Effect of two sinusoidal protuberances on natural convection in a verticalconcentric annulus

A numerical study is presented for laminar flow and heat transfer in a vert ical concentric annulus with two sinusoidal protuberances on the external a nd internal surfaces of the inner and external cylinders, respectively. The basis of the method used is an algebraic nonorthogonal coordinate transfor mation that maps the complex fluid domain onto a rectangle. The transformed equations and the entire discretization procedure were solved by a finite volume methodology. Representative results were found for laminar flow, uni form wall temperature (case I), uniform heat flux (case O), a range of Rayl eigh numbers, Prandtl number, various values of aspect ratio, and the heigh t of the sinusoidal protuberances. As seen from the streamlines, the flow p atterns are highly perturbed by the presence of the protuberance, including recirculation zones. It is also noted that the presence of the protuberanc e leads to an increase in heat transfer rates in the location of the obstru ction along the wall. The pressure drops and thermal correlation results ar e higher than the corresponding values for the cylinders without protuberan ces.