US2585777A - Ionizing structure - Google Patents

Description

Feb. 12, 1952 H L 2,585,777

IONIZING' STRUCTURE Filed March 1, 1947 m f /4 /5 l\" l Fly 2 y Hg 3 9 l 3 Muenfor Q CZMAfM Patented Feb. 12, 1952 assignments, to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 1, 1947, Serial No. 731,734

This invention relates to the production of ionization and more particularly to an improved apparatus for producing ions for theprocess of electrostatic precipitation of particles of solids or liquids from gases, asin the cleaning of air for air conditioning.

In electrostatic precipitators which are used for air conditioning, the air to be cleaned is first drawn or blown through an ionizing zone or chamber, where the foreign particles to be removed are first ionized or charged, and then through a precipitating zone or chamber where the charged particles of dust are made to precipitate or collect on a plurality of spaced, parallel, collector plates parallel to the general direction of gas flow, adjacent ones of which are at diiferent potentials with respect to each other, so that the charged particles will be deflected toward a plate and precipitated thereon. v

For eificient and commercially acceptable operation of this type of precipitator, the ionizing field must be sufficiently intense to charge substantially all of the particles of dust flowing through it, but, the ionizing currents preferably are such that negligible ozone generation occurs. In ionizing means generally used at present, fine wires are placed alternately between plane or curved electrodes having large radii of curvature, and the wires are placed at either a positive or negative potential of such magnitude with respect to the large curved electrodes that the 'gas to be'cleaned is ionized as it passes between the electrodes. In order to obtain sufficient ion ization with ionizing structures of this type, itis necessary to use very high voltages or very fine 5 Claims. (Cl. 183--7) them so that they cause large nonuniformities of ionizing wires or both. In many ionizers, both voltages as high as 15,000 volts, and wires as fine as 5 mils in diameter are used in order to obtain the required results. These wires must. be supported by high voltage insulators and often are suspended in lengths of several feet with no other supports than at their ends. This makes for mechanical structures that are extremely fragile and easily broken. Because of the necessary placement of the ionizing chamber on the intake side of the gas cleaner, large quantities of lint, dust, and other particles may have to 4 pass through the ionizing chamber often causing electrical arcs to occur between the fine wires and their cooperafting electrodes, which arcs may melt the fine wires thus putting the apparatus out of operation. In view of the fact that the ionizing wires collect large amounts of grease, dust and other matter, it is very difficult to clean them because of danger of breaking or stretching the electrical field in the ionizing chamber and even electrical arcs or flash-overs. These disadvantages cannot be eliminated by merely supporting the wires at more points or all along their lengths with insulating means because of the fact that any dielectric placed near an ionizing wire causes a reduction in ionization. Actual measurements which I have made show that the amount of ionization produced by a wire 11 mils in diameter excited at 20,000 volts'D. C. with respect to its cooperating electrodes drops to less than ten percent of its former value when a diameter glass rod is brought near it.

The reason for this is that if the wirewere, say, positive, positive ions would be repelled from it and collect on thesurface of the glass rod placed near it. The effect of these ions collecting on the glass rod is to cause the rod to reach a potential substantially the same as that'of the ionizing wire with the result that the electrostatic lines of force formerly coming from the relatively large negative electrodes of the ionizing structure and terminating on the ionizing wire now terminate on the glass rod instead, thus reducing the field gradient in the immediate vicinity of the wire to such an extent that the ionization produced by the wire decreases tr'e mendously. I have further found that by superimposing an alternating component of voltage of several hundred kilocycles on the voltage applied to the ionizing wire that the amount of ioniza tion produced by the wire actually increases rather than decreases when a dielectric material is brought near the wire. This increase in ionization due to the presence of the dielectric not only makes possible the operation of the ionizing wire at a lower potential, but makes possible the fastening of the wire to a dielectric member along its entire length thus giving great rigidity to the ionizing structure. The use of a dielectric backing for the ionizing conductor makes possiblethe economical construction of ionizing electrodes of other shapes than fine wires such as electrodes having many points which electrodes can be metal sprayed, plated, sputtered, evaporated yor otherwise placed'on a dielectric such as glass in the form of a thin film.

It is therefore van object of my invention to provide an ionizing means which is mechanically rugged, and can be cleaned without any substan tial danger of breaking, bending, stretching, or otherwise misaligning it. It is a further object'bf my invention to provide an ionizing means that requires a smaller magnitude of voltagefor its With the foregoing and other objects in view,

my invention consists of the featuresfiel'ements, combination and apparatus hereinafter described and claimed, and illustrated'in'jthe' accompany ing drawing,'in which:

Figure l is an end view of 'n'ibnizing struc ture showing the lines of force existing between the electrodes.

Figure 2 is an enlarged end view of theiqniz:

ing wire and dielectric rod forming part of the ionizing structureof Figure 1.

Figure '3 is an" end 'view'together with tiresment of a top view of an'iorii'zing electr'odewhich is representative of 'a'second embodiment'ofmy invention. 1

Figure 4 is an end view of an ionizing electrode which is a variation of the electrodeof Figure 3. Figure 5 is an end view and aifragmentof atop view of another embodiment of myinvention.

Figure 6 is'a circuit diagram illustrating one manneriri which the"dielectric'-backed electrodes of my invention could be excited from a source of alternating current energy;

Referring to Figure '1 of the drawing electrodes [2 represent a plurality of electrodes of relatively large radii of curvature between which electrodes and'ionizing wire it the exciting voltage'of-the ionizing structure i's' 'applied. Member leis a rod made of some dielectric material such as glass which is maintained 'incontact with -wire I I by suitable means substantially throughout the len'g'th'of'the wire. "Because "of th'epresence 0f the dielectric "l3, the'electrical capacitance of the discharge path'between the wire and'electrodes l2 through'the dielectric 13 is "increased,

since "the dielectric constantof themember -IB is greater than that"of"air,-or'-the =gas to-be cleaned, 'This' increased'electrical capacitance means that there is a'greater'number of-electrostatic lines of force linking electrodes 12 with electrode H for -the'same voltage 'difierence .between the electrodes- ['2 and-electrodeI-l. This increased number oflinesof force terminating onfelectrode' ll means thatthere is=an increased 'field gradient in theimmediate vicinity-of electrode II with a resulting increase in-ionization. As the dielectric I3 'is'not positioned directly in the path between the electrodes H and l2-,-'and there is a free path between the electrodes through the gas medium unobstructed by the-dielectric, the overall capacity between the-electrodes is not substantially more'than that vided by the gas medium;

The amount of ionization produced is -increased still 'further by another phenomenon. Figure 2 shows an enlarged-view of dielectric rod l3 and wire ll. Due to the fact that both'the rod and the wire have the form of circular cylinders in this embodiment ofmyinvention they touch each other only along a'single line parallel to the axes of the two cylinders. The largest number of electrostatic lines of force that terminate on the conductor l I reach it by passing upward through the dielectric rod due to thetfact thatthe rod has a greater electrical permittivity than does the gas surrounding it; These lines of 'progreater stress concentration can be seen experimentallylby observing the corona discharge from such a wire backed by a dielectric and excited *withjfa source containing a high frequency com- 'ponent offaltefrnating voltage. The side of the wire fagthest'flfr', the dielectric appears dark as if numerate discharge from it at all but vthe'side of-the-wire nearest the dielectric glows verybrightly with streamers that spread downward'toward the dielectric rod on each side of the wire.

As explained earlier the desirableeffects of the addition ofthe dielectric red could not bere'alize'd if the ionizing electrode were excited-with' d'irect current alone. This'-is'-because'--ions produced in the gas between the regions 14 on the wire an'd regions 15 on the dielectric rod -tend,--as-all ionsin gases do, to-move'parallel 'to the lines ofiorcein the electrical field and reduce the charges on the electrodes-'thathave setup-the field. This means that'if electrode H were'charged positively that positive ions wouldmove away from it along-lines of force'and would deposit themselves on' rTegions l5 of the dielectric rod l3. --A-s=soon:as enoug-h ions haddeposited themselves on red 13 its potential in'the'regi'ons l5 -would-.becor"ne substane tiallyequal tothat on thewir e l-l' and the :field existing between regions l-ii or the wire andde of the 'rod'would be reduced to-such a--value that ion production would-be reduced to an extremely low value or "cease entirelyl T- c n phenomenon may be likened to :the phenomenon occurring in an electrical circuit in which the ionized and therefore conductive pathwthroug-h the gas between'regions 1-4 and" l5 may bemcomlpared to an electrical resistance whicn..iis. .cone nected 'in serieswith a condenser .(which. condenser has as itsdielectric the' seriescombination of the dielectric er rod "I3 and the gasthrough which the lines of-fo'r'cel'fio'w' in linking electrodes ll and'l2,and which condenser. haszas itselectrodes the charged region l5 andxthe electrode 12) "Upon' the" application of a direct.;volta 9 across the series combination of lthecresistancfi and the capacitance there is a surge or. current which lasts 1mm the acapacitance has become charged and then subsides. '.By applying analternating voltage across this series combinationihe condenser continually charges :anddischarges so that there is a continualiiowof alternating current through the resistance. V .This current is in: creased'b'y increasing' the frequency of. thesource. In thissame manner when anialternating vol ge is applied 'between' the' electrodes. and ilz of Figured; there is a-continualflowlo'f alternating currentfrom the electrode -l l' with the resulting continuous production of ions. By applying addition to "the alternating component f .voltage between the electrcde's' of" theiionizingi Structure a direct component of voltage, the ionslof charge opposite to that of tha electrodes I2 are pulled outwardfrom the region near the'wirein which they are formed toward the larger .electrodes l2 and thus permeate the 'entire'spacel between electrodes l land 12 through which the gas to becleaned is 'directed. I havefound extreme?- 1y good ionization to"'be obtained" with a frequency of the alternatingvoltage component-of excitation of the order of 200 lrilocyclesper secand though, frequencies as ,low as commercial powerline" frequencies can be used."'

In aisecond embodiment 01. my invention-was shown in Figure 3, a dielectric member or red It has a conducting film' such 'asialuminum-sor copper or other conductive material sprayed. plated, sputtered, evaporated or otherwiselfasjr tened to its as'illustratedby reference character I! in the diagram. A This condii'cting film may serve as an ionizing electrodeiand is of such shape that various portions of it form a' series of-point such that when an alternating potential of sufficient amplitude is applied between the conduction film l1 and cooperating electrodes placed nearby an electrical discharge takes place from the points formed by the conducting film into the gas surrounding the points causing ionization of the gas.

The addition of a second member of dielectric material I8 placed near and arranged substantially parallel to the conducting film 11 as illustrated in Figure 4 increases the electric field gradient in the vicinities of the points formed by the films ll thus allowing the ionizing electrode I! to operate at a lower value of alternating current potential. A small space must be maintained between the film I1 and the dielectric member It in order that a discharge into the gas surrounding the electrode may take place and in order that the ions formed near the points may have a path through the gas through which to fiow outward into the stream of gas to be cleaned.

Figure 5 illustrates another embodiment of my invention in which member I9 is a dielectric rod substantially rectangular in shape which forms the main supporting member of the ionizing electrode 20. Electrode 20 may take the form of a thin metallic stamping, so stamped or otherwise formed so that it has a plurality of pointed sections curved upward and away from the dielectric members I9. Members i9 and 2t are fastened together by means of small rivets 2i only one of which'is shown in the diagram. The pointed sections of member 20 are curved away from the dielectric member so that there exists an air space between the points and the dielectric member through which an electrical discharge can take place. When properly excited a bluish glow can be seen to fan outward and downward from the various points toward portions of the dielectric member IS in the immediate vicinities of the points.

Figure 6 illustrates a typical electrical circuit which may be used to excite all of the ionizing structures described above. In it reference numeral 25 represents a source of alternating current electrical energy such as the secondary winding of a high voltage transformer. Connected in series with each other and with the resulting series combination connected across source 25 are respectively an electrical capacitor 26 and a rectifying device such as an electron discharge device 24. As the cathode 28 of the electron discharge device is connected to one terminal of the alternating current source and as the anode 21 is connected to one terminal of the capacitor 26 the capacitor will be charged to a voltage equal substantially to the peak value of the voltage appearing between the terminals of source 25. The two terminals of the ionizing structure to be excited, namely the ionizing electrode 29 supported by its dielectric rod means 22 and the cooperating electrodes 23, are connected to the cathode and anode respectively ofxrthe rectifyingdevioa 24.1 Inthis mannerZthe-Jphs tential difference 'applied'zbe'twe'en electrodes':;23; and 29 consist's 'of the :1 sum of tw'o I components which 'are 'the' direct currentc'omponent of -volt:i-

age existing across capacitor2=B and thealternatw' izrg component 'of'i-voltag'e existing across source;

In the'following claim it is tobe understood that radius of curvature may; at times bay-so; small that sharp corners or-edges are meant 'andmay at times be infinite suchlthatiplane. sure; faces are meant.

While three embodiments of my invention have been described for the purpose of illustration, it should be understood that the invention is not limited to the exact circuits and arrangements of apparatus herein described, or specifically covered by my claims, as modifications thereof may be suggested by those skilled in the art without departure from the essence of the invention.

What is claimed is:

1. An electrical ionizing apparatus including in combination, a gas medium, a cylindrical conducting electrode having relativelysmall radius, a solid dielectric cylinder having a radius larger than that of said cylindrical electrode and being made of a material having a dielectric constant substantially greater than that of said gas medium, said dielectric cylinder being parallel to said cylindrical electrode and being in contact therewith through substantially the entire length thereof, at least one cooperating conducting electrode spaced from said first conducting electrode and said dielectric cylinder and having a radius of curvature substantially greater than that of said dielectric cylinder,-said dielectric cylinder being positioned with respect to said conducting electrodes to provide a free path through said gas medium between said electrodes unobstructed by said dielectric cylinder so that the electrical capacity between said electrodes is not substantially more than that provided by said gas medium, and a high voltage energizing source coupled across said conducting electrodes for applying a voltage thereto having a direct current component and an alternating current component.

' 2'. An electrical ionizing apparatus including in combination, a gas medium, first and second elongated conducting electrodes extending parallel to eachother in said medium, a high voltage energizing source coupled across said electrodes for applying a voltage thereto having a direct cur--. rent component and an alternating current com ponent, said first electrode having surface regions of small radius of curvature, a dielectric rod made of a material having a dielectric constant substantially greater than that of said gas medium extending parallel to and substantially in contact with said first electrode so that a short discharge path is provided from said first electrode to said dielectric rod, said dielectric rod being positioned with respect to said conducting electrodes to provide a free path through said gas medium between said electrodes unobstructed by said dielectric rod so that the capacity between said electrodes is not substantially more than that provided by said gas medium.

3. An electric ionizing apparatus in accordance with claim 2 in which said alternating current component of said high voltage energizing source has a frequency greater than ten thousand cycles per second, with said alternating

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