The Precipitation Coupling Feature
The Precipitation () multiphysics coupling can be used to simulate a space-independent system containing one or more solute species that are present in a precipitation process. The coupling feature adds an extra reaction to the precipitating species to ensure mass conservation.
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 pffg1.
Coupled Interfaces
This section defines the physics involved in the multiphysics coupling. The 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 Size-Based Population Balance is deleted, then the Population balance 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 Reaction Engineering 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. The additional reaction rate is
where ρp and Mp is the density and molar mass of the precipitate respectively, Vav,j is the average volume, ΔLj is the interval length and ST,j is the total source term (1/m4/s) of size interval j of the population balance defined as
The reaction rate is added under the assumption that the molar mass of the precipitant and precipitate are equal.
When the Size-Based Population Balance interface defines the nucleation, growth, or dissolution using the concentration and diffusion coefficient of a dissolved species, additional input fields may be available. Enter an equilibrium concentration in the Equilibrium concentration field.
precipitate
Enter the precipitate molar mass in the corresponding text field. The Molar mass field is only available when the molar mass is not defined in the Reaction Engineering interface.