JPS63171322A - Flow velocity measuring instrument - Google Patents

Abstract

PURPOSE:To enable mean flow velocity to be easily measured by constituting a flow velocity measuring instrument such that the flow velocity of fluid to be measured is calculated from difference between the values of negative pressures generated by the flow of the fluid to be measured in first and second flow velocity detecting pipes. CONSTITUTION:A pipe 1 is like, for example, a duct and fluid to be measured flows in a direction shown by an arrow in the pipe 1. A composite flow velocity detecting pipe 4 composed of first and second flow velocity detecting pipes 2 and 3, respectively, is arranged in the pipe 1 so as to cross the flow of the fluid to be measured. The detecting pipe 2 is provided with openings 5 and 6 having elevation angles theta1 and theta2, respectively, four by four at approximately equal spacings with the upstream side of the fluid to be measured as a reference. Further, the detecting pipe 3 is provided with four openings 7 having elevation angles 180 deg. with the upstream side of the fluid to be measured as a reference. The distal ends of the detecting pipes 2 and 3 are closed and the other ends are connected to pressure gages 9 and 10, respectively, outside the pipe 1 via connecting ports. The output of the pressure gates 9 and 10 is supplied to arithmetic means 11 and difference between negative pressure in the detecting pipes 2 and 3 is calculated. The flow velocity of the fluid to be measured is calculated in arithmetic means 12 in accordance with a characteristic curve obtained in advance.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a flow velocity measuring device, and particularly to a flow velocity measuring device suitable for measuring the flow velocity of a fluid containing dust and the like flowing through a huge pipe. It is something.

[Conventional technology]

2. Description of the Related Art As flow rate or flow rate measuring devices for measuring the flow rate or flow rate of a fluid, devices based on various principles have been proposed and put into practical use. Examples thereof include an orifice type flow rate measuring device, a pitot tube type flow rate measuring device, a hot wire current meter, a magnetic current meter, and the like.

[Problem that the invention seeks to solve]

However, for example, the inner diameter of the equipment installed in steel factories, etc. is 5.
Currently, there is no suitable method for measuring the flow velocity or flow rate of air containing a large amount of dust flowing through huge blast pipes or combustion waste gas pipes that can extend up to 10 m.

In an orifice-type flow rate measuring device, the orifice itself is not practical to be attached to a pipe of a huge diameter, and dust in the pipe adheres to it, making it difficult to obtain sufficient measurement accuracy.

In a pitot tube type flow rate measuring device, the large diameter of the pipe is not a problem, but clogging of the pitot tube is a problem. That is, the total pressure hole of the pitot tube, which opens toward the flow to measure the total pressure of the flow, becomes blocked by dust and the like contained in the fluid to be measured, such as combustion waste gas.

Hot wire anemometers, which cool a thermistor or the like heated by Joule heat with a fluid to be measured and measure the flow velocity based on the degree of cooling, also have the disadvantage of large changes over time due to adhesion of dust, etc. in the fluid.

This hot wire anemometer also has the disadvantage that it is very fragile because the sensor element, which is a metal filament or a thermistor, is directly exposed to the fluid.

Furthermore, electromagnetic flowmeters that utilize Faraday's law of electromagnetic induction can measure even if the fluid is highly viscous or contains fine particles, as long as the fluid is conductive. Since the method is limited to electrically conductive fluids, it is not possible to measure the flow rate of non-conductive fluids such as air.

[Means for solving problems]

The flow rate measuring device of the present invention has been developed in view of the above-mentioned problems. exposed to the measured fluid at an elevation angle that is smaller than the minimum stable angle (the minimum angle with respect to the upstream of the measured fluid at which the negative pressure received from the measured fluid remains approximately constant regardless of the angle). a first opening having an elevation angle greater than the critical negative pressure angle and less than the minimum stable angle; 2nd exposed
a second flow velocity detection tube having a third opening exposed in the fluid to be measured with an elevation angle greater than the minimum stable angle; The flow rate of the fluid to be measured is calculated from the difference between the negative pressure generated in the second flow rate detection tube and the negative pressure generated in the second flow rate detection tube.

In addition, the angle of elevation in the fluid to be measured is larger than the critical negative pressure angle and smaller than the maximum negative pressure angle (the angle with respect to the upstream of the fluid to be measured at which the negative pressure received from the fluid to be measured is the maximum). a first opening exposed into the fluid to be measured with an elevation angle larger than the maximum negative pressure angle and smaller than the stable minimum angle; a second flow velocity detection tube having a third opening exposed in the fluid to be measured with an elevation angle greater than and calculation means for calculating the flow velocity of the fluid to be measured from the difference.

[Effect]

Due to the flow of the fluid to be measured, negative pressure states with different values are formed inside the first flow velocity detection tube and inside the second flow velocity detection tube, and the negative pressure difference changes depending on the flow velocity of the fluid to be measured. Therefore, the flow velocity of the fluid to be measured can be determined from the negative pressure difference.

Furthermore, even if fluctuations occur in the flow of the fluid to be measured, the changes in the negative pressure at the first opening and the changes in the negative pressure at the second opening contradict each other.
There is no change in the internal negative pressure inside the flow rate detection tube.On the other hand, the negative pressure at the third opening does not change much due to fluctuations in the flow of the fluid to be measured. There is almost no measurement error due to flow fluctuations.

〔Example〕

Hereinafter, the present invention will be described in detail along with examples.

FIG. 1 is a schematic diagram showing an embodiment of the present invention. The pipe 1 shown in cross section is, for example, a duct, through which air containing dust, which is the fluid to be measured, flows in the direction of the arrow shown in outline. Inside pipe 1,
A composite flow velocity detection tube 4 consisting of a first flow velocity detection tube 2 and a second flow velocity detection tube 3 is arranged to cross the flow of the fluid to be measured. FIG. 2 is a perspective view showing the entire composite flow velocity detection tube 4, and FIG. 3 is a cross-sectional view taken along the line mm'.

The first flow velocity detection tube 2 has an opening 5 having an elevation angle of θl (76° in this example) in the clockwise direction and an elevation angle of θ2 (=θ1) in the counterclockwise direction with respect to the upstream of the fluid to be measured. Four openings 6 each are provided at approximately equal intervals. The second flow velocity detection tube 3 is provided with four open lowers having an elevation angle of 1800 with respect to the upstream of the fluid to be measured, that is, facing in the downstream direction.

The tips of the first flow rate detection tube 2 and the second flow rate detection tube 3 are both closed, and each end has a connecting port 16.
．． 17 is formed. The connecting ports 16 and 17 protrude outside the pipe 1, and are connected to pressure gauges 9 and 10 by tubes (not shown), respectively, as shown by dashed lines.

The pressure gauges 9 and 10 are means for detecting the internal pressure of the first flow rate detection tube 2 and the second flow rate detection tube 3, respectively, and their output terminals are connected to the input terminal of the calculation means 11, respectively. The calculation means 11 calculates the difference between the negative pressure in the first flow rate detection tube 2 and the negative pressure in the second flow rate detection tube 3 from the outputs of the pressure gauges 9 and 10.
．． Together with 10, it constitutes negative pressure difference detection means 8.

The output terminal of the negative pressure difference detection means 8, that is, the output terminal of the calculation means 11 is connected to the input terminal of the calculation means 12. The calculation means 12 calculates the flow velocity of the fluid to be measured corresponding to the output of the negative pressure difference detection means 8 according to a characteristic curve determined in advance by measurement.

The flow velocity of the fluid to be measured determined in this way is
It is displayed on a display means or serves as an input signal to a control system.

Here, the operating principle of the present invention, that is, the first flow velocity detection tube 2
We will explain how the flow velocity of the fluid to be measured can be determined from the difference between the negative pressure produced within the second flow velocity detection tube 3 and the negative pressure produced within the second flow velocity detection tube 3.

First, Fig. 4 shows an outline of the experimental apparatus. The experiment was conducted by creating an air flow with a fan motor 50 and an air pipe 51 connected to it, and measuring the internal pressure of a flow velocity detection tube inserted into the air pipe 51 (at point A) with a manometer 52. It was conducted.

The flow velocity of the air in the air pipe 51 can be changed by adjusting the power supply voltage supplied to the fan motor 50 using the slider 53, and the air flow velocity can be measured separately using a commercially available current meter.

As shown in FIG. 5, the flow rate detection tube used in this experiment has a diameter of 1 mm or 2 mm on the surface of a circular tube 54 with a sealed tip.
A plurality of openings 55a to 55e are formed at equal intervals. This pipe 54 is vertically and rotatably inserted into the pipe wall of the air pipe 51, and has openings 55a to 55e.
The direction of the air can be freely changed with respect to the air flow (white arrow). Openings 55a-55
e is the angle to the air flow, i.e. the upstream of the flow is 0
The angle in degrees is the elevation angle θ (however, o″≦θ≦18
0°). In other words, when you are completely facing away from the airflow, it is 180 degrees.

In this experimental device, when the elevation angle θ was varied while keeping the flow velocity of the air in the air pipe 51 constant, results as shown in FIG. 6 were obtained. FIG. 6 shows the dependence of the internal pressure in the flow rate detection tube 54 on the elevation angle θ, and in both cases, the horizontal axis shows the elevation angle θ, and the vertical axis shows the gauge pressure of the internal air pressure, and the unit is water column (mAq). . In the same figure, the characteristic A plotted at the 0 point is 5 from the opening 55a.
This is the case where the diameter of 5e is IR, and the characteristic B plotted at the point Δ is the case where the diameter is 2 cranes. In addition, Fig. 7 is an enlarged view of the elevation angle θ = 45° to 90'' in Fig. 6. In this experiment, the air flow velocity was set to 5
It was set at m/s.

From this experimental data, it has become clear that the internal air pressure of the tube 54 becomes negative when the elevation angle θ is greater than a predetermined value (and that this internal pressure changes depending on the elevation angle θ. For example, the experiment shown in FIG. 6 Looking at the data, the elevation angle θ (hereinafter referred to as the critical negative pressure angle) at which the internal pressure starts to become negative is around 45″ for an opening diameter of 1 m, and around 54″ for an opening diameter of 2 am, which is the maximum. The elevation angle θ indicating the negative pressure (hereinafter referred to as the maximum negative pressure angle) is approximately 70 degrees regardless of the opening diameter. ) is approximately 80° regardless of the opening diameter.The values of these critical negative pressure angles, maximum negative pressure angles, or stable minimum angles are approximately 80° regardless of the opening diameter.
This is just an example, as it varies depending on the shape and number of flow plates, Reynolds number, presence or absence of a rectifying plate provided in front of the flow, etc. From the above experiments, it has become clear that different negative pressures are generated depending on the elevation angle with respect to the flow of the fluid to be measured.

Further experiments based on this basic phenomenon revealed that the negative pressure increases as the flow rate of the fluid being measured increases, and in particular, the negative pressure difference between two points with different negative pressures increases. It was confirmed that it increases as the fluid flow rate increases. For example, the difference between the negative pressure at the maximum negative pressure angle (around 70 degrees) and the negative pressure at the minimum stable angle (around 80'') increases as the flow rate of the fluid to be measured increases.

The embodiment shown in FIGS. 1 to 3 utilizes this principle, and the first flow velocity detection tube 2 is provided with openings 5.6 at the top and bottom with an elevation angle of 76", and the second flow velocity detection tube 3
An open lower part with an elevation angle of 180° is provided, and the negative pressure difference detected by the flow rate detection tubes 2 and 3 is applied to the characteristic curve determined in advance in the negative pressure difference detection means 8 and the calculation means 12, and the This is to calculate the flow velocity.

Incidentally, the openings 5 and 6 of the first flow velocity detection tube 2 are provided so as to be opposite to each other with respect to the basic flow direction of the fluid to be measured regulated by the pipe 1. That is, in FIGS. 1 to 3, the opening 5 is provided on the upper side and the opening 6 is provided on the lower side. On the other hand, the open lower portion of the second flow velocity detection tube 3 is provided with an elevation angle much larger than the minimum stable angle.

Setting the elevation angle in this manner makes it possible to perform sufficiently stable flow velocity measurements even when fluctuations occur in the flow of the fluid to be measured.

For example, suppose that the flow velocity of the fluid to be measured remains constant, but only the flow direction is shifted by α0 from the basic flow direction 1 shown in FIG. 3 to become direction 2. This angular displacement substantially reduces the elevation angle of the opening 5 formed on the upper side of the first flow velocity detection tube 2 by α°, and substantially increases the elevation angle of the opening 6 formed on the lower side by α0. ing. Therefore, as shown in the characteristic diagram of FIG. 8, the negative pressure with respect to the opening 5 increases, and the negative pressure with respect to the opening 6 decreases. Therefore, the changes in the negative pressure of the openings 5 and 6 with respect to the angular displacement α0 of the flow of the fluid to be measured cancel each other out, and as a result, the internal negative pressure of the first flow velocity detection tube 2 is almost equal to that for flow 1. Become.

On the other hand, the open lower portion of the second flow velocity detection tube 3 has an elevation angle α0 substantially smaller than the angular displacement α0 of the fluid to be measured. However, as is clear from FIG. 6, at angles larger than the minimum stable angle, the negative pressure hardly changes even if the elevation angle changes, so the internal negative pressure of the second flow velocity detection tube 3 also remains the same as when flow 1. Almost equal.

Therefore, even if there is some angular displacement α0 in the flow direction of the fluid to be measured, the negative pressure difference between the first flow velocity detection tube 2 and the second flow velocity detection tube 3 hardly changes.

Note that in this embodiment, the openings 5 and 6 of the first flow velocity detection tube 2
from the maximum negative pressure angle (approximately 70°) to the stable minimum angle (approximately 8
0°), but the angle may be smaller than the maximum negative pressure angle as long as it is larger than the critical negative pressure angle and smaller than the minimum stable angle. For example, if the elevation angle of the opening 5.6 is set to 65'' with respect to the basic flow 1, the negative pressure at the opening 5 will increase and the negative pressure at the opening 6 will decrease, as seen from the characteristic diagram in Figure 7. Therefore, although the direction of increase and decrease is opposite to that in this embodiment, the negative pressure in the first flow velocity detection tube 2 is as follows.
Similar to this embodiment, there is almost no change.

In addition, in this embodiment, although the openings 5.6 are oriented in opposite directions with respect to the flow direction of the fluid to be measured, their absolute values are both 76'' and the same. However, the absolute values are not necessarily the same. They do not need to be equal. For example, even if the opening 5 is 74° and the opening 6 is 78", the negative pressure increases at the opening 5 and decreases at the opening 6 with respect to the angular displacement α0. The pressure becomes stable.

Further, the negative pressure difference detection means 8 of this embodiment includes the flow velocity detection tube 2,
3, and a calculation means 11 for calculating the pressure difference between the pressure gauges 9 and 10, and a communication pipe 18 and a minute flow rate detection means 19 as shown in FIG. You can also do that.

That is, the negative pressure phenomenon occurring in the first flow velocity detection tube 2 and the second
Due to the difference between the negative pressure phenomenon that occurs in the flow rate detection tube 3, the communication tube 1
8, and the negative pressure difference can be determined from the velocity or flow rate of the fluid flowing through the communication pipe 18. The output of this minute flow rate detection means 19 is
2 and is converted into the flow velocity of the fluid to be measured. In addition,
The relationship between the output of the minute flow rate detection means 19 and the flow velocity of the fluid to be measured is determined in advance by measurement, and this relationship is written in the calculation means 12 as a calibration curve.

FIG. 10 shows an example suitable as the minute flow rate detection means 19. This minute flow rate detection means 19 is
The thermal wind speed detector is constructed using a bridge structure based on semiconductor anisotropic etching technology, and since the detection part is thermally separated from the semiconductor substrate, it is possible to detect even extremely small flow speeds. There are characteristics. Figure (a)
is a perspective view, and (b) is a BB sectional view thereof. A through hole 24 that communicates the left and right openings 22 and 23 is formed directly below the region 21 surrounded by the broken line. That is, area 2
1 is spatially separated from the semiconductor base 25 in the form of a bridge, and as a result, the region 21 is thermally insulated from the semiconductor base 25. On the surface of this region 21, a thin film heater element 26 and thin film temperature measuring resistors 27 and 28 sandwiching it are formed, as schematically shown in FIG. 2(c). When the fluid moves in the direction indicated by the arrow in FIG. It's warm. Therefore, a difference occurs between the outputs of the temperature measuring resistance elements 27 and 28, and from this output difference, the flow velocity of the fluid can be detected as shown in FIG. 2(d).

Next, a second embodiment of the present invention will be described.

This embodiment, like the first embodiment described above, is composed of a composite flow velocity detection tube consisting of two flow velocity detection tubes, negative pressure difference detection means, and calculation means. However, unlike the first embodiment, the first flow velocity detection tube 2 has a plurality of openings 13 and 14 on the same side with different elevation angles, as shown in the perspective view of FIG. 11 and the cross-sectional view of FIG. (three in this embodiment) are drilled. The elevation angle θ3 of the opening 13 is set to 65°, which is smaller than the maximum negative pressure angle (approximately 70°), and the opening 14
The elevation angle θ4 is set to 756, which is larger than the maximum negative pressure angle.

This embodiment is also based on the same principle as the first embodiment, by detecting the difference between the negative pressure inside the first flow velocity detection tube 2 and the negative pressure inside the second flow velocity detection tube 3. The flow velocity of the fluid to be measured can be detected.

Furthermore, stable values can be obtained for angular displacement of the flow of the fluid to be measured as shown below.

For example, the flow direction of the fluid to be measured is α with respect to the basic flow direction 1, as in the above embodiment.

Suppose that it is displaced and becomes direction 2. This angular displacement substantially reduces the elevation angle of both apertures 13.14 by α°. This effect results in an increase in the negative pressure with respect to the opening 13 and a decrease in the negative pressure with respect to the opening 14, as shown in the characteristic diagram of FIG.

These negative pressures cancel each other out, and as a result, the negative pressure inside the first flow rate detection tube 2 does not change.

In this example, θ3 and θ4 are each a value of the maximum negative pressure angle ±5°, but the value is not limited to this, and θ3 is larger than the critical negative pressure angle and smaller than the maximum negative pressure angle. It can take any value, and θ4 can take any value that is larger than the maximum negative pressure angle and smaller than the minimum stable angle.

In the above two embodiments, the cylindrical flow velocity detection tubes 2.3 are simply arranged in parallel as the composite flow velocity detection tube 4, but the shape is not limited to such a shape. Taking the composite flow velocity detection tube 4 used in the first embodiment as an example, it may have a shape as shown in the cross-sectional views of FIGS. 14(a) to 14(C). Also, openings 5, 6, 7.13
．． 14 are circular in shape, but an elliptical shape as shown in the perspective view of FIG. 15 is also conceivable. Furthermore, the first
As shown in the cross-sectional view of FIG. 6, the flow velocity detection tube may have an opening at its tip.

〔Effect of the invention〕

As explained above, according to the flow rate measuring device of the present invention, negative pressure states of different values are formed inside the first flow rate detection tube and inside the second flow rate detection tube due to the flow of the fluid to be measured, and The flow velocity of the measured fluid is determined from the difference in the negative pressure values, and even if the diameter of the pipe through which the measured fluid flows is large, the average flow velocity can be easily determined.

Furthermore, since a negative pressure phenomenon is utilized, even if dust is contained in the fluid to be measured, the dust is unlikely to flow into the flow velocity detection tube. Therefore, maintenance-free measurement is possible over a long period of time.

Furthermore, even if fluctuations occur in the flow of the fluid to be measured, the changes in the negative pressure at the first opening and the changes in the negative pressure at the second opening due to the fluctuations contradict each other. There is no change in the internal negative pressure in the first flow velocity detection tube, and on the other hand, the negative pressure in the third opening does not change much in response to fluctuations in the flow of the fluid to be measured. There are no measurement errors due to flow fluctuations. Therefore, very highly accurate flow velocity measurement is possible.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of the present invention, Fig. 2 is a perspective view of a composite flow velocity detection tube 4 in this embodiment, Fig. 3 is a cross-sectional view along the mm-m'' line, and Fig. 4 is a diagram of the present invention. Fig. 5 is a perspective view of the flow velocity detection tube used in this experiment, and Fig. 6 shows the experimental results, showing the internal pressure and elevation angle of the flow velocity detection tube. Graph showing the relationship between θ and FIG. 9 is a configuration diagram showing another example of the negative pressure difference detection means 8, FIG. 10 is an explanatory diagram of the minute flow rate detection means 19 in FIG. 9, and FIG. 11 is a diagram showing the composite flow rate used in the second embodiment of the present invention. A perspective view of the detection tube, Fig. 12 shows its x
u-xn' sectional view, FIG. 13 is a characteristic diagram for explaining the change in negative pressure at the opening 13.14 with respect to fluctuations in the flow of the fluid to be measured, and FIG. 14 shows another example of the composite flow velocity detection tube 4. 15 is a perspective view showing another example of the composite flow rate detection tube 4, and FIG. 16 is a sectional view showing another example of the flow rate detection tubes 2 and 3. 1... Pipe, 2... First flow velocity detection tube, 3...
Second flow velocity detection tube, 4... Composite flow velocity detection tube, 5, 6.
7゜13.14...Opening, 8...Negative pressure difference detection means,
9.10...Pressure gauge, 11.12...Calculating means.

Claims (2)

[Claims] (1) Critical negative pressure angle (the minimum angle with respect to the upstream of the fluid to be measured that can receive negative pressure from the fluid to be measured)
, and smaller than the minimum stable angle (the minimum angle with respect to the upstream of the measured fluid at which the negative pressure received from the measured fluid is approximately constant regardless of the angle). a first aperture that is exposed and an elevation angle that is greater than the critical negative pressure angle and less than the minimum stable angle; a second flow velocity detection tube having a second opening exposed to the measured fluid; a second flow velocity detection tube having a third opening exposed into the fluid to be measured with an elevation angle greater than the minimum stable angle; A flow rate measuring device comprising a calculation means for calculating a flow rate of a fluid to be measured from a difference between a negative pressure generated in a flow rate detection tube and a negative pressure generated in a second flow rate detection tube. (2) The fluid to be measured has an elevation angle that is larger than the critical negative pressure angle and smaller than the maximum negative pressure angle (an angle based on the upstream of the fluid to be measured, at which the negative pressure received from the fluid to be measured is maximum). a first flow velocity sensing tube having a first opening exposed into the fluid to be measured with an elevation angle greater than the maximum negative pressure angle and less than the stable minimum angle; a second flow velocity detection tube having a third opening exposed in the fluid to be measured with an elevation angle greater than the angle; a negative pressure generated within the first flow velocity detection tube; and a negative pressure generated within the second flow velocity detection tube. a calculation means for calculating the flow velocity of a fluid to be measured from the difference between the two.