應用二維真實孔隙微模型於多相流置換及殘餘量變化之研究

Experimental study on fluid displacement and residual saturation variation of multiphase flow using X-ray image inspired Micro-models.

林子維(Tsu-Wei Lin)

指導教授 ： 張良正 ； 許少瑜

國立交通大學/工學院/土木工程系所/碩士(2020年)

摘要

地底下的多相流體置換是生態循環及環境整治的重要環節之一，因土壤孔隙的不可透視，利用透明的微模型透過直接觀測的方式進行多相流研究，有助於了解多相流在孔隙介質中的置換現象，故本研究目的在以真實土壤之X-ray CT 掃描影像製作PDMS微模型，並以此微模型探討土壤孔隙中多相流體汲取與排退時，濕潤相與非濕潤相的置換過程、殘餘相的形成機制及不同含水量下新酒精與舊酒精間的交替過程。實驗方法為以微流幫浦將流體以五種不同流量注入至PDMS微模型中，並使用高速相機紀錄注入過程及結果，再以影像分析進行量化並進行注入流量影響殘餘量之機制分析。實驗結果顯示雙相流實驗中，在主汲取過程中非濕潤相殘餘量隨著濕潤相注入流量增加而增加，此現象與角隅流有關，低注入流量時角隅流有充分的時間填滿流體界面附近角隅，此使整體潤濕前緣(流體界面)較連續可較完整的排除非濕潤相，使非濕潤相殘餘量減少；隨著注入流量增加，濕潤相前進速度加快，以致角隅流無充分時間填滿流體界面附近角隅，此時濕潤相前進速度主要由孔隙大小決定，而複雜的孔隙大小變化，使濕潤相分散前進導致非濕潤相易被濕潤相包夾無法及時排出而被封存(trapping)。在主排退過程中濕潤相殘餘量亦隨非濕潤相注入流量增加而增加，其主要原因在於毛細壓力及黏滯力的相對影響程度，低流量時黏滯力較小，毛細壓力影響較大，因此非濕潤相(流體界面)逐步依孔隙之大小前進而排出濕潤相；當高流量時，因黏滯力所產生之能量損失對整個排退過程影響較大，致使非濕潤相(流體界面)循能量損失較小，即平均孔隙半徑較大之路徑前進，產生非潤濕相前進之類優勢流現象，致使潤濕相之殘餘量相對增大。本研究亦進行雙相流之次汲取實驗，以觀測新舊酒精間的交互作用，研究結果指出，流量對於殘餘量的影響較不明顯，但是本研究在觀測影像中發現舊酒精易殘留在空氣泡周圍，空氣氣泡的大小、數量與位置亦影響舊酒精殘餘量；三相流置換機制較為複雜，由實驗可看出，注入水時水同時置換出油與空氣，惟水置換油為排退，油置換空氣則為汲取。本研究結果顯示，孔隙大小之空間分布變化，對整個多相流體之流動置換過程有相當大的影響，本研究之真實土壤孔隙微模型實驗，不但觀測到以往孔隙大小變化相對較規則的人工網路微模型所不易觀測的現象，同時亦提供後續更多待進一步研究的方向。

關鍵字

PDMS微模型 ； 孔隙介質多相流 ； 汲取及排退 ； 新水與舊水 ； 角隅流

並列摘要

Multiphase fluid displacement is one of important links of ecological cycle and environmental improvement under the ground. However, the invisibily of porous media limits the study of multiphase flow. Using transparent micro-models help to understand the displacement of multiphase flow in the porous media. Therefore, the purpose of this study is to investigate displacement of multiphase flow in the porous media by using X-ray image of soil pores inspired Micro-models, the experiment of this study include imbibition, drainage, displacement between New ethanol and Old ethanol and displacement of three-phase flow to observe residual saturation variation. The experimental method is to inject fluid into the PDMS micro-model with micro-flow pumps at five different flows, and use a high-speed camera to record the injection process and results, and then use image analysis to quantify and analyze the mechanism of the influence of the injected flow on the residual volume. two-phase flow. In the two-phase flow experiment: The results of Primary Imbibition show the residual volume increases as the injection flow rate of wetting fluid increases. This phenomenon is related to the corner flow. At low injection flow, the corner has enough time to be filled up by corner flow. This makes the overall wetting front more continuous and can completely remove the non-wetting phase, reducing the residual volume(non-wetting phase); as the injection flow rate increases, the wetting phase advances faster, so that the corner flow does not have enough time to fill up the corner. The advancing speed of the wetting phase is mainly determined by the pore size, however the complex pore size makes the wetting phase discretely advance, which causes the non-wetting phase to be easily trapped. The results of Primary Drainage show the residual volume increases as the injection flow rate of wetting fluid increases. The reason is the relative influence of capillary pressure and viscous force. The viscous force is smaller and the capillary pressure has a greater influence at low flow rates, so the non-wetting phase gradually advances according to the pore size to discharge the wetting phase; When the flow rate is high, the energy loss due to the viscous force has a greater impact on the Drainage process, causing the non-wetting phase to follow the path with a smaller energy loss and a larger average pore radius to produce The moving path is similar to preferential flow such as phase advancement leads to a relative increase in the residual volume(wetting phase). This study also conducted the experiment of secondary imbibition to observe the interaction between new ethanol and old ethanol in the two-phase flow. The results of secondary imbibition indicate that the influence of the flow rate on the residual volume has no obvious trend, but we found in the images that the residual phase of old ethanol often remain around the air bubbles, and the size, number and location of air bubbles also affect the residual volume of old ethanol. The displacement mechanism of three-phase flow is more complicated. It can be seen from the experiment that when water is injected, water replaces oil and air at the same time, but water replaces oil for drainage and oil replaces air for imbibition. The results of this study show that the spatial distribution of pore size has a considerable influence on the flow replacement process of the multiphase fluid.

並列關鍵字

PDMS ； Micro model ； Multiphase flow in the porous media ； Imbibition ； Drainage ； New water and Old water ； Corner flow

參考文獻

1. Berkowitz, B., Interchange of Infiltrating and Resident Water in Partially Saturated Media, in Transport and Reactivity of Solutions in Confined Hydrosystems. 2014, Springer. p. 55-66.

2. Chang, L.-C., et al., Experimental study on imbibition displacement mechanisms of two-phase fluid using micro model. 2009. 59(4): p. 901.

3. Davis, E. and B. Lien, Laboratory study on the use of hot water to recover light oily wastes from sands. 1993, Environmental Protection Agency, Ada, OK (United States). Robert S. Kerr ….

4. Dong, M., I.J.J.o.c. Chatzis, and i. science, The imbibition and flow of a wetting liquid along the corners of a square capillary tube. 1995. 172(2): p. 278-288.

5. Gervais, T., et al., Flow-induced deformation of shallow microfluidic channels. 2006. 6(4): p. 500-507.