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EP1064827A1 - Appareil de chauffage par micro-ondes - Google Patents

Appareil de chauffage par micro-ondes

Info

Publication number
EP1064827A1
EP1064827A1 EP99910915A EP99910915A EP1064827A1 EP 1064827 A1 EP1064827 A1 EP 1064827A1 EP 99910915 A EP99910915 A EP 99910915A EP 99910915 A EP99910915 A EP 99910915A EP 1064827 A1 EP1064827 A1 EP 1064827A1
Authority
EP
European Patent Office
Prior art keywords
applicator
mode
microwave
microwave heating
load
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.)
Withdrawn
Application number
EP99910915A
Other languages
German (de)
English (en)
Inventor
Per Olov Risman
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.)
Rubbright Group Inc
Original Assignee
Rubbright Group Inc
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
Application filed by Rubbright Group Inc filed Critical Rubbright Group Inc
Publication of EP1064827A1 publication Critical patent/EP1064827A1/fr
Withdrawn legal-status Critical Current

Links

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
    • H05B6/70—Feed lines
    • 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
    • H05B6/6402—Aspects relating to the microwave cavity
    • 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
    • H05B6/70—Feed lines
    • H05B6/705—Feed lines using microwave tuning

Definitions

  • Microwave heating apparatus and system using same.
  • the present invention relates to the field of microwave heating, in particular to a microwave heating apparatus and a system using such apparatuses.
  • the invention is particularly suitable for heating flat loads heated while passing a microwave apparatus and carried on a suitable conveyor.
  • One prior art microwave heating apparatus typically operates at a predetermined frequency and comprises an open-ended microwave waveguide applicator which preferably has a rectangular cross-section and a longitudinal dimension from a closed end to second open end.
  • a metal plate is positioned opposite said open end parallel thereto and spaced therefrom such that a load can be in- serted into the space between said open end of the appli ⁇ cator and said metal plate.
  • the load is typically carried by a microwave transparent conveyor passing through said space close to said plate.
  • Means are provided for feeding microwaves of said predetermined frequency into the ap- plicator such that said microwaves propagate from said closed end towards said open end for being absorbed by the load so as to heat the same.
  • a microwave heating apparatus of the above-mentioned kind is disclosed in the European patent application No. 96108790.5. That application addresses the problems of even heating of the load, high efficiency and low leakage 2 of microwave energy away from the apparatus.
  • the application teaches a solution to these problems by using a particular combination of hybrid modes of a specific nature, undesired modes being prevented by making them non- resonant.
  • the excitation of a desirable combination of specific hybrid modes while suppressing undesired modes means rather complicated dimensioning and feeding consid ⁇ erations .
  • the object of this invention is to provide a further improved microwave heating apparatus while at the same time giving simplified considerations with regard to dimensioning of the applicator and the feeding of microwaves into it.
  • the above-mentioned object is achieved by means of a microwave heating apparatus, a microwave heating system incorporating such apparatuses and a use of such apparatuses having the features defined in the appended claims.
  • the invention is based upon an insight that the mode to be used in the applicator should be a resonant quarterwave mode when the relative effective permittivity (here called ⁇ ) of the load is low, typically below about 40, that is, the wave impedance of the mode be- ing higher within the load than in the applicator space. Consequently, according to a first aspect of the invention, there is provided a microwave heating apparatus having a waveguide applicator dimensioned so as to sup- 3 port a resonant quarterwave mode when heating a load having a low ⁇ .
  • the applicator is dimensioned so as to support a so-called Brewster mode when said ⁇ of the load is high, that is, typically above about 40.
  • a so-called Brewster mode when said ⁇ of the load is high, that is, typically above about 40.
  • a typical example in this respect is a drying process where the load initially is quite wet, thus having a very high ⁇ , and ends up being quite dry, thus having a very low ⁇ .
  • the use of a resonant quarterwave mode means that the heating effect will be substantially less sensitive to the height or thickness of the load than in prior art system, thereby also improving efficiency and flexibility of the microwave heating process.
  • the microwave leakage out from the microwave heating apparatus will be very low despite the resonance of the quarterwave mode, because the field components of said mode at the open end of the applicator will be such that no substantial Poynting vector out from the applicator will be created. Also, the induced currents in the applicator walls at the open end will be controlled in a favourable way.
  • the applicator is dimensioned and fed so as to support substantially only one dominating mode. It has surprisingly 4 been found that this can be achieved quite easily by having an excitation such as to eliminate unwanted modes, namely by having a suitable coupling slot positioned in the centre of the closed end of the applicator, the slot having an extension parallel to one of the side walls of the applicator, preferably parallel to a smaller dimension of a rectangular cross-section of the applicator.
  • the effective longitudinal dimension of the applicator corresponds to one quarter of the mode wavelength.
  • said longitudinal dimension could be increased by a number of full half wavelengths.
  • TM mn a dominating heating mode of the type TM mn .
  • m should be even and n should be odd.
  • n should be low, advantageously 1. It has been found that a particularly advantageous mode type is TM 6 ⁇ .
  • a microwave heating system comprising a plu- rality of microwave heating apparatuses of the kind dis- 5 cussed, said apparatuses being arranged in at least one row in a staggered configuration such that a load passing said apparatuses while being heated will be subjected to a very even heating.
  • the apparatuses of the row are mutually staggered a distance which is about a quarter of the free space wavelength of the applicator mode, whereby in the line of the row a cold spot of the heating pattern of an apparatus of the row will be followed by a hot spot of the heating pattern of the follow- ing apparatus of the row.
  • the staggered distance can be the transverse offset between two adjacent apparatuses of the row.
  • a third aspect of the invention means a use of a dominating resonant quarterwave mode in a so-called open- ended microwave waveguide applicator for heating a load at the open end of said applicator.
  • a fourth aspect of the invention means a use of a dominating resonant quarterwave mode/Brewster mode in a so-called open-ended microwave waveguide applicator for heating a load at the open end of said applicator, the dominating mode being a resonant quarterwave mode when the relative effective permittivity ⁇ of the load is low and a Brewster mode when said relative effec- tive permittivity ⁇ of the load is high.
  • Figure 1 is a schematic plan view of an embodiment of a microwave heating apparatus according to the invention.
  • Figure 2 is a schematic cross-sectional view of the apparatus of Figure 1, taken along line II-II in Figure 1.
  • FIG 3 is a schematic plan view of an embodiment of a microwave heating system comprising several microwave heating apparatuses of the kind disclosed in Figures 1 and 2, some of the microwave feeding means being removed for the sake of clarity.
  • Figure 4 is a schematic cross-sectional view of the system of Figure 3, taken along line IV-IV in Figure 3.
  • FIGS 1 and 2 schematically show an embodiment of an industrial microwave heating apparatus in accordance with the invention.
  • the apparatus shown comprises a metal waveguide applicator 1 having a rectangular horizontal cross-section and a vertical propagation direction of the microwaves excited in the applicator.
  • the upper horizontal end 3 of the applicator is closed.
  • a rectangular coup- ling slot 5 is provided in the centre of said closed end 3 of the applicator, the slot 5 extending parallell to the longer dimension of the rectangular cross-section of the applicator.
  • the coupling slot is fed by a conventional rectangular TEio waveguide 7 extending vertically and at its upper end connected to a microwave source 8, waveguide 7 being fed with an antenna 9.
  • Source 8 is mounted on the waveguide 7.
  • the end of waveguide 7 connecting to slot 5 has a decreasing internal height (so-called b-dimension) so as to finally being the same as the width of the slot.
  • the opposite end 11 of applicator 1 is horizontal and open while co-acting with a metal plane or plate 13 7 parallel to and spaced from said end 11 such that a tunnel-like load space 15 is provided therebetween.
  • the smaller side walls 16, 17 of applicator 1 are extended downwards and connected to said plate 13, thereby confin- ing said load space on two opposite sides, that is, the sides corresponding to the smaller dimension of the applicator cross-section.
  • the respective lower edges of applicator side walls 19, 20 of said two other sides are each provided with outwardly projecting metal flanges 21 and 22, re- spectively, that is, parallel to the metal plate 13.
  • metal flanges 21 and 22 help reducing microwave leakage to the outside.
  • said loads 25 can be wet objects, the microwaves heating the objects for drying purposes.
  • Applicator 1 is dimensioned and fed by means of cou- pling slot 5 in the closed end of the applicator so as to support only one dominating mode which is a resonant quarterwave mode when the relative effective permittivity ⁇ of the load in space 15 is low and which is a Brewster- mode when said ⁇ is high, there being an automatic change 8 of mode dependent on the actual ⁇ of the load.
  • the mode is of a general TM type in the load.
  • the effective vertical length or heigth of applicator is the distance between its closed end 3 and the load 25 and is preferably one quarter of the applicator mode wavelength. This means that there will be a long vertical wavelength resulting in low sensitivity to variations of the load height. Also, those field components which could produce leaking microwaves will be comparitively small over the entire height of the load space, that is, the tunnel opening.
  • the standing wave of the vertically directed E field will be minimum at the load.
  • the standing wave of the horizontal H field components will be minimum at the load, whereby there will be no substantial Poynting vector causing leakage of microwave to the outside.
  • the field components creating the heating of the load will be substantial.
  • their field "loops" advantageously should have a marked “ellipticity” (cf. Figure 3 to be described below) , so as to give a stronger excitation of the desired mode.
  • elongated H field ellipses are preferred, the direction of the elongation preferably being parallell to the extension of the coupling slot.
  • First cross-section dimension about 375-380 mm
  • Second cross-section dimension about 300 mm
  • Coupling slot width about 72 mm
  • Coupling slot length about 18 mm
  • the feeding waveguide 7 has a wide dimension (a) which is the same as the length of the slot 5. This results in a reduction of the strong currents in the waveguide iris which is otherwise created. A reduction of current concentrations is advantageous in view of the quite low wave impedance of the quarterwave resonant mode.
  • a plurality of microwave heating apparatuses of the kind described so as to give a microwave heating system that can take care of several loads at a time and can provide effective and even heating also when the ⁇ of the load varies during the heating process.
  • a microwave heating system is schematically shown in Figures 3 och 4, the microwave ge- nerating and feeding means being omitted but for the coupling slot 5, for clarity reasons.
  • the system of Figures 3 och 4 comprises eight apparatuses of the kind shown in Figures 1 and 2.
  • eight applicators 31 are arranged in two parallel rows above a common metal plate 33, each row thus having four applicators.
  • Adjacent applicators of each row are staggered relative to each other, so that the coupling slots of such adjacent applicators are transversly displaced or offset relative each other a certain distance.
  • 10 the coupling slots of the applicators of one row are transversly alternatingly displaced half said distance relative to a row centre line.
  • Each row of applicators heat an associated row of loads 35 carried by a common conveyor belt.
  • the applicators 31 all have circumferentially outwardly projecting flanges 39 (corresponding to flanges 21 and 22 in Figure 1) at their open end, the flanges of adjacent applicators being interconnected so as to provide a totally confined structure seen from above.
  • the respective flanges 39 are connected to vertical metal side elements 41, 43 which are connected to metal plate 33, thereby providing a completely confined tunnel-like configuration.
  • laterally adjacent applicators of the two parallel rows of applicators are spaced a suitable distance which in combination with the above- mentioned staggering of the applicators of a row will gi- ve an overall even heating pattern, that is, over the entire width of the heating system.
  • Using a microwave heating system in accordance with the invention means that the microwave energy of each applicator will be well confined by each applicator and the co-acting metal plate so that surprisingly there will be very little coupling (so-called crosstalk) between adjacent applicators in addition to a low leakage to the outside at the two slot-like openings of the tunnel-like load space.
  • the very low coupling between adjacent applicators eliminates the risk of loosing control of the hea- ting pattern as well as loss of power due to interaction of the multiple microwave generators used (that is, one generator for each applicator) .
  • an automatic mode alteration can be very advantageous when heating a load in a system having many applicators in series, because the 12 modes and the heating effects of the applicators automatically and successively will adjust to a changing ⁇ of the load, for instance due to a drying effect thereon.
  • the orientation of the applicators need not be vertical but can be changed due to specific operating conditions.
  • various configurations of mutually staggered microwave heating, apparatuses are possible in view of demands on length and width of the microwave heating system.
  • the cross section may also be allowed to vary somewhat, in order to accommodate needs for higher impedance in the ceiling (feeding) region, which is accomplished by larger dimensions there - or needs to achieve a stronger quarterwave resonance effect (with all its advantages) for load with reather high ⁇ , which is accomplished by making the applicator slightly smaller near its open end.
  • TM the type of TM in , where n is an integer.
  • Another embodiment which is space-saving is the use of regular hexagonal applicators in a honeycomb pattern.
  • the modes in such cross section applicators can be approximated by the modes in circularly cylindrical applicators. Analogous constraints and preferences thus apply.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Constitution Of High-Frequency Heating (AREA)

Abstract

L'invention concerne un appareil de chauffage par micro-ondes et un système de chauffage par micro-ondes comprenant une pluralité de tels appareils dans une configuration en quinconce. Chaque appareil comprend un applicateur guide d'onde à micro-ondes à extrémité ouverte dimensionné et alimenté de façon à tolérer un mode résonnant quart d'onde pour une charge de faible permittivité relative efficace.
EP99910915A 1998-03-16 1999-03-11 Appareil de chauffage par micro-ondes Withdrawn EP1064827A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
SE9800857 1998-03-16
SE9800857A SE512162C2 (sv) 1998-03-16 1998-03-16 Mikrovågsvärmningsapparat
PCT/SE1999/000375 WO1999048335A1 (fr) 1998-03-16 1999-03-11 Appareil de chauffage par micro-ondes

Publications (1)

Publication Number Publication Date
EP1064827A1 true EP1064827A1 (fr) 2001-01-03

Family

ID=20410558

Family Applications (1)

Application Number Title Priority Date Filing Date
EP99910915A Withdrawn EP1064827A1 (fr) 1998-03-16 1999-03-11 Appareil de chauffage par micro-ondes

Country Status (6)

Country Link
EP (1) EP1064827A1 (fr)
AU (1) AU2967399A (fr)
BR (1) BR9908773A (fr)
CA (1) CA2324155A1 (fr)
SE (1) SE512162C2 (fr)
WO (1) WO1999048335A1 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE0201755D0 (sv) 2002-06-07 2002-06-07 O Risman Improvements of hybrid mode rectangular heating applicators
SE526169C2 (sv) * 2003-09-02 2005-07-19 Exh Llc Mikrovågsvärmningsapplikator
WO2007069980A1 (fr) * 2005-12-13 2007-06-21 Exh Llc Applicateur de chauffage par micro-ondes

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB896422A (en) * 1958-10-16 1962-05-16 Philips Electrical Ind Ltd Improvements in or relating to the heating in tunnel furnaces of various substances by very high frequencies
FR2275961A1 (fr) * 1974-06-21 1976-01-16 Anvar Four tunnel a chauffage hyperfrequence
FR2478930A1 (fr) * 1980-03-20 1981-09-25 Technics Lambda Internal Applicateur a micro-ondes, notamment pour la vulcanisation ou la reticulation en continu de profiles, de tuyaux ou de cables a base de caoutchouc
US5828040A (en) * 1995-05-31 1998-10-27 The Rubbright Group, Inc. Rectangular microwave heating applicator with hybrid modes

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9948335A1 *

Also Published As

Publication number Publication date
SE512162C2 (sv) 2000-02-07
AU2967399A (en) 1999-10-11
BR9908773A (pt) 2000-11-14
CA2324155A1 (fr) 1999-09-23
SE9800857D0 (sv) 1998-03-16
SE9800857L (sv) 1999-09-17
WO1999048335A1 (fr) 1999-09-23

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