Laminar gas micro-flow convection characteristics due to steep density gradients

¹ Department of Aerospace Engineering, Indian Institute of Technology Bombay P.O. IIT, Powai, Mumbai, 400 076, India
² Technische Thermodynamik, Technische Universität Hamburg-Harburg Arbeitsbereich 6-08 - Denickestr. 17, D-21073 Hamburg, Germany

Corresponding author: spm@aero.iitb.ac.in

Received: 6 July 2004
Accepted: 25 October 2004

Abstract

We report numerical simulation of pure continuum-based laminar gas micro-flow convection with steep density gradients, which cause, for the case of heated air, flattening and rate of flattening of axial velocity profile. This flattening is similar to the characteristics in constant-properties slip flow, and high rate of flattening can cause hydrodynamic undevelopment of flow —the reverse process of hydrodynamic development. By continuity, radially outward velocities and radial convection are induced, which degrades convection performance. The low densities near the wall reduce the axial mass flux near the wall, which also degrades convection performance. In heated-gas micro-flows, these negative effects dominate to dictate the net convection characteristics, which differ considerably from the known characteristics of conventional continuum models. The identification of such microscale effects also has implications in possibly extending the limits of applicability of continuum models to higher Knudsen numbers.