Ultrasonic probe, probe mounting device, and ultrasonic flow measurement system

Abstract

The present invention provides a means to increase the refraction angle of ultrasound on the inner surface of a pipe carrying cryogenic fluid compared to conventional methods, and to reduce ultrasound waves other than the central wave entering the cryogenic fluid, thereby improving the accuracy of detecting the propagation time of ultrasound. [Solution] The wedge 20 has a first surface 21, a second surface 22, and a third surface 23 that are perpendicular to the central plane 4 containing the central axis Z. The first surface is located parallel to the central axis and has a reference point A to which the transverse wave center wave TC is incident. The second surface has a reflection point B that converts the longitudinal wave center wave PC into a transverse wave center wave TC and reflects it. The third surface has a longitudinal wave transmission point C to which the ultrasonic transducer 12 is attached and which emits the longitudinal wave center wave PC. The incident angle θ1 of the reference point A is set to be between 65° and 75°, and the incident angle θ3 of the reflection point B is set to be between 65° and 75°. In addition, the contact medium 30 is located in an usable angle range α of 5° to 10° with respect to the incident angle θ1.

Description

Technical Field

[0001] The present invention relates to a means for measuring the flow rate of cryogenic fluids such as liquid oxygen, liquid nitrogen, liquefied natural gas, etc. using ultrasonic waves.

Background Art

[0002] In engine combustion test facilities for conducting combustion tests such as rocket engines, in the measurement of the flow rate of cryogenic fluids such as liquid oxygen and liquid nitrogen, conventionally, in-line turbine flow meters have been mainly used.

[0003] However, the in-line turbine flow meter had the following problems. (1) To prevent the turbine from idling, pre-cooling work before the test requires time and cost. (2) Removal work is required for equipment calibration, and it cannot be used during that period. (3) Due to the large inertia of the turbine, the responsiveness is low and transient phenomena cannot be measured. Therefore, it has been proposed to measure the flow rate of cryogenic fluids using ultrasonic waves (for example, Patent Documents 1 and 2).

[0004] The "ultrasonic flow meter" of Patent Document 1 includes a flow path body having a measurement flow path through which the measurement fluid flows, a pair of opening holes provided in the flow path body at a predetermined angle with respect to the flow direction of the measurement flow path, a pair of ultrasonic transceivers attached to the pair of opening holes, and a measurement calculation unit. The measurement calculation unit measures the propagation time of ultrasonic waves between the pair of ultrasonic transceivers and calculates the flow velocity and flow rate of the measured fluid.

[0005] The "ultrasonic flow meter probe mounting jig for cryogenic use" of Patent Document 2 includes an annular frame formed by connecting an upper frame having a substantially inverted U shape and a lower frame having a substantially U shape while supporting the ultrasonic probe. The gaps between the ends of the upper and lower frames are made expandable and contractible by a spring mechanism. Two ultrasonic probes, each holding a transmitting and receiving ultrasonic transducer, are mounted on the outer wall of the tube through which the cryogenic fluid flows, facing each other across the tube using probe mounting fixtures. The measurement and calculation unit measures the propagation time of ultrasound between the two ultrasonic probes and calculates the flow rate of the cryogenic fluid. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2024-15189 [Patent Document 2] Japanese Patent Application Publication No. 10-221137 [Overview of the project] [Problems that the invention aims to solve]

[0007] Patent documents 1 and 2 describe a method in which a pair of ultrasonic transducers (or ultrasonic probes) are mounted opposite each other across a pipe through which a fluid flows, and the propagation time of the ultrasonic waves between them is measured to calculate the flow velocity and flow rate of the fluid being measured. Therefore, the aforementioned problems of turbine flow meters can be avoided.

[0008] However, in the case of Patent Document 1, it is necessary to separately manufacture a flow channel body having a pair of openings and insert it into the middle of an existing facility such as an engine combustion test facility (a pipeline through which cryogenic fluid flows). Furthermore, the flow of cryogenic fluid through a flow channel is affected because the flow channel area is not uniform and changes, which can negatively impact the flow of the cryogenic fluid.

[0009] On the other hand, in the case of Patent Document 2, existing equipment (pipelines through which cryogenic fluid flows) is used as is, so the problems of Patent Document 1 can be avoided. However, Patent Document 2 had the following problems.

[0010] (1) Because the ultrasonic probe is an oblique probe using a conventional wedge-shaped blade, the ultrasonic waves emitted by the ultrasonic transducer are longitudinal waves (hereinafter referred to as "longitudinal ultrasonic waves"). Therefore, the angle of refraction of the ultrasonic waves when they enter the cryogenic fluid from the inner surface of the pipe (the angle with respect to the plane perpendicular to the central axis of the pipe) is small. This refraction angle is approximately 14° when the angle of incidence of longitudinal ultrasound is 70°. Therefore, when the inner diameter of a pipe through which cryogenic fluid flows is small, the propagation time of ultrasound is short, resulting in low accuracy in detecting time differences.

[0011] (2) The central wave of the ultrasonic waves incident on the surface of the pipe has a divergence angle (direction angle), and ultrasonic waves within the direction angle range are emitted into the cryogenic fluid via the contact medium sandwiched between the wedge and the outer surface of the pipe. Ultrasound waves outside the central wave's directional angle range are incident on the receiving ultrasonic probe and detected as noise. This reduces the accuracy of detecting the ultrasonic wave propagation time.

[0012] This invention was devised to solve the problems described above. Specifically, the object of this invention is to provide a means that can increase the refraction angle of ultrasound on the inner surface of a pipe carrying cryogenic fluid compared to conventional methods, and reduce ultrasound waves other than the central wave entering the cryogenic fluid, thereby improving the detection accuracy of the ultrasound propagation time. [Means for solving the problem]

[0013] According to the present invention, an ultrasonic transmitter / receiver that transmits and receives longitudinal ultrasonic waves, A metal wedge that converts the longitudinal ultrasonic waves into transverse ultrasonic waves and transmits them to the outside, An ultrasonic probe having a metal contact medium sandwiched between the wedge and the outer surface of a pipe through which a cryogenic fluid flows, thereby propagating the transverse ultrasonic waves between them, The wedge has a first surface, a second surface, and a third surface that are perpendicular to the central plane containing the central axis of the piping, The first surface is located parallel to the central axis and close to the outer surface of the pipe, and has a reference point A to which the transverse wave center of the transverse ultrasonic wave is incident. The second surface has a reflection point B that converts the longitudinal wave center wave of the longitudinal wave ultrasonic wave into the transverse wave center wave of the transverse wave ultrasonic wave and reflects it. The third surface has a longitudinal wave transmission point C to which the ultrasonic transmitter / receiver is attached and that transmits the longitudinal wave center wave. The incident angle θ1 of the transverse wave center wave at the reference point A is set to be 66° or more and 74° or less. The incident angle θ3 of the longitudinal wave center wave at the reflection point B is set to be 60° or more and 70° or less. An ultrasonic probe is provided, in which the contact medium is located within the utilization angle range of the transverse wave ultrasonic wave with respect to the incident angle θ1, and the utilization angle range α is set to an angle smaller than the directivity angle.

[0014] Further, according to the present invention, there is provided a probe mounting device that presses the ultrasonic probe inward in the radial direction of the pipe to attach the wedge to the outer surface of the pipe, wherein the probe mounting device includes: a probe side member that sandwiches the wedge between it and the outer surface of the pipe; a counter-probe side member that is positioned opposite to the probe side member with the pipe sandwiched therebetween; and a connecting member that elastically connects the probe side member and the counter-probe side member. The connecting member applies a compression force within a predetermined range to the wedge on the outer surface of the pipe in the measurement temperature range of the cryogenic fluid, and a probe mounting device is provided.

[0015] Furthermore, according to the present invention, there is provided an ultrasonic flow measurement system including: the ultrasonic probe as described above; and a signal detection device that detects transmission signals and reception signals of ultrasonic waves between the ultrasonic probe attached to the outer surface of the pipe on the upstream side and the ultrasonic probe attached to the outer surface of the pipe on the diametrically opposite side and downstream side of the pipe in a central plane including the central axis; and a flow rate calculation device that calculates the flow rate of the fluid from the transmission signals and the reception signals.

[0016] In order to increase the refraction angle of ultrasonic waves on the inner surface of the cryogenic fluid pipe (the angle with respect to the plane perpendicular to the central axis of the pipe), the incident angle of the ultrasonic waves at the reference point A on the first surface is preferably as close to 90° as possible. However, in the case of an incident angle exceeding the critical angle (about 74.6° in the case of titanium), most of the ultrasonic waves are totally reflected on the inner surface of the wedge, so the ratio of the ultrasonic waves entering the cryogenic fluid through the pipe becomes very small. Therefore, in the present invention, the incident angle θ1 of the ultrasonic waves at the reference point A is set to be 66° or more and 74° or less, which is less than the critical angle.

[0017] Further, according to the present invention, since the longitudinal wave ultrasonic waves are mode-converted into transverse wave ultrasonic waves and reflected on the second surface of the wedge, the transverse wave center wave of the transverse wave ultrasonic waves is incident on the reference point A of the first surface. Since the sound velocity of the ultrasonic waves in the metal wedge is different for longitudinal waves and transverse waves, the refraction angle of the ultrasonic waves on the inner surface of the cryogenic fluid pipe, for example, is about 27° when the incident angle of the transverse wave ultrasonic waves is 70°, which can be larger than that in the case of the incidence of longitudinal wave ultrasonic waves (about 14°).

[0018] Further, according to the present invention, since the incident angle θ3 of the longitudinal wave center wave at the reflection point B on the second surface is set to be 60° or more and 70° or less, most (about 90%) of the longitudinal wave ultrasonic waves can be reflected as transverse wave ultrasonic waves at the reflection point B.

[0019] Note that a part of the longitudinal wave ultrasonic waves is reflected as longitudinal wave ultrasonic waves at the reflection point B, but the reflection angle of the longitudinal wave center wave is equal to the incident angle θ3, while the reflection angle of the transverse wave center wave is significantly smaller than the incident angle θ3. For example, when the incident angle θ3 of the longitudinal wave center wave is 67°, the reflection angle of the transverse wave center wave is about 28°. With this configuration, the longitudinal wave center wave reflected on the second surface can be separated from the transverse wave center wave and diffused and eliminated in the wedge, so that the noise incident on the ultrasonic probe on the receiving side can be reduced.

[0020] Furthermore, according to the present invention, the contact medium is located within the usable angle range of transverse ultrasonic waves with respect to the incident angle θ1 of ultrasonic waves at reference point A, and the usable angle range α is set to an angle smaller than the directional angle (for example, 5° or more and 10° or less). This configuration allows only the transverse ultrasonic waves near the transverse wave center to be transmitted from the wedge to the outer surface of the pipe for use, while transverse ultrasonic waves outside the usable angle range α are diffused and annihilated within the wedge. This prevents transverse ultrasonic waves outside the usable angle range α from entering the receiving ultrasonic probe and being detected as noise.

[0021] Therefore, according to the present invention, the refraction angle of ultrasound on the inner surface of a pipe carrying cryogenic fluid can be increased compared to conventional methods, and the ultrasound waves other than the central wave entering the cryogenic fluid can be reduced, thereby improving the accuracy of detecting the ultrasound propagation time. [Brief explanation of the drawing]

[0022] [Figure 1] This is a cross-sectional view of the ultrasonic probe according to the present invention, attached to the outer surface of a pipe. [Figure 2] This diagram shows the relationship between the incident angle of longitudinal ultrasonic waves and the sound pressure reflectance of longitudinal and transverse waves within pure titanium. [Figure 3] This is a view from the direction of arrow XX in Figure 1. [Figure 4] This is a view from the YY arrow in Figure 1. [Figure 5] This is a diagram illustrating the shape of the contact medium. [Figure 6] This is an overall configuration diagram of the ultrasonic flow measurement system according to the present invention. [Figure 7] This is a schematic diagram of one pair of transmitted signals and one pair of received signals. [Figure 8] This is an explanatory diagram of the method for calculating time difference according to the present invention. [Figure 9] This figure shows the test results of the flow rate measurement test. [Figure 10] This diagram shows the relationship between the standard flow rate and the measured flow rate. [Figure 11] This diagram shows the relationship between test time and measured flow rate in a combustion test. [Modes for carrying out the invention]

[0023] Preferred embodiments of the present invention will be described below with reference to the drawings. In each figure, common parts are denoted by the same reference numerals, and redundant explanations are omitted.

[0024] Figure 1 is a cross-sectional view of the ultrasonic probe 10 according to the present invention when attached to the outer surface of a pipe. In this example, 1 is the cryogenic fluid, 2 is the pipe, 3 is the outer surface of pipe 2, Z is the central axis of pipe 2, and 4 is the central plane. The cryogenic fluid 1 is, for example, liquid oxygen or liquid nitrogen. The temperature of liquid oxygen or liquid nitrogen is, for example, -183°C to -164°C. Pipe 2 is, for example, a circular pipe made of stainless steel (SUS304) or titanium. The central plane 4 is the plane containing the central axis Z of pipe 2, which in this example is parallel to the plane of the paper.

[0025] In Figure 1, the ultrasonic probe 10 includes an ultrasonic transducer 12, a wedge 20, and a contact medium 30.

[0026] The ultrasonic transducer 12 transmits and receives longitudinal ultrasonic waves (hereinafter referred to as "longitudinal ultrasonic waves P"). In other words, the ultrasonic transducer 12 can be used as a transmitter or receiver of longitudinal ultrasonic waves P. The ultrasonic transducer 12 is preferably a piezoelectric element made of lithium niobate. This is because lithium niobate has a stable structure in a temperature range from cryogenic temperatures to 1650°C, and the piezoelectric effect is not impaired.

[0027] The wedge 20 receives longitudinal ultrasonic waves P from the ultrasonic transducer 12, converts the mode to transverse ultrasonic waves (hereinafter referred to as "transverse ultrasonic waves T") and transmits them to the outside (in this example, the cryogenic fluid 1), and receives transverse ultrasonic waves T from the outside, converts the mode to longitudinal ultrasonic waves P and inputs it to the ultrasonic transducer 12. The wedge 20 is made of metal, preferably pure titanium.

[0028] The ultrasonic transducer 12 is directly brazed to the wedge 20 with an aluminum-based brazing material. Furthermore, since one end of the piezoelectric element (ultrasonic transducer 12) is at the same potential as the wedge 20, the wedge 20 is grounded via the jig and piping. With this configuration, the interface between the ultrasonic transducer 12 and the wedge 20 is completely filled with the brazing material, preventing the formation of an air gap, thus increasing the propagation efficiency of ultrasonic waves between the ultrasonic transducer 12 and the wedge 20.

[0029] The contact medium 30 is sandwiched between the wedge 20 and the outer surface 3 of the pipe 2 through which the cryogenic fluid 1 flows (hereinafter referred to as "pipe outer surface 3"), and transmits transverse ultrasonic waves T between them. The contact medium 30 can be installed at room temperature or low temperature, and is preferably a substance that does not generate a gas layer at the contact surface with the outer surface of the pipe at the extremely low temperature (-183°C to -164°C) of an cryogenic fluid (liquid oxygen or liquid nitrogen). The contact medium 30 is preferably a metal with a coefficient of thermal expansion similar to that of the piping and less likely to generate a gas layer at the contact surface due to temperature changes. Furthermore, it is preferable that the contact medium 30 is flexible at the temperature in which it is used.

[0030] In the embodiment described later, annealed oxygen-free copper was used as the contact medium 30. The coefficient of linear expansion of copper is approximately 16.8 (×10⁻⁶). -6 It is approximately 17.3 (×10) for stainless steel. -6 It has a value close to ( / °C). Furthermore, "annealed oxygen-free copper" is a solid that is flexible and easily deformable in a temperature range from extremely low temperatures (e.g., -200°C) to room temperature, and has the characteristic of adhering closely to the curved surface of the outer surface of pipes.

[0031] In Figure 1, the wedge 20 has a first surface 21, a second surface 22, and a third surface 23 that are perpendicular to the central plane 4 (a plane parallel to the plane of the paper) containing the central axis Z of the piping.

[0032] The first surface 21 is located parallel to the central axis Z and close to the outer surface 3 of the pipe, and has a reference point A to which the transverse wave center wave TC of the transverse wave ultrasonic T is incident. The second surface 22 has a reflection point B that reflects the longitudinal wave center wave PC of the longitudinal wave ultrasonic wave P after mode conversion to the transverse wave center wave TC of the transverse wave ultrasonic wave T. The third surface 23 has a longitudinal wave source point C to which an ultrasonic transducer 12 is attached and which emits a longitudinal wave center wave PC. The transverse wave center wave TC and longitudinal wave center wave PC mentioned above are located in the central plane 4.

[0033] In Figure 1, the incidence angle θ1 of the transverse wave center wave TC at reference point A is set to 66° or more and 74° or less (preferably 70°). In this case, the transverse wave center wave TC propagates through the contact medium 30 and the pipe 2 to the inner surface 2a of the pipe, and then refracts and enters the cryogenic fluid from the inner surface 2a of the pipe. The angle of incidence of the transverse wave center wave TC at the refraction point D on the inner surface of the pipe can be considered to be the same as the angle of incidence θ1 at the reference point A, because the speed of sound in the contact medium 30 and the pipe 2 are substantially equal.

[0034] In order to increase the refraction angle θ2 of the ultrasonic waves on the inner surface of the pipe through which the cryogenic fluid 1 flows (the angle with respect to a plane perpendicular to the central axis of the pipe), it is preferable that the incident angle θ1 of the ultrasonic waves at reference point A on the first surface 21 be as close to 90° as possible. However, in the case of an incident angle exceeding the critical angle, most of the ultrasonic waves are totally reflected on the inner surface of the wedge (first surface 21), so the proportion of ultrasonic waves that enter the cryogenic fluid through the pipe becomes very small. Assuming the refractive index of titanium is 2.153 and that of air is 1.0, the critical angle is approximately 74.6°. Therefore, by setting the incidence angle θ1 of the transverse wave center wave at reference point A to 66° or more and 74° or less, which is less than the critical angle, the proportion of ultrasonic waves reflected by the outer surface 3 of the pipe can be reduced, and the proportion of ultrasonic waves refracted from the inner surface 2a of the pipe into the cryogenic fluid can be increased.

[0035] Figure 2 shows the relationship between the incident angle of longitudinal wave ultrasonic waves P and the sound pressure reflectance of longitudinal and transverse waves within pure titanium. This figure shows that when the incidence angle θ3 of the longitudinal wave center wave PC is between 60° and 70°, most of the longitudinal wave ultrasound P (approximately 90%) is converted to transverse wave ultrasound T and reflected. Therefore, in Figure 1, the incident angle θ3 of the longitudinal wave center wave PC at reflection point B is set to 60° or more and 70° or less (preferably 67°) so that most of the longitudinal wave ultrasonic waves P are converted into transverse wave ultrasonic waves T and reflected at reflection point B.

[0036] In this case, at reflection point B, the longitudinal wave velocity c1, the transverse wave velocity c2, the incident angle θ3 of the longitudinal wave ultrasound P (longitudinal wave center PC), and the reflection angle θ4 of the transverse wave ultrasound T (transverse wave center TC) are related by the following equation: c2·sin(θ3)=c1·sin(θ4)···(1).

[0037] Table 1 shows the velocities of longitudinal and transverse waves in air, stainless steel, and titanium.

[0038] [Table 1]

[0039] From Table 1, the longitudinal wave velocity c1 in pure titanium is approximately 6100 m / s and the transverse wave velocity c2 is approximately 3120 m / s. Therefore, from equation (1), if the incidence angle θ3 of the longitudinal wave center PC is 67°, the reflection angle θ4 of the transverse wave center TC is approximately 28°.

[0040] Furthermore, in Figure 1, the second surface 22 is set to have a first obtuse angle θ5 = θ1 + θ4 ... (2) relative to the first surface 21. In the embodiment described later, the incidence angle θ1 of the transverse wave center wave TC at reference point A was set to 70°, the incidence angle θ3 at reflection point B was set to 67°, and the first obtuse angle θ5 was set to 98° (=70+28). With this configuration, at any position on the second surface 22, the angle of incidence θ1 and the angle of reflection θ4 relative to the angle of incidence θ3 can be set to angles that satisfy equation (1).

[0041] Furthermore, in Figure 1, the third surface 23 is set to a first acute angle θ6 = θ3···(3) with respect to the second surface 22. In the embodiment described later, the incident angle θ3 of the reflection point B was set to 67°, and the first acute angle θ6 was set to 67°. This configuration allows the angle of incidence θ3 with respect to the second surface 22 to be set to the first acute angle θ6 at any position on the third surface 23.

[0042] Note that at reflection point B, some of the longitudinal wave ultrasound P is reflected as longitudinal wave ultrasound P, but in this case the reflection angle of the longitudinal wave center wave PC is equal to the incident angle θ3. Therefore, if the incident angle θ3 of the longitudinal wave center wave PC is 67°, the reflection angle of the longitudinal wave center wave PC will also be 67°. Therefore, in Figure 1, the longitudinal wave center wave PC reflected by the second surface 22 has a significantly different reflection angle from the transverse wave center wave TC, and can be reflected and diffused within the wedge outside the contact medium 30, thereby being eliminated. This reduces the noise incident on the receiving ultrasonic probe.

[0043] In Figure 1, the contact medium 30 is located within the usable angle range α of the transverse ultrasonic wave T, with respect to the incidence angle θ1 of the transverse wave center wave TC at reference point A. In this example, the usable angle range α is set to an angle smaller than the directional angle (in this example, 5° or more and 10° or less). The directionality of ultrasound varies depending on the ultrasonic transducer (piezoelectric element), but it is usually greater than 10°.

[0044] This configuration allows only the transverse ultrasonic waves T near the transverse wave center wave TC to be transmitted from the wedge 20 to the outer surface 3 of the pipe via the contact medium 30 and utilized, while the transverse ultrasonic waves T outside the usable angle range α can be diffused within the wedge. This configuration prevents transverse ultrasonic waves T outside the usable angle range α from being transmitted to the outer surface 3 of the pipe and detected as noise incident on the receiving ultrasonic probe.

[0045] In Figure 1, the first surface 21 has a first a surface 21a and a first b surface 21b.

[0046] Surface 1a 21a includes reference point A and is located within the usable angle range α of transverse ultrasonic wave T. The first b surface 21b is closer to the outer surface 3 than the first a surface 21a, and surrounds the first a surface 21a, with a step 21c between them. The step 21c is preferably 0.5 to 1 mm. Furthermore, the contact medium 30 is in close contact with the first a surface 21a and housed inside the step 21c, and protrudes radially inward from the first b surface 21b of the pipe 2, and is positioned in close contact with the outer surface 3.

[0047] Figure 3 is a view from the direction of arrow XX in Figure 1.

[0048] In Figure 3(A), the usable angle range α of the transverse ultrasonic wave T has an ellipse with the central plane 4 as its central axis (axis of symmetry). Note that the reference point A may be offset from the center of the ellipse within the central plane. In Figure 3(A), the shape of the step 21c coincides with the usable angle range α. Furthermore, the plan view shape of the contact medium 30 is located inside the step 21c, and its plan view shape coincides with the usable angle range α.

[0049] As shown in Figure 3(B), the shape of the step 21c may be located inside the usable angle range α, and the contact medium 30 may also be located inside the step 21c. In this case, the shape of the step 21c and the contact medium 30 may be circular, rectangular (rectangle or square), or any other shape, as shown in this figure.

[0050] Furthermore, as shown in Figure 3(C), if the ratio of the first a surface 21a to the first surface 21 is small, the step 21c and a portion of the contact medium 30 may be located outside the usable angle range α. In this case, the area near the central plane 4 is strongly pressed against the outer surface 3 of the pipe by the probe mounting device 40 (described later), making it difficult for a gas layer to form on the contact surface. On the other hand, at positions away from the central plane 4 (outside the usable angle range α in this example), the pressing force is relatively low, making it easier for a gas layer to form and potentially preventing the contact medium from functioning properly.

[0051] The configuration of the step 21c and the contact medium 30 described above allows the contact medium 30 to be positioned at an optimal location including the reference point A, and prevents the contact medium 30 from shifting position when the ultrasonic probe 10 is attached and positioned.

[0052] In Figure 1, the wedge 20 is located radially outward of the pipe 2, opposite the first surface a 21a, and has a fourth surface 24 parallel to the first surface a 21a.

[0053] The probe mounting device 40 according to the present invention is a device that attaches the wedge 20 to the outer surface 3 of the pipe by applying pressure to the ultrasonic probe 10 described above in the radial direction inward of the pipe 2.

[0054] Figure 4 is a view along the YY arrow in Figure 1. In this figure, the probe mounting device 40 comprises a probe-side member 42, an anti-probe-side member 44, and a connecting member 46.

[0055] The probe-side member 42 sandwiches the wedge 20 between itself and the outer surface 3 of the pipe. In this example, the probe-side member 42 has a pressurizing portion 42a having a pressurizing surface 43 that contacts the fourth surface 24 of the wedge 20, and a pair of first protruding portions 42b extending in opposite directions from the pressurizing portion 42a to the radially outer side of the pipe.

[0056] The anti-probe side member 44 is positioned opposite the probe side member 42, with the pipe 2 in between. In this example, the anti-probe side member 44 has a pressure-receiving portion 44a having a pressure-receiving surface 45 that faces the fourth surface 24 and contacts the outer surface 3 of the pipe, and a pair of second protrusions 44b. The pair of second protrusions 44b extend in the opposite direction from the pressure-receiving portion 44a to the radially outer side of the pipe 2 and are positioned opposite the pair of first protrusions 42b.

[0057] In this example, a pair of first protrusions 42b are located radially outward from the pipe 2 and have a pair of first through holes 42c that are perpendicular to the central axis Z of the pipe 2 and parallel to the central plane 4. The pair of second protrusions 44b are positioned opposite the pair of first through holes 42c and have a pair of second through holes 44c that are perpendicular to the central axis Z of the pipe 2 and parallel to the central plane 4.

[0058] The connecting member 46 presses the wedge 20 against the outer surface 3 of the pipe with a predetermined range of compressive force within the measurement temperature range of the cryogenic fluid 1. In this example, the connecting member 46 elastically connects the probe-side member 42 and the anti-probe-side member 44 on the radially outer side of the pipe 2.

[0059] The connecting member 46 has a pair of bolts 47 extending through a first through hole 42c and a second through hole 44c, and a pair of nuts 49 that are screwed onto the pair of bolts 47 via a pair of metal coil springs 48. The coil spring 48 is set to maintain a predetermined range of compressive force within the measurement temperature range of the cryogenic fluid.

[0060] With the configuration of the probe mounting device 40 described above, a predetermined range of compressive force can be applied to the contact medium 30 within the measurement temperature range of the cryogenic fluid, and ultrasonic waves can be stably propagated between the wedge 20 and the outer surface 3 of the pipe.

[0061] Figure 5 is an explanatory diagram of the shape of the contact medium 30. In this figure, (A) is a partially enlarged view of Figure 4, and (B) and (C) are schematic diagrams of the contact medium 30 before the wedge 20 is pressed against the outer surface 3 of the pipe.

[0062] As shown in Figure 5(A), in the operating state, the contact medium 30 preferably has its upper surface perpendicular to the central plane 4 (horizontal plane) and its lower surface a concave arc surface along the outer surface 3 of the pipe. Therefore, the shape of the contact medium 30 before pressing the wedge 20 against the outer surface 3 of the pipe is preferably such that the top surface is flat and the bottom surface is a flat surface parallel to the top surface (see Figure 5(B)), or a cylindrical surface that bulges downward in the center (see Figure 5(C)).

[0063] Furthermore, according to the embodiments of the present invention described above, the longitudinal ultrasonic waves P are converted to transverse ultrasonic waves T and reflected by the second surface 22 of the wedge 20, so that the transverse wave center wave TC of the transverse ultrasonic waves T is incident on the reference point A of the first surface 21. Because the speed of sound in a metal wedge differs between longitudinal and transverse waves, the refraction angle θ2 of ultrasound on the inner surface of a pipe carrying cryogenic fluid can be made larger than that of longitudinal ultrasound (approximately 14°), for example, when the incidence angle of transverse ultrasound is 70°, which is about 27°. The refraction angle θ2 of ultrasound is the angle with respect to a plane perpendicular to the central axis of the pipe.

[0064] Furthermore, according to the embodiments of the present invention described above, since the incidence angle θ3 of the longitudinal wave center wave PC at reflection point B is set to 60° or more and 70° or less, most of the longitudinal wave ultrasonic waves P (approximately 90%) can be reflected as transverse wave ultrasonic waves T at reflection point B.

[0065] While some of the longitudinal ultrasonic waves P are reflected as they are, the reflection angle of the longitudinal wave center wave PC is equal to the incident angle θ3, whereas the reflection angle of the transverse wave center wave TC is significantly smaller than the incident angle θ3. For example, if the incidence angle θ3 of a longitudinal wave center wave PC is approximately 67°, the reflection angle of a transverse wave center wave TC is approximately 28°. This configuration allows the longitudinal wave center wave PC reflected by the second surface 22 to be separated from the transverse wave center wave TC, diffused and canceled out within the wedge, thereby reducing noise incident on the receiving ultrasonic probe.

[0066] Furthermore, according to the embodiments of the present invention described above, the contact medium 30 is located within the usable angle range α of the transverse ultrasonic wave T with respect to the incident angle θ1 of the ultrasonic wave at the reference point A, and the usable angle range α is set to be 5° or more and 10° or less. This configuration allows only the transverse ultrasonic waves T near the transverse wave center wave TC to be transmitted from the wedge 20 to the outer surface 3 of the pipe for use, while transverse ultrasonic waves outside the usable angle range α are diffused and annihilated within the wedge. This prevents transverse ultrasonic waves outside the usable angle range α from entering the receiving ultrasonic probe and being detected as noise.

[0067] Accordingly, according to the embodiments of the present invention described above, the refraction angle θ2 of ultrasonic waves at the inner surface 2a of the pipe of the cryogenic fluid 1 can be made larger than in the conventional method, and ultrasonic waves other than the central wave entering the cryogenic fluid 1 can be reduced, thereby improving the detection accuracy of the ultrasonic wave propagation time.

[0068] Figure 6 is an overall configuration diagram of the ultrasonic flow measurement system 100 according to the present invention. In this figure, the ultrasonic flow measurement system 100 comprises a pair of the aforementioned ultrasonic probes 10, a signal detection device 50, and a flow rate calculation device 60.

[0069] A pair of ultrasonic probes 10 consists of an upstream ultrasonic probe 10A attached to the outer surface 3 of the upstream pipe, and a downstream ultrasonic probe 10B attached to the outer surface 3 of the downstream pipe 2, within a central plane containing the central axis Z. The upstream ultrasonic probe 10A and the downstream ultrasonic probe 10B are located on opposite sides of the piping in the diametrical direction.

[0070] Furthermore, the axial distance between the piping of the upstream ultrasonic probe 10A and the downstream ultrasonic probe 10B is set so that the refraction angle θ2 of the ultrasonic waves is equal to the plane in which the line connecting the refraction points D described above is perpendicular to the central axis Z. Note that this axial distance does not need to be exactly the refraction angle θ2 and may be finely adjusted as appropriate.

[0071] In Figure 6, L is the straight-line distance between the upstream and downstream refraction points D, θ is the angle of this straight line with respect to a plane perpendicular to the central axis Z, d is the inner diameter of the pipe, V is the average flow velocity of the cryogenic fluid 1, and c is the speed of sound in the cryogenic fluid. Furthermore, the propagation time of ultrasound from the upstream ultrasound probe 10A to the downstream ultrasound probe 10B is defined as the first propagation time t1, and the propagation time of ultrasound from the downstream ultrasound probe 10B to the upstream ultrasound probe 10A is defined as the second propagation time t2.

[0072] In this case, the following equation holds true. t1=L / (c+Vcosθ), t2=L / (c-Vcosθ)...(4)

[0073] From equation (4), if we set t2-t1=Δt, the flow rate Q of the cryogenic fluid can be calculated using the following equation. Q=(πd 2 / 4) × (c 2 Δt) / 2L(cos(90-θ))···(5)

[0074] The signal detection device 50 applies a transmission signal S1 to one of the pair of ultrasonic probes 10 to transmit ultrasonic waves into the cryogenic fluid, and detects the received signal S2 from the ultrasonic transducer 12 on the other probe. Furthermore, the signal detection device 50 detects a pair of transmitted signals S11, S12 and a pair of received signals S21, S22 when ultrasound is transmitted from the upstream ultrasonic probe 10A and when ultrasound is transmitted from the downstream ultrasonic probe 10B.

[0075] Figure 7 is a schematic diagram of a pair of transmitted signals S11 and S12 and a pair of received signals S21 and S22.

[0076] The flow rate calculation device 60 calculates the fluid flow rate from a pair of transmitted signals S11 and S12 and a pair of received signals S21 and S22. In other words, in this example, the flow rate calculation device 60 calculates the fluid flow rate from the time difference Δt between the pair of received signals S21 and S22 shown in Figure 7 using equation (5).

[0077] In Figure 7, the pair of transmission signals S11 and S12 should preferably have a pulse waveform preceded by a negative pulse and an oscillation frequency of 1.

[0078] Figure 8 is an explanatory diagram of the method for calculating the time difference Δt according to the present invention. Figure 8(A) is a schematic diagram of the received signal S21 (hereinafter referred to as the "forward received signal") when ultrasound is transmitted from the upstream ultrasound probe 10A and the received signal S22 (hereinafter referred to as the "reverse received signal") when ultrasound is transmitted from the downstream ultrasound probe 10B.

[0079] (range selection) In this invention, the ranges for the forward received signal and the reverse received signal are specified first. The range specification defines a signal processing range that includes both the forward and reverse received signals, assuming that the ultrasonic transmission times coincide, and extracts the signals within this signal processing range. Figure 8(B) shows the waveforms after range selection. The waveform extracted from the forward received signal is called the "forward waveform," and the waveform extracted from the reverse received signal is called the "reverse waveform." Furthermore, during this extraction process, the amplitude is corrected so that the peak heights of the forward and reverse waveforms are the same.

[0080] (Cross-correlation) Next, in this invention, the forward waveform and the reverse waveform are cross-correlated to generate (create) a processed waveform. Cross-correlation processing corrects the inverse waveform so that its correlation with the forward waveform is maximized, using the peak position of the forward waveform as the origin. "Peak position" refers to the location in the measured waveform data where the amplitude value is largest.

[0081] Figure 8(C) shows the processed waveform after cross-correlation processing.

[0082] (True peak position) Next, in this invention, the true peak position is calculated. In Figure 8(C), if there is only one position with the maximum peak height, that position is considered the "true peak position". Furthermore, in Figure 8(C), if there are two adjacent points with substantially the maximum peak height, the true peak position is considered to lie between them, and the true peak position is calculated by interpolation using the three points with peak heights near the maximum.

[0083] (Flow rate of cryogenic fluid) The flow rate of the cryogenic fluid is calculated using equation (5) with the time difference Δt from the origin (peak position of the forward waveform) to the true peak position of the processed waveform. [Examples]

[0084] Ultrasonic flow measurement was performed using the ultrasonic flow measurement system described above (hereinafter referred to as "this system"). The test conditions were as follows. (Piping) As a substitute for piping through which cryogenic fluids flow, stainless steel piping (SUS304, 40A) was attached to the existing kerosene inspection line, and the ultrasonic probe 10 described above was attached to this stainless steel piping using the probe mounting device 40 described above. (Fluid conditions) Kerosene was used as a substitute for the cryogenic fluid, and tests were conducted within a temperature range of 22°C to 28°C and a flow rate range of 20 to 1000 L / min. (Flow rate measuring device) For comparative flow measurement, a volumetric flow meter standard meter (hereinafter referred to as the "standard") and a comparative ultrasonic flow meter (PT878, manufactured by GE, hereinafter referred to as the "other company's meter") were used. (Data acquisition conditions) The data acquisition interval was set to 100 S / sec, the waveform sampling frequency to 100 MHz, the high-pass filter to 2 MHz, and the low-pass filter to 5 MHz. (flow rate) The flow rate of the standard instrument (test flow rate) was gradually changed to 280, 250, 200, 250, 100, and 50 L / min, and the flow rate was measured using this system and a meter from another company.

[0085] Figure 9 shows the test results of the flow rate measurement test. In this figure, the horizontal axis represents the passage of time, and the vertical axis represents the measured flow rate. The wide band A in the figure represents the measured values ​​of this system, line B located approximately in the center of the band represents the moving average of the measured values ​​of this system, and line C located below the center of the band represents the measured values ​​of another company's meter.

[0086] A "moving average" is a value obtained by taking the average value for time-series data within a certain range, shifting that range, and then averaging the result to smooth the data. In this example, the moving average is a "100-period moving average".

[0087] As shown in Figure 9, the measured values ​​for A, B, and C all yielded results similar to those of the test flow rate change. In particular, the moving average of B accurately matched the test flow rate. Furthermore, a comparison of the measured values ​​of B and C reveals that when the test flow rate changes, the measured value of C may not keep pace with the flow rate change and may become interrupted, while the moving average of B is able to keep pace with the flow rate change. [Examples]

[0088] The same test as in Example 1 was performed by varying the standard flow rate from 0 to 1000 L / min.

[0089] Figure 10 shows the relationship between the standard flow rate and the measured flow rate, with (A) showing the relationship for the entire range of the standard flow rate from 0 to 1000 L / min, and (B) showing the relationship for a partial range of the standard flow rate from 100 to 500 L / min. In each figure, the horizontal axis represents the standard instrument flow rate, the vertical axis represents the measured flow rate, ● in the figure represents the moving average according to the present invention, ▲ represents the measured value of another company's meter, and the space between the upper and lower horizontal lines (-) represents the maximum and minimum measured values ​​of this system.

[0090] The following points were confirmed from these test results. (1) The moving average according to the present invention is in good agreement with the standard flow rate (flow rate of a volumetric flow meter), and linearity can be confirmed in the range of 0 to 1000 L / min. (2) The relative error between the moving average and the standard instrument flow rate according to the present invention is ±5% or less in the range of 0 to 1000 L / min and ±2% or less in the range of 100 to 300 L / min. (3) Under steady conditions, the flow rate measurements obtained by this system have the same accuracy as those of standard instruments and meters from other companies. [Examples]

[0091] This system was used to measure the flow rate of LNG during engine combustion tests. In this example, a turbine flow meter was used as the standard instrument. The moving average according to the present invention is a "10-period moving average" in this example.

[0092] Figure 11 shows the relationship between test time and measured flow rate in a combustion test, where (A) shows the entire combustion time from 55 to 95 seconds, (B) shows the period immediately after ignition from 62 to 67 seconds, and (C) shows the period towards the end of combustion from 80 to 90 seconds. Furthermore, in each figure, the band-shaped portion A, which has width vertically, represents the measured values ​​of this system, while lines B and C, located approximately in the center of the band-shaped portion, represent the moving average and the measured values ​​of the standard instrument (turbine flow meter) according to the present invention.

[0093] The following points were confirmed from these test results. (1) The moving average according to the present invention exhibits low variability and can capture transient phenomena. In particular, in Figures 11(B) and 11(C), a discrepancy is observed between the moving average according to the present invention and the measured value of the standard instrument, indicating that the moving average according to the present invention tracks transient phenomena more effectively. (2) At the maximum LNG flow rate (80-82 seconds), the relative error was -1.11%. (3) The discrepancy with the turbine flow meter is small at high LNG flow rates, but large at low flow rates. This is likely because the turbine's inertia causes larger errors in the turbine flow meter when measuring low flow rates.

[0094] With the configuration of the ultrasonic flow measurement system 100 described above, the time difference Δt between a pair of received signals S21 and S22 can be accurately detected, and the fluid flow rate can be accurately calculated using equation (5). Furthermore, as shown in the above-described embodiments, the ultrasonic flow measurement system 100 of the present invention provides a moving average that closely matches the standard flow rate (flow rate of a volumetric flow meter), has less variation than a turbine flow meter, and can capture transient phenomena.

[0095] It should be noted that the present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit of the invention. [Explanation of Symbols]

[0096] A Reference point, B Reflection point, C Longitudinal wave source point, c Speed ​​of sound in cryogenic fluid, D Refraction point, d Pipe inner diameter, c1 Longitudinal wave velocity, c2 Transverse wave velocity, P Longitudinal wave ultrasound, PC Longitudinal wave center wave, S1, S11, S12 Transmitted signals, S2, S21, S22 Received signals, T Transverse wave ultrasound, TC Transverse wave center wave, Δt Time difference, L Straight-line distance to refraction point, θ1 Incidence angle of transverse wave center wave, θ2 Refraction angle of ultrasound, θ3 Incidence angle of longitudinal wave center wave, θ4 Reflection angle of transverse wave center wave, θ5 First obtuse angle, θ6 First acute angle, α Usable angle range, 1 Cryogenic fluid, 2 Pipe, 2a Inner surface of pipe, 3 Outer surface of pipe, Z Central axis of pipe, 4 Center plane, 10 Ultrasonic probe, 10A Upstream ultrasonic probe, 10B Downstream ultrasonic probe, 12 Ultrasonic transducer, 20 wedge, 21 first surface, 21a first a surface, 21b first b surface, 21c step, 22 second surface, 23 third surface, 24 fourth surface, 30 contact medium, 40 probe mounting device, 42 probe side member, 42a pressurizing part, 42b first protrusion, 42c first through hole, 43 pressurizing surface, 44 anti-probe side member, 44a pressure receiving part, 44b second protrusion, 44c second through hole, 45 pressure receiving surface, 46 connecting member, 47 bolt, 48 coil spring, 49 nut, 50 signal detection device, 60 flow rate calculation device, 100 ultrasonic flow rate measurement system

Claims

1. An ultrasonic transmitter / receiver that transmits and receives longitudinal ultrasonic waves, A metal wedge that converts the longitudinal ultrasonic waves into transverse ultrasonic waves and transmits them to the outside, An ultrasonic probe having a metal contact medium sandwiched between the wedge and the outer surface of a pipe through which a cryogenic fluid flows, thereby propagating the transverse ultrasonic waves between them, The wedge has a first surface, a second surface, and a third surface that are perpendicular to the central plane containing the central axis of the piping, The first surface is located parallel to the central axis and close to the outer surface of the pipe, and has a reference point A to which the transverse wave center wave of the transverse ultrasonic wave is incident. The second surface has a reflection point B that reflects the longitudinal wave center wave of the longitudinal wave ultrasonic wave after mode conversion to the transverse wave center wave of the transverse wave ultrasonic wave. The third surface has a longitudinal wave source point C to which the ultrasonic transducer is attached and which emits the longitudinal wave center wave, The incidence angle θ1 of the transverse wave center wave at the aforementioned reference point A is set to 66° or more and 74° or less. The incidence angle θ3 of the longitudinal wave center at the reflection point B is set to 60° or more and 70° or less. The contact medium is located within the usable angle range of the transverse ultrasonic wave with respect to the incident angle θ1, and the usable angle range α is set to an angle smaller than the directional angle.

2. The longitudinal wave velocity c1, transverse wave velocity c2, incidence angle θ3, and reflection angle θ4 of the transverse wave ultrasound at the reflection point B are: The relationship c² sin(θ³) = c¹ sin(θ₄) ... (1) holds, The second surface is set to a first obtuse angle θ5 = θ1 + θ4 ... (2) with respect to the first surface, The ultrasonic probe according to claim 1, wherein the third surface is set to a first acute angle θ6 = θ3 ... (3) with respect to the second surface.

3. The first surface includes a first a surface that includes the reference point A and is located within the usable angle range of the transverse ultrasonic wave, and a first b surface that is closer to the outer surface of the pipe than the first a surface, surrounds the first a surface, and has a step between them. The ultrasonic probe according to claim 1, wherein the contact medium is housed inside the step in close contact with the first a surface, and protrudes radially inward from the first b surface and is positioned in close contact with the outer surface of the pipe.

4. The ultrasonic probe according to claim 3, wherein the wedge is located radially outward of the piping opposite to the first a surface and has a fourth surface parallel to the first a surface.

5. The aforementioned wedge is made of pure titanium, The ultrasonic transducer is a piezoelectric element made of lithium niobate, and one end thereof is directly brazed to the wedge. The ultrasonic probe according to claim 1, wherein the wedge is grounded.

6. The ultrasonic probe according to claim 1, wherein the contact medium is a substance that does not generate a gas layer on the contact surface at the cryogenic temperature of a cryogenic fluid.

7. A probe mounting device for attaching the wedge to the outer surface of the pipe by applying pressure to the ultrasonic probe described in claim 1 radially inward of the pipe, A probe-side member that sandwiches the wedge between itself and the outer surface of the piping, A non-probe side member is positioned opposite the probe side member, with the piping in between, The system includes a connecting member that elastically connects the probe-side member and the anti-probe-side member, The connecting member is a probe mounting device that applies a predetermined range of compressive force to the outer surface of the pipe using the wedge within the measurement temperature range of the cryogenic fluid.

8. The probe-side member has a pressurizing portion having a pressurizing surface that contacts a fourth surface parallel to the first surface, and a pair of first protruding portions extending in opposite directions from the pressurizing portion to the radially outer side of the piping. The anti-probe side member has a pressure-receiving portion having a pressure-receiving surface that faces the fourth surface and contacts the outer surface of the pipe, and a pair of second protrusions that extend in the opposite direction from the pressure-receiving portion to the radially outer side of the pipe and are located opposite the pair of first protrusions. The probe mounting device according to claim 7, wherein the connecting member elastically connects the probe-side member and the anti-probe-side member on the radially outer side of the piping.

9. The pair of first protrusions are located radially outward from the piping and have a pair of first through holes perpendicular to the central axis and parallel to the central plane. The pair of second protrusions are positioned opposite the pair of first through holes and have a pair of second through holes that are perpendicular to the central axis and parallel to the central plane. The connecting member comprises a pair of bolts extending through the first through hole and the second through hole, It has a pair of bolts and a pair of nuts that screw into each of them via a pair of metal coil springs, The probe mounting device according to claim 8, wherein the coil spring has a predetermined range of compressive force within the measurement temperature range of the cryogenic fluid.

10. The ultrasonic probe according to claim 1, A signal detection device for detecting ultrasonic transmission and reception signals between an ultrasonic probe attached to the upstream outer surface of the pipe and an ultrasonic probe attached to the downstream outer surface of the pipe on the opposite side in the diametrical direction of the pipe, within a central plane including the central axis, An ultrasonic flow measurement system comprising a flow rate calculation device that calculates the flow rate of a fluid from the transmitted signal and the received signal.

11. The signal detection device detects a pair of transmitted signals and a pair of received signals when ultrasound is transmitted from the upstream ultrasonic probe and when ultrasound is transmitted from the downstream ultrasonic probe. The ultrasonic flow rate measurement system according to claim 10, wherein the flow rate calculation device calculates the flow rate of a fluid from the time difference of a pair of received signals.

12. The pair of received signals consists of a forward received signal when ultrasound is transmitted from the upstream side and a reverse received signal when ultrasound is transmitted from the downstream side. The flow rate calculation device, with the ultrasonic transmission timings coinciding, specifies the signal processing range for a pair of received signals and extracts the forward waveform from the forward received signal and the reverse waveform from the reverse received signal. The ultrasonic flow measurement system according to claim 11, further comprising correcting the amplitude so that the peak heights of the forward waveform and the reverse waveform are the same.

13. The flow rate calculation device further performs cross-correlation processing to correct the reverse waveform so that the correlation with the forward waveform is maximized, using the peak position of the forward waveform as the origin, and creates a processed waveform after cross-correlation processing. The true peak position of the processed waveform is calculated, The ultrasonic flow rate measurement system according to claim 12, wherein the flow rate of the cryogenic fluid is calculated using the time difference from the origin to the true peak position of the processed waveform.

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