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What happened to thread on Centrifuagal Pumps and head squared

What happened to thread on Centrifuagal Pumps and head squared

What happened to thread on Centrifuagal Pumps and head squared

(OP)
Where did the thread go on the discussion of centrifugal pump head versus the rotational speed squared. I started the thread and hate to lose it because there was good info contained within.  

RE: What happened to thread on Centrifuagal Pumps and head squared

"Much ado about nothing." I believe is how the saying goes.
 

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: What happened to thread on Centrifuagal Pumps and head squared

I looked for it this morning as well.

It was becoming a somewhat passionate discussion.  It might (quite justifiably) not have withstood "moderator scrutiny".  In any event, I think the thread had run its course.

Regards,

SNORGY.

RE: What happened to thread on Centrifuagal Pumps and head squared

If you believe, you can, was the take away lesson.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: What happened to thread on Centrifuagal Pumps and head squared

(OP)
Oh well. Thanks to all who participated in a somewhat "passionate" and "imaginative" but very informative discussion. It would seem I should have received notification my thread had been pulled and by whom, but I did not receive any such notification. Thanks again!

amptramp

RE: What happened to thread on Centrifuagal Pumps and head squared

Yep, gone to the happy hunting ground where it can be discussed over and over without any hard feelings, whether it is ever resolved is another discussion.

RE: What happened to thread on Centrifuagal Pumps and head squared

I apologize if anyone didn't like my tone.  The regulars on this forum all know a lot more about pumps then I ever will.

A small attempt to summarize the conclusions:

For a centrifugal pump attached to a fixed fluid system, the "operating point characteristics" (*) will follow the complete pattern Q~N, DP~N^2, FHP~N^3  if and only if the fluid system satisfies DP~Q^2

I think most agree with the above. Some comments/objections were raised:
1 – It is not likely that many fluid systems are fixed – often there is some control valve.
2 – Perhaps there are not a lot of systems that obey DP~Q^2 to begin with.  Very turbulent systems do on a first view, although Snorty had some more comments on that.  In any case more in depth analysis is usually in order than trying to give a simple generalization as this.
3 – Who cares shadeshappy
* "operating point characteristics" represents change in operating point of the fixed system as a functio of speed. It is not to be confused with pump laws. Pump laws depend on the pump only, nothing to do with the system.

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RE: What happened to thread on Centrifuagal Pumps and head squared

I am very susceptible to typo's as you guys may have noticed. The g key is next to the t.  Sorry about that Snorgy.

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RE: What happened to thread on Centrifuagal Pumps and head squared

I certainly subscribe to one of Snorgy's last comments - no harm no foul.  Today is a new day.  I have no emotional investment in this topic anymore.

If anyone wants to correct, revise, or addend my summary, please do.

Thanks.

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RE: What happened to thread on Centrifuagal Pumps and head squared

My take away and search results are that the pump characteristic curves follow the affinity laws.  The operating point is dependant on the system curve and where it intersects the pump curve.
The system curve does not follow the affinity laws.
Predicting the operating point does not necessarily follow the affinity laws since it is dependant on both the pump and the system characteristics.  It is necessary to know both the system curve and the pump curve(s) to determine the new operating point for the new pump curve.

Thanks to the participants for making me review what I used to know are research to understand the rest.

Ted

RE: What happened to thread on Centrifuagal Pumps and head squared

It wasn't me that flagged it.

Likewise I don't mean anything personal in anything I say, nor take it personally in what I see.  Just calling it like I see it.  Hope no harm was done.

If by chance anyone wants to discuss this, or anything else for that matter, in private, my contact info is in the link.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: What happened to thread on Centrifuagal Pumps and head squared

No worries, Electricpete.

Sincerely,

Snorty.

smile

It's actually pretty funny...I mean...how much worse than "Snorgy" could it get, anyway?

 

Regards,

SNORGY.

RE: What happened to thread on Centrifuagal Pumps and head squared

Electripete
- I would suggest that many many thousands probably millions of installations are fixed, within very small variations - fixed inlet conditions and disharge conditions, no change to SG, Vis. Temp. etc - the only significant change woud be increasing head overtime due to pipeline fouling.


Hydtools
 - The friction component to a system curve does follow the Q^2 law all things being equal with no change in conditions other than flow

Given a flow, the total head and knowing the static head  component of a system curve you can calculate a head new for an increase in flow using the following parabolic equation:

H = Hs + KQ^2

H  = total head
Hs = static head
K  = constant
Q  = Capacity / flow



 

RE: What happened to thread on Centrifuagal Pumps and head squared

If its 1 phase flow, only 1 fluid in the pipe, newtonian ...

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: What happened to thread on Centrifuagal Pumps and head squared

Agreed, but I can only think water - so no problem to me as I like to keep everything simple.

RE: What happened to thread on Centrifuagal Pumps and head squared


Allow me to be the devil's advocate when referring to some special cases.

Pressure drop is admitedly proportional to the friction factor [f] multiplied by velocity squared [V2], and since [f] is sometimes proportional to Re-0.2, as for water flowing through tube banks, the resulting pressure drop is proportional to V1.8.

Any comments ?

RE: What happened to thread on Centrifuagal Pumps and head squared

There is only one system characteristic that allows us to predict change in operating point with change in speed WITHOUT consulting the pump curve: and that system is:
DP~Q^2 (same as DP~V^2)

For all others we would need to utilize the pump curve to make any prediction about changes to the operating point with speed.

The best you can do for DP~Q^1.8 is say it is CLOSE to the result predicted above.... OR ELSE dig out the pump curve, adjust it for speed and compare to system curve.

The fact that DP~Q^2 is unlikely does not contradict my summary statement which has DP~Q^2 in the IF part of IF/THEN logic, but perhaps makes it of less practical value to some.

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RE: What happened to thread on Centrifuagal Pumps and head squared

Quote:

The best you can do for DP~Q^1.8 is say it is CLOSE to the result predicted above
For what little it's worth, you could also predict  the direction of the deviations as well.... for example when doubling speed, the DP~Q^1.8 system will have a new DP somewhere less than factor of 4 above original operating point and new Q somewhere less than factor of 2 above the original operating point.

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RE: What happened to thread on Centrifuagal Pumps and head squared

CORRECTION IN BOLD:
"For what little it's worth, you could also predict  the direction of the deviations as well.... for example when doubling speed, the DP~Q^1.8 system will have a new DP somewhere less than factor of 4 above original operating point and new Q somewhere MORE than factor of 2 above the original operating point"

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RE: What happened to thread on Centrifuagal Pumps and head squared

To support my previous statement (in case it's not already obvious), attached is a  picture.

Assumed a form of system characteristic: DP~Q^m

Plotted three different systems m=1.8, m=2.0, m=2.2... all connected to identical pumps and all initially at the same operating point (V=4.698, DP=44.14).

Then double the speed of the pump.  We know that where the m=2 operating point ends up:  twice the flow rate and 4 times the DP as initial operating point.  The new m=2.2 operating point is above and to-the-left of the new m=2 operating point.  The new m=1.8 operaring point is below and to-the-right of the new m=2 operating point.

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RE: What happened to thread on Centrifuagal Pumps and head squared

As long as friction factor doesn't change faster than the prediction you need to make and the value you get is good enough to suit your purposes, I don't see a problem with using that method.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: What happened to thread on Centrifuagal Pumps and head squared

Electripete, the pump curves you show in your spread sheet are for centrifugal pumps while the discussion was supposed to be about positive displacement pumps.
 

RE: What happened to thread on Centrifuagal Pumps and head squared

Quote - 25362 (Chemical) 13 Dec 09 12:08  

Allow me to be the devil's advocate when referring to some special cases.

Pressure drop is admitedly proportional to the friction factor [f] multiplied by velocity squared [V2], and since [f] is sometimes proportional to Re-0.2, as for water flowing through tube banks, the resulting pressure drop is proportional to V1.8.

Any comments ?- Unquote  

Yes, I disagree.  

After 30+ years of having used the likes of Cameron Hydraulic data and other friction charts for asphalt-dipped cast iron and new steel pipe to give a good approximation of the friction loss, do I now find out that I and a couple of the worlds leading pump companies for whom I have worked have also been wrong all this time.

For example, a random number of selections from the above tables which shows that head increases near enough to Q2/Q1^2 , There is a slight variance but guess this variations is the roughness factors / pipe diameter etc playing their part.
   
1000 GPM  6" sch 40# pipe = 6.23 ft/100
2000 GPM  6" sch 40# pipe = 24.1 ft/100

3000 GPM 18" sch 40# pipe = 0.294 ft /100
6000 GPM 18" sch 40# pipe = 1.11 ft / 100

70 000 GPM   72" pipe     =0.137 ft / 100
140 000 GPM  72" pipe      =0.419 ft /100     

The above of course is based on standard water at 60F etc.

If talking about fluids other than water there is more to consider than just the change of system head losses due to an increase of pump speed, which I will leave to others more experienced to comment on.

Just for interest, when pumping paper stocks below 6% AD the water friction tables can be used, but once a certain velocity is reached (depending on pulp type, consistency etc)the friction loss drops below that of water.
 

RE: What happened to thread on Centrifuagal Pumps and head squared


Artisi, I referred to "special cases" where the friction factor is not a linear function of the Re number (as implied by BigInch).

For example, for water flow through staggered tubes or for air through a finned air cooler:

f ∝ Re-0.316

or flow in some spirals where:

f ∝ Re-0.25

In those cases and many more, the pressure drop is not proportional to V2.

RE: What happened to thread on Centrifuagal Pumps and head squared


Correction. I should have said, when referring to BigInch, where the friction factor is not independent (not: a linear function as written) of the Re number.

 

RE: What happened to thread on Centrifuagal Pumps and head squared

Or just pumping vertically into a tank where density pressure changes could be far more significant than head loss due to other factors, one might be tempted to write
pressure as a function of height alone.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: What happened to thread on Centrifuagal Pumps and head squared

amptramp

I don't believe anything happened to your original post -- it's just in a different forum.

I believe you're talking about thread378-148264: Positive Displacement Pump Modeling (which I found by clicking on your name and then clicking on the number of threads started).

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

RE: What happened to thread on Centrifuagal Pumps and head squared

We wish it was that one.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: What happened to thread on Centrifuagal Pumps and head squared

Quote (CompositePro):

Electripete, the pump curves you show in your spread sheet are for centrifugal pumps while the discussion was supposed to be about positive displacement pumps.
Please see original post:

Quote (AmpTramp):

Where did the thread go on the discussion of centrifugal pump head versus the rotational speed squared. I started the thread and hate to lose it because there was good info contained within
Both the referenced deleted thread and the current thread are about centrifugal pumps, not positive displacement pumps. You must be three or four threads removed from the current thread.

Speaking of removed threads, do you have any idea what happened to the thread on inductive current interruption?

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RE: What happened to thread on Centrifuagal Pumps and head squared


Artisi, it seems to me that the Δp for the 72-in pipe at 70,000 GPM as 0.137 ft/100 ft, is too high, would you kindly confirm ?

RE: What happened to thread on Centrifuagal Pumps and head squared

25262 (chemical), you are correct just re-checked Camerons  - 72"I.D. New Steel Pipe is 0.085 ft loss / 100ft. Sorry for that - I looked at the wrong column.  

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