Online measurement method for temperature, concentration and pressure intensity of complex flow field

Abstract

The invention relates to the technical field of flow field parameter measurement, and discloses a complex flow field temperature, concentration and pressure online measurement method, which comprises the following steps: selecting an absorption component and a corresponding absorption spectral line according to a to-be-measured target, and the selected absorption spectral line needs to meet the following requirements: building a tunable semiconductor laser absorption spectrum measurement system; the method comprises the following steps of: calculating an initial temperature through an obtained absorptivity curve, then carrying out Voigt linear fitting on a fixed temperature, iteratively updating the temperature until convergence, and finally calculating the gas concentration and the gas pressure of the absorption component by utilizing the convergence temperature and fitting parameters of an absorption spectral line. By optimizing the flow field parameter measurement technology, the efficiency and safety of the industrial process can be improved, energy consumption and environmental pollution are reduced, and therefore remarkable economic benefits are brought.

Description

Technical Field

[0001] The invention relates to the technical field of flow field parameter measurement, and in particular to an online measurement method for temperature, concentration and pressure of a complex flow field. Background Art

[0002] In fluid dynamics and thermodynamics research, accurate measurement of flow field parameters is crucial to understanding fluid behavior and optimizing thermal systems. These flow field parameters include temperature, concentration, and pressure, which directly affect energy conversion, combustion efficiency, and fluid properties. Flow field parameter measurement technology plays a key role in aerospace, chemical engineering, environmental monitoring, and energy conversion. For example, it is crucial to improving aircraft engine performance, optimizing chemical reactions, monitoring air pollution, and improving energy conversion efficiency.

[0003] However, traditional invasive measurement technologies, such as wall sensors and thermocouples, have problems such as interfering with the flow field, only being able to measure a single parameter, high maintenance costs, low sensitivity, and slow response speed, which limit their application in extreme environments. Faced with challenges such as high temperature, high pressure, and high-speed flow, technological innovation is needed to ensure the accuracy and reliability of measurement. With the advancement of laser technology, non-invasive measurement technologies, such as tunable semiconductor laser absorption spectroscopy (TDLAS), provide more accurate and rapid measurement methods, promoting the development of flow field parameter measurement technology.

[0004] Although flow field parameter measurement technology has made certain progress, existing invasive measurement technologies, such as wall sensors, pneumatic probes, and thermocouples, still have certain limitations. These technologies may interfere with the flow field, resulting in inaccurate measurement data. In addition, these technologies can usually only measure a single parameter and cannot simultaneously obtain parameter information such as gas temperature, concentration, and pressure. They have high installation and maintenance costs, low sensitivity, slow response speed, and are difficult to adapt to measurement requirements in extreme environments such as high temperature and high pressure. These limitations restrict the in-depth study of fluid dynamics and thermodynamics, and also affect the optimization of industrial processes and the accuracy of environmental monitoring. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides an online measurement method for temperature, concentration and pressure of a complex flow field, provides a non-invasive measurement method, does not interfere with the flow field, and can measure multiple parameters simultaneously, providing support for the research of modern fluid dynamics and thermodynamics.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for online measurement of temperature, concentration and pressure in a complex flow field includes the following steps:

[0008] Step 1: Select the absorption component and the corresponding absorption spectrum according to the target to be measured. The selected absorption spectrum must meet the following requirements: the absorption rate and signal-to-noise ratio meet the set standards, avoid the influence of adjacent absorption spectrum, and the temperature sensitivity of the selected absorption spectrum within the temperature range to be measured is greater than the set value;

[0009] Step 2: Build a tunable semiconductor laser absorption spectrum measurement system, including a laser, a laser controller, a signal generator, a fiber coupler, a collimator, a detector, an FP standard and an oscilloscope;

[0010] The signal generator sends a sawtooth wave signal to the laser controller, so that the laser generates a laser signal with the same frequency. The two laser signals are coupled and split by the fiber coupler and collimated by the collimator. One laser signal is directly calibrated by the FP standard tool for frequency and time signal, and the other laser signal is sent to the flow field to be measured. Finally, it is received by the detector and the absorption signal is collected by the oscilloscope to obtain the absorption rate curve.

[0011] Step 3: Obtain the initial temperature through the obtained absorption rate curve calculation, then perform Voigt line fitting at a fixed temperature, iteratively update the temperature until convergence, and finally calculate the gas concentration X and gas pressure P of the absorbing component using the convergence temperature and the fitting parameters of the absorption spectrum.

[0012] Furthermore, step one specifically includes:

[0013] Two-color laser is used to measure flow field parameters, that is, two laser absorption lines are used;

[0014] The temperature sensitivity is defined as follows:

[0015]

[0016] Wherein, R=A1 / A2 is the ratio of the integrated absorption rates A1 and A2 of the two laser absorption lines; the physical parameter k represents the Boltzmann constant, h is the Planck constant, c is the propagation speed of light in the medium, E″1, E″2 are the low-energy level energies of the transitions of the two laser absorption lines, and T is the gas temperature of the absorbing component.

[0017] Furthermore, step three specifically includes the following steps:

[0018] S31, calculate the integrated absorption rate A of the two laser absorption lines through the absorption rate curve 1，0 , A 2,0 , based on the integrated absorption rate A 1，0 , A 2，0 Calculate an initial temperature T1;

[0019] S32, then fix the temperature T = T1 and calculate the Gaussian half-maximum full width Δv of the two laser absorption linesD1 , Δv D2 , with the Lorentz full width at half maximum Δv C1 , Δv C2 , center wave number v 1,0 , v 2,0 The integral absorption rates A1 and A2 are free parameters. The absorption rate curves of the two laser absorption lines are fitted by Voigt line type to obtain the corresponding parameters. The integral absorption rates A1 and A2 of the two laser absorption lines are extracted and fitted. 1，1 , A 2，1 , calculate the new temperature T2;

[0020] S33, determine whether |T2-T1|<ξ is satisfied. If not, update the temperature T=T2 and return to step S32; if satisfied, output the temperature T and obtain the Lorentz half-maximum full width Δv of the two laser absorption spectra after fitting. C1 , Δv c2 , center wave number v 1,0 , v 2,0 , integrated absorption rate A1, A2;

[0021] S34, using the temperature T and the fitting parameters of any laser absorption spectrum line, iteratively calculate the gas concentration X of the absorbing component and the gas pressure P of the absorbing component.

[0022] Compared with the prior art, the beneficial technical effects of the present invention are:

[0023] 1. Accurately measuring flow field parameters is of great significance to scientific research fields such as verifying fluid dynamics theory, developing new combustion technology, and monitoring environmental changes. The progress of this invention in measurement technology not only promotes the development of scientific theories, but also provides an experimental basis for the development and application of new technologies.

[0024] 2. The present invention can improve the efficiency and safety of industrial processes, reduce energy consumption and environmental pollution, and thus bring significant economic benefits by optimizing flow field parameter measurement technology. For example, in chemical production, accurate flow field parameter control can reduce the waste of raw materials and improve product quality and output.

[0025] 3. Improving flow field parameter measurement technology helps reduce industrial emissions, protect the environment, and has a positive impact on sustainable development. By precisely controlling the combustion process and fluid mixing, greenhouse gas emissions can be reduced, pollutant release can be reduced, and the atmospheric environment and ecosystem can be protected. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the variation of absorption line intensity and temperature sensitivity with temperature;

[0027] Figure 2is a schematic diagram of a TDLAS measurement system in an embodiment of the present invention;

[0028] Figure 3a and Figure 3b The H2O in the embodiment of the present invention under 294K, 1atm, 98cm environment is located at 7168.437cm -1 and 7185.6cm -1 Schematic diagram of nearby absorbance and Voigt line type fitting;

[0029] Figure 4 Schematic diagram of H2O temperature measurement results in an embodiment of the present invention;

[0030] Figure 5 Schematic diagram of H2O pressure measurement results in an embodiment of the present invention;

[0031] Figure 6 Schematic diagram of H2O concentration measurement results in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] A preferred embodiment of the present invention is described in detail below with reference to the accompanying drawings.

[0033] In this embodiment, a method for online measurement of temperature, concentration, and pressure of a complex flow field includes the following steps:

[0034] Step 1, absorption line selection:

[0035] This embodiment uses a two-color laser to measure flow field parameters, that is, two laser absorption spectra are required. First, determine the absorption component, which can be selected according to different occasions and different needs, and then select the appropriate absorption spectrum according to the absorption component. In this embodiment, H2O is selected as the target absorption component. Based on the description of the absorption spectrum selection rules, the spectrum selection principle needs to consider the following aspects:

[0036] 1) The absorption spectrum has good absorption and good signal-to-noise ratio;

[0037] 2) Avoid the influence of adjacent absorption;

[0038] 3) The temperature sensitivity of the selected spectral line within the temperature range to be measured should be high (generally required to be greater than 1).

[0039] The temperature sensitivity is defined as follows:

[0040]

[0041] Wherein, R = A1 / A2, which is the ratio of the integrated absorption rates A1 and A2 of the two laser absorption lines. The physical parameter k represents the Boltzmann constant. In the preferred embodiment, k = 1.381×10 -23; h is Planck's constant, h = 6.626 × 10 -34 ; c is the propagation speed of light in the medium, c≈3×10 10 cm / s, E″1, E″2 (unit: cm -1 ) is the low-level energy of the transition of the two laser absorption lines.

[0042] This example selects water vapor as the absorption component and determines two absorption lines near 1392nm and 1395nm. Both absorption lines meet the principle of line selection. The central wave numbers of these two absorption lines are 7185.6cm -1 and 7168.437cm -1 The detailed parameter information of these two spectral lines is listed in Table 1. Figure 1 As shown, by analyzing the intensity and temperature sensitivity of the two absorption lines, in the temperature range of 200 to 900 K, the temperature sensitivity is greater than 1, that is, the two selected absorption lines meet the temperature measurement requirements within a certain temperature range.

[0043] Table 1, absorption line parameters corresponding to H2O

[0044] <![CDATA[Central wave number v0 / (cm -1 )]]> <![CDATA[Line strength S(296K) / (cm-2·atm -1 )]]> <![CDATA[Low-level energy E″ / (cm -1 )]]> 7185.6 7.947E-22 1045.0579 7168.437 1.170E-20 173.3658

[0045] Step 2: TDLAS measurement system construction and operation:

[0046] The H2O absorption test was carried out at room temperature and pressure to verify the normal operation of the experimental equipment and the accuracy of the measurement method. Figure 2As shown, the signal generator sends a sawtooth wave signal to the laser controller, so that the 1395nm and 1392nm DFB lasers generate lasers of the same frequency. The signal generator uses Tektronix's AFG3000C series products. The signal generator can output dual channels and can output two signals separately to control lasers with different requirements. In this experiment, the output frequency is 1KHz and the phase difference is 180 degrees. The sawtooth wave signal. The two laser signals are coupled and split by the coupler. After the laser is collimated by the collimator, one signal is directly calibrated by the FP standard tool for frequency and time signal. The other signal leads to the flow field to be measured for parameter diagnosis and measurement. The laser uses a 14-pin butterfly package laser produced by NEL, with central wavelengths of 1395nm and 1392nm respectively. The detector uses the PDA05CF2 indium gallium arsenide amplified detector from Thorlabs. The laser controller is ILX Lightwave's LDC-3724C driver, and the near-infrared etalon uses Thorlabs' SA200-12B scanning Fabry-Perot interferometer, which is a resonant cavity etalon. The free spectrum range is 1.5 GHz (i.e. 0.05 cm -1 ), used to calibrate the frequency information of the laser and convert the time domain signal into the frequency domain signal. The signal is collected by an oscilloscope.

[0047] Step 3: Data collection and analysis:

[0048] Tunable diode laser absorption spectroscopy (TDLAS) technology is mainly based on the Beer-Lambert law, which describes the relationship between the incident light intensity and the transmitted light intensity before and after the laser passes through the flow field by the following formula:

[0049]

[0050] In the formula, I0 and I t are the incident light intensity and the transmitted light intensity, respectively. L is the effective absorption optical path, P is the gas pressure of the absorbing component, X is the gas concentration of the absorbing component, T is the gas temperature of the absorbing component, α(v) is the absorbance, S(T) is the intensity of the absorption spectrum, which describes the intensity of light energy absorption and radiation during molecular energy level transitions. φ(v) is the absorption spectrum line function, which satisfies the normalization condition. Note that the Beer-Lambert law is applicable to uniform flow field environments, where the temperature, pressure, and concentration of the absorbing component are all line-of-sight averages.

[0051] Since the absorption spectrum is affected by various broadening mechanisms, the absorption spectrum of the molecule is not a point on the central frequency, but presents a distribution form with a certain width; the present invention adopts the Voigt line type, which is the convolution of the Gaussian line function and the Lorentz line function.

[0052] Gauss full width at half maximum Δv D It can be expressed as:

[0053]

[0054] Lorentz full width at half maximum Δv C It can be expressed as:

[0055] Δv C =PX2r(T) self +P(1-X)2r(T) air ; (4)

[0056] In the formula, r(T) se l f (cm -1 ·atm -1 ) is the self-collision broadening coefficient of the absorbing component, r(T) air (cm -1 ·atm -1 ) is the collision broadening coefficient between the absorbing component and the non-absorbing component:

[0057]

[0058] Where n self and are the exponential factors for self-collision broadening and collision broadening with non-absorbing components, respectively, which can be retrieved from the HITRAN database or calibrated experimentally.

[0059] Define the integrated absorbance of an absorption line:

[0060]

[0061] By comparing the integrated absorption rates of the two absorption lines and taking their logarithms, we can obtain an analytical expression for temperature:

[0062]

[0063] Where A1 / A2 is the ratio of the experimentally measured double-line integrated absorbance, and the remaining parameters are physical constants or spectral parameters.

[0064] First, import the collected data into the computer, and then use the iterative fitting program to analyze the data. The specific operations are:

[0065] 1) Roughly calculate the integrated absorption rate A of the two spectral lines by using the experimentally measured absorption rate curve 1，0 , A 2，0 , an initial temperature T1 is calculated by formula (8).

[0066] 2) Then fix the temperature T = T1 and calculate the Gaussian half-maximum full width Δv of the two absorption lines according to formula (3): D1 , Δv D2 , with the Lorentz full width at half maximum Δv C1 , Δv C2 , absorption line center wave number v 1,0 , v 2,0 The integral absorption rates A1 and A2 are free parameters. The experimental absorption rate curve is fitted with Voigt line type to obtain the corresponding parameters. The integral absorption rates A of the two spectral lines are extracted and fitted. 1，1 , A 2，1 , calculate the new temperature T2 through formula (8).

[0067] 3) Determine whether |T2-T1|<ξ is satisfied. ξ can be set according to the requirements. In this embodiment, ξ is 0.1. If not satisfied, update the temperature T=T2 and return to step 2); if satisfied, output the temperature T and obtain the Lorentz half-maximum full width Δv of the two fitted spectral lines. C1 , Δv C2 , center wave number v 1,0 , v 2,0 , integrated absorption rate A1, A2.

[0068] 4) Using the temperature T and the fitting parameters of one of the absorption lines, such as Δv C1 , A1, and iteratively calculate through equations (4) to (7) to obtain the gas concentration X of the absorption component and the gas pressure P of the absorption component.

[0069] The processing results are as follows:

[0070] Figure 3a , Figure 3b They are 7168.437cm respectively -1 and 7185.6cm -1 Voigt fitting curve of absorbance at 294 K, 1 atm, 98 cm.

[0071] The flow field temperature can be calculated by fitting the absorbance curve with the Voigt line type. Since the measured indoor environment is a uniform flow field, the measured flow field parameters are processed as average values ​​to ensure the measurement accuracy. Figure 4 As shown, the final measured temperature is 300K, the indoor temperature is 294K, and the relative error is 2%.

[0072] The pressure measurement results of H2O are as follows Figure 5 As shown, the calculated pressure result is 0.9895 atm, with a relative error of -1.05%.

[0073] The concentration of H2O is measured as follows: Figure 6As shown, the calculated concentration result is 0.0166, and the water vapor concentration converted by the thermometer and hygrometer is 0.0162, and the relative error between the two is 2.47%.

[0074] In the test under normal temperature and pressure, the measured value by the measurement method provided in this embodiment is consistent with the reading of the thermometer and hygrometer, with small relative error and high accuracy, which verifies the feasibility of the system and method in this embodiment.

[0075] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention, and any reference numerals in the claims should not be regarded as limiting the claims involved.

[0076] In addition, it should be understood that although the present specification is described in terms of implementation modes, not every implementation mode contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for online measurement of temperature, concentration and pressure in a complex flow field, characterized in that: The following steps are involved: Step 1: Select the absorption component and the corresponding absorption spectrum according to the target to be measured. The selected absorption spectrum must meet the following requirements: the absorption rate and signal-to-noise ratio meet the set standards, avoid the influence of adjacent absorption spectrum, and the temperature sensitivity of the selected absorption spectrum within the temperature range to be measured is greater than the set value; Step 2: Build a tunable semiconductor laser absorption spectrum measurement system, including a laser, a laser controller, a signal generator, a fiber coupler, a collimator, a detector, an FP standard and an oscilloscope; The signal generator sends a sawtooth wave signal to the laser controller, so that the laser generates a laser signal with the same frequency. The two laser signals are coupled and split by the fiber coupler and collimated by the collimator. One laser signal is directly calibrated by the FP standard tool for frequency and time signal, and the other laser signal is sent to the flow field to be measured. Finally, it is received by the detector and the absorption signal is collected by the oscilloscope to obtain the absorption rate curve. Step 3: Obtain the initial temperature through the obtained absorption rate curve calculation, then perform Voigt line fitting at a fixed temperature, iteratively update the temperature until convergence, and finally calculate the gas concentration X and gas pressure P of the absorbing component using the convergence temperature and the fitting parameters of the absorption spectrum.

2. The method for online measurement of temperature, concentration and pressure in a complex flow field according to claim 1, characterized in that: Step 1 specifically includes: Two-color laser is used to measure flow field parameters, that is, two laser absorption lines are used; The temperature sensitivity is defined as follows: Wherein, R=A1 / A2 is the ratio of the integrated absorption rates A1 and A2 of the two laser absorption lines; the physical parameter k represents the Boltzmann constant, h is the Planck constant, c is the propagation speed of light in the medium, E″1, E″2 are the low-energy level energies of the transitions of the two laser absorption lines, and T is the gas temperature of the absorbing component.

3. The method for online measurement of temperature, concentration and pressure in a complex flow field according to claim 2, characterized in that: Step three specifically includes the following steps: S31, calculate the integrated absorption rate A of the two laser absorption lines through the absorption rate curve 1,0 ,A 2,0 , based on the integrated absorption rate A 1,0 ,A 2,0 Calculate an initial temperature T1; S32, then fix the temperature T = T1 and calculate the Gaussian half-maximum full width Δv of the two laser absorption lines D1 ,Δv D2 , with the Lorentz full width at half maximum Δv C1 ,Δv C2 , center wave number v 1,0 ,v 2,0 The integral absorption rates A1 and A2 are free parameters. The absorption rate curves of the two laser absorption lines are fitted by Voigt line type to obtain the corresponding parameters. The integral absorption rates A1 and A2 of the two laser absorption lines are extracted and fitted. 1,1 ,A 2,1 , calculate the new temperature T2; S33, determine whether |T2-T1|<ξ is satisfied. If not, update the temperature T=T2 and return to step S32; if satisfied, output the temperature T and obtain the Lorentz half-maximum full width Δv of the two laser absorption spectra after fitting. C1 ,Δv C2 , center wave number v 1,0 ,v 2,0 , integrated absorption rate A1, A2; S34, using the temperature T and the fitting parameters of any laser absorption spectrum line, iteratively calculate the gas concentration X of the absorbing component and the gas pressure P of the absorbing component.

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