Patent ID: 12251483

DETAILED DESCRIPTION

Briefly, the present invention includes apparatus for sterilizing surfaces and objects, and apparatus for sterilizing air using gliding arc discharge technology, whereby disinfecting products formed in the discharge are prevented from escaping from the apparatus into the ambient air.

Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. In the Figures, similar structure will be identified using identical reference characters. It will be understood that the FIGURES are presented for the purpose of describing particular embodiments of the invention and are not intended to limit the invention thereto. Turning now toFIG.1Aa schematic representation of an embodiment of a pair of divergent planar electrodes,10a, and10b, effective for generating a gliding arc discharge, when powered by high-voltage source,12, are shown. Electrical lead,14, can either be grounded or connected to high-voltage source12to complete the circuit, depending on the type of high-voltage source employed. Supports for electrodes10aand10bare not shown inFIG.1A, but many types of supports are envisioned. Air blower,16, directs air between flat faces,18a, and18b, of electrodes10aand10b. Air flow rates between 20 and 80 liters/min. were used. The discharge is initiated at the narrowest distance,20, between the electrodes and progresses down the electrode spacing,22, until conditions no longer permit a discharge to occur between electrodes10aand10b.

FIG.1Bis a schematic representation of another embodiment of electrodes effective for generating a gliding arc discharge, illustrating cylindrical common ground electrode,24, employed with at least two powered electrodes10, arranged in a divergent orientation around ground electrode24, one of which is shown attached to electrically insulating cone,26, which may be made of ceramic materials or machinable NO3inert materials such as Kynar or PEEK. The powered electrodes or blades10would be mounted in slots in insulating cone26, to where they are disposed slightly (between about 1 mm and 2 mm) beyond the inside surface,27, of cone26. As will be shown and described inFIGS.3A-3CandFIGS.4A-4D, below, multiple gliding arc discharge configurations may be envisioned.

Cylindrical ground electrode24would have a nominal diameter of about ¼″, in a range between about 8 mm and 12 mm, a nominal length of about 35 mm in a range between about 20 mm and 50 mm, and rounded edges. Distance 22 is nominally about 4 mm in a range between about 3 mm and 5 mm, (the closest distance between powered electrodes10and to ground electrode24), with a nominal distance of about 11 mm in a range between about 9 mm and 15 mm as the furthest distance therefrom. Nominal lengths of blades10for this plasma source would be 35 mm in a range between about 20 mm and 50 mm.

FIGS.1C and1Dshow electrical block diagrams of two embodiments of systems for powering an automobile ignition coils effective for generating a gliding arc discharge. InFIG.1C, an automobile ignition coil driver for a “dumb” coil-on-plug is illustrated. Function generator,28, provides the shape and duration of each pulse, driving switching module,30, powered by 12 V supply,32, with TTL signals, which causes coil,34, in electrical connection with a powered electrode in a gliding arc discharge configuration shown inFIGS.1A and1Bhereof to discharge, there being one coil34connected to each powered electrode. The output of switching module30is a pulse between about 4 V and 12 V. If several powered electrodes are employed, one wire to each coil from switching module30is used.FIG.1Dshows an automobile ignition coil driver for a “smart” coil-on-plug. Again, function generator28provides the shape and duration of each pulse, this time driving coil,36, powered by 12 V supply32, directly, since 5 V logic signals from function generator28now provides switching instructions to “smart” coil36.

Pulse power sources initially used for the gliding arc discharges of embodiments of the present invention were developed for and widely used for powering neon signs, since they are inexpensive, ubiquitous, and meet UL and other safety standards. Most of these sources operate at 110 V, but some may be operated using 12 V power supplies, but only deliver a maximum of about 12 kV to the plasma. Another disadvantage of such power supplies is that they cannot be located closer than about 2 in. between units, since they interact electrically and can shut down unexpectedly.

As stated above, the off-the-shelf automotive “coil-on-plug” (COP) ignition components used for initiating the gliding arc discharges employed in embodiments of the present invention operate with a pulsed 12 V DC signal provided to a high-voltage coil mounted directly on engine spark plugs, for automotive use, but in direct electrical contact with the powered electrodes hereof. The compact coils permit 8 gliding arc plasmas to occupy the same area as 2 of the neon sign power sources. The COP components are capable of delivering 30 kV-40 kV to the plasmas, depending on the coil, versus at most 12 kV for the neon sign power sources. The COP components can also be operated at lower voltages, including 12 kV, if desired. Such higher voltages are expected to generate increased numbers and types of plasma products effective for sterilization of surfaces and air. As an example, water will break down at about 25 kV. The voltage waveform is adjustable for each COP independently of the others, which will permit the breakdown voltage for each plasma discharge to be adjusted for variations due to electrode blade alignment. Additionally, plasma uniformity and density can also be controlled, as well as power density for heat management of the electrode blades. Some COP coils provide real-time ignition feedback signals which allows for diagnosis of the discharge.

FIG.2is a schematic representation of the side view of an embodiment gliding arc plasma apparatus,40, for decontaminating surface,42, showing two plasma generators,44, and46, using the electrode configuration illustrated inFIG.1A, above, and blowers,48, and50, enclosed in air-tight chamber,52, having flat side,54, a portion,56, of which is open to surface42. Chamber52also encloses inner chamber,58, also having flat side,60, a portion,62, of which is open to surface42, and having openings in opposing side or wall,64, for permitting blowers48and50to direct air into plasmas,66, and68, of plasma generators44and46, respectively, and out of inner chamber58through opening62. Gasket,70, prevents the plasma products from escaping from apparatus40as the apparatus is moved along surface42by directing the unused plasma products into opening56of chamber52, thereby recirculating plasma-activated air (PAA),71, through blowers48and50and again through plasmas66and68for increasing activated species concentrations. This configuration slightly pressurizes inner chamber58relative to outer chamber52. Atomizers,72, and74, are employed for introducing water into plasmas66and68, respectively, either directly or through blowers48and50, or both. Evacuation fan/filter,75, is triggered in the event that gliding arc discharge apparatus40is removed from surface42, or if one or more plasma discharge products exceeds a predetermined level in chamber52.

Clearly, additional plasma generators44and46can be employed in apparatus40, as needed. Additionally, surface42can be moved relative to chamber52, or the chamber moved relative to the surface, depending on the situation encountered.

FIG.3Ais a schematic representation of side view of an embodiment of a gliding arc plasma apparatus40for decontaminating surface42where several electrode blades can share a common ground when disposed in a circular configuration, as illustrated inFIG.1Bhereof. Automobile ignition coils34are illustrated as being used for powering plasmas66and68. Blowers48and50are shown circulating PAA through T-fitting,76, inserted through wall64of inner chamber52which directs the PAA through the plasmas, thereby increasing the concentrations of plasma activated species.

FIG.3Bis a schematic representation of a side perspective view of the gliding arc plasmas shown inFIG.3A. Eight ignition coils34supported by insulating block,78, are illustrated, each powering a blade electrode sharing a common ground electrode24, with each ignition coil separately powered by switching module30inFIG.1B.FIG.3Cis a schematic representation of a bottom view of the plasma discharges generated by the apparatus ofFIG.3A.

FIG.4Ais a schematic representation of a side view of another configuration of the gliding arc discharges effective for decontaminating a surface using automobile ignition coils34aand34bfor powering plasmas66and68, where two opposing, powered electrode blades10aand10bshare common cylindrical ground24therebetween.FIG.4Bis a schematic representation of a perspective side view of a linear configuration of pairs of opposing, powered electrodes shown inFIG.4A, suitable for use in embodiments of gliding arc discharge apparatus40for decontaminating surface42; andFIG.4Cis a schematic representation of the plasmas66and68formed by the gliding arc discharge configuration ofFIG.4B.

FIG.5is a schematic representation of another embodiment of gliding arc discharge apparatus40of the present invention for decontaminating a large surface, illustrating the use of extra fans,80, and82, to maintain circulation of the plasma activated air into the chamber after contacting surface42, thereby increasing the concentration of plasma generated species, and illustrating evacuation fan/filter76used to evacuate chamber52and the inner chamber58after the decontamination process has been completed, or if the concentration of nitrogen oxides exceeds a chosen level. Gliding arc discharge generators shown inFIG.1A or1B, or a combination thereof, may be used for this embodiment, which is anticipated to be useful as a robotic, “vacuum cleaner” style apparatus. As in the embodiments illustrated inFIGS.2and3Ahereof, the plasma may either be in contact with or in close proximity with surface42.

FIG.6Ais a schematic representation of the side view of air purifier embodiment,90, of the present invention, illustrating first chamber,92, containing a plurality of gliding arc discharges in blades10powered by power supply12, through which air is drawn by fan,94, through filter,96, plasma activated air generated in gliding arc discharges10then mixes with any air already in or introduced into chamber92in mixing zone,98, which is then directed into charcoal or carbon filter,100, to remove the plasma-generated species. In embodiments of air purifier90, all of incoming air,102, is shown passing through the discharges; however, additional air inlets which do not direct the air into the discharges, but into mixing zone98before leaving chamber92as disinfected air,104, are envisioned. It should be mentioned that either of the gliding arc discharge apparatus illustrated inFIGS.1A and1Band combinations thereof can be used in air purifier90in numbers necessary to handle the desired air flow.

FIG.6Bis a schematic representation of the side view of the air purifier shown inFIG.6A, illustrating air from chamber92being directed by blower,108into smaller second chamber,106, containing at least one pair of gliding arc discharge electrodes10powered by high-voltage power supply12, in order to increase the concentration of plasma-activated species. Either of the gliding arc discharge apparatus illustrated inFIGS.1A and1Band combinations thereof can be used in air purifier90, in numbers necessary to handle the desired air flow.

FIG.6Cis a schematic representation of an embodiment of the apparatus shown inFIG.6Bhereof used for determining the effectiveness of the air sterilizer. Air is pumped into air jet nebulizer,110, by air pump,112, forming mist of inoculate,114, which passes through 3-way valve,116, into mist chamber,118, through port,120. Outside air,122, entering chamber118through vent,124, mixes with mist114to form a uniform aerosolization of inoculate, and enters chamber92through holes,126, before passing through4discharge electrode pairs10a,10bpowered by high-voltage power supply12, forming thereby 4 gliding arc discharge plasmas,128(Primary Plasma). Vacuum pump,130, pumps the mixture of air with the inoculate mist,132, through air impact sampler or monitor,134, containing an agar plate, which absorbs airborne microbes from the air passing therethrough, where it is exhausted through 3-way valve,136, into filter,138, or back into mist chamber118through 3-way valve116through port120. Air from chamber92is directed by blower,108into smaller chamber,106, containing at least one pair of gliding arc discharge electrodes10powered by high-voltage power supply12, in order to increase the concentration of plasma-activated species, and/or for use for self-cleaning the system by being directed into chamber118through valves136and116and port120.

FIG.7is a schematic representation of a side view of object disinfectant embodiment,140, of the present invention, illustrating air-tight object enclosure,142, having sealing lid,144, for inserting object,146, to be disinfected, and second chamber106in fluid contact with object enclosure142for directing air from the object enclosure through gliding arc discharge electrode plates10powered by high-voltage power supply12, whereby a plasma is formed therebetween, and returning plasma-generated species and air to the object enclosure using blower108. Once lid144is closed, no air is admitted to object enclosure142, except for that circulated through chamber106, which originates in object enclosure142. Objects146may include packages, personal protective equipment, and the like. In operation, the blower/plasma combination recirculate the plasma air, thereby raising the NO concentration to an estimated 6000 ppm in about 30 min., thereby creating a strong disinfecting environment for the enclosed objects. Experiments have shown a 99.9% reduction inStaphylococcus aureusin 30 s, and 99.99% reduction in 60 s. After disinfection is completed, the NO is drawn through charcoal filter100by vacuum pump130to remove all of the NON.

It was found by detailed examination of the embodiment illustrated inFIG.6hereof that with the gliding arc discharge apparatus utilized without a blower, but with the electrodes suspended in the air stream, that 0.2 ppm of NO2was generated; that, if a blower was used in the same air stream under the electrodes, that 0.8 ppm of NO2was generated, and that, if a blower with a baffle were used in the same air stream, 1.2 ppm of NO2was generated. Thus, air disinfection device150was developed over purification embodiment90inFIG.6.

FIG.8Ais a schematic representation of the side view of another air disinfectant embodiment,150, of the present invention, illustrating chamber,152, containing at least one gliding arc discharge device,154, through which air is directed by blower108. Gliding arc discharge device154powered by power supply12disposed as part of power and control electronics,156, generates plasma,158. Air to be sterilized,160, is filtered using pre-filter,96, and drawn through chamber152by fan94. Gliding arc discharge device154is mounted, along with blower108, on ⅜″-0.5″ thick PVC sheet,161, and plasma158is not extinguished by air160since sheet161in conjunction with ⅜″-0.5″ PVC baffle,162, effectively shields plasma158from the affects of direct air flow. The NON-disinfected air is then purified by charcoal or carbon filter100to remove the plasma-generated NON-species, and released,163.FIG.8Bis a schematic representation of the side view of the air disinfectant embodiment of the present invention shown inFIG.8Ahereof, illustrating some dimensions of the apparatus as constructed, whileFIG.8Cis a schematic representation of a side perspective view of the gliding arc discharge similar to that illustrated inFIG.1Ahereof, and blower108disposed on mounting plate for preventing the plasma from being extinguished by the flow of air through the disinfectant apparatus. It should be mentioned that either of the gliding arc discharge apparatus illustrated inFIGS.1A and1B, and combinations thereof can be used in air purifier150in numbers necessary to handle the desired air flow.

Carbon or charcoal filter100, is constructed of two carbon-coated polyester felts stacked together along with a MERV (Minimum Efficiency Reporting Values) 13 fabric. Pre-filter96, electrode holder161are about 0.5″ thick, and pre-filter96is typically MERV 6-8, its ability to capture larger particles (between 3 μm and 10 μm) being between about 50% and about 85% between these values.

Having described the general details of embodiments of the present invention, the following EXAMPLES provides additional details.

Example 1

Using the apparatus illustrated inFIG.6Cabove, with and without activating smaller chamber106(Secondary Plasma), two colony forming units (CFU) ofStaphylococcus epidermisof about ⅛ in. diameter were harvested from a tryptic soy agar plate. The harvested CFUs were dissolved in 2 mL of 0.1 M phosphate buffer solution (pH 7.3-7.4), vortexed until homogeneous, and diluted with distilled water to 1:1000 and 1:10,000. Five mL of the diluted inoculate was placed in a home air jet nebulizer (Compressor Nebulizer) and using the manufacturer's specifications, the particle sizes ranged from about 0.5 μm to 10 μm, at a nebulizing rate of about 0.25 mL/min., and an air flow of about 7 L/min. A “no plasma” control was run for each process condition. The total flow rate was controlled by vacuum pump130attached to the air impact monitor134. The agar plates contained in the impact monitor were then incubated and counted.

Test results are shown in TABLE 1, where germ kill data result from a single pass (single turn) of air flow. The relative humidity of the incoming air was measured to be 59%, and the total air flow was measured at the exhaust of vacuum pump130. For each sample, the nebulizer was operational for 180 s, after which air pumping was continued for 60 s, blower108being continuously operated. The impact plates were incubated for 20 h at 37° C., after which the CFUs were counted.

TABLE 1AIRSECOND-%FLOWPRIMARYARYCFURE-DILUTION(LPM)PLASMAPLASMACOUNTDUCTION100010NN3476100010YN15695.5100010NY46686.6100010YY1399.6

It is seen from TABLE 1 that the lowest efficacy was using only the Secondary Plasma, with the best efficacy being obtained when both plasmas were used.

Example 2

Air disinfection unit (ADU)150(FIG.8A) was placed inside a clear plastic cube, 4′ per side having an approximate volume of 1.812 m3. Inoculum of Staph epidermidis was dispensed into the top of the cube using a syringe pump connected to a 120 kHz ultrasonic nozzle, which produced droplets having a mean diameter of about 18 μm. A mixing fan within the cube was continuously operated. Immediately after the inoculum was dispensed, ADU150was made operational. A sample pump mounted on the top of the cube withdrew about 10 Lpm of air at specific points in time. The impinger water samples were sent to an outside testing lab. Water samples were tested with a standard serial dilution/culture test, and the test results were in Colony Forming Units (CFU) per cubic meter of air.

TABLE 2 shows air disinfection data from ADU150: log germ kill vs. air turns. Note that no germs were detected after 6 air turns. For this TABLE, fan94inFIG.8Awas operated at 95 CFM (2690 liters per min.). At this flow, the cube volume will experience one air turn in approximately 40 s. The data shows that the time to complete germ removal was on the order of 6 air turns, 240 s, or 4 min.

TABLE 2Air turnslog10CFU/m30.05.602.05.604.05.306.0010.0017.8022.3035.5044.50

The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.