Film boiling is usually induced while a very hot object contacts with a coolant. Such phenomena will deteriorate the heat transfer and degrade the cooling process. Film boiling is of significant concern for the design of an emergency core cooling system after a hypothetical loss of coolant accident happens in a nuclear power plant. Furthermore, after a nuclear power plant is shut down, the fuel rods will continue to release heat due to the decay of fission products. Moreover, the subcooling of coolant might be changed dramatically during the reflood process. Therefore, it is of significant importance and interest to understand the effect of decay heat and subcooling of coolant on the quenching process of a hot object. This study demonstrates the quenching of a vertical brass cylinder without and with heating power of 105W in deionized water with different subcoolings. The diameter and length of the cylinder is 24 mm and 112 mm, respectively. Six K-Type thermocouples are embedded 2mm below the cylinder surface at different axial locations. The experimental results reveal that, with heating power of 105W, the duration of film boiling becomes much larger than the case without heating power under the same subcooling condition. Besides, the duration of film boiling decreases with increasing subcooling. This study also reveals that the Leidenfrost temperature increases significantly with increasing the subcooling with or without heating power. Significantly, a stable film boiling with approximately constant wall temperature can be sustained in saturated water. This is of significant concern for nuclear safety.

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