Abstract:
An ion filtration air cleaning device for cleaning air by use of electrostatic ion attraction. Air having suspended particles is drawn into the device through an inlet by a fan. An ionization source near the inlet generates ions. Electrical charge transfers from the ions to the suspended particles. The fan pushes the air and suspended charged particles toward an outlet. A filter located adjacent to the outlet operates by electrostatic attraction and filters the charged particles from the air, allowing cleansed air to be released from the device, with a reduced level of charged particle emission.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/453,060, filed Mar. 15, 2011, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to the field of air cleaning systems. More specifically, the present invention relates to an ion filtration device (“IFD”) for cleaning air by use of electrostatic ion attraction. 
     2. Description of the Related Art 
     Air having a high concentration of suspended particles (hereinafter, “dirty air”) can pose a health hazard to living beings from breathing the dirty air. The dirty air can also cause a higher rate of deposition of settled suspended particles (e.g., dust) thus causing more frequent cleaning of surfaces that are desired to be kept clean (e.g., surfaces inside a home). 
     In farming, high aerosol concentrations are found in situations such as poultry sheds and intensive pig rearing sheds etc., and thus the health of both workers and animals is at risk. 
     In industry a variety of processes such as welding, grinding, smelting and use of internal combustion engines in confined spaces all produce high concentrations of suspended particles in enclosed spaces. 
     In social and domestic situations, suspended particles are produced by tobacco smoking. Sneezing can produce aerosols of bacteria and viruses. Allergy producing pollen is found in high concentrations at various times of the year. Dust mite allergen particles are produced when making up beds and enter the air as suspended particles. 
     Conventional air cleaners may remove particles from the air by trapping them either in filters as in a filtration air cleaner (FAC), or by collecting them on plates as in an electrostatic precipitation air cleaner (ESPAC). The filters or plates may then be disposed of, washed or replaced. 
     Disadvantages of FAC devices include a drop in efficiency of the filter over time as particles clog the filter; the need for a fan powerful enough to overcome the partially-clogged filter; noise and power consumption associated with the fan; and the need to replace the filters regularly. 
     Disadvantages of ESPAC devices include: a need for costly shielding of high voltage plates; loss of efficiency and generation of ozone caused by electrical breakdown and leakage between the high voltage plates; and a need to space the high voltage plates relatively far apart to reduce electrical breakdown in the air between the high voltage plates, thus increasing size and reducing efficiency. 
     Electrostatic precipitation air cleaners operate by attracting charged particles and ions to collection plates charged with an opposite electrical charge from that of the charged particles and ions. A variation of the ESPAC device is to replace the high voltage plates with an air passage, the air passage having at least a portion thereof having an electrical potential, electrets properties, electrostatic properties, or the like. An example of such a device known in the art is U.S. Pat. No. 6,749,669 to Griffiths, et al., the contents of which are incorporated by reference herein. 
     However, the particles and ions that are to be collected may not ordinarily be in a charged state, so charge must be introduced onto the particles and ions in order to attract them to the collection plates. Conventional electrostatic air cleaners of this kind introduce charge onto the particles and ions as they leave the cleaner by use of an ionizer to electrically ionize the gas or air stream. The ionizer may include a primary corona discharge emitter and a secondary corona discharge emitter at a lower potential relative to the primary emitter. The primary corona discharge emitter is connected to a high negative potential while the secondary corona discharge emitter is connected to electrical ground. The primary corona discharge emitter may be a needle having a sharp tip and the secondary corona discharge emitter may be a needle having a relatively blunt tip. 
     Since the ionizer imparts charge upon particles and ions as they leave the cleaner, the ions so charged must travel back to an air inlet of the conventional electrostatic air cleaner in order to be collected. This presents a disadvantage of the known art, because some particles so ionized may not return to the air inlet, and particles which do return to the air inlet may lose some or all of their charge before returning. Unless the electrostatic air cleaner is operating in a confined space, few adequately charged ions may return to the air inlet. Consequently, there is a need for a more efficient electrostatic air cleaner 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention an ion filtration device (IFD) is disclosed. The IFD includes a housing, a fan that creates an airflow within the housing, a prefilter disposed within the housing, an ionizer disposed within the housing downstream from the prefilter, and an electrostatically charged main filter disposed within the housing downstream from the ionizer. The fan is preferably disposed within the housing. In some embodiments a serpentine pathway is disposed between the ionizer and the main filter, and the airflow passes through the serpentine pathway prior to passing through the main filter. In other embodiments baffles are disposed between the ionizer and the main filter, and the airflow passes through the baffles prior to passing through the main filter. 
     In another aspect of the invention a method for filtering air is disclosed. Air is passed through a prefilter disposed in a housing to remove at least a portion of particulates suspended in the air. The air is then passed by an ionizer disposed in the housing to ionize at least a portion of the particulates suspended in the air. Finally, prior to the air exiting the housing, the ionized particulates are passed through an electrostatically charged main filter disposed within the housing. In some embodiments air is passed through baffles subsequent to passing by the ionizer and prior to passing through the electrostatically charged main filter. In other embodiments the air is passed through a serpentine pathway subsequent to passing by the ionizer and prior to passing through the electrostatically charged main filter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various aspects and embodiments disclosed herein will be better understood when read in conjunction with the appended drawings, wherein like reference numerals refer to like components. For the purposes of illustrating aspects of the present application, there are shown in the drawings certain preferred embodiments. It should be understood, however, that the application is not limited to the precise arrangement, structures, features, embodiments, aspects, and devices shown, and the arrangements, structures, features, embodiments, aspects and devices shown may be used singularly or in combination with other arrangements, structures, features, embodiments, aspects and devices. The drawings are not necessarily drawn to scale and are not in any way intended to limit the scope of this invention, but are merely presented to clarify illustrated embodiments of the invention. In these drawings: 
         FIG. 1  is functional schematic view of a conventional electrostatic air cleaner apparatus as known in the art. 
         FIG. 2  is a functional schematic view of an electrostatic air cleaner apparatus according to an embodiment of the present invention. 
         FIG. 3  is a functional schematic view of an electrostatic air cleaner apparatus according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention generally relate to the field of air cleaning systems. More specifically, embodiments relate to an ion filtration device (“IFD”) for cleaning air by use of electrostatic ion attraction. 
     Referring to  FIG. 1 , a functional schematic of a conventional IFD  100  is illustrated. Within housing  111 , fan  104  creates an airflow  110  within IFD  100  such that air is drawn into IFD  100  through an inlet  101  and passes first through a prefilter  102 . Prefilter  102  removes large dust particles and fibers. Airflow  110  next passes through main filter  103 , which is electrostatically charged to attract the incoming particles which carry the opposite charge from that of main filter  103 . When IFD  100  is first turned on, it is expected that there will be few or no such charged particles in the confined space that IFD  100  is operating, therefore at first main filter  103  will not be very effective in removing charged particles. 
     Next, fan  104  pushes airflow  110  past ionizer  105  which releases charged ions (not shown in  FIG. 1 ) that enter airflow  110  and exit IFD through outlet  106 . Air expelled from outlet  106  may disperse in substantially any direction, as indicated by exemplary directions  107 ,  108  and  109 . As the air expelled from outlet  106  disperses throughout the space surrounding IFD  100 , ions may transfer charge to suspended particles in the space surrounding IFD  100 . A portion of the ions and/or charged particles eventually make their way back to inlet  101 , such as along exemplary path  109 . 
     It can be seen that conventional IFD  100  is not efficient, at least for the following reasons. First, main filter  103  is not fully effective until charged particles pass through it. Second, because there is no control over the direction of air and ions that are expelled through outlet  106 , only a fraction may reach their way back to the inlet  101 , and the flow from outlet  106  to inlet  101  may be entirely blocked by drafts and air currents exterior to IFD  100 . Third, charged particles may adhere to other surfaces in the space surrounding IFD  100 , thereby causing an unwanted buildup of particles in unwanted locations. Fourth, because there may be a significant time delay between ionization and the entry of particles charged by those ions into inlet  101 , the strength of the electrostatic charge may decay, causing reduced efficiency of main filter  103 . 
       FIG. 2  is a functional schematic of an improved IFD  200  according to an embodiment of the invention. In this embodiment, a structural difference compared to conventional IFD  100  is that a main filter  203 , which is electrostatically charged to attract the incoming particles carrying the opposite charge from that of main filter  203 , is located in airflow  210  downwind or downstream from an ionizer  205 . 
     In operation of IFD  200 , within a housing  211  a fan  204  creates an airflow  210  within IFD  200  such that air is drawn into IFD  200  through an inlet  201  and passes first through a prefilter  202 . Prefilter  202  removes large dust particles and fibers. Airflow  210  next passes adjacent to ionizer  205 , which creates ions (not shown in  FIG. 2 ). Charge from the ions may then be transferred to any suspended particles that had passed through prefilter  202 . 
     Next, fan  204  pushes airflow  210  through main filter  203 , which attracts the incoming particles that carry the opposite charge from that of the ions. Finally, airflow  210  exits from IFD  200  through outlet  206 . 
     The embodiment of  FIG. 2  may have a longer internal path for airflow  210  than the internal path for airflow  110  of a conventional IFD. The longer internal path allows for more effective mixing of ions with air, and provides a longer time for any particles suspended in airflow  210  to become charged. The longer path for airflow  210  is achieved by moving the main filter  203  to be near outlet  206 , and by placing the ionizer  205  just after prefilter  202 . This lengthens the path of airflow  210  between ionizer  205  and main filter  203 , allowing the particles in the air more time to become charged, and thus removing the suspended particles more effectively from the airflow  210  by main filter  203 . The air cleansed by main filter  203  will leave the improved IFD  200  in a relatively uncharged condition. 
     The operation of improved IFD  200  is more efficient than that of conventional IFD  100  at least for the following reasons. First, main filter  203  is fully effective more quickly because charged particles begin passing through it almost immediately after turning on improved IFD  200 . Second, the vast majority of suspended particles charged by ionizer  205  will likely pass through main filter  203 , regardless of air flows outside of improved IFD  200 . Third, charged particles are less likely to adhere to surfaces outside of improved IFD  200 . Fourth, there is less decay of charge on the charged particles before they are filtered by main filter  203 . 
     The effectiveness of this design can be improved by further lengthening the time that the air and emitted charge are together inside the unit between the inlet and the outlet, thereby maximizing the charge mixing and therefore maximizing the filter efficiency. This may be accomplished by further lengthening the path in order to lengthen the time available for charge transfer, and in particular the airflow path between ionizer  205  and filter  203 . For instance, as shown in  FIG. 3 , a serpentine path  208  can increase the length of airflow  210  without unduly increasing the exterior size of improved IFD  200 . Such a serpentine path  208  is preferably disposed downstream from the ionizer  205 , such as between fan  204  and main filter  203 , or between ionizer  205  and fan  204 . As shown in  FIG. 2 , baffles  207  or the like can also be introduced into airflow  210 , such as downstream from ionizer  205  and upstream from main filter  203 , in order to increase the path length, provide more turbulence for more effective mixing, and/or slow airflow  210  to provide more time for mixing. 
     While there have been shown, described, and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions, substitutions, and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit and scope of the invention. For example, it is expressly intended that all combinations of those elements and/or steps which perform substantially the same function, in substantially the same way, to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated. It is also to be understood that the drawings are not necessarily drawn to scale, but that they are merely conceptual in nature. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto. 
     Those skilled in the art will recognize that the present invention has many applications, may be implemented in various manners and, as such is not to be limited by the foregoing embodiments and examples. Any number of the features of the different embodiments described herein may be combined into one single embodiment, the locations of particular elements can be altered and alternate embodiments having fewer than or more than all of the features herein described are possible. Functionality may also be, in whole or in part, distributed among multiple components, in manners now known or to become known. 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention. While there have been shown and described fundamental features of the invention as applied to being exemplary embodiments thereof, it will be understood that omissions and substitutions and changes in the form and details of the disclosed invention may be made by those skilled in the art without departing from the spirit of the invention. Moreover, the scope of the present invention covers conventionally known, future developed variations and modifications to the components described herein as would be understood by those skilled in the art.