US3191866A - Hollow spray atomizing head having a knife edge construction - Google Patents

Description

June 2 9, 1965 c, s, WILSQN 3,191,866

HOLLOW SPRAY ATOMIZING HEAD HAVING A KNIFE EDGE CONSTRUCTION Filed March 21, 1963 3 Sheets-Sheet l I as N (\l 'l I CHARLES $.WILSON g INVENTOR.

AJ'TOR/VE VS C. 8. WILSON June 29, 1965 HOLLOW SPRAY ATOMIZING HEAD HAVING A KNIFE EDGE CONSTRUCTION 3 Sheets-Sheet 2 Filed March 21, 1963 J1me 1965 c. 5. WILSON 3,191,866

HOLLOW SPRAY ATOMIZING HEAD HAVING A KNIFE EDGE CONSTRUCTION Filed March 21, 1963 3 Sheets-Sheet 3 coo I 8 CHARLES s. W'ILS INVENTO ATTORN EYS United States Patent 3,191,866 HOLLOW SPRAY ATOMIZING HEAD HAVING A KNIFE EDGE CONSTRUCTION Charles S. Wilson, P.(). Box 5, Anchorage, Alaska Filed Mar. 21, 1963, Ser. No. 266,991 6 Claims. (Cl. 239-171) This invention relates to spray atomizers, and for its general object aims to provide an atomizer which is simple and inexpensive to produce, which has no moving parts in its atomizing head, and yet performs its intended function with greater efliciency than atomizers heretofore devised.

A further and particular object is to devise a spray atomizer peculiarized in its employment of a knife edge, feeding liquid which is to be atomized over one face thereof and flowing atomizing air over the other face, and in the design of the parts causing the body of fiowing air to create a strong current free of turbulence while maintaining the merging liquid in a thin boundary layer.

These and other objects and advantages in view will appear and be understood in the course of the following description and claims, the invention consisting in the novel construction and in the adaptation and combination of parts hereinafter described and claimed.

In the accompanying drawings:

FIGURE 1 is a fragmentary side elevational view illustrating a knife-edge atomizer embodying teachings of the present invention and engineered specifically for use on a moving object such as an airplane whose direction of flight is denoted by the arrow A, a part of the atomizer being shown in section on the line 1-1 of FIG. 2.

FIG. 2 is a fragmentary transverse vertical sectional view thereof on line 2-2 of FIG. 1.

FIG. 3 is a longitudinal vertical sectional view on line 3-3 of FIG. 2 incorporating a diagrammatic illustration of air currents.

FIG. 4 is a view similar to FIG. 3 with the atomizer shown tilted to accelerate the velocity of the atomizing air.

FIG. 5 is a fragmentary horizontal sectional view on line 55 of FIG. 3.

FIGS. 6 through 9 are fragmentary views diagramming the atomizing action of air passing over an edge and showing the result of making such edge sharp, round or square, and also of introducing the liquid parallel to the air current. v

FIG. 10 is a fragmentary vertical sectional view illustrating the invention embodied in a structure employing compressed air as the atomizing agent, the liquid and the air being represented by plain-shafted and feathered arrows, respectively; and

FIG. 11 is a fragmentary view partly in top plan and partly in horizontal section on line 1111 of FIG. 10.

Referring first to FIGS. 1 and 2 of said drawings, the numeral 20 denotes one of two hangers which are adapted to have their upper ends removably secured to an airplane of the type used in dusting and like operations, one said hanger upon one side and the other hanger upon the other side of the airplane. This attachment is or could be made to the wheel-carrying struts. Bearing hubs 21 are formed upon the illustrated lower ends of these hangers, and provided by such bearing hubs are co-axial bores each fitted with a respective bushing 22 to provide a rocking journal for a related one of two trunnions 23 extending from the two ends of a hollow atomizing head denoted generally by 24. One of the two trun nions has a center-bore 25 communicating with the hollow center 26 of the atomizing head. The other and non-illustrated trunnion is made solid. A threaded nipple 27 extends as an integral axial prolongation of the centerice bored trunnion, and connected by a nut 30 thereto is a flexible feed hose 32 leading by gravity flow from a supply tank (not shown) for the liquid chemical which is to be atomized. This tank is or may be mounted within the airplane and has its discharge controlled by a suitable valve.

The atomizing head is designed to be shifted about the center of its trunnions as an axis into selected adjusted positions within prescribed limits of rocking motion. For performing said shifting movement one of the two trunnions protrudes beyond its bearing hub and has a lever arm 33 clamped thereto, with the free end of such lever arm being raised and set from within the plane by a cable 34 against yielding resistance imposed by a spiral return spring 35. The spiral return spring has one end anchored to the bearing hub by a pin 36 and its other end secured to the trunnion by a screw 37.

Proceeding now with a detailed description of the atomizing head, the same is generally oblong as viewed from the end, with the upper side 40 warped and the underside 41 fiat, and with the two said surfaces, namely the warped surface and the flat surface, merging at the front or leading edge of the head by a rounded nose 43 and being separated at the trailing edge by the head's delivery orifice which is formed between two plates 44 and 45 which lie in obtuse angular (preferably relation to the flat side 41 and protrude beyond the latter. This orifice extends the full length of the head. The eX- posed lips which said protruding portions of the plates produce have their outer edges cut on a common plane which is normal, or approximately normal, to the plane of the flat side 41, thus placing the surfaces 46 and 47 in acute angular relation and forming a knife edge 48 therebetween.

I desirably fabricate the head proper from stainless steel, employing sheet stock which is bent to the described shape and has its two ends folded back to form inwardly directed paralleling wings 50 and 51. The two plates 44 and 45 seat against these wings and are soldered thereto, fillets 52 and 53 produced by such soldering filling the reentrant openings which would otherwise obtain where the plates and the sheet metal meet. Closure walls 54 and 55 for the two ends are or may be also solder-joined.

The throat which lies between the plates 44 and 45, while shown for purposes of illustration as being quite wide, is little more than a crack and shim-thickness spacers 56 are introduced at spaced intervals of the length to maintain the gap. These spacers have a triangular plan configuration with the narrow end located at the emission end of the throat, are or may be tapered inwardly toward said narrow end so as not to impede the flow to the emission end of the throat, and are fixed in position by cap screws 57 introduced through wall openings which are then solder-closed and ground flush.

The operation of the described structure can be explained as follows, in course of which reference will be had to the diagrammatic views FIGS. 6 through 9:

When a jet of air, in this case the wind stream created by the forward progress of the airplane, is blown over a knife-edge a region of reduced pressure develops on the down-wind side of that edge. Those molecules that thermal agitation bounce into the jet are immediately swept away and atmospheric pressure pushes other molecules into their places (FIG. 6). If the boundary layer is reduced to a minimum by making the knife-edge very sharp and smooth, this current becomes surprisingly strong, sufiicient to carry liquid up the blade for an appreciable distance and into the edge of the air stream where it is drawn out into a sheet that ruptures to form drops. The size of the drops produced depends not only on such factors as air velocity, rate of feed, surface tension and viscosity, but

also on the manner in which the force of the air bears on the liquid. Maximum shear (and break-up) results from vertical presentation of the liquid to the force of the air jet, especially when this presentation is made at a place where the boundary layer is then and there is little metal surface for the liquid to adhere to. The shear forces become less as the angle of presentation is reduced toward the extreme shown in FIGURE 7. In fact, they can be eliminated by applying pressure behind the liquid, for ejecting same, in such force as to expel the liquid with the same velocity as the surrounding air stream. In this event, the only break-up would be that which results from instability of the sheet as it falls through the air.

Certain standards of workmanship must be maintained if delivery is to be made in a narrow range of drop sizes and with the best mechanical efficiency. FIGURES 8 and 9 illustrate the effect of having a rounded or a square rather than a sharply defined knife-edge. The critical dimensions are all, however, of natures that are relatively easy to maintain. In general, it can be assumed that, given a knife-edged ejection throat of uniform width throughout its length, the atomization will be uniform throughout such length, and the throat can be straight or of any curve desired. These factors allow extreme flexibility in design and the two-dimensional nature of the action invites the quantitative analysis needed for the drawing of precise specifications.

In respect of an airplane, the dynamic pressure of the air passing a light plane in flight (90 to '100 m.p.h.) is not sufficient to give a reading on the gauge of an ordinary air compressor, yet, when a knife-edge atomizer is used, such pressure becomes suflicient to break insecticide solutions into very fine sprays. The insecticide must be delivered in a thin film but, an ample supply of air being available, the knife-edge can be given suflicient length to insure an adequate rate of output. For a fine atomization, the atomizing head is tilted, as shown in FIG. 4, so that air scooped up by the flat side 41 passes over the knife-edge at relatively high velocity. The warping of the other side is such that just enough air flows around the same to prevent formation of a burble that'would carry spray back onto the head. Control of the size .of the drops delivered is obtained by simply altering the tilt to increase or decrease the scooping action of the flat face 41.

The size range of the drops is largely dependent on uniformity of feed to the knife-edge. Wide spots in the slot will tend to flood corresponding parts of the knif edge, while a constriction in the feed line (such as might be caused by a partially closed supply valve) will leave dry spots. Gravity feed is adequate for all but the very exceptional cases in which drops of the largest possible size are desired. In under-the-belly mounts, the flat side or scoop side of the boom should face downwardly to prevent wetting of the tail of the airplane.

Proceeding now to describe the structure portrayed in FIGS. and 11, the same embodies knife-edge principle in an atomizing nozzle having its air delivered from a pressurized source of supply and lends itself to sundry uses such, for example, as an oil burner.

In the form in which I have illustrated same, a corepiece for the atomizing head is carried by a hollow stem 60 which is rigidly secured in a suitable manner to a foundation and has its hollow center 61 suitably connected with a source of the liquid to be atomized. The corepiece is formed with an externally threaded flange 62 at its back end and has a cylindrical neck portion 63 projecting as a reduced axial prolongation forwardly therefrom. The neck is bored and counter-bored from its forward end, with the bore 64 communicating with the hollow center 61 of the stem 60. At equidistantly spaced intervals about the circumference of a circle drawn about the center of the bore as an axis a set of holes 65 are drilled in said neck parallel with said bore and extend to the floor of the counter-bore 66 from a manifold chamber 67 formed at the base of the flange 62. Air from a pressure source of supply (not shown) is fed to this manifq d by a P p 68- Internal threads are provided by said bore 64 at its forward end. To isolate the center-bore from said drillholes a member having a center-bore 70 and made in the form of a cap-screw engages these threads and has its cap 71 firmly shouldered against the floor of the counterbore. The outer limit of this shoulder terminates short of the drill-holes 65, and the peripheral wall of the cap flares outwardly therefrom to a flat face 72 located flush with the end face 73 of the neck 63 in a plane normal to the axial line of the neck. The adjacent edges of said faces 72 and 73 are closely spaced to produce an interstice having a narrow and uniform width throughout the circumference.

A facing cone-shaped nose-piece 74 having a diameter slightly less than that of the face 72 is secured by screws 75 in paralleling overlying relation to the latter with the spacing therebetween being prescribed by washers 76 which surround the screws. The peripheral wall of the cone desirably has no greater than a 45 slope and by its intersection with the flat base of the cone produces the inner of two circular edges concentric to the heads axial center. The outer edge is produced by the intersection of inner and outer meeting walls of a tapering inturned lip 80 formed upon the front end of a shell 81 which threads onto the flange. Such inner edge and the outer edge are spaced inwardly and outwardly, respectively, from the corresponding sharp concentric edges of the emission throat through which the compressed air issues.

82 denotes a spacer shim introduced between the front face of the flange and a shoulder formed on the shell. A ring 83 surrounds the neck 63 and at intervals of its circumference carries needle separators 84, spacing the shell from the neck while permitting free travel of liquid up the outside of the neck from radial bores 85 leading outwardly from the center-bore 64.

Other than for its employment of air from a pressure source of supply rather than the air stream flowing past an airplane in flight, the two illustrated atomizing heads function in much the same way.

It is thought that the invention will have been clearly understood from the foregoing detailed description of my now-preferred illustrated embodiments. Changes in the details of construction may be resorted to without departing from the spirit of the invention and it is accordingly my intention that no limitations be implied and that the hereto annexed claims be given the broadest interpretation to which the employed language fairly admits.

What -I claim is:

1. A spray atomizer comprising a hollow atomizing head presenting two merging planar surfaces disposed in acute-angular relation to one another and at their line of juncture producing an exposed knife edge, means for flowing liquid which is to be atomized from the hollow interior of the head to said knife edge over one of said surfaces, and means for delivering a current of atomizing air to the knife edge over the other of said surfaces, the atomizing head presenting a planar exterior face and having said surface over which the current of air passes projecting from one edge thereof as a lip prolongation of the face disposed in obtuse-angular relation to the face, means being provided for suspending said head from an airplane so as to occupy a position below the belly of the latter and placing said planar face at the underside with the lip at the after end.

2. A spray atomizer according to claim 1 having means for setting the head in adjusted positions tilted about an axis paralleling the knife edge so as to vary the scoop action of the planar face upon the air stream which passes the airplane when the latter is in flight.

3. A spray atomizer according to claim 1, said head being elongated with a generally oblong configuration when viewed from an end with said planar face being at the bottom and having the upper face warped, the two 'said faces merging at the front by a rounded nose and being separated at the rear to form a parallel-sided emission slit leading from the hollow center of the head to said surface over which the liquid flows to the knife edge.

4. A spray atomizer according to claim 3 having a fluid-flow connection leading to the atomizer head from a remote source of supply of the liquid to be atomized for feeding said liquid from the source to the hollow center of the head.

5. A spray atomizer according to claim 3 in which the emission slit is defined between upper and lower plates projecting downwardly and rearwa-rdly beyond the plane of the flat face in planes biased therefrom and each having the outer edge ground on a coinciding plane which lies approximately normal to the plane of the flat face.

6. A spray atomizer according to claim 1 in which the means for flowing liquid from the hollow interior of the head comprises upper and lower plate-s defining a parallelsided emission slit therebetween, the plates projecting downwardly and rearwardly beyond the plane of the fiat face in planes biased therefrom and each having the outer edge ground on a coinciding axis which lies approximately normal to the plane of the fla-t face, a spacer being provided separating the two plates and formed to a triangular plan configuration with the narrow end located at the emission end of the throat.

References Cited by the Examiner UNITED STATES PATENTS 1,437,201 11/22 Schumann 239434 1,888,791 11/32 Cole 239-8 1,927,743 9/33 Ivey 239 2,361,144 10/44 Loepsinger 239-8 2,419,365 4/47 Loepsinger 239-8 2,427,987 9/47 Wilson 244-136 2,591,157 4/52 Hutchinson 244-136 2,659,556 11/53 Doblhofi 239-171 2,772,061 11/56 Sellers 239-171 2,884,204 4/59 Feis 239-426 3,049,304 8/62 Sears 239-318 3,050,261 8/62 Littlefield 239318 FOREIGN PATENTS 54,300 2/ 3 8 Denmark. 477,164 6/29 Germany.

EVERETT w. KIRBY, Primary Examiner.

Claims (1)

1. A SPRAY ATOMIZER COMPRISING A HOLLOW ATOMIZING HEAD PRESENTING TWO MERGING PLANAR SURFACES DISPOSED IN ACUTE-ANGULAR RELATION TO ONE ANOTHER AND AT THEIR LINE OR JUNCTURE PRODUCING AN EXPOSED KNIFE EDGE, MEANS FOR FLOWING LIQUID WHICH IS TO BE ATOMIZED FROM THE HOLLOW INTERIOR OF THE HEAD TO SAID KNIFE EDGE OVER ONE OF SAID SURFACES, AND MEANS FOR DELIVERING A CURRENT OF ATOMIZING AIR TO THE KNIFE EDGE OVER THE OTHER OF SAID SURFACES, THE ATOMIZING HEAD PRESENTING A PLANAR EXTERIOR FACE AND HAVING SAID SURFACE OVER WHICH THE CURRENT OF AIR PASSES PROJECTING FROM ONE EDGE THEREOF AS A LIP PROLONGATION OF THE FACE DISPOSED IN ABTUSE-ANGULAR RELATION TO THE FACE, MEANS BEING PROVIDED FOR SUSPENDING SAID HEAD FROM AN AIRPLANE SO AS TO OCCUPY A POSITION BELOW THE BELLY OF THE LATTER AND PLACING SAID PLANAR FACE AT THE UNDERSIDE WITH THE LIP AT THE AFTER END.

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