EFFECTS OF THERMAL BOUNDARY CONDITIONS ON ENTROPY GENERATION DURING NATURAL CONVECTION Tanmay Basak, Ram Satish Kaluri, and A. R. Balakrishnan Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai, India A comprehensive numerical study on entropy generation during natural convection is studied in a square cavity subjected to a wide variety of thermal boundary conditions. Entropy gen- eration terms involving thermal and velocity gradients are evaluated accurately based on the elemental basis set via the Galerkin finite element method. The thermal and fluid irreversi- bilities during the conduction and convection dominant regimes are analyzed in detail for various fluids (Pr ¼ 0.026,988.24) within Ra ¼ 10 3 –10 5 . Further, the effect of Ra on the total entropy generation and average Bejan number is discussed. It is observed that thermal boundary conditions significantly affect the thermal mixing, temperature uniformity, and the entropy generation in the cavity. A case where the bottom wall is hot isothermal with linearly cooled side walls and adiabatic top wall is found to result in high thermal mixing and a higher degree of temperature uniformity with minimum total entropy generation. 1. INTRODUCTION The phenomena of natural convection in enclosures continues to be the subject of prime importance in fundamental heat transfer studies as innumerable natural, scientific, and industrial applications are based on the mechanism of natural convec- tion. In contrast to the external flows, the internal buoyancy-driven flows are complex due to essential coupling between the fluid flow and heat transfer. The external flow problems may be simplified assuming that the region outside the boundary layer is unaffected by the boundary layer at a large Rayleigh number. However, such simpli- fication is not possible for confined natural convection flows as the flow field exterior to the boundary layers (core flow) is unknown and that cannot be readily determined from the imposed boundary conditions, as the core flow is in turn dependent on the boundary layers formed at the walls. The problem becomes further complicated when the subregions, such as cells and layers, are embedded in the global core flow. Thermal boundary conditions play a major role in thermal processing of mate- rials. Although, the conventional heating methodology involving differential heating from the bottom portion is the most common type of boundary condition, various researchers have investigated the effects of alternative thermal boundary conditions Received 22 October 2010; accepted 29 November 2010. Address correspondence to A. R. Balakrishnan, Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai 600 036, India. E-mail: arbala@iitm.ac.in Numerical Heat Transfer, Part A, 59: 372–402, 2011 Copyright # Taylor & Francis Group, LLC ISSN: 1040-7782 print=1521-0634 online DOI: 10.1080/10407782.2011.549075 372