# Homework Help: Question concerning Fluid Mechanics.

1. Jul 11, 2006

### lawtonfogle

Is their a easy formula to find out how strong a pump needs to be based upon the number of elbows in a piping system. I am working on some heat transfers of the piping system, but now I need to know about the pump, and I have no knowledge of fluid mechanics to use to answer find this formula.

If nothing else, does anyone have an easy to understand (non-cal based if possible) website they wouldn't mind sharing. Thanks.

2. Jul 12, 2006

### Cyrus

I will post something for you tomorrow.

3. Jul 13, 2006

### Cyrus

Ok, here is what you need to know. What you are going to use is essentially the extended bernoulli equation.

$$\frac {P_1}{ \rho} + \frac {V_1^2}{2g} + z_1 + h_s = \frac {P_2}{ \rho} + \frac {V_2^2}{2g} + z_2 + h_L$$

$$h_s$$ is the pressure head that your pump will have to provide to over come the losses in the flow, $$h_L$$.

Solving for $$h_s$$ will allow you to find the HP of the pump required.

$$h_L$$ is the losses that occur in your pipe.

These losses take on two forms, Minor losses and Major losses.

Major losses are due to the viscous effects (shear stresses) of the flow. This will be $$f \frac{ l}{D} \frac{V^2}{2g}$$

l -is the length of the piping.
D - is the inside diameter of the pipe.

In addition, you will have minor losses due to the elbows.

$$h_L = K_L \frac{ V^2}{2g}$$

The value of $$K_L$$ changes depending on the fixture. For example, $$K_L$$ of a threaded elbow is 1.5, flanged 0.3 etc.

You can combine all this mess to find the losses and the pump requirements.

Also, this is for turbulent flow. This means that this equation:

$$Re = \frac { \rho V D} {\mu} ~> 4000$$

You will also need to know approx the surface roughness of the pipe, $$\epsilon$$.

With these equations, you can use what's called a Moody chart to iterate a solution for f, V, $$\epsilon$$, D if necessary.

I can help calculate the losses if you show me some thoughts.

Last edited: Jul 13, 2006
4. Jul 13, 2006

### mbengtson

This seems like a good place to ask this question.

I am currently engaged in an High School science project. I was wondering if you guys could help me out.

After some brainstorming, I have narrowed my topic down to CPU cooling. I plan on researching water cooling and doing my project on the different coolants and the proportions of the actual coolants' chemicals to hopefully come up with a valid conclusion. For those of you who aren't familiar with water cooling, it's basically a bunch of tubes inside of your computer that are filled with a coolant. This coolant is what runs across the surface of the CPU and dissipates heat through a radiator.

So far, all of the research has led me to the conclusion that the study of this 'heat transfer' is basically centered on thermodynamics. I, however, have absolutely no idea what some of this physics jargon means. I am in the middle of teaching myself some of it from the basics, but was wondering if some of my questions could be answered here.

One of my questions relates to the actual testing process. I have 5 old pentium 2 300 mhz computers. I am trying to figure out the most efficient/effective way to do the testing. I plan on tesing each of the coolants on each of the (identical) computers twice, yielding 10 data points for each different variable. The computers will be running for 1 hour, and data (regarding CPU temperature) will be collected at the 0,5,10,30,and 60 minute marks. With the cleaning and setup involved, each different coolant will take 3+ hours to test (2 hours testing = 10 data, 1 hour cleaning, setting up). Does this seem viable?

My next question; is there any linear relationship between chemicals that demonstates the heat dissipation properties? I am trying to think of how I will be able to calculate/predict how much heat is going to be dissipated if I change the mixture (ie water + bleach) and/or proportions. I have looked over some thermodynamics literature, and here is a summary of the information that I have gathered;

Well there you go! I'm a physicist! Haha thank you for any and all of your help!

Last edited by a moderator: Jun 15, 2008
5. Jul 13, 2006

### Cyrus

Hello mbengtson,

First, I would suggest you delete your above post and make a thread for help. Second, CPUs can overheat in mere seconds. I hope you know what you are doing, or you will burn out your CPU's and not get any data.

Last edited: Jul 13, 2006