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Surface tension coefficient σ (SI unit: N/m).
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Parameter controlling interface thickness εpf (SI unit: m). The default expression is pftff.ep_default, a value proportional to the maximum element size with a proportionality factor dependent on the ratio of the maximum and minimum element sizes in the domain.
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Mobility tuning parameter χ (SI unit: m·s/kg). This parameter determines the time scale of the Cahn–Hilliard diffusion and it thereby also governs the diffusion-related time scale for the interface. Select User defined (default) or Calculate from velocity. For User defined enter a value or expression for the mobility tuning parameter χ. The default is 1 m·s/kg, which is a good starting point for most models.
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Keep the χ parameter value large enough to maintain a constant interface thickness but still low enough to not damp the convective motion. A too high mobility can also lead to excessive diffusion of droplets.
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