Thermodynamic modeling method for high-pressure hydrogen storage cylinder charging and discharging cycle process

Abstract

The application is suitable for the technical field of high-pressure hydrogen storage, and provides a thermodynamic modeling method for a high-pressure hydrogen storage cylinder charging and discharging cycle process, which comprises the following steps: establishing a thermodynamic model based on a real gas state equation, including a mass conservation equation and an energy conservation equation, and constructing a hydrogen cylinder-environment three-level heat transfer link; verifying grid independence and time step independence of the model; using the verified model to perform single-parameter and multi-parameter coupling quantitative analysis on the gas inlet flow, pre-cooling temperature and cylinder inner diameter respectively; and screening an optimal parameter combination meeting the national standard temperature limit value. In the application, a professional thermodynamic database REFPROP is used to describe high-pressure hydrogen properties, and after the independence verification, the model error is controlled within 5%; three-parameter synergistic regulation can effectively reduce the maximum temperature, and after optimization, the cycle temperature and pressure all meet the national standard, and hydrogenation efficiency and hydrogen storage operation safety are considered.

Description

Technical Field

[0001] This invention belongs to the field of high-pressure hydrogen storage technology, and particularly relates to a thermodynamic modeling method for the filling and discharging cycle of high-pressure hydrogen storage cylinders. Background Technology

[0002] Hydrogen energy, with its high calorific value and zero pollution, has become a mainstream low-carbon energy solution in the transportation sector. 70MPa plastic-lined carbon fiber wound Type IV gas cylinders, with their lightweight and high pressure resistance, have become the mainstream product for on-board hydrogen storage. The conventional filling and discharging process for on-board hydrogen storage cylinders consists of three stages: fast charging, settling, and venting. According to safety standards, the maximum temperature during the filling process of on-board high-pressure hydrogen storage cylinders must not exceed 85℃, and the minimum temperature during the venting process must not be lower than -40℃; otherwise, it will cause safety hazards such as degradation of the cylinder wall material, deformation of the inner liner, and even hydrogen leakage.

[0003] Currently, the industry generally uses CFD three-dimensional fluid simulation or single-condition testing to conduct performance analysis of the filling and discharging process of hydrogen storage cylinders, but existing technologies have the following multiple drawbacks:

[0004] (i) At the simulation methodology level, traditional 3D CFD models require massive fine meshes to capture the heat transfer process of hydrogen jets, and a single charge-discharge cycle simulation can take tens of hours, resulting in extremely high computational costs. Existing models mostly adopt the ideal gas assumption, but hydrogen under high pressure deviates from the ideal gas state, leading to large deviations in physical properties. In addition, most studies only analyze the charging stage separately, ignoring the cumulative temperature change effect of multiple charge-discharge cycles; and the mesh and time step have not been standardized and checked for independence, resulting in simulation errors that typically exceed 8%, making it difficult to meet engineering accuracy requirements.

[0005] (II) At the level of parameter research: Existing studies only analyze the impact of single parameters such as inlet flow rate, precooling temperature, or cylinder inner diameter, lacking coupled quantitative analysis methods for two or three parameters. During fast charging, the adiabatic compression and jet mixing of hydrogen cause a sudden rise in cylinder temperature, and the peak temperature under normal operating conditions easily exceeds the national standard upper limit of 85℃. High temperatures can cause debonding of the carbon fiber and resin interface; during the venting stage, the Joule-Thomson negative effect causes drastic low temperatures, with extreme conditions dropping below the -40℃ lower limit. The alternation of hot and cold generates significant thermal stress, and long-term cycling can easily cause stress concentration at the cylinder mouth and overload of the carbon fiber.

[0006] (III) At the level of operating condition control schemes: While simply reducing the gas flow rate can suppress temperature rise, it will significantly prolong the hydrogen refueling time and reduce the convenience of vehicle use; simply increasing the pre-cooling and temperature reduction will increase the cooling energy consumption of hydrogen refueling stations; and simply adjusting the inner diameter of the gas cylinder will simultaneously exacerbate the low temperature problem during the gas release stage. Existing technologies lack a synergistic optimization scheme that takes into account fast charging efficiency, temperature and pressure safety, and heat exchange performance.

[0007] (iv) Optimization system level: Existing research only provides simulation data for single working conditions and cannot provide the optimal parameter combination that meets the national standard limits. The problem of continuous temperature accumulation and increase under multiple cycles cannot be effectively solved.

[0008] In summary, there is an urgent need for a thermodynamic modeling and parameter control method for the filling and discharging cycle of high-pressure hydrogen storage cylinders that balances computational efficiency and accuracy and enables multi-parameter collaborative optimization and control. Summary of the Invention

[0009] The purpose of this invention is to provide a thermodynamic modeling method for the filling and discharging cycle of high-pressure hydrogen storage cylinders, aiming to solve the problems mentioned in the background art.

[0010] The present invention is implemented as follows: a thermodynamic modeling method for the filling and discharging cycle of high-pressure hydrogen storage cylinders includes the following steps:

[0011] Step 1: Establish a thermodynamic model of the filling and discharging cycle of high-pressure hydrogen storage cylinders;

[0012] Step 2: Verify the mesh independence and time step independence of the thermodynamic model;

[0013] Step 3: Using the thermodynamic model after irrelevance verification, perform single-parameter influence analysis and multi-parameter coupled quantitative analysis on the three parameters of inlet flow rate, pre-cooling temperature and cylinder inner diameter respectively;

[0014] Step 4: Based on the influence patterns obtained in Step 3, select the optimal parameter combination that meets the national standard temperature limit requirements.

[0015] In a further technical solution, in step 1, the thermodynamic model is established based on the following assumptions:

[0016] The external ambient temperature is constant;

[0017] The surface heat transfer coefficient of the outer wall is constant;

[0018] The temperature and pressure of the hydrogen gas inside the cylinder are evenly distributed;

[0019] The thermal conductivity of carbon fiber and high-density polyethylene is constant;

[0020] The inlet and outlet boundaries are variable mass flow rate boundaries;

[0021] The temperature of the hydrogen gas being introduced is constant;

[0022] Hydrogen is described using real gas state parameters.

[0023] A further technical solution involves using an external analysis method in step 1 to perform thermodynamic analysis on the hydrogen stored inside the gas cylinder. The specific details of the analysis are as follows:

[0024]

[0025] in, The surface heat transfer coefficient; For heat exchange area; For time; This refers to the mass flow rate of the intake air. This refers to the mass flow rate during gas discharge. This is a change in internal energy; This refers to the change in internal energy caused by heat exchange; The change in internal energy caused by the exchange of work; This refers to the change in internal energy caused by mass exchange. The temperature of the hydrogen gas inside the bottle; The temperature of the inner surface of the bottle; The specific enthalpy of the incoming hydrogen gas; The specific enthalpy of the emitted hydrogen gas;

[0026] Using the hydrogen gas inside the hydrogen storage cylinder as the control volume, establish the mass conservation equation and the energy conservation equation;

[0027] Controlling the density of hydrogen in the body The variation over time is determined by the constant mass inflation / deflation process:

[0028]

[0029] in, To control the volume, the unit is m. 3 ; The mass flow rate of hydrogen during charging. >0, during emission <0;

[0030] Controlling the ratio of hydrogen to internal energy in the body The change is contributed by two parts: firstly, the transport of internal energy carried by the fluid during the filling and discharging process; and secondly, the convective heat transfer between hydrogen and the inner surface of the cylinder. The energy conservation equation can be written as:

[0031]

[0032] in, The specific enthalpy of hydrogen flowing in / out. Satisfies Newton's law of cooling:

[0033]

[0034] in, The convective heat transfer coefficient between hydrogen gas and the inner surface; It is the internal surface area; The temperature of hydrogen gas; The temperature is the inner surface temperature of the bottle.

[0035] In a further technical solution, in step 1, the state update of the control body follows the thermodynamic equation of state, and the hydrogen density is updated in real time. Compared to hydrogen, internal energy Inputting into the REFPROP professional thermodynamic database, the real-time specific enthalpy is obtained through the inverse solution of the high-precision equation of state for hydrogen. Real-time temperature and real-time pressure :

[0036]

[0037]

[0038]

[0039] in, This indicates a function that calls the REFPROP professional thermodynamics database.

[0040] In a further technical solution, in step 1, the high-pressure hydrogen storage cylinder has a multi-layer composite material structure, consisting of i layers and i+1 temperature nodes. The heat transfer between the layers follows Fourier's law of thermal conductivity, and the heat exchange of the nth layer is... for:

[0041]

[0042] in, For the thermal resistance of the nth layer, Let n be the temperature of the nth node. When n=1, Let i be the temperature of the inner surface of the bottle, and n=i. The outer surface temperature of the bottle;

[0043] The changes corresponding to each temperature node are obtained by the following formula.

[0044]

[0045]

[0046]

[0047] in, Let the mass of the control body represented by the nth node be [the mass of the control body]. The specific heat of the control volume represented by the nth node. The heat transfer between the outer surface of the bottle and the environment is due to convection, which satisfies Newton's law of cooling.

[0048]

[0049] in, The convective heat transfer coefficient between the outer surface and the environment. external surface area, The outer surface temperature of the bottle. The ambient temperature;

[0050] The thermal resistance of each layer is calculated using the following formula:

[0051]

[0052] In the heat conduction analysis, R1 is the thermal resistance of the cylindrical wall, and R2 is the thermal resistance of the spherical shell. and These represent the outer wall diameter and the inner wall diameter of the cylinder, respectively. and These represent the radii of the outer and inner walls of the spherical shell, respectively. The thermal conductivity of the material The length of the cylindrical wall along the axial direction;

[0053] The total thermal resistance R after parallel connection satisfies R=1 / (1 / R1+1 / R2).

[0054] A further technical solution is that, in step 2, the time step independence verification includes: under the same model conditions, comparing the model calculation results with different time steps, and selecting the time step with the minimum error and the minimum amount of computation as the model calculation time step;

[0055] The mesh independence verification includes: under the same model conditions, comparing the model calculation results with different mesh layer numbers, and selecting the mesh layer number that makes the temperature curve change stable and has the least amount of computation as the model mesh partitioning scheme.

[0056] A further technical solution is to use the thermodynamic model after irrelevance verification in step 3 to conduct single-parameter influence analysis on the three parameters of inlet flow rate, pre-cooling temperature and cylinder inner diameter.

[0057] Analysis of the impact of air intake flow rate: Under the condition of keeping the pre-cooling temperature and the inner diameter of the gas cylinder constant, simulation calculations were performed with different values ​​of air intake flow rate to analyze the impact of air intake flow rate on the temperature rise rate, peak temperature and inflation time during the inflation stage.

[0058] Analysis of the impact of precooling temperature: Under the condition of keeping the air intake flow rate and the inner diameter of the gas cylinder constant, simulation calculations were performed with different values ​​of precooling temperature to analyze the impact of precooling temperature on the temperature rise and cooling energy consumption during the filling stage.

[0059] Analysis of the influence of cylinder inner diameter: Under the condition of keeping the inlet flow rate and pre-cooling temperature constant, simulation calculations were performed with different values ​​of cylinder inner diameter to analyze the influence of cylinder inner diameter on the temperature rise rate during the filling stage and the low temperature problem during the venting stage.

[0060] A further technical solution, in step 3, includes multi-parameter coupled quantitative analysis:

[0061] Two-parameter coupling analysis: Two-parameter coupling analysis was performed on three sets of parameter combinations: inlet flow rate-precooling temperature, inlet flow rate-cylinder inner diameter, and precooling temperature-cylinder inner diameter. By changing the values ​​of the two parameters, the influence of each combination on the changes in the highest temperature, lowest temperature and pressure inside the cylinder was quantified.

[0062] Three-parameter coordinated control analysis: The three parameters of air intake flow rate, precooling temperature and cylinder inner diameter are analyzed for coordinated control. By changing the combination of values ​​of the three parameters, the system quantifies the influence of each combination on the temperature and pressure characteristics inside the cylinder.

[0063] In a further technical solution, in step 4, the national standard temperature limits include a maximum temperature of no more than 85°C during the inflation stage and a minimum temperature of no less than -40°C during the deflation stage. The selection of the optimal parameter combination adopts the following criteria: under the premise of ensuring that the maximum temperature during the inflation stage does not exceed 85°C and the minimum temperature during the deflation stage does not fall below -40°C, the parameter combination with the shortest inflation time is selected first.

[0064] The thermodynamic modeling method for the filling and discharging cycle of high-pressure hydrogen storage cylinders provided in this invention has the following beneficial effects:

[0065] (1) High calculation accuracy: This invention uses the REFPROP professional thermodynamic database to describe the physical properties of high-pressure hydrogen, overcoming the defect of large deviation of the ideal gas assumption under high pressure. After verification of the independence of grid and time step, the calculation error of the model is controlled within 5%.

[0066] (2) High computational efficiency: The present invention uses a lumped parameter thermodynamic model to replace the traditional three-dimensional CFD fine mesh simulation, which greatly shortens the calculation time of a single charge-discharge cycle and overcomes the computational bottleneck of CFD simulation taking tens of hours.

[0067] (3) Multi-parameter synergistic optimization: This invention establishes a three-parameter coupled quantitative analysis system of air intake flow rate, pre-cooling temperature and cylinder inner diameter, which breaks through the limitation of existing technology that only analyzes a single parameter. The synergistic control of the three parameters can reduce the maximum temperature by 35.4K.

[0068] (4) Safe and reliable operation: The optimal parameter combination selected by the present invention can control the highest temperature in the stable cycle stage to within 85℃ and the lowest temperature to not be lower than -40℃, fully meeting the national standard requirements and taking into account both hydrogen addition efficiency and hydrogen storage operation safety.

[0069] (5) Strong engineering applicability: This invention provides a complete theoretical simulation tool and quantitative optimization scheme for the design of on-board hydrogen storage cylinders and the optimization of hydrogen refueling process at hydrogen refueling stations. Attached Figure Description

[0070] Figure 1 The structure of a vehicle-mounted high-pressure hydrogen storage cylinder;

[0071] Figure 2 This refers to the energy and mass exchange process during inflation and deflation.

[0072] Figure 3 To divide the gas cylinder into grids;

[0073] Figure 4 The result is the irrelevance verification result (where a is the time step and b is the grid).

[0074] Figure 5 The results are for validating the model (where a is the comparison between the simulated and real-world temperature changes inside the gas cylinder, and b is the comparison between the experimental and simulated pressure changes inside the gas cylinder). Detailed Implementation

[0075] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0076] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0077] One embodiment of the present invention provides a thermodynamic modeling method for the filling and discharging cycle of a high-pressure hydrogen storage cylinder, comprising the following steps:

[0078] Step 1: Establish a thermodynamic model of the filling and discharging cycle of high-pressure hydrogen storage cylinders;

[0079] This embodiment takes a 70MPa vehicle-mounted Type IV hydrogen storage cylinder as the object, establishes a thermodynamic model of the filling and discharging cycle process, and verifies it.

[0080] (1) Model parameter settings;

[0081] Cylinder parameters: Nominal working pressure 70MPa, inner liner material is high-density polyethylene (HDPE), outer layer is carbon fiber composite winding layer.

[0082] (2) Model building;

[0083] The thermodynamic model is based on the following reasonable assumptions:

[0084] The external ambient temperature is constant;

[0085] The surface heat transfer coefficient of the outer wall is constant;

[0086] The temperature and pressure of the hydrogen gas inside the cylinder are evenly distributed;

[0087] The thermal conductivity of carbon fiber and high-density polyethylene is constant;

[0088] The inlet and outlet boundaries are variable mass flow rate boundaries;

[0089] The temperature of the hydrogen gas being introduced is constant;

[0090] Hydrogen is described using real gas state parameters.

[0091] In the thermodynamic analysis of hydrogen stored inside the gas cylinder, an external analysis method was used as the research tool. This method allows for an in-depth exploration of the interrelationships between key parameters such as pressure, temperature, and volume of hydrogen inside the cylinder. The specific details of the analysis are as follows:

[0092]

[0093] in, Surface heat transfer coefficient, unit W / (m²) 2 ·K); The heat exchange area is expressed in meters (m²). 2 ; Time, in seconds; The mass flow rate of the intake air is expressed in kg / s. The mass flow rate at the outlet is measured in kg / s. The change in internal energy is expressed in W. The change in internal energy caused by heat exchange, measured in W. The change in internal energy caused by the exchange of work, measured in W. The change in internal energy caused by mass exchange. Temperature of the hydrogen gas inside the bottle, in K; Temperature of the inner surface of the bottle, in K. The specific enthalpy of the incoming hydrogen gas, in J / kg. The specific enthalpy of the emitted hydrogen gas is expressed in J / kg.

[0094] like Figure 1As shown, the thermodynamic conditions during the filling and discharging process of hydrogen storage cylinders include: the change in internal energy caused by the entry and exit of hydrogen, the convective heat transfer process between the inside of the cylinder and the inner wall, the heat conduction process between the layers of the cylinder body, and the convective heat transfer process between the outer wall of the cylinder and the external environment.

[0095] like Figure 2 As shown, with the hydrogen gas inside the hydrogen storage cylinder as the control volume, mass conservation equations and energy conservation equations are established.

[0096] Controlling the density of hydrogen in the body The variation over time is determined by the constant mass inflation / deflation process:

[0097]

[0098] in, To control the volume, the unit is m. 3 ; Hydrogen mass flow rate (during charging) >0, during emission <0), unit: kg / s.

[0099] Controlling the ratio of hydrogen to internal energy in the body The change is contributed by two parts: firstly, the transport of internal energy carried by the fluid during the filling and discharging process; and secondly, the convective heat transfer between hydrogen and the inner surface of the cylinder. .

[0100] The energy conservation equation can be written as:

[0101]

[0102] in, The specific enthalpy of hydrogen flowing in / out. Satisfies Newton's law of cooling:

[0103]

[0104] in, The convective heat transfer coefficient between hydrogen gas and the inner surface is expressed in W / (m²). 2 ·K); Internal surface area, unit m 2 ; The temperature of hydrogen gas is expressed in Kelvin (K). Temperature of the inner surface of the bottle, in K.

[0105] The state update of the control volume follows the thermodynamic equation of state. The hydrogen density will be updated in real time. Compared to hydrogen, internal energy Inputting into the REFPROP professional thermodynamic database, the real-time specific enthalpy is obtained through the inverse solution of the high-precision equation of state for hydrogen. Real-time temperature and real-time pressure :

[0106]

[0107]

[0108]

[0109] in, This indicates a function that calls the REFPROP professional thermodynamics database.

[0110] This operation was achieved. The state mapping provides a thermodynamic basis for subsequent heat transfer calculations and boundary condition updates.

[0111] The bottle body is a multi-layered composite material structure, such as Figure 3 As shown, the system is divided into i layers with a total of i+1 temperature nodes. The heat transfer between layers follows Fourier's law of thermal conductivity. The heat transfer of the nth layer is... for:

[0112]

[0113] in, For the thermal resistance of the nth layer, use formula 1 / R n =1 / R1+1 / R2 is calculated to obtain the result. Let n be the temperature of the nth node. When n=1, Let i be the temperature of the inner surface of the bottle, and n=i. This refers to the temperature of the outer surface of the bottle.

[0114] The changes corresponding to each temperature node are obtained by the following formula.

[0115]

[0116]

[0117]

[0118] in, Let the mass of the control body represented by the nth node be [the mass of the control body]. The specific heat of the control volume represented by the nth node. For the outer surface of the bottle and the environment (constant temperature) The convective heat transfer between them satisfies Newton's law of cooling:

[0119]

[0120] in, The convective heat transfer coefficient between the outer surface and the environment. external surface area, The outer surface temperature of the bottle. This represents the ambient temperature. In summary, this constitutes a complete three-stage heat transfer chain: hydrogen gas - cylinder - environment.

[0121] By analyzing the heat and mass exchange processes between hydrogen gas inside the cylinder and the external environment, the changing patterns of hydrogen's thermodynamic energy can be derived. Simultaneously, based on the law of conservation of mass and combined with the hydrogen mass flow rate data entering and leaving the cylinder, the dynamic relationship of hydrogen density changes over time can be accurately calculated. Furthermore, by using MATLAB software to access the REFPROP professional thermodynamic database, crucial thermodynamic parameters such as temperature, pressure, and specific enthalpy of hydrogen under its current state can be precisely retrieved. This provides a data foundation for subsequent, more in-depth thermodynamic analysis and numerical simulation calculations.

[0122] like Figure 3 The diagram shows the grid division of the gas cylinder. To simplify the calculation process and improve efficiency, it is assumed that the temperature distribution between each layer is uniform. Starting from the known initial temperature conditions and combining them with the given boundary conditions, the temperature values ​​at each time layer can be calculated and derived step by step.

[0123] Specifically, the thermal resistance of each layer will be calculated according to the following formula:

[0124]

[0125] In the heat conduction analysis, R1 is the thermal resistance of the cylindrical wall, and R2 is the thermal resistance of the spherical shell. and These represent the outer wall diameter and the inner wall diameter of the cylinder, respectively. and These represent the radii of the outer and inner walls of the spherical shell, respectively. The thermal conductivity of the material denoted as the axial length of the cylindrical wall. For multi-layer structures, the thermal resistance of each grid layer consists of two parallel thermal resistances. This means that the superposition effect of thermal resistances along different paths needs to be comprehensively considered during the calculation process to accurately reflect the distribution and transfer characteristics of heat flow in the multi-dimensional structure.

[0126] When calculating the thermal resistance of a multilayer structure, the thermal resistance of each layer is first determined. For each cylindrical wall or spherical shell structure, the single-layer thermal resistance is calculated using the corresponding thermal resistance calculation formula based on its geometric dimensions and material thermal conductivity. Since heat flow in a single-layer structure may be transferred through different paths, parallel thermal resistances exist. In this case, the thermal resistances of each layer are superimposed using the method for calculating the resistance of a parallel circuit. The total thermal resistance R after parallel superposition satisfies 1 / R = 1 / R1 + 1 / R2. The total thermal resistance of the single-layer structure is obtained through this calculation method.

[0127] After determining the total thermal resistance, and combining the known initial temperature and boundary conditions, the temperature values ​​at each time step are calculated step by step using the heat conduction equation. Starting from the initial moment, the calculation is advanced progressively according to the time step. Within each time step, the temperature values ​​at each location are updated using the heat conduction equation based on the temperature distribution at the previous moment and the boundary conditions at the current moment. In this way, the temperature field distribution of the gas cylinder at different moments can be obtained, thereby simplifying the calculation process and improving computational efficiency, while ensuring that the calculation results can accurately reflect the temperature changes of the gas cylinder during the actual filling and discharging process.

[0128] Step 2: Verify the mesh independence and time step independence of the thermodynamic model;

[0129] like Figure 4 As shown in Figure a, under the same model conditions, the analysis results of the impact of different time steps on the model data show that when the time step is 0.1s and 0.05s, the model calculation error is relatively large and cannot meet the requirements of high-precision simulation; however, when the time step is reduced to 0.01s and 0.008s, the error is significantly reduced and the simulation accuracy is significantly improved. Considering both computational accuracy and computational efficiency, in order to effectively reduce the amount of computation while ensuring the accuracy of the model data, 0.01s was finally selected as the time step for model calculation.

[0130] In terms of mesh generation, irrelevance verification is also performed. For example... Figure 4 As shown in b, by comparing the calculation results under different grid densities, it was found that when the grid has only one layer, the model cannot accurately capture the temperature changes inside the gas cylinder, resulting in a large deviation in the calculation results. When the number of grid layers increases to 50 and 100, the temperature curves nearly overlap, and further increasing the number of grid layers no longer significantly improves the calculation results; instead, it greatly increases the computational load. After weighing the options, a grid of 50 layers was ultimately chosen, reducing computation time while maintaining accuracy. The above verification of the independence between grid and time step lays a solid foundation for subsequent research on the high-pressure hydrogen charging and discharging cycle process based on this thermodynamic model, ensuring the high reliability and accuracy of the obtained research results.

[0131] Step 3: Using the thermodynamic model after irrelevance verification, perform single-parameter influence analysis and multi-parameter coupled quantitative analysis on the three parameters of inlet flow rate, pre-cooling temperature and cylinder inner diameter respectively;

[0132] (1) Single parameter influence analysis

[0133] This embodiment uses a thermodynamic model that has been verified for irrelevance to perform single-parameter influence analysis on three parameters: inlet flow rate, precooling temperature, and cylinder inner diameter.

[0134] Analysis of the impact of inlet flow rate: Under the condition of keeping the pre-cooling temperature and the inner diameter of the gas cylinder constant, simulation calculations were performed with different inlet flow rates. The results show that increasing the inlet flow rate significantly aggravates the temperature rise rate and peak temperature during the charging stage, while shortening the charging time. Although simply reducing the inlet flow rate can suppress the temperature rise, it will significantly prolong the hydrogen addition time.

[0135] Analysis of the impact of precooling temperature: Under the condition of keeping the inlet flow rate and cylinder inner diameter constant, simulation calculations were performed with different precooling temperatures. The results show that reducing the precooling temperature can effectively suppress the temperature rise during the filling stage, but it will significantly increase the cooling energy consumption of the hydrogen refueling station.

[0136] Analysis of the impact of cylinder inner diameter: Under the condition of keeping the inlet flow rate and pre-cooling temperature constant, simulation calculations were performed with different values ​​for the cylinder inner diameter. The results show that increasing the cylinder inner diameter can reduce the temperature rise rate during the filling stage, but it will simultaneously exacerbate the low temperature problem during the venting stage.

[0137] (2) Multi-parameter coupled quantitative analysis and parameter optimization

[0138] This embodiment performs two-parameter coupling analysis and three-parameter synergistic control analysis on three parameters: air intake flow rate, precooling temperature, and cylinder inner diameter.

[0139] Two-parameter coupling analysis: Two-parameter coupling analysis was performed on three parameter combinations: inlet flow rate-precooling temperature, inlet flow rate-cylinder inner diameter, and precooling temperature-cylinder inner diameter. By changing the values ​​of the two parameters, the influence of each combination on the changes in the highest temperature, lowest temperature, and pressure inside the cylinder was quantified. The results show that the cooling effect of two-parameter coupling control is better than that of single-parameter control, but there is a problem of limited control margin.

[0140] Three-parameter synergistic control analysis: A three-parameter synergistic control analysis was conducted on the inlet flow rate, precooling temperature, and cylinder inner diameter. By changing the combinations of values ​​for these three parameters, the system quantified the impact of each combination on the temperature and pressure characteristics inside the cylinder. The results show that three-parameter synergistic control can effectively reduce the maximum temperature.

[0141] Step 4: Based on the influence patterns obtained in Step 3, select the optimal parameter combination that meets the national standard temperature limit requirements.

[0142] The national standard temperature limits include a maximum temperature of 85℃ during the inflation phase and a minimum temperature of -40℃ during the deflation phase. The optimal parameter combination is selected based on the following criteria: prioritizing the parameter combination with the shortest inflation time, while ensuring that the maximum temperature during inflation does not exceed 85℃ and the minimum temperature during deflation does not fall below -40℃. The selected optimal parameter combination ensures that all temperature and pressure parameters during the cyclic stabilization phase meet the national standard requirements, while maintaining the inflation time within a reasonable range.

[0143] To further verify the effectiveness of the established thermodynamic model, relevant comparative experiments were conducted, such as... Figure 5 As shown in the figure. The experiment uses an actual high-pressure hydrogen storage tank as the object, simulates the working conditions under different filling and discharging conditions, and collects key parameters such as temperature and pressure of hydrogen in the tank in real time through high-precision sensors.

[0144] Comparative analysis of experimental data and model simulation results showed that, under the same charging and discharging conditions, the hydrogen temperature and pressure change curves calculated by the model were in high agreement with the experimental data. During the charging process, the model accurately predicted the rising trend of hydrogen temperature over time and the gradual increase in pressure; similarly, during the discharging phase, it could simulate the decrease in hydrogen temperature and pressure. This indicates that the established thermodynamic model can realistically reflect the physical phenomena during the high-pressure hydrogen charging and discharging cycle and has high predictive accuracy for the thermodynamic state changes of hydrogen inside the tank. After multiple rounds of comparative analysis and optimization adjustments, the simulation results for some time periods still showed some deviation from the experimental data. However, considering that the final state of the previous cycle is used as the initial condition for the next cycle, the current focus is more on ensuring the optimization of overall performance at the end of the cycle. The final results show that after a single cycle, the relative errors between the simulated values ​​and experimental measurements of the system's internal temperature, pressure, and external wall temperature are all controlled within 5%, meeting the engineering accuracy requirements.

[0145] Furthermore, the adaptability and robustness of the model were further verified by comparing experiments and simulations under different initial conditions. Whether changing the inlet flow rate, pre-cooling temperature, or adjusting the structural parameters of the gas cylinder, the model consistently produced results consistent with the experiments. This fully demonstrates that the model is not only applicable to specific operating conditions but can also accurately simulate the high-pressure hydrogen charging and discharging cycle within a wide range of parameters, providing a reliable tool and strong support for further in-depth research on the thermodynamic characteristics of high-pressure hydrogen storage and transportation.

[0146] This invention focuses on an in-depth study of the thermodynamic model of the high-pressure hydrogen charging and discharging cycle. First, the necessity of establishing a thermodynamic model is explained. Due to the large time span and complex heat and mass transfer involved in the charging and discharging cycle, traditional CFD simulations are computationally intensive and time-consuming. Therefore, reasonable assumptions and model simplification are necessary. Next, the reasonable assumptions of the model are detailed, including settings for external ambient temperature, convective heat transfer coefficient of the outer wall, and the temperature and pressure distribution of hydrogen inside the cylinder, providing a foundation for subsequent model establishment. In selecting the thermodynamic model, an external analysis method is adopted, revealing the thermodynamic state change law of hydrogen by analyzing the heat and mass exchange between hydrogen inside the cylinder and the external environment. During the model establishment and simplification process, the cylinder is divided into grids, assuming uniform temperature distribution between layers. The temperature values ​​at each time layer are derived step by step by calculating the thermal resistance of each layer and combining it with the heat conduction equation, while considering the parallel superposition effect of thermal resistance in the multi-layer structure. To ensure the accuracy and reliability of the model calculation results, the independence of the grid and time step is verified, and an appropriate time step and number of grid layers are determined. Finally, the effectiveness of the established thermodynamic model was verified by comparing it with experiments in the literature. The model can not only accurately predict the changes in hydrogen temperature and pressure under the same operating conditions, but also shows good adaptability and robustness under different initial conditions, providing a reliable tool for subsequent research on the thermodynamic characteristics of high-pressure hydrogen storage and transportation.

[0147] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A thermodynamic modeling method for the filling and discharging cycle of high-pressure hydrogen storage cylinders, characterized in that, Includes the following steps: Step 1: Establish a thermodynamic model of the filling and discharging cycle of high-pressure hydrogen storage cylinders; Step 2: Verify the mesh independence and time step independence of the thermodynamic model; Step 3: Using the thermodynamic model after irrelevance verification, perform single-parameter influence analysis and multi-parameter coupled quantitative analysis on the three parameters of inlet flow rate, pre-cooling temperature and cylinder inner diameter respectively; Step 4: Based on the influence patterns obtained in Step 3, select the optimal parameter combination that meets the national standard temperature limit requirements.

2. The thermodynamic modeling method for the filling and discharging cycle of high-pressure hydrogen storage cylinders according to claim 1, characterized in that, In step 1, the thermodynamic model is established based on the following assumptions: The external ambient temperature is constant; The surface heat transfer coefficient of the outer wall is constant; The temperature and pressure of the hydrogen gas inside the cylinder are evenly distributed; The thermal conductivity of carbon fiber and high-density polyethylene is constant; The inlet and outlet boundaries are variable mass flow rate boundaries; The temperature of the hydrogen gas being introduced is constant; Hydrogen is described using real gas state parameters.

3. The thermodynamic modeling method for the filling and discharging cycle of high-pressure hydrogen storage cylinders according to claim 2, characterized in that, In step 1, during the thermodynamic analysis of the hydrogen stored inside the gas cylinder, an external analysis method is used, and the specific content of the analysis is as follows: ； in, The surface heat transfer coefficient; For heat exchange area; For time; This refers to the mass flow rate of the intake air. This refers to the mass flow rate during gas discharge. This is a change in internal energy; This refers to the change in internal energy caused by heat exchange; The change in internal energy caused by the exchange of work; This refers to the change in internal energy caused by mass exchange. The temperature of the hydrogen gas inside the bottle; The temperature of the inner surface of the bottle; The specific enthalpy of the incoming hydrogen gas; The specific enthalpy of the emitted hydrogen gas; Using the hydrogen gas inside the hydrogen storage cylinder as the control volume, establish the mass conservation equation and the energy conservation equation; Controlling the density of hydrogen in the body The variation over time is determined by the constant mass inflation / deflation process: ； in, To control the volume, the unit is m. 3 ; The mass flow rate of hydrogen during charging. >0, during emission <0; Controlling the ratio of hydrogen to internal energy in the body The change is contributed by two parts: firstly, the transport of internal energy carried by the fluid during the filling and discharging process; and secondly, the convective heat transfer between hydrogen and the inner surface of the cylinder. The energy conservation equation can be written as: ； in, The specific enthalpy of hydrogen flowing in / out. Satisfies Newton's law of cooling: ； in, The convective heat transfer coefficient between hydrogen gas and the inner surface; It is the internal surface area; The temperature of hydrogen gas; The temperature is the inner surface temperature of the bottle.

4. The thermodynamic modeling method for the filling and discharging cycle of high-pressure hydrogen storage cylinders according to claim 3, characterized in that, In step 1, the state update of the control volume follows the thermodynamic equation of state, and the hydrogen density is updated in real time. Compared to hydrogen, internal energy Inputting into the REFPROP professional thermodynamic database, the real-time specific enthalpy is obtained through the inverse solution of the high-precision equation of state for hydrogen. Real-time temperature and real-time pressure : ； ； ； in, This indicates a function that calls the REFPROP professional thermodynamics database.

5. The thermodynamic modeling method for the filling and discharging cycle of high-pressure hydrogen storage cylinders according to claim 4, characterized in that, In step 1, the high-pressure hydrogen storage cylinder has a multi-layer composite material structure, consisting of i layers and i+1 temperature nodes. The heat transfer between the layers follows Fourier's law of thermal conductivity. The heat exchange of the nth layer is... for: ； in, For the thermal resistance of the nth layer, Let n be the temperature of the nth node. When n=1, Let i be the temperature of the inner surface of the bottle, and n=i. The outer surface temperature of the bottle; The changes corresponding to each temperature node are obtained by the following formula. ； ； ； in, Let the mass of the control body represented by the nth node be [the mass of the control body]. The specific heat of the control volume represented by the nth node. The heat transfer between the outer surface of the bottle and the environment is due to convection, which satisfies Newton's law of cooling. ； in, The convective heat transfer coefficient between the outer surface and the environment. external surface area, The outer surface temperature of the bottle. The ambient temperature; The thermal resistance of each layer is calculated using the following formula: ； In the heat conduction analysis, R1 is the thermal resistance of the cylindrical wall, and R2 is the thermal resistance of the spherical shell. and These represent the outer wall diameter and the inner wall diameter of the cylinder, respectively. and These represent the radii of the outer and inner walls of the spherical shell, respectively. The thermal conductivity of the material The length of the cylindrical wall along the axial direction; The total thermal resistance R after parallel connection satisfies R=1 / (1 / R1+1 / R2).

6. The thermodynamic modeling method for the filling and discharging cycle of high-pressure hydrogen storage cylinders according to claim 5, characterized in that, In step 2, the time step independence verification includes: under the same model conditions, comparing the model calculation results with different time steps, and selecting the time step with the minimum error and the minimum amount of computation as the model calculation time step; The mesh independence verification includes: under the same model conditions, comparing the model calculation results with different mesh layer numbers, and selecting the mesh layer number that makes the temperature curve change stable and has the least amount of computation as the model mesh partitioning scheme.

7. The thermodynamic modeling method for the filling and discharging cycle of high-pressure hydrogen storage cylinders according to claim 6, characterized in that, In step 3, the single-parameter influence analysis of the three parameters of inlet flow rate, pre-cooling temperature and cylinder inner diameter is performed using the thermodynamic model after irrelevance verification. Analysis of the impact of air intake flow rate: Under the condition of keeping the pre-cooling temperature and the inner diameter of the gas cylinder constant, simulation calculations were performed with different values ​​of air intake flow rate to analyze the impact of air intake flow rate on the temperature rise rate, peak temperature and inflation time during the inflation stage. Analysis of the impact of precooling temperature: Under the condition of keeping the air intake flow rate and the inner diameter of the gas cylinder constant, simulation calculations were performed with different values ​​of precooling temperature to analyze the impact of precooling temperature on the temperature rise and cooling energy consumption during the filling stage. Analysis of the influence of cylinder inner diameter: Under the condition of keeping the inlet flow rate and pre-cooling temperature constant, simulation calculations were performed with different values ​​of cylinder inner diameter to analyze the influence of cylinder inner diameter on the temperature rise rate during the filling stage and the low temperature problem during the venting stage.

8. The thermodynamic modeling method for the filling and discharging cycle of high-pressure hydrogen storage cylinders according to claim 7, characterized in that, In step 3, the multi-parameter coupled quantization analysis includes: Two-parameter coupling analysis: Two-parameter coupling analysis was performed on three sets of parameter combinations: inlet flow rate-precooling temperature, inlet flow rate-cylinder inner diameter, and precooling temperature-cylinder inner diameter. By changing the values ​​of the two parameters, the influence of each combination on the changes in the highest temperature, lowest temperature and pressure inside the cylinder was quantified. Three-parameter coordinated control analysis: The three parameters of air intake flow rate, precooling temperature and cylinder inner diameter are analyzed for coordinated control. By changing the combination of values ​​of the three parameters, the system quantifies the influence of each combination on the temperature and pressure characteristics inside the cylinder.

9. The thermodynamic modeling method for the filling and discharging cycle of high-pressure hydrogen storage cylinders according to claim 8, characterized in that, In step 4, the national standard temperature limits include a maximum temperature of no more than 85°C during the inflation stage and a minimum temperature of no less than -40°C during the deflation stage. The selection of the optimal parameter combination adopts the following criteria: under the premise of ensuring that the maximum temperature during the inflation stage does not exceed 85°C and the minimum temperature during the deflation stage does not fall below -40°C, the parameter combination with the shortest inflation time is selected first.

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