Fragmentation of a single molten metal droplet penetrating into sodium pool. IV. Thermal and hydrodynamic effects on fragmentation in copper

Abstract

To characterize the relationship between thermal and hydrodynamic effects on fragmentation of molten metallic fuels, with the interaction of the sodium coolant under a wide range of thermal and hydrodynamic conditions, in this paper, we focus on the fragmentation characteristics of a single molten copper droplet (1 and 5 g) with an ambient Weber number (We a) from 102 to 614 and superheating conditions from 15 to 574°C, which penetrates into a sodium pool at an initial temperature from 298 to 355°C. In our experiments, fine fragmentations of the single molten copper droplets with a high We a were clearly observed even under a supercooled condition that is well below the copper melting point of 1083°C. The dimensionless mass median diameters (D m /D 0) of molten droplets with a high We a are less than the molten droplets with a low We a under the same thermal condition. When We a was approximately >200, the hydrodynamic effect on fragmentation became dominant over the thermal effect under a relatively low superheating condition. For a higher We a range, the comparisons indicated that the fragment sizes of the molten copper droplets had similar distributions to those of copper and metallic fuel jets and stainless steel droplets even with different thermophysical properties and a 1000-fold mass difference, which implied the possibility that the fragment size characteristics of the molten metal jets could be evaluated by the interaction of a single droplet with the sodium coolant without consideration of dropping modes and mass.