Estimation of Flammability Limits of Selected Fluorocarbons with F(sub 2) and CIF(sub3) Page: 33 of 78
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prediction that most could react or explode in the absence of any oxidizer whatever. Empirically,
however, no rapid conversion to CF4 and elemental carbon is observed. Even at high
temperatures, decomposition proceeds to CF2 and CF3 with only a very slow buildup of species
of lower and higher fluorine content. Since we are interested in reactions that occur rapidly (omn
the time scale of the passage of a detonation wave), only those species are included which
experimentally are observed to be form in significant quantity under such conditions. Elemental
carbon (i.e. graphite) is not among such species, so graphite is simply not included in the list of
Thermodynamic data. Thermodynamic data for the species considered are derived largely from
the JANAF Thermochemical Tables when available. Tabular data for C, were fit to the
polynomial temperature function used by SOLGAS. The fit covers the temperature range from
300 K to at least 4000 K. Specific values used for each species are listed in Appendix C, Table
Flame limit calibration data. Data points known to be on or near flammability limits were
used for calibration of the empirical functions in the model. The data used are the same ones
used for calibrating the flammability limit prediction in the detonation pressure model.
Calibration details are discussed in Appendix D.
3. RESULTS AND DISCUSSION
3.1 DETONATION PRESSURES
The theory of detonations in combustible gas mixtures is well developed and well established.
However, no known available experimental data give shock pressures or temperatures for
fluorocarbon/fluorine systems with which to compare the results of these models. A variation of
the model was developed using an 8:1 hydrogen:oxygen mixture in order to compare results with
an example presented in ref. 11. When radical products were included in the modified
spreadsheet version, the shock temperature, pressure, and velocity computed by this model
agreed within 1.8% with the tabulated theoretical results and within 6% with the experimental
shock velocity. The small differences are likely due to differences in thermodynamic values used
or computational approximations made.
The detonation pressure models were developed as tools to apply to specific conditions as the
needs arise. No single narrow set of conditions are of special interest as this is being written,
however. Appendix A, which describes the operation of the spreadsheet versions of these
models, does so partly by detailed illustration of a sample problem.
Some general observations on the relative reactive potency of the coolants and oxidizers under
consideration can be made from results of these models. As a reference condition, consider the
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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/m1/33/: accessed May 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.