Device and method for measuring heat conductivity coefficient of sample under vacuum high-temperature condition

Abstract

The invention relates to the technical field of heat conductivity coefficient measurement, and discloses a device and a method for measuring a heat conductivity coefficient of a sample under a vacuum high-temperature condition, and the device comprises a high-temperature environment unit which can form a high-temperature test environment in a test cavity; the vacuumizing unit can vacuumize the test cavity; the inert gas conveying unit can convey inert gas into the test cavity; the test loop comprises a lock-in amplifier as well as a signal generator, a power amplifier and a hot-wire probe which are sequentially connected in series, the lock-in amplifier is connected to two ends of the hot-wire probe in parallel, and the hot-wire probe is mounted in the test cavity and can heat the sample and measure the temperature of the sample; the controller is electrically connected with the high-temperature environment unit, the vacuumizing unit, the inert gas conveying unit, the signal generator, the power amplifier, the hot wire probe and the lock-in amplifier, and the controller calculates the heat conductivity coefficient by obtaining voltage data measured by the lock-in amplifier. The measuring device can measure the heat conductivity coefficient of the material under the high-temperature condition.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermal conductivity measurement, in particular to a device and method for measuring thermal conductivity of a sample under vacuum and high temperature conditions. BACKGROUND

[0002] A thermal conductivity instrument is a key device for measuring the thermal conductivity of materials, and its measurement accuracy and adaptability directly affect the evaluation results of material thermal performance, and is widely used in the fields of aerospace, electronic chips, building energy saving, etc. The core components of circulating fluidized bed boilers, such as the furnace and the cyclone separator, are covered with thick wear-resistant refractory materials. Such materials need to withstand extreme working conditions of high temperature of 900-1400℃, high-speed material flow scouring and temperature sudden change for a long time. The accurate measurement of the thermal conductivity of such materials is of great significance to the design optimization and safe operation of the boiler.

[0003] At present, the thermal conductivity of wear-resistant refractory materials is usually measured by a thermal conductivity determination instrument using the hot-wire method. Specifically, a hot wire with heating and temperature measurement functions is arranged inside the sample of the refractory material to be measured. A constant power source is used to apply transient heating to the hot wire, and the temperature change curve of the hot wire itself over time is recorded in real time. The linear slope of the temperature-time curve is directly related to the thermal conductivity of the material by using the non-steady-state heat conduction equation, and the thermal conductivity value of the material is finally calculated. However, the thermal conductivity determination instrument using the hot-wire method has the following defects: 1. For actual testing scenarios of non-ideal infinite hot wires and non-symmetrical sample structures, additional correction terms such as boundary correction coefficients and probe geometry correction coefficients need to be introduced to compensate for the calculation of thermal conductivity. The selection of correction terms depends on empirical models, which is prone to introduce systematic errors and lead to inaccurate measurement. 2. The hot wire itself of the thermal conductivity determination instrument using the hot-wire method is prone to oxidation failure under high temperature conditions. SUMMARY

[0004] To solve the above technical problems, the present application provides a device and method for measuring the thermal conductivity of a sample under vacuum and high temperature conditions.

[0005] In a first aspect, the present invention provides a device for measuring the thermal conductivity of a sample under vacuum and high temperature conditions, comprising: a high-temperature environment unit having a test chamber capable of placing a sample, the high-temperature environment unit being able to create a high-temperature test environment within the test chamber; a vacuum pumping unit connected to the high-temperature environment unit, the vacuum pumping unit being able to evacuate the test chamber; an inert gas delivery unit connected to the high-temperature environment unit, the inert gas delivery unit being able to deliver inert gas into the test chamber to create an inert gas environment; a test circuit including a lock-in amplifier, and a signal generator, a power amplifier, and a hot-wire probe connected in series, the lock-in amplifier being connected in parallel across the two ends of the hot-wire probe, the hot-wire probe being installed in the test chamber, and being able to heat the sample and measure the temperature of the sample; and a controller electrically connected to the high-temperature environment unit, the vacuum pumping unit, the inert gas delivery unit, the signal generator, the power amplifier, the hot-wire probe, and the lock-in amplifier, the controller acquiring the voltage data measured by the lock-in amplifier and determining the thermal conductivity of the standard sample based on the... Voltage data obtained by the lock-in amplifier when the standard sample is tested Calculate the thermal conductivity.

[0006] Optionally, the signal generator can output a sinusoidal voltage signal with a frequency of f; the power amplifier can receive the sinusoidal voltage signal and amplify it into a high-current sinusoidal signal with a frequency of f to drive the hot wire probe; the lock-in amplifier has a reference input frequency of 2f, and can extract the harmonic components synchronized with the reference input frequency 2f from the AC voltage signal at both ends of the hot wire probe, and convert them into a DC voltage signal output; the controller can receive the DC voltage signal and, in conjunction with the voltage data measured under the same conditions by a standard sample with a known thermal conductivity, calculate the thermal conductivity of the test sample.

[0007] Optionally, the test circuit also includes an oscilloscope, whose probes are connected to the output of the signal generator, the output of the power amplifier, and both ends of the hot wire probe, respectively. The oscilloscope can simultaneously monitor the voltage signals output by the signal generator, the power amplifier, and the voltage signals at both ends of the hot wire probe.

[0008] Optionally, the vacuum unit includes a vacuum pump and a first valve. The vacuum pump and the high-temperature environment unit are connected through a first pipe, and the first valve is installed on the first pipe.

[0009] Optionally, the inert gas delivery unit includes a nitrogen cylinder, which is connected to the high-temperature environment unit via a second pipeline. A pressure reducing valve and a flow meter are sequentially installed on the second pipeline along the nitrogen delivery direction.

[0010] Optionally, a temperature sensor is installed inside the test chamber, and a temperature display electrically connected to the temperature sensor is installed outside the tube furnace.

[0011] Optionally, the high-temperature environment unit is a tubular furnace, and the test chamber is the furnace chamber of the tubular furnace.

[0012] Optionally, a support is provided inside the furnace, and the test sample is placed on the support.

[0013] Secondly, the present invention provides a method for measuring the thermal conductivity of a sample under vacuum high-temperature conditions, comprising: A measurement experiment was conducted using a sample thermal conductivity measuring device under vacuum and high temperature conditions. The voltage data measured by the lock-in amplifier was obtained when the test sample was a standard sample with known thermal conductivity. ; A measurement experiment was conducted using a sample thermal conductivity measuring device under vacuum and high temperature conditions to obtain the voltage data measured by the lock-in amplifier when the test sample was the sample to be tested. ; The controller is based on the standard sample. and ,as well as Calculate the thermal conductivity of the sample to be tested. : In the formula The thermal conductivity of the sample to be tested is... The thermal conductivity of the standard sample is given. Voltage data obtained by the lock-in amplifier when testing standard samples. Voltage data obtained by the lock-in amplifier when testing the sample.

[0014] Optionally, methods for conducting measurement tests include: Two test specimens are stacked vertically in the test chamber of the high-temperature environment unit, and the monitoring end of the hot wire probe is placed between the two test specimens. The vacuum unit is activated to evacuate the test chamber. The inert gas delivery unit is activated to deliver inert gas into the test chamber, creating an inert gas environment. The high-temperature environment unit is activated to raise the temperature inside the test chamber to the temperature required for the test and maintain the temperature for no less than the first preset time. The test circuit is powered and heats the test sample through a hot wire probe, while the temperature is monitored through the hot wire probe. The controller acquires the voltage data measured by the lock-in amplifier.

[0015] The technical solution provided by the embodiments of the present invention has the following advantages compared with the prior art: 1. By setting up a vacuum pumping unit and an inert gas delivery unit, an inert gas environment can be constructed to effectively protect the hot wire probe and ensure that the hot wire can achieve stable and accurate measurement under the extreme working conditions required by wear-resistant and refractory materials, thereby overcoming the problem of the hot wire itself being easily oxidized in a high-temperature environment.

[0016] 2. The measuring device of the present invention only requires placing the sample in the test chamber of the high-temperature environment unit. The high-temperature environment unit itself forms a high-temperature test environment in the test chamber, which can accurately simulate the environment in which the sample is located under actual working conditions. Therefore, the thermal conductivity measured by the sample is the thermal conductivity of the sample under high-temperature working conditions, thereby reducing variables that may interfere with the measurement results, so the measurement results are more accurate.

[0017] 3. The thermal conductivity can be directly calculated using the voltage data obtained by the lock-in amplifier through the measuring device of the present invention without the need for additional correction terms, thereby avoiding the introduction of systematic errors in the calculation process and the problem of inaccurate measurement. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a device for measuring the thermal conductivity of a sample under vacuum and high temperature conditions, provided in Embodiment 1 of the present invention.

[0019] Explanation of reference numerals in the attached diagram: 1. Vacuum pump; 2. First valve; 3. Temperature display; 4. Temperature sensor; 5. Test sample; 6. Lock-in amplifier; 7. Signal generator; 8. Hot wire probe; 9. Nitrogen cylinder; 10. Pressure reducing valve; 11. Flow meter; 12. Support; 13. Tube furnace; 14. Oscilloscope; 15. Power amplifier. Detailed Implementation

[0020] The following detailed description of a specific embodiment of the present invention is provided in conjunction with the accompanying drawings. However, it should be understood that the scope of protection of the present invention is not limited to the specific embodiment.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the technical solution of this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] Example 1: like Figure 1As shown, this embodiment provides a device for measuring the thermal conductivity of a sample under vacuum and high temperature conditions, comprising: a high-temperature environment unit having a test chamber capable of holding the sample, the high-temperature environment unit being able to create a high-temperature test environment within the test chamber; a vacuum pumping unit connected to the high-temperature environment unit, the vacuum pumping unit being able to evacuate the test chamber; an inert gas delivery unit connected to the high-temperature environment unit, the inert gas delivery unit being able to deliver inert gas into the test chamber to form an inert gas environment; a test circuit including a lock-in amplifier 6, and a signal generator 7, a power amplifier 15, and a hot-wire probe 8 connected in series, the lock-in amplifier 6 being connected in parallel across the two ends of the hot-wire probe 8, the hot-wire probe 8 being installed in the test chamber, and being able to heat the sample and measure the sample temperature; and a controller electrically connected to the high-temperature environment unit, the vacuum pumping unit, the inert gas delivery unit, the signal generator 7, the power amplifier 15, the hot-wire probe 8, and the lock-in amplifier 6, the controller calculating the thermal conductivity by acquiring the voltage data measured by the lock-in amplifier 6. In the formula The thermal conductivity of the sample to be tested is... The thermal conductivity of the standard sample is given. Voltage data obtained by lock-in amplifier 6 when testing standard samples. Voltage data obtained by lock-in amplifier 6 when testing the sample to be tested.

[0023] In this embodiment, the hot wire probe 8 is composed of a refractory metal wire core and an outer ceramic insulating coating. The refractory metal wire is a platinum-rhodium alloy, and the ceramic insulating coating is alumina. The probe is led out through a vacuum feedthrough electrode on the furnace wall, forming a composite element that simultaneously performs heating and temperature sensing functions. The signal generator 7 is used to generate a sinusoidal voltage signal with a frequency of f. The power amplifier 15 operates in constant current mode to receive the sinusoidal voltage signal and output a high-current sinusoidal signal with a frequency of f to drive the hot wire probe. The differential input terminal of the lock-in amplifier 6 is connected in parallel to the hot wire probe. The two ends of the circuit are connected, and its reference input frequency is set to 2f, which is used to extract the harmonic component with a frequency of 2f from the voltage signal at both ends of the hot wire and convert it into a stable DC voltage signal output; the oscilloscope 14 is a four-channel digital oscilloscope with a resolution of not less than 12 bits, which is used to synchronously monitor the output of the signal generator, the output of the power amplifier 15 and the original differential voltage signal at both ends of the hot wire; the controller includes a computer and a data acquisition system, which is used to control the furnace temperature, signal source and lock-in amplifier 6 parameters, and receive the final DC voltage signal, calculate and output the effective thermal conductivity of the material.

[0024] The signal generator 7 can output a sinusoidal voltage signal with a frequency of f; the power amplifier 15 can receive the sinusoidal voltage signal and output a large current sinusoidal signal with a frequency of f to drive the hot wire probe 8; the lock-in amplifier 6 has a reference input frequency of 2f, and can extract the harmonic components synchronized with the reference input frequency 2f from the voltage signal at both ends of the hot wire probe 8 and convert them into a DC voltage signal output; the controller can receive the DC voltage signal and, in conjunction with the voltage data measured under the same conditions by a standard sample with a known thermal conductivity, calculate the thermal conductivity of the test sample 5.

[0025] In this embodiment, the frequency f ranges from 1Hz to 100Hz, and its specific value is determined by frequency scanning so that the output signal of the lock-in amplifier 6 is in a plateau region that does not change with frequency.

[0026] The test circuit also includes an oscilloscope 14. The probe of the oscilloscope 14 is connected to the output of the signal generator 7, the output of the power amplifier 15, and both ends of the hot wire probe 8. The oscilloscope 14 can synchronously monitor the voltage signal output by the signal generator 7, the voltage signal output by the power amplifier 15, and the voltage signals at both ends of the hot wire probe 8.

[0027] A sinusoidal current signal with frequency f is emitted by signal generator 7. The oscilloscope 14 is used to detect that the signal is correct and the signal is amplified by power amplifier 15. The test sample is heated by hot wire probe 8. The lock-in amplifier 6 is used to extract the signal with frequency 2f generated during heating and output this signal as a voltage signal. By comparing the voltage signal measured under the same conditions with that of a standard sample with known thermal conductivity, the thermal conductivity of the test sample can be obtained.

[0028] The vacuum pumping unit includes a vacuum pump 1 and a first valve 2. The vacuum pump 1 and the high-temperature environment unit are connected through a first pipe, and the first valve 2 is installed on the first pipe.

[0029] In this embodiment, the vacuum level evacuated by the vacuum pumping unit is no higher than 1×10⁻²Pa.

[0030] The inert gas delivery unit includes a nitrogen cylinder 9, which is connected to the high-temperature environment unit via a second pipeline. A pressure reducing valve 10 and a flow meter 11 are sequentially installed on the second pipeline along the nitrogen delivery direction.

[0031] A temperature sensor 4 is installed inside the test chamber, and a temperature display 3, which is electrically connected to the temperature sensor 4, is installed outside the tubular furnace.

[0032] In this embodiment, the high-temperature environment unit is a tubular furnace, and the test chamber is the furnace chamber of the tubular furnace. The maximum operating temperature of the tubular furnace is not lower than 1600℃.

[0033] A support 12 is installed inside the furnace, and the test sample 5 is placed on the support 12.

[0034] Example 2: This embodiment provides a method for measuring the thermal conductivity of a sample under vacuum and high temperature conditions, including: Step 1: Using a sample thermal conductivity measuring device under vacuum and high temperature conditions, conduct a measurement experiment to obtain the voltage data measured by the lock-in amplifier 6 when the test sample 5 is a standard sample with a known thermal conductivity. ; Step 2: Using a sample thermal conductivity measuring device under vacuum and high temperature conditions, a measurement experiment is conducted to obtain the voltage data measured by the lock-in amplifier 6 when the test sample 5 is the sample to be tested. ; Step 3: The controller determines the thermal conductivity of the standard sample. , and Calculate the thermal conductivity of the sample to be tested. .

[0035] Methods for conducting measurement tests include: Step 1: Stack two test specimens 5 vertically in the test chamber of the high-temperature environment unit, and place the monitoring end of the hot wire probe 8 between the two test specimens 5. Step 2: Start the vacuum unit to evacuate the test chamber; Step 3: Activate the inert gas delivery unit to deliver inert gas into the test chamber to create an inert gas environment; Step 4: Activate the high-temperature environment unit to raise the temperature inside the test chamber to the temperature required for the test, and maintain the temperature for no less than the first preset time. In this embodiment, the first preset duration is not less than 30 minutes.

[0036] Step 5: Power supply to the test circuit, heat the test sample 5 through the hot wire probe 8, and monitor the temperature through the hot wire probe 8 at the same time; Step 6: The controller acquires the voltage data measured by the lock-in amplifier 6.

[0037] In this embodiment, the method is specifically used to measure the effective thermal conductivity of wear-resistant refractory materials for circulating fluidized bed boilers in the temperature range from room temperature to 1400°C.

[0038] The above inventions are merely a few specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A device for measuring the thermal conductivity of a sample under vacuum and high temperature conditions, characterized in that, include: The high-temperature environment unit has a test chamber that can hold the sample, and the high-temperature environment unit can create a high-temperature test environment within the test chamber; The vacuum unit is connected to the high-temperature environment unit and can evacuate the test chamber. The inert gas delivery unit is connected to the high-temperature environment unit. The inert gas delivery unit can deliver inert gas into the test chamber to form an inert gas environment. The test circuit includes a lock-in amplifier, and a signal generator, a power amplifier and a hot wire probe connected in series. The lock-in amplifier is connected in parallel across the two ends of the hot wire probe, which is installed in the test chamber and can heat the sample and measure the temperature of the sample. The controller is electrically connected to the high-temperature environment unit, vacuum unit, inert gas delivery unit, signal generator, power amplifier, hot-wire probe, and lock-in amplifier. The controller acquires the voltage data measured by the lock-in amplifier and, based on the thermal conductivity of the standard sample... Voltage data obtained by the lock-in amplifier when the standard sample is tested Calculate the thermal conductivity.

2. The device for measuring the thermal conductivity of a sample under vacuum high temperature conditions as described in claim 1, characterized in that, The signal generator can output a sinusoidal voltage signal with a frequency of f; the power amplifier can receive the sinusoidal voltage signal and amplify it into a high-current sinusoidal signal with a frequency of f to drive the hot wire probe; the lock-in amplifier has a reference input frequency of 2f, and can extract the harmonic components synchronized with the reference input frequency 2f from the AC voltage signal at both ends of the hot wire probe, and convert them into a DC voltage signal for output; the controller can receive the DC voltage signal and, in conjunction with the voltage data measured under the same conditions by a standard sample with a known thermal conductivity, calculate the thermal conductivity of the test sample.

3. The device for measuring the thermal conductivity of a sample under vacuum high temperature conditions as described in claim 1, characterized in that, The test circuit also includes an oscilloscope, whose probes are connected to the output of the signal generator, the output of the power amplifier, and both ends of the hot wire probe, respectively. The oscilloscope can simultaneously monitor the voltage signals output by the signal generator, the power amplifier, and the voltage signals at both ends of the hot wire probe.

4. The device for measuring the thermal conductivity of a sample under vacuum high temperature conditions as described in claim 1, characterized in that, The vacuum pumping unit includes a vacuum pump and a first valve. The vacuum pump and the high-temperature environment unit are connected through a first pipe, and the first valve is installed on the first pipe.

5. The device for measuring the thermal conductivity of a sample under vacuum high temperature conditions as described in claim 1, characterized in that, The inert gas delivery unit includes a nitrogen cylinder, which is connected to the high-temperature environment unit via a second pipeline. A pressure reducing valve and a flow meter are sequentially installed on the second pipeline along the nitrogen delivery direction.

6. The device for measuring the thermal conductivity of a sample under vacuum high temperature conditions as described in claim 1, characterized in that, The high-temperature environment unit is a tubular furnace, and the test chamber is the furnace chamber of the tubular furnace.

7. The device for measuring the thermal conductivity of a sample under vacuum high temperature conditions as described in claim 6, characterized in that, A temperature sensor is installed inside the furnace, and a temperature display electrically connected to the temperature sensor is installed outside the tubular furnace.

8. The device for measuring the thermal conductivity of a sample under vacuum high temperature conditions as described in claim 6, characterized in that, The furnace chamber is equipped with a support, and the test sample is placed on the support.

9. The measurement method of the sample thermal conductivity measuring device under vacuum high temperature conditions as described in any one of claims 1-8, characterized in that, include: A measurement experiment was conducted using a sample thermal conductivity measuring device under vacuum and high temperature conditions. The voltage data measured by the lock-in amplifier was obtained when the test sample was a standard sample with known thermal conductivity. ; A measurement experiment was conducted using a sample thermal conductivity measuring device under vacuum and high temperature conditions to obtain the voltage data measured by the lock-in amplifier when the test sample was the sample to be tested. ; The controller is based on the standard sample. and ,as well as Calculate the thermal conductivity of the sample to be tested. : In the formula The thermal conductivity of the sample to be tested is... The thermal conductivity of the standard sample is given. Voltage data obtained by the lock-in amplifier when testing standard samples. Voltage data obtained by the lock-in amplifier when testing the sample.

10. The measurement method of the sample thermal conductivity measuring device under vacuum high temperature conditions as described in claim 9, characterized in that, Methods for conducting measurement tests include: Two test specimens are stacked vertically in the test chamber of the high-temperature environment unit, and the monitoring end of the hot wire probe is placed between the two test specimens. The vacuum unit is activated to evacuate the test chamber. The inert gas delivery unit is activated to deliver inert gas into the test chamber, creating an inert gas environment. The high-temperature environment unit is activated to raise the temperature inside the test chamber to the temperature required for the test and maintain the temperature for no less than the first preset time. The test circuit is powered and heats the test sample through a hot wire probe, while the temperature is monitored through the hot wire probe. The controller acquires the voltage data measured by the lock-in amplifier.

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