Double-diffusive natural convection of Al2O3-water nanofluid in an enclosure with partially active side walls using variable properties

Abstract

Natural convection heat and mass transfer characteristics in a square enclosure using variable thermal conductivity and variable viscosity are numerically studied. The fluid in the enclosure is a water-based nanofluid containing Al2O3 nanoparticles. The top and bottom horizontal walls are insulated, while a source (Th, Ch) and a sink (Tc, Cc) are located at the vertical left and right walls as active parts, respectively, with Th>Tc and Ch>Cc. The governing equations in the two-dimensional space are discretized using the control volume method. A proper upwinding scheme is employed to obtain stabilized solutions. The study has been carried out for the Rayleigh numbers of 104 to 106, the buoyancy ratios of -5~5, and different configurations of the source and sink. Results are presented in the form of the streamlines, isotherms and iso-concentraions as well as the average Nusselt and Sherwood numbers. It is observed that average Nusselt number is increased by adding the nanoparticles, while average Sherwood number is reduced. Moreover, both Nusselt and Sherwood number are increased as absolute value of the buoyancy ratio or Rayleigh number is increased.