Effect of temperature difference on the thermal mixing phenomenon in a T-junction under inflow pulsation

Abstract

The effects of inlet temperature difference between the main and branch fluids on the flow and thermal mixing characteristics in the T-junction under inflow pulsation are numerically investigated by large eddy simulation (LES) turbulent model. The inlet velocities of both the main and branch pipes are assumed to be sinusoidal distribution, which is similar to the rolling condition in the ocean. Thermal mixing between hot and cold fluids with temperature differences of 15 K, 30 K and 45 K is carried out in the present study. The flow and mixing characteristics, including qualitative and quantitative analyses of temperature and velocity are studied. The results show that the reverse flow occurs in the unsteady thermal mixing processes due to the effect of inertia force, and the area of reverse flow decreases as the inlet temperature difference increases. Increasing inlet temperature difference induces a more stable thermal stratification flow with smaller thermal mixing length and lower temperature gradient. The maximum root mean square (RMS) of temperature fluctuation slightly decreases and shifts to the upper of main pipe as the inlet temperature difference increases. In addition, the spectral analysis of temperature fluctuation performed by Wavelet Transform (WT) indicates that the number of frequency peaks decreases as the temperature difference increases. Meanwhile, the main frequencies of wavelet power spectrum densities (WPSDs) for the lower points (points 1 ~ 3) decrease, while those for the upper points (points 5 ~ 7) increase as the temperature difference increases.