Basic knowledge of air volume and air pressure

Fundamentals of Air Volume and Air Pressure

1. Air volume and air pressure are the two most important performance indicators of a.

Air Volume: The volume of air passing through the cross-section of the fan outlet (or inlet) per unit time, usually expressed in CFM, i.. cubic feet per minute, or CMM, i.e. cubic metres per minute. Air volume is an overall measure of fan performance, which is not limited by size,, or method, and is not limited to brushless DC fans, but can be applied to any air guiding device.

Air Pressure: The pressure difference that the fan can between the outlet and the inlet. The unit is generally mmH2O, i.e. millimetres of water column (similar to the millimetre of mercury column to measure atmospheric pressure, but since the pressure difference is small, it is generally expressed in water columns). Air pressure is an important indicator of the "power" of the fan

2. PQ Curve

In the matching process between the fan and the system, there are various systems with different pressure differences (impedance) between the and the inlet; in order to understand the working performance of the fan under various pressure differences (specifically, impedance), we must measure the flow rate of the fan under variousances; all the test points connected together are the characteristic curve of the fan (PQ curve).

3. The measurement of the PQ curve requires the use of wind tunnel, as shown below is the basic structure of the wind tunnel.

4. How to measure the PQ curve

To measure the PQ curve, it must be done on a wind tunnel. By adjusting the no and auxiliary fan, the wind volume is controlled, and the corresponding values of wind volume and static pressure are recorded, and finally the static pressure-flow rate diagram (i.e, the characteristic curve diagram) is drawn.

5. Typical PQ curve

The following figure is a typical fan characteristic curve diagram. The solid line (F) in the figure is the fan characteristic curve, and the dotted line (SRC) is the system impedance curve.

The intersection of FPC and SRC is the point OP when the system and fan are used together, and Qb and Pb are the wind volume and pressure difference that can be achieved in use, respectively

6、The division of the three regions of the PQ curve

According to the flow condition of the airflow, the entire curve can be divided into three: the working region, the stall region, and the return flow region.