Entropy generation for unsteady natural convection and radiation within a tilted saturated porous channel K. Slimi Institut PreÂparatoire aux Etudes d'IngeÂnieurs, Avenue Ibn Eljazzar, 5019, Monastir, Tunisia Fax: (+216)73 500 512 E-mail: khalifa.slimi@ipeim.rnu.tn Abstract: The problem of entropy generation for unsteady natural convection and radiation in a tilted open-ended channel, submitted to uniform hot walls temperature and filled with an isotropic fluid saturated porous medium is outlined. The present study is carried out using the Darcy flow model. The local thermal equilibrium assumption is assumed. Viscous dissipation effects are taken into account. The radiative coupling problem is solved numerically by the finite volume method. Present solutions are compared with known results from previous published work. Excellent agreement was obtained between results that validate the used computer code. The results show that the global heat transfer rate depends slightly on the viscous dissipation term but is strongly subordinate to the tilted angle. Moreover, the calculation of entropy generation maps is feasible and gives us a measure of the degree of irreversibility of the convective flow. Keywords: entropy generation; porous medium; radiation; tilted channel; unsteady natural convection. Reference to this paper should be made as follows: Slimi, K. (2006) `Entropy generation for unsteady natural convection and radiation within a tilted saturated porous channel', Int. J. Exergy, Vol. 3, No. 2, pp.174±190. Biographical notes: Dr K. Slimi is at present a Researcher at the Laboratoire d'Etudes des SysteÁ mes Thermiques et Energe tiques (LESTE), ENIM, Tunisia, and his research is conducted within the framework of his preparation of the `Habilitation Universitaire' in Physics. 1 Introduction Great attention has been paid to the thermally-induced convection in fluid-saturated porous media coupled with thermal radiation because of its direct relevance to a variety of engineering and technical systems and applications operating at high temperatures such as industrial furnaces, heat storage, heat exchangers, solar collectors, transport in packed and circulating bed combustors and reactors, oil reservoir modelling and thermal insulation, to name a few. The radiative heat transfer in porous media has been investigated by an increasing number of researchers (Kaviany and Singh, 1993; Slimi et al., 2004; Tien, 1988). These studies have been restricted, from a thermodynamic point of view, to only the first law of thermodynamics' analyses which is simply an expression of the Int. J. Exergy, Vol. 3, No. 2, 2006 174 Copyright # 2006 Inderscience Enterprises Ltd.