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oai:recercat.cat:2117/4388402026-01-21T10:22:27Zcom_2072_1033col_2072_452950

Linking mixing interface deformation to concentration gradients in porous media Farhat, Saif Bolster, Diogo Solé Marí, Guillem Universitat Politècnica de Catalunya. Departament d'Enginyeria Civil i Ambiental Universitat Politècnica de Catalunya. GHS - Grup d'Hidrologia Subterrània Àrees temàtiques de la UPC::Matemàtiques i estadística::Anàlisi numèrica::Mètodes numèrics Chemical kinetics dynamics & catalysis Contact line dynamics Convection in porous media Granular mixing Laminar flows Laminar reacting flows Microfluidics Mixing enhancement Mixing in geophysical flows Scaling laws of complex systems Shear flows Stratified geophysical flows We study the pore-scale transport of a conservative scalar forming an advancing mixing front, which can be re-interpreted to predict instantaneous mixing-limited bimolecular reactions. We investigate this using a set of two-dimensional, high-resolution numerical simulations within a poly-disperse granular porous medium, covering a wide range of Péclet (Pe) numbers. The aim is to show and exploit the direct link between pore-scale concentration gradients and mixing interface (midpoint concentration isocontour). We believe that such a perspective provides a complementary new lens to better understand mixing and spreading in porous media. We develop and validate a theoretical model that quantifies the temporal elongation of the mixing interface and the upscaled reaction kinetics in mixing-limited systems accounting for pore-scale concentration fluctuations. Contrary to the classical belief that, given sufficient time, pore-scale fluctuations would eventually be washed out, we show that for Pe>1 advection generates pore-scale concentration fluctuations more rapidly than they can be fully dissipated. For such Péclet numbers, once incomplete mixing is established, it will persist indefinitely. We identify critical Péclet thresholds (Pe=18 for Poiseuille flow, Pe=48 for porous media) where reaction efficiency is minimized. Finally, our developed model accurately reproduces the reaction product mass in a three-dimensional porous media column over a wide range of Péclet numbers, demonstrating its applicability to more realistic systems. This research was funded by National Science Foundation Grant No. EAR2049688 and by the European Commission (MixUp, MSCA-101068306). The authors gratefully acknowledge the Center for Research Computing (CRC) at the University of Notre Dame for providing the computational resources used to conduct the simulations in this work. Peer Reviewed Postprint (author's final draft) 2025-02-14 Article Farhat, S.; Bolster, D.; Sole-Mari, G. Linking mixing interface deformation to concentration gradients in porous media. «Physical review fluids», 14 Febrer 2025, vol. 10, núm. 2, article 024501. 2469-990X https://hdl.handle.net/2117/438840 10.1103/PhysRevFluids.10.024501 eng https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.10.024501 Open Access 21 p. application/pdf American Physical Society (APS)