Comparison investigation on natural convection of cold water near its density maximum in annular enclosures with complex configurations

In order to compare the characteristics of natural convection of cold water near its density maximum in annular enclosures with various complex configurations, a series of numerical simulations were carried out using the finite volume method. The effects of the Rayleigh number, the density inversion parameter and the aspect ratio on natural convective flow and heat transfer were analyzed, and the variations of local and average Nusselt numbers were discussed in these enclosures. The results show that the flow pattern depends mainly on geometrical configurations of the enclosures, the Rayleigh number and the density inversion parameter. The Rayleigh-Bénard convection cells appear in the top or bottom region for the R-C, T-C, E-S and E-T configurations at a large Rayleigh number. With the increase of the aspect ratio, the number of the vortex in the flow cell increases and the cell splitting phenomenon happens at a large aspect ratio in the R-C, D-C, T-C, E-S and E-T configurations. The heat transfer correlations for various configurations have been proposed, and the enclosure with the best heat transfer performance among various configurations is assured based on the simulation results.