Designing a closed loop recirc cooling system

[hydronicengr]

Hi all,

I'm doing a project right now which deals with designing a closed loop recirculating system using water to cool multiple components. However, this post will only deal with the fluids portion.

Below is the diagram of a very simplified system. Note that the areas marked red are 90 degree fittings with a given k (loss coefficient) value.

I am only given a supply pressure (P_supply) of 100 psi, the lengths of each of the sections (the lengths from dot to dot), the diameter of the pipes, the pipe material, and the temperature of the incoming fluid (water). The diameter of the pipes are all the same, so it's constant diameter. Also, assume that the system is on the same plane, so there is no height or elevation.

I am required to find:
- The pressure at P_return
- The volume flow rate (Q or V_dot)
- The k_component

When I was given this project, it seemed somewhat confusing, so I asked for help from the project advisor. Unfortunately, he didn't give me a clear answer and he's unavailable for the next few days so I cannot ask him any questions for the time being.

He just said that the volume flow rate does not have to be given and that there's a relation somewhere and told me to read up on Hydraulic Grade Lines. Also, he said to split the system up into sections, which are the areas between the red dots. This made me a bit confused because I was wondering how I would account for the 90 degree bends so that I can add the loss coefficients, K, into the total head loss.

I have done many problems regarding finding pressure difference, total headloss, etc., but I am totally lost when it comes to finding these many unknowns. I am doing this analysis in Excel as well.

If any of you can give me some tips on how to find or solve this, please let me know.

Thanks!

 

[BigInch]

first assume a near zero outlet pressure. The pressure loss, or head loss, for any flowrate is found using any one of a number of equations, Darcy-Weisbach, or even better, the Churchill equation. Subtrace the equivalent pressure/head losses due to flow through the fittings. With a near 100 psi head loss, you can calculate flow. Now make the flow a little smaller, so that you will have a lesser pressure drop and have some pressure left over to meet NPSH requirements for whatever pump is driving this system. Recheck the pressure loss with the new flowrate. If NPSHR for the pump is available at the outlet, that's your answer.

What would you be doing, if you knew that you could not fail? Ans. Gov lobbyist.

 

[vpl]

Do you have a copy of Crane's Technical Paper 410 Flow of Fluids? It tells you how to solve these sorts of problems. You can buy from Amazon or direct here: [link]http://www.flowoffluids.com/[/url] You might ask around your place of work. Chances are, somebody owns one; they might let you borrow it if you promise to return it.

Patricia Lougheed

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[Latexman]

How is the heat removed from P_return? Heat exchanger, cooling tower, what?

Good luck,
Latexman

 

[MortenA]

Like do you own homework ?

Best regrads Morten

 

[hydronicengr]

For now, I'm just concentrating on the flow and disregarding any heat.

I will try to find a copy of Crane's No. 410 around here.

Thanks.

 

[Latexman]

I'm not asking about what's downstream of p_return for heat duty reasons, it's for flow and pressure reasons. How is the heat removed from P_return? Heat exchanger, cooling tower, what?

Good luck,
Latexman

 

[hydronicengr]

At the "resistor" k_component, is a component, let's say a generator. The generator produces heat so water is used for cooling purposes. The heat will be removed using a cooling tower.

 

[Latexman]

And the water goes to the cooling tower just downstream of p_return, right?

Good luck,
Latexman

 

[hydronicengr]

Correct.

 

[stanier]

Sounds as if the advisor does not want a numeric answer but to get you to understand the principles and express the solution algebraically.

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