Phase Distribution Characteristics Of Gas-liquid Two-phase Flow In Branching Micro-t-junctions With Different Branch Channel Diameters

with the development of micro-chemical technology,micro T-junctions are widely used as a micro-chemical reactor in biomedical synthesis,precise control of micro-droplets or micro-bubbles as a common split flow channel.Besides,micro T-junctions are widely applied as a micro heat exchanger in various occasions,such as in nuclear power plant reactor and solar thermal conversion and heat exchanger of heat pump because of the simple structure.As the channel measurement decreases from the macro scale to the micro scale,the gas-liquid two-phase separation mechanism also changes.So far,most of the studies are based on experimental methods,exploring the effects of various channel’s geometric factors and fluid physical properties on the two-phase distribution characteristics in equal branching micro-T-junctions,including gas and liquid superficial velocity,fluid physical properties（density,viscosity）,branch angle,etc.Whereas,the previous experimental study mainly focuses on the flow distribution in micro T-junctions with the same diameter due to the limitation of microscale channel fabrication technology,there are few studies on unequal branching micro-T-junctions,and the related phase distribution mechanism is urgently needed to be studied.In this paper,an experimental investigation was conducted to study the effect of branch channel diameters on phase distribution behaviors of the two-phase flow in horizontal branching micro-T-junctions.Branching micro-T-junctions with different branch channel diameters were designed.The cross section of the inlet channel was 1000μm×500μm and the cross section of the branch channel was 400μm×500μm,600μm×500μm and 800μm×500μm,respectively.Nitrogen and pure water at 120 k Pa（abs）and 25°C were chosen as the working fluids.A high speed camera was used to clarify the fluid dynamics of the gas–liquid two-phase flow in the test section.The main research contents are as follows:（1）The effects of the variation of branch channel diameters on phase distribution at slug flow,slug-annular flow and annular flow are studied respectively,and it is found that the phase distribution curve has different characteristics when the flow patterns changes.More liquid flows into the branch channel at the same gas fraction when the branch diameter decreases at slug flow while less liquid phase flows into the branch channel on the same condition at slug-annular flow.As for annular flow,there is no clear correlation between F_L3 and changes of branch diameter.Besides,the separation efficiency was used to survey the influence of branch’s diameter more accurately,It is found that the separation efficiency has different trends due to different flow patterns.（2）The formula which can be applied to predict the phase distribution of slug-annular flow is established,which fully considered the influence of width ratio between branch channel and main channel,inlet gas and liquid velocity,fluid viscosity,density and surface tension.（3）The observed flow phenomena of the slug flow,slug-annular flow and annular flow were further analyzed to explore the effect of the changes of branch channel diameters and gas taken off fractions on the flow phenomenon at different flow patterns.