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 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.
• a TM021-type of field which has a maximum effect in the center and a minimum at the periphery.
• 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.
• As the field in the load is not homogenous it is necessary to use an integral function. This one is approximately proportional to J 0 2 (kr) . kr, where k is so estimated that the peripheral field (in a loss-free case) is zero, when k.r
• 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 TMlll. 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 j°) and another radial function J 1 (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 3 -function.
• the two first said resonances have a radial function of the radial field component according to the J 0 (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)
• Yarns And Mechanical Finishing Of Yarns Or Ropes (AREA)
• Endoscopes (AREA)
• Air-Conditioning For Vehicles (AREA)
• Heating, Cooling, Or Curing Plastics Or The Like In General (AREA)
• Control Of High-Frequency Heating Circuits (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20339628

Family Applications (1)

Country Status (9)

Citations (3)

Family Cites Families (3)

• 1979
  • 1979-12-21 SE SE7910621A patent/SE419494B/sv unknown
• 1980
  • 1980-12-17 AU AU67022/81A patent/AU6702281A/en not_active Abandoned
  • 1980-12-17 WO PCT/SE1980/000340 patent/WO1981001936A1/en not_active Ceased
  • 1980-12-17 AT AT80850191T patent/ATE7734T1/de not_active IP Right Cessation
  • 1980-12-17 JP JP81500333A patent/JPS56501819A/ja active Pending
  • 1980-12-17 DE DE8080850191T patent/DE3068079D1/de not_active Expired
  • 1980-12-17 EP EP80850191A patent/EP0031313B1/en not_active Expired
  • 1980-12-20 ES ES498027A patent/ES498027A0/es active Granted
• 1981
  • 1981-08-18 DK DK365681A patent/DK365681A/da not_active Application Discontinuation

Patent Citations (3)

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