title: Determination of heat transfer coefficients in plastic French straws plunged in liquid nitrogen.
abstract: The knowledge of the thermodynamic process during the cooling of reproductive biological systems is important to assess and optimize the cryopreservation procedures. The time-temperature curve of a sample immersed in liquid nitrogen enables the calculation of cooling rates and helps to determine whether it is vitrified or undergoes phase change transition. When dealing with cryogenic liquids, the temperature difference between the solid and the sample is high enough to cause boiling of the liquid, and the sample can undergo different regimes such as film and/or nucleate pool boiling. In the present work, the surface heat transfer coefficients (h) for plastic French straws plunged in liquid nitrogen were determined using the measurement of time-temperature curves. When straws filled with ice were used the cooling curve showed an abrupt slope change which was attributed to the transition of film into nucleate pool boiling regime. The h value that fitted each stage of the cooling process was calculated using a numerical finite element program that solves the heat transfer partial differential equation under transient conditions. In the cooling process corresponding to film boiling regime, the h that best fitted experimental results was h=148.12±5.4 W/m(2) K and for nucleate-boiling h=1355±51 W/m(2) K. These values were further validated by predicting the time-temperature curve for French straws filled with a biological fluid system (bovine semen-extender) which undergoes freezing. Good agreement was obtained between the experimental and predicted temperature profiles, further confirming the accuracy of the h values previously determined for the ice-filled straw. These coefficients were corroborated using literature correlations. The determination of the boiling regimes that govern the cooling process when plunging straws in liquid nitrogen constitutes an important issue when trying to optimize cryopreservation procedures. Furthermore, this information can lead to improvements in the design of cooling devices in the cryobiology field.
authors.affiliation: Depto. de Ingeniería Química, Facultad de Ingeniería, Universidad Nacional de La Plata and Centro de Investigación y Desarrollo en Criotecnología de Alimentos (CONICET-UNLP), Calle 47 y 116, La Plata 1900, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas, A. Rivadavia 1917, CABA 1033, Argentina. Electronic address: mvsantosd@gmail.com.
authors.forename: M Victoria
authors.initials: MV
authors.lastname: Santos
authors.affiliation: Facultad de Ciencias Agrarias, Pontificia Universidad Católica Argentina, Cap. Gral. Ramón Freire 183, CABA 1426, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas, A. Rivadavia 1917, CABA 1033, Argentina.
authors.forename: M
authors.initials: M
authors.lastname: Sansinena
authors.affiliation: Facultad de Ciencias Agrarias, Pontificia Universidad Católica Argentina, Cap. Gral. Ramón Freire 183, CABA 1426, Argentina.
authors.forename: J
authors.initials: J
authors.lastname: Chirife
authors.affiliation: Depto. de Ingeniería Química, Facultad de Ingeniería, Universidad Nacional de La Plata and Centro de Investigación y Desarrollo en Criotecnología de Alimentos (CONICET-UNLP), Calle 47 y 116, La Plata 1900, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas, A. Rivadavia 1917, CABA 1033, Argentina.
authors.forename: N
authors.initials: N
authors.lastname: Zaritzky
mesh_terms: D000818:Animals; D002417:Cattle; D015925:Cryopreservation / Q000295:instrumentation* / Q000379:methods / Q000662:veterinary; D020342:Finite Element Analysis; D005615:Freezing; D006358:Hot Temperature; D008954:Models, Biological; D008956:Models, Chemical; D009584:Nitrogen / Q000737:chemistry; D012662:Semen Preservation / Q000295:instrumentation* / Q000379:methods / Q000662:veterinary
chemical_list: D009584:Nitrogen
keywords: Boiling correlations; Cooling; Film pool boiling; Finite element method; Freezing; French straws; Liquid nitrogen; Nucleate pool boiling; Surface heat transfer coefficient