Void fraction acquisition system and void fraction acquisition method

Abstract

This invention provides a void fraction acquisition system and a void fraction acquisition method that can accurately acquire the void fraction. [Solution] The void fraction acquisition system comprises a flow path through which a fluid that can be in a gas-liquid two-phase state containing bubbles in the liquid flows, an emission unit that emits pressure waves into the fluid, a detection unit that detects the pressure waves, and a control device. The control device comprises a resonance frequency acquisition unit that acquires the resonance frequency of bubbles in the fluid, a setting unit that sets the frequency of the pressure waves emitted by the emission unit to be lower than the resonance frequency, a velocity acquisition unit that acquires the propagation velocity of the pressure waves based on the detection information from the detection unit, and a void fraction acquisition unit that acquires the void fraction in the fluid based on the propagation velocity.

Description

Technical Field

[0001] The present disclosure relates to a void fraction acquisition system and a void fraction acquisition method.

Background Art

[0002] Void fraction is an important parameter in the analysis, modeling, and practical application of gas-liquid two-phase flow. For example, the void fraction measurement device described in Patent Document 1 irradiates a fluid containing gas as fine bubbles in liquid with pressure waves, and calculates the void fraction from the propagation velocity of the pressure waves.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0004] However, the void fraction measurement device described in Patent Document 1 may not be able to measure the void fraction with practically sufficient accuracy in some cases.

[0005] The present disclosure has been made to solve the above problem, and an object of the present disclosure is to provide a void fraction acquisition system and a void fraction acquisition method capable of accurately acquiring the void fraction.

Means for Solving the Problems

[0006] To solve the above problems, the void fraction acquisition system according to the present disclosure comprises a flow path through which a fluid that can be in a gas-liquid two-phase state containing bubbles in the liquid flows, an emission unit that emits a pressure wave into the fluid, a detection unit that detects the pressure wave, and a control device, wherein the control device comprises a resonance frequency acquisition unit that acquires the resonance frequency of bubbles in the fluid, a setting unit that sets the frequency of the pressure wave emitted by the emission unit to be lower than the resonance frequency, a velocity acquisition unit that acquires the propagation velocity of the pressure wave based on the detection information of the detection unit, and a void fraction acquisition unit that acquires the void fraction in the fluid based on the propagation velocity.

[0007] The method for obtaining void fraction according to this disclosure includes the steps of: obtaining the resonance frequency of bubbles in a fluid that can be in a gas-liquid two-phase state containing bubbles in the liquid; setting the frequency of a pressure wave emitted into the fluid to be lower than the resonance frequency; emitting the pressure wave into the fluid; detecting the pressure wave; obtaining the propagation speed of the pressure wave based on the detection information of the pressure wave; and obtaining the void fraction in the fluid based on the propagation speed.

[0008] The method for obtaining void fraction according to this disclosure includes the steps of: obtaining the resonance frequency of bubbles in a fluid that can be in a gas-liquid two-phase state containing bubbles in the liquid; working on the flow path through which the fluid flows so that the frequency of pressure waves propagating in the fluid when the flow path is struck becomes smaller than the resonance frequency; striking the flow path; detecting the pressure waves propagating in the fluid due to the striking of the flow path; obtaining the propagation velocity of the pressure waves based on the detection information of the pressure waves; and obtaining the void fraction in the fluid based on the propagation velocity. [Effects of the Invention]

[0009] According to the void fraction acquisition system and void fraction acquisition method of this disclosure, the void fraction can be accurately acquired. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of a void acquisition system according to the first embodiment of this disclosure. [Figure 2] This is a cross-sectional view along the line II-II in Figure 1. [Figure 3] This is a correlation diagram of sound velocity and frequency according to the first embodiment of this disclosure. [Figure 4] This is a correlation diagram between two-phase sound velocity and void fraction according to the first embodiment of this disclosure. [Figure 5] This is a functional block diagram of a control device according to the first embodiment of this disclosure. [Figure 6] This is a correlation diagram between the resonant frequency and the bubble diameter according to the first embodiment of this disclosure. [Figure 7] This is a flowchart showing the procedure for obtaining the void ratio according to the first embodiment of this disclosure. [Figure 8] A flowchart illustrating the procedure for acquiring the resonant frequency according to the first embodiment of this disclosure. [Figure 9] This is a flowchart showing the procedure for obtaining the transmission speed according to the first embodiment of this disclosure. [Figure 10] This is a schematic diagram of a void acquisition system according to the second embodiment of this disclosure. [Figure 11] This is a cross-sectional view along the line XI-XI in Figure 10. [Figure 12] This is a functional block diagram of a control device according to a second embodiment of the present disclosure. [Figure 13] This is a flowchart showing the procedure for obtaining the void ratio according to the second embodiment of this disclosure. [Figure 14] This is a schematic diagram of a void acquisition system according to the third embodiment of this disclosure. [Figure 15] This is a cross-sectional view along the line XV-XV in Figure 14. [Figure 16] This is a functional block diagram of a control device according to the third embodiment of this disclosure. [Figure 17] This is a flowchart showing the procedure for obtaining the void ratio according to the third embodiment of this disclosure. [Figure 18]This is a diagram showing an example of work performed on a flow channel according to a modification of the third embodiment of the present disclosure. [Figure 19] This is a schematic configuration diagram of a void acquisition system according to a modification of the third embodiment of the present disclosure. [Figure 20] This is a flowchart showing the procedure of a void fraction acquisition method according to the third embodiment of the present disclosure. [Figure 21] This is a hardware configuration diagram according to each embodiment of the present disclosure. [Mode for Carrying Out the Invention]

[0011] <First Embodiment> Hereinafter, a void fraction acquisition system 1 and a void fraction acquisition method according to the first embodiment of the present disclosure will be described with reference to FIG. 1 to FIG. 9.

[0012] The void fraction acquisition system 1 acquires the void fraction of a fluid 2 that can be in a gas-liquid two-phase state containing bubbles 2b in a liquid 2a.

[0013] The void fraction acquisition system 1 of the present embodiment is applied to plants such as chemical plants and nuclear power plants, for example. In boilers and condensers used in plants, the flow of the fluid 2 such as a refrigerant or working fluid in piping becomes a gas-liquid two-phase flow in which gas and liquid 2a are mixed. Note that such a fluid 2 may also be referred to as a gas-liquid two-phase flow (or gas-liquid two-phase fluid). The void fraction acquisition system 1 of the present embodiment acquires the void fraction of the fluid 2 flowing through the plant. The void fraction referred to herein is the volume ratio of the gas phase (gas) including the bubbles 2b occupying the interior of the fluid 2.

[0014] As shown in FIG. 1 and FIG. 2, the void fraction acquisition system 1 includes a flow channel 10, an emission unit 3, a detection unit 4, a control device 30, and an input device 6.

[0015] (Flow Channel) Fluid 2, whose void fraction is to be measured, flows through the flow path 10. Hereinafter, the main flow direction Df of this fluid 2 will be simply referred to as "flow direction Df". Furthermore, the upstream side Dfu of the flow direction Df will be simply referred to as "upstream Dfu", and the downstream side Dfd of the flow direction Df will be simply referred to as "downstream Dfd". Furthermore, the flow path 10 through which fluid 2 flows will be simply referred to as "flow path 10". Examples of flow path 10 include pipes and containers. In this embodiment, for the sake of simplicity, we will describe the case where the flow path 10 is a pipe extending in one direction. The flow path 10 is formed in the shape of a circular pipe. Hereinafter, the axis O of the flow path 10 will be simply referred to as axis O, and the direction in which axis O extends will be referred to as "axial direction Da". Furthermore, the radial direction of axis O will be referred to as "radial direction", and the circumferential direction of axis O will be referred to as "circumferential direction". The axial direction Da is assumed to be approximately located in the same position as the flow direction Df. Furthermore, the inner circumferential surface of the flow path 10 that is in contact with the fluid 2 is referred to as the "inner wall surface 11," and the outer circumferential surface of the flow path 10 is referred to as the "outer wall surface 12." Note that the shape of the flow path 10 is not limited to a cylindrical shape. The flow path 10 may be formed in the shape of a rectangular prism or a rectangular duct, for example.

[0016] (Ejection section) The discharge unit 3 emits a pressure wave 5 into the fluid 2. The pressure wave 5 is a type of longitudinal wave. Examples of pressure waves 5 include sound waves and ultrasound. The discharge unit 3 is installed on the outer wall surface 12 of the flow path 10. In this embodiment, the discharge unit 3 is a piezoelectric element. Hereinafter, this piezoelectric element will be referred to as the discharge-side piezoelectric element 3a. A voltage is applied to the discharge-side piezoelectric element 3a. When a voltage is applied, the discharge-side piezoelectric element 3a vibrates. The vibration of the discharge-side piezoelectric element 3a generates a pressure wave 5 in the flow path 10. The generated pressure wave 5 is emitted towards the detection unit 4.

[0017] (Detection unit) The detection unit 4 detects the pressure wave 5. The detection unit 4 is installed on the outer wall surface 12 of the flow path 10. In this embodiment, the detection unit 4 is a piezoelectric element. Hereinafter, this piezoelectric element will be referred to as the detection-side piezoelectric element 4a. The detection-side piezoelectric element 4a converts the detected pressure wave 5 into an electrical signal and transmits it to the control device 30.

[0018] The ejection unit 3 and the detection unit 4 are positioned opposite each other in a direction perpendicular to the fluid flow direction Df of the fluid 2. More specifically, the ejection unit 3 and the detection unit 4 are positioned radially opposite each other across the axis O. The ejection unit 3 and the detection unit 4 function as sensors that acquire parameters for obtaining the void fraction. For this reason, the ejection unit 3 may be referred to as the first sensor, and the detection unit 4 may be referred to as the second sensor.

[0019] (Control device) The control device 30 acquires the void fraction of the fluid 2 based on the detection information (detected value) of the pressure wave 5 (longitudinal wave). Specifically, the control device 30 acquires the propagation speed (two-phase sound velocity) of the pressure wave 5 in the gas-liquid two-phase system from the detection information of the pressure wave 5. Then, the control device 30 acquires the void fraction based on the acquired two-phase sound velocity. Here, the propagation speed (sound velocity) of the pressure wave 5 in the gas-liquid two-phase system is referred to as the two-phase sound velocity, and the propagation speed (sound velocity) in the liquid single-phase system is referred to as the reference sound velocity or liquid single-phase sound velocity.

[0020] Here, as shown in Figure 3, when the frequency of the pressure wave 5 is lower than the resonant frequency (also called the natural frequency) of the bubble 2b in the fluid 2, the propagation speed (speed of sound) of the pressure wave 5 becomes the two-phase sound speed. On the other hand, when the frequency of the pressure wave 5 is sufficiently higher than the resonant frequency of the bubble 2b in the fluid 2, the propagation speed (speed of sound) of the pressure wave 5 approaches the reference sound speed (single-phase sound speed of liquid). In Figure 3, the case where the two-phase sound speed is approximately 500 m / s to 1000 m / s (for example, approximately 700 m / s), the reference sound speed (single-phase sound speed of liquid) is approximately 1500 m / s, and the resonant frequency is approximately 60 kHz is illustrated.

[0021] Furthermore, as shown in Figure 4, there is a correlation between the propagation speed (two-phase sound velocity) of the pressure wave 5 (longitudinal wave) in the gas-liquid two-phase system and the void fraction. Therefore, the two-phase sound velocity can be obtained, and the void fraction can be obtained based on the obtained two-phase sound velocity. In particular, the change in two-phase sound velocity is large in the range where the void fraction is between 0 and 0.15 (0% to 15%). Therefore, by obtaining the two-phase sound velocity in the range where the void fraction is between 0 and 0.15 (0% to 15%), and then obtaining the void fraction based on the obtained two-phase sound velocity, the void fraction can be obtained accurately (with high precision). Based on these results, in this embodiment, the range where the void fraction is between 0 and 0.15 (0% to 15%) is considered a preferred measurement range.

[0022] The control device 30 is equipped with various functional units for acquiring the void fraction according to the principle described above. Specifically, as shown in Figure 5, the control device 30 includes a resonance frequency calculation information acquisition unit 31, a resonance frequency acquisition unit 32, a setting unit 33, an ejection operation unit 34, an ejection information acquisition unit 35, a detection operation unit 36, a detection information acquisition unit 37, a delay time acquisition unit 38, a distance acquisition unit 39 between sensors, a velocity acquisition unit 40, and a void fraction acquisition unit 41.

[0023] (Resonance frequency calculation information acquisition section) The resonance frequency calculation information acquisition unit 31 acquires the information (parameters) necessary for calculating the resonance frequency. Here, the resonance frequency is calculated, for example, from equation (1) below.

[0024]

number

[0025] Equation (1) is known as Minnaert's equation. In equation (1), f0 is the resonant frequency [Hz], P0 is the static pressure of liquid 2a [Pa(abs)], R0 is the diameter (radius) of bubble 2b [m], γ is the specific heat ratio [-], and ρ0 is the density of liquid 2a [kg / m³]. 3]. In other words, when calculating the resonant frequency based on equation (1), the information (parameters) required for calculating the resonant frequency are the static pressure of liquid 2a [Pa(abs)], bubble diameter [m], specific heat ratio [-], and density of liquid 2a [kg / m³]. 3 ]. According to equation (1), as shown in Figure 6, the resonant frequency tends to decrease as the bubble diameter increases. As an example, Figure 6 shows that the resonant frequency is approximately 60 kHz when the bubble diameter is approximately 110 μm. Also in Figure 6, the range of frequencies and bubble diameters for which the void fraction can be obtained (measured) is illustrated with hatching.

[0026] (1) Of the parameters required for the calculation of equation (1), the bubble diameter is either an estimated value obtained using knowledge from literature, etc., or a known bubble diameter is used. When estimating the bubble diameter from knowledge from literature, etc., the bubble diameter is estimated from, for example, temperature, pressure, fluid properties, heating conditions, etc. For example, equation (2) below is used to estimate the bubble diameter. Equation (2) is a formula for calculating the dimensionless bubble Sauter diameter based on the dimensionless Laplace length. In equation (2), the dimensionless bubble Sauter diameter corresponds to the bubble diameter used in the calculation of the resonance frequency.

[0027]

number

[0028] (Resonant frequency acquisition section) The resonance frequency acquisition unit 32 acquires the resonance frequency of the bubbles 2b in the fluid 2. In this embodiment, the resonance frequency acquisition unit 32 acquires the resonance frequency based on the information acquired by the resonance frequency calculation information acquisition unit 31.

[0029] (Settings section) The setting unit 33 sets the frequency of the pressure wave 5 emitted from the discharge unit 3 to be lower than the resonant frequency.

[0030] (Emission operation part) The injection control unit 34 operates the injection unit 3 to emit a pressure wave 5 into the fluid 2.

[0031] (Emission information acquisition unit) The emission information acquisition unit 35 acquires information (hereinafter referred to as emission information) when the emission unit 3 emits the pressure wave 5. The emission information includes, for example, information such as the time (timing) when the emission unit 3 emits the pressure wave 5.

[0032] (Detection operation unit) The detection operation unit 36 ​​activates the detection unit 4. This puts the detection unit 4 in a state where it can detect the pressure wave 5 from the discharge unit 3.

[0033] (Detection information acquisition unit) The detection information acquisition unit 37 acquires information (hereinafter referred to as detection information) when the detection unit 4 detects the pressure wave 5. The detection information includes, for example, information such as the time (timing) when the detection unit 4 detected the pressure wave 5.

[0034] (Delay time acquisition unit) The delay time acquisition unit 38 acquires the time (hereinafter referred to as delay time) that takes place from the time the pressure wave 5 is generated until the pressure wave 5 is detected. In this embodiment, the delay time is the time it takes for the pressure wave 5 to propagate from the emission unit 3 to the detection unit 4. The delay time acquisition unit 38 acquires the delay time based on the emission information and the detection information.

[0035] (Sensor distance acquisition unit) The sensor distance acquisition unit 39 acquires the distance over which the pressure wave 5 propagates before it is detected (hereinafter referred to as the sensor distance L). In this embodiment, the sensor distance L is the shortest distance between the emission unit 3 and the detection unit 4. The sensor distance L may be input to the control device 30 in advance, for example, via the input device 6 described later.

[0036] (Speed ​​acquisition part) The velocity acquisition unit 40 acquires the propagation speed (two-phase sound speed) of the pressure wave 5 based on the detection information from the detection unit 4. In this embodiment, the delay time and the distance L between sensors are acquired based on the detection information from the detection unit 4. The velocity acquisition unit 40 then acquires the propagation speed of the pressure wave based on the delay time and the distance L between sensors. Here, the setting unit 33 sets the frequency of the pressure wave 5 to be less than or equal to the resonance frequency between the bubbles 2b in the fluid 2 and the pressure wave 5. Therefore, the propagation speed of the pressure wave 5 acquired by the velocity acquisition unit 40 is the two-phase sound speed.

[0037] (Void fraction acquisition unit) The void fraction acquisition unit 41 acquires the void fraction in the fluid 2 based on the propagation speed (two-phase sound velocity). In this embodiment, the void fraction acquisition unit 41 uses the correlation between two-phase sound velocity and void fraction shown in Figure 3 to convert the two-phase sound velocity acquired by the velocity acquisition unit 40 into void fraction.

[0038] (Input device) The input device 6 is a device that inputs information necessary for calculating the void fraction to the control device 30. In this embodiment, the operator inputs information (parameters) necessary for calculating the resonant frequency, for example, through the input device 6.

[0039] (Procedure for obtaining void fraction) Next, an example of a method for obtaining the void ratio according to this embodiment will be explained with reference to the flowcharts in Figures 7 to 9.

[0040] As shown in Figure 7, first, the resonance frequency acquisition unit 32 acquires the resonance frequency of the bubble 2b in the fluid 2 (step S1). In step S1, first, as shown in Figure 8, the resonance frequency acquisition unit 32 acquires the information (parameters) necessary for calculating the resonance frequency (step S11). Then, the resonance frequency acquisition unit 32 calculates the resonance frequency based on the information obtained in step S11 (step S12).

[0041] For example, when the resonant frequency is obtained based on equation (1) above, the resonant frequency acquisition unit 32 obtains the static pressure [Pa(abs)] of liquid 2a, the bubble diameter [m], the specific heat ratio [-], and the density [kg / m³] of liquid 2a. 3 The following information is obtained. This information is entered, for example, by the operator through the input device 6. Note that, regarding the bubble diameter [m], if the resonant frequency is estimated using an equation such as equation (2), information necessary for estimating the bubble diameter (e.g., temperature, pressure, fluid properties, heating conditions, etc.) may be entered instead of the bubble diameter information.

[0042] Although this explanation describes a case where the resonant frequency is calculated within the control device 30, it is not limited to this case. For example, the resonant frequency may be input to the control device 30 in advance through the input device 6. In that case, the procedure in the resonant frequency calculation information acquisition unit 31 and step S11 becomes unnecessary.

[0043] Step S1 is completed by step S12. Then, returning to the flow in Figure 7, the setting unit 33 sets the frequency of the pressure wave 5 emitted into the fluid 2 to be lower than the resonant frequency (step S2). After step S2, the emission unit 3 emits the pressure wave 5 (longitudinal wave) into the fluid 2 (step S3). Immediately after step S3, the emission information acquisition unit 35 acquires emission information from the emission unit 3 (step S4). This emission information includes information on the time (timing) when the emission unit 3 emitted the pressure wave 5.

[0044] After step S4, the detection unit 4 detects the pressure wave 5 (step S5). Immediately after step S5, the detection information acquisition unit 37 acquires detection information from the detection unit 4 (step S6). This detection information includes information on the time (timing) when the detection unit 4 detected the pressure wave 5.

[0045] The steps S4 to S6 can be rearranged as needed. For example, steps S4 and S6 may be performed after step S5. However, step S6 must always be performed after step S5.

[0046] After step S6, the speed acquisition unit 40 acquires the propagation speed of the pressure wave 5 based on the detection information of the pressure wave 5 (step S7). In step S7, first, as shown in Figure 9, the delay time acquisition unit 38 acquires the delay time based on the emission information and the detection information (step S71). Here, for example, the delay time acquisition unit 38 calculates the time difference between when the emission unit 3 emits the pressure wave 5 and when the detection unit 4 detects the wave, and this time difference is taken as the delay time. After that, the sensor distance acquisition unit 39 acquires the sensor distance L (step S72). Note that the steps S71 to S72 can be rearranged as appropriate. For example, step S71 may be performed after step S72. Also, for example, step S72 may be performed before step S7.

[0047] After steps S71 to S72, the velocity acquisition unit 40 calculates the propagation speed (speed of sound) from the delay time and the distance L between sensors (step S73). One example of the simplest method for step S73 is for the velocity acquisition unit 40 to divide the distance L between sensors by the delay time (method of dividing the distance L between sensors by the delay time). In this embodiment, by following the procedures of steps S71 to S73, step S7 is completed and the propagation speed of the pressure wave 5 is acquired. Here, the setting unit 33 sets the frequency of the pressure wave 5 to be less than or equal to the resonance frequency between the bubbles 2b in the fluid 2 and the pressure wave 5. Therefore, in step S7, the two-phase sound speed of the pressure wave 5 is acquired.

[0048] After step S7, the void fraction acquisition unit 41 acquires the void fraction in the fluid 2 based on the propagation speed (two-phase sound speed) acquired in step S7 (step S8). In this embodiment, the void fraction acquisition unit 41 uses the correlation between two-phase sound speed and void fraction shown in Figure 3 to convert the two-phase sound speed acquired by the speed acquisition unit 40 into void fraction.

[0049] After following the steps above, the acquisition of the void fraction is complete.

[0050] (Effects and Benefits) According to this embodiment, the following effects and advantages are achieved.

[0051] In this embodiment, the void fraction acquisition system comprises a flow path 10, an injection unit 3, a detection unit 4, and a control device 30. A fluid 2 that can be in a gas-liquid two-phase state containing bubbles 2b in liquid 2a flows through the flow path 10. The injection unit 3 emits a pressure wave 5 into the fluid 2. The detection unit 4 detects the pressure wave 5. The control device 30 comprises a resonance frequency acquisition unit 32, a setting unit 33, a velocity acquisition unit 40, and a void fraction acquisition unit 41. The resonance frequency acquisition unit 32 acquires the resonance frequency of bubbles 2b in the fluid 2. The setting unit 33 sets the frequency of the pressure wave 5 emitted by the injection unit 3 to be lower than the resonance frequency. The velocity acquisition unit 40 acquires the propagation velocity of the pressure wave 5 based on the detection information from the detection unit 4. The void fraction acquisition unit 41 acquires the void fraction in the fluid 2 based on the propagation velocity.

[0052] Incidentally, since there is a correlation between the propagation speed (two-phase sound velocity) of the pressure wave 5 (longitudinal wave) in a gas-liquid two-phase system and the void fraction, the void fraction can be obtained based on the two-phase sound velocity. However, if the frequency of the pressure wave 5 is higher than the resonant frequency of the bubble 2b, the propagation speed of the pressure wave 5 becomes the propagation speed in the liquid single-phase system (single-phase sound velocity), and the two-phase sound velocity cannot be determined. Also, the resonant frequency tends to decrease as the bubble diameter increases. In contrast, with the above configuration, by setting the frequency of the pressure wave 5 (longitudinal wave) lower than the resonant frequency of the bubble 2b, the propagation speed (two-phase sound velocity) of the pressure wave 5 in a gas-liquid two-phase system can be obtained. As mentioned above, there is a correlation between the two-phase sound velocity and the void fraction, so the accurate void fraction in the fluid 2 can be obtained based on the obtained two-phase sound velocity. Therefore, accurate evaluation of the void fraction becomes possible.

[0053] Furthermore, the pressure wave 5 generated by the discharge section 3 is a sound wave. The speed of sound is sufficiently greater than the flow velocity of the fluid 2. Therefore, the flow direction of the fluid 2 can be ignored with respect to the propagation direction of the pressure wave 5 (sound wave).

[0054] Furthermore, when using a pressure wave 5 (sound wave) in the audible range, it becomes possible to measure bubbles 2b with higher resonant frequencies. Also, the higher the resonant frequency, the smaller the bubble diameter. Therefore, by using a pressure wave 5 (sound wave) in the audible range, it becomes possible to measure the void fraction of bubbles 2b with a diameter of a few millimeters or less.

[0055] In this embodiment, the discharge unit 3 and the detection unit 4 are installed on the outer wall surface 12 of the flow path 10.

[0056] With the above configuration, the ejection unit 3 and detection unit 4 can be installed outside the flow path 10. Therefore, even if the flow path 10 is under high pressure, the ejection unit 3 and detection unit 4 are not affected by that high pressure. Thus, the void fraction acquisition system 1 can be applied to high-pressure environments. In addition, the void fraction acquisition system 1 can be easily retrofitted to existing equipment. Maintainability is also improved.

[0057] In this embodiment, the discharge unit 3 is a discharge-side piezoelectric element 3a. The discharge-side piezoelectric element 3a vibrates when a voltage is applied, and this vibration generates pressure in the fluid 2. The detection unit 4 is a detection-side piezoelectric element 4a. The detection-side piezoelectric element 4a converts the detected pressure wave 5 into an electrical signal and transmits it to the control device 30.

[0058] With the above configuration, the control device 30 can electrically obtain emission information that the emission unit 3 has emitted the pressure wave 5, and detection information that the detection unit 4 has detected the pressure wave 5. Therefore, responsiveness is improved, and more accurate measurement of the void fraction becomes possible.

[0059] In this embodiment, the discharge unit 3 and the detection unit 4 are arranged opposite each other in a direction perpendicular to the fluid flow direction Df (for example, the radial direction).

[0060] With the above configuration, the detection unit 4 can receive the pressure wave 5 directly in front of it. As a result, the detection intensity by the detection unit 4 is maximized. Therefore, the detection accuracy is improved, making it possible to obtain the void fraction more accurately.

[0061] <Second Embodiment> Hereinafter, the void fraction acquisition system 101 and void fraction acquisition method according to the second embodiment of this disclosure will be described with reference to Figures 10 to 13. Configurations common to the embodiments described above will be given the same names or reference numerals, and their descriptions will be omitted as appropriate.

[0062] In this embodiment, as shown in Figures 10 and 11, the void fraction acquisition system 101 comprises a flow path 110, a heating element 7, an outlet unit 3, a detection unit 4, a control device 130, and an input device 6.

[0063] (Flow channel) In this embodiment, for the sake of simplicity, the flow path 110 is a rectangular parallelepiped (rectangular duct-shaped) container extending in one direction (flow direction Df). Hereinafter, the direction in which the flow path 110 extends will be referred to as the first direction D1, the direction perpendicular to the first direction D1 will be referred to as the second direction D2, and the direction perpendicular to both the first direction D1 and the second direction D2 will be referred to as the third direction D3. The first direction D1 coincides with the flow direction Df. The flow path 110 opens on both sides of the first direction D1. The flow path 110 has a pair of first side walls 113 facing the second direction D2 and a pair of second side walls 114 facing the third direction D3. One of the first side walls 113 has a heat transfer surface 115 on its inner wall surface 111. The heat transfer surface 115 transfers heat from the heat-generating element 7, which will be described later, to the fluid 2.

[0064] (heating element) The heating element 7 is provided on the outer wall surface 112 of one of the first side walls 113. The heat from the heating element 7 is transferred to the fluid 2 via the heat transfer surface 115.

[0065] (Ejection unit, detection unit) The discharge unit 3 is provided on the outer wall surface 112 of one of the second side walls 114. The detection unit 4 is provided on the outer wall surface 112 of the other second side wall 114. In this embodiment as well, the discharge unit 3 and the detection unit 4 are arranged opposite each other in a direction perpendicular to the flow direction Df. Furthermore, both the discharge unit 3 and the detection unit 4 are provided at the same position as the heating element 7 in the flow direction Df. Also, the discharge unit 3 and the detection unit 4 are provided at positions close to the heating element 7 in the second direction D2. The discharge unit 3 emits a pressure wave 5 along the heat transfer surface 115.

[0066] (Control device) As shown in Figure 12, the control device 130 includes a resonance frequency calculation information acquisition unit 31, a resonance frequency acquisition unit 32, a setting unit 33, an ejection operation unit 34, an ejection information acquisition unit 35, a detection operation unit 36, a detection information acquisition unit 37, a delay time acquisition unit 38, a distance acquisition unit 39 between sensors, a velocity acquisition unit 40, a void fraction acquisition unit 41, and a boiling determination unit 42.

[0067] (Boiling judgment section) The boiling determination unit 42 determines whether or not the fluid 2 is boiling based on the void fraction.

[0068] (Procedure for obtaining void fraction) Next, an example of a method for obtaining the void fraction according to this embodiment will be described with reference to the flowchart in Figure 13. As shown in Figure 13, in this embodiment, steps S1 to S8 are performed in the same procedure as in the first embodiment, for example.

[0069] After step S8, the boiling determination unit 42 determines whether or not the fluid 2 is boiling based on the void fraction obtained in step S8 (step S9). In step S9, the boiling determination unit 42 determines whether or not the void fraction is below a predetermined value. If the void fraction is below the predetermined value (step S9; YES), the boiling determination unit 42 determines that the fluid 2 is not boiling (step S10). On the other hand, if the void fraction is not below the predetermined value (step S9; NO), the boiling determination unit 42 determines that the fluid 2 is boiling (step S11). The predetermined value of the void fraction that serves as the basis for the determination in step S9 (hereinafter simply referred to as the predetermined value) is pre-entered by the operator, for example, via the input device 6. The predetermined value can be set as appropriate. For example, the predetermined value can be set in the range of 0 to 0.001 (0% to 0.1%). The setting range of the predetermined value is not limited to the above range and can be set as appropriate.

[0070] Furthermore, it is desirable that the predetermined value be 0 (0%). That is, in step S9, it is desirable to determine whether or not the void fraction is 0 (0%). In this case, if the void fraction is 0 (0%) or less (the void fraction is 0 (0%)) (step S9; YES), the boiling determination unit 42 determines that the fluid 2 is not boiling (step S10). On the other hand, if the void fraction is not the predetermined 0 or less (the void fraction is not 0 (0%)) (step S9; NO), the boiling determination unit 42 determines that the fluid 2 is boiling (step S11). After step S9, all the steps of the void fraction acquisition method of this embodiment are completed.

[0071] (Effects and Benefits) According to this embodiment, the following effects and advantages are achieved.

[0072] In this embodiment, the discharge unit 3 is positioned to emit pressure waves 5 along the heat transfer surface 115.

[0073] On the heat transfer surface 115, bubbles 2b are generated when the liquid 2a boils. With the above configuration, the void fraction near the heat transfer surface 115 can be obtained. This allows us to see, for example, that boiling does not occur when the void fraction is 0, and that boiling occurs when the void fraction is not 0.

[0074] For example, if the subcooling degree of the main fluid 2 is high, the generated boiling bubbles will condense and disappear. In contrast, in this embodiment, the discharge unit 3 and the detection unit 4 are installed near the heat transfer surface 115.

[0075] With the above configuration, the void fraction can be obtained before the generated boiling bubbles condense and disappear. Therefore, the presence or absence of boiling can be determined more accurately.

[0076] <Third Embodiment> Hereinafter, the void fraction acquisition system 201 and void fraction acquisition method according to the third embodiment of this disclosure will be described with reference to Figures 14 to 18. Components common to the embodiments described above will be given the same names or reference numerals, and their descriptions will be omitted as appropriate.

[0077] In this embodiment, as shown in Figures 14 and 15, the void fraction acquisition system 201 comprises a flow path 10, a heating element 7, an outlet unit 203, a detection unit 4, a control device 230, and an input unit 6.

[0078] (Ejection section) The discharge unit 203 in this embodiment is a striking device 203a that strikes the flow path 10. The striking device 203a emits a pressure wave 5 into the fluid 2 by striking the flow path 10. Hereinafter, the portion of the flow path 10 that is struck by the striking device 203a will be referred to as the striking point 204. The striking point 204 is located, for example, upstream Dfu of the detection unit 4. The striking point 204 may also be located downstream Dfd of the detection unit 4, or it may be located at the same position as the detection unit 4 in the flow direction Df.

[0079] (Control device) As shown in Figure 16, the control device 230 includes a resonant frequency calculation information acquisition unit 31, a resonant frequency acquisition unit 32, an ejection operation unit 234, an ejection information acquisition unit 35, a detection operation unit 36, a detection information acquisition unit 37, a delay time acquisition unit 38, a distance acquisition unit 39 between sensors, a velocity acquisition unit 40, and a void fraction acquisition unit 41.

[0080] (Emission operation part) The ejection control unit 234 operates the ejection unit 203 to strike the flow path 10. As a result, a pressure wave 5 (impact sound) is ejected into the fluid 2.

[0081] (Procedure for obtaining void fraction) Next, an example of a method for obtaining the void fraction according to this embodiment will be explained with reference to the flowchart in Figure 17.

[0082] As shown in Figure 17, first, the resonance frequency acquisition unit 32 acquires the resonance frequency of the bubble 2b in the fluid 2 (step S1A). In step S1A, for example, the resonance frequency is acquired using the same procedure as in the first embodiment (steps S11 to S12).

[0083] Subsequently, the worker performs a modification on the flow path 10 (step S2A). In step S2A, the flow path 10 is modified so that when the flow path 10 is struck in a later step, the frequency of the pressure wave 5 propagating in the fluid 2 becomes smaller than the resonant frequency. An example of the modification in step S2A is to attach adjustment members 13 such as fins or support materials to the inner wall surface 11 or outer wall surface 12 of the flow path 10, as shown in Figure 18. The shape of the flow path 10 changes as a result of the modification in step S2A. This changes the vibrations transmitted to the fluid 2 through the flow path 10, or the flow of the fluid 2 is disturbed by the adjustment members 13 in the flow path 10, causing the bubble diameter of the bubbles 2b in the fluid 2 to change (decrease). As the bubble diameter decreases, the resonant frequency becomes larger than the pressure wave 5. The installation location of the adjustment member 13 can be changed as appropriate. The adjustment member 13 may be provided on both the inner wall surface 11 and the outer wall surface 12 of the flow path 10, or on only one of the inner wall surface 11 or the outer wall surface 12. The shape and number of adjustment members 13 can also be changed as appropriate depending on the conditions. Furthermore, this is merely one example of a manufacturing method. The frequency of the pressure wave 5 may be adjusted to be lower than the resonant frequency of the flow path 10 by other manufacturing methods (for example, a method of creating irregularities in the flow path 10).

[0084] After step S2A, the ejection unit 203 (impact device 203a) strikes the flow path 10 (step S3A). This causes a pressure wave 5 (longitudinal wave, impact sound in this embodiment) to be ejected into the fluid 2. Immediately after step S3A, the ejection information acquisition unit 35 acquires ejection information from the ejection unit 203 (step S4A). This ejection information includes information on the time (timing) when the ejection unit 203 ejected the pressure wave 5.

[0085] After step S4A, the detection unit 4 detects the pressure wave 5 (step S5A). Immediately after step S5A, the detection information acquisition unit 37 acquires detection information from the detection unit 4 (step S6A). This detection information includes information on the time (timing) when the detection unit 4 detected the pressure wave 5.

[0086] The steps S4A to S6A can be rearranged as needed. For example, steps S4A and S6A may be performed after step S5. However, step S6A must always be performed after step S5A.

[0087] After step S6A, the velocity acquisition unit 40 acquires the propagation speed (two-phase sound speed) of the pressure wave 5 based on the detection information of the pressure wave 5 (step S7A). In step S7A, for example, the propagation speed of the pressure wave 5 is acquired using the same procedure as in the first embodiment (steps S71 to S73). The delay time acquisition unit 38 acquires the delay time based on the emission information and the detection information (step S71). In this embodiment, the delay time is the time it takes for the pressure wave 5 to propagate from the impact point 204 to the detection unit 4. Subsequently, the inter-sensor distance acquisition unit 39 acquires the inter-sensor distance L (step S72). In this embodiment, the inter-sensor distance L is the shortest distance between the impact point 204 and the detection unit 4. After steps S71 to S72, the velocity acquisition unit 40 calculates the propagation speed (sound speed) from the delay time and the inter-sensor distance L (step S73). By following the above procedure, step S7A is completed, and the propagation speed (two-phase sound velocity) of pressure wave 5 is obtained.

[0088] After step S7A, the void fraction acquisition unit 41 acquires the void fraction in the fluid 2 based on the propagation speed (two-phase sound speed) (step S8A). In this embodiment, the void fraction acquisition unit 41 uses the correlation between two-phase sound speed and void fraction shown in Figure 3 to convert the two-phase sound speed acquired by the speed acquisition unit 40 into void fraction. After the above procedure, the acquisition of the void fraction is completed.

[0089] (Effects and Benefits) According to this embodiment, the following effects and advantages are achieved.

[0090] In this embodiment, the void fraction acquisition method includes the steps of: acquiring the resonance frequency of bubbles 2b in a fluid 2 that can be in a gas-liquid two-phase state containing bubbles 2b in liquid 2a; working on the flow path 10 through which the fluid 2 flows so that the frequency of the pressure wave 5 propagating in the fluid 2 becomes smaller than the resonance frequency when the flow path 10 is struck; striking the flow path 10; detecting the pressure wave 5 propagating in the fluid 2 due to the striking of the flow path 10; acquiring the propagation speed of the pressure wave 5 based on the detection information of the pressure wave 5; and acquiring the void fraction in the fluid 2 based on the propagation speed.

[0091] According to the above configuration, a pressure wave 5 (longitudinal wave) with a frequency lower than the resonant frequency of the bubble 2b can be applied to the fluid 2. This makes it possible to obtain the propagation speed (two-phase sound velocity) of the pressure wave 5 in the gas-liquid two-phase system. Since there is a correlation between the two-phase sound velocity and the void fraction, the accurate void fraction in the fluid 2 can be obtained based on the obtained two-phase sound velocity. In addition, the impact sound generated by striking the flow path 10 is used as the pressure wave 5. The impact sound is generally more intense than the pressure wave 5 produced by the piezoelectric element. Therefore, the pressure wave 5 becomes easier to detect. Thus, the measurement accuracy of the void fraction is further improved.

[0092] Furthermore, the pressure wave 5 generated by the impact becomes an audible impact sound. Therefore, it becomes possible to measure the bubbles 2b and the void fraction in a frequency range higher than the audible range.

[0093] (Modified version of the third embodiment) Next, a modified example of the third embodiment, a void fraction acquisition system 201 and a void fraction acquisition method, will be described with reference to Figures 19 and 20.

[0094] In this modified example, as shown in Figure 19, the void fraction acquisition system 201 comprises two detection units 4. The detection units 4 are spaced apart in the flow direction Df. The striking device 203a is located in the flow direction Df, excluding the area between the two detection units 4. In the illustrated example, the striking device 203a is located upstream Dfu of the two detection units 4, but it may also be located downstream Dfd of the two detection units 4.

[0095] (Procedure for obtaining void fraction) Next, an example of a method for obtaining the void fraction according to this modified example will be explained with reference to the flowchart in Figure 20. In this modified example, the method for obtaining the void fraction is performed using the same procedure as in the third embodiment described above. In the following, the procedure that is the same as in the third embodiment described above will be omitted, and the procedure that differs from the third embodiment will be described.

[0096] Steps S1A to S3A are performed in the same manner as in the third embodiment. In this modified example, the step in which the ejection information acquisition unit 35 acquires ejection information from the ejection unit 203 (step S4A) is omitted. After step S5A is performed, the detection information acquisition unit 37 acquires detection information from the two detection units 4 (step S6B).

[0097] After step S6B, the speed acquisition unit 40 acquires the propagation speed (two-phase sound speed) of the pressure wave 5 based on the detection information of the pressure wave 5 (step S7B). In step S7B, for example, the propagation speed of the pressure wave 5 is acquired using the same procedure as in the first embodiment (steps S71 to S73). In this modified example, the delay time acquisition unit 38 acquires the delay time based on two pieces of detection information (step S71). In this modified example, the delay time is the time it takes for the pressure wave 5 to propagate from one detection unit 4 (the detection unit 4 closer to the impact point 204) to the other detection unit 4 (the detection unit 4 further from the impact point 204). In this modified example, the delay time acquisition unit 38 calculates the time difference between when one detection unit 4 detects the pressure wave 5 and when the other detection unit 4 detects the wave, and this time difference is taken as the delay time. After that, the inter-sensor distance acquisition unit 39 acquires the inter-sensor distance L (step S72). In this modified example, the inter-sensor distance L is the shortest distance between the two detection units 4. After steps S71 and S72, the velocity acquisition unit 40 calculates the propagation speed (sound speed) from the delay time and the distance L between sensors (step S73). By following the above procedure, step S7B is completed and the propagation speed (two-phase sound speed) of the pressure wave 5 is acquired.

[0098] After step S7B, step S8A is performed in the same manner as in the third embodiment to obtain the void fraction. The acquisition of the void fraction is completed through these steps.

[0099] (Effects and Benefits) According to this modified example, the following effects and benefits are achieved.

[0100] In this modified example, two detection units 4 are provided. This allows the control device 30 to obtain the propagation velocity (two-phase sound velocity) from the detection information of the two detection units 4, even if the ejection information of the ejection unit 203 (impact device 203a) cannot be obtained accurately or electrically, and to obtain the void fraction from the obtained propagation velocity.

[0101] In the third embodiment, the case in which the flow path 10 is struck by the ejection unit 203 (impact device 203a) to generate a pressure wave 5 was described. However, the ejection unit 203 (impact device 203a) is not required. In this case, the flow path 10 may be struck by, for example, the operator's hand.

[0102] Furthermore, the void fraction acquisition system 201 of the third embodiment may also have the boiling determination unit 42 of the second embodiment.

[0103] <Hardware Configuration> The control devices 30, 130, and 230 of the above embodiments and modified examples are implemented in the computer 1100 shown in Figure 21. Figure 21 is a schematic block diagram showing the configuration of the computer 1100 according to each embodiment. The computer 1100 includes a processor 1110, main memory 1120, storage 1130, and interface 1140.

[0104] The operations of each of the above-mentioned functional units of the control devices 30, 130, and 230 are stored in the storage 1130 in the form of a program. The processor 1110 reads the program from the storage 1130, loads it into the main memory 1120, and executes the above-mentioned processes according to the program. The processor 1110 also allocates storage space in the main memory 1120 according to the program.

[0105] The program may be for the purpose of realizing some of the functions that the computer 1100 is to perform. For example, the program may perform functions in combination with other programs already stored in the storage 1130, or in combination with other programs implemented in other devices. In addition, the computer 1100 may be equipped with a custom LSI (Large Scale Integrated Circuit) such as a PLD (Programmable Logic Device) in addition to or instead of the above configuration. Examples of PLDs include PAL (Programmable Array Logic), GAL (Generic Array Logic), CPLD (Complex Programmable Logic Device), and FPGA (Field Programmable Gate Array). In this case, some or all of the functions realized by the processor 1110 may be realized by the integrated circuit.

[0106] Examples of storage 1130 include magnetic disks, magneto-optical disks, and semiconductor memory. Storage 1130 may be an internal medium directly connected to the bus of computer 1100, or an external medium connected to computer 1100 via interface 1140 or a communication line. Furthermore, if this program is distributed to computer 1100 via a communication line, computer 1100 that receives the program may expand it into main memory 1120 and execute the above processing. Storage 1130 may also be a tangible storage medium that is not temporary.

[0107] Furthermore, the program may be intended to implement some of the functions described above. In addition, the program may be a so-called differential file (differential program) that implements the functions described above in combination with other programs already stored in the storage 1130.

[0108] (Other embodiments) Although embodiments of this disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and may include design changes and the like that do not depart from the gist of this disclosure.

[0109] In the embodiments described above, the case in which the flow paths 10 and 110 extend in one direction has been explained, but the invention is not limited to this. For example, the flow paths 10 and 110 may be curved. Also, the flow paths 10 and 110 may be partially narrowed or widened in diameter. Furthermore, the flow paths 10 and 110 may be branched.

[0110] <Note> The void fraction acquisition system and void fraction acquisition method described in each embodiment can be understood, for example, as follows.

[0111] (1) The void fraction acquisition system 1, 101 according to the first embodiment comprises a flow path 10, 110 through which a fluid 2 that can be in a gas-liquid two-phase state containing bubbles 2b in a liquid 2a flows, an ejection unit 3 that ejects a pressure wave 5 into the fluid 2, a detection unit 4 that detects the pressure wave 5, and control devices 30, 130, wherein the control devices 30, 130 comprises a resonance frequency acquisition unit 32 that acquires the resonance frequency of bubbles 2b in the fluid 2, a setting unit 33 that sets the frequency of the pressure wave 5 from the ejection unit 3 to be lower than the resonance frequency, a speed acquisition unit 40 that acquires the propagation speed of the pressure wave 5 based on the detection information from the detection unit 4, and a void fraction acquisition unit 41 that acquires the void fraction in the fluid 2 based on the propagation speed.

[0112] With the above configuration, by setting the frequency of the pressure wave 5 (longitudinal wave) lower than the resonance frequency of the bubble 2b, the propagation speed of the pressure wave 5 (two-phase sound velocity) in the gas-liquid two-phase system can be obtained. Since there is a correlation between the two-phase sound velocity and the void fraction, the accurate void fraction in the fluid 2 can be obtained based on the acquired two-phase sound velocity.

[0113] (2) The void fraction acquisition systems 1, 101 of the second embodiment are the void fraction acquisition systems 1, 101 of (1), wherein the ejection unit 3 and the detection unit 4 may be installed on the outer wall surfaces 12, 112 of the flow channels 10, 110.

[0114] With the above configuration, the discharge unit 3 and the detection unit 4 can be installed outside the flow paths 10 and 110. Therefore, even if the flow paths 10 and 110 are under high pressure, the discharge unit 3 and the detection unit 4 will not be affected by that high pressure. Thus, the void fraction acquisition systems 1 and 101 can be applied to high-pressure environments.

[0115] (3) A third embodiment of the void fraction acquisition system 1, 101 is the void fraction acquisition system 1, 101 of (1) or (2), comprising a heating element 7, wherein the flow channels 10, 110 have a heat transfer surface 115 on the inner wall surface 11, 111 that transfers the heat of the heating element 7 to the fluid 2, and the discharge section 3 may discharge the pressure wave 5 along the heat transfer surface 115.

[0116] On the heat transfer surface 115, bubbles 2b are generated when the liquid 2a boils. With the above configuration, the void fraction near the heat transfer surface 115 can be obtained. This allows us to see, for example, that boiling does not occur when the void fraction is 0, and that boiling occurs when the void fraction is not 0.

[0117] (4) A fourth embodiment of a method for obtaining void fraction includes the steps of: obtaining the resonance frequency of bubbles 2b in a fluid 2 that can be in a gas-liquid two-phase state containing bubbles 2b in a liquid 2a; setting the frequency of a pressure wave 5 emitted into the fluid 2 to be lower than the resonance frequency; emitting the pressure wave 5 into the fluid 2; detecting the pressure wave 5; obtaining the propagation speed of the pressure wave 5 based on the detection information of the pressure wave 5; and obtaining the void fraction in the fluid 2 based on the propagation speed.

[0118] (5) A fifth embodiment of the method for obtaining the void fraction includes the steps of: obtaining the resonance frequency of bubbles 2b in a fluid 2 that can be in a gas-liquid two-phase state containing bubbles 2b in a liquid 2a; working on the flow paths 10 and 110 through which the fluid 2 flows so that the frequency of the pressure wave 5 propagating in the fluid 2 becomes smaller than the resonance frequency when the flow paths 10 and 110 are struck; striking the flow paths 10 and 110; detecting the pressure wave 5 propagating in the fluid 2 due to the striking of the flow paths 10 and 110; obtaining the propagation speed of the pressure wave 5 based on the detection information of the pressure wave 5; and obtaining the void fraction in the fluid 2 based on the propagation speed.

[0119] According to the above configuration, a pressure wave 5 (longitudinal wave) with a frequency lower than the resonant frequency of the bubble 2b can be applied to the fluid 2. This makes it possible to obtain the propagation speed (two-phase sound velocity) of the pressure wave 5 in the gas-liquid two-phase system. Since there is a correlation between the two-phase sound velocity and the void fraction, the accurate void fraction in the fluid 2 can be obtained based on the acquired two-phase sound velocity. [Explanation of symbols]

[0120] 1. Void Factor Acquisition System 2 fluid 2a liquid 2b Air bubbles 3. Ejection section 3a Output side piezoelectric element 4. Detection Unit 4a Detecting side piezoelectric element 5. Pressure Waves 6 Input devices 7 Heating element 10 channels 11 Interior wall surface 12 Exterior wall surface 13 Adjustment Member 30 Control device 31 Resonance frequency calculation information acquisition section 32 Resonant frequency acquisition section 33 Settings Section 34 Output operation section 35 Emission information acquisition section 36 Detection operation unit 37 Detection Information Acquisition Unit 38 Delay Time Acquisition Unit 39 Sensor distance acquisition unit 40 Speed ​​acquisition section 41 Void fraction acquisition unit 42 Boiling judgment section 101 Void Factor Acquisition System 110 flow path 111 Interior wall surface 112 Exterior wall surface 113 First side wall 114 Second side wall 115 Heat transfer surface 130 Control device 201 Void Factor Acquisition System 203 Ejection section 203a Impact device 204 RBIs 230 Control device 234 Output operation section 1100 Computer 1110 processor 1120 Main Memory 1130 storage 1140 Interface Df flow direction Dfu upstream side Dfd downstream side Da axial direction D1 1st direction D2 2nd direction D3 Third direction L Distance between sensors O axis

Claims

1. A flow channel through which a fluid that can exist in a gas-liquid two-phase state containing air bubbles in the liquid flows, A discharge unit that emits pressure waves into the fluid, The detection unit for detecting the pressure wave, Control device and Equipped with, The control device is A resonance frequency acquisition unit that acquires the resonance frequency of bubbles in the fluid, A setting unit that sets the frequency of the pressure wave emitted by the emission unit to be lower than the resonance frequency, A speed acquisition unit that acquires the propagation speed of the pressure wave based on the detection information of the detection unit, A void fraction acquisition unit that acquires the void fraction in the fluid based on the aforementioned propagation speed, A void fraction acquisition system equipped with the following features.

2. The discharge unit and the detection unit are installed on the outer wall surface of the flow path. The void ratio acquisition system according to claim 1.

3. Equipped with a heating element, The flow path has a heat transfer surface on its inner wall surface that transfers the heat from the heating element to the fluid. The void fraction acquisition system according to claim 1 or 2, wherein the emission unit emits the pressure wave along the heat transfer surface.

4. A step of obtaining the resonant frequency of a bubble in a fluid that can be in a gas-liquid two-phase state containing a bubble in the liquid, The steps include setting the frequency of the pressure wave emitted into the fluid to be lower than the resonance frequency, The steps include: emitting the pressure wave into the fluid; The steps include detecting the pressure wave, A step of obtaining the propagation speed of the pressure wave based on the detection information of the pressure wave, A step of obtaining the void fraction in the fluid based on the propagation velocity, A method for obtaining the void fraction, including the void fraction.

5. A step of obtaining the resonant frequency of a bubble in a fluid that can be in a gas-liquid two-phase state containing a bubble in the liquid, The steps include: modifying the fluid passage so that when the fluid passage is struck, the frequency of the pressure wave propagating in the fluid becomes lower than the resonant frequency; The steps of striking the aforementioned flow path, The steps include detecting a pressure wave propagating in the fluid due to an impact on the flow path, A step of obtaining the propagation speed of the pressure wave based on the detection information of the pressure wave, A step of obtaining the void fraction in the fluid based on the propagation velocity, A method for obtaining the void fraction, including the void fraction.

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