JP3629338B2 - Void rate measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for measuring a void ratio in a fluid containing powder or liquid.
[0002]
[Prior art]
As an apparatus for measuring the void ratio of a gas-liquid two-phase flow, for example, as shown in Japanese Patent Laid-Open No. 53-66293, there is a method of obtaining by measuring the light transmittance using an optical detector. . In this case, a laser beam is used as a light source in order to avoid the influence of coloring of the test oil. However, even if a laser is selected as the light, the turbidity of the liquid to be measured affects the measurement in the optical means, so the state of the liquid to be measured is limited, and the measurement container also emits the measurement light. There is a drawback that it is limited to what is transmitted.
[0003]
Further, as a method using radiation, there is a method of calculating from a change in attenuation factor due to an object to be measured using X-rays and γ-rays as disclosed in, for example, Japanese Patent Application Laid-Open No. 58-143253. As described above, in the method using X-rays and γ-rays, in the case of measuring a hydrogen-containing fluid, since the attenuation rate of the pipe is larger than the attenuation rate of the fluid in the radiation transmission process, the measurement efficiency decreases, and the It is not effective for piping. Furthermore, when the dose intensity required for measurement falls within the scope of legal regulations, there is a problem that the place of use and the user are restricted.
[0004]
The method using neutrons is effective for measurement of hydrogen-containing liquid fluids because neutrons are effectively decelerated with respect to hydrogen atoms, and since there is usually almost no radiation in the natural world, the change in the count is extremely high. It is an excellent method that can measure efficiently. As a method using neutrons, there is JP-A-4-131744. In this method, fast neutrons emitted from the radiation source are attenuated by the fluid and lose energy, and change to thermal neutrons. However, if there are voids in the fluid, there is no energy loss. Using the point where the number of neutrons changes, the thermal neutron change rate is obtained with a BF3 counter tube, and the void rate is measured. The reason for using thermal neutrons, which are low directionality and slow neutrons, without using fast neutrons with excellent directionality in this method is thought to be because an appropriate measurement means for fast neutrons was not found. However, neutrons scattered many times, such as thermal neutrons, have a very low directionality, resulting in an error in measurement accuracy in the conventional apparatus. The total number of neutrons emitted from the neutron radiation source is only a small part of the number of neutrons detected by the conventional apparatus, the count value is low, and the resolution and measurement error are large.
[0005]
As described above, a method using light or radiation exists as a proposal. However, none of the methods for measuring bubbles in engine / transmission oil has been put into practical use, and the methods currently in practical use are as follows. Street.
[0006]
Part 1: Scoring method This is a method in which a glass tube is connected to a pipe connected to an oil passage, the flow of oil in the pipe is visually observed, and a score corresponding to the state is given. Although it is simple as a method, it has only a qualitative evaluation, and there are disadvantages that a difference in results by an observer is large, and a minute change in the amount of bubbles cannot be identified.
[0007]
Part 2: Weight measurement method This is a method of measuring the weight by connecting a removable pipe to the oil passage and removing the pipe through which oil flows during operation. This method can measure the void ratio fairly accurately by comparing the weight without foam and the weight with foam, but it is dangerous when the oil temperature is high because the piping is switched during operation. Need to get used to the work.
[0008]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a highly accurate and easy-to-handle measuring device with high safety for measuring the void fraction in a hydrogen-containing fluid using fast neutrons.
[0009]
[Means for Solving the Problems]
The present inventors have (a) a pipe through which a hydrogen-containing fluid flows, (b) a radiation source outside the pipe and capable of irradiating the pipe with fast neutrons, and (c) provided at a position facing the radiation source. And a neutron detector whose periphery is surrounded by a neutron moderator and (d) a neutron shielding material covering the periphery of the pipe, and a void ratio measuring apparatus.
[0010]
In the present invention, a radiation source is arranged outside a pipe through which a hydrogen-containing fluid flows, and a neutron detector surrounded by a neutron moderator is arranged at a position facing the low radiation source, and the circumference of the pipe is A configuration that efficiently detects only fast neutrons that have passed through the hydrogen-containing liquid in the pipe by thermal neutrons using the neutron moderator, among the fast neutrons emitted from the low radiation source It is what.
[0011]
Examples of the moderator include polyethylene and polypropylene. The moderator shape around the neutron detector is preferably the most efficient for the target fluid.
[0012]
Examples of the radiation source include Am-Be and Ra-Be utilizing a nuclear reaction, and it is particularly desirable to use a miniaturizable fast neutron source such as californium 252 ( ²⁵² Cf). Further, it is desirable from the viewpoint of safety that the radiation source is less than 3.7 MBq (100 microcurie).
[0013]
The neutron detector is preferably a neutron detector using BF ₃ gas or ³ He gas, and a decelerating neutron detector in which a substance containing a large amount of hydrogen atoms such as polyethylene or paraffin is wound around as a moderator.
[0014]
[Action]
Next, the operation will be described. Fast neutrons emitted from the radiation source are decelerated when passing through a hydrogen-containing liquid or powdery fluid in the pipe. Since neutrons lose more energy when the mass of the partner nucleus is smaller and the density thereof is higher, the attenuation rate due to the hydrogen-containing liquid or powder fluid is larger, and the gas contained in the liquid or powder fluid and The attenuation rate due to the piping material is small. Therefore, when the volume ratio (void ratio) of the gas contained in the hydrogen-containing liquid or powder fluid in the pipe is large, the number of neutrons passing through the pipe and reaching the detector is large, and the void ratio is small. Has a small number of neutrons reaching the detector. Most neutrons that have passed through a hydrogen-containing liquid or powdery fluid are fast neutrons. However, since the neutrons detected by the detector alone are only thermal neutrons, most of the neutrons that have reached cannot be detected as they are. Therefore, by arranging a moderately shaped moderator between the detector and the pipe, the fast neutrons that have passed through the pipe can be decelerated to thermal neutrons, and the number of neutrons detected by the detector can be increased. Furthermore, by surrounding the pipe with a moderator to prevent fast neutrons that have passed through other than the pipe from reaching the detector, the detector is prevented from counting thermal neutrons other than the target object. Good direction can be used effectively. It is also possible to measure the bubble change online by taking the count into a computer.
[0015]
There are no particular restrictions on the target liquid for void measurement, but examples include raw materials and products such as nuclear reactor plant / boiler and petroleum in chemical plants.
[0016]
Embodiment
Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a sectional view of an apparatus showing a specific example of the present invention. FIG. 2 is a sectional view taken along the piping axis of the apparatus shown in FIG. The hydrogen-containing liquid fluid 6 flows through the pipe 1. A radiation source 3 held by a holding member 7 is arranged on one side of the pipe 1, and a neutron detector 2 is arranged on the other side of the pipe 1 via a moderator 4. The radiation source 3 may be a low-strength sealed radiation source that is not regulated by the Radiation Hazard Prevention Act in Japan. In the case of this apparatus, a californium 252 sealed radiation source having a radiation intensity of less than 3.7 MBq (100 μCi) is used. The neutron detector 2 uses a BF ₃ proportional counter. This BF ₃ proportional counter is generally used as a neutron detector. The moderator 4 is arranged around the neutron detector 2 so as to have a uniform thickness. Since the neutron detector 2 has a cylindrical shape, the neutron detector 2 is arranged at a position where the axes of the pipes 1, which are the positions where the neutron detection efficiency is best, are orthogonal. Neutrons detected by the neutron detector 2 are measured by the counter 9 using, for example, the measurement system shown in FIG. The shielding material 5 uses a polyethylene block and is arranged uniformly around the pipe 1. The holding member 7 of the radiation source 3 also uses a polyethylene block. Since the hydrogen-containing liquid fluid 6 flowing in the pipe 1 may become a high temperature, the pipe 1 is an air layer as the heat insulating layer 11 between the pipe holding member 10 and the shielding material 5 in consideration of the heat resistance of polyethylene. Is provided and held. In the apparatus shown in FIG. 1, the pipe 1 is U-shaped, and a radiation source 3 is provided at one bent portion thereof, and a neutron detector 2 covered with a moderator is provided at the other bent portion. As one aspect, the radiation source 3 can be provided outside one of the pipes in the diametrical direction, and the neutron detector 2 can be provided at the opposing position.
[0017]
Next, a method for measuring the void ratio will be described. The energy of neutrons passing through the pipe 1 is distributed from the range of thermal neutrons to the range of fast neutrons. In the present invention, fast neutrons that have passed through the pipe 1 can be efficiently detected by decelerating the neutrons after passing through the pipe with the moderator before entering the detector, so that the change in detected neutrons per hour can be measured. Can do. Since the number of neutrons emitted from the radiation source is proportional to time, the number of measured neutrons decreases when the measurement time is short. In general, neutron measurement errors have a deviation of ± √n when n is the number of measurements, so the larger the number of measurements, the better the void rate measurement accuracy. Must be set.
[0018]
The number of neutrons emitted from the radiation source, passing through the pipe 1 and reaching the detector 9 is the number of measurements per hour if the deceleration rate in the pipe is constant, that is, if the void ratio is a steady flow. It is constant. Since hydrogen atoms have a great effect of decelerating neutrons, when the pipe 1 is filled with a hydrogen-containing liquid fluid, that is, when the void ratio is 0%, the number of neutron measurements is small, and conversely, the entire pipe is gas. That is, when the void ratio is 100%, the number of neutron measurements increases. Therefore, a theoretical curve of the void ratio and the number of measurements can be obtained by measuring the number of neutron measurements at these two points in advance. Therefore, the void ratio can be calculated from the number of measurements of the hydrogen-containing fluid containing bubbles.
[0019]
The method for obtaining the calibration curve is as follows.
Number of neutrons emitted by the radiation source I ₀
Attenuated length x
Decay coefficient μ
Then, the number of neutrons I after deceleration is theoretically expressed by the following formula.
I = I ₀ exp (−μx) 1)
here,
Number of measured neutrons when the measuring part is 100% oil I ₂
Distance x ₂ when the measuring part is 100% oil.
Number of neutrons measured when the measurement part is 0% oil I ₁
Distance of attenuation x ₁ when the measurement unit is 0% oil
Number of measured neutrons when the measurement part is oil Y% I
Attenuated distance when the measurement part is oil Y% x
Then, the volume ratio Y of oil is Y = (x−x ₁ ) / (x ₂ −x ₁ )
Therefore, if the void ratio is Z, Z = (x ₂ −x) / (x ₂ −x ₁ )
From equation 1), I / I ₂ = exp [μ (x ₂ −x)]
_{I 1} / I 2 = exp [μ _(x 2 -x _1)]
Therefore,
Z = In (I / I ₂ ) / In (I ₁ / I ₂ )
From the above, a theoretical calibration curve can be obtained by measuring the number of measurements (I ₂ ) when the measurement unit is filled with oil and the number of measurements (I ₁ ) when empty. Further, the void ratio can be obtained by measuring the number of measurements (I) when there is oil mixed with bubbles.
[0020]
The effect of the moderator 4 will be described. In FIG. 3, the horizontal axis represents the energy of neutrons, and the vertical axis represents the number of neutron measurements. The influence of the thickness of the moderator on the measurement efficiency is shown. When the thickness of the moderator is small, A efficiently measures neutrons in a low energy range, that is, thermal neutrons, but when measuring fast neutrons, it is preferable to increase the thickness of the moderator as in C Therefore, it is preferable that the moderator has a thickness that matches the energy of the neutron to be measured. B indicates an intermediate case between A and C.
FIG. 4 shows the measurement results for each of the cases where the thickness of the moderator is 125 mm, 60 mm, 30 mm, and 10 mm, with the wave height distribution of the signal on the horizontal axis and the number of detections on the vertical axis. In the case of the present example, the thickness of around 60 mm shows the highest total count value, and it can be seen that this is the optimum thickness. As shown in FIG. 4, by using a moderator having an appropriate thickness for a specific radiation source, in other words, by a combination of a moderator having an appropriate thickness corresponding to the distance that the radiation passes through the liquid in the pipe. The number of neutron measurements can be increased. That is, when the distance that the radiation passes through the liquid in the pipe is short as shown in FIG. 5A, the thickness of the moderator is increased, and as shown in FIG. When the distance passing through the liquid inside is long, the number of neutrons can be increased by reducing the thickness of the moderator. It is clear that fast neutrons with high directivity are efficiently measured, and the sensitivity of the number of measurements to the gas ratio is improved.
[0021]
The effect of the shielding material 5 will be described. FIG. 6 is a graph showing the influence of the presence of the shielding material 5. In FIG. 6, the solid line indicates the case where the shielding material is used, the broken line indicates the case where there is no shielding material, the horizontal axis indicates the gas ratio in the liquid, and the vertical axis indicates the number of neutron measurements. By arranging a shielding material around the pipe 1, it is clear that the sensitivity of the number of measurements with respect to the gas ratio (void ratio) is improved.
[0022]
FIG. 7 shows the result of actually measuring the void ratio in ATF (automatic transmission fluid) as a hydrogen-containing liquid. In FIG. 7, the horizontal axis represents the void fraction in the liquid, and the vertical axis represents the number of neutron measurements. In FIG. 7, the solid line is the theoretical curve obtained as a result of calculation from the neutron measurement value of the present invention, and the plot (◯) is the result of actual measurement of the gas volume ratio in the liquid by weight measurement. From FIG. 7, the void ratio calculation result by neutron and the void ratio measurement result by weight measurement are in good agreement, and the effectiveness of the device of the present invention is clear.
[0023]
【The invention's effect】
According to the present invention, in the void ratio measuring apparatus using the radiation source, the shielding material is arranged around the pipe and the moderator is arranged between the detector and the pipe, so that an optimum and effective measuring method is realized. did it. This method can efficiently measure the void ratio even when a weak-intensity radiation source that is not subject to legal regulations is used. Moreover, it is safer and cheaper than a void ratio measuring apparatus using other radiation. Furthermore, there are few restrictions on the material of the pipe (glass material, iron material, etc.), and the target fluid can be applied to any hydrogen-containing gas-liquid two-phase flow or solid-gas two-phase flow. In particular, the device of the present invention is an epoch-making device capable of measuring bubbles in oil in a running automobile engine and transmission.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an apparatus showing a specific example of the present invention.
2 is a cross-sectional view taken along the piping axis of the apparatus shown in FIG.
FIG. 3 is a graph for showing the influence of the thickness of the moderator on the measurement efficiency; A shows a case where the thickness of the moderator is small, and B shows a case where the thickness of the moderator is between A and C. C represents the case where the thickness of the moderator is large, the horizontal axis represents the energy of neutrons, and the vertical axis represents the number of neutron measurements.
FIG. 4 shows the relationship between the thickness of the moderator and the number of detections when the thickness of the moderator is changed to 125 mm, 60 mm, 30 mm, and 10 mm.
FIG. 5A shows a state where the thickness of the moderator is reduced when the liquid layer through which the radiation passes is thick, and FIG. 5B shows a moderator when the liquid layer through which the radiation passes is thin. It is the schematic which shows the state which is thickening.
FIG. 6 is a graph showing that the presence or absence of a shielding material affects the measurement number measurement sensitivity with respect to the void ratio.
FIG. 7 shows the data obtained by actually measuring the void ratio in the hydrogen-containing liquid fluid by weight measurement, and shows the theoretical curve of the void ratio obtained from the result calculated from the neutron measurement value of the present invention by a solid line.
FIG. 8 is a block diagram of a measurement system used in an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Piping 2 Neutron detector 3 Radiation source 4 Moderator 5 Shielding material 6 Hydrous liquid fluid 7 Holding member 8 Bubble 9 Counter 10 Pipe holding member 11 Heat insulation layer 12 Power supply 13 Signal amplification device 14 In-pipe pressure detection means 15 In piping Temperature detection means 16 Void ratio calculation circuit 17 Display section

Claims (1)

(A) a pipe through which a hydrogen-containing fluid flows; (b) a radiation source outside the pipe that can irradiate the pipe with fast neutrons; (c) provided at a position facing the radiation source; A void ratio measuring apparatus comprising: a neutron detector surrounded by a moderator; and (d) a neutron shielding material covering the periphery of the pipe.

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