Investigation on mixing behavior and heat transfer in a horizontally arranged tee pipe under turbulent mixing of hot and cold fluid

Highlights: • The whole model of the tee pipe (not only the T-junction) are employed directly for studying. • Three different zones are divided according to different characteristics of mixing behaviors. • Normalized mean and RMS temperature are employed to distinguish different zones. • Relationship between mass flow rate ratio and characteristics of mixing behaviors are found. - Abstract: Tee pipes are commonly used in piping systems and multichannel networks in various industries. When two fluids at different temperatures mixing turbulently in a tee pipe, and the mass flow rate ratio Q_m,m/Q_m,b is large, both the turbulent penetration and the thermal stratification may appear simultaneously in the branch pipe. The temperature fluctuation induced by the turbulent penetration may lead to high-cycle thermal fatigue of the pipe structure, and the thermal stratification may lead to the pipeline distortion and pipeline support damage. This test section has reference meaning in some typical pipelines in nuclear power plant. In this study, the mixing behavior and heat transfer phenomena in a horizontally arranged tee pipe under turbulent mixing of hot and cold fluids are studied by us with the experiment and the numerical simulation based on the CFD software package FLUENT 16.0. Results show that both the length of the turbulent penetration zone "L_tp" and the length of the thermal stratification zone "L_ts" tend to increase with the increase of the mass flow rate ratio Q_m,m/Q_m,b. As the root cause of different mixing behaviors and heat transfer phenomena in the branch pipe is the combined effect of the buoyancy lift and the inertia force. To obtain a complete description of the mixing behavior, numerical simulations are still essential.