What happened to thread on Centrifuagal Pumps and head squared

[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.

 

[BigInch]

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.

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"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/

 

[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.

 

[Artisi]

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.

 

[25362]

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.

 

[25362]

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.

 

[BigInch]

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/

 

[vpl]

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 (which I found by clicking on your name and then clicking on the number of threads started).

Patricia Lougheed

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

 

[BigInch]

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/

 

[electricpete]

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:

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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[25362]

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

 

[Artisi]

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.