WO2009074163A1

WO2009074163A1 - Ultrasonic flowmeter

Info

Publication number: WO2009074163A1
Application number: PCT/EP2007/010752
Authority: WO
Inventors: Henrik Lyck; Morten Storgaard Nielsen
Original assignee: Siemens Aktiengesellschaft
Priority date: 2007-12-10
Filing date: 2007-12-10
Publication date: 2009-06-18

Abstract

The present invention provides an apparatus (10, 50) for measuring a flow characteristic of a fluid (17, 57) flowing through a conduit. The apparatus (10, 50) comprises a generally cylindrical tube (16, 56) forming a portion of said conduit. The apparatus (10, 50) further comprises a pair of transducers (12, 14, 52, 54) clamped on exteriorly to said tube (16, 56) and located in relative upstream-downstream positions. The pair of transducers (12, 14, 52, 54) comprise means for transmitting ultrasonic energy for propagation therebetween, and said pair of transducers (12, 14, 52, 54) used for measuring said flow characteristic in dependance on the propagation time. The generally cylindrical tube (16, 56) further comprises a pair of surfaces (22, 24, 62, 64) for clamping on said pair of transducers (12, 14, 52, 54) thereto. These surfaces (22, 24, 62, 64) are configured such that the normals (26, 28, 66, 68) to these surfaces (22, 24, 62, 64) are parallel to each other, whereby said pair of transducers (12, 14, 52, 54), when clamped on to said pair of surfaces (22, 24, 62, 64), define a chordal measurement path (20, 60) therebetween through said fluid (17, 57).

Description

ULTRASONIC FLOWMETER

The present invention relates to fluid flow measurement and in particular to ultrasonic measurement of a flow rate of a fluid flowing through a conduit.

An ultra-sound based flow measurement device, also referred to as an ultra-sound flow-meter, is a device used for measuring flow characteristics, such as the flow-rate of a fluid flowing through a conduit. The measurement principle primarily involves measurement of velocity of the fluid based upon propagation times of ultrasonic energy emitted and received by a pair of transducers located at relative upstream-downstream positions along the conduit.

Based upon construction, ultra-sound flow-meters may be classified as those comprising spool-piece type transducers and those comprising clamp-on type transducers. Spool-piece transducers are wetted transducers that can be installed by drilling and tapping the conduit, which typically comprises a cylindrical tube, at the points of measurement. Spool-piece type flow-meters suffer from the disadvantage causing a disturbance in the fluid flow since the transducers are in direct contact with the flowing fluid. Further the associated manufacturing and installation costs of spool-piece type flow-meters are much higher than the clamp-on type.

A clamp-on type flow-meter uses ultra-sound transducers that are attached to the outer periphery of the conduit, to make measurements from the exterior of the conduit. This construction is relatively simple, and advantageously obviates the problems associated with the wetted transducers. However, clamp-on type ultra-sound flow-meters usually function as one path meter, i.e. capable of measurement only along the center-plane of the conduit. This is because of the inherent limitations of ultrasonic refraction at the surface of the conduit. One path measurements result in bad linearity and poor adjustments to odd installation conditions.

It is an object of the present invention to provide an improved apparatus for fluid flow measurement.

The above object is achieved by an apparatus for measuring a flow characteristic of a fluid flowing through a conduit, said apparatus comprising: - a generally cylindrical tube forming a portion of said conduit,

- a pair of transducers clamped on exteriorly to said tube and located in relative upstream-downstream positions, said pair of transducers comprising means for transmitting ultrasonic energy for propagation therebetween, and said pair of transducers used for measuring said flow characteristic in dependance on the propagation time, wherein said generally cylindrical tube further comprises a pair of surfaces for clamping on said pair of transducers thereto, wherein the normals to said pair of surfaces are parallel to each other, such that said pair of transducers, when clamped on to said pair of surfaces, define a chordal measurement path therebetween through said fluid.

The underlying idea of the present invention is to provide an apparatus which enables the use of clamp-on type ultra-sound transducers for out-of-plane measurement of a fluid flow characteristic, which was hitherto not possible as described earlier. This is advantageous over ordinary clamp-on type flow-meters that provide only flow information in the center plane .

In one embodiment, said generally cylindrical tube comprises a pair of circumferential bulges that define said pair of surfaces for clamping on said pair of transducers thereto. The bulges advantageously provide a suitable place to mount the transducers to provide out-of-flow flow measurements. Further advantageously, both surfaces of a bulge may be used for clamping on a transducer, thereby facilitating flow measurements along multiple chordal paths.

In another embodiment, said generally cylindrical tube comprises a pair of angular dents that define said pair of surfaces for clamping on said pair of transducers thereto. The dents advantageously provide a suitable place to mount the transducers and are easy to manufacture both in large and small volumes, and are further possible to be manufactured without welding.

In a preferred implementation of the above embodiment, said angular dents comprise an included angle between 110 degrees to 130 degrees. Particularly, for an included angle of about 120 degrees, the resulting strain of the material of the tube is minimum during manufacturing, in comparison to dents with angle of about 90 degrees. This allows use of a lower grade material to manufacture the tube. Also, when the included angle lies in the given range, it is possible to use both faces of the dent for clamp-on mounting of transducers.

In a further embodiment, said flow characteristic is measured along multiple chordal paths defined by a plurality of pairs of transducers clamped on to a plurality of pairs of surfaces on said tube. The above feature advantageously improves accuracy and linearity of the flow measurements and also obviates the disadvantages of spool piece type ultra-sound flow meters.

The present invention is further described hereinafter with reference to illustrated embodiments shown in the accompanying drawings, in which:

FIG 1 is a schematic sectional front view of a flow measurement apparatus having a cylindrical tube with bulges for clamping on transducers thereto, FIG 2 is a schematic longitudinal sectional view of the apparatus shown in FIG 1,

FIG 3 is a schematic sectional front view of a flow measurement apparatus having a cylindrical tube with dents for clamping on transducers thereto,

FIG 4 is a schematic longitudinal sectional view of the apparatus shown in FIG 2, and

FIG 5 is a schematic front view of a flow measurement apparatus having a cylindrical tube with bulges as well as dents for clamping on transducers thereto.

The embodiments described herein below provide an apparatus which enables the use of clamp-on type ultra-sound transducers for out-of-plane measurement of a fluid flow characteristic, which was hitherto not possible as described earlier. In accordance with the principles of the invention, the conduit carrying the fluid comprises a generally cylindrical tube that is provided with a pair of surfaces suitable for clamping on the transducers thereto, such that the normals to these surfaces are parallel to each other. This facilitates clamping on the transducers on the exterior of the tube in such a way that they define, between themselves, a chordal measurement path through the fluid. Specific embodiments of the above-described idea are illustrated below.

Referring jointly to FIG 1 and FIG 2, a flow measurement apparatus 10 (also referred to as a flow-meter) is illustrated for measurement of a flow characteristic, such as a flow-rate of a fluid 17, according to one embodiment of the present invention. FIG 2 represents a longitudinal view of the apparatus 10, while FIG 1 is a cross-sectional view of a section I-I of the apparatus 10 indicated in FIG 2. The fluid 17 is shown to flow in a direction represented by arrows 30 and 32 in FIG 2, through a conduit. The portion of the conduit where the flow measurement is intended to be made comprises a tube 16 having a generally cylindrical profile. A pair of transducers 12 and 14 are clamped on to the exterior of the tube 16 for measurement of the flow-rate of the fluid 17. As shown, the transducers 12 and 14 are clamped in relative upstream-downstream locations. As in case of conventional ultra-sound transducers, the transducers 12 and 14 comprise ultrasonic energy emitters and receivers, i. e. means for transmitting ultrasonic energy for propagation between the transducers. The pair of transducers 12, 14 is used for measuring said flow characteristic in dependance on the propagation time of the ultra-sonic energy waves through the fluid 17. The propagation time of these ultrasonic waves is indicative of the velocity of the fluid 17 along a plane containing these two transducers 12 and 14. Multiple such pairs of transducers (not shown herein) may be used to measure fluid velocity along various planes of measurement. Unlike in case of conventional clamp-on type flow-meters, in the present embodiment, the planes of measurement do not pass through the center of the conduit. Such measurements, which are not along the center-plane of the conduit are also referred to as out-of-plane measurements. The flow-rate of the fluid may be computed by integrating the velocity information so obtained with respect to the cross-sectional area of the tube 16.

In the shown embodiment, the generally cylindrical tube 16 is provided with at least one pair of bulges 21 and 23. These bulges 21 and 23 provide a pair of suitable surfaces 22 and 24 for clamping on the transducers 12 and 14 respectively to the tube 16. As can be seen, the normals 26 and 28 to the pair of surfaces 22 and 24 are parallel to each other. The transducers 12 and 14, when clamped on to the surfaces 22 and 24 respectively, thus define a chordal measurement path 20 therebetween through the fluid 17. As used herein, the term ^λchordal measurement path' , or ^λchordal path' refers to a flow measurement path across the conduit that does not pass though the center plane of the conduit

It should be appreciated that multiple pairs of bulges may be provided on the tube 16, to facilitate measurement of fluid flow along multiple chordal measurement paths. In the illustrated embodiment, the tube 16 further comprises bulges 25 and 27 as shown in FIG 1. Further, as shown, each bulge comprises two surfaces suitable for mounting of a transducer thereto. Thus, as shown, bulge 21 comprises surfaces 22 and 17, bulge 23 comprises surfaces 19 and 24, bulge 25 comprises surfaces 34 and 35 and bulge 27 comprises surfaces 36 and 37. In this embodiment, any two of the above-mentioned surfaces with their normals parallel to each other (for example surfaces 17 and 35, or surfaces 19 and 37), may be used for clamping on a pair of transducers to measure fluid velocity along a chordal measurement path defined between them.

Thus in the embodiment illustrated above, the bulges 21, 23, 25 and 27 facilitate use of conventional clamp-on type transducers for out-of-plane flow measurements, thus providing a multi-path ultra-sound flow-meter. In one embodiment, the tube 16 is a continuous pipe-line forming a conduit for fluid flow, in which case the fluid carrying pipe-line is custom-built to comprise the bulges in the desired measurement locations as described above. In another embodiment, the tube 16 comprising bulges may be separately manufactured and inserted between an existing fluid flow pipe-line at the desired measurement location, thus providing a continuous conduit for fluid flow. Further, advantageously, the above illustrated design is less costly to manufacture in comparison to spool-piece ultra-sound flow-meters. The bulges proposed in this embodiment facilitate mounting of the transducers without corners and crevices, reducing the risk of corrosion, and making it a more sanitary design. Further, herein, the transducers may be mounted or dismounted without affecting the use of the conduit tube at all. Another advantageous feature lies in the fact that the transducers and their electronics are based upon existing clamp-on flowmeters and thus may be used in the present invention without substantial modification.

Referring now jointly to FIG 3 and FIG 4, a flow measurement apparatus 50 is illustrated according to another embodiment of the present invention. FIG 4 represents a longitudinal view of the apparatus 50, while FIG 3 is a cross-sectional view of a section III-III of the apparatus 50 indicated in FIG 4.

Herein, the fluid 57 is shown to flow in a direction represented by arrows 82 and 84 in FIG 4, through a conduit. The measurement portion of the conduit comprises a tube 56 having a generally cylindrical profile. As in the previous embodiment, a pair of ultra-sound transducers 52 and 54 are clamped on to the conduit 56 for measurement of the flow-rate of the fluid 57, the transducers 52 and 54 being clamped in relative upstream-downstream locations. The transducers 52 and 54 are functionally similar to the transducers 12 and 14 and are capable of performing out-of-plane velocity and flow- rate measurements as described earlier.

In the shown embodiment, the generally cylindrical tube 56 is provided with at least one pair of angular dents 51 and 53. These angular dents 51 and 53 provide a pair of suitable surfaces 62 and 64 for clamping on the transducers 52 and 54 respectively to the exterior of the tube 56. As can be seen, the normals 66 and 68 to the pair of surfaces 62 and 64 are parallel to each other. The transducers 52 and 54, when clamped on to the surfaces 62 and 64 respectively, thus define a chordal measurement path 60 therebetween through the fluid 57.

It should be appreciated that multiple pairs of angular dents may be provided on the conduit 56, to facilitate measurement of fluid flow along multiple chordal measurement paths. In the illustrated embodiment, the tube 56 further comprises dents 55 and 57 as shown in FIG 3. Further, as shown, each dent comprises two surfaces suitable for mounting of a transducer thereto. Thus, as shown, dent 51 comprises surfaces 61 and 62, dent 53 comprises surfaces 63 and 64, dent 55 comprises surfaces 76 and 77 and dent 57 comprises surfaces 78 and 79.

As shown, each dent is formed by two surfaces having an included angle between them. For example, the included angle in the dent 55 is denoted by the reference numeral 80. In a preferred embodiment, the included angle of the dent has a value between 110 degrees to 130 degrees. At such an angle, particularly at an angle of 120 degrees, the resulting plane strain on the material of the tube during manufacture is minimized. Said strain is much higher for angles of about 90 degrees. Having an angular dent with an angle within said range thus allows use of a lower grade of material for manufacture of the tube.

It has been found that if the included angle is about 120 degrees, the plastic strain of the dent is of the order of approximately 0.16, allowing for processing of mild steel (for example) with a deformation hardening coefficient of up to 0.2, whereas a dent of 90 degrees has a plastic strain of the order of 0.34 only requiring very high grade stainless steel with a deformation hardening up to 0.4 to 0.45. As known to one skilled in the art, the plastic strain should be lower than the deformation hardening coefficient at plane strain, or else the material will rapture.

The above-described embodiment is easy to manufacture with pressing tools in large volumes or with single point incremental forming (SPIF) in low volume. Further, it is possible to manufacture the tube without welding. Also, when the included angle of the dent is about 120 degrees, the manufacturing stress is well below the stretch limit of most metallic materials. Such dents can be easily manufactured by forming operations. In this embodiment, the dents also do not involve any seams or crevices reducing the risk of corrosion, and making it a more sanitary design. The above embodiment is also less costly to make than spool-piece type flow-meters. Also, as in the earlier described embodiment, the transducers and their electronics are based upon existing clamp-on flowmeters and thus may be used in the present embodiment without substantial modification.

In one embodiment, the tube 56 is a continuous pipe-line providing a conduit for fluid flow, in which case the fluid carrying pipe-line is custom-built to comprise the dents in the desired measurement locations as described above. In another embodiment, the tube 56 comprising dents may be separately manufactured and inserted between an existing fluid flow pipe-line at the desired measurement location, thus providing a continuous conduit for fluid flow.

In FIG 5, a further embodiment is proposed wherein the conduit tube 104 of a flow-meter 100 comprises multiple bulges 106 and 108 and multiple dents 110 and 112, each bulge or dent providing the necessary surfaces for mounting of a transducer thereto, for measurements along multiple chordal measurement paths as explained above.

Summarizing, the present invention provides an apparatus for measuring a flow characteristic of a fluid flowing through a conduit. The apparatus comprises a generally cylindrical tube forming a portion of said conduit. The apparatus further comprises a pair of transducers clamped on exteriorly to said tube and located in relative upstream-downstream positions. The pair of transducers comprises means for transmitting ultrasonic energy for propagation therebetween, and said pair of transducers is used for measuring said flow characteristic in dependance on the propagation time. The generally cylindrical tube further comprises a pair of surfaces for clamping on said pair of transducers thereto. These surfaces are configured such that the normals to these surfaces are parallel to each other, whereby said pair of transducers, when clamped on to said pair of surfaces, define a chordal measurement path therebetween through said fluid.

Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present invention as defined.

Claims

Patent claims

1. An apparatus (10, 50) for measuring a flow

' characteristic of a fluid (17, 57) flowing through a conduit, comprising:

- a generally cylindrical tube (16, 56) forming a portion of said conduit, and

- a pair of transducers (12,14, 52,54) clamped on exteriorly to said tube (16, 56) and located in relative upstream-downstream positions, said pair of transducers (12,14, 52,54) comprising means for transmitting ultrasonic energy for propagation therebetween, and said pair of transducers (12,14, 52,54) used for measuring said flow characteristic in dependance on the propagation time, wherein said generally cylindrical tube (16, 56) further comprises a pair of surfaces (22,24, 62,64) for clamping on said pair of transducers (12,14, 52,54) thereto, wherein the normals (26,28, 66,68) to said pair of surfaces (22,24, 62,64) are parallel to each other, such that said pair of transducers (12,14, 52,54), when clamped on to said pair of surfaces (22,24, 62,64), define a chordal measurement path (20, 60) therebetween through said fluid (17, 57) .

2. The apparatus (10) according to claim 1, wherein said generally cylindrical tube (16) comprises a pair of circumferential bulges (21, 23) that define said pair of surfaces (22, 24) for clamping on said pair of transducers (12, 14) thereto.

3. The apparatus (50) according to claim 1, wherein said generally cylindrical tube (56) comprises a pair of angular dents (51, 53) that define said pair of surfaces (62, 64) for clamping on said pair of transducers (52, 54) thereto.

4. The apparatus (50) according to claim 3, wherein said angular dents (51, 53) comprise an included angle between 110 degrees to 130 degrees.

5. The apparatus (10, 50) according to any of the preceding claims, wherein said flow characteristic is measured along multiple chordal paths defined by a plurality of pairs of transducers clamped on to a plurality of pairs of surfaces on said tube (16, 56) .