Immersion chiller temperature control system

Abstract

The application relates to an immersion refrigeration temperature control system, and relates to the technical field of immersion refrigeration temperature control. The system realizes temperature control during the immersion refrigeration process, reduces the formation of large ice crystals in the refrigeration process, reduces the damage to the inside of food, reduces energy consumption and reduces costs. The system comprises a temperature acquisition module, a liquid pump driving module, an upper computer, a data transmission module, a control module and a refrigeration equipment control module; the upper computer and the control module realize data interaction through the data transmission module; the temperature acquisition module collects the temperature of a refrigeration object and an external environment, converts the collected temperature signals into electric signals and sends the electric signals to the control module; the control module controls the power of the liquid pump driving module according to the temperature signals of the refrigeration object and the influence value of the external environment on the refrigeration liquid through a cascade control strategy and a PID control algorithm; and the control module also controls the start and stop of the refrigeration equipment control module according to the real-time temperature of the refrigeration object. The application is suitable for the field of immersion refrigeration temperature control.

Description

Technical Field

[0001] The present invention relates to the technical field of immersion freezing temperature control, and in particular to a temperature control system for an immersion freezing device. Background Art

[0002] Freezing preservation technology is an important technology for improving the quality of my country's export products. Among the traditional freezing methods, air blast freezing and indirect contact freezing are widely used. These two methods have simple equipment and are easy to operate, but they have high energy consumption, long freezing time, and large ice crystals, resulting in poor quality of frozen products. Immersion freezing (ICF) is a process that uses low-temperature freezing liquid to directly contact food, that is, the frozen product is placed in a coolant for freezing, thereby achieving rapid freezing of the food. Immersion freezing has the advantages of fast freezing rate, low energy consumption, low dryness loss, and high freezing quality. It is widely used in food freezing processing. At present, immersion freezing has been deeply studied abroad, and in recent years, research on it has gradually increased in China. By designing a temperature control system, the freezing rate can be further optimized and the high frequency of use of freezing equipment can be reduced.

[0003] Immersion freezing is an important food processing technology that combines immersion and freezing to improve the taste, flavor, and nutritional value of food. Temperature control systems play a crucial role in the immersion freezing process. Precise temperature control reduces the formation of large ice crystals during freezing, minimizing damage to the food's interior, thereby preserving the food's nutritional content and significantly improving product quality. A temperature control system effectively controls the immersion freezing rate. By adjusting the freezing temperature and time, the speed and size of ice crystal formation within the food can be precisely controlled. This control not only preserves the food's appearance and taste but also prevents structural damage caused by overly large ice crystals, thereby ensuring food quality and safety. Temperature control systems effectively monitor and control the temperature during the immersion freezing process, preventing food spoilage caused by temperature fluctuations. Temperature control systems provide strong support for optimizing immersion freezing process parameters. By monitoring and analyzing temperature changes during the freezing process, it is possible to understand the impact of different process parameters on food freezing results, enabling optimization of these parameters and improving the efficiency and quality of immersion freezing. Precise temperature control accelerates immersion freezing, thereby increasing production efficiency. By optimizing process parameters and reducing temperature fluctuations, freezing times can be shortened, production line throughput can be increased, production costs can be reduced, and enterprise competitiveness can be enhanced. The application of temperature control systems in immersion freezing has driven innovation and development in related technologies. With the continuous advancement of temperature control technology, more precise and efficient immersion freezing processes can be achieved, bringing more innovations and breakthroughs to the food processing industry. By further studying the application of temperature control systems in immersion freezing, we can further expand its application areas. Summary of the Invention

[0004] The purpose of the present invention is to provide an immersion freezing device temperature control system to achieve temperature control during the immersion freezing process, ensure that the formation of large ice crystals in the food during the freezing process is reduced, thereby reducing damage to the interior of the food, while reducing energy consumption and reducing costs.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] The present invention provides a temperature control system for an immersion freezing device, the system comprising a temperature acquisition module, a liquid pump drive module, a host computer, a data transmission module, a control module and a refrigeration equipment control module;

[0007] The host computer is used to exchange data with the control module through the data transmission module;

[0008] The temperature acquisition module is used to collect the temperature of the frozen object and the external environment in real time, and convert the collected temperature signal into an electrical signal and send it to the control module;

[0009] The control module is used to control the power of the liquid pump drive module through a cascade control strategy and a PID control algorithm according to the temperature signal of the frozen object and the influence of the external environment on the freezing liquid;

[0010] The control module is also used to control the start and stop of the refrigeration equipment control module according to the real-time temperature of the frozen object.

[0011] Furthermore, in a preferred embodiment, the control module is embedded with a cascade control strategy and a PID control algorithm;

[0012] The interaction process between the cascade control strategy and the PID control algorithm is:

[0013] Set up two control closed loops, the inner loop and the outer loop, with the outer loop as the main loop and the inner loop as the secondary loop, and the two closed loops work together;

[0014] The main loop is used to convert the difference between the rated temperature and the actual temperature of the frozen object into the set value of the secondary loop through the PID control algorithm;

[0015] The secondary loop is used to control the power of the liquid pump drive module according to the set value and the difference between the collected temperature of the refrigerant and the actual temperature.

[0016] Furthermore, there is a preferred embodiment in which the control module is embedded with a main program, a temperature sensor subroutine, a digital PID algorithm subroutine, a PWM subroutine, a display subroutine, a host computer reading subroutine, and a relay control subroutine;

[0017] The main program is used to control the temperature of the immersion freezing equipment by calling different subroutines at regular intervals.

[0018] Furthermore, in another preferred embodiment, the main program calls different subroutines as follows:

[0019] After initializing each module, perform a system loop;

[0020] Read the PID value set by the host computer and the temperature data detected by the temperature sensor, perform PID calculation, obtain the PWM value of the liquid pump drive module, and display all the data;

[0021] Determine whether the temperature meets the requirements. If not, start the refrigeration equipment control module until the requirements are met.

[0022] Furthermore, there is a preferred embodiment in which the host computer uses LABVIEW software, which is used to store the data transmitted by the control module, draw curves and display them in real time with the data, and send KP, KI, KD, and TS values ​​to the control module for intelligent regulation of the PID control algorithm.

[0023] Furthermore, in a preferred embodiment, the temperature controlled by the temperature control system is divided into three stages: 20°C to 4°C, 4°C to -4°C, and -4°C to -18°C.

[0024] The present invention further provides an immersion freezing process control method, which is implemented based on any one of the above-mentioned immersion freezing device temperature control systems, and the method is:

[0025] S1: The freezing process of frozen materials is divided into three stages: pre-cooling stage, phase change stage and supercooling stage;

[0026] S2: The refrigerant flow rate is controlled to be low in the pre-cooling stage and the super-cooling stage, and is controlled to be high in the phase change stage.

[0027] Furthermore, in a preferred embodiment, a flow rate less than or equal to 4 m / s is considered a low flow rate, and a flow rate greater than 4 m / s is considered a high flow rate.

[0028] Furthermore, there is another preferred embodiment, the above S2 is specifically:

[0029] The freezing process of frozen materials under different flow rate conditions is simulated and analyzed to determine the influence of different flow rates on the freezing rate at different stages, so as to determine that the refrigerant flow rate is controlled to be low in the pre-cooling stage and the supercooling stage, and the refrigerant flow rate is controlled to be high in the phase change stage.

[0030] Furthermore, in another preferred embodiment, the above simulation analysis is specifically as follows:

[0031] S21: According to the freezing process of the frozen object, determine the material parameters of the simulation process: the heat released from the frozen object from room temperature to the freezing point temperature, the specific heat capacity, thermal conductivity and viscosity of the coolant;

[0032] S22: Construct the fluid mechanics calculation model of the coolant and the heat transfer equation of the freezing process;

[0033] S23: Use the fluid mechanics calculation model and the heat transfer equation of the freezing process as the calculation basis of the fluid simulation software;

[0034] S24: Construct a frozen model and put it into mesh drawing software for mesh drawing;

[0035] S25: Place the drawn grid into the fluid simulation calculation software for calculation and solution, input different flow rates of the coolant, and obtain the center temperature data;

[0036] S26: generating a curve showing the change of the core temperature over time based on the core temperature data, and generating a temperature cloud map and a heat transfer cloud map after processing;

[0037] S27: The influence of flow rate on freezing time and freezing effect is obtained based on the temperature cloud map and the heat transfer cloud map, so as to determine that the flow rate of the refrigerant is controlled to be low in the pre-cooling stage and the supercooling stage, and the flow rate of the refrigerant is controlled to be high in the phase change stage.

[0038] The beneficial effects of the present invention are:

[0039] 1. This invention proposes a temperature control system for an immersion freezer, comprising a temperature acquisition module, a liquid pump drive module, a host computer, a data transmission module, a control module, and a refrigeration equipment control module. The control module receives temperature signals from the temperature acquisition module and adjusts the power of the liquid pump drive module based on these temperature signals and a pre-set control strategy (cascade control and PID control algorithm). This control increases the freezing rate by controlling the flow rate of the refrigerant, reduces energy consumption, minimizes the formation of large ice crystals, and preserves the nutritional content of the food. Furthermore, the refrigeration equipment control module is activated and deactivated based on the real-time temperature of the frozen product, minimizing energy consumption.

[0040] Furthermore, compared to traditional single-loop PID control, the present invention utilizes a cascade control strategy to effectively increase system response speed, suppress noise interference, and improve system dynamic quality. The present invention also enables precise adjustment and flexible control of freezing temperatures to meet the freezing requirements of different foods. Furthermore, by optimizing the temperature control system, the present invention can better control the quality and temperature of the cryogenic liquid, ensuring that the cryogenic liquid remains safe and non-toxic during use, thereby preventing food contamination.

[0041] 2. The present invention provides an immersion freezing process control method. First, based on the computational fluid dynamics theory and heat transfer principles, a simulation model is constructed by numerical simulation software. The effects of different refrigerant flow rates on the freezing speed and freezing quality of the frozen material under constant speed and variable speed conditions are simulated, and the time-varying curve of the center temperature of the frozen material and the temperature distribution cloud map of the center section are obtained. The results show that with the increase of the refrigerant flow rate, the cooling and freezing time is shortened. Therefore, the present invention can achieve the effect of increasing the freezing rate and reducing energy consumption by detecting and controlling the flow rate and temperature during immersion freezing, using a low flow rate in the pre-cooling and supercooling stages of the freezing process, and using a high flow rate in the phase change stage.

[0042] Furthermore, existing immersion freezing control methods typically use a fixed-speed method, where the refrigerant is frozen at a fixed speed. However, to ensure the freezing effect, full power output is used, resulting in high energy consumption. The present invention adopts a variable-speed control method for immersion freezing. That is, by controlling the refrigerant flow rate to a low rate during the pre-cooling and supercooling stages and a high rate during the phase change stage, the refrigerant flow rate is controlled to reduce freezing time while selecting different flow rates at different stages, avoiding full power output, reducing energy waste, and lowering costs.

[0043] The invention is applicable to the field of immersion freezing temperature control. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is the principle diagram of the serial port circuit of the present invention;

[0045] Figure 2 This is the circuit diagram of the temperature acquisition module terminal design of the present invention;

[0046] Figure 3 It is a schematic diagram of the relay described in the present invention;

[0047] Figure 4 is a circuit diagram of the power module of the present invention;

[0048] Figure 5 It is the PID theoretical diagram of the present invention;

[0049] Figure 6 This is the cascade control principle diagram of the present invention;

[0050] Figure 7 This is a flow chart of the main program of the temperature control system of the present invention calling different subroutines;

[0051] Figure 8 This is a flowchart of the OLED display subroutine programming described in the present invention;

[0052] Figure 9 is a flow chart of the display program of the present invention;

[0053] Figure 10 Schematic diagram of three stages of the freezing process of the frozen product according to the present invention;

[0054] Figure 11 It is the simulation analysis flow chart of the present invention;

[0055] Figure 12 is the curve of the central temperature of the frozen product changing with time according to the present invention;

[0056] Figure 13 yes Figure 12 Magnified image of;

[0057] Figure 14 It is a bar graph of the brine flow rate and freezing time according to the present invention;

[0058] Figure 15 is the variable speed freezing curve of the present invention;

[0059] Figure 16 yes Figure 15 Magnified image of . DETAILED DESCRIPTION

[0060] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings. The following embodiments will help those skilled in the art further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that those skilled in the art may make various changes and improvements without departing from the scope of the present invention, and these are all within the scope of protection of the present invention.

[0061] Embodiment 1. This embodiment provides a temperature control system for an immersion freezing device, the system comprising a temperature acquisition module, a liquid pump drive module, a host computer, a data transmission module, a control module and a refrigeration equipment control module;

[0062] The host computer is used to exchange data with the control module through the data transmission module;

[0063] The temperature acquisition module is used to collect the temperature of the external environment of the frozen object in real time, and convert the collected temperature signal into an electrical signal and send it to the control module;

[0064] The control module is used to control the power of the liquid pump drive module through a cascade control strategy and a PID control algorithm according to the temperature signal of the frozen object and the influence of the external environment on the freezing liquid;

[0065] The control module is also used to control the start and stop of the refrigeration equipment control module according to the real-time temperature of the frozen object.

[0066] In practical applications, this embodiment involves designing a temperature acquisition module, a liquid pump driver module, a host computer, a data transmission module, a control module, and a refrigeration equipment control module to ensure that food reaches the desired freezing temperature in the shortest possible time while minimizing energy consumption. The control module receives temperature signals from the temperature acquisition module and adjusts the power of the liquid pump driver module based on these signals and a pre-defined control strategy (cascade control and PID control algorithm). This control increases the freezing rate by controlling the flow rate of the refrigerant, reduces energy consumption, minimizes the formation of large ice crystals, and preserves the nutritional content of the food. Furthermore, the refrigeration equipment control module is activated and deactivated based on the real-time temperature of the frozen food, minimizing energy consumption.

[0067] The data transmission module realizes the communication between the host computer and the control module through USB to serial communication. The connection between the host computer and the "DB9 interface" of the control module is established through the serial signal line. The serial signal line uses the "RS-232 standard" to transmit data signals. Since the RS-232 level standard signal cannot be directly recognized by the controller, this embodiment uses a level conversion chip to convert it into the "TTL standard" level signal that the controller can recognize. The serial port baud rate is configured to be 11500, the data bit is 8, there is no parity bit, the stop bit is 1, and the serial port is selected as COM3 or COM5. The serial port circuit is as follows Figure 1 shown.

[0068] The STM32F103C8T6 microcontroller serves as the control module's main chip, completing functions such as data acquisition, transmission, and display. The STM32F103C8T6 is a 32-bit microcontroller based on the STM32 series ARM Cortex-M core. It has a 64KB program memory capacity, requires a voltage of 2V to 3.6V, and operates in a temperature range of -40°C to 85°C.

[0069] The DS18B20 temperature sensor is used as the temperature acquisition module. By connecting two DS18B20 temperature sensors to measure the temperature of the frozen object and the external environment, the collected temperature signal is converted into an electrical signal and stored in the single chip microcomputer. The circuit diagram of the temperature acquisition module terminal design is shown in the figure. Figure 2 shown.

[0070] The power supply voltage of the liquid pump drive module and the refrigeration equipment control module is 220 AC, but the power supply voltage of the circuit board is 24V. In order to protect the entire circuit board, two DC 3.3V to AC 220V relays are connected. The relay is Aoyan DC-AC SSR-25DA, with an actual current of 12A. The relay schematic is as follows Figure 3 shown.

[0071] It is also necessary to power the 24V motor, 3.3V microcontroller and LCD screen. The external power supply 220V AC is adjusted to 24V through the power adapter and connected to the control board. Then 24V is converted to 12V, 12V to 5V, and 5V to 3.3V. Therefore, the power module circuit is designed. The power module circuit is as follows Figure 4 shown.

[0072] The temperature control system proposed in this implementation needs to accurately maintain a stable temperature between -20°C and 25°C in the freezing environment. Therefore, a DS18B20 temperature sensor is selected as the control system's temperature data acquisition component. The temperature control system must maintain stable performance over extended periods of operation, resisting degradation due to minor environmental changes or aging of internal components. Therefore, this article chooses an STM32 microcontroller as the core control system. The hardware is modularized for ease of maintenance and optimization.

[0073] The temperature control system proposed in this embodiment requires a stable PCB board during the design process. Therefore, when designing the PCB board in this embodiment, the following contents need to be designed:

[0074] ① Wiring rules and strategies: Wiring should follow the shortest path principle. To reduce signal delay and interference, avoid parallel wiring and reduce coupling noise. For high-frequency signal lines, use differential pair wiring to reduce electromagnetic radiation. Select appropriate line width and line spacing based on different signal types to ensure signal transmission quality.

[0075] Component layout principles: Components should be partitioned and arranged according to functional modules to facilitate maintenance and debugging. High-frequency components should be placed close to their driver circuits to minimize signal transmission distances. The spacing between components should meet process requirements to avoid short circuits or poor contact. Considering the mechanical strength of the PCB board, components should be arranged rationally to reduce stress concentration.

[0076] ③ Electrical Performance and Safety: Before designing, thoroughly analyze the circuit's electrical performance requirements, including voltage, current, and impedance. Ensure that the PCB's insulation meets safety standards to prevent leakage and breakdown. For high-voltage components, implement protective measures such as isolation trenches or the use of insulating materials.

[0077] ④ Heat dissipation and thermal design: Design the heat dissipation structure appropriately based on the power consumption and heat dissipation requirements of the components. For high-power components, add heat sinks, fans, and other heat dissipation measures. Optimize the PCB layout to reduce thermal resistance and improve heat dissipation efficiency.

[0078] ⑤ Electromagnetic compatibility and shielding: Consider electromagnetic compatibility during design to reduce electromagnetic interference and radiation. For critical signal lines, use shielded cables or add shielding layers to improve anti-interference capabilities. Arrange grounding appropriately to avoid ground loops and potential differences.

[0079] ⑥ Reliability and durability: Select components and materials that meet the requirements to ensure the reliability of the PCB board. Strictly control the process to ensure the stable quality of the PCB board. Conduct sufficient reliability tests such as vibration, shock, and temperature cycling.

[0080] ⑦ Process and Manufacturability: Designs should consider manufacturing feasibility, avoiding overly complex or difficult-to-implement processes. Rationally select PCB material, thickness, and number of layers to meet performance requirements and production efficiency. Optimize drilling, pad design, and other details to improve production yield.

[0081] ⑧ Cost Optimization and Control: Minimize PCB board costs while meeting performance requirements. Reduce costs through rational component selection and layout optimization. Effective cost control is achieved by comprehensively considering factors such as production efficiency and material utilization.

[0082] In actual application, this embodiment needs to be tested on the entire circuit to determine the feasibility of each module. Specifically:

[0083] Relay on / off circuit test: Adjust the current input and output of the relay to realize the circuit test of the relay;

[0084] Liquid pump drive circuit test: Perform circuit tests on the liquid pump drive circuit using three sets of flow rate values: fixed value, stage fixed value, dynamic value under PID control, to ensure that the circuit can be used.

[0085] Implementation 2: This implementation is to specifically explain the cascade control strategy and PID control algorithm embedded in the control module described in Implementation 1 above.

[0086] The interaction process between the cascade control strategy and the PID control algorithm is:

[0087] Set up two control closed loops, the inner loop and the outer loop, with the outer loop as the main loop and the inner loop as the secondary loop, and the two closed loops work together;

[0088] The main loop is used to convert the difference between the rated temperature and the actual temperature of the frozen object into the set value of the secondary loop through the PID control algorithm;

[0089] The secondary loop is used to control the power of the liquid pump drive module according to the set value and the difference between the collected temperature of the refrigerant and the actual temperature.

[0090] In practical applications, this embodiment adopts a combination of a cascade control strategy and a PID control algorithm to achieve power control of the liquid pump drive module.

[0091] Among them, such as Figure 5As shown, the PID control algorithm uses the deviation between the set value and the actual measured value to perform linear algebraic operations through proportional (P), integral (I), and differential (D) information to gradually reduce the system deviation to zero, thereby achieving the purpose of precise control. The purpose of this embodiment is to reduce energy consumption and increase the freezing rate by intelligently controlling the difference between the real-time temperature of the frozen object and the rated temperature, thereby improving the immersion freezing effect. Therefore, the digital position PID control algorithm is selected. The specific PID calculation formula is:

[0092]

[0093] Among them, T i 、T d are all time constants.

[0094] like Figure 6 As shown, two closed-loop control systems are designed, with the inner loop being the secondary loop and the outer loop being the primary loop. The primary loop is a fixed-value control system, while the secondary loop is a follower control system. These two closed-loops work together to accurately control the temperature of the frozen product. The input of the primary regulator is the rated temperature of the frozen product, while the output of the primary regulator is the setpoint of the secondary regulator. The secondary regulator's output controls the pump's power, which in turn influences the flow rate and, in turn, cools the frozen liquid.

[0095] In the main loop, e1(t) is the difference between the setpoint temperature of the frozen material and the actual temperature of the frozen material y1(t). e2(t) is the difference between the liquid pump controller input and the actual temperature of the frozen liquid y2(t).

[0096] The main regulator output u1(t) is:

[0097]

[0098] The output u2(t) of the sub-regulator is:

[0099]

[0100] u2(t) is the driving voltage acting on the liquid pump.

[0101] Among them, T i 、T d are all time constants.

[0102] The temperature control system described in this embodiment is a thermal inertia system, and the heat transfer process can be affected by adjusting the water flow rate through a water pump. The temperature control system is a second-order system.

[0103] In a temperature control system, the water pump speed directly affects the water flow rate, which in turn affects the heat transfer rate and temperature response.

[0104] The heat transfer process of the temperature control system can be expressed as the following differential equation:

[0105]

[0106] Where, T(t) represents the temperature response equation; Q(t) represents the pump speed; K represents the gain of the system; τ is the time constant; ζ represents the damping ratio;

[0107] Perform Laplace transform to convert the equation into frequency domain, and the differential equation can be expressed as:

[0108] τ 2 s 2 T(s)+2ζτsT(s)+T(s)=KQ(t)

[0109] By simplifying the above equation and extracting T(s), we can obtain the transfer function G(s):

[0110]

[0111] Where Q(s) is the pump speed and T(s) is the temperature.

[0112] When the pump speed increases from 0 m / s to 5 m / s, the temperature decreases from 25°C to -18°C. Calculate the system gain.

[0113]

[0114] Wherein, time constant τ = 30s; damping ratio ζ = 0.7; ζ > 1 is overdamping; ζ = 1 is critical damping; 0 < ζ < 1 is underdamping;

[0115] Substitute the parameters and calculate:

[0116]

[0117] Implementation 3: This implementation is to specifically explain the control module described in the above implementation;

[0118] The control module also embeds the main program, temperature sensor subroutine, digital PID algorithm subroutine, PWM subroutine, display subroutine, host computer reading subroutine, and relay control subroutine;

[0119] The main program is used to control the temperature of the immersion freezing equipment by calling different subroutines at regular intervals.

[0120] In actual application of this embodiment, the program of the temperature control system is compiled in a long polling structure. All programs are integrated into a main program and the main program is called in a self-loop to work.

[0121] The whole program is shown in Figure 7 After the initialization of each function, the program enters the system cycle to read the PID value set by the host computer and detect the temperature for calculation of the PWM value. At the same time, all data are displayed on the display screen.

[0122] The digital PID algorithm subroutine is specifically as follows:

[0123] The single-chip microcomputer program is written according to the positional PID formula. In the program, err(k) is temperature1_temp-SET_Temp, representing the temperature error of one time minus the temperature error of the previous time. Since the temperature control system has three stages of temperature control (20℃~4℃, 4℃~-4℃, -4℃~-18℃), Δu(k) in the formula is set as PWM_DUTU in the program, and Derror represents the error accumulation value. The error accumulation value and the PWM value generated according to the PID iterative calculation are represented by u(k).

[0124] The PID formula is as follows:

[0125] Δu(k)=K p err(k)+K i ∑err(k)+K d (err(k)-err(k-1))

[0126] Wherein: k is the serial number of sampling; err(k) is the error of the kth time; u(k) is the output; K p is constant.

[0127] The relay on-off subroutine is specifically as follows:

[0128] According to the design scheme of the control system, the condenser and the compression pump need to be closed at -18℃, so the PA12 and PA15 pins of the single-chip microcomputer are used to control the power supply to the relay to be stopped at -18℃.

[0129] The calling of the host computer value subroutine is specifically as follows:

[0130] The overall PID program needs to be measured for the specific K P , K I values through experiments. If the K P , K I values are modified through the program, it is too cumbersome and inconvenient. Therefore, the values can be changed at any time by calling the values of the host computer. The host computer sends the changed values to the STM32 single-chip microcomputer through the serial port, and the single-chip microcomputer stores the data sent by the host computer in the array named USART_RX_BUF[*].

[0131] The OLED display subroutine is specifically as follows:

[0132] Set up the STM32103's IO connections to the OLED module. Set the PB11-PB15 IO ports connected to the OLED module to outputs. Write a subroutine based on the timing diagram to meet the requirements. The program design sequence is shown in the figure.

[0133] Use functions to display characters and numbers on the OLED module, such as Figure 8 shown.

[0134] The temperature detection subroutine is as follows:

[0135] The temperature sensor selected for the temperature control system described in this embodiment is DS18B20. The temperature reading process of DS18B2 is as follows: Figure 9 shown.

[0136] Implementation 4: This implementation is a specific description of the host computer described in the above implementation.

[0137] LABVIEW was used to create the host computer. This software stores, displays, and plots data transmitted from the control board. KP, KI, KD, and TS values ​​are sent to the circuit board via serial communication for intelligent PID control. This in turn controls the entire device's temperature control process. The host computer is divided into serial communication, PID settings, data storage, and temperature curve plotting.

[0138] In practical application, this embodiment requires a front panel design to help users better understand and utilize the entire system. This panel allows for data storage settings, serial port selection, and real-time display of both the frozen product and the refrigerant temperature. KP, KI, KD, and the set temperature are set and transmitted to the control board program. The program performs PID calculations and generates PWM output power for the liquid pump. The host computer's front panel displays the real-time PWM value, a date string, and two waveform charts representing the temperature data transmitted by the temperature sensor.

[0139] The host computer provides the microcontroller with the values ​​of KP, KI, KD, and the set temperature via serial communication. The switch for sending parameters is set. The four numeric components for inputting numerical values ​​are set to a string length of 3, allowing for accurate 3-digit input. To improve precision in the microcontroller program, the set values ​​are multiplied by 10 to conform to the microcontroller's calculation rules. Since this article is controlling the freezing state and involves subzero temperatures, a conditional structure is added to determine whether the set temperature input is greater than 0. If the set temperature is less than 0, a sign is applied to the input to the microcontroller. Finally, all values ​​are combined into a concatenated string and transmitted to the microcontroller via the serial port.

[0140] The host computer first intercepts the data transmitted by the single-chip microcomputer. Since the data transmitted by the single-chip microcomputer is a multiple of the required data, it needs to be divided by 10 first. Then a conditional structure is added to determine the positive or negative of the temperature data. If it is a positive number, it is multiplied by 1, and if it is a negative number, it is multiplied by -1. A display component is added to the processed data to display the real-time temperature. The two data are automatically generated into a temperature change curve through the waveform image component. The PWM value is calculated and transmitted directly by the single-chip microcomputer. Only the hexadecimal value needs to be converted into a decimal value. This system also has an experimental time function (specific to year, month, and day). Finally, the two temperature data, PWM value, and time value are bundled together and each data is automatically recorded by the software's write text component. This facilitates the generation of data in the subsequent experimental stage and is finally analyzed with the simulation data.

[0141] Implementation method five, see Figure 10 This embodiment provides an immersion freezing process control method, which is implemented based on the immersion freezing device temperature control system described in any one of the above embodiments. The method is specifically as follows:

[0142] Step S1: The freezing process of the frozen product is divided into three stages: a pre-cooling stage, a phase change stage, and a supercooling stage;

[0143] Step S2: controlling the brine flow rate to be low in the pre-cooling stage and the super-cooling stage, and controlling the brine flow rate to be high in the phase change stage.

[0144] In practical application of this embodiment, the freezing process of frozen objects is divided into three stages, such as Figure 10 As shown, it includes pre-cooling stage, phase change stage and super-cooling stage;

[0145] Among them, pre-cooling stage: This embodiment analyzes that the temperature of food or substance gradually decreases from above 0°C. During the decrease, the heat of the food or substance is gradually removed, but the water inside it still exists in liquid form. Therefore, this embodiment defines this stage as the pre-cooling stage, which is the beginning of the freezing process. The goal of this stage is to reduce the temperature of the substance to below the freezing point.

[0146] Phase Transition Stage: This embodiment analyzes that when the temperature of a food or substance drops below freezing, moisture begins to transform into solid ice crystals. The formation and growth of ice crystals directly affect the structure and taste of the food or substance. If the cooling rate is too fast, the ice crystals will form quickly and become small, which helps maintain the texture of the food or substance. However, if the cooling rate is too slow, the ice crystals will grow larger, causing structural damage to the food or substance. Therefore, this embodiment designates this stage as the phase transition stage, which is the most critical stage in the freezing process. This is because the formation and growth of ice crystals directly affect the structure and taste of the food or substance.

[0147] Supercooling stage: This embodiment analyzes the stage when most of the water in the food or substance has been converted into ice crystals, and the substance enters the freezing stage. In this stage, the temperature of the food or substance continues to drop until the desired freezing temperature is reached. At this time, the water in the food or substance mainly exists in the form of solid ice crystals, and the substance can be stored at low temperature for a long time. Therefore, this embodiment defines this stage as the supercooling stage.

[0148] Understanding these three stages of the freezing process is of great significance for optimizing freezing technology and improving the quality of frozen food or substance. By controlling the cooling rate and temperature, the formation and growth of ice crystals can be influenced, thereby maximizing the preservation of the original structure and taste of the food or substance.

[0149] Therefore, this embodiment simulates and analyzes the freezing process of the frozen substance under different flow conditions to determine the influence of different flow rates on the freezing rate at different stages, thereby determining that the flow rate of the refrigerant should be low (less than or equal to 4 m / s) in the precooling and supercooling stages, and the flow rate of the refrigerant should be high (greater than 4 m / s) in the phase change stage.

[0150] Preferably, the low flow rate is selected as 4 m / s, and the high flow rate is selected as 5 m / s.

[0151] Embodiment six, see Figure 11 This embodiment is a specific description of step S2 in the immersion freezing process control method described in Embodiment One above;

[0152] By simulating and analyzing the freezing process of the frozen substance under different flow conditions, the influence of different flow rates on the freezing rate at different stages is determined, thereby determining that the flow rate of the refrigerant should be low in the precooling and supercooling stages, and the flow rate of the refrigerant should be high in the phase change stage.

[0153] The simulation analysis is specifically:

[0154] Step S21: According to the freezing process of the frozen substance, determine the material parameters of the simulation process: the heat release of the frozen substance from room temperature to the freezing point temperature, the specific heat capacity of the refrigerant, the thermal conductivity and the viscosity;

[0155] Step S22: Construct a fluid mechanics calculation model of the refrigerant and a heat transfer equation of the freezing process;

[0156] Step S23: Take the fluid mechanics calculation model and the heat transfer equation of the freezing process as the calculation basis of the fluid simulation software;

[0157] Step S24: Construct a freezing model and put it into a mesh drawing software for mesh drawing;

[0158] Step S25: Place the drawn grid into fluid simulation software for calculation and solution, input different flow rates of the brine, and obtain the center temperature data;

[0159] Step S26: generating a curve showing the change of the core temperature over time based on the core temperature data, and generating a temperature cloud map and a heat transfer cloud map after processing;

[0160] Step S27: The influence of flow rate on freezing time and freezing effect is obtained based on the temperature cloud map and the heat transfer cloud map, so as to determine that the refrigerant flow rate is controlled to be low in the pre-cooling stage and the supercooling stage, and the refrigerant flow rate is controlled to be high in the phase change stage.

[0161] In practical application, the material parameters of the simulation process need to be determined: the freezing process of the frozen object is the heat release process of the object, and the simulation process of the design is fluid-solid heat transfer. The heat released from the frozen object from room temperature to the freezing point is:

[0162] Q1=mc1(T 初 -T 冻 )

[0163] Where m represents the mass of the frozen material and c represents the specific heat capacity of the frozen material.

[0164] The specific heat capacity, thermal conductivity and viscosity of the coolant can be obtained based on actual work.

[0165] In order to reflect the freezing process of immersion freezing, the flow process of the fluid and the heat transfer process with the frozen material, the basic theory and model calculation basis are provided for the entire freezing process, and the control equations and numerical simulation solution equations required for the fluid are explained.

[0166] The basic control equations for fluid flow include the continuity equation, the momentum conservation equation, and the energy conservation equation.

[0167] The continuity equation is:

[0168]

[0169] Where u, v, and w are the velocity components in the x, y, and z directions, respectively, in m / s. ρ is the density, in kg / m 3 .

[0170] The momentum conservation equation is:

[0171]

[0172] Where ρ is density, unit is Kg / m 3 ; P is pressure, unit is N; F bx 、F by 、F bzF is the volume force on the x, y, and z axes, in N; P xx ,P xy ,P yz is the component of P, unit N;

[0173] The energy conservation equation is:

[0174]

[0175] Among them, c p is the specific heat capacity, unit is J / kg·℃; T is the thermodynamic temperature, unit is ℃; k is the fluid heat transfer coefficient, unit is W / m 2 ℃; S T It is the part of the fluid's mechanical energy that changes into other energy under the action of viscosity, unit is J.

[0176] The above three formulas are combined into the (NS) Navier-Stokes equations, which can be solved numerically through computer calculation and iteration to calculate the computational model of fluid mechanics.

[0177] The heat transfer equation for the freezing process is:

[0178] The circulation of the refrigerant accelerates the exchange of heat between the frozen object and the refrigerant, which is called convection heat transfer. The convection heat at the contact surface between the solid and the fluid can be expressed by Newton's law of cooling:

[0179] Q=αA Δ T

[0180] Where Q is the heat transfer rate, that is, the heat transfer per unit time, unit W; α is the surface heat transfer coefficient, unit W / (m 2 ·K); A is the surface area of ​​the frozen object in contact with the freezing liquid medium, unit is m 2 ; Δ T is the temperature difference between the food surface and the freezer, measured in degrees Kelvin. Since the surface area A of the frozen product in contact with the freezer is typically constant and the freezer temperature is determined by the refrigeration equipment, the convective heat flow is primarily related to the convective surface heat transfer coefficient, which in turn is determined by other factors, such as the type and properties of the freezer and the surface condition of the frozen product.

[0181] The governing equation for heat transfer is:

[0182]

[0183] in:

[0184]

[0185] In the formula, Vx, Vy, and Vz are the conduction rates of the medium; q' is the heat generation per unit volume; k nnis the thermal conductivity, unit is W / (mg·℃); ρ is the density; c is a constant; It is the temperature gradient in the direction of heat conduction, in K / m.

[0186] The above heat transfer control equations are set up in the fluid simulation software to set up the corresponding energy equations to help with subsequent solutions.

[0187] This embodiment requires solving the freezing process of the frozen product and generating a curve of the center temperature change over time based on the center temperature data obtained from the solution. Then, post-processing is performed to generate a temperature cloud map and a heat transfer cloud map. The overall simulation process requires pre-processing, solution processing, and post-processing. These three parts exist independently and are also necessary steps for the entire simulation. The specific simulation process is as follows Figure 11 As shown:

[0188] (1) The freezing model is simplified and constructed using modeling software.

[0189] (2) Place the constructed model into the mesh drawing software and set the basic parameters such as fluid inflow, outflow direction, fluid domain, solid domain, container wall, mesh size, etc. to draw the mesh.

[0190] (3) Place the drawn grid into the fluid simulation software for calculation and solution

[0191] (4) Generate cloud images through post-processing software.

[0192] Embodiment 7: This embodiment is an overall description of the immersion freezing process control method described in the above embodiment;

[0193] In this embodiment, beef is used as the frozen product, and the freezing process under different flow rate conditions is simulated and analyzed. Then, the freezing rate is improved by changing the flow rate during the freezing process, and an overall analysis of the temperature curves and cloud maps that change with time are performed on the two types of simulation processes (constant speed and variable speed). It is determined that the refrigerant flow rate is controlled to be low in the pre-cooling stage and the supercooling stage (less than or equal to 4m / s is a low flow rate), and the refrigerant flow rate is controlled to be high in the phase change stage (greater than 4m / s is a high flow rate).

[0194] The freezing process of frozen materials is divided into three stages: pre-cooling stage, phase change stage and supercooling stage. Figure 10 shown.

[0195] Determine the material parameters for the simulation process:

[0196] The freezing process of frozen objects is a heat release process of the object, and the simulation process of the design is fluid-solid heat transfer. The heat released from the frozen object from room temperature to the freezing point is:

[0197] Q1=mc1(T初 -T 冻 )

[0198] wherein m represents the mass of the frozen material and c represents the specific heat capacity of the frozen material.

[0199] The specific heat capacity of beef is shown in Table 1:

[0200] Table 1

[0201]

[0202]

[0203] The thermal conductivity of beef is shown in Table 2:

[0204] Table 2

[0205] t / ℃ -5.0 -10.0 -15.0 -20.0 -25.0 λ 1.06 1.35 1.44 1.57 1.65

[0206] The density of beef is 1.03 g / cm 2 .

[0207] The refrigeration medium of the present embodiment is SH-7A food-grade refrigerant, and Tables 3 to 4 are attribute data of the refrigerant recorded in the refrigerant specification at different temperatures.

[0208] Table 3 is the specific heat capacity of the refrigerant:

[0209] Table 3

[0210] t / ℃ -5.0 -10.0 -15.0 -20.0 -25.0 kj / (kg·k) 3.355 3.325 3.272 3.224 3.186

[0211] Table 4 is the thermal conductivity of the refrigerant:

[0212] Table 4

[0213] t / ℃ -5.0 -10.0 -15.0 -20.0 -25.0 λ 0.372 0.360 0.354 0.350 0.345

[0214] Table 5 is the viscosity of the refrigerant:

[0215] Table 5

[0216] t / ℃ -5.0 -10.0 -15.0 -20.0 -25.0 μ / mPa·s 3.97 4.11 4.37 4.53 4.81

[0217] A fluid mechanics calculation model of the refrigerant and a heat transfer equation of the freezing process are constructed.

[0218] The present embodiment needs to solve the freezing process of the frozen material and generate a curve of the center temperature changing with time according to the center temperature data obtained by solving, and perform post-processing to generate a temperature cloud map and a heat transfer cloud map, etc. The overall simulation process needs to perform pre-processing, solving processing, and post-processing. These three parts exist independently, and are also necessary steps for the entire simulation. The specific simulation process is shown in Figure 11 .

[0219] The simulation pre-processing is as follows:

[0220] The overall model was created using 3D modeling software, and the inflow, outflow, wall, fluid domain, and solid domain were set using ICEM CFD. The freezing chamber was a rectangular parallelepiped with dimensions of 200 mm × 200 mm × 100 mm, and the frozen product (beef) was a small rectangular parallelepiped with dimensions of 40 mm × 30 mm × 20 mm.

[0221] Since the model required by this embodiment is relatively simple, the results of selecting the structural grid for division and the grid quality are as follows: in the discretization software, the structural three-dimensional grid division unit type is a regular hexahedron, with a total of 8976 units. When the grid quality is detected to be high, the solution can be output.

[0222] This embodiment takes into account that the purpose of the simulation is to obtain data under relatively ideal conditions. Therefore, some factors that affect the simulation results are not considered to establish a mathematical model of the composite freezing process. Therefore, the following assumptions are made:

[0223] (1) The refrigerant is an incompressible liquid.

[0224] (2) Eliminate the reduction of water content in frozen products during the freezing process.

[0225] (3) The freezer compartment does not exchange heat with the outside world.

[0226] (4) The freezing liquid is a radiation transparent medium and there is no thermal radiation.

[0227] (5) Since the material parameters of the frozen material and the freezing liquid will change as the temperature continues to decrease, the piecewise linear function parameter input is selected.

[0228] Calculation settings are required during solution processing, specifically:

[0229] The pre-processed model was placed in Fluent for solution calculation. The model's solver type (solver) selected pressure equation (Pressure-Based), velocity equation (Velocity Formulation) set to absolute velocity (Absolute), time type (Time) set to transient (Transient), and gravity term (Gravity) was applied. The vertical acceleration of gravity was set to -9.81m / s2.

[0230] The boundary conditions are set. Since the freezing experiment is carried out at room temperature (25℃), the initial temperature of the frozen material is 25℃, and the freezing liquid needs to be cooled to -20℃ first. In the simulation process, the temperature value is set to -20℃. Since the temperature of the freezing liquid is maintained at -20~-25℃, the related specific heat capacity, viscosity and thermal conductivity will not change, and they are set as constant values in the simulation software.

[0231] Wherein, the flow inlet is a velocity inlet, and the flow outlet is a pressure outlet. The center temperature point of the frozen material is selected as the data extraction point.

[0232] The simulation results and analysis are as follows:

[0233] The simulation grouping under the conditions of constant flow rate and dynamic flow rate is shown in Tables 6 and 7. The simulation experiment is carried out according to the temperature values of the grouping.

[0234] Table 6 is the constant flow rate simulation grouping:

[0235] Table 6

[0236] Number Flow rate (m / s) 1 0 2 1 3 2 4 3 5 4 6 5

[0237] Table 7 is the stage flow rate simulation grouping:

[0238] Table 7

[0239]

[0240] The influence of constant flow rate on the freezing time and freezing effect of the frozen material is analyzed:

[0241] The temperature distribution of the immersion freezing equipment during the freezing process is simulated by Fluent software, which is shown in the overall three-dimensional structure diagram. In order to better observe the temperature distribution, the center point x-y section is selected to observe the freezing process and the corresponding temperature gradient cloud chart, so as to better judge the freezing effect.

[0242] First, the flow rate at the inlet was set to 0 m / s, 1 m / s, 2 m / s, 3 m / s, 4 m / s, and 5 m / s. Six constant flow rate simulations generated temperature contours and a temperature curve for the frozen product's center, yielding freezing data. A summary analysis revealed the impact of flow rate on freezing time and effectiveness. The following temperature contours and xy-plane temperature contours are generated for 200 seconds at the six constant flow rates. The temperature distribution within the freezer compartment is shown in the legend on the left, indicating a progression from high to low temperatures from red to blue. The xy-cross-sectional diagram reveals a freezing temperature of -18°C. Except for the case of no flow rate, where the coolant temperature remains at -20°C, heat transfer between the frozen product and the coolant is clearly visible at a flow rate of 0 m / s. Single immersion freezing involves direct contact between the frozen product and the coolant, lowering the temperature to the target temperature through heat transfer. Adding a fluid field accelerates heat transfer through the circulation of the coolant, resulting in a faster freezing rate and shorter freezing time.

[0243] Extract the data of the center point of 6 simulated frozen objects to obtain the curve of temperature change over time. Figure 11 and Figure 12 As shown in the figure, when freezing begins, the core temperature drops rapidly, but after a certain period of time, an inflection point appears, and the slope of the curve of the core temperature drop gradually becomes flat. As the brine flow rate increases, the inflection point moves leftward along the coordinate axis. This is because when food is frozen, the free water molecules within the cells condense into small ice crystals, which gradually aggregate to form ice crystal bands. The freezing time before the inflection point is the time it takes for the largest ice crystal band to form. The shorter this period, the higher the freezing quality of the food. Therefore, the simulation data shows that as the brine flow rate increases, the freezing quality of the frozen food improves. As the brine flow rate increases, the freezing time gradually decreases.

[0244] according to Figure 12 to Figure 14 It can be seen that increasing the refrigerant flow rate affects the freezing speed of beef. As the refrigerant flow rate increases, the freezing time of the frozen product gradually decreases. However, the improvement in freezing efficiency shows a decreasing trend, meaning that as the refrigerant flow rate increases, the improvement in freezing efficiency gradually decreases and eventually approaches zero.

[0245] Among them, the refrigerant flow rate and freezing time efficiency are shown in Table 8.

[0246] Table 8

[0247] Flow rate (m / s) Freezing time (s) Year-on-year growth (%) 0 1780 \ 1 897 49.6 2 804 10.3 3 713 12.3 4 684 4.06 5 666 2.63

[0248] It can be seen that the refrigerant flow rate reaches saturation at 4 m / s due to the influence of the size of the frozen object. The simulation results show that the freezing rate increases very slowly when the flow rate is continuously increased.

[0249] Analyze the effect of changing flow rate on freezing time and freezing effect of frozen products:

[0250] Based on the above analysis, a higher flow rate shortens the simulation time, but also requires more power and consumes more energy. Therefore, this embodiment proposes to simulate the process by varying the flow rate at different temperature stages during the freezing process. This achieves both a high freezing rate and reduced energy consumption.

[0251] During the freezing process, the temperature range from 4°C to -4°C is where water transforms from an ice-water mixture into ice crystals, where the largest ice crystals form, and where water density reaches its maximum. Therefore, increasing the flow rate between 4°C and -4°C ensures the formation of small ice crystals, minimizing damage to the frozen material's cells and demonstrating the advantages of immersion freezing. Table 9 shows the time required to reduce the final frozen material temperature from 4°C to -4°C for six flow rate groups during constant flow rate simulations.

[0252] Table 9

[0253] Flow rate (m / s) Time (s) 0 233 1 150 2 133 3 122 4 114 5 109

[0254] Use the expression function in Fluent software to set an expression that changes the flow rate as the temperature changes. The expression is: IF(T <= 269.15[K], X[m / s], IF(T >= 277.15[K], X[m / s], Y[m / s])). Where Y is the flow rate at 4°C to -4°C, and X is the flow rate at other temperatures.

[0255] According to the research purpose and the analysis of constant flow rate, the freezing time required for different stages of the freezing process at different flow rates was obtained, and 10 groups of simulations were formulated as shown in Table 7 for summary analysis. An accurate flow rate combination was obtained to provide a flow rate combination with high freezing rate and energy saving for the subsequent R&D control board and experimental stage.

[0256] According to the simulated data, the temperature curve is summarized as follows Figure 15 As shown, Figure 15 is the overall temperature curve of 10 groups of images, Figure 16 This is an enlarged image showing the inflection point starting at 4°C.

[0257] The time required for variable-speed freezing and the time difference are obtained as shown in Table 10.

[0258] Table 10

[0259]

[0260]

[0261] According to the above constant flow rate on the frozen time and the effect of frozen effect and the influence of the change of flow rate on the frozen time and the effect of frozen effect analysis, respectively, the corresponding energy consumption calculation.

[0262] By simulation, the constant speed and variable speed 16 groups of freezing time are solved, and the energy calculation of the simulation results of the two speeds is carried out.

[0263] Constant speed energy consumption calculation:

[0264] Referring to the existing immersion freezing experimental equipment, the liquid pump power (maximum) is 48w·h; the freezing unit is 165w·h; the controllable flow rate of the pump is 1m / s, 2m / s, 3m / s, 4m / s, 5m / s. Finally, the time obtained in table 2-9 is multiplied to solve the formula:

[0265] W=p·t

[0266] The results show that the constant speed energy consumption is shown in table 11.

[0267] Table 11

[0268] Flow rate (m / s) Time (t) Energy consumption (w·h) 1 897 55.096 2 804 51.456 3 713 49.6036 4 684 48.3275 5 666 48.4256

[0269] Variable speed energy consumption calculation:

[0270] This embodiment is to accelerate the flow rate at 4℃~-4℃, so the time of 10 groups of variable speed freezing simulation to increase the flow rate is shown in table 12. The time required at 4℃~-4℃ is multiplied by the power required by the increased flow rate, and the power of other flow rates is multiplied by the remaining time to obtain the power consumption calculation formula:

[0271] W=p 快 ·t 快 +p 慢 ·t 慢

[0272] Table 12 is the time required for freezing 4℃~-4℃:

[0273] Table 12

[0274]

[0275] The variable speed energy consumption is solved and shown in table 13:

[0276] Table 13

[0277]

[0278] Result analysis:

[0279] According to the above table 11 and table 13, it can be seen that the energy consumption gradually decreases with the increasing flow rate. When the full power is running, the energy consumption generated is 48.4256 W. In the calculation of variable speed energy consumption, the energy consumption required for the 4-5-4 flow rate group is 48.3193 W. It can be seen that the energy consumption required under variable speed condition is reduced. The existing equipment has low power. When a large-scale immersion freezing equipment is designed subsequently, the amount of energy consumption reduction will be greater, and when the freezing equipment is running at full power, it will also damage the service life of the liquid pump. Therefore, high flow rate is used when ice crystals are formed (phase change stage), and low flow rate is used at other temperatures, which can not only improve the freezing rate, but also protect the experimental equipment. Therefore, the present embodiment adopts 4 m / s as the slow flow rate of variable speed freezing. Thus, ideas are provided for the subsequent construction of the control system, and control data are provided for the subsequent experimental data to judge the accuracy of the control board and the correctness of the experiment.

[0280] In summary, the present embodiment solves the time required for the maximum ice crystal zone through the simulation analysis of 16 groups of constant speed and variable speed, and the time required for 16 groups of flow rate. Finally, through the calculation of energy consumption, the control board program of the flow rate group suitable for temperature control in subsequent experiments is obtained, and idealized data for the correctness of the experimental data of subsequent experiments is determined, and the overall design of the control system is carried out according to the simulation results.

[0281] The above only describes the embodiments of the present application and does not limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the scope of the claims of the present application.

Claims

1. Immersion freezer temperature control system, characterized in that: The system includes a temperature acquisition module, a liquid pump drive module, a host computer, a data transmission module, a control module and a refrigeration equipment control module; The host computer is used to exchange data with the control module through the data transmission module; The temperature acquisition module is used to collect the temperature of the frozen object and the external environment in real time, and convert the collected temperature signal into an electrical signal and send it to the control module; The control module is embedded with a cascade control strategy and a PID control algorithm. The control module is used to control the power of the liquid pump drive module through the cascade control strategy and the PID control algorithm according to the temperature signal of the frozen object and the influence of the external environment on the frozen liquid; The interaction process between the cascade control strategy and the PID control algorithm is: Set up two control closed loops, the inner loop and the outer loop, with the outer loop as the main loop and the inner loop as the secondary loop, and the two closed loops work together; The main loop is used to convert the difference between the rated temperature and the actual temperature of the frozen object into the set value of the secondary loop through the PID control algorithm; The secondary loop is used to control the power of the liquid pump drive module according to the set value and the difference between the collected temperature of the refrigerant and the actual temperature; The control module is also used to control the start and stop of the refrigeration equipment control module according to the real-time temperature of the frozen object.

2. The immersion freezer temperature control system according to claim 1, characterized in that: The control module is embedded with the main program, temperature sensor subroutine, digital PID algorithm subroutine, PWM subroutine, display subroutine, host computer reading subroutine, and relay control subroutine; The main program is used to control the temperature of the immersion freezing equipment by calling different subroutines at regular intervals.

3. The immersion freezer temperature control system according to claim 2, characterized in that: The main program calls different subroutines as follows: After initializing each module, perform a system loop; Read the PID value set by the host computer and the temperature data detected by the temperature sensor, perform PID calculation, obtain the PWM value of the liquid pump drive module, and display all the data; Determine whether the temperature meets the requirements. If not, start the refrigeration equipment control module until the requirements are met.

4. The immersion freezer temperature control system according to claim 1, characterized in that: The upper computer uses LABVIEW software, which is used to store the data transmitted by the control module, draw curves and display the data in real time. It is also used to send KP, KI, KD, and TS values ​​to the control module for intelligent regulation of the PID control algorithm.

5. The immersion freezer temperature control system according to claim 1, characterized in that: The temperature controlled by the temperature control system is divided into three stages: 20℃~4℃, 4℃~-4℃, and -4℃~-18℃.

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