Marangoni Effect
The Marangoni Effect 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.
Settings
The Label is the default multiphysics coupling feature name.
The Name 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 Name field. The first character must be a letter.
The default Name (for the first multiphysics coupling feature in the model) is mar1.
Coupled Interfaces
This section defines the physics involved in the multiphysics coupling. The Fluid flow and Heat transfer lists include all applicable physics interfaces.
The default values depend on how this coupling node is created.
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If it is added from the Physics ribbon (Windows users), Physics 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.
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If it is added automatically when a multiphysics interface is chosen in the Model Wizard or Add Physics window, then the two participating physics interfaces are selected.
You can also select None from either list to uncouple the node from a physics interface. If the physics interface is removed from the Model Builder — for example, Heat Transfer in Fluids is deleted — then the Heat transfer list defaults to None 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.
Surface Tension
Select a Surface tension coefficient type: Library coefficient, liquid/gas interface, or User defined (the default).
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For Library coefficient, liquid/gas interface choose an option from the Library surface tension coefficient list.
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For User defined enter a Surface tension coefficient σ (SI unit: N/m).
Contact Angle
The attachment angle between the fluid/fluid interface and the adjacent walls can be specified in this section.
Select an option from the Specify contact angle list — Directly (the default) or Through Young’s equation.
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For Directly enter a Contact angle θw (SI unit: rad). The default is π/2 radians.
For Through Young’s equation enter values or expressions for Phase 1-Solid surface energy density γs1 (SI unit: J/m2) and Phase 2-Solid surface energy density γs2 (SI unit: J/m2).