Study On Gas-liquid Two-phase Flow Characteristics In Horizontal Helical Rectangular Channel

With the rapid development of China's economy,the energy demand increasingly strained and the contradiction between supply and demand of energy increasingly prominent,to improve energy utilization or development of new energy is imminent.The single screw expander system,for its low speed,large expansion ratio,high efficiency,wide applicable scope,etc,is considered as an efficient way to solve the contradiction of energy,which is widely used in the waste heat recovery,low temperature geothermal power generation,etc.But the study of the single screw expander system mainly concentrated on its processing and performance,and lack of the research on its characteristics of multiphase flow though the channel,which is also the important factors that affect its operation.However,because of its complex structure with irregular cross-section,it is difficult for experimental observation.Based on the single screw expander,a rectangular helical channel is designed and the characteristics of gas-liquid two-phase flow in the channel are observed,which provide a necessary foundation for the single screw expander system.Firstly,based on the single screw expander with a diameter of 175 mm,a rectangular section helical channel is processed using transparent organic glass.The features of gas-liquid two-phase flow are observed by using high speed camera method in the horizontal rectangular channel,and the working mediums are air and water.The flow characteristics of unstable pulse flow,bubble flow,intermittent flow and annular flow in different round angle location are analyzed.The flow pattern map is given and the effects of spiral cycle and round angle for flow pattern are also observed.Then,the method of dimensional is adopted to analyze the flow pattern transitions from intermittent flow to bubble flow and annular flow.In addition,the slug size and liquid film distribution are studied in intermittent flow pattern.Secondly,the pressure drop of single phase and gas-liquid two-phase are collected by pressure transmitter in the helical rectangular channels.Based on the Ito model and L-M split phase flow model,the correlations of pressure drop of single phase and gas-liquid two-phase in horizontal helical rectangular channels are investigated.In addition,the differential pressure fluctuations in different flow patterns are analyzed.Lastly,in order to reveal the phase holdup distribution characteristics,the quick closing valve methold is used to measure the average gas holdup around the whole pipe,and the conductivity probe measurement technique is used to measure the local gas holdup in the position of 540°.The distributions of (?) and ? are observed under different flow patterns.The results show that the flow patterns effect the distribution of gas holdup.The method of split flow pattern is used to analyze the correlations between the average gas holdup (?) and gas volume holdup ?.According to the results,the signal of probe measurement technique can be used as the basis of the flow pattern identification,and the local gas holdup has its own unique characteristics under different flow patterns along the radial direction of measuring points.