This thesis describes the transient heat transfer phenomenon when the small object is suddenly plunged into the subcooled liquid nitrogen. The cooling experiment was performed with the thin plates to simulate the rapid cooling process of cryopreservation and to observe the detailed fast temperature variation. The temperature history was precisely measured during cooling process under various subcooled conditions of liquid nitrogen(from 64 K to 77 K) and various plunging speeds(from 0.1 m/s to 0.7 m/s). The instantaneous heat transfer rate was obtained by lumped capacitance method from the measured temperature data. The high speed camera was also utilized to observe the boiling characteristic of this process. The heat flux of the cooled object was increased as the plunging speed increased and the increase was influenced by the degree of subcooling. The enhanced cooling characteristic due to the plunging speed and the degree of subcooling was more noticeable in the film boiling regime than nucleate boiling regime. The shape of the rapid cooling curve was greatly modified by this effect. From the experimental data, the thesis presented the heat transfer coefficient in the cooling process.
