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Exhaust Air Velocity Profile

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marksummers

Mechanical
Joined
Aug 29, 2007
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27
Location
US
I am looking for some help with what seems to be a simple engineer fluid dynamics problem.

I have a pressurized electronics rack with a 550 cfm exhaust fan mounted on the top, exhausting to atmospheric pressure. My customer wants to know how much "non-obstruction area" is required above the rack to prevent a reduction in the exhaust flow.

Obviously, an obstruction at even a long distance away will theoretically obstruct the flow, so my approach was to determine the air flow velocity as a function of height above the rack. Assuming the fan can provide 550 cfm and the fan opening is 12" diameter, any thoughts on how to develop a flow velocity profile?
 
I cannot help with the velocity profile, but would suggest ensuring that the customer doesn't just want to know how close an obstruction can be without causing your rack to overheat.
 
Correct. The ultimate requirement is to not have the rack overheat. But I already know from other analysis that the rack will not overheat with the system as it is currently designed.

I thought the velocity profile would help me understand at what height an obstruction might start having an impact on the fans.
 
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