Analysis Of Internal Flow Field And Hydraulic Performance Of Two-stage Liquid Ring Compressor

Liquid ring pump is a kind of fluid machinery which uses liquid as working medium to pump or compress gas.It has the advantages of large flow rate,small gas temperature rise and no metal contact in the pump.It has important applications in petroleum,chemical,electric power and other industries.Liquid ring pump can be used as both vacuum pump and compressor.At present,the design of multi-stage liquid ring compressor still depends on the traditional theoretical analysis method,and the internal flow characteristics of multi-stage liquid ring compressor and the distribution mechanism of compression ratio between impellers are not clear enough.Based on the combination of numerical simulation and experiment,this study studies the relationship between hydraulic performance and internal flow field of two-stage liquid ring compressor under different working conditions and different impeller width ratios.The main work and innovative research results of this study are as follows:(1)Through the combination of experiment and numerical simulation,the complex gas-liquid two-phase flow in the two-stage liquid ring compressor is analyzed.The results show that the numerical simulation is in good agreement with the experimental test,and the numerical simulation results are slightly higher than the experimental values.Because the compression ratio of the secondary impeller is smaller than that of the primary impeller,the gas-liquid interface in the exhaust port area of the secondary impeller is smoother than that of the primary impeller.The pressure change trend along the circumferential direction in the two impellers is basically the same.There is obvious backflow at the beginning of the first-stage suction port,and no backflow occurs at the second-stage suction port.(2)The influence of outlet pressure on the flow field and hydraulic performance of the compressor is analyzed.The results show that the efficiency of the first stage impeller decreases slowly with the increase of the inlet and outlet pressure ratio,and the efficiency of the second stage impeller increases first and then decreases.With the increase of outlet pressure,the compression ratio of the two-stage impeller increases gradually,and the ratio of the compression ratio of the first stage impeller decreases first and then increases.With the increase of outlet pressure,the serrated gas-liquid interface of the first-stage impeller gradually intensifies,the pressure along the circumferential direction in the two-stage impeller gradually increases,and the flow velocity in the suction and exhaust port area gradually increases.There is obvious vortex secondary flow in the impeller passage of the two-stage impeller,and the vortex secondary flow intensity is the largest in the transition zone.The pressure in the impeller channel at the beginning of the first-stage suction port is greater than the suction pressure,and the backflow phenomenon occurs.The backflow of the suction port changes periodically with the rotation of the impeller.(3)The pressure fluctuation characteristics of the inner wall of the first and secondary stage impeller are compared and analyzed.The results show that the main frequency of the pressure fluctuation at the suction port and the exhaust port of the inner wall of the first stage impeller is the blade frequency f_b.Under the same outlet pressure,the amplitude of pressure pulsation at the exhaust port of the inner wall of the shell is greater than that at the suction port.With the increase of outlet pressure,the frequency domain distribution characteristics of pressure pulsation at the same position are basically the same,and the amplitude of pressure pulsation increases gradually.The main frequency of the pressure pulsation on the inner wall of the two-stage impeller shell is the blade frequency f_b.The frequency domain characteristics of the two-stage impeller along the rotation direction of the impeller are basically the same.The amplitude of the pressure pulsation from the transition zone to the end of the suction port gradually decreases,and the amplitude of the pressure pulsation from the end of the suction port to the transition zone gradually increases.Because the compression ratio of the first-stage impeller is larger than that of the second-stage impeller,the pressure pulsation amplitude in the exhaust port area of the first-stage impeller is larger than that of the second-stage impeller.Due to the uneven distribution of pressure in the circumferential direction,the radial force of the impeller in the x direction is greater than that in the y direction,and the periodicity is more obvious.The characteristic frequencies of the radial force in the x and y directions are shaft frequency f_n and blade frequency f_b.(4)The influence of the first stage impeller width ratio on the performance of the two-stage liquid ring compressor is analyzed.The results show that the flow rate of the compressor increases gradually with the decrease of the first stage impeller width ratio k.With the decrease of k value,the efficiency of the compressor increases gradually under the condition of small pressure ratio,and increases first and then decreases under the condition of large pressure ratio.At the same time,the compression capacity of the secondary impeller gradually increases,and its pressure ratio curve gradually moves upward,while the pressure ratio curve of the primary impeller gradually moves downward.Under the same working condition,with the decrease of the width ratio of the first stage impeller,the shaft power of the first stage impeller decreases gradually,and the shaft power of the second stage impeller increases gradually.With the increase of pump outlet pressure,the ratio of the first stage impeller pressure ratio gradually tends to be gentle,and the ratio of the two stage impeller pressure ratio gradually tends to be 1.1 when the k value is 2.2.(5)The variation law of the internal flow field characteristics of the first stage impeller under different impeller width ratios is analyzed.The results show that under the same pressure ratio,with the decrease of the first stage impeller width ratio,the serrated gas-liquid interface in the exhaust port area of the second stage impeller is obviously intensified.The pressure at the beginning of the exhaust port of the secondary impeller gradually increases;the flow velocity in the suction and exhaust port area of the two-stage impeller increases gradually,and the backflow phenomenon in the first suction port and the second exhaust port area is improved.