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

Abstract

The bubble rate sensor disclosed herein comprises: an insulating inner tube having a through-hole for the flow of a cryogenic liquid; at least one pair of electrodes disposed on the outer surface of the inner tube; and a heat-insulating layer covering the outer periphery of the inner tube. The flow meter disclosed herein measures the flow rate of the cryogenic liquid flowing through the through-hole of the inner tube, and comprises: the aforementioned bubble rate sensor; and a flow meter for measuring the flow velocity of the cryogenic liquid flowing through the through-hole.

Description

Technical Field

[0001] This disclosure relates to a void fraction sensor for measuring the bubble fraction of cryogenic liquids such as liquid hydrogen, a flow meter using the same, and a cryogenic liquid transfer tube. Background Technology

[0002] Recently, with the reduction of greenhouse gas emissions, the utilization of hydrogen as a powerful energy storage medium has attracted attention. In particular, liquid hydrogen has been developed for various utilization technologies due to its high volumetric efficiency and long-term storage capacity. However, a proper method for measuring the required flow rate for large-scale liquid hydrogen disposal has not been established in industry. The main reason for this is that liquid hydrogen is a fluid that is very easily vaporized and has a highly variable gas-to-liquid ratio.

[0003] That is, because liquid hydrogen is a liquid at extremely low temperatures (boiling point -253°C), it has very high thermal conductivity and low latent heat, thus exhibiting the characteristic of immediately generating bubbles (void). Therefore, liquid hydrogen becomes a so-called two-phase flow, a gas-liquid mixture, within the piping used for transfer.

[0004] Therefore, because the proportion of bubbles varies greatly, simply measuring the flow rate as is done for ordinary liquids in order to determine the flow rate of liquid hydrogen flowing through the piping cannot provide the accurate flow rate.

[0005] Therefore, the development of bubble rate meters that measure the bubble rate representing the gas phase volume ratio of a gas-liquid two-phase flow has been promoted. As such a bubble rate meter, Non-Patent Document 1 proposes a capacitance-type bubble rate meter that uses a pair of electrodes to measure the electrostatic capacitance.

[0006] Prior art literature

[0007] Non-patent literature

[0008] Non-patent literature 1: Norihide MAENO, 5 others, "Void Fraction Measurement of Cryogenic Two Phase Flow Using a Capacitance Sensor", Trans. JSASS AerospaceTech. Japan, Vol. 12, No. ists29, pp. Pa_101-Pa_107, 2014 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] The bubble rate sensor disclosed herein comprises: an insulating inner tube having a through hole for flowing through a cryogenic liquid; at least one pair of electrodes disposed on the outer peripheral surface of the inner tube; and a heat insulation layer covering the outer peripheral side of the inner tube.

[0011] The flow meter disclosed herein measures the flow rate of an extremely low temperature liquid flowing through a through-hole in an inner tube, and includes: the bubble rate sensor described above; and a flow meter for measuring the flow velocity of the extremely low temperature liquid flowing through the through-hole.

[0012] In addition, this disclosure provides a cryogenic liquid transfer tube equipped with the aforementioned flow meter. Attached Figure Description

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

[0014] Figure 2 This is a schematic cross-sectional view showing a bubble rate sensor according to other embodiments of this disclosure.

[0015] Figure 3A It means Figure 2 The diagram shows a cross-sectional view of the assembled structure of the inner tube.

[0016] Figure 3B It means Figure 3A An explanatory diagram of a divisible ceramic component.

[0017] Figure 4 It means Figure 2 A three-dimensional view showing a partial fracture of a deformed example of a bubble rate sensor.

[0018] Figure 5 It means Figure 4 A three-dimensional view showing a partial fracture of the inner tube and its surrounding structure.

[0019] Figure 6 It means Figure 4 The diagram shows a three-dimensional view of the inner tube. Detailed Implementation

[0020] The following describes the bubble rate sensor according to embodiments of this disclosure. Additionally, the following description will explain a bubble rate sensor used to measure the bubble rate when liquid hydrogen is used as a cryogenic liquid.

[0021] Figure 1 This refers to a bubble rate sensor 1 according to one embodiment of the present disclosure. For example... Figure 1 As shown, the bubble rate sensor 1 includes: an insulating inner tube 2 with a through hole 3 through which liquid hydrogen flows; and an even number (two in this embodiment) of electrodes 4 mounted on the outer surface of the inner tube 2.

[0022] Furthermore, annular portions 5 are installed on the outer periphery of both ends of the inner tube 2, and the outer tube 6 is joined to the outer periphery of the annular portions 5. The outer tube 6 has a first insertion hole 7 that opens radially. A first airtight terminal 8 is provided in the first insertion hole 7, and a conductive pin 9, which is separately connected to the electrode 4, is fixed in the first insertion hole 7.

[0023] The so-called insulating inner tube 2 refers to a tube with an inherent volume resistivity of 10 Ω at 20°C. 10 Inner tubes with an Ω·m or higher.

[0024] A vacuum venting valve 15 (e.g., a needle valve for vacuum venting) is provided in the outer tube 6, forming a vacuum space 10 (insulation layer) between the inner tube 2 and the outer tube 6. Thus, because a vacuum space 10 is provided on the outer periphery of the inner tube 2, the insulation performance of the inner tube 2 is ensured. As a result, the accuracy of bubble rate measurement is improved because the generation of bubbles caused by the influence of external air temperature is suppressed. That is, if the insulation performance between the inside and outside of the inner tube 2 through which cryogenic liquids such as liquid nitrogen flow is insufficient, the bubbles generated in the inner tube 2 cannot be adequately controlled due to the influence of external temperature. Therefore, it becomes difficult to accurately measure the bubble rate of cryogenic liquids.

[0025] Furthermore, since the leakage of liquid hydrogen from the inner tube 2 to the outside is controlled by the first airtight terminal 8, the accuracy of the bubble rate measurement is further improved.

[0026] The inner tube 2 can contain ceramic, such as ceramic with alumina as the main component. If alumina is the main component, the inner tube 2 can be made with relatively inexpensive raw materials and manufacturing costs, and has excellent mechanical properties.

[0027] When the inner tube 2 contains a ceramic with alumina as the main component, it may contain, for example, silicon, magnesium, and calcium. If these elements in the total 100% by mass of the ceramic components are converted into oxides, for example, SiO2 is 0.3% to 1% by mass, MgO is 0.1% to 0.4% by mass, and CaO is 0.04% to 0.08% by mass.

[0028] It can also contain anorthite (CaAl2Si2O8). Since anorthite has a lower coefficient of linear expansion than alumina, its inclusion improves thermal shock resistance. In particular, the inner tube 2 can contain low-thermal-expansion ceramics. Low-thermal-expansion ceramics are defined as ceramics with a linear expansion rate of 0 ± 20 ppb / K or less at 22°C. Due to the low linear expansion rate of low-thermal-expansion ceramics, the possibility of breakage is reduced even when subjected to thermal shock from extremely low-temperature liquids containing liquid hydrogen.

[0029] Specifically, the low thermal expansion ceramic can have cordierite as the main crystalline phase, and include alumina, mullite, and pseudosapphire as secondary crystalline phases, with an amorphous phase containing Ca present in the grain boundary phase. Preferably, the crystallinity of the main crystalline phase is 95% by mass or more and 97.5% by mass or less, the crystallinity of the secondary crystalline phase is 2.5% by mass or more and 5% by mass or less, the Ca content relative to the total amount (converted to CaO) is 0.4% by mass or more and 0.6% by mass or less, and it further includes zirconium oxide, with a zirconium oxide content relative to the total amount of 0.1% by mass or more and 1.0% by mass or less. Since the relative permittivity of the ceramic forming the inner tube 2 becomes close to that of the cryogenic liquid, the high-frequency characteristics are improved, and therefore, the accuracy of bubble rate measurement is further improved.

[0030] By using an X-ray diffraction apparatus with CuKα rays to analyze the diffraction angle range of 2θ = 8 to 100°, the Rietveld method can be used to analyze the crystalline phases and their ratios in low thermal expansion ceramics.

[0031] Furthermore, the inner tube 2 may contain ceramics primarily composed of silicon nitride or silane. These ceramics have high mechanical strength and thermal shock resistance, thus reducing the likelihood of breakage even under thermal shock.

[0032] Specifically, the aforementioned ceramic comprises oxides of calcium oxide, aluminum oxide, and rare earth elements. Relative to 100% by mass of the total mass of these oxides, the content of calcium oxide and aluminum oxide is 0.3% to 1.5% by mass and 14.2% to 48.8% by mass, respectively, with the remainder being oxides of the rare earth elements. The silicon nitride is composed of the formula Si. 6-Z Al Z O Z N 8-Z β-Syrone characterized by (z = 0.1 to 1) has an average crystal grain size of less than 20 μm (excluding 0 μm).

[0033] The term "major component" in ceramics refers to a component that constitutes 60% or more of the total 100% mass of the components constituting the ceramic. Specifically, the major component can be 95% or more of the total 100% mass of the components constituting the ceramic. The composition of ceramics can be determined using X-ray diffraction (XRD). Regarding the content of each component, after identification, the elemental content of the constituent components is determined using X-ray fluorescence (XRF) or intracellular optical emission spectrophotometry (ICP), and then converted into the identified components.

[0034] The relative density of ceramics is, for example, above 92% and below 99.9%. Relative density is characterized as the percentage (proportion) of the apparent density of ceramics relative to the theoretical density of ceramics, as determined in accordance with JIS R1634-1998.

[0035] The ceramic has closed pores, and the value of the average distance between the centroids of adjacent closed pores minus the average equivalent circle diameter of the closed pores (hereinafter referred to as the spacing between closed pores) can be greater than 8 μm and less than 18 μm. The closed pores are independent of each other.

[0036] When the spacing between the closed pores is 8 μm or more, the mechanical strength is higher because the closed pores exist in a relatively dispersed state. On the other hand, when the spacing between the closed pores is 18 μm or less, even if repeated thermal shocks are applied, the probability of microcracks originating from the contours of the closed pores protruding due to the surrounding closed pores is higher. Accordingly, if the spacing between the closed pores is 8 μm or more and 18 μm or less, the inner tube 2 containing this ceramic can be used for a long time.

[0037] The skewness of the equivalent circle diameter of a closed vent can be greater than the skewness of the distance between the centroids of the closed vent. Here, skewness is an indicator (statistic) representing how much a distribution deviates from a normal distribution, that is, an indicator of the left-right symmetry of the distribution. When the skewness is greater than 0, the tail of the distribution tends to the right; when the skewness is 0, the distribution is left-right symmetrical; and when the skewness is less than 0, the tail of the distribution tends to the left.

[0038] If the histograms of the equivalent circle diameter of the vent and the distance between the centroids of the vents are superimposed, then when the skewness of the equivalent circle diameter of the vent is greater than the skewness of the distance between the centroids of the vents, the mode of the equivalent circle diameter is located to the left (zero side) than the mode of the distance between the centroids. That is, there are more vents with smaller equivalent circle diameters, and these vents are more sparsely distributed, which can produce an inner tube 2 that combines mechanical strength and resistance to thermal shock.

[0039] For example, the deviation of the equivalent circle diameter of the closed air hole is 1 or more, and the deviation of the distance between the centroids of the closed air hole is 0.6 or less. The difference between the deviation of the equivalent circle diameter of the closed air hole and the deviation of the distance between the centroids of the closed air hole is 0.4 or more.

[0040] To determine the distance between the centroids of the closed pores and the equivalent circle diameter, firstly, one end face of the ceramic component is axially oriented using the average grain size D. 50 3μm diamond abrasive grains were ground using a copper disc. Then, by using an average grain size D... 50 0.5μm diamond abrasive grains were ground with a tin disc to obtain a ground surface with an arithmetic mean roughness Ra of less than 0.2μm in the roughness curve.

[0041] The arithmetic mean roughness Ra of the polished surface is the same as the above-mentioned measurement method.

[0042] The polished surface is observed at a magnification of 200 times, an average range is selected, and for example, an area of 7.2×10 4 μm 2 (with a horizontal length of 310 μm and a vertical length of 233 μm) is photographed with a CCD camera to obtain an observation image.

[0043] Taking this observation image as an object, for example, using image analysis software "A Image-kun (ver2.52)" (registered trademark, manufactured by Asahi Kasei Engineering Co., Ltd.), the distance between the centroids of closed pores is obtained by a method such as the distance between centroids method for measuring dispersion. Hereinafter, when the image analysis software is described as "A Image-kun", it means the image analysis software manufactured by Asahi Kasei Engineering Co., Ltd.

[0044] As the setting conditions for this method, for example, the threshold value, which is an index indicating the brightness and darkness of the image, is set to 165, the brightness is set to dark, the area for removing small figures is set to 1 μm 2 , and the noise removal filter can be set to none. In addition, the threshold value can be adjusted according to the brightness of the observation image. The brightness is set to dark, and by means of the binary method, on the basis of setting the area for removing small figures to 1 μm 2 and setting the noise removal filter to be present, the threshold value is adjusted so that the marks presented in the observation image are consistent with the shape of the closed pores. Regarding the equivalent circle diameter of the closed pores, taking the above-mentioned observation image as an object, the equivalent circle diameter of the open pores can be obtained by a method such as particle analysis. The setting conditions can be the same as those used for obtaining the distance between the centroids of the closed pores. The skewness of the equivalent circle diameter and the distance between the centroids of the closed pores can be obtained using the function Skew provided in Excel (registered trademark, Microsoft Corporation).

[0045] An example of the manufacturing method of the inner tube formed of such ceramics will be described. The case where the main component of the ceramics forming the inner tube is alumina will be described.

[0046] Powders of alumina (purity 99.9 mass% or more) as the main component, magnesium hydroxide, silicon oxide, and calcium carbonate are put into a grinding mill for pulverization together with a solvent (ion-exchanged water), and after pulverizing until the average particle diameter (D 5o ) becomes 1.5 μm or less, an organic binder and a dispersant for dispersing the alumina powder in Japanese style are added and mixed to obtain a slurry.

[0047] In this composition, the total 100% by mass of the aforementioned powders contains 0.3–0.42% by mass of magnesium hydroxide powder, 0.5–0.8% by mass of silicon dioxide powder, and 0.06–0.1% by mass of calcium carbonate powder. The remainder consists of alumina powder and unavoidable impurities. Organic binders include, for example, acrylic emulsions, polyvinyl alcohol, polyethylene glycol, and polyethylene oxide.

[0048] Next, after spray granulation of the slurry to obtain granules, a single-axis pressing forming device or a cold-air hydrostatic pressing forming device is used to apply pressure at a setting of 78 MPa or higher but less than 118 MPa, thereby obtaining a columnar shaped body. The shaped body is then machined as needed to create recesses that become concave sections after firing.

[0049] A ceramic-containing inner tube is obtained by firing a molded body at a firing temperature of 1580°C or higher and 1780°C or lower, and holding it for 2 hours or higher and 4 hours or lower. To obtain a ceramic with a pore spacing of 8 μm or higher and 18 μm, the molded body is fired at a firing temperature of 1600°C or higher and 1760°C or lower, and holding it for 2 hours or higher and 4 hours or lower. A ground surface can be created by grinding the surface of the ceramic component opposite the tube. Additionally, the bottom surface can be created by grinding the surface of the recessed portion where the electrode is located. Furthermore, the inner tube 2 can have an inner diameter of 50 mm or higher.

[0050] The annular portion 5 may, for example, comprise a Kovar alloy, Fe-Ni alloy, Fe-Ni-Cr-Ti-Al alloy, Fe-Cr-Al alloy, Fe-Co-Cr alloy, Fe-Co alloy, Fe-Co-C alloy, or austenitic stainless steel with a nickel content of 10.4% by mass or more. The outer diameter of the annular portion 5, while achieving sufficient thermal insulation performance, is 1 mm or more relative to the outer diameter of the inner tube 2, preferably 10 mm or more, and may be 200 mm or less, preferably 100 mm or less. The annular portion 5 is hermetically bonded to the outer circumferential surface of the metallized inner tube 2 by brazing.

[0051] The outer tube 6 may contain metals such as austenitic stainless steel (e.g., SUS316L) with a nickel content of 10.4% or more, silicon nitride, silane, or other ceramics.

[0052] The first airtight terminal 8 constitutes a so-called sealed connector, comprising: a guide pin 9; a circular first ceramic substrate 17 having a first pin hole (not shown) in the thickness direction for inserting the guide pin 9; and a first annular body 18 surrounding the outer peripheral surface of the first ceramic substrate 17. The first annular body 18 functions as a sleeve for holding the first ceramic substrate 17, and may, for example, contain Kovar alloys, Fe-Ni alloys, Fe-Ni-Cr-Ti-Al alloys, Fe-Cr-Al alloys, Fe-Co-Cr alloys, Fe-Co alloys, Fe-Co-C alloys, or austenitic stainless steel with a nickel content of 10.4% by mass or more. Therefore, since embrittlement caused by liquid hydrogen is difficult to occur, the accuracy of bubble rate measurement can be maintained for a long period.

[0053] Austenitic stainless steels with a nickel content of 10.4% by mass or more, such as SUS310S, SUS316L, SUS316LN, SUS316J1L, SUS317L, etc.

[0054] Electrode 4 may include, for example, copper foil, aluminum foil, etc. To form electrode 4 on the outer peripheral surface of inner tube 2, methods such as vacuum evaporation, metallization, or active metal deposition can be used. Furthermore, a metal plate that forms electrode 29 can be bonded to the bottom surface of recess 28 (described later). The thickness of electrodes 41 and 42 can both be 10 μm or more, preferably 20 μm or more, and less than 1 mm, preferably less than 2 mm.

[0055] Metal tubes 20 with flanges 19 are disposed at both ends of the inner tube 2, and the annular portion 5 and the flanges 19 are welded or brazed together. In this way, by connecting the metal tubes 20 to the inner tube 2, it becomes less susceptible to damage from external impacts, and by welding or brazing the annular portion 5 and the flanges 19, leakage of liquid hydrogen from the inner tube 2 to the outside is suppressed, thus further improving the accuracy of bubble rate measurement. Additionally, the metal tubes 20 can be liquid hydrogen transfer tubes for transferring liquid hydrogen.

[0056] Next, based on Figure 2 Figure 3 illustrates other embodiments of this disclosure. The bubble rate sensor 11 of this embodiment has a structure in which a housing 22 surrounds an inner tube 21, and an outer tube 26 covers the outer side of the housing 22. The housing 22 has a second through-hole 23 that opens radially on its outer peripheral surface, and further, a connecting hole 24 that opens axially along the inner tube 21 and communicates with a through-hole 31 of the inner tube 21. Metal tubes 25, communicating with the through-hole 31 of the inner tube 21 via the connecting hole 24, are disposed at both ends of the housing 22.

[0057] The inner tube 21 has a recess 28 that opens to the outside, and an electrode 29 is mounted on the bottom surface of the recess 28. Furthermore, as... Figure 3A , 3BAs shown, the inner tube 21 contains an even number (four in this embodiment) of divisible ceramic components 21a, 21b, 21c, and 21d arranged circumferentially.

[0058] To assemble the inner tube 21 from these ceramic components 21a, ... 21d, so that their sides overlap, annular binding bodies 30 are provided on the outer peripheral surface to bind the ceramic components 21a, ... 21d together to form the inner tube 21. In this state, a housing 22 is installed on the outer peripheral side of the inner tube 21. In other words, the housing 22 is provided to accommodate the separable inner tube 21.

[0059] That is, the housing 22 includes: a frame portion 22a for housing the inner tube 21; and a cover portion 22b for sealing the opening of the frame portion 22a. After the bundled ceramic components 21a, ... 21d are housed in the frame portion 22a, the frame portion 22a and the cover portion 22b are joined together by welding or brazing. The frame portion 22a and the cover portion 22b each have an opening communicating with the through hole of the inner tube 21. The metal tube 25 is welded or brazed to the frame portion 22a and the cover portion 22b respectively, so that it communicates with the through hole through each opening.

[0060] like Figure 3A , 3B As shown, the cross-section of the inner tube 21 is approximately quadrilateral, and its corners 211 are chamfered (C-face or R-face). Therefore, the annular binding body 30, by pressing the chamfered corners 211 together, can securely bind each ceramic component 21a, ... 21d. Examples of binding bodies 30 include flexible plastic films in the form of strips or metal strips. The binding body 30 then joins its two ends by means of heat fusion, welding, or other joining methods.

[0061] In addition, the ceramic components 21a, ... 21d constituting the inner tube 21, like the inner tube 2, may contain ceramics with low thermal expansion ceramics or alumina, silicon nitride or silane as the main components.

[0062] At least one of the ceramic components 21a, ... 21d has closed pores, with the spacing between the closed pores being more than 8 μm and less than 18 μm.

[0063] Back Figure 2 An annular portion 51 is provided on the axially outer side of the housing 22. The annular portion 51 has a shaft hole on the same axis as the inner tube 21, and is welded or brazed to the outer peripheral surface of a metal tube 25 inserted through the shaft hole. An outer tube 26 is joined to the outer peripheral portion of the annular portion 51. The outer tube 26 has a first through hole 27 that opens radially on its outer peripheral surface.

[0064] A first hermetic terminal 81 for fixing the conductive pin 91 is provided in the first insertion hole 27 and is individually connected to each electrode 29. The first hermetic terminal 81, like the first hermetic terminal 8, includes: a conductive pin 91; a circular plate-shaped first ceramic substrate 50 having a first pin hole (not shown) in the thickness direction for inserting the conductive pin 91; and a first annular body 52 surrounding the outer peripheral surface of the first ceramic substrate 50.

[0065] Furthermore, a second airtight terminal 82 for fixing the guide pin 91 is also provided in the second insertion hole 23 on the outer peripheral surface of the housing 22. The second airtight terminal 82 includes: a guide pin 91; a circular plate-shaped second ceramic substrate 50′ having a second pin hole (not shown) for inserting the guide pin 91 in the thickness direction; and a second annular body 52′ surrounding the outer peripheral surface of the second ceramic substrate 50′.

[0066] A vacuum exhaust valve 15 (e.g., a needle valve for vacuum exhaust) is provided in the outer tube 26, forming a vacuum space 100 (insulation layer) between the shell 22 and the outer tube 26. At this time, the space between the inner tube 21 and the shell 22 can also be a vacuum space. Thus, because a vacuum space 100 is provided between the shell 22 and the outer tube 26, the vaporization of liquid hydrogen caused by external air temperature is suppressed, improving the insulation performance of the inner tube 21, suppressing bubble formation, and improving the accuracy of bubble rate measurement. Other factors related to… Figure 1 The implementation method shown is the same, so detailed descriptions are omitted.

[0067] Next, Figure 2 as well as Figure 3A , 3B Variations of the embodiments shown in Figures 4-6 As shown in the image. Additionally, regarding... Figure 2 as well as Figure 3A , 3B The components of the bubble rate sensor 11 shown are labeled with the same symbols and their descriptions are omitted.

[0068] like Figure 4 As shown, in this modified example, the bubble rate sensor 111 is directly joined to the metal tube 25' in the inner tube 21'. Furthermore, the frame portion 22a' and the cover portion 22b' constituting the housing 22' are integrally formed with or joined to the metal tube 25'. The outer tube 26' is joined to the outer peripheral surface of the housing 22'. The joining can be performed, for example, by welding or brazing.

[0069] A vacuum exhaust valve 15 is provided in the outer tube 26′, forming a vacuum space 100′ (insulation layer) between the inner tube 21′ and the outer tube 26′.

[0070] like Figure 5 as well as Figure 6As shown, the inner tube 21′ is composed of four ceramic components 21a′, 21b′, 21c′, and 21d′, which are integrally joined by a binding body 30′. Details are as follows... Figure 3A , 3B As shown.

[0071] Furthermore, in this disclosure, the inner tube is not limited to having a roughly square cross-section; it can also have a circular or other polygonal cross-section. In this case, the number of ceramic components constituting the inner tube is an even number, such as 2, 4, 6, or 8. This is because, in order to measure electrostatic capacitance, at least a pair of opposing electrodes are required, with each electrode mounted on a separate ceramic component.

[0072] Furthermore, since electrostatic capacitance is measured between opposing electrodes, even if electrodes are not provided on all even-numbered ceramic components, electrodes can be provided only on at least one pair of opposing ceramic components.

[0073] Next, the flow meter according to the embodiments of this disclosure will be described. This flow meter measures the flow rate of liquid hydrogen flowing through inner tubes 2, 21, 21', and includes: the aforementioned bubble rate sensors 1, 11, 111; and a flow velocity meter (not shown) for measuring the flow velocity of cryogenic liquid flowing through through-holes 3, 31. The bubble rate sensors 1, 11, 111 and the flow velocity meter are mounted in a liquid hydrogen transfer tube (not shown) (hereinafter sometimes simply referred to as the transfer tube).

[0074] Since the liquid hydrogen flowing through the through holes 3 and 31 becomes a two-phase flow of gas and liquid mixture, the density d (kg / m³) of the liquid hydrogen can be calculated by measuring the electrostatic capacitance of the liquid hydrogen using bubble rate sensors 1, 11, and 111. 3 ).

[0075] Then, the flow rate of liquid hydrogen (m / s) obtained from the flow meter is set as v, and the cross-sectional area (m²) of the through holes 3 and 31' is set as v. 2 When is set as a, the flow rate F (kg / s) is obtained by the following formula.

[0076] F=d×v×a

[0077] The flow meter also includes a calculation device that connects to bubble rate sensors 1, 11, and 111, as well as a flow velocity meter, to perform the aforementioned calculations. Therefore, since the flow rate of liquid hydrogen can be easily measured, management becomes easier in industrial applications involving large-scale transfers of liquid hydrogen.

[0078] The above description describes bubble rate sensors 1, 11, and 111 for liquid hydrogen and flow meters using them, but the same applies to other cryogenic liquids such 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, the term "cryogenic liquid" in this disclosure refers to a liquid that liquefies at temperatures below -162°C.

[0079] The above describes the embodiments of this disclosure, but the bubble rate sensor of this disclosure is not limited to the above embodiments and can be modified and improved in various ways within the scope of this disclosure.

[0080] Symbol Explanation

[0081] 1, 11, 111 Bubble Rate Sensor

[0082] 2, 21, 21′ Inner tube

[0083] Ceramic components 21a, 21b, 21c, 21d

[0084] Ceramic components 21a′, 21b′, 21c′, 21d′

[0085] 211 corner

[0086] 3.31 Through Hole

[0087] 4.29 electrodes

[0088] 5. Circular portion

[0089] 6. Outer tube

[0090] 7. First through hole

[0091] 8.81 First airtight terminal

[0092] 82 Second airtight terminal

[0093] 9, 91 guide pin

[0094] 10, 100, 100′ Vacuum space

[0095] 15 Vacuum exhaust valve

[0096] 17, 50 First ceramic substrate

[0097] 18, 52 First ring body

[0098] 19. Flange portion

[0099] 20, 25, 25′ metal pipes

[0100] 22, 22′ Shell

[0101] Frame section 22a, 22a′

[0102] 22b, 22b′ Cover

[0103] 23 Second through hole

[0104] 24 Connecting holes

[0105] 26, 26′ outer tube

[0106] 27 First through hole

[0107] 28 recess

[0108] 29 electrodes

[0109] 30 bundles

[0110] 50′ Second ceramic substrate

[0111] 51. Circular portion

[0112] 52′ Second ring.

Claims

1. A bubble rate sensor, comprising: An insulating inner tube with a through-hole for the flow of extremely low temperature liquids; At least one pair of electrodes is mounted on the outer surface of the inner tube; A heat insulation layer covers the outer periphery of the inner tube; An annular portion is provided at both ends of the inner tube; The outer tube engages with the outer periphery of the annular portion; and A metal tube having a flange at at least one end of the inner tube. The annular portion and the flange portion are welded or brazed together.

2. The bubble rate sensor according to claim 1, wherein, The outer tube has a first insertion hole. The bubble rate sensor includes: The first airtight terminal is located inside the first insertion hole, and a conductive pin that is separately connected to the electrode is fixed inside the first insertion hole.

3. The bubble rate sensor according to claim 2, wherein, The insulation layer is a vacuum space located between the inner tube and the outer tube.

4. The bubble rate sensor according to claim 2 or 3, wherein, The first airtight terminal includes: The guide pin; A circular ceramic substrate has a first pin hole in its thickness direction for inserting the guide pin; and A ring-shaped body surrounds the outer peripheral surface of the ceramic substrate. The annular structure comprises Kovar alloys, Fe-Ni alloys, Fe-Ni-Cr-Ti-Al alloys, Fe-Cr-Al alloys, Fe-Co-Cr alloys, Fe-Co alloys, Fe-Co-C alloys, or austenitic stainless steels with a nickel content of 10.4% by mass or more.

5. The bubble rate sensor according to claim 3, wherein, The inner tube comprises an even number of divisible ceramic components arranged circumferentially. The bubble rate sensor includes: The housing, surrounding the inner tube, has a second through hole and a connecting hole communicating with the through hole of the inner tube; The annular portion, located on the outside of the housing, has a shaft hole on the same axis as the inner tube; The outer tube, which is joined to the outer periphery of the annular portion, has a first through hole; The first airtight terminal has a conductive pin, which is separately connected to the electrode, fixed in the first insertion hole; and The second airtight terminal secures the guide pin within the second insertion hole. The vacuum space is located at least between the outer tube and the shell.

6. The bubble rate sensor according to claim 5, wherein, Both the first airtight terminal and the second airtight terminal have: The guide pin; A circular ceramic substrate has a pin hole in its thickness direction for inserting the guide pin; and A ring-shaped body surrounds the outer peripheral surface of the ceramic substrate. The annular structure comprises Kovar alloys, Fe-Ni alloys, Fe-Ni-Cr-Ti-Al alloys, Fe-Cr-Al alloys, Fe-Co-Cr alloys, Fe-Co alloys, Fe-Co-C alloys, or austenitic stainless steels with a nickel content of 10.4% by mass or more.

7. The bubble rate sensor according to any one of claims 5 to 6, wherein, The inner tube has a recess that opens to the outside, and the electrode is mounted on the bottom surface of the recess.

8. The bubble rate sensor according to any one of claims 5 to 6, wherein, The electrodes are respectively disposed on at least one pair of ceramic components that are opposite each other among an even number of the ceramic components.

9. The bubble rate sensor according to any one of claims 5 to 6, wherein, An annular binding body for binding the ceramic component is provided on the outer periphery of the inner tube.

10. The bubble rate sensor according to any one of claims 5 to 6, wherein, At least one of the end face and the outer side of the inner tube abuts against the inner surface of the shell.

11. The bubble rate sensor according to any one of claims 5 to 6, wherein, The housing includes: The frame section houses the inner tube; and The cover seals the opening of the frame. The frame and the cover each have an opening that communicates with the through hole of the inner tube. The metal tube is welded or brazed to the frame and the cover so that it communicates with the through hole through each opening.

12. The bubble rate sensor according to claim 11, wherein, The annular portion is welded or brazed to the metal tube.

13. The bubble rate sensor according to any one of claims 1 to 3, wherein, The inner tube contains low thermal expansion ceramic.

14. A flow meter for measuring the flow rate of a cryogenic liquid flowing through a through-hole in the inner tube, the flow meter comprising: The bubble rate sensor according to any one of claims 1 to 13; and A flow meter is used to measure the flow rate of the cryogenic liquid through the through-hole.

15. A cryogenic liquid transfer tube, comprising: The flow meter according to claim 14.

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