Numerical Simulation On Phase Split Of Gas-liquid Two-phase Flow At A Micro-junction

As a special form micro-channel, the micro-junction has even been applied toelectronic cooling, chemical process engineering, medical and genetic engineering,bioengineering, etc. Recently, the behavior of two-phase flow in micro-channelsattracted the attention of researchers. When two-phase flow comes into amicro-junction, the liquid and gas will show different preferential route. It is alsoknown as uneven phase split in micro-junctions. For heat exchangers, phasemaldistribution is harmful. Because some of the tubes lack liquid due to phasemaldistribution, the local heat transfer will be deteriorated. It seriously affects thenormal operation of the downstream equipment, even damage to equipment.The method of computation fluid dynamics (CFD) is adopted. Numericalsimulation for micro-junction of different branch pipe dip angle was carried out. Thephase split characteristic of annular flow in micro-junction was investigated. The flowfield characteristics of the velocity field distribution law, the phase volume fractiondistribution law were analyzed. The results show that when the branch pipe dip angleis90°、120°、150°,the liquid preferentially enters the side branch; When the branchpipe dip angle is30°, the gas preferentially enters the side branch; when the branchpipe dip angle is60°, the phase split characteristic is uniformity.When the phase split is the slug flow, the results show that when the branch pipedip angle is20°,30°,60°,90°,120°and150°, the gas preferentially enters the sidebranch. The larger the branch pipe dip angle, the higher the quality separationefficiency.Phase separation is the more obvious; Mass separation efficiency isgradually decreased when the inclination angle of the branch pipe is reduced. For thebranch pipe dip angle of20°and30°, the quality of separation efficiency difference isless than5%, causing lowest quality separation efficiency. The micro-channel branchpipe structural improvements can reduce the nonuniformity of phase. Calculated the phase distribution of two phase flow at the different time, thebubble separation process through the tee was investigated. With air and pure wateras working fluid, the relationship of the quality produced fraction and separationefficiency at the different gas velocity and liquid velocity was studied. The separationefficiency decreases with the increase of liquid velocity at a certain gas velocity.Phase separation is the more obvious; the separation efficiency is a little changed withthe increase of gas velocity at a certain liquid velocity.By comparing the results of slug and annular flow, it is shown that phase splitcharacteristic of micro-junction is very dependent on inlet flow pattern. If the flowpattern is slug flow, the gas preferentially enters the side branch. If the flow pattern isannular, the liquid preferentially enters the side branch.