Numerical simulation of double-diffusive mixed convection in an enclosure filled with nanofluid using Bejan’s heatlines and masslines

Abstract

In this study, double-diffusive mixed convection of temperature-dependent alumina-water nanofluid in a lid-driven square enclosure is numerically investigated. The governing equations are discretized using finite volume method and solved by SIMPLER algorithm. The temperature and concentration of the left wall are higher than those of the right wall, while the two other walls are adiabatic and impermeable. The simulations are conducted for Richardson numbers of 0.01≤Ri≤100, buoyancy ratios of −5≤Br≤5, and nanoparticle volume fractions of 0≤ϕ≤4%. The results show that at high Richardson numbers, increasing the nanoparticle volume fraction results in a decrease in the average Nusselt number, while at low Richardson numbers this leads to an increase in the average Nusselt number. Additionally, by comparing the Nusselt or Sherwood numbers for positive and negative values of a same buoyancy ratio, the positive values always lead to higher average Nusselt or Sherwood number. Moreover, the heatlines are more compressed for nanofluid than pure fluid, which demonstrates better convective heat transfer by nanofluid than pure fluid. Masslines are always similar to streamlines due to domination of mass transfer on fluid flow at high Lewis numbers.