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Old   May 14, 2020, 06:14
Default Mixture Properties
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Hi everyone,

I am writing a UDF to find the change in Gibbs free energy for a volumetric reaction in FLUENT, which is a function of the enthalpy and entropy of the reaction species.
I've created a gaseous mixture for the reaction in FLUENT and selected the Peng-Robinson method for calculating the density of the mixture in the mixture panel.
In the UDF, when I use C_H(c,t) to access the enthalpy of the mixture in the cell, I want to know will it return me the enthalpy which is a sum of Partial Molar enthalpies of the gas mixture species and not the sum of the enthalpies of pure species in the gas mixture. Does anybody have any idea about this?

I am also not sure if I'm using the right macro C_H(c,t) to retrieve the enthalpy. Should I use the MIXTURE_enthalpy macro (given in the example of Real gas UDF, Multispecies UDF section, p466) to retrieve the total enthalpy instead?
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Old   May 14, 2020, 07:02
Default Enthalpy
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There is no macro or function called Mixture_Enthalpy. The one you are referring to is a user defined function that returns value of enthalpy to Fluent for a real gas. C_H is the macro that stores enthalpy of whole mixture and not of individual species. To fetch enthalpy of individual species, either you could back calculate using C_H and C_YI (macro for storing mass fractions of species) or you can use generic_property function along with PROP_hform and PROP_href to fetch enthalpy of formation and reference enthalpy for each species.
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Old   May 16, 2020, 13:43
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Thank you, Sir, for clarifying. I really appreciate it.
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enthalpy equation, entropy production, mixture of gases, reaction modelling, udf customize

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