U.S. patent application number 11/993517 was filed with the patent office on 2010-02-25 for electrostatic atomiser.
Invention is credited to Jeffrey Allen, Paul Bartholomew Ravenhill.
Application Number | 20100044474 11/993517 |
Document ID | / |
Family ID | 34896911 |
Filed Date | 2010-02-25 |
United States Patent
Application |
20100044474 |
Kind Code |
A1 |
Allen; Jeffrey ; et
al. |
February 25, 2010 |
ELECTROSTATIC ATOMISER
Abstract
The present invention relates to (with reference to FIG. 1) an
electrostatic fluid atomiser which has a fluid inlet (2) and a
fluid channel (3) leading fluid to a wall (6) in which orifices
(100) are formed. Fluid passing out of the orifices (100) is
atomised into droplets which fall into a first set of larger
droplets (12) and a second set of smaller droplets (13). Two
charging electrodes (4,6) charge fluid passing through the channel
(3). A droplet separator (200) has a separator electrode (16) which
applies an electrical force on the droplets and deflects the
smaller droplets (13) to he collected by a droplet collector (15)
while the larger droplets (12) continue undeflected out of a
droplet (201) of the atomiser.
Inventors: |
Allen; Jeffrey; ( Norfolk,
GB) ; Ravenhill; Paul Bartholomew; (Norfolk,
GB) |
Correspondence
Address: |
LUEDEKA, NEELY & GRAHAM, P.C.
P O BOX 1871
KNOXVILLE
TN
37901
US
|
Family ID: |
34896911 |
Appl. No.: |
11/993517 |
Filed: |
July 6, 2006 |
PCT Filed: |
July 6, 2006 |
PCT NO: |
PCT/GB2006/002506 |
371 Date: |
December 21, 2007 |
Current U.S.
Class: |
239/690 |
Current CPC
Class: |
B05B 5/08 20130101; B05B
5/025 20130101 |
Class at
Publication: |
239/690 |
International
Class: |
F23D 11/32 20060101
F23D011/32 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 8, 2005 |
GB |
0514000.9 |
Claims
1. An electrostatic atomiser, comprising: a fluid inlet; one or
more orifices out of which the fluid emerges in an atomised form
which comprises at least a first set of droplets of comparable size
to each other and a second set of droplets of comparable size to
each other and of a smaller size to the droplets of the first set;
a fluid channel connecting the fluid inlet to the orifice(s); and
at least two charging electrodes for applying a charge to fluid
passing through the fluid channel; wherein the electrostatic
atomiser comprises a fluid droplet separator extending downstream
of the orifices having a first separator electrode which is either
earthed or electrically charged and which applies an electrical
force on the droplets which deflects the second set of smaller
droplets to a droplet collector while allowing the first set of
larger droplets to continue out of a droplet outlet of the
atomiser; and the droplet collector is located upstream of the
fluid outlet whereby only the larger droplets of the first set are
output by the atomiser out of the droplet outlet, the smaller
droplets of the first set having been collected within the atomiser
by the droplet collector.
2. An electrostatic atomiser according to claim 1 wherein said
droplet collector comprises an absorbent layer.
3. An electrostatic atomiser as claimed in claim 1 wherein the
first separator electrode applies an attractive electrical force on
the fluid droplets attracting the fluid droplets to move towards
the first separator electrode.
4. An electrostatic atomiser as claimed in claim 1 wherein the
first separator electrode is a cylindrical wall disposed around the
orifices and extending downstream.
5. An electrostatic atomiser as claimed in claim 4 comprising a
second separator electrode extending spaced apart from and parallel
to the cylindrical wall and either earthed or charged to apply an
attractive electrical force on the droplets, the atomiser having a
second fluid droplet collector which collects the droplets
attracted by the second separator electrode.
6. An electrostatic atomiser as claimed in claim 5 wherein the
second fluid droplet collector is connected to a fluid return via a
conduit which passes through passages formed in the charging
electrodes, the fluid return returning fluid collected by the
droplet collector to the fluid inlet.
7. An electrostatic atomiser as claimed in claim 1 wherein the
orifices are provided in an orifice wall and said fluid droplet
separator comprises a plurality of fluid collectors spaced apart
from each other and extending from locations on the orifice wall
located between the orifices and extending from the orifice wall in
a downstream direction.
8. An electrostatic atomiser as claimed in claim 7 wherein each of
the fluid collectors is associated with a separator electrode
individual thereto which is electrically charged to attract the
fluid droplets to the fluid collector.
9. An electrostatic atomiser as claimed in claim 7 wherein the
orifice wall functions as a charging electrode.
10. An electrostatic atomiser as claimed in claim 3 comprising a
second separator electrode spaced apart from the first separator
electrode and electrically charged with a voltage of a different
polarity to the first separator electrode, and which applies a
repelling electrical force on the fluid droplets repelling the
fluid droplets away from the second electrode towards the droplet
collector.
11. An electrostatic atomiser as claimed in claim 1 wherein the
orifices are provided in an orifice wall which also functions as
one of the charging electrodes.
12. An electrostatic atomiser as claimed in claim 1 further
comprising a fluid return for returning fluid collected by the
droplet collector to the fluid inlet.
13. An electrostatic atomiser as claimed in claim 1 wherein the
atomiser incorporates multiple orifices in close proximity to a
substantially planar surface of a charging electrode which spans
said multiple orifices.
14. An electrostatic atomiser as claimed in claim 1 comprising
orifices angled to generate converging streams of droplets.
15. An electrostatic atomiser as claimed in claim 1 comprising
orifices angled to generate diverging streams of droplets.
16. An electrostatic atomiser as claimed in claim 1, wherein the
first separator electrode is electrically connected to one of said
charging electrodes.
17. An electrostatic atomiser as claimed in claim 5 wherein the
second separator electrode is electrically connected to one of said
charging electrodes.
18. An electrostatic atomiser as claimed in claim 2 wherein the
first separator electrode applies an attractive electrical force on
the fluid droplets attracting the fluid droplets to move towards
the first separator electrode.
19. An electrostatic atomiser as claimed in claim 3 wherein the
first separator electrode is a cylindrical wall disposed around the
orifices and extending downstream.
20. An electrostatic atomiser as claimed in claim 19 comprising a
second separator electrode extending spaced apart from and parallel
to the cylindrical wall and either earthed or charged to apply an
attractive electrical force on the droplets, the atomiser having a
second fluid droplet collector which collects the droplets
attracted by the second separator electrode.
21. An electrostatic atomiser as claimed in claim 20 wherein the
second fluid droplet collector is connected to a fluid return via a
conduit which passes through passages formed in the charging
electrodes, the fluid return returning fluid collected by the
droplet collector to the fluid inlet.
22. An electrostatic atomiser as claimed in claim 21 wherein the
orifices are provided in an orifice wall and said fluid droplet
separator comprises a plurality of fluid collectors spaced apart
from each other and extending from locations on the orifice wall
located between the orifices and extending from the orifice wall in
a downstream direction.
23. An electrostatic atomiser as claimed in claim 22 wherein each
of the fluid collectors is associated with a separator electrode
individual thereto which is electrically charged to attract the
fluid droplets to the fluid collector.
24. An electrostatic atomiser as claimed in claim 23 wherein the
orifice wall functions as a charging electrode.
25. An electrostatic atomiser as claimed in claim 3, wherein the
first separator electrode is electrically connected to one of said
charging electrodes.
Description
[0001] The invention relates to electrostatic atomisers which may
have a wide variety of applications, particularly in the fields of
drying, coating and mixing, where, despite a need for large flow
rates, it is very important that the drops are of a consistent
size, i.e. their diameters fall within a selected range of
diameters.
[0002] The closest prior art known is the applicant's own prior
published patent application, PCT/GB2004/000458. This prior
published patent application discloses the use of multiple orifice
atomisers with a primary charging electrode spanning an array of
orifices. With constant fluid flow such electrostatic atomisers
produce two distinctly differently sized sets of droplets. Due to
the physics of droplet formation each pair of larger sized droplets
are separated by a smaller droplet. For example, the smaller sized
droplets may have diameters between 20 and 80 microns, whilst the
larger sized droplets may have diameters between 150 and 350
microns. Due to such differences in size, the smaller droplets will
have much lower mass whilst having much higher specific electrical
charge than the larger droplets. Since in many applications it is
desirable to obtain fluid droplets of a consistent size, i.e.
within a selected range of diameters, there is a need for an
electrostatic atomiser which acts to separate larger droplets from
smaller droplets.
[0003] In a first aspect, the present invention provides an
electrostatic fluid-atomiser, comprising: a fluid inlet; one or
more orifices out of which fluid emerges in an atomised form which
comprises at least a first set of droplets of comparable size to
each other and second set of droplets of comparable size to each
other and of a smaller size to the droplets of the first set; a
fluid channel connecting the fluid inlet to the orifice(s); and at
least two charging electrodes for applying a charge to fluid
passing through the fluid channel; wherein the electrostatic
atomiser comprises a fluid droplet separator downstream of the
orifices having a separator electrode which is either earthed or
electrically charged and which applies an electrical force on the
droplets which deflects the second set of smaller droplets to a
droplet collector of the atomiser while allowing the first set of
larger droplets to continue out of a droplet outlet of the
atomiser.
[0004] This configuration is advantageous because it allows the
electrostatic fluid atomiser to output only fluid droplets of sizes
falling within a selected range.
[0005] The droplet collector can comprise an absorbent wall or a
porous wall. The wall can be cylindrical and disposed surrounding
the droplets as they leave the orifices. The fluid droplet
connector can be connected to a fluid return line. The fluid return
line can easily avoid crossing the path of the orifices when the
droplet collector comprises a cylindrical wall surrounding the
droplets emerging from the orifices.
[0006] The fluid return line returns the collected droplets to the
fluid input. This configuration maximises the efficiency of the
electrostatic atomiser; there is no waste or only minimal
waste.
[0007] The orifices may comprise multiple orifices in close
proximity to a substantially flat surface of one of the charging
electrodes which spans the multiple orifices. This configuration
will provide an ideal combination of evenly spread atomisation
across multiple orifices and efficient collection of a second set
of droplets.
[0008] The orifices can be angled to generate a converging or a
diverging stream of atomised droplets. In certain applications,
generating directed streams will allow improved collection by the
droplet collector, when compared to the use of parallel straight
orifices.
[0009] The orifices are preferably provided in an orifice wall and
the droplet collector can then be provided with a plurality of
portions projecting from the orifice wall between the orifices in a
downstream direction. This will allow improved collection of small
droplets within a central portion of an array of orifices as well
as maintaining excellent small droplet collection from the outer
portions of the ejected jet of fluid.
[0010] The separator electrode of the fluid droplet separator could
be electrically connected to one of said charging electrodes.
[0011] Preferred embodiments of the present invention will now be
described with reference to the accompanying drawings, in
which:
[0012] FIG. 1 is a perspective view, partly in cross-section, of a
first embodiment of an electrostatic fluid atomiser according to
the present invention with components external to the atomiser
shown schematically;
[0013] FIGS. 2a and 2b show alternative geometries of orifices of
the atomiser of FIG. 1 (or of the atomiser of FIGS. 3 and 4);
[0014] FIG. 3 shows in cross-section a second embodiment of
electrostatic fluid atomiser according to the present invention,
with components external to the atomiser again shown schematically;
and
[0015] FIG. 4 shows a third embodiment of electrostatic fluid
atomiser according to the present invention, with components
external to the atomiser once more shown schematically.
[0016] FIG. 1 shows an electrostatic atomiser 1 with a fluid inlet
2. A fluid channel 3 connects the fluid inlet 3 to an array of
multiple orifices 100 provided in an orifice wall 6. Fluid passing
through the channel 3 is electrostatically charged by a pair of
charging electrodes comprising an electrode 4 and the orifice wall
5. In the figure it can be seen that a high voltage source 18 is
connected to apply a charge of a first polarity to the charging
electrode 4 and to apply a charge of the opposite polarity to the
wall 6. The electrode 4 has a tip 5 which is substantially flat and
spans the array of multiple orifices 100. The fluid, which may be
of the any kind of chargeable fluid, is pumped into the fluid inlet
by a pump 7. Prior to pumping, the fluid is filtered by a filter
8.
[0017] On emerging from the orifices 6 the fluid is atomised,
initially forming so-called "ligament" jets 9, 10 and 11, which
shortly thereafter break up into substantially two sets of droplets
which differ in size, a first set comprising droplets such as
droplet 12 (a relatively large droplet) and a second set comprising
droplets such as droplet 13 (a relatively small droplet). The small
droplets will each inevitably have a lower mass with a much higher
specific electrical charge than the large droplets.
[0018] The atomiser 1 is provided with a fluid droplet separator
200 for separating the set of small-sized droplets (e.g. 12) from
the set of large-sized droplets (e.g. 13), so that only the
large-sized droplets leave a fluid outlet 201 of the atomiser. The
separator 200 has a cylindrical wall 16 which surrounds the
droplets leaving the orifices 100. The wall 16 functions as a
separator electrode and is either appropriately charged or earthed,
in order to attract the droplets. In the figure the wall 16 is
connected to the high voltage source and charged with the same
polarity as the wall 6. The smaller droplets are attracted to a
greater extent than the larger droplets. Consequently, the smaller
droplets are deflected to the wall 16 whilst the larger droplets
will continue largely undeflected and exit the fluid outlet 201.
The separator 200 has a layer 14 of a porous absorbent material
located radially inwardly of the wall 16. The wall 16 has a
downstream portion which extends around a downstream end of the
porous layer 14, the wall 16 extending radially inwardly to form a
fluid channel 15 at the downstream end of layer 14.
[0019] Collected fluid is withdrawn from channel 15 by a scavenge
pump 17. The scavenge pump 17 draws the fluid from the droplet
collector 100 and relays the fluid to an accumulator tank 101.
Fluid from the tank 101 is then filtered and pumped back into the
fluid inlet 2.
[0020] The voltage applied to the charging electrodes 4, 6 and to
the wall 16 (which functions as the separator electrode) and the
sizes of orifices 100 may be adjusted in accordance with the
properties of the fluid used, the flow rate chosen and the desired
output droplet sizes.
[0021] In the FIG. 1 embodiment the wall 6 is provided with
multiple straight parallel orifices 100. An alternative geometry of
orifices is shown in FIGS. 2a and 2b. FIG. 2a shows a diverging
array of orifices 110 which would provide diverging streams of
droplets. FIG. 2b shows a converging array of orifices 111 which
would provide converging streams of droplets. The use of the
orifices 110, 111 of FIGS. 3a or 3b may be preferred for certain
fluids.
[0022] FIG. 3 shows a second embodiment of electrostatic atomiser
19. This embodiment shares many components in common with the first
embodiment of FIG. 1 and identical components are given identical
reference numerals. The atomiser has two charging electrodes 26,
27. They are both connected to the high voltage source 18 and a
voltage of a first polarity is applied to electrode 26 and a
voltage of a second opposite polarity is applied to the electrode
formed by orifice wall 27. The orifice wall 27 has a number of
orifices referenced 20, 21, 22, 23. Fluid passing through orifices
20, 21, 22, 23 is atomised and forms droplets in two sets, one set
of smaller-sized droplets and one set of larger-sized droplets. The
droplets all pass into a droplet separator 24. The droplet
separator 24 has an outer wall 25 which is charged or earthed to
attract and collect small droplets from outer jets 28, 29. In the
figure it can be seen that the separator wall 25 is connected to
the high voltage source 18 and is charged with the same polarity as
the orifice wall 27. The droplet separator 24 also has a central
collecting rod 30, which is charged or earthed to attract and so
collect droplets of central streams 31 and 32. In the figure the
electrode 30 is electrically connected to charging electrode 27 and
is charged with the same polarity. Both the outer wall 25 and the
rod 30 are provided with an absorbent layer; there is a layer 34
for wall 25 and a layer 35 for rod 30. A scavenge pump 33 is
provided to extract fluid collected by the rod 27 through a pipe 36
to be passed to an accumulator tank 101. The pipe 36 passes through
a central passage provided through electrode 26.
[0023] The lowermost surface of charging electrode 26 is provided
with a roughened surface opposite the orifices 20, 21, 22, 23 to
improve the charging of the fluid, e.g. by the provision of faceted
elements in a diamond coating or similar (as described in the
applicant's own previous patent application PCT/GB2004/000458).
Only the part of the surface opposite the orifices 20, 21, 22, 23
need be roughened/coated.
[0024] The invention also envisages using several spaced apart rods
of the same type as rod 30 in a large multi-orifice array so as to
minimise the occurrence of any small droplets exiting the atomiser.
The rods would extend from the orifice wall 27 downwardly (i.e.
downstream), would be spaced apart from one another and would
extend from parts of the wall 27 located between the orifices in
the wall 27.
[0025] FIG. 4 shows a further embodiment of electrostatic atomiser
39, which has components identical to those of FIG. 1; identical
components having identical reference numerals. As with the FIG. 1
embodiment, it has an input fluid line 40, charging electrode 41,
an array of multiple orifices 42, 43, 44, 45 in an orifice wall 46
which also functions as a second charging electrode, and a droplet
separator 47 with a charged or earthed external cylindrical droplet
collector wall 48. As shown in the figure the collector wall 48 is
connected to the high voltage source 18 and charged with the same
polarity as the orifice wall 46. Additionally, a central rod 50 is
located within a spray channel 49 in the separator 47 and the rod
50 is appropriately charged to repel the small charged droplets
towards the wall 48 where they are collected. The top of the rod 50
is separated from the orifice wall 46 by an insulator 51. The rod
50 is electrically connected to the charging electrode 41 by
connector 52. The planar bottom face of electrode 41 is provided
with faceted elements only in the region facing the orifices 42,
43, 44, 45.
* * * * *