Laboratory liquid nitrogen ultralow temperature control system and control method thereof

Abstract

The invention is suitable for the technical field of temperature control, and provides a laboratory liquid nitrogen ultralow temperature control system and a control method thereof.The laboratory liquid nitrogen ultralow temperature control system comprises a stainless steel box body; the electrical control assembly comprises an anti-explosion electrical cabinet, an anti-explosion computer and an operating part, and a PLC control system is integrated in the anti-explosion electrical cabinet; the pipeline assembly comprises a system inlet pipeline, a pump, a pump outlet pipeline, a heat exchanger, an expansion tank assembly, an electric heater, a liquid nitrogen inlet pipeline and a liquid nitrogen outlet pipeline; one end of the system inlet pipeline is connected with the reaction kettle jacket, and the other end of the system inlet pipeline is connected with the pump inlet; one end of the pump outlet pipeline is connected with the pump outlet, and the other end of the pump outlet pipeline is connected with the heat exchanger shell pass inlet; one end of the electric heater is connected with a shell pass outlet of the heat exchanger, the other end of the electric heater is connected with a system outlet pipeline, and high-power, stable and high-precision temperature control can be automatically achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of temperature control, in particular to a laboratory liquid nitrogen ultra-low temperature control system and a control method thereof. Background Art

[0002] Currently, in order to achieve laboratory low-temperature reaction test conditions, existing traditional laboratories use dry ice acetone baths to achieve -78°C cooling conditions when conducting chemical reaction experiments under ultra-low temperature (below -100°C). This is applied in an open system. This will generate a large amount of acetone volatilization and VOCS during the experiment, increasing the burden of environmental treatment. Another application form is that the refrigeration system uses a single or multi-stage compressor to achieve -100°C conditions. Since the compressor needs to perform compression, condensation and evaporation under high pressure to achieve this low-temperature condition, it has the disadvantages of high noise, bulky size, high maintenance cost, and difficulty in continuously providing high-power cooling capacity. The dynamic temperature control capability is weak, and it is difficult to meet the needs of rapid temperature rise and fall and high-power, continuous cooling during chemical reaction experiments.

[0003] Therefore, in view of the above situation, there is an urgent need to provide a laboratory liquid nitrogen ultra-low temperature control system and a control method thereof to overcome the shortcomings in current practical applications. Summary of the Invention

[0004] The object of the present invention is to provide a laboratory liquid nitrogen ultra-low temperature control system and a control method thereof, aiming to solve the problems in the above-mentioned background technology.

[0005] The present invention is achieved by a laboratory liquid nitrogen ultra-low temperature control system comprising:

[0006] Stainless steel box;

[0007] Electrical control components, including an explosion-proof electrical cabinet, an explosion-proof computer and operating components, wherein the explosion-proof electrical cabinet is integrated with a PLC control system;

[0008] Piping components, including system inlet piping, pump, pump outlet piping, heat exchanger, expansion tank assembly, electric heater, liquid nitrogen inlet piping, and liquid nitrogen outlet piping;

[0009] One end of the system inlet pipeline is connected to the reactor jacket, and the other end of the system inlet pipeline is connected to the pump inlet;

[0010] One end of the pump outlet pipeline is connected to the pump outlet, and the other end of the pump outlet pipeline is connected to the shell side inlet of the heat exchanger;

[0011] One end of the electric heater is connected to the shell outlet of the heat exchanger, and the other end of the electric heater is connected to the system outlet pipeline.

[0012] As a further solution of the present invention: the heat exchanger is a wound tube heat exchanger;

[0013] The pump is a stainless steel magnetic drive pump;

[0014] The pump outlet pipeline is provided with a pump outlet stop valve and a pressure gauge valve, and the pressure gauge valve is connected to a pressure gauge 1.

[0015] As a further solution of the present invention: the expansion tank assembly is connected to a second pressure gauge, and the expansion tank assembly includes an expansion tank and an expansion tank outlet arranged on the expansion tank, the expansion tank outlet is provided with an expansion tank outlet valve, the expansion tank is also provided with an oil filling pipeline, an emptying pipeline, a pressure gauge pipeline, a nitrogen inlet pipeline and a liquid level gauge, the emptying pipeline is provided with a first unloading valve and an emptying valve, and the first unloading valve and the emptying valve are installed in parallel, the pressure gauge pipeline is connected to the second pressure gauge, and a pressure reducing valve is provided on the nitrogen inlet pipeline.

[0016] As a further solution of the present invention: the system inlet pipeline includes a temperature transmitter and a drain outlet, and the system inlet pipeline is also connected to a pressure relief bypass through a tee. The drain outlet is arranged at the inlet of the pump, and the inlet of the pump is connected to the outlet of the expansion tank assembly and the expansion tank outlet valve through a tee.

[0017] As a further solution of the present invention: the liquid nitrogen outlet pipeline is provided with a liquid nitrogen outlet two-way valve, a temperature transmitter three and a safety valve, the liquid nitrogen outlet two-way valve and the safety valve are installed in parallel, one end of the liquid nitrogen outlet pipeline is connected to the heat exchanger pipe outlet, and the other end of the liquid nitrogen outlet pipeline is connected to the nitrogen outlet main pipe.

[0018] As a further solution of the present invention: a pressure transmitter valve, a second temperature transmitter and a pressure transmitter are provided on the system outlet pipeline.

[0019] As a further solution of the present invention: a liquid nitrogen inlet stop valve is provided on the liquid nitrogen inlet pipeline, one end of the liquid nitrogen inlet pipeline is connected to the heat exchanger pipe inlet, and the other end of the liquid nitrogen inlet pipeline is connected to the liquid nitrogen inlet main pipe.

[0020] As a further solution of the present invention: a second unloading valve is provided on the pressure relief bypass, one end of the second unloading valve is connected to the system inlet pipeline, and the other end of the second unloading valve is connected to the system outlet pipeline.

[0021] A method for controlling the ultra-low temperature of liquid nitrogen in a laboratory, using the above-mentioned ultra-low temperature control system for liquid nitrogen in a laboratory, the method comprising the following steps:

[0022] By setting the target temperature and temperature control parameters on the explosion-proof computer;

[0023] Start the pump to drive the medium to circulate in the system;

[0024] The PLC control system collects the signals of temperature transmitter 1, temperature transmitter 2 and temperature transmitter 3 in real time;

[0025] If cooling is required, the PLC controls the opening of the liquid nitrogen outlet two-way valve to adjust the liquid nitrogen flow rate;

[0026] If the temperature needs to be increased, the PLC controls the power output of the electric heating;

[0027] The system pressure is maintained stable through the expansion tank assembly and the pressure relief bypass.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. High degree of automation. You only need to set the appropriate temperature value, and the system will automatically control the temperature at the set value without frequent manual operation;

[0030] 2. This system is a relatively closed system, without any waste liquid or waste gas, and is environmentally friendly;

[0031] 3. It can be customized according to user needs within a certain temperature range;

[0032] 4. Flexible heating and cooling loads;

[0033] 5. Low overall investment, high cost performance and low maintenance cost;

[0034] 6. Fast heating and cooling speed;

[0035] 7. The unit has a wide operating temperature range, which can realize multi-purpose functions and the output temperature can be adjusted according to user needs;

[0036] 8. The temperature control accuracy of the unit is high, and the temperature control accuracy of the unit system can reach ±1℃;

[0037] 9. The system configuration is perfect with automatic protection functions, including under-pressure protection, low-flow protection, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 The present invention provides a flow chart of a method for controlling ultra-low temperature of liquid nitrogen in a laboratory.

[0040] Figure 2 This is a structural schematic diagram of a laboratory liquid nitrogen ultra-low temperature control system provided by the present invention.

[0041] Figure 3 for Figure 2 Schematic diagram of the internal structure.

[0042] Figure 4 This is a structural schematic diagram of an electrical control component in a laboratory liquid nitrogen ultra-low temperature control system provided by the present invention.

[0043] Figure 5 A schematic diagram of the structure of the piping assembly in a laboratory liquid nitrogen ultra-low temperature control system provided by the present invention Figure 1 .

[0044] Figure 6 A schematic diagram of the structure of the piping assembly in a laboratory liquid nitrogen ultra-low temperature control system provided by the present invention Figure 2 .

[0045] Figure 7 A schematic diagram of the structure of the piping assembly in a laboratory liquid nitrogen ultra-low temperature control system provided by the present invention Figure 3 .

[0046] In the attached figure: 1-stainless steel box, 2-electrical control components, 3-pipeline components, 4-explosion-proof electrical cabinet, 5-explosion-proof computer, 6-operating parts, 7-system inlet pipeline, 8-pump, 9-pump outlet pipeline, 10-heat exchanger, 11-expansion tank assembly, 12-pressure gauge 1, 13-pressure gauge, 14-pressure relief bypass, 15-electric heating, 16-system outlet pipeline, 17-liquid nitrogen outlet pipeline, 18-liquid nitrogen inlet pipeline, 19-temperature transmitter 1, 20-expansion Tank outlet valve, 21-sewage outlet, 22-pump outlet stop valve, 23-pressure gauge valve, 24-expansion tank, 25-oil filling line, 26-unloading valve one, 27-pressure gauge line, 28-emptying valve, 29-pressure reducing valve, 30-liquid level gauge, 31-expansion tank outlet, 32-unloading valve two, 33-pressure transmitter valve, 34-temperature transmitter two, 35-liquid nitrogen outlet two-way valve, 36-temperature transmitter three, 37-safety valve, 38-pressure transmitter. DETAILED DESCRIPTION

[0047] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0048] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0049] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0050] The present invention will be further explained below with reference to specific embodiments.

[0051] The present invention provides continuous and stable cooling capacity at -100°C by automatically and precisely controlling the amount of liquid nitrogen. Meanwhile, electric heating is used to restore the system's low temperature to a temperature within the 100°C range, automatically achieving high-power, stable, and high-precision temperature control. This provides an efficient, energy-saving, safe, and environmentally friendly automated temperature control device capable of continuously providing stable cooling capacity and high temperature control accuracy. This compact ultra-low temperature TCU addresses the existing problems of high energy consumption, slow response speed, narrow applicable temperature range, and low cooling capacity, meeting the demand for high-power and stable cooling capacity in continuous chemical reactions.

[0052] See also Figure 1-Figure 7The embodiment of the present invention provides a laboratory liquid nitrogen ultra-low temperature control system, including a stainless steel box 1, an electrical control component 2, a pipeline component 3, an explosion-proof electrical cabinet 4, an explosion-proof computer 5, an operating component 6, a system inlet pipeline 7, a pump 8, a pump outlet pipeline 9, a heat exchanger 10, an expansion tank component 11, a pressure gauge 12, a pressure gauge 2 13, a pressure relief bypass 14, an electric heater 15, a system outlet pipeline 16, a liquid nitrogen outlet pipeline 17, a liquid nitrogen inlet pipeline 18, a temperature transmitter 19, an expansion tank outlet valve 20, and a sewage outlet. 21, pump outlet stop valve 22, pressure gauge valve 23, expansion tank 24, oil filling pipeline 25, unloading valve 1 26, pressure gauge pipeline 27, emptying valve 28, pressure reducing valve 29, liquid level gauge 30, expansion tank outlet 31, unloading valve 2 32, pressure transmitter valve 33, temperature transmitter 2 34, liquid nitrogen outlet two-way valve 35, temperature transmitter 3 36, safety valve 37 and pressure transmitter 38, and electrical control components 2 are all concentrated in the stainless steel box 1, fully considering the space layout and facilitating subsequent maintenance and repair.

[0053] The electrical control assembly 2 includes an explosion-proof electrical cabinet 4, an explosion-proof computer 5 and an operating element 6. All electrical components are arranged in the explosion-proof electrical cabinet 4. The operating element 6 includes but is not limited to switches, indicator lights, etc.

[0054] The pipeline assembly 3 includes a system inlet pipeline 7, a pump 8, a pump outlet pipeline 9, a heat exchanger 10, an expansion tank assembly 11, a pressure gauge 12, a pressure gauge 2 13, a pressure relief bypass 14, an electric heater 15, a system outlet pipeline 16, a liquid nitrogen outlet pipeline 17 and a liquid nitrogen inlet pipeline 18;

[0055] The system inlet pipeline 7 includes a temperature transmitter 19 and a sewage outlet 21. One end of the system inlet pipeline 7 is connected to the glass kettle jacket, and the other end is connected to the pump 8 inlet; the system inlet pipeline 7 is provided with a temperature transmitter 19 for measuring the temperature of the medium in the jacket after entering the system; after entering the system, the system inlet pipeline 7 is connected to the pressure relief bypass 14 through a tee; the inlet of the pump 8 where the system inlet pipeline 7 is located is connected to the expansion tank outlet 31 through a tee and is provided with an expansion tank outlet valve 20; the inlet of the pump 8 where the system inlet pipeline 7 is located is provided with a sewage outlet 21 for emptying the medium in the pipeline during maintenance.

[0056] The pump 8 is a stainless steel magnetic pump, and the flow rate and lift are determined according to actual needs;

[0057] The pump outlet pipeline 9 includes a pump outlet stop valve 22 and a pressure gauge valve 23. One end of the pump outlet pipeline 9 is connected to the outlet of the pump 8, and the other end is connected to the shell inlet of the heat exchanger 10. The pump outlet pipeline 9 is provided with a pump outlet stop valve 22. The pump outlet of the pump outlet pipeline 9 is provided with a pipeline connection pressure gauge valve 23, and the pressure gauge valve 23 is connected to the pressure gauge 12.

[0058] The heat exchanger 10 is a wound tube heat exchanger, and the heat exchange area is determined according to actual needs; the shell side of the heat exchanger 10 is connected to heat transfer oil or other medium in the jacket, and the tube side of the heat exchanger 10 is connected to liquid nitrogen for cooling the medium;

[0059] The expansion tank assembly 11 includes an expansion tank 24, an oil filling pipeline 25, an unloading valve 26, a pressure gauge pipeline 27, an emptying valve 28, a pressure reducing valve 29, a liquid level gauge 30 and an expansion tank outlet 31;

[0060] The volume of the expansion tank 24 is determined according to actual needs; the expansion tank 24 is provided with an oil filling pipeline 25, an emptying pipeline, a pressure gauge pipeline 27, a nitrogen inlet pipeline and a liquid level gauge 30; the emptying pipeline is provided with an unloading valve 1 26 and an emptying valve 28, and the unloading valve 1 26 and the emptying valve 28 are installed in parallel; the pressure gauge pipeline 27 is connected to the pressure gauge 2 13, and the nitrogen inlet pipeline is provided with a pressure reducing valve 29;

[0061] The pressure gauge 12 is connected to the pump outlet pipeline 9 and is used to measure the pressure at the pump outlet;

[0062] The second pressure gauge 13 is connected to the expansion tank assembly 11 and is used to measure the pressure in the expansion tank;

[0063] The pressure relief bypass 14 is provided with a second unloading valve 32, one end of which is connected to the system inlet pipe 7, and the other end is connected to the system outlet pipe 16;

[0064] The heat exchange power of the electric heater 15 is determined according to actual needs; one end of the electric heater 15 is connected to the shell outlet of the heat exchanger 10, and the other end is connected to the system outlet pipe 16;

[0065] The system outlet pipeline 16 is provided with a pressure transmitter valve 33, a second temperature transmitter 34 and a pressure transmitter 38; the pressure transmitter 38 is used to measure the pressure of the medium at the system outlet; the second temperature transmitter 34 is used to measure the temperature of the medium at the system outlet; one end of the system outlet pipeline 16 is connected to the outlet of the electric heater 15, and the other end is connected to the jacket inlet;

[0066] The liquid nitrogen outlet pipeline 17 is provided with a liquid nitrogen outlet two-way valve 35, a temperature transmitter 36 and a safety valve 37. One end of the liquid nitrogen outlet pipeline is connected to the outlet of the heat exchanger 10, and the other end is connected to the nitrogen outlet main pipe; the liquid nitrogen outlet two-way valve 35 and the safety valve 37 are installed in parallel; the temperature transmitter 36 is used to measure the temperature of the nitrogen outlet;

[0067] The liquid nitrogen inlet pipeline 18 is provided with a liquid nitrogen inlet stop valve, one end of the liquid nitrogen inlet pipeline is connected to the pipe inlet of the heat exchanger 10, and the other end is connected to the liquid nitrogen inlet main pipe.

[0068] In an embodiment of the present invention, the system is powered on and relevant parameters are set on an explosion-proof computer or display screen. After the system is powered on, the heat transfer oil is pumped into the reactor jacket and then returned to the pump for repeated circulation.

[0069] Based on the temperature sensor at the system outlet, the temperature control instrument automatically verifies the temperature under PLC control. When the oil in the jacket needs to be cooled, the system automatically controls liquid nitrogen to enter the heat exchanger tube from the liquid nitrogen inlet, thereby cooling the thermal oil in the system. When the oil in the jacket needs to be heated, the system automatically controls the electric heater to heat the medium in the system, thereby bringing the medium in the jacket to the set temperature.

[0070] See also Figure 1-Figure 7 The embodiment of the present invention provides a method for controlling the ultra-low temperature of liquid nitrogen in a laboratory, which uses the above-mentioned ultra-low temperature control system of liquid nitrogen in a laboratory. The method includes the following steps:

[0071] The target temperature and temperature control parameters are set by explosion-proof computer;

[0072] Start the pump to drive the medium to circulate in the system;

[0073] The PLC control system collects the signals of temperature transmitter 1, temperature transmitter 2 and temperature transmitter 3 in real time;

[0074] If cooling is required, the PLC controls the opening of the liquid nitrogen outlet two-way valve to adjust the liquid nitrogen flow rate;

[0075] If the temperature needs to be increased, the PLC controls the power output of the electric heating;

[0076] The system pressure is maintained stable through the expansion tank assembly and the pressure relief bypass.

[0077] The PLC control system also includes the following protection functions:

[0078] Underpressure protection: When the pressure transmitter detects that the pressure is lower than the set threshold, it automatically closes the liquid nitrogen inlet stop valve and electric heating;

[0079] Low flow protection: When the pump flow is abnormal, an alarm is triggered and the pump stops;

[0080] Over-temperature protection: When the temperature exceeds the safe range, the pressure relief bypass is forced to open and the heating / cooling source is cut off.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A laboratory liquid nitrogen ultra-low temperature control system, comprising a stainless steel box (1), characterized in that: Also includes: An electrical control assembly (2) includes an explosion-proof electrical cabinet (4), an explosion-proof computer (5), and an operating element (6), wherein a PLC control system is integrated in the explosion-proof electrical cabinet (4); A pipeline assembly (3), comprising a system inlet pipeline (7), a pump (8), a pump outlet pipeline (9), a heat exchanger (10), an expansion tank assembly (11), an electric heater (15), a liquid nitrogen inlet pipeline (18), and a liquid nitrogen outlet pipeline (17); One end of the system inlet pipeline (7) is connected to the jacket of the reactor, and the other end of the system inlet pipeline (7) is connected to the inlet of the pump (8); One end of the pump outlet pipeline (9) is connected to the outlet of the pump (8), and the other end of the pump outlet pipeline (9) is connected to the shell side inlet of the heat exchanger (10); One end of the electric heater (15) is connected to the shell outlet of the heat exchanger (10), and the other end of the electric heater (15) is connected to the system outlet pipeline (16).

2. The laboratory liquid nitrogen ultra-low temperature control system according to claim 1, characterized in that: The heat exchanger (10) is a wound tube heat exchanger; The pump (8) is a stainless steel magnetic drive pump; The pump outlet pipeline (9) is provided with a pump outlet stop valve (22) and a pressure gauge valve (23), and the pressure gauge valve (23) is connected to a pressure gauge 1 (12).

3. The laboratory liquid nitrogen ultra-low temperature control system according to claim 2, characterized in that: The expansion tank assembly (11) is connected to a second pressure gauge (13), and the expansion tank assembly (11) comprises an expansion tank (24) and an expansion tank outlet (31) arranged on the expansion tank (24), an expansion tank outlet valve (20) being arranged on the expansion tank outlet (31), an oil filling pipeline (25), an emptying pipeline, a pressure gauge pipeline (27), a nitrogen inlet pipeline and a liquid level gauge (30) being arranged on the expansion tank (24), an unloading valve (26) and an emptying valve (28) being arranged on the emptying pipeline, and the unloading valve (26) and the emptying valve (28) being installed in parallel, the pressure gauge pipeline (27) being connected to the second pressure gauge (13), and a pressure reducing valve (29) being arranged on the nitrogen inlet pipeline.

4. The laboratory liquid nitrogen ultra-low temperature control system according to claim 3, characterized in that: The system inlet pipeline (7) includes a temperature transmitter (19) and a sewage outlet (21), and the system inlet pipeline (7) is also connected to a pressure relief bypass (14) through a tee. The sewage outlet (21) is arranged at the inlet of the pump (8), and the inlet of the pump (8) is connected to the outlet of the expansion tank assembly (11) and the expansion tank outlet valve (20) through the tee.

5. The laboratory liquid nitrogen ultra-low temperature control system according to claim 4, characterized in that: The liquid nitrogen outlet pipeline (17) is provided with a liquid nitrogen outlet two-way valve (35), a temperature transmitter (36) and a safety valve (37). The liquid nitrogen outlet two-way valve (35) and the safety valve (37) are installed in parallel. One end of the liquid nitrogen outlet pipeline (17) is connected to the pipe outlet of the heat exchanger (10), and the other end of the liquid nitrogen outlet pipeline (17) is connected to the nitrogen outlet main pipe.

6. The laboratory liquid nitrogen ultra-low temperature control system according to claim 5, characterized in that: The system outlet pipeline (16) is provided with a pressure transmitter valve (33), a second temperature transmitter (34) and a pressure transmitter (38).

7. The laboratory liquid nitrogen ultra-low temperature control system according to claim 6, characterized in that: The liquid nitrogen inlet pipe (18) is provided with a liquid nitrogen inlet stop valve, and one end of the liquid nitrogen inlet pipe (18) is connected to the pipe inlet of the heat exchanger (10), and the other end of the liquid nitrogen inlet pipe (18) is connected to the liquid nitrogen inlet main pipe.

8. The laboratory liquid nitrogen ultra-low temperature control system according to claim 7, characterized in that: The pressure relief bypass (14) is provided with a second unloading valve (32), one end of which is connected to the system inlet pipeline (7), and the other end of which is connected to the system outlet pipeline (16).

9. A method for controlling ultra-low temperature of liquid nitrogen in a laboratory, characterized in that: Using the laboratory liquid nitrogen ultra-low temperature control system as claimed in claim 8, the method comprises the following steps: The target temperature and temperature control parameters are set by an explosion-proof computer (5); Starting the pump (8) to drive the medium to circulate in the system; The PLC control system collects signals from temperature transmitter 1 (19), temperature transmitter 2 (34) and temperature transmitter 3 (36) in real time; If cooling is required, the PLC controls the opening of the liquid nitrogen outlet two-way valve (35) to adjust the liquid nitrogen flow rate; If the temperature needs to be increased, the PLC controls the power output of the electric heater (15); The system pressure is maintained stable through the expansion tank assembly (11) and the pressure relief bypass (14).

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