B O U N D A R Y S E L E C T I O N

From the Selection list, choose the interior boundaries to apply a flux discontinuity

boundary condition.

P A I R S E L E C T I O N

If Flux Discontinuity is selected from the Pairs menu, choose the pair to define. An identity pair has to be created first. Ctrl-click to deselect.

F L U X D I S C O N T I N U I T Y

Specify the jump in species mass flux. Use a positive value for increasing flux when going from the downside to the upside of the boundary. The boundary normal points in the direction from the downside to the upside of an interior boundary and can be plotted for visualization. Select the check boxes for the species to specify a flux discontinuity, and enter a value or expression for the mass flux jump in the corresponding field. To use a different boundary condition for a specific species, click to clear the check box for that species’ flux discontinuity.

Symmetry

The Symmetry feature can be used to represent boundaries where the species concentration is symmetric; that is, there is no mass flux in the normal direction across the boundary:

n iu + ji = 0

This boundary condition is identical to that of the No Flux feature, but applies to all species and cannot be applied to individual species.

B O U N D A R Y S E L E C T I O N

From the Selection list, choose the boundaries to apply a symmetry condition.

Open Boundary

Use the Open Boundary node to set up mass transport across boundaries where both convective inflow and outflow can occur. Use the feature to specify an exterior species composition on parts of the boundary where fluid flows into the domain. A condition equivalent to the Outflow feature applies to parts of the boundary where fluid flows out of the domain.

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The direction of the flow across the boundary is typically calculated by a

Fluid Flow interface, and is entered as Model Inputs.

Tip

B O U N D A R Y S E L E C T I O N

From the Selection list, choose the boundaries to apply the open boundary condition.

E X T E R I O R C O M P O S I T I O N

Enter a value or expression for the species composition. These quantities can be selected:

•The mass fraction (default): 0

•The mole fraction: x x0

•The molar concentration (SI unit: mol/m3) c c0

•The number density, which describes the number of particles per volume (SI unit: 1/m3): n n0

A concentration quantity other than the mass fractions can only be used

when all species are defined.

Tip

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T h e R e a c t i n g F l o w , C o n c e n t r a t e d S p e c i e s I n t e r f a c e

The Reacting Flow, Concentrated Species multiphysics interface (), found under the

Chemical Species Transport branch () in the Model Wizard, combines the Transport of Concentrated Species and the Free and Porous Media Flow interfaces. This means that mass and momentum transport can be modeled from a single physics interface, with the couplings between velocity field and mixture density set up automatically. Also, the effective transport coefficients in a porous matrix domain are derived based on the corresponding values in for a non-porous domain. This interface is applicable for fluid flow in the laminar regime.

Except where included below, many features for this interface are described in detail for The Transport of Concentrated Species Interface and The Free and Porous Media Flow Interface. Links to the

Note documentation are included when it is the same information, otherwise the section or feature is described.

When this interface is added, these default nodes are also added to the Model Builder— Transport Properties, No Flux, Wall, and Initial Values. Right-click the main node to add other features with appropriate boundary conditions.

I N T E R F A C E I D E N T I F I E R

The interface identifier is a text string that can be used to reference the respective physics interface if appropriate. Such situations could occur when coupling this interface to another physics interface, or when trying to identify and use variables defined by this physics interface, which is used to reach the fields and variables in expressions, for example. It can be changed to any unique string in the Identifier field.

The default identifier (for the first interface in the model) is rfcs.

D O M A I N S E L E C T I O N

The default setting is to include All domains in the model to define the dependent variables and the equations. To choose specific domains, select Manual from the

Selection list.

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S P E C I E S

This section is described for The Transport of Concentrated Species

Interface.

Note

P H Y S I C A L M O D E L

Diffusion model is described under Transport Mechanisms for The

Transport of Concentrated Species Interface.

Compressibility is described under Physical Model for The Free and Porous

Note

Media Flow Interface.

D E P E N D E N T V A R I A B L E S

The dependent variables (field variables) are for the Velocity field u (SI unit: m/s),

Pressure p (SI unit: Pa), and Mass fractions. Use the Add Concentration () and

Remove Concentration () buttons as required. Add or remove species in the model and also change the names of the dependent variables that represent the species concentrations. Enter the Number of species.

The names can be changed but the names of fields and dependent variables must be unique within a model.

•Model Builder Options for Physics Feature Node Settings Windows

•Theory for the Reacting Flow, Concentrated Species Interface

•Transport Properties

•Diffusion

•Porous Matrix Properties

• Initial Values

See Also

•Domain Features for the Reacting Flow, Concentrated Species Interface

•Boundary Conditions for the Reacting Flow, Concentrated Species Interface

•Reacting Boundary

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