A temperature control device for cryogenic mechanical tests and its control method

Abstract

The present invention discloses a temperature control device for low-temperature mechanical tests, which includes a liquid nitrogen tank, a central control box and a test box. The liquid nitrogen tank is connected to the central control box through a first transport pipeline. The central control box and the test box are connected through a second transport pipeline and a reflux pipeline. A heating unit and a pressure sensor are arranged in the liquid nitrogen tank. A vacuum pump is arranged in the central control box, and the outlet end of the vacuum pump is connected to the port of the second transport pipeline. Semiconductor refrigeration chips are arranged on both the second transport pipeline and the reflux pipeline and the central control box. An air valve is arranged on the reflux pipeline. Temperature sensors are arranged in both the central control box and the test box. In this solution, the heating unit heats to generate liquid nitrogen vapor, which can achieve rapid refrigeration of the test box, and has a large low-temperature refrigeration range and precise temperature adjustment. And by adopting the methods of liquid nitrogen vapor circulation and refrigeration compensation, the temperature in the test box is always maintained at the set temperature, thereby providing a stable low-temperature environment for the test box.

Description

Technical Field

[0001] The present invention relates to the technical field of temperature control, and particularly relates to a temperature control device for low-temperature mechanical tests and a control method thereof. Background Art

[0002] Environmental test equipment can be used to simulate high and low temperature environments to monitor the reliability of engineering materials or test the basic mechanical properties of materials, so as to ensure that the engineering materials can exert their designed performance during actual use; the mechanical experiments of engineering materials in different temperature environments are also the main sources for obtaining important technical parameters in the field of materials research. For common mechanical property tests such as uniaxial compression, tension, and dynamics, they have some common points, that is, the experimental specimens are small, the test process is exposed to the air, and the conventional test devices cannot achieve the function of keeping the specimen at a certain ambient temperature during low-temperature performance tests.

[0003] Existing high-temperature environment equipment has been relatively mature, while a stable low-temperature environment is relatively difficult to achieve. Directly using traditional PID control and fuzzy control algorithms for temperature regulation is likely to result in a large overshoot and a long adjustment time; therefore, how to ensure the cooling rate and the stability of the ambient temperature in the environmental chamber is an extremely important issue. Summary of the Invention

[0004] Aiming at the above deficiencies of the prior art, the present invention provides a temperature control device for low-temperature mechanical tests and a control method thereof, which solves the problems of slow refrigeration and poor stability of the existing low-temperature environment control equipment.

[0005] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0006] In a first aspect, a temperature control device for low-temperature mechanical tests is provided, which includes a liquid nitrogen tank, a central control box, and a test chamber. The liquid nitrogen tank is connected to the central control box through a first transport pipeline, and the central control box and the test chamber are connected through a second transport pipeline and a return pipeline. A heating unit and a pressure sensor are arranged in the liquid nitrogen tank, a vacuum pump is arranged in the central control box, and the outlet end of the vacuum pump is connected to the port of the second transport pipeline. Semiconductor refrigerators are arranged at both the connection end of the second transport pipeline to the test chamber and the connection end of the return pipeline to the central control box. An air valve is arranged on the return pipeline, and a pressure relief valve is arranged at the top of the test chamber. Temperature sensors are arranged in both the central control box and the test chamber; the heating unit, the pressure sensor, the vacuum pump, the semiconductor refrigerators, the air valve, and the temperature sensors are all electrically connected to the control module.

[0007] The beneficial effects of adopting the above technical solution are as follows: Through the heating unit in this solution, liquid nitrogen in the liquid nitrogen tank can be evaporated to generate low-temperature liquid nitrogen vapor. Under the action of the vacuum pump, the liquid nitrogen vapor enters the test chamber after passing through the first transport pipeline, the central control box, and the second transport pipeline in sequence, thus realizing rapid refrigeration of the test chamber. At the same time, through the cooperation of the second transport pipeline and the return pipeline, the liquid nitrogen vapor can circulate between the central control box and the test chamber, and the cold loss during the circulation process is compensated by the semiconductor refrigeration sheet. After the test chamber reaches the set temperature, it is possible to stably maintain the temperature inside the test chamber without continuing to generate liquid nitrogen vapor, avoiding waste of liquid nitrogen while ensuring a stable low-temperature environment inside the test chamber.

[0008] Further, the first transport pipeline, the second transport pipeline, and the return pipeline are all silica gel hoses, and the outside of the silica gel hoses is covered with thermal insulation materials. Metal hoses are provided at both ends of the first transport pipeline, the second transport pipeline, and the return pipeline for passing through the inside of the liquid nitrogen tank, the central control box, and the test chamber.

[0009] The beneficial effects of adopting the above technical solution are as follows: The silica gel hose has a soft texture and good deformability, which is convenient for the movement of the liquid nitrogen tank, the central control box, and the test chamber. At the same time, it has a low thermal conductivity, minimizing the loss of cold energy to the greatest extent. The metal hose is used for connecting the silica gel hose to the liquid nitrogen tank, the central control box, and the test chamber respectively, avoiding pipeline damage caused by the brittleness of the silica gel tube at low temperatures. The thermal insulation material can effectively prevent excessive cold loss due to too large a temperature difference with the outside world.

[0010] Further, low-temperature sealant is applied to the connections between the metal hose and the liquid nitrogen tank, the central control box, and the test chamber respectively to ensure the airtightness of the pipeline connections.

[0011] Further, the upper end of the liquid nitrogen tank is open, and the opening is sealed with polyurethane foam. The front end of the first transport pipeline and the connecting wires of the heating unit and the pressure sensor are hermetically passed through the polyurethane foam.

[0012] The beneficial effects of adopting the above technical solution are as follows: The setting of the polyurethane foam makes the disassembly and assembly of the first transport pipeline, the heating unit, and the pressure sensor convenient. After the test is completed, the polyurethane foam can be removed, and the lid of the liquid nitrogen tank can be covered to realize the sealed storage of the liquid nitrogen tank.

[0013] Further, the pressure sensor and the heating unit are respectively arranged at the upper end and the lower end inside the liquid nitrogen tank, and the upper end of the liquid nitrogen tank is connected to the gas chamber; the gas chamber can store liquid nitrogen vapor for subsequent recycling.

[0014] Further, both the central control box and the test chamber are of double-layer shell structure, and a thermal insulation layer is provided in the hollow part between the double-layer shell structures, which is beneficial to the heat preservation and heat insulation of the central control box and the test chamber.

[0015] Second aspect, a control method for a temperature control device is provided, which includes the following steps:

[0016] S1: Turn on the vacuum pump, and when the air pressure monitored by the air pressure sensor drops to the set lower limit pressure, turn off the vacuum pump;

[0017] S2: Preset the set temperature for the low-temperature test in the test chamber;

[0018] S3: Turn on the heating unit. The liquid nitrogen vapor generated in the liquid nitrogen tank enters the central control box through the first transport pipeline. When the air pressure monitored by the air pressure sensor rises to the set upper limit pressure, turn on the vacuum pump. The liquid nitrogen vapor enters the test chamber through the second transport pipeline, and the hot air in the test chamber is discharged through the pressure relief valve. When the temperature in the test chamber drops to the set temperature, turn off the heating unit;

[0019] S4: Turn on the air valve and the semiconductor refrigeration chip. The liquid nitrogen vapor circulates between the central control box and the test chamber through the second transport pipeline and the return pipeline. After the semiconductor refrigeration chip compensates for the cold loss during the transportation of the liquid nitrogen vapor in the second transport pipeline and the return pipeline, the low-temperature mechanical test can be started.

[0020] Furthermore, the method for adjusting the set temperature includes the following steps:

[0021] A1: When it is necessary to lower the set temperature, then execute step A2; when it is necessary to raise the set temperature, then execute step A3;

[0022] A2: Close the air valve and the vacuum pump, and re-execute steps S2 - S4;

[0023] A3: Convert the current of the semiconductor refrigeration chip, and use the semiconductor refrigeration chip to heat the second transport pipeline and the return pipeline until the temperature in the test chamber rises to the new set temperature, then reset the current of the semiconductor refrigeration chip, and use the semiconductor refrigeration chip to continue to compensate for the cold loss of the second transport pipeline and the return pipeline.

[0024] Furthermore, the magnitude of the working voltage of the vacuum pump in step S3 is proportional to the difference between the set temperature and the temperature in the test chamber within a preset range.

[0025] The beneficial effects of adopting the above technical solutions are as follows: The vacuum pumps under different working voltages can transport the low-temperature working medium vapor into the test chamber at different rates. When the vacuum pump starts to operate at first, the working voltage is adjusted to the maximum to enable the maximum cooling rate in the test chamber. As the difference between the temperature inside the test chamber and the preset temperature continuously decreases, the working voltage of the vacuum pump is adjusted by the microcomputer module to a stable value, and at this time, the temperature in the test chamber is also stable at the preset target temperature. Description of the Drawings

[0026] Figure 1 This is a schematic structural diagram of the temperature control device of this solution.

[0027] Figure 2 This is a schematic process diagram of this solution.

[0028] Among them, 1. Liquid nitrogen tank; 2. Heating unit; 3. Pressure sensor; 4. Gas chamber; 5. Polyurethane foam; 6. Metal hose; 7. Thermal insulation material; 8. First transport pipeline; 9. Central control box; 10. Temperature sensor; 11. Vacuum pump; 12. Thermoelectric cooler; 13. Test chamber; 14. Pressure relief valve; 15. Gas valve; 16. Second transport pipeline; 17. Return pipeline; 18. Control module. Specific implementation manners

[0029] The following describes the specific implementation manners of the present invention to facilitate those skilled in the art of this technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation manners. For those of ordinary skill in the art of this technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions created using the concept of the present invention are within the scope of protection.

[0030] Embodiment 1

[0031] As Figure 1 shown, the temperature control device for low-temperature mechanical tests of this solution includes a liquid nitrogen tank 1, a central control box 9, and a test chamber 13. The liquid nitrogen tank 1 is connected to the central control box 9 through a first transport pipeline 8, and the central control box 9 and the test chamber 13 are connected through a second transport pipeline 16 and a return pipeline 17.

[0032] A pressure sensor 3 and a heating unit 2 are arranged in the liquid nitrogen tank 1, and the pressure sensor 3 and the heating unit 2 are respectively arranged at the upper and lower ends inside the liquid nitrogen tank 1. The heating unit 2 is in contact with the liquid nitrogen in the liquid nitrogen tank 1. When it starts, the temperature rises, and it can evaporate the liquid nitrogen to form low-temperature liquid nitrogen vapor. The pressure sensor 3 can monitor the pressure in the liquid nitrogen tank 1; the upper end of the liquid nitrogen tank 1 is connected to a gas chamber 4, and the gas chamber 4 can store the liquid nitrogen vapor for subsequent use.

[0033] A vacuum pump 11 is arranged in the central control box 9, and the outlet end of the vacuum pump 11 is connected to the port of the second transport pipeline 16. Thermoelectric coolers 12 are arranged at both the connection end of the second transport pipeline 16 to the test chamber 13 and the connection end of the return pipeline 17 to the central control box 9. A gas valve 15 is arranged on the return pipeline 17, a pressure relief valve 14 is arranged on the top of the test chamber 13, and temperature sensors 10 are arranged in both the central control box 9 and the test chamber 13; the heating unit 2, the pressure sensor 3, the vacuum pump 11, the thermoelectric cooler 12, the gas valve 15, and the temperature sensor 10 are all electrically connected to the control module 18.

[0034] The upper end of the liquid nitrogen tank 1 is open, and the opening is sealed with polyurethane foam 5. The front end of the first transport pipeline 8 and the connection lines of the heating unit 2 and the pressure sensor 3 are all hermetically penetrated through the polyurethane foam 5. The setting of the polyurethane foam 5 makes the disassembly and assembly of the first transport pipeline 8, the heating unit 2 and the pressure sensor 3 convenient. After the test is over, the polyurethane foam 5 can be removed, and the lid of the liquid nitrogen tank 1 can be covered to achieve the sealed storage of the liquid nitrogen tank 1. The central control box 9 and the test box 13 are both of double-layer shell structures, and a heat insulation layer is provided in the hollow part between the double-layer shell structures, which is beneficial to the heat insulation of the central control box 9 and the test box 13.

[0035] In this solution, the heating unit 2 can cause the liquid nitrogen in the liquid nitrogen tank 1 to evaporate to generate low-temperature liquid nitrogen vapor. Under the action of the vacuum pump 11, the liquid nitrogen vapor sequentially passes through the first transport pipeline 8, the central control box 9 and the second transport pipeline 16 and then enters the test box 13, so as to realize the rapid refrigeration of the test box 13, and the low-temperature refrigeration range is large. At the same time, through the cooperation of the second transport pipeline 16 and the return pipeline 17, the liquid nitrogen vapor can circulate between the central control box 9 and the test box 13, and the semiconductor refrigeration chip 12 compensates for the cold loss during the circulation process, so that after the test box 13 reaches the set temperature, it is not necessary to continue to generate liquid nitrogen vapor, and the temperature in the test box 13 can also be stably maintained, avoiding the waste of liquid nitrogen and ensuring a stable low-temperature environment in the test box 13.

[0036] Embodiment 2

[0037] Based on Embodiment 1, the preferred solution of this embodiment is that the first transport pipeline 8, the second transport pipeline 16 and the return pipeline 17 are all silica gel hoses, and the outside of the silica gel hoses is covered with a heat insulation material 7. Metal hoses 6 for penetrating into the liquid nitrogen tank 1, the central control box 9 and the test box 13 are provided at both ends of the first transport pipeline 8, the second transport pipeline 16 and the return pipeline 17, and low-temperature sealant is applied at the joints of the metal hoses 6 with the liquid nitrogen tank 1, the central control box 9 and the test box 13 respectively to ensure the airtightness of the pipeline joints. Among them, the texture of the silica gel hose is soft and the deformability is good, which is convenient for the movement of the liquid nitrogen tank 1, the central control box 9 and the test box 13. At the same time, the thermal conductivity is low, which minimizes the cold loss. The metal hose 6 is used for the connection of the silica gel hose with the liquid nitrogen tank 1, the central control box 9 and the test box 13 respectively, to avoid pipeline damage caused by the brittleness of the silica gel tube at low temperatures. The heat insulation material 7 can effectively prevent excessive cold loss caused by too large a temperature difference with the outside world.

[0038] Combining the above Embodiments 1-2, this solution also provides a control method for a temperature control device, which includes the following steps:

[0039] S1: Turn on the vacuum pump 11. When the air pressure monitored by the air pressure sensor 3 drops to the set lower limit pressure, turn off the vacuum pump 11. By using the pre-pumping method, the hot air in the liquid nitrogen tank 1 and the central control box 9 can be pre-extracted. At the same time, setting the lower limit pressure can prevent the liquid nitrogen from being extracted due to too low pressure.

[0040] S2: Preset the set temperature for the low-temperature test in the test chamber 13.

[0041] S3: Turn on the heating unit 2. A part of the liquid nitrogen vapor generated in the liquid nitrogen tank 1 is stored in the air chamber 4, and the other part enters the central control box 9 through the first transport pipeline 8. When the air pressure monitored by the air pressure sensor 3 rises to the set upper limit pressure, turn on the vacuum pump 11. The liquid nitrogen vapor enters the test chamber 13 through the second transport pipeline 16, and the hot air in the test chamber 13 is discharged through the pressure relief valve 14. When the temperature in the test chamber 13 drops to the set temperature, turn off the heating unit 2.

[0042] Among them, the magnitude of the working voltage of the vacuum pump 11 within the preset range is proportional to the difference between the temperature in the test chamber 13 and the set temperature. The vacuum pump 11 under different working voltages can transport the liquid nitrogen vapor to the test chamber 13 at different rates. When the vacuum pump 11 starts to operate at the beginning, the temperature difference is the largest, and the working voltage is adjusted to the maximum, so that the maximum cooling rate can be achieved in the test chamber 13. As the difference between the temperature in the test chamber 13 and the set temperature gradually decreases, the working voltage of the vacuum pump 11 is gradually lowered to a stable value by the control module 18, and finally the temperature in the test chamber 13 is stably maintained at the set temperature.

[0043] S4: Turn on the air valve 15 and the semiconductor refrigeration chip 12. Under the action of the vacuum pump 11, the liquid nitrogen vapor circulates between the central control box 9 and the test chamber 13 through the second transport pipeline 16 and the return pipeline 17. After the semiconductor refrigeration chip 12 compensates for the cold loss during the transportation of the liquid nitrogen vapor in the second transport pipeline 16 and the return pipeline 17, the low-temperature mechanical test can be started.

[0044] In particular, the central control box 9 of this solution is connected to the air chamber 4. The air chamber 4 can supply the liquid nitrogen vapor during the circulation process, and at the same time make the circulation volume of the whole liquid nitrogen vapor much higher than the amount of liquid nitrogen vapor in the experimental chamber, so that the temperature of the circulating liquid nitrogen vapor is not easy to change.

[0045] The adjustment method of the set temperature in this solution includes the following steps:

[0046] A1: When it is necessary to lower the set temperature, then execute step A2. When it is necessary to raise the set temperature, then execute step A3.

[0047] A2: Close the air valve 15 and the vacuum pump 11, and re - execute steps S2 - S4 to lower the temperature in the test chamber 13 to the new set temperature;

[0048] A3: Convert the current of the semiconductor refrigeration chip 12 through the current conversion circuit, and use the semiconductor refrigeration chip 12 to heat the second transport pipeline 16 and the return pipeline 17 until the temperature in the test chamber 13 rises to the new set temperature, then reset the current of the semiconductor refrigeration chip 12, and use the semiconductor refrigeration chip 12 to continue to perform refrigeration compensation on the second transport pipeline 16 and the return pipeline 17.

[0049] In summary, in this solution, the rapid refrigeration of the test chamber 13 can be achieved by heating the heating unit 2 to generate liquid nitrogen vapor, and the low - temperature refrigeration range is large, the controllability is strong, and the temperature regulation is accurate; and by adopting the liquid nitrogen vapor cycle and refrigeration compensation methods, the temperature in the test chamber 13 can always be maintained at the set temperature, and at the same time, the set temperature can be adjusted according to the requirements of low - temperature mechanical tests, and its practicability is strong.

Claims

1. A temperature control device for low-temperature mechanical tests, characterized in that, It includes a liquid nitrogen tank (1), a central control box (9) and a test chamber (13). The liquid nitrogen tank (1) is connected to the central control box (9) through a first transport pipeline (8). The central control box (9) and the test chamber (13) are connected through a second transport pipeline (16) and a return pipeline (17). A heating unit (2) and a pressure sensor (3) are arranged in the liquid nitrogen tank (1). A vacuum pump (11) is arranged in the central control box (9), and the outlet end of the vacuum pump (11) is connected to the port of the second transport pipeline (16). Semiconductor refrigeration chips (12) are arranged at the connection end of the second transport pipeline (16) with the test chamber (13) and the connection end of the return pipeline (17) with the central control box (9). An air valve (15) is arranged on the return pipeline (17). A pressure relief valve (14) is arranged at the top of the test chamber (13). Temperature sensors (10) are arranged in both the central control box (9) and the test chamber (13); The heating unit (2), the pressure sensor (3), the vacuum pump (11), the semiconductor refrigeration chip (12), the air valve (15) and the temperature sensor (10) are all electrically connected to a control module (18).

2. The temperature control device for cryogenic mechanical tests according to claim 1, characterized in that, The first transport pipeline (8), the second transport pipeline (16) and the return pipeline (17) are all silica gel hoses, and the outside of the silica gel hoses is covered with a heat insulation material (7). Metal hoses (6) for passing through the inside of the liquid nitrogen tank (1), the central control box (9) and the test chamber (13) are arranged at both ends of the first transport pipeline (8), the second transport pipeline (16) and the return pipeline (17).

3. The temperature control device for low-temperature mechanical tests according to claim 2, characterized in that Low-temperature sealant is filled at the connection parts of the metal hoses (6) with the liquid nitrogen tank (1), the central control box (9) and the test chamber (13) respectively.

4. The temperature control device for cryogenic mechanical tests according to claim 1, wherein, The upper end of the liquid nitrogen tank (1) is open, and the opening is blocked by polyurethane foam (5). The front end of the first transport pipeline (8) and the connecting wires of the heating unit (2) and the pressure sensor (3) are hermetically arranged on the polyurethane foam (5).

5. The temperature control device for cryogenic mechanical tests according to claim 1, characterized in that The pressure sensor (3) and the heating unit (2) are respectively arranged at the upper end and the lower end inside the liquid nitrogen tank (1), and the upper end of the liquid nitrogen tank (1) is connected to an air chamber (4).

6. The temperature control device for cryogenic mechanical tests according to claim 1, characterized in that, Both the central control box (9) and the test chamber (13) are of a double-layer shell structure, and a heat insulation layer is arranged in the hollow part between the double-layer shell structures.

7. The control method of the temperature control device for low-temperature mechanical tests according to any one of claims 1-6, characterized in that, It includes the following steps: S1: Turn on the vacuum pump (11), and when the pressure monitored by the pressure sensor (3) drops to the set lower limit pressure, turn off the vacuum pump (11); S2: Preset the set temperature for the low-temperature test of the test chamber (13); S3: Turn on the heating unit (2). The liquid nitrogen vapor generated in the liquid nitrogen tank (1) enters the central control box (9) through the first transport pipeline (8). When the pressure monitored by the pressure sensor (3) rises to the set upper limit pressure, turn on the vacuum pump (11). The liquid nitrogen vapor enters the test chamber (13) through the second transport pipeline (16), and the hot air in the test chamber (13) is discharged through the pressure relief valve (14). When the temperature in the test chamber (13) drops to the set temperature, turn off the heating unit (2); S4: Open the air valve (15) and the semiconductor refrigeration chip (12). The liquid nitrogen vapor circulates between the central control box (9) and the test chamber (13) through the second transport pipeline (16) and the reflux pipeline (17). After the semiconductor refrigeration chip (12) compensates for the cold loss during the transportation of the liquid nitrogen vapor in the second transport pipeline (16) and the reflux pipeline (17), the low-temperature mechanical test can be started.

8. The control method of the temperature control device for low-temperature mechanical tests according to claim 7, characterized in that The method for adjusting the set temperature includes the following steps: A1: When it is necessary to lower the set temperature, step A2 is executed; when it is necessary to raise the set temperature, step A3 is executed. A2: Close the air valve (15) and the vacuum pump (11), and re-execute steps S2 - S4. A3: Convert the current of the semiconductor refrigeration chip (12), and use the semiconductor refrigeration chip (12) to heat the second transport pipeline (16) and the reflux pipeline (17) until the temperature in the test chamber (13) rises to the new set temperature. Then reset the current of the semiconductor refrigeration chip (12), and use the semiconductor refrigeration chip (12) to continue compensating for the cold loss of the second transport pipeline (16) and the reflux pipeline (17).

9. The control method of the temperature control device for low-temperature mechanical tests according to claim 7, characterized in that, In step S3, the magnitude of the working voltage of the vacuum pump (11) within the preset range is proportional to the difference between the set temperature and the temperature in the test chamber (13).

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