Heat Transfer and Friction Characteristics of Internal Helical-Rib Roughness

Abstract

This paper provides heat transfer and friction data for single-phase flow in seven 15.54-mm inside diameter tubes having internal helical-rib roughness. The range of geometric parameters were number of rib starts (18 to 45), helix angle (25 to 45 deg), and rib height (0.33 to 0.55 mm). These geometries provide data on a new class of internal enhancement that is typical of commercially rough tubes presently used. The tested geometries provide enhancement by flow separation at the ribs, and by a significant surface area increase. The data were taken with water having 5.08⩽Pr⩽6.29. Two different correlations were employed to predict the Stanton number and friction factor as a function of geometric variables and Reynolds number. The average deviation of the multiple regression heat transfer and correlations were 2.9 percent and 3.8 percent, respectively. Heat transfer and friction correlations based on the heat-momentum transfer analogy for rough surfaces yielded standard deviations of 1.4 percent and 5.4 percent, respectively. The correlations were shown to reasonably predict the heat transfer and friction for commercially used helical-rib roughened tubes. [S0022-1481(00)03001-2]