In centrifugal fans, increasing the number of impeller blades can increase the theoretical pressure of the impeller, because it can reduce the influence of the relative eddy current. However, the increase of the number of blades will increase the friction loss of impeller passage, which will reduce the actual pressure of the fan and increase the energy consumption. Therefore, for each type of impeller, there exists an optimal number of blades. The exact number of blades is sometimes determined by the experience of the designer. According to the current application situation, the selection range of blade number is recommended. When designing centrifugal fans, the actual pressure is always given in advance. The impeller is the only component that the fan transmits to the gas energy, so its design has great influence on the fan. Whether the main structure of the impeller can be determined correctly plays a key role in the performance parameters of the fan. It includes the key technology of centrifugal fan design - blade design. The most critical part of blade design is how to determine the blade exit Angle β2A.

The outer dimension of the volute should be as small as possible. For high specific RPM fans, a shortened cochlear shape can be used, and for low specific RPM fans, a standard cochlear shape is generally selected. Sometimes in order to reduce the size of the volute, the outlet velocity of the volute can be chosen to be greater than the fan inlet velocity, at this time, the outlet diffuser is used to improve its static pressure value. Blade exit Angle is one of the main geometrical parameters to be selected first in design. For the convenience of application, we classify the blades into strong backward-curved blade, backward-curved arc blade, backward-curved straight blade and backward-curved airfoil blade. Radial outlet blade and radial straight blade; Front bent blade, strong front bent blade.