Abstract:The second law performance of double diffusive forced convection in a horizontal porous channel with thick walls was considered. The Soret effect is included in the concentration equation and the first order chemical reaction was chosen for the concentration boundary conditions at the porous-solid walls interfaces. This investigation is focused on two principal types of boundary conditions. The first assumes a constant temperature condition at the outer surfaces of the solid walls, and the second assumes a constant heat flux at the lower wall and convection heat transfer at the upper wall. After obtaining the velocity, temperature and concentration distributions, the local and total entropy generation formulations were used to visualize the second law performance of the two cases. The results indicate that the total entropy generation rate is directly related to the lower wall thickness. Interestingly, it was observed that the total entropy generation rate for the second case reaches a minimum value, if the upper and lower wall thicknesses are chosen correctly. However, this observation was not true for the first case. These analyses can be useful for the design of microreactors and microcombustor systems when the second law analysis is taken into account.

The objective of the current investigation is to investigate the entropy generation inside porous media utilizing a pore scale modeling approach. The current investigation improves the thermodynamics performance of the recent analysis (Int. J. Heat Mass Transfer, 2016, 99, pp. 303–316) by considering different cross-sectional configurations and analyzing the thermal system for various Reynolds numbers, porosities, and a comparison between the previous and current investigation. The Nusselt number, the dimensionless volume-averaged entropy generation rate, Bejan number, and performance evaluation criterion (PEC) are all presented and discussed. The dimensionless volume-averaged entropy generation rate was found to increase with increasing Reynolds number, with the increase being higher for lower porosity medium. A slight variation of the dimensionless volume-averaged entropy generation rate is observed for higher Reynolds numbers which is confirmed for both cross-sectional configurations. Examination of the Bejan number demonstrates heat transfer irreversibility (HTI) dominance for most of the Reynolds number ranges examined. The results indicate that the longitudinal elliptical cross-sectional configuration with porosity equals to 0.53 provides superior performance when applying the performance evaluation criterion utilized.

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