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Forced Convection 1

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GreenRoger

Mechanical
Joined
Aug 12, 2009
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9
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GB
I have a problem similar to a thread I found here:

thread391-227383

I am designing a generator cooling system. The generator is in a sealed steel tube which is air filled and under water. I intend to weld a steel channel to the side of the tube and blow air down it to power circulation. So I need to work out how big a fan I need.

HeatPower = GeneratorPower x (1- Efficiency)

TempGenerator = TempWater + HeatPower x Area x Coefficient

The previous thread recommended a coefficient of 100W/m2K. That's a good start but it doesn't tell me how big a fan I need. I suppose I'll need to use CFD to get a better value than that but is there a rough formula I can use to relate the fans flow rate to the coefficient?

(Relating to the previous thread, under water vehicles use an electrical umbilical which may carry was much as 2MW. These are wrapped on a winch drum which is water cooled.)
 
I've corrected the attached spreadsheet. It doesn't take account of changes in pressure in my enclosed volume pod. Would pressure effect the air's Specific Heat, Thermal Conductivity or Dynamic Viscosity?
 
 http://files.engineering.com/getfile.aspx?folder=3775c594-a979-429b-a250-6cc6e06cdbda&file=forced_convection_r03.xls
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