多孔介质中NAPLs流体毛细管指进形态及分形表征

Fractal Characteristics of Capillary Finger Flow for NAPLs Infiltrated in Porous Media

非水相流体(non-aqueous phase liquids,NAPLs)如石油烃类和有机溶剂类污染土壤和地下水引起了广泛关注.不同粒径多孔介质中不同性质流体入渗形态的识别是确定污染范围、有效修复土壤和地下水的前提.本研究选取不同性质的4种NAPLs流体,建立可视化砂箱模型,比较4种流体在不同粒径石英砂中指流形态差异,并引入分形理论对迁移形态进行定量描述.结果表明,NAPLs流体指进过程属于毛细管指进,主要驱动力为毛细力;同种污染物或同一黏度数量级污染物之间指流宽度和渗流面积变化趋势与毛细管数和邦德数变化趋势呈负相关;指流宽度和渗流面积随着介质粒径的减小和流体黏度的增大而增加;指流宽度和渗流面积与渗流面的质量分形维数呈正相关,质量分形维数可以作为指流宽度和渗流面积的指示指标.

Non-aqueous phase liquids （NAPLs） like petroleum hydrocarbons and chlorinated solvents have resulted in contamination of soils and ground water, which aroused widespread concern. It＇s quite important to delineate pollution area for remediation according to different soil types with pollutants properties in consideration. In this paper, a two-dimension visual sand box apparatus was constructed, with four typical NAPLs selected for infiltration experiments conducted in initially dry porous media. The main driving force was identified and fingering patterns were compared. The fractal dimension was used to give quantitative description. The present work indicates that the main driving force was capillary forces and the mechanism was the capillary fingering. The fingers varied from skeletal patterns to fleshy patterns and the infiltration area increased when the capillary number and the bond number decreased for NAPLs with the same level of viscosity. The high viscous force resulted in larger finger width and infiltration area. The same change between fluids happened in finer media. Fractal dimensions were positively correlated with the finger width and infiltration area, which is helpful in the pollution area characterization.