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 ‧ Selection of AIR FLOW to cool an apparatus

P : represents the power to be dissipated (in watts)
Δt : represents the temperature difference between internal temperature of the equipment and ambient temperature
Q : represents the air flow of the fan = P(w)1.2XΔt L/s
THE AIR FLOW IS DETERMINED BY THE PROJECTION ON THE GRAPH BELOW FROM THE INTERSECTION POINT OF THE LINES AND Δt ON THE AIR FLOW SCALE.
Example given a power to dissipate of 400 W and t of 10℃

REQUIRED AIR FLOW TO COOL = 34 L/s = 72 CFM
  ‧Conversion Chart
(CFM = L/s x 0.0353 x 60)  
  ‧Air Measurement

Determination of the air performance curves is obtained by using the double chamber method based on AMCA standard. The difference between the pressures before and after the nozzle (differential pressure Pn) is measured so as to obtain the air flow at the nozzle and the different pressure between those in the twochambers (static pressure Ps). The air flow is calculated from the differential pressure by using equation (A). The auxiliary blower enables to cancel out the aerodynamic resistance.

Q = 60 AV…..(A)
where
Q: Air flow rate (m3/ min)
A: Nozzle sectional area = π D2 / 4
V: Average flow velocity from nozzle

r: Specific gravity (kg / m3) of air (r = 1.2 kg / m3 at 20℃, 1atm)
g: Gravitational acceleration = 9.8 m/s2
Pn: Differential pressure mm H2O)
Ps: Static pressure (mm H2O)
  ‧Table of Temperature Vs. Air Flow
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