Heat Transfer to Air, Carbon Dioxide and Helium Flowing through Smooth Circular Tubes under Conditions of Large Surface/Gas Temperature Ratio

Abstract

In this paper, experiments are described on the transfer of heat from a heated tube to a gas flowing through it. Three gases were used: air, helium and carbon dioxide. The difference in temperature between the tube and the gases was large and the main objective of the work was to study the effects of radial variations of the gas properties with temperature. The conditions under which the experiments were performed were (1) essentially fully developed velocity and temperature profiles, (2) approximately uniform wall heat flux and (3) low subsonic turbulent flow. Some analysis has been developed to cover the present experimental work. Predicted Nusselt number-Reynolds number relations for the constant properties case are found to be in reasonable agreement with the experimental data for Reynolds numbers above about 10 000, provided the ratio of eddy diffusivities is assumed to vary from about 1·0 at Re = 104 to about 1·2 at Re = 105. The effects of variations of surface/gas temperature ratio, predicted by the analysis, are found to be in quite good agreement with the experimental data of both this and earlier investigations.