Surface Chemistry Workflow

Use the following procedure to simulate surface reactions which occur when a gaseous or liquid mixture contacts a reacting surface in a fluid or porous region.

The steps in this workflow are intended to follow on from the initial steps in the Reacting Flow General Workflow.

For the physics continuum which contains the reacting surface, select the following models in order—in addition to the models that are previously selected, with Auto-select recommended models activated.


Group Box	Model
Reacting Flow Models (when Reacting is selected)	Reacting Species Transport
Reacting Species Models (when Reacting is selected)	For detailed mechanisms, select Complex Chemistry. For simple mechanisms, select Eddy Break-Up.
Turbulence Chemistry Interactions (when Complex Chemistry is selected)	For steady-state diffusion flames, select Eddy Dissipation Concept For premixed, partially-premixed, and unsteady flames, Laminar Flame Concept
Optional Models	Surface Chemistry
Enabled Models	Surface-Gas Interaction: Selected automatically when Non-Reacting is selected, or when Reacting and Eddy Break-Up are selected.

Select any Optional models that are necessary. For example:
- NOx Emission or Soot Emissions—to model the formation of these pollutants.
- Porous Media—to model surface reactions on porous phases. See Porous Media Models.
- The Radiation model is useful for modeling applications in which radiative heat transfer is important, such as in glass furnaces. The soot emission models influence the Participating Media Radiation (DOM) and Gray Thermal Radiation models by contributing to the absorption coefficient of the continuous phase (the absorption coefficient describing both absorption and emission).
Import the surface mechanism as follows:
1. Right-click the Complex Chemistry node (or Surface-Gas Interaction node) and select Import Chemistry Definition (Chemkin format).
2. In the Import Chemkin Files dialog, select appropriate files as shown below, then click OK.
  - Chemical Mechanism File
    If multiple surface mechanisms are required, you define them all within this file.
  - Thermodynamic Properties File
  - Transport Properties File (optional)
  - Surface Chemical Mechanism File
  - Surface Thermodynamic Properties File
  Upon import, the Surface Chemistry > Surface Mechanism Manager node becomes populated with the surface mechanism.
See Importing Species and Reactions.

The Chemkin mechanism must contain, at a minimum, the description of the NASA polynomials for all the species that are involved in the mechanism. Put this information into the mechanism file itself or in separate files.

Note

You can use open site formalism for surface chemistry mechanisms in Simcenter STAR-CCM+. For the surface site species to be defined as open (have no elemental composition and molecular mass of 0), the open site species name must include OPEN in its name. For more details, please refer to the Chemkin manuals.

Define the surface for each reacting surface mechanism:

Option	Description
On a Boundary Not Associated With an Interface	When the reacting surface is represented by a boundary that is not associated with an interface, you define the mechanism at the boundary. Select the Boundaries > [boundary] > Physics Conditions > Surface Mechanism Option node and set Mechanism to one of the available mechanisms for your simulation. Expand the [boundary] > Physics Values node and define the properties.
On a Baffle Interface	When different surface mechanisms are required on either side of a baffle interface, you define a mechanism at each specific boundary—instead of at the interface. Select the Boundaries > [boundary] > Physics Conditions > Surface Mechanism Option node and set Mechanism to one of the available mechanisms for your simulation. Expand the [boundary] > Physics Values node and define the properties. Surface Chemistry Model Reference: Boundary Settings.
On Any Other Interface	For an interface other than a baffle interface, you define a surface mechanism at the interface for the reacting surface. Select the Interfaces > [interface] > Physics Conditions > Surface Mechanism Option node and set Mechanism to one of the available mechanisms for your simulation. Expand the [interface] > Physics Values node and define the properties. See Surface Chemistry Model Reference: Interface Settings.
On Surfaces in a Porous Region	To allow the internal surfaces within a porous region to become reactive surfaces, you define a surface mechanism for the porous region. Select the Regions > [region] > Physics Conditions > Surface Mechanism Option node and set Mechanism to one of the available mechanisms for your simulation. Expand the [region] > Physics Values node and define the properties. Surface Chemistry Model Reference: Region Settings.

If the Eddy Break-Up model or Complex Chemistry model is selected, define the parameters of the Reacting Species physics model:
- For the Complex Chemistry model, define the Properties of the Complex Chemistry model and its sub-nodes.
  1. Select the Models > Complex Chemistry node and set the required Properties.
  2. Select the Complex Chemistry > Chemistry Acceleration node and if necessary, you can activate ISAT, Clustering, or Dynamic Mechanism Clustering. Then define the Properties.
  For more information, see Complex Chemistry Model Reference.
- For the EBU model, define the EBU Properties.
  The EBU property, Reaction Control, is set to Hybrid by default—which is appropriate for most simulations. Hybrid specifies the reaction rate as the minimum of the rate predicted by turbulent mixing and the rate predicted by finite-rate chemical kinetics. However, if the turbulent mixing scale solely defines the rate, select Standard EBU instead.
  See Eddy Break-Up Model Reference.
Set the parameters of any other [Continuum] > Models, as required.
When using the Eddy Dissipation Concept model or the Laminar Flame Concept model, you can adjust the flame position by changing the Multi-Component Gas > Material Properties > Turbulent Schmidt Number.
For the continuum, define any necessary parameters for the Reference Values and Initial Conditons.
Define any necessary Physics Conditions and Values for the Region and Boundaries.
- If you are modeling surface reactions on porous phases, make sure that you set the porosity within the fluid region, and the volume fraction within the porous phase. See Porous Media Model Region Settings and Porous Media Model Phase Settings.
- To limit the surface reaction rate to the minimum of the reaction rate and the diffusive flux, activate the physics condition Enable Reaction-Diffusion Flux Limiting. See Surface-Gas Interaction Model Reference: Region Inputs.
Return to the Reacting Flow General Workflow.