Thermoelectric device analysis method considering variable-temperature elastic-plastic mechanical properties of thermoelectric material

Abstract

The invention provides a thermoelectric device analysis method considering the variable-temperature elastic-plastic mechanical property of a thermoelectric material, and the method comprises the steps: firstly obtaining a real variable-temperature mechanical property curve of the thermoelectric material in a set temperature range through a performance experiment test, and carrying out the fitting to obtain a variable-temperature damage model of the thermoelectric material; then establishing a thermoelectric device model in finite element software, and defining material attributes of each component; carrying out bearing performance simulation on the hot arm component to obtain a stress-strain response simulation curve; comparing the stress-strain response simulation curve with the real variable-temperature mechanical property curve, and judging whether the finite element simulation process is accurate or not; thermal field boundary conditions and load boundary conditions of all components of the thermoelectric device are set, design parameters are adjusted, the bearing performance and damage of the adjusted thermoelectric device are analyzed, and the thermoelectric device configuration with the optimal performance is selected. According to the method, the real mechanical response of the thermoelectric material in a high-temperature and high-load service environment is considered, and the structure optimization design of the thermoelectric device is realized.

Description

Technical Field

[0001] The invention relates to the field of performance analysis and structural design of thermoelectric devices, and in particular to a thermoelectric device analysis method that takes into account the temperature-dependent elastic-plastic mechanical properties of thermoelectric materials. Background Art

[0002] As fossil energy shortages and environmental pollution become more prominent, energy diversification and efficient multi-level utilization have become important technical approaches to systematically solve energy and environmental problems. As a green energy technology, thermoelectric conversion technology has attracted widespread attention from industry and academia.

[0003] Thermal power generation technology uses the Seebeck effect of materials to convert thermal energy into electrical energy under the action of temperature gradients. However, when serving in a large temperature difference environment, thermoelectric devices are very prone to thermal arm material damage, resulting in reduced device load-bearing capacity and performance degradation. Current research on thermoelectric materials is mainly focused on improving their thermal power generation performance indicators, while relatively few studies have considered the mechanical properties of thermoelectric materials in high-temperature environments (such as thermal expansion coefficient and elastic modulus). This means that existing thermoelectric device design methods can only analyze and optimize thermoelectric materials as linear elastic models, making it difficult to accurately evaluate and predict their actual load-bearing and failure behaviors in high-temperature and high-pressure service environments. Summary of the invention

[0004] In order to overcome the problems existing in the prior art, the present invention proposes a thermoelectric device analysis method taking into account the variable temperature elastic-plastic mechanical properties of thermoelectric materials. Combined with the special needs of thermoelectric devices in high temperature and high load service environments, the variable temperature mechanical properties of thermoelectric materials are fully considered, and a thermoelectric device analysis model that simulates service behavior is established to improve the service stability of thermoelectric devices and promote the engineering application of thermoelectric devices.

[0005] The technical solution of the present invention is:

[0006] A thermoelectric device analysis method considering the temperature-dependent elastic-plastic mechanical properties of thermoelectric materials comprises the following steps:

[0007] Step 1: Through performance experimental testing, obtain the real temperature-dependent mechanical performance curve of the thermoelectric material to be studied within the set temperature range;

[0008] Step 2: Using the real temperature-dependent mechanical property curve of the thermoelectric material to be studied within a set temperature range obtained in step 1, a temperature-dependent damage model of the thermoelectric material to be studied is obtained by fitting;

[0009] Step 3: Create or import the thermoelectric device model to be analyzed in the finite element software;

[0010] Step 4: defining the material properties of each component in the thermoelectric device model in finite element software, wherein the material of the hot arm component is the thermoelectric material to be studied in step 1, and the material properties of the thermoelectric material to be studied are defined by the variable temperature damage model obtained in step 2;

[0011] Step 5: In finite element software, the load-bearing performance of the hot arm component in the thermoelectric device model is simulated, and failure judgment is performed on each unit of the hot arm component to obtain the stress-strain response simulation curve of the hot arm component at several temperatures within the set temperature range;

[0012] Step 6: Compare the stress-strain response simulation curve obtained in step 5 with the actual variable temperature mechanical property curve at the same temperature in step 1 to obtain the curve difference at each temperature. If the curve difference at all temperatures is less than the set requirement, it is considered that the finite element simulation process in steps 2 to 5 is accurate, otherwise return to step 2 and re-establish the variable temperature damage model;

[0013] Step 7: According to the actual service temperature range of the thermoelectric device, set the thermal field boundary conditions of each component of the thermoelectric device in the finite element software, and according to the structural constraints, set the load boundary conditions of each component of the thermoelectric device;

[0014] Step 8: In the finite element software, mesh the remaining components in the thermoelectric device model and assign mesh unit attributes;

[0015] Step 9: In the finite element software, the design parameters of each component in the thermoelectric device model are adjusted, the load-bearing performance and damage analysis of the adjusted thermoelectric device are performed, and the thermoelectric device configuration with the best performance is selected.

[0016] Furthermore, in step 1, the mechanical properties include bending properties, shear properties, compression properties or tensile properties.

[0017] Furthermore, the variable temperature damage model is:

[0018]

[0019] in is stress, For strain, is the damage evolution factor, is the initial elastic modulus of the thermoelectric material to be studied.

[0020] Furthermore, the damage evolution factor for:

[0021]

[0022] in , and is an intermediate variable, specifically:

[0023] , ,

[0024] represents the compressive strength of the thermoelectric material to be studied, for The corresponding strain value is is the fitting coefficient describing the stress-strain curve, is the correction factor.

[0025] Furthermore, in step 6, the curve difference is measured by the statistic of the stress difference corresponding to the same strain; at a certain temperature, the average value of the stress difference corresponding to the same strain in the entire strain range is calculated, and then the average value of the average values ​​corresponding to all temperatures is taken. If the average value is less than the set threshold, it is considered that the finite element simulation process in steps 2 to 5 is accurate.

[0026] Furthermore, in step 9, the optimal performance means that when the equivalent structural bearing capacity meets the requirements, the cross-sectional area of ​​the hot arm perpendicular to the high and low temperature directions is the largest; the equivalent structural bearing capacity is the structural bearing performance per unit area of ​​the cross-section of the hot arm perpendicular to the high and low temperature directions.

[0027] Furthermore, the equivalent structural bearing capacity According to the formula

[0028]

[0029] Calculated, where It is the cross-sectional area of ​​the hot arm after chamfering perpendicular to the high and low temperature directions. for The corresponding absolute structural bearing capacity of the thermoelectric device, It is the area of ​​the hot arm after the cross section perpendicular to the high and low temperature directions is chamfered into the inscribed circle of the initial prismatic hot arm cross section.

[0030] Furthermore, in step 9, the heat arm component is initially designed as a prismatic heat arm structure, and the design parameters are the four-edge chamfer parameters of the prismatic heat arm. The optimal heat arm chamfer configuration is selected by analyzing the load-bearing performance and damage of the thermoelectric device under different chamfer radii.

[0031] The present invention has the following beneficial effects:

[0032] (1) The present invention achieves actual service performance testing and evaluation of thermoelectric application technology material level and device level through coupling experimental testing, theoretical analysis and numerical analysis, and further carries out structural optimization design of thermoelectric devices, which breaks the limitation of linear elastic model in the design and analysis of thermoelectric devices in the past.

[0033] (2) The device model construction and structural optimization design based on the real temperature-dependent elastic-plastic mechanical properties of thermoelectric materials were realized. This enables the analysis method to evaluate the load-bearing and failure modes of thermoelectric devices under high-temperature and high-load service environments, and to provide structural optimization design recommendations.

[0034] (3) Evaluate the load-bearing and damage performance of thermoelectric devices in a wide temperature gradient service environment, and then select the thermoelectric devices with the best load-bearing performance, improve the design efficiency, thereby improving the service reliability and stability of thermoelectric devices and promoting the engineering application of thermoelectric conversion technology.

[0035] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0037] Figure 1 The present invention is a flow chart of a thermoelectric device analysis method that takes into account the temperature-dependent elastic-plastic mechanical properties of thermoelectric materials.

[0038] Figure 2 This is a test diagram of the variable temperature mechanical properties of a typical medium and high temperature range thermoelectric material system in the present invention.

[0039] Figure 3 It is a comparison chart between simulation and experiment of the variable temperature mechanical properties of the thermoelectric material at different temperatures in the present invention.

[0040] Figure 4 This is the geometric model of a typical π-type thermoelectric device.

[0041] Among them: 1. Insulating ceramic plate; 2. Electrode; 3. Hot arm.

[0042] Figure 5 The strength calculation results obtained by carrying out different chamfer optimization designs on typical thermoelectric devices in the present invention.

[0043] Figure 6The simulation diagrams of thermal arm damage and destruction obtained by carrying out different chamfer optimization designs on typical thermoelectric devices in the present invention, and the chamfer radii r corresponding to (a) to (e) are (r=0 mm, 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm), respectively. DETAILED DESCRIPTION

[0044] Embodiments of the present invention are described in detail below. The embodiments are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0045] Thermoelectric energy conversion devices are based on the Seebeck effect, which directly converts the temperature gradient between the hot and cold ends into electrical energy output through semiconductor thermoelectric materials. In engineering application scenarios, the internal hot arm of the thermoelectric module is not only subjected to the high gradient temperature field under the typical working temperature field, but also the nonlinear mechanical response of the material due to temperature dependence, resulting in a significant nonlinear characteristic of the force-heat coupling constitutive relationship. The existing thermoelectric device analysis model based on the linear elastic constitutive assumption is difficult to accurately characterize the interaction mechanism between the elastic-plastic deformation and thermal stress evolution of the material under high temperature difference conditions, resulting in theoretical deviations in the device structural integrity assessment. In response to this key technical bottleneck, the present invention proposes a thermoelectric device analysis method that considers the variable temperature elastic-plastic mechanical properties of thermoelectric materials. First, the variable temperature complete mechanical response of the core component "hot arm material" in the thermoelectric device is considered, and then the corresponding device analysis model is established to carry out the load-bearing and damage analysis of the typical device structure; finally, the physical parameters and variable parameters of the device structure are optimized to improve the device structure load-bearing. The present invention provides for the first time a theoretical and simulation analysis basis for the design of temperature difference devices in a real service environment, and provides suggestions and guidance for their structural optimization design, thereby improving the reliability and stability of thermoelectric devices in a real temperature difference service environment.

[0046] Due to the large number of thermoelectric material systems, this embodiment selects ZrNiSn-based half-Heusler material as a typical thermoelectric material. The mechanical properties of this material change from linear elasticity to nonlinear plasticity as the temperature increases. Its complexity covers the common variable temperature linear elasticity and variable temperature plasticity models. Therefore, the selection of this thermoelectric material for case discussion is representative.

[0047] Figure 1 A schematic flow chart of a thermoelectric device analysis method considering the temperature-dependent elastic-plastic mechanical properties of thermoelectric materials provided in this embodiment specifically includes the following steps:

[0048] Step 1: Obtain the real temperature-dependent mechanical performance curve of the thermoelectric material to be studied within a set temperature range through performance experimental testing. The mechanical performance curve is a stress-strain response curve. The set temperature range covers the service temperature range of the thermoelectric material to be studied. The mechanical properties include bending properties, shear properties, compression properties or tensile properties.

[0049] In this embodiment, ZrNiSn-based half-Heusler material is selected as a typical thermoelectric material. According to its typical service temperature and load environment, a variable temperature compression experiment is carried out from 300 K to 1100 K to obtain the variable temperature compression response of the thermoelectric material in a wide temperature range service environment. Figure 2 shown.

[0050] Step 2: Using the actual variable temperature mechanical property curve of the thermoelectric material to be studied within the set temperature range obtained in step 1, a variable temperature damage model of the thermoelectric material to be studied is fitted to achieve a quantitative description of the stress-strain response of the thermoelectric material to be studied at different temperatures.

[0051] In this embodiment, the variable temperature damage model is:

[0052]

[0053] in is stress, For strain, is the damage evolution factor, is the initial elastic modulus of the thermoelectric material to be studied.

[0054] According to the variable temperature compression mechanical response of the ZrNiSn-based half-Heusler material measured in step 1, its stress-strain curve at medium and low temperatures (300, 500, 700 K) is a linear elastic response, and the stress-strain relationship at high temperatures (900 and 1100 K) is a nonlinear elastoplastic response, which goes through the elastic stage, hardening stage and softening stage. Therefore, the damage evolution factor in the variable temperature damage model is for:

[0055]

[0056] in , and is an intermediate variable, specifically:

[0057] , ,

[0058] represents the compressive strength of the thermoelectric material to be studied, for The corresponding strain value is is the fitting coefficient describing the stress-strain curve, is the correction coefficient. In this embodiment, when T=900K, 0.155, 1.063, T = 1100K, 0.102, 1.093.

[0059] Step 3: Create or import the thermoelectric device model to be analyzed in the finite element software.

[0060] In this embodiment, Abaqus finite element analysis software is used to establish a prismatic hot arm (4 mm×4 mm×8 mm), a copper electrode plate, and an insulating ceramic plate, and assemble them into a complete thermoelectric device model.

[0061] Step 4: Define the material properties of each component in the thermoelectric device model in the finite element software, wherein the material used for the hot arm component is the thermoelectric material to be studied in step 1, and the material properties of the thermoelectric material to be studied are defined by the variable temperature damage model obtained in step 2 and embedded in the finite element software. For example, the variable temperature damage model is embedded in the Abaqus finite element analysis software through a custom subroutine.

[0062] Step 5: In the finite element software, the load-bearing performance of the hot arm component in the thermoelectric device model is simulated, and failure judgment is performed on each unit of the hot arm component to obtain the stress-strain response simulation curve of the hot arm component at several temperatures within the set temperature range.

[0063] The failure criterion selected in this embodiment is the maximum principal stress criterion, that is, when the principal stress of the thermoelectric material during the load-bearing process reaches the corresponding load-bearing strength, the material is damaged and its material performance is reduced.

[0064] Step 6: Compare the stress-strain response simulation curve obtained in step 5 with the actual variable temperature mechanical property curve at the same temperature in step 1 to obtain the curve difference at each temperature. If the curve difference at all temperatures is less than the set requirement, the finite element simulation process in steps 2 to 5 is considered accurate. Otherwise, return to step 2 and re-establish the variable temperature damage model.

[0065] In this embodiment, the curve difference is measured by the statistic of the stress difference corresponding to the same strain. For example, at a certain temperature, the average value of the stress difference corresponding to the same strain in the entire strain range is calculated, and then the average value of the average values ​​corresponding to all temperatures is taken. If the average value is less than the set threshold, it is considered that the finite element simulation process in steps 2 to 5 is accurate. Figure 3 The stress-strain response curves of the prismatic hot arm under uniaxial compression conditions at different measurement temperatures are given and compared with the actual variable temperature mechanical property curves at the same temperature (i.e., experimental measured results). It can be seen that the two have good consistency, indicating that the finite element simulation process in steps 2 to 5 is accurate, and the established variable temperature damage model can be further used for subsequent simulation analysis and optimization.

[0066] Step 7: According to the actual service temperature range of the thermoelectric device, set the thermal field boundary conditions of each component of the thermoelectric device in the finite element software, and set the load boundary conditions of each component of the thermoelectric device according to the structural constraints.

[0067] In this embodiment, Figure 4 The figure shows the finite element analysis model of a typical π-type thermoelectric device. The hot arm (4 mm × 4 mm × 8 mm) uses the aforementioned half-Heusler thermoelectric material, the electrode uses copper material, and the insulating ceramic plate uses alumina ceramic material. The service temperature of the cold end of the thermoelectric device is 550 K, the service temperature of the hot end is 1050 K, and the structural constraint is that the cold end of the thermoelectric device is fixed and a compressive load is applied to the hot end.

[0068] Step 8: In the finite element software, mesh the remaining components in the thermoelectric device model and assign mesh unit properties, such as sequential or direct coupling of thermal-mechanical analysis units, thermal-electrical analysis units, and other multi-field unit types.

[0069] In step 5, the load-bearing performance of the hot arm component has been simulated. Here, the remaining components, including the insulating ceramic plate and the electrode, are meshed with a mesh size of 0.15 mm, and the mesh unit properties are assigned.

[0070] Step 9: In the finite element software, adjust the design parameters of each component in the thermoelectric device model, analyze the load-bearing performance and damage evolution of the adjusted thermoelectric device, and select the thermoelectric device configuration with the best performance. For example, the design parameters can be material properties such as modulus, strength, thermal expansion coefficient, Poisson's ratio, thermal conductivity, electrical conductivity, etc., or geometric parameters of the components. The load-bearing performance can be shear load-bearing strength, tensile load-bearing strength, compressive load-bearing strength, structural load-bearing toughness, etc.

[0071] In the present invention, the performance of the thermoelectric device considered includes the structural bearing performance and the thermoelectric conversion performance. Generally speaking, without considering the cost and structural weight, the larger the cross-sectional area of ​​the hot arm perpendicular to the high and low temperature direction, the better the structural bearing performance and the thermoelectric conversion performance. However, in actual engineering, the cost and structural weight constraints need to be considered. For this reason, the present invention uses the structural bearing performance per unit area of ​​the cross section of the hot arm perpendicular to the high and low temperature direction as the judgment basis, which is called the equivalent structural bearing capacity.

[0072] The optimal performance means that when the equivalent structural bearing capacity meets the requirements, the cross-sectional area of ​​the hot arm perpendicular to the high and low temperature direction is the largest, so as to achieve the best thermoelectric efficiency. The high and low temperature direction is the connection direction of the hot and cold ends of the hot arm component.

[0073] In this embodiment, the other parameters of the thermoelectric device model are kept unchanged, and the adjusted design parameters are the chamfer parameters of the four edges of the prismatic hot arm. The chamfer radii are respectively taken as r=0mm, 0.5mm, 1.0mm, 1.5mm, and 2.0mm. By analyzing the load-bearing performance and damage of the thermoelectric device under different chamfer radii, the optimal hot arm chamfer configuration is selected.

[0074] The calculated results of mechanical properties of thermoelectric devices under different chamfer radii and the thermal arm damage diagram are shown in Figure 2. Figure 5 and Figure 6 As shown. Figure 5 The black line shows that as the chamfer radius of the hot arm increases, the absolute structural bearing capacity of the thermoelectric device This is because as the chamfer increases, the absolute area of ​​the thermal arm load decreases, but as the chamfer radius increases, the equivalent structural load-bearing capacity of the thermoelectric device Initially, when the chamfer radius of the hot arm is 1.5mm to 2.0mm, the equivalent structural bearing capacity does not change much. Figure 6 It can be found that as the chamfer size of the hot arm increases, the damage to the hot arm gradually decreases. When the chamfer radius is 1.5mm to 2.0mm, the damage to the hot arm is less. The hot arm structure with a chamfer radius of 1.5mm has a larger cross-sectional area perpendicular to the high and low temperature directions, so the hot arm structure with a chamfer radius of 1.5mm is selected as the final optimized structure.

[0075] In this embodiment, the structural load-bearing test is the uniaxial compression performance, so the structural load-bearing capacity is the cross-sectional compression strength, and the equivalent structural load-bearing capacity is According to the formula

[0076]

[0077] Calculated, where It is the cross-sectional area of ​​the hot arm after chamfering perpendicular to the high and low temperature directions. for The corresponding absolute structural bearing capacity of the thermoelectric device, It is the area of ​​the hot arm after the cross section perpendicular to the high and low temperature directions is chamfered into the inscribed circle of the initial prismatic hot arm cross section.

[0078] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A thermoelectric device analysis method considering the temperature-dependent elastic-plastic mechanical properties of thermoelectric materials, characterized by: The following steps are involved: Step 1: Through performance experimental testing, obtain the real temperature-dependent mechanical performance curve of the thermoelectric material to be studied within the set temperature range; Step 2: Using the real temperature-dependent mechanical property curve of the thermoelectric material to be studied within a set temperature range obtained in step 1, a temperature-dependent damage model of the thermoelectric material to be studied is obtained by fitting; Step 3: Create or import the thermoelectric device model to be analyzed in the finite element software; Step 4: defining the material properties of each component in the thermoelectric device model in finite element software, wherein the material of the hot arm component is the thermoelectric material to be studied in step 1, and the material properties of the thermoelectric material to be studied are defined by the variable temperature damage model obtained in step 2; Step 5: In finite element software, the load-bearing performance of the hot arm component in the thermoelectric device model is simulated, and failure judgment is performed on each unit of the hot arm component to obtain the stress-strain response simulation curve of the hot arm component at several temperatures within the set temperature range; Step 6: Compare the stress-strain response simulation curve obtained in step 5 with the actual variable temperature mechanical property curve at the same temperature in step 1 to obtain the curve difference at each temperature. If the curve difference at all temperatures is less than the set requirement, it is considered that the finite element simulation process in step 2 to step 4 is accurate, otherwise return to step 2 and re-establish the variable temperature damage model; Step 7: According to the actual service temperature range of the thermoelectric device, set the thermal field boundary conditions of each component of the thermoelectric device in the finite element software, and according to the structural constraints, set the load boundary conditions of each component of the thermoelectric device; Step 8: In the finite element software, mesh the remaining components in the thermoelectric device model and assign mesh unit attributes; Step 9: In the finite element software, the design parameters of each component in the thermoelectric device model are adjusted, the load-bearing performance and damage analysis of the adjusted thermoelectric device are performed, and the thermoelectric device configuration with the best performance is selected.

2. According to claim 1, a thermoelectric device analysis method considering the temperature-dependent elastic-plastic mechanical properties of thermoelectric materials is characterized by: In step 1, the mechanical properties include bending properties, shear properties, compression properties or tensile properties.

3. A thermoelectric device analysis method considering the temperature-dependent elastic-plastic mechanical properties of thermoelectric materials according to claim 1 or 2, characterized in that: The variable temperature damage model is: in is stress, For strain, is the damage evolution factor, is the initial elastic modulus of the thermoelectric material to be studied.

4. A thermoelectric device analysis method considering the temperature-dependent elastic-plastic mechanical properties of thermoelectric materials according to claim 3, characterized in that: The damage evolution factor for: in , and is an intermediate variable, specifically: ， ， represents the compressive strength of the thermoelectric material to be studied, for The corresponding strain value is is the fitting coefficient describing the stress-strain curve, is the correction factor.

5. The thermoelectric device analysis method according to claim 1, wherein the thermoelectric material temperature-dependent elastic-plastic mechanical properties are considered, characterized in that: In step 6, the curve difference is measured by the statistic of the stress difference corresponding to the same strain; at a certain temperature, the average value of the stress difference corresponding to the same strain in the entire strain range is calculated, and then the average value of the average values ​​corresponding to all temperatures is taken. If the average value is less than the set threshold, it is considered that the finite element simulation process in steps 2 to 4 is accurate.

6. A thermoelectric device analysis method considering the temperature-dependent elastic-plastic mechanical properties of thermoelectric materials according to claim 1, characterized in that: In step 9, the optimal performance means that when the equivalent structural bearing capacity meets the requirements, the cross-sectional area of ​​the hot arm perpendicular to the high and low temperature directions is the largest; the equivalent structural bearing capacity is the structural bearing performance per unit area of ​​the cross section of the hot arm perpendicular to the high and low temperature directions.

7. A thermoelectric device analysis method considering the temperature-dependent elastic-plastic mechanical properties of thermoelectric materials according to claim 6, characterized in that: Equivalent structural load capacity According to the formula Calculated, where It is the cross-sectional area of ​​the hot arm after chamfering perpendicular to the high and low temperature directions. For the corresponding The absolute structural load-bearing capacity of It is the area of ​​the hot arm after the cross section perpendicular to the high and low temperature directions is chamfered into the inscribed circle of the initial prismatic hot arm cross section.

8. A thermoelectric device analysis method considering the temperature-dependent elastic-plastic mechanical properties of thermoelectric materials according to claim 6, characterized in that: In step 9, the heat arm component is initially designed as a prismatic heat arm structure, and the design parameters are the four-edge chamfer parameters of the prismatic heat arm. The optimal heat arm chamfer configuration is selected by analyzing the load-bearing performance and damage of the thermoelectric device under different chamfer radii.

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