# OpenFOAM: sensible enthalpy/internal energy for a reactive case

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 August 15, 2022, 04:17 OpenFOAM: sensible enthalpy/internal energy for a reactive case #1 Member   K Join Date: Jul 2017 Posts: 97 Rep Power: 8 Hi foamers, I have a question regarding the calculation of the sensible enthalpy/interal energy. I first start by explaining what I expect to see in the algorithem based on thermodynamic text books and after, I 'll compare it with the codes in OpenFoam. For an inviscid/adiabatique reactive case exchanging no work with the environment, we have: with where and are, respectively, the enthalpy of formation of species i and the mass fraction of species i. In the same way, can be calculated; However, as the nature of species change in presence of chemical reactions, for enthalpy (the same applies for internal energy) we HAVE to take a reference. The standard reference is = 25°C and = 1 atm. As such h, is calculated based on a reference value: Now, my question is how this reference temperature is considered in OpenFOAM (we know that the sensible enthalpy/interal energy do not change a lot with pressure). I cannot find any track of this reference temperature in OpenFOAM. For instance, if we take a look at temperature calculation based on Newton’s method in src/thermophysicalModels/specie/thermo/thermo/thermoI.H, we have something as*: However, we know that: Therefore: We know that is different from and we can NOT have the following simplification: to deduce: I would be grateful if someone could explain that to me. Am I missing a step here? P.S.: I read carefully http://caefn.com/openfoam/temperature-calculation and tried to search a lot on different forums. But, I could not find my answer there. * that expression is coming from Temperature calculation from sensible internal energy . Last edited by mkhm; August 15, 2022 at 07:05.