Abstract:
This specification discloses an air purifying apparatus having an ozone generator and an electrostatic filter. The air purifier includes two charge carrying plates abutting opposite sides of a planar dielectric layer along the entire width of each plate, one of the plates being relatively narrow in width in comparison to the other plate. The plate configuration prolongs the life of the dielectric layer and permits easy cleaning of the air purifier.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to air purifying apparatus; and, more particularly, to air purifying apparatus having an electrostatic filter and ozone generator. 
     The prior art teaches air purifying apparatus having two electrodes with an intervening dielectric layer for producing a corona to ionize air thus producing ozone as well as acting as an electrostatic filter. The shape of the electrodes has often included a plurality of pin-like protrusions or an interwoven mesh. Such structures have been difficult to clean and produce undesirably high concentrations of electric field on the dielectric layer thereby causing a burn out of the dielectric layer and subsequent shorting of one electrode to the other electrode. Shorting is undesirable because it can damage the air purifying apparatus thereby creating a need for repair work which is both costly and time consuming. Easy cleaning is very important in a device which attracts particle impurities in the air because, periodically, all the partical impurities attracted to the electrodes must, of course, be removed. Difficult cleaning tends to lead to longer intervals between cleaning thus reducing the efficiency of the air purifier. 
     SUMMARY OF THE INVENTION 
     An air purifying apparatus in accordance with this invention has two substantially planar electrodes carrying electrical charges of opposite polarity butting against opposite sides of a common dielectric layer. The planar surfaces of the electrodes are either substantially parallel or perpendicular to the dielectric layer thus avoiding an undesirable concentration of electric field on the dielectric layer which prolongs the life of the dielectric layer and prevents shorting of the two electrodes. 
     In the preferred embodiment, each electrode is sufficiently spaced from the such electrodes to provide for easy cleaning. Air flow passing the electrodes can generally follow the planar sides of the electrodes. Therefore, access to the electrodes for cleaning can follow the path of the air and can be readily accomplished by various cleaning apparatus because of the flat and spaced sides of the electrodes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of an air purifying apparatus in accordance with an embodiment of this invention; 
     FIG. 2 is a cross sectional view along section line II--II of FIG. 1 of an air purifying apparatus in accordance with an embodiment of this invention; 
     FIG. 3 is a cross sectional view along section line III--III of FIG. 2 of an air purifying apparatus in accordance with an embodiment of this invention; 
     FIG. 4 is a partial interior end view of the air purifying apparatus shown in FIGS. 2 and 3; and 
     FIG. 5 is a schematic electrical circuit diagram of an air purifying apparatus in accordance with an embodiment of this invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, an air purifier 10 as an exterior cover comprising a housing top 28 having perforations for passing air, a housing bottom 29 also having perforations for passing air, a cover 16 for shielding interior components and a housing base 13 for supporting a plurality of interior components. Mounted to housing base 13 are a transformer 14, a fuse 36 retained by a clip-type fuse holder 36a, and an electrostatic grid assembly 18 for producing an electrostatic charge to remove impurity particles from the air and for producing an electric field having a sufficient voltage gradient for producing a corona to produce ozone. 
     Referring particularly to FIG. 5 with FIG. 1, an electrical schematic drawing of air purifier 10 includes a alternating current voltage source 35 coupled through a potentiometer 12, fuse 36, and wires 15, 17a and 17b to the primary winding 14a of transformer 14. The secondary winding of transformer 14 has one terminal coupled by wire 19 to inside backing plates 27 and another terminal coupled by wire 21 to central plates 22 so plates 22 and 27 carry charges of opposite electrical polarity. The two plates 27 are electrically connected by metallic securing bolts 34 as will be described hereinafter. Between plates 22 and 27 are insulating mica sheets 24 and surrounding plates 22 and 27 is housing base 13, indicated as a dotted line in FIG. 5 and grounded for safety. Plates 27 are electrically insulated from housing 13 by planar sheets of dielectric insulation material 26, 26a. Potentiometer 12, mounted on cover 16, is electrically coupled to voltage source 35 through an electric plug 55 and a grounded, 3-wire line cord 15a, located outside cover 16, and includes a knob 37 on the outside of cover 16 for varying the resistance of potentiometer 12. 
     Grid assembly 18 includes a grid central portion 20 which is preferably negatively charged and includes a plurality of planar, parallel, spaced conductive central plates 22. Central plates 22 are rectangular and have major side surfaces 32 and first extremities having end surfaces 33, and second extremities having apertures 38. Surfaces 33 are generally perpendicular to side surfaces 32 and to the top and bottom edges of plates 22. Central plates 22 are mounted by an electrically conductive core pin 31, typically a nut and bolt combination, passing through apertures 38 and are oriented so alternate plates 22 extend in radially opposed directions from core pin 31. End surfaces 33 of central plates 22 extending in a common direction from core pin 31 are oriented along a common plane and firmly contact dielectric sheets or layers 24. Core pin 31 is conductively connected to central plates 22 and the negative terminal of transformer 14 by wire 21. Between each pair of adjacent central plates 22 extending in opposite directions is a spacer 30 for separating the central plates from one another. Spacer 30 has a cylindrical shape with a longitudinal central opening for passing core pin 31 and planar ends for butting against central plates 22. This spacing is advantageous for providing access to central plates 22 for cleaning and for providing a space for corona discharge. The orientation of central plate side surfaces 32 is parallel to the path of a direct flow of air between the perforations in housing bottom 29 and housing top 28. A typical grid central portion 20 has, for example, 14 central plates 22 in seven double plate groupings. A larger capacity air purifier 10 can have more central plates 22. 
     Abutting central plate end surfaces 33 are planar, rectangular mica sheets 24, one mica sheet being positioned on either side of core pin 31 generally perpendicular to central plates 22. Preferably, mica sheets 24 each have a thickness in the range of about 0.004- 0.005 inches. A double or greater thickness of mica sheeting may be used on either side of core pin 31, if desired, for a total thickness of about 0.012-0.014 inches. Backing plates 27 abut mica sheets 24 on the other side of mica sheets 24 from central plates 22 and are conductively connected to the positive terminal of transformer 14 by wire 19 to carry a positive charge. Plates 27 each have a substantially planar and rectangular shape with mounting openings at each of their four corners. Accordingly, the two conductive electrodes, central plates 22 and backing plates 27, are separated from one another by an intermediate insulating layer mica sheets 24. An electrically conductive, connecting screw 34 passes through the corresponding corner openings of each of backing plates 27 to connect those plates to each other and to compress mica sheets 24 and central plates 22 therebetween. Electrical connection between backing plates 27 may also be accomplished by a low resistance wire connected between the plates. Connecting screw 34 is typically a metallic bolt with a nut fastener which is tightened snugly and then one or two turns more to produce a tight fit of central plates 22 against mica sheets 24. This compression is advantageous to produce an even pressure on end surfaces 33 and to prevent air gaps which might cause sparking betwen mica sheets 24 and end surfaces 33 of central plates 22 and backing plates 27. Thus, the electric field which ionizes the air surrounding central plates 22 has electric field lines extending from the relatively broad side surfaces 32 thereby avoiding a concentrated electric field, and undesirably high voltage on the portions of mica sheets 24 between adjacent central plates 22 thus preventing their burn out. To show how a concentration of electric fields lines is avoided on mica sheets 24, FIG. 2 shows dotted lines 55 representing electric field lines between adjacent central plates 22. Note that there is a relatively constant density of electric field lines on mica sheet 24 between central plates 22. Additionally, sparking and an undesirably high electric field concentration between end surfaces 33 of central plates 22 and backing plates 27 is avoided because end surfaces 33 are relatively planar and butt against mica sheets 24 without any intervening air space whereby sparking could occur. 
     Preferably a rectangular insulation backing sheet or layer 26 can be placed adjacent backing plates 27 when mounting of grid assembly 18 to housing base 13. Layer 26 prevents the charge on plates 27 from being transferred to housing 13, 16 and is preferably a plastic material having a dielectric strength of approximately 10,000 volts per each 1/4 inch of thickness. An additional layer 26a of fellon insulation or fiberglass insulation having a thickness of about 3/8 inch may also be used. Alternatively, additional stainless steel backing plates for strength and rigidity of the grid assembly may be used in place of layers 26a. If desired, a micro switch (not shown) can be mounted on housing base 13 so air purifier 10 is activated only when cover 16 is in place. This prevents exposure of personnel to the high voltage generated on central plates 22. 
     In the preferred embodiment, cover 16, housing top 28 and housing base 13 have a plurality of apertures 50 which can be selectively aligned to pass screws 51 thus coupling the housing elements of air purifier 10. Also, if desired, a fan can be used to aid air flow through air purifier 10. Further, if desired, an elongated opening 95 (FIG. 1) can be located along the bottom portion of cover 16 for passing air when air purifier 10 is mounted on a horizontal surface and the perforations of housing bottom 29 are obstructed. Transformer 14 is advantageously an iron core, double coil, isolated transformer in which coils can be replaced. An example of a suitable transformer is a Hyboer transformer, Product No. HT-14581. Replacement of coils is advantageous for easy repair of air purifier 10. A typical transformer 14 has a turns ratio of 1 to 44. Accordingly, a voltage applied between central plates 22 and inside backing plate 27 is in the range of about 3,800 volts to about 5,200 volts depending on the setting of potentiometer 12 and based on a typical line voltage of 110-120 volts. The grid assembly 18 including spacers 30, central plates 22, inside backing plates 27, and core pin 31 are advantageously stainless steel to resist corrosion and oxidation which are very prevalent in an ozone producing apparatus. A typical thickness for central plates 22 and backing plates 27 is about 0.062 inch. Similarly, housing base 13, cover 16, housing top 28 and housing bottom 29 are preferably anodized aluminum to prevent corrosion. An alternative to fuse 36 is the use of a circuit breaker, having, for example, a magnitude of one ampere, with a reset button extending through cover 16. For safety, cover 16 housing top 28 and housing bottom 29 are grounded. 
     In operation, plug 55 is electrically coupled to voltage source 35 and appropriately grounded. Knob 37 of potentiometer 12 is turned to decrease the resistance, from an initially high resistance setting, thereby increasing the charge on central plates 22 and backing plates 27. An electric field forms between the static charge on plates 22 and 27 and thus surrounds central plates 22. When the voltage gradient of this electrical field is sufficiently large, the air ionizes, there is a corona discharge and ozone is produced. Normally, a minimal electric current of 1 milliamp passes through mica sheeting 24. Fuse 36 preferably has a 1 amp capacity. Ozone is a powerful oxidizing agent and useful for eliminating odors. Additionally, the charge on plates 22 and 27 attracts airborne impurity particles to plates 22, 26 and 27. As a result, air passing through air purifier 10 is electrostatically filtered and purged of odors. 
     To clean air purifier 10, voltage source 35 is disconnected and housing top 28 is removed, thereby exposing grid assembly 18. Cleaning instruments such as brushes can be readily inserted between parallel central plates 22 to clean central plate side surfaces 32 and inside and outside backing plates 26 and 27. Cleaning solutions may also be easily applied and wiped across and along the grid plates. Any impurity particles attracted to plates 22, 26 and 27 can be removed and typically dropped through openings in housing bottom 29. If desired, housing bottom 29 can also be removed. 
     Various modifications and variations will no doubt occur to those skilled in the various arts to which this invention pertains. For example, the particular connection of the central electrode plates to each other and the housing may be varied from that disclosed herein. These and all other variations which basically rely on the teachings through which this disclosure has advanced the art are properly considered within the scope of this invention.