An experimental investigation on dynamics and heat transfer associated with a single droplet impacting on a hot surface above the Leidenfrost point temperature

摘要

During large loss-of-coolant accidents in nuclear reactors, water splatters as the quench front propagates at the quenching surface, and many droplets of different sizes and velocities are generated and carried with the steam in the cooling channel. Heat transfer due to droplets striking an overheated fuel rod above the Leidenfrost point temperature is important for predicting the peak cladding temperature. This study investigated the dynamics and heat transfer characteristics when a single droplet at room temperature collided with a surface at 425 degrees C experimentally, using synchronized high-speed video and infrared cameras. Various physical parameters related to heat transfer model development were measured, including the residence time, spreading diameter, local heat flux distribution, effective heat transfer area, average vapor film thickness, and total heat transfer per collision. The measured data were compared with the values of the physical parameters predicted by existing mechanistic models.