FIELD OF THE INVENTION
This invention relates to air filtration systems. In particular it relates to an air filtration system based upon forming an air current of ionized air and the collection from such air current of dust particles by means of a charged surface.
BACKGROUND TO THE INVENTION
U.S. Pat. No. 5,538,692 to Joannou describes an ionizing type air cleaner having an exposed ionizing needle and a collector element in the form of a charged, partially conducting, surface. (See FIG. 1) Ions released from the needle spread-out through the air of the surrounding environment in the form of an “ion wind”, charging particles of dust present therein. By reason of the charge on the collecting surface, such dust particles are drawn to and become attached upon the collecting surface. Dust removed from the air in this manner may be readily disposed of by simply wiping the collecting surface with a rag or the like.
Although the collecting plate will attract and hold a substantial part of the dust present in the air flow, nevertheless some dust and oily aerosols will still be present in the air flow that moves past the collecting plate. A number of these particles will still be charged. It has been found that such ionized particles as are not collected on the collecting plate have a tendency to collect on adjacent uncharged surfaces, such as walls. Over time, the collection of particles on wall surfaces can become visible as a discoloration. This is an undesirable effect. This disadvantage arises because this air cleaner acts as a “fountain of ions” with its collection surface positioned beneath the ion source, requiring ions to flow outwardly before being collected.
A need exists for an ionization-based air cleaner that has a reduced tendency to produce discoloration on adjacent surfaces. The invention herein addresses that objective. This invention is a continuation-in-part of U.S. application Ser. No. 10/067,433 filed Feb. 10, 2002 (the contents of which are adopted herein by reference) which application partially provides part of the disclosure and solution set-out herein.
It has been disclosed in U.S. Pat. Nos. 6,176,977, and 6,312,507 to Taylor et al to provide a pointed ion source upstream in an ion induced airflow, with washer-like ring electrodes positioned downstream. Dust charged by ions is collected on the flat surfaces of the ring-like electrodes facing the ion source as well as between plates.
The design of U.S. Pat. No. 6,176,977 does not, however, address confining the ion-wind induced airflow, or providing an airflow path that will minimize interference with such airflow. The invention disclosed herein, however, incorporates such features.
The invention in its general form will first be described and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.
SUMMARY OF THE INVENTION
According to the invention in one aspect, an ion-emitting source or “ion source”, preferably in the form of a needle, releases ions to charge dust particles in the surrounding air. This ion source is placed in a position whereby charged dust particles will flow, along with the flow of air that is induced to flow by an “ion wind”, away from the needle to pass through the center of a dust collecting guide that is preferably in the form of a dust collecting cylinder.
This cylinder serves as a guide or duct for the flow of air. This dust collecting cylinder includes, at least and preferably only on its inner surface, a conductive plate or element connected to a potential source which acts as a charged dust collection surface. This dust collection surface is optionally but preferably in the form of a substantially encircling collecting plate, that contains the flow of the air as it collects charged dust particles. The dust-depleted air then passes on, outwardly, from the collecting cylinder. Alternately, the dust collection surface can be intermittently formed on the inside of a cylinder of non-conductive materials or as mutually opposed inwardly directed electrodes in the form of discrete conductive panels.
The dust collection surface carries an ion-inducing potential which, based on its proximity to the needle and its electrical potential, serves as well as a counter-electrode to induce the release of ions from the ion source.
According to one variant of the invention, this guide cylinder and charged collecting plate are located vertically above the ion-emitting needle source. By placing the charged collecting plate above the ion source, an upwardly directed ion wind is formed. Air entrained by the ion wind approaches the ion source laterally and is then swept upwardly by the flux of ions introduced into the airflow by the ionizing needle. The collecting plate, located above the needle, does not block this upward flow of air but rather serves to guide the air flow.
The volume of air treated for dust removal is increased by the airflow arising from the ion wind that is created. This airflow may also be directed horizontally by placing the ion source and dust collecting guide in horizontal opposition.
A further advantage of providing a collecting plate in the form of opposed dust collecting electrode surfaces, preferably carried by a cylinder, that are positioned downstream from the ion source is that the opposed dust collecting surfaces will contain the air flow while attracting dust. Thus a cylinder with opposed inner dust collecting electrode surfaces may be positioned in the direct path of the ion wind originating from an ion source so that the quantity of charged particles that will be released laterally for potential collection on wall surfaces is reduced from that created by the fountain-form collector where the collection surface is positioned beneath the ion source.
The focusing of an ion wind, and hence the capacity for protection of wall surfaces from discoloration, can be further increased in another variant of the invention. In this variant the charged ion source is mounted on an insulating charge-collecting surface that is preferably otherwise exposed to the environment, producing a directed flow of ions. The ion source and charge-collecting surface are then positioned to direct the ion wind into the core of the opposed dust collection electrode surfaces. The ion source insulating surface is preferably made of a non-conducting or dielectric material, (polymeric plastic for example), which becomes charged with the same polarity as the ion source by the deposition of charge from the ions. This fixed charge repels the ions coming out of the ion source and directs them or focuses them in the direction of the collector. With the help of the repulsion surface and its positioning with respect to the collector electrodes, fewer ions are emitted in directions away from the collector. Thus, for example, when a cylindrical collector is oriented horizontally and positioned in sufficiently close proximity to the ion source so that virtually all of the focused ion wind passes horizontally through the core of the collector, this arrangement can ensure that charged dust particles in the ion wind are directed away from a wall, minimizing or excluding the formation of discolorization on the wall surface. Ideally, all ions emitted will become entrained in the air flow of the ion wind and be directed to pass through the dust collecting guide.
While an ion source may consist of a single needle, multiple needles and repulsion surfaces may be provided. Preferably such multiple needles should be sufficiently separated to avoid the mutual suppression of ions that may arise when similarly charged needles are placed in close proximity to each other.
The tendency for ions to form is proportional to the electrical field potential gradient present at the needle tip. This gradient may be enhanced by ensuring that the leading, upstream edge of the ion-inducing charged collection plate (located in front of the ion source, down-wind from the needle tips), is in relatively close proximity to the ion source, sufficient to induce the release of ions. This positioning also helps suppress the lateral escape of ions and charged dust particles. Of course, the collection surface should not be so close to the needle(s) as to risk arcing and preferably not so close as to induce the release of excessive amounts of ozone.
To protect persons handling this air cleaner device, it is preferable to provide mechanical shielding means around each needle. Shielding is appropriate because the ion source and dust collecting electrodes of the invention are fully exposed for possible human contact and are not protected within a housing. Such mechanical shielding means is preferably in the form of thin plastic posts or plates protruding from the repulsion surface. Preferably two, three or four such posts surrounding the needle are of a length sufficient to prevent injury to a hand passing over the needle tip. By using short posts, the surface around the needle tip may be conveniently cleaned with a simple brush, eg. a toothbrush.
The dust collecting surface(s) may be in the form of one or more opposed plate members or in the form of one or more conductive layers formed along the inwardly facing airflow guide surface(s). In the case of a cylindrical guide support the interior surface(s) may be circular or optionally may be generally oval-shape. According to this preferred arrangement the invention dust is principally collected on the opposed interior collecting surface(s). The dust collecting electrode surfaces may be either self-supporting or carried on the inner face of a cylindrical support. While an entire dust collecting guide may be conductive, only the interior surface or an effective portion of the interior surface need be conductive. The exterior surface of the airflow guide, or cylinder, when employed, may be non-conductive. An advantage of providing the airflow guide of the invention with an exterior, insulating, fixed charge supporting surface, at least in the vicinity of its upstream edge proximate to the ion source, is that fixed charges formed on such a surface by arriving ions will tend to repel further ions and similarly charged dust particles. This effect will further enhance the channeling effect of employing a focused ion source as well as an airflow guide to contain the flow of dust-laden air.
A convenience of all of these variants arising from the cylindrical shape is that the collecting cylinder with its interior dust collecting surface may conveniently be removed for cleaning, and presents no sharp corners to conceal dust.
A further salutary feature of the invention is that the minor portion of ions not trapped on or discharged by the collecting surface may mix with surrounding air away from wall surfaces, if so directed, and if negative ions are employed and escape the collection surface(s), provide the reported health benefits arising from the presence of such ions in the air.
Another optional feature of the invention is the provision of a protective circuit which is incorporated within the power supply of the unit. Because the ionizing needles and collection cylinder are open to the outside world, a person can place his or her hand inside the device, close to the ionizing needles. In this case, a charge will be imparted on the body of the person and if the person then touches the collector electrode, he or she may get an unpleasant spark between their hand and such collector. To eliminate this effect, a sensing circuit is incorporated in the power supply that turns off the unit as soon as the slightest discharge occurs on the collector. Conveniently, the reset switch for this safety circuit can also serve as an on-off switch.
The foregoing summarizes the principal features of the invention and some of its optional aspects. The invention may be further understood by the description of the preferred embodiments, in conjunction with the drawings, which now follow.