Estimation of Flammability Limits of Selected Fluorocarbons with F(sub 2) and CIF(sub3) Page: 29 of 78
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and the other for lean mixtures
Ti.= A,. / X0,di., + Blea.
"Rich" mixtures were defined as those having an excess of fuel and "lean" mixtures as having an
excess of oxidizer relative to the ideal stoichiometric fuel/oxidizer ratio which would burn the
fuel to CF4. The parameters A and B were calibrated using available experimental data so that
the adiabatic temperature computed for any lean mixture on or within a flammability boundary
would equal or exceed the value of T1. (and similarly for rich mixtures). To allow the predicted
temperature to make a smooth transition between lean and rich mixtures, a smoothing function
Tthshold = (TeanN + TrichN )IIN
where a reasonable smoothing was achieved using a value for N of minus 4. Values of
parameters used in in the 1992 model were as follows: A,,, = 71, B1 = 1036, An, = 55, and
Bdch = 758.
The model as previously described, was essentially conceptual, tied to no particular software. It
was tied to data in that the experimental flame boundary data points used in the calibration
defined which mixtures are deemed to burn and also was tied to thermodynamics data (and
choice of product species), which determined the calculated adiabatic temperatures associated
those mixtures. In practice, since many calculations had to be performed either for generating
the adiabatic temperatures used in calibration or for computing points on the composition limits
of flammability, automated systems were developed. All were based around SOLGASMIX, a
computational thermodynamics program of long genealogy. The version used in 1992 predates
the one described in refs. 15 and 16, and is incompatible with current data libraries and utilities
for that program.
2.2.2 1999 Version of Equilibrium-Based Flame Limit Model
One part of the original commission of this present work was to adequately document the 1992
model so that it could be routinely applied to current GDP problems relating to gas flammability.
Examination of the 1992 model revealed that to provide a usable version, some revision would be
necessary to render it compatible with current operating systems (e.g. Microsoft Windows 95 or
98) and the most recent documented version of SOLGAS .
126.96.36.199 Design Intent
At its simplest, this model is a prescription for estimating the flammability of a potentially
combustible gas mixture based on the observed behavior of similar chemical systems. It requires
thermodynamic data for a reasonable set of reactants and reaction products and a means
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Trowbridge, L.D. Estimation of Flammability Limits of Selected Fluorocarbons with F(sub 2) and CIF(sub3), report, September 1, 1999; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc623234/m1/29/: accessed May 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.