Entropy generation due to natural convection with non-uniform heating of porous quadrantal enclosure - A numerical study

Abstract

Industrial processes optimization for higher energy efficiency may be effectively carried out based on the thermodynamic approach of entropy generation minimization (EGM). This approach provides the key insights on how the available energy (exergy) is being destroyed during the process and the ways to minimize its destruction. In this study, EGM approach is implemented for the analysis of optimal thermal mixing and temperature uniformity due to natural convection in quadrantal cavity filled with porous medium for the material processing applications or for cooling of electrical equipments. Effect of the permeability of the porous medium and the role of non-uniform heating in enhancing the thermal mixing, temperature effects and minimization of entropy generation is analyzed. The numerical solutions are obtained using finite element method. Stream lines, Isotherms and Entropy generation results are depicted for Ra=106, 1.7x105, 104 and for Da=10-3, 10-4 and 10-5 at Pr=0.71.It is found that at lower Darcy number (Da), the thermal mixing is low and the heat transfer irreversibility dominates the total entropy generation. In contrast, thermal mixing is improved due to enhanced convection at higher Da. It is observed that fluid friction irreversibility dominates over heat transfer irreversibility for only Da=10-3 at Ra=106. The local entropy generation is maximum at the bottom wall, while at the center and top of the enclosure it becomes minimum. Based on EGM analysis, it is established that total entropy production is not significant with larger thermal mixing at high Darcy number, and can be recommended for material processing process or for cooling of electrical equipments.