An experimental investigation of heat transfer and pressure drop in the transition region for a horizontal tube with different inlets and uniform wall heat flux

摘要

Scope and method of study. The purpose of this study was to experimentally investigate the effect of inlet configuration on the heat transfer and non-isothermal pressure drop transition regions. Systematic experiments of heat transfer and pressure drop measurements were conducted to develop an accurate and broad forced and mixed convection heat transfer and pressure drop database for a wide range of Reynolds, Prandtl and Grashof numbers in the entrance and fully developed regions of an electrically heated horizontal circular tube. The experimental data was then used to study the influence of inlet configuration and buoyancy on the laminar, transition, and turbulent regions. After all these effects had been investigated, heat transfer and skin friction coefficient correlations for engineering purposes were developed.;Findings and conclusions. Inlet configuration was found to play an important role in heat transfer and pressure drop transition region. The Reynolds number for the start and end of transition were different for different inlet configurations. The existence of mixed convection was also proven to be inlet configuration dependent. A flow regime map based on the experimental data was developed to predict the existence of free convection and the correct flow region at a certain condition. The flow regime map is unique in the sense that it is the first attempt at developing such a map for the case of a horizontal tube with uniform wall heat flux. Effect of buoyancy due to different heating rates on non-isothermal pressure drop was proven to play a significant role in the laminar and transition regions. Empirical correlations for heat transfer in the laminar, transition, and turbulent flow regions and for non-isothermal pressure drop in the laminar and transition regions were developed for the reentrant, square-edged, and bell-mouth inlets. All these correlations predicted the experimental data well.