Numerical Study Of Phase Split Characteristics Of Slug Flow At A Dividing Micro-T-junction

The branching micro-T-junction is widely used as a special form during various types of micro-pipes in micro/nano electromechanical systems,electronic cooling,food engineering and other fields.When the gas-liquid two-phase flow passes through the T-junction,due to the structural characteristics of the junction and the difference in gas-liquid two-phase fluid properties,the uneven distribution of the phases will inevitably take place between the branch and main.This phenomenon is known as mal-distribution.The micro-T-junction are usually used as the heat exchanger elements of the microelectronic equipment.The uneven distribution of the phases will cause the downstream branch tubes to have different dryness,which will affect the heat transfer and mass transfer performance,and serious phase misalignment will cause damage to the equipment..In this paper,the method of computation fluid dynamics(CFD)was adapted to study the phase split behavior of slug flow in a branching micro-T-junction,under the condition of fixed unit slug length.The reliability of the model is verified through comparison with experimental results and mesh independence test.Then the phase split behavior and flow field characteristics of slug flow are simulated.The flow pattern of bubble breakup observed in microfluidic T-junctions were breakup with permanent obstruction and breakup with tunnels.The driving force for breakup with permanent obstruction originates from the upstream pressure.As for flow pattern of breakup with tunnels,the role of shear force becomes important with the thickening of the tunnel between the bubble and the channel wall.The influences of velocity,liquid viscosity,surface tension and branching angle on the phase split results were studied under the condition of fixed unit slug length.The results show that when the bubble length is long,velocity,liquid viscosity,and surface tension have little effect.With the decrease of bubble length,the role of velocity and surface tensions should not be slighted.What's more,the degree of mal-distribution decreases with the decrease of velocity and increase of surface tension.In addition,as the branch angle increases,the phase split curve moves to the gas enrichment zone which means that the degree of mal-distribution increases.The predictive model of phase split at a branching micro-T-junction was studied.By comparison the phase split results of micro-scale with macro-scale,the effect ofscale effect was analyzed and a conventional phase split prediction model was established.What's more,the liquid slug length has a negligible effect on the split results of gas phase.Thus,the results of two phase split could be obtained from the gas split ratio solely.By analyzing the influence of various factors on the bubble breakup process,the critical conditions for the transition of breakup with permanent obstruction and breakup with tunnels are obtained.Finally,based on different flow pattern of bubble breakup,a new phase distribution prediction formula is proposed formulated with the regression analysis of numerical data.