EP0031313A1 - Through passing microwave heater - Google Patents
Through passing microwave heater Download PDFInfo
- Publication number
- EP0031313A1 EP0031313A1 EP80850191A EP80850191A EP0031313A1 EP 0031313 A1 EP0031313 A1 EP 0031313A1 EP 80850191 A EP80850191 A EP 80850191A EP 80850191 A EP80850191 A EP 80850191A EP 0031313 A1 EP0031313 A1 EP 0031313A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- applicator
- microwave
- load
- wall structure
- racterized
- 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.)
- Granted
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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
- H05B6/80—Apparatus for specific applications
- H05B6/802—Apparatus for specific applications for heating fluids
Definitions
- the present invention relates to a cylindrical microwave applicator for heating purposes with special arrangements for adjusting the heating density in a section through the cylindrical load, which is conveyed through the applicator along or parallelly with its longitudinal direction.
- Microwave applicators in which the load stuff is conveyed through a heating zone and heated to a predetermined temperature are known. If the stuff is in the form of a liquid it is conveyed through a microwave transparent tube through the zone.
- a microwave transparent tube through the zone.
- a TM021-applicator of a cylindrical shape is used for creating a heating zone in a rod-like load extended along the longitudinal direction of the applicator.
- the heating must be more effective in the center than at the periphery.
- TM021-type of field which has a maximum effect in the center and a minimum at the periphery.
- the TM021-resonator has properties which solve the problem of overheating of some parts of the load cross section and allows greater load diameters than priorly known types of applicators.
- the heating at the periphery of the load shall not, proportionally, be so small, as in the above said type of applicator.
- the applicator diameter for a given diameter and dielectric constant of the load can be calculated by an exact solution of the transcendental equations of the zero order of Bessel- and Neumann-functions and their first derivatives.
- the microwave heating in an applicator with modified measures according to the above-said but otherwise according to the Swedish Patent Specification No. 363 462 eminates substantially from the resonance amplification of the dominating TM020 field, if the length of the applicator in the axial direction is about the same as its diameter.
- other oscillation modes can arise. Among several oscillation modes are just such ones of the TM-type possible in practice, first for the reason that the introduction of microwave energy to the applicator is effected by a loop connected to the magnetic field and then for the reason that the major part of connection of the field to the load is effected when the electric field vector is substantially parallell to the surface of the load.
- the resonance field patterns which can generally prevail during the above given circumstances are TM011, TM012, TM110 and TM111. These notations for modes are generally accepted and are explained as follows:
- the first index after "TM" means the number of hole cycles in the angular direction during one revolution around the axis, the second index states the number of minima of the E-field in a radial direction from the axis to the periphery, the third and last index is the number of half wave lengths in the axial direction of a standing wave in the applicator.
- the two first said modes have no field variation in the angular direction in the cylindrical applicator, but the two others have an angular function (cos 10) and another radial function J l (kr) of the radial field component which is zero on the axis and has a maximum at a somewhat less value of r than the zero point of the J -function.
- the two first said resonances have a radial function of the radial field component according to the J (kr) function, i.e. the same as the "basic mode" TM020 - yet another value of k which will be different owing to the different connection to the rod-like load. All four "distorsion modes" have variations in the axial direction (z-) bringing about a tendency of an increase of the heating at the periphery of the load.
- the purpose of the invention consists of an embodiment of an applicator with variable inner cross section dimensions.
- the arrangement for enabling this feature is stated in detail in the characterizing clause of Claim 1.
- Fig. 1 a perspective view of the applicator, wave guide and generator, Fig. 2 a cross section through the applicator.
- FIG. 1 An apparatus of a through passing type and microwave heating based on the theory of the microwave field according to the foregoing is shown in Fig. 1.
- the load is conducted in a tube 1 through a cylindrical applicator 2 provided with end walls 3 penetrated by the tube.
- This one can be displaced in a radial direction and by such a displacement the field pattern can be located to the axial center of the load.
- the displacement of the load has been carried out by means of a flange 4 on the tube 1 at each end wall, where the tube pass through in a rather big hole.
- the tube can then be displaced laterally in this hole and fixed in an adjusted position by means of a couple of retainers 5, which by means of screws keep the flange pressed against the end wall.
- the position of the tube at the one end can be adjusted independent of its position at the other end.
- the technical embodiment of the arrangement for adjustment of the diameter of the applicator is shown on the drawing in the shape of a flexible sheet 6, which resiliently abuts the cylindrical surface 7 of the applicator and the inner surfaces of the end walls.
- the sheet is kept in this position by a couple of adjusting screws 8 each one penetrating a hole in the cylindrical wall and having a nut 9 on its end.
- the length of the screws determines how far the position of the sheet can be changed and thus how much the cross section of the applicator cavity can be decreased.
- the surface currents on its inside will have components in the axial direction but not in the angular direction. This will mean that special arrangements for achieving a good contact between the sheet 6 and the cylindrical surface 7 need not be used.
- a higher demand for a good contact is put on the abutment of the sheet against the inside of the end walls 3, where the edge of the sheet is slitted so that thus produced contact tongues 10 can slide against the inside of the end wall making a good contact when the sheet edge is moved over the inside.
- the cross section of the load is predetermined as the stuff to be heated has a determined thickness.
- the applicator shall be, e.g. a TM020-resonator, the designer choses a somewhat great value of the diameter of the applicator casing than what is chosen according to an ordinary dimensioning of a TM020-resonator.
- the position of the load in the applicator is adjusted empirically (by means of the flanges 4) and the cross section of the applicator cavity (adjustments of the sheet) so that the heating density in the load in the cross section thereof will be symmetrical, i.e. constant in the angular direction.
- a matching adjustment can be carried out by a stub in the wave guide so that a sufficiently good microwave matching of the applicator to the microwave generator is achieved.
- the described embodiment may be regarded as example of the invention with a reservation for other possible applicator apparatus for a variable determining of the cross section, which in fact need not have the illustrated circular shape but, for instance, a polygon.
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Constitution Of High-Frequency Heating (AREA)
- Resistance Heating (AREA)
- Endoscopes (AREA)
- Air-Conditioning For Vehicles (AREA)
- Yarns And Mechanical Finishing Of Yarns Or Ropes (AREA)
- Heat Treatment Of Articles (AREA)
- Heating, Cooling, Or Curing Plastics Or The Like In General (AREA)
- Control Of High-Frequency Heating Circuits (AREA)
Abstract
Description
- The present invention relates to a cylindrical microwave applicator for heating purposes with special arrangements for adjusting the heating density in a section through the cylindrical load, which is conveyed through the applicator along or parallelly with its longitudinal direction.
- Microwave applicators in which the load stuff is conveyed through a heating zone and heated to a predetermined temperature are known. If the stuff is in the form of a liquid it is conveyed through a microwave transparent tube through the zone. Such a device is known from the Swedish Patent Specification No. 363 462. In this one a TM021-applicator of a cylindrical shape is used for creating a heating zone in a rod-like load extended along the longitudinal direction of the applicator. As a flow in a tube, owing to friction, does not have the same flow velocity at the periphery of the cross section area as in the center, the heating must be more effective in the center than at the periphery. In order to achieve such a distribution of the heating effect in the cross section it is used in a known applicator a TM021-type of field which has a maximum effect in the center and a minimum at the periphery. By such a distribution of the effect over the cross section area of the load it is possible to avoid more heating of some parts than others and over-heating of the peripherial parts. It is shown in the said patent specification that the TM021-resonator has properties which solve the problem of overheating of some parts of the load cross section and allows greater load diameters than priorly known types of applicators.
- However, if the load is conveyed through the applicator in contact with a conveying tube, band or the like it is desirable that the heating at the periphery of the load shall not, proportionally, be so small, as in the above said type of applicator. In fact, the applicator diameter for a given diameter and dielectric constant of the load can be calculated by an exact solution of the transcendental equations of the zero order of Bessel- and Neumann-functions and their first derivatives. However, it may be successful to use approximative calculation methods. As the field in the load is not homogenous it is necessary to use an integral function. This one is approximately proportional to Jo 2 (kr) . kr, where k is so estimated that the peripheral field (in a loss-free case) is zero, when k.r = 2,405.
- The microwave heating in an applicator with modified measures according to the above-said but otherwise according to the Swedish Patent Specification No. 363 462 eminates substantially from the resonance amplification of the dominating TM020 field, if the length of the applicator in the axial direction is about the same as its diameter. However, also other oscillation modes can arise. Among several oscillation modes are just such ones of the TM-type possible in practice, first for the reason that the introduction of microwave energy to the applicator is effected by a loop connected to the magnetic field and then for the reason that the major part of connection of the field to the load is effected when the electric field vector is substantially parallell to the surface of the load.
- The resonance field patterns which can generally prevail during the above given circumstances are TM011, TM012, TM110 and TM111. These notations for modes are generally accepted and are explained as follows: The first index after "TM" means the number of hole cycles in the angular direction during one revolution around the axis, the second index states the number of minima of the E-field in a radial direction from the axis to the periphery, the third and last index is the number of half wave lengths in the axial direction of a standing wave in the applicator. The two first said modes have no field variation in the angular direction in the cylindrical applicator, but the two others have an angular function (cos 10) and another radial function Jl (kr) of the radial field component which is zero on the axis and has a maximum at a somewhat less value of r than the zero point of the J -function. The two first said resonances have a radial function of the radial field component according to the J (kr) function, i.e. the same as the "basic mode" TM020 - yet another value of k which will be different owing to the different connection to the rod-like load. All four "distorsion modes" have variations in the axial direction (z-) bringing about a tendency of an increase of the heating at the periphery of the load.
- By the arrangement described in the Swedish Patent Specification No. 7801280-4 a possibility is introduced to displace the load parallelly with the cylinder axis in a radial direction, whereby a certain change in the connection of the basic oscillation in the applicator is achieved. This change can easily be compensated as known per se by a so called stub in the wave guide feeding the applicator.
- In consequence of the useful changes of the applicator and the load positioning therein in relation to the theoretical basic principles the appearance of the composite field pattern will be difficult to calculate. It is therefore suggested also to change the diameter of the applicator and in an empirical way achieve an improvement of the applicator. In principle, this change brings about a diplacement of all resonances of the system - thus, in practice, a possibility to change the balance between the basic mode and other modes. As all the above said other modes make an amplification of the electric field of the periphery of the load they contributes to an equalization of the composite field strength and thus also of the heating velocity over the hole cross section area of the load. As only the two added modes TM110 and TM111 have variations in the angular direction but locked in one and the same position in relation to the antenna member a field adjustment is possible to achieve just by making the changes of the tube in the radial direction and the diameter of the applicator. Such an adjustment involves in general that the operating frequency of the microwave generator does not correspond to any of the considered resonance frequency peaks. However, it is stated in the Swedish Patent Specification No. 363 462 that the Q-value is proportionally small and thus the band width, where a good efficiency is obtained, so great that just by a matching adjustment with the aforesaid stub it is possible to reach a sufficiently good microwave matching within a necessary generator frequency range.
- The purpose of the invention consists of an embodiment of an applicator with variable inner cross section dimensions. The arrangement for enabling this feature is stated in detail in the characterizing clause of
Claim 1. - An embodiment of the applicator according to the invention is described in the following with references to the accompanying drawing which shows in Fig. 1 a perspective view of the applicator, wave guide and generator, Fig. 2 a cross section through the applicator.
- An apparatus of a through passing type and microwave heating based on the theory of the microwave field according to the foregoing is shown in Fig. 1. The load is conducted in a
tube 1 through a cylindrical applicator 2 provided with end walls 3 penetrated by the tube. This one can be displaced in a radial direction and by such a displacement the field pattern can be located to the axial center of the load. In the shown embodiment of the applicator the displacement of the load has been carried out by means of aflange 4 on thetube 1 at each end wall, where the tube pass through in a rather big hole. The tube can then be displaced laterally in this hole and fixed in an adjusted position by means of a couple of retainers 5, which by means of screws keep the flange pressed against the end wall. The position of the tube at the one end can be adjusted independent of its position at the other end. - The technical embodiment of the arrangement for adjustment of the diameter of the applicator is shown on the drawing in the shape of a
flexible sheet 6, which resiliently abuts the cylindrical surface 7 of the applicator and the inner surfaces of the end walls. The sheet is kept in this position by a couple of adjusting screws 8 each one penetrating a hole in the cylindrical wall and having anut 9 on its end. The length of the screws determines how far the position of the sheet can be changed and thus how much the cross section of the applicator cavity can be decreased. As it is designed for TM-modes the surface currents on its inside will have components in the axial direction but not in the angular direction. This will mean that special arrangements for achieving a good contact between thesheet 6 and the cylindrical surface 7 need not be used. A higher demand for a good contact is put on the abutment of the sheet against the inside of the end walls 3, where the edge of the sheet is slitted so that thus producedcontact tongues 10 can slide against the inside of the end wall making a good contact when the sheet edge is moved over the inside. - This now added feature to change the cross section of the applicator offers a greater liberty to dimension the cross section of the load which no longer needs to follow the formula from the Patent Specification 363 462 strictly, i.e. the radius of the cross section of the load = the first minimum in the function J (r).Jo*(r) where
- In many practical cases the cross section of the load is predetermined as the stuff to be heated has a determined thickness. By assuming that the applicator shall be, e.g. a TM020-resonator, the designer choses a somewhat great value of the diameter of the applicator casing than what is chosen according to an ordinary dimensioning of a TM020-resonator. By way of experimental measuring and adjustments the position of the load in the applicator is adjusted empirically (by means of the flanges 4) and the cross section of the applicator cavity (adjustments of the sheet) so that the heating density in the load in the cross section thereof will be symmetrical, i.e. constant in the angular direction. As said in the introduction a matching adjustment can be carried out by a stub in the wave guide so that a sufficiently good microwave matching of the applicator to the microwave generator is achieved.
- The described embodiment may be regarded as example of the invention with a reservation for other possible applicator apparatus for a variable determining of the cross section, which in fact need not have the illustrated circular shape but, for instance, a polygon.
Claims (4)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT80850191T ATE7734T1 (en) | 1979-12-21 | 1980-12-17 | MICROWAVE CONTINUOUS HEATING OVEN. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
SE7910621 | 1979-12-21 | ||
SE7910621A SE419494B (en) | 1979-12-21 | 1979-12-21 | MICROWAG TYPE FLOW HEATER CONTAINING A CYLINDRIC MICROWAG APPLICATOR |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0031313A1 true EP0031313A1 (en) | 1981-07-01 |
EP0031313B1 EP0031313B1 (en) | 1984-05-30 |
Family
ID=20339628
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP80850191A Expired EP0031313B1 (en) | 1979-12-21 | 1980-12-17 | Through passing microwave heater |
Country Status (9)
Country | Link |
---|---|
EP (1) | EP0031313B1 (en) |
JP (1) | JPS56501819A (en) |
AT (1) | ATE7734T1 (en) |
AU (1) | AU6702281A (en) |
DE (1) | DE3068079D1 (en) |
DK (1) | DK365681A (en) |
ES (1) | ES8200988A1 (en) |
SE (1) | SE419494B (en) |
WO (1) | WO1981001936A1 (en) |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3344254A (en) * | 1967-09-26 | Radio frequency heating apparatus | ||
DE2162851A1 (en) * | 1970-12-31 | 1972-07-20 | Soulier J | Oven working with hyperfrequency waves for the continuous treatment of foils or strips made of a material that absorbs these waves |
DE1907448B2 (en) * | 1969-02-14 | 1976-02-26 | Fritz, Karl, Dr., 4973 Vlotho | Variable wavelength microwave oven using cooking medium - allows adjustment of wavelength to suit the cooked object which is embedded in an efficiency improving medium |
DE2345706B2 (en) * | 1972-09-13 | 1976-06-10 | Husqvama AB, Jönköping (Schweden) | METHOD AND DEVICE FOR MICROWAVE HEATING OF A ROD-SHAPED HEATING MATERIAL |
DE2903984A1 (en) * | 1978-02-03 | 1979-08-16 | Husqvarna Ab | METHOD AND EQUIPMENT FOR PREPARING FOOD WITH PROTEIN CONTENT |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB579317A (en) * | 1942-02-13 | 1946-07-31 | Albert Frederick Pearce | Improvements in or relating to electron discharge devices employing hollow resonators |
FR1569046A (en) * | 1968-03-29 | 1969-05-30 | ||
US3597567A (en) * | 1969-09-24 | 1971-08-03 | Ray M Johnson | Microwave applicator for heating continuous web |
-
1979
- 1979-12-21 SE SE7910621A patent/SE419494B/en unknown
-
1980
- 1980-12-17 DE DE8080850191T patent/DE3068079D1/en not_active Expired
- 1980-12-17 AT AT80850191T patent/ATE7734T1/en not_active IP Right Cessation
- 1980-12-17 AU AU67022/81A patent/AU6702281A/en not_active Abandoned
- 1980-12-17 EP EP80850191A patent/EP0031313B1/en not_active Expired
- 1980-12-17 JP JP81500333A patent/JPS56501819A/ja active Pending
- 1980-12-17 WO PCT/SE1980/000340 patent/WO1981001936A1/en unknown
- 1980-12-20 ES ES498027A patent/ES8200988A1/en not_active Expired
-
1981
- 1981-08-18 DK DK365681A patent/DK365681A/en not_active Application Discontinuation
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3344254A (en) * | 1967-09-26 | Radio frequency heating apparatus | ||
DE1907448B2 (en) * | 1969-02-14 | 1976-02-26 | Fritz, Karl, Dr., 4973 Vlotho | Variable wavelength microwave oven using cooking medium - allows adjustment of wavelength to suit the cooked object which is embedded in an efficiency improving medium |
DE2162851A1 (en) * | 1970-12-31 | 1972-07-20 | Soulier J | Oven working with hyperfrequency waves for the continuous treatment of foils or strips made of a material that absorbs these waves |
DE2345706B2 (en) * | 1972-09-13 | 1976-06-10 | Husqvama AB, Jönköping (Schweden) | METHOD AND DEVICE FOR MICROWAVE HEATING OF A ROD-SHAPED HEATING MATERIAL |
DE2903984A1 (en) * | 1978-02-03 | 1979-08-16 | Husqvarna Ab | METHOD AND EQUIPMENT FOR PREPARING FOOD WITH PROTEIN CONTENT |
Also Published As
Publication number | Publication date |
---|---|
DK365681A (en) | 1981-08-18 |
ES498027A0 (en) | 1981-11-16 |
ES8200988A1 (en) | 1981-11-16 |
AU6702281A (en) | 1981-07-22 |
SE419494B (en) | 1981-08-03 |
WO1981001936A1 (en) | 1981-07-09 |
DE3068079D1 (en) | 1984-07-05 |
ATE7734T1 (en) | 1984-06-15 |
EP0031313B1 (en) | 1984-05-30 |
SE7910621L (en) | 1981-06-22 |
JPS56501819A (en) | 1981-12-10 |
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