Inverse relationship between air volume and wind pressure

The concept of air volume is relatively easy to understand, refers to the volume flow per unit time, the simplest way to calculate is Q=vA, v is the fluid speed, A is the area of flow. The unit of air volume in the cooling fan is usually CFM (cubic feet per minute, cubic feet per minute), and is also useful in units such as m3/h.

We often notice that there is basically a "maximum air volume" parameter in the fan specification, and the maximum air volume refers to the output air volume of the fan when the system impedance is 0.

What is system impedance?

Revised sentence: In technical terms, system impedance refers to the resistance of airflow within a device's system. The lower the impedance, the faster the flow rate and higher air volume. For instance, an open empty chassis has an impedance close to zero; however, when components such as motherboards, radiators, hard disks and video cards are installed and side plates sealed off, system impedance increases. Radiator fins with greater density or larger surface area have higher impedances. Typically cold rows have greater impedances than air-cooled radiators. In industry settings Bernoulli method is used to calculate pressure differences caused by fluids flowing from large tubes into smaller ones. Our air pressure test devices measure air volume using orifice plate flowmeters. Air volumes in systems are not static; for example, chassis fan intakes change depending on internal situations (system impedance). Generally speaking, higher air volumes indicate better performance.

Similarly, in a system, the static pressure is not constant; it increases proportionally with the impedance of the system. It is impossible for maximum static pressure and maximum air volume to occur simultaneously. In fan design, one must choose between prioritizing either main air volume or main air pressure. If both need improvement, motor power and conversion efficiency can be enhanced by increasing speed. A high-speed fan with large air volume and high wind pressure would be an optimal choice of product.