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 bounded by two horizontal, isothermal eccentric cylinders by solving the governing two‐dimensional Darcy‐Boussinesq equations on a very fine grid for different values of the eccentricity ε. For a radius ratio of 2 and ε < 0.5, both a bicellular and a tetracellular flow patterns remain stable for moderate Rayleigh numbers. For ε ≥ 0.5, the transition from one flow regime to the other 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 physically realizable than to the value that minimizes the heat transfer when the flow pattern is bicellular. The net gain with respect to a concentric insulation can be of the order of 10 per cent.