Water Cooling Calculations for Water Cooled Motor

[PrecisionMechDesign]

I'm designting a motor that will be running hot, and needs some water cooling.

Are there some simple equations relating water flow to temperature, etc. of the motor?

From what I remember from Heat Transfer in college (and reminded by opening my Heat Transer book), this stuff just isn't that simple.

This stuff isn't as simple as F=ma, equations of motion, etc. This stuff is pretty hairy.

But it still seems I should somehow be able to do some sort of energy balance.

I'm looking at a steady-state condition.

Things I want to play with are:

1) Water inlet and outlet temperatures

2) Water Pressure

3) Size and length of my cooling "tubing" wrapped around the motor.

Thank you in advance for any help.

 

[willard3]

BTU/hr = 500 x gpm x delta t
You'll have to convert kw to btu/hr 3413 btu = 1 kw

For the tubing heat exchanger, you're going to have to get a book on heat exchangers as it's complicated. I'm not sure what you propose will work because Underwriters are going to look pretty hard at home-brew heat exchangers on electric motors.

 

[vpl]

Well the equation to start off with is pretty simple:

Q/A= m_dotc_p(T₁-T₂) where

Q = heat to be removed
A = area of heat transfer (or, in your words, the size and length of cooling tubing)
m_dot = mass flow rate
c_p = specific heat = 1 for water
T₁ = inlet temperature
T₂ = outlet temperature

This will give you some rough ideas, since you say you have control over most of the major parameters involved.

Patricia Lougheed

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

 

[PrecisionMechDesign]

Great info. Thank you both!

Patricia, what is this "formula" called?

I want to dig through my old heat transfer book and fully understand what's going on here.

Willard, what formula are you using?

 

[PrecisionMechDesign]

Patricia, I found it in my heat transfer book, as I'd figured would be the case, it's an "energy balance", in the "Internal Flow" section of my book.

Thanks very much for your help!

I love these simple first-order approximation formulas when they fit your situation. This will do nicely for my application.