BUOYANCY-INDUCED FLOW AND HEAT-TRANSFER IN A CYLINDRICAL ANNULUS WITHMULTIPLE PERTURBATIONS

The present work focuses on the effects of multiple geometric perturba tions on the three-dimensional buoyancy-driven flow and heat transfer in an annular cavity with impermeable end walls. The three-dimensional (3-D) study carried out involved the fluid flow and heat transfer ana lysis in a horizontal annulus with multiples of geometric perturbation s placed on the inner cylinder of the annulus. The flow field structur e corresponding to these different perturbations is analyzed. Heat tra nsfer results were obtained up to a Ra of 10(4), and the heat transfer effects were studied by analyzing the local and average Nusselt numbe rs. It is observed that with the introduction of multiple perturbation s on the inner cylinder, the overall heat transfer rate increases subs tantially. For example, the average Nusselt number at a Ra of 10(4) fo r the annulus with four perturbations was found to be about 25% higher than that for the annulus with a single perturbation, which itself wa s about 50% higher than that for the annulus without any perturbation. It was found that the average Nusselt number could be correlated as N u = 0.71 Ra-0.1(1+0.12P), where P refers to the number of perturbation s on the inner cylinder. The results show an interesting method for su bstantially augmenting heat transfer within an enclosed annulus. (C) 1 998 Elsevier Science Ltd. All rights reserved.