Patent Publication Number: US-2010126343-A1

Title: Electrically Enhanced Air Filter Apparatus With A Perpendicular Field Ionizer

Description:
TECHNICAL FIELD OF INVENTION 
     The invention relates to electrically enhanced air filter apparatus that ionize particles in the air for improving the efficiency of the filter to remove and retain the particles from the air. In particular, the electrically enhanced air filter apparatus has an ionizer that generates an electric field having a direction perpendicular to the direction of the air flowing through the ionizer at an ionizer speed to ionize the particles in the air, and then passes the air through a filter element at a filter speed less than the ionizer speed, thereby increasing the efficiency of the filter. 
     BACKGROUND OF INVENTION 
     It is known to ionize particles in air prior to filtering to improve the efficiency of a filter. Particles are ionized by passing through an ionizing field having sufficient electric field strength. It is believed that minimizing the speed that the ionized particles approach a filter improves filter efficiency, thereby encouraging large filter areas. Electrically enhanced air filters with ionizer areas similar to the filter areas generate ionizing fields that are spread out, thereby requiring a high ionizing voltage source to establish an ionizing field. Furthermore, arrangements of needle and brush ionizers may not create a uniform ionizing field, so the particles in the air may not be uniformly ionized. Thus, electrically enhanced air filters are compromised with respect to size and effectiveness to balance the needs of electric field strength, ion current, airflow, packaging constraints, and aesthetics. 
     What is needed is a compact electrically enhanced air filter apparatus having a smaller ionizer that creates an ionizing field to ionize air particles moving through the ionizer at an ionizer speed and then reduces the speed of the particles approaching the filter. 
     SUMMARY OF THE INVENTION 
     In accordance with this invention, an electrically enhanced air filter apparatus is provided for filtering particles from moving air. The apparatus has a housing that defines an inlet, an outlet, and a filter chamber between the inlet and the outlet. Air moves through the housing by moving into the inlet, through the filter chamber and out of the outlet. Within the housing is a filter disposed in a first passageway that defines a filter area. The filter is adapted to filter ionized particles from air moving through the filter. The apparatus also has an ionizer disposed in a second passageway within the filter chamber between the filter and the inlet. The area of the ionizer is smaller than the filter area. The second passageway guides the air in an ionizer airflow direction. The ionizer is configured to establish an electric field to form an ionizing curtain across the second passageway, where the ionizing curtain is arrayed along a plane substantially perpendicular to the ionizer flow direction. The configuration is effective to ionize particles moving through the ionizing curtain. 
     An embodiment of a method of filtering particles from air utilizing an air filtering apparatus comprising an ionizer generating an ionizing curtain having an ionizer field direction and a filter is described. The method includes moving a quantity of air through the ionizer in an ionizer airflow direction substantially perpendicular to the ionizing curtain and substantially perpendicular the ionizer field direction at an ionizer speed, and moving air through the filter at a filter speed less than the ionizer speed. 
     Further features and advantages of the invention will appear more clearly on a reading of the following detail description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       This invention will be further described with reference to the accompanying drawings in which: 
         FIG. 1  is a sectional side-view of an electrically enhanced air filter apparatus housing with a ionizer and a fan of a type preferred in the practice of this invention; 
         FIG. 2  is a detailed sectional side-view of the ionizer in  FIG. 1 ; 
         FIG. 3  is a detailed sectional top-view of the ionizer in  FIG. 1 ; and 
         FIG. 4  is a perspective view of the ionizer and a portion the housing in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     In accordance with a preferred embodiment of this invention,  FIG. 1  shows an electrically enhanced air filter apparatus  10  for filtering particles from air moving in an airflow direction  11 . The air is moved by a fan  40  through an ionizer  30 , in which particles in the air are ionized, and then through a filter  20  where particles adhere to the filter and are thereby removed from the air. A housing  12  defines an inlet  14 , shown in  FIG. 4 , for supplying air to fan  40 , an outlet  16 , for expelling filtered air from the filter apparatus and a filter chamber  18  between inlet  14  and outlet  16 . Housing  12  provides a guide for the air such that air moves in airflow direction  11  into inlet  14 , through ionizer  30  and filter  20 , and out of outlet  16 . The housing is preferably made from an electrically isolative material so the housing does not dissipate electric charge created by the ionizer. The housing is configured so that all of the air entering inlet  14  passes through the ionizer  30 , through filter  20 , and exits outlet  16 , whereby none of the particles can bypass either ionizer  30  or filter  20 . 
     Housing  12  defines filter chamber  18  that includes filter  20  disposed in a first passageway  22 . Filter  20  is formed of a filter media selected to filter or entrap particles in the air being filtered. The filter media selected has characteristics that cooperate with the particles being ionized to more efficiently remove the particles from the air. An exemplary filter media is High Air Flow (HAF) Air Filtration Media sold by the 3M corporation. Filter  20  shown in  FIG. 1  has a planar configuration and is arranged in the housing so that air flows through the filter in a direction substantially perpendicular to the plane established by the body of the filter. Alternate filter configurations are possible such as circular filter elements similar to those found in automotive engine air-cleaner assemblies. Filter  20  and first passageway  22  define a cross-sectional area that determines a filter area. Filter areas proposed for an electrically enhanced air filter apparatus are in a range of about 0.1 square meters to about 4 square meters. An exemplary filter area for an electrically enhanced air filter apparatus for filtering air in a room is 0.25 square meters, where filter  20  has a square shape of 0.5 m on each side. 
     Filter chamber  18  also includes ionizer  30  disposed in a second passageway  24  between inlet  14  and filter  20 . Ionizer  30  and second passageway  24  define a cross-sectional area that determines the ionizer area.  FIGS. 2 and 3  are detailed views of ionizer  30  having an ionizer electrode  38  and a reference electrode  36 . The electrodes  38  and  36  are arranged to generate an ionizing electric field depicted by jagged lines  34  in response to a sufficient voltage difference applied from the ionizer electrode  38  to the reference electrode  36 . In general, ionizers operate by applying a sufficient voltage from an ionizer electrode to a reference electrode to establish an ionizing electric field and create a cloud of ions within the electric field that have a sufficient ion density to ionize particles passing through the cloud. The arrangement shown in  FIGS. 2 and 3  creates an ionizing electric field that forms an ionizing cloud across the second passageway arrayed along a plane substantially perpendicular to an ionizer airflow direction as depicted by ionizer flow arrows  32 . Second passageway  24  guides airflow direction  11  to flow in ionizer airflow direction depicted by ionizer flow arrows  32  substantially perpendicular to the ionizing electric field depicted by jagged lines  34 . With this configuration, particles are ionized by passing through an ionizing cloud resembling a curtain across the second passageway  24  created by the ionizer  30 . 
       FIG. 3  is a detailed sectional top-view of ionizer  30  showing ionizer electrode  38  and reference electrode  36  having substantially the same length. Portions of housing  12  cooperate with reference electrode  36  to define second passageway  24 . The electric field depicted by jagged lines  34  extends from ionizer electrode  38  to reference electrode  36 , and the ionizer airflow direction is substantially normal to the page of the drawing, and substantially perpendicular to electric field depicted by jagged lines  34 . At any position between the electrodes, the ionizing electric field is substantially uniform across the width of the ionizer, the width being a direction parallel to the electrodes. This generates an ionizing curtain having an ion density that is substantially uniform along a line parallel to the electrodes. With this arrangement, the particles passing through the filter apparatus are exposed to a more uniform ion density and are thereby more uniformly ionized. The ionizer can be smaller than comparably effective needle type ionizers because the electrode arrangement generates a more organized electric field when compared to the omni-directional kind of field generated by a needle type electrode. Thus, the ionizing electric field generated by the ionizer arrangement in  FIGS. 1-3  is effective to ionize particles in the air moving through the ionizer at speeds higher than the preferred speed for particles approaching the filter. Furthermore, the smaller ionizer allows for a more compact electrically enhanced air filter apparatus and can use lower voltages across the electrodes to be sufficient to establish an ionizing electric field. 
     Ionizer  30  is shown having an area rectangular in shape where rectangle size is determined by a minor axis or height and a major axis or width greater than the height. Having a rectangle shape with the electrode arrangement shown provides a more consistent electric field intensity across the width of the ionizer and therefore a more uniform ion density. Exemplary values for the height and the width are 40 mm and 500 mm respectively, thereby defining an ionizer area of 0.02 meters square. Reference electrode  36  is formed by two rectangular plates made of conductive material having plate lengths substantially equal to the width of the ionizer and electrically connected to each other. The plates are arranged parallel to each other on opposing widthwise walls of the ionizer upon the surface of second passageway  24 . The ionizer electrode  38  is arranged parallel to and intermediate the plates forming reference electrode  36  so the ionizing electric field forms a uniform ionizing curtain through which particles in the air pass. Electrodes  36  and  38  are electrically coupled to a voltage source (not shown), typically with wires (not shown), and a voltage is applied to the electrodes effective to establish an ionizing electric field. The rectangular shape allows the distance between the ionizing electrode and reference electrode to be adjusted to provide an electric field intensity sufficient to create an ionizing electric field for a given applied voltage. A suggested range of sufficient electric field intensity values is about 400 kV/m to about 1000 kV/m. An exemplary electric field intensity value that creates an ionizing electric field in the electrically enhanced air filter apparatus shown in  FIG. 1  is about 600 kV/m. 
     Ionizer electrode  38  in this embodiment is formed of wire. Smaller diameter wires have greater ionizing efficiencies because of increased corona discharge effects, while larger diameter wires have greater durability. A range of exemplary ionizer electrode  38  wire diameters is about 0.001 mm to about 0.1 mm. An optimum ionizer electrode  38  wire diameter for an electrically enhanced air filter apparatus similar to the design shown in the figures is about 0.025 mm. An ionizer configured as shown having height of 40 mm, a width of 500 mm, a wire diameter of 0.025 mm, a field intensity of 600 kV/m is suitable for ionizing typical indoor room air at a flow rate of about 150 cubic feet per minute. Based on these dimensions, a voltage of about 12 kV applied across the 20 mm distance between the electrodes is a sufficient voltage to generate a field intensity of 600 kV/m. If the flow rate is increased, the exemplary ionizer may become less effective. If the flow rate is decreased, the exemplary ionizer may be physically larger than necessary. 
     A ratio of the filter area to the ionizer area is an electrically enhanced air filter apparatus design variable that can be varied. The ratio is adjusted to the area of ionizer  30  occupies as small an area as possible while still being effective to ionize the particles in the air traveling through the ionizer at an ionizer speed. The ionizer speed is determined by the area of the ionizer and the volume or mass of air passing through the electrically enhanced air filter apparatus. As the ionizer speed increases, ionizer  30  becomes less effective, so there is an upper limit for the ionizer speed based on a desired effectiveness. The filter area is also determined by a desired filter effectiveness based on a filter speed of a particle approaching filter  20 . The effectiveness of filtering is increased by increasing the filter area thereby reducing the filter speed of the particles approaching the filter. There is an upper limit for the area of filter  20  based on a desired maximum size of the electrically enhanced air filter apparatus. An exemplary range of a ratio of filter area to ionizer area is 6:1 to 20:1. For the electrically enhanced air filter apparatus in  FIG. 1 , a ratio of 10:1 has been suggested. 
       FIG. 1  also shows fan  40  as part of electrically enhanced air filter apparatus  10 . The exemplary fan shown in  FIG. 1  is a squirrel cage type fan. Alternate embodiments of an electrically enhanced air filter apparatus could use any device capable of moving air such as an axial fan like those found in home computers. Alternately, the fan could be located remote from the housing and coupled to the housing by ducting, or coupled to the outlet and configured to draw air through the filter chamber.  FIG. 4  is a perspective view of the lower portion of  FIG. 1  and shows the relative orientation of ionizer  30 , electric field depicted by jagged lines  34 , and inlet  14 . The air flow is established by the fan and the rate of air flow is at least a function of fan speed or fan effort. If the fan speed is increased, more air moves through the air filter apparatus, but the efficiency of the filter apparatus may decrease. If a room has a relatively large number of particles in the air, then a higher fan speed may be desirable to more quickly filter a greater portion of the air in the room at a reduced efficiency. Alternately, if the air has a relatively low number of particles, than a lower fan speed may be desirable to increase the efficiency of the filter system and reduce the amount of fan noise generated by the filter system. 
       FIG. 1  shows filter  20  as a planar element having a filter plane, and the housing is configured so the ionizer airflow direction depicted by ionizer flow arrows  32  is substantially parallel to and offset from the filter plane. This arrangement reduces the size of electrically enhanced air filter apparatus  10 . Alternately, the arrangement allows for a larger area filter  20  for a given electrically enhanced air filter apparatus size, thereby increasing filtering efficiencies. 
     Thus, an electrically enhanced air filter apparatus having a compact ionizer  30  that generates an ionizing electric field and reduces the filter speed of the particles approaching filter  20  is provided. The arrangement of ionizer  30  creates a uniform ionizing electric field by establishing an ionizing curtain perpendicular to the direction of the particles flowing through ionizer  30 . The compactness of the ionizer reduces the voltage requirements necessary to generate an electric field intensity sufficient to ionize the particles in the air flowing therethrough. Furthermore, the cross-sectional area of the filter  20  is larger than the cross sectional area of the ionizer  30 . Thus, for a given volume or mass of air flowing through filter  20 , increasing the cross-sectional area of the filter reduces the filter speed of particles approaching the filter, thereby increasing the probability that a particle will be intercepted by the filter and reducing the probability that the particle will pass through the filter. 
     While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.