Entropy generation of viscous dissipative nanofluid convection in asymmetrically heated porous microchannels with solid-phase heat generation

Abstract

Nanofluid exhibits great potential in enhancing thermal performance of cooling devices. From the second-law point of view, we investigate the entropy generation of nanofluid flow in asymmetrically heated porous microchannels with solid-phase heat generation. Based on two-energy-equation model, the closed-form temperature distributions of porous medium solid phase and nanofluid are obtained. The thermal non-equilibrium entropy generation function is derived by using differential method. The results show that the thermal asymmetries significantly affect the temperature distribution and hence the heat transfer irreversibility in the system. However, the fluid friction irreversibility is barely affected by the thermal asymmetries. For the case without solid-phase heat generation, the entropy generation can be minimized when the wall heat flux ratio is 1/2. Besides, there is an optimum Reynolds number at Re=22 which further reduces the entropy generation. For the case with solid-phase heat generation, the entropy generation is minimized at wall heat flux ratio of 3/4, but the optimum Reynolds number vanishes. The solid-phase heat generation irreversibility dominates other irreversibilities and intensifies the entropy generation conspicuously. The second-law performance of nanofluid can be enhanced only when the internal heat generation is relatively low. When the suspended nanoparticle is smaller than the threshold size, the entropy generation can be reduced as much as 42%. The intensification of solid-phase heat generation significantly reduces the discrepancy between the thermal equilibrium and non-equilibrium models to less than 1%. This signifies the importance of considering thermal asymmetries and internal heat generation in the performance characterization of nanofluid flow in porous media.