Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~ DUST PRECIPITATION FROM AIR BY NEGATIVE IONIZATION
'`'`BACKGROUND OF THE INVENTION
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This invention relates to a system for dust
' precipitation from air using negative ionization of the air.
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~- The concept and prospective commeccialization of
negative ionization techniques has been around foc decades with
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very little progress due to the lack of credibility arising
from inappropriate, largely unsuccessful applications and
clouded by exaggerated unsubstantiated claims.
- At the same time the effectiveness of the
technique suffered because the equipment to generate and
distribute the required volumes of negative ions was initially
bulky, expensive, requiring constant maintenance and was
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generally unreliable. These circumstances meant that the
effectiveness of applications deteriorated rapidly and became
totally suspect in operation.
` The increasing employment of the technology is
~; being brought about by some basic trends:
- the development of equipment utilizing
`~ electronics and new materials which provide a safe, reliable,
inexpensive, and non polluting source of negative ions and
their distribution.
- an increasing need to improve the air quality
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in enclosed environments which have been designed to minimizeenecgy costs for heating, ventilating and aic conditioning
installations.
- higher standards of safety and health in the
workplace in regard to the contcol of micconic and submicronic
pollutants identified as a health hazacd.
- zero defect objectives in manufacturing
operations requicing more effective means to contcol the
migration of fine dust and pollutants.
- hard evidence of the effectiveness of
industrial applications and increasing supportive scientific
evidence as cegards propec electco climate conditions for human
` comfort and working efficiency.
Off-shore countries, particularly Iscael have
maintained a fairly high level of reseacch and development
effort into pucsuing the effectiveness of negative ionization
techniques in a wide range of applications with considerable
success.
Progre~s in North America in this respect,
industrially at least, has been limited to the elimination of
static electricity, but with strong indications of a recent
revival of air treatment by modular, fan assisted negative ion
dispersal units.
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, Conventional systems to obtain super clean aic
1 with filtration efficiencies in the micronic and sub-micronic
ranges are capital intensive and expensive to run in tecms of
energy consumption and maintenance costs.
At the same time the systems while fully
effective on the air circulated can have little influence to '5"~
prevent small particulants and pollutants originating in the
working plennum producing problems, apart from the inherent
,~ dilution refreshening process allowed by the cycle of air
changes supplied to the area. An investigation into further
; prior art suggests that while the use of negative ionization
techniques to impcove air quality and contain dust pollution in
a general way is gaining ground, there is little doubt that the
level of technology available is relatively crude.
Ions are created in natuce by sunlight, cosmic
and terrestrial radiation and the friction of moving air and
water that causes electrons to leave hydrogen, nitrogen and
other molecules and to attach themselves to oxygen molecules.
Molecules with extra electrons from negative ions
and have a positive effect on the environment. They neutralize
odoucs and contribute to the clear air and the fresh smell we ---
find in non-industrial, sparsely populated areas and at the
seaside or healthy holiday resorts. ~ -
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,~In the Pcairie regions of Canada, the phenomenon -~
best manifests itself by the invigoration experienced after a
summer storm with lightning, which relieves the heavy
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`depressing conditions which gradually build up periodically in
such areas during the summer.
;Positive ions are produced by car and factory
exhausts, cigarette smoke, dust, soot, fumes from new processes
and other domestic and industrial pollutants.
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'r~lIn the wide open spaces these pollutants are
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attracted to the negative ground and are harmlessly discharged.
But in the enclosed environments of modern society - metals,
cars, builings lined and furbished with synethetic materials,
etc., these pollutions cannot be discharged to earth.
At the same time the enveloping car bodies and
building structures that keep the positive ions in, also keep
the beneficial negative ions out because their electrical
charges are absorbed by steel and concrete, bricks and siding
material.
A controlled output of negative ions can be
produced by electronic means/corona discharge and this source
is an approved alternative for the Polonium Ionizers withdrawn
from the market by 3M in February 1988. The source generation
of ozone is 90 low as to be almost immeasurable and well below
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the FDA maximum of 0.05 ppm.
SUMMARY OF THE INVENTION
It is one object of the present invention to
provide an improved method for cleaning air within a building
using the negative ionization principles in a unique manner to
obtain air which is cleaned to a high degree with low capital
and maintenance costs.
According to a first aspect of the invention,
therefore, there is provided a method of precipitating
particles from air within a building comprising defining a zone
within the building at least partly partitioned from a
remaining part of the building, separating the zone from the
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building by a screen which is perforated to allow transmission
therethrough of air and light, and mounting within the zone a
~ plurality of emitters of negatively charged air ions.~
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. According to a second aspect of the invention,
therefore, there is provided an emitter of negatively charged
air ions for use in precipitating particles from air within a
building comprising an elongate member defining a channel
~ therealong and having a closed front surface, a conductor ;-~
IR,~ ~ mounted in the channel member, means defining a plurality of
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openings in front surface through which portions of the
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!~ conductor pcoject, and connector means on the channel member
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for connecting a high voltage to the conductoc such that the
exposed portions of the conductor generate ions in air exposed
to the conductor focwardly of the fcont face.
The provision of the elongate multiple emittec
enables a high very degree of flexibility to be used in the
location and mounting of the emittecs foc the negative
ionization tceatment so that the units can be installed very
quickly and at low capital cost.
The use of the screen to separate the zone to be
cleaned fcom the remaindec of the building enables a system ~o
be used known as a "clean-zone" or as an altecnative a "reverse
clean-zone" in which the major dust emitting pcocess is mounted
within the zone and the negative ionization treatment used to
extract the dust from the aic pcioc to its celease to the
remainder of the building.
The screen is pceferably focmed of a matecial
which is pecmeable to air and light ~qo that the zone can be
mounted within the building without cegard to the location of
the ventilation units and provision of lighting. In many
cases, therefoce, the zone can be developed at an area leaving
the ventilation systems and lighting systems outside of the
zone so that there is no interference whatever with the ; ~-
existing utilities within the building. The light and air
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movement necessacy for ventilation can then take place through
the screen with the screen and the negative ionization system
cooperating to extract the dust and to prevent its penetration
through the scceen.
The system as installed, constantly and
efficiently will precipitate about 99% of the fine dust
particles and pollutants in a work area defined and isolated by
specially constructed barriec screens.
With the correctly calculated and distributed
negative ion density within the zone, all further migration of
the precipitation micronic and submicronic pacticles will be
effectively and continuously prevented, as a result of the
electro-climate created and maintained in the "Clean Zone" `
area.
The emitters are pceferably separated from any
aic flow generating systems such as fans or aic duct outlets so
that the ions are freely emitted into the are to be cleaned
wihtout passage of the ions or any air stream carrying the ions
through a filter. Thus the particles are separated from the
air by a precipitation technique which causes the particles to
fall to the floor for collection by conventional house cleaning
techniques. -~
The enclosuce which acts as a cage to isolate and
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define the area/volume required for the application, is
considered to be a basic and essential feature of the "clean
zone" concept. The design, constcuction and materials
employed, all con~ribute to ensucing the effectiveness of the
system.
Installation of the "Clean Zone" enclosure is
simple and flexible and easily fitted ee~ro-actively with the
minimum difficulty to accomodate existing equipment.
The light open nature of the enclosure gives
little sense of restriction to employees inside the zone and it
is generally unnecessary to upgrade lighting levels in the area
after the installation of the zone.
The effectiveness of the system is readily
measurable and can be demonstrated by the simple action of
energizing and deenergizing the AC power input.
The results in regard ~o the control of fine
dust, and reduction of inclusions are fully substantiated in
practical cost effective terms by satisifed industrial end
users in regard to~
- reduced level of rejections due to inclusions;
- increased productivity
- improved working environment inside and outside
the zone.
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Accocding to a ~hird aspect of the invention,
thece is pcovided a method of cleaning particles fcom air
within an area of a building comprising mounting emitters of
negatively chacged ions in the acea of the building ~eparate
from any aic flow acrangements foc causing aic flow within the
acea, causing the ions to engage particle~ in the area and to
precipitate the pacticles downwardly onto a flooc of the area
and collecting the particles fcom the flooc.
Preferably the method includes a canopy which
assists in dicecting the particles away from a source of the
particle~ e.g. a dust pcoducing machine towacds sides of the
machine for precipitation on the floor.
With the foregoing in view, and other advantages
as will ~ecome apparent to those skilled in the art to which
~his i~v~ention relates as this specification proceeds, the
inven~ion is herein describ~d by reference to the accompanying
~acawings focming a part hereof, which includes a descciption of
the best mode known to the applicant and of the prefecred
typical embodiment of the prin~ciples of the present invention,
in vhich~
DESCRIPTIO~ OF THE DRAWINGS
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Figure 1 i~ an isometric view showing a screen
sy~tem defining a zon~ for ~eparatiQn f~om the remaindec of
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building and including ionization generating elements mounted
within the zone.
Figure 2 is a top plan view of the zone of Figuce
1 showing the location of the ion emitters.
Figuce 3 is a cross-sectional view showing a
modified arrangement of screen assembly defining a zone within ~ ~
a building. ~ ~-
Figure 4 is a cross-sectional view through an
emitter element of a type shown schematically in Figures 1 and
2.
Figure 5 is an isometric view of the emitter
element of Figure 4.
Figure 6 is a cross-sectional view through a
second emitter element of the type illustrated schematically in
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Figure 1.
Figure 7 is an isometric view of the emittec of
Figure 6.
Figure 8 is a cros3 sectional view showing a
modified arrangement of the screen assembly of Figure 3.
In the drawings like characters of reference
indicate corresponding parts in the different figures.
DETAILED DESCRIPTION
In Figures 1 and 2 i9 illustrated a zone defined
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by a surrounding wall stcucture generally indicated at 10
within which i9 mounted a machine 11 which is illustcated ~ ;
schematically and is wholly enveloped by the surrounding wall
structure defining the zone.
The wall structure compcises two side walls 12
and 13 togethec with end walls 14 and 15 each of which includes
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an opening 16 and a slidable closing dooc 17. Accoss the top - ~;
of the walls is pcovided a ceiling 19. The height of the walls
is arcanged to be approximately equal to the minimum wocking
height of the ocdec of eight feet and up to a maximum of the
ocdec of ten feet so that the ceiling 19 is genefally
positioned beneath the roof or ceiling stcucture of the
building and is separate from the lighting, duct wock and othec
utilities which ace often pcovided in stcuctural buildings of
an industrial type.
This ccitical acea or zone is enclosed using a
slotted metal ~tcuctuce as the main suppoctive fcamewock,
housing panels coveced with perforated scceen matecial of a
type which is permeable to aic and light but is cesistant to ;-
teh pa sage of dust oc other fine pacticles. One example of
material which can be used is known as TAK Barrier Screening.
The TAK Barcier Screening is a fine gauge fabcic, treated with
a special tacky cesin. This Baccier screening is
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electronically compatible with negative ion presence and wocks
harmoniously to create a dust free enclosuce, trapping large
pacticles, yet allowing the zone to bceathe without any
increase in air speeds across the fabric.
The enclosure which acts as a cage to isolate and
define the area/volume required for the application is
considered to be a basic and essential feature of the "clean
zone" concept. The design, construction and matecials
employed, all contribute to ensuring the effectiveness of the
system.
Installation is simple and flexible and easily
fitted cetcoactively with the minimum difficulty to accommodate
existing equipment.
The light open nature of the enclosure gives
little sense of restriction to employees inside the zone and it
i9 genecally unnecessary to upgrade lighting levels in the area
after the installation of the screens.
Strategically located emittecs at ceiling level
within the enclosure produces a bombardment of negative ions to
precipitate particles inside the zone. At the same time a high
density is created within the confines of the enclosure which
will not allow particles to penetrate the screens, in either
direct1on.
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All openings into the zone required for access
ace pcotected by a curtain of ions which comprises a pecipheral
distcibution of emitters to form an high density concentration
of directed negative ions to precipitate any dust which might
othecwise migrate into the area. Altogether a total scceened,
"cage" effect is produced with a fully isolated Clean Zone
separate and distinct from the general working area of the
facility.
On completion of a Clean Zone, and activation of
the ion generation system, an ultra Clean Zone will be
established for process within 24 hours. This protection will
be available as long as the system is in operation with the
necessacy negative ions densities being maintained
automatically at the pcoper levels.
The slotted steel frame wock is indicated at 20
and is of a conventional nature available for receiving wall
panelq and for bug screens. A solid panel is indicated at 21
and the scceen material iR indicated at 22.
The ceiling is formed in the same structure
employing wholly the screen material 22. The enclosure can
thu~ be formed relatively ~imply by the assembly of the frame
work following which the panels are simply flipped into place
to define the completed zone. In Figures 1 and 2 there is
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provided a plurality of emitters of negative ions including two
separate types of emitters indicated at 25 and 26 cespectively.
The details of the emitters 25 are shown in Figures 6 and 7 and
the details of the emitters 26 are shown in Figures 4 and 5.
Turning thecefore to the emittecs 25 shown in
Figures 6 and 7, this emitter comprises an elongate channel
member 30 focmed in two halves 31 and 32 which are snap fit
togethec along a joining line 33 to form an enclosed elongate
tubular membec. End caps 34 are provided of a type shown in
Figure 4 which comprise a press fit into the end of the tubular
member thus focming a complete enclosure. The emitter 26 as
shown in Figures 4 and 5 comprises the same basic housing
stfuctufe. The length of the housing can be selected according
to requirements as shown in Figures 4 and 5 the emitter is of a
celatively short length whe~eas in Figure 6 and 7 the emitter
25 can be significantly longer.
Each of the housings includes a connector 36 of a
type including a body 37 which has an outer screw thread 38 and
an end cap 39. The body can thus be attached through an
opening in the housing simply by clamping into place by one or
more nuts 40 and 41. In the arrangement shown in Figure 6
there are two nuts provided each on a respective side of a wall
of the housing so as to space the end cap 39 away from the
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wall. In the arrangement shown in Figure 4, the end cap is
clamped against the end face of the housing by the nut 40 on
the opposed side of the wall of the housing. The housing
includes a central bore which cacries a conductoc 42 and a
volume of the sleeve which projects outwardly beyond the inner
end of the body to connect to a conductor 43 provided within
the housing. The tubular connector 42 is thus of a type which
can receive simply a single pole connector by which high
voltage fcom a generator 45 (Figuce 2) can be connected to the
emitter with a plurality of emitters arranged in series by
connection of a wire fcom each to the next.
The conductor 43 is formed of a yarn of a
conductive fibre material for example carbon fibres which are
cut into staple fibres and then spun and twisted to form a
multi fold yarn. The housing i9 focmed of very suitable
insulating plastics matecial so that the conductor yarn can
simply be thceaded into the housing and can cest against the
housing without forming a short circuit.
In Figures 4 and 5, a front face of the emitter
which is defined by the upper face of the uppec part 31 has a
plurality of openings 48 substantially equidistantly spaced
along the front face in a single line across the centre of the
front face. The yarn is then threaded simply in a stitch
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pattern so that portions of the yarn are exposed on the outer
side of the front face and portions of the yarn are maintained
on the inner side of the fcont face that is within the housing
as indicated at 49 and 50 respectively.
This form of emitter is substantially
multidirectional so that when a high voltage of the ocder of
6000 volts is applied to the conductor 43 the exposed portions
49 of the yarn generate a corona effect causing the creation of
ions in the area of the corona effect with those ions tending
to escape from the exposed portion of the yarn 49 in all
directions away from the front surface. The ions thus tend to
spread away from the emitter in all directions and to attach to
particles within the air. As the particles are heavier than
air the particles tend towacd the ground surface and in view of
the generally positive charge on the ground surface, the
negatively chacged particles are attracted to the ground
surface and fall to the ground surface for collection on the
ground surface both in view of gravity and in view of the
electrostatic attraction.
As shown in Figure 2, the emitters 26 are
arranged in array around the centre of the zone. In the
example shown there are four rows of the emitters arranged
substantially equadistantly spaced across the width of the
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zone. In this way the full area of the interior of the zone iB
bombarded with the ions which are spread equally thcoughout the
centcal acea of the zone. As shown in Figure 1 the emitters 26
are mounted at the ceiling area on suitable supports (not
shown). This places the height of the emitters generally at
the height of the ceiling which would be in the ocdec of eight
to ten feet from the gcound which has been found to be
pacticularly effective since the ions are thus pcevented fcom
dissipation to othec areas of the building before they can
carry out their function of attachment to particles and
transpocting those pacticles to the ground surface.
The emitter 25 shown in Figures 6 and 7 is
modified celative to the emittec 26 in that the conductor 43 is
confined into shoct poctions which project outwacdly from the
front face of the channel membec 31. Thus the front face 31
includes foc each portion a paic of holes 55 and 56 which are
closely positioned togethec with only a narrow sepacating
poction 57. The conductoc i~ then threaded through the holes
55 and 56 and passes~thcough a collar membec 58 surcounding the
holes and supporting the outerly projecting portion of the
conductor 43 as indicated at 59. The collar membec 58 can be
bonded to the front surface of the channel member oc can
comprise a separately manufactured product which inserts from
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an undecside of the uppec sucface of the channel membec thcough
a single hole in the wall 31 and pcovides by itself the pcopec
suppoct foc the projecting portion 59.
The projecting portion 59 is confined to a short
length of the front face of the channel member is caused to
tucn back upon itself at a shacp angle. This tends to cause
individual ones of the staple fibres 60 to pcoject outwacdly
from the yarn at the point whece it is turned sharply thus
forming a plucality of spikes which pcoject outwardly from the
shacply turned poction of the conductoc 43. These spikes have
been found to generate ions in a highly directional mannec in
that the ions ace pceferentially genecated at the apex of the
fibce ~pike and thus tend to be emitted in a direction
generally at right angles to the front face.
The emitter 25 is therefore much more directional
than the emittecs 26. In view of this propecty, the emittecs
25 ace thus arcanged to generate a curtain of ions lying in a
plane longitudinal of the emitter 25 and at right angles to the
fcont face.
Turning therefore to Figure 1 the emitters 25 are
mounted around the opening 16 along the sides of the opening
and along the top of the opening with the emitters facing
inwardly to generate a curtain across the plane of the opening
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of a high concentration of ions. This curtain acts to "attack"
any dust pacticles attempting to pass through the opening so
that those particles are acted upon quickly and tend quickly to
fall to the ground at the area of the opening. As a back up
for the emittecs 25 at the opening, one or more rows of furthec
emitters 25 can be positioned inwardly of the opening. Thus in
Figure 2 there are two further .ows of emitters one positioned
just inside the opening and the next behind the first thus
forming three curtains of ions acting specifically on the dust
tending to move thsough the opening carried by persons or
equipment passing through that opening or by air movement
through the opening.
The curtain of ions thus act at the openings in
the zone and in addition the general level of ions within the
zone acts in cooperation with the permeable tacky screen to
cause dust and other particles to be collected at the screen
rathec than to pass through the screen. It has been noted that
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the ions have a tendancy to act upon the dust just outside of
the screen so that large quantities of particles fall to be
collected on ground or other horizontal surfaces just outside
the screen thus preventing the dust from passing through the
screen.
As shown in Figure 3 there is provided a modified
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arrangement including a floor surface 70, a machine 71, a
screen 72, an uppec ceiling 73 of the building and utilities
including duct wock 74 and lighting 75.
In this case the scceen is modified in that it
comprises simply a canopy supported from the ceiling oc roof on
support wires 76. The canopy includes a ceiling 77 focmed in
panels similac to the ceiling 19 togethec with fouc side wall
portions 78 which hang down from the side edges of the ceiling.
The details of the construction ace not shown but are similar
to that shown in Figuce l. This of course leaves the side
walls of the zone open foc passage of persons or equipment but
generates enough of a separation of the zone from the building
to enable the cleaning of dust from around the machine 71.
Figuce 3 also illu~trates the arcangement in which the zone is
sepacated from the ventilation systems including the duct work
74 and fcom the lighting systems which ace maintained without
modification in the building. The light into the zone is thus
provided by the conventional lighting of the building. The
ventilation or aic movement within the zone is provided by the
conventional building ventilation systems including the duct
work 74 and a nozzle 80 which projects aic to move downwardly -~
through the screen and into the zone. ~ ;
In the arrangement of Figure 3, the dust is
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pcevented fcom passing into the interior of the zone through
the open side walls by the generation of a curtain of ions
similar to that at the opening 16. Thus the emitters 25 are
positioned so as to generate a curtain projecting downwardly at
the open side walls and this can be backed up by one or more
further rows of emitters 25 positioned inwardly of the side -
walls. Also similac to the construction shown in Figures 1 and
2, interior emitters can be of the type illustrated at 26 to
generate a moce even spread of ions throughout the zone. -~
In Figures 1 and 2 the machine 11 illustrated
schematically comprises a machine for carrying out an
industrial process of a type which requires very clean air fof
example a paint spraying machine or part molding machine so
that this machine is maintained within a clean zone in which
the dust in the remainder of the building is kept outside of
the zone and is prevented from entering the zone and from
remaining within the zone once it has entered. The clean zone
must of course be backed up with good housingkeeping practices ;~
which will not be explained in detail here. -
In the arrangement shown in Figure 3, the zone is
effectively a "reverse clean zone" in which the machine 71 is
of a type which generates high levels of dust, for example a
paper cutting machine or a textile spinning machine. In this
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case the machine itself is surrounded by a zone which protects
the cemainder of the building from receiving the high
quantities of dust generated by the machine itself. In this
way instead of maintaining the whole of the building cleaned,
it is only necessary to clean the acea surcounding the machine
concerned so that the dust from that machine is prevented from
escaping to the remaindec of the building and is also contained
within that area by the action of the negative ions on the dust
particles and the tendency to precipitate and thus to collect
on the gfound surfaces from which they can be readily removed
by normal housekeeping systems.
The emitters are entirely fcee from any forced
air effect so that neither the ions noc any pacticle laden air
passes through a filter. Thus the negatively charged ions
collect onto the particles causing them to conglomerate and to
precipitate onto the floor. The floor thus acts as a collector
for the particles and this can be readily cleaned by
conventional housekeeping practices. In addition, the tendancy
of the particles at the area above the machine is to rise 80
that the bombardment of the particles in the air space of the
canopy with the ions causes the particles to tend to flow
outwards of the machine and to precipitate out onto the floor
at the sides of the machine.
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The details of the electrical equipment
generating the high voltage are not shown as these are well
known to one skilled in the art. In addition the wiring
connection3 and the necessary conduit are not shown.
As an alternative arrangement for use in some
building structures, the emitte~ 25 can be used at the exit
nozzle of the ventilation duct work so that the ions are
directed into the air stream which passes through the nozzle as
the aic emerges from the nozzle and is communicated into the
building. The use of the emitters in the elongate or strip
focm enables the emitters to be tailored to the specific
nozzles concerned by simply cutting to length or selection from
a number of available lengths and attachment at the nozzle.
Turning now to Figure 8, there is shown a canopy
arrangement similar to that of Figure 3 including the source 71
mounted upon the floor sucface 70 and including a canopy
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generally indicated at 82. The canopy is again formed
including a ceiling portion 83 and depending side walls 84 ~;
acfanged around the periphery of the ceiling and depending
therefrom to a position at a height from the floor sufficient
to allow persons and machinery to pass under without
obstruction. -
In this case the canopy is modified by the ;~
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addition of two elements.
Firstly the ion emittecs of the type generally
described above are pcovided in six rows indicated at 85, 86,
87, 88, 89 and 90. The two central rows 87 and 88 positioned
above the source 71 are acranged instead of the previously
described negative ion emitters to pcovide emission of positive
ions. The construction of the device is substantially
identical to that previously described but the electrical
controls provide a positive voltage foc emission of the
positive ions from the fibcous conductors.
Outside of the vertical area above the source 71
are provided the rows 85, 86 and 89, 90 positioned closely
adjacent the sides of the rectangulac canopy. These emitters
ace of the negative ion type previously desccibed.
In addition two further rows of emitters 91 and
92 ace provided located at a position approximately halfway
down the ~ide walls 84 from a ceiling to the flooc. In a
practical example, the canopy can have a ceiling height of
twenty feet in which case the rows 91 and 92 will be positioned
at a distance of approximately ten feet from the ground. The
lowermost edge of the side walls is then positioned
appcoximately six and one half feet from the g~ound to allow
ceady cleacance. The emitters 91 and 92 ace arranged to emit
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negative ions.
This acrangement of the emitters tends to
generate a flow of the particles indicated by the acrows 93 in
which the particles rise from the source 71, move outwacdly
undec the canopy and then precipitate downwardly toward the
floor adjacent the sides of the canopy. This tendancy is
enhanced by the positive ion emittecs at the central area and
in addition the tendancy of the air to rise ovec the source in
view of the fact that the source tends to generate heat and aic
flow due to vacious moving pacts. The shape of the canopy and
the location of the negative ion emittecs then tends to turn
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the pacticles to move outwacdly and downwardly foc :
pcecipitation downwardly towacd the floor 70. ~ -
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To provide an additional collection of the
particles, there is pcovided a paic of collection sucfaces 94
and 95 each arcanged along a respective longitudinal side edge
of the canopy. Each collection surface comprises a simple
shelf type element extending outwardly and connected from the
lowec most edge and inclined upwardly thecefrom and inwardly of
the canopy to define between the wall 84 and the shelf element
a V-shaped area in which the particles tend to collect. The
negative ion emitters 91, 92 positioned just above the shelf
element also assist in the collection of the particles in that
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area.
Automatic extcaction devices may be pcovided in
the V-shaped area foc continual removal of the particles
collecting in that acea. Foc example vacuum acrangements may
pcovide along the length of the collection zone foc extcaction
of the pacticles as they pcecipitate into the V-shaped area.
In a further modification of the emitters (not
shown), each emitter is formed as a module in which the
electrical supply unit for the module is connected to the end
of the channel section forming the emitter. In this case the
channel section forming in the emitter fcom which the
electcodes protrude can have a length of the ocder of the eight
feet and be dicectly connected to its own electrical supply and
contcol unit. The modules can then be suspended from the
ceiling of the canopy with a numbec and acrangement of the
modules being selected according to design cequicements. This
accangement has the advantage that the wiring necessary for
insulation can now be provided by the conventional electrical
supply system at conventional voltages within the building and
is no longec necessary to pcovide high voltage wiring which
requires different safety constructions.
Since various modifications can be made in my
invention as hereinabove described, and many apparently widely
diffecent embodiments of same made within the spirit and scope
of the claims without departing from such spirit and scope, it
is intended that all matter contained in the accompanying
specification shall be interpreted as illustrative only and not
in a limieing sense.
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