ENHANCEMENT OF HEAT-TRANSFER USING POROUS CONVECTION-TO-RADIATION CONVERTER FOR LAMINAR-FLOW IN A CIRCULAR DUCT

The convection-to-radiation converter (CRC) made of porous ceramics ha s been proven to be an effective means in the enhancement of heat tran sfer in burners, combustors, industrial furnaces and high temperature plug flow systems. The paper proposes a novel application using this C RC technique in a partial bypass flow system for potential heat transf er enhancement. Hydrodynamically fully-developed and thermally develop ing laminar how is assumed in a circular duct which is fitted with a p orous core to enhance both convective and radiative transfer from a hi gh-temperature gaseous medium to a heat-absorbing wall. The Navier-Sto kes and modified Darcy equations are applied, respectively, to the flo w held in a gas layer and porous core region. The radiation held is mo deled by a two-dimensional S-type integral equation of transfer for it s accuracy and efficiency in the numerical calculations. The effects o f heat transfer augmentation using a porous CRC are investigated numer ically for various flow and thermal parameters. Numerical solutions wh ich include velocity profiles and flow characteristics of the CRC syst em as well as isotherm patterns, parameterization of the heat fluxes, mean bulk temperature and Nusselt number distributions along the how d irection are presented. Copyright (C) 1996 Elsevier Science Ltd.