Mathematical modeling of electrothermal couple stress nanofluid flow and entropy in a porous microchannel under injection process

Abstract

We examine the effects of ion diffusion coefficient on steady electroosmotic couple stress nanofluid flow and heat transfer in a porous microchannel bounded by two permeable beds. The study considers the nanofluid injection process through porous beds. The combined effects of ion diffusivity and injected nanofluid velocity on EDL (Electric double layer) thickness are analytically expressed. The differential transform method (DTM) is used to solve the flow equations. The DTM solution is then compared with the exact analytical solution of velocity, Zeta potential function and a square averaged residual analysis is conducted. These comparisons show excellent matching. We observe that the enhancement of ion diffusion coefficient increases nanofluid velocity at the edge of EDL but diminishes with intrinsic couple stress. The bulk nanofluid flow rate is found to follow a quadratic like relationship with the couple stress parameter. We have investigated the nanofluid temperature and nanoparticle concentration distribution in microchannel for variations of the diffusive Reynolds number, porous permeability parameter and couple stress parameter. The nanofluid temperature is found to increase with an enhancement of ion diffusion coefficient, which is related with experimental results observed by Kong et al. (Phys. Chem. Chem. Phys. 19 (2017) 7678) for NaCl electrolyte solution confined in a graphene nanochannel. Moreover, the nanofluid temperature decreases with enhancement of both porous permeability of the medium and couple stress parameter.