A method for designing and optimizing a single-mode microwave resonant cavity internal heating transmission device

Abstract

The present application relates to the technical field of microwave heating, in particular to a single-mode microwave resonant cavity heating transmission device design and optimization method. The cavity width is changed by means of the design of the carrier box, and the internal components of the carrier box are designed to optimize the heating mode of the food. The present application gives a detailed description of the optimization technical scheme for the metal design of the carrier box, and preferentially adopts the inward collection of the metal plate to control the microwave heating cavity at a minimal cost. The balanced metal rod is designed, and on the basis of keeping balance, the optimization adjustment of the heating uniformity for different foods can be realized without changing the main structure of the single-mode cavity. Starting from the carrier box which is lower in cost and easier to process, the precise optimization of the targeted heating mode for different foods can be realized.

Description

Technical Field

[0001] This invention relates to the field of microwave heating technology, and specifically to a design method for a heating and transmission device within a single-mode microwave resonant cavity. Background Technology

[0002] Based on the laws governing electric field distribution, the non-uniformity of microwave heating can only be reduced, not eliminated. Therefore, to better utilize microwave energy for food processing, the resonant cavity and its internal structure need to be designed to improve the uniformity of the food being processed. For single-mode industrial microwave sterilization systems, the cavity size affects the temperature distribution of the food. For example, the inventor's previously published Chinese patent CN120124371A, "A Uniform Electric Field Cavity Design Method for a Single-Mode Liquid Microwave Resonant Cavity," can effectively determine the optimal resonant cavity size and its limitations for microwave energy-powered devices at a certain frequency, effectively improving the uniformity of the microwave electric field distribution within the microwave liquid single-mode resonant cavity.

[0003] However, in industrial applications, different foods need to be heated in the same microwave resonant cavity, but these foods may have inherent differences, such as variations in dielectric or thermal properties. Therefore, using a single resonant cavity for heating is highly unsuitable, potentially resulting in uniform heating for some foods while causing highly uneven heating for others. To achieve optimal heating, each food requires a precisely matched microwave field distribution, meaning each food needs an optimally matched cavity width. However, it is difficult to equip every food with a suitable cavity. Therefore, it is necessary to develop effective and feasible methods to optimize microwave heating uniformity. Summary of the Invention

[0004] The technical problem that this invention aims to solve is that existing technical solutions mainly focus on the overall design of the cavity, without designing a material carrier box for a specific food, thus failing to achieve precise and uniform optimization for a particular food.

[0005] To address the problems of existing technologies, this invention provides a design method for a single-mode microwave resonant cavity heating and conveying device. This method utilizes the design of a material carrier box to modify the cavity width, and simultaneously optimizes the heating mode of food by designing the internal components of the material carrier box. The research results of this invention reduce the non-uniformity of the microwave heating process, which is beneficial to the standardization of microwave sterilization systems and promotes the development of microwave sterilization systems in industrial applications.

[0006] To achieve the above objectives, the present invention provides a design method for a single-mode microwave resonant cavity heating and transfer device, comprising the following steps:

[0007] (1) Select the microwave frequency. According to GB / T 11450.2-1989 Hollow Metal Waveguide Part 2: Specifications for Ordinary Rectangular Waveguides, select the rectangular waveguide used for the microwave resonant cavity corresponding to the microwave frequency. The long side of the rectangular waveguide is a and the short side is b.

[0008] (2) Design the food conveying device and obtain specific dimensional parameters. Use finite-difference time-domain software, finite element software, method of moments software, etc. to draw a geometric model; the geometric model includes forming a stable rectangular shape in the XY plane in the single-mode microwave resonant cavity, maintaining a rectangular shape with thickness in the XZ plane, and providing the main mechanical stress support in the YZ direction to obtain a three-dimensional shape of the material box that is almost impossible to change.

[0009] Specifically, it includes: well-functioning; including two side plates and front and rear fixing devices, making it a complete material conveying device;

[0010] (3) Establish a numerical simulation model. You can use the time-domain finite element software Quickwave or the finite element software COMSOL Multiphysics to build a coupled simulation model that includes electromagnetic field and heat transfer field. The software must include the movement of metal components for the simulation movement of the material box.

[0011] (4) Set the heat source for the numerical simulation model, including the energy generated by microwaves and the energy generated by hot water;

[0012] (5) For microwave resonant cavities, metallic boundary conditions should be set: the material properties of the inner wall of the resonant cavity and all components of the carrier box should be set to metallic (so that microwaves cannot pass through in the microwave field, cannot absorb microwave energy, and can only reflect microwaves).

[0013] (6) Determine the width parameter of the microwave resonant cavity; since the microwave rectangular waveguide can only propagate microwaves into the resonant cavity without loss, the electric field distribution range is hardly changed; therefore, in the actual microwave equipment design process, tapered waveguides are often used to achieve the gain of the electric field radiation range; therefore, the minimum width of the microwave resonant cavity is at least 1b. Simulation results show that when it is greater than 2b, the microwave energy gradually diffuses from the center region of the XY plane of the resonant cavity to both ends of the Y direction, so most of the energy cannot be used for food heating, so the maximum value is selected as 2b. The microwave cavity width is selected with a maximum value of 2b and a minimum value of 1b. At least one width gradient should be set in the middle to facilitate optimization to obtain the best microwave resonant cavity width; considering the tolerance and difficulty of actual processing, a certain error (within ±2mm) is allowed in actual processing.

[0014] (7) Material box design:

[0015] (7-1) The side metal sheet of the material box simulates the width of the microwave resonant cavity. The side is divided into height A and width B. The side metal edge is called the electric field adjustment plate. The thickness of the electric field adjustment plate is set: different lengths and widths are combined to obtain the size combination model of the electric field adjustment plate.

[0016] (7-2) Metal rods are installed at the front and rear of the material box, and the diameter of the metal rods is set;

[0017] (7-3) Center distance between the front and rear metal bars of the material carrier box; After determining the optimal setting diameter, further analyze the center distance between the metal bars of the material carrier box and set different center distances;

[0018] (7-4) Set the food to be heated statically directly below the microwave source, and set the distance between the metal rod and the food to D;

[0019] (8) Perform numerical simulation of the food carrier box, and calculate that the food and the food carrier box are stationary together in the center of the cavity during the simulation process, facing the waveguide heating.

[0020] (8-1) Numerical simulation processing was performed on the width of microwave resonant cavities with different widths;

[0021] (8-2) Numerical simulation was performed on the models of different combinations of the width and height of the electric field adjustment plates; the differences between the numerical simulations of adjusting the width of the electric field adjustment plate and adjusting the width of the microwave resonant cavity were compared, and the correlation between the heights of different electric field adjustment plates was compared.

[0022] (8-3) Simulate the diameter of the metal rods on the material carriers of different diameters and compare the effects of different metal rod diameters on the food heating effect;

[0023] (8-4) Simulate the center spacing between metal rods with optimized diameters and compare the effects of different center spacings of metal rods on food heating effect;

[0024] (8-5) Numerical simulation was performed on the distance between the metal rods with optimized diameter and center spacing and the food to compare the effect of different metal rod center spacing on the food heating effect.

[0025] (8-6) The optimized food resonant cavity width, material box side plate parameters, metal adjusting rod diameter, center distance between metal adjusting rods, and distance between metal adjusting rods and food are obtained, in mm.

[0026] Furthermore, after obtaining the optimized parameters, a verification step is also included:

[0027] (9) Prepare experimental verification samples;

[0028] (10) Simulated food microwave treatment: The simulated food was cut into pieces, put into a heat-resistant retort bag, vacuum-packed and placed on a food carrier box, and then processed in a microwave sterilization system; the experimental parameters in the microwave sterilization process matched the parameters set in the simulation.

[0029] (11) Machining is performed on the food resonant cavity width, the side plate parameters of the loading box, the diameter of the metal adjusting rod, the center distance between the metal adjusting rods, and the distance between the metal adjusting rod and the food, etc., after optimization in step (8); and the metal object of the loading box is obtained.

[0030] (12) Add the material carrier box into the simulated food resonant cavity, set the microwave power and the microwave source used, and carry out microwave sterilization treatment; after the treatment is completed, take out the heat-resistant cooking bag and put it into cold water for cooling treatment.

[0031] (13) Analysis of the heat pattern of simulated food: After cooling, the simulated food sample with the cooking bag removed was placed in the photography studio to take pictures of the front, back and middle cross-section, and the pictures were converted into pseudo-color pictures; the heating pattern obtained in the experiment was compared with the heating pattern obtained in the simulation model to verify the stability of the simulation model.

[0032] (14) Temperature monitoring of simulated cold spots in food: After determining the heating mode, place the probe of the metal wireless temperature sensor at a representative location (such as a hot spot or a cold spot) according to the heating mode diagram, and measure the time-temperature curve. Compare the time-temperature curve obtained from the experiment with the time-temperature curve obtained from the simulation model to further verify the accuracy and stability of the simulation model.

[0033] Furthermore, in step (7-1), ① the width B is the flange surface folded inward from both sides of the material box in the Y direction towards the center in the Y direction within the XY plane. Therefore, changing the width B will affect the width of the microwave resonant cavity that can transmit microwaves, which is equivalent to modifying the width of the microwave resonant cavity. To explore the influence of different resonant cavity widths on the heating effect, based on the theory of equivalent microwave resonant cavity widths, starting from the maximum microwave resonant cavity width (2.0 b≈247 mm), since the thickness of the side plate where the material box width B is located is about 2 mm, the maximum distance that can be used for microwave transmission inside is 243 mm. The minimum value of width B needs to take into account the limit of mechanical processing, which can bear a certain mechanical strength and can be processed into shape, and is selected as 18 mm. The maximum value of width B considers that after adding width B, the middle area can still place common food, and the maximum value of width B is selected as 48 mm. At this time, the microwave transmission area inside the resonant cavity is 147 mm. In summary, when the width B is set to 18 mm, 33 mm and 48 mm, the middle value is the average of the maximum and minimum values. There are two inwardly folded flanges on the left and right sides, so the actual width of the resonant cavity that can actually transmit microwaves is 243-2*(18 or 33 or 48)=207, 177, 147mm.

[0034] ② Height A primarily affects the height of the food container. Considering the need to hold food inside, the thickness of common food items typically ranges from 5 to 20 mm. Given the need for vacuum packaging and securing with straps, a certain thickness range must be maintained; therefore, the minimum height A is set at 25 mm. Considering the need for smooth mechanical operation within the microwave resonant cavity, the maximum height A should fully consider the distances between the food container and the upper and lower parts of the resonant cavity; therefore, it is set at 65 mm. Intermediate values ​​are selected based on the average of the maximum and minimum values. In summary, height A is set to 25 mm, 45 mm, and 65 mm.

[0035] Furthermore, the setting of the distance D between the food and the metal rod in step (7-4) mainly considers the feasibility in practical applications. One side of the container needs to maintain a certain distance from the food to avoid uncontrollable effects on the food due to changes in the electric field caused by the metal material of the container. Based on actual conditions, the distance between the food and the front and rear ends of the container should be at least 35 mm. For the food (150 mm × 90 mm × 16 mm), the distance from the left side of the food to the left side of the metal rod is 35 mm. Figure 2As shown, the distance between the metal rods on both sides of the food container is (990+950) / 2=970 mm. The distance from the left side of the food at the far right to the resonant cavity should be (970-35-150=785mm). Therefore, the distance from the left side of the food to the left end of the food container ranges from 35 mm to 785 mm. Taking the average of two values ​​yields two values: 222.5 mm, 410 mm, and 597.5 mm. Since the food container enters through the inlet, is microwave-heated, and then exits through the outlet, all food items will undergo the complete microwave heating process. Based on the principle of symmetry, 35 mm from the left side of the food near the left metal rod of the food container is equivalent to 35 mm from the right metal rod. Therefore, the right side portion centered at 410 mm is omitted, and is set to selectable values ​​of 35 mm, 222.5 mm, and 410 mm; where D=35 and D=410 are the minimum and maximum values ​​within the research range, and D=222.5 mm is the median value within the research range.

[0036] Further, step (9) uses gellan gum as a food simulation for experimental verification. A certain proportion of gellan gum powder is dissolved in deionized water at 90°C. After it is fully dissolved, calcium chloride is added, and the mixture is heated until completely melted. Then, it is cooled to 65°C at room temperature. Finally, a certain amount of L-lysine and D-ribose are added. After mixing evenly, the solution is quickly poured into a prepared container, and the cooled and solidified food simulation is stored in a refrigerator.

[0037] Further, in step (10), the simulated food is cut into 150mm×90mm×16mm pieces.

[0038] Further, in step (11), a polytetrafluoroethylene mesh track is bound in the middle of the material box, and the polytetrafluoroethylene mesh is fixed to the side of the metal adjustment plate and the metal rod with metal screws or strips no larger than 3mm; the polytetrafluoroethylene mesh is cut and fixed according to the size of the simulated food, the simulated food is placed into the mesh bag, and the opening is sealed with strips.

[0039] A single-mode microwave resonant cavity heating and transfer device prepared by the above method has a carrier box with a specific size for a particular food, thereby achieving precise and uniform microwave heating of the specific food.

[0040] The beneficial effects of this invention are as follows:

[0041] (1) This invention provides a detailed description of the optimized technical solution for the metal design of the material carrier box. Without changing the main structure of the single mold cavity, starting with the material carrier box which is cheaper and easier to process, it can achieve precise optimization of the heating mode for different foods.

[0042] (2) The method of inward retraction of metal plates was adopted to control the microwave heating cavity at a very low cost.

[0043] (3) A metal rod for maintaining balance was designed, which can optimize the heating uniformity of different foods while maintaining balance. Attached Figure Description

[0044] Figure 1 This is a design flowchart of the present invention.

[0045] Figure 2 The material carrier box is constructed with hinges that adjust the electric field, including electric field width adjustment index B and material carrier box height adjustment index A.

[0046] Figure 3 The top view, front view, and side view of the loading box for the electric field adjustment plate have been added.

[0047] Figure 4 Mark the position and distance when food is placed on the container.

[0048] Figure 5 These are the food heating modes corresponding to different cavity widths.

[0049] Figure 6 These are simulation results of food heating modes corresponding to "electric field adjustment plates" of different sizes.

[0050] Figure 7 These are simulation results of food heating modes corresponding to metal rods of different diameters.

[0051] Figure 8 These are simulation results of the heating modes of food corresponding to the center-to-center spacing between different metal rods.

[0052] Figure 9 The simulation results show the food heating mode corresponding to the distance between the metal rod and the food.

[0053] Figure 10 This is a comparison of the results of simulated and experimental food heating modes (food dimensions: 150 mm × 90 mm × 16 mm; "electric field adjustment plate": width 45 mm, height 50 mm; metal rod: diameter 5 mm, center distance 25 mm). Figure (a) shows the food at a distance of 35 mm from the metal rod. Figure (b) shows the food at a distance of 410 mm from the metal rod.

[0054] Figure 11 This is a comparison of the time-temperature curves between the simulation results and the experimental results. Figure (a) shows the time-temperature curve of the hot spot. Figure (b) shows the time-temperature curve of the cold spot.

[0055] Figure 12 This is an introduction to the BJ9 rectangular waveguide standard. Detailed Implementation

[0056] The following description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0057] The following embodiments can be understood as illustrating only a part of the structure or method of the present invention, or as a combination of embodiments explaining the broader structure or method of the present invention. Unless otherwise specified, all raw materials of the present invention are commercially available.

[0058] Example 1:

[0059] A design method for a single-mode microwave resonant cavity heating and transfer device includes the following steps:

[0060] (1) such as Figure 12 As shown, a microwave frequency of 915 MHz was selected, and the BJ9 rectangular waveguide was determined as the intermediate module of the microwave resonant cavity from the microwave source. According to GB / T 11450.2-1989 "Hollow Metal Waveguides Part 2: Specifications for Ordinary Rectangular Waveguides", the long side of the rectangular waveguide was determined to be a (247.65 mm) and the short side was determined to be b (123.82 mm).

[0061] (2) For example Figure 2 , Figure 3 As shown, a food conveying device is designed. Geometric modeling is performed using the QW-Editor component in Quickwave 2018, and a scaled-down geometric model is drawn. This model should include a sound mechanical foundation for operation within a single-mode microwave resonant cavity, specifically: the microwave resonant cavity, waveguide, and all components affecting the electric field of the material carrier box; two metal connecting rods on each side; and two metal adjustment plates (with dimensions limited by height A and width B). Other components, such as fixing screws, hinges, and the outermost metal plate, are omitted during modeling because they do not affect the electric field distribution. This makes it a material conveying device (material carrier box).

[0062] (3) Establishing a numerical simulation model. In this embodiment, the QW-Simulator component in Quickwave 2018 software is used to perform dual-field modeling for microwave heating, and to analyze and perform coupled calculations of electromagnetic and thermal fields. The specific calculation process is as follows: ① Define the material properties of the microwave equipment, the loading box, and the food inside after geometric modeling, so as to solve the Maxwell equations for electromagnetic fields. The microwave equipment and the loading box are made of metal, and their dielectric and thermal properties are derived from the Quickwave material library. The dielectric constant of the simulated food is 64, the dielectric loss is -10J, the specific heat is 4.35 J / (g·℃), and the thermal conductivity is 0.48 W / (m·K). ② Configure the microwave equipment with microwave sources and set the emission direction, phase, and power of the microwave sources. The microwave sources are emitted simultaneously from opposite directions above and below into the microwave resonant cavity. The phase difference between the upper and lower microwave sources is 180°, and the power is 7.2kW. ③ Boundary settings and mesh optimization were performed. All metal materials were set as metal boundaries, and the maximum mesh size for each component was less than one-tenth of the microwave wavelength within the medium. The mesh size for air inside the waveguide was 33 mm, and for water and food, it was 4 mm. The mesh sizes for air were 4 mm × 4 mm × 18 mm, for water 4 mm × 4 mm × 1 mm, and for food 4 mm × 4 mm × 1 mm. ④ The electromagnetic heat consumed inside the food was calculated, yielding the heat energy obtained by the microwave electric field within the food through dielectric loss. The calculation formula is: Where P represents the energy output by microwaves per unit volume of food, expressed in W. The frequency is microwave, in MHz; Let E be the dielectric loss of the food in the dielectric material; E is the instantaneous electric field strength (vector) obtained from the numerical simulation software. This software needs to include the movement of metal components and can be used to simulate the movement of the food container.

[0063] (4) The heat source is set for the numerical simulation model, including the energy generated by microwaves and the energy generated by hot water. Specifically, in this embodiment, the heat transfer coefficient between water and the food surface is set to 180 W•m. -2 •K -1 The temperature of the hot water inside the resonant cavity is set to a constant 90℃.

[0064] (5) The material properties of the inner wall of the microwave resonant cavity and all components of the carrier box are set to metal; the metal boundary condition is an ideal electrical conductor. This material has the characteristic of completely reflecting the incident electromagnetic waves, and no energy will pass through the PEC surface material to enter the material interior.

[0065] (6) Determining the microwave resonant cavity width parameters: The maximum limit for the microwave resonant cavity width is set to 2b, and the minimum limit is set to 1b. The actual microwave resonant cavity width is selected from 1b to 2b. In this embodiment, the resonant cavity width is determined to be 247 mm, 207 mm, 177 mm, and 147 mm. The maximum value is 2b (approximately 247 mm), and the minimum value is 147 mm, which can accommodate a width of 140 mm and be reasonably fixed. The remaining gradients are selected as 207 mm and 177 mm according to the actual product requirements.

[0066] (7) Material container design: The design of the material container is mainly divided into three parts:

[0067] (7-1) The side metal sheet of the material box simulates the width of the microwave resonant cavity. The side is divided into height and width, which are set as A and B respectively. The side metal edge is also called the electric field adjustment plate. The thickness of the electric field adjustment plate of the material box is 2mm.

[0068] ① The width B is set to 18 mm, 33 mm, and 48 mm. The width of the microwave resonant cavity corresponds to the maximum width of the microwave resonant cavity: 2*b - 2*(width B) - 2*metal thickness (2*2). At this point, microwaves can pass through microwave sterilization systems with resonant cavity widths of 207 mm, 177 mm, and 147 mm. Width B is used to adjust the actual area within the microwave cavity that can transmit microwaves in practical applications. Width B is set to a minimum size (18 mm) that allows for practical processing and provides good mechanical support, and a maximum size of 48 mm to accommodate larger food items (140 mm wide).

[0069] ② Height A is set to 25mm, 45mm, and 65mm. The minimum height of height A is 25mm, which is the minimum acceptable height for successfully placing most food items, and the maximum height is 65mm, which is the maximum size that allows for smooth operation inside the resonant cavity. 45mm is the average of the maximum and minimum values.

[0070] ③ By combining different lengths and widths, a size combination model of the electric field adjustment plate is obtained.

[0071] (7-2) Metal rods are installed at the front and rear of the material box. The diameter of the metal rods affects the heating mode. The diameters are set to 3mm, 5mm, 7mm, 9mm, and 11mm. The diameter of 3mm is the minimum diameter that can support the three-dimensionality of the material box after machining, and 11mm is the maximum electric field strength that does not adversely affect the electric field distribution.

[0072] (7-3) Set the center distance between the front and rear metal bars of the material carrier box. After determining the optimal setting diameter, further analyze the center distance between the metal bars of the material carrier box and set three different center distances, namely 50mm, 25mm and 12.5mm.

[0073] (7-4) For example Figure 4 As shown, the distance between the metal connecting rod and the food in the X direction is set. After determining the influence of the diameter and center distance of the metal rod on the heating of the food, the range of influence of the metal rod on the food is investigated. The food is set to be heated statically directly below the microwave source, and the distance between the metal rod and the food is set as D. D can be set to 35mm, 222.5mm, or 410mm. 35mm is the minimum distance that can be achieved when the food is softly packaged and fixed in the carrier box. The distance between the left and right metal rods of the food in the carrier box is 970mm. Since the carrier box is symmetrical, the food can be fully subjected to the microwave heating process in the carrier box. Due to the principle of symmetry, only the left part of the carrier box is considered. The distance between the food in the center of the carrier box and the left metal rod is half the distance between the metal rods (970mm / 2) - half the length of the food in the X direction (150mm / 2) = 410mm. Therefore, D=35 and D=410 are the minimum and maximum values ​​of the research range, and D=222.5mm is the median value of the research range.

[0074] (8) Perform numerical simulation of the food carrier box, and calculate that the food and food carrier box are stationary together in the center of the cavity during the simulation process, facing the waveguide heating for 60s.

[0075] (8-1) Numerical simulation processing was performed on the width of microwave resonant cavities with different widths;

[0076] (8-2) Numerical simulation was performed on different combinations of the height and width of the electric field adjustment plate; the differences between numerical simulations using the electric field adjustment plate width adjustment and the microwave resonant cavity width adjustment were compared, and the correlation between different electric field adjustment plate heights was compared.

[0077] (8-3) Simulate the diameter of the metal rods on the material carriers of different diameters and compare the effects of different metal rod diameters on the food heating effect;

[0078] (8-4) Simulate the center spacing between metal rods with optimized diameters and compare the effects of different center spacings of metal rods on food heating effect;

[0079] (8-5) Numerical simulation was performed on the distance between the metal rods with optimized diameter and center spacing and the food to compare the effect of different metal rod center spacing on the food heating effect.

[0080] (8-6) The optimized width of the food resonant cavity, the height and width of the side plate of the material box (metal adjustment plate), the diameter of the metal adjustment rod, the center distance between the metal adjustment rods, and the distance between the metal adjustment rod and the food are obtained, in mm.

[0081] (9) Sample preparation for experimental verification: Gellan gum was used as a food simulant for experimental verification. 1% low-acyl gellan gum powder was dissolved in deionized water at 90℃. After complete dissolution, 0.2% calcium chloride was added, and the mixture was heated until completely melted. Then, it was cooled to 65℃ at room temperature. Finally, a certain amount of 1.5% L-lysine and D-ribose was added. After mixing evenly, the solution was quickly poured into a prepared container, and the cooled and solidified food simulant was stored in a refrigerator.

[0082] (10) Simulated microwave food processing: The simulated food was cut into 150mm×90mm×16mm pieces. It was placed in a heat-resistant retort pouch, vacuum-packed, and then placed on a food carrier box. Subsequently, it was processed in a microwave sterilization system. The experimental parameters in the microwave sterilization process were matched with the parameters set in the simulation.

[0083] (11) Machining is performed according to the optimized parameters, including the width of the food resonant cavity, the height and width of the side plate of the material box (metal adjustment plate), the diameter of the metal adjustment rod, the center distance between the metal adjustment plates, and the distance between the metal adjustment rod and the food. The metal material box is then obtained.

[0084] (11-1) Bind a polytetrafluoroethylene mesh track in the middle of the loading box, and use metal screws or strips no larger than 3mm to fix the polytetrafluoroethylene mesh to the side of the metal adjustment plate and the metal rod.

[0085] (11-2) Cut and fix the polytetrafluoroethylene mesh according to the size of the simulated food, place the simulated food into the mesh, and seal it with a tape.

[0086] (12) Place the material carrier into the simulated food resonant cavity, set the microwave power and the microwave source used, and perform microwave sterilization. After the treatment is completed, take out the heat-resistant retort bag and put it into cold water for cooling.

[0087] (13) Simulated food thermal pattern analysis: After cooling, the simulated food sample with the cooking bag removed was placed in a photography studio to take front, back and middle cross-section images, and the photos were converted into pseudo-color images. The heating pattern obtained from the experiment was compared with the heating pattern obtained from the simulation model to verify the stability of the simulation model.

[0088] (14) Temperature monitoring at simulated cold spots in food: Once the heating mode is determined, the probe of the metal wireless temperature sensor can be placed at representative locations (such as hot spots and cold spots) according to the heating mode diagram, and the time-temperature curve can be measured. The time-temperature curve obtained from the experiment is compared with the time-temperature curve obtained from the simulation model to further verify the accuracy and stability of the simulation model.

[0089] Experimental results:

[0090] (1) Figure 5 The numerical simulation results of Example 1 from step 1 to steps 6 and 8-1 are shown. a, b, c, and d represent food heating modes with cavity widths of 247 mm, 207 mm, 177 mm, and 147 mm, respectively. These four heating modes, with their different cavity widths, exhibit a cold-hot-cold-cold distribution along the Y-direction. The main difference lies in the proportion of the hot spot region in the Y-direction. A larger proportion of the hot spot region in the Y-direction indicates better continuity of the food's heat profile in the Y-direction, i.e., better heating uniformity.

[0091] Comparing Figures a and b, the heating patterns of the foods corresponding to these two cavity widths are similar, but the heating intensity corresponding to a cavity width of 247 mm is higher than that corresponding to a cavity width of 207 mm. Compared to the heating patterns corresponding to Figures a and b, the hot spot area in Figure c occupies a smaller proportion of the entire food, with the hot spot concentrated in the middle of the food, and the overall heating intensity of the food is relatively low. The hot spot area in Figure d occupies a larger proportion in the Y direction, indicating that the food shown in Figure d has better heating uniformity.

[0092] The above results indicate that the cavity width affects the heating pattern of food. Changing the cavity width can improve heating uniformity, but there is no fixed rule between changes in cavity width and heating pattern. For the experimental food in this embodiment, the heating effect was best when the cavity width was 147 mm.

[0093] (2) Determine the parameters of the metal adjustment plate according to step 7-2 to obtain the combination of the height and width of the electric field adjustment plate. The specific names and combination parameters are shown in Table 1.

[0094] Table 1. Combinations of height and width of the electric field adjustment plate

[0095]

[0096] Based on the numerical simulation scheme in 8-2, the following results are obtained: Figure 6The simulation results for food heating modes corresponding to different sizes of "electric field adjustment plates" are shown. Models 1-9 represent the simulation results for the food heating modes corresponding to nine simulation models. Overall, according to Models 1-9, all food heating modes exhibit a similar heating pattern of cold spot region-hot spot region-cold spot region in the Y direction. The main difference lies in the proportion of the hot spot region in the Y direction, i.e., the width of the hot spot region.

[0097] The "electric field adjustment plate" of Models 1-3 has a width of 18 mm and heights of 25 mm, 45 mm, and 65 mm, respectively. These three models have similar heating modes but different heating intensities. Model 3 has the highest heating intensity, followed by Model 2, and Model 1 has the lowest. Two parallel strip-shaped cold spot areas are distributed along the top and bottom edges of the food. A hot spot area runs between the two cold spot areas, and both the cold and hot spots are evenly distributed along the X-direction.

[0098] The "electric field adjustment plate" in Models 4-6 has a width of 33 mm and heights of 25 mm, 45 mm, and 65 mm, respectively. The heating pattern of these three models also consists of two cold spot strips and one hot spot strip. The hot spot strip is located in the center of the food, while the two cold spot strips are distributed along the Y-axis on either side of the hot spot strip, located at the edge of the food. The main difference between the three models' heating patterns lies in the proportion of the hot spot strip in the Y-axis; Model 5 has the largest proportion, resulting in better continuity in the Y-axis and thus better heating uniformity.

[0099] The "electric field regulating plate" in Models 7-9 has a width of 48 mm and heights of 25 mm, 45 mm, and 65 mm, respectively. The hot spots in these three models are also distributed in the center of the food, while the cold spots are distributed at the edges. Compared to "electric field regulating plate" widths of 18 mm and 33 mm, the height of the "electric field regulating plate" has a more significant impact on heating when the plate is 48 mm wide. The heating intensity of Model 8 is significantly higher than that of Models 7 and 9, and the heating uniformity of Models 7 and 9 is inferior to that of Model 8.

[0100] The simulation results above show that both the width and height of the "electric field regulating plate" affect the heating pattern of the food, but there is no fixed relationship between the specific heating pattern change and the size of the "electric field regulating plate". The food as a whole exhibits a cold-hot-cold heating pattern along the Y direction. Among these nine models, Model 8 has the best heating effect. This indicates that for the experimental food, a food container with an "electric field regulating plate" (50 mm wide and 45 mm high) can achieve a better heating effect. This shows that the metal "electric field regulating plate" can effectively regulate the electric field distribution within the cavity, and designing an "electric field regulating plate" to improve the heating uniformity of food is effective.

[0101] (3) Process according to steps 7-2, 8-2 and 8-3 to obtain the following: Figure 7 The simulation results show the heating mode of the food corresponding to the metal rod shown. The main hot spots of the food heating mode shown in the figure are divided into region 1 and region 2.

[0102] Figure a shows the food heating pattern without a metal rod, where the temperature is high in the center and low at the edges. A large hot spot is located in the center of the food. There is a cold spot on each side of the hot spot along the Y direction. Figures b to f show the food heating patterns with metal rods of different diameters. Compared to the heating pattern without a metal rod, the presence of the metal rod divides the relatively large hot spot into two hot spot regions. This indicates that the metal rod affects the electric field distribution. The heating pattern of the food with a 3 mm diameter metal rod (Figure b) is closest to that without a metal rod (Figure a). As the diameter of the metal rod increases, the overall heating pattern of the food remains unchanged, but the heating intensity of regions 1 and 2 changes. These results show that the presence of a metal rod affects the heating pattern of the food, and the smaller the diameter of the metal rod, the smaller the impact. Increasing the diameter of the metal rod reduces the heating intensity in the area near the metal rod and increases the heating intensity of hot spot regions 1 and 2. This is because the metal rod is made of metal, and metal can regulate the electric field distribution.

[0103] The primary function of the metal connecting rod is to connect the food container, so its impact on the food heating mode should be minimized. Simulation results show that a smaller diameter metal rod has less impact on the food heating mode. However, considering practical applications, a metal rod that is too thin is unsuitable for installation on the food container for connection; therefore, the optimal metal rod diameter is determined to be 5 mm.

[0104] (4) Determine the parameters according to step 7-3, and perform numerical simulation processing according to step 8-4 to obtain the following results: Figure 8The simulation results show the heating modes of food corresponding to different center-to-center distances of the metal rods. Based on the research results on the influence of the metal rod diameter on the food heating mode, the optimal metal rod diameter was determined to be 5 mm. Therefore, this section uses a 5 mm diameter metal rod to study the influence of the center-to-center distance between the upper and lower metal rods on the food heating mode. Considering practical factors, three different center-to-center distances were studied: 50 mm, 25 mm, and 12.5 mm. When studying the center-to-center distance of the metal rods, the following... Figure 4 The study focused on the heating position of the food shown, with the food being heated statically for 60 seconds. Figure 8 The results show the effect of the center-to-center distance between the upper and lower metal rods on the heating pattern of food. Figure a shows the heating pattern without metal rods. Figures b to d show the center-to-center distances of the upper and lower metal rods, which are 50 mm, 25 mm, and 12.5 mm, respectively. Dashed boxes are used to divide the main hot spots of each food item. The heating pattern in Figure c is closest to that in Figure a, meaning that the metal rods have the least impact on the heating pattern when the center-to-center distance is 25 mm. Compared to the heating pattern corresponding to a center-to-center distance of 25 mm (Figure c), when the center-to-center distance is 50 mm (Figure b), the hot spots (including 1 and 2) receive greater heating intensity, while the areas near the metal rods receive less heating intensity. When the center-to-center distance is 12.5 mm, the hot spots are divided into three areas, with areas 2 and 3 receiving higher heating intensity than area 1. Similarly, the areas near the metal rods receive lower heating intensity. These results indicate that the center-to-center distance of the metal rods affects the heating pattern of food, with the smallest impact at a distance of 25 mm. Therefore, 25 mm can be chosen as the optimal center-to-center distance for the metal rods.

[0105] (5) Determine the parameters according to step 7-4, and perform numerical simulation processing in step 8-5 to obtain the following results. Figure 9 The heating mode is shown by the distance between the metal rod and the food.

[0106] Figure 9This presents simulation results of food heating patterns at different distances between the metal rod and the food. All food heating patterns exhibit an alternating hot and cold (cold-hot-cold) distribution in the Y direction. There is a parallel cold spot region along the X direction at the top and bottom edges of the food, with a hot spot region parallel to the cold spot region located between the two cold spot regions. Compared to the hot spot region in the center of the food, the hot spot region at the edge of the food has a lower temperature. The dotted box in the figure encloses the hot spot region located in the center of the food. When D is 35 mm and 85 mm, the presence of the metal rod changes the hot spot region in the center of the food from one relatively large hot spot region to two hot spot regions. When D is 128.75 mm, 222.5 mm, and 410 mm, the food heating patterns with and without the metal rod are basically the same. The results show that when the distance between the metal rod and the food is less than 128.75 mm, the metal rod affects the food heating pattern.

[0107] (6) Perform numerical simulation of the optimized parameters according to step 8-6, and conduct experimental verification according to step 9-13. Fix the simulated food on the carrier box and put it into the single-mode microwave heating system for microwave treatment. Figure 10 This is a comparison of the results of simulation and experimental food heating modes. Figure 10 -a corresponds to the result when the food is 35 mm away from the metal rod. Figure 10 -b corresponds to the results when the food is 410 mm away from the metal rod. When the food is 35 mm away from the metal rod, the heating pattern of the food shows a cold-hot-cold distribution along the Y direction, and both the cold and hot spot areas are distributed in stripes along the X direction. When the food is 410 mm away from the metal rod, the overall heating pattern is similar to that when the food is 35 mm away, but the continuity of the hot spot area in the X direction is better at this distance. This is because at this distance, the food is not affected by the metal rod. Figure 10 The simulation results of the heating mode of the computer simulation model established in this study are basically consistent with the experimental results. This indicates that the established simulation model is reliable.

[0108] (7) In order to further verify the simulation model, the following were selected Figure 10 The cold and hot spots marked in b were used to determine the time-temperature curves at these two locations according to step 14. Figure 11 -a and Figure 11 -b represents the time-temperature curves from both the simulation and experiment. The time-temperature curves for the cold and hot spots obtained from the simulation and experiment are basically consistent, indicating that the established computer simulation model is accurate. These results demonstrate that the computer simulation model is stable and accurate.

[0109] All aspects, embodiments, and features of this invention should be considered illustrative in all respects and not limiting of the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0110] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.

[0111] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A design and optimization method for a single-mode microwave resonant cavity heating and transmission device, characterized in that... Includes the following steps: (1) Select the microwave frequency and determine the rectangular waveguide used in the microwave resonant cavity based on the microwave frequency. The long side of the rectangular waveguide is a and the short side is b. (2) Design the food conveying device and draw a geometric model; the geometric model includes forming a stable rectangular shape in the XY plane in the single-mode microwave resonant cavity, maintaining a rectangular shape with thickness in the XZ plane, and providing the main mechanical stress support in the YZ direction to obtain a three-dimensional shape of the material box that is almost impossible to change. (3) Establish a numerical simulation model. The software used in the simulation model includes the movement of metal components for simulating the movement of the material box. (4) Set the heat source for the numerical simulation model, including the energy generated by microwaves and the energy generated by hot water; (5) Set the metal boundary condition for the microwave resonant cavity, and set the material properties of the inner wall of the resonant cavity and all components of the carrier box to metal; (6) Determine the width parameters of the microwave resonant cavity; select a microwave cavity width with a maximum value of 2b and a minimum value of 1b, and set at least one width gradient in between; (7) Material box design: (7-1) The side metal sheet of the material carrier simulates the width of the microwave resonant cavity. The side is divided into height A and width B. The side metal edge is called the electric field adjustment plate. The thickness of the electric field adjustment plate is set: different lengths and widths are combined to obtain the size combination model of the electric field adjustment plate. Among them, the metal design of the material carrier has been optimized without changing the main structure of the single-mode cavity. Starting from the material carrier, the precise optimization of the targeted heating mode for different foods can be achieved. (7-2) Metal rods for maintaining balance are installed at the front and rear of the material box, and the diameter of the metal rods is set. (7-3) Center distance between the front and rear metal bars of the material carrier box; After determining the optimal setting diameter, further analyze the center distance between the metal bars of the material carrier box and set different center distances; (7-4) Set the food to be heated statically directly below the microwave source, and set the distance between the metal rod and the food to D; (8) Perform numerical simulation of the food carrier box, and calculate the food and food carrier box being stationary together in the center of the cavity during the simulation process, facing the rectangular waveguide for heating; (8-1) Numerical simulation processing was performed on the width of microwave resonant cavities with different widths; (8-2) Numerical simulation was performed on the models of different combinations of the width and height of the electric field adjustment plates; the differences between the numerical simulations of adjusting the width of the electric field adjustment plate and adjusting the width of the microwave resonant cavity were compared, and the correlation between the heights of different electric field adjustment plates was compared. (8-3) Simulate the diameter of the metal rods on the material carriers of different diameters and compare the effects of different metal rod diameters on the food heating effect; (8-4) Simulate the center spacing between metal rods with optimized diameters and compare the effects of different center spacings of metal rods on food heating effect; (8-5) Numerical simulation was performed on the distance between the metal rods with optimized diameter and center spacing and the food to compare the effect of different metal rod center spacing on the food heating effect. (8-6) The optimized food resonant cavity width, material box side plate parameters, metal adjustment rod diameter, center distance between metal adjustment rods, and distance between metal adjustment rods and food are obtained.

2. The method as described in claim 1, characterized in that... After obtaining the optimized parameters, a verification step is also included: (9) Prepare experimental verification samples; (10) Simulated food microwave treatment: The simulated food was cut into pieces, put into a heat-resistant retort bag, vacuum-packed and placed on a food carrier box, and then processed in a microwave sterilization system; the experimental parameters in the microwave sterilization process matched the parameters set in the simulation. (11) After optimizing the parameters in step (8), determine the optimal parameters of the food resonant cavity width, the side plate parameters of the loading box, the diameter of the metal adjusting rod, the center distance between the metal adjusting rods, and the distance between the metal adjusting rod and the food, and perform mechanical processing to obtain the metal object of the loading box; (12) Add the material carrier box into the simulated food resonant cavity, set the microwave power and the microwave source used, and carry out microwave sterilization treatment; After processing, remove the heat-resistant retort bag and place it in cold water to cool it down. (13) Analysis of the heat pattern of simulated food: After cooling, the simulated food sample with the cooking bag removed was placed in the photography studio to take pictures of the front, back and middle cross-section, and the pictures were converted into pseudo-color pictures; the heating pattern obtained in the experiment was compared with the heating pattern obtained in the simulation model to verify the stability of the simulation model. (14) Temperature monitoring of simulated cold spots in food: After determining the heating mode, the probe of the metal wireless temperature sensor is placed at a representative location according to the heating mode diagram, and the time-temperature curve is measured. The time-temperature curve obtained in the experiment is compared with the time-temperature curve obtained in the simulation model to further verify the accuracy and stability of the simulation model.

3. The method as described in claim 1, characterized in that: In step (7-1), ① the width B is set to 18 mm, 33 mm, and 48 mm, respectively, to correspond to microwave sterilization systems with cavity widths of 207 mm, 177 mm, and 147 mm; ② the height A is set to 25 mm, 45 mm, and 65 mm.

4. The method as described in claim 1, characterized in that: In step (7-4), D is set to 35 mm, 222.5 mm, or 410 mm; where D=35 mm and D=410 mm are the minimum and maximum values ​​of the research range, and D=222.5 mm is the intermediate value of the research range.

5. The method as described in claim 2, characterized in that: Step (9) uses gellan gum to simulate food for experimental verification.

6. The method as described in claim 2, characterized in that: Step (10) Cut the simulated food into 150mm×90mm×16mm pieces.

7. The method as described in claim 2, characterized in that: Step (11) Bind the PTFE mesh track in the middle of the material box, and fix the PTFE mesh to the side of the metal adjustment plate and the metal rod with metal screws or strips no larger than 3mm; cut and fix the PTFE mesh according to the size of the simulated food, place the simulated food into the mesh bag, and seal it with strips.

Images