WO2016101903A1 - Heat transfer coefficient measurement device - Google Patents

Abstract

Provided is a heat transfer coefficient measurement device, comprising a test chamber (9), a hot-end heating system (10), a cold-end cooling system (14), an evacuation system (12), a temperature acquisition system and processing system (13), and a pressure control system (11); a test bench (15) is arranged inside the test chamber (9), the test bench (15) being an overall upper and lower structure: in sequence from bottom to top are a heating block (8), a lower pressure head (7), a sample to be tested (5), an upper pressure head (2), and a cooling block (1). A temperature-measurement-point horizontal multipoint arrangement simulates the horizontal temperature gradient of the tested sample, so as to objectively reflect the heat transfer attributes of the tested sample, and with the aid of data processing, obtain a more objective heat transfer coefficient value. At the same time, a flexible thin sheet (16) having a high thermal conductivity is arranged between the sample to be tested (5) and the pressure heads (7, 2), reducing thermal contact resistance and improving the accuracy of test values. Moreover, a limiting ring (4) is arranged between the pressure heads so as to ensure testing operability and precision when testing flexible samples. The accuracy and objectivity of heat transfer coefficient testing is significantly improved.

Description

Thermal conductivity measuring device Technical field

The present invention relates to a measuring device for thermal conductivity, and more particularly to a measuring device for measuring the thermal conductivity of a solid material.

Background technique

The thermal conductivity of materials is an important parameter for studying the physical properties of materials. In the research, teaching, production and other departments, it is required to predict or measure the thermal conductivity of materials. The thermal conductivity is a physical quantity that reflects the thermal conductivity of a material. It is not only a basis for evaluating the thermal properties of materials, but also a design basis for materials. Therefore, the measurement of thermal conductivity of materials has become a new development in scientific experiments and engineering techniques. The key to the material.

At present, there are three main methods for measuring the thermal conductivity of materials:

First, the laser flash method. The method uses a transient method. The principle is that a laser beam is applied to the upper surface of the sample, and the temperature change of the lower surface is tested by an infrared detector. The actual measured data is the thermal diffusivity of the sample, and is compared with the standard sample. The density and specific heat of the sample are obtained, and the thermal conductivity of the sample can be calculated by the formula. The method has the advantages of rapid measurement, non-contact method, suitable for high temperature, high thermal conductivity samples, but not suitable for multilayer structures, coatings, foams, liquids, anisotropic materials, and the like. The reason is that the laser method tests the thermal diffusivity and the mathematical model is based on isotropic materials. In addition, other methods are needed to measure the density, which can be converted into thermal conductivity, which increases the source of the error.

Second, the thermal conductivity method. The method also uses the transient method. The principle is to use a thermal resistance material - nickel to make a flat probe, as a heat source and temperature sensor. The thermal resistance coefficient of nickel is linear with the relationship between temperature and resistance. That is, the loss of heat can be known by understanding the change of resistance, thereby reflecting the thermal conductivity of the sample. These characteristics of the material can be calculated by recording the temperature and the response time of the probe. The thermal conductivity and the thermal diffusion coefficient can be directly obtained from the mathematical model, and the ratio of the two is obtained by volumetric heat. The advantages are fast, convenient, no special sample preparation, and can be used for in-situ/single-sided testing. It is suitable for many types of samples such as solids, powders, liquids, coatings, honeycomb materials, etc., but limited by the surface coating of the probe. The temperature range can only reach 700 ° C, and the probe cost is high, the design is complex, and can not be effectively promoted.

Third, the temperature gradient method. The method is to place the sample to be tested between the heat source and the cryogenic refrigeration device. After the temperature distribution is stabilized, the thermal conductivity of the material is calculated by measuring parameters such as heat flux and temperature gradient flowing through the sample. Ideally, all the heat of the heat source is transmitted to the low temperature refrigerating end through the sample to be tested, and in fact, some heat is inevitably radiated from other directions, which inevitably leads to a temperature gradient in the cross section of the same sample, resulting in Measuring error and reducing the accuracy of the measurement. At the same time, there is inevitably a contact thermal resistance between the sample to be tested and the heat source and the cold end, resulting in inaccurate measurement data. Therefore, the measurement accuracy of this method mainly depends on two aspects: on the one hand, how to reduce the heat dissipation from other directions during the transfer process; on the other hand, reduce the contact thermal resistance. At present, from the domestic and foreign literatures, insulation materials are generally used as insulation layers to isolate the heat source from the outside world, minimizing heat loss, but there will still be some heat. External conduction, how to improve the accuracy of detection in this case has become a major technical problem. The theoretical basis of this method is the Fourier heat conduction law, as described in equation (1).

Where A: the cross-sectional area of the sample to be tested perpendicular to the direction of heat flow;

H: the thickness of the sample to be tested in the direction parallel to the heat flow;

The heat flow through the cross-sectional area A per unit time;

T ₁ : the center temperature of the lower surface of the upper pressing head;

T ₂ : the center temperature of the upper surface of the lower indenter;

λ: the sample to be tested is at temperature

Thermal conductivity

A negative sign indicates that the direction of heat flow is opposite to the direction of the temperature gradient.

In the formula (1), λ is the amount to be determined,

A, H, T ₁ and T ₂ are unknowns, of which

The measurement is the most difficult, and several other quantities can be measured directly.

Under ideal conditions, that is, under the adiabatic condition of the measuring device, the heating power of the hot end heating system is

The size, but in reality it is inevitable that some of the heat will be dissipated from other directions, which inevitably leads to a temperature gradient in the cross section of the same sample.

At the same time, there is inevitably a contact thermal resistance between the sample to be tested and the heat source and the cold end, resulting in inaccurate measurement data.

Summary of the invention

In view of the deficiencies of the prior art, in order to improve the accuracy of the thermal conductivity testing device, the present invention designs a new solid material thermal conductivity measuring device, which overcomes the large errors, complicated operation, low accuracy and cost in the prior art. High disadvantages.

The technical solution of the present invention is: a thermal conductivity measuring device, comprising: a test chamber 9, a hot end heating system 10, a cold end cooling system 14, a vacuuming system 12, a temperature collecting system 13, a pressure control system 11; A test stand 15 is disposed in the cavity, and the test stand is generally upper and lower structures, and is a heating block 8, a lower pressing head 7, a sample to be tested 5, an upper pressing head 2, and a cooling block 1 from bottom to top; The head surface is provided with a temperature sensor group 3, and the temperature sensor is connected to the temperature collecting and processing system 13; the heating block 8 is connected to the hot end heating system 10, and the cooling block 1 and the cold end cooling system 14 are connected, and the temperature is collected. And the processing system 13 completes data acquisition, online processing, and test result output in a timely manner; the temperature sensor group 3 is a first group of temperature sensors, a second group of sensors, and a third group respectively disposed along a cross-sectional direction of the upper and lower indenters Pass a sensor, wherein the first group of temperature sensors are three first temperature measurement points 3-A, a second temperature measurement point 3-B, and a third temperature measurement point 3-C, which are uniformly distributed in the same plane. The second and third sets of temperature sensors are set in the same way as the first set of temperature sensors.

The temperature collecting and processing system 13 processes the temperature values measured by the three sets of temperature measuring sensors of the upper and lower indenters, and calculates the thermal conductivity coefficient after fitting.

According to the law of thermal Ohm, as described in the formula (2).

Among them, Q _scattered : the heat emitted by the upper and lower indenters from all sides;

λ ₀ : thermal conductivity of the material used for the upper and lower indenters;

ΔT: The temperature gradient measured by the temperature sensor.

In the formula (2), λ ₀ is a determination parameter, and ΔT is a measurable temperature gradient. From this function, a set of Q- _scatters can be obtained, and the data obtained by the obtained set of numbers can be fitted to obtain a fitting function of Q- _scatter .

Compared with the prior art, the invention has the beneficial effects that an accurate Q- _scatter value can be obtained by using a material with a known thermal conductivity to make the upper and lower indenters, thereby obtaining a more accurate measurement.

Further more accurately measure the thermal conductivity of the sample.

A limiting ring 4 is disposed between the upper and lower indenters, and the limiting ring is made of a ceramic material with good thermal insulation effect, and has a circular shape and an inner flange. A highly thermally conductive flexible sheet 16 is disposed between the sample to be tested and the upper and lower indenters. The high thermal conductive flexible sheet is composed of a carbon material and a bonding material, and the thickness of the sheet is from 10 μm to 1 mm. The carbon material is one or more of carbon nanotubes, carbon fibers, and graphene, and the bonding material is a high thermal conductivity organic high molecular polymer. The carbon material is regularly arranged in the sheet, and the a-b axis direction is substantially the same as the heat transfer direction. The test chamber 9 is connected to an evacuation system and is capable of withstanding a vacuum of up to 10 Pa in a sealed state. A layer of insulating thermal insulation material 6 is disposed on the periphery of the test stand 15.

The invention simulates the lateral temperature gradient of the sample to be tested by the lateral multi-point setting of the temperature measuring point, and objectively reflects the heat transfer characteristics of the sample to be tested by the multi-point temperature test, and obtains a more objective thermal conductivity coefficient value by means of data processing. . At the same time, the invention provides a high thermal conductive flexible sheet between the sample to be tested and the indenter, reduces contact thermal resistance, and improves the accuracy of the test value. In addition, the present invention provides a stop ring between the indenters to ensure test operability and accuracy in testing flexible samples. The invention greatly improves the accuracy and objectivity of the thermal conductivity test.

DRAWINGS

Figure 1 is a system diagram of a thermal conductivity measuring device system

Figure 2 shows the distribution of the test surface temperature sensor

Figure 3 is a structure diagram of the limit ring

Figure 4 is the internal structure of the thermal conductive sheet

Wherein, reference numeral, 1 cooling block, 2 upper indenter, 3 temperature measuring sensor group, 3-A first temperature measuring point, 3-B second temperature measuring point, 3-C third temperature measuring point, 4 limit Bit ring, 5 test specimens, 6 thermal insulation material layer, 7 lower pressure head, 8 heating block, 9 test chamber, 10 hot end heating system, 11 pressure control system, 12 vacuum system, 13 temperature acquisition and processing system , 14 cold end cooling system, 15 test benches, 16 high thermal conductivity flexible sheets

Specific embodiment 1

A rigid material thermal conductivity measuring device comprising: a test chamber 9, a hot end heating system 10, a cold end cooling system 14, a vacuuming system 12, a temperature collecting system 13, a pressure control system 11; and a test station 15 disposed in the test chamber The test bench as a whole is a top and bottom structure, and the bottom of the bottom is a heating block 8, a lower pressing head 7, a sample to be tested 5, an upper pressing head 2, a cooling block 1; and a temperature measuring sensor group is disposed on the surface of the upper and lower indenters 3. The temperature sensor is connected to the temperature acquisition and processing system 13; the heating block 8 is connected to the hot end heating system 10, the cooling block 1 is connected to the cold end cooling system 14, and the temperature acquisition and processing system 13 completes the data in a timely manner. Acquisition, on-line processing and test result output; the temperature measurement points are arranged in three ways equidistantly in the radial direction in the cross section; the test chamber 9 is connected to the vacuum system and can withstand in a closed state 10 degrees vacuum. A layer of insulating thermal insulation material 6 is disposed on the periphery of the test stand 15.

For rigid materials, the amount of denaturation is extremely small when the upper and lower indenters are pressurized, and the surface roughness of the sample to be tested is different. When the upper and lower indenters are in contact with the sample to be tested, the contact areas are not the same, and there is a difference between the contact faces. A certain contact thermal resistance, the existence of contact thermal resistance leads to an error in the test results. In order to obtain a more accurate test result of the thermal conductivity, the present invention is newly set up between the sample to be tested and the upper and lower indenters. A highly thermally conductive flexible sheet 16 comprising a carbon material and a bonding material, the sheet having a thickness of 1 mm. The carbon material graphene, the bonding material is a high thermal conductivity silicone resin, the carbon material is regularly arranged in the sheet, and the a-b axis direction is substantially the same as the heat transfer direction. On the one hand, the high thermal conductivity flexible material itself has extremely high thermal conductivity and can transfer heat to the adjacent medium instantaneously. On the other hand, the high thermal conductivity flexible material has certain flexibility and toughness, and the flexible substance occurs when a certain pressure is applied to the upper and lower indenters. The deformation makes it more closely contact with the sample to be tested and the indenter, thereby eliminating contact thermal resistance due to surface roughness.

Furthermore, the inventors of the present invention found that there is a temperature gradient in the cross section of the sample to be tested due to the inability to achieve the desired adiabatic condition, which results in different temperatures at different positions in the cross section, and the conventional test means are only in the center position. The temperature measurement point is set, and the true heat flux passing through the test sample cannot be measured, which leads to a decrease in the accuracy of the test, and it is impossible to objectively and accurately reflect the true thermal conductivity value. In order to solve this technical problem, the inventive cross-section is more creative. Set the temperature measurement point, set the first temperature measurement point (3-A) at the center position in the cross section, set the second temperature measurement point (3-B) at the midpoint of the radius, and set the third temperature measurement on the outer edge. Point (3-C), for the convenience of setting three temperature measurement points can be dispersed, or can be set on one radius line as needed. In the same way, three sets of temperature measuring points for the upper and lower indenters are set. The temperature values collected for each of the three temperature measurement points can objectively reflect the temperature gradient of the cross section.

According to the law of thermal Ohm, as described in the formula (2).

Among them, Q _scattered : the heat emitted by the upper and lower indenters from all sides;

λ ₀ : thermal conductivity of the material used for the upper and lower indenters;

ΔT: The temperature gradient measured by the temperature sensor.

In the formula (2), λ ₀ is a determination parameter, and ΔT is a measurable temperature gradient. From this function, a set of Q- _scatters can be obtained, and the data obtained by the obtained set of numbers can be fitted to obtain a fitting function of Q- _scatter .

Compared with the prior art, the invention has the beneficial effects that an accurate Q- _scatter value can be obtained by using a material with a known thermal conductivity to make the upper and lower indenters, thereby obtaining a more accurate measurement.

Further more accurately measure the thermal conductivity of the sample.

Specific embodiment 2

The flexible material thermal conductivity determining device comprises: a test chamber 9, a hot end heating system 10, a cold end cooling system 14, a vacuuming system 12, a temperature collecting system 13, a pressure control system 11; and a test bench 15 is arranged in the test chamber. The test bench as a whole is a top and bottom structure, and the bottom of the bottom is a heating block 8, a lower pressing head 7, a sample to be tested 5, an upper pressing head 2, a cooling block 1; and a temperature measuring sensor group is disposed on the surface of the upper and lower indenters 3. The temperature sensor is connected to the temperature acquisition and processing system 13; the heating block 8 is connected to the hot end heating system 10, the cooling block 1 is connected to the cold end cooling system 14, and the temperature acquisition and processing system 13 completes the data in a timely manner. Acquisition, on-line processing and test result output; the temperature measurement points are arranged in three ways equidistantly in the radial direction in the cross section; the test chamber 9 is connected to the vacuum system and can withstand in a closed state 10Pa vacuum. A layer of insulating thermal insulation material 6 is disposed on the periphery of the test stand 15.

The inventors have found that there is a temperature gradient in the cross section of the sample to be tested, which results in different temperatures at different positions in the cross section, and the conventional test means only longitudinally arranges the temperature measurement point at the center position, which leads to the accuracy of the test. Decreasing, it is impossible to objectively and accurately reflect the true thermal conductivity value. In order to solve this technical problem, the inventive creative method uses a cross-section multi-point setting of the temperature measuring point, and sets the first temperature measuring point at the center position in the cross section (3- A), set the second temperature measurement point (3-B) at the midpoint of the radius, and set the third temperature measurement point (3-C) on the outer edge. In order to conveniently set the three temperature measurement points, the settings can be dispersed, or as needed. Set centrally on a radius line. After the setting of the three temperature measurement points, the collected temperature values can objectively reflect the temperature field in the cross section, and the thermal conductivity values obtained by statistically and fitting the three temperature values are more accurate.

When testing the thermal conductivity of flexible materials, large deformation occurs when the flexible material is applied with appropriate pressure on the upper and lower indenters. In extreme cases, the indenter cannot be centered on the sample to be tested, even when the sample is deformed. The sample to be tested is extruded from the upper and lower indenters, resulting in failure to fix. In order to solve this problem, the present invention is between the upper and lower indenters A limiting ring 4 is disposed. The material of the limiting ring is a ceramic material with good thermal insulation effect, and has a circular shape and an inner flange. The diameter of the inner flange of the limiting ring is slightly smaller than the diameter of the pressing head, the outer diameter of the limiting ring is slightly larger than the diameter of the pressing head, and the inner flange height of the limiting ring is slightly smaller than the height of the standard sample to be tested, The limit ring is first placed on the lower pressing head, and then the sample to be tested is placed, and the pressure head is pressurized, and the pressure head is fed back in accordance with the feedback of the pressure controller to contact the inner flange of the limiting ring, and then the subsequent testing process is started.

The TP215 thermal silica gel gasket was made into 16 samples with a thickness of 1 mm, and the thermal conductivity was used as a measurement index. The experiment was carried out under the same reaction conditions. The results are shown in Table 1. Experimental conditions: heating power 70W, cold end temperature 20 ° C, ambient temperature 30 ° C.

Table 1 experimental results

Sample serial number	Thermal conductivity (W/m·K)	Sample serial number	Thermal conductivity (W/m·K)
01	1.598	09	1.595
02	1.537	10	1.638
03	1.495	11	1.695
04	1.612	12	1.538
05	1.545	13	1.462
06	1.482	14	1.486
07	1.563	15	1.612
08	1.489	16	1.583

The experimental accuracy is calculated as follows:

It can be seen from Table 1 that the number of measurements is n=16, and the theoretical value of the thermal conductivity of the TP215 thermal silica gel gasket is λ=1.5, which results in:

Mean square error

Mean square error coefficient

It can be seen from the above calculation that the accuracy of the thermal conductivity measurement result of the instrument is relatively high.

The present invention has been described in detail with reference to FIGS. 1 to 4, but the present invention is not limited to the embodiments, and various modifications can be made without departing from the spirit and scope of the invention. It is obvious.

Claims (10)

1. A thermal conductivity measuring device, characterized in that the device comprises: a test chamber (9), a hot end heating system (10), a cold end cooling system (14), a vacuum system (12), a temperature collecting and processing system ( 13), pressure control system (11); a test bench (15) is set in the test cavity, the test bench as a whole is upper and lower structure, and the heating block (8) and the lower pressing head (7) are sequentially tested from bottom to top. a sample (5), an upper pressing head (2), a cooling block (1); a temperature measuring sensor group (3) is disposed on the surface of the upper and lower indenters, and the temperature measuring sensor group is connected to the temperature collecting system (13); The heating block (8) is connected to the hot end heating system (10), the cooling block (1) is connected to the cold end cooling system (14), and the temperature collecting and processing system (13) completes data acquisition, online processing and test results in a timely manner. Output.
2. The thermal conductivity measuring device according to claim 1, wherein the temperature measuring sensor group (3) is a first group of temperature measuring sensors and a second group of sensors respectively disposed along a cross section of the upper and lower indenters. And a third group of sensors, wherein the first group of temperature sensors are three first temperature measurement points (3-A), second temperature measurement points (3-B), and third, which are uniformly distributed in the same plane The temperature measurement point (3-C), the second group and the third group of temperature sensor are set in the same way as the first group of temperature sensors.
3. The thermal conductivity measuring device according to claim 2, wherein the temperature collecting and processing system (13) processes the temperature values measured by the three sets of temperature measuring sensors of the upper and lower indenters, and calculates the values after fitting. The thermal conductivity is obtained.
4. A thermal conductivity measuring apparatus according to claim 1 or 2, wherein a stopper ring (4) is provided between the upper and lower indenters.
5. The thermal conductivity measuring device according to claim 4, wherein the material of the limiting ring is made of a ceramic material having a good heat insulating effect, and has a circular shape and an inner flange.
6. The thermal conductivity measuring apparatus according to claim 1, wherein a highly thermally conductive flexible sheet (16) is disposed between the sample to be tested and the upper and lower indenters, and the highly thermally conductive flexible sheet is made of carbon. The material and the bonding material are composed, and the thickness of the sheet is from 10 μm to 1 mm.
7. The thermal conductivity measuring device according to claim 6, wherein the carbon material is one or more of carbon nanotubes, carbon fibers, and graphene, and the bonding material has high thermal conductivity. Organic high molecular polymer.
8. A thermal conductivity measuring apparatus according to claim 7, wherein said carbon material is regularly arranged in the sheet, and the a-b-axis direction is substantially the same as the heat transfer direction.
9. A thermal conductivity measuring apparatus according to claim 1 or 2, wherein the test chamber (9) is connected to the vacuuming system and is capable of withstanding a vacuum of up to 10 Pa in a sealed state.
10. A thermal conductivity measuring apparatus according to claim 1 or 2, wherein a heat insulating material layer (6) is provided on the periphery of the test stand (15).

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