GB2186975A - Improvements in or relating to vortex-shedding fluid flowmeters - Google Patents

Abstract

A fluid flowmeter has a conduit 11 and an obstacle 12, 14 in the fluid flow which extends to outside the conduit. Successive vortices break away from the obstacle transmitting movement to the obstacle 12, 14 outside the conduit. This movement is sensed e.g. by a laser interferometer or a piezoelectric sensor which may be outside a containment wall 18. The obstacle may be symmetrical in a cross-section taken parallel to the flow and eg of rectangular or circular shape or it may be of semi-circular cross-section. <IMAGE>

Description

SPECIFICATION Improvements in or relating to fluid flowmeters This invention relates to fluid flowmeters.

According to this invention a fluid flowmeter comprises a conduitforfluid flow, an obstacle in the conduit for producing successive vortices when fluid flows, the vortices breaking away from the obstacle to produce movement of the obstacle, means for transmitting said movement to a location external of the conduit, and sensor means responsive to said movement at said location for providing a measure ofthe fluid flow.

The obstacle may extend through the conduit wall.

The sensor means may comprise on electro magnetic radiation accelerometer.

The radiation may be produced by a laser.

The radiation may pass through a window in a wall of a protective vessel around the conduitand obstacle.

The invention may be performed in various ways and one specific embodiment with possible modifications will now be described byway of example with reference to the accompanying diagrammatic drawings in which: Figure lisa section through part of a radioactive plant, for example part of a nuclear reactor, and Figure2 shows other forms of flow obstacle.

A vortex-shedding fluid flowmeter 10 comprises a conduit 11 forflowoffluid, an obstruction member9 provides an obstruction 12 in the flow arrangedto produce eddies or vortices shown at 13. The obstruction member 9 extends in sealing manner through the conduit wall 1 5to provide a portion 14 external of the wall. The obstruction member is preferably welded at 16 to the exterior of the wall 15.

The obstruction 12 acts as a so-called bluff body, that is it produces successive vortices which break free of the obstruction 12 and move downstream. A bluff body is a fluid dynamic oscillatorwhose frequency is regulated and maintained by feedback which is constituted by transfer, in the flow downstream of the obstacle 12, across the wake of some of the energy in each successive vortex. The frequency at which vortices are produced is related to fluid flow velocity. The obstacle 12 is usually symmetrical in a cross-section taken parallel to the flow. Vortices are shed on both sides of the obstacle.

When a vortex is shed from the obstacle 12 it produces movement of the obstacle 12 which is transmitted to the external portion as shown by arrows B, because of a small flexibility in wall 15 and obstacle 12. The movement or vibration ofthe obstacle portion 14 is sensed by a laser accelerometer 20 which sends an electromagnetic radiation beam 17 to the portion 14 and derivesfrom the beam reflected from the portion 14 a measure of thefrequencyofthevibration and thus of the fluid flow. The accelerometer may use a laser doppler vibrometer system.

The measured flow may be in the form of an output which varies with the rate of fluid flow or in form of an output which detects a particularflow rate or in theform of an outputwhichindicatesa changeof flowthrough a particular flow rate.

The output signal from the accelerometer may, for example, go to a visual display unitora computeror other signal handling apparatus.

Inthe caseshown of a radioactiveplanttheconduit 11 and obstacle member 9 are in a containment vessel having a containment wall 18 which has a window 19, sealed to prevent egress of radiation, through which the beam 17 passes. If the flow and its environmentarenon-hazardousthewall 18 can be omitted andthe sensor maytake otherforms; for examplethe sensor may take the form of a piezo electric sensor attached to the external obstacle portion 14.

It will be observed that there is no direct contact between the sensorandthefluid intheconduit 11.

The fluid can be liquid or gas.

The frequency at which the vortices are shed is proportional tothe Reynolds number (Re) overran extensive range of Re for a fixed geometry of bluff body.

In one form the sensor comprises an optical fibre viewing a reflective surface on the portion 14, but this is not suitable for a radiation zone or plant.

Figure 2 shows other possible cross-sections for the obstacle 12.

1. Afluid flowmetercomprising a conduitfor fluid flow, an obstacle in the conduit for producing successive vortices when fluid flows, the vortices breaking away from the obstacle to produce movement ofthe obstacle, means fortransmitting said movement to a location external ofthe conduit, and sensor means responsive to said movement at said location for providing a measure of the fluid flow.

2. Afluidflowmeteras claimed in claim 1, in which the obstacle extends through the conduit wall to transmit the movement to said location.

3. Afluid flowmeter as claimed in claim 1 or claim 2, in which the sensor means comprises an electro-magnetic radiation accelerometer.

4. Afluid flowmeteras claimed in claim 3, in which the radiation is produced by a laser.

5. Afluidflowmeterasclaimed in Claim3or Claim 4, in which the radiation passes through a window in a wall of a protective-vessel around the conduit and the obstacle.

6. Afluidflowmeter as claimed in any preceding claim, in which the obstacle has a circular cross-section.

7. Afluidflowmeteras claimed in-any of Claims 1 to 5, in which the obstacle has a rectangular cross-section with the major dimension at right angles to the conduit axis.

8. Afluidflowmeteras claimed in any of Claims 1 to 5, in which the cross-section of the obstacle is semi-circularwith the diameter at right angiesto the conduit axis and facing upstream.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to fluid flowmeters This invention relates to fluid flowmeters. According to this invention a fluid flowmeter comprises a conduitforfluid flow, an obstacle in the conduit for producing successive vortices when fluid flows, the vortices breaking away from the obstacle to produce movement of the obstacle, means for transmitting said movement to a location external of the conduit, and sensor means responsive to said movement at said location for providing a measure ofthe fluid flow. The obstacle may extend through the conduit wall. The sensor means may comprise on electro magnetic radiation accelerometer. The radiation may be produced by a laser. The radiation may pass through a window in a wall of a protective vessel around the conduitand obstacle. The invention may be performed in various ways and one specific embodiment with possible modifications will now be described byway of example with reference to the accompanying diagrammatic drawings in which: Figure lisa section through part of a radioactive plant, for example part of a nuclear reactor, and Figure2 shows other forms of flow obstacle. A vortex-shedding fluid flowmeter 10 comprises a conduit 11 forflowoffluid, an obstruction member9 provides an obstruction 12 in the flow arrangedto produce eddies or vortices shown at 13. The obstruction member 9 extends in sealing manner through the conduit wall 1 5to provide a portion 14 external of the wall. The obstruction member is preferably welded at 16 to the exterior of the wall 15. The obstruction 12 acts as a so-called bluff body, that is it produces successive vortices which break free of the obstruction 12 and move downstream. A bluff body is a fluid dynamic oscillatorwhose frequency is regulated and maintained by feedback which is constituted by transfer, in the flow downstream of the obstacle 12, across the wake of some of the energy in each successive vortex. The frequency at which vortices are produced is related to fluid flow velocity. The obstacle 12 is usually symmetrical in a cross-section taken parallel to the flow. Vortices are shed on both sides of the obstacle. When a vortex is shed from the obstacle 12 it produces movement of the obstacle 12 which is transmitted to the external portion as shown by arrows B, because of a small flexibility in wall 15 and obstacle 12. The movement or vibration ofthe obstacle portion 14 is sensed by a laser accelerometer 20 which sends an electromagnetic radiation beam 17 to the portion 14 and derivesfrom the beam reflected from the portion 14 a measure of thefrequencyofthevibration and thus of the fluid flow. The accelerometer may use a laser doppler vibrometer system. The measured flow may be in the form of an output which varies with the rate of fluid flow or in form of an output which detects a particularflow rate or in theform of an outputwhichindicatesa changeof flowthrough a particular flow rate. The output signal from the accelerometer may, for example, go to a visual display unitora computeror other signal handling apparatus. Inthe caseshown of a radioactiveplanttheconduit 11 and obstacle member 9 are in a containment vessel having a containment wall 18 which has a window 19, sealed to prevent egress of radiation, through which the beam 17 passes. If the flow and its environmentarenon-hazardousthewall 18 can be omitted andthe sensor maytake otherforms; for examplethe sensor may take the form of a piezo electric sensor attached to the external obstacle portion 14. It will be observed that there is no direct contact between the sensorandthefluid intheconduit 11. The fluid can be liquid or gas. The frequency at which the vortices are shed is proportional tothe Reynolds number (Re) overran extensive range of Re for a fixed geometry of bluff body. In one form the sensor comprises an optical fibre viewing a reflective surface on the portion 14, but this is not suitable for a radiation zone or plant. Figure 2 shows other possible cross-sections for the obstacle 12. CLAIMS

1. Afluid flowmetercomprising a conduitfor fluid flow, an obstacle in the conduit for producing successive vortices when fluid flows, the vortices breaking away from the obstacle to produce movement ofthe obstacle, means fortransmitting said movement to a location external ofthe conduit, and sensor means responsive to said movement at said location for providing a measure of the fluid flow.

2. Afluidflowmeteras claimed in claim 1, in which the obstacle extends through the conduit wall to transmit the movement to said location.

3. Afluid flowmeter as claimed in claim 1 or claim 2, in which the sensor means comprises an electro-magnetic radiation accelerometer.

4. Afluid flowmeteras claimed in claim 3, in which the radiation is produced by a laser.

5. Afluidflowmeterasclaimed in Claim3or Claim 4, in which the radiation passes through a window in a wall of a protective-vessel around the conduit and the obstacle.

6. Afluidflowmeter as claimed in any preceding claim, in which the obstacle has a circular cross-section.

7. Afluidflowmeteras claimed in-any of Claims 1 to 5, in which the obstacle has a rectangular cross-section with the major dimension at right angles to the conduit axis.

8. Afluidflowmeteras claimed in any of Claims 1 to 5, in which the cross-section of the obstacle is semi-circularwith the diameter at right angiesto the conduit axis and facing upstream.

9. Afluidflowmeter substantially as hereinbefore described with reference to and as shown in Figure 1, or Figure 2, or Figure 3, or Figure 4 ofthe accompanying drawings.