FIELD OF THE INVENTION
[0001] This application generally relates to the creation of an aerosol created by the directed
flow of fluids.
BACKGROUND OF THE INVENTION
[0002] Devices for creating finely directed streams of fluids and/or creating aerosolized
particles of a desired size are used in a wide range of different applications, such
as, for example, finely directed streams of ink for ink jet printers, or directed
streams of solutions containing biological molecules for the preparation of microarrays.
The production of finely dispersed aerosols is also important for (1) aerosolized
delivery of drugs to obtain deep even flow of the aerosolized particles into the lungs
of patients; (2) aerosolizing fuel for delivery in internal combustion engines to
obtain rapid, even dispersion of any type of fuel in the combustion chamber; or (3)
the formation of uniform sized particles which themselves have a wide range of uses
including (a) making chocolate, which requires fine particles of a given size to obtain
the desired texture or "mouth feel" in the resulting product, (b) making pharmaceutical
products for timed release of drugs or to mask flavors and (c) making small inert
particles which are used as standards in tests or as a substrate onto which compounds
to be tested, reacted or assayed are coated.
[0003] EP-A-0 899 017 discloses a method according to the preamble of claim 1, comprising a liquid atomization
process based on the formation of a capillary microjet upon sucking a liquid by means
of a high speed gas flow through a small diameter orifice. According to a parametric
determination, the liquid sucked forms a stationary capilar jet having a very small
diameter, and accelerated and stabilized by the tangential viscous efforts exerted
by the gas on the liquid surface, going through the orifice and coming out to the
outside wherein finally the microjet is broken up into microdroplets having an extremely
small size and scarce dispersity. The disclosed process applies to mechanisms requiring
homogenous atomization of liquids and specially to the electronic injection of fuel.
[0004] It is an object of the invention to improve the known methods.
SUMMARY OF THE INVENTION
[0005] According to the present invention there is provided the method of claim 1.
[0006] There is hereinafter disclosed a method of creating small particles and aerosols
by a technology referred to here as "violent focusing" of a liquid to break up and
disperse a liquid, along with devices for generating such violent flow focusing. In
general, a "violent focusing" method comprises the steps of forcing a first liquid
through a feeding tube and out of an exit opening of the feeding tube positioned inside
a pressure chamber which is continually filled with a second fluid which may be a
second liquid immiscible in the first liquid or a gas. The exit opening of the feeding
tube is positioned such that the liquid flowing out of the tube flows toward and out
of an exit or discharge orifice of the chamber surrounding the exit opening of the
feeding tube. The first liquid exiting the tube is focused to a substantially reduced
diameter and subjected to a violent action created by the second liquid or gas, breaking
up the flow into particles substantially smaller than if the reduced diameter flow
underwent spontaneous capillary breakup. The exit opening of the feeding tube preferably
has a diameter in the range of about 5 to about 10,000 microns and the exit opening
of the tube is positioned at a distance in a range of from about 5 to about 10,000
microns, more preferably about 15 to about 200 microns from an entrance point of the
exit orifice.
[0007] A stream of the first liquid flows out of the tube and is focused by the flow of
the second liquid or gas in the surrounding pressure chamber. The focused stream then
exits out of the discharge orifice of the pressure chamber, destabilizing and forming
small particles. The size of the particles of the first liquid is governed by the
balance between the surface tension forces of the first liquid particle formed, and
the amplitude of the turbulent pressure fluctuations at, and outside of the exit orifice
of the pressure chamber. When the particles are sufficiently small that their surface
tension forces substantially match the amplitude of the pressure fluctuation then
the particles are stabilized and will not break up into still smaller particles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008]
Figure 1 is a schematic cross-sectional plan view of a nozzle of the invention;
Figure 2 is another embodiment of the nozzle of Figure 1 showing and labeling various
angles and areas of the nozzle;
Figure 3 is the same embodiment as shown in Figure 1 with various angles and areas
labeled;
Figure 4 is another embodiment of the nozzle of Figure 1 with certain areas and angles
labeled;
Figure 5 is an embodiment of the nozzle of Figure 1 with various parameters labeled;
Figure 6 is a graph of the volume median diameter (VMD) vs the liquid supply flow
rate for four different liquids;
Figure 7 is a graph of the dimensionless volume median diameter (VMD) versus dimensionless
liquid flow rate with a line through the data points showing the best power-fit;
Figure 8 is a graph of the data with the line shown in Figure 7 compared to a theoretical
line for the Rayleigh breakup prediction of a flow-focused jet; and
Figure 9 is a graph of data obtained with the different liquids listed of the geometric
standard deviation (GSD) vs. dimensionless liquid flow rates.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0009] Before the present aerosol device and method are described, it is to be understood
that this invention is not limited to the particular components and steps described,
as such may, of course, vary. It is also to be understood that the terminology used
herein is for the purpose of describing particular embodiments only, and is not intended
to be limiting, since the scope of the present invention will be limited only by the
appended claims.
[0010] It must be noted that as used herein and in the appended claims, the singular forms
"a", "and," and "the" include plural referents unless the context clearly dictates
otherwise. Thus, for example, reference to "a particle" includes a plurality of particles
and reference to "a fluid " includes reference to a mixture of fluids, and equivalents
thereof known to those skilled in the art, and so forth.
[0011] Unless defined otherwise, all technical and scientific terms used herein have the
same meaning as commonly understood by one of ordinary skill in the art to which this
invention belongs. Although any methods and materials similar or equivalent to those
described herein can be used in the practice or testing of the present invention,
the preferred methods and materials are now described.
[0012] The publications discussed herein are provided solely for their disclosure prior
to the filing date of the present application. Nothing herein is to be construed as
an admission that the present invention is not entitled to antedate such publication
by virtue of prior invention. Further, the dates of publication provided may be different
from the actual publication dates which may need to be independently confirmed.
GENERAL METHODS
[0013] The method is carried out by forcing a liquid from a liquid supply means, e.g. a
tube. The liquid exits the supply means into a pressure chamber filled with a second
fluid which is preferably a gas. The chamber has an exit port preferably positioned
directly in front of and preferably downstream of the flow of liquid exiting the supply
means. The exit port may be positioned slightly upstream of the liquid supply means
exit. The liquid is focused by the gas to substantially smaller dimensions as it exits
the supply means e.g. a tubular stream of liquid one unit in diameter is focused to
a stream 1/2 - 1/400 of a unit in diameter or smaller depending on operating conditions.
In this proposed example, a focused cylindrical stream of one unit in diameter would
be expected to undergo Rayleigh breakup and form particles which are about 1.89 times
the diameter of the focused stream. However, by correctly adjusting parameters (such
as positioning the exit of the liquid supply means relative to the chamber exit port)
the liquid stream is first focused by the gas flowing out of the chamber thereby forming
a stream with a much smaller diameter. That stream leaves the chamber and forms particles
which are smaller in diameter than the focused stream.
[0014] Based on the above it will be understood that the nozzles and methods of the present
invention are capable of producing extremely small particles. As an example, consider
producing particles using a cylindrical liquid supply means having a diameter of 1000
units. The stream from such a supply means would be expected to undergo normal Rayleigh
breakup of the 1000 unit diameter stream to form spherical particles having a diameter
of about 1.89 x 1000 or 1890 units in diameter. If the stream having a diameter of
1000 units is focused to a stream or jet of smaller dimension by a surrounding gas
the jet might have a diameter of one tenth that size or 100 units. That 100 unit diameter
focused jet would be expected to undergo normal Rayleigh breakup to form particles
having a diameter of 1.89 x 100 or 189 units.
[0015] Focusing the diameter of the stream to a narrow focused jet or "stable microjet"
jet has been referred to as flow focusing technology. When using the flow focusing
technology the focused jet has a diameter
dj at a given point A in the stream characterized by the formula:
wherein
dj is the diameter of the stable microjet, ≅ indicates approximately equally to where
an acceptable margin of error is ± 10%, ρ
1 is the density of the liquid and ΔPg is change in gas pressure of gas surrounding
the stream at the point A. The diameter of the jet (d
j) can be any reduced dimension smaller than that of liquid stream exiting the supply
means, e.g. can have a cross-sectional diameter of from about one half to about 1/100
the area of the stream exiting the liquid supply means.
[0016] In accordance with the violent flow focusing of the present invention the liquid
flow exiting the supply means with a diameter of 1000 units is focused as it leaves
the supply means so that the end of the exiting drop exiting the liquid supply tube
is focused by the surrounding gas to a reduced dimension (e.g. ½ to 1/100 the cross-sectional
diameter of the liquid supply means). For purposes of example we will say the 1000
unit stream is reduced to a diameter of about 100 units. That 100 unit end of the
drop is subjected to turbulent action by the gas exiting the pressure chamber thereby
forming particles which are 10 units in diameter. Thus, the above proposed examples
can be summarized as follows:
|
Supply Means Diameter |
Particle Diameter |
Rayleigh |
1000 |
∼1890 |
Flow Focusing |
1000 |
∼189 |
Violent Flow Focusing |
1000 |
∼1 |
[0017] Based on the above it will be appreciated that the method of the invention can produce
particles which are substantially smaller than (e.g. ½ to 1/100) the size of particles
produced using flow focusing technology. Further, flow focusing technology can produce
particles which are substantially smaller than (e.g. ½ to 1/100) the size of particles
produced by normal capillary breakup of a stream.
GENERAL DEVICE
[0018] The basic device or nozzle of the invention can have a plurality of different configurations.
However, each configuration or embodiment will comprise a means for supplying a liquid
or first fluid and a means for supplying a second fluid (preferably a gas) in a pressure
chamber which surrounds at least an exit of the means for supplying a liquid. The
liquid supply means and pressure chamber are positioned such that turbulent action
takes place between the liquid exiting the liquid supply means and the second fluid,
a liquid or a gas, exiting the supply chamber. Preferably, the exit opening of the
pressure chamber is downstream of and more preferably it is directly aligned with
the flow path of the means for supplying the liquid. To simplify the description of
the invention, the means for supplying a liquid is often referred to as a cylindrical
tube (tube shape could be varied, e.g. oval, square, rectangular). The first fluid
or liquid can be any liquid depending on the overall device which the invention is
used within. For example, the liquid could be a liquid formulation of a pharmaceutically
active drug used to create dry particles or liquid particles for an aerosol for inhalation
or, alternatively, it could be a hydrocarbon fuel used in connection with a fuel injector
for use on an internal combustion engine or heater or other device which bums hydrocarbon
fuel. Further, for purposes of simplicity, the second fluid is generally described
herein as being a gas and that gas is generally air or an inert gas. However, the
first fluid is a liquid and the second fluid may be a gas or a liquid provided the
first and second fluids are sufficiently different from each other (e.g. immiscible).
It is possible to have situations wherein the liquid exits either the liquid supply
means or the pressure chamber vaporizes to a gas on exit. Such is not the general
situation. Notwithstanding these different combinations of liquid-gas, and liquid-liquid,
the invention is generally described with a liquid formulation being expelled from
the supply means and interacting with surrounding gas flowing out of an exit of the
pressure chamber. Further, the exit of the pressure chamber is generally described
as circular in cross-section and widening in a funnel shape (Fig. 1), but could be
any configuration.
[0019] Referring to the figures a cross-sectional schematic view of the nozzle 1 is shown
in Figure 1. The nozzle 1 is comprised of two basic components which include the pressure
chamber 2 and the liquid supply means 3. The pressure chamber 2 is pressurized by
fluid flowing into the chamber by the entrance port 4. The liquid supply means 3 includes
an inner tube 5 where liquid flows. The inner tube 5 of the liquid supply means 3
is preferably supplied with a continuous stream of a fluid which fluid is preferably
in the form of a liquid. The pressure chamber 2 is continuously supplied with a pressurized
fluid which may be a liquid or a gas. When the fluid is a liquid the liquid is preferably
insoluble and incompatible with the liquid being provided from the inner tube 5 (e.g.
oil and water which do not readily mix and form a distinct interface). The inner tube
5 of the liquid supply means 3 includes an exit point 6. The pressurized chamber 2
includes an exit point 7. The exit point 7 of the pressure chamber is preferably positioned
directly downstream of the flow of liquid exiting the exit point 6. The liquid supply
means exit and the exit of the pressure chamber are configured and positioned so as
to obtain two effects (1) the dimensions of the stream exiting the liquid supply means
are reduced by the fluid exiting the pressure chamber; and (2) the liquid exiting
the liquid supply means and the fluid exiting the pressure chamber undergo a violent
interaction to form much smaller particles than would form if the stream of liquid
in reduced dimensions underwent normal capillary instability, e.g. formed spherical
particles 1.89 times the diameter of the cylindrical stream.
[0020] Preferably, the exit port of the chamber 2 is directly aligned with the flow of liquid
exiting the liquid supply means 3. An important aspect of the invention is to obtain
small particles 8 from the liquid 9 flowing out of the exit port 6 of the inner tube
5. Obtaining the desired formation of particles 8 is obtained by correctly positioning
and proportioning the various components of the liquid supply means 3 and the chamber
2 as well as the properties of the fluids including the speed of these fluids which
flow out of both the liquid supply means 3 and the chamber 2. Specifically, there
are some important geometric parameters that define the nozzle 1 of the present invention.
Those skilled in the art will adjust those parameters using the information provided
here in order to obtain the most preferred results depending on a particular situation.
[0021] Preferably, the liquid 9 is held within the inner tube 5 which is cylindrical in
shape. However, the inner tube 5 holding the liquid 9 may be asymmetric, oval, square,
rectangular or in other configurations including a configuration which would present
a substantially planar flow of liquid 9 out of the exit port 6. Thus, the nozzle of
the invention applies to all kinds of round (e.g., axi-symmetric) and planar (e.g.,
symmetric two-dimensional) configurations that have a convergent passage for the outer
fluid. For example, a round but not axi-symmetric geometry would be one in which the
surfaces of the orifice plate are faceted at different azimuthal angles. Accordingly,
the figures including Figure 1 are used only to define the variables but are not intended
to imply any restrictions on the type of geometry or the specific details of the design
of the nozzle 1 of the present invention. There are infinite degrees of freedom of
design. For example, corners which are shown as sharp could be rounded or finished
in different ways.
[0022] Formation of the microjet and its acceleration and ultimate particle formation are
based on the abrupt pressure drop associated with the steep acceleration experienced
by the liquid on passing through an exit orifice of the pressure chamber which holds
the second fluid (i.e. the gas).
[0023] Without being limited to any one theory, the creation of the violently focused aerosol
(in an axisymmetric configuration) may occur as follows. The strong radial fluid flow
(10) that exists in the very narrow gap between the points 6 and 7 becomes circulatory
as it passes through and out of the orifice of the exit 7 of the pressure chamber
2. At the same time, the liquid (9) meniscus is sucked in towards the center of the
exit point 7 of the chamber 2. As the gas 10 exits the hole at point 7, its strong
circulatory motion induces the fluid dynamic effect referred to as a vortex breakdown.
This is an instability in which fluid particles gain so much centrifugal inertia that
they spin off away from the axis. As a result, a bubble of gas is created along the
axis downstream from this point, in which the outer fluid (preferably a gas) flow
reverses, flowing upstream back towards the nozzle. Consequently, the droplets are
accelerated radially outwards resulting in enhanced dispersion.
[0024] Referring now to Figure 2 in order to describe the relationships between some of
the components shown in Figure 1. First, a dashed line C---C' is shown running through
the center of the inner tube 5 in which the liquid 9 flows as well as the exit of
the chamber 2. In symmetric atomizers the line C--C' represents the plane of symmetry
intersection of the plane of view. The line B--B' represents the bisector of the convergent
passage near the center of the nozzle. The area referred to as the "convergent passage"
is the region which is the open area between the terminal face 11 of the liquid supply
means 3 and the front face 12 of the chamber 2. To obtain desired results with the
nozzle of the present invention the following characteristics must be present:
- (a) a strong convergence of the outer fluid (liquid of gas) in the chamber 2 towards
and around the inner fluid 9 coming out of the inner tube 5;
- (b) sufficient momentum for the fluid 10 in the chamber 2 before it interacts with
the fluid 9;
- (c) a focusing or compression of the stream of liquid 9 by the surrounding fluid 10.
[0025] The above characteristics (a)-(c) combine with each and with other characteristics
in order to result in the desired (d) vortex breakdown of the stream of fluid 9 exiting
the inner tube 5. For example, other characteristics will include sonic speeds and
shock waves (e) when the outer fluid 10 is a gas.
[0026] In order to more fully understand the invention each of the characteristics (a)-(e)
referred to above are described in further detail below.
(a) Strong convergence of outer fluid:
[0027] The primary characteristic of the present invention is the facilitation of a strongly
convergent (imploding) flow of outer fluid 10 towards and around the inner liquid
9. The fluid 10 in the pressure chamber should preferably not merely flow parallel
to the liquid 9 exiting the liquid supply means, i.e. should preferably not intersect
at a 0 degree angle. Further, the fluid 10 in the pressure chamber should preferably
not flow directly perpendicular to the liquid stream 9 exiting the liquid supply means,
i.e. should preferably not interact at a 90 degree angle or more. Thus, convergence
of the two fluids is preferably at an angle of more than 0 degrees and less than 90
degrees. However, the fluid 10 of the pressure chamber could, in some situations be
directed at the liquid 9 from the liquid supply means at an angle of 90 degrees or
more, i.e., at an angle such that the fluid 10 is flowing back toward the liquid 9
and is converging on the liquid 9 at an angle of up to 150 degrees.
[0028] Flow convergence improves the transfers of momentum and kinetic energy from the outer
fluid 10 to the inner liquid 9 required to breakup the inner fluid 9 into particles
8. Improving the efficiency of such transfer results in energy savings for a given
amount of inner liquid 9 atomized and a given droplet size requirement. A greater
efficiency of atomization is achieved by transferring a greater fraction of pressure
energy originally in the outer fluid 10 per unit mass of the outer fluid to the inner
liquid 9.
(b) Incident momentum in outer fluid:
[0030] To ensure sufficient momentum in the outer fluid at the point where it meets the
inner liquid 9, the convergent passage separation between R and P (see Figure 2) must
be chosen appropriately. This distance can be defined as the distance between points
R and P in Figure 2. For given conditions of pressure and temperature in the outer
fluid chamber and outside region, this variable regulates the relative average velocity
between the inner liquid 9 and the outer fluid 10 at the point of encounter (inner
rim of tube exit indicated by point P' in Figures 2 and 3). For example, a very narrow
convergent passage is one in which frictional losses dissipate the outer fluid momentum
significantly. Widening such a passage will encourage coupling between outer fluid
10 and inner liquid 9. On the other hand, if the separation between R and P is made
too wide, then the effect of efficient atomization is lost, because the fastest speed
is encountered then in the discharge orifice, not at the end of the convergent passage.
[0031] In general, thus, one desires to have as high a momentum as possible in the outer
fluid 10 for a certain amount of outer fluid mass flow (and pressure and temperature
conditions). The ratio between momentum and mass fluxes is similar to its average
speed (in fact, is very nearly such value when variations in local speed are negligibly
small across the convergent passage). The fastest speed is generally obtained in the
narrowest part of the outer fluid flow path. Again, if the distance between R and
P is too large, then the narrowest part will be at the discharge orifice. Thus, if
the distance ofR to P is H the largest value of H compatible with this requirement
typically is:
[0032] For axi-symmetric configurations, β equals 0.25; while for planar-two dimensional
configurations, β equals 0.5.
[0033] On the other hand, H must be large enough to preclude excessive friction between
the outer fluid and the convergent passage walls that can slow down the flow and waste
pressure energy (stagnation enthalpy) into heat (internal energy). An approximate
guiding principle is that H should be greater than H
min, defined as a few times the thickness of the viscous boundary layer δ
L that develops inside the outer fluid 10 in its acceleration through the convergent
passage:
[0034] The thickness of the boundary layer at point P' (Figure 2) for the case when the
outer fluid is near the speed of sound is approximately given by the following expression:
[0035] Here µ
2 is the dynamic viscosity coefficient of the outer fluid 10, ρ
2 is its density, and P
o2 is the pressure of the outer fluid 10 in the upstream chamber. λ is a numerical factor,
which generally is between 1 and 10. L is the length of the convergent passage (Figure
3)
[0036] These expressions neglect the presence of liquid in the discharge orifice, or the
possibility of swirling in the flow. Therefore, the equations provided above should
be considered as approximate guides, e.g. ±30% error factors.
(c) Flow-focusing of the inner liquid:
[0037] In the presence of airflow, the inner liquid 9 coming out of the inner tube 5 gets
funnel-shaped into a jet that gets thinner as it flows downstream. The jet can have
a variety of different configurations, e.g. a circular cross-section, or a flat planar
one. Any configuration can be used which provides flows through the center of the
discharge orifice 7, and can become much thinner as it enters the discharge orifice
7 than at the exit 6 of the inner tube 5. This phenomenon has previously been termed
"flow-focusing" (see
WO 99/31019 published June 24, 1999). The forces responsible for the shaping of the inner liquid 9 are believed to arise
from the pressure gradients that set within the outer fluid 10 as it flows through
the discharge orifice 7. For example, in axi-symmetric configurations, a round inner
liquid jet is expected to attain a diameter dj determined by the ½ power law with
liquid flow rate Q (in volume per unit of time, e.g. cubic meter per second; Gañán-Calvo
A. M., 1998):
ρ
1 is the inner liquid density, π is pi, and ΔP
g is the pressure drop in the outer fluid between the upstream value and the value
at the point where d
j is taken and ∼ means approximately equal to with about a ± 10% error margin. This
equation will be herein referred to as the "flow-focusing" formula and only applies
for a uniform velocity distribution along the inner liquid jet radius.
[0038] A notable consequence of flow-focusing is that the inner liquid is stabilized towards
the center of the discharge orifice. For example, in one of the preferred device embodiments
(Figure 5), the exit of both the inner tube 5 and the chamber 2 at point 7 were of
equal diameter. However, in all the tests done the inner liquid 9 was observed to
flow through the center of the discharge orifice without impacting or wetting its
side walls. (Due to the random nature of the drop trajectories under conditions of
very high inner liquid flow rates used for violent focusing, a small degree of wetting
has indeed been detected, but is associated with an insignificant fraction of the
inner liquid.)
(d) Vortex breakdown:
[0039] A theoretical model based on the existence of a vortex cell near the region of breakup
is proposed to explain the effectiveness of atomization obtained by the present invention
in the case of axi-symmetric geometries. In such cases, it is hypothesized that the
strong radial forces provided by the outer fluid flow between the orifice body and
the liquid dispenser (a cylindrical tube in its simplest form) result in a violent
swirl in the outer fluid (Shtem and Hussain 1999). The swirling motion results in
a vortex which breaks down near the region of breakup. Such breakdown is the centrifugal
explosion of the fluid streamlines due to their rapid spinning motion. The entrained
particles and filaments of the inner liquid are spun away and dispersed before they
get a chance to coalesce (two or more particles forming one). The benefits of vortex
breakdown in promoting liquid breakup and drop dispersion have previously been reported
(Hopfinger and Lasheras 1996; Lasheras et al. 1998). In the new invention any swirling
of the outer fluid is not created upstream by means of swirling vanes or other shapes
of the atomizer body. Instead, the swirling is induced locally by the strong converging
motions forced by the very simple geometry of the atomizer.
(e) Gas sonic speeds and shock waves:
[0040] Sonic speeds and shock waves take place when the outer fluid is a gas. In all tests
to date using that configuration, the pressure drop across the atomizer was such that
the gas attained sonic and supersonic speeds. Under these conditions shock waves are
also expected to be present.
[0041] Characteristics of supersonic flow such as shock waves may improve atomization. However,
such are not believed to be required.
[0042] Unique characteristics of the present invention include: (f) High frequency of droplet
generation, (g) Low requirements on liquid pressure, (h) Low sensitivity of drop size
to inner liquid flow rate, (i) Little apparent effect of atomizer size on droplet
size. These characteristics are described further below.
(f) High frequency of droplet generation:
[0043] When the outer fluid is a gas and the inner fluid a liquid, the data demonstrate
that the droplets are much smaller than predicted from the spontaneous capillary breakup,
such as Rayleigh breakup in axi-symmetric configurations; (Rayleigh 1882) of an inner
liquid column of size dj equal to that predicted by the flow-focusing formula discussed
earlier. Or, what is the same, for given values of the liquid properties and operational
variables, the final size of the droplets is many times smaller than the flow-focusing
diameter dj discussed earlier. As a result, the frequency of droplet production is
much higher than predicted by spontaneous capillary breakup of the flow focused jet.
Accordingly, particles formed via the method described here are substantially smaller
(e.g. 1/2 the size or less or 1/20 the size or less) than would be obtained due to
spontaneous capillary break-up of the stream exiting the tube 5 and chamber 2. (See
Figure 7)
(g) Low requirements on liquid pressure:
[0044] The inner liquid 9 does not have to be pushed out of its inner tube 5 with a sufficiently
high pressure capable of maintaining a stable liquid jet in the absence of outer fluid
flow and solid surfaces in its way. It is not necessary for the inner liquid to form
a stable microjet structure. Further, pre-existent inner liquid jet structure coming
directly out of the exit opening 6 is not required because, a explained in (c), the
liquid meniscus is focused by the action of the outer fluid pressure forces.
(h) Low sensitivity of drop size to inner liquid flow rate:
[0045] In the cases tested thus far, a low sensitivity of droplet size on flow rate has
been observed. The dependence is close to a power law with exponent 1/5 of the liquid
flow rate.
(i) Small apparent effect of atomizer size:
[0046] Based on the experimental data available thus far (reported later herein), the drop
size dependence with inner liquid flow rate, outer fluid pressure and inner liquid
physical properties does not seem to involve any variables characterizing the size
of the atomizer. (See the EXAMPLES.) However, under certain conditions of operation,
for example at high flow rates that lead to a large fraction of the discharge orifice
occupied by the liquid, one would expect certain dependence.
EXAMPLES
[0047] The following examples are put forth so as to provide those of ordinary skill in
the art with a complete disclosure and description of how to make and use the present
invention, and are not intended to limit the scope of what the inventors regard as
their invention nor are they intended to represent that the experiments below are
all or the only experiments performed. Efforts have been made to ensure accuracy with
respect to numbers used (
e.g. amounts, temperature, etc.) but some experimental errors and deviations should be
accounted for. Unless indicated otherwise, parts are parts by weight, molecular weight
is weight average molecular weight, temperature is in degrees Centigrade.
[0048] Figures 6-9 show results for aerosols produced by methods of the present invention
using dry air and dry nitrogen as outer fluids 10, and a range of liquids as inner
fluids 9: distilled water, 2-propanol, 20 % (v/v) by volume of ethanol in water ("20%EtOH"),
and 0.1 % weight in volume (w/v) Polysorbate-20 in distilled de-ionized water ("0.1%Tween").
Tests were performed in four separate experiments with different atomizers. The atomizers
were of an axi-symmetric type and had dimensions as specified below in Table A.
[0049] The droplet size was determined by phase Doppler anemometry (Lefebvre 1989; Bayvel
and Orzechowski 1993) along the axis of the aerosol plume a few centimeters downstream
from the exit of the atomizer. This measurement technique led to notoriously low rates
of validated counts, i.e. low rates of detected light pulses ("bursts"). This problem
appears to result from a combination of high droplet concentrations and high velocities.
Validation count rates lower than 50% have been excluded from the sets of data presented
here. As a consequence, all of the droplet size measurements in experiments 3 and
4 with were excluded from the graphs. Nevertheless, atomizer dimensions have been
included in table A to indicate that stable aerosols were obtained in a third and
fourth experiment with an atomizer of similar characteristics as in experiment 2,
but otherwise of a very different design.
TABLE A
Atomizer geometric dimensions (in micron unless indicated) used in the experiments
(refer to figure for key); typical tolerance +/-15%, (α=0 degrees; β=90 degrees) |
Experiment |
Do |
Dt |
D1 |
H |
T |
ϕ, degrees |
θ, degrees |
1 |
62 |
50 |
90 |
19 |
50 |
13 +/-7 |
60 |
2 |
200 |
200 |
400 |
35 |
75 |
0 |
0 |
3 |
200 |
200 |
400 |
50 |
75 |
0 |
0 |
4 |
200 |
200 |
400 |
50-80 |
75 |
0 |
0 |
[0050] Figure 6 is a graph of the volume median diameter (VMD) vs the liquid supply flow
rate for four different liquids.
[0051] In Figure 7 the volume median diameter and liquid flow rates have been non-dimensionalized
using similar variables to those identified in the flow-focusing literature (Gañán-Calvo
1998), d
o and Q
o:
and
where σ is the interfacial tension of the liquid-gas interface (newton/meter). However,
the definition of the pressure drop ΔP
g used here is based not on the upstream (stagnation) and downstream (ambient) values
of the pressure, but on the upstream value P
o and the value P* at the sonic point. The sonic pressure was computed using the well-known
isentropic expression:
where k is the heat capacity ratio of the gas (equal to 1.4 for dry air and dry nitrogen;
White 1994). Therefore
Thus, for both dry air and nitrogen,
In these experiments P
o was varied between 200 kPa and 700 kPa.
The best power law fit to the available data (Figure 7) is:
Figure 8 graphs the new fit characteristic of the new method together with the one
which would correspond to the Rayleigh breakup of a flow focused jet at the same conditions
of liquid properties, flow rate, and gas pressure (thus equal d
o, Q, and Q
o). The results shown in Figure 8 are based on the theoretical assumption that Rayleigh
breakup of a flow-focused jet would result in droplets of uniform diameter (VMD) equal
to 1.89 times the jet diameter (Brodkey 1995). Applying the equation for the jet diameter
given earlier leads to:
This expression can be cast into dimensionless form using the definitions of d
o and Q
o:
[0052] In Figure 8 the "Rayleigh breakup" line has been represented between the limits believed
to occur in reality. If this expression could be extrapolated to higher Q/Qo values,
it would predict larger drop sizes at equal conditions of Q/Qo and do. But, more importantly,
because the dependence with Q/Qo is much less pronounced than for flow-focused jets,
the range of liquid flow rates over which a certain band of desired drop sizes can
be generated is much wider than from Rayleigh breakup of flow-focused jets. These
conclusions should apply as well when a comparison is being made to non-Rayleigh breakup
of flow-focused jets, provided the droplet diameters become similar to the jet diameter.
[0053] Another notable result is that data from dissimilar atomizers seems to follow the
same scaling law. In other words, based on currently available data, the scaling law
appears to be relatively insensitive to the scale of the atomizer.
[0054] The proposed atomization system obviously requires delivery of the liquid to be atomized
and the gas to be used in the resulting spray. Both should be fed at a rate ensuring
that the system lies within the desired parameter window. Multiplexing is effective
when the flow-rates needed exceed those obtained for an individual cell. More specifically,
a plurality of feeding sources 3 or holes therein forming tubes 3 may be used to increase
the rate at which aerosols are created. The flow-rates used should also ensure the
mass ratio between the flows is compatible with the specifications of each application.
[0055] The gas and liquid can be dispensed by any type of continuous delivery system (e.g.
a compressor or a pressurized tank the former and a volumetric pump or a pressurized
bottle the latter). If multiplexing is needed, the liquid flow-rate should be as uniform
as possible among cells; this may entail propulsion through several capillary needles,
porous media or any other medium capable of distributing a uniform flow among different
feeding points.
[0056] Although a single liquid supply means 3 is shown in Figures 1-5 it, of course, is
possible to produce a device with a plurality of feeding members where each feeding
member feeds fluid to an array of outlet orifices in a single surrounding pressure
chamber. In addition, the liquid supply means may be planar with grooves therein,
but need not be strictly planar, and may be a curved feeding device comprised of two
surfaces that maintain approximately the same spatial distance between the two pieces
of the liquid supply means. Such curved devices may have any level of curvature, e.g.
circular, semicircular, elliptical, hemi-elliptical, etc.
DRUG DELIVERY DEVICE
[0057] A device of the invention may be used to provide particles for drug delivery, e.g.
the pulmonary delivery of aerosolized pharmaceutical compositions. The device would
produce aerosolized particles of a pharmaceutically active drug for delivery to a
patient by inhalation. The device is comprised of a liquid feeding source such as
a channel to which formulation is added at one end and expelled through an exit opening.
The feeding channel is surrounded by a pressurized chamber into which gas is fed and
out of which gas is expelled from an opening. The opening from which the gas is expelled
is positioned directly in front of the flow path of liquid expelled from the feeding
channel. Various parameters are adjusted so that pressurized gas surrounds liquid
flowing out of the feeding channel in a manner so as to reduce the dimension of the
flow which is then broken up on leaving the chamber. The aerosolized particles are
inhaled into a patient's lungs and thereafter reach the patient's circulatory system.
PRODUCTION OF DRY PARTICLES
[0058] The method of the invention is also applicable in the mass production of dry particles.
Such particles are useful in providing highly dispersible dry pharmaceutical particles
containing a drug suitable for a drug delivery system, e.g. implants, injectables
or pulmonary delivery. The particles formed of pharmaceutical are particularly useful
in a dry powder inhaler due to the small size of the particles (e.g. 1-5 microns in
aerodynamic diameter) and conformity of size (e.g. 3 to 30% difference in diameter)
from particle to particle. Such particles should improve dosage by providing accurate
and precise amounts of dispersible particles to a patient in need of treatment. Dry
particles are also useful because they may serve as a particle size standard in numerous
applications.
[0059] For the formation of dry particles, the first fluid is preferably a liquid, and the
second fluid is preferably a gas, although two liquids may also be used provided they
are generally immiscible. Atomized particles are produced within a desired size range
(e.g., 1 micron to about 5 microns). The first fluid liquid is preferably a solution
containing a high concentration of solute. Alternatively, the first fluid liquid is
a suspension containing a uniform concentration of suspended matter. In either case,
the liquid quickly evaporates upon atomization (due to the small size of the particles
formed) to leave very small dry particles.
FUEL INJECTION APPARATUS
[0060] The device of the invention is useful to introduce fuel into internal combustion
engines by functioning as a fuel injection nozzle, which introduces a fine spray of
aerosolized fuel into the combustion chamber of the engine. The fuel injection nozzle
has a unique fuel delivery system with a pressure chamber and a fuel source. Atomized
fuel particles within a desired size range (e.g., 5 micron to about 500 microns, and
preferably between 10 and 100 microns) are produced from a liquid fuel formulation
provided via a fuel supply opening. Different size particles of fuel may be required
for different engines. The fuel may be provided in any desired manner, e.g., forced
through a channel of a feeding needle and expelled out of an exit opening of the needle.
Simultaneously, a second fluid, e.g. air, contained in a pressure chamber which surrounds
at least the area where the formulation is provided (e.g., surrounds the exit opening
of the needle) is forced out of an opening positioned in front of the flow path of
the provided fuel (e.g. in front of the fuel expelled from the feeding needle). Various
parameters are adjusted to obtain a fuel-fluid interface and an aerosol of the fuel,
which allow formation of atomized fuel particles on exiting the opening of the pressurized
chamber.
[0061] Fuel injectors of the invention have two significant advantages over prior injectors.
First, fuel generally does not contact the periphery of the exit orifice from which
it is emitted because the fuel stream is surrounded by a gas (e.g. air) which flows
into the exit orifice. Thus, clogging of the orifice is eliminated or substantially
reduced. In addition, formation of carbon deposits around the orifice exit is also
substantially reduced or eliminated. Second, the fuel exits the orifice and forms
very small particles which may be substantially uniform in size, thereby allowing
faster and more controlled combustion of the fuel.
MICROFABRICATION
[0062] Molecular assembly presents a 'bottom-up' approach to the fabrication of objects
specified with incredible precision. Molecular assembly includes construction of objects
using tiny assembly components, which can be arranged using techniques such as microscopy,
e.g. scanning electron microspray. Molecular self-assembly is a related strategy in
chemical synthesis, with the potential of generating nonbiological structures with
dimensions as small as 1 to 100 nanometers, and having molecular weights of 10
4 to 10
10 daltons. Microelectro-deposition and microetching can also be used in microfabrication
of objects having distinct, patterned surfaces.
[0063] Atomized particles within a desired size range (e.g., 0.001 micron to about 0.5 microns)
can be produced to serve as assembly components to serve as building blocks for the
microfabrication of objects, or may serve as templates for the self-assembly of monolayers
for microassembly of objects. In addition, the method of the invention can employ
an atomizate to etch configurations and/or patterns onto the surface of an object
by removing a selected portion of the surface.
[0064] The instant invention is shown and described herein in a manner which is considered
to be the most practical and preferred embodiments. It is recognized, however, that
departures may be made therefrom which are within the scope of the invention and that
obvious modifications will occur to one skilled in the art upon reading this disclosure.