CONJUGATE CONDUCTION AND LAMINAR MIXED CONVECTION IN VERTICAL PIPES FOR UPWARD FLOW AND UNIFORM WALL HEAT FLUX

Abstract

This paper presents the results of a numerical investigation of conjugate conduction and laminar mixed convection in vertical pipes for upward flow and uniform wall heat flux. The Prandtl number was fixed at 5; the Grashof number, based on heat flux, was set at 5000; and Reynolds numbers of 1 and 10 were used. Results are presented for four different values of solid-to-fluid thermal conductivity ratio K and three different values of wall thickness-to-pipe diameter ratio Δ. The effects of axial conduction in the pipe wall are quite pronounced when K and Δ are high and Re is low. In one case, upstream axial wall conduction distorted the parabolic velocity profile at the entrance of an upstream section to the point that the centerline velocity was negative at the entrance of the heated section, which established a zone of recirculation. Experimental flow visualization results and corresponding numerical predictions of these recirculation zones are also presented.