The Flow And Performance Analysis In Liquid Ring Pump Based On Flow Thermal Coupling

Liquid ring vacuum pump is a kind of fluid machinery that uses liquid as an intermediate medium for energy conversion to pump gas.As the development trend of liquid ring vacuum pumps in industrial applications is gradually becoming larger and more complete,the performance requirements of liquid ring vacuum pumps are becoming higher and higher.The high speed rotation of the liquid ring in the liquid ring pump causes strong viscous dissipation loss and the loss of compression work in the gas compression process is mostly converted into heat,causing the temperature of the circulating medium to rise,which leads to a decrease in the suction vacuum and efficiency of the pump.The mechanism of internal flow-thermal coupling in liquid ring pumps is not yet clear enough.Therefore,this study will analyze the flow-thermal characteristics by calculating the energy dissipation and gas compression work in the flow field inside the liquid ring pump from the perspective of flow-thermal coupling.The main research contents and innovative results are as follows:(1)Conducting thermodynamic characteristics tests and temperature rise tests on liquid ring vacuum pumps,monitoring temperature changes of liquid ring and exhaust water discharge,The experimental results showed that:After a period of operation,the internal flow field and temperature field will reach thermodynamic equilibrium,and the external characteristic index and temperature change at each measurement point will stabilize.As the cooling water volume decreases,the cooling effect decreases and the liquid ring temperature gradually increases.In small cooling water flow(0.5m~3/h)conditions,the maximum temperature of the liquid ring can reach 42.5℃,which is converted into heat dissipation loss of about 53.8%of the shaft work.At different suction flow rates,the exhaust gas temperature gradually increases with the increase of gas pressure ratio,while the liquid ring temperature shows a trend of first decreasing and then increasing,and there is an optimal working condition to minimize the heat loss power.(2)The thermodynamic equilibrium process in a liquid ring pump is a long time period problem,which is difficult to be simulated numerically in a non-stationary manner.In this study,we propose to initialize the flow field by experimentally testing the steady-state liquid ring and outlet medium temperature in order to accelerate the convergence of numerical simulation,and realize the non-stationary numerical simulation of the long-time periodic problem of thermal equilibrium process to obtain the stable temperature field distribution characteristics inside the liquid ring pump.(3)Through unsteady flow-thermal coupling numerical simulation,we analyze the distribution law of compression work and dissipation term of two internal energy terms of gas in liquid ring pump,and the results show that the high dissipation area generally appears in the velocity shear location in the flow field,and its distribution characteristics are basically the same as the vortex distribution.The high dissipation area of liquid ring vacuum pump is mainly concentrated in the friction loss area near the wall of the casing and the vortex area at the tip of the vane.The distribution of compression work in the impeller changes periodically,and the distribution rules of compression work in different cycles are basically the same.The work done by the liquid ring on gas compression is mainly concentrated in the compression area and the beginning of the exhaust port,and the end of the exhaust port shows alternate changes of compression-expansion.(4)Based on the dissipation function and compression work analysis of the liquid ring pump suction flow and speed conditions,it can accurately calculate the liquid ring friction,vortex loss occurring parts and the gas compression process and compression work distribution characteristics.The results show that:the change of cooling water has a small effect on the fluid flow characteristics,with the increase of cooling water,the liquid ring thickness increases,and the friction loss near the wall of the casing increases.Under different suction flow rates,as the suction flow rate decreases,the area of high dissipation area on the wall of the cavity gradually increases,and the total dissipation increases,while the gas outlet return flow rate keeps increasing,so that the pump efficiency keeps decreasing;under different rotational speeds,when the rotational speed increases,the liquid ring flow speed increases,and the dissipation intensity increases in the casing and impeller,while the liquid ring’s ability to compress the gas in the cavity increases.