This physics interface can be used to create reaction kinetics and optionally compute transport and thermodynamic properties for direct use in 1D, 2D, or 3D models. This is similar to The Reaction Engineering Interface, except that it does not solve for an ideal reactor model.

The Chemistry (chem) interface () is found under the Chemical Species Transport branch () when adding a physics interface. The Chemistry interface is also created when the Generate Space-Dependent Model feature is used in the Reaction Engineering interface, collecting all mixture variables and properties for use in a space-dependent model.

Many of the fields and nodes described in this section are only made available when either a Reaction or a Species (or both) subnode is added to the Model Builder. All predefined constants and expressions can be overwritten by user-defined expressions. This makes it possible to go beyond the modeling assumptions set as defaults in this physics interface.

The following is a description of the features and fields available on the Settings window for the Chemistry interface.

The Label is the default physics interface name.

The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different 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 physics interface in the model) is chem.

This section sets the Temperature, Pressure and Electrode potential (only available with a Batteries & Fuel Cells, Corrosion, Electrochemistry or Electrodeposition module license) to be used by the current interface. Use the lists to select a temperature, pressure or electrode potential defined and announced by another interface in the model. For example, when a heat transfer interface is also included, the temperature solved for is available in the Temperature list.

For Temperature or Pressure, you can also select Common model input to use a globally available common model input. In all three cases, select User defined to manually define the variable in question.

Select the Calculate thermodynamic properties check box to enable the interface to compute thermodynamic properties, especially critical if the reaction kinetics are defined at nonisothermal conditions. The setting here also controls whether thermodynamic mixture properties becomes available in Calculate Transport Properties section.

Select the Calculate mixture properties check box to calculate mixture properties that can be picked up in the space-dependent model interfaces. The properties that can be calculated are shown beneath the check box. Consider also if the built-in Automatic expressions fits the model or if User defined expressions are more suitable. In general, the Chemistry interface calculates properties in the same way as the Reaction Engineering interface.

All property parameters and property functions required by the interface can be automatically created by coupling to a system added to the Thermodynamics node. To do so, click the Thermodynamics check box and select an existing Thermodynamic System.

The Thermodynamics check box is enabled when the Thermodynamics node, including one or more systems, is available under Global Definitions. Also, the Chemistry interface needs to include at least one species.

Use the Phase list to specify the state of aggregation of the mixture.

Mixture density always has two settings available: Automatic or User defined. The Thermodynamics options is available when the interface is coupled to a Thermodynamic System, and all interface species has been matched to species in the system. In this case the density is defined by a function automatically added under the thermodynamic system coupled to.

The Automatic setting uses the following logic:

Use the Species concentration input table to specify the concentrations to be used as arguments in variables generated by the Reaction and the Species features (the reaction rate for example). The species concentrations are also used in the mixture properties (transport and thermodynamic properties).

Select Diluted species from the Mixture type list to use the concentration variables from a Transport of Diluted Species interface. The same setting should be used for any other interface solving for species concentrations using a diluted species assumption. Enter the names of the dependent variables in the Molar concentration column.

Select Concentrated species from the Mixture type list to use the mass fractions from a Transport of Concentrated Species interface. Enter the names of the dependent variables in the Mass fraction column.

When coupled to Thermodynamics is enabled, the species in the Chemistry interface can be matched to the species in the Thermodynamic System. This is needed to ensure that arguments for the thermodynamic functions are correctly defined. Use the drop-down lists in the From Thermodynamics column to match each species in the interface to a species in the coupled thermodynamic system. For each species matched, the required property parameters and functions are added under the corresponding thermodynamic system. When all species are matched, the interface is considered fully coupled and functions representing mixture properties, such as the density, are also added automatically under the corresponding thermodynamic system.

The name of the reaction rate variables for each species generated by the interface can be seen in the Reaction Rate column of the Species concentration input table. The syntax of the reaction rate variables depend on the Species type selected in the Species Settings window. Bulk species and Solvent use the syntax R_speciesname, while Surface species uses R_speciesname_surf. Selecting Concentrated species for the Mixture type, the base of syntax for the reaction rate is changed to Rw_speciesname.

This table is only available when equilibrium reactions are present in the interface. Use the Reaction rate column to specify the rate for each equilibrium reaction. By doing so the post processing variable for the total reaction rate for each species, of form chem.Rsum_species, will be updated correctly. For a mass transport interface, say Transport of Diluted Species, the reaction rate needed for an equilibrium reaction is typically a dependent variable. In that case the name of the variable can be found in the Shape Function section of the Equation View of the node.

When the Chemistry interface is created using from the Generate Space-Dependent Model the table is automatically set up in accordance with the added equilibrium reaction nodes.

Select Define variables in extra dimension when the current Chemistry interface is coupled to a feature on an extra dimension. An example of this is when the concentrations in the Concentration input column of the Model Inputs, Concentration corresponds to pellet concentrations from a Reactive Pellet Bed feature in a Transport of Diluted Species interface.

Select the Use activity check box to solve for species activities instead of species concentrations, which is a common approach when non-ideal fluids are modeled.

An activity coefficient other than 1 can be set for each species for the Species node in the Species Concentration/Activity section.