Enhanced reaction kinetics and reactive mixing scale dynamics in mixing fronts under shear flow for arbitrary Damköhler numbers - INSU - Institut national des sciences de l'Univers Access content directly
Journal Articles Advances in Water Resources Year : 2017

Enhanced reaction kinetics and reactive mixing scale dynamics in mixing fronts under shear flow for arbitrary Damköhler numbers

Aditya Bandopadhyay
  • Function : Correspondent author
Tanguy Le Borgne
  • Function : Author
  • PersonId : 905951
Yves Méheust

Abstract

Mixing fronts, where fluids of different chemical compositions mix with each other, are known to represent hotspots of chemical reaction in hydrological systems. These fronts are typically subjected to velocity gradients, ranging from the pore scale due to no slip boundary conditions at fluid solid interfaces, to the catchment scale due to permeability variations and complex geometry of the Darcy velocity streamlines. A common trait of these processes is that the mixing interface is strained by shear. Depending on the Péclet number Pe , which represents the ratio of the characteristic diffusion time to the characteristic shear time, and the Damköhler number Da , which represents the ratio of the characteristic diffusion time to the characteristic reaction time, the local reaction rates can be strongly impacted by the dynamics of the mixing interface. So far, this impact has been characterized mostly either in kinetics-limited or in mixing-limited conditions, that is, for either low or high Da . Here the coupling of shear flow and chemical reactivity is investigated for arbitrary Damköhler numbers, for a bimolecular reaction and an initial interface with separated reactants. Approximate analytical expressions for the global production rate and reactive mixing scale are derived based on a reactive lamella approach that allows for a general coupling between stretching enhanced mixing and chemical reactions. While for Pe < Da , reaction kinetics and stretching effects are decoupled, a scenario which we name ”weak stretching”, for Pe > Da , we uncover a ”strong stretching” scenario where new scaling laws emerge from the interplay between reaction kinetics, diffusion, and stretching. The analytical results are validated against numerical simulations. These findings shed light on the effect of flow heterogeneity on the enhancement of chemical reaction and the creation of spatially localized hotspots of reactivity for a broad range of systems ranging from kinetic limited to mixing limited situations.

Domains

Hydrology
Fichier principal
Vignette du fichier
reaction_diffusion_v7.pdf (906.67 Ko) Télécharger le fichier
Origin : Files produced by the author(s)

Dates and versions

insu-01424302 , version 1 (02-01-2017)

Identifiers

Cite

Aditya Bandopadhyay, Tanguy Le Borgne, Yves Méheust, Marco Dentz. Enhanced reaction kinetics and reactive mixing scale dynamics in mixing fronts under shear flow for arbitrary Damköhler numbers. Advances in Water Resources, 2017, 100, pp.78-95. ⟨10.1016/j.advwatres.2016.12.008⟩. ⟨insu-01424302⟩
178 View
273 Download

Altmetric

Share

Gmail Facebook X LinkedIn More