CN115802534A

CN115802534A - High-temperature microwave heating device

Info

Publication number: CN115802534A
Application number: CN202211233146.1A
Authority: CN
Inventors: 王清源
Original assignee: Wuxi Carbon Technology Co ltd
Current assignee: Wuxi Carbon Technology Co ltd
Priority date: 2022-10-10
Filing date: 2022-10-10
Publication date: 2023-03-14

Abstract

The invention provides a high-temperature microwave heating device which comprises a reaction cavity, at least one microwave feed port positioned at the bottom of the reaction cavity, a microwave source communicated with the other end of the microwave feed port, and a metal wire conveyor belt used for bearing a heated object and driving the heated object to move along the Z direction. The microwave feed port is rectangular, and the wide edge of the microwave feed port is parallel to the axial direction of the metal wire of the conveyor belt along the X direction. The conveyor belt passes through the reaction chamber. The invention can be used in household oven and high temperature treatment of various materials, such as ferrite and lithium gold ore.

Description

High-temperature microwave heating device

Technical Field

The invention relates to the field of uniform and efficient microwave heating or drying, in particular to a high-temperature microwave heating device.

Background

Microwave heating can replace various traditional heating modes. Microwave 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.

A tunnel furnace is a production facility that can continuously heat or dry materials. The microwave tunnel oven adopts an integral heating mode to replace the traditional conduction heating modes such as electric heating or gas and the like, can improve the production speed by several times to tens of times, and has great application prospect. The microwave tunnel oven generally comprises a reaction cavity, at least one microwave feed port, a microwave source communicated with the microwave feed port and at least one conveyor belt for bearing a heated object and driving the heated object to move. The conveyor belt passes through the reaction chamber. Each microwave source inputs microwave energy to the microwave feed port through one microwave feed port.

Despite its principle advantages, the use of microwave tunnel ovens is still in the beginning of the world. Three key technical problems that severely limit the application of microwave energy: non-uniformity of heating, low energy efficiency of heating, and mismatched burnout of microwave sources.

In a traditional microwave tunnel furnace, a reaction cavity is mostly a rectangular cavity, and the sizes of the reaction cavity in three directions are far larger than the working wavelength of a microwave source. The length and width of the reaction chamber are large, which is required for increasing the productivity. The height of the reaction chamber is large, one reason being to facilitate cleaning. In any cavity such as a reaction chamber of this kind, electromagnetic waves will resonate in the form of various natural modes of the cavity, the modes being excited in common, the electric field being of large amplitude at some locations in space and of small amplitude at other locations. At a typical microwave energy application frequency of 2450MHz, the distance between these electric field concentrations is half the operating wavelength, on the order of 62 mm, resulting in non-uniformity of the heated object over the corresponding dimension.

In order to solve the problem of uniformity of microwave heating, international and domestic companies have made continuous efforts. 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. Meanwhile, control of the electric field distribution in the reaction chamber and measurement of the temperature distribution inside the heated material are also difficult. Thus, the world's colleagues seek answers to questions on an "uncertain" road. On the premise of increasing the number of microwave sources to dozens to hundreds, people adopt microwave feed ports with different shapes, arrange the microwave sources on the inner top surface, the inner bottom surface, even the inner left surface and the inner right surface of the reaction cavity, change the polarization direction of an electric field at the microwave feed port of the rectangular waveguide, simultaneously adopt microwave sources with different frequencies, and adopt microwave sources with the frequency spectrum as wide as possible \8230. Attempts have been made to improve the uniformity of heating by increasing the complexity of the scheme. The method lacks theoretical guidance and mainly depends on continuous trial and error debugging. Three major bottleneck problems of microwave ovens, particularly large microwave tunnel ovens, namely the problem of non-uniformity of heating, the problem of low energy efficiency of heating and the problem of mismatched burning of microwave sources, are not solved well all the time.

Disclosure of Invention

The invention aims to provide an innovative scheme, and solves the problems of non-uniformity in heating, low heating energy efficiency and easy burning of a microwave source in the traditional microwave tunnel oven.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a high-temperature microwave heating device comprises a reaction cavity, at least one microwave feed port and a microwave source, wherein the microwave feed port is positioned at the bottom of the reaction cavity along the-Y direction and is communicated with the reaction cavity, and the microwave source is communicated with the microwave feed port. Typically, one said microwave feed and one said microwave source are provided at each end of a length of waveguide. The high-temperature microwave heating device also comprises at least one conveyor belt which is used for bearing the heated object and driving the heated object to move along the Z direction. The wide edge of the conveyor belt is along the X direction, and the conveyor belt penetrates through the reaction cavity.

To ensure that the apparatus can operate at high temperatures, such as 500 ℃,1000 ℃,1500 ℃, or even 2000 ℃, the conveyor is a wire conveyor. The conveyor belt comprises at least 10 adjacent wires in the Z-direction. The conveyor belt is formed of wires having an axis at an angle of less than 40 degrees to the X direction. In a preferred design, the angle between the axis of the conveyor belt and the X direction is 0 degree. The conveyor belt is formed of such adjacent wires and has the overall shape of a loop with its axis in the X-direction. A plurality of side chains are respectively arranged in the X direction and the-X direction. The number of side chains in one direction is one, and a plurality of side chains may be provided as necessary. The wires are connected to the side links in the X-direction and the-X-direction. The ends of the wire may be located inside, flush with or outside the outermost side chains in the X and-X directions, as desired. The region between the two side chains located at the center in the X direction is a heated object placing region. The metal wires and the side chains form a metal wire conveyor belt. Gaps exist between adjacent metal wires along the Z direction, and the sizes of the gaps along the Z direction are equal. In order to prevent the wire conveyor belt from shielding the microwaves, the cross-sectional dimensions of the wires making up the conveyor belt must be sufficiently small: the projected size of the wire in the XZ plane is less than one fifth of the minimum of the operating wavelengths of all the microwave sources. If a microwave source with a frequency of 2450MHz is used, the wire preferably has a maximum cross-sectional dimension of less than 10 mm. Further, the metal wire is a cylindrical body with a cross section shape which is constant along the axial direction, and the cross section shape of the metal wire is generally rectangular, and can also be circular, square, oval or other polygons. In order to prevent sparking at high microwave powers, the wire is generally rounded at sharp outward corners in its cross-sectional profile.

Further, the minimum dimension in the Z direction of the gap between adjacent wires in the Z direction is greater than five thousandths of the minimum value of the operating wavelengths of all microwave sources. The minimum gap in the Z direction between adjacent wires is greater than half the projected dimension of the cross section of the wire in the XZ plane.

The distance between adjacent wires cannot be too small, since the microwaves need to propagate upwards through said wires. For some applications, particularly very high temperature applications such as microwave ceramic sintering and microwave powder metallurgy, where it may be desirable to provide a dielectric plate or vessel, such as a crucible or the like, on the wire conveyor, the spacing of adjacent wires in the Z direction may be one or even tens of times the minimum of the operating wavelengths of all microwave sources. In this case, one function of the wire is to push the medium plate or medium vessel in the Z direction.

In a preferred design, the cross section of the microwave feed port in the XZ plane is rectangular. The cross section of the rectangular microwave feed port in the XZ plane is provided with a wide side and a narrow side which are perpendicular to each other. The included angle between the wide side of the cross section of the rectangular microwave feed port and the X direction is smaller than 40 degrees. In a better design, the included angle between the wide side of the cross section of the rectangular microwave feed port and the X direction is 0 degree. Due to the above arrangement of the axes of the wires of the conveyor belt and the broadside direction of the rectangular microwave feed opening, when the wires in the conveyor belt move in the Z-direction, the axial direction of the wires is perpendicular to the direction of the electric field in the rectangular microwave feed opening. This arrangement minimizes the reflection of microwaves near the microwave feed opening by the wires in the conveyor belt.

It can thus be seen that the present invention is configured with a metal structured conveyor belt for application to high temperatures. Wherein, a gap is formed among the metal wires of the conveyor belt, the gap is rectangular in an XZ plane, the wide edge of the gap is along the X direction, and the narrow edge of the gap is along the Z direction; the microwave feed port is arranged on the wide side of the rectangle of the XZ plane along the X direction, and the narrow side of the rectangle of the XZ plane along the Z direction. The metal wire of the conveyor belt and the microwave feed port are mutually cooperated, and the projection part of the conveyor belt at the microwave feed port along the Y direction is not provided with any connection along the Z direction, so that the influence of the metal wire on the microwave field near the microwave feed port is reduced as much as possible. Microwave energy may pass through the gap to heat the heated object above.

In order to isolate the different microwave feed openings well, a two-dimensional loading metal body or a pit is arranged on the inner surface of the top surface of the reaction chamber. Near the center point of at least one of the microwave feeds, there are at least 5 equally spaced loaded metal bodies or dimples in at least two mutually perpendicular directions in the XZ plane. In a preferred design, near the center point of each microwave feed opening, there are at least 5 equally spaced loading metal bodies or pits in at least two mutually perpendicular directions in the XZ plane. In this way, all microwave feed openings arranged at the bottom of the reaction chamber are isolated from each other by the use of the two-dimensional loading metal body or the recess.

In order to solve the problem of low interaction energy efficiency of the equipment, a microwave tuner is arranged between at least one microwave source and the microwave feed port communicated with the microwave source. In a preferred design, a microwave tuner is disposed between each microwave source and the microwave feed port communicated with the microwave source. The microwave tuner here is most commonly a rectangular waveguide pin tuner.

In order to protect the microwave source or prevent the working state of the microwave source from being influenced by the state of the heated object, an isolator is arranged between at least one microwave source and the microwave tuner communicated with the microwave source. Preferably, an isolator is arranged between each microwave source and the microwave tuner communicated with the microwave source. The isolator here is most commonly a rectangular waveguide isolator.

In order to reduce the total height of a microwave source assembly comprising a microwave source and a microwave tuner connected thereto, and possibly an isolator, a curved waveguide is provided at the end of at least one microwave tuner remote from the microwave feed. In a preferred design, a bent waveguide is disposed at an end of each microwave tuner away from the microwave feed port. Typically, the waveguide bends are 90-degree E-plane rectangular waveguide bends.

The invention provides a high-temperature microwave heating device. The innovation points of the invention are as follows: 1) The use of wires to form the conveyor belt in combination with a microwave source allows the heated material to be treated at high temperatures, such as 500 c, 1000 c, 1500 c, or even 2000 c. 2) The cross sections of all the microwave feed ports are rectangular, the wide sides of the cross sections of the rectangular microwave feed ports are along the X direction, and the axial direction of the metal wires in the conveyor belt is along the X direction. With this arrangement, the axial direction of the wires in the conveyor belt is perpendicular to the direction of the electric field in the rectangular microwave feed opening, minimizing the effect of the wires in the conveyor belt on the microwave field in the vicinity of the microwave feed opening. 3) The bent waveguide is additionally arranged outside each microwave tuner, so that the height of each microwave source assembly can be reduced, and the space below the reaction cavity of the equipment is saved.

Drawings

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

FIG. 2 is a schematic side view of example 2.

Fig. 3 is a schematic view showing the AA direction of fig. 1 and 2.

Fig. 4 is a schematic structural view of the vicinity of a microwave feed port of embodiment 3.

FIG. 5 is a graph showing the variation of the electric field amplitude (unit: V/m) in the microwave feed plane of the model of FIG. 3 with the narrow side direction of the waveguide.

FIG. 6 is a graph showing the variation of the electric field amplitude (unit: V/m) at 5 mm above the microwave feed plane of the model of FIG. 3 obtained by simulation along the narrow side direction of the waveguide.

The reference numbers in the drawings correspond to the names: 1-reaction cavity, 2-microwave feed port, 3-microwave source, 4-conveyor belt, 5-metal wire, 51-side chain, 6-loading metal body, 7-microwave tuner, 8-isolator, 9-bent waveguide and 10-heated object.

Some of the terms specified in this specification are as follows:

the working wavelength is the wavelength in the air corresponding to the central working frequency of a certain microwave source of the microwave tunnel oven.

Feeding a microwave port: a microwave source of the heating apparatus feeds a transmission line of microwave energy into the reaction chamber at an interface with an interior surface of the reaction chamber.

Detailed Description

Example 1

As shown in fig. 1 and 3.

A high-temperature microwave heating device comprises a

reaction cavity

1, 3 microwave feed ports 2 which are positioned at the bottom of the reaction cavity 1 along the-Y direction and are communicated with the reaction cavity 1, a total of 3 microwave sources 3 which are communicated with the other ends of the microwave feed ports 2, and a conveyor belt 4 which is used for bearing a heated object 10 and driving the heated object 10 to move along the Z direction. The wide edge of the conveyor belt 4 is along the X direction, and the conveyor belt 4 passes through the reaction chamber 1.

The conveyor belt 4 comprises at least 10 adjacent metal wires 5 along the Z direction, each side chain 51 is arranged in the X direction and the-X direction of the metal wires 5, the ends of the metal wires 5 in the X direction and the-X direction are arranged on the side chains 51, the area between the two side chains 51 is a heated object 10 placing area, the metal wires 5 and the side chains 51 form an annular conveyor belt, and the axes of the metal wires 5 are along the X direction. Gaps are present between adjacent wires 5 and the gaps are all equal in size in the Z-direction.

The maximum cross-sectional dimension of the wire 5 is less than one fifth of the minimum value of the operating wavelengths of all the microwave sources 3.

The size of the gap between the adjacent metal wires 5 along the Z direction is larger than five thousandths of the minimum value of the working wavelengths of all the microwave sources 3. The minimum gap in the Z direction between adjacent wires 5 is greater than half the projected dimension of the cross section of the wire 5 in the XZ plane.

The cross section of the microwave feed port 2 in the XZ plane is rectangular. The wide side of the cross section of the rectangular microwave feed port 2 on the XZ plane is along the X direction, and the narrow side is along the Z direction.

Referring to fig. 3, it can be seen that the present invention is configured with a metal structured conveyor belt in order to accommodate higher temperature heating. Gaps are formed among the metal wires of the conveyor belt, the gaps are rectangular in the XZ plane, the wide sides of the gaps are arranged along the X direction, and the narrow sides of the gaps are arranged along the Z direction. Moreover, the microwave feed port is arranged along the X direction on the wide side of the rectangle of the XZ plane, and the narrow side of the microwave feed port is also arranged along the Z direction. The two parts cooperate with each other to ensure that the conveyor belt is not provided with any connection along the Z direction at the projection part of the microwave feed port. The wire therefore has less influence on the microwave field in the vicinity of the microwave feed, the microwaves can pass through the gap with lower losses, and energy can pass through the gap to heat the heated object 10 above.

A two-dimensional loading metal body 6 is provided on the upper inner surface of the reaction chamber 1. Near the center point of each of said microwave feeds 2, there are at least 5 equally spaced loading metal bodies 6 in at least two mutually perpendicular directions in the XZ plane.

Between each microwave source 3 and the microwave feed port 2 communicated with it, 1 microwave tuner 7 is arranged.

Between each of the microwave sources 3 and the microwave tuner 7 connected thereto, 1 isolator 8 is provided.

At the end of each microwave tuner 7 remote from the

microwave feed

2, 1 curved waveguide 9 is provided.

Example 2

As shown in fig. 2 and 3.

On the basis of the above embodiment 1, the present embodiment is different from embodiment 1 in that: this embodiment is not provided with any bent waveguides.

Example 3

As shown in fig. 4-6.

The model is a part near a microwave feed port of a high-temperature microwave heating device and comprises a

reaction cavity

1 and 3 microwave feed ports 2 which are positioned at the bottom of the reaction cavity 1 along the-Y direction and are communicated with the reaction cavity 1.

The conveyor belt 4 comprises 11 adjacent wires 5 in the Z-direction, the axes of the wires 5 all being in the X-direction. Gaps are present between adjacent wires 5 and the gaps are all equal in size in the Z-direction.

The cross section of the metal wire 5 is circular, the maximum cross section size of the metal wire is 1 millimeter, and the maximum cross section size is about eight thousandths of the minimum value of the working wavelengths of all the microwave sources 3.

The size of the gap between the adjacent metal wires 5 along the Z direction is 4, which is larger than five thousandths of the minimum value of the working wavelength of all the microwave sources 3. The minimum gap between adjacent wires 5 in the Z direction is 4, which is greater than half the projection dimension of the cross section of the wire 5 in the XZ plane.

The height of the channel of the high-temperature microwave heating device is 30 mm. The width dimension of the microwave feed port is 86.36 mm, and the narrow side dimension is 43.18 mm. The loading metal body was a metal column having a length of 21.3 mm and a circular cross-sectional shape of 10 mm in diameter. The spacing between the axes of adjacent metal posts is 29.4 mm.

It can be seen from fig. 5 that at the microwave feed, the magnitude of the electric field strength along the narrow edge of the waveguide (not including the wire-according to the microwave principle, the electric field strength in the wire is 0) is between 900 and 1200V/m. At a distance from the microwave feed, the electric field strength decreases rapidly.

As can be seen from FIG. 6, the electric field intensity along the narrow side of the waveguide is very uniform in magnitude between 750 and 780V/m at a distance of 5 mm above the microwave feed. And the electric field intensity is rapidly reduced by a certain distance from the position right above the microwave feed port.

It can be seen from this embodiment that by arranging the axis of the wire parallel to the broad side of the microwave feed opening, the microwaves can well pass through the wire to reach the reaction chamber. When an object is placed in the high-temperature microwave heating apparatus, the object is effectively heated by microwaves from the microwave feed port.

The invention provides a high-temperature microwave heating device, which comprises a reaction cavity, at least one microwave feed port positioned at the bottom of the reaction cavity, a microwave source communicated with the other end of the microwave feed port, and a metal wire conveyor belt for bearing a heated object and driving the heated object to move along the Z direction. The microwave feed port is rectangular, and the wide edge of the microwave feed port is parallel to the axial direction of the metal wire of the conveyor belt along the X direction. The conveyor belt passes through the reaction chamber. The invention can be used in domestic ovens and also for treating various materials, such as ferrites and lithium gold ores.

The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. For example, in the present invention, the conveyor belts are all in a horizontal plane. In practical application, the bottom of the reaction chamber and the conveyor belt can be at various angles to the horizontal plane. The main innovation points of the invention are as follows: the metal wires are adopted to form the conveyor belt and are combined with the microwave source, and the heated object can be treated at high temperature, such as 500 ℃,1000 ℃,1500 ℃ or even 2000 ℃; the cross sections of all the microwave feed openings 2 are rectangular, the wide sides of the cross sections of the rectangular microwave feed openings 2 are along the X direction, and the axial direction of the metal wires in the conveyor belt is along the X direction. With this arrangement, the axial direction of the wires in the conveyor belt is perpendicular to the direction of the electric field in the rectangular microwave feed opening, minimizing the effect of the wires in the conveyor belt on the microwave field in the vicinity of the microwave feed opening. The bent waveguide is additionally arranged outside each microwave tuner, so that the height of each microwave source assembly can be reduced, and the space below the reaction cavity of the equipment is saved. According to the technical spirit of the present invention, any simple modification, equivalent replacement, and improvement made to the above embodiments within the spirit and principle of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A high-temperature microwave heating device comprises a reaction cavity (1), at least one microwave feed port (2) which is positioned at the bottom of the reaction cavity (1) along the-Y direction and is communicated with the reaction cavity (1), a microwave source (3) which is communicated with the microwave feed port (2), and at least one conveyor belt (4) which is used for bearing a heated object (10) and driving the heated object (10) to move along the Z direction; the conveyor belt (4) passes through the reaction cavity (1);

the conveyor belt (4) comprises at least 10 metal wires (5) which form an included angle of less than 40 degrees between the adjacent axial direction along the Z direction and the X direction, and side chains (51) which are respectively arranged in the-X direction and the-X direction; the metal wire (5) is connected with the side chain (51) in the X direction and the-X direction; gaps between adjacent metal wires (5) along the Z direction are equal; the directions X, Y, and Z constitute a rectangular coordinate system.

2. A high-temperature microwave heating device according to claim 1, characterized in that the projected size of the cross-section of the wire (5) in the XZ plane is less than one fifth of the minimum of the operating wavelengths of all the microwave sources (3).

3. A high temperature microwave heating device according to claim 1, characterized in that the minimum gap in the Z direction of adjacent wires (5) is more than five thousandths of the minimum value of the operating wavelength of all microwave sources (3).

4. A high-temperature microwave heating device according to claim 1, characterized in that the minimum gap in the Z-direction of adjacent wires (5) is greater than half the projection dimension of the cross-section of the wire (5) in the XZ-plane.

5. A high temperature microwave heating device according to claim 1, characterized in that the cross-section of the microwave feed (2) in the XZ plane is rectangular in shape.

6. A high temperature microwave heating device according to claim 5, characterized in that the angle between the broad side of the cross section of the microwave feed (2) in the XZ plane and the X direction is less than 40 degrees.

7. A high-temperature microwave heating device according to claim 1, characterized in that a two-dimensional loading metal body (6) or a pit is provided on the upper inner surface of the reaction chamber (1); near the center point of at least one of the microwave feeds (2), there are at least 5 equally spaced loading metal bodies (6) or dimples in at least two mutually perpendicular directions in the XZ plane.

8. A high-temperature microwave heating device according to claim 1, characterized in that between at least one of said microwave sources (3) and said microwave feed (2) communicating therewith, there is provided 1 microwave tuner (7).

9. A high temperature microwave heating apparatus according to claim 8, wherein 1 isolator (8) is further provided between at least one of said microwave sources (3) and said microwave tuner (7) communicating therewith.

10. A high-temperature microwave heating device according to claim 9, characterized in that between at least one of said isolators (8) and said microwave tuner (7) communicating with the isolator (8), there is provided 1 bent waveguide (9).