title: Numerical investigation into thermal effects of pre-cooling zone in vitrification-based cryopreservation process.
abstract: Most studies on ultra-fast cryopreservation assume an immediate placement of the cryopreservation tube in the liquid nitrogen tank. However, in practice, before the tube is placed into the liquid nitrogen, it passes through a space containing gaseous nitrogen (pre-cooling zone) formed via the evaporation of the bulk liquid nitrogen. Comparing with ultra-fast cryopreservation, the cooling rate is insufficiently high during the falling transition to vitrify the liquid. As the tube passes through this region, its temperature may fall to the temperature required for the formation of ice crystals, and thus cell damage may occur. Consequently, in optimizing the cryopreservation process, the effects of this transition region should be properly understood. Accordingly, the present study utilizes a thermal model to investigate the temperature variation in the tube as it falls through the pre-cooling region. The simulation results show that the cooling rate within the tube increases with an increasing tube velocity. Furthermore, the results reveal that the cooling rate at the front end of the tube is higher than that at any other position of the tube. Thus, to prevent the formation of ice crystals, the material used to seal the front end of the tube should have a low thermal conductivity. In addition, a streamlined design of the front end of the tube is advised. Finally, the cooling rate within the tube depends on the tube material as well as the falling speed. The height of the pre-cooling zone needs to be carefully designed based on the tube material and falling speed, thus the ice crystal formation can be prevented.
authors.affiliation: Department of Biomechatronics Engineering, National Pingtung University of Science and Technology, Taiwan, ROC.
authors.forename: Hsun-Heng
authors.initials: HH
authors.lastname: Tsai
authors.affiliation: Department of Vehicle Engineering, National Pingtung University of Science and Technology, Taiwan, ROC.
authors.forename: Chien-Hsiung
authors.initials: CH
authors.lastname: Tsai
authors.affiliation: Department of Biomechatronics Engineering, National Pingtung University of Science and Technology, Taiwan, ROC.
authors.forename: Wei-Te
authors.initials: WT
authors.lastname: Wu
authors.affiliation: Industrial Technology Research Institute, Taiwan, ROC.
authors.forename: Fu-Zen
authors.initials: FZ
authors.lastname: Chen
authors.affiliation: Advanced Institute of Manufacturing with High-Tech Innovations, Department of Mechanical Engineering, National Chung Cheng University, Taiwan, ROC.
authors.forename: Pei-Ju
authors.initials: PJ
authors.lastname: Chiang
mesh_terms: D003080:Cold Temperature; D015925:Cryopreservation / Q000379:methods*; D006358:Hot Temperature; D008962:Models, Theoretical; D009584:Nitrogen / Q000737:chemistry; D013814:Thermal Conductivity; D058989:Vitrification
chemical_list: D009584:Nitrogen
keywords: Convective–conductive heat transfer; Ice crystal formation; Pre-cooling; Ultra-fast cryopreservation; Vitrification