Study On Flow Characteristic In Rectangular Sudden Expansion Micro-channels

Heat transfer enhancement by phase change at micro-channel has always been a research hotspot in the field of microelectronics,and the flow pattern and pressure drop analysis of two-phase flow in micro-channel are the basis of the design and control of microfluidic system.In this paper,the characteristics of two-phase flow in a rectangular micro-channel with a sudden expansion structure are studied by means of measurement,visualization and numerical simulation.Finally,a more comprehensive prediction model of pressure drop is established by considering comprehensive factors of pressure drop in two-phase flow.The pressure drop components of the rectangular micro-channel with sudden expansion structure,the pressure drop of the sudden contraction,the pressure drop of the sudden expansion and the pressure drop of the straight channel,are analyzed by measuring experiments.The results show that the pressure drop of the straight channel accounts for more than 50% of the total pressure drop.It means that the pressure drop of the straight channel is the main type of the total pressure drop.Besides,with the increase of mass flux of two-phase flow,the percentage of the pressure drop of the straight channel is relatively weakened,and the proportion of sudden contraction and sudden expansion are relatively increased.It can be seen that improving the accuracy of the pressure drop in the straight channel is the main way to improve the accuracy of total pressure drop.In addition,this paper analyzes the influence factors of pressure drop.The results show that three kinds of pressure drop all increase with mass flux,and the pressure drop of the straight channel is greatly affected by mass flux.And three kinds of pressure drop all increase with liquid Reynolds number,and the pressure drop of the straight channel is most affected by liquid Reynolds number.The bubble behavior in a rectangular micro-channel is observed by visualization experiments.Five typical flow patterns,bubble flow,plug flow,slug flow,jet like flow and annular flow,are observed.The formation of the flow patterns are analyzedby bubble behavior analysis.In this paper,the typical flow patterns are simulated by numerical simulation.The flow patterns observed in the experiments are simulated.The pressure distribution of the flow patterns are studied.It is found that the pressure drop gradient at the interface between gas and liquid is very large.It indicates that the pressure drop of the two-phase flow in the micro-channel with sudden expansion structure is closely related to flow pattern.Finally,a more comprehensive pressure drop model is established by introducing dimensionless capillary number(Ca),and the average prediction error of the model is21.3%.Because of the introduction of the dimensionless parameter Ca,the model of the pressure drop prediction which can express the quantitative relationship between flow pattern and pressure drop,provides theoretical basis for further study of two-phase flow in micro-channel.