During the actual operation of the fan, a“illusion”——Why does this situation occur when there is only air volume but no wind pressure?

In fact, the relationship between air volume and air pressureA slap won't make a soundThis sentence is the most appropriate description, as the two constrain and complement each other, together forming the performance of the fan.

Firstly, let's understand the definitions of air volume and air pressure from a fundamental theoretical perspective.

air volumeIt refers to the volumetric or mass flow rate of gas passing through the inlet section of a ventilation fan per unit time. Used for volumetric flow rateQv stands for m ^ 3/s, m ^ 3/min, or m ^ 3/h; Mass flow rate is expressed in Qm, with units of kg/h or kg/s.

wind pressureIt refers to the energy obtained by a unit volume of working medium flowing through a fan, and its unit is the same as the pressure,Pa or mmAq. The pressure of a fan is divided into three types: static pressure, dynamic pressure, and total pressure, with the relationship being: total pressure=static pressure+dynamic pressure.

Next, let's talk about why air volume and air pressure areCan't a slap make a sound?

After testing, any fan can draw its airflow~Wind pressure performance curve, as shown in the following figure:

This curve is composed of an infinite number of points, and the air volume and pressure usually written on the nameplate are only one point on this line. For example, the performance point required by the customer as shown in the above figure is air volume100m^3/minWind pressure300mmAqDifferent air volumes will inevitably correspond to different wind pressures, so it is said that“A slap won't make a sound”.

Speaking of which, the question at the beginning of the article already has an answer.

As mentioned above, the performance curve is constructed from countless performance points, including those shown in the figureAPoint: Airflow165m^3/minThe wind pressure is0.

During the initial acceptance and trial operation of most projects, the system was not debugged to its optimal level, and even the fan inlet and outlet were tested and accepted without being taken over. At this point, the resistance is very small, even zero, and the operating point of the fan is directly shifted towards the high flow area, with the maximum deviation reachingAPoint, causing such on-site incidents“illusion”.

How can we retrieve the wind pressure?

As long as a pipeline is connected to the inlet or outlet of the fan and a regulating air valve is added, the resistance of the system can be simulated by adjusting the air valve to adjust the operating point of the fan to the required performance.

For such situations, especially when configuring large fans on site, it is recommended that customers install regulating air valves at the front or back of the fan. When starting, the inlet regulating air valve can be closed and slowly opened after reaching the rated speed. This can not only test the air volume and pressure, but also better protect the motor and prevent overcurrent situations from occurring.