CN117309699A - Mixing acoustic solid-liquid two-phase flow particle concentration and particle size distribution detection system and method - Google Patents
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Abstract
The invention relates to a mixed acoustic solid-liquid two-phase flow particle concentration and particle size distribution detection system and method, comprising a mixed signal generation unit, wherein the mixed signal generation unit is used for generating a mixed signal, and the signal output end of the mixed signal generation unit is connected with an ultrasonic piezoelectric driving control system; the signal output end of the ultrasonic piezoelectric driving control system is connected with the ultrasonic transducer; the ultrasonic transducer is used for outputting a mixing signal and receiving an echo signal scattered by suspended matters in the solid-liquid two-phase flow; the signal input end of the operation unit is connected with the echo signal output end of the ultrasonic transducer, and the operation unit is used for calculating the concentration and the particle size of suspended particles according to the echo signal. The invention can effectively improve the detection precision.
Description
Technical Field
The invention relates to a mixed acoustic solid-liquid two-phase flow particle concentration and particle size distribution detection system and method.
Background
Solid-liquid two-phase flow is a common phenomenon in nature, and typically includes streams, rivers, pipeline fluids and the like. The solid particles are mixed with the liquid and move simultaneously, and the original flowing state of the pipeline liquid is changed due to the existence of various solid particle substances such as flour, silt, salts and the like with different sizes and shapes, so that the flowing structure and the flowing form are changed differently. When studying the sedimentation velocity of solid particulate matter in liquid flow, the particle suspension stability and the movement capability of liquid carrying particulate matter, not only the gravity, the two-phase flow velocity, but also the particle size and concentration of solid particulate matter, it is necessary to know and measure the influence of the particle size and concentration of solid particulate matter on the solid-liquid two-phase flow system.
The existing particle size measuring methods for detecting particles are mainly classified into screening methods, microscopy methods, light scattering methods, ultrasonic methods and the like. The screening method is to select a series of standard screens with different screen hole diameters, and the screening of the particles with different particle diameters can be realized through automatic vibration. Due to the limitation of sieve mesh division, the measurement accuracy is affected to a certain extent. The microscopic method can measure the particle size as low as nanometer, is convenient and reliable, takes longer time and is operated in an off-line state. The light scattering method has high accuracy and simple operation, but the accuracy degree has large dependence on a distribution model. The principle of ultrasonic measurement of particle concentration and particle size in solid-liquid two-phase flow is based on the propagation characteristics of sound waves in a medium and the scattering effect of particles on sound waves. When the sound wave passes through the particles in the solid-liquid two-phase fluid, the particles can interact with the sound wave, so that parameters such as amplitude, propagation direction and the like of the sound wave are changed. These changes can be received by the ultrasonic sensor and the particle concentration and particle size inferred from the inversion algorithm. And the ultrasonic frequency band is wider, the particle size range of the particles can be measured, the sound wave transmittance is strong, the measurement response is quick, the anti-pollution capability is strong, and the online particle measurement can be performed. The positive problem of measuring the particle size distribution by an ultrasonic method is to establish an ultrasonic attenuation forward model through an ultrasonic attenuation mechanism, predict the attenuation and phase velocity of ultrasonic in a two-phase system, and the negative problem is to invert the particle size distribution based on the ultrasonic attenuation model. The current method for ultrasonically measuring particle size distribution mainly comprises the steps of obtaining an ultrasonic spectrum through excitation of a given frequency and carrying out inversion through an ultrasonic attenuation theoretical model in combination with an inversion algorithm.
In the existing ultrasonic measurement method, an ultrasonic transducer correlation mode is adopted, and particle size measurement is achieved through propagation and scattering of ultrasonic waves. Ultrasonic waves are mechanical waves, in which sound waves generated by an ultrasonic transducer propagate in a medium. In correlation mode, the transmitter and receiver are typically located on either side of the measurement area and produce orthogonal beams. When the acoustic wave encounters a particle, scattering occurs. The presence of the particles causes scattering of the acoustic wave, causing a portion of the acoustic wave to change direction of propagation. The scattering pattern will vary depending on the size and shape of the particles. The scattering pattern is related to parameters such as particle size, shape and distribution. The receiver receives the sound wave scattered by the particles and measures the intensity of the received sound wave. By analyzing the received sonic intensity information, information about the presence, size, and distribution of particles can be inferred.
The existing ultrasonic measurement method has the defect that an ultrasonic transducer in an opposite-emission mode can be limited by the measurement depth when measuring the particle size. Larger particles or larger measurement depths may require more powerful ultrasound transducers or more complex measurement configurations. And secondly, the back scattering measurement can obtain not only scattering signals related to the particle size, but also parameters related to the speed according to actual needs, so that multi-parameter detection of the particle size, the concentration and the speed of the pipeline is realized. The correlation mode of the ultrasonic transducer can be interfered by environmental noise, scattering, attenuation and other factors in the measuring process, and the interference can influence the accuracy and precision of measurement.
When the particle size is measured based on the existing ultrasonic measurement method, a multi-frequency acoustic method is adopted. The multi-frequency acoustic method is a method for realizing acoustic measurement and analysis by simultaneously using a plurality of acoustic signals with different frequencies, and solves the problem that the particle size information cannot be synchronously measured by a single frequency signal. In multi-frequency acoustics, sound waves of different frequencies are simultaneously transmitted to a measured object, and returned multi-frequency signals are received through a receiver. As the sound waves with different frequencies have different scattering behaviors on particles with different sizes, such as front scattering, back scattering and the like, the multi-frequency signals are processed, analyzed and compared, and the characteristic information of the target object can be extracted by comparing the characteristics and amplitude changes of the signals with different frequencies.
The existing multi-frequency acoustic method for measuring the particle size has the defects that the multi-frequency ultrasonic signals are used for measuring, a plurality of ultrasonic transmitters and receivers are involved, signals with a plurality of frequencies are required to be processed and analyzed, and the complexity and the cost of the system are increased. In solid-liquid two-phase flow, the multi-frequency ultrasonic signals may interfere or cross-influence each other. When ultrasonic signals of a plurality of frequencies are simultaneously present in a medium, mutual influence of the signals may occur, resulting in interference and error generation. If receiving transducers corresponding to different frequencies are used to receive the ultrasonic signals. Each frequency has a dedicated receiving transducer. This approach allows for more accurate reception and measurement of signals at different frequencies and avoids propagation differences and the need for calibration and compensation. However, the use of multiple receiving transducers increases the complexity and cost of the system.
Disclosure of Invention
The invention aims to provide a mixed acoustic solid-liquid two-phase flow particle concentration and particle size distribution detection system and method, which can effectively improve detection accuracy.
Based on the same inventive concept, the invention has two independent technical schemes:
1. a mixed acoustic solid-liquid two-phase flow particle concentration and particle size distribution detection system comprises: the signal output end of the mixing signal generating unit is connected with the ultrasonic piezoelectric driving control system;
the signal output end of the ultrasonic piezoelectric driving control system is connected with the ultrasonic transducer;
the ultrasonic transducer is used for transmitting the mixed signals to the solid-liquid two-phase fluid and receiving echo signals scattered by suspended matters in the solid-liquid two-phase fluid;
the signal input end of the operation unit is connected with the echo signal output end of the ultrasonic transducer, and the operation unit is used for calculating the concentration and the particle size of suspended particles according to the echo signal.
Further, the ultrasonic piezoelectric driving control system comprises a bias voltage signal generating unit, wherein the signal output end of the bias voltage signal generating unit is connected with the ultrasonic piezoelectric driving control system, and the bias voltage signal generating unit is used for generating a bias voltage signal.
Further, the signal output end of the mixing signal generating unit is connected with the ultrasonic piezoelectric driving control system through the digital-to-analog converter and the low-pass filter in sequence.
Further, the mixing signal generating unit and the bias voltage signal generating unit are integrated in an FPGA module, and the FPGA module is externally connected with a storage unit.
Further, the echo signal output end of the ultrasonic transducer is connected with an operation unit through a gain amplifier, an analog-to-digital converter and an FPGA module in sequence.
Further, the bias voltage signal generating unit is connected with the ultrasonic piezoelectric driving control system through a buffer and a low-pass filter in sequence.
2. The detection method utilizing the mixed acoustic solid-liquid two-phase flow particle concentration and particle size distribution detection system comprises the following steps:
step 1: the frequency mixing signal generating unit generates a frequency mixing signal, and the frequency mixing signal is output to the ultrasonic piezoelectric driving control system;
step 2: the ultrasonic piezoelectric driving control system outputs signals to the ultrasonic transducer, the ultrasonic transducer outputs mixed signals, and the mixed signals are scattered by suspended matters in the solid-liquid two-phase flow to form mixed echo signals which are received by the ultrasonic transducer;
step 3: the ultrasonic transducer transmits the echo signals to the operation unit, and the operation unit calculates the concentration and the particle size of suspended particles according to the echo signals.
Further, in step 3, the particle size of the two-phase flow particles is calculated by the following formula,
in the method, in the process of the invention,V i 、 V j respectively represent the corresponding frequenciesiSum frequencyjIs used for the echo voltage of the (c), K t,i 、K t,j respectively represent the corresponding frequenciesiSum frequencyjIs used for controlling the system parameters of the ultrasonic transducer, α w,i 、 α w,j respectively represent the corresponding frequenciesiSum frequencyjIs the absorption attenuation coefficient of water body ，rRepresenting the distance between the particle and the ultrasonic transducer;
f i /f j representing energy ratio functions for different frequencies of particle size, according to energy ratiof i /f j The particle size of the particles is obtained.
Further, in step 3, the two-phase flow particle concentration is calculated by the following formula,
in the method, in the process of the invention,Mthe concentration of the particles is indicated and,psi represents a near field correction factor, V rms The echo voltage is represented by a value representing the echo voltage,K t representing the parameters of the ultrasonic transducer system,αindicating the total attenuation in both the solid and liquid phases,rrepresenting the distance between the particles and the ultrasonic transducer,K s indicating the backscatter characteristic parameter of the suspended particles,K s can be obtained by calculation according to the particle size of the particles.
Further, the output signal of the ultrasonic electric drive control system is enabled to move upwards, and the transistor normally works in an amplifying state, so that correct transmission and undistorted amplification of the output signal are ensured.
Further, in step 3, when the ultrasonic piezoelectric driving control system outputs signals, a tailing removing function is adopted when the response of the transmitting signals is cut off, so that zero setting and residual vibration removing are carried out on the tail parts of the transmitted mixed signals, and the interference of noise signals is eliminated.
The invention has the beneficial effects that:
the invention comprises a mixed signal generating unit, wherein the mixed signal generating unit is used for generating a mixed signal, and the signal output end of the mixed signal generating unit is connected with an ultrasonic piezoelectric driving control system; the signal output end of the ultrasonic piezoelectric driving control system is connected with the ultrasonic transducer; the ultrasonic transducer is used for outputting a mixing signal and recovering an echo signal scattered by suspended matters in the solid-liquid two-phase flow; the signal input end of the operation unit is connected with the echo signal output end of the ultrasonic transducer, and the operation unit is used for calculating the concentration and the particle size of suspended particles according to the echo signal. The frequency mixing signal generating unit generates a frequency mixing signal, and the frequency mixing signal is output to the ultrasonic piezoelectric driving control system; the ultrasonic piezoelectric driving control system outputs signals to the ultrasonic transducer, the ultrasonic transducer outputs mixed signals, and the mixed signals are scattered by suspended matters in the solid-liquid two-phase flow to form mixed echo signals which are received by the ultrasonic transducer; the ultrasonic transducer transmits the echo signals to the operation unit, and the operation unit calculates the concentration and the particle size of suspended particles according to the echo signals.
The ultrasonic transducer can output a mixing signal and recover an echo signal scattered by suspended matters in the solid-liquid two-phase flow, namely, the transmitting and receiving signals are realized by the same ultrasonic transducer. The existing ultrasonic multi-frequency detection unit is characterized in that a plurality of transducers emit single-frequency signals with different frequencies to be combined, and corresponding ultrasonic transducers are arranged to receive the single-frequency signals, so that multi-frequency measurement is realized. The invention is based on the multi-frequency measurement of an ultrasonic transducer, which is realized by simultaneously transmitting mixed signals with different frequencies. The invention transmits and receives by the same transducer, which eliminates errors caused by alignment, stability or uniformity problems which may exist between two independent transducers, thereby improving the detection accuracy, and the self-receiving transducer reduces the number of devices, thereby reducing the device cost and maintenance cost.
According to the invention, the concentration and the particle size of suspended matters are detected through the mixing signals, and as the sensitivity degree of ultrasonic signals with different frequencies to particles with different particle sizes is different, the mixing signals can be used for more accurately analyzing the characteristics of materials and distinguishing and comparing the influence degree of different frequency components on the materials, and compared with single-frequency signals, the mixing signals can effectively prevent the interference of external noise signals such as environment and the like, and improve the anti-interference capability of the signals. Mixing signals can avoid frequency selection difficulties, and when using multi-frequency signals, multiple frequencies need to be selected to obtain optimal detection performance, and determining the optimal frequency can require extensive experimentation and experience. Mixing the signals can then avoid this problem, as the signals can be optimized by adjusting the frequency combinations. The invention utilizes the mixing acoustic technology to detect the particle concentration and the particle size distribution of the solid-liquid two-phase flow, which is an original method, and the traditional method can only detect one parameter, while the invention can detect the concentration and the particle size distribution simultaneously. The invention can effectively improve the detection accuracy, reduce the sample preparation time required by the traditional measurement method, possibly repeatedly measure, improve the detection efficiency and save the detection cost, and does not need to add any chemical reagent or substance, thus being a green and environment-friendly detection method.
When the ultrasonic piezoelectric driving control system outputs signals, the tail of the emitted mixed signal is subjected to zero setting and aftershock removal by adopting a tailing removal function when the response of the emitted signals is cut off, so that the interference of noise signals is eliminated. Depalletizing is an important means of reducing dead zones of spontaneous, self-retracting mode transducers because the mechanical oscillations of the transducer still last some time after the signal is sent out, and in order to shorten the tailing time, after the signal is sent out, the mechanical energy is released through a circuit, thereby reducing the tailing time. The shorter the tailing time is, the shorter the time from transmitting to receiving is, so that the dead zone is smaller, the detection range is enlarged, and the detection accuracy is improved.
The invention comprises a bias voltage signal generating unit
The signal output end is connected with the ultrasonic piezoelectric driving control system, and the bias voltage signal generating unit is used for generating bias voltage signals so as to ensure that the ultrasonic piezoelectric driving control system works in a normal range. The signal output end of the mixing signal generating unit is connected with the ultrasonic piezoelectric driving control system through the digital-to-analog converter and the low-pass filter in sequence. The frequency mixing signal generating unit and the bias voltage signal generating unit are integrated in an FPGA module, and the FPGA module is externally connected with a storage unit. The echo signal output end of the ultrasonic transducer is connected with an operation unit through a gain amplifier, an analog-to-digital converter and an FPGA module in sequence. The bias voltage signal generating unit is connected with the ultrasonic piezoelectric driving control system through the buffer and the low-pass filter in sequence. The bias voltage signal generating unit, the ultrasonic piezoelectric driving control system, the mixing signal generating unit, the ultrasonic transducer and the operation unit are connected through specific circuits, so that effective guarantee is further provided for improving detection precision.
In the step 3 of the invention, the particle size of the two-phase flow particles is calculated by the following formula,
in the method, in the process of the invention,V i 、V j respectively represent the corresponding frequenciesiSum frequencyjIs used for the echo voltage of the (c), K t,i 、K t,j respectively represent the corresponding frequenciesiSum frequencyjIs used for controlling the system parameters of the ultrasonic transducer,α w,i 、α w,j respectively represent the corresponding frequenciesiSum frequencyjIs the absorption attenuation coefficient of water body ，rRepresenting the distance between the particle and the ultrasonic transducer;
f i /f j representing energy ratio functions for different frequencies of particle size, according to energy ratiof i /f j The particle size of the particles is obtained.
In step 3, the particle concentration of the two-phase flow is calculated by the following formula,
in the method, in the process of the invention,Mthe concentration of the particles is indicated and,ψrepresenting the near field correction factor,V rms the echo voltage is represented by a value representing the echo voltage,K t representing the parameters of the ultrasonic transducer system,αindicating the total attenuation in both the solid and liquid phases,rrepresenting the distance between the particles and the ultrasonic transducer,K s indicating the backscatter characteristic parameter of the suspended particles,K s can be obtained by calculation according to the particle size of the particles. According to the method, the particle size and the concentration of the two-phase flow particles are calculated through the method and the specific formula, so that the detection precision is further effectively ensured.
The ultrasonic piezoelectric driving control system inputs the voltage bias signal, so that the ultrasonic piezoelectric driving control system is ensured to work in a normal range; a mixed signal with a center frequency of 2MHz and a bandwidth of 1 MHz. The invention ensures the reliability of detection through the bias signal input and the selection of the frequency of the mixed signal.
Drawings
FIG. 1 is a schematic block diagram of a system for detecting particle concentration and particle size distribution of mixed acoustic solid-liquid two-phase flow in the present invention;
FIG. 2 is a flow chart of a method for detecting particle concentration and particle size distribution of mixed-frequency acoustic solid-liquid two-phase flow according to the invention;
fig. 3 is a schematic diagram of a de-tailing circuit of the ultrasonic piezoelectric driving control system of the present invention.
Description of the embodiments
The present invention will be described in detail below with reference to the embodiments shown in the drawings, but it should be understood that the embodiments are not limited to the present invention, and functional, method, or structural equivalents and alternatives according to the embodiments are within the scope of protection of the present invention by those skilled in the art.
Examples
Mixing acoustic solid-liquid two-phase flow particle concentration and particle size distribution detection system
As shown in fig. 1, the mixed acoustic solid-liquid two-phase flow particle concentration and particle size distribution detection system of the invention comprises:
the signal output end of the mixing signal generating unit is connected with the ultrasonic piezoelectric driving control system.
The signal output end of the bias voltage signal generating unit is connected with the ultrasonic piezoelectric driving control system, and the bias voltage signal generating unit is used for generating a bias voltage signal.
And the signal output end of the ultrasonic piezoelectric driving control system is connected with the ultrasonic transducer.
In specific implementation, the mixing signal generating unit and the bias voltage signal generating unit are integrated in an FPGA module, and the FPGA module is externally connected with a storage unit. The frequency mixing signal is to establish a sine table in the FPGA module, output sine data through table lookup, change the table lookup to obtain the step size, change the frequency of the output sine data, add a plurality of different sine data to obtain multi-frequency sine frequency mixing data, and the above steps are completed in the FPGA module. The signal output end of the mixing signal generating unit is connected with the ultrasonic piezoelectric driving control system through the digital-to-analog converter and the low-pass filter in sequence. The bias voltage signal generating unit is connected with the ultrasonic piezoelectric driving control system through the buffer and the low-pass filter in sequence. Because the last stage of amplifying driving circuit is an analog circuit, the MOS transistor of the last stage of amplifying driving circuit enters an amplifying semiconductor conduction state and needs a certain bias voltage, and therefore the circuit can enter a normal working state. By adding the bias voltage signal, the whole output signal of the ultrasonic electric drive control system is moved upwards, the transistor normally works in an amplifying state, namely, a static working point of the transistor is set, correct transmission and undistorted amplification of the output signal are ensured, and the load carrying capacity of the circuit is improved.
And the ultrasonic transducer is used for outputting the mixing signal and recovering the echo signal scattered by suspended matters in the solid-liquid two-phase flow. The ultrasonic transducer adopts a self-receiving ultrasonic measurement mode of back scattering signals (namely, the ultrasonic transducer adopts a self-receiving working mode, and the mixed signals realize the acquisition and the reception of echo signals through the back scattering of solid particles in solid-liquid two-phase flow).
When the ultrasonic piezoelectric driving control system outputs signals, a tailing removing function is adopted when the response of the transmitting signals is cut off, so that the tail part of the transmitted mixing signals is subjected to zero setting and residual vibration removing, and the interference of noise signals is eliminated. Depalletizing is an important means of reducing dead zones of spontaneous, self-retracting mode transducers because the mechanical oscillations of the transducer still last some time after the signal is sent out, and in order to shorten the tailing time, after the signal is sent out, the mechanical energy is released through a circuit, thereby reducing the tailing time. The shorter the tailing time is, the shorter the time from transmitting to receiving is, so that the dead zone is smaller, the detection range is enlarged, and the detection accuracy is improved.
In specific implementation, as shown in fig. 3, the tailing removing circuit includes a switching triode Q3, a first NMOS tube Q5, a second NMOS tube Q6, a diode D5, a base electrode of the switching triode Q3 is connected to a positive terminal of the diode D5, a negative terminal of the diode D5 is connected to a resistor R23, and the other end (a signal control terminal of the tailing removing circuit) out_to_gnd of the resistor R23 is connected to the FPGA module, and a collector electrode of the switching triode Q3 is connected to gates of the first NMOS tube Q5 and the second NMOS tube Q6. After the mixed signal output by the FPGA module is amplified by the transformer T1, the mixed signal is output to the ultrasonic transducer by the signal output end OUT.
When the mixing signal output by the FPGA module is ended, the out_to_gnd is changed from a high level to a low level from the FPGA, the switching triode Q3 is conducted, the first NMOS tube Q5 and the second NMOS tube Q6 are conducted, and energy is released to the ground through the first NMOS tube Q5 and the second NMOS tube Q6, so that the mixing signal of the FPGA module is subjected to zero setting and aftershock elimination, interference of noise signals is eliminated, the resolving power of the transmitting signal is improved, and the accuracy of a measuring result is further improved. The initial turn-on voltage of diode D5 is 2.5V, which acts as: since the output of the FPGA is 3.3V and the emitter voltage of Q3 is 5V, if 3.3V is directly output from the FPGA, the switching transistor Q3 is also turned on, and when the voltage of out_to_gnd needs to be lower than 1.9V after the diode D5 is added, the switching transistor Q3 is turned on, and when out_to_gnd is 3.3V, the switching transistor Q3 is turned off.
In the concrete implementation, the echo signal output end of the ultrasonic transducer is connected with an operation unit through a gain amplifier, an analog-to-digital converter and an FPGA module in sequence.
The signal input end of the operation unit is connected with the echo signal output end of the ultrasonic transducer, and the operation unit is used for calculating the concentration and the particle size of suspended particles according to the echo signal. In specific implementation, the arithmetic unit adopts a micro controller MCU.
During operation, the DDS module in the FPGA module generates a mixed signal with the center frequency of 2MHz and the bandwidth of 1MHz, the mixed signal is converted into an analog signal through the DAC and is filtered by the low-pass filter, and meanwhile, the FPGA module generates a bias voltage signal for outputting, and the bias voltage is used for shifting an input voltage signal to a set working range, so that the normal operation and the operation of the system are ensured. After passing through the buffer area and the low-pass filter, the mixed signal enters the ultrasonic piezoelectric driving control system together with the mixed signal, and reaches the ultrasonic transducer to generate the mixed sound wave signal.
After the mixed sound wave signals are reflected in the solid-liquid two-phase fluid, the particles have scattering effect on sound waves, and the ultrasonic transducer receives the signals. The signals enter an input buffer unit, the buffer signals then enter an analog signal gain amplifier, the signals pass through a high-speed analog-to-digital converter, an FPGA module receives mixed echo signals carrying particle concentration and particle size information, the mixed echo signals are sent to a micro controller MCU for decomposition and Fourier transformation, suspended matter particle concentration and particle size data are obtained through calculation, and finally the MCU transmits the data to a differential transceiver through an RS485 bus communication interface to achieve data acquisition.
The FPGA module and the microcontroller MCU are communicated in an SPI mode of USART1, the microcontroller MCU and the differential transceiver are communicated in 485, and because the RAM structure is adopted inside the FPGA module, data can be lost when power is lost, so that logic configuration data needs to be stored externally, an EPCS4 memory is required to be equipped, and the FPGA module and the EPCS4 memory are communicated in SPI mode.
Examples
The detection method utilizing the mixed acoustic solid-liquid two-phase flow particle concentration and particle size distribution detection system comprises the following steps:
in the specific implementation, the ultrasonic piezoelectric driving control system inputs a voltage bias signal to ensure that the ultrasonic electric driving control system works in a normal range. The mixing signal adopts a mixing signal with a central frequency of 2MHz and a bandwidth of 1 MHz.
The particle size of the two-phase flow particles is calculated by the following formula,
in the method, in the process of the invention,V i 、 V j respectively represent the corresponding frequenciesiSum frequencyjIs used for the echo voltage of the (c), K t,i 、K t,j respectively represent the corresponding frequenciesiSum frequencyjIs used for controlling the system parameters of the ultrasonic transducer, α w,i 、 α w,j respectively represent the corresponding frequenciesiSum frequencyjIs the absorption attenuation coefficient of water body ，rRepresenting the distance between the particle and the ultrasonic transducer;
f i /f j energy ratio function representing different frequencies with respect to particle sizeNumber, according to the energy ratiof i /f j The particle size of the particles is obtained. The energy ratio function is prior art.
The two-phase flow particle concentration is calculated by the following formula,
in the method, in the process of the invention,Mthe concentration of the particles is indicated and,psi represents a near field correction factor, V rms The echo voltage is represented by a value representing the echo voltage,K t representing the parameters of the ultrasonic transducer system,αindicating the total attenuation in both the solid and liquid phases,rrepresenting the distance between the particles and the ultrasonic transducer,K s indicating the backscatter characteristic parameter of the suspended particles,K s can be obtained by calculation according to the particle size of the particles.
As shown in fig. 2 and 1, first, the system performs necessary initialization, including elements such as a micro controller MCU communication interface, a calculation module, and a system variable, and an FPGA module. The FPGA module generates and mixes three sine waves with different frequencies and amplitudes. Before preparing to send a signal, the FPGA module disables the received signal and grounds the amplifier input. The FPGA module generates PWM signals and Offset_Adj level, and outputs mixed waves through the ultrasonic piezoelectric driving control system and the digital-to-analog converter, so as to drive the ultrasonic transducer. The system confirms whether the transmission signal is finished or not, and after the transmission is finished, the system waits for delay and prepares to receive the signal. The FPGA module receives and processes the returned echo signals, including amplification, digitization and harmonic analysis. The microcontroller MCU reads and calculates concentration data according to a preset mathematical model and outputs the concentration data through a communication interface.
On the measurement flow of the FPGA module, the FPGA program is designed into a working mode of timing circulation, after power-on, the microcontroller MCU sets the FPGA initialization parameter, sets the detection time interval parameter, namely how long to detect, the detection flow is as follows, mixed analog signals can be sent by setting the signal sending time, the delay time is set to 60us and the acquisition signals are prepared, the acquisition time is set, the acquisition data is started, the acquisition point number is 1 ten thousand acquisition points, the acquisition period is 24MHz, the AD acquisition is finished, the FPGA output state is notified to the microcontroller MCU to read the acquired data, the data is processed in one detection time interval, then the FPGA module waits for one detection time interval, the timing is finished, the next detection is automatically started, and the initialization FPGA module only occurs when the detection is performed for the first time, and the initialization parameter setting can be modified in the detection process.
The working principle of the present invention is described in further detail below.
In the process of solid-liquid two-phase flow propagation of sound waves generated by an ultrasonic transducer, the sound wave penetration range is divided into a near field and a far field. Because of the existence of the transducer protective shell in practical application, the radius measurement difficulty of the sound wave is high when the sound wave propagates in the near field, and the continuous oscillation of the sound wave can also cause the signal to be interfered, so that the sound wave propagates in the near field more complex. Distance transducer when acoustic wave propagates in far fieldrSound pressure amplitude atpDistance to propagation ofrInversely proportional. During near field propagation, a near field correction factor needs to be added to correct the signal of the interfered part. Therefore, in practical application, only far-field echo signal data are generally collected to ensure the reliability of the experiment.
The sound wave intensity can be attenuated in the propagation process of the solid-liquid two-phase flow, and the attenuation is divided into absorption attenuation of a water bodyα w And scattering attenuation of sound waves by suspended particles in a body of waterα s . The absorption decay of a body of water is related to the temperature of the body of water, the absorption, depth of the relaxation process of metal ions, and the frequency of the sound wave, with the absorption decay increasing with increasing propagation distance. Scattering attenuation is caused by the interaction of solid particles, which is related to the concentration of suspended particles, particle size distribution, and frequency of sound waves. The calculation of the scatter attenuation is related to the normalized scatter cross-sectional area of the suspended particles. The normalized cross-sectional area describes the scattering attenuation capability of suspended particles for sound waves, but the accuracy of the measurement is lower when scattering irregularly shaped particles. Wherein both absorption and scattering attenuation can be calculated. The present invention uses a formal function to describe the backscattering properties of suspended particles to sound waves due toThe formal function is directed to backscattering and empirical analysis of the irregular particles is performed to obtain an empirical formula of the formal function for irregularly shaped suspended particles in an actual measurement environment:
(2.1)
falso known as a form function, consider the effect of particle size distribution effects on backscattering capacity.Is the average particle size of the suspended particles,K s is a backscatter characteristic parameter of suspended particles.
Since the form function is difficult to describe suspended particles of irregular shape, reasonable assumption is generally required for particle size distribution in the actual measurement process, and the particle size distribution is mainly classified into lognormal distribution, normal distribution, uniform distribution, and the like. The particle size distribution of the suspended particles is relatively suitable for the case of lognormal distribution.
The backscattering sound pressure received by the ultrasonic transducer is integrated on the propagation path of the sound wave, so that the backscattering sound pressure of the transducer is related to the concentration of solid-liquid two-phase flow particles, and the voltage amplitude and the backscattering sound pressure have the following relation:
(2.2)
Ris the sensitivity coefficient of the ultrasonic transducer,T v is the piezoelectric coefficient of the transducer;V rms is the equivalent echo voltage;P rms is the back-scattered sound pressure.
The concentration of suspended particles and the echo voltage received by the ultrasonic transducer can be expressed by the following formula:
(2.3)
K s is a backscattering characteristic parameter of suspended particles;K t as a system parameter of the transducer,ψis a near field correction factor, corrects near field signals, and is in far field conditionψ=1；MIs the concentration of suspended particles;αis the total attenuation in the solid-liquid phase;Mis the concentration of suspended particles;ris a distance transducerrParticles at the same.
In the formula (2.3), the received back scattering sound pressure is used forP rms Integration in the propagation path and in the spherical coordinates, establishes a relationship between the echo voltage and the concentration of suspended particles,K t as the parameters of the transducer system, the system is calibratedK t It is known that the number of the components,K s the backscattering characteristic parameter concerning the particle diameter information can be obtained by the formula (2.1) if the particle diameter information is knownK s Then the relation between the particle concentration and the echo voltage can be established, and the concentration can be further calculated.
The working principle of quantitative detection of the split-phase content of multiphase flow is as follows:
the ultrasonic transducer outputs a short-time pulse signal (a signal is generated by the control of a formula (2.2)), suspended matters in a water body scatter the signal when the signal propagates in a solid-liquid two-phase flow, the ultrasonic transducer receives a backward scattering echo signal, the echo signal carries parameters such as suspended matter concentration, particle size and the like, and the suspension matter concentration and particle size parameters can be obtained by processing the echo signal through a proper inversion algorithm, so that the volume fraction of solid-liquid two-phase fluid solid-phase substances is further achieved. The basic equation:
(2.4)
(2.5)
(2.6)
K s is a backscatter property parameter of suspended particles;K t is a system parameter of the transducer;V rms is equivalent echo voltage;ris the propagation distance;α s andα w the scattering attenuation coefficient of suspended particles and the absorption attenuation coefficient of the water body are respectively;ρ s is the density of the particles;Nnumber of suspended particles per unit volume;α 0 is the average particle size of the suspended particles.
Energy ratio method (particle size inversion algorithm):
the particle size of the particle is tested based on mixed frequency acoustics, echo signals obtained under a plurality of different frequencies can be measured simultaneously through mixed frequency acoustics, the echo signals generated by the acoustic wave signals with different frequencies on the particle with the same particle size are different, the energy ratio method is based on the fact that different incident frequency signals are adopted on the same measurement system, the concentration of suspension obtained through inversion is consistent according to the signals with different frequencies, and the particle size is measured through the ratio of the concentration. The principle of measuring the particle size by the energy ratio method is given below.
In the multi-frequency measurement mode, the ratio relation of different frequency data to concentration results of the same place is obtained according to the formula (2.5), and inversion concentrations of different frequency data are consistent, then:
(2.7)
(2.8)
(2.9)
i,jwhich means that the different frequencies are to be represented,is the average particle size of the suspended matter;f i andf j is a formal function of suspended particles subjected to a certain particle size distribution for acoustic waves of different frequencies.
Equation (2.7) is obtained by subjecting equation (2.4) to a ratio of 1 at different frequencies, and then to transformation with equation (2.8) (2.9) to obtain equation (2.10). Neglecting the effect of scattering attenuation, for far field information,ψ=1, then it can be reduced to:
(2.10)
the left side of the above formula (2.10) can be calculated, the right sidef i /f j Is an energy ratio function of different frequencies related to particle size, and is fixed on a lookup function chartyCorresponding to the valuexValue [(s) ]xThe axis is the particle size), the particle size can be found out.
Then for a calibrated acoustic suspended sediment measurement system (i.e.K t Known), in the case of known particle size information (i.e.K s Known), the information of the concentration of suspended sediment in the water body can be obtained directly by using the formula (2.4).
When the particle size information is ambiguous, if the system is calibrated (i.eK t Known), the left side of the formula (2.10) can be calculated, the frequency form function on the right side of the formula is a function on particle size, then the particle size information can be obtained, and then the solid phase concentration information of the solid-liquid two-phase medium can be obtained according to the formula (2.4).
The above list of detailed descriptions is only specific to practical embodiments of the present invention, and they are not intended to limit the scope of the present invention, and all equivalent embodiments or modifications that do not depart from the spirit of the present invention should be included in the scope of the present invention.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (10)
1. A mixing acoustic solid-liquid two-phase flow particle concentration and particle size distribution detection system is characterized by comprising:
the signal output end of the mixing signal generating unit is connected with the ultrasonic piezoelectric driving control system;
the signal output end of the ultrasonic piezoelectric driving control system is connected with the ultrasonic transducer;
the ultrasonic transducer is used for outputting a mixing signal and receiving an echo signal scattered by suspended matters in the solid-liquid two-phase flow;
the signal input end of the operation unit is connected with the echo signal output end of the ultrasonic transducer, and the operation unit is used for calculating the concentration and the particle size of suspended particles according to the echo signal.
2. The mixed acoustic solid-liquid two-phase flow particle concentration and particle size distribution detection system according to claim 1, comprising a bias voltage signal generating unit, wherein the signal output end of the bias voltage signal generating unit is connected with an ultrasonic piezoelectric driving control system, and the bias voltage signal generating unit is used for generating a bias voltage signal.
3. The mixed acoustic solid-liquid two-phase flow particle concentration and size distribution detection system according to claim 2, wherein: the signal output end of the mixing signal generating unit is connected with an ultrasonic piezoelectric driving control system through a digital-to-analog converter and a low-pass filter in sequence; the frequency mixing signal generating unit and the bias voltage signal generating unit are integrated in an FPGA module, and the FPGA module is externally connected with a storage unit.
4. The mixed acoustic solid-liquid two-phase flow particle concentration and size distribution detection system according to claim 3, wherein: the echo signal output end of the ultrasonic transducer is connected with an operation unit through a gain amplifier, an analog-to-digital converter and an FPGA module in sequence.
5. The mixed acoustic solid-liquid two-phase flow particle concentration and size distribution detection system according to claim 2, wherein: the bias voltage signal generating unit is connected with the ultrasonic piezoelectric driving control system through the buffer and the low-pass filter in sequence.
6. A detection method using the mixed acoustic solid-liquid two-phase flow particle concentration and particle size distribution detection system according to any one of claims 1 to 5, comprising the steps of:
step 1: the frequency mixing signal generating unit generates a frequency mixing signal, and the frequency mixing signal is output to the ultrasonic piezoelectric driving control system;
step 2: the ultrasonic piezoelectric driving control system outputs signals to the ultrasonic transducer, the ultrasonic transducer outputs mixed signals, and the mixed signals are scattered by suspended matters in the solid-liquid two-phase flow to form mixed echo signals which are received by the ultrasonic transducer;
step 3: the ultrasonic transducer transmits the echo signals to the operation unit, and the operation unit calculates the concentration and the particle size of suspended particles according to the echo signals.
7. The method of detecting according to claim 6, wherein: in step 3, the particle size of the two-phase flow particles is calculated by the following formula,
；
in the method, in the process of the invention,V i 、 V j respectively represent the corresponding frequenciesiSum frequencyjIs used for the echo voltage of the (c),K t,i 、K t,j respectively represent the corresponding frequenciesiSum frequencyjIs used for controlling the system parameters of the ultrasonic transducer,α w,i 、α w,j respectively represent the corresponding frequenciesiSum frequencyjIs characterized by that the absorption attenuation coefficient of water body,rrepresenting the distance between the particle and the ultrasonic transducer;
f i /f j representing energy ratio functions for different frequencies of particle size, according to energy ratiof i /f j The particle size of the particles is obtained.
8. The method of detecting according to claim 7, wherein: in step 3, the particle concentration of the two-phase flow is calculated by the following formula,
；
in the method, in the process of the invention,Mrepresents particle concentration, ψ represents near field correction factor, V rms The echo voltage is represented by a value representing the echo voltage,K t representing the parameters of the ultrasonic transducer system,αindicating the total attenuation in both the solid and liquid phases,rrepresenting the distance between the particles and the ultrasonic transducer,K s indicating the backscatter characteristic parameter of the suspended particles,K s can be obtained by calculation according to the particle size of the particles.
9. The method of detecting according to claim 6, wherein: in the step 1, the ultrasonic piezoelectric driving control system inputs a voltage bias signal, so that the output signal of the ultrasonic piezoelectric driving control system moves upwards, and the transistor normally works in an amplifying state, thereby ensuring the correct transmission and undistorted amplification of the output signal.
10. The method of detecting according to claim 6, wherein: in step 3, when the ultrasonic piezoelectric driving control system outputs signals, a tailing removing function is adopted when the response of the transmitting signals is cut off, so that the tail part of the transmitted mixed signals is subjected to zero setting and residual vibration removing, and the interference of noise signals is eliminated.
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