The Precipitation in Fluid Flow Coupling Feature
The Precipitation in Fluid Flow () multiphysics coupling is used to simulate a fluid flow containing one or multiple solute species that act as reactants in precipitation. The coupling feature accounts for the mass transport of species and precipitate in the fluid flow, as well as the consumption of selected species resulting from precipitation.
Domain Level Synchronization
The Precipitation in Fluid Flow coupling feature synchronizes the features of the fluid flow interface with the in the transport interfaces. When using the Precipitation in Fluid Flow, the velocity field used by the Transport of Diluted Species and Size-Based Population Balance interfaces are synchronized to the one computed by the Laminar Flow interface.
Turbulent Mass Transfer
When a turbulence model is used, the Precipitation in Fluid Flow coupling applies turbulence modeling for the population balance and species transport interfaces in the following manners:
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Turbulent mass transport is added. The additional mass transport contribution is defined from the turbulent viscosity and a turbulent Schmidt number (for more information, see Turbulent Mass Transport Models).
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Mass transport wall functions are added if the turbulence model also uses wall functions. The coupling automatically adds wall functions for the mass transport on the same boundaries as those defined by the fluid flow interface (for more information, see Mass Transport Wall Functions).
Wall functions are not added for the Size-Based Population Balance interface.
Settings
The Label is the default multiphysics coupling 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 underscore (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first multiphysics coupling in the model) is pff1.
Domain Selection
The selection of the Precipitation in Fluid Flow coupling feature is automatically defined on the intersection of the selections for the coupled interfaces.
Coupled Interfaces
This section defines the physics involved in the multiphysics coupling. The Fluid flow, Species transport, and Population balance 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 (macOS 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 Laminar Flow is deleted, then the Fluid flow list defaults to None as there is nothing to couple to.
Click the Go to Source buttons () to move to the main physics interface node for the selected physics interface.
To reestablish the coupling if a physics interface is deleted and then added to the model again, you need to choose the physics interface again from the Fluid flow, Species transport, or Population balance 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.
Precipitant
Each species defined in the Transport of Diluted Species interface, is available as a reactant in the precipitation and can be selected in the list. When a species is selected, an additional reaction rate is added to that species. For the added reaction rate, refer to the Precipitant section of the Precipitation interface.
precipitate
Enter the precipitate molar mass in the corresponding text field.
Turbulence
When the fluid flow interface uses a turbulence model, select an option from the Mass transport turbulence model list — Kays–Crawford, High Schmidt Number, or User-defined turbulent Schmidt number.
For User-defined turbulent Schmidt number, enter a Turbulent Schmidt number ScT (dimensionless).
The turbulent mass transfer added to the concentration equation is defined as
where μT is the turbulent viscosity defined by the flow interface, and the turbulent Schmidt number, ScT depends on the Mass transport turbulence model used.