US3769833A

US3769833A - Bubble generator

Info

Publication number: US3769833A
Application number: US00257787A
Authority: US
Inventors: D Ordway; R Hale
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1972-05-30
Filing date: 1972-05-30
Publication date: 1973-11-06
Anticipated expiration: 1990-11-06

Abstract

A device for the rapid generation of massive quantities of gasfilled, neutrally buoyant bubbles is provided. The device consists of a plurality of parallel struts each streamlined like an airfoil and containing a gas manifold and a bubble film material (BFM) manifold. The generating elements comprise two concentric tubes with the inner tubes connected to the gas manifold and the outer tubes connected to the BFM manifold. The struts are disposed near the discharge end of a cylindrical housing through which an axial air flow is created by a motor and fan plus screens and flow straighteners. The bubbles are pulled off the tips of the outer tubes by the air flow, with the size of the bubbles governed principally by the velocity of the air flow.

Description

United States Patent Ordway et al. [4 1 Nov. 6, 1973 BUBBLE GENERATOR 1,676,984 7/1928 Fales CI al 73 147 75 I t D Id nven Ors f gfg of Primary Examiner-Herbert Goldlstein NY Attorney-R. S. Sciascia et a1.

[73] Assignee: The United States of America as [57 ABS Q'G LP the SDecetary of the A device for the rapid generation of massive quantities as mgton of gas-filled, neutrally buoyant bubbles is provided. [22] Filed: M 30, 1972 The device consists of a plurality of parallel struts each streamlined like an airfoil and containing a gas manim] APPl- 2571787 fold and a bubble film material (EBFM) manifold. The generating elements comprise two concentric tubes [52] [1.8. CL. 73/147, 46/6 with the inner tubes nn cted to th gas manifold and 51 161. CI. G01m 9/00 the outer tubes ted to the BFM manifold. The 58 Field 61 Search 46/6, 7, 8; 73/147; struts are disposed near the discharge end of a cylindri- 239/557; 261/76, 124 cal housing through which an axial air flow is created by a motor and fan plus screens and flow straighteners. [56] Refe n Cit d The bubbles are pulled off the tips of the outer tubes UNITED STATES PATENTS by the air flow, with the size of the bubbles governed 2 134 890 11/1938 RedOll 73/147 principally by the velocity of the 2,616,291 11/1952 Benedum 73/147 2 Claims, 5 Drawing Figures PATENIEDHuv 6 Ian sum -1 or 2 WISS Fig. I

Fig.5

alvsslass same BF 2 BUBBLE GENERATOR The present invention relates to bubble generating means and, more particularly, to means for generating gas-filled bubbles at a rate of substantially six million bubbles per minute.

The use of bubbles which conform to or follow the flow of low to medium velocity gases is replacing a similar use of smoke primarily because of the movement of gases within certain velocity ranges. A hand gun for the production of a single stream of bubbles is described in U. S. Pat. application Ser. No. 112,992, filed Feb. 5, 1971, now abandoned, however, it is often desirable to have a massive flow of bubbles, and, obviously, the pistol device in the forementioned application would not serve such a purpose.

The present invention provides a device for generating massive quantities of bubbles which is both desired and necessary in the art of airflow or fluid flow in applications such as the flow of air past outdoor structures or a flow in a very large cross-sectional area where a multiplicity of bubbles in a single plane at the origin of the bubbles is necessary. The method is accomplished in one embodiment of an apparatus wherein a multiplicity of bubble forming heads are deployed across the outlet of a large internal diameter bubble generating means. A desired flow rate is produced by an axial fan disposed at the opposite end of the generating means, and fluctuation damping and flow straighteners are interposed between the heads and the fan to provide a parallel flow of air. A gas reservoir and a reservoir of bubble film material are connected by appropriate valves to transverse manifolds, with bubble film material being introduced through one manifold which is connected to the outer of two co-axial tubes and a gas such as helium introduced into the other manifold which is connected to the inner of the co-axial tubes.

Accordingly, it is an object of the present invention to provide a novel apparatus for generating massive quantities of gas-filled bubbles.

It is another object of the invention to provide a device for the generation of massive quantities of gasfilled bubbles wherein a bubble flow rate on the order of 6 million bubbles per minute is achieved.

A further object of the invention is to provide a device for generating a massive quantity of gas-filled bubbles wherein the bubbles are entrained in a parallel flow of air prior to exiting the device.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description thereof when considered in conjunction with the accompanying drawings in which like numerals represent like parts throughout andwherein:

FIG. 1 is an end view of the bubble generating device.

showing the array of bubble forming orifices and surrounding structural members;

FIG. 2 is a longitudinal section taken along a line sub stantially identical to line 2-2 in FIG. 1;

FIG. 3 is a plan view partly cut away of the discharge end of the device shown in FIG. 2;

FIG. 4 is a plan view partly cut away of an individual strut in the device; and

FIG. 5 is a sectional view of the strut of FIG. 4 taken along a line substantially identical to line 55 in FIG. 4.

Referring to FIGS. 1, 2 and 3, a means for generating an axial flow 11 is shown which includes a cylindrical housing 12 having a bellmouth inlet 13 at one end and a plurality of bubble forming heads 15 at the opposite end. The general configuration of housing 12 is cylindrical in the embodiment shown to enable a substantially straight flow of air to be produced. It will be appreciated that other configurations than cylindrical may be used to accomplish this result. Disposed in housing 12 adjacent bellmouth inlet 13 is an axial flow motor 16 and a fan 17 connected thereto, with the motor 16 positioned concentrically within the housing by supports 18. Interposed between the head elements 15 and fan 17 are a plurality of means for producing a desirably uniform and straight flow of air such as a primary screen 21 of selected fine mesh in which a high loss of velocity takes place for the advantage of removing non-uniformities in the flow of air. After passing through screen 21, the air is directed through a flowstraightener 22 which is comprised of a multiplicity of parallel passages 23 for taking out swirls in the flow of air which may still exist. The air flow is then directed through a plurality of secondary screens 24 27 which are inserted for the purpose of damping remaining fluctuations and thereafter the straightened flow of air is directed past the multiplicity of head elements 15.

FIG. 1 is an end view of the device showing an array of struts 30, a gas reservoir 31, a valve 32 for controlling the gas admittedinto reservoir 31 and a plurality of bubble film material valves 35 for controlling the flow of bubble film material (BFM) in struts 30. FIG.

3 is a plan view of the discharge end of the device partly cutaway to illustrate an individual strut 30 in which the head elements 15 are positioned.

An individual strut 30 is shown cutaway in FIG. 4 to illustrate the manner in which gas is directed to the head elements via a manifold 36 for a lighter-than-air gas such as helium and in which bubble film material is directed to the head element via a manifold 37. FIG. 5 illustrates the exterior shape of the struts 30, having an airfoil contour at the end 38 which is disposed nearest the secondary screens and nozzle or head end 15 at which bubbles are formed. 1

In operation, a straightened flow of air which is produced by the combined effect of fan 17, primary screen 21, flow straightener 22 and secondary screens 24 27, is directed against airfoil section 38 to cause a flow of air along the outer surface of nozzle 15 which is nonturbulent and uniform. With gas being introduced through manifold 36 and bubble film material being introduced through manifold 37, a bubble necessarily is formed at the end of nozzle 15 which grows in size as additional gas is forced out from the manifold. Each bubble formed in this manner is swept away from the head element when the drag created by air friction is sufficient to exert the force necessary to remove the bubble. Bubble size can be controlled by the velocity of the air flow, with larger bubbles being produced at lower airflow rates and smaller bubbles at a higher density rate being produced at higher airflow rates. By proper adjustment of fan speed and

valves

32 and 35, gas-filled bubbles may be generated continuously and for extremely long periods of time.

In the embodiment shown, which. includes small gage tubing, bubbles of from about one-sixteenth inch to one-half inch in diameter or somewhat larger may be generated. For this size bubble, the corresponding massive generating rate is about 15,000 bubbles per minute. per liead so that for a generator having 20 strutswith 3 20 heads each, or a total of 400 heads altogether, a

total generation rate of million bubbles per minutemay be realized.

The bubble generator described herein provides a valuable and unique tool previously unavailable for the rapid generation of massive quantities of bubbles. A more compact unit of a substantially smaller number of heads, for example, a semi-portable unit, not shown, having from about to 40 bubble forming elements could be employed in visualizing the complex airflow patterns either about various objects or within enclosures. Applications of the smaller unit are to determine air flow in aerodynamic air tunnels, in heating and ventilation installation, through blowers and fans, in natural convection studies, in wind flow about buildings, plants etc., in air cooling of electronic systems, in ground testing of propellers, rotors, and aircraft, and in internal flow studies such as in pipes, ducts, etc., among other uses.

The unique capabilities of the helium-filled bubbles for visualization of complex air motions lie in their suitable size and light weight. The size described, of about one-sixteenth inch to one-half inch in diameter, allows the motion of individual bubbles to be traced independently while their neutral or substantially neutral buoyancy allows them to follow even very low speed flows accurately. The lifetimes of the bubbles can be adjusted from several seconds up to an indefinite period of time by using various bubble film solutions. Bubble lifetime is controlled primarily by the evaporation rate of the bubble film which may be formed from various soap solutions but for superior characteristics the SA] 1035 Bubble Film Solution made by Sage Action, Inc., P. O.

Box 416, Ithaca, N.Y. 14850 may be used. Bubbles from higher quality solutions have a longer life, a thinner bubble film and are formed more easily than those made by ordinary soap solutions. Films of bubbles made with the SA] 1035 solution have been demonstrated to possess a minimum lifetime of 30 seconds which is sufficient for most uses. At low speeds, the bubbles appear to be colored and therefore are more visible with respect to human perception. Bubble streaks are best photographed for permanent records and for accurate analysis when the shutter speed of the camera is slower than the time to generate a single bubble. Consequently, higher generation rates allow faster shutter speeds which help to cut down unfavorable background lighting and overexposure of the models under study, thereby gaining better contrast for good streak photographs. The higher quality bubble solution leaves a minimum of residue when the film dries and can be made so as not to stain surfaces or clothing.

The bubble motions can be easily photographed by means of conventional film and light sources. With an interrupted light source, the motion appears as broken streaks on the photograph which can be used then to obtain a quantitative measurement of local velocity.

Other means of airflow visualization such as smoke do not possess these capabilities since with regards to smoke they are only visible when there is a sufficiently high concentration of smoke particles and, in turbulent flows particularly, smoke defuses too rapidly to be of any value. Other means such as balsa dust have larger particles which are also heavy relative to air and so do not follow rapid fluctuations in velocity or low-speed flows accurately. On the contrary, helium-filled bubbles have been shown to trace airflow patterns at speeds in excess of fps. Because of their ability to follow flow steamlines, the bubbles rarely collide with objects in the air stream and are extremely durable. For

example, bubbles have been observed to flow through a fan without impact on the moving blades.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. For example, the bubble generator may be wired for remote operation of the fan, the helium supply and the bubble film material supply.

What is claimed is:

1. A device for rapidly generating massive quantities of gas-filled neutrally buoyant bubbles for following complex laminar and turbulent airflows comprising:

means for generating a straight, uniform flow of air at controlled flow rates, including flow straightening passages disposed in said device and'turbulence removing screens disposed on opposite sides of said flow straightening passages,

means for forming a multiplicity of streams of neutrally buoyant bubbles containing a lighter-than-air gas within said flow of air,

said bubble forming means including a plurality of pairs of bubble film material manifolds and gas manifolds and a conduit connected to each of said manifolds,

said gas manifolds disposed upstream of said bubble film material manifolds and the conduits connected to said gas manifolds extending through said bubble film manifolds concentrically into the conduits connected thereto and terminating a selected distance from the ends thereof to form bubbles at the ends of said conduits connected to said bubble film material manifolds,

said bubble film material and gas manifolds arranged parallel to one another and said concentric pairs of conduits spaced equally from one another to uniformly dispense said bubbles into said airflows.

2. The device as defined in claim 1 wherein said pairs of manifolds are disposed in struts having an airfoil configuration so as to introduce a minimum of turbulence into said flow of air;

said struts disposed in parallel rows across said generating means so that said streams of bubbles are dispensed uniformly throughout a cross section of said flow of air.

l l =8 t i

Claims

1. A device for rapidly generating massive quantities of gasfilled neutrally buoyant bubbles for following complex laminar and turbulent airflows comprising: means for generating a straight, uniform flow of air at controlled flow rates, including flow straightening passages disposed in said device and turbulence removing screens disposed on opposite sides of said flow straightening passages, means for forming a multiplicity of streams of neutrally buoyant bubbles containing a lighter-than-air gas within said flow of air, said bubble forming means including a plurality of pairs of bubble film material manifolds and gas manifolds and a conduit connected to each of said manifolds, said gas manifolds disposed upstream of said bubble film material manifolds and the conduits connected to said gas manifolds extending through said bubble film manifolds concentrically into the conduits connected thereto and terminating a selected distance from the ends thereof to form bubbles at the ends of said conduits connected to said bubble film material manifolds, said bubble film material and gas manifolds arranged parallel to one another and said concentric pairs of conduits spaced equally from one another to uniformly dispense said bubbles into said airflows.

2. The device as defined in claim 1 wherein said pairs of manifolds are disposed in struts having an airfoil configuration so as to introduce a minimum of turbulence into said flow of air; said struts disposed in parallel rows across said generating means so that said streams of bubbles are dispensed uniformly throughout a cross section of said flow of air.