Pore-scale study on reactive mixing of miscible solutions with viscous fingering in porous media

In this paper, the reactive mixing process with viscous fingering of two miscible solutions is studied at pore scale using the lattice Boltzmann method. This single-phase flow obeys the Navier-Stokes equations with a concentration-dependent viscosity. The concentration transport is governed by the advection-diffusion-reaction equation, in which the interfacial reaction rate is described by a function of the concentration of a single reacting solute and admits two stable states separated by an unstable one. The reaction effects on mixing process with viscous fingering are explored in a single pore with different reaction rates, Péclet numbers and viscosity ratios. It is found that generally the reaction can suppress the mixing process significantly by sharping the solution interfaces. Such restriction is more obvious with increasing reaction rate, and even shares the similar fashion for different Péclet numbers and viscosity ratios. The reactive mixing process with viscous fingering is further investigated in artificial homogeneous and heterogeneous porous media with different parameters, and similar results are observed.