Numerical Simulation Of Gas-Liquid Interfacial Mass Transfer With Rayleigh Convection And Mass Transfer Coefficient Prediction

In the process of gas-liquid interfacial mass transfer,the system is termed as Rayleigh unstable system if there is reverse density gradient caused by the concentration gradient of solute at the interface.The Rayleigh convection can be induced at the interface once the instability reaches the critical value and there is a disturbance at the interface.Subsequently,the convective structure of Rayleigh will evolve into the main part of liquid phase,which has an important influence on the interfacial mass transfer.Take CO₂-ethanol absorption process as an example,a random disturbance interfacial model based on Lattice-Boltzmann method-Finite Difference method?LBM-FDM?was proposed for numerical simulation of Rayleigh convection occurred in the gas-liquid interfacial mass transfer process.The critical onset time of Rayleigh convection was used as a criterion for judgment to determine the disturbance parameters of random disturbance model.The simulated results were compared with the Schlieren experimental results in order to verify the effectiveness of numerical noise control and accuracy of Rayleigh convection characteristics,in preparations of reliable data for the next step for mass transfer coefficient prediction.Due to the complexity of interfacial fluid flow and interfacial properties,there is no universal model for predicting mass transfer coefficient.In this paper,the mass transfer coefficient of absorption mass transfer process with Rayleigh convection was studied.Mass transfer coefficient of mass transfer process with Rayleigh convection depends on the concentration field and velocity field near the interface,which could be provided by the numerical simulation.It was assumed that the mass transfer process with Rayleigh convection was a special type of turbulence.Then several mass transfer coefficient prediction models?equations?were derived by using physical quantities from turbulent mass transfer model?small eddy model and surface divergence model?and computational mass transfer for reference.Different models?equation?had advantages in different aspects,such as fitting degree,peak value of mass transfer coefficient,the time to peak value of mass transfer coefficient,phase difference,and instantaneous value of mass transfer coefficient in full development stage of Rayleigh convection.The good results of the mass transfer coefficient prediction showed that eddies affected the mass transfer in the same way,not dependent on the means of turbulence generating,thus proved the assumption.Subsequently,the numerical simulation method of desorption process and its mass transfer coefficient was predicted by analogizing.And some optimization work about mass transfer coefficient prediction was done based on particular characteristics.On the basis of two dimensional numerical simulation,gas phase random disturbance model in the frame of Lattice-Boltzmann method-Finite Difference method?LBM-FDM?was established for three dimensional numerical simulation.The simulation results were in good agreement with the Schlieren experimental images,and characteristics which were unobservable in experiments were investigated.Based on the two-dimensional mass transfer coefficient prediction method,the three dimensional predictions formula of mass transfer coefficient were obtained by following the two dimensional mass transfer coefficient prediction methods.