Analytical Model Development And Numerical Simulation Of Gas-Liquid Interface Mass Transfer

In industry, a lot of reaction processes are carried out in gas-liquid two phase dispersion equipment, such as bubble columns, packed towers, etc. Have a good understanding of the interfacial mass transfer is of great significance for the designingand optimizing of these devices. Currently, research about the gas-liquid interfacial mass transfer theory is not perfect, many of the existing theoretical models have drawbacks, for example, some models are too idealized(ie. penetration model, surface renewal model), parameters in some models cannot be accurately measured and so on. Therefore, using these models to guide and optimize the industrial production process has great limitations. So, deeply investigate the mechanism of interfacial mass transfer and developing a universal theoretical model for understanding the mass transfer and guiding industrial production is very meaningful. This work focused on the mass transfer process of the gas-liquid interface, we will study the gas-liquid interfacial mass transfer in two parts.The first part is the gas-liquid interfacial mass transfer model. This model was derived from a 3-D unsteady-state convection and diffusion equation through a characteristics method. The different scale of fluid elements structure contribution to mass transfer was considered within the scope of the full energy spectrum in this article, this model can be used to predict the liquid side mass transfer coefficient in turbulent flow. Meanwhile, our model introduces a new concept of arriving frequency density which can represent the probability of the eddies arrived at the surface. It has been abandoned the assumption adopted by the previous model that all the eddies can reach the gas liquid interface. Furthermore,this model also consider the impact of the amount of fluid structures of different scales existing in the turbulent flows, size of bubbles, the deformation and oscillation of bubbles on mass transfer. At last, the overall mass transfer coefficient predicted by our model showed a better agreement with the reported experimental data.For the second part, the numerical simulation method was employed to analyze the gas-liquid interfacial mass transfer. Firstly, a novel quasi one-fluid equation is derived from the convection- diffusion equations on both sides of the gas and liquid. In order to solve the equation, we used the finite volume method(FVM) to discrete this equation. Meanwhile, a VOF method was used to track the gas-liquid interface. Meanwhile, in this paper, a new solver is developed in the open source software OpenFoam to simulate the different size bubbles rising in quiescent fluid. We chose the PIMPLE algorithms of OpenFoam to solve the pressure and velocity equation. The bubble rising trajectory, bubble rising velocity and bubble shape which have a great influence on the gas-liquid interfacial mass transfer and estimation of the local mass transfer coefficient. Finally, the numerical simulation results are in good agreement with the reported experimental data.