Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
127~ Aven-t 3
An air transporting arrangement
The present invention relates to an arrangement for
transporting air with the aid of a so-called ion wind
or corona wind and being of the kind set forth in the
pre-characterizing clause of Claim 1.
It is known that air can, in principle, be transported
witn tne aid of a so-called electric ion-wind or corona-
wind. An electric ion-wind is created when a corona
electrode and a target electrode are placed at a distance
from one another and each connected to a respective
terminal of a d~c. voltage source, the corona electrode
and the d.c. voltage source being such as to cause a
corona discharge at the corona electrode. This corona
discharge results in ionization of the air, with the air
ions having the same polarity as the polarity of the
corona electrode, and possibly also in the production of
electrically charged aerosols, i.e. air-suspended solid
particles or liquid droplets which are electrically char-
ged as a result of collisions with the electrically char-
ged air ions. The air ions move rapidly from the coronaelectrode to the target electrode, under the influence
of the electric field, where they relinquish their
electric charge and return to electrically neutral air
molecules. During their movement from the corona elec-
trode to the target electrode, the air ions are in con-
stant collision with the electrically neutral air mole-
cules, therewith transferring electrostatic forces to
the neutral air molecules, so as to draw these molecules
from the corona electrode to the target electrode, result-
ing in the transportation o air in the form of a so-
called ion wind or corona wind.
Earlier proposed arrangements for transporting air with
the aid of ion-wind are found described, for example, in
DE-OS-2854716, DE-OS-2538959, GB-A-2112582, EP-A1-
29421, US 3,374,941 and US 4,38Q,720. These prior art
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arrangements have been found extremely ineffective,
however, and have not achieved any significance in prac-
tice. Air transporting arrangements which utilize the
ion-wind principle and which display marked improvemen-ts
over the aforesaid known arrangements, both with regard
to efficiency and to practical utility, are described in
our copending Canadian patent application 506,412.
It has been found, however, that air transporting arrange-
ments of this latter kind are encumbered with a particu-
lar problem, especially when there is used an elongated
corona electrode, for example an electrode which comprises
one or more mutually parallel, rectilinear thin wires
which extend across the airflow path between suitably
constructed holders at the ends of the electrode. When
using a corona electrode of this kind it has been found
that the electrode tends to produce a much higher corona
current per unit of length in the region of its centre,
i.e. within the central region of the airflow path, than
at its end regions. It would seem that this phenomenon
is the result of a screening effect created by the faste-
ners securing the ends of the electrode,
and by the wall of the airflow duct normally
surrounding the electrode arrangement. In the case of
low corona currents, a major part of the two end portions
of the corona electrode may even be "extinguished". This
phenomenon results in ureven distribution of the ion
current over the whole cross-section of the airflow path
and therewith in uneven flow velocity within said path.
In those cases where the airflow passage is defined by
duct walls, those parts of the path cross-section that
are located axially opposite the two end parts of the
corona electrode may even
have an airflow which is counterdirectional to
that desired. The phenomenon is particularly paramount
in the case of airflow ducts which have a narrow, elonga-
ted rectangular or slit-like cross-section. It will be
understood that this phenomenon greatly impairs the total
air throughput of the arrangement. In an extreme case,
the transportation of air through the duct may cease
altogether.
The object of the present invention is to provide an air
transporting arrangement of the kind described in the
introduction with which the aforementioned problems are
no longer found.
This is achieved in accordance with the invention by
means of an arrangement of the construction defined in
the following claims.
The invention will now be described in more detail with
reference to the accompanying drawings, in which
Figures 1-3 illustrate in perspective and by way of
example various embodiments of the invention in which
the target electrode comprises electrically conductive
surfaces located on or adjacent the wall of an airflow
duct surrounding the path of air flow;
Figures 4-6 illustrate schematically and by way of
example further embodiments of the invention in which
the target electrode comprises a net or grid; and
Figures 7-9 illustrate schematically, and by way of
example, other embodiments of the invention in which the
target electrode comprises a plurality of mutually paral-
lel, electrode plates or lamellae arranged perpendicular
to the longitudinal axis of the corona electrode.
Figure 1 illustrates schematically an air transporting
arrangement which operates in accordance with the ion
wind principle. The arrangement includes an airflow duct
1, shown in chain lines, a corona electrode K, and a
target electrode M. The electrodes are spaced axially
apart within the airflow duct 1, with the target elec-
trode M located downstream of the corona electrode K,
as seen in the desired direction 2 of air flow through
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the duct 1. In the illustratecl embodiment the airflow
duct 1 has a narrow, elongated rectangular or slit-like
cross-section. The corona electrode K comprises a thin,
rectilinear wire which extends across the airflow duct 1
along the major axis of the rectangular cross-section of
the duct, whereas the target electrode M comprises an elec-
trically conductive surface, or coating which i5 applied
adjacent to or directly on the inner surface of the duct
wall, and which extends fully around the wall. The corona
electrode K and the target electrode M are each connected
to a respective terminal of a d.c. voltage source 3. The
voltage of this source is such as to create a corona
discharge at the corona electrode K, thereby generating
air ions ~hich migrate to the target electrode under the
influence of the electric field, thereby creating an air-
flow 2 through the duct 1. With regard to a more detailed
description of the manner in which the illustrated arrange-
ment operates, the reader is referred to the complete
description found in the aforementioned Canadian
patent application 506,412.
In order to obtain substantially uniform distribution of
the corona current along the whole length of the corona
electrode K, and therewith a uniform flow of air over
2, the entire cross-section of the airflow duct 1, the
electrically conductive surface constituting the target
electrode M of the embodiment illustrated in Figure 1 is
formed so as to present at a location axially opposite
the end parts of the corona electrode K, surface parts Ma
which are situated at a shorter axial distance from the
cross-sectional plane that contains the corona electrode
K than the parts of the target electrode M located axial-
ly opposite the centre part of the corona electrode K.
It has been found that the corona current can be distri-
buted more uniformly along the whole length of the coronaelectrode K, when the target electrode M is constructed
in this manner.
With an air transporting arrangement constructed in
accordance with the invention, the target electrode may
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incorporate a plurality of mutually separated, electri-
cally conductive surfaces or electrode elements that are
connected to mutually different potentials, all having, however,
-the sam~ polarity relative-me potential of the eorona electrode.
Figure 2 illustrates schematically and by way of example,
an embodiment of the invention in which the target elec-
trode has the aforedescribed form. As with the embodiment
illustrated in Figure 1, the Figure 2 embodiment includes
an airflow duct 1 of elongated rectangular or slit-like
cross-section, a corona electrode K in the form of a
thin, rectilinear wire which extends across the airflow
duct 1, and a first target electrode M1 in the form of an
electrically conductive surface or coating applied adja-
cent -to or on the inner surface of the wall of the air-
flow duct 1 such as to extend fully therearound, the
corona electrode K and the target electrode M each being
connected to a respective terminal of the d.c. source 3.
In addition hereto, the Figure 2 embodiment also includes
a second target electrode M2 which, similar to the first
electrode M1, comprises an electrically conductive surface
or coating arranged adjacent to or on the inside surface
of the wall of the airflow duct 1 and extends fully
around the duct, this second target electrode M2 being
connected to the same terminal of the d.c. voltage source
3 as the first target electrode M1 through a large
resistance 4. Consequently, the second electrode M2 will
only receive and conduct a small part of the total ion
flow from the corona electrode K and will adjust to a
potential which may differ from the potential of the
first target electrode M1, but which, of course, has in
relation to the potential of the corona electrode K,
the same polarity as the potential of the first target
electrode M1. The two electrodes M1 and M2 can be said
to form together a target electrode arrangement for the
ion current from the corona electrode K. The objective
of the second target electrode M2 and the manner in which
it functions are described more fully in the aforementio-
32
ned Canadian patent application 506,412. In the exempli-
fying embodiment of the invention illustrated in Figure
2, the first target electrode M1 has a uniform axial
extension around the full circumference of the duct 1.
The second target electrode M2, on the other hand, which
is located closer to the corona electrode than the first
electrode M1, has the same form as the target electrode
M in the Figure 1 embodiment. The electrically conductive
surface or coating forming the second electrode M2 thus
has parts M2a which extend axially towards the corona
electrode, or wire K at regions opposite respective end
parts of the corona electrode, and which are thus located
at a shorter axial distance from the cross-sectional plane
incorporating the corona electrode K than the remaining
parts of the second target electrode M2 located opposite
the centre section of the corona electrode K. As a result,
the corona current will be distributed uniformly over the
whole length of the corona electrode K, in the manner
desired.
In the case of an air transporting arrangement provided
with a second target electrode M2 in the manner illustra-
ted in Figure 2, the first target electrode M1 may be
given the same form as the target electrode M illustrated
in Figure 1, so that both the electrode M2 and the elec-
trode M1 extend closer to the corona electrode K at re-
gions located axially opposite the end parts of said
corona electrode.
Figure 3 illustrates schematically and by way of example
a further conceivable embodiment of the invention. Similar
to the arrangements illustrated in Figures 1 and 2, ~he
arrangements illustrated in Figure 3 includes an airflow
duct 1 having a narrow, elongated rectangular or slit-
like cross-section, a wire-like corona electrode K which
extends across the duct 1, and a target electrode M1 in
the form of an electrically conductive surface or coating
on the inside of the airflow duct 1, the corona electrode
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and the target electrode each being connected to a
respective terminal of the d.c. voltage source 3. In
addition, two further electrodes M2 are arranged axially
opposite respective end parts of the corona wire K. These
further electrodes M2 comprise electrically conductive
surfaces or coatings located adjacent to or on the inside
surface of the wall of the airflow duct 1 and are each
connected to the same terminal of the d.c. voltage source
3 as the target electrode M1, through a large resistance
4. These further electrodes M2, which are located solely
opposite the two end parts of the corona wire K, contri-
bute towards providing a more uniform distribution of the
corona current over the whole length of the corona wire K.
The two electrodes M2 may also serve, at the same time,
as excitation electrodes, in a similar manner to that
described in the aforementioned Canadian patent
application serial No. 506,412.
Figure 4 is a schematic, axial sectional view of a
further embodiment of the invention, in which the target
electrode M comprises an electrically conductive net or
grid. In this case, the net or grid is so curved, or
arched, that i~s axial distance to the cross-sectio-
nal plane extending through the duct 1 and incorporating
the corona electrode K is shorter at those locations
opposite the end parts of the corona electrode than at
locations opposite the centre part of said corona
electrode. In this way the magnitude of the corona current
is balanced evenly over the whole length of the corona
electrode K, in the manner described.
In order to ensure that the velocity of the airflow
is as uniform as possible over the entire cross-sectional
area of the airflow duct, it is important not only to
distribute the corona current as evenly as possible over
the whole length of the elongated corona electrode, but
also to spread out the ion current from the corona elec-
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trode in a lateral direction, i.e. in a direction atright angles to the longitudinal axis of the corona
electrode, as evenly as possible over the airflow duct,
i.e. even towards the duct side-walls extending parallel
with the longitudinal extension of the elongated corona
electrode. This can be achieved with a target electrode
of the aforedescribed kind illustrated in Figure 4 in
the manner illustrated schematically in Figure 5, which
is a sectional view of the arrangement according to
Figure 4 taken at right angles to the section shown
therein. The section in Figure 5 is thus perpendicular
to the elongated corona electrode K. As illustrated in
Figure 5, the net or grid target electrode M is also
curved, or arched, so that the axial distance between the
cross-sectional plane incorporating the corona electrode
K and the target electrode M is shorter at the duct side
walls extending parallel with the longitudinal extension
oE the corona electrode K than within the central part
of the duct 1. Thus, the net-like or grid-like target
electrode M has, in principle, the configuration of a
double-curve or hemisphere. This ensures better propa-
gation of the ion current from the corona electrode K
over the whole cross-sectional area of the airflow duct 1.
The same result can be achieved when the corona electrode
is comprised of a plurality of mutually parallel, elonga-
ted, e.g. wire-like, electrode elements placed side-by-
side, in the manner illustrated schematically in Figure 6,
which is a secticnal view of the air transporting arrange-
ment taken at right angles to the section in Figure 4.As shown in Figure 6, the target electrode M is, in this
case, formed so that the axial distance between the
cross-sectional plane in the duct 1 that contains the
corona electrode elements K and the target electrode M
is shorter in the region opposite the interspace between
said elements than in regions opposite thereto. This
affords more uniform propagation of the ion current from
the corona electrode elements K over the whole cross-
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sectional area of the duct 1. It will be understoodthat the net-like or grid-like target electrode M is,
at the same time, curved or arched in the manner illustra-
ted in Figure 4, so that the axial distance between the
cross-sectional plane containing the corona electrode
elements K and the target electrode M is shorter at
regions opposite the end parts of said elements K than
at regions opposite the centre portions thereof.
The target electrode may also have a grid-like configu-
ration which comprises mutually intersecting plate-like
or lamella-like strips which extend parallel with the
intended direction of air flow, such that the target
electrode has a substantial extension in said airflow
direction. In the case of target electrode of such
construction, the side of the grid facing the corona
electrode is formed in the manner aforedescribed with
reference to the illustrations of Figures 4-6.
Figure 7 illustrates schematically a further embodiment
of the invention which can be applied to particular
advantage in the case of an air transporting arrangement
in which the airflow duct 1 has a broader rectangular
cross-section, or even a square cross-section, and in
which the corona electrode comprises a plurality of wire-
like electrode elements K arranged in mutually parallel,
side-by-side relationship. In order to ensure that the
corona current is distributed as evently as possible over
the whole length of the wire-like corona electrodes X,
and in order to ensure that the velocity of the airflow
is as uniform as possible over the whole cross-sectional
area of the airflow duct 1, the target electrode M of
this embodiment comprises a plurality of plate-like or
lamella-like electrode elements 5 which extend parallel
with one another and also with the direction of the air
flow 2, and the longitudinal extension of which elements
5 is located at right angles to the longitudinal extension
of the wire-like corona electrodes K. The lamella-like
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target electrodes 5 are also so arranged that the axial
distance between the plane incorporating the corona
electrodes K and the edges of the target electrode
elements 5 facing the corona electrode wires K gradually
decreases from the target electrode elements 5 located
opposite the centre parts of the corona electrode wires
K to the target electrode elements 5 located opposite
the end parts of the corona electrode wires K. In this
way propagation of the corona discharge is achieved
right to the ends of the corona electrode wires K, and
a more uniform velocity distribution of the air flow is
obtained over the whole cross-sectional area of the air-
flow duct 1. An advantage is afforded when the target
electrode M also includes plate-like or lamella-like
electrode elements 6 which are arranged at the respective
ends of the lamella-like target electrode elements 5 and
located in the proximity of and adjacent to a respective
opposing wall in the airflow duct 1. The upstream facing
edges of these target electrode elements 6 are therewith
advantageously located at the shorter axial distance from
the plane containing the corona electrode wires K. This
also contributes towards evening out the ion current
from the corona electrode wires K in a direction towards
the walls of the airflow duct 1, so as to obtain a more
uniform flow velocity over the whole cross-sectional area
of the flow duct. These additional target electrode
elements 6 are particularly valuable when the target
electrode elements 5 extend out to an electrically insula-
ted duct wall. In the exemplifying embodiment illustrated
in Figure 7, the lamella-like target electrode elements 5
are of varying widths, which does not, however, have any
important significance with regard to the function of the
target electrode in the aforedescribed respects. The
important fact is that the edges of the target electrode
elements 5 which face the corona electrode wires K are
positioned and located in the aforedescribed manner.
In the case of a target electrode constructed in the man-
1 1
ner illustrated in principle in Figure 7, the plate-
like or lamella-like target electrode elements 5 may
advantageously have the form illustrated schematically
in Figure 8, which is a sectional view of the air trans-
porting arrangement taken at right anyles to the lGngitu-
dinal axis of the wire-like corona electrode elements K.
As illustrated in Figure 8, the upstream facing edge of
the plate-like or lamella-like target elec~rode elements
5 directed towards the cross-sectional plane that con-
tains the corona electrode elements K is, in this case,profiled in a manner such that the axial distance between
said cross-sectional plane and said edge of the target
electrode elements is shorter at a location centrally
opposite the interspaces between the corona electrode
elements K than opposite said elements. Similar to the
manner described with reference to the embodiment illu-
strated in Figure 6, there is also obtained here a more
uniform dispersal of the ion current from the corona
electrode elements K over the whole cross-sectional area
of the airflow duct 1.
When the corona electrode comprises solely one single
wire-like electrode element, the plate-like or lamella-
like target electrode elements 5 are suitably formed in
the manner illustrated schematically in Figure 9, which
is a sectional view of the air transporting arrangement
taken at right angles to the longitudinal axis of the
wire-like corona electrode K. The configuration of the
edge surfaces of the target electrode elements 5 facing
the corona electrode K corresponds to the configuration
of the target electrode described in the aforegoing and
illustrated in Figure 5, and affords an improved and
more uniform distribution of the ion current from the
corona electrode K over the whole cross-sectional area
of the airflow duct 1.
An embodiment of the plate-like or lamella-like target
electrode elements 5 according to Figure 8 or Figure 9
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can be used to advantage despite the fact that the
target electrode has no plate-like electrode elements 6
located adjacent the duct sidewalls which extend
parallel with the longitudinal extension of the corona
electrode K.
It will be evident from the aforegoing that many mutually
different embodiments of the invention are conceivable.
In summary it can be said that the essential feature of
the invention is that the target electrode is so formed
that the axial distance between the cross-sectional plane
which contains the corona electrode and the nearest part
of the target electrode is shorter at the end parts of
the corona electrode than at the centre regions thereof.
Furthermore, when the arrangement comprises a plurality
of mutually parallel elongated corona electrodes the
target electrode may be so formed that the axial distance
between the cross-sectional plane containing the corona
electrode and the nearest part of the target electrode
is shorter at the duct sidewalls which extend parallel
with the longitudinal extension of the corona electrode,
and also at the region opposite the interspaces between
mutually adjacent corona electrodes, than at the region
opposite the actual electrode or electrodes.
In the illustrated and described embodiments the corona
electrode K comprises one or more thin rectilinear
wires. It will be understood, however, that the invention
can also be applied with other types of elongated corona
electrodes which extend across the airflow path.
Furthermore, the invention has been described and illu-
strated with reference to an airflow duct or airflow
path, of rectangular or slit-like cross-section, since
it is with such cross-sectional configurations that the
problem concerned is most prevalent. It will be under-
stood,however, that the invention can be applied with
airflow ducts or paths of other cross-sectional shapes,
127088;~
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such as circular for instance, since the problem with
which this invention is concerned can also occur in those
cases.
In the aforegoing an air transporting arrangement accord-
ing to the invention has been described in detail solely
with respect to the configuration of the target electrode.
With regard to the remaining construction of an arrangement
according to the invention the reader is referred to the
aforementioned Canadian patent application 506,412. Thus,
the arrangement need not include a duct which embraces
the electrodes with physical walls. In addition,
a suitable screen may be provided upstream of the corona
electrode, in order to prevent an ion current from passing
upstream from the corona electrode, as described in said
internat-ional patent application. In all other respects,
the configuration and positioning of the various electro-
des and the voltage supply thereto may be in acc~rd with
the proposals set forth in the aforesaid-in~ernational
patent application.
In those instances in the aforegoing when the target
electrode has been referred to as comprising electrically
conductive surfaces or elements, it should be observed
that the current strength of the ion current passing from
the corona electrode to the target electrode in arrange-
ments of the kind described here is very low, and that
the term "electrically conductive" must be understood in
relation hereto.
