1, the selection of volute shape size, volute shape size should be as small as possible. For high specific revolution fans, the shortened volute shape can be used, while for low specific revolution fans, the standard volute shape is generally used. Sometimes, in order to reduce the size of the volute, the outlet speed of the volute can be selected to be greater than the inlet speed of the fan. At this time, the outlet diffuser is used to improve the static pressure value.



2. Selection of blade number. In a centrifugal fan, increasing the number of blades in the impeller can improve the theoretical pressure of the impeller, because it can reduce the influence of relative eddy current. However, the increase of blade number will increase the friction loss of impeller channel, which will reduce the actual pressure of the fan and increase energy consumption. Therefore, for each impeller, there is an optimal number of blades. Specific determination of the number of blades, sometimes depending on the designer's experience.



3, the selection of fan transmission mode, if the fan selection of transmission mode A, D, F, the fan speed and motor speed is the same; B, C and E are all variable speed, and the fan speed can be flexibly selected during design. Generally, small fans are widely used to drive A directly connected with electric motors. For large fans, sometimes belt transmission is not suitable, and most of them are driven by D and F.



4. Selection of blade outlet Angle. Blade outlet Angle is one of the main geometric parameters to be selected in design. In order to facilitate the application, the blades are classified into strong backward curved blades, backward curved arc-shaped blades, backward curved straight blades, and backward curved airfoil shaped blades. Radial outlet blade and radial straight blade; Fore-curved blade, strong fore-curved blade.



5, the reasonable choice of blade type, common fan at a certain speed, the pressure coefficient of the rear impeller is small, the impeller diameter is large, and its efficiency is high, on the front impeller is the opposite.