The enhancement of mixed convection in a metal foam-filled elliptic annulus by a spatially variable heat flux

Abstract

Thermal performance enhancement is obtained when the same heat input that is uniformly imposed on a conduit wall is concentrated over short axial bands that are separated by adiabatic bands. This study explores numerically the heat transfer enhancement, with a variable concentrated heat flux, for the three-dimensional mixed convection in a metal foam-filled elliptic annulus. This work studies the effect and synergy of the spatially periodic or aperiodic heat flux, the metal foam structure, the annulus orientation and geometry and the dynamic and thermal controlling parameters on the mixed convection heat transfer performance, the axial evolution of the cross-section temperature difference and the annulus pressure drop. The results of the spatially variable heat flux are compared with those of the constant and uniform heat flux. For the same heat input and the same flow rate, in most of the considered cases in this study, the spatial variation of the heat flux enhances the heat transfer, decreases slightly the pressure drop but increases the cross-section temperature variation along the heated bands. A totally adiabatic end portion of the annulus is found to considerably enhance the homogenization of the cross-section temperature towards the annulus exit.