Experimental study and software simulation of air-water periodic flooding in a 3×3 bundle channel

Investigating the behavior of gas-liquid two-phase flow within rod bundle channels can provide theoretical support for the smooth operation and emergency response of reactor systems. The characteristics of flow in a 3 × 3 rod bundle channel under periodic flooding conditions were investigated using numerical simulation methods. Comparing the simulation results with the experimental data revealed a high degree of agreement in the gas-liquid behavior and the time fractions across different flooding regions. This study examines the evolution of the void fraction along the axial direction and the variation of liquid phase velocity within the subchannels. The study of the local liquid phase velocity field analyzes the mechanisms underlying the onset of the flooding front and the formation of liquid phase accumulation. The relationship between the dimensionless pressure gradient and liquid holdup was analyzed, and an examination of the force conditions on the liquid film led to the conclusion that periodic flooding results from the alternating effects of the gas phase's carrying force and the gravity of the liquid phase in different regions. These research findings further enhance the understanding of thermal-hydraulic characteristics within rod bundle channels.