Effects of density and thermal conductivity variations on entropy generation in gas micro-flows

Abstract

Abstract High temperature gradients in heat sinks of micro devices cause substantial properties variations in gas-micro-convection; which constitutes an important strategic research area in non-rarefaction scaling effects. In present analysis, compressible Navier–Stokes equations incorporating temperature dependent density and thermal conductivity variations, for steady, viscous flow of gas at subsonic speeds (Mach number ≪ 1) are numerically solved. Circular micro-pipe geometry, subjected to constant wall heat flux was chosen. The key observations are: In addition to known effects, two additional physical mechanisms increasingly surface at micro scale; and also determine the micro convection characteristics within continuum regime. They are, induced radial convection due to density variations in radial and axial directions and axial conduction induced due to thermal conductivity variations along the flow. High density variations in radial and axial directions, cause velocity gradients and increase fluid friction irreversibility. High thermal conductivity variations cause flattening of temperature profile, induce axial conduction and substantially increase in entropy generation. The results highlight the need for incorporating fluid properties variation in thermal designs of heat sinks for micro devices. Two-way link between velocity profile and temperature, influence entropy generation. Corner effects at entrance and exit influence entropy generation in all cases studied.