Passive Heat Transfer Augmentation in a Cylindrical Annulus Utilizing a Porous Perturbation

In this work, free convective fluid flow and heat transfer are analyzed in a horizontal cylindrical annulus in the presence of a porous geometric perturbation. The flow in the porous region is modeled using the Brinkman-Forchheimer-Darcy model. The numerical scheme used in the present study is based on a Galerkin method of the finite element formulation. The nature of the three-dimensional flow field has been analyzed in detail, and the local and average Nusselt numbers have been obtained for a range of Rayleigh numbers of practical interest. In order to evaluate the effect of a porous perturbation, the flow and heat transfer characteristics were compared with those for a regular annulus without a perturbation and one with a solid perturbation. This study reports on the dependence of the flow and heat transfer characteristics on the governing parameters such as the ratio of the conductivity of the porous material to that of the fluid and the permeability. A correlation has been obtained that captures the variations of the overall heat transfer as a function of the Rayleigh number, the permeability, and the conductivity ratio. The results of this study show that both heat transfer retardation and enhancement can be achieved with the introduction of a porous perturbation.