A two-way coupling numerical simulation method for the translational heating process of a regular or irregular food in a microwave cavity

Abstract

The application discloses a two-way coupling numerical simulation method for the translational heating process of regular or irregular food in a microwave cavity, and belongs to the technical field of microwave heating. The application can improve the precision of the electric heating characteristic parameters of food by adopting the liquid nitrogen freezing homogenization treatment of food samples; the two-way coupling translational movement mode can improve the prediction precision of the numerical simulation of microwave heating. The accurate modeling of regular food and the approximate modeling method of the platform or the round corner of the edge corner of irregular food can effectively meet the finite element and finite time domain difference principles. For the microwave-assisted heating model of various heat sources, the fluid dynamics grid division method provided by the application can effectively reduce the false cooling phenomenon occurring in the initial stage of the heating translational movement operation, and is more consistent with the actual microwave-assisted heating process. The application can greatly reduce the time and economic cost of sample testing, and can realize the accurate prediction of the temperature change of regular food and irregular food in the microwave treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of microwave heating, in particular to a numerical simulation method for microwave translation motion heating of regular or irregular food. BACKGROUND

[0002] Microwaves have different heating effects in different microwave fields. When designing a microwave system, a translation motion method can be used to make food experience different electric field distributions, and through time superposition, more uniform microwave heating can be achieved.

[0003] In addition to conventional rectangular and circular shapes, there are still different shaped foods that need to be heated. The microwave heating process of different shaped foods still needs to be further explored, and better ways are needed to accurately predict the microwave heating effect of food. SUMMARY

[0004] The purpose of the present application is to provide a numerical simulation method for microwave translation motion heating of regular or irregular food, to make up for the shortcomings of the prior art.

[0005] To achieve the above purpose, the present application adopts the following technical solutions:

[0006] A numerical simulation method for microwave translation motion heating of regular or irregular food, comprising the following steps:

[0007] S1: Construct a regular or irregular food model;

[0008] S2: Homogenize the food by liquid nitrogen freezing;

[0009] S3: Measure the electric heating simulation parameters of the food;

[0010] S4: Add food material parameters to the food model, including but not limited to dielectric properties, specific heat, thermal conductivity, electrical conductivity, etc. of the food;

[0011] S5: Determine the heat source: electromagnetic wave and / or heat conduction heat source;

[0012] S6: Divide the microwave translation heating process, determine the distance step of each movement, determine the time t1 of staying at each position, set the total time of microwave processing as t, and the number of movements n = t / t1, wherein 24≤n≤48;

[0013] S7: Model the microwave equipment using numerical simulation software to realize the bidirectional coupling simulation process of microwave translation motion;

[0014] S8: Microwave grid division;

[0015] S9: Microwave translation heating two-way coupling process selection frequency domain-transient study to cover the analysis of the distribution of microwave in food, electric field intensity, heating mode changes and temperature changes; and set the waveguide type, set the microwave port position and power;

[0016] S10: Calculate the distribution of electromagnetic field in food using existing food temperature material parameters, calculate microwave dissipation power to get electromagnetic energy conversion in food, take microwave dissipation power as heat source of heat transfer equation, if there is other heat source, take it as heat flux as heat source 2 for accumulation, calculate the food temperature distribution at the end of t1 time step;

[0017] S11: Save the food temperature after heating at t1 time step in S10, judge whether the food moves to the end of microwave translation movement, if not, move the food by a distance step, and take the saved food temperature as the initial temperature of the new position;

[0018] S12: Update the dielectric properties, electrical conductivity, thermal conductivity, specific heat, density and other food material parameters according to the existing temperature of the food, as the parameter source for calculating electromagnetic field and microwave dissipation power;

[0019] S13: Repeat steps S10-S12 until the microwave translation movement heating reaches the end point.

[0020] Further, in S1, for regular or irregular food, direct modeling or 3D modeling using 3D scanning related equipment or 1:1 three-dimensional model established by professional modeling software; and for uniform size food, single sample simulation can be performed, and for the same food but with size difference, multi-size simulation modeling is performed; specifically:

[0021] S1-1: For regular shapes such as cuboids, direct geometric modeling is mostly used for modeling, and sweep or boundary layer mesh is used as much as possible during mesh division to improve accuracy;

[0022] S1-2: For irregularly shaped food such as starfish, seahorse, sea cucumber, small lobster, whole fish, etc., special attention should be paid to the edges and corners during modeling, and the edges can be rounded or flattened as much as possible to simplify the model and improve the feasibility of numerical simulation program running.

[0023] Further, in S2, the liquid nitrogen freezing time of food samples below 5g is 15s or more; the liquid nitrogen freezing time of food samples above 10g is 45s or more.

[0024] Further, in S3, if the food ingredients have different compositions, separate measurements should be taken between different compositions; and the required temperature range for measurement should be determined, the temperature range for freezing should be-20℃ to 20℃, the heating or curing should be set to 20-95℃, and the high temperature sterilization should be set to the actual temperature rise starting temperature and final temperature.

[0025] Further, S3 includes:

[0026] S3-1: Measure the thermal conductivity of the food, use probe method, plate method or other related instruments and equipment to measure the thermal conductivity, the unit of thermal conductivity is W / m 2 ·K;

[0027] S3-2: Measure the specific heat of the food, use differential scanning calorimetry or probe method to measure the specific heat, the unit of specific heat is kJ / kg·K;

[0028] S3-3: Calculate the electrical conductivity of the food, use conductivity meter or other instruments that can measure electrical conductivity. The density of the food is measured by drainage method or other methods that can measure density. The parts with large differences in properties should be measured separately.

[0029] Further, in S5, according to formula 1 as the formula for conversion of microwave energy to heat energy:

[0030]

[0031] The power of the microwave source (P(z)) is used as one of the heat sources in the heat transfer equation, and the heat conduction As another heat source.

[0032] Further, in S7, the numerical simulation software can use finite element or finite time domain difference software; according to the actual situation, set the type of microwave source, phase, set the position and power of microwave port in the electromagnetic wave interface, select the food as the research object in the solid heat transfer interface and set the initial value.

[0033] Further, in S8: In the process of single-mode microwave translation, the grid division of the food should be kept consistent, and for the microwave grid division with heat conduction as the heat source, fluid dynamics grid should be used, and for irregular food, sweep grid should be added to improve the simulation accuracy; and for irregular food, block processing method should be used to appropriately improve the grid quality. More than 80% of the grid quality should be above 0.8.

[0034] Further, S8 includes:

[0035] S8-1: Divide the grid according to the order of food and microwave equipment to ensure that the grid division of the food is consistent at each time step;

[0036] S8-2: The grid maximum size in food should be less than half of the wavelength of the microwave in the medium inside the food, according to the above-mentioned limited size, determine the size of the maximum unit in the food where only microwave is the heat source; if there is an additional heat source, the maximum unit size should be less than half of the microwave single heat source unit size; the grid division maximum size of the microwave equipment other than food is less than half of the wavelength of the microwave inside the medium (air or liquid medium);

[0037] S8-3: Sweep grid should be adopted for regular food grid type, and for irregular food, regular surface should be swept or boundary layer grid should be selected to improve the grid quality, and free tetrahedral grid division should be performed in the area that cannot be regularly divided;

[0038] S8-4: After the grid division is completed, the grid division of the food at different moving positions should be confirmed, and whether the grid changes is observed. According to the simulation software, the food can be cut in the thickness direction (Z>0), and whether the grid division inside the food changes in the movement process is observed. When the food grid does not change, it can be determined that the food can inherit the temperature after heating in the previous period as the initial value at the next position.

[0039] S8-5: The translation movement of the food can be selected to move the food or move the microwave equipment to realize the relative displacement of the food and the microwave equipment.

[0040] Further, in S10, the calculation by the numerical simulation software can also be selected, or the Maxwell equation set can be directly calculated.

[0041] Further, in S13, the condition for the cycle is that the existing moving distance of the food is less than the moving position required to reach the end point; the content of the cycle is to determine the solution of the last heating as the initial value, establish a geometric model, divide the grid, run the model, obtain a new solution and number it in sequence, and move an interval distance.

[0042] The iterative repetition process involved in step S13 should be combined with finite element or finite time domain difference software, commercial mathematical software, etc. to complete the automatic running process. The main pseudo code includes the definition of the initial position, the number of running times, the condition of the loop condition, the content of the loop, the loop exit condition, the loop end method, the solution inheritance method.

[0043] After the above simulation method is finished, the research results are post-processed, and the distribution of the microwave in the food, the temperature change and distribution of the food in the translation movement heating process are analyzed. If necessary, the cold and hot spots in the microwave heating process are analyzed.

[0044] Compared with the prior art, the present application has at least the following beneficial effects:

[0045] The application can improve the precision of food electric heating characteristic parameters by using liquid nitrogen freezing homogenization treatment on food samples; the two-way coupling translation movement method can improve the prediction precision of microwave heating numerical simulation. The grid division of regular food and irregular food is constrained and suggested, which improves the fitting effect of numerical simulation and actual heating condition; the movement times are specified, which can ensure good fitting effect and smoothly simulate the geometric modeling of regular food and irregular food. The accurate modeling of regular food and the platform or round corner approximation modeling method of the corners of irregular food can effectively meet the finite element and finite time domain difference principle, and obtain higher numerical simulation precision. For the microwave-assisted heating model of multiple heat sources, the fluid dynamics grid division method provided by the application can effectively reduce the false cooling phenomenon at the initial stage of heating translation movement operation, and is more consistent with the actual microwave-assisted heating process. Through numerical simulation and experimental research on regular food and irregular food, it is proved that the technical scheme can better fit the microwave heating condition prediction under the conditions of single microwave heat source and microwave-heat conduction double heat source.

[0046] The simulation method provided by the application can greatly reduce the time and economic cost of sample testing, and can realize accurate prediction of the temperature change of regular food and irregular food in microwave processing. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 The flowchart of the technical scheme of the application.

[0048] Figure 2 The grid division of the gelling gum food at different positions.

[0049] Figure 3 The temperature distribution of the gelling gum food obtained by the two-way coupling method.

[0050] Figure 4 The temperature values of the hot spots and cold spots of the gelling gum food obtained by the two-way coupling method.

[0051] Figure 5 The temperature distribution of the gelling gum food obtained by the one-way coupling method.

[0052] Figure 6 The hot spot and cold spot temperature of the gelling gum food obtained by the one-way coupling method.

[0053] Figure 7 The dielectric constant and dielectric loss of the liquid nitrogen frozen homogeneous rainbow trout meat.

[0054] Figure 8 The dielectric constant and dielectric loss of the liquid nitrogen frozen homogeneous flavored sea cucumber.

[0055] Figure 9 Dielectric constant and dielectric loss of direct-frozen homogenized rainbow trout meat.

[0056] Figure 10 Dielectric constant and dielectric loss of direct-frozen homogenized sea cucumber.

[0057] Figure 11 Temperature distribution of spherical food with 24-48 steps of movement.

[0058] Figure 12 Temperature distribution of spherical food with less than 24 steps of movement or more than 48 steps of movement.

[0059] Figure 13 Numerical simulation calculation of round or flat angle processing of irregularly shaped food sea horse.

[0060] Figure 14 Numerical simulation calculation of irregularly shaped food sea horse without round or flat angle processing.

[0061] Figure 15 Two-way coupling numerical simulation heating mode results of microwave single heat source regular shape food (surimi products).

[0062] Figure 16 Two-way coupling simulation and experimental hot spot and cold spot temperature curve of microwave single heat source regular shape food (surimi products).

[0063] Figure 17 Fluid dynamics grid division two-way coupling numerical simulation heating mode results of microwave-thermal water double heat source regular shape food (surimi products).

[0064] Figure 18 Fluid dynamics grid division two-way coupling numerical simulation hot spot and cold spot temperature curve of microwave-thermal water double heat source regular shape food (surimi products).

[0065] Figure 19 Conventional grid division two-way coupling numerical simulation heating mode results of microwave-thermal water double heat source regular shape food (surimi products).

[0066] Figure 20 Conventional grid division two-way coupling numerical simulation hot spot and cold spot temperature curve of microwave-thermal water double heat source regular shape food (surimi products).

[0067] Figure 21 Two-way coupling numerical simulation heating mode results of microwave-thermal water double heat source irregular shape food (sea cucumber).

[0068] Figure 22The application discloses a two-way coupling numerical simulation and experimental cold point temperature curve of an irregularly shaped food (sea cucumber) with microwave and hot water as double heat sources. DETAILED DESCRIPTION

[0069] For the purpose, technical solutions and advantages of the present application, the following will be further described in detail in combination with specific examples and with reference to the drawings. Obviously, the described examples are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0070] For regular food: a relatively fine vernier caliper and other measuring tools should be used to obtain the length, width and thickness parameters of the cuboid; for cylindrical food, the diameter and height of the cylinder should be measured; for spherical food, the diameter of the food should be obtained. The model construction is realized by using the geometric design page of the simulation software, and compared with the actual sample.

[0071] For irregular food: the modeling of irregular food can be carried out in two ways. First, for irregular food with low complexity, the geometric drawing page of the simulation software or other structure drawing software such as Solidworks, 3ds Max and AutoCAD can be used. In the operation process, the sharp or very detailed parts of the food can be simplified to realize the numerical simulation process. Second, for irregular food, 3D scanning entity equipment such as Creality ScanFerret, RevopointPOP 3, Matter and Form 3D Scanner V2, Scan Dimension Sol or scanning software Reality Composer, Reality Scan combined with mobile communication equipment can be used. When scanning, a rotating platform is preferably equipped.

[0072] Note: Regular shape: cuboid, cylinder, sphere, trapezoid, regular tetrahedron, parallelepiped, etc.; irregular shape: for example, natural biological food such as sea cucumber, sea horse, crab and mussel.

[0073] The overall technical solution of the application is shown in Figure 1 The application mainly comprises numerical simulation modeling and two-way coupling translation motion setting. The application will be described below through specific examples and comparative examples.

[0074] Example 1: A two-way coupling microwave translation motion heating simulation scheme for a gellan gum food

[0075] The example comprises the following specific steps:

[0076] S1. Clear the numerical simulation case: the size of the gelatin food is 90mm*90mm*10mm, and the initial temperature of the food is set to 20℃. The microwave source frequency is 433MHz, the microwave source power is 3kW, and the single resonant cavity is used.

[0077] S2. Since the gelatin simulation food is a regular food, the geometry modeling is directly performed in the numerical simulation model. Sweep or boundary layer mesh should be used when meshing.

[0078] S3. Since the gelatin food is a uniform product after stirring plasticity, it is not necessary to homogenize it.

[0079] S4. Measure the electrical heating simulation parameters of the gelatin, and set the heating or curing temperature to 20-120℃.

[0080] S4.1 Measure the thermal conductivity of the gelatin food, use probe method, plate method or other related instruments to measure the thermal conductivity, the unit of thermal conductivity is W / m2·K.

[0081] S4.2 Measure the specific heat of the gelatin food, use differential scanning calorimetry or probe method to measure the specific heat, the unit of specific heat is kJ / kg·K.

[0082] S4.3 Measure and calculate the electrical conductivity of the gelatin food, use conductivity meter or other instruments that can measure electrical conductivity. The density of the gelatin food is measured by drainage method or other methods that can measure density.

[0083] S5. Add material parameters to the geometry model of the gelatin food, including but not limited to dielectric properties, specific heat, thermal conductivity, electrical conductivity, etc.

[0084] S6. Determine the heat source: determine the electromagnetic wave as the heat source; determine the heat conduction as the heat source. According to the following formula as the formula of microwave energy conversion to heat energy. The input microwave source power P(z) is the only heat source of the heat transfer equation, and the heat conduction is 0.

[0085]

[0086] S7. Divide the translation motion step and the motion time. The number of motion steps is 24-48. According to the actual situation, set the required parameters, set the total heating time to 120s, set the number of forward times to 24, set the time of each small section to 10s, set the distance of each forward time to 50mm, and the overall forward distance is 1200mm.

[0087] S8. The finite element software COMSOL Multiphysics 6.1 is used to build the simulation model of the two-way coupled translational motion. According to the case, a rectangular waveguide is set in the electromagnetic wave-frequency domain, and the microwave port position and power are set. The food is selected as the research object in the solid heat transfer interface, and the food heating initial value (20°C) is set.

[0088] S9. Keep the food grid consistent during the single-mode microwave translational motion. Since only microwaves are used as the heat source in this case, there is no heat conduction, and the gellan gum is a regular-shaped food, so the sweeping method can be directly used for grid division.

[0089] S9-1. First, divide the gellan gum food into grids, and then divide the microwave equipment into grids.

[0090] S9-2. The maximum size of the gellan gum grid should be less than one-half of the wavelength of 433 MHz in gellan gum (38 mm).

[0091] S9-3. The upper and lower planes (90 mm*90 mm) of the gellan gum food are used as the source plane, and the number of cells is 10. The size of each cell is 9 mm*9 mm, and the overall grid quality is >0.95.

[0092] S9-4. After the grid division is completed, the consistency of the grid division of the gellan gum food at 200 mm, 400 mm, 600 mm, 800 mm, 1000 mm, and 1200 mm is checked. Set the expression z>0 to view the grid changes.

[0093] S9-5. The two-way coupling technology solution needs to realize the translational motion of the gellan gum food. Since the food needs to maintain the consistency of the grid, based on the symmetry principle, the microwave heating equipment is selected to move. After modeling, the entire geometry is moved in the same direction to the distance of the sample translational motion.

[0094] S10. The study of the microwave translational heating two-way coupling process should select the frequency domain-transient study to cover the analysis of the microwave distribution in the food, the electric field intensity, the heating mode change, and the temperature change.

[0095] S11. In addition to the gellan gum food, all components are selected to move, and the moving distance is 0. Calculate the microwave heating at the first position. (1) Set the moving position to 0, and perform study 1, which is a frequency domain transient study. The output step end is 10 s, and the step can be selected, for example, 5 s. range(0, 5, 10), unit: s. Set the frequency to 433 MHz, and click Calculate. (2) To accurately match the initial value of the next study, modify the initial step of the transient solver in the study to 10 -5 s.

[0096] (3) Click to calculate study 1. Get the result as time step 10 -5 s. After the calculation is completed, get the heating result at the last time of the first transient heating.

[0097] S12. Save the temperature value of the microwave heating obtained in S11, and determine whether the translation motion endpoint is reached. The translation motion endpoint has not been reached at present, and the gelling food is moved forward by one step (50 mm). The saved temperature value is used as the initial temperature at this position.

[0098] S13. According to the existing temperature value, update the food material parameters such as dielectric properties, electrical conductivity, thermal conductivity, specific heat, density, etc., as the parameter source for calculating electromagnetic field and microwave dissipation power.

[0099] S14. Repeat steps S11-S13 until the endpoint of microwave translation motion heating is reached. The repeated process is written by using COMSOL Multiphysics 6.1 software to complete the automation process. The main pseudo code includes the definition of the initial position (0 mm), the number of runs (24 times), the condition of the loop condition, the content of the loop, the loop exit condition, the graph drawing method after the loop ends, and the way of solution inheritance.

[0100] S14-1 The condition for the loop to run is that the existing moving distance of the food is less than the moving position required to reach the endpoint (position < 1200 mm).

[0101] S14-2 The content of the loop is to determine the copied solution of the last heating as the initial value, establish the geometric model, divide the grid, run the model, get the new solution and number it in sequence (solution number = solution number + 1), and move an interval distance (50 mm).

[0102] S15 Post-process the research results, analyze the distribution of microwaves in the food, the temperature change and distribution of the food in the translation motion heating process, and analyze the cold and hot spots in the microwave heating process if necessary.

[0103] In Example 1, a rectangular parallelepiped is subjected to translation motion numerical simulation, Figure 2 The microwave heating grid distribution result during the microwave translation motion treatment is shown. It can be seen that according to the above-mentioned grid division method, the grid inside the food remains consistent at each position, and the grid inside the resonant cavity is then divided after each running position is changed. Figure 3 For the temperature distribution of the food section obtained by using the bidirectional coupling technical solution, it can be seen that the food cold and hot spot area obtained by the bidirectional coupling technical solution has a relatively smooth temperature gradient line. Figure 4The temperature values of the bidirectional coupling hot spot and cold spot are well fitted with the real-time experimental hot spot and cold spot temperatures.

[0104] Comparative Example 1: A unidirectional coupling technology translation motion simulation scheme for a gellan gum food

[0105] The same equipment and translation motion times as in Comparative Example 1 were used, and the following conventional unidirectional coupling technology scheme was selected. The contents of S1-S7 are consistent with the bidirectional coupling scheme in Example 1.

[0106] S8. A unidirectional coupling translation motion simulation model was built using the finite element software COMSOL Multiphysics 6.1. In component 1, the microwave equipment was simulated and modeled, and the gellan gum food was modeled according to the steps of S1 and S2. In addition, a component 2 with only gellan gum food was also established for the single coupling scheme.

[0107] S9. The gellan gum food was meshed, and the physical field was divided or free tetrahedron or user-defined. The meshing method and size of the gellan gum food in component 1 needed to be consistent with the meshing method of the gellan gum food in component 2.

[0108] S10. Two studies were selected for unidirectional coupling, Study 1 for electromagnetic wave, frequency domain (emw), and Study 2 for solid heat transfer (ht). The calculation of electromagnetic field and the calculation of heat transfer field were divided.

[0109] S11. The electromagnetic field of the food in component 1 was calculated. The electromagnetic field of the food at the initial position was calculated, the food position was moved, and the electromagnetic field at the next position was calculated. The above process was repeated to obtain the electromagnetic field distribution at different positions. The specific operation was to set the parameterized scan range (0, 50, 1200) with the unit set as mm.

[0110] S12. The electromagnetic field distribution data of the food at each position was saved after the calculation in step S11.

[0111] S13. The heating of the food in component 2 was studied. The microwave electromagnetic field data obtained in S12 was added as a heat source in the solid heat transfer module.

[0112] S14. The results were post-processed, and the distribution of microwaves in the food, the temperature change and distribution of the food during the translation motion heating process, and the cold and hot spots during the microwave heating process were analyzed.

[0113] Figure 5 The temperature distribution obtained using the unidirectional coupling technology was 47.5-104°C, which was larger than the temperature range of 49.5-94.9°C obtained by the bidirectional coupling technology.Figure 6 The temperature development curve of the numerical simulation temperature result of the single-direction coupling hot spot and the experimental result shows that in the single-direction coupling, there is a temperature rising process fitting time separation, the hot spot temperature is higher than the experimental value, and the cold spot temperature is lower than the experimental value. The temperature deviation of the single-direction coupling is larger than that of the double-direction coupling.

[0114] For the single-direction coupling model, the following principle problems cause the actual temperature of heating to be greatly different from other methods.(1) The single-direction coupling technical scheme first calculates the microwave distribution. Then, the temperature is calculated by taking the electric field of the food at each place as a heat source. In actual production and life, the electric heating characteristics of the food will change, thereby affecting the electric field distribution in the electromagnetic field.

[0115] (2) Because the calculation of solid heat transfer is performed in the single-direction coupling, the heating time of the food under the microwave treatment condition is replaced by the multiple magnification of the heat source. When the thermal characteristic parameters of the food change greatly with temperature, the temperature rising of 10 times the heat source per unit time may not be completely the same as the temperature rising of 10 times the heat source per unit time 1 times.

[0116] The above two reasons are the reasons why the temperature of the single-direction coupling technical scheme may be greatly different from that of the double-direction coupling.

[0117] Example 2: Measuring the dielectric constant, dielectric loss and penetration depth after freezing with liquid nitrogen and homogenizing

[0118] Figure 7 The dielectric constant and dielectric loss of the rainbow trout homogenized by freezing with liquid nitrogen are measured. The dielectric constant of the rainbow trout is between 35-55, and the dielectric constant decreases with the increase of temperature. The dielectric loss of the rainbow trout is between 20-55, and the dielectric loss increases with the increase of temperature. Figure 8 The dielectric constant and dielectric loss of the seasoned sea cucumber homogenized by freezing with liquid nitrogen are measured. The dielectric constant of the seasoned sea cucumber ranges from 20 to 75, and the dielectric loss ranges from 55 to 200. The overall curve is relatively smooth, the dielectric properties and dielectric loss of the rainbow trout are consistent with those of similar unseasoned fish, and the dielectric properties and dielectric loss of the seasoned sea cucumber are consistent with those of other high-moisture seasoned products. The dielectric constant and dielectric loss of the food have a great influence on the electric response in the microwave field. If there is a large error in the dielectric property measurement, it will cause the dissipation power calculation of the microwave heating to be distorted, and will have an adverse effect when the temperature conversion is performed by taking the heat source.

[0119] Comparative Example 2: Measuring the dielectric constant, dielectric loss and penetration depth after directly freezing and homogenizing

[0120] Figure 9The dielectric constant and dielectric loss of the directly homogenized rainbow trout meat. The dielectric constant ranges from 40 to 70, and the dielectric loss ranges from 20 to 70. The dielectric constant is overall higher than the liquid nitrogen freezing treatment, and the dielectric loss is also significantly higher than the liquid nitrogen freezing treatment. When directly homogenizing fish meat food, it may cause cell rupture to produce a large amount of water, and more water will be precipitated at the probe contact, and its dielectric constant will be higher. The umami substances in fresh aquatic products such as nucleotides will rapidly degrade during the homogenization process. The inorganic salts between the muscles rapidly dissolve into the liquid, and the dielectric loss caused by ion conduction rapidly increases. Overall, for fish and other foods, when directly homogenized, the dielectric constant may be higher, and the dielectric loss may also be higher.

[0121] Figure 10 The dielectric constant and dielectric loss of the directly homogenized sea cucumber. The dielectric constant of sea cucumber ranges from 20 to 55, and the dielectric loss ranges from 30 to 150. The overall results are smaller than the liquid nitrogen homogenization treatment.

[0122] For foods rich in collagen fibers, especially sea cucumber products containing collagen fibers, direct homogenization may result in incomplete homogenization, and the sea cucumber may present small fiber blocks after normal temperature homogenization. When testing the dielectric properties, there is a gap between the homogenized sea cucumber fragments and the probe, and the dielectric properties and dielectric loss measured at this time are contributed by air and seasoned sea cucumber. The dielectric properties measured at this time are the combined results of air and sea cucumber, and the dielectric constant and dielectric loss are smaller.

[0123] Example 3: Two-way coupling simulation of the number of k-carrageenan food movements is 24-48

[0124] Taking k-carrageenan simulated food as an example, its shape is modified to a sphere to simulate fish balls and other food types, and the research steps are the same as in Example 1. The number of movement steps in the numerical simulation is 24. Figure 11 It can be seen that when the number of movements is 24, the hot area in the XY plane is on the left and right sides, and the temperature on the left side is higher than that on the right side, with a maximum temperature of 37.7°C and a minimum temperature of 33.4°C. The YZ plane presents a hot spot area in the form of an outward convex eye, with the highest temperature in the middle. The XZ plane presents an inward concave upper and lower symmetric condition, with the hottest point on the left. The running time of Dell workstation T7920 at this time is 28 hours and 20 minutes. When the number of movement steps is further increased to 48 steps, the running time is further increased to 58 hours and 37 minutes. At this time, the overall temperature distribution of the XY plane is basically the same as that when the number of steps is 24, and the temperature difference between the left side and the right side is further increased. The temperature distribution of the YZ and XZ planes is basically the same as that when the number of steps is 24.

[0125] Compared with the numerical simulation parameters of 120 steps in Comparative Example 3, the results show that the temperature distribution and temperature value of 48 steps are almost consistent with that of 120 steps, but the time is saved by about three quarters. This will greatly reduce the requirements and occupation of computing resources.

[0126] Comparative Example 3: Two-way coupling simulation of gelatin food motion step length less than 24 and motion step length greater than 48

[0127] Taking the gelatin food as an example, the shape is modified to a sphere for simulating food types such as fish balls, and the steps are the same as in Example 1. The number of motion steps in the numerical simulation is 12. Figure 12 The first row shows the temperature distribution when the motion number is 12, at this time the XY direction presents the situation that the left side is lower in temperature and the right side is higher in temperature. This is contrary to the temperature distribution of 24 steps, 48 steps and 120 steps. This shows that when the number of steps is small, some electric field peak or valley regions may be missed, and at this time the rectangular integral of the electric field of 12 positions is different from the real-time curve integral of different positions.

[0128] Figure 12 The second row shows the temperature distribution when the motion number is 120. It can be known that the accuracy of 120 steps is not much different from that of 48 steps. However, the calculation time of the numerical simulation model increases from 59 hours of 48 steps to 219 hours. At this time, the occupation of computing resources is large, and the long-time calculation increases the cost of using numerical simulation technology for calculation, and also causes the temporary termination of the machine due to the long occupation time of the workstation or other calculators.

[0129] Example 4: Microwave vacuum drying experiment of sea horse with round corner or platform treatment

[0130] According to the steps of Example 1, the sea horse is modeled and numerically simulated, and the difference is that the platform treatment is needed for the irregular food sea horse. Figure 13 is the geometric modeling and numerical simulation process of the processed sea horse. The results show that the convergence is good when the sea horse is dried, and the step length reciprocal has decreased to below 2*10-4 at about 10 time steps. The air flow velocity in the XY plane of the sea horse and the pressure distribution inside the sea horse can be well simulated.

[0131] Comparative Example 4: Microwave vacuum drying experiment of sea horse without round corner or platform treatment

[0132] Figure 14 The geometric modeling of the sea horse without round corner or platform treatment is shown. At this time, the tail of the sea horse presents a relatively sharp shape, and at this time the grid quality of the tail may be reduced, which may affect the calculation.Figure 14 The right graph of FIG. 19 shows the convergence of the hippocampus geometric model. When no rounding or platform processing is performed, the convergence of the hippocampus model decreases, and the undefined value cannot be found. When the Vanka equation is solved, inf or NaN is found. In summary, it is very important to reasonably model the irregular model, which is the key to whether the subsequent simulation program can run normally.

[0133] Example 5 Numerical simulation results of micro wave single heat source regular shape food (surimi product)

[0134] S1. Directly model the surimi product. Since the surimi product is uniformly produced by the factory, it has a stable and uniform size. The length, width and height of the surimi product are measured, and a geometric model is established. The size of the surimi product is 120mm*60mm*16mm. The initial temperature of the surimi is 25℃. The microwave source frequency is 433MHz, the power is 3kW, and it passes through two resonant cavities.

[0135] S2. Since the surimi is a food with uniform size and regular shape, direct numerical simulation modeling is performed.

[0136] S3. The surimi is homogenized by liquid nitrogen freezing. Since the surimi is large as a whole, it should be cut first with a knife and divided into small pieces of about 5g. Liquid nitrogen is used for freezing for more than 15s until it is successfully broken by knocking with a metal such as a forceps.

[0137] S4. Measure the thermal simulation parameters of the surimi. The food composition of the surimi is uniform, and direct measurement can be performed. In this case, microwave heating technology is used, and the heating temperature is set to 20-95℃.

[0138] S4.1 Measure the thermal conductivity of the surimi product. The thermal conductivity is measured by using a probe method, a plate method or other related instruments and equipment for measuring thermal conductivity. The unit of thermal conductivity is W / m 2 ·K.

[0139] S4.2 Measure the specific heat of the surimi product. The specific heat is measured by using a differential scanning calorimetry method or a probe method. The unit of specific heat is kJ / kg·K.

[0140] S4.3 Calculate the electrical conductivity of the surimi product. The electrical conductivity is measured by using an electrical conductivity measuring instrument or other instruments that can measure electrical conductivity. The density of the surimi product is measured by using a drainage method or other methods that can measure density. The parts with large property differences should be measured separately.

[0141] S5. Add material parameters to the geometric model of the surimi product in the model tree, including but not limited to electrical properties, specific heat, thermal conductivity, electrical conductivity, etc.

[0142] S6. Determine the heat source situation: determine that electromagnetic waves are the heat source; determine that there is no heat conduction as the heat source. According to the following formula as the formula for the conversion of microwave energy to heat energy. The power P(z) of the microwave source is input as the only heat source of the heat transfer equation, and the heat conduction

[0143]

[0144] S7. Divide the step length and motion time of the surimi product in the microwave resonant cavity. The number of motion steps is 24-48. According to the actual situation, set the required parameters, set the total heating time to 150s, set the number of advances to 30 times, set the time of each small section to 5s, and set the distance of each advance to 80mm. The total distance of the translation motion is 2400mm.

[0145] S8. A two-way coupled translation motion simulation model is built using the finite element software COMSOL Multiphysics 6.1. According to the situation of the present embodiment, a rectangular waveguide is set in the electromagnetic wave-frequency domain, the microwave port position and power are set. The food is selected as the research object in the solid heat transfer interface, and the initial value of food heating (20℃) is set.

[0146] S9. In the process of single-mode microwave translation motion, the food grid division is consistent. Since only microwave is used as the heat source in this case, there is no heat conduction, and the surimi is a regular shaped food, the sweeping method can be directly used for grid division.

[0147] S9-1. First, the surimi product is divided into a grid, and then the microwave equipment is divided into a grid.

[0148] S9-2. The maximum size of the surimi product grid should be less than one-half of the wavelength of 433MHz in the gelatin (45mm).

[0149] S9-3. The grid design preferably uses fluid mechanics grid. The surimi product is a regular shaped product, one side of 120mm*60mm is selected as the source side, a sweeping grid is constructed, and the sweeping unit number is set to 20. The grid quality is inspected, and the overall grid quality is >0.95.

[0150] S9-4. After the grid division is completed, the consistency of the grid division of the gelatin food at different positions is checked. The expression z>0 is set, and the grid change is viewed.

[0151] S9-5. The two-way coupling technology scheme needs to realize the translation motion of the surimi product. Since the food needs to maintain the consistency of the grid, based on the symmetry principle, the microwave heating equipment is selected to move. After modeling, the entire geometry is moved in the same direction by the distance of the sample translation motion.

[0152] S10. The study of microwave translation heating two-way coupling process should choose frequency domain-transient study to cover the analysis of microwave distribution in food, electric field intensity, heating mode change and temperature change.

[0153] S11. All components except surimi products are selected to move, and the moving distance is 0. Calculate the microwave heating situation of the first position.

[0154] (1) The position of movement is set to 0, and study 1, frequency domain transient study, is conducted. The output step end is set to 10 s, and the step can be selected by yourself, for example, 5 s. range(0, 5, 10), unit: s. Set the frequency to 433 MHz, and click Calculate.

[0155] (2) In order to accurately match the initial value of the next study, the initial step of the transient solver in the study is modified to 10 -5 s.

[0156] (3) Click Calculate Study 1. The result is time step 10 -5 s. After the calculation is completed, the heating result at the last time after the first transient heating is obtained.

[0157] S12. Save the microwave heating temperature value obtained in S11, and determine whether the translation motion endpoint has been reached. The gelling food is moved forward by one step (80 mm) since the translation motion endpoint has not been reached. The saved temperature value is used as the initial temperature at this position.

[0158] S13. According to the existing temperature value, update the food material parameters such as dielectric properties, electrical conductivity, thermal conductivity, specific heat, density, etc., as the source of parameters for calculating electromagnetic field and microwave dissipation power.

[0159] S14. Repeat steps S11-S13 until the endpoint of microwave translation motion heating is reached. The involved repeating process is written in COMSOL Multiphysics 6.1 software to complete the automation process. The main pseudo code includes the definition of the initial position (0 mm), the number of runs (24), the condition of the loop condition, the content of the loop, the loop exit condition, the graph drawing method after the loop ends, and the way of solution inheritance.

[0160] S14-1 The condition for the loop to run is that the existing moving distance of the food is less than the moving position required to reach the endpoint (position < 2400 mm).

[0161] S14-2 The content of the loop is to determine the copy of the last heating solution as the initial value, establish the geometric model, divide the grid, run the model, get the new solution and number it in sequence (solution number = solution number + 1), and move an interval distance (80 mm).

[0162] S15 post-processing of the results, analysis of the distribution of microwave in the food, the temperature change and distribution of food in the process of translation movement heating. If there is a need to analyze the cold spots and hot spots in the process of microwave heating.

[0163] The results analysis: the electric field distribution and heat distribution of surimi products in the system are shown in Figure 15 For 120mm*60mm*16mm surimi products, the center position is effectively heated, and the highest temperature reaches about 128℃. In addition to the high temperature hot spot in the center, the central part of the left and right sides also has a high temperature area with a temperature of about 112℃.

[0164] Figure 16 A shows the numerical simulation temperature of the hot spot of surimi products and the measured temperature curve of the hot spot. The image shows that the surimi products have experienced two rapid heating stages, which is that the surimi products are passing through the first microwave resonant cavity and the second microwave resonant cavity in turn. The hot spot temperature slowly decreases at 50s-90s. At this time, the surimi products are experiencing the middle of the two microwave resonant cavities, and the electric field distribution at the connecting part reaches the minimum.

[0165] Figure 16 B shows the numerical simulation temperature of the cold spot of surimi products and the measured temperature curve of the cold spot. The image shows that the temperature of the cold spot also experiences two rapid heating stages, and the cold spot of the surimi products also experiences rapid heating when passing through the first microwave resonant cavity and the second microwave resonant cavity. At 50s-90s, unlike the hot spot, the temperature at the cold spot slowly increases. This shows that although the electric field strength here is low enough to raise the temperature, the heat from the hot spot of the surimi products with high temperature is transferred to the cold spot, causing the temperature to slowly rise.

[0166] In summary, the bidirectional coupling technology can better fit the temperature rise of surimi products, clearly correspond to the time through the microwave resonant cavity, and has high curve consistency. The research scheme set by the present application has good temperature monitoring effect, and can realize effective temperature prediction of surimi products.

[0167] Example 6: Numerical simulation results of surimi products processed by microwave-thermal water double heat source fluid mechanics grid and sweeping method

[0168] Unlike the addition of heat conduction for research. When there is heat conduction, the requirement for grid division is higher. On the basis of example 4, heat conduction is added, and the corresponding step 9 is modified as follows: the rest of the conditions are the same.

[0169] 9. Determine the heat source condition: determine whether there is an electromagnetic wave as a heat source; determine that there is heat conduction as a heat source. According to the following formula as the formula for the conversion of microwave energy to heat energy. The power P(z) of the input microwave source is taken as one of the heat sources of the heat transfer equation, and the heat conduction as another heat source.

[0170]

[0171] The hot water heat source is added as a heat flux, all the surfaces of the food are selected as all the boundaries, the material type is selected as solid, the flux type is selected as generalized inward heat flux, and q0 = h_T (Twater-T).

[0172] Result analysis: Figure 17 The heating mode of the surimi product with microwave and heat conduction as common heat sources is shown. Compared with the heating mode of the surimi product with only microwave as a heat source in Example 5, the temperature difference at the hot spot and the cold spot is significantly reduced. The temperature gradient curve is more smooth, the overall maximum temperature is reduced from 128℃ to 125℃, the minimum temperature is increased from 51.3℃ to 60℃, and the temperature range is reduced. Figure 18 A shows the temperature change of the hot spot of the surimi product with microwave and heat conduction as common heat sources. Figure 18 B shows the temperature change of the cold spot of the surimi product with microwave and heat conduction as common heat sources. The hot spot and the cold spot have good mathematical fitting effect with the experimental values. In summary, the technical scheme of the present application is also applicable to the heating mode with heat conduction and microwave as common heat sources. The predicted temperature change is good, and has good practicability.

[0173] Comparative Example 6: Numerical simulation results of regular grid processing of regular food (surimi product) with microwave-hot water double heat source

[0174] The same grid refinement degree as in Example 6 is selected, and the numerical simulation results of regular grid processing are shown in Figure 19 The results show that when regular processing (free tetrahedral mesh division) is used, the thermal pattern after numerical simulation of regular grid division presents a similar temperature distribution to Example 6 when heat conduction is added, except that the temperature gradient horizontal line changes from smooth to irregular. Further statistics of the numerical simulation temperature and the experimental temperature at the hot spot and the cold spot are obtained Figure 20 A shows the hot spot temperature curve, and Figure 20 B shows the cold spot temperature graph. The fitted temperature of the hot spot is higher than the actual temperature, and the fitted temperature of the cold spot decreases below the initial temperature before 40s, which is obviously a problem with the simulation strategy. Therefore, in the presence of heat conduction, the temperature prediction of the hot spot and the cold spot by regular free tetrahedral mesh division has a very large error.

[0175] Example 7: Numerical simulation results of microwave-hot water dual heat source irregularly shaped food (sea cucumber)

[0176] S1. Since sea cucumbers are natural organisms, their sizes are inconsistent, so they should be first classified by size. This case only demonstrates a model of one size of sea cucumber, and models of sea cucumbers of other sizes can be realized by modifying the model size. The initial temperature of the sea cucumber is 30°C. The microwave source frequency is 433 MHz, and the power is 3 kW, which passes through two resonant cavities.

[0177] S2. Sea cucumbers are irregular foods, so a 3D scanner should be used for three-dimensional solid modeling. Import or directly establish the 3D model of the sea cucumber in the numerical simulation software.

[0178] S2-1. Round the spines of the sea cucumber or perform platform processing, so that there are no infinitely small sharp corners at the top.

[0179] S3. Perform liquid nitrogen freezing homogenization on the sea cucumber, as the skin layer and inner wall of the sea cucumber have large material property differences. The skin and inner wall of the sea cucumber should be first separated by a knife or other tools, and if conditions permit, the skin layer and collagen layer of the sea cucumber can be further separated. The separated sea cucumber parts are frozen and homogenized in liquid nitrogen.

[0180] S4. Measure the electrical heating simulation parameters of different parts of the sea cucumber. In this case, microwave heating technology is used, and the heating temperature is set to 20-95°C.

[0181] S4.1 Measure the thermal conductivity of different parts of the sea cucumber, using the probe method, plate method, or other related instruments for measuring thermal conductivity. The thermal conductivity unit is W / m 2 ·K.

[0182] S4.2 Measure the specific heat of different parts of the sea cucumber using differential scanning calorimetry or the probe method. The specific heat unit is kJ / kg·K.

[0183] S4.3 Calculate the electrical conductivity of different parts of the sea cucumber using an electrical conductivity meter or other instruments that can measure electrical conductivity. The density of different parts of the sea cucumber is measured using the drainage method or other methods that can measure density. Parts with large property differences should be measured separately.

[0184] S5. Add material parameters to the model tree of the sea cucumber geometry model, including but not limited to dielectric properties, specific heat, thermal conductivity, electrical conductivity, etc.

[0185] S6. Determine the heat source: determine that electromagnetic waves are the heat source; determine that there is no heat conduction as the heat source. According to the following formula as the microwave energy to heat energy conversion formula. Input the power P(z) of the microwave source as the only heat source of the heat transfer equation, and the heat conduction The heat flux is represented by the heat flux method.

[0186]

[0187] The heat flux brought by hot water selects all surfaces of the food as all boundaries, the material type selects solid, the flux type selects generalized inward heat flux, and q0 = h_T(Twater-T).

[0188] S7. The step length and movement time of the sea cucumber translation movement in the microwave resonant cavity are divided. The number of movement step lengths is 24-48. According to the actual situation, the required parameters are set, the total heating time is set to 120 s, the number of advances is set to 24 times, the time of each small section is set to 5 s, and the distance of each advance is set to 100 mm. The total distance of the translation movement is 2400 mm.

[0189] S8. The two-way coupling translation movement simulation model is built by using the finite element software COMSOL Multiphysics 6.1. According to the case, a rectangular waveguide is set in the electromagnetic wave-frequency domain, the microwave port position and power are set. The food is selected as the research object in the solid heat transfer interface, and the initial value of food heating (20℃) is set.

[0190] S9. The food grid division is consistent during the single-mode microwave translation movement. Since this case is a microwave-hot water double heat source, it has two ways of electromagnetic heating and heat conduction. Therefore, the grid division of the irregular food sea cucumber should be carried out by using the fluid dynamics grid.

[0191] S9-1. The sea cucumber is first divided into a grid, and then the microwave equipment is divided into a grid.

[0192] S9-2. The maximum size of the sea cucumber should be less than one half (39 mm) of the wavelength of the 433 MHz microwave.

[0193] S9-3. On the basis of completing the rounding or platforming in S2-1, the sea cucumber is divided into a free tetrahedral grid, and the grid design preferentially selects the fluid dynamics method for grid division. The grid quality should be removed at the sharp corner, and the overall grid quality should be >0.65.

[0194] S9-4. After the grid division is completed, the consistency of the grid division of the sea cucumber at different moving positions is checked. The expression z>0 is set, and the grid change is viewed.

[0195] S9-5. The two-way coupling technical solution needs to realize the translation movement of the sea cucumber food, and since the food needs to maintain the consistency of the grid, based on the symmetry principle, the moving microwave heating equipment is selected. After modeling, the whole geometry is moved in the same direction to the distance of the sample translation movement.

[0196] S10. The study of microwave translation heating two-way coupling process should choose frequency domain-transient study to cover the analysis of microwave distribution, electric field intensity, heating mode change and temperature change in food.

[0197] S11. All components except sea cucumber are selected to move, and the moving distance is 0. Calculate the microwave heating situation of the first position.

[0198] (1) Set the moving position to 0, and perform study 1, frequency domain-transient study. Set the output step end to 10 s, and the step can be selected by yourself, for example, select 5 s. range(0, 5, 10), unit: s. Set the frequency to 433 MHz, and click Calculate. (2) In order to reduce the calculation results of the previous step and accurately match the initial value of the next step of study, modify the initial step of the transient solver in the study to 10 -5 s.

[0199] (3) Click Calculate Study 1. Get the result of time step 10 -5 s. After the calculation is completed, the heating result at the last time after the first transient heating is obtained.

[0200] S12. Save the microwave heating temperature value obtained in S11, and determine whether the translation motion endpoint is reached. The translation motion endpoint has not been reached yet, so move the gelling food forward by one step (100 mm). Save the temperature value as the initial temperature at this position.

[0201] S13. According to the existing temperature value, update the food material parameters such as dielectric properties, electrical conductivity, thermal conductivity, specific heat, density, etc., as the source of parameters for calculating electromagnetic field and microwave dissipation power.

[0202] S14. Repeat steps S11-S13 until the endpoint of microwave translation motion heating is reached. The repeated process involved is written in COMSOL Multiphysics 6.1 software to complete the automation process. The main pseudo code includes the definition of the initial position (0 mm), the number of runs (24), the condition of the loop condition, the content of the loop, the loop exit condition, the graph drawing method after the loop ends, and the way of solution inheritance.

[0203] S14-1 The condition for the loop to run is that the existing moving distance of the food is less than the moving position required to reach the endpoint (position < 2400 mm).

[0204] S14-2 The content of the loop is to determine the copy of the previous heating solution as the initial value, establish the geometric model, divide the grid, run the model, get the new solution and number it in sequence (solution number = solution number + 1), and move an interval distance (100 mm).

[0205] S15 post-processing of the research results, analysis of the distribution of microwave in the food, temperature change and distribution of food in the process of translation movement heating. If necessary, analyze the cold and hot spots in the process of microwave heating.

[0206] Results analysis: the irregular shape of sea cucumber was treated with round corner or platform, and the sharp angle at the top end was removed. It can more truly fit the shape of the relatively round and smooth thorn at the top end of the real sea cucumber. Figure 21 The temperature distribution of the two-way coupled numerical simulation is shown by using liquid nitrogen freezing homogenization, geometric modeling platform processing and fluid dynamics mesh division. The results show that the lowest temperature is above the thorn side of the sea cucumber, followed by the center of the lower part, and the temperature on the left and right sides is higher. The highest temperature is the outer wall of the sea cucumber in contact with hot water.

[0207] Figure 22 The numerical simulation and experimental cold spot temperature change of irregular sea cucumber are shown. The results show that for irregular food sea cucumber, the two-way coupled technical scheme involved in the present application can better fit the temperature change of irregular seasoned sea cucumber in the microwave heating system.

[0208] The above specific embodiments further illustrate the purpose, technical scheme and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A numerical simulation method of microwave translation heating of a regular or irregular food product, characterized in that, The method comprises the following steps: S1: constructing a regular or irregular food model; S2: liquid nitrogen freezing homogenization of the food; S3: measuring the electric heating simulation parameters of the food; S4: adding food material parameters to the food model, including the dielectric properties, specific heat, thermal conductivity, and electrical conductivity of the food; S5: determining the heat source: electromagnetic wave and / or heat conduction heat source; S6: dividing the microwave translation heating process, determining the distance step of each movement, determining the time t1 of staying at each position, and setting the total microwave processing time as t, and the number of movements n = t / t1; S7: modeling the microwave equipment using numerical simulation software to realize the bidirectional coupling simulation process of microwave translation movement; S8: microwave grid division; S9: selecting the frequency domain-transient study for the microwave translation heating bidirectional coupling process to cover the analysis of the microwave distribution in the food, the electric field intensity, the heating mode change, and the temperature change; and setting the waveguide type, setting the microwave port position and power; S10: based on the existing food temperature material parameters, calculating the distribution of the electromagnetic field in the food, calculating the microwave dissipation power to obtain the thermal energy converted by the electromagnetic energy in the food, taking the microwave dissipation power as the heat source of the heat transfer equation, and taking other heat sources as the heat flux for accumulation, and calculating the food temperature distribution at the end of the t1 time step; S11: saving the food temperature after heating at the t1 time step in S10, and judging whether the food moves to the end of the microwave translation movement, if not, the food moves a distance step, and the saved food temperature is taken as the initial temperature of the new position; S12: updating the dielectric properties, electrical conductivity, thermal conductivity, specific heat, and density of the food material parameters according to the existing temperature of the food, as the parameter source for calculating the electromagnetic field and microwave dissipation power; S13: repeating steps S10-S12 until the microwave translation movement heating reaches the end.

2. The numerical simulation method of claim 1, wherein, The S1 comprises: S1-1: for regular shape food modeling, direct geometric modeling is adopted, and sweep or boundary layer mesh is used in grid division to improve accuracy; S1-2: for irregular shape food, the model needs to be simplified by rounding or beveling the edges for numerical simulation program running.

3. The numerical simulation method of claim 1, wherein, In S2, the liquid nitrogen freezing time of food samples below 5g is 15s or more; the liquid nitrogen freezing time of food samples above 10g is 45s or more.

4. The numerical simulation method of claim 1, wherein, In S3, the electric heating simulation parameters include: measuring the thermal conductivity of the food; measuring the specific heat of the food; calculating the electrical conductivity of the food, and determining the density of the food.

5. The numerical simulation method of claim 1, wherein, In S5, formula 1 is used as the formula for microwave energy conversion to thermal energy: The power of the input microwave source (P(z)) is used as one of the heat sources in the heat transfer equation, heat conduction as another heat source.

6. The numerical simulation method of claim 1, wherein, In S7, the numerical simulation software uses finite element or finite time domain difference; and according to the actual situation, the microwave source type, phase, microwave port position and power are set in the electromagnetic wave interface, and the food is selected as the research object and the initial value is set in the solid heat transfer interface.

7. The numerical simulation method of claim 1, wherein, In S8, the grid division of the food needs to be consistent during the single-mode microwave translation movement. For the microwave grid division with the heat conduction as the heat source, the fluid dynamics grid is used. For the irregular food, the swept grid is added to improve the simulation accuracy. For the irregular food, the partition block processing method is used to appropriately improve the grid quality.

8. The numerical simulation method of claim 7, wherein, S8 includes: S8-1: The grid division is performed according to the order of the food and the microwave equipment, so as to ensure that the grid division of the food is consistent at each time step; S8-2: The maximum size of the grid in the food should be less than half of the wavelength of the microwave in the food medium. According to the limited size, the size of the maximum unit of the food with only the microwave as the heat source is determined. If there is an additional heat source, the maximum unit size should be less than one-half of the microwave single heat source unit size. The grid division of the microwave equipment other than the food is less than half of the wavelength of the microwave in the internal medium; S8-3: For the regular food grid type, the swept grid is used. For the irregular food, the regular surface is preferentially swept or the boundary layer grid is used to improve the grid quality. The free tetrahedral grid division is performed on the area that cannot be regularly divided; S8-4: After the grid division is completed, the grid division of the food at different moving positions is confirmed, and whether the grid changes is observed. When the food grid does not change, it is determined that the food can inherit the temperature after the heating at the previous time period as the initial value at the next position; S8-5: The translation movement of the food can be selected to move the food or the microwave equipment to realize the relative displacement of the food and the microwave equipment.

9. The numerical simulation method of claim 1, wherein, In S13, the conditions for the circulation are that the existing moving distance of the food is less than the moving position required to reach the end point. The contents of the circulation are to determine the solution of the last heating as the initial value, to establish the geometric model, to divide the grid, to run the model, to obtain the new solution and to number the new solution in sequence, and to move an interval distance.

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