Air bubble rate sensor, flow meter using same, and liquid transfer pipe

Abstract

A bubble fraction sensor according to the present disclosure comprises: an insulating tube having a plurality of through-holes for causing a liquid to flow; and a plurality of electrodes which are located inside or on the outer surface of the insulating tube, and face each other while sandwiching each of the plurality of through-holes. The plurality of through-holes each have, in a cross-section perpendicular to the flow direction of the liquid, an elongated shape that has a first direction and a second direction that is shorter than the first direction. The plurality of electrodes sandwich the plurality of through-holes and face each other in the second direction.

Description

[Technical Field]

[0001] The present disclosure relates to a void fraction sensor for measuring the void fraction of a liquid such as liquid hydrogen, and a flow meter and a liquid transfer pipe using the same. [Background technology]

[0002] Recently, the use of hydrogen as a potential energy storage medium has been attracting attention in line with efforts to reduce greenhouse gas emissions. Liquid hydrogen, in particular, has high volumetric efficiency and can be stored for long periods, leading to the development of various technologies for its use. However, an accurate method for measuring the flow rate required for handling large amounts of liquid hydrogen has not yet been established industrially. The main reason for this is that liquid hydrogen vaporizes very easily, and its gas-to-liquid ratio changes significantly.

[0003] Liquid hydrogen is a cryogenic liquid (boiling point -253°C), and because it has very high thermal conductivity and little latent heat, it quickly generates bubbles (voids). As a result, liquid hydrogen flows in a two-phase flow, a mixture of gas and liquid, inside the transfer pipe. As the bubble content varies greatly, it is not possible to accurately measure the flow rate of liquid hydrogen flowing through the transfer pipe by simply measuring the flow velocity, as is done with normal liquids.

[0004] Therefore, development of a bubble fraction meter that measures the bubble fraction, which indicates the volume fraction of the gas phase in a gas-liquid two-phase flow, is underway. As such a bubble fraction meter, Non-Patent Document 1 proposes a capacitance-type void fraction sensor that measures capacitance using a pair of electrodes. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Norihide MAENO, 5 others, "Void Fraction Measurement of Cryogenic Two Phase Flow Using a Capacitance Sensor", Trans. JSASS Aerospace Tech. Japan, Vol. 12, No. ist29, pp. Pa_101-Pa_107, 2014 Summary of the Invention

[0006] The air bubble rate sensor of the present disclosure includes an insulating tube and at least two electrodes. The insulating tube has a plurality of through holes for allowing a liquid to flow. The at least two electrodes are located inside or on the outer surface of the insulating tube and face each other across one of the plurality of through holes. The plurality of through holes have an elongated shape in a cross section perpendicular to the direction of liquid flow, and have a first side in a first direction and a second side in a second direction that is shorter than the first side. The at least two electrodes face each other in the second direction, and the plurality of through holes are located between the at least two electrodes.

[0007] The flow meter of the present disclosure measures the flow rate of a liquid flowing in a transfer pipe. The flow meter includes the air bubble rate sensor and a flow meter. The flow meter can measure the flow rate of the liquid flowing through the through-hole. Furthermore, the liquid transfer pipe of the present disclosure includes the flow meter. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic perspective view illustrating an air bubble rate sensor according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic side view of the air bubble rate sensor shown in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view of the air bubble rate sensor shown in FIG. 2 taken along line II-II. [Figure 4] FIG. 4 is a cross-sectional view of the air bubble rate sensor shown in FIG. 2 taken along line IV-IV. [Figure 5] FIG. 4 is a cross-sectional view of the air bubble rate sensor shown in FIG. 3 along line VV. [Figure 6]FIG. 4 is an enlarged cross-sectional view of a portion P of the air bubble rate sensor shown in FIG. 3. [Figure 7A] FIG. 6 is a schematic perspective view showing an insulating tube in the air void rate sensor shown in FIGS. 3, 4 and 5. [Figure 7B] 7B is a cross-sectional view taken along the line MM of the insulating tube shown in FIG. 7A. [Figure 7C] 7B is a cross-sectional view of the insulating tube taken along line NN in FIG. 7A. [Figure 8A] FIG. 2 is a schematic perspective view showing a supply pipe and a discharge pipe in the air bubble rate sensor shown in FIG. [Figure 8B] 8B is a schematic perspective view of the supply pipe and the discharge pipe shown in FIG. 8A, viewed from the opposite side. FIG. [Figure 8C] FIG. 8C is a longitudinal cross-sectional view of the supply and discharge pipes shown in FIGS. 8A and 8B. [Figure 8D] 8D is a cross-sectional view of the supply pipe and the discharge pipe shown in FIG. 8C taken along line ZZ. [Figure 9] FIG. 9 is a cross-sectional view of the air bubble rate sensor shown in FIG. 2 taken along line IX-IX. [Figure 10] FIG. 10 is a schematic cross-sectional view showing an air bubble rate sensor according to another embodiment of the present disclosure. [Figure 11] 1 is a schematic explanatory diagram showing an example of a liquid transfer pipe equipped with an air bubble rate sensor according to the present disclosure. FIG. [Figure 12] FIG. 2 is a schematic explanatory diagram showing the relationship between the air bubble rate sensor and the transfer pipe. [Figure 13A] FIG. 10 is a schematic explanatory diagram showing another example of a liquid transfer pipe equipped with an air bubble rate sensor according to the present disclosure. [Figure 13B] 13B is a schematic side view of the liquid transfer pipe of FIG. 13A as viewed in the direction of arrow Q. FIG. [Figure 14] FIG. 10 is a schematic side view showing another example of a liquid transfer pipe according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] In the capacitance-type void fraction meter proposed in Non-Patent Document 1, the cross-sectional shape of the pipe through which liquid nitrogen flows is a perfect circle. Therefore, increasing the supply rate of liquid, such as liquid nitrogen, required increasing the diameter of the pipe. However, increasing the diameter of the pipe also increases the distance between the electrodes facing each other across the pipe. As a result, the strength of the electrical signal decreases, resulting in a decrease in measurement accuracy. To improve this, the electrode area can be increased or the applied voltage can be increased. However, increasing the electrode area increases the risk of breakage due to the bonding stress of the large electrodes. Furthermore, increasing the voltage may make it difficult to ensure sufficient safety.

[0010] Therefore, the present disclosure provides a bubble rate sensor that can improve the accuracy of measuring the bubble rate of a liquid even at low temperatures without reducing the amount of liquid supplied, as well as a flow meter and a liquid transfer pipe that use the same.

[0011] Hereinafter, an air bubble rate sensor according to an embodiment of the present disclosure will be described with reference to the drawings.

[0012] Fig. 1 is a schematic perspective view showing an air bubble rate sensor 1 according to one embodiment of the present disclosure, and Fig. 2 is a schematic side view thereof. The air bubble rate sensor 1 measures the air bubble rate of a liquid. As shown in Fig. 1, a supply-side transfer pipe 2 and a discharge-side transfer pipe 3 for the liquid are connected to both ends of the air bubble rate sensor 1, respectively.

[0013] FIG. 3 is a cross-sectional view of the air bubble rate sensor 1 shown in FIG. 2 taken along line II-II, and FIG. 4 is a cross-sectional view of line IV-IV in FIG. 2. The air bubble rate sensor 1 includes a vacuum vessel 4. An insulating tube 5 is located at the center of the vacuum vessel 4. The insulating tube 5 has two through-holes 6a and 6b for allowing a liquid to flow (see FIG. 4). The liquid may be a low-temperature liquid or a cryogenic liquid as long as it has the ability to store electric charge so that its capacitance can be measured. In the following description of this disclosure, the liquid may be referred to as a low-temperature liquid or a cryogenic liquid, for example. Electrodes 7a and 7b are located on the outer surface of the insulating tube 5 (see FIG. 3). The electrode 7a faces the electrode 7b. The through-holes 6a and 6b are located between the electrodes 7a and 7b. The vacuum vessel 4 includes a vacuum exhaust valve 12. The vacuum exhaust valve 12 maintains the interior of the vacuum vessel 4 in a vacuum space 26. The vacuum space 26 acts as a thermal insulating layer.

[0014] The configuration of the insulating tube 5 will be described in more detail using Figure 5, which is a cross-sectional view taken along line VV in Figure 3. As described above, the insulating tube 5 has two through-holes 6a and 6b for flowing the cryogenic liquid, and a pair of electrodes 7a and 7b are located on the outer surface of the insulating tube 5, facing each other with the through-holes 6a and 6b between them. The through-holes 6a and 6b each have an elongated cross-section perpendicular to the flow direction of the cryogenic liquid (i.e., the direction perpendicular to the paper surface in Figure 5), and each have first sides 6a1 and 6b1 in a first direction (the longitudinal direction, indicated by the x-direction in Figure 5) and second sides 6a2 and 6b2 in a second direction (indicated by the y-direction in Figure 5) that are shorter than the first side 6a1. The second sides 6a2 and 6b2 can be defined as sides connecting the two parallel first sides 6a1 and 6b1, and include straight and curved lines. The elongated shape refers to, for example, a rectangular shape, a flattened elliptical shape, or the like.

[0015] Because the through-holes 6a, 6b are elongated, the distance between the electrodes 7a, 7b can be shortened. This increases the capacitance accumulated between the electrodes 7a, 7b, improving the accuracy of measuring the bubble rate of the cryogenic liquid and maintaining the supply rate of the cryogenic liquid. Furthermore, because the first partition wall 11 between adjacent through-holes 6a, 6b functions as a support, the pressure resistance of the insulating tube 5 is improved.

[0016] Furthermore, the two through holes 6a, 6b are aligned in the first direction (x direction), which enables the insulating tube 5 to be made thinner. The aspect ratio (long axis / short axis) of the long axis parallel to the first direction (x direction) and the short axis parallel to the second direction (y direction) is, for example, not less than 5 and not more than 8. The long axis is an axis that passes through the axial centers of the through holes 6a, 6b and is parallel to the first direction (x direction), and the short axis is an axis that passes through the axial centers of the through holes 6a, 6b and is parallel to the second direction (y direction).

[0017] As shown in Figures 5 and 6 (enlarged views of part P in Figure 3), the electrodes 7a, 7b face each other in the second direction, sandwiching the through holes 6a, 6b. A conductive pin 8 is individually connected to each of the electrodes 7a, 7b. The conductive pin 8, together with an insulating substrate 9 having an insertion hole and a flange 10, constitutes an airtight terminal. The insulating substrate 9 is circular, and the conductive pin 8 is fixed in the insertion hole with brazing material or the like. The flange 10 surrounds the insulating substrate 9. The flange 10 is fixed to the vacuum vessel 4. Thus, the airtight terminal is connected to the vacuum vessel 4. The airtight terminal reduces leakage of the cryogenic liquid from the bubble rate sensor 1 to the outside. As a result, the accuracy of measuring the bubble rate is improved.

[0018] As shown in Figures 7A to 7C, the insulating tube 5 has two through holes 6a, 6b in the first direction and an opening 13 in the second direction for accommodating plate-shaped electrodes 7a, 7b, and the electrodes 7a, 7b are located in a recess 131 located at the bottom of the opening 13.

[0019] The electrodes 7a, 7b include, for example, a copper thin film, an aluminum thin film, or the like. The electrodes 7a, 7b can be formed on the bottom surface of each recess 131 by, for example, vacuum deposition, metallization, or an active metal method. Alternatively, a metal plate that will become the electrodes 7a, 7b may be adhered to the bottom surface of the recess 131. The thickness of each of the electrodes 7a, 7b may be 0.1 μm or more, preferably 20 μm or more, or 2 mm or less, or preferably 1 mm or less.

[0020] The insulating tube 5 contains ceramics containing, as a main component, for example, zirconia, alumina, sapphire, aluminum nitride, silicon nitride, sialon, cordierite, mullite, yttria, silicon carbide, cermet, β-eucryptite, etc. When the ceramics contain ceramics containing alumina as a main component, the ceramics may contain silicon, calcium, magnesium, sodium, etc. as oxides.

[0021] The term "major component" in ceramics refers to a component that accounts for 60% by mass or more of the total 100% by mass of the components that make up the ceramic. In particular, the major component is preferably a component that accounts for 95% by mass or more of the total 100% by mass of the components that make up the ceramic. The components that make up the ceramic can be determined using an X-ray diffraction analyzer (XRD). The content of each component can be determined by identifying the component, then using an X-ray fluorescence analyzer (XRF) or an ICP optical emission spectrometer to determine the content of the elements that make up the component, and converting it into the identified component.

[0022] The insulating tube 5 preferably contains low thermal expansion ceramics. Low thermal expansion ceramics refer to ceramics whose linear expansion coefficient at 22°C is 0±20 ppb / K or less, with the temperature range for measuring the linear expansion coefficient being 0°C to 50°C. Because low thermal expansion ceramics have a low linear expansion coefficient, there is a reduced risk of breakage even when subjected to thermal shock from cryogenic liquid. The linear expansion coefficient of low thermal expansion ceramics can be determined, for example, using an optical heterodyne optical path interferometer.

[0023] Specifically, the low-thermal expansion ceramic preferably has a main crystalline phase of cordierite, alumina, mullite, and sapphirine as secondary crystalline phases, and an amorphous phase containing Ca in the grain boundary phase. The crystalline phase ratio of the main crystalline phase may be 95% to 97.5% by mass, and the crystalline phase ratio of the secondary crystalline phase may be 2.5% to 5% by mass. The Ca content relative to the total amount may be 0.4% to 0.6% by mass, calculated as CaO, and the ceramic may further contain zirconia, with the zirconia content relative to the total amount being 0.1% to 1.0% by mass. This allows the low-thermal expansion ceramic to be resistant to expansion and contraction even when the temperature of the cryogenic liquid fluctuates significantly, allowing for long-term use. Such low-thermal expansion ceramics are described, for example, in Japanese Patent No. 5,430,389.

[0024] The ceramics that make up the insulating tube 5 preferably have a relative dielectric constant of 11 or less in the operating temperature range. Because cryogenic liquids have a low relative dielectric constant, if the ceramics have a low relative dielectric constant, it approaches the relative dielectric constant of the cryogenic liquid, improving high-frequency characteristics and further improving the accuracy of measuring the porosity. In particular, if the relative dielectric constant is 11 or less, the accuracy of measuring the porosity of the cryogenic liquid can be further improved. The operating temperature range refers to the temperature range of the ceramics that make up the insulating tube 5 when the cryogenic liquid is being transferred.

[0025] Furthermore, the insulating tube 5 may contain ceramics containing silicon nitride or sialon as a main component. These ceramics have high mechanical strength and thermal shock resistance, so there is a reduced risk of breakage even when subjected to thermal shock.

[0026] Specifically, the ceramics contain calcium oxide, aluminum oxide, and oxides of rare earth elements. The contents of calcium oxide and aluminum oxide are 0.3% by mass or more and 1.5% by mass or less, and 14.2% by mass or more and 48.8% by mass or less, respectively, relative to a total of 100% by mass of calcium oxide, aluminum oxide, and oxides of rare earth elements. The remainder is oxides of the rare earth elements. Silicon nitride has a composition formula of Si 6-Z Al Z O Z N8-Z (z=0.1 to 1) and has an average crystal grain size of 20 μm or less (excluding 0 μm). Such ceramics are described in Japanese Patent No. 5430389, for example.

[0027] At least in the insulating tube 5, the arithmetic mean roughness Ra of the roughness curve of the inner wall surface in the direction parallel to the axis of the through holes 6a, 6b is preferably 0.2 μm or less. When the arithmetic mean roughness Ra of the roughness curve of the inner wall surface is 0.2 μm or less, the increase in flow resistance of the cryogenic liquid caused by the inner wall surface is reduced, thereby stabilizing the flow velocity distribution of the cryogenic liquid. In other words, the variation in flow velocity is reduced, thereby improving the accuracy of measuring the bubble fraction of the cryogenic liquid.

[0028] The arithmetic mean roughness Ra can be measured in accordance with JIS B 0601:2001 using a laser microscope (Keyence Corporation, Ultra-Deep Color 3D Shape Measuring Microscope (VK-X1000 or its successor model)). The measurement conditions are as follows: coaxial illumination, 240x magnification, no cutoff value λs, 0.08mm cutoff value λc, end effect correction, and a measurement range of 1425μm x 1067μm. Four lines to be measured are drawn at approximately equal intervals within the measurement range, and the line roughness is measured. The length of each line to be measured is 1280μm.

[0029] The relative density of ceramics is, for example, 92% or more and 99.9% or less, and is expressed as a percentage (proportion) of the apparent density of the ceramics determined in accordance with JIS R 1634-1998 to the theoretical density of the ceramics.

[0030] The insulating tube 5 includes ceramics having a plurality of closed pores, and the value obtained by subtracting the average value of the circle-equivalent diameter of the closed pores from the average value of the distance between the centers of gravity of adjacent closed pores (hereinafter, this value is referred to as the distance between closed pores) is 8 μm or more and 18 μm or less. belowThe closed pores are independent of each other. When the distance between the closed pores is 8 μm or more, the closed pores are relatively dispersed, resulting in high mechanical strength. On the other hand, when the distance between the closed pores is 18 μm or less, even if microcracks originating from the contours of the closed pores are generated due to repeated thermal shocks, the surrounding closed pores are likely to prevent the cracks from expanding. For this reason, when the distance between the closed pores is 8 μm or more and 18 μm or less, the insulating tube 5 can be used for a long period of time.

[0031] The skewness of the circle equivalent diameter of closed pores may be greater than the skewness of the distance between the centers of gravity of closed pores. Here, skewness is an index (statistic) that indicates how much the distribution is distorted from a normal distribution, that is, the symmetry of the distribution. When the skewness is greater than 0, the tail of the distribution is to the right. When the skewness is 0, the distribution is symmetric. When the skewness is less than 0, the tail of the distribution is to the left.

[0032] When the histograms of the circle-equivalent diameter of closed pores and the distance between the centers of gravity of closed pores are superimposed, if the skewness of the circle-equivalent diameter of closed pores is greater than the skewness of the distance between the centers of gravity of closed pores, the mode of the circle-equivalent diameter is located to the left (zero side) of the mode of the distance between the centers of gravity. In other words, there are many closed pores with small circle-equivalent diameters, and these closed pores are more sparsely distributed, resulting in a ceramic member that combines mechanical strength with thermal shock resistance.

[0033] For example, the skewness of the circle-equivalent diameter of closed pores is 1 or more, and the skewness of the distance between the centers of gravity of closed pores is 0.7 or less. The difference between the skewness of the circle-equivalent diameter of closed pores and the skewness of the distance between the centers of gravity of closed pores is 0.3 or more.

[0034] To find the distance between the centers of gravity of the closed pores and the equivalent circle diameter, first, measure the average particle diameter D 50 The sample is polished on a copper plate using diamond abrasive grains with an average grain size of 3 μm. 50 By polishing with a tin disk using diamond abrasive grains with a roughness of 0.5 μm, a polished surface with an arithmetic mean roughness Ra of 0.2 μm or less on the roughness curve is obtained.

[0035] The arithmetic mean roughness Ra of the polished surface can be measured by the above-mentioned measurement method. The polished surface is observed at a magnification of 200 times, and the average range is selected. For example, if the area is 7.2 × 10 4 μm 2 An image of the area (310 μm horizontal length, 233 μm vertical length) is captured with a CCD camera, and an observation image is obtained. Using this observation image, the image analysis software "A-zo-kun (ver2.52)" (registered trademark, manufactured by Asahi Kasei Engineering Co., Ltd.) is used to determine the distance between the centers of gravity of closed pores using the distance between the centers of gravity method for measuring dispersity. Hereinafter, the image analysis software "A-zo-kun" refers to the image analysis software manufactured by Asahi Kasei Engineering Co., Ltd.

[0036] The setting conditions for this method are, for example, a threshold value, which is an index showing the brightness of an image, of 165, brightness is dark, and the area for removing small figures is 1 μm 2 The noise reduction filter can be omitted. The threshold value can be adjusted according to the brightness of the observed image. The brightness is dark, the binarization method is manual, and the small figure removal area is 1 μm 2 The threshold value can be adjusted so that the markers appearing in the observation image match the shape of the closed pores, with the noise reduction filter enabled. The circle-equivalent diameter of the closed pores can be determined using a technique called particle analysis on the observation image. The setting conditions should be the same as those used to determine the distance between the centers of gravity of the closed pores. The circle-equivalent diameter and the skewness of the distance between the centers of gravity of the closed pores can be determined using the Skew function provided in Excel (registered trademark, Microsoft Corporation).

[0037] An example of a method for manufacturing the insulating tube 5 containing such ceramics will be described below. The case where the main component of the ceramics constituting the insulating tube 5 is alumina will be described.

[0038] The main component, aluminum oxide powder (purity of 99.9% by mass or more), and powders of magnesium hydroxide, silicon oxide, and calcium carbonate are placed in a grinding mill together with a solvent (ion-exchanged water). The average particle size (D50 After pulverizing the powder to a particle size of 1.5 μm or less, an organic binder and a dispersant for dispersing the aluminum oxide powder are added and mixed to obtain a slurry.

[0039] Here, the content of magnesium hydroxide powder is 0.3 to 0.42 mass%, the content of silicon oxide powder is 0.5 to 0.8 mass%, and the content of calcium carbonate powder is 0.06 to 0.1 mass% in a total of 100 mass% of the above powders. The remainder is aluminum oxide powder and unavoidable impurities. The organic binder is an acrylic emulsion, polyvinyl alcohol, polyethylene glycol, polyethylene oxide, etc.

[0040] Next, the slurry is spray-granulated to obtain granules, which are then compressed using a uniaxial press or cold isostatic press at a molding pressure of 78 MPa to 118 MPa to obtain a columnar green body. The green body is optionally machined to form recesses that will become recesses 131 after firing. The green body is fired at a firing temperature of 1580°C to 1780°C for a holding time of 2 hours to 4 hours to obtain insulating tube 5.

[0041] To obtain an insulating tube 5 having a closed pore spacing of 8 μm to 18 μm, the compact may be fired at a firing temperature of 1600°C to 1760°C for a holding time of 2 to 4 hours. To obtain an insulating tube 5 in which the skewness of the circle-equivalent diameter of the closed pores is greater than the skewness of the distance between the centers of gravity of the closed pores, the compact may be pressed at a molding pressure of 96 MPa to 118 MPa, and then fired at a firing temperature of 1600°C to 1760°C for a holding time of 2 to 4 hours. The inner wall surfaces of the through holes 6a and 6b of the insulating tube 5 may be ground. Furthermore, the bottom surfaces of the recesses 131 in which the electrodes 7a and 7b are attached may be ground.

[0042] As described above, the insulating tube 5 has two elongated through holes 6a and 6b. On the other hand, the cross sections of the flow paths of the supply-side transfer tube 2 and the discharge-side transfer tube 3 connected to the bubble rate sensor 1 may have a circular shape. Therefore, in order to flow the cryogenic liquid from the supply-side transfer tube 2 through the insulating tube 5 to the discharge-side transfer tube 3, it is necessary to change the cross-sectional shape of the flow path.

[0043] 3 and 4, a supply-side converter 14 and a discharge-side converter 15 for converting the cross-sectional shape of the flow path are located on both sides (i.e., the supply side and the discharge side) of the insulating tube 5 inside the vacuum vessel 4. The supply-side converter 14 and the discharge-side converter 15 have flow holes 14a and 15a through which the cryogenic liquid flows. The cross-sectional shape of one end 141a and one end 151a of the flow holes 14a and 15a is circular, to which the circular supply-side transfer pipe 2 and the discharge-side transfer pipe 3 are connected. The cross-sectional shape of the other end 141b and one end 151b is elongated, with the length in the second direction of the insulating tube 5 (i.e., the y direction shown in FIG. 5) being shorter than the length in the first direction of the insulating tube 5 (i.e., the x direction shown in FIG. 5). This allows the supply rate of the cryogenic liquid to be maintained without any drop.

[0044] The supply-side converter 14 and the discharge-side converter 15 may be directly connected to the insulating pipe 5, but in this embodiment, as shown in Figures 3 and 4, the supply-side converter 14 is connected to the insulating pipe 5 via a supply pipe 16, and the discharge-side converter 15 is connected to the insulating pipe 5 via a discharge pipe 17.

[0045] Figures 8A to 8D show supply pipe 16 and discharge pipe 17. Figure 8A is a perspective view of supply pipe 16 and discharge pipe 17 as seen from the supply-side converter 14 side and the discharge-side converter 15 side, and Figure 8B is a perspective view as seen from the insulating pipe 5 side. Figure 8C is a vertical cross-sectional view of supply pipe 16 and discharge pipe 17 shown in Figures 8A and 8B, and Figure 8D is a cross-sectional view taken along line ZZ shown in Figure 8C.

[0046] 4 is disposed on the supply side of the insulating tube 5 and has two supply holes 16a, 16b. Each of the supply holes 16a, 16b has an elongated shape in a cross section perpendicular to the flow direction of the cryogenic liquid, the same as the shape of each of the plurality of through holes 6a, 6b in the cross section. The two supply holes 16a, 16b may face the two through holes 6a, 6b of the insulating tube 5, respectively.

[0047] In this way, the two supply holes 16a, 16b face the two through holes 6a, 6b. As a result, the generation of bubbles is reduced where the supply holes 16a, 16b connect to the through holes 6a, 6b, further improving the accuracy of measuring the bubble content of the cryogenic liquid. Furthermore, a second partition wall 18 exists between the adjacent supply holes 16a, 16b, separating the two supply holes 16a, 16b. Therefore, the second partition wall 18 functions as a support, improving the pressure resistance of the supply pipe 16.

[0048] As described above, the portion separating adjacent through holes 6a, 6b of insulating tube 5 is defined as first partition wall 11 (see FIG. 5), and the portion separating adjacent supply holes 16a, 16b of supply pipe 16 is defined as second partition wall 18. In this case, as shown in FIG. 8C, second opposing surface 18a of second partition wall 18 on the insulating tube 5 side is not in contact with first opposing surface 11a of first partition wall 11 on the supply pipe 16 side, and there is a gap D1 between the opposing surfaces 11a, 18a.

[0049] In this way, the first opposing surface 11a has a gap D1 with the second opposing surface 18a and is not joined, so that it is possible to reduce stress generated on the first opposing surface 11a of the first partition wall 11. The gap D1 is preferably 1 mm or less (but not 0 mm). This reduces stress generated on the first opposing surface 11a and also reduces the generation of bubbles due to mixing of the cryogenic liquid flowing through the adjacent through holes 6a, 6b, thereby improving the accuracy of measuring the bubble rate of the cryogenic liquid.

[0050] Discharge pipe 17, which is located on the opposite side of supply pipe 16, has the same structure, configuration, and function as supply pipe 16. Therefore, discharge pipe 17 will also be described below with reference to Fig. 8C. Specifically, discharge pipe 17 has two discharge holes 17a, 17b, each of which faces two through-holes 6a, 6b. Between the two adjacent discharge holes 17a, 17b, there is a third partition wall 19 that separates the two discharge holes 17a, 17b and functions as a support.

[0051] When the portion separating adjacent through holes 6a, 6b of insulating tube 5 is defined as first partition wall 11 (see FIG. 5), and the portion separating adjacent discharge holes 17a, 17b of discharge pipe 17 is defined as third partition wall 19, as shown in FIG. 8C, third opposing surface 19a of third partition wall 19 on the insulating tube 5 side is not in contact with fourth opposing surface 11b of first partition wall 11 on the discharge pipe 17 side, and a gap D2 is formed between the opposing surfaces 11b, 19a. Like gap D1 described above, gap D2 is preferably 1 mm or less (but not 0 mm). Since the remaining features are the same as those of supply pipe 16, detailed description thereof will be omitted.

[0052] A first covering portion including a metallized layer is located on the end surface of the insulating tube 5 facing the supply pipe 16, except for the first opposing surface 11a. The reason for excluding the first opposing surface 11a is to reduce unintended adhesion of brazing material to the metallized layer on the first opposing surface 11a when joining the insulating tube 5 and the supply pipe 16 by brazing. This reduces the bonding of the first opposing surface 11a to the second opposing surface 18a of the supply pipe 16, thereby reducing an increase in stress occurring in the first opposing surface 11a of the first partition wall 11. Similarly, a second covering portion including a metallized layer is located on the end surface of the insulating tube 5 facing the discharge pipe 17, except for the fourth opposing surface 11b.

[0053] 9 is a cross-sectional view taken along line IX-IX in FIG. 2. As shown in the figure, a supply pipe 16 and a discharge pipe 17 for a cryogenic liquid are connected to both ends of an insulating pipe 5. Furthermore, a supply-side converter 14 is connected upstream of the supply pipe 16, and a discharge-side converter 15 is connected downstream of the discharge pipe 17. The supply pipe 16 and the discharge pipe 17 are made of metal and brazed to the insulating pipe 5. Specifically, the supply pipe 16 and the discharge pipe 17 are preferably made of austenitic stainless steel (e.g., SUS316L) containing 10.4 mass% or more of nickel, a Fernico alloy, an Fe-Ni alloy, an Fe-Ni-Cr-Ti-Al alloy, an Fe-Cr-Al alloy, or an Fe-Co-Cr alloy. The supply-side converter 14 and the discharge-side converter 15 are also preferably made of the same metal.

[0054] 3 and 4, the supply-side transfer pipe 2 connected to the supply-side converter 14 is surrounded by a flexible tube, supply-side bellows 20. When a cryogenic liquid flows, the supply-side transfer pipe 2 tends to contract, whereas the vacuum vessel 4 itself does not. Therefore, the supply-side bellows 20 functions as a buffer to mitigate the difference in contraction. In addition, the discharge-side transfer pipe 3 connected to the discharge-side converter 15 is also surrounded by a discharge-side bellows 21 that is the same as or similar to the supply-side bellows 20.

[0055] The supply-side bellows 20 and the discharge-side bellows 21 are connected to both ends of the cylindrical vacuum vessel 4 via flanges 22. The connection is vacuum-tight. The upstream opening of the supply-side bellows 20 and the downstream opening of the discharge-side bellows 21 are sealed with bellows joints 23, maintaining vacuum-tightness. At least one of the outer circumferential surfaces of the supply-side transfer pipe 2, supply-side converter 14, discharge-side converter 15, and insulating pipe 5, which are surrounded by the supply-side bellows 20, and the discharge-side transfer pipe 3, which is surrounded by the discharge-side bellows 21, is preferably covered with a heat insulating material 27. The heat insulating material 27 is, for example, a film of polyester, polystyrene, polypropylene, or the like.

[0056] 10 shows another embodiment of the present disclosure. As shown in the figure, an air bubble rate sensor 1' has a plurality of through-holes 61 for flowing a cryogenic liquid in an insulating tube 51, and a plurality of electrodes 71 are disposed in the insulating tube 51, facing each other across each through-hole 61. Each of the plurality of through-holes 61 has an elongated shape having a first direction (x direction) and a second direction (y direction) in a cross section perpendicular to the flow direction of the cryogenic liquid. The plurality of electrodes 71 face each other in the second direction, with the plurality of through-holes 61 in between. As in the previously described embodiment, the plurality of through-holes 61 are connected to converters 14 and 15 via a supply pipe 16 and a discharge pipe 17, respectively. The rest is the same as in the previously described embodiment.

[0057] Next, a flow meter according to an embodiment of the present disclosure will be described. This flow meter can measure the flow rate of the cryogenic liquid flowing through the through-holes 6a, 6b or the through-hole 61. The flow meter includes the bubble rate sensor 1 or the bubble rate sensor 1' and a flow velocity meter (not shown). The bubble rate sensor 1 or the bubble rate sensor 1' and the flow velocity meter are attached to the supply-side transfer pipe 2 and / or the discharge-side transfer pipe 3.

[0058] The cryogenic liquid flowing through the supply-side transfer pipe 2 and the discharge-side transfer pipe 3 is a two-phase flow of gas-liquid mixture. Therefore, the bubble rate is measured by the bubble rate sensor 1 or the bubble rate sensor 1', and the density d (kg / m 3 ) can be obtained. This is because the density d of the cryogenic liquid corresponds to the relative dielectric constant, and therefore also corresponds to the capacitance measured by the bubble rate sensor 1 or the bubble rate sensor 1'.

[0059] The flow velocity (m / sec) of the cryogenic liquid measured by the flow meter is v, and the cross-sectional area (m 2 ) is taken as a, the flow rate F (kg / sec) can be calculated using the following formula: F=d×v×a

[0060] In order to perform the above calculations, the flow meter further includes a calculation unit to which the bubble rate sensor 1 or 1' and the flow velocity meter are connected. This makes it easy to measure the flow rate of the cryogenic liquid, facilitating management when transporting large amounts of cryogenic liquid industrially.

[0061] Fig. 11 shows an example of a transfer pipe 24 of the present disclosure equipped with the above-described flow meter. Fig. 11 shows a schematic example of a flow meter in which the bubble rate sensor 1 or the bubble rate sensor 1' is attached to a bent transfer pipe 24, and wiring 25 is connected to the conductive pin 8 of the bubble rate sensor 1 or the bubble rate sensor 1'.

[0062] In this case, if the supply side or discharge side of the bent transfer pipe 24 is close to the air bubble rate sensor 1 or the air bubble rate sensor 1', this may hinder the installation of the wiring 25. For this reason, as shown in FIG. 12, it is preferable that the air bubble rate sensor 1 or the air bubble rate sensor 1' be inclined with respect to the bent portion of the transfer pipe 24 (hereinafter referred to as the bent portion). The inclination angle θ of the air bubble rate sensor 1 or the air bubble rate sensor 1' is preferably 10° or more and 90° or less with respect to the axis of the bent portion of the transfer pipe 24 shown in FIG. 12. The transfer pipe 24 is, for example, a U-shaped pipe or a J-shaped pipe.

[0063] In particular, when the insulating tube 51 is large, as in the case of the air bubble rate sensor 1' according to another embodiment of the present disclosure, the wiring 25 may be inclined with respect to the transfer tube 24, as shown in FIGS. 13A and 13B. FIG. 13B is a schematic side view of the air bubble rate sensor 1' shown in FIG. 13A, as viewed in the direction of arrow Q. In FIG. 13B, the wiring 25 is inclined at 90° with respect to the axis of the bent portion of the transfer tube 24, but the inclination may be any angle between 10° and 90°. As long as it does not interfere with the installation of the wiring 25, the wiring 25 may be arranged in the same direction as the bent portion of the transfer tube 24, as shown in FIG. 14.

[0064] Cryogenic liquids to be measured by the bubble rate sensor 1 and the bubble rate sensor 1' of the present disclosure include liquid hydrogen (-253°C), as well as liquid nitrogen (-196°C), liquid helium (-269°C), liquefied natural gas (-162°C), and liquid argon (-186°C) (the liquefaction temperature is indicated in parentheses). Therefore, in the present disclosure, "cryogenic liquid" means a liquid that liquefies at an extremely low temperature of -162°C or lower.

[0065] As described above, according to the present disclosure, the multiple through holes 6a, 6b, and 61 located in the insulating tube 5 and 51 have an elongated shape in a cross section perpendicular to the liquid flow direction, with a first side in a first direction and a second side in a second direction that is shorter than the first side. Furthermore, the multiple electrodes 7a and 7b or the electrode 71 face each other in the second direction, sandwiching the multiple through holes 6a and 6b or the through holes 61 therebetween. This allows the distance between the electrodes 7a and 7b or the electrode 71 to be shortened. As a result, the capacitance accumulated between the electrodes 7a and 7b or the electrode 71 increases, which improves the accuracy of measuring the bubble rate of the liquid and maintains the supply amount of the liquid.

[0066] Although the embodiments of the present disclosure have been described above, the air bubble rate sensor of the present disclosure is not limited to the above-described embodiments, and various modifications and / or improvements are possible within the scope of the present disclosure. [Explanation of symbols]

[0067] 1,1´ Air bubble rate sensor 2 Supply side transfer pipe 3 Discharge side transfer pipe 4 Vacuum container 5, 51 Insulating tube 6a, 6b, 61 through hole 6a1, 6b1 First side 6a2, 6b2 Second side 7a, 7b, 71 electrodes 8 Conduction Pins 9. Insulating substrate 10 flange 11 First Partition Wall 11a 1st facing surface 11b 4th facing surface 12 Vacuum exhaust valve 13 Opening 131 recess 14 Supply-side converter 14a Flow hole 141a one end 141b other end 15 Discharge side converter 15b Flow hole 151a one end 151b other end 16 Supply pipe 16a Supply hole 17 Discharge pipe 17a Discharge hole 18 Second Partition Wall 18a 2nd facing surface 19 Third Partition Wall 19a Third facing surface 20 Supply side bellows 21 Discharge side bellows 22 flange 23 Bellows joint 24 Transfer pipe 25 Wiring 26 Vacuum space 27 Insulation D1, D2 gap

Claims

1. an insulating tube having a plurality of through holes for allowing a liquid to flow; at least two electrodes located inside or on the outer surface of the insulating tube and facing each other across the plurality of through holes; the plurality of through holes have an elongated shape in a cross section perpendicular to the flow direction of the liquid, the elongated shape having a first side in a first direction and a second side in a second direction that is shorter than the first side; The at least two electrodes face each other in a second direction, and the plurality of through holes are located between the at least two electrodes.

2. The air bubble rate sensor according to claim 1 , wherein the plurality of through holes are aligned in the first direction.

3. The air bubble rate sensor according to claim 1 , wherein the plurality of through holes are aligned in the second direction.

4. a supply pipe having a plurality of supply holes is disposed on the supply side of the insulating pipe; 2. The air bubble rate sensor according to claim 1, wherein each of the plurality of supply holes has the same shape as the cross section of each of the plurality of through holes in a cross section perpendicular to the flow direction of the liquid, and faces each of the plurality of through holes.

5. 5. The air bubble rate sensor according to claim 4, wherein when a portion of the insulating tube that separates adjacent through holes is defined as a first partition wall and a portion of the supply pipe that separates adjacent supply holes is defined as a second partition wall, a second opposing surface of the second partition wall on the insulating tube side is not in contact with a first opposing surface of the first partition wall on the supply pipe side.

6. 6. The air bubble rate sensor according to claim 5, wherein the gap between the first opposing surface and the second opposing surface is 1 mm or less.

7. 6. The air bubble rate sensor according to claim 5, wherein a first covering portion including a metallized layer is located on the end face of the insulating tube on the supply tube side, excluding the first opposing surface.

8. a discharge pipe having a plurality of discharge holes is disposed on the discharge side of the insulating pipe; 2. The air bubble rate sensor according to claim 1, wherein each of the plurality of discharge holes has the same shape as the cross section of each of the plurality of through holes in a cross section perpendicular to the flow direction of the liquid, and faces each of the plurality of through holes.

9. 9. The air bubble rate sensor according to claim 8, wherein when a portion of the insulating tube that separates adjacent through holes is defined as a first partition wall and a portion of the exhaust pipe that separates adjacent discharge holes is defined as a third partition wall, a third opposing surface of the third partition wall on the insulating tube side is not in contact with a fourth opposing surface of the first partition wall on the exhaust pipe side.

10. 10. The air bubble rate sensor according to claim 9, wherein a gap between the third opposing surface and the fourth opposing surface is 1 mm or less.

11. 10. The air bubble rate sensor according to claim 9, wherein a second covering portion including a metallized layer is located on the end surface of the insulating tube on the discharge pipe side, excluding the fourth opposing surface.

12. A flow meter for measuring the flow rate of a liquid flowing through a through hole, comprising a bubble rate sensor described in any one of claims 1 to 11 and a flow rate meter for measuring the flow rate of the liquid flowing through the through hole.

13. A liquid transfer pipe equipped with the flow meter according to claim 12.

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