News Column

Researchers Submit Patent Application, "Apparatus for Air Purification and Disinfection", for Approval

July 15, 2014



By a News Reporter-Staff News Editor at Life Science Weekly -- From Washington, D.C., NewsRx journalists report that a patent application by the inventor TSUI, Herman Yik Wai (Kowloon, HK), filed on December 24, 2012, was made available online on July 3, 2014 (see also Patents).

No assignee for this patent application has been made.

News editors obtained the following quote from the background information supplied by the inventors: "Available air purification apparatus in the marketplace can be broadly grouped into two principal types: i) removal of unwanted particles through trapping and filtration, and ii) destruction of unwanted particles to eliminated the associated harmful effects or render the harmful microbes (such as bacteria) unviable. Filtration based apparatus have air circulating through an air filtration device (filter) and particles above a certain size are trapped by the filter. Depending on the materials that make up the filter and its construction method, particles with a diameter of a few micrometers or larger can be removed from the circulating air. Some filtration devices incorporate additional apparatus (such as electrostatic precipitators) to introduce charges to the particles to enhance the trapping efficiency. Viruses are generally small enough to pass through these filters and microbes can also be carried by aerosol of sufficiently small size to pass through the filters. Filters trap them but do not destroy them. Some existing air purification systems incorporate ultraviolet (UV) light to destroy trapped microbes. Un-trapped microbes remain in the air.

"Ion generators are also provided in the marketplace for the removal of airborne particles. They produce negative electrical charge and when the charge is applied to airborne particles, the airborne particles will fall out and cling to nearby surfaces. Therefore, these devices function only to separate and remove airborne harmful particles but not to destroy them.

"There are also ozone (O.sub.3) generators in the marketplace for the destruction of airborne microbes. Ozone is not an effective biocide for airborne microbes except at extremely high and unsafe levels, for example, more than 3,000 ppb. As a result, ozone generators cannot destroy airborne microbes or pathogenic microorganisms effectively to achieve any benefits to human health. If these devices accidentally generate excessive levels of ozone, it will be detrimental to health. In fact, there are many articles published giving warnings about use of excessive ozone for air disinfection.

"UV has been successfully applied in some applications for disinfection. Research in UV disinfection of airborne microbes demonstrated that a residence time (i.e. the duration that an air stream needs to be radiated with UV) of the order minutes and hours is required to achieve noticeable level of disinfection. This level of efficiency is considered low in practical terms.

"There are also articles reported that charged particles (ion clusters) can have disinfection effect. Similar to UV disinfection, the efficiency of this disinfection mechanism is also low and an exposure to the ion clusters of the order hours is typically required.

"Plasma is an electrically neutral, ionized gas composed of freely moving ions, electrons, and neutral particles. Plasma is used today for a variety of commercial applications including for air purification and disinfection. Depending on the operation regime, plasma can consist of charged particles (electrons and ions), excited species, free radicals, ozone and UV photons, which are capable of decomposing chemical compounds and destroying microbes. Existing commercially available plasma air purifiers operate either indirectly by using ozone or UV photons generated by plasma contained in a separate device or by charging up the airborne particles in a similar fashion as ion generators operate.

"Plasma can be created by electrical means in the form of gaseous discharges whereby a high voltage is applied to a set of electrodes, the anode and the cathode. When the applied voltage is sufficiently high and becomes greater than the breakdown voltage, arcs begin to develop across the electrodes. The threshold for electrical breakdown or arc formation follows the well-known Paschen law, which relates the breakdown voltage to the gap size between the electrodes and the gas pressure.

"Breakdown occurs when the applied voltage, or more precisely the local electric field, is sufficiently large for electrons to acquire enough energy to compensate the energy losses due to collisions, excitation and other energy loss processes. The breakdown process begins with presence of some free or residual electrons accelerating towards the anode under the influence of the externally applied electric field. As they accelerate towards the anode, the streaming electrons collide with the gas atoms causing ionization directly by impact or indirectly through photo-ionization. An electron cloud begins to build up and propagates towards the anode together with an ionization or breakdown front ahead of the electron cloud, leaving an ion trail behind, resulting in a plasma channel with an electric dipole opposing the applied electric field. The formation of such streamer, if unrestrained, leads to a rapid increase in charge density, fast growth of an avalanche, and the transformation of the streamer into an arc.

"By introducing suitable current limiting or quenching mechanism(s) to prevent the development of major arcs, a quasi-steady state can be established with micro-arcs or filaments (of dimension of the order of 10.sup.-4 m) filling up the gap between the electrodes. Traditionally this is achieved by placing dielectric barrier or insulator covering one or both electrodes. Discharge having an insulating or dielectric layer incorporated on one or both of the electrodes is known as dielectric-barrier discharge. The non-conducting property of the dielectric or insulating layer allows charge accumulation on the surface, which produces an opposite electric field to the applied electric field. In addition, the space charge built up next to the dielectric or insulating layer adds to the electron repelling electric field. The opposing electric field cancels the applied electric field and prevents a filament from developing into a major arc and causes a discharge filament to extinguish. Therefore, the low charge mobility on the dielectric leads to self-arresting of the filaments and also limits their lateral extension, thereby allowing multiple filaments to form in close proximity to one another. Furthermore, when coalescence of multiple ionization fronts occurs, the filamentary discharge transforms to a diffuse glow discharge that has spatially more uniform properties. Current quenching can also be achieved by carefully controlling the applied voltage to prevent transition into an arc. It can be created by the use of needle-like electrodes to create a space charge region around the smaller or sharper electrode. It can also be achieved by including non-conducting packing materials in a bed residing between the electrodes.

"In a dielectric-barrier discharge operating in the near-atmospheric pressure range, electron energy is typically in the range of 1 to 10 eV and ion energy is close to the ambient gas temperature. Because of the energy disparity between the electron and ion species, these discharges are classified as non-thermal plasma. Typically, the density of the charge particles is much less than the neutral ambient gas and the plasma behavior is dominated by collisional effects. The energy of the electrons can be utilized for exciting atoms and molecules, thereby initiating chemical reactions and/or emission of radiations. The energetic electrons are able to induce the breakdown of some chemical bonds of the molecules, collide with the background molecules resulting in the breakdown of molecular chain, ionization and excitation, and generation of free atoms and radicals such as O, OH or HO.sub.2. The radicals can attack hazardous organic molecules and are useful in decomposing pollutants in air. The disassociation of O.sub.2 provides the required O to combine with O.sub.2 to form ozone. The low energy electrons can attach to neutral atoms or molecules to form negative ions, which can enhance reactions in decomposing pollutants and destruction of microbe. Through collision, electrons can destroy organic compounds including bacteria and virus directly. Emissions, particularly in the UV spectral region, through recombination and relaxation, can initiate photo-physical and photo-chemical process by breaking molecular bonds and hence destroying microbe resulting in disinfection effect.

"The harmful contaminants can be broadly grouped into chemical contaminant, volatile organic compounds, bacteria, fungi and viruses; each group is characterized by the amount and complexity of the constituent molecules or radicals. Plasma properties have to be optimized in order to destroy and/or to prevent the growth of these harmful contaminants. One major requirement is to ensure that these harmful contaminants have an adequate residence time within the reactor device while supporting a sufficiently high flow rate for practical applications.

"While plasma can be utilized to reduce the harmful particles, the generation of plasma also creates by-product gas which can be hazardous. Typical examples of bi-product gas are ozone and nitrogen dioxide (NO.sub.2).

"Therefore it would be desirable to provide an apparatus to generate plasma for indoor air purification and disinfection which adequate residence time and effective plasma power deposition to achieve efficient destruction of pollutants while minimizing the generation unwanted bi-product gases."

As a supplement to the background information on this patent application, NewsRx correspondents also obtained the inventor's summary information for this patent application: "An apparatus for air purification and disinfection is provided. In one aspect, the apparatus includes at least one elongated reactor having an elongated inner electrode and an elongated outer electrode. The outer electrode encompasses at least a portion of the inner electrode along a longitudinal axis of the reactor. The outer and inner electrodes are positioned in a substantially concentric relationship and define a reaction chamber therebetween. The apparatus also includes an inner electrode mounting member holding the inner electrode at an end of the inner electrode and an outer electrode mounting member holding the outer electrode at an end of the outer electrode. The apparatus further includes a power supply adapted to supplying electrical power to the inner and outer electrodes to generate plasma within the reaction chamber to purify and disinfect air flowing therethrough.

"The reaction chamber of the reactor may include an air inlet and an air outlet positioned at opposite ends thereof. The outer electrode mounting member may include an opening corresponding to the air inlet or the air outlet of the reaction chamber of the reactor.

"In one embodiment, the inner electrode is longer than the outer electrode. In another embodiment, the inner electrode mounting member includes a protruded portion holding the inner electrode.

"In one embodiment, the apparatus includes a plurality of elongated reactors positioned in generally parallel with each other.

"In one embodiment, the outer electrode includes an insulator layer and an electrode conductor covered at the outer surface of the insulator layer, while the inner electrode includes an insulator layer and an electrode conductor covered at the inner surface of the insulator layer. In another embodiment, the outer electrode includes an insulator layer and an electrode conductor embedded in the insulator layer, while the inner electrode includes an insulator layer and an electrode conductor embedded in the insulator layer.

"In one embodiment, the power supply includes a control unit adapted to control the electrical power supplied to the inner and outer electrodes of the reactor. The waveform period and the on/off cycle of the electrical power are set to be shorter than the time that the air stays inside the reaction chamber.

"In another aspect, the apparatus for air purification and disinfection includes at least one elongated reactor having an elongated inner electrode and an elongated outer electrode. The outer electrode encompasses the inner electrode along a longitudinal axis of the reactor. The outer and inner electrodes are positioned in a substantially concentric relationship and define a reaction chamber therebetween. The insulator layer of the inner electrode and the insulator layer of the outer electrode are integrally joined together. The apparatus further includes a power supply adapted to supplying electrical power to the inner and outer electrodes to generate plasma within the reaction chamber to purify and disinfect air flowing therethrough.

"The reaction chamber of the reactor may include an air inlet and an air outlet positioned at opposite ends thereof.

"In one embodiment, the insulator layer of the inner electrode and the insulator layer of the outer electrode are integrally joined at a first end of the reactor. The insulator layer of the inner electrode and the insulator layer of the outer electrode may be integrally joined at a second end of the reactor. In another embodiment, the insulator layer of the inner electrode and the insulator layer of the outer electrode are integrally built along the longitudinal axis of the reactor.

"In one embodiment, the apparatus includes a plurality of elongated reactors positioned in generally parallel with each other.

"In one embodiment, the outer electrode includes an insulator layer and an electrode conductor covered at the outer surface of the insulator layer, while the inner electrode includes an insulator layer and an electrode conductor covered at the inner surface of the insulator layer. In another embodiment, the outer electrode includes an insulator layer and an electrode conductor embedded in the insulator layer, while the inner electrode includes an insulator layer and an electrode conductor embedded in the insulator layer.

"In one embodiment, the power supply includes a control unit adapted to control the electrical power supplied to the inner and outer electrodes of the reactor. The waveform period and the on/off cycle of the electrical power are set to be shorter than the time that the air stays inside the reaction chamber.

"In another aspect, the apparatus for air purification and disinfection includes at least one elongated reactor having an elongated inner electrode, an elongated outer electrode and a first end cap. The outer electrode encompasses the inner electrode along longitudinal axis of the reactor. The outer and inner electrodes are positioned in a substantially concentric relationship and define a reaction chamber therebetween. The first end cap couples the inner electrode and the outer electrode at a first end of the reactor. The apparatus further includes a power supply adapted to supplying electrical power to the inner and outer electrodes to generate plasma within the reaction chamber to purify and disinfect air flowing therethrough.

"The apparatus may includes a second end cap coupling the inner electrode and the outer electrode at a second end of the reactor.

"The reaction chamber of the reactor may include an air inlet and an air outlet positioned at opposite ends thereof.

"In one embodiment, the apparatus includes a plurality of elongated reactors positioned in generally parallel with each other.

"In one embodiment, the outer electrode includes an insulator layer and an electrode conductor covered at the outer surface of the insulator layer, while the inner electrode includes an insulator layer and an electrode conductor covered at the inner surface of the insulator layer. In another embodiment, the outer electrode includes an insulator layer and an electrode conductor embedded in the insulator layer, while the inner electrode includes an insulator layer and an electrode conductor embedded in the insulator layer.

"In one embodiment, the power supply includes a control unit adapted to control the electrical power supplied to the inner and outer electrodes of the reactor. The waveform period and the on/off cycle of the electrical power are set to be shorter than the time that the air stays inside the reaction chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1a is a perspective view of an embodiment of a reactor assembly of an air purification and disinfection apparatus.

"FIG. 1b is an enlarged view of the circled portion of the reactor assembly shown in FIG. 1a.

"FIG. 2 is an exploded view of the reactor assembly of FIG. 1a, showing the arrangement of the reactors.

"FIG. 3a is a perspective view of one of the reactors of the reactor assembly of FIG. 1a.

"FIG. 3b is a cross-sectional front view of the reactor of FIG. 3a, showing the reaction chamber between the inner and outer electrodes.

"FIG. 3c is a cross-sectional side view of the reactor of FIG. 3a, showing two electrodes and the reaction chambers between the two electrodes.

"FIG. 4 is a schematic diagram of an electrical circuit of an air purification and disinfection apparatus which utilize at least one reactor of FIG. 3a.

"FIG. 5a is a perspective view of an air purification and disinfection apparatus incorporating the reactor assembly of FIG. 1a.

"FIG. 5b is an exploded view of the air purification and disinfection apparatus shown in FIG. 5a.

"FIG. 6a is a perspective view of another embodiment of a reactor.

"FIG. 6b is a cross-sectional front view of the reactor of FIG. 6a.

"FIG. 6c is a cross-sectional side view of the reactor of FIG. 6a.

"FIG. 7a is a top view of a corresponding reactor assembly for the reactors shown in FIG. 6a.

"FIG. 7b is a cross-sectional side view of the reactor assembly of FIG. 7a.

"FIG. 8a is a perspective view of another embodiment of a reactor.

"FIG. 8b is a cross-sectional front view of the reactor shown in FIG. 8a.

"FIG. 8c is an exploded view of the reactor shown in FIG. 8a.

"FIG. 9 is a perspective view of a corresponding reactor assembly for the reactors shown in FIG. 8a.

"FIG. 10 is a cross-sectional side view of another embodiment of a reactor assembly showing a reactor and electrode mounting members.

"FIG. 11a is a cross-sectional side view of another embodiment of a reactor assembly showing a reactor and electrode mounting members.

"FIG. 11b is a cross-sectional front view of the reactor assembly of FIG. 11a."

For additional information on this patent application, see: TSUI, Herman Yik Wai. Apparatus for Air Purification and Disinfection. Filed December 24, 2012 and posted July 3, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3784&p=76&f=G&l=50&d=PG01&S1=20140626.PD.&OS=PD/20140626&RS=PD/20140626

Keywords for this news article include: Ozone, Patents.

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Source: Life Science Weekly


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