We implement the Multi-Rate Mass Transfer (MRMT) model for mobile-immobile transport in porous media within open-source finite volume library \textsc{OpenFOAM}\reg \citep{Foundation2014}. Unlike other codes available literature [Geiger, S., Dentz, M., Neuweiler, I., SPE Reservoir Characterisation and Simulation Conference Exhibition (2011); Silva, O., Carrera, J., Kumar, Alcolea, A., Willmann, ...