高サブクール水による非定常冷却過程における膜沸騰の発生機構と沸騰冷却不安定現象
1993 年 79 巻 1 号 p. 55-61
詳細
1993 年 79 巻 1 号 p. 55-61
The unstable boiling-cooling phenomena in transient cooling process of hot steel bring about dispersion in steel temperature during cooling with subcooled water.The dispersion phenomena of cooling curves are resulted from co-existence of film and transition boiling on the cooling surface of steel in earlier period of cooling. This paper discusses the mechanism of this phenomena in terms of the cooling-curve shape and the average cooling rate in the film boiling region.
It has been made clear that the unstable boiling-cooling phenomena are not random but have a kind of regularity. The quench point temperature and average cooling rate immediately after the quench point are determined only by the average cooling rate in film boiling region, which is inversely proportional to the thickness of vapor film.
For the transient cooling process of steels with highly subcooled water, it is suggested that the onset condition of film boiling depends on the roughness because the cavities on the steel surface have a great influence on the capability in trapping air in the bottoms of cavities. The onset of film boiling, namely, depends on the combined effect of geometry and wettability of the cavity wall. The mechanism of unstable boiling cooling can also be understood based on the initiation of film boiling.
