Laminar mixed convection in horizontal concentric annuli with non-uniform circumferential heating

Steady, laminar, mixed convection in the fully developed region of horizontal concentric annuli has been investigated numerically for the case of non-uniform circumferential heating. Two heating conditions were studied, one in which a 180° arc encompassing the top half of inner surface of the inner cylinder is uniformly heated while the bottom half is kept insulated, and the other in which the heated and the insulated surfaces were reversed. The fluid flow and heat transfer characteristics were found to be affected by the heating conditions. For the investigated range of the governing buoyancy parameter, the modified Grashof number (Gr*), it was found that bottom heating arrangement gives rise to a vigorous secondary flow, with the result that the average Nusselt numbers are much higher than those for pure forced convection. On the other hand, the local Nusselt numbers are nearly circumferentially uniform. In the case of top heating arrangement, a less vigorous secondary flow is induced because of temperature stratification, with average Nusselt numbers that are substantially lower than those for bottom heating and with large circumferential variation of the local Nusselt number.