Comparison of Turbulent Thermal Entrance Regions for Pipe Flows With Developed Velocity and Velocity Developing From a Sharp-Edged Inlet

Abstract

The thermal entrance region for turbulent flow in circular tube has been analytically investigated for two types of velocity distributions. In one case, the flow is hydrodynamically developed throughout the entire length of the thermal entrance region. In the other, the velocity is uniform at the inlet of the heated section, so that there is a hydrodynamic development of the flow which occurs simultaneously with the thermal development. The latter situation is rarely, if ever, encountered in practice and is, in fact, difficult to achieve in a laboratory experiment. The effect of various types of velocity distributions on the turbulent heat transfer coefficients in the thermal entrance region of an isothermal-walled tube was investigated experimentally by Boelter et al. The different velocity distributions were attained by use of different configurations of the inlet of the heated section. As noted in Kays and Crawford, the insufficiencies of the experimental technique used by Boelter et al. suggest that the results be regarded as qualitative rather than quantitative. The objective of the present research is to provide definitive thermal entrance region heat transfer results for an isothermal-walled tube for two types of turbulent velocity distributions that are of practical relevance. The two setsmore » of results will be compared to yield the quantitative response of the thermal entrance region to the nature of the velocity condition at the tube inlet. The work to be reported here is experimental and covers the Reynolds number range from approximately 5,000 to 85,000.« less