Convection heat transfer coefficient integration test method and system based on transient liquid crystal

Abstract

The invention relates to the field of aero-engine heat transfer and mass transfer, and discloses a convective heat transfer coefficient integrated test method and system based on transient liquid crystal, a narrow-band thermochromic liquid crystal coating is sprayed on the surface of a test piece, and test airflow in an air inlet channel can realize temperature step through a wire mesh heater. By synchronously measuring the color developing time of a narrow-band thermochromic liquid crystal coating on the surface of a test piece and a temperature step curve of test airflow, non-contact two-dimensional test of the convective heat transfer coefficient of the test piece is realized by utilizing the corresponding relation between the color changing characteristic of narrow-band thermochromic liquid crystal and the temperature; not only can great influence on the accuracy of test data caused by asynchronous signal acquisition be avoided, but also the problems of heat conduction error and influence on flow field distribution caused by interference on fluid in the traditional test technology are avoided, and the test precision of the convective heat transfer coefficient of the test piece is ensured. And powerful technical support is provided for research on convective heat transfer characteristics of complex flow fields in the aerospace field.

Description

Technical Field

[0001] The present invention relates to the field of heat transfer and mass transfer of aero-engines, and discloses an integrated test method and system for convective heat transfer coefficient based on transient liquid crystals. Background Art

[0002] Increasing the turbine inlet temperature is one of the important ways to increase the thrust of aero-engines. In order to ensure the life and working reliability of turbine blades, efficient blade cooling technologies must be adopted. Commonly used turbine blade cooling structures include internal enhanced heat transfer and external film cooling. To achieve the refined design of turbine blade cooling structures, it is crucial to accurately measure the convective heat transfer coefficients of the internal and external cooling structures of the blades.

[0003] Currently, the measurement of convective heat transfer coefficients mostly uses thermocouples, broadband thermochromic liquid crystals (steady-state method) or infrared thermal imagers. Among them, thermocouples belong to single-point measurement and cannot achieve two-dimensional surface measurement of convective heat transfer coefficients. At the same time, the thermocouple probes have a certain volume, which will have a certain impact on the flow field distribution and thus also affect the distribution of convective heat transfer coefficients. For broadband thermochromic liquid crystals, although the two-dimensional distribution of test data can be obtained, it is difficult to accurately and quantitatively evaluate the influence of heat conduction by the steady-state method, resulting in large test errors. For infrared thermal imagers, not only is it difficult to eliminate the errors of the steady-state method, but there are also certain calibration errors in the thermal imagers themselves. Summary of the Invention

[0004] The purpose of the present invention is to provide an integrated test method and system for convective heat transfer coefficient based on transient liquid crystals, which can not only avoid the significant impact on the accuracy of test data caused by asynchronous signal acquisition, but also avoid the problems of heat conduction errors and interference with the fluid in traditional test technologies, affecting the flow field distribution, ensuring the test accuracy of the convective heat transfer coefficient of the test piece, and providing strong technical support for the research on the convective heat transfer characteristics of complex flow fields in the aerospace field.

[0005] In order to achieve the above technical effects, the technical solution adopted by the present invention is: An integrated test method for convective heat transfer coefficient based on transient liquid crystals, comprising: Installing a test piece with a narrowband thermochromic liquid crystal coating on its surface in an intake channel, introducing a test air flow into the intake channel, and heating the test air flow to generate a temperature step in the test air flow; Synchronously collecting the temperature step curve of the test air flow and the image information of the narrowband thermochromic liquid crystal coating on the surface of the test piece, where the image information includes the color development time of the narrowband thermochromic liquid crystal coating at a fixed color value; Analyzing and obtaining the convective heat transfer coefficient of the test piece according to the color development time and the temperature step curve of the test air flow; where the convective heat transfer coefficient of the test piece is based on Obtained through analysis, where is the temperature when the narrow-band thermochromic liquid crystal displays a fixed color value, is the initial temperature of the test piece surface, is the segmented temperature step of the test air flow collected, is the time corresponding to the segmented temperature step, ， represents the number of segments of the temperature step curve during summation, is the total number of segments of the temperature step curve, is the natural constant, is the density of the test piece material, is the specific heat capacity of the test piece material, is the thermal conductivity of the test piece material, is the convective heat transfer coefficient of the test piece, is the time when the narrow-band thermochromic liquid crystal displays a fixed color value, represents the complementary error function.

[0006] To achieve the above technical effects, the present invention also provides an integrated test system for the convective heat transfer coefficient based on transient liquid crystals, for implementing the integrated test method for the convective heat transfer coefficient based on transient liquid crystals, including: An air inlet channel, used to provide a test piece installation assembly and a test air flow, and heat the test air flow to generate a temperature step for the test air flow; A collection module, used to synchronously obtain the temperature step curve of the test air flow and the image information of the narrow-band thermochromic liquid crystal coating on the surface of the test piece, where the image information includes the color display time of the narrow-band thermochromic liquid crystal coating at a fixed color value; A data processing module, used to analyze and obtain the convective heat transfer coefficient of the test piece according to the color display time and the temperature step curve of the test air flow.

[0007] Furthermore, it further includes a computer terminal, used to issue instructions for the start and end of the test to the outside world, and control the heating device to heat the test air flow in the air inlet module after the test starts to achieve a temperature step of the gas; and control the collection module to synchronously obtain the temperature step curve of the test air flow and the image information of the narrow-band thermochromic liquid crystal coating on the surface of the test piece.

[0008] Furthermore, the collection module includes: A thermocouple, which is used to measure the temperature signal of the test air flow; An analog-to-digital conversion unit, used to receive the temperature signal transmitted by the thermocouple and convert the temperature signal into a digital signal and transmit it to the data processing module.

[0009] Further, the thermocouple is a semi-exposed thermocouple, mainly composed of a sleeve, an insulating film, and a nickel-chromium - nickel-silicon thermocouple wire.

[0010] Further, the intake passage is made of a transparent material, and the device for collecting the image information of the narrow-band thermochromic liquid crystal coating on the surface of the test piece is a CCD camera.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses narrow-band thermochromic liquid crystals to achieve non-contact two-dimensional testing of the convective heat transfer coefficient of the test piece, and during the testing process, it ensures that the gas temperature data collection in the intake passage and the liquid crystal color display image information collection process are synchronized. This not only avoids the significant impact on the accuracy of test data caused by asynchronous signal collection, but also avoids the problems of conduction error and interference with the fluid in the traditional testing technology, which affects the flow field distribution, and ensures the testing accuracy of the convective heat transfer coefficient of the test piece. Description of the Drawings

[0012] Figure 1 is the flowchart of the integrated test method for the convective heat transfer coefficient in Embodiment 1 or 2; Figure 2 is the structural block diagram of the integrated test system for the convective heat transfer coefficient in Embodiment 1 or 2; Among them, 1. Narrow-band thermochromic liquid crystal coating; 2. Test piece; 3. Intake passage; 4. Computer terminal; 5. Thermocouple; 6. Digital-to-analog conversion unit; 7. CCD camera; 8. Signal acquisition unit; 9. High and low level output unit; 10. Relay; 11. DC power supply; 12. Wire mesh heater; 13. Fan. Detailed Embodiments

[0013] The present invention will be further described in detail below in conjunction with the embodiments and the drawings. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following embodiments. All technologies implemented based on the content of the present invention belong to the scope of the present invention.

[0014] Embodiment 1 Refer to Figure 1 and Figure 2 , an integrated test method for the convective heat transfer coefficient based on transient liquid crystals, includes: Install the test piece 2 with a narrow-band thermochromic liquid crystal coating 1 on its surface in the intake passage 3, introduce a test air flow into the intake passage 3, and heat the test air flow to generate a temperature step; Synchronously collect the temperature step curve of the test air flow and the image information of the narrow-band thermochromic liquid crystal coating 1 on the surface of the test piece 2, and the image information includes the color display time of the narrow-band thermochromic liquid crystal coating 1 at a fixed color value; According to the color development time and the temperature step curve of the test air flow, the convective heat transfer coefficient of the test piece 2 is obtained through analysis; wherein the convective heat transfer coefficient is based on obtained through analysis, wherein is the temperature when the narrow-band thermochromic liquid crystal shows a fixed color value, is the initial temperature of the surface of the test piece 2, is the segmented temperature step of the collected test air flow, is the time corresponding to the segmented temperature step, ， represents the number of segments of the temperature step curve when summing, is the total number of segments of the temperature step curve (which can be adjusted according to the actual test conditions), is the natural constant, is the material density of the test piece 2, is the specific heat capacity of the material of the test piece 2, is the thermal conductivity of the material of the test piece 2, is the convective heat transfer coefficient of the test piece 2, is the time when the narrow-band thermochromic liquid crystal shows a fixed color value, represents the complementary error function.

[0015] In this embodiment, by spraying a narrow-band thermochromic liquid crystal coating 1 on the surface of the test piece 2, the test air flow in the intake passage 3 can achieve a temperature step through the wire mesh heater 12. When the temperature of the test piece 2 in the intake passage 3 reaches a certain value, the narrow-band thermochromic liquid crystal shows color. By synchronously measuring the color development time of the narrow-band thermochromic liquid crystal coating 1 on the surface of the test piece 2 and the temperature step curve of the test air flow, and using the corresponding relationship between the color change characteristics of the narrow-band thermochromic liquid crystal and the temperature, a non-contact two-dimensional test of the convective heat transfer coefficient of the test piece 2 is realized. This not only reduces the conduction error and avoids the significant impact on the test accuracy caused by asynchronous signal acquisition, but also circumvents the problems of interfering with the fluid and affecting the flow field distribution in traditional test technologies, ensuring the test accuracy of the convective heat transfer coefficient of the test piece 2 and providing strong technical support for the research on the convective heat transfer characteristics of complex flow fields in the aerospace field.

[0016] Based on the same inventive concept, this embodiment also provides an integrated test system for the convective heat transfer coefficient based on transient liquid crystals, including: An intake passage 3 for providing an installation component for the test piece 2 and a test air flow, and heating the test air flow to cause a temperature step in the test air flow; A collection module for synchronously obtaining the temperature step curve of the test air flow and the image information of the narrow-band thermochromic liquid crystal coating 1 on the surface of the test piece 2, where the image information includes the color development time when the narrow-band thermochromic liquid crystal coating 1 shows a fixed color value; A data processing module, configured to analyze and obtain the convective heat transfer coefficient of the test piece 2 according to the color development time and the temperature step curve of the test air flow.

[0017] The convective heat transfer coefficient integrated test system in this embodiment further includes a computer terminal 4, which is configured to issue instructions for the start and end of the test to the outside world, and after the test starts, control the heating device to heat the test air flow in the intake module to achieve a temperature step of the gas; and control the acquisition module to synchronously acquire the temperature step curve of the test air flow and the image information of the narrow-band thermochromic liquid crystal coating 1 on the surface of the test piece 2.

[0018] In this embodiment, the intake passage 3 is made of a transparent material, and the device for collecting the image information of the narrow-band thermochromic liquid crystal coating 1 on the surface of the test piece 2 is a CCD camera 7.

[0019] Using the convective heat transfer coefficient integrated test system proposed in this embodiment, after the computer terminal 4 issues an instruction, the video information input of the CCD camera 7, the heating of the test air flow, and the temperature signal acquisition can be carried out simultaneously, realizing the synchronous measurement of the color development time of the narrow-band thermochromic liquid crystal coating 1 and the temperature step curve of the gas, ensuring the accuracy of the test.

[0020] Moreover, the convective heat transfer coefficient integrated test system of this embodiment can realize the integration of multiple test modules. When conducting the test, only one instruction needs to be issued on the computer terminal 4 to realize the video shooting of the video recorder, the temperature signal acquisition, and the power supply of the DC power supply 11; when the test ends, only one instruction needs to be issued to stop the above functions, and all the above test processes are carried out synchronously, reducing the complexity of the test system.

[0021] Embodiment 2 Refer to Figure 1 and Figure 2 , taking the convective heat transfer coefficient test of a certain type of turbine blade structure as an example, this embodiment details the process of an integrated test method for convective heat transfer coefficient based on transient liquid crystals of the present invention. The specific test process is as follows: Step 1: Install the test piece 2 with a narrow-band thermochromic liquid crystal coating 1 on its surface in the intake passage 3; In this embodiment, before data acquisition, the narrow-band thermochromic liquid crystal coating 1 is pre-sprayed on the surface of the test piece 2, and then the test piece 2 is installed at the corresponding installation position in the intake passage 3 and fixed.

[0022] Step 2: Use the fan 13 to introduce the test air flow into the intake passage 3 and heat the test air flow to cause a temperature step of the test air flow; synchronously collect the temperature step curve of the test air flow and the image information of the narrow-band thermochromic liquid crystal coating 1 on the surface of the test piece 2, and the image information includes the color development time of the narrow-band thermochromic liquid crystal coating 1 at a fixed color value. In this embodiment, the computer terminal 4 is used to issue instructions for the start and end of the experiment to the outside world. The core acquisition module is an acquisition box, which mainly includes six parts: an analog-to-digital conversion unit 6, a signal acquisition unit 8, a thermocouple 5, a high and low level output unit 9, a relay 10, and a DC power supply 11. Next, the main functions of each part will be introduced in detail: Analog-to-digital conversion unit 6: It is mainly used for analog-to-digital conversion. It can convert the analog signal of the signal acquisition unit 8 of the thermocouple 5 into a digital signal and transmit it to the computer terminal 4, and convert the high and low level digital signal output by the computer terminal 4 into an analog signal and transmit it to the high and low level output unit 9.

[0023] Signal acquisition unit 8: It is mainly used to collect the temperature signal of the thermocouple 5 and transmit it to the analog-to-digital conversion unit 6.

[0024] Thermocouple 5: It is mainly used to measure the gas temperature step curve; the semi-exposed thermocouple 5 is selected in this embodiment, which is mainly composed of a low thermal conductivity sleeve, an insulating film, and a nickel-chromium-nickel silicon thermocouple 5 wire. This thermocouple 5 can ensure the stability of the thermocouple 5 wire under high-speed air flow. At the same time, the low thermal conductivity sleeve can greatly reduce the influence of heat conduction and improve the measurement accuracy of the gas temperature step curve.

[0025] High and low level output unit 9: It receives the analog signal of the analog-to-digital conversion unit 6 and outputs high and low levels, including but not limited to 0 / 5V / 12V / 24V according to the selection of the relay 10.

[0026] Relay 10: It receives the level signal of the high and low level output unit 9 and is used to control the on and off of the DC power supply 11. According to the actual use environment, it can be selected whether to integrate the relay 10 with the DC power supply 11.

[0027] DC power supply 11: It supplies power to the wire mesh heater 12 to realize the temperature step of the test gas in the intake passage 3. According to the actual use power, the input voltage can be selected as 220V / 380V. At the same time, the DC power supply 11 can provide two use modes - constant voltage output (the output voltage remains unchanged) and constant current output (the output current remains unchanged).

[0028] During the specific acquisition process, after the instruction is issued on the computer side, the video information input, high and low level signal output, and temperature signal input of the CCD camera 7 are carried out simultaneously, realizing the synchronous measurement of the liquid crystal coating color development time and the gas temperature step curve, ensuring the accuracy of the test method, and integrating the test system.

[0029] Step 3: Analyze and obtain the convective heat transfer coefficient of the test piece 2 according to the color development time and the temperature step curve of the test air flow; In this embodiment, the convective heat transfer coefficient of the test piece 2 is based on Analysis obtained, where is the temperature when the narrow-band thermochromic liquid crystal displays a fixed color value, is the initial temperature of the surface of Test Piece 2, is the segmented temperature step of the test air flow collected, is the time corresponding to the segmented temperature step, ， represents the number of segments of the temperature step curve during summation, is the total number of segments of the temperature step curve (which can be adjusted according to the actual test conditions), is the natural constant, is the material density of Test Piece 2, is the specific heat capacity of the material of Test Piece 2, is the thermal conductivity of the material of Test Piece 2, is the convective heat transfer coefficient of Test Piece 2, is the time when the narrow-band thermochromic liquid crystal displays a fixed color value, represents the complementary error function.

[0030] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An integrated test method for convective heat transfer coefficient based on transient liquid crystal, characterized in that: include: A test piece having a narrow-band thermochromic liquid crystal coating on its surface is installed in an air inlet passage, a test airflow is introduced into the air inlet passage, and the test airflow is heated to generate a temperature step in the test airflow; synchronously collecting the temperature step curve of the test airflow and the image information of the narrow-band thermochromic liquid crystal coating on the surface of the test piece, wherein the image information includes the color development time of the narrow-band thermochromic liquid crystal coating at a fixed color value; According to the color development time and the temperature step curve of the test airflow, the convective heat transfer coefficient of the test piece is analyzed and obtained; wherein the convective heat transfer coefficient of the test piece is based on The analysis obtained is the temperature at which the narrow-band thermochromic liquid crystal displays a fixed color value, is the initial temperature of the test piece surface, is the segmented temperature step of the collected test airflow, is the time corresponding to the segmented temperature step, ， represents the number of temperature step curve segments when summing, is the total number of segments of the temperature step curve, is a natural constant, is the material density of the test piece, is the specific heat capacity of the test piece material, is the thermal conductivity of the test piece material, is the convective heat transfer coefficient of the test piece, The time it takes for narrow-band thermochromic liquid crystal to display a fixed color value. represents the complementary error function.

2. A transient liquid crystal based convective heat transfer coefficient integrated test system, used to implement the transient liquid crystal based convective heat transfer coefficient integrated test method according to claim 1, characterized in that: include: An air inlet passage, used for providing a test piece mounting assembly and a test airflow, and heating the test airflow to produce a temperature step of the test airflow; An acquisition module is used to synchronously acquire a temperature step curve of the test airflow and image information of the narrow-band thermochromic liquid crystal coating on the surface of the test piece, wherein the image information includes the color development time of the narrow-band thermochromic liquid crystal coating at a fixed color value; The data processing module is used to analyze and obtain the convective heat transfer coefficient of the test piece according to the color development time and the temperature step curve of the test airflow.

3. The integrated test system for convective heat transfer coefficient based on transient liquid crystal according to claim 2 is characterized in that: It also includes a computer terminal, which is used to issue instructions for starting and ending the test to the outside world, and control the heating device to heat the test airflow in the air intake module to achieve a temperature step of the gas after the test starts; and control the acquisition module to synchronously obtain the temperature step curve of the test airflow and the image information of the narrow-band thermochromic liquid crystal coating on the surface of the test piece.

4. The integrated test system for convection heat transfer coefficient based on transient liquid crystal according to claim 2, characterized in that: The acquisition module comprises: A thermocouple, wherein the thermocouple is used to measure a temperature signal of a test air flow; The digital-to-analog conversion unit is used to receive the temperature signal transmitted by the thermocouple and convert the temperature signal into a digital signal to transmit to the data processing module.

5. The integrated test system for convection heat transfer coefficient based on transient liquid crystal according to claim 4 is characterized in that: The thermocouple is a semi-exposed thermocouple, which is mainly composed of a sleeve, an insulating film and a nickel-chromium-nickel-silicon thermocouple wire.

6. The integrated test system for convective heat transfer coefficient based on transient liquid crystal according to claim 2, characterized in that: The air inlet passage is made of transparent material, and the device used to collect image information of the narrow-band thermochromic liquid crystal coating on the surface of the test piece is a CCD camera.

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