Regular Article

Active chimney effect using heated porous layers: optimum heat transfer^*

¹ LTPMP Laboratory, Faculty of Mechanical and Process Engineering, University of Science and Technology Houari Boumediene, Algiers, Algeria
² Key Lab of Refrigeration Technology, Tianjin University of Commerce, 300134 Tianjin, P.R. China
³ LMT/ENS-Cachan/CNRS/Université Paris Saclay, 61 av. du Prés. Wilson, 94235 Cachan, France

^a e-mail: tofik.mehiris@outlook.fr

Received: 25 October 2016
Revised: 13 January 2017
Accepted: 20 February 2017
Published online: 12 May 2017

Abstract

The purpose of the present work is to treat numerically the problem of the steady mixed convection that occurs in a vertical cylinder, opened at both ends and filled with a succession of three fluid saturated porous elements, namely a partially porous duct. The flow conditions fit with the classical Darcy-Brinkman model allowing analysing the flow structure on the overall domain. The induced heat transfer, in terms of local and average Nusselt numbers, is discussed for various controlling parameters as the porous medium permeability, Rayleigh and Reynolds numbers. The efficiency of the considered system is improved by the injection/suction on the porous matrices frontier. The undertaken numerical exploration particularly highlighted two possible types of flows, with and without fluid recirculation, which principally depend on the mixed convection regime. Thus, it is especially shown that recirculation zones appear in some domain areas under specific conditions, obvious by a negative central velocity and a prevalence of the natural convection effects, i.e., turnoff flow swirls. These latter are more accentuated in the areas close to the porous obstacles and for weak permeability. Furthermore, when fluid injection or suction is considered, the heat transfer increases under suction and reduces under injection.