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Show Paper #21 COMBINED CONVECTION-RADIATION HEAT TRANSFER IN A SURFACE COMBUSTOR-HEATER -- -- ABSTRACT A.A. Mohamad and R. Viskanta Heat TransCer Laboratory School oC Mechanical Engineering Purdue University West LaCayette, IN 47g07 The paper presents a model to predict combined conduction-convection-radiation heat transCer in a porous bed Crom which heat is extracted by a coolant circulated in tubes embedded in the porous matrix. The two-dimensional model is based on first principles oC mass, momentum and energy conservation. The flow is modeled using the Brinkman-Forchheimer modified Darcy's equations, and the differential approximation is used Cor radiative transCer in the porous bed. Energy balances are made on the solid and the gas separately. The model equations are solved numerically using the SIMPLER algorithm. The numerical results reported in the paper show that the opacity oC the bed and the product oC the heat transCer coefficient and the surCace area per unit volume oC the bed are important parameters which control the thermal perCormance oC the system. NOMENCLATURE Ae surCace area oC the porous matrix per unit volume C inertia coefficient, C = 0.5 Cp specific heat D dimension oC square duct, see Fig.1 Eb Planck black body emitted flux, aT" -+ -+ -+ -+ ~ radiative flux vector, fF = iF x + jF y <'D irradiance g asymmetry Cactor H height oC porous matrix, see Fig.1 MIc chemical heat release rate per unit volume h heat transCer coefficient between solid matrix and gas ho heat transCer coefficient between solid matrix and ambient K permeability k thermal conductivity L length oC porous matrix, see Fig.1 ~ total heat extraction rate Crom system defined by equation (17) q heat flux at the tube surCace s distance measured around the duct perimeter T temperature Vi inlet velocity u,v velocity components in the x- and y-directions x,y coordinates |
