How to differentiate between forward-curved and backward-curved fans, and what are the differences?

This should be the basic knowledge of fluid mechanics. The difference between forward-curved and backward-curved fans lies in the size of the exit angle of the fan blades. As shown in the figure, when the exit angle is greater than 90 degrees, it is called forward-curved (or forward-bent), when it is less than 90 degrees, it is called backward-curved (or backward-bent), and when it is equal to 90 degrees, it is called radial. When the size and speed of the fan are the same, the larger the exit angle, the higher the pressure generated (the specific equation is not listed here and can be obtained from the velocity triangle). Therefore, the advantage of the forward-curved fan compared to the backward-curved fan is that the total pressure head is larger (as shown in the following figure, it should be noted that the theoretical total pressure head is not considered limited number of blades and hydraulic losses). However, the dynamic pressure head of the forward-curved fan also accounts for a larger proportion of the total pressure head, and the air flow velocity is high, resulting in greater losses when converting to static pressure, so the efficiency is not as high as the backward-curved fan.