Numerical Simulation Of Gas-liquid Two-phase Flow And Mass Transfer Of CO₂ Absorption In A Microreactor

The microreactor is one of the cores of microchemical technology,and the microchannel is the core component in the microreactor.In this paper,the hydrodynamic characteristics of gas-liquid two-phase flow in the microreactor were studied by numerical simulation,the velocity distribution in the slug flow was obtained,and the change of velocity in the each part of liquid phase were analyzed in detail.On the basis of flow,the mass transfer of CO₂absorption and flow were coupled to further simulate the mass transfer of CO₂absorption in slug flow.The liquid phase for physical absorption is water and ethanol solution,the liquid phase for chemical absorption is 0.2M monoethanolamine solution and 0.2M Na OH solution,and the gas phase is a mixture of 5 vol.%CO₂and 95 vol.%N₂.The flow and mass transfer characteristics in the microchannel are different in different liquid phases.Based on the permeation theory,the concentration field distribution of CO₂absorption was obtained and described in depth through the local simulation of the coupling of flow and mass transfer.The effects of contact time and bubble velocity on the mass transfer process were discussed.The volumetric mass transfer coefficient of bubble cap and liquid film,CO₂absorption rate and enhancement factor under physical and chemical absorption were calculated and analyzed.The effects of model changes on the mass transfer of CO₂absorption under physical absorption were analyzed.The results show that the vortex in the flow field enhanced the mass transfer,the CO₂absorption rate increased with the increase of the flow velocity and the length of the liquid slug,which decreased with the increase of the channel diameter and bubble length,while the increase of the unit length had little effect on the CO₂absorption rate.The volumetric mass transfer coefficient of chemical absorption was between 3.5 and 7.5,which is about 3 to 10 times that of physical absorption.The absorption of CO₂is more complete in chemical absorption,and the absorption rate is close to 100%,while the absorption rate of physical absorption is not more than 50%.The new empirical correlations for predicting the volumetric mass transfer coefficient of liquid phase were proposed respectively in physical absorption and chemical absorption,which were compared with the empirical formulas in some literature.The volumetric mass transfer coefficients obtained by predictive correlations were in good agreement with those obtained by simulation in this paper.Finally,the model of slug flow in the microreactor was optimized,and the mass transfer of CO₂absorption was compared in different models.It was found that the effect of mass transfer in the unit cell with concave diameter was better than that in the unit cell with convex diameter.This work made a basic prediction for industrial realization of CO₂absorption in microreactor and laid a foundation for the following experimental research.