Abstract
The flammability of vapors above aqueous solutions of ethanol and
acetonitrile was studied experimentally in a 20-L combustion apparatus.
No liquid was present in the apparatus, but the vapor concentrations
were adjusted to correspond to the vapor in equilibrium with a specified
aqueous solution. The experimental results for these two systems
show that - As water is added to the vapor, the lower boundary of
the flammability zone decreases. For ethanol, the lower flammability
limits (LFL) decreases from 3.7% for pure vapor to 3.2% with saturated
water vapor. For acetonitrile, the decrease is from 4.2% to 3.8%.
Thus, to a good approximation, the water vapor can be treated as
an inert, enabling the data to be displayed on a single flammability
triangle diagram. This provides a very simplified method for estimating
the flammable behavior for aqueous solutions. - The upper boundary
of the flammability zone is unchanged with the addition of water.
- The limiting oxygen concentration (LOC) is essentially constant
for all concentrations of aqueous solutions. The LOC for the pure
solvent may be used as a universal LOC for all solvent concentrations.
- The vapor mixture above the aqueous solution is not flammable below
a certain liquid mol fraction of flammable. The flammable concentration
at which this occurs can be called the maximum safe solvent concentration
(MSSC). A method is presented to determine the MSSC from experimental
flammability data. - The oxygen concentration defining the flammable
boundary for the vapor decreases rapidly from the MSSC and then increases
as the liquid solvent concentration increases. The calculated adiabatic
flame temperature (CAFT) method qualitatively predicts the same behavior
as the experimental data.
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