The Phase Field Thin-Film Flow, Shell (pftffs) interface () and the Phase Field Thin-Film Flow, Edge (pftffs) interface (), found under the Mathematics>Moving Interface branch () when adding a physics interface, are used to track moving interfaces by solving two transport equations, one for the phase field variable, , and one for the mixing energy density, ψ, in thin-film flows. The fluids are assumed to flow in a narrow channel, that is represented, within the geometry, by a surface in the Phase Field Thin-Film Flow, Shell (pftffs) interface and an edge in the Phase Field Thin-Film Flow, Edge (pftffs) interface. The position of the interface is determined by minimizing the free energy.

The main node is the Phase Field Model feature, which adds the phase field thin-film flow equations and provides an interface for defining the phase field model properties.

When the Phase Field Thin-Film Flow, Shell (pftffs) physics interface is added, the following default nodes are also added in the Model Builder — Phase Field Model, Wetted Wall (the default boundary condition), Initial Values, and Initial Values, Fluid 2. And when the Phase Field Thin-Film Flow, Edge (pftffs) physics interface is added, the following default nodes are also added in the Model Builder — Phase Field Model, Initial Values, and Initial Values, Fluid 2. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions. You can also right-click Phase Field Thin-Film Flow, Shell (pftffs) or Phase Field Thin-Film Flow, Edge (pftffs) to select physics features from the context menu.

The Label is the default physics interface name.

The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.

The default Name (for the first physics interface in the model) is pftffs.

To display this sections, click the Show More Options button () and select Advanced settings options in the Show More Options dialog box.

Specify the Convective term as Nonconservative form (default) or Conservative form.

By default, the Phase Field Thin-Film Flow interface uses Linear elements.

This interface defines the dependent variables (fields) Phase field variable and Phase field help variable ψ. If required, edit the name, but dependent variables must be unique within a model.