The main processes that occur in the freezing of humid soils are phase transition of water and mass transfer, the latter being discernible in the thawed as well as in the frozen zone. Experiments reveal that the front of macroscopic ice formation lags significantly behind the boundary of incipient freezing. To this phenomeno is attributable the existence of a region of vigorous phase transition, or kinetc zone, in which migration and crystallization of moisture take place simultaneously.

In theoretical studies no allowace is made for the kinetic zone, and the phase front is treated as a mathematical surface. Yet the zone delimiting the phase transistions occurring in any temperature spectrum and the migratory processes that take place in this zone are the key to understanding the formation of schlieren textures and to describing the processes of formation of cryogenic structures consistently.

In the work reported here, a model is constructed of freezing of disperse media which allows for heat and moisture transfer in the thawed and frozen zones, phase transition in any temperature spectrum, and relaxation effects in the process of crystallization of moisture and melting of ice.

Numerical analysis is used to obtain the characteristic distributions of the temperature fields, total moisture content (including ice capacity), and many other significant results. Thus, the dimensions of the kinetic zone and its transformations are calculated, and a study is made of the region where phase transition does not take place even at temperatures below the point of onset of freezing, owing to migration processes in the frozen zone. Under certain conditions the phase front advances in an oscillating manner corresponding to the process of intensive ice formation.

The principal results obtained in this work show satisfactory agreement with experimental data.

Dr. Eli Korin
Department of Chemical Engineering
Ben-Gurion University of the Negev
P.O. Box 653
Beer-Sheva 84105, ISRAEL
Phone: 972-7-461820
Fax: 972-7-472916
E-mail: EKORIN@bgumail.bgu.ac.IL