Equilibrium Reaction
Use this node to model an equilibrium reaction, involving two or more species, in a domain. Note that a necessary requirement for this is feature to be available is that two or more species are solved for by the interface.
The equilibrium reaction is defined by the relation between the chemical activities of the chemical species participating in the reaction (the equilibrium condition) and the stoichiometry of the reaction.
The node solves for an additional degree of freedom (the reaction rate) to fulfill the equilibrium condition at all times in all space coordinates.
If the Apply equilibrium condition on inflow boundaries check box is selected, the specified inflow concentration values in all active Inflow boundary nodes for the physics interface are modified to comply with the equilibrium condition.
Equilibrium Condition
The list defaults to Equilibrium constant or select User defined. For either option, the Apply equilibrium condition on inflow boundaries check box is selected by default.
For Equilibrium constant, enter an Equilibrium constant Keq (dimensionless). The default is 1. Enter a value or expression for the Unit activity concentration Ca0 (SI unit: mol/m3). The default is 1·10-3 mol/m3. Equilibrium constant creates an equilibrium condition based on the stoichiometric coefficients, the species activities, and the law of mass action.
For User defined, enter an Equilibrium expression Eeq (dimensionless).
Stoichiometric Coefficients
Enter a value for the stoichiometric coefficientνc (dimensionless). The default is 0. Use negative values for reactants and positive values for products in the modeled reaction.
Species with a stoichiometric coefficient value of 0 are not affected by the Equilibrium Reaction node.
Further Reading
See