PNNL

Abstract

Darcy scale description of multi-component reactive transport can significantly over-predict the extent of mixing-controlled reactions. In this letter we describe a systematic pore- and Darcy-scale study of multicomponent reactive transport for various Peclet ($Pe$) and Damkohler ($Da$) numbers. We used pore-scale models to parameterize and validate Darcy scale simulations. We found that for small $Pe$, the Darcy scale model of mixing-controlled reactions is accurate, but its accuracy deteriorates with increasing $Pe$. The dilution index was calculated based on the pore-scale simulations as a measure of the degree of true solute mixing (dilution) for different $Pe$. We found that true mixing decreases with increasing $Pe$. A strong correlation was found between the magnitude of the dilution index and the error in the Darcy scale model prediction. The error (over-prediction of the mass of a product of the mixing controlled reaction) increases with decreasing dilution index (reduced dilution).