Entropy Generation of Double Diffusive Forced Convection in Porous Channels with Thick Walls and Soret Effect

Abstract

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.

Non-Equilibrium Thermodynamic Analysis of Double Diffusive, Nanofluid Forced Convection in Catalytic Microreactors with Radiation Effects

“…The present study advances the previous investigation of Torabi et al [13] by two important modifications: (1) nanofluid flow has been considered through the microchannel and (2) LTNE model of thermal transport has been applied to the porous section of the system. As internal heat generation is an intrinsic feature of many microreactors, the use of LTNE model instead of LTE approach provides more accurate predictions of the temperature field [24,25].…”

“…It is emphasised that the assumption of fully developed flow has been included in the derivation of Equations (2b) and (2c). The dispersion equation, which is coupled with the temperature of the nanofluid via the thermodiffusion coefficient can be written as [13]:…”

“…The thermophysical problem described above includes three main governing equations, namely momentum, energy and dispersion expressed by Equations (12), (13) and (15), respectively. Each of these equations can be solved analytically by a straightforward mathematical manipulation and integration.…”

“…This could be due to the peculiar features of microstructure devices that complicate the analysis. For example, the small dimensions of microreactors warrants inclusion of the solid walls of microchannels within the thermophysical calculations of the system [12,13]. Further, due to the internal heat generation within the microreactor, the local thermal non-equilibrium (LTNE) approach should be applied to the thermal analyses of porous microreactors [14,15].…”

“…Yet, to the best of the authors' knowledge so far, there exists only one investigation on the double diffusive forced convection in microreactors. Recently, Torabi et al [13] have investigated the entropic characteristics of porous microchannels with thick walls, when a first order chemical reaction occurs at the porous-solid wall interfaces. An LTE model was used to model the heat transport through the porous section of the microchannel and internal radiation heat transfer was also considered in the analysis.…”