CN111398205B - Infrared absorption spectrum isotope abundance detection method based on temperature gradient field compensation - Google Patents
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Abstract
A method for detecting isotope abundance of infrared absorption spectrum based on temperature gradient field compensation belongs to the field of infrared laser absorption spectrum, and comprises the steps of firstly, carrying out three-dimensional grid division on a gas to be detected according to the distribution and the optical path of a measuring optical path, so that only one measuring light source passes through each grid; establishing a measured gas temperature gradient field model, and acquiring a measured gas temperature gradient field theoretical database; then measuring the outer surface temperature of the measured gas container by using a high-precision temperature sensor to obtain the characteristic temperature of the measured gas, and fitting a temperature gradient field by using a fitting algorithm according to the characteristic temperature of the measured gas to obtain the temperature gradient field of the measured gas; and finally, controlling a signal excitation device through a microcomputer, exciting a laser to respectively emit light and heavy isotope detection light, acquiring a detection result through an acquisition device, and combining a temperature gradient field of the gas to be detected to obtain the isotope abundance.
Description
Technical Field
The invention belongs to the field of infrared laser absorption spectroscopy, and particularly relates to an infrared absorption spectroscopy isotope abundance detection method based on temperature gradient field compensation.
Background
With the development of science and technology, isotope analysis has been widely researched and applied in the fields of science and environmental protection, ecological environment, ecological agriculture, food, medical detection, mineral exploration, nuclear industry, geochemistry, and the like, and is increasingly paid attention to. In particular in the field of geochemistry, early in the 80's of the 20 th century, researchers have noted problems with environmental isotope technology in exploring scientific aspects related to seismic prediction, and accurate measurement of isotope abundances is the basis for these studies and applications.
Currently, the detection of isotopic abundance is mainly based on mass spectrometry and infrared absorption spectroscopy (TDLAS). The mass spectrometry technology has the longest development history and higher precision and sensitivity, and is the main mode for isotope detection at present. However, the mass spectrometry has some defects, such as complex structure, large volume, sample pretreatment, complex operation process and high cost, which greatly limit the application of the mass spectrometry. Compared with the prior art, the infrared absorption spectrum technology has the advantages of simple structure, small volume, low cost, capability of adapting to complex application environments and the like, and is favored by scholars at home and abroad.
In recent years, infrared absorption spectroscopy technology has been developed greatly, and detection performance is improved continuously. Becker in Joseph F.S. utilizes a tunable semiconductor laser to obtain closer CO based on double-light-source scanning 2 Isotope absorption lines and use of this technique for detecting CO 2 Isotope abundance, and accuracy reaches 0.4%. Dvaid E.Cooper et al, based on TDLAS technology, have detected CO in human respiratory gases using a 1.6 μm band laser 2 In gas 13 C isotope, the accuracy reaches 0.4 percent. Kasyutich et al in UK based on continuous thermoelectric cooling distributed feedback quantum cascade laser and uses absorption spectroscopy technology to CO 2 The isotope is detected with the accuracy of 0.05-0.2 per mill. Yangchunhua et al invented a temperature compensation method for detecting oxygen concentration in a glass bottle by using a wavelength modulation spectrum, and the accuracy of the system was improved. Although the method improves the detection accuracy, the influence of the temperature field of the detected gas on the measurement is not considered, so that the detection result still has errors compared with the actual value.
Disclosure of Invention
The invention aims to provide an infrared absorption spectrum isotope abundance detection method based on temperature gradient field compensation, which aims to solve the problem that the detection result still has errors compared with a real value because the influence of a temperature field of a detected gas on measurement is not considered when isotope abundance is detected in the prior art.
The purpose of the invention is realized by the following technical scheme: the infrared absorption spectrum isotope abundance detection method based on temperature gradient field compensation is characterized by comprising the following steps which are sequentially carried out:
step 1: according to the distribution of the measuring light path and the light path, three-dimensional grid division is carried out on the measured gas, so that only one measuring light source in each grid passes through the grid, and the temperature field grid data of the measured gas are obtained;
step 2: establishing a measured gas temperature gradient field model, acquiring a measured gas temperature gradient field theoretical database by using the temperature field grid data of the measured gas in the step 1, and storing the database in a microcomputer;
the input quantity of the measured gas temperature gradient field model is constant heating power p, temperature field grid data and heating time T of the measured gas, and the output quantity is measured gas temperature gradient field theoretical data T;
and 3, step 3: measuring the temperature of the outer surface of a container containing the measured gas, and storing the measured temperature data into a microcomputer to obtain the characteristic temperature of the measured gas, wherein the characteristic temperature is the temperature of the outer surface of the container containing the measured gas when the isotope abundance is measured;
and 4, step 4: determining the temperature gradient field of the measured gas: comparing the characteristic temperature of the measured gas in the step 3 with the theoretical database of the temperature gradient field of the measured gas obtained in the step 2, traversing all the theoretical data T of the temperature gradient field of the measured gas in the step 2, and searching data consistent with the characteristic temperature of the measured gas to obtain the temperature gradient field of the measured gas;
and 5: and (4) controlling a signal excitation device to emit an excitation signal through a microcomputer, driving a laser to emit light and heavy isotope detection light respectively by the excitation signal, storing the output light intensity to the microcomputer by a collection device, and combining the temperature gradient field of the detected gas obtained in the step (4) to obtain the isotope abundance.
In step 1, the three-dimensional mesh division process is as follows: the method comprises the steps of dividing a gas to be measured into n equal parts on a cross section perpendicular to a light path, wherein each part is provided with a light spot, the part on a path parallel to the light path is divided into m equal parts, the length of the light path in each grid is L/m, L is the length of a container for containing the gas to be measured, and the total part of three-dimensional grids of the gas to be measured is nxm.
Further, in step 2, the measured gas temperature gradient field theoretical database is a set of measured gas temperature gradient field theoretical data obtained through an established unsteady state heat conduction equation and boundary conditions in the measured gas temperature gradient field model, wherein the input quantity of the measured gas temperature gradient field model is constant heating power p, the temperature field grid data and heating time T of the measured gas, and the output quantity is measured gas temperature gradient field theoretical data and is represented by T (p, n, m, T);
unsteady state heat conduction equation:
boundary conditions:
wherein, the ratio of x,
z is the axial, angle and radial coordinate of the cylindrical coordinate system, and n in the theoretical database of the temperature gradient field of the measured gas is n (x, is greater than or equal to n)>
) Denotes that m is m (` H `)>
z) represents that R is the radius of a circular surface of a container for containing the measured gas, lambda is a heat conductivity coefficient, rho is the density of the measured gas, c is the heat capacity of the measured gas, T is the theoretical temperature of the measured gas at a certain position, R is a heat conduction boundary, R is the temperature of the measured gas MPC Is a coordinate set of the outer surface of the measured gas, T 1 Is the initial temperature of the gas being measured.
Further, in step 3, the method for measuring the characteristic temperature of the measured gas comprises: taking X temperature measuring points on the outer surface of a container containing the measured gas, measuring the temperature by using a temperature sensor to obtain the characteristic temperature T of the measured gas i And i is 1 to X, and the characteristic temperature of the gas to be measured is the temperature of the outer surface of the container containing the gas to be measured when the isotopic abundance is measured.
Further, in step 4, the method for determining the temperature gradient field of the measured gas comprises: according to the measured gasCharacteristic temperature T of body i Searching the theoretical database of the temperature gradient field of the measured gas, traversing all the theoretical data of the temperature gradient field of the measured gas in the step 2 to ensure that T is equal to T i And T (p, n) i M, T) or T (p, n, m) i And t) are identical.
Further, in step 5, the isotope abundance is calculated by selecting absorption lines of the light and heavy isotopes to perform infrared absorption spectroscopy detection respectively, the temperature gradient distribution conditions of the light and heavy isotopes are substituted in formula (3) respectively,
simultaneously measuring the emergent light intensity I of the measured gas 0 Absorption intensity of light I t And pressure P, the isotope abundance can be obtained after the concentrations of the light isotope and the heavy isotope are compared; wherein, L is optical path, M is relative molecular mass, C is measured isotope concentration, n is the number of equal parts of measured gas according to the section vertical to the optical path, each part has a light spot, M is the number of equal parts of the path parallel to the optical path, S is line intensity, and g is line type.
Through the design scheme, compared with the prior art, the invention can bring the following beneficial effects: according to the infrared absorption spectrum isotope abundance detection method based on temperature gradient field compensation, the unsteady-state temperature gradient field of the measured gas is obtained by establishing the temperature gradient field model of the measured gas, and the temperature gradient field of the measured gas during measurement is combined with the isotope abundance calculation method, so that the measured temperature value of the measured gas during measurement is more in line with the actual situation, and the accuracy of isotope abundance calculation is improved.
Drawings
Fig. 1 is a block diagram of a device structure adopted in an infrared absorption spectrum isotope abundance detection method based on temperature gradient field compensation in an embodiment of the present invention;
FIG. 2 is a detection flow chart of the method for detecting isotope abundance in infrared absorption spectrum based on temperature gradient field compensation according to the present invention;
fig. 3 is a temperature gradient field when the initial temperature of the gas to be detected is 22.5 degrees celsius and the gas is heated for 30 minutes in the method for detecting isotope abundance by infrared absorption spectroscopy based on temperature gradient field compensation according to the embodiment of the present invention;
fig. 4 is an analysis diagram of experimental measurement data in the infrared absorption spectrum isotope abundance detection method based on temperature gradient field compensation according to the embodiment of the present invention.
Detailed Description
The invention provides an infrared absorption spectrum isotope abundance detection method based on temperature gradient field compensation, which comprises the steps of firstly, carrying out three-dimensional grid division on a gas to be detected according to the distribution and the optical path of a measuring optical path, and enabling only one measuring light source in each grid to pass through; establishing a measured gas temperature gradient field model, and acquiring a measured gas temperature gradient field theoretical database; then measuring the outer surface temperature of the measured gas container by using a high-precision temperature sensor to obtain the characteristic temperature of the measured gas, and fitting a temperature gradient field by using a fitting algorithm according to the characteristic temperature of the measured gas to obtain the temperature gradient field of the measured gas; finally, controlling a signal excitation device through a microcomputer, exciting a laser to respectively emit light and heavy isotope detection light, acquiring a detection result through an acquisition device, and combining a temperature gradient field of a gas to be detected to obtain isotope abundance;
the method specifically comprises the following steps which are carried out in sequence:
step 1: according to the distribution of the measuring light path and the light path, three-dimensional grid division is carried out on the measured gas, so that only one measuring light source in each grid passes through the grid, and the temperature field grid data of the measured gas are obtained;
step 2: establishing a temperature gradient field model of the measured gas: acquiring a temperature gradient field theoretical database of the measured gas by using the temperature field grid data of the measured gas in the step 1;
the input quantity of the measured gas temperature gradient field model is constant heating power p, temperature field grid data and heating time T of the measured gas, and the output quantity is measured gas temperature gradient field theoretical data T;
and step 3: measuring the temperature of the outer surface of a container containing the measured gas, and storing the measured temperature data into a microcomputer to obtain the characteristic temperature of the measured gas, wherein the characteristic temperature is the temperature of the outer surface of the container containing the measured gas when the isotope abundance is measured;
and 4, step 4: determining the temperature gradient field of the measured gas: comparing the characteristic temperature of the measured gas with the theoretical database of the temperature gradient field of the measured gas obtained in the step 2 according to the step 3, traversing all the theoretical data T of the temperature gradient field of the measured gas in the step 2, and searching data consistent with the characteristic temperature of the measured gas to obtain the temperature gradient field of the measured gas;
and 5: and (4) controlling a signal excitation device to give an excitation signal through a microcomputer, driving a laser to respectively send out light and heavy isotope detection light, storing the output light intensity to the microcomputer through an acquisition device, and combining the temperature gradient field of the gas to be detected acquired in the step (4) to obtain the isotope abundance.
In the step 1, the three-dimensional mesh division process is to divide the gas to be measured into n equal parts on a cross section perpendicular to the light path, each part has a light spot, and the part is divided into m equal parts on a path parallel to the light path, the length of the light path in each mesh is L/m, L is the length of a container for containing the gas to be measured, and the total number of the three-dimensional meshes of the gas to be measured is n × m.
The measured gas temperature gradient field theoretical database in the step 2 is a set of measured gas temperature gradient field theoretical data obtained through an established unsteady heat conduction equation and boundary conditions in a measured gas temperature gradient field model, wherein the input quantity of the measured gas temperature gradient field model is constant heating power p, the temperature field grid data and heating time T of the measured gas, and the output quantity is measured gas temperature gradient field theoretical data and is represented by T (p, n, m, T);
unsteady state heat conduction equation:
boundary conditions:
wherein, the ratio of x,
z is axial, angle and radial coordinate of the cylindrical coordinate system, and n is n (x, in the temperature gradient field theory database of the measured gas temperature>
) Denotes that m is m (` H `)>
z) represents that R is the radius of a circular surface of a container for containing the measured gas, lambda is a heat conductivity coefficient, rho is the density of the measured gas, c is the heat capacity of the measured gas, T is the theoretical temperature of the measured gas at a certain position, R is a heat conduction boundary, R is the temperature of the measured gas MPC Is a coordinate set of the outer surface of the measured gas, T 1 Is the initial temperature of the gas being measured. />
The method for measuring the characteristic temperature of the measured gas in the step 3 comprises the following steps: taking X temperature measuring points on the outer surface of a container containing the measured gas, and measuring the temperature by using a temperature sensor to obtain the characteristic temperature T of the measured gas i And i is 1 to X, and the characteristic temperature of the gas to be measured is the temperature of the outer surface of the container containing the gas to be measured when the isotopic abundance is measured.
The method for determining the temperature gradient field of the measured gas in the step 4 comprises the following steps: according to the characteristic temperature T of the measured gas i Searching the theoretical database of the temperature gradient field of the measured gas, traversing all the theoretical data of the temperature gradient field of the measured gas in the step 2 to ensure that T is equal to T i And T (p, n) i M, T) or T (p, n, m) i And t) are identical.
Wherein, the calculation method of the isotope abundance in the step 5 is to select the absorption lines of the light isotope and the heavy isotope to respectively carry out infrared absorption spectrometry detection, the temperature gradient distribution conditions of the light isotope and the heavy isotope are respectively substituted in the formula (3),
simultaneously measuring the emergent light intensity I of the measured gas 0 Absorption intensity of light I t And pressure P, the isotope abundance can be obtained after the concentrations of the light isotope and the heavy isotope are compared; wherein, L is optical path, M is relative molecular mass, C is measured isotope concentration, n is the number of parts of gas to be measured which are equally divided on a section perpendicular to the optical path, each part has a light spot, M is the number of parts of the path parallel to the optical path, S is line intensity, g is line type, wherein the line type g can be expressed as follows by taking Lorentz line type as an example:
wherein P is 0 And T 0 Respectively reference pressure and reference temperature, v air Is the air broadening coefficient;
the line strength S can be expressed as:
wherein S (T) 0 ) Is the initial value of linear intensity, Q (T) is the molecular distribution function of the absorbed gas, E n The three are given by HITRAN database as lower energy level energy, h is Planck constant, c is speed of light, k is Boltzmann constant, Q (T) 0 ) Assigning an initial value of a function, v, to the absorbed gas molecule 0 The center wavelength.
In order to better understand the technical scheme of the invention, the following description is further provided for the implementation mode of the invention with the accompanying drawings; well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.
As shown in fig. 1, the device adopted by the infrared absorption spectrum isotope abundance detection method based on temperature gradient field compensation comprises a multi-pass cell, a laser, a signal excitation device, a microcomputer, an acquisition device and a temperature sensor. Using a microcomputer as a core, controlling a signal excitation device to excite a laser to output detection light with corresponding wavelengths of light isotopes and heavy isotopes through the microcomputer, and emitting the detection light into a multi-channel cell to measure a gas to be detected; acquiring a signal with isotope abundance information by an acquisition device, and storing the signal into a microcomputer; meanwhile, the temperature gradient field model of the measured gas is stored in the microcomputer, the temperature field of the measured gas is retrieved by collecting signals of the temperature sensor, compensation calculation is further carried out, and accurate isotope abundance is obtained, wherein the specific detection process is shown in fig. 2.
With CO 2 Is/are as follows 13 C/ 12 The isotope C is taken as an example to explain the implementation process of the infrared absorption spectrum isotope abundance detection method based on temperature gradient field compensation, and comprises the following steps:
step 1: the multi-pass tank for containing the gas to be measured is of a hollow cylindrical structure, the radius is 30mm, the length is 190mm, and 300 light spots are uniformly distributed on the circular surface of the multi-pass tank; thus, the round surface was divided into 300 portions each having an area of 12mm 2 A square of (a); dividing each square into 19 parts perpendicular to the direction of the round surface, wherein the length of each part is 10mm; therefore, each three-dimensional grid is provided with a section of light spot with the length of 10mm, and 570 three-dimensional grids are provided;
and 2, step: according to the actual situation, establishing an unsteady heat conduction equation and boundary conditions of the measured gas, setting the initial temperature condition of the measured gas to be 22.5 ℃, the heating power to be 10W and the target temperature to be 23 ℃, obtaining unsteady solutions under different heating powers, forming a measured gas temperature gradient field theoretical database, and showing that the initial temperature of the measured gas is 22.5 ℃ and the measured gas temperature gradient field is heated for 30 minutes in fig. 3;
and step 3: uniformly taking 10 temperature measuring points on the outer surface of a multi-pass cell containing the measured gas, which is vertical to the circular surface, and measuring the temperature by adopting a high-precision temperature sensor to obtain 10 characteristic temperatures of the measured gas;
and 4, step 4: comparing the 10 measured gas characteristic temperatures obtained in the step 3 with the measured gas temperature gradient field theoretical database obtained in the step 2, and retrieving to obtain the temperature gradient field of the measured gas at the moment;
and 5: selecting 13 CO 2 、 12 CO 2 Respectively 4078.022cm -1 And 4978.202cm -1 Respectively exciting the laser with the wavelength output by using a signal excitation device, and acquiring a detection result by using an acquisition device; output of 13 CO 2 、 12 CO 2 Respectively substituting the detection results into I in formula (3) t Respectively substituting the other parameters into the temperature gradient field of the measured gas obtained in the step 4 to obtain 13 CO 2 、 12 CO 2 The concentration of the isotope is obtained by dividing the two, the isotope abundance can be obtained, the obtained result is shown in figure 4, along with the change of time, the temperature field is close to uniform, the isotope abundance is close to a standard value, and when the temperature difference inside and outside the multi-pass cell containing the gas to be measured is more than 100mK, the isotope measurement accuracy can be improved by more than 0.15 per thousand.
Claims (4)
1. The infrared absorption spectrum isotope abundance detection method based on temperature gradient field compensation is characterized by comprising the following steps which are sequentially carried out:
step 1: according to the distribution and the optical path of the measuring optical path, three-dimensional grid division is carried out on the measured gas, only one measuring light source in each grid passes through the three-dimensional grid division, and temperature field grid data of the measured gas are obtained;
step 2: establishing a measured gas temperature gradient field model, acquiring a measured gas temperature gradient field theoretical database by using the temperature field grid data of the measured gas in the step 1, and storing the database in a microcomputer;
the input quantity of the measured gas temperature gradient field model is constant heating power p, temperature field grid data and heating time T of the measured gas, and the output quantity is measured gas temperature gradient field theoretical data T;
and step 3: measuring the outer surface temperature of a container containing the measured gas, and storing the measured temperature data into a microcomputer to obtain the characteristic temperature of the measured gas, wherein the characteristic temperature is the outer surface temperature of the container containing the measured gas when the isotope abundance is measured;
and 4, step 4: determining the temperature gradient field of the measured gas: comparing the characteristic temperature of the measured gas with the theoretical database of the temperature gradient field of the measured gas obtained in the step 2 according to the step 3, traversing all the theoretical data T of the temperature gradient field of the measured gas in the step 2, and searching data consistent with the characteristic temperature of the measured gas to obtain the temperature gradient field of the measured gas;
and 5: controlling a signal excitation device to emit an excitation signal through a microcomputer, driving a laser to emit light and heavy isotope detection light respectively through the excitation signal, storing output light intensity to the microcomputer through an acquisition device, and combining the temperature gradient field of the gas to be detected acquired in the step 4 to obtain isotope abundance;
in step 1, the three-dimensional mesh division process is as follows: dividing the gas to be measured into n equal parts on a section perpendicular to a light path, wherein each part is provided with a light spot, the path parallel to the light path is divided into m equal parts, the length of the light path in each grid is L/m, L is the length of a container for containing the gas to be measured, and the total number of three-dimensional grids of the gas to be measured is nxm;
in step 2, the measured gas temperature gradient field theoretical database is a set of measured gas temperature gradient field theoretical data obtained through an established unsteady state heat conduction equation and boundary conditions in a measured gas temperature gradient field model, wherein the input quantity of the measured gas temperature gradient field model is constant heating power p, the temperature field grid data and heating time T of the measured gas, and the output quantity is measured gas temperature gradient field theoretical data and is represented by T (p, n, m, T);
unsteady state heat conduction equation:
boundary conditions are as follows:
wherein, the ratio of x,
z is the axial, angle and radial coordinate of the cylindrical coordinate system, and n in the theoretical database of the temperature gradient field of the measured gas body is used for ^ n>
Denotes that m is m->
The expression that R is the radius of a circular surface of a container for containing the measured gas, lambda is the heat conductivity coefficient, rho is the density of the measured gas, c is the heat capacity of the measured gas, T is the theoretical temperature of the measured gas at a certain position, R is a heat conduction boundary, R is the temperature of the measured gas MPC Set of coordinates of the outer surface of the measured gas, T 1 Is the initial temperature of the gas being measured.
2. The infrared absorption spectrum isotope abundance detection method based on temperature gradient field compensation as claimed in claim 1, characterized in that: in step 3, the method for measuring the characteristic temperature of the measured gas comprises the following steps: taking X temperature measuring points on the outer surface of a container containing the measured gas, measuring the temperature by using a temperature sensor to obtain the characteristic temperature T of the measured gas i And i is 1 to X, and the characteristic temperature of the gas to be measured is the temperature of the outer surface of the container containing the gas to be measured when the isotopic abundance is measured.
3. The infrared absorption spectrum isotope abundance detection method based on temperature gradient field compensation as claimed in claim 2, characterized in that: in step 4, the method for determining the temperature gradient field of the measured gas comprises the following steps: according to the characteristic temperature T of the measured gas i Searching the theoretical database of the temperature gradient field of the measured gas, and traversing the temperature gradient field of the measured gas in the step 2All measured gas temperature gradient field theoretical data of the theoretical database enable T i And T (p, n) i M, T) or T (p, n, m) i And t) are identical.
4. The infrared absorption spectrum isotope abundance detection method based on temperature gradient field compensation as claimed in claim 3, characterized in that: in the step 5, the isotope abundance is calculated by selecting absorption lines of light and heavy isotopes to respectively carry out infrared absorption spectrometry detection, the temperature gradient distribution conditions of the light and heavy isotopes are respectively substituted in the formula (3),
simultaneously measuring the emergent light intensity I of the measured gas 0 Absorption intensity of light I t And pressure P, obtaining isotope abundance after the concentrations of the light and heavy isotopes are compared; wherein, L is an optical path, M is relative molecular mass, C is measured isotope concentration, n is the number of parts of measured gas evenly divided on a section vertical to the optical path, each part is provided with a light spot, M is the number of parts evenly divided on a path parallel to the optical path, S is line intensity, and g is line type.
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