A pare-scale model is developed to simulate mass transfer between two fluid
phases in a porous medium. The approach uses a network description of the
pore space and builds on explicit tracking of the fluid-fluid interfaces in
the pore network. Mass transfer is computed as local mass fluxes across ea
ch interface, and transport equations are solved in the pore network by a c
haracteristic method. The concept of stagnant-layer diffusion is used to de
scribe the interface mass transfer, where calculated local concentrations c
ontrol the rates of mass transfer. The model results predict dissolution fr
onts developed in column experiments of porous media initially at residual
nonaqueous phase saturation. The definition of macroscopic mass transfer co
efficients is investigated, and comparisons are made for rigorously upscale
d quantities.