Phase Field Model

The Equations for the Phase Field Thin-Film Flow Method are added in the node. The node defines the associated phase field parameters including surface tension and interface thickness.

Phase Field Parameters

Define the following phase field parameters. Enter a value or expression for the:

•

σ (SI unit: N/m).

•

epf (SI unit: m). The default expression is pf.hmax/2, which means that the value is half of the maximum mesh element size in the region through which the interface passes.

•

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 (default) or . For enter a value or expression for the mobility tunning parameter χ. The default is 1 m·s/kg, which is a good starting point for most models.

For enter a value for the expected velocity at the interface U (SI unit: m/s). χ is then computed as:

where hmax is the largest mesh cell size.


	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.

External Free Energy

Add a source of external free energy to the phase field equations. This modifies the last term on the right-hand side of the equation:

The external free energy f (SI unit: J/m3) is a user-defined free energy. In most cases, the external free energy can be set to zero. Manually differentiate the expression for the external free energy with respect to

and then enter it into the

field

Convection

Enter values or expressions for the components (u, v, and w in 3D, for example) of the u (SI unit: m/s). The applied velocity field transports the phase field variables through convection.


	Additional Sources of Free Energy