Bubble rate sensor, flow meter using the same, and extremely low temperature liquid transfer tube

Abstract

A bubble rate sensor of the present disclosure is provided with: an insulating tube having a through hole for flowing an extremely low temperature liquid; and a pair of planar electrodes fitted to an outer wall surface of the insulating tube. The insulating tube has an electrode fitting portion, and a distance D1 between inner wall surfaces in a direction perpendicular to an electrode surface of the electrode of the electrode fitting portion is shorter than a distance D2 between inner wall surfaces in a direction parallel to the electrode surface of the electrode.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a void fraction sensor for measuring a void fraction of an extremely low-temperature liquid such as liquid hydrogen, a flowmeter using the void fraction sensor, and an extremely low-temperature liquid transfer pipe. BACKGROUND

[0002] Recently, with the reduction of emission of greenhouse gases, the use of hydrogen as a powerful energy storage medium has attracted attention. In particular, liquid hydrogen has high volumetric efficiency and can be stored for a long period of time, and thus various techniques for using liquid hydrogen have been developed. However, an accurate measurement method for the flow rate required for handling a large amount of liquid hydrogen has not yet been established in industry. The main reason for this is that liquid hydrogen is a fluid in which the ratio of gas to liquid changes greatly because it is very easily vaporized.

[0003] That is, liquid hydrogen is an extremely low-temperature (boiling point -253°C) liquid, has very high thermal conductivity and small latent heat, and thus has the characteristic of immediately generating bubbles (voids). Therefore, liquid hydrogen becomes a so-called two-phase flow of gas-liquid mixture in a pipe for transfer.

[0004] Therefore, since the proportion of bubbles changes greatly, in order to measure the flow rate of liquid hydrogen flowing in the pipe, only the flow rate is measured as with a general liquid, and an accurate flow rate cannot be obtained.

[0005] Therefore, the development of a void fraction meter that measures the void fraction indicating the volume ratio of the gas phase of the gas-liquid two-phase flow has been promoted. As such a void fraction meter, in Non-Patent Literature 1, a capacitance type void fraction sensor using a pair of electrodes to measure the electrostatic capacitance is proposed.

[0006] PRIOR ART DOCUMENTS

[0007] NON-PATENT LITERATURE

[0008] Non-Patent Literature 1: Norihide MAENO et al., “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

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] The bubble rate sensor disclosed herein comprises: an insulating tube having a through hole for supplying cryogenic liquid flow; and a pair of face-shaped electrodes mounted on the outer wall surface of the insulating tube. The insulating tube has an electrode mounting portion, wherein the distance D1 between the inner wall surfaces of the electrode mounting portion in the direction perpendicular to the electrode surface of the electrode is shorter than the distance D2 between the inner wall surfaces in the direction parallel to the electrode surface of the electrode.

[0011] The flow meter disclosed herein measures the flow rate of a cryogenic liquid flowing within a through-hole, wherein the flow meter comprises: the aforementioned bubble rate sensor; and a flow velocity meter that measures the flow velocity of the cryogenic liquid flowing within the through-hole.

[0012] This disclosure provides a cryogenic liquid transfer tube having the aforementioned flow meter. Attached Figure Description

[0013] Figure 1 This is a schematic perspective view showing a bubble rate sensor according to one embodiment of the present disclosure.

[0014] Figure 2 It is shown Figure 1 A schematic perspective view of the vertical cross-section of the bubble rate sensor shown.

[0015] Figure 3 It is shown Figure 1 A schematic perspective view of the horizontal cross-section of the bubble rate sensor shown.

[0016] Figure 4 yes Figure 1 The image shows a vertical cross-sectional view of the bubble rate sensor.

[0017] Figure 5 yes Figure 1 The image shows a horizontal cross-sectional view of the bubble rate sensor.

[0018] Figure 6 yes Figure 1 The image shows a cross-sectional view of the bubble rate sensor along line IV-IV.

[0019] Figure 7 yes Figure 1 The image shows a VV-line cross-sectional view of the bubble rate sensor.

[0020] Figure 8 yes Figure 1 The bubble rate sensor shown is a cross-sectional view along line VI-VI.

[0021] Figure 9 This is a schematic perspective view of a bubble rate sensor with binding bodies installed on the outer peripheral surfaces of the inlet and outlet of the insulating tube.

[0022] Figure 10 It shows thatFigure 1 Fig. 7 is a perspective view of the bubble rate sensor shown in Fig. 1, which is housed in a state of the case.

[0023] Figure 11 Fig. 8 is a perspective view of the bubble rate sensor shown in Fig. 1, which is housed in a state of the case. Figure 10 Fig. 9 is a perspective view of the bubble rate sensor shown in Fig. 1, which is housed in a state of the case.

[0024] Figure 12 Fig. 10 is a perspective view of the bubble rate sensor shown in Fig. 1, which is housed in a state of the case. Figure 11 Fig. 11 is a perspective view of the bubble rate sensor shown in Fig. 1, which is housed in a state of the case.

[0025] Figure 13 Fig. 12 is a perspective view of the bubble rate sensor shown in Fig. 1, which is housed in a state of the case. Figures 1-5 Fig. 13 is a vertical sectional view of a modification of the bubble rate sensor shown in Fig. 1.

[0026] Figure 14 Fig. 14 is a perspective view of a bubble rate sensor according to another embodiment of the present disclosure.

[0027] Figure 15 Fig. 15 is a perspective view of the bubble rate sensor shown in Fig. 14, which is housed in a state of the case. Figure 14 Fig. 16 is a perspective view of the bubble rate sensor shown in Fig. 14, which is housed in a state of the case.

[0028] Figure 16 Fig. 17 is a perspective view of the bubble rate sensor shown in Fig. 14, which is housed in a state of the case. Figure 14 Fig. 18 is a perspective view of the bubble rate sensor shown in Fig. 14, which is housed in a state of the case. DETAILED DESCRIPTION

[0029] Hereinafter, a bubble rate sensor according to an embodiment of the present disclosure will be described.

[0030] Figure 1 Fig. 1 is a perspective view of a bubble rate sensor 1 according to an embodiment of the present disclosure, Figure 2 and Figure 3 Fig. 2 is a perspective view of a vertical cross section of the bubble rate sensor 1 and a perspective view of a horizontal cross section. As shown in Figs. 1 and 2, the bubble rate sensor 1 is provided with an insulating tube 2 having a through hole 3 for flowing an extremely low temperature liquid, and a pair of planar electrodes 4, 4 fitted to an outer wall surface of the insulating tube 2. Figure 2 and Figure 3 As shown in Figs. 1 and 2, the bubble rate sensor 1 is provided with the insulating tube 2 having the through hole 3 for flowing the extremely low temperature liquid, and the pair of planar electrodes 4, 4 fitted to the outer wall surface of the insulating tube 2.

[0031] As shown in Figs. 1 and 2, the insulating tube 2 is formed by overlapping two insulating tube members 21, 21 of a half-split shape with each other. The insulating tube 2 has a pair of recesses 6, 6 which are opened in a direction perpendicular to an axis of the through hole 3. The pair of electrodes 4, 4 are respectively fitted to bottom surfaces of the recesses 6, 6 provided in the insulating tube 2, and oppose each other (see Fig. 3). Figure 1 Figure 2

[0032] ​​Each electrode 4 is connected to a conductive pin 7. An airtight terminal 8 is mounted on the conductive pin 7. The airtight terminal 8 will be described later.

[0033] The insulating tube 2 has recesses 6, 6 as described above, thus narrowing the distance between the electrodes 4, 4 mounted on the bottom surface of these recesses 6, 6. This increases the electrostatic capacitance accumulated between the electrodes 4, 4, improving the accuracy of measuring the bubble rate of the cryogenic liquid flowing within the through-hole 3. The positions of the electrodes 4, 4 and the area of ​​the electrode surface 41 can be set to achieve optimal measurement accuracy.

[0034] Here, electrode surfaces 41 and 41 refer to the surfaces on which electrodes 4 and 4 are assembled at the bottom of recesses 6 and 6.

[0035] On the other hand, in order to avoid reducing the supply of cryogenic liquid, this embodiment is configured such that... Figure 2 and Figure 3 As shown, at the electrode assembly part 5 of the insulating tube 2, the distance D1 between the inner wall surfaces 3a, 3a in the direction perpendicular to the electrode surfaces 41, 41 of the electrodes 4, 4 is shorter than the distance D2 between the inner wall surfaces 3b, 3b in the direction parallel to the electrode surfaces 41, 41. Conversely, since the distance D2 in the parallel direction is larger than the distance D1 in the vertical direction, it is assumed that even if the distance between the electrodes 4, 4 becomes narrower, i.e., the distance D1 becomes smaller, the supply of cryogenic liquid can be maintained without decreasing. This also means that even if the supply of cryogenic liquid is increased, the accuracy of the bubble rate measurement can be maintained without decreasing.

[0036] In the electrode assembly part 5, the distance D1 between the inner wall surfaces 3a and 3a refers to the shortest distance, and the distance D2 between the inner wall surfaces 3b and 3b refers to the longest distance. Here, the distances D1 and D2 can be appropriately determined according to the supply amount of cryogenic liquid, the accuracy of bubble rate measurement, etc., and there are no particular restrictions. However, it is generally preferred that the distance D1 is a length that is 10% or more, preferably 20% or more, and 67% or less, preferably 50% or less relative to the distance D2.

[0037] Therefore, the shape of the through hole 3 in the section perpendicular to the axis of the through hole 3 in the electrode assembly part 5 can be elliptical or rectangular. In this way, the shape of the through hole 3 in the aforementioned section becomes a simple shape, and it becomes a shape without edges along the axis, thereby suppressing the deviation of bubble generation and improving the accuracy of bubble rate measurement.

[0038] It should be noted that the electrode assembly part 5 refers to the part for assembling electrodes 4 and 4, specifically the part that includes the bottom surface of the recesses 6 and 6 for assembling electrodes 4 and 4, and is sandwiched by the bottom surface.

[0039] like Figure 4As shown, in the vertical cross-section of the insulating tube 2 in the direction perpendicular to the electrode surfaces 41, 41, the distance between the inner wall surfaces 3a, 3a gradually decreases smoothly from the circular inlet 31 and outlet 32 ​​of the cryogenic liquid to the end of the parallel region E2. On the other hand, as Figure 5 As shown, in the horizontal cross-section of the insulating tube 2 in the direction horizontal to the electrode surfaces 41, 41, the distance between the inner wall surfaces 3b, 3b smoothly decreases from the parallel region E2 toward the inlet 31 and outlet 32 ​​of the through hole 3. In the parallel region E2, the inner wall surfaces 3a, 3a of the through hole 3 are parallel to each other, and the distance D1 is minimized. In addition, the inner wall surfaces 3b, 3b of the through hole 3 are parallel to each other, and the distance D2 is maximized. In this way, by changing the distance between the inner wall surfaces 3a, 3a and the distance between the inner wall surfaces 3b, 3b, the cross-sectional area of ​​the through hole 3 in the section perpendicular to the axial direction of the through hole 3 can be kept constant. Furthermore, the parallel region E2 includes an electrode assembly region E1 (i.e., electrode assembly part 5), which is preferably located approximately at the center of the parallel region E2.

[0040] Thus, in the vertical section perpendicular to the electrode surfaces 41, 41, the distance between the inner wall surfaces 3a, 3a smoothly increases from the parallel region E2 toward the inlet 31 and outlet 32 ​​of the through hole 3. Therefore, compared to the case where the distance between the inner wall surfaces 3a, 3a increases in stages toward the inlet 31 and outlet 32, stress concentration is less likely to occur on the inner wall surfaces 3a, 3a, allowing for long-term use. Similarly, in the horizontal section horizontal to the electrode surfaces 41, 41, the distance between the inner wall surfaces 3b, 3b smoothly decreases from the parallel region E2 toward the inlet 31 and outlet 32 ​​of the through hole 3. Therefore, compared to the case where the distance between the inner wall surfaces 3b, 3b increases in stages toward the inlet 31 and outlet 32, stress concentration is less likely to occur on the inner wall surfaces 3b, 3b, allowing for long-term use. In addition, by having a parallel region E2 and an electrode assembly region E1 in the parallel region E2, the electric field lines generated between the electrode surfaces 41, 41 vertically penetrate the cryogenic liquid flowing from the inlet 31 toward the outlet 32, thereby improving the measurement accuracy.

[0041] The length of the parallel region E2 is preferably 105% or more, more preferably 150% or more, and more preferably less than 5000% of the length of the electrode region E1.

[0042] It should be noted that, alternatively, the inner wall surfaces 3a, 3a may not have the parallel region E2, and at least one of the inner wall surfaces 3a, 3a may be bent such that the distance D1 between them continuously decreases from the inlet 31 and the outlet 32 ​​toward the electrode assembly portion 5. The bending direction of the inner wall surfaces 3a, 3a is preferably concave when viewed from the axis of the through hole 3.

[0043] Likewise, it can also be that the inner wall surfaces 3b, 3b do not have the parallel region E2, and at least one of the inner wall surfaces 3b, 3b is curved in a manner that the distance D2 therebetween continuously increases from the flow inlet 31 and the flow outlet 32 toward the electrode mounting portion 5. It can also be that the direction of the curvature of the inner wall surfaces 3b, 3b is convexly curved when viewed from the axis of the through-hole 3.

[0044] Figures 6-8 The case where the shape of the through-hole 3 gradually changes from the flow inlet 31 of the through-hole 3 toward the electrode mounting portion 5 is shown. For the Figures 6-8 The area of the cross section perpendicular to the axis of the through-hole 3 is the same for each of the through-holes 3 shown. Thereby, it is possible to maintain the supply amount of the extremely low-temperature liquid without decreasing.

[0045] The insulating tube 2 in the present embodiment is formed by overlapping the two insulating tube members 21, 21 in a split shape as described above. Also, as shown in Figure 9 The split-shaped insulating tube members 21, 21 are integrally joined by installing the annular binding body 9 around the outer peripheral surface of the flow inlet portion and the flow outlet portion of the insulating tube 2.

[0046] Note that the insulating tube members 21, 21 can also be bound with the binding body 9 without using a joining material. Alternatively, the joining surfaces of the insulating tube members 21, 21 can also be joined to each other with a sealing material that is stable with respect to the extremely low-temperature liquid flowing in the insulating tube 2 instead of or in addition to the binding body 9.

[0047] Figure 10 The state where the bubble rate sensor 1 is housed in the case 10 is shown. The bubble rate sensor 1 is surrounded by the case 10.

[0048] The outline perspective view of the case 10 shown in FIG. 6 is a vertical cross-sectional view. Figure 11 The outline perspective view of the case 10 shown in FIG. 7 is a horizontal cross-sectional view. Figure 12 As shown in the outline perspective view of the case 10 shown in FIG. 6 and the outline perspective view of the case 10 shown in FIG. 7, the case 10 has a frame portion 101 that houses the bubble rate sensor 1, and a cover portion 102 that seals the opening of the frame portion 101.

[0049] Figure 9 The bubble rate sensor 1 whose insulating tube members 21, 21 are bound by the binding body 9 is joined by welding or brazing the frame portion 101 and the cover portion 102 after being housed in the frame portion 101. The first connection tube 11 and the second connection tube 12 are respectively connected to the both end openings (the flow inlet 31 and the flow outlet 32) of the through-hole 3 of the bubble rate sensor 1.

[0050] The first connecting pipe 11 is inserted into the inlet 31, and its outer peripheral surface is joined to the cover 102 by welding or brazing. The second connecting pipe 12 is integrally formed with the frame 101, but it can also be joined to the frame 101 in the same way as the cover 102.

[0051] An insertion hole 13 is formed in the frame portion 101 of the housing 10. An airtight terminal 8 is assembled in the insertion hole 13, and a conductive pin 7, which is respectively connected to the electrode 4, is fixed in the insertion hole 13.

[0052] Furthermore, a vacuum exhaust valve 14 (such as a needle valve for vacuum exhaust) is provided in the housing 10, forming a vacuum space 15 (heat insulation layer) between the bubble rate sensor 1 and the housing 10. Thus, the vacuum space 15 exists on the outer periphery of the bubble rate sensor 1, ensuring heat insulation performance for the bubble rate sensor 1. As a result, the generation of bubbles caused by the influence of external gas temperature is suppressed, thereby improving the accuracy of bubble rate measurement. Additionally, leakage of cryogenic liquid from the bubble rate sensor 1 to the outside is suppressed by the airtight terminal 8, further improving the accuracy of bubble rate measurement.

[0053] like Figure 11 , Figure 12 As shown, preferably, the first connecting pipe 11, which has a supply hole on the inlet 31 side of the through hole 3, is connected to the insulating pipe 2, and the cross-sectional area of ​​the through hole 3, which is perpendicular to the axis of the through hole 3, is 90% or more and 110% or less of the cross-sectional area of ​​the supply hole, which is perpendicular to the axis of the supply hole. Normally, if the cryogenic liquid flows at a high speed, the pressure loss near the connection between the supply hole and the through hole 3 tends to increase, but with the configuration described above, the increase in pressure loss is suppressed. As a result, the generation of bubbles can be suppressed, thus improving the accuracy of the bubble rate measurement of the cryogenic liquid.

[0054] Similarly, preferably, the second connecting pipe 12, which has a discharge hole on the outlet 32 ​​side of the through hole 3, is connected to the insulating pipe 2, and the cross-sectional area of ​​the through hole 3, which is perpendicular to the axis of the through hole 3, is 90% or more and 110% or less of the cross-sectional area of ​​the discharge hole, which is perpendicular to the axis of the discharge hole. This suppresses the increase in pressure loss. As a result, the generation of bubbles can be suppressed, thus improving the accuracy of the bubble rate measurement of cryogenic liquids.

[0055] The frame portion 101 and the cover portion 102 constituting the housing 10 are formed of metal or ceramic. The first connecting pipe 11 and the second connecting pipe 12 are preferably metal pipes. Specifically, the frame portion 101 is preferably formed of, for example, austenitic stainless steel (e.g., SUS316L) with a nickel content of 10.4% by mass or more, silicon nitride, silane, or other ceramics.

[0056] The lid portion 102 is preferably formed of, for example, an iron-nickel-cobalt alloy, an Fe-Ni alloy, an Fe-Ni-Cr-Ti-Al alloy, an Fe-Cr-Al alloy, an Fe-Co-Cr alloy, or the like.

[0057] In order to obtain sufficient thermal insulation performance, the inner diameter of the frame portion 101 is preferably 1 mm or more with respect to the outer diameter of the insulation tube 2, and preferably 10 mm or more with respect to the outer diameter of the insulation tube 2, and is preferably 200 mm or less with respect to the outer diameter of the insulation tube 2, and preferably 100 mm or less with respect to the outer diameter of the insulation tube 2. The lid portion 102 is hermetically joined to the outer peripheral surface of the insulation tube 2 by brazing.

[0058] The electrodes 4, 4 can be formed of, for example, a copper foil, an aluminum foil, or the like. In order to form the electrodes 4 on the bottom surfaces of the recesses 6, for example, a vacuum evaporation method, a metallization method, or an active metal method can be used. Alternatively, a metal plate that becomes the electrodes 4 can be bonded to the bottom surfaces of the recesses 6. The thickness of each of the electrodes 4, 4 is preferably 10 μm or more, and preferably 20 μm or more, and is preferably 2 mm or less, and preferably 1 mm or less.

[0059] The insulation tube 2 is formed of, for example, a ceramic in which zirconia, alumina, sapphire, aluminum nitride, silicon nitride, sialon, cordierite, mullite, yttria, silicon carbide, a cermet, β-eucryptite, or the like is a main component. In the case where the ceramic is composed of a ceramic in which alumina is a main component, the ceramic can contain silicon, calcium, magnesium, sodium, or the like as an oxide.

[0060] The main component in the ceramic refers to a component that accounts for 60% by mass or more in the total of 100% by mass of components that constitute the ceramic. In particular, the main component is preferably a component that accounts for 95% by mass or more in the total of 100% by mass of components that constitute the ceramic. The components that constitute the ceramic can be found using an X-ray diffractometer (XRD). As for the content of each component, after identifying the components, the content of elements that constitute the components can be found using a fluorescence X-ray analysis device (XRF) or an ICP emission spectrometer, and converted into the identified components.

[0061] The insulation tube 2 is preferably composed of a low thermal expansion ceramic. As the low thermal expansion ceramic, a ceramic in which the temperature range in which the linear expansion rate is measured is set to 0°C to 50°C, and the linear expansion rate at 22°C is 0 ± 20 ppb / K or less is referred to. The low thermal expansion ceramic has a low linear expansion rate, and thus even if subjected to thermal shock of an extremely low-temperature liquid including liquid hydrogen, the possibility of breakage is reduced. The linear expansion rate of the low thermal expansion ceramic can be found using, for example, an optical heterodyne method-optical path interferometer.

[0062] Specifically, for the low thermal expansion ceramic, it is preferable that the main crystal phase is cordierite, the secondary crystal phase includes alumina, mullite, and sapphirine, and the amorphous phase including Ca exists in the grain boundary phase. It is preferable that the crystal phase ratio of the main crystal phase is 95 mass% or more and 97.5 mass% or less, the crystal phase ratio of the secondary crystal phase is 2.5 mass% or more and 5 mass% or less, the content of Ca with respect to the total amount is 0.4 mass% or more and 0.6 mass% or less in terms of CaO, and zirconia is included, the content of zirconia with respect to the total amount is 0.1 mass% or more and 1.0 mass% or less. Thus, even if the temperature of the extremely low temperature liquid greatly varies, the low thermal expansion ceramic is not easily stretched and contracted, and thus can be used for a long period of time. As such a low thermal expansion ceramic, for example, the ceramic described in Japanese Patent No. 5430389 can be used.

[0063] The relative dielectric constant of the ceramic constituting the insulating tube 2 in the use temperature range thereof is preferably 11 or less. The relative dielectric constant of the extremely low temperature liquid is small, and thus if the relative dielectric constant of the ceramic is small, it is close to the relative dielectric constant of the extremely low temperature liquid, the high frequency characteristics are improved, and thus the measurement accuracy of the bubble rate is further improved. In particular, if it is 11 or less, the measurement accuracy of the bubble rate of the extremely low temperature liquid can be further improved. The above use temperature range refers to the temperature range at the time of transfer of the extremely low temperature liquid.

[0064] In addition, the insulating tube 2 can also be constituted by a ceramic in which silicon nitride or sialon is the main component. These ceramics are high in mechanical strength and thermal shock resistance, and thus even if subjected to thermal shock, the possibility of breakage is reduced.

[0065] Specifically, the above ceramic includes calcium oxide, aluminum oxide, and oxides of rare earth elements, and with respect to 100 mass% of the total of the calcium oxide, the aluminum oxide, and the oxides of rare earth elements, the contents of the calcium oxide and the aluminum oxide are respectively 0.3 mass% or more and 1.5 mass% or less and 14.2 mass% or more and 48.8 mass% or less, and the balance is the oxides of the rare earth elements. The silicon nitride is β-sialon represented by the composition formula Si 6-Z Al Z O Z N 8-Z (z = 0.1 to 1) and has an average grain diameter of 20 μm or less (where 0 μm is excluded). As such a ceramic, for example, the ceramic described in Japanese Patent No. 5430389 can be used.

[0066] The arithmetic average roughness Ra in the roughness curve of the inner wall surface 3a, 3b of the electrode assembly portion 5 in the direction parallel to the axis of the through-hole 3 is preferably 0.2 μm or less. If the arithmetic average roughness Ra in the roughness curve of the inner wall surface 3a, 3b is 0.2 μm or less, the increase in the flow resistance of the extremely low-temperature liquid generated by the inner wall surface 3a, 3b is suppressed, and thus the flow rate distribution of the extremely low-temperature liquid is stabilized. That is, the deviation of the flow rate is suppressed, and thus the measurement accuracy of the bubble rate of the extremely low-temperature liquid can be improved.

[0067] The arithmetic average roughness Ra can be measured in accordance with JIS B0601:2001, using a laser microscope (manufactured by Keyence Co., Ltd., super depth color 3D shape measuring microscope (VK-X1000 or subsequent models)). As the measurement conditions, the illumination method is set to coaxial illumination, the measurement magnification is set to 240 times, the cutoff value λs is set to none, the cutoff value λc is set to 0.08 mm, the correction of end effect is set to yes, and the measurement range is set to 1425 μm x 1067 μm. Within the measurement range, four lines as measurement targets are drawn at substantially equal intervals, and the line roughness is measured. The length of each line as a measurement target is 1280 μm.

[0068] The relative density of the ceramic is, for example, 92% or more and 99.9% or less. The relative density is expressed as a percentage (ratio) of the apparent density of the ceramic with respect to the theoretical density of the ceramic, which is calculated in accordance with JIS R1634-1998.

[0069] The insulating tube 2 is composed of ceramic having a plurality of closed pores. The value obtained by subtracting the average value of the equivalent circle diameters of the closed pores from the average value of the distances between the centers of gravity of the adjacent closed pores (hereinafter, referred to as the interval between the closed pores) is 8 μm or more and 18 μm or less. The closed pores are independent of each other.

[0070] In the case where the interval between the closed pores is 8 μm or more, the closed pores exist in a relatively dispersed state, and thus the mechanical strength is high. On the other hand, in the case where the interval between the closed pores is 18 μm or less, even if a microcrack starting from the profile of the closed pore is generated by repeated application of cold and heat shocks, the probability that the extension of the microcrack is blocked by the surrounding closed pores is high. Thus, if the interval between the closed pores is 8 μm or more and 18 μm or less, the insulating tube 2 can be used for a long period of time.

[0071] The skewness of the equivalent circle diameter of the closed pores can also be greater than the skewness of the center-to-center distance of the closed pores. Here, the skewness Sk is an index of how much a distribution deviates from a normal distribution, that is, an index (statistic) of the left-right symmetry of a distribution, and in the case where the skewness is greater than 0, the tail of the distribution is oriented to the right, in the case where the skewness is 0, the distribution is left-right symmetrical, and in the case where the skewness is less than 0, the tail of the distribution is oriented to the left.

[0072] When the respective histograms of the equivalent circle diameter of the closed pores and the center-to-center distance of the closed pores are overlaid, in the case where the skewness of the equivalent circle diameter of the closed pores is greater than the skewness of the center-to-center distance of the closed pores, the mode of the equivalent circle diameter is located at a position that is more to the left (zero side) than the mode of the center-to-center distance. That is, the closed pores having a small equivalent circle diameter are more numerous, and these closed pores are more sparsely present, and it is possible to obtain a ceramic member that has both mechanical strength and cold and hot impact resistance.

[0073] For example, the skewness of the equivalent circle diameter of the closed pores is 1 or more, and the skewness of the center-to-center distance of the closed pores is 0.7 or less. The difference between the skewness of the equivalent circle diameter of the closed pores and the skewness of the center-to-center distance of the closed pores is 0.3 or more.

[0074] In order to obtain the center-to-center distance and the equivalent circle diameter of the closed pores, first, from one end surface of the ceramic forming insulating tube 2 toward the axial direction, the average particle diameter D 50 of 3 μm and using a copper disk. Then, by using diamond abrasive grains having an average particle diameter D 50 of 0.5 μm and using a tin disk, a polished surface having an arithmetic average roughness (Ra) of 0.2 μm or less in the roughness curve was obtained.

[0075] The arithmetic average roughness Ra of the polished surface was the same as the measurement method described above. The polished surface was observed at a magnification of 200 times, and an average range was selected, for example, an area of 7.2 x 10 4 μm 2 (length in the lateral direction: 310 μm, length in the vertical direction: 233 μm) was obtained.

[0076] Using this observation image as an object, the center-to-center distance of the closed pores was obtained by a method such as the center-to-center distance method measured by a dispersity meter using an image analysis software "Akenken (ver 2.52)" (registered trademark, manufactured by Asahi Chemical Industry Co., Ltd.). Hereinafter, in the case where it is described as the image analysis software "Akenken", it indicates the image analysis software manufactured by Asahi Chemical Industry Co., Ltd.

[0077] As the setting conditions of this method, for example, the index indicating the brightness of the image, that is, the threshold value was set to 165, the brightness was set to dark, and the small figure removal area was set to 1 μm2 The noise removal filter is set to OFF. Note that the threshold value is adjusted according to the brightness of the observation image, and the brightness is set to dark, the method of binarization is set to manual, the small pattern removal area is set to 1 pm, and the noise removal filter is set to ON. The threshold value is adjusted in such a manner that the shape of the mark appearing in the observation image matches the shape of the closed-end pore. The equivalent circle diameter of the closed-end pore is obtained by particle analysis using the above observation image as the object. The same setting conditions as those for obtaining the distance between the centers of gravity of the closed-end pores are used. 2 The equivalent circle diameter of the closed-end pore and the skewness of the distance between the centers of gravity are obtained using the function Skew provided by Excel (registered trademark, Microsoft Corporation).

[0078] The equivalent circle diameter of the closed-end pore and the skewness of the distance between the centers of gravity are obtained using the function Skew provided by Excel (registered trademark, Microsoft Corporation).

[0079] An example of a method for manufacturing an insulating tube composed of ceramic will be described. A case where alumina is used as the main component of the ceramic constituting the insulating tube will be described.

[0080] An alumina powder (purity of 99.9 mass% or more) as the main component, and each of a magnesium hydroxide powder, a silicon oxide powder, and a calcium carbonate powder are put together with a solvent (ion exchange water) into a pulverizing mill, and after being pulverized to an average particle diameter (D 50 ) of 1.5 pm or less, an organic binder and a dispersant for dispersing the alumina powder are added and mixed, thereby obtaining a slurry.

[0081] In this case, the content of the magnesium hydroxide powder in the total 100 mass% of the above powders is 0.3 to 0.42 mass%, the content of the silicon oxide powder is 0.5 to 0.8 mass%, the content of the calcium carbonate powder is 0.06 to 0.1 mass%, and the balance is the alumina powder and unavoidable impurities.

[0082] The organic binder is an acrylic emulsion, polyvinyl alcohol, polyethylene glycol, polyethylene oxide, or the like.

[0083] Next, after the slurry is spray granulated to obtain granules, a uniaxial press molding device or a cold isostatic press molding device is used to pressurize the molding pressure to 78 MPa or more and 118 MPa or less, thereby obtaining a columnar molded body.

[0084] As needed, a recess that becomes a concave portion after firing is formed on the molded body by cutting processing.

[0085] The molded body is fired at a firing temperature of 1580°C or more and 1780°C or less and a holding time of 2 hours or more and 4 hours or less, thereby obtaining an insulating tube.

[0086] To obtain an insulating tube with a closed pore spacing of 8 μm or more and 18 μm, the molded body is fired at a firing temperature of 1600°C or more and 1760°C or less, and for a holding time of 2 hours or more and 4 hours or less. To obtain an insulating tube where the deviation of the equivalent circular diameter of the closed pores is greater than the deviation of the distance between the centroids of the closed pores, the molded body obtained by applying a forming pressure of 96 MPa or more and 118 MPa or less is fired at a firing temperature of 1600°C or more and 1760°C or less, and for a holding time of 2 hours or more and 4 hours or less. Alternatively, the surface opposite the through hole of the insulating tube can be ground to form the inner circumferential surface. Additionally, the surface of the recess where the electrode is mounted can be ground to form the bottom surface.

[0087] Figure 13 It shows Figures 1-3 Variations of the illustrated implementation. For example... Figure 13 As shown, the recess 6' has a first recess 61 that opens to the outside and a second recess 62 disposed on the bottom surface of the first recess 61. The opening area of ​​the second recess 62 is smaller than that of the first recess 61, and the electrode 4' is mounted on the bottom surface of the second recess 62. This further improves the positioning accuracy of the electrode 4', thus improving the accuracy of the bubble rate measurement of the cryogenic liquid. Other aspects are the same as in the aforementioned embodiment, therefore detailed descriptions are omitted.

[0088] Next, based on Figures 14-16 Other embodiments of this disclosure will be described. It should be noted that, regarding... Figures 1-13 Components that are identical to those shown are labeled with the same reference numerals and their descriptions are omitted.

[0089] Figure 14 A bubble rate sensor 1' surrounded by a housing 10 is shown. Figure 15 and Figure 16 It is a schematic perspective view showing its vertical cross-section and a schematic perspective view showing its horizontal cross-section.

[0090] like Figure 15 As shown, the bubble rate sensor 1' of this embodiment has a pair of recesses 6a, 6b, 6c that open in a direction perpendicular to the axis of the through hole 3' of the insulating tube 2. Electrodes 4a, 4b, 4c are respectively mounted on the bottom surface of each recess 6a, 6b, 6c. The recesses 6a, 6b, 6c are arranged along the axis of the through hole 3'.

[0091] In this embodiment, the electrode assembly part 5' refers to the part for assembling the plurality of electrodes 4a, 4b, 4c, for example, the part in which the recesses 6a, 6b, 6c are formed.

[0092] In this embodiment, the electrode assembly part 5' is also formed such that the distance D1 between the inner wall surfaces in the direction perpendicular to the electrode surfaces of electrodes 4a, 4b, and 4c is shorter than the distance D2 between the inner wall surfaces in the direction parallel to the electrode surfaces of electrodes 4a, 4b, and 4c.

[0093] By using multiple electrodes 4a, 4b, and 4c to measure the bubble rate, the measurement accuracy is further improved. The rest is the same as the previously described implementation method.

[0094] Next, the flow meter according to an embodiment of the present disclosure will be described. This flow meter is used to measure the flow rate of cryogenic liquid flowing within through-holes 3, 3', and includes the aforementioned bubble rate sensors 1, 1' and a flow velocity meter (not shown). The bubble rate sensors 1, 1' and the flow velocity meter are mounted in a cryogenic liquid transfer tube (hereinafter, sometimes simply referred to as the transfer tube).

[0095] The cryogenic liquid flowing inside the transfer tube becomes a two-phase flow of gas and liquid mixture. Therefore, the bubble rate is measured using bubble rate sensors 1 and 1', and the density d (kg / m³) of the cryogenic liquid is calculated from this. 3 The density d of cryogenic liquids corresponds to the relative permittivity, and therefore also to the electrostatic capacitance measured by bubble rate sensors 1 and 1'.

[0096] Furthermore, the flow velocity (m / s) of the cryogenic liquid determined by the flow meter is set as v, and the cross-sectional area (m²) of the through hole 3 in the electrode assembly part 5 is set as... 2 When ) is set as a, the flow rate F (kg / s) can be calculated using the following formula.

[0097] F=d×v×a

[0098] To perform the above calculations, the flow meter also includes a calculation device that connects to bubble rate sensors 1 and 1' and a flow velocity meter. This allows for simple measurement of the flow rate of cryogenic liquids, thus simplifying management in industrial applications involving large-scale transfers of cryogenic liquids.

[0099] The cryogenic liquids measured by the bubble rate sensors 1 and 1' of this disclosure include, in addition to liquid hydrogen (-253°C), 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, the cryogenic liquids in this disclosure refer to liquids that liquefy at extremely low temperatures below -162°C.

[0100] The embodiments of this disclosure have been described above, but the bubble rate sensor of this disclosure is not limited to the above embodiments, and various changes and improvements can be made within the scope of this disclosure.

[0101] Explanation of reference numerals in the attached figures:

[0102] 1, 1'... bubble rate sensor;

[0103] 2... insulation tube;

[0104] 21... insulation tube member;

[0105] 3, 3'... through hole;

[0106] 3a, 3b... inner wall surface;

[0107] 31... inflow port;

[0108] 32... outflow port;

[0109] 4, 4', 4a, 4b, 4c... electrode;

[0110] 5, 5', 5a, 5b, 5c... electrode assembly portion;

[0111] 6, 6', 6a, 6b, 6c... recess;

[0112] 61... first recess;

[0113] 62... second recess;

[0114] 7... conductive pin;

[0115] 8... airtight terminal;

[0116] 9... bundled body;

[0117] 10... housing;

[0118] 101... frame portion;

[0119] 102... cover portion;

[0120] 11... first connection tube;

[0121] 12... second connection tube;

[0122] 13... insertion hole;

[0123] 14... vacuum exhaust valve;

[0124] 15... vacuum space;

[0125] D1... (shortest) distance;

[0126] D2... (longest) distance.

Claims

1. A bubble rate sensor, wherein, The bubble rate sensor includes: An insulating tube having a through-hole for the flow of cryogenic liquids; and A pair of face-shaped electrodes are mounted on the outer wall surface of the insulating tube. The insulating tube has an electrode assembly portion, and the distance D1 between the inner wall surfaces of the electrode assembly portion in the direction perpendicular to the electrode surface of the electrode is shorter than the distance D2 between the inner wall surfaces in the direction parallel to the electrode surface of the electrode.

2. The bubble rate sensor according to claim 1, wherein, At least in the electrode assembly, the opposing inner wall surfaces at the distance D1 are determined to be parallel to each other, or at least one of the opposing inner wall surfaces at the distance D1 is determined to be concave when viewed from the axis of the through hole.

3. The bubble rate sensor according to claim 1 or 2, wherein, At least in the electrode assembly, the opposing inner wall surfaces at the distance D2 are determined to be parallel to each other, or at least one of the opposing inner wall surfaces at the distance D2 is determined to be convexly curved when viewed from the axis of the through hole.

4. The bubble rate sensor according to claim 1 or 2, wherein, A first connecting pipe having a supply hole on the inlet side of the through hole is connected to the insulating pipe, and the cross-sectional area of ​​the through hole perpendicular to the axis of the through hole is more than 90% and less than 110% of the cross-sectional area of ​​the supply hole perpendicular to the axis of the supply hole.

5. The bubble rate sensor according to claim 1 or 2, wherein, A second connecting pipe having a discharge hole on the outlet side of the through hole is connected to the insulating pipe. The cross-sectional area of ​​the through hole, which is perpendicular to the axis of the through hole, is more than 90% and less than 110% of the cross-sectional area of ​​the discharge hole, which is perpendicular to the axis of the discharge hole.

6. The bubble rate sensor according to claim 1 or 2, wherein, The arithmetic mean roughness Ra of the roughness curve of the inner wall surface in the direction parallel to the axis of the through hole in at least the electrode assembly is 0.2 μm or less.

7. The bubble rate sensor according to claim 1 or 2, wherein, At least the cross-sectional shape of the through hole in the electrode assembly that is perpendicular to the axis of the through hole is elliptical or rectangular.

8. The bubble rate sensor according to claim 1 or 2, wherein, The insulating tube has at least a pair of recesses in the electrode assembly portion that open in a direction perpendicular to the electrode surface of the electrode, and the outer wall surface for assembling the electrode is the bottom surface of the recesses.

9. The bubble rate sensor according to claim 8, wherein, The recess has: a first recess that opens to the outside; and a second recess disposed on the bottom surface of the first recess, with an opening area smaller than that of the first recess, and the outer wall surface for assembling the electrode is the bottom surface of the second recess.

10. The bubble rate sensor according to any one of claims 1, 2, and 9, wherein, The insulating tube is made of low thermal expansion ceramic.

11. The bubble rate sensor according to any one of claims 1, 2, and 9, wherein, The insulating tube is made of ceramic with silicon nitride or silane as the main components.

12. The bubble rate sensor according to any one of claims 1, 2, and 9, wherein, The insulating tube is made of ceramic with a relative permittivity of 11 or less in the operating temperature range.

13. The bubble rate sensor according to any one of claims 1, 2, and 9, wherein, The insulating tube is made of ceramic with multiple closed pores, and the value obtained by subtracting the average equivalent circular diameter of the closed pores from the average distance between the centroids of adjacent closed pores is 8 μm or more to 18 μm.

14. The bubble rate sensor according to claim 13, wherein, The deviation of the equivalent circle diameter of the closed vent is greater than the deviation of the distance between the centroids of the closed vent.

15. A flow meter for measuring the flow rate of a cryogenic liquid flowing within a through-hole, wherein, The flow meter has the following features: The bubble rate sensor according to any one of claims 1 to 14; and A flow meter that measures the flow rate of the cryogenic liquid within the through-hole.

16. A cryogenic liquid transfer tube, wherein, The cryogenic liquid transfer tube is equipped with the flow meter as described in claim 15.

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