Droplet breakup and entrainment at PWR spacer grids

A detailed photographic study of droplet grid interactions has been carried out to provide a basis for improvements in the modelling of heat transfer in the vicinity of a grid in dispersed flows characteristic of PWR reflood. The fragmentation associated with impact of drops onto the leading edge of a grid has been studied and an understanding of the mechanisms governing the resulting drop size gained. Additionally for a wet grid the process of entrainment of drops from the training edge of the grid has been investigated, and the dependence of entrained droplet size on the flow conditions has been established. The results indicate that adequate modelling of the droplet breakup due to impact is important in the calculation of heat transfer at a dry grid and may be significant in the modelling of grid rewetting. At a wet grid modifications to the droplet phase are shown to be of less significance since steam desuperheating is dominated by film evaporation