| Summary: | 碩士 === 逢甲大學 === 環境工程與科學學系 === 101 === This study assesses density-driven flow and gravity-induced transport of dense gas mixture in unsaturated soil. We conducted experiments which use Sulfur hexafluoride (SF6) mixed with nitrogen to represent dense gas mixtures. This study includes three parts：First, transport experiment was carried out in a soil column which was placed in horizontal, vertically upward and downward directions to assess density-driven and gravitational effects on the migration of the dense gas mixture along the column, and then to compare with the results of Cheng (2011) and Pan (2012); second, Dusty Gas Model (DGM) theory and Fick’s first law were applied to calculate diffusive flux components, as well as to assess total flux of the transport system; third, time-varied SF6 density in the transport system was simulated with MISER model and compared with experimental results.
Experimental results show that density and pressure variations are substantial, especially near the entrance of the column. Besides, the trends of the pressure and density variations along the soil column were affected by the transport direction and initial SF6 concentration in the inlet chamber (IC). Computations of flux components show that diffusion component driven by molar-fraction gradient accounting for at most 66.8% is the dominant one in the DGM. However, diffusion driven by nonequimolar effect and gravity may account for more than 19 % and 33.5 %, respectively. Viscous flux induced by gravity is dominant from the entrance to the soil column for transport in a vertical direction. Further, predictions from the transport modeling with MISER may not entirely agree with the experiment results due to the inadequacy of formulating the diffusion term by only considering molecular fraction variations.
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