Abstract:
An air purifier includes a housing, a high voltage power supply, a first electrode assembly in which a wire-like first electrode is either the only first electrode or, alternatively, is spaced sufficiently far from any other such first electrodes so as to avoid undesirable effects upon each other, and a second electrode assembly in which there are a plurality of blade-like second electrodes. The air purifier can be of the type in which air flows through the housing as a result of electro-kinetic effects. To increase air flow velocity, the voltage between first and second electrodes is relatively high, such as 23-50 kV, and the first and second electrodes are accordingly spaced apart a relatively great distance, such as at least 30 mm.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to electrostatic or ionic air purifiers and, more specifically, to an ionic air purifier having a high air flow volume and clean air delivery rate (CADR). 
         [0003]    2. Description of the Related Art 
         [0004]    An ionic air purifier typically includes a louvered or grilled housing in which an ionizer unit electrostatically attracts and removes particulate matter from the air. The ionizer unit includes two spaced-apart arrays of electrodes coupled to the respective positive and negative high voltage output ports of a power supply. The electrodes of one array, which are sometimes referred to in the art as a corona electrodes, are typically thin and wire-like, and electrodes of the other array, which are sometimes referred to as collector electrodes, are typically blade-shaped. The voltage between the electrodes is typically on the order of 10-20 kilovolts. 
         [0005]    Ionic air purifiers typically utilize electro-kinetic principles to produce air flow without the use of fans or other mechanically moving parts. The electric field that is generated between the first and second electrode arrays produces an electro-kinetic airflow moving from the first array toward the second array. Ambient air, including dust particles and other undesired particulate matter, enters the housing through the grill or louver openings on the upstream side of the housing, is charged by the corona electrode array, and particulate matter entrained in the air is electrostatically attracted to the surface of the collector electrode array, where it remains, thus removing particulate matter from the flow of air exiting the housing through the grill or louver openings on the downstream side of the housing. The collector electrode array can be cleaned of trapped particulate matter by removing the assembly from the housing and wiping the blades with a cloth. 
         [0006]    The high voltage electric field present between electrode arrays can cause a corona effect that generates ozone (O 3 ) and nitrogen oxides (NO x ). Ozone inhibits the growth of bacteria, molds and viruses and helps eliminate odors in the output air, but as high concentrations of ozone are harmful to human health, it is desirable to control the release of ozone. 
         [0007]    Low air flow velocity and concomitant low air flow volume, i.e., the amount of air that moves through the purifier in a given amount of time, are problems with conventional ionic air purifiers of the type described above. While it is known that increasing the power drawn by the electrode arrays will increase the electro-kinetic airflow, it can also increase generation of undesirable amounts of ozone and nitrogen oxides. 
         [0008]    It would therefore be desirable to provide an ionic air purifier that maximizes air flow volume yet controls generation of ozone and other corona effect products. The present invention addresses these problems and deficiencies and others in the manner described below. 
       SUMMARY OF THE INVENTION 
       [0009]    An air purifier includes a housing, a high voltage power supply, a first electrode assembly in which a wire-like first electrode (or corona electrode) is either the only first electrode or, alternatively, is spaced sufficiently far from any other such first electrodes so as to avoid undesirable effects upon each other, and a second electrode assembly in which there are a plurality of blade-like second electrodes. The air purifier can be of the type in which air flows through the housing as a result of electro-kinetic effects. 
         [0010]    It has been discovered in accordance with the present invention that, as the first electrode&#39;s electrical field is a vector, and only the component in the desired direction of air flow through the housing contributes to the desired electro-kinetic effect, the presence of nearby electric fields from other such first electrodes can undesirably increase air flow in directions other than the desired direction of air flow through the housing. The resulting turbulent flow can inhibit maximum air flow in the desired direction. In embodiments of the invention in which there are more than one first electrode, any first electrode is preferably spaced no closer than about 40 millimeters (mm) (and more preferably 75 mm) from any other first electrode, though the spacing can depend upon the voltage (electrical potential) between the first and second electrodes. 
         [0011]    Preferably, the power supply provides an electrical potential between the first electrode and the second electrodes that is substantially higher than that which conventional air purifiers of this general type provide, such as 23-50 kilovolts (kV). The relatively high voltage (in comparison with conventional air purifiers) results in relatively high air flow velocity and concomitant high air flow volume, thereby providing a relatively high clean air delivery rate (CADR). 
         [0012]    Other features of the invention address issues relating to high voltage. For example, is it preferred that no portion of a second electrode be closer than about 30 mm from any portion of the first electrode, though the spacing can depend upon the voltage. In the exemplary embodiment of the invention, the voltage is 23-50 kilovolts, and the spacing between the closest respective points on the first electrode and any second electrode is 30-50 mm. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a perspective view of elements of an air purifier in accordance with an embodiment of the present invention. 
           [0014]      FIG. 2  is a top view of elements of an air purifier in accordance with another embodiment of the present invention. 
           [0015]      FIG. 3  is a perspective view of the electrode assemblies of  FIG. 1 , illustrating a dielectric guard in the first electrode assembly. 
           [0016]      FIG. 4  is a cross-sectional view taken on line  4 - 4  of  FIG. 3 . 
           [0017]      FIG. 5  is a block diagram of a power supply circuit of the air purifier of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    As illustrated in  FIG. 1 , in an exemplary embodiment of the invention, an ionic air purifier includes a wire-like first electrode  10  (sometimes referred to in the art as a corona electrode) and a plurality of blade-like second electrodes  12  (sometimes referred to in the art as collection electrodes). Although three second electrodes  12  are shown in  FIG. 1  for purposes of illustration, there can be more or fewer such second electrodes in other embodiments. A positive terminal of a high voltage power supply  14  is coupled to first electrode  10  via a current-limiting resistor  16 , a negative terminal of power supply  14  is coupled to each of second electrodes  12  via another current-limiting resistor  18 , and a ground terminal is coupled to earth ground or equivalent. 
         [0019]    First electrode  10  preferably comprises a thin wire, about 0.2 millimeters (mm) in diameter, but wires or other thin, elongated structures between about 0.1 and 0.3 mm in diameter or width may be suitable. For example, a razor-thin strip or ribbon may be suitable. Second electrodes  12  are blade-like or paddle-like in that they have broad, substantially similar opposing surfaces. Although the opposing surfaces are flat or planar and parallel to each other in the illustrated embodiment of the invention, in other embodiments they can be curved, cambered, contoured, etc., can have surface features, or any other suitable blade-like shape. Nevertheless, smooth, featureless surfaces are believed to minimize undesirable corona. To further minimize corona, one or both edges of second electrodes has a blunt, rounded shape, preferably with a radius of curvature greater than about 1 mm. Electrodes  10  and  12  can be made of any suitable conductive material, though a material that resists corrosion and is easily cleanable, such as stainless steel, is preferred. 
         [0020]    The above-described elements can be housed in a suitable housing  20  and retained in suitable mechanical assemblies (not shown for purposes of clarity), for example, as described in U.S. Pat. No. 6,946,103, entitled “AIR PURIFIER WITH ELECTRODE ASSEMBLY INSERTION LOCK,” the specification of which is incorporated herein in its entirety by this reference. With reference to a desired direction of air flow through housing  20 , indicated by the arrow  22 , an upstream side of housing  20  has grill-like or louver-like intake apertures  24 , and a downstream side of housing  20  has similar exhaust apertures  26 . When the indicated electrical potential is applied between first electrode  10  and second electrodes  12 , the resulting electro-kinetic effect causes air to enter housing  20  through intake apertures  24 , flow through housing  20  past electrodes  10  and  12 , and exit the housing  20  through exhaust apertures  26 . Particulate matter entrained in the air is electrostatically attracted to the surfaces of electrodes  12  and collects upon the surfaces. 
         [0021]    Note that in the exemplary embodiment illustrated in  FIG. 1 , there is only a single first electrode  10 . It has been discovered in accordance with the present invention that the presence of nearby electric fields from other such first (i.e., corona) electrodes, as in some conventional purifiers, can undesirably increase air flow in directions other than that indicated by arrow  22 , thereby interfering with air flow in the desired direction. 
         [0022]    The amount of kinetic energy imparted to the air through the electro-kinetic effect increases with an increase in power consumed by the circuit defined by first and second electrodes  10  and  12 . Thus, to maximize air flow velocity, it may at first glance seem optimal to maximize power. However, high electrode current can result in the corona effect generating undesirable amounts of ozone and nitrogen oxides. Rather than maximizing current, as power is the mathematical product of voltage and current, the present invention maximizes voltage (within what are believed to be safe and otherwise desirable limits for a consumer product) and controls electrode current. 
         [0023]    Although power supply  14  is described in further detail below, it can be noted here that in the exemplary embodiment it provides an electrical potential between first electrode  10  and each of second electrodes  12  of about 23-50 kilovolts (kV). Still more preferably, it provides a potential of about 30 kV. With a potential of about 23-50 kV, the electrode current is generally less than about 500 microamperes (μA). To avoid applying excessive voltage to any one electrode (with respect to ground), the potential can be divided equally or at least approximately equally between first electrode  10  and each second electrode  12 . Thus, for example, in an embodiment in which power supply  14  provides a potential of 30 kV between first electrode  10  and each of second electrodes  12 , power supply  14  can provide a potential of +15 kV with respect to ground to first electrode  10  and a potential of −15 kV with respect to ground to each of second electrodes  12 . Nevertheless, in other embodiments the reference ground can be omitted. 
         [0024]    The optimal distance or spacing between first electrode  10  and the closest point on any of second electrodes  12  depends upon the electrical potential between them. A higher potential militates a greater distance or spacing to minimize corona. A portion of the axis  28  shown in  FIG. 1  extends between respective closest points on first electrode  10  and a second electrode  12 . The spacing between respective closest points along axis  28 , i.e., between the trailing edge of first electrode  10  and the leading edge of the middle second electrode  12  (“leading” and “trailing” referring to the direction of air flow), is preferably at least 30 mm and, more preferably, 30-50 mm. An optimal spacing is believed to be about 35-45 mm. The spacing between the respective closest points on adjacent second electrodes is preferably 25-40 mm. 
         [0025]    Although in this embodiment of the invention, axis  28  is parallel to the direction of air flow (arrow  22 ), in other embodiments the axis extending between respective closest electrode points may be oriented in any other suitable manner. Similarly, although in this embodiment second electrodes  12  are parallel to the direction of air flow, parallel to each other, and parallel to first electrode  10 , in other embodiments they can be oriented in any other suitable manner. Nevertheless, orienting electrodes  12  in the manner shown in  FIG. 1  and with first electrode  10  and one of second electrodes  12  along the same axis  28  as the direction of air flow is believed to maximize air flow. 
         [0026]    As illustrated in  FIG. 2 , in another embodiment of the invention two first electrode assemblies  30  and  31 , respectively include first electrodes  32  and  34 , and two second electrode assemblies  36  and  37 , respectively include two groups of second electrodes  38  and  39 . Although in this embodiment each group of second electrodes  38  and  39  corresponds to one of first electrode assemblies  30  and  32 , in other embodiments the number of first electrode assemblies may be different from the number of second electrode assemblies. For example, in a similar embodiment (not shown), electrodes  38  and  39  can be included in the same assembly. 
         [0027]    Electrodes  32 ,  34  and  36  are as described above with regard to the embodiment illustrated in  FIG. 1 . Importantly, there is a spacing or distance  40  between first electrodes  32  and  34  of at least about  75  mm to avoid undesirable electric field interaction that is believed to inhibit air flow. Thus, they are included in separate assemblies  30  and  31 . As described above with regard to the embodiment illustrated in  FIG. 1 , the spacing or distance  42  between the closest points on first electrodes  32  and  34  and any second electrode  38  or  39  is preferably at least about 30 mm and, still more preferably, between about 30 and 50 mm. Optimally, distance  42  is between about 38 and 40 mm. Nevertheless, as noted above, the optimal distance and electrode voltage are inter-dependent. In all other respects, this embodiment of the invention is as described above with regard to the embodiment illustrated in  FIG. 1 . Note the above-described radius of curvature  44  of at least about 1 mm of the leading edges of second electrodes  38  and  39 . 
         [0028]    The manner in which a first electrode (e.g., electrode  10  in  FIG. 1 ) is retained in a first electrode assembly and shielded with a guard  46  that enhances distribution of the magnetic field is illustrated in  FIGS. 3-4 . Guard  46  is made of a dielectric material suitable for shielding against corona discharge, such as plastic or ceramic. Guard  46  comprises a hollow tubular portion  48  and a semi-tubular extension  50 . One end of first electrode  10  is retained in a retainer  52  inside guard  46  made of a suitable dielectric material such as plastic or ceramic. Similarly, the corresponding end of each second electrode  12  is retained in a suitable dielectric retainer  54  that is part of the second electrode assembly. Although retainer  54  is shown in generalized or conceptualized form in  FIGS. 3-4  for purposes of clarity, the electrode assembly can have a structure along the lines of that described in the above-referenced U.S. Pat. No. 6,946,103 or as otherwise known in the art. The other end of first electrode  10  is retained in a retainer  56  that can be similar to retainer  52 , and the corresponding other end of each second electrode  10  is retained in a retainer  58  that can be similar to retainer  54 . Features of retainers  54  and  58  and the electrode assembly in which they are included that allow the electrode assembly to be removed from housing  12  ( FIG. 1 ) for cleaning and retained or locked in housing  12  during operation are described in the above-referenced U.S. Pat. No. 6,946,103. 
         [0029]    Note that the end  60  of retainer  54  extends to a location between the ends of first electrode  10 , approximately even or level with the end of  62  of tubular portion  62 . It has been found that the electrical field can be unevenly distributed because first electrode  10  and second electrode  12  have unequal lengths, which can result in electrical discharge noise emanating primarily from the areas where the ends of electrode  10  are retained. To adjust the distribution of the electric field and thereby maintain quiet operation, semi-tubular extension  50  extends a distance  64  beyond this location. Preferably, distance  64  is at least  5  mm. Although this double-wall shielding arrangement with tubular portion  62  and extension  50  is suitable, in other embodiments guard  46  can be structured differently. For example, tubular portion  62  can be longer, extending approximately distance  64  beyond the end  60  of retainer  54 . 
         [0030]    As illustrated in  FIG. 5 , power supply  14  ( FIG. 1 ) operates in a closed-loop or feedback manner to regulate electrode current. As described below in further detail, the circuit responds to changes in electrode current that can occur as a result of changes in humidity and particulate matter in the air by controlling electrode voltage. 
         [0031]    The power supply circuit primarily comprises a microcontroller  66 , a pulse-width modulation (PWM) signal generator  68 , a line filter  70 , a low voltage power supply  72 , a rectifier  74 , a MOSFET  76 , a transformer  78 , and a high voltage multiplier  80 . As controlled by a main power switch  81 , line filter  70  receives and filters household utility power (e.g., 120 VAC). Low voltage power supply  72  receives the filtered utility power and provides the digital voltage (e.g., 5 VDC) required to power microcontroller  66 . Rectifier  74  converts the AC power to DC, and transformer  78  steps up the voltage. High voltage multiplier  80  similarly multiplies the stepped-up voltage to the (e.g., +15 and −15 kV) electrode voltages. The circuit through the primary side of transformer  78  is coupled to ground through the drain terminal of MOSFET  76  and a resistor  82 . This circuit also provides a feedback signal, representative of electrode current, to microcontroller  66 . A peak voltage rectifier  84  tapping into the output of transformer  78  allows microcontroller  66  to monitor peak voltage. A reset switch  86  and two control switches  88  and  90  allow a user to control the operation of the power supply (e.g., “on”, “off”, etc.) and thus of the air purifier as a unit. Microcontroller  66  also controls a number of status indicator LED&#39;s  92 . 
         [0032]    Microcontroller  66  digitizes the feedback signal and, in response to the corresponding digital value, adjusts the digital signal it provides to PWM signal generator  68 . The pulse train output by PWM signal generator  68  controls MOSFET  76 . Changes in the duty cycle and frequency of the pulse train cause MOSFET  76  to adjust the output voltage (indicated by “+” and “−” at the output of high voltage multiplier  80 ) accordingly. If the circuit senses an increase in electrode current above a predetermined normal operational value (e.g., 300 μA), the circuit responds by lowering the output voltage by an amount needed to maintain essentially constant power. In addition, if microcontroller  66  senses an electrode current that is beyond normal operational range by a predetermined amount, it responds by shutting off power to avoid potentially harmful conditions. 
         [0033]    It will be apparent to those skilled in the art that various modifications and variations can be made to this invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided that they come within the scope of any claims and their equivalents. With regard to the claims, no claim is intended to invoke the sixth paragraph of 35 U.S.C. Section 112 unless it includes the term “means for” followed by a participle.