Mixing-limited bimolecular chemical reactions at pore-scale
A cargo de: Lazaro Perez (IDAEA-CSIC)
Fecha: Jueves 13 de septiembre a las 12:15 h
Lugar: Departamento de Ingeniería Civil y Ambienta, Modulo D2-Aula CIHS, Planta Baja
Mixing processes control chemical transformations such as precipitation/dissolution or degradation reactions that are fast compared to mass transfer processes. Chemical
reactions are intrinsically local phenomena, while many applications require predictions at large scales. Physical and chemical heterogeneities are found at all scales and are
at the root of complex spatial concentration distributions, segregation of reactants and phenomena related to the notion of incomplete mixing.
In order to assess the impact of medium and flow heterogeneity at pore-scale on mixingcontrolled reactions, we study the bimolecular irreversible chemical reaction A + B !
C. We consider the reactive displacement of B by a continuous injection of A in a 2-dimensional porous medium characterized by a random distribution of grain size and
position. We use a reactive random walk particle tracking (RWPT) method to simulate the reactive transport problem. This approach is fully equivalent to the advection-diffusionreaction-
equation. We observe three different regimes for the evolution of the product mass mC(t). In the first regime the reaction is controlled by diffusion, in the intermediate regime
it is dominated by advective heterogeneity and characterized by incomplete mixing, in the third, asymptotic regime, mass production is controlled by hydrodynamic dispersion. We
quantify the full evolution of the product mass through the dispersive lamella model (Perez et al., 2018), based on an effective dispersion coefficient, which captures the features of
stretching, compression and coalescence of the mixing front. The effective model predicts accurately the total mass of C. The developed methodology is applied to the pore-scale
experiments reported by Jim´enez-Mart´ınez et al. (2015).