Microwave heating device and microwave heating system

Abstract

A microwave heating device and a microwave heating system are provided. The microwave heating device includes a cavity, a microwave source, at least a pair of conductive columns, and a tubular furnace body. The cavity has a first surface. The microwave source is disposed on the cavity and located at the center of the first surface, wherein the microwave source is connected with the cavity. At least a pair of conductive columns are disposed in the cavity and form a TE 22resonance mode together with the microwave source and the cavity. The tubular furnace body is disposed in the cavity and penetrates through the cavity, wherein the tubular furnace body includes a tubular furnace core and a ceramic coating layer, and the ceramic coating layer covering the tubular furnace core.

Description

[Technical Field]

[0001] This disclosure relates to microwave heating equipment, and more particularly to microwave heating devices and microwave heating systems. [Previous Technology]

[0002] To improve or enhance the properties of materials, these materials can be heat-treated using heating equipment. For example, heating equipment may include conventional electric furnace heating devices or modern microwave heating devices. However, electric furnace heating technology, which heats layer by layer from the outermost layer to the innermost layer, has a long heating time and high energy consumption, making it unsuitable for materials requiring high-temperature heat treatment. Furthermore, electric furnace heating technology requires filling the cavity with insulation materials such as refractory bricks, graphite felt, or graphite frames. These insulation materials have a short lifespan, further increasing the cost of electric furnace heating technology.

[0003] On the other hand, using a traveling wave microwave heating device to heat materials through penetration allows energy to act directly on the inner layer material, offering the advantage of a shorter heating time compared to traditional electric furnace heating. However, the microwave energy generated by this type of microwave heating device is usually evenly distributed throughout the cavity, rather than concentrated at the material placement area (e.g., the center), resulting in relatively low microwave energy utilization. Therefore, how to develop a manufacturing equipment for more efficient continuous heat treatment, such as the heat treatment of continuous bundles or fabric materials, has become an urgent issue to be addressed. [Summary of the Invention]

[0004] In one or more embodiments disclosed herein, a microwave heating device is provided, comprising a cavity, a microwave emitting source, at least a pair of conductive pillars, and a tubular furnace body. The cavity has a first surface. The microwave emitting source is disposed on the cavity and located at the center of the first surface, wherein the microwave emitting source is in communication with the cavity. At least a pair of conductive pillars are disposed in the cavity and together with the microwave emitting source and the cavity form a TE 22 resonant mode. The tubular furnace body is disposed in the cavity and extends through the cavity, wherein the tubular furnace body includes a tubular furnace core and a ceramic coating layer, and the ceramic coating layer covers the tubular furnace core.

[0005] In one or more embodiments disclosed herein, a microwave heating system is provided, which includes a plurality of microwave heating devices as described above, and these microwave heating devices are connected in series.

Implementation Method

[0006] The following disclosure provides many different embodiments or examples for implementing the provided apparatus. Specific examples of the components and their configurations are described below to simplify the embodiments of this disclosure, and are not intended to limit this disclosure. For example, if the description mentions that a first component is formed on a second component, it may include embodiments where the first and second components are in direct contact, or embodiments where an additional component is formed between the first and second components, so that the first and second components are not in direct contact. Furthermore, this disclosure may repeat element symbols and / or characters in different embodiments or examples. Such repetition is for brevity and clarity, and is not intended to indicate a relationship between the different embodiments and / or examples discussed.

[0007] In some embodiments disclosed herein, terms such as "setup," "connection," and similar terms, unless specifically defined, may refer to two components in direct contact, or to two components not in direct contact, wherein an additional connecting component is located between the two structures. Terms such as "setup" and "connection" may also include situations where both structures are movable or both structures are fixed.

[0008] In addition, the terms "first", "second" and similar terms mentioned in this specification or the claims are used to name different components or to distinguish different embodiments or scopes, and are not used to limit the upper or lower limit of the number of components, nor to limit the manufacturing order or the order of installation of components.

[0009] In this document, the terms "approximately," "about," and "substantially" generally mean within 10%, 5%, 3%, 2%, 1%, or 0.5% of a given value or range. The given quantities are approximate, meaning that the terms "approximately," "about," or "substantially" are implied even without specific mention. The phrase "the range is between the first value and the second value" means that the range includes the first value, the second value, and other values ​​in between. Furthermore, any two values ​​or directions used for comparison may have a certain degree of error. If the first value equals the second value, it implies that there may be an error between the first value and the second value within approximately 10%, 5%, 3%, 2%, 1%, or 0.5%. If the first direction is perpendicular to the second direction, the angle between the first and second directions can be between 80 and 100 degrees. If the first direction is parallel to the second direction, the angle between the first and second directions can be between 0 and 10 degrees.

[0010] It should be understood that, for clarity, some components of the device are omitted in the drawings, and only some components are schematically shown. In some embodiments, additional components may be added to the device described below. In other embodiments, some components of the device described below may be replaced or omitted. It should be understood that, in some embodiments, additional operating steps may be provided before, during, and / or after the method of manufacturing the device. In some embodiments, some operating steps may be replaced or omitted, and the order of some operating steps is interchangeable.

[0011] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art. It is understood that such terms, for example, as defined in commonly used dictionaries, should be interpreted as having a meaning consistent with the relevant art and the background or context of this disclosure, and should not be interpreted in an idealized or overly formal manner, unless specifically defined in the embodiments of this disclosure.

[0012] This disclosure provides a resonant microwave heating device and microwave heating system, which effectively concentrates microwave energy at the center by means of the cavity and conductive column configuration, so as to improve the heating rate at the center and reduce the overall energy consumption.

[0013] Please refer to Figures 1 to 3, which respectively show a perspective view, a perspective view, and a cross-sectional view of a microwave heating device according to some embodiments of this disclosure. As shown in the figures, the microwave heating device 1 includes a cavity 10, a microwave emission source 11, at least a pair of conductive pillars 12, and a tubular furnace body 13. Specifically, the tubular furnace body 13 is used to carry or transport a workpiece (not shown). During transport, the microwave emission source 11, the conductive pillars 12, and the cavity 10 of the microwave heating device 1 together form at least one resonant mode, and the workpiece in the tubular furnace body 13 is heated (or modified) by this or these resonant modes to form a modified material with specific properties. In this disclosure, the resonant mode is mainly the TE 22 resonant mode. That is, the TE 22 resonant mode accounts for (or is allocated to) at least 80% of the energy of the microwave signal. To make this disclosure clearer and easier to understand, each of the above components or their possible variations will be described in detail below.

[0014] As shown in Figures 1 to 3, the cavity 10 is used to house components located therein (e.g., conductive pillar 12 and tubular furnace body 13), and is used to form one or more resonant modes including the TE 22 resonant mode together with the microwave emission source 11 and the conductive pillar 12.

[0015] In some embodiments, the cavity 10 is a rectangular cavity and has a first surface 10A to a sixth surface 10F. The first surface 10A is opposite to the second surface 10B, and the distance between them can be defined as a height H1. The third surface 10C is opposite to the fourth surface 10D, and the distance between them can be defined as a length L. The fifth surface 10E is opposite to the sixth surface 10F, and the distance between them can be defined as a width W. In some embodiments, adjacent surfaces 10A to 10F are substantially perpendicular to each other, but this disclosure is not limited thereto.

[0016] In some embodiments, the cavity 10 has a first opening 101 located on a first surface 10A of the cavity 10. The microwave emission source 11 communicates with the interior of the cavity 10 via the first opening 101 (e.g., fluid communication). In some embodiments, the cavity 10 further has a second opening 102 and a third opening 103 located on a third surface 10C and a fourth surface 10D of the cavity 10, respectively. A tubular furnace body 13 enters the cavity 10 through the second opening 102 and exits from the cavity 10 through the third opening 103. In some embodiments, the cavity 10 further has a fourth opening 104 located on a second surface 10B of the cavity 10. In some embodiments, the internal temperature of the cavity 10 can be sensed from the fourth opening 104 using a temperature sensing element (not shown), such as an infrared thermometer. It is worth noting that the above configuration is merely an example and is not intended to limit this disclosure. For example, in other embodiments, the fourth opening 104 may be located on the first surface 10A, the third surface 10C, or the fourth surface 10D of the cavity 10.

[0017] In some embodiments, the housing of the cavity 10 includes a conductive material. The conductive material includes metal or graphite. For example, the metal may be tin (Sn), copper (Cu), gold (Au), silver (Ag), nickel (Ni), indium (In), platinum (Pt), palladium (Pd), iridium (Ir), titanium (Ti), chromium (Cr), tungsten (W), aluminum (Al), molybdenum (Mo), titanium (Ti), magnesium (Mg), zinc (Zn), alloys thereof, or combinations thereof, but this disclosure is not limited thereto.

[0018] In some embodiments, the ratio of the length L to the width W of the cavity 10 is between 2:1 and 2.2:1. In some embodiments, the ratio of the length L to the height H1 of the cavity 10 is between 2:1 and 2.2:1. In some embodiments, the ratio of the width W to the height H1 of the cavity 10 is between 0.9:1 and 1.1:1. In other words, the cavity 10 is a rectangular cavity, and its front cross-section (i.e., viewed towards the third surface 10C or the fourth surface 10D of Figure 1) is approximately square or square. In some embodiments, the ratio of the length L, width W, and height H1 of the cavity 10 is between 2:1:1 and 2.2:1:1, and the length L, width W, and height H1 of the cavity 10 can be proportionally enlarged or reduced according to the wavelength of the microwave signal used.

[0019] For example, when the frequency of the microwave signal emitted by the microwave source 11 is 2.45 GHz (corresponding to a microwave wavelength of 12.5 cm), the length L of the cavity 10 can be between 410 mm and 430 mm, for example, 420 mm; the width W of the cavity 10 can be between 190 mm and 210 mm, for example, 200 mm; and the height H1 of the cavity 10 can be between 190 mm and 210 mm, for example, 200 mm.

[0020] Alternatively, when the frequency of the microwave signal emitted by the microwave transmitter 11 is 915MHz (corresponding to a wavelength of 32.8cm), the length L, width W, and height H1 of the cavity 10 can be proportionally increased with the wavelength of the microwave signal. In this example, 32.8cm / 12.5cm = 2.7, therefore the length L, width W, and height H1 of the cavity 10 can be proportionally increased by 2.7 times. In other words, the length L of the cavity 10 can be between 1107mm and 1161mm, for example, 1134mm; the width W of the cavity 10 can be between 513mm and 567mm, for example, 540mm; and the height H1 of the cavity 10 can be between 513mm and 567mm, for example, 540mm. Therefore, in practical applications, the dimensions of the cavity 10 can be adjusted according to the frequency (or wavelength) of the selected microwave signal.

[0021] As shown in Figures 1 to 3, a microwave emission source 11 is disposed on the cavity 10 and located at the center of the first surface 10A. The microwave emission source 11 is in communication with the cavity 10 and is used to provide microwave signals to the cavity 10. In some embodiments, the microwave emission source 11 includes a waveguide and a microwave magnetron. In some embodiments, the microwave magnetron can emit microwave signals with a frequency between 800 MHz and 13 GHz and transmit them to the cavity 10 via the waveguide. For example, the frequency of the microwave signal can be any value or range between 800 MHz, 2.2 GHz, 2.45 GHz, 2.6 GHz, 5.8 GHz, and 13 GHz. It is worth mentioning that in this disclosure, the single cavity 10 is equipped with a single microwave emission source 11, and the microwave emission source 11 is located at the geometric center of one of the surfaces of the cavity 10 (e.g., the first surface 10A) to form one or more resonant modes including the TE 22 resonant mode together with the entire cavity 10 and the conductive pillar 12.

[0022] As shown in Figures 1 to 3, a pair of conductive pillars 12 are disposed in the cavity 10. Specifically, the conductive pillars 12 are symmetrically disposed on the inner surface of the cavity 10, centered on the microwave emission source 11, along the tubular furnace body 13. In this disclosure, the conductive pillars 12 are used to form the TE 22 resonant mode together with the microwave emission source 11 and the cavity 10. Specifically, the microwave signal emitted by the microwave emission source 11 interacts with the cavity 10 and generates various resonant modes, such as the TE 01 resonant mode, TE 02 resonant mode, TE 11 resonant mode, TE 12 resonant mode, TE 22 resonant mode, TE 23 resonant mode, TE 33 resonant mode, or other possible resonant modes. Each resonant mode has a different electromagnetic field profile. Compared with resonant modes such as the TE 01 resonant mode and the TE 21 resonant mode, the electromagnetic field profile of the TE 22 resonant mode is most suitable for heating the tubular furnace body 13.

[0023] Referring also to Figure 4A, which shows a simulation diagram of the electromagnetic field of the TE 22 resonant mode in a cavity according to some embodiments of this disclosure. Solid lines represent contour lines of the electric field, and dashed lines represent contour lines of the magnetic field. As shown in the figure, from a cross-sectional view of a rectangular cavity, the electromagnetic field profile of the TE 22 resonant mode is mainly concentrated at the center. In other words, increasing the energy of the microwave signal allocated to the TE 22 resonant mode (i.e., making the TE 22 resonant mode the dominant resonant mode) can make the electromagnetic field more concentrated at the center of the cavity 10. To this end, this disclosure adjusts the energy of the microwave signal allocated to the TE 22 resonant mode by setting conductive pillars 12 and adjusting the size, position, and material of the conductive pillars 12. Table 1 No conductive pillars were installed. Set conductive pillars Resonance mode Energy distribution rate of microwave signals Energy distribution rate of microwave signals TE 01 40% 2% TE 02 25% 1.4% TE 11 15% 0.5% TE 12 10% 0.3% TE 22 5% 90% TE 23 3% 0.8% TE 33 2% 0%

[0024] Continuing from the foregoing and referring to Table 1, which shows simulated numerical results of the energy distribution rate of microwave signals with and without conductive pillars according to some embodiments of this disclosure. In one simulation result of this disclosure, after setting the conductive pillar 12 in a specific manner, the energy distribution rate of the TE 22 resonant mode can be increased from 5% to over 80%, for example, to 90%. In this way, the resonant mode in the cavity 10 can be dominated by the TE 22 resonant mode. Since the electromagnetic field of the resonant mode TE 22 is mainly concentrated at the center of the cavity 10, the heating efficiency at the center of the cavity 10 can be improved with the same input power. In other words, this disclosure effectively improves the heating efficiency of the entire microwave heating device 1 or effectively reduces the energy consumption of the entire microwave heating device 1 by setting the conductive pillar 12.

[0025] Referring also to Figures 4B and 4C, which respectively show front electromagnetic field simulation diagrams (e.g., viewed towards the third surface 10C or fourth surface 10D of Figure 1) and side electromagnetic field simulation diagrams (e.g., viewed towards the fifth surface 10E or sixth surface 10F of Figure 1) of a microwave heating apparatus according to some embodiments of the present disclosure. After simulating the interaction between the conductive pillar 12 and the tubular furnace body 13 and the cavity 10, the electromagnetic field in the entire microwave heating apparatus 1 has the general outline shown in the figures. It can be observed from the figures that the electromagnetic field is mainly concentrated at the center of the cavity 10 (i.e., where the tubular furnace body 13 is located). In this way, the energy of the microwave signal can be effectively used to heat the tubular furnace body 13, and the energy distribution of the microwave signal to the periphery of the cavity 10 can be reduced. In addition, it can be observed from the figures that the electric field is concentrated in a very small diameter area. For the workpiece to be processed in the tubular furnace body 13, its surface may also generate a large surface current due to the strong electric field. In some embodiments, these surface currents can further modify the workpiece.

[0026] Returning to Figure 3, in some embodiments, the two conductive pillars 12 are spaced apart by a distance S along the length of the cavity 10, with the microwave source 11 as the center. In some embodiments, when the frequency of the microwave signal is 2.45 GHz, the distance S between the two conductive pillars 12 can be between 60 mm and 170 mm, for example, 110 mm. In some embodiments, when the ratio of the length L, width W, and height H1 of the cavity 10 is 2.1:1:1, the ratio between the length L of the cavity 10 and the distance S between the conductive pillars 12 is between 4.2:1 and 3.5:1. For example, when the length L of the cavity 10 is 420 mm, the width W is 200 mm, and the height H1 is 200 mm, the distance S between the conductive pillars 12 can be between 60 mm and 170 mm, for example, 110 mm.

[0027] In some embodiments, the conductive post 12 has a height H2, and the height H2 is related to the reflectivity of the microwave signal. Specifically, the lower the reflectivity of the microwave signal, the higher the amount of unreflected microwave signal. In other words, more microwave signal remains in the cavity 10 for heating. Therefore, the height H2 of the conductive post 12 can be determined based on the frequency of the microwave signal, the size of the cavity 10, or other factors. In some embodiments, the height H2 of the conductive post 12 can be adjusted by various parameters in simulation or actual application. For example, when the frequency of the microwave signal is 2.45 GHz, the height H2 of the conductive post 12 can be between 3 mm and 10 mm, for example, 6 mm. In some embodiments, when the ratio between the length L, width W, and height H1 of the cavity 10 is 2.1:1:1, the ratio between the height H1 of the cavity 10 and the height H2 of the conductive post 12 is between 140:1 and 42:1. For example, when the length L of the cavity 10 is 420 mm, the width W is 200 mm, and the height H1 is 200 mm, the height H2 of the conductive post 12 can be between 3 mm and 10 mm, for example, 6 mm. In some embodiments, the ratio between the height H1 of the cavity 10 and the height H2 of the conductive post 12 can be between 25:1 and 35:1. For example, when the height H1 of the cavity 10 is 200 mm, the height H2 of the conductive post 12 can be between 5.7 mm and 8 mm, for example, 7 mm.

[0028] It is worth mentioning that this disclosure is not limited to the number of conductive pillars 12. In other embodiments, conductive pillars 12 can be symmetrically arranged in more pairs within the cavity 10. For example, two, three, four, or more pairs of conductive pillars 12 can be provided in the cavity 10 to more precisely control the profile of the electromagnetic field of the resonant mode and the energy allocated thereto. In some embodiments where there are two, three, four, or more pairs of conductive pillars 12, the conductive pillars 12 can be symmetrically arranged on the inner surface of the cavity 10 with the microwave emission source 11 as the center, along the length direction (i.e., the direction parallel to the extension direction of the tubular furnace body 13) or the width direction (i.e., the direction perpendicular to the extension direction of the tubular furnace body 13). In some embodiments, different pairs of conductive pillars 12 can also be located on different inner surfaces of the cavity 10 (e.g., inside the fifth surface 10E or the sixth surface 10F) to more precisely control the profile of the electromagnetic field of the resonant mode and the energy allocated thereto.

[0029] In some embodiments, the material of the conductive post 12 includes a conductive material such as a metal. For example, the metal may be tin (Sn), copper (Cu), gold (Au), silver (Ag), nickel (Ni), indium (In), platinum (Pt), palladium (Pd), iridium (Ir), titanium (Ti), chromium (Cr), tungsten (W), aluminum (Al), molybdenum (Mo), titanium (Ti), magnesium (Mg), zinc (Zn), alloys of the foregoing, or combinations thereof, but this disclosure is not limited thereto. In some embodiments, the material of the conductive post 12 may also be a metal compound or other suitable conductive material.

[0030] As shown in Figures 1 to 3, a tubular furnace body 13 is disposed within a cavity 10 and extends through the cavity 10 along its length. In some embodiments, the tubular furnace body includes a tubular furnace core 131 and a ceramic cladding layer 132, with the ceramic cladding layer 132 covering the tubular furnace core 131. Specifically, the tubular furnace core 131 is a hollow tube and is used to transport the workpiece located therein. On the other hand, the ceramic cladding layer 132 is used for heat preservation to maintain the temperature of the tubular furnace core 131. For example, the workpiece can enter the cavity 10 from the third surface 10C of the cavity 10 along the tubular furnace core 131. Then, the workpiece moves along the tubular furnace core 131. During the entire movement, since the tubular furnace body 13 is heated by the TE 22 resonant mode generated by the microwave signal, the workpiece located therein can be modified by the temperature. Finally, the workpiece can leave the cavity 10 along the tubular furnace core 131 from the fourth surface 10D of the cavity 10.

[0031] In some embodiments, the tubular furnace core 131 is made of silicon carbide, and the ceramic cladding layer 132 is made of porous ceramic, but this disclosure is not limited thereto. In other embodiments, different materials or combinations of materials may be used to form the tubular furnace core 131 and the ceramic cladding layer 132.

[0032] The possible parameters of each component, such as structure, shape, size, material, and relative relationships, have been given above. However, in practical applications, the type of resonant mode, the allocated energy ratio, or the electromagnetic field profile are related to the frequency band of the microwave signal, as well as the dielectric and thermal conductivity (material-related), size, shape, and relative positions of the cavity 10, conductive pillar 12, and tubular furnace body 13. Therefore, given that these parameters interact with each other, this disclosure is not limited to the specific parameters of these components. For those skilled in the art, the structure, shape, size, material, and relative relationships of these components can be further adjusted according to actual needs, with the TE 22 resonant mode as the primary resonant mode.

[0033] Referring to Figure 5, which is a perspective view of a microwave heating system according to some embodiments of the present disclosure. As shown, in some embodiments, multiple microwave heating devices 1 can be connected in series to allow the workpiece to undergo a longer or more refined heating or modification process in the tubular furnace body 13. For example, two, three, four or more microwave heating devices 1 can be connected in series sequentially, and the tubular furnace bodies 13 in each microwave heating device 1 can be connected to realize the microwave heating system 2 shown in the figure.

[0034] In some embodiments, the microwave heating devices 1 in the microwave heating system 2 can be independent of each other. For example, a material that blocks electromagnetic waves can be provided between two adjacent microwave heating devices 1. In this case, the microwave signals emitted by each microwave source 11 will not interfere with each other, but will only heat the tubular furnace body 13 in the corresponding cavity 10. In this way, the power and resonance mode of the microwave sources in different microwave heating devices 1 can be adjusted separately according to product requirements, so as to meet the different heating temperatures required by the characteristics of the processed workpiece, so as to modify the workpiece more precisely.

[0035] In summary, the embodiments disclosed herein provide a resonant microwave heating device and microwave heating system, which effectively concentrates microwave energy at the center by means of the cavity and conductive pillar configuration, thereby increasing the heating rate at the center and reducing the overall energy consumption.

[0036] Several embodiments have been summarized above to enable those skilled in the art to better understand the viewpoints of the embodiments disclosed herein. Those skilled in the art should understand that other processes and structures can be designed or modified based on the embodiments disclosed herein to achieve the same purpose and / or advantages as the embodiments described herein. Those skilled in the art should also understand that such equivalent processes and structures do not depart from the spirit and scope of this disclosure, and various changes, substitutions, and replacements can be made without departing from the spirit and scope of this disclosure. [Simplified Explanation of the Diagram]

[0037] The viewpoints of the embodiments disclosed herein can be better understood through the following detailed description in conjunction with the accompanying drawings. It is worth noting that, according to industry standard practice, some features may not be drawn to scale. In fact, the dimensions of different features may be increased or decreased for clear description. Figure 1 is a perspective view of a microwave heating device according to some embodiments of the present disclosure. Figure 2 is a perspective view of a microwave heating device according to some embodiments of the present disclosure. Figure 3 is a cross-sectional view of a microwave heating device according to some embodiments of the present disclosure. Figure 4A is an electromagnetic field simulation diagram of the TE 22 resonant mode in a cavity according to some embodiments of the present disclosure. Figure 4B is a front electromagnetic field simulation diagram of a microwave heating device according to some embodiments of the present disclosure. Figure 4C is a side electromagnetic field simulation diagram of a microwave heating device according to some embodiments of the present disclosure. Figure 5 is a perspective view of a microwave heating system according to some embodiments of the present disclosure.

Claims

1. A microwave heating device, comprising: A cavity having a first surface; A microwave emission source is disposed on the cavity and located at the center of the first surface, wherein the microwave emission source is in communication with the cavity; at least a pair of conductive pillars are disposed in the cavity and together with the microwave emission source and the cavity form a TE22 resonant mode, wherein the TE22 resonant mode accounts for at least 80% of the energy provided by the microwave emission source; and a tubular furnace body is disposed in the cavity and extends through the cavity, wherein the tubular furnace body includes a tubular furnace core and a ceramic coating layer, and the ceramic coating layer covers the tubular furnace core.

2. The microwave heating apparatus as claimed in claim 1, wherein the at least one pair of conductive pillars are symmetrically arranged on the inner surface of the cavity along the tubular furnace body with the microwave emission source as the center.

3. The microwave heating apparatus as claimed in claim 1, wherein the cavity is a rectangular cavity and the ratio between the length, width and height of the cavity is between 2:1:1 and 2.2:1:

1.

4. The microwave heating apparatus as claimed in claim 3, wherein the ratio between the height of the cavity and the height of the at least one pair of conductive pillars is between 25:1 and 35:

1.

5. The microwave heating apparatus as claimed in claim 3, wherein the tubular furnace body extends through the cavity along its length.

6. The microwave heating apparatus as claimed in claim 1, wherein the microwave emitting source comprises a waveguide and a microwave magnetron.

7. The microwave heating apparatus as claimed in claim 1, wherein the material of the tubular furnace core comprises silicon carbide, and the material of the ceramic coating layer comprises porous ceramic.

8. The microwave heating apparatus as claimed in claim 1, wherein the material of the at least one pair of conductive pillars includes metal.

9. A microwave heating system comprising a plurality of microwave heating devices as described in any one of claims 1 to 8, wherein the microwave heating devices are connected in series.

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