Experimental determination of surface heat transfer coefficient in a dry ice-ethanol cooling bath of using a numerical approach

SANTOS, MV; SANSINENA, M.; CHIRIFE, J; ZARITZKY, N

CRYO-LETTERS

CRYO LETTERS

Año: 2017 vol. 38 p. 119 - 124

0143-2044

BACKGROUND: Dry ice (solid CO2) -ethanol baths (-78 ºC) have been widely used in low temperature biological research to attain rapid cooling of samples below freezing temperature. The prediction of cooling rates of biological samples immersed in dry ice-ethanol bath is of practical interest in the area of cryopreservation. These cooling rates can be obtained using mathematical models that represent the heat conduction equation in transient state. Additionally at the solid cryogenic-fluid interface, knowledge of the surface heat transfer coefficient (h) is necessary for the convective boundary condition in order to correctly establish the mathematical problem. OBJECTIVE: The objective of the study was to apply numerical modeling in order to obtain the surface heat transfer coefficient of a cooling bath commonly used in cryobiology. MATERIALS AND METHODS: A numerical finite element solution of the heat conduction equation was used to obtain surface heat transfer coefficients from measured temperatures at the center of polytetrafluoroethylene (Teflon) and polymethylmetacrylate cylinders immersed in a dry ice-ethanol cooling bath. The numerical model considered the temperature dependence of the thermophysical properties of the plastic materials utilized. RESULTS: A straight line relationship with negative slope is observed between cylinder diameter and heat transfer coefficient in the liquid bath. CONCLUSION: Numerical results showed that calculated heat transfer coefficients were consistent among several replicates; heat transfer coefficients in dry ice-ethanol showed an inverse relationship with cylinder diameter.Keywords: heat transfer coefficient, cooling bath, dry ice-ethanol, unsteady state heat conduction, cryobiology