Conservative and Nonconservative Formulations
When the velocity field is divergence free, you can use either the conservative or the nonconservative formulation of the phase field thin-film flow equation. The conservative form perfectly conserves the mass of each fluid, but the computational time is generally longer.
When the Phase Field Thin-Film Flow interface are coupled to a Thin-Film Flow interface by means of or The Two-Phase Thin-Film Flow, Phase Field Coupling Feature, improved conservation of the integral of the phase field variable is obtained using the nonconservative form provided that the discretization order of the phase field variable is equal to or lower than the order of the film pressure.