Thermal design and optimization of vertical convergent channels in natural convection

In this study, design charts for the evaluation of thermal and geometrical parameters, when some of these are known, are proposed for natural convection in air, in vertical convergent channels. A simple procedure to obtain thermal design charts is presented. The optimal spacing and convergence angle, in terms of thermal performance, is obtained from composite correlations of average Nusselt number and dimensionless maximum wall temperature as a function of Rayleigh numbers. Results are carried out for symmetrically heated channels with walls at uniform heat flux. The proposed charts are obtained starting from data of numerical investigation in the following parameter ranges: surface emissivity from 0.10 to 0.90, convergence angle from 0° to 10°, 2.0 ⩽ L/bmax ⩽ 60, 0.048 ⩽ bmin/bmax ⩽ 1.0 and