Effect of horizontal and vertical elliptic baffles inside an enclosure on the mixed convection of a MWCNTs-water nanofluid and its entropy generation

Abstract

In the present study, the effect of horizontal and vertical elliptic baffles on the flow, heat transfer and entropy generation of a MWCNTs-water nanofluid was investigated. Experimental data were used to calculate the viscosity and thermal conductivity of the nanofluid at different temperatures and volume fractions. A square enclosure with a central elliptic baffle was numerically studied. The elliptic baffle was located in two horizontal and vertical positions. The hot baffle was at temperature Th and the walls of the enclosure, except for the lower insulated wall, were at temperature Tc. A FORTRAN code based on the finite volume method and SIMPLER algorithm was used to analyze mixed convection. Nanoparticle volume fractions of 0, 0.002, 0.004, 0.008, and 0.01 at Richardson numbers of 0.01, 0.1, 1 and 100 at a constant Grashof number of 104 were studied. Horizontal placement of thermal baffle led to a higher heat transfer rate, which is more favorable in terms of heat exchange. The entropy generation values in the horizontal position were higher than the vertical position. The highest mean Nusselt number and total entropy generation were 7.9 and 20.4, respectively. For the horizontal placement, the highest mean Nusselt number happens at a volume fraction of 0.01 and a Richardson number of 0.01. Studies often focus on higher heat transfer rates. However, a horizontal baffle is more favorable than the vertical position considering that the greatest difference in the total entropy generation is about 8%.