The post AFFINITY LAWS FOR SLOWER OR FASTER SPINNING IMPELLERS appeared first on The Process Technology and Operator Academy.
]]>("My Head is Spinning," by the Pet Shop Boys, 1993)
CHANGING PUMP PERFORMANCE WITH IMPELLER RPMs
PTOA Readers and Students just learned how Affinity Laws #1, #2, and #3 can be used to predict the change in Capacity, Total Dynamic Head (TDH), and Brake Horsepower when a Centrifugal Pump's Impeller is replaced by an Impeller with a shorter or longer diameter.
Yep!
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order already know that a longer diameter Impeller will generate a greater TDH Curve (aka Characteristic Curve) compared to a shorter diameter Impeller that is being spun around at the same speed.
And vice versa, PTOA Readers and Students likewise learned in PTOA Segment #169 that a shorter Impeller will decrease the TDH generated whilst spinning at the same speed.
An alternate method for "stepping up" or "stepping down" the performance of a Centrifugal Pump is to vary the speed of the Impeller by rotating it faster or slower.
An Impeller that is spinning faster will complete a greater amount of revolutions ... or complete circles ... over the time interval of one minute.
So an Impeller that is now completing more revolutions per minute .... rpms ... is spinning faster than it was ...
and vice versa ...
An Impeller that is completing less rpms than it was previously is spinning more slowly.
To repeat loud and clear:
RPMs are a totally different way of measuring speed when compared to driving a car really fast down a highway!
AFFINITY LAWS FOR VARYING IMPELLER SPEEDS
The nearby graphic shows the predicted performance of a Scot 57 pump with Impeller sizes that range from 5.50 to 6.88 inch.
The top most Characteristic Curve shown in the diagram is the TDH generated with a 6.88 inch Impeller over a Capacity range of 0 to 1100 gpm.
PTOA Readers and Students should notice the box of data on the middle-right side of the graphic:
The boxed data shows the (maximum) Horsepower that is required to spin the 6.88 inch Impeller at speeds which vary in increments of 500 rpm from a low range of 1500 rpm to a high range of 3500 rpm.
The data table shows that a maximum of 2.4 Hp is needed to spin the Impeller at 1500 rpm and a maximum of 30.0 Hp is needed to spin the Impeller at 30 rpm.
Doesn't it just make sense in your gut that spinning an Impeller faster would require more Hp?
AFFINITY LAW #4: THE IMPACT OF RPMs ON PUMP CAPACITY
Affinity Law #4 is:
The pump Capacity varies directly with the RPM speed of the spinning Impeller.
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order will notice the similarity between Affinity Law #4 and Affinity Law #1 which was featured in PTOA Segment #169:
Affinity Law #1 stated that the pump Capacity varied directly as the diameter of the Impeller.
So PTOA Readers and Students will not be surprised to learn that the Capacity of a pump can be "stepped up" or "stepped down" by multiplying a "known" Capacity by the ratio of the "new"/"known" Impeller speed ... for example:
As stated previously above, the top TDH Curve results with a 6.88 inch diameter Impeller.
Check it out and verify that at a Capacity of 800 gpm, the TDH generated by the 6.88 inch Impeller is just real close to 150 feet.
Assume the Impeller is spinning at a known speed of 3500 rpm and then use Affinity Law #4 to predict the Capacity when the rotation speed is decreased to a new speed of 3000 rpm:
Capacity at 3000 rpm = 800 gpm *(3000 rpm/3500 rpm)
= 800 gpm * (3000/3500) = 686 gpm
Voila!
"Stepping down" the performance of the Scot 57 Centrifugal Pump by decreasing the Impeller speed from 3500 rpm to 3000 rpm will decrease the pump Capacity from 800 gpm to 686 gpm.
Remember!
The Capacity of Centrifugal pumps can be "stepped up" using the same relationship between a "known" Capacity and rpm and a "new and faster" rotation speed.
AFFINITY LAW #5: THE IMPACT OF RPMs ON TDH
Affinity Law #5 can be used to determine the TDH that will be generated when the pump is "stepped up" or "stepped down" by increasing or decreasing the speed of the Impeller.
Affinity Law #5:
The TDH varies directly with THE SQUARE of the RPM speed that spins the Impeller.
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order cannot help but notice how similar Affinity Law #5 is to Affinity Law #2.
Affinity Law #2 stated that the TDH varies directly with the square of the diameter of the Impeller!
Brilliant PTOA Readers and Students can easily extrapolate and modify what they learned about Affinity Law #2 to "step down" the TDH of the Scot Pump by applying Affinity Law #5 and decreasing the Impeller speed from 3500 rpms to 3000 rpms.
First thing is to remember that ... with the 6.88 inch Impeller ... the Scot 57 pump has a Capacity of 800 gpm and a TDH of 150 feet.
Next ...
"Stepping down" the pump TDH via decreasing Impeller speed can be calculated as follows:
TDH at 3000 rpm = 150 feet (3000 rpm)^{2} / (3500 rpm)^{2}
= 150 * 0.7347 = 110 Feet
Aha!
"Stepping down" the Scot 57 pump by reducing the speed of the rotating Impeller from 3500 rpms to 3000 rpms reduces the TDH of 150 feet to 110 feet.
By selecting a few more known points on the TDH-Capacity Curve (aka Characteristic Curve) shown for the 6.88 inch Impeller, Affinity Laws #5 and #6 can be used to predict the entire 3000 rpm Characteristic Curve for the Scot 57 pump.
And don't forget!
The TDH of Centrifugal pumps can likewise be "stepped up" using the same relationship between a "known" TDH and rpm and a "new and faster" rotation speed.
AFFINITY LAW #6:
THE IMPACT OF RPMS ON BRAKE HORSEPOWER
Affinity Law #6 states how the Brake Horsepower will change as the speed of the Impeller is increased or decreased:
The Brake Horsepower of the Pump will vary directly with THE CUBE of the RPM speed of the spinning Impeller.
PTOA Readers and Students already know that "cubing a number" means to raise it to the power of 3 ... one more power than squaring!
And by now who is surprised to notice the similarity between Affinity Law #6 and Affinity Law #3 which states that the Brake Horsepower of the Pump will vary directly as THE CUBE of the Impeller diameter?
Ergo ...
Affinity Law #6 can be used to predict how the performance of the Scot 57 pump can be "stepped down" from 3500 rpms to 3000 rpms after first grabbing some data from the data box that is shown in the middle-right of the Scot Pump Performance Curve chart.
When the 6.88 inch Impeller is installed in the Scot 57 Pump ...
The data in the box states that a maximum BHP of 30 is required when the Impeller speed is 3500 RPMs.
So ...the
BHP required with 3000 rpm speed = 30 hp (3000 rpm)^{3} / (3500 rpm)^{3}
= 30 * (0.6297) = 18.89 = 19 hp
Hey!
Check it Out!
The calculated maximum 19 Hp predicted after "stepping down" the Scot 57 pump from 3500 to 3000 rpm matches the 19 Hp listed in the data box! That's because Affinity Law #6 was used to generate the data listed in the table!
And, of course it goes without saying...
The BHP of a Centrifugal pump can be "stepped up" using the same relationship between a "known" BHP and rpm and a "new and faster" rpm.
HOW DOES THE SPEED OF THE IMPELLER RPMs IMPACT THE PUMP'S EFFICIENCY?
In a future PTOA Segment, PTOA Readers and Students will learn how the design of the Impeller can also change the Characteristic Curve of a Centrifugal pump (aka, the TDH-Capacity relationship).
Spoiler alert!
PTOA Readers and Students will learn that the Impeller is designed with vane angles which accommodate a restricted range of speed variance.
Therefore, there are Real World limits with respect to how much the Impeller's speed can be increased or decreased.
For this reason, PTOA Readers and Students can assume that the Efficiency of a Centrifugal Pump remains constant over the small step changes made to Impeller speed rotation.
THE REAL WORLD COMBINATION PERFORMANCE CHART
FOR THE VARIABLE SPEED PUMP
A real-world "Combination" Performance Curve Chart for a Scot 57 variable speed pump is shown nearby.
Guess what?
The Combination Performance Curve Chart for the Scot pump has the same type of information that PTOA Readers and Students observed on the Combined Performance Curve Chart for the constant speed 4BC Pump which was featured in PTOA Segment #169 and is shown below.
Both the nearby Constant Speed Performance Curve Chart for the 4BC pump and the Variable Speed Performance Curve Chart for the Scot 57 Pumps include TDH-Capacity "Characteristic Curves" with different sizes of Impellers.
The Efficiency of both the Constant Speed 4BC Pump and the Variable Speed Scot 57 Pump are expressed as "U" shaped lines.
Both the Constant Speed 4BC Pump and the Variable Speed Scot 57 Pump represent BHP as downward-right slanting straight lines.
So...
The clues that the Scot 57 Pump Chart is for a Variable Speed pump are simply:
Yeah!
PTOA Readers and Students can now claim a familiarity with respect to being able to interpret the Performance Curves for Variable Speed and Constant Speed Pumps!
By the way, the Affinity Laws also apply to fans!
Hang in there!
The next PTOA Segment features the last and final remaining important line on the chart of Performance Curves ... Net Positive Suction Head Required!
TAKE HOME MESSAGES: Once a Centrifugal Pump is purchased and installed, it may not perform optimally in the real world until it is modified by "stepping up" or "stepping down" its performance.
Affinity Laws are used to estimate the pump performance that will result after the pump is "stepped up" or "stepped down."
The previous PTOA Segment #169 featured Affinity Laws #1,#2, and #3 which are used to "step up" or "step down" pump performance by substituting longer or shorter diameter Impellers.
This PTOA Segment #170 featured Affinity Laws #4, #5, and #6 which are used to estimate pump performance after "stepping up" or "stepping down" the pump by varying the speed of the pump.
The speed of a pump is measured by how many revolutions per minute (rpms) are completed by the spinning Impeller; the greater the number of rpms, the greater the speed of the Impeller ... and vice versa.
Once a set of TDH, Efficiency, and BHP Performance Curves for a pump have been established for a pump with a specified Impeller, correlating Performance Curves can be generated by using the Affinity Laws which will predict the impact of changing the speed of Impeller rotation. These Affinity Laws are:
The Efficiency of a Variable Speed Pump does not change much and can be assumed to be constant no matter what the speed of Impeller rotation is.
The above assumption can be made because ... in the Real World ... the vane angles of Impellers are designed to accommodate a small range of rotational speed.
The Combined Performance Curve Charts for both the Constant and Variable Speed pumps are extremely similar and contain a wide range of information that characterizes pump performance.
©2017 PTOA Segment 0170
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study
The post AFFINITY LAWS FOR SLOWER OR FASTER SPINNING IMPELLERS appeared first on The Process Technology and Operator Academy.
]]>The post AFFINITY LAWS appeared first on The Process Technology and Operator Academy.
]]>("Love and Affection," by Joan Armatrading, 1976)
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order just learned that Centrifugal Pumps are selected for service based upon their chart of Performance Curves.
Quickie review:
Here's some new information about Performance Curves and Centrifugal Pumps:
Each Performance Curve will specify either:
Gee ...
What the heck happens after the purchased Centrifugal Pump is installed and then found to be incapable of generating the actual TDH that is required in the real processing world application?
Fortunately there are several ways to improve Centrifugal Pump performance so that the purchased and installed pump can work well in the real world. Two of the methods are:
This PTOA Segment #169 features the impact that changing the size of an Impeller has on Centrifugal Pump Performance.
The next PTOA Segment will feature the impact that changing the speed of the Impeller has on Centrifugal Pump Performance.
In either case, the adjusted performance of the Centrifugal Pump is easy to predict from the original Performance Curve that is supplied by the pump's manufacturer because ...
The Affinity Laws are used to generate parallel Capacity, TDH, and Brake Horsepower Performance Curves.
The Performance Curves that are generated from Affinity Laws represent "stepping up" or "stepping down" the pump's performance.
Do Process Operators need to memorize The Affinity Laws by heart to do a good job?
Heck No!
Process Operators won't ever directly use The Affinity Laws!
However, Process Operators who have been exposed to The Affinity Laws will have a better understanding of the challenges Mechanics have with respect to getting a new pump to optimally operate.
Because efficient pump operation translates into less pump failure and less downtime ...
all Process Operators benefit from understanding how a pump's performance is optimized!
THE IMPACT OF CHANGING A PUMP'S IMPELLER
ON CAPACITY AND TDH
The nearby graphic shows the TDH Performance Curves for three Impellers with the following diameters:
Affinity Law #1: The Impact of Impeller Size on Capacity
The family of Performance Curves shown above could be generated from any one of the curves using Affinity Laws #1 and #2.
Affinity Law #1 is:
The Capacity varies directly with the diameter of the Impeller.
Sounds fancy. What does that mean?
Well, let's focus on the TDH-Capacity curve for the 12 inch Impeller ... that is the curve in the middle.
Check it out and verify that:
At Capacity=2400 gpm, the TDH=2000 feet.
The Capacity that will be achieved with a longer (or shorter) Impeller can be determined by the following expression:
Capacity with 12.75 inch Impeller = 2400 gpm * (12.75 in/12.0 in)
= 2400 (12.75/12.0) = 2550 gpm
In other words,
"Stepping up" the performance of the Centrifugal Pump by substituting a 12.75 in Impeller for the 12.0 inch Impeller will increase the Capacity from 2400 gpm to 2550 gpm.
Wow! Is that all there is to it?
The above example shows that the procedure to determine the Capacity for a different size Impeller is:
Just multiply the "old" or "known" Capacity by the ratio of the "new"/"old" Impeller diameters!
Affinity Law #2: The Impact of Impeller Size on TDH
Affinity Law #2 can be used to determine the TDH that will be generated when the pump is "stepped up" by substituting a 12.75 inch Impeller for the original 12.0 inch Impeller.
Affinity Law #2:
The TDH varies directly with THE SQUARE of the diameter of the Impeller.
More fancy talk. Translation, please!
This is what Affinity Law #2 means:
First ...
Remember that the middle curve on the nearby diagram showed that a TDH created with the 12 inch Impeller is 2000 feet when the Capacity is 2400 gpm.
Ergo,
To determine the TDH generated with a 12.75 inch Impeller, multiply the "old" or "known" TDH by the squared ratio of the (New Impeller Diameter)^{2} / ("Old" Impeller Diameter)^{2} like this:
TDH with 12.75 inch Impeller = 2000 feet (12.75 in)^{2} / (12.0 in)^{2}
= 2000 * (12.75)^{2} / (12.0)^{2} = 2258 Feet
Voila!
"Stepping up" the pump by replacing the 12.0 Inch Impeller with a 12.75 inch Impeller will create an increased TDH of 2258 feet at an increased Capacity of 2550 gpm.
By selecting a few more points on the 12.0 Inch Impeller TDH-Capacity Curve (aka Characteristic Curve), the Affinity Laws #1 and #2 can be used to predict the entire 12.75 inch Impeller Characteristic Curve.
Likewise ...
The expected outcome of "stepping down" the performance of a Centrifugal Pump by replacing the 12.0 inch Impeller with a shorter, 11.0 inch Impeller can be predicted via The Affinity Laws.
Remember that at the "old" or "known" Capacity of 2400 gpm, a 12.0 inch Impeller creates a TDH = 2000 feet.
Using Affinity Law #1, the Capacity for a 11.0 inch Impeller can be determined:
Capacity with 11.0 inch Impeller = 2400 gpm * (11.0 in / 12.0 in)
= (2400) * (11 / 12 ) = 2200 gpm
Using Affinity Law #2, the TDH can be predicted for a 11.0 inch Impeller:
TDH for an 11.0 inch Impeller = 2000 feet (11.0 in)^{2} / (12.0 in)^{2}
= 2000 (121 / 144) = 1681 feet
Aha!
"Stepping down" the performance of a Centrifugal pump by substituting a 11.0 inch Impeller for a 12.0 inch Impeller will result in generating a 1681 foot TDH at a Capacity of 2200 gpm.
Using a couple more points from the 12.0 inch TDH-Capacity curve, the entire 11.0 inch curve can be fleshed out.
THE REAL WORLD APPLICATION REGARDING
CHANGING THE IMPELLER DIAMETER
Why The Impeller Diameter Can't Be Too Long
Increasing the diameter of the Impeller sure seems like an easy fix to increase TDH and Capacity!
So what is the limit on how long the Impeller diameter can be?
PTOA Readers and Students will soon learn the important role that the Volute plays with respect to directing the desired flow of the pumped liquid.
See the two upper most arrows in the nearby graphic?
These two arrows indicate the flow of the pumped fluid is entering the Pump Discharge instead of taking another spin around the Volute.
These two arrows show the pumped fluid clearing the Cutwater of the Pump.
The Cutwater of the Pump is the edge of the Volute interior right where the spinning fluid either flows into the Pump Discharge or makes another revolution around the Volute.
If the diameter of the Impeller is too long, the Impeller will rub against the Cutwater of the Volute.
The second great reason to limit the Impeller diameter is that some Efficiency would be sacrificed with the maximum-most-possible Impeller diameter.
A maximum diameter Impeller will have slightly lower Efficiency than the optimally-sized Impeller because of turbulence that would be created near the Cutwater.
Why The Impeller Diameter Can't Be Too Short
Brilliant PTOA Readers and Students can easily Imagine the reduction in Efficiency that results if the Impeller is cut down to the minimum diameter!
In that case a greater amount of pumped liquid is circulated around and around instead of entering the Pump Discharge.
The circulating liquid creates its own special brand of undesired turbulence!
The Optimally Sized Impeller
The optimally sized Impeller may require physical modifications made by expert pump Mechanics.
The outcomes that result after physically modifying an Impeller are not predictable by The Affinity Laws and are performed by experts only.
The nearby graphic (labelled "Figure 1") shows how the original vanes on an Impeller are trimmed back from the labelled "Original vane thickness" by "underfiling" which results in a significantly thinner vane.
As the nearby graphic labelled "Figure 2" shows, the underfiling modification has made a significant impact on the TDH and Capacity.
The Pump's TDH and Efficiency Curves before underfiling are shown as solid lines.
The Pump's TDH and Efficiency Curves after underfiling are represented as dotted lines.
Comparing the before and after vane underfiling reveals:
The maximum pump Efficiency is slightly greater than the Efficiency that the same pump had before the vanes of its Impeller were filed.
The maximum Efficiency occurs where there is a 20% increase in pump Capacity with absolutely no sacrifice in TDH!
Wow! This pump can efficiently handle 20% more Capacity!
Volute Modifications
Although not an Impeller modification, this is as good a place as any to mention that the Cutwater of the Volute and Pump Discharge may also be modified to improve Centrifugal Pump Performance.The nearby graphic (which is labelled "Figure 3") shows the Cutwater of a Volute.
Warning ... don't become confused! The label in the graphic refers to the Cutwater as "the Casing Tongue."
The darkened area of the Cutwater is the part that is trimmed away by an expert pump specialist.
The modifications to the Cutwater indicate the same favorable impacts that were observed when the Impeller vanes were underfiled!
The nearby graphic (labelled "Figure 4") compares the performance of the pump before and after modification of the Cutwater.
Solid lines represent pump performance "before Cutwater trimming" and dotted lines represent pump performance "after Cutwater was trimmed."
The impacts of the Cutwater modification on pump performance are:
The maximum pump Efficiency is slightly greater after the Cutwater is trimmed.
The maximum Efficiency occurs where there is a 20% increase in pump Capacity with absolutely no sacrifice in TDH!
Wow! This type of modification to the pump can also improve pump efficiency AND make it possible to handle 20% more Capacity!
AFFINITY LAW #3:
HOW IMPELLER DIAMETER IMPACTS BRAKE HORSEPOWER
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order already know exactly what is meant by the phase "Brake Horsepower" because they have read PTOA Segment #168.
Affinity Law #3 states how the Brake Horsepower will change as the Impeller diameter is changed:
The Brake Horsepower of the Pump will vary directly as THE CUBE of the Impeller diameter.
Cubing a number means to raise it to the power of 3 ... one more power than squaring!
Here's an example of how Affinity Law #3 is used to predict the BHP that is required when pump performance is "stepped-up."
PTOA Readers and Students will remember that the 12 inch Impeller shown in the nearby graphic creates a 2000 foot TDH at a Capacity of 2400 gpm.
PTOA Readers and Students must also remember Affinity Laws #1 and #2 were used to determine a 12.75 Impeller creates a 2258 ft TDH when the Capacity is 2550 gpm.
Affinity Law #3 predicts what will happen when the Pump's Performance is "stepped up" by replacing the 12 inch Impeller with a 12.75 inch Impeller:
First, assume the BHP required to generate a 2000 ft TDH at 2400 gpm is 131 hp.
Then:
BHP required for 12.75 inch Impeller = 131 hp (12.75 in)^{3} / (12.0 in)^{3}
= 131 * (2072)/(1728) = 157 hp
Aha!
When the 12.75 inch Impeller replaces the 12.0 inch Impeller, the BHP required increases from 131 hp to 157 hp for a TDH = 2558 ft at a Capacity of 2550 gpm.
DIY Exercise:
Do it Yourself and figure out what the BHP required is when an 11 inch Impeller replaces the 12.0 inch Impeller.
PTOA Readers and Students who want to delve into the Affinity Laws further might enjoy using this handy dandy link tool provided by Systek Technologies Inc:
Systek Technologies Affinity Rule Calculator
HOW DOES THE PUMP IMPELLER IMPACT THE PUMP'S EFFICIENCY?
PTOA Readers and Students have already learned that there are limits as to how long or short an Impeller can be.
Because there is a limit to an Impeller's diameter, the impact of changing out an Impeller does not impact the pump's Efficiency that much.
Otherwise stated:
Over the real world ranges of an Impeller's diameter, the Efficiency can be assumed to remain constant.
That means if an optimal Efficiency of 80% for a 12.0 inch Impeller is observed, the Efficiency for a 12.75 inch Impeller or an 11.0 inch Impeller can be assumed to be 80%, too!
Below PTOA Readers and Students will see a real world Combination Performance Curve. Note that ... in the operating range of interest for this pump ... the Efficiency changes from 80% to 83%.
REAL WORLD COMBINATION PERFORMANCE CHARTS
Real world Performance Curve charts typically show the predicted pump performance with several Impeller diameters.
The nearby graphic describes the Performance Curves for a 4 BC Pump which spins the Impeller at the constant speed of 1750 rpms ... no matter what the size of the Impeller is.
PTOA Readers and Students should notice that the TDH Curves shown are for Impeller diameters that range from 7.5 to 9.5 inch.
The real world Combined Performance Curves chart cannot represent the Efficiency and Brake Horsepower Curves in the same format that is used for single TDH-Capacity relationship.
The Efficiency at each 'step' is shown in the region of interest as a looping downward curve that looks like the letter "U."
Each point on each U-shape curve represents the same stated Efficiency.
In the nearby graphic the Efficiency U-shaped curves range from 80% (the largest "U") to 83% (the smallest "U" that sort of looks like a "V").
There are other lines of Efficiency that do not make a complete U. For example there are lines of Efficiency marked "75%" and even "60%." These lines are for informational purpose only; in the real world the pump would not be selected to operate everyday in this region.
Note that Brake Horsepower is shown as dashed lines that slant downward and to the right.
Each point on the separate slanted lines represents the same stated HP ... which appears on the right side of the slanted lines.
The labels at the right side of the slanted lines indicate the range of BHP to be 7 ^{1}/_{2} (bottom-most BHP line) to 20 HP (highest-most BHP line).
Gad Zooks! There sure is a lot of information on any combined chart of Performance Curves!
And now PTOA Readers and Students have a fairly good idea of how to interpret the real world Centrifugal Pump Performance Chart of a constant speed Centrifugal Pump!
TAKE HOME MESSAGES: Once a Centrifugal Pump is purchased and installed, it may not perform optimally in the real world until it is modified and may have to be "stepped up" or "stepped down."
One way to change the performance of a Centrifugal Pump is to change the size of the Impeller. The size of the Impeller is "the diameter of the Impeller."
Once a set of TDH, Efficiency, and BHP Performance Curves for a pump have been established, correlating Performance Curves that correspond to changing the Impeller Diameter can be calculated via the Affinity Laws.
Affinity Law #1: The Capacity varies directly with the diameter of the Impeller.
Affinity Law #2: The TDH varies directly with THE SQUARE of the diameter of the Impeller.
Affinity Law #3: The Brake Horsepower of the Pump will vary directly as THE CUBE of the Impeller diameter.
There are limitations on the maximum and minimum length of an Impeller. For example, an Impeller that is too long will rub on the Cutwater of the Volute.
The Cutwater of the Volute is the point where the spinning water either enters the Pump Discharge or spins around the pump again.
Real world Centrifugal Pump Performance charts combine information for several sizes of Impellers and show their impact on the TDH-Capacity relationship.
For constant speed Centrifugal Pumps:
Physical changes to the Impeller and Volute can be made by professionals to significantly change the performance of a pump. Physical changes to the Impeller and Volute are not part of the Affinity Laws and are performed by pump specialists only.
©2017 PTOA Segment 0169
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study
The post AFFINITY LAWS appeared first on The Process Technology and Operator Academy.
]]>The post WHAT CONDITION THE PUMP’S CONDITION IS IN appeared first on The Process Technology and Operator Academy.
]]>I said I just dropped in to see what condition my condition was in
Yeah
Yeah
Oh yeah
["I Just Dropped In (To See What Condition My Condition Was In)," made famous by The First Edition, but written by Mickey Newberry, 1967]
PTOA Readers and Students just learned that the Capacity of a Centrifugal Pump can exceed what is optimal and move into a Capacity range that will cause a harmful pump problem called Cavitation.
Wouldn't the safer, more simple option be to design the pump to operate in the smack middle of the Capacity range?
The answer to the above question would be Yes Indeedo were it not for the fact that the Dynamic Head (TDH) versus Capacity relationship is not the only important relationship displayed by a Performance Curve.
Two other curves help define the optimal Capacity where the Centrifugal Pump should be operated:
All PTOA Readers and Students should be able to look at the nearby chart of Performance Curves and understand that every Capacity point on the chart's X-Axis has a corresponding and unique TDH, Efficiency, and BHP point.
In other words ...
For every Capacity of throughput for the pump in gpm ... there is a definite Pump Efficiency that corresponds to a specific, required TDH which is only achievable with a pump that is selected to provide the designated Brake Horsepower (BHP).
These three points define the "Condition of the Pump" at every value of the Centrifugal Pump's Capacity.
By the time PTOA Readers and Students complete this PTOA Segment #168 they will be able to determine the optimal Condition of the Pump from assessing the changes observed between Pump Efficiency, TDH, and Brake Horsepower (BHP) as the pump Capacity changes.
This PTOA Segment also features background information regarding the meaning and definition of:
There's one other noteworthy curve that will be discussed in a future PTOA Segment yet shows up on most Performance charts:
NPSHr will be featured soon in the PTOA Segment that focusses on Cavitation.
ISOLATING THE CAPACITY-TDH RELATIONSHIP
The nearby graphic isolates the TDH-Capacity relationship.
The TDH-Capacity curve is sometimes called The Pump Characteristic Curve.
Who amongst the brilliant PTOA Readers and Students remembers that the change in Capacity ...
from 0 gpm on the left hand side of the X axis to the maximum amount on the right hand side ...
is what happens in the real world when the Outside Process Operator opens the Discharge Valve from 'totally blocked in' position to 100% open?
So guess what?
Friction Losses explain why the head that the pump can discharge (aka TDH) decreases as the Capacity increases!
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order are not surprised to connect these dots because they recently learned the following fun facts about PV Pressure Losses in PTOA Segment #165:
Therefore ...
The greater the Capacity on the X-axis ...
The greater the PV Pressure losses due to Friction ... and thus the arcing downward shape of the TDH curve!
HORSEPOWER DEFINED
The Brake Horsepower Curve (BHP Curve) is another unique point that helps define the Pump's Condition.
There are two prerequisites that lead up to understanding BHP:
And prior to learning the above concepts ...
Everyone must understand what is meant by the phrase "horsepower."
What is "Horsepower?"
The Industrial Revolution (roughly 1760-1840) is described as a time wherein the handiwork of Humankind was replaced by machines ...
which is still a timely subject considering Artificial Intelligence is predicted to replace large segments of manual labor during the 21st century!
In the 1780s, Scottish inventor James Watt promoted the use of his steam engine by proving how much more work the steam engine could perform compared to the work that horses performed while hauling water out of coal mines.
Before Watt could prove how much more powerful his steam engine was he needed to develop the basis for measuring "power" ... which is the amount of work performed over a unit of time.
Watt determined that a horse can vertically lift a weight of 550 lbs a distance of one foot over a time interval of one second.
Watt's mathematical description-definition of hydraulic horsepower can be converted to the time basis of one minute via the following conversion:
1 hp = 550 ft-lbf/sec * 60 sec/1 min = 33,000 ft-lb_{f}/min
1 hp = 33,000 ft-lb_{f}/min
Note the units that express hydraulic horsepower are:
(height-weight) / time.
Every PTOA Reader and Student who reads the PTOA Segments in the intended sequential order already knows that "weight" is simply a mass that has the force of gravity acting upon it ...
that concept was explained in PTOA Segment #143.
Ergo, "hydraulic horsepower" is a unit of power that complies to the rule that everything is derived from the three basic units of measurement ... mass, length, and time ... as was mentioned way, way back in PTOA Segment #60.
Fun fact:
A weight lifter raising a bar bell over his/her head is likewise expending horsepower by lifting the weight over a vertical distance in a short amount of time.
Yabba Dabba Do!
Time to apply all of the above to understanding:
Wow!
There sure is a lot of background information to learn before learning how to identify the optimal Condition of the Pump from a chart of Performance Curves!
HYDRAULIC HORSEPOWER OF A CENTRIFUGAL PUMP
An improved yet equivalent expression for "hydraulic horsepower" that applies to pumps is:
The amount of work required to change a liquid from a beginning elevation, Pressure, and velocity to a final elevation, Pressure, and velocity over a set period of time.
It doesn't take much imagination to figure out that the power of a Centrifugal Pump moves a mass of liquid from the Suction-side Head elevation, Suction-side Pressure, and Suction-side Flowrate/Capacity to the Discharge-side Head, Discharge-side Pressure, and Discharge-side Flowrate/Capacity.
Otherwise stated ...
The hydraulic horsepower of the liquid being pumped can be thought of as the is the increased energy state of the liquid at Pump Discharge because of a change in elevation (aka TDH), change in Pressure, and change in velocity (aka Flowrate/Capacity) between the Discharge and Suction.
The generalized expression that defines Hp ...
Hp = (Weight)(Height) ÷ (Time)
Can be converted into an expression that describes the hydraulic horsepower transferred into the pumped liquid:
Hp = [(Capacity in gal/min) * (TDH in ft) * (Spec.Gravity of Liquid)]
÷ 3960
Does a Process Operator need to memorize the above defining expression for hydraulic horsepower to perform his/her job well?
Heck No!
Hydraulic horsepower doesn't even appear on the chart of Performance Curves ... it's Brake Horsepower that appears on the chart!
Just be mindful that:
EFFICIENCY DEFINED FOR ANY MACHINE
What is meant by a Machine's "Efficiency?"
Who is John Galt?
John Galt is/was a make-believe protagonist conjured up by author Ayn Rand for her 1957 rant entitled "Atlas Shrugged." John Galt supposedly defied the laws of physics and invented a "frictionless motor."
Galt's invention is as much a fairy tale as Goldilocks' wrong choice of the perfect porridge featured in PTOA Segment #79 because the Universe has decreed that some power shall always be sacrificed to friction and the emission of noises. Therefore:
There is no such thing as a 100% efficient machine!
PTOA Readers and Students who can access the below link will be mesmerized by the myriad of simple mechanical machines incorporated into OK-Go's Paint Gun Machine You Tube that was created to promote their song "This Too Shall Pass."
Note that:
ACCESS HERE FOR OK GO's "THIS TOO SHALL PASS" PAINT BALL MACHINE
EFFICIENCY DEFINED FOR A CENTRIFUGAL PUMP
No Centrifugal Pump has 100% Efficiency either.
Otherwise stated ...
All of the power that the driver does to spin the shaft and impeller will not be transferred into the pumped liquid. An 80% Efficiency for an operating pump is darn good!
The Efficiency of the Centrifugal Pump will be reduced by:
The Efficiency of the Pump can be calculated using the below equation:
Hydraulic Hp of the pumped liquid
÷
Hp put into the machine to make it operate
Which can be rewritten as shown below by inserting the definition PTOA Readers and Students just learned for hydraulic horsepower:
Efficiency (expressed as a Decimal Fraction) =
[Hp = [(Cap in gal/min) * (TDH in ft) * (Sp.Gr of Liquid)]÷ 3960]
÷
Hp of the Driver
Does a Process Operator need to memorize the above defining expression for pump Efficiency to perform his/her job well?
Heck No!
But a Process Operator should be vaguely aware of these Pump Efficiency phenomena:
A typical Pump Efficiency Curve in red is featured on the nearby chart of Performance Curves.
Naturally, Pump Efficiency= 0 at 0 Capacity gpm because ... with no flow through the pump ... the pump is not in the process of changing the elevation, Pressure, or velocity of the liquid.
The Pump Efficiency Curve increases with increasing pump Capacity up until the increase in Capacity creates large friction losses that make the Efficiency Curve arc downward.
Unless told otherwise, PTOA Readers and Students should assume the chart of Performance Curves is describing a Centrifugal Pump that does not have a variable speed driver.
Therefore ...
Operating the pump at any point other than the maximum Efficiency-Capacity condition would waste the utility expense that pays for rotating the shaft of the pump.
Thus:
The optimal Capacity to operate a Centrifugal Pump is at the pump Condition described by the maximum Pump Efficiency ...which is just prior to where the Efficiency begins to decrease.
The Pump Efficiency Curve in some Performance charts appears to flatten out a bit over a Capacity range. In that case, the optimal Condition of the Pump is the Capacity with the maximum Pump Efficiency AND greatest TDH. The TDH Curve will never flatten out and will always be plunging downward with increased Capacity!
BRAKE HORSEPOWER (BHP)
Let's be honest.
"Brake Horsepower" is a confusing term that makes one think of stopping power or something like that. Some committee should have decreed a new name by now.
The modifier "Brake" refers to the instrument that is used to scientifically measure Brake Horsepower ... the "brake dynamometer."
Brake Horsepower (BHP) is the horsepower an engine could supply before any losses in power occur.
Why measure BHP instead of Hp?
Remember how each of the simple machines in the OK Go Paint Gun Machine had to overcome friction AND deliver enough punch to keep the machine working?
Likewise ...
The person who selects the Centrifugal Pump must size the pump to provide the amount of horsepower needed to move the required amount of liquid AND account for power losses throughout the machine.
BHP is simply calculated by dividing the Hydraulic Hp of the liquid by the pump's Efficiency (expressed as a decimal fraction):
BHP = Hp ÷ Pump Efficiency
Because Pump Efficiency is always less than one, BHP will always be GREATER THAN the Hydraulic Horsepower.
PTOA Readers and Students who desire to understand how BHP is calculated from Pump Efficiency and hydraulic horsepower can access the below link:
Does the Process Operator need to memorize the above definition/expression for BHP to perform his/her job well?
Heck No!
However, the Process Operator should be familiar with the meaning of Pump Efficiency and BHP and understand that the two are intimately related ... BHP is determined by dividing Hp by Pump Efficiency.
IDENTIFYING THE OPTIMAL THE CONDITION OF A PUMP
Shazam!
PTOA Readers and Students who have not dozed off by this point have now learned all the concepts that support a chart of Performance Curves!
The optimal Condition of the Pump can be determined!
The below chart of Performance Curves is for a pump that has an impeller spinning at 1750 revolutions per minute (rpm).
The size of the impeller has a major impact on the Performance Curves; the magnitude of the impact will be featured in an upcoming PTOA Segment.
All PTOA Readers and Students should confirm that the optimal condition for the Centrifugal Pump described by the above chart is:
TAKE HOME MESSAGES: Every chart of Performance Curves shows the unique values of TDH, Pump Efficiency, and BHP that extend across the range of Pump Capacity.
Each TDH-Pump Efficiency-BHP-Capacity family describes a Condition of the Pump.
Because of the assumption that the driver is not a variable speed driver ...
The optimal Condition of a Pump is where the Capacity is at maximum Efficiency which identifies the TDH requirement. To achieve the specified TDH the pump must be sized for the Brake Horsepower (BHP) that works at the Maximum Efficiency-TDH condition.
The Efficiency of a Pump is the hydraulic horsepower of the pumped liquid divided by the energy used to make the pump work.
No machine is 100% Efficient. No machine can transfer or perform all of the work it is built to do because of power losses.
The Efficiency of a Pump will be a decimal fraction that is less than 1.0; Note the Efficiency Curve on a Performance chart is typically expressed as a percentage.
Brake Horsepower is the power an engine has before power losses occur in the operation of the machine.
In a pump, the Brake Horsepower will always be greater than the hydraulic horsepower transferred into the pumped liquid.
Understanding the terms "Efficiency" and "Brake Horsepower" required understanding these terms:
The TDH Curve is sometimes called the pump's "Characteristic Curve."
©2017 PTOA Segment 0168
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study
The post WHAT CONDITION THE PUMP’S CONDITION IS IN appeared first on The Process Technology and Operator Academy.
]]>The post WELL I THINK I’M GOIN’ OUT OF MY HEAD appeared first on The Process Technology and Operator Academy.
]]>Well, I think I'm goin' out of my head
Yes, I think I'm goin' out of my head
("Goin' Out of My Head," made famous by Little Anthony and the Imperials but written by T. Randazzo & B,Weinstein, 1964)
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order were recently introduced to Performance Curves.
Performance Curves can be used to determine the optimal Capacity of a Centrifugal Pump.
PTOA Readers and Students already know that the X-axis of a Performance Curve shows the Capacity range of the pump ... aka the amount of fluid that the pump can handle ... from 0 gpm to a maximum design flowrate.
And PTOA Readers and Students already know that the Y-axis is the Total Head of the pump, expressed in feet.
This is a good place to mention that Performance Curves do not apply to Positive Displacement type pumps because the operating principle of a Positive Displacement Pump is not related to centrifugal action.
Centrifugal action is illustrated in the nearby graphic; the pumped liquid is fed into the Suction-side eye of the spinning impeller and is thence flung outwards.
Centrifugal action will be explored soon in a future PTOA Segment so don't stress about understanding it now.
PTOA Readers and Students will soon learn exactly how the fabricated casing of the Centrifugal Pump ... aka the Volute ... changes the direction and velocity of the pumped fluid that has been spun out from the center of the impeller.
This PTOA Segment #167 continues the focus on Centrifugal Pump Performance Curves. PTOA Readers and Students will learn the difference between Total Dynamic Head and Total Static Head ... which will involve defining a myriad of other head types.
Whoa Pardner! Stop right here if you are confused by the phrase "Total Head!" The rest of us got knowed-up about Total Head just recently in PTOA Segment #166 and you need to do yourself a favor and catch up.
Alert!
This PTOA Segment is gonna get kind of wonky explaining and differentiating Pump Head types.
By the end of this PTOA Segment everyone's mind will be blown and everyone's head will be spinning!
HEAD DISSECTION
First and foremost, PTOA Readers and Students must figuratively understand what the Centrifugal Pump lingo "head" means.
The nearby graphic exhibits many features found in the Typical Pump Set Up which was described in PTOA Segment #164.
This graphic also shows a "Real" versus "Imagined" pumping situation.
In real life, the pumped-up liquid flows out the Pump Discharge into the Discharge Line.
In real life, the Discharge Line is initially vertical but soon makes a turn to the horizontal plane via an elbow in the pipe. The jagged line on the Discharge Line infers that the pipe is too long to show any more of the pipe in the diagram.
The blue vertical line that is shown extending from the pump's Discharge is the figurative expression of "Total Discharge Head."
The height of the figurative head gives a visual idea as to the amount of PV Pressure energy that has been infused into the liquid so that it has sufficient energy to flow where it is needed.
So ... in YOUR HEAD ...when you hear the word "head" in pump lingo ...
visually Imagine a vertical stack of liquid ... and remember:
The taller the stack, the more PV Pressure energy the liquid has within it so that it can flow to where it is needed to be.
The Suction-side PV Pressure of the Centrifugal Pump can also be figuratively expressed as a vertical line.
As the nearby photo shows, the vertical blue line that figuratively illustrates the Total Suction Head is not as tall as the vertical blue line that figuratively represents the Total Discharge Head.
Who amongst the brilliant PTOA Readers and Students is asking themselves:
"Since all the fuss is about Pressure ... Why isn't the Y-axis of the Performance Curve plotted in units of Pressure (psi) instead of feet of head?"
An excellent question that can be answered by another question:
Who amongst the brilliant PTOA Readers and Students has noticed that two different types of forces are creating Pressure on the Suction and Discharge sides of the pump?
The Suction-side Pressure is mainly caused by the Gravity force of hydrostatic head.
When the pump is operating, Centrifugal force creates the PV Pressure on the Discharge-side of the pump.
Righteeo!
Once the pump is turned on and whirling liquid around...
The Centrifugal force that creates the PV Discharge Pressure is not the same thing as the gravity force that creates the PV Pressure on the Suction-side of the Centrifugal pump.
By now every dedicated PTOA Reader and Student who is reading the PTOA Segments in the intended sequential order can recite in their sleep that the magnitude of the Suction-side Pressure is created by the Suction-side Static Head and depends only upon the Specific Gravity and height of the liquid ... ergo ..
The greater the density of the liquid the more Pressure is exerted at the bottom of the hydrostatic head.
Alternatively stated, a liquid with a S.G less than 1.0 (the S.G. of water) will require a greater head to exert the same pressure as water would.
And vice versa, a liquid with a S.G. greater than 1.0 will require less head to exert the same pressure as water.
Yeah. We all know that by now.
HOWEVER ...
On the Discharge-side of the operating pump, Centrifugal action rules in the process of creating PV Pressure energy.
Once the Centrifugal Pump is operating, the liquid being pumped is no longer "static" ... it is moving and is therefore described as "dynamic."
Your Mentor will never be convinced that Process Operators need to know the particulars of math-modelling dynamic fluid flow to perform their jobs well.
Just file it in the back of your head that the PV Pressure created by Centrifugal force depends upon the square of the velocity of the liquid ... but not the density of the liquid.
And accept that the two noteworthy outcomes of the PV Pressure created by Centrifugal Force are:
"A centrifugal pump with a given impeller diameter that is rotating at a specified speed will develop the SAME FEET OF TOTAL DYNAMIC DISCHARGE HEAD no matter what the liquid is."
Yes Indeedo!
Be it water or gasoline or whatever ... the impeller will spin the fluid to the same imaginary height.
However ...
Process Operators must be aware ...
The Discharge Pressure that the Process Operator reads on the Discharge PI DOES INCREASE with increasing liquid Specific Gravity!
The two Centrifugal action phenomena described above explain why the manufacturers of Centrifugal Pumps prefer to plot the Total Head on the Y-axis of Performance Curves in feet of liquid instead of Pressure in psig.
Ergo ...
PTOA Readers and Students must slog through learning what Total Head is ... which they did in PTOA Segment #166.
Incidentally, the Pump Manufacturing Industry is not nearly as anal retentive as the Instrumentation Industry; they haven't convened for hours and days of meetings to settle on common terminology for Performance Curves.
So don't be confused when Total Head on the Y-axis is described as "Total Discharge Head" or "Total Dynamic Head" or "Characteristic Curve" ... yadda yadda yadda.
HEAD TYPES AND PERFORMANCE CURVES
One chart that attempts to define the different types of Pump Head is shown below.
The phrases that appear in this Pump Head chart will be shown in red writing when mentioned in the below text.
Total Static Head = Total Head at 0 gpm
Total Static Head in the above chart is almost the same thing PTOA Readers and Students learned to determine in PTOA Segment #166.
"Static" means not moving ... thus at rest and standing still.
Imagine how the Total Static Head relates to the Centrifugal Pump Set Up shown below ... before power to the Centrifugal Pump's driver is engaged.
Imagine:
Since the pump is not spinning, no Friction Losses have been generated.
Thus, only the Static Head and Pressure Head on both sides of the pump contribute to Total Head ... not Friction Losses.
On any chart of Performance Curves, the static situation is the leftmost vertical line ... where Capacity = 0 gpm.
So what Your Mentor is trying to tell ya is that the maximum Total Head of a Centrifugal Pump is also known as the Total Static Head when the Capacity = 0 gpm.
On the nearby chart of Performance Curves, the "0 gpm flow" is where Total Static Head and Total Head both equal 105 feet.
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order will not be surprised to learn that:
Total Static Head =
(Total Static Discharge Head) - (Total Static Suction Head)
and in the case of lift:
(Total Static Discharge Head) - (Total Static Suction Lift).
No Process Operator will ever be asked to calculate Total Static Head ... but the value of the knowledge is understanding how the term is incorporated into the Performance Curves.
For example PTOA Readers and Students will know that Total Static Head is the maximum value of Total Head and is plotted on the Y axis where Capacity = 0 gpm.
Total Dynamic Head
Now Imagine that:
Shazam!
The Centrifugal Pump is now operating in a dynamic mode ... doing what it was built to do ...
Adding PV Pressure energy to the liquid that enters the Pump Suction ...
which is expressed on the Performance Curve as Total Dynamic Head (TDH) at any Capacity above 0 gpm.
The change in TDH with the pump Capacity appears as the top curve on the vast majority of Centrifugal Pump Performance Curves.
This is the mathematical expression for the TDH Curve:
Total Dynamic Head (TDH) =
(Total Dynamic Discharge Head) - (Total Dynamic Suction Head)
and in the case of lift TDH =
(Total Dynamic Discharge Head) - (Total Dynamic Suction Lift).
No Process Operator will ever be asked to calculate Total Dynamic Head ... but the value of the knowledge is understanding how the term is incorporated into the Performance Curves.
TDH is the Total Head curve that is plotted at all values of Capacity above 0 gpm.
APPLYING ABOVE TO THE TDH PERFORMANCE CURVE
Wow!
All Performance Curve charts show that ...
A relatively small increase in flow rate (aka Capacity) correlates to a rapid decrease in Total (Dynamic) Head.
A nearby Performance Curve graphic illustrates where the Capacity/Total Head combination falls into the cavitation range.
Notice that the Capacity point labelled "V" is considerably beyond and therefore greater in magnitude than the maximum Capacity which is labelled V_{max}.
In the real world, the left side of the cavitation range indicates where the pump begins sucking liquid into the eye of its impeller at a rate that is too great for the Suction-side to keep supplying sufficient Total Dynamic Suction Head.
Wait! I see Fred waving his hand!
What do you have to say, Fred?
"The Centrifugal Pump that is operating at V has done gone out of its Total Dynamic Head!
Yuk! Yuk! Yuk!"
TAKE HOME MESSAGES: Performance Curve charts only apply to Centrifugal Pumps.
Figuratively speaking, the phrase "head" should conjure up the vision of a vertical "stack" of liquid.
The Pressure that is built up by Centrifugal action is proportional to the square of the liquid velocity but is not at all impacted by the liquid's density or specific gravity.
Therefore the Total Dynamic Discharge Head of a Centrifugal Pump with a given impeller diameter rotating at a specified speed will be the same for any liquid, regardless of specific gravity.
However, the Discharge Pressure of a Centrifugal Pump is still impacted by the pumped liquid's specific gravity; the greater the specific gravity of the liquid, the greater the Discharge Pressure observed by the Process Operator.
"Static" means at rest or not moving. With respect to Centrifugal Pumps the phrase describes the state wheren the pump is primed liquid full but the power to the driver has not been supplied so the impeller is not spinning.
"Dynamic" means moving. With respect to Centrifugal Pumps the phrase describes the pump operating and the impeller spinning.
Total Static Head is the maximum value of Total Head and is plotted on the Y axis of a Performance Chart Curve where Capacity = 0 gpm.
The calculation of Total Static Head does not include any Friction Loss because the liquid is at rest.
Total Dynamic Head is the value of Total Head at all points on the Performance Chart Curve where Capacity is greater than 0 gpm.
Every Total (Dynamic) Head Curve for a Centrifugal Pump will indicated that a small increase in flow rate (aka Capacity) correlates to a rapid decrease in Total (Dynamic) Head.
©2017 PTOA Segment 0167
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study
The post WELL I THINK I’M GOIN’ OUT OF MY HEAD appeared first on The Process Technology and Operator Academy.
]]>The post THE THREE-HEADED CENTRIFUGAL PUMP MONSTER … AND PERFORMANCE CURVES appeared first on The Process Technology and Operator Academy.
]]>("Scary Monsters," by David Bowie, 1980)
INTRODUCTION TO CENTRIFUGAL PUMP PERFORMANCE CURVES
Modern Plant Managers want modern Process Operators to understand why it is important to operate Centrifugal Pumps at their optimal flow through rate.
Process Operators who do not understand the basics of Centrifugal Pump operation may inadvertently cause the pump to cavitate.
The best way to illustrate the optimal pump operating range is to learn how to interpret the myriad of lines that appear on a Centrifugal Pump Performance Curve.
The X-axis on every Performance Curve is the Capacity of the pump, aka the flow of liquid that the pump can handle in gallons per minute (gpm).
For example, the Capacity scale of the nearby Performance Curve could be 0 gpm on the far left side of the X-axis to 1400 gpm on the far right side.
The Total Head is shown plotted on the nearest Y-axis of the nearby Centrifugal Pump Performance Curve.
The Total Head curve is the blue curve that decreases in an arc as the Capacity of the pump increases.
Unlike the pump's Capacity, Total Head takes a bit more brainwork to understand.
The goal of this PTOA Segment #166 is to define the Total Head that a pump must achieve to successfully add sufficient PV Pressure energy into the liquid so that it can get to where it is going and do what it is supposed to do.
Otherwise stated:
The Total Head is the difference in PV Pressure measured between the Pump Discharge and Pump Suction.
The word "Total" in "Total Head" is a big hint that "Total Head" is derived from several contributing sources.
Righteoo!
Albeit invisible, there is a Three-Headed Centrifugal Pump Monster on both the Suction and Discharge sides of any Centrifugal Pump.
The Total Head of a Centrifugal Pump is determined after quantifying these three sources that contribute to the Total Suction-side Head and the Total Discharge-side Head of any Centrifugal Pump:
QUICKIE REVIEW OF HYDROSTATIC HEAD
In PTOA Segments #146 and #147, PTOA Readers and Students learned all about hydrostatic head.
In fact, PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order used the hydrostatic head of sea water at the Strait of Gibraltar to determine how much pressure was bearing down upon the hull of U Boat 96 via this expression for hydrostatic Pressure:
Pressure (psi) = SG * 0.433 psi/1 foot * h (feet)
where:
The above expression can be easily rearranged to find the hydrostatic head when the Pressure in psi is known:
h (in feet) = Pressure (psi) / (SG * 0. 433 psi/foot)
For example:
1 psi of water is created by a hydrostatic head of 2.31 feet
because:
h (in feet) = 1 psi / (1.0 * 0.433 psi/foot)
= (1) / (1.0 * 0.433) = 2.31
Hey! That's a handy conversion factor to know:
2.31 Static Head Water in Feet / 1 psi Water Pressure
Because if 1 psi of water is created by a hydrostatic head of 2.31 feet, that means any multiple of Pressure in psi can be created by an equal multiple of head in feet!
For example:
10 psi water = 23.1 Static Head in Feet
because:
h (in feet) = 10 psi / (1.0 * 0.433 psi/foot)
= (10) / (1.0 * 0.433) = 23.1
and
100 psi water = 231 Static Head in Feet
because:
h (in feet) = 100 psi / (1.0 * 0.433 psi/foot)
= (100) / (1.0 * 0.433) = 231
HEAD #1: THE STATIC HEAD
The first head of the Three Headed Centrifugal Pump Monster is the Static Head which is created by any standing vertical distance of liquid.
Static Suction Head of a Centrifugal Pump
In PTOA Segment #164, PTOA Readers and Students learned that the Typical Pump Installation Set Up includes a tank which stores the inventory of liquid that will soon be fed into the Pump Suction Line and thence to the Pump Suction.
The nearby graphic illustrates that the Static Suction Head is the vertical distance from the Centerline of the pump's Suction Line to the liquid level in the Suction-side tank.
In other words, the Static Suction Head includes the hydrostatic head of the liquid contained in the Suction-side tank plus the hydrostatic head of the liquid that is contained in the liquid-filled vertical piping.
The definition of Static Suction Head makes perfect sense because ....
as any brilliant PTOA Reader and Student can recite by heart ...
"the Pressure exerted by a liquid only depends upon the height and the density of the liquid ... not the volume or shape of the container holding the liquid."
Quantifying Static Suction Head is easy because it is just the depth of the contained liquid added to the length of vertical pipe that extends from the bottom of the tank.
For example ... assume:
Then ... voila!
Static Suction Head = 3 + 5 Feet!
Static Discharge Head
Extending what was just learned about Static Suction Head to the other side of the pump ...
PTOA Readers and Students are probably not surprised to learn that the Static Discharge Head is the vertical distance between Centerline of the Pump Suction Pipe and the top of the liquid level contained in the Discharge-side Tank.
Static Discharge Head is also easy to determine!
If the vertical distance between the Centerline of the Suction Pipe and the top of the Discharge-side Tank is 25 feet, then:
The Static Discharge Head is 25 feet!
Now that PTOA Readers and Students have been made aware of the Static Head Monster that lives in the Suction-side and Discharge-side of a Centrifugal Pump ... it's time to learn about Pressure Head.
HEAD #2: PRESSURE HEAD
The Suction-side and Discharge-side tanks in the above drawings indicate that the tanks are open to atmospheric pressure because they are not enclosed.
When the Suction-side and Discharge-side Tanks/Vessels/Receivers are enclosed, the Pressure Head must be determined.
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order already learned in PTOA Segments #147 and #162 that the vapor space above any enclosed tank is occupied by either the vapor of the contained liquid or a gas blanket (like nitrogen or natural gas).
Either way, the vapors or gas blanket generate a pressure above the liquid level.
In pump lingo, when the vapor or blanket gas pressure is converted into equivalent feet, the outcome is called a "Pressure Head."
Assume the Suction-side tank in the graphic above has a 25 psig gas blanket.
Since 1 psi is equal to 2.31 feet of water ...
the Pressure Head of the Suction-side tank is:
h (in feet) = 25 psig * (2.31 feet H2O)/1 psig
= 57.8 feet
The Discharge-side Tank/Vessel/Receptacle will most likely also have a vapor space occupied by vapor or a gas blanket.
The Discharge-side Tank/Vessel/Receptacle Pressure Head is calculated exactly as shown above for the Suction-side Tank.
What If the Vapor Space Is Measured in PSIA?
What happens if the vapor space pressure is measured in units of Absolute Pressure ... psia?
In that case the first step is to convert the vapor space pressure measurement into the same basis that will be used to eventually determine the Total Head.
In the vast majority of cases on Earth, gauge pressure is the basis of measurement.
Ergo, the Absolute Pressure measurement in psia must first be converted into a gauge pressure, psig.
PTOA Readers and Students learned in PTOA Segment #150 that:
P_{abs} = P_{gauge} + P_{atm}
and that P_{atm }is equal to 14.7 psi and 101.3 kPa at sea level.
To determine P_{gauge} the above expression can be rearranged:
P_{gauge} = P_{abs} - P_{atm}
Ergo ... if the Suction-side vapor space pressure was measured as 25 psia, the gauge pressure equivalent is:
P_{gauge} = 25 - 14.7 = 10.3 psig
So now the conversion to Pressure Head can occur:
h = (2.31 feet / psig) * 10.3 psig = 23.8 feet
Aha! It is time to learn about the third and last head of the Three Headed Centrifugal Pump Monster ... Friction Head!
HEAD #3: FRICTION HEAD
PTOA Readers and Students very recently learned in PTOA Segment #165 that just the action of flowing through a pipe causes a liquid to lose some of the PV Pressure to friction losses.
For example ... in the below Typical Pump Installation Set Up ...
Friction losses will occur:
The "friction factors" that are assigned to pipes, pipe fittings, valves, etc have been quantified by nerdy engineer-scientists and can be found in resources such as Crane's Technical Paper #410.
However, no PTOA Reader or Student needs to invest in such resources because they are used in the design phase of the Processing Facility, not operating phase.
Generally speaking, the factors that determine the magnitude of the "friction factor" assigned to hardware are:
Naturally ... the viscosity of the liquid impacts the magnitude of the Friction Loss, but this factor is a characteristic of the liquid ... not the pipe that the liquid is flowing through.
Your Mentor just wants PTOA Readers and Students to be aware of where the statements related to quantified friction losses come from.
For now friction losses will simply be stated as a specific amount of Friction Head expressed in feet.
TOTAL HEAD =
(TOTAL DISCHARGE HEAD) - (TOTAL SUCTION HEAD)
Okay! PTOA Readers and Students now have sufficient knowledge to calculate the Total Head of a Centrifugal Pump!
Total Head = (Total Discharge Head) - (Total Suction Head)
First Step: Determine Total Suction Head
Total Suction Head is determined stepwise by:
Who amongst the brilliant PTOA Readers and Students can visualize that the Suction-side Static Head and Pressure Head in the nearby Typical Pump Installation Set Up are beneficial to the Centrifugal Pump because they help add PV Pressure to the liquid by just gravity and not any applied power?
However, the Suction-side Friction Head decreases the amount of PV Pressure on the Suction Side of the Centrifugal Pump.
So here's an example of ...
How to Calculate Total Suction Head for the Centrifugal Pump shown installed below:
Given:
Then:
Thus:
Total Suction Head = (10 + 46.2) - 1.3 = 54.9 ft
Second Step: Determine Total Discharge Head
Total Discharge Head is determined by adding:
Here's an example of ...
How to Calculate Total Discharge Head for the Centrifugal Pump shown installed below:
Given:
Then:
Thus:
Total Discharge Head = (60 + 231 + 17.6) = 308.6 feet
Ta-Dah! Finally Ready to Calculate Total Head!
Total Head = (Total Discharge Head) - (Total Suction Head)
For example ... given:
Total Discharge Head = 308.6 feet
Total Suction Head = 54.9 feet
Then:
Total Head = 308.6 - 54.9 = 253.7 feet
Gosh, it has taken so long to get to this point who remembers what Total Head means?
A Total Head of 253.7 feet means that an equivalent amount of PV Pressure energy must be added into the pumped liquid so that it can be distributed where it needs to go to do what it needs to do!
Hey! A Total Head of 45.8 feet means (253.7 * 2.31) = 586 psi must be added to the liquid flowing through the pump!
Note that the Total Head decreases in an arc as the Capacity of the pump increases.
The pump described by the nearby Performance Curve was designed for the horizontal Total Head and vertical Capacity combination indicated by the black triangle.
The optimal Total Head and Capacity is always closely associated with the optimal Pump Efficiency. Pump Efficiency is shown as a red line in the nearby Performance Curve.
Mission Accomplished!
All PTOA Readers and Students now understand what goes into the determination of Total Head for a Centrifugal Pump!
Now there's just one more thing to cover for the Not So Typical Pump Installation Set Up!
HOW TO DETERMINE TOTAL HEAD FOR LIFTING PUMPS
"Static Suction Head" changes into "Static Suction Lift" when the liquid in the Suction-side Tank/Reservoir is situated vertically below the Centrifugal Pump.
The nearby drawing shows a "Static Suction Head" pump installation on the left side and a "Static Suction Lift" pump installation on the right side.
Both Static Suction Head and Static Suction Lift are the vertical distance between the liquid surface and the Centerline of the pump's Suction Line.
However ...
Note that the Centrifugal Pump on the right must perform more work on the pumped liquid because it doesn't have the benefit of gravity contributing to the Static Suction Head or Pressure Head.
Ergo ...
The Static Suction Lift, Suction-side Pressure Head, and Suction-side Friction Head of a lifting pump are all negative ... and thus end up being added to the Total Discharge Head to determine Total Head!
Uh-oh Fred's sweating.
Here's an example for you, Fred:
Assume the following bullet items apply to the lifting pump installation shown on the right side of the nearby diagram:
Therefore Total Suction Head = -11.3 feet
Therefore Total Discharge Head = 60 + 60 + 17.6 = 137.6 feet
Next ...
Total Head is calculated exactly as before ... yet beware that a subtracting a negative is the same as adding!
Total Head = (Total Discharge Head) - (Total Suction Head)
= 137.6 - (-11.3)
= 137.6 + 11.3 = 148.9 feet
The lift pump must add the equivalent of 149 feet of PV Pressure energy to the liquid to get it where it needs to go!
Hey! That's 148.9 * 2.31 = 344 psi!
TAKE HOME MESSAGES: PTOA Readers and Students were introduced to Centrifugal Pump Performance Curves as a first step to learning how to operate a Centrifugal Pump in the optimal range.
Every Centrifugal Pump is supplied to the Processing Facility with its own Performance Curve.
A Centrifugal Pump Performance Curve includes the relationship between the pump's Capacity and Total Head.
In the USA, the Capacity of a pump is expressed in units of gallons per minute, gpm.
The Total Head of a Centrifugal Pump is defined:
Total Discharge Head - Total Suction Head
The Total Head of a Centrifugal Pump is the PV Pressure that must be added to the liquid by the pump ... expressed in units of feet.
The three components that go into the determination of both Total Suction Head and Total Discharge Head were featured:
Both the Static Suction Head and Static Discharge Head are determined from the Centerline of the Pump Suction Line.
Before converting into the head equivalent of pressure, all the components of Static, Pressure, and Friction Head must be on the same basis ... which is typically gauge pressure.
The conversion factor 2.31 feet / 1 psi water is used to convert Pressure Head from the pressure measured in the vapor space of a contained liquid.
When determining Total Head for a lifting pump it is important to remember that subtracting a negative means adding!
©2017 PTOA Segment 0166
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study
The post THE THREE-HEADED CENTRIFUGAL PUMP MONSTER … AND PERFORMANCE CURVES appeared first on The Process Technology and Operator Academy.
]]>The post WHERE OH WHERE DOES THE PV PRESSURE GO? appeared first on The Process Technology and Operator Academy.
]]>I'm looking through you,
Where did you go?
I thought I knew you,
What did I know?
You don't look different, but you have changed.
I'm looking through you, you're not the same.
("I'm Looking Through You," by The Beatles, 1967)
WHERE OH WHERE DOES THE PV PRESSURE GO?
Who amongst the brilliant PTOA Readers and Students has noticed that Your Mentor has yet to explain exactly why it is necessary to keep adding the PV Pressure to flowing process streams?
Of course, PTOA Readers and Students know: No ΔP = No Flow!
But why doesn't the flowing liquid just stay at the pump's Discharge Pressure?
Guess what?
Just the act of flowing through the pipe will reduce the PV Pressure of any fluid ... liquid or gas.
Pressure Drop caused by Friction Losses is a BIG DEAL!
Uh-oh!
Fred's getting all panicky and sweaty again.
Don't worry, Fred!
This PTOA Segment #165 explores what Friction Losses and Pressure Drop are and how they impact any piping and pumping system.
FRICTION LOSSES AND PRESSURE DROP
IN ONCE-THROUGH AND CIRCULATING PUMPING SYSTEMS
Consider Alaska's 800 mile long Trans-Alaska Pipeline which delivers crude oil from Prudhoe Bay to Valdez.
Pressure Drop due to Friction Losses eat up the Discharge Pressure delivered by the pumps at Pump Station 1 (PS1) so Pumping Station 2 (PS2) is strategically placed to restore the PV Pressure on the 48-inch diameter pipeline and keep the flow a-going!
The pumps installed at each successive Pumping Station are sized to create a Discharge Pressure that can deliver the oil to the next Pumping Station.
Without Pumping Stations, the PV Flowrate of the oil would cease.
The Trans-Alaska Pipeline is an example of a one-direction, series pumping system.
Some pumping systems are like the Lube Oil System shown below and use the same pump to restore the PV Pressure to the lube oil that is circulating in a closed loop.
The PV Pressure in the circulating lube oil line decreases from its maximum at the Pump Discharge as it flows through the pipes that deliver the fluid to → Coolers→ Filters →Check Valve → Compressor Train → Pump Suction Line.
Whew! Flowing through all that piping and hardware would consume the flow energy ... aka PV Pressure ... out of any fluid!
That's why IN ANY CIRCULATING PUMP OR COMPRESSOR SYSTEM:
The Suction Pressure is the Lowest Pressure in a Circulating Closed Loop System
and
The Discharge Pressure is the Highest Pressure in a Circulating Closed Loop System
All the PIs on the pipes of the circulating system will indicate progressively less PV Pressure between the maximum observed at Pump Discharge and the minimum observed at the Pump Suction.
Okay! Okay! The above information falls under the category of "Good To Know."
But why does the darn PV Pressure of a flowing fluid decrease in the first place and where or where does that PV Pressure go?
POOF ... PV PRESSURE CHANGES INTO FRICTION!
The PV Pressure of a flowing fluid is lost due to the Friction created by rubbing on the interior pipe wall.
Hey! You've already been sort of introduced to this concept!
The Velocity Profile of Laminar flow that was featured in PTOA Segment #159 is caused by Friction between the flowing fluid and the interior surface of the pipe.
PTOA Readers and Students know that the Velocity Profile shows how the fluid Velocity gradually increases "in radial layers" from the slowest flow velocity observed at the pipe's interior surface to the fastest flow velocity observed at the center of the pipe.
So PTOA Readers and Students already know that the Velocity Profile of Laminar flow can be identified by a cone shape.
The cone shape develops because of the rubbing of the outermost liquid on the interior of the pipe wall ...
and this rubbing causes some of the PV Pressure of the flowing fluid to just ...
POOF!
Change into Friction Losses that lower the PV Pressure in the process flow line ... thereby creating a noticeable Pressure Drop.
No kidding! ... The PTOA Department of Redundancy Department repeats:
Even with no restriction in the process fluid line, the mere interaction of a flowing fluid with the interior walls of a pipe creates a noticeable Pressure Drop due to Friction Losses.
The nearby schematic shows fluid flowing from left to right in a blue pipe. The decreasing PV Pressure is depicted as a decreasing red level in a gauge ... kind of like a barometer!
Here's another redundant way to look at it:
If a set of PIs were stabbed into a length of pipe, the PV Pressure indicated on the PIs would be less and less as the fluid flowed through the pipe.
For example:
The 60 psi PV Pressure in the top left of the nearby pipe drawing decreases to 57 psi after the fluid has flowed through a 50 foot length of Pipe ...
Heck yeah that's a noticeable Pressure Drop of 3 psi!
Otherwise stated ...
Friction Losses have eaten up 3 PSI of the PV Pressure as the process fluid flowed through just 50 feet of pipe!
The Pressure Drop due to Friction Losses is even more severe in a pipe with a smaller diameter!
The first 50 feet of pipe has a pipe diameter of 3/4 inch.
The second 50 feet of pipe has a reduced pipe diameter of 1/2 inch.
This decrease in pipe diameter from 3/4 inch to 1/2 inch greatly increases the Friction Losses that create Pressure Drop!
The 57 psi PV Pressure at the mid point of the top pipe reduces to 42 psi after the pipe diameter is reduced!
Wow! Decreasing the diameter of the pipe by a third creates 5 times the Pressure Drop due to Friction Losses (15 psi versus 3 psi).
OMG!
The Total Pressure Drop due to Friction Losses over just 100 total feet of pipe in the above pipe drawing is 18 psi!
That means (18/60 * 100 =) 30% of the initial PV Pressure was just chomped up by Friction and therefore did not help transport the fluid to its intended destination.
Wow! The above observation also means ...
Thirty percent of the utilities spent on generating the spinning or pushing action of a pump to create the PV Pressure did not even go into doing useful work ... like delivering the fluid where it is needed!
Thirty percent of the utilities spent on generating the PV Pressure of 60 psi is just wasted as Friction Losses!
SOURCES OF FRICTION LOSS ... AND THUS PRESSURE DROP
PTOA Readers and Students just learned that there is a direct link between wasted utilities expense and Friction Losses.
Understanding the sources of Friction Losses is the first step to designing pumping systems that minimize Pressure Drop.
Friction Loss and Pressure Drop Caused by Flow Through a Pipe
Pipe Flow Friction Losses that result in Pressure Drop are impacted by:
Pipe Length ... the longer the pipe, the greater total Pressure Drop.
Now PTOA Readers and Students understand why Your Mentor made the below statement that appeared in PTOA Segment #163:
In the real world, the Suction Pipe that delivers lube oil from the Reservoir to the Lube Oil Circulating Pump will be the shortest, straightest run of pipe possible.
Fluid Properties Impact Friction Losses, Too!
The nitty-gritty details that describe math modelling and quantifying Pressure Drop due to Friction Losses are well beyond the scope of the PTOA and are not fundamental information that Process Operators must know to do their job well.
However, the factors that influence the Pressure Drop of a flowing liquid are easy to understand and reason out.
Who amongst the PTOA Readers and Students would be surprised to learn that the fluid properties that were featured in PTOA Segment #162 contribute to how much Pressure Loss is observed?
The Fluid's Properties of Density, Specific Gravity and Viscosity logically impact Friction Losses and Pressure Drop.
Imagine water and then honey flowing through a pipe. Honey is much more dense and viscous than water and of course has a Specific Gravity greater than 1.0.
No PTOA Reader or Student would be surprised to know that:
Pipe Hardware Fittings and Components
Are Additional Sources of Friction Losses and Pressure Drop
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order just learned in PTOA Segment #164 that typical hardware components are found in the Suction and Discharge Lines of the Typical Pump Installation Set Up.
Who amongst the PTOA Readers and Students would be surprised to learn that each hardware fitting ...
like a Gate Valve or Check Valve ...
causes yet more Pressure Drop due to Friction Losses?
Heck! That makes sense!
Because if merely flowing through a pipe causes a Pressure Drop so would flowing through the twists and turns of a Valve because the fluid makes contact with more surfaces than just the interior pipe wall!
The nearby Check Valve animation and graphic together show why Check Valves cause significant Pressure Drop.
The normal flow through the nearby Check Valve animation is from right to left; the Pump Discharge Line would be to the right of the animated diagram.
In the event the ΔP changes and thus changes the flow direction from left to right, the Check Valve closes ... which is desired because the Check Valve was installed to protect the pump internals.
However, the normal flow route must always flow around the flapper of the Check Valve.
This constant contact with the flapper converts the PV Pressure into Friction Losses 24/7!
Friction Losses that cause Pressure Drop in hardware fittings and components explain why Your Mentor made the below statement in PTOA Segment #164:
PTOA Readers and Students will learn that each Valve is installed for a specific purpose ... no Valve is just randomly stuck in there for grins.
Fred! Please confirm that you understand all the TAKE HOME MESSAGES below.
And Fred ...
Have you realized that the Friction Losses that cause a Pressure Drop support the statement: "No ΔP, No Flowrate!"
Good! That means it's time to introduce everybody to the Three Headed Pump Monster!
TAKE HOME MESSAGES: Contact between a flowing liquid and the interior surface of the pipe that the fluid is flowing in creates Friction Losses that result in Pressure Drop.
That means the mere necessity of having a fluid flow through a pipe results in some of the PV Pressure in the line being changed into useless Friction ... with the result being a decrease in the PV Pressure.
Friction Losses are unavoidable yet wasteful because they result in continually wasting the Utilities Expense item in the Plant's Daily Operating Expenses.
The amount of Pressure Drop observed in the flowing fluid depends upon pipe and fluid properties and are listed below:
Pressure Drop due to Friction Losses is also caused by every hardware component in the piping, like Gate Valves and Check Valves, etc.
In a circulating pump or compressor system, the Suction Pressure is the lowest PV Pressure in the system and the Discharge Pressure is the highest PV Pressure in the system.
©2017 PTOA Segment 0165
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study
The post WHERE OH WHERE DOES THE PV PRESSURE GO? appeared first on The Process Technology and Operator Academy.
]]>The post THE TYPICAL PUMP INSTALLATION SET UP appeared first on The Process Technology and Operator Academy.
]]>("What Do You Expect?," by J. J. Cale, 1981)
THE EXPECTED, TYPICAL PUMP INSTALLATION SET UP
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order just learned that ...
No matter which kind of pump is chosen for a process industry service ...
each pump will have:
In this PTOA Segment #164, PTOA Readers and Students will learn about the hardware components that will be installed on the Suction and Discharge Pipes of all pumps ...
No matter which type of pump is chosen for whatever process industry service.
The Typical Pump Installation Set Up is evident in the nearby photo.
The Suction Valve, Discharge Valve, Strainer, and Check Valve are labelled.
All PTOA Readers and Students who stick with the PTOA will soon be able to identify the hardware components found in the Typical Pump Installation Set Up without any labels ...
and that will certainly impress any potential Process Industry employer!
REAL & SYMOBLIZED PIPE HARDWARE COMPONENTS
INSTALLED ON PUMP SUCTION AND DISCHARGE LINES
ISA Valve Symbols
The future PTOA PV Flowrate Focus Study Area will focus upon piping hardware and the various methods used to connect pipe segments together ... so don't sweat the details now.
At this juncture PTOA Readers and Students just need to realize that pipe hardware components include Valves and Filters.
Spoiler Alert!
PTOA Readers and Students will learn that ... although there are many types of Valves ... there are only 4 reasons to add a Valve into the process flow piping.
The above graphic shows the ISA symbols for popular process industry Valves.
For example, one of the most common process industry Valves is the Gate Valve.
Gate Valves are used to start or stop the process flow.
That means that Gate Valves will either be totally open or totally closed.
The ISA symbol for a Gate Valve looks like a bow tie.
A real world manually operated Gate Valve is in the nearby photo.
This model has a blue hand wheel.
The Typical Pump Installation Set Up
The Typical Pump Installation Set-up is shown in the below diagram ...
Don't fret, the symbols will be explained, right after a little "decoding of the schematic."
Note that the Centrifugal Pump in the diagram does not have the "backwards C." The symbol is also missing the Discharge Line spout ... because it was drawn with a cheap CAD program.
In this case Your Mentor can infer the diagram is showing a Centrifugal Pump that adds the PV Pressure to liquids and not a Centrifugal Compressor that adds the PV Pressure to gases.
The drains are a dead giveaway. Liquids drain. Gases don't drain.
Now direct your attention to the bottom left of the diagram.
Although there are no arrows indicating flow, believe Your Mentor that the process stream liquid is flowing from its Tank/Reservoir and enters the diagram on the bottom left.
Find the below hardware components on the Typical Pump Installation Set Up diagram.
The purpose of a Check Valve is to prevent flow from going in the non-desirable, reverse direction. The arrow on the check valve body indicates the desired flow direction.
PTOA Readers and Students will soon learn why ...
Each Valve is installed for a specific purpose ... no Valve is just randomly stuck in there for grins.
Don't stress about the piping hardware shown in the upper region of the schematic; PTOA Readers and Students will learn all about it in the future PTOA PV Flowrate Focus Study Area.
In the nearby real world photo, the Suction and Discharge Gate Valves are easily identified by their black hand wheels.
The Check Valve is on the Discharge Line, bolted in-between two segments of piping that have flanged ends... (just look for a drain spout pointing down).
Hardware Components That are Needed for Pump Malfunction
The Typical Pump Installation Set Up must take into account this question:
What happens if the Pump malfunctions?
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order already know that critical-service pumps are installed in pairs ... a Primary Pump and a Back-Up Pump.
Logically, the Back Up Pump is placed in service while the malfunctioning pump is repaired.
So also logically, some piping component hardware must exist to "block in and isolate" the malfunctioning pump from the process fluid ...
because the process fluid must still continue flowing so that raw materials can continuously be upgraded to more valuable products.
The General Steps To Prepare a Pump for Maintenance
The hardware piping components that are purposely installed to make it possible to "swap a pump out for maintenance" are explained below ...
While the actions that an Outside Process Operator follows to bring the malfunctioning pump "off-line" are simultaneously explained.
In general the procedure will include the following actions:
The Outside Process Operator will either initiate the written procedures to start the Back Up Pump or it will be started up automatically via automatic instrumentation.
In Process Operator jargon, the phrase "Block in" means "to close tightly and completely."
The Typical Pump Installation Set Up must also take into account this question:
What would happen if the Suction Valve or Discharge Valve were found to be leaking ... and maintenance still must be completed on the pump?
Opening up the two drains to sewer would encourage the leaking process fluid to "take the easy way out" and flow to the drain or sewer ... but this plan-of-attack would not be a safe procedure nor would it comply with environmental permitting.
The designed-in solution is:
The spectacle blinds on the diagram are those Figure 8 shaped things that look like spectacles (eyeglasses).
The dark circle represents a metal surface that, when swung into place, creates a physical barrier in the pipe that prevents flow from getting through. (Don't Stress! Pipe Fittings will be featured in the PTOA PV Flowrate Focus Study Area).
Although not shown on the Typical Pumping Installation Setup schematic, there will always be a Filter or Strainer of some type on the Suction side of the Pump.
The Filter/Strainer removes debris that would scratch the internal working surfaces of any Pump.
Centrifugal Pumps Require Suction Line Contraction
Followed by Discharge Line Expansion
See the two thimble-looking things, one piped in prior to the Pump Suction and the other piped in after the Pump Discharge?
These symbols indicate the pipe diameter is intentionally decreased just prior to the Pump Suction and increased after the Pump Discharge.
The change in piping diameters is a permanent, planned feature of the piping scheme that is needed for centrifugal action to work properly and is not related to the maintenance interval.
So the complete Typical Pump Installation Setup For A Centrifugal Pump is shown in the below schematic:
PTOA Readers and Students will soon expertly understand centrifugal action ... do don't fret about that now!
TAKE HOME MESSAGES: There is a Typical Pump Installation Set Up that is common to all pumps, no matter what their style of process service is.
The component hardware in the Typical Pump Installation Set Up includes:
The typical component pump piping hardware may also include:
This PTOA Segment included the general procedure that all Outside Process Operators follow to "swap out a pump for maintenance".
The Outside Process Operator must always verify the status of the Back Up Pump prior to shutting down the Primary Pump (a limping Primary Pump is better than no pumping action at all).
©2017 PTOA Segment 0164
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study
The post THE TYPICAL PUMP INSTALLATION SET UP appeared first on The Process Technology and Operator Academy.
]]>The post EXPLORING THE FIRST SYMBOL IN THE PTOA LOGO appeared first on The Process Technology and Operator Academy.
]]>The more I learn, the less I know
And what I do ... it's all too much
("It's All Too Much," G. Harrison of The Beatles, 1969)
COMMON FEATURES OF ALL PUMPS
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order already know that pumps are rotating equipment which add the PV Pressure to liquid process streams.
The pump chosen for a process industry service might be a Centrifugal Pump, a Positive Displacement Plunger/Piston Pump or a Positive Displacement Rotary Pump.
Although the pumping service varies, there are common features of each pumping environment.
This PTOA Segment #163 and the upcoming PTOA Segment #164 familiarize PTOA Readers and Students with the "common pumping environment" ...while using Centrifugal Pump systems as an example.
Pump Discharge Pressure
is ALWAYS GREATER Than Pump Suction Pressure
The pipe that delivers flow into the Pump Suction is logically called "the Pump Suction Pipe."
There will always be a Pressure Indicator (PI) installed on the Pump Suction Pipe.
This Suction Pressure PI logically measures and indicates the PV Pressure of the liquid that is flowing into the Pump Suction.
Likewise, there will always be a Discharge Pressure PI installed on the Pump Discharge Pipe that measures and indicates the Discharge Pressure of the pumped-up liquid.
The Pump Suction PI located on the Pump Suction Pipe will always indicate a Pressure that is less than the Pump Discharge Pressure ...
Because that's what pumps do!
That's their raison d'etre ...
their reason to exist!
Pumps add the PV Pressure to process stream liquids!
For example ...
The Suction Pressure PI on the Pump Suction Pipe in the below schematic indicates 50 psi. The Discharge Pressure PI on the Pump Discharge Pipe indicates 250 psi.
So the schematic above conveys the following information:
ISA SYMBOLS FOR ROTATING EQUIPMENT
ISA Symbols for Centrifugal Pumps
and Centrifugal Compressors
This ISA symbol for a Centrifugal Pump is shown in the nearby photo.
A correctly drawn ISA Centrifugal Pump symbol will have a "backwards C" drawn in the center of the symbol.
Frequently the "backwards C" is omitted; sometimes it is drawn as a complete circle.
That's not very helpful ... but hey, that's life.
The "backwards C" or complete circle distinguishes the ISA Centrifugal Pump symbol from the ISA Centrifugal Compressor symbol ... the process industry equipment that adds the PV Pressure to gases.
The ISA symbol for a Centrifugal Compressor does not have the "backwards C" in the center ... it's just empty.
In the nearby symbol chart, the (correctly drawn) ISA symbol for a Centrifugal Pump appears in the top row.
The symbol for a generic Centrifugal Compressor appears in the bottom row, second column.
When a Centrifugal Pump is incorrectly drawn without a "backwards C" in the center and is therefore blank, PTOA Readers and Students must use their decoding skills to determine if the symbol represents a Centrifugal Pump or Centrifugal Compressor.
For example, when PTOA Readers and Students know the process fluid is a liquid, that will be sufficient information to assume that the symbol in a schematic is a Centrifugal Pump, not a Centrifugal Compressor.
ISA Symbols for Centrifugal Pumps, Plunger/Piston Pumps,
and Rotary Pumps
The top row on the below ISA symbol chart shows three typical drawings of Centrifugal Pumps labelled "Centrifugal Pump," "Centrifugal Pump 2," and "Centrifugal Pump 3."
However it is drawn, the Centrifugal Pump symbol is easy to distinguish from the symbol used for:
Who amongst the brilliant PTOA Readers and Students noticed that the first symbol in the Process Technology and Operator Academy logo is a Centrifugal Pump?
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order are now aware of what three of the four ISA symbols in the PTOA logo represent.
ASSESSING THE PUMPING SITUATION
So far in this PTOA Segment #163, PTOA Readers and Students have learned:
Guess what?
There's even more common features that will be found in the pumping environment, no matter what kind of pump is in service!
The Pump Will Be Placed Close To A Tank or Reservoir
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order were introduced to the Lube Oil System block diagram below in the recent PTOA Segment #161.
To analyze the flow in the block diagram, locate the block labelled "Pumps" in the bottom right of the below diagram.
The plural form of the word "Pumps" implies there is a Primary Pump and an identical Back Up Pump represented by the block.
The block labelled "Reservoir" is a container or tank of some type that holds the liquid inventory of lube oil that is available to circulate through the Lube Oil System.
Note that the lube oil flows from the Reservoir into the Suction Line of the block labelled "Pumps."
In the real world, the Suction Pipe that delivers lube oil from the Reservoir to the Lube Oil Circulating Pump will be the shortest, straightest run of pipe possible.
From the Pumps Block, the lube oil flows through the Discharge Line to a Cooler → Filter → and finally to the Compressor Train that needs the lube oil to keep functioning.
The used lube oil is then drained from the Compressor and returned to the Reservoir.
The above Lube Oil System has a lot in common with the Cooling Water System shown below that was first introduced way back in PTOA Segment #40.
Instead of lube oil, cooling water is circulated in a Cooling Water System.
PTOA Readers and Students should recall that the "Heat Exchanger" labelled in the graphic represents several heat exchangers that use the circulated, cool Supply Water for heat transfer,
The warmer water effluent from the shell and tube heat exchangers collects in the Return Header that is piped to the top of the Cooling Tower.
Find the (Cooling Water Supply) Pump in the lower right of the above drawing. The ISA symbol indicates this is a Centrifugal Pump.
The water supplied to the Suction of this Centrifugal Pump comes from the Cooling Water Basin, which contains a large volume of water that will insure the Suction Line is always filled.
The basin of a real world Cooling Tower can be seen in the nearby photo.
Another nearby photo shows a bank of real world Cooling Water Supply Pumps that are drawing their Suction from the water basin shown above.
Aha!
PTOA Readers and Students should notice a common feature in both the Lube Oil and Cooling Water Systems:
A Tank ... or Reservoir ... or Large Container of some type CONTINUOUSLY supplies a steady process stream flow into the Pump's Suction.
"Running a pump dry" will ruin the pump ...
because pumps are made to add the PV Pressure to liquids ... not gases like air!
Any type of pump will always be associated with an identifiable holding Tank or Reservoir which contains an inventory of the liquid that is going to be pumped.
The Suction-side piping that connects any pump to the Tank/Reservoir will have common hardware components ... no matter what kind of pump is in service.
Likewise, the Discharge-side piping that connects the pump to its intended process industry service will have common hardware components ... no matter what kind of pump is in service.
The common hardware components that are found in the piping of the pumping environment are featured in the upcoming PTOA Segment #164.
TAKE HOME MESSAGES: Pumps are selected and matched to their specific process industry service. Common types of pumps are:
No matter what kind of pump or process industry service, each pump will have:
The Tank/Reservoir insures that there is continuous process stream flow into the Pump Suction. Running a pump "dry" will ruin it.
Important pump service will be sustained by installing two pumps ... a Primary Pump and a Back Up Pump.
The ISA symbol for a Centrifugal Pump and Centrifugal Compressor are very similar; an accurately drawn Centrifugal Pump ISA symbol has a "backwards C" drawn in the middle, but sometimes it is omitted or drawn as a circle.
The ISA symbol for a Centrifugal Compressor is just like the symbol for a Centrifugal Pump but does not have anything drawn in the center.
Because of their similarity, PTOA Readers and Students will have to use decoding to distinguish between ISA symbols for Centrifugal Pumps and Compressors.
©2017 PTOA Segment 0163
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study
The post EXPLORING THE FIRST SYMBOL IN THE PTOA LOGO appeared first on The Process Technology and Operator Academy.
]]>The post YOU OUGHTA KNOW BY NOW! appeared first on The Process Technology and Operator Academy.
]]>You oughta know by now
You oughta know ...you oughta know by now
("Words of Love," by J.Phillips of The Mamas and The Papas, 1966)
CONNECTING THE PV PRESSURE DOTS
In this PTOA Segment #162, Your Mentor will begin connecting the dots between the PV Pressure fundamentals and how those fundamentals apply to the operation of Centrifugal Pumps.
Centrifugal Pumps are the go-to rotating equipment used to increase the PV Pressure in liquids and condensed vapors.
"Condensed vapors" are gases that are maintained in their liquid state by increased Pressure and lower Temperature.
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order will cruise through this essential information that directly applies to the operation of Centrifugal Pumps and other rotating equipment.
If the above paragraph does not describe yourself ...
STOP RIGHT HERE!
Do yourself a big favor and access the below link that will jump you back to the beginning of the PTOA PV Pressure Focus Study Area.
Your success with respect to learning what Plant Managers expect you to know about Centrifugal Pumps depends upon taking this opportunity to "own" the PV Pressure fundamentals.
STUFF YOU OUGHTA KNOW BY NOW
Absolute Pressure Vs. Gauge Pressure
PTOA Readers and Students must understand the difference between Gauge Pressure (psig) and Absolute Pressure (psia) measurements.
Gauge and Absolute Pressure measurement were featured in PTOA Segment #150.
PTOA Students and Readers learned that:
P_{abs} = P_{gauge} + P_{atm}
Prior to assessing the performance of Centrifugal Pumps, the PV Pressure measurements recorded around the pump must be on the same measurement basis.
The above statement means that PTOA Readers and Students must be vigilantly alert to first recognize when information that describes the pumping situation is given in multiple Pressure-measuring bases and then be ready to convert all information into one consistent basis.
Although the choice between Absolute and Gauge Pressure is arbitrary, most processing industry pump performance assessments are performed on the basis of Gauge Pressure, psig.
With advanced apologies to the PTOA Readers and Students who do not use the English system of measurement, the PTOA PV Pressure Rotating Equipment Focus Study will only use English measuring units to assess the performance of pumps and compressors.
The PV Pressure ↔ Fluid Velocity Swap
PTOA Readers and Students learned liquids are not "compressible" in PTOA Segment #153.
So PTOA Readers and Students know that suddenly decreasing the Volume of a liquid by half WILL NOT result in doubling the PV Pressure of a liquid as it will for a gas.
Centrifugal Pumps add the PV Pressure to liquids and gases by combining centrifugal force with the PV Pressure ↔ Fluid Velocity Swap, a fluid-flow phenomenon that was explored thoroughly in PTOA Segment #159.
PTOA Readers and Students must invest whatever time and effort is needed to understand the conditions that allow a fluid to swap its velocity for a gain in the PV Pressure.
FLUID PROPERTIES YOU OUGHTA KNOW BY NOW
Describing Fluids with Fluid Properties
The properties of fluids that are listed below are used to describe the expected behavior of one fluid when compared to a different fluid.
The standard fluid which provides the basis from which all other fluid characteristics and properties are defined is Water for liquids and Air for gases (measured at 1 Atm Pressure and a specified Temperature).
Since all rotating equipment adds the PV Pressure to fluids, it would behoove PTOA Readers and Students to become "bilingual" with respect to understanding and expertly using the below list of fluid properties.
Density
The term "Density" was defined in PTOA Segment #145.
The definition expression for Density is:
Density = Mass ÷ Volume
PTOA Readers and Students learned that any expression of a Mass divided by a Volume is describing the Density of the mass ... be it a mass of solid or liquid or a gas.
Closer scrutiny of the Density definition reveals that the Density of a substance can change in the following ways:
For example ...
The visual aid that was used to illustrate Charles' (common sense) Gas Law in PTOA Segment #152 clearly showed how a change in the PV Temperature causes a change in the Volume of a gas.
Although it wasn't brought up at the time and saved to this very moment ...
The PV Temperature-Volume relationship observed by Charles also applies to liquids; the Volume change for liquids is not as dramatic compared to gases but nevertheless is sufficiently significant for some liquids to be useful.
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order learned way back in PTOA Segment #98 that liquid-in-glass Temperature measuring instruments ... aka "common glass Thermometers" ... work because the enclosed liquid mercury expands and contracts according to the heat transferred into or out of it.
So the general cause-effect statement between a changing PV Temperature and the Volume of a fluid can be stated in shorthand:
Fluid Temperature ↑ = Fluid Volume ↑
and vice versa:
Fluid Temperature ↓ = Fluid Volume ↓
Wow!
That must mean that the change in Temperature which causes a Volume change in a fluid must also change the Volumetric Flowrate of the fluid ... for example the gallons per minute being pumped through a pump!
Yes Indeedo!
The above cause-effect relationship can be expanded:
Fluid Temperature ↑ = Fluid Volume ↑ & Volumetric Flowrate ↑
and vice versa:
Fluid Temperature ↓ = Fluid Volume ↓ & Volumetric Flowrate ↓
Connecting even more dots ...
The change in PV Temperature that causes a change in Volume and Volumetric Flowrate must also cause a change in the fluid's Density!
Righteeo!
Density =
Mass / Volume
Hence ... the cause/effect relationship on a fluid's properties when the PV Temperature changes can be expanded to:
Fluid Temperature ↑ =
Fluid Volume ↑ & Volumetric Flowrate ↑
& Fluid Density ↓
and vice versa:
Fluid Temperature ↓ =
Fluid Volume ↓ & Volumetric Flowrate ↓
& Fluid Density ↑
Specific Gravity
The fluid property called Specific Gravity was also defined in PTOA Segment #145.
PTOA Readers and Students learned that Specific Gravity was simply a quickie way to evaluate the relative density of a gas or liquid compared to the density of water (for liquids) and air (for gases) measured at standard conditions.
PTOA Readers and Students who put their thinking caps on can easily figure out why the cause-effect relationship string that results when the PV Temperature changes can be expanded as shown below to include the impact on Specific Gravity:
Fluid Temperature ↑ =
Fluid Volume ↑ & Volumetric Flowrate ↑
& Density ↓ & Specific Gravity ↓
and vice versa:
Fluid Temperature ↓ =
Fluid Volume ↓ & Volumetric Flowrate ↓
& Density ↑ & Specific Gravity ↑
In summary, PTOA Readers and Students must understand the impact of the PV Temperature changes on the above fluid properties ... and one more ... Viscosity.
Viscosity
Although it wasn't emphasized at the time and saved for this very moment, PTOA Readers and Students were introduced to the fluid property Viscosity in PTOA Segment #145.
PTOA Readers and Students were asked to consider which liquid would flow faster ... honey or water?
The Viscosity of a liquid characterizes how easily the fluid will flow.
However those who defined Viscosity must have been glass-half-empty folks because they defined it in terms of "a fluid's resistance to flow."
Basically the more goopy looking a fluid, the longer time it will take to pour. This "resistance to flow" means that the Viscosity of a goopy fluid will be greater than the Viscosity of a different fluid that is observed to flow more freely.
Honey takes a longer time to pour than water. Therefore Honey is more viscous than water.
The nearby chart shows that honey and corn syrup are 2000 to 3000 times more viscous than water (measured at 70 °F).
Viscosity is yet another fluid property that is definitely impacted by Temperature ... think about how much easier honey or syrup flows when it is heated and how much harder it pours when first removed from a refrigerator.
Viscosity is typically measured in centistokes (cSt); The amount of cSt measured for cool honey will decrease as the honey is warmed up.
So the final cause-effect relationship string that shows the impact of Temperature on fluid properties is:
Fluid Temperature ↑ =
Fluid Volume ↑ & Volumetric Flowrate ↑
& Density ↓ & Specific Gravity ↓ & Viscosity ↓
and vice versa:
Fluid Temperature ↓ =
Fluid Volume ↓ & Volumetric Flowrate ↓
& Density ↑ & Specific Gravity ↑ & Viscosity ↑
Fluid Properties and Phenomena Related to a Gas/Liquid Interface
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order have already devoted brainwork contemplating what happens at the liquid/vapor interface of a liquid that is stored in a container.
The Vapor Pressure that is created by the gas/vapors that linger above the liquid level can have a significant impact on Centrifugal Pump operations.
Ergo, it is worthwhile to review the below liquid/gas interface case studies to completely understand how a Centrifugal Pump works.
Case 1: The Total Pressure Exerted By A Gas Blanketed Tank
In PTOA Segment #147, PTOA Readers and Students learned that a gas blanket ...
typically nitrogen or in some cases natural gas ...
is purposely piped into a tank to occupy the vapor space above the liquid level and thereby intentionally prevent the volatile liquid from interacting with the oxygen content in air.
The pressure of the blanket is regulated and typically stated as a gauge pressure (psig).
PTOA Readers and Students must always remember to take the gas blanket pressure into account when determining the Total Pressure exerted on the bottom of the tank.
The Total Pressure exerted on the bottom is determined by adding the gas blanket pressure to the head pressure generated by the liquid.
Total Pressure exerted on Bottom of Tank =
(S.G. * 0.433 lb_{f}/ft * h (ft)) + Blanket Pressure (psi)
PTOA Readers and Students who do not understand the above paragraphs absolutely must return to the beginning of the PTOA PV Pressure Focus Study Area at this juncture.
Case 2: The Total Vapor Pressure exerted on the Liquid Level
When there is no gas blanket, the vapor space is filled with a combination of vaporized gas particles that have escaped from the liquid mixture's surface.
The Pressure that is generated by the vaporized liquid particles and which is exerted on the liquid level is the "Total Vapor Pressure of the liquid."
The Total Vapor Pressure of the liquid must likewise be taken into account when determining the total PV Pressure exerted on the bottom of a tank.
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order have already been introduced to the concept of an individual component's vapor pressure:
PTOA Readers and Students learned that Dalton's Gas Law of Partial Pressures determines the Total Vapor Pressure exerted on a liquid level by adding up the individual Vapor Pressure contributions from each component in the liquid mixture.
The example liquid mixture that was used to define and explore the Total Vapor Pressure that hovered above a liquid level was a simple binary mixture of two components, Hexane and Heptane.
Not clarified at any previous point and saved to define exactly right now is how the individual component Vapor Pressure is determined.
The fluid property called "Vapor Pressure" is determined by measuring the pressure that a gas/vapor exerts on the liquid surface of a container that is storing just the pure liquid component.
The container is held at a constant reference Temperature while the Vapor Pressure measurement is recorded.
A high Vapor Pressure indicates the tendency for the liquid to easily change into its vapor state.
A table or graph of compared components and their individual Vapor Pressures quickly reveals which components will most easily vaporize and therefore be present in a higher concentration in the vapor state that hovers above the liquid level of a mixture.
Here are more Vapor Pressure Fun Facts:
So, Fred wants to know:
Why do we care about the Vapor Pressure of a gas that will form from a liquid when just liquid is supposed to be flowing through a Centrifugal Pump?
The question practically answers itself; the main goal of successfully operating a Centrifugal Pump is to make certain the fluid flowing through it remains in the liquid state and thus prevent the formation of bubbles from vaporizing liquid.
The pump impeller in the nearby photo was not so lucky.
TAKE HOME MESSAGES: PTOA Readers and Students must expertly understand the fundamentals related to the PV Pressure so that they can apply the fundamentals to the operation of Centrifugal Pumps ... and other types of rotating equipment.
Liquids are defined by the following characteristics, all of which are impacted by a change in the PV Temperature.
A Cause-Effect statement is a string of relationships that uses arrows to easily indicate how a change in a Process Variable ... for example, Temperature ... will impact other properties ... for example, the properties of fluids.
The Vapor Pressure of a liquid component is the pressure that its vaporized particles will exert on the surface of a stored sample of the pure liquid ; the Temperature at which the Vapor Pressure is measured must be recorded because Vapor Pressure changes with Temperature.
Vapor Pressure is inversely related to Boiling Point Temperature; Liquid components with high Vapor Pressures will have low Boiling Point Temperatures and vice versa.
The Total Vapor Pressure of a mixture is the additive vapor pressure contribution from each component in the mixture.
If the PV Pressure of a pumped fluid decreases below the Total Vapor Pressure of the pumped fluid, the lightest components in the pumped fluid will start vaporizing and ruin the impeller of a Centrifugal Pump.
©2017 PTOA Segment 0162
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study
The post YOU OUGHTA KNOW BY NOW! appeared first on The Process Technology and Operator Academy.
]]>The post THE RELATIONSHIP BETWEEN PROCESS OPERATORS & ROTATING EQUIPMENT appeared first on The Process Technology and Operator Academy.
]]>You and me chasing paper
Getting nowhere
On our way back home
We're on our way home
We're on our way home
We're going home
("Two of Us," by The Beatles, 1971)
INTRODUCTION TO ROTATING EQUIPMENT
We have arrived!
The time has come for PTOA Readers and Students to learn about Rotating Equipment ... the complex and expensive process industry equipment that increases the PV Pressure within fluids and thus keeps those fluids flowing through pipes.
The important relationship between the Process Operator and Rotating Equipment goes like this:
The Process Operator who competently understands how Rotating Equipment fundamentally works will properly start up, daily monitor, and properly shutdown the Rotating Equipment and its Auxiliary Systems.
Plant Managers have demanded that Process Technology instruction include a thorough exploration of Rotating Equipment because ...
No PV Pressure → No ΔP.
No ΔP → No Fluid Flow.
No Fluid Flow → Plant Shutdown!
PTOA Readers and Students who embrace learning the myriad of details related to Rotating Equipment will gain knowledge that is both desired by Plant Managers and useful at the processing plant.
So hang in there ... because it's going to get wonky!
ONWARD!
What is meant by "Rotating Equipment?"
The PV Pressure in fluids is increased by movement that can be described as spinning around in circles ...
OR ...
"repetitious displacement" ... which means the process fluid is pushed out of its container by more of the same process fluid.
Because of the required repetitious movement, the equipment that increases the PV Pressure is called "Rotating Equipment."
Rotating Equipment is "Coupled With" A Driver
A Driver is needed to provide the motive force that makes the spinning and displacing motion possible.
Examples of Drivers are Electric Motors and Steam Turbines.
The Driver and Rotating Equipment are carefully matched and "coupled together."
The device called a Shaft Coupling transmits power from the Driver (aka "primary mover") to the Rotating Equipment (aka "driven machine").
Axial and Thrust Bearings
Without any restraint, the constant spinning and displacing motions would create axial thrust and outward radial forces. Eventually, the excessive vibration would cause equipment failure.
Axial Bearings and Thrust Bearings are important components that adorn the Rotating Equipment shaft and offset undesired axial and thrusting motion.
Lubrication Reduces Friction
Lube Oil is required to lubricate the hardware components and any metal-to-metal contact area.
Circulating lubrication oil reduces friction as well as removes heat and dirt from the working surfaces of the Rotating Equipment.
Lube oil is selected to accommodate its intended service; a variety of chemical additives like Viscosity Index Improvers, Anti-Foam Agents, Anti-Rust/Corrosion Inhibitors, etc. may be added to it.
So a Lubricating Oil System is a complete subsystem ... aka Auxiliary System ... that is required to support Rotating Equipment.
Preventing Process Fluid Leakage
Assuming the Rotating Equipment is not a vacuum-creating pump ...
The process fluid that is being pressurized will be at a higher PV Pressure than the atmospheric pressure that surrounds the Rotating Equipment-Driver assembly.
The ΔP that results will thus favor leaking the process fluid from the internals of the Rotating Equipment to the lower pressure of the surrounding environment.
Therefore ...
Seal Oil is use to prevent the process fluid from leaking into the atmosphere.
Alternatively, a mechanic means like mechanical seals, O-rings, and glands may perform the sealing function.
In some applications, the lube oil can meet the specifications of the seal oil.
When that is not the case, a separate Seal Oil Auxiliary System must likewise be installed to support the Rotating Equipment.
Gee!
It sure takes a lot of supporting components and auxiliary systems to create what would otherwise be the simple spinning and repetitive displacement motion that increases the PV Pressure in fluids!
That's why Mechanic Techs and Process Operators must freely communicate and work together to extend the working life of Rotating Equipment.
COMMON PROCESS INDUSTRY "ROTATING EQUIPMENT"
Examples of Rotating Equipment and their uses are:
Turbines are Rotating Equipment AND Drivers!
Steam and Gas Turbines are Rotating Equipment Drivers because the spinning motion they produce provides the motive force that drives a coupled piece of Rotating Equipment.
Since the spinning rotation of Turbines can be increased and decreased, Turbines are typically installed when there is a need for a Variable Speed Driver.
THE PTOA PV PRESSURE ROTATING EQUIPMENT FOCUS STUDY CONTENT
This PTOA PV Pressure Rotating Equipment Focus Study will feature Pumps, Compressors, and Steam Turbines.
(Natural) Gas Turbines (GTs), Water Turbines, and Wind Turbines will be featured in the future PTOA Electricity Generation and Distribution Focus Study Area.
The modern Process Operator is expected to possess core competency with respect to identification of Rotating Equipment internal hardware and understanding the purpose of each component.
In addition, modern Process Operators must understand the following terms and how they each impact proper operations of Rotating Equipment:
Pumps: Affinity Laws, Cavitation, PD Safety Pressure Relief, Fluid Viscosity, Internal Fluid Slip, Available and Required Net Positive Suction Head (NPSH), Preparing Pumps for Maintenance, Priming, Pump Characteristic Curve, Pump Efficiency, Pump Failure Causes and Troubleshooting, Total Head, Vapor Pressure of Pumped Fluid.
Compressors: After Coolers, Compressor Efficiency, Compressor Failure Causes, Interstage Cooler, Dryers and Flash Drums, Failure Causes and Troubleshooting, Internal Slip, PD Safety Pressure Relief, Discharge/Suction Pressure Ratio, Snubbers, Surge Awareness and Control.
Steam Turbines: Governor, Heat Soaking, Hunting, Overspeed Trip, Sentinel valve, Steam Quality/Steam Trap, Thermal Shock Avoidance.
EVERYTHING ELSE IS CLASSIFIED AS "STATIONARY EQUIPMENT"
Since Rotating Equipment has been defined, this is about as good a place as any to describe the other category of process industry equipment, "Stationary Equipment."
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order already possess a core competent understanding of the Stationary Equipment that is associated with the PV Temperature, for example:
The future PTOA PV Flowrate Focus Study Area will feature the Stationary Equipment that distributes the fluids that flow throughout the processing complex:
The future PTOA PV Level Focus Study Area will feature the Stationary Equipment that contains and separates fluids into separate phases:
The future PTOA Process Industry Systems Focus Study Area will illustrate how each of the common examples of Stationary Equipment are incorporated into value-added processing systems.
TAKE HOME MESSAGES: Rotating Equipment increases the PV Pressure in fluids.
Process Operators must understand the fundamental operating theory of Rotating Equipment so that they are aware how to properly start up, daily monitor, and shutdown the equipment and associated Auxiliary Equipment.
Modern Plant Managers demand that modern Process Operators competently understand the design and efficient operation of Rotating Equipment.
The movement that increases the PV Pressure in Rotating Equipment is simple spinning or repetitious displacement of the process fluid ...
However, successful operation of Rotating Equipment requires complex technology so that the simple movement will be sustained:
All Rotating Equipment is carefully coupled to and aligned with a Driver that provides the motive force which creates the spinning or displacement movement.
Examples of Drivers are Electric Motors and Steam Turbines.
The Shaft Coupling has the important duty of transferring power from the Driver (aka "primary mover") to the Rotating Equipment (aka "driven machine").
Pumps and Compressors are common Rotating Equipment which is installed to increase the PV Pressure in process fluids so that they can flow and circulate throughout a processing facility.
Steam Turbines, Water Turbines, and Wind Turbines are examples of Variable Speed Drivers that are coupled to drive a different piece of Rotating Equipment ...
For example, a Steam Turbine, Gas Turbine, and Wind Turbine can spin an electricity generator.
The other general classification of process industry equipment is "Stationary Equipment." PTOA Readers and Students already possess a core competent understanding of the Stationary Equipment that is associated with the PV Temperature.
©2017 PTOA Segment 0161
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study
The post THE RELATIONSHIP BETWEEN PROCESS OPERATORS & ROTATING EQUIPMENT appeared first on The Process Technology and Operator Academy.
]]>The post THE RELATIONSHIP BETWEEN THE PV PRESSURE + THE PV LEVEL appeared first on The Process Technology and Operator Academy.
]]>("Mother Nature's Son," by the Beatles, 1968)
THE PROCESS VARIABLE LEVEL
The obvious prerequisite to understanding how the PV Pressure interfaces with the PV Level is to be knowed-up on what is meant by the phrase "PV Level."
The PV Level applies to a liquid level ...
and sometimes even a solid level ... for example ...
The HMI screen of a DCS control system shown below displays an FCC Reactor (right) and its Catalyst Regenerator (left).
The PV Level of the catalyst in each vessel is represented as a "dipstick" outlined in blue with variable white light area which the Control Board Operator can easily interpret with one glance to be a current PV Level indication of 75% in both vessels.
The point is that the PV Level does not apply to gases or vapors.
A gas or vapor would have to condense into its liquid form before the PV Level would apply.
And the above statement provides the perfect segue to begin focusing on the two relationships between the PV Pressure and the PV Level.
TWO IMPORTANT PV PRESSURE + PV LEVEL RELATIONSHIPS
The PV Pressure has two important relationships with the PV Flowrate and the same can be said with respect to the PV Level.
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order already learned in PTOA Segment #146 that the liquid stored in any container creates a hydrostatic head and a Pressure Profile which is minimum at the liquid's surface and maximum at the bottom of the container.
In the future PTOA PV Level Focus Study Area, PTOA Readers and Students will learn how the hydrostatic head Pressure of a contained liquid can be used to monitor the changing PV Level in a tank.
Sneak Preview:
The tank is calibrated so that the maximum hydrostatic head Pressure will be indicated as a 100% Level (right side of above graphic) which declines linearly to 0% Level as the hydrostatic head likewise declines (left side of the above graphic).
The remainder of this PTOA Segment #160 is dedicated to exploring the second important PV Pressure + PV Level relationship which is a bit more complex as it only occurs when a "saturated vapor" occupies the vapor space above its corresponding "saturated liquid."
QUICKIE REVIEW OF SATURATED LIQUIDS AND THEIR VAPORS
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order were first introduced to the classic example of a saturated liquid and its vapor while learning how Saturated Steam is generated from Boiler Feed Water (BFW) in a Package Boiler (featured in PTOA #26).
So PTOA Readers and Students already know that steam is none other than the vapor/gas that hovers above the surface of its liquid form ... which is known as Boiler Feed Water (BFW).
In the Steam Drum, the BFW water droplets at the surface of the BFW are just as likely to vaporize into steam as the steam particles above the BFW surface are likely to condense back into BFW ...
Hence .. the criteria to meet the fancy scientific phrase ... "a saturated liquid in equilibrium with its saturated vapor" have been met!
And logically ...
Since there is the same amount of vaporizing and condensing going on between the saturated liquid and the saturated vapor ...
The PV Level of the BFW in the Steam Drum does not change at all. Like, Duh!
Of course there is itty, bitty caveat:
Were it not for the BFW being added to the Steam Drum to balance the flow of the Saturated Steam product exiting the Steam Drum ...
The PV Level of the Steam Drum most certainly would decrease!
With that important caveat understood, the Steam Drum of a successfully operating Package Boiler still provides a go-to example of "a saturated liquid/vapor system that is in equilibrium between the two phases."
But what happens when the PV Pressure of the Boiler is increased or decreased?
Guess what?
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order already know the answer to that question!
THE RELATIONSHIP BETWEEN THE PV PRESSURE AND THE PV LEVEL
PTOA Readers and Students just recently learned in PTOA Segment #157 that an increase in the PV Pressure over a boiling pot of water will require a simultaneous increase in the PV Temperature if the goal is to keep the water boiling ... aka changing state into its corresponding vapor composition.
Thus, in the absence of a simultaneous increase in the PV Temperature ...
PTOA Readers and Students can conclude the same outcome for ANY saturated system of water and vapor:
An increase in the PV Pressure will make it harder for water droplets to vaporize into Saturated Steam.
Since less BFW can vaporize into the vapor state, the PV Level in the Steam Drum will increase.
Likewise ...
When a decrease in the PV Pressure of the Steam Drum occurs with no compensating decrease in the PV Temperature ...
the water droplets feel less pressure above them and are more able to vaporize into the Saturated Steam phase thus decreasing the PV Level in the Steam Drum.
In other words, the PV Pressure + PV Level relationship of any saturated liquid/vapor system in equilibrium can be summarized:
WHEN PV PRESSURE ↑, THEN PV LEVEL ↑
WHEN PV PRESSURE ↓ , THEN THE PV LEVEL ↓
Spoiler Alert:
So ... who amongst the brilliant PTOA Readers and Students would be surprised to learn that the modern automatic control scheme on a Package Boiler:
THE RELATIONSHIP BETWEEN THE PV PRESSURE + PV LEVEL
APPLIES TO ANY LIQUID/VAPOR EQUILIBRIUM
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order have already learned what happens to a saturated vapor that is occupying the space above a saturated liquid when there is more than one component in the both phases.
In the very recent PTOA Segment #157, PTOA Readers and Students learned that a multi-component mixture of n-hexane and n-heptane could be physically separated from each other because of the variance between their Boiling Point Temperatures.
Therefore no PTOA Reader or Student will be surprised to learn that ...
In the absence of a corresponding increase in the PV Temperature applied to a multi-component saturated liquid/vapor system ...
An increase in the PV Pressure results in an increase in the PV Level because neither the n-hexane or the n-heptane can vaporize as easily as they could prior to the PV Pressure increase.
and vice versa ...
A decrease in the PV Pressure results in a decrease in the PV Level because both the n-hexane and n-heptane can vaporize more easily than they could prior to the PV Pressure decrease.
In summary ... the same rule applies for any multi component system that has a saturated liquid and its corresponding saturated vapor on the verge of vaporizing or condensing at equal rates ...
WHEN PV PRESSURE ↑, THEN PV LEVEL ↑
WHEN PV PRESSURE ↓ ,THEN PV LEVEL ↓
And that statement applies even when there are dozens and dozens of components in the liquid and vapor phases.
Control Board Operators Must Beware!
The change in the PV Level will not be instantaneous because it takes time for the liquid/vapor system to reach a new equilibrium.
Also ... since vapors/gases have much more space between particles ...
it takes a LOT of vapor/gas condensing to noticeably change the saturated liquid's level.
CONCLUSIONS OF THE PV PRESSURE + DIFFERENT PV FOCUS STUDIES
That's it!
PTOA Readers and Students have learned all about how the PV Pressure interacts with the PV Temperature, the PV Flowrate, and the PV Level ...
and are now ready to move on and learn about the process industry equipment that is purposely purchased and installed to create, maintain, or decrease the PV Pressure in an industrial complex.
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order are ready to move on because they possess a core competency with respect to the PV Pressure Fundamentals and understand the following PV Pressure relationships with:
TAKE HOME MESSAGES: The phrase "PV Level" refers to a liquid ... and sometimes a granular solid ... but not to a gas or vapor.
There are two important PV Pressure + PV Level relationships.
#1. The hydrostatic head of a contained liquid creates a Pressure and Pressure Profile that can be used to measure and monitor the PV Level of the liquid that is contained.
#2. When a liquid/vapor system is in equilibrium:
PTOA Readers and Students can now predict how the PV Pressure will interact with the PV Temperature, PV Flowrate, and PV Level.
The next section in the PV Pressure Focus Study Area features the process industry equipment that is intentionally purchased and installed to increase, maintain, and decrease the PV Pressure in the processing complex.
©2017 PTOA Segment 0160
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Interrelationship with PV Level
The post THE RELATIONSHIP BETWEEN THE PV PRESSURE + THE PV LEVEL appeared first on The Process Technology and Operator Academy.
]]>The post THE PV PRESSURE ↔ FLUID VELOCITY SWAP appeared first on The Process Technology and Operator Academy.
]]>("Will It Go Round in Circles," Billy Preston & B. Fisher, 1973)
THE PV PRESSURE SWAP WITH FLUID VELOCITY
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order just learned in PTOA Segment #158 that the PV Flowrate is totally dependent upon a Pressure Differential (aka ΔP) to exist.
There is a second crucial relationship between the PV Pressure and the Velocity component of the PV Flowrate:
An increase in the Velocity of a flowing fluid will result in a decrease of the fluid's PV Pressure and then ...
The recovery and increase of the PV Pressure in the flowing fluid will result in a corresponding decrease of its Velocity.
Oh no.
Fred's a little confused and getting jittery.
But he won't be after finishing this PTOA Segment #159 which is dedicated to defining and understanding
The PV Pressure ↔ Fluid Velocity Swap!
THE PV (VOLUMETRIC) FLOWRATE HAS TWO COMPONENTS:
VELOCITY AND (FLOW THROUGH) AREA
By now, PTOA Readers and Students could create a Power Point presentation in their sleep that explains the dependent relationship between the PV Flowrate and ΔP.
A quality presentation would not fail to mention that the Universe demands that this dependent relationship apply to ALL flowing fluids, not just those confined to flow within the pipes of a processing facility.
Heck ...
It's easier to observe the PV Pressure - PV (Volumetric) Flowrate relationship in nature because nobody has x-ray vision to see what's going on in all those pipes!
For example ...
All rivers also flow from an area of HIGH PRESSURE to an area of LOW PRESSURE.
In fact,
a "river" that is not flowing because of loss of ΔP is not a river at all but rather what we Earthlings recognize as the pooled water of "a lake!"
The "Flowrate" of a river is what we Earthlings call "a current."
Yet the current of a river is none other than how fast the water is flowing ... aka its Velocity.
The river's Velocity ..."V" ... is one of the two components that comprise its (Volumetric) Flowrate, "Q."
The other component of "Q" is (Flow Through) Area, "A."
Multiplying the Velocity and (Flow Through) Area of any flowing fluid results in quantifying its Volumetric Flowrate "Q" in units of Volume/time ...
like "standard cubic feet per hour" (scft^{3}/hr) or "cubic meters per hour" (M^{3}/hr) which could be converted into English unit equivalents of, say, "barrels per day" (Bbls/day) or "gallons per hour" (gal/hr).
The units are consistent on both sides of the expression that defines "Q" because:
Velocity is measured in units of length per unit time ...
For example "feet/min" or "feet/sec" or "meters/minute" or "meters/sec."
And (Flow Through) Area is exactly what it says it is ...
the cross-sectional area that the fluid is flowing through! Like, Duh!
As you would expect ...
the (Flow Through) Area is measured in units of area ... like "ft^{2}" or "m^{2}."
It's a little tricky to calculate the exact (Flow Through) Area for riverbeds because they are basically partially filled ducts ... and the geological features below the surface of the water must be taken into account because they impact the total (Flow Through) Area.
Fortunately a study of current flow (aka river Velocity) can help reveal what lies beneath the river surface that obstructs flow!
A STUDY OF A RIVER'S FLUID VELOCITY
The Santa Clara River graphic below colorfully depicts how the Velocity of the Santa Clara River changes as it flows through several of its bends.
Aha!
The dark blue color that indicates the fastest river Velocity always occurs where the river has a "pinch point" ... a place where the width of the river narrows.
Why does the Velocity of the flowing river increase at a pinch point?
If the river Velocity did not increase at a pinch point, then the flowing water would "bunch up" and flood the surrounding area.
The high dollar instructional jargon word to use here is "continuity" as in:
To maintain the overall flow continuity of the river, the river's Velocity changes with the width of the river;
The river's Velocity increases when the width of the river narrows and decreases when the width of the river widens.
THE OBSERVATIONS OF A FLOWING RIVER DIRECTLY APPLY TO A FLUID THAT FLOWS THROUGH A RIGID PIPE
PTOA Readers and Students should not be at all surprised to learn that the Velocity behavior observed with the flowing Santa Clara River is the same Velocity behavior that would be observed in the fluids that flow through all the processing pipes ... if we just had the x-ray vision to look inside the mess of pipes that distribute all those fluids from one processing point to the other!
There is one noteworthy difference between the two case studies:
The (Flow Through) Area of a rigid metal or plastic pipe is constant and determined from the interior pipe radius.
So the (Flow Through) Area of any pipe is easy to calculate because it is simply the area of the circle with the interior diameter (and hence radius) of the pipe:
(Flow Through) Area = π * (Internal Radius of Pipe) ^{2}
Since the (Flow Through) Area is unchangeable, only the Velocity component of the PV (Volumetric) Flowrate "Q" can change in a fluid-filled pipe.
So the "Velocity Profile" that the flowing fluid develops is caused by only the fluid's Velocity and looks like the schematic below:
Brilliant PTOA Readers and Students will notice these similarities between the above Velocity Profile graphic and the map of the Santa Clara River current:
If we were to apply color mapping to define the fluid Velocities shown in the above rigid pipe graphic the result would be something like this:
The red flow at the center would have the fastest Velocity.
The yellow flow that radially surrounds the red area would have the next fastest Velocity.
The green area that radially surrounds the yellow area would have a slower Velocity than the yellow Velocity area ... but a greater Velocity than ...
The light blue Velocity area which radially surrounds the green area. This radial area has the slowest fluid Velocity area because it is hung up by friction while interacting with the dark blue interior wall.
Take another look at the flow gushing from the pipe in the nearby photo.
Who can discern the "Velocity Profile?"
The trained eye can discern the significantly greater Velocity of the water that protrudes outward from the center of the pipe as compared to the Velocity of the water that is hindered by friction at the wall of the pipe.
If that "Velocity Profile" was too hard to see ... can you discern the "Velocity Profile" of the fluid flowing through the laboratory-study glass pipe below?
The "Velocity Profile" can be seen fully developed on the far right side of the photo; its cone shape looks remarkably like the graphic below:Congratulations!
All PTOA Readers and Students just learned how to identify what is called "Laminar Flow" and now know that it can be identified by:
Now ... let's throw a monkey wrench into this perfect Laminar Flow "Velocity Profile" by changing the diameter of the pipe that the fluid must flow through!
TA-DA! THE PV PRESSURE ↔ FLUID VELOCITY SWAP
Which brilliant PTOA Readers and Students wish to predict what will happen to the Velocity of a flowing fluid when the diameter of the rigid pipe is swaged down into a tighter throat?
Hint! Remember the concept of "continuity" ... the fluid is not allowed to "bunch up" when the (Flow Through) Area is reduced.
Who thinks the fluid Velocity will increase as it did in the Santa Clara River?
If you said YES INDEEDO then you are CORRECTAMUNDO!
The above graphic illustrates how the fluid's Velocity and the PV Pressure swap in magnitude as they pass through an area of restriction.
The graphic shows:
The PV Pressure indicators and Velocity meters tell the following tale:
While passing through the restriction, the fluid's Velocity increases temporarily while the PV Pressure decreases.
Once further "downstream" from the restriction, the fluid's PV Pressure increases and recovers to where it was originally as the fluid's Velocity decreases to where it had been originally.
This swapping of the PV Pressure for an increase in fluid Velocity ... and back again is called
THE PV PRESSURE ↔ FLUID VELOCITY SWAP
Got it, Fred?
THE POWER OF THE SWAP
Mankind has learned how to harness the power of the PV Pressure ↔ Fluid Velocity Swap to create amazing process technologies.
The PV Pressure ↔ Fluid Velocity Swap is used to measure the PV Flowrate of gases or liquids ... as long as the fluids meet the criteria that characterizes "Laminar flow."
In the future PTOA PV Flowrate Focus Study Area, PTOA Readers and Students who desire to know more about automatic instrumentation ...
will learn how an intentionally placed restriction in the path of a fluid that meets the criteria of Laminar flow ....
can utilize the pressure-change to generate a head measurement which can thence be converted into a PV Flowrate measurement!
My, my that's pretty nifty!
Another nifty use of the PV Pressure ↔ Fluid Velocity Swap is adding Pressure to liquids.
In the relatively recent PTOA Segment #153, PTOA Readers and Students learned that gases are compressible but liquids are not.
Since compression won't work to increase the PV Pressure of a liquid, Mankind has ingeniously harnessed the power of the PV Pressure ↔ Fluid Velocity Swap to build up the PV Pressure of a liquid by decreasing the liquid's Velocity.
Centrifugal Pumps will be featured soon in this PTOA PV Pressure Focus Study Area. Stay tuned!
ANSWER TO DIY IN PTOA SEGMENT #158:
Is there flow going through this pipe?
The pipe is pressurized with a fluid but is currently blocked in from any flow. We can conclude that there is no flow ongoing through the pipe because there is no pressure drop in the line. No pressure drop, no flow!
If so, in what direction is the flow going?
Since there is no flow through the pipe, there is no direction to the flow.
When flow commences in the future, the flow will be from the source of higher pressure ...
For example, if the fluid in the pipe is a liquid ...
The source of high pressure might be from the head pressure provided by a liquid filled tank or from the discharge of a pump.
If the fluid in the pipe is a gas, the source of high pressure might be from the discharge of a compressor.
TAKE HOME MESSAGES: The purpose of PTOA Segment #159 was to explore the second important PV Pressure - PV Flowrate relationship ... the PV Pressure ↔ Fluid Velocity Swap.
Simply stated, the PV Pressure ↔ Fluid Velocity Swap is the exchange of increased flow Velocity with decreased PV Pressure observed when a fluid flows through a restricted area.
Further downstream from the restriction, the PV Pressure increases ... or "swaps back" ... until it is restored to its original amount while the Velocity of the fluid correspondingly decreases ... or "swaps back" ... to its original amount.
The PV Pressure ↔ Fluid Velocity Swap ensures continuity of fluid flow even when the area of flow is decreased ... or increased.
Process technologies have harnessed the power of the PV Pressure ↔ Fluid Velocity Swap to:
Subject matter that supported full comprehension of the PV Pressure ↔ Fluid Velocity Swap included:
The two PV Pressure-PV Flowrate relationships featured in PTOA Segments #158 and #159 universally apply to freely flowing fluids AND fluids that flow through rigid plastic and metal pipes.
Without x-ray vision, the PV Pressure-PV Flowrate relationships cannot be observed at the processing plant but can be observed in freely flowing fluids.
©2017 PTOA Segment 0159
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Interrelationship with PV Flowrate
The post THE PV PRESSURE ↔ FLUID VELOCITY SWAP appeared first on The Process Technology and Operator Academy.
]]>The post THE RELATIONSHIP BETWEEN THE PV PRESSURE + THE PV FLOWRATE appeared first on The Process Technology and Operator Academy.
]]>I can't live if living is without you
I can't live, I can't give anymore
I can't live if living is without you
I can't give, I can't give anymore
("Without You," P.Ham & T. Evans of Badfinger, 1971)
NO CHANGE IN PRESSURE? THEN NO FLOW!
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order know that this PTOA Segment #158 is the second in a series that focuses on the interrelationship between the PV Pressure and another PV ... in this case the PV Flowrate.
Actually ...
There are two crucial relationships between the PV Pressure and the PV Flowrate that will be featured in this and the next PTOA Segments.
Guess what!
The PV Pressure - PV Flowrate relationship is totally one-way!
From the point of view of the PV Flowrate ...
the relationship looks like:
Because ...
The PV Flowrate cannot exist without the PV Pressure!
To be more specific, the PV Flowrate is dependent upon a Pressure Differential ...
which is interchangeably known as:
On the other hand ...
The PV Pressure can and does exist independently without creating the PV Flowrate.
For example,
PTOA Readers and Students already learned in PTOA Segments #146 and #147 that the PV Pressure exists anytime a pooled, homogenous liquid is stored in a container ... like a tank.
So, from the point of view of the PV Pressure, the relationship between the PV Pressure and the PV Flowrate is more like the relationship shown in the nearby photo.
The purpose of PTOA Segment #158 is to clarify the one way relationship between a change in the PV Pressure (aka Pressure Differential) and the PV Flowrate.
QUICKIE REVIEW OF "TRANSPORT PHENOMENA" & THEIR DRIVING FORCES
PTOA Readers and Students were first introduced to the cosmic sounding "Transport Phenomena" that rule the Universe way back in PTOA Segment #57.
"Transport Phenomena" just means that:
Quickie Review of the Heat Transfer and Delta Temperature (ΔT)
When it comes to HEAT that is being "transported" ... aka transferred...
PTOA Readers and Students already expertly understand that HEAT flows from a warmer area to a colder area ...
and that it is the difference in Temperature between the two areas (ΔT) which provides the driving force that automatically results in HEAT being transferred ... or moved ... between the two areas.
Furthermore, the greater the ΔT, the greater the amount of heat that will flow between the two areas over a unit of time ...
until the entire area is at the same final Temperature!
So the driving force for HEAT TRANSFER is the ΔT between the hotter area and the colder area.
PTOA Readers and Students learned all about Heat Transfer in PTOA Segment #58, one of the first focus studies in the PTOA Heat Transfer Focus Study series.
So PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order already thoroughly understand how and why a ΔT provides the driving force for the three methods of HEAT TRANSFER: conduction, convection, and radiation.
Quickie Review of Electrical Current and Delta Voltage (ΔV).
PTOA Readers and Students also learned that a difference in Voltage (ΔV) is needed before electrons can flow around a circuit.
ΔV is often called a "Potential Difference" or even more simply "Potential."
Electrons will always flow from the area of highest voltage (usually supplied by a battery) to an area of less voltage.
Furthermore the greater the ΔV, the greater the amount of current that flows around a circuit.
The relationship between current and ΔV was introduced in PTOA Segment #57 and further explored during PTOA Segment #106 which introduced electrical instruments that measure the PV Temperature.
FLUID FLOW DEPENDS UPON DELTA P (ΔP)
The last "Transport Phenomena" that has many applications in the process industries is the dependence that the PV Flowrate has upon the existence of a Pressure Differential.
Without a Pressure Differential, a fluid Flowrate cannot exist!
PTOA Readers and Students learned a long time ago in PTOA Segment #3 that the term "fluid" applies to both liquids and gas/vapors.
In the much more recent PTOA Segment #140, PTOA Readers and Students learned that ... under certain conditions ...
even solids like catalysts can be made to "fluidize."
In all cases ...
getting a fluidized solid or a liquid or a gas/vapor to flow requires a Pressure Differential.
Beware and always remember!
The term "Pressure Differential" can interchangeably be called:
The other parts of the "Transport Phenomena" also apply to the ΔP - Flowrate Relationship:
MEASURING FLUID FLOWRATES WITH LIQUID HEAD INSTRUMENTS
As all PTOA Readers and Students would expect ...
Mankind has devoted hours observing the relationship between ΔP and Flowrate to whittle it down into a mathematical expression.
The complexity of the final version of the mathematical expression exceeds the purview of the PTOA and is not a requirement for Process Operators to know.
However,
the simplified expression shown below applies when the PV Flowrate is measured via intentionally generating a ΔP from a head of fluid:
PTOA Readers and Students will learn about Flowrate measuring instruments in the PTOA PV Flowrate Focus Study Area that follows the PTOA PV Pressure Focus Study Area.
The terms in the above expression are:
Q ... the VOLUMETRIC FLOWRATE that in the real world is expressed with units like "cubic meters per hour" (M^{3}/hr) or "gallons per hour" (gal/hr) or "cubic feet per hour" (ft^{3}/hr) or "barrels per day" (Bbls/day), etc.
Note that Q is not the same Q that was used in HEAT TRANSFER equations for Btu/hr ... that was a different Q!
K is, of course... another "fudge factor" that helps the units on both sides of the equation work out as well as takes into account stuff like the density of the fluid that is flowing and the diameter of the pipe that the fluid is flowing through.
ΔP is the Pressure Differential (aka Delta P aka dP aka Pressure Drop aka Pressure Gradient) created between taps that are inserted to sense an area of High Pressure and the area of Low Pressure.
Hey!
There's something kind of weird about the ΔP - Flowrate expression above so let's scrutinize it again:
Aha!
The expression clearly shows that the amount of Flowrate (Q) is proportional ...but NOT LINEAR ... to the ΔP that is generated by the head-producing instrument.
Unlike the flow of Heat and its driving force, ΔT ...
Unlike the flow of Current and its driving force, ΔV ...
Flowrate is proportional to the SQUARE ROOT of the ΔP !
To get ΔP out from under the square root sign, both sides of the equation must be squared ... that's just how math works!
That makes ΔP equal to the square of the Flowrate (Q^{2})!
The below graphic shows that version of the ΔP - Flowrate relationship ...
That weird little symbol between both sides of the ΔP - Flowrate expression means "approximates" ...
because once the fudge factor K is taken out of the expression the best one can do is an approximation!
The graphic below is just like the graphic above except that it has a real Flowrate expressed as gallons per minute (gpm).
The ΔP is in units of pounds per square inch (psi).
Your Mentor demonstrated how to convert a liquid head into a psi pressure in PTOA Segment #149.
Nowadays modern Process Operators are not consciously aware that the ΔP - Flowrate relationship is not linear!
Your Mentor is old enough to remember when Flowrates were displayed on square-root chart paper.
But today's modern DCS systems automatically apply a "square root extraction function/algorithm" which modifies the Flowrate standard signal that is transmitted into the modern Man-Machine Interface.
So this linearizing algorithm takes the real-world relationship shown on the left side of the graphic below and straightens it into a one-to-one linear correspondence between the square root of ΔP and Flowrate ... as shown in the right side of the graphic below:
So Your Mentor can't really fault modern Process Operators who never knew or don't remember that when Flowrate is inferred from a Head Instrument ... the Flowrate is proportional to the SQUARE ROOT OF ΔP.
However, Instrumentation Technicians must never forget the special relationship between ΔP - Flowrate because they frequently calibrate flowrate instruments that intentionally generate a liquid head Pressure specifically for the purpose of inferring a Flowrate measurement.
And one thing all of the ΔP - Flowrate graphics above show ...
corrected for square root function or not ...
When the ΔP goes to zero ... so does the Flowrate!
DIY ΔP - FLOWRATE EXERCISE:
So let's see which of the smart PTOA Readers and Students got the main points of the ΔP - Flowrate relationship by answering the following questions:
You are the Outside Process Operator doing rounds checking the local TIs, PIs, and FIs (Flow Indicators).
While checking the below long pipeline you notice that a Pressure Indicator (PI) indicates 150 psi (1034 kPa).
You walk down 200 more feet and notice the next PI that is sensing the pipeline Pressure also indicates 150 psi (1034 kPa).
Is there flow going through this pipe?
If so, in what direction is the flow going?
The answer will be in the next PTOA Segment.
TAKE HOME MESSAGES: The ΔP - Flowrate relationship is the third of three Transport Phenomena that govern how Heat, Current, and now Fluid flow in the Universe ... and therefore also in the process industries.
Flowrate is also known as "Volumetric Flowrate" and has units of Volume divided by time. For example:
The PV Flowrate cannot exist without a Pressure Differential. Otherwise stated, ΔP is the driving force that supports all fluid flow.
The term Pressure Differential can also appear as:
The Flowrate always flows from the area of higher pressure to the area of lower pressure.
The greater the Pressure Differential, the greater the flowrate.
When liquid head Pressure instruments are used to measure Flowrate, the Flowrate is proportional to the square root of the ΔP that is created.
Nowadays, the transmitters which transmit Flowrate measurements as standard signals apply an algorithm called a "square root extractor" that linearizes the Flowrate reading into a one-to-one correspondence with the square root of ΔP.
©2017 PTOA Segment 0158
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Interrelationship with PV Flowrate
The post THE RELATIONSHIP BETWEEN THE PV PRESSURE + THE PV FLOWRATE appeared first on The Process Technology and Operator Academy.
]]>The post THE RELATIONSHIP BETWEEN THE PV PRESSURE + THE PV TEMPERATURE appeared first on The Process Technology and Operator Academy.
]]>Baby's good to me, you know
She's happy as can be, you know
She said so
I'm in love with her and I feel fine
("I Feel Fine," the Beatles, 1964)
THE PV PRESSURE - PV TEMPERATURE RELATIONSHIP
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order are already aware that this PTOA Segment #157 is the first in a series which focusses on the relationship between the PV Pressure and a different process variable ... in this case the PV Temperature.
When the stuff we're talking about is a gas held in a rigid-walled container ...
PTOA Readers and Students have already predicted that an increase in the PV Temperature will cause a corresponding increase in the PV Pressure ... and vice versa.
Yes, indeedo!
Gay Lussac's common sense "Gas Law" was recently featured in PTOA Segment #152 ... so let's not waste paragraphs repeating all that information!
However, the PV Pressure - PV Temperature relationship is very different when the container is holding a liquid that is being heated up to its Boiling Point Temperature.
THIS PTOA Segment #157 begins with focusing on what happens when water is heated in a container ...just as it would be to make a cup of tea at three different worldwide locations:
At sea level in New York City, where the P_{atm} = 14.7 psia (29.92 in Hg = 101.3 kPa = 1 Atm).
For each of the above case studies ...
The Atmospheric Pressure (P_{atm}) above the surface of the water will represent the PV Pressure ...and the increasing Temperature of the heated water will represent the PV Temperature.
MAKING A CUP OF TEA AT WORLDWIDE LOCATIONS
The below graphic illustrates how Altitude (aka "Feet Above Sea Level"), Atmospheric Pressure (aka P_{atm}), and the Boiling Point Temperature of Water are related.
This graphic was prominently featured in PTOA Segment #149 which explained why P_{atm} at sea level is 101.3 kPa = 14.7 psia ... and how it decreases with increasing Altitude.
But why exactly does a change in P_{atm} change the Boiling Point Temperature of Water?
And since it apparently can change ...
What exactly is meant by "Boiling Point Temperature" of a Liquid?
Case Study 1:Boiling Water at Sea Level
Sitting at an altitude of just 10 feet above sea level, New York City is essentially at sea level.
Therefore, the air pressure that surrounds and lingers above the liquid's surface as it is being heated to a boil in NYC is 101.3 kPa (aka 14.7 psia = 29.92 in Hg = 1 Atm).
Before the first water particles on the surface of the water can change their physical state and move into the vapor/gas phase, their pressure must exceed that of the P_{atm} that is pressing down upon them.
Ergo ...
As the water particles absorb the heat that is transferred into them via conduction and convection, their Temperature increases ...
until they have finally absorbed sufficient energy to break their liquid-state bonds ...
and begin to change their physical state into that of a vapor/gas.
The Temperature of the water when vaporization starts happening will be the Boiling Point Temperature of water at sea level ... 100 °C = 212 °F
So the Boiling Point Temperature is the Temperature that the liquid particles attain when the liquid has sufficient thermal energy to do these two things:
Case Study 2: Boiling Water at High Altitude
Now assume that the pot of water being boiled for tea is located at the top of Mt. Sagarmatha (aka Mt. Everest in the nearby graphic).
As the nearby chart shows, the highest altitude of Mt. Sagarmatha is 29,028 feet (8848 meters).
The chart also shows that P_{atm} at this high altitude has decreased significantly from the 101.3 kPa (14.7 psia) measured at sea level to just 32 kPa (aka 4.64 psia = 9.4 in Hg = 0.32 Atm).
OMG!
The P_{atm} at the top of Mt Sagarmatha is slightly less than one-third of what it is at sea level!
Another way to look at it is:
On a barometer, the length of the column of mercury ...
(aka "head of mercury," H) ...
that is used to measure P_{atm} would be just 9.96 in Hg high compared to the 29.92 in Hg head observed at sea level (don't remember that? Go to PTOA Segment # 149).
Ergo ...
The water particles in the teapot have significantly less P_{atm} pressing down upon them and squishing them together while they are absorbing thermal energy from whatever source is supplying heat.
Therefore ...
The water particles do not need to absorb as much heat to get excited and start breaking up the water bonds and ...
now in their newly vapor state ...
the water vapor particles can push through the air pressure that is pressing down upon them.
Thus, the particles of water vapor can mix and mingle with the air particles hovering above the liquid level at a much lower Boiling Point Temperature.
As the chart shows, the Boiling Point Temperature of water on top of Mount Sagarmatha (aka Mt. Everest) is just 70 °C (aka 158 °F).
Aha! A pattern is emerging!
The Boiling Point Temperature of a liquid (in this case water) decreases as the Pressure above the liquid level in the container decreases!
The above conclusion pertains to all liquids ... not just water!
Case Study 3: Boiling Water where P_{atm }is High
The "Siberian High" is a mass of cold, dry air that hangs around Lake Baikal in Russia from September through April.
During this time interval, the P_{atm} is typically 15.23 psia (aka 31 in Hg = 105 kPa = 1.03 Atm).
Wow!
A barometer measuring P_{atm} at sea level is 29.92 in Hg! So the taller mercury head of 31 in Hg that would be measured at Lake Baikal during a "Siberian High" is a noteworthy increase in P_{atm}!
Your Mentor predicts that all smart PTOA Readers and Students can deduce how this significantly higher P_{atm} will impact the Boiling Point Temperature of Water.
Water particles being boiled for tea during the "Siberian High" have a significantly greater pressure above them that must be overcome before they can get sufficiently excited to start changing into the vapor/gas state.
The water particles will need to absorb significantly more thermal energy before they can start to vaporize and join the gas phase that is lingering above the liquid level.
In fact, the water in the teapot where the P_{atm} is 15.23 psia (aka 31 in Hg = 105 kPA = 1.03 Atm) will not begin to boil until 221 °F (aka 105 °C).
Aha! The pattern that emerged above still applies!
The Boiling Point Temperature of a liquid (in this case water) increases as the Pressure above the liquid level in the container increases!
And once again, the important addendum ...
The above conclusion pertains to ALL liquids, not just water!
WHAT IS OBSERVED IN NATURE
IS LIKEWISE OBSERVED IN PROCESS INDUSTRY
The Pressures that are created in the process industries via mechanical means are much greater and much lower than the Atmospheric Pressure (P_{atm}) that is measured with a barometer at different altitudes on the Earth's surface.
Yet, the above relationship that was observed to naturally exist between the PV Pressure (represented as P_{atm}) and the PV Temperature (represented as the Boiling Point Temperature of water) universally applies to Pressures that are created by mechanical means:
The higher the PV Pressure in the Vessels and Towers and Tanks that are used in the process industries to contain liquids ...
the greater the Boiler Point Temperature that will be required to convert the contained liquids into gases .. and vice versa!
REAL WORLD EXAMPLES
OF THE PV PRESSURE - PV TEMPERATURE RELATIONSHIP
APPLIED IN THE PROCESS INDUSTRIES
PV Pressure and Water Tube Package Boilers
PTOA Readers and Students learned all about boilers in PTOA Segments #24 and #25.
The Operating Pressure (PV Pressure) of a water tube boiler that is sized to generate 4 million pounds of steam per hour could easily be 2321 psi (aka 16.2 MEGAPascal = 158 Atm = 160 Bar).
On any scale of measurement ... that's a high pressure! A lot more pressure than P_{atm} at any altitude on Earth!
So who amongst the brilliant PTOA Readers and Students would be surprised to learn that the water in this boiler will not be able to boil and start turning into steam until the Operating Temperature (PV Temperature) is around 1022 °F (550 °C).
Wow!
That's a lot higher Boiling Point Temperature than the 212 °F (100 °C) observed at the sea level P_{atm} = 14.7 psia!
PV Pressure and Atmospheric Crude Towers
PTOA Readers and Students were first introduced to the (Atmospheric) Crude Tower Distillation process way back in PTOA Segment # 34 which focused on shell and tube heat exchanger trains.
Much more recently, PTOA Segment #154 explained how the hydrocarbons n-hexane and n-heptane can be separated from each other by taking advantage of their different Boiling Point Temperatures.
The binary example of separating n-hexane from n-heptane by Boiling Point Temperature can be extrapolated to separate the stew of hydrocarbons that are in the Crude Tower feedstock.
In the future PTOA Separating Systems Focus Study Area, PTOA Readers and Students will learn that each tray in the Atmospheric Distillation Tower has a distinct relationship between the liquid hydrocarbon stew that is on each tray and the combination of vapors/gases that linger above the tray.
When the Control Board Operator changes the Operating Pressure of the Tower, the composition of the gas and liquid phases will change over a 24 hour interval.
If the Operating Pressure is increased (PV Pressure ↑) and a corresponding increase in Temperature is not supplied by a heat source ...
the liquid layer on each tray will not be able to maintain the level of excitement and agitation that was needed to convert the same amount of liquid into gas as it could do before the PV Pressure was changed.
Thus, a greater percentage of the hydrocarbons with higher Boiling Point Temperatures will remain on the tray in the liquid phase.
So ...over the 24 hour interval, the composition of the gas phase that lingers above each tray will changed into a gas with a lighter density and the liquid level on each tray will become a liquid with a heavier density.
Of course the opposite happens when the Operating Pressure of the Crude Tower is decreased.
In that case the liquid components with the lowest Boiling Point Temperatures on each tray will have an easier time getting excited and agitated enough to change into the gas phase.
In 24 hours the gas phase will have a heavier density and the liquid on each tray will become a liquid with a lighter density.
Hey!
Don't stress out if you did not follow what happens on each tray of a Crude Distillation Tower. The subject matter will be repeated in the future PTOA Separating Systems Focus Study Area.
TAKE HOME MESSAGES: PTOA Readers and Students already know that a gas contained in a rigid-walled container exhibits a one-to-one linear relationship between the PV Pressure and the PV Temperature:
If the PV Temperature increases, so does the PV Pressure of the gas ... and vice versa.
When a rigid container has a liquid level, the PV Pressure of the gas that hovers over the liquid level will impact the Boiling Point Temperature of the liquid:
The higher the PV Pressure above the liquid level, the higher the Boiling Point Temperature that will be needed to turn the liquid into a vapor/gas ... and vice versa.
A Boiling Point Temperature is the temperature of a liquid that signifies the liquid has sufficient thermal energy to perform these two functions:
©2017 PTOA Segment 0157
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Interrelationship with PV Temperature
The post THE RELATIONSHIP BETWEEN THE PV PRESSURE + THE PV TEMPERATURE appeared first on The Process Technology and Operator Academy.
]]>The post DIY ANSWERS FOR THE PV PRESSURE INTRO appeared first on The Process Technology and Operator Academy.
]]>Why do we never get an answer
When we're knocking at the door?
("Question," by J. Hayward of the Moody Blues, 1970)
WRAPPING UP THE PTOA's
PV PRESSURE INTRODUCTION FOCUS STUDY
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order ...
are already aware that PTOA Segments #145, #146, and #147 included Do It Yourself (DIY) challenges that helped explain some of the PV Pressure fundamentals.
The answers to those challenges are included in this PTOA Segment #156.
However ...
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order probably noticed that the review of SI (metric) and English conversion units was skipped... so that subject will be covered first.
CONVERTING BETWEEN ENGLISH AND SI UNITS
PTOA Segment #148 formally introduced and compared the English, SI, and metric measuring units.
Why was the discussion on conversion factors delayed until the 148th PTOA Segment?
There was no need to bring up how to covert between the English and SI (metric) measuring units for the PV Temperature.
PTOA Readers and Students have grown up observing a variety of Temperature scales posted throughout society ... many that show the correspondence between the °F and ° C scales.
Thus, PTOA Readers and Students have grown up with a cognitive awareness about the differences between these two Temperature scales.
When it comes to the PV Pressure, converting between the English and SI (metric) measuring systems is not as straightforward.
By now PTOA Readers and Students can probably predict that some of the confusion equating the English to SI (metric) measuring systems is due to Sir Isaac Newton creating confusion between the meaning of a lb_{f} and a lb_{m}.
Until the difference between a lb_{f} is delineated from a lb_{m}, the person performing the conversion exercise may erroneously attempt to convert a lb_{m} (a unit of Mass) into a kPa (the SI/metric unit of Force).
And this happenstance conveniently segues into another conversion challenge:
The SI (metric) system avoided mistaking Mass for Force by using "derived definitions"...
for example "Newton" is the SI measuring unit for Force and ...
the SI measuring unit for Pressure is the "Pascal."
Hence ... unlike the PV Temperature ...
It is simply more challenging to acquire an intuitive understanding of the correspondence between the English and SI (metric) systems used to measure the PV Pressure!
A PI that indicates BOTH psi and kPa units for Gauge Pressure certainly helps to correlate the relative difference between the English and SI pressure-measuring units.
And of course, nowadays there "an app" for instant conversion between English and SI measuring units.
Still ...
PTOA Readers and Students are living in a globalized world and should devote some effort to gain a sense of the quantitative difference between the measuring systems.
After all ...
Even traveling "abroad" from the USA to processing plants located in Canada and Mexico requires a working knowledge of metric units applied in the processing industries.
Ergo,
PTOA Segment #48 included a handy dandy conversion chart that has served Your Mentor well throughout the years since the days of the dinosaur... when conversion calculations were done by hand and brain!
DIY ANSWERS FOR THE PTOA'S
PV PRESSURE INTRODUCTION FOCUS STUDY
DIY ANSWERS for PTOA Segment # 145:
Determine Fred's Specific Gravity and, based on the answer, state whether Fred will sink or float in water.
Fred's Mass = 175 lb_{m} (79 kg)
Note: Fred's mass was inferred from his weight!
Fred's Volume = 6.25 ft * 1.5 ft * 1 ft = 9.38 ft^{3} (0.26 m^{3})
Fred's Density = 175 / 9.38 = 18.69 lb_{m}/ft^{3} (304 kg/m^{3})
Fred's Specific Gravity = 18.7 lb_{m}/ft^{3} ÷ 62.4 lb_{m}/ft^{3} = 0.30
or in SI/Metric Units 304 kg/m^{3} ÷ 1000 kg/m^{3} = 0.30
Fred's Specific Gravity is less than 1.0 so Fred will float in water!
NOTE: Specific Gravity is a dimensionless number ... but STILL very useful as it instantly reveals the relative density of the two liquids.
DIY ANSWERS PTOA Segment #146
#1. Determine the Pressure on the hull of the sunk U-96
Pressure (psi) = SG_{seawater} * 0.433 / l ft * h (in ft) =
The SG_{seawater} is the same for the Kursk: SG =1.2
Pressure (psi) =1.2 * 0.433 * 919 = 477.5 psi (3292 kPa)
NOTE: Even the Pressure exerted by the liquid in an extremely large container ... like the ocean ... is easy to calculate!
#2. What are the maximum pressures exerted by 3 feet and 9 feet of water ... the depth of the shallow and deep ends of a swimming pool?
Pressure (psi) = SG * 0.433 * h
Pressure at 3 feet = 1.0 * 0.433 * 3 = 1.3 psi
Pressure at 9 feet = 1.0 * 0.433 * 9 = 3.9 psi
NOTE: The volume of the contained water in the swimming pool does not impact the Pressure that the liquid exerts on the sides and bottom of the swimming pool.
DIY ANSWER PTOA Segment #147:
Why is the dam shown in the schematic wider at the base than at the top?
The Pressure Profile of the head pressure exerted on the reservoir-side wall of the dam would
The trapezoid structure of the dam with the wide base at the bottom geometrically limits the length of the head ... and hence Pressure ... at each level of the dam.
NOTE: The outcome of the trapezoidal construction shape is a less severe Pressure Profile impacting the dam as compared to the pressure that would be exerted on the flat face of a square or rectangle dam structure.
TAKE HOME MESSAGES: PTOA Readers and Students have finished The PTOA PV Pressure Focus Study Area.
Onto the relationship between the PV Pressure with the PV Temperature, PV Flowrate, and PV Level!
©2017 PTOA Segment 0156
PTOA Process Variable Pressure Focus Study Area
PTOA Introduction to PV Pressure Focus Study
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