Heat transfer measurements and correlations in the transition region for a circular tube with three different inlet configurations

Abstract

Local forced and mixed convective heat transfer measurements were made in a horizontal circular straight tube with reentrant, square-edged, and bell-mouth inlets under uniform wall heat flux condition. For the experiments the Reynolds number of the liquid ranged from about 280 to 49,000, the Prandtl number varied from 4 to 158, and the Grashof number ranged from about 1000 to 2.5 × 10 5. From the experiments the heat transfer transition Reynolds number range was determined to be about 2000–8500 for the reentrant inlet, 2400–8800 for the square-edged inlet, and 3800–10,500 for the bell-mouth inlet. A correlation for prediction of the developing and fully developed forced and mixed convection heat transfer coefficients in the transition region for each inlet is recommended. Heat transfer correlations for the laminar and turbulent regions for the three inlets are also proposed. Some of the available heat transfer correlations are compared with our experimental data for different inlets.