Will Bainbridge authored Oct 19, 2017 and Andrew Heather committed May 16, 2018

Two boundary conditions for the modelling of semi-permeable baffles have
been added. These baffles are permeable to a number of species within
the flow, and are impermeable to others. The flux of a given species is
calculated as a constant multipled by the drop in mass fraction across
the baffle.

The species mass-fraction condition requires the transfer constant and
the name of the patch on the other side of the baffle:

boundaryField
{
    // ...

    membraneA
    {
        type            semiPermeableBaffleMassFraction;
        samplePatch     membranePipe;
        c               0.1;
        value           uniform 0;
    }
    membraneB
    {
        type            semiPermeableBaffleMassFraction;
        samplePatch     membraneSleeve;
        c               0.1;
        value           uniform 1;
    }
}

If the value of c is omitted, or set to zero, then the patch is
considered impermeable to the species in question. T...