Anti-dielectric constant drift gas-liquid two-phase flow holdup measurement method based on resonant cavity

Abstract

The invention provides an anti-dielectric constant drift gas-liquid two-phase flow holdup measurement method based on a resonant cavity. The method comprises the following steps: obtaining a relative dielectric constant according to a resonant frequency change; obtaining an effective dielectric constant according to a gas-liquid two-phase position relation; obtaining a gas-phase resonant frequency and a liquid-phase resonant frequency according to the relative dielectric constant and the effective dielectric constant; obtaining a normalized resonant frequency through the gas-phase resonant frequency and the liquid-phase resonant frequency; fitting the normalized resonant frequency into a theoretical phase volume fraction reference value through a perturbation method based on a resonant cavity working mode; based on the theoretical phase holdup reference value, combining the change of the liquid phase holdup and the liquid phase dielectric constant to obtain the resonant frequency variation; and obtaining a quality factor through a perturbation method, and carrying out decoupling operation on the resonant frequency variation to obtain a real phase volume fraction. According to the method, by introducing a quality factor variable and decoupling liquid phase volume fraction fluctuation caused by electrical property change and phase volume fraction change, the precision and accuracy of phase volume fraction measurement are improved.

Description

Technical Field

[0001] The present invention relates to the field of electronic information technology, and particularly to a method for measuring the gas-liquid two-phase flow void fraction based on a resonant cavity and resistant to dielectric constant drift. Background Art

[0002] A microwave resonant cavity is an electrical detection device that can interact with the electromagnetic properties (such as dielectric constant) of a target object to detect changes in these physical parameters. When the electromagnetic properties of an object change, it will affect the electromagnetic field distribution in the resonant cavity, thereby changing the resonant frequency and quality factor of the cavity. Since a multiphase flow is composed of a mixture of different media, factors such as the phase void fraction and the type of medium will affect the overall dielectric constant of the multiphase flow. By measuring the change in the dielectric constant, the microwave resonant cavity can effectively calculate data such as the phase void fraction.

[0003] Monitoring of multiphase flow in industrial processes often requires long-term on-site testing, and changes in external environmental factors (such as temperature, pressure, etc.) may cause changes in the electrical properties of the fluid to be measured. As the measurement time extends, physical and chemical properties such as the salinity, salt content, and viscosity of the fluid may fluctuate, and these changes will directly affect the electrical characteristics of the fluid, thereby introducing cumulative errors. Therefore, it is very necessary to design a method for measuring the gas-liquid two-phase flow void fraction based on a resonant cavity and resistant to dielectric constant drift. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for measuring the gas-liquid two-phase flow void fraction based on a resonant cavity and resistant to dielectric constant drift. By introducing a quality factor variable and decoupling the liquid-phase volume fraction fluctuations caused by changes in electrical properties and changes in the phase void fraction, the accuracy and precision of the phase void fraction measurement are improved.

[0005] To achieve the above purpose, the present invention provides the following scheme:

[0006] A method for measuring the gas-liquid two-phase flow void fraction based on a resonant cavity and resistant to dielectric constant drift includes the following steps:

[0007] Calculate the relative dielectric constant based on the change in the resonant frequency of the resonant cavity;

[0008] Obtain the equivalent dielectric constant according to the positional relationship between the gas phase and the liquid phase;

[0009] Obtain the gas-phase resonant frequency and the liquid-phase resonant frequency respectively based on the relative dielectric constant and the equivalent dielectric constant;

[0010] Obtain the normalized resonant frequency through the gas-phase resonant frequency and the liquid-phase resonant frequency;

[0011] Based on the working mode of the resonator, the normalized resonance frequency is fitted to the theoretical phase fraction reference value by the perturbation method; the working modes include: TE mode and TM mode; the TE mode includes: the first TE mode and the second TE mode;

[0012] Based on the theoretical phase fraction reference value, the change in resonance frequency is obtained by combining the changes in liquid phase fraction and liquid phase dielectric constant; the change in resonance frequency includes: the resonance frequency change due to phase fraction and the resonance frequency change due to dielectric constant;

[0013] The quality factor is obtained by the perturbation method, and the decoupling operation is performed on the resonance frequency change using the quality factor to obtain the true phase fraction.

[0014] Optionally, the calculation formula for the relative dielectric constant is: where ε r is the relative dielectric constant, Δf is the resonance frequency offset, r1 is the radius of the cylindrical perturbation, a, b, and l are the length, width, and height of the resonator respectively, p is the number of standing waves in the Z-axis direction, dv is the volume element of the resonator, E0 is the electric field strength in the cavity before perturbation, and f r is the resonance frequency before perturbation.

[0015] Optionally, the calculation formula for the equivalent dielectric constant is: ε || = ρ1ε pipe + ρ2ε liquid + ρ3ε gas ; where ε ∥ is the equivalent dielectric constant, ρ1, ρ2, and ρ3 are the phase fractions of the pipe, liquid phase, and gas phase respectively, and ε pipe , ε liquid and ε gas are the dielectric constants of the pipe, liquid phase, and gas phase respectively.

[0016] Optionally, the calculation formulas for the gas phase resonance frequency and the liquid phase resonance frequency are respectively: where f empty is the gas phase resonance frequency, and f full is the liquid phase resonance frequency.

[0017] Optionally, the calculation formula for the normalized resonance frequency is: where f' holdup and f holdup are the normalized resonance frequency and the resonance frequency in a certain liquid phase fraction state respectively, and ρ liquid,holdup is the proportion of the liquid phase volume in the total volume of the gas-liquid two-phase flow in the pipe.

[0018] Optionally, the calculation formula for the theoretical phase fraction reference value is: where, is the proportion of the liquid volume in the second TE mode to the total volume of the gas-liquid two-phase flow in the pipeline, f′ TE2,holdup is the normalized resonance frequency in the second TE mode, is the quadratic coefficient of the fitting, is the linear coefficient of the fitting.

[0019] Optionally, the calculation formula for the change in the resonance frequency of the phase holdup is: where, Δf′ holdup and Δf holdup are the change in the resonance frequency of the normalized phase holdup and the change in the resonance frequency of the phase holdup respectively, and Δρ2 is the change in the liquid phase holdup;

[0020] The calculation formula for the change in the resonance frequency of the dielectric constant is: where, Δf′ permittivity and Δf permittivity are the change in the resonance frequency of the normalized dielectric constant and the change in the resonance frequency of the dielectric constant respectively, and Δε liquid is the change in the liquid phase dielectric constant.

[0021] Optionally, the calculation formula for the quality factor is: where, Q is the quality factor after perturbation, and Q0 is the quality factor before perturbation.

[0022] Optionally, the calculation formula for the true phase holdup is: where, is the true phase holdup, f′ TE2,total is the change in the resonance frequency of the phase holdup in the second TE mode, and Δf′ TE2,permittivity is the change in the resonance frequency of the dielectric constant in the second TE mode.

[0023] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: The method for measuring the gas-liquid two-phase flow holdup based on a resonant cavity provided by the present invention, which includes: calculating the relative dielectric constant according to the change in the resonance frequency of the resonant cavity; obtaining the equivalent dielectric constant according to the position relationship between the gas phase and the liquid phase; obtaining the gas phase resonance frequency and the liquid phase resonance frequency according to the relative dielectric constant and the equivalent dielectric constant respectively; obtaining the normalized resonance frequency through the gas phase resonance frequency and the liquid phase resonance frequency; based on the working mode of the resonant cavity, fitting the normalized resonance frequency to the theoretical phase holdup reference value by the perturbation method; based on the theoretical phase holdup reference value, obtaining the change in the resonance frequency in combination with the change in the liquid phase holdup and the liquid phase dielectric constant; obtaining the quality factor by the perturbation method, and decoupling the change in the resonance frequency using the quality factor to obtain the true phase holdup. This method improves the accuracy and precision of the phase holdup measurement by introducing the quality factor variable and decoupling the fluctuations in the liquid phase volume fraction caused by the changes in the electrical properties and the phase holdup. Brief Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 It is a flowchart of the gas-liquid two-phase flow void fraction measurement method of the present invention. Detailed Embodiments

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0027] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0028] As Figure 1 shown, the present invention provides a method for measuring the gas-liquid two-phase flow void fraction based on a resonant cavity, including the following steps:

[0029] Step 100: Calculate the relative permittivity according to the change in the resonant frequency of the resonant cavity;

[0030] Specifically, the calculation formula for the relative permittivity is:

[0031]

[0032] where ε r is the relative permittivity of the perturbation, Δf is the offset of the resonant frequency, r1 is the radius of the cylindrical perturbation, a, b, and l are the length, width, and height of the resonant cavity respectively, p is the number of standing waves in the Z-axis direction, dv is the volume element of the resonant cavity, E0 is the electric field strength in the cavity before perturbation, and f r is the resonant frequency before perturbation.

[0033] Further, according to whether there are electric and magnetic field components in the Z-axis direction of the resonant cavity, the working modes of the resonant cavity are divided into two modes: the TE mode (the electric field component is 0 and the magnetic field component is not 0) and the TM mode (the electric field component is not 0 and the magnetic field component is 0). In this embodiment, to ensure that the electric field direction in the resonant cavity is consistent and only exists in the x or y direction, and the electric field magnitude in the Z-axis direction is 0, the TE mode is selected. The p value of 1 or 2 corresponds to the first TE mode TE1 and the second TE mode TE2, respectively.

[0034] Step 200: Obtain the equivalent dielectric constant according to the positional relationship between the gas-liquid two-phase.

[0035] Specifically, when the gas-liquid interface is parallel to the electric field lines, the equivalent dielectric constant ε ∥ is:

[0036] ε || = ρ1ε pipe + ρ2ε liquid + ρ3ε gas ;

[0037] where ρ1, ρ2, and ρ3 are the phase holdups of the pipeline, liquid phase, and gas phase, respectively, and ε pipe , ε liquid and ε gas are the dielectric constants of the pipeline, liquid phase, and gas phase, respectively.

[0038] Step 300: Obtain the gas-phase resonant frequency and the liquid-phase resonant frequency according to the relative dielectric constant and the equivalent dielectric constant, respectively.

[0039] Specifically, stratified flow is used as the flow pattern of the measured gas-liquid two-phase flow, and by changing the height of the gas-liquid interface, the liquid-phase holdup traverses from 0% to 100%. The conversion relationship between the liquid level height and the phase holdup is:

[0040]

[0041] where ρ is the liquid-phase holdup, h is the liquid level height, and R is the radius of the pipeline to be measured. In the laminar flow pattern, the gas-liquid interface is parallel to the electric field lines. According to the comprehensive calculation of the relative dielectric constant and the equivalent dielectric constant, the resonant frequency f can be obtained:

[0042]

[0043] When the medium is all gas phase (empty field) or liquid phase (full field), the gas-phase resonant frequency f empty and the liquid-phase resonant frequency f full are respectively:

[0044]

[0045] Step 400: Obtain the normalized resonance frequency from the gas-phase resonance frequency and the liquid-phase resonance frequency;

[0046] Specifically, the resonance frequencies of the empty field and the full field can be directly measured by injecting gas or liquid into the sensor. After that, the frequencies under any other liquid-phase holdup states can be normalized using f empty and f full That is:

[0047]

[0048] where f' holdup and f holdup are the normalized resonance frequency and the resonance frequency under a certain liquid-phase holdup state respectively, ρ liquid,holdup is the proportion of the liquid-phase volume in the total volume of the gas-liquid two-phase flow in the pipeline, and the parameters with the word "holdup" in the subscript all represent those obtained from the change in the phase holdup.

[0049] Step 500: Based on the working mode of the resonant cavity, fit the normalized resonance frequency to the theoretical phase holdup reference value by the perturbation method;

[0050] Specifically, when the dielectric constants of the gas and liquid in the pipeline remain unchanged, the change in the normalized resonance frequency caused by the perturbation is equal to the liquid-phase holdup of the gas-liquid two-phase flow. When the resonant cavity resonates in the TE2 mode, the electric field intensity around the pipeline position is the largest, and a higher sensitivity can be obtained. Therefore, in this embodiment, the resonance frequency f2 in the TE2 mode is selected to calculate the liquid holdup.

[0051] In the TE2 mode, if the pipeline volume does not meet the condition of being much smaller than the resonant cavity volume, the perturbation method assumption is not satisfied. Therefore, the formula is used to fit the normalized resonance frequency f′ TE2,holdup in the second TE mode to the theoretical phase holdup reference value where is the quadratic coefficient of the fit, is the linear coefficient of the fit

[0052] Step 600: Based on the theoretical phase holdup reference value, obtain the resonance frequency change amount by combining the changes in the liquid-phase holdup and the liquid-phase dielectric constant; the resonance frequency change amount includes: the phase holdup resonance frequency change amount and the dielectric constant resonance frequency change amount;

[0053] Specifically, due to the changes in external factors such as temperature and pressure during the long-term process of the sensor, the actual liquid-phase dielectric constant ε liquid may also change. For long-term measurements, these factors will bring inevitable cumulative errors to the liquid-phase volume measurement. In this embodiment, it is assumed that the current liquid-phase holdup is ρ2, so as to obtain the change Δρ2 in the liquid-phase holdup and the change Δε liquidThe corresponding resonant frequency changes caused are respectively:

[0054]

[0055] Among them, Δf′ holdup and Δf holdup are respectively the normalized phase fraction resonant frequency change and the phase fraction resonant frequency change, and Δf′ permittivity and Δf permittivity are respectively the normalized dielectric constant resonant frequency change and the dielectric constant resonant frequency change. However, Δf' holdup and Δf' permittivity have similar forms. When both of them change simultaneously, it is impossible to distinguish the effects of the phase fraction and the dielectric constant on the volume fraction. Therefore, by introducing the quality factor, the changes of the phase fraction and the dielectric constant are decoupled.

[0056] Step 700: Obtain the quality factor by the perturbation method, and use the quality factor to perform a decoupling operation on the resonant frequency change to obtain the true phase fraction.

[0057] Specifically, the calculation formula of the quality factor Q is:

[0058]

[0059] Among them, Q is the quality factor after perturbation, and Q0 is the quality factor before perturbation.

[0060] The quality factor reflects the overall energy storage capacity of the resonant cavity. In this embodiment, the quality factor Q of the TE1 mode of the resonant cavity is used TE1 . Replace f holdup in the normalized resonant frequency calculation formula with Q TE1 to obtain the normalized quality factor Q' TE1,holdup , and through the formula

[0061]

[0062] obtain the phase fraction of Q TE1 where and and are respectively the coefficients of the quadratic term and the linear term.

[0063] Furthermore, when ε r changes, Q will increase by a certain additional change amount. A parameter k calculated by least squares estimation is introduced into the change amount of the dielectric constant ΔQ' permittivity caused by the change of the quality factor to improve the change amount of the dielectric constant. The relevant formula is as follows:

[0064]

[0065] k = ΔQ' TE1,permittivity × (Δf′ TE2,permittivity ) + ;

[0066] wherein, Δf' permittivity and ΔQ' permittivity are both measurement result matrices under multiple experimental conditions, and (Δf' permittivity ) + is the pseudo-inverse matrix of Δf' permittivity .

[0067] Furthermore, when the phase fraction and the dielectric constant change simultaneously, only the total contribution of the two changes can be observed, and the equation is as follows:

[0068]

[0069] wherein, the parameter with subscript "total" indicates that this parameter is the result of the combined action of the phase fraction change and the dielectric constant change. Solving the equation gives:

[0070]

[0071] wherein, is the true phase fraction, f′ TE2,total is the change in the phase fraction resonance frequency in the second TE mode, and Δf′ TE2,permittivity is the change in the dielectric constant resonance frequency in the second TE mode.

[0072] The beneficial effects of the present invention are as follows:

[0073] 1) Quantitatively describes the relationship among the phase fraction, the change in the dielectric constant, and the change in the resonance frequency;

[0074] 2) By introducing the quality factor, the deviation caused by the dielectric constant and the measured value of the phase fraction are decoupled, improving the accuracy and precision of the measurement of the phase fraction in gas-liquid two-phase flow, and enhancing the compensation ability for the influence of the external environment and the change of the fluid's own properties.

[0075] In this specification, each embodiment is described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same and similar parts among the embodiments, reference can be made to each other.

[0076] In the present invention, specific examples are used to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for measuring the holdup of a gas-liquid two-phase flow with resistance to dielectric constant drift based on a resonant cavity, characterized in that: The steps include: The relative dielectric constant is calculated based on the change in the resonant frequency of the resonant cavity; The equivalent dielectric constant is obtained according to the positional relationship between the gas and liquid phases; Obtaining a gas phase resonance frequency and a liquid phase resonance frequency respectively according to the relative dielectric constant and the equivalent dielectric constant; Obtaining a normalized resonant frequency through the gas phase resonant frequency and the liquid phase resonant frequency; Based on the working mode of the resonant cavity, the normalized resonant frequency is fitted to a theoretical phase content reference value by a perturbation method; The working modes include: TE mode and TM mode; the TE mode includes: a first TE mode and a second TE mode; Based on the theoretical phase content reference value, the resonant frequency change is obtained in combination with the changes in the liquid phase content and the liquid phase dielectric constant; the resonant frequency change includes: the phase content resonant frequency change and the dielectric constant resonant frequency change; The quality factor is obtained by the perturbation method, and the quality factor is used to perform a decoupling operation on the resonant frequency variation to obtain the true phase content.

2. The method for measuring the holdup of a gas-liquid two-phase flow with dielectric constant drift resistance based on a resonant cavity according to claim 1, characterized in that: The calculation formula of the relative dielectric constant is: Among them, ε r is the relative dielectric constant, Δf is the resonant frequency offset, t1 is the radius of the cylindrical perturbation, a, b and l are the length, width and height of the resonant cavity respectively, p is the number of standing waves in the Z-axis direction, dv is the volume element of the resonant cavity, E0 is the electric field strength in the cavity before the perturbation, and f r is the resonant frequency before perturbation.

3. The method for measuring the holdup of a gas-liquid two-phase flow with dielectric constant drift resistance based on a resonant cavity according to claim 2, characterized in that: The calculation formula of the equivalent dielectric constant is: ε || =ρ1ε pipe +ρ2ε liquid +ρ3ε gas ; where ε ∥ is the equivalent dielectric constant, ρ1, ρ2 and ρ3 are the phase contents of the pipeline, liquid phase and gas phase respectively, ε pipe , ε liquid and ε gas are the dielectric constants of the pipe, liquid phase, and gas phase, respectively.

4. The method for measuring the holdup of a gas-liquid two-phase flow with dielectric constant drift resistance based on a resonant cavity according to claim 3, characterized in that: The calculation formulas of the gas phase resonance frequency and the liquid phase resonance frequency are respectively: Among them, f empty is the gas phase resonance frequency, f full is the liquid phase resonance frequency.

5. The method for measuring the holdup of a gas-liquid two-phase flow with dielectric constant drift resistance based on a resonant cavity according to claim 4, characterized in that: The calculation formula of the normalized resonant frequency is: Among them, f' holdup and f holdup are the normalized resonant frequency and the resonant frequency under a certain liquid holdup state, ρ liquid,holdup It is the ratio of the liquid phase volume to the total volume of the gas-liquid two-phase flow in the pipeline.

6. The method for measuring the holdup of a gas-liquid two-phase flow with dielectric constant drift resistance based on a resonant cavity according to claim 1, characterized in that: The calculation formula of the theoretical phase content reference value is: in, is the ratio of the liquid phase volume in the second TE mode to the total volume of the gas-liquid two-phase flow in the pipeline, f T ' E2,holdup is the normalized resonant frequency in the second TE mode, is the coefficient of the quadratic term of the fit, is the coefficient of the first-order term of the fit.

7. The method for measuring the holdup of a gas-liquid two-phase flow with dielectric constant drift resistance based on a resonant cavity according to claim 4, characterized in that: The calculation formula for the change in phase holdup resonant frequency is: Where Δf h ' oldup and Δf holdup are the normalized changes in the resonance frequency of phase content and the changes in the resonance frequency of phase content, respectively, and Δρ2 is the change in the liquid content; The calculation formula of the dielectric constant resonant frequency change is: Where Δf p ' ermittivity and Δf permittivity are the normalized dielectric constant resonant frequency change and the dielectric constant resonant frequency change, Δε liquid is the change in the dielectric constant of the liquid phase.

8. The method for measuring the holdup of a gas-liquid two-phase flow with dielectric constant drift resistance based on a resonant cavity according to claim 2, characterized in that: The calculation formula of the quality factor is: Among them, Q is the quality factor after disturbance, and Q0 is the quality factor before disturbance.

9. The method for measuring the holdup of a gas-liquid two-phase flow with resistance to dielectric constant drift based on a resonant cavity according to claim 6, characterized in that: The calculation formula of the true phase content is: in, is the real phase content, f T ' E2,total is the change in the phase content resonant frequency in the second TE mode, Δf T ' E2,permittivity is the change in the dielectric constant resonance frequency in the second TE mode.

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