role of plenum in forced air cooling of electronics

[nigelt]

I need to understand the role of the plenum in forced air cooling of electronics, please.
I have observed two quite different types of structures being called plenums, though they may operate on the same principle.

First is a fan fed box (typically a scroll type fan) from which air goes to an electronics enclosure that needs cooling - one subject housing, no distribution, and the enclosure inlet may be similar size as the fan outlet. This suggests to me that the plenum has a role that is principally one of pressure management?

Second is a structure, again fan fed, that increases, perhaps many times the sq area of the fan outlet - such as feeding a heat exchanger or a filter. Is this a plenum also?

Any references or guides on sizing and designing plenums (plena?) particularly the second type (I have searched).

Thanks in advance,
NigelT

"You will master any feeling of inadequacy you may be having"
....from my fortune cookie @ the buffet!

 

[drawoh]

nigelt,

I have designed electronics enclosures that contained things that I refered to as plenums, or that I could have called plenums if I had wanted to.

You should try to figure out what problem the designer is trying to solve. Generally, I am trying to fit a dust/EMI filter in front of the fan. These cause head losses, so I select ones that are significantly bigger than the fan, as you have noted above. This causes fit problems that are easily solved by a transitional structure of some sort.

In the past, I have fallen into the trap of thinking that air on the high pressure side of the fan has more cooling capacity. The effect, whatever it is, is negligible. The pressure heads of ventilation fans are small compared to atmospheric pressure.

JHG

 

[Heckler]

I also design electronic enclosures for harsh environments and cooling is always a struggle especially with the wide spread use of commerical electronics. This book is a great resource for any designer of electronics equipment.

Cooling Techniques for Electronic Equipment by Dave S. Steinberg published by John Wiley & Sons, inc

http://www.efisystemsgroup.com/system.htm

http://www.coolingzone.com/

Best Regards,

Heckler
Sr. Mechanical Engineer
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