In order to account for consumption or production of the different phases due to one or more reactions or other physical processes at a boundary, the Boundary Mass Source node adds mass flux terms at the selected boundaries.

Add an expression for the mass source for each individual phase present. The net mass transfer corresponds to the sum of the mass sources for all phases and should be accounted for in the computation of the flow field. When the Phase Transport in Porous Media interface is coupled to a Darcy’s Law interface using a Multiphase Flow in Porous Media multiphysics coupling node, this is done automatically.