Method for quickly estimating dangerous range of small-aperture leakage of liquid hydrogen

Abstract

The invention discloses a method for quickly estimating a liquid hydrogen small-aperture leakage dangerous range. The method comprises the following steps: step 1, establishing a liquid hydrogen leakage numerical model; solving the liquid hydrogen leakage numerical model by using CFD software FLUENT, and simulating a three-dimensional liquid hydrogen leakage small-aperture diffusion behavior; step 2, determining a hydrogen dangerous area range and a liquid hydrogen leakage diffusion process under the influence of different factors, and obtaining a factor with the most significant influence; and step 3, fitting and correcting a liquid hydrogen leakage numerical model: normalizing the liquid hydrogen leakage ejection axis distance and the most significant influence factor to obtain an engineering model of jet flow axial hydrogen mass fraction attenuation distribution, and fitting simulation data under different working conditions to obtain the liquid hydrogen leakage numerical model. Obtaining a correction coefficient of the engineering model of the jet flow axial hydrogen mass fraction attenuation distribution; and 4, calculating a danger range. The method has the advantages of being simple and small in calculation amount, the liquid hydrogen small-aperture leakage axial hydrogen concentration extended range distribution condition can be obtained, and the dangerous distance can be rapidly estimated.

Description

Technical Field

[0001] This invention relates to the field of liquid hydrogen transportation safety assessment technology, specifically to a method for rapidly estimating the hazardous range of small-diameter liquid hydrogen leaks. Background Technology

[0002] Hydrogen, as an important clean energy source, has been widely used in many fields such as chemical engineering and aerospace propulsion. Because the storage of cryogenic liquid hydrogen is more feasible than that of room-temperature hydrogen with lower energy density, liquid hydrogen storage and transportation are commonly used. However, this method is susceptible to leaks due to structural failures. During the storage, transportation, and refueling of liquid hydrogen, common leak points include refueling hose inlets, instrument components, welded joints at flange connections, and cracks or pinholes in the liquid hydrogen delivery pipeline. The leaked hydrogen appears as vaporized cryogenic hydrogen gas. Under the influence of the pressure difference between the inside and outside of the pipeline, and the combined effects of initial momentum and buoyancy, a jet phenomenon occurs. Over time, the dangerous concentration distribution and spatial expansion of the hydrogen gas reach an equilibrium state. In emergency response to liquid hydrogen leaks and diffusion accidents, accurately predicting the diffusion trend and concentration distribution of this gas, i.e., determining the danger zone, is crucial for effective emergency response and handling.

[0003] Gaussian diffusion theory model. The Gaussian diffusion model can effectively reflect the turbulent diffusion of pollutants in the atmosphere. It is mainly divided into puff diffusion model and plume diffusion model. For instantaneous leaks or light winds (u < 1 m / s), the Gaussian puff diffusion model is often used; for continuous sources, the plume diffusion model is more reasonable. For liquid hydrogen leaks with small apertures, the Gaussian plume diffusion model can be used to describe the gas cloud concentration distribution under steady-state conditions, thereby obtaining the hazardous area. [Paper: Research on a rapid estimation method for chlorine leak concentration distribution based on the Gaussian model].

[0004] CFD numerical simulation method. Computational fluid dynamics (CFD) is a discrete computational method based on the continuity equation, momentum conservation equation, and energy conservation equation, capable of simulating physicochemical processes under complex three-dimensional terrain conditions. A three-dimensional liquid hydrogen small-aperture leakage and diffusion model was established using CFD software, and the diffusion characteristics and hazardous range were calculated. [Paper: CFD Simulation Analysis of Liquid Hydrogen Leakage and Diffusion Characteristics at Rocket Launch Sites].

[0005] Experimental Methods. The UK Safety Institute (HSL) conducted a liquid hydrogen leak experiment on a transport vehicle in a large space. The mass flow rate of the hydrogen leak in the experiment was 60 L / min, the leak time was 2 min, and the horizontal danger distance of the flammable hydrogen cloud was found to be 9 m. [Paper: Hooker P, Willoughby DB, Royle M. Experimental releases of liquid hydrogen, Proceedings of 4th International Conference on Hydrogen Safety, 2011; San Francisco, Paper 160.]

[0006] Currently, the main methods used are theoretical models, CFD numerical simulations, and experiments, but these methods have the following drawbacks: (1) The Gaussian diffusion model is suitable for uniform atmospheric conditions. It is better to use the Gaussian model to simulate and calculate gases with densities close to those of air. However, the low-temperature hydrogen gas formed by the vaporization of liquid hydrogen after leakage has a large density. The calculation using the Gaussian diffusion model will result in a large error. Furthermore, it is necessary to use software such as Matlab to solve the model, which is not convenient and quick for on-site workers.

[0007] (2) In terms of numerical simulation, the liquid hydrogen leakage and diffusion model is complex, involving physical processes such as multi-component transport, turbulent flow, gas-liquid phase change, and heat transfer. It requires a hardware platform with strong computing power to run the model, resulting in problems such as high hardware cost and long calculation time.

[0008] (3) In terms of testing, hydrogen-air mixtures are flammable in the concentration range of 4% to 75%, with a wide flammability range and very low ignition energy, resulting in a high risk factor. Furthermore, a lot of preparation is required in the early stages of testing, and there are currently few ways to obtain liquid hydrogen, which presents problems such as the high effort required for liquid hydrogen leak testing and the danger of the process. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to avoid the shortcomings of the above-mentioned existing methods and to quickly estimate the dangerous range of liquid hydrogen leakage through small orifices. In order to solve the above problem, a method for quickly estimating the dangerous range of liquid hydrogen leakage through small orifices is provided.

[0010] The object of this invention is achieved in the following manner: A method for rapidly estimating the hazardous extent of liquid hydrogen leaks in small-diameter orifices, the method comprising: Step 1: Based on the physical properties of liquid hydrogen and the leakage scenario, establish a numerical model of liquid hydrogen leakage; considering the physical processes of multi-component transport, turbulent flow, and heat transfer, use the CFD software FLUENT to solve the numerical model of liquid hydrogen leakage and simulate the three-dimensional liquid hydrogen leakage small-aperture diffusion behavior. Step 2: Consider the diffusion pattern of liquid hydrogen leakage under different influencing factors, determine the range of the hydrogen hazard zone, the diffusion process of liquid hydrogen leakage under different factors, and obtain the most significant influencing factor; Step 3: Fitting and correction of the numerical model of liquid hydrogen leakage: After normalizing the axial distance of the liquid hydrogen leakage and the most significant factors, an engineering model of the axial hydrogen mass fraction decay distribution of the jet is obtained. By fitting simulation data under different working conditions, the correction coefficient of the engineering model of the axial hydrogen mass fraction decay distribution of the jet is obtained. Step 4: Calculate the danger range: After transforming the engineering model formula for the axial hydrogen mass fraction decay distribution of the jet, the relationship between the danger distance and the parameters of the leakage source is obtained, and the danger distance is directly calculated through the relationship.

[0011] Step 1, establishing a numerical model for liquid hydrogen leakage, specifically includes: A typical physical condition is proposed and the flow field is simplified into a three-dimensional cuboid structure, where the X direction is the axis of liquid hydrogen leakage and the Z direction is the height direction of the liquid hydrogen leakage port. Considering the physical processes of multi-component transport, turbulent flow and heat transfer, the liquid hydrogen leakage diffusion model is solved using the CFD software FLUENT to simulate the three-dimensional liquid hydrogen leakage small aperture diffusion behavior.

[0012] The influencing factors in step 2 include leakage height, leakage amount of different orifice sizes, leakage temperature, and ambient temperature. The most significant factor is the leakage orifice size.

[0013] The engineering model for the axial hydrogen mass fraction attenuation distribution in step 3 is as follows: The mass fraction decay curve at the center of the corrected jet: (4) Expression for dimensionless characteristic length: (5) (6) (7) (8) In the formula Fr The Frod number represents the ratio of inertial force to gravity. Y clrepresents the mass fraction at the center of the jet; A and B are correction coefficients; L represents the danger distance; d* represents the dimensionless characteristic length. Indicates the diameter of the leak opening; Indicates hydrogen export density; The density of the surrounding environment is represented by s, and the cross-sectional area of ​​the leak is represented by u. exit The velocity at the leak outlet is represented by g, and g represents the acceleration due to gravity.

[0014] Step 4 includes: Transforming formula (4), we obtain the relationship between the danger distance and the parameters of the leakage source: (9).

[0015] The beneficial effects of this invention are: This invention is characterized by its simplicity and low computational complexity. It can obtain the axial hydrogen concentration distribution over a small-diameter liquid hydrogen leak, enabling rapid estimation of the danger distance. Attached Figure Description

[0016] Figure 1 This is a flowchart of a method for quickly estimating the hazardous area of ​​a liquid hydrogen leak.

[0017] Figure 2 It is a geometric model for leakage diffusion in small flow rates.

[0018] Figure 3 It refers to the leakage and diffusion behavior of liquid hydrogen under the influence of different factors.

[0019] Figure 4 It is the axial mass fraction decay curve of hydrogen gas with a leak radius of 0.015m.

[0020] Figure 5 It is the axial mass fraction decay curve of hydrogen gas with a leak radius of 0.01m.

[0021] Figure 6 It is the axial mass fraction decay curve of hydrogen gas with a leak radius of 0.005m.

[0022] Figure 7 This is a graph verifying the simulation results and calculation formulas. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same technical meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0025] A method for rapidly estimating the hazardous extent of liquid hydrogen leaks in small-diameter orifices, the method comprising: Step 1: Based on the physical properties of liquid hydrogen and the leakage scenario, establish a numerical model of liquid hydrogen leakage; considering the physical processes of multi-component transport, turbulent flow, and heat transfer, use the CFD software FLUENT to solve the numerical model of liquid hydrogen leakage and simulate the three-dimensional liquid hydrogen leakage small-aperture diffusion behavior. Step 2: Consider the diffusion pattern of liquid hydrogen leakage under different influencing factors, determine the range of the hydrogen hazard zone, the diffusion process of liquid hydrogen leakage under different factors, and obtain the most significant influencing factor; Step 3: Fitting and correction of the numerical model of liquid hydrogen leakage: After normalizing the axial distance of the liquid hydrogen leakage and the most significant factors, an engineering model of the axial hydrogen mass fraction decay distribution of the jet is obtained. By fitting simulation data under different working conditions, the correction coefficient of the engineering model of the axial hydrogen mass fraction decay distribution of the jet is obtained. Step 4: Calculate the danger range: After transforming the engineering model formula for the axial hydrogen mass fraction decay distribution of the jet, the relationship between the danger distance and the parameters of the leakage source is obtained, and the danger distance is directly calculated through the relationship.

[0026] Step 1, establishing a numerical model for liquid hydrogen leakage, specifically includes: A typical physical condition is proposed and the flow field is simplified into a three-dimensional cuboid structure, where the X direction is the axis of liquid hydrogen leakage and the Z direction is the height direction of the liquid hydrogen leakage port. Considering the physical processes of multi-component transport, turbulent flow and heat transfer, the liquid hydrogen leakage diffusion model is solved using the CFD software FLUENT to simulate the three-dimensional liquid hydrogen leakage small aperture diffusion behavior.

[0027] The influencing factors in step 2 include leakage height, leakage amount of different orifice sizes, leakage temperature, and ambient temperature. The most significant factor is the leakage orifice size.

[0028] The engineering model for the axial hydrogen mass fraction attenuation distribution in step 3 is as follows: The mass fraction decay curve at the center of the corrected jet: (4) Expression for dimensionless characteristic length: (5) (6) (7) (8) In the formula Fr The Frod number represents the ratio of inertial force to gravity. Ycl represents the mass fraction at the center of the jet; A and B are correction coefficients; L represents the danger distance; d* represents the dimensionless characteristic length. Indicates the diameter of the leak opening; Indicates hydrogen export density; The density of the surrounding environment is represented by s, and the cross-sectional area of ​​the leak is represented by u. exit The velocity at the leak outlet is represented by g, and g represents the acceleration due to gravity.

[0029] Step 4 includes: Transforming formula (4), we obtain the relationship between the danger distance and the parameters of the leakage source: (9).

[0030] Example: The flowchart of the method for rapidly estimating the hazardous range of liquid hydrogen leakage in small apertures proposed in this invention is as follows: Figure 1 As shown, CFD numerical simulation is first used to obtain the diffusion characteristics of liquid hydrogen in space after leakage, including leakage location, leakage amount, and ambient temperature. The main monitoring range is the dangerous concentration of hydrogen, from 4% to 75%. Based on this, a multi-parameter comprehensive influence analysis is conducted to identify the most significant influencing factors. Relevant dimensionless formulas are derived, allowing for rapid estimation of the dangerous range of liquid hydrogen leakage. The main steps are as follows: (1) Establish a numerical model for liquid hydrogen leakage A typical physical condition is abstracted: a storage tank experiences a crack and leak; the liquid hydrogen temperature is 20K, the leaked cryogenic hydrogen gas is 40K, and the ambient temperature is 300K. The flow field is simplified as a three-dimensional cuboid structure with dimensions of 8000mm × 2000mm × 2000mm. The X-axis represents the axis of the leaking liquid hydrogen, and the Z-axis represents the height of the leak point. The leak point is very small relative to the overall flow field, approximating a small circular hole with its center coordinates (0, 1000, 1000). Figure 2 As shown.

[0031] Considering physical processes such as multi-component transport, turbulent flow, and heat transfer, the CFD software FLUENT was used to solve the liquid hydrogen leakage diffusion model and simulate the three-dimensional liquid hydrogen leakage small-aperture diffusion behavior.

[0032] Considering the diffusion patterns of liquid hydrogen leakage under various influencing factors, including leakage height, leakage volume (for different orifice sizes), leakage temperature, and ambient temperature, the extent of the hydrogen hazard zone is determined, and the diffusion process of liquid hydrogen leakage under the influence of different factors is analyzed. Figure 3 As shown, the simulation results are used to fit the hydrogen mass fraction decay curve, correct the dimensionless formula, and verify the accuracy of the engineering model.

[0033] (3) Fitting and correction of the liquid hydrogen diffusion engineering model Based on the research results of the influencing factors of each single leakage source, it was found that the influence of each influencing factor is different, among which the leakage orifice diameter has the most significant impact.

[0034] a) Fitting and correcting engineering models Birch AD's study found that after normalizing the axial distance and the leakage orifice diameter, it was positively correlated with the reciprocal of the average mass fraction of the leaked gas, passing through the origin under the influence of no changes in the external environment. [Birch AD, Brown DR, Dodson MG, Swaffield F. The structure and concentration decay of high pressure jets of natural gas[J]. Combust Sci Technol 1984;36(5-6):249-61.] After normalizing the experimental data using a planar laser Rayleigh scattering system, Li Xuefang et al. from Tsinghua University obtained the mass fraction decay curve of the subsonic jet center (Equation (1)) and the mass fraction decay curve of the underexpanded jet center (Equation (2)). The dimensionless characteristic length expression is given in (3). The formulas are applicable to room temperature hydrogen jets without the influence of external environmental factors. [Li X, Hecht ES, Christopher DM. Validation of areduced-order jet model for subsonic and underexpanded hydrogenjets[J]. International journal of hydrogen energy, 2016, 41(2):1348-1358.] The mass fraction decay curve at the center of the subsonic jet is as follows: (1) In the formula: Y cl — Mass fraction at the center of the jet; z—Axial distance, in meters; d* — dimensionless characteristic length; The mass fraction decay curve at the center of the underexpanded jet is as follows: In the formula: —Diameter of the leak opening, in meters; — Hydrogen outlet density, kg / m³ 3 ; —Ambient density, kg / m³ 3 ; This invention studies the small-aperture diffusion of liquid hydrogen leakage as a subsonic jet. Data under various influencing factors are processed, and changes in the parameters of the leakage source lead to… d exit and ρ exit Changes, changes in environmental parameters make Change. The mass fraction decay curve at the center of the corrected jet: (4) Expression for dimensionless characteristic length: (5) (6) In the formula Fr The Frode number represents the ratio of inertial force to gravity.

[0035] Figures 4-6 The hydrogen mass fraction decay curves for different leakage radii were plotted and fitted. The figure shows that the fitting effect is better when the distance to the leak is closer. This is because the temperature of the low-temperature hydrogen increases with the diffusion distance, causing gas expansion and a greater influence from buoyancy.

[0036] The values ​​of correction coefficients A and B were obtained by fitting the curve: (7) (8) in S This represents the cross-sectional area of ​​the leak.

[0037] b) Formula verification The above formula was verified by selecting a leakage pressure of 0.15 MPa and different ambient temperatures to measure the mass fraction of leaked hydrogen.

[0038] Depend on Figure 7 It can be seen that, compared with typical working conditions, the maximum error of the engineering model calculation results does not exceed 13%, therefore it is believed that this diffusion engineering model can reflect the simulation results well.

[0039] (4) Calculate the danger zone Transforming formula (4), we obtain the relationship between the danger distance and the parameters of the leakage source: (9) The danger distance is mainly determined by five parameters: hydrogen density at the leak outlet, leak outlet velocity, leak equivalent diameter, atmospheric density, and danger concentration value. The lower limit of the volume fraction of hydrogen danger concentration is generally set at 4%, which translates to 0.299% by mass. Substituting into equation (9), we get: (10) Taking a leak under a certain operating condition as an example, the hydrogen density at the leak outlet... Leakage exit speed Leakage equivalent diameter Atmospheric density Substituting into equation (10), we obtain a danger distance of 13.8m.

[0040] The steps 1 (establishing a numerical model for liquid hydrogen leakage), 2 (the diffusion law of liquid hydrogen under the influence of different factors), and 3 (fitting and correcting the diffusion engineering model) of this invention only need to be performed once.

[0041] This invention is characterized by its simplicity and low computational complexity. It can obtain the axial hydrogen concentration distribution over a small-aperture leak in liquid hydrogen, enabling rapid estimation of the danger distance. In emergency rescue operations following liquid hydrogen leaks and diffusion accidents, it can predict the diffusion trend and concentration distribution of this gas, determine the danger zone, and provide important guidance for personnel to take appropriate protective measures.

[0042] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several changes and improvements without departing from the overall concept of the present invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A method for rapidly estimating the hazardous range of liquid hydrogen leakage through small-diameter orifices, characterized in that: The method includes: Step 1: Based on the physical properties of liquid hydrogen and the leakage scenario, establish a numerical model of liquid hydrogen leakage; considering the physical processes of multi-component transport, turbulent flow, and heat transfer, use the CFD software FLUENT to solve the numerical model of liquid hydrogen leakage and simulate the three-dimensional liquid hydrogen leakage small-aperture diffusion behavior. Step 2: Consider the diffusion pattern of liquid hydrogen leakage under different influencing factors, determine the range of the hydrogen hazard zone, the diffusion process of liquid hydrogen leakage under different factors, and obtain the most significant influencing factor; Step 3: Fitting and correction of the numerical model of liquid hydrogen leakage: After normalizing the axial distance of the liquid hydrogen leakage and the most significant factors, an engineering model of the axial hydrogen mass fraction decay distribution of the jet is obtained. By fitting simulation data under different working conditions, the correction coefficient of the engineering model of the axial hydrogen mass fraction decay distribution of the jet is obtained. Step 4: Calculate the danger range: After transforming the engineering model formula for the axial hydrogen mass fraction decay distribution of the jet, the relationship between the danger distance and the parameters of the leakage source is obtained, and the danger distance is directly calculated through the relationship.

2. The method for rapidly estimating the hazardous range of liquid hydrogen leakage through small apertures according to claim 1, characterized in that: Step 1, establishing a numerical model for liquid hydrogen leakage, specifically includes: A typical physical condition is proposed and the flow field is simplified into a three-dimensional cuboid structure, where the X direction is the axis of liquid hydrogen leakage and the Z direction is the height direction of the liquid hydrogen leakage port. Considering the physical processes of multi-component transport, turbulent flow and heat transfer, the liquid hydrogen leakage diffusion model is solved using the CFD software FLUENT to simulate the three-dimensional liquid hydrogen leakage small aperture diffusion behavior.

3. The method for rapidly estimating the hazardous range of liquid hydrogen leakage through small apertures according to claim 1, characterized in that: The influencing factors in step 2 include leakage height, leakage amount of different orifice sizes, leakage temperature, and ambient temperature. The most significant factor is the leakage orifice size.

4. The method for rapidly estimating the hazardous range of liquid hydrogen leakage through small apertures according to claim 1, characterized in that: The engineering model for the axial hydrogen mass fraction attenuation distribution in step 3 is as follows: The mass fraction decay curve at the center of the corrected jet: （4） Expression for dimensionless characteristic length: （5） （6） （7） （8） In the formula Fr The Frod number represents the ratio of inertial force to gravity. Y cl The mass fraction at the jet center is represented by A and B, which are correction coefficients; L represents the danger distance. d* represents the dimensionless characteristic length; Indicates the diameter of the leak opening; Indicates hydrogen export density; The density of the surrounding environment is represented by s, and the cross-sectional area of ​​the leak is represented by u. exit The velocity at the leak outlet is represented by g, and g represents the acceleration due to gravity.

5. The method for rapidly estimating the hazardous range of liquid hydrogen leakage through small apertures according to claim 3, characterized in that: Step 4 includes: Transforming formula (4), we obtain the relationship between the danger distance and the parameters of the leakage source: （9）。

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