GB2088141A

GB2088141A - Air Ion Propagation Element

Info

Publication number: GB2088141A
Application number: GB8135004A
Authority: GB
Original assignee: EATON WILLIAMS RAYMOND HERBERT
Current assignee: EATON WILLIAMS RAYMOND HERBERT
Priority date: 1980-11-21
Filing date: 1981-11-20
Publication date: 1982-06-03
Also published as: GB2088141B

Abstract

A device of the corona discharge type for generating ions for use in conditioning the air, comprising a multiplicity of carbon fibre filaments (10) at respective ends of which the ions are generated when the device is in use. The carbon fibre filaments are preferably surrounded by an electrically-insulating plastics tube (12), and are connected to a high voltage generator. <IMAGE>

Description

SPECIFICATION A Device for Generating lons of the Corona Discharge Type The present invention relates to a device for generating ions of the corona discharge type, for use in producing electrically negatively charged ions and/or electrically positively charged ions in the atmosphere, for example in conjunction with other air-conditioning apparatus.

It has been found that negatively charged ions in the atmosphere are beneficial physically and psychologically to people breathing the ionised air, and is also effective in treating certain ailments. Various atmospheric ionisers have therefore been designed. One type is a corona ioniser which comprises a high voltage generator and a plurality of sharply pointed metallic needles connected to the high voltage generator so that a sufficiently large electric field is produced around the tips of the needles to create electrically negatively charged ions within that field. The ions may be discharged into the atmosphere of a room or directed towards a particular individual undergoing treatment.

Tests have shown that, when such an ioniser is switched on, one or more of the needles are often inoperative. Furthermore, the needle or needles which are inoperative may change from one use of the ioniser to the next.

As a result, the ion output from the ioniser tends to be uncertain, even though the failure of operation of one needle will tend to cause an increase in ion productivity from the other needles when all the needles are in fairly close proximity.

A further problem encountered with an ioniser having needles is the necessity of an electrically conductive grid or other member positioned behind the needles and connected to earth potential, or a potential somewhere between earth potential (zero) and the high voltage of the needles themselves. Without this backing member, the needles will often fail to produce ions altogether. Unfortunately, however, the presence of the backing member increases the likelihood of a spark discharge across the gap between the needles and the member, particularly with increasing age of the ioniser since the needle points tend to be easily corrbded or covered with dust or other dirt. Spark discharging is very undesirable as it produces ozone. This is harmful to health and negates any beneficial effect obtained from the negative ions.

A very different construction has been proposed which is much less prone to these problems. It comprises a bunch of copper filaments in place of a plurality of needles.

Because there are so many filaments each providing a tip from which a corona discharge may develop, it makes little difference if one or two are inoperative at any instant. Furthermore, there is no necessity for an electrically conductive backing member, so that a higher voltage may be applied to the filaments without danger of spark discharging.

This construction still suffers from a limitation imposed by the use of an open bunch of copper filaments. To obtain a high production of ions, a sharp tip is required to produce a very strong localized electric field. A sharper tip is obtainable by using thinner copper filaments. But this also weakens them, so that they easily break away from the rest of the bunch, making the ioniser messy and shortlived.

It is an aim of the present invention to obviate this disadvantage.

Accordingly, the present invention provides a device for generating ions of the corona discharge type for use in conditioning the air, comprising a multiplicity of carbon fibre filaments at respective ends of which the ions are generated when the device is in use. The carbon fibre filaments are advantageous because they have a small crosssectional diameter and yet are relatively very strong.

Because the copper filaments of the previously proposed ioniser are coarse and spread out like a wire brush, they may be unsightly and the ions may be projected diffusely over a wide angle. This limits the extent to which ions can be directed to penetrate deep into the atmosphere of a room. It also increases the likelihood of dust staining of surrounding fabrics. One form of the present invention is therefore directed to an air ion propagation element in which the carbon fibre filaments extend at least partially within a tube or tubular portion made of an electrically insulating material, or are otherwise surrounded, at least in part, by electrically insulating material.

Advantages obtainable from an air ion propagation element made in accordance with the present invention are as follows: (a) relatively high output of negatively charged ions; (b) relatively low or zero production of ozone; (c) acceptable aesthetic appearance bearing in mind that the element may be visible in the occupied space; (d) capability of being adapted to existing air diffusion systems; and (e) directional or beamed propagation properties, to minimise dust staining of surrounding fabrics or ceiling.

To ascertain the most desirable constructional features of an air ion propagation element, a range of experiments-have been conducted with different constructions for comparison purposes, not all these constructions embodying the present invention. The comparison was achieved by using an ion detecting meter, setting this to scale 5 with a ten times multiplier operative, and adjusting the distance of the instrument from the propagation element until the reading on the meter was 50 negative. The distance between the receiving disc of the ion sensing meter and the tip of the ion propagation element was then measured. This gave an inverse indication of the ion output.

Unfortunately, this inverse measure of distance is far from linear in relation to ion output so a further experiment was carried out to determine the relationship of this distance to the ion output.

As this is fundamental to an evaluation of other readings, details of this experiment are given first below.

For this experiment, the ion sensing meter was set to scale 3 with the times 10 multiplier in circuit and the distance was measured from a typical propagation element for scale readings of between ten and fifty in intervals of ten. The results are tabulated below-

Meter Reading Distance (cms.) 50 30 40 33.5 30 37 20 43 10 54 An analysis of these readings indicates that the ion intensity at a given point decreases with distance from the propagation element inversely to the distance raised to the power of 2.67.

That is: k 1=- d2.67 where i is the ion intensity at the point measured, k is a constant and d is the distance between the point at which the measurement is taken and the ion propagation element.

This formula can clearly be used to compare the ion output from differing ion propagation elements, by applying it to the distances at which similar meter readings are noted.

The following is a summary of test carried out over a period of three days, noting the type of ion propagation element used and the distances in centimetres between the propagation element and the meter receiving disc to produce a reading of 50 negative.

Description of Element Distance (cms.) The following were all connected to a 6kV supply.

Earlier construction-a blue 1 5 cm cube unit comprising nine point discharge elements 110 Stainless steel wire (30 micron) 127 Stainless steel wire (50 micron) 111 Twenty tow carbon fibreopen 134 Twenty tow carbon fibre inside a six millimetre diameter plastics tube a) with carbon flush with end oftube 121 b) with carbon recessed three millimetres inside tube 113 Second Series of Tests Six millimetre plastics tube, carbon flush with end, twenty tow carbon fibre 130 12.5 millimetre tube, carbon flush with end, eighty tows 132 18 millimetre tube, carbon flush with end, eighty tows 138 Third Series of Tests Twenty tow carbon fibre in 7 millimetre bore polypropalene tube 94 Twenty tow carbon fibre in 6 millimetre bore plastics blue tube 127 Twenty tow carbon fibre in 6 millimetre blue tube flush with end and with 4 cm square reflector 6 cms from end a)-reflector earthed 127 b) -reflector at 2 kV 132 Twenty tow carbon-no tube 123 Eighty tow carbon-no tube 1 28 The following tests were carried out with the elements connected to a 1 5 kV supply.

Eighty tow carbon fibre in 1 8 millimetre tube flush with end 214 Twenty tow carbon fibre in 6 millimetre blue tube flush with end 227 Bunch of copper filaments open 216 From the above it would seem likely that an optimum ion propagation element comprises a twenty tow carbon fibre contained within a plastics tube of highly insulating material of 6 millimetres internal diameter, and with the carbon fibre ends flush with the end of the tube.

From the experiments carried out with the 1 5kV generator, it would appear that the number of ions propagated from an element of optimal construction as outlined above, is increased by approximately 4.7 times by raising the applied voltage from 6 kV to 15 kV. These, and other experiments, show that ionisers with between 1 and 80 two carbon fibres are useful, connected to an electrical-voltage generator of between 5 kV and 1 5 kV. The diameter of each filament may be in the range from 6 to 16 microns.

Examples of devices in accordance with the present invention are illustrated in the accompanying drawings, in which: Figure 1 shows an axial, partly sectional view of an air ion propagation element; Figure 2 shows a part of the element shown in Figure 1, on an enlarged scale; Figures 3 to 5 show axial, partly sectional views of modified forms of the air ion propagation element; Figure 6 shows three elements projecting through an outlet grille of an air-conditioning system; and Figure 7 shows a different example of a device for generating ions of the corona discharge type.

With reference to Figure 1, approximately 2x 105 Grafil (Registered Trade Mark) XA-S carbon fibre filaments 10 extend axially within a highly electrically-insulating plastics tube 12 at an open end 14 thereof, with ends of the filaments 10 being substantially flush with the end 14. The cross-section of the tube at that end is substantially filled with carbon fibre filaments 10.

This is not essential, but is desirable since it confines the ends of the filaments and prevents them splaying apart when they are at a high electrical potential. As is shown more clearly in Figure 2, the carbon fibre filaments 10 are bent double into a U, the base of the U being looped with bared ends of copper filaments 1 6 of a length of electrical flex 1 8. A piece of tough wire 20 is wound around the looped base end of the carbon fibre filaments 10 to secure them, and solder metal 22 is applied around the looped base end of the filaments, the wire 20 and looped bared filament ends 1 6 to ensure a good connection between the carbon filaments 10 and the copper filaments 1 6 both physically and electrically.The whole connection is protected by a sheath 24 of electrically insulating plastics material.

The flex 1 8 extends axially within the tube 12 and out through a rear tapered end 26 thereof. A small strap 28 of plastics material is fastened to the flex 1 8 at the appropriate position to ensure that when the strap 28 abuts the tapered end 26 of the tube, the free ends of the carbon fibre filaments 10 are substantially flush with the end 14 of the air ion propagation element.

The end of the flex 1 8 further from the element is connected to a high voltage generator 30, for example a Cockcroft and Walton ladder generating a voltage in the range from 6 kV to 1 5 kV, usually about 8 kV. The generator 30 is itself supplied with an alternating electrical current from the mains.

When the generator 30 is switched on, negatively charged ions are produced at the free ends of the carbon fibre filaments 10. These ions are directed in a stream axially away from the tube 12.

Figures 3 to 5 show respective modifications in which (a) the free ends of the carbon fibre filaments project 5 mm from the forward end of the tube, (b) those ends project 10 mm from the tube end, and (c) the element has no surrounding tube.

Figure 6 shows how three air ion propagation elements 32 may be arranged to project downwardly through an outlet grille 34 of an air conditioning system. The downdraught of air through the grille 34 when the air-conditioning system is operating assists in carrying the ions further into the room interior, so that less ions are lost to surrounding objects and more are carried deeper into the atmosphere of the room.

Preferably the elements 32 are spaced more than 1 foot (0.3 metre) away from one another, since it has been found that they adversely affect the performance of one another if they are any closer. They may project through holes 36 specially bored through a central portion 38 of the grille 34 for the elements. Alternatively, if the elements are sufficiently slim, they may project through cracks or holes 40 which are present incidentally in the designs of existing outlet grilles. Slim elements are also desirable because they can project from an outlet grille without being obtrusive. It is not necessary to find a space in the grille 34 for the generator 30 since this may be positioned some way from the elements. In this case, however, it is desirable for the flex 18 to be high tension wire to keep leakage of electrical charge to a minimum.

The most preferred dimensions for the element are 6 millimetres for the internal diameter of the tube 12, and 8 microns for the diameter of each carbon fibre filament 10.

Possible materials for the tube 12 are PTFE, polystyrene, polypropalene and polyphenol oxide (PPO). The material should be a very high electrical insulator exhibiting substantially no water absorption properties.

Thus it will be seen that the present invention is concerned with an ion propagation element which may be used for the production and propagation of negative ions, for example for restoration of satisfactory ion levels, in ion depleted environments, although it will be readily appreciated that the element could equally well be used to produce positive ions where this is required. The illustrated ion propagation element comprises an assembly or conglomerate of multifilament conducting fibres, so disposed as to display a multiplicity of filament ends to the area to which the ions are to be propagated. The most important aspect of this propagation element is the use of carbon fibre as a material for the filaments.

The propagation element may be made relatively small, of unobtrusive and neat appearance, such that it will be aesthetically acceptable in most decorative situations. A typical size for the part of the propagation element which would usually be visible is typically between 8 mm and 12 mm external diameter and between 4 cms and 10 cms in length. The multi-filaments are cut off flush with the end of the tube, such that they do not appear separately outside the tube. The outward appearance is therefore simply that of the tube itself.

As mentioned earlier, it is of assistance (but not in any way necessary) to promote better propagation of the ions, to locate the tube in the airstream of an air-conditioning supply diffuser.

Such a tube may readily be fitted to most types of existing air-conditioning supply diffusers without extensive modification and without adverse results to their decorative appearance. If it can be arranged that the tube is located completely within an enclosing air-flow, the chances of ions being attracted back to earthed surfaces such as walls or ceilings and causing staining are greatly diminished.

Experiments have shown that the smaller the size of the conducting filament, the greater is the quantity of ion discharge at a given voltage.

Furthermore, it seems that with very small filaments, it is not necessary to provide a neighbouring earthed or lower voltage electrode in order to create an electric field of sufficient intensity to initiate a corona discharge. Carbon fibre elements in their most commonly available form are typically between 8 and 10 microns in diameter. This diameter is considerably less than the filament size of other available materials, for example stainless steel wire. Such material is generally not available in a fibre size less than 20 microns in diameter.

Examples of stainless steel wire in diameters of 30 microns and 50 microns have been tried, but have been found to be slightly less effective in ion propagation than carbon fibre and more seriously have been found to be mechanically fragile and prone to damage. In contrast, carbon fibre is mechanically very stable, maintains its linear form extremely well, is not brittle, and is very resistant to most forms of chemical attack which may be found in a normal air environment. Furthermore, in its normal form it is in continuous filaments which are mechanically strong and stable and may be anchored effectively at one end, or perhaps better, looped through a U-shaped retaining component of copper wire or similar.

The chance of carbon fibre filaments breaking or otherwise migrating into the treated atmosphere is therefore almost eliminated. This is in contrast to the copper "Fuzz" type of element in which the propagating device comprises a very large number of random fibre copper filaments which are arranged in a three dimensional fuzz, but which are not effectively retained mechanically.

It is possible to construct the element in a way which minimises the possibility of spark discharge occurring and therefore of ozone being produced.

This is because the tube itself may be manufactured from very highly insulating material and because it is not necessary to provide an earthed conductor or a conductor connected to a lower voltage in close proximity to the fibre ends in order to promote the initiation of a corona discharge. This latter requirement has been found to be an essential feature to ensure effective ion propagation when using the well known needle point types of propagation element. These features also allow the use of a considerably higher voltage without the danger of spark discharge and hence of ozone production than is possible with the more usual needle type propagation element. Such higher voltage enables a much larger output of ions to be achieved.

Should it be found necessary to wash the fibres of the propagation element to clean them, the flex 1 8 may be pushed further into the tube 12 of the tapered end 26 so that the carbon fibres 10 project outwardly from the end 14 of the tube 12.

Experiments have shown that it is not essential for the carbon fibres to be completely dry before the propagation element is fully operational.

Ions may be projected further into the surrounding air if a fan is positioned behind the ion generating ends of the carbon fibre filaments.

In the device shown in Figure 7, a box 60 of synthetic plastics material houses a voltagegenerator (not shown) connected to apply a high voltage to carbon fibre filaments 62. The free ends of the latter project slightly through respective apertures in otherwise closed ends of two tubular portions 64 made of synthetic plastics material. These portions act as hoods around the free ends of the carbon fibre filaments to assist in directing the ions away from the device. The box 60 is provided with an on/off rocker switch 66, and two feet 68 at its bottom front and to raise the latter in relation to the rear end of the box slightly, so as to tilt the tubular portion 64 upwardly.

Claims

1. A device for generating ions of the corona discharge type for use in conditioning the air, comprising a multiplicity of carbon fibre filaments at respective ends of which the ions are generated when the device is in use.

2. A device according to claim 1, in which the carbon fibre filaments are provided by a between 1 and 80 tow carbon fibre.

3. A device according to claim 1 or claim 2, in which the filaments are bent double and electrical contact means loop the filaments where they are bent.

4. A device according to any preceding claim, in which the filaments each have a diameter which is in the range from 6 to 1 6 microns.

5. A device according to any preceding claim, in which the carbon fibre filaments are connected to an electrical-voltage generator.

6. A device according to claim 5, in which the electrical-voltage generator comprises a Cockcroft and Walton ladder.

7. A device according to claim 5 or claim 6, in which the electrical-voltage generator generates a voltage of between 5 kV and 15 kV when in use.

8. A device according to any preceding claim, in which the carbon fibre filaments are surrounded, at least in part, by electricallyinsulating material.

9. A device according to claim 8, in which the electrically insulating material comprises PTFE, polystyrene, polypropalene or polyphenol oxide (PPO).

1 0. A device according to claim 8 or claim 9, in which the carbon fibre filaments extend within a tube or tubular portion made of the electrically insulating material.

11. A device according to claim 10, in which the ion-generating ends of the carbon fibre filaments are within the tube or tubular portion, and rearward of one end thereof.

1 2. A device according to any one of claims 8 to 11, in which an internal cross-section of the surrounding electrically insulating material is substantially filled by the filaments.

1 3. A device according to any preceding claim, having a fan behind the ion-generating ends of the filaments to assist in propagating the ions.

14. A device according to any preceding claim, arranged at an outlet of an air-conditioning system.

1 5. A device for generating ions for use in conditioning the air, substantially as described herein with reference to Figures 1 and 2 or any one of Figures 3 to 7 of the accompanying drawings.