JPH0518981A - Gas-liquid two phase flow measurement device - Google Patents

Abstract

PURPOSE:To apply the measurement device for detecting gas-liquid two-phases and the velocity of bubbles and the like by the use of an optical fiber under an environment of high temperature and pressure. CONSTITUTION:An optical fiber 1 for beam emission is centered and a group of optical fibers arranging another optical fiber 2 for beam receiving in the circumference thereof are brought into contact with a transparent sapphire probe 3 for passing a beam A laser beam is irradiated from the end face of the optical fiber l for beam emission, introduced to the optical fiber 2 for beam receiving as a reflection beam of different reflectance in response to gas-liquid two-phases and at the same time the reflection beam Doppler-shifted on the surface of bubbles 5 and the like is guided to the optical fiber 1 for beam emission. As the result, a bubble speed and a bubble diameter are measured on the basis of the level difference of the reflection beam and a Doppler shift frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring bubble velocity, bubble diameter, etc. in a gas-liquid two-phase flow.

[0002]

2. Description of the Related Art As a conventional gas-liquid two-phase flow measuring device, a gas-liquid two-phase flow measuring device using an optical fiber has been proposed, as disclosed in Japanese Patent Publication No. 62-58441. In this, one end of the optical fiber is arranged so as to be perpendicular to the flow direction of the gas-liquid two-phase flow, and laser light is incident from the other end of the optical fiber. The level of the reflected light obtained from the end face of the optical fiber changes when it is in contact with the gas phase and the liquid phase, and Doppler shift occurs.Therefore, the bubble velocity is higher than the high frequency component of the reflected light and the bubble passes from the low frequency component. It is designed to calculate speed.

[0003]

However, in such a conventional gas-liquid two-phase flow measuring device, when it is used in a high temperature and high pressure environment, the end face of the optical fiber is improved in order to improve the environmental resistance. It is necessary to cover it with a protective cover. In that case, there is a drawback that the level of the reflected light from the optical fiber is low and a signal of a low frequency component cannot be detected.

The present invention has been made in view of the above problems of the conventional measuring apparatus for gas-liquid two-phase flow, and the bubble velocity and bubble diameter of the gas-liquid two-phase flow are high even under the environment of high temperature and high pressure. It is a technical subject to be able to measure.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to a light source for generating light having a constant plane of polarization at a single frequency, a polarizing beam splitter for transmitting light provided by the light source, and a light source for transmitting the polarized beam splitter. An optical fiber for projecting light from one end face of the optical fiber, abutting the end face of the projecting optical fiber, and a transparent probe arranged opposite to the flow direction of the gas-liquid two-phase flow, Reflection from the interface between the two phases of gas and liquid given to the polarization beam splitter from the multiple optical fibers for receiving light, one end of which contacts the probe around the other end face of the optical fiber for projecting light. A first light receiving element arranged so as to give light that is reflected again by the polarization beam splitter of the light, and a bubble speed calculation for obtaining a bubble speed from a high frequency component of a signal obtained from the first light receiving element A step, a second light receiving element for converting the reflected light of the light receiving optical fiber into an electric signal, and a passage time measuring means for obtaining a bubble passage time based on a change in the signal level of the second light receiving element. It is characterized by that.

[0006]

According to the present invention having such characteristics, the light from the light source is guided to the light projecting optical fiber through the polarization beam splitter. Since the level of light received by the light-receiving optical fiber differs depending on whether the tip of the probe is in contact with the liquid phase or the gas phase, the reflected light signal is detected based on this. Further, the Doppler shift frequency is detected from the high frequency component obtained in the light projecting optical fiber, and the moving speed of the gas phase or the liquid phase is detected.

[0007]

FIG. 1 is a principle diagram for explaining the principle of gas-liquid two-phase flow according to an embodiment of the present invention. In this figure, an optical fiber 1 for projecting light and an optical fiber 2 for receiving light are configured so as to abut on the end of a cylindrical sapphire probe 3 whose only lower end is formed in a truncated cone shape as shown. .. Here, a plurality of, for example, 19 optical fibers 2 for receiving light are arranged around a specific circumference around the optical fiber for projecting light. Now, the light emitting / receiving optical fibers 1 and 2 and the probe 3 are fixed, and the tip end surface 3a is fixed so as to face the gas-liquid two-phase flow. Here, 4 represents a liquid phase, and 5 represents a bubble. In FIG. 1A, the end face 3a of the probe 3 faces the adjacent bubble 5, and in FIG. 1B, the end face in contact with the bubble 5. 3a shows a state where the bubble 5 penetrates the surface of the bubble 5 and is contained therein, and FIG. 1 (c) shows a state in which the bubble 5 has finished passing through the end face 3a. The arrow indicates the direction of gas-liquid two-phase flow.

When light passes through the light projecting optical fiber 1 and is applied to the sapphire probe 3, most of the light passes through the end face 3a, but part of the light is reflected by the end face 3a and the optical fiber 1 and The light is incident on the optical fiber 2 for receiving light again. This reflected light intensity varies depending on the refractive index of the medium with which the end face 3a is in contact, but assuming that the refractive index nc of sapphire is 1.7, the refractive index n1 of liquid phase such as water is 1.3, and the refractive index na of bubbles such as air is 1. As shown in FIGS. 1 (a) and 1 (c), the reflected light intensity is about 0.2 to 0.5% when the end face 3a is in contact with the liquid phase, which is smaller than about 6.7% when it is in contact with bubbles. Therefore, as shown in FIGS. 1A to 1C, when the bubble 5 approaches the end face 3a of the sapphire probe 3 and passes through the end face 3a, the light intensity obtained by the optical fiber 2 for receiving light is increased. Is as shown in FIG. Here at time t ₂ is the bubble 5 in contact with the end face 3a, t ₄ shows the time when the end face 3a began contact with the liquid phase finishes passing through the bubble, during the time t ₂ ~t ₄ end surface Since 3a is in contact with the bubbles, the intensity of the reflected light is high only during that time.

In FIGS. 1A and 1B, the light transmitted through the end surface 3a of the sapphire probe 3 is reflected on the outer surface and the inner surface of the bubble 5, that is, the boundary surface between the two phases, and enters the sapphire probe 3 again. Incident. A part of this light will be incident on the light receiving optical fiber 2 and the light projecting optical fiber 1 again. Since the bubble 5 is moving at the velocity V in the direction of the arrow, the frequency of the reflected light from the bubble surface is slightly increased due to the Doppler effect. Now, if the frequency of the incident light is fi, the frequency shift amount due to the Doppler effect at the time of approaching a bubble, that is, the Doppler shift frequency is Δfi, and the luminous flux is c, the relationship of the following formula (1) is established.

[Equation 1] Further, when the Doppler shift frequency due to the Doppler effect before the air bubbles have finished passing through the end face 1a is Δf ₀ , the following equation (2) is established similarly to the equation (1).

[Equation 2] Since the frequency of the reflected light from the end face 3a of the sapphire probe 3 is equal to the frequency fi of the light from the light source, the Doppler shift frequency due to the Doppler effect can be detected by taking an optical beat with the reflected light from the bubble surface. .. FIG. 2B shows the temporal change of the light intensity of the reflected light from the bubble surface, and the time axis is aligned with that of FIG. 2A. As shown in this figure, from the time t ₁ immediately before the bubble 5 contacts the end face 3a to the time t ₂ just before contacting the end face 3a, and from the time t ₃ just before the bubble 5 finishes passing the end face 3a, finishes passing. in between times t _4, the bubble surface, i.e. the reflected light from the two-phase boundary surface is obtained, the level gradually increases. Since the frequencies of these reflected lights have frequency shifts due to the Doppler effect, the Doppler shift frequency obtained by performing heterodyne detection using the reflected light as the reference light at the light source part of the optical fiber for projection is measured. Then, the bubble velocity V can be measured by the above equations (1) and (2). Further, as shown in FIGS. 2A and 2B, the bubble passing time can be measured by detecting the time interval between the times t ₂ and t ₄ . Further, the bubble diameter can be measured from the bubble velocity and bubble passage time.

FIG. 3 is a block diagram showing the overall construction of a gas-liquid two-phase flow measuring apparatus according to an embodiment of the present invention. In the figure, 11 is a laser oscillator having a single frequency, and the polarization plane of the laser beam is changed to a polarization beam splitter 12
Set the direction to pass through. Then, the laser light emitted from the laser oscillator 11 passes through the polarization beam splitter 12 and is guided to the light projecting optical fiber 1 through the lens 13. The polarization plane of the laser light becomes random in the process of being transmitted through the optical fiber 1. Of the reflected light obtained from the light projecting optical fiber 1, a first light receiving element, for example, an avalanche type photodiode (A
PD) 15 is placed. The photodiode 15 performs heterodyne detection for converting a light beam from the original laser light source 11 and a laser beam of a single wavelength into an electric signal corresponding to the frequency, and its output is frequency-dependent through the amplifier 16. It is given to the measuring device 17. The amplifier 16 and the frequency measuring device 17 are bubble velocity calculating means for obtaining the bubble velocity from the high frequency component obtained from the photodiode 15.

On the other hand, a photodiode (PD) 22 as a second light receiving element is provided on the end face of the optical fiber 2 for receiving light via a condenser lens 21. Photodiode 22
Generates an electric signal corresponding to the light intensity of the reflected light, and its output is given to the time interval measuring device 24 via the amplifier 23. The amplifier 23 and the time interval measuring device 24 constitute a passage time measuring means for obtaining the passage time of bubbles based on the change in the signal level of the photodiode 22. The outputs of the frequency measuring device 17 and the time interval measuring device are transmitted to the signal processing circuit 25. As described above, the signal processing circuit 25 is configured to calculate the bubble diameter and the void rate based on the bubble velocity and the bubble passage time, and display them on the display 26.

As shown in FIG. 4, the optical fiber is constructed so that the optical fibers 1 and 2 for projecting and receiving light are integrated at the tip surface of the probe. FIG. 4A is a cross-sectional view showing a tip portion of an optical fiber forming a probe, FIG.
Is an enlarged cross-sectional view taken along the line AA, in which an optical fiber 1 for projecting light is located in the central portion, and a plurality of, for example, 19 optical fibers 2-1 to 2-19 for receiving light are surrounded by a circle. Place it on the circumference.
The end faces of these optical fibers are in contact with the end face of the sapphire probe 3 which is cylindrical and has only a tip formed in a truncated cone shape as shown in the figure. The root portion of the sapphire probe 3 is covered with a metal sleeve 6 as shown in the figure. Then, electron beam welding is performed on a part of the sleeve 6 to fix the light projecting optical fiber 1 and the light receiving optical fibers 2-1 to 2-19 therein. Here, all of the light-receiving optical fibers 2-1 to 2-19 are constructed so as to be guided to the photodiode 22 shown in FIG.

Next, the operation of this embodiment will be described. When the laser light source 11 is driven, the laser light enters the light projecting optical fiber 1 through the polarization beam splitter 12 and is guided to the tip portion thereof as shown in the figure. Then, the gas-liquid two-phase flow is irradiated through the sapphire probe 3. As described above, the bubble 5 approaches the tip of the sapphire probe 3 and the end face 3a becomes reflected light having different intensities depending on whether it is in the liquid phase or in the gas phase. It is provided to the diode 22. Therefore, a signal based on the reflected light intensity of the photodiode 22 is obtained. This signal is used as a signal for determining whether the end face of the probe is in the liquid phase or the gas phase. Time interval measuring device 2
In 4, the signal is discriminated and the time interval in contact with the gas phase and the liquid phase is measured.

The light emitted from the tip 3a of the sapphire probe 3 is also partially reflected at the boundary surface of the gas-liquid two-phase flow and returns to the optical fiber 1 for projecting light. Since the polarization planes of these reflected lights are all random, part of the reflected light is reflected by the polarization beam splitter 12 via the light projecting optical fiber 1 and transmitted to the photodiode 15. The photodiode 15 generates an electric signal having a Doppler shift frequency (Δfi at the time of entering the gas phase and Δf ₀ at the time of entering the liquid phase), which is the difference in the frequency of the reflected light. This signal is the photodiode 15
By the heterodyne detection by, a signal as shown in FIG. 2C is obtained. Information about the bubble velocity is obtained by measuring this signal with the frequency measuring device 17. In this way, the signal processing circuit 25 calculates the bubble velocity and bubble passage time and the bubble diameter and void ratio (volume ratio of gas and liquid) based on these, and displays them on the display 26.

As known from the equations (1) and (2),
The ratio of the Doppler shift frequencies Δfi and Δf ₀ is equal to the ratio of the refractive indices n1 and na of the liquid and gas phases. Therefore, if the refractive index of one of the liquid phase and the gas phase is known, it is possible to obtain many refractive indexes from the ratio of the Doppler shift frequencies. Although the present embodiment has described the gas-liquid two-phase flow in which bubbles pass through the liquid phase, the gas-liquid two-phase flow also alternates for the gas-liquid two-phase flow where droplets pass through the gas phase. It goes without saying that the apparatus of the present invention can be applied to a gas-liquid two-phase flow passing through the. Further, although sapphire is used as the probe in this embodiment,
It is also possible to construct the probe using another transparent substance as long as it can withstand high pressure and has a high refractive index.

[0016]

As described in detail above, according to the present invention, since the tip of the optical fiber is covered with the transparent probe to separate the optical fiber for projecting light and the optical fiber for receiving light, high temperature and high pressure are applied. The effect that the gas-liquid two-phase flow measuring device can be applied even under the environment is obtained.

[Brief description of drawings]

FIG. 1 is a principle diagram showing the principle of the present invention.

2A and 2B are graphs showing changes in the intensity of reflected light at the optical fiber end face and the bubble end face, respectively, and FIG. 2C is an output waveform diagram of the photodiode.

FIG. 3 is a block diagram showing a configuration of a signal processing unit of a gas-liquid two-phase flow measuring apparatus according to an embodiment of the present invention.

FIG. 4A is a sectional view showing a probe portion of a gas-liquid two-phase flow measuring apparatus according to the present embodiment, and FIG. 4B is a sectional view taken along line AA.

[Explanation of symbols]

 1 Optical fiber for projecting light 2, 2-1 to 2-19 Optical fiber for receiving light 3 Sapphire probe 3a End face 5 Bubble 11 Laser oscillator 12 Polarizing beam splitter 15 Avalanche photodiode 17 Frequency measuring instrument 22 Photodiode 24 Time interval measuring instrument 25 signal processing circuit 26 indicator

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshihiro Taki 1-5-20 Yaesu, Chuo-ku, Tokyo Japan Lignite Liquefaction Co., Ltd.

Claims (1)

Claim: What is claimed is: 1. A light source for generating light having a constant polarization plane at a single frequency, a polarizing beam splitter for transmitting light provided by the light source, and a polarizing beam splitter. A light-transmitting optical fiber to which light from a light source is given to one end surface, and a transparent probe arranged so as to bring the end surface of the light-projecting optical fiber into contact with each other and facing each other in the flow direction of the gas-liquid two-phase flow. A plurality of light-receiving optical fibers, one end of which abuts on the probe around the other end face of the light-projecting optical fiber, and a gas-liquid two-phase provided from the light-projecting optical fiber to the polarization beam splitter. From the first light receiving element arranged so as to give the light that is reflected again by the polarization beam splitter among the light reflected from the boundary surface, and from the high-frequency component of the signal obtained from the first light receiving element, A bubble velocity calculating means for obtaining a bubble velocity, a second light receiving element for converting the reflected light of the light receiving optical fiber into an electric signal, and a bubble passing time based on a change in the signal level of the second light receiving element. A gas-liquid two-phase flow measuring device comprising: a transit time measuring means.