阅读说明：本技术 一种基于热成像的平板状样品导热性能测试装置 (Flat-plate-shaped sample heat-conducting property testing device based on thermal imaging ) 是由 侯德鑫 叶树亮 于 2021-09-03 设计创作，主要内容包括：本发明公开了一种基于热成像的平板状样品导热性能测试装置。本发明包括热像仪、可控温恒温槽和隔热板,在所述的可控温恒温槽内设置有待测试的平板状样品,所述的可控温恒温槽通过隔热板将样品控温区与观测区进行隔热分离,所述的隔热板上开槽,用于热像仪对所述的平板状样品的观测。所述的平板状样品的观测面喷涂有黑体漆,观测面的相对面设置有用于热激励的电热片。本发明可测定多个热参数,采用热像仪作为温度数据采集器,其数据量大且直接获得二维平面数据及50Hz以上的时间变量数据,给基于三维传热模型进行测试和反演分析带来了足够数据源支撑,且无需破坏制样,可直接对多层薄膜堆叠制品的等效导热系数进行准确测试。(The invention discloses a device for testing the heat-conducting property of a flat-plate-shaped sample based on thermal imaging. The thermal imager comprises a thermal imager, a temperature-controllable constant temperature groove and a thermal insulation plate, wherein a flat-plate-shaped sample to be tested is arranged in the temperature-controllable constant temperature groove, the temperature-controllable constant temperature groove is used for carrying out thermal insulation separation on a temperature-controlled area and an observation area of the sample through the thermal insulation plate, and a groove is formed in the thermal insulation plate and used for the thermal imager to observe the flat-plate-shaped sample. The observation surface of the flat-plate-shaped sample is sprayed with black body paint, and the opposite surface of the observation surface is provided with an electric heating sheet for thermal excitation. The invention can measure a plurality of thermal parameters, adopts the thermal imager as a temperature data collector, has large data volume, directly obtains two-dimensional plane data and time variable data above 50Hz, brings enough data source support for testing and inversion analysis based on a three-dimensional heat transfer model, does not need to destroy sample preparation, and can directly and accurately test the equivalent thermal conductivity coefficient of a multilayer film stacking product.)

1. The utility model provides a flat sample thermal conductivity testing arrangement based on thermal imaging, includes thermal imager, controllable temperature constant temperature groove and heat insulating board, its characterized in that:

a flat-plate-shaped sample to be tested is arranged in the temperature-controllable constant temperature groove, the temperature-controllable constant temperature groove is used for carrying out heat insulation separation on a sample temperature control area and an observation area through a heat insulation plate, and a groove is formed in the heat insulation plate and is used for observing the flat-plate-shaped sample by a thermal imager;

the observation surface of the flat-plate-shaped sample is sprayed with black body paint, and the opposite surface of the observation surface is provided with an electric heating sheet for thermal excitation.

2. The device for testing the thermal conductivity of the flat plate-shaped sample based on thermal imaging according to claim 1, wherein: the slotting mode of the heat insulation plate is a straight slot or a cross slot.

3. The device for testing the thermal conductivity of the flat plate-shaped sample based on thermal imaging according to claim 1, wherein: and a synchronous heating signal area is also configured for assisting in recording the heating starting time of the thermal flat-plate-shaped sample.

4. The device for testing the thermal conductivity of the flat plate-shaped sample based on thermal imaging according to claim 1, wherein: and a cooperative black body for eliminating the temperature drift of the thermal imager is arranged in the observation area.

5. The device for testing the thermal conductivity of the flat plate-shaped sample based on thermal imaging according to claim 1, wherein: the sample is heated by the electrothermal sheet in a transmission mode, and the heating excitation mode is a pulse cycle or a double pulse cycle.

6. The device for testing the thermal conductivity of the flat plate-shaped sample based on thermal imaging according to claim 1, wherein: the thermal imager is provided with laser positioning coordinates and is used for realizing the alignment of the thermal imager and the spatial position of the flat-plate-shaped sample.

Technical Field

The invention belongs to the field of heat conductivity test, and relates to a flat-plate-shaped sample heat conductivity test device based on thermal imaging.

Background

Conventional thermal conductivity tests are steady state, flash, Hot wire, and Hot Disk.

The steady-state method has higher requirements on the size of a sample, and the multilayer heterogeneous characteristics cannot meet ideal test conditions; in addition, in order to reduce the thermal contact resistance between the sample to be tested and the test element, a certain pressure is usually applied to the sample, which causes the internal state of the sample to change, the measured result cannot reflect the thermal properties of the sample in a normal state, and the test time is usually too long, and the efficiency is low. Therefore, the conventional steady-state method is not suitable for samples with complicated structures and large differences in shapes and sizes.

The flash method has high requirements on a test object, a sample needs to be made into a thin sheet, and finally the overall thermal conductivity of the sample is obtained through theoretical calculation, but the method cannot correctly evaluate the influence of an internal complex structure, and the calculation result has a large difference from the real thermal conductivity.

The hot wire method is similar to the flash method, and the complex packaging structure makes the method unable to carry out in-situ measurement on the sample and can only be used for measuring the heat conductivity coefficient of the battery cell component of the lithium battery.

The Hot Disk method is only suitable for samples such as lithium batteries which are uniform media in principle, and the thermal physical properties of a battery core and a shell package of the sample are obviously different, so that the measurement result is easily influenced by an external aluminum-plastic film and the overall thermal conductivity of the battery cannot be correctly measured.

From the above analysis, the conventional thermal conductivity test is not suitable for the thermal parameter test of the anisotropic plate and the multi-layer anisotropic plate.

The thermal parameter test of the anisotropic flat plate and the multilayer anisotropic flat plate represented by the lithium battery has the advantages of complex multilayer film, porosity, looseness, solid-liquid two phases, irregular edge, various specifications and incapability of processing and changing the shape and the size due to the particularity of a test object. The thermal related problems of samples such as power lithium batteries relate to the performance, safety, life and cost of the batteries. The risk of thermal runaway may occur at higher cell temperatures, and the energy and power density of the cell may be reduced at lower temperatures. Therefore, the lithium battery must be thermally designed and thermally managed. The thermal conductivity is one of the important thermal physical parameters of the battery, and reflects the thermal conductivity of the battery. In thermal simulation of the battery, the difference that thermal physical parameters such as thermal conductivity are close to one order of magnitude can cause the difference of predicted temperature gradient to be one order of magnitude, so accurate measurement of the thermal conductivity of the battery has very important significance for analyzing the thermal characteristics of the battery and using thermal control measures in a targeted manner.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: aiming at the thermal parameter test of an anisotropic flat plate and a multilayer heterogeneous flat plate represented by a multilayer composite plate and a lithium battery, the thermal conductivity testing device for the flat sample based on thermal imaging is provided, the evolution data of the surface temperature field of the sample is recorded by a thermal imager, and a plurality of thermal parameters of the battery, such as the thermal conductivity coefficient, the longitudinal thermal conductivity coefficient, the specific heat capacity, the thermal diffusion coefficient, the contact thermal resistance, the interface heat exchange coefficient, the total thermal resistance and the like, can be simultaneously inverted, so that uncertain factors introduced by the traditional contact type surface temperature measurement are avoided.

The technical scheme adopted by the invention for solving the technical problem is as follows:

the thermal imager comprises a thermal imager, a temperature-controllable constant temperature bath and a thermal insulation board, wherein a flat-plate-shaped sample to be tested is arranged in the temperature-controllable constant temperature bath, the temperature-controllable constant temperature bath is used for carrying out thermal insulation separation on a temperature-controlled area and an observation area of the sample through the thermal insulation board, and a groove is formed in the thermal insulation board and is used for the thermal imager to observe the flat-plate-shaped sample;

the observation surface of the flat-plate-shaped sample is sprayed with black body paint, and the opposite surface of the observation surface is provided with an electric heating sheet for thermal excitation.

Furthermore, the slotting mode of the heat insulation plate is a straight slot or a cross slot.

Furthermore, a synchronous heating signal area is configured for assisting in recording the heating start time of the thermal flat-plate-shaped sample.

Furthermore, a cooperative black body for eliminating the temperature drift of the thermal imager is arranged in the observation area.

Furthermore, the sample is heated by the electrothermal sheet in a transmission mode, and the heating excitation mode is a pulse period or a double pulse period.

Furthermore, the thermal imager is provided with laser positioning coordinates and used for realizing the alignment of the thermal imager and the spatial position of the flat-plate-shaped sample.

The invention has the beneficial effects that: the invention can be applied to the heat-conducting performance parameters of the flat-plate material and is suitable for homogeneous or non-homogeneous samples with different specifications, surface hardness, roughness and porosity; the device adopts a thermal imager as a temperature data collector, has large data volume, directly obtains two-dimensional plane data and time variable data above 50Hz, brings enough data source support for testing and inversion analysis based on a three-dimensional heat transfer model, does not need to destroy sample preparation, and can directly and accurately test the equivalent heat conductivity coefficient of a multilayer film stacked product.

Drawings

FIG. 1 is a block diagram of the present invention.

Detailed Description

For the purpose of making clear the objects, technical solutions and advantages of the present invention, the present invention will be further described with reference to the accompanying drawings in which:

the invention relates to a professional testing device for measuring the heat conduction performance of a flat sample, in particular to a professional testing device for measuring various thermal parameters of an anisotropic flat plate and a multilayer anisotropic flat plate, which can not be solved by a conventional method: such as face-to-face thermal conductivity, longitudinal thermal conductivity, specific heat capacity, thermal diffusivity, contact thermal resistance, interfacial heat transfer coefficient, total thermal resistance, and the like. The thermal imager is used as temperature observation equipment, two-dimensional temperature data and one-dimensional time data information are directly obtained, and a foundation is provided for later sample data testing and model inversion.

The invention adopts a transmission type pulse heating mode, the back surface of the sample is heated by the electric heating sheet, the front surface of the sample is sprayed with black body paint to be used as an observation surface, the emissivity of the sample is ensured to be 0.94 or above, and the thermal response of the observation surface can reflect the integral heat-conducting property of the sample. Because the temperature measurement of the thermal imager is easily influenced by environmental noise, in order to ensure the reliability of data, the maximum temperature rise of the observation surface of the sample is about 3-5 ℃ as a standard test condition, so that the temperature of the sample is obviously higher than the environmental temperature. And recording the temperature change of the heated sample by the thermal imager, and establishing a three-dimensional heat transfer model for testing and inversion analysis to calculate the thermal parameters of the sample in an inversion way.

The invention controls the temperature of the sample environment, and the temperature control mode can be as follows: and (3) a constant temperature tank, wherein the temperature range is-10-80 ℃, so as to measure the thermal parameters of the sample at a specific temperature. A heat insulation plate with one end capable of being turned is designed, a sample temperature control area and an observation area (an area surrounded by an observation surface and a thermal imager is used as the observation area) are subjected to heat insulation separation, air convection is prevented, and the interference of a thermal imager lens by a heat source is reduced as much as possible. The observation window (namely at the position of the heat insulation plate) is opened with a line shape or other-shaped openings with the line shape for observing the temperature, wherein the cross shape is particularly common.

The invention is also provided with a synchronous heating signal area, particularly a synchronous heating small electric heating piece can be adopted, and the heating starting time is recorded. When the experiment is started, the heating sheet and the small electric heating sheet which are stuck on the sample start to heat at the same time, after 2s, the power supply of the small heating sheet is turned off, and the temperature rise speed can reach more than 5 ℃/s through actual measurement because the small electric heating sheet has small heat capacity and large power density. Therefore, the small electric heating piece can be used as a synchronous signal through self quick heating and is recorded by the thermal imager, a temperature-rising curve can be fitted according to the data of the local high-temperature area of the small electric heating piece during data processing, and the frame number corresponding to the heating starting time of the small electric heating piece is calculated according to the approximate straight line and is used as a time zero point. Obviously, the precision of the time zero point calculated by the method is better than that of the initial heating frame directly determined according to the temperature rise, and the maximum error of the time zero point is not more than 1 frame, so that the time synchronization error mainly comes from the sampling frame frequency of the thermal imager.

The present invention also designs a cooperative black body. A small metal plate sprayed with black body paint is placed in the observation window (above the heat insulation plate), and the surface emissivity of the small metal plate can reach 0.94. And the observation data of the cooperative black body is used as the reference data of the thermal imager for observing the sample, so that the deviation of the thermal imager caused by temperature drift at different times is eliminated.

The invention is also provided with laser positioning coordinates for realizing the alignment of the thermal imager and the space position of the sample.

Example (b):

as shown in fig. 1: the thermal imager 1 is arranged right above, the space formed by the thermal insulation board 2 and the thermal imager is used as an observation window to form an observation area, and the cooperation black body 6 and the synchronous heating small electric heating piece 7 are arranged above the thermal insulation board: the thermal baffle is provided with a linear window 8, and the positioning of the cross laser coordinate center is consistent with the sample center and the thermal imager center. The lithium battery 3 is arranged in the temperature-controllable thermostatic bath 5, blackbody paint with emissivity of 0.94 is uniformly sprayed on the surface of the sample and is fully dried, thermal excitation of any rule is provided for the non-observation surface through the electric heating sheet 4, and a fan is designed in the thermostatic bath to improve the constant temperature efficiency.

The test method using the device comprises the following steps:

before testing, the front side of the lithium battery is uniformly sprayed with black body paint for at least two times, so that the emissivity of an observation surface is ensured to be 0.94 or more; the back of the lithium battery is adhered with the electric heating piece, the electric heating piece is generally considered to be adhered to the central position, the proportional relation between the size of the electric heating piece and the size of the lithium battery is noticed, the calculation model of the heat conduction inversion is directly influenced, the electric heating piece is tightly attached, and the contact thermal resistance is reduced as much as possible.

Opening the heat insulation plate, putting the lithium battery on the test board, connecting a lead and starting a power supply; and setting the heating and cooling time and voltage of the synchronous small electric heating pieces.

Taking the sprayed black body paint surface as an observation surface, turning on laser, aligning the position of the lithium battery, and aligning the centers of the sample, the thermal imager and the straight groove by using the laser; and (4) closing the laser and closing the heat insulation plate (the heat insulation plate is designed to be a turnover plate with one end fixed). Setting the temperature of the thermostatic bath, and starting a power supply of the thermostatic bath; and (4) turning on the fan, turning off the fan after a certain time, and standing for a certain time (waiting for the lithium battery to reach the set temperature of the thermostatic bath).

And setting heating and cooling time, period and voltage parameters of the heating plate to record the cooperative black body data.

The specific inversion calculation method of the thermal conductivity coefficient comprises the following steps: knowing the geometric size, heat source distribution, boundary conditions and initial conditions of the lithium battery, all thermophysical parameters except the thermal conductivity, and temperature field data under specific thermal excitation, solving the thermal conductivity is a typical inverse problem of thermal conduction. Solving the thermal parameter inversion problem by a nonlinear least square method, wherein the basic idea is that the deviation between the generated numerical calculation result and the actual experimental data is minimized by adjusting the parameters to be solved, and the optimization target of the inversion can be written as the following formula

In the formula: j (x) is an inversion target function, and x is a parameter vector to be inverted; n is the number of temperature measurement points;the value is calculated for the value of the temperature at the measuring point,is an experimental measurement of the temperature at the measurement point.

Thermal parametric inversion seeks an optimal set of x such that the objective function j (x) is minimized, i.e.:

when longitudinal and facing heat conductivity coefficients are calculated simultaneously, a rectangular area with the size equal to that of the electric heating sheet in the center of the lithium battery is selected as an area of interest to ensure inversion accuracy. And when the deviation is calculated in each iteration, comparing the data of all temperature measuring points in the region of interest of the thermal image at all times with the numerical simulation data, calculating the total deviation value, and taking the group of data with the minimum deviation as a result.

And clicking to start the test, waiting for the end of the experiment, and returning the heating power and other thermal parameter information.

The embodiments described in this specification are merely illustrative of implementations of the inventive concept and the scope of the present invention should not be considered limited to the specific forms set forth in the embodiments but rather by the claims that follow the summary of the invention in equivalents thereof as may be devised by those skilled in the art based on the teachings of the present invention.