It is of great significance to study the mass transfer and mixing of gas in natural convection flow caused by density gradient resulted from thermal conditions because chemical reactions mainly depend on the gas molecular concentration in fluids and the natural convection can strengthen the transport of gas molecules.The diffusion process of oxygen molecules is simulated with the natural convection developed in a simplified container

coupling with the effects of thermal and mass diffusion.On the basis of impressible flow of lattice Boltzmann(LB) model D2G9

a two-dimensional nine-speed lattice Boltzmann model D2Q9 of diffusion-natural convection is first built up to simulate the diffusion processes of heat energy and mass

with non-equilibrium extrapolation boundary scheme.Then the thermal natural convection and gas mass transfer process are simulated with three kinds of thermal boundary conditions in order to analyze and explore how the thermal conditions influence the fluid flow and mass transfer of gas.The calculated results are consistent with the published data.The effect of thermal condition on the natural convection flow is analyzed and the differences in velocity distribution between the numerical data and published data are discussed.The thermal flow dependent mass transfer provides a basis for designing appropriate thermal conditions to control the chemical reaction processes.