NASA CASE NO.

PRINT FIG. _l(a)

t_3_T_ICE

The invention disclosed in this document resulted from research in aeronautical and

space activities performed under programs of the National Aeronautics and Space

Administration. The invention is owned by NASA and is, therefore, available for

licensing in accordance with the NASA Patent Licensing Regulation (14 Code of

Federal Regulations 1245.2).

To encourage commercial utilization of NASA-owned inventions, it is NASA policy to

grant licenses to commercial concerns. Although NASA encourages nonexclusive

licensing to promote competition and achieve the widest possible utilization, NASA

will provide the necessary incentive to the licensee to achieve early practical

application of the invention.

Address inquiries and all applications for license for this invention to NASA Patent

Counsel, Langley Research Center, Code 212, Hampton, Virginia 23681-0001.

Serial No.: 08/359,320

11/28/94 LaRC

(NASA-Case-LAR-15058-1) VAPOR

GEMERATOR WAND Patent Application

(NASA. Langley Research Center)

12 p

83/09

N95-20080

Unclas

0039291
VAPOR GENERATOR WAND 

Awards Abstract 

NASACaseNo. LAR 15058-1 

In low speed wind tunnels it is oRen desireable to visualize airflow to augment observations made 

with instruments such as strain and pressure gages. Current technology devices for delivery of a 

vapor are bulky and thus disrupt local airflow. It is the object of this invention to provide a device 

capable of delivering a stream of vapor with a minimal effect on local airflow. 

The present invention achieves this object by utilizing a narrow tube as a heating device for 

producing the vapor. Running an electrical current through the tube provides resistive heating to 

a liquid which produces a vapor when boiled. As the entire heating and delivery portion of the 

device is simply a small cylinder the disruption to airflow within the tunnel is minimized. This 

allows an experimenter to place the source of vapor fairly close to a model without causing too 

much change to the model data. 

The novelty of the present invention lies in reducing the bulk of current technology devices by 

combining the acts of heating and delivery. .... 

Inventor: David B. Robelen 

Address: 1 1 7 River Point Dr. 

Yorktown, VA 23 693 

S SN: 

Employer: LaRC 

Initial Evaluator: Dana G. Dunham 

Serial No.: 08/359,320 

Filed: 1 1/28/94 
LAR 15058-1 -1- PATENT APPLICATION

VAPOR GENERATOR WAND

Ori,qin of the Invention

5 The invention described herein was made by an employee of the United

States Government and may be manufactured and used by or for the

Government for governmental purposes without the payment of any royalties

thereon or therefor.

10 Back.qround of the Invention

.

E

Field of the Invention

The invention relates to the field of vapor production and distribution. It

15 may find more specific use in the field of wind tunnel flow visualization.

.

m Description of the Related Art

Applications for vapor production can be found in a variety of fields. In

20 theater settings vapor may be produced as a visual special effect. For training

exercises vapor production may serve to simulate a fire. Yet another use is in

wind tunnel airflow visualization.

In wind tunnel airflow visualization, a model is placed in a low speed

wind tunnel, an airflow is provided and the interaction between the airflow and

25 the model is observed. In order to render visible the motions of the air the

experimenter provides what is known as a smoke plume, in practice this is not

usually smoke but rather a vapor created by heating an oil or other substance

until a vapor is produced. The resulting vapor is not the product of combustion

so is not properly called a smoke. The plume of vapor, when properly

30 illuminated provides the experimenter with a visible indication of direction of
LAR 15058-1 -2- PATENT APPLICATION

airflow in a given region.

It is desirable to be able to provide the vapor without disturbing the

natural airflow of the observed system. It is also often desirable to be able to

move the source of vapor to various points in the wind tunnel so that airflows

5 around different portions of the model may be observed.

The currently available selection of vapor producing devices does not

meet the needs of the airflow visualization community. These devices tend to

be bulky, having a heater, liquid reservoir, and controlling electronics

contained in one device. In general, they produce a low density smoke

10 stream. They may be unsuitable for use in airflow visualization due to the

downwind effects produced by airflow around the generator itself. While these

effects may be diminished by careful selection of test geometry, that step will

necessarily reduce the tester's ability to move the vapor source.

Parrish (US 3,964,304) discloses a compact smoke generator for use in

15 airflow visualization. This device makes use of a heating element with the fluid

heated in a coil wrapped around the heating element.

Weinstein (US 4,493,211) discloses a smoke generator that makes use

of a heating tube that is closed on one end and has an output hole drilled

through a portion of the heating tube's sidewall. Weinstein specifically

20 addresses the problem of producing a compact generator that is capable of

producing laminar flow.

Each of these devices is capable of producing a vapor that may be used

for airflow visualization. Each is more compact than prior art devices, however

both must still be employed at a distance from the area of interest in testing

25 because they still have somewhat bulky bodies.

It is an object, therefore, of the present invention to provide a vapor

generating device that causes minimal interference with airflow in the region

surrounding the device.

It is a further object of the present invention to provide a device that may

30 be easily relocated within a wind tunnel.
LAR 15058-1 -3- PATENT APPLICATION

Another object of the present invention is to provide a device that is

easily scalable so that it may be employed in a wide range of wind tunnel

situations.

5 Summary of the Invention

10

15

20

These objects and others are accomplished by providing a wand device

that incorporates the heating process into the output portion of the device. A

tube is provided that has resistive heating properties. This tube is fed with a

vapor producing fluid that is under pressure. An electrical current is passed

through the tube, causing it to heat up. The fluid boils and produces a vapor

which proceeds to pass through the end of the tube.

The portion of the device that needs to be placed in the wind tunnel

airflow thus consists only of the tube which itself acts as a heater and a vapor

output portion. This tube does not have a large adverse effect on airflow in its

immediate region. It is clear that the tube may be easily relocated at various

points of interest around a test specimen.

It can be easily seen that by changing the size of the tube the device

may be scaled for various applications.

Brief Description of the Drawin,qs

25

30

FIG. la is a schematic of the heating and delivery portion of the vapor

generator wand.

FIG. lb is a cross section of FIG. la taken across line A-A of FIG. lb.

FIG. 2 is a drawing of a sample set up for employing the vapor

generator wand in a demonstration wind tunnel.

FIG. 3 is a drawing prepared from a photograph of the vapor generator

wand in use in a wind tunnel.
LAR 15058-1 -4- PATENT APPLICATION

Description of the Preferred Embodiments

Examples of the practice of the present invention follow, making

5 reference to FIGS. la, 2 and 3 above.

In FIG. la is shown the detailed construction of the heating and delivery

portion of the present invention. A thin stainless steel tube 11 acts as the

heating portion of the vapor generator wand 10. A brass tube 12 forms the

return portion of the electrical circuit. Copper wire leads 14, 16 are provided at

10 the base of each tube. The leads are connected to a variable power supply 40

(not shown in FIG. la). The brass tube 1:) is of larger diameter than the

stainless steel tube 11 and is coaxial. The annular space between the brass

and stainless steel tubes is thermally and electrically insulated with a

fiberglass layer 18. Near the output end 21 of the stainless steel tube 11, the

15 brass tube 12 is electrically connected to the stainless steel tube 11 with a

brass adaptor plug 20. All joints are connected with a silver solder and the

brass tubing is annealed prior to assembly. The input end of the wand is

connected to a supply of fluid with plastic tubing 22.

Making reference to FIG. 2, the fluid tank 30 is kept under pressure of

20 about 5-15 psi by an air source 32 Plastic tubing 22 leads out of the fluid tank

30 to the base of the vapor generator wand 10. Flow through this tubing is

controlled by a needle valve :34.

An adjustable power supply 40 provides electrical current through the

thin stainless steel tube 11. To provide the necessary heating in the stainless

25 steel tube it is desirable to utilize a high amperage current. To reduce the risk

of shock to an operator a low voltage is employed.

The fluid flows under pressure through the plastic tubing 22 into the

stainless steel tubing 11 where it is heated to boiling. The boiling fluid

produces a vapor which escapes through the output end 21 of the stainless
LAR 15058-1 -5- PATENT APPLICATION

steel tube 11. The vapor then enters the wind tunnel inlet 50.

As an example of the power considerations in implementing the present

invention one can examine an exemplar embodiment as illustrated in FIG. la.

The stainless steel tubing 11 is .020" in outside diameter with .005" wall

5 thickness and is 10" long. A fiberglass insulating layer 18 having outside

diameter of .120" is provided. The return portion of the circuit is a 9" long

brass tube 12 having an outside diameter of 5/32". For this configuration,

using propylene glycol as the vapor producing liquid, the power requirements

are 3A at 5V. As the device is scaled in size, it obviously becomes necessary

10 to increase power to maintain the necessary temperature.

It is preferable to use propylene glycol as the vapor producing fluid, it

has good vapor producing properties and is considered to be non-toxic.

An additional insulating coating may be added to the outside of the

brass tubing to reduce the danger of burn to an operator.

15 The vapor generator wand may be constructed within a model, such that

the output end of the heating tube protrudes slightly. This embodiment allows

for production of vapor at a single invariant point. This may be useful when it

is desirable to observe one region of an aircraft model as it is exposed to

varying angles of attack.

20 The vapor generator wand may also be placed at the end of a long

boom. This embodiment allows a technician to move the wand to various

positions within the wind tunnel so that different regions of flow may be readily

observed. This is shown in FIG. 3.

A modular system may be employed wherein a plurality of wands of

25 various sizes may be utilized with a single power supply and fluid supply

means.

The present invention may also find uses in other fields. For example it

may be used in manufacturing to provide a vapor for deposition on a substrate.

Other variations and uses will be apparent to those skilled in the art.

30 The above embodiments are not exhaustive but rather are given by way of
LAR 15058-1 -6- PATENT APPLICATION

example. It is understood that the present invention is capable of numerous

modifications within the scope of the following claims.
LAR 15058-1

,/

PATENT APPLICATION

VAPOR GENERATOR WAND

Abstract

5 A device for producing a stream of vapor for wind tunnel airflow

visualization is described. A tube is used to resistively heat a vapor producing

liquid. The heating and delivery systems are integrated to allow the device to

present a small cross section to the air flow, thereby reducing disturbances

due to the device. The simplicity of the design allows for inexpensive

10 implementation and for construction utilizing off the shelf components. The

design is readily scaled for use in various wind tunnel applications. The

device may also find uses in manufacturing, producing a vapor for deposition

on a substrate.
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