Convective Flow in Annuli of Stationary and Rotating Horizontal Cylinders

Heat transfer and fluid flow processes in enclosed spaces have been extensively studied due to their importance in energy conversion, storage and transmission systems. Concentric and eccentric annular geometries are most commonly encountered in solar collector-receiver system, cooling system in nuclear reactors etc. For mixed flow in the annulus between concentric or eccentric cylinders in a rotating system, most work were performed for the cases of vertical cylindrical annulus. More recently, the effects of recirculation on the natural convection between the annular region in horizontal rotating cylinders have become a topic of interest to researchers. The applications of these studies include food processing and the interest in seeking improved methods for crystallographic perfection in industrial processes, above studies are for air with Pr≅1.0. However, other effects of rotation on heat transfer characteristics for low Prandtl number fluids are encountered in high power electric machines with heated shafts, such as a mercury slip ring assembly. For the present study, natural convection is driven by vertical temperature gradient and vertical gravity force. The interaction with the effect of rotation of the inner cylinder is expected to lead to complicated flows. Studies show that the mean Nusselt number increases with Rayleigh number. At a Prandtl number of order 1.0 with a fixed Rayleigh number, when the inner cylinder is made to rotate, the mean Nusselt number decreases through out the flow. At lower Prandtl number of the order 0.1 to 0.01, the mean Nusselt number remained fairly constant with respect to the rotational Reynolds number.