| Recent years,with the development of high-tech,header-channels systems attracted more and more interests,which could be encountered in a wide range of advanced equipment.There are some unique academic value and prospects of application for micro-channels compared with conventional size channels.For instance,high specific surface area of micro-channels allows more effective heat and mass transfer;the high-risk exothermic reaction can be carried out with more safety in narrow space;high-throughput drug screening can be performed by massively identical parallel-production lines;the reaction process can be precisely controlled in the form of plug flow.However,when a two-phase flow passes through the parallel channels,uneven distributions always happen in the branch channels.Maldistribution strongly influences the performance and even the safety of downstream equipments.Therefore,many researchers pay close attention to the study of phase distribution in the branch channels.Whereas,most scholars focused on mini-scale systems(1 mm< diameters?5 mm)or a single channel and T-junction.The dominant factors change substantially when the size of system is decreasing from macro-scale to micro-scale.The flow behavior in header and the interaction effect between the channels are also diffferent.Therefore,it's important to solve the problem of maldistribution by understanding the mechanism of two-phase flow distribution in parallel micro-channels.In this paper,the investigation of gas-liquid two-phase flow distribution in transparent parallel micro-channels is conducted based on the high speed photography and micro fluids control/measurement systems.1.The effect of typically related fluid properties in micro-scale on the phase distribution characteristics is studied,including surface tension and viscosity.The experimental results indicate that the gas phase distribution can be improved with a low surface tension,while the effect of surface tension on the uniformity of liquid phase distribution depends on the inlet flow patterns.Besides,the increase of viscosity will make the distribution uniformity of the liquid phase significantly better but that of the gas phase worse.2.The effect of operating conditions on the phase distribution characteristics is studied,including inlet conditions(superficial velocity of gas and liquid,etc.),orientaitons of header & channels and flow directions.The experimental results demonstrate that a uniform distribution of can be achieved by adjusting the inlet conditions for slug flow,while the inlet conditions has little effect on the phase distribution of annular flow.For slug-annular flow,the phase distribution is unstable but the duration of varying process and distribution results in stable state show regularity with different inlet conditions.What's more,the diverse impact of the orientations of header and channels is embodied not only on the effectiveness but also on the extent with different inlet flow patterns.3.The effect of relevant geometrical factors on the phase distribution characteristics is studyied,including the branch spacing,hydraulic diameter,number of channels and hydraulic diameter of header.The results show that the influence of branch spacing and hydraulic diameter of header is significant,and the hydraulic diameter of channels only has a significant influence on phase distribution of gas.In addition,the the phase distribution characteristics are similar with different numbers of branch channels.4.Based on the analysis of experimental data and the exploration of the key factors affecting the phase distribution of gas-liquid two-phase flow in parallel micro-channels,the empirical formulae for predicting the phase distribution of slug flow and slug-annular flow are established,which reflect the influence of inlet conditions,flow state inside the header and branch spacing on the phase distribution characteristics. |
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