CFD Simulation On Hydrodynamics And Internal Circulation Of Liquid-liquid Slug Flow In Microchannels

Microstructure reactor has a broad application prospect in the fields of organic synthesis,drug screening and chemical engineering.Study on hydrodynamics parameters and internal circulation of two phase flow in microchannels can provide guidance for optimizing the operation conditions of reactors and developing a novel reactor with high performance.Based on the computational fluid dynamics software ANSYS Fluent16.2,the two-dimensional T model of microchannel was established,the hydrodynamics and internal circulation of the liquid-liquid slug flow in the microchannel were simulated.The main contents included the following aspects:The droplets formation mechanism of slug flow is divided into dripping regime and squeezing regime.The critical capillary number(Ca_cr)of the two mechanisms is between 0.013 and 0.016.The effects of the capillary number and two phase flow rate on the hydrodynamic parameters such as the length of the dispersed phase slug,the thickness of the liquid film,and the velocity of dispersed phase slug were investigated.The dependence of slug length on flow rates and other parameters like capillary number was determined.The results show that slug length increases as the flow rates of the dispersed phase increases and it decreases as the flow rates of the continuous phase and capillary number increase.The film thickness is well predicted by available models with an average error of 11%.Due to the existence of liquid film,the slug velocity is greater than mixing velocity.Correlation of slug length and slug velocity is developed based on the simulated data which are???,respectively.The average error between the correlation and experimental values are 20%and17.7%,respectively.By changing the inlet geometry and dimensions of T-junction channel and its influence on the hydrodynamic parameters of the slug flow was studied.The inlet geometry has little effect on the hydrodynamic parameters,while the inlet size has great influence on the hydrodynamic parameters.At the end of this paper,we study the internal circulation of slug flow.The velocity field inside the slug flow has a parabolic shape and is symmetrical about the central axis of the channel,the velocity reaches a maximum at the channel core.Two typical counter-rotating vortices which symmetrical to the channel centerline were found in dispersed phase slug.The position of vortices are related to the dispersed phase flow rate.When the flow rates of dispersed phase and continuous phase are equal,the best mixing effect can be achieved.