TURBULENT NATURAL-CONVECTION FROM A VERTICAL CYLINDER TO AN ARRAY OF COOLED TUBES

In order to determine whether available correlations are adequate to t reat a complicated, turbulent natural convection problem encountered i n industrial practice, experiments were conducted by resistively heati ng a slender, vertical cylinder centered inside a concentric perforate d tube, which was, in turn, surrounded by an array of three larger-dia meter cooled tubes. The ratio of the test section temperature to the c ooling tube temperature was varied up to 2.6; and the Rayleigh number, based on tube diameter and properties evaluated at the cooling tube t emperature, ranged from 2.9 x 10(4) to 9.2 x 10(5). Results indicate t hat the convective heat transfer parameters for the perforated tube ar e about 15 percent higher than for the smooth bare tube centered in th e same position relative to the array. The Nusselt number for convecti ve heat transfer across the annulus between the heated test section an d the perforated tube corresponded approximately to parallel laminar f low (i. e., Nu(s) almost-equal-to 1).