Liquid-vapor interface behaviors during quenching and cooling of vials containing cryoprotectants immersed in liquid nitrogen

The vapor film layer during cryovials quenching in LN2 has been thought to severely impede heat transfer for cryopreservation of biomaterials. The current work mainly investigates both liquid-vapor interface behaviors and heat transfer characteristics when cryovials with CPAs immersed into LN2 by high-speed camera and data processing techniques. The results show that a shorter film boiling regime occurs for the vial with lower thermal effusivity, which implies that the vapor film was not the major obstacle to heat transfer for this case, but rather a result of the low thermal diffusivity of the vial. For example, the film boiling regime, for PP vial containing Vs55, lasted 1 s. Whereas for the case of Al vial containing Vs55, it lasted about 50 s, and the quenching time for Al vial to reach cryogenic temperature was 24.49 % faster than that for PP vial. For the vial with high thermal diffusivity, the solution inside the vial and its crystallization behaviors during quenching significantly affect the vapor film thickness and development of film boiling regime. For example, the heat released due to crystallization maintains the vapor film thickness stable over time for Al vial containing water. Vs55 in Al vials raise the Leidenfrost temperature by 22.3 degrees C compared to water. Based on the above experimental phenomena and results, further analysis shows that the vapor film of the vial filled with water is thicker than that of the vial containing Vs55 within 2 mm. For Al vials, the interfacial velocity and wavelength are higher than those of PP vials. This work is valuable for understanding the key issues in the quenching process of cryopreserved biomaterials.