Nucleate boiling

Japanese: 核沸騰 - かくふっとう

…On the other hand, it is known that the mechanism of boiling heat transfer changes with the increase in the heat transfer surface temperature. For example, if a thin platinum wire is stretched horizontally in water at atmospheric pressure and heated by Joule heat generated by an electric current, natural convection occurs around the wire when the difference between the heat transfer surface temperature and the saturation temperature of the liquid is very small, and when the amount of heat increases and the temperature difference exceeds a certain level, discrete bubbles are generated and a state called nucleate boiling is reached. If the electric current is further increased, the heat transfer surface temperature rises rapidly at a certain limit of heat flux conditions, the thin wire is covered with a vapor film, and a state called film boiling is reached in which the heat transfer surface and the liquid no longer come into direct contact with each other. …

From [Boiling]

…Superheated liquids can suddenly and explosively boil, a phenomenon known as bumping. There are two main types of boiling: nucleate boiling, in which the liquid turns directly into steam on the high-temperature surface of the vessel wall and creates bubbles, and film boiling, in which the steam forms a continuous thin film on the high-temperature surface. In the case of film boiling, the steam film impedes the transfer of heat, so the rate at which heat is transferred is slower than in the case of nucleate boiling. …

*Some of the terminology that refers to "nucleate boiling" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…一方，沸騰伝熱の機構は伝熱面温度の上昇とともに変化することが知られている。例えば，大気圧の水中に白金細線を水平に張ってこれを電流によるジュール熱で加熱した場合，伝熱面温度と液体の飽和温度との差がごく小さいときは細線周囲に自然対流が発生し，加熱量が増してある温度差以上になると初めて離散的な気泡が発生して核沸騰と呼ばれる状態になる。さらに電流を大きくすると，ある限界の熱流束条件において伝熱面温度は急上昇して細線は蒸気膜に覆われて，もはや伝熱面と液体が直接触れ合わない膜沸騰と呼ばれる状態になる。…

【沸騰】より

…過熱状態の液体は突然爆発的に沸騰することがあり，この現象を突沸という。沸騰の型としては，おもなものは器壁の高温面で液体が直接蒸気になって気泡ができる核沸騰と，高温面で蒸気が連続な薄膜を形成する膜沸騰の二つがある。膜沸騰の場合は，蒸気の膜が熱の伝達を妨げるので，核沸騰の場合に比べ熱の伝わる速度は小さい。…

※「核沸騰」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典第２版について | 情報

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