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15.14 Defining Non-Premixed Physical Properties

When you use the non-premixed combustion model, the material used for all fluid zones is automatically set to pdf-mixture. This material is a special case of the mixture material concept discussed in Section  14.1.2. The constituent species of this mixture are the species that you defined for the look-up table calculation; you cannot change them. When the non-premixed model is used, heat capacities, molecular weights, and enthalpies of formation for each species considered are extracted from the chemical database, so you will not modify any properties for the constituent species in the PDF mixture. For the PDF mixture itself, the mean density and mean specific heat are determined from the look-up tables.

The physical property inputs for a non-premixed combustion problem are therefore only the transport properties (viscosity, thermal conductivity, etc.) for the PDF mixture. To set these in the Materials panel, choose mixture as the Material Type, pdf-mixture (the default, and only choice) in the Mixture Materials list, and set the desired values for the transport properties.

Define $\rightarrow$ Materials...

See Chapter  8 for details about setting physical properties. The transport properties in a non-premixed combustion problem can be defined as functions of temperature, if desired, but not as functions of composition. In practice, since turbulence effects will dominate, it will be of little benefit to include even the temperature dependence of these transport properties.

If you are modeling radiation heat transfer, you will also input radiation properties, as described in Section  8.8. Composition-dependent absorption coefficients (using the WSGGM) are allowed.


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