Boundary Conditions for the Reacting Flow, Concentrated Species Interface

•Reacting Boundary

•See The Transport of Concentrated Species Interface for Mass Fraction, Inflow, Outflow, Flux, No Flux, Symmetry, and Open Boundary.

•See Boundary Conditions for the Free and Porous Media Flow Interface for Wall, Inlet, Outlet, Boundary Stress, Symmetry, Microfluidic Wall Conditions, and Flow Continuity. Also see Periodic Flow Condition and Pressure Point Constraint as described for Laminar Flow interface.

Reacting Boundary

Use the Reacting Boundary node to define the boundary conditions for a reactive surface over which there is net mass flux. The flow velocity across the boundary is set up automatically based on the sum of the species fluxes.

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 reacting boundary.

I N W A R D F L U X

Specify the Inward flux for each species individually by selecting the check box for the species to prescribe a flux. Then enter a value or expression for the flux in the corresponding field. Click to clear the check box for that species’ flux to set the flux to zero. Use a positive value for an inward flux.

C O N S T R A I N T S E T T I N G S

To display this option, click the Show button () and select Advanced Physics Interface Options. Select a Constraint type—Bidirectional, symmetric or Unidirectional. If required, select the Use weak constraints check box.

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

The Reacting Flow, Diluted Species interface (), found under the Chemical Species Transport branch () in the Model Wizard, merges the functionality of the Transport of Diluted Species and the Free and Porous Media Flow physics interfaces into a multiphysics interface. In this way coupled mass and momentum transport in free and porous media can be modeled from a single physics interface, with the model coupling for the velocity field set up automatically. In addition, the effective transport coefficients in a porous matrix domain can be derived based on the corresponding values in for a non-porous domain.

This interface is applicable for solutions (fluids) where the transported species have concentrations at least one order of magnitude less than their solvent, and where the fluid flow is in the laminar regime. More information on the applicability of the interface can be found in the individual documentation for the Transport of Diluted Species and the Free and Porous Media Flow interfaces.

Except where noted below, many features for this interface are described in detail for The Transport of Diluted Species Interface in the COMSOL

Multiphysics Guide and The Free and Porous Media Flow Interface in Note this guide. Links to the 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 rfds.

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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.

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

The Migration in electric field is described for The Transport of Diluted Species Interface in the COMSOL Multiphysics Guide.

Compressibility, Neglect inertial term in free flow (Stokes flow), Swirl flow

(2D axisymmetric models), and Neglect inertial term in porous media flow

Note

(Stokes-Brinkman) are described under Physical Model for The Free and Porous 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) and

Pressure p (SI unit: Pa). The name can be changed but the names of fields and dependent variables must be unique within a model.

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. Use the Add Concentration () and Remove Concentration () buttons as required.

•Model Builder Options for Physics Feature Node Settings Windows

•Theory for the Reacting Flow, Diluted Species Interface

•Transport Properties

•Porous Matrix Properties

• Initial Values

See Also

• Domain Features for the Reacting Flow, Diluted Species Interface

• Boundary Conditions for the Reacting Flow, Diluted Species Interface

• Pair and Point Conditions for the Reacting Flow, Diluted Species Interface

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