Measurement system

Abstract

This disclosure provides a measurement system that can be applied to metal piping and is capable of measuring the void ratio with high precision. [Solution] A measuring system comprising: a pipe made of metal through which a two-phase fluid to be measured flows; a first electrode made of metal attached to the pipe so as to be in contact with the fluid to be measured; a second electrode made of metal attached to the pipe opposite the first electrode so as to be in contact with the fluid to be measured; a measuring unit for measuring the capacitance between the first electrode and the second electrode; and a calculation unit for calculating the gas-liquid ratio of the fluid to be measured based on the capacitance measured by the measuring unit, wherein the first electrode is larger than the second electrode.

Description

Technical Field

[0001] The present disclosure relates to a measurement system.

Background Art

[0002] Patent Document 1 discloses an apparatus for measuring the mass flow rate of two-phase flows such as gas-liquid, solid-liquid, and solid-gas flowing in a pipe using a capacitance detector and a cross-correlation method. Patent Document 1 discloses that a narrow-width electrode plate for flow velocity detection and a wide-width electrode plate for concentration detection arranged so as to surround the narrow-width electrode plate are arranged on one side of the pipe wall, and a wide-width common electrode plate is arranged at a position facing the narrow-width electrode plate.

[0003] Patent Document 2 discloses a two-phase flow measurement method in which the inner diameter of a pipe through which a fluid flows is changed midway, the void fraction and pressure before and after the pipe inner diameter change portion are measured, and the outlet-side liquid-phase flow velocity and the outlet-side gas-phase flow velocity are obtained based on the liquid-phase density, gas-phase density, inlet-side pipe cross-sectional area, and outlet-side pipe cross-sectional area. Patent Document 2 discloses that since the void meter for measuring the void fraction is a capacitance type, the material of the pipe needs to be non-metallic.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] For example, cryogenic fluids such as liquid hydrogen are used as propellants and fuels for aerospace transport vehicles. Furthermore, demand for liquid hydrogen is increasing in the hydrogen supply chain. Cryogenic fluids have very low boiling points and boil easily. Because cryogenic fluids boil easily, they tend to form a complex gas-liquid two-phase flow state where gas and liquid coexist. Therefore, understanding the flow characteristics of gas-liquid two-phase flow is crucial for fluid control in cryogenic fluids.

[0006] Metal piping is used for transporting ultra-low temperature fluids. Conventionally, voidometers have been incompatible with metal piping, making it difficult to measure the void fraction in ultra-low temperature fluids. Furthermore, voidometers often have poor linearity in their response, limiting their measurement range.

[0007] This disclosure provides a measurement system applicable to metal piping that can measure the void ratio with high precision. [Means for solving the problem]

[0008] According to one aspect of the present disclosure, a measurement system is provided comprising: a pipe made of metal through which a two-phase fluid to be measured flows; a first electrode made of metal attached to the pipe so as to be in contact with the fluid to be measured; a second electrode made of metal attached to the pipe so as to be in contact with the fluid to be measured, opposite to the first electrode; a measuring unit for measuring the capacitance between the first electrode and the second electrode; and a calculation unit for calculating the gas-liquid ratio of the fluid to be measured based on the capacitance measured by the measuring unit, wherein the first electrode is larger than the second electrode. [Effects of the Invention]

[0009] The measurement system disclosed herein is applicable to metal piping and can measure the void ratio with high accuracy. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a diagram illustrating the schematic configuration of the measurement system according to the first embodiment. [Figure 2] Figure 2 is a perspective view of the detection unit included in the measurement system according to the first embodiment. [Figure 3] Figure 3 is an exploded perspective view of the detection unit of the measurement system according to the first embodiment. [Figure 4] Figure 4 is a cross-sectional view of the detection unit included in the measurement system according to the first embodiment. [Figure 5] Figure 5 shows the capacitance measurement results using the measurement system according to the first embodiment. [Figure 6] Figure 6 shows the relationship between the low-potential electrode angle and the error in the measurement system according to the first embodiment. [Figure 7] Figure 7 is a perspective view of the detection unit included in the measurement system according to the second embodiment. [Figure 8] Figure 8 is a side view of the detection unit included in the measurement system according to the second embodiment. [Modes for carrying out the invention]

[0011] The embodiments of this disclosure will be described below with reference to the attached drawings. Note that, in the description and drawings of each embodiment, components having substantially the same or corresponding functional configurations may be denoted by the same reference numerals, thereby omitting redundant explanations. Furthermore, for ease of understanding, the scale of each part in the drawings may differ from that of actual parts.

[0012] A degree of deviation is permissible in directions such as parallel, right angles, orthogonal, horizontal, vertical, up and down, left and right, and front and back, as long as it does not impair the effects of the embodiment. The shape of the corners is not limited to right angles and may be rounded. Parallel, right angles, orthogonal, horizontal, and vertical may include approximately parallel, approximately right angles, approximately orthogonal, approximately horizontal, and approximately vertical, respectively.

[0013] For example, “substantially parallel” means that even if two lines or two planes are not completely parallel to each other, they can be treated as parallel to each other within an acceptable range in manufacturing. Similarly, for each of “substantially right angle”, “substantially orthogonal”, “substantially horizontal” and “substantially vertical”, it is intended that they are applicable respectively as long as the relative positional relationship between two lines or planes is within an acceptable range in manufacturing.

[0014] <First Embodiment> A measurement system according to the first embodiment will be described. The measurement system according to the first embodiment includes a pipe, a first electrode, a second electrode, a measurement unit that measures the capacitance between the first electrode and the second electrode, and a calculation unit that calculates the gas-liquid ratio of the measurement target based on the capacitance measured by the measurement unit. The pipe in the measurement system according to the first embodiment is formed of metal, and a two-phase fluid as the measurement target flows through it. The first electrode in the measurement system according to the first embodiment is attached to the pipe so as to contact the measurement target, and is formed of metal. The second electrode in the measurement system according to the first embodiment is attached to the pipe so as to face the first electrode and contact the measurement target, and is formed of metal. The first electrode in the measurement system according to the first embodiment is larger than the second electrode.

[0015] Also, in the measurement system according to the first embodiment, each of the first electrode and the second electrode is used by being embedded in the pipe.

[0016] The measurement system according to the first embodiment will be described in detail with reference to the drawings. FIG. 1 is a diagram for explaining the schematic configuration of a measurement system 1 which is an example of the measurement system according to the first embodiment.

[0017] The measurement system 1 includes a conversion unit 10 and a detection unit 20.

[0018] The detection unit 20 includes an electrode unit 21. The electrode unit 21 includes a high-potential electrode 21a and a low-potential electrode 21b. A two-phase fluid TPF as the measurement target flows between the high-potential electrode 21a and the low-potential electrode 21b.

[0019] The conversion unit 10 includes a measurement unit 11 that measures the capacitance C of the two-phase fluid TPF flowing between the high-potential electrode 21a and the low-potential electrode 21b, and a calculation unit 12 that calculates the gas-liquid ratio (void fraction) of the object to be measured based on the capacitance C measured by the measurement unit 11.

[0020] The detection unit in the measurement system according to the first embodiment will be described in more detail. Figure 2 is a perspective view of the detection unit 20 included in measurement system 1, which is an example of the measurement system according to the first embodiment. Figure 3 is an exploded perspective view of the detection unit 20 included in measurement system 1, which is an example of the measurement system according to the first embodiment.

[0021] The detection unit 20 has an internal structure 20p through which the two-phase fluid TPF to be measured flows. The detection unit 20 comprises an electrode section 21 and a pipe 22. The detection unit 20 is used to measure the capacitance of the two-phase fluid TPF flowing between the electrode sections 21.

[0022] The electrode unit 21 includes a high-potential electrode 21a and a low-potential electrode 21b. The measuring unit 11 generates a predetermined potential difference between the high-potential electrode 21a and the low-potential electrode 21b. The measuring unit 11 applies a higher voltage to the high-potential electrode 21a than to the low-potential electrode 21b.

[0023] The high-potential electrode 21a has a curved shape. The high-potential electrode 21a is made of metal. The high-potential electrode 21a is attached to the pipe 22 so as to be in contact with the two-phase fluid TPF to be measured. The high-potential electrode 21a is used embedded in the pipe 22.

[0024] The low-potential electrode 21b has a curved shape. The low-potential electrode 21b is made of metal. The low-potential electrode 21b is mounted in the piping 22 opposite the high-potential electrode 21a, in contact with the two-phase fluid TPF to be measured. The low-potential electrode 21b is used embedded in the piping 22.

[0025] The piping 22 is made of metal. The piping 22 has openings 22u and 22d through which the two-phase fluid TPF flows in and out. The piping 22 also has a mounting hole 22s into which a high-potential electrode 21a is attached, and a mounting hole 22t into which a low-potential electrode 21b is attached.

[0026] The high-potential electrode 21a, the low-potential electrode 21b, and the piping 22 may be made of the same type of metal. For example, the high-potential electrode 21a, the low-potential electrode 21b, and the piping 22 may each be made of stainless steel.

[0027] The high-potential electrode 21a is embedded and installed in the mounting hole 22s of the pipe 22. The low-potential electrode 21b is embedded and installed in the mounting hole 22t of the pipe 22. Both the high-potential electrode 21a and the low-potential electrode 21b are installed so as to be electrically insulated from the pipe 22. For example, both the high-potential electrode 21a and the low-potential electrode 21b are installed in the pipe 22 with an insulating material in between. Alternatively, for example, an insulating film may be formed on the portion of both the high-potential electrode 21a and the low-potential electrode 21b that is installed in the pipe 22 before installation in the pipe 22.

[0028] The high-potential electrode 21a is larger than the low-potential electrode 21b. First, the sizes of the high-potential electrode 21a and the low-potential electrode 21b in the circumferential direction in the pipe 22 will be described. Figure 4 is a cross-sectional view of the detection unit 20 of the measurement system 1, which is an example of a measurement system according to the first embodiment. Specifically, Figure 4 is a cross-sectional view showing a section of the detection unit 20 that includes the high-potential electrode 21a and the low-potential electrode 21b, perpendicular to the longitudinal direction of the pipe 22.

[0029] The high-potential electrode 21a is formed in the circumferential direction within an angle θa with respect to the central axis of the pipe 22. The angle θa is, for example, 180 degrees. In other words, the arc size of the high-potential electrode 21a is, for example, half the circumference on the inner surface of the pipe 22. Note that when we say that the angle θa is 180 degrees, it is not limited to the case where the angle θa is exactly 180 degrees. For example, it also includes cases where the angle θa is 180 degrees within the normal manufacturing tolerance range. The same applies to the arc size of the high-potential electrode 21a. The same also applies to the following explanation. The angle θa is made larger than the angle θb, which will be described later. For example, the angle θa should be an angle that falls within the range of 160 degrees to 200 degrees.

[0030] The low-potential electrode 21b is formed in the circumferential direction within an angle θb with respect to the central axis of the pipe 22. The angle θb is, for example, 150 degrees. In other words, the arc size of the low-potential electrode 21b is, for example, 5 / 12 of the circumference on the inner surface of the pipe 22. For example, the angle θb may be an angle that falls within the range of 140 degrees to 155 degrees.

[0031] Next, the sizes of the high-potential electrode 21a and the low-potential electrode 21b in the longitudinal direction of the pipe 22 will be described. The longitudinal length La of the high-potential electrode 21a is at least three times the pipe diameter D of the pipe 22. The longitudinal length Lb of the low-potential electrode 21b is greater than or equal to the pipe diameter D of the pipe 22, and less than or equal to one-third of the longitudinal length La of the high-potential electrode 21a. Length La is longer than length Lb.

[0032] As described above, the high-potential electrode 21a is larger than the low-potential electrode 21b in both the circumferential and longitudinal directions of the pipe 22. In the measurement system according to this embodiment, the high-potential electrode only needs to be larger in at least one of the circumferential and longitudinal directions of the pipe.

[0033] The measurement unit 11 is connected to the high-potential electrode 21a and the low-potential electrode 21b in the electrode unit 21. The measurement unit 11 measures the capacitance C in the two-phase fluid TPF between the high-potential electrode 21a and the low-potential electrode 21b. The measurement unit 11 outputs the measured capacitance C to the calculation unit 12.

[0034] The calculation unit 12 calculates the void fraction (gas-liquid ratio). The void fraction is the area ratio of gas to the cross-sectional area of ​​the pipe. The calculation unit 12 calculates the void fraction using the capacitance in the pipe 22, which is measured by two electrodes, a high-potential electrode 21a and a low-potential electrode 21b, in the measurement unit 11. The dielectric constant differs between gases and liquids. Generally, the dielectric constant of a liquid is greater than that of a gas. Therefore, as the void fraction changes from 100% to 0%, the capacitance shows an increasing response.

[0035] In the calculation unit 12, in order to convert the capacitance measured by the measurement unit 11 into void fraction, it is necessary to create a calibration curve from values ​​calculated by actual measurement or simulation. An example of the void fraction calculation formula in the calculation unit 12 is shown below.

[0036] For example, the void coefficient can be determined using Equation 1, based on the void coefficient and capacitance at two measurement points, measurement point 1 and measurement point 2.

[0037]

number

[0038] However, CM is the capacitance measured at the measurement unit 11. α is the void fraction to be calculated (unit: %), CL is the capacitance of the liquid phase (capacitance when the void fraction is 0%), α1 is the void fraction at measurement point 1, α2 is the void fraction at measurement point 2, c1 is the capacitance at measurement point 1, and c2 is the capacitance at measurement point 2.

[0039] Furthermore, for example, the void fraction can be determined based on Equation 2 using the capacitance when the pipe is filled with only gas or only liquid.

[0040]

number

[0041] However, CG is the capacitance of the gas phase (capacitance when the void fraction is 100%).

[0042] The above example is just one example; for instance, a conversion formula that converts capacitance to void fraction using two or more measurement data points may also be used.

[0043] To calculate the void fraction from capacitance, a linear proportional relationship where capacitance uniquely determines the void fraction is desirable. However, depending on the electrode structure, the response may not be uniquely determined. This non-unique response is thought to be due to factors such as the size of the electrodes and the electric field distribution. For example, the electric field passing through the pipe may be distorted, resulting in an uneven electric field distribution.

[0044] Furthermore, there is a growing need for liquid hydrogen flow measurement in the hydrogen supply chain. Because liquid hydrogen is easily vaporized by heat input, measurement is required at cryogenic temperatures and in a gas-liquid mixed-phase state. Therefore, it is necessary to establish measurement technology for multiphase flow in cryogenic environments. To achieve durability against strong loads such as fluid pressure and vehicle vibration, and compatibility with the cryogenic fluid used as fuel, void fraction sensors with metal piping and electrodes are required. Since the metal piping acts as a shield, the electrodes need to be embedded inside the piping.

[0045] Therefore, the inventors invented a measurement system consisting of metal piping and electrodes by fitting electrodes into the piping. The detection unit of the measurement system according to the first embodiment has mounting holes formed in the piping and has a fitting structure into which two types of electrodes are fitted. With the detection unit of the measurement system according to the first embodiment, two electrodes are fitted into the piping, and by connecting the two electrodes to the measurement unit, the capacitance inside the piping can be measured.

[0046] Using measurement system 1, which is an example of a measurement system according to the first embodiment, the detection unit 20 of measurement system 1 has mounting holes 22s and 22t formed in the pipe 22. A high-potential electrode 21a is attached to mounting hole 22s. A low-potential electrode 21b is attached to mounting hole 22t. The detection unit 20 has a fitting structure in which the two electrodes, the high-potential electrode 21a and the low-potential electrode 21b, are fitted into the pipe 22. The high-potential electrode 21a and the low-potential electrode 21b are each connected to the measurement unit 11, so that the capacitance of the two-phase fluid TPF can be measured and the void fraction can be calculated.

[0047] Furthermore, the inventors have found that in a void fraction sensor in which electrodes are embedded in a metal pipe, the relationship between capacitance and void fraction becomes closer to a proportional relationship by having asymmetric electrodes. In the detection unit of the measurement system according to the first embodiment, the two electrodes are of different sizes. According to the detection unit of the measurement system according to the first embodiment, by making the high-potential electrode larger and the low-potential electrode smaller, the response of capacitance to void fraction can be linearized, thereby improving measurement accuracy.

[0048] Using measurement system 1, which is an example of a measurement system according to the first embodiment, the high-potential electrode 21a is larger than the low-potential electrode 21b, and the electrode portion 21 is composed of an asymmetric electrode. By making the high-potential electrode 21a larger than the low-potential electrode 21b, the electric field between the high-potential electrode 21a and the low-potential electrode 21b in the two-phase fluid TPF can be made approximately perpendicular to the flow of the two-phase fluid TPF. By making the electric field between the high-potential electrode 21a and the low-potential electrode 21b approximately perpendicular to the flow of the two-phase fluid TPF, the capacitance response to the void fraction can be linearized, thereby improving the measurement accuracy of the void fraction.

[0049] The measurement results of the measurement system according to the first embodiment will now be described. Figure 5 shows the results of capacitance measurement obtained from simulation using measurement system 1, which is an example of the measurement system according to the first embodiment. In Figure 5, the horizontal axis is the set void fraction (unit: dimensionless), and the vertical axis is the measured capacitance (unit: femtofarad (fF)). Note that a set void fraction of 1 in Figure 5 indicates that the set void fraction is 100%.

[0050] As shown in Figure 5, the measurement system 1 exhibits a linear change in capacitance with respect to the set void fraction. In other words, in the measurement system 1, the capacitance responds linearly to the set void fraction. Therefore, according to the measurement system 1, the void fraction can be uniquely determined from the measured capacitance value.

[0051] Furthermore, in measurement system 1, the difference in size between the high-potential electrode 21a and the low-potential electrode 21b affects the linear response. In particular, the arc length of the piping for each of the high-potential electrode 21a and the low-potential electrode 21b relative to the circumference, and especially the size of the low-potential electrode, are related to accuracy.

[0052] Next, the relationship between the angle θb of the low-potential electrode 21b and the error will be explained. Figure 6 is a diagram showing the relationship between the angle θb of the low-potential electrode 21b and the error in measurement system 1, which is an example of a measurement system according to the first embodiment. In Figure 6, the horizontal axis represents the angle θb of the low-potential electrode 21b (unit: °), and the vertical axis represents the error (unit: %).

[0053] In the simulation shown in Figure 6, the angle θa of the high-potential electrode 21a is set to 180 degrees (Figure 4), and the angle θb of the low-potential electrode 21b is varied. The measurement accuracy is then evaluated when the angle θb of the low-potential electrode 21b is varied. Figure 6 shows the average error and the maximum error. A large average error indicates that the response is deviating from linearity overall, and a large maximum error indicates that the response is significantly deviating at some void fractions.

[0054] As shown in Figure 6, the error is reduced when the angle θb of the low-potential electrode is 150 degrees or less. Based on these results, it can be concluded that the optimal design is one in which the angle θa of the high-potential electrode 21a is 180 degrees and the angle θb of the low-potential electrode is 150 degrees.

[0055] According to the measurement system of the first embodiment, it is applicable to metal piping and can measure the void ratio with high accuracy.

[0056] <Second Embodiment> A measurement system according to the second embodiment will now be described. In the measurement system according to the second embodiment, the first electrode and the second electrode of the measurement system according to the first embodiment are each installed inside a pipe and used.

[0057] Figure 7 is a perspective view of a detection unit 120, which is an example of a detection unit included in the measurement system according to the second embodiment. In Figure 7, hidden lines are indicated by dashed lines. Figure 8 is a side view of a detection unit 120, which is an example of a detection unit included in the measurement system according to the second embodiment. For configurations other than the detection unit 120, please refer to the description of measurement system 1, which is an example of a measurement system according to the first embodiment.

[0058] The detection unit 120 comprises an electrode unit 121 and a pipe 122. The electrode unit 121 comprises a high-potential electrode 121a and a low-potential electrode 121b. Each of the high-potential electrode 121a and the low-potential electrode 121b has a curved shape. Each of the high-potential electrode 121a and the low-potential electrode 121b is used attached to the inner surface 122S of the pipe 122.

[0059] The piping 122 is insulated from the high-potential electrode 121a and the low-potential electrode 121b. For example, the high-potential electrode 121a and the low-potential electrode 121b may be installed with an insulating member in between them and the inner surface 122S, thereby insulating the piping 122 from the high-potential electrode 121a and the low-potential electrode 121b. The piping 122 also has through holes 122h at the positions where the high-potential electrode 121a and the low-potential electrode 121b are installed. The high-potential electrode 121a and the low-potential electrode 121b may be connected to the conversion unit 10 through the through holes 122h.

[0060] According to the measurement system of the second embodiment, it is applicable to metal piping and can measure the void ratio with high accuracy.

[0061] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The above embodiments may be omitted, replaced, or modified in various ways without departing from the scope and spirit of the appended claims. [Explanation of Symbols]

[0062] 1. Measurement System 10 Conversion section 11 Measuring part 12 Arithmetic section 20, 120 detection unit 20p internal 21, 121 Electrode section 21a, 121a High potential electrode 21b, 121b Low potential electrode 22, 122 Piping 22d, 22u aperture 22s, 22t mounting holes θa, θb angle

Claims

1. A pipe made of metal through which the two-phase fluid to be measured flows, A first electrode, made of metal, is attached to the aforementioned piping so as to be in contact with the object to be measured, A second electrode, made of metal, is attached to the piping opposite the first electrode and in contact with the object to be measured, A measuring unit for measuring the capacitance between the first electrode and the second electrode, A calculation unit calculates the gas-liquid ratio of the object to be measured based on the capacitance measured by the measurement unit, Equipped with, The first electrode is larger than the second electrode. Measurement system.

2. The arc size of the first electrode is half the circumference of the inner surface of the pipe, and the arc size of the second electrode is 5 / 12 of the circumference. The measurement system according to claim 1.

3. The longitudinal size of the first electrode is at least three times the diameter of the pipe, and the longitudinal size of the second electrode is greater than or equal to the diameter of the pipe and one-third the size of the first electrode. The measurement system according to either claim 1 or claim 2.

4. Each of the first electrode and the second electrode is formed of the same type of metal as the piping. The measurement system according to either claim 1 or claim 2.

5. Each of the first electrode and the second electrode has a curved shape and is used by being installed inside the pipe or embedded in the pipe. The measurement system according to either claim 1 or claim 2.

Images