H024-02
Three-dimensional Vortex-Induced Reaction Hot Spots at Pore and Fracture Intersections

Monday, 7 December 2020: 19:04
Virtual
Peter K. Kang, University of Minnesota, Department of Earth and Environmental Sciences, Minneapolis, MN, United States, Sang Lee, University of Minnesota Twin Cities, Earth and Environmental Sciences, Minneapolis, MN, United States and Woonghee Lee, University of Minnesota Twin Cities, Minneapolis, MN, United States
Recorded Presentation
Abstract:
The vortex, a region in a fluid in which the flow revolves around an axis line, commonly occurs in various channel flow systems, such as rock fractures, porous media, pipe flows, micromixers, and blood vessels. Vortices can have a distinctive flow topology, and the topology of a flow field is known to control mixing processes, which in turn control reaction dynamics. Vortices at fracture intersections are particularly important because fluids with distinctive biogeochemical properties can mix and react at intersections [1]. Nevertheless, the role of three-dimensional (3D) vortices on mixing and reaction at flow intersections is still elusive.

In this study, we combine microfluidics experiments and 3D pore-scale numerical simulations to understand how 3D flow structures control reaction dynamics at flow intersections. PDMS microfluidic chips with straight and rough intersections are prepared to study the reaction dynamics of a biomolecular chemiluminescent reaction. The two solutions A and B are mixed and reacted at the intersection and the reaction rate, dC/dt, is estimated by analyzing the light intensity. We vary Reynold number (Re) from 1 to 300, which are typically observed values in fractured media, by varying injection rate. Flow and reactive transport simulations are conducted by directly solving 3D Navier-Stokes and advection-diffusion-reaction equations.

We show the emergence of reaction hot spots induced by 3D vortices [2]. 3D vortices form at spiral-saddle-type stagnation points, and the 3D vortex flow topology is essential for initiating reaction hot spots. The effect of vortices on mixing and reaction becomes more vigorous for rough-walled channels, and our findings are valid over wide ranges of channel dimensions and Damköhler numbers (Fig. 1). This study highlights the fundamental importance of pore-scale 3D flow effects on reactive transport in porous and fractured media.

Figure 1. Reaction rate, dC/dt, map obtained from microfluidics experiments (at Re = 1 and 100).

[1] Bochet, O., Bethencourt, L., Dufresne, A., Farasin, J., Pédrot, M., Labasque, T., Chatton, E., Lavenant, N., Petton, C., Abbott, B.W. and Aquilina, L., 2020. Nature Geoscience, 13(2), pp.149-155.

[2] Lee, S.H. and Kang, P.K., 2020. Physical Review Letters, 124(14), p.144501.

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