Natural Convection Heat Transfer From Cylinders of Arbitrary Cross Section

Abstract

Analytical, numerical, and experimental studies of free convection heat transfer from the external surface of isothermal two-dimensional bodies, especially circular cylinders and vertical flat plates, have been conducted by many investigators. A review of the existing literature shows that most workers have focused mainly on experimental data of circular cylinders and vertical plates with air (Pr[approximately]0.71) as working fluid. The results of these studies have been empirical correlations restricted either to some simple geometries or to a narrow range of Rayleigh numbers. Only a few scientists have carried out numerical techniques, which unfortunately, are also restricted to simple geometries such as circular cylinders. There are a few analytical solutions for cylinders of fairly arbitrary cross section, but, unfortunately, those solutions are restricted to a very narrow range of Rayleigh were the boundary layer is thin compared to the local radius of curvature of the cylinder. The approximate method suggested by Raithby and Hollands, however, is capable of predicting heat transfer from cylinders of various cross sections and for wide ranges of Prandtl and Rayleigh numbers. Unfortunately, following the steps of their approximate method is complex, and engineers might be discouraged from using it. Therefore it is the goal of thismore » study to simplify this approximate method and introduce an expression for predicting natural convection heat transfer from isothermal two-dimensional bodies of arbitrary cross section over a wide range of Rayleigh and Prandtl numbers. In this paper, following a similar procedure to that outlined by Hassani and Hollands, an expression for predicting the convection heat transfer from two-dimensional bodies (cylinders of different convex cross sections) is derived.« less