Developing Laminar Mixed Convection Heat Transfer Through Vertical Concentric Annuli With Adiabatic Inner Cylinder

Abstract

ABSTRACTTheoretical and experimental investigations have been carried out on developing laminar combined free and forced convection heat transfer in a vertical concentric annulus with uniformly heated outer cylinder (constant heat flux) and adiabatic inner cylinder for both aiding and opposing flows. The theoretical investigation involved a mathematical modeling and numerical solution for two dimensional, symmetric, simultaneously developing laminar air flows was achieved. The governing equations of motion (continuity, momentum and energy) are solved by using implicit finite difference method and the Gauss elimination technique. The theoretical work covers heat flux range from (200 to 1500) W/m2, Re range from 400 to 2000 and (1.36×105 ≤ Ra ≤ 1.1×107) with radius ratio of 0.555 which is the same radius ratio used in the experimental part of this study and Pr=0.7. The experimental work includes construct a rig consists essentially of an annulus with uniformly heated outer cylinder and adiabatic inner cylinder to give clear insight into heat transfer process and compare its results with that obtained in theoretical part, the range of the study are (Re= 383, 724, 1000, 1500) and heat flux equal to (q =370, 422, 588, 980) W/m2. Numerical results were represented by the temperature profile, axial velocity profile, outer surface temperature and the distribution of local Nusselt number along the dimensionless axial distance. The velocity and temperature profile results have revealed that the secondary flow created by natural convection have significant effects on the heat transfer process. Results reveal also that the experimental local Nusselt number along the annulus follows the same trend as present theoretical results with mean difference 10.23 %.