33.4.24 Reactions Dialog Box

The Reactions dialog box (opened by clicking on the Edit... button next to Reaction Model in the Create/Edit Materials dialog box) allows you to define the reactions that comprise a mixture material. See Section  15.1.3 for details about using this dialog box.

(Note that the Reactions dialog box is a modal dialog, which means that you must tend to it immediately before continuing the property definitions.)

Controls

Mixture   shows the name of the mixture material for which you are defining the species. This field is not editable.

Total Number of Reactions   sets the total number of reactions (fluid-phase reactions and surface reactions occurring at wall boundaries). Use the arrows to change the value, or type in the value and press RETURN.

Reaction Name   contains the name of the reaction.

ID   sets the number of the reaction you want to define. (Again, if you type in the value be sure to press RETURN.)

Reaction Type   contains options that allow you to specify the type of reaction.

Volumetric   specifies, if enabled, that the current reaction is a volumetric reaction.

Wall Surface   specifies, if enabled, that the current reaction is a wall surface reaction.

Particle Surface   specifies, if enabled, that the current reaction is a particle surface reaction.

Number of Reactants   indicates the number of reactants in the specified reaction.

Species   contains drop-down lists of all species in the mixture. (The number of lists will be equal to the Number of Reactants.) Select each reactant in one of these lists.

Stoich. Coefficient   specifies the stoichiometric coefficient of the reactant species in the reaction.

Rate Exponent   specifies the rate constant for the reactant species in the reaction.

Number of Products   indicates the number of products in the specified reaction.

Species   contains drop-down lists of all species in the mixture. (The number of lists will be equal to the Number of Products.) Select each product in one of these lists.

Stoich. Coefficient   specifies the stoichiometric coefficient of the product species in the reaction.

Rate Exponent   specifies the rate constant for the product species in the reaction.

Arrhenius Rate   contains inputs related to the Arrhenius rate. (If you have chosen Eddy-Dissipation for the Turbulence-Chemistry Interaction in the Species Model dialog box, these inputs are not required.)

Pre-exponential Factor   is the constant $A_r$ in this equation in the separate Theory Guide. The units of $A_r$ depend on the other rate constant inputs, but must be defined such that the units of the reaction rate $R_{i,r}$ ( this equation in the separate Theory Guide) are in (kg/m $^3$-s) if you are using SI units.

It is important to note that if you have selected the British units system, the Arrhenius factor should still be input in SI units. This is because ANSYS FLUENT applies no conversion factor to your input of $A_r$ (the conversion factor is 1.0) when you work in British units, as the correct conversion factor depends on your inputs for $\nu_{j,r}$, $\beta_r$, etc.

Activation Energy   is the constant $E_r$ in the forward rate constant expression, this equation in the separate Theory Guide).

Temperature Exponent   is the value for the constant $\beta_r$ in this equation in the separate Theory Guide.

Include Backward Reaction   specifies that the reaction is reversible. The backward reaction rate constant will be computed from this equation in the separate Theory Guide.

Third-Body Efficiencies   enables the input and use of third-body efficiencies ( $\gamma_{j,r}$ in this equation in the separate Theory Guide). These inputs are optional. (This item is available only if you have selected Volumetric for the Reaction Type.)

Pressure-Dependent Reaction   enables the modeling of a pressure fall-off reaction. See Section  15.1.3 for details. (This option is available only if you have chosen Laminar Finite-Rate or Eddy-Dissipation Concept for the Turbulence-Chemistry Interaction in the Species Model dialog box and have selected Volumetric for the Reaction Type.)

Coverage-Dependent Reaction   is used when modeling Wall Surface reactions with site-balancing and reaction rates depend on site coverages.

Specify...   opens the Reaction Parameters dialog box, the Pressure-Dependent Reaction dialog box, or Coverage-Dependent Reaction dialog box in which you can specify the third-body efficiencies, pressure-dependent reaction parameters, or coverage parameters.

Mixing Rate   contains inputs related to the mixing rate. (If you have chosen Laminar Finite-Rate or Eddy-Dissipation Concept for the Turbulence-Chemistry Interaction in the Species Model dialog box, these inputs are not required.)

A   is the constant $A$ in the turbulent mixing rate ( this equation and  this equation in the separate Theory Guide) when it is applied to a species that appears as a reactant in this reaction. The default setting of 4.0 is based on the empirically derived values given by Magnussen et al. [ 47].

B   is the constant $B$ in the turbulent mixing rate ( this equation in the separate Theory Guide) when it is applied to a species that appears as a product in this reaction. The default setting of 0.5 is based on the empirically derived values given by Magnussen et al. [ 47].

Particle Surface Reaction   contains inputs related to a particle surface reaction. See Section  15.3.1 for details. (This section will appear only if you have selected Particle Surface for the Reaction Type.)

Diffusion Limited Species   is a drop-down list that allows you to select the species for which the concentration gradient between the bulk and the particle surface is the largest when there is more than one gaseous reactant taking part in the particle surface reaction. See Section  15.3.1 for details.

Diffusion Rate Constant   is the constant $C_{1,r}$ in this equation in the separate Theory Guide.

Effectiveness Factor   is the constant $\eta_r$ in this equation in the separate Theory Guide.