Fundamental Study of Laminar Low-Subsonic Micro-Convective Air-Flow with Density Variations Due to Temperature Gradients

摘要

Examining non-rarefaction effects in laminar micro-convective low subsonic (with negligible compressibility effects) gas flows is as important as the well-explored rarefaction effects. This study numerically analyzes one of the important non-rarefaction effects arising from steep density variations due to the steep temperature-gradients, in micro-convective air-flow. For the constant wall heat flux boundary condition with air-heated along the flow, density-variation over the cross-section sharpens the radial mass flux profile. This sharpening of radial mass flux profile is reduced along the flow by the flattening of axial velocity profile along the flow. Net sharpening of radial mass flux profile relative to the constant properties case reduces the axial advection, which reduces the Nusselt number. The varying radial mass flux profile along the flow induces a weak radially outward flow i.e. induces a radially outward advection that is not weak, which also degrades Nusselt number. The low Nusselt number values in this study relative to its value of the case of all constant properties (including density), highlight the significant role of density variations in laminar micro-convective gas flow.