Magnetic field auxiliary circulating liquid microcrystal freezing system and freezing method thereof

Abstract

The invention discloses a magnetic field auxiliary circulating liquid microcrystal freezing system which comprises a refrigerator body, a magnetic field generator is arranged in the refrigerator body, the magnetic field generator is connected with a transformer through an external control port, the magnetic field generator comprises two symmetrically-arranged coils, and a freezing liquid groove is formed between the two coils. A sample tank is placed in the refrigerating fluid tank, refrigerating fluid is contained in the refrigerating fluid tank, the refrigerating fluid tank is connected with an electric self-priming diaphragm pump through a refrigerating fluid circulating pipe and a silica gel hose, and thermocouple temperature measuring equipment is arranged beside the magnetic field generator. According to the invention, the sample is accurately regulated and controlled to enter a supercooled metastable state, and uniform and fine ice crystals can be formed in the food sample in combination with uniform alternating magnetic field auxiliary crystallization generated by the symmetrical coil, so that the mechanical damage of the ice crystals to food cells is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of freezing and preservation technology, and in particular to a magnetic field-assisted circulating liquid microcrystal freezing system and its freezing method. Background Technology

[0002] In the food freezing process, traditional freezing methods, due to the large size and uneven distribution of ice crystals, easily cause severe mechanical damage to the food's cellular structure. This leads to a series of quality problems after freeze-thaw processing, such as darkening of color, significant moisture loss, reduced texture, and deterioration of flavor. As people's demands for food quality and safety continue to rise, the market urgently needs new freezing technologies that are energy-efficient, have no thermal effects, are environmentally friendly, and are convenient and efficient. The freezing process is essentially a transformation of food from a liquid to a solid state. This process is accompanied by key characteristics and phenomena at both the microscopic and macroscopic scales. The core requirement of new freezing technologies is to reduce freezing damage and maintain the original quality of food by controlling the ice crystal formation process.

[0003] Magnetic field technology has demonstrated remarkable characteristics in the food processing field, exhibiting significant biological and non-thermal effects. It can function without generating high temperatures and possesses excellent sterilization capabilities, helping to control microbial growth and improve preservation performance, thus providing a new technological approach to improving the quality of frozen food. In freezing applications, magnetic field-assisted freezing technology, by influencing supercooling and regulating the ice crystal formation process, can effectively reduce damage to food cells caused by ice crystals, thereby better preserving the sensory characteristics, nutritional value, and safety of food, making it one of the important development directions of new freezing technologies.

[0004] To address the issue of food quality deterioration during freezing, various solutions have emerged in existing technologies, including ultra-low temperature freezing, ultrasonic-assisted freezing, the addition of bioactive antifreeze, radio frequency technology, high-pressure freezing, and low-temperature spray freezing. However, these technologies all have significant limitations in the freezing and processing of muscle foods: ultra-low temperature freezing and ultrasonic-assisted freezing equipment are expensive and can further damage food cells; bioactive antifreeze requires the addition of additional chemical reagents, posing food safety risks; and high-pressure freezing and low-temperature spray freezing equipment are complex in structure, difficult to operate, and unsuitable for large-scale industrial production.

[0005] Compared to the aforementioned technologies, magnetic field-assisted freezing technology has significant advantages, but its application in the food freezing field is still in its early stages. Existing related technical solutions, such as pull-out freezing chambers built with constant magnetic field plates, quick-freezing systems based on permanent magnet arrays, and pulsed magnetic field amorphous deep-crystallization systems, all have many shortcomings that urgently need to be addressed, severely limiting their industrial application and promotion. Firstly, existing technologies mostly use permanent magnet freezing systems with constant magnetic fields, which presents the core problem of uncontrollable magnetic fields. Since different types and volumes of materials have different requirements for magnetic field parameters, uncontrollable magnetic fields are difficult to adapt to various conditions. Firstly, the diverse freezing requirements of various materials make it difficult to guarantee the stability and consistency of freezing effects. Secondly, most existing magnetic field-assisted freezing systems are not equipped with matching coil cooling facilities, resulting in large fluctuations in temperature distribution within the freezing chamber, which cannot guarantee the uniformity of sample quality after freezing. Thirdly, the applicable temperature range of some existing magnetic field-assisted technologies is concentrated between 0℃ and -8℃. Within this temperature range, microorganisms can still survive and many biochemical reactions continue, making it impossible to achieve deep freezing preservation. However, in actual industrial production, deep freezing of products such as muscle foods often requires temperatures of -20℃ and below, which existing technologies cannot meet. Summary of the Invention

[0006] Therefore, the purpose of this invention is to provide a magnetic field-assisted circulating liquid microcrystal freezing system, which can solve the technical problems of uncontrollable magnetic field, large temperature distribution fluctuations in the freezing chamber leading to uneven sample quality, and inability to adapt to the deep freezing requirements of -20℃ and below in existing magnetic field-assisted freezing technologies. At the same time, this invention also provides a magnetic field-assisted circulating liquid microcrystal freezing method, which is applied to the aforementioned magnetic field-assisted circulating liquid microcrystal freezing system.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A magnetic field-assisted circulating liquid microcrystal freezing system includes a refrigerator body. A magnetic field generator is installed inside the refrigerator body. The magnetic field generator has an external control port and is connected to a transformer via the external control port. The magnetic field generator is an alternating magnetic field generator, connected to an AC power source via the transformer. The magnetic field strength is precisely controlled by adjusting the output current of the transformer. The magnetic field generator includes two symmetrically arranged coils, with a freezing liquid tank placed between the two coils. A sample tank is placed inside the freezing liquid tank, which is filled with freezing liquid. The freezing liquid tank is circulated by a cooling... The cryo-fluid circulation pipe and the silicone hose are connected to an electric self-priming diaphragm pump. The cryo-fluid in the cryo-fluid tank is drawn into the cryo-fluid circulation pipe by the suction provided by the electric self-priming diaphragm pump, cooled down, and then returned to the cryo-fluid tank through the silicone hose, thus forming a cryo-fluid recycling system. A thermocouple temperature measuring device is installed next to the magnetic field generator. The thermocouple temperature measuring device can monitor the temperature change of the sample during the freezing process and the temperature change of the cryo-fluid in the cryo-fluid tank in real time and accurately. It includes a temperature measuring probe I and a temperature measuring probe II. The temperature measuring probe I extends into and is fixed inside the sample in the sample tank, and the temperature measuring probe II is placed inside the cryo-fluid tank.

[0008] Furthermore, the magnetic field generator consists of two symmetrically arranged coils with a certain distance between them, and the two coils are connected in series. The distance between the two coils is equal to the distance from the center point of the inner and outer coils to the center of the coil. The area between the two symmetrical coils is the freezing working area, and the freezing liquid tank is fixedly placed in the freezing working area. The transformer integrates a voltage display module and a current display module to facilitate real-time monitoring of operating parameters. Changes in magnetic field strength are precisely controlled by adjusting the knob on the transformer to change the output current.

[0009] Furthermore, a sample tank is fixedly installed in the center of the cryo-liquid tank. The edge of the sample tank is higher than the edge of the cryo-liquid tank, which can effectively prevent the cryo-liquid in the cryo-liquid tank from entering the sample tank and contaminating the sample. Both the sample tank and the cryo-liquid tank are made of PET material. The cryo-liquid inside the cryo-liquid tank is a mixture of 65% edible propylene glycol and 35% water, which can ensure that it will not freeze at -60°C.

[0010] Furthermore, the refrigerant tank is detachably connected to the electric self-priming diaphragm pump via a refrigerant circulation pipe and a silicone hose through food-grade quick connectors, thus forming a closed refrigerant circulation loop. The detachable connection points between the refrigerant tank and the refrigerant circulation pipe and silicone hose are equipped with a sealing structure suitable for a low-temperature environment. The refrigerant circulation pipe is a multi-layered structure with a horizontally arranged central axis, formed by multiple bends of a single copper pipe. Hot melt adhesive is applied to the bends of each layer of copper pipe as a buffer layer and a protective layer to prevent metal fatigue. At the same time, the refrigerant circulation pipe is fixed below the magnetic field generator inside the refrigerator body by a stainless steel frame. The refrigerant circulation pipe is located near the refrigeration components inside the refrigerator body. The refrigerant is cooled by convective heat exchange between the copper pipe and the refrigeration components and the low-temperature environment inside the refrigerator body. The electric self-priming diaphragm pump provides power for the circulation of the refrigerant.

[0011] Furthermore, the thermocouple temperature measuring device can capture the temperature changes of key objects in real time and accurately during the freezing process, providing data support for freezing parameter adjustment and process control, and ensuring the stability and consistency of the freezing effect. The temperature probe I extends into and is fixed at the center of the sample in the sample tank, making close contact with the sample. It can accurately capture the temperature changes of the sample during the freezing process, determine whether the sample has entered a supercooled metastable state (i.e., the temperature drops below 0°C), accurately determine the supercooling limit (the inflection point where the temperature rebounds back to the freezing point after dropping to the lowest point, which must reach below -4°C), and monitor the temperature return during the crystallization stage. During the process of raising the temperature to the freezing point and confirming whether the sample is ultimately stable at the target freezing temperature of -20℃ to -40℃, the temperature probe II is in direct contact with the cryo-liquid, monitoring the temperature change of the cryo-liquid in the cryo-liquid tank in real time. This ensures that the cryo-liquid temperature is stable at -12℃ during the preparation stage and accurately drops to the target range of -20℃ to -40℃ during the rapid freezing stage, avoiding uneven freezing caused by local temperature fluctuations in the cryo-liquid. The data from temperature probe I and temperature probe II work together to provide accurate data support for operators to adjust temperature and magnetic field parameters, avoiding poor freezing results due to inaccurate temperature monitoring.

[0012] This invention also provides a magnetic field-assisted circulating liquid microcrystal freezing method, which is applied to the above-mentioned magnetic field-assisted circulating liquid microcrystal freezing system, and the specific steps include: Step S1: Preparation Phase First, check the connection status of each component to ensure that the external control port of the magnetic field generator is securely connected to the transformer, and that the closed loop formed by the cryo-liquid tank, cryo-liquid circulation pipe, silicone hose, and electric self-priming diaphragm pump is well sealed. Ensure that the temperature probe I of the thermocouple temperature measuring device is positioned at the center of the sample and is functioning correctly, and that temperature probe II is installed in the cryo-liquid tank and is functioning correctly. Inject cryo-liquid into the cryo-liquid tank according to a specific ratio. Based on the type of sample to be frozen, preset the initial current parameters using the transformer knob to generate the corresponding magnetic field strength. Start the equipment for preheating, and stabilize the cryo-liquid temperature at -12℃ through the cryo-liquid circulation loop. Step S2: Supercooling stage Place the food sample to be frozen into the sample chamber, ensuring that the center of the sample is in close contact with the temperature probe I of the thermocouple temperature measuring device, and that the freezing liquid is in contact with the temperature probe II of the thermocouple temperature measuring device, for accurate temperature monitoring. At this time, the sample is in a freezing liquid environment of -12℃, and the temperature will gradually decrease. When the thermocouple temperature measuring device shows that the sample temperature has dropped below 0℃, the sample enters a supercooled metastable state. At this time, it is necessary to strictly maintain the stable operation of the equipment, eliminate interference factors such as temperature fluctuations and equipment vibration, and ensure that the sample continues to accumulate cold in the metastable state. During this stage, the sample temperature needs to be continuously monitored until the temperature drops to the supercooling limit (i.e., the inflection point where the temperature rebounds back to the freezing point after dropping to the lowest point, which requires the supercooling limit to reach below -4℃). Step S3: Crystallization Stage When the sample temperature reaches the supercooling limit below -4℃, it will instantly break through the metastable state and enter the crystallization state. The sample temperature will quickly rise back to the freezing point and remain there for a period of time. During this process, the alternating magnetic field generated by the magnetic field generator will continuously act on the water molecules in the sample, inhibiting the growth of large ice crystals and promoting the formation of uniform small crystal nuclei. Step S4: Rapid freezing stage: After the sample is kept at a stable freezing point temperature for 5-10 minutes, the temperature of the cryo-fluid is adjusted through the cryo-fluid circulation loop to rapidly drop the temperature of the cryo-fluid to the target range of -20°C to -40°C, guiding the sample into a rapid freezing state. During this stage, the electric self-priming diaphragm pump works continuously to drive the cryo-fluid to flow rapidly in the circulation tube and cool down efficiently. Then, it flows back to the cryo-fluid tank through the silicone tubing to achieve continuous circulation and cooling of the cryo-fluid, ensuring that the sample freezes rapidly in a low-temperature environment, further fixing the uniform small ice crystal structure and preventing ice crystals from growing and damaging food cells. Step S5: End Phase When the thermocouple temperature measuring device shows that the sample temperature is stable at the target freezing temperature (i.e., -20℃ to -40℃) and no longer changes, the sample freezing is complete. Turn off the transformer and the electric self-priming diaphragm pump, stop the magnetic field generation and the circulation of the freezing liquid, and take out the frozen sample after the equipment has cooled down slightly.

[0013] Compared with the prior art, the technical solution described in this invention has the following beneficial effects: 1. This invention achieves controllable alternating magnetic field through the combination of "AC power supply - transformer - symmetrical coil of magnetic field generator", achieves temperature uniformity through the heat exchange design of "cooling liquid circulation pipe - refrigerator refrigeration system", and achieves deep freezing through precise control of subcooling limit (below -4℃). The synergistic effect of the three significantly improves the quality of frozen food. 2. This invention precisely controls the sample to enter a supercooled metastable state, and combines the uniform alternating magnetic field generated by the symmetrical coil to assist crystallization, which can promote the formation of uniform and fine ice crystals in the food sample, and greatly reduce the mechanical damage of ice crystals to food cells. 3. The present invention uses PET material to make sample tanks and cryo-fluid tanks, which effectively avoids the interference of metal materials on alternating magnetic fields, ensures the uniformity and stability of the magnetic field area, and ensures the consistency of magnetic field-assisted crystallization effect; the cryo-fluid circulation pipe is fixed by a hot melt adhesive buffer layer and a stainless steel frame, which effectively prevents copper pipes from freezing and cracking or deforming at low temperatures, ensures the sealing and stability of the circulation loop, reduces the impact of equipment failure on the freezing process, and improves the reliability of system operation. 4. This invention achieves the recycling and reuse of cryocooling through a cryocooling circulation loop. Driven by an electric self-priming diaphragm pump, the cryocooling flows rapidly through a copper tube with good thermal conductivity, efficiently cooling down and returning to the cryocooling tank. This ensures uniform temperature distribution within the cryocooling tank, avoiding the problem of low freezing efficiency caused by local temperature differences. At the same time, precise control of the supercooled state allows the sample to fully accumulate cold energy in the metastable stage. Subsequent crystallization and rapid freezing stages can achieve rapid freezing of the sample without consuming a large amount of additional energy. Compared with traditional freezing technology, this invention effectively improves freezing efficiency and reduces energy consumption while ensuring freezing quality. Other beneficial effects of this invention will be further explained in the following specific embodiments. Attached Figure Description

[0014] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Figure 1 This is a schematic diagram of the structure of the magnetic field-assisted circulating liquid microcrystal refrigeration system described in this invention; Figure 2 A comparative chart showing the thawing drip loss in the experimental examples shown in this invention; Figure 3 A comparative chart of cooking losses in the experimental examples shown in this invention; The components include: 1. Refrigerator body; 2. Magnetic field generator; 3. Transformer; 4. Coil; 5. Refrigerant tank; 6. Sample tank; 7. Refrigerant circulation pipe; 8. Silicone tubing; 9. Electric self-priming diaphragm pump; 10. Thermocouple temperature measuring device; 11. Temperature probe I; 12. Temperature probe II. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] like Figure 1 As shown, this invention provides a magnetic field-assisted circulating liquid microcrystal refrigeration system. It includes a refrigerator body 1, inside which a magnetic field generator 2 is installed. The magnetic field generator 2 has an external control port, through which a transformer 3 is connected. The magnetic field generator 2 includes two symmetrically arranged coils 4, with a refrigerant tank 5 placed between the two coils 4. A sample tank 6 is placed inside the refrigerant tank 5, which is filled with refrigerant. The refrigerant tank 5 is connected to an electric self-priming diaphragm pump 9 through a refrigerant circulation pipe 7 and a silicone hose 8. The cryogenic fluid is drawn into the cryogenic fluid circulation pipe 7 by the suction provided by the electric self-priming diaphragm pump 9, cooled down, and then pumped back into the cryogenic fluid tank 5 through the silicone hose 8 to form a cryogenic fluid recycling system. A thermocouple temperature measuring device 10 is installed next to the magnetic field generator 2. The thermocouple temperature measuring device 10 can monitor the temperature change of the sample in real time and accurately during the freezing process. It includes a temperature measuring probe I 11 and a temperature measuring probe II 12. The temperature measuring probe I 11 extends into and is fixed inside the sample in the sample tank 6, and the temperature measuring probe II 12 is placed in the cryogenic fluid tank 5.

[0017] In the embodiments described in this invention, the magnetic field generator 2 consists of two symmetrically arranged coils 4, with a certain distance between them. The two coils 4 are connected in series, and the distance between them is equal to the distance from the center point of the inner and outer coils of the coil 4 to the center of the coil 4. The magnetic field generator 2 is an alternating magnetic field generator, which is connected to an AC power supply through a transformer 3. The magnetic field strength is positively correlated with the output current of the transformer 3. The magnetic field strength can be precisely controlled by adjusting the current. Specifically, the AC power supply is 220V / 50Hz, and the inner diameter of each coil 4 is 16cm and the outer diameter is 22cm. Each coil 4 has 1000 turns, and the inside of the coil 4 is wound with copper wire with a diameter of 0.8mm. The spacing between two coils 4 is 9.5cm. By using two coils 4 with identical parameters and symmetrical arrangement, along with precise spacing settings, a uniform and stable alternating magnetic field region can be formed. This ensures that the magnetic field acting on all parts of the sample is uniform during freezing, laying the foundation for the subsequent formation of uniform crystal nuclei. The optimized design of the specific parameters of the coil 4 (number of turns, copper wire diameter, inner and outer coil diameter) can generate a magnetic field strength of 2mT-8mT under reasonable current input, adapting to the freezing needs of different samples (fruits and vegetables, meat products). The area between the two symmetrical coils 4 is the freezing working area, and the freezing liquid tank 5 is fixedly placed in this freezing working area, that is, between the two coils 4; The transformer 3 integrates a voltage display module and a current display module, facilitating real-time monitoring of operating parameters. Changes in magnetic field strength are precisely controlled by adjusting the output current using a knob on the transformer 3. Combined with the voltage and current display modules, operators can easily monitor the operating status in real time. For example, when the current is 1A, the magnetic field strength is 4mT; when the current is 1.5A, the magnetic field strength is 6mT; and when the current is 2A, the magnetic field strength is 8mT. This clear correlation between current and magnetic field strength makes magnetic field strength adjustment more intuitive and controllable, eliminating the need for additional magnetic field detection equipment and reducing operational difficulty. Here, the coil 4 operates with a current ≤2A and a heat output ≤10W, so natural heat dissipation is sufficient.

[0018] It should be noted that, according to Biosavart's law, when current is passed through coil 4 of magnetic field generator 2, an alternating magnetic field is generated. The magnetic field strength is positively correlated with the current magnitude. The alternating magnetic field can act on water molecules in the sample, changing the motion state and interaction of water molecules. During the sample crystallization process, it can inhibit the growth of large ice crystals and promote the formation of uniform small crystal nuclei. At the same time, the magnetic field can improve the stability of the supercooled state, reduce the interference of factors such as temperature fluctuations and vibrations on the supercooled state, and ensure that the crystallization process is controllable.

[0019] In the embodiments described in this invention, a sample tank 6 is fixedly installed at the center of the interior of the cryo-liquid tank 5. The edge height of the sample tank 6 is higher than the edge height of the cryo-liquid tank 5, which effectively prevents the cryo-liquid in the cryo-liquid tank from entering the sample tank 6 and contaminating the sample. Preferably, the edge of the sample tank 6 is 3 cm higher than the edge of the cryogenic tank 5; It should be noted that both the sample tank 6 and the cryo-liquid tank 5 are made of PET material. The reason for not using metal materials is to avoid interference from metal materials with the alternating magnetic field generated by the magnetic field generator 2, ensuring the uniformity and stability of the magnetic field area and ensuring the magnetic field-assisted freezing effect. At the same time, PET material has good low-temperature resistance and can adapt to freezing environments from -20°C to -40°C, avoiding damage at low temperatures. The cryo-liquid tank 5 is filled with a mixture of 65% edible propylene glycol and 35% water, which gives the cryo-liquid a low freezing point and good thermal conductivity. This ratio of cryo-liquid can meet the low-temperature freezing requirements of -60°C, and the edible propylene glycol meets the standards. Even if there is a small amount of contact with the food sample, it will not affect the food safety.

[0020] In the embodiments described in this invention, the refrigerant tank 5 is detachably connected to the electric self-priming diaphragm pump 9 via a refrigerant circulation pipe 7 and a silicone hose 8, respectively, through food-grade quick-connect fittings, thus forming a closed refrigerant circulation loop. The detachable connections between the refrigerant tank 5 and the refrigerant circulation pipe 7 and silicone hose 8 are equipped with sealing structures suitable for low-temperature environments to ensure the airtightness of the circulation loop under low-temperature conditions. The refrigerant circulation pipe 7 is a multi-layered structure formed by multiple bends of a single copper tube, arranged horizontally along a central axis to increase the heat exchange area. To prevent the copper tube from freezing and cracking or deforming due to thermal expansion and contraction under low-temperature conditions, hot melt adhesive is applied to the bends of each layer of copper tube. As a buffer layer and a protective layer to prevent metal fatigue, the refrigerant circulation pipe 7 is fixed below the magnetic field generator 2 inside the refrigerator body 1 by a stainless steel frame. Specifically, the refrigerant circulation pipe 7 is located near the refrigeration components installed inside the refrigerator body 1. The refrigerant is cooled by convective heat exchange between the copper pipe and the refrigeration components and the low-temperature environment inside the refrigerator body 1. The refrigerator body 1 has a cooling capacity below -40℃, providing energy support for the refrigerant circulation and cooling. The bottom of the refrigerator body 1 is equipped with a shock-absorbing structure to reduce vibration. The refrigerator body 1 itself is equipped with a high-precision temperature control capability to control the refrigerant temperature fluctuation within a precision range of ±0.5℃. Preferably, the refrigerant circulation pipe 7 has a 30-layer structure, with each layer having a diameter of 20cm; The hot melt adhesive is a low-temperature elastic polyurethane hot melt adhesive with a low temperature resistance limit of not less than -80℃. The design of the hot melt adhesive buffer layer, protective layer and stainless steel frame fixing structure effectively solves the problems of copper pipe freezing cracking, deformation and fatigue under low temperature and high pressure environment. It reduces the vibration and friction between copper pipe and refrigerator body 1 at low temperature, ensures the sealing and stability of the refrigerant circulation loop, ensures smooth refrigerant circulation, improves freezing efficiency. The copper pipe material has good thermal conductivity, which can quickly cool the refrigerant and further improve the freezing effect. The electric self-priming diaphragm pump 9 provides power for the circulation of the refrigerant. It has a power of 50W and a rated flow rate of 8-10L / min. Under the suction force generated by the electric self-priming diaphragm pump 9, the refrigerant in the refrigerant tank 5 is drawn into the refrigerant circulation pipe 7 for cooling. The cooled refrigerant is then returned to the refrigerant tank 5 through the silicone hose 8, realizing the recycling of the refrigerant.

[0021] In the embodiments described in this invention, the thermocouple temperature measuring device 10 is a prior art device. The thermocouple temperature measuring device 10 has the function of capturing the temperature changes of key objects in real time and accurately during the freezing process, providing data support for freezing parameter adjustment and process control, and ensuring the stability and consistency of the freezing effect. The temperature measuring probe I 11 extends into and is fixed at the center of the sample in the sample tank 6, making close contact with the sample. It can accurately capture the temperature changes of the sample during the freezing process, determine whether the sample has entered the supercooled metastable state (i.e., the temperature drops below 0°C), and accurately determine the supercooling limit (the inflection point where the temperature rebounds back to the freezing point after dropping to the lowest point, which needs to reach below -4°C). The process of monitoring the temperature rise to the freezing point during the crystallization stage and confirming whether the sample is finally stable at the target freezing temperature of -20℃ to -40℃ is monitored. The temperature probe II12 is in direct contact with the freezing liquid and monitors the temperature change of the freezing liquid in the freezing liquid tank 5 in real time. This ensures that the freezing liquid temperature is stable at -12℃ during the preparation stage and accurately drops to the target range of -20℃ to -40℃ during the rapid freezing stage. This avoids uneven freezing caused by local temperature fluctuations in the freezing liquid. The data from temperature probe I11 and temperature probe II12 work together to provide accurate data support for operators to adjust temperature and magnetic field parameters, avoiding poor freezing effect due to inaccurate temperature monitoring. Thermocouple temperature measuring device 10 and temperature probes I 11 and II 12 can accurately identify "critical temperature nodes" in the freezing process, providing a clear basis for process switching at each stage: Supercooling node: When the temperature probe I11 shows that the sample temperature is <0℃, the sample is determined to have entered a supercooled metastable state; Crystallization trigger point: When the temperature probe I11 shows that the sample temperature has dropped to the supercooling limit (below -4℃) and then rebounds, it is determined that the sample has entered the crystallization stage, ensuring that the alternating magnetic field continues to act on the ice crystal formation process; Rapid freezing start-up node: When the temperature probe I11 shows that the sample temperature has stabilized at the freezing point, the rapid freezing stage is triggered, and the cooling liquid is adjusted to cool down to the target range. Freezing completion point: When the temperature probe I11 shows that the sample temperature is stable at -20℃ to -40℃ and no longer changes, freezing is considered complete, and the operator is instructed to shut down the equipment.

[0022] This invention addresses the issue of different supercooling points among various types of meat by using variable frequency and voltage regulation, enabling a single device to adapt to the freezing needs of multiple meat samples and ensuring that all types of meat samples achieve optimal freezing quality. During the cooling process, when the temperature is below the freezing point but crystallization has not yet occurred, the substance enters a supercooled metastable state. At this point, cold energy continues to accumulate but does not reach the crystallization condition. When the supercooling limit is reached, it freezes instantaneously, forming small ice crystals that do not damage the food structure. Therefore, this invention utilizes the energy provided instantaneously during the metastable state transition to achieve controllable crystallization, further ensuring uniform crystal nucleus formation, forming small ice crystals, and avoiding damage to the food structure. The supercooling limit is the inflection point at which the temperature rebounds back to the freezing point after dropping to the lowest point. The supercooling limit of the sample is required to reach below -4°C. The lower the supercooling degree at this stage, the better the effect. Therefore, the magnetic field-assisted circulating liquid microcrystal freezing system described in this invention can currently reduce the temperature to around -7°C.

[0023] This invention also provides a magnetic field-assisted circulating liquid microcrystal freezing method, which is applied to the above-mentioned magnetic field-assisted circulating liquid microcrystal freezing system, and the specific steps include: Step S1: Preparation Phase First, check the connection status of each component to ensure that the external control port of the magnetic field generator 2 is firmly connected to the transformer 3, the closed loop formed by the cryo-liquid tank 5, the cryo-liquid circulation pipe 7, the silicone hose 8, and the electric self-priming diaphragm pump 9 is well sealed, the temperature probe I 11 of the thermocouple temperature measuring device 10 is placed in the center of the sample and is working normally, and the temperature probe II 12 is installed in the cryo-liquid tank 5 and is working normally; inject cryo-liquid prepared according to a certain ratio into the cryo-liquid tank 5, and according to the type of sample to be frozen, preset the initial current parameters through the knob of the transformer 3 to generate the corresponding magnetic field strength; start the equipment to preheat, and stabilize the cryo-liquid temperature at -12℃ through the cryo-liquid circulation loop; Step S2: Supercooling stage Place the food sample to be frozen into sample tank 6, ensuring that the center of the sample is in close contact with the temperature probe I 11 of the thermocouple temperature measuring device 10, and that the freezing liquid is in contact with the temperature probe II 12 of the thermocouple temperature measuring device 10, for accurate temperature monitoring. At this time, the sample is in a freezing liquid environment of -12℃, and the temperature will gradually decrease. When the thermocouple temperature measuring device 10 shows that the sample temperature has dropped below 0℃, the sample enters a supercooled metastable state. At this time, it is necessary to strictly maintain the stable operation of the equipment, eliminate interference factors such as temperature fluctuations and equipment vibration, and ensure that the sample continues to accumulate cold in the metastable state. During this stage, the sample temperature needs to be continuously monitored until the temperature drops to the supercooling limit (i.e., the inflection point where the temperature rebounds back to the freezing point after dropping to the lowest point, which requires the supercooling limit to reach below -4℃). Step S3: Crystallization Stage When the sample temperature reaches the supercooling limit below -4℃, it will instantly break through the metastable state and enter the crystallization state. The sample temperature will quickly rise back to the freezing point and remain there for a period of time. During this process, the alternating magnetic field generated by the magnetic field generator 2 will continuously act on the water molecules in the sample, inhibiting the growth of large ice crystals and promoting the formation of uniform small crystal nuclei. Step S4: Rapid freezing stage: After the sample is kept at a stable freezing point temperature for 5-10 minutes, the temperature of the cryo-liquid is adjusted through the cryo-liquid circulation loop to rapidly drop the temperature of the cryo-liquid to the target range of -20°C to -40°C, guiding the sample into a rapid freezing state. During this stage, the electric self-priming diaphragm pump 9 works continuously to drive the cryo-liquid to flow rapidly in the circulation tube and cool down efficiently. Then, it flows back to the cryo-liquid tank 5 through the silicone hose 8 to achieve continuous circulation and cooling of the cryo-liquid, ensuring that the sample freezes rapidly in a low-temperature environment, further fixing the uniform small ice crystal structure and preventing ice crystals from growing and damaging food cells. Step S5: End Phase When the thermocouple temperature measuring device 10 displays that the sample temperature is stable at the target freezing temperature (i.e., -20℃ to -40℃) and no longer changes, the sample freezing is complete. Turn off the transformer 3 and the electric self-priming diaphragm pump 9 to stop the magnetic field generation and the circulation of the freezing liquid. After the equipment has cooled down slightly, the frozen sample can be taken out.

[0024] It should be noted that, for different types of meat, due to the differences in their supercooling points, the magnetic field frequency and current parameters (i.e., magnetic field strength) can be flexibly adjusted by using variable frequency and voltage regulation of the magnetic field generator and transformer. This ensures that each type of meat can complete the supercooling to crystallization process under optimal magnetic field conditions, ultimately achieving the best frozen quality. This avoids the problem of unstable frozen quality caused by parameter mismatch, significantly improving the versatility and practical application value of the technology.

[0025] To further verify the technical effectiveness of the magnetic field-assisted circulating liquid microcrystal freezing system and method of the present invention, based on the above, the present invention selects beef foreleg meat as the experimental object and provides the following experimental examples: Experimental parameter settings: The target freezing temperature of the refrigerator body was set to -30℃, and the magnetic field strength parameters were set to 2mT, 4mT, 6mT, and 8mT. At the same time, a normal freezing group without magnetic field was set up as a control group. The other experimental conditions of the control group (such as target freezing temperature, sample size, etc.) were kept the same as those of the experimental group. Experimental results: Under the above parameters, the experimental group of beef foreleg meat was supercooled to an average of -6.6℃ during magnetic field-assisted freezing, which is 6.6℃ supercooled compared to the freezing point of 0℃; while the control group of beef foreleg meat did not exhibit supercooling, with a supercooling of 0℃. The following are the comparative results of the quality data of beef foreleg meat from the two experimental groups: 1. Water loss due to thawing dripping: such as Figure 2 As shown, the control group underwent ordinary freezing (freezing 1-4 days) without a magnetic field, while the experimental group underwent magnetic field-assisted freezing (2mT / 4mT / 6mT / 8mT). The thawing drip loss of beef foreleg meat in the magnetic field-assisted freezing group was significantly lower than that in the ordinary freezing control group. This indicates that beef foreleg meat treated with magnetic field-assisted freezing has superior water retention. The core reason is that the ice crystals formed during the freezing process are smaller, which significantly reduces the mechanical damage to the beef foreleg meat cells caused by ice crystals and reduces the loss of intracellular water.

[0026] It needs to be explained that, Figure 2 The chromaticity data in the table shown are used to help verify the color stability of the samples. The color change of the magnetic field-assisted freezing group was smaller than that of the control group.

[0027] 2. Comparison of cooking losses: such as Figure 3 As shown, control group 1 was subjected to ordinary freezing (freezing 1-3 times), control group 2 was quick-frozen, and the experimental group was subjected to magnetic field-assisted freezing (magnetic field 1-magnetic field 3). The cooking loss of beef foreleg meat in the magnetic field-assisted freezing group was not only lower than that in the ordinary freezing control group, but also lower than that in the quick-frozen group. This further confirms that beef foreleg meat frozen with magnetic field assistance can still maintain good water retention during subsequent processing, and its cell structure integrity is effectively protected, highlighting the advantages of the freezing system and method of this invention.

[0028] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A magnetic field-assisted circulating liquid microcrystal refrigeration system, characterized in that: The refrigerator includes a main body, inside which is installed a magnetic field generator. The magnetic field generator has an external control port, through which a transformer is connected. The magnetic field generator is an alternating magnetic field generator, connected to an AC power source via the transformer. The magnetic field strength is precisely controlled by adjusting the transformer's output current. The magnetic field generator includes two symmetrically arranged coils, with a refrigerant tank placed between them. Inside the refrigerant tank is a sample tank containing refrigerant. The refrigerant tank is connected to a refrigerant circulation pipe and a silica gel container. The hose is connected to an electric self-priming diaphragm pump. The cryosol in the cryosol tank is drawn into the cryosol circulation pipe by the suction provided by the electric self-priming diaphragm pump, cooled down, and then returned to the cryosol tank through the silicone hose to form a cryosol recycling system. A thermocouple temperature measuring device is installed next to the magnetic field generator. The thermocouple temperature measuring device can monitor the temperature change of the sample during the freezing process and the temperature change of the cryosol in the cryosol tank in real time and accurately. It includes temperature probe I and temperature probe II. Temperature probe I extends into and is fixed inside the sample in the sample tank, and temperature probe II is placed inside the cryosol tank.

2. The magnetic field-assisted circulating liquid microcrystal refrigeration system according to claim 1, characterized in that: The magnetic field generator consists of two symmetrically arranged coils with a certain distance between them. The two coils are connected in series, and the distance between them is equal to the distance from the center point of the inner and outer coils to the center of the coil. The area between the two symmetrical coils is the freezing working area, and the freezing liquid tank is fixedly placed in the freezing working area. The transformer integrates a voltage display module and a current display module to facilitate real-time monitoring of operating parameters. Changes in magnetic field strength are precisely controlled by adjusting the output current through a knob on the transformer.

3. The magnetic field-assisted circulating liquid microcrystal refrigeration system according to claim 1, characterized in that: A sample tank is fixedly installed in the center of the cryo-liquid tank. The edge of the sample tank is higher than the edge of the cryo-liquid tank, which can effectively prevent the cryo-liquid in the cryo-liquid tank from entering the sample tank and contaminating the sample. Both the sample tank and the cryo-liquid tank are made of PET material. The cryo-liquid inside the cryo-liquid tank is a mixture of 65% edible propylene glycol and 35% water, which can ensure that it will not freeze at -60℃.

4. The magnetic field-assisted circulating liquid microcrystal refrigeration system according to claim 1, characterized in that: The refrigerant tank is detachably connected to the electric self-priming diaphragm pump via a refrigerant circulation pipe and a silicone hose through food-grade quick connectors, thus forming a closed refrigerant circulation loop. The detachable connections between the refrigerant tank, the refrigerant circulation pipe, and the silicone hose are equipped with a sealing structure suitable for low-temperature environments. The refrigerant circulation pipe is a multi-layered structure with a horizontally arranged central axis, formed by multiple bends in a single copper tube. Hot melt adhesive is applied to the bends of each layer of the copper tube as a buffer layer and a protective layer to prevent metal fatigue. The refrigerant circulation pipe is fixed to the refrigerator body below the magnetic field generator via a stainless steel frame. The refrigerant circulation pipe is located near the refrigeration components inside the refrigerator body. Cooling of the refrigerant is achieved through convective heat exchange between the copper pipe and the refrigeration components and the low-temperature environment inside the refrigerator body. The electric self-priming diaphragm pump provides power for the circulation of the refrigerant.

5. A magnetic field-assisted circulating fluid microcrystal freezing method, wherein the method is applied to the magnetic field-assisted circulating fluid microcrystal freezing system according to any one of claims 1 to 4, characterized in that: The specific steps include: Step S1: Preparation Phase First, check the connection status of each component to ensure that the external control port of the magnetic field generator is securely connected to the transformer, and that the closed loop formed by the cryo-liquid tank, cryo-liquid circulation pipe, silicone hose, and electric self-priming diaphragm pump is well sealed. Ensure that the temperature probe I of the thermocouple temperature measuring device is positioned at the center of the sample and is functioning correctly, and that temperature probe II is installed in the cryo-liquid tank and is functioning correctly. Inject cryo-liquid into the cryo-liquid tank according to a specific ratio. Based on the type of sample to be frozen, preset the initial current parameters using the transformer knob to generate the corresponding magnetic field strength. Start the equipment for preheating, and stabilize the cryo-liquid temperature at -12℃ through the cryo-liquid circulation loop. Step S2: Supercooling stage Place the food sample to be frozen into the sample chamber, ensuring that the center of the sample is in close contact with the temperature probe I of the thermocouple temperature measuring device, and that the freezing liquid is in contact with the temperature probe II of the thermocouple temperature measuring device, for accurate temperature monitoring. At this time, the sample is in a freezing liquid environment of -12℃, and the temperature will gradually decrease. When the thermocouple temperature measuring device shows that the sample temperature has dropped below 0℃, the sample enters a supercooled metastable state. At this time, it is necessary to strictly maintain the stable operation of the equipment, eliminate interference factors such as temperature fluctuations and equipment vibration, and ensure that the sample continues to accumulate cold in the metastable state. During this stage, the sample temperature needs to be continuously monitored until the temperature drops to the supercooling limit (i.e., the inflection point where the temperature rebounds back to the freezing point after dropping to the lowest point, which requires the supercooling limit to reach below -4℃). Step S3: Crystallization Stage When the sample temperature reaches the supercooling limit below -4℃, it will instantly break through the metastable state and enter the crystallization state. The sample temperature will quickly rise back to the freezing point and remain there for a period of time. During this process, the alternating magnetic field generated by the magnetic field generator will continuously act on the water molecules in the sample, inhibiting the growth of large ice crystals and promoting the formation of uniform small crystal nuclei. Step S4: Rapid freezing stage: After the sample is kept at a stable freezing point temperature for 5-10 minutes, the temperature of the cryo-fluid is adjusted through the cryo-fluid circulation loop to rapidly drop the temperature of the cryo-fluid to the target range of -20°C to -40°C, guiding the sample into a rapid freezing state. During this stage, the electric self-priming diaphragm pump works continuously to drive the cryo-fluid to flow rapidly in the circulation tube and cool down efficiently. Then, it flows back to the cryo-fluid tank through the silicone tubing to achieve continuous circulation and cooling of the cryo-fluid, ensuring that the sample freezes rapidly in a low-temperature environment, further fixing the uniform small ice crystal structure and preventing ice crystals from growing and damaging food cells. Step S5: End Phase When the thermocouple temperature measuring device shows that the sample temperature is stable at the target freezing temperature (i.e., -20℃ to -40℃) and no longer changes, the sample freezing is complete. Turn off the transformer and the electric self-priming diaphragm pump, stop the magnetic field generation and the circulation of the freezing liquid, and take out the frozen sample after the equipment has cooled down slightly.

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