Heat Migration and Solute Transport in a Discrete Fracture
Bou Jaoude, Issam
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The study of heat and solute transport in fractured rock can provide complementary information in aid of understanding the interaction between surface and groundwater, the long-term isolation of energy by products, the application of renewable energy storage systems, and the treatment of contaminated sites. Employing numerical modeling, this research was undertaken to assess the most influential factors controlling heat migration in discretely fractured rock under natural groundwater flow conditions, to address the effect of fracture aperture variability on the spatial distribution of a migrating thermal front, and to compare heat and solute transport mechanisms. Using factorial analyses, it is shown that the most influential factor controlling heat propagation in a single fracture setting is the velocity of the fluid in the fracture. The combination of effects of the thermal conductivity of the matrix with the velocity of the fluid, and of the thermal conductivity of the matrix with the aperture of the fracture dominantly control the attenuation of the thermal front migration. By integrating variable aperture fields with contact points, it is demonstrated that the effect of aperture variability on the spatial distribution of the thermal front is defined mainly by the thermal conductivity of the rock matrix. The effect of groundwater flow channeling on the spatial distribution of the thermal front is small, contrary to solute transport in a discrete fracture setting, where channeling is sometimes a major contributor to widespread solute migration rates and directions. The thermal plume in the fracture does not reach equilibrium over the 3-year period of the simulation in contrast to the solute plume that reaches steady state in less than ten days, mainly due to thermal conduction in the matrix which remains in disequilibrium. Two-dimensional conduction in the plane of the fracture and three-dimensional conduction in the matrix are important factors to consider when assessing the thermal plume in contrast to solute transport, whereas one-dimensional diffusion in the matrix and two-dimensional dispersion in the fracture are good assumptions.
URI for this recordhttp://hdl.handle.net/1974/26704
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