Three-dimensional study of heat and fluid flow of air and dielectric liquids filling containers partially heated from below and entirely cooled from above

In this work, a numerical procedure based on the finite volume method coupled with a full multigrid acceleration is utilized to study three-dimensional flow structures and heat transfer characteristics in partially heated 3-D containers having a heated strip on the lower horizontal wall. The opposite horizontal wall is cooled to a uniform low temperature and the four remaining walls are insulated. Two different fluids, one air (Pr = 0.7) and the other a dielectric liquid (Pr = 25) are employed encompassing descriptive Rayleigh numbers Ra that range three orders of magnitude from 103 to 106. Typical plots of streamlines and isotherms are presented to analyze the circulatory flow patterns set up by the buoyancy force of the fluids. At low Ra, the flow structures and average Nusselt numbers are similar for both fluids under consideration. On the contrary, for higher Ra, a systematic comparison illuminates heat transfer augmentation when the Prandtl number is switched from air to the dielectric fluid. At high Ra = 106, the air flow (Pr = 0.70) becomes unsteady whereas the dielectric liquid flow (Pr = 25) remains steady. At the end, monomial correlations are presented for the quantification of the heat transfer that emanates from the heated bottom strip in harmony with the various Rayleigh number associated with the two dissimilar fluids.