JPS5845648B2 - Eddy current flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION SUMMARY OF THE DISCLOSURE A vortex flow meter in which an obstruction assembly mounted within a flow tube generates thinning with a degree of intrusion that is a function of flow rate.

The flow meter comprises a block fixed across the flow tube at right angles to the direction of flow, the block having a substantially square cross section and a flat surface facing the incoming fluid. do.

The width of this block is maximum at its midpoint and gradually narrows toward both ends, reaching its minimum value at the ends, where the upper and lower surfaces of the block swell, making the front surface biconvex.

While the maximum width provides effective flow outflow, the average width of the block is much less than the maximum to substantially reduce the pressure drop created by the flow meter.

[Background of the invention]

TECHNICAL FIELD This invention relates to vortex flow meters and, more particularly, to vortex flow meter geometries that minimize pressure drop across the flow meter without compromising the operating efficiency of the flow meter.

In some circumstances, periodic sluggishness occurs when there is an obstruction in the flow tube.

When the Reynolds number is small, the downstream wake exhibits a laminar flow, but as the Reynolds number increases, it becomes a regular vortex pattern.

This pattern is called the Kalman thin sequence.

The frequency with which light is emitted into Karman's light train is a function of flow rate.

In this vortex flow meter, disclosed in U.S. Pat. No. 3,589,185, an obstruction assembly mounted within a flow tube is configured such that its longitudinal axis is perpendicular to the direction of fluid flow. It consists of a block placed across the flow tube, with a strip supported at a distance from the block to create a gap behind the block, which traps the Kármán vortex and strengthens the vortex line. This is to ensure stability.

This thin line is detected and a signal having a frequency proportional to the flow rate is generated.

The obstruction assembly disclosed in U.S. Pat. No. 3,867.839 utilizes a block mounted across the flow tube, the cross section of which is triangular, and the apex of the block is triangular in cross section. It is directed towards the incoming fluid.

Other shapes of cross-sectional obstacles, including cylindrical, are disclosed in U.S. Pat.
No. 116.639 and U.S. Pat. No. 3,572,117.

The benefits of a cylindrical swirl generator are that it is physically strong, mechanically stable, and provides more interior space for mounting multiple sensing devices.

However, these benefits do not come without the disadvantages of using a cylindrical vortex generator, in addition to the many disadvantages of using a cylindrical vortex generator. offset by facts.

It is well known that flat plates have a strong effect on eddy formation.

However, flat plates are physically weak and do not have enough internal space to accommodate sensing devices.

For example, the obstructing object of U.S. Pat. A rod passing through the internal conduit of the object allows for mechanical transmission to the external connection.

However, this is difficult to do if the obstacle is a flat plate.

The problems encountered with obstruction assemblies of the previously known type are concentrated in relatively small flow meters.

Therefore, only one manufacturer can produce a vortex flow meter with a flow tube diameter of 5 cf/L and a flat plate obstruction.

However, the constraints imposed on the sensing device by the shape of this obstacle and the accompanying hydraulic problems are the limits to which these flowmeters can operate.

U.S. patent application Ser. Disclosed is a small diameter eddy current flow meter obstruction assembly that is capable of generating high currents and exhibits instrument linearity of ±1% or better.

The assembly disclosed in said patent application comprises a block disposed across the flow tube at right angles to the direction of fluid flow and a sensing plate cantilevered behind the block by an elastic beam. The fluid vibration generated by the block causes the plate to vibrate at a frequency proportional to the flow rate.

The flat front face of the block faces the incoming fluid, and the rear edges of the block are beveled to define a narrow area flat rear face.

The shape of the block enhances the eddy generation characteristics of the obstruction assembly to produce a substantially linear flow measurement at low Reynolds numbers.

In a flowmeter of the type disclosed in the said application, its eddy generation characteristics are determined primarily by the width of the block; the wider the obstruction, the less frequently eddies occur for a given flow rate. .

It has long been recognized that for a flowmeter to operate satisfactorily, the ratio of the width of the obstruction to the inside diameter of the flow tube must not be too small.

However, this relationship is not critical and, as noted in the aforementioned patent application, the acceptable width of the obstruction may be within the range of about 0.15 to 0.35 of the inside diameter of the flow tube. .

Insertion of a vortex flow meter into a flow tube creates a pressure drop within the flow tube approximately equal to the square of the width of the obstruction.

Therefore, the wider the obstacle, the greater the pressure effect.

Obstacles that are widened to improve eddying characteristics therefore typically result in significant pressure drops.

There are some practical drawbacks when the pressure drop is large.

That is, pump power is required to compensate for the pressure drop, which ultimately affects the equipment and operating costs of the device.

Furthermore, at low system pressures the flow meter cavitates at high flow rates - conventionally known obstruction shapes, including those in the above-mentioned application, include:
Although it has been possible to reduce the pressure drop across the flowmeter simply by narrowing the width of the obstruction, this reduction in pressure drop is achieved exclusively at the expense of its eddy-generating properties.

Therefore, heretofore it has not been possible to substantially reduce the pressure drop without adversely affecting the operation of the flow meter.

[Summary of the invention]

In view of the foregoing, it is a principal object of the present invention to provide an obstruction assembly for a vortex flow meter that is mechanically and hydraulically effective and has a relatively low pressure drop.

More specifically, an object of the present invention is to provide an obstacle assembly having a shape that can effectively generate thinning at low Reynolds numbers and maintain instrument linearity of ±1% or more. .

Indeed, it is a feature of this invention that it combines all the benefits of obstruction assemblies of the type disclosed in the above-mentioned U.S. patent application, and that the resulting pressure drop is far greater than that produced by the inventive assembly of that application. The goal is to make it as low as possible.

Therefore, in the obstruction assembly according to the present invention, the pressure drop is kept to a minimum, eliminating the need for pump power to compensate for the pressure drop, and avoiding the possibility of cavitation.

Briefly, the above quantities are accomplished by a vortex flow meter with an obstruction assembly mounted within a flow tube of a predetermined internal diameter, the assembly being oriented in the direction of fluid flow. It consists of a block of generally rectangular cross-section placed across the flow tube at right angles to the flow tube so as to be impinged by the incoming fluid on a flat front surface of the block.

A sensing plate is cantilevered behind the block by an elastic beer, and the eddies created by the block create fluid vibrations that cause the plate to vibrate at a frequency proportional to the flow rate.

The vibrations of this plate are transmitted to an external sensor by an internal linkage.

The width of the block is maximum at its center, gradually decreases toward both ends, and reaches a minimum at both ends.

The top and bottom surfaces of the block were bell-shaped, and the front surface was biconvex, and the shape of the finished block conformed to a typical flow velocity profile.

It is preferable that the maximum width of the block is approximately 0.20 to 0.35 times the inner diameter of the flow tube, and this relationship allows for effective eddy generation. Desirably, it is about 1.05 to 2 times greater than the minimum value.

Therefore, the average width is significantly smaller than the maximum width.

Since the pressure drop experienced by a flowmeter is a function of the square of the average width, it is considerably lower than the pressure drop for a flowmeter with a constant width obstruction of the maximum width.

[Description of the invention]

In the eddy current flowmeter disclosed in U.S. Pat. Suitable for vibrating at a rate corresponding to a number.

These mechanical vibrations are sensed by one or more strain gauges placed within the swingable section, producing a signal whose frequency is proportional to the flow rate of the fluid.

In the flowmeter of the present invention shown in FIGS. 1-4, vibrations of the swingable portion of the obstruction assembly are detected by force sensors external to the flow tube.

However, although the present invention is shown as an external sensor device to show that the obstruction assembly provides adequate space for the sensing device, the invention is broadly intended to be used to reduce pressure drop. Since the shape of the obstruction assembly is the main focus, the present invention can be applied not only to the external sensor device of the eddy current flowmeter, but also to the internal sensor device, as well as other sensing devices such as thermistors, pressure sensors, etc. It can also be applied to vortex flowmeters equipped with

The flowmeters shown in Figures 1 to 4 are inserted into water pipes of water flooding equipment and other water pipes in environments where the flow rate often needs to be checked to determine whether the flow conditions are correct. A flow tube 10 is provided.

As such, the flow tube may be provided with an end flange for convenient connection to the water line.

An obstruction assembly 11 is mounted within flow tube 10 .

The assembly includes a swingable portion.

This part responds to the Karman spiral train and vibrates at a frequency proportional to the flow rate.

A vibration transmitter consisting of a rod 12 and a probe 13 is incorporated into the obstacle assembly.

The flow tube 10, shown as of circular cross-section, is provided with an inlet 10A into which the fluid to be measured is introduced.

The flow impinges on the obstacle assembly 11, splitting the flow around the obstacle and creating a fluid turbulence in the form of a Karman diagonal.

The obstacle assembly consists of a laterally extended block-like front section 14 and a rear section 15 extended behind the front section with cantilevered support members in the form of flexible beams 16.

The front block 14 has a roughly rectangular cross section;
Its axis is perpendicular to the flow axis of the flow tube and the flat surface FF faces the incoming fluid.

The ends of the front section flock 14 are fixed to the tube wall of the flow tube, so that this block is anchored within the flow tube.

The width of the block is maximum at its center, gradually decreases towards both ends, and reaches its minimum width at the ends, so the upper surface UF and lower surface LF are convex, and the front surface F
F has a biconvex shape.

The shape of the resulting block is therefore in the shape of a bulbous bullet, which is typical of the flow velocity of the fluid entering the flow tube, with a maximum in the middle of the flow tube and tapering off towards the tube wall. There is.

The rear part 15 consists of a rectangular sensing plate and is spaced apart from the front part by a beam 16.

The plane of the sensing plate is perpendicular to the front surface of the block 14 in the front section.

This rear part is shaped to interfere with the row of vortices, and the gap formed between the block of the front part and the sensing plate of the rear part captures the shank and thereby strengthens the row of vortices. Stabilize.

The rear section 15 is cantilevered by a flexible beam 16 so that it can swing.

Although the beam can bend, it has enough rigidity to allow the rear part to swing slightly.

The fluid vibrations produced in the flow tube cause the swingable rear portion 15 to vibrate at a rate corresponding to the frequency of the fluid vibrations.

Since the natural resonance frequency of the swingable rear section is far different from the flow meter's normal frequency range, there is no mechanical resonance peak and the vibration amplitude faithfully reflects the fluid vibration amplitude.

The downstream sensing plate of the assembly not only interferes with the wake to stabilize it and increase its detection, but also because its vibrations produce an output signal, this sensing plate performs two functions.

Since the part that can swing is relatively rigid, the total amplitude of the rear part is minimal even at the maximum amplitude of fluid vibration.

Therefore, fatigue of the support beam as a result of vibration effects is minimized and failures do not occur even after long-term operation.

Flow rate information is given by vibration frequency,
The magnitude of the runout is not the most important consideration since it is not due to the amplitude of the vibration.

Although the magnitude of the runout is kept extremely small in order to obtain favorable conditions for fatigue life, this does not in any way prevent the reading of outputs at various frequencies.

Very slight vibrations of the swingable rear portion of the obstruction assembly are sensed outside the flow tube 10 rather than within it.

To this end, the vibrations are transmitted by means of a vibration transmitter.

The transmitter includes a rod 12 whose rear end is fitted into a hole 18 in a beam 16.

Further, the hole 18 extends to a region adjacent to the swingable portion 15.

The front portion of the rod 12 is free into a relatively large diameter longitudinally extending hole 19 which communicates with a small diameter hole 18 and extends all the way into the forward portion 14.

Rod 12 terminates in collar 12A.

This collar surrounds the end of the probe 13 and provides a link between the rod and the probe.

Probe 13 passes through a longitudinal passageway of forward section 14 and projects from an opening in the wall of flow tube 10.

The opening in the tube wall is then covered with a flexible diaphragm 20 and the probe 13 terminates in a coupling head 21.

A force sensor 22 capable of generating a corresponding electrical signal in response to a force at the coupling head 21 is used to generate a signal indicative of the flow rate.

As previously mentioned, a simple rectangular or rectangular cross-section obstruction object is a mechanically effective shape, with a size more than adequate to accommodate the rod and probe for transmitting the vibrations to an external sensing site. It has an internal volume.

However, those with a simple rectangular cross-sectional shape have a relatively poor dust generation effect.

However, if we change the shape of the block as shown in the drawing,
The vortex-generating properties are significantly changed and the obstructing object becomes an excellent vortex-generating member without significant pressure drop.

This vortex generating member is a small eddy current flowmeter (inner diameter 2.54
to 20.32 CIrL) are of particular benefit.

The mode of change will be explained.

The block in the front part of the rectangular cross section has a maximum width A1 at its midpoint and a minimum width A2 at both ends.

The ratio between the maximum width A1 and the minimum width A2 is within the range of about 1.05 to 2.

Therefore, the average width of a block is significantly smaller than the maximum width.

The front surface FF faces the incoming fluid flow and the rear surface RF is parallel to the front surface, both of which are perpendicular to the direction of flow.

If the distance between the front surface FF and the rear surface RF is indicated by the symbol C, this distance is almost equal to the width A1.

Both rear edges of the block 14 are cut diagonally, and the upper slope b1 and the lower slope b2 are located within the rear region B', which is about 1/3 of the distance C.

Therefore, the ex-husband part B, which occupies both the upper and lower flat surfaces, is 2/3 of the distance C.

The angle of slopes b1 and b2 may be in the range of about 45 to 60 degrees.

Therefore, the area of the rear RF is smaller than the area of the front FF.

The value of the maximum width A1 of the block relative to the inner diameter of the flow tube is not critical, but is preferably in the range of about 0.20 to 0.35.

The distance along the beam 16 between the rear face RF of the block and the front edge of the sensing plate 15 is approximately 1-1/2D, and the length F of the sensing plate 15 is approximately 1/4 wavelength.

Wavelength is defined as the flow velocity divided by the frequency of eddy occurrence.

With a vortex generator having the geometric relationships described above, excellent instrument linearity of better than ±1% can be achieved at Reynolds numbers as low as 7000.

Since the relationship between A1 and A1 is not strict, it is widely used as a meter.

The value of maximum A1 relative to minimum A2 constitutes a block with a contour that matches a typical bulge flow velocity profile, and the eddy characteristics of the block are similar to those of the type described in the aforementioned U.S. patent application. , does not vary at least from a uniform value A corresponding to the maximum value A1 over the width of the block or its longitudinal axis.

The shape of the blocks of this invention is such that the average width of the blocks is substantially smaller than the maximum value A1.

Since the pressure drop is a function of the square of the mean value, the pressure drop is much smaller than that induced by an obstacle assembly in which the uniform width of the blocks is equal to the value A.

Although the preferred embodiments of the eddy current flow meter obstruction assembly of the present invention have been described, many changes may be made without departing from the spirit of the invention.

Accordingly, the present invention is not limited to the shape of the obstruction assembly shown above, but includes a vortex generating block mounted across the flow tube, the shape of the block being at its midpoint. The width has a maximum width at each end, and the width decreases toward both ends, and reaches a minimum value at the ends, so that the average value of the widths is considerably smaller than the maximum value.

[Brief explanation of the drawing]

1 is a longitudinal cross-sectional view of a vortex flow meter equipped with an obstruction assembly according to the present invention; FIG. 2 is a cross-sectional view of the flow meter taken along the plane indicated by line 2--2 in FIG. 1; The figure shows the front view of the flowmeter.
FIG. 4 is a perspective view of a block included in the obstacle assembly. The symbols of main parts in the drawings are as follows. 10...flow tube, 11...obstacle assembly, 12...rod, 13...probe,
14... Front block, 15...
- Sensing plate in the rear part, 16...Flexible beam. The relationship between the symbols is as follows. AI/D22.0
~2.5. C2, A, , B22/3C. B"=1/3C, E=3/4~1-D, F=A wavelength. 4 The angles of bl and b2 with respect to FF are within the range of 45° to 60°.

Claims (1)

[Scope of Claims] 1. A vortex flow meter in which a fluid to be measured is guided into a flow tube having an obstacle assembly therein to generate a vortex with a frequency that is a function of the flow rate. , ■ a block of substantially rectangular cross-section presenting a flat front face to the flow and fixed across said flow tube;
The width of the block is set to the maximum value at the center, and gradually reduces toward both ends until it reaches the minimum value at the ends, and a bulge is created in which the maximum value is 1.05 times to 2 times the minimum value. a block having a contour that matches a representative flow velocity profile; ■ an eddy sensing plate cantilevered to said block by a flexible beam; and ■ a flow meter passing through said block to detect vibrations of said sensing plate. A vortex flow meter characterized by comprising a connecting means for transmitting information to the outside. 2. A flowmeter according to claim 1, wherein both upper and lower rear edges of the block are cut diagonally to form a narrow flat surface that enhances the outflow characteristics of the obstruction assembly. 3. The flowmeter according to claim 1, wherein the maximum value is about 0.20 to 0.35 times the flow tube. 4. The flowmeter according to claim 2, wherein the diagonally cut rear edge occupies a rear area within about one-third of the distance between the rear face and the front face of the block. . 5. The flowmeter of claim 4, wherein the slope is at an angle within the range of about 45 to 60 degrees.