Surface Chemistry

The Surface Chemistry model is used to represent surface reaction mechanisms on interfaces, boundaries, or surfaces in porous regions. You can use this model to simulate applications such as monolithic catalysts, chemical vapor deposition (CVD), and packed bed reactors.

Surface Chemistry Model

There are two options available for simulating surface chemistry reactions.
  • If the simulation involves reacting flow reactions other than the surface reactions, you can: follow another reacting flow workflow, select Surface Chemistry as an optional model, and then follow the surface chemistry workflow.
  • If the simulation only involves surface reactions and does not involve any other reacting flow reactions, you can follow the surface chemistry workflow.

You can simulate surface chemistry reactions on fluid or porous regions (or porous phases) with reacting surfaces when using the following models:

  • The Complex Chemistry model.
  • The Eddy Break-Up (EBU) model.
  • The Non-Reacting and Segregated Species models.
You can simulate surface chemistry reactions and electrochemical surface reactions within the same region, using both the Surface Chemistry model and the Electrochemical Reactions model. See Modeling Electrochemical Surface Reactions.
The Surface Chemistry model provides the Surface Mechanism Manager node which contains details of the bulk species, site species, and reactions within the Reacting Surface and Solid Composition model nodes.
Note You can import surface mechanisms which contain multiple sites or bulk mixtures within the same surface mechanism.
The way in which the ODEs (Ordinary Differential Equations) that arise from the reaction mechanism are solved depends on the other physics models that are selected.
  • When Surface Chemistry is selected with the Complex Chemistry model, the CVODE solver resolves the reaction system.
  • When Surface Chemistry is selected with the Eddy-Break Up model, or with the Non-Reacting and Segregated Species models, the Surface-Gas Interaction model resolves the reaction system.

The Reacting Surface Model

The Reacting Surface model defines chemical reactions for the surface mechanism in the same manner that the Reacting model defines reactions for the continuum gas or liquid phase. See Reacting Model Reference.

The Solid Composition Model

The Solid Composition model is a multi-component material model that allows you to specify two distinct types of surface species:

  • Solid Composition > Site Solid Mixture (surface species that occupy a surface site that is next to the gas or liquid)
  • Solid Composition > Bulk Solid Mixture (species that are underneath the site layer)

    When the Complex Chemistry model uses the CVODE solver to resolve surface chemistry reaction mechanisms, the Site Solid Mixture and Bulk Solid Mixture managers cannot be manipulated explicitly. No adding, removing, or renaming species is possible. However, when a complex chemistry definition is imported, these nodes are populated with the mechanisms and surface species that are involved in surface-gas or surface-liquid reactions.

    When the Surface-Gas Interaction model is used, you can define the surface chemistry by importing the Chemkin-formatted surface chemistry definition.

The Surface-Gas Interaction Model

The Surface-Gas Interaction model is activated when the Surface Chemistry model is chosen together with either, the EBU model, or the Non-Reacting and Segregated Species models. The Surface-Gas Interaction model solves the ODEs that arise from the surface reaction system using the CVODE solver from the Sundials kit. If you are using the Surface-Gas Interaction model with the Surface Chemistry model, first import a chemical library for the Surface Chemistry model.

Limitations Modeling Surface Chemistry

  • No energy equations are solved for the reactive surface. Fixed temperature boundary conditions apply.
  • Surface growth and shrinking are not taken into account.

You specify the surface reaction mechanism, which you can import (see Reaction Mechanism Formats). The surface reaction rate is defined per unit surface area—different from fluid-phase reactions, which are based on unit volume.