Temperature control system of dipping type freezing device

Abstract

The invention discloses a temperature control system of an immersion type freezing device and relates to the technical field of immersion type freezing temperature control. Temperature control in the dipping and freezing process is achieved, it is ensured that large ice crystals are reduced in the food freezing process, damage to the interior of food is reduced, and meanwhile energy consumption and cost are reduced. 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 performs data interaction with the control module through the data transmission module; the temperature acquisition module acquires the temperature of the frozen object and the external environment, converts the acquired temperature signal into an electric signal and sends the electric signal to the control module; the control module controls the power of the liquid pump driving module through a cascade control strategy and a PID (Proportion Integration Differentiation) control algorithm according to the temperature signal of the frozen object and the influence value of the external environment on the freezing liquid; and starting and stopping of the refrigeration equipment control module are controlled according to the real-time temperature of the frozen object. The method is suitable for the field of dipping type freezing 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 to improve 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 convenient operation, but 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 material is placed in a coolant for freezing, so as to achieve rapid freezing of food. Immersion freezing has the advantages of fast freezing rate, low energy consumption, low dry 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 in China has gradually increased. 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 the two methods of immersion and freezing to improve the taste, flavor and nutritional value of food. The temperature control system plays a vital role in the immersion freezing process. By accurately controlling the temperature, it can be ensured that the formation of large ice crystals is reduced during the freezing process, thereby reducing the damage to the inside of the food, thereby maintaining the nutritional content of the food and greatly improving the quality of the product. The temperature control system can effectively control the rate of immersion freezing. By adjusting the freezing temperature and freezing time, the speed and size of ice crystal formation inside the food can be accurately controlled. This control can not only maintain the appearance and taste of the food, but also prevent the damage to the food structure caused by excessive ice crystals, thereby ensuring the quality and safety of the food. The temperature control system can effectively monitor and control the temperature during the immersion freezing process to prevent food deterioration caused by temperature fluctuations. The temperature control system provides strong support for the optimization of immersion freezing process parameters. By monitoring and analyzing the temperature changes during the freezing process, it is possible to understand the effects of different process parameters on the freezing effect of food, and then optimize the process parameters to improve the efficiency and quality of immersion freezing. Accurate temperature control can speed up the immersion freezing process, thereby improving production efficiency. By optimizing process parameters and reducing temperature fluctuations, freezing time can be shortened, production line throughput can be increased, production costs can be reduced, and the competitiveness of enterprises can be increased. The application of temperature control systems in immersion freezing has promoted the innovation and development of related technologies. With the continuous advancement of temperature control technology, we can achieve a more precise and efficient immersion freezing process, bringing more innovations and breakthroughs to the food processing industry. By deeply studying the application of temperature control systems in immersion freezing, we can further expand its application areas. Summary of the invention

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

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

[0006] The present invention provides an immersion freezing device temperature control system, 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 value 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, there is a preferred embodiment in which a cascade control strategy and a PID control algorithm are embedded in the control module;

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

[0013] Two control closed loops are set, namely the inner loop and the outer loop, with the outer loop being the main loop and the inner loop being the secondary loop, and the two closed loops work with each other;

[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] Further, there is a preferred embodiment, the control module is embedded with a main program, a temperature sensor subroutine, a digital PID algorithm subroutine, a PWM subroutine, a display screen 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, there is a preferred embodiment in which 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 adopts 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 also 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 objects is divided into three stages: precooling stage, phase change stage and supercooling stage;

[0026] S2: The flow rate of the refrigerant is controlled to be low in the precooling stage and the supercooling stage, and the flow rate of the refrigerant is controlled to be high in the phase change stage.

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

[0028] Furthermore, there is a 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, there is a 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 refrigeration 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 freezing model and put it into mesh drawing software for mesh drawing;

[0035] S25: Put 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 of the change of the center temperature over time according to the center 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. The present invention proposes a temperature control system for an immersion freezing device, which respectively designs 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; wherein the control module is responsible for receiving the temperature signal from the temperature acquisition module, and adjusting the power of the liquid pump drive module according to these temperature signals and the preset control strategy (cascade control and PID control algorithm), thereby controlling the flow rate of the coolant, increasing the freezing rate, reducing energy consumption, reducing the formation of large ice crystals, and maintaining the nutritional components of food. At the same time, the start and stop of the refrigeration equipment control module is controlled according to the real-time temperature of the frozen object to minimize energy consumption.

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

[0041] 2. The present invention provides an immersion freezing process control method. First, a simulation model is constructed through numerical simulation software based on computational fluid dynamics theory and heat transfer principles. The influence of different refrigerant flow rates on the freezing speed and freezing quality of frozen objects under constant speed and variable speed conditions is simulated, and the time-varying curve of the center temperature of the frozen object and the temperature distribution cloud map of the center section are obtained. The results show that as the refrigerant flow rate increases, 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 a high flow rate in the phase change stage.

[0042] Furthermore, the existing immersion freezing control method usually adopts a fixed speed mode, that is, the coolant is frozen in a fixed speed mode, but in order to ensure the freezing effect, full power output will be used, resulting in high energy consumption. The present invention adopts a variable speed mode to control the immersion freezing control, that is, by controlling the coolant flow rate to a low flow rate in the precooling stage and the supercooling stage, and controlling the coolant flow rate to a high flow rate in the phase change stage, while reducing the freezing time, different flow rates are selected in different stages, avoiding full power output, reducing energy waste, and reducing 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 It is the circuit diagram of the terminal design of the temperature acquisition module described in the present invention;

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

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

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

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

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

[0051] Figure 8 It is a program flow chart of the OLED display subroutine of the present invention;

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

[0053] Fig.10 It is a schematic diagram of three stages of the freezing process of the frozen object of the present invention;

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

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

[0056] Fig.13 yes Fig.12 A magnified image of

[0057] Fig.14 It is a bar graph of the flow rate of the coolant and the freezing time of the present invention;

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

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

[0060] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope 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 value 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 application, in order to ensure that the food can reach the required freezing temperature in the shortest time and the required energy consumption is lower, the temperature acquisition module, liquid pump drive module, host computer, data transmission module, control module and refrigeration equipment control module are designed respectively; the control module is responsible for receiving the temperature signal from the temperature acquisition module, and adjusting the power of the liquid pump drive module according to these temperature signals and the preset control strategy (cascade control and PID control algorithm), thereby controlling the flow rate of the refrigerant, increasing the freezing rate, reducing energy consumption, reducing the formation of large ice crystals, and maintaining the nutritional content of the food. At the same time, the start and stop of the refrigeration equipment control module is controlled according to the real-time temperature of the frozen object to minimize energy consumption.

[0067] Among them, 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 a "TTL standard" level signal that can be recognized by the controller. 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, the serial port selection is COM3 or COM5, and the serial port circuit is as follows Figure 1 shown.

[0068] The STM32F103C8T6 microcontroller is used as the main control chip of the control module to complete data acquisition, transmission, display and other functions. The STM32F103C8T6 microcontroller is a 32-bit microcontroller based on the ARM Cortex-M core STM32 series. The program memory capacity is 64KB, the voltage required is 2V~3.6V, and the operating temperature is -40℃~85℃.

[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, the actual current is 12A, and the relay schematic is as follows Figure 3 shown.

[0071] It is also necessary to power the 24v motor, 3.3v microcontroller and LCD display. 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 be able to accurately control the freezing environment to stabilize at -20℃~25℃, so the DS18B20 temperature sensor is selected as the component for temperature data acquisition of the control system. The temperature control system should be able to maintain stable performance during long-term operation, and will not cause performance degradation due to slight changes in the external environment or aging of internal components. Therefore, this paper chooses to design the control system with the STM32 microcontroller as the control core. And the hardware part is made modular for easy 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 follows 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. Choose appropriate line width and line spacing according to different signal types to ensure signal transmission quality.

[0075] ② Component layout principles: Components are partitioned and laid out according to functional modules for easy maintenance and debugging. High-frequency components are placed close to their driving circuits to reduce signal transmission distances. The spacing between components meets process requirements to avoid short circuits or poor contact. Considering the mechanical strength of the PCB board, components are laid out reasonably to reduce stress concentration.

[0076] ③Electrical performance and safety: Before designing, fully analyze the electrical performance requirements of the circuit, including voltage, current, impedance, etc. Ensure that the insulation performance of the PCB board meets safety standards to avoid leakage and breakdown. For high-voltage parts, take protective measures, such as setting isolation grooves or using insulating materials.

[0077] ④ Heat dissipation and thermal design: Design the heat dissipation structure reasonably according to 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, 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 key signal lines, use shielded wires or add shielding layers to improve anti-interference capabilities. Rationally lay out grounding 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, temperature cycling, etc.

[0080] ⑦ Process and manufacturability: The design should consider the feasibility of production and manufacturing, and avoid processes that are too complicated or difficult to achieve. Reasonably select the material, thickness and number of layers of the PCB board to meet performance requirements and production efficiency. Optimize the design of details such as drilling and pads to improve production yield.

[0081] ⑧ Cost optimization and control: Under the premise of meeting performance requirements, try to reduce the cost of PCB boards. Reduce costs through reasonable component selection, layout optimization, etc. Comprehensively consider factors such as production efficiency and material utilization to achieve effective cost control.

[0082] In actual application, this implementation mode needs to be tested for 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 method 2: This implementation method specifically describes the cascade control strategy and PID control algorithm embedded in the control module described in the implementation method 1 above;

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

[0087] Two control closed loops are set, namely the inner loop and the outer loop, with the outer loop being the main loop and the inner loop being the secondary loop, and the two closed loops work with each other;

[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 application, this embodiment adopts a combination of cascade control strategy and PID control algorithm to realize power control of the liquid pump drive module.

[0091] Among them, 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, so that the system deviation is gradually reduced to zero, thereby achieving the purpose of precise control. The purpose of this embodiment is to reduce energy consumption and enhance the freezing rate by intelligently controlling the difference between the real-time temperature of the frozen object and the rated temperature, thereby improving the effect of immersion freezing. Therefore, the numbers in the position PID control algorithm are selected, and the PID calculation formula is specifically as follows:

[0092]

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

[0094] like Figure 6 As shown, two control closed loops are designed, in which the inner loop is the secondary loop and the outer loop is the main loop. The main loop is a fixed value control system, and the secondary loop is a follow-up control system. The two closed loops work together to accurately control the temperature of the frozen object. The input of the main regulator is the rated temperature of the frozen object, and the output of the main regulator is the set value of the secondary regulator. The power of the liquid pump is controlled by the output value of the secondary regulator. The power affects the flow rate, thereby cooling the frozen liquid.

[0095] In the main loop, e1(t) is the difference between the rated value of the frozen material temperature and the actual frozen material temperature y1(t). e2(t) is the difference between the liquid pump controller input and the actual refrigerant temperature 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 get the transfer function G(s):

[0110]

[0111] Among them, Q(s) is the pump speed and T(s) is the temperature.

[0112] When the pump speed increases from 0m / s to 5m / s, the temperature will decrease from 25℃ to -18℃. 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 method 3: This implementation method is to specifically explain the control module described in the above implementation method;

[0118] The control module also has embedded main program, temperature sensor subprogram, digital PID algorithm subprogram, PWM subprogram, display subprogram, host computer reading subprogram, and relay control subprogram;

[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 with a long polling structure, and all programs are integrated into a main program, which is called in a self-loop manner to work.

[0121] The whole procedure is as follows Figure 7 As shown, the program of each function is initialized first and then enters the system cycle to first read the PID value set by the host computer and the detected temperature to calculate the PWM value, and all the data are displayed on the display screen.

[0122] Among them, the digital PID algorithm subroutine is specifically as follows:

[0123] Write a microcontroller program based on the positional PID formula. Among them, err(k) is temperature1_temp-SET_Temp in the program, which represents the temperature error of one time minus the temperature error of the previous time. Since the temperature control of the temperature control system is divided into three stages (20℃~4℃, 4℃~-4℃, -4℃~-18℃), Δu(k) in the formula is set to the PWM_DUTU value in the program, and Derror represents the accumulated error value. Among them, it represents the accumulated value of the error and the PWM value generated by the PID iterative calculation.

[0124] The PID formula is:

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

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

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

[0128] According to the design of the control system, the condenser and the compression pump need to be shut down at -18 degrees Celsius, so the PA12 and PA15 pins of the microcontroller are used to control the relay to stop being powered at -18 degrees Celsius.

[0129] The specific steps of calling the upper computer numerical subroutine are as follows:

[0130] The overall PID program needs to be tested to determine the specific K P , K I If you modify the program to control K P , K I The value is too cumbersome and inconvenient, so the value can be changed at any time by calling the host computer. The host computer sends the changed value to the STM32 microcontroller through the serial port, and the microcontroller stores the data sent by the host computer in an array named USART_RX_BUF[*].

[0131] The specific OLED display subroutine is:

[0132] Set the IOs of STM32103 connected to the OLED module. Set the IO ports PB11-PB15 connected to the OLED module as outputs. Write a subroutine according to the timing diagram to meet the requirements. The design sequence of the program 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: Fig. 9 shown.

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

[0137] LABVIEW is used to make the host computer part, and LABVIEW software is used to store the data transmitted from the control board, display it in real time, and draw curves. And the KP, KI, KD, and TS values ​​are sent to the circuit board through serial communication for intelligent regulation of the PID algorithm. Then the temperature control process of the entire device is controlled. The entire host computer is divided into serial communication, PID setting, data storage, and temperature curve drawing.

[0138] In actual application, this embodiment also needs to design a front panel so that users can better understand and use the function of the whole system. The front panel is used to set the data storage address, serial port selection, and real-time display of the two temperature values ​​of the frozen object and the frozen liquid. KP, KI, KD, and the set temperature are set and sent to the program of the control board. The program calculates PID and forms PWM as the output power of the liquid pump. The front panel of the host computer is equipped with real-time PWM value display, date string, and two waveform charts representing the temperature data transmitted by the temperature sensor.

[0139] The host computer provides the MCU with the values ​​of KP, KI, KD, and set temperature through serial communication, sets the switch for sending parameters, and the numerical components of the four input values. The string length is set to 3, which can accurately input 3 digits of numerical values. For the MCU program, there is a situation where the accuracy needs to be improved, so when setting the value, it is necessary to multiply by 10 to comply with the calculation rules of the MCU. Since this article is to control the freezing state involving sub-zero temperatures, a conditional structure is added to determine whether the input set temperature is greater than 0. If the set temperature is less than 0, a sign will be applied when it is transmitted to the MCU. Finally, all the values ​​are summarized into a connection string and transmitted to the MCU through 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 in multiples with the required data, it needs to be divided by 10 first, and then a conditional structure is added to determine the positive and 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. Add a display component to the processed data to display the real-time temperature. The two data are automatically generated through the waveform image component. The temperature change curve. The PWM value is directly transmitted by the single-chip microcomputer calculation. It only needs to process the hexadecimal conversion into a decimal value. This system also sets the experimental time function (specific to the 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. It is convenient for the generation of data in the subsequent experimental stage, and finally analyzed with the simulation data.

[0141] Implementation method 5: See Fig.10 This embodiment is described. This embodiment provides an immersion freezing process control method. The method 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: dividing the frozen product into three stages during the freezing process: a pre-cooling stage, a phase change stage, and a super-cooling stage;

[0143] Step S2: Control the coolant flow rate to be low in the precooling stage and the supercooling stage, and control the coolant flow rate to be high in the phase change stage.

[0144] In actual application of this embodiment, the freezing process of frozen objects is divided into three stages, such as Fig.10 As shown, it includes a precooling stage, a phase change stage and a supercooling stage;

[0145] Among them, pre-cooling stage: This embodiment analyzes the temperature of food or substance gradually decreasing from above 0°C. During the decreasing process, 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 change stage: This embodiment analyzes that when the temperature of food or substance drops below the freezing point, the water begins to transform into solid ice crystals. The formation and growth of ice crystals will directly affect the structure and taste of food or substance. If the cooling rate is too fast, ice crystals will form quickly and become very small, which helps to maintain the texture of food or substance; but if the cooling rate is too slow, ice crystals will grow larger, resulting in structural damage to food or substance. Therefore, this embodiment defines this stage as the phase change stage, which is the most critical stage in the freezing process. Because the formation and growth of ice crystals will directly affect the structure and taste of food or substance.

[0147] Supercooling stage: This embodiment analyzes that when most of the water in the food or substance is converted into ice crystals, the substance enters the freezing stage. In this stage, the temperature of the food or substance continues to drop until it reaches the required freezing temperature. 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 for a long time at low temperatures. 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 foods or substances. By controlling the cooling rate and temperature, the formation and growth of ice crystals can be affected, thereby maximizing the preservation of the original structure and taste of food or substances.

[0149] Therefore, this embodiment simulates and analyzes the freezing process of frozen materials under different flow rate conditions to determine the impact of different flow rates on the freezing rate at different stages, thereby determining 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 that the refrigerant flow rate is controlled to be high in the phase change stage (greater than 4m / s is a high flow rate).

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

[0151] Implementation Method 6: See Fig.11 This embodiment is described. This embodiment specifically describes step S2 in the immersion freezing process control method described in the first embodiment above.

[0152] By simulating and analyzing the freezing process of frozen materials under different flow rate conditions, the influence of different flow rates on the freezing rate at different stages is determined, 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.

[0153] The simulation analysis is as follows:

[0154] Step 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;

[0155] Step S22: constructing a fluid mechanics calculation model of the coolant and a heat transfer equation of the refrigeration process;

[0156] Step S23: using 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: constructing a freezing model and placing it into a mesh drawing software for mesh drawing;

[0158] Step S25: putting the drawn grid into the fluid simulation calculation software for calculation and solution, inputting different flow rates of the coolant, and obtaining the center temperature data;

[0159] Step S26: generating a curve of the core temperature changing with time according to 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 flow rate of the refrigerant is controlled to be low in the pre-cooling stage and the supercooling stage, and that the flow rate of the refrigerant is controlled to be high in the phase change stage.

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

[0162] Q1=mc1(T 初 -T 冻 )

[0163] Among them, 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 object, 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 controlling fluids include the continuity equation, the momentum conservation equation, and the energy conservation equation.

[0167] The continuity equation is:

[0168]

[0169] Where u, v, 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 Kg / m 3 ; P is pressure, unit N; F bx 、F by 、F bzis the volume force of F on the x, y, and z axes, in N; P xx ,P xy ,P yz is the component of P, in N;

[0173] The energy conservation equation is:

[0174]

[0175] Among them, c p is the specific heat capacity, in J / kg·℃; T is the thermodynamic temperature, in ℃; k is the fluid heat transfer coefficient, in 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, and then the computational model of fluid mechanics can be calculated.

[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 heat convection heat transfer. The convection heat at the contact surface between the solid and the fluid can be expressed by Newton's cooling law:

[0179] Q=αA Δ T

[0180] Where Q is the heat transfer rate, that is, the heat transfer per unit time, in W; α is the surface heat transfer coefficient, in W / (m 2 ·K); A is the surface area of ​​the frozen object in contact with the freezing liquid medium, unit: m 2 ; Δ T is the temperature difference between the food surface and the freezing liquid, in K. Since the frozen surface area A in contact with the freezing liquid is usually a constant, and the freezing liquid temperature is determined by the freezing equipment, it can be seen that the convective heat transfer heat flow is mainly related to the convective surface heat transfer coefficient, which is determined by other factors such as the type and physical properties of the freezing liquid 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, 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 heat conduction direction, 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 assist in the subsequent solution.

[0187] This implementation method needs to solve the freezing process of the frozen object and generate a curve of the central temperature change over time based on the central temperature data obtained by the solution, and then perform post-processing 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 Fig.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 maps 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 a simulation analysis is performed on the freezing process under different flow rate conditions. Then, a simulation analysis is performed by changing the flow rate during the freezing process to increase the freezing rate, and an overall analysis of the temperature curves and cloud diagrams that change with time in the two types of simulation processes (constant speed and variable speed) is performed. Thus, 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 objects is divided into three stages: precooling stage, phase change stage and supercooling stage. Fig.10 shown.

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

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

[0197] Q1=mc1(T初 -T 冻 )

[0198] Among them, 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: 1.03g / cm 2 .

[0207] The freezing medium of this embodiment is SH-7A food grade refrigerant. Tables 3 and 4 are the property data of the refrigerant at different temperatures recorded in the refrigerant manual.

[0208] Table 3 shows the specific heat capacity of the coolant:

[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 shows the thermal conductivity of the coolant:

[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 shows the viscosity of the coolant:

[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] Construct the fluid mechanics calculation model of the coolant and the heat transfer equation of the refrigeration process.

[0218] This implementation method needs to solve the freezing process of the frozen object and generate a curve of the central temperature change over time based on the central temperature data obtained by the solution, and then perform post-processing 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 Fig.11 shown.

[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 freezer was a rectangular block of 200 mm × 200 mm × 100 mm, and the frozen product (beef) was a small rectangular block 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 simulation is to obtain data under relatively ideal conditions, so some factors that affect the simulation results are not considered to establish a mathematical model of the composite freezing process, so 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 does not exchange heat with the outside world.

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

[0227] (5) Since the material parameters of the frozen material and the refrigerant 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 is placed in Fluent for solution and calculation. The model's solver type (solver) selects the pressure equation (Pressure-Based) to solve, the velocity equation (Velocity Formulation) is absolute velocity (Absolute), the time type (Time) is transient (Transient), and the gravity term (Gravity) is applied, and the gravity acceleration in the vertical direction is set to -9.81m / s2.

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

[0231] The inlet is the velocity inlet, and the outlet is the pressure outlet. The central temperature point of the frozen object is selected as the data extraction point.

[0232] The simulation results and analysis are:

[0233] The simulation groups under the conditions of constant flow rate and dynamic flow rate are shown in Tables 6 and 7, and the simulation experiments are carried out according to the temperature values ​​of the groups.

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

[0235] Table 6

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

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

[0238] Table 7

[0239]

[0240] Analyze the influence of constant flow rate on freezing time and freezing effect of frozen products:

[0241] The temperature distribution of the freezing process of the immersion freezing equipment simulated by Fluent software is presented through the overall three-dimensional structure diagram. In order to better see the temperature distribution, the freezing process and the corresponding temperature gradient cloud diagram are observed by selecting the center point xy section to better judge the freezing effect.

[0242] First, the flow rate at the inlet is set to 0m / s, 1m / s, 2m / s, 3m / s, 4m / s, and 5m / s. The temperature cloud map generated by the 6 sets of constant flow rate simulations and the temperature detection curve of the frozen object center are used to obtain the freezing data. The influence of flow rate on the freezing time and freezing effect is summarized and analyzed. The temperature cloud map and the temperature cloud map on the xy plane generated by the 6 constant flow rates when freezing for 200s are shown. It can be seen that the temperature distribution in the freezing chamber is from red to blue, which represents the temperature from high to low. From the xy cross-sectional diagram, it can be seen that the internal temperature of the frozen animal is -18℃. Except when there is no flow rate, the temperature of the freezing liquid is kept at -20℃. When the flow rate is 0m / s, it can be clearly seen that heat is transferred between the frozen object and the freezing liquid. Single immersion freezing is that the frozen object is in direct contact with the freezing liquid and the temperature of the frozen object is reduced to the target temperature through heat transfer. Adding a fluid field is to accelerate the heat transfer through the circulation of the freezing liquid, so that the freezing rate is greater and the freezing time is shorter.

[0243] Extract the data of the center point of the 6 simulated frozen objects to obtain the curve of temperature change over time. Fig.11 and Fig.12 As shown. It can be seen that when freezing begins, the center temperature drops rapidly, but after a certain period of time, an inflection point will appear, and the slope of the curve of the center temperature drop gradually tends to be gentle. As the flow rate of the coolant increases, the inflection point will move to the left along the coordinate axis. This is because when the food is frozen, the free water molecules in the cells will condense into small ice crystals, and the small ice crystals will slowly gather to form an ice crystal belt. The freezing time before the inflection point is the time to form the largest ice crystal belt. The shorter this period of time, the higher the freezing quality of the food. Therefore, it can be seen from the simulation data that as the flow rate of the coolant increases, the freezing quality of the frozen food improves. As the flow rate of the coolant increases, the freezing time gradually decreases.

[0244] according to Figure 12 to Figure 14 It can be seen that increasing the flow rate of the refrigerant will affect the freezing speed of beef. As the flow rate of the refrigerant increases, the freezing time of the frozen food will gradually decrease. However, the improvement of the freezing efficiency shows a decreasing trend, which means that as the flow rate of the refrigerant increases, the improvement of the freezing efficiency gradually decreases and eventually tends to 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 due to the influence of the size of the frozen object, the refrigerant flow rate reaches a saturated state at 4m / s. The simulation results show that the freezing rate increases very slowly if the flow rate is continuously increased.

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

[0250] According to the above analysis, the higher the flow rate, the shorter the time required in the simulation process, but the higher the power required and the more energy consumed. Therefore, this embodiment proposes to adopt a method of changing the flow rate at different temperature stages during the freezing process to perform simulation. This can achieve both maintaining an efficient freezing rate and reducing energy consumption.

[0251] During the freezing process, 4℃~-4℃ is the temperature range when water goes from ice-water mixture to ice crystals, the maximum ice crystal formation zone and the water density is the highest. Therefore, the flow rate is increased at 4℃~-4℃ to ensure the formation of small ice crystals, reduce the damage to the frozen cells, and reflect the advantages of immersion freezing. When simulating at a constant flow rate, the time required for the six flow rates to reduce the final temperature of the frozen product from 4℃ to -4℃ is shown in Table 9.

[0252] Table 9

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

[0254] By using the expression function in Fluent software, an expression is set to change 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])). Among them, Y is the flow rate at 4℃~-4℃, 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, and an accurate flow rate combination was obtained to provide a high freezing rate and energy-saving flow rate combination for the subsequent R&D control board and experimental stage.

[0256] According to the simulated data, the temperature curve is summarized as follows Fig.15 As shown, Fig.15 is the overall temperature curve of 10 groups of images, Fig.16 This is an enlarged image of 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 analysis of the influence of constant flow rate on the freezing time and freezing effect of frozen materials and the influence of variable flow rate on the freezing time and freezing effect of frozen materials, corresponding energy consumption calculations are carried out respectively.

[0262] The freezing time of 16 groups of fixed speed and variable speed is solved through simulation, and the energy calculation of the simulation results of the two speeds is carried out below.

[0263] Calculation of energy consumption at constant speed:

[0264] Refer to the existing immersion freezing experimental equipment, where the liquid pump power (maximum): 48w·h; refrigeration unit: 165w·h; pump controllable flow rate is 1m / s, 2m / s, 3m / s, 4m / s, 5m / s. Finally, multiply it with the time term solved in Table 2-9 to obtain the solution formula:

[0265] W=p·t

[0266] The results of the constant speed energy consumption are 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] Calculation of variable speed energy consumption:

[0270] This embodiment is to speed up the flow rate at 4℃~-4℃, so the time of increasing the flow rate for 10 groups of variable speed freezing simulations is summarized as shown in Table 12. The power consumption calculation formula is obtained by multiplying the time required for 4℃~-4℃ by the power required for the increased flow rate and adding the power of other flow rates multiplied by the remaining time:

[0271] W=p 快 ·t 快 +p 慢 ·t 慢

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

[0273] Table 12

[0274]

[0275] The energy consumption of speed change is shown in Table 13:

[0276] Table 13

[0277]

[0278] Result analysis:

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

[0280] In summary, this embodiment solves the time required for the maximum ice crystal band and the time required for 16 groups of flow rates through 16 groups of simulation analyses of constant speed and variable speed, and finally calculates the energy consumption to obtain the control board program for the flow rate group required for temperature control in subsequent experiments, and makes idealized data for the correctness of the experimental data of subsequent experiments, determines the correctness of the experimental data, and performs an overall design of the control system based on the simulation results.

[0281] The above description is only the implementation mode of the present invention and is not limited to the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the claims of the present invention.

Claims

1. An 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 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 value of the external environment on the freezing liquid; 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 cascade control strategy and PID control algorithm; The interaction process between the cascade control strategy and the PID control algorithm is: Two control closed loops are set, namely the inner loop and the outer loop, with the outer loop being the main loop and the inner loop being the secondary loop, and the two closed loops work with each other; 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.

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

4. The immersion freezer temperature control system according to claim 3, 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.

5. The immersion freezer temperature control system according to claim 1, characterized in that: 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.

6. 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℃, -4℃~-18℃.

7. An immersion freezing process control method, characterized in that: The method is implemented based on the immersion freezer temperature control system according to any one of claims 1 to 6, and the method is: S1: The freezing process of frozen objects is divided into three stages: precooling stage, phase change stage and supercooling stage; S2: The flow rate of the refrigerant is controlled to be low in the precooling stage and the supercooling stage, and the flow rate of the refrigerant is controlled to be high in the phase change stage.

8. The immersion freezing process control method according to claim 7, characterized in that: Less than or equal to 4m / s is a low flow rate, and greater than 4m / s is a high flow rate.

9. The immersion freezing process control method according to claim 8, characterized in that: S2 is specifically: 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.

10. The immersion freezing process control method according to claim 9, characterized in that: The simulation analysis is as follows: 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; S22: Construct the fluid mechanics calculation model of the coolant and the heat transfer equation of the refrigeration process; 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; S24: construct a freezing model and put it into mesh drawing software for mesh drawing; S25: Put 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; S26: generating a curve of the change of the center temperature over time according to the center temperature data, and generating a temperature cloud map and a heat transfer cloud map after processing; 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.

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