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How to calculate the fan air volume
For customers, manufacturers are obligated to assist them in selecting appropriate air volume cooling fans. The calculation method for air volume demand is now introduced as follows：
一、Firstly, it is necessary to understand some known conditions:
1、1 calorie is equal to the amount of heat required to raise the temperature by 1 ℃ by 1 gram of water weighing 0 ℃.
2、1 calorie is equal to the amount of heat required to raise the temperature by 1 ℃ by 1 gram of water weighing 0 ℃. One watt of power per second is equivalent to one joule.
3、1 calorie equals 4.2 joules
4、Constant pressure (10mmAq) specific heat of air (Cp)=0.24 (Kcal/Kg ℃)
5、Standard state air: Wet air with a temperature of 20 ℃, atmospheric pressure of 760mmHg, and humidity of 65% is the standard air. At this time, the unit volume the weight of accumulated air (also known as specific weight) is 1200g/M * 3
6、CMM and CFM both refer to the volume of air discharged per minute, with the former unit being cubic meters per minute; The latter unit is cubic feet per hour.
1CMM=35.3CFM。
二、 Formula calculation
1、It is known that the total heat output of the fan (H)=specific heat (Cp) × Weight (W) × Allowable temperature rise of container (△ Tc)
because：Weight W=Volume multiplied by density between units (per second)
That is to say：weightW=(CMM/60) ×D
That is to say：weightW=(CMM/60)•1200g/M*3
That is to say：weightW=(Q/60) ×1200g/M*3
so ：calories(H)=0.24(Q/60) •1200g/M*3•△Tc
2、Electrical heat (H)=(P [power] t [seconds])/4.2
3、From 1 and 2, it can be concluded that: 0.24 (Q/60) • 1200g/M * 3 • △ Tc=(P • t)/4.2
Decipher: Q=(P×60)/1200•4.2•0.24•△Tc
Decipher: Q=0.05P/△Tc……………………………………………… (CMM)
Decipher: Q=0.05•35.3 P/△Tc=1.76 P/△Tc…………………………(CFM)
4、The conversion of Fahrenheit degrees (temperature difference of 1.8 degrees Fahrenheit for every 1 degree Celsius) is:
Q=0.05•1.8 P/△Tf=0.09 P/△Tf………………………(CMM)
Q=1.76•1.8 P/△Tf=3.16 P/△Tf…………………………(CFM)
三、Example
Example 1: There is a computer that consumes 150 watts of power and a fan that consumes 5 watts. When the summer temperature reaches 30 ℃, the CPU is allowed to operate at 60 ℃ and the required fan air volume is required. The calculation is as follows:
P=150W+5W=155W；△Tc=60-30=30
Q=0.05×155/30=0.258CMM=9.12CFM ( Air volume required for work)
Example 2: There is a SWITCHING power supply that consumes 250 watts of power and a fan that consumes 20 watts. The highest temperature in the local summer is 55 ℃, and the supply is allowed to operate at 95 ℃. 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 ( Air volume required for work)
In this way, the main parameter of the air volume required for the cooling fan of the product can be confirmed, and the cooling fan that suits the customer's product can be basically selected through other parameters.
