Pump impeller how to adjust the pump impeller is turning?
Bladeinletangle, usually more than imports relative flow angle, namely, beta 1 beta 1 'angle is a p = P 1- beta 1'. Angle value is typically a p (3~10) = DEG to 15 DEG in individual cases. The positive impact angle can improve the anti cavitation performance, and the efficiency is not affected, the reasons are as follows: (1) increase the blade inlet angle beta 1, which can reduce the bending of leaves, increase the blade inlet flow area, reduce the crowding of leaves. These factors are reduced by 0 and W0, improve the anti cavitation performance of the pump. (2) with the positive impact angle, the liquid will flow off the back of the blade at the designed flow rate. Because the back side is the low pressure side of the blade passage, the vortex caused by the flow is not easy to diffuse to the high pressure side, so the vortex is controlled locally, and the cavitation is less affected. On the contrary, when the negative impact angle occurs, the liquid produces vortices in the working surface of the blade, which is easy to diffuse to the low pressure side, and has a greater impact on the cavitation. In the positive impact angle, pressure drop coefficient in very little change at Taisho angular range, the negative angle of attack, a sharp rise. The transformation in the appropriate increase of blade, make a p =12. (3) when the pump flow increases, the beta 1 increases, and the use of positive angle can avoid the pump flow at a large negative angle.
Obviously, increasing the K0 can reduce the V0, thus reducing the NPSHr and improving the anti cavitation performance of the pump. However, when K0 is too large, the diffusion of liquid flow at the inlet is serious, which destroys the flow smoothness and stability, and forms vortices, resulting in the decrease of hydraulic efficiency. On the other hand, the Dj increases and the inner diameter of the mouth ring becomes larger. The leakage of the mouth ring increases with the increase of the leakage flow area and reduces the volumetric efficiency of the pump. K0 is generally chosen according to the following principles:For the impeller with high anti cavitation performance, take K0=4.5~5.5;Take into account the anti cavitation performance and efficiency of the impeller, take K0=4.0~4.5;For the main consideration of increasing efficiency of impeller, take K0=3.5~4.0;For this design, take k0=5.5.Select impeller inlet diameter: Dj=D0=538mm.Improve suction performance - change the inlet angle of the blade.
Centrifugal pump cavitation damage principle, cavitation is a liquid dynamics phenomenon, the root cause is that the liquid flow in the process of local pressure drop, forming a low pressure zone. When the pump suction pressure is reduced to the corresponding saturated steam temperature under pressure, liquid boiling vaporization, the original flow of fluid flow in the bubble, the bubble contains vapor and a small amount of the original dissolved in liquid air escaping. When the bubbles flow along the liquid flow from the low pressure region to the high pressure zone, the bubble rapidly shrinks and condenses rapidly under the action of the surrounding high pressure liquid. Because the steam condensation process very quickly and suddenly, resulting in partial vacuum in the bubble disappear around the place, the pressure changes in the fluid flow very quickly from the periphery to the vacuum space impact extrusion to produce severe water hammer, forming a great impact. Because of the size of the bubbles are extremely small, so the impact force in micro bubble contact on the surface of the parts above, the pressure up to hundreds of atmospheric pressure, water hammer frequency up to 25000 /s. so that the material on the wall under repeated load of high frequency and high pressure gradually lead to the fatigue damage; at the same time, if the bubbles also mixed with inert gas (such as oxygen etc.), with the help of bubble condensation heat of metal chemical corrosion, resulting in metal surface pitting to cause perforation, metal grain serious when loosening and stripping showed a honeycomb and even the wall erosion wear. This bubble is formed, the growth and rupture of the crash, so that the process of damage to the material, collectively referred to as cavitation.
