MMA Memo #203

Forced Air Cooling at High Altitude

Jingquan Cheng [1]

March 24, 1998

Keywords:

This memo discusses the efficiency change of the forced air cooling process when the site is located at 5,000 m above sea level. Formulae provided give theoretical numbers on efficiency loss. The calculation shows that for a larger characteristic length object, the loss in efficiency may be very large (78 %) since there is a transition between laminar to turbulent flow. For objects with smaller characteristic length, the efficiency loss will be of the order between 17 % and 39 %. At the same time, the memo also discusses the practical situation of the fan efficiency problem. The memo includes a number of useful figures of the cooling efficiency and a table of efficiency loss for electrical equipment at altitude.

[1] NRAO-Tucson

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Last modified: 09 December, 1999