Turbulent Natural Convection From a Vertical Cylinder to an Array of Cooled Tubes

In order to determine whether available correlations are adequate to treat a complicated, turbulent natural convection problem encountered in industrial practice, experiments were conducted by resistively heating a slender, vertical cylinder centered inside a concentric perforated tube, which was, in turn, surrounded by an array of three larger-diameter cooled tubes. The ratio of the test section temperature to the cooling tube temperature was varied up to 2.6; and the Rayleigh number, based on tube diameter and properties evaluated at the cooling tube temperature, ranged from 2.9×10⁴ to 9.2×10⁵. Results indicate that the convective heat transfer parameters for the perforated tube are about 15 percent higher than for the smooth bare tube centered in the same position relative to the array. The Nusselt number for convective heat transfer across the annulus between the heated test section and the perforated tube corresponded approximately to parallel laminar flow (i.e., Nu_s≈1).