Numerical study on the combined effects of Brownian motion and thermophoresis on an unsteady magnetohydrodynamics nanofluid boundary layer flow

Abstract

Buongiorno’s two-phase model is adopted to study the impacts of the thermophoresis effect and Brownian motion on an unsteady nanofluid flow through an irregular channel due to a stretching sheet in the presence of magnetic field. The copper oxide nanoparticles are dispersed in the base solution (i.e., water) and the nanofluid thus developed is considered as an operating fluid. The thermophysical properties such as density, thermal conductivity, viscosity, heat capacitance and thermal expansion of the considered nanofluid are determined using established laws and mixture theory. The flow and heat transfer are described by the boundary layer equations that correspond to the flow field, temperature, and concentration, and associated boundary conditions are solved numerically by employing an effective and optimized finite difference technique. The convergence criteria of the developed numerical algorithm for the obtained solutions are verified. The significant features of momentum, temperature, and concentration distributions are due to the influence of key parameters which are of physical interest such as magnetic parameter, the amplitude of a wavy channel, particle–density increment parameter, Brownian diffusion coefficient, nanoparticle Lewis number are analyzed in detail.Dissecting the impact of the wavy wall, magnetic field, Brownian motion, and thermophoresis effect are a few core objectives of the study. The substantial findings are that the enhancement in the amplitude of the wavy wall impacts the flow markedly and it increases the shear stress, heat, and mass transfer rates. The strength of the magnetic field boosts the friction factor and heat transfer rate. The Brownian motion and thermophoresis effects are to increase the momentum and heat transfer rate in the boundary layer while the concentration field is noticed to be decreasing. The fluid mechanisms behind these physical reasons are discussed in detail.