Thermal management of a symmetrically heated channel–chimney system

A parametric analysis of natural convection in air, in a channel–chimney system, symmetrically heated at uniform heat flux, obtained by means of a numerical simulation, is carried out. The analyzed regime is two-dimensional, laminar and steady-state. Results are presented in terms of wall temperature profiles in order to show the more thermally convenient configurations which correspond to the channel–chimney system with the lowest maximum wall temperature. For the considered Rayleigh number, the difference between the highest and the lowest maximum wall temperatures increases with increasing the channel aspect ratio. The optimal expansion ratio values depend strongly on the Rayleigh number and extension ratio values and slightly on the channel aspect ratio. Correlations for dimensionless mass flow rate, maximum wall temperature and average Nusselt number, in terms of Rayleigh number and dimensionless geometric parameters are presented in the ranges: 5⩽Ra∗⩽2.0×104, 1.5⩽L/Lh⩽4.0 and 1.0⩽B/b⩽4.0.