Interaction of Porosity and Chemical Reaction on the Evolution of Solute Transport Processes
Date Issued
2007
Date
2007
Author(s)
Chang, Yuan-Yao
DOI
zh-TW
Abstract
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.
Subjects
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
Type
thesis
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