JP6351028B2 - Perforated plate for rectifier, rectifier and flow rate measuring device - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a rectifier for a rectifier, two rectifiers arranged to rectify a flow in a circular tube, and a flow rate measuring device including the rectifier.

  In the field of handling air, water, and petroleum fluids, various types of flow meters are used. Specifically, the flow meters are roughly classified into volume flow meters and mass flow meters, and the volume flow meters are actually measured formulas (for example, a self-acting type such as a rotor type, servo type) or estimation formulas (eg differential pressure type, turbine type). Type, vortex type, electromagnetic type, ultrasonic type, etc.). On the other hand, the mass flow meter includes a direct type (for example, a thermal type, a Coriolis type, etc.) and an indirect type for simply obtaining a flow rate under a predetermined condition.

  Here, for example, a speculative flow meter is used after calibration under the condition of a sufficiently developed pipe flow (also called a developed flow or a turbulent flow velocity distribution in the pipe). Therefore, a sufficient straight pipe length is required upstream of the flow meter. However, it is difficult to secure a sufficient straight pipe length when the diameter of the pipe is increased and the installation space is rationalized by increasing the size of the plant. Therefore, for example, Patent Document 1 discloses a technique including a rectifier upstream of a flow meter.

  On the other hand, the rectifying device of Patent Document 1 is formed of a single perforated plate, and a rectifying effect on a flow accompanied by swirling cannot be expected. Specifically, piping with piping elements such as elbows, joints, and valves tends to generate swirling flow and uneven flow. This is because a single perforated plate cannot provide both functions. Thus, for example, Non-Patent Document 1 discloses a rectifier that simultaneously removes the effects of swirling flow and disturbance.

  The rectifier of Non-Patent Document 1 is formed of two perforated plates. And in order to satisfy the three conditions of removing the swirling component, that the upstream flow does not affect the downstream flow, and that the downstream flow has a sufficiently developed turbulent velocity distribution in the pipe, The perforated plate for swirl rectification is arranged on the upstream side, and the perforated plate for velocity distribution is arranged on the downstream side. As a result, the swirl flow with bias is removed, and a sufficiently developed turbulent flow velocity distribution is obtained with a short straight pipe length.

Japanese Patent Publication No. 51-37022

K. Hisayoshi, 4 others, “Study on rectifier using perforated plate”, Transactions of the Japan Society of Mechanical Engineers (B), January 1985, 51, 461, p. 106-114

However, since both Patent Document 1 and Non-Patent Document 1 are rectifiers for obtaining a sufficiently developed turbulent flow velocity distribution necessary for measuring the flow rate of, for example, a differential pressure-type throttle flow meter, When performing flow rate measurement based on a flow having a uniform axial velocity distribution necessary for flow rate measurement of an ultrasonic flowmeter (also referred to as an average flow velocity in the pipe), there is a problem that it is difficult to improve measurement accuracy.
In addition, when using a rectifier using two perforated plates, the resistance coefficient is not practical with the resistance coefficient value (for example, K = 5.0) shown in ISO5167.

  The present invention has been made in view of the above circumstances, and provides a perforated plate for a rectifier, a rectifier, and a flow measurement device that can achieve improvement in measurement accuracy when measuring flow rate based on the average flow velocity in the pipe. The purpose is to do.

In order to solve the above problems, a first technical means of the present invention is a perforated plate for a rectifier that rectifies a flow in a circular pipe, and the perforated plate penetrates the plate with a predetermined thickness. A plurality of through-holes having the same diameter, and the through-hole is arranged in a concentric circle with one central hole disposed at the center of the plate. Six first concentric holes arranged at equal intervals, six second concentric holes arranged at equal intervals on the outer side of the first concentric hole and concentrically with the central hole, and the second Six third concentric holes arranged equidistantly on the outer side of the concentric hole and concentrically with the central hole, and arranged equidistantly on the concentric circle with the central hole outside the third concentric hole. and 12 of the fourth concentric hole, and a 24 fifth concentric holes are arranged at equal intervals at the outside of the fourth concentric hole central hole concentric with In which was characterized by Rukoto.

  In a second technical means, when the inner diameter of the circular tube is D, the first concentric hole is placed on the concentric circle defined by 0.26D from the center of the plate, and the second concentric hole is placed on the plate. On the concentric circle defined by 0.42D from the center, the third concentric hole on the concentric circle defined by 0.54D from the center of the plate, and on the fourth concentric hole from the center of the plate by. The fifth concentric holes are respectively arranged on the concentric circles defined by 0.92D from the center of the plate on the concentric circles defined by 68D.

  The third technical means is characterized in that the third concentric hole communicates with the fourth concentric hole adjacent on both sides thereof.

  A fourth technical means is a rectifier including an upstream perforated plate and a downstream perforated plate, wherein the upstream perforated plate is provided through a plate having a predetermined thickness and the plate. A plurality of through-holes having the same diameter, and the through-holes of the upstream perforated plate are arranged such that the distance between adjacent ones is smaller at the center of the plate and larger toward the periphery of the plate, The plate is any one of the above-described perforated plates for a rectifying device.

  A fifth technical means is a flow rate measuring device provided with the rectifying device described above and having a flow meter for measuring a flow rate based on an average flow velocity in the pipe downstream of the downstream perforated plate. is there.

  According to the present invention, there are one central hole, six first to third concentric holes, twelve fourth concentric holes, and a through-hole consisting of 24 fifth concentric holes on the outside thereof. Since it is provided, the flow velocity near the wall of the circular tube increases, and a velocity distribution close to the average flow velocity in the tube is obtained, so that the axial velocity distribution can match the measurement result of the ultrasonic flowmeter. For this reason, for example, when the flow rate measurement is performed based on the average flow velocity in the pipe such as an ultrasonic flow meter or a thermal flow meter, it is possible to improve the measurement accuracy.

It is a perspective view explaining the piping composition provided with the rectifier of the present invention. It is a fragmentary sectional view explaining the rectifier of FIG. FIG. 3 is a front view illustrating the upstream perforated plate in FIG. 2. It is a front view explaining the perforated plate for downstream of FIG. It is a front view explaining the porous plate for downstream of 2nd Embodiment. It is a figure explaining the turning angle with respect to a present Example and a comparative example. It is a figure explaining the axial velocity distribution with respect to a present Example and a comparative example.

Hereinafter, preferred embodiments of a perforated plate for a rectifying device, a rectifying device, and a flow rate measuring device of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view illustrating a piping configuration provided with a rectifying device of the present invention.
The piping configuration 1 is, for example, a space double curved pipe, and the pipe inlet 10 to the pipe outlet 15 have a circular cross section (for example, inner diameter D = 100 mm). The pipeline inlet 10 opens toward the negative direction of the Z axis shown in FIG. 1, and the pipeline outlet 15 opens toward the positive direction of the Y axis.

The piping configuration 1 includes a first elbow 11, a second elbow 12, a rectifier 13, and a flow meter 14 between the pipe inlet 10 and the pipe outlet 15.
The distance from the pipe inlet 10 to the start end of the first elbow 11 can be indicated by, for example, a running section 25D where a developmental flow is obtained. The starting end of the first elbow 11 opens toward the negative direction of the Z axis, and the end of the first elbow 11 opens toward the negative direction of the X axis. The distance from the end of the first elbow 11 to the start of the second elbow 12 can be indicated by D, for example. The starting end of the second elbow 12 opens toward the positive direction of the X axis, and the end of the second elbow 12 opens toward the positive direction of the Y axis. Note that the radii of curvature of the first and second elbows 11 and 12 are set to 0.62D, for example, in order to generate a relatively strong swirling flow.

  Although the detailed structure of the rectifier 13 will be described with reference to FIG. 2 and the like, the rectifier 13 is disposed, for example, at a distance 2D from the end of the second elbow 12. The straight line is formed from the rectifier 13 to the pipe outlet 15, and the flow meter 14 is disposed at a position of, for example, a distance 8D from the end of the rectifier 13. In addition, the distance from the terminal end of the rectifier 13 to the pipe outlet 15 can be shown by 10D, for example.

(First embodiment)
FIG. 2 is a partial cross-sectional view for explaining the rectifier of FIG. 1, and shows a downstream side of the second elbow 12 in a cross-sectional view except for the flow meter 14 and the subsequent parts.
The rectifying device 13 includes two perforated plates including a swirl rectifying perforated plate 20 on the upstream side and a perforated plate 30 for velocity distribution on the downstream side. The swirl rectifying perforated plate 20 mainly has a function of removing swirl components, and the distance from the end of the second elbow 12 to the start end of the swirl rectifying perforated plate 20 can be represented by 2D as described above.

As shown in FIG. 2, the starting end of the swirl rectifying perforated plate 20 is Y = 0, and the center of the cross section where Y = 0 is the origin of coordinates (X, Y, Z) = (0, 0, 0 ).
On the other hand, the velocity distribution porous plate 30 mainly has a function of removing disturbance, and the starting end of the velocity distribution porous plate 30 is disposed at a distance L ₁ from the end of the swirl rectifying porous plate 20.
The swirl rectifying porous plate 20 corresponds to the upstream porous plate of the present invention, and the velocity distribution porous plate 30 corresponds to the downstream porous plate of the present invention.

The flow meter 14 can be represented by, for example, 8D as described above when the distance L ₂ from the end of the velocity distribution porous plate 30 is set. The flow meter 14 is provided with a device that measures the flow rate based on the average flow velocity in the pipe, for example, an ultrasonic flow meter or a thermal flow meter.

3 is a front view for explaining the upstream perforated plate of FIG. 2, FIG. 3 (A) is a front view of the swirl rectifying perforated plate 20, and FIG. 3 (B) is a view of the swirl rectifying perforated plate 20. A cross-sectional view is shown.
The swirl rectifying perforated plate 20 includes a disk-shaped plate 21 and a through-hole 22 formed through the plate 21. Similar to the structure shown in Non-Patent Document 1, for example, a total of 35 through-holes 22 are formed, and the upstream edge portion is chamfered, and both are formed with the same hole diameter d.

However, the hole diameter d of the through-hole 22 is set to 10 mm, for example. The opening ratio β of the swirl rectifying perforated plate 20 is 0.56. The plate thickness t of the plate 21 can be represented by 0.13D.
Here, the swirl rectifying perforated plate 20 is designed such that the resistance coefficient K has a uniform value in the radial direction and the outflow angle coefficient α is zero, and the through-holes 22 are adjacent to each other. The distance is smaller at the center of the plate 21 and larger at the periphery of the plate 21.

  Specifically, as shown in FIG. 3A, twelve through-holes 22 are provided in the first quadrant of the ZX coordinate (corresponding to a quarter circle of the plate 21). If each hole is represented by the ZX coordinates, first, the first hole h1 (Z, X) = (0,0), the second hole h2 (Z, X) = (0,0.142D), It can be shown that the third hole h3 (Z, X) = (0,0.283D) and the fourth hole h4 (Z, X) = (0,0.423D).

  Subsequently, the fifth hole h5 (Z, X) = (0.129D, 0.078D), the sixth hole h6 (Z, X) = (0.134D, 0.225D), the seventh Hole h7 (Z, X) = (0.156D, 0.381D), eighth hole h8 (Z, X) = (0.252D, 0), ninth hole h9 (Z, X) = (0.255D, 0.146D), 10th hole h10 (Z, X) = (0.288D, 0.288D), 11th hole h11 (Z, X) = (0.396D, 0), the 12th hole h12 (Z, X) = (0.400D, 0.151D).

Then, when these are expanded in a line-symmetrical position with respect to the ZX axis, in other words, when the through-holes are developed in the second to fourth quadrants of the ZX coordinates, a total of 35 through-holes 22 are formed at the center of the plate 21. While the hole distribution is dense, the hole distribution is sparse around the plate 21.
In FIG. 3, the example of the swirl rectifying perforated plate made of one plate has been described. However, in order to reduce the weight and save the material, the tube is fitted to the plate and the plate thickness t is set. A swirl rectifying perforated plate may be formed. Further, when the perforated plate for swirl rectification is sandwiched between the flanges, a region in which no hole is provided between the through-circular hole (for example, h4, h7, h10, h11, h12) located on the outermost periphery and the outer peripheral edge of the plate May be formed.

4 is a front view for explaining the downstream porous plate of FIG. 2, FIG. 4 (A) is a front view of the velocity distribution porous plate 30, and FIG. 4 (B) is for explaining the arrangement of the holes. The figure which extracted a part (30 degrees) of the perforated plate 30 for speed distribution is shown.
The velocity distribution porous plate 30 includes a disk-shaped plate 31 and a through-circular hole 32 drilled through the plate 31. The through-holes 32 are composed of, for example, a total of 55 pieces, and all are formed with the same hole diameter d.

However, the hole diameter d of the through-hole 32 is set to, for example, 10 mm, similarly to the swirl rectifying perforated plate 20, and is larger than the hole diameter 7 mm disclosed in Non-Patent Document 1. The aperture ratio β of the velocity distribution porous plate 30 is 0.54. The plate thickness t of the plate 31 can be represented by 0.035D.
Here, the velocity distribution porous plate 30 is designed such that its resistance coefficient K has a uniform value in the radial direction, and its outflow angle coefficient α also has a uniform value. According to the structure design method disclosed in Patent Document 1, holes are provided on a plurality of concentric circles.

Specifically, as shown in FIG. 4A, the through-hole 32 has one central hole H0 provided at the center of the plate 31, and, for example, a five-fold concentric circle is set around the central hole H0. Yes.
First, the first concentric holes H1 are, for example, six, and are arranged at equal intervals (for example, every 60 °) on the concentric circle with the central hole H0. As shown in FIG. 4B, the radius r1 of the concentric circle related to the first concentric hole H1 can be represented by 0.26D.

  The number of the second concentric holes H2 is, for example, six, and they are arranged at equal intervals (for example, every 60 °) on the outer side of the first concentric hole H1 and concentrically with the central hole H0. The radius r2 of the concentric circle with respect to the second concentric hole H2 can be shown as 0.42D. The third concentric holes H3 are also composed of, for example, six, and are arranged at equal intervals (for example, every 60 °) outside the second concentric holes H2 and concentrically with the central hole H0. The radius r3 of the concentric circle for the third concentric hole H3 can be shown as 0.54D.

Next, the fourth concentric hole H4 is composed of, for example, twelve. The fourth concentric holes H4 are arranged at equal intervals (for example, every 30 °) outside the third concentric hole H3 and concentrically with the central hole H0. The radius r4 of the concentric circle with respect to the fourth concentric hole H4 can be shown as 0.68D.
However, the number of the fifth concentric holes H5 is not twelve as in Non-Patent Document 1, but 24, for example, and is equidistant (for example, 15) outside the fourth concentric hole H4 and concentrically with the central hole H0. Are arranged at every °). For this reason, compared with the structure of a nonpatent literature 1, the flow velocity near the wall of a circular pipe can be enlarged. The concentric radius r5 for the fifth concentric hole H5 can be shown as 0.92D.

  The velocity distribution porous plate 30 reduces the number of concentric circles compared to the structure of Non-Patent Document 1 and increases the diameter of each concentric circle in order to increase the diameter of each hole and facilitate the manufacture of the porous plate. The value has been changed. FIG. 4 also illustrates an example of a velocity distribution perforated plate made of a single plate. However, in order to reduce weight and save material, a tube is fitted to the plate and the plate thickness t is reduced. A perforated plate for velocity distribution may be formed. Further, when the perforated plate for speed distribution is sandwiched between the flanges, a region where no hole is provided may be formed between a through-hole (for example, H5) located on the outermost periphery and the outer peripheral edge of the plate.

(Second Embodiment)
FIG. 5 is a front view for explaining the downstream porous plate of the second embodiment, FIG. 5 (A) is a front view of the velocity distribution porous plate 40, and FIG. 5 (B) is an explanation of the hole arrangement. In order to do so, the figure which extracted a part (30 degrees) of the perforated panel 40 for speed distribution is shown.
Similarly to the velocity distribution porous plate 30, the velocity distribution porous plate 40 has a through hole 42 having the same hole diameter d (for example, 10 mm) in one plate 41 (plate thickness t = 0.035D). However, the total number of through-holes 42 is 43, for example.

  Specifically, in the through-circular hole 42, for example, five concentric circles are set around one central hole H <b> 0 similarly to the through-circular hole 32, and the concentric circle radii r <b> 1 to r <b> 5 have the same value as the through-circular hole 32. However, it can be seen that the distance between the third concentric hole H3 and the fourth concentric hole H4 indicated by a two-dot chain line in FIG. 5 is narrow. Therefore, the third concentric hole H3 communicates with the adjacent fourth concentric holes H4 on both sides of the plate 41 when viewed in the circumferential direction. For this reason, the number of through-holes 42 is 12 fewer than the through-holes 32 of FIG. The aperture ratio β of the velocity distribution porous plate 40 is 0.58.

As described above, when the third concentric hole H3 and the fourth concentric hole H4 are arranged close to each other, the diameter of each hole is increased so that the third concentric hole H3 and the fourth concentric hole H4 communicate with each other. As compared with the case where no is communicated, the production of the velocity distribution porous plate is facilitated.
Then, the analysis result of the said rectifier is demonstrated. In the rectifier studied in this analysis, the swirl rectifying perforated plate 20 described in FIG. 3 and the velocity distribution perforated plate 40 described in FIG. 5 are combined. Then, a rectifying device (hereinafter referred to as Example A) set to a distance L ₁ = D from the terminal end of the swirl rectifying porous plate 20 to the start end of the velocity distribution porous plate 40, A rectifying device (hereinafter referred to as the present embodiment B) set to a distance L ₁ = 2D from the end to the starting end of the velocity distribution porous plate 40 and a rectifying device including only the swirl rectifying porous plate 20 described in FIG. The following examples A and B show the rectifying effect at the position of the distance L ₂ = 8D from the end of the velocity distribution porous plate 40, and the comparative example shows the end of the swirl rectifying perforated plate 20 The rectification effect at the position of the distance L ₂ = 8D from the center was examined (FIGS. 6 and 7).

6A and 6B are diagrams for explaining the swirl angle with respect to the present embodiment and the comparative example. FIG. 6A shows the swirl flow angle with respect to the vertical (X) direction, and FIG. 6B shows the horizontal (Z) direction. The flow angles of the swirling flow with respect to are respectively shown. Φ _u = tan ⁻¹ (U / V), φ _w = tan ⁻¹ (W / V), U is the velocity X component, V is the velocity Y component, and W is the velocity Z component. ordinate the absolute value of phi _u of 6 (a), the vertical axis in FIG. 6 (B) shows the absolute value of phi _w. R is the radius of the pipe, and the horizontal axis in FIGS. 6A and 6B represents the measurement position in the X coordinate or Z coordinate as dimensionless.

The solid line in FIG. 6 indicates a swivel angle of 2 °, and is a value that is considered that the influence of the swirl flow does not affect the measurement accuracy of the speculative flow meter. In addition, the broken line of FIG. 6 is an analysis value when there is no perforated plate.
The above comparative example is indicated by ● in FIGS. 6 (A) and 6 (B). Although the swirl component can be removed from the broken line in FIG. 6, it appears at a value near the solid line in FIG. It can be seen that it is difficult to remove the swirl flow accompanied by bias with the perforated plate.

On the other hand, as shown by a circle in FIGS. 6A and 6B, in Example A (L ₁ = D), many smaller values appear than in the comparative example. Further, as indicated by □ in FIGS. 6A and 6B, in Example B (L ₁ = 2D), many smaller values appear than in Example A. For this reason, both of Examples A and B are excellent in the function of removing the swirling component, and it can be seen that the present Example B is particularly an effective rectifier for removing the swirling component.

7A and 7B are diagrams for explaining the axial speed distribution for the present example and the comparative example. FIG. 7A shows the axial speed distribution of this example A, and FIG. 7B shows the axial speed of this example B. FIG. 7C shows the axial velocity distribution of the comparative example. Note that Vm is the average flow velocity in the pipe, and the vertical axis in FIGS.
For the measurement of the axial velocity distribution, for example, an ultrasonic flowmeter based on the reciprocal difference in propagation time of four measuring lines is used, and a running section is sufficiently provided to generate a development flow, and gasoline is used as a working fluid. Measurement was performed in the range of Reynolds number Re = 10 ⁴ to 10 ⁷ . That is, since the measured flow velocity is the average flow velocity (linear average flow velocity) on the path along which the ultrasonic wave propagates, after correcting to the average flow velocity in the pipe (average surface flow velocity) by the flow correction coefficient, The flow rate is calculated by multiplying the cross-sectional area. The measurement interval is on the order of microseconds. Here, the measured values (14,550) were averaged in order to grasp the tendency of the velocity distribution. In this analysis, the fluid is air (viscosity coefficient μ = 1.822 × 10 ⁻⁵ Pa · s, density ρ = 1.205 kg / m ³ ), and the Reynolds number is in the above-described range of Reynolds number (10 ⁴ to 10 ⁷ ) The value was close to the lower limit (7.3 × 10 ⁴ ).

In the above comparative example, in FIG. 7C, the axial velocity on the vertical plane (X / R) indicated by ●, the axial velocity on the horizontal plane (Z / R) indicated by ○ is the ultrasonic flow rate indicated by ◇. It turns out that it does not correspond with the measurement result of the total.
On the other hand, as shown by ● and ◯ in FIG. 7A, Example A (L ₁ = D) is concentrated at the position of V / Vm = 1.0, and ◇ compared with the comparative example. Many portions that coincide with the measurement results of the ultrasonic flowmeter shown appear. Further, as shown by ● and ○ in FIG. 7B, in this example B (L ₁ = 2D), there are many portions that match the measurement result of the ultrasonic flowmeter indicated by ◇ compared to this example A. Appears.

  As described above, both of Examples A and B are excellent in reproducibility and repeatability test when the flow rate is measured based on the average flow velocity in the pipe such as an ultrasonic flow meter and a thermal flow meter. It can be seen that it demonstrates its performance. As a result, according to Examples A and B, it is possible to achieve an improvement in measurement accuracy by a flow meter that performs flow rate measurement based on the average flow velocity in the pipe, and to provide a practical rectifier.

  Further, the resistance coefficient K of the rectifier is K = 3.94 in the present embodiment A, and K = 3.98 in the present embodiment B. Here, for example, considering the value of Example B, it is 1.73 to 2.65 times that of the comparative example (K = 1.5 to 2.3), but is described in ISO5167. Since the value is smaller than the resistance coefficient (for example, K = 5.0), it can be seen that the rectifier is sufficiently practical.

  In addition, although the said test result uses the porous plate 40 for speed distribution demonstrated in FIG. 5, this is employ | adopted in consideration of the ease of processing of a through-hole, and it demonstrates in FIG. It is considered that the same test results can be obtained using the perforated plate 30 for velocity distribution.

DESCRIPTION OF SYMBOLS 1 ... Piping structure, 10 ... Pipe | line inlet, 11 ... 1st elbow, 12 ... 2nd elbow, 13 ... Rectifier, 14 ... Flowmeter, 15 ... Pipe line outlet, 20 ... Perforated plate for swirl rectification, 21 ... Plate 22 through holes, 30 and 40 perforated plates for velocity distribution, 31 and 41 plates and 32 and 42 through holes.

Claims (5)

A perforated plate for a rectifier that rectifies the flow in a circular pipe,
The perforated plate has a plate having a predetermined thickness, and a plurality of through-holes provided through the plate and having the same diameter.
The through-holes include one central hole arranged at the center of the plate, six first concentric holes arranged at equal intervals on a concentric circle with the central hole, and the first concentric holes. Six second concentric holes arranged equidistantly on the outer side and concentrically with the central hole, and six outer parts arranged equidistantly on the concentric circle with the central hole outside the second concentric hole A third concentric hole, twelve fourth concentric holes arranged equidistantly on the outer side of the third concentric hole and concentrically with the central hole, and a concentric circle with the central hole outside the fourth concentric hole rectifier for perforated plate, wherein the 24 fifth concentric hole and Tona Rukoto arranged at equal intervals at the top.   When the inner diameter of the circular tube is D, the first concentric hole is defined on the concentric circle defined by 0.26D from the center of the plate, and the second concentric hole is defined by 0.42D from the center of the plate. The third concentric hole is defined on the concentric circle defined by 0.54D from the center of the plate, and the fourth concentric hole is defined by 0.68D from the center of the plate. The rectifier perforated plate according to claim 1, wherein the fifth concentric holes are arranged on the concentric circles defined by 0.92D from the center of the plate.   The perforated plate for a rectifying device according to claim 1 or 2, wherein the third concentric hole communicates with the fourth concentric hole adjacent on both sides thereof. A rectifier including an upstream porous plate and a downstream porous plate,
The upstream perforated plate includes a plate having a predetermined thickness and a plurality of through-holes provided through the plate and having the same diameter. The through-holes of the upstream perforated plate The distance between adjacent ones is smaller at the center of the plate and larger at the periphery of the plate,
The rectifying device according to claim 1, wherein the downstream porous plate is the rectifying device porous plate according to claim 1.   A flow rate measuring device comprising the rectifying device according to claim 4, wherein a flow meter for measuring a flow rate based on an in-tube average flow velocity is disposed downstream of the downstream porous plate.

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