Pore-Scale Modeling of Mixing-Induced Reaction Transport through a Single Self-Affine Fracture

Abstract

This pore-scale modeling study in single self-affine fractures showed that the heterogeneous flow field had a significant influence on the mixing-induced reaction transport. We generated the single self-affine fracture by the successive random additions (SRA) technique. The pore-scale model was developed by coupling the Navier-Stoke equation (NSE) and advection-diffusion equation with reaction (ADER). Eddies were captured in the self-affine fracture due to the increasing Reynolds number and the sudden expansion of aperture. The flux-weighted breakthrough curves (BTCs) of reaction product showed the typical non-Fickian characteristics (i.e., "early arrival" and "heavy tail"). It was found that the reactant was involved in eddies and then reacted inside the eddy-controlled domain. Consequently, eddies played a significant role in delaying the mass exchange process between the eddycontrolled domain and the main flow channel, which resulted in the "heavy tail" in BTCs. As the Reynolds number increased, the breakthrough time increased while the concentration peaks of BTCs decreased. Furthermore, the dilution index presenting the exponential of the Shannon entropy of a concentration probability distribution was used to quantify the degree of reactant mixing. The results showed that the quantification of dilution for nonreaction transport was in good agreement with the outcomes of mixing-induced reaction transport. The high Reynolds number and Peclet number had a negative influence on the mixing process at the early time whereas they led to the enhanced mixing process at the late time.

Three-Dimensional Vortex-Induced Reaction Hot Spots at Flow Intersections

“…We performed experiments on a rough channel intersection to study the roughness effect on vortex-induced reaction hotspots. For generating rough surfaces, the Hurst exponent of 0.7 was used [28,32,33]. The channel had a constant aperture of 100 µm and a depth of 70 µm.…”

Temporal Mixing Behavior of Conservative Solute Transport through 2D Self-Affine Fractures

“…It has been widely recognized that fractures can play an important role in the transport and fate of contaminants. Characterizing the spreading and mixing processes of conservative solute through the fractures is very important for the understanding of reaction rates and mass transport rates associated with nuclear waste disposal, enhanced oil recovery, and bioremediation [1][2][3][4][5][6]. Although, in recent decades, many studies have provided new insights into the mechanisms and properties of mixing processes in homogeneous and heterogeneous porous media [7][8][9][10][11][12][13][14][15][16][17], to date, little attention has been focused on mixing behavior in fractures.…”