GB2179474A - Vortex amplifier - Google Patents

Abstract

Vortex amplifiers are used to control by-pass gas flow through an inspection pig Fig. 7, not shown, propelled through the pipeline by gas pressure. Each amplifier is of compact design so as to optimise arrangement of several amplifiers in limited space around the pig body. One form of amplifier has a diffuser 64 which is inclined to the central axis 62 of the amplifier. Four tangential control inlets open into a vortex chamber 50. The main inlet flow enters the chamber by an arcuate inlet 56 which extends 180 DEG about the chamber 50. The array of amplifiers is controlled digitally, a valve being provided for each amplifier to switch control flow on and off. Alternatively, the control inlets are commoned and a single analogue control valve adjusts control flow of all the amplifiers together. The designs are such that the controllability of the amplifier is improved. The operating characteristic has a major proportion to the left of the line at which the control pressure ratio is unity. <IMAGE>

Description

SPECIFICATION Vortex amplifier The invention relates to vortex amplifiers.

A vortex amplifier is a fluidic device having no moving parts and capable of operating like a valve to control flow. It has already been proposed in British Patent No 2097537 to provide a pipeline inspection pig with mechanical valves to control a flow of gas or liquid via a path which by-passes the seal cups as the pig travels along the pipeline. The speed of the pig can thus be controlled. However, the operation of such mechanical valves is adversely affected by particulate matter in the fluid in the pipeline and operation requires a source of power to move the valve members.

The object of the invention is to provide a vortex amplifier which is applicable to the control of such by-pass flow in a pipeline pig.

For such an application, the amplifier must be relatively compact because only limited space is available in the pig in which to accommodate the amplifier. Also, the control flow can be provided only as a direct branch flow from flow of fluid in the pipeline i.e. the maximum pressure difference available for the control flow cannot exceed the pressure difference between the upstream and downstream ends of the pig.

A vortex amplifier, according to the invention, comprises a circular vortex chamber which is enclosed between first and second opposed wails and by a circumferential wall, the chamber being rotationally symmetrical about an axis transverse to the opposed walls, the main flow entering the chamber through at least one main inlet which extends through the first wall and is offset from said axis, and the flow leaving the chamber through an outlet which extends through the second wall and through which said axis passes, the control flow entering the chamber, in a direction to cause rotation in the chamber, through at least one control inlet which extends through the circumferential wall, and the ratio of the diameter of the chamber to the diameter or minimum dimension of the outlet is less than four and over at least half the operating range of the amplifier the control pressure ratio is less than one.

The main inlet, or each main inlet, is in one form of the invention a circular aperture through the first wall; or alternatively it is, or each is, an arcuate aperture; or where there is more than one main inlet each is an aperture and the apertures are not all of the same shape.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section on the line I-I in Fig. 2 through a first embodiment of amplifier; Figure 2 is a longitudinal section on the line Il-Il in Fig. 1; Figures 3 and 4 are longitudinal sections similar to the sections shown in Figs. 1 and 2 on the lines Ill-Ill and IV-IV in Figs. 4 and 3, respectively; Figures 5 and 6 are graphs showing, for the embodiments shown in Figs. 1 and 2 and in Figs. 3 and 4, respectively, the operating characteristics for main flow and for control flow; and Figure 7 is a schematic longitudinal vertical section through a pipeline inspection pig showing one vortex amplifier the other amplifiers being omitted for simplicity.

Figs. 1 and 2 show the amplifier as having the following main components: a plenum chamber 10 having a supply connection spigot 12; a central housing 14 having an outlet spigot 16 connected to the chamber 10 and to a divergent pressure recovery nozzle 18. Two machined plates 20, 22 are located in the housing 14 retained by the chamber 10. The chamber 10, housing 14 and nozzle 18 are each of circular transverse cross-section.

The plates 20, 22 form opposed first and second walls and their marginal portions extend towards each other so as together they form a circumferential wall.

A circular vortex chamber 24 is enclosed between the opposed walls and by the circumferential wall. Each wall presents a radically inner circular portion to the other, the inner portion of the first wall 20 being plane.

Each wall presents to the other a radically outer concave, annular portion of generally semi-circular transverse cross-section, so that the radically outer portion 26 of the chamber 24 is toroidal. The chamber 24 is rotationally symmetrical about an axis 27 transverse to the walls 20, 22.

Two arcuate apertures 28, 30 extend through the first wall 20 and open into the toroidal portion 26 of the chamber 24 to form main inlets into the chamber 24 for flow passing from the plenum chamber 10. An outlet from the chamber 24 is formed by a central, circular aperture 32 extending through the second wall 22 and aligned with the internal opening through the spigot 16.

The housing 14 has a tangential control flow inlet branch 34 the opening through which is aligned with a control flow inlet formed by an aperture 36 through the circumferential wall of the chamber 24.

Typically, the ratio of the maximum diameter of the chamber 24 to the diameter of the outlet 32 is 2.75 and the ratio of the total area of the two inlets 28 and 30 to the area of the outlet 32 is 4. The total angle of divergence of the diffuser 18 ia typically 7 , for example.

Figs. 3 and 4 show part of a second embodiment of amplifier, the plenum chamber having been omitted and the central housing having been dispensed with. The vortex chamber 50 is circular and enclosed between first and second walls formed by machined plates 52, 54. The chamber 50 has a toroidal outer portion as before into which a single arcuate inlet 56.

The outlet from the chamber 50 is formed by a cylindrical passage 58 through a cylindrical conduit 60 included to the central axis 62 of the chamber 50. The conduit 60 is received in a circular inclined aperture extending through the second wall 54. The conduit presents an elliptical open end to the interior of the vortex chamber 50. The conduit 60 is connected to a divergent diffuser nozzle 64.

The vortex chamber 50 has four equi-angularly spaced control inlets 66, 68, 70 and 72, which are supplied by respective branch connections 74 to 80, respectively arranged in the same rotational sense.

Fig. 5 shows characteristics for the amplifier shown in Figs. 1 and 2 plotted for a supply pressure of 2068 kilopascals (300 Ibs. per square inch) and a pressure drop accross the amplifier of 41 pascals (6 Ibs. per square inch). The quotient: supply flow Qs divided by maximum flow Qmax is plotted as ordinate for the main flow characteristic 100. The quotient: control flow Qc divided by maximum flow Qmax is plotted as ordinate for the control flow characteristic 102. The corresponding plottings for the abscissa are Pc divided by P1-PD where Pc is the control pressure, PD is the pressure at the diffuser throat and P, is the pressure at the inlet. That quotient is also known as the control pressure ratio.

Fig. 6 shows corresponding characteristics 104, 106 for the amplifier shown in Figs. 3 and 4.

In Fig. 5, some 50% of the characteristic lies to the left of the line through G= 1; 73% lies to the left of the line through G= 1.05 and 80% to the left of the line through G= 1.1.

The characteristic is displaced leftwards at higher pressures and with larger amplifier exhaust throats. In Fig. 6 some 75% of the characteristic lies to the left of the G= 1 line; 85% to the left of the G=1.05 line; and 100% to the left of the G=1.08 line.

The main characteristic 104 in Fig. 6 is relatively linear, with little noise exhibited i.e. no point at which the slope changes from negative to positive.

Either of the amplifiers described above can be used in a pipeline pig to control by-pass flow. For example, several amplifiers, say nine, can be arranged in an array and switched separately into or out of action so that a required number of amplifiers can be selected by switching to give a desired overall by-pass flow, or no flow. Some 11 % of change is available for each amplifier. Alternatively, all the control inlets can be commoned so that only one control valve is needed (instead of nine separate switching valves) to control the array. Thus, instead of digital control, an analogue mode of control is available by analogue control of the control valve.

The amplifiers described are relatively compact, enabling good use to be made of the limited space available in the pig. The inclined exhaust nozzle or diffuser of the amplifier shown in Figs. 3 and 4 not only allows better use of pig space, but it has been found that that feature of the amplifier improves the linearity of the characteristic as already mentioned, reduces the control pressure ratio G and increases the proportion of the characteristic to the left of the G= 1 line. In other words, the controllability of the amplifier is improved especially in the context of use in a pig, where the control pressure must equal the inlet pressure.

Typically, a pig may be some 915 millimetres in diameter (36 inches) and made up of two pig vehicles connected by a Hooke's joint. The amplifiers would be fitted in an array around the central cylindrical pressure vessel of the leading vehicle, between the two circumferential rubber cup seals. The gas flowing in a pipeline propels the pig through the line. The control inlets of the amplifiers communicate with the upstream end of the trailing vehicle. The axial inlets of the amplifiers communicate with the upstream end of the leading vehicle. When control flow is turned off, the amplifiers present low resistance to main flow and substantial gas flow can by-pass the leading vehicle. The force on the pig overcoming friction is reduced and the pig decelerates.As the control flow increases or as more amplifiers have their control flow switched on, the point of operation of each amplifier moves down its characteristic increasing resistance to main flow so that by-pass flow is reduced and the pig accelerates. Eventually the only bypass flow is the control flow, all main flow having ceased.

Fig. 7 shows one module of a pipeline inspection pig which comprises one or more other modules (not shown) interconnected to form a train. The module shown comprises a steel pressure vessel 100 having two external flanges 102, 104 each carrying an annular sealing cup 106 of synthetic elastomeric material, which engages the inside of the pipeline 108 to be inspected by the pig. The module shown is the leading module and is connected to a second module (not shown) by a rod 110. The rod 110 is pivotally connected to the module by a pivot pin 112 and is connected to the other module by another pin (not shown) at right angles to the pin 112.

Several vortex amplifiers 114, for example nine, are equally distributed around the pressure vessel 100. Each amplfier 114 is positioned between the flanges 102, 104 and, for example, is of the kind shown in Figs. 3 and 4. Each amplifier 114 comprises a vortex chamber 116 and a diffuser 118 which are relatively inclined so that each amplifier and particularly each vortex chamber 116 lies wholly within a notional envelope 120 of waisted shape. The envelope 120 represents the working outline of the module beyond which the surface of the pipeline 108 may intrude between the flanges 102, 104 as the pig traverses bends in the pipeline 108.

The inlets to the vortex chambers 1 extend through one flange 104 and the outlet ends of the diffusers extend through the other flange 102. The direction of travel of the pig through the pipeline 108 and the direction of by-pass flow through the amplifiers is as indicated by the arrow in Fig. 7.

Each vortex chamber 116 is connected to a respective pipe 122 providing a passage which extends through the flange 104 and is connected to a control arrangement (not shown) for controlling the control flow to the control inlets, such as the four inlets (not shown) corresponding to the inlets 66 to 72 shown in Figs. 3 and 4. The control flow is in each case drawn from the gas or liquid in the pipeline 108 preferably upstream of the last module in the pig train. The gas or liquid is fed from that zone to the control arrangement via a continuation of the passage through a respective conduit, which is flexible in parts and which extends through the flanges of the other modules. Similarly, the control arrangement is connected in each case to the pipe 122 by a flexible conduit, completing the respective passage.

The control arrangement may conveniently, for example, be of the kind described in British patent No. 2097537.

The other modules typically, for example, do not have sealing cups and are supported by parts engaging the pipeline which do not effect a seal. Accordingly, the module shown in Fig. 7 is the driving module and the by-pass flows through the amplifiers 114 determine the speed of the pig. The flows through the amplifiers can never be zero, since the control flows are present as flows through the amplifiers when the amplifiers present maximum resistances to the main flows.

Claims (17)

1. A vortex amplifier comprising a circular vortex chamber which is enclosed between first and second opposed walls and by a circumferential wall, the chamber being rotationally symmetrical about an axis transverse to the opposed walls, the main flow entering the chamber through at least one main inlet which extends through the first wall and is offset from said axis, and the flow leaving the chamber through an outlet which extends through the second wall and through which said axis passes, the control flow entering the chamber, in a direction to cause rotation in the chamber, through at least one control inlet which extends through the circumferential wall, and the ratio of the diameter of the chamber to the diameter or minimum dimension of the outlet is less than four and over at least half the operating range of the amplifier the control pressure ratio is less than one.

2. An amplifier according to claim 1, in which the, or each, main inlet is a circular aperture through the first wall.

3. An amplifier according to claim 1, in which the, or each, main inlet is an arcuate aperture through the first wall.

4. An amplifier according to claim 1, in which there is more than one main inlet, each being an aperture through the first wall and the apertures not all being of the same shape.

5. An amplifier according to any preceding claim, in which the outlet is a passage which is inclined to said axis.

6. An amplifier according to claim 5, in which the outlet is a cylindrical passage the entrance to which is an elliptical opening in the second wall, the passage leading to a divergment flow diffuser coaxial with the passage.

7. An amplifier according to any preceding claim, in which each of the walls presents a radically inner circular portion to the other and each presents a radically outer concave, annu lar portion to the other of generally semi-circular transverse cross-section so that the outer portion of the chamber is toroidal, and in which the, or each, main inlet, opens into the toroidal outer portion of the chamber.

8. An amplifier according to any preceding claim, in which the, or each, main inlet directs flow in a direction parallel to said axis.

9. An amplifier according to any claim of claims 1 to 8, in which the, or each, main inlet directs flow in a direction inclined to said axis so as to induce or correspond to rotation in the chamber in the same sense as rotation caused by control flow.

10. An amplifier according to any preceding claim provided in a pipeline inspection pig to control flowing pipeline gas by-passing seal means carried by the pig and engageable with the internal surface of the pipeline.

11. Amplifiers each according to claim 10, in which for each amplifier there is a valve for controlling flow through the respective control inlet.

12. Amplifiers each according to claim 10, in which the flows through the control inlets of the amplifiers are controiled by a common control valve.

13. An amplifier according to claim 10, or each of the amplifiers according to claim 11 or claim 12, in which the pig comprises a train of interconnected modules, the leading module having said seal means in the form of two annular seals carried by respective supports, the main inlet of the amplifier passing through the upstream support, the outlet of the amplifier being connected to a diffuser which passes through the downstream sup port and in which the or each control inlet is connected by a passage which extends through the upstream support and which leads to a zone upstream of the last module in the train, said valve or each said valve controlling flow through the respective passage.

14. An amplifier according to claim 1, substantially as herein described with reference to Figs. 1 and 2 of the accompanying drawings.

15. An amplifier according to claim 1, substantially as herein described with reference to Figs. 3 and 4 of the accompanying drawings.

16. An amplifier according to claim 1, substantially as herein described with reference to Fig. 7 of the accompanying drawings.

17. A pipeline pig having amplifiers each according to claim 1 substantially as herein described with reference to Fig. 7 of the accompanying drawings.