PNNL

Abstract

In this paper we present a smoothed particle hydrodynamics (SPH) pore scale reactive transport model of competitive adsorption of a binary system in a porous media. SPH is a Lagrangian, particle based modeling method which uses the particles as interpolation points to directly discretize the governing equations of the system. The theory and details of the SPH pore scale model are presented along with a novel method for handling surface reactions based on the continuum surface force model [1]. The numerical accuracy of the model is validated with analytical and finite difference solutions, and the effects of spatial and temporal resolution on the accuracy of the model are also discussed. The pore scale model is used to study competitive adsorption for different Damköhler and Peclet numbers in a binary system where a plume of species B is introduced into a system which initially contains species A. The pore scale model results are compared with a Darcy scale model to investigate the accuracy of a Darcy scale reactive transport model for a wide range of Damköhler and Peclet numbers. The results demonstrate that the Darcy model is able to accurately predict the total mass of aqueous and adsorbed species of both species A and B for low Damköhler numbers. For high Damköhler numbers the Darcy model is able to accurately model the aqueous and absorbed mass of species A, but is unable to accurately predict the total mass of aqueous and adsorbed species B, which moves through the domain as a plume. At high Peclet numbers, the Darcy model was able to accurately predict the aqueous and adsorbed masses of species A and B at higher Damköhler numbers then low Peclet number simulations, however at both high and low Peclet numbers the Darcy model was not able to accurately predict the total mass of species B at high Damköhler numbers. The simulation results demonstrate the limitations of simple Darcy scale models with constant transport coefficients.