Numerical simulation of the evaporator in two-phase thermosyphon loop for passive containment cooling system

This study applied experimental data as numerical simulation input conditions to calculate the evaporator operating states of a two-phase thermosyphon loop for a passive containment cooling system. The numerical model comprised a vertically arranged steel tube operating in a steam environment at 134 degrees C, with an inner diameter of 17 mm and an length of 800 mm, and the working fluid was water. The evaporator exhibited different flow and heat transfer characteristics under filling ratios (FRs) ranging from 40 % to 65 %. The results indicated that bubbly, cap, and slug flows could be sequentially observed along the flow direction. The starting position of the bubble flow varied with the subcooling of the inlet fluid. The flow patterns in the upper part of the tube were similar for the 55 % and 65 % FRs. Compared with the experiment, the simulated liquid-level fluc-tuation was smaller.