CN107044865A - A kind of minimum pressure drop speed decision method based on electrostatic signal approximate entropy - Google Patents

Abstract

The invention provides a method for judging the minimum pressure drop velocity based on the approximate entropy of an electrostatic signal, which is used to measure the minimum pressure drop velocity of a gas-solid two-phase flow in a horizontal pipeline. The four-electrode electrostatic sensor includes four arcs fixed inside the horizontal pipeline The electrodes, marked with numbers 1-4, are fixed on the upper, right, lower and left sides of the circumference of the pipe section in turn. The determination method is as follows: under different solid phase mass flow conditions, collect four For the electrostatic signals of four electrodes, the wavelet transform is used to filter the electrostatic signals to filter out high-frequency noise signals; for the electrostatic signals of the four electrodes after filtering, the respective approximate entropy values are calculated respectively, and electrodes 1 to 4 correspond to Approximate entropy values E ₁ , E ₂ , E ₃ and E ₄ ; calculate the average E _mean of the approximate entropy values corresponding to the three electrodes No. 1, 2 and 4; calculate E _mean and the approximate entropy value E ₃ corresponding to the electrode No. 3 Relative difference, the superficial gas velocity corresponding to the maximum is the minimum pressure drop velocity.

Description

A Judgment Method of Minimum Voltage Drop Velocity Based on Approximate Entropy of Electrostatic Signal

technical field

The invention belongs to the technical field of gas-solid two-phase flow detection, in particular to a method for judging the minimum pressure drop velocity of horizontal pipeline pneumatic conveying.

Background technique

Pneumatic conveying has been used more and more in the industrial and living fields. The minimum pressure drop velocity is a key parameter in the design of a pneumatic conveying system, and it is the minimum boundary condition to maintain conveying stability [1]. Due to the interaction between particles-gas, particles-particles and particles-pipe wall inside the pipeline, the pneumatic conveying process is a very complex turbulent flow process[2]. Existing models [3-5] are based on empirical formulas, and these models are only applicable to the researchers' own experimental data and are not transplantable. In addition, the pressure signal in the pipeline is time-varying, and current models are based on static pressure drop values.

The minimum pressure drop velocity can be determined indirectly by analyzing the different characteristics of different flow patterns near the minimum pressure drop velocity. Hui Li used the wavelet multi-resolution analysis method to study and found that the larger root mean square appeared in the high-frequency part of the signal in the suspended state, while the larger root mean square appeared in the low-frequency part of the signal in the non-floating state [6]. Klinzing used the energy spectrum method to analyze the pressure signal, and concluded that the pressure signal has a high frequency and a low amplitude in the suspension flow, while the main frequency appears near 0 Hz and has a large amplitude in the laminar flow [7 ]. These methods provide the possibility for the accurate determination of the minimum pressure drop velocity, but the pressure fluctuation signal mainly reflects the overall state of the pipeline at the pressure taking part. For horizontal pipelines, due to gravity, different flow conditions near the minimum pressure drop velocity will Different flow states are generated in different regions of the pipe section, and their relationship characteristics may provide a more reliable basis for determining the minimum pressure drop velocity.

Non-invasive electrostatic sensors have the advantages of simple structure and high sensitivity, and are widely used in the detection of gas-solid two-phase flow [8-10]. How to process and analyze electrostatic signals and effectively determine the minimum pressure drop velocity of gas-solid two-phase flow poses new challenges for electrostatic detection.

references

[1]Jama G A, Klinzing G E, Rizk F.An investigation of the prevailingflow patterns and pressure fluctuation near the pressure minimum and unstable conveying zone of pneumatic transport systems[J].Powder Technology,2000,112(1/2):87- 93.

[2] Herbreteau C, Bouard R. Experimental study of parameters which influence the energy minimum in horizontal gas—solid conveying[J]. Powder Technology, 2000, 112(3): 213-220.

[3] R.D.Marcus, L.S.Leung, G.E.Klinzing, et al. Pneumatic Conveying of Solids: A Theoretical and Practical Approach [J]. Drying Technology, 1993, 11(4): 859-860.

[4] Dhodapkar S V, Klinzing G E. Pressure fluctuations in pneumatic conveying systems [J]. Powder Technology, 1993, 74(2): 179-195..

[5] M.G.JONES, K.C.WILLIAMS. Solids Friction Factors for Fluidized Dense-Phase Conveying [J]. Particulate Science & Technology, 2003, 21(1): 45-56.

[6] Hui L. Application of wavelet multi-resolution analysis to pressure fluctuations of gas–solid two-phase flow in a horizontal pipe [J]. Powder Technology, 2002, 125(125): 61-73.

[7] GREGORY A. JAMA, GEORGE E. KLINZING, FARID RIZK. Analysis of unstable behavior of pneumatic conveying systems [J]. Particulate Science & Technology, 1999, 17(1): 43-68.

[8]Ma J, Yan Y.Design and evaluation of electrostatic sensors for themeasurement of velocity of pneumatically conveyed solids[J].Flow Measurement&Instrumentation,2000,11(3):195-204.

[9] Zhang W, Wang C, Wang Y. Parameter Selection in Cross-Correlation-Based Velocimetry Using Circular Electrostatic Sensors [J]. Instrumentation&Measurement IEEE Transactions on, 2010, 59(5): 1268-1275.

[10] Xu C, Zhou B, Yang D, et al. Velocity measurement of pneumatically conveyed solid particles using an electrostatic sensor [J]. Measurement Science & Technology, 2008, 19(2): 211-218.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, and provide a method for judging the minimum pressure drop speed of horizontal pipeline pneumatic conveying with 4-electrode electrostatic sensors based on the approximate entropy of electrostatic signals. For this reason, the present invention adopts following technical scheme:

A method for judging the minimum pressure drop velocity based on the approximate entropy of an electrostatic signal, which is used to measure the minimum pressure drop velocity of a gas-solid two-phase flow in a horizontal pipeline. The detection device used consists of a four-electrode electrostatic sensor, four identical conditioning circuits, It consists of a data acquisition module and a host computer. The 4-electrode electrostatic sensor includes 4 arc-shaped electrodes fixed inside the horizontal pipe, marked with numbers 1-4, and fixed on the upper, right, lower and left sides of the circumference of the pipe section in turn, and each arc-shaped electrode is connected to a Conditioning circuit; the signal passed through the conditioning circuit is input to the upper computer for analysis and processing through the data acquisition module, and the detection steps of the minimum pressure drop speed of pneumatic conveying are as follows:

(1) Under different solid-phase mass flow conditions, collect the electrostatic signals of four electrodes corresponding to different superficial gas velocities, and use wavelet transform to filter the electrostatic signals to filter out high-frequency noise signals;

(2) For the electrostatic signals of the four electrodes that have been filtered, calculate their respective approximate entropy values, and electrodes 1 to 4 correspond to approximate entropy values E ₁ , E ₂ , E ₃ and E ₄ ;

(3) average E _mean to the approximate entropy values corresponding to No. 1, No. 2 and No. 4 electrodes;

(4) Calculate the relative difference between E _mean and the approximate entropy value E ₃ corresponding to electrode No. 3, which is recorded as the relative approximate entropy E _d , and the superficial gas velocity corresponding to the maximum E _d is the minimum pressure drop velocity.

Description of drawings

Figure 1. Schematic diagram of the minimum pressure drop detection system for horizontal pipeline pneumatic conveying;

Figure 2. Schematic diagram of the structure of the four-electrode electrostatic sensor;

Figure 3. The flow chart of detecting the minimum pressure drop speed of pneumatic conveying based on approximate entropy;

The reference signs are as follows:

1. Horizontal pipeline; 2. Left electrode; 3. Upper electrode; 4. Right electrode; 5. Lower electrode; 6 Conditioning circuit; 7. Data acquisition module; 8. Insulation layer; 9. Arc electrode group ; 10, flange

Specific implementation method

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Referring to Fig. 1, the detection device includes a 4-electrode electrostatic sensor 2-5, four identical conditioning circuits 6, a data acquisition module 7 and a host computer. Referring to Figure 2, the electrostatic sensor is composed of a pipeline insulation layer 8, an arc-shaped electrode group 9, a shielding pipe wall 1, and a flange 10; The digital marks of 4 are respectively installed on the upper side, right side, lower side and left side of the circumference of the pipe section, the electrode width is 6mm, and the arc is 60 degrees; the signal conditioning circuit is used to filter and amplify the signal of the electrostatic sensor; The signal is input to the upper computer for analysis and processing through the data acquisition module; the upper computer is responsible for calculating and processing the collected 4 signals.

The determination steps of the minimum pressure drop velocity are as follows:

(1) Use wavelet transform to filter the electrostatic signal

Under different solid phase mass flow conditions, the electrostatic signals of the four electrodes corresponding to different superficial gas velocities were collected. Using wavelet transform to filter the electrostatic signal, using "db3" wavelet base to decompose the electrostatic signal into 4 layers, and reconstruct the signal below 1000Hz, so as to filter out the noise signal above 1000Hz.

(2) Calculate the approximate entropy values of the electrostatic signals of the four electrodes

Calculate the approximate entropy values of the electrostatic signals of the four electrodes respectively, and the electrodes 1 to 4 correspond to the approximate entropy values E ₁ , E ₂ , E ₃ and E ₄ respectively.

Take a piece of electrostatic signal data {x(i)} with a length of N, and reconstruct it into an m-dimensional signal (generally m is selected as 2), and its vector y(i) is expressed as

y(i)={x(i),x(i+1),x(i+2),...,x(i+m-1)}1≤i≤N-m+1 (1)

In the formula, m is called the window length. d[y(i),y(j)] is defined as the maximum distance between each vector, which is

For a single vector sequence {y(i)}(i≤N-m+1), define

In the formula, B[y(j)|d[y(i), y(j)]≤r the number of y(j) (r generally chooses 0.1~0.2 times the standard deviation of the signal); It represents the probability that d[y(i), y(j)] is less than r with y(i) as the center when the window length is m and the allowable deviation is r, so that all y(j )(j≠i) and y(i), that is, the degree of regularity of the sequence {y(j)}. make

In the formula, Φ ^m (r) represents the average autocorrelation degree of the sequence {y(j)}. The larger m is, the rarer the state points in the phase space are, and the corresponding correlation opportunities are smaller, so Both Φ m (r) and Φ ^m (r) decrease with the increase of m, and the deviation of Φ ^m (r) can be expressed by the following formula:

For different signals, the result of formula (5) will be very different. White noise uniformly fills all dimensions of the phase space, Not big, but Φ ^m is very small, as m increases, Φ ^m (r)-Φ ^m+1 (r)→∞. But for regular signals, when m increases to a certain extent, Φ ^m (r) does not increase with the increase of m, close to 0. Therefore, Φ ^m (r)-Φ ^m+1 (r) can describe the degree of randomness of the system, and the approximate entropy E is defined as

E＝Φ ^m (r)-Φ ^m+1 (r) (6)

(3) Judgment method of minimum pressure drop velocity based on approximate entropy

Calculate the average E _mean of the approximate entropy values corresponding to the three electrodes 1, 2 and 4

E _mean ＝(E ₁ +E ₂ +E ₄ )/3 (7)

Calculate the relative difference between E _mean and the approximate entropy value E ₃ corresponding to electrode No. 3, which is recorded as the relative approximate entropy E _d

The superficial gas velocity corresponding to the maximum approximate entropy difference E _d is the minimum pressure drop velocity.

Calculate the relative approximate entropy values corresponding to different superficial gas velocities under the three solid phase mass flow rates, as shown in Table 1.

Table 1 Relative approximate entropy values corresponding to different superficial gas velocities under three solid phase mass flow rates

When the conveying speed reaches the minimum pressure drop speed, the sum of the solid phase pressure loss and the gas phase pressure loss reaches the minimum. At this time, it is the suspension flow with the lowest degree of turbulence, and the degree of chaos in the flow is the lowest. The magnitude of the approximate entropy value represents the complexity of the flow in the pipeline, so the maximum value of the relative approximate entropy of the electrostatic signal represents the minimum point of chaos in the pipeline, which has the same effect as the minimum pressure drop velocity. Establish the following mathematical model:

where v _mp is the minimum pressure drop velocity, is the apparent gas velocity corresponding to the maximum value of the relative approximate entropy of the electrostatic signal. It can be seen from Table 1 that the apparent gas velocity corresponding to the approximate entropy of the electrostatic signal of the lower electrode is The air velocity is 9.88m/s, 9.62m/s, 9.20m/s respectively.

Claims (1)

1. A minimum pressure drop velocity determination method based on the approximate entropy of electrostatic signals, which is used to measure the minimum pressure drop velocity of gas-solid two-phase flow in horizontal pipelines. The detection device used consists of four-electrode electrostatic sensors, four identical conditioning circuit, a data acquisition module and a host computer. The 4-electrode electrostatic sensor includes 4 arc-shaped electrodes fixed inside the horizontal pipe, marked with numbers 1-4, and fixed on the upper, right, lower and left sides of the circumference of the pipe section in turn, and each arc-shaped electrode is connected to a Conditioning circuit; the signal passed through the conditioning circuit is input to the upper computer for analysis and processing through the data acquisition module. The detection steps of the minimum pressure drop speed of pneumatic conveying are as follows: (1) Under different solid-phase mass flow conditions, collect the electrostatic signals of four electrodes corresponding to different superficial gas velocities, and use wavelet transform to filter the electrostatic signals to filter out high-frequency noise signals; (2) For the electrostatic signals of the four electrodes that have been filtered, calculate their respective approximate entropy values, and electrodes 1 to 4 correspond to approximate entropy values E ₁ , E ₂ , E ₃ and E ₄ ; (3) average E _mean to the approximate entropy values corresponding to No. 1, No. 2 and No. 4 electrodes; (4) Calculate the relative difference between E _mean and the approximate entropy value E ₃ corresponding to electrode No. 3, which is recorded as the relative approximate entropy E _d , and the superficial gas velocity corresponding to the maximum E _d is the minimum pressure drop velocity.