Numerical simulation of thermal mixing of liquid sodium in a Y-junction

Numerical simulations are conducted to investigate the flow and heat transfer behaviour of liquid sodium in a Y-junction. Three thermal hydraulic parameters - the fluid momentum ratio, the temperature difference between the inlets of the two branches, and the inlet Reynolds number - are studied to understand their impact on flow development, mixing characteristics, and heat transfer in the main pipe. Results indicate that the momentum ratio is a key factor affecting flow development and temperature distribution. When the momentum ratio lies outside a certain range, flow impingement on the opposite wall occurs. If the ratio falls within this range, two jet flows merge into a turn/deflecting slab-shaped jet, accompanied by two pairs of counter-rotating vortices in the main pipe. The Reynolds number has a negligible impact on flow and thermal mixing patterns for the turbulent flows considered. However, lower Reynolds numbers result in stronger velocity variation and weaker temperature differences at the cross-section in the mixing area. Lastly, the inlet temperature difference has a very limited impact on flow and thermal mixing, and changes in physical property variables negligibly affect velocity and temperature distributions in flow and thermal mixing.