Simulation Research On Flow Dynamics And Mass Transfer Of Slug Flow In Microchannel

As a new method of process intensification,microreaction technology has several specific advantages,such as the enhancement of heat and mass transfer,high safety characteristics,large surface volume ratio and so on.Due to these unique advantages,some reactions which are difficult to operate in traditional reactors,can be realized in microreactors and commercially produced.This work is supported by the National Natural Science Foundation of China(No.21676257).In this paper,the fluid dynamics including flow patterns,pressure drop,and mass transfer characteristics in gas-liquid two-phase flow of microchannel reactor are analyzed by numerical simulation.And the results can provide a theoretical reference for the optimal design of microchannels and the mass transfer between gas and liquid in industry.The work and main conclusions are as follows:(1)In this paper,CFD software was used to simulate the flow characteristics of the water-carbon dioxide system in the T-junction microchannel with diameter of 0.8mm.By comparing the elastic flow field in the fixed reference frame and the moving reference frame,it is found that the fluid in the liquid membrane is in reverse flow,which reduces the gas-liquid contact time,and the liquid vortex is symmetrical at both ends of the bubble,which promotes the diffusion of molecules and strengthens the mass transfer.At the same time,the simulation method of the moving reference frame is feasible.(2)The physical mass transfer process of water-carbon dioxide in a single bubble unit is simulated by using the single-phase flow and two-phase flow models in a moving reference frame,and it is found that the concentration distribution and velocity field in the fluid domain have good synergy.The effects of different factors on gas absorption process were simulated and analyzed.It was found that the shorter the residence time was,the greater the mass transfer coefficient was.The diffusion coefficient and the bubble velocity have the greatest influence,the higher bubble velocity and the larger diffusion coefficient can increase the volume mass transfer coefficient by nearly 1.2 times and 1.5 times,respectively.And the liquid film length has the least influence,only in the early mass transfer effect is significant,can increase by 20%.By comparing the obtained data with the experimental results,the reliability of the model is verified,and the prediction formula of the volume mass transfer coefficient in the initial stage and the reaction stage is proposed,with an error of ±20%(3)The chemical mass transfer process of carbon dioxide absorption by alcohol-amine solution in a single bubble unit was simulated.The results show that chemical reaction can further enhance the mass transfer effect of gas-liquid phase,and the volume mass transfer coefficient after adding the reaction is 1-2 times of that under pure physical absorption.The reaction is mainly carried out in the liquid domain.Under the influence of the flow field,the closer the product is to the center of the flow field vortex,the greater the concentration is.The mass transfer processes at different reaction rates were studied,and it was found that with the increase of reaction rates,the reactant consumption was accelerated,and the mass transfer was promoted.It is found that the higher the concentration,the higher the volume mass transfer coefficient and the faster the reaction.The influence of various model factors on the mass transfer enhancement factor is analyzed.The results show that chemical reaction and physical absorption affect each other.