How to choose air volume

In order to meet the needs of different customers in different regions, we are obliged to know how customers choose the appropriate air volume. The air volume selection method is introduced as follows:

There are some known conditions that must be understood first:

1 cal is equal to the heat required to raise the temperature of 1 gram of water at 0°C by 1°C.

1 watt of power work for 1 second equals 1 joule

1 card equals 4.2 joules

Constant pressure of air (10mmAq) specific heat (Cp) = 0.24 (Kcal/Kg°C)

Standard air: the temperature is 20°C, the atmospheric pressure is 760mmHg, and the humid air with a temperature of 65% is the standard air. At this time, the weight of the unit volume of air (also known as the specific weight) is 1.2Kg/m3

CMM and CFM both refer to the volume of air discharged per minute, the former unit is cubic meters/minute; the latter unit is cubic feet/minute. 1CMM=35.3CFM

1. Know that: the total exhaust heat of the fan (H) = specific heat (Cp) × weight (W) × container allowable temperature (△Tc)

Because: weight W = (CMM/60) × D = volume per unit time (per second) multiplied by density

=(CMM/60)×1.2Kg/m3

=(Q/60)×1.2Kg/m3

So: total heat (H)=0.24(Q/60)×1.2Kg/m3×△Tc

2. Electrical heat (H) = (P [power] t [seconds])/4.2

3. Known from 1 and 2: 0.24(Q/60)×1.2Kg/ m3×△Tc=(P×t)/4.2

Q=(P×60)/1200×4.2×0.24×△Tc

Q=0.05P/△Tc…………………………………………(CMM)

=0.05×35.3P/△Tc=1.76 P/△Tc………………(CFM)

4. The conversion in degrees Fahrenheit is: Q=0.05×1.8P/△Tf=0.09P/△Tf………………(CMM)

=1.76×1.8P/△Tf=3.16P/△Tf…………(CFM)

Example 1: A computer consumes 150 watts of power and a fan consumes 5 watts. The local summer temperature is up to 30°C. If the CPU is allowed to work at 60°C, the required fan air volume is calculated as follows:

P=150W+5W=155W;△Tc=60-30=30

Q=0.05×155/30=0.258CMM=9.12CFM (for the air volume required at the working point)

Example 2: A SWITCHING power supply consumes 250 watts, the fan consumes 20 watts, and the local summer temperature is up to 55°F. Assuming that the power supply is allowed to work at 95°F, the required fan air volume is calculated as follows:

P=250W+20W=270W;△Tf=95-55=40

Q=0.09×270/40=0.6075CMM=21.44CFM (for the air volume required at the working point)