System and method for testing mechanical property of material in ultralow-temperature high-pressure environment

Abstract

The invention discloses an ultralow-temperature high-pressure environment material mechanical property test system and method, the test system comprises a medium circulation system and a cold source supply system, the medium circulation system comprises a heat exchanger tube pass, a circulation pump and a test box, the heat exchanger tube pass, the circulation pump and the test box are connected in sequence, and a medium outlet of the test box is connected with a blow-down pipe; the cold source supply system comprises a heat exchanger shell pass, a first valve bank, a second valve bank, a gas-liquid mixer, a liquefied gas pump, a normal-temperature gas storage tank and a first liquefied gas storage tank, the heat exchanger shell pass accommodates the heat exchanger tube pass, an outlet of the first liquefied gas storage tank is connected to the first valve bank and the liquefied gas pump, and the liquefied gas pump is connected to the second valve bank. The first valve group and the second valve group are both connected to an inlet of the gas-liquid mixer, the second valve group is further connected to a pipeline where the circulating pump is located, an outlet of the gas-liquid mixer is connected to one end of the heat exchanger shell side, and the other end of the heat exchanger shell side is connected to the blow-down pipe through a discharge pipeline.

Description

Technical Field

[0001] The present invention belongs to the field of testing the mechanical properties of materials, and particularly relates to a testing system and method for the mechanical properties of materials in an ultra-low temperature and high-pressure environment. Background Art

[0002] The liquefaction temperatures of industrial gases under normal pressure are very low. For example, the temperature of liquid nitrogen is -196°C, the temperature of liquefied natural gas is -163°C, and the temperature of liquid hydrogen is -253°C. When developing pressure-bearing equipment related to the production, storage, and transportation of these cryogenic liquefied gases, such as liquid hydrogen storage tanks, on-vehicle cryogenic high-pressure hydrogen storage tanks, high-pressure liquid nitrogen pumps, etc., the first thing to do is to study the mechanical properties of materials at ultra-low temperatures.

[0003] Existing experimental devices for the low-temperature mechanical properties of materials can be roughly divided into two forms: liquid cooling and non-liquid cooling.

[0004] Liquid cooling means directly cooling the test environmental chamber with cryogenic liquefied gas. For example, the test environmental chamber is cooled with liquid nitrogen at -196°C, and the tensile specimen is immersed in the liquid nitrogen environment for tensile testing. The advantage of liquid cooling is that the temperature during the test process can be relatively stably controlled. The disadvantage is that the test can only be carried out at certain specific saturation temperature points corresponding to the liquefied gas, and the test temperature and pressure cannot be adjusted.

[0005] Non-liquid cooling means realizing the low-temperature environment of the test chamber in the form of an active refrigerator and refrigerant. For example, a GM refrigerator is usually used as the cold source. The advantage of non-liquid cooling is that the temperature and pressure environment required for the test can be conveniently adjusted. Its disadvantage is that the temperature and pressure in the environmental chamber cannot be accurately controlled during the test process. For the test in a liquid hydrogen or liquid helium environment with a temperature lower than -196°C, there is also a major defect in non-liquid cooling that the time required to achieve the required temperature and pressure environment of the test chamber is very long, and the test efficiency is low. In addition, the non-liquid cooling method cannot characterize the influence of the medium itself on the material properties. For example, for metal materials used to manufacture liquid hydrogen equipment, when tested in a non-liquid cooling device with helium as the refrigerant, the influence of the liquid hydrogen medium on the material, such as hydrogen embrittlement, cannot be characterized.

[0006] In addition, although a testing system for the mechanical properties of materials at low temperatures is mentioned in related designs, this system can use the liquefied gas in direct contact with the test material during actual application as the refrigeration cold source required for the experiment, solving the problem of low experimental efficiency existing in the traditional technology. However, since this technical solution fails to consider the strong coupling relationship between the temperature, pressure, and strength of the gas at low temperatures, it is difficult to accurately adjust the temperature and pressure simultaneously during the actual operation process due to the mutual influence of temperature and pressure and uneven liquid filling. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiencies existing in the prior art and provide a mechanical property testing system and method for materials in an ultra-low temperature and high-pressure environment.

[0008] To solve the technical problem, the solution of the present invention is as follows: On the one hand, the present application provides a mechanical property testing system for materials in an ultra-low temperature and high-pressure environment, including: a medium circulation system and a cold source supply system. The medium circulation system includes a heat exchanger tube side, a circulation pump, and a test chamber. The test chamber is suitable for accommodating a universal testing machine for mechanical tests. The heat exchanger tube side, the circulation pump, and the test chamber are connected in sequence. The medium outlet of the test chamber is connected to a vent pipe. The cold source supply system includes a heat exchanger shell side, a first valve group, a second valve group, a gas-liquid mixer, a liquefied gas pump, a normal temperature gas storage tank, and a first liquefied gas storage tank. The heat exchanger shell side houses the heat exchanger tube side. The outlet of the first liquefied gas storage tank is respectively connected to the first valve group and the liquefied gas pump. The liquefied gas pump is connected to the second valve group. Both the first valve group and the second valve group are connected to the inlet of the gas-liquid mixer. The second valve group is also connected to the pipeline where the circulation pump is located. The outlet of the gas-liquid mixer is connected to one end of the heat exchanger shell side. The other end of the heat exchanger shell side is connected to the vent pipe through a discharge pipeline. The heat exchanger shell side and the heat exchanger tube side form a countercurrent heat exchange.

[0009] According to an embodiment of the present application, the cold source supply system further includes a second liquefied gas storage tank. The outlet of the second liquefied gas storage tank and the outlet of the first liquefied gas storage tank are both connected to a first reversing valve. The first reversing valve is also respectively connected to the first valve group and the liquefied gas pump. Among them, the second liquefied gas storage tank is equipped with a GM refrigerator and a low-temperature thermostat.

[0010] According to an embodiment of the present application, the media in the normal temperature gas storage tank, the first liquefied gas storage tank, and the second liquefied gas storage tank are the same substance.

[0011] According to an embodiment of the present application, the heat exchanger shell side has a cylindrical tank structure, and the heat exchanger tube side is configured as a spiral tube structure disposed inside the tank structure.

[0012] According to an embodiment of the present application, a fully enclosed hollow inner cylinder is provided inside the heat exchanger shell side, and the spiral tube structure is arranged around the hollow inner cylinder.

[0013] According to an embodiment of the present application, the test chamber includes a box body and a door body. The door body is connected to the box body through a dynamic sealing structure with three-stage spring energy storage.

[0014] According to an embodiment of the present application, a thermometer and a pressure sensor are provided inside the test chamber, a safety valve is provided on the test chamber, and the medium outlet of the test chamber is connected to a vent pipe through the safety valve.

[0015] According to an embodiment of the present application, a thermometer and a flow meter are provided at the outlet of the normal temperature gas storage tank, and a pressure reducing valve is equipped at the outlet of the gas-liquid mixer.

[0016] According to an embodiment of the present application, a first pressure control valve is provided on the pipeline between the tube side of the heat exchanger and the vent pipe, a second pressure control valve is provided on the vent pipe, and a stop valve is provided on the pipeline between the test chamber and the tube side of the heat exchanger.

[0017] According to an embodiment of the present application, the end of the vent pipe is connected to an exhaust gas recovery device.

[0018] On the other hand, the present application proposes a method for testing the mechanical properties of materials in an ultra-low temperature and high-pressure environment. This testing method is applied to the above-mentioned testing system for the mechanical properties of materials in an ultra-low temperature and high-pressure environment. The testing method includes: Adjust the first valve group to transport the normal temperature gaseous medium in the normal temperature gas storage tank to the test chamber through a liquefied gas pump to provide a circulating medium for the test chamber. Adjust the second valve group to allow the liquid medium in the first liquefied gas storage tank to enter the shell side of the heat exchanger through a gas-liquid mixer. Start the circulation pump, and the medium in the test chamber exchanges heat with the medium in the shell side of the heat exchanger in the tube side of the heat exchanger, so that the circulating medium in the test chamber becomes the experimental target medium.

[0019] According to an embodiment of the present application, if the density of the experimental target medium is lower than the corresponding density of the normal temperature gas under the design pressure of the test chamber, by adjusting the pressure of the gas already filled in the circulation system, the gas density is made to be consistent with the density of the experimental target medium. If the density of the experimental target medium is equal to or higher than the corresponding density of the normal temperature gas under the design pressure of the test chamber, density adjustment needs to be carried out by combining temperature reduction and pressure supplementation.

[0020] According to an embodiment of the present application, the density adjustment by combining temperature reduction and pressure supplementation includes: First, connect the normal temperature gas storage tank and the liquefied gas storage tank to the gas-liquid mixer simultaneously to form a cold source with controllable temperature, introduce the cold source into the shell side of the heat exchanger to exchange heat with the circulating medium in the tube side of the heat exchanger to lower its temperature, and the pressure of the circulating medium will decrease simultaneously with the temperature. Use the normal temperature gas in the normal temperature gas storage tank to supplement the pressure of the circulating medium, and then continue to lower the temperature. Through multiple operations of pressure supplementation and temperature reduction, the density of the medium in the circulation system is made to be consistent with the density of the experimental target medium.

[0021] According to an embodiment of the present application, the testing method further includes a rewarming operation after the test experiment: Discharge the circulating medium from the test chamber to the vent pipe, and then connect the normal temperature gas storage tank to the medium circulation system to inject normal temperature gas into the medium circulation system; Start the circulation pump to circulate the normal temperature gas in the medium circulation system until the rewarming of the metal wall surface of the test chamber and the shell side of the heat exchanger is completed.

[0022] Compared with the prior art, the beneficial effects of the present application are as follows: 1. Compared with the traditional liquidless cooling method, the present application can use the liquefied gas that is directly in contact with the test material during actual application as the refrigeration cold source required for the test, thereby solving the problem of low test efficiency existing in the use of an active refrigerator in the liquidless cooling method. At the same time, since the test system can be placed in the medium corresponding to the service conditions, the influence of the medium on the material can be considered.

[0023] 2. Compared with the traditional liquid cooling method, the present invention controls the temperature and pressure conditions required for the test by setting a heat exchanger. Since the heat exchanger is large enough compared to the volume of the test chamber and has a large enough heat transfer area. If there are fluctuations in pressure and temperature during the test process, the temperature control power can increase as the temperature rises. Although there is a coupling situation of temperature and pressure changes for high-pressure gas at low temperatures, this solution realizes a one-to-one mapping relationship between temperature and pressure of the gas or liquefied gas at a specific density by determining the density of the gas or liquefied gas in the test chamber, thereby solving the problem that it is difficult to adjust temperature and pressure simultaneously. Therefore, the present invention can stably control the temperature and pressure of the test chamber and can withstand a large heat load, solving the problem of temperature and pressure coupling and instability in the existing liquid cooling low-temperature test device.

[0024] 3. The ultra-low temperature and high-pressure material performance testing system provided by the present invention can use a gas-liquid mixer and a heat exchanger to control the temperature and pressure of the liquefied gas or the gas after gasification. Therefore, this system can not only cover most of the process conditions in the existing hydrogen liquefaction or helium liquefaction devices in research work, but also provide test conditions in the low-temperature gaseous application scenario. Thus, the test requirements of materials under various typical medium, temperature, and pressure combination conditions are realized, solving the problem that the existing liquid cooling test device can only conduct tests at specific temperature points and pressure points.

[0025] 4. In the ultra-low temperature and high-pressure material performance testing system of the present invention, the configured equipment form, cold insulation technology, and liquefied gas circulation equipment can all adopt existing mature technologies; therefore, the overall system construction cost is low, and it has very good feasibility and is suitable for widespread promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] To more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 It is a schematic diagram of a mechanical property test system for materials in an ultra-low temperature and high-pressure environment according to an embodiment of the present application; Figure 2 It is a schematic diagram of the structure of the shell side and the tube side of a heat exchanger according to an embodiment of the present application; Figure 3 It is a flowchart of a method for testing the mechanical properties of materials in an ultra-low temperature and high-pressure environment according to an embodiment of the present application.

[0028]

Description of the reference numerals

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0030] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs; the terms used in the description of the present application in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "including" and "having" and any variations thereof in the specification and claims of the present application and the above drawings are intended to cover non-exclusive inclusion. The terms "first", "second", etc. in the specification and claims of the present application or the above drawings are used to distinguish different objects and are not used to describe a specific order or primary-secondary relationship.

[0031] References to "embodiments" in this application mean that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described in this application can be combined with other embodiments.

[0032] In the description of this application, it should be noted that unless otherwise clearly specified and limited, the terms "install", "connect", "couple", and "attach" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0033] The term "and / or" in this application is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this application generally represents an "or" relationship between the associated objects before and after.

[0034] The term "a plurality of" appearing in this application refers to two or more (including two). Similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of sheets" refers to two or more sheets (including two sheets).

[0035] Description of the inventive principle: 1. In related technical solutions, the cold source in the cold source storage tank is first introduced into the temperature and pressure regulation chamber, and then the temperature and pressure are increased through the normal temperature gas storage tank; during the test, the internal pressure is stabilized through a pressure control valve, and the temperature in the temperature and pressure regulation chamber is adjusted through the cold source storage tank. The most prominent drawback of this technical solution is that it does not consider the coupling relationship between the temperature and pressure of the low-temperature gas. During the actual operation process, due to the mutual influence of temperature and pressure, and the uneven filling phenomenon of the liquid in the temperature and pressure regulation chamber (this unevenness is particularly obvious when far from the boiling point of the cold source), it is difficult to adjust the filling speed of the cold source storage tank, further resulting in an unclear control logic of the liquid pump during the design of the control system, and also posing high requirements for the layout method of the temperature sensors.

[0036] In this application, the applicant proposes an innovative solution. First, a normal-temperature gas storage tank is connected to the tube side of the heat exchanger to inject normal-temperature gas into the medium circulation system. Relying on the pressure difference between the normal-temperature gas storage tank, the test chamber, and the tube side of the heat exchanger, the gas in the circulation system is pressurized to adjust the density of the gas to be consistent with the operating conditions required for the test, and then cooling continues. Or, according to the situation where the pressure of the circulating medium decreases simultaneously with the temperature, the pressure is replenished, and then the density of the gas is adjusted to be consistent with the operating conditions required for the test, and then cooling continues. This solution takes into account and utilizes the coupling relationship between temperature and pressure. Based on the principle of mass conservation, when the temperature is adjusted, the pressure of the circulating medium is also adjusted simultaneously.

[0037] During the test process of this application, by mixing normal-temperature gas and liquid through a gas-liquid mixer, the cold source in the shell side of the heat exchanger can be maintained at the temperature required by the test, and stepless temperature adjustment within a large temperature range can be achieved through heat exchange with the circulating medium in the tube side. This temperature adjustment solution is simple and mature and can maintain good accuracy.

[0038] 2. In related technical solutions, to maintain the stability of the temperature and pressure in the test chamber, the designed volume of the temperature and pressure adjustment chamber needs to be large enough. This temperature and pressure adjustment chamber is essentially a spiral tube heat exchanger. If the shell side of the heat exchanger is to withstand high internal pressure and the tube side is to withstand high external pressure, when using S31608 material, the wall thickness is very thick. Not only is the processing of the spiral tube difficult, but also due to the large wall thickness of the temperature and pressure adjustment chamber, a large amount of cooling capacity is required for cooling. If liquefied gas is used for cooling, a large amount of liquid hydrogen is required to make the temperature of the temperature and pressure adjustment chamber reach the corresponding temperature range, and the cost of a single test is extremely high. And in fact, only the temperature and pressure conditions of hydrogen in the test chamber need to be maintained, and most of the cooling capacity in the temperature and pressure adjustment chamber is wasted on the cooling wall surface, and it will also cause difficulties in the rewarming process after the test.

[0039] In the solution of this application, only the tube side of the heat exchanger withstands high internal pressure; and because its diameter is small, the wall thickness does not need to be too thick; at the same time, the shell side of the heat exchanger only needs to withstand a relatively low design pressure, and the wall thickness can be significantly reduced compared to the original solution considering a relatively conservative safety factor. On the other hand, since only the outlet temperature of the tube side of the heat exchanger needs to be controlled, the volume of the shell side of the heat exchanger does not need to be very large. Even a fully enclosed hollow inner cylinder with a relatively low wall thickness requirement can be placed inside it to reduce the volume of the shell side, which not only simplifies the processing technology but also avoids waste of cooling capacity.

[0040] 3. In related technical solutions, the influence of the work done by the high-pressure liquid pump on the liquid temperature is not considered, resulting in the inability to achieve most key operating conditions. Taking liquid hydrogen as an example, in fact, when using a liquid hydrogen pump to pressurize liquid hydrogen to a high pressure, a large amount of heat will be input into the liquid hydrogen. This influence is small in the scenario of a large flow rate and a high-power GM refrigerator in a hydrogen refueling station. However, in the circulating pump or liquid hydrogen pump in the laboratory test scenario, the flow rate is small, and the influence of the heat introduced by the pump operation cannot be ignored and will become the main influence. Therefore, for the tests of a large number of key operating conditions such as high-pressure tests in the range of temperature 33K - 50K and pressure 35 - 45MPa (this test corresponds to the truck transportation use scenario of low-temperature high-pressure hydrogen), due to the influence of the circulating pump or liquid hydrogen pump, it has become impossible to achieve. Moreover, pumps with a large pressure and a small flow rate need to be customized and are expensive.

[0041] In this application, the liquefied gas pump is not directly used to adjust the circulating medium to a high pressure; instead, innovatively, the combination of a gas-liquid mixer and a heat exchanger is used to exchange heat between a cold source with controllable temperature and the hydrogen for high-pressure tests, ultimately achieving temperature and pressure adjustment. Considering that even using a low-pressure liquefied gas pump will generate a certain amount of heat, this application further proposes to set up a liquefied gas storage tank equipped with a GM refrigerator and a cryostat, and a small-power GM refrigerator is used to give a certain degree of subcooling to the liquefied gas in the storage tank, so as to meet the requirements of tests under extreme conditions such as a temperature of 20K. At the same time, on the premise of maintaining the circulation, the flow rate of the circulating pump is gradually reduced to reduce the introduced heat until the temperature of the medium in the test chamber reaches the experimental target value.

[0042] 4. The solution of this application breaks through the conventional technical thinking and is not restricted to the usual experimental experience of adjusting the temperature and pressure of the test chamber simultaneously; instead, the high-pressure gas in the normal-temperature gas storage tank is used to inject the experimental medium into the circulation system for pressure regulation and pressure supplementation, realizing the density control of the medium in the test chamber, and then the temperature control in the heat exchanger is used to further control the temperature of the experimental medium, thus solving the problem of gas temperature and pressure coupling at low temperatures that is difficult to avoid in traditional test technologies. Therefore, in the solution of this application, since the density of the medium remains unchanged, the medium pressure will decrease simultaneously with the temperature. When the temperature of the medium in the test chamber is adjusted, the pressure will definitely be adjusted simultaneously. Since the entire adjustment process is a steady and smooth transition, the situation of frequently opening and closing the safety valve will not occur, reducing the problem of heat leakage in the test chamber.

[0043] 5. In traditional temperature and pressure control schemes, whether using a temperature and pressure regulating chamber or a heat exchanger, the main purpose is only to consider achieving temperature reduction, and the pressure control is achieved by a separate liquid pump, without ever considering the strong coupling relationship between the temperature and pressure of the experimental medium under low-temperature conditions. Although the scheme of this application also uses a conventional shell-and-tube heat exchanger, while using the heat exchanger to achieve the conventional use of cooling high-temperature gas with low-temperature liquid, the present invention further breaks through the conventional thinking. By cooperating with a gas-liquid mixer and taking advantage of the large volume difference between the tube side and the shell side, during the cooling process, through the liquefied gas rapid cooling test chamber, and during the mechanical experiment, by changing the gas-liquid mixing ratio in the gas-liquid mixer to control the temperature of the shell side of the temperature and pressure regulating chamber, thereby achieving stepless regulation of the temperature of the test chamber during the experiment.

[0044] 6. In traditional cooling schemes, there are also cases where a GM refrigeration unit and heating resistors are directly used to adjust the temperature of the experimental medium. However, such schemes are not suitable for high-pressure gas environment tests. On the one hand, it is dangerous to electrically heat a part of the high-pressure gas. On the other hand, due to the need to achieve high-pressure conditions, the wall thickness of the test chamber is greatly thickened, so the heat capacity is large. The disadvantage of the GM refrigeration machine is that its refrigeration efficiency is low when below the liquid temperature range, so the test time required is further extended; if the time needs to be shortened, existing schemes often increase the number of GM refrigeration machines or use liquid cooling, resulting in a further increase in the comprehensive experimental cost.

[0045] For working conditions where the temperature is close to or lower than the boiling point of the target medium, this scheme innovatively proposes to adopt a hierarchical cooling strategy. First, use the liquid in the low-pressure liquefied gas storage tank to cool the experimental medium; then use the liquid in the liquefied gas storage tank equipped with a GM refrigeration unit and a low-temperature thermostat to further cool the experimental medium. Since the heat leakage of the liquefied gas storage tank is much smaller than that of the cold source supply system and the medium circulation system, the scheme of this application can, while ensuring the cooling rate, greatly reduce the requirement for the refrigeration power of the GM refrigeration machine and further reduce the comprehensive experimental cost.

[0046] This application proposes a mechanical property testing system for materials in an ultra-low temperature and high-pressure environment. The system includes a medium circulation system and a cold source supply system. Among them, the medium circulation system includes the tube side 12 of the heat exchanger, a circulation pump 10, and a test chamber 17. The test chamber 17 is suitable for accommodating a universal testing machine for mechanical tests. The tube side 12 of the heat exchanger, the circulation pump 10, and the test chamber 17 are connected in sequence. The medium outlet of the test chamber 17 is connected to a vent pipe 18; The test chamber 17 is suitable for carrying a universal testing machine for mechanical tests in its inner cavity. The test chamber 17 has a double-layer box structure, with a spacing maintained between the two layers of boxes and a vacuum maintained. A medium outlet and a medium inlet are respectively provided on the top and bottom panels of the box structure. The universal testing machine carried inside the test chamber 17 can perform mechanical tests such as tension, compression, and fracture toughness by changing the fixtures.

[0047] As an alternative, to reduce heat leakage and avoid air leakage, the door body of the test chamber 17 adopts a dynamic sealing structure with three-stage spring energy storage. Specifically, the test chamber 17 can include a box body and a quick-opening flat cover, and the quick-opening flat cover can be connected to the box body through a dynamic sealing structure with three-stage spring energy storage.

[0048] A thermometer and a pressure sensor are provided inside the test chamber 17, and a safety valve is provided on the test chamber 17. The medium outlet of the test chamber 17 can be connected to the safety valve, and the safety valve is connected to the vent pipe 18 through a pipeline. When the pressure inside the test chamber 17 exceeds the limit, the test medium will be quickly discharged through the safety valve to prevent the test chamber 17 from failing.

[0049] The test chamber 17, the circulation pump 10, and the tube side 12 of the heat exchanger are connected by pipelines to form a circulation loop, thereby obtaining a medium circulation system. The medium outlet of the test chamber 17 can be connected to the vent pipe 18 through an outlet pipeline, and the end of the vent pipe 18 can be connected to the waste gas recovery device 16, and the waste gas recovery device 16 can carry an air-bath type vaporizer.

[0050] The cold source supply system can include the shell side 11 of the heat exchanger, the first valve group 4, the second valve group 7, the gas-liquid mixer 8, the liquefied gas pump 6, the normal temperature gas storage tank 3, and the first liquefied gas storage tank 1. The shell side 11 of the heat exchanger houses the tube side 12 of the heat exchanger. The shell side 11 of the heat exchanger housing the tube side 12 of the heat exchanger can form a complete heat exchanger, and this heat exchanger can be a spiral tube heat exchanger.

[0051] The outlet of the first liquefied gas storage tank 1 is respectively connected to the first valve group 4 and the liquefied gas pump 6. The liquefied gas pump 6 is connected to the second valve group 7. Both the first valve group 4 and the second valve group 7 are connected to the inlet of the gas-liquid mixer 8. The second valve group 7 is also connected to the pipeline where the circulation pump 10 is located. The outlet of the gas-liquid mixer 8 is connected to one end of the shell side 11 of the heat exchanger. The other end of the shell side 11 of the heat exchanger is connected to the vent pipe 18 through a discharge pipeline. The shell side 11 of the heat exchanger and the tube side 12 of the heat exchanger perform countercurrent heat exchange. That is to say, the flow direction of the medium inside the shell side 11 of the heat exchanger and the flow direction of the medium inside the tube side 12 of the heat exchanger can be opposite.

[0052] In some embodiments of the present application, the cooling supply system further includes a second liquefied gas storage tank 2. The outlet of the second liquefied gas storage tank 2 and the outlet of the first liquefied gas storage tank 1 are both connected to a first reversing valve 5, and the first reversing valve 5 is also respectively connected to a first valve group 4 and a liquefied gas pump 6; wherein, the second liquefied gas storage tank 2 is equipped with a GM refrigerator and a low-temperature thermostat.

[0053] The outlet pipeline of the first liquefied gas storage tank 1 and the outlet pipeline of the second liquefied gas storage tank 2 can be connected in parallel to the first reversing valve 5. The pipeline after the first reversing valve 5 can be divided into two paths. One path is connected to the first valve group 4 on the outlet pipeline of the normal-temperature gas storage tank 3, and the other path is connected to the second valve group 7 through the liquefied gas pump 6; the first valve group 4 is also respectively connected to the inlet of a gas-liquid mixer 8 through a pipeline; the second valve group 7 is also respectively connected to the inlet of the gas-liquid mixer 8 and the pipeline where a circulation pump 10 is located through a pipeline; the outlet of the gas-liquid mixer 8 is connected to one end of the shell side 11 of a heat exchanger through a pipeline, and the other end of the shell side 11 of the heat exchanger is connected to a vent pipe 18 through a discharge pipeline. The shell side 11 of the heat exchanger and the tube side 12 of the heat exchanger form a countercurrent heat exchange.

[0054] As an alternative, the shell side 11 of the heat exchanger has a cylindrical tank structure, and inlets and outlets are respectively arranged on the two end heads thereof. The tube side 12 of the heat exchanger is a spiral tube structure arranged inside the shell side 11 of the heat exchanger, and inlets and outlets connecting the tube side 12 of the heat exchanger are arranged on the shell side 11 of the heat exchanger in a centrosymmetric manner; a fully enclosed hollow inner cylinder 19 is nested inside the spiral tube structure, and the spiral tube structure can be arranged around the hollow inner cylinder 19 to further reduce the volume for accommodating the cold medium in the shell side 11 of the heat exchanger, reduce the consumption of the cold source, and can avoid short-circuit flow and uneven flow, improving the heat exchange efficiency. The thickness of the tube side of the spiral tube heat exchanger structure needs to meet the strength requirements, the radial dimension of the spiral coil needs to meet the design specifications, and the spiral tube needs to ensure a certain heat exchange area to achieve heat exchange of a certain power, ensuring that the test cooling time will not be too long. A first pressure control valve 13 can be arranged on the pipeline between the tube side 12 of the spiral tube heat exchanger and the vent pipe 18; a second pressure control valve 14 can be arranged on the vent pipe 18; a stop valve 15 can be arranged on the pipeline between the test chamber 17 and the tube side 12 of the spiral tube heat exchanger. The circulation pump 10 can adopt a plunger-type high-pressure diaphragm pump to ensure the circulation of experimental media with different components; and the flow rate of the circulation pump should be adjustable, and during the mechanical test, the flow rate can be reduced while maintaining the circulation, minimizing the heat leakage during the test and reducing the consumption of the cold source.

[0055] As an alternative, the normal-temperature gas storage tank 3 can be a spherical storage tank, with the internal gas pressure much greater than the highest pressure required for the test, and the volume is sufficient to provide sufficient normal-temperature high-pressure gas to the test chamber 17; a thermometer and a flowmeter can be provided at the outlet of the normal-temperature gas storage tank 3, and the real-time density of the liquefied gas or gas in the test chamber 17 can be obtained through the flow formula by measuring the flow rate at the outlet. A pressure reducing valve can be equipped at the outlet of the gas-liquid mixer 8; the circulation pump 10 is a diaphragm reciprocating pump; a check valve 9 can be provided on the pipeline between the circulation pump and the tube side 12 of the heat exchanger. The pressure reducing valves inside the first valve group 4 and the second valve group 7 can be used to reduce the pressure of the gas or liquefied gas to the required pressure. The volumes of the first liquefied gas storage tank 1 and the second liquefied gas storage tank 2 are both much larger than the volume of the test chamber, and the liquefied gas in the tanks is directly provided by the liquid-making equipment, with low requirements for subcooling degree. The GM refrigeration unit can complete the cooling of the liquefied gas within a certain period of time and overcome the heat leakage of the storage tank itself through the cryostat. When cooling the system, first, the liquefied gas storage tank at a higher temperature provides the cooling capacity. When the temperature cannot continue to drop, the liquefied gas storage tank at a lower temperature equipped with a set of GM refrigerators and a cryostat further provides the cooling capacity to reach the temperature required for the test. The temperature of the cold source at the outlet can be adjusted by regulating the pressure and flow rate of the liquefied gas and gas at the inlet of the gas-liquid mixer; by using the pressure reducing valves in the valve group and equipping a pressure reducing valve at the outlet of the liquefied gas pump, it can be ensured that the liquefied gas or gas flowing into the shell side 11 of the heat exchanger does not exceed the design pressure.

[0056] The present application also provides a method for testing the mechanical properties of materials in an ultra-low temperature and high-pressure environment. This testing method is applied to the above-mentioned testing system for the mechanical properties of materials in an ultra-low temperature and high-pressure environment, and the testing method includes: Adjust the first valve group to transport the normal-temperature gaseous medium in the normal-temperature gas storage tank to the test chamber through the liquefied gas pump to provide a circulating medium for the test chamber; Adjust the second valve group to make the liquid medium in the first liquefied gas storage tank enter the shell side of the heat exchanger through the gas-liquid mixer; Start the circulation pump, and the medium in the test chamber exchanges heat with the medium in the shell side of the heat exchanger in the tube side of the heat exchanger, so that the circulating medium in the test chamber becomes the experimental target medium.

[0057] It should be noted that when the normal-temperature gaseous medium in the normal-temperature gas storage tank 3 first enters the test chamber 17, since the temperature and pressure do not meet the requirements, it is a common medium at this time. After cooling and pressurization, the temperature and pressure meet the conditions, and the medium in the test chamber 17 becomes the experimental target medium. At this time, various performance manifestations of the material in the test chamber 17 can be tested.

[0058] According to some embodiments of the present application, if the density of the experimental target medium is lower than the corresponding density of the normal-temperature gas at the designed pressure of the test chamber 17, the pressure of the gas already filled in the circulation system is adjusted to make the gas density consistent with the density of the experimental target medium; if the density of the experimental target medium is equal to or higher than the corresponding density of the normal-temperature gas at the designed pressure of the test chamber 17, density adjustment needs to be carried out by combining temperature reduction and pressure compensation.

[0059] According to some embodiments of the present application, the density adjustment by combining temperature reduction and pressure compensation includes: First, the normal-temperature gas storage tank 3 and the first liquefied gas storage tank 1 are simultaneously connected to the gas-liquid mixer 8 to form a cold source with controllable temperature. The cold source is introduced into the shell side 11 of the heat exchanger to exchange heat with the circulating medium in the tube side 12 of the heat exchanger to reduce its temperature. The pressure of the circulating medium will decrease simultaneously with the temperature. The normal-temperature gas in the normal-temperature gas storage tank 3 is used to compensate the pressure of the circulating medium, and then the temperature is continuously reduced. Through multiple operations of pressure compensation and temperature reduction, the density of the medium in the circulation system is made consistent with the density of the experimental target medium.

[0060] According to some embodiments of the present application, the test method further includes the rewarming operation after the experiment: The circulating medium is discharged from the test chamber 17 to the vent pipe 18, and then the normal-temperature gas storage tank 3 is connected to the medium circulation system to fill the medium circulation system with normal-temperature gas. The circulation pump 10 is started to make the normal-temperature gas circulate in the medium circulation system until the metal wall surface of the test chamber 17 and the shell side of the heat exchanger are rewarmed.

[0061] A cold source supply system is constructed by using the shell side 11 of the heat exchanger, the gas-liquid mixer 8, the normal-temperature gas storage tank 3, the liquefied gas pump 6 and at least one liquefied gas storage tank (the first liquefied gas storage tank 1 and / or the second liquefied gas storage tank 2) to provide the experimental target medium and serve as the cold source for heat exchange; a medium circulation system is constructed by using the test chamber 17, the circulation pump 10 and the tube side 12 of the heat exchanger to cool the circulating medium through heat exchange; the experimental target medium and the cold source are the same substance, and its state is gaseous, liquid or supercritical fluid.

[0062] Connect the normal-temperature gas storage tank 3 to the tube side 12 of the heat exchanger and the test chamber 17, fill the medium circulation system with normal-temperature gas, and pressurize the already filled gas depending on the pressure difference between the normal-temperature gas storage tank 3 and the medium circulation system. If the density of the experimental target medium is lower than the corresponding density of the normal-temperature gas at the design pressure of the test chamber, adjust the pressure of the gas charged in the circulation system to make the gas density consistent with the density of the experimental target medium; if the density of the experimental target medium is equal to or higher than the corresponding density of the normal-temperature gas at the design pressure of the test chamber 17, density adjustment needs to be carried out by combining temperature reduction and pressure compensation: first, simultaneously connect the normal-temperature gas storage tank 3 and the liquefied gas storage tank (the first liquefied gas storage tank 1 or / and the second liquefied gas storage tank 2) to the gas-liquid mixer 8 to form a cold source with controllable temperature, introduce the cold source into the shell side 11 of the heat exchanger to exchange heat with the circulating medium in the tube side 12 of the heat exchanger to reduce its temperature; the pressure of the circulating medium will decrease simultaneously with the temperature; use the normal-temperature gas in the normal-temperature gas storage tank 3 to compensate the pressure of the circulating medium, and then continue to reduce the temperature; through multiple pressure compensation and temperature reduction operations, the density of the medium in the circulation system is finally made consistent with the density of the experimental target medium; Control the ratio of the gas and liquefied gas entering the gas-liquid mixer 8 to keep the temperature in the shell side 11 of the heat exchanger consistent with the experimental target temperature; gradually reduce the flow rate of the circulation pump 10 under the premise of maintaining circulation to reduce the introduced heat until the medium temperature in the test chamber 17 reaches the experimental target value; since the density of the medium in the circulation system remains unchanged, based on the principle of mass conservation, the adjustment of the medium temperature and pressure can be completed simultaneously.

[0063] The rewarming operation after the test: first, discharge the circulating medium from the test chamber 17 to the vent pipe 18; then connect the normal-temperature gas storage tank 3 to the medium circulation system and charge normal-temperature gas into the system; start the circulation pump 10 to make the normal-temperature gas circulate in the medium circulation system until the rewarming of the metal wall surface of the test chamber 17 and the shell side of the heat exchanger is completed.

[0064] The present invention is applicable to a variety of experimental conditions, and the experimental target medium can be hydrogen, liquid hydrogen or supercritical hydrogen fluid, or nitrogen, liquid nitrogen or supercritical nitrogen fluid. During the process of adjusting the density of the experimental medium, when pressurizing or compensating the pressure, hydrogen or nitrogen stored in the normal-temperature gas storage tank is used, and the pressure range can be selected from 50 to 98 MPa. There are two liquefied gas storage tanks, one of which provides liquid hydrogen (such as temperature 22K), liquid nitrogen (such as temperature 80K) or liquefied natural gas (such as temperature 115K); the other is equipped with a GM refrigerator and a low-temperature thermostat, and provides liquid hydrogen with a relatively lower temperature (such as temperature 18K), liquid nitrogen (such as temperature 75K) or liquefied natural gas (such as temperature 105K); in the case of extremely low temperature experimental conditions, first use the liquid with a higher temperature to cool the medium in the circulation system, and then use the liquid with a lower temperature to cool it.

[0065] Specific application examples under different experimental conditions.

[0066] Example 1: Target medium and conditions: medium is hydrogen gas, pressure is 5 MPa, and temperature is 100 K; 1. Preparation stage: (1) Standby of normal-temperature high-pressure gas: Hydrogen is supplemented to the normal-temperature gas storage tank 3 through an external compressor to reach the designed pressure.

[0067] (2) Purge and discharge air: Adjust the first valve group 4 and the second valve group 7, open the first pressure control valve 13 and the second pressure control valve 14, and use the normal-temperature hydrogen in the normal-temperature gas storage tank 3 to purge the gas-liquid mixer 8, the shell side 11 of the heat exchanger, the tube side 12 of the heat exchanger, and the test chamber 17. The purge gas is finally discharged to the waste gas recovery device 16 through the vent pipe 18.

[0068] 2. Adjust the density of the hydrogen gas for the test: Adjust the first valve group 4 to connect the normal-temperature gas storage tank 3 to the tube side 12 of the heat exchanger and the test chamber 17 through the liquefied gas pump 6. Use the pressure reducing valve in the first valve group 4 to adjust the outlet pressure to 16.2 MPa, that is, maintain the pressure of the hydrogen gas in the test chamber 17 at 16.2 MPa. The density of hydrogen gas with a pressure of 5 MPa and a temperature of 100 K is the same as that of hydrogen gas with a pressure of 16.2 MPa and a temperature of 298 K, both being 12 kg / m³.

[0069] When adjusting the temperature under the condition of keeping the density the same, the coupling relationship between temperature and pressure can be utilized; when subsequent temperature adjustment is carried out, pressure adjustment can be achieved simultaneously. Use the first pressure control valve 13 to maintain the pressure not exceeding the designed pressure of the shell and tube sides of the heat exchanger.

[0070] 3. Temperature adjustment stage: (1) Adjust the reversing valve 5 and use the liquid hydrogen in the second liquefied gas storage tank 2 to cool down the system. Specifically, adjust the second valve group 7 so that the liquid hydrogen enters the shell side 11 of the heat exchanger through the gas-liquid mixer 8. Use the second pressure control valve 14 on the vent pipe to maintain the pressure of the shell side of the heat exchanger not exceeding the designed pressure, and the excess liquid hydrogen is discharged. Turn on the circulation pump 10 to circulate the hydrogen gas in the test chamber 17 and the tube side 12 of the heat exchanger, and conduct convective heat exchange with the low-temperature liquid hydrogen in the shell side 11 of the heat exchanger to achieve a stable temperature drop until the temperature approaches 100 K.

[0071] (2) Control the first valve group 4 and the second valve group 7, and adjust the flow rate and pressure of the hydrogen gas and liquid hydrogen flowing into the gas-liquid mixer 8. Mix the liquid hydrogen from the first liquefied gas storage tank 1 and the normal-temperature hydrogen from the normal-temperature gas storage tank 3 in a certain proportion so that the temperature of the hydrogen gas at the outlet of the gas-liquid mixer 8 remains at 100 K, and finally make the temperature of the shell side 11 of the heat exchanger stable at 100 K. Gradually reduce the flow rate of the circulation pump 10 to reduce the heat introduced by the pump operation, and precisely adjust the temperature of the hydrogen gas in the test chamber 17 until the temperature in the test chamber 17 reaches the set test temperature.

[0072] Since the density of hydrogen in the test chamber 17 and the tube side 12 of the heat exchanger remains unchanged and mass is conserved, the pressure is also adjusted simultaneously. And because the tube side 12 of the heat exchanger is of a spiral tube design, it has a large heat transfer area and can be moderately deformed, and can withstand the heat leakage of the system environment and the heat generated due to the change in the shape of the specimen during the test.

[0073] 4. Rewarming stage: (1) Drain the low-temperature hydrogen for the test: Open the first pressure control valve 13, the second pressure control valve 14 and the stop valve 15, and gradually drain the low-temperature hydrogen in the test chamber 17.

[0074] (2) Introduce normal-temperature hydrogen to rewarm the metal wall surface: Close the second pressure control valve 14, adjust the first valve group 4 so that normal-temperature low-pressure hydrogen enters the tube side 11 of the heat exchanger and the test chamber 17 through the liquid hydrogen pump (i.e., the liquefied gas pump 6), and complete the rewarming of the metal wall surface of the test chamber 17 through the circulation of hydrogen by the circulation pump 10. On the other hand, because the tube side 12 of the heat exchanger is of a spiral tube structure, the rewarming of the shell side 11 of the heat exchanger can also be completed simultaneously during the circulation process.

[0075] Embodiment 2: Target medium and conditions: Medium is nitrogen, pressure is 5 MPa, temperature is 250 K; 1. Preparation stage: (1) Reserve normal-temperature high-pressure gas: Supply nitrogen to the normal-temperature gas storage tank 3 through an external compressor to reach the design pressure.

[0076] (2) Purge and drain air: Adjust the first valve group 4 and the second valve group 7, open the first pressure control valve 13 and the second pressure control valve 14, and use normal-temperature nitrogen to purge the gas-liquid mixer 8, the shell side 11 of the heat exchanger, the tube side 12 of the heat exchanger and the test chamber 17, and the purge gas is finally discharged through the vent pipe 18.

[0077] 2. Adjust the density of the nitrogen for the test: Adjust the first valve group 4 to connect the normal-temperature gas storage tank 3 with the tube side 12 of the heat exchanger and the test chamber 17 through the liquid hydrogen pump 6, and use the pressure reducing valve in the first valve group 4 to adjust the outlet pressure to 6.1 MPa, that is, maintain the pressure of nitrogen in the test chamber 17 at 6.1 MPa (the density of nitrogen at a pressure of 5 MPa and a temperature of 250 K is the same as the density of nitrogen at a pressure of 6.1 MPa and a temperature of 298 K, both are 70 kg / m3).

[0078] 3. Temperature adjustment stage: (1)Adjust the reversing valve 5 and use the low-pressure liquid nitrogen in the second liquefied gas storage tank 2 to cool down the system. Adjust the second valve group 2 so that the liquid nitrogen enters the shell side 11 of the heat exchanger through the gas-liquid mixer 8. Turn on the circulation pump 10 to make the nitrogen gas circulate in the test chamber 17 and the tube side 12 of the heat exchanger, and conduct convective heat exchange with the low-temperature and low-pressure liquid nitrogen in the shell side 11 of the heat exchanger to achieve a stable temperature drop until the temperature approaches 250K.

[0079] (2)Adjust the first valve group 4 and the second valve group 7, and adjust the flow rate and pressure of the nitrogen gas and liquid nitrogen flowing into the gas-liquid mixer 8 so that the low-pressure liquid nitrogen from the first liquefied gas storage tank 1 and the normal-temperature nitrogen gas from the normal-temperature gas storage tank 3 are mixed in a certain proportion, so that the nitrogen gas temperature at the outlet of the gas-liquid mixer 8 reaches 250K, and finally make the temperature of the shell side 11 of the heat exchanger stable at 250K. Reduce the flow rate of the circulation pump 10 to reduce the input heat, so that the nitrogen gas in the test chamber 17 is accurately temperature-controlled to reach the corresponding test temperature.

[0080] Since the hydrogen density in the test chamber 17 and the tube side 12 of the heat exchanger remains unchanged and mass is conserved, the medium pressure is also adjusted simultaneously during the temperature control process. And because the tube side 12 of the heat exchanger is a spiral tube structure, it has a large heat exchange area and can be moderately deformed, and can withstand the heat leakage of the system environment and the heat generated due to the change of the specimen shape during the test.

[0081] 4. Rewarming stage: (1)Discharge the low-temperature nitrogen gas for the test: Open the second pressure control valve 14 and gradually discharge the low-temperature nitrogen gas in the test chamber 17.

[0082] (2)Introduce normal-temperature hydrogen to rewarm the metal wall surface: Close the second pressure control valve 14, adjust the first valve group 4 so that the normal-temperature low-pressure nitrogen gas enters the tube side 11 of the heat exchanger and the test chamber 17 through the liquid nitrogen pump (i.e., the liquefied gas pump 6), and complete the rewarming of the metal wall surface of the test chamber 17 through the circulation of the nitrogen gas by the circulation pump 10. On the other hand, because the tube side 12 of the heat exchanger is a spiral tube structure, the rewarming of the shell side 11 of the heat exchanger is also completed at the same time.

[0083] Embodiment 3: Target medium and conditions: The medium is supercritical hydrogen, the pressure is 50 MPa, and the temperature is 50K; 1. Preparation stage: (1)Standby normal-temperature high-pressure gas: Supply hydrogen to the normal-temperature gas storage tank 3 through an external compressor to reach the design pressure.

[0084] (2)Purge and discharge air: Adjust the first valve group and the second valve group, open the first pressure control valve 13 and the second pressure control valve 14, and use normal-temperature hydrogen to purge the gas-liquid mixer 8, the shell side 11 of the heat exchanger, the tube side 12 of the heat exchanger, and the test chamber 17. The purge gas is finally discharged through the vent pipe 18.

[0085] 2. Adjust the density of supercritical hydrogen for the adjustment test: (1) Adjust the first valve group 4 so that the normal-temperature gas storage tank 3 is connected to the tube side 12 of the heat exchanger through the liquid hydrogen pump (i.e., the liquefied gas pump 6). The pressure reducing valve in the first valve group adjusts the outlet pressure to 50 MPa, and 50 Mpa is the maximum pressure that the shell of the test chamber 17 can withstand.

[0086] (2) Adjust the reversing valve 5 and use the liquid hydrogen in the second liquefied gas storage tank 2 to cool down the system. Adjust the second valve group 7 so that the liquid hydrogen enters the shell side 11 of the heat exchanger through the gas-liquid mixer 8. Turn on the circulation pump 10 to make the hydrogen (i.e., the circulating medium) in the test chamber 17 and the tube side 12 of the heat exchanger circulate, and conduct convective heat exchange with the low-temperature liquid hydrogen in the shell side 11 of the heat exchanger to achieve a stable temperature drop. At this time, due to the law of conservation of mass, the temperature and pressure of the hydrogen in the test chamber 17 decrease simultaneously. When the pressure drops to 5 MPa, stop cooling. At this time, the gas pressure in the test chamber 17 is lower than the maximum pressure that the shell of the test chamber 17 can withstand. Adjust the first valve group 4 to continue to connect the normal-temperature gas storage tank 3 to the tube side 12 of the heat exchanger through the liquid hydrogen pump (i.e., the liquefied gas pump 6), and use the pressure reducing valve in the first valve group 4 to adjust the outlet pressure to 50 MPa to pressurize the test chamber 17 and the tube side 12 of the heat exchanger. After the pressurization is completed, continue to cool down. Through multiple operations of pressurization and cooling, the density of the supercritical hydrogen in the test chamber 17 finally reaches the density corresponding to the supercritical hydrogen at a pressure of 50 MPa and a temperature of 50 K.

[0087] 3. Temperature adjustment stage: Adjust the first valve group 4 and the second valve group 7, and adjust the flow rate and pressure of the hydrogen and liquid hydrogen flowing into the gas-liquid mixer 8 so that the liquid hydrogen from the second liquefied gas storage tank 2 and the hydrogen from the normal-temperature gas storage tank 3 are mixed in a certain proportion, so that the temperature of the hydrogen at the outlet of the gas-liquid mixer 8 reaches 50 K, and finally the temperature of the shell side 11 of the heat exchanger is stabilized at 50 K. Reduce the flow rate of the circulation pump 10 to reduce the input heat, so that the supercritical hydrogen in the test chamber 17 is accurately temperature-adjusted to the corresponding test temperature.

[0088] Since the density of the supercritical hydrogen in the test chamber 17 and the tube side 12 of the heat exchanger remains unchanged, that is, the law of conservation of mass, the pressure is also adjusted simultaneously. And because the tube side 12 of the heat exchanger is a spiral tube structure, the heat transfer area is large and can be deformed moderately, and it can withstand the heat leakage of the system environment and the heat generated due to the change of the specimen shape during the test.

[0089] 4. Rewarming stage: (1) Drain the supercritical hydrogen for the test: Open the second pressure control valve 14 and gradually drain the supercritical hydrogen inside the test chamber 17.

[0090] (2)Re-warm the metal wall by introducing normal-temperature hydrogen: Close the second pressure control valve 14, and adjust the first valve group 4 so that normal-temperature low-pressure hydrogen enters the tube side 11 of the heat exchanger and the test chamber 17 through the liquid hydrogen pump (i.e., the liquefied gas pump 6), and the circulation pump 10 is used to circulate hydrogen to complete the re-warming of the metal wall of the test chamber 17. On the other hand, since the tube side 12 of the heat exchanger is of a spiral tube structure, the re-warming of the shell side 11 of the heat exchanger is also completed at the same time.

[0091] Implementation Case Four: Target medium and conditions: Medium is liquid hydrogen, pressure is 0.4 MPa, and temperature is 20 K; 1. Preparation stage: (1)Reserve normal-temperature high-pressure gas: Supplement hydrogen to the normal-temperature gas storage tank 3 through an external compressor to reach the design pressure.

[0092] (2)Purge and discharge air: Adjust the first valve group 4 and the second valve group 7, open the first pressure control valve 13, the second pressure control valve 14 and the stop valve 15, and use normal-temperature hydrogen to purge the gas-liquid mixer 8, the shell side 11 of the heat exchanger, the tube side 12 of the heat exchanger and the test chamber 17. The purge gas is finally discharged through the vent pipe 18.

[0093] 2. Adjust the density of the liquid hydrogen for the test (1)Adjust the first valve group 4 to connect the normal-temperature gas storage tank 3 to the tube side 12 of the heat exchanger through the liquid hydrogen pump (i.e., the liquefied gas pump 6), and use the pressure reducing valve in the first valve group 4 to adjust the outlet pressure to 50 MPa. 50 MPa is the maximum pressure that the shell of the test chamber 17 can withstand.

[0094] (2)Adjust the reversing valve 5, and first use the liquid hydrogen in the first liquefied gas storage tank 1 to cool down the system. Adjust the second valve group 4 so that the liquid hydrogen enters the shell side 11 of the heat exchanger through the gas-liquid mixer 8. Turn on the circulation pump 10 to circulate the hydrogen gas (i.e., the circulating medium) in the test chamber 17 and the tube side 12 of the heat exchanger, and perform convective heat transfer with the low-temperature liquid hydrogen in the shell side 11 of the heat exchanger to achieve a stable temperature drop. At this time, due to the law of conservation of mass, the temperature and pressure of the hydrogen gas in the test chamber 17 both drop. When the pressure drops to 5 MPa, stop cooling. At this time, the gas pressure in the test chamber 17 is lower than the maximum pressure that the shell of the test chamber 17 can withstand. Adjust the first valve group 4, and continue to connect the normal-temperature gas storage tank 3 to the tube side 12 of the heat exchanger. Use the pressure reducing valve in the first valve group 4 to adjust the outlet pressure to 50 MPa, and pressurize the test chamber 17 and the tube side 11 of the heat exchanger. After the pressurization is completed, continue to cool down. Through multiple pressurization and cooling operations, the hydrogen density in the test chamber 17 reaches the density corresponding to the liquid hydrogen with a pressure of 0.4 MPa and a temperature of 20 K. And through this operation, the temperature inside the test chamber 17 can be stabilized at 22 K. Relatively speaking, in the prior art, since the heat leakage of the relevant temperature and pressure adjustment system is much higher than the heat leakage of the liquefied gas storage tank, in order to achieve a strict temperature of 20 K in the liquid hydrogen temperature range, it is necessary to use a more expensive and more powerful refrigerator or use a large amount of scarce liquid helium in a single test to offset the heat leakage of the relevant equipment of the system and the heat input by the liquid hydrogen pump.

[0095] 3. Temperature adjustment stage: Adjust the first reversing valve 5, use the second liquefied gas storage tank 2 equipped with a set of GM refrigerators and a cryostat as the cold source, adjust the first valve group 4 and the second valve group 7, directly introduce 20 K liquid hydrogen into the shell side 11 of the heat exchanger, and finally make the temperature of the shell side 11 of the heat exchanger stable at 20 K. Gradually reduce the flow rate of the circulation pump 10 to reduce the input heat, so that the liquid hydrogen in the test chamber 17 reaches the corresponding test temperature through precise temperature adjustment.

[0096] Since the liquid hydrogen density in the test chamber 17 and the tube side 12 of the heat exchanger remains unchanged, that is, the law of conservation of mass, the pressure is also adjusted simultaneously. And because the tube side 12 of the heat exchanger is a spiral tube structure, it has a large heat transfer area and can be moderately deformed, and can withstand the heat leakage of the system environment and the heat generated due to the change of the specimen shape during the test.

[0097] That is to say, in this application, first cool the circulating medium in the experimental chamber 17 through the medium in the first liquefied gas storage tank 1. When the temperature drops to a certain level, then use the medium in the second liquefied gas storage tank 2 to cool the circulating medium in the experimental chamber 17. Thus, the cooling cost is greatly reduced.

[0098] 4. Rewarming stage: (1)Discharge the test liquid hydrogen: Open the second pressure control valve 14 and gradually discharge the liquid hydrogen in the test chamber 17.

[0099] (2) Introduce normal-temperature hydrogen to rewarm the metal wall: Close the second pressure control valve 14, and adjust the first valve group 4 so that normal-temperature low-pressure hydrogen enters the tube side 11 of the heat exchanger and the test chamber 17 through the liquid hydrogen pump (i.e., the liquefied gas pump 6), and the circulation of hydrogen is completed through the circulation pump 10 to rewarm the metal wall of the test chamber 17. On the other hand, since the tube side 12 of the heat exchanger is of a spiral tube structure, the shell side 11 of the heat exchanger is also rewarmed simultaneously.

[0100] As can be seen from the above description and application examples, the cryogenic high-pressure environmental material performance test system provided by the present invention uses the liquefied gas required for the test as the refrigeration cold source, which can solve the problem of low test efficiency existing in the active refrigerator using the liquid-free cooling method. The temperature and pressure conditions required for the test are controlled by the heat exchanger, solving the problem of unstable temperature and pressure in the existing liquid-cooled or liquid-free cooled low-temperature test devices. By ensuring a certain density of the test gas or liquefied gas, the temperature-pressure coupling problem in the test is solved. The cryogenic high-pressure material performance test system provided by the present invention can cover most of the process conditions in the existing hydrogen liquefaction or liquefied gas storage and transportation devices, realizing the test requirements of materials under typical medium, temperature, and pressure combination conditions, and solving the problem that the existing liquid-cooled test devices can only conduct tests at specific temperature points and pressures. At the same time, the temperature-pressure coupling problem during the temperature and pressure adjustment process is solved, and the test cost is reduced and the required refrigeration power is reduced by using a liquefied gas storage tank and a low-pressure liquefied gas storage tank equipped with a group of GM refrigerators and a low-temperature thermostat. The cryogenic test chamber and heat exchanger configured in the present invention can adopt vacuum-wrapped insulation, which is a mature insulation technology. Therefore, the present invention has very high feasibility.

[0101] It should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. Without further limitation, the element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, commodity or device including the said element.

[0102] Each embodiment in this specification is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0103] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

[0104] Although the embodiments of the present application have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present application, and such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A mechanical properties testing system for materials in ultra-low temperature and high pressure environments, characterized in that: include: A medium circulation system, comprising a heat exchanger tube, a circulation pump and a test box, wherein the test box is suitable for accommodating a universal testing machine for mechanical testing, the heat exchanger tube, the circulation pump and the test box are connected in sequence, and the medium outlet of the test box is connected to a vent pipe; A cold source supply system comprises a heat exchanger shell, a first valve group, a second valve group, a gas-liquid mixer, a liquefied gas pump, a normal temperature gas storage tank and a first liquefied gas storage tank. The heat exchanger shell accommodates the heat exchanger tube side. The outlet of the first liquefied gas storage tank is respectively connected to the first valve group and the liquefied gas pump. The liquefied gas pump is connected to the second valve group. The first valve group and the second valve group are both connected to the inlet of the gas-liquid mixer. The second valve group is also connected to the pipeline where the circulating pump is located. The outlet of the gas-liquid mixer is connected to one end of the heat exchanger shell side. The other end of the heat exchanger shell side is connected to the vent pipe through a discharge pipeline. The heat exchanger shell side and the heat exchanger tube side form countercurrent heat exchange.

2. The ultra-low temperature and high pressure environment material mechanical properties testing system according to claim 1 is characterized in that: The cold source supply system further includes a second liquefied gas storage tank, the outlet of the second liquefied gas storage tank and the outlet of the first liquefied gas storage tank are both connected to a first reversing valve, and the first reversing valve is also respectively connected to the first valve group and the liquefied gas pump; Wherein, the second liquefied gas storage tank is equipped with a GM refrigerator and a low-temperature thermostat.

3. The ultra-low temperature and high pressure environment material mechanical properties testing system according to claim 2 is characterized in that: The medium in the normal temperature gas storage tank, the medium in the first liquefied gas storage tank, and the medium in the second liquefied gas storage tank are the same substance.

4. The ultra-low temperature and high pressure environment material mechanical properties testing system according to claim 1, characterized in that: The shell side of the heat exchanger is a cylindrical tank structure, and the tube side of the heat exchanger is a spiral tube structure arranged inside the tank structure.

5. The ultra-low temperature and high pressure environment material mechanical properties testing system according to claim 4 is characterized in that: A fully enclosed hollow inner cylinder is arranged in the shell side of the heat exchanger, and the spiral tube structure is arranged around the hollow inner cylinder.

6. The ultra-low temperature and high pressure environment material mechanical properties testing system according to claim 1, characterized in that: The test box comprises a box body and a door body, and the door body is connected to the box body through a three-stage spring energy storage dynamic sealing structure.

7. The ultra-low temperature and high pressure environment material mechanical properties testing system according to claim 6, characterized in that: A temperature measuring instrument and a pressure sensor are arranged inside the test box, a safety valve is arranged on the test box, and a medium outlet of the test box is connected to a vent pipe through the safety valve.

8. The ultra-low temperature and high pressure environment material mechanical properties testing system according to claim 1, characterized in that: A thermometer and a flow meter are provided at the outlet of the normal temperature gas storage tank, and a pressure reducing valve is provided at the outlet of the gas-liquid mixer.

9. The ultra-low temperature and high pressure environment material mechanical properties testing system according to claim 1, characterized in that: A first pressure control valve is arranged on the pipeline between the heat exchanger tube and the vent pipe, a second pressure control valve is arranged on the vent pipe, and a stop valve is arranged on the pipeline between the test box and the heat exchanger tube.

10. The ultra-low temperature and high pressure environment material mechanical properties testing system according to claim 1, characterized in that: The end of the vent pipe is connected to the waste gas recovery device.

11. A method for testing mechanical properties of materials in ultra-low temperature and high pressure environments, characterized in that: The test method is applied to the ultra-low temperature and high pressure environment material mechanical property test system described in any one of claims 1 to 10, and the test method comprises: The first valve group is adjusted to transport the normal temperature gaseous medium in the normal temperature gas storage tank to the test box through the liquefied gas pump to provide circulating medium for the test box; The second valve group is adjusted to allow the liquid medium in the first liquefied gas storage tank to enter the shell side of the heat exchanger through the gas-liquid mixer; Turn on the circulation pump, and the medium in the test box will exchange heat with the medium in the shell side of the heat exchanger in the tube side of the heat exchanger, so that the circulating medium in the test box becomes the experimental target medium.

12. The method for testing mechanical properties of materials in ultra-low temperature and high pressure environments according to claim 11, characterized in that: If the density of the experimental target medium is lower than the corresponding density of the gas at room temperature under the design pressure of the test chamber, the pressure of the gas filled in the circulation system is adjusted to make the gas density consistent with the density of the experimental target medium; If the density of the experimental target medium is equal to or higher than the corresponding density of the gas at room temperature under the design pressure of the test chamber, it is necessary to adjust the density by combining cooling and pressure replenishment.

13. The method for testing mechanical properties of materials in ultra-low temperature and high pressure environments according to claim 12, characterized in that: The density adjustment by combining temperature reduction and pressure supplementation includes: First, the normal temperature gas storage tank and the first liquefied gas storage tank are connected to the gas-liquid mixer at the same time to form a temperature-controllable cold source, and the cold source is introduced into the shell side of the heat exchanger to exchange heat with the circulating medium in the tube side of the heat exchanger to cool it down. The pressure of the circulating medium will decrease simultaneously with the temperature; The circulating medium is pressurized with the normal temperature gas in the normal temperature gas storage tank, and then the temperature is continuously lowered. Through multiple pressurization and temperature reduction operations, the density of the medium in the circulation system is kept consistent with the density of the experimental target medium.

14. The method for testing mechanical properties of materials in ultra-low temperature and high pressure environment according to claim 11, characterized in that: The test method also includes a rewarming operation after the test experiment: Discharge the circulating medium from the test chamber to the vent pipe, then connect the normal temperature gas storage tank to the medium circulation system, and fill the medium circulation system with normal temperature gas; Start the circulation pump to circulate the room temperature gas in the medium circulation system until the metal wall of the test box and the shell of the heat exchanger are fully reheated.

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