Method and system for achieving partial freezing heat transfer control of muscle food

Abstract

The application discloses a heat transfer control method and system for realizing partial freezing of muscle food, and the method comprises the following steps: obtaining the ice fraction of muscle food samples and the moisture state change in the partial freezing and thawing process of the muscle food samples through experiments; comprehensively analyzing the juice loss rate, shear force, ice fraction and moisture state change of the muscle food samples to obtain a suitable partial freezing temperature of the muscle food; establishing a three-dimensional heat transfer model, predicting the temperature data of the muscle food, and calculating the time for the muscle food to reach the suitable partial freezing temperature; and switching the refrigerator between the rapid cooling mode and the maintenance mode according to the time for reaching the suitable partial freezing temperature, so that the temperature of the muscle food is rapidly reduced in the rapid cooling mode and is maintained at the suitable partial freezing temperature in the maintenance mode. The method can accurately control the temperature of the muscle food, and thus the control target of short-term high-quality storage of the muscle food is achieved.

Description

Technical Field

[0001] This invention belongs to the field of food storage technology, specifically relating to a heat transfer control method and system for partially freezing muscle foods. Background Technology

[0002] Meat and seafood play a vital role in the human diet, but they are highly perishable. Freezing food by lowering the temperature to convert the liquid water within it into solid ice can extend its shelf life.

[0003] Ice fraction refers to the proportion of liquid free water that transforms into solid ice during the freezing process, and it can be used to determine the moisture state of food during freezing. Partial freezing is considered an alternative freezing method for short-term storage of meat products. Compared to the common method of freezing meat products at -18℃ to -40℃, it can save energy costs and provide better short-term food quality. Achieving partial freezing requires precise control of the food freezing process, and real-time accurate temperature acquisition is a prerequisite for precise control.

[0004] The current methods for determining the appropriate ice fraction and controlling the temperature of muscle products still have some shortcomings and limitations, mainly:

[0005] (1) There is a lack of analysis and measurement on the changes in ice fraction of specific muscle foods at different freezing temperatures; (2) There is a lack of parameters on the appropriate ice fraction and moisture state of specific muscle foods in a partially frozen state, so it is impossible to determine the corresponding freezing temperature control range for the appropriate ice fraction control range of specific muscle foods; (3) There is a lack of more accurate and convenient calculation methods for the heat transfer process of muscle foods during freezing, so it is impossible to obtain real-time temperature data of muscle foods during freezing; (4) Currently, the control of the frozen state of food requires the installation of multiple sensors, which increases the production cost of freezing equipment. Summary of the Invention

[0006] The main objective of this invention is to overcome the shortcomings and deficiencies of the prior art and to propose a heat transfer control method and system for partially freezing muscle foods.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for controlling heat transfer to achieve partial freezing of muscle products, comprising the following steps:

[0009] A three-dimensional heat transfer model of the muscle food and the refrigerator cavity was established using simulation software. The fluid flow in the refrigerator cavity and the unidirectional coupling heat transfer behavior between the fluid and the muscle food were predicted, and the time for the muscle food to reach the appropriate partial freezing temperature was calculated.

[0010] Based on the time required to reach the appropriate partial freezing temperature, the refrigerator switches between rapid cooling mode and maintenance mode, so that the temperature of the muscle food is rapidly reduced in rapid cooling mode and maintained at its appropriate partial freezing temperature in maintenance mode.

[0011] The present invention also includes a heat transfer control system for partially freezing muscle food. The system applies the heat transfer control method provided by the present invention and includes a module for obtaining ice fraction and moisture state change, a module for obtaining partial freezing temperature, a module for predicting partial freezing temperature time, and a module for controlling partial freezing temperature.

[0012] The ice fraction and moisture state change acquisition module is used to place a glass sample tube containing a muscle food sample into the VT-NMR instrument, start the liquid nitrogen temperature control system, set the required temperature, collect the transverse relaxation signal of the sample, and obtain the ice fraction of the muscle food sample and its moisture state changes during partial freezing and thawing.

[0013] The partial freezing temperature acquisition module is used to determine the juice loss rate and shear force of muscle food samples after thawing. By comprehensively analyzing the juice loss rate, shear force, ice fraction and moisture state changes of the samples, the appropriate partial freezing temperature of the muscle food is obtained.

[0014] The partial freezing temperature and time prediction module is used to establish a three-dimensional heat transfer model, predict the temperature data of the muscle food, and calculate the time it takes for the muscle food to reach the appropriate partial freezing temperature.

[0015] The partial freezing temperature control module controls the refrigerator to switch between rapid cooling mode and maintenance mode based on the time required to reach the appropriate partial freezing temperature, so that the temperature of the meat food is rapidly reduced in rapid cooling mode and maintained at its appropriate partial freezing temperature in maintenance mode.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0017] 1. This invention utilizes VT-NMR to achieve rapid, in-situ determination of the ice fraction and moisture state of different muscle foods, which can determine the partial freezing temperature range and suitable partial freezing temperature for different muscle foods.

[0018] 2. This invention uses the computer simulation software COMSOL Multiphysics to establish a three-dimensional heat transfer model to predict temperature changes during the freezing process of meat products. It has universality; for different types, shapes, and sizes of meat products and different working conditions, the prediction results can be obtained simply by modifying the model parameters and running the program again.

[0019] 3. This invention regulates the temperature of food by using a heat transfer model of the food freezing process, which can reduce the use of sensors in the refrigerator, reduce the manufacturing cost of the refrigerator, and reduce control errors caused by interconnecting multiple sensors.

[0020] 4. The numerical model of this invention is composed of code, which can be easily combined with the control logic code of the microcomputer in the freezing equipment, providing reference and guidance for further development of intelligent refrigerator freezing technology and equipment upgrades. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the method of the present invention;

[0022] Figure 2 This is a schematic diagram of the VT-NMR device in the embodiment;

[0023] Figure 3 This is a graph showing the relationship between the ice fraction of the pork tenderloin sample and different temperatures in the example;

[0024] Figure 4 This is a transverse relaxation time spectrum of the pork tenderloin sample during partial freezing and thawing in the embodiment;

[0025] Figure 5 This is a geometric model structure diagram of the three-dimensional heat transfer model in the embodiment;

[0026] Figure 6 This is a graph showing the relationship between the thermal conductivity of pork tenderloin and temperature in the embodiment.

[0027] Figure 7 This is a graph showing the specific heat capacity of pork tenderloin versus temperature in the example. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0029] like Figure 1 As shown, the present invention provides a heat transfer control method for partially freezing muscle food, comprising the following steps:

[0030] Perform VT-NMR instrument calibration; place the glass sample tube containing the muscle food sample in the VT-NMR instrument, set the required temperature, and use VT-NMR to collect the transverse (T2) relaxation signal of the sample to obtain the ice fraction of the muscle food sample and the changes in water state during partial freezing and thawing.

[0031] Among them, such as Figure 2 As shown, the VT-NMR equipment includes a nuclear magnetic resonance control system, a data recording system, a magnet device, and a liquid nitrogen temperature control system;

[0032] The nuclear magnetic resonance control system is used to control the performance of the magnet equipment, including the spectrometer unit, radio frequency unit, magnet temperature control unit, and two gradient units;

[0033] The data logging system is used for the acquisition of data and transverse relaxation signals;

[0034] The magnet device includes a 10mm insulated probe coil and a 1.0T permanent magnet, with a proton resonance frequency of 40.69MHz at 32℃.

[0035] The liquid nitrogen temperature control system is used to control the temperature of the sample tube, including a temperature control system, a liquid nitrogen system, and a heating chamber; the liquid nitrogen system is located between the temperature control system and the heating chamber; the heating chamber is located between the liquid nitrogen system and the magnet device.

[0036] Specifically, the calibration of VT-NMR equipment involves:

[0037] Place a 10mm diameter glass sample tube containing a standard silicone oil solution into a 10mm insulated probe coil, select the FID sequence, and determine the instrument’s center frequency and 90° and 180° pulse widths to calibrate the instrument.

[0038] An optical fiber was inserted into a 10 mm diameter glass sample tube containing a standard silicone oil solution. The sample tube was then placed in a 10 mm insulated probe coil. The liquid nitrogen temperature control system was activated to adjust the temperature inside the sample tube to the required temperature. After the temperature stabilized, the transverse (T2) relaxation signal of the sample was acquired using the CPMG sequence of the VT-NMR equipment, and signal intensity correction was performed.

[0039] The specific method for obtaining the ice fraction and moisture state changes during partial freezing and thawing of muscle food samples using VT-NMR equipment is as follows:

[0040] An optical fiber was inserted into a glass sample tube containing a muscle food sample wrapped in plastic wrap, with a diameter of 10 mm. The sample tube was placed in a 10 mm insulated probe coil. The liquid nitrogen temperature control system was activated and the temperature inside the sample tube was adjusted to the required temperature. The transverse (T2) relaxation signal of the sample was continuously acquired every 2 minutes using the CPMG sequence of the VT-NMR device until the transverse relaxation signal remained unchanged. The acquisition was then stopped to obtain the CPMG attenuation curve.

[0041] To eliminate the influence of mass magnitude on signal strength, the transverse (T2) relaxation signal was subjected to mass normalization processing.

[0042] The CPMG decay curve was continuously fitted with multiple exponentials using the MultiExp Inv analysis software and the synchronous iterative reconstruction algorithm to obtain the transverse relaxation time spectrum. The transverse relaxation time was calculated from the peak position. The area under each peak (corresponding to the relative content of water molecules) was calculated by cumulative integration. The transverse relaxation signal and peak area need to be multiplied by the correction coefficient during the calculation.

[0043] The ice fraction was calculated from the difference in total peak area and correction factor of the transverse relaxation time spectra of fresh and partially frozen samples.

[0044] The correction factor is the ratio of the total peak area measured at a certain standard temperature to the total peak area measured at the temperature required for the experiment.

[0045] The CPMG pulse sequence parameters are set as follows:

[0046] Sampling frequency: 200kHz; Main frequency: 40MHz; RF delay: 0.02ms; Analog gain: 20dB; Digital gain: 3; Waiting time: 3000ms; Accumulation count: 16; Echo time: 0.2ms; Number of echoes: 15000.

[0047] The juice loss rate and shear force of muscle food samples after thawing were measured. A comprehensive analysis of the juice loss rate, shear force, ice fraction, and changes in moisture state during partial freezing and thawing was conducted to determine the appropriate partial freezing temperature for the muscle food. Specifically:

[0048] The mass of a muscle food sample before freezing and after thawing was determined to obtain the sample juice loss rate.

[0049] The shear force of thawed muscle food samples was determined using a muscle tenderness meter.

[0050] By comprehensively analyzing the juice loss rate, shear force, ice fraction, peak area loss rate of bound water and free water after partial freezing, and peak area loss rate of bound water after thawing of muscle food samples, the appropriate partial freezing temperature for muscle food can be obtained.

[0051] A three-dimensional heat transfer model of the muscle food and the refrigerator cavity was established using simulation software. The fluid flow in the refrigerator cavity and the unidirectional coupling heat transfer behavior between the fluid and the muscle food were predicted, and the time it took for the muscle food to reach the appropriate partial freezing temperature was calculated.

[0052] The physical processes involved in heat transfer to muscle products are highly complex, considering the influence of the external fluid environment. To date, no fluid flow model can perfectly simulate the flow behavior of turbulent fluids. After years of development in fluid mechanics and research into related applications, the turbulent, low Reynolds number k-ε model is considered to be able to simulate the flow behavior of fluids within a refrigerator cavity relatively accurately.

[0053] Specifically, establishing a three-dimensional heat transfer model includes:

[0054] Measure the size of the refrigerator cavity, the location and size of the air inlet and outlet, and determine the size and location of the muscle food in advance, and build a matching geometric model in the computer simulation software COMSOL Multiphysics.

[0055] Define the geometric model and physical parameters, including:

[0056] Set boundary and initial conditions according to the required operating parameters of the muscle food product;

[0057] Set physical property parameters based on the characteristics of muscle food materials;

[0058] The boundary mesh of the muscle food geometric model was refined, while other parts were divided using a physics-controlled mesh.

[0059] The fluid flow field is solved using a steady-state solver, while the heat transfer physical field is solved using a transient solver.

[0060] The physics interface is set to turbulence, low Reynolds number k-ε interface, and solid and fluid heat transfer interface to calculate the velocity and temperature of the fluid flow field in the physical model during the freezing process.

[0061] The governing equations of the three-dimensional heat transfer model are:

[0062] Flow behavior of fluid flow field:

[0063]

[0064]

[0065]

[0066]

[0067] Where, ρ a Let be the density of air, and t be the freezing time of the muscle product. Let P be the vector velocity of the air; P be the pressure at various points in the fluid flow field; and μ be the dynamic viscosity of the air. t S is the turbulent viscosity. Ti Here, k is the source term of the fluid kinetic energy equation, σ is the turbulent kinetic energy, and k is the turbulent kinetic energy. k P is the Prandtl number of the turbulent flow, ε is the kinetic energy dissipation of the fluid; k G k C1 and C3 are the sources of turbulent kinetic energy; C1 and C3 are the turbulence constants of the k-ε model; f1 and f2 are the damping functions of the k-ε model.

[0068] Heat transfer behavior:

[0069]

[0070]

[0071] Among them, C pa Here, T is the specific heat capacity of air, and k is the temperature. a σ is the thermal conductivity of air. T For turbulence, ρ is the Prandtl number. f C is the density of muscle food. pf For the specific heat capacity of muscle foods, k f The thermal conductivity of muscle foods;

[0072] The thermal conductivity of the muscle food is used as an interpolation function of temperature and input into the model.

[0073] The specific heat capacity of the muscle food is used as an interpolation function of temperature and input into the model.

[0074] The density of the muscle food is calculated by measuring the size and mass of the muscle food and then input into the model.

[0075] The control equations of the three-dimensional heat transfer model were solved using the computer simulation software COMSOL Multiphysics to obtain the temperature change relationship of each point of the muscle food over time. The temperature change relationship of the geometric center point of the muscle food over time was analyzed. The temperature of the geometric center point was reduced from the initial temperature to the appropriate freezing temperature of the muscle food. The time taken for the cooling process is the time to reach the appropriate freezing temperature.

[0076] Based on the time required to reach the appropriate partial freezing temperature, the refrigerator is controlled to switch between rapid cooling mode and maintenance mode, so that the temperature of the muscle food is reduced in rapid cooling mode and maintained at its appropriate partial freezing temperature in maintenance mode. Specifically:

[0077] Place the meat in the refrigerator and turn on the quick-cool mode. The three-dimensional heat transfer model calculates the time required for the meat to reach the appropriate partial freezing temperature under the quick-cool mode. When the working time of the quick-cool mode reaches the time required calculated by the three-dimensional heat transfer model, it is considered that the appropriate partial freezing temperature of the meat has been reached. At this time, switch the refrigerator from quick-cool mode to maintenance mode to keep the current temperature of the meat unchanged.

[0078] Example

[0079] The present invention will be further described in detail below using pork tenderloin as an example, but the embodiments of the present invention are not limited thereto.

[0080] First, after VT-NMR instrument and signal intensity calibration, the T2 relaxation signal of the pork tenderloin sample was acquired using VT-NMR to obtain the ice fraction of the pork tenderloin and the changes in water state during partial freezing and thawing.

[0081] In this embodiment, the VT-NMR device is as follows: Figure 2 As shown; the sample tube is made of pure SiO2 glass, and the effective testing area inside the sample tube is 10mm in diameter and 20mm in height. The specific operation steps are as follows:

[0082] (1) After removing the fascia from the surface of the pork tenderloin, cut it into pieces with a size of 2.0cm×0.5cm×0.5cm (0.21±0.03g) perpendicular to the fiber direction;

[0083] (2) Place a glass sample tube containing standard silicone oil solution with a diameter of 10 mm into a 10 mm insulated probe coil, select the FID sequence, and determine the center frequency of the instrument and the 90° and 180° pulse widths to calibrate the instrument.

[0084] (3) Insert the optical fiber into a glass sample tube containing a standard silicone oil solution with a diameter of 10 mm, place the sample tube into a 10 mm insulated probe coil, start the liquid nitrogen temperature control system, adjust the temperature inside the sample tube to the temperature required for the experiment, and after the temperature stabilizes, use the CPMG sequence of VT-NMR to acquire the transverse (T2) relaxation signal of the sample 3 times and perform signal intensity correction.

[0085] (4) Insert the optical fiber into a glass sample tube containing a pork tenderloin sample wrapped in plastic wrap with a diameter of 10 mm, and place the sample tube into a 10 mm insulated probe coil.

[0086] (5) Start the liquid nitrogen temperature control system and adjust the temperature inside the sample tube to 25℃ and -2℃~-20℃ to study the relationship between the ice fraction of different pork tenderloin samples and different temperatures in situ; then, based on the ice fraction measurement results, adjust the temperature inside the sample tube to 25℃, -2℃, -2.5℃, -3℃, -3.5℃, -4℃ and 4℃ to analyze the changes in the water state of the pork tenderloin samples during partial freezing and thawing.

[0087] (6) The transverse (T2) relaxation signal of the pork tenderloin sample was continuously collected every 2 minutes using the same CPMG sequence until the transverse (T2) relaxation signal remained basically unchanged. The collection was then stopped to obtain the CPMG decay curve.

[0088] (7) To avoid the randomness of the results, three parallel experiments were conducted;

[0089] (8) The quality of the transverse (T2) relaxation signal was normalized.

[0090] (9) Using the MultiExp Inv analysis software, the synchronous iterative reconstruction technology algorithm is used to continuously fit the CPMG decay curve to obtain the transverse (T2) relaxation time spectrum. The relaxation time is calculated from the peak position, and the area under each peak (corresponding to the relative water content) is determined by cumulative integration. The transverse (T2) relaxation signal and peak area need to be multiplied by the correction coefficient.

[0091] (10) The ice fraction was calculated from the total peak area of ​​the transverse (T2) relaxation time spectrum of fresh and partially frozen pork tenderloin samples and the correction coefficient. The specific formula is ice fraction (%) = (A0-A1×k) / A0×100, where A0 is the total peak area of ​​the transverse (T2) relaxation time spectrum of fresh pork tenderloin sample, A1 is the total peak area of ​​the transverse (T2) relaxation time spectrum of partially frozen pork tenderloin sample, and k is the correction coefficient of the required temperature (T℃), that is, the ratio of the total peak area measured at 25℃ to the total peak area measured at T℃.

[0092] Then, the juice loss rate and shear force of the thawed pork tenderloin samples were measured. By comprehensively analyzing the juice loss rate, shear force, ice fraction, and changes in moisture state of the pork tenderloin, a suitable partial freezing temperature for the pork tenderloin was obtained; in this embodiment, specifically:

[0093] The juice loss rate of pork tenderloin reflects its water-holding capacity. The specific formula is: juice loss rate (%) = (M0-M1) / M0×100, where M0 is the mass of the pork tenderloin sample before partial freezing and M1 is the mass of the pork tenderloin sample after thawing.

[0094] The surface liquid of the sample was absorbed with filter paper, and the required shear force (N) for each sample was measured by a C-LM 3B digital muscle tenderness meter.

[0095] like Figure 3 As shown in the figure, the relationship between the ice fraction of the sample and different temperatures can be analyzed. It can be found that the change of ice fraction of pork tenderloin sample in the temperature range of -2℃ to -20℃ can be divided into three stages: the stage of slow increase of ice fraction, the stage of ice fraction jump, and the stage of significant increase of ice fraction.

[0096] like Figure 4 As shown, the T2 relaxation time spectra during the partial freezing and thawing of the samples reveal that, under normal circumstances, partial freezing has little effect on myofibrils and muscle membranes related to bound water in pig tenderloin samples, while the capillaries of muscle tissue connected to free water may be damaged by ice crystals during partial freezing.

[0097] Comprehensive analysis criteria: For indicators such as juice loss rate, peak area loss rate of bound water and free water after partial freezing, and peak area loss rate of bound water after thawing, the highest score is achieved when these indicators are significantly minimized; for the shear force indicator, the highest score is achieved when the temperature is significantly closest to that of a fresh sample. The temperature with the highest final total score is the suitable partial freezing temperature.

[0098] Table 1 below shows the effects of different partial freezing temperatures on the ice fraction, juice loss rate, shear force after thawing, peak area loss rate of bound water and free water after partial freezing, and peak area loss rate of bound water after thawing in pork tenderloin. Table 1 shows that the pork tenderloin that was partially frozen at -4℃ and then thawed at 4℃ had the highest juice loss rate (p<0.05). Since the shear force of fresh pork tenderloin is 3.465N, the shear force of pork tenderloin that was partially frozen at -4℃ and then thawed at 4℃ was poorly maintained (p<0.05). There was no significant difference in the ice fraction of partially frozen pork tenderloin at the five partial freezing temperatures. The pork tenderloin that was partially frozen at -3.5℃ and then thawed at -3.5℃ had the highest bound water peak area loss rate (p<0.05), indicating that the water holding capacity of pork tenderloin that was partially frozen at -3.5℃ and then thawed at -3.5℃ was relatively weak. Furthermore, the pork tenderloin that was partially frozen at -4°C had the largest free water peak area loss (p<0.05), indicating that the tenderness of the pork tenderloin was not well preserved after partial freezing at -4°C.

[0099] The analytical criteria are as follows: A score of 10 is awarded. A score of 0 is awarded for the sample juice loss rate, the peak area loss rate of bound and free water after partial freezing, and the peak area loss rate of bound water after thawing, with a median of 5 and a significant minimum of 10. Similarly, a score of 0 is awarded for the sample shear force after thawing that is significantly least close to that of a fresh sample, with a median of 5 and a significant minimum of 10. Therefore, the scores for -2℃, -2.5℃, -3℃, -3.5℃, and -4℃ are 40, 40, 40, 25, and 20, respectively.

[0100] In summary, the suitable freezing temperature for pork tenderloin is -2 to -3℃.

[0101]

[0102]

[0103] Table 1

[0104] Next, a three-dimensional heat transfer model of the pork tenderloin and the refrigerator cavity was established using the computer simulation software COMSOL Multiphysics. This model predicted the fluid flow within the refrigerator cavity and the coupled heat transfer process between the fluid and the pork tenderloin, obtaining the time required for the pork tenderloin to reach a suitable partial freezing temperature. The accuracy of this model was verified through experimental measurements. This embodiment uses the pork tenderloin temperature dropping to -2℃ as an example.

[0105] (1) First, based on the external dimensions of the refrigerator cavity and the pork tenderloin, a three-dimensional geometric model was created in COMSOL Multiphysics. The geometric model was constructed based on the actual dimensions of the refrigerator cavity and the pork tenderloin. The refrigerator cavity is an irregular hexahedron with an overall axisymmetric design. The specific dimensions are as follows: Figure 5 As shown.

[0106] (2) Set the physical field interface to turbulence, low Reynolds number k-ε interface and solid and fluid heat transfer interface;

[0107] (3) Set boundary conditions and initial conditions according to the required operating parameters;

[0108] The initial temperature of the sample was 20℃, and the initial temperature of the environment was 5℃.

[0109] Boundary conditions:

[0110] The inlet boundary fluid temperature is -10℃, the flow velocity is 1m / s, and the pressure is 0Pa;

[0111] For the exit boundary, apply the exit boundary condition (i.e., outflow boundary condition) to the fully developed flow section, and set the gradient perpendicular to the flow direction of other variables to zero in the exit section;

[0112] The inner wall boundary of the cavity is defined as a zero-roughness, non-slip wall, and the velocity vector on all walls is zero.

[0113] (4) Set the physical property parameters according to the material characteristics of pork tenderloin; the physical property parameters need to be set for thermal conductivity, specific heat capacity, and density. Thermal conductivity and specific heat capacity should be set as follows: Figure 6 and Figure 7 The interpolation function shown is input into the model. The density is calculated by measuring the length, width, height, and mass of the pork tenderloin sample.

[0114] (5) The mesh generation tool provided by COMSOL Multiphysics was used to generate the mesh. The boundary mesh of the geometric model of the pork tenderloin sample was refined, and the other parts were divided using the physical field control mesh.

[0115] (6) The fluid flow field is solved by a steady-state solver, and the heat transfer physics field is solved by a transient solver. The heat transfer physics field requires the steady-state solution of the fluid flow field, which is input through the dependent variable setting. The heat transfer physics field is solved by the backward difference method, and the initialization method is the backward Euler method.

[0116] (7) Set the transient solver to solve for 300 minutes with a time step of 1 second;

[0117] (8) Predict the relationship between temperature and time of pork tenderloin samples and compare it with the subsequent verification results.

[0118] Finally, the pork tenderloin is kept at a suitable freezing temperature by switching between the rapid cooling mode and the maintenance mode in the refrigerator's cooling module. In this embodiment, a household refrigerator is used for the experiment, and temperature data is obtained by inserting a thermocouple into the pork tenderloin. The specific steps are as follows:

[0119] (1) After removing the fascia on the surface of the pork tenderloin, cut it into pieces with dimensions of 10.0cm×10.0cm×2.0cm along the direction perpendicular to the fibers;

[0120] (2) Place the cut pork tenderloin at the bottom center of the refrigerator cavity and insert the thermocouple at its geometric center;

[0121] (3) When the ambient temperature sensor detects that the refrigerator door is open, the refrigeration module immediately starts the rapid cooling mode and starts working. At the same time, the temperature sensor's recording software is opened to collect sample temperature data.

[0122] (4) When the temperature of the pork tenderloin drops to -2℃, the refrigeration module will switch from rapid cooling mode to maintenance mode;

[0123] (5) To avoid the randomness of the results, three parallel experiments were conducted;

[0124] (6) Compare and analyze the collected data with the calculation results of the model.

[0125] It should be noted that the refrigeration module in this embodiment includes the entire refrigeration system, including a compressor, condenser, expansion valve, and evaporator. The rapid cooling mode and the sustaining mode of the refrigeration module represent different cooling capacities of the refrigeration module for the refrigerator cavity, with the rapid cooling mode having a stronger cooling capacity and the sustaining mode having a weaker cooling capacity.

[0126] Results analysis showed that, based on model calculations and experimental measurements, the temperature of pork tenderloin rapidly decreased from 0 to 135 minutes. After approaching its freezing point, the temperature gradually leveled off before resuming its downward trend. In this example, the time required for the pork tenderloin sample to cool from 20°C to -2°C was 480 minutes. Experiments verified the accuracy of the model calculations. The goodness-of-fit calculation showed that the predicted temperature had a good fit of 0.9436 to the measured temperature, indicating a good fit.

[0127] In another embodiment, a heat transfer control system based on the heat transfer control method of the above embodiment is also provided. The system includes an ice fraction and moisture state change acquisition module, a partial freezing temperature acquisition module, a partial freezing temperature time prediction module, and a partial freezing temperature control module.

[0128] The ice fraction and moisture state change acquisition module is used to place a glass sample tube containing a muscle food sample into the VT-NMR instrument, start the liquid nitrogen temperature control system, set the required temperature, collect the transverse relaxation signal of the sample, and obtain the ice fraction of the muscle food sample and its moisture state changes during partial freezing and thawing.

[0129] The partial freezing temperature acquisition module is used to determine the juice loss rate and shear force of muscle food samples after thawing. By comprehensively analyzing the juice loss rate, shear force, ice fraction and moisture state changes of the samples, the appropriate partial freezing temperature of the muscle food is obtained.

[0130] The partial freezing temperature and time prediction module is used to establish a three-dimensional heat transfer model, predict the temperature data of the muscle food, and calculate the time it takes for the muscle food to reach the appropriate partial freezing temperature.

[0131] The partial freezing temperature control module controls the refrigerator to switch between rapid cooling mode and maintenance mode based on the time required to reach the appropriate partial freezing temperature, so that the temperature of the meat food is rapidly reduced in rapid cooling mode and maintained at its appropriate partial freezing temperature in maintenance mode.

[0132] It should also be noted that, in this specification, terms such as "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0133] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling heat transfer to achieve partial freezing of muscle food, characterized in that, Includes the following steps: A three-dimensional heat transfer model of the muscle food and the refrigerator cavity was established using simulation software. The fluid flow in the refrigerator cavity and the unidirectional coupling heat transfer behavior between the fluid and the muscle food were predicted, and the time for the muscle food to reach the appropriate partial freezing temperature was calculated. The appropriate freezing temperature for a portion of the muscle product can be obtained using the following method: Glass sample tubes containing muscle food samples were placed in a VT-NMR instrument. The required temperature was set, and the transverse relaxation signal of the sample was acquired using VT-NMR to obtain the ice fraction of the muscle food sample and the changes in water state during partial freezing and thawing. The juice loss rate and shear force of muscle food samples after thawing were measured. A comprehensive analysis of the juice loss rate, shear force, ice fraction, and changes in moisture state during partial freezing and thawing was conducted to determine the appropriate partial freezing temperature for the muscle food. Specifically: The mass of a muscle food sample before freezing and after thawing was determined to obtain the sample juice loss rate. The shear force of thawed muscle food samples was determined using a muscle tenderness meter. By comprehensively analyzing the juice loss rate, shear force, ice fraction, bound water peak area loss rate after partial freezing, free water peak area loss rate after partial freezing, and bound water peak area loss rate after thawing of muscle food samples at different partial freezing temperatures, the appropriate partial freezing temperature for muscle food was determined; comprehensive analysis standards: For the indicators of juice loss rate, bound water peak area loss rate after partial freezing, free water peak area loss rate after partial freezing, and bound water peak area loss rate after thawing, the minimum score is the highest. For the indicator of shear force, the score is the highest when it is closest to that of a fresh sample. With 10 points as the maximum score, the maximum score for the sample juice loss rate, bound water peak area loss rate after partial freezing, free water peak area loss rate after partial freezing, and bound water peak area loss rate after thawing is 0 points, the median is 5 points, and the minimum is 10 points. The score for the shear force after thawing that is least close to that of a fresh sample is 0 points, the median is 5 points, and the closest is 10 points. The scores for juice loss rate, shear force, bound water peak area loss rate after partial freezing, free water peak area loss rate after partial freezing, and bound water peak area loss rate after thawing are added together, and the partial freezing temperature corresponding to the highest total score is the appropriate partial freezing temperature. Establishing a three-dimensional heat transfer model specifically includes: Measure the size of the refrigerator cavity, the location and size of the air inlet and outlet, and determine the size and location of the muscle food in advance, and build a matching geometric model in the computer simulation software COMSOL Multiphysics. Define the geometric model and physical parameters, including: Set boundary and initial conditions according to the required operating parameters of the muscle food product; Set physical property parameters based on the characteristics of muscle food materials; The boundary mesh of the muscle food geometric model was refined, while other parts were divided using a physics-controlled mesh. The fluid flow field is solved using a steady-state solver, while the heat transfer physical field is solved using a transient solver. The physics interface is set to turbulence, low Reynolds number k-ε interface, and solid and fluid heat transfer interface to calculate the velocity and temperature of the fluid flow field in the physical model during the freezing process. The specific time required to reach the appropriate freezing temperature for muscle products is calculated as follows: The control equations of the three-dimensional heat transfer model were solved using the computer simulation software COMSOL Multiphysics to obtain the temperature change relationship of each point of the muscle food with time. The temperature change relationship of the geometric center point of the muscle food with time was analyzed. The temperature of the geometric center point was reduced from the initial temperature to the appropriate freezing temperature of the muscle food. The time taken for the cooling process is the time to reach the appropriate freezing temperature. Based on the time required to reach the appropriate partial freezing temperature, the refrigerator switches between rapid cooling mode and maintenance mode, so that the temperature of the muscle food is rapidly reduced in rapid cooling mode and maintained at its appropriate partial freezing temperature in maintenance mode.

2. The heat transfer control method according to claim 1, characterized in that, VT-NMR equipment includes a nuclear magnetic resonance control system, a data recording system, a magnet device, and a liquid nitrogen temperature control system; The nuclear magnetic resonance control system is used to control the performance of the magnet equipment, including the spectrometer unit, radio frequency unit, magnet temperature control unit, and two gradient units; The data logging system is used for the acquisition of data and transverse relaxation signals; The magnet device includes a 10mm insulated probe coil and a 1.0T permanent magnet; The liquid nitrogen temperature control system is used to control the temperature of the sample tube, including a temperature control system, a liquid nitrogen system, and a heating chamber; the liquid nitrogen system is located between the temperature control system and the heating chamber; the heating chamber is located between the liquid nitrogen system and the magnet device.

3. The heat transfer control method according to claim 2, characterized in that, The specific method for obtaining the ice fraction and moisture state changes during partial freezing and thawing of muscle food samples using VT-NMR equipment is as follows: Place a 10mm diameter glass sample tube containing a standard silicone oil solution into a 10mm insulated probe coil, select the FID sequence, and determine the instrument’s center frequency and 90° and 180° pulse widths to calibrate the instrument. Insert the optical fiber into a 10 mm diameter glass sample tube containing a standard silicone oil solution. Place the sample tube into a 10 mm insulated probe coil. Start the liquid nitrogen temperature control system to adjust the temperature inside the sample tube to the required temperature. After the temperature stabilizes, use the CPMG sequence of the VT-NMR equipment to acquire the transverse relaxation signal of the sample and perform signal intensity correction. An optical fiber was inserted into a glass sample tube containing a muscle food sample wrapped in plastic wrap, with a diameter of 10 mm. The sample tube was placed in a 10 mm insulated probe coil. The liquid nitrogen temperature control system was activated, and the temperature inside the sample tube was adjusted to the required temperature. The transverse relaxation signal of the sample was continuously acquired every 2 minutes using the CPMG sequence of the VT-NMR equipment until the transverse relaxation signal remained unchanged. The acquisition was then stopped to obtain the CPMG attenuation curve. The transverse relaxation signal was subjected to quality normalization. The CPMG decay curve was continuously fitted by the MultiExp Inv analysis software using the synchronous iterative reconstruction algorithm to obtain the transverse relaxation time spectrum. The transverse relaxation time was calculated from the peak position. The area under each peak was calculated by cumulative integration. The transverse relaxation signal and the peak area need to be multiplied by the correction coefficient during the calculation. The ice fraction was calculated from the difference in total peak area and correction factor of the transverse relaxation time spectra of fresh and partially frozen samples. The correction factor is the ratio of the total peak area measured at a certain standard temperature to the total peak area measured at the temperature required for the experiment.

4. The heat transfer control method according to claim 3, characterized in that, The CPMG pulse sequence parameters are set as follows: Sampling frequency: 200kHz; Main frequency: 40MHz; RF delay: 0.02ms; Analog gain: 20dB; Digital gain: 3; Waiting time: 3000ms; Accumulation count: 16; Echo time: 0.2ms; Number of echoes: 15000.

5. The heat transfer control method according to claim 1, characterized in that, The governing equations of the three-dimensional heat transfer model are: Flow behavior of fluid flow field: in, For the density of air, This refers to the freezing time of muscle products. The vector velocity of the air; This represents the pressure at various points in the fluid flow field. The dynamic viscosity of air. For turbulent viscosity, This is the source term of the fluid kinetic energy equation. For turbulent kinetic energy, For the Prandtl number of turbulence, This refers to the dissipation of kinetic energy in the fluid. , It is a source of turbulent kinetic energy; , For k- The turbulence constants of the model; , For k- The damping function of the model; Heat transfer behavior: in, Let T be the specific heat capacity of air, and T be the temperature. The thermal conductivity of air. For the Prandtl number of turbulence, For the density of muscle food, The specific heat capacity of muscle foods. The thermal conductivity of muscle foods; The thermal conductivity of the muscle food is used as an interpolation function of temperature and input into the model; The specific heat capacity of muscle foods is used as an interpolation function of temperature and input into the model; The density of the muscle food is calculated by measuring the size and mass of the muscle food and then input into the model.

6. The heat transfer control method according to claim 5, characterized in that, To control the refrigerator's switching between quick-cooling mode and maintain mode, the following steps are taken: Place the meat in the refrigerator and turn on the quick-cool mode. The three-dimensional heat transfer model calculates the time required for the meat to reach the appropriate partial freezing temperature under the quick-cool mode. When the working time of the quick-cool mode reaches the time required calculated by the three-dimensional heat transfer model, it is considered that the appropriate partial freezing temperature of the meat has been reached. At this time, switch the refrigerator from quick-cool mode to maintenance mode to keep the current temperature of the meat unchanged.

7. A heat transfer control system for partially freezing muscle food products, characterized in that, The system applies the heat transfer control method according to any one of claims 1-6, and the system includes an ice fraction and moisture state change acquisition module, a partial freezing temperature acquisition module, a partial freezing temperature time prediction module, and a partial freezing temperature control module. The ice fraction and moisture state change acquisition module is used to place a glass sample tube containing a muscle food sample into the VT-NMR instrument, start the liquid nitrogen temperature control system, set the required temperature, collect the transverse relaxation signal of the sample, and obtain the ice fraction of the muscle food sample and its moisture state changes during partial freezing and thawing. The partial freezing temperature acquisition module is used to determine the juice loss rate and shear force of muscle food samples after thawing. By comprehensively analyzing the juice loss rate, shear force, ice fraction and moisture state changes of the samples, the appropriate partial freezing temperature of the muscle food is obtained. The partial freezing temperature and time prediction module is used to establish a three-dimensional heat transfer model, predict the temperature data of the muscle food, and calculate the time it takes for the muscle food to reach the appropriate partial freezing temperature. The partial freezing temperature control module controls the refrigerator to switch between rapid cooling mode and maintenance mode based on the time required to reach the appropriate partial freezing temperature, so that the temperature of the meat food is rapidly reduced in rapid cooling mode and maintained at its appropriate partial freezing temperature in maintenance mode.

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