Note: Descriptions are shown in the official language in which they were submitted.
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Title: IONIZING APPARATUS FOR AN ELECTRONIC AIR FILTER
Field of the Invention
This invention relates to gas and air filtration
systems. In particular, it relates to the removal of fine
S particulates like dust from gaseous flows.
Hackaround of the Invention
Iii the previous art, various combinations of
. ionizing and dust collecting elements have been used to
.produce high efficiency electronic air filters. One
.classic example is the standard precipitator type
electronic air filter in which ionizing fine wires of about
0.01 millimetres diameter, charged at about 7 kilovolts,
are placed between grounded plates to generate a corona and
charge the dust particles passing therethrough. Further
down the air flow path, alternating charged and grounded
plates collect the charged particles of dust.
Precipitating filters, while highly efficient,
produce large numbers of ions and generate ozone. They
also consume distinct quantities of current at high
voltage, thereby requiring substantial power supplies.
Another type of electronic air filter is the non-
ionizing, polarized dielectric media type. This is
not as efficient as the precipitator type but it is
cheaper and easier to maintain. This filter uses filament
pads of non-conducting, dielectric material sandwiched
between charged and grounded screens which produce
electrostatic fields to polarize these pads. Any
part~iculates passing through the filter also get polarized
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and they are attracted and collected by the packed
filaments within the pads. This type of system produces
very few ions, if any at all, no ozone and consumes
virtually no current. The power supply required is thus of
a low power type.
Two examples of prior art patents based on the
polarization principle are U.S. No. 4,549,833 and No.
4,828,586. The first patent describes a pair of outer
hinged screens for enclosing a pair of glass fibre pads
with a central grid located therebetween. The central
grid, made of coarse wire mesh that is on the order of 0.5
millimetres in diameter, is charged to around 7000 volts
and the outer screerus are grounded. This combination does
not generate ions significantly. The spacing between the
charged screens is between two and five centimetres,
producing an electr.l.c field gradient. This field gradient
polarizes the non-conducting glass fibres rendering them
active in trapping dust particles, and more effective than
non-polarized pads.
An advantage of this type of filter is that the
accumulated dust is readily removed by exchanging the glass
fibre pads for fresh pads.
Both of the above designs. have disadvantages.
The precipitator type, although it is very efficient when
2~5 clean, because of the limited surface of the collecting
plates, its efficiency drops as the filter loads up with
dust. The filter':a loading capacity, especially for the
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larger particles, is very low. Maintenance of the
precipitator type filters is very tedious especially in
industrial and commercial applications as the plates must
be individually wiped to clean them. Also they are
expensive both in original investment and operating costs.
This is because they have very elaborate construction and
have large, high voltage power supplies that consume
anywhere from 80 to 150 watts.
The polarizing filter systems do not have the
disadvantages of the precipitator filters but they lack
efficiency.
United States Patent No. 5, 403, 383 to Jaisinghani
depicts an "Ionizing Field Electrically Enhanced Filter"
wherein air passes through ionizing wires before reaching
a separately-spaced pad of dielectric material that has a
grounded electrode on its downstream side. To effect
increased ionization Jaisinghani provides a further charged
"control grid" upstream from the ionizing wires in the air
flow to provide field gradients that will create the
desired degree of ionization. Filter replacement does not
disturb the ionizing wires which are separated from the
filters and are permanently connected to the supporting
body.
Both United States Patents Nos. 945,917 and
2,593,869 to Cottrell and Fruth respectively describe a
precipitator-type air purifier that relies upon an ionizing
electrode incorporating multiple, conducting, frayed
strands of wire or thread that provide an array of pointed
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ends. A steep, ionizing potential gradient is formed at
the sharp points of the frayed strands. Ionized dust
particles are collected on charged walls or plates which,
as with all precipitators, must be cleaned regularly.
A further reference that combines ionization and
polarization is U.S. patent No. 3,763,633 to Soltis. In
this .patent wires are used to charge particles by
ionization of the air. The use of wires requires higher
applied voltages for the production of ions, and this
increases the risk of producing ozone.
A major concern in the process of ionizing air is
to minimize the production of ozone. Ozone is offensive to
some and can be injurious above certain levels. Any system
that relies on ionization should also minimize the
production of ozone.
In view of the foregoing, it is the object of my
present invention to provide an electronic filter which is
highly efficient, easy to maintain and inexpensive to
install and operate.
The invention in its general form will first be
described, and then its implementation in terms of specific
embodiments will be detailed with reference to the drawings
following hereafter. These embodiments are intended to
demonstrate the principle of the invention, and the manner
of its implementation. The invention in its broadest and
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more specific forms will then be further described, and
defined, in each of the individual claims which conclude
this Specification.
Summary of the Invention
5 The invention herein is based on ionizing dust
particles to enhance their entrapment by a filter pad.
T' Ionization to effect charging of dust particles
is achieved by providing an active ionizing grid in the
form of a conductive path having multiple, exposed,
ionizing points that, when charged, produce ions because of
the high potential gradient formed around such sharp
points.
The ionizing grid of the invention is located
directly adjacent, and preferably bonded to a fibrous
filter pad. Located on the opposite side of the pad from
the grid, a conducting screen held at differing potential
will provide an electrical field gradient across the
thickness of the fibrous filter pad to induce ionization.
Electrical coupling means are further provided to ensure
that voltage is applied to and between the ionizing grid
and: screen when the pad is installed in a filter support
frame_
- A preferred way of providing an ionizing grid is
to render a cord of multi-stranded filaments of short
fibres, such as cotton, conductive. Each fibre provides an
end that is pointed and has around it a higher field
gradient than the fibre itself, thereby creating ions in
the region of the steep field gradient.
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This grid of broken fibre lengths joined in a
conductive string may be prepared by applying a conductive
material, such as a high carbon ink, to the fibres. A
conductive path may similarly be deposited onto a fabric
having similar filaments and fiber ends therein.
It is desirable in such systems to minimize the
production of ozone. The provision of ionization with
minimal production of ozone can be effected by a selection
of the field gradient condition at the ionizing grid. As
well, such grid can be positively charged as a positive
electrode has a lesser tendency to create ozone.
In this manner, a source of ionization is
provided that is substantially less expensive than a system
based upon use of a filter support frame that carries a
separate, fragile ionizing grid of fine wires. Further,
maintenance of the system is facilitated by the ease by
which the filter pad and ionizing grid, provided together
in cartridge form, may be replaced. In this manner the
convenience of a throw-away pad is combined with
efficiencies based upon the use of ionization.
The features of both polarization and
ionization may be combined in one simple design by use of
a fibrous filter pad of dielectric material positioned
between a charged, active ionizing grid and an oppositely
charged, preferably grounded, screen. The active ionizing
grid is positioned adjacent to and in contact with the pad
upstream in the air flow in respect to the pad.
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By selection of the appropriate level of charge
and grid-to-screen spacing, the charged, active grid
provides a degree of ionization within the air flow thus
charging dust particles passing thr4ugh the filter and
thereby constituting it an "ionizing grid". The closeness
of the ionizing grid and screen on opposite sides of the
pad form a polarizing field gradient within the dielectric
material of the pad that polarizes the dielectric material.
This combination of charged dust particles and a polarized
pad of dielectric fibers achieves high efficiency as an air
filter, removing such dust particles from a stream of air
more effectively than with either feature used separately.
To conceal and protect the ionizing grid, pads
may be provided on both sides of such grid. An optional,
complementary second screen grid may be placed against the
outside surface of this additional pad on the upstream side
from which the airflow is originating. The upstream pad in
such case is advantageously exposed to rapidly diffusing
ions which flow upstream against the air flow, charging
dust particles present inside the first, upstream filter
pad of a two pad unit. This increases the trapping
efficiency of the combined assembly.
As a further alternate embodiment, an additional
ionizing grid may be placed on the upstream surface of the
upstream, second screen of an air filter that has an
upstream screen. This additional ionizing grid is
separated from and supported on the upstream screen by an
insulating layer, such as a polyester film. By charging
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this additional ionizing grid to an ionizing potential,
dust particles in the air flow may be charged before they
enter the first polarized air filter pad, increasing
filtering efficiency even further.
The convenience of this invention is that the
filter pad material may be separately removable from
between the~ionizing grid and screen to further increase
the efficiency of this air filter system.
Alternately, .the ionizing grid and filter pad
material are bonded together for replacement and disposal
as a unit.
In yet another variant a replaceable "cartridge"
may include:
1) two dielectric fiber pads;
2) an ionizing grid between the pads;
3) two external screens.
An optional second ionizing grid may be fixed on the
outside of one screen.
The foregoing summarizes the principal features
of the invention and some of its optional aspects. The
invention may be further understood by the description of
the preferred embodiments, in conjunction with the
drawings, which now follow.
Several embodiments of the present invention will
hereinafter be described by way of example only and with
reference to the following drawings herein.
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Summar~r of the Ficrures
Figure 1 shows .an exploded, perspective view of
the components of a basic filter assembly with fine wires
as the ionizing grid that is not claimed as the invention.
Figure 2 shows the construction of the assembled
filter of Figure 1 in cross-sectional view.
Figure 3 shows a central grid composed of fine,
ionizing wires for use in the filter assembly of figures 1
and 2.
Figures 4, 5 and 6 show the invention based on an
ionizing grid that differs from the configurations of
Figures 1 - 3 by the presence multiple, exposed ionizing
points that form ions when charged to an ionizing
potential.
Figure 7 shows an exploded perspective view of a
filter assembly wherein the ionizing grid of Figure 4 is
attached to one of the fibrous pads.
Figure 8 shows a perspective view of a hinged
filter arrangement where the two outside screens are hinged
together and a central ionizing grid is composed of
wires and not claimed as the invention supported with
insulating hinges. Power to the central grid is supplied
by a high voltage power supply attached to one of the
outside screen frames.
Figure 9 is a similar embodiment to that of
Figure 8 except that the central ionizing grid incorporates
the ionizing points of the invention and is attached to and
carried by one of the fibrous pads. High voltage to the
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grid is supplied via a conducting strip connected to a high
voltage power supply.
Figure 10 is a similar arrangement to Figure 9
except that the ionizing~grid is sandwiched between the
5 fibrous pads that are bonded together enclosing a portion
of the ionizing grid. The conducting strip is exposed
between portions of the pads that are not bonded together.
Figure 11 is an arrangement where the ionizing
grid of the invention and conducting strip are fully
10 contained between the fibrous pads which are bonded
together to enclose the grid and strip.
Figure 12 shows how the arrangement of Figure 11
is used in a filter frame.
Figure 13 is a graph showing the removal of
particles over time from a room using respectively a prior
art polarized filter, and a filter according to the
invention relying on an ionizing grid of conductive string
with multiple ionizing points.
Figure 14 is a perspective view of a cartridge
filter with an exterior ionizing grid of conductive string,
according to the invention, fixed over an exterior screen
by being mounted on insulating tape.
Figure 15 is an edge view of Figure 14.
Figure 16 is a graph showing the improved performance used
by having a second, upstream ionizing grid.
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Description of the Preferred Embodiment
Referring to the drawings, Figure 1 shows one
example of an assembly of components not incorporating a
cartridge filter based on the invention, but instead
relying upon use of very fine ionizing wires. Two outside
perforated retainers 1 form the outside frames of the
filter. Two outside conducting polarizing screens 2 are
mounted within the frames 1. Two dielectric fibrous pads
3, preferably made of glass fibres, are placed centrally
between the polarizing screens 2. Preferably, the screens
2 are grounded.
Located centrally between the pads 3 is the
ionizing grid 4. Ionizing grid 4 in this embodiment
comprises fine wires S which ionize the surrounding air
when high voltage is applied to them by virtue of a high
potential gradient which is present around the wires. The
diameter of wires 5 is preferably between 0.030 and 0.06
millimetres causing ionization when charged to a potential
of between 5,000 and 10,000 volts, depending on the spacing
of the screens 2. The spacing between such wires is
preferably from about 1 to 5 centimetres. The spacing
r between the grid 4 and screens 2 is between one and two and
one half centimetres in order to produce the desired
polarizing field gradient. Preferably, the grid 4 charged
with positive potential ions as this reduces the production
of ozone.
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While Figure 1 depicts a symmetrical cartridge
with the ionizing grid 4 carried between and adjacent to
two filter pads 3, only one filter pad 3 need be employed.
Use of a second filter pad~3 helps shield and protect the
charged ionizing grid 4 and provides improved filtration
efficiency.
Figure 2 shows a cross-sectional view of the
cartridge filter shown in Figure 1 when -assembled with a
high voltage power supply 6~mounted along one side. This
power supply is connected to ionizing grid 4 via a high
voltage contacting means in the form of a probe 7. Power
supply 6 and probe 7 may be mounted in an air filter
support frame (not shown) but are preferably detachably
attached to one side of the cartridge frame 1. (See U.S.
Patent No. 4,828,586).
Figure 3 shows a detail of construction of
central grid 4 which comprises fine ionizing wires S.
Operation of the filter is as follows: High
voltage (about 5 to 10 KV) is applied to central grid 4
which, by virtue of its fine wires, ionizes the air and
dust particles in the space between grid 4 and outside
screens 2. At the same time, because of the high voltage
applied to grid 4, an electrostatic field is also created
between grid 4 and grounded screens 2 and thus polarizes
the non-conducting, dielectric fibrous pads 3. Dust
particles or any particulate matter entering the filter
become charged due to ionization and are attracted and
collected by the polarized fibrous pads 3. This double
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". .
action of ionization and polarization makes for a filter of
improved efficiency.
Figure 4 shows an alternate construction of the
central ionizing grid 4~ which is ;the basis of the
invention, identified herein. A length of fibrous string 8,
such as one made of cotton having broken fibre ends, is
treated wi>:.h a conducting solution, such as colloidal
graphite, to render it conducting. String 8 is attached to
a conducting frame 9. Fibrous string 8 which has been
rendered conducting, because of its composition of fine
fibres or filaments with multiple, sharp ends, functions
the same way as fine wires in ionizing dust particles but
produces more ions and less ozone.
Figure 5 shows another alternate construction of
the invention where a fabric-based ionizing grid 10 laid
over a pad 3 is formed by depositing conducting paint or
colloidal graphite on a sheet of gauze 11. Gauze 11,
because of its composition of fine fibres and because it is
rendered conducting, provides within the conductive
material a grid 10 which functions the same way as fine
wires 5 in effecting ionization.
'' Figure 6 shows another alternate construction for
the central ionizing grid 4. In this case, a paper-based
grid 12 is formed by painting conducting paint or colloidal
graphite on coarse, fibrous paper 13. This paper 13 is
perforated with perforations 14 to allow air to pass
through. This arrangement also functions the same way as
grid 10 in effecting ionization of dust particles because
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the coarse fibrous paper also has fine fibers which act in
the same manner as the fibers in string 8 of Figure 4.
Figure 7 shows an alternate construction for a
cartridge filter assemblywhich is similar to the
mechanical filter assembly shown in Figures 1 and 2 and an
ionizing grid as in Figure 4. In this case, the ionizing
grid element is based on use of an electrical conductor in
the form of a fibrous conductive string 5a composed of fine
filaments with multiple filament ends attached to one of
the fibrous filter trapping pads 3. The fibrous string
with its multiple filament ends is again made conductive by
coating it with conductive material like colloidal
graphite. Conductive string Sa is connected to a high
voltage power supply in a similar manner as shown in Figure
2. Operation of this filter is as described above.
When the ionizing grid 4 is based upon use of a
conducting element that provides multiple protruding point
ends, it has been found that satisfactory ionization with
minimum ozone production can be produced using the
following parameters:
ionizing grid voltage from SKV to 10KV kilovolts
depending on the space between the ionizing grid on
the grounded screens
- ionizing grid charged with positive potential
- conducting element separation or spacing from 10mm to
30mm
- grid to screen separation from 10mm to 30mm
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1S
Figure 8 shows a filter arrangement not claimed
as the invention wherein~two outer, conducting screens 2
within frames 1 are hinged together to form the outside of
a filter cartridge. (See also U.S. patent No. 4,549,883).
Replaceable fibrous pads 3 are positioned on either side of
central ionizing grid 4 of wires. Grid 4, through its'
supportingframe, is attached to one of frames 1 by
insulating hinges 17. A high .voltage power supply 6 is
attached to one of the outside~frames 1 and connects to
grid 4 via electrode probe 7 when the filter assembly is
closed. When closed, the grid 4 lies directly adjacent to
the fibrous pad 3. A cord 20 is connected to a low
voltage power supply for supplying power to high voltage
power supply 6. Operation of this filter is the same as
described above for the cartridge filter shown in Figures
1 and 2.
Figure 9 shows a similar arrangement as that of
Figure 8 except that in this case a conducting ionization
grid 4a having multiple ionizing points according to the
invention is attached on one side of one of the fibrous
pads 3. Again, these fibrous pads 3 are removable for easy
replacement. Grid 4a is made by attaching fibrous,
conducting elements with multiple ionizing ends directly
onto the surface of fibrous pad 3. Thus in Figure 9, the
grid 4a is also removable and replaced with the
installation of fresh pads.
Grid 4a is connected to power supply 6 via a
frame-mounted conducting strip 22 and wire 23. Strip 22 is
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attached to one of the frames 1 by insulating hinges 24.
Grid 4a functions the same way as the grid formed by the
fibrous string 5a in Figure 7. As it is bonded to a pad 3
and is composed of an inexpensive ionizing structure that
provides ionization at multiple pointed ends, it is readily
disposable.
Figure 10 shows another filter arrangement
similar to that of Figure 9. In this case, the two filter
media pads 3 are bonded together over part of .their opposed
surfaces as by gluing or stitching but~portions of each of
the pads 3 are left free so that, when placed collectively
in the filter frame 1, metal strip 22 may be inserted
between pads 3 to make contact with ionizing grid 5a. In
this embodiment the two bonded pads 3 with ionizing grid 4a
there between make a convenient package for filter
replacement.
Figure 11 shows another arrangement where the
filter media pads 3 are bonded together over their entire
opposed faces. Between the pads 3 ionizing grid 4a is held
in place as by stitching or gluing, by friction, or by
other suitable means. Metal strip 22 is also held in place
between pads 3 to make contact with grid 4a.
Figure 12 shows how the arrangement of Figure 11
is used in a filter frame similar to that of Figures 8, 9
and 10. Here, high voltage from power supply 6 is supplied
to strip 22 by insulated electrode 31 which connects to the
high voltage power supply 6 through frame 1. Electrode 31
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is thin and narrow, enabling it to pierce one of pads 3 and
touch strip 22 to complete the electrical circuit.
Figure 13 shows the results of comparative tests
made on a 20" x 20" x~2" prior art, cartridge-type,
polarizing filter and a filter of similar dimensions with
conductive fibrous strings to serve as an ionizing grid as
ion contemplated by the invention. The high voltage used
was 10 KV on both cartridge filters.
The tests were made by generating smoke in
.asealed 570 cubic feet room. A ventilator was used to
circulate air through the filters and the level of
contamination was measured using a CLIMET INNOVATION~TM~S00
particle counter. The particle counter is capable of
counting different particle sizes in the air as the air is
drawn through the tube into the instrument. The counts
used were for particles down to a .3 micron size, which is
the most difficult particle size to capture, and the most
numerous. The instrument was set to count the particles in
.2 cubic feet of air every minute. All tests were made
with 1000 cubic feet per minute (CFM) of air circulating
through the filters as measured by an EBTRON~T"'~ air velocity
meter.
The results show that by using ionization as well
as polarization, (lower curve) the efficiency of filter
improves as compared to using only polarization. A
precipitator would be more efficient but it uses much more
energy to operate. It has much less loading capacity and
it is far more expensive to operate. The precipitator
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requires between 80 to 100 watts of power to operate while
both the polarized media and the new polarized
media/ionization type filters use only about 1.5 watts to
operate. In both of the Tatter cases, the trapping pads,
once coated with dust, may be readily removed and exchanged
for fresh, clean pads.
Another variant of the invention is shown in
Figures 14 and 15. In these Figures a thin insulating
strip of plastic such as polyester 37, is applied over and
fastened to an outer upstream screen 36 of a cartridge
filter assembly 35, in this case in the shape of the letter
"H". On top of strip 37 and along its middle line, a
fibrous conducting string 38 is attached. A high voltage
power supply (not shown in the drawings) is connected
between string 38 and grounded screen 36. String 38 is
thereby charged to a voltage of between 5 KV and 12KV. A
high resistance value limiting resistor (not shown) in the
high voltage source ensures that no danger of injurious
electric shock can arise from contacting the charged string
38 _
Operation of this arrangement is as follows: The
conducting string 38 ionizes the air in the vicinity of the
string by emitting charges 39 via its fine fibre ends.
These charges ionize (charge) the dust particles in the
space in front of the filter 35. The dust particles are
then drawn into the filter 35 by the air flow and are
collected by. the filter pad 40. The filter's efficiency
improves by this arrangement because charged particles of
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dust are more readily captured by a filter pad 40,
especially a polarized- filter pad 40, than neutral
particles. This arrangement produces results even more
favourable than those shown in the graph of Figure 13. The
improved results are shown in the graph of Figure 16.
while two fibrous pads have been shown throughout
as embracing the high voltage grid, only one is essentially
required. Two pads are preferred to cover the high voltage
grid and prevent inadvertent contact. The~symmetrical two
pad format also protects the contained ionizing grid when
the invention is applied in its preferred, replaceable
cartridge with ionizing string format.
Conclusion
The foregoing has constituted a description of
specific embodiments showing how the invention may be
applied and put into use. These embodiments are only
exemplary. The invention in its broadest, and more
specific aspects, is further described and defined in the
claims which now follow.
2O These claims, and the language used therein, are
to be understood in terms of the variants~of the invention
which have been described. They are not to be restricted
to such variants, but are to be read as covering the full
scope of the invention as is implicit within the invention
and the disclosure that has been provided herein.
AMENDED S~'LE'fi
