CA1097390A

CA1097390A - Microcapillary nebulizer and method

Info

Publication number: CA1097390A
Application number: CA301,459A
Authority: CA
Inventors: Darrel R. Resch; Elisha W. Erb
Original assignee: ERB ELISHA; Resch D R
Current assignee: ERB ELISHA; Resch D R
Priority date: 1977-08-04
Filing date: 1978-04-19
Publication date: 1981-03-10
Also published as: DE2823643A1; FR2400965A1; GB1600306A

Abstract

MICROCAPILLARY NEBULIZER AND METHOD
Abstract of the Disclosure A pneumatic microcapillary nebulizer adapted to accept a supply of flowable liquid, such as water, and reduce the liquid to an ultrafine dispersion of particles in a propellant gas, such as air. The microcapillary nebulizer comprises a mixing element having a liquid conduit comprising a microporous capil-lary element having a multiplicity of liquid passages and exit orifices, a gas conduit having a gas orifice and a filming-surface having an edge comprising said gas orifice and communi-cating with said liquid exit orifices. All the liquid flowing to said filming surface must pass through said capillary element wherein it is retained in the absence of external forces and whereby it may be rendered substantially free of undesirable solid impurities of microscopic size or larger. The filming sur-face has an affinity for the liquid, which affinity coupled with the cohesive forces acting on the liquid and the pressure acting on the liquid, cause the liquid to flow out of the capillary ele-ment and across the filming surface to form a continuous thin liquid film on the filming surface which is drawn to the edge of the filming surface comprising the gas orifice and is reduced to an ultrafine dispersion of said liquid in the gas flowing through said gas conduit.

Description

~973~C~

Background of the Invention Copending Canadian Application Serial No. 2~5,222, filed August 22, 1977, relates to pneumatic nebulizers which contain a filming surface between the narrow exit orifices of the liquid passages and the gas conduit. The exit orifices are so small as to retain the liquid therein by capillary attraction unless a force is applied, such as a pressurized liquid supply or a vacuum beyond the exit orifice, to force the liquid out of the exit orifices and onto the filming sur-face. The :liquid has an affinity for the filming surface ;-which is contiguous with the exit orifices of the liquid passages, which affinity causes the liquid film to spread over the filming surface as a very thin continuous liquid film which flows to the edge of the filming surface and is drawn into the gas flow. The flowing gas shatters the liquid film and dis-perses it as an ultrafine dispersion of particles of liquid in the gas flow.
Prior pneumatic nebulizers have encountered two differ-ent problems, both related to the presence of solid impurities in the liquid belng nebulized. ~'irstly, if the nebulizer is of the type having a limited number of very fine or narrow liquid passages and exit orifices, such passages and/or ori-fices can become contaminated and blocked with~deposits of solid impurities, such as minerals, rust andior dirt dispersed ln the water or other liquid being nebulized. This causes the nebulizers, such as humidif'iers, to malfunction and requires that they be disassembled due to blockage of the liquid pass-ages and/or orifices, cleanèd and/or replaced in cases where the liquid passages and/or orificies cannot be cleared or where co~rosion has oecurred.
Seeondly~ if the nebulizer is used in hospitals or other areas where a sterile atmosphere free of microbiological con-

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tamination must be maintained, it is essential that the ultra-fine dispersion emitted by the nebulizer be sterile, i~e., free of germs and o-ther solid impurities, even those which are micro-scopic in size. Such requirement is most important in the case of nebulizers used for -the direct inhalation of ultrafine dis-persions of liquid medicines by seriously ill patients having li-ttle or no resistance to the inhalation of germs or other solid impurities. This requirement is also importan-t in a wide variety of o-ther locations where the exclusion of germs, micro~
biological organisms and other solids dispersed in the atmos-phere is essential, such as humidifiers used in hospital nurser-ies, incubators, burn units t operating rooms, intensive care units and medical research facilities.
Precautions are currently taken to avoid -the introduction of germs and other solid impurities into atmospheres which are intended to be maintained sterile. Thus gases, such as air, are filtered and llquids, such as water, are sterilized and filtered in an ef~ort to remove germs and other impurlties. Steriliza-tion by means of heat can be effecti~e in killing germs, but filtratlon is necessary to remove the dead germs since the pre-sence of foreign solids, such as dead germs, can be detrimental to the healing and recovery of the patient~ A variety of fil-ters are currently used for these purposes, inclùding micropor-ous membrane filters commercially available from Nillipore Corp-oratlon, Bedford, Uass. and having mean pore sizes r~nging down to as small~as 25 nanometers (0.025 micrometer).
While such procedures~are eXfective in producing sterile .
supplies of liquids and gases, such liquids and gases can become recontaminated with germs, microbiological organisms and/or foreign substances when they are introduced into a nebulizer, such as a humidifier or an inhalation device. Even though pre-cautions are taken -to maintain such machines or devices clean, ~7~
it is difficult to exclude all contamination. Even the presence of tiny amounts o~ minute contaminants can be critically impor-tant Summary of the Invention The present inven-tion relates to a novel pneumatic micro-capillary nebulizer which comprises a mixing element for intro-ducing a supply of liquid through a liquid conduit having a mul-tiplic~ty of microporous liquid passages and exit orifices, onto a filming surface having an affinity for said liquid to film the 10 liquid for introduction into a gas flow which reduces the film of liquid into an ultrafine dispersion. ~he mixing element com-prises a liquid conduit, a microporous element comprising a mul-tiplicity of capillary liquid passages and exit orifices of said liquid conduit, and a filming surface which communicates with said microporous element and has an edge thereof closely spaced from said microporous element and communicating with the orifice of a gas conduit. In cases where a sterile atmosphere is re-quired, the gas conduit may also be provided with a microporous element so that both the liquid on -the filming surface and the 20 gas supplled a~ainst the edgé of sald Iilmlng surface are fil~
tered of all solid impurities, including those which are micro--scopic i~ size.

;~ The dimensions of the~present nebullzer device, including - . ~
the pore sizes of the microporous capillary element are such that llquid will not~flow from~said~microporous capillary element onto said filming sur~ace under -the effects of the forces acting on -the liquid, unless the combined effect of such forces other than capillary force, exceeds the force due to the capillary attrac- -tion which tends to retain said liquid within the pores of the microporous capillary element. However, when a pressure differ-ential is crea-ted, such as by opening a valve between a pressur-ized liquid supply and said liquid passage or by applying suction or a vacuum external ~o the microporous capillary element, liquid is caused to flow through the capillary element onto the ~ilming surface where it lays down as a continuous thin film which is drawn to the edge of the filming surface where it meets the gas flowing through the gas conduit. The thin liquid film is drawn into the gas flow from the edge of the filming surface and shat-tered to form an ultrafine dispersion of the liquid in the gas.
Essentially, the nebulizer devices and methods of the present invention are the same as those of our aforementioned 10 application Serial No. 285,222 with the exception that the pre-sent capillary liquid passages and exit orifices of the liquid~
supplying conduit comprise a myriad of capillaries present within a relatively uniform microporous element having an open cell structure, i.e., being permeable to said liquid under operating conditions. Thus, rather than relying upon -the narrow spacing between two discs to provide the liquid passages and their exit orifices, or upon a limited number of coplanar recesses im-pressed or scratched into the surface of a disc, the present invention employs a microporous capillary element containing a 20 myriad of pores therethrough which may communicate with each other and which are open at the surfaces of said eleme~t in the form of capilllary exit ori~ices. Such elements can be manufac-tured to provide a multitude of uniform pores of any desired mi-croscoplc size and are commercially-available, such as from the Millipore Corporation9 as discussed supra. Different capillary sizes are required for different liquids having different surface tensions and viscosities and also for different filtering proper-ties in cases where ~iltratlon of the liquid is required.
Brief_Descr~ion of the Drawings FIG. 1 is a perspecti~e view of a nebulizer assembly according to one embodiment of the present invention, the ele-ments thereof being shown spaced for purposes of illustration;
FIG. 2 is a diagrammatic partial cross-section of the nebulizer device of FIG. 1, illustrating the elements in magni-fied assembled position and in operation;
FIG. 3 is a perspective view of a unitary mixing element suitable for use in the nebulizer assembly of FIG. 1; and FIGS. 4, 5 and 6 are diagrammatic cross-sections of nebulizer-assemblies according -to other embodiments of the pre-10 sent invention;
FIG. 7 is a view of the nebulizer of FIG. 6 taken alongthe line 7-7 thereof.

Detailed Description Capillary nebulizers, such as those of the present inven- - --tion and those o~ our aforementioned parent application Serial No. :28~.2~, cause a liquid, such as wat~r, to be filmed and dlspersed in a propellant gas, such as air, in the form of a - -continuous and uniform, stable, ultrafine dispersion having the 20 appearance of a natural fog and containing the llquid in the form of particles having a geometric mean diameter of less than ~: ~ about ~ microns. This is accomplished by subJecting the liquid ~ to three different, yet cooperative, forces whlch cause the li-: quid to flow from its container, -to be drawn into thé thinnest possible continuous film and to be dispersed in the propellant gas as an ultrafine disperslonf and equilibrium being established between the rate of supply and dispersio~ of said liquid, which equilibrium is not affected by gravity, vibration or other ex-ternal forces.
~0 The nebulizers of our parent application, as well as those of the present invention comprise a mixing element having thin liquid passages adapted to convey liquid therethrough as a thin liquid stream, and capillary liquid orifices or exits from said liquid passages opening onto a filming surface. The rnixing ele-ment also comprises a propellant gas orifice which is an edge of said filming surface, sufficiently spaced from said liquid ori-fice that the thin liquid stream which exits said liquid orifices and adheres -to said filming surface is caused to flow over said filming surface, forming a continuous film of the liquid which is even thinner than the thin liquid stream which exits the li-10 quid orifices and which reaches its thinnes-t possible, yet con-tinuous, state at the edge of -the filming surface which comprises the gas orifice. At this point, the thin liquid film is drawn into the flow of propellan-t gas flowing through the gas passage which comprises the gas orifice.
The three separate forces acting upon the liquid in the nebulizer devices of the parent application and of the present invention are (1) sufficient pressure on the liquid up stream (behind) the liquid orifice to overcom~ the capillary forces which retain the liquid within the liquid passage(s) and/or the 20 liquid orifice(s) thereof to ~orce the liquid out of -the liquid orifices; (2) adhesive force between the llquid and filming sur-face, which adhesive force causes the liquid e~iting the liquid orifices to~adhere to and spread over the filming sur~ace; and - (3) cohesive force which (a) causes the thin liquid film to re-tain its continuity as the liquid is drawn over the fllming sur-face, and (b) also causes the liquid being removed from the edge of the filming surface at the gas orifice into the flow of pro-pellant gas to draw to the edge o~ the filming surface liquid on the f:ilming surface. An equilibrium is es-tablished between the 30 rate at which the liquid is supplied to and removed from the filming surface to maintain liquid on the filming surface in the form of a continuous film extending from the liquid orifices to the gas orifice. The thinnest possible continuous ~ilm on the filming sur~ace produces the finest possible uninterrupted fog and such a state of preferred equilibrium can be attained by either reducing the rate of the liquid supply or increasing the rate of the gas flow until the liquid film breaks as evidenced by a cessation or pulsation o~ fog emission. Thereafter, the liquid supply rate is increased slightly or the gas supply rate 10 is reduced slightly until continuous fog emission resumes.
If the exceedingly thin liquid film is drawn from the ~ilming surface into the gas ~low substantially simultaneously with the dispersion of said gas flow into a large receptacle or open space, -the expansion of the gas disperses the thin liquid ~ ;
film as fine particles and prevents the fine particles of liquid from coalescing into large droplets.
The present invention resides in the discovery of a novel means for providing capillary liquid passages and exit orifices for pneumatic nebulizers of the general type disclosed in our 20 aforementioned parent application, Serial Mo. 285,2~, which :
no~el means has the advantages of (a) providing a myriad of ran-dom, interconnected, capillar~ liquid passages~and exit orifices which provide alternate liquid routes when portlons thereof be-co~e blocked with solid impurities carried by the liquid; (b) being available in different known capillary sizes to provide precise filtering properties 1~here desirable, and (c) being inter-changeable and replaceable if necessary or desira~le.
Small liquid exit ori~ices are essential to the present nebulizers because capillary ~orce tends to hold the liquid in 30 the liquid passages, if the exit ori~ices are very small, until C201~A
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the combined pulling and pushing effects of the various other forces acting on the liquid exceeds the capillary force. The smaller the liquid exit orifices, the greater the capillary force, and consequently, the greater must be the combined pulling and pushing effects of the various other forces acting on the liquid -to draw-push liquid out of the liquid orifices. The force required to cause liquid to ~low out of the very small, capillary liquid orifices can be greater than the net effect of the com-bined push and pull on the liquid in the liquid passages and ~0 orifices resulting from (a) the cohesive force which draws the liquid across -the filming surface; (b) the adhesive force which draws the liquid onto the filming surface; (c) the gravitational force on the liquid in the liquid passages and orifices; and (d) the differences between the liquid pressure behind the liquid orifices and the ambient pressure at the mau~h of the liquid ori- ~-fices. When the strength of the capillary force retaining the liquid in the small liquid passages and orifices is greater than the net effect of the combined push-pull effect on the liquid in the liquid passages and orifices of the adhesive force, the co-20 hesive force, gravity and the difference in pressure - the liquid will not flow out of the liquid orifices. As a consequence, it is possible by use of sufficiently small liquid exit orifices to ; supply liquid to the filming surface at an adjustable stable very ]ow rate of flow regardless of the drawing power of the cohesive force, andlor regardless of the drawing power of the adhesive force, and/or regardless of the ambient pressure at the mouth of ; - the liquid orifibe by simply controlling the rate at which li-quid is supplied to the liquid passages at a sufficient pressure to ~orce the liquid therethrough. This would not be possible -30 i.e., supplying liquid to the filming surface at an adjus-table C201-~

stable low rate of flow by simply regulating the rate a-t which liquid is supplied to the liquid passages and exit orifices -if the liquid exit orifices were not critically small as defined herein. This is because if the liquid exit orifices were not critically small and liquid was supplied thereto at a controlled low rate, the cohesive force between the liquid being removed from the filming surface at the gas orifice and the liquid ~ilm on the filming surface, which cohesive force draws liquid from the liquid orifices across the filming surface to the gas ori-10 fice, in conjunction with the adhesive force, and for downwardsloping liquid orifices -- in conjunction with gravity, would draw liquid out from within the interior of the liquid passages, i.e., tunneling into -the liquid orifices. As liquid is supplied to the liquid orifices at a controlled low rate, liquid would be drawn from the mouth of the liquid orifices faster than liquid was supplied to the liquid orifices until the interior of the - liquid orifices had been emptied for some distance within the liquid passages and the liquid ceased flowing out of the liquid orifices. Thereafter, liquid flowing into the liquid passages 20 at the controlled low rate would refill the liquid orifices and ultimately cause liquid to flow out of the liquid orifices onto the filming surface. When the liquid on the filming surface con- -tacte~ the gas flowing from -the gas orifice, the liquid on the filming surface would be drawn into the gas flow, re-establishing the drawing force between the liquid being removed from the film-ing surface and the liquid on the filming surface, starting the cycle again. The end result is the pneumatic nebulizer operated in pulses.
The fact that for critically small capillary liquid ori-30 fices, liquid may be supplied to the filming surface a-t an adjust-able low ra-te of flow which is steady and continuous regardless of the orientation in space of the liquid orifices or the strength of the adhesive and cohesive forces, makes it possible to set the rate of flow to less than the rate at which the cohesive force between the liquid being removed at -the gas orifice and the li-quid remaining on the filming surface is capable of drawing li-quid from the liquid orifices. This rate differential makes it possible to s-tretch the liquid on the filming surface to a stable stretched exceedingly thin liquid film.
It is critical to the invention described herein that the liquid orifices be sufficiently small so that the net push-pull 10 effect of the various forces acting on the liquid in the liquid orifices) other than capillary force, can be adjusted to be less than the capil~ary force, i.e., can be adjusted to stop the li-quid flow at the mouth of the liquid orifices. The critical di-mensions of the liquid orifices for any particular application depends on the relationship between the size of the liquid ori-fices and the strength o~ the capillary force, the strength of the pulling effect on the liquid in the liquid orifices of the cohesive force which draws the liquid across the filming surface, the strength of the pulling effect on the liquid in the liquid 20 ori~ices of the adhesive force between the liquid and the filming surface, the positi~e or negative strength of gravitational force along the axis of the liquid orlfices and the positi~e or nega tive strength of the difference between the pressure in the li-quid behind the liquid orifices and the ambient pressure at the mouth of the liquid orlfices.
An additional consequence of the liquid exlt arifices being sufficiently small so that the net push-pull effect of the ~arious forces acting on the liquid in -the liquid exit orifices 9 other than capillary force, ~an be adjusted to be less than the 30 capillary force, is that pneumatic nebulizers based on the within in~ention may be operated in any direction, such as straight down, -1~-and will also operate under vibration. Because the li~uid ori-fices of pneumatic nebulizers based on the within invention are of critical size as defined herein or smaller, liquid will not flow from the liquid orifices at a rate greater than the con-trolled supply rate. This fact, in conjunc-tion with the fact that the adhesive force between the liquid and -the filming sur-~ace causes the liquid on the filming surface to adhere to the filming surface, prevents liquid from dripping from the pneumatic nebulizer regardless of its orientation in space or ~ibration, ~0 so long as the liquid supply rate does not exceed the rate at which li~uid is remo~ed from the filming surface by the gas flow.
The present inv~ntion is based upon the discovery that the size requirements for the liquid exit orifices of pneumatic nebu-lizers of the general type disclosed by our aforementioned appli-cation Serial No. 2~5,2Z2 are satisfied conveniently and most beneficially by the use of a microporous member or filter of the type which is commercially-available for ultrafine or microscopic fi}tration purposes. ~uch members are available in the form of sheets or membranes of various thicknesses, as thin as from about 20 125 to about 150 ~ m, and comprislng a skeletal network or sponge system of pure, biologically-inert cellulose esters or ~arious ot~e-r polymeric materials containing an interconnected capillary pore system extending therethrough in all directions. They are available in a variety of different precie-~ mean pore sizes rang-ing down to about 0.025 ~ m and ha~e high porosity, with as much as about 84% of their volume consisting of pores. They have high degrees of permeability permitting hi~h flow rates with respect to liquids and gases. They also have excellent retention or fil-tra-tion properties for solid particles carried by the liquids or 30 gases ~eing passed therethrough, the minimum size of the solid -12~

~201-A ~7~

particles being retained thereby being determined by the mean pore size of the particular microporous member selected. rne microporous members consist o~ a myriad of pores per square inch of surface area which may be interconnected so that a large num-ber of solid particles or impurities can be retained or trapped at the entrances of the pores passing through the member without substantially reducing the flow rate of the liquid or gas being pass0d therethrough due to the availability of a myriad of alter-nate random passages throughout the thickness of the member.
FIGS. 1 and 2 of the drawing illustrate a uni-tary nebu-lizer device adapted to be connected by valve means to adjustable sources of a liquid and a gas to cause atomization of the liquid in the form of an ultrafine stable ~og. The de~ice 10 comprises a circular base plate 11 having a central opening 12 adapted to be connected to a pneumatic conduit 13 and having an offset open-ing 14 connected to a liquid-supply tube 15. The base plate 11 is seallngly connected to a cir~u~ar:top~;1p~ate 16 by means of a compressible outer ring gasket 17 and a compressible inner washer gasket 18 which sealingly confines between itself and the under-20 surface of top plate 16 circular mloroporous disc 19 and circular filming disc 20. Four bolts 21 and nùts 22 unite plates 11 and 16 with an adjustable pressure~ due -to the oompressibility of gaskets 17 and 18. The plates 11 and ~6 and gaske-t 1~ are pro-vided with central openings 12, 23 a-nd 24 respectively, and the discs 19 a~d 20 are also pro~ided with central openings 25 and 26) the latter being smaller in diameter than openings 23~ 24 and 25, and forming a restricted sharp-edged gas orifice through which the gas from the pneumatic conduit 13 must pass. Hole 25 in the microporous disc 19 is substantially larger in diameter 30 than hole 26 in filming disc 20. The liquid which passes through the pores 28 in microporous disc 19, which pores comprise the myriad o~ capillary liquid passages, exits through the numerous small liquid exit orifices 30, which comprise the pores exposed at central opening 25. The liquid exits onto the filming sur-~ace 29 of lower disc 20 within hole~ 25 of top disc 19 and lays down as a thin layer on surface 29 in the center of disc 20, shown by broken lines, as it is drawn to the edge of the ~ilming surface a-t central opening 26 ~hich comprises a restriction in the gas conduit.
All ~ive central openings are coaxial in the assembled device to form a gas-flow passage. The ~low o~ the gas through the most restric-ted ori~ice 26, which is the gas orifice, causes the gas to ~orm a vena contracta at a distance beyond orifice 26 equa1 to approximately one-half the diame-ter thereo~, and then to expand in a pattern as illustrated by FIG. 2.
As illustrated, the sealed confinement of gaskets 17 and 18 between plates 11 and 16 provides a circular chamber 27 to which liquid supplied to the device through supply tubé 15 has access. - -The circular discs 19 and 20, with their aligned central openings 25 and 26, have conforming surfaces which lie in sealing engagement with each o-ther. Upper microporous disc 19 is pro-vided with a myriad of uni~orm pores which form liquid passages located between the filming disc 20 and the undersurface of top plate 16, which passages or pores have entrances at the periphery of disc 19 and communicate with the central opening 25 of disc 19 by means of numerous liquid exit orifices 30 which exit into the central opening 25 adjacent filming surface area 29 of filming disc 20, shown by broken lines in FIG. 1 and also shown in FIG. 2.
In operation~ a gas lS supplied through pneumatlc conduit 13 so that it ~lows force~ully through openings 12~ 24, 26, 25 . ' ; , ~

and 23 and exits into the atmosphere, forming a vena contracta and an unobstructed flow pattern as shown by FIG. 2. A liquid is supplied at a controlled rate -through supply tube 15 to cir-cular chamber 27 where it is sealingly confined except for escape through the pores 28 of rnicroporous disc 19, which pores comprise very narrow liquid passages or capillaries through disc 19, which passages have their exit orifices 30 at central disc opening 25. The pressure of the liquid provides a con-tinuous supply of the liquid so that the microporous disc is saturated with the liquid and the liquid extends to and fills the exit orifices 30 adjacen-t the filming surface 29. As illus-trated by FIG. 6, the liquid is attracted to receptive filming surface 29 in the area between the central openings 25 and 26 of the discs and forms a very thin film of the liquid ha~ing a thickness of less than 0.010 inch.
The thin liquid film covers surface 29 and extends to central gas orifice 26 where i-t is e.xposed to the blast of the gas flow from pneumatic conduit 13. The thin liquid film is immediately reduced to an ultrafine dispersion of liquid parti-: 20 cles having a geometric mean diameter of about 3 microns or lesswhich are carried through opening 25 by the propellant gas in the form of a stable fog ~s illustrated by FIG. 2. In the em-~: bodiment illustrated by FIG. 2, the thin liquid film enters the gas flow as:the gas flow approaches its vena contracta and the liquid i5 reduced to the ultrafine dispersion. mereafter, the gas expands in a patternt as illustrated, and flows unobstructed into the atmosphere due to the chamfered structure of orifice 23 of the top plate 16. If oriflce 23 is not chamfered~ the gas flow might strike the inner surface of the orifice depending upon the gas pressure and the thickness of the plate 16. Thiswould cause the dispersed liquid particles to wet said surface ~15~

and flow back into orifice 25 and would also cause a vacuurn to be created in orifice 23 above disc 19.
The filming disc 20 of FIGS. 1 and 2 is preferably formed of smooth stainless steel having a thickness of at least about 0.01 inch -to prevent flexing of the disc. Because of the tight supporting contact between the discs 19 and 20 and plate 16, liquid is prevented from passing therebetween and must flow through the microporous disc 19.
It appears that the impro~ed performance of the present nebulizer devices is due to a number of important cooperative features. First, the constant supply of the liquid -through the myriad of uniform capillaries of the microporous disc 19 causes the liquid to exit from orifices 30 in the area of the central -disc opening 25 at a uniform, const~n-t rate, regardless of the accumulation of a substantial number of solid impurities in disc 19 or on its periphery, and causes the liquid to be drawn across filming surface 29 as a very thin filament or film of liquid s~ having a thickness of from about~h~t inch down to the smallest possible continuous thickness, from which condition the liquid is reduced to a multiplicity of extremely fine liquid particles at gas orifice 26.
A second cooperative feature of the present devices is the provision of a continuous gas flow at an angle to, preferably substantially perpendicular to, the direction of flow of the li-quid film on filming surface 29, which gas flow passes through the central disc opening 26 and draws or pulls the thin liquid filament or film from surface 29 at the edges of Gentral gas orifice 26 as an exceedingly thin liquid filament or film and disperses the liqui~ in the form o~ minute particles. Because the liquid film adjacent gas orifice 26 is exceedingly thin, it shatters when drawn into and struck by the gas flow, forming a .

multiplicity of microscopic liquid particles having a geometric mean diameter of less than about 3 microns which are carried along in -the gas flow.
A third cooperative feature~ according to a preferred embodiment, is the abrupt restriction in the gas flow provided by central orifice 26 in disc 20 which forms a sharp-edged gas orifice. The gas flow contracts as it flows from the wide area under disc 20 through the narrow area of hole 26 in disc 20.
The gas flow continues to contract for some distance beyond disc 20. The point of greatest contraction is the vena con-tracta o~ the gas flow pattern and is shown in FIG. 2 as the most narrow portion of the illustrated gas flow pattern. The gas flow reaches its greatest velocity at this point and there-after the gas flow pattern diverges. Because the gas flow carries away everything contacting it as it leaves gas orifice 26 in disc 20~ a slight vacuum is created in the area of ori-fice 26 which helps the cohesive force between the departing liquid and the liquid on surface 29 drawn or pull the thin liquid film towards orifice 26 and into the gas flow. The rate at which the liquid film is drawn over the filming surface 29 and into the gas flow will depend in part upon the characteristics of the li quid and in part upon the pressure under which the gas is forced through gas ori~ice 26 and in part upon the rate at which the liquid is supplied to liquid chamber 27~and through the micro-porous disc 19. The finest possible fog is produced by main-taining the rate of removal and the rate of supply of liquid to ~ilming surface 29 at that equilibrium which results in an exceedingly thin continuous filament or film of liquid on sur-fa¢e 29 adjacent gas orifice 26 This is accomplished by supplying liquid through conduit 15 at a slow and steady rate and under slight, but sufficient, pressure to force a slow steady flow of liquid through the microporous disc 19 and out C201-A ~ ~ ~

of orifices 30 at opening 25 onto filming surface 29 where the liquid can be drawn across surface 29 as a very thin filament or film by the cohesive forces between the liquid being re-moved from surface 29 at gas orifice 26 and -the remaining li-quid on surface 29 and by the suction created by the gas flow.
A fourth coopera-tive feature of the present devices, according to a preferred embodiment of the present invention, is the unobstructed passage of the liquid-particle-carrying gas flow into the atmosphere or into a larger chamber being supplied thereby. This is accomplished by excluding from the pa-th of the gas flow any portion of the device which could be contracted by the diverging gas flow pattern. Thus, if the device has a top plate or other element beyond the central discs, which would normally be contracted by the expanding gas flow, the central orifice of such top plate or other element must be sufficiently large or the plate must be sufficiently thin or must be outward-ly chamfered, as shown by FIG. 2, -to prevent -the gas flow from striking the surface of the plate or other element before it escapes into the atmosphere. If the expanding gas flo~ pattern strikes the surface of the plate or a~y other solid surface in the vicinity of the disc openings, the dispersed liquid particles will coalesce on that surface and increase in size until the sur-face becomes wet with the liquid and droplets form thereon.
Many of said droplets will be blown off the surface on which they form by the flowing gas, thereby contaminatlng with rela-tively large droplets the fine dlspersed liquid particles con-tained in the flowing gas. In addition, if the expanding gas flow pattern strikes the central orifice of the top plate, some of said droplets will run dow~ thè sides of the central orifice and onto disc 19, eventually entering central opening 25 and flooding the filming surface 29, This is a second source of C201-A ~ ~ ~ ~

large liquid particles in the gas flow because the liquid which enters in the area of the cen-tral disc opening 25 augments, and thereby makes thick, the -thin liquid film on the filming sur-face 29, resul-ting in a flooding of gas orifice 26 and the forma-tion of oversize droplets in the dispersion.
In some instances where the atmosphere being treated is itself contained within a confined receptacle, such as in the case of automobile carburetors, face mask~, inhalation devices, etc., the advantages discussed above resùlting from the unob-struc-ted passage of the liquid-containing gas flow or fog must be compromised to some extent, but in all cases the liquid on the filming sur~ace 29 is in the form of a very thin film having a thickness of less than 0.001 inch when the gas flow contacts the liquid at orifice 26. ~he gas then flows into a larger area so that the gas may expand for at least some distance to permit at least a substantial percentage of the fine liquid particles to become widely dispersed.
As discussed supra, the passage of the gas flow from a large space to a confined, narrow space as it passes from the `
space under disc 20 through the sharp-edged, restricted central opening 26 thereof and into the larger space in the area of opening~25, causes the formation of a vena contracta and then a substantial dispersement o~ the gas flow7 ~ith attendant reduc-tion in gas pressure. The thin liquid film is drawn into the gas ~low in the vicinity of the vena contracta. This causes the already-thin ~ilm of liquid to be torn apart by the fast moving gas in the vena contracta with resultant formation of exceptionally fine liquid particles to the apparent exclusion of liquid particles greater than about 20 microns in diameter and probably even to the exclusion of liquid particles~greater than about 10 microns in diameter. The liquid particles are immediately dispersed by the expansion of the gas flow beyond the vena contracta. The emitted liquid dispersion has the appearance of a fine, stable fog.
It is an important requirement of the present invention that the gas flow be substantially continuous and of sufficient velocity that the liquid film be blown from the edge of filming surface 29 at orifice 26, causing liquid to be drawn at a regu-lar uniform, rate across surface 29 from the exit orifices 30 10 of microporous disc 19.
Preferably, the gas and liquid supply are pressurized but this is not necessary in cases where there is a vacuum in the receptacle or atmosphere being treated such as in the case of an automobile manifold. The manifold vacuum creates a suction in the area of the gas orifice 26 and the liquid exit orifices 30, causing the gas, i.e., air, to be sucked through-its orifice and causing the liquid, i.e., gasoline, to be sucked through its orifices and dispersed into the air flow for vaporization and perfect combustion.
. 20 FIG. 3 illustrates a disc 31 which may be substituted ~ for disc 19 of FIGS. 1 and 2, disc 31 being illustrated with ; disc 20 in inverted position for purposes of illustration.
Thus, filming disc 20 has a smooth upper-surface and a small central opening 26 comprising the gas orifice, while the disc 31 has a larger central opening 32 and a surface 33 comprising a multiplicity of interconnected recessed areas 34 of uniform size and depth surrounded by a multiplicity of peaks or plateaus 35 of uniform height. Such disc surfaces may be formed by sand-blasting or otherwise chemically or mechanically etching the 30 surface in a uniform and controlled manner whereby the original ~'~

thickness of the disc is substantially retained in spaced areas of plateaus 35 surrounded by valleys or recessed areas 34 which are interconnected and which extend from the periphery of' the disc to the central orifice 32, as illustrated. Uni~ormly roughened surfaces of this type are receptive to liquids, due to their proslty. ~he passages are particularly resistant to becoming clogged because of the myriad of liquid orifices which provide alternative routes or passages for the liquid. When the discs 31 and 20 are placed together with the surface 33 being pressed tightly against the smooth surface of lower disc 20, they constitute micorporous means defining a multiplicity of interconnected capillary passages formed by the recesses 34 and extending from entrances at the outer periphery of disc 31 to exit orifices at central orifice 32 opening onto the filming surface 29 of disc 20.
Suitable surfaces for the disc 31 may also be formed by pressing the disc against a die having an inversely-correspond-ing rough surface or, in the case of plastic discs, casting or molding the disc against a casting or molding surface having 20 an inversely-corresponding rough surface. It should be no~ed that the filmirlg surface 29, being that part of the upper sur-face of lower disc 20 lying between opening 32 in upper disc 31 and opening 26, need not be smooth. The cohesive force between the liquid being drawn into the gas flow and the liquid still present on the filming surface will draw the liquid across both rough or smooth surfaces.

As an alternative means f'or forming the surface on disc 31, it is possible to apply a discontinuous layer of suitable material in a thickness of 0.01 inch or less to the surface 30 o~ the discs or plates rather than removing surface material . , . ~ .

`from the discs or plates. The end result is similar in appear-ance and function to the disc 31 of ~IG. 3, for instance, the raised areas 35 surrounding the shallow recessed areas or pores 34 being formed by applying a uniformly-thin discon~inuous coating of inert material such as synthetic resin or metal to the smooth surface of' the disc. This may be done using photo-sensitive resinous compositions which are exposed through a negative and then removed f'rom the unexposed areas which will correspond to recessed areas 34, or by vacuum deposition of a metallic layer using a stencil to prevent deposition in the spaced areas which will correspond to recessed areas 34. The discontinuous coating may also be applied by speckle coating techniques where specks of suitable composition are sprayed onto the surface of the plate or disc to form a muliplicity of spaced peaks 35 of uniform height equal to 0.01 inch or less - over the entire surface of the plate or disc. A similar result may be obtained by applying uniformly-sized particles of heat-fusible metal or plastic powder to the disc surface, such as by electrostatic techniques, and then heat-fusing or sintering the particles to each other and to the disc surf'ace. Other suitable methods will be apparent to those skilled in the art in the light of the present disclosure, the essential require-ment being that the eventual passages are suffi`ciently fine to retain the particlar liquid used therewit~h by capillary attrac-- tion.
FIGS. 4 and 5 illustrate alternative designs for pneu-matic nebulizers which are particularly adapted for oil burner use. Referring to FIG. 4, the nebulizer 36 thereof comprises an outer casing 37 which may be cylindrical. Within the outer 30 casing 37 is an interior gas conduit or tube 39 having a gas passage 40 having an entrance communicating with a pressurized .LP
~11 `. ~, . . .: . . ~ .

~7~

gas supply and having an exit at gas orifice 41. The outer diameter of tube 39 is sufficiently smaller than the inner diameter of casing 37 as to provide therebetween an annular -22a-;'~ ' ~!

.. ..

space comprising a li~lid passage 42 having an entrance com-municating with a pressurized liquid supply and having an exit comprising an a~nular microporous capillary member 43 which functions as a liquid-permeable seal between casing 37 and gas conduit 39. Member 43 is similar -to the microporous disc 19 of FIGS. I and 2 in that it consists of a relatively rigid skele-tal network, such as a sintered bronze pellet ~ilter, con-taining a myriad of interconnected pores which communicate with each other to form liquid passages which extend generally per-pendicular to the plane of -the filming surface and which open to the atmosphere at upper surface 44 in the form of a myriad of small liquid exi-t orifices adjacent to and generally on the same plane as the smooth, annular, flat filming surface 38 of the gas conduit 39. The upper surface 44 of the microporous member 43 is on the same plane~as~ or on a slightly higher plane than, the ~ilming surface 38 so that liquid e~iting mem-ber 43 at surface 44 is drawn towards the gas orifice 41 and forms a ~ery thin film on the filming surface 38 for which it has an affinity. me gas flowing through passage 40 contacts the thin liquid film at the inner edge of -the filming surface 38 at gas orifice 41 and reduces the liquid film to an ultra~
fine dispersion, The capillary properties of member 43 are such that the liquid will be retained therein, even if the nebulizer is turned upside down, unless the liquid is forced therefrom under pressure.
The nebulizer 45 of FIG. 5 is similar to that of FIG. 4 and identical numbers are used to identify identical elements thereof. Thus, it comprises an outer casing 37, which may be cylindrical, an interior gas sonduit or tube, numbered 47 in FIG. 5, a gas passage 40, a liquid passage 42 and a microporous member 43 at the exit of the liquid passage 42 which opens to - ~201-A

the atmosphere at upper surface 44 of the microporous member 43.
The essential dif~erence between the nebulizers of FIGS. 4 and 5 resides in the fact that the gas conduit or tube 47 has a re-stricted sharp-edged gas orifice 48 so tha-t -the filming sur-face 49 extends beyond the inner surface 46 of the gas conduit 47. The movement of the gas through the restricted gas orifice 48 produces a vena contracta in the gas flow, resulting in a greater shock to the liquid film at the upper edge of the film-ing surface 49 at orifice 48 and the production of a most ultra fine dispersion of the liquid in the gas.
In cases where -the nebulizers of FIGS. 4 and 5 are used to produce sterile dispersions, member 43 should be a micro-porous member of sufficiently small pore size and a similar mi-croporous member of sufficiently small pore size should be placed as an obstruction within -the gas conduit 39 or 47 so that the liquid and the gas passing through each is cleansed of all dust, germs, microorganisms or other minute solid particles.
Since the microporous members can have the required degree of uni~orm microscopic porosity and permit high flow ra-tes, they may be located as described herein -to provide any high degree of ~i!ltr~ion of both liquid and gas immediately prior -to the dispersion of the liquid in the gas, therbby minimizing solid contamination in either mate~ial.
e oil burner of FIG. 4 or FIG. 5 may be provided with a spaced baffle plate, combustion cone and/or exterior chimney eleme~t as illustrated by FIGS. 5 and 6 of our parent applica-tion, Serial No. 285,2Z~ Such elements permit the intake of additional atmo$pheric air for combustion purposes, shield the nebulizer and microporous member from the heat of the combus-tion, and improve ~he heat-radiation properties of the burner, as taught by said co-pending application.

FIG. 6 and 7 illustrate a simplified, unitary nebulizer 51 which is adapted for single, throw-away use, if desired.
Nebulizer 51 comprises a unitary metal or plastic casing 52 which sealingly confines a ring-shaped microporous element 53 in cen-tered position between the top wall 54 and the bottom wall 55 thereof, The bottom wall 55 of the casing 52 is pro-vided with a small central hole comprising a gas orifice 56 and with a downwardly-extendin~ flange or short gas conduit 57 which has an inside diameter larger than gas orifice 56 and an 20 outside diameter adapted to be tightly engaged by a flexible -rubber hose which is connected to an adjustable pressurized gas supply. Also illustrated is the presence of an optional microporous, gas-permeable member 58 within gas conduit 57 adjacent gas orifice 56 which functions to filter the gas, such as air, passlng therethrough in cases where such is neces-sary. Bottom wall 55 is also provided with a peripheral down-wardly-ex~ending flange or short liquid conduit 59 which opens in*o an annular space or liquid passage 60 which extends ar~und the periphery of the microporous ring member 53 due to the fact that the outer diameter of centered member 53 is less than the inside diameter of casing 52, as shown in FIG. 7. Liquid con- -- -duit 59~has an outside diameter adapted to be tightly engaged by a flexible rubber hose connected to an adjustable pressurized liquid source. Finally~ the top~wall 54 of casing 52 is pro- -vided with a relativ0ly large central hole 61 which is similar in size to the central hole 62 in the microporous member 53 and is bevelled downwardly adjacent said hole to provide a centering, restraint edge whlch engages the interior edge or exit ori~ice wall 63 of the ring-shaped microporous member 53 to maintain said member in centered position relative -to the gas orifice 56.

~25-The pneumatic nebulizer of FIGS. 6 and 7 lunctions in the same manner as those of FIGS. 2 and ~ in providing a gas flow which forms a vena contracta due to its passage through the sharp-edged, restricted gas orifice 56. When a pressurized liquid is supplied to -the annular liquid passage 60 through li-quid conduit 59, it fills passage 60 and impregnates the micro-porous member 53, being absorbed within all of the capillary passages extending therethrough. If the liquid supply is shut off a-t this point, the liquid will be retained within the micro-porous member 53 by capillary attraction and will not flow outonto the upper central surface or filming surface 64 of the bottom casing wall 55 even if the device is turned on end or upside down When the pressurized liquid supply is resumed and pressur-ized gas is supplied through gas conduit 57, filter 58 and ori-fice 56, the capillary restraint to the liquid flow is overcome and liquid flows out of the myriad of micropore~or liquid exit orifices present at the interior wall 63 of the microporous member 5~ said liquid being drawn over the filming surface 64, which has an affinity there~o~, in the form of a very thin, con- -tinuous liquid film whi¢h becomes thinner as it is drawn towards the central edge of the filming surface comprlsing the gas ori-fice 56. The force o~ the filtered gas flow~ as it approaches its vena contracta, bla~ts the thin li~uid fllm into mi~te par-ticles forming an ultra~ine dispersion.
The present nebulizer devioes, suoh~as those o~ FIGS. 6 and 7, can be made exceptionall~ small in size and sufficiently , inexpensive as to~justify disposing thereof after a single use or a limited period of use, i.e., they may bé used on sealed ~0 aerosol spray cans containing a liquid and a pressurized pro- -pellant gas. Since microporous members useful according to the ~'~
present invention may be made at any desired size, it is clear that unitary nebulizer devices of the structure illustrated by FIGS. 6 and 7 can be made exceptionally small.
It should be understood that microporous members of various types, sizes and qualities may be used according to the present invention, depending upon the specific requirements.
Such members are generally relati~ely rigid so as to resist com-pression and change in pore size but such is not a requirement where the member is mounted in fixed relaxed position within a casing or other container, pro~ided that the member is suffi-ciently rigid to resist major distortion under the ~orce of the pressurized liquid supply.
~ iologically-inert microporous members of very small pore size, such as Millipore membrane filters, may be required ~or both the llquid supply and -the gas supply where sterile dispersions are necessary, such as in inhalation therapy de-~ices, hospital humidifier systems, incubators, etc. However, where filtration of the liquid is not required and the micro-porous member functions only to pro~ide a myriad of liquid capillaries which offer capillary restralnt against the ~low or drawing of the liquid contained therein, in the absence of applied force, numerous other microporous materials may be used provided they are substantially inert to the particular liquids and gases used therewith and are heat-resistant, ~Jhere necessary. Such materials include fine sponges, both natural and of the synthetic resin type, dense fabrics such as felt~
heat-resistant, sintered metal as currently used to filter fuel oil in fuel burners, heat-resistant, porous ceramics as currently used in gasoline filters and any other inert microporous materials which pro~ide capillary attraction for the particular liquids with which they are used.

C201~A

An essential feature of the presen-t invention is that the microporosity of the exit orifices of the microporous element or filter be sufficiently small or fine so that liquid is not drawn from the liquid exit orifice excep-t as liquid is supplied to the liquid-saturated microporous element, That is, liquid is no-t dra~n ou-t from -the interior of the microporous element because of the smallness or fineness of the liquid exit orifices. The net combined effects of the other forces acting on the liquid, in the absence of more liquid being supplied to 10 the microporous member, are insufficient to overcome the capil-lary forces which restrain the liquid flow, Consequently, liquid does not flow from the liquid exit orifices onto the filming sur-face except as liquid is supplied to the microporous element.
It is this essential feature -- liquid flows onto -the filming sur-face from the liquid exit orifices at the same steady rate at which more liquid is supplied to the liquid orifice -- which makes it possible to supply a steady flow of liquid to the film-ing surface at a controlled low rate, which rate can be set to be less than the rate at which the cohesive force between the liquid 20 being dispersed at the gas orifice and the liquid on the filming surface is capable of drawing liquid from the liquid orifice.
The fact that the liquid may be supplied to the filming surface at a steady rate which is less than the rate at which the cohe-sive force between the liquid being dispersed at the gas orifice and the liquid on the filming surface is capable of drawing li-quid from the liquid orifice makes it possible to stretch the liquid on the filming surface to a stable stretched exceedingly thin liquid film~ This essential feature, in conjunction with the adhesive force between the liquid and the filming surface, 30 permits pneumatic nebulizers based on the present invention to operate in any direction, such as straight down, and/or under vibration.

I

The controlled flow of liquid through the narrow liquid orifices can be achieved by any of a number of possible means which either control -the pressure of the liquid upstream of the exit orifices relative to the ambient pressure at the mouth of the exit orifices or control the rate at which liquid of suffi-cient pressure is supplied to the exit orifices. The rate of flow of the liqllid through the orifices may also be controlled en-tirely or in part by utilizing various sized orifices, pro-vided~ of course, they are sufficiently small as described above and the liquid's upstream pressure is sufficiently high.
It should be ~mderstood that -the specific structures of the nebulizer devices set forth in the figures of the drawing ~ -are not critical except with respect to accommodating the pre-sent mixing elements and that variations will be apparent to those skilled in the art for purposes of simplification or modi- -fication of the devices to a par-ticular use where size, shape, appearance or other factors are to be considered.
~ ariations and modifications may be made within the scope of the claims and portions of the improvements may be used with-out others, ~0

Claims

The embodiment of the invention in which an exclusive property or privilege is claims are defined as follows:

1. A nebulizer device capable of reducing a flowable liquid to an ultrafine dispersion of liquid particles in a pro-pellant gas, comprising a mixing element comprising (a) a mi-croporous member having a multiplicity of liquid passages therethrough, said passages having entrance orifices adapted to receive a supply of said flowable liquid and exit orifices sufficiently small that when filled with said liquid, the li-quid is retained therein by capillary attraction and is pre-vented from flowing therefrom under ambient conditions except as liquid is supplied through said liquid passages to said exit orifices, (b) a filming surface communicating with said exit orifices and having some affinity for said liquid, and (c) a gas orifice comprising an edge of said filming surface spaced from said exit orifices and communicating with a gas conduit adapted to transmit a supply of gas through said gas orifice, whereby liquid which flows through said liquid pass-ages is adapted to exit said exit orifices as thin liquid streams which adhere to said filming surface as a continuous thin liquid film which extends to the edge of said filming surface comprising said gas orifice where the thin liquid film is adapted to be drawn into the gas flowing through said gas passage, the drawing of said liquid film into said gas flow causing said film to be stretched across said filming surface as a very thin continuous film of said liquid for introduction into said gas flow to form said ultrafine dispersion.

2. A nebulizer device according to claim 1 in which said microporous member comprises a skeletal network of a solid material containing an interconnected pore system comprising said liquid passages.

3. A nebulizer device according to claim 2 in which said solid material is biologically-inert.

4. A nebulizer device according to claim 2 in which said solid material comprises a polymeric material.

5. A nebulizer device according to claim 4 in which said polymeric material comprises a cellulose ester.

6. A nebulizer device according to claim 2 in which said solid material comprises sintered particles of metal.

7. A nebulizer device according to claim 2 in which said solid material comprises a ceramic material.

8. A nebulizer device according to claim 1 in which said mixing element is a unitary element comprising said mi-croporous member contained within a casing, a portion of said casing extending beyond said microporous element to form said filming surface.

9. A nebulizer device according to claim 1 in which said microporous member comprises a microporous disc or plate having a transverse opening with which said exit orifices oommunicate and which communicates with said filming surface.

10. A nebulizer device according to claim 1 in which said mixing element comprises said microporous member and a smooth member which is pressed thereagainst to form said film-ing surface.

11. A nebulizer device according to claim 1 in which the liquid passages of said microporous member extend in a direction generally perpendicular to said filming surface and said exit orifices are generally on the same plane as said filming surface.

12. A nebulizer device according to claim 1 in which said gas orifice comprises a restricted, sharp-edged orifice.

13. A nebulizer device according to claim 1 which further comprises means for controlling the rate of flow of the liquid through the exit orifices, predetermined variations in the rate of flow of said liquid causing various predetermined amounts of liquid to combine with said gas at the gas orifice to provide ultrafine dispersions having variable predetermined con-centrations.

14. A nebulizer device according to claim 1 which further comprises means of controlling the rate of flow of the gas through the gas orifice, predetermined variations in the rate of flow of said gas causing various predetermined amounts of gas to combine with the liquid at the gas orifice to produce ultrafine dispersions having variable predetermined concentra-tions.

15. A nebulizer device according to claim 1 which further comprises means for maintaining the liquid upstream of said exit orifices at a sufficiently greater pressure than the ambient pressure at the outlet of said exit orifices to force liquid through said liquid passages and out of said exit ori-fices onto said filming surface.

16. A nebulizer device according to claim 1 in which said filming surface comprises a material which has good affi-nity for the particular liquid used therewith.

17. A nebulizer device according to claim 1 in which a microporous, gas-permeable member is present in said gas conduit to filter and remove microscopic impurities from the gas being supplied to the gas orifice.

18. A nebulizer device according to claim 1 comprising a fuel burner in which said microporous member comprises a heat-resistant material and said gas orifice communicates with a combustion chamber.

19. A nebulizer device capable of reducing a flowable liquid to an ultrafine dispersion of liquid particles in a pro-pellant gas, comprising (a) a microporous member having a multi-plicity of liquid passages therethrough, said passages having entrance orifices adapted to receive a supply of said flowable liquid and exit orifices sufficiently small that when filled with said liquid, the liquid is retained therein by capillary attraction and is prevented from flowing therefrom under ambient conditions except as liquid is supplied through said liquid pass-ages to said exit orifices, (b) a liquid compartment communi-cating with said entrance orifices and adapted to supply a flow-able liquid thereto, (c) a filming surface communicating with said exit orifices and having some affinity for said liquid, (d) a gas conduit having a gas orifice comprising an edge of said filming surface spaced from said exit orifices and adapted to transmit a supply of gas through said gas orifice, and (e) means for controlling the rate of flow of said liquid through said small liquid passages, whereby liquid which flows through said liquid passages at a controlled rate is adapted to exit said exit orifices as thin liquid streams which adhere to said filming surface as a continuous thin liquid film which extends to the edge of said filming surface comprising said gas orifice where the thin liquid film is adapted to be drawn into the gas flowing through said gas passage, the drawing of said liquid film into said gas flow causing said film to be stretched across said film-ing surface as a very thin continuous film of said liquid for introduction into said gas flow to form an ultrafine dispersion containing variable predetermined amounts of said liquid and said gas.

20. A nebulizer device according to claim 19 in which said microporous member comprises a skeletal network of a solid material containing an interconnected pore system comprising said liquid passages.

21. A nebulizer device according to claim 20 in which said solid material is biologically-inert.

22. A nebulizer device according to claim 20 in which said solid material comprises a polymeric material.

23. A nebulizer device according to claim 22 in which said polymeric material comprises a cellulose ester.

24. A nebulizer device according to claim 20 in which said solid material comprises sintered particles of metal.

25. A nebulizer device according to claim 20 in which said solid material comprises a ceramic material.

26. A nebulizer device according to claim 19 comprising a unitary element including said microporous member contained within a casing, a portion of said casing extending beyond said microporous element to form said filming surface.

27. A nebulizer device according to claim 19 in which said microporous member comprises a microporous disc or plate having a transverse opening with which said exit orifices com-municate and which communicates with said filming surface.

28. A nebulizer device according to claim 19 comprising said microporous member and a smooth member which is pressed thereagainst to form said filming surface.

29. A nebulizer device according to claim 19 in which the liquid passages of said microporous member extend in a direction generally perpendicular to said filming surface and said exit orifices are generally on the same plane as said filming surface.

30. A nebulizer device according to claim 19 in which said gas orifice comprises a restricted, sharp-edged orifice.

31. A nebulizer device according to claim 19 which com-prises valve means for controlling the rate of flow of the li-quid to the liquid compartment and through the exit orifices, predetermined variations in the rate of flow of said liquid causing various predetermined amounts of liquid to combine with said gas at the gas orifice to provide ultrafine dispersions having variable predetermined concentrations.

32. A nebulizer device according to claim 19 which further comprises means of controlling the rate of flow of the gas through the gas orifice, predetermined variations in the rate of flow of said gas causing various predetermined amounts of gas to combine with the liquid at the gas orifice to produce ultrafine dispersions having variable predetermined concentra-tions.

33. A nebulizer device according to claim 19 which further comprises means for maintaining the liquid upstream of said exit orifices at a sufficiently greater pressure than the ambient pressure at the outlet of said exit orifices to force liquid through said liquid passages and out of said exit orifices onto said filming surface.

34. A nebulizer device according to claim 19 in which said filming surface comprises a material which has good affi-nity for the particular liquid used therewith.

35. A nebulizer device according to claim 19 in which a microporous, gas-permeable member is present in said gas conduit to filter and remove microscopic impurities from the gas being supplied to the gas orifice.

36. A nebulizer device according to claim 19 compris-ing a fuel burner in which said microporous member comprises a heat-resistant material and said gas orifice communicates with a combustion chamber.

37. Method for reducing a flowable liquid to an ultra-fine dispersion of liquid particles in a propellant gas com-prising the steps of:
(a) confining a flowable liquid within a microporous element comprising a multiplicity of microscopic liquid pass-ages having entrances communicating with a supply of liquid and having as the only means for escape a multiplicity of exit ori-fices sufficiently small that when filled with liquid, the li-quid is retained therein by capillary attraction and is pre-vented from flowing therefrom under ambient conditions except as liquid is supplied to said exit orifices, (b) causing said flowable liquid to flow into said entrances, through said liquid passages and out of said exit orifices onto a filming surface having some affinity for said liquid whereby said liquid forms a thin continuous liquid film having a thickness of about 0.01 inch or less on said filming surface extending from said exit orifices to an edge of said filming surface which is spaced from said exit orifices, and (c) causing a supply of gas to flow at sufficient velo-city through a gas orifice which communicates with said edge of said filming surface and against said continuous liquid film which extends to said edge, thereby causing said continuous liquid film to become stretched as a very thin continuous film of said liquid on said filming surface and to be drawn into said gas flow to form said ultrafine dispersion.

38. Method according to claim 37 which comprises main-taining the liquid upstream of said exit orifices at a suffi-ciently greater pressure than the ambient pressure at the outlet of said exit orifices to force liquid through said liquid pass-ages and out of said exit orifices onto said filming surface.

39. Method according to claim 37 which comprises con-trolling the rate of flow of said liquid through the liquid passages and their exits to cause various predetermined amounts of the liquid to combine with the gas at the gas orifice to pro-duce ultrafine dispersions having variable predetermined concen-trations.

40. Method according to claim 37 which comprises con-trolling the rate of flow of said gas through the gas orifice, predetermined variations in the rate of flow of said gas causing various predetermined amounts of gas to combine with the liquid at the gas orifice to produce ultrafine dispersions having vari-able predetermined concentrations.

41. Method according to claim 37 in which the said mi-croporous element used functions to filter and remove impuri-ties from the liquid being supplied through the microporous element.

42. Method according to claim 37 in which the gas is passed through a microporous gas-permeable member to filter and remove impurities therefrom prior to passage of said gas through said gas orifice.

43. Method according to claim 37 on which said gas ori-fice is a restricted, sharp-edged orifice and said gas forms a vena contracta into which the liquid film is drawn to form said ultrafine dispersion.

44. Method according to claim 37 in which said ultra-fine dispersion is released directly into a larger receptacle without striking any solid surface.

45. Method according to claim 37 in which said liquid is a combustible liquid and said ultrafine dispersion is re-leased into a combustion chamber and ignited.