Heat transfer enhancement due to water accumulation near grid spacers during reflood

Reflood experiments in a 36-rod bundle have been performed to investigate the effect of grid spacers on heat transfer and water accumulation behavior above the quench front. The heat transfer above grid spacers was significantly enhanced; the degree of enhancement was inversely proportional to the distance from the grid spacer in both dispersed and slug flows. In the dispersed flow region, a decrease of droplet diameter above the grid spacers, a rewetting of the spacer wall, and the onset of water accumulation above the grid spacers were observed. In the slug flow region, water accumulation just above the grid spacer was larger than below the grid spacer. Among parameters tested, the water accumulation in the core was mostly affected by the flooding rate