A method and system for transient calculation of temperature field of phase change capsules based on thermal network

Abstract

The application discloses a kind of based on heat network's phase change capsule temperature field transient calculation method and system, it is related to phase change capsule technical field, including: constructing phase change capsule physical model and parameter initialization;Four-node heat network model is constructed;Phase change process: preheating stage: all solid surface heat is used for temperature rise, solve four-node coupled heat transfer equation group, output each node transient temperature value;Melting stage: solid surface temperature is fixed at phase change temperature, solve equation group, according to gas phase, liquid phase net heat flow calculation two-phase mixture enthalpy, update solid-liquid mass and volume and output each node transient temperature value;Complete liquefaction stage: solid disappears, liquid node directly exchanges heat with shell wall, calculate heat transfer coefficient, solve equation group, output each node transient temperature value;To each node preheating stage and melting stage between and each node melting stage and complete liquefaction stage between with stage transition smoothing processing.The application greatly improves calculation efficiency, physical model is complete, and numerical stability is good.

Description

Technical Field

[0001] This invention relates to the field of phase change capsule technology, and in particular to a method and system for transient calculation of the temperature field of a phase change capsule based on a thermal network. Background Technology

[0002] Phase change thermal energy storage technology utilizes phase change materials (PCMs) to absorb or release a large amount of latent heat during solid-liquid phase change to achieve thermal energy storage. It is widely used in fields such as solar thermal utilization, building energy conservation, and industrial waste heat recovery. Encapsulated phase change particle thermal accumulators are composed of a large number of spherical phase change capsules, which have the advantages of large heat exchange area and high heat storage density.

[0003] In existing technologies, the following methods are mainly used to calculate the temperature field of phase change particle heat accumulators:

[0004] (1) CFD method: A complete three-dimensional numerical simulation of the interior of each phase change capsule is performed, including physical processes such as solid-liquid phase change, natural convection, and heat conduction of the phase change material. This method has high calculation accuracy, but the computational load is extremely large. For actual heat storage systems containing thousands or even tens of thousands of capsules, the calculation time can reach several weeks or even months, which is difficult to meet the engineering design requirements.

[0005] (2) Equivalent thermal conductivity method: The phase change capsule is simplified as a solid sphere with equivalent thermal properties, and internal convection and phase change interface movement are ignored. This method is fast, but it cannot accurately describe the latent heat release / absorption characteristics during the phase change process, especially with large errors during melting / solidification.

[0006] (3) Enthalpy-Porous Media Method: The phase transition region is treated as a mushy region, and the phase transition interface is tracked by the enthalpy method. This method has a certain ability to describe the phase transition process, but its ability to handle complex multiphase flows (bubbles, floating ice, etc.) inside spherical capsules is limited, and a finer grid resolution is still required.

[0007] The common problems of the above methods are: (1) they cannot balance computational efficiency and accuracy; (2) they are difficult to accurately describe the influence of complex physical phenomena such as the internal bubble space of the phase change capsule, the eccentricity of the floating ice, and the natural convection of liquid water on heat transfer; and (3) they lack a smooth transition processing mechanism for the three stages of preheating-melting-complete liquefaction. Summary of the Invention

[0008] This invention addresses the problems and shortcomings of existing technologies by providing a transient calculation method and system for the temperature field of a phase change capsule based on a thermal network. By establishing a multi-node thermal network model inside the phase change capsule and combining it with a quasi-steady-state heat transfer correlation, the calculation efficiency is significantly improved while ensuring calculation accuracy.

[0009] The present invention solves the above-mentioned technical problems through the following technical solution:

[0010] This invention provides a transient calculation method for the temperature field of a phase change capsule based on a thermal network, characterized by comprising the following steps:

[0011] S1. The internal structure of the phase change capsule is layered under the action of gravity. The top is a gas space, and the rest is a liquid working medium and a solid working medium. The solid working medium floats in the liquid working medium. Its position depends on the density difference between the solid and liquid phases and the current solid-liquid mass distribution. Based on this, a physical model of the phase change capsule is constructed and the parameters are initialized. The parameters include the outer radius, wall thickness and inner radius of the shell wall of the phase change capsule, the filling rate of the inner cavity of the phase change capsule, the phase change temperature and the latent heat of phase change.

[0012] S2. Construct a thermal network model with at least four nodes, including: constructing a heat capacity calculation model for each node, constructing a geometric parameter calculation model for each node, and constructing a heat transfer calculation model between each node. The four nodes are shell wall nodes, gas nodes, liquid nodes, and solid nodes.

[0013] S3. The phase transition process is divided into three stages.

[0014] Preheating stage: All heat on the solid surface is used for heating, no phase change occurs, and the solid surface temperature is treated as an unknown variable in the solution. A solver is used to solve the four-node coupled heat transfer equations and outputs the transient temperature values ​​of each node.

[0015]

[0016] In the formula, Let be the transient temperature value of the i-th node, and represent the temperature change value of the i-th node within one time step. The net heat transfer rate is calculated using the heat transfer calculation model associated with the i-th node. For time steps, The heat capacity of the i-th node is calculated from the heat capacity calculation model of each node.

[0017] Melting stage: The solid surface temperature is fixed at the phase transition temperature. The four-node coupled heat transfer equations are solved using a solver. The enthalpy of the two-phase mixture is calculated according to the net heat flow of the gas and liquid phases. The solid and liquid mass and volume are updated, and the transient temperature values ​​of each node are output.

[0018] Complete liquefaction stage: Solids disappear, liquid nodes directly exchange heat with the shell wall. The heat transfer coefficient is calculated using the natural convection correlation inside the Churchill-Chu sphere. The four-node coupled heat transfer equations are solved using a solver, and the transient temperature values ​​of each node are output.

[0019] A smooth transition process is applied between the preheating stage and the melting stage of each node, and between the melting stage and the complete liquefaction stage of each node.

[0020] This invention also provides a transient calculation system for the temperature field of a phase change capsule based on a thermal network, characterized in that it includes:

[0021] The physical model building module is used to construct a physical model of the phase change capsule based on the layered structure inside the capsule under the action of gravity, with a gas space at the top and liquid and solid working fluids in the rest. The solid working fluid floats in the liquid working fluid, and its position depends on the density difference between the solid and liquid phases and the current solid-liquid mass distribution. The module initializes the parameters, including the outer radius, wall thickness and inner radius of the capsule shell, the filling rate of the capsule cavity, the phase change temperature and the latent heat of phase change.

[0022] The computational model building module is used to build a thermal network model with at least four nodes, including: building a heat capacity calculation model for each node, building a geometric parameter calculation model for each node, and building a heat transfer calculation model between each node. The four nodes are shell node, gas node, liquid node, and solid node.

[0023] The phase change processing module is used to divide the phase change process into three stages:

[0024] Preheating stage: All heat on the solid surface is used for heating, no phase change occurs, and the solid surface temperature is treated as an unknown variable in the solution. A solver is used to solve the four-node coupled heat transfer equations and outputs the transient temperature values ​​of each node.

[0025]

[0026] In the formula, Let be the transient temperature value of the i-th node, and represent the temperature change value of the i-th node within one time step. The net heat transfer rate is calculated using the heat transfer calculation model associated with the i-th node. For time steps, The heat capacity of the i-th node is calculated from the heat capacity calculation model of each node.

[0027] Melting stage: The solid surface temperature is fixed at the phase transition temperature. The four-node coupled heat transfer equations are solved using a solver. The enthalpy of the two-phase mixture is calculated according to the net heat flow of the gas and liquid phases. The solid and liquid mass and volume are updated, and the transient temperature values ​​of each node are output.

[0028] Complete liquefaction stage: Solids disappear, liquid nodes directly exchange heat with the shell wall. The heat transfer coefficient is calculated using the natural convection correlation inside the Churchill-Chu sphere. The four-node coupled heat transfer equations are solved using a solver, and the transient temperature values ​​of each node are output.

[0029] A smooth transition process is applied between the preheating stage and the melting stage of each node, and between the melting stage and the complete liquefaction stage of each node.

[0030] The present invention also provides an electronic device, characterized in that it includes: a processor; a memory for storing processor-executable instructions; wherein the processor is configured to invoke the instructions stored in the memory to execute the above-described transient calculation method for the temperature field of the phase change capsule.

[0031] The present invention also provides a computer-readable storage medium storing computer program instructions thereon, characterized in that the computer program instructions, when executed by a processor, implement the above-described transient calculation method for the temperature field of the phase change capsule.

[0032] The positive and progressive effects of this invention are as follows:

[0033] (1) Significantly improved computational efficiency: Compared with existing full CFD methods, the computational cost of a single phase change capsule is reduced from millions of grids to 4 lumped nodes, and the computational speed is improved by about 3-4 orders of magnitude, making it possible to simulate system-level transients containing tens of thousands of phase change capsules.

[0034] (2) Complete physical model: It correctly describes various physical mechanisms such as gas space, solid eccentricity, natural convection, radiation heat transfer, and contact thermal resistance, as well as the smooth transition of the three stages of preheating-melting-liquefaction.

[0035] (3) Good numerical stability: Through the smoothing processing strategy, the stability and convergence of long-term transient calculations are guaranteed. Attached Figure Description

[0036] Figure 1 This is a flowchart of a preferred embodiment of the transient calculation method for the temperature field of a phase change capsule.

[0037] Figure 2 This is a schematic diagram of the phase change capsule according to a preferred embodiment of the present invention.

[0038] Figure 3 The diagram shows the temperature results at each node in a preferred embodiment of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] like Figure 1 As shown, this embodiment of the invention provides a transient calculation method for the temperature field of a phase change capsule based on a thermal network, which includes the following steps:

[0041] Step 101: Under the influence of gravity, the phase change capsule exhibits a layered structure. The top is a gas space, and the rest consists of liquid and solid working fluids. The solid working fluid floats within the liquid working fluid, and its position depends on the density difference between the solid and liquid phases and the current solid-liquid mass distribution. Based on this, a physical model of the phase change capsule is constructed (see...). Figure 2 The parameters are initialized, including the outer radius, wall thickness and inner radius of the phase change capsule shell, the filling rate of the phase change capsule cavity, the phase change temperature and the latent heat of phase change.

[0042] Specifically, the shell of the phase change capsule is a metal spherical shell, and in this example, the outer radius R_outer = 5*10 -3 m, wall thickness t_shell = 3*10 -4 m, inner radius R_inner = 4.7*10 -3 m; The inner cavity of the phase change capsule is filled with phase change material, which is water / ice in this example, with a filling rate of φ = 87.2%, and the remainder is gas, which is air in this example; Phase change temperature: T_m = 273.15 K, latent heat of phase change L_f = 333.5 kJ / kg.

[0043] Step 102: Construct a thermal network model with at least four nodes, including: constructing a heat capacity calculation model for each node, constructing a geometric parameter calculation model for each node, constructing a heat transfer calculation model between each node, and constructing a solid internal temperature distribution model; wherein, the four nodes are shell wall nodes, gas nodes, liquid nodes, and solid nodes.

[0044] In this example, the definitions of each node are shown in Table 1.

[0045] Table 1

[0046]

[0047] (1) Construct the heat capacity calculation model for each node:

[0048] The heat capacity of a shell wall node is C_wall = V_shell × ρ_wall × cp_wall

[0049] The heat capacity of a gas node is C_gas = m_gas × cp_gas, where m_gas = ρ_gas(T_gas) × V_gas

[0050] The heat capacity of the liquid node is C_liq = m_w × cp_w(T_liq).

[0051] The heat capacity of a solid node is C_core = m_i × cp_i

[0052] In the formula, C is the heat capacity, in J / K; V is the volume, in m³. 3 ρ is density, in kg / m³ 3 ;cp is the specific heat at constant pressure, in J / (kg·K); m is the mass, in kg; wall and shell represent the shell wall, gas represents gas (air in this example), liq and w represent liquid (water in this example), and core and i represent solid (ice core in this example).

[0053] (2) Construct the geometric parameter calculation model for each node:

[0054] As the phase transition process proceeds, the volume distribution and interface position of ice / water / gas will continuously change, requiring dynamic updates to the geometric parameters. This necessitates the construction of a geometric parameter calculation model for each node.

[0055] 1) Volume of each phase: Based on the current solid mass m_i and liquid mass m_w, and using the temperature-dependent density function, calculate the volume of each phase:

[0056] Solid volume V_i = m_i / ρ_i

[0057] Liquid volume V_w = m_w / ρ_w(T_liq)

[0058] The volume of the gas spherical cap is V_g = V_cavity - V_i - V_w

[0059] In the formula, V represents volume, in meters (m³). 3 ρ is density, in kg / m³ 3 m represents mass in kg; V_cavity represents the volume of the phase change capsule cavity; i represents solid; w represents liquid; g represents gas; and ρ_w(T_liq) represents the liquid density related to the liquid temperature.

[0060] 2) The solid is equivalent to a sphere, and the radius of the equivalent sphere is r_s = (3V_i / 4π)^(1 / 3).

[0061] In the formula, r is the radius, in meters (m).

[0062] 3) Height of the air cap: The height h_g of the air space is calculated using the inverse operation of the spherical cap volume formula.

[0063] V_g = πh_g²(3R_inner - h_g) / 3

[0064] In the formula, R_inner is the inner radius of the shell wall.

[0065] 4) Interface area: Inner wall surface - gas contact area A_ex = 2πR_inner × h_g, unit m 2 ;

[0066] The inner wall surface-liquid contact area A_wet = A_inner - A_ex, in meters. 2 A_inner is the inner surface area of ​​the shell wall;

[0067] The solid-liquid interface area A_ls and the solid-gas interface area A_sg are calculated based on the solid immersion depth, and the specific calculation formula is the existing formula.

[0068] (3) Construct a heat transfer calculation model between each node:

[0069] The heat transfer calculation model includes formulas for calculating the heat transfer rate of the inner wall surface to gas, the heat transfer rate of the inner wall surface to gas radiation, the heat transfer rate of the inner wall surface to liquid convection, the heat transfer rate of the liquid-solid interface convection, the heat transfer rate of the wall surface to solid contact surface, the heat transfer rate of the gas-solid interface, and the heat transfer rate of the solid surface to solid core (see Table 2).

[0070] Table 2

[0071]

[0072] In the formula, G is the heat transfer rate in W; k is the thermal conductivity in W / (m·K); k_air(T) is the temperature-dependent gas thermal conductivity; ΔT is the heat transfer temperature difference between the two connection nodes in K, and the value of ΔT varies depending on the specific connection nodes; σ is the radiation constant, i.e., the Stefan-Boltzmann constant, with a value of 5.669 × 10⁻⁶. -8 W / (m 2 ·K 4 ε is the surface emissivity, unitless; T is the surface Kelvin temperature, in Kelvin; δ is the thermal resistance thickness, in meters; k_eff is the effective thermal conductivity of the wall-ice interface; A_contact is the ice-wall contact area; δ_gap is the equivalent thermal resistance thickness of the wall-ice micro-gap (calibrated, 2.0 × 10⁻⁶). -5 m), λ1 is the first characteristic value of transient thermal conductivity of the sphere, and α_i is the thermal diffusivity of ice.

[0073] Among them, the heat transfer rate G_ws between the wall and ice (contact) is calculated: Under the condition of direct solid-solid contact between ice and the wall (m_i > 0), the interfacial thermal resistance is equivalently considered as a micro-gap with a thickness of δ_gap, and the effective thermal conductivity of the wall-ice contact interface is taken as the harmonic average of the wall and ice: k_eff = 2 / (1 / k_wall + 1 / k_i) h_c = k_eff / δ_gap, G_ws = h_c ×A_contact×ΔT In the formula, k_wall is the thermal conductivity of the shell wall, and k_i is the thermal conductivity of ice.

[0074] In this example, the natural convection heat transfer correlation between concentric spherical shells proposed by Teertstra et al. is adopted. This correlation takes into account both boundary layer and transition flow modes.

[0075] Calculate the convective heat transfer rate G_wl between the inner wall and the liquid and the convective heat transfer rate G_ls between the liquid and the ice interface: G_wl = f_area × h_o,eff × A_o×ΔT G_ls = f_area × h_i,eff × A_i×ΔT f_area is the effective area ratio coefficient, ∈ [0, 1], which is the ratio of the wetted area to the geometric area. Its physical meaning is: when the capsule is not fully filled or the ice core is not completely submerged, the actual area participating in heat exchange is the proportion of the area of ​​the complete sphere.

[0076] h_o,eff and h_i,eff are the natural convection heat transfer coefficients of the spherical annulus (W·m). -2 ·K -1 h_o,eff corresponds to the capsule inner wall-liquid interface, and h_i,eff corresponds to the ice core outer surface-liquid interface. Both are obtained from the Teertstra correlation: h_o,eff=Nu·k_water(T) / R_inner×2 h_i,eff =Nu·k_air(T) / r_s×2 Nu is the Nusselt number, k_water(T) is the thermal conductivity of water as a function of temperature, and A_o and A_i are the reference geometric areas (m²). 2 ), A_o = 4πR_inner 2 Let A_i be the area of ​​the spherical inner wall of the capsule, and A_i = 4πr_s 2 Let be the outer surface area of ​​the ice core, and be the geometric area of ​​a perfect sphere.

[0077] (4) Construct a model of temperature distribution inside a solid.

[0078] For the internal temperature distribution of a solid, the radial distribution function of its internal temperature is calculated using the first mode of the transient thermal conductivity equation of a sphere. Its equivalent thermal conductivity is obtained by solving the first eigenvalue λ1 using the Biot number through the characteristic equation 1 - λ·cot(λ) - Bi = 0.

[0079] Step 103: Divide the phase transition process into three stages.

[0080] (1) Preheating stage (ice surface temperature T_sf < phase change temperature T_m)

[0081] All the heat on the solid surface (ice in this example) is used for heating, with no phase change occurring. The solid surface temperature is treated as an unknown variable in the solution. A solver is used to solve the four-node coupled heat transfer equations, outputting the transient temperature values ​​of each node (see...). Figure 3 ):

[0082]

[0083] In the formula, Let be the transient temperature value of the i-th node, and represent the temperature change value of the i-th node within one time step. The net heat transfer rate is calculated using the heat transfer model associated with the i-th node. For time steps, The heat capacity of the i-th node is calculated from the heat capacity calculation model of each node.

[0084] (2) Melting stage (ice surface temperature T_sf = phase change temperature T_m, ice mass m_i > 0)

[0085] The solid surface temperature is fixed at the phase transition temperature T_m. A solver is used to solve the four-node coupled heat transfer equations. The enthalpy of the two-phase mixture is calculated based on the net heat flux of the gas and liquid phases. The solid and liquid masses and volumes are updated, and the transient temperature values ​​of each node are output (see...). Figure 3 ).

[0086] Specifically, the enthalpy of the two-phase mixture is calculated based on the net heat flow of the gas and liquid phases, and the solid and liquid masses and volumes are updated accordingly.

[0087] Q_latent = G_ws+ G_gs+ G_ls- G_sr

[0088] Δm = Q_latent × Δt / L_f

[0089] ΔV =Δm / ρ_i

[0090] In the formula, Q_latent is the latent heat change of the ice-water mixture, Δt is the time step, and L_f is the latent heat of phase change.

[0091] (3) Complete liquefaction stage (ice mass m_i≈0)

[0092] With the solid phase eliminated, the liquid nodes directly exchange heat with the shell wall. The heat transfer coefficient is calculated using the natural convection correlation within the Churchill-Chu sphere. A solver is used to solve the four-node coupled heat transfer equations, and the transient temperature values ​​of each node are output (see...). Figure 3 ).

[0093] A smooth transition process is applied between the preheating stage and the melting stage of each node, and between the melting stage and the complete liquefaction stage of each node.

[0094] Specifically, a smooth transition process is implemented between the preheating and melting stages at each node:

[0095] T1 i = (1-α)T_preheat i +α×T_melt1 i T1 i T_preheat is the temperature value obtained after smoothing the i-th node. i T_melt1 is the current temperature value calculated for the i-th node according to the preheating state. i Let be the current temperature value calculated for the i-th node according to the melting state; where the phase transition activation factor α = max(α_T, α_m), α_T is a smooth step function based on the current solid surface temperature, and α_m is the wetting fraction based on the current liquid mass. To avoid numerical jumps during stage switching, a phase transition activation factor is introduced in this example.

[0096] Smoothing the transition between the melting stage and the complete liquefaction stage at each node:

[0097] T2 i = (1-α) T_melt2 i +α×T_liquefy i T2 i T_melt2 represents the temperature value obtained after smoothing the i-th node. i T_liquefy represents the current temperature value calculated for the i-th node according to its melting state. i The current temperature value is calculated for the i-th node under the condition of complete liquefaction.

[0098] This invention also provides a transient calculation system for the temperature field of a phase change capsule based on a thermal network, including a physical model construction module, a computational model construction module, and a phase change processing module.

[0099] The physical model building module is used to construct a physical model of the phase change capsule based on the layered structure inside the capsule under gravity, with a gas space at the top and liquid and solid working fluids in the rest. The solid working fluid floats in the liquid working fluid, and its position depends on the density difference between the solid and liquid phases and the current solid-liquid mass distribution. The module initializes the parameters, including the outer radius, wall thickness and inner radius of the capsule shell, the filling rate of the capsule cavity, the phase change temperature and the latent heat of phase change.

[0100] The computational model building module is used to build a thermal network model with at least four nodes, including: building a heat capacity calculation model for each node, building a geometric parameter calculation model for each node, and building a heat transfer calculation model between each node. The four nodes are shell node, gas node, liquid node, and solid node.

[0101] The phase change processing module is used to divide the phase change process into three stages, specifically including:

[0102] Preheating stage: All heat on the solid surface is used for heating, no phase change occurs, and the solid surface temperature is treated as an unknown variable in the solution. A solver is used to solve the four-node coupled heat transfer equations and outputs the transient temperature values ​​of each node.

[0103]

[0104] In the formula, Let be the transient temperature value of the i-th node, and represent the temperature change value of the i-th node within one time step. The net heat transfer rate is calculated using the heat transfer calculation model associated with the i-th node. For time steps, The heat capacity of the i-th node is calculated from the heat capacity calculation model of each node.

[0105] Melting stage: The solid surface temperature is fixed at the phase transition temperature. The four-node coupled heat transfer equations are solved using a solver. The enthalpy of the two-phase mixture is calculated according to the net heat flow of the gas and liquid phases. The solid and liquid mass and volume are updated, and the transient temperature values ​​of each node are output.

[0106] Complete liquefaction stage: Solids disappear, liquid nodes directly exchange heat with the shell wall. The heat transfer coefficient is calculated using the Churchill-Chu sphere internal natural convection correlation. A solver is used to solve the four-node coupled heat transfer equations and output the transient temperature values ​​of each node.

[0107] A smooth transition process is applied between the preheating stage and the melting stage of each node, and between the melting stage and the complete liquefaction stage of each node.

[0108] This invention also provides an electronic device, including: a processor; and a memory for storing processor-executable instructions; wherein the processor is configured to invoke the instructions stored in the memory to execute the aforementioned transient calculation method for the temperature field of a phase change capsule.

[0109] This invention also provides a computer-readable storage medium storing computer program instructions, which, when executed by a processor, implement the aforementioned transient calculation method for the temperature field of a phase change capsule.

[0110] This invention can be a method, apparatus, system, and / or computer program product. The computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for performing various aspects of the invention.

[0111] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A transient calculation method for the temperature field of a phase change capsule based on a thermal network, characterized in that, It includes the following steps: S1. The internal structure of the phase change capsule is layered under the action of gravity. The top is a gas space, and the rest is a liquid working medium and a solid working medium. The solid working medium floats in the liquid working medium. Its position depends on the density difference between the solid and liquid phases and the current solid-liquid mass distribution. Based on this, a physical model of the phase change capsule is constructed and the parameters are initialized. The parameters include the outer radius, wall thickness and inner radius of the shell wall of the phase change capsule, the filling rate of the inner cavity of the phase change capsule, the phase change temperature and the latent heat of phase change. S2. Construct a thermal network model with at least four nodes, including: constructing a heat capacity calculation model for each node, constructing a geometric parameter calculation model for each node, and constructing a heat transfer calculation model between each node. The four nodes are shell wall nodes, gas nodes, liquid nodes, and solid nodes. S3. The phase transition process is divided into three stages. Preheating stage: All heat on the solid surface is used for heating, no phase change occurs, and the solid surface temperature is treated as an unknown variable in the solution. A solver is used to solve the four-node coupled heat transfer equations and outputs the transient temperature values ​​of each node. ； In the formula, Let be the transient temperature value of the i-th node, and represent the temperature change value of the i-th node within one time step. The net heat transfer rate is calculated using the heat transfer calculation model associated with the i-th node. For time steps, The heat capacity of the i-th node is calculated from the heat capacity calculation model of each node. Melting stage: The solid surface temperature is fixed at the phase transition temperature. The four-node coupled heat transfer equations are solved using a solver. The enthalpy of the two-phase mixture is calculated according to the net heat flow of the gas and liquid phases. The solid and liquid mass and volume are updated, and the transient temperature values ​​of each node are output. Complete liquefaction stage: Solids disappear, liquid nodes directly exchange heat with the shell wall. The heat transfer coefficient is calculated using the natural convection correlation inside the Churchill-Chu sphere. The four-node coupled heat transfer equations are solved using a solver, and the transient temperature values ​​of each node are output. A smooth transition process is applied between the preheating stage and the melting stage of each node, and between the melting stage and the complete liquefaction stage of each node.

2. The transient calculation method for the temperature field of a phase change capsule based on a thermal network as described in claim 1, characterized in that, Smoothing the transition between the preheating and melting stages at each node: T1 i = (1-α)T_preheat i +α×T_melt1 i T1 i T_preheat is the temperature value obtained after smoothing the i-th node. i T_melt1 is the current temperature value calculated for the i-th node according to the preheating state. i The current temperature value calculated for the i-th node according to its melting state; Wherein, the phase change activation factor α = max(α_T, α_m), α_T is a smooth step function based on the current solid surface temperature, and α_m is the wetting fraction based on the current liquid mass.

3. The transient calculation method for the temperature field of a phase change capsule based on a thermal network as described in claim 2, characterized in that, Smoothing the transition between the melting stage and the complete liquefaction stage at each node: T2 i = (1-α) T_melt2 i +α×T_liquefy i T2 i T_melt2 represents the temperature value obtained after smoothing the i-th node. i T_liquefy represents the current temperature value calculated for the i-th node according to its melting state. i The current temperature value is calculated for the i-th node under the condition of complete liquefaction.

4. The transient calculation method for the temperature field of a phase change capsule based on a thermal network as described in claim 1, characterized in that, In S2, a model of the internal temperature distribution of the solid is also constructed: For the internal temperature distribution of a solid, the radial distribution function of its internal temperature is calculated using the first mode of the transient thermal conductivity equation of a sphere. Its equivalent thermal conductivity is obtained by solving the first eigenvalue λ1 using the Biot number through the characteristic equation 1 - λ·cot(λ) - Bi = 0.

5. The transient calculation method for the temperature field of a phase change capsule based on a thermal network as described in claim 1, characterized in that, Construct a heat capacity calculation model for each node: The heat capacity of a shell wall node is C_wall = V_shell × ρ_wall × cp_wall The heat capacity of a gas node is C_gas = m_gas × cp_gas, where m_gas = ρ_gas(T_gas) × V_gas The heat capacity of the liquid node is C_liq = m_w × cp_w(T_liq). The heat capacity of a solid node is C_core = m_i × cp_i In the formula, C is the heat capacity, in J / K; V is the volume, in m³. 3 ; ρ is density, in kg / m³ 3 ;cp is the specific heat at constant pressure, in J / (kg·K); m is the mass, in kg; wall and shell represent the shell wall, gas represents gas, liq and w represent liquid, and core and i represent solid.

6. The transient calculation method for the temperature field of a phase change capsule based on a thermal network as described in claim 1, characterized in that, Construct a geometric parameter calculation model for each node: 1) Volume of each phase: Calculate the volume of each phase based on the current solid mass m_i and liquid mass m_w, combined with the temperature-dependent density function; Solid volume V_i = m_i / ρ_i Liquid volume V_w = m_w / ρ_w(T_liq) The volume of the gas spherical cap is V_g = V_cavity - V_i - V_w In the formula, V represents volume, in meters (m³). 3 ρ is density, in kg / m³ 3 m is mass in kg; V_cavity is the volume of the phase change capsule cavity; i represents solid; w represents liquid; g represents gas; ρ_w(T_liq) represents the liquid density related to the liquid temperature. 2) The solid is equivalent to a sphere, and the radius of the equivalent sphere is r_s = (3V_i / 4π)^(1 / 3). In the formula, r is the radius, in meters (m). 3) Height of the air cap: The height h_g of the air space is calculated using the inverse operation of the spherical cap volume formula. V_g = πh_g²(3R_inner - h_g) / 3 In the formula, R_inner is the inner radius of the shell wall; 4) Interface area: Inner wall surface - gas contact area A_ex = 2πR_inner × h_g, unit m 2 ; The inner wall surface-liquid contact area A_wet = A_inner - A_ex, in meters. 2 A_inner is the inner surface area of ​​the shell wall; The solid-liquid interface area A_ls and the solid-gas interface area A_sg are calculated based on the solid immersion depth.

7. The transient calculation method for the temperature field of a phase change capsule based on a thermal network as described in claim 1, characterized in that, Construct a heat transfer calculation model between the nodes: The heat transfer calculation model includes formulas for calculating the heat transfer rate of the inner wall surface to gas, the heat transfer rate of the inner wall surface to gas radiation, the heat transfer rate of the inner wall surface to liquid convection, the heat transfer rate of the liquid-solid interface convection, the heat transfer rate of the wall surface to solid contact surface, the heat transfer rate of the gas-solid interface, and the heat transfer rate of the solid surface to the solid core.

8. A transient calculation system for the temperature field of a phase change capsule based on a thermal network, characterized in that, include: The physical model building module is used to construct a physical model of the phase change capsule based on the layered structure inside the capsule under the action of gravity, with a gas space at the top and liquid and solid working fluids in the rest. The solid working fluid floats in the liquid working fluid, and its position depends on the density difference between the solid and liquid phases and the current solid-liquid mass distribution. The module initializes the parameters, including the outer radius, wall thickness and inner radius of the capsule shell, the filling rate of the capsule cavity, the phase change temperature and the latent heat of phase change. The computational model building module is used to build a thermal network model with at least four nodes, including: building a heat capacity calculation model for each node, building a geometric parameter calculation model for each node, and building a heat transfer calculation model between each node. The four nodes are shell node, gas node, liquid node, and solid node. The phase change processing module is used to divide the phase change process into three stages: Preheating stage: All heat on the solid surface is used for heating, no phase change occurs, and the solid surface temperature is treated as an unknown variable in the solution. A solver is used to solve the four-node coupled heat transfer equations and outputs the transient temperature values ​​of each node. ； In the formula, Let be the transient temperature value of the i-th node, and represent the temperature change value of the i-th node within one time step. The net heat transfer rate is calculated using the heat transfer calculation model associated with the i-th node. For time steps, The heat capacity of the i-th node is calculated from the heat capacity calculation model of each node. Melting stage: The solid surface temperature is fixed at the phase transition temperature. The four-node coupled heat transfer equations are solved using a solver. The enthalpy of the two-phase mixture is calculated according to the net heat flow of the gas and liquid phases. The solid and liquid mass and volume are updated, and the transient temperature values ​​of each node are output. Complete liquefaction stage: Solids disappear, liquid nodes directly exchange heat with the shell wall. The heat transfer coefficient is calculated using the natural convection correlation inside the Churchill-Chu sphere. The four-node coupled heat transfer equations are solved using a solver, and the transient temperature values ​​of each node are output. A smooth transition process is applied between the preheating stage and the melting stage of each node, and between the melting stage and the complete liquefaction stage of each node.

9. An electronic device, characterized in that, include: processor; Memory used to store processor-executable instructions; The processor is configured to invoke instructions stored in memory to execute the transient calculation method for the temperature field of the phase change capsule as described in any one of claims 1-7.

10. A computer-readable storage medium having computer program instructions stored thereon, characterized in that, When the computer program instructions are executed by the processor, they implement the transient calculation method for the temperature field of the phase change capsule as described in any one of claims 1-7.

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