Through in-depth analysis, the parameters that determine the performance and structure of water ring vacuum pump are impeller radius R, impeller wheel ratio v, eccentricity e, impeller blade number Z, impeller width B, blade inclination angle, impeller submergence in the liquid ring h, impeller speed n, pumping rate and ultimate pressure, etc. The shape, position, blade outlet angle beta and circumferential velocity U of suction and exhaust outlet have great influence on the performance of water ring vacuum pump.
Impeller design is a universal problem. Comparing the shape design of radial impeller, tangential impeller and curved impeller, the structure of curved impeller is reasonable, the compression is good and the efficiency is high. But through the comparison of various impellers, the stress and strain values of radial impeller and curved impeller are larger, which is determined by their structure. For the design of impeller, not only the influence of shape characteristics, but also the strength and manufacturing problems should be considered.
The flow process in the water ring vacuum pump is much more complicated than that in the vane pump. Considering the complexity of the force acting on the impeller of a water ring vacuum pump during its rotating cycle, this paper divides a cycle of the impeller into intake zone, compression zone, exhaust zone and dead zone. According to the pressure of each zone, this regular variable force is found to analyze the strength of the impeller. From the analysis of stress, strain and displacement diagram, it can be seen that the stress and strain of the impeller are maximum in the compression zone because of the uneven distribution of pressure on the impeller, but the stress and strain of any impeller are within the allowable range. It should be noted that when the rotating speed is high and the pressure is high, the reaction effect of the liquid ring needs to be considered. In addition, the blade on the impeller is always in alternating state with the impeller's rotation, and the fatigue effect should also be considered.
In the design of water ring pump, it is very important to determine the circumferential speed of impeller, because the circumferential speed has a great influence on the pump performance, which can be said to be global. Other parameters of the pump, such as critical compression ratio, limit vacuum, efficiency and so on, are closely related to the circumferential velocity. Generally speaking, if the circumferential velocity is too small, the pump will not reach the predetermined critical compression ratio, and the limit vacuum will also decrease, resulting in the narrowing of the working range of the pump and the increase of the axial power in the high vacuum region. On the other hand, if the circumferential velocity is too large, the critical compression ratio of the pump can be improved, although it can be improved. And the limit vacuum, but excessive cycle speed will reduce the efficiency of the pump, and the shaft power will also rise. Moreover, under the influence of the vaporization pressure of the liquid ring medium, excessive cycle speed will not increase the critical compression ratio proportionally. Therefore, the selection of cycle speed should not be too large. How to reasonably select the cycle speed so that the pump has satisfactory performance and small energy consumption is worth discussing when designing the water ring pump. Problem.
When the impeller rotates and drives the liquid to rotate to form a liquid ring, the liquid ring, as a boundary of the closed chamber, continuously obtains kinetic energy from the impeller in the suction zone, and its velocity increases continuously until the circumferential velocity of the impeller at the maximum eccentric point on the impeller reaches the maximum value at the site. In the compression zone, it works on the gas in the form of "active cold", and transfers part of the kinetic energy obtained from the impeller to the gas so as to make the gas pressure. With the increase of force, the working process of the water ring pump is actually the most energy conversion process among impellers, liquid rings and gases, which abides by the law of energy level street. Among them, the kinetic energy of the liquid ring depends on the circumferential velocity of the impeller. If the circumferential velocity is high, the kinetic energy obtained by liquid from impeller is large, and the function of liquid to gas is strong, which means that a certain volume of gas can obtain a higher compression ratio; on the contrary, the function of liquid to gas is weak.
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