Generator is simple in construction, efficient, and extremely easy to start and regulate. It can be of such small size and weight that it can be installed easily inside a model. Size can be changed to suit needs, as long as operating temperatures can be attained and identified controls are utilized

Parrish, K. L.

English

NASA Technical Reports Server

Bakelite 
Plug
Boron 
Nitride	 t 
Plug	 1-1/2 in. 
(3.8 cm) 
April1974
	 B73-10414 
NASA TECH BRIEF 
Langley Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Smoke Generator 
Outer Case	 Quartz 
Insulation 
Thermocouple
Smoke Generator 
. 
.
A smoke generator used at Langley Reseatch Center 
wind tunnel for visualizing the air flow could be utilized 
as a fogger for insect control. While air-pressurized 
foggers are available commercially, they are charged with 
insecticides which vaporize rapidly at warm outdoor 
temperatures. The result is that insecticides must be 
frequently applied to maintain proper insect control. The 
smoke generator, on the other hand, could be charged 
with an insecticide that vaporizes at higher than outdoor 
temperatures. One spraying then would be sufficient to 
provide a lasting insect control. In use, such an insecti-
cide could be mixed with the fuel, or even used as fuel 
to feed the smoke generator. 
The components of a smoke generator of this type 
are shown in the illustration. The size can be changed to 
suit needs, as long as operating temperatures can be 
attained and identified controls are utilized. 
The generator shown is 1-1/2 inches (3.8 cm) in 
diameter and 6 inches (15.2 cm) long. It consists of 
tubing coiled around a heating element, a thermocouple, 
insulation, and an outer case. The heating element is 
rated at 300 watts and is 3/8 inch (1 cm) in diameter 
by 4 inches (10.1 cm) long. Seven feet (2.1 m) of Monel 
tubing (0.060-inch, 1.5-mm, diameter) is tightly coiled 
around the heating element and extends 4 inches 
(10.1 cm) beyond the element on the input side and 2
inches (5.1 cm) on the output side. The tube is spot 
welded to the heating unit with Nichrome strips. A 
ceramic-insulated Chromel-Alumel thermocouple is spot 
welded to the tubing at the center of the coil and extends 
past the heater end with the heater leads. A 1/2-inch 
(1.3-cm) layer of quartz batting insulation is placed 
around the heater and coil, to reduce heat loss and 
concentrate heat in the coil; and the assembly is 
installed in the case. A boron nitride plug 1/4-inch 
(0.6-cm) thick is installed in the case with the output 
tube end extending through it, and a Bakelite plug is 
placed in the other end of the case. 
Temperature is controlled by a 0- to 140-volt 
variable transformer which supplies power to the heating 
element. Fuel is supplied by a pump or a pressure tank 
that will maintain 50 lb/in. 2
 (345 x 10 3 N/rn2 ) of 
pressure, and a needle valve is inserted between the 
supply and the generator assembly to regulate fuel 
flow. The fuel used, in this instance, is a silicone 
diffusion pump oil, which is nontoxic, noncorrosive, 
nonorganic, chemically inert, and dielectric; but this 
does not preclude the use of other fuels. This oil does 
not decompose at operating temperatures and emits a 
large volume of smoke per quantity of fuel used. The 
thermocouple output may be monitored by any meter 
designed for this purpose.
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000414 2020-03-17T07:27:43+00:00Z
In operation, the fuel needle valve is opened until 
the tube is filled with oil and is then closed. Approxi-
mately 110 volts of power are supplied to the heater 
and maintained until the temperature reaches 800° F 
(698 K). (The temperatures given are for Dow Coming 
704 fluid and normally would be different for other 
fuels.) The fuel valve is reopened, and the voltage is 
increased and adjusted to hold the temperature near 
900° F (755 K). As oil is forced through the tubing 
coil, it is vaporized and produces a dense smoke when 
forced out of the tube. To reduce the smoke rate, the 
fuel supply is decreased while maintaining temperature 
near 900 F (755 K). The generator is turned off by 
removing the heater voltage and closing the fuel valve, 
when temperature drops below 300° F (422 K).
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Langley Research Center 
Mail Stop 139-A 
Hampton, Virginia 23665 
Reference: B73-10414 
Patent status: 
Inquiries concerning rights for the commercial use of 
this invention should be addressed to: 
Patent Counsel 
Langley Research Center 
Code 456 
Hampton, Virginia 23665 
Source: Kemp-L. Parrish 
Langley Research Center
(LAR-1 1433)
. 
B73-10414	 Category 05


Smoke generator

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