Joint correction method of flash vaporization and evaporation condensation for liquid hydrogen tank filling simulation

Abstract

The application discloses a flash evaporation and condensation combined correction method for liquid hydrogen storage tank filling simulation, which comprises the following steps: determining a phase change calculation area of liquid hydrogen storage tank filling simulation; determining a grid unit with pressure reduction flash evaporation in a pipe flash evaporation candidate area, and obtaining a pipe flash evaporation source term according to a balanced gas phase mass proportion calculation; determining a grid unit with evaporation or condensation in a gas-liquid interface and gas pillow candidate area, and determining an evaporation and condensation mass source term; obtaining a local gas phase generation amount and consumption amount, combining a whole gas phase mass change amount of the storage tank, and determining a tank pressure response displacement amount; jointly correcting the pipe flash evaporation, evaporation and gas pillow condensation source terms according to the tank pressure response displacement amount; writing back the corrected source terms, and outputting a simulation result. The flash evaporation and condensation combined correction method for liquid hydrogen storage tank filling simulation can improve the accuracy and interpretability of liquid hydrogen storage tank filling pressure, temperature and gas-liquid phase distribution simulation.

Description

Technical Field

[0001] This invention relates to the field of computer-aided simulation technology, specifically to a combined correction method for flash evaporation and evaporation-condensation in liquid hydrogen storage tank filling simulation. Background Technology

[0002] Liquid hydrogen is characterized by extremely low temperature, low density, low viscosity, and low latent heat of vaporization, making it prone to complex phase transitions during the filling process of liquid hydrogen storage tanks. When liquid hydrogen enters the storage tank through the filling pipeline, the internal pressure of the tank, the inlet liquid hydrogen temperature, the local pressure drop at the pipe inlet, heat transfer at the gas-liquid interface, and the condensation process in the gas pillow area all collectively affect the pressure, temperature, and gas-liquid phase distribution within the tank. For liquid hydrogen flow rate standards, liquid hydrogen storage and transportation equipment, and liquid hydrogen filling equipment, failure to accurately predict pressure changes and gas-liquid phase distribution during the filling process can easily affect tank safety assessments, filling process control, and flow metering accuracy.

[0003] Current simulations of liquid hydrogen tank filling typically employ computational fluid dynamics (CFD) methods to establish a flow field model within the tank and use the fluid volume method to describe the distribution of the liquid and gas phases of liquid hydrogen. This approach usually combines turbulence models, surface tension models, evaporation-condensation models, and energy equations to solve for the pressure field, temperature field, and gas-liquid phase volume fraction field.

[0004] In evaporation-condensation processes, a common approach is to compare the current temperature of a grid cell with the local saturation temperature at the current pressure. Evaporation is determined to have occurred when the current temperature of the grid cell is higher than the local saturation temperature; condensation is determined to have occurred when the current temperature of the grid cell is lower than or equal to the local saturation temperature. This type of method is suitable for describing evaporation or condensation caused by heat exchange at the gas-liquid interface.

[0005] However, in the initial stage after liquid hydrogen enters the low-pressure storage tank, there is often a significant pressure drop in the inlet area. When the saturation pressure corresponding to the inlet liquid hydrogen is higher than the local pressure inside the storage tank, the liquid hydrogen will undergo pressure-reducing flash evaporation near the inlet. This process is mainly triggered by a sudden change in pressure state and is not equivalent to ordinary temperature difference evaporation. Inlet flash evaporation will form a local gas phase peak near the inlet, causing the gas phase volume fraction in the inlet area to increase rapidly.

[0006] Meanwhile, the introduction of cryogenic liquid hydrogen into the storage tank cools the gas pillow area and the gas-liquid interface, causing condensation of the gas phase and thus weakening or even delaying the overall pressure rise of the tank. This results in a peculiar phenomenon: strong local gas phase generation near the nozzle, but the overall tank pressure response does not necessarily increase synchronously, manifesting as a temporal, spatial, and intensity misalignment between the local gas phase peak at the nozzle and the overall tank pressure response. Chinese Patent CN110043791A discloses a device and method for reducing the evaporation rate of liquid hydrogen storage tanks using liquid nitrogen cooling, but this still fails to solve the aforementioned problem. Summary of the Invention

[0007] Existing simulation models tend to conflate intrapipeline pressure reduction flash evaporation with interfacial evaporation and condensation, leading to mismatches between flash evaporation source terms, condensation source terms, and the overall gas phase response of the storage tank. To address this, this invention proposes a joint correction method for flash evaporation and evaporation / condensation in liquid hydrogen storage tank filling simulation, improving the accuracy and interpretability of simulations of filling pressure, temperature, and gas-liquid phase distribution in liquid hydrogen storage tanks.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a combined correction method for flash evaporation and evaporation-condensation in liquid hydrogen storage tank filling simulation, comprising the following steps: S1, determine the phase change calculation region for the liquid hydrogen storage tank filling simulation; S2, grid cells with depressurized flashing are identified within the candidate region of pipe flashing, and the pipe flashing source term is calculated based on the equilibrium gas phase mass ratio; S3, Identify the grid cells where evaporation or condensation occurs at the gas-liquid interface and within the candidate region of the gas pillow, and determine the evaporation-condensation mass source term; S4, obtain the local gas phase generation and consumption, and combine them with the overall gas phase mass change of the storage tank to determine the tank pressure response misalignment. S5, based on the tank pressure response misalignment, jointly correct the source terms of pipe flash evaporation, evaporation and gas pillow condensation; S6 writes back the corrected source term and outputs the simulation results.

[0009] In this technical solution, by identifying the pressure reduction flash evaporation and gas-liquid interface evaporation and condensation at the pipe outlet, the tank pressure response misalignment is calculated, and the phase change source terms are jointly corrected based on the misalignment, so that the local phase change source terms form a closed-loop correspondence with the overall gas phase response of the storage tank, thereby improving the accuracy and interpretability of the simulation of the filling pressure, temperature and gas-liquid phase distribution of the liquid hydrogen storage tank.

[0010] Further, step S1 includes: S11, Construct a transient two-phase flow simulation model of the liquid hydrogen storage tank filling process and obtain parameter information of each grid cell in the storage tank; S12. Based on the outlet location of the filling pipeline, the outlet location of the diffuser, and the volume fraction distribution of the gas and liquid phases, determine the candidate regions for flash evaporation at the pipe inlet, the candidate regions for the gas-liquid interface, and the candidate regions for the gas pillow.

[0011] In this technical solution, the parameter information of each grid cell in the storage tank includes the pressure, temperature, liquid volume fraction, gas volume fraction, and specific enthalpy of the mixture for each grid cell.

[0012] Further, step S2 includes: S21, In the candidate region of flash evaporation at the pipe opening, the grid cell containing the liquid phase is compared with the current pressure to determine whether the grid cell has pressure reduction flash evaporation. S22, if there is pressure reduction flash evaporation in the grid cell, determine the equilibrium gas phase mass ratio based on the grid cell parameter information; obtain the inlet flash evaporation source term based on the equilibrium gas phase mass ratio and the current gas phase mass ratio.

[0013] In this technical solution, within the candidate region for flash evaporation at the nozzle, for each grid cell containing a liquid phase, the liquid hydrogen saturation pressure is determined based on the current temperature of the grid cell, and the liquid hydrogen saturation pressure is compared with the current pressure of the grid cell; when the liquid hydrogen saturation pressure is higher than the current pressure of the grid cell, it is determined that the grid cell has pressure-reducing flash evaporation; when the liquid hydrogen saturation pressure is not higher than the current pressure of the grid cell, no nozzle flash evaporation source term is generated.

[0014] Further, step S3 includes: For grid cells in the gas-liquid interface and candidate area of ​​the gas pillow, the current temperature of the grid cell is compared with the local saturation temperature to determine whether the grid cell has undergone evaporation or condensation. If evaporation or condensation occurs in a grid cell, the evaporation / condensation mass source term is determined based on the heat change and latent heat of vaporization of liquid hydrogen in the current time step.

[0015] In this technical solution, within the candidate regions of the gas-liquid interface and the candidate regions of the gas pillow, for each grid cell, the local saturation temperature is determined based on the current pressure of the grid cell, and the current temperature of the grid cell is compared with the local saturation temperature. When the current temperature of the grid cell is higher than the local saturation temperature, it is determined that the grid cell has undergone evaporation; when the current temperature of the grid cell is lower than or equal to the local saturation temperature, it is determined that the grid cell has undergone condensation.

[0016] Furthermore, step S3 also includes: Condensation source terms located in the candidate region of the air pillow or the gas-liquid interface region on the side of the air pillow are air pillow condensation source terms.

[0017] Further, step S4 includes: The nozzle flash source term is integrated within the nozzle flash candidate region to obtain the amount of nozzle flash vapor phase generated at the current time step; the gas pillow condensation source term is integrated within the gas pillow candidate region and the gas pillow side gas-liquid interface region to obtain the amount of gas pillow condensation vapor phase consumed at the current time step. The tank pressure response misalignment is determined based on the amount of flash vapor generated at the pipe inlet, the amount of condensed vapor consumed in the gas pillow, and the overall change in the gas phase mass of the storage tank.

[0018] Further, step S5 includes: When the amount of flash vapor generated at the pipe outlet exceeds the preset generation threshold and the overall gas phase quality change of the storage tank does not increase synchronously, the gas pillow condensation source item or the pipe outlet flash vapor source item is corrected according to the tank pressure response misalignment. When the overall change in gas phase mass of the storage tank is greater than the net amount generated after deducting the amount of gas phase consumed by the gas pillow condensation from the amount of gas phase generated by the flash vapor phase at the pipe inlet, the evaporation source term is compensated based on the tank pressure response misalignment.

[0019] In this technical solution, based on the tank pressure response misalignment obtained in step S4, the flash evaporation source term obtained in step S2 and the evaporation source term and air cushion condensation source term obtained in step S3 are jointly corrected.

[0020] Further, step S6 includes: The corrected pipe flash source term, the corrected evaporation source term, and the corrected gas pillow condensation source term are written back to the continuity equation, volume fraction equation, and energy equation of the liquid hydrogen storage tank filling simulation, respectively. Resolve the pressure field, temperature field, and gas-liquid phase volume fraction field at the current time step, and proceed to the next time step until the liquid hydrogen storage tank filling simulation is completed.

[0021] In this technical solution, for the modified flash evaporation source term at the pipe inlet, a liquid phase mass reduction term and a gas phase mass increase term are set in the candidate region of flash evaporation at the pipe inlet; for the modified evaporation source term, a liquid phase mass reduction term and a gas phase mass increase term are set in the candidate region of the gas-liquid interface; for the modified condensation source term in the gas pillow, a gas phase mass reduction term and a liquid phase mass increase term are set in the candidate region of the gas pillow and the gas-liquid interface region on the side of the gas pillow. Simultaneously, energy terms corresponding to the latent heat of vaporization or latent heat of condensation are added to the energy equation.

[0022] Furthermore, the steps for determining the overall gas phase mass change of the storage tank are as follows: Based on the gas phase volume fraction and gas phase density of all grid cells in the storage tank, the overall gas phase mass change of the storage tank between the current time step and the previous time step is calculated.

[0023] Further, step S22 includes: determining the equilibrium gas phase mass ratio based on the saturated liquid hydrogen specific enthalpy, the saturated hydrogen specific enthalpy, and the mixture specific enthalpy of the grid cell at the current pressure; converting the portion of the equilibrium gas phase mass ratio that is higher than the current gas phase mass ratio into a mass source term for the liquid phase to gas phase conversion within the current time step, thereby obtaining the nozzle flash evaporation source term.

[0024] The present invention can bring about the following beneficial effects.

[0025] First, we distinguish between the triggering mechanisms of pressure drop flash evaporation at the nozzle and evaporation and condensation at the gas-liquid interface. This allows us to calculate the source terms of flash evaporation caused by a sudden pressure drop and evaporation and condensation caused by heat imbalance separately. This avoids simply equating flash evaporation with ordinary evaporation and thus more accurately describes the process of rapid increase in the gas phase volume fraction near the inlet and the formation of a flash plume at the nozzle when liquid hydrogen first enters the low-pressure storage tank.

[0026] The present invention further calculates the tank pressure response misalignment based on the amount of flash vapor generated at the inlet, the amount of condensed vapor consumed in the gas pillow, and the overall change in the gas phase mass of the storage tank. Therefore, it can identify the asynchronous relationship between the local gas phase peak at the inlet and the overall gas phase response of the storage tank, and avoid judging the overall pressure change only from the local source term.

[0027] This invention utilizes the tank pressure response misalignment to jointly correct the flash evaporation source term, evaporation source term, and gas pillow condensation source term, thereby forming a closed-loop correspondence between the local phase change source term and the overall gas phase response of the storage tank. Therefore, it can reduce the pressure prediction deviation caused by the asynchronous relationship between the local gas phase peak at the pipe inlet and the overall tank pressure response, and improve the simulation reliability of the pressure curve, temperature curve, and gas-liquid phase volume fraction distribution of the liquid hydrogen storage tank. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a simulation scenario for filling a liquid hydrogen storage tank according to the present invention.

[0029] Figure 2 This is a schematic diagram illustrating the scenario where the flash plume and the condensation clamping mechanism of the pipe in this invention coexist.

[0030] Figure 3 This is a graph illustrating the coexistence mechanism of flash plume and air cushion condensation clamping at the nozzle in this invention.

[0031] Attached reference numerals: 1. Storage tank; 2. Filling port; 3. Diffuser; 4. Liquid phase zone; 5. Gas-liquid interface; 6. Air cushion zone; 7. Flash plume zone; 8. Air cushion condensation zone. Detailed Implementation

[0032] Example 1: During the simulation of liquid hydrogen tank filling, when liquid hydrogen enters the low-pressure tank through the filling pipe, flash evaporation preferentially occurs in the pipe-inlet area due to the sudden local pressure drop, forming a local gas phase peak. Meanwhile, the cryogenic liquid hydrogen will also cause condensation in the gas pillow area and the gas-liquid interface, so that the local gas phase generation cannot be synchronously reflected in the overall pressure rise of the tank. Existing simulation models tend to confuse the pipe-inlet pressure drop flash evaporation with the interface evaporation and condensation, resulting in a mismatch between the flash evaporation source term, the condensation source term, and the overall gas phase response of the tank, thus causing distortion of the simulation results of liquid hydrogen tank pressure, temperature, and gas-liquid phase distribution.

[0033] The existing solutions have the following specific drawbacks.

[0034] First, since the triggering condition for pressure reduction flash evaporation at the inlet is mainly the imbalance between the liquid hydrogen saturation pressure and the local pressure, rather than simply being triggered by the grid temperature being higher than the local saturation temperature, if the existing method judges the phase change direction only by comparing the temperature with the saturation temperature, it is easy to misjudge pressure reduction flash evaporation at the inlet as ordinary evaporation, resulting in inaccurate prediction of the gas phase volume fraction and gas phase generation near the inlet.

[0035] Second, flash evaporation at the nozzle causes rapid local gas phase generation, but the cryogenic liquid hydrogen entering the tank promotes condensation in the gas pillow area and at the gas-liquid interface. If existing methods only treat gas pillow condensation as a result of local heat exchange without analyzing its offsetting effect on the overall tank pressure response, a lack of correspondence between the local gas phase peak and the overall tank pressure response will result.

[0036] Third, in the simulation of liquid hydrogen tank filling, the overall pressure response of the tank is essentially closely related to the overall gas phase mass change of the tank. If there is a lack of closed-loop verification at the mass conservation level between the flash evaporation source term at the nozzle, the condensation source term in the gas pillow, and the overall gas phase mass change of the tank, the simulation model may exhibit distortions such as strong local phase change source terms but weak overall tank pressure changes, or an overall tank pressure increase but insufficient contribution from local source terms.

[0037] To address these shortcomings, this embodiment proposes a joint correction method for flash evaporation and evaporation-condensation in liquid hydrogen storage tank filling simulation. By identifying the sources of pressure reduction flash evaporation at the pipe inlet and evaporation-condensation at the gas-liquid interface, the tank pressure response misalignment is calculated. Based on this misalignment, the phase change source terms are jointly corrected, forming a closed-loop correspondence between the local phase change source terms and the overall gas phase response of the storage tank. This improves the accuracy and interpretability of the simulation of liquid hydrogen storage tank filling pressure, temperature, and gas-liquid phase distribution.

[0038] refer to Figure 1 , Figure 2 and Figure 3 It includes a storage tank 1, a filling port 2, a diffuser 3, a liquid phase zone 4, a gas-liquid interface 5, a gas pillow zone 6, a flash plume zone 7, and a gas pillow condensation zone 8.

[0039] This embodiment proposes a combined correction method for flash evaporation and evaporation-condensation for liquid hydrogen storage tank filling simulation, which includes the following steps.

[0040] Step S1: Determine the phase change calculation region for the liquid hydrogen storage tank filling simulation.

[0041] Step S1 includes the following sub-steps.

[0042] Step S11: Construct a transient two-phase flow simulation model of the liquid hydrogen storage tank filling process and obtain parameter information of each grid cell in the storage tank; Step S12: Based on the outlet location of the filling pipeline, the outlet location of the diffuser, and the gas-liquid phase volume fraction distribution, determine the candidate areas for flash evaporation at the pipe inlet, the candidate areas for the gas-liquid interface, and the candidate areas for the gas pillow.

[0043] In this technical solution, the parameter information of each grid cell in the storage tank includes the pressure, temperature, liquid volume fraction, gas volume fraction, and specific enthalpy of the mixture for each grid cell.

[0044] For a transient two-phase flow simulation model, it includes at least the tank cavity, the filling pipeline outlet, the diffuser outlet, the gas-liquid interface region, and the gas pillow region.

[0045] More specifically, for the candidate regions of flash evaporation at the nozzle, gas-liquid interface, and gas pillow, grid cells adjacent to the outlet of the filling pipeline or the outlet of the diffuser and containing liquid phase are identified as candidate regions of flash evaporation at the nozzle; grid cells where both liquid and gas phase volume fractions exist are identified as candidate regions of gas-liquid interface; and continuous gas phase grid cells above the candidate regions of gas-liquid interface are identified as candidate regions of gas pillow.

[0046] Step S2: Within the candidate region for flash evaporation at the pipe inlet, grid cells exhibiting pressure-reducing flash evaporation are identified. The source term for flash evaporation at the pipe inlet is calculated based on the equilibrium gas phase mass ratio. Step S2 includes the following sub-steps.

[0047] Step S21: In the candidate region of flash evaporation at the pipe opening, the liquid hydrogen saturation pressure of the grid cell containing the liquid phase is compared with the current pressure to determine whether the grid cell has pressure reduction flash evaporation. Step S22: If there is depressurization flash evaporation in the grid cell, determine the equilibrium gas phase mass ratio based on the grid cell parameter information; obtain the inlet flash evaporation source term based on the equilibrium gas phase mass ratio and the current gas phase mass ratio.

[0048] For step S22, more detailed, it includes the following process: determining the equilibrium gas phase mass ratio based on the saturated liquid hydrogen specific enthalpy, the saturated hydrogen specific enthalpy, and the mixture specific enthalpy of the grid cell at the current pressure; converting the portion of the equilibrium gas phase mass ratio that is higher than the current gas phase mass ratio into a mass source term for the liquid phase to gas phase conversion within the current time step, thereby obtaining the nozzle flash evaporation source term.

[0049] In this technical solution, within the candidate region for flash evaporation at the nozzle, for each grid cell containing a liquid phase, the liquid hydrogen saturation pressure is determined based on the current temperature of the grid cell, and the liquid hydrogen saturation pressure is compared with the current pressure of the grid cell; when the liquid hydrogen saturation pressure is higher than the current pressure of the grid cell, it is determined that the grid cell has pressure-reducing flash evaporation; when the liquid hydrogen saturation pressure is not higher than the current pressure of the grid cell, no nozzle flash evaporation source term is generated.

[0050] For grid cells with depressurization flash evaporation, the equilibrium gas phase mass ratio is determined based on the parameter information of the current grid cell, namely the saturated liquid hydrogen specific enthalpy, the saturated hydrogen specific enthalpy, and the mixture specific enthalpy of the grid cell at the current pressure.

[0051] Based on the enthalpy conservation relationship under vapor-liquid equilibrium conditions, after liquid hydrogen enters the low-pressure region, if the current pressure is lower than the saturation pressure corresponding to its temperature, part of the liquid phase will be converted into the gas phase. The conversion ratio can be determined by the position of the current mixture specific enthalpy between the saturated liquid hydrogen specific enthalpy and the saturated hydrogen gas specific enthalpy.

[0052] Finally, the portion of the equilibrium gas phase mass ratio that is higher than the current gas phase mass ratio is converted into a mass source term for the liquid phase to gas phase conversion within the current time step, thereby obtaining the nozzle flash evaporation source term.

[0053] Step S3: Identify the grid cells where evaporation or condensation occurs at the gas-liquid interface and within the candidate region of the gas pillow, and determine the evaporation-condensation mass source term; Step S3 includes the following processes: For grid cells in the gas-liquid interface and candidate area of ​​the gas pillow, the current temperature of the grid cell is compared with the local saturation temperature to determine whether the grid cell has undergone evaporation or condensation. If evaporation or condensation occurs in a grid cell, the evaporation / condensation mass source term is determined based on the heat change and latent heat of vaporization of liquid hydrogen within the current time step. The condensation source term located in the candidate region of the gas pillow or the gas-liquid interface region on the side of the gas pillow is the gas pillow condensation source term. The upper part of the liquid hydrogen storage tank is the hydrogen gas phase region, and the lower part is the liquid hydrogen liquid phase. The gas-liquid interface is the thin layer of grid at the boundary between the gas and liquid hydrogen. The gas-liquid interface region on the side of the gas pillow specifically refers to the gas-liquid interface grid on the side immediately adjacent to the gas phase of the gas pillow, near the top gas phase space of the tank. Low-temperature liquid hydrogen will continuously condense hydrogen gas here, which is the region where the gas pillow condensation source term is generated. The layer of interface grid near the top gas phase (gas pillow) is the layer of grid at the liquid surface.

[0054] In this technical solution, within the candidate regions of the gas-liquid interface and the candidate regions of the gas pillow, for each grid cell, the local saturation temperature is determined based on the current pressure of the grid cell, and the current temperature of the grid cell is compared with the local saturation temperature. When the current temperature of the grid cell is higher than the local saturation temperature, it is determined that the grid cell has undergone evaporation; when the current temperature of the grid cell is lower than or equal to the local saturation temperature, it is determined that the grid cell has undergone condensation.

[0055] Based on the latent heat equilibrium of phase change, in the evaporation process, liquid hydrogen absorbs latent heat and transforms from the liquid phase to the gas phase; in the condensation process, hydrogen releases latent heat and transforms from the gas phase to the liquid phase. Therefore, determining the phase change mass source term by the ratio between the heat of phase change and the latent heat of vaporization has a clear thermodynamic basis.

[0056] When the corresponding liquid phase transforms into the gas phase, it is used as an evaporation source term; when the corresponding gas phase transforms into the liquid phase, it is used as a condensation source term. Among them, the condensation source terms located in the candidate region of the gas pillow or the gas-liquid interface region on the side of the gas pillow are determined as gas pillow condensation source terms.

[0057] Step S4: Obtain the local gas phase generation and consumption, and determine the tank pressure response misalignment by combining the overall gas phase mass change of the storage tank.

[0058] Step S4 includes the following process: the inlet flash evaporation source term is integrated in the inlet flash evaporation candidate region to obtain the amount of inlet flash vapor phase generated at the current time step; the gas pillow condensation source term is integrated in the gas pillow candidate region and the gas pillow side gas-liquid interface region to obtain the amount of gas pillow condensation vapor phase consumed at the current time step. The tank pressure response misalignment is determined based on the amount of flash vapor generated at the pipe inlet, the amount of condensed vapor consumed in the gas pillow, and the overall change in the gas phase mass of the storage tank.

[0059] The steps for determining the overall gas phase mass change of the storage tank are as follows: based on the gas phase volume fraction and gas phase density of all grid cells in the storage tank, calculate the overall gas phase mass change of the storage tank between the current time step and the previous time step.

[0060] In this technical solution, within the current calculation time step, the flash evaporation source term obtained in step S2 is integrated in the flash evaporation candidate region to obtain the flash vapor generation amount at the pipe opening in the current time step; the condensation source term obtained in step S3 is integrated in the condensation candidate region and the gas-liquid interface region on the condensation side to obtain the condensation vapor consumption amount at the current time step.

[0061] Simultaneously, based on the gas phase volume fraction and gas phase density of all grid cells within the storage tank, the overall gas phase mass change of the storage tank between the current time step and the previous time step is calculated. Then, based on the amount of flash vapor generated at the nozzle, the amount of condensed vapor consumed in the gas pillow, and the overall gas phase mass change of the storage tank, the tank pressure response misalignment is determined.

[0062] Based on the principle of gas phase mass conservation, the gas phase mass generated by flash evaporation at the nozzle is not necessarily entirely reflected in the overall gas phase mass increase of the storage tank; it may be offset by condensation in the gas pillow or at the interface. Therefore, the tank pressure response misalignment can characterize the degree of misalignment between the local gas phase peak at the nozzle and the overall gas phase response of the storage tank.

[0063] Step S5: Based on the tank pressure response misalignment, perform joint correction on the pipe flash evaporation, evaporation, and air cushion condensation source items.

[0064] Step S5 includes the following process: When the amount of flash vapor generated at the pipe outlet exceeds the preset generation threshold, and the overall gas phase mass change of the storage tank does not increase synchronously, the gas pillow condensation source item or the pipe outlet flash vapor source item is corrected according to the tank pressure response misalignment. The generation threshold is preset according to the actual situation. When the overall gas phase mass change of the storage tank is greater than the net generation amount after deducting the gas pillow condensation vapor consumption from the amount of flash vapor generated at the pipe outlet, the evaporation source item is compensated according to the tank pressure response misalignment.

[0065] In this technical solution, based on the tank pressure response misalignment obtained in step S4, the flash evaporation source term obtained in step S2 and the evaporation source term and air cushion condensation source term obtained in step S3 are jointly corrected.

[0066] When the amount of flash vapor generated at the inlet is large, but the overall change in the gas phase mass of the storage tank does not increase synchronously, it indicates that the gas phase generated by local flash evaporation at the inlet is partially offset by condensation of the gas pillow or interface. At this time, the gas pillow condensation source term or the flash evaporation source term at the inlet is corrected according to the tank pressure response misalignment, so that the corrected net gas phase generation amount matches the overall gas phase change of the storage tank.

[0067] When the overall change in gas phase mass of the storage tank is greater than the net amount generated after deducting the amount of gas phase consumed by the gas pillow condensation from the amount of gas phase generated by the flash vapor at the pipe inlet, it indicates that the contribution of interface evaporation is underestimated. In this case, the evaporation source term is compensated based on the tank pressure response misalignment.

[0068] The correction amount is not allocated using preset fixed parameters, but rather according to the proportion of the original source term in each grid cell within the total source term in the corresponding region. The same proportion allocation principle is used for evaporation source terms and confined space condensation source terms, distributing the correction amount to the grid cells where evaporation or condensation actually occurs.

[0069] Step S6: Write back the corrected source terms and output the simulation results.

[0070] Step S6 includes the following process: The corrected pipe flash source term, the corrected evaporation source term, and the corrected gas pillow condensation source term are written back to the continuity equation, volume fraction equation, and energy equation of the liquid hydrogen storage tank filling simulation, respectively. Resolve the pressure field, temperature field, and gas-liquid phase volume fraction field at the current time step, and proceed to the next time step until the liquid hydrogen storage tank filling simulation is completed.

[0071] In this technical solution, for the modified flash evaporation source term at the pipe inlet, a liquid phase mass reduction term and a gas phase mass increase term are set in the candidate region of flash evaporation at the pipe inlet; for the modified evaporation source term, a liquid phase mass reduction term and a gas phase mass increase term are set in the candidate region of the gas-liquid interface; for the modified condensation source term in the gas pillow, a gas phase mass reduction term and a liquid phase mass increase term are set in the candidate region of the gas pillow and the gas-liquid interface region on the side of the gas pillow. Simultaneously, energy terms corresponding to the latent heat of vaporization or latent heat of condensation are added to the energy equation.

[0072] After completing the source term writeback, the pressure field, temperature field, and gas-liquid phase volume fraction field of the current time step are solved again, and the process proceeds to the next time step until the simulation of the liquid hydrogen storage tank filling process is completed.

[0073] The technical solutions described above in this embodiment can bring about the following technical effects.

[0074] This embodiment first distinguishes between the triggering mechanisms of pressure drop flash evaporation at the inlet and evaporation and condensation at the gas-liquid interface, so that the source terms of flash evaporation caused by sudden pressure drop and the source terms of evaporation and condensation caused by heat imbalance are calculated separately. Therefore, it can avoid simply equating flash evaporation with ordinary evaporation, and thus more accurately describe the process of rapid increase in the volume fraction of the gas phase near the inlet and the formation of a flash plume at the inlet when liquid hydrogen just enters the low-pressure storage tank.

[0075] This embodiment further calculates the tank pressure response misalignment based on the amount of flash vapor generated at the inlet, the amount of condensed vapor consumed in the gas pillow, and the overall change in the gas phase mass of the storage tank. Therefore, it can identify the asynchronous relationship between the local gas phase peak at the inlet and the overall gas phase response of the storage tank, avoiding the judgment of the overall pressure change based solely on local source terms.

[0076] This embodiment utilizes the tank pressure response misalignment to jointly correct the flash evaporation source term, evaporation source term, and gas pillow condensation source term, so that a closed-loop correspondence is formed between the local phase change source term and the overall gas phase response of the storage tank. Therefore, it can reduce the pressure prediction deviation caused by the asynchronous relationship between the local gas phase peak at the pipe inlet and the overall tank pressure response, and improve the simulation reliability of the pressure curve, temperature curve, and gas-liquid phase volume fraction distribution of the liquid hydrogen storage tank.

[0077] In this embodiment, the correction amount is allocated according to the proportion of the original source term of each grid cell to the total source term of the corresponding region, rather than using preset fixed parameters. Therefore, the accumulation of empirical parameters is reduced, and the interpretability and applicability of the method are improved.

[0078] In another alternative embodiment, the candidate region for flash evaporation at the nozzle can be determined based on the outlet radius of the filling pipeline, the outlet angle of the diffuser, and the inlet liquid volume fraction distribution, rather than being limited to the grid cells directly adjacent to the nozzle.

[0079] In another alternative embodiment, the overall gas phase mass change of the storage tank can be obtained by integrating the gas phase density and gas phase volume fraction of all gas phase grid cells in the storage tank, or by calculating the gas phase region volume change and average gas phase density.

[0080] In another alternative embodiment, the liquid hydrogen saturation pressure, local saturation temperature, saturated liquid hydrogen specific enthalpy, saturated hydrogen specific enthalpy, and latent heat of vaporization can be obtained from a liquid hydrogen property database, a lookup interpolation method, or a thermophysical property calculation program.

[0081] In another alternative embodiment, the modified phase change source term can be loaded into the Fluent solver via a user-defined function, or via a user-defined source term interface, script interface, or secondary development interface in other computational fluid dynamics solvers.

[0082] In another alternative embodiment, when jointly correcting source terms, in addition to using the original source term proportion allocation, the proportion of change in gas phase volume fraction, the proportion of phase change heat, or the proportion of local gas phase mass change in each grid cell can also be used for allocation, as long as the allocation method can reflect the phase change contribution and maintain the gas phase mass conservation relationship.

[0083] For ease of understanding, some technical terms involved in this embodiment are explained here.

[0084] Liquid hydrogen storage tank filling simulation: refers to simulating the changes in pressure, temperature, velocity, gas-liquid phase distribution, and phase change process during the process of liquid hydrogen entering the storage tank using a computer numerical model.

[0085] Fluid volume method: This refers to a two-phase flow numerical method that captures the position and morphology of the gas-liquid interface by calculating the volume fraction of different fluid phases within a grid cell.

[0086] Pipe flash evaporation: refers to the phenomenon where liquid hydrogen enters a low-pressure storage tank area through a filling pipeline or diffuser, and due to the local pressure being lower than the saturation pressure of liquid hydrogen at the current temperature, a portion of the liquid phase rapidly transforms into the gas phase.

[0087] The flash source term at the nozzle refers to the liquid phase mass reduction and gas phase mass increase caused by pressure reduction flash evaporation within the nozzle flash candidate region.

[0088] Evaporation source term: refers to the mass source term formed in the gas-liquid interface region by the absorption of latent heat by the liquid phase and its conversion into the gas phase.

[0089] Gas pillow condensation source term: refers to the mass source term formed by the release of latent heat of hydrogen and its conversion into liquid phase in the gas pillow region or the gas-liquid interface region on the side of the gas pillow.

[0090] Tank pressure response misalignment: This refers to the quantity calculated based on the overall gas phase mass change of the storage tank, the amount of flash vapor phase generated at the inlet, and the amount of condensed vapor phase consumed by the gas pillow. It can characterize the degree of asynchrony between the local gas phase peak at the inlet and the overall gas phase response of the storage tank.

[0091] Joint correction of phase change source terms refers to the process of simultaneously adjusting the flash evaporation source term, evaporation source term, and gas pillow condensation source term based on the tank pressure response misalignment, so that the local phase change contribution is consistent with the overall gas phase quality change of the storage tank.

Claims

1. A combined correction method for flash evaporation and evaporation-condensation in liquid hydrogen storage tank filling simulation. Its characteristics include the following steps: S1, determine the phase change calculation region for the liquid hydrogen storage tank filling simulation; S2, grid cells with depressurized flashing are identified within the candidate region of pipe flashing, and the pipe flashing source term is calculated based on the equilibrium gas phase mass ratio; S3, Identify the grid cells where evaporation or condensation occurs at the gas-liquid interface and within the candidate region of the gas pillow, and determine the evaporation-condensation mass source term; S4, obtain the local gas phase generation and consumption, and determine the tank pressure response misalignment by combining the overall gas phase mass change of the storage tank; integrate the pipe flash source term in the pipe flash candidate region to obtain the pipe flash gas phase generation at the current time step; integrate the gas pillow condensation source term in the gas pillow candidate region and the gas pillow side gas-liquid interface region to obtain the gas pillow condensation gas phase consumption at the current time step. The tank pressure response misalignment is determined based on the amount of flash vapor generated at the pipe inlet, the amount of condensed vapor consumed in the gas pillow, and the overall change in the vapor mass of the storage tank. S5, based on the tank pressure response misalignment, jointly correct the source terms of pipe flash evaporation, evaporation and gas pillow condensation; S6 writes back the corrected source term and outputs the simulation results.

2. The method for combined flash evaporation and evaporation-condensation correction for liquid hydrogen storage tank filling simulation according to claim 1, characterized in that, Step S1 includes: S11, Construct a transient two-phase flow simulation model of the liquid hydrogen storage tank filling process and obtain parameter information of each grid cell in the storage tank; S12. Based on the outlet location of the filling pipeline, the outlet location of the diffuser, and the volume fraction distribution of the gas and liquid phases, determine the candidate regions for flash evaporation at the pipe inlet, the candidate regions for the gas-liquid interface, and the candidate regions for the gas pillow.

3. The method for combined flash evaporation and evaporation-condensation correction for liquid hydrogen storage tank filling simulation according to claim 1 or 2, characterized in that, Step S2 includes: S21, In the candidate region of flash evaporation at the pipe opening, the grid cell containing the liquid phase is compared with the current pressure to determine whether the grid cell has pressure reduction flash evaporation. S22, if there is pressure reduction flash evaporation in the grid cell, determine the equilibrium gas phase mass ratio based on the grid cell parameter information; obtain the inlet flash evaporation source term based on the equilibrium gas phase mass ratio and the current gas phase mass ratio.

4. The method for combined flash evaporation and evaporation-condensation correction for liquid hydrogen storage tank filling simulation according to claim 3, characterized in that, Step S3 includes: For grid cells in the gas-liquid interface and candidate area of ​​the gas pillow, the current temperature of the grid cell is compared with the local saturation temperature to determine whether the grid cell has undergone evaporation or condensation. If evaporation or condensation occurs in a grid cell, the evaporation / condensation mass source term is determined based on the heat change and latent heat of vaporization of liquid hydrogen in the current time step.

5. The method for combined flash evaporation and evaporation-condensation correction for liquid hydrogen storage tank filling simulation according to claim 4, characterized in that, Step S3 also includes: Condensation source terms located in the candidate region of the air pillow or the gas-liquid interface region on the side of the air pillow are air pillow condensation source terms.

6. The method for combined flash evaporation and evaporation-condensation correction for liquid hydrogen storage tank filling simulation according to claim 1, 2, or 5, is characterized in that, Step S5 includes: When the amount of flash vapor generated at the pipe outlet exceeds the preset generation threshold and the overall gas phase quality change of the storage tank does not increase synchronously, the gas pillow condensation source item or the pipe outlet flash vapor source item is corrected according to the tank pressure response misalignment. When the overall change in gas phase mass of the storage tank is greater than the net amount generated after deducting the amount of gas phase consumed by the gas pillow condensation from the amount of gas phase generated by the flash vapor phase at the pipe inlet, the evaporation source term is compensated based on the tank pressure response misalignment.

7. The method for combined flash evaporation and evaporation-condensation correction for liquid hydrogen storage tank filling simulation according to claim 1, 2, or 5, characterized in that, Step S6 includes: The corrected pipe flash source term, the corrected evaporation source term, and the corrected gas pillow condensation source term are written back to the continuity equation, volume fraction equation, and energy equation of the liquid hydrogen storage tank filling simulation, respectively. Resolve the pressure field, temperature field, and gas-liquid phase volume fraction field at the current time step, and proceed to the next time step until the liquid hydrogen storage tank filling simulation is completed.

8. The method for combined flash evaporation and evaporation-condensation correction for liquid hydrogen storage tank filling simulation according to claim 1, characterized in that, The steps for determining the overall gas phase mass change of the storage tank are as follows: Based on the gas phase volume fraction and gas phase density of all grid cells in the storage tank, the overall gas phase mass change of the storage tank between the current time step and the previous time step is calculated.

9. The method for combined flash evaporation and evaporation-condensation correction for liquid hydrogen storage tank filling simulation according to claim 3, characterized in that, Step S22 includes: determining the equilibrium gas phase mass ratio based on the saturated liquid hydrogen specific enthalpy, the saturated hydrogen specific enthalpy, and the mixture specific enthalpy of the grid cell at the current pressure; converting the portion of the equilibrium gas phase mass ratio that is higher than the current gas phase mass ratio into a mass source term for the liquid-to-gas phase conversion within the current time step, thereby obtaining the nozzle flash evaporation source term.

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