Note: Descriptions are shown in the official language in which they were submitted.
~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-
-2- ~
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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,
--3--
C201-A
~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
C201-A
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
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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
C201
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
C201-A
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
--8--
C201~A
~3~
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
-10-
G201-A
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~-
G201-A
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
-13-
C201-A
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
. '
-14-
; , ~
C201-A
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~
- C201-A
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
.
-16-
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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
-17-
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
-19-
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
-20-
~'~
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
- 21 -
. , . ~ .
`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
-22-
`. ~,
. . .: . . ~ .
~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-
;'~ ' ~!
.. ..
C201-A
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
-23-
- ~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.
-24-
-- CZ01-A
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-
- CZ01-A
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
26
- C201-A
~'~
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.
-27-
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.
-28-
I
C201-A
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
-29
