Method and system for testing static boil-off rate of liquid hydrogen storage tank

Abstract

This invention discloses a method and system for testing the static evaporation rate of a liquid hydrogen storage tank. The method involves pre-cooling the liquid hydrogen storage tank to a preset internal temperature; filling the pre-cooled tank with cryogenic helium; closing all valves and allowing the tank to stand for a preset time; collecting temperature and pressure parameters of the helium inside the tank at the beginning and end of the preset time; determining the internal energy of the helium at the beginning and end based on these parameters; calculating the mass of helium in the tank based on its volume and density; calculating the heat absorbed by the tank during the preset time based on the helium mass and the difference in internal energy between the beginning and end times; and calculating the static evaporation rate of the liquid hydrogen storage tank based on the heat absorbed and the physical properties of the liquid hydrogen. This method uses the sensible heat change of cryogenic helium instead of the latent heat of liquid hydrogen phase change, ensuring safety, reliability, and improved testing accuracy.

Description

Technical Field

[0001] This invention relates to the field of liquid hydrogen storage tank testing technology, and in particular to a method and system for testing the static evaporation rate of liquid hydrogen storage tanks. Background Technology

[0002] Static evaporation rate is a core indicator for evaluating the insulation performance of cryogenic insulated containers. It refers to the percentage of mass lost due to natural evaporation of the cryogenic liquid within 24 hours when the container is in a static state, relative to the total fill mass. Domestic standards such as GB / T18443.5 "Performance Test Methods for Vacuum Insulated Cryogenic Equipment Part 5: Measurement of Static Evaporation Rate" have been issued, explicitly defining static evaporation rate as a core acceptance indicator for liquid hydrogen insulated pressure vessels.

[0003] However, testing the static evaporation rate of liquid hydrogen storage tanks currently faces many technical challenges, mainly in the following aspects: 1. Extremely low temperatures and the difficulty of safety management Liquid hydrogen needs to be stored at an ultra-low temperature of -253°C, and hydrogen gas is highly flammable and explosive. The testing process places extremely stringent requirements on cryogenically adapted instruments and explosion-proof safety facilities. In addition, the supply channels for civilian liquid hydrogen are limited, and the threshold and risks of directly conducting liquid hydrogen field tests are very high, making it difficult to scale up in engineering practice.

[0004] 2. Accurate prediction of phase change and heat transfer processes is difficult. The phase change heat transfer and unsteady-state heat and mass transfer characteristics of liquid hydrogen are highly complex. Effects such as the conversion of normal to secondary hydrogen and thermal stratification directly affect the evaporation rate. Existing multiphase flow numerical methods struggle to accurately predict the mass transfer characteristics at the liquid-gas interface, often resulting in errors in pressure and evaporation rate predictions.

[0005] 3. The accuracy of conversion in alternative tests is difficult to guarantee. To mitigate the high risks of liquid hydrogen testing, the industry standard practice is to use liquid nitrogen instead. However, liquid nitrogen and liquid hydrogen differ significantly in their boiling points (the difference is approximately 57K, far exceeding the national standard's allowable temperature difference limit of 20K), densities (liquid nitrogen is about 11 times denser than liquid hydrogen), and latent heat of vaporization. Their evaporation characteristics differ, necessitating precise corrections for insulation and structural heat leakage, making the conversion factor extremely difficult to control. The evaporation rate ratio of liquid hydrogen to liquid nitrogen is highly sensitive to insulation performance and the liquid nitrogen filling rate, with the conversion factor fluctuating significantly between 2.9 and 8.3, making accuracy and reliability difficult to guarantee. Furthermore, the measurement principle, based on the latent heat of phase change, faces the complexity and uncertainty arising from the phase change of the test medium.

[0006] 4. Difficulty in removing interference factors and calibrating data During the test, there are many interfering factors such as ambient temperature and humidity, atmospheric pressure, and residual gas thermal conductivity. At the same time, the system error control requirements for high-precision flow measurement and weighing verification are stringent, and data needs to be collected continuously for a long time to obtain stable thermal balance results. Summary of the Invention

[0007] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a method and system for testing the static evaporation rate of liquid hydrogen storage tanks. It uses cryogenic helium as the test medium and utilizes the sensible heat change caused by the heat absorption and temperature rise of helium in the liquid hydrogen storage tank. This fundamentally avoids the high risks of direct testing of liquid hydrogen, while also avoiding the conversion errors caused by differences in physical properties and complex phase transitions in the liquid nitrogen substitution method. The method is simple to operate and has high testing accuracy.

[0008] On one hand, embodiments of the present invention provide a method for testing the static evaporation rate of a liquid hydrogen storage tank, comprising: The liquid hydrogen storage tank under test is pre-cooled to bring the internal temperature of the liquid hydrogen storage tank to the preset temperature. Cryogenic helium gas is introduced into the pre-cooled liquid hydrogen storage tank; Close all valves on the liquid hydrogen storage tank and allow the liquid hydrogen storage tank to stand for the preset set time. Collect the temperature and pressure parameters of helium gas in the liquid hydrogen storage tank at the start and end of the preset settling time; Based on the temperature and pressure parameters of helium at the start and end, the internal energy values ​​of helium at the start and end are obtained by consulting the helium property parameter table. The mass of helium in the liquid hydrogen storage tank is then calculated based on the volume of the liquid hydrogen storage tank and the density of helium. Based on the helium mass and the difference in internal energy of the helium at the start and end, calculate the heat absorption of the liquid hydrogen storage tank during the preset static time. Based on the heat absorption and the physical properties of liquid hydrogen, the static evaporation rate of the liquid hydrogen storage tank is calculated.

[0009] According to some embodiments of the present invention, the precooling of the liquid hydrogen storage tank under test includes: First pre-cooling: The liquid hydrogen storage tank under test is cooled with liquid nitrogen until the liquid nitrogen fill rate reaches more than 90% of the effective volume of the liquid hydrogen storage tank, and the cooling time is not less than 48 hours, and then the liquid nitrogen is discharged; Second pre-cooling: Cool the helium gas to below -253℃ to perform a second pre-cooling on the liquid hydrogen storage tank. Record the temperature of the circulating helium gas at the outlet of the liquid hydrogen storage tank back to the refrigerator. When the outlet temperature tends to stabilize and is below -253℃, the pre-cooling is complete.

[0010] According to some embodiments of the present invention, in the first pre-cooling, the liquid nitrogen filling rate does not exceed 50 L / min, and temperature measuring points are set at three height positions (upper, middle, and lower) of the liquid hydrogen storage tank. When the temperature at all three measuring points drops below -190°C and the temperature difference between each measuring point does not exceed 10°C, the first pre-cooling is deemed complete. Liquid nitrogen is discharged by a combination of bottom discharge and top nitrogen pressurized purging, and the discharge time is not less than 2 hours. During the second precooling, the circulating helium flow rate is controlled at 5~20g / s. When the outlet temperature stabilizes below 20K and the fluctuation does not exceed ±0.5K within 30 minutes, the second precooling is considered complete.

[0011] According to some embodiments of the present invention, in the step of calculating the mass of helium in the liquid hydrogen storage tank based on the liquid hydrogen storage tank volume and helium density, the formula for calculating the mass of helium in the liquid hydrogen storage tank is as follows: m = V · ρ; In the formula, m is the mass of helium gas in the liquid hydrogen storage tank, in kg; V is the volume of the storage tank, in m³. 3 ρ is the density of helium gas in the liquid hydrogen storage tank, in kg / m³. 3 .

[0012] According to some embodiments of the present invention, the formula for calculating the heat absorption of the liquid hydrogen storage tank during the preset settling time is as follows: Q = m · (u2- u1); In the formula, Q is the heat absorbed by the liquid hydrogen storage tank, in kJ; m is the mass of helium in the liquid hydrogen storage tank, in kg; u1 is the internal energy of helium in the liquid hydrogen storage tank at the beginning, in kJ / kg; u2 is the internal energy of helium in the liquid hydrogen storage tank at the end, in kJ / kg.

[0013] According to some embodiments of the present invention, the formula for calculating the static evaporation rate of liquid hydrogen is as follows: d test = Q / (η · γ · V · ρ H2 ) × 100%; In the formula, d test η represents the static evaporation rate of liquid hydrogen, expressed as % / d; Q represents the heat absorption of the liquid hydrogen storage tank; η represents the rated fill rate of the liquid hydrogen storage tank; γ represents the latent heat of vaporization of liquid hydrogen at atmospheric pressure, expressed as kJ / kg; and V represents the tank volume, expressed as m³. 3 ;ρ H2 The density of liquid hydrogen at atmospheric pressure is expressed in kg / m³. 3 .

[0014] According to some embodiments of the present invention, the calculation of the static evaporation rate of the liquid hydrogen storage tank further includes: The static evaporation rate of the test is converted to the static evaporation rate of liquid hydrogen under standard conditions using the following formula: d std = d test · (0.7·(T std - T s ) / (T h - T s ) + 0.3·(T std 4 - T s 4 ) / (T h 4 - T s 4 )) ; In the formula, d std The static evaporation rate of liquid hydrogen under standard conditions is expressed as % / d; d test The static evaporation rate of liquid hydrogen is measured in % / d; T std The standard state temperature is 293.15 K; T s T represents the saturation temperature of liquid hydrogen at atmospheric pressure, expressed in Kelvin (K). h The average ambient temperature during the test is expressed in Kelvin (K).

[0015] According to some embodiments of the present invention, after the step of calculating the heat absorption of the liquid hydrogen storage tank during the preset settling time, the method further includes: The heat absorption of liquid hydrogen storage tanks is verified using the integral method based on constant volume specific heat capacity. The verification formula is as follows: ; In the formula, Q represents the heat absorbed by the liquid hydrogen storage tank, in kJ; m represents the mass of helium gas in the liquid hydrogen storage tank, in kg; c v (T) represents the constant-volume specific heat capacity of helium at temperature T, in kJ / (kg·K); T1 represents the initial temperature of helium in the liquid hydrogen storage tank, in K; T2 represents the final temperature of helium in the liquid hydrogen storage tank, in K; dT ​​represents the temperature element, i.e., the integral variable. The verification was conducted based on pressure changes, and under constant volume conditions, pressure and temperature satisfy the following formula: P2 / T2 = P1 / T1; In the formula, P1 is the initial helium pressure, and P2 is the final helium pressure. If the measured ratio of P2 / T2 to P1 / T1 deviates by more than 3%, then helium deviates from the ideal gas behavior within the test temperature range and needs to be corrected.

[0016] According to some embodiments of the present invention, the method further includes repeated resting and data collection steps: The static evaporation rates d1 and d2 are obtained within two consecutive preset resting times, wherein the preset resting time is 24 hours. The test result is considered valid when the difference between d1 and d2 does not exceed 5%. If the difference exceeds 5%, continue with the third test for the preset resting time. If it still exceeds 5%, repeat the test.

[0017] In another aspect, embodiments of the present invention provide a static evaporation rate testing system for liquid hydrogen storage tanks, used to implement the above-described static evaporation rate testing method for liquid hydrogen storage tanks. The system includes: Liquid hydrogen storage tank, equipped with pressure detection interface and temperature detection interface; A pressure detection module, located at the pressure detection interface, is used to detect the pressure inside the liquid hydrogen storage tank; A temperature detection module is located at the temperature detection interface and is used to detect the temperature of helium inside the liquid hydrogen storage tank. A helium supply module is used to fill a liquid hydrogen storage tank with cryogenic helium. The helium supply module includes a helium cylinder and a helium refrigerator. The helium cylinder is connected to the liquid hydrogen storage tank through a pipeline, and a control valve is installed on the pipeline. The data processing unit, connected to the pressure detection module and temperature detection module, is used to collect the pressure and temperature parameters of helium in the liquid hydrogen storage tank at the start and end of a preset settling time; calculate the mass of helium in the storage tank based on the tank volume and helium density; calculate the heat absorption of the liquid hydrogen storage tank during the preset settling time based on the helium mass and the difference in internal energy of the helium at the start and end; and calculate the static evaporation rate of the liquid hydrogen storage tank based on the heat absorption and the physical properties of liquid hydrogen.

[0018] The method and system for testing the static evaporation rate of liquid hydrogen storage tanks according to embodiments of the present invention have at least the following beneficial effects: Cryogenic helium is used as the testing medium for the static evaporation rate of liquid hydrogen storage tanks. The heat leakage is calculated by measuring the sensible heat change caused by helium's endothermic temperature rise, and then converted into the liquid hydrogen evaporation rate. First, helium is an inert gas, non-toxic, non-flammable, and non-explosive, completely avoiding the high risks of flammability and explosion associated with liquid hydrogen. Testing requires no explosion-proof site or complex safety facilities, significantly reducing operational barriers and personnel risks. Second, helium remains gaseous throughout the test, avoiding complex interferences such as liquid hydrogen phase transitions, ortho- and para-hydrogen conversions, and thermal stratification. It has good gas diffusion, a relatively stable temperature field inside the tank, and high accuracy and reproducibility of test parameters, meeting engineering precision requirements. Third, the heat leakage is calculated directly based on helium's physical properties, eliminating the need for a liquid nitrogen-liquid hydrogen conversion model or numerical simulation iterations, resulting in simple calculations and clear physical meaning. Fourth, helium does not condense under test conditions of 20K to 50K, stably reproducing the heat transfer environment of liquid hydrogen containers. Helium is readily available, used in small quantities, and recyclable, eliminating reliance on scarce and expensive liquid hydrogen resources, resulting in a short testing cycle and low overall cost. Fifth, helium emissions are pollution-free and environmentally friendly, and it is widely used in the factory inspection, periodic inspection and insulation performance evaluation of liquid hydrogen tank containers, tank trucks and stationary storage tanks.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a flowchart of the static evaporation rate test method for liquid hydrogen storage tanks according to an embodiment of the present invention; Figure 2 This is a functional block diagram of the static evaporation rate testing system for liquid hydrogen storage tanks according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the static evaporation rate testing system for liquid hydrogen storage tanks according to an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the change of helium temperature over time in a liquid hydrogen storage tank as part of the static evaporation rate test method for a liquid hydrogen storage tank according to an embodiment of the present invention. Figure 5 This is a schematic diagram illustrating the change of helium pressure over time in a liquid hydrogen storage tank, as described in the static evaporation rate test method for liquid hydrogen storage tanks according to an embodiment of the present invention. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0022] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0023] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," "exceeding," etc. are understood to exclude the stated number, and "above," "below," "within," etc. are understood to include the stated number. If "first," "second," etc. are used in the description, they are only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the order of the indicated technical features.

[0024] Static evaporation rate measures the amount of liquid evaporation, based on the physical principle of latent heat of phase change. Current technologies all use liquid media such as liquid hydrogen or liquid nitrogen, measuring evaporation through flow rate, gravimetric analysis, or level-pressure methods. The conventional approach is: to measure evaporation rate, the medium must evaporate; to replace liquid hydrogen, a cryogenic liquid with similar physical properties should be found. Under this approach, gaseous helium neither evaporates nor generates latent heat of phase change, thus it is not a candidate medium. While the liquid nitrogen substitution method suffers from unstable conversion factors, the current improvement path involves optimizing the conversion model, establishing thermodynamic simulations, and iteratively solving for the conversion factors, rather than changing the test medium or measurement principle. When facing substitution testing problems, the usual practice is to patch things up within the "liquid nitrogen + conversion model" framework, rather than considering completely breaking free from the liquid medium and phase change measurement framework.

[0025] Helium is commonly used in cryogenic applications as a refrigerant, leak detection gas, protective gas, or pressurizing gas. Helium is typically associated with its inertness, low boiling point, and tendency to leak; there seems to be no technical connection between its conventional uses and static evaporation rate testing. Choosing helium presents several technical obstacles and lessons learned: First, traditional evaporation rate testing requires a phase change in the medium; helium does not evaporate, so it's generally considered unsuitable for evaporation rate measurement. Second, helium's small molecular weight and high leakage rate make it difficult to maintain a constant mass of helium within the container during long-term static testing, leading conventional thinking to consider it unsuitable as a quantitative testing medium. Third, helium has a relatively low specific heat capacity at constant volume, resulting in larger temperature and pressure rises for the same amount of heat leakage, raising concerns about deviations from ideal gas behavior and insufficient measurement accuracy. Finally, using helium requires additional helium cylinders, helium refrigerators, and recovery systems, increasing system complexity and cost, further hindering the choice of helium.

[0026] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] This embodiment provides a method for testing the static evaporation rate of a liquid hydrogen storage tank. Please refer to [link to relevant documentation]. Figure 1 The method for testing the static evaporation rate of liquid hydrogen storage tanks mainly includes steps S101 to S107: S101. Pre-cool the liquid hydrogen storage tank under test so that the internal temperature of the liquid hydrogen storage tank reaches the preset temperature.

[0028] S102. Fill the pre-cooled liquid hydrogen storage tank with cryogenic helium.

[0029] S103. Close all valves of the liquid hydrogen storage tank and allow the liquid hydrogen storage tank to stand for the preset standing time.

[0030] S104. Collect the temperature and pressure parameters of helium in the liquid hydrogen storage tank at the start and end of the preset settling time.

[0031] S105. Based on the temperature and pressure parameters of helium at the start and end, look up the helium physical property parameter table to obtain the internal energy values ​​of helium at the start and end, and calculate the mass of helium in the liquid hydrogen storage tank based on the volume of the liquid hydrogen storage tank and the density of helium.

[0032] S106. Calculate the heat absorbed by the liquid hydrogen storage tank during the preset settling time based on the mass of helium and the difference in internal energy of helium at the start and end.

[0033] S107. Based on the heat absorption and the physical properties of liquid hydrogen, the static evaporation rate of the liquid hydrogen storage tank is calculated.

[0034] Please see Figure 2 This embodiment also provides a static evaporation rate testing system for liquid hydrogen storage tanks, used to implement the above-described static evaporation rate testing method for liquid hydrogen storage tanks. The system includes: Liquid hydrogen storage tank 100 is equipped with pressure detection interface and temperature detection interface; The pressure detection module 200 is located at the pressure detection interface and is used to detect the pressure inside the liquid hydrogen storage tank 100. Temperature detection module 300 is located at temperature detection interface and is used to detect the temperature of helium inside liquid hydrogen storage tank 100. The helium supply module 400 is used to fill the storage tank with cryogenic helium. The helium supply module 400 includes a helium cylinder 410 and a helium refrigerator 420. The helium cylinder 410 is connected to the liquid hydrogen storage tank 100 through a pipeline, and a control valve is installed on the pipeline. The data processing unit 500 is connected to the pressure detection module 200 and the temperature detection module 300. It is used to collect the pressure and temperature parameters of helium in the liquid hydrogen storage tank 100 at the beginning and end of the preset static time; calculate the mass of helium in the liquid hydrogen storage tank 100 based on the tank volume and helium density; calculate the heat absorption of the liquid hydrogen storage tank 100 during the preset static time based on the helium mass and the difference in internal energy of the helium at the beginning and end; and calculate the static evaporation rate of the liquid hydrogen storage tank 100 based on the heat absorption and the physical properties of liquid hydrogen.

[0035] Please see Figure 3 The system also includes a liquid nitrogen tank 600 and a helium refrigerator. The liquid nitrogen tank 600 is used to store liquid nitrogen and perform initial precooling on the liquid hydrogen storage tank 100. The helium refrigerator is used to cool helium to below 20K and perform secondary precooling on the liquid hydrogen storage tank 100.

[0036] The system also includes an automatic filling module and a safety interlock module. The automatic filling module includes a mass flow controller, an electric regulating valve, and a PLC controller, which automatically fills the helium tank according to a preset filling rate and termination pressure. During the filling process, the pressure inside the tank is monitored in real time, and filling is automatically paused when the pressure exceeds the limit. The safety interlock module is used to monitor the pressure inside the tank in real time, and automatically open the vent valve to release pressure when the pressure exceeds the limit; it also monitors the ambient hydrogen concentration in real time, and automatically alarms and shuts off all valves when the concentration exceeds the limit; it is equipped with an emergency stop button, which can terminate the test with one click.

[0037] The data processing unit stores a table of helium physical properties, including the density, internal energy, and specific heat capacity of helium at different temperatures and pressures.

[0038] The static evaporation rate testing method and system for liquid hydrogen storage tanks provided in the embodiments of the present invention will be described in detail below.

[0039] 1. Precooling of liquid hydrogen storage tank The liquid hydrogen storage tank 100 under test is pre-cooled to reduce the internal temperature of the liquid hydrogen storage tank 100 to a preset temperature, which is below 20K (i.e. below -253℃).

[0040] The precooling process for liquid hydrogen storage tanks includes two stages: a first precooling and a second precooling. First pre-cooling: The tested liquid hydrogen storage tank 100 is cooled using liquid nitrogen. The liquid nitrogen filling rate should reach more than 90% of the effective volume, and the filling rate should be controlled within the range of 30~50L / min to prevent thermal stress damage to the inner container due to excessive temperature difference. For example, for a 40m³ storage tank, a filling rate of 40L / min will require approximately 15 hours to complete 90% filling. Temperature measuring points are set at three heights (upper, middle, and lower) of the inner container of the liquid hydrogen storage tank 100 to continuously monitor the temperature distribution of each part of the tank. After sufficient cooling for at least 48 hours, the first pre-cooling is considered complete when the temperature at all three measuring points drops below -190℃ and the temperature difference between the measuring points does not exceed 10℃. Then, the liquid nitrogen is drained using a combination of bottom purging and top nitrogen pressurization, with a purging time of no less than 2 hours to ensure that no residual liquid nitrogen remains in the tank.

[0041] Second pre-cooling: Helium gas is cooled to below 20K (below the boiling point of liquid hydrogen, 20.27K) using a helium refrigerator to perform a second deep pre-cooling of liquid hydrogen storage tank 100. The circulating helium flow rate is controlled between 5 and 20 g / s; too high a flow rate will result in wasted cooling capacity, while too low a flow rate will lead to insufficient pre-cooling efficiency. The temperature of the circulating helium at the outlet of liquid hydrogen storage tank 100 back to the refrigerator is recorded. When the outlet temperature tends to stabilize below 20K and the fluctuation does not exceed ±0.5K within 30 minutes, the second pre-cooling is considered complete.

[0042] Since the critical temperature of helium is 5.19K, which is far below the test operating temperature range (20K~50K), the cryogenic helium introduced is gaseous helium. The helium remains in a gaseous state throughout the test, does not undergo a phase change, and there is no risk of liquefaction.

[0043] The two-stage precooling process ensures that the internal temperature of the storage tank is sufficiently reduced to near the liquid hydrogen temperature range, creating suitable initial conditions for subsequent helium testing.

[0044] 2. Replacement and filling with cryogenic helium After the secondary precooling is completed, the helium refrigeration circulation loop is shut down. The interior of the liquid hydrogen storage tank 100 is purged and replaced three times with high-purity helium gas (i.e., purity not less than 99.999%). After each purging, the vacuum is evacuated to below 10 Pa to completely remove residual liquid nitrogen vapor and other impurity gases from the tank.

[0045] After the purging is completed, cryogenic helium is introduced into the liquid hydrogen storage tank 100 through a helium cylinder. The introduced helium is gaseous helium, and its temperature should be below 20K to ensure that the helium remains gaseous throughout the test and does not undergo any phase change.

[0046] The filling rate of cryogenic helium should not exceed 10 g / s to prevent a sudden pressure rise and uneven temperature field inside the tank. The filling termination pressure is set to 0.08~0.15 MPa (absolute pressure), determined according to the design pressure and testing requirements of the liquid hydrogen storage tank 100. After filling, all valves are closed, and the tank is allowed to stand for at least 2 hours, during which time the pressure and temperature changes inside the tank are continuously monitored. When the pressure change rate is less than 0.001 MPa / h and the temperature change rate is less than 0.1 K / h, the tank is considered to have reached thermal equilibrium, and initial parameters are recorded.

[0047] 3. Settling and Data Acquisition Close all valves of liquid hydrogen storage tank 100 to allow it to settle for a preset settling time. During the settling process, the temperature difference between the inside and outside of liquid hydrogen storage tank 100 causes heat to continuously enter the tank from the external environment. This heat is absorbed by the helium gas inside liquid hydrogen storage tank 100, resulting in an increase in helium temperature and pressure.

[0048] Record the pressure P1 and temperature T1 of the helium gas in the storage tank at the start of the preset settling time. Record the pressure P2 and temperature T2 of the helium gas in the storage tank at the end of the preset settling time.

[0049] Throughout the test, the ambient temperature T was continuously recorded. h The weighted arithmetic mean of the ambient temperature at each sampling time within 24 hours during the test period is taken.

[0050] Temperature measurement accuracy should be no less than ±0.1K, and the temperature sensor response time should not exceed 1 second. The temperature sensor should preferably be a platinum resistance thermometer (such as Pt100 or Pt1000 low-temperature type) or a low-temperature thermocouple (such as a T-type thermocouple) suitable for ultra-low temperature environments, with a measurement range covering 4K~100K. Pressure measurement accuracy should be no less than ±0.1%FS (full scale), and the pressure sensor response time should not exceed 0.5 seconds. The pressure sensor range should cover 0~1.0MPa.

[0051] During the first two hours of the test, the sampling frequency was maintained at no less than 1 Hz. After the two hours, the slope of the linear fit of the temperature data from the 1.5-hour to the 2-hour period was taken as the rate of temperature change. If this rate of change was less than 0.5 K / h, the sampling frequency was reduced to 0.1 Hz. All data were recorded and stored in real time, and temperature-time and pressure-time curves were plotted to determine whether thermal equilibrium had been reached.

[0052] The preset settling time was set to 24 hours. To verify the reliability of the test results, the above settling and data acquisition steps were repeated to obtain the static evaporation rates d1 and d2 for two consecutive preset settling times.

[0053] When |d1-d2| / d1×100%≤5%, the test result is deemed valid, and the average of d1 and d2 is taken as the final result; when the deviation exceeds 5%, the test continues for the third preset settling time. If the deviation of any two of the three data exceeds 5%, the test conditions are deemed to be problematic, and the liquid hydrogen storage tank needs to be pre-cooled again, and the test is repeated.

[0054] 4. Calculate the heat absorption of the liquid hydrogen storage tank. Based on the temperature and pressure parameters of helium at the start and end, the internal energy u1(P1,T1) of helium at the start and the internal energy u2(P2,T2) of helium at the end are obtained by consulting the helium property parameter table.

[0055] The volume of liquid hydrogen storage tank 100 is V, and its unit is m³. Since all valves of the storage tank are closed during the test, the volume V of the storage tank remains constant, and the mass m of helium in the tank remains constant. Therefore, the helium density ρ = m / V is a constant throughout the entire test.

[0056] (1) The mass of helium in the liquid hydrogen storage tank is calculated according to the following formula: m = V · ρ; In the formula, m is the mass of helium in the liquid hydrogen storage tank, V is the volume of the storage tank, and ρ is the density of helium in the liquid hydrogen storage tank, in kg / m³, which is obtained by looking up the helium physical property parameter table, that is, based on the initial state P1 and T1, and remains unchanged throughout the test.

[0057] (2) The heat absorption Q of the liquid hydrogen storage tank during the preset settling time (e.g., 24 hours) is calculated according to the following formula: Q = m · (u2- u1); In the formula, Q is the heat absorbed by the liquid hydrogen storage tank, in kJ; m is the mass of helium in the liquid hydrogen storage tank, in kg; u1 is the internal energy of the helium in the tank at the beginning, in kJ / kg; u2 is the internal energy of the helium in the tank at the end, in kJ / kg.

[0058] The physical basis of this formula is the first law of thermodynamics: under constant volume conditions, all the heat absorbed by the system is used to increase its internal energy. This is the thermodynamic basis for the use of "sensible heat change" rather than "latent heat of phase change" in this invention, i.e., the use of the helium sensible heat method.

[0059] To verify the reliability of the heat absorption calculation results of the helium sensible heat method, the internal energy difference method and the constant volume specific heat capacity integral method were used for mutual verification, and the rationality was checked by combining the pressure change verification method.

[0060] (1) Based on the constant volume specific heat capacity integral method When helium is approximately an ideal gas within the test temperature range and its specific heat capacity at constant volume varies with temperature: ; In the formula, Q represents the heat absorbed by the storage tank during the preset settling time, in kJ; m represents the mass of helium gas in the storage tank, in kg; c v (T) represents the constant volume specific heat capacity of helium at temperature T, in kJ / (kg·K); T1 represents the temperature of helium in the tank at the start of the preset settling time, in K; T2 represents the temperature of helium in the tank at the end of the preset settling time, in K; dT ​​represents the temperature element (integral variable).

[0061] (2) Verification method based on pressure change For helium gas in a closed, rigid container, under constant volume conditions, the pressure and temperature satisfy: P2 / T2 = P1 / T1; In the formula, P1 is the initial helium pressure, and P2 is the final helium pressure.

[0062] If the measured ratio of P2 / T2 to P1 / T1 deviates by more than 3%, this threshold is derived from the maximum deviation (approximately 1%) of the compressibility factor of helium from 1 within this temperature and pressure range, multiplied by a safety factor of 3, to cover measurement errors and real gas effects. This indicates that the following situations may exist: helium deviates from ideal gas behavior within the test temperature range, requiring correction using the real gas equation of state; or there is a minor leak in the storage tank; or there is a systematic error in the temperature or pressure measurement.

[0063] By verifying each other using the methods described above, the reliability of the heat absorption calculation results can be improved.

[0064] Helium's physical properties (including density, internal energy, specific heat capacity at constant pressure, and specific heat capacity at constant volume) are obtained by consulting a professional cryogenic fluid thermophysical property database, yielding helium's thermophysical parameters over a wide temperature and pressure range. Alternatively, a table of helium's physical properties within a specific temperature and pressure range can be prepared in advance, allowing for direct lookup of the required parameters during testing.

[0065] 5. Calculate the static evaporation rate of liquid hydrogen. The calculated heat absorption Q is converted into the amount of liquid hydrogen evaporation if the internal storage medium is liquid hydrogen, thus obtaining the liquid hydrogen evaporation rate.

[0066] (1) Test static evaporation rate d of liquid hydrogen test Calculate according to the following formula: d test = Q / (η·γ·V·ρ H2 ) × 100%; In the formula, d testη represents the static evaporation rate of liquid hydrogen, expressed as % / d; Q represents the heat absorption of the liquid hydrogen storage tank; η represents the rated fill rate of the liquid hydrogen storage tank; γ represents the latent heat of vaporization of liquid hydrogen at atmospheric pressure, expressed as kJ / kg; and V represents the tank volume, expressed as m³. 3 ;ρ H2 The density of liquid hydrogen at atmospheric pressure is expressed in kg / m³. 3 .

[0067] (2) Convert the tested static evaporation rate to the static evaporation rate of liquid hydrogen under standard conditions: d std = d test · (0.7·(T std - T s ) / (T h - T s ) + 0.3·(T std 4 - T s 4 ) / (T h 4 - T s 4 )) ; In the formula, d std The static evaporation rate of liquid hydrogen under standard conditions is expressed as % / d; d test The static evaporation rate of liquid hydrogen is measured in % / d; T std The standard state temperature is 293.15 K; T s T represents the saturation temperature of liquid hydrogen at atmospheric pressure, expressed in Kelvin (K). h The average ambient temperature during the test is expressed in Kelvin (K), which is the weighted average of the ambient temperature at each sampling time. The standard pressure is 101325 Pa.

[0068] Here, coefficients 0.7 and 0.3 represent the empirical proportions of convective heat transfer and radiative heat transfer in the total heat loss of the liquid hydrogen storage tank, respectively. For a high-vacuum multilayer insulation structure, convective heat transfer accounts for approximately 70% of the total heat loss, and radiative heat transfer accounts for approximately 30%. Coefficient 0.7 corresponds to the temperature correction of the convective heat transfer component in the heat loss, and is proportional to the temperature difference; coefficient 0.3 corresponds to the temperature correction of the radiative heat transfer component in the heat loss, and is proportional to the fourth power of the temperature difference. This ratio can be adjusted according to the actual type of insulation structure of the storage tank.

[0069] In some embodiments of the present invention, anomaly identification and removal processing is also performed on the test data: (1) Moving average filtering The pressure and temperature data continuously collected during the test were processed using a moving average filter. The moving average window width was set to 60 sampling points (corresponding to 1 minute of data, with a sampling frequency of 1Hz), and each data point was replaced with the arithmetic mean of the data within the window. The moving average filter effectively eliminated high-frequency random noise while preserving the true trend of the signal.

[0070] (2) Identification and removal of outlier data points When the pressure or temperature data at a certain moment deviates from the average of the data over the preceding and following 5 minutes by ±3 times the standard deviation, it is judged as an outlier and is removed.

[0071] (3) Determination of test validity If more than 5% of the data points are removed, the test data quality is deemed unacceptable and must be retested.

[0072] (4) Uncertainty assessment Provide an assessment of the uncertainty of the test results, including Type A uncertainty and Type B uncertainty.

[0073] Type A uncertainty (statistical assessment): calculated using statistical methods based on the standard deviation of continuously collected data and the number of samples.

[0074] Type B uncertainty (non-statistical evaluation): Evaluate the uncertainty introduced by temperature measurement, pressure measurement, and volume measurement based on the instrument calibration certificate and manufacturer's technical specifications.

[0075] The following is an example of a 40m 3 The test method of the present invention is illustrated using a liquid hydrogen storage tank as the test object.

[0076] 1. Test object parameters The main parameters of the liquid hydrogen storage tank under test are as follows: Internal container geometric volume: 40m³ 3 ; Effective internal volume: 36m³ 3 ; Rated fill rate: 90%; Thermal insulation structure: high vacuum multilayer thermal insulation.

[0077] 2. Test Procedure (1) First pre-cooling Liquid nitrogen was used to cool the liquid hydrogen storage tank 100 under test. Liquid nitrogen was filled into the liquid hydrogen storage tank 100 at a rate controlled at 40 L / min, so that the liquid nitrogen filling rate reached more than 90% of the effective volume. Platinum resistance thermometers were installed at three height points (upper, middle, and lower) inside the liquid hydrogen storage tank 100 to continuously monitor the temperature distribution of various parts of the liquid hydrogen storage tank 100.

[0078] The liquid hydrogen storage tank 100 was kept fully cooled under this condition for 48 hours. After 48 hours, the temperature at all three measuring points dropped below -190℃, and the temperature difference between the measuring points was 6℃, which met the criteria for the completion of the first pre-cooling.

[0079] Open the drain valve at the bottom of liquid hydrogen storage tank 100, and use a combination of bottom venting and top nitrogen pressurization purging to completely drain the liquid nitrogen from the tank. The venting time is approximately 2.5 hours, ensuring that no liquid nitrogen remains in the tank. This completes the first pre-cooling. After liquid nitrogen pre-cooling, the internal temperature of liquid hydrogen storage tank 100 has been significantly reduced to approximately 77K (-196℃), but is still above the liquid hydrogen temperature range.

[0080] (2) Second precooling The helium refrigeration unit is activated to cool the helium gas to below 20K (i.e., below -253℃). Cryogenic helium gas is then introduced into the liquid hydrogen storage tank 100, with the circulating helium flow rate controlled at 10g / s, to perform a secondary deep pre-cooling of the liquid hydrogen storage tank 100. During this secondary pre-cooling process, the cryogenic helium gas circulates within the liquid hydrogen storage tank 100, continuously absorbing residual heat from the tank's walls and internal components, further reducing the internal temperature of the liquid hydrogen storage tank 100 to the liquid hydrogen temperature range.

[0081] During the second precooling process, the temperature of the circulating helium at the outlet of the liquid hydrogen storage tank 100 back to the refrigerator was continuously monitored. After approximately 8 hours of the second precooling, the outlet temperature stabilized at 19.5K, and the fluctuation within 30 minutes did not exceed ±0.3K, meeting the criteria for the completion of the second precooling.

[0082] (3) Displacement After the second precooling is completed, the helium refrigeration circulation loop is shut down. The interior of the liquid hydrogen storage tank 100 is purged and replaced three times with high-purity helium gas (99.999% purity). After each purging, the vacuum is evacuated to below 10 Pa to completely remove residual liquid nitrogen vapor and other impurity gases from the tank.

[0083] (4) Fill with helium and collect initial parameters After the purging is completed, cryogenic helium is introduced into the liquid hydrogen storage tank 100 through a helium cylinder at a rate controlled at 8 g / s. The filling termination pressure is set at 0.1031 MPa. After filling, all valves are closed, and the tank is left to stand for 2 hours, during which time the pressure and temperature changes inside the tank are continuously monitored. When the pressure change rate is less than 0.001 MPa / h and the temperature change rate is less than 0.1 K / h, the thermal equilibrium condition is met. After the pressure and temperature of the helium in the liquid hydrogen storage tank 100 stabilize, the pressure P1 and temperature T1 of the helium in the liquid hydrogen storage tank 100 at the initial moment are recorded. The pressure P1 and temperature T1 are the arithmetic mean of the data from the last 10 minutes.

[0084] Simultaneously, the ambient temperature T is continuously recorded by an ambient temperature sensor installed around the liquid hydrogen storage tank 100. h The sampling frequency was set to 1Hz for the first 2 hours. After 2 hours, the slope of the linear fit of the temperature data from the 1.5th hour to the 2nd hour was 0.15K / h, which is less than 0.5K / h. Therefore, the sampling frequency was reduced to 0.1Hz.

[0085] (5) Let stand for 24 hours The liquid hydrogen storage tank 100 was left to stand in a completely sealed state for 24 hours. During this period, due to the large temperature difference between the outside and inside of the liquid hydrogen storage tank 100 (the outside temperature is about 293K, and the inside temperature is about 20K), heat continuously entered the liquid hydrogen storage tank 100 from the outside environment through the insulation layer. This heat was absorbed by the helium gas inside the tank, causing the temperature and pressure of the helium gas to gradually increase.

[0086] (6) Acquire termination parameters Please see Figure 4 and Figure 5 After 24 hours of settling, record the helium pressure P2 and helium temperature T2 in the liquid hydrogen storage tank 100 at the end time. The helium pressure P2 and helium temperature T2 are both taken as the arithmetic mean of the data in the last 10 minutes.

[0087] The actual recorded parameters are as follows: Initial helium pressure P1: 0.1031 MPa; Initial helium temperature T1: 21 K; The helium pressure at termination, P2, is 0.2047 MPa. The helium temperature at termination, T2, is 43 K. The average ambient temperature T during the test period h 275.65 K (approximately 2.5℃); liquid hydrogen saturation temperature T s : 20.27 K.

[0088] 3. Calculation of heat absorption Based on the initial conditions (P1=0.1031MPa, T1=21K), the helium density ρ = 2.3 kg / m³, and the initial internal energy u1 is 65.49 kJ / kg. Based on the final conditions (P2=0.2047MPa, T2=43K), the final internal energy u2 is 134.13 kJ / kg. Since the liquid hydrogen storage tank 100 is a closed rigid container with a constant volume V and a constant helium mass m, the helium density ρ remains constant throughout the test, at 2.30 kg / m³.

[0089] (1) Calculate the mass of helium in the liquid hydrogen storage tank: m = V·ρ = 40 × 2.3 = 92kg.

[0090] The tank volume V is 40m³. Since helium exists in gaseous form during the test, it will fill the entire space of the tank's inner container. Therefore, the calculation takes the geometric volume of the inner container (i.e., 40m³) rather than the rated filling volume of liquid hydrogen.

[0091] (2) The heat absorption is calculated using the internal energy difference method: Q=m·(u2- u1)=92 × (134.13 - 65.49)=6314.88kJ.

[0092] The endothermic heating process of helium is a isochoric process, and the isochoric specific heat capacity of helium is c. v The average value over the temperature range of 21K to 43K is approximately 3.12 kJ / (kg·K).

[0093] (3) The heat absorption is calculated using the average constant volume specific heat capacity method: Q = m·c v ·(T2- T1) = 92 × 3.12 × (43 - 21) = 92 × 3.12 × 22 =6314.88kJ.

[0094] The calculation results of the internal energy difference method and the average constant-volume specific heat capacity method are completely consistent. Using the internal energy difference method eliminates the need for averaging the specific heat capacity, resulting in higher accuracy. The two methods are essentially equivalent; under constant-volume conditions and with the specific heat capacity approximately constant, the internal energy difference method can be simplified to the specific heat capacity multiplied by the temperature difference.

[0095] 4. Calculation of static evaporation rate Physical properties of liquid hydrogen at atmospheric pressure: Latent heat of vaporization γ: 445 kJ / kg; Saturation temperature T s 20.27 K; Liquid hydrogen density ρ H2 70.97 kg / m 3 ; (1) Calculate the static evaporation rate (under the test ambient temperature) d test = Q / (η·γ·V·ρ H2 ) × 100% = 6314.88 / (0.9 × 445 × 40 × 70.97) × 100% = 0.555% / d.

[0096] (2) Static evaporation rate converted to standard conditions The evaporation rate at the test ambient temperature was converted to standard conditions: d std = d test ·(0.7·(T std - T s ) / (T h - T s ) + 0.3·(T std 4 - T s 4 ) / (T h 4 - T s 4 )) = 0.555 × (0.7 × (293.15 - 20.27) / (275.65 - 20.27) + 0.3 × (293.15) 4 - 20.27 4 ) ) / (275.65 4 - 20.27 4 ) ≈ 0.628% / d.

[0097] 5. Comparison and verification with the direct testing method using liquid hydrogen To verify the accuracy of the method of the present invention, the same 40m... 3 The liquid hydrogen storage tank was directly tested according to the standard method of GB / T 18443.5, using liquid hydrogen as the test medium. After the liquid hydrogen storage tank reached thermal equilibrium, continuous measurements were taken for 24 hours, and the cumulative mass flow rate of the evaporated gas was recorded. The average evaporation rate over 24 hours was calculated to be 14.77 kg / d.

[0098] (1) The latent heat of vaporization of liquid hydrogen at atmospheric pressure is 445 kJ / kg. Calculate the heat absorbed: Q H2 = 14.77 × 445 = 6572.65kJ.

[0099] (2) Heat absorption measured using the helium sensible calorimetry method: Q He = 40 × 2.3 × 3.12 × (43 - 21) = 6314.88kJ.

[0100] (3) Calculate the deviation in heat absorption: E = (Q H2 - Q He ) / Q H2× 100% = (6572.65 - 6314.88) / 6572.65 × 100% ≈3.92%.

[0101] (4) Calculate the static evaporation rate Liquid hydrogen density ρ H2 Given a hydrogen density of 70.97 kg / m³, calculate the mass of liquid hydrogen to be filled: m H2 =η·V·ρ H2 =0.9×40×70.97=2554.92kg; The static evaporation rate was calculated as follows: D test,H2 =14.77 / 2554.92×100%=0.578% / d; The evaporation rate at the test ambient temperature was converted to standard conditions: d std,H2 = d test,H2 ·(0.7·(T std - T s ) / (T h - T s ) + 0.3·(T std 4 - T s 4 ) / (T h 4 - T s 4 )) = 0.578 × (0.7 × (293.15 - 20.27) / (275.65 - 20.27) + 0.3 × (293.15) 4 - 20.27 4 ) ) / (275.65 4 - 20.27 4 ) ≈0.654% / d.

[0102] (5) Calculate the evaporation rate deviation: E d = (d std,H2 - d std ) / d std,H2 × 100% = (0.654 - 0.628) / 0.654 × 100% ≈3.98%.

[0103] Please refer to Table 1 for a comparison of the test results.

[0104] Table 1. Comparison of test results between the test method of this invention and the test results using the direct liquid hydrogen test method. 6. Test Result Analysis The above test results show that: (1) Using helium as the test medium, the heat leakage of the liquid hydrogen storage tank is calculated by measuring the sensible heat change of helium, and then the static evaporation rate of liquid hydrogen is calculated. The method is feasible and the results are accurate.

[0105] (2) Compared with direct testing of liquid hydrogen, the heat absorption deviation is only 3.92% and the standard state evaporation rate deviation is about 3.98%, which fully meets the engineering accuracy requirements (usually the deviation is required to be no more than 5%).

[0106] (3) Helium remains in a gaseous state throughout the test, without the complexity and uncertainty caused by phase transition, and the test results have good reproducibility.

[0107] (4) Helium is an inert gas, and the testing process is safe and reliable, without the need for complicated explosion-proof facilities.

[0108] This application does not simply replace liquid hydrogen or liquid nitrogen with helium; rather, it changes the measurement principle from "measuring the latent heat of phase change" to "measuring the sensible heat change," and then converts the sensible heat change into the liquid hydrogen evaporation rate. It overcomes the conventional thinking that "evaporation rate must be measured by the amount of evaporation," and redefines the testing logic: the increase in internal energy absorbed by helium represents the heat leakage of the liquid hydrogen storage tank, and the amount of liquid hydrogen evaporation is then calculated using this heat leakage. By employing the helium sensible heat method, the following beneficial effects are achieved.

[0109] 1. Significantly Enhanced Safety: Helium is an inert gas, non-toxic, non-flammable, and non-explosive, completely avoiding the high risks associated with the flammability and explosiveness of liquid hydrogen. The testing process requires no complex explosion-proof equipment, lowering the operational threshold and fundamentally ensuring personnel safety.

[0110] 2. Higher test stability and accuracy: Helium is used for testing, avoiding the complex and unpredictable test results caused by liquid hydrogen phase change and positive-negative hydrogen conversion. At the same time, helium exists in gaseous form. Since the diffusion of gases is much better than that of liquids, the temperature field of the medium inside the container is easier to stabilize when using helium for testing than that of liquid hydrogen. The test parameters are more accurate, and the accuracy and reproducibility of the obtained static evaporation rate value are better.

[0111] 3. Adaptable to ultra-low temperature testing scenarios: Helium has a boiling point as low as 4.2K and a critical temperature of 5.19K, which is far below the operating temperature range of the test method in this application. Therefore, it will not condense during the test and will maintain a stable gaseous state, which can accurately reproduce the heat transfer environment inside the cryogenic pressure vessel and is suitable for the insulation performance testing requirements of liquid hydrogen containers.

[0112] 4. Lowering the threshold for test implementation: Helium is readily available and does not rely on scarce liquid hydrogen resources. The pretreatment process before testing is simple and it is widely used for static evaporation rate testing of various liquid hydrogen storage tanks (such as liquid hydrogen tank containers, liquid hydrogen tank trucks, stationary liquid hydrogen storage tanks and liquid hydrogen spherical tanks), which can shorten the test cycle and reduce the overall test cost.

[0113] 5. No need for complex conversion factors: Unlike the liquid nitrogen substitution method, the heat loss is calculated directly based on the physical properties of helium. There is no need to establish a complex liquid nitrogen-liquid hydrogen evaporation rate conversion model or to perform numerical simulation iterations. The calculation process is simple and the physical meaning is clear.

[0114] 6. Experimental verification shows that the deviation between the helium sensible calorimetry method and the direct liquid hydrogen method is less than 5%, which is within the acceptable range for engineering applications and has high accuracy and reliability.

[0115] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for testing the static evaporation rate of a liquid hydrogen storage tank, characterized in that, include: The liquid hydrogen storage tank under test is pre-cooled to bring the internal temperature of the liquid hydrogen storage tank to the preset temperature. Cryogenic helium gas is introduced into the pre-cooled liquid hydrogen storage tank; Close all valves on the liquid hydrogen storage tank and allow the liquid hydrogen storage tank to stand for the preset set time. Collect the temperature and pressure parameters of helium gas in the liquid hydrogen storage tank at the start and end of the preset settling time; Based on the temperature and pressure parameters of helium at the start and end, the internal energy values ​​of helium at the start and end are obtained by consulting the helium property parameter table. The mass of helium in the liquid hydrogen storage tank is then calculated based on the volume of the liquid hydrogen storage tank and the density of helium. Based on the helium mass and the difference in internal energy of the helium at the start and end, calculate the heat absorption of the liquid hydrogen storage tank during the preset static time. Based on the heat absorption and the physical properties of liquid hydrogen, the static evaporation rate of the liquid hydrogen storage tank is calculated.

2. The method for testing the static evaporation rate of a liquid hydrogen storage tank according to claim 1, characterized in that, The precooling of the liquid hydrogen storage tank under test includes: First pre-cooling: The liquid hydrogen storage tank under test is cooled with liquid nitrogen until the liquid nitrogen fill rate reaches more than 90% of the effective volume of the liquid hydrogen storage tank, and the cooling time is not less than 48 hours, and then the liquid nitrogen is discharged; Second pre-cooling: Cool the helium gas to below -253℃ to perform a second pre-cooling on the liquid hydrogen storage tank. Record the temperature of the circulating helium gas at the outlet of the liquid hydrogen storage tank back to the refrigerator. When the outlet temperature tends to stabilize and is below -253℃, the pre-cooling is complete.

3. The method for testing the static evaporation rate of a liquid hydrogen storage tank according to claim 2, characterized in that, During the first pre-cooling, the liquid nitrogen filling rate shall not exceed 50L / min. Temperature measuring points shall be set at the upper, middle and lower heights of the liquid hydrogen storage tank. When the temperature at all three measuring points drops below -190℃ and the temperature difference between the measuring points does not exceed 10℃, the first pre-cooling shall be deemed complete. Liquid nitrogen shall be discharged by a combination of bottom discharge and top nitrogen pressurization purging, and the discharge time shall not be less than 2 hours. During the second precooling, the circulating helium flow rate is controlled at 5~20g / s. When the outlet temperature stabilizes below 20K and the fluctuation does not exceed ±0.5K within 30 minutes, the second precooling is considered complete.

4. The method for testing the static evaporation rate of a liquid hydrogen storage tank according to claim 1, characterized in that, In the step of calculating the mass of helium in the liquid hydrogen storage tank based on the liquid hydrogen storage tank volume and helium density, the formula for calculating the mass of helium in the liquid hydrogen storage tank is as follows: m = V · ρ; In the formula, m is the mass of helium gas in the liquid hydrogen storage tank, in kg; V is the volume of the storage tank, in m³. 3 ρ is the density of helium gas in the liquid hydrogen storage tank, in kg / m³. 3 .

5. The method for testing the static evaporation rate of a liquid hydrogen storage tank according to claim 4, characterized in that, The formula for calculating the heat absorption of the liquid hydrogen storage tank during the preset settling time is as follows: Q = m · (u2- u1); In the formula, Q is the heat absorbed by the liquid hydrogen storage tank, in kJ; m is the mass of helium in the liquid hydrogen storage tank, in kg; u1 is the internal energy of helium in the liquid hydrogen storage tank at the beginning, in kJ / kg; u2 is the internal energy of helium in the liquid hydrogen storage tank at the end, in kJ / kg.

6. The method for testing the static evaporation rate of a liquid hydrogen storage tank according to claim 5, characterized in that, The formula for calculating the static evaporation rate of liquid hydrogen is: d test = Q / (η·γ·V·ρ H2 ) × 100%; In the formula, d test η represents the static evaporation rate of liquid hydrogen, expressed as % / d; Q represents the heat absorption of the liquid hydrogen storage tank; η represents the rated fill rate of the liquid hydrogen storage tank; γ represents the latent heat of vaporization of liquid hydrogen at atmospheric pressure, expressed as kJ / kg; and V represents the tank volume, expressed as m³. 3 ; ρ H2 The density of liquid hydrogen at atmospheric pressure is expressed in kg / m³. 3 .

7. The method for testing the static evaporation rate of a liquid hydrogen storage tank according to claim 6, characterized in that, The calculation of the static evaporation rate of the liquid hydrogen storage tank also includes: The static evaporation rate of the test is converted to the static evaporation rate of liquid hydrogen under standard conditions using the following formula: d std = d test · (0.7·(T std - T s ) / (T h - T s ) + 0.3·(T std 4 - T s 4 ) / (T h 4 - T s 4 )) ; In the formula, d std The static evaporation rate of liquid hydrogen under standard conditions is expressed as % / d; d test The static evaporation rate of liquid hydrogen is measured in % / d; T std The standard state temperature is 293.15 K; T s T represents the saturation temperature of liquid hydrogen at atmospheric pressure, expressed in Kelvin (K). h The average ambient temperature during the test is expressed in Kelvin (K).

8. The method for testing the static evaporation rate of a liquid hydrogen storage tank according to claim 5, characterized in that, After the step of calculating the heat absorption of the liquid hydrogen storage tank during the preset settling time, the method further includes: The heat absorption of liquid hydrogen storage tanks is verified using the integral method based on constant volume specific heat capacity. The verification formula is as follows: ； In the formula, Q represents the heat absorbed by the liquid hydrogen storage tank, in kJ; m represents the mass of helium gas in the liquid hydrogen storage tank, in kg; c v (T) represents the constant-volume specific heat capacity of helium at temperature T, in kJ / (kg·K); T1 represents the initial temperature of helium in the liquid hydrogen storage tank, in K; T2 represents the final temperature of helium in the liquid hydrogen storage tank, in K; dT ​​represents the temperature element, i.e., the integral variable. The verification was conducted based on pressure changes, and under constant volume conditions, pressure and temperature satisfy the following formula: P2 / T2 = P1 / T1; In the formula, P1 is the initial helium pressure, and P2 is the final helium pressure. If the measured ratio of P2 / T2 to P1 / T1 deviates by more than 3%, then helium deviates from the ideal gas behavior within the test temperature range and needs to be corrected.

9. The method for testing the static evaporation rate of a liquid hydrogen storage tank according to claim 1, characterized in that, The method also includes repeating the settling and collection steps: The static evaporation rates d1 and d2 are obtained within two consecutive preset resting times, wherein the preset resting time is 24 hours. The test result is considered valid when the difference between d1 and d2 does not exceed 5%. If the difference exceeds 5%, continue with the third preset resting time test. If it still exceeds 5%, repeat the test.

10. A static evaporation rate testing system for a liquid hydrogen storage tank, characterized in that, The method for testing the static evaporation rate of a liquid hydrogen storage tank according to any one of claims 1 to 9 includes: Liquid hydrogen storage tank, equipped with pressure detection interface and temperature detection interface; A pressure detection module, located at the pressure detection interface, is used to detect the pressure inside the liquid hydrogen storage tank; A temperature detection module is located at the temperature detection interface and is used to detect the temperature of helium inside the liquid hydrogen storage tank. A helium supply module is used to fill a liquid hydrogen storage tank with cryogenic helium. The helium supply module includes a helium cylinder and a helium refrigerator. The helium cylinder is connected to the liquid hydrogen storage tank through a pipeline, and a control valve is installed on the pipeline. The data processing unit, connected to the pressure detection module and temperature detection module, is used to collect the pressure and temperature parameters of helium in the liquid hydrogen storage tank at the start and end of a preset settling time; calculate the mass of helium in the liquid hydrogen storage tank based on the tank volume and helium density; calculate the heat absorption of the liquid hydrogen storage tank during the preset settling time based on the helium mass and the difference in internal energy of the helium at the start and end; and calculate the static evaporation rate of the liquid hydrogen storage tank based on the heat absorption and the physical properties of liquid hydrogen.

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