Heterogeneous Multi-Rate mass transfer models in OpenFOAM

In this work, we present a numerical implementation of the Multi-Rate mass transfer (MRMT) model \citep{Haggerty1995,gmrmt2019} in the opensource finite volume library OpenFOAM\reg \citep{Foundation2014}. Unlike other codes available in literature \citep{Geiger2011,Silva2009}, the one we propose can be applied to general geometries and highly heterogeneous fields, where the parameters of the MRMT can arbitrarily vary in space. Furthermore, being built over the widely diffused OpenFOAM\reg library, it can be easily installed and modfied, as well as run in parallel architectures. First, we briefly describe the structure of the \emph{multiContinuumModels} library that includes the formulation of the MRMT based on the works of \citet{Haggerty1995} and \citet{gmrmt2019}, and we verify our method against manufactured solutions. Furthermore, we show how heterogeneity plays a significant role in the mass transfer when permeability and porosity are represented using Gaussian random fields.