Ridge waveguide design method and system for microwave heating of liquid material

Abstract

The invention discloses a ridge waveguide design method and system for liquid material microwave heating, and belongs to the technical field of liquid microwave heating. The ridge-shaped waveguide structure comprises a stepped discontinuous waveguide, stepped ridges, a double-ridge waveguide, a pipeline and a standard waveguide, the stepped ridges are located on the two sides of the stepped discontinuous waveguide, the double-ridge waveguide is connected with the stepped discontinuous waveguide, the pipeline is installed in the double-ridge waveguide, and the standard waveguide is connected with the stepped discontinuous waveguide. The standard waveguide is connected with the stepped discontinuous waveguide, parameters of each structure are determined, a simulation model is established for analysis, and a ridge waveguide structure matching form is obtained. According to the method, the compatibility of different pipeline thicknesses and liquid food dielectric range changes can be realized through geometric and matching optimization. The ridge waveguide heating system designed by the method can effectively deal with the impedance mismatch problem caused by the change of the dielectric property of the liquid material along with the temperature, reduces the energy reflection loss in the hot working process, and improves the operation stability of the system.

Description

Technical Field

[0001] This invention relates to the field of liquid microwave heating technology, specifically to a ridge waveguide design method and system for microwave heating of liquid materials. Background Technology

[0002] Heat treatment of liquid materials is a core process in the food, pharmaceutical, and chemical industries. Traditional heat treatment processes for liquid materials, such as pasteurization and UHT sterilization, have long relied on steam conduction heating, which has inherent problems such as high thermal inertia, coking on pipe walls, and low energy utilization.

[0003] In recent years, microwave heating technology has been regarded as an ideal alternative due to its advantages such as rapid heating, selective heating, and no dielectric residue. However, its large-scale application in industrial continuous flow processing scenarios still faces core bottlenecks: existing microwave continuous flow devices generally adopt multiple magnetrons in parallel or high-power single-cavity structures to achieve the material temperature rise target, resulting in bulky equipment and excessively high system power consumption, which seriously restricts its applicability in space-constrained production lines and special processing scenarios. In addition, when conventional rectangular waveguides are used for continuous flow dynamic heating, the insufficient coordination between the electromagnetic field distribution and the fluid flow state leads to the discretization of the energy density in the effective heating area, forcing the system to compensate for thermal efficiency losses by increasing the input power.

[0004] Ridge waveguides can overcome the problem of low energy utilization in rectangular waveguides. Through the unique field strength focusing effect of ridge waveguides, they can achieve directional enhancement of electromagnetic field energy flux density while reducing the microwave propagation cutoff frequency. The power requirement is lower than that of traditional rectangular waveguide devices, providing a brand-new implementation path for continuous flow microwave heating technology.

[0005] Chinese patent document CN114007292B discloses a microwave heating thin film device and system based on ridge waveguides, which uses ridge waveguides to heat the thin film. Chinese patent document CN113078432A discloses a microwave heating filament device based on ridge waveguides, capable of heating filaments. However, currently, ridge waveguide structures in the field of microwave heating are mainly used for solid media. These technologies rely on small ridge spacing to concentrate the electric field, making them suitable for solid materials with thin and fine structures. When the medium becomes a liquid material, ridge waveguide design faces significant challenges: on the one hand, if the original ridge spacing is directly introduced into the liquid pipeline, even with optimization, a direct fit cannot be achieved, resulting in the microwave energy not being effectively absorbed by the liquid material; on the other hand, the small ridge spacing of conventional ridge waveguides cannot adapt to larger pipeline diameters. If the ridge spacing is directly increased, the field strength is significantly weakened, losing the field concentration advantage of the ridge waveguide, and the heating rate and uniformity cannot meet the requirements for rapid heating of liquid materials. Furthermore, the dynamic flow characteristics of liquids significantly alter the impedance matching conditions of ridge waveguides, easily leading to a surge in energy reflectivity or localized overheating. A single geometric design of the ridge waveguide cannot balance the contradiction between pipe size and field strength concentration, making it difficult to achieve high efficiency and stability for industrial-grade continuous flow heating. Existing technologies include patents attempting to address the microwave processing problem of liquid media with ridge waveguides. For example, Chinese patent CN 119503950 A discloses a device combining a single ridge waveguide with an electrodeless ultraviolet lamp for water disinfection. In this patent, microwave energy is used to synergistically with ultraviolet light for liquid disinfection, but the temperature rise is limited (<45°C), failing to meet the demand for rapid high-temperature heating. Liquid materials requiring higher heating often need to have their dielectric properties considered simultaneously, as these properties change significantly with increasing temperature. When dielectric loss varies considerably, the matching effect becomes unbalanced. Therefore, utilizing the field strength concentration effect of ridge waveguides to heat liquid materials still lacks a systematic design method and cannot effectively solve the problem of microwave energy coupling efficiency under material flow conditions. Summary of the Invention

[0006] To address the aforementioned issues, this invention provides a ridge waveguide design method and system for microwave heating of liquid materials. By optimizing the matching form and structure between the ridge waveguide and the liquid material, it adapts to the dielectric change characteristics of the liquid material during heating. Furthermore, based on the heating requirements of different pipelines and liquid materials, this method can optimize the design of the ridge waveguide structure, thereby improving the application stability of different types of liquid materials in the ridge waveguide.

[0007] In a first aspect, the present invention provides a ridge waveguide design method for microwave heating of liquid materials, using a ridge waveguide structure, the ridge waveguide structure including a stepped discontinuous waveguide, a stepped ridge, a double-ridge waveguide, a conduit and a standard waveguide, the stepped ridge being located on both sides of the stepped discontinuous waveguide, the double-ridge waveguide being connected to the stepped discontinuous waveguide, the conduit being installed in the double-ridge waveguide, and the standard waveguide being connected to the stepped discontinuous waveguide; The ridge waveguide design method includes: Step 1: Determine the dimensions a of the first side and b of the second side of the cross-section of the double-ridge waveguide based on the inner diameter d of the pipeline containing the liquid material. Step 2: The double ridges of the double-ridged waveguide are located in the middle of the first side, and the relative orientation of the conduit and the ridges of the double-ridged waveguide is determined; Step 3: Determine the spacing c of the double-ridge waveguide ridges based on Step 1 and Step 2; Step 4: Determine the width w of the double-ridge waveguide ridge, which must satisfy: 0.1≤w / a≤0.4; Step 5: Determine the length gl and shape of the pipeline. The length gl of the pipeline must satisfy: gl > b; Step 6: Determine the number n and length jl of the double-ridge waveguides; Step 7: Select a standard waveguide that meets the design requirements and determine the number of the stepped discontinuous waveguides; Step 8: Establish a finite element simulation model of the continuous flow microwave system based on the above parameters and matching methods, and set material parameters at different locations; Step 9: Determine the number m2, width rw, and height rh of the stepped ridges based on the dielectric properties of the liquid material and the dimensions of the double-ridge waveguide and the standard waveguide; Step 10: Multiphysics simulation optimization improves the robustness of the ridge waveguide structure, making the structure of the ridge cavity compatible with liquid materials. By fixing the relevant parameters of the double-ridge waveguide, the length rl of the stepped ridge of the matching section is set as the parameter to be optimized, and the calculation target is set as S11≤-10dB; where S11 is the input reflection coefficient. Step 11: Determine all parameters of the designed ridge waveguide structure cavity and the pipeline through the above process. Select the dielectric constant values ​​of the designed liquid material at three arbitrary points within the heating range to verify the reflection, ensuring that S11 ≤ -10dB during the heating process.

[0008] In one embodiment of the present invention, in step 1, the dimension b of the second side is [2d, 10d], and the dimension a of the first side is 2b.

[0009] In one embodiment of the present invention, the number of double-ridged waveguides n=1, and the length jl of the double-ridged waveguides is greater than 4 / 3gl.

[0010] In one embodiment of the present invention, the number of double-ridged waveguides n > 1, and the length of the double-ridged waveguides jl = gl / n.

[0011] In one embodiment of the present invention, a slot is provided on the standard waveguide, the length of the slot l ∈ [0.4λc, 0.5λc], and the width fw of the slot needs to satisfy 10. <e / fw<40; Where λc is the wavelength in free space at the resonant frequency, and e is the length of the third side of the standard waveguide where the slit surface is located, that is, the width dimension of the cross section of the standard waveguide (5).

[0012] In one embodiment of the present invention, the ratio of the dimension a of the first side to the dimension e of the standard waveguide, i.e., a / e≤2, the number m1 of the stepped discontinuous waveguides≥2, and the length of the stepped discontinuous waveguides is an integer multiple of a quarter wavelength.

[0013] In one embodiment of the present invention, the number of stepped ridges m2=1, the height rh of the stepped ridge is consistent with the width w of the upper ridge of the double-ridge waveguide, and the width rw of the stepped ridge is calculated based on the distance between the two stepped ridges, rw=(tb-c) / 2; where tb is the narrow side length of the stepped discontinuous waveguide. The number of step ridges m2 > 1. The relevant parameters of the first step ridge are the same as when m2 = 1. The distance between the two ridges of the secondary step ridge must be twice the distance between the ridges of the previous step ridge, and the height must be consistent with the previous step.

[0014] In one embodiment of the present invention, the pipeline is a straight pipe, the pipeline is perpendicular to the ridge of the ridge waveguide, and the relationship between the spacing c of the ridges on the double-ridge waveguide and the inner diameter d and the thickness t of the pipeline must satisfy: c > (d + 2t + 1) mm.

[0015] In one embodiment of the present invention, the conduit is an L-shaped tube, the conduit is parallel to the ridge of the ridge waveguide, and the relationship between the spacing c of the ridges on the double-ridge waveguide and the inner diameter d and the thickness t of the conduit must satisfy: c > (d + 2t + 4) mm.

[0016] Secondly, the present invention provides a system for microwave heating of liquid materials, which uses the aforementioned ridge waveguide design method for microwave heating of liquid materials. The liquid material microwave heating system includes the ridge waveguide structure, material pipeline, microwave source generator, cooling device, and back pressure valve, wherein the back pressure valve is adapted according to the expected range of temperature heating.

[0017] The beneficial effects of this invention are: 1. This invention provides a ridge waveguide design method for microwave heating of liquid materials. Compared with existing ridge waveguide heating systems, this method can achieve compatibility with different pipe diameters and varying dielectric ranges of liquid foods through geometric and matching optimization, avoiding the application limitations of existing technologies, such as short transmission distances or impedance mismatch during heating.

[0018] 2. The design method of this invention provides a closed-loop optimization framework, including parameter determination and simulation verification steps for ridge waveguides. It realizes a waveguide structure design method based on differences in pipe dimensions and material properties, improving the application stability of different types of liquid materials in ridge waveguides. The ridge waveguide heating system designed based on this method can effectively address the impedance mismatch problem caused by temperature changes in the dielectric properties of liquid materials, reduce energy reflection losses during thermal processing, and improve system operational stability. It is widely applicable to industrial pharmaceuticals, chemicals, food processing, and other fields. Furthermore, using this method for ridge waveguide structure design can reduce R&D time, accelerate R&D speed, and lower R&D costs. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the ridge waveguide microwave cavity in Embodiment 1.

[0020] Figure 2 This is a schematic diagram of the ridge waveguide microwave cavity from another perspective in Embodiment 1.

[0021] Figure 3 This is a bottom view of the ridge waveguide microwave cavity in Embodiment 1.

[0022] Figure 4 This is a top view of the gap in Example 1.

[0023] Figure 5 This is a schematic diagram of the ridge waveguide microwave cavity in Embodiment 2.

[0024] Figure 6 This is a structural schematic diagram of the ridge waveguide microwave cavity from another perspective in Embodiment 2.

[0025] Figure 7 This is a front view of the ridge waveguide microwave cavity in Embodiment 2.

[0026] Figure 8 This is a right view of the ridge waveguide microwave cavity in Embodiment 2.

[0027] Figure 9 This is a temperature distribution diagram of the microwave cavity heating liquid material in the ridge waveguide of Example 1.

[0028] Figure 10 This is a temperature distribution diagram of the ridge waveguide microwave cavity used in Example 2 to heat liquid materials.

[0029] Figure 11 This is an electric field distribution diagram of the ridge waveguide microwave cavity in Example 1.

[0030] Figure 12 This is an electric field distribution diagram of the ridge waveguide microwave cavity in Example 2.

[0031] Figure 13 This is the electric field distribution diagram of the standard waveguide in Comparative Example 1.

[0032] Figure 14 This is the electric field distribution diagram of the ridge waveguide in Comparative Example 1.

[0033] Figure 15 This is the electric field distribution diagram of the microwave cavity of the ridge waveguide in Comparative Example 2 before optimization.

[0034] Figure 16 This is the electric field distribution diagram after optimization of the ridge waveguide microwave cavity in Comparative Example 2.

[0035] In the picture: 1. Stepped discontinuous waveguide; 2. Stepped ridge; 3. Double ridge waveguide; 31. First side; 32. Second side; 4. Pipeline; 5. Standard waveguide; 51. Third side; 6. Gap; 7. Support. Detailed Implementation

[0036] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "first position" and "second position" refer to two different positions.

[0038] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0039] like Figures 1 to 16 As shown, this invention provides a ridge waveguide structure for microwave heating of liquid materials. The ridge waveguide structure includes a stepped discontinuous waveguide 1, a stepped ridge 2, a double-ridge waveguide 3, a conduit 4, and a standard waveguide 5. The stepped ridge 2 is located on both sides of the stepped discontinuous waveguide 1. The double-ridge waveguide 3 is connected to the stepped discontinuous waveguide 1. The conduit 4 is installed in the double-ridge waveguide 3. The standard waveguide 5 is located on the side of the stepped discontinuous waveguide 1 opposite to the double-ridge waveguide 3 and is connected to the stepped discontinuous waveguide 1. A gap 6 can also be provided at the connection between the standard waveguide 5 and the stepped discontinuous waveguide 1 to uniformly distribute the fed microwaves.

[0040] In some embodiments, the double-ridged waveguide 3 includes a first side 31 and a second side 32, where the first side 31 is the wide side of the cross-section of the double-ridged waveguide 3 and the second side 32 is the narrow side of the cross-section of the double-ridged waveguide 3. The standard waveguide 5 includes a third side 51, where the third side 51 is the wide side of the cross-section of the standard waveguide 5.

[0041] In some embodiments, the pipe 4 can be a straight pipe or an L-shaped pipe. When the pipe 4 is an L-shaped pipe, since the pipe 4 is long, a support 7 is needed to provide support for the pipe 4.

[0042] This invention provides a method for designing a ridge waveguide structure for microwave heating of liquid materials, the method comprising: Step 1: Determine the dimension b of the second side 32 of the cross section of the double-ridge waveguide 3 based on the inner diameter d of the liquid material pipeline 4, b ∈ [2d, 10d], and calculate the dimension a of the first side 31 of the cross section of the double-ridge waveguide 3, a=2b; Step 2: The double ridges of the double-ridged waveguide 3 are located in the middle of the first side 31, which can compress the field strength of the second side and determine the relative direction of the ridges of the conduit 4 and the double-ridged waveguide 3. When the conduit 4 is perpendicular to the ridge of the double-ridged waveguide 3, the local field strength can be further enhanced by reducing the ridge spacing. This coupling method can more effectively coordinate with the wave propagation direction, thereby optimizing the field strength distribution. When the conduit 4 is parallel to the ridge of the double-ridged waveguide 3, the interference of the conduit 4 on the guided wave mode can be effectively avoided by increasing the ridge spacing, thus ensuring the effective transmission of the wave.

[0043] Step 3: Determine the spacing c of the ridges on the double-ridged waveguide 3 based on Step 1 and Step 2; When the conduit 4 is perpendicular to the ridge of the double-ridged waveguide 3, the relationship between the spacing c of the ridges on the double-ridged waveguide 3 and the inner diameter d and thickness t of the conduit 4 must satisfy: c > (d + 2t + 1) mm. When the conduit 4 is parallel to the ridge of the double-ridged waveguide 3, the relationship between the spacing c of the ridges on the double-ridged waveguide 3 and the inner diameter d and thickness t of the conduit 4 must satisfy: c > (d + 2t + 4) mm.

[0044] The thickness t of pipe 4 is ≤ 4 mm. If the thickness t exceeds this range, it will affect the microwave energy absorption of the liquid in pipe 4.

[0045] Step 4: Determine the width w of the upper ridge of the double-ridged waveguide 3. The width w of the upper ridge of the double-ridged waveguide 3 affects the wave compression and matching effect, and must satisfy: 0.1≤w / a≤0.4; Step 5: Determine the length gl and shape of pipe 4.

[0046] The length gl of pipe 4 must satisfy: gl > b; The shape of pipe 4 can be either a straight pipe or an L-shaped pipe; When pipe 4 is an L-shaped pipe, the inlet position of the heating cavity needs to be set according to the dominant mode of electromagnetic waves (TE) transmitted in the waveguide. 10 The electromagnetic field distribution characteristics of the module and the design structure are optimized. The design principle is to preferably be located at a position with a relatively moderate electric field strength amplitude, that is, between the antinode (the position where the electric field strength reaches its maximum value) and the node (the position where the electric field strength reaches its minimum value). The specific position y of the pipe entering the cavity (y represents the vertical coordinate of the pipe center, and the horizontal coordinate x=b / 2) should be around y = a / 4 or 3a / 4. When the liquid material enters the microwave field, it can withstand a uniform and moderate field strength, avoiding excessive field strength at the inlet of pipe 4 to absorb microwave energy and cause local overheating inside pipe 4.

[0047] Step 6: Determine the number n of the double-ridged waveguides 3 and the length jl of the double-ridged waveguides 3.

[0048] When the number of double-ridged waveguides 3 is n=1, the length jl of the double-ridged waveguide 3 is greater than 4 / 3gl; When the number of double-ridged waveguides 3 n > 1, the length of a single-segment ridged waveguide jl = gl / n.

[0049] Step 7: Select a standard waveguide 5 that meets the design resonant frequency. The length of the standard waveguide 5 has little impact on subsequent optimization and can be set to 40-80mm. Determine the dimensions of the matching structure between the standard waveguide 5 and the double-ridge waveguide 3: Adopt the matching method of the stepped discontinuous waveguide 1 combined with the stepped ridge 2. Except for the standard waveguide 5, the number of stepped discontinuous waveguides 1, m1≥1, and the number of stepped ridges 2, m2≥1; the cross-sectional dimensions of the stepped discontinuous waveguide 1 also need to satisfy that the length of the wide side is twice the length of the narrow side.

[0050] When the ratio of the dimension a of the first side of the double-ridge waveguide 3 to the dimension e of the third side 51 of the standard waveguide 5 is ≤2, the number of stepped discontinuous waveguides 1, m1 = 1, and the cross-sectional dimensions of the stepped discontinuous waveguide 1 are determined according to the geometric dimension average of the side dimensions of the double-ridge waveguide 3 and the standard waveguide 5; When the ratio of the dimension a of the first side of the double-ridge waveguide 3 to the dimension e of the third side 51 of the standard waveguide 5 is >2, the number of stepped discontinuous waveguides 1, m1≥2, can be set according to the linear gradient geometric average principle. The length of the stepped discontinuous waveguide 1 is an integer multiple of a quarter wavelength, and the cross-sectional dimensions and length of the stepped discontinuous waveguide 1 can be rounded on this calculation basis without significantly affecting the transmission effect.

[0051] When multiple double-ridge waveguides 3 are used, a slit 6 can be set on the wide surface of the standard waveguide 5 to uniformly feed microwave energy into multiple double-ridge waveguides 3. The number of slits is the same as the number of double-ridge waveguides 3. The length l of the slit 6 ∈ [0.4λc, 0.5λc], where λc is the wavelength in free space at the designed resonant frequency; the length direction of the slit 6 is parallel to the waveguide axis, and the width fw of the slit 6 needs to satisfy 10 < e / fw < 40. For example: it is 3 - 8 mm under the BJ26 waveguide at a resonant frequency of 2.45 GHz, and the offset p of the slit 6 relative to the center ∈ [0.25a, 0.7a], and the offset of the slit ensures the best intensity of the wave fed through the slit.

[0052] Step 8: Establish a finite element simulation model of the continuous-flow microwave system according to the above parameters and matching method, and set the material parameters at different positions. Among them, the inside of the cavity is an air domain, and the dielectric property is set to 1. The dielectric property of the fluid pipeline 4 area is set according to the selected material, and the dielectric property of the fluid area is set according to the targeted liquid material, and is set to the dielectric property value with lower loss of this liquid material within the entire temperature rise range.

[0053] Step 9: Determine the number m2, width rw, and height rh of the stepped ridge 2 according to the dielectric property of the liquid material, as well as the dimensions of the double-ridge waveguide 3 and the standard waveguide 5.

[0054] The design of the number m2 of the stepped ridges 2 can refer to the following principles: When the dielectric loss increases significantly with the increase of temperature, since this material property is relatively easier to be heated to a higher temperature, the number m2 of the stepped ridges 2 can be appropriately reduced; When dielectric loss decreases with increasing temperature, dielectric adaptability can be improved by adding multiple stepped ridges 2, i.e., increasing the number of stepped ridges 2 m2. When the cross section of the double-ridged waveguide 3 differs significantly from that of the standard waveguide 5, the matching degree can be improved and the reflection reduced by adding multiple stepped ridges 2. When the number of stepped ridges 2 is m2=1, the height rh of stepped ridge 2 is consistent with the width w of the upper ridge of the double-ridge waveguide 3. The width rw of stepped ridge 2 is calculated based on the distance between the two stepped ridges 2, rw=(tb-c) / 2; where tb is the narrow side length of the stepped discontinuous waveguide 1, that is, the distance between the two stepped ridges 2 is consistent with the spacing c of the double-ridge waveguide 3. When the number of step ridges 2, m2 > 1, the relevant parameters of the first step ridge 2 (the side adjacent to the double-ridge waveguide 3 is the first section) are the same as when m2 = 1. The distance between the two ridges of the second step ridge 2 must be twice the distance between the previous step ridge 2, and the height must be consistent with the previous level. Step 10: Multiphysics simulation optimization enhances the robustness of the ridge waveguide structure, adapting the ridge cavity structure to the dielectric changes of the liquid material. Relevant parameters of the double-ridge waveguide 3 are fixed, with the length rl of the stepped ridge 2 in the matching section as the parameter to be optimized. The calculation target is set as S11 ≤ -10dB. Here, S11 is defined as the input reflection coefficient, and its amplitude (|S11|) reciprocal is often expressed in decibels (dB), called return loss. This parameter directly reflects the impedance matching between the microwave source and the load. In the design of microwave heating devices, optimizing S11 aims to maximize the absorption efficiency of microwave energy by the heated load, thereby improving the overall system energy efficiency.

[0055] The optimization method could be to optimize each step ridge 2 step by step, using parametric scanning; Alternatively, the number of step ridges 2 can be determined through the above design, and the Monte Carlo simulation method can be selected for optimization, defining each step ridge 2 with different parameters and performing scanning simultaneously.

[0056] Step 11: Determine all parameters of the designed cavity and pipeline 4 through the above process. Select three dielectric constant values ​​of the designed liquid material within the heating range to verify the reflection situation, so as to ensure that different S11 ≤ -10dB.

[0057] Optionally, the material of pipe 4 can be quartz, polytetrafluoroethylene or glass.

[0058] This invention also provides a rapid microwave heating system for liquid materials. This system can match the characteristics of the dielectric properties of liquid materials as a function of temperature, and has a good reflection efficiency, i.e., S11≤-10dB, to achieve efficient heating of liquid materials. The system specifically includes a ridge waveguide designed by the above method and its matching method. The ridge waveguide structure is connected to the material pipeline, microwave source generator, cooling device, back pressure valve, etc. The cooling device (water cooling) is usually located between the ridge waveguide structure and the microwave source generator, or is installed on the microwave source generator in the form of air cooling. The material pipeline is located inside the cavity of the ridge waveguide. The back pressure valve can be selected according to the expected temperature range (>100℃) and connected to the pipeline outlet section.

[0059] Example 1 like Figures 1 to 4 As shown, this embodiment provides a ridge waveguide structure designed for liquid materials with phosphate buffer as the medium. The ridge waveguide structure includes a stepped discontinuous waveguide 1, a stepped ridge 2, a double-ridge waveguide 3, a conduit 4, and a standard waveguide 5.

[0060] The design process is as follows: The ridge waveguide structure for microwave heating of liquid materials, as described above, is employed. Step 1: The inner diameter d of the conduit 4 is 3mm. The second side dimension b of the double-ridge waveguide 3 is determined to be 20mm, and the first side dimension a is determined to be 40mm. Step 2: Select the relative direction of the conduit 4 and the double-ridged waveguide 3 so that the ridges of the conduit 4 and the double-ridged waveguide 3 are perpendicular.

[0061] Step 3: Determine the ridge spacing c of the double-ridge waveguide 3 to be 5mm; select the thickness t of the conduit 4 to be 1mm.

[0062] Step 4: The width w of the upper ridge of the double-ridge waveguide 3 is 10mm; Step 5: The length of pipe 4 (gl) is 120mm, and the shape of pipe 4 is a straight pipe; Step 6: The number of double-ridged waveguides 3, n, is 4, and the length jl of each double-ridged waveguide 3 is 30mm; Step 7: Standard waveguide 5 is a BJ22 standard waveguide with a wide side of 109.2 mm and a narrow side of 54.6 mm. The number of stepped discontinuous waveguides 1 is m1=2. The first section of the two-stage stepped discontinuous waveguide 1 (the section adjacent to the double-ridge waveguide 3) has a wide side of 60 mm and a narrow side of 30 mm. The second section has a cross-sectional dimension of 80 mm wide and 40 mm narrow. The lengths of the two-stage stepped discontinuous waveguide 1 are 20 mm and 40 mm, respectively. The length of slot 6 is 50 mm, the width of slot 6 is 4 mm, the thickness of slot 6 is 2 mm, and the offset of slot 6 relative to the center is 14 mm. For ease of fabrication and uniform microwave energy distribution, the distance between the centers of the two slots 6 is 86.36 mm.

[0063] Step 8: Establish a finite element model in COMSOL software, draw the dimensions in the geometry, set the material parameters for different regions, the cavity is the air region, the dielectric property is set to 1, the material of pipe 4 is selected as polytetrafluoroethylene, the dielectric parameter is set to 2.3, and the dielectric constant function of the fluid region is ε=0.00002 T. 2 - 0.25559 T + 81.62038: The loss tangent function is: tanδ = 0.00000004T 4 - 0.00000853T 3 + 0.00067288 T 2 - 0.02110217T +0.49861945, set the dielectric property of the material to 70-21j; set the boundary conditions, the inner wall of the cavity is an ideal electrical conductor; where T: represents temperature, j: represents the unit of the imaginary part of the dielectric constant.

[0064] Step 9: The dielectric function of the liquid material increases with increasing temperature. The number of stepped ridges 2, m2, is set to 2. The stepped ridges 2 are located at the middle position of each stepped surface, so that it gradually compresses and transforms from the standard waveguide 5, through the transition stepped discontinuous waveguide 1, into the resonant cavity of the designed double-ridged waveguide 3. The width of the stepped ridge 2 of the first stepped waveguide is rw1=12.5mm, rh1=10mm. The ridge spacing of the stepped ridge 2 of the second stepped waveguide is 10mm, rw2=15mm, rh2=10mm.

[0065] Step 10: The optimization method is selected as Monte Carlo simulation method for simultaneous optimization. S11 is set to -10, and the lengths of the first and second step ridges are both determined to be 20mm.

[0066] Step 11: Input the dielectric constant values ​​of the liquid material at 25℃, 45℃, and 80℃ respectively, and obtain the S11 parameters as -12, -14, and -11, indicating that the structure has good dielectric adaptability.

[0067] The above design method yields a ridged waveguide structure for microwave heating of liquid materials using phosphate buffer solution as the medium. Stepped ridges 2 are located on both sides of the stepped discontinuous waveguide 1. A double-ridged waveguide 3 connects to the stepped discontinuous waveguide 1. A straight pipe 4 runs through the double-ridged waveguide 3. A standard waveguide 5 is located on the side of the stepped discontinuous waveguide 1 opposite to the double-ridged waveguide 3 and connects to the stepped discontinuous waveguide 1. A gap 6 can be provided at the connection between the standard waveguide 5 and the stepped discontinuous waveguide 1 to uniformly distribute the fed microwaves. There are four standard waveguides 5, four double-ridged waveguides 3, and four stepped waveguides 1. Stepped ridges 2 are placed within the stepped discontinuous waveguide 1 to improve the matching effect.

[0068] like Figure 9 and Figure 11 The image shows the electric field distribution cloud map inside the cavity of the ridge waveguide structure. Inputting the dielectric constant function and dielectric loss tangent function of the liquid material in this embodiment, when heating the liquid material at a flow rate of 0.01 m / s and a power of 300 W, the average surface temperature at the outlet of pipe 4 can reach 80°C when using this ridge waveguide structure for heating.

[0069] Example 2: like Figures 5 to 8 As shown, this embodiment provides a ridge waveguide structure designed for liquid materials with high concentrations of nutrients as the medium. The ridge waveguide structure includes a stepped discontinuous waveguide 1, a stepped ridge 2, a double-ridge waveguide 3, a conduit 4, and a standard waveguide 5. The design process is as follows: A ridge waveguide structure design method for microwave heating of liquid materials, as described above, is employed. Step 1: The inner diameter d of pipe 4 is 8mm. The second side dimension b of the double-ridge waveguide is determined to be 30mm, and the first side dimension a is determined to be 60mm. Step 2: Select the relative direction of conduit 4 and double-ridged waveguide 3 so that the ridges of conduit 4 and double-ridged waveguide 3 are parallel.

[0070] Step 3: Determine the ridge spacing c of the double-ridge waveguide 3 to be 18mm; select the thickness t of the conduit 4 to be 3mm; Step 4: The width w of the upper ridge of the double-ridged waveguide 3 is 24mm; Step 5: The length of pipe 4 (gl) is 180mm, and the shape of pipe 4 is an L-shaped pipe; Step 6: The number of double-ridged waveguides 3, n, is 1, and the length jl of each double-ridged waveguide 3 is 300mm; Step 7: Standard waveguide 5 is a BJ22 standard waveguide with a wide side of 109.2 mm and a narrow side of 54.6 mm. The number of stepped discontinuous waveguides 1 is m1=1, and the cross-sectional dimensions of stepped discontinuous waveguide 1 are 80 mm wide, 40 mm narrow, and 40 mm long. Step 8: Establish a finite element model in COMSOL software, draw the dimensions in the geometry, set the material parameters for different regions, the cavity is the air region, the dielectric property is set to 1, the material of pipe 4 is selected as quartz, the dielectric parameter is set to 4.2, and the dielectric constant function of the fluid region is ε=-0.000001 T. 5 + 0.000183T 4 - 0.018328T 3 + 0.876336T 2 - 20.029088T + 242.177350: The loss tangent function is: tanδ = 0.000186T 2 - 0.00352T +0.592167, set the dielectric properties of the fluid material to 72-49j; set the boundary conditions, the inner wall of the cavity is an ideal electrical conductor.

[0071] Step 9: The dielectric function of the liquid material increases with increasing temperature. The number of step ridges 2 is set to 1. The width of the step surface of the first section of the discontinuous waveguide 1 is rw=15mm and the height is rh=24mm.

[0072] Step 10: The optimization method is selected as parametric scanning, S11 is set to -10, and the length of the step ridge 2 is determined to be 20mm.

[0073] Step 11: Input the dielectric constant values ​​of the liquid material at 25℃, 45℃, and 80℃ respectively, and obtain the S11 parameters as -13, -10, and -11, indicating that the structure has good dielectric adaptability.

[0074] The ridge waveguide structure for microwave heating of liquid materials with high concentration of nutrients obtained by the above design method has a stepped ridge 2 located on both sides of the stepped discontinuous waveguide 1, a double-ridge waveguide 3 connected to the stepped discontinuous waveguide 1, a pipe 4 being an L-shaped pipe installed inside the double-ridge waveguide 3, and a standard waveguide 5 located on the side of the stepped discontinuous waveguide 1 away from the double-ridge waveguide 3 and connected to the stepped discontinuous waveguide 1.

[0075] like Figure 10 and Figure 12The image shows the electric field distribution cloud map inside the ridge waveguide structure cavity. Inputting the dielectric constant function and dielectric loss tangent function of the liquid material in this embodiment, with the power set to 500 W and the liquid flow rate at 0.14 m / s, the average surface outlet temperature of pipe 4 is 123℃. With the power set to 200 W and the liquid flow rate at 0.06 m / s, the average surface outlet temperature of pipe 4 is 116℃. In practical use, this cavity, combined with a back pressure valve to pressurize the pipeline, can achieve rapid ultra-high temperature heating of the liquid without prior heating. It can also achieve heating at high flow rates in a short time. For example, with the power set to 200 W and the liquid flow rate at 0.06 m / s, the average surface outlet temperature of the pipe is 87℃. This cavity is suitable for different heating purposes.

[0076] Comparative Example 1 like Figure 13 and Figure 14 As shown in this comparative example, referring to the pipeline configuration in Example 2, a standard rectangular waveguide was established in COMSOL software. When the same power of 500W and the same flow rate of 0.14m / s were set, the S11 parameter of the resonant cavity was >-10, indicating that energy could not be concentrated in pipeline 4 and the liquid could not be heated.

[0077] Furthermore, using three pins for adjustment, although S11=-13 under the same S11 parameters, the electric field strength of the cavity near pipe 4 is significantly lower than that of the waveguide designed in Example 2. Therefore, with the same material parameters, the average outlet temperature of pipe 4 is 95°C, which still cannot reach the temperature of Example 2 (123°C). Even when the conventional rectangular waveguide cavity is adjusted to the same energy absorption conditions, it cannot be heated to a higher temperature.

[0078] Comparative Example 2 like Figure 15 and Figure 16 As shown, in this comparative example, the ridge waveguide was not designed using this method. The form of the ridge waveguide and cavity is similar to that of Example 2, except that the cross-sectional dimensions of the ridge waveguide were adjusted so that the wide side is 50 mm and the narrow side is 25 mm; everything else remains unchanged. Although the field strength through the ridge can still be compressed, the maximum electric field strength is 1.46 × 10⁻⁶. 5V / m, but the reflection coefficient increases under this cavity structure, S11=-2. Therefore, the size of the ridge waveguide needs to meet certain design requirements to achieve a good matching effect with the liquid material. According to the design method of this invention, the size of the standard waveguide is changed to the BJ26 standard waveguide, and the cross-sectional size of the stepped waveguide is changed to a wide side of 70mm and a narrow side of 35mm. By optimizing the length of the stepped ridge, when the length of the stepped ridge is optimized to 15mm, it is still possible to achieve S11<-10 under this structure. Compared with the case of a higher reflection coefficient, the field strength will be further compressed after optimizing and reducing the reflection coefficient. The highest field strength after optimization is 3.05×10. 5 V / m.

[0079] Comparative Example 3 In this comparative example, when the dielectric constant and loss tangent function in Example 2 are replaced with another liquid material with different dielectric properties, S11 increases (S11=-6). Although it can still be used for heating, reflection increases, and the microwave absorption efficiency of the liquid material decreases. Using the same power and flow rate parameters as in Example 2: power set to 500 W and flow rate to 0.14 m / s, the average surface outlet temperature after changing the dielectric parameters of the liquid material is significantly reduced, with an average outlet temperature of only 45°C (compared to 123°C in Example 2). The dielectric constant of liquid material 1 in Example 2 changes with temperature as a function of ε=-0.000001 T. 5 + 0.000183T 4 - 0.018328T 3 + 0.876336 T 2 - 20.029088T+242.177350, the loss tangent as a function of temperature is tanδ=0.000186T 2 - 0.00352T +0.592167, the dielectric constant of liquid material 1 at 21.3℃ is approximately 42.3, and the loss tangent is 0.6. The dielectric constant of the replaced liquid material 2 as a function of temperature is ε=0.0011T. 2 - 0.35T + 84.877; The loss tangent as a function of temperature is tanδ = 0.00005 T 2 - 0.00207 T + 0.28704. The dielectric constant of liquid material 2 at 21.3℃ is approximately 77.9℃, and the loss tangent is 0.27. This indicates that although the designed ridge waveguide has a certain degree of dielectric adaptability, its structure cannot be adapted when the dielectric properties of the liquid material differ significantly from the dielectric properties of the material on which the design is based. This prevents it from achieving a higher and wider temperature heating range, necessitating further dimensional optimization.

[0080] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for designing a ridge waveguide for microwave heating of liquid materials, characterized in that, A ridge waveguide structure is used, which includes a stepped discontinuous waveguide (1), a stepped ridge (2), a double-ridge waveguide (3), a conduit (4), and a standard waveguide (5). The stepped ridge (2) is located on both sides of the stepped discontinuous waveguide (1). The double-ridge waveguide (3) is connected to the stepped discontinuous waveguide (1). The conduit (4) is installed in the double-ridge waveguide (3). The standard waveguide (5) is connected to the stepped discontinuous waveguide (1). The ridge waveguide design method includes: Step 1: Determine the dimensions a of the first side (31) and the second side (32) of the cross section of the double-ridge waveguide (3) based on the inner diameter d of the pipeline (4) containing the liquid material; Step 2: The double ridges of the double-ridged waveguide (3) are located in the middle of the first side (31), and the relative directions of the pipeline (4) and the ridges of the double-ridged waveguide (3) are determined; Step 3: Determine the ridge spacing c of the double-ridge waveguide (3) according to Step 1 and Step 2; Step 4: Determine the width w of the ridge of the double-ridge waveguide (3), which must satisfy: 0.1≤w / a≤0.4; Step 5: Determine the length gl and shape of the pipe (4). The length gl of the pipe (4) must satisfy: gl > b; Step 6: Determine the number n and length jl of the double-ridge waveguides (3); Step 7: Select a standard waveguide (5) that meets the design requirements and determine the number of the stepped discontinuous waveguides (1); Step 8: Establish a finite element simulation model of the continuous flow microwave system based on the above parameters and matching methods, and set material parameters at different locations; Step 9: Determine the number m2, width rw, and height rh of the stepped ridges (2) based on the dielectric properties of the liquid material and the dimensions of the double-ridge waveguide (3) and the standard waveguide (5); Step 10: Multiphysics simulation optimization improves the robustness of the ridge waveguide structure, making the structure of the ridge cavity compatible with liquid materials. By fixing the relevant parameters of the double ridge waveguide (3), the length rl of the stepped ridge (2) of the matching section is set as the parameter to be optimized, and the calculation target is set as S11≤-10dB; where S11 is the input reflection coefficient. Step 11: Determine all parameters of the designed ridge waveguide structure cavity and the pipeline (4) through the above process. Select any three dielectric constant values ​​of the designed liquid material within the heating range to verify the reflection situation and ensure that S11≤-10dB of the liquid material during the heating process.

2. The ridge waveguide design method for microwave heating of liquid materials according to claim 1, characterized in that, In step 1, the dimension b of the second side (32) is in the range [2d, 10d], and the dimension a of the first side (31) is 2b.

3. The ridge waveguide design method for microwave heating of liquid materials according to claim 2, characterized in that, The number of double-ridged waveguides (3) is n=1, and the length of the double-ridged waveguides (3) is jl>4 / 3gl.

4. The ridge waveguide design method for microwave heating of liquid materials according to claim 2, characterized in that, The number of double-ridged waveguides (3) is n>1, and the length of the double-ridged waveguides (3) is jl=gl / n.

5. A ridge waveguide design method for microwave heating of liquid materials according to claim 4, characterized in that, A slot (6) is provided on the standard waveguide (5), the length l of the slot (6) ∈ [0.4λc, 0.5λc]; the width fw of the slot (6) must satisfy 10 <e / fw<40; Where λc is the wavelength in free space at the resonant frequency, and e is the length of the third side of the standard waveguide where the slit surface is located, that is, the long side dimension of the cross section of the standard waveguide (5).

6. A ridge waveguide design method for microwave heating of liquid materials according to claim 3 or 5, characterized in that, The ratio of the dimension a of the first side (31) to the dimension e of the standard waveguide (5), i.e. a / e≤2, the number m1 of the stepped discontinuous waveguides (1)≥2, and the length of the stepped discontinuous waveguides (1) is an integer multiple of a quarter wavelength.

7. A ridge waveguide design method for microwave heating of liquid materials according to claim 6, characterized in that, The number of the stepped ridges (2) is m2=1. The height rh of the stepped ridges (2) is consistent with the width w of the upper ridge of the double-ridge waveguide (3). The width rw of the stepped ridges (2) is calculated based on the distance between the two stepped ridges (2), rw=(tb-c) / 2; where tb is the narrow side length of the stepped discontinuous waveguide (1). The number of step ridges (2) is m2>1. The relevant parameters of the first step ridge are the same as when m2=1. The distance between the two ridges of the secondary step ridge must be twice the distance between the upper step ridges, and the height must be consistent with the upper step.

8. A ridge waveguide design method for microwave heating of liquid materials according to claim 2, characterized in that, The pipe (4) is a straight pipe, and the pipe (4) is perpendicular to the ridge of the ridge waveguide (3). The relationship between the spacing c of the ridges on the double-ridge waveguide (3), the inner diameter d of the pipe (4), and the thickness t of the pipe (4) must satisfy: c > (d + 2t + 1) mm.

9. A ridge waveguide design method for microwave heating of liquid materials according to claim 2, characterized in that, The pipe (4) is an L-shaped pipe, and the pipe (4) is parallel to the ridge of the ridge waveguide (3). The relationship between the spacing c of the ridges on the double-ridge waveguide (3), the inner diameter d of the pipe (4), and the thickness t of the pipe (4) must satisfy: c > (d + 2t + 4) mm.

10. A system for microwave heating of liquid materials, characterized in that, The method for designing a ridge waveguide for microwave heating of liquid materials according to any one of claims 1-9 is used. The microwave heating system for liquid materials includes the ridge waveguide structure, material pipeline, microwave source generator, cooling device and back pressure valve, wherein the back pressure valve is adapted according to the expected range of temperature heating.

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