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. MATERIALS AND 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, h1
= 120 W/(m2·K) while due to film boiling and nucleate boiling
= 5 W/(m2·K) followed by hn
= 245 W/(m2·K). These values were verified by the differential cooling rates at the three locations of a cryovial. CONCLUSION: The heat transfer process during cooling in liquid
nitrogen is better modeled as film boiling followed by nucleate boiling.
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CONVECTIVE HEAT TRANSFER COEFFICIENT;
FINITE ELEMENT METHOD
Document Type: Research Article
Publication date: July 1, 2015
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CryoLetters is a bimonthly international journal for low temperature sciences, including cryobiology, cryopreservation or vitrification of cells and tissues, chemical and physical aspects of freezing and drying, and studies involving ecology of cold environments, and cold adaptation
The journal publishes original research reports, authoritative reviews, technical developments and commissioned book reviews of studies of the effects produced by low temperatures on a wide variety of scientific and technical processes, or those involving low temperature techniques in the investigation of physical, chemical, biological and ecological problems.