期刊
THERIOGENOLOGY
卷 77, 期 8, 页码 1717-1721出版社
ELSEVIER SCIENCE INC
DOI: 10.1016/j.theriogenology.2011.10.044
关键词
Cooling rate; Slush nitrogen; Heat transfer coefficient; Numerical simulation; Cryopreservation; Sperm
Slush nitrogen (SN2) is a mixture of solid nitrogen and liquid nitrogen, with an average temperature of -207 degrees C. To investigate whether plunging a French plastic straw (commonly used for sperm cryopreservation) in SN2 substantially increases cooling rates with respect to liquid nitrogen (LN2), a numerical simulation of the heat conduction equation with convective boundary condition was used to predict cooling rates. Calculations performed using heat transfer coefficients in the range of film boiling confirmed the main benefit of plunging a straw in slush over LN2 did not arise from their temperature difference (-207 vs. -196 degrees C), but rather from an increase in the external heat transfer coefficient. Numerical simulations using high heat transfer (h) coefficients (assumed to prevail in SN2) suggested that plunging in SN2 would increase cooling rates of French straw. This increase of cooling rates was attributed to a less or null film boiling responsible for low heat transfer coefficients in liquid nitrogen when the straw is placed in the solid liquid mixture or slush. In addition, predicted cooling rates of French straws in SN2 tended to level-off for high h values, suggesting heat transfer was dictated by heat conduction within the liquid filled plastic straw. (c) 2012 Elsevier Inc. All rights reserved.
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