title: DETERMINATION OF CONVECTIVE HEAT TRANSFER COEFFICIENT AT THE OUTER SURFACE OF A CRYOVIAL BEING PLUNGED INTO LIQUID NITROGEN.
abstract: BACKGROUND
  Cell survival upon cryopreservation is affected by the cooling rate. However, it is difficult to model the heat transfer process or to predict the cooling curve of a cryoprotective agent (CPA) solution due to the uncertainty of its convective heat transfer coefficient (h).
  
  
  OBJECTIVE
  To measure the h and to better understand the heat transfer process of cryovials filled with CPA solution being plunged in liquid nitrogen.
  
  
  METHODS
  The temperatures at three locations of the CPA solution in a cryovial were measured. Different h values were selected after the cooling process was modeled as natural convection heat transfer, the film boiling and the nucleate boiling, respectively. And the temperatures of the selected points are simulated based on the selected h values. h was determined when the simulated temperature best fitted the experimental temperature.
  
  
  RESULTS
  When the experimental results were best fitted, according to natural convection heat transfer model, h(1) = 120 W/(m(2)·K) while due to film boiling and nucleate boiling regimes h(f) = 5 W/(m(2)·K) followed by h(n) = 245 W/(m(2)·K). These values were verified by the differential cooling rates at the three locations of a cryovial.
  
  
  CONCLUSIONS
  The heat transfer process during cooling in liquid nitrogen is better modeled as film boiling followed by nucleate boiling.
authors.affiliation: Centre for Biomedical Engineering, Department of Electronic Science and Technology, University of Science and Technology of China, Hefei, China.
authors.forename: T
authors.initials: T
authors.lastname: Wang
authors.affiliation: Centre for Biomedical Engineering, Department of Electronic Science and Technology, University of Science and Technology of China, Hefei; Anhui Provincial Engineering Technology Research Center for Biopreservation and Artificial Organs, Hefei, China. zhaog@ustc.edu.cn.
authors.forename: G
authors.initials: G
authors.lastname: Zhao
authors.affiliation: Centre for Biomedical Engineering, Department of Electronic Science and Technology, University of Science and Technology of China, Hefei, China.
authors.forename: H Y
authors.initials: HY
authors.lastname: Tang
authors.affiliation: Centre for Biomedical Engineering, Department of Electronic Science and Technology, University of Science and Technology of China, Hefei, China.
authors.forename: Z D
authors.initials: ZD
authors.lastname: Jiang
mesh_terms: D003080:Cold Temperature; D015925:Cryopreservation / Q000295:instrumentation*; D003451:Cryoprotective Agents / Q000737:chemistry; D004867:Equipment Design; D020342:Finite Element Analysis; D009584:Nitrogen / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D013814:Thermal Conductivity
chemical_list: D003451:Cryoprotective Agents; D012996:Solutions; D009584:Nitrogen