A Testing Method for the Peltier Coefficient of a Bulk Material

Abstract

The present invention relates to a method for testing the Peltier coefficient of a bulk material, and the specific steps are as follows: 1) Prepare a cuboid-shaped sample to be tested, weld a pair of thermocouples at the top and bottom positions on one side of the sample to be tested, test and calculate the system error ΔT<subgt;0< / subgt; of the two pairs of thermocouples before energization, and then pass a constant current I to test and calculate the temperature difference ΔT<subgt;t< / subgt> between the two pairs of thermocouples. Subtract ΔT<subgt;0< / subgt> from ΔT<subgt;t< / subgt> to obtain the temperature difference ΔT at this current; 2) Model according to the parameters of the sample to be tested in the COMSOL simulation software to obtain the optimized boundary heat source coefficient B at the corresponding current. Perform linear regression on different constant currents I and the measured boundary heat source coefficient B, and the intercept of the obtained regression curve is the Peltier coefficient Π. The testing method of the present invention can measure the Peltier coefficient of the bulk material, takes into account the influence of interfacial Joule heat, has high precision, and this measurement method can also be applied in a magnetic field.

Description

Technical Field

[0001] The present invention belongs to the technical field of testing or analyzing materials by thermal methods, and particularly relates to a method for testing the Peltier coefficient of bulk materials. Background Art

[0002] Thermoelectric materials have a unique Peltier effect and can generate electricity through temperature difference or directly pump heat through electric energy. The Peltier coefficient of thermoelectric materials is defined as the ratio of the heat released by the energized joint per unit time to the current, and this Peltier coefficient can be used to evaluate the refrigeration ability of thermoelectric materials.

[0003] In the thermoelectric effect, the Peltier coefficient Π is defined as shown in formula (1):

[0004] dQ / dt = ΠI Formula (1)

[0005] Where dQ / dt is the heat absorption or release amount per unit time at the contact surface between the thermoelectric material and the electrode, and I is the applied current. This formula describes the Peltier effect from the perspective of power, so the Peltier coefficient can be indirectly obtained by measuring the heat flow.

[0006] Currently, there is no commercial device specifically for measuring the Peltier coefficient. Generally, the Seebeck coefficient is indirectly converted into the Peltier coefficient, and this relationship is usually called the second Kelvin relationship, as shown in formula (2):

[0007] Π = αT Formula (2)

[0008] Where Π is the Peltier coefficient, α is the Seebeck coefficient, and T is the average temperature of the test sample. This formula does not hold under a magnetic field.

[0009] KOYANO et al. from the Japan Advanced Institute of Science and Technology used tip contact in 2009 and measured the Peltier coefficient of (Bi,Sb)2Te3 by AC and DC methods. However, the Peltier coefficient measured by this method is only limited to the contact point and cannot measure the Peltier coefficient of the bulk material. Hilmar et al. from the Max Planck Institute for Microstructure Physics measured the Peltier coefficient of polycrystalline silicon solar panels using lock-in thermography. This method can only measure thin film materials, and the measurement results are affected by the emissivity of the sample surface. GARRIDO et al. from the University of Valencia measured the Peltier coefficient of thermoelectric modules using the energy balance relationship during 2009 - 2013. The thermoelectric module consists of multiple groups of P / N type thermoelectric materials forming Π-shaped thermoelectric arms. Therefore, this Peltier coefficient is the difference between the two P / N type thermoelectric materials and is not the Peltier coefficient of a single material. Moreover, this measurement method does not consider the influence of interfacial Joule heat. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a test method for the Peltier coefficient of bulk materials in view of the above deficiencies in the prior art.

[0011] To solve the above technical problem, the technical solution provided by the present invention is:

[0012] Provide a test method for the Peltier coefficient of bulk materials, and the specific steps are as follows:

[0013] 1) Prepare a cuboid-shaped sample to be measured, place the length direction of the sample to be measured perpendicular to the ground, weld a pair of thermocouples at the top and bottom positions on one side of the sample to be measured for temperature measurement, make an electrode on the upper and lower surfaces of the sample to be measured respectively, and then install the sample to be measured on a copper heat sink. First, use a temperature measuring instrument to test and calculate the system error ΔT0 (temperature difference at both ends) before energizing the two pairs of thermocouples. Then, under vacuum conditions, pass a constant current I through the electrodes at both ends of the sample to be measured through the electrode wires. After 300 seconds, the temperature distribution of the sample to be measured reaches a stable state. At this time, test and calculate the temperature difference ΔT between the two pairs of thermocouples t , ΔT t Subtract ΔT0 from ΔT to obtain the temperature difference ΔT at this current.

[0014] 2) Select the three-dimensional space dimension and the physical field of the thermoelectric effect in the COMSOL simulation software, add a steady-state study, and then establish a corresponding geometric model of the thermoelectric device with the same shape as the model to be measured according to the sample to be measured described in step 1). Modify the Peltier coefficient built into the software to the boundary heat source coefficient B (the COMSOL simulation software has built in the second Kelvin relation and does not consider the influence of the interfacial Joule heat). Define the boundary heat source coefficient B and the current I in the "Global Parameters", and add the material property parameters of the geometric model of the thermoelectric device. Set the initial value (ambient temperature, consistent with the experimental temperature) and boundary conditions (temperature of the heat sink, adiabatic on the four sides and the top surface) of the geometric model of the thermoelectric device. Calculate the temperature field of the sample to be measured when a constant current I is passed through using the COMSOL simulation software, and extract the steady-state temperature difference ΔT in the COMSOL simulation software. c , and by continuously adjusting to obtain an optimized boundary heat source coefficient B, such that the temperature difference ΔT simulated by the COMSOL simulation software c is consistent with the temperature difference ΔT actually measured under the same temperature and the same constant current I in step 1). Adjust the value of the constant current I, repeat the above steps, obtain the optimized boundary heat source coefficient B corresponding to the current, perform a linear regression on different constant currents I and the measured boundary heat source coefficient B, and obtain a regression curve, the intercept of which is the Peltier coefficient Π.

[0015] Before modifying the software parameters, the boundary heat source power P at the free end is P = ΠI, with only a first-order term, and Π = αT. The present invention takes into account the Joule heat at the boundary in an actual thermoelectric device, that is, P = ΠI + R×I 2 . After modifying the software configuration, the boundary heat source power P = BI, then B = Π + R×I, where R is the resistance value of the interfacial Joule heat source.

[0016] According to the above scheme, the diameter of the thermocouple wire of the thermocouple described in step 1) is less than 30 microns, the length is 30 - 40 mm, and the distance from the thermocouple welded to the top of the sample to be measured to the upper surface of the sample to be measured is equal to the distance from the thermocouple welded to the bottom of the sample to be measured to the lower surface of the sample to be measured. Selecting a thermocouple wire of this specification can reduce the heat transfer influence of the thermocouple wire and reduce the measurement error.

[0017] According to the above scheme, the thickness of the electrode described in step 1) is 0.1 - 0.5 mm. The preferred electrode is a silver electrode, and the electrode covers the upper and lower surfaces of the sample to be measured.

[0018] According to the above scheme, the measurement accuracy of the temperature measuring instrument described in step 1) is ±0.02 K. For the measurement of the steady-state temperature, the number of data acquisition points is not less than 20.

[0019] According to the above - mentioned scheme, the diameter of the electrode wire in step 1) is less than 0.1 mm, and the length is 40 - 50 mm. Selecting this specification can reduce the influence brought by heat transfer of the wire.

[0020] According to the above - mentioned scheme, the physical field of the thermoelectric effect in step 2) is obtained by coupling the physical field of solid heat transfer and the physical field of electric current.

[0021] According to the above - mentioned scheme, the material property parameters of the geometric model of the thermoelectric device in step 2) are the performance parameters of the sample to be measured, specifically the electrical conductivity (measured by the four - probe method), the thermal conductivity (measured by the steady - state method), the Seebeck coefficient (measured by the steady - state method), the constant - pressure heat capacity (measured by DSC), the density (measured by the drainage method), and the relative dielectric constant (since there is no alternating current involved, the relative dielectric constant is 1).

[0022] According to the above - mentioned scheme, the temperature difference ΔT simulated by the COMSOL simulation software in step 2) c is consistent with the temperature difference ΔT actually measured under the same temperature and the same constant current I in step 1), and it is required to satisfy the following formula:

[0023] (ΔT c - ΔT) / ΔT < 0.01.

[0024] The beneficial effect of the present invention is that: by using the testing method of the present invention, the Peltier coefficient of the bulk material can be measured, and considering the influence of interfacial Joule heat, the accuracy is high, and this measurement method can also be applied in a magnetic field. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic structural diagram of the thermoelectric device test piece in Embodiment 1 of the present invention;

[0026] Figure 2 is a geometric model diagram of the thermoelectric device constructed by the COMSOL simulation software in Embodiment 1;

[0027] Figure 3 is a curve graph of the temperature difference change between two thermocouples when a constant current of 0.1 A is passed in a vacuum environment at 300 K in step 1) of this embodiment;

[0028] Figure 4 is a linear regression curve graph of the current I and the corresponding boundary heat source coefficient B in Embodiment 1;

[0029] Figure 5 is the Peltier coefficient curve obtained at different temperatures in Embodiment 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the drawings.

[0031] Example 1

[0032] The Peltier coefficient of the bulk material is tested, and the specific test method is as follows:

[0033] 1) Prepare a cuboid-shaped sample to be tested (bismuth telluride thermoelectric material, with length, width and height of 3 mm×3 mm×10 mm). Place the sample to be tested vertically with its length direction perpendicular to the ground. Weld a pair of thermocouples on one side of the sample to be tested near the top and bottom positions for temperature measurement (the diameter of each thermocouple wire is less than 30 microns and the length is 40 mm). The distance between the two pairs of thermocouples is d (6.7 mm). Make a silver electrode on the upper and lower surfaces of the sample to be tested (the electrode thickness is 0.5 mm). Then install the sample to be tested on a copper heat sink to obtain a thermoelectric device test piece (for the schematic diagram, see Figure 1 ). First, use a temperature measuring instrument (temperature control accuracy ±0.02 K, for the measurement of steady-state temperature, the data acquisition points are 20) to test and calculate the system error ΔT0 (temperature difference at both ends) of the two pairs of thermocouples at room temperature (300 K) before energization. This temperature difference is caused by the system error. Then, under vacuum conditions (vacuum degree below 10 -3 Pa), energize the electrodes at both ends of the sample to be tested through the electrode wires (length 40 mm, diameter 0.1 mm). Test the stable temperature difference ΔT of the two pairs of thermocouples after being energized with a constant current I (0.1 A) for 300 s at 300 K in a vacuum environment and remaining in the energized state. t ΔT t Subtract ΔT0 from ΔT to obtain the temperature difference ΔT at this current. Adjust I to -0.1 A, -0.05 A, and 0.05 A respectively, and the corresponding temperature difference data are shown in Table 1 below:

[0034] Table 1

[0035] Current I Temperature difference ΔT I1 -0.1 dT1 4.17K I2 -0.05 dT2 1.95K I3 0.05 dT3 -1.77K I4 0.1 dT4 -3.29K

[0036] 2) Select "Model Wizard" on the main interface of COMSOL simulation software. Select "Three-dimensional" in "Spatial Dimension", select "Thermoelectric Effect" in the sub-module of the solid heat transfer module of the physical field, and select "Steady State" in "Study". Then, establish a geometric model of the thermoelectric device with the same shape as the model to be tested according to the sample to be tested described in step 1). Select "Cuboid" in the "Geometry" tab page, set the "Width", "Depth", and "Height" of the "Cuboid" to 3 mm, 3 mm, and 11 mm respectively. Then expand the "Layer" option, set the thickness of "Layer 1" to 0.5 mm (to construct the electrode model), and set "Bottom" and "Top" in "Layer Position" to the checked state. Select "All Build" in the "Form Union" option. The geometric model diagram of the constructed thermoelectric device is shown in Figure 2, then modify the Peltier coefficient built into the software to the boundary heat source coefficient B (the boundary heat source coefficient B is a quantity matrix, i.e., Bxx = Byy = Bzz, Bij = 0 (i ≠ j)). In the "Multiphysics" - "Thermoelectric Effect" - "Equation View" in the "Model Builder", modify "tee1.S*T" to B, and define the boundary heat source coefficient B and the current I in the "Global Parameters". Select "Empty Material" in the material main window, and input the known material properties (electrical conductivity, thermal conductivity, Seebeck coefficient, constant-pressure heat capacity, density, and relative permittivity) of the thermoelectric material to be measured into this "Empty Material", click Figure 2 the 2 in Figure 2 , assign the material properties to domain 2, select "copper" in "Browse Materials" and add it to the model tree, and click 1 and 3 to assign it to domain 1 and domain 3 (electrode materials). Set the initial values and boundary conditions of the geometric model of the thermoelectric device. Set the initial temperature in "Solid Heat Transfer" in the "Model Builder" to 300K, add a "Temperature" node, and set Figure 2 the lower bottom surface in Figure 2 to 300K. In the "Current" module, add a "Ground" node, and set Figure 2 the lower bottom surface in Figure 2 to the ground surface, add a "Terminal" node, and select Figure 2 the upper end surface in Figure 2 , fill in the actually applied current I into the "Current" selection box. After the settings are completed, perform a steady-state calculation to calculate the temperature field of the sample to be measured when a constant current I (0.1A) is passed through. Use the "mphinterp" command to extract the steady-state temperature difference ΔT in the COMSOL simulation software c , and continuously adjust to obtain an optimized boundary heat source coefficient B such that the temperature difference ΔT simulated by the COMSOL simulation software c is consistent with the temperature difference ΔT measured actually at the same temperature and the same constant current I in step 1), that is, it satisfies the following relationship:

[0037] (ΔT c - ΔT) / ΔT < 0.01

[0038] Adjust the current I to -0.1A, -0.05A, and 0.05A respectively, repeat the above steps to obtain the boundary heat source coefficient B corresponding to the respective currents, and use Origin to perform a linear regression operation on the current I and the corresponding boundary heat source coefficient B to obtain a regression curve, as Figure 4 shown. Its intercept is the Peltier coefficient Π (-60.3 mV). Through linear regression, the slope R can also be calculated, and R×I 2 is the magnitude of the interfacial Joule heat.

[0039] Figure 3For this embodiment, at 300K and in a vacuum environment, when a constant current of 0.1A is passed, the temperature difference change curve between the two thermocouples can be seen. After maintaining the power supply for 180s, the temperature difference tends to be stable.

[0040] Figure 5 The Peltier coefficient curves obtained in this embodiment at different temperatures. cal.αT is the calculated value obtained according to the Seebeck coefficient formula (1), and meas. is the measured value using the method of this embodiment. It can be seen that there is a certain difference between the two, and the method of this embodiment has higher accuracy.

Claims

1. A test method for the Peltier coefficient of a bulk material, characterized in that, The specific steps are as follows: 1) Prepare a sample to be measured in the shape of a cuboid. Place the sample vertically with its length direction perpendicular to the ground. Weld a pair of thermocouples at the top and bottom positions on one side of the sample to measure temperature. Make an electrode on each of the upper and lower surfaces of the sample. Then install the sample to be measured on a copper heat sink. First, use a temperature measuring instrument to test and calculate the systematic error ΔT0 of the two pairs of thermocouples before energization. Then, under vacuum conditions, pass a constant current I through the electrodes at both ends of the sample to be measured through the electrode wires. After 300 seconds, the temperature distribution of the sample to be measured reaches a steady state. At this time, test and calculate the temperature difference ΔT between the two pairs of thermocouples. t , ΔT t Subtract ΔT0 from it to obtain the temperature difference ΔT at this current. 2) Select the three-dimensional space dimension and the physical field of the thermoelectric effect in the COMSOL simulation software, add a steady-state study, and then establish a corresponding geometric model of the thermoelectric device with the same shape as the model to be measured according to the sample to be measured described in step 1). Modify the Peltier coefficient built into the software to the boundary heat source coefficient B, define the boundary heat source coefficient B and the current I in the "Global Parameters", and add the material property parameters of the geometric model of the thermoelectric device. Set the initial values and boundary conditions of the geometric model of the thermoelectric device. Calculate the temperature field of the sample to be measured when a constant current I is passed through by the COMSOL simulation software, and extract the steady-state temperature difference ΔT in the COMSOL simulation software. c , and continuously adjust to obtain an optimized boundary heat source coefficient B, so that the temperature difference ΔT simulated by the COMSOL simulation software c is consistent with the temperature difference ΔT measured actually under the same temperature and the same constant current I in step 1). Adjust the value of the constant current I, repeat the above steps, obtain the optimized boundary heat source coefficient B corresponding to the current, perform a linear regression on different constant currents I and the measured boundary heat source coefficients B, and obtain a regression curve. The intercept of the curve is the Peltier coefficient Π.

2. The testing method for the Peltier coefficient of the bulk material according to claim 1, wherein, Step 1) The diameter of the thermocouple wire of the thermocouple is less than 30 microns, and the length is 30 - 40 mm. The distance from the thermocouple welded to the top of the sample to the upper surface of the sample is equal to the distance from the thermocouple welded to the bottom of the sample to the lower surface of the sample.

3. The test method for the Peltier coefficient of the bulk material according to claim 1, characterized in that, Step 1) The thickness of the electrode is 0.1 - 0.5 mm.

4. The method for testing the Peltier coefficient of the bulk material according to claim 1, wherein Step 1) The measurement accuracy of the temperature measuring instrument is ±0.02 K. For the measurement of the steady-state temperature, the number of data acquisition points is not less than 20.

5. The test method for the Peltier coefficient of the bulk material according to claim 1, characterized in that, Step 1) The diameter of the electrode wire is less than 0.1 mm, and the length is 40 - 50 mm.

6. The method for testing the Peltier coefficient of a bulk material according to claim 1, characterized in that, Step 2) The physical field of the thermoelectric effect is obtained by coupling the physical field of solid heat transfer and the physical field of electric current.

7. The method for testing the Peltier coefficient of the bulk material according to claim 1, wherein Step 2) The material property parameters of the geometric model of the thermoelectric device are the performance parameters of the sample to be measured, specifically conductivity, thermal conductivity, Seebeck coefficient, constant-pressure heat capacity, density, and relative permittivity.

8. The method for testing the Peltier coefficient of a bulk material according to claim 1, characterized in that, Temperature difference ΔT simulated by COMSOL simulation software in step 2) c is consistent with the temperature difference ΔT actually measured at the same temperature and the same constant current I in step 1), and it is required to satisfy the following formula: (ΔT c -ΔT) / ΔT < 0.01.

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