GB2162697A - Slot ionizer - Google Patents

Abstract

The ionizer comprises one or more needle probes (6) suitably insulated from and mounted between two substantially parallel side-cheeks (1) through which air may be passed. The side-cheeks are of insulating material and carry conductive screens (2, 3), both on the inner surfaces, facing the needle probes, and on the outer surfaces of the side-cheeks. The needle probes and screens are so arranged that when held at suitable potentials a stream of ionized air is produced, the production and free passage of which to the outside air is not affected by adjacent metal or insulated members in or near which the ionizer may be mounted, and so that unwanted electrostatic fields due to the said needle probes and or screens are suppressed. The ionizer is particularly for use in a ventilating system. <IMAGE>

Description

SPECIFICATION Slot ionizer This invention relates to air ionizers of the type in which a corona discharge is produced at the point of a sharp needle, wire, conductive fibre etc., termed the corona electrode or probe, by connecting it to a source of high potential, typically 3000 to 7000 volts. The corona gives rise to a stream of elecrtically charged molecules of the gas or gases constituting the air in which the corona discharge takes place. These air-"ions", the sign of which is determined by the sign of the applied potential, are normally propelled away from the corona electrode by the well known "electric wind" effect.

In many applications the use of an exposed corona electrode, or probe, gives rise to a problem in that airborne dust particles become charged by the emitted air-ions and are then propelled towards nearby surfaces at a lower potential, or at earth potential, or at a potential of opposite sign, by virtue of the electric field existing between the corona electrode and the said surfaces. This disposition of ionizing means and surfaces of earth or opposite potential corresponds in essence to an open electrostatic dust precipitator of known principle.

In order to prevent the deposition of ionized, or charged, dust particles on to the adjacent surfaces it is necessary to remove or suppress the electrostatic field existing between the corona electrode and its associated wires and equipment, and the external surfaces. This can be done by enclosing the corona device in a metal box or container, as in Figure 1, but in this case the passage of ions through aperture 3 to outside the box is suppressed due to one or other of two possible effects. Referring to Figure 1, this shows a needle probe 1, suitably mounted in and insulated from a conductive container 2, having an outlet aperture 3 and inlet apertures 4 through which air, A, may be passed under pressure through the container and out via the outlet aperture 3.If now the container 2 is earthed and a potential of, say, 6kV applied to the needle proble 1, a corona will be maintained at the sharp needle point of the probe 1, so that air passing through the container will be ionized.

However, the strong electrostatic field existing between electrode 1 and the inner surfaces of the earthed container 2 will cause the ionized air to impinge directly on the container, as at 5, and an ionization current will flow. Because of this, little or no ionized air will emerge from aperture 3, even when induced air, A, is passing through the container.

A different condition will exist in the case where the container 2 is insulated from earth, or the container itself is made from insulating material such as plastics. In this case the air-ions emitted from electrode 1 will serve to charge the inner surface of the container and this rising potential will approach that of electrode 1 until a condition is reached where the electric field- strength between the container and the probe is insufficient to maintain the corona. At this point the generation of airions will cease.

Either one or the other of the two conditions described is met with when attempts are made to pass ionized air through conductive, or insulated grilles or diffusers, as used in air- conditioning systems, by mounting an ionizing probe behind them.

This applies particularly in the case of the narrow "slot" type of ceiling diffuser in Figure 2. Grille and diffuser type air dispensers of many types are used extensively in heating, ventilation and air-conditioning systems and it is the purpose of this invention to provide a means of generating and distributing air-ions through such devices with a high level of efficiency and without the deposition of airborne dirt on to adjacent surfaces or the generation of 03 due to heavy earth currents.

The principles employed in this invention, hereinafter called the "slot ionizer", will be described with reference to Figure 3 and Figure 4. In this embodiment, two side-cheeks 1, are suitably mounted and spaced by insulators 11, or similar, so as to lie parallel to each other. Each side-cheek 1 consists of a board or plate of insulating material, on to which are mounted or deposited a first conductive screen 2, and a second conductive screen 3, the first conductive screens 2 being positioned so as to face each other as shown in Figure 3. A further board 4, hereinafter called a "probe strip", is suitably mounted between the two side-cheeks by insulators 11, and consists of a strip of insulating material carrying a conductive strip 5 and one or moe conductive probes 6, which are connected to it.

The slot ionizer illustrated here in principle may be constructed in any length suited to the application, the spacing between the conductive probes 6 being a function of the spacing between the side cheeks 1 and the probe strip 4, and the length of ionization required.

In operation a potential of, say, 6kV is applied to the conductive strip 5 to which the probes 6, are connected. With the side-cheeks 1 in close proximity to the probe strip this would normally lead to the charging of the inner surfaces of side-cheeks 1 by the action of the corona produced at the point of the probe 6. As previously described, the potential of the side-cheek charge would gradually increase towards that of the proble 6 to reduce the field strength at the probe tip until the corona discharge could no longer be maintained. To overcome this, the conductive screens 2 are held at a potential, typically 2 kV and of the same sign as the probe potential, such as to produce an electric field between screens 2 and probe 6 of sufficient strength to maintain the coronoa discharge.At the same time, the potential at screens 2 is also chosen so as to repel the air-ions of like sign produced by the corona and thus prevent a flow of current to the screens which would result in a loss of ions and the production of 03. The inner surfcaes 7, of the side-cheeks not covered by screens 2 acquire a charge potential from the air-ions which also affects the strength of the corona discharge at probes 6, and which is taken in account in the design of screens 2 and the potential applied to them. The field pattern existing between screens 2, the surfaces 7, and the probes 6 and conductor 4, is such as to focus the air-ions emitted and accelerated by probe 6 into a beam in the direction indicated by arrow 8.

However, the charge potential on surface 7 will be significantly increased by any intermittent external contact with the outer surfaces of the insulated side-cheeks 1, due to charge transfer and this can seriously affect the intensity, and even suppress, the corona discharge at the probe 6. To overcome this problem and stabilise the charge potential at surfaces 7, additional conductive screens 3, are secured to the outer surfaces of the side-cheeks 1 as shown, said screens being maintained at earth or other suitable potential. A further important function of screens 3 is to suppress any side fields, generally in the direction of arrow 10, arising from or due to the probes 6, screens 2 or side-cheek surfaces 7.

It will be seen, therefore, that if the slot ionizer described is mounted, for example, totally inside a section of metal slot-type ventilator, as illustrated in Figure 5, air A passing through the ventilator will be ionized by probe 6 and accelerated and focused by the surrounding electric fields as described to emerge, without loss of ions to the metal "slot" member, through the exit orifice 12.

Since all external electric fields, other than that remaining in the direction of arrow 8 have been suppressed, dirt deposition on surround surfaces will also be suppressed. Typically, the slot ventilator assembly shown in Figure 5 would be mounted in a ceiling ventilating system with a clean unobstructed space in front of the downward-facing exit orifice 12.

In a further application, the slot ionizer may be mounted in a grille-type diffuser as illustrated in Figs. 6 and 7. Fig. 6 shows a typical grille construction with vertical (v) and horizontal (h) vanes. The vanes are normally mounted so as to rotate by a small amount about their length and may be set to deflect the air flow in the required direction.

Fig. 7 shows, in plane, one typical arrangement in which a slot ionizer (I) is mounted in place of one of the rear vertical vanes.

The horizontai vanes (h) are preferably insulated, for instance, by a suitable varnish, paint, or membrane, in order to minimise or suppress the flow of any ionization current to the vanes. The presence of the vanes, whether conductive or insulating, will not affect the operation of the ionizer (I) since the necessary field conditions are internally determined by its own arrangement of electrodes and screens operating at predetermined potentials It will be clearly apparent that the use of ordinary exposed ionizer probes behind the grille vanes will, as explained with reference to Fig. 1, result in all air-ions being either lost or suppressed.

Claims (15)

1. An air ionizer comprising one or more needle probes suitably insulated from and mounted between two side-cheeks through which air may be passed, the said side-cheeks being constructed from insulating material, the said side-cheeks carrying conductive screens or electrodes, both on the inside surfaces facing the needle probes, and on the outer surfaces, said needle probes and screen electrodes being so arranged that when held at suitable potentials a stream of ionized air is produced, the production and free passage of which to the outside air is not effected by adjacent metal or insulated members in or near which the ionizer may be mounted, and so that unwanted electrostatic fields due to the said needle probes and or electrodes are suppressed.

2. An ionizer according to Claim 1 wherein the needle probes take the form of metal or plated metal needles, or wires, mounted on a conductive or insulating member.

3. An ionizer according to Claim 1, wherein the probes take the form of conductive fibres.

4. An ionizer according to Claim 1 wherein the probes take the form of one or more stretched thin wires.

5. An ionizer according to any one of Claims 2 to 4, in which the probe mounting member takes the form of a printed circuit board.

6. An ionizer according to Claim 1, wherein the side-cheeks take the form of printed circuit board laminate on which the necessary conductive screens and electrodes are formed on one or both sides by an etching or other suitable process.

7. An ionizer according to Claim 1, in which the probe assembly is insulated from and positioned between, the side-cheeks by insulators affixed to said side cheeks.

8. An ionizer according to Claim 7 in which the side-cheeks and probe assembly are independently insulated and mounted so as to preserve the desired spatial relationship.

9. An ionizer according to Claim 7 or 8 in which the side-cheeks and probe assembly are so mounted as to allow the free passage of air between the side-cheeks and past or over the probes.

10. An ionizer according to any one of Claims 1 to 9 in which the parallel mounted side-cheeks and the concentrically mounted probe assembly may be formed into an arc, circle or other required form.

11. An ionizer according to anyone of Claims 6 to 10, in which more than one independent conductive screen or electrode may be placed on either side of the side cheeks.

12. An ionizer according to any one of Claims 6 to 11 in which the conductive screens and/or electrodes derive their operating potentials from an external power supply.

13. An ionizer according to any one of Claims 6 to 12 in which some or all of the conductive screens and electrodes derive their working potentials from a resistor or reversed diode by virtue of an ionization current deriving from the corona discharge.

14. An ionizer according to any one of Claims 2 to 13 wherein at least one probe or conductive screen or electrode may be connected to an indicator for indicating the operating efficiency of said ionizer.

15. An air ionizer constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as shown in, Figures 1 to 7 of the accompanying diagrammatic drawings.