According to the compilation of the centrifugal fan manufacturer, the pressure coefficient of the backward impeller of the common centrifugal fan at a certain speed Ψ T is smaller, the impeller diameter is larger, and its efficiency is higher; The opposite is true for the forward impeller. If the transmission mode is A, D and F, the fan speed is the same as the motor speed; However, B, C and E are variable speed, so the fan speed can be flexibly selected during design. Generally, the drive A directly connected with the motor is widely used for small fans. For large fans, sometimes the belt drive is not suitable, and the drive mode D and F are mostly used. For high temperature and dusty conditions, the protection and cooling of motors and bearings should also be considered in the transmission mode.
In centrifugal fans, increasing the number of blades of the impeller can increase the theoretical pressure of the impeller, because it can reduce the impact of relative eddy current. However, the increase of the number of blades will increase the friction loss of the impeller channel, which will reduce the actual pressure of the fan and increase energy consumption. Therefore, there is a better number of blades for each impeller. The specific number of blades is sometimes determined according to the experience of the designer.
According to the current application in China, the selection range of blade number is recommended. When designing centrifugal fans, the actual pressure is always preset. The impeller is the element that the fan transmits energy to the gas, so its design has a great impact on the fan; Whether the main structure of the impeller can be correctly determined plays a key role in the performance parameters of the fan. It includes the key technology of centrifugal fan design - blade design. The key link of blade design is how to determine the blade outlet angle β 2A。
The overall dimension of spiral case shall be as small as possible. Shortened volute can be used for fans with high specific speed, and standard volute can be used for fans with low specific speed. Sometimes, in order to reduce the size of the volute, the scheme that the outlet speed of the volute is greater than the inlet speed of the fan can be selected. At this time, the outlet diffuser is used to increase its static pressure value. The blade outlet angle is one of the main geometric parameters to be selected in design. In order to facilitate the application, we classify the blades as follows: strong backward curved blades, backward curved arc blades, backward curved straight blades, and backward curved airfoil blades; Radial outlet blade, radial straight blade; Forward curved blade, strong forward curved blade.