Thermal battery activation time simulation prediction method based on level set
By constructing the mobile heat source function of the internal heating system of the thermal battery based on the horizontal set method, the problem of large error in the activation time prediction in the prior art is solved, and the accurate prediction of the activation time of the thermal battery is achieved.
Patent Information
- Application Number
- CN202411888543.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-20
- Publication Date
- 2025-04-25
AI Technical Summary
In the existing thermal battery simulation research, there is a large error in the activation time prediction, which cannot meet the prediction accuracy requirements of fast activation thermal batteries, mainly because the heat source position of the heating system changes with time and the combustion reaction area is ignored.
The moving heat source function of the internal heating system of the thermal battery was constructed by a horizontal set-based method. The solid heat transfer physics interface of COMSOL was used for transient research, and the internal phase change distribution of the thermal battery was analyzed and calculated to obtain the activation time of the thermal battery.
Accurate and reliable prediction of the heat transfer and phase transition process in the activation stage of the thermal battery is achieved, eliminating the error of reaching the melting point as the basis for judging, and improving the accuracy of activation time prediction.
Smart Images
Figure CN119885725A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of thermal batteries, and in particular to a thermal battery activation time simulation prediction method based on a level set. Background Art
[0002] Thermal batteries are primary storage batteries that use insulating solid inorganic salts as electrolytes (such as LiCl+KCl). They have the characteristics of high reliability, short activation time, wide operating temperature range, and high current discharge. Activation time is a key indicator of thermal battery technical requirements. At present, the test method for evaluating the activation time of thermal batteries is mainly completed through the discharge test of thermal batteries. There is a lack of efficient and accurate prediction and analysis methods for the activation time before the test, which is not conducive to the exposure of thermal battery design defects during the design and development process.
[0003] The rapid maneuverability of modern weapons and the rapid ejection of ejection seats place more stringent requirements on the activation speed of thermal batteries, which puts higher requirements on the activation time prediction accuracy in the thermal battery design stage. In existing thermal battery simulation research, for the prediction of thermal battery activation time, the heat source of its internal heating system generally uses a uniform body heat source or a simplified heat source using a dynamic grid method. These two methods ignore the change of the position of the heat source of the heating system over time, as well as the combustion reaction area of the heat source system, which leads to the distortion of the prediction of the temperature change and phase change process of each part of the thermal battery activation stage. In terms of the judgment method of activation time prediction, the existing simulation method uses the average temperature of the electrolyte or the highest temperature reaching the melting point as the judgment basis. This method has a large error and cannot meet the prediction accuracy requirements of fast-activated thermal batteries. Summary of the invention
[0004] In view of the problems existing in the prior art, the present invention provides a method for simulating and predicting the activation time of a thermal battery based on a level set. A transient study is conducted through the solid heat transfer physical field interface of COMSOL, and the internal phase change distribution of the thermal battery is analyzed and calculated to obtain the activation time of the thermal battery.
[0005] The present invention is implemented as follows: a thermal battery activation time simulation prediction method based on level set, comprising the following steps:
[0006] (1) Establishing a thermal battery model including internal structure according to the selected thermal battery model parameters;
[0007] (2) Grid division of the thermal battery complex;
[0008] (3) Define the materials for the thermal battery model and set the phase change domain properties of the positive electrode layer and the electrolyte layer according to the electrolyte material used;
[0009] (4) defining initial values and boundary conditions according to the external working environment of the thermal battery;
[0010] (5) Define the moving heat source function using the level set method and load it into the model
[0011] (6) After solving the problem, the change of phase distribution inside the thermal battery is obtained. By analyzing the conduction time of the electrolyte phase change, the activation time of the thermal battery can be obtained.
[0012] In step (1), a two-dimensional model of a thermal battery including an internal structure is established according to the selected thermal battery model parameters, including: in a geometric module, according to the thermal battery design parameters, a battery shell bottom, a lower insulation, a single cell 1-single cell n, an upper insulation, an ignition sheet, a battery cover, a side insulation, an ignition structure and a battery shell are sequentially constructed from the bottom of the battery upward to form a joint body, wherein each single cell includes a positive electrode layer, a negative electrode layer, an electrolyte layer and a heating sheet layer.
[0013] In step (2), the quadrilateral structured grid is first divided into monomers 1 to n through the edge option of the grid module, and then the insulation structure, ignition plate, battery cover, battery shell bottom and battery shell are divided outwardly by mapping the boundaries formed by them, so that the overall grid of the thermal battery is structured to ensure the efficiency and accuracy of the calculation.
[0014] In step (3), in the material module, the material used for the thermal battery is defined, wherein the battery cover, battery shell, and battery shell bottom are set to stainless steel or titanium alloy, the upper insulation, lower insulation, and side insulation are set to insulation materials, the ignition structure is set to ignition material, and the negative electrode layer and heating plate layer of monomer 1 to monomer n are set to corresponding materials; the positive electrode layer and electrolyte layer of monomer 1 to monomer n are set by the phase change material module in the solid heat transfer physical field, the phase change function adopts the Heaviside function, and the phase change temperature and phase change latent heat are set according to the material properties of the molten salt used for the electrolyte.
[0015] In step (4), in the Initial Values option of the Solid Heat Transfer module, define the initial temperature T0 according to the thermal battery usage conditions; in the Heat Flux option, define the external temperature T ext , convection q on the thermal battery boundary c and radiant heat q r Calculation formula:
[0016] -n·q c =h(T ext -T)
[0017]
[0018] Where h is the equivalent convection heat transfer coefficient, ε is the Stefan-Boltzmann constant, σ is the surface emissivity, T is the finite element temperature, and n is the unit vector.
[0019] In step (5), the model does not consider the detailed chemical reaction of the combustion process of the heating system, but instead uses the level set method to equate it to a mobile heat source;
[0020] The level set Φ of heat source movement is as follows:
[0021]
[0022] Among them, z ig is the axial coordinate of the top ignition piece, v heat and v ig are the burning rates of the heating plate and the ignition plate, respectively; r is the distance from the ignition starting point; and z is the axial coordinate of the center point of the heat source;
[0023] Heat source function Q h The expression is as follows:
[0024] Q h =ρvq h / a
[0025] Where ρ is the heat source density, q h and v are the calorific value and burning rate of the heater respectively, and a is the combustion reaction area.
[0026] First, create variable options in the component definition module and define three variables:
[0027] Variable 1, :x _ foc, this variable is defined by the level set method to determine the location of the heat source at each moment in the transient model. The expression is: (Z ig -y)*v heat / v ig -v heat *t+r;
[0028] Variable 2: f_jud, this variable is used to determine the combustion reaction area at each moment, the expression is: if (abs (x-x_foc)) <= a, 1, 0);
[0029] Variable 3: Q h , this variable is the heat source function, the expression is: f_jud*ρ*v*q h / a;
[0030] Then, load the heat source option in the Solid Heat Transfer Module, select the generalized source and define it as Q h .
[0031] In step (6), the PARDISO solver is used to directly solve the problem, and the thermal battery activation time is obtained based on the transient analysis of the phase change conduction time points of each layer of monomer electrolyte.
[0032] In the study module, add a transient study step, select solid heat transfer as the physics interface, set the output time step range to 1s, and set the time step to 10 -3 s, the solver configuration is selected as full coupling, and the PARDISO solver is used for direct solution. The phase change cloud diagram of the thermal battery is calculated, and the activation time of the thermal battery is determined according to the calculation results.
[0033] The advantages and technical effects of the present invention are as follows: Based on the level set method, the present invention constructs a mobile heat source function for the internal heating system of a thermal battery, which can accurately locate the combustion reaction area of the heat source of the heating system during the simulation process, restore the change process of the position of the heat source of the heating system over time, and make the heat transfer and phase change process of the thermal battery activation stage accurate and reliable. The electrolyte is set as a phase change material, and the phase change of the electrolyte during the activation process is transiently tracked. The time point of the phase change conduction of each layer of electrolyte is used as the activation time, eliminating the error of using the average temperature or the highest temperature of the electrolyte to reach the melting point as the judgment basis for predicting the activation time of the thermal battery, and realizing the accurate prediction of the activation time of the thermal battery. BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Figure 1 is a two-dimensional geometric model of a thermal battery provided by an embodiment of the present invention;
[0035] Figure 2 The thermal battery monomer structure provided by the embodiment of the present invention;
[0036] Figure 3 The thermal battery grid structure provided by the embodiment of the present invention;
[0037] Figure 4 This is a phase change cloud diagram of a thermal battery provided by an embodiment of the present invention. DETAILED DESCRIPTION
[0038] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation methods described herein are only used to explain the present invention and are not used to limit the present invention.
[0039] The present invention discloses a method for simulating and predicting the activation time of a thermal battery based on a level set. The method uses the solid heat transfer physical field interface of COMSOL to conduct transient research, analyze and calculate the phase change distribution inside the thermal battery, and obtain the activation time of the thermal battery. Specifically, the method includes:
[0040] (1) Establish a thermal battery model including an internal structure according to the selected thermal battery model parameters. Specifically, establish a two-dimensional thermal battery model including an internal structure according to the selected thermal battery model parameters. Specifically, in the geometry module, construct the battery shell bottom, lower insulation, cells 1 to 8, upper insulation, ignition sheet, battery cover, side insulation, ignition structure and battery shell in sequence from the bottom of the battery upward according to the thermal battery design parameters to form a joint body, refer to Figure 1 Each monomer includes a positive electrode layer, a negative electrode layer, an electrolyte layer and a heating layer, referring to Figure 2 .
[0041] (2) Mesh the thermal battery complex. Specifically, first use the edge option of the mesh module to perform quadrilateral structured meshing on cells 1 to 8, and then use the boundaries formed to map outward to divide the insulation structure, ignition plate, battery cover, battery shell bottom and battery shell, so that the overall mesh of the thermal battery is structured to ensure the efficiency and accuracy of the calculation. The mesh structure is referenced Figure 3 .
[0042] (3) Define the materials for the thermal battery model, and set the phase change domain properties of the positive electrode layer and the electrolyte layer according to the electrolyte material used. Specifically, in the material module, the material used for the thermal battery is defined, where the battery cover, battery shell, and battery shell bottom are set to stainless steel or titanium alloy, the upper insulation, lower insulation, and side insulation are set to insulation materials, the ignition structure is set to ignition material, and the negative electrode layer and heating plate layer of monomer 1 to monomer 8 are set to corresponding materials; the positive electrode layer and electrolyte layer of monomer 1 to monomer 8 are set through the phase change material module in the solid heat transfer physics field, the phase change function uses the Heaviside function, and the phase change temperature and phase change latent heat are set according to the material properties of the molten salt used for the electrolyte.
[0043] (4) Define the initial values and boundary conditions according to the external working environment of the thermal battery. Specifically, in the Initial Values option of the Solid Heat Transfer module, define its initial temperature T0 according to the thermal battery usage conditions; in the Heat Flux option, define the external temperature T ext , convection q on the thermal battery boundary c and radiant heat q r Calculation formula:
[0044] -n·q c =h(T ext -T)
[0045]
[0046] Where h is the equivalent convection heat transfer coefficient, ε is the Stefan-Boltzmann constant, σ is the surface emissivity, T is the finite element temperature, and n is the unit vector.
[0047] (5) The mobile heat source function is defined by the level set method and loaded into the model. Specifically, the model does not consider the detailed chemical reaction of the combustion process of the heating system, but equates it to a mobile heat source by the level set method;
[0048] The level set Φ of heat source movement is as follows:
[0049]
[0050] Among them, z ig is the axial coordinate of the top ignition piece, v heat and v ig are the burning rates of the heating plate and the ignition plate, respectively; r is the distance from the ignition starting point; and z is the axial coordinate of the center point of the heat source;
[0051] Heat source function Q h The expression is as follows:
[0052] Q h =ρvq h / a
[0053] Where ρ is the heat source density, q h and v are the calorific value and burning rate of the heater respectively, and a is the combustion reaction area.
[0054] (6) Load the heat source in the solid heat transfer of the model. Specifically, first, create a variable option in the component definition module and define three variables:
[0055] Variable 1, :x _ foc, this variable is defined by the level set method to determine the location of the heat source at each moment in the transient model. The expression is: (Z ig -y)*v heat / v ig -v heat *t+r;
[0056] Variable 2: f_jud, this variable is used to determine the combustion reaction area at each moment, the expression is: if (abs (x-x_foc)) <= a, 1, 0);
[0057] Variable 3: Q h , this variable is the heat source function, the expression is: f_jud*ρ*v*q h / a;
[0058] Then, load the heat source option in the Solid Heat Transfer Module, select the generalized source and define it as Q h .
[0059] (7) Use the PARDISO solver to solve directly. Specifically, add a transient study step in the study module, select solid heat transfer as the physical field interface, set the output time step range to 1s, and set the time step to 10 -3 s, the solver configuration is selected as fully coupled, and the PARDISO solver is used for direct solution.
[0060] (8) After solving, the phase distribution change inside the thermal battery is obtained as follows: Figure 4 As shown, the electrolyte phase change conduction moment is analyzed: the calculation results show that the electrolyte begins to melt 50ms after the battery is activated, and the electrolyte is basically completely melted at 226ms. At this time, the electrolytes of all monomers are melted and conductive. According to the transient analysis of the phase change conduction time points of each layer of monomer electrolyte, the thermal battery activation time is obtained: at 226ms, the battery has full load-carrying capacity, so the activation time of this type of thermal battery is predicted to be 226ms.
[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.
Claims
1. A thermal battery activation time simulation prediction method based on level set, characterized in that: The following steps are involved: (1) Establishing a thermal battery model including internal structure according to the selected thermal battery model parameters; (2) Grid division of the thermal battery complex; (3) Define the materials for the thermal battery model and set the phase change domain properties of the positive electrode layer and the electrolyte layer according to the electrolyte material used; (4) defining initial values and boundary conditions according to the external working environment of the thermal battery; (5) Define the moving heat source function using the level set method and load it into the model (6) After solving the problem, the change of phase distribution inside the thermal battery is obtained. By analyzing the conduction time of the electrolyte phase change, the activation time of the thermal battery can be obtained.
2. The thermal battery activation time simulation prediction method based on level set according to claim 1 is characterized in that: In step (1), a two-dimensional model of a thermal battery including an internal structure is established according to the selected thermal battery model parameters, including: in a geometric module, according to the thermal battery design parameters, a battery shell bottom, a lower insulation, a single cell 1-single cell n, an upper insulation, an ignition sheet, a battery cover, a side insulation, an ignition structure and a battery shell are sequentially constructed from the bottom of the battery upward to form a joint body, wherein each single cell includes a positive electrode layer, a negative electrode layer, an electrolyte layer and a heating sheet layer.
3. The thermal battery activation time simulation prediction method based on level set according to claim 2 is characterized in that: In step (2), the quadrilateral structured grid is first divided into monomers 1 to n through the edge option of the grid module, and then the insulation structure, ignition plate, battery cover, battery shell bottom and battery shell are divided outwardly by mapping the boundaries formed by them, so that the overall grid of the thermal battery is structured to ensure the efficiency and accuracy of the calculation.
4. The thermal battery activation time simulation prediction method based on level set according to claim 3 is characterized in that: In step (3), in the material module, the material used for the thermal battery is defined, wherein the battery cover, battery shell, and battery shell bottom are set to stainless steel or titanium alloy, the upper insulation, lower insulation, and side insulation are set to insulation materials, the ignition structure is set to ignition material, and the negative electrode layer and heating plate layer of monomer 1 to monomer n are set to corresponding materials; the positive electrode layer and electrolyte layer of monomer 1 to monomer n are set by the phase change material module in the solid heat transfer physical field, the phase change function adopts the Heaviside function, and the phase change temperature and phase change latent heat are set according to the material properties of the molten salt used for the electrolyte.
5. The method for simulating and predicting thermal battery activation time based on level sets according to claim 4 is characterized in that: In step (4), in the Initial Values option of the Solid Heat Transfer module, define the initial temperature T0 according to the thermal battery usage conditions; in the Heat Flux option, define the external temperature T ext , convection q on the thermal battery boundary c and radiant heat q r Calculation formula: -n·q c =h(T ext -T) Where h is the equivalent convection heat transfer coefficient, ε is the Stefan-Boltzmann constant, σ is the surface emissivity, T is the finite element temperature, and n is the unit vector.
6. The thermal battery activation time simulation prediction method based on level set according to claim 5 is characterized in that: In step (5), the model does not consider the detailed chemical reaction of the combustion process of the heating system, but instead uses the level set method to equate it to a mobile heat source; The level set Φ of heat source movement is as follows: Among them, z ig is the axial coordinate of the top ignition piece, v heat and v ig are the burning rates of the heating plate and the ignition plate, respectively; r is the distance from the ignition starting point; and z is the axial coordinate of the center point of the heat source; Heat source function Q h The expression is as follows: Q h =ρvq h / a Where ρ is the heat source density, q h and v are the calorific value and burning rate of the heater respectively, and a is the combustion reaction area.
7. The thermal battery activation time simulation prediction method based on level set according to claim 6 is characterized in that: First, create variable options in the component definition module and define three variables: Variable 1, :x _ foc, this variable is defined by the level set method to determine the location of the heat source at each moment in the transient model. The expression is: (Z ig -y)*v heat / v ig -v heat *t+r; Variable 2: f_jud, this variable is used to determine the combustion reaction area at each moment, the expression is: if (abs (x-x_foc)) <= a, 1, 0); Variable 3: Q h , this variable is the heat source function, the expression is: f_jud*ρ*v*q h / a; Then, load the heat source option in the Solid Heat Transfer Module, select the generalized source and define it as Q h .
8. The method for simulating and predicting thermal battery activation time based on level sets according to claim 6 is characterized in that: In step (6), the PARDISO solver is used to directly solve the problem, and the thermal battery activation time is obtained based on the transient analysis of the phase change conduction time points of each layer of monomer electrolyte.
9. The thermal battery activation time simulation prediction method based on level set according to claim 8 is characterized in that: Add a transient study step in the study module, select Solid Heat Transfer as the physics interface, set the output time step range to 1s, and set the time step to 10 -3 s, the solver configuration is selected as full coupling, and the PARDISO solver is used for direct solution. The phase change cloud diagram of the thermal battery is calculated, and the activation time of the thermal battery is determined according to the calculation results.