Container heat leak detection method and system using liquid nitrogen instead of liquid hydrogen

Abstract

The present invention discloses a container heat leakage detection method and system using liquid nitrogen instead of liquid hydrogen. Liquid nitrogen is filled into the liquid hydrogen container to be tested, and the liquid nitrogen filling process is controlled by step-by-step pre-cooling; the container is left to stand for a preset time, and the pressure data and ambient temperature data inside the liquid hydrogen container are synchronously collected; a pressure-time curve is formed according to the pressure data, and the liquid nitrogen evaporation heat absorption is calculated based on the pressure-time curve; the liquid nitrogen evaporation heat absorption is converted into liquid hydrogen equivalent heat leakage based on a heat flux equivalent conversion model. The system includes a liquid nitrogen supply module, a multi-channel data acquisition module, a wireless communication module, and an equivalent calculation module. By establishing an equivalent conversion model between the liquid nitrogen detection heat flux result and the liquid hydrogen equivalent heat load, the problems of high risk and high cost of traditional liquid hydrogen detection are solved. The system is suitable for factory inspection and thermal insulation performance evaluation of in-service containers; safe and efficient detection of liquid hydrogen containers is achieved, with low detection risk and reduced detection cost.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal insulation performance testing, and in particular to a container heat leakage detection method and system using liquid nitrogen instead of liquid hydrogen. Background Art

[0002] Liquid hydrogen storage and transportation containers are key hydrogen energy infrastructure, and their thermal insulation performance is directly related to safety and operating costs. The current method for detecting heat leakage in liquid hydrogen containers mainly uses liquid hydrogen medium to perform pressurization or evaporation tests. This method has the following problems:

[0003] 1. High risk: Liquid hydrogen is highly flammable and explosive, posing an obvious safety hazard;

[0004] 2. High cost: The high cost of liquid hydrogen preparation and testing is not conducive to large-scale testing;

[0005] 3. Narrow application: It is not suitable for in-service equipment testing, and most liquid hydrogen tankers or storage tanks cannot be connected to the liquid hydrogen source on site.

[0006] Therefore, a low-risk, low-cost detection method that can replace liquid hydrogen is urgently needed. Liquid nitrogen, as a cryogenic medium with similar physical properties and easy access, has broad application potential. However, there is currently a lack of scientific equivalent detection theory, and static evaporation rate testing with liquid nitrogen can only be performed based on experience. The test indicators are unfounded and have large errors, which can easily lead to problems later. Summary of the Invention

[0007] The present invention aims to address at least one of the technical problems existing in the prior art. To this end, the present invention proposes a container heat leak detection method and system that uses liquid nitrogen instead of liquid hydrogen. By establishing an equivalent conversion model between the liquid nitrogen detection heat flux results and the liquid hydrogen equivalent heat load, the present invention enables safe and efficient detection of liquid hydrogen containers, reduces detection risks, and reduces detection costs.

[0008] In one aspect, an embodiment of the present invention provides a container heat leakage detection method using liquid nitrogen instead of liquid hydrogen, comprising:

[0009] Fill the liquid hydrogen container to be tested with liquid nitrogen, and control the filling process of liquid nitrogen through step-by-step pre-cooling;

[0010] Allow the container to stand for a preset period of time, and simultaneously collect the pressure data and ambient temperature data inside the liquid hydrogen container;

[0011] forming a pressure-time curve according to the pressure data, and calculating the amount of heat absorbed by evaporation of liquid nitrogen based on the pressure-time curve;

[0012] Perform dual-channel verification on the liquid nitrogen evaporation heat absorption to obtain the verified liquid nitrogen evaporation heat absorption;

[0013] Based on the heat flux equivalent conversion model, the verified liquid nitrogen evaporation heat absorption is converted into liquid hydrogen equivalent heat leakage;

[0014] Wherein, the heat flux equivalent conversion model satisfies:

[0015]

[0016] Where, Q H2 is the equivalent heat leakage of liquid hydrogen, Q N2 is the heat absorbed by evaporation of liquid nitrogen, k is the equivalent conversion coefficient, ρ N2 is the density of liquid nitrogen, L v,N2 is the latent heat of vaporization of liquid nitrogen, ρ H2 is the density of liquid hydrogen, L v,H2 is the latent heat of vaporization of liquid hydrogen, α is the thermal boundary layer correction coefficient, and β is the phase change heat transfer correction factor.

[0017] According to some embodiments of the present invention, the liquid nitrogen filling process controlled by step-by-step pre-cooling includes:

[0018] In the first stage, the liquid hydrogen container to be tested is filled with 5% liquid nitrogen and maintained for 10 minutes;

[0019] In the second stage, the liquid hydrogen container to be tested is filled with liquid nitrogen to 30% of its volume and maintained for 20 minutes;

[0020] In the third stage, the liquid hydrogen container to be tested is filled with liquid nitrogen to a preset filling rate, and the preset filling rate is dynamically adjusted according to the ambient temperature;

[0021] The full rate is dynamically adjusted based on the ambient temperature adjustment full rate formula, and the ambient temperature adjustment full rate formula is:

[0022]

[0023] Where R is the filling rate, T amb is the ambient temperature.

[0024] According to some embodiments of the present invention, calculating the amount of heat absorbed by evaporation of liquid nitrogen based on the pressure-time curve includes:

[0025] Perform linear fitting on the pressure data during the static stage to obtain the slope kp of the pressure-time curve:

[0026] kp = dP / dt

[0027] Determine and calculate the gas phase space volume Vg based on the filling parameters:

[0028] V g = V total (1-R)

[0029] Where V g is the gas phase space volume, V total is the total volume of the container, R is the filling rate;

[0030] Calculate the evaporation mass rate dm / dt:

[0031]

[0032] Where dm / dt is the evaporation mass rate, V g is the gas phase space volume, M N2 is the molar mass of nitrogen, R gas is the filling rate, T is the average temperature of the gas phase, dP / dt is the slope of the pressure-time curve;

[0033] Calculate the evaporation heat Q N2 :

[0034]

[0035] Where, Q N2 is the heat absorbed by evaporation of liquid nitrogen, dm / dt is the evaporation mass rate, L v,N2 is the latent heat of vaporization of liquid nitrogen.

[0036] According to some embodiments of the present invention, the dual-channel verification of the heat absorption of liquid nitrogen evaporation includes:

[0037] The liquid nitrogen evaporation heat absorption calculated based on the pressure-time curve is set as the first liquid nitrogen evaporation heat absorption;

[0038] The mass loss rate of liquid nitrogen evaporation is obtained by weighing, and the second liquid nitrogen evaporation heat absorption is calculated based on the weighing method calculation formula. The weighing method calculation formula is:

[0039]

[0040] Where, Q N2 The heat absorbed by the evaporation of liquid nitrogen is is the mass loss rate of liquid nitrogen evaporation, L v,N2 is the latent heat of vaporization of liquid nitrogen;

[0041] If the deviation between the first liquid nitrogen evaporation heat absorption and the second liquid nitrogen evaporation heat absorption is ≤5%, the average of the two is taken;

[0042] If the deviation between the first liquid nitrogen evaporation heat absorption value and the second liquid nitrogen evaporation heat absorption value is greater than 5%, pressure data verification is performed.

[0043] According to some embodiments of the present invention, before the step of forming a pressure-time curve according to the pressure data, the step includes:

[0044] The pressure data is compensated for ambient temperature using an ambient temperature compensation formula, which is:

[0045] P real = P meas + 0.021 •(T amb -20)

[0046] Where, P real is the real pressure, P meas To measure pressure, the unit is kPa, T amb is the ambient temperature.

[0047] According to some embodiments of the present invention, the thermal boundary layer correction coefficient α ranges from 1.05 to 1.15 and is associated with the container volume. The associated formula is:

[0048]

[0049] Where α is the thermal boundary layer correction coefficient, V is the volume of the liquid hydrogen container in cubic meters, and ΔT is the difference between the ambient temperature and the boiling point of liquid nitrogen.

[0050] According to some embodiments of the present invention, the phase change heat transfer correction factor β ranges from 0.92 to 0.98, satisfying:

[0051]

[0052] Where β is the phase change heat transfer correction factor, h fg,H2 is the boiling heat transfer coefficient of liquid hydrogen, h fg,N2 is the boiling heat transfer coefficient of liquid nitrogen.

[0053] According to some embodiments of the present invention, after the step of converting the heat absorbed by evaporation of liquid nitrogen into equivalent heat leakage of liquid hydrogen based on the heat flux equivalent conversion model, the method further includes:

[0054] According to the equivalent heat leakage of liquid hydrogen Q H2 Derivation of the static evaporation rate B of liquid hydrogen container H2 , the derivation formula is:

[0055]

[0056] Where, B H2 is the static evaporation rate of the liquid hydrogen container,Q H2 is the equivalent heat leakage of liquid hydrogen, ρ H2 is the density of liquid hydrogen, L v,H2 is the latent heat of vaporization of liquid hydrogen, and V is the volume of the container.

[0057] On the other hand, an embodiment of the present invention provides a container heat leakage detection system using liquid nitrogen instead of liquid hydrogen, comprising:

[0058] A liquid nitrogen supply module, including a volume control valve, is used to provide the liquid nitrogen medium required for container thermal leakage detection, and the liquid nitrogen filling rate is dynamically adjusted by the volume control valve;

[0059] Multi-channel data acquisition module, including pressure sensor, temperature sensor and weighing sensor, used to collect pressure data, temperature data and weight data;

[0060] Wireless communication module, used to upload data to the backend server in real time;

[0061] Equivalent calculation module, with built-in dynamic calculation model of thermal boundary layer correction coefficient α and phase change heat transfer correction factor β.

[0062] According to some embodiments of the present invention, the equivalent calculation module includes:

[0063] Physical property database, used to store the liquid density ρ and latent heat of vaporization L of liquid hydrogen and liquid nitrogen v and boiling heat transfer coefficient h fg parameter;

[0064] α calibration module, used to calibrate the thermal boundary layer correction coefficient α based on standard container experimental data;

[0065] The dynamic compensator is used to dynamically compensate for the difference between the ambient temperature and the boiling point of liquid nitrogen according to the ambient temperature.

[0066] The embodiments of the present invention have at least the following beneficial effects:

[0067] Liquid nitrogen is used instead of liquid hydrogen to detect heat leakage in containers, and a dual-factor heat flux conversion model based on the thermal boundary layer correction coefficient α and the phase change heat transfer correction factor β is established. The detection system includes a liquid nitrogen supply module, a multi-channel data acquisition module, a wireless communication module, and an equivalent calculation module. Multi-source fusion is used to eliminate local temperature differences in the tank caused by solar radiation, such as the temperature difference between the sunny and shady sides of the tank; thermal inertia modeling is used to solve the temperature response lag problem of large containers; derivative advance compensation is used to suppress the interference of sudden changes in ambient temperature; and volume adaptation is used to cover 1~100m 3Full-scale container. This achieves four major benefits: First, safety, eliminating the risk of liquid hydrogen explosion and ensuring safe operations in high-risk environments; second, economic, reducing detection costs by over 85%, with the cost of liquid nitrogen as a medium only 7.5% of that of liquid hydrogen; third, precision, the dual-factor model overcomes the difficulty of physical property differences, resulting in a small error in evaporation rate detection, comparable to the accuracy of direct liquid hydrogen measurement; fourth, efficiency, the detection system can be quickly deployed on-site, shortening the detection cycle and improving the efficiency of liquid hydrogen container heat leak detection.

[0068] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0070] Figure 1 This is a flow chart of a container heat leakage detection method using liquid nitrogen instead of liquid hydrogen according to an embodiment of the present invention;

[0071] Figure 2 A flow chart of a liquid nitrogen filling process controlled by step-by-step pre-cooling in a container heat leak detection method using liquid nitrogen instead of liquid hydrogen according to an embodiment of the present invention;

[0072] Figure 3 This is a flow chart of calculating the amount of heat absorbed by evaporation of liquid nitrogen based on a pressure-time curve in a method for detecting heat leaks in a container using liquid nitrogen instead of liquid hydrogen according to an embodiment of the present invention;

[0073] Figure 4 This is a flow chart of dual-channel verification of the amount of heat absorbed by evaporation of liquid nitrogen in a container heat leakage detection method using liquid nitrogen instead of liquid hydrogen according to an embodiment of the present invention;

[0074] Figure 5 This is a module diagram of a container heat leakage detection system that uses liquid nitrogen instead of liquid hydrogen according to an embodiment of the present invention.

[0075] Reference numerals:

[0076] Liquid nitrogen supply module 100, multi-channel data acquisition module 200, wireless communication module 300, equivalent calculation module 400. DETAILED DESCRIPTION

[0077] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0078] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention.

[0079] In the description of the present invention, "several" means one or more, "multiple" means more than two, "greater than," "less than," and "exceed" are understood to exclude the number itself, and "above," "below," and "within" are understood to include the number itself. The use of terms such as "first" and "second" is solely for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly specifying the number of the indicated technical features, or implicitly specifying the order of the indicated technical features.

[0080] In the description of the present invention, unless otherwise clearly defined, words such as “set,” “install,” “connect,” and “connected” should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above words in the present invention based on the specific content of the technical solution.

[0081] The technical solution of the present invention is described in detail below through the accompanying drawings and specific embodiments.

[0082] See Figure 1 This embodiment provides a container heat leakage detection method using liquid nitrogen instead of liquid hydrogen, which mainly includes steps S101 to S105:

[0083] S101, filling liquid nitrogen into the liquid hydrogen container to be tested, and controlling the liquid nitrogen filling process through step-by-step pre-cooling;

[0084] S102, leaving the container to stand for a predetermined period of time, and simultaneously collecting pressure data and ambient temperature data inside the liquid hydrogen container;

[0085] S103, forming a pressure-time curve according to the pressure data, and calculating the heat absorbed by evaporation of liquid nitrogen based on the pressure-time curve;

[0086] S104, performing dual-channel verification on the liquid nitrogen evaporation heat absorption to obtain a verified liquid nitrogen evaporation heat absorption;

[0087] S105. Based on the heat flux equivalent conversion model, the verified liquid nitrogen evaporation heat absorption is converted into liquid hydrogen equivalent heat leakage. The heat flux equivalent conversion model satisfies:

[0088]

[0089] Where, QH2 is the equivalent heat leakage of liquid hydrogen, Q N2 is the heat absorbed by evaporation of liquid nitrogen, k is the equivalent conversion coefficient, ρ N2 is the density of liquid nitrogen, L v,N2 is the latent heat of vaporization of liquid nitrogen, ρ H2 is the density of liquid hydrogen, L v,H2 is the latent heat of vaporization of liquid hydrogen, α is the thermal boundary layer correction coefficient, and β is the phase change heat transfer correction factor.

[0090] It should be noted that since the density of liquid nitrogen (808 kg / m³) is significantly higher than that of liquid hydrogen (71 kg / m³), the thermal boundary layer formed between it and the container wall is thicker, which inhibits the heat transfer efficiency. Therefore, the thermal boundary layer correction factor α is used to correct the thermal boundary layer. Liquid hydrogen has a small molecular weight (2 g / mol) and low surface tension (1.93 mN / m), and its nucleate boiling intensity is 6% to 8% higher than that of liquid nitrogen. Therefore, the phase change heat transfer correction factor β is used to quantify the difference in boiling heat transfer efficiency.

[0091] See Figure 2 The liquid nitrogen filling process in the above step S101 by step-by-step pre-cooling control includes:

[0092] S201, the first stage, fill the liquid hydrogen container to be tested with 5% liquid nitrogen and maintain it for 10 minutes;

[0093] S202, the second stage, filling the liquid hydrogen container to be tested with liquid nitrogen to 30% of its volume and maintaining it for 20 minutes;

[0094] S203, the third stage, filling the liquid hydrogen container to be tested with liquid nitrogen to a preset filling rate, and the preset filling rate is dynamically adjusted according to the ambient temperature;

[0095] The filling rate is dynamically adjusted based on the ambient temperature adjustment filling rate formula. The ambient temperature adjustment filling rate formula is:

[0096]

[0097] Where R is the filling rate, T amb is the ambient temperature.

[0098] See Figure 3 Calculating the heat absorbed by evaporation of liquid nitrogen based on the pressure-time curve in step S103 includes:

[0099] S301. Perform linear fitting on the pressure data during the static stage to obtain the slope kp of the pressure-time curve:

[0100] kp = dP / dt

[0101] S302. Determine and calculate the gas phase space volume Vg based on the filling parameters:

[0102] V g = V total (1-R)

[0103] Where V g is the gas phase space volume, V total is the total volume of the container, R is the filling rate;

[0104] S303. Calculate the evaporation mass rate dm / dt:

[0105]

[0106] Where dm / dt is the evaporation mass rate, V g is the gas phase space volume, M N2 is the molar mass of nitrogen, R gas is the filling rate, T is the average temperature of the gas phase, dP / dt is the slope of the pressure-time curve;

[0107] S304. Calculate the evaporation heat Q N2 :

[0108]

[0109] Where, Q N2 is the heat absorbed by evaporation of liquid nitrogen, dm / dt is the evaporation mass rate, L v,N2 is the latent heat of vaporization of liquid nitrogen.

[0110] See Figure 4 The double-channel verification of the liquid nitrogen evaporation heat absorption in the above step S103 to obtain the verified liquid nitrogen evaporation heat absorption includes:

[0111] S401, setting the liquid nitrogen evaporation heat absorption calculated based on the pressure-time curve as a first liquid nitrogen evaporation heat absorption;

[0112] S402. Obtain the mass loss rate of liquid nitrogen evaporation by weighing, and calculate the second liquid nitrogen evaporation heat absorption based on the weighing method calculation formula. The weighing method calculation formula is:

[0113]

[0114] Where, Q N2 The heat absorbed by the evaporation of liquid nitrogen is is the mass loss rate of liquid nitrogen evaporation, Lv,N2 is the latent heat of vaporization of liquid nitrogen;

[0115] S403. If the deviation between the first liquid nitrogen evaporation heat absorption amount and the second liquid nitrogen evaporation heat absorption amount is less than or equal to 5%, take the average value of the two;

[0116] S404: If the deviation between the first liquid nitrogen evaporation heat absorption amount and the second liquid nitrogen evaporation heat absorption amount is greater than 5%, perform pressure data verification.

[0117] It should be noted that when verifying pressure data, if sensor drift is detected, the historical calibration curve is used; if temperature compensation is abnormal, dynamic compensation is performed. Liquid nitrogen evaporation heat absorption is cross-validated using a pressure method and a weight method. The pressure method provides real-time performance, while the weight method provides direct measurement and offers higher accuracy.

[0118] In some embodiments of the present invention, before the step of forming a pressure-time curve according to the pressure data in step S103, the following steps are included:

[0119] The pressure data is compensated for ambient temperature using the ambient temperature compensation formula. The ambient temperature compensation formula is:

[0120] P real = P meas + 0.021 •(T amb -20)

[0121] Where Preal is the actual pressure, Pmeas is the measured pressure, both in kPa, T amb is the ambient temperature.

[0122] The thermal boundary layer correction coefficient α in the above step S105 has a value range of 1.05 to 1.15 and is associated with the container volume. The associated formula is:

[0123]

[0124] Where α is the thermal boundary layer correction coefficient, V is the volume of the liquid hydrogen container in cubic meters, and ΔT is the difference between the ambient temperature and the boiling point of liquid nitrogen.

[0125] The phase change heat transfer correction factor β in the above step S105 ranges from 0.92 to 0.98, satisfying:

[0126]

[0127] Where h fg,H2 is the boiling heat transfer coefficient of liquid hydrogen, h fg,N2 is the boiling heat transfer coefficient of liquid nitrogen.

[0128] In some embodiments of the present invention, after the above step S105, the method further includes:

[0129] According to the equivalent heat leakage of liquid hydrogen Q H2 Derivation of the static evaporation rate B of liquid hydrogen container H2 , the derivation formula is:

[0130]

[0131] Where, B H2 is the static evaporation rate of the liquid hydrogen container, Q H2 is the equivalent heat leakage of liquid hydrogen, ρ H2 is the density of liquid hydrogen, L v,H2 is the latent heat of vaporization of liquid hydrogen, and V is the volume of the container.

[0132] See Figure 3 This embodiment further discloses a container heat leakage detection system using liquid nitrogen instead of liquid hydrogen, which is used to implement the above-mentioned container heat leakage detection method using liquid nitrogen instead of liquid hydrogen, including:

[0133] The liquid nitrogen supply module 100 includes a volume control valve for providing the liquid nitrogen medium required for container thermal leakage detection and dynamically adjusting the liquid nitrogen filling rate through the volume control valve;

[0134] The multi-channel data acquisition module 200 includes a pressure sensor, a temperature sensor, and a weighing sensor, and is used to collect pressure data, temperature data, and weight data;

[0135] Wireless communication module 300, used to upload data to the backend server in real time;

[0136] The equivalent calculation module 400 has a built-in dynamic calculation model of the thermal boundary layer correction coefficient α and the phase change heat transfer correction factor β.

[0137] For example, the pressure sensor inside the container uses an absolute pressure transmitter, the liquid nitrogen temperature is monitored using a three-wire PT100 platinum resistor, the weighing sensor uses an explosion-proof weighing sensor, and the ambient temperature is monitored using a digital temperature and humidity sensor. The explosion-proof design ensures safety, the dual verification mechanism ensures reliability, and edge computing ensures real-time performance. The wireless communication module 300 uses a LoRa wireless communication module.

[0138] In some embodiments of the present invention, the equivalent calculation module includes:

[0139] Physical property database, used to store the liquid density ρ and latent heat of vaporization L of liquid hydrogen and liquid nitrogen v and boiling heat transfer coefficient h fg parameter;

[0140] α calibration module, used to calibrate the thermal boundary layer correction coefficient α based on standard container experimental data;

[0141] The dynamic compensator is used to dynamically compensate for the difference between the ambient temperature and the boiling point of liquid nitrogen according to the ambient temperature.

[0142] Specifically, the physical properties database stores liquid hydrogen physical properties, liquid nitrogen physical properties and container characteristic parameters. Among them, the liquid hydrogen physical properties include liquid hydrogen density ρ H2 =70.8kg / m 3 , latent heat of vaporization of liquid hydrogen L v,H2 =446kJ / kg; liquid nitrogen physical properties include liquid nitrogen density ρ N2 =808kg / m 3 , latent heat of vaporization of liquid nitrogen L v,N2 =199kJ / kg, molar mass of nitrogen M N2 = 0.028kg / mol; container characteristic parameters include material thermal conductivity and volume deformation coefficient. The α calibration module pre-stores calibration curves for containers of different volumes.

[0143] The dynamic compensator collects and fuses multi-source temperatures, adopts thermal inertia modeling and hysteresis compensation, and dynamically outputs ΔT. It can calculate the difference ΔT between the ambient temperature and the boiling point of liquid nitrogen in real time, solve the three major interferences of ambient temperature fluctuations, solar radiation, and container thermal inertia, and ensure the calculation reliability of the α coefficient under variable working conditions.

[0144] The thermal boundary layer correction coefficient α is calibrated through standard container calibration experiments and meets the following requirements:

[0145]

[0146] Where α is the thermal boundary layer correction coefficient, Q H2 The heat absorbed by the evaporation of liquid hydrogen is Q N2 The heat absorbed by the evaporation of liquid nitrogen is ρ N2 is the density of liquid nitrogen, L v,N2 is the latent heat of vaporization of liquid nitrogen, ρ H2 is the density of liquid hydrogen, L v,H2 is the latent heat of vaporization of liquid hydrogen.

[0147] The calibration experimental steps are as follows:

[0148] (1) In liquid hydrogen reference mode, inject liquid hydrogen into the heating / cooling jacket to maintain the inner tank at -253°C;

[0149] The target ΔT (e.g. 224°C) is set in the environmental chamber, and the heat absorption Q of liquid hydrogen evaporation is measured by a heat flow meter.H2 .

[0150] (2) In liquid nitrogen replacement mode, switch to liquid nitrogen to maintain the inner liner at -196℃; measure the liquid nitrogen evaporation heat absorption Q at the same ΔT N2 .

[0151] (3) According to the heat absorption Q of liquid hydrogen evaporation H2 , Liquid nitrogen evaporation heat absorption Q N2 Calculate the α value.

[0152] (4) Generate the surface α = f(V, ΔT).

[0153] The empirical dependence of the α coefficient is solved through dual-path closed-loop calibration and in-situ verification of the thermal boundary layer.

[0154] Below 1m 3 Liquid hydrogen cylinder factory inspection and 50m 3 Taking the in-service inspection of liquid hydrogen tankers as an example, the process of using liquid nitrogen instead of liquid hydrogen to perform container heat leakage detection is explained in detail.

[0155] 1. 1m 3 Liquid hydrogen cylinder factory inspection

[0156] (1) The pre-cooling and filling ambient temperature is 28°C, and the target filling rate is 52%.

[0157] The first stage: charging 0.05m 3 Liquid nitrogen (5%), close the valve and let it stand for 10 minutes, the inner tank temperature dropped from 20℃ to -80℃;

[0158] Stage 2: Continue charging to 0.3m 3 (30%), let it stand for 20 minutes, and the temperature stabilizes to -170℃;

[0159] The third stage: charging to 0.52m 3 (52%), filling is completed.

[0160] (2) Data Collection

[0161] Physical parameters: Liquid hydrogen density ρ H2 =70.8kg / m 3 , latent heat of vaporization of liquid hydrogen L v,H2 =446kJ / kg, density of liquid nitrogen ρ N2 =808kg / m 3 , latent heat of vaporization of liquid nitrogen L v,N2 =199kJ / kg, molar mass of nitrogen M N2 = 0.028kg / mol, ideal gas constant R = 8.314 J / (mol·K), average gas phase temperature T = 77K.

[0162] After filling with liquid nitrogen, let it stand for 48 hours; data were collected synchronously during the standing period.

[0163] According to the pressure data collected by the pressure sensor, P meas =0.073kPa / min;

[0164] After temperature compensation, we get P real =0.073+0.021×(28-20)=0.241kPa / min;

[0165] Among them, the coefficient 0.021 is the linear expansion experimental value of 304 stainless steel.

[0166] Calculate the evaporation mass rate dm / dt:

[0167] dm / dt = (V g ·M N2 ·P real ) / (R ·T)

[0168] = (0.48 × 0.028× 0.241× 1000 / 60) / (8.314 × 77) = 0.000084kg / s

[0169] The total evaporation mass in 48 hours was measured to be 14.58 kg. The evaporation mass loss rate of liquid nitrogen was calculated. ;

[0170] =14.58 / (48 × 3600) = 8.436× 10 -5 g / s;

[0171] The heat absorption of liquid nitrogen evaporation is cross-validated using the pressure method + weighing method:

[0172] Calculation of the heat absorption Q of liquid nitrogen evaporation by pressure method N2 :

[0173] Q N2= dm / dt ·L v,N2 = 0.000084 × 199000 = 16.72W;

[0174] Calculate the heat absorption Q of liquid nitrogen evaporation by weighing method N2 :

[0175] Q N2 = ·L v,N2 = 8.436 × 10 -5 × 199 × 10 3 = 16.79W;

[0176] The deviation between the two is 0.4%, which meets the requirement of ≤5%. The average value of the two is taken to obtain the heat absorption of liquid nitrogen evaporation Q N2 It is 16.76W.

[0177] (3) Equivalent conversion

[0178] Calculate the thermal boundary layer correction factor α:

[0179]

[0180] Among them, the boiling point of liquid nitrogen is -196℃, ΔT=28-(-196)=224 ∘ C;

[0181] α=1.1+0.02×ln(1)-0.03×224=1.12.

[0182] Calculate the phase change heat transfer correction factor β:

[0183]

[0184] Take h fg,H2 =1200W / (m 2 ·K), h fg,N2 =700W / (m 2 K),

[0185] β=0.95×(1200 / 700) 0.12 =0.96;

[0186] Calculate the equivalent conversion coefficient k:

[0187] k=(70.8×446) / (808×199)× 1.12 × 0.96=0.21;

[0188] Convert liquid hydrogen equivalent heat leakage Q H2 :

[0189] Q H2 = k ·Q N2 = 0.21×16.76=3.52W.

[0190] (4) Derivation of static evaporation rate B H2 B H2 = Q H2 / ( ρ H2 · L v,H2 V) ×24×3600×100%

[0191] = 3.52 / (70.8×446×1000)×24×3600×100%=0.963% / day

[0192] The deviation from the direct test results of liquid hydrogen in the same container (0.97% / day) is 0.72%, which is lower than the 5% error value allowed by the industry.

[0193] 2.50m 3 In-service inspection of liquid hydrogen tank trucks

[0194] A modified liquid nitrogen tanker truck provides a mobile liquid nitrogen source, equipped with an adaptive volume control valve that automatically matches the filling rate to the truck's pipeline pressure capacity. An explosion-proof data acquisition box is installed on top of the tanker truck, with a pressure sensor and temperature sensor secured via a magnetic base.

[0195] (1) Liquid nitrogen filling (2.5 hours)

[0196] Volume V=50m 3 , ambient temperature -5℃;

[0197] Calculate the maximum fill rate:

[0198] R max =50% - 0.4×(T amb +40)=50% - 0.4×(-5+40)=36%

[0199] The first stage: fill with 2.5m3 of liquid nitrogen (5%), close the valve and let it stand for 10 minutes, the temperature of the inner tank drops from -5℃ to -80℃;

[0200] Second stage: Continue charging to 15m 3 (30%), let it stand for 20 minutes, and the temperature stabilizes to -170℃;

[0201] The third stage: charging to 18m 3 (36%), filling is completed.

[0202] (2) Data Collection

[0203] Physical parameters: Liquid hydrogen density ρ H2 =70.8kg / m 3 , latent heat of vaporization of liquid hydrogen L v,H2 =446kJ / kg, density of liquid nitrogen ρ N2 =808kg / m 3 , latent heat of vaporization of liquid nitrogen L v,N2 =199kJ / kg, molar mass of nitrogen M N2 = 0.028kg / mol, ideal gas constant R = 8.314 J / (mol·K), average gas phase temperature T = 77K.

[0204] After filling with liquid nitrogen, the container was left to stand for 72 hours. Data was collected during this period, and the total evaporated mass over 72 hours was 890 kg.

[0205] Q N2 = 890 / (72 × 3600) × 199 × 10 3 = 683.29W;

[0206] (3) Equivalent conversion

[0207] Input the ambient temperature sequence {start, -5°C; 36 hours, 2°C; 72 hours, 8°C}, run the dynamic compensator, and calculate the ΔT dynamic value.

[0208]

[0209] Among them, the boiling point of liquid nitrogen is -196℃, and the volume compensation coefficient is τ = 0.4×V 0.5 .

[0210] Calculate the thermal boundary layer correction factor α:

[0211]

[0212] α=1.1+0.02×ln(50)-0.03×201.3=1.05.

[0213] For every 1°C change in ambient temperature, the ΔT dynamic value error is ≤0.1°C, ensuring that the α coefficient accuracy reaches 99%.

[0214] Calculate the phase change heat transfer correction factor β:

[0215]

[0216] Pick h fg,H2 =1200W / (m 2 K), h fg,N2 =700W / (m 2 K),

[0217] β=0.95 × (1200 / 700) 0.12 =0.96.

[0218] Calculate the equivalent conversion coefficient k:

[0219] k=(70.8×446) / (808×199) × 1.05 × 0.96=0.20;

[0220] Convert liquid hydrogen equivalent heat leakage Q H2 :

[0221] Q H2 = k ·Q N2 = 0.20× 683.29=136.66W.

[0222] (4) Derivation of static evaporation rate B H2 B H2 = Q H2 / ( ρ H2 · L v,H2 V) ×24×3600×100%

[0223] =136.66 / (70.8×446×1000×50)×24×3600×100%=0.748% / day.

[0224] The deviation from the direct test results of liquid hydrogen in the same container (0.740% / day) is 1.08%, which is lower than the 5% error limit allowed by the industry.

[0225] Due to the increase in volume and the prolonged standing time, the test took 72 hours and the total cost was 21,000 yuan, which was 86% lower than the liquid hydrogen test cost (150,000 yuan).

[0226] Liquid nitrogen is used instead of liquid hydrogen for container heat leakage detection. By establishing a conversion model between the liquid nitrogen detection heat flux results and the liquid hydrogen equivalent heat load, a derivation method for the equivalent coefficient k is proposed, and a dual-factor heat flux conversion model based on the thermal boundary layer correction coefficient α and the phase change heat transfer correction factor β is established. Through the α / β dual-factor physical model, the technical prejudice that liquid nitrogen cannot be directly equivalent to liquid hydrogen is broken, and the hardware acquisition data stream is bound. The detection system includes a liquid nitrogen supply module 100, a multi-channel data acquisition module 200, a wireless communication module 300 and an equivalent calculation module 400. Multi-source fusion is used to eliminate the local temperature difference of the tank caused by solar radiation, such as the temperature difference between the sunny and shady sides of the tank; thermal inertia modeling is used to solve the temperature response lag problem of large containers; derivative advance compensation is used to suppress the interference of sudden changes in ambient temperature; and volume adaptation is used to cover 1~100m 3Full-scale container. Through closed-loop control of heat flux conversion, safe, efficient and economical detection of liquid hydrogen containers is achieved, solving the problems of high risk and high cost of traditional liquid hydrogen detection. It is suitable for factory inspection and thermal insulation performance evaluation of in-service containers, making liquid nitrogen a reliable industrial-grade solution for liquid hydrogen detection. It has four major beneficial effects: 1. In terms of safety, it eliminates the risk of liquid hydrogen explosion and ensures the safety of operations in high-risk environments; 2. In terms of economy, the detection cost is reduced by more than 85%, of which the cost of liquid nitrogen medium is only 7.5% of liquid hydrogen; 3. In terms of accuracy, the dual-factor model overcomes the problem of physical property differences, and the evaporation rate detection error is small, comparable to the direct measurement accuracy of liquid hydrogen; 4. In terms of efficiency, the detection system can be quickly deployed on-site, shortening the detection cycle and improving the efficiency of liquid hydrogen container heat leakage detection.

[0227] The embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the scope of the present invention.

Claims

1. A container heat leakage detection method using liquid nitrogen instead of liquid hydrogen, characterized in that: include: Fill the liquid hydrogen container to be tested with liquid nitrogen, and control the filling process of liquid nitrogen through step-by-step pre-cooling; Allow the container to stand for a preset period of time, and simultaneously collect the pressure data and ambient temperature data inside the liquid hydrogen container; forming a pressure-time curve according to the pressure data, and calculating the amount of heat absorbed by evaporation of liquid nitrogen based on the pressure-time curve; Perform dual-channel verification on the liquid nitrogen evaporation heat absorption to obtain the verified liquid nitrogen evaporation heat absorption; Based on the heat flux equivalent conversion model, the verified liquid nitrogen evaporation heat absorption is converted into liquid hydrogen equivalent heat leakage; Wherein, the heat flux equivalent conversion model satisfies: Where, Q H2 is the equivalent heat leakage of liquid hydrogen, Q N2 is the heat absorbed by evaporation of liquid nitrogen, k is the equivalent conversion coefficient, ρ N2 is the density of liquid nitrogen, L v,N2 is the latent heat of vaporization of liquid nitrogen, ρ H2 is the density of liquid hydrogen, L v,H2 is the latent heat of vaporization of liquid hydrogen, α is the thermal boundary layer correction factor, and β is the phase change heat transfer correction factor; The calculation of the heat absorption of liquid nitrogen evaporation based on the pressure-time curve includes: Perform linear fitting on the pressure data during the static stage to obtain the slope kp of the pressure-time curve: kp = dP / dt Determine and calculate the gas phase space volume Vg based on the filling parameters: V g = V total · (1-R) Where V g is the volume of the gas phase space, V total is the total volume of the container, R is the filling rate; Calculate the evaporation mass rate dm / dt: Where dm / dt is the evaporation mass rate, V g is the gas phase space volume, M N2 is the molar mass of nitrogen, R gas is the filling rate, T is the average temperature of the gas phase, dP / dt is the slope of the pressure-time curve; Calculate the heat absorption Q of liquid nitrogen evaporation N2 : Where, Q N2 is the heat absorbed by evaporation of liquid nitrogen, dm / dt is the evaporation mass rate, L v,N2 is the latent heat of vaporization of liquid nitrogen; The dual-channel verification of the heat absorption of liquid nitrogen evaporation includes: The liquid nitrogen evaporation heat absorption calculated based on the pressure-time curve is set as the first liquid nitrogen evaporation heat absorption; The mass loss rate of liquid nitrogen evaporation is obtained by weighing, and the second liquid nitrogen evaporation heat absorption is calculated based on the weighing method calculation formula. The weighing method calculation formula is: Where, Q N2 The heat absorbed by the evaporation of liquid nitrogen is is the mass loss rate of liquid nitrogen evaporation, L v,N2 is the latent heat of vaporization of liquid nitrogen; If the deviation between the first liquid nitrogen evaporation heat absorption and the second liquid nitrogen evaporation heat absorption is ≤5%, the average of the two is taken; If the deviation between the first liquid nitrogen evaporation heat absorption value and the second liquid nitrogen evaporation heat absorption value is greater than 5%, pressure data verification is performed.

2. The container heat leakage detection method using liquid nitrogen instead of liquid hydrogen according to claim 1, characterized in that: The process of controlling the filling of liquid nitrogen by step-by-step pre-cooling includes: In the first stage, the liquid hydrogen container to be tested is filled with 5% liquid nitrogen and maintained for 10 minutes; In the second stage, the liquid hydrogen container to be tested is filled with liquid nitrogen to 30% of its volume and maintained for 20 minutes; In the third stage, the liquid hydrogen container to be tested is filled with liquid nitrogen to a preset filling rate, and the preset filling rate is dynamically adjusted according to the ambient temperature; The full rate is dynamically adjusted based on the ambient temperature adjustment full rate formula, and the ambient temperature adjustment full rate formula is: Where R is the filling rate, T amb is the ambient temperature.

3. The container heat leakage detection method using liquid nitrogen instead of liquid hydrogen according to claim 1, characterized in that: Before the step of forming a pressure-time curve according to the pressure data, the method includes: The pressure data is compensated for ambient temperature using an ambient temperature compensation formula, which is: P real = P meas + 0.021 •(T amb -20) Where, P real is the real pressure, P meas To measure pressure, the unit is kPa, T amb is the ambient temperature.

4. The container heat leakage detection method using liquid nitrogen instead of liquid hydrogen according to claim 1, characterized in that: The thermal boundary layer correction coefficient α ranges from 1.05 to 1.15 and is related to the container volume. The correlation formula is: Where α is the thermal boundary layer correction coefficient, V is the volume of the liquid hydrogen container in cubic meters, and ΔT is the difference between the ambient temperature and the boiling point of liquid nitrogen.

5. The container heat leakage detection method using liquid nitrogen instead of liquid hydrogen according to claim 1, characterized in that: The phase change heat transfer correction factor β ranges from 0.92 to 0.98, satisfying: Where β is the phase change heat transfer correction factor, h fg,H2 is the boiling heat transfer coefficient of liquid hydrogen, h fg,N2 is the boiling heat transfer coefficient of liquid nitrogen.

6. The container heat leakage detection method using liquid nitrogen instead of liquid hydrogen according to claim 1, characterized in that: After the step of converting the verified liquid nitrogen evaporation heat absorption into liquid hydrogen equivalent heat leakage based on the heat flux equivalent conversion model, the method further includes: According to the equivalent heat leakage of liquid hydrogen Q H2 Derivation of the static evaporation rate B of liquid hydrogen container H2 , the derivation formula is: Where, B H2 is the static evaporation rate of the liquid hydrogen container, Q H2 is the equivalent heat leakage of liquid hydrogen, ρ H2 is the density of liquid hydrogen, L v,H2 is the latent heat of vaporization of liquid hydrogen, and V is the volume of the container.

7. A container heat leakage detection system using liquid nitrogen instead of liquid hydrogen, characterized in that: The method for detecting heat leakage of a container using liquid nitrogen instead of liquid hydrogen as claimed in any one of claims 1 to 6 comprises: A liquid nitrogen supply module, including a volume control valve, is used to provide the liquid nitrogen medium required for container thermal leakage detection, and the liquid nitrogen filling rate is dynamically adjusted by the volume control valve; Multi-channel data acquisition module, including pressure sensor, temperature sensor and weighing sensor, used to collect pressure data, temperature data and weight data; Wireless communication module, used to upload data to the backend server in real time; Equivalent calculation module, with built-in dynamic calculation model of thermal boundary layer correction coefficient α and phase change heat transfer correction factor β.

8. The container heat leakage detection system using liquid nitrogen instead of liquid hydrogen according to claim 7, characterized in that: The equivalent calculation module includes: Physical property database, used to store the liquid density ρ and latent heat of vaporization L of liquid hydrogen and liquid nitrogen v and boiling heat transfer coefficient h fg parameter; α calibration module, used to calibrate the thermal boundary layer correction coefficient α based on standard container experimental data; The dynamic compensator is used to dynamically compensate for the difference between the ambient temperature and the boiling point of liquid nitrogen according to the ambient temperature.

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