Study On Flow Characteristics Of Gas-liquid Two-phase Flow In Rectangular Channels With Large Aspect Ratios

Leakage channel is one of the key factors affecting the efficiency of the expander.The height of the leakage channel is generally less than 0.1 mm,while the width is generally several centimeters long,featuring aspect ratios much greater than 100.Scholars have analyzed and studied the leakage line and leakage model of the single screw expander,and the leakage channel,which has a greater impact on the volumetric efficiency,is transformed into a flat leakage model.In order to improve the efficiency of the expander,the flow characteristics and flow mechanism of the oil and gas two-phase flow in the leakage channel need to be studied,which will provide theoretical basis and guidance for optimizing the performance of the singlescrew expander and improving its efficiency.Five rectangular channels with aspect ratios of 100,125,200,333,and 1000 dimensions were experimentally studied.Nitrogen was used as the gas phase and water,ethanol,20%glycerol solution and 40% glycerol solution as the liquid phase.Four stable flow patterns were found in the horizontal direction using visualization studies,namely,wavy flow,annular flow,bubble flow,and diffuse annular flow.The effects of aspect ratio,liquid viscosity and surface tension on the flow pattern transition were analyzed and flow patterns were plotted.The results show that: with the increase of aspect ratio,the bubble flow appears earlier,and the transition line of flow pattern of wavy flow and bubble flow moves toward the lower superficial gas velocity;the increase of viscosity has a more significant effect on the flow pattern,the range of bubble flow increases and the range of wavy and annular flow decreases;when the liquid phase was ethanol,the decrease of surface tension makes the annular flow replaced by slug flow;the signal of differential pressure fluctuation under each flow pattern was plotted,and the The differential pressure fluctuation signals of each flow type were plotted and analyzed.The frictional pressure drop of two-phase flow was analyzed from the aspects of gas-liquid phase velocity,aspect ratio,liquid viscosity,surface tension,and roughness,respectively.The results show that: the pressure drop increases with the increase of gas-liquid phase velocity,in which the liquid phase velocity has a greater influence on the pressure drop and plays a dominant role;the pressure drop increases significantly with the increase of aspect ratio and liquid viscosity;the pressure drop increases with the decrease of surface tension;the pressure drop does not change significantly with the increase of roughness.The prediction results of the homogeneous flow model and the separated flow model method were compared with the experimental results for analysis,and it was found that the existing correlation equation could not fit the experimental data well.The Chisholm parameter C was modified by the separated flow model,and the aspect ratio was used as a dimensionless number to fit the new correlation formula,which can predict the friction pressure drop in a rectangular channel with aspect ratio from 100 to 1000 well with an average deviation within±25%.In this experiment,the pressure drop and flow characteristics of gas-liquid two-phase flow in rectangular channel with high aspect ratio were studied which provided data support for leakage channel of single screw expander and further developed the understanding of two-phase flow characteristics in rectangular channel with high aspect ratio.