How do I calculate how much airflow I need?
Several pieces of information are needed:
The amount of heat to dissipate or “get rid of”, in watts;
The allowable temperature rise in Celsius or Fahrenheit; and
The derived factor of 1.76 for Celsius and 3.16 for Fahrenheit.
With that, the formulas are:
Airflow(CFM) =1.76 X Watts divided by allowable temperature rise in Celsius (Delta T).
Airflow(CFM) =3.16 X Watts divided by allowable temperature rise in Fahrenheit (Delta T.)
This is a general rule of thumb for calculating airflow needed. Other factors that also need to be considered are altitude, hot spots, and humidity.

What is the relationship between RPM and airflow?
RPM and airflow are directly proportional. In other words, increasing RPM by 20% also increases airflow by 20%.

What can we do to lower the noise level in a fan?
1) Lower the RPM or the fan operating speed (this also lowers airflow.)

2) Check for obstacles in front of and behind the fan. If they exist, move the fan farther away. In general, obstacles on the intake side of the fan negatively impact the noise level more than on the exhaust side.

How do I determine my system's static pressure?
This is difficult to do without an airflow chamber. Typical system impedance for electronics equipment ranges between .05" and .15" of water.

范例 (网友补充, 是否正确,请自己判定):
　　例一：有一电脑消耗功率150瓦，风扇消耗5瓦，当夏季气温最噶30℃，设CPU 允许工作60℃，所需风扇风量计算如下：   
　　P=150W+5W=155W；△Tc=60-30=30  
　　Q=0.05×155/30=0.258CMM=9.12CFM(为工作所需风量)  
　　所以,应选择实际风量为Qa之风扇  
　　  
　　  例二：有一SWITCHING电源供应器消耗功率250瓦，风扇消耗20瓦，当地夏季气温最高55℃，设该供应器允许工作95℃，所需风扇风量计算如下：   
　　P=250W+20W=270W；△Tf=95-55=40  
　　Q=0.09×270/40=0.6075CMM=21.44CFM(为工作所需风量)  
　　所以,应选择实际风量为Qa之风扇
 

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