US3748421A

US3748421A - Microwave melter apparatus

Info

Publication number: US3748421A
Application number: US00167301A
Authority: US
Inventors: R Peterson
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1971-07-29
Filing date: 1971-07-29
Publication date: 1973-07-24
Anticipated expiration: 1990-07-24

Abstract

Apparatus is disclosed for effecting a change in the state of materials from, for example, solid to fluid, or a viscous fluid to a freer-flowing fluid. A compartmentalized enclosure is provided with means for indirectly radiating electromagnetic microwave energy to heat, by absorption, the material to be treated. Continuous drainage of the resultant material is provided. The energy is radiated within an empty heating compartment which is dimensioned to define a cavity resonator structure. The material is contained within a superimposed upper treatment compartment and comprises the load exposed to the microwave energy. A common separation wall of an energy permeable material provides for the admittance of the heating energy to successively erode the load as a fluid medium which is removed by drainage means. Appropriate valve and sensing means in combination with the material treatment compartment are provided to prevent operation of the energy generator when no load is present. In treating viscous, gelatinous materials for film, the apparatus is appropriately rendered lightproof.

Description

United States Patent Peterson 1 July 24, 1973 MICROWAVE MELTER APPARATUS state of materials from, for example, solid to fluid, or

17s I Inventor when A Peterson Canton Mass a viscous fluid to a freer-flowing fluid. A compartmentalized enclosure is provided with means for indirectly [73] Assignee: Raytheon Company, Lexington, radiating electromagnetic microwave energy to heat,

Mass. by absorption, the material to be treated. Continuous drainage of the resultant material is provided. The en- [22] July ergy is radiated within an empty heating compartment [21 App]. No.: 167,301 which is dimensioned to define a cavity resonator structure. The material is contained within a superimposed [52] U 8 Cl 219/10 55 upper treatment compartment and comprises the load [51] 1.0 Hush 9206 exposed to the microwave gy A common p tion wall of an gy permeable material provides for [58] Field of Search 219/ 10.55 the admittance of the heating gy to successively 56] References Cited erode the load as a fluid medium which is removed by drainage means. Appropriate valve and sensing means UNITED STATES PATENTS in combination with the material treatment compart- 3,336,142 8/1967 Lawson 2l9/l0.55 X ment are provided to prevent operation of the energy goschnel' generator when no load is present. In treating viscous, om

Primary Examiner-J. V. Truhe Assistant Examiner-Hugh D. Jaeger A ttorney Harold A. Murphy, Edgar O. Rost et al.

[57] ABSTRACT Apparatus is disclosed for effecting a change in the VALVE CONTROL gelatinous materials for film, the apparatus is appropriately rendered lightproof.

6 Claims, 3 Drawing Figures SYSTEM MICROWAVE =ECE VIN;

MICROWAVE MELTER APPARATUS BACKGROUND OF THE INVENTION The invention relates to indirect heating by electromagnetic energy to change the state of materials to have a lower density.

The utilization of electromagnetic microwave energy for heating has found wide acceptance in the processing of poor thermally conductive materials, including foodstuffs, paper, wood, rubber, leather, and viscous materials.

An energy generator of microwaves is the magnetron oscillator of World War II radar systems fame. The text Microwave Magnetrons, Radiation Laboratory Series, Vol. 6, by G. B. Collins, McGraw-Hill Book Company, Inc., 1948, provides a detailed description of the construction and operation of such devices. Conventionally the operating frequencies allocated by the Federal Communication Commission for oven apparatus are 915 and 2,450 megahertz. For the purposes of the present specification, the term microwaves is defined as electromagnetic energy radiation in that portion of the spectrum having wavelengths in the order of approximately I meter to one millimeter and frequencies in excess of 300 megahertz.

Thawing of frozen masses utilizing the heating energy under consideration has been the subject of several prior art United States Letters Patents. U.S. Pat. No. 3,336,142 issued Aug. 15, 1967 to J. L. Lawson describes a device of interest providing for the melting of frozen juices by direct exposure to microwave energy within a chamber with the melted liquid or mass being withdrawn while the energy is applied. The material to be treated is placed directly within the oven enclosure and a top feed is utilized with the liquefied mass being withdrawn from an empty lower container.

Another patent of interest is U. S. Pat. No. 3,505,490 issued Apr. 7, 1970 to E. J. Gorn and assigned to the present assignee wherein rotation of the frozen mass is provided to assist in the rapid removal of the thawed liquid and/or masses from the oven enclosure to compensate for the changing dielectric constant value of the mass as it thaws.

In both the foregoing prior art patents the microwave heating energy is radiated within the enclosure containing the material to be treated. Certain masses, however, which are extermely dense, such as, for example, a gelatinous mass cannot be treated by direct radiation within an enclosure to change the state of the material because of the length of time for the microwaves to penetrate. Further, in certain instances the material would be seriously damaged by direct exposure to the heating energy. For this reason the prior art has also provided for hot water coil-type heating systems which are both costly and time consuming. A need arises, therefore, for an apparatus which incorporates the disposition of the material to be treated in a compartment removed from the heating means.

SUMMARY OF THE INVENTION In accordance with the teachings of the present invention, a microwave melter is disclosed for heating a localized region of a dense mass by indirect radiation from a heating compartment cavity resonator structure. An energy permeable wall member separates the respective compartments. As the less dense material is generated in the interface region by the radiated microwave energy it is rapidly removed by drainage perforations in the wall member through the empty heating compartment. In this manner dense masses which would require a long time period for penetration of any heating energy may be successfully treated by the gradual erosion of the interface layer of material adjacent to the energy permeable wall member.

The load within the treatment compartment which for foodstuffs may be of stainless steel composition is thereby gradually reduced until a no-load condition exists. Suitable circuitry for sensing and controlling the energy generator in such no-Ioad conditions are pro vided. Valving means for controlling the continuous flow of the incoming material to be treated with the outflow of the less dense material is also described in exemplary embodiments of the invention. The microwave energy is fed from underneath the material treatment compartment to indirectly radiate the interface region supported on the separation boundary wall.

The invention permits the selection of the treatment compartment independently of the heating compartment requirements. Hence where conductive walls are necessary for direct exposure ovens, modification is possible to include nonconductive materials. For photographic emulsions the apparatus is rendered lightproof by opaque surfaces on the inside of the treatment chamber and energy input lines. Numerous solid products such as coal with the chunks often frozen when stored outside in the winter environment in piles or railroad cars are another illustrative application where indirect heating by microwaves of dense masses is advantageous.

BRIEF DESCRIPTION OF THE DRAWING Details of an illustrative embodiment of the invention will be readily understood after consideration of the following description and reference to the accompanying drawings, wherein:

FIG. I is a vertical cross-sectional view of the apparatus embodying the invention;

FIG. 2 is a view, partly in section, taken in the direction indicated by line 2-2 in FIG. I; and

FIG. 3 is a fragmentary cross-sectional view of an alternative exemplary embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, apparatus 10 comprises a body member 12 which may, for example, be a cylindrical tank, is compartmentalized to provide treatment and heating regions. A cover member 14 is provided and may not be necessary in certain applications. Tapered bottom wall 16 terminates the opposing end of body member 12. Drainage pipe 18 together with suitable valve means 20 is provided in this wall for removal of the liquefied mass during the treatment. Pipe 18 is suitably dimensioned to minimize any loss of the microwave energy.

The material 22 to be treated is fed by means of a hopper-shaped input tank 24 through a pipe conductor 26 and valve means 28 in cover member 14 into treatment compartment 30 of a metallic or any desired compatible composition. Hollow heating compartment 32 having metallic walls defines a cavity resonator structure and is separated by means of a microwave energy permeable common wall member 34. Member 34 is illustratively of a disc-shaped configuration and defines a slightly concave top wall 36 extending upward. Circular support member 35 which may also be ofa compatiblc composition is joined to the walls of body member 12 to position the disc-shaped member. Drainage perforations 38 are circumferentially disposed adjacent the peripheral edge of wall member 34 to provide for removal of the condensate in the form of droplets 40 which flow along metal sidewalls of the empty heating compartment and are directed by bottom wall 16 and drainage pipe 18 into receiving tank 42 for distribution to further processing stages.

Microwave energy from a source 44, for example, a magnetron oscillator or any other well-known energy generator, is radiated within the empty heating compartment 32 by means of a transmission line 46 of a rectangular waveguide configuration. The inner end 48 is slightly tilted to prevent the flow of the condensate into the transmission line to create a mismatch condition. Line 46 also has a substantially S-shaped configuration to thereby prevent the entrance of any light from the outside within the apparatus when film emulsion materials are being processed. The microwave energy radiates from the metallic walls of heating compartment 32 which responds as a cavity resonator. The energy is directed to the common wall member 34 for indirect transmission therethrough to contact the layer of material to be treated at the interface region. The gradual erosion and successive decreasing of the quantity of the interface material thereby results. The side waveguide feed is preferred for certain applications while in other applications a bottom feed with the transmission line extending through wall 16 may be favored. In such structure the waveguide end projects far enough within the heating compartment 32 to be above the level of the condensate flow along the bottom wall 16. The waveguide transmission line is oriented with the electric field plane of the transmission mode in a horizontal direction so that the condensate material does not perturb this field. In those applications. where the less dense condensate material may emit vapors or moisture which would affect energy propagation, an energypermeable window may be provided at the end of the waveguide transmission line.

As the interface layer of material is depleted, compartment 30 reaches a no-load condition with a considerable portion of the microwave energy being reflected back through the waveguide transmission line to possibly cause the failure of the energy generator. The energy source may be adequately protected by means of a circulator 50 to direct the reflected energy in the reverse direction to an energy absorber 52. The heating of the absorbing load through an appropriate sensor to activate a relay 54 will decouple the microwave energy source 44 from the apparatus when the compartment 30 is empty.

Compartment 30 is provided with input valve means 28 in pipe 26 and drainage perforations 38 can also be provided with appropriate well-known valve means oriented at point 56 to permit drainage only when the heating energy is applied. A valve control system 60 with appropriate relay means 62 and switch 64 conductively energized by

leads

66 and 68 will open the drainage perforations 38 when the heating cycle commences with the opening of valve 28. The inner wall dimensions of the heating compartment 32 are selected to provide for resonance at the desired frequency of operation. Conventionally, a height of one-half or a multiple of a half wavelength will suffice.

in H6. 3 the adaptability of the invention to solid materials is illustrated in the form of chunks 70 of coal which have become frozen together by reason of being stores outside in a cold environment. A railroad car containing the solid material would be substantially similar to the walls of body member 12. A microwave energy permeable common wall member 34 supported by suitable means 35 provides for the exposure of the interface region of the mass to microwave energy indirectly radiates from below the resultant generation of droplets 72 of the melting liquid. Such liquid may be rapidly removed through the empty heating compartment 32 by appropriate means. The solidified mass may also be transported through the apparatus by conveyorized means to provide for the exposure of the interface region to the indirect mirrowave energy. Particulate materials may be treated with the disclosed apparatus to provide for the gradual decreasing of the interface mass exposed to the energy until the treatment compartment is emptied.

An efficient microwave melter apparatus is thus disclosed for the treatment of viscous, dense or solid masses to liquefy or reduce the density of the material. Numerous variations, alterations and modifications of the disclosed apparatus will be evident to those skilled in the art. It is intended, therefore, that the foregoing description of the invention and illustrative embodiments be considered in the broadest aspects and not in a limiting sense.

i l. A microwave heating apparatus comprising:

a body member including wall structure defining a compartment for material to be treated;

said member further including conductive wall structure defining a hollow heating compartment dimensioned to approximate a cavity resonator;

a nonmetallic perforated electromagnetic energy permeable common wall member separating said compartments; and

means for radiating electromagnetic energy within said heating compartment to heat and liquefy material in said treatment compartment resting on said common wall member.

2. Microwave apparatus as set forth in claim 1 wherein said common wall member is disc-shaped.

3. Microwave apparatus as set forth in claim 1 wherein said common wall member has a concave configuration.

4. Microwave apparatus as set forth in claim 1 wherein said energy is fed into said heating compartment by a sidewall feed.

5. Microwave apparatus as set forth in claim 1 wherein said energy is fed into said heating compartment by a bottom wall feed.

6. Mircowave apparatus as set forth in claim 1 wherein said compartments are superimposed in a vertical array with said treatment compartment comprising the upper position.

it t t 8

Claims

1. A microwave heating apparatus comprising: a body member including wall structure defining a compartment for material to be treated; said member further including conductive wall structure defining a hollow heating compartment dimensioned to approximate a cavity resonator; a nonmetallic perforated electromagnetic energy permeable common wall member separating said compartments; and means for radiating electromagnetic energy within said heating compartment to heat and liquefy material in said treatment compartment resting on said common wall member.