A Computer Model for Predicting Two-Phase Ground Water Transport in the Soil Surrounding a Growing Melt in the In Situ Vitrification Process

摘要

Two different computer models are tested for their usefulness in predicting the water balance and pressure field surrounding a growing hemispherical In Situ Vitrification (ISV) melt. The melt is centered under the flat surface of a hemisphere of soil contained by an impervious wall. The control volume method is employed for balancing heat, and mass in each model. The soil is considered a porous media; consequently, fluid velocity can be modeled by Darcy's equation. Both computer models employ grids which adapt to the transient boundary of the growing melt. Computational Grid I (CGI) adapts with the melt boundary by contracting in the radial direction only. In addition to adapting to the melt boundary, Computational Grid II (CGII) also adapts to the liquid-vapor interface which moves outward from the 1700°C melt in response to the formation of vapor. CGII has been devised in order to attempt to reduce, at a reasonable CPU cost, the numerical pressure oscillation which arises when the grid is too coarse. A very fine CGI is used as a benchmark to test CGII and a coarser version of CGI. Results from the two CGI and the one CGII cases are presented graphically to illustrate the mass flux of liquid and vapor water and the build-up in pressure as the melt boundary approaches the impermeable wall.