CN107421713B - System for measuring wave frequency and wave speed of wave liquid film in pipe - Google Patents
System for measuring wave frequency and wave speed of wave liquid film in pipe Download PDFInfo
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- CN107421713B CN107421713B CN201710647411.3A CN201710647411A CN107421713B CN 107421713 B CN107421713 B CN 107421713B CN 201710647411 A CN201710647411 A CN 201710647411A CN 107421713 B CN107421713 B CN 107421713B
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- 239000007788 liquid Substances 0.000 title claims abstract description 50
- 238000012360 testing method Methods 0.000 claims abstract description 10
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- 238000010219 correlation analysis Methods 0.000 abstract description 5
- 238000005259 measurement Methods 0.000 abstract description 4
- 239000010408 film Substances 0.000 description 31
- 238000000034 method Methods 0.000 description 8
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- 230000003595 spectral effect Effects 0.000 description 5
- 238000005314 correlation function Methods 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 4
- 238000009434 installation Methods 0.000 description 4
- 238000012546 transfer Methods 0.000 description 4
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- 238000010586 diagram Methods 0.000 description 2
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- 230000008859 change Effects 0.000 description 1
- 238000003889 chemical engineering Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
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- 238000009833 condensation Methods 0.000 description 1
- 238000010612 desalination reaction Methods 0.000 description 1
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- 239000011552 falling film Substances 0.000 description 1
- 238000002795 fluorescence method Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M10/00—Hydrodynamic testing; Arrangements in or on ship-testing tanks or water tunnels
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Abstract
The measuring system provided by the invention converts the intensity signal of light into a current signal by using the photoelectric sensor, thereby realizing the measurement of the wave frequency and the wave speed of the fluctuating liquid film. The invention relates to the following principle: light emitted by the infrared light-emitting diode is dispersed when passing through the interface of the fluctuating liquid film, and only part of the light is absorbed by the infrared photodiode. A pair of infrared light emitting diodes and infrared photoelectric diodes which are installed on the outer wall of the test section pipe form an upstream sensor and a downstream sensor, the sensors convert light intensity signals into current signals, the current signals are amplified by an amplifier and then converted into discrete digital signals by an A/D converter, and the digital signals are processed by adopting an MATLAB software programming program based on Fourier transform (FFT) and a cross-correlation analysis principle to obtain the wave frequency and the wave speed of a fluctuating liquid film. The invention has the advantages that the wave frequency and the wave speed of the fluctuating liquid film can be measured simultaneously, and the statistical uncertainty of the measured data is lower than 5 percent.
Description
Technical Field
The invention belongs to the technical field of measurement of fluctuation characteristic parameters of a fluctuation liquid film in a falling film evaporator, and particularly relates to a system for obtaining wave frequency and wave speed of the fluctuation liquid film in a tube through Fast Fourier Transform (FFT) and cross-correlation analysis of a current signal received by a photoelectric sensor.
Background
The steam condensation is widely applied to the fields of petroleum, chemical engineering, refrigeration, energy, aerospace, seawater desalination and the like as an efficient heat transfer technology. The heat and mass transfer process is strengthened by the fluctuation characteristic of the condensed liquid film in the practical application process. The fluctuation of the condensed liquid film has complex dynamic characteristics in time and space, and due to the limitation of a test technology and a test method, the wave frequency and the wave speed which characterize the dynamic characteristics of the fluctuation of the condensed liquid film cannot be accurately measured, so that the mechanism of strengthening heat and mass transfer by the fluctuation of the condensed liquid film is to be further researched.
At present, the dynamic parameters of the fluctuating liquid film are mainly measured by an induced fluorescence method, images of the same wave shot at different positions are manually identified, and the wave velocity of the fluctuating liquid film is obtained by measuring the fluctuating displacement within a shooting time interval. The following main problems exist in the measuring technology: identifying that the same wave depends on subjective judgment of a measurer; the physical property of the liquid film is easy to change by adding the fluorescence factor into the liquid; only the wave velocity of the liquid film can be measured, but the wave frequency cannot be measured. Therefore, a system capable of accurately measuring the wave frequency and the wave speed of the fluctuating liquid film is required to be developed, the mechanism process of the condensed liquid film fluctuation enhanced heat and mass transfer is explored and researched, and theoretical basis and technical reserve are provided for the innovative development of the high-efficiency heat exchange technology.
Disclosure of Invention
The invention aims to solve the problem of providing a system for measuring the wave frequency and the wave speed of a fluctuating liquid film in a pipe, which can accurately measure the wave frequency and the wave speed of the fluctuating liquid film in real time. The device for measuring the wave frequency and the wave speed of the fluctuating liquid film provided by the invention is required to be used under no light or weak light.
The technical solution of the invention is realized as follows:
a system for measuring wave frequency and wave velocity of a fluctuating liquid film in a pipe, comprising: the infrared LED display device comprises two infrared light emitting diodes, two infrared photodiodes, an amplifier, an A/D converter, a computer, a power supply, a lead and a data wire;
the infrared light emitting diode and the infrared photodiode form a pair of optical sensors which are respectively called as an upstream sensor and a downstream sensor according to the flowing direction of liquid;
the two infrared light-emitting diodes are arranged on the same side of the outer wall of the test section pipe, and the distance between the two infrared light-emitting diodes is L;
the two infrared photodiodes are arranged on the outer wall of a tube testing section which is symmetrical to the infrared light emitting diode, receive light emitted by the infrared light emitting diode and convert intensity signals of the received light into current signals;
the signal amplifier is connected with the infrared photodiode through a lead, and amplifies a weak current electric signal generated by the infrared photodiode;
the A/D converter is connected with the signal amplifier through a data line, and converts amplified continuous signals into discrete digital signals;
the computer is connected with the A/D converter through a data line, and the MATLAB software is used for writing a program to process the digital signal so as to obtain the wave frequency and the wave speed of the fluctuating liquid film.
The other technical scheme of the invention is that the installation distance L of the two optical sensors is 9-11 cm.
The other technical scheme of the invention is that the infrared light emitting diode emits infrared rays with the wavelength of 935-945 nm.
The other technical scheme of the invention is that the intensity of the light emitted by the infrared light-emitting diode can be adjusted according to the thickness of the fluctuating liquid film in the tube.
The other technical scheme of the invention is that the light received by the infrared photodiode is infrared with the wavelength of 935-945 nm, which is the same as that of the infrared light-emitting diode.
The light emitted by the infrared light-emitting diode is dispersed when passing through the interface of the wave liquid film, one part of light is refracted or reflected by the wave interface, the other part of light is absorbed by the infrared photodiode, and then the intensity signal of the light is converted into an electric signal.
The use method of the system for measuring the wave frequency and the wave speed of the wave liquid film in the pipe comprises the following steps:
1) and device installation: installing two infrared light emitting diodes at the same side of the outer wall of a tube at a distance of L, installing two infrared photodiodes at the outer wall of the tube test section symmetrical to the infrared light emitting diodes, connecting a signal amplifier and the infrared photodiodes through a lead, connecting an A/D converter and the signal amplifier through a data line, and connecting a computer and the A/D converter through a data line;
2) and adjusting the device: adjusting the relative positions of the infrared light-emitting diode and the infrared photoelectric diode to ensure that the centers of the infrared light-emitting diode and the infrared photoelectric diode are kept on a straight line and are vertical to the axial direction of the circular tube;
3) and debugging the device: the current signal generated by the infrared photodiode is recorded by electrifying under the condition that water is not introduced into the tube, and if the current value changes, the signal amplifier needs to be adjusted to fix the current value;
4) and water test: the wave frequency and the wave speed of the wave liquid film in the pipe can be measured by introducing water into the round pipe;
5) and data acquisition and analysis: and the computer acquires and stores the discrete signals obtained by the conversion of the A/D converter, and then utilizes MATLAB software to write a program to process the discrete digital signals to obtain the wave frequency and the wave speed of the fluctuating liquid film.
The digital signal processing process by writing a special program by using MATLAB software is as follows:
the signal output by the upstream sensor is x (t), and the signal output by the downstream sensor is y (t);
respectively carrying out Fast Fourier Transform (FFT) on the signals x (t) and y (t) by a written program to obtain corresponding power spectral density function graphs;
the frequencies corresponding to the peaks in the corresponding power spectral density map are respectively f1、f2；
The wave frequency of the fluctuating liquid film is:
f＝(f1+f2)/2
taking the signal x (t) as an input signal and the signal y (t) as an output signal, and performing cross-correlation analysis on the signals by using a programmed program to obtain a cross-correlation function graph;
the value of tau corresponding to the peak in the cross-correlation function graph is time displacement tau0；
The fluctuating liquid film velocity is then:
V＝L/τ0
the advantages of the invention are obvious and mainly appear as follows:
1. the invention has high measurement precision, and the statistical uncertainty of wave frequency and wave velocity data is lower than 5 percent;
2. the invention can simultaneously measure the wave velocity and the wave frequency of the liquid film;
3. the invention can process the signal in real time and obtain the transient distribution of wave frequency and wave speed.
The invention has the advantages of simple structure, convenient installation and debugging, high measurement precision, capability of realizing real-time processing of signals to obtain the transient distribution of wave frequency and wave speed and the like.
Drawings
The invention has 6 figures in total, wherein:
FIG. 1 is a schematic diagram of the system of the present invention;
FIG. 2 is a schematic representation of a signal function image output by an upstream sensor employing the present invention;
FIG. 3 is a graph of power spectral density obtained by fast Fourier transforming a signal x (t);
FIG. 4 is a schematic representation of a signal function image output by a downstream sensor employing the present invention;
FIG. 5 is a plot of the power spectral density of a signal y (t) after fast Fourier transform;
FIG. 6 is a schematic diagram of a cross-correlation function image obtained by cross-correlation analysis of signals x (t) and y (t).
In the figure: 1. the device comprises an infrared light emitting diode 2, a round tube 3, an infrared photodiode 4, a signal amplifier 5, an A/D converter 6, a computer 7, a fluctuating liquid film, X, a liquid flowing direction, L and an installation distance.
Detailed Description
The embodiment of the invention is shown in figure 1, and the system for measuring the wave frequency and the wave speed of the fluctuating liquid film in the pipe comprises: the system comprises an infrared light emitting diode 1, an infrared photodiode 3, a signal amplifier 4, an A/D converter 5, a computer 6, a lead and a data line;
the infrared light emitting diode 1 and the infrared photodiode 3 form a pair of optical sensors which are respectively called as an upstream sensor and a downstream sensor according to the flowing direction of liquid;
the two infrared light-emitting diodes 1 are arranged on the same side of the outer wall of the test section pipe, and the distance between the two infrared light-emitting diodes is L, and the L is 10 cm;
the two infrared photodiodes 3 are arranged on the outer wall of the tube testing section which is symmetrical to the infrared light-emitting diode 1, receive light emitted by the infrared light-emitting diode 1 and convert intensity signals of the received light into current signals;
the signal amplifier 4 is connected with the infrared photodiode 3 through a lead, and amplifies a weak current electric signal generated by the infrared photodiode 3;
the A/D converter 5 is connected with the signal amplifier 4 through a data line, and converts the amplified continuous signals into discrete digital signals;
and the computer 6 is connected with the A/D converter 5 through a data line, and the digital signal is processed by utilizing an MATLAB software programming program to obtain the wave frequency and the wave speed of the fluctuating liquid film.
The infrared light emitting diode 1 emits infrared rays with the wavelength of 935-945 nm; the intensity of the emitted light can be adjusted according to the flowing state of the liquid in the tube.
The light received by the infrared photodiode 3 is the infrared ray with the wavelength of 935-945 nm which is the same as that of the infrared light-emitting diode 1
Fig. 2 to 6 are images obtained in this example:
FIGS. 2 and 4 are respectively an image of the signal x (t) output by the upstream sensor and an image of the signal y (t) output by the downstream sensor;
fast Fourier Transform (FFT) is respectively performed on the signals x (t) and y (t) by a written program to obtain corresponding power spectral density function graphs as fig. 3 and 5;
frequency corresponding to peak in fig. 3
f1＝39.06Hz
Frequency corresponding to peak in fig. 5
f2＝41.99Hz
The wave frequency of the fluctuating liquid film is as follows:
f＝(f1+f2)/2＝40.53Hz
taking the signal x (t) as an input signal and y (t) as an output signal, and performing cross-correlation analysis by using a programmed program to obtain a cross-correlation function graph as a graph shown in FIG. 6;
the value of τ corresponding to the peak in fig. 6 is the time shift τ0，
τ0＝13.8ms
The wave speed of the wave liquid film is as follows:
V＝L/τ0＝0.1/0.0138＝7.2m/s 。
Claims (5)
1. a system for measuring wave frequency and wave velocity of a fluctuating liquid film in a pipe, comprising: an infrared light emitting diode (1) and an infrared photodiode (3); the infrared light emitting diode (1) and the infrared photodiode (3) form a pair of optical sensors which are respectively called as an upstream sensor and a downstream sensor according to the flowing direction of liquid; the two infrared light-emitting diodes (1) are arranged on the same side of the outer wall of the test section pipe, and the distance between the two infrared light-emitting diodes is L; the two infrared photodiodes (3) are arranged on the outer wall of the tube testing section which is symmetrical to the infrared light-emitting diode (1) and used for receiving light emitted by the infrared light-emitting diode (1) and converting intensity signals of the received light into current signals;
the system for measuring the wave frequency and the wave speed of the wave liquid film in the pipe is characterized by further comprising: a signal amplifier (4), an A/D converter (5), a computer (6), a lead and a data line;
the signal amplifier (4) is connected with the infrared photodiode (3) through a lead and amplifies a weak current electric signal generated by the infrared photodiode (3);
the A/D converter (5) is connected with the signal amplifier (4) through a data line, and converts amplified continuous signals into discrete digital signals;
the computer (6) is connected with the A/D converter (5) through a data line, and the digital signal is processed by utilizing an MATLAB software programming program to obtain the wave frequency and the wave speed of the fluctuating liquid film.
2. The system for measuring the wave frequency and the wave speed of the fluctuating liquid film in the pipe according to claim 1, wherein the two optical sensors are installed at a distance L ranging from 9 to 11 cm.
3. The system for measuring the wave frequency and the wave speed of the fluctuating liquid film in the pipe according to claim 1, wherein the infrared light emitting diode (1) emits infrared rays with the wavelength of 935-945 nm.
4. The system for measuring the wave frequency and the wave speed of the fluctuating liquid film in the pipe according to claim 1, wherein the intensity of the light emitted from the infrared light emitting diode (1) is adjusted according to the thickness of the fluctuating liquid film in the pipe.
5. The system for measuring the wave frequency and the wave speed of the fluctuating liquid film in the pipe according to claim 1, wherein the infrared photodiode (3) receives the same infrared rays with the wavelength of 935-945 nm as the infrared light emitting diode (1).
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| CN201710647411.3A CN107421713B (en) | 2017-08-01 | 2017-08-01 | System for measuring wave frequency and wave speed of wave liquid film in pipe |
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| CN107421713B true CN107421713B (en) | 2020-02-18 |
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH074943A (en) * | 1993-06-14 | 1995-01-10 | Ulvac Japan Ltd | Film-formation monitoring and control apparatus |
| CN105701842A (en) * | 2016-01-08 | 2016-06-22 | 天津大学 | Liquid film fluctuation speed measurement method based on chain code contour features |
| CN107314738A (en) * | 2017-06-13 | 2017-11-03 | 中国科学院力学研究所 | The thick measurement experiment system of hypersonic overflow liquid film cooling film and data processing method |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3893888B2 (en) * | 2001-03-19 | 2007-03-14 | 株式会社日立製作所 | Plasma processing equipment |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH074943A (en) * | 1993-06-14 | 1995-01-10 | Ulvac Japan Ltd | Film-formation monitoring and control apparatus |
| CN105701842A (en) * | 2016-01-08 | 2016-06-22 | 天津大学 | Liquid film fluctuation speed measurement method based on chain code contour features |
| CN107314738A (en) * | 2017-06-13 | 2017-11-03 | 中国科学院力学研究所 | The thick measurement experiment system of hypersonic overflow liquid film cooling film and data processing method |
Non-Patent Citations (1)
| Title |
|---|
| Optical measurement of liquid film thickness and wave velocity in liquid film flows";E. T. Hurlburt 等;《Experiments in Fluids》;19961231;第21卷;第357-362页 * |
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