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 (網(wǎng)友補(bǔ)充, 是否正確,請(qǐng)自己判定):
　　例一：有一電腦消耗功率150瓦，風(fēng)扇消耗5瓦，當(dāng)夏季氣溫最噶30℃，設(shè)CPU 允許工作60℃，所需風(fēng)扇風(fēng)量計(jì)算如下：   
　　P=150W+5W=155W；△Tc=60-30=30  
　　Q=0.05×155/30=0.258CMM=9.12CFM(為工作所需風(fēng)量)  
　　所以,應(yīng)選擇實(shí)際風(fēng)量為Qa之風(fēng)扇  
　　  
　　  例二：有一SWITCHING電源供應(yīng)器消耗功率250瓦，風(fēng)扇消耗20瓦，當(dāng)?shù)叵募練鉁刈罡?5℃，設(shè)該供應(yīng)器允許工作95℃，所需風(fēng)扇風(fēng)量計(jì)算如下：   
　　P=250W+20W=270W；△Tf=95-55=40  
　　Q=0.09×270/40=0.6075CMM=21.44CFM(為工作所需風(fēng)量)  
　　所以,應(yīng)選擇實(shí)際風(fēng)量為Qa之風(fēng)扇
 

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