JP2008226510A - Microwave heating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out a continuous heating treatment of a flowing fluid load in a waveguide efficiently in a short time. <P>SOLUTION: In the apparatus provided with a waveguide 1 transmitting a TE10 mode with its either end blocked by a short-circuiting plate, a matching element 3 fitted at a side of the center inner wall face of a long side of the waveguide 1, a magnetron 4 fitted to an end of the waveguide for supplying microwave energy, a cylindrical tube 5 fitted at one end side of the waveguide 1 in penetration through top and bottom wall faces of the long side at an up-and-down center of the long side of the waveguide 1, and a fluid load 6 freely flowing in the cylindrical tube 5, a distance S between the cylindrical tube 5 and the waveguide short-circuiting plate 2 is to be (λg/4)+(n×λg/2), (provided, λg is an inner-tube wavelength, and n denotes 0, 1, 2, 3, ...). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a microwave heating apparatus that continuously heats a flowing liquid load in a waveguide.

  This type of conventional microwave heating apparatus moves the short-circuit plate installed near the load at the end of the waveguide in the tube axis direction and short-circuits in order to efficiently irradiate and heat the load with microwave energy. Adjust the plate insertion position and adjust the phase so that the microwave energy incident in the load direction generated by the magnetron and the microwave energy reflected back from the short-circuit plate are in phase at the load position. Trying to heat the load. (For example, Patent Documents 1 and 2). It is known to adjust this short-circuit plate, and the flange portion is connected to the flange portion of the waveguide terminal opening by screwing, and the adjustment of the short-circuit plate is carried out manually by using a screw screw connected to the short-circuit plate. It is rotated using a power source such as a motor so as to move back and forth along the tube axis.

JP 2006-181533 A JP-A-11-225007

  In the above prior art, the adjustment of the short-circuit plate is mainly aimed at the phase adjustment of the incident wave and the reflected wave of the microwave energy generated by the magnetron, and in order to efficiently heat the load in a short time, the phase adjustment of the short-circuit plate In parallel, the most important thing is to make the magnetron itself oscillate at the maximum output. In order for the magnetron to oscillate at the maximum output, the impedance viewed from the load side from the magnetron has capacitive and inductive characteristics so that it oscillates in the maximum output region on the Reike diagram showing the operating characteristics of the magnetron. It is necessary to adjust the phase and reflection by using a diaphragm or a stub as a matching element to achieve matching with the load. That is, it is difficult to achieve matching with the microwave heating device by adjusting only the short-circuit plate.

  Matching with the microwave heating device suppresses the reflected wave from the load and efficiently absorbs the microwave energy radiated by the magnetron, while also causing abnormal oscillation, antenna spark, abnormal heating of the anode, etc. Without adjusting the load to be heated so that the maximum output is stably radiated, and the reflection from the transmission line and load generally described in microwave engineering (in the phase It is different from (unless much) adjusting the minimum to suppress the reflected wave returning to the oscillator. That is, in the matching of the microwave heating device, in addition to reducing the reflected wave from the transmission path and the load, there is a difference in adjusting so that the output of the magnetron is maximized (weighting on the phase).

  Also, in microwave heating devices, the type of liquid load rarely changes with each heating, and the same type of liquid is often heated, so the dielectric constant for each type of food, such as a microwave oven that heats food. ε and dielectric loss angle tanδ do not change greatly. Therefore, it is only necessary to adjust the short-circuit plate once for the liquid load so as to increase the electric field strength, and adjustment for each heating is unnecessary in most cases, and the conventional method is a waste of time, labor and cost. there were. Furthermore, providing a movable part such as a short-circuit plate in a waveguide through which high-power microwave energy is transmitted can cause microwave leakage, abnormal heating, sparks, etc. in the gap between the inner walls of the waveguide in contact with the short-circuit plate. May occur.

  An object of the present invention is to solve the above-mentioned problems of the prior art and realize safe and highly efficient short-time heating without occurrence of microwave leakage, abnormal heating, sparks and the like.

  The present invention has been made to solve the above problems, and since the magnetron oscillates at the maximum output, the operating impedance when the liquid load side is viewed from the magnetron oscillates in the maximum output region on the Reike diagram. Thus, a matching element is provided on the inner wall surface side of the long side of the waveguide, and matching with the liquid load is performed by adjusting the phase and reflection. Furthermore, the shorting plate is fixed to the end of the waveguide, and the distance S between the cylindrical tube axis and the shorting plate is set so that the incident wave and the reflected wave are in phase at the liquid load position, that is, the electric field strength at the liquid load is maximized. (Λg / 4) + (n × λg / 2) (where λg is the guide wavelength, n is 0, 1, 2, 3,...). In addition, the angle α between the tube axis of the cylindrical tube containing the liquid load and the waveguide tube axis that passes through the upper and lower wall surfaces of the long side at the upper and lower centers of the waveguide is reflected. It was tilted from the minimum 14 degrees to 18 degrees.

  The microwave heating device of the present invention is provided with a matching element on the inner wall surface side of the long side of the waveguide so that the impedance when the liquid load side is viewed from the magnetron operates in the maximum output region as described above, and the phase and reflection are provided. Is adjusted to match the liquid load, and the short-circuit plate is fixed at the end of the waveguide, and the distance S to the cylindrical tube axis clogged with the liquid load is set to (λg / 4) + (n × (λg / 2), where λg is the guide wavelength and n is 0, 1, 2, 3,..., so that the liquid load is installed at the maximum electric field position. In addition, the inclination angle α between the tube axis of the cylindrical tube provided through the long side upper and lower wall surfaces at the upper and lower centers of the waveguide and the waveguide tube axis is inclined from 14 degrees to 18 degrees. As a result, the reflection is reduced and the microwave energy is efficiently absorbed by the liquid load. Therefore, there is no occurrence of microwave leakage, abnormal heating, sparks, etc., and safe and highly efficient heating can be realized in a short time.

  An embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 is a longitudinal sectional view of an essential part of a microwave heating apparatus showing an embodiment of the present invention, and FIG. 2 is a sectional view as seen from aa ′ in FIG. FIG. 3 is an external view of a matching element showing one embodiment. FIG. 4 is a Reike diagram showing the operating characteristics of the magnetron. FIG. 5 shows the analysis of the reflection coefficient Γ when the liquid load is tilted in the waveguide.

  Reference numeral 1 denotes a waveguide that transmits a TE10 mode in which both ends are closed by a short-circuit plate 2. A matching element 3 made of a conductor such as aluminum is provided on the inner wall surface side of the long side of the waveguide 1. A magnetron 4 for supplying microwave energy is provided at one end of the waveguide 1, and the other side of the waveguide 1 has upper and lower walls on the long side and at the center below the long side of the waveguide 1. A cylindrical tube 5 made of a material having a small dielectric loss such as quartz is provided. The cylindrical tube 5 is filled with a liquid load 6. Although not shown in this figure, a pump is actually provided in connection with the cylindrical tube 5 so that the liquid load 6 flows through the cylindrical tube 5.

  In the cylindrical tube 5 filled with the liquid load 6, the distance S between the center of the cylindrical tube 5 and the short-circuit plate 2 fixed to the waveguide 1 is (λg / 4) + (n × λg / 2). ) (Where λg is the guide wavelength, and n is 0, 1, 2, 3,...). Reference numeral 4 ′ denotes an antenna for radiating the microwave energy generated by the magnetron 4 into the waveguide 1. In this embodiment, the inclination angle α between the tube axis of the cylindrical tube 5 and the tube axis of the waveguide 1 is 90 degrees. However, the inclination angle α can be selected from 14 degrees to 18 degrees. It has become.

  Next, the effect | action by the above structure is demonstrated.

  The microwave energy generated from the magnetron 4 propagates through the waveguide 1 and is irradiated to the liquid load 6, and the microwave energy that has passed through the liquid load 6 is reflected by the short-circuit plate 2 and irradiated to the liquid load 6 again. . At this time, the matching element 3 is previously matched with the liquid load 6 so that the oscillation output of the magnetron 4 is maximized. Specifically, a pseudo antenna probe portion corresponding to the antenna 4 ′ of the magnetron 4 is attached to the waveguide 1 instead of the antenna 4 ′, and an oscillator that outputs microwave power of low power of several milliwatts instead of the magnetron 4 is output. Connect. The pseudo antenna probe unit is provided by a magnetron manufacturer.

  Next, the maximum output on the Reike diagram of the magnetron 4 is observed while observing the phase and reflection by moving the height and diameter of the matching element 3 in the tube axis direction with the waveguide 1 using a network analyzer. Adjust to get into the resulting area. As shown in Fig. 4, the Reike diagram is a Smith diagram used to calculate the impedance of an electric circuit or the like, and the magnetron iso-output lines and iso-frequency lines are described. The reflection is zero at the concentric center. Perfect matching at a standing wave ratio ρ = 1), the outermost circumference shows perfect reflection with infinite reflection, and the phase is clockwise with the reference of the antenna 4 'at the 12 o'clock position (clockwise) A half wavelength (λg / 2) is obtained by making a round around the load side.

  In the Reike diagram, the state of reflection is not shown by the reflection coefficient Γ but by the voltage standing wave ratio ρ, but it can be easily converted to the reflection coefficient Γ using a conversion formula. Here, λg is an in-tube wavelength obtained from the oscillation frequency f and the long side dimension of the waveguide 1. The long side dimension is a cross-sectional view of the rectangular waveguide 1 taken along a plane perpendicular to the tube axis direction, and is the horizontal width of the upper and lower wall surfaces, while the short side dimension is the height of the left and right side wall surfaces. It is. Next, regarding the operation of the matching element, for example, when the matching element 3 is not provided, assuming that the impedance in FIG. 4 is at the position P ′, the matching element 3 is placed in the waveguide and matched. P points. As can be seen, the output of the magnetron is 650 W at the point P ′, whereas an output difference of 900 W and 250 W is caused by the presence or absence of the matching element at the point P where matching is achieved. In other words, the matching element 3 itself is a kind of microwave three-dimensional circuit whose reflection can be adjusted mainly at the position where the matching element 3 is installed in the waveguide 1, and the impedance can be moved to a desired region.

  In this embodiment, the matching element 3 is made of an aluminum cylinder. However, the matching element 3 need not be a cylinder and can be made of a conductor having a low microwave loss if it has a rectangular shape such as a rectangular parallelepiped. The liquid load 6 is such that the phase of the microwave energy incident on the liquid load 6 generated by the magnetron 4 and the microwave energy reflected back from the short-circuit plate 2 is in phase at the position of the liquid load 6. Because the distance S to the short-circuit plate 2 is (λg / 4) + (n × λg / 2) (where λg is the wavelength in the tube, n is 0, 1, 2, 3,...) And is fixedly installed. In addition, since the liquid load 6 is irradiated with both incident wave and reflected microwave energy, heating is promoted. By adding the matching element 3 and using the fixed short-circuit plate 2 as described above, the maximum output of the magnetron 4 is extracted, the electric field strength of the liquid load 6 is increased, the heating is performed efficiently in a short time, and it is inexpensive and energy saving. It is a safe and reliable device.

  Next, the action of the inclination angle α between the waveguide 1 tube axis and the cylindrical tube 5 tube axis will be described. FIG. 5 shows reflection by varying the inclination angle α between the tube axis of the waveguide and the tube axis of the cylindrical tube provided through the upper and lower wall surfaces at the upper and lower sides of the waveguide. The coefficient Γ is obtained by magnetic field analysis. In this embodiment, the cylindrical tube 5 is installed perpendicularly (90 degrees) to the tube axis of the waveguide 1. As can be seen from the analysis result, the reflection is the highest when the inclination angle α is 16 degrees. It can be confirmed that the reflection is gradually small before and after that. There is an incident angle (Brewster angle in terms of optics) that minimizes reflection when the microwave is applied to the load. In this embodiment, the analysis results show that α is between 14 degrees and 18 degrees. It was. Therefore, by tilting the liquid load 6 within this angular range, it is expected that reflection is reduced and the liquid load 6 is efficiently absorbed by microwave energy.

It is a principal part longitudinal cross-sectional view of the microwave heating apparatus which shows one Example of this invention. It is sectional drawing seen from aa 'in FIG. It is an external view which shows one Example of a matching element. It is a Reike diagram which shows the operational characteristic of a magnetron. It is the result of analyzing the reflection coefficient Γ when the liquid load is tilted in the waveguide.

Explanation of symbols

1 Waveguide 2 Short-circuit plate 3 Matching element 4 Magnetron 5 Cylindrical tube 6 Liquid load

Claims (2)

  A waveguide that transmits a TE10 mode with both ends closed by a short-circuit plate, a matching element provided on the inner wall surface of the long side of the waveguide, and microwave energy provided at one end of the waveguide. A magnetron, a cylindrical tube provided on one end side of the waveguide through the long side upper and lower wall surfaces at the upper and lower sides of the waveguide, and a liquid load freely flowing in the cylindrical tube; The distance S between the cylindrical tube and the waveguide short-circuit plate is (λg / 4) + (n × λg / 2), where λg is the wavelength in the tube, n is 0, 1, 2, 3,. ...) A microwave heating apparatus characterized by that.   2. The microwave heating apparatus according to claim 1, wherein an inclination angle α between the tube axis of the cylindrical tube and the tube axis of the waveguide is inclined from 14 degrees to 18 degrees.

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