Effect of hybrid nanoparticles on conjugate mixed convection of a viscoplastic fluid in a ventilated enclosure with wall mounted heated block

Abstract

We consider the thermal performance due to mixed convection and conjugate heat transfer of a Al2O3- Cu/viscoplastic hybrid nanofluid in a ventilated enclosure. A cold viscoplastic hybrid nanofluid is injected through the inlet port placed at the lower left corner of the enclosure and an outlet is placed at lower right corner. A heated solid obstacle is mounted at the bottom wall of the enclosure and the left wall of the enclosure is considered to be uniformly heated. The viscoplastic nanofluid is modeled as the Casson fluid, in which the plastic viscosity is considered to be temperature dependent. Nanoparticles mass flux due to both Brownian and thermophoretic diffusion along with convection is taken into account. The Corcione model for the thermal conductivity and viscosity of the hybrid nanofluid is adopted. The presence of the heated obstacle at the lower wall induces a recirculating vortex above it, which reduces the heat transfer from the enclosure. This vortex disappears when higher range of Reynolds number is considered. Our results show that the inclusion of Cu-nanoparticles in the Al2O3-viscoplastic fluid manifests the heat transfer. The yield stress of the fluid reduces the heat transfer but enhances the entropy generation. The thermal performance of the system is evaluated by presenting the heat transfer to entropy generation ratio. An enhancement of the solid-to-fluid conductivity ratio intensifies the heat transfer as well as entropy generation. Hybrid nanofluid enhances both heat transfer as well as entropy generation with the rate of heat transfer higher than the rate of entropy generation. A comparison with the corresponding homogeneous model is provided to analyze the effect of slip velocity created by Brownian diffusion and thermophoresis of nanoparticles.