Experiments and Investigation on the Multi-phase Flow Mechanism in Porous Media Using Micro-models
Hung H. Chen
|關鍵字:||非水相液;微模型;相對滲透係數;飽和度;毛細壓力;實驗;NAPLs;micro-model;relative permeability;saturation;capillary pressure;experiment|
|摘要:||有機溶劑被大量的應用於工業製程及一般的生活中，如晶圓製造的清洗，及 隨處可見的加油站等，由於其在水中的溶解度甚低，故又稱為非水相液（NAPLs），一般而言，因其毒性高且於自然界中不易被分解，若不慎滲入含水層時，會導致地下水長期的污染，若不慎飲用對人體健康將造成很大的影響，故研究NAPLs於地表下的傳輸分佈，乃一重要的課題。惟NAPLs在土壤中為複雜的多相流傳輸，其機制複雜且仍有許多問題待進一步的釐清，其中相對滲透係數-飽和度-毛細壓力（Kr-S-P）特性曲線，為分析NAPLs傳輸最基本也最重要的關係曲線，因此本研究以微模型實驗平台探討非水相液體於孔隙介質中主要流動機制。學術上貢獻如下：(1) 微模型實驗技術開發：整合高精度雷射雕刻，壓克力表面處理及數位影像分析等技巧，發展微模型實驗平台，以可透視微模型模擬多孔介質，可清楚的觀察到多孔介質中多相流體的流動機制，配合數位影像技術分析實驗所得之影像，可精確的求得介質中各相的飽和度，進而獲得在水、空氣及NAPLs等多相共存下之完整Kr-S-P關係曲線，由於微模型本身可重複使用，因此整個研究成果之再現性甚佳。(2)二相流體對微模型實驗之Kr-S-P關係：包括以孔頸尺寸比例組成微模型板實驗平台去證實多相流流動主要特性曲線正確性與適用性; 驗證水和空氣二相流之P-S微模型實驗，與前人以幾何形狀所推估出來的置換機制門檻值大致吻合;以連通性及潤濕性等解釋多組二相流體對Kr-S曲線實驗之遲滯現象;以微模型實驗結果配合van Genuchten特性曲線經驗式互推估二相流體對之P-S與Kr-S 曲線，推估結果良好;以比例原則(Scaling rule) 推估多組二相流體於毛細壓力-飽和度曲線的結果，顯示在水和空氣二相流體對為參考流體對時，推估其他組流體對吻合度最佳。(3) 三相流體共存時之Kr-S-P關係曲線：以微模型實驗取得水、空氣、柴油（LNAPL）和四氯乙烷（DNAPL）各三相共存時之Kr-S-P關係曲線，由單一實驗直接得到Kr-S-P的關係，此乃前人所無的實驗；本研究同時也發現，在三相共存的情形下，在同組實驗中各相進入多孔介質（微模型）的順序對於Kr-S-P關係有一定的影響，且在三相共存時，當非濕潤相之柴油與空氣兩者飽和度的比例不同時，會影響濕潤相的相對滲透。|
Organic solvents are largely used in manufacturing process such as: the cleaning of solar wafers. They can also be commonly encountered in daily routine at gas stations. The solubility of organic solvents, also known as Non-Aqueous-Phase-Liquids (NAPLs), is low in water. NAPLs are high-toxic and non-decomposable. The infiltration of NAPLs in underground water will cause long term contamination. Eventually the polluted water presents serious threats to human health once it is consumed. Therefore, it is crucial to characterize the transmission and spreading of the NAPLs under the ground surface. The diffusion mechanism of the NAPLs in soil is subtle and can be portrayed as multi-phase flows. The curve demonstrating the relationships between relative permeability, saturation, and capillary pressure (Kr-S-P) of NAPL plays a pivotal role in revealing the transmission of NAPLs in the ground. This study utlizes the perspective micro-model to examine the micro-behavior of multi-phase flows in porous media and obtains the corresponding curves between relative permeability, saturation, and capillary pressure between every two and three phases of water, air, LNAPL and DNAPL. The major accomplishments of this study include three parts: (1) Developing experimental micro-model techniques. A laboratory testing bed of micro-models are established integrating high precision carving machines, surface treatment apparatus of acrilans, and image process engines to clearly observe the phenomenon of the multi-phase flow in the micro-model. All of the experimental results are video taped using digital camcorders. Moreover, by using laser tools, a large number of porous media subject to identical conditions can be generated allowing numerous comparative sets of specific experiment. The saturation of each phase is computed once the digital image analysis is performed at images. The research results are highly reproducible owing to the repeatable micro-model technique. (2) Quantifying the Kr-S-P curves in two-phase flow. The validity and adaptability of multi-phase curves are verified using micro-model testing bed tailored to adequate scale of pores. Results obtained from the P-S micro-model tests generally agree with the threshold values of displacement mechanism offered by researchers using geometric shapes. The hysteresis of .experimental Kr-S curves of numerous two-phase flows are depicted in terms of connectivity and humidification. The P-S and Kr-S curves of two-phase flow are well-derived in conjunction with micro-model test results and empirical van Genuchten model. For the curve expressing the relation between saturation and capillary pressure, experimental results of water-air flow system corresponds to the theoretical data. Additionally, the proportion derived from the scaling rule is congruous to the experimental data. (3)Deriving the Kr-S-P cuves at the co-existence of three-phase flow. This study successfully obtains the experimental micro-model data showing the Kr-S-P curves that includsthe water, air, LNAPL and DNAPL are coexist. No such effort has ever been attempted. The experimental results also show that the sequence of entering into the micro-model for the three phases will have certain impact at the Kr-S-P relation. It is remarkable that the relative permeability of wetting phase varies with varying percentage of saturation of the non-wetting diesel and air in three phase co-existence case.
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