In setting up a new Ansys Chemkin mechanism for use with KINetics, you must specify thermodynamic and composition data for all of the species in the system, either by specifying a thermodynamic database file that contains all species, by including thermodynamic data in the reaction-mechanism input file(s), or by a combination thereof. The Chemkin standard thermodynamic database is a source for over 800 species and is available to KINetics users. However, it may be necessary at times to either assemble a new thermodynamic database file or augment an existing one by adding thermodynamic data for certain species. This section describes the format of the thermodynamic data file and of the thermodynamic data when included within the gas-phase or surface chemistry mechanism files.

The thermodynamic data file consists of polynomial coefficients for fits to temperature of specific heats, enthalpies and entropies for each species in the system. The thermodynamic data entries also contain the species' name, its elemental composition, its electronic charge, and an indication of its phase (gas, solid, liquid or solid).

For each species, seven polynomial coefficients are needed for fits over each of two temperature ranges, as shown in Equation 3–1 through Equation 3–3. These fits take the following form, where the temperatures are in Kelvin:

(3–1)

(3–2)

(3–3)

The format allows for the specification of a midpoint temperature, where the fits are constrained to match for two temperature ranges. This midpoint temperature may be specified independently for each chemical species. In addition to the temperature-fit coefficients, the thermodynamic data entries define the species elemental composition.

The data for each species requires four formatted lines, each with a maximum length of 80 characters. Example 3.1: Excerpts from the Chemkin therm.dat Thermodynamic database file provides a sample of the lines required for entering a set of thermodynamic data. The first two lines in Example 3.1: Excerpts from the Chemkin therm.dat Thermodynamic database file are required at the top of a thermodynamic database file; the first line identifies the file as containing thermodynamic data, while the second line provides the three temperatures used in the fitting process (a low temperature, break temperature, and high temperature). The remaining input in Example 3.1: Excerpts from the Chemkin therm.dat Thermodynamic database file consists of four lines for each species containing the elemental composition information and fitting coefficients.

Implemented as a figure so that automatic figure numbering and xrefs behave normally. A text copy is provided here for reference.

THERMO
   300.000  1000.000  5000.000
(CH2O)3     70590C   3H 6O 3 G 0300.00   4000.00  1500.00  1
 0.01913678E+03 0.08578044E-01-0.08882060E-05-0.03574819E-08 0.06605142E-12   2
 -0.06560876E+06-0.08432507E+03-0.04662286E+02 0.06091547E+00-0.04710536E-03  3
 0.01968843E-06-0.03563271E-10-0.05665403E+06 0.04525264E+03  4
 AL     62987AL 1 G 0300.00  5000.00  0600.00 1 
 0.02559589E+02-0.10632239E-03 0.07202828E-06-0.02121105E-09 0.02289429E-13   2
 0.03890214E+06 0.05234522E+02 0.02736825E+02-0.05912374E-02-0.04033937E-05    3
 0.02322343E-07-0.01705599E-10 0.03886794E+06 0.04363879E+02 4
END

Table 3.1: Summary of the rules for thermodynamic data summarizes the rules for thermodynamic data input. Each species includes the species name, the elemental composition of the species, and the temperature ranges over which the polynomial fits to thermodynamic data are valid. The fits to , , and consist of seven coefficients for each of two temperature ranges.