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Anonymous Poster

Problem Process Cooling Water System

06/15/2009 4:45 PM

I am looking for information on how to calculate head loss on a process cooling water system.

This system has 1 supply pump with 4 HX feed off the supply main. All HX return to a common return which passes thru a heat recovery HX and then flows to 2 cooling towers and drains to a common sump tank.

The system is under performing and i question it's design. ie pump undersized or piping undersized.

I am looking for answer on system head loss calculation. On an open system is total head loss everthing from pumps back to tower?

Any help would be greatly appreciated.

Jeffrey Bull

Jbb1944@sbcglobal.net
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The Prof
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#1

Re: Problem Process Cooling Water System

06/15/2009 8:44 PM

Jeff,

Try modelling your system using the free downloadable software from here http://www.pumpsystemsmatter.org/ Go to Downloadable Tools on the left of the page and download the PSIM Software.

Sugggest that you sign up so that you can follow the thread more easily.

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PWSlack
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#2

Re: Problem Process Cooling Water System

06/16/2009 3:45 AM

Start by installing an accurate pressure gauge either side of the pump, and a clamp-on ultrasonic flowmeter to the pipework, and find out where the pump is performing on its published characteristic curve.

Several possibilities:

  • The pump impeller is knackered.
  • The heat exchangers or the pipes leading to them are partially blocked.
  • The system has been added to willy-nilly over the years and the pump can't keep up with the flow requirements.

The instruments should give a better picture of what is going on and determine where maintenance effort would be best applied.

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agua_doc
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#5
In reply to #2

Re: Problem Process Cooling Water System

06/16/2009 10:18 AM

If you have info on the HX, you might want to then do a check of overall heat transfer coefficient (Ud) and compare with expected values.

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PWSlack
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#6
In reply to #5

Re: Problem Process Cooling Water System

06/17/2009 4:32 AM

It would be far better for the original poster to do that.

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betomachine
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#3

Re: Problem Process Cooling Water System

06/16/2009 8:30 AM

Do you have any information on the HXs and the CT pump (datasheets, nameplates, etc)? As PW and others suggest, you need some basic tools to gather some data if you want to do an analysis.

Also, have you ever opened up the suction strainer on the pump?

You should sign up for this board as well, it is a good time.

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PWSlack
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#8
In reply to #3

Re: Problem Process Cooling Water System

06/23/2009 4:04 AM

<...Also, have you ever opened up the suction strainer on the pump?...>

Good point.

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cingold
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#4

Re: Problem Process Cooling Water System

06/16/2009 8:41 AM

I agree with PW. For an existing system, the easiest way to find pressure drop is to just add pressure gauges.

The only benefit I can see to calculating here is to create a model of the system in order to predict the effects of future alterations.

If you really want to calculate it (without purchasing a program or finding a free one), use the Bernoulli equation.

The good thing for you is that you are using water which means you can use the Moody Chart and you are looking for pressure drop. I only see 1 branch in your description, so for pressure drop, it's a tedious equation but it's a direct one. Of course I say it's direct assuming you know the flow rate. If not you better be ready to iterate through it.
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PWSlack
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#7
In reply to #4

Re: Problem Process Cooling Water System

06/17/2009 4:35 AM

Yep. It can be done. The calculations are iterative and somewhat tedious. All any software will do is speed the calculation up.

All calculations are based on assumptions. An invalid assumption can throw the whole lot out of the window.

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Previous in Forum: difference between SA106 GR B and SA 516 GR 70N   Next in Forum: Scale Drawings for a 1:7.5 DH 98 Mosquito
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