COMSOL 6.4 - Mixture Properties

The node adds the equations described in . The node defines the associated phase field parameters, including the surface tension coefficients and parameters controlling the thickness of the interfaces.

The surface tension coefficients can be defined through user inputs, variables, or by selecting a material. For the latter option, an additional input, the temperature, may be required to define these properties.

By default, the model input is set to , and the temperature is controlled from Default Model Inputs under or by a locally defined Model Input. If a Heat Transfer interface is included in the component, it controls the temperature . Alternatively, the temperature field can be selected from another physics interface. All physics interfaces have their own tags (). For example, if a Heat Transfer in Fluids interface is included in the component, the option is available for T.

You can also select from the model input in order to manually prescribe T

	Model Inputs and Multiphysics Couplings in the COMSOL Multiphysics Reference Manual

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

ε. The default expression is terpf.ep_default*sqrt(2), 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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M0. This parameter determines the time scale of the Cahn–Hilliard diffusion and it thereby also governs the diffusion-related time scale for the interface. Keep the mobility tuning parameter value large enough to maintain a constant interface thickness but still low enough to not damp the convective motion. A mobility that is too high can also lead to excessive diffusion of droplets. By default, M0 is set to 1·10−4 m3/s, which is a good starting point for most models.

Specify the surface tension coefficients for the three types of interfaces present.

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To use a predefined expression, select or Then select an option from the list that displays below (, , and so forth).

The predefined correlations are based on the data in Ref. 3, Ref. 4, and Ref. 5.

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