| Twin-screw multiphase pumps are the core equipment of oil and gas mixed transport technology,which has been widely used in marginal,offshore,and deep-sea oil and gas extraction and transport systems.The operation performance and inlet-outlet two-phase flow characteristics of the twin-screw multiphase pump are of great significance for efficient oil-gas two-phase transportation and safe and stable operation of the system.In this paper,a multiphase pump test bench was built.And then,the performance,vibration acceleration at the bearing end and outlet pipe of the twin-screw multiphase pump were tested under different inlet gas volume fraction(IGVF),rotational speed,and outlet pressure conditions.The two-phase flow patterns at the inlet and outlet of the multiphase pump were photographed.The performance,vibration characteristics,and inlet-outlet flow patterns of the multiphase pump were studied.The influence of the inlet flow pattern on the performance and vibration of the multiphase pump is analyzed.The main research contents and conclusions are as follows:(1)Based on the external characteristic test,the influence of operating parameters on the performance of the multiphase pump was analyzed.The results show that the volumetric efficiency of the multiphase pump increases gradually with the increase of IGVF,but the increased range decreases gradually.The main reason is that with the increase of IGVF,the gap leakage flows become a gas-liquid two-phase flow,the leakage decreases,and the volumetric efficiency increases.Volumetric efficiency increases with the increase of rotational speed and decreases with the increase of outlet pressure.In the pure liquid condition,the hydraulic efficiency increases first and then decreases with the outlet pressure,and reaches the maximum value in the design condition.The hydraulic efficiency decreases gradually with the increase of IGVF,and the hydraulic efficiency under 40%IGVF condition is 63%of that under pure liquid condition.When the speed increases,the hydraulic efficiency increases linearly.(2)Based on the vibration test data,the influence of different working conditions on the peak-to-peak value and dominant frequency of vibration acceleration at the position of the driving end bearing seat and outlet pipe of the twin-screw multiphase pump was studied by using time and frequency domain analysis.The results show that the peak-to-peak vibration acceleration of the driving end-bearing seat in the vertical direction is greater than that in the horizontal direction and axial direction under various working conditions.Under the condition of 0.6-0.8MPa outlet pressure,the peak-to-peak values of vibration acceleration in all directions of the driving end bearing seat are smaller than those of other outlet pressures.With the increase of rotational speed,the peak-to-peak values of vertical and axial vibration acceleration reach the maximum value at 1450r·min-1.The peak-to-peak value of vertical vibration acceleration in the mixed transport condition is larger than that in the pure liquid condition,and the maximum value appears in the 7.5%IGVF condition,which is 1.94 times that in the pure liquid condition.The vibration of the outlet pipe is more severe than that of the bearing seat,and the maximum peak-to-peak value of the acceleration is 3.71 times the maximum value of the bearing seat.According to frequency domain analysis,the primary frequency of vibration acceleration of the bearing seat in the horizontal direction is 3fn,in the vertical direction is 50fn,in the axial direction is 25fn,and at the outlet pipe is 50fn.(3)Based on the visualized image of gas-liquid two-phase flow in inlet and outlet,the flow pattern of inlet and outlet pipelines varies with working conditions.The results show that when the rotational speed is 1650r·min-1,the inlet IGVF increases from 2.5%to 20%,the diameter of the maximum number of bubbles in the inlet and outlet increases,and the flow type is bubble flow.However,when the IGVF is higher than 20%,the inlet flow pattern changes to plug flow,and large bubbles appear at the outlet.When the speed increases from 850r·min-1 to 1650r·min-1 at the IGVF of 10%,the diameter of the maximum number of bubbles at the inlet and outlet decreases,and the flow pattern is bubble flow.(4)The influences of different inlet flow patterns on the external characteristics and vibration of the twin-screw multiphase pump were compared.The conclusions were as follows:the hydraulic efficiency and volume efficiency of the twin-screw multiphase pump were better in the bubbling inflow condition than in the wavy inflow condition,and the efficiency difference between the bubbling flow and the wavy flow increased with the increase of the IGVF when the IGVF is below 20%.When the IGVF is higher than 20%,the mixing effect weakens,and the efficiency difference between bubble flow and wave flow decreases gradually.The peak-to-peak value of vibration acceleration of wave-flow bearing in the vertical direction is higher than that in the bubble flow condition.However,the changes in the horizontal direction and axial direction are close to that in the bubble flow condition.The installation of a pipeline mixer can reduce the vibration of the pump body and improve its hydraulic efficiency. |
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