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標題: | 孔隙率與化學反應之交互作用之溶質傳輸歷程 Interaction of Porosity and Chemical Reaction on the Evolution of Solute Transport Processes |
作者: | Yuan-Yao Chang 張元耀 |
指導教授: | 林俊男 |
共同指導教授: | 劉振宇 |
關鍵字: | 孔隙率,動力,溶解反應,強度,反應速率,常數,波鋒行,為圖, porosity,kinetic dissolution reaction,strength,reaction rate constant,front behavior diagram, |
出版年 : | 2007 |
學位: | 碩士 |
摘要: | 地下水與流經之孔隙介質將產生各種不同化學反應,使固相部份之孔隙介質溶解或沉澱,進而改變孔隙率,同時,水中溶質濃度亦隨之增減,且孔隙率之改變亦影響地下水流場,因而形成一複雜交互作用之系統。目前常用於模擬地下水流之模式鮮少考慮孔隙率改變之影響, 即地下水流況不受反應作用影響。本研究之目的為探討影響地下水-孔隙介質間動力溶解反應與地下水流況之重要因子,將以數值方法分析地下水系統受不同上游壓力梯度、反應速率常數、初始雙擾動擾動間距與強度等因子影響下,其孔隙率與水中溶質濃度隨時間與空間變化之歷程,並將結果繪製成波鋒行為圖,藉以探討各重要因子之影響機制。
模擬結果指出上游壓力梯度較低時(<0.3),初始雙擾動皆發展為平波鋒。而上游壓力梯度>0.5時,初始雙擾動則會合併為單波鋒或發展成雙波鋒。隨著強度因子由0.2增加至1.0,初始雙擾動發展為雙波鋒之情況亦隨之增加。強度因子為1.0時,初始雙擾動最容易發展為雙波鋒。隨著強度因子由1.0增大至2.0,初始雙擾動合併為單波鋒之情況增加。此外,反應速率常數較小( 值為0.2或0.4)時,初始雙擾動容易發展為單波鋒。改變 值對波鋒延伸速度影響較大,整體之波鋒延伸速度隨 值增加而減少,而 值為0.4之波鋒延伸速度最慢。故不同強度因子與反應速率常數對於地下水中溶解傳輸交互作用有顯著之影響。 自然界中因溶解反應之岩/水交互作用,形成不同型態之複雜現象,可經由本研究考慮之上游壓力梯度、反應速率常數、初始雙擾動間距及強度等因子,在不同組合條件下重建其形成之歷程,並提供了部份定量分析上之解釋,有助於進一步解開造物者創造自然之神奇面紗。未來研究可考慮較高流速之地下水流況,並加入延散之效應。化學反應亦可考慮沉澱、吸附與脫附等反應,或考慮多溶質之傳輸與化學反應,擴大模式之應用範圍。孔隙率之改變機制可考慮微生物之作用,期能更接近真實現地之情況。 When groundwater flows through porous media of subsurface, various water/rock reactions are developed, including dissolution and precipitation, and the porosity is also changed. Accordingly, the concentration in the groundwater may increase or decrease. The change of the porosity affects the groundwater flow field, resulting a feed-back complex system. However, the change of the porosity is not considered in most of numerical models of which are commonly used to simulate the groundwater flow and solute transport. The objective of this study is hence to evaluate the interaction of porosity and kinetic dissolution reaction on the evolution of groundwater flow and solute transport using the developed numerical model, NSPCRT. Four important factors, including upstream pressure gradient, reaction rate constant, initial two perturbations spacing and strength are comprehensively considered. According to the simulation results, front behavior diagram are plotted to illustrate the evolution of dissolution fronts under various conditions of these four factors. Simulation results indicate that initial two perturbations develop to a planar front under low upstream pressure gradient (<0.3) and merge to a single front, or develop to a double front under high upstream pressure gradient greater (>0.5). Moreover, the tendency of initial two perturbations will develop to a double front as the strength factor increases from 0.2 to 1.0, and to a single front as the strength factor increases from 1.0 to 2.0. The optimum condition for developing a double front is the strength factor equal to 1.0. As the reaction rate constant is small ( is equal to 0.2 or 0.4), initial two perturbations likely merge to a single front. Changes of value significantly affect the front moving velocity. The front moving velocity decreases with increasing . The slowest front moving velocity occurred with =0.4. Based on these results, strength factor and reaction rate constant are considered as two important factors that govern the interaction of dissolution and solute transport in the groundwater system. In this study, the numerical model can reproduce the natural observed phenomenon of water/rock interaction with dissolution chemical reaction using a combination of various conditions of upstream pressure gradient, reaction rate constant, initial two perturbations spacing and strength. The result provides some quantitative clue to disclose the nature process formation of the Karst rock. Future study can consider high flow velocity condition, and includes the dispersion effect. In addition to precipitation chemical reaction, adsorption and desorption, or multiple-species reactive chemical transport can also be incorporated to the NSPCRT model. Moreover, the modeling of porosity change induced by microbial mediation is another active research area in the field of biogeochemistry which can be included in the future study. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/28673 |
全文授權: | 有償授權 |
顯示於系所單位: | 生物環境系統工程學系 |
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