Thermal design of artificial soil freezing systems

Appropriate thermal design of an artificial soil freezing system should include the linking between the performance of the refrigeration system and the thermal regime in the soil, as well as the influence of variable thermal properties and complicated geometries.

The paper presents design systems, based on computer programs, where these features are demonstrated. The refrigeration capacity is given as a boundary condition at the freezing pipe, either as temperature or flux.

Two programs are discussed; a one-dimensional (1-D), finite difference program for the analysis of a single pipe, and a two-dimensional (2-D), finite element code, with seepage flow as an option, more suited for real problems.

The programs are used to display the influence of various design parameters, such as refrigeration capacities, material properties and geometries.

A comparison is made between the 2-D program and a simplified method developed by K.R. Khakimov, which shows that the simplified method gives a very conservative estimate of the frozen volume vs. elapsed time.

Finally, the 2-D program computing combined heat and seepage flow is applied to a laboratory model of a soil freezing system, and the agreement between measured and computed values of temperature and water flow is shown to be acceptable.