Direct numerical simulations of Rayleigh-Bénard convection of a gas-liquid medium near its density maximum

•Rayleigh-Bénard convection in the oxidation of hydrocarbons process is simulated.•Density inversion phenomenon plays a role of enhancing the stability of convection.•Flow pattern evolution strongly relies on the density inversion parameter.•A scaling relationship for average Nusselt number is successfully proposed. Oxidation of hydrocarbons is a commonly used chemical reaction due to the prominent economic value of its products in plasticizers, resins and other intermediate manufacturing processes. However, there is a significant explosion danger of the gas-liquid medium in this chemical reaction. Thus, it is necessary to make sense of the flow and thermal fields in the gas-liquid medium to manage the convection, avoid overheating and prevent explosion in the industry. A comprehensive numerical work of Rayleigh-Bénard convection of a gas-liquid medium near its density maximum was presented in this paper. The influences of the density inversion parameter and Rayleigh number on the flow stability, flow pattern evolution, and heat transfer ability of Rayleigh-Bénard convection were analyzed. The results show that the critical Rayleigh numbers for onsets of a steady convection and an unsteady convection rise with the increase of the density inversion parameter. The flow pattern evolution strongly relies on the density inversion parameter. The strength and heat transfer ability of Rayleigh-Bénard convection are enhanced as the Rayleigh number rises, while they are suppressed along with the density inversion parameter. A scaling relationship for the average Nusselt number on the bottom wall in terms of the Rayleigh member and density inversion parameter is successfully proposed. In addition, the predicted results based on the scaling correlation are consistent with those from simulations.