Heat transfer and vapor behavior on microstructure surface in liquid nitrogen for application to cryopreservation of living cells

Abstract Heat transfer characteristics during the cryopreservation of living cells both of the cooling and the thawing process are investigated. In the present study, heat transfer in the case of the rapid cooling such as a direct immersion in the liquid nitrogen is tried to promote by adding the microstructure on the surface of cooling objects. The microstructures on cooling surface are machined by using a computer numerical control lathe (CNC lathe). Temperature is measured at a depth of 1 mm from the inner surface of the cooling object. Variations of heat transfer with the surface condition including the vapor behaviors both of the film and the nucleate boiling in liquid nitrogen are examined. It is confirmed that in the case of the cooling object with the surface microstructure, the cooling rate is improved by about 90 % compared with the no-machining condition. It is considered that the boiling heat transfer in liquid nitrogen is promoted by the microstructures that act on the departure of vapor bubbles from vapor layer.