Use the Reaction node to specify the reaction kinetics for a single homogeneous chemical reaction. The resulting mass source terms for the species involved in the reaction are automatically defined and added on the selected domains. For turbulent flow, the Reaction node includes the Eddy-dissipation turbulent-reactions model.
Select a Reaction rate —
Automatic (the default), or
User defined. Selecting
Automatic the laminar flow reaction rate is computed using the mass action law
For User defined, input a custom expression or constants for the
Reaction rate r.
When the Use Arrhenius expressions check box is not selected, input custom expressions or constants for the
Forward rate constant kf and
Reverse rate constant kr.
When the Use Arrhenius expressions check box is selected, enter values for the following parameters of the forward and reverse reactions:
When the Turbulent-reaction model is set to
None, laminar flow is assumed and the reaction source terms are defined from the reaction stoichiometry and reaction rates prescribed.
When the Turbulent-reaction model is set to
Eddy-dissipation, turbulent flow will be accounted for in the reaction mass sources. In this case, enter values for the
Turbulent reaction model parameters αED and
β ED (dimensionless).
The Eddy-dissipation model also requires an estimation of the turbulent mixing time of the fluid flow turbulence. When a Fluid Flow interface defining it is present in the model, it can be selected from the
Turbulence time scale list. For example, select
Turbulence time scale (spf/fp1) to use the time scale defined by the
Fluid Properties node
fp1 in a Turbulent Flow,
k-
ε interface with the
Name set to
spf.
Select Rate expression in order to regularize the individual rate expressions that are added to each species. If the mass fraction for a reactant species
ωi becomes smaller than its
damping limit,
ωidl, the rate expression added to species
ωi is reduced linearly. If
ωi ≤ 0 for a reactant species, the reaction rate contribution to that species is completely removed. Similarly, the if the mass fraction for a product species
ωj becomes larger than
1 − ωjdl, the rate expression added to that species is damped linearly. If
ωj ≥ 1 for a product species, the reaction rate contribution to that species is completely removed.
The default value for the damping limit,
ωidl, is
10−6, which is appropriate for most applications, but can require adjustment when working with for example catalytic trace species.