Natural Convection Heat Transfer Between Concentric Rectangular Pipes

Abstract

Natural convection heat transfer between concentric rectangular pipes was studied numerically. It has been found that rolls of even number form in the region on the top surface of the inner pipe. The number of rolls depends on both Rayleigh number and aspect ratio. An oblong circulation of flow forms in the region between the side surface of the inner pipe and the surface of the outer pipe. The aspect ratio does not have much effect on the average Nusselt number at the side surface of the inner pipe. The relation between Nusselt and Rayleigh numbers at the top surface resembles that of the Rayleigh-Benard convection obtained by Silveston [Chandrasekhar. S., Hydrodynamic and Hydromagnetic Stability. (1961), 68, Oxford University Press]. The average Nusselt number at the bottom surface of the inner pipe decreases with increasing aspect ratio because the region where heat transfer is affected significantly by convection is limited.