Investigating thermal mixing and reverse flow characteristics in a T-junction by way of experiments

T-junctions are usually designed in piping systems for industries. A comprehensive understanding of mixing characteristics in a T-junction can contribute to its optimal design and functionality. In this study, the experiments are conducted to investigate the thermal mixing and reverse flow characteristics in an in-house T-junction with hot water flowing in the main pipe and cold water in the branch. The degree of thermal mixing can be found in the measured temperature distributions on the cross-sections in the main pipe downstream of this T-junction. Additionally, the reverse flow from the branch injection can be revealed in the lower temperature near the bottom of the cross-section upstream of the T-junction. Based on the previous works, the flowrate ratio (or velocity ratio) is adopted to discriminate the flow pattern, reverse flow phenomenon, and thermal mixing. Therefore, different branch/main pipe flowrates are considered in this study. The thermal mixing for a T-junction can be enhanced as the flowrate in the branch increases or the flowrate in the main pipe decreases, as clearly revealed in the comparison results of different flowrate ratios. The effect of different flowrates in the branch/main pipe on the reverse flow at the upstream of a T-junction has a similar trend to the degree of thermal mixing. In addition, the measured distributions on the cross-sections located upstream, within, and downstream of a T-junction can provide useful data to validate the CFD simulation models, which will be presented in the next paper.