A high spatiotemporal resolution temperature sensor for simultaneously measuring tangential and normal heat fluxes

Abstract

The present invention discloses a temperature measurement system for measuring the facing and normal heat fluxes and a method for measuring the heat flux. The system includes a temperature measurement unit, a data acquisition unit, and a high-temperature flame test bench. Among them, the high-temperature flame test bench includes an acetylene high-temperature flame generator and a positioning assembly. The positioning assembly is arranged close to the acetylene high-temperature flame generator, and the temperature measurement unit is fixed on the positioning assembly. The temperature measurement unit includes a substrate and at least one set of temperature measurement elements. The temperature measurement elements have metal thin-film electrodes. The data acquisition system is electrically connected to the temperature measurement unit. This system can better simulate the aerodynamic heat characteristics of the surface of a hypersonic vehicle. The temperature measurement unit has good facing and normal heat flux followability and sensitivity, and both the spatial and temporal resolutions are relatively high.

Description

Technical Field

[0001] The present invention relates to the field of thermoelectric performance testing. Specifically, it relates to a high spatio-temporal resolution temperature sensor for simultaneously measuring the tangential and normal heat fluxes. More specifically, it relates to a temperature measurement system for measuring the tangential and normal heat fluxes and a method for measuring the heat flux. Background Art

[0002] A hypersonic vehicle refers to a vehicle with a flight Mach number greater than 5. With its high speed and high maneuverability characteristics, it has a high success rate of penetration while achieving precise and rapid strikes over ultra-long distances, thus having great military value. At high Mach numbers, the aerodynamic environment in which the vehicle is located will have very complex thermal and flow characteristics.

[0003] Specifically, in terms of flow, the flight altitude of a hypersonic vehicle is generally between 40 - 70 km, located in the near-space region. The low density of air makes the mean free path of air molecules non-negligible compared to the scale of the vehicle itself, and the assumption of a continuous medium may no longer hold, and conventional numerical calculation methods may no longer be applicable; secondly, a detached shock wave will be generated at the leading edge of the hypersonic vehicle, and the gas will be violently compressed to convert its kinetic energy into heat energy, resulting in a sharp increase in local temperature. At the same time, the friction between the airflow and the vehicle surface will further increase the temperature, and the aerodynamic heating can make the temperature at the leading edge of the vehicle reach 2000 - 3000 K. At the same time, under the influence of high temperature and high-speed collisions of gas molecules, the gas will experience changes in vibrational heat capacity, dissociation, and ionization, so it cannot be regarded as an ideal gas, and the effects of high-temperature real gases need to be considered. The above complex flow states, local high temperatures, chemical reactions, and radiation heating effects will result in non-linear and high-frequency oscillating heat transfer characteristics. At present, the heat transfer characteristics of hypersonic vehicles in complex aerodynamic environments have received increasing attention. Accurately predicting the complex aerodynamic heating characteristics of the vehicle and performing effective thermal protection and thermal design are crucial for ensuring the safe operation of the vehicle.

[0004] To meet the requirements of the above precise prediction, there are three common research methods in related technologies: theoretical prediction, ground tests, and free flight experiments. In terms of theoretical prediction, traditional computational fluid dynamics methods are difficult to provide an accurate flow image under complex aerodynamic heating conditions. G.A. Bird proposed the DSMC method in 1969. Although the DSMC does not directly solve the Boltzmann equation, it directly simulates the physical processes described by the Boltzmann equation. By decoupling collisions and motions to simplify calculations, and presetting the intermolecular interaction potential to simulate collision effects, and finally statistically averaging the motions of molecules to obtain the variation law of macroscopic quantities; similarly, factors such as molecular vibration heat capacity, ionization, dissociation, or thermal radiation can be simulated under certain conditions. After more than 50 years of research, the DSMC method has been widely applied. Even so, although the DSMC method starts directly from the perspective of molecular kinetic theory, its results are not necessarily the closest to the real situation. Especially under complex aerodynamic heating conditions in the near space, strong nonlinear effects such as chemical reactions and radiation will significantly affect the calculation accuracy. And large-scale DSMC calculations consume extremely high computer resources, limiting its practical application in engineering.

[0005] In summary, the current theoretical prediction methods are difficult to solve complex flow, aerodynamic heating, and heat transfer problems, and accurate experimental measurements are important research means. In terms of thermal measurement, contact point heat flux measurement and non-contact surface heat flux measurement are two main methods. There are mainly two contact measurement methods: (1) Thin film heat flux sensor: It is mainly applied under conditions of low heat flux and good flow field conditions, with high accuracy, and the uncertainty is generally between ±5% and ±8%. Its response speed is the fastest in the millisecond order, but due to the temperature resistance limitation of the thin film material, it cannot work under high temperature conditions for a long time; (2) Coaxial thermocouple: It is mainly used under harsh working conditions such as high temperature and high pressure, with the advantages of erosion resistance, reusability, large output, stable performance, and high signal-to-noise ratio, but the sensor has a large size, long response time, and low spatial and temporal accuracy.

[0006] The main principle of the non-contact method is to use a camera system to sense the temperature-sensitive source to collect the surface temperature of the experimental model. It has a high spatial resolution and the characteristics of being vivid, intuitive, easy to use, and having little interference with the original thermal field. The temperature-sensitive sources mainly include temperature-sensitive paint, temperature-sensitive phosphorescent coating, thermochromic liquid crystal, and infrared radiation, etc. The uncertainty of measuring temperature using temperature-sensitive materials is about ±10% - ±12%. However, the thickness of the temperature-sensitive material has a great influence on the measurement accuracy and signal-to-noise ratio, and the accuracy decreases with the increase of the thickness. In addition, due to the temperature resistance limitation of the temperature-sensitive material and the problem of material shedding at high temperatures, this method cannot measure high-temperature objects. Another infrared radiation temperature measurement method needs to first determine the emissivity of the material surface and it is difficult to accurately measure samples with unknown surface characteristics and accompanied by high-temperature chemical reactions.

[0007] It should be noted that when the Mach number is very high, the flow regime on the surface of the aircraft will exhibit strong locality. The flow characteristics at different positions along the hypersonic aircraft are different, and there are significant localization characteristics in the flow and heat transfer characteristics of the surface airflow. The characteristic size of local gas vortices is on the order of millimeters or even micrometers. The strong aerodynamic heating and complex flow effects will cause the small disturbances between different flow fields to be amplified, resulting in high-frequency oscillation phenomena in the flow field and temperature field, and the characteristic time is on the order of microseconds. In addition, the external environment of the hypersonic aircraft during flight is harsh, and high-frequency oscillation, local high temperature, chemical corrosion, and large temperature difference deformation will all significantly shorten the service life of the sensor. Currently, existing contact or non-contact thermal measurement methods cannot simultaneously meet the requirements of localization, high spatio-temporal accuracy, and long-term stable operation.

[0008] Therefore, it is necessary to design a sensor with a spatial resolution on the micron scale, a time response on the order of microseconds, and high mechanical strength. Summary of the Invention

[0009] To solve the above technical problems, the present invention proposes a high spatio-temporal resolution temperature sensor capable of simultaneously measuring the heat flux facing the flow and the normal heat flux, as well as a measurement method. This method can solve the problem of difficult measurement of the aerodynamic heat characteristics on the surface of hypersonic aircraft, and provide monitoring data for the thermal protection and thermal design of high-speed aircraft.

[0010] In view of this, the present invention proposes a temperature measurement system for measuring the heat flux facing the flow and the normal heat flux. This system can be used to simulate the measurement of the complex aerodynamic heat environment in the rarefied flow field, can accurately measure the heat flux facing the flow and the normal heat flux, and has high spatio-temporal resolution. The system includes: a temperature measurement unit and a high-temperature flame test bench. Among them, the high-temperature flame test bench includes an acetylene high-temperature flame generator and a positioning component. The positioning component is arranged close to the acetylene high-temperature flame generator, and the temperature measurement unit is fixed on the positioning component. The temperature measurement unit includes a substrate and at least one group of temperature measurement elements. The temperature measurement elements include platinum thin film temperature sensors.

[0011] In one aspect of the present invention, the present invention proposes a temperature measurement system for measuring the heat flux facing the flow and the normal heat flux. The system includes: a temperature measurement unit, a data acquisition unit, and a high-temperature flame test bench. Among them, the high-temperature flame test bench includes an acetylene high-temperature flame generator and a positioning component. The positioning component is arranged close to the acetylene high-temperature flame generator, and the temperature measurement unit is fixed on the positioning component. The temperature measurement unit includes a substrate and at least one group of temperature measurement elements. The temperature measurement elements have metal thin film electrodes, and the data acquisition system is electrically connected to the temperature measurement unit. This system can better simulate the aerodynamic heat characteristics on the surface of hypersonic aircraft. The temperature measurement unit has good followability and sensitivity to the heat flux facing the flow and the normal heat flux, and both the spatial and time resolutions are relatively high.

[0012] According to an embodiment of the present invention, the metal thin film electrode is formed of a platinum thin film. The metal thin film electrode includes a first electrode block and a second electrode block, and the first electrode block and the second electrode block are connected by a serpentine portion. The line width of the serpentine portion is 10 - 3 microns. Thus, the temperature measurement sensing unit can have a good heat transfer sensing effect.

[0013] According to an embodiment of the present invention, the thickness of the metal thin film electrode is 200 - 80 nm.

[0014] According to an embodiment of the present invention, the width and length of the temperature measurement unit are independently 80 - 200 microns respectively.

[0015] According to an embodiment of the present invention, the substrate of the temperature measurement unit is aluminum nitride ceramic.

[0016] According to an embodiment of the present invention, the substrate is a quadrilateral substrate, the temperature measurement unit includes 4 groups of the temperature measurement elements, and the temperature measurement elements are arranged at the four corners of the quadrilateral substrate respectively.

[0017] According to an embodiment of the present invention, the system further includes a constant temperature unit. The constant temperature unit includes a constant temperature vacuum chamber, a molecular pump connected to the constant temperature vacuum chamber, a constant temperature table for placing the temperature measurement unit in the constant temperature vacuum chamber, and a plurality of independently powered electrodes for connecting to the temperature measurement unit.

[0018] According to an embodiment of the present invention, the constant temperature unit further has a detection circuit structure. The detection circuit structure has a port for accessing the temperature measurement unit. The detection circuit at least includes a variable resistor, a fixed resistor, and at least two voltmeters. The fixed resistor, the variable resistor, and the temperature measurement unit are connected in series, and the at least two voltmeters are respectively used to detect the voltages of the fixed resistor and the temperature measurement unit.

[0019] In another aspect of the present invention, the present invention provides a method for measuring heat flow by using the temperature measurement system described above. The method includes:

[0020] Obtaining the resistance values of the temperature measurement elements in the temperature measurement unit at different temperatures and when the power is 0, fitting to obtain the resistance - temperature linear response relationship, and the initial resistance of the temperature measurement unit, and obtaining the resistance temperature coefficient β of the temperature measurement unit according to the slope of the resistance - temperature linear response relationship and the initial resistance, and obtaining the correction relationship of the temperature measurement value of the temperature measurement element:

[0021] T = T0 + ΔR / (R0β);

[0022] Place the temperature measurement unit in a high-temperature flame test bench, and rely on the positioning component to move the position of the temperature measurement unit to obtain the temperature at different distances between the temperature measurement unit and the acetylene high-temperature flame generator, and obtain the heat flux data of the high-temperature acetylene flame according to the correction relationship of the temperature measurement values.

[0023] This method can preferably obtain the heat flux data of the high-temperature acetylene flame, and further can preferably simulate the aerodynamic heat characteristics of the hypersonic vehicle surface, and is suitable for obtaining the aerodynamic heat characteristics of the hypersonic vehicle surface.

[0024] According to an embodiment of the present invention, the correction relationship of the temperature measurement value of the temperature measurement element is obtained by placing the temperature measurement unit in a constant temperature unit: on the premise that a fixed voltage is connected to the constant temperature table in the constant temperature unit, control the electrode in the constant temperature table in the constant temperature unit that is connected to the temperature measurement element to change the input voltage of the temperature measurement element, and use a voltmeter to measure the voltage changes of the fixed resistor connected in series with the temperature measurement unit and the temperature measurement element respectively to obtain the resistance and power data of the temperature measurement element at different temperatures, draw an R-P diagram, and obtain the resistance value of the temperature measurement element when the power P = 0; when no external voltage is applied to the constant temperature table, measure the initial resistance R0 of the temperature measurement element at room temperature; change the input voltage of the constant temperature table to obtain multiple groups of temperatures and the resistance values of the temperature measurement element when the power is 0, and perform fitting to obtain the resistance-temperature linear response relationship of the temperature measurement element, and obtain the resistance temperature coefficient β of the temperature measurement unit:

[0025] β = ΔR / (R0ΔT)

[0026] Wherein, ΔR is the resistance difference between any two points in the resistance-temperature linear response relationship. Description of the Drawings

[0027] Figure 1 is a schematic structural diagram of a temperature measurement unit according to an embodiment of the present invention;

[0028] Figure 2 is a temperature measurement unit under an optical microscope according to an embodiment of the present invention;

[0029] Figure 3 is a digital photo of a temperature measurement unit according to an embodiment of the present invention;

[0030] Figure 4 is the wiring condition of the calibration circuit according to an embodiment of the present invention;

[0031] Figure 5 is the wiring condition of the circuit when facing heat flux measurement according to an embodiment of the present invention;

[0032] Figure 6It is a schematic structural diagram of a temperature measurement system according to an embodiment of the present invention. Detailed implementation manners

[0033] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements. The solutions of the present invention will be explained in conjunction with the embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0034] In one aspect of the present invention, the present invention provides a temperature measurement system for measuring the facing and normal heat fluxes. This system can be used in the complex aerodynamic heat environment in the rarefied flow regime, can accurately measure the facing heat flux and the normal heat flux, and has high spatio-temporal resolution. Referring to Figure 6 , the system includes: a temperature measurement unit (platinum temperature sensor) and a high-temperature flame test bench. Among them, the high-temperature flame test bench includes an acetylene high-temperature flame generator and a positioning component (such as the x and y positioning scales shown in the figure). The positioning component is disposed close to the acetylene high-temperature flame generator, and the temperature measurement unit is fixed on the positioning component. The temperature measurement unit includes a substrate and at least one group of temperature measurement elements. The temperature measurement elements include platinum thin film temperature sensors. This system can achieve high spatio-temporal resolution temperature measurement for simultaneously measuring the facing and normal heat fluxes. For the convenience of understanding, the structure of the sensor used in this method will be briefly described first:

[0035] The sensor used in the method proposed by the present invention uses a platinum thin film on the micron scale as the temperature measurement element. Specifically, physical vapor deposition technology excited by high-energy electron beams can be used to fabricate the Pt thin film, with a thickness of about 100 nm. Ultraviolet lithography technology is used to fabricate the serpentine structure of the Pt thin film, where the minimum line width can reach 5 μm, and the size of a single temperature measurement unit can be about 100 μm × 100 μm. Using ultraviolet lithography technology to fabricate the serpentine structure of the Pt thin film can increase the length of the Pt thin film per unit area to improve the sensitivity. Platinum maintains a good resistance-temperature linear response relationship in a large temperature range of 200 - 1300 degrees Celsius, has stable chemical properties and good repeatability. By measuring the resistance change of the Pt thin film, the change in temperature can be accurately obtained. The Pt thin film is deposited on a dense aluminum nitride ceramic thin sheet with a thickness of about 127 μm, so that the sensor can achieve a spatial resolution on the micron scale. The aluminum nitride ceramic thin sheet has high mechanical strength, so the sensor has high mechanical strength. The aluminum nitride ceramic material has good mechanical strength and high thermal conductivity of 200 - 300 W m -2 K-1 and advantages such as a low coefficient of thermal expansion, which can ensure that the Pt thin film sensor will not be damaged under strong aerodynamic heating conditions and meet the requirements for long-term online operation of the heat flux sensor. Multiple temperature measurement elements can be arranged on an aluminum nitride ceramic chip to form a temperature measurement unit as shown in Figure 1 . Since the size of the temperature measurement element reaches the micron level, through theoretical calculation, a pure platinum sensor can achieve a time resolution of the microsecond level. A single-layer temperature measurement unit can be used to measure the heat flux facing the object and the local temperature, and a double-layer bonded temperature measurement unit can be used to measure the normal heat flux of the object. The sensor has a small size, which is convenient for realizing localized measurement. The arrangement of multiple sensors can ensure the detection of temperature and heat flux in an array form, and is particularly suitable for thermal measurement during the study of complex flows, aerodynamic heating, and heat transfer problems.

[0036] Furthermore, the system may further include a constant temperature unit. The constant temperature unit includes a constant temperature vacuum chamber, a molecular pump connected to the constant temperature vacuum chamber, a constant temperature table for placing the temperature measurement unit in the constant temperature vacuum chamber, and multiple independently powered electrodes for connecting to the temperature measurement unit. The constant temperature unit further has a detection circuit structure. The detection circuit structure has ports that can be connected to the temperature measurement unit. The detection circuit at least includes a variable resistor, a fixed resistor, and at least two voltmeters. The fixed resistor, the variable resistor, and the temperature measurement unit are connected in series, and the at least two voltmeters are respectively used to detect the voltages of the fixed resistor and the temperature measurement unit. This constant temperature unit can be used to obtain the correction relationship of the temperature measurement values of the temperature measurement elements and detect and evaluate the sensor performance of the temperature measurement unit.

[0037] Specifically, the preparation process of the temperature measurement unit can be as follows:

[0038] Use high-purity platinum (Pt) as the target source, such as Pt with a purity of 99.9999%, and use high-energy electron beam-excited physical vapor deposition technology to fabricate a Pt thin film as a sensor for temperature measurement (i.e., the temperature measurement element). The thickness of the Pt thin film is 100 nm. Use ultraviolet lithography technology to fabricate the serpentine structure of the Pt thin film. The Pt thin film is deposited on a dense aluminum nitride ceramic thin sheet with a thickness of 127 μm. This structure can increase the length of the Pt thin film per unit area to improve the sensitivity. Refer to Figure 1 , the temperature measurement element may have two electrodes and a serpentine part connecting the two electrodes. Figure 1 shows a schematic diagram of a temperature measurement unit according to an embodiment of the present invention, that is, the case where 4 groups of temperature measurement elements are fabricated on an aluminum nitride ceramic chip, and the 4 groups of temperature measurement elements are arranged at the four corner positions of the ceramic chip. Refer to Figure 2 and Figure 3 , the minimum line width of the serpentine part in the temperature measurement unit is only 5 μm, and the size of a single temperature measurement unit is 100 μm × 100 μm.

[0039] For the convenience of understanding, first, the temperature sensing method using this system and the specific steps for detecting and evaluating the sensor performance of the temperature measuring unit included in this method will be described below. Specifically, this method may include the following steps:

[0040] S100: Place the temperature measuring unit in a constant temperature vacuum chamber and calibrate the temperature of the temperature measuring element

[0041] According to an embodiment of the present invention, in this step, the temperature measuring unit is placed in a constant temperature vacuum chamber to calibrate the temperature of the temperature measuring element. The structure of the temperature measuring unit may be as described above, that is, multiple groups of Pt thin film electrodes are arranged on the aluminum nitride ceramic thin film, such as a total of 4 groups are arranged at the four corners. The constant temperature vacuum chamber is used to fix the temperature measuring unit, and the temperature measuring element and the vacuum chamber are electrically connected, such as connecting the Pt thin film electrode and the vacuum chamber with a copper wire and silver glue, so as to ensure the stability of the Pt thin film electrode during the measurement process. Subsequently, the temperature measuring element is connected to the measurement circuit, and different ambient temperatures are obtained by controlling the input voltage on both sides of the constant temperature table, so as to calibrate the temperature of the temperature measuring element.

[0042] Specifically, multiple independent electrodes can be arranged in the constant temperature vacuum chamber for power-on detection. For example, 12 independent electrodes can be arranged. Two-stage molecular pumps can also be connected in the vacuum chamber, so as to maintain a high vacuum degree of 10 -4 Pa, avoiding the influence of air convection on the calibration result. The constant temperature table can ensure a temperature control accuracy of 0.001K. The structure of the constant temperature table. The temperature measurement circuit may include a power supply, a rheostat, a fixed resistor, and a temperature measuring unit. The temperature measurement circuit may include a power supply, a rheostat, a fixed resistor, and a temperature measuring unit connected in series. The temperature measuring unit is fixed on the constant temperature table, and a voltmeter is added to each of the fixed resistor and the temperature measuring unit to detect the voltage. Specifically, the equivalent circuit of the temperature measurement circuit may be as Figure 4 shown in, the fixed resistor R1 and the temperature measuring element (R2 shown in the figure) are connected in series. The temperature measuring unit is fixed on the constant temperature table, and a voltmeter is added to each of the fixed resistor and the temperature measuring element to detect the voltage (V1 and V2 shown in the figure).

[0043] According to an embodiment of the present invention, the temperature inside the constant temperature table can be controlled by controlling the input voltage on both sides of the constant temperature table, so as to obtain different ambient temperatures. After the voltage changes (that is, the ambient temperature changes), let it stand for 30 min, and then use the thermocouple in the vacuum chamber to read the temperature inside the chamber as the temperature reached by the temperature measuring element. Then, the input voltage of the temperature measuring element is changed from large to small, and the voltage changes of the fixed resistor R1 and the temperature measuring element are measured respectively. The resistance data of the temperature measuring element after the temperature change is processed, and an R-P diagram is drawn to obtain the resistance value of the temperature measuring element when the power P = 0. This value can reflect the temperature value measured by the thin film sensor only in the environment, and is thus used to eliminate the interference of the external voltage.

[0044] Subsequently, the access voltage of the constant temperature stage can be changed multiple times to change the temperature of the Pt temperature measuring element, and the voltage values of the fixed resistor and the sensor at different temperatures can be obtained. Subsequently, calculate the resistance values when their power P = 0, and then obtain multiple sets of temperature and the resistance values of the temperature measuring element when the power is 0, and perform fitting to obtain the resistance-temperature linear response relationship of the Pt temperature measuring element.

[0045] According to an embodiment of the present invention, after obtaining the resistance-temperature linear response relationship of the Pt temperature measuring unit, the slope of the linear curve of this linear relationship can be obtained. At this time, the initial resistance R0 of the temperature measuring element at room temperature can be measured (when no external voltage is applied to the constant temperature stage, the voltage across the temperature measuring element is at the level of a dozen millivolts), and according to the obtained initial resistance and the slope of the linear curve, the resistance temperature coefficient β of the temperature measuring unit can be obtained from the resistance temperature coefficient relationship formula:

[0046] β = ΔR / (R0ΔT),

[0047] where ΔR is the resistance difference between any two points on the resistance-temperature curve. For example, when the fixed resistor R1 is 150 ohms and the temperature measuring element has the aforementioned structure, the resistance temperature coefficient β = 0.0017477 of the temperature measuring element can be obtained.

[0048] The temperature measurement value of the temperature measuring element can be corrected according to the resistance-temperature linear response relationship curve obtained previously according to the following formula:

[0049] T = T0 + ΔR / (R0β) Equation 1

[0050] where T0 is the temperature when the initial resistance R0 is measured.

[0051] S200: Obtain the response of the temperature measuring unit to the heat flux facing it, and obtain the resolution of the heat flux density

[0052] According to an embodiment of the present invention, in this step, to measure the response of the sensor to the heat flux facing it, the temperature measuring element located in the center of the adjacent pair of Pt temperature measuring elements can be used to measure the temperature response facing it, and at the same time, the resolution of the heat flux density can be obtained.

[0053] Specifically, in this step, the adjacent pair of Pt temperature measuring elements are used to measure the temperature response facing it. A relatively large voltage is applied to one temperature measuring element as the heat source end; a relatively small voltage is applied to the other pair of temperature measuring elements on the other side to measure the temperature change. Specifically, the two groups of temperature measuring elements are respectively connected as Figure 5In the described measurement circuit. Subsequently, in this step, first ensure that the power supply voltage in the temperature measurement element circuit of the small voltage group remains unchanged, and change the voltage across the temperature measurement elements of the large voltage group to gradually increase the temperature. At this time, the heat flow will flow from the high-temperature region to the low-temperature region, causing the local temperature of the small voltage platinum temperature measurement element to increase and the resistance to increase accordingly. By accurately measuring the resistance change, the temperature rise data can be obtained. That is, at different voltages, the voltage values of R1 and R2 at different temperatures can be obtained through the voltmeters 1 and 2 shown in Figure 5 to calculate the resistance of the temperature measurement element at different temperatures, and substitute it into the aforementioned formula 1 to calculate and obtain the value of T, and then obtain the linear relationship between temperature and resistance.

[0054] According to an embodiment of the present invention, in this step, two groups of temperature measurement elements can be selected for repeatability experiments to verify the followability and sensitivity of the temperature measurement elements with the aforementioned structure to the heat flow. Specifically, the temperature measurement elements with the applied large and small voltages can be interchanged to obtain the temperature rise data of the two groups of temperature measurement elements, and then the synchronous linear change of the temperature of the temperature measurement elements can be tested. The consistency of the temperature rise straight lines obtained from the two groups of temperature rise data is high, indicating that the temperature measurement element is sensitive to the heat conduction phenomenon, has good followability and sensitivity to temperature changes, excellent repeatability in temperature measurement of the sensor composed of Pt film, and strong stability, and is suitable as a temperature measurement unit for local heat flow under complex aerodynamic conditions. And because the aforementioned platinum sensor unit has a thickness of only 100 nm and a minimum line width of 5 μm, the self-heat capacity of the sensor is extremely small, and the response time is in the microsecond order, thus ensuring that there is no time lag between the temperature measurement units at different positions and having good synchronism.

[0055] According to an embodiment of the present invention, the heat flow measurement value q facing the heat flow can be determined in the following way: Denote the temperatures measured by two adjacent temperature measurement elements on the same plane as T1 and T2 respectively, and the distance is L (such as the straight-line distance between the inflection points of the serpentine parts of two adjacent temperature measurement elements shown in Figure 1 ), and take the temperature rise at the minimum power in the experiment, then the heat flow measurement value facing the heat flow is:

[0056]

[0057] where λ is the thermal conductivity of the ceramic sheet. Using a high-precision temperature measurement platform to calibrate the temperature of the temperature measurement element, the results show that the temperature measurement accuracy of the temperature measurement unit can reach 0.001 K, and the heat flux density resolution is calculated as 110 W / m 2 .

[0058] Due to the very close distance of the temperature measurement elements, a situation of large heat flow with a small temperature difference is caused. In actual applications, the temperature measurement spacing of the sensor must be larger than 10 -3It is two to three orders of magnitude larger. At this time, the measurement accuracy of the heat flux will be further improved. Therefore, high-precision heat flux measurement can be carried out based on the aforementioned temperature measuring elements.

[0059] The uncertainty of heat flux measurement can be calculated by the error transfer formula. The uncertainty is related to the uncertainty of thermal conductivity (λ), the uncertainty of measurement distance (x), and the uncertainty of voltage (i.e., U1 and U2 in the following formula for fixed resistance and the resistance to be measured (temperature measuring element)). Specifically:

[0060]

[0061] Among them, the uncertainty of the thermal conductivity estimated by simulation calculation is 3%. Therefore, the uncertainty of heat flux measurement is also better than 10%. It can be seen that the aforementioned structure has good measurement accuracy for measuring the heat flux facing.

[0062] S300: Obtain the response of the temperature measuring unit to the normal heat flux

[0063] According to an embodiment of the present invention, in this step, the response of the temperature measuring unit to the normal heat flux is evaluated. Specifically, to measure the response of the sensor to the normal heat flux, two temperature measuring units are bonded together with thermal conductive glue, and two groups of temperature measuring units as shown in Figure 1 are bonded with thermal conductive glue. The side of the Pt thin film in the two temperature measuring units is in contact with the thermal conductive glue. Subsequently, the relative platinum sensors are connected to the vacuum chamber with silver glue and copper wires and connected to the measurement circuit to measure the response of the sensor to the normal heat flux. During the detection process of the normal heat flux response, the temperature measuring unit is kept in a vertical state.

[0064] According to an embodiment of the present invention, the circuit connection and measurement method for measuring the response are the same as those for the response measurement facing, which will not be elaborated here. From the aforementioned steps, it can be obtained that the sensors on the following side are sensitive and can measure the temperature change in a timely manner.

[0065] S400: Conduct a simulation experiment through COMSOL finite element simulation software to obtain the thermal conductivities of Pt and aluminum nitride in the temperature measuring unit

[0066] The inventor found that through a large number of experiments, it was confirmed that the thermal conductivity of a thin film with a thickness of nanoscale is significantly lower than that of a conventional scale material. Since the temperature measuring element, that is, the sensor, proposed by the method of the present invention has a small design size, when calculating the heat flux, even if the temperature difference and the distance difference are known, the accurate heat flux value cannot be calculated. Therefore, in this step, first, a simulation experiment is carried out through COMSOL finite element simulation software to obtain the thermal conductivities of platinum and aluminum nitride in the temperature measuring unit. Specifically, the thermal conductivity of Pt is 26 W m -2 K -1 , and the thermal conductivity of aluminum nitride is 230 W m-2 K -1 The process of obtaining the aforementioned thermal conductivity is briefly described below:

[0067] First, the data obtained in the response temperature experiment for the measurement surface in the previous step is used as the data reference for modeling. The model consists of three layers, from top to bottom, namely a deposited platinum layer (100 nm), an aluminum nitride ceramic sheet layer (0.127 mm), and an alumina ceramic sheet layer (4.5 cm). Among them, the deposited platinum layer and the aluminum nitride ceramic sheet layer are the sensor parts, and the alumina ceramic sheet layer is the material of the constant temperature stage. The geometric construction of the model is established in a 1:1 correspondence with the actual temperature measurement unit size. In the simulation, a constant temperature stage is established to set the boundary conditions. Therefore, only the alumina ceramic sheet layer with the surface area of the sample size is taken, which can reduce the number of grids and improve the solution speed. The purpose of this simulation is to solve the thermal conductivities of the platinum thin layer and the aluminum nitride ceramic sheet layer. Therefore, these two parameters are set as λ pt and λ AIN It can be known from the temperature field control equation of constant physical properties, steady state, three-dimensional and with internal heat sources (shown below) that the temperature field is independent of the density and heat capacity of the material:

[0068]

[0069] After assigning material parameters to the geometric model, boundary conditions need to be set for it. This simulation is carried out in the solid heat transfer module. First, the initial value of the model temperature is set to the ambient temperature T0 = 300.85 K. The bottom of the alumina ceramic sheet is set to the ambient temperature, and the remaining surfaces are set to thermal insulation. Since the platinum is deposited on the aluminum nitride ceramic sheet non-compactly, there is an interfacial thermal resistance at the deposition interface. Through debugging, the interfacial thermal conductivity r of the contact interface between platinum and aluminum nitride is determined to be 2.1×10 7 Wm -2 K -1 .

[0070] At this time, heat sources are applied to the two groups of electrodes respectively. The different powers applied to the two temperature measurement units can be obtained from the experimental measurement results. From the magnitude of the external heat source can be obtained, where P is the power and V is the volume of the platinum wire.

[0071] Through the simulation of the response situation by COMSOL, the error between the simulation value and the experimental value is minimized. The calculated thermal conductivity of platinum is 26 W m -2 K -1 , the thermal conductivity of aluminum nitride is 230 Wm -2 K -1 , and the interfacial thermal conductivity of the thermal contact gap is 2.1×10 7 W m -2 K -1 . The thermal conductivity of bulk material platinum is about 70 W m -2 K-1 It can be seen therefrom that the thermal conductivity of the thin film material is lower than that of the bulk material, which is consistent with the existing research results. The thermal conductivity of the aluminum nitride ceramic sheet is 200 - 300 Wm -2 K -1 , so the calculated value is reasonable. When there is no gap at the contact interface between the platinum and the aluminum nitride ceramic sheet, the interfacial thermal conductivity is infinite. However, since it is impossible to achieve zero gap during actual operation and the gap of the material fabricated by the high-energy electron beam excited physical vapor deposition method is extremely small, the interfacial thermal conductivity is also within a reasonable range.

[0072] S500: Obtain the response time of the temperature measuring element through data fitting

[0073] According to an embodiment of the present invention, in this step, a data acquisition card is used to measure the change of the sensor temperature over time, and the response time t = 0.66 s of transient heat transfer is obtained through data fitting. Since platinum is deposited on the aluminum nitride ceramic sheet at this time, a large amount of heat energy is dissipated from the ceramic sheet with high thermal conductivity. Therefore, this response time only represents the situation of the sensor with the aluminum nitride ceramic sheet. Through theoretical derivation, the response time of the sensor can be obtained as 1.3×10 -7 s. Therefore, theoretically, this temperature measuring element can achieve a time resolution of the microsecond order.

[0074] Specifically, the suspended platinum thin film sensor is beneficial to further improve the time measurement accuracy. However, the mechanical strength of the suspended micron sensor is not high, and it is very easy to break during the measurement process, and its high-temperature resistance performance is not good. Therefore, according to the method of the embodiment of the present invention, a micron sensor supported by a ceramic sheet is selected. On the one hand, it improves the mechanical strength of the sensor, and on the other hand, it also greatly improves the high-temperature resistance performance of the device. Since the size and heat capacity of the ceramic sheet are much larger than those of the platinum micron sensor, it takes a longer time for the ceramic sheet-supported sensor to reach a steady state.

[0075] Specifically, in this step, a data acquisition card NI-PXI-5592 is used to measure the voltage of the energized temperature measuring element. The circuit connection is the same as that for the response experiment, and only one temperature measuring unit is connected. The temperature measurement of the sensor reaches a stable value at about 6 s for this temperature measuring unit. Using COMSOL simulation, by adding the parameters of density and specific volume on the basis of the steady-state model, the transient heat transfer problem can be calculated. The curve of the calculated simulation value is fitted using matlab, and the response time is obtained as 0.66 s.

[0076] As mentioned above, since platinum is deposited on the aluminum nitride ceramic sheet at this time, a large amount of heat energy is dissipated from the ceramic sheet with high thermal conductivity. Therefore, this response time only represents the situation of the sensor with the aluminum nitride ceramic sheet. From theoretical analysis, the size of the platinum micron sensor is in the micro-nano order of magnitude, and its heat capacity is extremely small, and the time resolution of temperature measurement is extremely high. The following is its derivation process:

[0077] ∵q = hAΔT

[0078]

[0079]

[0080] Therefore, theoretically, it can be concluded that a pure platinum sensor can achieve a response time in the microsecond order and can achieve a time resolution in the microsecond order.

[0081] In summary, the temperature measurement unit and the temperature measurement element with the aforementioned structure can have a relatively fast response time, and have good corresponding sensitivity and followability for both the facing and normal heat fluxes, and are suitable for measuring the heat flux characteristics in the aerodynamic environment where a simulated hypersonic vehicle is located.

[0082] Next, according to specific embodiments of the present invention, a method for measuring the heat flux under the aerodynamic flight conditions of a simulated hypersonic vehicle using the aforementioned temperature measurement unit will be introduced in detail:

[0083] According to an embodiment of the present invention, to simulate the aerodynamic flight conditions of a hypersonic vehicle, the present invention designs and provides an acetylene flame platform equivalent to the aerodynamic heating effect of a hypersonic vehicle. By building a high-temperature flame test bench, the sensor measures the temperature change during position transformation to observe the sensitivity and followability of the temperature measurement unit. The structural schematic diagram of this platform is as Figure 6 shown. Acetylene high-temperature flame is selected to simulate the aerodynamic heating effect. The combustion temperature of acetylene can reach 3200 °C, which is equivalent to the aerodynamic heating effect of a hypersonic vehicle. To simulate the aerodynamic flight conditions of a hypersonic vehicle, by building a high-temperature flame test bench as Figure 6 shown, the temperature measurement unit can measure the temperature change during position transformation, so as to observe the sensitivity and followability of the temperature measurement unit. Similarly, during the measurement, the temperature measurement unit is connected to an equivalent circuit as Figure 6 shown. For the change in temperature response, the voltages of the fixed resistor and across the sensor are collected using a data acquisition card. By changing the position of the sensor relative to the flame, the change in the obtained voltage value is observed. According to the calibration result, the voltage value change is converted into resistance, and the temperature change obtained by the temperature measurement unit is obtained by substituting it into Equation 1 mentioned above.

[0084] Specifically, referring to Figure 6, the high-temperature flame test bench includes an acetylene high-temperature flame generator and a positioning component. Among them, the positioning component includes a first-direction positioning scale and a second-direction positioning scale. The first direction can be the x direction shown in the figure, and the second direction is the y direction shown in the figure. The positioning component is connected to the temperature measurement unit, used to control the position of the temperature measurement unit, and can directly read the displacement of the temperature measurement unit moving in the first and second directions between two movements. During the temperature measurement process, the position of the temperature measurement unit is moved to make it far away from or close to the acetylene high-temperature flame generator, so as to obtain the increase or decrease of the temperature around the temperature measurement unit. Since acetylene flame is used as the heat source, this process can better simulate the aerodynamic heating effect of hypersonic vehicles.

[0085] From the experimental results, it can be concluded that the followability of the temperature measured by the sensor is strong and the temperature response is sensitive. Since when the temperature measurement unit is far away from the flame, the interference of the flame movement can be ignored as the distance increases, therefore, in the temperature drop curve, the overall drop trend is obvious and there is no large fluctuation. There are some interferences in the data acquisition of the data acquisition card. The temperature fluctuation is affected by the airflow movement on the one hand and by interferences such as noise on the other hand. Limited by the connection method of the sensor and the wire and the connection method on the position control bracket, too close a distance will cause the silver glue to melt and the adhesive tape to burn, so the distance is controlled to make its temperature not exceed 150°C.

[0086] According to the embodiments of the present invention, the test experimental results show that the sensor has high time resolution and temperature measurement accuracy. The transient fluctuations and details of the flame heating can be clearly captured, fully reflecting the advantages of the aerodynamic heating test bench, being able to better evaluate the performance of the sensor, reflecting the excellent response characteristics of the sensor, and being able to perform localized measurements of the temperature rise and heat flux of the solid wall surface in practical applications. Arranging multiple sensors can obtain the distribution maps of the temperature and heat flux along the path.

[0087] It should be noted that the present invention is not limited to the above specific embodiments. A high-spatiotemporal resolution temperature sensor and method capable of measuring the heat flux in the facing and normal directions proposed in the present invention can be widely applied to thermoelectric performance testing and other related fields. The present invention can be implemented in other various specific embodiments. Any design that adopts the design concept of the present invention and makes some simple changes or modifications falls within the protection scope of the present invention.

[0088] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A temperature measurement system for measuring the facing and normal heat fluxes, characterized in that, Comprising: A temperature measurement unit, a data acquisition unit, and a high-temperature flame test bench. Among them, the high-temperature flame test bench includes an acetylene high-temperature flame generator and a positioning component. The positioning component is arranged close to the acetylene high-temperature flame generator, and the temperature measurement unit is fixed on the positioning component. The temperature measurement unit includes a substrate and at least one group of temperature measurement elements. The temperature measurement elements have metal thin film electrodes, and the data acquisition unit is electrically connected to the temperature measurement unit; Further comprising a constant temperature unit. The constant temperature unit includes a constant temperature vacuum chamber, a molecular pump connected to the constant temperature vacuum chamber, a constant temperature table for placing the temperature measurement unit in the constant temperature vacuum chamber, and a plurality of independently power-supplied electrodes for connecting to the temperature measurement unit; The constant temperature unit further has a detection circuit structure. The detection circuit structure has a port that can access the temperature measurement unit. The detection circuit at least includes a variable resistor, a fixed resistor, and at least two voltmeters. The fixed resistor, the variable resistor, and the temperature measurement unit are connected in series, and the at least two voltmeters are respectively used to detect the voltages of the fixed resistor and the temperature measurement unit.

2. The temperature measurement system according to claim 1, wherein The metal thin film electrode is formed of a platinum thin film. The metal thin film electrode includes a first electrode block and a second electrode block, and the first electrode block and the second electrode block are connected by a serpentine part. The line width of the serpentine part is 3-10 microns.

3. The temperature measurement system according to claim 2, characterized in that, The thickness of the metal thin film electrode is 80-200 nm.

4. The temperature measurement system according to claim 2, wherein The width and length of the temperature measurement unit are independently 80-200 microns.

5. The temperature measurement system according to claim 1, characterized in that The substrate of the temperature measurement unit is aluminum nitride ceramic.

6. The temperature measurement system according to claim 5, wherein The substrate is a quadrilateral substrate. The temperature measurement unit includes 4 groups of the temperature measurement elements, and the temperature measurement elements are arranged at the four corners of the quadrilateral substrate.

7. A method for measuring heat flux using the temperature measurement system according to any one of claims 1-6, characterized in that, Comprising: Obtain the resistance values of the temperature measurement elements in the temperature measurement unit at different temperatures and when the power is 0, fit to obtain the resistance-temperature linear response relationship, and the initial resistance of the temperature measurement unit. According to the slope of the resistance-temperature linear response relationship and the initial resistance, obtain the resistance temperature coefficient β of the temperature measurement unit, and obtain the correction relationship of the temperature measurement value of the temperature measurement element: T = T0 + ΔR / (R0β) Wherein, T0 is the temperature when the initial resistance R0 is measured, Place the temperature measurement unit in the high-temperature flame test bench, rely on the positioning component to move the position of the temperature measurement unit to obtain the temperatures of the temperature measurement unit at different distances from the acetylene high-temperature flame generator, and obtain the heat flux data of the high-temperature acetylene flame according to the correction relationship of the temperature measurement value; the correction relationship of the temperature measurement value of the temperature measurement element is obtained by placing the temperature measurement unit in the constant temperature unit: On the premise that a fixed voltage is connected to the constant temperature table in the constant temperature unit, control the electrodes in the constant temperature table in the constant temperature unit that are connected to the temperature measurement elements to change the input voltage of the temperature measurement elements, and use voltmeters to respectively measure the voltage changes of the fixed resistor connected in series with the temperature measurement unit and the temperature measurement elements to obtain the resistance and power data of the temperature measurement elements at different temperatures, draw an R-P diagram, and obtain the resistance value of the temperature measurement element when the power P = 0; When no external voltage is applied to the constant temperature stage, the initial resistance R0 of the temperature measuring element at room temperature is measured; Change the applied voltage of the constant temperature stage to obtain multiple sets of temperatures and the resistance values of the temperature measuring element at a power of 0, and perform fitting to obtain the resistance-temperature linear response relationship of the temperature measuring element, and obtain the resistance temperature coefficient β of the temperature measuring unit: β = ΔR / (R0ΔT) where ΔR is the resistance difference between any two points in the resistance-temperature linear response relationship.

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