In defining the chemistry used in an Ansys Chemkin reactor simulation, users must first supply the thermodynamic data for each species in the chemical system. These data are in the form of polynomial fits to temperature, for species enthalpy, entropy, and specific heat capacity. Sources of this data, as well as the utility that generates the needed polynomial-fit parameters, are described in detail in the Chemkin Getting Started Guide . Once these data are defined, they are used during a Chemkin simulation to determine species thermodynamic properties, thermal transport properties, and reaction equilibrium constants. This chapter describes the mathematical relationships, formulations, and conversions used in such calculations.

These formulas are used internally within Ansys Chemkin program executables. In addition, the Chemkin/API, allows users to call Chemkin subroutines to perform many of the calculations described within their own programs. Such calls can be made from a user’s C, C++, or FORTRAN program or to create interfaces to 3rd-party programs. Details on the API for such calls are provided in the Chemkin Application Programming Interface Manual . However, to aid in programming and formulation of a problem, the descriptions of formulas and conversions in the following section contain references to the Chemkin/API, giving the name of the subroutine that performs the particular calculation.

Species can exist in the gas phase, on surface sites, or in bulk mixtures. In some cases it is desirable to refer to information about species without regard to the phases, and in other cases it is desirable to determine information about species in one particular phase or group of phases. Therefore, before discussing surface state variables, it is helpful to first introduce a nomenclature that facilitates the mathematical expression of species information.