Method and device for measuring plane thermal conductivity of flaky material

Abstract

The invention relates to a method and a device for measuring the plane thermal conductivity of a flaky material. According to the method, after a to-be-measured sheet material is obtained, the temperature difference between the center position and the edge position of the current to-be-measured sheet material and the first heat flow passing through the to-be-measured sheet material are measured firstly, then the thickness of the to-be-measured sheet material is changed, the heat flow is adjusted to enable the temperature difference to be kept unchanged, and the heat flows corresponding to different thicknesses are obtained; and finally, according to the first heat flow, the temperature difference and a heat conduction amount correction value, the plane heat conductivity of the to-be-measured sheet material is calculated, and the heat conduction amount correction value is obtained based on the first heat flow and heat flows corresponding to different thicknesses. Compared with the prior art, the method has the advantages of effectively improving the accuracy of plane thermal conductivity measurement and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of material physical property measurement, and in particular to a method and device for measuring the planar thermal conductivity of sheet materials. Background Art

[0002] The thermal conductivity of a material is a main parameter for evaluating the heat conduction or heat insulation ability of the material. For materials that are isotropic in terms of their organizational structure, their thermal conductivity has no directionality; for materials with significant directional differences in their organizational structure, such as certain woven sheet materials, the thermal conductivity in the direction perpendicular to the plane and the thermal conductivity in the direction parallel to the plane will vary due to different orientations of the microstructures.

[0003] Currently, when measuring the thermal conductivity of a material using the heat flux method, for the case where the sample itself is already in the shape of a thin sheet, due to the structure of the measuring device, for example, Chinese Patent CN211927759U discloses a test accessory for a heat flux method thermal conductivity meter. This accessory is used on a heat flux method thermal conductivity meter, which includes an upper radiator, an upper Peltier plate temperature control system, a hot plate, a sample, a cold plate, a lower Peltier plate temperature control system, and a lower radiator arranged in parallel from top to bottom. During the test, the sample is placed between two flat plates, the cold plate and the hot plate. By setting the test conditions, the upper and lower plates reach different constant temperatures respectively, and then the thermal conductivity is calculated. However, this scheme can only measure the heat transfer from one side of the thin sheet to the other side, that is, in the direction perpendicular to the plane of the thin sheet, and the obtained thermal conductivity is the thermal conductivity in the direction perpendicular to the plane, and it is unable to effectively measure the thermal conductivity of the sheet material in the direction parallel to the plane. In addition, existing schemes capable of measuring the anisotropy of sheet materials ignore possible measurement errors during calculation, which will affect the accuracy of the measurement results. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects existing in the prior art and provide a method and device for measuring the planar thermal conductivity of sheet materials, which can accurately measure the thermal conductivity of thin sheet-shaped materials along their planar direction.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] According to a first aspect of the present invention, there is provided a method for measuring the planar thermal conductivity of a sheet material, comprising the following steps: S1, obtaining the sheet material to be measured; S2, measuring the temperature difference between the central position and the edge position of the current sheet material to be measured and the first heat flux passing through the sheet material to be measured, wherein the central position coincides with a preset heating zone, the edge position coincides with a preset temperature measuring zone, and there is a heat insulation zone between the heating zone and the temperature measuring zone; S3, changing the thickness of the sheet material to be measured, adjusting the heat flux to keep the temperature difference unchanged, and obtaining the heat fluxes corresponding to different thicknesses respectively; S4, calculating the planar thermal conductivity of the sheet material to be measured according to the first heat flux, the temperature difference and the heat conduction correction value, and the heat conduction correction value is obtained based on the first heat flux and the heat fluxes corresponding to different thicknesses.

[0007] As a preferred technical solution, when the sheet material to be measured is circular, the heating zone is circular, the edge position is located in a preset annular temperature measuring zone, and the planar thermal conductivity is expressed as:

[0008]

[0009] In the formula, ρ is the planar thermal conductivity of the sheet material to be measured, Q1 is the first heat flux at the initial thickness, DQ is the heat conduction correction value, r1 is the inner radius of the annular temperature measuring zone, r0 is the radius of the heating zone, d is the thickness of the sheet material to be measured, and DT is the temperature difference between the central position and the edge position.

[0010] As a preferred technical solution, the heat conduction correction value is obtained by the least squares method, and is specifically expressed as:

[0011]

[0012] In the formula, Q2 and Q3 are the heat fluxes corresponding to two different thicknesses of the sheet material to be measured after changing the initial thickness respectively.

[0013] As a preferred technical solution, the heat conduction correction value is obtained by the graphical method. The specific process includes: forming data pairs of different thicknesses of the sheet material to be measured and the corresponding heat fluxes; plotting multiple data pairs on a two-dimensional thickness-heat flux diagram and drawing a straight line as much as possible through each data pair; determining the intersection point of the straight line and the vertical axis of the two-dimensional diagram as the heat conduction correction value.

[0014] According to a second aspect of the present invention, there is provided a planar thermal conductivity measuring device for a sheet material, which is used to implement the method described above. The device includes measuring components that are oppositely arranged and have the same structure. Each measuring component includes a heating block, a temperature measuring block, and a heat insulation element located between the heating block and the temperature measuring block. Both the heating block and the temperature measuring block include contact surfaces that contact the sheet material to be measured, and the contact surfaces of the two are flush. During the measurement process, both sides of the sheet material to be measured are in close contact with the corresponding measuring components, and the heating powers of the heating blocks of different measuring components are the same, and the temperatures of the temperature measuring blocks are the same.

[0015] As a preferred technical solution, the heating block is cylindrical, and the temperature measuring block is annular.

[0016] As a preferred technical solution, the temperature measuring block has a hollow structure and is internally provided with a circulating coolant.

[0017] As a preferred technical solution, the heating block integrates a temperature sensor and a heat flux sensor.

[0018] As a preferred technical solution, the heat insulation element is one of plastic foam and quartz wool.

[0019] As a preferred technical solution, after the device is loaded with the sheet material to be measured, one of the measuring components is fixed, and the other measuring component is movable.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. When the method provided by the present invention measures the planar thermal conductivity of a sheet material, considering that due to the too thin thickness of the material to be measured and the too large heat-receiving area of the heat insulation area, the heat flow leaking through the heat insulation area is not negligible relative to the material to be measured. Therefore, a heat conduction correction value is introduced. Compared with the existing thermal conductivity measurement method, this method can reduce errors and effectively improve the accuracy of planar thermal conductivity measurement.

[0022] 2. The measuring device provided by the present invention has a simple structure and strong applicability. Different thicknesses of sheet materials to be measured can be loaded between the symmetrically arranged measuring components, which is convenient for introducing and calculating the heat conduction correction value to improve the accuracy of planar thermal conductivity measurement of the sheet material. Description of the Drawings

[0023] Figure 1 is a schematic flow chart of the method provided by the present invention;

[0024] Figure 2 is a side sectional view of the device in the embodiment of the present invention;

[0025] Figure 3 is a top view of the device in the embodiment of the present invention;

[0026] Figure 4 This is the two-dimensional thickness-heat flux diagram drawn in the embodiment of the present invention;

[0027] Wherein: 201, upper measurement component; 202, lower measurement component; 200, sheet material to be measured; 301, heating block; 302, temperature measurement block; 303, heat insulation element. Detailed implementation manners

[0028] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and gives detailed implementation manners and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0029] Embodiment

[0030] As Figure 1 shown, this embodiment provides a method for measuring the planar thermal conductivity of a sheet material. After obtaining the sheet material to be measured, the method first measures the temperature difference between the central position and the edge position of the current sheet material to be measured and the first heat flux passing through the sheet material to be measured, and then by changing the thickness of the sheet material to be measured and adjusting the heat flux to keep the temperature difference unchanged, obtains the heat fluxes corresponding to different thicknesses respectively. Finally, according to the first heat flux, the temperature difference and the heat conduction correction value, calculates the planar thermal conductivity of the sheet material to be measured, and the heat conduction correction value is obtained based on the first heat flux and the heat fluxes corresponding to different thicknesses. Among them, the central position of the sheet material to be measured coincides with a preset heating area, the edge position coincides with a preset temperature measurement area, and there is a heat insulation area between the heating area and the temperature measurement area.

[0031] The foregoing method can be implemented by a device as Figure 2 and Figure 3 shown. The device includes measurement components that are oppositely arranged and have the same structure, specifically an upper measurement component 201 and a lower measurement component 202. During measurement, the sheet material 200 to be measured is loaded between the upper measurement component 201 and the lower measurement component 202. After the device loads the sheet material 200 to be measured, the upper measurement component 201 is movable, and the lower measurement component 202 is immovable.

[0032] Each measurement component includes a heating block 301, a temperature measurement block 302, and a heat insulation element 303 located between the heating block 301 and the temperature measurement block 302. Both the heating block 301 and the temperature measurement block 302 include contact surfaces that contact the sheet material 200 to be measured, and the contact surfaces of the two are flush; during the measurement process, the upper and lower sides of the sheet material 200 to be measured are in close contact with the corresponding measurement components respectively, and the heating powers of the heating blocks of the two measurement components are the same, and the temperatures of the temperature measurement blocks are the same.

[0033] Exemplarily, Figure 2 and Figure 3The heating block 301 therein is cylindrical, and the temperature measuring block 302 is annular. Specifically, the cylindrical heating block 301 is the center of the measuring device with a radius of r0, integrating a temperature sensor and a heat flux sensor. Inside the annular temperature measuring block 302 concentric with the heating block 301 is a hollow structure where the coolant circulates to ensure the temperature of the temperature measuring block 302 remains stable during the test and does not fluctuate significantly with the test duration. The inner diameter of the temperature measuring block 302 is r1, and the outer diameter is r2, satisfying r0 < r1 < r2 < R, where R is the radius of the sheet-like material 200 to be measured; the contact material surfaces of the heating block 301 and the temperature measuring block 302 are kept flush; between the heating block 301 and the temperature measuring block 302, there is filled with a high thermal resistance heat insulation material such as plastic foam, quartz wool and other high thermal resistance materials; during the measurement process, the heating powers of the heating blocks at the centers of the upper and lower measurement components are kept consistent, and the temperatures of the coolant flowing through the temperature measuring blocks of the upper and lower measurement components are kept consistent. In actual use, exemplarily, heat is transferred to the heating block through a common heating element. Since the heating block is in close contact with the sheet-like material, heat is then transferred to the sheet-like material. The temperature sensor is used to measure and monitor the temperature of the sheet-like material at the central position, and the heat flux sensor is used to monitor the heat flux to facilitate the subsequent adjustment of the heat flux; temperature measuring elements can also be installed on the temperature measuring block to monitor the temperature at the edge position, so as to obtain the temperature difference from the central position. When heat is transferred from the heating area to the temperature measuring block, the coolant in the temperature measuring block will take away the corresponding heat to ensure the temperature of the temperature measuring block remains stable during the test.

[0034] In the device, the action area of the heating block corresponds to the heating area in the measuring method, the action area of the temperature measuring block corresponds to the temperature measuring area in the measuring method, and the action area of the heat insulation material corresponds to the heat insulation area. Based on this, exemplarily, the specific implementation steps of the foregoing method are as follows:

[0035] (1) Obtain the sheet-like material to be measured, cut the material into circular sample pieces, with the number of pieces being 3, the thickness d of a single sample piece, and the radius R.

[0036] (2) Place the single sample piece obtained after cutting on the device and apply pressure to the sample to ensure close contact between the sample and the device, and ensure that the center position of the sample coincides with the center heating area position of the device.

[0037] (3) During the measurement process, measure the temperature difference DT between the central position and the edge position of the sample and the heat flux Q1 passing through the sample (i.e., the first heat flux corresponding to the initial thickness).

[0038] (4) Overlap the second and third sample pieces with the initial single sample piece respectively, repeat processes (2) to (3), and ensure that the temperature difference DT during the test is consistent with that of the single sample piece test by adjusting the value of the heat flux, and the corresponding heat fluxes are Q2 and Q3 respectively.

[0039] (5) Calculate the planar thermal conductivity ρ of the sample (i.e., the planar thermal conductivity of the sheet material to be measured) according to the following formula:

[0040]

[0041] In the formula, DQ is the corrected value of the heat conduction quantity, r0 is the radius of the central cylindrical heating block of the device (i.e., the radius of the heating area), r1 is the inner radius of the annular temperature measurement ring (i.e., the inner radius of the annular temperature measurement area), and π is the pi.

[0042] (6) The specific value of DQ can be obtained by the least squares method based on the values of Q1, Q2, and Q3, or can be obtained by graphing. Specifically:

[0043] For some ultra-thin samples, although their thermal conductivity is much greater than that of the heat insulation material, due to the too thin thickness of the sample and the too large heat-receiving area of the heat insulation material, the heat leakage through the heat insulation material cannot be ignored relative to the sample.

[0044] During the test of samples with different thicknesses, since the temperature difference ΔT is ensured to be the same, it can be considered that the heat flow transmitted through the heat insulation material is constant, all being DQ. Also, because the heat flow Qs transmitted along the annular sample and the thickness δ of the sample (having the same meaning as d in the previous text, here δ is used for principle analysis) satisfy:

[0045]

[0046] Therefore, the relationship between the total heat flow Q during the measurement process and the sample thickness is:

[0047] Q = k * δ + DQ.

[0048] Based on the foregoing analysis, the specific process of obtaining the corrected value DQ of the heat conduction quantity by the least squares method is as follows:

[0049] When the data pairs (xi, yi) satisfy the linear equation y = k * x + b, the expression for b obtained by the least squares method is b = (A * D - C * B) / (A * n - B * B), where:

[0050]

[0051] In the formula, n is the total number of data pairs.

[0052] Substitute xi = d, 2d, 3d, yi = Q1, Q2, Q3 into the above expression, and calculate to obtain:

[0053]

[0054] That is:

[0055]

[0056] Optionally, the specific process of calculating the corrected heat conduction value DQ by the graphical method is as follows:

[0057] As Figure 4 shown, plot the data pairs (d, Q1), (2d, Q2), and (3d, Q3) on a two-dimensional thickness-heat flow diagram, and draw a straight line that passes through the three points as much as possible. The intersection of the straight line and the vertical axis is the value of DQ.

[0058] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative labor. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention through logical analysis, reasoning, or limited experiments based on the concept of the present invention on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A method for measuring the planar thermal conductivity of a sheet material, characterized in that, Including the following steps: S1. Obtain the sheet material to be measured; S2. Measure the temperature difference between the central position and the edge position of the current sheet material to be measured and the first heat flux passing through the sheet material to be measured. The central position coincides with a preset heating zone, the edge position coincides with a preset temperature measurement zone, and there is a heat insulation zone between the heating zone and the temperature measurement zone; S3. Change the thickness of the sheet material to be measured, adjust the heat flux to keep the temperature difference unchanged, and obtain the heat fluxes corresponding to different thicknesses respectively; S4. Calculate the planar thermal conductivity of the sheet material to be measured according to the first heat flux, the temperature difference and the heat conduction correction value. The heat conduction correction value is obtained based on the first heat flux and the heat fluxes corresponding to different thicknesses.

2. The method for measuring the planar thermal conductivity of a sheet material according to claim 1, characterized in that, When the sheet material to be measured is circular, the heating zone is circular, the edge position is located in a preset annular temperature measurement zone, and the planar thermal conductivity is expressed as: In the formula, ρ is the planar thermal conductivity of the sheet material to be measured, Q1 is the first heat flux at the initial thickness, DQ is the heat conduction correction value, r1 is the inner radius of the annular temperature measurement zone, r0 is the radius of the heating zone, d is the thickness of the sheet material to be measured, and DT is the temperature difference between the central position and the edge position.

3. The method for measuring the planar thermal conductivity of the sheet material according to claim 2, wherein, The heat conduction correction value is obtained by the least square method, and is specifically expressed as: In the formula, Q2 and Q3 are the heat fluxes corresponding to two different thicknesses of the sheet material to be measured after changing the initial thickness respectively.

4. The method for measuring the planar thermal conductivity of a sheet material according to claim 1, characterized in that, The heat conduction correction value is obtained by the graphical method. The specific process includes: Form data pairs with different thicknesses and the corresponding heat fluxes of the sheet material to be measured; Plot multiple data pairs on a two-dimensional thickness-heat flux diagram, and draw a straight line as far as possible through each data pair; Determine the intersection point of the straight line and the vertical axis of the two-dimensional diagram as the heat conduction correction value.

5. A planar thermal conductivity measurement device for sheet materials, characterized in that, The device is used to implement the method according to any one of claims 1-4. The device includes measurement components arranged oppositely and having the same structure. Each measurement component includes a heating block, a temperature measurement block and a heat insulation element located between the heating block and the temperature measurement block. The heating block and the temperature measurement block both include contact surfaces in contact with the sheet material to be measured, and the contact surfaces of the two are flush. During the measurement process, both sides of the sheet material to be measured are in close contact with the corresponding measurement components respectively, and the heating powers of the heating blocks of different measurement components are the same and the temperatures of the temperature measurement blocks are the same.

6. The planar thermal conductivity measuring device for sheet materials according to claim 5, characterized in that, The heating block is cylindrical and the temperature measurement block is annular.

7. The planar thermal conductivity measuring device for sheet materials according to claim 6, characterized in that, The temperature measurement block is of a hollow structure and is internally provided with a circulating coolant.

8. The planar thermal conductivity measuring device for sheet materials according to claim 5, characterized in that, The heating block integrates a temperature sensor and a heat flux sensor.

9. The planar thermal conductivity measuring device for sheet materials according to claim 5, wherein, The heat insulation element is one of plastic foam and quartz wool.

10. The planar thermal conductivity measuring device for sheet materials according to claim 5, characterized in that, After the device loads the sheet material to be measured, one of the measurement components is fixed and the other measurement component is movable.

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