Estimation of Flammability Limits of Selected Fluorocarbons with F(sub 2) and CIF(sub3) Page: 34 of 78
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case of a gas at 25*C and 1 atm total pressure in which 60 mol % of a gas mixture consists of
diluent, the diluent consisting of UF6 at its vapor pressure (14.7%) and N2 comprising the
balance of the diluent (45.3%). The remaining 40% of the gas will be a fuel/oxidizer mix, with
the ratio being chosen as that which gives the highest detonation pressure. For the six
combinations of fuel and oxidizer, the results are shown in Table 2.
Table 2. Pressure results-for the most potent fuel/oxidizer mixtures.
The gas mixture consists of a diluent comprising 14.7% UF6 and 45.3% N2,
with the remaining 40% being the fuel/oxidizer mixture at the listed ratio.
Isentropic Detonation Impulse,
Ratio of (const. vol.) pressure, (atm)
Oxidizer Fuel oxid:fuel pressure, (atm)
F2 CFC-114 3:1 7.4 14.4 24.3
F2 c-C4F 4:1 9.8 19.1 33.5
F2 C4F,0 3:1 8.7 17.0 29.5
ClF3 CFC-114 4:3 8.8 17.1 29.5
CIF3 c-C4F8 2:1 10.4 20.3 35.9
CIF3 C4F10 3:1 8.6 16.7 28.8
The pressures listed in the table are the isentropic value (i.e., the final constant volume adiabatic
pressure that the heat of reaction can generate prior to any heat loss to the surroundings); the
detonation pressure, (i.e., the transient pressure within a fully developed shock wave); the
impulse, (a combination of the detonation pressure and the momentum of the gas in the direction
of motion of the shock wave). To reiterate earlier comments, the fact that the model computes a
detonation pressure and impulse is no guarantee that a fully developed shock will arise; these
values simply represent the upper limit of transient pressures that could possibly be generated.
Viewed in this way, it can be seen that the two perfluorocarbons can generate higher pressures
than CFC-114, and that CIF3 has the potential to generate slightly higher pressures than F2. The
order of "potency" however, could change if the rules of comparison changed - for example, a
series of 1:1 oxidizer:fuel ratio mixtures would yield higher pressures for CFC-114 explosions
than for the perfluorocarbon.
3.2 FLAMMABILITY LIMITS
The detonation pressure models also evaluate the predicted adiabatic temperature of the gas
mixture against the threshold temperature and predict whether or not the gas mixture is ignitable.
One can generate a list of points predicted to lie on the boundary by seeking compositions for
which the two temperatures are identical, a process that can be very laborious if done manually.
The process can be automated somewhat but such automation is not incorporated into the six
detonation model spreadsheets.
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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/m1/34/: accessed May 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.