US2661195A

US2661195A - Method and apparatus for atomizing liquids

Info

Publication number: US2661195A
Application number: US212844A
Authority: US
Inventors: Pieter Martinus Van Bemmel; Milborn Hans
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1950-02-28
Filing date: 1951-02-27
Publication date: 1953-12-01
Anticipated expiration: 1970-12-01

Description

1953 P. M. VAN BEMMEL ET AL 2,661,195

METHOD AND APPARATUS FOR ATOMIZING LIQUIDS Filed Feb. 27, 1951 1nvzn+ors= Px'eizr Marfinus van bemrnel Hans Mil-born 59 a rhcir Ari'ornzg Patented Dec. 1, 1953 METHOD AND APPARATUS FOR ATOMIZING LIQUIDS Pieter Martinus van Bemmel and Hans Milborn,

Delft, Netherlands, assignors to Shell Development Company, Emeryville, Calif., a corporation of Delaware Application February 2'7, 1951, Serial No. 212,844

Claims priority, application Netherlands February .28, 1950 18 Claims. 1

This invention relates to the art of atomizing liquids, including solutions, emulsions and suspensions, by the formation of a liquid film whlch is disrupted and thus divided into fine droplets by means of an atomizing gas stream. The invention finds particular although not exclusive application in situations wherein it is desired to atomize liquids into small droplets, and wherein it is desirable that the diameters of the droplets be of greater uniformity than is possible w th other simple atomizing devices and methods and/or wherein the complication of moving parts is to be avoided. Thus, the invention may be applied to the spraying of biocides from aeroplanes or from the ground, in driers, in chemical reactors wherein small drops of liquid are to be contacted with a gaseous reagent, such as air, oxygen, halogens, etc. in oil burners, carburetors and atomizers for internal combustion engines.

The atomization of liquids by atomizing gas currents is often effected by causing a film of liquid to be formed on a rotating body having a surface of revolution, e. g., a rotating disc or cup, to which the liquid is supplied at or near the axis of rotation, the liquid moving outwards from said axis as a film adhering to the surface of the rotating body; upon reaching the periphery of the body it is discharged therefrom as a film or as liquid filaments and caught by a stream of atomizing gas which divides the film or filaments into fine drops. In such an arrange ment the friction between the rotating body and the liquid produces the force necessary for accelerating the movement of the liquid outwards towards the circumference, thereby causing a reduction in the thickness of the liquid film as it aproaches the circumference. This reduction in thickness of the film is further due to the fact that as the liquid moves outwards the surface of the disc that is to be covered by a given quantity of liquid becomes larger, this area being directly proportional to the radius on which the liquid moves when the radial velocity of the liquid is constant. Such a technique requires rapidly rotating parts and motive power for driving them; moreover, the size of the resulting drops is often far from uniform because the thickness of the liquid film at the periphery has a tendency to be non-uniform. this being aggravated when even minute irregularities occur on the surface of the disc or cap or particles of adventitious solids are deposited on the surface.

The droplet diameter with the rotating disc is inversely proportional to the circumferential speed of the disc (diameter of the disc times rotating sp 2 If, instead of a. rotating disc or cup, a stationary liquid distributing body, such as a round disc or cone, were to be used, to which the liquid is supplied at or near the center in such a man-- nor that at that point the liquid acquires a certain radial velocity, then the liquid, if friction and surface tension were to play no part, would retain this radial velocity up to the circumference and the thickness of the film in an outward lirection would diminish and be always in inverse u'oportion to the radius. The friction occurring etween the stationary body and the liquid, however. causes a significant reduction in the radial velocity; this causes the radial velocity at the circumference of the disc or cone to be reduced materially. The consequence is that the thickness of the film is substantially greater than if there were no friction, so that it is diificult to divide by means of a gas stream the liquid discharged from the stationary body into droplets having diameters of such small values as are required for many purposes. Moreover, in order to maintain an adequate radial velocity of the liquid moving on the stationary liquid distributing body and, consequently, a uniform distribu-- tion of the liquid over the circumference of the body, the diameter of the body must be kept small.

With a stationary disc the thinness of the liquid fim emerging from the disc and consequently the droplet diameter resulting from breaking up such a film by an air stream is theoretically inversely proportional to the disc diameter. For the reasons mentioned above, however, (friction losses and even distribution), the disc must be small, which, however, implies that the film is not extended over a large area before reaching the periphery and therefore remains thicker than is desirable for a subdivision into fine droplets.

It is an object of the invention to provide an improved method and apparatus for atomizing liquids by means of an atomizing gas stream wherein the liquid film is thinned by radial fiow without being subjected to such frictional forces rior to being disrupted by the atomizing gas.

A further object is to provide an improvedmethod and apparatus for atomizing liquids by disrupting a film thereof with an atomizing gas that does not require the use of a rotating body.

The instant invention is based on the concept that the film of liquid discharged from a liquid distributing body, such as a stationary disc, must be given an opportunity to be thinned further by rendering possible a continued radial movement of the liquid film after leaving the body and before being engaged by the atomizing gas stream. In this continued radial movement the liquid iswthen nolongerihamp ered by-the fric tion with the disc, but only by the much smaller forces due to friction with the substantially quiescent gas through which the film moves and:

the surface tension. The liquid consequently retains practically the radial speed" it h'adwhen leaving the distributing body, on account of which the thickness of the film reducesrfurther to assume a thickness thatisapproximately inversely proportional to the radius*measuredfrom:

fore the latter has undergone radial flow beyond:

the periphery of the distributing body and'has acquired the thinness indicated by the drop size desired.

According to the invention the liquidis'supplied to an intermediate part,'preferably a point substantially at the center, of a'liquid distributing body that has, preferably, a circular outline in a'manner to impart to different portions of the liquid divergent, preferably radial velocities along saidsurface, and is thereafter flowed outwardly as a film onthe surface of the body and discharged from the periphery thereof as a divergent film; the film is then passed outwardly in divergent'directions through a substantially quiescent space for a distance necessary to effect the desired thinning and'is, upon emergence from the quiescent'space, attacked by a' current of atomizing gas: that flows more or less perpendicular to the liquidfilm. The atomizing gasflow'is-conducted in' such a mannerthat the gas passes the distributing body only'at some distance spaced radially'outwardly from the periphery of the body and thus encounters the liquid film at some dis tance:from the latter. This can-be-effected in asimple mannerby arranging ahead of the-discharge edge of the' distributing body, (i; e., upstream with regardto the direction of the atomizir'rg gas flow) a'gas deflectoror screen of a larger diameter than that'ofthe distributing body, to' provide an annular quiescent thinning space'be hind the deflector: The surfaceof'the liquid distributor on'which the liquid film is formed may;

be directed" either upstream or downstream with respect to the direction offiow of the atomizinggas: enceto the preferredemb'odiment' wherein the liquid distributing body 'is'a stationary body 0nt0 whichtheliquid is directedtqform a liquid film traveling radially outwardly and wherein the dis-- tributing' body has :a' circular periphery forming the :discharge edge; but neither of these two limitationsis-inevery case essential, it"being'evidentthat any suitable -:means: maybe employed to. impart a radial velocity V to the liquid supplied at the centerof the-distributing body, and that" The invention will be described with refer tion in general terms, the invention will be described with reference to the accompanying drawings forming a part of thisspecificationiand illustrating certain preferred;embodimerrts..the1'eof, wherein:

Figs. 1 and 2 are a longitudinal, axial section and an end elevation view, respectively, of one embodiment suitable for application to an aeroplane;

Fig. 3 :isarlongitudinal, axial section view of a modified construction suitable for like application; and

Fig; 4 is a-vertical, axial section view of a third form suitable for use with a blower to supply atomizing gas, parts being shown in elevation.

Thecdevice'ofFigs. 1 and 2 is supported by a supply pipe I 0 which may be secured to a moving object such as a vehicle or an aeroplane which may be given a substantial velocity relative to the ambient air and connected to a source of liquidto be-atomized, not shown. An annular disc I I of circular outline, forming a gas'clefiector, is"fixed-to'front end of the pipe and astationary; fl'atsmaller liquid distibuting disc I2, also of circular outline and forming a stationary liquid dis= tributing body is mounted a suitable distance from the air deflector. The I distributing body may be mounted by beingbolted'to asupport l3 that is supported by streamlined arms H'from a threaded ring IE-that can be-adjusted-'axially on a threaded collar [6 fixedto'the pipe, a locknut ll being, provided to retain the ring I 5.

Of course the liquid distributing disc 12 can, instead of by outside supporting arms l4; be'carried by' an inside supporting 'rod, fixed' centrallyto the disc l2, situated in'the centre of the liquidstream and fixed with its other end to the inside of the supply pipe 10 somewhere upstream away fromthe orifice of the pipe l0-.

The liquidto beatomized flowed through the pipe l0with a velocity suificient toflow'beyond the end of the pipeandto form a film of liquidon' the disc IZ'that flows evenly in all radial directions. The liquid velocity should be adequatetoeffect distribution but not so great as to produce rebounding drops-or splash. This film flows outwardly to the perimeter of the disc [2 and continuesto move in divergent radial directions beyond'theperimeter as a gradually thinning film. The-velocity is advantageously chosen so that the film'discharged from the disc retains its cohesion at least until the film attains a diameter equal to that of the deflector l I; The stream of atomizing gas, indicated by thearrows' marked l8,,

flows relatively to the atomizer from left to right;

it may be generated, for example,.by movement of the vehicleor aeroplane on .which the atomizer. isfitted towardtheleftasrseen in-Fig. 1,..or by afanor therlike, as describedhereinafter. Thedefiector H, havinga greater.diametenthamdis tributing; disc l2, prevents the atomizingj gas streamlfl from reachingthe disc.l2 or immediate vicinity thereof. and forms"v an annular; substa-mtially,quiescent'thinningspace to'the downstream sidethereof; As a consequence'the liquid film is notseized by the gas stream until'itreaches a circular line having a diameteralmost as great as that of the deflector H and indicated by the number l9, but flows throughthe substantially quiescent thinning space containing substantially quiescent gas after discharge from the distributing-disc-and until reaching the circular, line I9. Upon passing radially. beyond thelatter the film is attacked by the gas current and disrupted into.-

fine droplets which are entrained by'the gas stream, as indicated by the number 20.

It is evident that the size of these droplets may be controlled by selecting a deflector disc H of suitable diameter, and that the relation between the diameters of the discs II and [2 may be selected in accordance with the type of atomization desired and other conditions, such as the properties of the liquid (density, viscosity, surface tension) and of the atomizing gas. The dimensions will, further, depend upon the rate at which liquid is to be atomized. By way of specific example, in one arrangement according to Figs. 1 and 2, the mouth of the pipe It had a diameter of about 5 mm., the liquid distributing disc I2 had a diameter of about mm., the gas deflector disc had a diameter of about 40 mm, and the distance between these discs was about 5 mm. A liquid having the nature of gas oil was atomized at a rate of 500 liters pcr hour and the air was used as the atomizing gas, the air velocity relative to the atomizer being 100 km. per hour and generated by moving the atomizer through the atmosphere. An adequate atomization was attained and the drops had diameters of from about 150 to 200 microns. In most cases the substantially quiescent thinning space extends through a radial distance that is at least half as great as the radius of the surface of the liquid distributor, i. e., the diameter of the disc ll is at tributing disc I2 is from 1.5 to 2.5 times the diameter of the orifice of the pipe l0 and the diameter of the gas deflector disc ll exceeds that of the liquid distributing disc by about 2 to about 6 cm. The distance between the two discs in this embodiment may vary from a few millimeters to a few centimeters.

' In the modification shown in Fig. 3 the liquid distributor and gas deflector comprise streamlined bodies 2l and 22, respectively, having approximately the same maximum diameters and outer surfaces of revolution that converge upstream and downstream away from each other and supported from a bracket 23 by longitudinally

streamlined supports

24 and 25. The distributor body is provided with a longitudinal bore 26 into which is fitted the liquid supply pipe 2'! which is connected directly to the support and carries the distributor body. The gas deflector 22 has a small protrusion 23 extending toward the orifice of the bore and providing a flat liquid deflecting surface 22 for deflecting the liquid directed against it from the bore back against a fiat annular liquid distributing face of the distributor as an annular film at the central part iereof. The liquid then forms a film on the face 39 and debouches beyond the margin thereof. The outside diameter of the fiat face 32 preferably exceeds that of the liquid deflecting face 29, as shown, and this face 30 is the liquid distributor proper; beyond the face til the body is cut away as shown at 3| to provide an annular, substantially quiescent gas space for the thinning liquid film until the latter reaches the circle H3, at which line it is attacked by the atomizing gas stream 18, disrupted into droplets, and entrained as indicated by 22-. The'optimum dimensions previously given are applicable also to this embodiment, it being noted that the surface 30 corresponds to the distributing disc I2 and the greatest diameter of the gas deflector '22 corresponds to the diameter of the disc I I; the spacing between the surfaces 29 and 30 will, however, usually be of the order of a few millimeters.

The two embodiments just described are particularly suitable (although not limited) for operation within a stationary atmosphere forming the atomizing gas through which the atomizer moves to produce a relative velocity. An application of this principle is encountered when biocide liquids are atomized from an aeroplane. The

plane need only be equipped with a number of atomizers, say 10 to 20, distributed uniformly over the width of the plane, whilst the movement of the plane causes the air to flow relatively to the atomizers.

As was previously indicated, the stream. of atomizing gas will often have to be generated by a separate fan or like blowing device. Such an installation is shown in Fig. 4 which, further, illustrates a modified shape for the surface of the liquid distributor and an arran ement wherein the surface of the distributor is directed downstream. In this view the device comprises" a cylindrical casing 32 that may, for example, form the upper part of a drying space or chemical reaction space; it is surmounted by an upwardly convergent hood 33 communicating with a gas supply conduit 34 supplied with a suitable atomiz-' ing gas, such as air or some other gas that is to react with the liquid, from a blower 35. The atomizer proper is mounted within the

parts

32 and 33 and comprise a pair of streamlined bodies 36 and 31, the latter having a bore 38 connected to a liquid supply pipe 39 and supported through the latter from the casing by radial struts 4B. The upper end of the bore is formed as a convergent nozzle to discharge a liquid stream having a uniform flow velocity over the area thereof, and the upstream (upper) face of the body 31 is preferably cut away as indicated at 3| in Fig. 3. The body 36 is supported by struts 4!; it forms the gas deflector and also has a part thereof shaped to form the liquid distributor. The latter is, in this embodiment, made separate from the streamlined body although this feature is optional; it has the form of a button 42 having a threaded stem carrying a loeknut 43 by which it is fastened'to the body 35. The face of the liquid distributor nearer the body 3'! forms the distributing surface and is shaped as a surface of revolution coaxial with the bore 38. This surface has a frusto-conical marginal portion 44 which is joined smoothly by a curved portion to a point 45.

In operation, liquid from the pipe 39 is discharged from the nozzle of the bore 28 against. the liquid distributing body 42 and distributedby the latter uniformly in different radial direc-.

tions to form a divergently flowing film thereon. The liquid film, after discharging from the distributor, flows through the annular, substantially quiescent space between bodies 36 and 3! and retains its cohesion while being gradually thinned until it reaches a circle indicated at 89, where it is attacked by the gas stream, disrupted into droplets, and entrained as indicated at 23. The optimum relations between the outer diameters of the body 38, the liquid distributor 32 and the orifice of the bore 33 are as indicated for Figs. 1 and 2.

The various features combined for purposes of illustration in the different views may be substituted individually one for another.

The invention can be applied for many pur-- poses, e. g., for atomizing biocide liquids, liquid '7? fuel 1 (in liquid fuel burning plants; and internal combustionz nsinesl; solutions, cmulsi nsorz usi pensions of solids in liquidstdbereduced ,or dried by: vapor tion-z r reacted; chemically; wi the atomizing gas or with a gas or other substances.

We claim as our invention:

1.; Method .of zatomizingy liquids, into fine drop: lets comprising the steps of supplying the liquid to be atomized onto an intermediate part of the surface of a liquid distributor and forming thereon afilm of said liquiddifferent parts of-which have divergent velocities along said surface; flowingthe liquid film divergently on said surface; discharging the liquid film from the saidsurface and flowing the discharged liquid as a .diverging film through a substantially quiescent thinning space for a substantial distance to effect a thinning thereof, said liquid film being entirely out of engagement with anysolid object after being discharged from said surface; continuing the flow of the thinned film beyond said'quiescent thinning space; generating av current of atomizing' gas and flowing-said current substantially perpendicularly, to the thinned film immediately beyond; said: quiescent thinning space; and r engagingthe thinned; film, only after emergencefrom said quiescent thinning space with said current of atomizing gas and thereby disrupting the thinned film into dropletsand entraining said droplets in the current.

2. Method according to claim 1 wherein the film-is p assed through the-thinning space after discharge from said surface of the distributorand prior to engagement with the atomizing gas current for a distance equal-to at leasthalf of the distance of -movemen.t of said film on the said surface.

3. Method according to claiml; wherein the distributor is rotationally stationary; and said parts-;. of; the; liquid film are. given, said .-diVergent velocities along saidisurface by. directing the liq-H uid against the said surface.

4. Method of atomizing liquids into fine dropletscompris.ing the steps-ofsupplying the liquid to be atomized substantially onto the central part of the surface of a liquid distributor, said surface being a surface of revolution with a substantially circular margin, and forming thereon a film of said liquid different parts of which have divergent radial velocities; flowing the liquid film divergently radially outwardly on said surface; discharging theliquid film from said margin of the surface and flowing the dischaiged -liquid as aradially diverging film through a substantially space surrounding'said margin for a substantial distance to effect thinning thereof; said liq uid film being entirely outof contactwith any solid object after being discharged from said surface; continuing-the flow of the thinned filin beyondi said quiescent thinning space; generating a current of atomizing gas and flowing said current substantially perpendicularly to the thinned film as a substantially annular current surrounding said quiescent thinning space; and engaging the thinned film only after emergence from said quiescent thinning space with said annular current of atomizing gas and thereby disrupting the thinned film into droplets and entraining said droplets in the current;

5. Method according to claim 4 wherein thefilm is passed through the thinning space after discharge from the margin of the saidsurface-of the distributor for adistance equal to at least half of, the radial distance of movementof said film on the said surface.

Me ed ccordin tos aimfl herei he outer d met r:- f; h m: s id uiescent; thinning. pecee x eeds the ime print the, mar in: of th d s fac of. 1 the dis ributor y betweeniabout 1 1. ndf L me.

'7. A liquid; atomizer fonatomizingliquid by m ns of ac r ntpf a mizin as flowing-melee, tively thereto; comprising; a; liquid distributor having a--- liquid; distributing surface with a: dis-.- charge edge disposedg;substantially transversely: to the direction'of :relativefiow of said current 021 atomizin as; me ns-1101y upplyi gl quid toe-be; a o ized to-;an intermediate-part OfcSaid ur a e and forming on said surface a=,film of :liquid -dif-i ferent parts of; which have, divergent velocities. along said surfaces and a;, gas deflector -locatcd upstream from saiddischargeedgewith regard to, the direction of fiowo f said current and extende ing laterally a; ,sub stantial; distance beyond-1 saided e topr vi ea 11 st nt a y qu escent thinning:

space beyond said edgaand downstream fromzthe, deflector, the part'of said distributing surfacead-. joining the said discharge edgqthereof extend. ing in directions clear of ;any:.b 0dy ;bounding.-said= 4, thinning space whereby a liquid-film discharged divergently from said; edge, must; flow, as a thinning film, beyond; saididischarge edge :for said substantial distance entirelyiollt-of 'contact with any solid object beforetbeingrengagedand--dise. rupted by said; current -.of:at0mizing;ga s

8 A, liquid atomizer according to claim 7'. wherein the deflector extendslaterallyibeyond the; discharge edge of theiliquiddistributingr surface, fora distance between about cm., and=3:cmi

9. A liquid atomizer according to, claim 7? wherein the liquid distributorr-is stationary with respect tothe atomizeras awhole.

10. A liquid: atomizer according: to claim: 7': wherein the .liquid distributor i -stationary with respect to. the atomizeras-ayvholeand rth'etmeans: for supplying liquid onto the surface'thereof com-. prises a liquid supplyv conduit havingran outlet orifice directed toward the said intermediate part of the liquid distributing surface;

11. A liquid atomizer according to claim 'li wherein the liquid distributorisstationary with respect to the atomizer as aiwhole-and the said means for supplying liquid-onto thesurfacethere of comprises a liquid supply conduit having -a flow passage openingthrough the. liquid distributingsurface for discharging liquid in a-directionaway from said surface, and a-liquid deflector in spaced relation to said liquid distributing surface and opposite said flow passage-f0r deflectingtheliquid back against theliquid distributing surface.

12. A liquid atomizer foratomizing liquid by means of a current of atomizing-gas fiowing-relatively thereto comprisingz a liquid distributor having a liquid distributing-surfacewith--a:substantiallycircular discharge edgedisposed sub stantially transversely tothe'direction of relative flow of said current of'atomizing-gas; means for supplying liquid to beatomized substantially to the central part-of said surface; and forming on said surface a film of liquid different parts ofwhich have divergent radial velocities; and-agesdeflector having a substantially Y circular outline located upstreamfrom said discharge edgewith regard tothe directionofflow. of said-current an extending radially asubstantial distance beyond' said edge to provide an annular, substantiallyquiescent thinning spacesurrounding said edge and downstream from the gas deflector, the .part of said distributing surface.adjoining--the said discharge" edge. thereof extending in directions clear of any body bounding said thinning space, whereby a liquid film discharged radially divergently from said edge must flow as a thinning film beyond said discharge edge for said substantial distance entirely out of contact with any solid object before being engaged and disrupted by said current of atomizing gas.

13. A liquid atomizer according to claim 12 wherein said deflector is in the shape of a streamlined body having an outer surface that converges upstream and having, in combination therewith, a second streamlined body spaced downstream from the deflector to form a downstream Wall for said quiescent thinning space, said second body having an outer diameter extending radially outwardly at least as far as said deflector.

14. A liquid atomizer according to claim 12 wherein said deflector has a diameter equal to at least 1.5 times the diameter of said discharge edge of the distributing surface.

15. A liquid atomizer according to claim 12 wherein said deflector has a diameter that exceeds the diameter of said discharge edge of the distributing surface by between about 1 cm. and 6 cm.

16. A liquid atomizer according to claim 12 wherein the means for supplying the liquid to the distributing surface comprises a supply conduit having an orifice with the axis thereof substantially at the center of said surface and perpendicular thereto, the diameter of said discharge edge being between about 1.5 and 2.5 times the diameter of said orifice.

17. A liquid atomizer for atomizing liquid by means of a current of atomizing gas flowing relatively thereto comprising: a stationary liquid distributor having a liquid distributing surface with a substantially circular discharge edge disposed substantially transversely to the direction of relative fiow of said gas current, said surface being a surface of revolution; means for supplying liquid to be atomized substantially to the central part of said surface and forming on said surface a film of liquid diiferent parts of which have divergent radial velocities comprising a liquid supply conduit having a discharge orifice with the axis thereof substantially coincident with the axis of said surface of revolution; and a gas deflector having a substantially circular outline located upstream from said discharge edge with regard to the direction of flow of said current and extending radially beyond said edge for a distance between about 0.5 cm. and 3 cm. to provide an annular, substantially quiescent thinning space surrounding said edge and downstream from the gas deflector, the part of said distributing surface adjoining the said discharge edge thereofextending in directions clear of any body bounding said thinning space, whereby a liquid film discharged radially divergently from said edge must fiow as a thinning film beyond said discharge edge for a distance between about 0.5 cm. and 3 cm. entirely out of contact with any solid object before being engaged and disrupted by said current of atomizing gas.

18. A liquid atomizer according to claim 17 wherein said liquid distributing surface is a flat disc and the diameter of said discharge edge is between about 1.5 and 2.5 times the diameter of said orifice.

PIETER MARTINUS VAN BEMMEL. HANS MILBORN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,184,873 Raymond May 30, 1916 1,427,910 Quinn Sept. 5, 1922 1,457,408 Sunderman June 5, 1923 1,598,624 Taylor Sept. 7, 1926 1,895,470 Mathieu Jan. 31, 1933 2,364,987 Lee Dec. 12, 1944 2,541,316 Winkler Feb. 13, 1951 FOREIGN PATENTS Number Country Date 9,246 Great Britain June 29, 1887