Thermo-electrokinetic rotating non-Newtonian hybrid nanofluid flow from an accelerating vertical surface

Prakash, J, Tripathi, D, Beg, OA ORCID: https://orcid.org/0000-0001-5925-6711, Tiwari, AK and Kumar, R 2022, 'Thermo-electrokinetic rotating non-Newtonian hybrid nanofluid flow from an accelerating vertical surface' , Heat Transfer, 51 (2) , pp. 1746-1777.

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Abstract

This paper explores the combined effects of Coriolis force and electric force on the rotating boundary layer flow and heat transfer in a viscoplastic hybrid nanofluid from a vertical exponentially accelerated plate. The hybrid nanofluid comprises two different types of metallic nanoparticles, namely silver (Ag) and magnesium oxide (MgO) suspended in an aqueous base fluid. The Casson model is deployed for non-Newtonian effects. An empirical model is implemented to determine the thermal conductivity of the hybrid nanofluid. Rosseland’s radiative diffusion flux model is also utilized. Axial electrical field is considered and the Poisson-Boltzmann equation is linearized via the Debye-Hückel approach. The resulting coupled differential equations subject to prescribed boundary conditions are solved with Laplace transforms. Numerical evaluation of solutions is achieved via MATLAB symbolic software. A parametric study of the impact of key parameters on axial velocity, transverse velocity, nanoparticle temperature and Nusselt number is conducted for both hybrid (Ag-MgO)-water nanofluid and also unitary (Ag)-water nanofluid. With increasing volume fraction of silver nanoparticles there is a reduction in both axial velocity and temperatures whereas there is a distinct elevation in transverse velocity for both unitary and hybrid nanofluid. Elevation in heat absorption parameter strongly decreases axial velocity whereas it enhances transverse velocity. Increasing radiation parameter strongly boosts temperatures. Increasing heat absorption parameter significantly accelerates the transverse flow. Negative values of Helmholtz-Smoluchowski velocity decelerate the axial flow whereas positive values accelerate it; the opposite behavior is observed for transverse velocity. Increasing Taylor number significantly damps both the axial (primary) and transversal (secondary) flow. Increasing thermal Grashof number strongly enhances the axial flow but damps the transverse flow. Unitary nanofluid achieves higher Nusselt numbers than hybrid nanofluid but these are decreased with greater radiative effect (since greater heat transport away from the plate surface), Prandtl number and heat absorption. Nusselt number is significantly reduced with greater time progression and values are consistently higher for unitary nanofluid compared with hybrid nanofluid. The computations provide insight into more complex electrokinetic rheological nanoscale flows of relevance to biomedical rotary electro-osmotic separation devices.

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