Solid state regenerative bed design method for nitrogen phase transition process and related device

Abstract

The application belongs to the technical field of cryogenic cold storage, and discloses a solid-state cold storage packed bed design method for nitrogen phase transition process and related devices. First, the initial size of the packed bed is determined through working condition parameters and filler characteristics, and a geometric and numerical simulation model is established. Then, the phase change processes such as liquid nitrogen evaporation and cold storage, nitrogen condensation and cold release are dynamically simulated. The packed bed structure is optimized according to the comparison result of the phase change stable time obtained by simulation and the design requirement. The method breaks through the limitation of the traditional sensible heat storage mode by accurately simulating the latent heat transfer process of the phase state transition of the working medium. At the same time, the high density characteristics of the liquid nitrogen phase change are used to overcome the heat transfer defects of the gas working medium. The method can significantly improve the cold storage density and heat exchange rate, effectively suppress the formation of the thermocline, and avoid the safety risk of liquid medium, thereby providing a solid-state cold storage solution with high cold storage efficiency and engineering feasibility for the liquid air energy storage system.

Description

Technical Field

[0001] This invention belongs to the field of cryogenic cold storage technology, and particularly relates to a solid-state cold storage packed bed design method and related apparatus for nitrogen phase transition process. Background Technology

[0002] Large-scale energy storage technology is a key support for energy system transformation. Currently, mainstream technologies include pumped hydro storage, battery energy storage, compressed air energy storage, and liquid air energy storage. Among them, liquid air energy storage has become one of the most promising large-scale energy storage technologies due to its advantages such as no geographical limitations, high flexibility, and strong scalability. The cold storage process, as a key link, has a significant impact on the system's round-trip efficiency. Solid-state cold storage technology is widely used in liquid air energy storage systems due to its low cost, safety, and technological maturity.

[0003] Existing cryogenic packed bed cold storage systems for liquid air energy storage have significant shortcomings. Their heat exchange fluids are mostly gases, resulting in low storage density, slow heat transfer rates, and the formation of wide thermoclines, leading to low cold storage efficiency. Although researchers in this field have proposed improvement schemes such as graded management of cold capacity and the use of liquid-phase heat transfer fluids, these have not yet overcome the limitations of existing technologies. Furthermore, current research and patents on solid-state cold storage packed beds are all based on sensible heat storage mechanisms, failing to utilize the large amount of latent heat released or absorbed during the phase transition of the heat exchange fluid. Moreover, there is a lack of modeling, numerical simulation, and engineering design methods for the phase change process of the heat transfer medium inside the packed bed, and related technical solutions still need improvement. In addition, all existing cold storage technologies have shortcomings; liquid-phase cold storage media pose safety hazards, and phase change material cold storage is still in the research and development stage, making it difficult to meet the high-efficiency cold storage requirements of liquid air energy storage systems.

[0004] In summary, existing solid-state cold storage beds in liquid air energy storage lack mature system engineering modeling and design methods for the phase change process of the heat transfer medium, and therefore cannot meet the high-efficiency cold storage requirements of liquid air energy storage systems. Summary of the Invention

[0005] This invention provides a solid-state cold storage packed bed design method and related apparatus for nitrogen phase transition process. This method can supplement the mature system engineering modeling and design methods for heat transfer working fluid phase change process, and effectively meet the high-efficiency cold storage requirements of liquid air energy storage system.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A solid-state cold storage packed bed design method for a nitrogen phase transition process includes: Based on the pre-set design parameters and the pre-screened types of packing materials, the volume of the solid-state cold storage packed bed is determined in order to obtain the packed bed diameter and height. A geometric model and a numerical simulation model of the filling bed are constructed based on the filling bed diameter and filling bed height. Based on numerical simulation models and packed bed geometric models, the processes of low-temperature liquid nitrogen evaporation and cold storage, gas filling and pressurization, room temperature and high pressure nitrogen condensation and cold release, and exhaust and depressurization in the packed bed are simulated to obtain the simulation time of liquid nitrogen evaporation process and nitrogen condensation process corresponding to the steady state. Based on the larger of the simulation time for the liquid nitrogen evaporation process and the simulation time for the nitrogen condensation process under steady-state conditions, and the preset design time, the structure of the packed bed is adjusted to obtain the height of the solid-state cold storage packed bed under the design operating parameters, so as to complete the design of the solid-state cold storage packed bed.

[0007] Furthermore, before determining the volume of the solid-state cold storage packed bed based on preset design operating parameters and pre-screened packed bed filler types, the process also includes: The specific steps for screening the types of packed bed packing materials are as follows: By comprehensively evaluating the density, specific heat, thermal conductivity, volumetric heat capacity, and economic efficiency of packed bed packings, the types of packed bed packings were selected.

[0008] Furthermore, determining the volume of the solid-state cold storage packed bed based on preset design operating parameters and pre-screened packed bed filler types to obtain the packed bed diameter and height includes: Obtain the preset design operating condition parameters, which include the target duration of the liquid nitrogen evaporation and cold storage process and the target duration of the high-pressure nitrogen condensation and cold release process; Based on the preset design parameters and the type of packing material, the volume of the solid-state cold storage packed bed is calculated using the following formula: When the target duration of the liquid nitrogen evaporation and cold storage process is greater than the target duration of the high-pressure nitrogen condensation and cold release process, the formula for calculating the volume of the solid-state cold storage packed bed is as follows: The heat transfer of the fluid during the cold storage process is:

[0009] The theoretical heat exchange capacity of solid packing is:

[0010]

[0011]

[0012] In the formula, For the heat exchange of fluids during the liquid nitrogen evaporation process; The fluid mass flow rate at the inlet of the packed bed during the liquid nitrogen evaporation process; The target duration for the liquid nitrogen evaporation and cold storage process; The volume of the solid-state cold storage packed bed; Porosity of the packed bed; The density of liquid nitrogen at the inlet of the packed bed; The percentage of liquid nitrogen in the packed bed at the end of the evaporation process, ranging from 0 to 1. The enthalpy of the fluid at the inlet of the packed bed during the nitrogen condensation process; The enthalpy of the fluid at the inlet of the packed bed in the liquid nitrogen evaporation and cold storage process; For the heat exchange of solid packing material in the liquid nitrogen evaporation process; This is the ratio of fluid heat transfer to the theoretical heat transfer of the packing material; The density of the solid filler; Specific heat capacity of solid filler; This refers to the inlet temperature of the packed bed during the nitrogen condensation process. The inlet temperature of the packed bed in the liquid nitrogen evaporation and cold storage process; When the target duration of the liquid nitrogen evaporation and cold storage process is less than the target duration of the high-pressure nitrogen condensation and cold release process, the formula for calculating the volume of the solid-state cold storage packed bed is as follows: The heat transfer rate of the fluid during the nitrogen condensation and cooling process is:

[0013] The theoretical heat exchange capacity of solid packing is:

[0014]

[0015]

[0016] In the formula, The heat exchange of the fluid during the nitrogen condensation process; This refers to the fluid mass flow rate at the outlet of the packed bed during the nitrogen condensation process. The target duration for the high-pressure nitrogen condensation and release process; The percentage of liquid nitrogen in the packed bed after the nitrogen condensation process is complete, ranging from 0 to 1. For the heat exchange of solid packing material in the nitrogen condensation process; According to the preset filling bed diameter D The height of the filling bed was calculated. L :

[0017] In the formula, Pi is the mathematical constant of a circle.

[0018] Furthermore, the construction of the geometric model and numerical simulation model of the packed bed based on the packed bed diameter and packed bed height includes: Construct a geometric model of the filling bed based on its diameter and height. A numerical simulation model was constructed using the Fluent platform; wherein the numerical simulation model includes a porous medium model and a two-phase flow model; The density and thermal conductivity of the solid packing were set to 0; during the numerical simulation model solution process, a scalar variable was added to represent the temperature of the solid packing. Establish the solid energy equation for scalar variables:

[0019] In the formula, Represents the gradient operator; Indicates the thermal conductivity of solid fillers; Indicates the temperature of the solid packing material; Indicates the temperature of the heat transfer fluid; This represents the volumetric convection heat transfer coefficient.

[0020] Furthermore, based on the numerical simulation model and the packed bed geometric model, the processes of cryogenic liquid nitrogen evaporation and cold storage, gas charging and pressurization, room temperature high-pressure nitrogen condensation and cold release, and exhaust and depressurization within the packed bed are simulated to obtain the simulation duration of the liquid nitrogen evaporation process and the simulation duration of the nitrogen condensation process corresponding to the steady state, including: A numerical simulation model was used to simulate the processes of cryogenic liquid nitrogen evaporation and cold storage, gas charging and pressurization, nitrogen condensation and release at room temperature and high pressure, and exhaust and depressurization within a packed bed geometric model. During the gas charging and pressurization and exhaust and depressurization processes, nitrogen properties were obtained based on a pre-built user-defined real gas model to determine nitrogen properties according to the current temperature and pressure. The specific steps are as follows: The nitrogen property relationships are written into the user-defined function to define the material; the nitrogen density is described using the ideal gas law; the nitrogen specific heat capacity is described using a pressure-segmented and intra-segment temperature polynomial approach, dividing the pressure range into multiple intervals, and expressing the nitrogen specific heat capacity as a polynomial function dependent only on temperature within each pressure interval; the enthalpy of nitrogen is defined as follows:

[0021] In the formula, This refers to the enthalpy of nitrogen. For temperature, This is a reference temperature; the reference temperature is set as the saturation temperature of nitrogen at different pressures. The enthalpy of nitrogen at the reference temperature; This represents the specific heat of nitrogen at the corresponding pressure and temperature. After simulation, the simulation time for the liquid nitrogen evaporation process and the nitrogen condensation process corresponding to the steady state are obtained.

[0022] Furthermore, before adjusting the packed bed structure based on the greater of the simulation time for the liquid nitrogen evaporation process and the simulation time for the nitrogen condensation process under steady-state conditions, and the preset design time, to obtain the height of the solid-state cold storage packed bed under the design operating parameters, the following steps are also included: Compare the simulation durations of liquid nitrogen evaporation and nitrogen condensation, and obtain the larger of the two simulation durations. Output the larger of the two simulation durations as the simulation duration.

[0023] Furthermore, the height of the solid-state cold storage packed bed is adjusted based on the greater of the simulation time for the liquid nitrogen evaporation process and the simulation time for the nitrogen condensation process under steady-state conditions, and the preset design time, including: The simulation duration is compared with the preset design duration for judgment: If the difference between the two is within the preset ratio range, it is determined that the structural parameters of the packed bed meet the design requirements, and the current height of the packed bed is output as the height of the solid-state cold storage packed bed under the design working conditions. If the difference between the two exceeds the preset ratio range, the filling bed height will be adjusted to the original filling bed height × ratio coefficient; where the ratio coefficient = design duration ÷ simulation duration. Repeat the simulation process until the design duration requirement is met, and output the adjusted packed bed height as the height of the solid-state cold storage packed bed under the design operating conditions.

[0024] A solid-state cold storage packed bed design system for a nitrogen phase transition process includes: The data acquisition module is used to determine the volume of the solid-state cold storage packed bed based on the preset design operating parameters and the pre-screened packed bed filler types, so as to obtain the packed bed diameter and packed bed height. The model building module is used to construct geometric and numerical simulation models of the filling bed based on the filling bed diameter and filling bed height. The simulation module is used to simulate the processes of cryogenic liquid nitrogen evaporation and cold storage, gas charging and pressurization, room temperature and high pressure nitrogen condensation and cold release, and exhaust and depressurization in a packed bed based on numerical simulation models and packed bed geometric models, and to obtain the simulation time of liquid nitrogen evaporation process and nitrogen condensation process corresponding to the steady state. The structure adjustment module is used to adjust the structure of the packed bed based on the greater of the simulation time of the liquid nitrogen evaporation process and the simulation time of the nitrogen condensation process under the steady state and the preset design time, so as to obtain the height of the solid cold storage packed bed under the design working conditions and complete the design of the solid cold storage packed bed.

[0025] A solid-state cold storage packed bed design device for a nitrogen phase transition process includes: Memory, used to store computer programs; A processor is used to execute the computer program to implement the steps of the solid-state cold storage packed bed design method for the nitrogen phase transition process described above.

[0026] A computer-readable storage medium storing a computer program, which, when executed by a processor, is used to implement the steps of the solid-state cold storage packed bed design method for the above-described nitrogen phase transition process.

[0027] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a solid-state cold storage packed bed design method for nitrogen phase transition processes. First, the initial dimensions of the packed bed are determined by operating parameters and packing characteristics, and a geometric and numerical simulation model is established. Then, dynamic simulations are performed on phase transition processes such as liquid nitrogen evaporation and nitrogen condensation. The packed bed structure is optimized based on the comparison between the simulated phase transition stabilization time and design requirements. This method overcomes the limitations of traditional sensible heat cold storage models by accurately simulating the latent heat transfer process of the working fluid phase transition, while utilizing the high-density characteristics of liquid nitrogen phase transitions to overcome the heat transfer defects of gaseous working fluids. This method can significantly improve cold storage density and heat exchange rate, effectively suppress thermocline formation, and avoid the safety risks of liquid media, providing a solid-state cold storage solution for liquid air energy storage systems that combines high cold storage efficiency with engineering feasibility. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the implementation of a solid-state cold storage packed bed design method for a nitrogen phase transition process, as provided in an embodiment of the present invention. Figure 2 This is a core flowchart of a solid-state cold storage packed bed design method for a nitrogen phase transition process provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of a solid-state cold storage packed bed design system for a nitrogen phase transition process provided in an embodiment of the present invention. Detailed Implementation

[0029] To further understand the content of this invention, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0030] As mentioned in the background section, liquid nitrogen, as one of the most commonly used working fluids in cryogenic environments, possesses characteristics such as stable physical properties and wide availability. Using liquid nitrogen as the heat exchange fluid to study the processes of liquid nitrogen evaporation and high-pressure nitrogen condensation and release under cryogenic conditions within a packed bed has broad application value for cryogenic cold storage scenarios such as liquid air energy storage systems, air separation energy storage, and cryogenic cooling systems. However, current research on solid-state cold storage packed beds in liquid air energy storage is still based on sensible heat storage mechanisms, meaning that the heat exchange fluid within the packing only undergoes temperature changes without phase transitions. In contrast, if the heat exchange fluid evaporates or condenses within the packed bed, it can absorb or release a large amount of latent heat during phase transitions, thereby significantly increasing the cold storage density, greatly enhancing the heat transfer coefficient between the fluid and the solid packing, and forming a relatively stable temperature plateau within the packed bed. Currently, there is a lack of modeling, numerical simulation, and engineering design methods for the phase change process of the heat transfer working fluid within a packed bed. Mature and systematic engineering modeling and design methods are still lacking, and related technical solutions require further improvement.

[0031] To address the aforementioned issues, this embodiment provides a solid-state cold storage packed bed design method for the nitrogen phase transition process. This method fully utilizes the latent heat of phase change for high-density cold energy storage and efficient release, breaking through the dependence of traditional solid-state cold storage packed beds on single-phase flow and constant pressure conditions, and providing a new cold storage path for cryogenic energy storage systems.

[0032] like Figure 2 As shown, this embodiment provides a solid-state cold storage packed bed design method for a nitrogen phase transition process, including: Based on the pre-set design parameters and the pre-screened types of packing materials, the volume of the solid-state cold storage packed bed is determined in order to obtain the packed bed diameter and height. A geometric model and a numerical simulation model of the filling bed are constructed based on the filling bed diameter and filling bed height. Based on numerical simulation models and packed bed geometric models, the processes of low-temperature liquid nitrogen evaporation and cold storage, gas filling and pressurization, room temperature and high pressure nitrogen condensation and cold release, and exhaust and depressurization in the packed bed are simulated to obtain the simulation time of liquid nitrogen evaporation process and nitrogen condensation process corresponding to the steady state. Based on the larger of the simulation time for the liquid nitrogen evaporation process and the simulation time for the nitrogen condensation process under steady-state conditions, and the preset design time, the structure of the packed bed is adjusted to obtain the height of the solid-state cold storage packed bed under the design operating parameters, so as to complete the design of the solid-state cold storage packed bed.

[0033] The prediction method provided in this embodiment will be further explained below with reference to the accompanying drawings: Step 1: Screening the types of packing materials suitable for cryogenic conditions: Investigate and evaluate parameters such as density, specific heat, thermal conductivity, volumetric heat capacity and economy of solid particles in the liquid nitrogen temperature range (100K-300K) to finally determine the types of solid packing materials suitable for cryogenic cold storage packed beds.

[0034] Step 2: Determine the packed bed volume based on operating parameters and packing type: Given the target duration of the liquid nitrogen evaporation and cold storage process. Target duration of high-pressure nitrogen condensation and release process ;Pick and The larger value in the equation is T, which is used for subsequent adjustments to the packed bed size; it is assumed that the ratio of fluid heat transfer to the theoretical heat transfer of the packing is [value missing]. ; when The volume of the packed bed is calculated as follows: The heat transfer rate of the fluid during the cold storage process is approximately:

[0035] The theoretical heat transfer of solid packing is approximately:

[0036]

[0037]

[0038] For the heat exchange of fluids during the liquid nitrogen evaporation process; The fluid mass flow rate at the inlet of the packed bed during the liquid nitrogen evaporation process; The target duration for the liquid nitrogen evaporation and cold storage process; The volume of the solid-state cold storage packed bed; Porosity of the packed bed; The density of liquid nitrogen at the inlet of the packed bed; The percentage of liquid nitrogen in the packed bed at the end of the evaporation process, ranging from 0 to 1. The enthalpy of the fluid at the inlet of the packed bed during the nitrogen condensation process; The enthalpy of the fluid at the inlet of the packed bed in the liquid nitrogen evaporation and cold storage process; For the heat exchange of solid packing material in the liquid nitrogen evaporation process; This is the ratio of fluid heat transfer to the theoretical heat transfer of the packing material; The density of the solid filler; Specific heat capacity of solid filler; This refers to the inlet temperature of the packed bed during the nitrogen condensation process. The inlet temperature of the packed bed in the liquid nitrogen evaporation and cold storage process; when The volume of the packed bed is calculated as follows: The heat transfer rate of the fluid during the nitrogen condensation and release process is approximately:

[0039] The theoretical heat transfer of solid packing is approximately:

[0040]

[0041]

[0042] In the formula, The heat exchange of the fluid during the nitrogen condensation process; This refers to the fluid mass flow rate at the outlet of the packed bed during the nitrogen condensation process. The target duration for the high-pressure nitrogen condensation and release process; The percentage of liquid nitrogen in the packed bed after the nitrogen condensation process is complete, ranging from 0 to 1. For the heat exchange of solid packing material in the nitrogen condensation process; Based on a given packed bed diameter D The height of the filling bed was calculated. L : .

[0043] Step 3: Establish the geometric model and numerical simulation model of the filling bed: based on the height of the filling bed L and the diameter of the packed bed D Establish a packed bed geometric model; enable the porous medium model and two-phase flow model in the simulation software, and use the User-Defined Scalar (UDS) function to achieve a joint solution of the two-phase flow-porous medium non-thermal equilibrium, wherein: Since simulation software cannot directly simulate the non-thermal equilibrium flow heat transfer process of phase change porous media, the solution in this embodiment is to use a combination of "software-built-in fluid energy equations + custom solid energy equations" and secondary development based on the Fluent platform to achieve the joint solution of two-phase flow-porous medium non-thermal equilibrium. The implementation steps are as follows: Calculate fluid temperature: In the property settings, set the density and thermal conductivity of the packing to 0 so that the built-in energy equation of the Fluent platform software no longer includes the heat capacity term of the solid packing and the heat conduction term inside the solid, ensuring that the built-in energy equation is only used to solve the temperature change of the fluid in the pores. Solving for solid temperature: Using UDS, add a new scalar variable. Indicates the solid temperature of the filler, and for Establish the solid energy equation; The solid energy equation is:

[0044] In the formula, Represents the gradient operator; Indicates the thermal conductivity of solid fillers; Indicates the temperature of the solid packing material; Indicates the temperature of the heat transfer fluid; This represents the volumetric convection heat transfer coefficient.

[0045] In the equation, This is the unsteady-state term in the solid energy equation. This refers to the diffusion term in the solid-state energy equation. The source term in the solid energy equation represents the fluid-solid heat transfer. Functions were written to express the unsteady-state term, diffusion term, and source term in the solid energy equation. The unsteady-state term describes the temperature change of the solid packing over time, the diffusion term describes the heat conduction inside and between the packings, and the source term is the convective heat transfer between the fluid and the solid. These were loaded into the UDS equation in Fluent, and the fluid temperature and solid temperature were solved respectively. A heat and mass transfer model for porous media considering non-thermal equilibrium was established, and the accurate simulation of the phase change process in porous media was achieved.

[0046] Step 4: Based on the numerical simulation model, the processes of cryogenic liquid nitrogen evaporation and cold storage, gas charging and pressurization, room temperature and high pressure nitrogen condensation and cold release, and exhaust and depressurization in the packed bed are simulated. During the gas charging and pressurization process and the exhaust and depressurization process, the nitrogen properties are simulated using a User Defined Real Gas Model (UDRGM) to obtain property data that varies with both pressure and temperature, thereby improving calculation accuracy. The above processes are iteratively calculated until a steady state is reached. The larger of the simulation durations for the liquid nitrogen evaporation process and the nitrogen condensation process is obtained, and this larger value is taken as the simulation duration t. During the pressurization and depressurization processes within a packed bed, the pressure of nitrogen gas fluctuates significantly, causing substantial changes in its physical properties such as density, specific heat capacity, and enthalpy with increasing pressure and temperature. Therefore, this embodiment proposes a method for defining gas phase properties during the pressurization and depressurization processes. The core approach is to allow simulation software to obtain nitrogen gas properties based on the current temperature and pressure, thereby ensuring simulation accuracy. The specific implementation process is as follows: By using a user-defined real gas model, materials are defined by writing gas property relationships into user-defined functions (UDFs). Nitrogen density is described using the ideal gas law, making the density change with pressure and temperature. Nitrogen specific heat capacity is expressed in the form of pressure segmentation and temperature polynomial within the segment. The pressure range is divided into multiple intervals, and the nitrogen specific heat capacity is expressed as a polynomial function that is only related to temperature within each pressure interval, thus balancing the accuracy of property settings and the stability of numerical calculations. The enthalpy of a gas is defined as follows:

[0047] in, This refers to the enthalpy of a gas. For temperature, The reference temperature is set as the saturation temperature of nitrogen at different pressures. This refers to the enthalpy of nitrogen at a reference temperature, i.e., the saturated gas phase enthalpy of nitrogen at different pressures. Let represent the specific heat of nitrogen at the corresponding pressure and temperature. The above formula can accurately calculate the enthalpy of nitrogen at different temperatures and pressures, and obtain the saturation enthalpy of nitrogen at different pressures, thereby accurately calculating the latent heat of phase change at different pressures during the pressure increase and decrease process, improving simulation accuracy. Liquid nitrogen properties are not sensitive to pressure; during the pressure increase and decrease process, the main phase of the multiphase flow is set to the properties of liquid nitrogen under high pressure, and the secondary phase is real-gas-fluid.

[0048] Through the above settings, this embodiment achieves continuous, stable, and accurate updates of gas phase properties during pressurization / depressurization, enabling more accurate acquisition of enthalpy and latent heat of phase change under different pressures, thereby improving the accuracy and repeatability of numerical simulation of pressurization / depressurization processes and the design of packed bed structures.

[0049] Step 5: Compare the simulation duration t and the design duration T to adjust the packed bed structure: If the difference between the simulation duration and the design duration is within m% (m is a preset ratio range), the structural parameters of the packed bed are considered to meet the design requirements; if the deviation exceeds m%, the height of the packed bed is adjusted to the original T / t, and the simulation steps are repeated until the design duration requirement is met, and the height L of the packed bed under the design working conditions is obtained.

[0050] It should be noted that the reason for using different pressures for the evaporation and condensation processes in this embodiment is that if both are at the same pressure, the evaporation and condensation temperatures will be the same. After evaporation, the unavoidable heat leakage will cause the temperature of the packing material inside the packed bed to rise, making condensation of the heat transfer fluid difficult and hindering the effective completion of the cold storage-release cycle. Therefore, a pressure-partitioning operation mode of low-pressure evaporation and high-pressure condensation is used to drive the phase change.

[0051] The working process of the solid-state cold storage packed bed in this embodiment is as follows: the pressure inside the packed bed is at... During this process, supercooled or saturated liquid nitrogen enters the packing area from the bottom of the packed bed, contacting the high-temperature solid packing and releasing cooling energy, causing the temperature to gradually rise. When the temperature reaches the saturation temperature, an evaporative phase change occurs, absorbing a large amount of latent heat, and the solid temperature rapidly decreases until it drops to the phase change temperature. At this point, the liquid nitrogen stops evaporating, the liquid level gradually rises, and the nitrogen gas produced by evaporation is discharged from the top of the packed bed. After the cooling process is complete, most of the inside of the packed bed is immersed in liquid nitrogen. To increase the pressure of the packed bed, nitrogen gas needs to be introduced from the top for pressurization. The bottom inlet of the packed bed is sealed, and nitrogen gas is introduced from the top until the pressure inside the packed bed reaches the condensation pressure. During the pressurization process, as the phase transition temperature increases, a small amount of nitrogen condenses into liquid nitrogen. Subsequently, room-temperature, high-pressure nitrogen is introduced from the top of the packed bed, contacting the low-temperature packing. Due to the fluid-solid temperature difference, the nitrogen absorbs the cooling energy from the packing, causing the temperature to gradually decrease, while the solid temperature gradually increases. When the nitrogen temperature drops to the high-pressure saturation temperature, the gas phase absorbs a large amount of cooling energy and condenses. The original liquid nitrogen and the condensed liquid nitrogen in the packed bed are discharged from the bottom. To proceed with the next cycle of low-pressure evaporation, the packed bed needs to be depressurized by sealing the bottom outlet and discharging the gas from the top, reducing the internal pressure of the packed bed to a lower level. This completes the heat storage and release process involving phase change of the heat transfer fluid inside the solid packed bed.

[0052] Therefore, this embodiment provides a solid-state cold storage packed bed design method for nitrogen phase transition processes, which has the following advantages: This embodiment constructs a solid-state energy equation using UDS functionality, achieving non-thermal equilibrium coupling between two-phase flow and porous media. This allows for independent solution of solid and fluid temperatures, significantly improving the accuracy of the cold storage model involving phase change of the heat transfer fluid within the packed bed. Combined with UDRGM, the specific heat capacity under different pressure segments is set to improve the prediction accuracy of nitrogen properties changing with temperature and pressure. This embodiment introduces a pressure-switching phase change cold storage mechanism into the solid-state packed bed cold storage system. By controlling the evaporation and condensation processes of the heat transfer fluid under different pressures, the cold energy storage in the packed bed is no longer limited to sensible heat. This invention fully utilizes the latent heat of phase change for high-density cold energy storage and efficient release, breaking through the dependence of traditional solid-state cold storage beds on single-phase flow and constant pressure conditions, and providing a new cold storage path for cryogenic energy storage systems. The solid-state cold storage bed with internal heat transfer fluid phase change designed in this embodiment can be used as a cold storage unit in liquid air energy storage systems, as well as for the storage and recovery of gas products in the air separation industry, and can also be used in other applications involving phase change of heat transfer fluid in porous media. This embodiment can not only select liquid nitrogen as the heat transfer fluid, but also other cryogenic fluids such as oxygen and air.

[0053] For example, taking the solid-state cold storage packed bed design process of liquid nitrogen evaporation / nitrogen condensation as an example, the solid-state cold storage packed bed design method for the nitrogen phase transition process provided in this embodiment is specifically described as follows: Basalt was selected as the filling material for the packed bed, with a density of 2702.3 kg·m³. -3 The particles have a diameter of 11.6 mm and a porosity of 0.45. The operating temperature range is 102.14 K–303 K, and the average specific heat of the basalt within this temperature range is 760.8 J·kg⁻¹. -1 ·K -1 .

[0054] The target duration for the liquid nitrogen evaporation process is set at 9.5 hours, and the design target duration for the condensation process is also set at 9.5 hours. Based on the operating parameters and the design target duration, the packed bed structural parameters are determined. The required operating parameters are shown in Table 1. Table 1 shows the relevant operating parameters of the packed bed.

[0055] Assuming the ratio of fluid cold storage capacity to the theoretical cold storage capacity of the packing is n, the calculation method is as follows: The heat transfer rate of the fluid during the cold storage process is approximately:

[0056] The theoretical heat transfer of solid packing is approximately:

[0057]

[0058]

[0059] In the formula, For the heat exchange of fluids during the liquid nitrogen evaporation process; The fluid mass flow rate at the inlet of the packed bed during the liquid nitrogen evaporation process; The target duration for the liquid nitrogen evaporation and cold storage process; The volume of the solid-state cold storage packed bed; Porosity of the packed bed; The density of liquid nitrogen at the inlet of the packed bed; The percentage of liquid nitrogen in the packed bed at the end of the evaporation process, ranging from 0 to 1. The enthalpy of the fluid at the inlet of the packed bed during the nitrogen condensation process; The enthalpy of the fluid at the inlet of the packed bed in the liquid nitrogen evaporation and cold storage process; For the heat exchange of solid packing material in the liquid nitrogen evaporation process; This is the ratio of fluid heat transfer to the theoretical heat transfer of the packing material, taken as 0.5; The density of the solid filler; The specific heat capacity of the solid packing is taken as the average value within the working temperature range of the packing, and the qualitative temperature is used. This refers to the inlet temperature of the packed bed during the nitrogen condensation process. The inlet temperature of the packed bed in the liquid nitrogen evaporation and cold storage process is given; the calculated packed bed volume is 2.385 m³. 3 Based on the volume of the packed bed and its diameter of 0.6m, the height of the packed bed is calculated to be 8.435m.

[0060] Establish the geometric and numerical simulation models of the packed bed: A geometric model of the packed bed was established based on a height of 8.435 m and a diameter of 0.6 m. To simplify calculations, the inlet and outlet regions of the packed bed were not considered; the internal micropore structure of the packed bed was not considered, and the following assumptions were made: fluid flow was treated as one-dimensional plug flow; the porosity within the packed bed was uniform; the working fluid flowed laminarly within the packed bed; thermal radiation within the packed bed was not considered; the internal temperature gradient of the solid particles was not considered; the insulation effect was good, and the wall was considered adiabatic; the porous medium model and two-phase flow model were opened in the simulation software, and the governing equations of the model are as follows: Continuity equation:

[0061]

[0062] In the formula, This indicates the mass of phase transfer during the evaporation and condensation process. Represents either liquid or gas phase. This represents the phase volume fraction. The evaporation-condensation process can be realized using the evaporation-condensation model, also known as the Lee model. This model simplifies this process to a phase transition dominated by temperature difference under quasi-thermal equilibrium conditions. The governing equations for the evaporation and condensation processes are as follows: when At that time, the evaporation process takes place:

[0063] when At that time, the condensation process takes place:

[0064] The key to using the Lee model lies in the value of the mass transfer intensity factor. To use this model, it is necessary to ensure that the coefficient value is not too large and that the calculation converges. The coefficient needs to be adjusted based on experimental results.

[0065] Momentum equation:

[0066] In the formula, The pressure of the working fluid; The dynamic viscosity of the working fluid.

[0067] The pressure drop of the fluid entering the packed bed can be expressed by the Ergun equation:

[0068] In the formula, is the height of the filling bed; Where the filler diameter is. Permeability. Viscous resistance is Inertial drag is Based on the packed bed particle diameter of 11.6 mm and porosity of 0.45, the viscous resistance is calculated to be 3700523 and the inertial resistance is 1821. Heat transfer fluid energy equation:

[0069] Solid packing energy equation:

[0070] Volumetric convective heat transfer coefficient :

[0071] In the formula , , The value represents the thermal conductivity, with subscripts f and s representing the heat transfer fluid and solid packing, respectively, and subscript eff representing the effective value.

[0072] In simulation software, porous media models cannot directly simulate the non-thermal equilibrium flow heat transfer process of phase change porous media. Therefore, a combined solution of the two-phase flow-porous media non-thermal equilibrium is achieved using a combination of the software's built-in fluid energy equation and a user-defined solid energy equation. The steps are as follows: In the property settings, the density and thermal conductivity of the packing are set to 0, so that the software's built-in energy equation no longer includes the heat capacity term of the solid packing and the internal thermal conductivity term of the solid, ensuring that the built-in energy equation is only used to solve the temperature change of the fluid within the pores; a new scalar variable is added using the User-Defined Scalar (UDS) function. Indicates the solid temperature of the filler, and for Establish the solid energy equation; In the equation This is the unsteady-state term in the solid energy equation. This refers to the diffusion term in the solid-state energy equation. The source term in the solid energy equation is used to couple the solid energy equation written in UDS with the fluid energy equation in the simulation software through the convection heat transfer term. The transient term, diffusion term, and source term in the solid energy equation are written using different macro commands, as shown in Table 2.

[0073] Table 2 lists the macro commands corresponding to different items.

[0074] Numerical simulations were performed on the processes of low-temperature, low-pressure liquid nitrogen evaporation and cold storage, gas filling and pressurization, room-temperature, high-pressure nitrogen condensation, and exhaust and depressurization inside the packed bed. The physical property settings are as follows: The density, specific heat capacity, thermal conductivity, and viscosity of oxygen and liquid oxygen were fitted to the NIST data using polynomials. The relevant fitting formulas are as follows:

[0075] in, For fluid temperature; , , , fluids Density, specific heat capacity, thermal conductivity, and viscosity; For constant terms, This represents the coefficient of the i-th term. During evaporation or condensation, the physical properties of liquid nitrogen or nitrogen gas are set as polynomials with respect to temperature at the corresponding pressures. During pressurization or depressurization, the gas phase physical properties use UDRGM, and the fluid property relationships are written into the UDF to define the material. The gas density adopts an ideal gas model.

[0076] The specific heat capacity of nitrogen is determined by dividing the pressure range into multiple segments, with the specific heat capacity within each 0.1 MPa interval being a polynomial of temperature.

[0077] The enthalpy of a gas is defined as follows:

[0078] in, The reference temperature is set as the saturation temperature of nitrogen under different pressures. The relationship between the saturation temperature and pressure is fitted as a polynomial:

[0079] In the formula The unit is Pa.

[0080] The values ​​represent the saturated vapor phase enthalpy of nitrogen under different pressures. Let represent the specific heat of nitrogen at the corresponding pressure and temperature. The above formula can accurately calculate the enthalpy of nitrogen at different temperatures and pressures, and obtain the saturation enthalpy of nitrogen at different pressures, thereby accurately calculating the latent heat of phase change at different pressures during the pressure increase and decrease process, improving simulation accuracy. Liquid nitrogen properties are not sensitive to pressure; during the pressure increase and decrease process, the main phase of the multiphase flow is set to the properties of liquid nitrogen under high pressure, and the secondary phase is real-gas-fluid.

[0081] A two-dimensional axisymmetric, transient, non-thermal equilibrium flow and heat transfer model was established. The UDS was compiled, and the solid-state energy equation was established. For the evaporation process, a VOF multiphase flow model was used, and the Lee model was adopted for evaporation and condensation, with an evaporation coefficient of 1 and a condensation coefficient of 100. The phase change temperature was set to 102.14 K (nitrogen saturation temperature) at 0.9 MPa. The primary phase was liquid nitrogen at 0.9 MPa, and the secondary phase was nitrogen gas at 0.9 MPa. The reference temperature was the phase change temperature, and the reference enthalpies were the corresponding saturated liquid and gas phase enthalpies. Density and thermal conductivity were set to 0 in the solid properties. A porous media model was established, and viscous drag coefficients and inertial drag coefficients were set. Liquid nitrogen was introduced at the inlet under mass flow conditions at a temperature of 102.14 K, and the outlet was a pressure outlet at a pressure of 0.9 MPa. The walls were adiabatic, and initially, the temperature of the packing material and nitrogen gas inside the packed bed was the same (303 K), with a pressure of 0.9 MPa. When the outlet temperature drops to 243.15K, the evaporative cooling process is stopped.

[0082] Next, a UDF (User-Defined Function) was compiled to set the nitrogen properties. The primary phase was liquid nitrogen at 2.6 MPa, and the secondary phase was the nitrogen obtained after compiling the UDF, named "real-gas-fluid". The bottom boundary was changed to "wall" for insulation. The top boundary was changed to a mass flow inlet, through which 303 K nitrogen was introduced. Once the pressure inside the packed bed reached 2.6 MPa, the pressurization process was stopped.

[0083] The secondary phase is changed to nitrogen at 2.6 MPa, the bottom boundary is changed to a mass flow outlet, and the top boundary is changed to a pressure inlet at 2.6 MPa, with nitrogen at 303 K introduced. The nitrogen condenses into liquid nitrogen upon contact with the cryogenic packing material, and this liquid nitrogen, along with the initial liquid nitrogen present in the packed bed, is discharged from the bottom of the packed bed. The condensation process is stopped when the volume fraction of liquid nitrogen inside the packed bed drops below 10%.

[0084] The secondary phase is changed to real-gas-fluid, the bottom boundary is changed to a wall for insulation, and the top boundary is changed to a mass flow outlet to discharge nitrogen. The venting and depressurization process is stopped when the internal pressure of the packed bed drops from 2.6 MPa to 0.9 MPa.

[0085] This completes one cycle of liquid nitrogen evaporation / nitrogen condensation and storage in the packed bed. Repeat this process until stability is achieved, obtaining the duration t of the liquid nitrogen evaporation process.

[0086] The packed bed structure is adjusted based on the stabilization time t of the evaporation process. If the difference between the simulation time and the design time is within m%, the structural parameters of the packed bed are considered to meet the design requirements. If the deviation exceeds m%, the height of the packed bed is adjusted to the original T / t and the simulation steps are repeated until the design time requirement is met, thus completing the solid-state cold storage packed bed design.

[0087] Under these conditions, when the diameter of the packed bed is 0.6m and the evaporation process lasts for 9.47h, the corresponding height of the packed bed is 9.6m.

[0088] like Figure 3 As shown, this embodiment also provides a solid-state cold storage packed bed design system for nitrogen phase transition process, including: a data acquisition module, used to determine the volume of solid-state cold storage packed bed based on preset design operating parameters and pre-screened packed bed filler types, so as to obtain the packed bed diameter and packed bed height; The model building module is used to construct geometric and numerical simulation models of the filling bed based on the filling bed diameter and filling bed height. The simulation module is used to simulate the processes of cryogenic liquid nitrogen evaporation and cold storage, gas charging and pressurization, room temperature and high pressure nitrogen condensation and cold release, and exhaust and depressurization in a packed bed based on numerical simulation models and packed bed geometric models, and to obtain the simulation time of liquid nitrogen evaporation process and nitrogen condensation process corresponding to the steady state. The structure adjustment module is used to adjust the structure of the packed bed based on the greater of the simulation time of the liquid nitrogen evaporation process and the simulation time of the nitrogen condensation process under the steady state and the preset design time, so as to obtain the height of the solid cold storage packed bed under the design working conditions and complete the design of the solid cold storage packed bed.

[0089] The present invention also provides a solid-state cold storage packed bed design device for a nitrogen phase transition process, comprising: a memory for storing a computer program; and a processor for executing the computer program to implement the steps of the solid-state cold storage packed bed design method for the nitrogen phase transition process.

[0090] The present invention also provides a computer program product, including a computer program / instruction that, when executed by a processor, implements the steps of the solid-state cold storage packed bed design method for the nitrogen phase transition process.

[0091] When the processor executes the computer program, it implements the following steps for designing a solid-state cold storage packed bed for the aforementioned nitrogen phase transition process: Based on pre-set design parameters and pre-selected types of packing materials, the volume of the solid-state cold storage packed bed is determined to obtain its diameter and height; a geometric model and a numerical simulation model of the packed bed are constructed based on its diameter and height; based on the numerical simulation model and the geometric model, the processes of cryogenic liquid nitrogen evaporation and cold storage, pressurization, condensation and release of nitrogen at room temperature and high pressure, and depressurization are simulated within the packed bed to obtain the simulation durations of the liquid nitrogen evaporation process and the nitrogen condensation process under stable conditions; based on the larger of the simulation durations of the liquid nitrogen evaporation process and the nitrogen condensation process under stable conditions and the preset design duration, the structure of the packed bed is adjusted to obtain the height of the solid-state cold storage packed bed under the design parameters, thus completing the design of the solid-state cold storage packed bed.

[0092] Exemplarily, the computer program can be divided into one or more modules / units, which are stored in the memory and executed by the processor to complete the present invention. The one or more modules / units can be a series of computer program instruction segments capable of performing preset functions, wherein the instruction segments describe the execution process of the computer program in the solid-state cold storage packed bed design device for the nitrogen phase transition process. For example, the computer program can be divided into a data acquisition module, a model building module, a simulation module, and a structure adjustment module. The data acquisition module is used to determine the volume of the solid-state cold storage packed bed based on preset design operating parameters and pre-selected packed bed filler types, so as to obtain the packed bed diameter and height. The model building module is used to build a geometric model and a numerical simulation model of the packed bed based on the packed bed diameter and height. The simulation module is used to simulate the processes of cryogenic liquid nitrogen evaporation and cold storage, gas charging and pressurization, room temperature high-pressure nitrogen condensation and cold release, and exhaust and depressurization in the packed bed based on the numerical simulation model and the packed bed geometric model, so as to obtain the simulation time of the liquid nitrogen evaporation process and the simulation time of the nitrogen condensation process corresponding to the steady state. The structure adjustment module is used to adjust the structure of the packed bed based on the larger of the simulation time of the liquid nitrogen evaporation process and the simulation time of the nitrogen condensation process corresponding to the steady state and the preset design time, so as to obtain the height of the solid-state cold storage packed bed under the design operating parameters, so as to complete the design of the solid-state cold storage packed bed.

[0093] The solid-state cold storage filled bed design device for the nitrogen phase transition process can be a computing device such as a desktop computer, laptop, handheld computer, or cloud server. This device may include, but is not limited to, processors and memory. Those skilled in the art will understand that the above are examples of a solid-state cold storage filled bed design device for the nitrogen phase transition process and do not constitute a limitation on the device. It may include more components than described above, or combine certain components, or use different components. For example, the solid-state cold storage filled bed design device for the nitrogen phase transition process may also include input / output devices, network access devices, buses, etc.

[0094] The processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor, or any conventional processor. The processor is the control center of the solid-state cold storage filled bed design for the nitrogen phase transition process, connecting various parts of the solid-state cold storage filled bed design equipment for the entire nitrogen phase transition process via various interfaces and lines.

[0095] The memory can be used to store the computer program and / or modules. The processor realizes various functions of the solid-state cold storage packed bed design equipment for the nitrogen phase transformation process by running or executing the computer program and / or modules stored in the memory and calling the data stored in the memory.

[0096] The memory may primarily include a program storage area and a data storage area. The program storage area may store the operating system and at least one application program required for a function (such as sound playback, image playback, etc.). The data storage area may store data created based on the use of the mobile phone (such as audio data, phonebook, etc.). Furthermore, the memory may include high-speed random access memory and non-volatile memory, such as hard disks, RAM, plug-in hard disks, smart media cards (SMC), secure digital cards (SD cards), flash cards, at least one disk storage device, flash memory device, or other volatile solid-state storage devices.

[0097] The present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the solid-state cold storage packed bed design method for a nitrogen phase transition process.

[0098] If the modules / units integrated into the solid-state cold storage packed bed design system for the nitrogen phase transition process are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium.

[0099] Based on this understanding, all or part of the processes in the solid-state cold storage packed bed design method for the nitrogen phase transition process described above can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium. When executed by a processor, the computer program can implement the steps of the solid-state cold storage packed bed design method for the nitrogen phase transition process described above. The computer program includes computer program code, which can be in the form of source code, object code, executable file, or a preset intermediate form, etc.

[0100] The computer-readable storage medium may include: any entity or device capable of carrying the computer program code, recording media, USB flash drive, portable hard drive, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal, and software distribution medium, etc.

[0101] It should be noted that the content contained in the computer-readable storage medium may be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, the computer-readable storage medium does not include electrical carrier signals and telecommunication signals.

[0102] The above embodiments are merely one of the implementation methods for achieving the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes any variations, substitutions and other implementation methods that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A solid-state cold storage packed bed design method for a nitrogen phase transition process, characterized in that, include: Based on the pre-set design parameters and the pre-screened types of packing materials, the volume of the solid-state cold storage packed bed is determined in order to obtain the packed bed diameter and height. A geometric model and a numerical simulation model of the filling bed are constructed based on the filling bed diameter and filling bed height. Based on numerical simulation models and packed bed geometric models, the processes of low-temperature liquid nitrogen evaporation and cold storage, gas filling and pressurization, room temperature and high pressure nitrogen condensation and cold release, and exhaust and depressurization in the packed bed are simulated to obtain the simulation time of liquid nitrogen evaporation process and nitrogen condensation process corresponding to the steady state. Based on the larger of the simulation time for the liquid nitrogen evaporation process and the simulation time for the nitrogen condensation process under steady-state conditions, and the preset design time, the structure of the packed bed is adjusted to obtain the height of the solid-state cold storage packed bed under the design operating parameters, so as to complete the design of the solid-state cold storage packed bed.

2. The solid-state cold storage packed bed design method for a nitrogen phase transition process according to claim 1, characterized in that, Before determining the volume of the solid-state cold storage packed bed based on preset design operating parameters and pre-screened packed bed filler types, the following steps are also included: The specific steps for screening the types of packed bed packing materials are as follows: By comprehensively evaluating the density, specific heat, thermal conductivity, volumetric heat capacity, and economic efficiency of packed bed packings, the types of packed bed packings were selected.

3. The solid-state cold storage packed bed design method for a nitrogen phase transition process according to claim 1, characterized in that, The process of determining the volume of the solid-state cold storage packed bed based on pre-set design parameters and pre-screened packed bed filler types, in order to obtain the packed bed diameter and height, includes: Obtain the preset design operating condition parameters, which include the target duration of the liquid nitrogen evaporation and cold storage process and the target duration of the high-pressure nitrogen condensation and cold release process; Based on the preset design parameters and the type of packing material, the volume of the solid-state cold storage packed bed is calculated using the following formula: When the target duration of the liquid nitrogen evaporation and cold storage process is greater than the target duration of the high-pressure nitrogen condensation and cold release process, the formula for calculating the volume of the solid-state cold storage packed bed is as follows: The heat transfer of the fluid during the cold storage process is: The theoretical heat exchange capacity of solid packing is: In the formula, For the heat exchange of fluids during the liquid nitrogen evaporation process; The fluid mass flow rate at the inlet of the packed bed during the liquid nitrogen evaporation process; The target duration for the liquid nitrogen evaporation and cold storage process; The volume of the solid-state cold storage packed bed; Porosity of the packed bed; The density of liquid nitrogen at the inlet of the packed bed; The percentage of liquid nitrogen in the packed bed at the end of the evaporation process, ranging from 0 to 1. The enthalpy of the fluid at the inlet of the packed bed during the nitrogen condensation process; The enthalpy of the fluid at the inlet of the packed bed in the liquid nitrogen evaporation and cold storage process; For the heat exchange of solid packing material in the liquid nitrogen evaporation process; This is the ratio of fluid heat transfer to the theoretical heat transfer of the packing material; The density of the solid filler; Specific heat capacity of solid filler; This refers to the inlet temperature of the packed bed during the nitrogen condensation process. The inlet temperature of the packed bed in the liquid nitrogen evaporation and cold storage process; When the target duration of the liquid nitrogen evaporation and cold storage process is less than the target duration of the high-pressure nitrogen condensation and cold release process, the formula for calculating the volume of the solid-state cold storage packed bed is as follows: The heat transfer rate of the fluid during the nitrogen condensation and cooling process is: The theoretical heat exchange capacity of solid packing is: In the formula, The heat exchange of the fluid during the nitrogen condensation process; This refers to the fluid mass flow rate at the outlet of the packed bed during the nitrogen condensation process. The target duration for the high-pressure nitrogen condensation and release process; The percentage of liquid nitrogen in the packed bed after the nitrogen condensation process is complete, ranging from 0 to 1. For the heat exchange of solid packing material in the nitrogen condensation process; According to the preset filling bed diameter D The height of the filling bed was calculated. L : In the formula, Pi is the mathematical constant of a circle.

4. The solid-state cold storage packed bed design method for a nitrogen phase transition process according to claim 3, characterized in that, The construction of the geometric model and numerical simulation model of the packed bed based on the packed bed diameter and packed bed height includes: Construct a geometric model of the filling bed based on its diameter and height. A numerical simulation model was constructed using the Fluent platform; wherein the numerical simulation model includes a porous medium model and a two-phase flow model; The density and thermal conductivity of the solid packing were set to 0; during the numerical simulation model solution process, a scalar variable was added to represent the temperature of the solid packing. Establish the solid energy equation for scalar variables: In the formula, Represents the gradient operator; Indicates the thermal conductivity of solid fillers; Indicates the temperature of the solid packing material; Indicates the temperature of the heat transfer fluid; This represents the volumetric convection heat transfer coefficient.

5. The solid-state cold storage packed bed design method for a nitrogen phase transition process according to claim 1, characterized in that, The numerical simulation model and the packed bed geometric model are used to simulate the processes of cryogenic liquid nitrogen evaporation and cold storage, gas filling and pressurization, room temperature and high pressure nitrogen condensation and cold release, and exhaust and depressurization within the packed bed. The simulation durations for the liquid nitrogen evaporation process and the nitrogen condensation process at steady state are obtained, including: A numerical simulation model was used to simulate the processes of cryogenic liquid nitrogen evaporation and cold storage, gas charging and pressurization, nitrogen condensation and release at room temperature and high pressure, and exhaust and depressurization within a packed bed geometric model. During the gas charging and pressurization and exhaust and depressurization processes, nitrogen properties were obtained based on a pre-built user-defined real gas model to determine nitrogen properties according to the current temperature and pressure. The specific steps are as follows: The nitrogen property relationships are written into the user-defined function to define the material; the nitrogen density is described using the ideal gas law; the nitrogen specific heat capacity is described using a pressure-segmented and intra-segment temperature polynomial approach, dividing the pressure range into multiple intervals, and expressing the nitrogen specific heat capacity as a polynomial function dependent only on temperature within each pressure interval; the enthalpy of nitrogen is defined as follows: In the formula, This refers to the enthalpy of nitrogen. For temperature, This is a reference temperature; the reference temperature is set as the saturation temperature of nitrogen at different pressures. The enthalpy of nitrogen at the reference temperature; This represents the specific heat of nitrogen at the corresponding pressure and temperature. After simulation, the simulation time for the liquid nitrogen evaporation process and the nitrogen condensation process corresponding to the steady state are obtained.

6. The solid-state cold storage packed bed design method for a nitrogen phase transition process according to claim 1, characterized in that, Before adjusting the packed bed structure based on the larger of the simulation time for the liquid nitrogen evaporation process and the simulation time for the nitrogen condensation process under steady-state conditions, and the preset design time, to obtain the height of the solid-state cold storage packed bed under the design operating parameters, the following steps are also included: Compare the simulation durations of liquid nitrogen evaporation and nitrogen condensation, and obtain the larger of the two simulation durations. Output the larger of the two simulation durations as the simulation duration.

7. The solid-state cold storage packed bed design method for a nitrogen phase transition process according to claim 6, characterized in that, The height of the solid-state cold storage packed bed is adjusted based on the larger of the simulation time for the liquid nitrogen evaporation process and the simulation time for the nitrogen condensation process under steady-state conditions, and the preset design time. This adjustment includes: The simulation duration is compared with the preset design duration for judgment: If the difference between the two is within the preset ratio range, it is determined that the structural parameters of the packed bed meet the design requirements, and the current height of the packed bed is output as the height of the solid-state cold storage packed bed under the design working conditions. If the difference between the two exceeds the preset ratio range, the filling bed height will be adjusted to the original filling bed height × ratio coefficient; where the ratio coefficient = design duration ÷ simulation duration. Repeat the simulation process until the design duration requirement is met, and output the adjusted packed bed height as the height of the solid-state cold storage packed bed under the design operating conditions.

8. A solid-state cold storage packed bed design system for a nitrogen phase transition process, characterized in that, include: The data acquisition module is used to determine the volume of the solid-state cold storage packed bed based on the preset design operating parameters and the pre-screened packed bed filler types, so as to obtain the packed bed diameter and packed bed height. The model building module is used to construct geometric and numerical simulation models of the filling bed based on the filling bed diameter and filling bed height. The simulation module is used to simulate the processes of cryogenic liquid nitrogen evaporation and cold storage, gas charging and pressurization, room temperature and high pressure nitrogen condensation and cold release, and exhaust and depressurization in a packed bed based on numerical simulation models and packed bed geometric models, and to obtain the simulation time of liquid nitrogen evaporation process and nitrogen condensation process corresponding to the steady state. The structure adjustment module is used to adjust the structure of the packed bed based on the greater of the simulation time of the liquid nitrogen evaporation process and the simulation time of the nitrogen condensation process under the steady state and the preset design time, so as to obtain the height of the solid cold storage packed bed under the design working conditions and complete the design of the solid cold storage packed bed.

9. A solid-state cold storage packed bed design device for a nitrogen phase transition process, characterized in that, include: Memory, used to store computer programs; A processor, configured to execute the computer program to implement the steps of the solid-state cold storage packed bed design method for the nitrogen phase transition process according to any one of claims 1-7.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it is used to implement the steps of the solid-state cold storage packed bed design method for the nitrogen phase transition process according to any one of claims 1-7.

Images