可透視微模型實驗於毛細壓力-飽和度關係之研究

Abstract

由於有機溶劑於水中的溶解度甚低並在自然界中不易被分解，故又稱非水相液（NAPLs），其污染能力比水溶性污染物更為嚴重，一旦滲入含水層時，極易導致地下水污染，故研究NAPLs於地表下的傳輸分佈進而解決此類污染問題是刻不容緩的。 本研究以可透視微模型並應用數位影像分析觀察有孔介質中多相流微觀的流動行為，並取得水對空氣、柴油對空氣等毛細壓力對飽和度的資料，並探討比例原則(Scaling rule)於毛細壓力-飽和度曲線推估之應用。由實驗結果可知，以比例原則推估毛細壓力-飽和度曲線時，其誤差約正比於推估之毛細壓力值，即毛細壓力值愈大誤差也愈大。另外，由微觀的觀察可看出，在汲取過程中，部分濕潤相液體將沿著其在固體表面的液體流動，此種現象將會大幅增加比例原則推估汲取過程中之毛細壓力-飽和度曲線的誤差。

In addition to having a low solubility in water, most organic solvents are difficult to decompose naturally. While leaking into the aquifer, the organic compounds can more seriously contaminate the aquifer than other high soluble pollutants do. Therefore, understanding the fate and transport mechanism of the organic compounds in aquifer is a relevant task. This study utilizes perspective micro-model experiments and digital image analysis to obtain capillary pressure-saturation relationships for several two-phases systems including the water-air and NAPLs-air and to observe the micro-scale behavior of a multi-phases system in porous media. The experimental data from the micro-model are then used to investigate the accuracy of scaling rule. For the same porous media, the scaling rule has been widely used to estimate the capillary pressure-saturation curve of a target two-phases system based on the observed data of other two-phases system. The result indicates that the error of the estimation is proportional to the value of capillary pressure for the target phases. The higher the capillary pressure the larger the error. The micro-scale observation also reveals that a thin film of wetting fluid exists on the surface of porous matrix and that become a preferential path of the wetting phase during the imbibition process. Therefore, applying the scale rule to estimate the capillary pressure-saturation curve for the imbibition process is questionable.