Retardation of ice growth in glass capillaries: Measurement of the critical capillary radius

An experiment was designed to compare the freezing of an aqueous solution in glass microcapillaries and in thin films. The velocity dependence of the ice front propagation in glass capillaries with radii of 87.5 μm–1.5 μm was observed. A critical capillary radius r₀, corresponding to certain thermal conditions, was obtained, below which the ice growth inside the capillaries was retarded. This critical capillary radius is further related to λ₀, the smallest wavelength used in the Mullins-Sekerka criterion for the instability analysis of bulk solidifications [Mullins and Sekerka, J. Appl. Phys. 35, 444 (1964)]. It was found that for the present hypothesis, r₀=λ₀/4 gives good predictions. The relation between the propagation velocity (or cooling rate) and the critical radius (or pore size) is summarized in a chart for applications in capillary-porous media, such as in the freezing of biological tissues.