A test method for high heat flux density aerodynamic heating test

Abstract

The application relates to the technical field of heat flow meters, and discloses a heat flow meter for high-heat-flow-density aerodynamic heating tests and a testing method, wherein the heat flow meter for high-heat-flow-density aerodynamic heating tests comprises a coaxial thermocouple outer electrode, a coaxial thermocouple inner electrode, an insulating adhesive tape and a phase change material wrapping layer; the coaxial inner electrode is in the innermost layer, the coaxial thermocouple outer electrode is sleeved on the outer side, the two are in contact to form a measurement junction through a protrusion on the top of the coaxial thermocouple inner electrode, and the gap between the coaxial thermocouple inner electrode and the coaxial thermocouple outer electrode is filled with the insulating adhesive tape. The heat flow meter for high-heat-flow-density aerodynamic heating tests improves the measurement precision of the heat flow meter through the cold compensation device of the cold end of the coaxial thermocouple by the latent heat of phase change of the phase change material.

Description

TECHNICAL FIELD

[0001] The application relates to a coaxial thermocouple-based heat flow meter cold end compensation technology, in particular to a cold end compensation technology suitable for a high heat flux density aerodynamic heating test heat flow meter, cold compensation of a coaxial thermocouple is performed through a phase change material, and the measurement precision of the heat flow meter is improved. BACKGROUND

[0002] The thermal protection system design of a hypersonic vehicle requires accurate thermal environment parameter measurement. Ground tests are an important means of obtaining these parameters, and wind tunnel tests and rocket sled tests are two commonly used aerodynamic heating ground test methods.

[0003] A wind tunnel test measures the temperature, heat flux and other parameters of a vehicle surface by simulating the aerodynamic heating environment of the vehicle in a wind tunnel. The wind tunnel test has the advantages of controllable test conditions and good repeatability, but due to the size of the wind tunnel and the limitations of the incoming flow conditions, it is difficult to completely simulate the real flight environment, especially at high supersonic flight conditions, the static temperature and density of the incoming flow of the wind tunnel test are small, resulting in some uncertainty in the test results.

[0004] A rocket sled test simulates the speed, acceleration and mechanical environment of a hypersonic vehicle by using a rocket engine to propel a sled at high speed on a special track. The rocket sled test can better simulate the real flight environment, especially the aerodynamic heating environment in the dense atmosphere, and has higher test accuracy. However, the test time of the rocket sled test is short, usually within a few seconds to tens of seconds, and the heat flux changes dramatically during the test, which puts higher requirements on the heat flux measurement technology.

[0005] In a rocket sled test, accurate measurement of heat flux is crucial for designing a low-redundancy thermal protection system. A coaxial thermocouple is commonly used in aerodynamic heating tests due to its fast response, high precision, compact structure and other significant advantages in measuring heat flux. However, in long-term high-temperature measurement, the cold end temperature of the thermocouple will deviate significantly from the preset reference temperature point, resulting in increased measurement error. Traditional cold end compensation techniques mainly include internal compensation and external compensation.

[0006] Internal compensation techniques usually implement temperature correction inside the measurement device through integrated temperature sensors, bridge methods or thermistor methods. External compensation techniques place the cold end of the thermocouple in a temperature-stable environment and use an external temperature sensor to measure and compensate the cold end temperature in real time.

[0007] Due to the particularity of the rocket sled test, the traditional cold end compensation technology has many deficiencies in application. The internal compensation technology needs complex circuit design and additional electronic components, which increases the system complexity and cost, and is difficult to effectively implement in the compact space of the hypersonic vehicle. The external compensation technology needs external sensors to measure and compensate the reference end temperature in real time, but in the rocket sled test, the measuring equipment needs to accompany high-speed movement, and the installation and operation of the external compensation equipment are greatly limited, making it difficult to achieve effective temperature control. Therefore, a simple and effective cold end compensation device is needed to improve the measurement accuracy of the heat flow meter. SUMMARY

[0008] In view of the above problems existing in the prior art, a heat flow meter for high heat flux density aerodynamic heating test and a test method are provided.

[0009] In one aspect of the present application, a heat flow meter for high heat flux density aerodynamic heating test is provided, which aims to improve the measurement accuracy of the heat flow meter by using a device that uses the latent heat of phase change of a phase change material to cold compensate the cold end of a coaxial thermocouple.

[0010] The technical solution of the present application is: a heat flow meter for high heat flux density aerodynamic heating test, comprising a coaxial thermocouple outer electrode, a coaxial thermocouple inner electrode, an insulating tape and a phase change material wrapping layer. The coaxial inner electrode is in the innermost layer, and the outer side is sleeved with the coaxial thermocouple outer electrode. The two are in contact through the protrusion at the top of the coaxial thermocouple inner electrode to form a measurement junction. The gap between the coaxial thermocouple inner electrode and the coaxial thermocouple outer electrode is filled with the insulating tape.

[0011] Further, the starting temperature of the phase change temperature zone of the phase change material wrapping layer should be higher than the rocket sled test environment temperature by 2℃ or less, and should meet the requirements of high latent heat of phase change and low thermal conductivity.

[0012] Further, the cold end of the coaxial thermocouple is connected to the measuring instrument through a wire, and the phase change material wrapping layer is arranged at the connection part between the cold end and the measuring instrument to slow down the change trend of the cold end temperature.

[0013] Further, the outer side of the coaxial thermocouple outer electrode is sleeved with an outer shell.

[0014] Further, the material of the coaxial thermocouple inner electrode is nickel-aluminum alloy; the material of the coaxial thermocouple outer electrode is nickel-chromium alloy; the material of the insulating tape is Teflon; the material of the phase change material wrapping layer is paraffin-based phase change material; and the material of the outer shell is stainless steel.

[0015] Further, the thermal physical parameters of the materials of the coaxial thermocouple inner electrode, the coaxial thermocouple outer electrode and the outer shell are close to each other, so as to reduce the influence of lateral heat transfer on the measurement results.

[0016] Further, the structure of the inner electrode of the coaxial thermocouple is a cylinder with a small protrusion at the measuring end, which contacts the outer electrode of the coaxial thermocouple to form a measuring junction.

[0017] Further, the diameter of the inner electrode of the coaxial thermocouple is 10 mm, the length is 21.2 mm; the thickness of the insulating tape is 0.1 mm, the length is 18.15 mm; the inner diameter of the outer electrode of the coaxial thermocouple is 10 mm, the outer diameter is 20 mm, the length is 18.15 mm; the inner diameter of the shell is 20 mm, the outer diameter is 40 mm, the length is 23.70 mm; the bottom of the phase change material wrapping layer is 2.5 mm away from the cold end of the coaxial thermocouple.

[0018] Another aspect of the present application provides a test method for high heat flux density aerodynamic heating test, which adopts a heat flow meter for high heat flux density aerodynamic heating test, comprising the following steps:

[0019] Step one: insert the heat flow meter into the surface of the rocket sled so that the measuring surface is in the same plane as the surface of the rocket sled;

[0020] Step two: expose the heat flow meter to the harsh aerodynamic heating environment of the rocket sled test for a long time, when the heat on the surface of the heat flow meter causes the temperature of the cold end to change through heat conduction, the phase change material wrapping layer absorbs heat through the phase change process to maintain the relative stability of the cold end temperature, thereby realizing cold compensation, so that the measurement result will not have a large error due to the deviation of the cold end temperature, and finally the surface heat flux is inversely calculated according to the surface temperature measured by the thermocouple, the thermal physical parameters of the thermocouple and the formula of the semi-infinite assumption; the relationship formula of the surface transient heat flux density and temperature of the semi-infinite assumption is:

[0021] ;

[0022] In the formula, is the density of the material; is the specific heat capacity of the material; is the thermal conductivity of the material; t is the heat load loading time; is the continuous function of the surface temperature and the heat load loading time.

[0023] The beneficial effects of the present application are:

[0024] The device for cold compensation of the cold end of the coaxial thermocouple by the phase change latent heat of the phase change material improves the measurement accuracy of the heat flow meter. Compared with the traditional internal compensation technology, the cold compensation technology based on the phase change material does not depend on complex electronic circuits, which can effectively avoid the influence of electromagnetic interference on the measurement accuracy in the hypersonic state. In addition, compared with the external compensation technology, the cold end of the thermocouple does not need to be placed in an external temperature stable environment, which simplifies the system structure and improves the applicability and reliability in the rocket sled test. Attached Figure Description

[0025] Figure 1 is a schematic diagram illustrating the principle of thermocouple temperature measurement provided in an embodiment of the present invention;

[0026] Figure 2 is a schematic diagram of the structure of phase change material for cold junction compensation of coaxial thermocouple provided in an embodiment of the present invention;

[0027] Figure 3 shows a comparison between the simulated thermocouple temperature and the measured temperature.

[0028] Figure 4 shows the heat flux density values ​​derived from the actual temperature and the measured temperature based on the semi-infinite assumption.

[0029] In the picture:

[0030] 1. Coaxial thermocouple outer electrode; 2. Coaxial thermocouple inner electrode; 3. Insulating tape; 4. Phase change material wrapping layer; 5. Measuring junction; 6. Coaxial thermocouple cold junction; 7. Outer shell. Detailed Implementation

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0032] Example 1, referring to Figures 1-4 This is the first embodiment of the present invention, which provides a heat flow meter for high heat flux density aerodynamic thermal experiments.

[0033] The purpose of this invention is to provide a heat flow meter containing phase change material suitable for high heat flux density aerodynamic experiments. This device utilizes the latent heat of phase change of the phase change material to perform cold compensation on the cold junction of a coaxial thermocouple, thereby improving the measurement accuracy of the heat flow meter. Compared to traditional internal compensation techniques, the phase change material-based cold compensation technique does not rely on complex electronic circuits and can effectively avoid the impact of electromagnetic interference on measurement accuracy under hypersonic conditions. Furthermore, compared to external compensation techniques, this invention eliminates the need to place the thermocouple cold junction in a stable external temperature environment, simplifying the system structure and improving its applicability and reliability in rocket sled tests.

[0034] Figure 1 illustrates the measurement principle of a thermocouple. The thermocouple measurement principle is based on the Seebeck effect, which states that when two different conductors or semiconductors are connected to form a closed circuit, a thermoelectric electromotive force (EMF) will be generated in the circuit if the two connection points are at different temperatures. By measuring the magnitude of the EMF, the temperature difference between the two connection points can be calculated.

[0035]

[0036]

[0037] Wherein, SB is the absolute Seebeck coefficient of material B, unit V / K; SA is the absolute Seebeck coefficient of material A, unit V / K; SBA is the relative Seebeck coefficient of material B relative to A, that is, the Seebeck coefficient of the thermocouple, unit V / K; T1 is the temperature of the measuring end of the thermocouple, unit K; T0 is the temperature of the cold end of the thermocouple, unit K.

[0038] The temperature difference between the cold end and the measuring end is obtained according to the measured thermoelectric potential, and the reference temperature of the cold end is added to obtain the actual temperature of the measuring end. In the test time of several seconds to tens of seconds of the rocket sled, since the thermocouple is exposed to a severe aerodynamic heat environment, long-time measurement will cause the cold end temperature to deviate from the reference temperature seriously, resulting in that the measured temperature is low and the inverted heat flux density value is small.

[0039] The specific structure of the heat flow meter for high heat flux aerodynamic heat test is shown in Fig. 2, and the structure includes a coaxial thermocouple outer electrode 1, a coaxial thermocouple inner electrode 2, an insulating tape 3 and a phase change material wrapping layer 4. The coaxial inner electrode is in the innermost layer, and the coaxial thermocouple outer electrode 1 is sleeved on the outside. The structure of the coaxial thermocouple inner electrode 2 is a cylinder and has a small protrusion at the measuring end, which is in contact with the coaxial thermocouple outer electrode 1 to form a measuring junction 5. The gap between the coaxial thermocouple inner electrode 2 and the coaxial thermocouple outer electrode 1 is filled with the insulating tape 3. The thermal physical parameters of the coaxial thermocouple inner electrode 2, the coaxial thermocouple outer electrode 1 and the outer shell 7 are close to each other, so as to reduce the influence of lateral heat transfer on the measurement result. The phase change material has excellent heat preservation characteristics and can absorb or release a large amount of latent heat during the phase change, so as to maintain a relatively constant temperature in the phase change temperature range. This characteristic enables the phase change material to effectively buffer the change of the cold end temperature of the thermocouple and reduce the influence of temperature fluctuation on the measurement accuracy.

[0040] The purpose of the present application is achieved by the following technical solutions:

[0041] The cold end compensation device of the heat flow meter of the present application comprises a coaxial thermocouple, a phase change material wrapping layer 4 and an outer shell 7. The coaxial thermocouple is used for measuring temperature, the phase change material wrapping layer 4 is used for compensating the cold end of the thermocouple, and the outer shell 7 is used for avoiding lateral heat transfer.

[0042] The cold end compensation method of the heat flow meter of the present application comprises the following steps:

[0043] 1. Selecting a phase change material: the starting temperature of the phase change temperature range of the phase change material wrapping layer 4 should be higher than the rocket sled test environment temperature by 2℃ or less, and should meet the requirements of high phase change latent heat and low thermal conductivity.

[0044] 2. The phase change material is wrapped around the cold end of the thermocouple to form a phase change material wrapping layer 4. The cold end of the coaxial thermocouple is connected to the measuring instrument through a wire, and the phase change material wrapping layer 4 is arranged at the connection position between the cold end and the measuring instrument to slow down the temperature change trend of the cold end.

[0045] 3. The shell 7 is wrapped around the outer layer of the thermocouple to reduce lateral heat transfer and improve measurement accuracy.

[0046] The technical scheme of the embodiment provides a relatively stable temperature for the cold end of the thermocouple through the latent heat of the phase change of the phase change material. When the phase change material changes from solid to liquid, it will absorb a large amount of latent heat, which can effectively maintain the temperature stability of the cold end 6 of the coaxial thermocouple. When the cold end temperature rises, the phase change material undergoes phase change and stores the excess heat, thereby inhibiting the rise of the cold end temperature. In this way, the phase change material provides a stable temperature buffer environment for the cold end 6 of the coaxial thermocouple, ensuring the measurement accuracy and reliability.

[0047] As can be seen from the technical scheme provided by the above invention, the cold end compensation device of the heat flow meter provided by the invention compensates the cold end of the thermocouple through the phase change material, improves the measurement accuracy of the heat flow meter, prolongs the effective measurement time, and is suitable for heat flow measurement in high heat flux density aerodynamic heating tests such as rocket sled tests.

[0048] As shown in FIG. 2, the structure of the phase change material compensating the cold end 6 of the coaxial thermocouple is shown. The main body of the thermocouple is composed of an inner electrode, an insulating tape 3, and an outer electrode. The coaxial inner electrode is in the innermost layer, and the outer electrode 1 is wrapped outside. The two are in contact through the protrusion at the top of the coaxial inner electrode 2 to form a measurement junction 5, and the gap between the coaxial inner electrode 2 and the coaxial outer electrode 1 is filled with insulating tape 3. In order to avoid the influence of lateral heat transfer and electromagnetic interference during the rocket sled test on the measurement of the coaxial thermocouple, a shell 7 is wrapped around the outer side of the coaxial thermocouple as a whole. The inner electrode is processed by grinding to form the measurement junction 5; then the inner electrode is wrapped with insulating tape 3 to combine with the outer electrode, so that the inner and outer electrodes form an electric circuit through the measurement junction 5; the temperature difference between the cold end and the measurement end can be obtained by measuring the potential difference between the electric circuits, and the actual temperature of the measurement end, i.e. the temperature of the measurement junction 5, can be obtained by adding the reference temperature of the cold end.

[0049] The selected phase change material of the phase change material wrapping layer 4 of the embodiment needs to meet the following requirements:

[0050] 1. The lower limit of the phase change temperature range of the phase change material needs to be slightly higher than the test environment temperature;

[0051] 2. The latent heat of the phase change material is as high as possible;

[0052] 3. The thermal conductivity of the phase change material should be as low as possible.

[0053] The phase change material coating layer 4 is made as follows: the phase change material is heated and melted, then introduced into a mold, and a coaxial thermocouple is inserted so that the cold end of the thermocouple is immersed in the phase change material. After the phase change material solidifies, the thermocouple and the phase change material are removed.

[0054] This embodiment determines the feasibility of the phase change material compensating for the cold end 6 of the coaxial thermocouple by thermodynamic simulation. The model structure is shown in FIG. 2. The inner electrode has a diameter of 10 mm and a length of 21.2 mm. The outer electrode has an inner diameter of 10 mm, an outer diameter of 20 mm, and a length of 18.15 mm. The shell 7 has an inner diameter of 20 mm, an outer diameter of 40 mm, and a length of 23.70 mm. The insulating tape 3 has a thickness of 0.1 mm and plays an insulating role in the thermocouple. The effect of insulating tape 3 on insulating lateral heat transfer can be ignored, so the insulating tape 3 is omitted in the model establishment. The thermal physical parameters of the phase change material are referenced from a commercial paraffin phase change material, as shown in Table 1.

[0055]

[0056] The applied boundary condition is a heat flux of 1 MW / m2 for 20 s. The material of the cold end coating layer is selected to be a phase change material or stainless steel for comparison, and the results are shown in FIG. 3. The actual temperature refers to the actual temperature of the measurement junction of the coaxial thermocouple. The measurement temperature is determined by the following formula, and 300 K refers to the reference temperature of the cold end:

[0057] ;

[0058] Firstly, the material of the coating layer, whether it is a phase change material or stainless steel, does not affect the actual temperature of the measurement junction 5. Secondly, the use of a phase change material for the coating layer can slow down the deviation of the cold end temperature from the reference temperature. Then, the heat flux is inversely calculated according to the temperature based on the semi-infinite assumption, and the results are shown in FIG. 4. The use of the latent heat of the phase change material for cold compensation of the cold end 6 of the coaxial thermocouple indeed slows down the deviation of the cold end from the reference temperature, thereby achieving the purpose of prolonging the effective measurement time. Compared with existing compensation techniques, the device for compensating the cold end of the thermocouple using the phase change material does not require complex circuit compensation or additional temperature sensors, simplifying the system structure, reducing the cost and maintenance difficulty. The device has the characteristics of passive compensation and does not require external energy input, which is suitable for use in energy-limited or harsh environments such as the head of a rocket sled.

[0059] Embodiment 2, with reference to Figures 1-4 The second embodiment of the present application provides a test method for high heat flux density aerodynamic heating tests, which uses a heat flow meter for high heat flux density aerodynamic heating tests, and includes the following steps:

[0060] Step one: heat flow meter is inserted into the surface of the rocket sled, so that the measurement surface and the surface of the rocket sled in the same plane;

[0061] Step two: heat flow meter is exposed to the harsh aerodynamic heat environment of the rocket sled test for a long time, when the heat of the heat flow meter surface changes the cold end temperature through heat conduction, the phase change material coating layer 4 absorbs heat through the phase change process, maintains the relative stability of the cold end temperature, so as to realize the cold compensation, so that the measurement result will not produce larger error because of the cold end temperature deviation, finally according to the surface temperature measured by the thermocouple, the thermal physical parameters of the thermocouple and the formula of the semi-infinite assumption to inverse the surface heat flow; the relationship between the surface transient heat flux density and the temperature of the semi-infinite assumption is:

[0062] ;

[0063] In the formula, The density of the material is; The specific heat capacity of the material is; The thermal conductivity of the material is; t is the heat load loading time; The surface temperature and the heat load loading time are continuous functions.

[0064] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalent, without departing from the spirit and scope of the technical solutions of the present application, which should be covered in the scope of the claims of the present application.

Claims

1. A test method for high heat flux density aero-thermal test using a heat flux meter for high heat flux density aero-thermal test, characterized by, It comprises the following steps: Step one: insert the heat flow meter into the surface of the rocket sled, so that the measurement surface is in the same plane as the surface of the rocket sled; Step two: the heat flow meter is exposed to the harsh aerodynamic heat environment of the rocket sled test for a long time, when the heat on the surface of the heat flow meter causes the cold end temperature to change through heat conduction, the phase change material wrapping layer (4) absorbs heat through the phase change process, maintains the relative stability of the cold end temperature, thereby realizing cold compensation, so that the measurement result will not produce larger error due to the deviation of the cold end temperature, finally the surface heat flow is inversely calculated according to the surface temperature measured by the thermocouple, the thermal physical parameters of the thermocouple and the formula of the semi-infinite assumption; the relationship formula of the semi-infinite assumption surface transient heat flow density and temperature is: ； wherein is the density of the material; is the specific heat capacity of the material; is the thermal conductivity of the material; t is the thermal load application time; is a continuous function of the surface temperature and the thermal load application time; The heat flow meter for high heat flow density aerodynamic heat test, comprising coaxial thermocouple outer electrode (1), coaxial thermocouple inner electrode (2), insulating tape (3) and phase change material wrapping layer (4), the coaxial inner electrode (2) is in the innermost layer, the outer side is sleeved with the coaxial thermocouple outer electrode (1), the two are in contact through the protrusion on the top of the coaxial thermocouple inner electrode (2) to form a measurement junction (5), the gap between the coaxial thermocouple inner electrode (2) and the coaxial thermocouple outer electrode (1) is filled with insulating tape (3).

2. The test method for high heat flux density aerodynamic heating tests according to claim 1, characterized in that: The starting temperature of the phase change temperature zone of the phase change material wrapping layer (4) should be higher than the rocket sled test environment temperature by 2℃ or less, and meet the high phase change latent heat and low thermal conductivity.

3. The test method for high heat flux density aerodynamic heating tests of claim 1, wherein: The cold end (6) of the coaxial thermocouple is connected with the measuring instrument through a wire, and the phase change material wrapping layer (4) is arranged at the connecting part between the cold end and the measuring instrument, used for slowing down the change trend of the cold end temperature.

4. The test method for high heat flux density aerodynamic heating tests of claim 1, wherein: The outer side of the coaxial thermocouple outer electrode (1) is sleeved with an outer shell (7).

5. The test method for high heat flux density aerodynamic heating tests of claim 1, wherein: The material of the coaxial thermocouple inner electrode (2) is nickel-aluminum alloy; the material of the coaxial thermocouple outer electrode (1) is nickel-chromium alloy; the material of the insulating tape (3) is Teflon; the material of the phase change material wrapping layer (4) is paraffin phase change material; and the material of the outer shell (7) is stainless steel.

6. The test method for high heat flux density aerodynamic heating tests of claim 1, wherein: The thermal physical parameters of the materials of the coaxial thermocouple inner electrode (2), the coaxial thermocouple outer electrode (1) and the outer shell (7) are close, so as to reduce the influence of transverse heat conduction on the measurement result.

7. The test method for high heat flux density aerodynamic heating tests of claim 1, wherein: The structure of the coaxial thermocouple inner electrode (2) is a cylinder and has a small protrusion at the measurement end, the protrusion is in contact with the coaxial thermocouple outer electrode (1) to form a measurement junction (5).

8. The test method for high heat flux density aerodynamic heating tests of claim 1, wherein: The diameter of the coaxial thermocouple inner electrode (2) is 10 mm, the length is 21.2 mm; the thickness of the insulating tape (3) is 0.1 mm, the length is 18.15 mm; the inner diameter of the coaxial thermocouple outer electrode (1) is 10 mm, the outer diameter is 20 mm, the length is 18.15 mm; the inner diameter of the outer shell (7) is 20 mm, the outer diameter is 40 mm, the length is 23.70 mm; the distance from the bottom of the phase change material wrapping layer (4) to the coaxial thermocouple cold end (6) is 2.5 mm.

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