The Dispersed Two-Phase Flow, Diluted Species Coupling Feature
The Dispersed Two-Phase Flow, Diluted Species () multiphysics coupling is used to simulate the fluid flow of a liquid containing a dispersed phase, together with mass transport occurring in the continuous phase and the dispersed phase. The coupling feature also support mass transfer (solute extraction) between the phases.
Domain Level Synchronization
The Dispersed Two-Phase Flow, Diluted Species coupling synchronizes the features in a Mixture Model interface, with those in the transport interfaces for each of the phases (Continuous Phase Transport of Diluted Species and Dispersed Phase Transport of Diluted Species). When added, the velocity field and the volume fraction of each of the phases, computed by the Mixture Model interface, is synchronized to the species transport interface for each phase.
Solute Extraction
Extraction is the process where a species is transferred between two immiscible phases due to different relative solubilities in each phase. Physically this transfer process occurs at the phase separating interfaces, the bubble or droplet surfaces in the case of dispersed two phase flow.
Use the check boxes to select which of the species that can be dissolved in both phases and is subjected to extraction. When multiple species are present in each phase, the species in the two mass transport interfaces are paired by position, from top to bottom, in the Concentrations list (in the Dependent Variables section when selecting an interface). During extraction, the species in the continuous phase physics interface is transferred into, or from, the corresponding species in the dispersed phase physics interface. The rate at which species is removed from the continuous phase is
(8-11)
where cc and cd are the concentration in the continuous and the dispersed phase respectively. Kp is the partition coefficient determining the phase partitioning at equilibrium, as is the dispersed phase specific surface area (m2/m3), and km is a mass transfer coefficient governing the transport from the bubble or droplet surfaces to the bulk of each phase. Note same source term but with opposite sign is added for the corresponding species in the dispersed phase.
Assuming that the dispersed phase particles are spherical, the specific surface area is computed from the dispersed phase volume fraction ϕd and the particle radius rp in the manner of
(8-12)
When modeling phase transfer with a net mass change between the phases, and a corresponding change in the particle radius, Solve for interfacial area can be enabled in the settings of the coupled Mixture Model interface. In this case the resulting specific area is used in the extraction rate.
Turbulent Mass Transfer
When a turbulence model is used, the Dispersed Two-Phase Flow, Diluted Species coupling applies turbulence modeling for species transport interface in the following manners:
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Turbulent mass transport is added, 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. When a turbulence model using wall functions is used for the fluid flow, the coupling node automatically adds wall functions for the mass transport on the same boundaries (for more information, see Mass Transport Wall Functions).
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 dds1.
Domain Selection
The Dispersed Two-Phase Flow, Diluted Species coupling is automatically defined on the intersection of the selections for the coupled interfaces.
The Selection list displays the domains where the coupling feature is active.
Coupled Interfaces
This section defines the physics involved in the multiphysics coupling. The lists Dispersed Two-Phase Flow, Continuous phase species, and Dispersed phase species include the applicable physics interfaces of each kind.
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 Mixture Model, Laminar Flow is deleted, then the Dispersed Two-Phase 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.
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 using the lists in the Coupled Interfaces section. 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.
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 equations 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.