A method to improve the temperature uniformity of microwave heating

Abstract

A method for improving the temperature uniformity of microwave heating is characterized by adding auxiliary materials containing temperature-sensitive electromagnetic materials simultaneously inside, outside, or both inside and outside the material. This causes the heating capacity of the material as a whole or a specific local area within a desired temperature range to decrease as the temperature increases, thereby making the temperatures of hot and cold areas within this temperature range more similar. This invention can significantly improve the temperature uniformity of microwave heating, eliminates the need for complex temperature monitoring methods, and has a wide range of applications.

Description

Technical Field

[0001] This invention relates to a microwave heating technology for composite materials, and more particularly to a method for improving the temperature uniformity of composite materials during microwave heating, specifically a method for improving the temperature uniformity of the heated material during microwave heating. Background Technology

[0002] Microwaves are electromagnetic waves with frequencies ranging from 300 MHz to 300 GHz. Microwave heating is an energy-efficient and highly effective heating method, offering advantages such as rapid heating, selective heating, and ease of control. Therefore, it is widely used in food processing, material handling, chemical synthesis, and other fields. However, the uneven distribution of the electromagnetic field within the microwave cavity results in relatively hot and relatively cold regions on the material, leading to temperature inhomogeneity. This problem severely affects the heating quality of the material and hinders the application of microwave heating technology.

[0003] There are three main methods to improve the uniformity of microwave heating temperature: (1) Optimize the distribution of electromagnetic field in the cavity before heating. By optimizing the shape, size or position of the microwave cavity or microwave source, the distribution of electromagnetic field in the cavity can be made more uniform. However, the nature of electromagnetic wave resonance in the cavity determines that this method cannot achieve a uniform distribution of electromagnetic field in principle. (2) On this basis, random relative motion between the electromagnetic field and the heated material can be made during the heating process (such as using a material rotating tray or a mode stirrer). Overall, the uniformity of microwave heating can be further improved, but it cannot avoid the situation where cold areas are colder and hot areas are hotter in some parts of the material. (3) Therefore, based on the real-time monitoring results of the material temperature distribution during the heating process, directional compensation for the non-uniform temperature field is a new idea in recent years, but it still needs to be accompanied by further development of temperature field monitoring technology (especially surface temperature measurement technology).

[0004] Unlike existing methods, this invention proposes adding auxiliary materials containing temperature-sensitive electromagnetic materials inside, outside, or both inside and outside the material simultaneously. This causes the overall temperature rise of the material or a specific local area within the desired temperature range to decrease as the temperature increases. Consequently, the temperature rise of the hot zone within this temperature range is lower than that of the cold zone, thus bringing the temperatures of the hot and cold zones closer together (related principles are as follows). Figure 1 (As shown). This invention does not require real-time monitoring of the temperature distribution of materials, but can achieve the effect of directional compensation of the temperature field. It is easy to implement and has broad application prospects. Summary of the Invention

[0005] The purpose of this invention is to address the problem of uneven temperature distribution in microwave heating of materials, and to develop a new method to improve the temperature uniformity of microwave heating, thereby fundamentally overcoming the problem of uneven microwave heating.

[0006] The technical solution of this invention is: A method for improving the temperature uniformity of microwave heating is characterized by adding auxiliary materials containing temperature-sensitive electromagnetic materials simultaneously inside, outside, or inside and outside the material, so that the heating capacity of the material as a whole or a certain local area within the desired temperature range decreases as the temperature increases, thereby making the heating capacity of the hot area of ​​the material as a whole or a certain local area within this temperature range lower than that of the cold area, so as to make the temperatures of the hot and cold areas closer.

[0007] The addition of auxiliary materials containing temperature-sensitive electromagnetic materials to the material refers to mixing powder containing temperature-sensitive electromagnetic materials into the material, so that the material can obtain wave absorption performance that decreases with increasing temperature within the required temperature range.

[0008] The powder of the temperature-sensitive electromagnetic material is one or a mixture of several of the following: strontium titanate, barium titanate, or barium strontium titanate.

[0009] The method used to mix the temperature-sensitive electromagnetic material inside the material depends on the shape and size of the material, such as melt blending, mechanical blending, etc.

[0010] The addition of auxiliary materials containing temperature-sensitive electromagnetic materials to the outside of the material refers to covering the outside of the material with a temperature-sensitive film having two or more layers; the temperature-sensitive film consists of one or more dielectric layers and one or more subwavelength conductive patterns, and at least one dielectric layer or conductive pattern is made of or contains temperature-sensitive electromagnetic materials, so that the overall wave absorption performance of the "temperature-sensitive film and material" decreases with increasing temperature within the required temperature range.

[0011] The conductive pattern has negligible dimensions in the thickness direction (less than 500 micrometers) and a specific geometry in the plane. Its shape and size can be easily determined by electromagnetic simulation once the material selection is determined (i.e., the material parameters are determined).

[0012] The addition of auxiliary materials containing temperature-sensitive electromagnetic materials to the outside of the material refers to covering the outside of the material with microwave-absorbing material; the microwave-absorbing material is made of or contains temperature-sensitive electromagnetic materials, and has microwave absorption performance that decreases as the temperature increases within the required temperature range, thereby transferring heat to the heated material more evenly after absorbing microwaves.

[0013] When adding auxiliary materials containing temperature-sensitive electromagnetic materials to the outside of the material, special attention should be paid to ensuring that the auxiliary materials and the heated material are in close contact. This can be achieved through methods such as coating, attaching, plating, and vacuum adsorption.

[0014] The aforementioned temperature-sensitive electromagnetic material refers to a material whose electromagnetic parameters change with temperature; such as alloys of metals such as copper, aluminum, silver, and chromium; phase change metal oxides such as vanadium dioxide; ferroelectric materials such as strontium titanate and barium titanate; liquid crystal materials; and materials containing the above components.

[0015] The electromagnetic parameters referred to are resistivity, dielectric constant, permeability, or a combination of the above parameters.

[0016] The beneficial effects of this invention are: This invention does not require real-time monitoring of the temperature distribution of materials, but can achieve the effect of directional compensation of the temperature field. It is easy to implement and has broad application prospects. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the principle of the method of the present invention.

[0018] Figure 2 This is a schematic diagram of a double-layer temperature-sensitive film according to the present invention.

[0019] Figure 3 This is a schematic diagram showing the change of the real part of the dielectric constant of a double-layer thermosensitive film of the present invention with temperature at a frequency of 2.45 GHz.

[0020] Figure 4 This is a schematic diagram showing the change of 2.45 GHz microwave absorptivity with temperature of a double-layer thermosensitive film and a carbon fiber reinforced epoxy resin matrix composite material according to the present invention. Detailed Implementation

[0021] The method solution of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0022] like Figure 1 As shown.

[0023] One method for improving the temperature uniformity of microwave heating involves adding auxiliary materials containing temperature-sensitive electromagnetic materials inside, outside, or both inside and outside the material. This causes the heating capacity of the material as a whole or a specific local area within the desired temperature range to decrease as the temperature increases. Consequently, the heating capacity of the hot zone within this temperature range is lower than that of the cold zone, thus bringing the temperatures of the hot and cold zones closer together. Figure 1 As shown.

[0024] Adding auxiliary materials containing temperature-sensitive electromagnetic materials (not shown in the figure) to the material (not shown in the figure) refers to mixing powders containing temperature-sensitive electromagnetic materials, such as strontium titanate, barium titanate, barium strontium titanate, and their mixtures, into the material. This allows the material to achieve microwave absorption properties that decrease with increasing temperature within the desired temperature range. The method used to mix the temperature-sensitive electromagnetic material into the material depends on the material's shape and size, and may include methods such as melt blending and mechanical blending.

[0025] Adding auxiliary materials containing temperature-sensitive electromagnetic materials to the outside of materials refers to covering the outside of materials with a temperature-sensitive film with two or more layers, such as... Figure 2 As shown; the temperature-sensitive film consists of one or more dielectric layers and one or more subwavelength conductive patterns, and at least one dielectric layer or conductive pattern is made of or contains a temperature-sensitive electromagnetic material, so that the overall absorption performance of the "temperature-sensitive film and material" decreases with increasing temperature within the desired temperature range. The conductive pattern has negligible dimensions in the thickness direction (less than 500 micrometers) and has a specific geometry in the plane (e.g., Figure 2 The shape and size of the ring (or square ring) are easily determined through electromagnetic simulation once the material selection (i.e., material parameters) are determined. Adding auxiliary materials containing temperature-sensitive electromagnetic materials to the outside of the material refers to covering the material with microwave-absorbing material. The microwave-absorbing material is made of or contains temperature-sensitive electromagnetic materials, and its absorption performance decreases with increasing temperature within the desired temperature range, thus transferring heat to the heated material more uniformly after absorbing microwaves. When adding auxiliary materials containing temperature-sensitive electromagnetic materials to the outside of the material, special attention must be paid to ensuring close contact between the auxiliary material and the heated material, which can be achieved through methods such as coating, attaching, plating, and vacuum adsorption. The temperature-sensitive electromagnetic materials refer to materials whose electromagnetic parameters change with temperature; such as alloys of metals like copper, aluminum, silver, and chromium; phase-change metal oxides like vanadium dioxide; ferroelectric materials like strontium titanate and barium titanate; liquid crystal materials; and materials containing the above components. The electromagnetic parameters refer to resistivity, dielectric constant, permeability, or a combination of the above parameters.

[0026] The invention will be further illustrated below by showing several implementation examples.

[0027] Example 1.

[0028] A carbon fiber reinforced epoxy resin matrix composite material with a two-layer temperature-sensitive film outer coating is microwave-heated. The carbon fiber reinforced epoxy resin matrix composite material is hand-laid from unidirectional prepreg with layup angles of [0° / 90°]. 10 The dimensions of the composite material are 250 (length) × 250 (width) × 2 (height) mm. 3 .like Figure 2The dual-layer temperature-sensitive film consists of a conductive pattern layer and a dielectric layer. The upper conductive pattern layer is made of copper, with a thickness of 18 μm and a conductivity of 5.813 × 10⁻⁶. 7 The S / m dielectric constant, consisting of square ring-shaped units, is arrayed on the dielectric layer. The pattern is obtained by laser etching of copper foil. The dielectric layer is prepared by curing a 1:1 mass ratio of epoxy resin and strontium titanate powder, with a thickness of 0.52 mm and a particle size of 1 μm. The real part of the dielectric constant of the dielectric layer material at 2.45 GHz monotonically increases with increasing temperature in the range of 25–150 °C, as shown in the figure. Figure 3 "Double-layer temperature-sensitive film with [0° / 90°]" 10 The overall absorption rate of the carbon fiber reinforced epoxy resin composite material for 2.45 GHz microwaves decreased from 91.28% at 25°C to 57.17% at 150°C, as shown in the figure. Figure 4 A double-layer temperature-sensitive film is vacuum-adsorbed onto a carbon fiber reinforced epoxy resin matrix composite material using a vacuum bag, and then placed in a microwave heating cavity for heating, which significantly improves temperature uniformity.

[0029] Example 2.

[0030] A glass fiber plate covered with a microwave-absorbing material containing a temperature-sensitive material is microwave-heated. This utilizes the "double-layer structure temperature-sensitive film and [0° / 90°]" described in Example 1. 10 The carbon fiber reinforced epoxy resin matrix composite material is used as a microwave absorbing material containing temperature-sensitive materials, covering an area with dimensions of 250 (length) × 250 (width) × 2 (height) mm. 3 On the fiberglass board, a "double-layer temperature-sensitive film with [0° / 90°]" 10 The carbon fiber reinforced epoxy resin composite material absorbs microwave heating as a whole, and transfers the heat to the glass fiber board in a relatively uniform way.

[0031] Example 3.

[0032] Microwave heating is used to heat the internally mixed temperature-sensitive epoxy resin. Bisphenol A type epoxy resin and its curing agent are mixed evenly at a mass ratio of 10:3 and then poured into a container measuring 200 (length) × 200 (width) × 50 (height) mm. 3 The silicone mold was then filled with barium strontium titanate nanoparticles (Ba) in a mass ratio of 1:2 with epoxy resin. 0.6 Sr 0.4 TiO3 was used to monotonically decrease the absorptivity of the mixture to 915MHz microwaves within the temperature range of 25-150℃. When placed in a microwave heating cavity, it achieved uniform microwave heating within the temperature range of 25-120℃.

[0033] All parts not covered in this invention are the same as or can be implemented using existing technologies.

Claims

1. A method for improving the temperature uniformity of microwave heating, characterized in that: By adding auxiliary materials containing temperature-sensitive electromagnetic materials to the outside or inside of the material simultaneously, the heating capacity of the material as a whole or a certain local area within the desired temperature range decreases as the temperature increases. This results in the heating capacity of the hot zone within this temperature range being lower than that of the cold zone, thus bringing the temperatures of the hot and cold zones closer together. Adding auxiliary materials containing temperature-sensitive electromagnetic materials inside the material refers to mixing powder containing these materials into the material, thereby enabling the material to achieve wave absorption properties that decrease with increasing temperature within the desired temperature range. Adding auxiliary materials containing temperature-sensitive electromagnetic materials to the outside of the material refers to covering the material with a temperature-sensitive film having two or more layers; the temperature-sensitive film consists of one or more dielectric layers and... The material comprises one or more subwavelength conductive patterns, with at least one dielectric layer or conductive pattern made of or containing a temperature-sensitive electromagnetic material, such that the overall microwave absorption performance of the "temperature-sensitive film and material" decreases with increasing temperature within the desired temperature range. Adding an auxiliary material containing a temperature-sensitive electromagnetic material to the outside of the material refers to covering the material with a microwave-absorbing material. The microwave-absorbing material is made of or contains a temperature-sensitive electromagnetic material, and its microwave absorption performance decreases with increasing temperature within the desired temperature range, thereby transferring heat to the heated material more uniformly after absorbing microwaves. The temperature-sensitive electromagnetic material refers to a material whose electromagnetic parameters change with temperature. The electromagnetic parameters refer to resistivity, dielectric constant, permeability, or a combination of these parameters. The temperature-sensitive film consists of a conductive pattern layer and a dielectric layer, wherein the conductive pattern material is copper. The dielectric layer is prepared by uniformly mixing epoxy resin and strontium titanate powder in a 1:1 mass ratio and then curing it.

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