Microwave drying and sanitizing of articles

Abstract: The invention features a sanitization method and apparatus utilizing multiple microwave sources. Bacteria are killed by the combination of microwave heated water vapor and the microwave field effect. Articles such as moist fabrics, that are contained within a substantially sealed chamber, can be sanitized and dried by this method.

Description: Field of the Invention The Invention relates to a microwave apparatus and method, and more particularly to a method and apparatus for both drying and sanitizing articles, such as clothes or fabric, during the drying cycle. Background of the Invention As far back as twenty years ago, suggestion was made that clothes could be sterilized by irradiation with microwaves. Such suggestion can be found in United States Patent No. 3,605,272; issued: September 20, 1971. However, despite this disclosure, very little is definitively known about killing bacteria using microwave energy. A careful survey of scientific articles and journals indicated that parameters and mechanisms by which bacteria can be killed by microwaves is not well understood. In fact, there are published articles that even suggest that bacteria growth can be enhanced by microwave irradiation. On this note, the present inventive research, set the task of developing a verifiable method for sanitizing clothes and fabrics heated and dried by microwaves. Using an apparatus similar to that described and shown in U.S Patent application, Serial No. 092,621, clothes and fabrics were heated and dried by multiple magnetron units, each producing approximately 700 Watts, and operating at approximately 2,450 MHz. The multiple microwave sources were cross-polarized. The tested fabric articles respectively contained different strains of bacteria, such as: E. Coli; Salmonella; Shigella, etc. It was discovered that bacteria could be killed using microwaves, and that the effective mechanism by which this was accomplished was not entirely heat dependent. In other words, the microwave field effect itself was a contributing mechanism by which decontamination was accomplished. Thus, heating and drying by microwaves provides a sanitizing advantage that ordinary heating and drying techniques cannot accomplish. Furthermore, it was also discovered that the airflow necessary for carrying away evaporated moisture, could seriously complicate the sanitizing process by introducing air-borne contaminants. It was further discovered during the testing, that the fabrics could be heated by microwaves without removing the moisture from the drying chamber. Heated in this way, it was observed that an enhanced sanitizing effect was obtained. Bacteria were more easily killed by the combination of the microwave field effect and the accumulated and heated moist air which was now trapped within the heating chamber. However, the microwave field effect in combination with the confined, heated water vapor (steam) provides a synergy in sanitizing fabric heretofore unknown. A system for sanitizing matresses using this technique is disclosed in DE-A-3505571. Brief Summary of the Invention : The invention features a method and apparatus whereby moist fabrics that are heated and dried by microwaves can be simultaneously sanitized. The method establishes at least one sanitization sub-cycle during a portion or portions of the microwave heating cycle. The sanitization sub-cycle comprises the step of accumulating and heating the vaporized moisture effluent emanating from the microwave irradiated fabrics during a portion of the microwave heating cycle. The trapped moisture is confined within a "heating zone", which for the purposes of definition shall mean either a heating and drying chamber as used in a stationary, commercial system, or a heated work station adjacent a conveyor, as would be utilized in an industrial, bulk, or continuous system. When the vaporized moisture (steam) is allowed to remain and be further heated within the "heating zone", the microwave field effect in combination with the heated vaporized moisture causes a sanitizing of the fabrics. The portion of the microwave heating cycle in which the sanitization sub-cycle is accomplished is generally at the beginning thereof; after which, the fabric is further heated with application of a conventional airflow to complete the drying process. In addition, there is a second, or additional sanitization sub-cycle at an end portion of the microwave heating cycle, in order to kill any air-borne contaminants introduced by the subsequent drying airflow. It is also contemplated that the drying airflow can be adequately filtered to prevent introduction of air-borne contaminants. In the sanitization of other articles in addition to fabrics and clothing, such as: plastics, instruments, and sealed non-perishables, moisture may be introduced to the heating zone. The sanitization sub-cycle does not increase the drying time for the fabrics, since it is itself a fractional cycle of the heating step. The sanitization sub-cycle will comprise up to 50% of the microwave heating cycle. The moist fabrics are tumbled within a rotatable microwave-permeable drum which is disposed within the "heating zone". The microwaves penetrate the tumbling drum, causing the moisture within the fabrics to evaporate. In continuous systems featuring a conveyor belt, the clothes may be agitated by rotating vanes as they travel through the "heating zone". There may be several heat work stations for the above purpose. It is an object of this invention to provide an improved microwave drying system wherein fabrics and other articles can be sanitized as they are dried. It is another object of this invention to provide a sanitization method and apparatus which utilizes both microwave field effect and heated moisture to kill bacteria. These and other objects of the invention will be better understood and will become more apparent with reference to the following detailed description considered in conjunction with the accompanying drawings. Brief Description of the Drawings : Figure 1 is a perspective schematic view of an apparatus used for the drying and sanitizing of fabrics in accordance with the teachings of this invention; and Figure 2 is a schematic sectional view of the apparatus shown in Figure 1, depicting in more detail the airflow system used for the drying and sanitization of the fabrics. Detailed Description of the Invention : Generally speaking, the invention pertains to a method and apparatus for heating, drying, and sanitizing moist fabric articles by microwave energy. The vaporized moisture driven off by the microwave irradiation, is accumulated within the heating zone. The accumulated moisture is itself heated during the irradiating process. This heated vapor in combination with the microwave field effect kills bacteria entrained within the fabric articles in a more facile manner heretofore unknown. Now referring to Figure 1, a moist fabric microwave heating and drying apparatus 10 comprising heating chamber 9, is illustrated in schematic view. The airflow system shown in the sectional view of Figure 2 has been deleted from Figure 1 for the sake of brevity, but will be understood to be part of the entire apparatus 10 therein. For purposes of clarity and brevity, the same elements will carry the same designation throughout the figures. Moist fabrics (not shown) are loaded into a removable, rotatable tumbling drum 11, which has internal vanes 12 for tumbling the moist fabric as the drum rotates (arrow 25). The tumbling drum 11 is microwave permeable, being made of a plastic such as Lexan, so that moist fabrics disposed within the drum can be irradiated. Microwaves are directed at drum 11 from magnetron fed waveguides 13, 14, 15 and 16, respectively disposed about heating chamber 9, as illustrated. The chamber 9 can be of a generally rectangular shape with two side walls 17 and 18, respectively configured with pyrimidal-shaped quarter panels. At the apex of walls 17 and 18, are respective internal bearings 19 and 20, for rotatively supporting drum shaft 21 which is fixedly attached to respective distal ends 22 and 23 of drum 11 (Figure 2). A motor 24 rotatively drives the drum shaft 21, thus causing drum 11 to rotate (arrow 25) within end bearing 19 and 20. The end walls 17 and 18 are each pyrimidal-shaped so that the respective magnetron waveguides 13, 14, 15 and 16 project the microwaves inwardly toward the center of drum 11. Waveguides 13 and 14 are vertically oriented, while waveguides 15 and 16 are horizontally oriented, such that the microwaves projected from chamber walls 17 and 18 are cross-polarized with respect to each other. The airflow system of this invention is illustrated in Figure 2. There are two air ducts 26, only one of which is shown in the sectional view of Figure 2. Each duct 26 has two squirrel-cage blowers 27 and 28, respectively disposed therein as shown. Each of the blowers 27 and 28 feeds air (arrows 29) through duct 26 towards, and into, a common chamber inlet 30. Each blower 27 and 28 cools a magnetron 31 disposed adjacent its respective waveguide. There are a total of four magnetrons 31. Each magnetron 31 produces approximately 700 watts at 2,450 MHz. There are two magnetrons 31 in each air duct 26. During the drying portion of the microwave heating cycle, air enters inlet 30 of chamber 9 from the two air ducts 26, and is directed with aid of a microwave permeable deflector 42 across the heating chamber 9 (arrows 32) towards chamber outlet 33. The airflow 32 passes through tumbler drum 11 as it rotates and tumbles the fabric (arrow 25). Evaporated moisture resulting from the microwave heating of the moist fabric is then carried away by airflow 32, and exits chamber 9 at outlet 33. An exhaust duct 34 and fan (not shown) disposes of the moist air, as shown by arrow 35. An average fabric load of approximately 4 pounds can be dried in approximately 15 to 18 minutes during the microwave heating cycle. The drying sub-cycle is approximately 50% or more of the microwave heating cycle. The remaining portion of the microwave heating cycle comprises a sanitization sub-cycle which ranges from approximately one-third to one-half of the microwave heating cycle (between 5 to 9 minutes). During the sanitization sub-cycle, gate 37 is opened, such that there is no airflow 32 through drum 11 and chamber 9. Airflow 29 is continuous throughout the heating cycle, but is caused to exit (arrow 36) through outlet 41 of ducts 26 by means of gate 37, which is caused to be opened about hinge 38. In the drying sub-cycle, gate 37 is kept shut, so that all of the airflow 29 is directed into chamber 9 via inlet 30. Airflow 32 passes through drum 11 by means of perforations (not shown) on distal ends 39 of drum 11. Whether airflow 29 is directed into chamber 9 via inlet 30, or is caused to exit outlet 41, air is continuously passed over magnetrons 31 in order to cool them. During the sanitization sub-cycle when inlet 30 is closed to the airflow 29, evaporated moisture from the wet fabric in drum 11 is caused to accumulate and become heated within chamber 9. It is the heated effluent in combination with the microwave field effect which has been shown to sanitize the fabrics. The sanitization experiments tested fabric impregnated with many different bacterial strains, some of which include: E. Coli; Salmonella; Shigella and P. aeruginosa, etc. The heated, accumulated effluent emanating from the fabrics was allowed to reach a maximum temperature of approximately 60° C. Higher temperatures may be reached for short periods of time without harming the fabric, analogous to a pasturization technique. In the many tests which were conducted, many bacterial strains were found to be non-viable after 72 hours of incubation on an appropriate medium after removal from the drum 11. Generally speaking, the sanitization sub-cycle is conducted at the beginning portion of the microwave heating cycle, and then the remainder of the cycle is substantially comprised of the drying sub-cycle. In addition, a second sanitization sub-cycle of approximately 0.5 to 1.5 minutes in duration is performed at the very end of the drying sub-cycle. This second sanitization sub-cycle may be necessary where air-borne contaminants may be excessive, or where the fabric is excessively loaded with virulent strains of bacteria. A filter may be provided at inlet 30 and/or in ducts 26. In another embodiment, more than one heating chamber may be provided.

Claims: A method of heating, drying and sanitizing moist fabric articles in a microwave heating zone, wherein a microwave heating cycle comprises the steps of: (a) directing microwaves into a heating zone containing moist fabric articles for causing moisture effluent to emanate from the fabric articles; (b) tumbling said fabric articles during said microwave heating cycle; (c) establishing at least one sanitization sub-cycle during at least one portion of said microwave heating cycle by accumulating and heating evaporated moisture effluent vapor from said fabric articles in said heating zone whereby bacteria in said fabric articles are killed by heated moist air in combination with the microwave field effect; (d) establishing an airflow through said heating zone during a further portion of said microwave heating cycle which carries away said moisture effluent from said fabric articles; and (e) subsequent to step (d), carrying out a second sanitization sub-cycle by directing microwaves into said fabric articles whereby contaminants carried by said airflow are irradiated. The method of Claim 1, wherein a sanitization sub-cycle is provided at a beginning portion of said microwave heating cycle. The method of claim 1 or 2, wherein a sanitization sub-cycle is provided at an end portion of said microwave heating cycle. The method of Claim 2 wherein said sanitization sub-cycle comprises up to 50% of the microwave heating cycle. The method of Claim 2 comprising the further step of filtering the airflow of step (d). The method of Claim 2, wherein said moist fabric articles move through said heating zone on a conveyor means. The method of Claim 2, wherein the airflow of step (d) is used to cool microwave generating sources during said sanitization sub-cycle.

Inventors: CLOUTIER MICHEL JACQUES, O'CONNOR MARY ELLEN, SOREN JAMES R JR, STRATTAN ROBERT D, CLOUTIER, MICHEL JACQUES, O'CONNOR, MARY ELLEN, SOREN, JAMES R., JR., STRATTAN, ROBERT D.
Applicants: MICRO DRY INC, MICRO DRY, INCORPORATED
Application year: 1988
Main classification: A61L2
IPC codes: D06F58, A61L2, F26B3