| Summary: | 碩士 === 逢甲大學 === 環境工程與科學所 === 90 === In this study, a multicomponent flow and transport model, MVFT, was applied to simulate migration of volatile organic compounds (VOCs) in unsaturated soils, MVFT model is a transient, two-dimensional finite element model, which incorporates different diffusion approaches, including Dusty Gas Model (DGM), Stefan-Maxwell (SM) equations and Fick’s law of diffusion. Besides, this model considers dynamic steady-state phase partitioning of organic compounds with assuming linear isotherm within liquid, gas and solid phases.
This study examines concentration distribution and flux of organic vapors under five different pollution scenarios with considering three kinds of source boundary conditions. The result shows that soil permeability, gas type, system condition (steady-state and transient), domain size, dimensionality and source boundary condition may have a significant effect on producing discrepancies between predictions from the DGM and the other diffusion approaches. All of these discrepancies arise from nonequimolar effect and diffusion-induced advection. The latter is due to volatilization and phase partioning of organic compounds from nonaqueous and dissolved phases and may only be analyzed by the approach of solving the coupled flow and transport equations. The nonequimolar effect may be more significant when ratio of organic compounds increases in the gas mixture. Besides, this study proposes to modify the effective diffusion coefficient with considering Knudsen effect in applying to the Fick’s law model. This may improve applicability of Fick’s law of diffusion to gas diffusion problems in low permeable soil systems.
|
|---|
