CN112255155B - Rotation measurement system and method for two-dimensional distribution of particle concentration and particle size - Google Patents

Rotation measurement system and method for two-dimensional distribution of particle concentration and particle size Download PDF

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CN112255155B
CN112255155B CN202011167981.0A CN202011167981A CN112255155B CN 112255155 B CN112255155 B CN 112255155B CN 202011167981 A CN202011167981 A CN 202011167981A CN 112255155 B CN112255155 B CN 112255155B
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王飞
范金惠
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Zhejiang University ZJU
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
    • G01N15/06—Investigating concentration of particle suspensions
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/032—Analysing fluids by measuring attenuation of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/24—Probes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G01N29/4409—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison
    • G01N29/4418—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison with a model, e.g. best-fit, regression analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G01N29/4472—Mathematical theories or simulation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/01—Indexing codes associated with the measuring variable
    • G01N2291/015—Attenuation, scattering
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/024—Mixtures
    • G01N2291/02408—Solids in gases, e.g. particle suspensions

Abstract

The invention belongs to the technical field of online real-time measurement in an industrial production process, and particularly relates to a rotation measurement system and method for two-dimensional distribution of particle concentration and particle size. Comprises an ultrasonic air coupling transducer; the ultrasonic air coupling transducer is arranged on a measuring window arranged on the particle pipeline, the signal input end of the ultrasonic air coupling transducer is connected with the signal generator, and the signal output end of the ultrasonic air coupling transducer is sequentially connected with the echo signal filter, the echo signal acquisition module and the industrial personal computer through signal lines. The invention also provides a method for carrying out rotation measurement on the two-dimensional distribution of the particle concentration and the particle size by using the system. In practical application, the invention can realize two-dimensional measurement only by drilling at one angle, and plays a role in promoting the practicability of the field parameter method.

Description

Rotation measurement system and method for two-dimensional distribution of particle concentration and particle size
Technical Field
The invention belongs to the technical field of online real-time measurement in an industrial production process, and particularly relates to a system and a method for measuring particle concentration and particle size two-dimensional distribution in a gas-solid two-phase medium.
Background
The accurate measurement of the particle concentration and the particle size in the gas-solid two-phase medium has important significance for controlling and saving energy in the production processes of energy, electric power, chemical industry, pharmacy and the like. For example, the ratio of pulverized coal to air in a pulverized coal boiler burner of a power plant has a significant impact on combustion efficiency. Firstly, if the mass flow of the pulverized coal at the outlet of each burner is not uniform, the flame center of a hearth can be deflected, and the phenomena of local overtemperature, coking and the like of a heating surface in a furnace can be caused. Secondly, too high a coal dust concentration may result in insufficient combustion, reducing combustion efficiency and increasing pollutant emissions. Therefore, it is very critical to control the mixing ratio of pulverized coal and air entering the furnace. This requires that accurate measurements of the coal dust concentration and particle size in each pipe must be mastered. However, in the transportation process of the gas-solid two-phase medium, the problems of high particle concentration, uneven distribution, many influencing factors and the like are faced, so that the difficulty in accurately measuring the flow parameters is high.
The single-point measurement of the concentration and the particle size of the particles in the gas-solid two-phase medium has been studied at home and abroad, such as an optical method, an electrical method, a microwave method, an acoustic method, a differential pressure method and the like, but they all have certain limitations, for example, see utility model patent No. CN93212914.5, it discloses an industrial capacitance type gas-solid two-phase flow phase concentration detection device, which belongs to a non-contact type measurement system, the principle is that the capacitance value is changed due to the change of the equivalent dielectric constant caused by the change of the concentration of the discrete phase, the detection of the gas-solid two-phase flow phase concentration is realized by detecting the change of the capacitance value, but in practical application, the electromagnetic interference of an industrial field is strong generally, and the establishment of an analytic function relation between the absolute measurement value of the particle concentration and the electrostatic induction signal is difficult, so the application effect is limited.
Moreover, the single-point measurement of the concentration and the particle size cannot comprehensively reflect the actual distribution condition of the particles, so that the method cannot be used for adjusting the concentration of the pulverized coal in a pipeline in real time, and safe, efficient, clean and stable production is realized. The reconstruction method has great significance for measuring the two-dimensional distribution on the section of the gas-solid two-phase medium, and certainly has more challenge. Due to difficulties related to multi-detector arrangement, signal processing, reconstruction algorithm selection and the like, the study of reconstruction of two-dimensional distribution of flow parameters is not as extensive as single-point measurement, and the two-dimensional reconstruction of parameters of multiphase flow by using a tomography method is a main research hotspot. One of the tomographic methods is reconstruction by rotation of an optical system, which is similar to the principle of Computer Tomography (CT) scanning, but has certain difficulties in actual flow measurement, and the actual device cannot rotate and cannot be installed with such a large mirror. Another method that is more frequently adopted is to arrange a plurality of emission-detection unit devices in a plurality of directions for reconstruction, but this method needs to open a plurality of windows to install an emitter and a receiver, and obtains a plurality of groups of projection values by using different measurement paths, although the efficiency can be effectively improved, the reconstruction quality is affected by the limited number of projections, and a large number of holes are difficult to arrange on the measurement section in the industrial field, thereby causing the practical application to be more difficult.
In conclusion, the measurement of the two-dimensional distribution on the section of the gas-solid two-phase medium faces huge challenges at present, and no breakthrough technical scheme is available. Therefore, how to overcome the deficiencies of the prior art has become a major problem to be solved in the field of the current industrial production online real-time measurement technology.
SUMMARY OF THE PATENT FOR INVENTION
The invention aims to solve the technical problem of overcoming the defects in the prior art and provides a rotation measuring system and method for particle concentration and particle size two-dimensional distribution.
In order to solve the technical problem, the invention adopts the technical scheme that:
the rotation measuring system for the two-dimensional distribution of the particle concentration and the particle size comprises an ultrasonic air coupling transducer; the ultrasonic air coupling transducer is arranged on a measuring window arranged on the particle pipeline, the signal input end of the ultrasonic air coupling transducer is connected with the signal generator, and the signal output end of the ultrasonic air coupling transducer is sequentially connected with the echo signal filter, the echo signal acquisition module and the industrial personal computer through signal lines;
the signal generator controls the ultrasonic air coupling transducer to emit ultrasonic waves, and the ultrasonic waves enter the echo signal acquisition module through the echo signal filter and are finally uploaded to the industrial personal computer; the industrial personal computer controls the screw feeder to feed the particle pipeline.
As an improvement, the ultrasonic air coupling transducer is a self-generating and self-receiving transmitting transducer or two transducers which are adjacently arranged and can realize synchronous rotation, and the transmission and the reception of ultrasonic waves are realized.
A method for carrying out rotation measurement on two-dimensional distribution of particle concentration and particle size by using the system comprises the following steps:
(1) an ultrasonic air coupling transducer is used as a core to establish a measuring system, and a particle echo signal sound spectrum is obtained; the system mainly comprises an ultrasonic air coupling transducer, a signal generator, an echo signal filter, an echo signal acquisition module, a feeding system, an industrial personal computer and the like. The ultrasonic air coupling transducer can emit high-frequency pulse ultrasonic signals under the excitation of an ultrasonic signal source, can emit exponential attenuation pulses, attenuation oscillation pulses and square modulation pulses under the control of an electric signal of an emitting end, can be used as an echo receiving end at the same time, can achieve the level of mu s in response time precision, and can provide quite abundant frequency spectrum information by a broadband pulse probe. Thus, the measurement mode is to obtain a backscattered echo signal of the ultrasonic wave passing through the particles at a certain frequency, and the receiving transducer records the echo signal.
(2) Determining the distance of a pulse ultrasonic echo signal measuring point; for the pulse ultrasonic radar, the position of an echo measuring point from a transmitting end can be determined according to the flight time of an echo, so that initial data is provided for the next step of calculating a one-dimensional concentration field and a particle size distribution field of particulate matters. After the pulse ultrasonic wave passes through the particle, an echo signal is generated, and because the echo signal comes and goes between the ultrasonic radar and the target, the echo signal lags behind the emission pulse by a time t, and the distance of the particle is z, then the following results are obtained:
Figure BDA0002746368670000031
t is the time that the echo signal generated by the pulse ultrasonic wave after passing through the particles lags behind the emission pulse, z is the distance between the particles and the transducer, and c is the sound velocity in the air;
(3) according to the superposition of a laser radar equation and a coupling phase and dense phase scattering attenuation model, a linear equation set of the acoustic parameters of echo sound spectrum signals, the concentration and the particle size of the particles under two different frequencies is established, and the one-dimensional particle concentration and particle size distribution can be obtained by solving the equation set:
Figure BDA0002746368670000032
I(zi)ffor a distance z from the transducer at a certain frequencyiEcho signal sound intensity at distance I0Beta (z) is z for the acoustic intensity of the emitted waveiThe back scattering coefficient of the particles, f,
Figure BDA0002746368670000033
r is the ultrasonic frequency, particle volume concentration and particle size, respectively, and P is a vector containing various parameters, F1And F2Model for respectively representing scattering attenuation of coupled phase and concentrated phaseThe attenuation coefficient as a function of the parameter.
Before establishing a linear equation set of acoustic parameters of echo sound spectrum signals and the concentration and particle size of particles, firstly, describing an acoustic model of sound attenuation change in the process of particle measurement in a gas-solid two-phase medium: a coupled phase model and a dense phase scattering model are introduced. This theory is only applicable to dilution systems, since in the basic acoustic model the particles are considered as individual individuals and the interactions between the particles are not accounted for. At high concentrations (e.g. coal dust concentration measurements) two effects have to be considered: complex scattering and particle interactions. Aiming at the defect, a coupled phase model developed under the conditions of high concentration, long wavelength and large density difference between particle phase and fluid phase can be applied to the measurement of the concentration and the particle size of high-concentration particles in the pipeline.
Harker and Temple examine the phenomenon of sound wave in two-phase flow from the viewpoint of fluid dynamics, and derive the viscous resistance equation of the interaction between phases, and the momentum and mass conservation equation independent of each phase. The complex wave number equation can be obtained by simultaneously solving the differential equations, and the derivation process is as follows:
two-phase flow equivalent density:
Figure BDA0002746368670000034
wherein rho' is the solid phase density of the particles and rho is the density of the continuous phase.
Equivalent compression factor:
Figure BDA0002746368670000041
in the formula, ka' -solid phase compressibility of the particles, ka-continuous phase compression factor.
One-dimensional conservation of mass equation for acoustic wave motion propagating in the x-direction from a hydrodynamic perspective:
for the particles:
Figure BDA0002746368670000042
for the continuous phase:
Figure BDA0002746368670000043
the conservation of momentum equation can also be written:
for the particles:
Figure BDA0002746368670000044
for the continuous phase:
Figure BDA0002746368670000045
wherein the resistance coefficient of the interphase resistance action:
Figure BDA0002746368670000046
Figure BDA0002746368670000047
the ratio of the particle radius to the viscous thickness y is R/deltas，
Figure BDA0002746368670000048
Substituting the parameters into a differential equation to solve a final complex wave number equation as follows:
Figure BDA0002746368670000049
for the coupled phase model, the acoustic attenuation is mainly composed of viscous attenuation, and is therefore by definition:
κ＝ω/cs(ω)+jαvisc(ω) (12)
the acoustic attenuation of the coupled phase model can be determined from equations (10) and (11), and is expressed as:
Figure BDA00027463686700000410
here, the number of the first and second groups, f,
Figure BDA0002746368670000051
r is the ultrasonic frequency, particle volume concentration and particle size, respectively, and P is a vector containing various parameters.
For the coupled phase model, the calculation is simpler than that of a basic acoustic model (ECAH model) which needs 14 physical parameters, only the density and sound velocity of particles and continuous phase and the viscosity of the continuous phase are needed, and the model is convenient to use in practice. Coupled phase models tend to macroscopically understand the different differences between the two phases, and in this case the individual particles are also replaced by the concept of discrete, since there are no interfaces and no scattering phenomena.
However, in order to measure the concentration and the particle size of the echo signal by scattering high-concentration particles, the scattering attenuation cannot be ignored. The dense phase scattering model starts from Lambert-Beer law, and similar to the scattering method in optics, when sound waves propagate in a particle suspension medium, the transmission intensity after passing through the medium is weakened due to the scattering and absorption of the particles, and the attenuation degree can be expressed by an attenuation coefficient, and the parameter represents the size of sound attenuation caused by pure scattering, which is related to the size and the number (concentration) of the particles, so that a scale is provided for particle measurement.
The dense phase scattering model starts from the balance of sound intensity in a thin layer with the thickness dL in two-phase flow, and comprises
dI＝-IαExt,DSdL (14)
Wherein, I is the sound intensity,
Figure BDA0002746368670000052
called coefficient of sound attenuation. Integrating the above formula, and obtaining the expression as follows according to the definition of the attenuation coefficient:
Figure BDA0002746368670000053
KExtcalled sound-deadening efficiency, given by
Figure BDA0002746368670000054
σ ═ ω R/c referred to as the particle size coefficient, infinite series AnReferred to as the scattering coefficient.
By substituting formula (15) for formula (14), it is possible to obtain:
Figure BDA0002746368670000055
in keeping with the viscous damping loss expression, it can be expressed as:
Figure BDA0002746368670000056
in the two-phase flow, the viscosity loss and the scattering loss alternately increase and decrease with the change of the particle size, and it can be considered that the viscosity loss is dominant at long wavelength and the scattering loss is dominant at short wavelength, and the coupled phase model and the dense phase scattering model represent the solution for the case of long wavelength and short wavelength, respectively. But in multiphase flow measurements, at medium wavelengths is quite common. On one hand, because the micron-level particles are more, and on the other hand, the technology of the ultrasonic transducer with the frequency of about 10MHz or below is mature, the establishment of the medium-wavelength acoustic wave attenuation model which meets the requirements of measurement under high concentration and comprehensively describes absorption loss and scattering loss has important application value. However, a complex acoustic wave loss model capable of accurately describing medium wavelength is still lacked, so the invention provides a method for describing the change of acoustic attenuation in the process of measuring particles in a gas-solid two-phase medium by adopting a coupling phase model and a dense phase scattering model to be superposed.
Therefore, after pulse ultrasonic waves transmitted by the ultrasonic probe enter particles with different concentrations and particle sizes, a linear equation set of the acoustic parameters of the echo sound spectrum signals and the concentrations and particle sizes of the particles can be established by utilizing a superposition method of the coupling phase model and the dense phase scattering model. Considering the viscosity factor and the scattering effect, the acoustic loss can be described in a "viscosity + scattering" manner. Referring to the method for calculating the energy of a scattered echo signal in a laser radar equation,
the ultrasonic echo signal sound intensity I (z) at different concentrations can be obtained:
I(z)＝I0β(z)T2(z) (19)
wherein, I0Beta (z) is the particle backscattering coefficient at z, and T (z) is the ultrasonic transmission rate, for the emitted acoustic intensity.
The particle backscattering coefficient β (z) at z can be determined by the rayleigh scattering equation:
Figure BDA0002746368670000061
the ultrasonic wave transmittance T (z) is:
Figure BDA0002746368670000062
wherein alpha isvis(z) and alphasca(z) is a viscosity attenuation coefficient and a scattering attenuation coefficient, respectively, and can be obtained from the coupled phase model and the dense phase scattering model. Considering that the concentration and the particle size distribution of the particulate matters are not uniform in the actual pneumatic transportation process, in order to facilitate the solution, the concentration and the particle size of the particulate matters are a certain value on the distance between every two echo measuring points, so that the formula (20) can be further discretized into:
Figure BDA0002746368670000063
can also be expressed as:
Figure BDA0002746368670000064
the integral expression of the viscous attenuation coefficient and the scattering attenuation coefficient of the ultrasonic wave transmittance on the one-dimensional measuring path can be dispersed into the sum of the viscous attenuation coefficient and the scattering attenuation coefficient on each measuring distance by the above expression, and then the sound attenuation can be expressed as a function relation expression of the ultrasonic wave frequency, the particle phase concentration and the particle size.
The position of each measurement point can be determined from the time of flight of each echo measurement point, and the attenuation loss on the measurement path can be discretized by assuming that the concentration and particle size between two measurement points are constant, resulting in a series of linear equations as follows:
Figure BDA0002746368670000071
the set of linear equations includes the particle phase concentration
Figure BDA0002746368670000072
And two unknowns of the particle size R, in order to solve the equation set, the ultrasonic probe may be used to sequentially transmit pulsed ultrasonic waves of two frequencies at certain transmission time intervals, that is, the equation set at two frequencies may be obtained, for example, when z is 1:
Figure BDA0002746368670000073
solving the equation set to obtain z1The concentration value and the particle size value of the particles are measured, and then the concentration value and the particle size value are sequentially measured on z on the measurement path2、z3、……、zkAnd (4) carrying out iterative solution on the equation set at the position, and obtaining the concentration value and the particle size value at each echo position.
(4) According to time of flight and transducer rotation rate (theta)0/s) determining the two-dimensional cross-section of each echo pointAnd establishing an equation set for echo points on a plurality of measurement paths by utilizing a one-dimensional concentration and particle size solution inversion algorithm of the particles, wherein each echo point corresponds to one equation set, the concentration and particle size value at the moment can be obtained, the concentration and particle size value of each measurement point are calculated and solved for many times, and finally, the discrete concentration value and particle size value distribution field parameter on the two-dimensional section are obtained.
Figure BDA0002746368670000074
I(zi)fFor a distance z from the transducer at a certain frequencyiEcho signal sound intensity at distance I0Beta (z) is z for the acoustic intensity of the emitted waveiThe back scattering coefficient of the particles, f,
Figure BDA0002746368670000075
r is the ultrasonic frequency, particle volume concentration and particle size, respectively, and P is a vector containing various parameters, F1And F2Respectively representing the function relation of attenuation coefficients and parameters in the coupled phase scattering attenuation model and the concentrated phase scattering attenuation model.
Compared with the prior art, the invention has the beneficial effects that:
1. the widely applied CT tomography scheme is skipped, the principle of radar measurement is utilized, ultrasonic pulses with low propagation speed are selected as signals, the simultaneous reconstruction of the two-dimensional concentration and the particle size distribution of the cross section is realized, and the method is an innovation in the two-dimensional measurement aspect of combustion and multiphase flow.
2. Aiming at the problem that the high concentration of particles in a gas-solid two-phase medium is difficult to measure, a sound wave transmission equation comprehensively considering a coupling phase model and a concentrated phase scattering model is established, and the quantitative relation between the sound attenuation coefficient and the ultrasonic frequency, the particle concentration and the particle size is established, so that the method is a model innovation for applying the radar reconstruction theory to the high-concentration particle scattering.
3. Aiming at the problem that the CT tomography technology is difficult to realize multi-angle installation in industrial application, the radar reconstruction method is adopted to complete one-dimensional measurement in a single direction firstly and then scan to obtain two-dimensional information, and in practical application, the two-dimensional measurement can be realized only by opening a hole at one angle, so that the practicability of a field parameter method is promoted.
Drawings
FIG. 1 is a diagram of an experimental system for particle parameter measurement of a pulsed ultrasonic radar according to the present invention;
FIG. 2 is a schematic view of the backscattering of the present invention;
FIG. 3 is a schematic diagram of the operation of the dual transmission-reception probe of the present invention;
FIG. 4 is a schematic diagram of an echo signal for pulsed ultrasonic radar ranging in accordance with the present invention;
FIG. 5 is a schematic diagram of a single pulse ultrasonic echo signal spectrum of the present invention;
FIG. 6 is a schematic diagram of a two-dimensional measurement principle based on a pulsed ultrasonic radar;
FIG. 7 is a schematic diagram of two-dimensional measurement paths and echo points according to the present invention.
Reference numerals: 1-an ultrasonic air-coupled transducer; 2-an echo signal filter; 3-echo signal acquisition module; 4-an industrial personal computer; 5-a signal generator; 6-a screw feeder; 7-driving a motor; 8-particle pipeline.
Detailed Description
One specific embodiment is given below. It should be noted that, in the implementation process of the invention patent, a plurality of hardware functional modules may be involved. The applicant believes that the technology he or she knows can be fully utilized to realize the present invention in conjunction with the prior art after a detailed reading of the application document, an accurate understanding of the principle of realization of the present invention and the object of the present invention patent. The applicant does not enumerate themselves to the extent that all documents cited in the present application fall within the scope of this patent. In addition, the realization of the invention depends on the application of various computers and board cards, and the instruments are all in the prior art, and mature products can be obtained in the market.
The invention is further described with reference to the following figures and detailed description.
Referring to fig. 1, a rotation measuring system for two-dimensional distribution of particle concentration and particle size comprises an ultrasonic air coupling transducer 1; the ultrasonic air coupling transducer 1 is arranged on a measuring window arranged on the particle pipeline 8, the signal input end of the ultrasonic air coupling transducer 1 is connected with the signal generator 5, and the signal output end is sequentially connected with the echo signal filter 2, the echo signal acquisition module 3 and the industrial personal computer 4 through signal lines;
the signal generator 5 controls the ultrasonic air coupling transducer 1 to emit ultrasonic waves, and the ultrasonic waves enter the echo signal acquisition module 3 through the echo signal filter 2 and are finally uploaded to the industrial personal computer 4; the industrial personal computer 4 controls the screw feeder 6 to feed the particle pipeline 8.
The ultrasonic air coupling transducer 1 is a self-generating and self-receiving transmitting transducer or two adjacent transducers which can realize synchronous rotation, and realizes the transmission and the reception of ultrasonic waves.
When the system is used, the system can be matched with a powder feeding experiment table, the powder feeding experiment table is composed of a driving motor 7, a feed hopper and a screw feeder 6, the screw feeder 6 continuously feeds materials to an experiment pipeline under the action of the driving motor 7 to manufacture gas-solid two-phase flow with uniform concentration, and the feed hopper plays a role in supplementing the feeding materials in time, so that the powder feeding experiment table realizes the function of providing the gas-solid two-phase flow for experiments.
The principle of the invention is to simulate the radar principle, and the backscattering of ultrasonic waves by particles is used as the analysis basis of particle concentration and particle size distribution. Radar is an electronic device that detects a target using electromagnetic waves, also called "radio positioning," and is capable of emitting electromagnetic waves to irradiate the target and receiving an echo thereof, thereby obtaining information on a distance, a distance change rate (radial velocity), an azimuth, an altitude, and the like of the target to an electromagnetic wave emission point. Referring to the basic principle of radar, the present invention utilizes ultrasonic waves to make incident on particles and receive their backscattered echoes. According to Mie scattering theory, when an ultrasonic wave is incident on isotropic particles, scattering occurs in all directions in space, and can be classified into forward scattering, side scattering and backward scattering according to the scattering angle, as shown in fig. 2, in the measurement, the scattering angle is defined as the angle between the ultrasonic propagation direction and the straight line of the receiving transducer, and is forward scattering when the scattering angle is less than 90 °, and is side scattering when the scattering angle is between 90 ° and 180 °, and is backward scattering when the scattering angle is 180 °.
The core instrument of the invention is an ultrasonic probe, also called ultrasonic transducer or ultrasonic sensor, which is a device capable of generating or receiving ultrasonic waves, mainly including a piezoelectric transducer and a magnetic sensor, and the piezoelectric transducer is widely used at present. When the external force is removed, it can be restored to its uncharged state, and when the direction of the applied force is changed, the polarity of the charge can be changed. In the present invention, the ultrasonic probe belongs to a dual-purpose transmitting-receiving probe which can not only transmit pulsed ultrasonic waves under the control of an ultrasonic controller, but also receive echoes reflected by particles (shown in fig. 3). The echo reflected by the particles enters the signal acquisition module after being filtered by the echo signal filter 2, the acquired signal is transmitted to the industrial personal computer 4 for analysis and research, and finally the signal obtained on the industrial personal computer 4 is a change curve of the sound pressure reflected by the particles received by the transducer along with the time.
In a specific embodiment, the transducer is first made to emit ultrasonic waves at a certain angle, and the signals reflected by the particles and received by the transducer are filtered and data-collected and then uploaded to the industrial personal computer 4, so that a reflected sound pressure-time relation curve can be obtained. Corresponding transmitted pulse and received echo diagrams are shown in fig. 4, and echo signals of the pulse ultrasonic wave after being reflected by the particles are transmitted to and from the ultrasonic radar and the target, so that the distance z corresponding to each time point t can be expressed as:
Figure BDA0002746368670000101
therefore, the acquired signal can be converted from the variation relation of the sound pressure along with time to the variation relation of the sound pressure along with distance. For sound waves, the sound intensity is proportional to the square of sound pressure and inversely proportional to the density of the medium and the sound velocity, and is specifically expressed as:
Figure BDA0002746368670000102
wherein ρ and c are respectively expressed as the density and the sound velocity of air, so that finally, according to the measurement result, the change relation of the sound intensity I reflected by the particles along with the propagation distance z can be obtained. With reference to the method for calculating the energy of the scattered echo signal in the lidar equation, the sound intensity i (z) of the ultrasonic echo signal at different distances z can be expressed as:
I(z)＝I0β(z)T2(z) (3)
wherein, I0Beta (z) is the particle backscattering coefficient at z, and T (z) is the ultrasonic transmission rate, for the emitted acoustic intensity. For the particle backscattering coefficient at z:
Figure BDA0002746368670000103
wherein f is frequency, R is particle size, and c is sound velocity in air, so that the backscattering coefficient of the particles is a fixed value for specific gas-solid two-phase flow. That is, after the variation of the sound intensity I reflected by the particles with the propagation distance z is experimentally obtained, the ultrasonic wave transmittance t (z) at different propagation distances z can be obtained. The ultrasonic wave transmittance t (z) is defined as:
Figure BDA0002746368670000104
wherein α (z) is an attenuation coefficient. The attenuation coefficient is briefly described below: the acoustic wave does not dissipate when traveling in an ideal medium because there is no interaction between the ideal medium and the acoustic wave. However, in practical situations, there is no ideal medium, and thus the sound wave will react with the medium when propagating in the medium, so that the intensity of the sound wave decreases with the distance, which is called sound attenuation. The sound attenuation is characterized by a sound attenuation coefficient (alpha), and causes of sound wave attenuation are many and can be mainly divided into three types, namely absorption attenuation, scattering attenuation and diffusion attenuation. Where absorption attenuation and scattering attenuation are mainly affected by the propagation medium, while diffusive attenuation is generally caused by the acoustic source characteristics. When studying the propagation law of sound waves in two-phase media, the third form of attenuation is generally ignored, and particularly when studying with sensors, it is often assumed that the sound attenuation is caused by absorption and scattering effects, and that the absorption effects dominate.
In the basic acoustic model above, the particles are considered as individual individuals and the interactions between the particles are not counted, so this theory is only applicable to dilution systems. At high concentrations (e.g. coal dust concentration measurements) two effects have to be considered: complex scattering and particle interactions. Aiming at the defect, a coupled phase model developed under the conditions of high concentration, long wavelength and large density difference between particle phase and fluid phase can be applied to the measurement of the concentration and the particle size of high-concentration particles in the pipeline.
Harker and Temple examine the phenomenon of sound wave in two-phase flow from the viewpoint of fluid dynamics, and derive the viscous resistance equation of the interaction between phases, and the momentum and mass conservation equation independent of each phase. Solving the differential equations simultaneously can be carried out on the complex wave number equation, and the derivation process is as follows:
two-phase flow equivalent density:
Figure BDA0002746368670000111
wherein rho' is the solid phase density of the particles and rho is the density of the continuous phase.
Equivalent compression factor:
Figure BDA0002746368670000112
of formula (II) k'a-solid phase compressibility of the particles, ka-continuous phase compression factor.
One-dimensional conservation of mass equation for acoustic wave motion propagating in the x-direction from a hydrodynamic perspective:
for the particles:
Figure BDA0002746368670000113
for the continuous phase:
Figure BDA0002746368670000114
the conservation of momentum equation can also be written:
for the particles:
Figure BDA0002746368670000115
for the continuous phase:
Figure BDA0002746368670000116
wherein the resistance coefficient omega of the interphase resistance action:
Figure BDA0002746368670000121
Figure BDA0002746368670000122
the ratio of the particle radius to the viscous thickness y is R/deltas，
Figure BDA0002746368670000123
Substituting the parameters into a differential equation to solve and derive a final complex wave number equation as follows:
Figure BDA0002746368670000124
for the coupled phase model, the acoustic attenuation is mainly composed of viscous attenuation, and is therefore by definition:
κ＝ω/cs(ω)+jαvisc(ω) (15)
the acoustic attenuation of the coupled phase model can be determined from equations (14) and (15) and is expressed as:
Figure BDA0002746368670000125
here, the number of the first and second groups, f,
Figure BDA0002746368670000126
r is the ultrasonic frequency, particle volume concentration and particle size, respectively, and P is a vector containing various parameters.
However, in order to measure the concentration and the particle size of the echo signal by scattering high-concentration particles, the scattering attenuation cannot be ignored. The dense phase scattering model starts from Beer-Lambert law, and similar to the scattering method in optics, when sound wave propagates in a particle suspension medium, the transmission intensity after passing through the medium is weakened due to the scattering and absorption of particles, and the attenuation degree can be expressed by an attenuation coefficient, and the parameter represents the size of sound attenuation caused by pure scattering, which is related to the size and the number (concentration) of the particles, so that a scale is provided for particle measurement.
The dense phase scattering model starts from the sound intensity balance in a thin layer with the thickness dL in two-phase flow, and comprises the following components:
dI＝-IαExt,DSdL (17)
wherein, I is the sound intensity,
Figure BDA0002746368670000127
referred to as the sound damping coefficient. Integrating the above equation and based on the attenuation coefficient alphasThe expression is obtained by defining (1):
Figure BDA0002746368670000128
KExtreferred to as the muffling efficiency, given by:
Figure BDA0002746368670000129
σ ═ ω R/c referred to as the particle size coefficient, infinite series AnReferred to as the scattering coefficient.
By substituting formula (19) for formula (18), a compound of formula
Figure BDA00027463686700001210
In keeping with the viscous damping loss expression, it can be expressed as:
Figure BDA0002746368670000131
the viscous loss and the scattering loss alternately increase and decrease with the change of the particle size in the two-phase flow, and it can be considered that the viscous loss is dominant at long wavelength and the scattering loss is dominant at short wavelength, and the coupled phase model and the dense phase scattering model represent the solution for the case of long wavelength and short wavelength, respectively. But in multiphase flow measurements, at medium wavelengths is quite common. On one hand, because the micron-level particles are more, and on the other hand, the technology of the ultrasonic transducer with the frequency of about 10MHz or below is mature, the establishment of the medium-wavelength acoustic wave attenuation model which meets the requirements of measurement under high concentration and comprehensively describes absorption loss and scattering loss has important application value. However, a complex acoustic wave loss model capable of accurately describing medium wavelength is still lacked, so the project proposes a method for describing the change of acoustic attenuation in the process of measuring particles in a gas-solid two-phase medium by adopting a coupling phase model and a dense phase scattering model.
After the coupled phase model and the dense phase scattering model are selected as the attenuation model, the ultrasonic wave transmittance t (z) is defined as:
Figure BDA0002746368670000132
αvis(z) and alphasca(z) is a viscosity attenuation coefficient and a scattering attenuation coefficient, respectively, and can be obtained from the coupled phase model and the dense phase scattering model. Considering that the concentration and the particle size distribution of the particulate matters are not uniform in the actual pneumatic transportation process, in order to facilitate the solution, the concentration and the particle size of the particulate matters are a certain value on the distance between every two echo measuring points, so that the formula (22) can be further discretized into:
Figure BDA0002746368670000133
can also be expressed as:
Figure BDA0002746368670000134
the integral expression of the viscous attenuation coefficient and the scattering attenuation coefficient of the ultrasonic wave transmittance on the one-dimensional measuring path can be dispersed into the sum of the viscous attenuation coefficient and the scattering attenuation coefficient on each measuring distance by the above expression, and then the sound attenuation can be expressed as a function relation expression of the ultrasonic wave frequency, the particle phase concentration and the particle size.
As shown in fig. 5, the position of each measurement point can be determined from the flight time of each echo measurement point, and the attenuation loss on the measurement path can be discretized by the assumption that the concentration and particle size between two measurement points are a certain value, thereby obtaining a series of linear equations as follows:
Figure BDA0002746368670000135
the set of linear equations includes the particle phase concentration
Figure BDA0002746368670000141
And two unknowns of the particle size R, to solve forThe system of equations can be obtained by using an ultrasonic probe to sequentially transmit pulsed ultrasonic waves of two frequencies at certain transmission time intervals, for example, when z is 1:
Figure BDA0002746368670000142
solving the equation set to obtain z1The concentration value and the particle size value of the particles are measured, and then the concentration value and the particle size value are sequentially measured on z on the measurement path2、z3、……、zkAnd (4) carrying out iterative solution on the equation set at the position, and obtaining the concentration value and the particle size value at each echo position.
After the concentration and particle size values at each distance z in one dimension are obtained, the concentration and particle size distribution in the other dimension can be measured by rotating the transducer as shown in fig. 6. Finally, the positions of echo points on the two-dimensional section (shown in fig. 7) are determined according to the flight time and the rotation rate, the black solid points are echo measuring points on each path, an equation set is established for the echo points on a plurality of measuring paths by utilizing a one-dimensional concentration and particle size solution inversion algorithm of the particles, the concentration and particle size values of each measuring point are solved through multiple iterations, and finally discrete concentration values and particle size value distribution field parameters on the two-dimensional section are obtained. The calculation formula is as follows:
Figure BDA0002746368670000143

Claims (2)

1. a method for rotation measurement of two-dimensional distribution of particle concentration and particle size is characterized in that:
the method is realized based on a rotation measuring system with two-dimensional distribution of particle concentration and particle size: the system includes an ultrasonic air-coupled transducer; the ultrasonic air coupling transducer is arranged on a measuring window arranged on the particle pipeline, the signal input end of the ultrasonic air coupling transducer is connected with the signal generator, and the signal output end of the ultrasonic air coupling transducer is sequentially connected with the echo signal filter, the echo signal acquisition module and the industrial personal computer through signal lines; the signal generator controls the ultrasonic air coupling transducer to emit ultrasonic waves, and the ultrasonic waves enter the echo signal acquisition module through the echo signal filter and are finally uploaded to the industrial personal computer; the industrial personal computer controls the screw feeder to feed the particle pipeline;
the measuring method comprises the following steps:
(1) an ultrasonic air coupling transducer is used as a core to establish a measuring system, and a particle echo signal sound spectrum is obtained;
(2) determining the distance of a pulse ultrasonic echo signal measuring point;
Figure FDA0003185715270000011
t is the time that the echo signal generated by the pulse ultrasonic wave after passing through the particles lags behind the emission pulse, z is the distance between the particles and the transducer, and c is the sound velocity in the air;
(3) establishing a linear equation set of the acoustic parameters of the echo sound spectrum signals, the concentration and the particle size of the particles under two different frequencies, and solving the equation set to obtain the one-dimensional particle concentration and particle size distribution;
Figure FDA0003185715270000012
I(zi)fis a distance z from the transducer at a certain frequencyiOf the echo signal at the measuring point, I0The sound intensity of the transmitted wave of the ultrasonic air coupling transducer is shown, and beta (z) is ziThe back scattering coefficient of the particles, f,
Figure FDA0003185715270000013
r is the ultrasonic frequency, particle volume concentration and particle size, respectively, and P is a vector containing various parameters, F1And F2Respectively representing the functional relation between attenuation coefficients and parameters in the coupling and dense phase scattering attenuation models;
(4) determining the position of each echo point on a two-dimensional section according to the flight time and the rotation rate of the transducer, establishing an equation set for the echo points on each measuring path by utilizing a one-dimensional concentration and particle size solution inversion algorithm, corresponding one equation set to each echo point, calculating the concentration and particle size value of each echo point, calculating and solving the concentration and particle size value of each measuring point for multiple times, and finally obtaining the discrete concentration value and particle size value distribution field parameters on the two-dimensional section.
2. The method of claim 1, wherein the ultrasonic air-coupled transducer is a self-transmitting and self-receiving transducer or two adjacently disposed transducers capable of synchronous rotation for transmitting and receiving ultrasonic waves.
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