The effects of temperature-dependent viscosity and coefficient of thermal expansion on the stability of laminar, natural convective flow along an isothermal, vertical surface

Abstract

The effects of temperature-dependent viscosity and coefficient of thermal expansion on the stability of laminar, natural convective boundary-layer flow of a liquid along an isothermal, vertical surface are studied employing linear stability theory for Prandtl numbers 7–10. Numerical solutions indicate that the temperature-dependent viscosity stabilizes the flow along a heated wall and destabilizes it along a cooled wall. The temperature-dependent coefficient of thermal expansion initially stabilizes the flow for a heated wall but farther downstream it destabilizes the flow. Flow visualization studies in water with an isothermal, vertical copper pipe (outside diameter 41.3mm and length 1 m) for various combinations of wall and ambient temperatures in the range 5–35°C support the numerical predictions.