HK1118249B - Air cleaning device - Google Patents

Description

Air purifying equipment

The patent application of the invention is a divisional application of an invention patent application with the application number of 00806175.0, the application date of 2000-4-12 and the name of 'air purifying equipment'.

Technical Field

The present invention relates to an air cleaning apparatus for reducing the concentration of airborne fine dust in a confined space such as a factory, shed, greenhouse, hall, shopping store or room.

Background

High airborne particulate concentrations can be a health hazard by inhalation of suspended particles.

In agriculture, where there is a high airborne dust concentration in, for example, poultry sheds, intensive pig sheds, etc., the health of both workers and animals can be compromised.

In industry, the use of internal combustion engines in many processes such as welding, grinding, smelting, and in confined spaces produces a highly contaminated airborne particulate concentration in the enclosed space.

In social and domestic environments, smoking produces airborne particulate pollution. Sneezing can produce airborne dust of bacteria and viruses. Allergic pollen is found in high concentrations throughout the year. Dust mite allergen particles can be generated in the bed and enter the air as airborne dust particles.

Conventional air purification devices remove particles from air by trapping the particles in a filter (filtered air purification devices (FAC's), or by collecting the particles on a panel (electrostatic precipitator air purification devices (ESPAC's)).

US4234324 discloses an electrostatic air cleaner comprising closely spaced planar electrodes of electrically conductive material spaced at their edges by corrugated spacers.

The disadvantages of FAC's are:

1. the efficiency of the filter tends to drop significantly over time.

2. The pressure drop across the filter tends to be high, requiring powerful fans.

3. Powerful fans tend to be noisy and consume considerable power.

4. The filter needs to be replaced periodically.

The advantages of ESPAC's are:

1. the pressure drop is low.

2. Low noise and low power.

3. A cleanable collection plate.

The disadvantages of ESPAC's are:

1. the shielding cost of the high voltage metal collector plate is high. The user needs to be protected from possible electric shocks from a high voltage power supply (typically several kilovolts). The charge stored on the board is at risk of electrocution even when the power supply is turned off. The plates need to be removed for cleaning and therefore a safety interlock is usually provided to automatically discharge the plates before they are accessible.

2. Electrical breakdown and leakage between the plates can cause efficiency losses and ozone generation.

3. The plates need to be spaced relatively widely apart to reduce electrical breakdown in the air between the plates, which reduces efficiency.

Disclosure of Invention

It is an object of the present invention to provide a practical apparatus for removing particles from air or gas streams that is substantially free of the disadvantages of ESPAC's.

To achieve the above object, according to the present invention there is provided a particle deposition apparatus for removing particles entrained in a gas stream, comprising an array of channels through which the gas stream can pass relatively freely, the channels being formed by enclosure with plastic walls having dielectric properties; for forcing an air stream through the array so that particles are collected from the air stream in channels provided by the upper and lower stacks of corrugated plastic sheets.

The channels are preferably provided by a corrugated plastic sheet, preferably having an electrically conductive material on opposite surfaces thereof. For example, the sheets of corrugated plastic may be stacked on top of each other, folded concertina-wise, formed into a spiral, or formed into a concentric array.

Alternatively, the channels may be provided by plastic tubes arranged side by side. The plastic tube may be of rectangular cross-section or of circular cross-section.

Channels may also be formed between the corrugated plastic sheets, or between the flat plastic sheets and the corrugated conductive material.

The plastic used in the present invention is preferably polypropylene, polyethylene or copolymers thereof, although other plastics such as PVC, PET, PTFE and polycarbonate may also be suitable.

For the first aspect of the invention, the regions of conductive material are preferably of a high impedance material, but may be of a low impedance material. The interleaved plastic sheets may have regions of high and low impedance material, respectively.

The high impedance material is preferably a cellulose based material, such as paper. The interleaved high impedance material comprises paint or ink or an antistatic coating.

The low resistance material may be selected from a metal sheet, a metal film, a carbon-based film, and a carbon-based paint.

The conductive material is preferably spaced inwardly from the edges of the plastic wall except where it is to be connected to an applied voltage.

Preferred embodiments of the invention further comprise means for charging particles in the gas stream prior to the array of channels. Such a device may be a corona discharge device or a radiation ionization device.

The high-resistance material used in the present invention preferably has a thickness of 10 per square⁹To 10¹¹Film resistivity in the ohmic range.

The apparatus of the preferred embodiment of the present invention also includes means for ionizing the gas stream as it exits the array. The means for ionising the gas stream as it leaves the array preferably comprises a primary electrical discharge emitter and a secondary corona emitter at a lower potential than the primary emitter. The primary transmitter is preferably connected to a high negative potential and the secondary transmitter is preferably connected to ground. The primary emitter is preferably a needle having a sharp tip and the secondary emitter is preferably a needle having a relatively blunt sharp tip.

In a preferred embodiment of the invention, the plastic wall is charged before being incorporated into the device. The plastic wall may be charged by means of electrodes which apply a high voltage difference to opposite sides of the wall. Alternatively, the plastic wall may be charged by applying an electric field at a higher temperature and then cooling to a lower temperature in the presence of the electric field. The plastic wall can also be charged by moving the plastic wall between a high potential corona discharge on one side and a grounded conductive plate on the other side.

In another preferred embodiment of the invention, the plastic wall may be provided by the surface of a corrugated plastic sheet material, and the charging may be carried out by injecting a conductive liquid into the corrugated grooves, connecting the corrugated grooves internally to a ground potential, and connecting the outer surface of the sheet material to a high negative and positive potential, respectively.

Another means of charging the plastic wall is to transport it between rolls of conductive or semiconductive material which are kept at a high and a low potential, respectively.

Another preferred way is to make opposite sides of the wall electrically conductive and electrically connected to each other. Making the plastic wall conductive can be done by coating with a conductive paint or applying a conductive sheet.

The apparatus of the present invention basically comprises a series of spaced plates which are alternately at high and low potential. The high potential plate is insulated from the low potential plate. The high potential plate may be positive or negative with respect to the low potential plate. The low potential plates may constitute a linearly spaced array of plates or a circularly spaced array of plates or a helically spaced array of plates or other suitable spaced array. The high potential plates are made of a special high impedance material instead of metal, which is a Low Impedance Material (LIM). The High Impedance Material (HIM) of the high potential plate raises the plate to its full operating potential without causing electrical shock damage. When a High Impedance (HIM) high potential plate is touched by a person, for example by a user, the current is limited to a low value which does not produce an electric shock and is not harmful to health. Thus, the series of spaced apart collector plates need not be hidden for protection in the air cleaning apparatus and can be mounted externally, if desired, for easy access and removal for cleaning.

The high potential plate needs to be connected with a high voltage power supply. According to the invention, a special wire is provided for connection to a high potential plate made of a High Impedance Material (HIM). The HIM wire can be insulated in a conventional manner, but if the insulation is broken, it will not cause electrical shock damage due to the low limit of current from within the wire.

Air entering the series of spaced plates is typically blown or drawn through the plate array by an electric fan. As it passes through the plate, the charged particles (positively or negatively charged) and any electrically neutral particles are subjected to a strong electric field which causes them to adsorb and collect on the plate. The plate may be designed to be disposable or washable.

In a preferred embodiment, both the high and low potential sets of the plates are made of HIM.

In another preferred embodiment of the present invention, the high potential HIM plate is covered with an insulating film.

In another preferred embodiment of the present invention, both the high potential HIM plate and the low potential plate are covered with an insulating film.

In another preferred embodiment, the gap between the high and low potential plates is occupied by an insulating plastic double-walled corrugated sheet through which air can pass.

In another preferred embodiment, the high and low potential plates sandwiching the insulating plastic double-walled corrugated sheet material are initially connected to a high voltage power supply and then disconnected.

The particle collection apparatus of the present invention may be based on a dielectric, which is a piece of insulating material exhibiting a durable electrical charge. The dielectric charge may consist of a surface charge layer, a charge within an insulating material, a polarization charge, or a combination thereof.

If the polarization and space charge of the thin film dielectric do not compensate each other everywhere within the insulating material, the thin film dielectric exhibits an external electrostatic field. This external electrostatic field is utilized in air cleaning filter materials made of thin film polymer dielectrics. The film polymer is electrically charged to form a nonwoven filter fabric. As the air containing the suspended particles passes through the fabric, the particles are subjected to a strong electrostatic field as they approach the dielectric fibers. These forces result in the deposition of particles on the fibers. Such fibrous dielectric polymer filter materials have an advantage over conventional fibrous filter media (e.g., microfine glass fibers) in that high efficiency can be achieved with relatively low pressure drop.

However, there is a further need for a filter medium that should provide high efficiency at even lower pressure drops.

Plastic sheets, particularly double-walled corrugated plastic sheets, may be pre-treated to impart dielectric properties thereto, and the materials are used in air purifying collection apparatus. Plastics suitable for making such sheets include Polyethylene (PE), polypropylene (PP), copolymers of ethylene and propylene, PVC, PET, PTFE, polycarbonate and other plastics. The plastic used preferably provides channels that facilitate the passage of air through the corrugated slots, thereby reducing the pressure drop through such air purification arrays. The particles in the passing gas stream are subjected to a strong electric field within the channel. The charged particles move in an electric field (by means of a so-called electrophoretic process) towards the channel walls, adhere to them and are thus trapped.

As the electric field in the channel is non-linear, uncharged or neutral particles also move (by means of so-called dielectrophoresis) to the walls and become trapped.

Although most dielectric air purification materials are made to exhibit an external electric field on the surface of the polymer film, in the present invention, it is of interest to maximize the electric field strength in the space in the plastic channel.

Drawings

The invention will now be further described with reference to the following drawings.

FIG. 1 schematically illustrates a first embodiment of the invention;

FIG. 2 schematically illustrates a second embodiment of the invention;

FIG. 3 schematically illustrates a third embodiment of the present invention;

FIGS. 4A and 4B schematically illustrate a fourth embodiment of the present invention;

FIG. 5 schematically illustrates a fifth embodiment of the present invention;

FIG. 6 schematically represents a linearly spaced array of plates;

FIG. 7 schematically shows a circular array of spaced plates;

FIG. 8 schematically represents a helically spaced array of plates;

FIG. 9 schematically illustrates a ninth embodiment of the invention;

FIG. 10 schematically illustrates a system for charging particles in a gas stream;

FIG. 11 schematically illustrates a tenth embodiment of the invention;

FIG. 12 schematically illustrates an eleventh embodiment of the invention;

FIG. 13 schematically illustrates a twelfth embodiment of the invention;

FIG. 14 schematically illustrates a system for generating ion leakage for charging particles in a gas stream;

FIG. 15 schematically illustrates a system for reducing the risk of electrostatic shock of the apparatus of the present invention;

FIGS. 16 and 17 schematically illustrate the operation of the particle abatement apparatus of the present invention;

fig. 18 schematically shows a prior art electrostatic air cleaner;

FIG. 19 schematically illustrates a thirteenth embodiment of the invention;

FIG. 20 shows a fourteenth embodiment of the invention;

figure 21 schematically shows a first means of dielectrically charging the collector plates of the apparatus of the invention;

FIG. 22 shows a second means of dielectrically charging the collector plates of the apparatus of the invention;

FIG. 23 shows a third means for dielectrically charging the collector plates of the apparatus of the invention;

FIG. 24 shows a fourth means for dielectrically charging the collector plates of the apparatus of the invention;

FIG. 25 schematically illustrates a fifteenth embodiment of the invention;

FIG. 26 schematically illustrates a sixteenth embodiment of the invention;

FIG. 27 schematically illustrates a seventeenth embodiment of the invention;

FIG. 28 schematically illustrates an eighteenth embodiment of the invention;

FIG. 29 schematically illustrates a charged particle detector in accordance with the present invention;

fig. 30 schematically shows a particulate contamination measurement apparatus according to the present invention.

Detailed Description

In the following description of fig. 1 to 8, for the sake of simplicity, the same parts are given the same reference numerals and the main differences between the embodiments are described in detail.

Referring now to fig. 1, the particle removal apparatus comprises at least two plates 1 and 2 (only two plates are shown for simplicity) spaced apart to allow substantially free flow of air or gas between the plates.

The plate 1 at high potential is constructed of or covered with a High Impedance Material (HIM). The plate need not be very thick, a thickness of 1mm or less being suitable for most applications. Suitable high impedance materials include card, cardboard, paper-bonded cellulose tape and some other material, or alternatively, the sheet 1 may be an insulating plastic coated with a film of HIM. Such coating materials include certain plastics, certain specialty coatings, and certain antistatic coatings. Suitable High Impedance Materials (HIM) preferably have a per square (per square) of 10⁹To 10¹¹Film resistivity in the ohmic range. In comparison, Low Impedance Materials (LIMs) typically have a film resistivity of 0.1 to 1.0 ohm per square for metals of about 50 microns thickness and a film resistivity of 10 to 1000 ohms per square for carbon paint films of about 50 microns thickness. The surface resistance of the insulator or insulating material is typically 10 per square¹³To 10¹⁶In the ohmic range.

A high voltage power supply 4 is connected to the high voltage board 1 by means of a special wire 5. The wire 5 is made of a conductive core of HIM sheathed in an insulating material. The HIM wires 5 need to be sufficiently conductive to supply current to the panel array sufficient to sustain a high potential, but not sufficiently conductive to cause electrical shock to the user after the dielectric material is broken. A range of materials may be used to construct the core of the lead 5, including cellulose thread or similar materials used in high impedance material sheets.

The plate 2 is a low-pressure plate and is constructed of HIM. The plate 2 is connected to a power source 4 by means of a conventional insulated metal conductive core wire 6. The plate 2 is at low or ground potential and does not cause electrical shock damage and can therefore also be made of a more conductive material such as metal, metal foil or carbon coated plastic.

As an example, an array of 13 HIM plates was constructed of 0.4mm thick cellulose card separated by a distance of 4 mm. The array was 100mm deep in terms of the distance of the air flow through the array. Air was passed through the array at a velocity of 2.0 m/s. The high potential HIM plate maintains-13 dc kilovolts with respect to the low potential plate. The air passing through the array contained approximately 500 microns per cubic meter of negatively charged salt particles with an average diameter of 0.5 microns. The capture efficiency of the assay was 93%.

In the embodiment of fig. 2 (which does not show power and wiring for clarity), the high potential HIM board 1 is covered or coated with an insulating material 8. This reduces leakage or loss of potential at the plates if the high and low potential plates are bridged by dirt or foreign matter.

The insulating material 8 may be one or more non-conductive paint film plastic tape films, heat-sealable plastic films, or other suitable insulating materials.

The low potential plate 7 may be constructed of a high impedance material or a metallic conductive material, a material coated with a conductive carbon paint, a conductive carbon-containing plastic, or any other similar suitable material.

In the embodiment of fig. 3, both the high potential plate 1 and the low potential plate 7 are covered or coated with an insulating material 8.

The high potential plate is constructed of a high impedance material covered with an insulating material 8.

The low potential plate may be constructed of any suitable high or low impedance material, the plate being covered with an insulating material 8.

The advantage of insulating the two sets of plates is that even if the plates touch together, there is no loss of high potential and therefore no loss of function.

In the embodiment of fig. 4a and 4b, the high and low potential plates are separated by a double-walled corrugated sheet 9 of insulating plastic. The sheet 9 may be made of polypropylene, polyethylene, polycarbonate, p.t.f.e or other suitable insulating material. Figure 4a shows the airflow through the wave shaped slots. Figure 4b shows a view at right angles to figure 4a as if air were flowing into the page. Air can freely flow through the wave-shaped grooves of the plastic sheet 9. The groove wall 10 is an integral part of the sheet 9. The corrugated plastic sheet 9 is structurally rigid and can be simply constructed of a multi-sheet array itself.

The recommended material for the high and low potential plates is a High Impedance Material (HIM), but a low impedance material may also be suitable since the double-walled plastic corrugated sheet material 9 is a good insulator.

In the embodiment of fig. 4, the elimination of particles is achieved by applying a continuous high potential between the high potential plate 1 and the low potential plate 2.

As an example, a circular array of 410mm diameter and 100mm depth is constructed using a stack of insulated plastic double wall corrugated sheets (IPTSMs) separated by high and low potential sheets made of HIMs. The IPTSFSM was constructed from polypropylene with an open air gap of 4 mm. The wall thickness of the IPTSFSM was 0.4 mm. The HIM used was a bonded cellulose tape with a thickness of 0.13 mm. The high potential HIM plate is held at-10 dc kilovolts relative to the low potential plate. Air (containing approximately 500 micrograms per cubic meter of salt particles with an average diameter of 0.5 microns) passed through the array at an average velocity of 1.8 m/s. Clean Air Delivery Rate (CADR) was measured at 717 cubic meters per hour.

In another embodiment (see again fig. 4), an initial high voltage potential is applied between the plates and then the high voltage power supply is disconnected. Particle capture efficiency is expected to decrease, but this is not the case. The initial high electric field strength generated between the plates appears to cause the corrugated plastic sheet 9 to constitute a dielectric material that stores a fixed charge within the sheet 9. The electric field strength generated by this stored fixed charge is sufficient to cause particles to settle on the corrugated walls of the sheet 9.

Another embodiment involves the use of the stacked array 11 as an air purifying collection device without the need to pre-treat the corrugated sheet material 9. Such sheets are typically made by extruding molten plastic, the raw material typically having some degree of dielectric properties, and exhibiting cleaning performance without any further treatment.

Figures 6, 7 and 8 show linear, circular and spiral spaced arrays of plates, respectively. In each case the high potential plate is numbered 13 and the low potential plate is numbered 12. The air flow appears to flow into the paper sheet.

Fig. 9 shows a situation where the air filter may be made of a double-walled corrugated plastic plate 10. The outer surfaces 30a and 30b of the plates are coated or covered with a conductive or highly resistive electrode material. The sheet is then folded in a concertina fashion into an overlapping array of air channels. One outer surface 30b serves as a high potential side, and the other outer surface 30b serves as a low potential side. The surfaces 30a and 30b are suitably connected to a source of high and low electrical potential to provide the necessary electric field to create an inductively charged field within the wave shaped slot so that airborne particulate can be drawn towards the wave shaped slot from the air flow passing through the wave shaped slot. The figures do not show fans or other means of drawing or blowing air through the array.

In various embodiments of the present invention, the particles are preferably pre-charged prior to entering the filter array. This can be achieved by two ion emitters 36, 38 placed in the plastic airflow outlet conduit of the air filter of the present invention. An emitter 36 having a sharp tip with a radius of curvature of typically less than 0.1mm, at a high negative potential, is disposed at a distance Z from an ion emitter 38 having a blunt tip (the radius of curvature of the tip is typically 0.5mm to 2.0 mm).

Due to the high electric field strength between the emitters, both emitters enter corona emission. The sharp emitter 36 emits a large amount of negative ions. The blunt emitter 38 emits positive ions in a small amount. The negative ion flow substantially neutralizes the positive ion flow. The net effect of blowing air across both emitters results in a cloud of negative ions leaving.

These ions leave the air purifier and tend to diffuse charge the particles in the room. Air ions generated by means of an ion emitter are blown into the room, where they impart a small amount of charge to the indoor particles by means of diffusion charging. When the charged particles are drawn into the air cleaner, they are trapped by the electrostatic field within the wave shaped grooves of the sheet material. It is desirable to place the ion emitter within the air purifier to reduce localized deposition and reduce the potential for electrostatic shock. External ion emitters produce localized contaminant deposits near the emitter and can also cause electrostatic damage to users of the air purifier. This is in contrast to the situation where two sharp emitters are used. If two sharp emitters are used, a greater amount of positive ions will be generated. The positive ions in the outlet air stream will effectively neutralize the negatively charged particles, thus reducing the efficiency of particle capture within the wave shaped grooves. Optimization of negative ionization (and unipolar charging) is achieved by adjusting the emitter potential, the radius of curvature of the emitter tip, the distance Z, and the direction and velocity of the airflow.

In the embodiment of the invention schematically illustrated in fig. 11, the insulated double-walled plastic sheet material is replaced by an array of square plastic insulating tubes 40 sandwiched between layers 42, 44 of electrode material.

Air flows through the length of square tube 40 in the same manner as air flows through the wave shaped grooves of the sheet material. The square slots are preferably made by a continuous plastic extrusion process and the tube is cut to length to accommodate different air purification applications. As shown, each tube is aligned with the high and low voltage electrode materials 42, 44 so as to pinch the square tube.

Alternatively, as shown in fig. 12, a circular cross-section plastic tube 50 may be used, again sandwiched between the electrode materials 42, 44.

Referring now to fig. 13, the particle collection apparatus of the present invention may have air passages provided in the pleats of a corrugated or undulating plastic sheet 60 sandwiched between electrode materials 62, 64 at high and low potentials, respectively.

The air containing particles is sucked or blown along the corrugations. This arrangement lends itself readily to the formation of a folded rectangular air cleaning array or a circular air cleaning array.

Preferred embodiments of the present invention may utilize the positioning of electrodes or electrode materials to provide particle charging through the plastic, particularly the corrugated plastic sheet array itself, thereby eliminating the need for external charging of the particles.

Figure 14 shows the arrangement of the electrode material 70 relative to a corrugated plastic sheet 72 (only one sheet in the array is shown, with the corrugated grooves arranged above and below the page). The distances X, Y and Z are creepage distances for providing sufficient insulation of one (high potential) electrode from the next (low potential above or below it) electrode in the electrode sandwich.

If the distance Y is decreased, the high voltage current leakage increases. By appropriate selection of distance and voltage, ionization at the array surface can be achieved by ion leakage. If the ionization arrangement is such that ionization occurs at the air inlet surface of the air purification array, then the neutral particles are charged just prior to entering the array. This improves the capture efficiency. If the ionization arrangement is such that it is generated at the air outlet surface of the air purification array, these ions are blown out into the room where they are charged before being drawn into and retained by the air purification array.

To reduce the likelihood of electrostatic shock due to handling of the air purifying array of the particle collection apparatus of the present invention, fig. 15 shows an electrode arrangement of a corrugated plastic sheet, wherein the electrodes are made of paper 80, covered with an aluminum foil connecting strip 82, two layers of paper (surge blocking) 82 and an aluminum foil tab 86. The paper layer is a high resistance material, limiting the current to a few microamperes. Another approach utilizes a high resistance material directly connected between high and low voltage electrodes. The resistor is adjusted to a value that does not unduly load the power supply (and reduce the voltage), but that will discharge the air purification array for a few seconds once the power supply is turned off. In this way, the array is quickly secured for disposal.

Fig. 16 shows a typical complete air purification system 100 for an indoor environment, and fig. 17 shows the air purification system 100 in the room, showing particle charging and collection. The system 100 has a collector 102 in the form of a corrugated plastic sheet and high and low potential electrodes (as shown in fig. 4B) and a fan 104 for drawing air through the array in the direction of the arrows. The array and fans are enclosed between an inlet grill 106 and an outlet grill 108. The corona emitter 110 behind the fan ionizes the air leaving the collector.

In conventional electrostatic air cleaners, a substantially uniform electric field exists between two parallel conductive (typically metal) plates or electrodes 112, 114 (fig. 18).

Charged particles passing between the plates are subjected to a force (by so-called electrophoresis) to move towards one of the plates and attach to it. Neutral particles passing between the plates are subjected to little or no force and pass through without being substantially trapped.

In the embodiment of the invention (fig. 4B) in which an insulating plastic double-walled corrugated sheet material is sandwiched between high and low potential plates or electrodes, the electric field within the corrugated slots is substantially non-linear.

Although the potential across the conductive or semi-conductive plate is uniform, the electric field within the wave-shaped groove is non-linear. The non-linearity of the electric field may be due to different displacements of the charge within the plastic, and due to the action of the walls of the wave-shaped slot.

The charged particles passing through the wave-shaped grooves are subjected to an electric field and deposited by electrophoresis. Neutral particles passing through the wave-shaped grooves are subjected to a non-linear electric field and move (by means of a so-called dielectrophoretic process) and a similar deposition takes place.

Forces act on the neutral particles by virtue of the polarization of the particles and the nonlinearity of the electric field, with the result that the neutral particles move and settle.

Thus, in this embodiment, both charged and neutral particles are deposited. The deposition efficiency of the charged particles is greater than that of the neutral particles. However, the deposition efficiency of the neutral particles is also significant.

In another embodiment, the electrodes may be sealed in a plastic sheet to prevent water ingress. Thus, such a composite collector can be periodically cleaned with water or detergent, dried, and reused.

As shown in fig. 19, instead of a corrugated plate array, electrodes 120 may be corrugated or corrugated, such electrodes being separated by plastic film 122.

Air is blown or sucked through the sandwich formed by the corrugations and the plastic film.

For purposes of illustration, semiconductive material is meant to have about 10 per square⁹To 10¹¹Ohmic film resistivity.

The invention is further described below, by way of example only, with reference to fig. 4B, illustrating high efficiency at low pressure drops.

The plastic double-wall corrugated plate is selected, wherein the square meter of the plastic double-wall corrugated plate is 300 g, the plate thickness is 2.1 mm, the spacing between corrugated grooves is 2-7 mm, and the wall thickness is 150 micrometers. The panels were cut and assembled into air purification arrays using 80 g.s.m. paper electrodes.

The dimensions of the array are such that the air flow delivery depth is 70 mm. One set of electrodes was grounded and the other set was held at-12,000 volts.

Approximately 1 milligram of 0.5 micron salt airborne particulates per cubic meter are formed in the detection chamber. As shown in fig. 10, particle charging is achieved by diffusion charging by blowing room air at two electrodes (one at ground potential and the other at-12 KV).

A series of experiments were conducted using an airborne mote monitor to determine the efficiency of salt particle capture at different velocities of air across the array. The experimental results are as follows:

air velocity (m/s)	Capture efficiency (%)	Pressure drop (Pa)
			0.5	99.99	3
1.0	99.97	7
			2.0	99.95	14
3.0	99.23	27

In another experiment, a plastic double-walled corrugated sheet was simply made into an air purification array.

Referring now to FIG. 5, a preferred embodiment is described which is suitable for dielectric charging of a plastic double-walled corrugated sheet material 10.

This embodiment includes an array 11 of insulated plastic double-walled corrugated sheets 9. In this embodiment there are no high and low potential plates. Alternatively, each plate 9 is "charged" between high and low voltage potential plates, removed, and then stacked to form the array 11. The efficiency with which the array deposits particles flowing through it depends on the stored dielectric charge in the sheet 9. A large amount of charge can be stored by applying a high potential difference before the sheets 9 are removed and stacked in an array 11.

Removable metal or semi-conductive flat electrodes are applied to the top and bottom of sheet 10. A high voltage difference is applied across the two electrodes. After sufficient charging time, the high voltage is disconnected and the electrode is removed from the newly formed dielectric sheet.

The dielectric sheets are now cut and an air cleaning array 200 (see fig. 5) is simply formed by stacking the sheets. The electric field within the wave shaped grooves effects retention of particles in the air flow flowing through the wave shaped grooves. No external power supply is required to maintain the electric field in the wave shaped groove, since the dielectric charge in the plastic is stable with respect to time (lifetime can reach several years).

In the embodiment of fig. 20, it is preferred that both sides of each panel 10 (all sides of all panels of the air purification array) be electrically connected together (after dielectric charging of the panel material). This is done to maximize the electric field strength within the wave shaped grooves and thereby maximize the filtration efficiency.

In order to electrically connect the two sides of each plate together, it is necessary that all of the plastic plate surfaces be conductive or semi-conductive. This is accomplished by applying a conductive paint film or antistatic paint, or an additional paper or metal film 198 on each side of the sheet.

The conductive surfaces of all of the plates in the array are then connected using wires 202, conductive tape, semi-conductive tape, conductive paint, semi-conductive paint, or similar means.

When so connected, the electric field in the wave-shaped groove space can be maximized, thereby maximizing particle capture efficiency.

The embodiment of fig. 20 will now be further described by way of the following example.

A plastic double-walled corrugated sheet material 10 made from a copolymer of ethylene and propylene is selected. The weight of the plate is 300 g per square meter, the plate thickness is 2.1 mm, the spacing of the wave-shaped grooves is 2.7 mm, and the wall thickness is 150 microns.

And arranging a paper electrode to clamp the plate. One electrode was grounded and the other electrode was connected to a potential of-33,000 volts for 15 minutes. The electrodes were disconnected, removed, and the dielectrically charged plastic sheet was cut and sandwiched in the array shown in figure 20.

The dielectric sheet was cut to a gas flow delivery depth of 70 mm. A series of experiments were conducted using an airborne mote monitor to determine the efficiency of capturing 0.5 micron salt particles at different velocities of air across the array.

The experimental results using uncharged airborne micronic salt particles at a concentration of about 1 milligram per cubic meter are as follows:

air velocity (m/s)	Capture efficiency (%)	Pressure drop (Pa)
			1	93	6
2	88	13
			3	84	26
4	79	37

5

74

52

The experimental results using negatively charged airborne micronic salt particles at a concentration of about 1 milligram per cubic meter are as follows:

air velocity (m/s)	Capture efficiency (%)	Pressure drop (Pa)
			1	99	6
2	99	13
			3	99	26
4	98	37
			5	96	52

Dielectric charging of the plastic double-walled corrugated sheet 10 may be accomplished by applying an electric field to the sheet at a higher temperature and then cooling to a lower temperature in the presence of the electric field.

Figure 21 shows another arrangement for dielectrically charging a plastic double-walled corrugated sheet material using a high potential corona wire 210 placed above the sheet with a grounded conductive or semi-conductive sheet placed below the sheet. The plastic sheet is slowly moved and the charging takes place along the length of the plastic sheet.

In fig. 22, dielectric charging of a plastic double-walled corrugated sheet 10 is accomplished using a high potential corona tip emitter 214 placed above the sheet, with a grounded conductive or semi-conductive sheet 216 placed below the sheet. The plastic panel is moved slowly and the charging takes place along the length of the plastic panel.

In order to achieve the maximum amount of charge stored in the dielectric material, it is generally preferred to apply a high potential difference across the dielectric material. The higher the applied potential difference, the more stored charge is available after the applied potential is removed. However, the potential difference must be controlled because if the potential difference is too high, breakdown of the insulation occurs, thereby reducing the dielectric charge.

The corrugated structure of the plastic double-walled sheet material 10 lends itself to dielectric charging by another preferred means as shown in figure 23. The interior of the wave shaped groove is passed or filled with water or other liquid 220 to render the liquid suitably conductive. The interior of the now temporarily conductive wave-shaped groove is connected to ground potential and the top and bottom surfaces of the plastic plate are covered with conductive or semi-conductive electrodes 222, 224. The top electrode 222 is connected to a suitably high negative potential and the bottom electrode 224 is connected to a suitably high positive potential. In this way, a dielectric charge is formed in the insulating material of the top and bottom surfaces of the sheet.

After a suitable time, the electrodes are disconnected and the conductive liquid is removed from the wave shaped grooves, allowing the wave shaped grooves to dry. In this way, a high electric field strength is formed in the wave-shaped groove.

The newly formed dielectric corrugated sheet material is cut and arranged into the air cleaning array previously described.

As shown in FIG. 24, dielectric charging of a plastic double-walled corrugated sheet 10 is accomplished by slowly passing the sheet through rollers 230, 232 of conductive or semi-conductive material. The rollers are kept at appropriate high and low potentials. To increase the transfer of charge, the roll is wet or treated with a suitable conductive liquid.

Dielectric charging of the plastic double-walled corrugated sheet material may be accomplished in a manner similar to that described in connection with fig. 5, except that one or both of the removable electrodes are wetted or treated with a suitable conductive liquid to increase charge transfer.

Materials other than plastic corrugated sheets may advantageously be charged with a dielectric and then used to construct the air purification array of the present invention. Fig. 25 shows this situation. As shown, a rectangular cross-section tube 300 is dielectrically charged by means of two planar electrodes 302, 304. The charging of the dielectric may be carried out in a batch mode or, preferably, continuously.

Alternatively, as shown in fig. 26, the rectangular cross-section tube 300 is dielectrically charged via two L-shaped cross-section electrodes 306.

Figure 27 shows that a tube 310 of circular or elliptical cross-section can be dielectrically charged by means of suitably shaped electrodes 312, 314.

After dielectric charging, rectangular or circular cross-section plastic tubes 300 or 310 can be cut and assembled into air purification arrays as shown in fig. 28, respectively.

Fig. 29 shows that a dielectrically charged waveform array (similar to the array shown in fig. 20) is used not as an air cleaning device but as a charged particle detector. Charged particles entering the wave shaped groove 10 are subjected to an electric field across the wave shaped groove. The particles move to the wall, attach to the wall and discharge their charge. The charge moves to electrode 198. Positively charged particles or ions move to one side of the wave-shaped groove and negatively charged particles or ions move to the other side.

By ensuring the correct orientation of the polarized dielectrically charged plates, and by connecting the interleaved electrodes, two currents can be measured, one attributable to the positive charge collected (a1) and the other attributable to the negative charge collected (a 2).

The ability of such an array to collect charged particles can be used to construct a sensitive particle contamination detection device 400 (see fig. 30). Such a device is briefly described below. An electrically conductive tube 402 has an inlet grid 404 and leads to a dielectric array 406 of the type shown in figure 20. The conductive tube 402 is grounded. A corona emitting pin 408 is disposed within tube 402. A fan 410 and an outlet grill 412 are positioned beyond the array 406. The array 406 is grounded by an ammeter a to measure the current induced by the charge from the particles collected on the array.

The fan 410 draws air into the device. All of the gas streams are subjected to a unipolar corona charge (technically referred to as field charging). All particles are charged as they pass through the corona charger. If the corona charge is negative, then all particles are negatively charged regardless of the charge status of the entering particles, i.e., positive, neutral, and negative particles entering the corona charger will be negatively charged away.

If all of these negatively charged particles are captured by the dielectrically charged array 406, then the current flowing from the array is proportional to the density of particles entering the device and proportional to the air flow through the device.

Such a device has a range of advantages over other particle contamination measuring devices, including high sensitivity (low pressure drop allows high air flow rates), zero state stability (no particles, no current), no leakage or interference problems (collection array is not connected to any high voltage).

The embodiment of fig. 30 is now described by way of the following example.

Airborne dust of smoke is generated in the room and sucked into a conductive tube of circular cross-section of 100mm diameter. (air velocity 1.5 meters per second). Airborne dust particles passed through a centrally located insulated needle held at-6,000 volts. The corona discharge from the needle produced a 4.5 microampere ion flow, charging the incoming particles. All of the high flow excess negative ions are captured by the surrounding conductive tube. The charged particles are conveyed by their low mobility along the gas stream into a square dielectrically charged array 70mm deep. Negatively charged particles in the gas stream are captured in the array, allowing the current meter to measure the current.

The experimental results are as follows:

airborne mote concentration (microgram/cubic meter)	Current from the array (nanoampere)
		1000	6.2
800	5.0
		600	3.7
400	2.5
		200	1.3
0	0.0

These numbers show a linear relationship between airborne particulate concentration and the current collected by the array.

Claims (26)

1. A particle deposition apparatus for removing particles entrained in a gas stream, comprising an array of channels through which the gas stream can pass relatively freely, the channels being bounded by plastics walls having dielectric properties imparted to the walls outside the channels after they have been formed, wherein: the channels are provided by a corrugated plastic sheet, the plastic walls upon charging resulting in a substantially uniform electric field within the corrugated grooves after formation; means for forcing an air flow through the array whereby particles are collected from the air flow in the channel is also included.

2. The apparatus of claim 1, wherein: the corrugated plastic plates are stacked up and down.

3. The apparatus of claim 1, wherein: the corrugated plastic plate is folded in a concertina manner.

4. The apparatus of claim 1, wherein: the corrugated plastic plate forms a spiral.

5. The apparatus of claim 1, wherein: the channels are formed by the side-by-side placement of plastic tubes.

6. The apparatus of claim 5, wherein: the plastic tube is rectangular in cross-section.

7. The apparatus of claim 5, wherein: the plastic tube is of circular cross-section.

8. The apparatus of claim 1, wherein: the plastic is selected from the group consisting of: polypropylene, polyethylene or copolymers thereof, polyvinyl chloride, PET, PTFE and polycarbonate.

9. The apparatus of claim 1, wherein: means for electrically charging particles in the gas stream prior to the array of channels is also included.

10. The apparatus of claim 9, wherein: including a corona discharge device for charging particles in the gas stream.

11. The apparatus of claim 9, wherein: including a radioionization device for charging particles in the gas stream.

12. The apparatus of claim 1, wherein: means for ionizing the gas stream as it exits the array are also included.

13. The apparatus of claim 12, wherein: the means for ionizing the gas stream as it exits the array comprises a primary corona discharge emitter and a secondary corona discharge emitter at a lower potential than the primary emitter.

14. The apparatus of claim 13, wherein: the main corona discharge emitter is connected to a high negative potential, and the auxiliary corona discharge emitter is grounded.

15. The apparatus of claim 13, wherein: the primary corona discharge emitter is a needle with a sharp tip, the sharp tip has a radius of curvature less than 0.1mm, the secondary corona discharge emitter is a needle with a relatively blunt tip, and the relatively blunt tip has a radius of curvature of 0.5 to 2.0 mm.

16. The apparatus of claim 1, wherein: the plastic wall is charged prior to installation into the device.

17. The apparatus of claim 16, wherein: the plastic wall is charged by means of electrodes applying a high voltage difference on opposite sides of the wall.

18. The apparatus of claim 16, wherein: the plastic wall is charged by applying an electric field at a higher temperature and then cooling to a lower temperature in the presence of the electric field.

19. The apparatus of claim 16, wherein: the plastic wall is charged by moving between a high potential corona discharge on one side and a grounded conductive plate on the other side.

20. The apparatus of claim 16, wherein: the plastic walls are provided by the surface of a corrugated plastic sheet and charging is achieved by injecting a conductive liquid into the corrugated grooves, connecting the interior of the corrugated grooves to ground potential, and connecting the exterior surface of the plastic sheet to high negative and positive potentials, respectively.

21. The apparatus of claim 16, wherein: the plastic wall is charged by transporting it between rolls of conductive or semiconductive material held at high and low potentials, respectively.

22. The apparatus of claim 17, wherein: making the opposite sides of the wall electrically conductive and electrically connected.

23. The apparatus of claim 22, wherein: the opposite sides of the wall are grounded.

24. The apparatus of claim 22, wherein: the plastic wall is made conductive by coating with a conductive paint or by applying a conductive sheet.

25. The apparatus of claim 1, wherein: it takes the form of a contamination monitor in which the plastic wall is grounded by an ammeter to measure the current due to collected particles.

26. A particle deposition apparatus for removing particles entrained in a gas stream, comprising an array of channels through which the gas stream can pass relatively freely, the channels being provided by a corrugated plastic sheet having outer walls connected by inner walls, the corrugated plastic sheet having dielectric properties imparted to its outer walls after it has been formed so as to generate a substantially uniform electric field within the channels defined by the corrugated channels; means for forcing an air flow through the array whereby particles are collected from the air flow in the channel is also included.