Mixed convective boundary layer flow over a vertical cylinder embedded in a porous medium saturated with a nanofluid

Abstract

Purpose

The purpose of this work is to study the mixed convection boundary layer flow past a vertical cylinder in a porous medium saturated with a nanofluid. Numerical results for friction factor, surface heat transfer rate and mass transfer rate have been presented for parametric variations of the buoyancy ratio parameter Nr, Brownian motion parameter Nb, thermophoresis parameter Nt and Lewis number Le. The dependency of the surface heat transfer rate (Nusselt number) and mass transfer rate on these parameters has been discussed.

Design/methodology/approach

Solutions of the set of non-similarity equations are obtained by employing the implicit finite difference method together with Keller box elimination method.

Findings

It was found that the heat transfer rate decreases and mass transfer rates increase as Lewis number increases. The heat and mass transfer rates increase as the buoyancy ration parameter increases. As the thermophoresis parameter Nt increases, the heat transfer rate decreases where as the mass transfer rate increases. As the Brownian parameter Nb increases, the heat transfer rate decreases. Brownian motion decelerates the flow in the nanofluid boundary layer. Brownian diffusion promotes heat conduction. The heat and mass transfer rates increase as the buoyancy ratio number Nr increases. The Brownian motion and thermophoresis of nanoparticles increases the effective thermal conductivity of the nanofluid. Both Brownian diffusion and thermophoresis give rise to cross diffusion terms that are similar to the familiar Soret and Dufour cross-diffusion terms that arise with a binary fluid.

Research limitations/implications

The analysis is valid for steady, mixed convection two-dimensional boundary layer flow in a nanofluid-saturated Darcy porous medium. An extension to non-Darcy porous medium is left as a part of future study.

Practical implications

The research is applicable for enhancing heat exchanger effectiveness by employing nanofluids.

Originality/value

The study is useful to engineers interested in designing heat exchangers, water and atmospheric pollution.

Citation

Gorla, R.S.R. and Hossain, A. (2013), "Mixed convective boundary layer flow over a vertical cylinder embedded in a porous medium saturated with a nanofluid", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 23 No. 8, pp. 1393-1405. https://doi.org/10.1108/HFF-03-2012-0064