Convection mixte défavorable et conjuguée dans un tube vertical

Abstract

This paper presents the results of a numerical study aimed at quantifying the effects of wall conduction on laminar mixed convection in vertical pipes for a downward flow and a uniform wall heat flux boundary condition. Results are presented for water ( Pr = 5) and two values of the ratio Gr q/ Re 2 (50 and 5000). Results indicate that a significant amount of heat is redistributed upstream of the heated section when the solid-to-fluid thermal conductivity and/or the wall thickness-to-pipe diameter ratios are high. Furthermore, for Gr q/ Re 2 = 5000, a recirculation cell is established near the wall. This cell extends approximately 25 diameters upstream of the heated section. Over this distance, the cell acts as an insulator and, consequently, heat is transferred longitudinally in the wall up to the start of the cell where it is released in the fluid.