Numerical Simulation Of Gas-liquid Flow And Mass Transfer In Bubble Column Based On WA-PBM Coupled Model

Bubble column has been widely used in petroleum,biology,metallurgy,environment and other industrial processes because of its low cost and high efficiency of mass and heat transfer.However,the gas-liquid hydrodynamic behavior and transfer characteristics in the reactor are complex,which makes it difficult to design,scale-up and optimize the bubble column reactor.In this case,the construction of a numerical model with high calculation efficiency and low cost to accurately describe the flow and mass transfer behavior of bubbles and liquids in the bubble column is of great significance.In this paper,considering the interphase interaction,Wray-Agarwal（WA）one-equation turbulence model coupled with population balance model（PBM）was used for the first time to construct the three-dimensional computational fluid dynamics（CFD）model to simulate the gas-liquid two-phase flow and mass transfer in bubble column.The effects of outlet boundary conditions,interphase force model,gas-liquid mass transfer model and operating conditions on gas-liquid flow and mass transfer processes were investigated.The main research results are as follows:（1）Taking the bubble column as the research object,using the WA-PBM coupled model,the numerical simulation of its gas-liquid two-phase flow behavior was carried out.The effects of different interfacial force models on gas axial velocity and liquid axial velocity are studied by 18 groups of orthogonal numerical tests,and the optimal combination of interphase force models and outlet boundary condition was determined.On this basis,the coefficients of the wall lubrication force model were optimized.Finally,the simulated values of the CFD model of liquid axial velocity,turbulent kinetic energy,average bubble diameter and bubble plume oscillation period were in good agreement with the experimental values,and the average deviation is within^?20%.（2）The optimized gas-liquid two-phase CFD model in the bubble column was extended to different bubble column gas-liquid systems.The gas-liquid flow under different operating conditions was numerically simulated.The simulated liquid axial velocity was in good agreement with the experimental values,and the deviation was within^?20%,indicating the effectiveness of the WA-PBM-interphase force model in the bubble column gas-liquid system.With the increase of gas superficial velocity,the gas and liquid axial velocity increases,the turbulent kinetic energy increases,the bubble size distribution widens,and the average bubble diameter increases.（3）In order to explore the mechanism of gas-liquid mass transfer in the bubble column,combining the experimental measurements,the three-dimensional CFD model of the CO₂physical absorption processes in the bubble column was further established.The predicted value and experimental data of the CO₂mass fraction in the liquid using different mass transfer models were compared.The results show that compared with the other two models,the simulated values of the modified eddy cell mass transfer model were in the best agreement with the experimental values,and the error was less than±20%.At the beginning of the mass transfer process,the gas holdup and bubble diameter of the system were lower than 50%of those in the process without mass transfer.With the increase of gas flow rates,the gas holdup,average bubble diameter,gas-liquid interface area and mass transfer coefficient all increased gradually,but the growth rate of mass transfer coefficient was small.With the increase of the static liquid height,the gas holdup,the gas-liquid interface area,and the mass transfer coefficient decrease gradually.When static liquid height increased from 0.4 m to 1.2 m,the gas-liquid interfacial area decreased by 28%,and the volumetric mass transfer coefficient decreased by 43%.