A method and apparatus for measuring steady-state thermal conductivity with self-calibration of heat loss.

Abstract

This invention discloses a method and apparatus for measuring steady-state thermal conductivity with self-calibrated thermal loss. Combining the theory of self-calibrated thermal loss, it utilizes a layered thermal barrier of high and low thermal conductivity materials to achieve quasi-one-dimensional heat conduction. This invention eliminates the need for additional thermal loss calibration, using easily measurable physical quantities to account for thermal loss and calculate the accurate thermal conductivity and thermal resistance of the sample. Compared to traditional quasi-steady-state testing methods, this invention is applicable to measuring the thermal conductivity and contact thermal resistance of both extremely high thermal conductivity thin films and extremely low thermal conductivity materials under wide temperature ranges and varying pressure conditions. This invention eliminates the need for additional thermal protection and thermal loss calibration; the accurate thermal conductivity can be directly calculated from the measurement data, simplifying the steady-state measurement process and improving the repeatability and accuracy of the measurement. It can be used to measure the thermal conductivity and thermal resistance of samples under different temperatures and pressures.

Description

Technical Field

[0001] This invention belongs to the field of material thermal property measurement research, specifically relating to a method and device for measuring steady-state thermal conductivity with self-calibrated thermal loss. Background Technology

[0002] Thermophysical properties determine the application conditions and usage environment of materials and are important intrinsic characteristics of materials. Among them, thermal conductivity describes the magnitude of a sample's heat transfer ability. Accurate thermal conductivity and contact thermal resistance data are required in fields such as aerospace, electronic circuits, and new energy.

[0003] Thermophysical property measurement methods are generally divided into steady-state methods and transient methods. The steady-state method establishes stable boundary conditions and calculates the results after the thermal system has stabilized. The transient method measures and records the temperature change of the sample under thermal excitation conditions to calculate the thermophysical parameters. Generally, the transient method has a shorter testing time and is more convenient, but its results are slightly less reliable than the steady-state method. The steady-state method is closer to the definition of thermophysical parameters, has a more complex testing procedure and a longer testing time, but its measurement results are more reliable.

[0004] Classical steady-state methods include the hot plate method and the heat flow meter method:

[0005] The protective hot plate method measures the thermal conductivity of a material by symmetrically placing two identical specimens on either side of a central heating plate. The central heating plate provides a constant heat source, and the internal protective plate keeps the temperature consistent with the heat source plate. The side protective plates maintain the consistency of heat flow, minimize edge losses, and ensure that the heat flow passes uniformly through the center of the specimen, thus constructing a one-dimensional heat transfer system and accurately calculating the thermal conductivity of the sample.

[0006] This method is best suited for testing relatively thick or homogeneous materials with low thermal conductivity, especially samples with a thermal conductivity range of 0–2 W / (m·K). Because the experiment is conducted in a controlled environment, environmental variables can be precisely controlled, effectively avoiding heat loss and resulting in very small experimental errors. The protective hot plate method can be used for measuring materials with higher thermal conductivity and conducting high-temperature tests; however, the influence of heat loss during this measurement process cannot be ignored, requiring additional heat loss compensation studies.

[0007] The heat flow meter method involves placing the sample between two metal rods with known high thermal conductivity. A force is applied to ensure the ends of the metal rods are pressed firmly against the sample, reducing air gaps and contact thermal resistance at the interface. Controllable heat input is provided by a hot plate, flowing through the metal rods → sample → metal rods. After reaching a steady state, the temperature difference at equal intervals within the metal rods is measured. The heat flow through the sample and the temperature difference at the sample surface are calculated using the thermal conductivity of the metal rods, thus determining the sample's equivalent thermal resistance. By measuring the equivalent thermal resistance of samples with different thicknesses, the surface contact thermal resistance of the sample can be fitted to its own thermal conductivity.

[0008] The heat flow method is widely used to evaluate thermal management materials in electronic devices. It is suitable for testing the equivalent thermal conductivity and contact thermal resistance of homogeneous and heterogeneous thermally conductive and electrically insulating thermal interface materials. It is adaptable to materials of different thicknesses and allows measurements to be performed under different temperature and pressure conditions, enabling it to simulate real-world application environments. However, the heat flow method requires calibration and standardization of the heat loss on the side of the metal rod, and the metal rod size is often relatively large for measuring samples with small thermal resistance.

[0009] In summary, the steady-state method for measuring thermal conductivity has the advantages of good repeatability and high accuracy. However, in order to meet the stringent one-dimensional heat transfer conditions during the measurement process, additional thermal protection or heat loss calibration is required. These two aspects need to be performed simultaneously, which significantly increases the measurement difficulty of the steady-state method. In thermal conductivity testing, the influence of heat loss mainly has two aspects:

[0010] The hot plate method disrupts one-dimensional heat transfer in the system and affects the calculated thermal conductivity. While the protective hot plate method maintains one-dimensional heat transfer through isothermal auxiliary hot plates and side protective plates, the heat flow method calculates the heat flow into and out of the sample using a high thermal conductivity metal rod and calibrates the heat loss on the sample's sides. The protective hot plate method suffers from reduced thermal protection when measuring high thermal conductivity samples and under high-temperature conditions, significantly impacting the measurement results. The heat flow method requires precise calibration of the heat loss on the sides of the high thermal conductivity metal rod itself to calculate the heat flow across the sample surface and estimate the sample surface temperature. Traditional steady-state methods require additional calibration and compensation for heat loss, affecting measurement efficiency and accuracy. Summary of the Invention

[0011] To address the problems existing in the prior art, the present invention aims to propose a method and device for measuring steady-state thermal conductivity with self-calibrated thermal loss. A steady-state heat transfer system with a high thermal resistance-sample-high thermal resistance structure is constructed. Combining the theory of self-calibrated thermal loss, a quasi-one-dimensional heat conduction is achieved by using a thermal barrier layered with high thermal conductivity and low thermal conductivity materials.

[0012] The technical solution adopted is as follows:

[0013] One aspect of the present invention provides a steady-state thermal conductivity measuring device with self-calibrated heat loss, comprising:

[0014] The thermal barrier includes an upper thermal barrier and a lower thermal barrier, which are located on both sides of the sample and in contact with the sample. The equivalent thermal resistance of the upper thermal barrier and the lower thermal barrier is much greater than the thermal resistance of the sample. The upper thermal barrier and the lower thermal barrier both include high thermal conductivity material and low thermal conductivity material, and the two materials are alternately stacked.

[0015] The cold plate includes an upper cold plate and a lower cold plate, wherein the upper cold plate is disposed at the end of the upper thermal barrier away from the sample, and the lower cold plate is disposed at the end of the lower thermal barrier away from the sample;

[0016] The load, located above the upper cold plate, is used to regulate the sample pressure;

[0017] A heating plate is disposed between the sample and the upper thermal barrier, and is used to apply a constant power heat source to the sample;

[0018] The first temperature sensor, the second temperature sensor, the third temperature sensor, and the fourth temperature sensor are embedded in the high thermal conductivity materials on the upper and lower sides, respectively, and are used to measure the temperature T1 of the upper surface of the upper thermal barrier, the temperature T2 of the upper surface of the sample, the temperature T3 of the lower surface of the sample, and the temperature T4 of the lower surface of the lower thermal barrier in steady state.

[0019] Based on the temperatures T1, T2, T3, and T4 measured by the first, second, third, and fourth temperature sensors, and the heating power of the heating plate... The equivalent thermal conductivity k of the sample is calculated using the following formula:

[0020]

[0021] Where d is the thickness of the sample and S is the cross-sectional area of ​​the sample perpendicular to the heat flow direction, this formula is based on the energy conservation relationship and incorporates the side heat loss into the calculation through the temperature difference ratio distribution, so as to achieve self-calibration of heat loss.

[0022] Another aspect of the present invention provides a steady-state thermal conductivity measurement method with self-calibrated heat loss, employing the above-mentioned apparatus and comprising the following steps:

[0023] Step 1: Place the sample between the upper and lower thermal barriers, and cool both ends of the thermal barriers with cold plates; apply a load to the top cold plate to regulate the sample pressure.

[0024] A first temperature sensor, a second temperature sensor, a third temperature sensor, and a fourth temperature sensor are embedded in the high thermal conductivity material on the top and bottom sides, respectively.

[0025] Step 2: After setting the cold plate temperature, apply a constant power heat source to the device through the heating plate placed between the sample and the thermal barrier, and measure and record the temperature at each measuring point.

[0026] Step 3: Determine whether a steady state has been reached based on the temperature change curve over time;

[0027] Step 4: Calculate the equivalent thermal conductivity k of the sample using the steady-state temperature measurement data:

[0028]

[0029] This formula is based on the law of conservation of energy and incorporates side heat loss into the calculation by proportionally allocating the temperature difference, thereby achieving self-calibration of heat loss.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] This invention eliminates the need for additional thermal loss calibration, using readily measurable physical quantities to account for thermal loss and calculate the accurate thermal conductivity and thermal resistance of the sample. Compared to traditional quasi-steady-state testing methods, this invention is applicable to the measurement of thermal conductivity and contact thermal resistance of both ultra-high thermal conductivity thin films (thermal conductivity > 100 W / mK) and ultra-low thermal conductivity materials (thermal conductivity < 1 W / mK) under wide temperature ranges (-20℃ to 300℃) and different pressure conditions (0 to 10 MPa).

[0032] This invention eliminates the need for additional thermal protection and thermal loss calibration. The accurate thermal conductivity can be directly calculated using the measurement data, greatly simplifying the steady-state measurement process and improving the repeatability and accuracy of the measurement. It can be used to measure the thermal conductivity and thermal resistance of samples under different temperatures and pressures. Attached Figure Description

[0033] Figure 1 This is a diagram of a steady-state thermal conductivity measurement device with self-calibrated heat loss according to an embodiment of this application.

[0034] Figure 2 This is a diagram showing the stacked structure of the thermal barrier and the arrangement of the temperature sensors according to an embodiment of this application.

[0035] Figure 3 These are the measurement results of the test sample in this application. Detailed Implementation

[0036] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0037] like Figure 1 As shown in the figure, this application provides a steady-state thermal conductivity testing device with self-calibrated thermal loss, including: load 1, upper cold plate 2, thermal insulation material 3, heating plate 4, sample 5, upper thermal barrier 6, lower thermal barrier 7, first temperature sensor 8, high thermal conductivity material 9, low thermal conductivity material 10, second temperature sensor 11, third temperature sensor 12, fourth temperature sensor 13, and lower cold plate 14.

[0038] The upper thermal barrier 6 and the lower thermal barrier 7 are located on both sides of the sample 5 and are in contact with the sample. Their equivalent thermal resistance is much greater than that of the sample.

[0039] The cold plate 2 includes an upper cold plate and a lower cold plate; the upper cold plate is disposed at the end of the upper thermal barrier that is farther from the sample, and the lower cold plate is disposed at the end of the lower thermal barrier that is farther from the sample.

[0040] The load 1 is located above the upper cold plate and is used to regulate the sample pressure.

[0041] A heating plate 4 is provided on one side of the sample 5.

[0042] Furthermore, both the upper thermal barrier 6 and the lower thermal barrier 7 are multilayered structures of high thermal conductivity material 9 and low thermal conductivity material 10, so as to achieve high thermal resistance while smoothing the isotherm through the high thermal conductivity layer, making the heat conduction closer to one-dimensional; at the same time, the embodiment of this application incorporates the heat loss to the environment generated by the upper and lower thermal barriers and the side of the sample 5 into the calculation to achieve heat loss self-calibration.

[0043] Preferably, the high thermal conductivity material uses a metal material with a thermal conductivity greater than 100 W / (mK), such as aluminum or copper.

[0044] Preferably, the low thermal conductivity material uses materials with a thermal conductivity of less than 10 W / (mK), such as polytetrafluoroethylene, aerogel, etc.

[0045] Furthermore, the sides of the thermal barrier 6 are wrapped with insulating material 3 to construct a quasi-one-dimensional heat transfer system.

[0046] like Figure 2 As shown, temperature sensors are embedded in the high thermal conductivity material on the upper and lower end faces of the upper and lower thermal barriers to measure the average temperature of the corresponding cross-section of the high thermal conductivity material, including:

[0047] The first temperature sensor 8 is used to measure the temperature of the upper surface of the upper thermal barrier in steady state. ;

[0048] The second temperature sensor 11 is used to measure the temperature of the sample's upper surface in a steady state. ;

[0049] The third temperature sensor 12 is used to measure the temperature of the lower surface of the sample in steady state. ;

[0050] The fourth temperature sensor 13 is used to measure the temperature of the upper surface of the thermal barrier in steady state. .

[0051] In this embodiment, load 1 applies a certain pressure to sample 5. When heating plate 4 heats with constant power, the heat flow flows approximately uniformly through the upper and lower thermal barriers and then enters the cold plate.

[0052] This application also provides a steady-state thermal conductivity measurement method with self-calibrated heat loss, applied to the above-mentioned device, comprising the following steps:

[0053] Step 1: The sample is placed in the middle of a thermal barrier whose equivalent thermal resistance is much greater than the sample's thermal resistance. The thermal barrier is cooled at both ends using water-cooled plates. A load is applied to the top water-cooled plate to regulate the sample pressure. Temperature sensors are embedded in highly thermally conductive materials on the upper and lower sides of the thermal barrier, forming a structure as follows: Figure 1 The test apparatus shown.

[0054] Furthermore, adjusting the thermal barrier resistance according to the sample thermal resistance can accelerate the steady-state construction time and improve testing efficiency while ensuring test accuracy. The thermal barrier resistance should be 10 times that of the sample thermal resistance.

[0055] Step 2: After setting the water-cooled plate temperature, apply a constant power heat source to the test device through the heating plate placed between the sample and the thermal barrier, and measure and record the temperature of each temperature measurement point (T1-T4).

[0056] Preferably, the temperature of the water-cooled plate should be 15 to 35 degrees lower than the sample test temperature to ensure that the temperature difference between the upper and lower surfaces of the sample is greater than 2 degrees, thereby improving the stability and accuracy of the measurement.

[0057] Step 3: Determine whether a steady state has been reached based on the temperature change curve over time.

[0058] As a preferred standard, the criterion for determining that a steady state has been reached is: the rate of temperature change at each temperature measurement point is less than 0.002℃ / min.

[0059] Step 4: Calculate the equivalent thermal conductivity and equivalent thermal resistance of the sample using the steady-state temperature measurement data.

[0060] Preferably, the equivalent thermal conductivity of the sample is calculated as follows:

[0061]

[0062] in, The equivalent thermal conductivity of the sample is given. For heating power, The temperature of the upper surface of the thermal barrier in steady state. The temperature of the upper surface of the sample in steady state. The temperature of the lower surface of the sample in steady state. The temperature of the lower surface of the thermal barrier in steady state. For the thickness of the sample, This is the cross-sectional area of ​​the sample perpendicular to the direction of heat flow.

[0063] Preferably, the equivalent thermal resistance of the sample is calculated as follows:

[0064]

[0065] Furthermore, the derivation of the formula for calculating the equivalent thermal conductivity of the sample is as follows:

[0066] After the system reaches steady state, according to the law of conservation of energy:

[0067]

[0068] in, This refers to the unknown heat loss from the side of the device to the environment. The equivalent thermal resistance of the thermal barrier after taking into account the effect of heat loss.

[0069] Based on the law of conservation of energy, heating power Some of it was lost into the environment from the side of the device, generating The remaining portion flows through the upper and lower thermal barriers and finally enters the water-cooled plate. Heat transfer analysis is performed on the lower thermal barrier structure on the underside of the sample.

[0070]

[0071] in, The actual heat flow through the lower thermal barrier is represented by the proportion of the temperature difference of the lower thermal barrier to the total temperature difference. Heating power The corresponding part of the lower thermal barrier is Similarly, the unknown heat loss from the side of the device to the environment The corresponding lower thermal barrier part is In actual measurements, For unknown terms, set parameters at this time. :

[0072]

[0073] Substituting formula (5) into formula (4), we get:

[0074]

[0075] when , hour,

[0076]

[0077] Substituting formula (7) into formula (6), we get:

[0078]

[0079] in, This represents the heat flow power of the sample as it passes through the lower thermal barrier. The heat loss is located slightly below the center of the sample. The sum of these two values ​​represents the actual heat flow passing through the central section of the sample, taking into account lateral heat loss. (Calculation...) Heat loss is taken into account, thus achieving adaptive calibration of heat loss. Based on the definitions of thermal conductivity and thermal resistance, calculation formulas (1) and (2) can be obtained.

[0080] In this application, under a 10MPa load, the thermal conductivity of quartz and aluminum alloy standard samples was tested using the measurement method provided in the above embodiments. The results are as follows: Figure 3 As shown.

[0081] Figure 3 The horizontal axis represents the test temperature, ranging from -20℃ to 300℃; the left vertical axis represents the thermal conductivity (W / m·K) of low thermal conductivity materials, corresponding to the quartz test results; the right vertical axis represents the thermal conductivity (W / m·K) of high thermal conductivity materials, corresponding to the aluminum alloy test results. It can be seen that the thermal conductivity of the quartz sample remained relatively stable at around 1.4 W / m·K across the entire temperature range, fluctuating only slightly with temperature; the thermal conductivity of the aluminum alloy sample remained stable at approximately 1.7 × 10² W / m·K, also showing relatively small variations with temperature.

[0082] The above measurement results are consistent with the typical literature thermal conductivity of the two materials, and the deviation is controlled within the allowable range for engineering applications. This indicates that the steady-state testing device and heat loss self-calibration method proposed in this application can accurately measure the thermal conductivity of extremely low and extremely high thermal conductivity materials with orders of magnitude variation over a wide temperature range (-20℃ to 300℃) and under certain load conditions (0 to 10MPa). This verifies that this application has high measurement accuracy and good applicability in thermal conductivity and contact thermal resistance testing, providing a reliable means for subsequent characterization of thermal conductivity performance under different material systems and pressure conditions.

[0083] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A self-calibrating, steady-state thermal conductivity measurement device that is immune to thermal damage, characterized in that, include: The thermal barrier includes an upper thermal barrier and a lower thermal barrier, which are located on both sides of the sample and in contact with the sample. The equivalent thermal resistance of the upper thermal barrier and the lower thermal barrier is much greater than the thermal resistance of the sample. The upper thermal barrier and the lower thermal barrier both include high thermal conductivity material and low thermal conductivity material, and the two materials are alternately stacked. The cold plate includes an upper cold plate and a lower cold plate, wherein the upper cold plate is disposed at the end of the upper thermal barrier away from the sample, and the lower cold plate is disposed at the end of the lower thermal barrier away from the sample; The load, located above the upper cold plate, is used to regulate the sample pressure; A heating plate is disposed between the sample and the upper thermal barrier, and is used to apply a constant power heat source to the sample; The first temperature sensor, the second temperature sensor, the third temperature sensor, and the fourth temperature sensor are embedded in the high thermal conductivity materials on the upper and lower sides, respectively, and are used to measure the temperature T1 of the upper surface of the upper thermal barrier, the temperature T2 of the upper surface of the sample, the temperature T3 of the lower surface of the sample, and the temperature T4 of the lower surface of the lower thermal barrier in steady state. Based on the temperatures T1, T2, T3, and T4 measured by the first, second, third, and fourth temperature sensors, and the heating power of the heating plate... The equivalent thermal conductivity k of the sample is calculated using the following formula: Where d is the thickness of the sample and S is the cross-sectional area of ​​the sample perpendicular to the heat flow direction, this formula is based on the energy conservation relationship and incorporates the side heat loss into the calculation through the temperature difference ratio distribution, so as to achieve self-calibration of heat loss.

2. The apparatus according to claim 1, characterized in that, The sides of the thermal barrier are all wrapped with insulating material to construct a quasi-one-dimensional heat transfer system.

3. The apparatus according to claim 1 or 2, characterized in that, The equivalent thermal resistance of the thermal barrier is more than 10 times that of the sample thermal resistance.

4. The apparatus according to claim 3, characterized in that, The high thermal conductivity material uses a metallic material with a thermal conductivity greater than 100 W / mK, and the low thermal conductivity material uses a material with a thermal conductivity less than 10 W / mK.

5. A method for measuring steady-state thermal conductivity with self-calibrated heat loss, using the apparatus described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Place the sample between the upper and lower thermal barriers, and cool both ends of the thermal barriers with cold plates; apply a load to the top cold plate to regulate the sample pressure. A first temperature sensor, a second temperature sensor, a third temperature sensor, and a fourth temperature sensor are embedded in the high thermal conductivity material on the top and bottom sides, respectively. Step 2: After setting the cold plate temperature, apply a constant power heat source to the device through the heating plate placed between the sample and the thermal barrier, and measure and record the temperature at each measuring point. Step 3: Determine whether a steady state has been reached based on the temperature change curve over time; Step 4: Calculate the equivalent thermal conductivity k of the sample using the steady-state temperature measurement data: This formula is based on the law of conservation of energy and incorporates side heat loss into the calculation by proportionally allocating the temperature difference, thereby achieving self-calibration of heat loss.

6. The method according to claim 5, characterized in that, The load provides a pressure range of 0–10 MPa.

7. The method according to claim 5 or 6, characterized in that, The test temperature range for the sample is -20℃ to 300℃.

8. The method according to claim 5, characterized in that, In step 2, the temperature of the cold plate is 15-35 degrees lower than the sample test temperature to ensure that the temperature difference between the upper and lower surfaces of the sample is greater than 2 degrees.

9. The method according to claim 5 or 8, characterized in that, The criterion for determining that a steady state has been reached in step 3 is that the temperature change rate at each temperature measurement point is less than 0.002℃ / min.

10. The method according to claim 9, characterized in that, It also includes calculating the equivalent thermal resistance of the sample. : 。

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