Centrifugal fans are mostly used in industrial production fans. One of the core components of this centrifugal fan is the impeller and blades. If the blades on the impeller change slightly, the performance of the fan will be affected. Usually, different types of centrifugal fans are used. There are different impeller and blade parameters, but in the process of fan customization and impeller blade repair (replacement), blades with different parameters are required for different working conditions. What are the effects of blade parameters and centrifugal fan performance?
Influence of Blade Parameters on Performance of Centrifugal Fan
1) The influence of blade shape
The basic shape of the blade is arc, straight and wing, which can be divided into forward, backward and radial according to the installation angle of the blade outlet. Different blade profiles have different effects on the pressure point, operating point, pressure curve shape and efficiency of the fan. From the perspective of the efficiency of the centrifugal fan, because the circumferential component of the outlet speed of the backward impeller is small, its reaction degree is large and the efficiency is high. In addition to being affected by the degree of reaction, the axial vortex makes the velocity distribution in the passage of the forward impeller more uneven and increases the loss, so the efficiency of the forward impeller is lower. The centrifugal fan with constant deceleration flow design has small flow loss inside the impeller, more regular pressure gradient change, weak jet-wake structure at the impeller outlet, uniform outlet velocity field and lower upper limit of velocity. In the rearward impeller, in order to reduce the inlet shock and improve the efficiency, airfoil-shaped blades are often used. However, in many cases, adding airfoils to the blades will not achieve good results in flow and wind pressure. Therefore, the method of adding airfoils should be adopted according to the specific situation to improve the performance of the fan.
2) The influence of the blade inlet installation angle
The blade inlet installation angle should be determined according to the principle of minimizing the impact loss of the airflow inlet, and one is determined according to the airflow angle. The blade inlet installation angle varies with the impeller form. Tests have shown that the higher efficiency point does not necessarily occur at the non-impact inlet, so it is recommended that the blade inlet angle should have a smaller attack angle (positive or negative). For the backward impeller, due to the small flow loss in the blade passage, the installation angle of the blade inlet should be selected so that the impeller inlet impingement loss is small; The angle will cause the blade to bend too much and the separation loss will increase. Experiments show that although the larger blade inlet installation angle increases the inlet impact loss, the flow separation loss of the blade channel is reduced. Compared with the two, the efficiency is improved. But compared with the backward impeller, its efficiency is still lower.
3) The influence of blade width
The principle of determining the blade width is to make the flow loss in the blade channel as small as possible. For the backward impeller, when other design parameters remain unchanged in the engineering design, the blade inlet and outlet width ratio increases, the outlet angle decreases, and the blade outlet width increases. The former is conducive to improving the efficiency, while the latter reduces the relative speed ratio at the impeller inlet, which has the opposite effect, because the impeller passage increases the diffusion, which is easy to cause separation. For the backward impeller, the ratio of the blade inlet and outlet width is often selected to be 0.7~0.8. For the forward impeller, the influence of the inlet geometry parameters is greater, and the blade inlet width should be much larger than the blade inlet width calculated directly by the blocking coefficient.
4)The influence of the number of leaves
If the number of blades is too small, the expansion angle of the blade path will generally be too large, which will easily cause the separation of the airflow boundary layer and reduce the efficiency; if the number of blades increases, the deflection of the airflow at the outlet of the impeller can be reduced and the pressure return can be increased. It will increase the friction loss along the way and the blockage of the blade inlet, and also reduce the efficiency. The increase of the number of blades can reduce the channel expansion and lag angle, which is beneficial to reduce the separation and improve the total pressure and efficiency, but at the same time increase the impeller channel, increase the friction loss, and reduce the total pressure and efficiency. Generally speaking, the smaller the wheel diameter ratio, the smaller the number of blades, so as to prevent the blades from being too dense at the inlet; the larger the wheel diameter, the more blades.
The above is the influence of the blade parameters explained by the centrifugal fan manufacturer on the performance of the centrifugal fan. I hope it can be helpful to everyone. It is not difficult to see that the blade parameters have a great influence on the performance of the fan, and in actual operation, the blades of the fan are prone to wear and tear, and it is easy to change the relevant parameters after repair and replacement, which will affect the performance of the fan. Relevant technicians are required to start maintenance, rather than just replacing a set of blades.
