ABRASIVE FLUID FLOW

Abstract: Abrasive fluid, which includes abrasive material and a carrier fluid, is transported through a conduit with minimum wear by directing the abrasive material along the centre of the flow channel within the conduit, accelerating the carrier fluid and entraining the abrasive material within the accelerated carrier fluid. A conduit for performing this method includes a flow channel, means (9) adjacent its upstream section (1) for directing abrasive material along the centre of the flow channel, a section (2) of reduced cross-section for accelerating carrier fluid in the flow channel and a down-stream section (3) for accelerating the abrasive material at the centre of the flow channel due to entrainment with the accelerated carrier fluid.

Description: ABRASIVE FLUID FLOW An abrasive fluid, that is a fluid with abrasive material entrained therein, causes wear on the surfaces of conduits through which it passes. The object of the present invention is to reduce such vrear. It is possible to construct nozzles in one or more grades of wear resistant materials such as ceramics (for example tungsten carbide, silicon carbide, aluminium oxide). These materials have been used in conventional nozzle shapes which are designed to accelerate the flow of fluid without undue loss of energy and without introducing disturbance which would cause the resulting > high velocity jet of fluid to break up. When such nozzles are used with abrasive 'fluids, the abrasive material still causes some wear on contact with the internal surfaces of the nozzle and they will be slowed down by iπpact with the nozzle. The present invention has the object of directing the abrasive material in abrasive fluids away frcm the internal surfaces of the nozzle in order to reduce such iπpact. According to one aspect of the invention there is provided a method of transporting an abrasive fluid comprising abrasive material and carrier fluid through a conduit comprising directing the abrasive material along the centre of the flow channel within the conduit, accelerating the carrier fluid and entraining the abrasive material within the accelerated carrier fluid. According to another aspect of the invention there is provided a fluid flow conduit comprising a flow channel, means adjacent to the upstream section of the conduit for directing abrasive material along the centre of the flow channel, a section of reduced cross section for accelerating carrier fluid in the flow channel and a down-stream section for accelerating the abrasive material at the centre of the flow channel due to entrainment with the accelerated carrier fluid. Examples of the invention will now be described as reference to the accαrpanying drawings in which: Figure 1 is a diametral cross-section through a nozzle assembly, Figures 2 to 4 are schematic diametral cross-sections through alternative nozzle assemblies, Figure 5 is a view on lines 5-5 in Figure 2, and Figure 6 is a view on lines 6-6 on Figure 4. In the nozzle assembly of Figure 1, abrasive fluid enters the up-stream section 1 of relatively large cross-section and abrasive material within * the fluid is deflected towards the centre of the flow channel by a tapered portion 4 between the upstream section 1 and the mid-stream section 2. The carrier fluid tends to flow in stream-line manner in contact with the internal surfaces of the flow channels 1 and 2, whereas the abrasive material tends to be deflected by the tapered portion 4 towards the centre of the flow channel within the section 2. Dcwn-strearr. of the mid-stream section 2 is a further tapered portion 5 which causes ' the carrier fluid to accelerate due to its decreasing cross-section, and as the abrasive fluid flows through the down-stream section 3 following the tapered section 5, there is an interchange of momentum between the carrier fluid and the abrasive material flowing in the centre of the flow channel, so that the abrasive material is accelerated and leaves the outlet 6 of the nozzle assembly at high velocity. It will be noted that there is a small shoulder between the mid-stream section 2 and the entrance to the tapered section 5 and the down-stream section 3 β enclosed within a cover whose outlet surface has a greater diameter than the down-stream section 3 * Typical dimensions of such a nozzle assembly include diameters of 17-0, 11.3 and 2.8mm for the up-stream section 1, mid-stream section 2 and down-stream section 3 > an entrance diameter of 9.5mm for the tapered section 5, a length of 27mm for the tapered section 4 and mid-stream section 2 together, and a length of 60mm for the tapered section 5 and down-stream section 3 together. The outer diameter of the down-stream section 3 s 12mm. The tapers of the sections 4 and 5 can be widely varied to achieve the desired effect of deflection of the abrasive material and acceleration of the carrier fluid, as will be seen from comparison of Figures 1 to 4- In Figure 2, the angle of taper of the section 4 is much greater, and the mid-stream section 2 and the tapered section 5 are combined into a single section of uniform taper and the down-stream section 3 is also tapered, to a smaller degree than the mid-stream section. A central flow deflector 9 is mounted i the centre of the up-stream section 1, supported by radial vanes as shown in Figure 5« The flow defector 9 has a conical up-stream section, a cylindrical mid-stream section and a conical down-stream section of very large included angle. The flow deflector serves to deflect particles towards the outside of the flow channel in section 1 , so tha the tapered section 5 which has an included angle of about 120° is able to deflect the particles to the centre of the flow channel in the mid-stream section 2. In the apparatus of Figure 3, the tapered section 4 has an included angle of more than l80°, in this case about 270°. This arrangement is particularly suitable when the abrasive material comprises large particles of high density. The flow deflector 9 has a domed up-stream portion and the re-entrant domed down-stream portion. The tapered portion 5 s in this case seperate from the mid-stream portion which is cylindrical and the taperd portion 5 is rounded and the down-stream portion 3 cylindrical. In Figure 4, the geometry of Figure 2 is followed, except that the flow deflector 9 is replaced by a centrifugal entry system 8, more clearly seen in the view in Figure 6, by which abrasive fluid enters the up-stream section tangentially so that abrasive material tends to flow around the outside of the up-stream section in a spiral flow before deflection by the tapered portion 4 * A number of ribs 11 are provided in the tapered mid-stream section to prevent the spiral flow of fluid extending through that section ip order to prevent abrasive material which has been deflected to the centre of the flow channel by the tapered portion 4 being carried to the outside of that section by further centrifugal action. The ribs 11 do not extend to the centre of the section 2 and consequently do not interfere with the abrasive particles which are concentrated at the centre of the flow channel.

Claims: AMENDED CLAIMS [received by the International Bureau on 6 October 1986 (06.10.86); original claim 3 amended; other claims unchanged (1 page)] 1. A method of transporting an abrasive fluid comprising abrasive material and carrier fluid through a conduit comprising directing the abrasive material along the centre of the flow channel within the conduit, accelerating the carrier fluid and mi in . -. the abrasive material with the accelerated carrier fluid characterised in that the steps are carried out in the order listed. 2. A method as claimed in Claim 1, wherein the directing step comprises deflecting abrasive material in the carrier luid towards the centre of the flow channel within the conduit. 3. A fluid flow conduit comprising a flow channel, means adjacent to the upstream of the section (1) of the conduit for directing abrasive material along the centre of the flow channel, a section (2) of reduced cross section for accelerating carrier fluid in the flow channel and a down-stream section (3) for accelerating the abrasive material at the centre of the flow channel due to .- mτ_ti_tg with the accelerated carrier fluid characterised in that the section (2) is located downsteam of the section (1) and upstream.of the section (3). 4. A conduit as claimed in Claim 3, wherein said directing means comprises deflecting means (4) adjacent the outside of the flow channel. 5. A conduit as claimed in Claim 4, wherein the deflecting means ccπprises a surface (4 in Figure 3) inclined at an angle greater than 90° to the downstream direction of the outside of the flew channel. 6. A conduit as claimed in anyone of Claims 3 to 5, comprising a central core (9) in the upstream section of the flow channel.

Inventors: HERON ROGER ARTINDALE, SAUNDERS DAVID HENRY, HERON, ROGER, ARTINDALE, SAUNDERS, DAVID, HENRY
Applicants: BRITISH HYDROMECHANICS, THE BRITISH HYDROMECHANICS RESEARCH ASSOCIATION
Application year: 1986
Main classification: B24C5
IPC codes: B24C5