Marangoni Effect

The multiphysics coupling (

) accounts for Marangoni convection. Marangoni convection occurs when the surface tension of a fluid-fluid interface (generally liquid-air) depends on the concentration of a species or on the temperature distribution. In the case of temperature dependence, the Marangoni effect is also called thermo-capillary convection. It is of primary importance in the fields of welding, crystal growth, and electron beam melting of metals.

The Marangoni effect is a shear stress that depends on the tangential and normal variations of surface tension with temperature gradient. It has the following contribution described by forces induced on the fluid/fluid interface:

where σ is the surface tension coefficient (N/m). The first term on the right-hand-side accounts for the normal forces related to curvature effects, while the second term stands for tangential forces. Note that this formulation is intended for laminar flow regimes only.

The is the default multiphysics coupling feature name.

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

The default (for the first multiphysics coupling feature in the model) is mar1.

This section defines the physics involved in the multiphysics coupling. The and lists include all applicable physics interfaces.

The default values depend on how this coupling node is created.

•

If it is added from the ribbon (Windows users), contextual toolbar (Mac and Linux users), or context menu (all users), then the first physics interface of each type in the component is selected as the default.

•

If it is added automatically when a multiphysics interface is chosen in the or window, then the two participating physics interfaces are selected.

You can also select from either list to uncouple the node from a physics interface. If the physics interface is removed from the — for example, is deleted — then the list defaults to as there is nothing to couple to.

	If a physics interface is deleted and then added to the model again, then in order to reestablish the coupling, you need to choose the physics interface again from the Fluid flow or Heat transfer lists. This is applicable to all multiphysics coupling nodes that would normally default to the once present interface. See Multiphysics Modeling Workflow in the COMSOL Multiphysics Reference Manual.

Select a : , or (the default).

•

For choose an option from the list.

The attachment angle between the fluid/fluid interface and the adjacent walls can be specified in this section. It influences the curvature of the interface provided a feature from the interface is active on the adjacent domain.

Select an option from the list — (the default) or .

•

For enter values or expressions for γs1 (SI unit: J/m2) and γs2 (SI unit: J/m2).

	Marangoni Effect: Application Library path Heat_Transfer_Module/Tutorials,_Forced_and_Natural_Convection/marangoni_effect

when any of the following interface is added together with (or another version of the Heat Transfer Interface):