The relationship between wind pressure, air volume, power and speed of the fan

Update:25-09-2019
Summary:

The speed n of the fan can be directly measured by the […]

The speed n of the fan can be directly measured by the tachometer, and its value is expressed in revolutions per minute (rev/min). Small fans typically have a high rotational speed and are often directly connected to the motor. The speed of a large fan is low. Generally, the belt drive is connected to the motor. The diameter of the pulley can be changed to adjust the speed of the fan. The relationship is as follows:
 n1/n2 = d2/d1
In the formula:
n1, n2 - fan; motor speed
d1, d2 - the diameter of the pulley of the fan and motor.
To change the speed of the fan, just change the diameter of any one of the fan or motor.

When the fan speed is changed, the characteristic parameters of the fan; the characteristic curve also changes, that is, the fan has its corresponding characteristic curve at each speed. When the speed changes, the change of the characteristic parameters Q, H, N of the fan can be calculated as follows:
Q/Q` = n/n`   H/H` = (n/n`)2   N/N` = (n/n`)3
It can be seen that if the speed of the fan is changed from n to nˊ, the change of the air volume of the fan is proportional to the primary of the speed ratio; the change of the wind pressure is proportional to the square of the speed ratio; the power change is proportional to the square of the speed ratio .
Therefore, when increasing the fan speed, you must recalculate the required power, and pay attention to whether the original motor will be overloaded. Several performance parameters of the fan are not fixed, and there is a certain internal relationship between them. When the fan works in the pipe network, these parameters are affected by the network characteristics, so choose a good fan, not only to be familiar with the performance of the fan, but also to understand the network characteristics and the relationship between them.