JPH11201787A - Insertion type vortex flowmeter and its length determining method for probe conduit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for finding the most reasonable length of a probe body in the flow direction of an inserting type vortex flowmeter and to provide the insertion type vortex flowmeter having the optimum probe body length found by this method. SOLUTION: This insertion type vortex flowmeter is constituted of a pipe to be measured in which a fluid to be measured flows, a vortex generator inserted through a hole bored on the measured pipe and fixed to face the flow in the measured pipe, a probe conduit surrounding the vortex generator, and a vertex detector. In the length L of the probe conduit, downstream side length L2 from the separation point position of an origin in the flow direction is set to 0.8a-1.0a, and the upstream side length L1 is set to 0.2a-0.4a, where (a) is the inter-vortex distance changed depending on the shape of the vortex generator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insertion type vortex flowmeter in which a small-diameter vortex flowmeter is inserted into a pipe to be measured, and a total flow rate is obtained from a measured partial flow rate. The present invention relates to an insertion type vortex flowmeter capable of reducing a mounting hole for mounting a probe body of a meter.

[0002]

2. Description of the Related Art As is well known, a vortex flowmeter comprises a pipe to be measured through which a fluid to be measured flows, a vortex generator fixed in the pipe to be measured so as to face the flow, and a vortex detector. It utilizes the fact that the number of Karman vortices per unit time (vortex frequency) flowing out of a vortex generator is proportional to the flow rate within a predetermined Reynolds number range regardless of gas or liquid. Called number. As a vortex detector, a heat change, a lift change, and the like due to a vortex can be detected by a heat sensor, a strain sensor, an optical sensor, a pressure sensor, an ultrasonic sensor, or the like. Such a vortex flow meter is a simple flow meter that can measure a flow rate without being affected by the physical properties of a measurement fluid, and is widely used for measuring the flow rate of a gas or a liquid.

Generally, in a vortex flowmeter, all of the measurement fluid passes through a pipe to be measured of the flowmeter. However, in a large-diameter flow measurement, a small-diameter vortex flowmeter is inserted into the pipe to be measured, and the flow rate is measured based on the partial flow rate. An insertion type vortex flowmeter for obtaining the total flow rate has been put to practical use. In the insertion type vortex flowmeter to which the present invention is applied, a probe body including a vortex generator, a probe line, and, in some cases, a sensor is inserted from the hole to be measured, and fixed to the probe body. The other side of the shaft unit is flange-connected to the flange to be measured.

[0004] Even if the flow is measured not on the entire pipe section but on a part thereof, if the flow is uniform, the entire flow rate can be estimated. That is, the insertion type vortex flowmeter is
The flow velocity distribution of the rectified fluid flowing through the straight pipe is a normal distribution given as a function of the Reynolds number.In the normal distribution, the ratio of the flow velocity at the center of the flow pipe to the average flow velocity is defined. It is a thing using. Such an insertion type vortex flowmeter can be made small,
Cost can be reduced.

[0005] In such an insertion type vortex flowmeter, it is more compact and shorter to make the body length in the flow direction as short as possible.
Inexpensive and easy to handle. Also, the hole to be drilled in the pipe to be measured for insertion mounting and inspection can be reduced. However, the length of the main body cannot be shortened ignoring the measurement accuracy. Conventionally, the optimal main body length has not been clearly defined, but has only been empirically determined.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a method for determining the most reasonable length of a probe body in the flow direction of an insertion type vortex flowmeter. The purpose is to provide.

Another object of the present invention is to provide an insertion type vortex flowmeter having an optimum probe body length determined by such a method.

[0008]

According to the present invention, an insertion type vortex flowmeter according to the present invention includes a tube to be measured 1 through which a fluid to be measured flows, and a tube inside the tube to be measured 1 inserted through a hole formed in the tube to be measured. A vortex generator 2 fixed to face the flow, a probe conduit 3 surrounding the vortex generator 2, and a vortex detector. When the distance between vortices that changes depending on the shape of the vortex generator 2 is a, the length L of the probe conduit 3 is
As the origin of the flow direction separation point position, the downstream side length L ₂ and 0.8A～1.0A, the upstream length L ₁ 0.2a~
0.4a (claim 1).

Further, in the insertion type vortex flowmeter of the present invention, a cross-sectional shape having a short vortex distance a is selected as the vortex generator 2,
Accordingly, the length L of the probe conduit 3 is shortened (claim 2). Further, as a vortex generator having a cross-sectional shape with a short inter-vortex distance, a vortex generator having a base d perpendicular to the flow downstream is provided. An isosceles triangle and 0.15d-
A vortex generator having a convex shape having a projection on the downstream side with a distance of 0.3 d or a composite vortex generator having a set of opposite sides perpendicular to the flow and a trapezoid having a long side on the upstream side is selected. 3).

[0010] The method for determining the length of the probe line according to the present invention comprises:
This is a method for determining the length of the probe line of the insertion type vortex flowmeter, wherein the length of the probe line 3 is defined as a, where the distance between vortices that changes depending on the shape of the vortex generator 2 is a. L, and the as the origin of the flow direction separation point position, the downstream side length L ₂ and 0.8A～1.0A, the upstream length L ₁ 0.2a~
0.4a (claim 4).

Further, in the method of determining the length of the probe conduit of the present invention, a cross-sectional shape having a short vortex distance a is selected as the vortex generator, and the length of the probe is shortened accordingly ( Claim 5) Further, as a vortex generator having a cross-sectional shape with a short inter-vortex distance, an isosceles triangle having a base d perpendicular to the flow on the downstream side and 0.15d on the downstream side of the isosceles triangle.
A vortex generator of a convex shape having a projection on the downstream side with a distance of ~ 0.3d or a composite vortex generator having a set of opposite sides perpendicular to the flow and a trapezoid having a long side on the upstream side is selected (claim). Item 6).

[0012]

FIG. 1 shows an example of an insertion type vortex flowmeter to which the present invention is applied in a cross-sectional view in the flow direction. FIG. 2 shows a cross section perpendicular to the flow direction in FIG. It is sectional drawing of a direction. In these figures, reference numeral 1 denotes a pipe to be measured through which a fluid to be measured flows. Although the tube to be measured 1 is illustrated as being horizontal, actual measurement can be performed not only horizontally but also vertically. 2 is a vortex generator, 3 is a probe line for detecting a flow velocity, 4 is a shaft unit for inserting a probe body consisting of the vortex generator 2 and the probe line 3 into the tube 1 to be measured, and 8 is a probe This is a probe connection flange for connecting the shaft unit. 10 is a shaft unit convex portion provided to reduce the turbulence effect of the fluid in the concave portion for inserting the probe, 7 is densely inserted so that the fluid in the tube to be measured does not leak, and the probe main body is inserted. This is a mounting flange that is fixedly supported. Reference numeral 6 denotes a converter for amplifying and shaping the vortex signal detected by the vortex detector, converting the signal into an output signal such as a digital or analog signal, and 5 a cable for electrically connecting the insertion type vortex flow meter to the outside. Wire connection port for

The vortex generator 2 has a cylindrical probe conduit 3.
As described later, they are arranged at positions at a fixed distance in the length direction as described later, and they are integrally attached to the shaft unit 4 by the probe connection flange 8. On the other side of the shaft unit 4, a shaft unit convex portion 10 is provided, and these are tightly packed on the pipe 1 to be measured via the mounting flange 7 and the mounting bolts so that the fluid flowing therethrough does not leak outside. Installed. The sensor configured as a thermal sensor is attached to the connection portion of the probe connection flange 8, and a signal from the sensor is input to the converter 6 through an electric wire arranged in the shaft unit 4.
The converter 6 converts the signal into an appropriate signal such as a digital signal and sends it to a remote display device from the wire connection port 5.

In order to reduce the influence on the measured value due to the hole formed in the tube 1 to be measured, the shaft unit convex portion 10 is provided. Can not. Furthermore, the influence of the shaft unit 4 cannot be neglected. Therefore, it is necessary to correct the measured value based on these influences. For example, the measured value can be calibrated by measuring with a test measuring tube whose flow rate is known.

As shown, the length of the probe body inserted into the tube to be measured is defined by the length L of the probe line 3. In other words, in order to shorten the length of the probe main body, it is necessary to shorten the length L of the probe pipe 3. In this example, the probe conduit 3 has a cylindrical shape, partitions a portion of the vortex generator 2 in the measured pipe 1, and measures a partial flow rate in the large-diameter measured pipe 1. It is for. As shown in the figure, the diameter of the probe line 3 and therefore the representative length of the vortex generator 2 is represented by d, and the diameter of the tube 1 to be measured is represented by D.

The smaller the diameter of the probe line 3 becomes, the smaller the vortex flowmeter body becomes, but a problem arises in measurement accuracy. For a tube to be measured with a diameter of 150 mm,
The probe diameter is 40 to 50 from Reynolds characteristics and the like.
About mm is necessary to maintain the performance, and generally, d / D = about 0.2 to 0.35 is practically used.

In this case, it is desired to make the length of the probe body shorter as long as it does not affect the performance.
A method for obtaining the most reasonable length of the probe body in the flow direction of the insertion type vortex flowmeter, which is a feature of the present invention, will be described.

FIG. 3 is a diagram for explaining the effect of the fluid pressure based on the vortex generator placed in the pipe to be measured through which the fluid flows. The vortex is a fluid in which the fluid flowing into the vortex generator 2 is separated from a position where the momentum change generated by the flow flowing along the vortex generator 2 is large. It becomes a peeling point. The vortices c that separate from the vortex generator 2 and flow out are generated alternately in a staggered manner according to the Karman stable vortex condition, and have a constant vortex distance a and a vortex row distance H
Flows out while forming a vortex street that maintains. The vortex distance a is
The number of vortices generated per unit time, that is, the vortex frequency,
Within a predetermined time, for example, it can be obtained from the flow rate per unit time calculated based on the flow rate obtained from the fluid flowing into the reference container such as the reference tank.

An actual measurement result will be described later with reference to FIG. 4. The pressure distribution in the flow direction based on the vortex generator can be obtained by changing the pressure or the flow rate of the flowing fluid.
Although the absolute value of the pressure changes, the relative pressure distribution along the flow direction all has the shape shown in the upper part of FIG. Here, the distance in the length direction is scaled with the separation point position of the edge portion as the origin, the diameter D of the tube to be measured as a unit, the downstream side as +, and the upstream side as −. . The longitudinal direction is graduated by fluid pressure.

Based on this vortex generator, it was found that a pressure fluctuation occurred downstream of the vortex generator, and the pressure fluctuation recovered as shown in FIG. 4 near 0.9D to 1.1D. In addition, there was a pressure fluctuation not only on the downstream side of the vortex generator but also on the upstream side of the separation point, and it was found that the position where this pressure fluctuation occurred was a position of about -0.4D to -0.2D. . It can be seen that the downstream pressure recovery position and the upstream pressure fluctuation start position do not change even if the flowing fluid pressure or fluid speed is changed.

It is also known that there is a certain correlation between the generation of a vortex and the pressure fluctuation. The diameter D of the tube to be measured and the inter-vortex distance a when the shape of the vortex generator is known are:
Since it is known, ｛a = Mf × 10 ⁶ / (πD ² /
4)｝, the distance expressed using the diameter D of the measured tube can be expressed in units of the vortex distance a (here, Mf
Is the meter coefficient, defined as "volume passed through the flow meter per unit pulse"). That is, when expressed using the vortex distance a, the pressure recovery position on the downstream side is 0.8a
1.0a, and the position where the upstream pressure fluctuation starts corresponds to -0.4a to -0.2a.

FIG. 4 shows the inside of a tube to be measured having a diameter D (= 53 mm).
The representative length d of a triangular shape as shown in the upper part of FIG.
(= 14.8 mm) vortex generator (d / D = 0.2
8) shows the measured pressure distribution. The measurement fluid is air
The measured fluid pressure (a certain distance upstream of the flow meter)
1.03 kg · f as shown in the figure.
/cm^Twoabs, 5.01 to 5.00 kg · f / cm^Twoabs, 8.
80 ~ 8.74kg ・ f / cm ^TwoAbout three kinds of abs, it
The flow rates are 6.2m / s, 9.3m / s and 12.4m / s, respectively.
Measured. Pressure distribution along its flow direction
Absolute value differs depending on the measurement fluid pressure and flow velocity.
However, the pressure is constant at the upstream side of the vortex generator.
(The above measured fluid pressure) and the position at which it starts to fluctuate
On the downstream side of the living body, the position where the pressure returns to a certain level is
In each case, the position is almost constant in the flow direction.
It is as expected.

As described above, on both the downstream side and the upstream side of the vortex generator, the position at which the pressure distribution stabilizes to a steady value, that is, the distance to the point where the vortex generator does not influence, depends on the change in pressure and flow velocity. Irrespective of this, it turned out that it depends only on the inter-vortex distance a. As described above, this is 0.8 a on the downstream side.
1.0a, and -0.4a to -0.2a on the upstream side. What can be said from this is that the function of the vortex generator is not adversely affected because the downstream or upstream side of the vortex generator is not affected by a certain distance. is there. It can be said that the length of the cylindrical probe conduit 3 surrounding the vortex generator should be at least in a range where the vortex generator affects the pressure distribution. The present invention determines the length L of the probe conduit, and therefore the length of the probe body, from such a viewpoint. Its length, as mentioned above, when expressed in the vortex tube distance a becomes constant, downstream length L ₂ is 0.8A～1.0A, upstream length L ₁ is 0.2a~0 .4a. Therefore, the length L of the probe main body is L ₁ + L ₂ .

Further, it can be said from the above that if the inter-vortex distance a of the vortex generator is reduced, the length of the probe conduit 3 can be reduced. The inter-vortex distance a is the number of vortices generated per unit time,
In other words, it is found from the vortex frequency f and the flow velocity per unit time that the vortex frequency f should be increased in order to reduce the inter-vortex distance a.

For example, as shown in FIG. 3, when the cross-sectional shape of the vortex generator is an isosceles triangle where the width of the side in the direction perpendicular to the upstream flow is d, and the flow velocity is V, The vortex frequency f is represented by f = St (V / d). Here, assuming that the width d is constant and the Strouhal number St is a constant, the vortex frequency f is proportional to the flow velocity V of the fluid. According to such a principle, the vortex flowmeter measures the flow velocity V by measuring the vortex frequency f.
If the Strouhal number St can be increased,
Obviously, high vortex frequencies can be obtained.

According to the experimental results of the present applicant, it has been found that in the cross-sectional shape of the vortex generator, the length h in the flow direction with respect to the representative length d perpendicular to the flow changes the Strouhal number St ( Japanese Patent Application No. 9-17075). This will be described below.

FIG. 5 generally shows the cross-sectional shape of the vortex generator,
It is a figure which shows the relationship with the Strouhal number St. In this figure, the inflow directions are all from left to right as indicated by arrows, and the cross-sectional shape of the vortex generator is (A) perpendicular to the flow on the upstream side under the condition that the representative length is all d. (B) is a trapezoid with a set of opposite sides perpendicular to the flow and has a long side on the upstream side, (C) is an isosceles triangle with a bottom side perpendicular to the flow on the downstream side, (D) Is a rectangle whose long side is perpendicular to the flow, and (E) is a convex shape having a bottom side perpendicular to the flow on the upstream side and a projection on the downstream side. In each of the cross-sectional shapes (A) to (E),
The St numbers are arranged from high to low.

In the case of (A) in which the cross-sectional shape of the vortex generator is an isosceles triangle having a base perpendicular to the flow on the upstream side, as described with reference to FIGS. Since the base angle becomes larger, the base angle becomes larger as θ1 <θ2 <θ3. In this order, (A) 1, (A) 2, (A) 3, St
The number will be smaller.

When the cross-sectional shape of the vortex generator is a trapezoid (B) having a pair of opposite sides perpendicular to the flow, the St number increases as the length t in the flow direction decreases, and the length t1 <t2 <. t
The number of Sts becomes smaller in the order of (B) 1, (B) 2, and (B) 3, which become three.

When the cross-sectional shape of the vortex generator is an isosceles triangle (C) having a base perpendicular to the flow on the downstream side, the St number increases as the base angle θ increases, and the base angle θ3> θ2
> Θ1, (C) 1, (C) 2, and (C) 3 in the order of
The t number becomes smaller.

In the case where the cross-sectional shape of the vortex generator is a rectangle (D) whose long side is a side perpendicular to the flow, the St number increases as the short side length t decreases, and the length becomes t4 <t5 <. The St number decreases in the order of (D) 1, (D) 2, and (D) 3, which are t6.

When the cross-sectional shape of the vortex generator is a convex shape (E) having a base perpendicular to the flow on the upstream side and a protrusion on the downstream side, the St number increases as the length h of the protrusion decreases,
(E) 1, (E) 2, whose lengths are h1 <h2 <h3,
(E) The number of Sts decreases in the order of 3.

FIG. 6 is a diagram showing the relationship between the cross-sectional shape of the vortex generator and the Strouhal number St. FIG. 7 shows the Strouhal number St measured for each vortex generator shown in FIG. ing. Under the condition that the cross-sectional area in the direction perpendicular to the flow is constant, the vortex generators (A) to (C) shown in FIG. 6 are all isosceles triangles having a base perpendicular to the flow on the upstream side. The lengths are both d and the heights are ha>hb> hc. The vortex generators (E) and (F) both have a bottom d perpendicular to the flow downstream.
And isosceles triangles e and f with heights he <hf
And 0.15d-0.0 downstream of the isosceles triangles e and f.
This is a composite vortex generator in which convex shapes e ′ and f ′ having projections on the downstream side with a distance of 3d are combined. Further, the vortex generator (G) includes an isosceles triangle g having a base perpendicular to the flow on the upstream side, and 0.15d to 0.15d on the downstream side of the isosceles triangle g.
FIG. 7 shows a composite vortex generator in which a trapezoid g ′ having a pair of opposite sides perpendicular to the flow is combined downstream with a 3d distance therebetween.
Is a diagram for explaining the experimental results of the Strouhal number St and Reynolds number Re characteristics of the vortex generator shown in FIG. 6, in which the horizontal axis represents the Re number and the vertical axis represents the St number. According to the experimental results shown in FIG. 7, isosceles triangular vortex generators (A) and (B)
In (C), the smaller the height h, that is, the smaller the base angle, the larger the St number. According to FIG. 7, the St number is C>B> A.
Becomes Further, St of the composite vortex generators (E) and (F)
Numbers are both isosceles triangular vortex generators (A) (B) (C)
It was found that the vortex generator (F) having an isosceles triangle f having a larger height and a higher height h, that is, an isosceles triangle f having a larger base angle has a larger St number than the vortex generator (E). . Similarly, it was found that the composite vortex generator (G) also had a large St number.

As can be seen from the results of FIGS. 5 to 7, by selecting a vortex generator having a large St number from the cross-sectional shape of the vortex generator, the vortex frequency f generated by the flow of the fluid is obtained.
Can be higher.

[0035]

The insertion type vortex flow meter and the method for determining the length of the probe line according to the present invention are characterized in that the distance between the vortices, which varies depending on the shape of the vortex generator, is a. The length is set to the separation point position as the origin in the flow direction, the downstream length is set to 0.8a to 1.0a, and the upstream length is set to 0.2a to 0.
By setting the length to 4a, it is possible to determine the length of the probe line, which has been conventionally only empirically determined, most rationally. As a result, the length of the probe body in the flow direction can be shortened as much as possible while maintaining the measurement accuracy, and the insertion type vortex flowmeter becomes smaller, less expensive, and easier to handle. In addition, there is an effect that a hole drilled in the pipe to be measured for insertion mounting and inspection can be reduced.

Further, according to the insertion type vortex flow meter and the method for determining the length of the probe conduit thereof of the present invention, by selecting a cross-sectional shape having a short inter-vortex distance a as the vortex generator, the probe main body can be adjusted accordingly. There is an effect that the length can be shortened.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view in the flow direction of an insertion type vortex flowmeter to which the present invention is applied.

FIG. 2 is a cross-sectional view of the insertion type vortex flow meter in a direction perpendicular to the flow direction in FIG.

FIG. 3 is a diagram illustrating the effect of fluid pressure based on a vortex generator placed in a pipe to be measured through which fluid flows.

FIG. 4 shows a pressure distribution measured by placing a triangular vortex generator in a tube to be measured.

FIG. 5 is a diagram showing the relationship between the cross-sectional shape of the vortex generator and the Strouhal number St.

FIG. 6 is a diagram illustrating a relationship between a cross-sectional shape of a vortex generator and a Strouhal number St.

FIG. 7 shows the Strouhal number St measured for each vortex generator shown in FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measurement pipe 2 Vortex generator 3 Probe conduit 4 Axis unit 5 Electric wire connection port 6 Converter 7 Mounting flange 8 Probe connection flange 10 Axis unit convex part

Claims (6)

[Claims] 1. A tube to be measured through which a fluid to be measured flows, a vortex generator fixed to face the flow inside the tube to be measured while being inserted through a hole formed in the tube, and the vortex generator In the insertion type vortex flow meter composed of a probe line surrounding the probe and a vortex detector, the length of the probe line is separated when the distance between vortices that changes depending on the shape of the vortex generator is a. With the point position as the origin in the flow direction, the downstream length is set to 0.8a to 1.0a,
An insertion type vortex flowmeter having an upstream length of 0.2a to 0.4a. 2. The insertion type vortex flowmeter according to claim 1, wherein a cross-sectional shape having a short inter-vortex distance a is selected as the vortex generator, and the length of the probe conduit is shortened accordingly. . 3. An isosceles triangle having a base d perpendicular to the flow on the downstream side and 0.15d to 0.3d on the downstream side of the isosceles triangle as a vortex generator having a cross section having a short inter-vortex distance. Convex with a projection on the downstream side, or one perpendicular to the flow
3. The insertion type vortex flowmeter according to claim 2, wherein a composite vortex generator having a pair of opposite sides and a trapezoid having a long side on the upstream side is selected. 4. A tube to be measured through which a fluid to be measured flows, a vortex generator fixed to face the flow inside the tube to be measured while being inserted through a hole formed in the tube to be measured, and the vortex generator In the method of determining the length of the probe line of the insertion type vortex flow meter composed of the probe line surrounding the vortex detector and the vortex detector, the distance between vortices that changes depending on the shape of the vortex generator is a In addition, the length of the probe channel, the separation point position as the origin of the flow direction, the downstream length is 0.8a ~ 1.0a,
A method for determining the length of a probe conduit, wherein the upstream length is 0.2a to 0.4a. 5. The length of a probe conduit according to claim 4, wherein a cross-sectional shape having a short inter-vortex distance a is selected as said vortex generator, and the length of the probe is shortened accordingly. Method. 6. An isosceles triangle having a base d perpendicular to the flow on the downstream side and 0.15d to 0.3d on the downstream side of the isosceles triangle as a vortex generator having a cross section having a short inter-vortex distance. Convex with a projection on the downstream side, or one perpendicular to the flow
6. The method for determining the length of a probe conduit according to claim 5, wherein a composite vortex generator having a pair of opposite sides and a trapezoid whose upstream side is a long side is selected.