T Wang1, G Zhao2, H Y Tang1, Z D Jiang1. 1. Centre for Biomedical Engineering, Department of Electronic Science and Technology, University of Science and Technology of China, Hefei, China. 2. 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.
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. 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, 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. CONCLUSION: The heat transfer process during cooling in liquid nitrogen is better modeled as film boiling followed by nucleate boiling.
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, 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. CONCLUSION: The heat transfer process during cooling in liquid nitrogen is better modeled as film boiling followed by nucleate boiling.