Effect of non-uniform diameter and fractal dimension of Al2O3 nanoparticle on double-diffusion in tilted enclosure

The present numerical work examines the effect of variable fractal dimension and non-uniform diameter of Al2O3 nanoparticle on heat and mass transfer due to natural convection in tilted square enclosures. Enclosures are filled with Al2O3/H2O nanofluid and under constant heat and mass fluxes boundary conditions. The Navier-Stokes, energy, and concentration equations are solved numerically by finite difference method. Xu’s model [1] and Jang’s model [2] have been used to compute effective thermal conductivity and dynamic viscosity, respectively. Present work validated with published work experimentally and numerically. Influence of Al2O3 nanoparticle’s non-uniform diameter, fractal dimension, and the ratio of minimum to maximum diameter are illustrated in the form of streamlines, heatlines, and masslines in addition to average Nusselt and Sherwood numbers at different enclosure tilt angles. Heat transfer increases with the decrement in mean nanoparticle diameter, and maximum at tilt angle of θ=45∘ is observed for all Rayleigh numbers. At weak buoyancy effect (Ra=5×103) and minimum mean nanoparticle diameter (dp=1nm), maximum of 30% enhancement in overall heat transfer is observed at tilt angle, θ=45∘ and nanoparticle volume fraction, ϕ=5%. At strong buoyancy effect (Ra=1×105), maximum of 66% enhancement in overall heat transfer is observed at same nanoparticle conditions and tilt angle. An increase in Rayleigh and Lewis number decreases the tilt angle at which maximum mass transfer occurred. Mass transfer is maximum in the range of mean nanoparticle diameter of dp=25−50 nm.