ON THE REDUCTION OF NATURAL-CONVECTION HEAT-TRANSFER IN HORIZONTAL ECCENTRIC ANNULI CONTAINING SATURATED POROUS-MEDIA

Studies numerically natural convection in a saturated porous medium bo unded by two horizontal, isothermal eccentric cylinders by solving the governing two-dimensional Darcy-Boussinesq equations on a very fine g rid for different values of the eccentricity epsilon. For a radius rat io of 2 and epsilon < 0.5, both a bicellular and a tetracellular flow patterns remain stable for moderate Rayleigh numbers. For epsilon grea ter than or equal to 0.5, the transition from one flow regime to the o ther occurs with one of the solutions losing stability. Suggests that in a real situation, insulation is more efficient if the eccentricity is set to the maximum value for which the four-cell flow pattern is ph ysically realizable than to the value that minimizes the heat transfer when the flow pattern is bicellular. The net gain with respect to a c oncentric insulation can be of the order of 10 per cent.