## 7.19. Chemistry Postprocessing

The components and reactions that are postprocessed are one-way coupled to the main simulation. This means that there is no effect on mixture properties or heat release. The list of components and reactions for postprocessing are specified by the user.

Postprocessing components:

- No contribution to mixture properties (density, static enthalpy)

- No contribution to total mass

Postprocessing reactions:

- Generate sources for components that are also postprocessed

- Generate no source for regular components (that is, not postprocessed ones)

- No heat release

The above model assumptions are justified if the component mass fractions and reaction turnover are small relative to the bulk mixture. A typical application is the simulation of pollutants; for example, NO formation. The transport equations for postprocessing components are solved at the end of the flow analysis after the solving of the main equations. When the postprocessing reactions require a temperature variance equation (reaction rate option is `Arrhenius with Temperature PDF`) and the variance equation was not solved during the analysis, then temperature variance will be postprocessed as well. In this case, the temperature variance equation will be solved first to convergence or maximum number of iterations and is then followed by the postprocessing components group.

Note: For steady-state cases, chemistry postprocessing is not performed at the end of the flow analysis if the termination of the flow analysis was due to a user-defined solver interrupt condition. For details, see Interrupt Control in the CFX-Pre User's Guide.

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