Thermal simulation method for thermal battery

Abstract

The application discloses a thermal simulation method of a thermal battery and belongs to the technical field of thermal batteries. The method is used for solving the problems existing in the simulation research of the thermal battery. The method comprises the following steps: S1, establishing a three-dimensional simulation model of the thermal battery; S2, loading the three-dimensional simulation model of the thermal battery into COMSOL software; S3, designing a control equation of a heat transfer physical model of the thermal battery; S4, designing a thermal equilibrium of a boundary of the thermal battery; S5, performing network division on the three-dimensional model of the thermal battery and setting a boundary condition; and S6, performing simulation calculation to obtain a temperature distribution nephogram of an activation process of the thermal battery and a stress distribution nephogram of the thermal battery.

Description

Technical Field

[0001] The invention relates to a thermal battery thermal simulation method based on COMSOL software, and belongs to the technical field of thermal batteries. Background Art

[0002] A thermal battery is a heat-activated primary power reserve that uses the battery's own heating system to heat and melt a non-conductive solid salt electrolyte into an ionic conductor, which then enters its operating state. Due to their high-power discharge, high specific energy and power, wide operating temperature range, long storage life, rapid and reliable activation, and compact structure, thermal batteries are ideal power sources for modern weapons and hold a crucial position in military power supply systems.

[0003] The basic structure of a thermal battery can be found in Figure 1 As shown, the battery stack 4 comprises a battery cover 1, an upper insulation component 2, a side insulation layer 3, a battery stack 4, a battery casing 5, a lower insulation component 6, and a battery bottom 7. The battery stack 4 is composed of multiple single cells 8 connected in series or parallel. The single cells 8 comprise a current collector 8-1, a separator 8-2, graphite paper 8-3, a heater 8-3, an anode 8-4, and a cathode 8-5. The stack is assembled in a stacked manner and is the core of a thermal battery. The cathode of a thermal battery is typically made of an active metal such as lithium, magnesium, or calcium; the anode is made of a high-performance oxide or salt such as vanadium pentoxide, iron disulfide, lead sulfate, or calcium chromate; and the electrolyte is a mixture of molten salt and fine clay, typically LiCl-KCl. At room temperature, the electrolyte inside a thermal battery is a non-conductive solid. The active electrode material and the electrolyte do not chemically react with each other, resulting in a non-operating state and minimal self-discharge. When in use, electric current is used to ignite the electric ignition head, which ignites the pyrotechnic heat source inside the battery, causing the internal temperature of the battery to rise rapidly to about 500°C, melting the electrolyte and forming a high-conductivity ion conductor, thereby activating the battery and supplying the required DC voltage and current to the electrical components in a short time.

[0004] After the thermal battery is activated, the voltage rises rapidly from 0V to the peak voltage. As the heat from the internal pyrotechnic heating source dissipates and the active electrode material is exhausted, the voltage eventually drops to 0V after a period of time. Figure 2 .

[0005] The internal temperature of a thermal battery must be maintained within a certain range for proper operation. This period of time is called its thermal life. Using lightweight, porous, and efficient insulation materials can extend the thermal life of a thermal battery. t1 is the activation time, t2 is the time it takes for the temperature to reach its maximum value, and t3 is the operating time. U1, U2, and U3 are the lower, maximum, and upper voltage limits for normal operation.

[0006] Since thermal design plays a vital role in the working life and performance of thermal batteries, thermal simulation of thermal batteries (including heat transfer process and heat distribution) has great scientific and practical value.

[0007] Research status of thermal batteries:

[0008] In 2008, Zhao Jinfeng and others used ANSYS software to simulate the transient heat distribution of the LiSi / FeS2 thermal battery during the discharge process. Based on the node temperature balance theory, they compared the temperature distribution of the upper, middle and lower parts of the battery stack with that of the actual discharge process of the thermal battery, and proved the practicality and feasibility of using ANSYS to simulate the LiSi / FeS2 thermal battery.

[0009] In 2012, Lan Wei and others briefly introduced the process of using ANSYS to perform thermal simulation on thermal batteries, and conducted a preliminary analysis on specific thermal batteries, proving that thermal simulation has guiding significance for battery thermal design.

[0010] In 2018, Wang Chao et al. simulated the activation process of electrically activated thermal batteries using ANSYS software, and proposed a simulation calculation method for the activation time of such thermal batteries. They also presented the internal temperature distribution characteristics of the thermal battery activation process, and compared the electrolyte melting processes of two different types of thermal batteries. It was shown that the temperature distribution trends of the two thermal batteries during the electrolyte melting process were consistent, such as Figure 3 and Figure 4 The cloud diagram shows the temperature distribution of two types of thermal batteries, battery No. 1 and battery No. 2, changing with time. After calculation, the simulation results of the activation time of the two thermal batteries are basically consistent with the measured values.

[0011] In 2020, Ran Ling and others used the ANSYS platform to decompose the entire working process of the thermal battery into appropriate working conditions and added each heat source according to the working stage, achieving a high-precision heat transfer simulation analysis of the entire process of thermal battery activation and discharge. By comparing the simulated and experimental values ​​of the temperature at two test points (1# and 2#) on the battery shell, the accuracy of the model was verified. The comparison curves are as follows: Figure 5 shown.

[0012] In the same year, Ye Danhong et al. used COMSOL to establish a two-dimensional axisymmetric thermal battery cell simulation model, simulating the activation time and surface temperature change process of the thermal battery at +60°C and -30°C, and gave a comparison chart of the measured and simulated values ​​of the battery shell temperature before and after the model correction, as shown in the figure. Figure 6 and Figure 7 As shown in the figure, the high temperature corresponds to +60°C and the low temperature corresponds to -30°C. Compared with the three-dimensional model, the calculation amount is greatly reduced while ensuring the simulation accuracy.

[0013] In summary, the research results on the simulation of thermal batteries are still not rich enough. However, based on the rapid development of numerical simulation technology and relying on mature numerical simulation platforms, a model for the simulation of the entire process of thermal batteries has been initially established, providing a basis for more comprehensive research. However, there are still great deficiencies in the research on the comprehensive working mechanism of thermal batteries and the changing characteristics of the internal physical properties of thermal batteries during the working process of thermal batteries. Summary of the Invention

[0014] In view of the problems existing in existing thermal battery simulation research, the present invention provides a thermal simulation method for thermal batteries.

[0015] The thermal simulation method of the thermal battery of the present invention comprises the following steps:

[0016] S1. Establish a three-dimensional simulation model of a thermal battery;

[0017] S2, loading the thermal battery three-dimensional simulation model into COMSOL software;

[0018] S3. The thermal battery heat transfer physical model is designed according to the following control equations:

[0019]

[0020] Where ρ is the density of each material of the thermal battery, C p is the specific heat capacity of each material, T is the temperature inside the thermal battery, and t is the time from the ignition of the thermal battery. is the gradient operator, k is the thermal conductivity of each material, χ is the electrolyte mass fraction, Δ is the difference operator, H L is the latent heat of electrolyte phase change, w is the mass fraction of solidified electrolyte, i A is the surface current density inside the thermal battery, R is the internal resistance of the thermal battery, Q rh It is the heat of chemical reaction during the operation of thermal battery;

[0021] S4. Thermal battery boundary is designed to achieve thermal balance;

[0022] S5. Perform network division on the three-dimensional model of the thermal battery and set boundary conditions;

[0023] S6. Perform simulation calculations to obtain a temperature distribution cloud map of the thermal battery activation process and a stress distribution cloud map of the thermal battery.

[0024] Preferably, the chemical reaction heat Q during the operation of the thermal battery rh Calculate as follows:

[0025]

[0026] Where U is the potential when the electrochemical reaction reaches equilibrium,

[0027] i v is the current volume density in the thermal battery, i v Get it as follows:

[0028]

[0029] Where d is the axial thickness of each component inside the thermal battery.

[0030] Preferably, the design process for achieving thermal balance of the thermal battery boundary in step S4 is:

[0031] S41. Natural convection heat transfer is carried out between the thermal battery and the environment, and the heat transfer amount is calculated as follows:

[0032] Q h =h w (T w -T s )A s

[0033] Where Q h is the heat exchange between the thermal battery and the environment, h w is the convection heat transfer coefficient between the thermal battery and the environment, T w is the ambient temperature, T s is the surface temperature of the thermal battery, A s is the effective area of ​​convective heat transfer between the thermal battery and the environment;

[0034] S42, the radial direction of the battery assembly is taken as the x direction, and the longitudinal direction of the battery assembly is taken as the y direction, and the effective thermal conductivity k in the x direction is calculated respectively. eff(x) and the effective thermal conductivity k in the y direction eff(y) :

[0035]

[0036] Where, l j is the radial thickness of the thermal battery assembly, k j is the radial thermal conductivity of the thermal battery assembly, l i is the axial thickness of the thermal battery assembly, k i is the axial thermal conductivity of the thermal battery assembly;

[0037] S43. The relationship equation for achieving thermal equilibrium at the thermal battery boundary according to step S41 and step S42 is designed as:

[0038]

[0039] Where, represents a radial unit vector.

[0040] Preferably, the boundary conditions in step S5 are set as follows:

[0041] Condition 1: Only heat conduction and contact thermal resistance between different components are considered inside the battery. The contact thermal resistance is set to 0.001K·m 2 / W;

[0042] Condition 2: Initial temperature setting: There is natural convection heat exchange between the thermal battery and the environment. Set the ambient temperature T w =293.15K; the initial temperature of each part of the thermal battery is equal to the ambient temperature;

[0043] Condition 3: Ignore radiation heat transfer in the entire heat transfer process

[0044] Condition 4: Activation process heat source setting: The heating power is set to the internal heat source evenly distributed inside the heating plate, and the heating time is 0 to 0.5s; according to the density of the heating plate 2.88g / cm 3 And the calorific value is 1084J / g to obtain the average heat value of 6243840000W / m 3 , that is, the activation process heat source S h =6243840000W / m 3 ;

[0045] Condition 5: Symmetric boundary condition: The central axis should be set to a symmetric boundary condition, that is, when the thermal battery radius r = 0, it satisfies Relational expression.

[0046] Preferably, the insulating and heat-preserving layer in the thermal battery is composed of fiber felt, QNJ nano thermal insulation paper, mica tape and aerogel stacked in sequence; the shell material of the thermal battery is set to stainless steel.

[0047] Beneficial effects of the present invention: Compared with the prior art, the physical model adopted by the present invention for thermal battery simulation adds a second phase change latent heat, a third Joule heat and a fourth chemical reaction heat. The heat transfer model is more complete and comprehensive, making the simulation results more referenceable and providing support for the technical improvement of thermal batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a schematic diagram of the thermal battery geometry, where Figure 1 (a) is the overall diagram, Figure 1 (b) is a schematic diagram of the structure of a single battery;

[0049] Figure 2 This is a schematic diagram of the typical output voltage of a thermal battery;

[0050] Figure 3 It is the cloud map of the temperature distribution of thermal battery No. 1 changing with time, and the cloud maps at 0s, 0.1s and 0.6s are given respectively;

[0051] Figure 4It is the cloud diagram of the temperature distribution of thermal battery No. 2 changing with time, and the cloud diagrams at 0s, 0.1s and 0.6s are given respectively;

[0052] Figure 5 is a comparison chart of simulation results and measured data, where Figure 5 (a) is a cloud map, Figure 5 (b) is a curve graph;

[0053] Figure 6 This is the battery case temperature curve before model correction at +60℃ and -30℃;

[0054] Figure 7 It is the battery case temperature curve after the +60℃ and -30℃ model correction;

[0055] Figure 8 is a flow chart of the thermal simulation method of the thermal battery of the present invention;

[0056] Figure 9 The contact thermal resistance is 0.0001K·m 2 Temperature distribution cloud diagram of thermal battery activation process at 100W;

[0057] Figure 10 The contact thermal resistance is 0.0001K·m 2 Temperature distribution cloud diagram of thermal battery activation process at 100W;

[0058] Figure 11 is the minimum temperature of the electrolyte in the middle unit cell T emin Curve change comparison chart;

[0059] Figure 12 is the average temperature of the electrolyte in the middle unit cell T eave Curve comparison chart;

[0060] Figure 13 is the average anode temperature T in the middle unit cell pa Curve comparison chart;

[0061] Figure 14 is the average cathode temperature T in the middle unit cell na Curve comparison chart;

[0062] Figure 15 is the average temperature of the current collector in the middle unit cell T ca Curve comparison chart;

[0063] Figure 16 is the average temperature of the single heating plate in the middle unit cell T have Curve comparison chart;

[0064] Figure 17 is the average substrate temperature T in the middle unit cell baCurve comparison chart;

[0065] Figure 18 is the average temperature of the electrolyte in the middle unit cell T eave Curve comparison chart;

[0066] Figure 19 is the average substrate temperature T in the middle unit cell ba Curve comparison chart;

[0067] Figure 20 is the average temperature of the current collector in the middle unit cell T ca Curve comparison chart;

[0068] Figure 21 is the average anode temperature T in the middle unit cell pa Curve comparison chart;

[0069] Figure 22 is the average cathode temperature T in the middle unit cell na Curve comparison chart;

[0070] Figure 23 is the average temperature of the heating plate in the middle unit cell T have Curve comparison chart. DETAILED DESCRIPTION

[0071] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0072] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0073] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0074] Specific implementation method 1: Figures 8 to 23 This embodiment describes a thermal simulation method for a thermal battery, which includes the following steps:

[0075] S1. Establish a three-dimensional simulation model of a thermal battery;

[0076] S2, loading the thermal battery three-dimensional simulation model into COMSOL software;

[0077] S3. The thermal battery heat transfer physical model is designed according to the following control equations:

[0078]

[0079] Where ρ is the density of each material of the thermal battery, C p is the specific heat capacity of each material, T is the temperature inside the thermal battery, and t is the time from the ignition of the thermal battery. is the gradient operator, k is the thermal conductivity of each material, χ is the electrolyte mass fraction, Δ is the difference operator, H L is the latent heat of electrolyte phase change, w is the mass fraction of solidified electrolyte, i A is the surface current density inside the thermal battery, R is the internal resistance of the thermal battery, Q rh It is the heat of chemical reaction during the operation of thermal battery;

[0080] S4. Thermal battery boundary is designed to achieve thermal balance;

[0081] S5. Perform network division on the three-dimensional model of the thermal battery and set boundary conditions;

[0082] S6. Perform simulation calculations to obtain a temperature distribution cloud map of the thermal battery activation process and a stress distribution cloud map of the thermal battery.

[0083] First, the structure of the thermal battery can be seen in Figure 1 As shown, thermal batteries are generally divided into cup-type structures and sheet-type structures according to their structures. The main structure includes a battery cover 1, an upper insulating and heat-preserving component 2, a side insulating and heat-preserving layer 3, a battery stack 4, a battery shell 5, a lower insulating and heat-preserving component 6 and a battery bottom 7. The battery stack 4 is composed of multiple single cells 8 connected in series or in parallel, and the single cell 8 is composed of a current collector 8-1, a diaphragm 8-2, a graphite paper 8-3, a heating plate 8-3, an anode 8-4 and a cathode 8-5. The battery stack is composed of a stacked assembly method, and the battery stack is the core of the thermal battery.

[0084] The specific embodiment of the thermal battery geometric structure parameters is shown in Table 1:

[0085] Table 1

[0086]

[0087]

[0088] Import the above-mentioned thermal battery three-dimensional model and specific geometric dimensions into COMSOL software.

[0089] The present invention adopts an innovative thermal battery heat transfer physical model, whose control equation is:

[0090]

[0091] Compared with the existing technology, the second term phase change latent heat, the third term Joule heat and the fourth term chemical reaction heat are added, and the heat transfer model is more complete and comprehensive. The definitions and units of the variables in the formula are shown in Table 2:

[0092] Table 2

[0093]

[0094] The left side of the equal sign in the control equation is the heat generated by temperature change; the first term on the right side of the equal sign is the heat conduction term; the second term is the latent heat during the phase change of the electrolyte, which only exists at the location where the electrolyte undergoes phase change and is zero everywhere else; the third term is the Joule heat generated during the operation of the thermal battery, which only exists at the location where the current passes and is zero everywhere else; the fourth term is the chemical reaction heat generated by the electrochemical reaction during the operation of the thermal battery, which is non-zero only at the location where the electrochemical process occurs.

[0095] Chemical reaction heat Q during the operation of thermal batteries rh Calculate as follows:

[0096]

[0097] Where U is the potential when the electrochemical reaction reaches equilibrium, V,

[0098] i v is the current volume density in the thermal battery, A / m 3 ,i v Get it as follows:

[0099]

[0100] Where d is the axial thickness of each component inside the thermal battery, m.

[0101] The design process for achieving thermal balance at the thermal battery boundary in step S4 is as follows:

[0102] S41. Natural convection heat transfer is carried out between the thermal battery and the environment, and the heat transfer amount is calculated as follows:

[0103] Q h =h w (T w -T s )A s

[0104] Where Q h is the heat exchange between the thermal battery and the environment, W, h w is the convection heat transfer coefficient between the thermal battery and the environment, W / (m2·K), T w is the ambient temperature, K, T s is the surface temperature of the thermal battery, K, A sis the effective area of ​​convective heat transfer between the thermal battery and the environment, m 2 ;

[0105] S42, the radial direction of the battery assembly is taken as the x direction, and the longitudinal direction of the battery assembly is taken as the y direction, and the effective thermal conductivity k in the x direction is calculated respectively. eff(x) and the effective thermal conductivity k in the y direction eff(y) :

[0106]

[0107] Where, l j is the radial thickness of the thermal battery assembly, m, k j is the radial thermal conductivity of the thermal battery assembly, W / (m·K), l i is the axial thickness of the thermal battery assembly, m, k i is the axial thermal conductivity of the thermal battery assembly, W / (m·K);

[0108] S43. The relationship equation for achieving thermal equilibrium at the thermal battery boundary according to step S41 and step S42 is designed as:

[0109]

[0110] Where, represents a radial unit vector.

[0111] The combustion process of the "single heater" is completely released at a constant power level within 0.5 seconds of battery operation. After the electrode temperature reaches the specified temperature (436°C), the "diaphragm" begins to absorb heat and melt. After the battery stack (including the positive electrode, diaphragm, negative electrode, current collector, and single heater) reaches its maximum temperature, the battery begins to slowly dissipate heat to the surrounding environment. After the electrode temperature drops to the specified temperature, the "diaphragm" begins to solidify and release heat, and battery operation is complete. The material configuration of each component of the thermal battery is shown in Table 3, and the physical properties of each component are shown in Table 4. The insulation layer of the thermal battery is composed of fiber felt, QNJ nano-insulation paper, mica tape, and aerogel in this order. The thermal battery shell is made of stainless steel.

[0112] Table 3

[0113]

[0114] Table 4

[0115]

[0116] Based on the above settings, the boundary conditions are set in step S5 as follows:

[0117] Condition 1: Only heat conduction and contact thermal resistance between different components are considered inside the battery. The contact thermal resistance is set to 0.001K·m2 / W;

[0118] Condition 2: Initial temperature setting: There is natural convection heat exchange between the thermal battery and the environment. Set the ambient temperature T w =293.15K; the initial temperature of each part of the thermal battery is equal to the ambient temperature;

[0119] Condition 3: Ignore radiation heat transfer in the entire heat transfer process

[0120] Condition 4: Activation process heat source setting: The heating power is set to the internal heat source evenly distributed inside the heating plate, and the heating time is 0 to 0.5s; according to the density of the heating plate 2.88g / cm 3 And the calorific value is 1084J / g to obtain the average heat value of 6243840000W / m 3 , that is, the activation process heat source S h =6243840000W / m 3 ;

[0121] Condition 5: Symmetric boundary condition: The central axis should be set to a symmetric boundary condition, that is, when the thermal battery radius r = 0, it satisfies Relational expression.

[0122] The first boundary condition is the setting of contact thermal resistance, which shows the importance of contact thermal resistance.

[0123] The internal structures of a thermoelectric battery's sheet-type cells generate contact thermal resistance when they come into contact. Contact thermal resistance refers to the reduction in heat transfer efficiency caused by imperfections in the contact surface (such as microscopic unevenness and air gaps). In a thermoelectric battery, the contact thermal resistance between the anode, electrolyte, and cathode sheets can affect the battery's overall thermal efficiency.

[0124] The magnitude of contact thermal resistance depends on factors such as the nature of the contact surface, pressure, surface roughness, and the thermal conductivity of the contact materials. During thermal battery operation, contact thermal resistance may vary due to factors such as temperature fluctuations, differences in material expansion coefficients, and creep caused by long-term use. The magnitude of contact thermal resistance is difficult to determine precisely because it is affected by multiple factors. During design and manufacturing, contact thermal resistance should be minimized, for example, by optimizing the flatness of the contact surface, using materials with high thermal conductivity, or employing specialized contact structure designs.

[0125] In actual situations, the influence of the contact thermal resistance between the components of the thermal battery on the thermal battery needs to be considered. Figure 9 、 Figure 10 The contact thermal resistance is 0.0001K·m 2 / W when the temperature distribution cloud diagram and contact thermal resistance of the thermal battery activation process are 0.0001K·m 2 / W temperature distribution cloud diagram of the electrochemical reaction process of the thermal battery. Figure 9 (a) to (d) are cloud diagrams at t = 0.1s, 0.5s, 0.6s and 0.9s respectively. Figure 10 (a) to (d) are cloud diagrams at t = 32s, 100s, 500s, and 700s, respectively.

[0126] See also Figure 9 When the thermal battery starts working after being activated, the heat from the heating plate in the thermal battery is quickly transferred to the battery stack over time. Figure 10 As shown in the figure, it can be seen that the temperature of the end of the thermal battery and the temperature inside the thermal battery stack tend to be consistent at a faster rate, indicating that the contact thermal resistance is 0.0001K·m 2 / W, the effect on the heat transfer performance of the thermal battery is small.

[0127] It can be seen that when the contact thermal resistance is 0.0001K·m2 / W, the temperature of the battery stack inside the thermal battery quickly converges to the same value within 1s.

[0128] The influence of contact thermal resistance on heat transfer is analyzed below.

[0129] The first is the influence of contact thermal resistance on the activation process of single battery, such as Figure 11 、 Figure 12 The following are the curves showing the change of the minimum temperature and average temperature of the electrolyte in the unit cell in the middle of the stack with time when the contact thermal resistance is 0.01K·m 2 / W and the ideal state without thermal resistance.

[0130] Whether at average or minimum temperatures, contact thermal resistance significantly prolongs the activation time of thermal batteries, indicating that, once contact thermal resistance reaches a certain level, its impact on thermal battery performance cannot be ignored. On the one hand, heat transfer is weakened, slowing the temperature drop of each component and improving thermal insulation. On the other hand, heat cannot be quickly transferred to the electrolyte, prolonging the activation time. Therefore, the impact of contact thermal resistance on thermal battery performance requires further discussion.

[0131] like Figure 13 、 Figure 14 、 Figure 15 、 Figure 16 and Figure 17 Shown are the comparisons of the time variation curves of the average temperature of each component of the unit cell in the thermal battery with and without thermal resistance.

[0132] During the activation process, the temperature change curve is smoother when there is contact thermal resistance between the components of the unit cell than when there is no thermal resistance. This is because when there is contact thermal resistance, the heat transfer process is hindered, so the temperature changes more slowly.

[0133] The contact thermal resistance not only hinders the heat transfer of the heating plate during the activation process, but also affects the heat transfer performance of the thermal battery during the electrochemical reaction process, and thus affects the thermal life of the thermal battery. Therefore, the influence of contact thermal resistance on the entire working process of the unit cell is analyzed.

[0134] like Figure 18 、 Figure 19 、 Figure 20 、 Figure 21 、 Figure 22 、 Figure 23 The thermal battery contact thermal resistance is 0.01K·m 2 Comparison of the temperature change curves of the electrolyte, substrate, current collector, anode, cathode and heater when the W and thermal batteries have no thermal resistance.

[0135] Similar to the activation process, when contact thermal resistance exists, the temperature change curve during the electrochemical reaction will have an inflection point later, especially for the electrolyte, which will extend the thermal life of the thermal battery to a certain extent. This is because the heat transfer is slower, which weakens the heat transfer between the components inside the battery stack, so the thermal life of the thermal battery is extended. At the same time, the activation time is also extended accordingly. That is, when contact thermal resistance exists, it has both positive and negative effects on the thermal battery.

[0136] In order to avoid adverse effects, the present invention imposes corresponding limitations on the contact thermal resistance.

[0137] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in conjunction with other described embodiments.

Claims

1. A thermal simulation method for a thermal battery, characterized in that: The method comprises the following steps: S1. Establish a three-dimensional simulation model of a thermal battery; S2, loading the thermal battery three-dimensional simulation model into COMSOL software; S3. The thermal battery heat transfer physical model is designed according to the following control equations: Where ρ is the density of each material of the thermal battery, C p is the specific heat capacity of each material, T is the temperature inside the thermal battery, and t is the time from the ignition of the thermal battery. is the gradient operator, k is the thermal conductivity of each material, χ is the electrolyte mass fraction, Δ is the difference operator, H L is the latent heat of electrolyte phase change, w is the mass fraction of solidified electrolyte, i A is the surface current density inside the thermal battery, R is the internal resistance of the thermal battery, Q rh It is the heat of chemical reaction during the operation of thermal battery; S4. Thermal battery boundary is designed to achieve thermal balance; S5. Perform network division on the three-dimensional model of the thermal battery and set boundary conditions; S6. Perform simulation calculations to obtain a temperature distribution cloud map during the thermal battery activation process and a stress distribution cloud map of the thermal battery; The design process of achieving thermal balance at the thermal battery boundary in step S4 is as follows: S41. Natural convection heat transfer is carried out between the thermal battery and the environment, and the heat transfer amount is calculated as follows: Q h =h w (T w -T s )A s Where Q h is the heat exchange between the thermal battery and the environment, h w is the convection heat transfer coefficient between the thermal battery and the environment, T w is the ambient temperature, T s is the surface temperature of the thermal battery, A s is the effective area of ​​convective heat transfer between the thermal battery and the environment; S42, the radial direction of the battery assembly is taken as the x direction, and the longitudinal direction of the battery assembly is taken as the y direction, and the effective thermal conductivity k in the x direction is calculated respectively. eff(x) and the effective thermal conductivity k in the y direction eff(y) : Where, l j is the radial thickness of the thermal battery assembly, k j is the radial thermal conductivity of the thermal battery assembly, l i is the axial thickness of the thermal battery assembly, k i is the axial thermal conductivity of the thermal battery assembly; S43. The relationship equation for achieving thermal equilibrium at the thermal battery boundary according to step S41 and step S42 is designed as: Where, represents the radial unit vector; In step S5, the boundary conditions are set as follows: Condition 1: Only heat conduction and contact thermal resistance between different components are considered inside the battery. The contact thermal resistance is set to 0.001K·m 2 / W; Condition 2: Initial temperature setting: There is natural convection heat exchange between the thermal battery and the environment. Set the ambient temperature T w =293.15K; the initial temperature of each part of the thermal battery is equal to the ambient temperature; Condition 3: Ignore the radiation heat transfer in the entire heat transfer process; Condition 4: Activation process heat source setting: The heating power is set to the internal heat source evenly distributed inside the heating plate, and the heating time is 0 to 0.5s; according to the density of the heating plate 2.88g / cm 3 And the calorific value is 1084J / g to obtain the average heat value of 6243840000W / m 3 , that is, the activation process heat source S h =6243840000W / m 3 ; Condition 5: Symmetric boundary condition: The central axis should be set to a symmetric boundary condition, that is, when the thermal battery radius r = 0, it satisfies Relational expression.

2. The thermal simulation method of a thermal battery according to claim 1, characterized in that: Chemical reaction heat Q during the operation of thermal batteries rh Calculate as follows: Where U is the potential when the electrochemical reaction reaches equilibrium, i v is the current volume density in the thermal battery, i v Get it as follows: Where d is the axial thickness of each component inside the thermal battery.

3. The thermal simulation method of a thermal battery according to claim 1, characterized in that: The insulating layer in the thermal battery is composed of fiber felt, QNJ nano thermal insulation paper, mica tape and aerogel stacked in sequence; the shell material of the thermal battery is set to stainless steel.

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