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No. 22
Thermal Condensation Generator Inert Gas Propellant
Applicable models: TDA-5A, TDA-5B & ATI 5C
Many customers inquire about the gas requirements
of the poly-dispersed aerosol generator manufactured by ATI.
The older version is the model TDA-5A and the current model
is the TDA-5B. The major difference between the two models
is not the capacity or capabilities of the generator, but
improvements requested by customers over the years. The heater
block assembly and heaters are the same in both units. The
major improvements are a larger reservoir which allows testing
up to four hours at full capacity whereas the old TDA-5A would
run out of liquid in twenty to thirty minutes and would have
to be refilled with whichever liquid was in use (DOP or PAO).
The other improvements include: a digital temperature indicator
of heater block temperature, controls mounted on the front
panel with the discharge on the rear panel, ergonomic handle,
and a larger cabinet.
Both units use approximately 20 standard
cubic feet per hour of compressed gas. An inert gas is used
since the heater block temperature is above the flashpoint
of either DOP or PAO. ATI recommends the use of nitrogen;
it makes no difference whether Oil Pumped (OP) or Water Pumped
(WP) nitrogen is used. The reason for this recommendation
is the availability of nitrogen at any gas supply house. Also,
there are B tanks or 60 cubic foot cylinders of this gas available.
The B tank will allow about 3 hours operation of the TDA-5A
or TDA-5B unit and the 60 cubic foot cylinder will allow about
4 hours of operation. Another advantage of the B tank or the
60 cubic foot cylinder is that they weigh only about 30 pounds,
are small, and are portable.
Other gases that are readily available are
CO2, argon, neon, and helium. CO2 is available in smaller
cylinders which lend themselves to portability. Over the years,
ATI customers have reported successful use of argon and neon.
At a demonstration of the TDA-5A unit to engineers at Dahlgren
Naval Surface Weapons Laboratory in VA, the only gas available
was helium, which worked fine.
The important factors about the gas are:
1) It will not support combustion &
2) A two-stage regulator is used to supply the pressure to
the TDA-5A or TDA-5B generator. A two-stage regulator maintains
a relatively constant output pressure, where a single stage
regulator's output varies extensively since the pressure of
the bottle starts at 2200 lbs. per square inch gauge and then
continually drops in pressure as it is used. It is imperative
that the pressure to the TDA-5B aerosol generator be adjusted
to 50 lbs. per square inch gauge. The reason for this is that
there is an internal pressure regulator which is factory adjusted
individually on each unit for optimum performance. If the
supplied generator inlet pressure to a pre-adjusted regulator is changed, its
output will also change, and this will affect operation of
the unit.
Nitrogen used by ATI for in-house testing purposes has the following properties:
Molecular Weight: 28.01
Specific Volume: 13.8 CF/lb
Flammable Limits: Nonflammable
CGA Valve: 580
DOT Name: Nitrogen, Compressed
UN No.: UN1066
DOT Class: 2.2
DOT Label: Nonflammable Gas
CAS Registry: 7727-37-9
Inert Gas Consumption rate: ~20 CFH @ 50 PSIG generator inlet pressure
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