When supplying boundary conditions for the coupled Phase Transport in Porous Media and Darcy’s Law interfaces, bear in mind that the Pressure boundary condition in the Darcy’s Law interface affects the pressure of the phase from the volume constraint, . If the pressure of another phase needs to supplied, then take into account the capillary pressure.

Since the coupled Darcy’s Law interface uses the conservation equation for the total mass (Equation 8-23) to solve for , the Mass Flux boundary condition in the Darcy’s Law interface should be used to prescribe the mass flux of all phases together.

If the mass flux of the phase computed from the volume constraint needs to be prescribed at a boundary, and the total mass flux is not known a priori, it might be necessary to compute for the total mass flux in the form of a Lagrange multiplier by using the weak constraint formulation for the pressure boundary condition in the Darcy’s Law interface.