Thermoelectric material thermal conductivity testing device and method

Abstract

The application discloses a material thermal conductivity testing device and method based on thermoelectric generation, and the device comprises a testing support, an upper heat transfer structure, a lower heat transfer structure, a stress loading device, a temperature sensor, a data acquisition element, an in-situ thickness measuring unit, a sample to be tested, an insulation layer and a heat insulation layer; a temperature equalizing heating plate and a temperature equalizing heat dissipating plate are started, temperature data of the temperature equalizing heating plate and the temperature equalizing heat dissipating plate are collected by using the temperature sensor, voltage data of the upper thermoelectric sheet and the lower thermoelectric sheet are collected by using the data acquisition element, the temperature of the sample to be tested and the heat flow through the sample are obtained by using the performance curve of the thermoelectric sheet voltage, the temperature and the heat flow, and the thermal conductivity of the sample is calculated. The device is simple in assembly and composition, the testing process is simple and clear, and the testing efficiency of the thermal conductivity is greatly improved; the contact thermal resistance in the calibration process makes the temperature information of the sample to be tested simple, accurate and convenient to operate.

Description

Technical Field

[0001] This invention belongs to the field of material thermal conductivity testing technology, and in particular relates to a material thermal conductivity testing device and method based on thermoelectric power generation. Background Technology

[0002] Thermal conductivity is a physical quantity characterizing the heat transfer performance of a material and is one of the most fundamental thermophysical parameters. Current methods for measuring thermal conductivity are based on the one-dimensional steady-state Fourier law of thermal conductivity. When the heated and cooled surfaces of a sample are kept at a constant temperature, a temperature gradient exists within the sample, and heat spontaneously transfers from the higher-temperature side to the lower-temperature side. If radial heat loss is ignored, axial one-dimensional steady-state heat flow can be considered as existing in the material. Based on the heat flux density through the sample and the temperature gradient across the sample, its thermal conductivity can be calculated using the one-dimensional Fourier law of thermal conductivity.

[0003] The thermal conductivity measurement method based on the one-dimensional steady-state Fourier thermal conductivity law requires the addition of a heat flux meter to the test system to obtain the heat flux density. The longitudinal temperature gradient is obtained by inserting a thermocouple through an opening into the heat flux meter and extrapolating it to obtain the interface temperature, which makes the device for testing thermal conductivity quite complex. The presence of the thermocouple not only affects the longitudinal one-dimensional heat flow transfer and causes heat transfer errors due to structural damage, but also introduces errors between the extrapolated end temperatures and the actual temperatures due to factors such as contact thermal resistance. This greatly affects the high-precision measurement requirements of the material's thermal conductivity. Summary of the Invention

[0004] The purpose of this invention is to provide a device and method for testing the thermal conductivity of materials based on thermoelectric power generation, so as to solve the problems in the prior art, such as large errors in the temperature difference measured by thermocouples at both ends of the material due to factors such as contact thermal resistance, heat transfer errors caused by the insertion of thermocouples damaging the structure, and the complexity of thermal conductivity testing devices.

[0005] To achieve the objective of this invention, a material thermal conductivity testing device based on thermoelectric power generation is disclosed, comprising a test support, an upper heat transfer structure, a lower heat transfer structure, a test sample, and an insulation layer. The test support includes a top plate, a support bracket, and a bottom plate, with the top and bottom plates respectively disposed at the top and bottom of the support bracket. The upper heat transfer structure, the test sample, and the lower heat transfer structure are sequentially assembled between the top and bottom plates from top to bottom. The upper heat transfer structure includes an insulation layer, a heating device, and an upper thermoelectric element, arranged sequentially from top to bottom. The lower heat transfer structure includes a lower thermoelectric element and a heat dissipation device, arranged sequentially from top to bottom. The test sample is covered with an insulation layer to reduce radial heat loss. By measuring the voltage and temperature difference of the thermoelectric elements in the upper and lower heat transfer structures, the temperature data of the upper and lower surfaces of the test sample are obtained, and the thermal conductivity of the test sample is calculated using Fourier's law of thermal conductivity.

[0006] Furthermore, the heating device includes a uniform heating plate, an upper electronic voltage regulator, and an upper temperature controller; the upper temperature controller is electrically connected to the upper electronic voltage regulator, and the upper electronic voltage regulator is electrically connected to the uniform heating plate, which provides a heat source for the test sample; the heat dissipation device includes a uniform heat dissipation plate, a lower electronic voltage regulator, and a lower temperature controller; the lower temperature controller is electrically connected to the lower electronic voltage regulator, and the lower electronic voltage regulator is electrically connected to the uniform heat dissipation plate, which serves as a heat sink for the test sample.

[0007] Furthermore, the upper or lower thermoelectric element is composed of a ceramic substrate, a metal conductor, a P-type semiconductor, and an N-type semiconductor; the P-type semiconductor and the N-type semiconductor are welded onto the metal conductor and encapsulated by the upper and lower ceramic substrates; when the heating device is activated, the uniform heating plate generates heat flow through the thermoelectric element, which can be approximated as one-dimensional heat transfer along the longitudinal direction of the thermoelectric element, and a temperature gradient is formed between the uniform heating plate at the top of the upper ceramic substrate and the test sample at the bottom of the lower ceramic substrate.

[0008] Furthermore, the temperature sensor is electrically connected to the uniform heating plate and the uniform heat dissipation plate to collect temperature data of the uniform heating plate and the uniform heat dissipation plate; the data acquisition element is electrically connected to the upper thermoelectric element and the lower thermoelectric element to collect voltage data of the upper thermoelectric element and the lower thermoelectric element.

[0009] Furthermore, the stress loading device is located at the bottom of the test bracket and is used to apply pressure to the test specimen; the pressure sensor is located between the stress loading device and the bottom plate of the test bracket and is used to measure the magnitude of the pressure applied by the stress loading device; the heat insulation layer is located between the top plate of the test bracket and the uniform heating plate; the in-situ thickness measurement unit is connected to the upper and lower surfaces of the test specimen and is used to measure the actual thickness of the test specimen.

[0010] To achieve the objectives of this invention, this invention also discloses a method for testing the thermal conductivity of materials based on thermoelectric power generation, comprising the following steps:

[0011] Step 1: Calibrate the thermoelectric performance curves of the upper and lower thermoelectric elements;

[0012] Step 2: After the upper and lower heating elements are calibrated, the testing device and the sample to be tested are pretreated.

[0013] Step 3: After the testing device and the test specimen are pretreated, the testing device and the test specimen are tightly fitted together. The stress loading device and heating device are started to apply compressive stress and heat flow.

[0014] Step 4: After the compressive stress and heat flow loading have stabilized, start the in-situ thickness measurement unit to measure the sample thickness d in real time during the thermal conductivity test.

[0015] Step 5: Obtain the temperature difference between the upper and lower surfaces of the test sample using the calibrated thermoelectric performance curves of the upper and lower thermoelectric plates, obtain the heat flow through the test sample using a uniform heating plate, obtain the actual thickness of the test sample using an in-situ thickness measurement unit, and calculate the thermal conductivity using Fourier's law of thermal conductivity.

[0016] Furthermore, step 1 specifically includes:

[0017] The upper thermoelectric element is tightly bonded to the heat exchanger and the heat sink. The heat exchanger and the heat sink are activated to generate a one-dimensional longitudinal heat flow. While keeping the temperature of the heat exchanger constant, the temperature of the heat sink is continuously changed, causing a change in the temperature difference between the upper and lower ceramic substrates. Due to the Seebeck effect, the upper thermoelectric element generates a pressure difference. The Seebeck effect formula is:

[0018]

[0019] The thermoelectric element absorbs heat from the uniform heating plate and transfers the heat longitudinally to the uniform heat dissipation plate. The heat transfer process of the thermoelectric element can be represented as follows:

[0020]

[0021] When the power supply is open, i.e., I = 0, the heat flow is only related to the temperature difference, which can be expressed as:

[0022] Q=λΔT

[0023] Where T1 is the cold junction temperature, T2 is the hot junction temperature, and S... B (T) is the Seebeck coefficient of the P-type semiconductor, S A (T) represents the Seebeck coefficient of the N-type semiconductor, ΔT = T2 - T1, which is the temperature difference between the high and low temperature heat sources; λ is the thermal conductivity of the material; r0 is the internal resistance of the power generation unit; I is the current of the thermoelectric element; S is the Seebeck coefficient. B (T) and S A (T) are all related to temperature. The temperature of the heat sink is continuously changed to change the temperature difference between the two ends of the upper heatsink. Temperature data T1 and T2 at the two ends of the upper heatsink are collected by temperature sensors. Voltage U1 and heat flow Q1 of the upper heatsink are collected by data acquisition elements. The data are imported into the computer for fitting to obtain the performance curve of voltage U1 of the upper heatsink as a function of temperature difference ΔT1 between the upper and lower ends and the performance curve of voltage U1 as a function of heat flow Q1. The calibration process of the lower heatsink is the same as that of the upper heatsink.

[0024] Furthermore, step 2 specifically involves:

[0025] A testing device for the thermal conductivity of materials based on thermoelectric power generation is set up and connected, so that the uniform heating plate and the upper thermoelectric element are in close contact, and the lower thermoelectric element and the uniform heat dissipation plate are in close contact. The processed sample is placed between the upper and lower thermoelectric elements. Temperature sensors are set on the uniform heating plate and the uniform heat dissipation plate to test the temperature T1 of the uniform heating plate and the temperature T2 of the uniform heat dissipation plate. Data acquisition elements are set on both the upper and lower thermoelectric elements to test the voltage of the thermoelectric elements.

[0026] Furthermore, step 3 specifically involves:

[0027] The pressure loading device is controlled to apply pressure to the test sample and the upper and lower thermoelectric plates to a specified load. The upper temperature controller is controlled to raise the temperature of the uniform heating plate to a specific temperature T1 and maintain it at a constant temperature, using the uniform heating plate as a heat source. The lower temperature controller is controlled to maintain the uniform heat dissipation plate at a specific temperature T2 and maintain it at a constant temperature, using the uniform heat dissipation plate as a heat sink. The temperatures T1 and T2 of the uniform heating plate are collected by temperature sensors. The voltages of the upper and lower thermoelectric plates are monitored by data acquisition elements. When the voltages stabilize, the voltages U1 and U2 of the upper and lower thermoelectric plates are read.

[0028] Furthermore, step 5 specifically includes:

[0029] In step 2, the temperatures T1 and T2 of the uniform heating plate and the uniform heat dissipation plate are obtained by temperature sensors, and the voltages U1 and U2 of the upper and lower thermoelectric elements are obtained by data acquisition elements. The following are determined by the performance curves of the calibrated voltage of the thermoelectric elements as a function of temperature difference: the temperature difference ΔT1 between the two ends of the upper thermoelectric element corresponding to the voltage U1 of the upper thermoelectric element, and the temperature difference ΔT2 between the two ends of the lower thermoelectric element corresponding to the voltage U2 of the lower thermoelectric element. The following are determined by the performance curves of the calibrated voltage of the thermoelectric elements as a function of heat flow: the heat flow Q1 through the upper thermoelectric element corresponding to the voltage U1 of the upper thermoelectric element, and the heat flow Q2 through the lower thermoelectric element corresponding to the voltage U2 of the lower thermoelectric element.

[0030] The calculated temperatures T1' (the temperature of the sample near the cold end of the upper thermoelectric element) and T2' (the temperature of the sample near the hot end of the lower thermoelectric element) are as follows:

[0031]

[0032] T2'=T2+△T2

[0033] The heat flow through the sample at this time can be expressed as:

[0034] Q = (Q1 + Q2) / 2

[0035] According to the one-dimensional steady-state Fourier thermal conductivity law, the thermal conductivity of the sample is calculated as follows:

[0036]

[0037] Where T1' is the temperature of the upper surface of the sample, T2' is the temperature of the lower surface of the sample, d is the thickness of the sample, and Q is the heat flow through the sample.

[0038] Furthermore, the heat insulation layer and the thermal insulation layer are made of heat insulation cotton.

[0039] Compared with existing technologies, the significant advancements of this invention are: 1) The testing device of this invention consists only of a testing bracket, an upper heat transfer structure, a lower heat transfer structure, a temperature sensor, a data acquisition element, an in-situ thickness measurement unit, the test sample, and an insulation layer. The device assembly is simple, the testing process is concise and clear, and the testing efficiency is greatly improved; 2) This invention uses a data acquisition element to collect the voltage data of the thermoelectric element. From this voltage data, the temperature difference and heat flow data of the test sample can be obtained through the performance curves of the calibrated voltage of the thermoelectric element changing with temperature difference and the performance curves of the calibrated voltage of the thermoelectric element changing with heat flow. The temperature and heat flow of the test sample are obtained through the simple relationship between the thermoelectric element voltage and temperature difference and heat flow. It eliminates the need to install a heat flow meter and insert a thermocouple in the testing system, which would damage the structure, lead to heat transfer errors, and affect the heat flow transfer process. At the same time, the accuracy of temperature data acquisition is greatly related to the experimental operation process. Due to the presence of contact thermal resistance during the calibration process, this invention makes the acquisition of temperature information at both ends of the test sample simple, accurate, and convenient.

[0040] To more clearly illustrate the functional characteristics and structural parameters of the present invention, further explanation is provided below in conjunction with the accompanying drawings and specific embodiments. Attached Figure Description

[0041] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0042] Figure 1 This is a schematic diagram of the overall structure of a material thermal conductivity testing device based on thermoelectric power generation.

[0043] Figure 2 This is a schematic diagram of a thermoelectric element structure for a material thermal conductivity testing device based on thermoelectric power generation.

[0044] Figure 3 This is a schematic diagram of the structure of a material thermal conductivity testing device based on thermoelectric power generation, used for calibrating the thermoelectric performance curves of the upper and lower thermoelectric elements during the process of testing the thermal conductivity of materials.

[0045] The attached figures are labeled as follows: 1. Uniform heating plate; 2. Upper thermoelectric element; 3. Test sample; 4. Lower thermoelectric element; 5. Uniform heat dissipation plate; 6. Upper electronic voltage regulator; 7. Upper electronic voltage regulator; 8. Lower electronic voltage regulator; 9. Lower electronic temperature controller; 10. Data acquisition element; 11. Temperature sensor; 12. Top plate; 13. Bottom plate; 14. Support bracket; 15. Insulation layer; 16. Stress loading device; 17. Pressure sensor; 18. Heat insulation layer; 19. In-situ thickness measurement unit. Detailed Implementation

[0046] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Example

[0048] like Figure 1 The device shown is a test device for the thermal conductivity of materials based on thermoelectric power generation. It mainly consists of a uniform heating plate 1, an upper thermoelectric element 2, a test sample 3, a lower thermoelectric element 4, a uniform heat dissipation plate 5, an upper electronic voltage regulator 6, an upper temperature controller 7, a lower electronic voltage regulator 8, a lower temperature controller 9, a data acquisition element 10, a temperature sensor 11, a top plate 12, a bottom plate 13, a support bracket 14, a thermal insulation layer 15, a stress loading device 16, a pressure sensor 17, a heat insulation layer 18, and an in-situ thickness measurement unit 19. The heat insulation layer 18, the uniform heating plate 1, the upper thermoelectric element 2, the test sample 3, the lower thermoelectric element 4, and the uniform heat dissipation plate 5 are installed sequentially from top to bottom. The top plate 12 and the bottom plate 13 support the heat insulation layer 18, the uniform heating plate 1, the upper thermoelectric element 2, the test sample 3, the lower thermoelectric element 4, and the uniform heat dissipation plate 5 in the middle. The pressure sensor 17 is located below the uniform heat dissipation plate 5 and above the stress loading device 16 at the center position, which can monitor and adjust the pressure on the test sample 3 and the upper and lower thermoelectric elements in real time. The stress loading device 16 is located below the bottom plate 13. The heat insulation layer 15 wraps the test sample 3 to reduce radial heat loss. The stress loading device 16 is activated and the position of the support bracket 14 is adjusted to ensure that the contact surfaces between the heat insulation layer 18, the uniform heating plate 1, the upper thermoelectric element 2, the test sample 3, the lower thermoelectric element 4, and the uniform heat dissipation plate 5 are tightly fitted.

[0049] like Figure 2The diagram shows the side view of the thermoelectric element. The thermoelectric element comprises a ceramic substrate, a metal conductor, P-type semiconductors, and N-type semiconductors. P-type and N-type semiconductor materials with known material properties are selected to fabricate the thermoelectric element. m sets of P / N-type semiconductors are soldered onto the metal conductor, and m sets of thermocouples are connected in series. The upper and lower ceramic substrates are then encapsulated. When a temperature difference exists between the two ends of the thermoelectric element, charge carriers at the hot end of the P-type and N-type semiconductors migrate to the cold end. The migration of holes in the P-type semiconductor and electrons in the N-type semiconductor creates a potential difference. If this forms a closed loop, a current will be generated.

[0050] The upper temperature controller 7 is connected to the upper electronic voltage regulator 8, which is connected to the uniform heating plate 1, providing a heat source for the test sample 3. The lower temperature controller 9 is connected to the lower electronic voltage regulator 8, which is connected to the uniform heat sink 5, serving as a heat sink for the test sample. The upper electronic voltage regulator 6 adjusts the current flowing through the uniform heating plate 1 to release heat, which flows into the test sample 3 and forms a one-dimensional steady-state heat transfer between them. The temperature sensor 11 can monitor and adjust the temperature of the uniform heating plate 1 and the uniform heat sink 5 in real time and can feed the temperature data back to the computer. The data acquisition element 10 can receive voltage data from the upper thermoelectric element 2 and the lower thermoelectric element 4. When the voltage data stabilizes within ±0.01V, the testing device can be considered to be operating stably. The voltage data is then fed back to the computer. The computer can calculate the temperature at the upper and lower ends of the sample and the heat flow through the sample based on the performance curves of the voltage calibrated for the thermoelectric elements as a function of temperature difference and heat flow. The thickness d of the sample under test can be directly measured by the in-situ thickness measurement unit.

[0051] A method for testing the thermal conductivity of materials based on thermoelectric power generation, characterized in that the thermal conductivity testing method includes the following steps:

[0052] The first step is to calibrate the thermoelectric performance curves of the upper and lower thermoelectric elements:

[0053] Figure 3 This is a schematic diagram of the structure for calibrating the thermoelectric performance curves of the upper and lower thermoelectric elements of the present invention. The upper thermoelectric element 2 is tightly attached to the uniform heating plate 1 and the uniform heat dissipation plate 5. The uniform heating plate 1 and the uniform heat dissipation plate 5 are activated to generate a one-dimensional longitudinal heat flow. While keeping the temperature of the uniform heating plate 1 constant, the temperature of the uniform heat dissipation plate 5 is continuously changed, causing the temperature difference between the upper and lower ceramic substrates of the upper thermoelectric element to change. Due to the Seebeck effect, the upper thermoelectric element generates a pressure difference. The Seebeck effect formula is:

[0054]

[0055] The thermoelectric element absorbs heat from the uniform heating plate 1 and transfers the heat longitudinally to the uniform heat dissipation plate 5. The heat transfer process of the thermoelectric element can be represented as follows:

[0056]

[0057] When the power supply is open, i.e., I = 0, the heat flow is only related to the temperature difference, which can be expressed as:

[0058] Where T1 is the cold junction temperature, T2 is the hot junction temperature, and S... B (T) is the Seebeck coefficient of the P-type semiconductor, S A (T) represents the Seebeck coefficient of the N-type semiconductor, ΔT = T2 - T1, which is the temperature difference between the high and low temperature heat sources, λ is the thermal conductivity of the material, and r0 is the internal resistance of the power generation unit; Seebeck coefficient S B (T) and S A (T) are all related to temperature. The temperature of the heat dissipation plate 5 is continuously changed to change the temperature difference between the two ends of the upper heat element 2. The temperature sensor 11 collects the temperature T1 and T2 data of the two ends of the upper heat element 2. The data acquisition element 10 collects the voltage U1 and heat flow Q1 data of the upper heat element 2. The data is imported into the computer for fitting to obtain the performance curve of the voltage U1 of the upper heat element 2 changing with the temperature difference ΔT1 between the upper and lower ends and the performance curve of the voltage U1 changing with the heat flow Q1. The calibration process of the lower heat element 4 is the same as that of the upper heat element.

[0059] The actual calibration process for the voltage performance curves of the upper thermoelectric element 2 and the lower thermoelectric element 4 as a function of temperature difference and voltage performance curves as a function of heat flow is as follows:

[0060] (1) The upper heating element 2 is tightly attached to the uniform heating plate 1 and the uniform heat dissipation plate 5;

[0061] (2) The temperature controller 7 starts the uniform heating plate 1, so that the temperature of the uniform heating plate 1 rises and maintains a constant temperature T1;

[0062] (3) After starting the uniform heating plate 1 in step (2), the temperature controller 9 is controlled to start the uniform heat dissipation plate 5 so that the uniform heat dissipation plate 5 maintains a constant temperature T2.

[0063] (4) After the entire system reaches equilibrium, the temperature sensor 11 collects the temperature data T1 of the uniform heating plate 1 and the temperature data T2 of the uniform heat dissipation plate 5, and the data acquisition element 10 collects the voltage U1 and heat flow Q1 of the upper thermoelectric element 2 (obtained by the power input of the heating plate).

[0064] (5) Keep the temperature of the uniform heating plate 1 constant, continuously change the temperature of the uniform heat dissipation plate 5 and repeat the process of steps (3)-(4) multiple times to obtain the relationship between the voltage U1 of multiple upper thermoelectric elements 2, the temperature difference ΔT1 = T1-T2 between the uniform heating plate 1 and the uniform heat dissipation plate 5, and the heat flow Q1.

[0065] (6) The voltage data of each group of thermoelectric elements measured in steps (3)-(5) are imported into the computer for linear fitting with the temperature difference and heat flow data of the uniform heating plate 1 and the uniform heat dissipation plate 5 to obtain the performance curve of the voltage U1 of the upper thermoelectric element 2 as the temperature difference △T1 between the upper and lower ends and the performance curve of the voltage U1 as the heat flow Q1.

[0066] Similarly, the relationship between temperature difference and voltage for the lower thermoelectric element 4 is calibrated:

[0067] (7) Fit the lower heating element 4 tightly with the uniform heating plate 1 and the uniform heat dissipation plate 5;

[0068] (8) Control the upper temperature controller 7 to start the uniform temperature heating plate 1, so that the temperature of the uniform temperature heating plate 1 rises and maintains a constant temperature T1;

[0069] (9) After starting the uniform heating plate 1 in step (8), the temperature controller 9 is controlled to start the uniform heat dissipation plate 5 so that the uniform heat dissipation plate 5 maintains a constant temperature T2.

[0070] (10) After the entire system reaches equilibrium, the temperature sensor 11 collects the temperature data T1 of the uniform heating plate 1 and the temperature data T2 of the uniform heat dissipation plate 5, and the data acquisition element 10 collects the voltage U2 and heat flow Q2 of the lower thermoelectric element 4 (obtained through the input power of the heating plate).

[0071] (11) Keep the temperature of the uniform heating plate 1 constant, continuously change the temperature of the uniform heat dissipation plate 5 and repeat the process of steps (9)-(10) multiple times to obtain the relationship between the voltage U2 of multiple lower thermoelectric elements 4, the temperature difference ΔT2 = T1-T2 between the uniform heating plate 1 and the uniform heat dissipation plate 5, and the heat flow Q2.

[0072] (12) The voltage data of each group of thermoelectric elements measured in steps (9)-(11) are imported into the computer for linear fitting with the temperature difference and heat flow data of the uniform heating plate 1 and the uniform heat dissipation plate 5 to obtain the performance curve of the voltage U2 of the lower thermoelectric element 4 as the temperature difference △T2 between the upper and lower ends and the performance curve of the voltage U2 as the heat flow Q2.

[0073] The second step is the preparation of test samples and equipment:

[0074] A testing device for the thermal conductivity of materials based on thermoelectric power generation is set up and connected, so that the uniform heating plate 1 is tightly attached to the upper thermoelectric element 2 and the heat insulation layer 18, and the lower thermoelectric element 4 is tightly attached to the uniform heat dissipation plate 5; the processed sample is placed between the upper thermoelectric element 2 and the lower thermoelectric element 4, and temperature sensors 11 are set on the uniform heating plate 1 and the uniform heat dissipation plate 5 to test the temperature T1 of the uniform heating plate 1 and the temperature T2 of the uniform heat dissipation plate 5; data acquisition elements 10 are set on both the upper thermoelectric element 2 and the lower thermoelectric element 4 to test the voltage of the thermoelectric element;

[0075] The third step is to activate the stress loading device 16 and the heating device to apply compressive stress and heat flow:

[0076] The stress loading device 16 is controlled to apply pressure to the test sample 3 and the upper and lower thermoelectric elements to a specified load. The upper temperature controller 7 is controlled to raise the temperature of the uniform heating plate 1 to a specific temperature T1 and maintain it at a constant temperature, with the uniform heating plate 1 as the heat source. The lower temperature controller 9 is controlled to maintain the uniform heat dissipation plate 5 at a specific temperature T2 and maintain it at a constant temperature, with the uniform heat dissipation plate 5 as the heat sink. The temperature T1 of the uniform heating plate 1 and the temperature T2 of the uniform heat dissipation plate 5 are collected by the temperature sensor 11. The voltage of the upper thermoelectric element 2 and the lower thermoelectric element 4 is monitored by the data acquisition element 10. When the voltage is stable, the voltage U1 of the upper thermoelectric element 2 and the voltage U2 of the lower thermoelectric element 4 are read.

[0077] Step 4, thermal conductivity calculation:

[0078] In the second step, the temperature T1 of the uniform heating plate 1 and the temperature T2 of the uniform heat dissipation plate 5 are obtained by the temperature sensor 11, and the voltage U1 of the upper thermoelectric element 2 and the voltage U2 of the lower thermoelectric element 4 are obtained by the data acquisition element 10. From the performance curve relationship of the voltage of the thermoelectric element as a function of temperature difference, it can be determined that: the temperature difference ΔT1 between the two ends of the upper thermoelectric element 2 corresponds to the voltage U1 of the upper thermoelectric element 2, and the temperature difference ΔT2 between the two ends of the lower thermoelectric element 4 corresponds to the voltage U2 of the lower thermoelectric element 4. From the performance curve relationship of the voltage of the thermoelectric element as a function of heat flow, it can be determined that: the heat flow Q1 through the upper thermoelectric element 2 corresponds to the voltage U1 of the upper thermoelectric element 2, and the heat flow Q2 through the lower thermoelectric element 4 corresponds to the voltage U2 of the lower thermoelectric element 4.

[0079] The temperatures T1' of the sample near the cold end of the upper thermoelectric element 2 and T2' of the sample near the hot end of the lower thermoelectric element 4 can be calculated as follows:

[0080] T1'=T1-△T1 (4)

[0081] T2' = T2 + △T2 (5)

[0082] The heat flow through the sample at this time can be expressed as:

[0083] Q = (Q1 + Q2) / 2 (6)

[0084] According to the one-dimensional steady-state Fourier thermal conductivity law, the thermal conductivity of the sample is calculated as follows:

[0085]

[0086] Where T1' is the temperature of the upper surface of the sample, T2' is the temperature of the lower surface of the sample, d is the thickness of the sample, and Q is the heat flow through the sample, where d can be directly measured by the in-situ side thickness unit.

[0087] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0088] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A material thermal conductivity testing device based on thermoelectric power generation, characterized in that, The test apparatus includes a test bracket, an upper heat transfer structure, a lower heat transfer structure, a test sample, and an insulation layer. The test bracket comprises a top plate, a support bracket, and a bottom plate, with the top and bottom plates respectively positioned at the top and bottom of the support bracket. The upper heat transfer structure, the test sample, and the lower heat transfer structure are sequentially assembled between the top and bottom plates from top to bottom. The upper heat transfer structure includes an insulation layer, a heating device, and an upper thermoelectric element, arranged sequentially from top to bottom. The lower heat transfer structure includes a lower thermoelectric element and a heat dissipation device, arranged sequentially from top to bottom. The test sample is covered with an insulation layer to reduce radial heat loss. By measuring the voltage and temperature difference of the thermoelectric elements in the upper and lower heat transfer structures, the temperature data of the upper and lower surfaces of the test sample are obtained, and the thermal conductivity of the test sample is calculated using Fourier's law of thermal conductivity. The heating device includes a uniform heating plate, an upper electronic voltage regulator, and an upper temperature controller; the upper temperature controller is electrically connected to the upper electronic voltage regulator, and the upper electronic voltage regulator is electrically connected to the uniform heating plate, which provides a heat source for the test sample; the heat dissipation device includes a uniform heat dissipation plate, a lower electronic voltage regulator, and a lower temperature controller; the lower temperature controller is electrically connected to the lower electronic voltage regulator, and the lower electronic voltage regulator is electrically connected to the uniform heat dissipation plate, which serves as a heat sink for the test sample; The upper or lower thermoelectric element is composed of a ceramic substrate, a metal conductor, a P-type semiconductor, and an N-type semiconductor. The P-type semiconductor and the N-type semiconductor are welded onto the metal conductor and encapsulated by the upper and lower ceramic substrates. When the heating device is activated, the uniform heating plate generates heat flow through the thermoelectric element, which can be approximated as one-dimensional heat transfer along the longitudinal direction of the thermoelectric element. A temperature gradient is formed between the uniform heating plate at the top of the upper ceramic substrate and the test sample at the bottom of the lower ceramic substrate. The temperature sensor is electrically connected to the uniform heating plate and the uniform heat dissipation plate to collect temperature data of the uniform heating plate and the uniform heat dissipation plate; the data acquisition element is electrically connected to the upper thermoelectric element and the lower thermoelectric element to collect voltage data of the upper thermoelectric element and the lower thermoelectric element. The stress loading device is located at the bottom of the test bracket and is used to apply pressure to the test specimen; the pressure sensor is located between the stress loading device and the bottom plate of the test bracket and is used to measure the magnitude of the pressure applied by the stress loading device; the heat insulation layer is located between the top plate of the test bracket and the uniform heating plate; the in-situ thickness measurement unit is connected to the upper and lower surfaces of the test specimen and is used to measure the actual thickness of the test specimen.

2. A method for testing the thermal conductivity of materials based on thermoelectric power generation, the method being based on the thermoelectric power generation thermal conductivity testing device described in claim 1, characterized in that, Includes the following steps: Step 1: Calibrate the thermoelectric performance curves of the upper and lower thermoelectric elements; Step 2: After the upper and lower heating elements are calibrated, the testing device and the sample to be tested are pretreated. Step 3: After the testing device and the test specimen are pretreated, the testing device and the test specimen are tightly fitted together. The stress loading device and heating device are started to apply compressive stress and heat flow. Step 4: After the compressive stress and heat flow loading have stabilized, start the in-situ thickness measurement unit to measure the sample thickness d in real time during the thermal conductivity test. Step 5: Obtain the temperature difference between the upper and lower surfaces of the test sample using the calibrated thermoelectric performance curves of the upper and lower thermoelectric plates, obtain the heat flow through the test sample using a uniform heating plate, obtain the actual thickness of the test sample using an in-situ thickness measurement unit, and calculate the thermal conductivity using Fourier's law of thermal conductivity.

3. The method for testing the thermal conductivity of materials based on thermoelectric power generation according to claim 2, characterized in that, Step 1 is as follows: The upper thermoelectric element is tightly bonded to the heat exchanger and the heat sink. The heat exchanger and the heat sink are activated to generate a one-dimensional longitudinal heat flow. While keeping the temperature of the heat exchanger constant, the temperature of the heat sink is continuously changed, causing a change in the temperature difference between the upper and lower ceramic substrates. Due to the Seebeck effect, the upper thermoelectric element generates a pressure difference. The Seebeck effect formula is: The thermoelectric element absorbs heat from the uniform heating plate and transfers the heat longitudinally to the uniform heat dissipation plate. The heat transfer process of the thermoelectric element can be represented as follows: When the power supply is open, i.e., I=0, the heat flow is only related to the temperature difference, which can be expressed as: Where T1 is the cold junction temperature, T2 is the hot junction temperature, and S... B (T) is the Seebeck coefficient of the P-type semiconductor, S A (T) represents the Seebeck coefficient of the N-type semiconductor, ΔT = T2 - T1, which is the temperature difference between the high and low temperature heat sources; λ is the thermal conductivity of the material; r0 is the internal resistance of the power generation unit; I is the current of the thermoelectric element; and S is the Seebeck coefficient. B (T) and S A (T) are all related to temperature. The temperature of the heat sink is continuously changed to change the temperature difference between the two ends of the upper heatsink. Temperature data T1 and T2 at the two ends of the upper heatsink are collected by temperature sensors. Data on voltage U1 and heat flow Q1 of the upper heatsink are collected by data acquisition elements. The data are imported into the computer for fitting to obtain the performance curve of voltage U1 of the upper heatsink as a function of temperature difference ΔT1 between the upper and lower ends and the performance curve of voltage U1 of the upper heatsink as a function of heat flow Q1. The calibration process of the lower heatsink is the same as that of the upper heatsink.

4. The method for testing the thermal conductivity of materials based on thermoelectric power generation according to claim 2, characterized in that, Step 2 is as follows: A testing device for the thermal conductivity of materials based on thermoelectric power generation is set up and connected, so that the uniform heating plate and the upper thermoelectric element are in close contact, and the lower thermoelectric element and the uniform heat dissipation plate are in close contact. The processed sample is placed between the upper and lower thermoelectric elements. Temperature sensors are set on the uniform heating plate and the uniform heat dissipation plate to test the temperature T1 of the uniform heating plate and the temperature T2 of the uniform heat dissipation plate. Data acquisition elements are set on both the upper and lower thermoelectric elements to test the voltage of the thermoelectric elements.

5. The method for testing the thermal conductivity of materials based on thermoelectric power generation according to claim 2, characterized in that, Step 3 specifically involves: The pressure loading device is controlled to apply pressure to the test sample and the upper and lower thermoelectric plates to a specified load. The upper temperature controller is controlled to raise the temperature of the uniform heating plate to a specific temperature T1 and maintain it at a constant temperature, using the uniform heating plate as a heat source. The lower temperature controller is controlled to maintain the uniform heat dissipation plate at a specific temperature T2 and maintain it at a constant temperature, using the uniform heat dissipation plate as a heat sink. The temperatures T1 and T2 of the uniform heating plate are collected by temperature sensors. The voltages of the upper and lower thermoelectric plates are monitored by data acquisition elements. When the voltages stabilize, the voltages U1 and U2 of the upper and lower thermoelectric plates are read.

6. The method for testing the thermal conductivity of materials based on thermoelectric power generation according to claim 4, characterized in that, Step 5 specifically involves: In step 2, the temperature T1 of the uniform heating plate and the temperature T2 of the uniform heat dissipation plate are obtained by temperature sensors, and the voltages U1 and U2 of the upper and lower thermoelectric elements are obtained by data acquisition elements. The following are determined by the performance curve relationship of the voltage of the thermoelectric element as a function of temperature difference: the temperature difference ΔT1 between the two ends of the upper thermoelectric element corresponding to the voltage U1 of the upper thermoelectric element, and the temperature difference ΔT2 between the two ends of the lower thermoelectric element corresponding to the voltage U2 of the lower thermoelectric element. The following are determined by the performance curve relationship of the voltage of the thermoelectric element as a function of heat flow: the heat flow Q1 through the upper thermoelectric element corresponding to the voltage U1 of the upper thermoelectric element, and the heat flow Q2 through the lower thermoelectric element corresponding to the voltage U2 of the lower thermoelectric element. The calculated temperatures T1' (the temperature of the sample near the cold end of the upper thermoelectric element) and T2' (the temperature of the sample near the hot end of the lower thermoelectric element) are as follows: T1'=T1-△T1 T2'=T2+△T2 The heat flow through the sample at this time can be expressed as: Q = (Q1 + Q2) / 2 According to the one-dimensional steady-state Fourier thermal conductivity law, the thermal conductivity of the sample is calculated as follows: Where T1' is the temperature of the upper surface of the sample, T2' is the temperature of the lower surface of the sample, d is the thickness of the sample, and Q is the heat flow through the sample.

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