A device and method for measuring the thermal conductivity of a flexible material

Abstract

The application discloses a kind of flexible material thermal conductivity measuring device and method.The device includes sensor part, signal acquisition data analysis part and current source control part.The application is through to sandwich structure heat transfer model numerical calculation, establishes the relationship library of the slope of the temperature rise curve of the thermal conductivity of the measured sample, standard side thermal conductivity and temperature rise curve slope.Collect average temperature rise curve slope, in relationship library according to signal curve slope and the thermal conductivity of standard side can obtain the thermal conductivity of the sample to be measured under the live environment.The measuring device provided by the application can be measured by the standard material to eliminate the experimental error caused by the influence of live environment on the properties of standard material, so that the measurement result is true and reliable;And the measurement result is obtained by temperature rise transient response, and transient measurement method can quickly obtain thermal physical property parameters.The measurement method has smaller heat loss, does not need vacuum environment, can carry out on-site real-time measurement, has strong adaptability, and can also realize the thermal physical property measurement of sample with internal heat source.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of thermophysical property measurement, and particularly relates to a method and device for measuring the thermal conductivity of flexible material. BACKGROUND

[0002] Flexible material has both deformability and flexibility, and is widely used in various fields. In addition to having high thermal and electrical conductivity, flexible thermal and electrical conductive material can also adapt to complex spatial structures, and thus has become the focus of academic research. Flexible thermal and electrical conductive material can be bent, folded, twisted, compressed, stretched, or even deformed into any shape while still maintaining high thermal and electrical performance and reliability. However, because of its easy deformation, and because materials like conductive cloth are woven and have complex structures, there are many difficulties in measuring the physical properties of flexible material.

[0003] Thermal conductivity is an important parameter for evaluating the thermal conductivity of a material, and can directly reflect the pros and cons of the thermal conductivity of the material. The methods for measuring the thermal conductivity of solid materials can be divided into steady-state method and transient method. However, these methods require the sample to be flat and require the material to be not easily deformed and have a complete structure. In engineering practice, it is extremely inconvenient to measure the thermal conductivity of tubular or irregular surface samples and flexible materials, and the real-time thermal conductivity is very important because the actual environment can cause changes in the thermal conductivity.

[0004] Patent CN110927209A discloses a method and apparatus for measuring the effective thermal conductivity of a vacuum insulation panel using a protective hot plate method. This method can directly measure the overall thermal conductivity of a vacuum insulation panel, including the "edge effect," solving the technical problem that existing technologies often result in errors between measured and actual values ​​of the thermal conductivity of vacuum insulation panels. The measured values ​​cannot represent the effective thermal conductivity of the entire panel, nor can they reflect the overall insulation performance. However, this apparatus requires high-performance insulation materials surrounding the test sample, and heat leakage from the perimeter significantly affects the measurement results. Furthermore, the experimental setup is complex, has specific requirements for sample size, and cannot meet the measurement needs of irregularly shaped solid materials or easily deformable flexible materials. CN106645284A discloses a system and method for measuring the thermal conductivity of a circular tube. Based on the transient heat source method, a sensor is placed on the outer surface of the circular tube, serving as both a heating element and a temperature measuring element. Current flows through the metal wire inside the sensor, generating heat to heat the tube. By analyzing the sensor's temperature-time response data, the thermal conductivity of the circular tube material can be calculated. However, this device can only measure circular tubular materials, making it difficult to measure irregularly shaped solid materials or easily deformable flexible materials. It also requires auxiliary equipment such as a constant temperature chamber, making the measurement system quite complex. Therefore, this invention proposes a method and device for measuring the thermal conductivity of flexible materials, suitable for real-time measurement of the thermal conductivity of irregularly shaped solid materials or easily deformable flexible materials. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method and apparatus for measuring the thermal conductivity of flexible materials. The measuring apparatus described in this invention is simple and, combined with relevant measurement methods, enables single-sided measurement of irregularly shaped solid materials or easily deformable flexible materials. It is suitable not only for laboratory measurements but also for real-time measurements under material operating conditions. Furthermore, through transient analysis, the measurement speed is fast, the delay is small, and the results are accurate.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a device for measuring the thermal conductivity of flexible materials, comprising an upper material, a sensor, a lower material, a data acquisition card, a data collection computer, and a current source;

[0008] The flexible material to be tested is placed between the standard material and the sensor to form a fitted sandwich structure;

[0009] The sensor is connected to a data acquisition card, which is then connected to a data collection computer;

[0010] The current source provides electrical energy.

[0011] Further, the sensor is a flexible sheet structure, and a heat source is provided. Preferably, the sensor is a double helix nickel metal sensor.

[0012] Further, the sensor has a thickness of 20-100 microns.

[0013] Further, the data acquisition card acquires the voltage change across the sensor in real time, transmits the voltage signal to the data collection computer for processing, and calculates the temperature of the heat source of the sensor.

[0014] In a second aspect, the present application provides a method for measuring the thermal conductivity of a flexible material using the device of the first aspect, comprising the following steps:

[0015] S1, the heat source is built in the middle of the upper and lower materials and diffuses heat to the two side materials. Due to the different thermal properties of the two side materials, the heat transfer is different. By analyzing the heat transfer model of the above sandwich structure and expanding the numerical calculation, the thermal conductivity of the two known materials is continuously changed to establish a three-dimensional surface relationship library of the thermal conductivity of the lower material, the thermal conductivity of the upper material and the slope of the temperature rise curve;

[0016] S2, standard material A is arranged on both sides of the sensor. After heating for a period of time, the data acquisition card acquires the voltage change across the sensor in real time, and transmits the voltage signal to the data collection computer. According to formula (2), the average temperature rise change curve of the sensor can be calculated:

[0017] (2)

[0018] Wherein: is the resistance value of the sensor at time t, is the resistance value of the sensor when it is not heated, which becomes the initial resistance, is the resistance temperature coefficient of the sensor, is the average temperature rise of the heat source;

[0019] S3, according to the slope of the temperature rise curve of standard material A, in the three-dimensional surface relationship library established

[0020] obtain the thermal conductivity of standard material A in the live environment, which is used to eliminate the experimental error caused by the influence of the live environment on the properties of standard material;

[0021] ​S4, respectively placing standard material A and the experimental sample to be measured on both sides of the sensor, substituting the thermal conductivity of standard material A in live environment into the heat transfer model of placing standard material A and the experimental sample to be measured on both sides respectively, correcting the thermal conductivity of standard material in live environment; the sensor heats the measuring sample, and the data acquisition card collects the voltage change of both ends of the sensor at a suitable measuring time after heating, and according to formula (2), the average temperature rise change curve of the sensor can be calculated; according to the slope of the temperature rise curve, the thermal conductivity of the sample to be measured in the live environment can be obtained according to the signal curve slope and the thermal conductivity of the standard side in the established three-dimensional curved surface relationship library.

[0022] Further, in the step S1, the relationship between the temperature of the heat source and the time dimensionless parameter in the heat transfer process of the sandwich structure is as follows:

[0023] (1)

[0024] wherein: is the average temperature rise of the heat source, is the dimensionless parameter, is the thermal diffusivity of the material, is the radius of the thin film heat source, t is the measuring time;

[0025] is the time dimensionless function:

[0026]

[0027] wherein is the number of turns of the thin film heat source, , n, l are all variables, e is the natural constant;

[0028] is the first type of modified function of Bessel function of zero order: , x , θ are all variables;

[0029] The slope of the temperature rise curve is only related to the thermal conductivity of the material.

[0030] Further, the thermal conductivity and thermal diffusivity of the standard material A are low, and the thickness is greater than the heat detection depth, i.e. to ensure that more heat flow flows to the sample material to be measured.

[0031] Further, in the step S4, the heat transfer model is as follows: Figure 2The heat source is embedded in the middle of the two known material or the material to be measured, and the heat is diffused to the two materials, because the thermal properties of the two materials are different, the heat transfer is different, and the temperature rise curve slope is different, forming a model.

[0032] Further, the size of the experimental sample to be measured should be much larger than the size of the sensor , and the thickness should be greater than the heat detection depth, that is .

[0033] Further, the data acquisition card acquisition time period should be after a period of time after heating, so as to eliminate the influence of contact thermal resistance, insulation layer and bonding layer thermal resistance, and the thermal property measurement of the sample with internal heat source can also be realized.

[0034] Further, the sensor is embedded as a heat source in the two materials, and the heat loss is small, without the need for a vacuum environment.

[0035] The beneficial effects of the present application are as follows:

[0036] On the one hand, the present application provides a method and device for measuring the thermal conductivity of flexible materials, which realizes the physical property measurement of solid materials with irregular surfaces or flexible materials prone to deformation. By numerical calculation of the sandwich structure heat transfer model, the relationship between the thermal conductivity of the measurement sample, the standard side thermal conductivity and the temperature rise curve slope can be established by continuously changing the thermal conductivity of the two materials. The average temperature rise curve slope of the sensor is collected by electrically controlling heating, and the thermal conductivity of the sample to be measured under the real environment is obtained according to the signal curve slope and the thermal conductivity of the standard side in the established relationship between the thermal conductivity of the measurement sample, the standard side thermal conductivity and the temperature rise curve slope. Because the sensor is a double helix nickel metal sensor with a thickness of 20-100 microns and good toughness, it can be deformed and can be used for physical property measurement of solid materials with irregular surfaces or flexible materials prone to deformation. For example, round pipe materials, textiles, and coating materials.

[0037] On the other hand, the measuring device provided by the present application obtains the thermal conductivity of the standard material under the real environment through the pre-measurement of the standard material, so as to eliminate the experimental error caused by the influence of the real environment on the properties of the standard material, so that the measurement result is true and reliable. The measurement result of the device is obtained by temperature rise transient response, and the transient measurement method can quickly obtain the thermal property parameters. At the same time, the sensor acts as a heat source and is contained in the two materials, with small heat loss and without the need for a vacuum environment, so that on-site real-time measurement can be carried out, and different sizes of measurement samples can be applied by changing the size of the sensor heat source. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is a structural schematic diagram of a method and device for measuring the thermal conductivity of flexible materials.

[0039] Figure 2 A heat transfer physical model for a method and device for measuring the thermal conductivity of flexible materials;

[0040] Figure 3 A flowchart of a method and apparatus for measuring the thermal conductivity of flexible materials;

[0041] Figure 4 This is a database of relationships between sample thermal conductivity, standard side thermal conductivity, and temperature rise curve slope established in the embodiments of the present invention.

[0042] Figure 5 This is an average temperature rise curve of the thin-film heat source (sensor) in an embodiment of the present invention; wherein, Configuration A and Configuration B are the average temperature rise curves for measuring two different samples, respectively.

[0043] In the diagram: 1-Standard material with low thermal conductivity; 2-Sensor; 3-Sample to be tested; 4-Data acquisition card; 5-Signal transmission line; 6-Data acquisition computer; 7-Current source. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0045] like Figure 1 As shown, a method and apparatus for measuring the thermal conductivity of flexible materials include a standard material 1 with low thermal conductivity, a sensor 2, a sample to be tested 3, a data acquisition card 4, a signal transmission line 5, a data acquisition computer 6, and a current source 7. In this embodiment, the standard material 1 is selected as a material with low thermal conductivity and thermal diffusivity to ensure that more heat flow is directed to the sample material being tested. The sensor 2 is a double-helix nickel metal sensor, which controls the heating amount of the heat source by controlling the current input, and the voltage change across the sensor can reflect the temperature change.

[0046] The sample to be tested 3 and the standard material 1 are in direct contact with and bonded together with the sensor 2. The sensor is a double-helix nickel metal sensor with a thickness of 20-100 micrometers. It has good toughness and can be deformed, and can be used to measure solid materials with irregular surfaces or flexible materials that are prone to deformation.

[0047] The current source 7 can control the current size inputted by the sensor 3, so as to realize the accurate control of the heat flow input; the data acquisition card 4 can collect the voltage change between the two ends of the sensor in real time, and transmit the voltage signal to the data collection computer 6, so as to convert the average temperature change of the real-time sensor heat source by the data collection computer 6;

[0048] The data acquisition card 4 should collect the time period after heating for a period of time, and the heat resistance of the heated contact, the insulation layer and the bonding layer has a great influence in the early heating stage, and the influence of the above heat resistance can be avoided in the later stage;

[0049] The sensor 2, the data acquisition card 4, the data collection computer 6 and the current source 7 are electrically connected through the signal transmission line 5.

[0050] As shown in Figure 3 , the application also provides a kind of measurement method of the thermal conductivity of flexible material, comprising the following steps:

[0051] Before measurement, the heat transfer model of the sandwich structure of the middle sensor 2, the two sides of the measurement sample 3 or the standard material 1 is analyzed, and the heat transfer model is as shown in Figure 2 The heat source is built in the middle of the two side materials with known physical properties and the material to be measured, and heat diffusion is carried out to the two side materials, and the heat transferred upward and downward by the heat source is as shown in Figure 2 In , As shown, due to the difference in thermal properties of the two side materials, the heat transferred is different, which leads to the difference in the slope of the temperature rise curve.

[0052] When the thin film heat source is heated for a period of time, there are:

[0053] (3)

[0054] Among them: is the average temperature rise of the heat source, is a dimensionless parameter, is the thermal diffusion coefficient of the material, is the radius of the thin film heat source, t is the measurement time;

[0055] is a dimensionless function of time:

[0056]

[0057] Among them is the number of turns of the thin film heat source, , n, l are variables, e is a natural constant;

[0058] is the first kind of modified function of Bessel function zero order: , x , θ are all variables;

[0059] is the slope of temperature rise curve, which is only related to the thermal conductivity of the material.

[0060] Through the numerical calculation of the heat transfer model of the sandwich structure, using known materials, the material type is changed to change the thermal conductivity, and the three-dimensional surface relationship library of the thermal conductivity of the measured sample, the thermal conductivity of the standard side and the slope of the temperature rise curve is established, as shown in Figure 4

[0061] First, the standard material 1 is arranged on both sides of the sensor 2, and the current source 7 controls the input current of the sensor 2 to realize the heating amount of the sensor 2 to the standard material 1. After heating for a period of time, the data acquisition card 4 can collect the voltage change of the two ends of the sensor 2 in real time, and transmit the voltage signal to the data collection computer 6. According to formula (4), the average temperature rise change curve of the sensor 2 can be calculated.

[0062] (4)

[0063] Wherein: is the resistance value of the sensor at moment, is the resistance value of the sensor when it is not heated, which becomes the initial resistance. is the resistance temperature coefficient of the sensor 2, and the value of the specific nickel metal sensor is known.

[0064] According to the slope of the temperature rise curve of the standard material 1 ( Figure 5 ), the thermal conductivity of the standard material under the live environment is obtained by interpolation in the established relationship library of the thermal conductivity of the measured sample, the thermal conductivity of the standard side and the slope of the temperature rise curve.

[0065] Then the measured standard material 1 and the to-be-measured experimental sample 3 are placed on both sides of the sensor 2 respectively, the thermal conductivity of the standard material under the live environment is substituted into the measurement model, and the thermal conductivity of the standard material under the live environment is corrected to eliminate the experimental error caused by the influence of the live environment on the properties of the standard material. The current source 7 controls the heating amount, and the data acquisition card 4 collects the voltage change of the two ends of the sensor 2 at a suitable measurement time after heating, and the data collection computer 6 can calculate the average temperature rise change curve of the sensor 2 according to formula (4). According to the slope of the temperature rise curve, the thermal conductivity of the to-be-measured sample 3 under the live environment can be obtained from the signal curve slope and the thermal conductivity of the standard side in the established relationship library of the thermal conductivity of the measured sample, the thermal conductivity of the standard side and the slope of the temperature rise curve.

[0066] ​The embodiment provides a kind of flexible material thermal conductivity measurement method and device.The device can measure the physical property of solid material with irregular surface or flexible material prone to deformation, and the real thermal conductivity of standard material in live environment is obtained by the pre-measurement of standard material, to eliminate the experimental error caused by the influence of live environment on the property of standard material, so that the measurement result is real and reliable;The measurement result of the device is obtained by temperature transient response, and the thermal physical property parameter can be quickly obtained, and the sensor is used as heat source and is contained in the material inside on both sides, with less heat loss, without vacuum environment, can carry out on-site real-time measurement, by changing the size of sensor heat source, different size measurement sample can be applied.

[0067] Although the preferred embodiments of the present application have been described, those skilled in the art who, once aware of the basic inventive concept, can make additional changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0068] Obviously, those skilled in the art can make various modifications and variations to the embodiments of the present application without departing from the spirit and scope of the embodiments of the present application. Thus, if these modifications and variations of the embodiments of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and variations.

Claims

1. A method for measuring the thermal conductivity of a flexible material, characterized in that: The method is implemented based on a measuring device, which includes a sensor, a data acquisition card, a data acquisition computer, and a current source. The sensor is placed between the flexible material to be tested and the standard material to form a fitted sandwich structure; The measurement method includes: S1. The heat source is embedded between the upper and lower layers of material and diffuses heat to the materials on both sides. By analyzing the heat transfer model of the sandwich structure and performing numerical calculations, the thermal conductivity of the known materials on both sides is continuously changed to establish a three-dimensional surface relationship library of the thermal conductivity of the lower layer material, the thermal conductivity of the upper layer material and the slope of the temperature rise curve. S2. Standard material A is arranged on both sides of the sensor. After heating for a period of time, the data acquisition card collects the voltage change at both ends of the sensor in real time and transmits the voltage signal to the data collection computer. According to equation (2), the average temperature rise curve of the sensor can be calculated: （2） in: It is the sensor in The resistance value at time t. The initial resistance is the resistance value of the sensor when it is not heated. It is the temperature coefficient of resistance of the sensor. It is the average temperature rise of the heat source; S3. Based on the slope of the temperature rise curve of standard material A, obtain the thermal conductivity of standard material A under actual conditions from the established three-dimensional surface relation library. S4. Place standard material A and the experimental sample to be tested on both sides of the sensor respectively. Substitute the thermal conductivity of standard material A under the actual environment into the heat transfer model of standard material A and the experimental sample to be tested placed on both sides respectively, and correct the thermal conductivity of standard material under the actual environment. The sensor heats the sample to be measured. The data acquisition card collects the voltage change at both ends of the sensor after heating for a suitable measurement time. According to formula (2), the average temperature rise curve of the sensor is calculated. According to the slope of the temperature rise curve, the thermal conductivity of the sample to be tested under the actual environment can be obtained from the established three-dimensional surface relation library based on the slope of the signal curve and the thermal conductivity of the standard side.

2. The method according to claim 1, characterized in that: The sensor is connected to a data acquisition card, which is then connected to a data collection computer; the current source provides electrical energy.

3. The method according to claim 1, characterized in that: The sensor has a flexible sheet structure and provides a heat source.

4. The method according to claim 1, characterized in that: The thickness of the sensor is 20-100 micrometers.

5. The method according to claim 1, characterized in that: The data acquisition card collects the voltage changes at both ends of the sensor in real time, transmits the voltage signal to the data collection computer for processing, and calculates the temperature of the sensor's heat source.

6. The method according to claim 1, characterized in that: In step S1, during the heat transfer process of the sandwich structure, the relationship between the heat source temperature and the dimensionless parameter of time is as follows: （1） in: It is the average temperature rise of the heat source. It is a dimensionless parameter. It is the thermal diffusivity of the material. Let be the radius of the thin-film heat source. t For measuring time; It is a dimensionless function of time: in This represents the number of revolutions in the thin-film heat source. n l All are variables. e It is a natural constant; It is a zeroth-order correction function of the first kind of Bessel function: , x , θ All are variables; The slope of the temperature rise curve is only related to the thermal conductivity of the material.

7. The method according to claim 1, characterized in that: The standard material A has a low thermal conductivity and thermal diffusivity, and its thickness is greater than the thermal detection depth.

8. The method according to claim 1, characterized in that: In step S4, the heat transfer model in which standard material A and the experimental sample to be tested are placed on both sides is formed when the heat source diffuses heat to the materials on both sides. Due to the different thermal properties of the materials on both sides, the heat transferred is different, which in turn leads to different slopes of the temperature rise curves.

9. The method according to claim 1, characterized in that: The data acquisition card should acquire data for a period of time after heating to eliminate the influence of contact thermal resistance, insulation layer and adhesive layer thermal resistance, and to enable the measurement of thermophysical properties of samples with internal heat sources.

10. The method as described in claim 1, characterized in that: The sensor is embedded inside the materials on both sides as a heat source, resulting in minimal heat loss and eliminating the need for a vacuum environment.

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