CN111356255A

CN111356255A - Uniform microwave heating equipment

Info

Publication number: CN111356255A
Application number: CN202010207751.6A
Authority: CN
Inventors: 王清源
Original assignee: Chengdu Saina Microwave Technology Co ltd
Current assignee: Chengdu Saina Microwave Technology Co ltd
Priority date: 2020-03-23
Filing date: 2020-03-23
Publication date: 2020-06-30

Abstract

The invention provides uniform microwave heating equipment which comprises two metal flat plates and at least one feed-in transmission line. The metal flat plate is provided with the two-dimensional periodic carrier, a broadband stop band is realized near the working frequency of the heating equipment, the feed-in transmission line is well isolated from other parts or other feed-in transmission lines, and the feed-in transmission line can be well matched through the tuner. The feed transmission line is a rectangular waveguide, the working mode of the feed transmission line is a TE10 mode, and the electric field of the feed transmission line is uniform in the transverse direction in a channel near a feed port of the feed transmission line, so that an object to be heated is uniformly heated in the transverse direction. The uniform microwave heating equipment has the advantages of simple structure and uniform heating, and can be widely used for heating and drying various materials, particularly low-cost, high-temperature and high-efficiency heating of low-humidity and low-absorption materials.

Description

Uniform microwave heating equipment

Technical Field

The invention relates to the field of uniform and efficient microwave heating, in particular to uniform microwave heating equipment.

Background

Microwave heating may be used in place of various conventional heating means. Microwave heating devices utilize microwave energy to heat various materials, including but not limited to wood, grain, medicinal materials, spices, dairy products, and the like. In the field of microwave chemistry, microwave energy is used to accelerate various chemical reactions. Microwave energy is also used in the production of new materials such as nanomaterials, synthetic diamonds, and the like.

In the conventional heating, because heat is conducted to the inside of the heated object through the outside of the heated object, the surface heating is adopted, and the temperature inside and outside the heated object is not uniform. Microwave heating is object heating in which the inside and outside of an object to be heated are heated simultaneously, and heat is generated by damping vibration of polar molecules in the object to be heated due to interaction between microwaves and the object to be heated. Thus, microwave heating may achieve faster and more uniform heating.

The size of a heating cavity of a common microwave oven is 3-5 times of the working wavelength. The size of a large heating cavity in the industrial microwave heating equipment is 20-1000 times of the working wavelength. The number of resonant modes that can be excited in these heating cavities at a certain operating frequency is several to several hundred. Any superposition of numerous resonant modes may produce a much greater electric field strength at some locations of the heating chamber than at others, severely affecting the uniformity of heating.

Technical personnel in international and domestic fields make continuous efforts to solve the problem of uniformity of microwave energy heating. Attempts have been made to improve the uniformity of heating by increasing the number of microwave feeds, changing the shape of the feeds, changing the position of the microwave feeds on the external surface of the heating chamber, or changing the polarization direction of the electric field at the microwave feeds, or simultaneously randomly changing the four variables. However, up to now, due to the high complexity of the problem, the microwave boundary lacks clear theoretical guidance for the problem, and the three-dimensional electromagnetic simulation is difficult to complete due to the huge calculation amount. Therefore, the problem of uniformity of heating in microwave ovens, particularly large microwave heating devices, has not been well solved.

Disclosure of Invention

The invention aims to provide uniform microwave heating equipment. Here we use a rectangular waveguide as the feed transmission line. The mode of operation of this waveguide is the TE10 mode, in which the electric field is uniform in the X direction. The microwave sources are isolated from each other, and each microwave source can be matched and adjusted through the adapter, so that the heated object can be uniformly and efficiently heated near the feed port of each feed transmission line. In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a uniform microwave heating device comprises a cover plate positioned in a Y direction, a bottom plate positioned in a-Y direction, at least 7 rows of carriers along an X direction and a Z direction, and at least 7 rows of carriers; the loading body is only contacted with the cover plate in the Y direction or contacted with the bottom plate in the-Y direction; a channel is arranged between the cover plate and the bottom plate; x, Y and the Z direction form a rectangular coordinate system.

The number of the carriers can be dozens of columns, dozens of rows to thousands of rows, and depends on the size of the heating device.

In general, in order to feed microwave energy into the channels of the heating apparatus, a plurality of feed transmission lines are required. These feed-in transmission lines can be arranged on the cover plate, on the base plate or on both the cover plate and the base plate. Due to the bandstop effect of the loading bodies distributed in the array, microwaves fed in from a feed-in transmission line are mainly present near the feed-in of the feed-in transmission line. In order to obtain a relatively uniform microwave field distribution at a level in the channel, the cover or the base plate, on which the feed transmission line is arranged, is preferably free of any loading bodies. Since the feed transmission line is disposed on a metal plate on which the loading body is disposed, the microwave in the feed path is disturbed by the loading body to affect the uniformity of the distribution thereof.

Typically, the cover plate, the base plate and the support are made of metal, such as aluminum alloy, stainless steel, etc.

The loading body is a cylindrical body with the axis parallel to the Y direction. The cross section of the material is round, rectangular or square.

In order to prevent the microwave from propagating on a horizontal plane in the channel in a wide frequency range near the working frequency of the heating device, a loading head is arranged at the top end of at least one loading body; the projection of the loading head along the Y direction comprises the projection of the loading body connected with the loading head along the Y direction. Further, a recess is provided in the cover plate or the bottom plate near the bottom end of the loading body. The groove surrounds the loading body.

To achieve microwave heating, the heating device further comprises an object to be heated located in the channel.

The invention provides uniform microwave heating equipment. The heating device comprises two metal plates. And a two-dimensional periodic loading body is arranged on one or two metal flat plates. Meanwhile, a loading head can be arranged on the loading body, and an annular groove can be arranged on the metal plate around the loading body. Such two metal plates can realize a microwave stop band within a wide bandwidth around the operating frequency of the heating device. When we feed microwave energy into the channel between two plates through a feed transmission line, the microwave will reach the channel but not propagate with the channel in the horizontal plane, but will be confined near the feed mouth of the feed transmission line. Since we use a rectangular waveguide as the feeding transmission line, the electric field of the TE10 mode is uniformly distributed in the X direction, which is beneficial to achieve uniform heating.

Drawings

Fig. 1 is a schematic top view of the present invention and example 1.

Fig. 2 is a schematic top view of embodiment 2.

Fig. 3 is a cross-sectional view in the direction AA of fig. 1 and 2.

FIG. 4 is a schematic top view of embodiment 3.

Fig. 5 is a cross-sectional view in the direction AA of fig. 4.

FIG. 6 is a schematic top view of embodiment 4.

Fig. 7 is a cross-sectional view in the direction AA of fig. 6.

Fig. 8 is an energy leakage coefficient (dB) of four sides of example 4.

Fig. 9 is a schematic top view of examples 5 and 6.

Fig. 10 is a cross-sectional view in the direction AA of fig. 9.

Fig. 11 is an energy leakage coefficient (dB) of four sides of example 5.

Fig. 12 is a cross-sectional view in the direction AA of fig. 9.

Fig. 13 is an energy leakage coefficient (dB) of four sides of example 6.

The reference numbers in the drawings correspond to the names: 1-cover plate, 2-bottom plate, 3-feed transmission line, 4-load carrier, 4A-load head, 4B-groove, 5-channel, 6-heated object.

Some of the terms (see FIGS. 1-2) in this specification are defined as follows:

horizontal, i.e. any plane parallel to the XZ plane.

Upward, i.e., Y-direction, i.e., vertically upward from the horizontal.

The lower, i.e. -Y direction, i.e. the direction vertically downwards from the horizontal.

And on the left, the X direction.

The right direction is the-X direction.

The bottom end of the loading body, i.e. the end of the loading body which is connected to the cover plate or the base plate.

The top end of the loading body, i.e. the end of the loading body remote from the top end thereof.

The operating wavelength is the wavelength in the air corresponding to the operating frequency of the microwave source of the heating device.

And (4) row: a plurality of targets having the same Z-direction position arrayed in the X-direction constitute one row.

The method comprises the following steps: a plurality of targets having the same X-direction position arrayed in the Z-direction constitute one column.

Feeding: the interface of any feed transmission line and any metal flat plate.

Detailed Description

Example 1

As shown in fig. 1 and 3.

A uniform microwave heating device comprises a cover plate 1 positioned in a Y direction, a bottom plate 2 positioned in a-Y direction, 7 columns of loading bodies 4 in an X direction and 7 rows of loading bodies in a Z direction; the loading body 4 is only contacted with the bottom plate 2 in the-Y direction; between the cover plate 1 and the base plate 2 a channel 5 is provided.

The channel 5 is shaped as a rectangular body, and three sides of the channel are parallel to the X direction, the Y direction and the Z direction respectively.

To feed the heating device with microwave energy, we have 1 feed transmission line 3. The transmission line 3 is arranged on the cover plate 1. Due to the bandstop effect of the loading bodies 4 distributed in an array, microwaves fed into the channel 5 from the feed transmission line 3 are confined only in the vicinity of the feed opening of the feed transmission line 3.

The cover plate 1, the bottom plate 2 and the loading body 4 are all made of metal.

The loading body 4 is a cylindrical body with the axis parallel to the Y direction.

The distance between the axes of the loading bodies 4 adjacent to each other in the X direction and the Z direction is 0.15-0.35 times of the working wavelength.

The height of the loading body 4 in the Y direction is 0.15-0.35 times of the working wavelength.

The cross-sectional shape of the loading body 4 is circular.

A loading head 4A is arranged at the top end of each loading body 4; the projection in the Y direction of the loading head 4A includes the projection in the Y direction of the loading body 4 connected thereto. The loading heads 4A are all in the shape of a circular tube, and the inner diameter of the loading heads is the same as the outer diameter of the loading body 4.

A recess 4B is provided in the bottom plate 2 near the bottom end of all the loading bodies 4. The groove 4B surrounds the loading body 4. The groove is circular, and the inner diameter of the groove is the same as the outer diameter of the loading body 4.

The feed transmission line 3 is a rectangular waveguide. The operating mode is TE10 mode. By this design, the microwave field is distributed relatively uniformly in the channel 5 in the X-direction in the horizontal plane in the vicinity of the feed transmission line 3. At this time, the electric field direction of the microwave in the rectangular waveguide is parallel to the X direction.

The height of the channel 5 in the Y direction is less than 0.5 times the operating wavelength.

An object to be heated 6 is provided in the tunnel 5.

Example 2

As shown in fig. 2 and 3.

Embodiment 2 differs from embodiment 1 only in that the cross-sections of the loading body 4, loading head 4A and recess 4B are all square.

Example 3

As shown in fig. 4 and 5.

Embodiment 3 differs from embodiment 1 only in that no groove 4B is provided.

Example 4

As shown in fig. 6-8.

Embodiment 4 differs from embodiment 1 only in that no loading head 4A is provided. No heated object 6 is provided.

The specific structure size is as follows: the loading body 4 is a metal cylinder with a diameter of 15.39 mm and a length of 21.82 mm. The distance between the axes of adjacent metal studs in the X-direction and in the Z-direction was 37.5 mm and the height of the channel 5 was 20 mm. The inner diameter of the groove 4B corresponds to the diameter of the loading body 4, and the width of the annular groove 4B in the radial direction is 4.51 mm and the depth thereof is 12.94 mm.

Fig. 8 is a graph of energy leakage coefficient (dB) with frequency for four sides of example 4 calculated by three-dimensional simulation. In the simulation calculations, microwave energy is fed from a rectangular waveguide into the transmission line 3 from the patch 1 into the channel 5. The four sides of the channel 5 are all arranged to match the boundary conditions. Any microwaves arriving from the feed transmission line 3 through the channel 5 to either side will be completely absorbed. From the energy leakage coefficient curve it can be seen how much microwave power entering the channel 5 from the feed transmission line 3 can propagate to the side and be absorbed over a certain frequency range.

It can be seen from fig. 8 that at many frequency points outside the 2.1 GHz-3.1 GHz bandwidth, most of the energy will pass through the channel 5 to its side. But in the 2.1 GHz-3.1 GHz band, only about 1% of the energy of the microwaves entering the channel 5 can propagate along the channel 5 to the side thereof.

Claims

1. A uniform microwave heating device, characterized by comprising a cover plate (1) located in Y direction, a bottom plate (2) located in-Y direction, at least 7 rows arranged in X direction and in Z direction, at least 7 rows of carriers (4); the loading body (4) is only contacted with the cover plate (1) in the Y direction or contacted with the bottom plate (2) in the-Y direction; the cover plate (1), the bottom plate (2) and the loading body (4) are all made of metal; at least one feed-in transmission line (3) is arranged on the cover plate (1) or the bottom plate (2); a channel (5) is arranged between the cover plate (1) and the bottom plate (2); the feed transmission line (3) transmits microwave energy to a channel (5) between the cover plate (1) and the bottom plate (2); the feed-in transmission line (3) is a rectangular waveguide, the working mode in the rectangular waveguide is a TE10 mode, and the electric field direction of the microwave in the rectangular waveguide is parallel to the X direction; x, Y and the Z direction form a rectangular coordinate system.

2. A uniform microwave heating device according to claim 1, characterized in that the loading body (4) is a cylindrical body with a circular, rectangular or square cross section with an axis parallel to the Y direction.

3. A homogeneous microwave heating device according to claim 1, characterized in that a loading head (4A) is provided at the top end of at least one of said loading bodies (4); the projection of the loading head (4A) along the Y direction comprises the projection of the loading body (4) connected with the loading head along the Y direction.

4. A uniform microwave heating device according to claim 1, characterized in that a recess (4B) is provided in the cover plate (1) or the bottom plate (2) near the bottom end of the loading body (4).

5. A uniform microwave heating device according to claim 4, characterized in that said recess (4B) surrounds said loading body (4).

6. A uniform microwave heating device according to claim 1, characterized in that in the channel (5) there is arranged an object (6) to be heated.