Performance Index in MHD Duct Nanofluid Flow Past a Bluff Body at High Re

Abstract

The quasi-two-dimensional Al 2 O 3 -water nanofluid magneto hydro-dynamics (MHD) flowing over a circular cylinder at higher Reynolds number has been modelled using Ansys FLUENT 15.0 in a rectangular duct to determine the viability of heat transfer enhancement. The effect of the numerical simulations on performance indices were analysed for the range of 1000 ≤ Re ≤ 3000 Reynolds numbers, 10 ≤ Ha ≤ 100 modified Hartmann numbers, 0.5 ≤ φ ≤ 2 nanoparticle volume concentrations, 0.1 ≤ β ≤ 0.4 blockage ratios, 1 ≤ γ ≤ 0.25 position ratios, 0.75 ≤ G/d ≤ 1.5 gap ratios and 0 ≤ d ≤ 10 distance downstream of cylinder along heated duct wall. The results are presented graphically and discussed quantitatively. Grid independence is achieved with the domain having 3 upstream and 20 downstream cylinder diameter distance lengths with element polynomial degree 7 with respect to mean drag coefficient and Strouhal number. Cylinder placement with gaps to the heated wall of diameters between 0.75 and 1.25 and 10 diameters downstream of cylinder performed best, achieving 117 % enhancement of the performance indices at Re = 3000, Ha = 20, φ = 2 %, β = 0.4, γ = 1 and G/d = 1. The performance indices were greater than one for all the cases tested, which indicates that the heat transfer enhancement for this flow is viable. The Nusselt number values of the present study were compared with the analytical and experimental data published earlier and found to be in perfect agreement validating the reliability of the present model. Highlights• A very high performance index enhancement is achieved, incorporating the impacts of Re, Ha and φ in rectangular duct flow. • A circular cylinder is used as bluff body in MHD nanofluid flow at higher Reynold numbers. • Ideal cylinder placement conditions of blockage, position and gap ratios are proposed. • Viable heat transfer enhancements analysed using numerical simulations and the resulting quasi-2D model predictions are validated.