A thermocouple temperature measuring device and correction method for ultra-high temperature test conditions

Abstract

The present invention relates to a thermocouple temperature measurement device and correction method for use under ultra-high temperature test conditions, belonging to the field of gas turbines. The device comprises an experimental channel, a mainstream thermocouple, a pitot tube, and a wall thermocouple. The mainstream thermocouple is used to measure the mainstream temperature, the pitot tube is used to measure the incoming flow velocity, and multiple wall thermocouples are arranged circumferentially along the experimental channel to measure the wall temperature. By considering the radiation heat transfer between the thermocouple and the inner wall of the channel, and applying convective heat transfer theory and empirical correlations to perform three iterative calculations and corrections, the device ultimately obtains a mainstream temperature that is closer to the actual value within the channel, significantly reducing experimental measurement errors and ensuring the accuracy of experimental data. This method for correcting the measured gas temperature using thermocouples has very important engineering application value and good universal applicability in high-temperature heat transfer experiments.

Description

Technical Field

[0001] The present invention belongs to the field of gas turbines, and in particular relates to a thermocouple temperature measuring device and a correction method for use under ultra-high temperature test conditions. Background Art

[0002] Gas turbines are widely used in power generation, aviation, and power machinery. The Brayton cycle of gas turbines demonstrates that increasing the combustor outlet temperature is one of the primary ways to improve gas turbine performance. Currently, the average temperature of the gas at the combustor outlet of advanced gas turbines exceeds 2000K, which increases the thermal load on the turbine. Ensuring the proper operation and extended life of turbine components under high temperatures and loads has become a technical challenge in gas turbine development. Gas turbine design requires the use of numerous cooling technologies, and experimental evaluation of these technologies is crucial to turbine design.

[0003] In heat transfer and cooling experiments, the heat load in the gas turbine blade cascade channels is primarily composed of convection and radiation. When the gas temperature is low, convection heat transfer within the channels is strong due to its high flow rate, and radiation heat transfer accounts for a relatively small portion of the total blade heat load. However, as the combustion chamber outlet gas temperature increases, the influence of radiation heat transfer becomes increasingly significant, and its share of the heat load also increases.

[0004] The primary purpose of heat transfer and cooling experiments is to experimentally determine the heat transfer coefficient between the gas and the wall it flows through, the gas heat transfer temperature, and the wall temperature, thereby calculating the heat transfer between the gas and the wall. The difficulty of many experiments lies in determining the surface heat transfer coefficient. In gas turbine heat transfer experiments, thermocouples are often used to measure the gas temperature in the flow path. They convert the received thermal energy into electrical energy and measure the temperature using the generated electromotive force. However, in actual measurements, the thermocouple contact point radiates heat with the surrounding environment, causing the measured gas temperature to be lower than the actual gas temperature. Furthermore, the error between the two increases as the gas temperature increases.

[0005] Therefore, the correction of the gas temperature measured by thermocouples under high temperature test conditions has very important engineering application value for its application in heat transfer and cooling experiments.

[0006] In "A Brief Analysis of Measurement Errors and Treatment Solutions of High-Temperature Thermocouples" published by Wang Junfang in the first issue of "Mechanical Management and Development" in 2017, the temperature measurement errors of thermocouples at high temperatures were attributed to structural deterioration. In existing gas turbine heat transfer experiments, the radiation heat exchange losses between the thermocouples and the surrounding environment were ignored, which increased the errors in the experimental data.

[0007] Therefore, when using thermocouples to measure the temperature of high-temperature combustion gas in a channel, the prior art fails to consider the radiation heat exchange between the thermocouple and the channel wall, resulting in a large error in temperature measurement. Summary of the Invention

[0008] Technical issues to be solved:

[0009] In order to avoid the shortcomings of the existing technology, the present invention proposes a thermocouple temperature measurement device and correction method for ultra-high temperature test conditions. By considering the radiation heat transfer between the thermocouple and the channel wall, the measured temperature is corrected using convective heat transfer theory and empirical correlation formulas. The result can be considered as the true mainstream temperature to ensure the accuracy of the experimental data.

[0010] The technical solution of the present invention is: a thermocouple temperature measuring device for use under ultra-high temperature test conditions, characterized in that it includes an experimental channel, a mainstream thermocouple, a Pitot tube, and a wall thermocouple; the mainstream thermocouple is used to measure the temperature of the mainstream, the Pitot tube is used to measure the incoming flow velocity, and multiple wall thermocouples are arranged circumferentially along the experimental channel to measure the wall temperature.

[0011] A further technical solution of the present invention is that the number of the wall thermocouples is 8 and they are evenly distributed along the circumference, that is, two wall thermocouples are set on each of the four walls of the experimental channel.

[0012] A further technical solution of the present invention is that the two thermocouples on the same wall are respectively located 7d upstream and downstream of the mainstream temperature measurement thermocouple probe along the mainstream direction, where d is the diameter of the thermocouple probe.

[0013] A correction method for a thermocouple temperature measuring device under ultra-high temperature test conditions, characterized by the following specific steps:

[0014] Step 1: Calculate the convective heat transfer between the mainstream thermocouple and the high-temperature gas:

[0015] Φ h =hA1(T f -T1)

[0016] Where A2 is the channel wall area, T f is the actual temperature of the mainstream, T1 is the measured temperature of the mainstream, and h is the average surface heat transfer coefficient of the fluid-swept sphere;

[0017] Step 2: Calculate the radiation heat transfer between the mainstream thermocouple and the inner wall of the channel:

[0018]

[0019] Where A1 is the surface area of ​​the thermocouple probe, T w is the wall temperature, ε is the thermocouple emissivity;

[0020] Step 3: When in steady state, Φ h =Φ r,Right now at this time The actual mainstream temperature T2 after the first correction can be obtained;

[0021] Step 4: Obtain the Prandtl number Pr, fluid thermal conductivity λ, and dynamic viscosity μ at the first correction temperature T2 by looking up the table ∞ and kinematic viscosity ν;

[0022] Repeat steps 3 and 4. After 3 iterations, the mainstream temperature T f The residual error is less than 1%, and the true mainstream temperature is obtained at this time.

[0023] A further technical solution of the present invention is: in step 1, the formula Φ h =hA1(T f The average surface heat transfer coefficient h of the fluid swept outward on a sphere with a flow rate of -T1) is determined using the following empirical correlation:

[0024]

[0025] Where, u is the mainstream velocity, l is the channel length, Pr is the Prandtl number, λ is the fluid thermal conductivity, μ ∞ is the dynamic viscosity, ν is the kinematic viscosity, μ w is the dynamic viscosity.

[0026] A further technical solution of the present invention is: in step 2, the surface area A1 of the mainstream thermocouple probe is less than the area A2 of the inner wall of the channel.

[0027] A further technical solution of the present invention is: w Measure the average wall temperature for multiple wall thermocouples.

[0028] Beneficial effects

[0029] The beneficial effect of the present invention is that in gas turbine heat transfer experiments, thermocouples are often used to measure the gas temperature in the flow channel. They convert the received thermal energy into electrical energy and use the generated electromotive force to measure the temperature. However, in actual measurements, the contact points of the thermocouples will radiate heat with the surrounding environment, resulting in the measured gas temperature being lower than the actual gas temperature. As the gas temperature increases, the error between the two gradually increases. Therefore, the method for correcting thermocouple temperature measurement under ultra-high temperature test conditions proposed in the present invention considers the radiation heat exchange between the thermocouple and the inner wall of the channel, and uses convective heat transfer theory and empirical correlations to perform three iterative calculations for correction. Ultimately, a mainstream temperature that is closer to the actual value in the channel is obtained, significantly reducing experimental measurement errors and ensuring the accuracy of experimental data. The application of this method for correcting the actual gas temperature measured by thermocouples in high-temperature heat transfer experiments has very important engineering application value and good universal applicability.

[0030] When conducting the film cooling characteristic experiment on the end wall of the ceramic matrix composite material flat plate, the above method is used to correct the mainstream temperature, such as Figure 4 As shown in the figure, it can be seen that the mainstream temperature is quite different before and after the correction, and the spanwise average cooling efficiency after the correction is closer to the experimental results than before the correction, which confirms the feasibility of this method. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the channel structure of the thermocouple temperature measurement correction under ultra-high temperature test conditions of the present invention;

[0032] Figure 2 It is a cross-sectional view of the experimental channel structure A;

[0033] Figure 3 It is the isometric cross-section of the experimental channel structure;

[0034] Figure 4 It is a comparison chart of experimental data before and after correction;

[0035] Figure 5 It is a flowchart of iterative calculation;

[0036] Explanation of reference numerals: 1- Pitot tube, 2- mainstream thermocouple, 3-10 wall thermocouple. DETAILED DESCRIPTION

[0037] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0038] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0039] The present invention provides a method for correcting thermocouple temperature measurement under ultra-high temperature test conditions. Figure 1 Figure 2 The experimental device includes an experimental channel, a Pitot tube 1 for measuring the incoming flow velocity, a thermocouple 2 for measuring the mainstream temperature, and eight thermocouples (3-10) for measuring the wall temperature.

[0040] Among them, the thermocouple emissivity ε, the thermocouple probe diameter d, the thermocouple probe surface area A1, the channel wall area A2, the mainstream measurement temperature T1, the mainstream velocity u, the channel length l, the wall temperature Actual mainstream temperature T f The main flow measurement temperature T1 is known, and the Prandtl number Pr, fluid thermal conductivity λ, and dynamic viscosity μ at this temperature can be obtained by looking up the table. ∞ And kinematic viscosity ν. Known wall temperature T w By looking up the table, we can get the dynamic viscosity μ at this temperature. w .

[0041] Step (1) Convection heat transfer between the mainstream thermocouple and the high-temperature gas Φ h =hA1(T f -T1).

[0042] Step (2) Since the surface area of ​​the mainstream thermocouple probe A1<<the area of ​​the inner wall of the channel A2, the radiation heat exchange between the mainstream thermocouple and the inner wall of the channel is

[0043] Step (3) where the formula Φ in step (1) is h =hA1(T f The average surface heat transfer coefficient h of the fluid swept sphere can be determined by the following empirical correlation:

[0044] in,

[0045] Step (4) When in steady state, Φ h =Φ r ,Right now at this time The actual mainstream temperature T2 after the first correction can be obtained.

[0046] Step (5) obtains the Prandtl number Pr, fluid thermal conductivity λ, and dynamic viscosity μ at the first corrected temperature T2 by looking up the table. ∞ and kinematic viscosity ν, repeat steps (3)(4)(5), and after 3 iterations the mainstream temperature T f The residual is less than 1%, which can be considered as the true mainstream temperature.

[0047] In the implementation of the present invention, since the channel has four inner wall surfaces, namely, upper, lower, left and right, a layout of two thermocouples is adopted on each surface, and the two thermocouples on the same wall are respectively located 7d upstream and downstream of the mainstream temperature measuring thermocouple along the mainstream direction. Finally, the average value of the total eight thermocouples is taken as the wall surface temperature T w , further reducing the error.

[0048] At the same time, the radiation heat transfer between the channel wall and the mainstream temperature measuring thermocouple is considered, and the measured temperature is corrected using the convection heat transfer theory and empirical correlation formula to obtain the mainstream temperature closer to the actual value.

[0049] The technical principles of the present invention are as follows:

[0050] As shown in the figure, by considering the radiation heat transfer between the thermocouple and the inner wall of the channel, multiple iterative calculations are performed using convective heat transfer theory and empirical correlation formulas to correct the measured temperature, ultimately obtaining a mainstream temperature that is closer to the actual value, greatly reducing the experimental measurement error and ensuring the accuracy of the experimental data.

[0051] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A correction method for a thermocouple temperature measuring device used under ultra-high temperature test conditions, characterized in that: The thermocouple temperature measuring device includes an experimental channel, a mainstream thermocouple, a pitot tube, and a wall thermocouple; the mainstream thermocouple is used to measure the mainstream temperature, the pitot tube is used to measure the incoming flow velocity, and multiple wall thermocouples are arranged along the circumference of the experimental channel to measure the wall temperature; There are eight wall thermocouples, which are evenly distributed along the circumference, that is, two wall thermocouples are set on each of the four walls of the experimental channel; The two thermocouples on the same wall are located 7 meters upstream and downstream of the mainstream temperature measurement thermocouple probe along the mainstream direction. d Department, d is the diameter of the thermocouple probe; The specific steps of the correction method are as follows: Step 1: Calculate the convective heat transfer between the mainstream thermocouple and the high-temperature gas: Where, A 2 is the channel wall area, T f is the actual mainstream temperature, T 1 is the mainstream measurement temperature, h is the average surface heat transfer coefficient of the fluid swept sphere; The formula The average surface heat transfer coefficient of the fluid swept outward on the sphere h Determine using the following empirical correlation: Where, , ; u For mainstream speed, l is the channel length, Pr is the Prandtl number, λ is the thermal conductivity of the fluid, is the dynamic viscosity, ν is the kinematic viscosity, is the dynamic viscosity; Step 2: Calculate the radiation heat transfer between the mainstream thermocouple and the inner wall of the channel: Where A1 is the surface area of ​​the thermocouple probe, is the wall temperature, ; is the thermocouple emissivity; Step 3: When in steady state, ,Right now ,at this time , you can get the actual mainstream temperature after the first correction ; Step 4: Get the first corrected temperature by looking up the table Prandtl number under Pr , fluid thermal conductivity λ , dynamic viscosity and kinematic viscosity ν ; Repeat steps 3 and 4, and after 3 iterations the mainstream temperature is calculated. The residual is less than 1%, and the true mainstream temperature is obtained.

2. The correction method for a thermocouple temperature measuring device used under ultra-high temperature test conditions according to claim 1, characterized in that: In step 2, the surface area of ​​the mainstream thermocouple probe A 1<<Channel inner wall area A 2.

3. The correction method for a thermocouple temperature measuring device used under ultra-high temperature test conditions according to claim 1, characterized in that: described Measure the average wall temperature for multiple wall thermocouples.

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