Effects of incomplete mixing on multicomponent reactive transport

Darcy-scale description of multicomponent reactive transport can significantly over-predict the extent of mixing-controlled reactions. Here we present a systematic pore- and Darcy-scale study of multicomponent reactive transport for various Peclet (Pe) and Damkohler (Da) numbers. We use pore-scale simulations to parameterize and validate Darcy-scale model. Our results reveal that for small Pe, the Darcy-scale model of mixing-controlled reactions is accurate, but its accuracy deteriorates with increasing Pe. The dilution index is calculated based on the pore-scale simulations as a measure of the degree of true solute mixing (dilution) for different Pe. We find that true mixing decreases with increasing Pe. A strong correlation is 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).