Method for on-line measuring temperature, concentration and pressure of complex flow field

Abstract

The application relates to the technical field of flow field parameter measurement, and discloses a temperature, concentration and pressure online measurement method for a complex flow field, which comprises the following steps: selecting an absorption component and a corresponding absorption spectral line according to a target to be measured; the selected absorption spectral line needs to meet the following conditions: a tunable semiconductor laser absorption spectrum measurement system is built; an initial temperature is calculated by using an obtained absorption rate curve; a Voigt line type fitting is carried out by fixing the temperature; the temperature is iteratively updated until convergence is achieved; and finally, the gas concentration of the absorption component and the gas pressure of the absorption component are calculated by using the converged temperature and the fitting parameters of the absorption spectral line. Through optimization of the flow field parameter measurement technology, the application can improve the efficiency and safety of an industrial process, reduce energy consumption and environmental pollution, and thus brings significant economic benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flow field parameter measurement, and particularly relates to a temperature, concentration and pressure online measurement method for complex flow fields. BACKGROUND

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

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

[0004] Although flow field parameter measurement technology has made some progress, existing invasive measurement techniques such as wall sensors, aerodynamic 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 only measure a single parameter, and cannot simultaneously obtain parameters 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 high temperature and high pressure measurement requirements in extreme environments. These limitations limit the in-depth study of fluid dynamics and thermodynamics, and affect the accuracy of industrial process optimization and environmental monitoring. SUMMARY

[0005] To solve the above technical problems, the present application provides a temperature, concentration and pressure online measurement method for complex flow fields, which provides a non-invasive measurement method that does not interfere with the flow field and can simultaneously measure multiple parameters, providing support for modern fluid dynamics and thermodynamics research.

[0006] To solve the above technical problems, the present application adopts the following technical solutions:

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

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

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

[0010] The signal generator sends a sawtooth wave signal to the laser controller, causing the laser to generate 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 for frequency and time by the FP standard tool, while the other laser signal is sent to the flow field to be measured. Finally, the detector receives the signal and the oscilloscope collects the absorption signal 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 use the convergence temperature and the fitting parameters of the absorption spectrum to calculate the gas concentration X and gas pressure P of the absorbing component.

[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] Where 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 integral 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 , Δv C1 , Δv C2 , v 1,0 , v 2,0 , A1, A2 1，1 , A 2，1 , Δv C1 , Δv c2 , v 1,0 , v 2,0 , A1, A2

[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 full width at half maximum Δv C1 , Δv c2 , v 1,0 , v 2,0 , A1, A2

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

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

[0023] 1. Accurate measurement of flow field parameters is of great significance for verifying fluid dynamics theory, developing new combustion technology, monitoring environmental changes and other scientific research fields. The progress in measurement technology not only promotes the development of scientific theory, but also provides experimental basis for the development and application of new technology.

[0024] 2. By optimizing the flow field parameter measurement technology, the present application can improve the efficiency and safety of industrial processes, reduce energy consumption and environmental pollution, thereby bringing significant economic benefits. For example, in chemical production, accurate flow field parameter control can reduce the waste of raw materials and improve the quality and yield of products.

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

[0026] Figure 1 is a schematic diagram of the absorption line intensity and temperature sensitivity with temperature change;

[0027] Figure 2A schematic diagram of a TDLAS measuring system in an embodiment of the present application;

[0028] Figure 3a and Figure 3b are a Voigt line type fitting schematic diagram of the absorbance of H2O near 7168.437 cm -1 and 7185.6 cm -1 in an environment of 294 K, 1 atm, 98 cm in an embodiment of the present application, respectively;

[0029] Figure 4 is a temperature measurement result schematic diagram of H2O in an embodiment of the present application;

[0030] Figure 5 is a pressure measurement result schematic diagram of H2O in an embodiment of the present application;

[0031] Figure 6 is a concentration measurement result schematic diagram of H2O in an embodiment of the present application. DETAILED DESCRIPTION

[0032] A preferred embodiment of the present application will be described in detail below with reference to the accompanying drawings.

[0033] The temperature, concentration, and pressure online measurement method of a complex flow field in the present embodiment includes the following steps:

[0034] Step one, absorption line selection:

[0035] In the present embodiment, two-color laser is used to measure flow field parameters, i.e. two laser absorption lines are needed. First, the absorption component is determined, which can be selected according to different needs in different situations, and then the appropriate absorption line is selected according to the absorption component. In the present embodiment, H2O is selected as the target absorption component. Based on the description of the selection rules of the absorption line, the following aspects need to be considered in the selection principle:

[0036] 1) The selected absorption line 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 line in the measured temperature range should be high (generally required to be greater than 1).

[0039] The temperature sensitivity is defined as follows:

[0040]

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

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

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

[0044] central wavenumber v0 / (cm -1 )]]> Line strength S (296 K) / (cm"2•atm -1 )]]> Low energy level energy E" / (cm -1 )]]> 7185.6 7.947E-22 1045.0579 7168.437 1.170E-20 173.3658

[0045] Step two: TDLAS measurement system building and operation

[0046] The H2O absorption test was carried out at room temperature and normal pressure to verify the normality of the experimental equipment and the accuracy of the measurement method. The designed TDLAS measurement system is shown in Figure 2 ​As shown, the sawtooth wave signal is given to the laser controller by the signal generator, so that the 1395nm and 1392nm DFB lasers generate laser of the same frequency. The signal generator adopts the product of the AFG3000C series of Tektronix. The signal generator can output two signals separately, and control the lasers with different needs. The output frequency of the experiment is 1KHz, and the phase difference of the sawtooth wave signal is 180 degrees. The two laser signals are coupled and split by the coupler. After collimation by the collimator, one signal is directly labeled by the F-P standard to the frequency and time signal. The other signal goes to the flow field to be measured for parameter diagnosis and measurement. The laser adopts the 14-pin butterfly package laser produced by NEL company, and the center wavelengths are 1395nm and 1392nm respectively. The detector is the PDA05CF2 indium gallium arsenide amplification detector of Thorlabs company. The laser controller is the LDC-3724C model driver of ILX Lightwave, and the near-infrared standard is the SA200-12B type scanning Fabry-Perot interferometer of Thorlabs company, which is a resonant cavity standard. The free spectral range is 1.5GHz (i.e. 0.05cm -1 ), which is used for labeling the frequency information of the laser and converting the time domain signal to the frequency domain signal. The signal acquisition is completed by the oscilloscope.

[0047] Step three: data acquisition and analysis processing:

[0048] The tunable diode laser absorption spectroscopy (TDLAS) technology is mainly based on Beer-Lambert law, and the relationship between the incident light intensity and the transmitted light intensity before and after the laser passing through the flow field is described 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 absorption component, X is the gas concentration of the absorption component, T is the gas temperature of the absorption component, α(v) is the absorbance, S(T) is the absorption line intensity, which describes the strength of the absorption and radiation of the molecular energy level transition. φ(v) is the absorption line shape function, which satisfies the normalization condition. It is noted that Beer-Lambert law is applicable to uniform flow field environment, and the temperature, pressure and absorption component concentration in the formula are all line-of-sight average values.

[0051] Due to the influence of various broadening mechanisms on the absorption spectrum, the molecular absorption spectrum is not a point at the center frequency, but a distributed form with a certain width; the Voigt line shape is adopted in the present application, which is the convolution of Gaussian line shape function and Lorentz line shape function.

[0052] Gaussian half width full width Δv D may be expressed as

[0053]

[0054] Lorentz half width full width Δv C may be expressed as

[0055] Δv C = P X2r(T) self + P (1 - X)2r(T) air ; (4)

[0056] where 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 of the absorbing component with the non-absorbing component:

[0057]

[0058] where n self and are the exponential factors of self-collision broadening and collision broadening with the non-absorbing component, respectively, which can be obtained from the HITRAN database or calibrated by experiments.

[0059] The integral absorption of the absorption line is defined as

[0060]

[0061] The ratio of the integral absorption of two absorption lines is taken and the logarithm is taken, and the analytical expression of the temperature can be obtained:

[0062]

[0063] where A1 / A2 is the ratio of the integral absorption of the two lines measured by experiments, and the rest of the parameters are physical constants or spectral parameters.

[0064] First, the collected data is imported into the computer, and then the iterative fitting program is used for data analysis, and the specific operation is:

[0065] 1) The integral absorption A 1，0 , A 2，0 of the two lines is roughly calculated by the measured absorption curve, and an initial temperature T1 is calculated by formula (8).

[0066] 2) Then fix the temperature T = T1, calculate the Gaussian half-peak full width Δv D1 , Δv D2 of the two absorption lines according to formula (3) C1 , Δv C2 , the center wave number v 1,0 , v 2,0 of the absorption lines, the integral absorption A1, A2 are free parameters, the Voigt line type fitting is performed on the absorption rate curve measured by experiment, the corresponding parameters are obtained, the integral absorption A 1，1 , A 2，1 of the two lines fitted out are extracted, and the new temperature T2 is calculated by formula (8).

[0067] 3) Determine whether it satisfies |T2-T1|<ξ, ξ can be valued according to requirements, and in the embodiment, ξ is 0.1, if it does not satisfy, update the temperature T = T2, and return to step 2); if it satisfies, output the temperature T, and obtain the Lorentz half-peak full width Δv C1 , Δv C2 , the center wave number v 1,0 , v 2,0 , the integral absorption A1, A2 of the two absorption lines after fitting.

[0068] 4) The gas concentration X of the absorption component and the gas pressure P of the absorption component are obtained by iterative calculation through formula (4) to formula (7) using the temperature T and the fitting parameters of one of the absorption lines, such as Δv C1 , A1.

[0069] The processing results are as follows:

[0070] Figure 3a 、 Figure 3b The Voigt fitting curves of the absorbance at 294K, 1atm, 98cm under the absorbance of 7168.437cm -1 and 7185.6cm -1 .

[0071] The flow field temperature can be calculated by making Voigt line type fitting on the absorbance curve, because the measured indoor environment is a uniform flow field, in order to ensure the measurement accuracy, the measured flow field parameters are all processed by average value, as shown in Figure 4 , the finally measured temperature is 300K, the indoor temperature is 294K, and the relative error is 2%.

[0072] The pressure measurement result of H2O is shown in Figure 5 , the pressure calculation result is 0.9895atm, and the relative error is-1.05%.

[0073] The concentration measurement result of H2O is shown in Figure 6The concentration calculation result is 0.0166, the hygrometer conversion water vapor concentration is 0.0162, and the relative error is 2.47%.

[0074] In the test at normal temperature and pressure, the measured value is consistent with the hygrometer reading, the relative error is small, the precision is high, and the feasibility of the system and method in the embodiment is verified.

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

[0076] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description manner of the specification is only for the sake of clarity, those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be combined to form other embodiments which can be understood by those skilled in the art.

Claims

1. A method for on-line measurement of temperature, concentration, pressure of complex flow field, characterized in that, The method comprises the following steps: Step one, selecting an absorption component and corresponding absorption spectrum line according to the target to be measured, wherein the selected absorption spectrum line needs to meet the following conditions: the absorption rate and signal-to-noise ratio reach a set standard, the influence of adjacent absorption spectrum lines is avoided, and the temperature sensitivity of the selected absorption spectrum line in the temperature range to be measured is greater than a set value; Step two, building 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 F-P standard device and an oscilloscope; A sawtooth wave signal is given by the signal generator to the laser controller, so that the laser generates a laser signal of the same frequency; after the two laser signals are coupled, split and collimated by the fiber coupler and the collimator, one laser signal is directly calibrated by the F-P standard device to obtain the frequency and time signal, and the other laser signal is directed to the flow field to be measured; finally, the absorption signal is received by the detector and collected by the oscilloscope to obtain the absorption rate curve; Step three, calculating the initial temperature by the obtained absorption rate curve, then fixing the temperature to perform Voigt line fitting, iteratively updating the temperature until convergence, and finally calculating the gas concentration X of the absorption component and the gas pressure P of the absorption component by using the converged temperature and the fitting parameters of the absorption spectrum line.

2. The method according to claim 1, wherein, Step one specifically comprises: Dual-color laser is used to measure the flow field parameters, that is, two laser absorption spectrum lines are used; The temperature sensitivity is defined as follows: In the formula, R=A1 / A2 is the ratio of the integral absorption rates A1 and A2 of the two laser absorption spectrum 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 and E''2 are the low-energy level energies of the two laser absorption spectrum line transitions, and T is the gas temperature of the absorption component.

3. The method of claim 2, wherein the temperature, concentration, and pressure of the complex flow field are measured on-line. Step three specifically comprises the following steps: S31, calculating the integral absorbance A of the two laser absorption lines from the absorbance curve 1,0 ,A 2,0 , calculating an initial temperature T1 based on the integral absorbance A 1,0 ,A 2,0 ​ S32, then fix the temperature T=T1, calculate the Gaussian half-height full width Δv of two laser absorption lines D1 ,Δv D2 , Lorentz half-height full width Δv C1 ,Δv C2 , center wave number v 1,0 ,v 2,0 , integral absorption A1, A2 as free parameters, Voigt line type fitting is carried out on the absorption curve of two laser absorption lines, the corresponding parameters are obtained, and the integral absorption A 1,1 ,A 2,1 of two laser absorption lines is extracted, and the new temperature T2 is calculated; S33, judging whether |T2-T1|<ξ is satisfied, if not, updating the temperature T=T2 and returning to step S32; if yes, outputting the temperature T and obtaining the Lorentz half-height full width Δv of the two fitted laser absorption spectral lines C1 ,Δv C2 、center wave number v 1,0 ,v 2,0 , integral absorption A1, A2; S34, iteratively calculating the gas concentration X of the absorption component and the gas pressure P of the absorption component by using the temperature T and the fitting parameters of any one laser absorption spectrum line.

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