U.S. patent number 3,584,792 [Application Number 04/817,370] was granted by the patent office on 1971-06-15 for device for liquid atomization and fluid blending.
This patent grant is currently assigned to Patent and Development of N.C., Inc.. Invention is credited to William H. Johnson.
United States Patent |
3,584,792 |
Johnson |
June 15, 1971 |
DEVICE FOR LIQUID ATOMIZATION AND FLUID BLENDING
Abstract
This disclosure relates to a method and a device for efficiently
atomizing liquids into extremely fine cloudlike particles by
discharging fluid thru one or more apertures located, preferably
between 1 mm. and 100 mm., above a controllable free surface of the
liquid to be atomized. The area adjacent to the fluid-discharging
aperture is linked to the liquid by at least two distinct wettable
surface means. In operation the liquid, at least partially due to
pressure differential, adhesion, cohesion, surface tension and
capillarity, rises to and surrounds completely the apertures. These
factors and means, along with a means of achieving a wide flat-fan
fluid dispersion and a means of varying the number of apertures,
produce a uniformly fine, highly stressed film on all sides of the
apertures and results in excellent metering control, uniform
atomization, efficient dispersion and atomization, and clogfree
operation. Secondary blending of the emitting fluid with atomized
liquid in the vicinity of the aperture by the removal of one or
more of the said liquid wettable surface means, permitting certain
apertures to emit only fluid while the remainder are emitting
atomized liquid, provides added efficiency and control.
Inventors: |
Johnson; William H. (Raleigh,
NC) |
Assignee: |
Patent and Development of N.C.,
Inc. (Raleigh, NC)
|
Family
ID: |
25222939 |
Appl.
No.: |
04/817,370 |
Filed: |
April 18, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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787974 |
Dec 30, 1968 |
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Current U.S.
Class: |
239/424;
128/200.21; 239/338; 239/433; 239/568; 128/203.12; 239/566 |
Current CPC
Class: |
B05B
7/00 (20130101); B05B 17/04 (20130101) |
Current International
Class: |
B05B
17/04 (20060101); B05B 7/00 (20060101); B05b
007/06 () |
Field of
Search: |
;239/318,358,312,337,338,418,566,421,424,433,568
;261/29,30,78,120,116 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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588,357 |
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Dec 1959 |
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CA |
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621,785 |
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Apr 1949 |
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GB |
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Primary Examiner: King; Lloyd L.
Assistant Examiner: Love; John J.
Parent Case Text
The present application is a continuation-in-part of my copending
application Ser. No. 787,974, filed Dec. 30, 1968.
Claims
I claim:
1. A device for liquid atomization and fluid blending comprising a
liquid reservoir with means for supplying liquid as required to
maintain a near constant free surface level, a fluid dispersion
nozzle means comprising a relatively large elongated fluid feed
conduit and a smaller elongated discharge orifice portion fluidly
communicating with the interior of said conduit including an
elongated wall portion having a semicylindrical internal curvature
substantially semicircular in cross section forming a corona
orifice cavity slitted transversely to provide at least one
discharge orifice or aperture for fan-shaped fluid dispersion, said
orifice cavity being unslitted on either side of said orifice for a
distance greater than its diameter, said dispersion nozzle being
disposed generally horizontally, with said orifice disposed above
said free surface such that adhesion forces between the liquid and
external surfaces of said nozzle means causes the liquid to rise
along said nozzle surfaces to the vicinity of said orifice slit,
means for supplying a fluid, at a pressure greater than the ambient
pressure above the said liquid free surface, into said fluid
dispersion nozzle means whereby said fluid discharges from said
orifice in a fan-shaped pattern, said dispersing fluid peripherally
entraining and divergently dispersing said liquid at orifice into
finely atomized particles blended uniformly with said fluid, said
liquid continuously rising up the external surface of said nozzle
means by forces of adhesion, cohesion, surface tension and pressure
differential, whereby said liquid is stressed into a thin film
along the upper portion of said discharge orifice portion which
with further stressing during entrainment provides fine atomization
and blending.
2. A device for liquid atomization and fluid blending comprising a
liquid reservoir with means for supplying liquid as required to
maintain a near constant free surface level, a fluid dispersion
nozzle means comprising a relatively large elongated fluid feed
conduit and a smaller elongated discharge orifice portion fluidly
communicating with the interior of said conduit including an
elongated wall portion having a semicylindrical internal curvature
substantially semicircular in cross section forming a corona
orifice cavity slitted transversely to provide at least one
discharge orifice or aperture for fan-shaped fluid dispersion, said
orifice cavity being unslitted on either side of said orifice for a
distance greater than its diameter, said dispersion nozzle being
disposed generally horizontally, with said orifice disposed above
said free surface, means for supplying a fluid, at a pressure
greater than the ambient pressure above the said orifice, into said
fluid dispersion nozzle whereby said fluid discharges from said
orifice in a fan-shaped pattern, at least two distinct wettable
surface means extending from below the free surface means and the
exterior side surfaces of said nozzle means for initial capillary
rise of liquid through said gaps which further rises by adhesion
forces to the vicinity of said aperture whereby, when said fluid is
discharged from said aperture, the liquid, at least partially due
to pressure differential, adhesion, cohesion, surface tension and
capillarity, rises continuously in said gap to surround said
aperture and is dispersed divergently by said fan-shaped fluid
discharge into finely atomized particles blended uniformly with
said fluid.
3. The device of claim 2 wherein means is provided for controlling
the flow of fluid from said aperture.
4. The device of claim 2 wherein means is provided for controlling
the flow of liquid rising to surround said aperture by regulating
the pressure differential between the fluid emitting from said
aperture and the ambient pressure above said free liquid
surface.
5. The device of claim 2 wherein the angle of contact between the
liquid and each of the wettable surface means is up to
90.degree..
6. The device of claim 2 wherein the wettable surface means are
removable.
7. The device of claim 2 wherein a multiplicity of apertures are
provided which give a parallel array of fluid discharge and
atomized liquid, at least one of which apertures is insulated from
the liquid to provide controlled blending of atomized liquid with
fluid discharged from nozzle means.
8. The device of claim 7 wherein the insulating means is an
integral part of a removable wettable surface means.
9. The device of claim 2 wherein the aperture is so formed to give
a flat-fantype dispersion of an angle up to approximately
190.degree..
10. The device of claim 2 wherein the free surface of the liquid is
maintained preferably between 1 mm. and 100 mm. from the nozzle
aperture
11. The device of claim 2 wherein the pressure differential between
the free surface of the liquid and the ambient atmosphere adjacent
the aperture is between 0.5 p.s.i. and 50 p.s.i.
Description
The present invention relates to an improved apparatus for
atomizing liquids into an emitting fluid medium, particularly
gaseous but not restricted thereto. More particularly, the
invention relates to a device for achieving unusually uniform and
fine atomization of a liquid in a highly efficient and simple
fashion. Furthermore, the invention achieves these two features,
uniform and fine atomization, over a wide range of volumetric
capacity. Utilizing the momentum of a fluid external to an aperture
to effect liquid feed and atomization, additional advantages of
control simplicity and dependable nonclogging operation become
apparent. In addition, secondary blending is easily accomplished by
preventing the feeding of liquid to one or more of a series of
fluid-dispersing apertures.
In carrying out this invention, particular reference is made but
not restricted to a fluid dispersion nozzle disclosed and claimed
in the copending application of William H. Johnson, on "Fluid
dispersion nozzle and method of making the same," Ser. No. 787,974
filed Dec. 30, 1968. This nozzle as disclosed pertains to a unique
design for achieving wide angle, flat-fan dispersion of both
liquids and gases uniformly and over a wide range of capacity and
pressure. In operation, a single fluid such as a liquid or a gas is
dispersed more completely than was heretofore possible because of
combined advantages in minimizing the orifice (aperture) area while
maximizing the dispersion angle. By utilizing this nozzle in
combination with auxiliary apparatus, the present invention makes
possible superior liquid atomization by forcing a fluid through the
aforesaid nozzle which in turn provides controlled liquid
dispersion and atomization.
The invention lends itself admirably to many applications where it
is desired to efficiently disperse and atomize a liquid into a
fluid medium, particularly gaseous. The usual applications of air
humidification, insecticide fogging, fuel atomization, spray
drying, etc. and numerous industrial operations could
advantageously employ the present invention. For example, home
humidification systems and greenhouses need fine atomization and
dispersion with little or no liquid fall out. Combustion processes
also need effective atomization and dispersion. In all cases
uniformity and efficiency of atomization are important
considerations. Efficiency is defined as the pounds of liquid
atomized per pound of gaseous fluid.
In order that a liquid remain dispersed in a gaseous medium for a
long time or until evaporation occurs, the drop size should be
small. For example water drops of 20 micron diameter fall at a
speed of 1 cm./sec. whereas drops of 200 micron diameter fall at 76
cm./sec. These and other points on drop size in relation to fall
speed and evaporation rate are discussed by Louis J. Battan in
"Cloud Physics and Cloud Seeding," published by Doubleday and
Company, Inc. Garden City, New York, 1962. Battan discusses rather
thoroughly investigations in measuring particle size distribution
in clouds and fogs and states that particles range from a few
microns to about 50 microns in diameter. The invention herein
disclosed accomplishes excellent liquid atomization with particle
size of about 50 microns diameter or less, that is with a particle
size distribution approximately that of a cloud or fog.
Several liquid atomizing devices are commercially available.
Although they may achieve satisfactory atomization, they generally
have certain disadvantages or limitations either in construction
complexity, operation or application. High-speed rotary atomizers
for example give capability of high capacity output with
dependable, nonclogging operation; however they are expensive, have
limited applicability and do not permit easy control of the
dispersion volume. On the other hand two-fluid atomizers such as
water-air devices are complex in construction, have fine openings
for liquid metering, are expensive per unit of liquid atomized, are
of low capacity, and are not applicable to all liquids because of
clogging problems.
The problem of clogging of the liquid channels cannot be
overemphasized. In many applications it is not possible, nor
feasible, to have a perfect liquid solution with no contaminants or
fine solid particles in suspension. For example, in spray drying it
may be desirable to form a fine slurry which is atomized and
dispersed in a drying environment. This problem is generally
handled by utilizing rotary atomizers wherein the liquid slurry
does not pass through a small orifice. The present invention has
the advantage over present two-fluid atomizers by providing designs
such that the liquid or slurry is not necessarily required to pass
through a fine orifice, hence it is virtually nonclogging in
operation. This advantage is realized in any application where
small solid particles in the liquid may pose a problem.
A further problem common to two-fluid atomizers is that of proper
metering of the liquid to achieve the desired degree and uniformity
of atomization and with high efficiency. With a given gaseous flow,
the liquid flow must be controlled rather critically to maintain a
given degree of atomization. An increased liquid flow relative to a
given gaseous flow causes larger particles. These problems are
overcome in the present invention since liquid metering and
atomization are both easily controlled. Also secondary blending can
be provided in a simple manner.
While the invention has its greatest usefulness in atomizing liquid
into a gaseous fluid medium emitting from an aperture, it is not
restricted thereto. Other emitting fluids such as water or kerosene
can be used, in which case the liquid to be atomized is simply
blended into the discharging liquid and results in the same
advantages such as uniformity and control. Hereafter gas as the
emitting fluid will be used mainly to describe and illustrate this
invention.
In view of the above considerations, it is an object of this
invention to provide an improved apparatus for wide dispersion and
fine uniform atomization of a liquid into a gaseous medium.
Another object of the invention is to provide liquid dispersion and
atomization wherein the liquid is uniformly and efficiently
entrained into a moving fluid. This is highly important in
applications where liquid flow should be responsive to an
intermittent fluid flow.
An additional object of the invention is to provide an improved
apparatus for liquid atomization wherein the liquid feed rate is
controlled by the difference in pressure of the free liquid surface
and the liquid at the orifice. Uniform and efficient atomization
over a wide range of operating conditions is further provided by
the control of the emitting fluid.
Another object of the invention is to provide an improved means for
achieving uniform, easily controlled secondary blending of a fluid
into the atomized liquid.
A further object of the invention is to provide an improved
apparatus for liquid atomization which virtually eliminate the
problem of clogging common to nonrotational atomizers. The feature
of nonclogging opens up many new areas of application for a
nonrotational device.
These and other objects and advantages of the invention will become
apparent in the following discussion of the method and apparatus
and in reference to the attached illustrations.
In the drawings:
FIG. 1 is a diagrammatic view partially in longitudinal section of
a multiple orifice nozzle means as disclosed and claimed in my
copending application, Ser. No. 787,974.
FIG. 2 is a diagrammatic sectional view of a suitably curved nozzle
end portion having a slot therein and illustrates how to maximize
the dispersion angle, that is to achieve up to at least
180.degree..
FIG. 3 is a vertical cross-sectional view of the nozzle of FIG. 1
and illustrates convergence of fluid within the nozzle.
FIG. 4 is a cross-sectional view of the nozzle of FIG. 1 and
illustrates how liquid is lifted from a lower level to be entrained
in the gaseous medium.
FIG. 5 is a sectional view, partly diagrammatic, of the nozzle of
FIG. 1 with the addition of liquid-feeding surfaces.
FIG. 6 is a vertical sectional view, partly diagrammatic, showing
an apparatus which utilizes the nozzle means of FIG. 1 for suitably
controlling liquid atomization such as in humidification.
FIG. 7 is a top view of the apparatus of FIG. 6, also partly
diagrammatic.
FIG. 8 is a vertical sectional view, partly diagrammatic,
illustrating a nozzle means, tubelike in structure and generally
horizontally disposed, with apertures cut in the topmost portion
thereof, and illustrating further a surrounding liquid-feeding
surface having openings in the bottom and top.
FIG. 9 is a top view of the apparatus of FIG. 8, also partly
diagrammatic.
FIG. 10 is a vertical sectional view, partly diagrammatic,
illustrating another tubelike nozzle means whose top surface, or a
portion thereof surrounding the apertures, is flat. As in FIG. 8
the liquid feeding surface generally conforms to the outer surface
of the container and has openings at the top and bottom.
FIG. 11 is a top view of the apparatus of FIG. 10, also partly
diagrammatic.
FIG. 12 is a vertical sectional view, partly diagrammatic,
illustrating an atomization device in which the liquid is lifted
from a free surface that is below the bottom of the nozzle
means.
FIG. 13 is a longitudinal section of FIG. 12, also partly
diagrammatic.
FIG. 14 is a vertical sectional view, partly diagrammatic,
illustrating how the liquid can be remotely located, as in the case
of combustible liquids, yet maintain its surface below the
apertures, without affecting satisfactory performance.
FIG. 15 is a top view of the device of FIG. 14, also partly
diagrammatic.
FIG. 16 is a vertical sectional view, partly diagrammatic,
illustrating a design having a single circular orifice in the top
of a tapered tubelike structure, positioned vertically and having
the exterior surface of the nozzle means and the liquid-feeding
surface converging like a cone, not necessarily circular in
section.
FIG. 17 is a top view of the device of FIG. 16, also partly
diagrammatic.
FIG. 18 is a vertical sectional view, partly diagrammatic,
illustrating a nozzle means which is a vertical tubelike structure,
dome shaped at the top with one aperture cut therein to give a
flat-fan dispersion to the emitting gas.
FIG. 19 is a top view of the device of FIG. 18, also partly
diagrammatic.
FIG. 20 is a vertical sectional view, partly diagrammatic,
illustrating liquid-feeding surfaces physically independent of the
nozzle means and therefore not dependent upon the external surface
of the nozzle means for the lifting of the liquid.
FIG. 21 is a top view of the device of FIG. 20, also partly
diagrammatic,
More efficient and uniform atomization, and wider dispersion, of
liquid into a gaseous medium are accomplished by: (1) discharging
upwardly and dispersing outwardly, a gas thru one or more discharge
orifices or apertures located within the 180.degree. top portion of
a nozzle means, (2) locating said point of discharge above a liquid
to be atomized (3) lifting said liquid by forces of adhesion,
cohesion, surface tension, and differential pressure acting singly
or in any combination thereof; the said liquid moving upwardly on
more than one side of the nozzle means and converging from more
than one direction to the region of the gaseous discharge from the
aperture, (4) entraining the liquid into the said discharging gas
along the greater portion of the aperture periphery, forming a
stressed liquid film within the unconfined fluid; further stressing
of the liquid film by dispersing and expanding the gas thru a
narrow aperture whose inner edge is minutely curved and has a large
included angle, (5) disrupting the liquid film surrounding the
aperture periphery by shear forces resulting from differential
velocities within the gas stream and between the gas and the liquid
to form extremely fine cloudlike particles.
Numerous tests and observations have been conducted to study the
atomization phenomenon and the significance of various forces
involved in causing liquid movement from a liquid surface to the
exit aperture. Several liquids and types of surface have been
utilized which indicate broad applicability of the method. In most
of the discussion, reference will be made, for illustrative
purposes only, to water as the liquid to be atomized and air as the
fluid-dispersing medium.
Reference to FIGS. 1 to 5 will permit a more complete understanding
of the method and will set the stage for the subsequent discussions
on specific apparatus for carrying out the method.
The nozzle shown in FIG. 1, and for which my copending application,
Ser. No. 787,974 supra, has been filed, has particular advantages
in permitting the formation of an arbitrarily small orifice inner
cavity while maximizing up to at least 180.degree. the angle of
fluid dispersion. This illustration is shown and discussed to
emphasize the nature of fluid dispersion from an orifice and to
point out the unique advantages of this design in accomplishing the
present invention. A fluid, either liquid or gas, enters the nozzle
1 and travels through the tube section 2 into the main nozzle
section beginning at 3. The nozzle section was originally a
straight length of circular tubing and has been brought to the
desired shape by pressure operations to form a central elongated
feed cavity or conduit 4 and at least one elongated corona
discharge portion or wing 5. As shown the central feed cavity 4 is
relatively large in cross section as compared with the smaller
cross section of the discharge wing portion 5 fluidly communicating
therewith. Two such wings are shown in FIG. 1. Each wing contains
within its surface a corona orifice cavity 6, fluidly connected to
said feed cavity 4. The wing and its cavity was referred to in the
copending application, Ser. No. 787,974 supra, as corona in that
they are crownlike and protrude outwardly. In this application the
main feed cavity, corona orifice cavity and aperture cut therein
are referred to as a nozzle means or a fluid-dispensing container.
Fluid moves unrestrictedly along the main feed cavity 4 until
finally terminating at a closed end. From the main feed cavity, the
fluid moves within the corona discharge wing 5 to its corona
orifice 7 formed by intersection of a surface slit with the corona
orifice cavity 6. The shape of the corona orifice cavity at its
outer extremity, as revealed by a cutting plane at right angles to
the longitudinal axis of the structure at my point, preferably an
arc of a circle of about 150.degree. to 190.degree. or
approximately a semicircle. Convergence of fluid flow at the
orifices establishes a fan dispersion pattern 8 as shown generally
at orifice 9. The angle of dispersion .theta. is determined by the
degree of intersection of the curves portion of the inner cavity 6
by the surface slit. In the case of the present invention, air is
forced through the nozzle where wide-angle fan dispersion occurs at
each discharge orifice or aperture 7.
As shown for example in FIG. 1 a plurality of widely spaced slits 7
are provided, the slits being spaced apart a sufficient distance so
that the orifice cavity is unslitted on either side of any orifice
for a distance greater than the diameter of the orifice cavity,
which as more fully set forth in my copending application Ser. No.
787,974 is an important feature from the standpoint of ensuring
uniform flow of fluid.
FIG. 2 illustrates how uniform dispersion is achieved by
intersection of the curved surface of the corona discharge wing
with a slit. The entering fluid 10 is dispersed through the angle
.theta. depending on the depth to which the surface slit 11 which
forms the discharge orifice intersects the corona cavity. The
emerging fluid 12 is discharged in a diverging fan pattern with
exceptional uniformity. It is to be noted that the diameter 13 of
the orifice at the line of intersection 11 can be made arbitrarily
small down to 0.001 inch. This feature, in combination with wide
angle dispersion, as more fully set forth in my copending
application Ser. No. 787,974, has particular importance to the
present invention in giving maximum dispersion per unit volume of
discharged gaseous substance. This will become evident in
subsequent discussions.
Consider now FIG. 3 which illustrates convergence of fluid within a
nozzle, necessary for the formation of a fan discharge pattern.
Fluid flow 14 converges to the surface slit 15 and produces a fan
discharge pattern 16, shown from the side, by nature of change in
fluid momentum within the orifice. The fluid at 17 is rapidly
changing direction near the center of the orifice and accelerating
outwardly. This action produces by entrainment low-pressure regions
18 along either side of the fan pattern. It is in fact this
low-pressure region, in combination with rapidly accelerating and
diverging gaseous flow, which permits certain unique advantages to
be achieved in the present invention. In tests in which air was
forced through the orifice at 30 p.s.i., suction pressures of 45
cm. water column were observed at the low-pressure regions 18,
utilizing a hypodermic needle carefully positioned from the side.
The suction pressure provides the capability for lifting a liquid
from a lower liquid level in a feed system wherein the liquid is
external to the orifice. FIGS. 1, 2 and 3 are more fully described
and claimed in my copending application Ser. No. 787,974 and their
application to the present invention will now be more fully
described.
FIG. 4 is a cross-sectional view of the nozzle of FIG. 1 located
with partial immersion in a liquid. As discussed above, a gaseous
substance such as air is forced through the nozzle means 19 and is
dispersed in a fan pattern by fluid behavior at the orifice 20. Air
within the corona orifice cavity or discharge orifice portion 21 is
under a higher pressure than the outside ambient pressure 22. FIG.
4 illustrates the manner by which a liquid such as water may be
lifted from a lower level 23 and caused to rise upward along the
outer surface of the corona discharge wing 24 to the orifice 20
where entrainment and atomization by the air stream occur. The
suction pressures along the side of the discharge orifice or
aperture 20 induce air movement 25 and 26 over the liquid surface
23, the air moving in the direction of the orifice from both sides
of the exposed nozzle portion 19. Low pressure and air movement
along the sides of the exposed nozzle portion 19 provides a lifting
effect which aids movement of liquid to the orifice.
A second factor which aids importantly in lifting the liquid to the
aperture is related to adhesive and cohesive properties of a
liquid. Surface phenomena and cohesive properties of liquids are
discussed rather completely by G. Shortley and D. Williams in
"Elements of Physics," published by Prentice-Hall, Inc., New York,
1955. Cohesive forces occur within liquids due to molecular
attraction between like molecules. A free liquid surface as 23 in
FIG. 4 tends to behave like a membrane stretched with constant
tension per unit width because of cohesive forces. The surface
tension varies for different liquids with mercury having a value of
0.465 joules/M.sup.2 while water has a value of 0.072, both at
20.degree. C. Surface tension becomes important for liquids which
tend to "wet" a surface in accounting for the phenomenon of
capillarity, or the tendency of a liquid to rise in a small tube or
between closely spaced plate or surfaces. A liquid tends to wet or
adhere to a surface when the liquid molecules at the interface are
attracted more strongly by the solid than they are attracted back
to the liquid. Liquid attraction forces with respect to the solid
surface are called adhesive or surface action forces. The tendency
of a liquid to wet a surface is often measured by the angle of
contact with a vertical surface. When the contact angle is between
90.degree. and 180.degree., the liquid does not wet the surface and
the liquid tends to drop at the interface with a vertical surface.
On the other hand when the contact angle is between 0.degree. and
90.degree., the liquid wets the surface and the liquid tends to
rise at the interface with a vertical surface. If the solid surface
is inclined, of course, the tendency to rise also exists. As shown
in FIG. 4 the liquid, for example water, wets the nozzle surface
and tends to rise or climb up the outer upper exposed surface of
the nozzle means 19. The liquid surface 27 is shown curved upward
as liquid approaches the liquid-solid interface. In the initial
stages of operation the liquid is lifted by both adhesion forces
and suction forces. When the liquid reaches the sides of the
aperture 20, it is almost instantaneously filmed along the sides of
the discharging, fan-shaped gaseous fluid (air in this example) and
is dispersed and atomized by entrainment into the high velocity air
stream. It is important to note that divergence of gaseous fluid
flow in the immediate vicinity of the orifice exit gives additional
stressing and disruption of any liquid film carried upward by the
gaseous fluid. The atomization so achieved 28 is exceptionally
uniform in terms of particle size and distribution. Once the liquid
is entrained by the air stream, continuous and uniform lifting is
achieved by forces of suction at the aperture, cohesion forces
within the liquid flowing up the sides of the nozzle, surface
tension along the free surface of the liquid, and by surface action
forces (adhesion) at the interface between the liquid and the solid
surface of the nozzle.
The mode of action described above has been observed to provide
satisfactory results for the liquids which wet the nozzle surface
such that the orifice can be located about 1 mm. or more above the
normal free surface level of the liquid. However, in the event the
liquid material and the nozzle surface are such that a minute
elevation difference is required to obtain feeding, say less than
about 1 mm., the observations indicate that instability and
irregular feeding may result due to turbulence in the liquid
surface 23 or slight variations in the liquid level. To circumvent
these problems, additional wettable surface means are employed.
FIG. 5 illustrates the use of surfaces external to the nozzle means
to direct the liquid upwardly. These are called surfaces because
they are the outside part of a plate that has length, breadth, and
thickness. And they feed liquid upwardly to the aperture. They are
also wettable, as previously discussed. The term wettable surface
means, also applies to the external surface of the nozzle means
which also helps direct the liquid upwardly. The mode of operation
is virtually the same as described for FIG. 4, except that
capillary forces are introduced and the liquid-feeding surfaces
allow propagation of the suction pressure over a further distance
to the lower liquid level. Considering air as the emitting fluid
and water as the liquid, air is forced into the main feed cavity 29
from which it moves into the corona cavity 30 and is discharged
through the orifice or aperture 31, forming a fan pattern 32. This
latter cavity 30 with apertures 31 in the top most portion has
heretofore been called a nozzle means. A more descriptive term is
"fluid-dispensing container" in that it contains the gas and
dispenses it thru an aperture. The emitting gas creates low
pressure regions at either side of the fan as previously described.
This suction pressure causes the water 37 to rise in the gaps 33
formed between the outer surfaces 34 of the fluid-dispensing
container 30, 31 and the wettable liquid-feeding surfaces 35. With
close spacing, capillarity with respect to these wettable surface
means also causes the water to rise within the gaps 33. Air 36
induced to flow laterally to the orifice 31 also aids in lifting
the water by nature of frictional effects. From the top of the
liquid directing plates 35 to the orifice, the water is
additionally lifted by adhesion forces as the surface becomes
"wet." When the water reaches the edge of the orifice, dispersion
and atomization occurs as discussed previously.
The advantages of utilizing the wettable feeding surfaces 35 are
(1) liquid may be lifted from one to several centimeters, (2)
capillary forces can be utilized in certain applications to aid
lifting of the liquid and to "hold" the liquid near the orifice for
intermittent air operation, (3) operation of the device is not
sensitive to the free surface level of the liquid and (4) apertures
can be located within 90.degree. of each side of the vertical axis
thru the nozzle means or fluid dispensing container 30, 31.
The capillary action under certain applications is quite effective
in aiding the initial lifting, even with a rather large gap. For
example with water rising between two parallel glass plates, the
following capillary rise is obtainable: ##SPC1##
The height of capillary rise between two vertical plates is
directly proportional to surface tension and inversely proportional
to the gap spacing, other factors being held constant. It is
considered that the rise of sap in trees to great heights is
largely attributable to capillary action. For liquid atomization,
however, it is important to make the gap as large as practicable,
especially where suspended particles are involved.
Once operation and atomization have started, continuous and uniform
liquid feeding to the orifice occurs as previously described, with
the exception that liquid moves into the gaps 33 from a subsurface
location. Trash and fine particles floating on the surface are
therefore no problem.
One additional, and unique advantage of the utilization of wettable
feeding surfaces, such as 35 in FIG. 5, is secondary blending. In a
nozzle means having a series of apertures in line, the wettable
feeding surfaces may be removed from one or more of the apertures,
say alternate ones. Since the apertures 31 are located some
distance above the free surface of the liquid, those with the
surfaces removed will emit only gas. And this gas will blend with
the gas and atomized liquid emitting from the remainder of the
apertures. The method and device as described above therefore
offers an effective additional control of the liquid to gas
ratio.
The above discussion describes the method rather completely;
however, general discussion related to specific operation and
performance will illustrate the effectiveness and utility of the
method. In numerous observations, the method has demonstrated
excellent atomization over a wide range of operating conditions.
The degree and uniformity of atomization are fairly easily observed
visually by directing a bright light into the region of atomized
particles with a dark background to offer contrast. Using air and
water, excellent dispersion and atomization are achieved at air
pressures as low as 0.5 p.s.i. At increasing air pressure and
airflow through the orifice, the quantity of rate of liquid
atomization does not appear to be appreciably changed. However, the
fineness of atomization is noticeably increased with higher air
discharge rate. Although elaborate, particle size distribution
measurements have not been made, the effect can be visually
observed by the increased volume of fog and smokelike particles at
the higher discharge pressure and by measured efficiency.
Apparently, the increased kinetic energy of the discharged air is
utilized in producing finer atomization. Since surface energy of a
given quantity of liquid is proportional to surface area, it is
logical that a given quantity of more finely atomized particles,
say 20 microns diameter, has considerably more surface energy than
the same quantity of 50 microns diameter. Calculations show that
the energy involved in atomizing 1 lb. of water to 50 micron
diameter particles if 4.12 watts-sec; whereas for 20 micron
diameter particles, the energy is 10.3 watts-sec. This information
supports the experimental observations. The following data gives
the effect of airflow rate on liquid atomization: ##SPC2##
It is to be noted that increases in airflow do not appreciably
affect the liquid atomization rate; however the fineness of
atomization is noticeably affected.
This method of liquid atomization, involving the use of one or more
forces to lift a liquid from a lower level and to feed the liquid
externally to an air stream passing through an orifice, offers
atomization improvements and control advantages. Consider the case
where a continuous flow of liquid is directed over a surface and an
aperture located in the surface, and then forcing a gas through the
aperture to effect atomization, as for example in the U. S. Pat.
No. 3,421,692 by Babington, et al. Since the liquid is directed
toward the aperture nonsymmetrically and from the upper side only,
the rate of liquid entrainment varies around the periphery of the
aperture. Furthermore, metering control is necessary on both liquid
and air supplies. In contrast, the method of this invention in
which the liquid is lifted from a lower level symmetrically from
both sides of an aperture, gives superior results in regards to
atomization uniformity. In addition, off-on control is simplified.
With air off, the liquid is quiescent; and with air on, the liquid
is almost instantaneously atomized. By varying the airflow rate,
the degree of atomization is simply accomplished. The upper limit
to airflow rate depends upon the maximum pressure which the
air-dispensing container can withstand. In practical situations,
however, fine atomization is accomplished at low pressures of 1
p.s.i. and above; 30--40 p.s.i. may represent practical upper
limits of operation for most applications.
It should be pointed out that efficiency of atomization, in terms
of pounds of liquid per pound of gas, is a variable depending upon
the degree of atomization. This is clear from the previous
discussion; in which the atomization rate remained fairly constant
while the airflow rate increased considerably. This method of
atomization is considered comparable, if not superior, to my
previous method in atomization efficiency. Since orifice size and
dispersion angle can be controlled in the nozzle of FIG. 1 to
optimize dispersion, efficiency of atomization will likewise be
optimal.
In addition to atomization improvements and control, the invention
offers control over the liquid feed rate. In the foregoing
discussion specific mention was made of the gaseous pressure above
the liquid surface being the same as the ambient pressure
surrounding the nozzle apertures. But, in practice the gaseous
pressure above the liquid surface is preferably controlled with
respect to the ambient pressure surrounding the nozzle apertures.
By controlling the amount of this differential pressure the amount
of liquid fed into the airstream is controlled accordingly.
Proceeding now to specific illustrations of apparatus which embody
the method of liquid atomization. In FIG. 6 and FIG. 7, air is
illustrated as the dispersing medium and the nozzle means of
fluid-dispensing container 45 with connecting fluid supply lines
are referred to as constructed of stainless steel; however, it is
to be understood that a variety of materials and different liquids
and gases could be used. A containing vessel 38 holds the liquid 56
which is to be atomized. The vessel 38 also contains the means for
liquid atomization, fluid supply lines, etc. The size of this
containing vessel may be quite variable, as small as a match box,
or several inches in each dimension, depending on application. In
this illustration, consider the vessel to be say 2 inches deep, 3
inches wide and 3 inches long. This is of ample size for providing
humidification for a home or small industrial plant. The liquid
(water) 56 is supplied by a pump 52 or suitable water supply means
having sufficient head pressure to cause water to move into the
vessel 38 when the valve 51 is open. As shown, liquid level probes
48 and 49 sense the liquid level 47 and serve to maintain the water
level constant. Whenever the water level falls and breaks contact
with probe 48, the liquid control unit 50 energizes the solenoid
valve 51 to admit water to the vessel. When the liquid touches
probe 48, the solenoid valve 51 is deenergized and closes, stopping
waterflow. Liquid level may be maintained by other suitable means,
such as the common float valve which is used in automobile
carburetors. Located within vessel 38 is a fluid-dispensing
container 45 which may be similar to the nozzle means of FIGS. 1 to
5, having a corona discharge wing 39 in its top portion with an
aperture 46 cut therein to provide a discharge orifice. It is shown
supported from beneath by the block 40 which locates the nozzle
means 45 partially immersed within the liquid 56 with the discharge
orifices 46 located above the liquid level 47. The height of the
orifices above the liquid level 47 may vary up to several inches.
Also located within the vessel are two wettable feeding surfaces 41
for aiding in lifting the liquid prior to and during operation as
previously discussed. These are shown attached to the lower portion
of vessel 38 and symmetrically and evenly spaced with respect to
the corona discharge wing 39. The gap 57 may be adjusted to provide
proper capillary effect for the liquid to be atomized; for this
illustration 0.050 inch provides ample clearance and effective
operation. A gas, air in this case, is supplied by the pump 42 or
other suitable air supply means to provide air under pressure
greater than the ambient pressure to the nozzle means
fluid-dispensing container 45. The valve 43 can be an electrical
solenoid valve, for example normally closed, which is actuated by a
humidistat 54 as required to maintain the desired humidity. When
the humidity falls below the set point, the valve 43 opens to admit
air through the supply line 44 to the fluid-dispensing container
45. The action and mode of operation at the discharge orifice or
aperture 46 to effect atomization of the water is exactly as
previously discussed for FIG. 5. The water is lifted from the lower
level, moving through the openings 53 in the liquid-feeding
surfaces 41 and passing up through the clearance gap 57 to the
apertures where dispersion and atomization occur in the fan
patterns 55. It is to be emphasized that better results are
achieved by utilizing an air supply device with a nozzle having the
configuration as shown in FIGS. 5 and 6 and as discussed
previously. This fluid dispersion nozzle gives the capability for
maximizing the dispersion angle, up to at least 180.degree., while
minimizing the aperture size. These two features provide the
capability for finer atomization and more uniform dispersion than
any other nozzle configuration. In this illustration, for example,
the apertures can be made simply and easily down to 0.001 inch
effective diameter with wide dispersion angle. Acceptable results
have been achieved using an orifice of about 0.008 inch diameter
with air pressure of only 2 p.s.i. One to four orifices 46 of 0.010
inch diameter and operating at 2--5 p.s.i. will provide ample
humidification capacity for an average-sized home. The number and
size of orifices can easily be modified to provide a wide range of
a capacity for varied applications.
Although results indicate a number of advantages to the apparatus
as illustrated in FIGS. 6 and 7, the applicability of the method is
not restricted to this specific example. For instance, the gaseous
supply and dispersion means may be of several configurations which
will achieve very satisfactory results for many applications, while
perhaps not achieving maximum dispersion, degree and efficiency of
atomization, or as simply. Furthermore the containing vessel 38 may
be of numerous sizes and configurations, while continuing to serve
the purpose as defined. Also the lqiuid-feeding surface 41 may
likewise be varied in size and configuration while continuing to
provide the defined supply channel through which the forces of
capillarity, cohesion and adhesion, and suction pressure remain in
effect. Alternate embodiments are therefore depicted in the
following discussion.
FIG. 8 and FIG. 9 illustrate an alternate nozzle means with a
different orifice configuration and different liquid-feeding
surfaces. All of the auxiliary apparatus is the same as in FIGS. 6
and 7. In this illustration there is provided a fluid-dispensing
container 58 tubelike and horizontally disposed and directly
connected to the gaseous supply line 44 and which is closed at the
end 59. This container, partially immersed in the liquid 56, has
one or more orifices 60 located at the top above the liquid surface
47. The orifices are shown as circular; however, they may be of any
shape such as oval, oblong or as a long slit. For efficient
atomization there is an advantage to having a large periphery of
the orifice in comparison to area. A number of small orifices is
then preferable to one large orifice. The liquid-feeding surfaces
previously shown in FIGS. 6 and 7 are shown in FIGS. 8 and 9 as a
concentric tube 61 which tends to encase symmetrically the tubelike
fluid-dispensing container or nozzle means 58. The gap 62 between
the fluid-dispensing container 58 and the liquid-feeding surface 61
may be varied in size as needed for the particular application.
Openings 63 in the liquid-feeding surface 61 are provided beneath
the surface 47 for liquid movement 64 into the gap 62. Discharge
openings 65 are also provided in the top portion 61 and are located
in exact alignment with the orifices 60. The openings 65 are
provided somewhat larger in size than the orifices 60 to assure
ample clearance for the discharging fluids 66. In operation the
apparatus works exactly as previously described with the gaseous
discharge entraining and atomizing the liquid which is lifted from
a lower level by various forces associated with suction pressure,
capillarity adhesion, cohesion, and surface tension. The design of
the atomizing device in FIGS. 8 and 9 is particularly simple in
construction and will give very satisfactory atomization. The
dispersion pattern 67 is circular and not as well dispersed as in
the design of FIGS. 6 and 7. Application simplicity is the major
advantage of this design.
Another alternate design, given in FIGS. 10 and 11, shows
respectively vertical sectional and top views of an atomization
apparatus which utilizes a rectangular tubelike fluid-dispensing
container. Again all of the auxiliary apparatus is the same as in
FIGS. 6 and 7. The rectangular fluid-dispensing container 68 is
directly connected to the gaseous supply line 44 and is closed at
the other end 69 to retain an internal pressure greater than the
outside pressure say above the liquid surface 47. This container 68
is partially immersed in the liquid 56 and is provided with one or
more orifices 70 located at the top and centered with respect to
the sides. The apertures, as noted, are above the liquid level
surface 47. They may be of any shape such as circular, oval,
oblong, or slitlike. Provided also is a liquid-feeding surface 71,
designed and arranged symmetric to the container 68 to provide a
gap 72 which may be varied in dimension according to the specific
application. The gap 72 allows liquid to enter from beneath the
surface 47 and to move upward through the gap. Discharge openings
73 are provided in the top portion of the liquid-feeding surface 71
and are located in exact alignment with the orifices 70. The
openings 73 are provided somewhat larger in size than the orifices
70 to provide clearance for the discharging fluids 74. Operation,
again, is exactly as previously described for this method of
atomization. The gaseous fluid discharging through the aperture 70
entrains and atomizes liquid which is lifted within the gap 72 from
a lower level.
The previous illustrative examples of apparatus for liquid
atomization have involved partial immersion of the fluid-dispensing
container within a liquid medium wherein the free surface is no
lower than the bottom of said container. In FIGS. 12 and 13 the
free surface is below the bottom of the fluid-dispensing container.
Initial lifting of the liquid 56 is by capillarity or by suction
pressure caused by the discharging gaseous fluid. Once feeding has
commenced, the liquid is continuously and uniformly lifted by
forces of suction, cohesion, capillarity, and surface tension. This
illustration shows the fluid dispensing container as a cylindrical
tube 75 into which a gas 76 is introduced; however any design as
discussed heretofore for this invention will work equally
satisfactorily. Two orifices 77 are provided for illustrative
purposes. In operation the liquid 56 enters the bottom opening 78
located below the free surface 47 and rises by capillarity or
suction pressure within the gap 80 provided between the liquid
direction surfaces 81. The height h of lifting to the bottom of the
gaseous containing tube 75 is adjustable depending upon application
requirements. The determining factors which limit h are (1) the
height of capillarity as determined by the liquid-surface adhesion
forces and width of gap 80 and (2) the amount of suction pressure
developed at the orifice 77. This may be up to several inches if
proper conditions are provided. The liquid moves freely around both
sides 82 of the cylindrical container 75 where it is drawn to the
aperture 77 and atomized at 83 through openings 84 as previously
discussed.
In all illustrations it may be pointed out that the free liquid
surface can easily be covered to prevent evaporation,
contamination, or for other reasons. For example if a combustible
liquid is being atomized and burned directly above the atomizer,
enclosure of the liquid may be necessary. Alternatively, a simple
modification in liquid feeding to the atomization device may be
made as illustrated in FIGS. 14 and 15. Again the cylindrical tube
for a fluid-dispensing container is illustrated. A gas 85 is
supplied from a source at a pressure above ambient 86 to the inside
87 of the container 88. The tube 88 is closed at the end 89 and is
shown containing three orifices 90 at the top. A cylindrical
liquid-feeding surface 91 is provided which symmetrically surrounds
the container 88 to provide a gap 92 for liquid feed. Liquid can
move freely beneath and around the container 88. At the top portion
of the liquid-feeding surface 91 are located openings 93,
symmetrical with respect to the orifices 90. In this design liquid
94 communicates or moves freely from a separate liquid supply
reservoir 95 having a free liquid surface at the same ambient
pressure 86 as surrounding the atomizer. This liquid surface must
be at a level below the orifices 90 to obtain proper operation.
Operation of the atomizer and forces involved are exactly as
previously discussed; the only difference is that the liquid is
remotely located. This principle is applicable to any of the
atomizer designs illustrated herein.
In all previous illustrations of this disclosure, the nozzle means
has been depicted as tubelike, with at least one orifice located
along the upper portion of the surface. Multiple orifices are
easily provided with these designs and would be located preferably
in a straight line along the upper surface and symmetric with
respect to a vertical line passing through the center of the
container. Symmetrical location of the orifices provides more
uniform lifting and feeding of the liquid from both sides of the
orifices through the gap than, for example asymmetric lifting of
the liquid from one side only. A nonsymmetrical arrangement of the
orifices with respect to the vertical line will work satisfactorily
if the liquid on either side can move freely to the aperture
without passing over a surface having a higher elevation than the
apertures. For example the nozzle means 45 in FIG. 6 can be rotated
right or left nearly 90.degree. with continued uniform feeding to
both sides of the apertures.
Consider now FIGS. 16 to 19 which illustrate alternate designs for
single orifices that are quite different from the previous designs.
In these designs, the liquid is lifted through a gap that surrounds
a vertically tapered gaseous dispensing container. The shapes could
be referred to as hollow conelike whose outer surface is also a
liquid-feeding surface. FIGS. 16 and 17 give a vertical sectional
and top view respectively of a liquid atomization device having a
single circular orifice. A gas 96 is supplied under pressure
greater than the ambient pressure 99 to the fluid-dispensing
container 98 which is tapered vertically. Located at the top of 98
is circular aperture 100 which provides an exit for the gaseous
fluid. A liquid 101 is shown provided from a separate liquid supply
reservoir 102 having a free liquid surface at the same ambient
pressure 99 as surrounding the atomizer. The liquid surface, as
discussed previously, must be lower than the aperture 100. The
liquid communicates freely within the supply tube 103 and up the
gap 105 between the liquid-feeding surface 104 and the outer
surface of the fluid-dispensing container 98. In operation the
discharging gaseous fluid atomizes the liquid 106 exactly as
previously discussed. One slight difference is that the liquid
feeds completely uniformly in the gap 105 around the circular
orifice; whereas, in previous designs illustrated the liquid feeds
approximately uniformly to the exit periphery of the discharging
gas.
FIGS. 18 and 19 similarly illustrate a single orifice design but
for flat-fan dispersion. A gas 107 is supplied under pressure
greater than ambient 110 to the gaseous dispensing container 108
which is tapered vertically and which has a single orifice 109 for
fan dispersion. A liquid 111 is provided from a separate liquid
supply reservoir 112 as in FIGS. 16 and 17. The liquid 111 moves
freely within the liquid supply tube 113 and up into the gap 114
between the liquid-feeding surface 115 and the gaseous container
108 outer surface. Operation again is exactly as previously
described to obtain fine atomization of the liquid 116.
In the previous designs, utilizing capillary forces to help lift
and hold the liquid near the gas emitting orifice, the exterior
surface of the nozzle means was described and illustrated as one of
the wettable feeding surfaces. An alternative is to utilize
completely separate, distinct, and removable if desired, wettable
surfaces such as is illustrated in FIGS. 20 and 21. Two concentric
surfaces, 115 being the inner one and 116 the outer one, are
closely spaced to provide gap 117 thru which the liquid 118 will
move by capillary forces, and otherwise, to the vicinity of the
nozzle. The circular orifice 119 emits fluid 120, such as a gas,
while the concentric orifice, 121 feeds the liquid into the gas
stream. Since the wettable feeding surfaces 115 and 116 are not a
physical part of the nozzle means 122, they can be removed easily
for cleaning, replacement such as for changing the material to
achieve different liquid angle contacts, or for secondary blending
control. Being separate, the gap 117 can be made and maintained
more precisely to specified dimensions. It is understood that the
physically separate removable wettable surfaces as described above
can be utilized with any design, including multiple orifices.
The foregoing designs showed the gaseous pressure above the free
liquid surface to be the same as the ambient pressure around the
nozzle apertures. It is to be emphasized that this is not a
requirement. By regulating the gaseous pressure above the free
liquid surface with respect to the pressure on the liquid at the
apertures the liquid flow rate is controlled. The latter design is
preferred in many instances. It should also be pointed out that
separate regulation of the liquid flow rate can be achieved by
means of an adjustable metering valve, in contrast to the
previously described solenoid "on-off" valve, located between the
liquid supply having a free surface and the nozzle means.
Without further discussion and illustration, the foregoing
illustrates the essential characteristics of the present invention
to the extent that ready adaptation can be made in various
applications. Such adaptations are considered to be within the
spirit and scope of the present invention.
* * * * *