A detection method and device for testing performance of thermal insulation material by using thermal resistance element in multi-temperature zone

Abstract

The application discloses a kind of heat insulation material performance detection method, by changing the thermal resistance of thermal resistance element between low-temperature liquid storage tank and test constant temperature surface, the temperature of constant temperature surface is adjusted and is used to test the performance of heat insulation material in different temperature zones.A kind of heat insulation material performance detection device using thermal resistance element to adjust the temperature of constant temperature surface, comprising: for providing and maintaining low-temperature temperature low-temperature liquid storage tank;Constant temperature surface simulating the cold end environment in the process of heat insulation material use;The resistance adjustable thermal resistance element connected constant temperature surface and low-temperature liquid storage tank;The flow meter of accurately testing the heat flux passing through heat insulation material.This method can use inert low-temperature liquid to test the performance of heat insulation material at multiple temperature zones cold boundary temperature;Cold end and hot end temperature can be regulated, meet different heat insulation test demand;There is also no security hidden trouble problem brought by dangerous gas such as liquid hydrogen or liquid oxygen.

Description

Technical Field

[0001] This invention relates to the field of low-temperature insulation, and more specifically to a testing device that uses thermal resistance elements to test the performance of insulation materials in multiple temperature zones. Background Technology

[0002] With the rapid development of aerospace, medical and health, industrial testing, and laboratory equipment in my country, the demand for cryogenic applications is becoming increasingly widespread. For example, hydrogen energy is a highly efficient and clean energy source, and its high-energy-density cryogenic liquid storage method has attracted much attention; liquid oxygen and liquid hydrogen are also widely used in aerospace propellants due to their high energy density; liquid helium is indispensable for cooling nuclear magnetic resonance medical imaging equipment; in addition, there are cryogenic refrigerators and cryostats in laboratories. These cryogenic applications have a large temperature difference with room temperature, resulting in more severe heat leakage. To avoid cryogenic failure caused by heat leakage and further safety hazards, efficient thermal insulation technology is crucial for the long-term storage, transportation, and use of cryogenic equipment.

[0003] The main performance evaluation indicators for thermal insulation materials include heat flux density and apparent thermal conductivity. Currently, the mainstream testing method is evaporation calorimetry. This method involves wrapping the outside of a cryogenic liquid storage tank with insulation material and obtaining the heat leakage of the insulation material by measuring the evaporation rate of the cryogenic liquid. Insulation materials are generally composed of alternating reflective screens with high emissivity and spacers with low thermal conductivity. Due to their excellent insulation performance under high vacuum conditions, they are widely used in liquid nitrogen storage tanks. Extensive test data exist for different structures in the cryogenic liquid nitrogen temperature range and the room temperature temperature range. However, the cold-end temperature of evaporation calorimetry is generally the boiling point of the cryogenic liquid, which is difficult to control or change. This limits the testing of insulation materials to the vicinity of their boiling point, while the wider temperature range without a cryogenic liquid boiling point can only be obtained through interpolation or reasonable calculation, which may differ from actual usage conditions. Furthermore, evaporation calorimetry is also limited by the price of liquid helium and the safety of hydrogen and oxygen, making widespread testing difficult.

[0004] Chinese patent CN 102809581B relates to a low-temperature vacuum insulation material performance testing device based on a thermal protection method. It utilizes liquid nitrogen to control the cold end temperature, employs upper and lower protective chambers to eliminate axial boundary effects, and obtains heat leakage through the evaporation rate of the low-temperature liquid. Chinese patent CN 207488217U relates to a device for testing the apparent thermal conductivity and outgassing rate of insulation materials. It uses liquid nitrogen as a cold source, and the calorimeter and high-vacuum chamber share a single vacuum pumping unit, saving the need for a separate vacuum pumping system and avoiding vacuum disruption caused by frequent disassembly. However, both of these devices can only test the insulation material performance at the boiling point of the low-temperature liquid (liquid nitrogen), and cannot meet further testing requirements for insulation materials in other temperature ranges. Chinese patent document CN 108614007A uses a two-stage refrigerator to maintain the cold end temperature and characterizes the heat flux through multiple layers of material by calculating the thermal conductivity of the heat-conducting rod. This calorimetric method requires the heat transfer rod to be calibrated before testing, and recalibration is required for different usage scenarios and conditions, which makes the testing process complicated. In addition, the calibration process may also introduce certain errors. Summary of the Invention

[0005] This invention addresses the safety and cost issues associated with using cryogenic liquids in the current common methods of testing the apparent thermal conductivity of insulation materials, as well as the lack of controllable cold-end temperature in existing evaporative calorimetry devices. It proposes a novel testing apparatus. This apparatus allows for adjustable hot and cold-end temperatures, enabling the measurement of insulation material performance in hazardous temperature ranges (such as liquid hydrogen or liquid oxygen) using inert gases (liquid helium or liquid nitrogen, etc.). This effectively avoids the safety concerns associated with using dangerous gases. Furthermore, the experimental setup includes a recovery, purification, and liquefaction device, which effectively saves on the cost of rare gases and avoids the complexity and potential calorimetric errors associated with using a refrigeration unit.

[0006] A testing method for evaluating the performance of thermal insulation materials in multiple temperature zones using a thermal resistance element is disclosed. The testing device used in this method includes a constant temperature surface, a cryogenic liquid storage tank for providing and maintaining a low temperature to the constant temperature surface, a thermal resistance element disposed between the cryogenic liquid storage tank and the constant temperature surface for adjusting the amount of cold energy transfer, and a flow meter for detecting the evaporation mass flow rate of the cryogenic liquid storage tank. The testing method includes: covering the thermal insulation material to be tested onto the constant temperature surface, adjusting the temperature of the constant temperature surface to the target testing temperature through the thermal resistance element, detecting the evaporation mass flow rate of the cryogenic liquid storage tank, and obtaining the performance data of the thermal insulation material after the evaporation flow rate stabilizes or the internal temperature of the thermal insulation material stabilizes.

[0007] This invention provides a method for testing the performance of thermal insulation materials by adjusting the temperature of a constant temperature surface using a thermal resistance element. By changing the thermal resistance of the thermal resistance element between the cryogenic liquid storage tank and the test constant temperature surface, the temperature of the constant temperature surface is adjusted and used to test the performance of thermal insulation materials in different temperature zones.

[0008] The constant temperature surface is used to simulate the cold end environment during the use of thermal insulation materials. The thermal insulation material to be tested is covered on the constant temperature surface, which further improves the accuracy of thermal insulation material testing.

[0009] Preferably, the heat flux of the insulation material is obtained using the evaporation mass flow rate; alternatively, the temperature difference between the inner and outer surfaces of the insulation material is detected simultaneously to obtain the apparent thermal conductivity of the insulation material.

[0010] The heat flux φ of the insulation material is obtained using the evaporation mass flow rate described above. MLI The following formula is used:

[0011]

[0012] Where: L v Latent heat of vaporization for cryogenic liquids, expressed in J / kg; This is the mass flow rate of the cryogenic liquid evaporation, measured in kg / s, and can be obtained by a flow meter.

[0013] As an alternative, the stability of the heat flux through the insulation material can be determined by measuring the evaporation mass flow rate of the cryogenic liquid storage tank. As a preferred option, the stability of the insulation material can be determined by detecting changes in the internal temperature of the insulation material.

[0014] As an alternative, the thermal resistance element is detachably connected, allowing adjustment of the cooling capacity transfer by replacing the thermal resistance element; alternatively, the thermal resistance element is an adjustable thermal resistance element. More preferably, the thermal resistance element is a gas gap thermal switch.

[0015] As an alternative, liquid helium is used as the cryogenic liquid when the cold boundary temperature to be tested is between 4K and 77K; and liquid nitrogen is used when the cold boundary temperature to be tested is between 77K and 300K. Here, the cold boundary temperature refers to the surface temperature of the insulation material near the cold source, measured in K.

[0016] As one possible implementation, the cryogenic liquid storage tank (liquid nitrogen container or liquid helium storage tank, etc.) is provided with an outlet pipe, and the flow meter is installed on the outlet pipe to detect the evaporation mass flow rate of the cryogenic liquid; or a cryogenic liquid inlet pipe is provided on the cryogenic liquid storage tank for filling with cryogenic liquid.

[0017] A testing device for testing the performance of thermal insulation materials in multiple temperature zones using thermal resistance elements includes: a constant temperature surface, which can maintain a uniform low temperature and is used to simulate the cold end environment during the use of thermal insulation materials, and the thermal insulation material to be tested is covered on the constant temperature surface.

[0018] A cryogenic liquid storage tank, wherein the cryogenic liquid storage tank is used to provide and maintain a cryogenic temperature for a constant temperature surface;

[0019] A thermal resistance element, one end of which is connected to a cryogenic liquid storage tank and the other end is connected to a test constant temperature surface. Its thermal resistance value can be changed by replacing the element or by using an adjustable thermal resistance element.

[0020] A flow meter used to accurately measure the heat flux through an insulating material.

[0021] Preferably, the thermal resistance element simultaneously achieves the fixation of the constant temperature surface relative to the cryogenic liquid storage tank.

[0022] As one possible implementation, it also includes temperature sensing elements for detecting the temperature of the inner and outer surfaces of the insulation material. These could be temperature sensors, etc.

[0023] As one possible implementation, the testing of vacuum insulation materials also includes a vacuum chamber for maintaining a vacuum environment, with the cryogenic liquid storage tank, thermal resistance element, constant temperature surface, and insulation material located inside the vacuum chamber. The vacuum chamber may also be equipped with a temperature control device.

[0024] The constant temperature surface can be flat, cylindrical, spherical, or other shapes. As one possible implementation, the cylindrical constant temperature surface is protected against heat leakage by using a protective cavity along its axial direction, and the temperature of the protective cavity is controlled by a cold source and a temperature controller.

[0025] As an alternative implementation, the cold source is a cryogenic liquid (liquid helium or liquid nitrogen), a refrigerator, or other refrigeration components. The cold source is capable of maintaining the same temperature between the protective cavity and the constant-temperature surface.

[0026] Preferably, the system also includes a cryogenic liquid recovery unit, with the vent pipe connected to the unit for recovering the evaporated cryogenic liquid. Simultaneously, a cryogenic liquid inlet pipe is provided on the cryogenic liquid storage tank for filling with cryogenic liquid or connecting to the cryogenic liquid recovery unit. For example, as an alternative implementation, when using liquid helium for testing, a helium purification and liquefaction system can be used for recycling, thereby reducing costs.

[0027] This invention provides a testing method that can use inert cryogenic liquids to test the performance of insulation materials at cold boundary temperatures in multiple temperature zones; it can also use other cryogenic liquid storage tanks such as refrigerators for testing, and the cold end and hot end temperatures can be adjusted to meet different insulation testing needs; and it does not pose any safety hazards caused by dangerous gases such as liquid hydrogen or liquid oxygen. Attached Figure Description

[0028] Figure 1 This is a simplified diagram of the testing device of the present invention.

[0029] Figure 2This is a graph showing the relationship between the thermal resistance of the thermal resistance element and the temperature of the isothermal surface in this invention.

[0030] Figure 3 This is a schematic diagram of the testing device of the present invention in the liquid nitrogen and above temperature range.

[0031] Figure 4 This is a schematic diagram of the testing device of the present invention in the liquid nitrogen to liquid helium temperature range. Detailed Implementation

[0032] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the invention. The specific details described below are illustrative and not restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0033] like Figure 1 As shown in the diagram, this invention discloses a simplified testing device for the performance of thermal insulation materials by adjusting the temperature of a constant-temperature surface using a thermal resistance element. The device includes: a cryogenic liquid storage tank 1 for providing and maintaining a low temperature; a test constant-temperature surface 2 for maintaining a uniform low temperature, the constant-temperature surface simulating the cold-end environment during the use of the thermal insulation material, the thermal insulation material 4 to be tested being covered on the constant-temperature surface; a thermal resistance element 3 connecting the constant-temperature surface and the cryogenic liquid storage tank, the thermal resistance element supporting the constant-temperature surface, used for fixing its position (i.e., achieving installation and fixation of the constant-temperature surface), and also for heat conduction, its thermal resistance value being changed by replacing the element or using an adjustable thermal resistance element; a flow meter 5 for accurately measuring heat; the relationship between the thermal resistance of the thermal resistance element 3 and the temperature of the constant-temperature surface 2 is as follows: Figure 2 As shown, the temperature of the isothermal surface 2 gradually increases with increasing thermal resistance. The intersection with the vertical axis is the boiling point of the low-temperature liquid. In other words, the lowest temperature that the isothermal surface can reach without thermal resistance is the boiling point of the low-temperature liquid.

[0034] like Figure 3As shown, this invention discloses an embodiment of a testing device for the performance of thermal insulation materials that utilizes a thermal resistance element to adjust the temperature of a constant-temperature surface. The device is tested in the liquid nitrogen and above temperature range. A cylindrical liquid nitrogen container 301 containing liquid nitrogen is used as the cryogenic liquid storage tank 1, which can continuously provide a low temperature of 77K. The constant-temperature surface 2 is the thin-shell outer wall of the cylindrical body corresponding to the liquid nitrogen container 301, and oxygen-free copper is used as the material to ensure temperature uniformity. A gas gap thermal switch 303 is used as the thermal resistance element, and the temperature of the constant-temperature surface 2 is controlled to the test cold boundary temperature (>77K) by adjusting the thermal resistance of the thermal switch. Liquid nitrogen is filled and replenished using the liquid nitrogen inlet pipe 307, and the outlet pipe is connected to the nitrogen flow meter 305 (i.e., in this embodiment, the flow meter 5 is a nitrogen flow meter); heat from the room temperature environment reaches the constant temperature surface through the insulation material and is collected in the liquid nitrogen container 301 through the thermal switch 303. The addition of heat causes the cryogenic liquid (liquid nitrogen) in the liquid nitrogen container 301 to evaporate. When a steady state is reached, the heat leakage through the multilayer material and the heat causing the cryogenic liquid to evaporate are the same and remain constant. The heat flux through the multilayer material can be obtained by calculating the latent heat, as shown in the following formula:

[0035]

[0036] Where: L v Latent heat of vaporization for cryogenic liquids, expressed in J / kg; This represents the mass flow rate of cryogenic liquid evaporation, expressed in kg / s.

[0037] The latent heat of vaporization of cryogenic liquids can be directly obtained from tables. The mass flow rate of cryogenic liquid evaporation can be directly obtained by measuring with a flow meter.

[0038] like Figure 4As shown, this invention discloses an embodiment of a testing device for the performance of insulating materials that utilizes thermal resistance elements to adjust the temperature of a constant-temperature surface, tested in the liquid hydrogen temperature range. A liquid helium storage tank 401 containing liquid helium is used as the cryogenic liquid storage tank 1. The constant-temperature cavity 402 is a hollow cylinder (which can be made of oxygen-free copper). The constant-temperature cavity and the cryogenic liquid storage tank are connected by a gas gap thermal switch 403. During testing, the thermal resistance of the thermal switch is adjusted to maintain the temperature of the constant-temperature cavity at 20K. An upper protective cavity 407 and a lower protective cavity 409 are respectively provided on the upper and lower end faces of the constant-temperature cavity 402 to eliminate heat leakage from the end faces of the constant-temperature cavity. The upper and lower protective cavities are maintained at a stable temperature of 20K using a first refrigerator 406 and a second refrigerator 408, respectively. The insulating material 4 wraps around the outer surface of the constant-temperature cavity, also covering the upper and lower protective cavities. At this time, the constant-temperature surface 2, the upper protective cavity 407, and the lower protective cavity 409 have the same temperature, and there is no axial heat transfer on the constant-temperature surface 2. The aforementioned constant temperature chamber 402, protective chamber, and refrigerator cold head are all located inside the vacuum enclosure 411. The vacuum enclosure 411 provides a safe operating environment for the refrigerator and also provides vacuum conditions for testing vacuum insulation materials. It can provide and maintain different pressure environments together with equipment such as pump units, and also facilitates the testing of vacuum insulation materials. The outlet pipe of the liquid helium storage tank 401 is connected to the helium flow meter 405, and the outlet end of the flow meter is connected to the helium recovery, purification, and liquefaction device 410. This device can purify and further liquefy the used helium to obtain usable liquid helium, which is then supplied back to the liquid helium storage tank 401 to achieve the purpose of recycling.

[0039] Test Procedure: First, open the vacuum chamber 411 and install the refrigerator, thermal switch, constant temperature surface, and protective chamber in sequence; wrap the outside of the constant temperature chamber 401 with insulation material, including the upper and lower protective chambers; close the vacuum chamber and adjust the vacuum pressure inside to be below 10. -3 Pa, turn on the first refrigerator 406 and the second refrigerator 408, and adjust the temperature of the upper and lower protective chambers to 20K; fill the liquid nitrogen storage tank 401 with liquid helium, at which time the surface temperature of the storage tank is about 4.2K; adjust the helium pressure inside the thermal switch 403 to change the thermal resistance of the thermal switch, and adjust the temperature of the constant temperature chamber 402 to 20K; use a flow meter to continuously detect the flow rate change, wait for the flow rate to stabilize and reach a steady state, and then send the helium through the flow meter to the helium purification liquefaction unit for recycling; obtain the heat transfer through the side of the constant temperature chamber based on the flow rate data measured by the flow meter, and use it to calculate the heat flux density and apparent thermal conductivity of the material.

[0040] The temperature difference Δt between the inner and outer surfaces of the insulating material in steady state can be obtained using formulas (1) and (2) through heat flux testing of multilayer materials. The apparent thermal conductivity of the multilayer material can be calculated using the following formula:

[0041]

[0042] Where: k e δ is the apparent thermal conductivity of the material, measured in W / (m·K); δ is the thickness of the insulation material, measured in meters (m); r in Δt is the outer radius of the thermostatic cavity, in meters (m); l is the height of the thermostatic cavity, in meters (m); Δt is the temperature difference between the inner and outer surfaces of the insulation material, in Kelvin (K).

[0043] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all possible modifications here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A testing method for evaluating the performance of thermal insulation materials in multiple temperature zones using a thermal resistance element, characterized in that, The detection device used in this method includes a constant temperature surface, a cryogenic liquid storage tank for providing and maintaining a low temperature to the constant temperature surface, a thermal resistance element disposed between the cryogenic liquid storage tank and the constant temperature surface for adjusting the amount of cold energy transfer, and a flow meter for detecting the mass flow rate of the cryogenic liquid evaporation; the detection method includes: covering the insulation material to be tested onto the constant temperature surface, adjusting the temperature of the constant temperature surface to the target detection temperature through the thermal resistance element, detecting the mass flow rate of the cryogenic liquid evaporation, and obtaining the performance data of the insulation material after the evaporation flow rate stabilizes or the internal temperature of the insulation material stabilizes; One end of the thermal resistance element is connected to the cryogenic liquid storage tank, and the other end is connected to the test constant temperature surface. The thermal resistance element simultaneously achieves the fixation of the constant temperature surface relative to the cryogenic liquid storage tank; The constant temperature surface is used to simulate the cold end environment during the use of insulation materials; The constant temperature surface is the hollow, thin-shell outer wall surrounding the cryogenic liquid storage tank.

2. The testing method for testing the performance of thermal insulation materials in multiple temperature zones using a thermal resistance element according to claim 1, characterized in that, The heat flux of the insulation material is obtained by using the evaporation mass flow rate; at the same time, the temperature difference between the inner and outer surfaces of the insulation material is detected to obtain the apparent thermal conductivity of the insulation material.

3. The testing method for testing the performance of thermal insulation materials in multiple temperature zones using a thermal resistance element according to claim 1, characterized in that, The thermal resistance element is connected in a detachable manner, and the amount of cold air transmission can be adjusted by replacing the thermal resistance element; or, the thermal resistance element is an adjustable thermal resistance element.

4. The testing method for testing the performance of thermal insulation materials in multiple temperature zones using a thermal resistance element according to claim 1, characterized in that, The temperature of the cryogenic liquid in the cryogenic liquid storage tank is lower than or equal to the cold boundary temperature required by the insulation material to be tested.

5. The testing method for testing the performance of thermal insulation materials in multiple temperature zones using a thermal resistance element according to claim 1, characterized in that, The cryogenic liquid is either liquid nitrogen or liquid helium.

6. A testing device for testing the performance of thermal insulation materials in multiple temperature zones using thermal resistance elements, characterized in that, include: The constant temperature surface is a hollow thin-shell outer wall surrounding the cryogenic liquid storage tank; the constant temperature surface can maintain a uniform low temperature and is used to simulate the cold end environment during the use of insulation materials. The insulation material to be tested is covered on the constant temperature surface. A cryogenic liquid storage tank, wherein the cryogenic liquid storage tank is used to provide and maintain a cryogenic temperature for the constant temperature surface; A thermal resistance element, one end of which is connected to a cryogenic liquid storage tank and the other end of which is connected to a test constant temperature surface. Its thermal resistance value can be changed by replacing the thermal resistance element or by using an adjustable thermal resistance element. Flow meter, used to detect the evaporation mass flow rate of cryogenic liquid storage tanks; The thermal resistance element simultaneously achieves the fixation of the constant temperature surface relative to the cryogenic liquid storage tank.

7. The testing device for testing the performance of thermal insulation materials in multiple temperature zones using a thermal resistance element according to claim 6, characterized in that, It also includes temperature sensing elements for detecting the temperature of the inner and outer surfaces of the insulation material.

8. The testing device for testing the performance of thermal insulation materials in multiple temperature zones using thermal resistance elements according to claim 6, characterized in that, The test of the vacuum insulation material also includes a vacuum chamber for maintaining the vacuum environment, inside which the cryogenic liquid storage tank, thermal resistance element, constant temperature surface and insulation material are located.

9. The testing device for testing the performance of thermal insulation materials in multiple temperature zones using thermal resistance elements according to claim 6, characterized in that, The constant temperature surface can be flat, cylindrical, or spherical.

10. The testing device for testing the performance of thermal insulation materials in multiple temperature zones using a thermal resistance element according to claim 6, characterized in that, The cryogenic liquid storage tank is equipped with a protective cavity to block the heat flux from the cold source without insulation material and the end effect of the cylindrical structure. The protective cavity is maintained at the same temperature as the constant temperature surface using a cold source, which is a cryogenic liquid or a cryogenic refrigerator.

Images