JP7405164B2 - Flow rate measuring device and method - Google Patents

Description

The present invention relates to a flow rate measuring device and method for measuring a fluid flow rate in a pipe from outside the pipe.

One method for measuring the flow rate of fluid in piping is a method using a differential pressure flowmeter (for example, Patent Document 1). A differential pressure flowmeter is a device in which an orifice (throttle valve) is installed as a sensor in a flow path through which fluid is flowing, generates pressure loss, detects the pressure difference before and after the orifice, and converts it into a flow rate. Flow rate measurement methods, such as differential pressure flowmeters, in which the fluid is in direct contact with a sensor such as an orifice, have the advantage of being able to perform reliable calibration and having high fluid detection accuracy. However, since this method incorporates piping parts with internal sensors such as orifices as part of the piping that forms the flow path, separate piping work is required to cut and replace the existing piping. The disadvantage is that the fewer measurement points there are, the higher the construction costs will be.

On the other hand, an ultrasonic flowmeter has been proposed as a flow rate measurement method that does not require direct contact between the fluid and the sensor and does not require processing of piping (Patent Document 2). An ultrasonic flowmeter has an oscillating part that oscillates ultrasonic waves in the thickness direction of the pipe, and a receiving part that receives ultrasonic waves including those propagated inside the pipe, which are installed on the outside of the pipe. A flow rate calculation unit that calculates the gas flow rate based on the results calculates the flow rate by performing spectrum analysis or the like. Therefore, no piping work is required, and the flow meter can be easily installed and removed. However, this method has a problem in that the cost of the flow meter equipment is high. Furthermore, flow rate measurement may become difficult due to restrictions on the mounting positions of the oscillating section and the receiving section. Note that this method is called an active type because it applies vibration (in this case, ultrasonic vibration) to the pipe.

In response, a so-called passive type was proposed as another flow rate measurement method that does not require piping processing, which directly measures the vibrations generated by the interaction between the piping and the fluid without applying vibration to the piping ( Patent Document 3). The passive flow rate measuring device of Patent Document 3 includes a signal level calculation section that calculates the relationship between frequency and signal level based on sensor data indicating fluid vibration from a sensor provided in a pipe, and a signal level calculation section that calculates a relationship between a frequency and a signal level based on the signal level. Based on a band signal level calculation unit that calculates band signal levels for multiple frequency bands, and a model representing the relationship between the band signal level and the flow rate and band signal level calculated for each frequency band, the frequency It has a flow rate calculation section that calculates the flow rate for each band for a plurality of frequency bands, and an estimation result judgment section that outputs an estimation result regarding the flow rate based on the plurality of calculated flow rates. In this method, compared to the differential pressure flowmeter and the ultrasonic flowmeter, the cost of sensors and installation is low, and installation is the simplest.

JP2009-53083A Japanese Patent Application Publication No. 2013-181812 JP 2019-109194 Publication

The passive flow rate measuring device disclosed in Patent Document 3 uses a model to determine the flow rate based on the frequency of vibrations that the fluid gives to piping. However, if the vibrations exerted by the fluid on the piping are superimposed on noise from mechanical vibrations around the piping caused by ancillary equipment such as a compressor on the supply side or rolling rolls, the frequency of the vibrations exerted by the fluid on the piping can be determined from this superimposed vibration. It is difficult to identify this as a signal, and therefore, there is a problem in that it is difficult to determine the flow rate based on the frequency of vibration that the fluid gives to the piping.

In view of the above-mentioned circumstances, the present invention provides a passive flow rate measuring device that allows vibrations exerted by the fluid on the piping to be easily identified even when mechanical vibrations around the piping are superimposed on vibrations exerted by the fluid on the piping. The purpose is to provide a measuring device and method.

In order to solve the above problems, the present inventors investigated a method for measuring flow rate without being affected by mechanical vibrations around piping in a passive flow rate measuring device, and obtained the following knowledge. .
(a) Measuring the frequency of piping vibration from outside the piping at locations where vortices occur within the piping makes it easy to distinguish between the frequency of vibrations exerted by the fluid on the piping and the frequency of mechanical vibrations around the piping.
(b) From the frequency of the vibration that the fluid gives to the piping identified above and the Strouhal number of the vortex St = f x d/v (where f is the frequency, d is the pipe diameter, and v is the flow velocity in the pipe), calculate the flow rate. can be found. Here, "pipe diameter" refers to the inner diameter of the pipe.

The present invention was completed through further study based on the above-mentioned knowledge, and the gist thereof is as follows.
[1] A device that measures the flow rate of fluid in piping,
comprising a vibration meter that measures the frequency f [Hz] of vibration of the piping from outside the piping, and a flow rate calculation means that calculates the flow rate based on the measurement results of the vibration meter,
The flow rate calculation means calculates the flow rate in the pipe from the Strouhal number St=f×d/v (where d is the pipe diameter [mm] and v is the flow velocity in the pipe [mm/s]) obtained in advance. Find the flow velocity v,
A flow rate measuring device characterized in that the flow rate is calculated by multiplying the flow velocity v in the pipe by a flow path cross-sectional area.
[2] The flow rate measuring device according to [1], wherein in the flow rate calculation means, the band of the frequency f is 500 Hz or less.
[3] The flow rate measuring device according to [1], wherein the Strouhal number St is fixed at 0.2 in the flow rate calculation means.
[4] The vibration meter is installed at a distance of not more than five times the diameter of the pipe on the downstream side from the base point, which is at least one of the bent part, valve part, flange part, and welded part of the pipe. The flow rate measuring device according to any one of [1] to [3], characterized in that the flow rate measuring device is located at a certain position.
[5] The flow rate measuring device according to [4], wherein the vibration meter is installed at a position further upstream from the base point by a distance equal to or less than the pipe diameter.
[6] A method for measuring the flow rate of fluid in piping, comprising:
a vibration measurement step of measuring the frequency f [Hz] of vibration of the pipe from outside the pipe;
a flow rate calculation step of calculating the flow rate from the measurement results of the vibration,
In the flow rate calculation step, the flow rate in the pipe is calculated from the Strouhal number St=f×d/v (where d is the pipe diameter [mm] and v is the flow velocity in the pipe [mm/s]) obtained in advance. Find the flow velocity v,
A flow rate measurement method characterized in that the flow rate is calculated by multiplying the flow velocity v in the pipe by a flow path cross-sectional area.
[7] The flow rate measurement method according to [6], wherein in the flow rate calculation step, the frequency f band is set to 500 Hz or less.
[8] The flow rate measuring method according to [6], wherein in the flow rate calculation step, the Strouhal number St is fixed at 0.2.
[9] The measurement position of the vibration is located downstream from a base point, which is at least one of a bent part, a valve part, a flange part, and a welded part of the pipe, at a distance of not more than five times the diameter of the pipe. The flow rate measurement method according to any one of [6] to [8], characterized in that the flow rate measurement method is performed at a position.
[10] The flow rate measurement method according to [9], wherein the vibration measurement position is further located upstream from the base point by a distance equal to or less than the pipe diameter.

According to the present invention, in a passive type flow rate measuring device and method, a flow rate can be measured without being affected by mechanical vibration around piping.

FIG. 1 is a factory layout diagram of piping, etc., showing an example of an embodiment of the present invention. It is a graph showing the velocity [mm/s] for each frequency [Hz] obtained by attaching the vibration meter 7a to the piping 3 of FIG. 1. It is a graph showing the velocity [mm/s] for each frequency [Hz] obtained by attaching the vibration meter 7b to the piping 4a of FIG. 1. It is a graph showing the velocity [mm/s] for each frequency [Hz] obtained by attaching the vibration meter 7c to the piping 4b in FIG. 1. It is a graph showing the velocity [mm/s] for each frequency [Hz] obtained by attaching a vibration meter 7d to the downstream side of the bent portion 5d of the pipe 4c in FIG. 1. It is a graph showing the velocity [mm/s] for each frequency [Hz] obtained by attaching the vibration meter 7e to the upstream side of the bent portion 5d of the pipe 4c in FIG. 1. 7 is a graph showing the result of subtracting the speed [mm/s] for each frequency [Hz] obtained in FIG. 5 by the speed [mm/s] for each frequency [Hz] obtained in FIG. 6. FIG. It is a graph showing the velocity [mm/s] for each frequency [Hz] obtained by attaching the vibration meter 7f to the straight pipe section 8 of FIG. 1. FIG. 2 is an explanatory diagram showing an outline of an offline experiment for obtaining the Strouhal number St in advance. 10 is a graph showing the relationship between frequency [Hz] and Strouhal number St [-] obtained by the offline experiment of FIG. 9. 10 is a graph showing the relationship between flow velocity [m/s] and Strouhal number St[-] obtained by the offline experiment of FIG. 9.

Hereinafter, an embodiment of the present invention (hereinafter also referred to as the present embodiment) will be described.
In the present invention, the frequency f [Hz] of vibration of the pipe is measured from outside the pipe, and the Strouhal number St = f x d/v (where d is the pipe diameter [mm] and v is the The flow velocity v in the pipe is determined from the flow velocity [mm/s] in the pipe, and the flow rate is calculated by multiplying this by the cross-sectional area of the flow path. As a result, in a passive type flow measuring device that is easy to install, the flow rate can be determined from the vibrations exerted on the pipe by the fluid without being affected by mechanical vibrations around the pipe.

[Vibration meter]
As a flowmeter that measures the frequency f [Hz] of vibration of piping from outside the piping, it is necessary to measure the magnitude of vibration at each frequency in order to distinguish between the frequency of vibration that the fluid gives to the piping and the frequency of mechanical vibration around the piping. A vibrometer with an output FFT (Fast Fourier Transform) analysis function is preferable. Vibration meters with FFT analysis functions are generally widely used and easily available. Note that there are displacement, velocity, and acceleration as measures of the magnitude of vibration, and it is desirable to measure using velocity. In this embodiment, the scale of vibration magnitude is hereinafter taken as speed [mm/s].

[Vibration meter installation position]
In the present invention, when calculating the flow rate from the measured frequency f, the Strouhal number St, which is defined in a state where a vortex (more specifically, a swirl vortex) is generated, is used. Therefore, the installation position of the vibration meter (vibration measurement position) is preferably a position where a vortex is generated. In this way, by using velocity data for each frequency measured at the location where the vortex is generated, even if mechanical vibrations around the piping are superimposed on vibrations exerted by the fluid on the piping as noise, the vibrations exerted by the fluid on the piping can be minimized. By identifying the frequency f of , the flow rate can be calculated from the Strouhal number St.

In piping that supplies fluid within a factory, the diameter of the pipe is not more than 5 times, preferably the It is known that a vortex is generated at a distance equal to or less than the pipe diameter. Therefore, it is preferable to adopt this position as the installation position of the vibration meter.

More preferably, the vibration meter is also installed at a position upstream from the base point at a distance equal to or less than the pipe diameter. According to this, if there is noise due to mechanical vibration or the like on the upstream side or downstream side from the base point, this can be removed and vibration data originating only from the vortex can be obtained.

[Frequency f band≦500Hz]
Vibration measurement experiment of factory piping during fluid flow by the present inventors (fluid is air, pipe diameter is 50A to 200A, fluid flow rate on the inlet side of the pipe is 50 to 550Nm ³ /h, fluid temperature is 10 to 25°C) According to the velocity data for each frequency obtained in , when vibrations caused by vortices and mechanical vibrations are applied to the piping at the same time, frequencies with velocity appear divided into a band below 500 Hz and a band above 500 Hz. When mechanical vibration is removed from this state, the velocity disappears from the band above 500 Hz and remains in the band below 500 Hz.

From these results, when mechanical vibrations around the piping are applied at the position where the vortex is generated, the band with a frequency of 500 Hz or less includes the frequency of vibrations exerted by the fluid on the piping, but it does not include the frequency of the mechanical vibrations around the piping. It can be seen that this is a band that does not include Note that this also applies to cases where the fluid is a gas other than air or a liquid. Therefore, the band of the frequency f for the Strouhal number St is preferably 500 Hz or less.

Next, as a method for selecting one frequency f (hereinafter also referred to as frequency f for St) used for calculating the Strouhal number St from a plurality of speed peaks within a band of 500 Hz or less, the following is preferable.
(a) Perform vibration measurement at a position downstream from the base point, where vortices are significantly generated, at a distance of five times the pipe diameter or less, and obtain frequency and velocity data (downstream data). .
(b) Let the frequency showing the highest velocity peak from the downstream data be the frequency f.
(c) More preferably, vibration measurement is further performed at a position upstream from the base point at a distance equal to or less than the diameter of the pipe, and frequency and velocity data (upstream data) are obtained.
(d) Overlap downstream data and upstream data with the same frequency, and use downstream data without overlap. This is done to remove noise such as mechanical vibrations occurring on the upstream and/or downstream sides.
(e) Among the data adopted above, it is assumed that the frequency showing the highest velocity peak is the frequency of vibration originating from the vortex, and this is set as the frequency f.
[Obtain Strouhal number St in advance]
To obtain the Strouhal number St in advance, set the fluid type, temperature, pipe diameter, and set flow rate within the range of actual pipe operating conditions, and conduct offline experiments to obtain multiple levels of set flow rate and pipe diameter d [mm]. , the frequency and flow velocity are measured at the position where the eddy current occurs, and at this position, the frequency is measured from outside the pipe using the vibration meter, and one frequency f [Hz] for St is selected from the band below 500 Hz, and the difference is The flow velocity v [mm/s] is measured using a pressure type flowmeter, and the Strouhal number St is calculated from the formula St=f×d/v.

Further, in experiments conducted by the present inventors, it has been confirmed that the swirl vortex is generated in a range larger than Reynolds number Re=10 ⁴ and St=0.2. Therefore, in the present invention, it is preferable that the Strouhal number St is fixed at 0.2 in the flow rate calculation means.

[Flow rate calculation means]
The flow rate calculation means for calculating the flow rate from the measured frequency f and the Strouhal number St acquired in advance can be easily configured as software installed in a personal computer.

Hereinafter, embodiments of the present invention will be described in more detail with reference to Examples.

FIG. 1 shows a factory layout diagram in this embodiment. As shown in FIG. 1, in this embodiment, a pipe 3 of 200A (input a number in □, □A means that the pipe diameter is □mm) runs from a compressor 1 installed outside the building. Compressed air is supplied to the factory 2, and is branched from a 200A pipe 3 through a 50A pipe 4a, a 50A pipe 4b, and a 100A pipe 4c, which are used for instrumentation instruments 6a, pneumatic equipment 6b, and dust removal, respectively. Compressed air is used in the nozzle 6c. The temperature of the compressed air is 10 to 25°C, and the pressure is 5.5 to 6 atmospheres. The pipes 3, 4a to 4c have bent portions 5a to 5d, respectively. It is known that when compressed air passes through a bend, a vortex is formed due to the formation of a secondary flow. In order to measure vibrations caused by vortices, we measure vibrations that allow us to obtain the velocity of each frequency using FFT analysis in the vicinity of each bend, more specifically, at a distance downstream from each pipe at a distance that is the diameter of each pipe. A total of 7a to 7d were installed. 2 to 5 respectively show graphs of velocity [mm/s] data for each frequency [Hz] obtained from the vibration meters 7a to 7d.

The installation position of the vibration meter 7a that acquired the data in Fig. 2 (a position 200 mm downstream from the bend 5a) is sufficiently far from the compressor 1, and is located at a position where no noise due to mechanical vibration is observed. be. In FIG. 2, a velocity peak was confirmed in the band of 10 to 200 Hz, and the band of 500 Hz or less was recognized to be the region where frequencies due to fluid vortex formation exist.

The installation position of the vibration meter 7b that acquired the data in FIG. 3 (a position 50 mm downstream from the bend 5b of the pipe 4a) is affected by noise caused by mechanical vibrations caused by the operation of the instrumentation device 6a to which air is supplied. This is a position where this is recognized. In Figure 3, velocity peaks are confirmed in the band of 10 to 500 Hz and in the band of 500 Hz or more, and from the results of Figures 2 and 3, the band of 500 Hz or less is the region where frequencies exist due to the formation of fluid vortices, and the frequency range of 500 Hz or more is found. It was recognized that the frequency range due to mechanical vibration exists.

The installation position of the vibration meter 7c that acquired the data in Fig. 4 (a position 80 mm downstream from the bend 5c of the pipe 4b) has noise associated with mechanical vibration of the pneumatic equipment 6b to which air is supplied. This is a position where it is impossible to In FIG. 4, a velocity peak was confirmed in the band of 10 to 500 Hz, and similarly to FIG. 2, the band of 500 Hz or less was recognized to be the region where frequencies due to fluid vortex formation exist.

The installation position of the vibration meter 7d that acquired the data in Fig. 5 (a position 100 mm downstream from the bend 5d of the pipe 4c) is affected by the vibration caused by the dust removal nozzle 6c at the air destination and surrounding incidental equipment. This is the location where mechanical vibrations due to the operation of (not shown) are observed. In FIG. 5, six large velocity peaks were confirmed in the band of 10 to 500 Hz. Therefore, the noise generated on the inlet side and/or the outlet side can be determined from the data in FIG. 5 using the data in FIG. It has become possible to reduce the influence of vortices and clarify the frequency of vortices (see Figure 7).

Furthermore, when compressed air passes through piping, no vortices are formed due to the formation of secondary flow, and mechanical vibrations extend through the piping. A vibration meter 7f was installed in the straight pipe section 8 of the pipe 3 connected from the pipe 3. This position is a position where mechanical vibrations due to incidental equipment (not shown) around the straight pipe portion 8 are observed. The velocity data for each frequency acquired from the vibration meter 7f is shown in a graph in FIG. From Fig. 8, a velocity peak was confirmed in the band above 500Hz, and as in Figs. 2 and 4, this band was recognized to be the region where frequencies due to mechanical vibration exist, but a velocity peak was observed in the band below 500Hz. did not appear, and no frequency band due to vibrations caused by the fluid was observed.

From the results shown in FIGS. 2 to 8, when compressed air passes through, velocity peaks appear conspicuously in the band below 500 Hz at locations where vortices are formed due to secondary flow formation, and at bends 5a to 5d, fluid It was possible to obtain the frequency from the vibration given by

On the other hand, FIG. 9 shows an outline of an offline experiment conducted to obtain the relationship between the frequency f [Hz] and the Strouhal number St [-] in advance. The experimental apparatus has a structure in which air is sent from a compressor 9 to a pipe 10, passes through a valve section 11 and a bent section 14, and is discharged from a nozzle 15. The flow rate was measured using the differential pressure type flowmeter 12, and the frequency f of the vibration given by the fluid was obtained at the bending portion 14 using the vibration meter 13. The formula for calculating the Strouhal number St is St=f×d/v, where d is the pipe diameter [mm] and v is the flow velocity [mm/s]. Note that the flow rate in the pipe was adjusted by manipulating the opening degree of the valve part 11, and the flow rate v was calculated by dividing the flow rate measured by the differential pressure flowmeter 12 by the cross-sectional area of the pipe.

The pipe diameter d [mm] of the pipe 12, which was varied in the range of 25 A to 100 A, the measured value of the flow velocity v [mm/s] by the differential pressure flowmeter 15, and the measured value of the frequency f [Hz] by the vibration meter 13 are as follows. The relationship between the calculated Strouhal number St and the frequency f applied to the formula for calculating the Strouhal number St is shown in FIG. 10, and the relationship between the calculated Strouhal number St and the flow velocity v is shown in FIG. However, in FIG. 11, the unit of the flow velocity v is [m/s]. From FIGS. 10 and 11, the Strouhal number St was constant at 0.2 regardless of the frequency f and the flow velocity v.

Based on the results shown in FIGS. 10 and 11, the flow rate of each facility in the factory in FIG. 1 was calculated using the flow rate calculation means (not shown) described above. As the frequency f for St, in Figures 2 to 5, the fluid gives the frequency at which the velocity peak is highest in the band below 500 Hz (if there are multiple highest velocity peaks, the frequency is the highest among them) It was adopted as the main vibration. The flow rate in the pipe is calculated from the pipe diameter d and the frequency f obtained from the vibration meters 7a to 7e and the Strouhal number St=0.2 using the formula v=f×d/St. Table 1 shows the flow rate calculated by multiplying the road cross-sectional area (=3.14×d ² /4).

Thus, according to the present invention, in the passive flow rate measuring device and method, the flow rate can be measured without being affected by mechanical vibrations around the piping.

In this example, air was used as the fluid, but the present invention can also be applied to gases or liquids other than air by obtaining the Strouhal number St in advance according to the type of fluid or the temperature. Applicable. Further, according to the present invention, it is preferable to install the vibration meter at a bent part, but for similar pressure loss parts such as valves and flanges, it is necessary to obtain the Strouhal number St in advance according to the type of fluid or even temperature. The present invention can be applied by setting the conditions.

1 Compressor 2 Factory building 3 Piping (200A)
4a Piping (50A)
4b Piping (50A)
4c Piping (100A)
5a Bend section 5b installed on piping 3 Bend section 5c installed on piping 4a Bend section 5d installed on piping 4b Bend section 6a installed on piping 4c Instrumentation equipment 6b Pneumatic equipment 6c Dust removal nozzle 7a At bent part 5a Vibration meter 7b installed Vibration meter 7c installed on bent portion 5b Vibration meter 7d installed on bent portion 5c Vibration meter 7e installed on the downstream side of bent portion 5d Vibration meter 7f installed on the upstream side of bent portion 5d Straight pipe section Vibration meter 8 installed near 8 Straight pipe section 9 Compressor 10 Air piping (25A to 100A)
11 Valve section 12 Differential pressure flow meter 13 Vibration meter 14 Bend section 15 Nozzle

Claims (8)

A device for measuring the flow rate of fluid in piping,
comprising a vibration meter that measures the frequency f [Hz] of vibration of the piping from outside the piping, and a flow rate calculation means that calculates the flow rate based on the measurement results of the vibration meter,
The vibration meter is installed at a position downstream from the base point, which is at least one of the bent part, valve part, flange part, and welded part of the pipe, at a distance of not more than five times the diameter of the pipe. ,
The flow rate calculation means calculates the flow rate in the pipe from the Strouhal number St=f×d/v (where d is the pipe diameter [mm] and v is the flow velocity in the pipe [mm/s]) obtained in advance. Find the flow velocity v,
A flow rate measuring device characterized in that the flow rate is calculated by multiplying the flow velocity v in the pipe by a flow path cross-sectional area. 2. The flow rate measuring device according to claim 1, wherein the frequency band of the frequency f is set to 500 Hz or less in the flow rate calculation means. 2. The flow rate measuring device according to claim 1, wherein the Strouhal number St is fixed at 0.2 in the flow rate calculation means. A claim characterized in that another vibration meter for measuring the frequency f [Hz] of vibration of the pipe from outside the pipe is installed at a position upstream from the base point by a distance equal to or less than the diameter of the pipe. The flow rate measuring device according to any one of Items 1 to 3 . A method for measuring the flow rate of fluid in a pipe, the method comprising:
a vibration measurement step of measuring the frequency f [Hz] of vibration of the pipe from outside the pipe;
a flow rate calculation step of calculating the flow rate from the measurement results of the vibration,
The measurement position of the vibration is a position downstream from a base point, which is at least one of a bent part, a valve part, a flange part, and a welded part of the pipe, at a distance of not more than five times the diameter of the pipe,
In the flow rate calculation step, the flow rate in the pipe is calculated from the Strouhal number St=f×d/v (where d is the pipe diameter [mm] and v is the flow velocity in the pipe [mm/s]) obtained in advance. Find the flow velocity v,
A flow rate measuring method characterized in that the flow rate is calculated by multiplying the flow velocity v in the pipe by a flow path cross-sectional area. 6. The flow rate measuring method according to claim 5 , wherein in the flow rate calculation step, the band of the frequency f is set to 500 Hz or less. 6. The flow rate measuring method according to claim 5 , wherein in the flow rate calculation step, the Strouhal number St is fixed at 0.2. Another vibration measurement position for measuring the vibration frequency f [Hz] of the pipe from outside the pipe is a position separated from the base point upstream by a distance equal to or less than the pipe diameter. 7. The flow rate measurement method according to any one of 5 to 7 .

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