Compelling Heat Transfer Augmentation of Laminar Natural Convection from Vertical Plates to Binary Gas Mixtures Formed with Light Helium and Selected Heavier Gases

Abstract

The present study addresses a remarkable behavior of certain binary gas mixtures in connection to laminar natural convection along a heated vertical plate at constant temperature. The binary gas mixtures are formed with light helium (He) as the primary gas and selected heavier secondary gases. The heavier secondary gases are nitrogen (N2), oxygen (O2), xenon (Xe), carbon dioxide (CO2), methane (CH4), tetrafluoromethane (CF4) and sulfur hexafluoride (SF6). The central objective in the study is to investigate the attributes of the set of seven He‒based binary gas mixtures for heat transfer enhancement with respect to the heat transfer with helium (He) and air. From heat convection theory, four thermo‒physical properties: viscosity η, density ρ, thermal conductivity λ, and isobaric heat capacity Cp affect the thermo‒buoyant convection of fluids. In this study it became necessary to construct a particular correlation equation consigned to the set of seven He‒based binary gas mixtures, which operate in the Prandtl number closed sub‒interval [0.1, 1]. The heat transfer rate with the set of seven He‒based binary gas mixtures from the vertical plate involves four thermo‒physical properties: density ρmix, viscosity ηmix, thermal conductivity λmix, and isobaric heat capacity Cp, mix that vary with the molar gas composition w. A case study is performed to elucidate the unique characteristics of the modified convective heat transport that the set of seven He‒based binary gas mixtures brings forward as compared to the convective heat transport of He and air. It was found that the He+SF6 binary gas mixture renders an absolute maximum heat transfer enhancement rate that is 39 times higher than the heat transfer rate provided by He and 78 times higher than air.