Numerical investigation on the rewarming heat transfer characteristics in cryogenic vials considering the influence of internal convection

The heat transfer characteristics significantly affect the rewarming process of cryopreserved biological samples. Currently, most numerical studies on the rewarming process merely consider the effect of heat conduction, while a description of convective heat transfer within the sample is still lacking. In this study, a comprehensive heat transfer model considering both heat conduction and convection is established by introducing a solid-liquid phase transition numerical calculation method. Under the water bath condition, the effects of oscillation, boundary conditions, and geometry on the rewarming process of cryogenic vials are investigated in detail. The results show that oscillating vials during thawing can effectively accelerate the process by approximately 21 % compared to static vials, and it also contributes to a more uniform temperature distribution within the vial. Higher water bath temperatures are available to accelerate thawing but it leads to excessive vial temperatures. Besides, the flow rate of the circulating water bath is suggested to be selected between 0.05 m center dot s  1 and 0.5 m center dot s  1. Smaller vial diameter and thinner wall thickness are favorable for accelerating the rewarming process, however, if maintaining a consistent outer diameter is necessary, reducing the wall thickness by 0.1 mm can advance the end time of rewarming by approximately 10 s. This study provides a numerical base for the design of rewarming equipment.