碩士 / 國立清華大學 / 工程與系統科學系 / 103 / 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 the heat due to 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. Besides, because the nuclear power plants are usually located in the place near the coast, the sea water is considered as an abundant source of coolant. Thus, it is also important to study the quenching behavior of sea water.
This study demonstrates the quenching of a vertical brass cylinder without and with heating power in deionized water or sea 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 cylinder is welled polished with the same process after every single test to maintain the surface condition approximately the same. The cylinder is first heated up to an initial temperature of about 550 °C in a radiant furnace, then the heater inside the cylinder is turned on and subsequently immersed into the quench pool by a pneumatic cylinder when the thermocouple (based on TC1, the lowest one ) reaches 600°C. The dimension of quench pool is 195 mm x 195 mm x 150 mm (depth), which is partially filled with deionized water or sea water. The temperatures of the quench pool are measured with T-Type thermocouples at four corner. The quenching behavior is visualized by a high-speed video camera simultaneously with the temperature measurements. The experimental results reveal that, with heating power of 105W, corresponding to the mean flux of 13.5kW/m2, which is to simulate the heat flux due to decay heat at about 1hour after reactor shut down, the duration of film boiling becomes much larger than the case without heating power under the same subcooling condition, especially for the low subcooling condition. For instance, the duration of film boiling in the case with heating power is 3.5 times longer than that in the case without heating power in deionized water with subcooling of 5˚C. Besides, the duration of film boiling increases with decreasing subcooling. The heating power and decreasing subcooling slow down the quench speed. The Leidenfrost temperature decreases significantly with decreasing subcooling. However, the heating power has no significant effect on the Leidenfrost temperature. This study also reveals that the sea water has better cooling capability than that of deionized water. The critical heat flux of sea water is 1.5 times larger than that of deionized water. Significantly, the formation of vapor film around the cylinder was not immediate as traditionally thought, but formed through the bubble coalescence of nucleate boiling at high temperature.
| Identifer | oai:union.ndltd.org:TW/103NTHU5593058 |
| Date | January 2015 |
| Creators | Ho, Yuan Hong, 何元宏 |
| Contributors | Pan, Chin, Su, Yu Chuan, 潘欽, 蘇育全 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 81 |
Page generated in 0.0025 seconds