Dual influence of temperature and gas composition of selected helium-based binary gas mixtures on the thermal convection enhancement in Rayleigh–Bénard enclosures

Abstract

This paper addresses the potential augmentation of natural convection heat transfer in Rayleigh–Bénard enclosures when filled with a certain type of binary gas mixture. To form the binary gas mixtures, helium (He) is the primary gas and the secondary gases are nitrogen (N 2), oxygen (O 2), carbon dioxide (CO 2) and methane (CH 4). Each of the thermo-physical properties participating in the binary gas mixtures viscosity η m, thermal conductivity λ m, density ρ m, and heat capacity at constant pressure C p,m depends on the molar gas composition, temperature and pressure. Results are presented in terms of the maximum allied heat transfer coefficient h m,max/ B at the optimal mole gas composition w opt, in the w-domain [0, 1] for the entire range of laminar and turbulent conditions. In the conduction regime, He provides the best heat transfer regardless of temperature. In the convection regime at 300 K a He–CO 2 mixture usually provides the maximum heat transfer, whereas at 1000 K pure methane CH 4 is the optimum. In addition, a detailed thermo-fluidic structure of the thermal convection patterns in the Rayleigh–Bénard enclosure was analyzed by performing 2-D numerical simulations.