Natural Convection in a Horizontal Cylindrical Annulus with Two Isothermal Blocks in Median Position: Numerical Study of Heat Transfer Enhancement

Natural convection is numerically investigated in a finned horizontal cylindrical annulus filled with air where two isothermal blocks are attached to the inner cylinder in a median position. A bi-vortex flow is observed and the influence of each vortex on heat transfer is analysed. Heat flux and transfer rate calculated per zone (superior, central and inferior) show that heat transfer is more important for the annulus superior zone. Compared to without blocks configuration, blocks presence contributes in the overall heat transfer improvement. This improvement is observed at the inferior zone (inferior vortex effect) and the central one. For the superior zone, despite its importance, heat transfer is deteriorated. This study also shows that the addition of inverted trapezoidal blocks to the medium increases heat transfer, relatively to the without blocks case, by 10.54% to 29.62% depending on Rayleigh number.