Use the Reacting Flow (
) multiphysics coupling to simulate mass transport and reactions in a gas or liquid mixture where the fluid flow can be dependent on the mixture composition. When a
Heat Transfer and a
Chemistry interface are selected, use this coupling to simulate heat transfer additionally to mass transport and reactions.
Select a Fluid Flow interface and a
Species transport interface to couple fluid flow with mass transport.
Chemistry and
Heat Transfer are optional. They can be set to
None when the coupling is used to simulate isothermal mixtures.
When a Chemistry interface is selected and
Heat Transfer is set to
None, fluid properties are taken from the Chemistry interface. Set the
Temperature to evaluate the fluid properties synchronized with all the physics interfaces at the given temperature.
Select a Chemistry interface and
Heat Transfer interface in order to account for the heat of reaction, enthalpy diffusion, viscous heating and mass fluxes contributing to the heat and energy balance.
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When Chemistry is set to None and a Heat Transfer interface is selected, the coupling is solved in the same way as when no Heat Transfer interface is selected. Thermodynamic properties are required by the Heat Transfer interface.
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The pressure, velocity, and temperature variables of the Reacting Flow coupling node are set to the Common Model Input values of the Default Model Inputs node on the complementary selection, that is, all domains except those from the Selection list. It allows to couple multiple fluid flow or transport of species interfaces with a single heat transfer interface. See Default Model Inputs in the COMSOL Multiphysics Reference Manual for details.
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The Reacting Flow coupling synchronizes the features from a Chemistry interface, Heat Transfer interface, Single-Phase Flow, or Brinkman Equations, interface and a Transport of Concentrated Species interface. When the Chemistry interface is not selected, the density in the Single-Phase Flow interface is automatically synchronized to the one defined by the Transport of Concentrated Species interface.
When a Chemistry interface is selected, the Reacting Flow coupling synchronizes the definition of the thermal conductivity, density, heat capacity, enthalpy and dynamic viscosity with the other coupled physics interfaces. The reference temperature is taken from the Heat Transfer interface.
The Reacting Flow coupling feature automatically couples mass transfer on boundaries and applies a corresponding velocity contribution for the flow. Prescribing a net mass boundary flux in the
Transport of Concentrated Species interface, either using a
Flux or
Mass Fraction feature, the
Reacting Flow feature computes
The Stefan Velocity and applies this in
Wall features using the same selection.
When coupled to the Brinkman Equations interface, the
Reacting Flow node automatically computes the net mass source or sink in a
Reactions (when
Mass transfer to other phases is enabled) node in the
Transport of Concentrated Species interface and adds the corresponding source/sink to the momentum equations of the
Fluid and Matrix Properties domains.
When a turbulence model is used, the Reacting Flow coupling applies turbulence modeling for the mass transport in the following manners:
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
nirf1.
The Reacting Flow coupling is automatically defined on the intersection of the selections for the coupled interfaces. When modeling porous media transport a
Porous Medium feature, applied on the same domains, is needed in all coupled transport interfaces.
Reacting Flow coupling supports porous media transport in
Fluid flow and
Species transport interfaces.
The Selection list displays the domains where the coupling feature is active.
This section defines the physics involved in the multiphysics coupling. The Fluid flow, Species transport, Chemistry, Heat Transfer lists include all applicable physics interfaces.
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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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You can also select None from a list to uncouple the node from a physics interface.
Click the Go to Source buttons (
) to move to the main physics interface node for the selected physics interface.
Click the Show or Hide Physics Properties Settings button (
) to toggle the display of physics properties settings affecting the coupling feature. When a turbulence model is used, turbulent heat and mass transfer is automatically accounted for (see the settings in the
Turbulence section below). Using Reacting Flow, the heat and mass transfer treatment at walls follows that applied for the fluid flow. Therefore the
Wall treatment setting is also displayed when using a turbulence model. For more information on turbulent mass transfer at walls, see the section
Mass Transport Wall Functions in the
CFD Module User’s Guide.
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).
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.
For Extended Kays-Crawford, enter a
Reynolds number at infinity Reinf (dimensionless).
For User-defined turbulent Prandtl number, enter a
Turbulent Prandtl number prT (dimensionless).
where μT is defined by the flow interface, and
PrT depends on the
Heat transport turbulence model. See
Turbulent Conductivity for details.
The Turbulence model type used by the fluid flow interface can be displayed by selecting the
Show or Hide Physics Property Settings button at the right of the
Fluid flow list.