Estimation of Flammability Limits of Selected Fluorocarbons with F(sub 2) and CIF(sub3) Page: 18 of 78
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
For calibration, compositions were taken from mixtures experimentally reported to be on the
boundary of the flame envelope for F2/CFC-114/N2, CIF3/CFC-114/N2, or F2/C4F,/UF6 systems.
These data were taken from refs. 2, 4, and 5. The association of the flammability limit question
with the 1992 explosion pressure spreadsheet models derives from the fact that the value of
T,,&, needed for the prediction is calculated as an intermediate value in the spreadsheet.
Extracting the adiabatic temperature from the spreadsheets was a manual operation; no explicit
reference to flammability prediction was present in any of the spreadsheets.
Dr. Barber's files did not contain any direct record of the specific parameters used in the
preceding fit. , A few months after the publication of K/ETO-111, the present author calculated
adiabatic temperatures for the same mixtures used by Barber and obtained the parameter values
A = 443.5 K and B= 1273 K. These parameters. were derived from thermodynamic equilibrium
rather than by forcing specific reactions to go to completion. It allowed only room-temperature-
stable species and (based on a memo) obtained fairly good temperature agreement with the
corresponding points generated by Barber. Neither a Barber temperature list nor values for fit
parameters survive. Possibly no mathematical fit was done, but rather the predictions were
Part of the original commission for the present work was to document the Barber model. The
implicit goal, however, was to have available at the GDPs a working set of models for prediction
of maximum explosion pressures that could be used for a wide variety of potential scenarios and
to ensure that those models are adequately documented. With this in mind, a detailed
examination of the 1992 spreadsheets was undertaken that revealed many inconsistencies from
one spreadsheet version to another. A fair amount of evolution evidently took place during the
preparation of the various versions, and the customization of each spreadsheet for specific
limited conditions and constituents led to a variety of errors and inconsistencies. Some of these
were operability errors, which did no harm to the results. Others were formula errors and led to
some degree of inaccuracy in the final results. In about half the versions, a numerical
convergence routine confused a Celsius with a Kelvin temperature, but this induced surprisingly
little error in the answer, 5 to 15 degrees in final temperature and about 1% in pressure. In all
versions, a factor relating the change in the number of moles of gas on burning was neglected,
which could result in overprediction or underprediction of final pressures by tens of percent in
practical cases and by multiples in pure fuel/oxidizer mixtures. A very few versions had mass
balance errors. That is, the intended reactions were not properly reflected in the reactant/product
conversion. Finally, there were data problems in some heat capacity information, leading to poor
predictions at high temperature. Converting a particular spreadsheet for use with a different
oxidizer or fuel was not at all straightforward, as many critical parameters (stoichiometry of
reactions, heat of reaction, heat capacity changes) are embedded in formulae rather than present
in tabular form. This difficulty of conversion almost surely led to many of the errors in some of
Here’s what’s next.
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
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/m1/18/: accessed May 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.