What will be given here is brief. For a good general reference on the subject, consult the book Cooling of Electronic equipment by Allen W. Scott, John Wiley & Sons, New York, NY, 1974.
Forced air cooling of electronic components results in a dramatic improvement over natural convection cooling. This effectiveness is the result of the following:
Although the best way to make an accurate determination of cooling requirements is by actual test of the equipment to be cooled, a good approximation of the amount of air required can be determined from the mass flow relationship:
| q=wCpD t | (eq. 1) | ||
| where | q = amount of heat absorbed by the air in BTU/hr. w = mass flow of air in lb/hr.
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This equation yields the following formula, which is more directly applied to electronics forced air-cooling:
| Q = 178.4(ti)(KW) (Dt)(Pb) |
(eq. 2) | |
| where | Q = airflow required in cubic feet per minute. t i = inlet temperature in R of (°F + 460°). Dt = temperature rise across the equipment in °F. kW = power to be dissipated in the equipment in kilowatts. Pb = barometric pressure at the air inlet in inches of Hg. |
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Here it is assumed that all of the heat to be dissipated is picked up by the air; i.e. conduction and radiation as well as natural convection effects on the external surfaces of the equipment are ignored. For standard conditions of 70°F and 29.92" Hg, equation 2 reduces to the familiar: Q = (3160) (KW) (eq. 3) Dt Recognizing that a given cooling application has numerous design considerations, a temperature rise of 15°F will usually yield effective cooling without incurring penalties of over sizing of the air moving device.
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