Bubble rate meter

Abstract

This bubble fraction meter for measuring a bubble fraction of a fluid being measured comprises: an insulator including a flow passage through which the fluid being measured flows; a pair of main electrodes which are disposed in positions in the insulator facing one another across the flow passage, and which measure an electrostatic capacitance of the fluid being measured that is inside the flow passage; and a processing unit which is provided with a temperature sensor for measuring a temperature of the fluid being measured that is inside the flow passage, a pressure sensor for measuring a pressure of the fluid being measured that is inside the flow passage, and an atmospheric pressure sensor for measuring atmospheric pressure, the processing unit including a fluid relative dielectric constant adjustment calculating circuit for calculating an adjusted dielectric constant of the fluid being measured, on the basis of the fluid temperature and a fluid absolute pressure, which is a value obtained by adding the pressure of the fluid being measured to the atmospheric pressure.

Description

Technical Field

[0001] The present disclosure relates to a void fraction meter for measuring the void fraction of cryogenic liquids such as liquid hydrogen.

Background Art

[0002] Recently, with the reduction of greenhouse gas emissions, the use of hydrogen as a promising energy storage medium has attracted attention. In particular, liquid hydrogen can significantly reduce its volume compared to gaseous hydrogen, making it easy to store large amounts for a long time. Therefore, various utilization technologies have been developed. However, an industrial method for accurately measuring the flow rate required when handling large amounts of liquid hydrogen has not been established. The main reason is that liquid hydrogen is a fluid that vaporizes very easily and has a large change in the ratio of gas to liquid.

[0003] That is, liquid hydrogen is a cryogenic liquid (boiling point -253°C) with very high thermal conductivity and low latent heat, and thus has the characteristic that bubbles (voids) are generated immediately. Therefore, liquid hydrogen in the transfer pipe is a so-called two-phase flow of gas-liquid mixture. Therefore, since the change in the content ratio of bubbles is large, it is impossible to accurately know the flow rate by simply measuring the flow velocity as in the case of ordinary liquids when measuring the flow rate of liquid hydrogen flowing through the pipe.

[0004] Therefore, the development of a void fraction meter for measuring the void fraction indicating the gas phase volume fraction of a gas-liquid two-phase flow has been underway. As such a void fraction meter, in Non-Patent Document 1, a capacitance type void fraction sensor that measures capacitance using a pair of electrodes has been proposed. Non-Patent Document 1 reports that the void fraction (i.e., void fraction) of liquid nitrogen was measured using this void fraction meter.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

[0006] The void fraction meter of the present disclosure is for measuring the void fraction of a fluid to be measured, and includes: an insulator having a flow path through which the fluid to be measured flows; a pair of main electrodes that are respectively installed at positions facing each other across the flow path in the insulator and measure the capacitance of the fluid to be measured in the flow path; a temperature sensor that measures the temperature of the fluid to be measured in the flow path, a pressure sensor that measures the pressure of the fluid to be measured in the flow path, and an atmospheric pressure sensor that measures the atmospheric pressure, and a processing unit having a fluid relative permittivity correction calculation circuit that calculates the corrected relative permittivity of the fluid to be measured based on the temperature and the fluid absolute pressure that is the sum of the pressure and the atmospheric pressure.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2A

Figure 2B

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Figure 4B

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Figure 6B

Figure 6C

Figure 6D

Figure 7A

Figure 7B

Figure 8

Embodiments for Carrying Out the Invention

[0008] Hereinafter, the bubble rate meter according to the embodiment of the present disclosure will be described with reference to the drawings. In the following description, the fluid to be measured includes cryogenic liquids such as liquid hydrogen and liquid nitrogen, but is not limited thereto.

[0009] FIG. 1 shows the basic configuration of a bubble rate meter 100 according to an embodiment of the present disclosure. In this bubble rate meter 100, a flow path 3 through which the fluid to be measured flows is formed in an insulator 4. A pair of main electrodes 1, 1 facing each other with the flow path 3 interposed therebetween are provided on the insulator 4, and the capacitance of the fluid to be measured flowing through the flow path 3 is measured by these main electrodes 1, 1. The insulator 4 is housed in a metal casing 5, and pipes 6 through which the fluid to be measured flows are connected to both ends of the flow path 3. A coaxial cable 8 is connected to the main electrodes 1, 1 via a connector 7. A temperature sensor 9a and a pressure sensor 9b are attached to a portion of the pipe 6 close to the flow path 3. The temperature sensor 9a is a sensor that measures the fluid temperature T1. The fluid temperature T1 is the temperature of the fluid to be measured flowing through the pipe 6 in the portion close to the flow path 3, and it is likely to vary until the temperature of the pipe 6 becomes constant while the fluid to be measured is flowing. The pressure sensor 9b is a sensor that measures the fluid gauge pressure Pg. Furthermore, near the pipe 6, an atmospheric pressure sensor 9c for measuring the atmospheric pressure is installed.

[0010] The insulator 4 is formed of insulating ceramics and is cylindrical. Examples of such ceramics include zirconia, alumina, sapphire, aluminum nitride, silicon nitride, sialon, cordierite, mullite, yttria, silicon carbide, cermet, β-eucryptite, etc. Also, the flow path 3 formed in the insulator 4 preferably has an inner diameter of 9 mm or more and 381 mm or less.

[0011] The main electrode 1 can be formed of, for example, copper foil, aluminum foil, etc. The main electrode 1 can be formed by, for example, vacuum evaporation method, metallization method, active metal method, etc., but it may also be adhered to the bottom surface of the recess formed on the outer peripheral surface of the insulator 4.

[0012] Generally, since a bubble rate meter handles a physical property value of capacitance, it is easily affected electrically by the external environment and prone to errors, and it is particularly difficult to accurately measure the bubble rate of the fluid to be measured over a wide temperature range from normal temperature to liquefied gas temperature. For example, as shown in FIG. 8 showing the relationship between the capacitance value and the bubble rate, when the absolute pressure and the temperature vary (indicated by the arrow T), the straight line A showing the relationship between the capacitance value and the bubble rate varies toward the straight line A1 or A2. That is, even if trying to obtain the bubble rate from the capacitance value measured by the bubble rate meter, the bubble rate can take values in the range sandwiched between the straight line A1 and the straight line A2 and cannot be uniquely determined.

[0013] Furthermore, when measuring the capacitance, the electric field lines (indicated by arrow E) from one main electrode 1 to the other main electrode 1 pass through the insulator 4 and the flow path 3. Therefore, when the main electrodes 1,1 measure the capacitance of the measured fluid, the influence of the insulator 4 cannot be ignored. That is, the relative dielectric constant of the insulator 4 is temperature-dependent in most materials, so that the capacitance value varies with temperature changes. Therefore, as described later, it is necessary to correct the capacitance value C1 measured by the main electrodes 1,1. Specifically, the capacitance measurement value C1 is a measurement value obtained by observing the combined capacitance of the measured fluid and the capacitance of the insulator 14.

[0014] As shown in FIG. 3, in the processing unit 20, the fluid relative dielectric constant correction calculation circuit 21 calculates the fluid temperature T1 measured by the temperature sensor 9a, the fluid absolute pressure P1, which is the sum of the atmospheric pressure Pa measured by the atmospheric pressure sensor 9c and the pressure (fluid gauge pressure Pg) measured by the pressure sensor 9b, in a known relative dielectric constant database εf(P1 , T1), the relative dielectric constant ε of the measured fluid when the bubble rate Br is 0% 0% and the relative dielectric constant ε of the measured fluid when the porosity Br is 100% 100% can be sought.

[0015] The capacitance measurement value C of the fluid to be measured when the bubble rate Br is 0% 0% can be calculated based on the following formula (1): C 0% =ε 0% ×(d / S) (d: distance between main electrodes 1, 1, S: area of ​​main electrode 1) (1) The capacitance measurement value C of the fluid to be measured when the bubble rate Br is 100% 100% can also be found using the above relational expression. Here, even if the porosity Br is 0%, if at least one of the fluid temperature T1 and the fluid absolute pressure P1 fluctuates, the relative dielectric constant ε 0% is different value (ε 1 , ε 3, ···) is shown. This is the same even when the void fraction Br is 100%, and the relative permittivity ε of the fluid to be measured varies according to the fluctuations in the fluid temperature T1 and the absolute fluid pressure P1 100% takes on different values (ε 2 , ε 4 , ···).

[0016] The measured capacitance value C1, the absolute fluid pressure P1, the fluid temperature T1, the relative permittivity ε of the fluid r r and the void fraction Br, which are the respective average values of the measured capacitance value C1 ave , the absolute fluid pressure P1 ave , the fluid temperature T1 ave , the relative permittivity of the fluid ε r ave and the void fraction Br ave are obtained, and then multiple regression analysis is performed. According to the following equations (2) and (3), the measured capacitance value C when the void fraction Br of the fluid to be measured is 0% 0% and the measured capacitance value C when the void fraction Br of the fluid to be measured is 100% 100% can be obtained. The measured capacitance value C 0% and the measured capacitance value C 100% The procedure for multiple regression analysis until the measured capacitance values C and C are obtained is, for example, to sequentially calculate the variance-covariance matrix shown in FIG. 6C, the inverse matrix shown in FIG. 6D, and the constant term shown in the following equation (4) using Excel (registered trademark, Microsoft Corporation). C 0% = D + d1×P1 + d2×T1 + d3×εr + d4×0 ·····(2) C 100% = D + d1×P1 + d2×T1 + d3×εr + d4×100···(3) However, D is the constant term obtained by multiple regression analysis and is the value obtained by the following equation (4). d1, d2, d3, and d4 are partial regression coefficients. D = C1 ave - d1×P1 ave - d2×T1 ave - d3×εr ave - d4×Br ave ···(4)

[0017] Note that the relative permittivity database εf(P1 , T1) is based on self-developed software. As shown in FIG. 6A, an example of this database shows how the relative permittivity of the fluid to be measured in a uniform equilibrium state changes due to the change in the fluid gauge pressure Pg and the change in the fluid temperature T1. The capacitance measurement values C1, C 0% and the capacitance measurement value C 100% obtained as described above are used to calculate the void fraction B r1 by the following formula (5). B r1 =(C 0% ―C1) / (C 0% ―C 100% )×100···(5)

[0018] By incorporating the atmospheric pressure Pa measured by the atmospheric pressure sensor 9c into the variables of the arithmetic function of the fluid relative permittivity correction arithmetic circuit 21, it is possible to correct the deviation of the relative permittivity of the fluid to be measured caused by the pressure difference generated between the reference atmospheric pressure Pa for formulating the arithmetic database and the current fluid absolute pressure P1.

[0019] FIG. 2A shows a void fraction meter 101 according to an embodiment of the present disclosure, and FIG. 2B shows the void fraction meter 101 including the housing 15. As shown in FIGS. 2A and 2B, recesses 10, 10 are formed on the outer peripheral surface of the insulator 14. These recesses 10, 10 are located at positions facing each other across the flow path 13 at the center of the insulator 14. Pipes 16 are connected to both ends of the flow path 13. A pair of main electrodes 1, 1 are formed on the bottom surfaces of the recesses 10, 10, respectively. These main electrodes 1, 1 measure the capacitance of the fluid to be measured in the flow path 13.

[0020] A coaxial cable 18 is connected to the main electrodes 1, 1. The coaxial cable 18 is drawn out of the housing 15 through the connector 17. As shown in Fig. 2A, a convex portion 40 is formed on a part of the insulator 14, and a pair of correction electrodes 2, 2 are provided facing each other on both side surfaces of the convex portion 40, and a coaxial cable 181 is connected to each correction electrode 2 (see Fig. 2B). The correction electrodes 2, 2 are for passing electric lines of force through the convex portion 40 to measure the capacitance of the insulator 14. In the example shown in Fig. 2A, the convex portion 40 is formed on a stepped portion formed from one end surface of the insulator 14. The correction electrode 2 can be formed, for example, by a vacuum evaporation method, a metallizing method, an active metal method, or the like.

[0021] The processing unit 20 shown in Fig. 3 has a capacitance scale correction circuit 22 that corrects one or both of the deviation when the bubble rate Br of the fluid to be measured caused by the insulator 14 is 0% and the deviation when the bubble rate Br of the fluid to be measured is 100% among the capacitance values C1 measured by the main electrodes 1, 1. The capacitance value C2 measured by the correction electrodes 2, 2 is used to correct the capacitance value C1 measured by the main electrodes 1, 1. That is, as shown in Fig. 3, the capacitance value measured by the correction electrodes 2, 2 (hereinafter, the insulator capacitance value C2) and the capacitance value measured by the main electrodes 1, 1 (hereinafter, the capacitance measurement value C1) are sent to the processing unit 20 together, and the capacitance scale correction circuit 22 calculates and outputs the bubble rate with the influence of the insulator 14 corrected. Here, the capacitance measurement value C1 is a measurement value obtained by combining the capacitance of the fluid to be measured and the capacitance of the insulator 14. The output bubble rate is displayed on a display device or recorded on a recording medium.

[0022] The function of the capacitance scale correction circuit 22 will be described in detail with reference to Figs. 7A and 7B. First, as shown in Fig. 7A, the fluid to be measured is flowed through the flow path 13 in a gaseous state (bubble rate Br is 100%), and data (capacitance measurement value C1, insulator capacitance value C2, fluid absolute pressure P1, fluid temperature T1, and fluid relative permittivity εr) in a region (for example, regions No. 1 to 4) where the insulator capacitance value C2 of the correction electrode 2 changes is acquired. The fluid temperature T1 is stable (T1 6 , T1 7 , T18 After a while with (...), the insulator capacitance value C2 also reaches a stable value. Obtain data (capacitance measurement value C1, insulator capacitance C2, fluid absolute pressure P1, fluid temperature T1, and fluid relative permittivity εr) in the region where the insulator capacitance value C2 is stable (for example, region No. 6 - 7).

[0023] As shown in FIG. 7B, for each measured value C2 of the insulator capacitance value C2 sandwiched between the maximum value C2 max and the minimum value C2 min , plot each measured value C2 2 , C2 3 , C2 4 , C2 5 , C2 6 on the horizontal axis of the graph, and plot each corresponding measured value C1 of the capacitance measurement value C1 when these measurements were taken 2 , C1 3 , C1 4 , C1 5 , C1 6 on the vertical axis of the graph.

[0024] For the approximate function showing the gradual decrease of the capacitance measurement value C1, for example, after setting it as a linear approximation using the graph tool provided in Excel (registered trademark, Microsoft Corporation), calculate the correlation coefficient R. Then, using the r - table (correlation coefficient test table), test the correlation coefficient R at a significance level of 5% (two - sided probability). If it is significant, the following regression equation (6) showing the gradual decrease of the capacitance measurement value C1 is determined. In regression equation (6), K is the slope and L is the intercept. C1 = K×C2 + L ··· (6)

[0025] Using the capacitance measurement values C 0% , C 100% obtained by equations (2) and (3), the slope (regression coefficient) K, and the intercept L, by using the following equations (7) and (8), the capacitance measurement values C’ 0% , C’ 100% of the fluid to be measured with the influence of the insulator 14 corrected respectively can be obtained. C’ 0% = K×C 0% + L ······ (7) C’ 100% = K × C 100% + L ···(8) (C’ 0% : Capacitance measurement value of the measured fluid corrected when the bubble rate is 0%, C’ 100% : Capacitance measurement value of the measured fluid corrected when the bubble rate is 100%)

[0026] Capacitance measurement value C’ of the measured fluid 0% 、C’ 100% Using C’ r2 the bubble rate B B r2 = (C’ 0% ― C1) / (C’ 0% ― C’ 100% ) × 100 ···(9)

[0027] Bubble rate meters 100, 101 use the obtained capacitance measurement values C1 2 、C1 3 、C1 4 、C1 5 、C1 6 、C1 7 It is also possible to convert from the fluid density. In this case, it is calculated based on the multivariate analysis provided in the capacitance / fluid density circuit. The fluid density refers to the density of the measured fluid in a state containing bubbles. The product of the converted fluid density, the cross-sectional area perpendicular to the axial direction of the flow path, and the flow velocity of the measured fluid flowing through the flow path is the mass flow rate of the measured fluid. With the capacitance scale correction circuit 22, it is also possible to correct the relative permittivity of the insulator 14 based on the temperature of the insulator 14.

[0028] The main electrodes 1, 1 and the correction electrodes 2, 2 are preferably applied with an alternating voltage for measurement alternately so as not to electrically interfere with each other. Also, in the same spirit, the facing direction of the main electrodes 1, 1 and the facing direction of the correction electrodes 2, 2 are preferably intersecting. In the present embodiment, they are orthogonal. Thereby, the lines of electric force of the main electrodes 1, 1 penetrating the fluid to be measured in the flow path 13 and the lines of electric force of the correction electrodes 2, 2 penetrating the convex portion 40 do not affect each other.

[0029] Next, another embodiment of the present disclosure will be described with reference to FIGS. 4A and 4B. The same components as those in FIGS. 2A, 2B, and 3 are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

[0030] As shown in FIGS. 4A and 4B, the void fraction meter 102 according to this embodiment includes an insulator 24 having a flow path 23 along the axial direction. Recesses 10, 10 are formed at positions facing each other across the flow path 23 (only one of the recesses 10 is shown in the figure), and a pair of main electrodes 1, 1 (see FIG. 2B) are formed on the bottom surfaces of the recesses 10, 10, respectively.

[0031] Further, a hole 30 is formed in the insulator 24 substantially parallel to the axial direction of the flow path 23. The hole 30 is formed so as not to pass through the flow path 23. A cylindrical correction electrode 25 is inserted into the hole 30. The cylindrical correction electrode 25 has a form in which an internal electrode 31 and an external electrode 32 are arranged on the inner peripheral surface and the outer peripheral surface of the cylindrical insulator 241, respectively, as shown in FIG. 4B. Note that the hole 30 is formed in a notch portion of the insulator 24, but it may be formed on the end face 24a of the insulator 24.

[0032] The cylindrical insulator 241 can be formed of the same or different insulating materials as the insulator 24 which is the main body. The internal electrode 31 is a columnar body inserted into the hole of the cylindrical insulator 241, and is preferably a conductor such as copper. The external electrode 32 can be formed by forming a metallized layer on the outer peripheral surface of the cylindrical insulator 241 or attaching a metal film. A coaxial cable (not shown) is connected to the internal electrode 31 and the external electrode 32. Also in this embodiment, since the internal electrode 31 and the external electrode 32 of the cylindrical correction electrode 25 are arranged to face each other at positions that do not pass through the flow path 23 of the insulator 24, the capacitance value measured by the main electrodes 1, 1 can be corrected based on the capacitance value measured by the cylindrical correction electrode 25.

[0033] A bubble rate meter according to still another embodiment of the present disclosure will be described with reference to FIG. 5. Note that the same components as those in FIGS. 4A and 4B are denoted by the same reference numerals, and detailed descriptions thereof are omitted. FIG. 5 shows the insulator 24' in this embodiment.

[0034] As shown in FIG. 5, the insulator 24' has a flow path 23', and recesses 10, 10 are formed at positions facing each other with the flow path 23' interposed therebetween (only one recess 10 is shown in FIG. 5). Electrodes 1, 1 (see FIG. 2B) are formed on the bottom surfaces of the recesses 10, 10 so as to face each other.

[0035] A hole 30' that intersects (is orthogonal to) the axial direction of the flow path 23' is formed in the insulator 24'. The cylindrical correction electrode 25 described above is inserted into the hole 30'. Other aspects are the same as those of the foregoing embodiment.

[0036] Note that in order to electrically isolate the main electrodes 1, 1 and the correction electrodes 2, 2, and also the main electrodes 1, 1 and the cylindrical correction electrodes 25, 25 from each other, a shield plate (not shown) such as a metal plate may be provided therebetween.

[0037] As described in detail above, according to the present disclosure, it is possible to correct the temperature dependence due to the material of the insulator when measuring the capacitance of the fluid to be measured. Furthermore, it is possible to correct even the variation in the individual differences of the insulators (for example, the differences that occur for each firing lot), enabling highly accurate measurement.

[0038] Although the embodiments of the present disclosure have been described above, the bubble rate meter of the present disclosure is not limited to the above embodiments, and various modifications and improvements are possible within the scope of the present disclosure.

Description of Reference Numerals

[0039] 1 Main electrode 2 Correction electrode 3, 13, 23 Flow paths 4, 14, 24, 24´ Insulators 24a End face 5, 15 Housings 6, 16 Pipes 7, 17 Connectors 8, 18, 181 Coaxial cables 9a Temperature sensor 9b Pressure sensor 9c Atmospheric pressure sensor 10 Recess 20 Processing unit 21 Dielectric constant correction calculation circuit 22 Capacitance scale correction circuit 241 Cylindrical insulator 25 Cylindrical correction electrode 30, 30´ Hole parts 31 Internal electrode 32 External electrode 100, 101 Bubble rate meters

Claims

1. A bubble rate meter for measuring the bubble rate of a fluid to be measured, comprising: an insulator having a flow path through which the fluid to be measured flows; a pair of main electrodes that are respectively installed at positions facing each other across the flow path in the insulator and measure the capacitance of the fluid to be measured in the flow path; a temperature sensor that measures the fluid temperature of the fluid to be measured in the flow path, a pressure sensor that measures the pressure of the fluid to be measured in the flow path, and an atmospheric pressure sensor that measures the atmospheric pressure, and a fluid relative permittivity correction calculation circuit that calculates the corrected relative permittivity of the fluid to be measured based on the fluid temperature and the fluid absolute pressure that is the value obtained by adding the pressure of the fluid to be measured to the atmospheric pressure; and a pair of correction electrodes that measure the capacitance of the insulator are provided in a region where the electric lines of force generated between the correction electrodes do not pass through the flow path. Bubble rate meter

2. The bubble rate meter according to claim 1, wherein an AC voltage for measurement is alternately applied to the main electrode and the correction electrode so as not to affect each other.

3. The bubble rate meter according to claim 1 or 2, wherein the facing direction of the main electrode and the facing direction of the correction electrode intersect.

4. The correction electrode is a cylindrical correction electrode including an internal electrode and an external electrode respectively arranged on the inner peripheral surface and the outer peripheral surface of a cylindrical insulator, and is housed in a hole provided in the insulator. The bubble rate meter according to claim 1 or 2.

5. The bubble rate meter according to claim 1 or 2, wherein a shield plate is interposed between the main electrode and the correction electrode.

6. The bubble rate meter according to claim 1 or 2, wherein the processing unit has a capacitance scale correction circuit that corrects one or both of the deviation when the bubble rate of the fluid to be measured caused by the insulator in the capacitance value measured by the main electrode is 0% and the deviation when the bubble rate of the fluid to be measured is 100%.

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