Measures to improve the cavitation resistance of centrifugal system
1) Select appropriate geometric parameters to reduce the necessary NPSH during pump design
In the design of the pump, increasing the impeller inlet area (by increasing the inlet diameter and width), selecting the blade inlet angle and blade number, increasing the curvature radius of the front cover plate inlet section of the impeller and the smoothness of the impeller surface can reduce the NPSH and improve the anti cavitation performance, as shown in Fig. 1-22 and Fig. 1-23.
2) The first stage impeller adopts double suction impeller
The flow through one side of the double suction impeller is half of the total flow, which reduces the inlet flow rate of the impeller, thereby reducing NPSH and improving the cavitation resistance。
安徽快3开奖结果3) Adopt front inducer
The inducer is installed in front of the first stage impeller of the pump, as shown in Figure 1-24。 When the liquid flows through the inducer, the inducer works on the liquid, which makes the liquid pressurized before entering the centrifugal pump, so as to improve the anti cavitation performance of the pump。 At the same time, because the inducer is axial-flow type, its outer edge speed is high, under the effect of centrifugal force, once bubbles are generated, they can only flow along the axial direction at the outer edge of the inducer, and will not block the flow channel。 Therefore, as an axial-flow impeller, inducer can prevent cavitation to a certain extent。
4) Adopt anti cavitation material
The impeller shall be made of materials with strong cavitation resistance to prolong its service life. It has been proved that the higher the strength, hardness, toughness and chemical stability of the material, the smoother the blade surface and the better the cavitation resistance. The commonly used materials are rare earth alloy cast iron, nickel chromium stainless steel, aluminum bronze and phosphor bronze.
5、 Calculation of cavitation performance parameters of special liquid
The necessary NPSH of the pump is obtained under the condition of clean water at 20c。 The NPSH 'required by the pump in the transportation of hydrocarbon medium and high temperature water is smaller than that in the transportation of normal temperature water。 Therefore, water is used to determine the specific
NPSH of different liquids is generally safe。 According to API 610, the reduction coefficient or correction coefficient shall not be used for the necessary NPSH of liquid (such as hydrocarbon) other than water, and the NPSH value obtained from clean water test shall be used。
The calculation formula of NPSH 'is: slurry pump
Figure 1-25 shows the curve of NPSH correction value △ h. for pumping carbon compound by American Hydraulic Association. Find the temperature of the liquid to be transported on the abscissa of the figure, and then make a line upward to intersect with the section level representing the vaporization pressure of the liquid at a point. Make a diagonal parallel to the correction curve through the point, intersect with the coordinate axis on the right, and the coordinate value of the intersection point is 0.