JPS60198413A - Vortex flowmeter - Google Patents

Abstract

PURPOSE:To make external oscillation and flow disturbance hard to exert influence by specifying the shapes and sizes of a vortex generation body and a detection pipe. CONSTITUTION:The detection pipe 28 of the vortex generation body 16 increases in sensitivity with its external diameter, but such a gap that the tube 28 does not contact the internal wall of a cavity part 24 is required to detect the strain of the pipe 28. The gap 26 needs to be determined so that there is no influence of foreign matter in fluid. For the purpose, the shapes and sizes of the generation body 16 and pipe 28 are specified to accelerate the flow at the periphery of the generation body 16 and the generate Karman's vortex streets behind the generation body 16. Then, pressure difference of the fluid generated between both flanks 42R and 42L of the generation body 16 operates on the pipe 28 as differential pressure to generate flexural stress, whose variation is detected by a magnetostrictive element. In this case, slits 44R and 44L are made long to improve linearity and then the Karman's vortex streets are generated stably even if the fluid to be measured is disordered owing to a drift current and a swivel current. Further, one end of the pipe 28 is formed cylindrically to increase the natural frequency, thereby reducing the influence of external oscillation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vortex flowmeter, and more particularly, a columnar vortex generator is disposed in a conduit, and a pressure difference on both sides of the vortex generator in parallel with the flow of fluid is detected. and relates to a vortex flowmeter for measuring flow rate.

Although vortex flowmeters have very good features in principle, they also have some drawbacks.

First, eddies are difficult to detect. Various methods have been used up to now, such as a thermal sensor method, an ultrasonic method, and a stress detection method, but each has advantages and disadvantages, and no method is considered definitive yet. However, for process applications, the stress detection method is becoming mainstream because it does not come into contact with liquid, is robust, and has a simple structure that requires no maintenance. However, the conventional stress detection method has the drawback of being susceptible to external vibrations.

A second disadvantage of vortex flowmeters is their sensitivity to flow velocity distribution within the conduit. If the flow velocity distribution in the conduit is disturbed by drift, swirling flow, etc., the flow velocity in the longitudinal direction of the vortex generating body will not be uniform, and a stable vortex train will not be generated.

For this reason, a relatively long straight pipe section is required before and after the vortex flowmeter, and some models require a front straight pipe section about 50 times the diameter.

A third drawback is that the detection signal of the vortex flowmeter contains many noise components, making signal processing difficult. The noise components differ depending on the vortex detection method, but
In general, high-frequency components higher than the vortex frequency and low-frequency components lower than the vortex frequency characteristically appear in each flow velocity region, and a fading phenomenon, also known as a narrow band irregular signal, frequently occurs, and these are complexly synthesized, resulting in electrical signals. Processing is not easy.

This situation is shown in FIGS. 9(al) and (b).

- FIG. 9(a) shows a case where fading has occurred, and there are places where the level has dropped to an undetectable state.

FIG. 9 fbl shows a state in which pulse loss is likely to occur and signal processing is difficult when low frequency component noise is superimposed on the vortex waveform. As described above, conventional vortex flowmeters have many drawbacks.

The present invention was made in view of these points, and its purpose is to reduce the influence of external vibrations, and to
It is an object of the present invention to provide a stress detection type vortex flowmeter that is less susceptible to flow disturbances, and to simplify electronic equipment by obtaining an essentially good vortex waveform. The feature is that in a vortex flow needle that utilizes Karman vortices, a vortex generator disposed in a fluid flow conduit has a rectangular cross-sectional shape in the fluid flow direction, and the vortex generator is orthogonal to the fluid flow of the vortex generator. A cavity for inserting a pressure-sensitive member in the direction is bored, and a slit is provided that passes through this cavity and communicates with both sides parallel to the fluid flow of the vortex generator, thereby forming a pressure guiding hole. , the inner diameter of the cavity of this pressure guiding hole is dO1, and the length of the side parallel to the fluid flow of the vortex generator is 11, and 0.71
1<do<tl, and the outer diameter of the pressure sensitive member is dl.
0.7dO<di<dO, and the width of the slit of the pressure guiding hole is h, 0.311<h<0.
611, and the slit is extended such that at least one of the ends of the slit is located outside the inner peripheral surface of the conduit.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. F is a cross-sectional view showing one embodiment of the present invention. 10
is a conduit through which the fluid to be measured flows; an opening 12 is provided at a predetermined position of this conduit 10;
It is formed by a cylindrical opening wall 14 extending in the outer circumferential direction. Reference numeral 16 denotes a vortex generator, which is inserted into the conduit 10 through the opening 12, is fixed to the flange 18 extending from the end of the opening wall 14 with bolts 20, and is connected to the opening wall 14. A slight spacing 22 is provided between them.

The vortex generator 16 has a rectangular cross-sectional shape as shown in the A-A sectional view of FIG. 1 shown in FIG. is bored in the cavity 24, and the detection tube 28, which is a pressure-sensitive member, is inserted into the cavity 24.
It is inserted so that there is a slight gap 26 with the inner wall surface. One end of this detection tube 28 is formed into a tubular shape and is open. Further, two holes 30 are bored at the other end of the detection tube 28, and a magnetostrictive element 32 is inserted into these holes 30, and an adhesive material 32 is inserted into the holes 30.
4 is filled and fixed to form a strain detection section. Further, a flange portion 36 extends from one end of the detection tube 28, and is fixed to one end of the vortex generator 16 with a port 40 via a presser flange 38.

Also, both side surfaces 42R parallel to the flow of the vortex generator 16
42L and the cavity 24 are connected to each other.
4R and 44L are provided to constitute a pressure guiding hole 46.

In the vortex flow needle configured in this manner, when fluid flows through the conduit 10, a regular Karman vortex street is generated behind the vortex generator 16, and at the same time as this vortex street is generated, both sides of the vortex generator 16 are generated. The pressures of 42R and 42L change. This pressure change acts on the detection tube 28 as a differential pressure and generates bending stress.
The magnetostrictive element 32 detects this stress change and converts it into an electrical signal.

Next, the shapes and dimensions of the vortex generator and the detection tube will be explained.

The width of the side surfaces 42R and 42L parallel to the flow of the vortex generator 16 is 11, and the slit 44 of the pressure guiding hole 46 is 11. The width of R, 4, 4L is h, the length is l, the inner diameter of the cavity 24 is dO1, the detection tube 2
The outer diameter of the tube 8 is 61, and the inner diameter of the conduit 10 is D.

The larger the outer diameter of the detection tube 28 inserted into the cavity 24 of the vortex generator 16, the better the sensitivity. It is necessary to form a gap 26 such that the detection tube 28 does not come into contact with it. Further, it is necessary to set the gap 26 in consideration so as not to be affected by foreign matter such as dust in the fluid to be measured.

Therefore, two contradictory conditions must be satisfied in the relationship between the cavity and the detection tube.

Therefore, the inventors of the present application conducted various experiments taking the above conditions into consideration. FIG. 6 is a diagram showing one of the results, and shows the inner diameter dO of the cavity 24 and the side surfaces 42R, 4 of the vortex generator.
, 2L to the width H, and the outer diameter d1 of the detection tube 28.
This shows the measurable range of vortex detection in the relationship of the ratio di/do between dO and the inner diameter dO of the cavity 240. According to this, the minimum measurable detection tube diameter d1 for the value of do/11
exists, and as the value of do/H approaches 1.0, the range of measurable detection tube diameter d1 expands. On the contrary, d
When the value of o/n decreases, the range of dl decreases, and the value of the minimum measurable detection tube diameter d1 increases.

Here, the measurable minimum detection tube diameter di exists because the vortex flowmeter of the present invention
This is based on the fact that the detection tube 28 detects a differential pressure of 42L. For example, as shown in FIG. 5(a), the cavity 2
4 and the detection tube 28 and when pressure is introduced from the direction of the arrow, the arcuate wall 4 of the cavity 24
A fluid flow occurs in the gap 26 along the line 8, which causes a differential pressure to escape, resulting in a decrease in pressure sensing capability. Furthermore, the flow of fluid within the gap 26 may generate fluid disturbances such as vortices around the detection tube 28, which may become noise and affect the vortex detection waveform, making measurement impossible.

Therefore, the detection tube 28 needs to be large enough to be unaffected by the flow generated around the detection tube 28, and there is a minimum measurable detection tube diameter d1.

Further, in FIG. 6, when the value of do/H changes in the reduction direction as described above, the value of di/do increases for the following reason. That is, when the inner diameter dO of the cavity 24 is a large value, the arcuate wall 48 is long as shown in FIG. 5+a), and when the inner diameter dQ of the cavity 24 is a small value,
The arcuate wall 48 is formed short as shown in FIG. Here the fifth
When a pressure difference due to vortex generation is introduced from the direction of the arrow as shown in FIGS. (al and b), if the width of the gap 26 is constant, the viscous resistance received from the wall surface is larger, and the shorter the arcuate wall 48 is, the smaller the arcuate wall 48 is. Therefore, as shown in FIG. As a result, disturbances such as vortices occur, which adversely affects vortex detection.Therefore, if the inner diameter dO of the cavity 24 is small, the di/doO value will inevitably increase, and the gap 26
There is a need to reduce the width of the fluid to suppress the flow of fluid.

The inventors took the above facts into consideration, and the inner diameter dO1 of the cavity
The following optimal conditions were set as the outer diameter d1 of the detection tube and the length of the side parallel to the flow of the vortex generator 1.

0.711<dO<H O, 7dO<di<dO Furthermore, the present inventors set the optimum condition for the slit as 1≦g/
The range was determined to be D O,3H<h<0.6H. The reason for this is explained below.

Generally, a vortex generator having a rectangular cross section has poor linearity. For this reason, Special Publication No. 55-20171 or Special Publication No. 55-28
There is a known method, as in No. 485, in which communicating holes are provided on both sides of the vortex generating body to cause suction and blow out, thereby improving linearity. However, in this embodiment, since the detection tube 28 is inserted into the cavity 24 of the vortex generator, fluid is not actually sucked in or blown out. In other words, although there are openings on both sides of the vortex generator, it is essentially the same as a columnar vortex generator.

Therefore, as a result of various experiments, the inventors of the present application found that the slit 4
It has been found that linearity can be significantly improved by positioning at least one of the ends of 4R and 44L outside the inner circumferential surface of the 0 conduit.

That is, the fluid displaced by the pressure difference between both side surfaces 42R and 42L of the vortex generating body I6 generated by the flow of fluid moves through the slit 44L of the side surface 42L on the suction side, as shown in FIGS. 1 and 4, for example. Rise and this slit 4
It escapes from the upper part of 4L to the interval 22, reaches the other side 42R along the opening wall 14, is sucked in at the upper part of the sulin I-44R of this side 42R, and is then drawn into the slit 44.
It descends along R and is blown out. These series of operations are
This is done through the slits 44R, 44L of the pressure guiding hole 46, the gap 26 between the cavity 24 and the detection tube 28, and the gap 22 between the opening wall 14 and the vortex generator 16, and eventually the slits 44R, 44L
The suction and blow-out of the air flow smoothly, which promotes and suppresses the separation of vortices, and improves linearity.

Therefore, at least one of the ends of the slits 44R, 44L may be positioned outside the inner circumferential surface of the conduit.

Furthermore, more preferably, the length β of the slits 44R and 44L is
It is desirable to form the inner diameter of the conduit 10 to be longer than the inner diameter of the conduit 10.

Furthermore, in order to efficiently release the pressure above the slit 44, it is conceivable to widen the width of the slit. This also results in good efficiency in introducing pressure into the pressure guiding hole 46. However, as shown in FIG. 5 (C1), the arcuate wall 48 becomes shorter, and fluid flows more easily in the gap 26, causing differential pressure to escape and reducing the pressure-sensing ability.On the other hand, when the width of the slit is narrowed, In this case, the differential pressure will not escape to the surroundings of the detection tube 28, but the linearity will deteriorate, making it difficult to efficiently detect the differential pressure.

The optimum conditions for the slit were determined from the above experimental results.

Next, the operation of the above embodiment will be explained.

By disposing the vortex flowmeter having the above configuration in which the vortex generator is set within the range of the optimum conditions in the conduit 10, the flow around the vortex generator 16 is strongly accelerated, and the flow behind the vortex generator 16 is strongly accelerated. Regular Karman vortices occur alternately. With the generation of this Karman vortex, both sides 42R142L of the vortex generator 16 parallel to the fluid
A pressure difference occurs between them. This pressure difference causes the slit 44
R, 44L and the distance 22 between the vortex generator 16 and the opening wall 14
Inhalation and blowout are efficiently performed through the sulin l□ 44R and 44L, and this pressure difference acts as a pressure difference on the detection tube 28 through the sulin l□ 44R and 44L to generate bending stress. The magnetostrictive element 32 detects this stress change and converts it into an electrical signal.

Therefore, although suction and blowout are not performed through the gap of the vortex generator 16, substantially the same effect is achieved by increasing the length of the slit, improving linearity and preventing the fluid to be measured from drifting. Karman vortices are generated stably even if they are disturbed by swirling flow.

In other words, it is a well-known fact through various experiments that suction and blow-out have the effect of stably generating Karman vortices, but even with pseudo suction and blow-out as in the present invention, the same effect can be obtained. It will be done.

Furthermore, since the detection tube 28 is installed inside the vortex generator 16, it is not affected by the drag force of the flow, and the differential pressure between the both sides 42R and 42L of the vortex generator 16 is applied to the detection tube 28. Since it works efficiently, a stable and good eddy detection waveform (see FIG. 7) can be obtained. Furthermore, the detection tube 2
Since one end of the detection tube 28 is formed into a cylindrical shape, the natural frequency is high and measurements can be made in the high-speed range, while the mass of one end of the detection tube 28 can also be reduced, making it less susceptible to external vibrations. There is.

In addition, since the detection tube 28 is located inside the vortex generator, there is no risk of wear, so lightweight materials such as aluminum may be used, and various weight reduction methods such as welding a thin-walled pipe to only one end of the cylindrical shape can be used. Therefore, the vibration resistance characteristics can be further improved.

In this respect, the conventional method of directly detecting the stress of the vortex generator cannot take such measures, resulting in an extremely large difference in performance from the present invention.

In the above embodiment, the cross-sectional shape of the vortex generating body 16 was formed into a rectangular shape, but this is easy to process, and it is possible to measure the flow from either the front or back direction. It has excellent characteristics such as good performance and eddy detection waveform. Further, since the slits 44R and 44t of the vortex generator 16 have a large area, they are not clogged by foreign matter contained in the fluid to be measured.

In addition, in the above embodiment, a strain detection sensor such as a piezoelectric element or a straight gauge may be used instead of the magnetostrictive element constituting the detection section of the detection tube.

Figures 8+a) and 8(b) are experimental data showing an example of the excellent characteristics of the vortex flowmeter of the present invention when the piping conditions were changed.

FIG. 8 (bl shows the instrumental error change when the vortex flow meter 50 of the present invention is installed immediately after the elbow 52 as shown in FIG. 8 611, and even under such adverse conditions) This shows that the instrumental difference change is small and can be used.

In this way, according to the present invention, it is possible to detect the differential pressure between the two sides parallel to the fluid of the vortex generator disposed in the conduit as an extremely stable and good vortex detection waveform, and also detect the turbulence of the fluid to be measured. It is not affected by. Furthermore, it is possible to shorten the straight pipe portions before and after the vortex flowmeter, which is a significant effect.

Various preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-mentioned embodiments. It can also be square (and of course, many modifications can be made within the scope of the spirit of the invention).

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, FIG. 2 is a cross-sectional view of A-AlJi in FIG. 1, FIG. 3 is a side view showing a part of the vortex generator, and FIG. BB sectional view in Figure 1, Figure 5 (a
l, (bl is a cross-sectional explanatory diagram showing the state of the vortex generator and the detection tube when h is set large; Figure 6 is a diagram showing the measurable range of the ratio of the inner diameter of the cavity to the outer diameter of the detection tube, and Figure 7 shows the waveform detected by the vortex flow needle of the present invention. FIG. 8 is an explanatory diagram in which the vortex flowmeter of the invention is installed (Bl is a line diagram showing the results. FIGS. 9A and 9B show detection waveforms that are difficult to detect in the vortex flowmeter. 10 ... Conduit, 12... Opening, 14... Opening wall, 16... Vortex generator, 18... Flange portion, 20...
... Bolt, 22 ... Spacing, 24 ... Hollow part, 26
...Gap, 28...Detection tube, 30...Hole. 32... Magnetostrictive element, 34... Adhesive. 36...flange part, 38...presser flange, 40
...Bolt, 42R, 42L...Side, 44R
,44L...slit. 46... Pressure hole, 48... Arc-shaped wall, 50... Vortex flow meter, 52... Elbow. Patent Applicant Nagano Keiki Seisakusho Co., Ltd. Representative Masayuki Mizo 7 6 K Tana Juku

Claims (1)

[Claims] ■ In a vortex flowmeter using Karman vortices, a vortex generator disposed in a conduit through which fluid flows has a rectangular cross-sectional shape in the fluid flow direction, and A cavity for inserting the pressure-sensitive member is bored, and a slit is provided that passes through this cavity and communicates with both sides of the vortex generator parallel to the fluid flow, thereby forming a pressure guiding hole. The inner diameter of the cavity of the pressure guiding hole is do, and the length of the side of the vortex generator parallel to the fluid flow is H, 0.7H.
<do<11, the outer diameter of the pressure-sensitive member is dl, 0.7dO<di<do, and the width of the slit of the pressure-conducting hole is h, 0.311<h<0 .6
H, and the slit extends so that at least one of the ends of the slit is located outside one peripheral surface within the conduit.