The impact of centrifugal pump structural design on cavitation in centrifugal pumps
Research shows that the direct factor affecting the cavitation performance of centrifugal pumps is the local flow uniformity at the impeller inlet. Therefore, the impeller structural design has a greater impact on centrifugal pump cavitation than the design of the pump body and is the main influencing factor.
(1) The impact of impeller structure on cavitation performance of centrifugal pumps
1) Blade inlet thickness. The displacing effect of the blades increases the fluid velocity at the inlet and causes pressure loss. You can choose a smaller blade inlet thickness to increase the flow area at the blade inlet and reduce blade crowding.
2) Surface roughness of the impeller inlet flow channel. The surface roughness of the impeller inlet channel of a centrifugal pump can be divided into two categories: one is isolated rough protrusions, and the other is rough protrusions evenly distributed along a certain part of the entire surface. Necessary grinding of the surface of the rough flow channel, especially the surface with isolated rough protrusions, is an effective measure to improve the anti-cavitation performance of the centrifugal pump.
3) Blade inlet throat area. If the blade inlet throat area is small, even if the ratio of the flow area at the blade inlet to the impeller inlet cross-sectional area is reasonably designed, it is still likely that the ideal cavitation performance will not be achieved. If the impeller blade inlet throat area is too small, the absolute speed of the blade inlet liquid flow will increase, resulting in a decrease in the anti-cavitation performance of the centrifugal pump.
4) Number of leaves. When selecting the number of impeller blades, on the one hand, it is necessary to minimize the displacement and friction surface of the blades, and on the other hand, the blade path must be of sufficient length to ensure the stability of the liquid flow and the full effect of the blades on the liquid.
(2) Effect of impeller suction inlet parameters on centrifugal pump cavitation performance
1) The blade inlet attack angle Δβ is generally a positive attack angle (3°~10°). Due to the positive attack angle, the blade inlet angle is increased, which can effectively reduce the bending of the blade, increase the blade inlet flow area, and reduce the displacement of the blade. The selection of the angle of attack has an optimal value for the anti-cavitation performance of the centrifugal pump. The larger the angle of attack, the better. The analysis and selection should be based on the actual situation.
2) Impeller inlet diameter. When the flow rate is constant, the absolute speed and relative speed of the liquid flow at the impeller inlet are both functions of the suction pipe diameter.
3) Blade inlet flow channel width. When the operating conditions of the centrifugal pump remain unchanged, increasing the width of the flow channel at the blade inlet will reduce the axial component of the absolute velocity of the liquid flow, thereby improving the cavitation characteristics of the centrifugal pump and affecting the hydraulic power of the centrifugal pump. Efficiency and volumetric efficiency have less impact.
4) Hub diameter. Reducing the hub diameter of the impeller will increase the actual inlet area of the impeller flow passage, thereby improving the cavitation performance of the centrifugal pump.
5) The radius of curvature of the impeller front cover. Using a larger curvature radius can weaken the change in flow velocity at the liquid flow turning point at the front cover, make the flow velocity uniform and stable, and improve the cavitation performance of the centrifugal pump.
