Natural Convention in a Horizontal Cylindrical Annulus with Equally Spaced Radially Divergent Longitudinal Solid Fins: Part I

Abstract

A numerical investigation was carried out to study laminar natural convection heat transfer in a stationary horizontal concentric cylindrical annulus with six equally spaced radially divergent round tip longitudinal solid metallic fins attached on the external surface of the inner cylinder. The surface ofthe inner cylinder as well as the surface of the outer cylinder was assumed to be at a uniform temperature. The non-dimensional thermal conductivity of the metallic fin to fluid was assumed to be high. Water was selected as the working fluid. The Rayleigh number based on the width of the annulus gap was variedfrom 103 to 106 and the ratio of the fin height to the annulus gap was varied as 0, 0.2, 0.4 and 0.6. The velocity vectors and the isotherm plots were depicted to investigate thefluidflow behavior and the heat transfer inside the annulus. It was found that the heat transfer rate from the inner cylinder increased with the increased of both the Rayleigh number and the fin height. The variations of the local equivalent thermal conductivity (ratio of Nusselt numbers due to convection and conduction heat transfer from the inner cylinder) were also presented. Four empirical correlations were developed for the average equivalent thermal conductivity as a function of Rayleigh number for three different fin heights and for the annulus without a fin. The heat transfer rate was much more pronounced in all of the fins fitted geometries compared to the case with no fins at the same Rayleigh number.