US3746822A - Split folded waveguide with leakage preventive apertures - Google Patents

Split folded waveguide with leakage preventive apertures Download PDF

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Publication number
US3746822A
US3746822A US00136727A US3746822DA US3746822A US 3746822 A US3746822 A US 3746822A US 00136727 A US00136727 A US 00136727A US 3746822D A US3746822D A US 3746822DA US 3746822 A US3746822 A US 3746822A
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US
United States
Prior art keywords
waveguide
conveyor
lips
elements
straight
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US00136727A
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English (en)
Inventor
Viet T Le
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Societe des Produits Nestle SA
Nestec SA
Original Assignee
Societe des Produits Nestle SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from CH707570A external-priority patent/CH515688A/fr
Priority claimed from CH255671A external-priority patent/CH528846A/fr
Application filed by Societe des Produits Nestle SA filed Critical Societe des Produits Nestle SA
Application granted granted Critical
Publication of US3746822A publication Critical patent/US3746822A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/78—Arrangements for continuous movement of material
    • A—HUMAN NECESSITIES
    • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23B—PRESERVATION OF FOODS, FOODSTUFFS OR NON-ALCOHOLIC BEVERAGES; CHEMICAL RIPENING OF FRUIT OR VEGETABLES
    • A23B2/00—Preservation of foods or foodstuffs, in general
    • A23B2/05—Preservation of foods or foodstuffs, in general by heating using irradiation or electric treatment
    • A23B2/08—Preservation of foods or foodstuffs, in general by heating using irradiation or electric treatment using microwaves or dielectric heating
    • A—HUMAN NECESSITIES
    • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23B—PRESERVATION OF FOODS, FOODSTUFFS OR NON-ALCOHOLIC BEVERAGES; CHEMICAL RIPENING OF FRUIT OR VEGETABLES
    • A23B2/00—Preservation of foods or foodstuffs, in general
    • A23B2/90—Preservation of foods or foodstuffs, in general by drying or kilning; Subsequent reconstitution
    • A23B2/92—Freeze drying
    • A—HUMAN NECESSITIES
    • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23F—COFFEE; TEA; THEIR SUBSTITUTES; MANUFACTURE, PREPARATION, OR INFUSION THEREOF
    • A23F5/00—Coffee; Coffee substitutes; Preparations thereof
    • A23F5/04—Methods of roasting coffee
    • A—HUMAN NECESSITIES
    • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23N—MACHINES OR APPARATUS FOR TREATING HARVESTED FRUIT, VEGETABLES OR FLOWER BULBS IN BULK, NOT OTHERWISE PROVIDED FOR; PEELING VEGETABLES OR FRUIT IN BULK; APPARATUS FOR PREPARING ANIMAL FEEDING- STUFFS
    • A23N12/00—Machines for cleaning, blanching, drying or roasting fruits or vegetables, e.g. coffee, cocoa, nuts
    • A23N12/08—Machines for cleaning, blanching, drying or roasting fruits or vegetables, e.g. coffee, cocoa, nuts for drying or roasting
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B3/00—Drying solid materials or objects by processes involving the application of heat
    • F26B3/32—Drying solid materials or objects by processes involving the application of heat by development of heat within the materials or objects to be dried, e.g. by fermentation or other microbiological action
    • F26B3/34—Drying solid materials or objects by processes involving the application of heat by development of heat within the materials or objects to be dried, e.g. by fermentation or other microbiological action by using electrical effects
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B2206/00—Aspects relating to heating by electric, magnetic, or electromagnetic fields covered by group H05B6/00
    • H05B2206/04—Heating using microwaves
    • H05B2206/046—Microwave drying of wood, ink, food, ceramic, sintering of ceramic, clothes, hair

Definitions

  • the straight elements are in even number, the length of the curved elements does not equal a whole multiple of a half-wavelength, the lips are grooved and the conveyor band carries the material from the end of the waveguide most remote from the microwave generator in the direction of the latter.
  • Other features of the invention are disclosed in the specification and drawing.
  • Microwave heating has, in principle, the advantage of speed.
  • the conditions of its application vary enormously with the materials.
  • the present invention concerns an apparatus for microwave heating granulated material, in particular for roasting cocoa beans and freeze-drying.
  • the heating time decreases with the increase of the frequency.
  • the distribution of the electric field along the waveguide would be extremely difficult to determine because of the major influence of the moisture of the material (up to l percent) and its variation along the tunnel.
  • the length of the tunnel could be found only be lengthy trial and error.
  • the invention provides a solution to these difficulties. It concerns an apparatus of the kind described, comprising a conveyor band carrying the material to be treated, a microwave generator and a split folded waveguide, the said waveguide having straight elements perpendicular to the direction of travel of the conveyor band, connected by curved elements, said straight elements being provided with slots for the passage of the conveyor'band and the material, and said slots having lips, the distance between said lips being not more than one-eighth of the wavelength in the waveguide.
  • FIG. 1 is a plan view.
  • FIG. 2 is a section of a transversal element of the waveguide along the line II II of FIG. 1.
  • FIG. 3 is an enlargement of a detail of FIG. 2.
  • FIG. 4 is a diagram of the stationary waves in two elements of the waveguide.
  • the apparatus comprises a microwave generator 1 connected to a split folded waveguide 2.
  • This waveguide has several straight elements 21, 22, 23, 24 connected by curved elements 31, 32, 33 and ends in an absorber 4 made of a water load or a cavity with ferrite walls.
  • This absorber is here purely as a safety measure because the energy emitted by the generator must be completely absorbed at the end of the waveguide for maximum efficiency.
  • the split folded waveguide has the advantage that straight elements can be added or removed to improve the efficiency.
  • the apparatus also comprises a conveyor band 5 driven by a motor 6.
  • This band is very thin and made of a material which is transparent" to microwaves, such as polytetrafluoroethylene (teflon) to prevent disturbances in the energy distribution.
  • the conveyor band is replaced by a vibrating bed.
  • the surface of the band is grained to reduce slippage between the band and the material carried on it.
  • a device equalises the thickness of the layer of material.
  • FIG. 2 is a section through a waveguide element.
  • the conveyor band 5 carries the material 7 and both pass through a slot 8 in the wall of the waveguide.
  • the slot has lips 9, the distance between them being not more than one-eighth of the wavelength in the waveguide.
  • the energy retained is reflected into the waveguide and tends to disturb the general distribution of energy inside the same.
  • the lips 9 are grooved inside as in 10 and the depth (1) of the groove is approximately equal to the distance h between the lips.
  • the cavity (of approximately square section) thus formed acts as a resonator in which the energy leakages remain stationary (FIG. 3).
  • This form is particularly necessary when the width of the slot (h) approaches a given fraction of the wavelength (Ag) in the waveguide. This fraction varies with the products; with cocoa beans (a difficult case because of their relatively large size) it is approximately one-eighth.
  • perforations are provided in the wall of the waveguide and/or of the tunnel. It has been found that if the diameter of the perforations does not exceed onefortieth of the wavelength, there are no energy losses. The perforations in the wall of the tunnel can even be larger because the energy leaking out of the lips and reaching the walls of the tunnel is very small.
  • the energy distribution along the waveguide is diagrammatically represented in FIG. 4.
  • the energy forms stationary waves with troughs 11 and peaks 12.
  • the curved element 3 should be of appropriate length, and must not equal a whole multiple of a half-wavelength.
  • the energy is progressively absorbed along the waveguide and therefore, if the power at the inlet of the upper element of FIG. 4 is 5W, by way of example, and is 4W at the outlet of this element, it will also be 4W at the inlet of the lower element and 3W at the outlet of the latter.
  • the apparatus is intended for roasting cocoa beans.
  • the generator provides 1,250W at 2,450 i 25 Megahertz, to which corresponds a wavelength of 12.24 cm in space.
  • the generator is connected to a waveguide type WR430 in which the wavelength Ag is 14.7716 cm.
  • the straight elements of the waveguide are perforated with circular holes of 3 mm diameter.
  • the height of the slots for the passage of the band and the material is 18 mm.
  • the beans, with a maximum diameter of 14 mm and an initial water content of 6.5 percent, are delivered at a rate of 15 kg/h. They are carried by a grained teflon band of 0.25 mm thickness and progress at 0.7 m/minute approximately.
  • the beans travel approximately 2 metres in 4 minutes. Their moisture content at the outlet is approximately 2 percent.
  • EXAMPLE 2 The apparatus is intended for freeze-drying frozen coffee extract.
  • the generator provides 1,500W.
  • the frequency, the wavelengths, the type of waveguide and the diameter of the perforations in the latter are the same as in Example 1.
  • the height of the slots for the passage of the band and the material is 14 mm, the thickness of the product layer 10 mm, the water content (in the form of ice) of the latter is 55 percent.
  • the material is carried by a grained teflon band of 28 cm width and 0.25 mm thickness travelling at 0.2 m/minute. The slippage being negligible, the output is 6 kg/h and the water content at the outlet 2 percent.
  • Microwave heating apparatus comprising a conveyor for carrying the material to be treated, a microwave generator and a split folded waveguide, the said waveguide having straight elements perpendicular to the direction of travel of the conveyor and curved elements alternately connecting said straight elements, said straight elements being provided with slots for the passage of the conveyor and the material and having spaced upper and lower lips adjacent said slots, each of said lips being provided with inwardly extending grooves together forming a resonator, the separation between said lips being not more than one-eighth-of the wavelength in the waveguide.
  • Microwave heating apparatus in which the width of the lip grooves is approximately one-ninth of the lip separation.

Landscapes

  • Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Food Science & Technology (AREA)
  • Polymers & Plastics (AREA)
  • Chemical & Material Sciences (AREA)
  • Microbiology (AREA)
  • Zoology (AREA)
  • Wood Science & Technology (AREA)
  • Health & Medical Sciences (AREA)
  • Electromagnetism (AREA)
  • Biomedical Technology (AREA)
  • Biotechnology (AREA)
  • Physics & Mathematics (AREA)
  • Molecular Biology (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Constitution Of High-Frequency Heating (AREA)
  • Drying Of Solid Materials (AREA)
  • Apparatuses For Bulk Treatment Of Fruits And Vegetables And Apparatuses For Preparing Feeds (AREA)
US00136727A 1970-05-13 1971-04-23 Split folded waveguide with leakage preventive apertures Expired - Lifetime US3746822A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH707570A CH515688A (fr) 1970-05-13 1970-05-13 Appareil pour la torréfaction de graines et produits analogues
CH255671A CH528846A (fr) 1971-02-23 1971-02-23 Appareil pour le chauffage de produits granulés

Publications (1)

Publication Number Publication Date
US3746822A true US3746822A (en) 1973-07-17

Family

ID=25690758

Family Applications (1)

Application Number Title Priority Date Filing Date
US00136727A Expired - Lifetime US3746822A (en) 1970-05-13 1971-04-23 Split folded waveguide with leakage preventive apertures

Country Status (7)

Country Link
US (1) US3746822A (enrdf_load_stackoverflow)
JP (1) JPS5323542B1 (enrdf_load_stackoverflow)
BE (1) BE766056A (enrdf_load_stackoverflow)
CA (1) CA923567A (enrdf_load_stackoverflow)
DE (1) DE2121229C3 (enrdf_load_stackoverflow)
FR (1) FR2091535A5 (enrdf_load_stackoverflow)
GB (1) GB1336181A (enrdf_load_stackoverflow)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4045639A (en) * 1973-01-16 1977-08-30 Food Processing Systems Corporation Continuous microwave and vacuum dryer
US4326114A (en) * 1978-12-11 1982-04-20 Gerling-Moore, Inc. Apparatus for microwave roasting of coffee beans
US20110174161A1 (en) * 2009-04-28 2011-07-21 Eugster/Frismag Ag Drink preparation machine, particularly espresso machine, comprising a height adjustable drink outflow unit
CN104667849A (zh) * 2015-02-06 2015-06-03 南京博炫生物科技有限公司 大功率微波反应器和微波连续压力反应系统
US20150351421A1 (en) * 2013-01-25 2015-12-10 Bühler Barth Gmbh Method and device for drying and/or roasting a food

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS55108798U (enrdf_load_stackoverflow) * 1979-01-23 1980-07-30
JPS567399U (enrdf_load_stackoverflow) * 1979-06-18 1981-01-22
DE3007143A1 (de) * 1980-02-26 1981-09-03 Eckhard Prof. Dr.-Ing. 1000 Berlin Krüger Verfahren zum darren von malz
JPS6094893U (ja) * 1983-12-02 1985-06-28 三菱電機株式会社 電子部品収納マガジン
JPS60163797U (ja) * 1984-04-06 1985-10-30 藤森工業株式会社 Ｉｃの係止機構
JPS6248991U (enrdf_load_stackoverflow) * 1985-09-13 1987-03-26
JPS6382786U (enrdf_load_stackoverflow) * 1986-11-17 1988-05-31
GB9009016D0 (en) * 1990-04-21 1990-06-20 Apv Baker Ltd Method and apparatus

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB882441A (en) * 1958-08-11 1961-11-15 Radyne Ltd Improvements in or relating to radio frequency dielectric heating apparatus
US3397296A (en) * 1964-06-02 1968-08-13 Ass Elect Ind Heating of substances by electrical energy at microwave frequencies
US3475577A (en) * 1966-11-02 1969-10-28 Philips Corp Apparatus for high frequency-heating in a wave guide
US3622733A (en) * 1970-01-28 1971-11-23 Cryodry Corp Method and apparatus for drying sheet materials
US3632945A (en) * 1969-04-16 1972-01-04 Cryodry Corp System and method for heating material employing oversize waveguide applicator

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB882441A (en) * 1958-08-11 1961-11-15 Radyne Ltd Improvements in or relating to radio frequency dielectric heating apparatus
US3397296A (en) * 1964-06-02 1968-08-13 Ass Elect Ind Heating of substances by electrical energy at microwave frequencies
US3475577A (en) * 1966-11-02 1969-10-28 Philips Corp Apparatus for high frequency-heating in a wave guide
US3632945A (en) * 1969-04-16 1972-01-04 Cryodry Corp System and method for heating material employing oversize waveguide applicator
US3622733A (en) * 1970-01-28 1971-11-23 Cryodry Corp Method and apparatus for drying sheet materials

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4045639A (en) * 1973-01-16 1977-08-30 Food Processing Systems Corporation Continuous microwave and vacuum dryer
US4326114A (en) * 1978-12-11 1982-04-20 Gerling-Moore, Inc. Apparatus for microwave roasting of coffee beans
US20110174161A1 (en) * 2009-04-28 2011-07-21 Eugster/Frismag Ag Drink preparation machine, particularly espresso machine, comprising a height adjustable drink outflow unit
US9585512B2 (en) * 2009-04-28 2017-03-07 Eugster/Frismag Ag Drink preparation machine, particularly espresso machine, comprising a height adjustable drink outflow unit
US20150351421A1 (en) * 2013-01-25 2015-12-10 Bühler Barth Gmbh Method and device for drying and/or roasting a food
CN104667849A (zh) * 2015-02-06 2015-06-03 南京博炫生物科技有限公司 大功率微波反应器和微波连续压力反应系统

Also Published As

Publication number Publication date
GB1336181A (en) 1973-11-07
BE766056A (fr) 1971-10-21
FR2091535A5 (enrdf_load_stackoverflow) 1972-01-14
DE2121229A1 (de) 1971-11-18
DE2121229C3 (de) 1974-03-07
JPS5323542B1 (enrdf_load_stackoverflow) 1978-07-15
CA923567A (en) 1973-03-27
DE2121229B2 (de) 1973-08-02

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