This is a sample fvOptions file that can be used to implement a degassing boundary condition for multiphase flows where the free surface is not modelled directly. At all cells adjacent to the degassing boundaries, a mass source is applied to remove the mass of gas within one timestep. To account for the mass sink, a force is also added to the momentum equations to balance the force due to the removal of mass.
The continous liquid phase should be set up as a slip wall on the degassing boundary, while the dispersed phase should be set up as a pressureInletOutletVelocity boundary. The pressure field, p_rgh should be set as prghPressure condition on the degassing boundary. This code has mainly been tested with the reactingTwoPhaseEulerFoam solver, but should work for any Eulerian solver provided the field names are specfied correctly in the fvOptions dictionaries. For reactingTwoPhaseEulerFoam the only entries that need to be changed are the patches entries in each of the degassingMassSource and degassingForce dictionaries. The patches entry must specify the name(s) of the boundary patches where the degassing boundary is applied. The folder tutorial contains a bubble column case that uses this boundary condition.