摘要
Through T-junction experiments, this paper investigates thermal mixing and thermal stripping characteristics. Different flowrates in the branch/main pipe and different branch injection directions are considered. The flow mixing pattern in a T-junction and the reverse phenomenon upstream a T-junction can be revealed in the measured temperature distributions and be observed from the blue dye distribution by the high-speed camera. The thermal stripping in a T-junction can be expressed using the non-dimensional power spectrum density (PSD ∗ ) versus the Strouhal (St) number since the degradation of thermal fatigue on the pipe wall depends strongly on the frequency of fluid temperature fluctuation. The frequency spectrum can be obtained from the time history data by way of the fast Fourier transform (FFT) analysis. Based on the measured results, the velocity ratio (Vr) can be used to indicate the thermal mixing characteristics in a T-junction; however, the momentum ratio (M R ) is suitable to discriminate the flow pattern and to reveal the reverse flow phenomenon from the branch injection. Detailed comparison of the present data and the measured results from the previous work reveals that the reverse flow upstream a T-junction can occur if M R is less than about 0.05, demonstrating that this conclusion has generality. In addition, according to the comparison of PSD ∗ versus St number for x/D = 1 and 9 under various Vr values, the piping degradation due to thermal fatigue for a T-junction is severe near its intersection and is stronger for the higher Vr values.