Study On Gas-liquid Two-phase Flow And Bubble Dynamics In Parallel Microchannels

The key step in micro-chemical technology from basic research to industrial applications is the scaling-up of micro-chemical processes.In order to realize the highthroughput,easy-to-control and uniform production of the products in the industrialized operation,the “numbering-up” of the micro-chemical process is mainly achieved from two directions: fluid distribution among the multi-channels and splitting of products step-by-step.In this paper,the key scientific issue of “uniformity of distribution of multiphase flow in parallel microchannels” is focused,the flow of gas-liquid two phases and dynamics of bubbles generation in parallel microchannels with typical structures were studied experimentally.The uniformity of the gas-liquid two-phase flow and slug bubble in a symmetrical parallelized branching microchannel were studied by using a high-speed camera system.Two flow patterns of slug flow and bubblly flow were observed,and the related flow patterns map and the transition lines for adjacent flow patterns were constructed by using flow rates of gas and liquid phases.The results show that the non-uniformity of bubbles is caused by the hydrodynamics interaction between the two channels,the hydrodynamics feedback of the downstream channels,and the manufacturing differences of microchannels.The bubble size distribution can be more uniform for low gas pressure,high flow rate and high viscosity of the liquid phase.Considering the feedback of fluid dynamics in the downstream microchannels,the prediction models of bubble size in both microchannels were established.The stability and distribution of gas-liquid two-phase flow in asymmetric parallel microchannels with four different configurations were focused.It is found that the stability of bubble formation is better under higher flow rates of gas and liquid,and when the flow rates ratio of gas and liquid is smaller,the uniformity of bubbles is better.The design of the cavities in the microchannel structure degrades stability,while results in better uniformity.The stability in bubble formation in the microchannel structured with a cavity in the rear is better than that in the front.The uniformity of the bubble size is the best in the microchannel engineered with cavity in both the front and rear.The uniformity of the bubble size in the microchannel with cavity in the front is better than that in the rear.The prediction models for relative deviation E(L)of bubble size in different microchannel structures were proposed.The mesoscale mechanism of the distribution with gas-liquid two-phase flow in parallel microchannels was explored.The dynamics of bubble formation and the complex interfacial behavior among multiple bubbles in the cavity affect the uniformity of the bubble size.There are synchronous and alternating two bubble formation mechanisms in symmetric parallel microchannels,resulting in different evolution of gas-liquid interface.As a result,the difference of pressure fluctuations in the two microchannels is generated.The bubble shape in the cavity and complex interfacial behavior among multiple bubbles affect the flow resistance in the downstream channel.Furthermore,the Laplace pressure in the bubble neck and the fluid resistance affect the uniformity of the bubble size.