CYCLONIC SEPARATION APPARATUS

Abstract: The invention provides cyclonic separation apparatus (10) comprising a cyclone body (14) having at least one fluid inlet (18) and a fluid outlet, the fluid outlet being concentric with the longitudinal axis of the cyclone body (14) and comprising a vortex finder (26) projecting from an end surface (24) of the cyclone body (14) into the interior thereof, and a proboscis (30) located partially within the vortex finder (26) and projecting beyond the distal edge thereof so that the distance between the end surface (24) of the cyclone body (14) and the furthermost end of the proboscis (30) is at least twice the smallest diameter of the vortex finder (26), wherein the cross-sectional area of the proboscis (30) is circular at any point along its length.

Description: Cyclonic Separation Apparatus The invention relates to cyclonic separation apparatus, particularly but not exclusively to cyclonic separation apparatus for use in a vacuum cleaner. Cyclonic separation apparatus consists generally of a frusto-conical cyclone body having a tangential inlet at its larger, usually upper, end and a cone opening at its smaller, usually lower, end. A fluid carrying particles entrained within it enters via the tangential inlet and follows a helical path around the cyclone body. The particles are separated out from the fluid during this motion and are carried or dropped through the cone opening into a collector from which they can be disposed of as appropriate. The cleaned fluid, usually air, travels towards the central axis of the cyclone body to form a vortex and exits the cyclonic separator via a vortex finder which is positioned at the smaller (upper) end of the cyclone body and is aligned with the central axis thereof. The vortex finder usually takes the form of a simple tube extending downwardly into the cyclone body so that the vortex of exiting fluid is reliably directed out of the cyclone. However, the vortex finder has a number of inherent disadvantages. One of these disadvantages is the fact that there is a significant pressure drop within the vortex finder due to the high angular velocity of the exiting fluid. In an attempt to overcome this problem, centerbodies have been introduced into known vortex finders in combination with tangential offtakes in order to straighten the flow passing through and out of the cyclone. Some attempts have been made to reduce the swirl of the flow using fixed vanes. A variety of these attempts are illustrated in the paper entitled " The use of tangential offtakes for energy savings in process industries" (T O'Doherty, M Biffin, N Syred: Journal of Process Mechanical Engineering 1992, Vol 206). Other arrangements incorporating centerbodies or vanes are illustrated in WO 97/46323, WO 91/06750 and US 5,444,982. In all of these pieces of prior art, the centerbody is wholly contained within the vortex finder or, if it is not, it projects only to a very minor extent into the cyclone body. This is because the single aim of the centerbody or vane is to remove the swirl from the flow within the vortex finder, rather than to stabilise it. Centerbodies have also been introduced to cyclonic separators for other reasons. One such reason, illustrated in US 4,278,452, is to expand the outgoing fluid so that an outermost annulus of fluid containing any particles remaining entrained is recirculated through the separator. However, by necessity, the major part of the centerbody must remain outside the vortex finder and therefore is incapable of stabilising the fluid flow inside the vortex finder. Another use of a centerbody is to support an electrode by means of which a Corona discharge is produced within the separation zone of the separator. This enhances the separation efficiency within the separation zone but, because the electrode must incorporate angular or pointed areas from which the Corona will discharge, there can be no stabilisation of the exiting fluid. Another problem associated with vortex finders is the fact that, during operation of the cyclonic separation apparatus, the vortex core precesses around the interior of the vortex finder causing a significant amount of noise. The provision of a centerbody wholly within the vortex finder has been recognised as contributing to the reduction of the noise associated with the exiting fluid to a certain extent but no attempt has been made to make use of a centerbody to reduce the noise still further. In domestic appliances such as vacuum cleaners, noise is always undesirable and there is an ongoing desire to reduce the noise associated with the appliance as far as possible. It is therefore an object of the present invention to provide cyclonic separation apparatus, suitable for incorporation into a domestic appliance, in which the noise level is improved. It is a further object of the invention to provide cyclonic separation apparatus in which the pressure drop appearing across the vortex finder is as small as possible. It is a still further object of the invention to provide cyclonic separation apparatus suitable for use in a domestic vacuum cleaner. The invention provides cyclonic separation apparatus as set out in claim 1. The invention also provides a proboscis as claimed in claim 22. Further and preferred features are set out in the subsidiary claims. The provision of a proboscis which protrudes beyond the lowermost end of the vortex finder to a distance at which the furthermost end of the proboscis is at least twice the smallest diameter of the vortex finder from the end surface of the cyclone body reduces the noise associated with the exiting vortex to an appreciable degree. The reduction has been found to be significantly better than in the case when the vortex finder does not protrude out of the vortex finder to any significant extent It is believed that precession of the vortex core when bounded by the walls of the vortex finder causes pressure perturbations within the airflow which are manifested as noise. Hence it is desirable to stabilise this rotation completely before the exiting air enters the vortex finder The extension of the proboscis into the core's low pressure area before it reaches the vortex finder causes the core to stabilise before it reaches the vortex finder. The noise level is thereby reduced. Experimentation with specific apparatus has shown that, for specific dimensions of cyclone, vortex finder and proboscis, there are optimum distances from the upper surface of the cyclone to which the proboscis must extend. It will be clear from the descπption and examples which follow that it is not necessary for the proboscis to extend all the way up the vortex finder to the upper surface of the cyclone Embodiments of the invention will now be descπbed with reference to the accompanying drawings, wherein: Figure 1 shows, in cross section, cyclonic separation apparatus according to the present invention and suitable for use in a vacuum cleaner; Figure 2a shows, to a larger scale, the proboscis forming part of the apparatus shown in Figure 1; Figure 2b shows a first alternative configuration of the proboscis of Figure 2a; Figure 2c shows a second alternative configuration of the proboscis of Figure 2a; Figure 3 is a cross-section through part of alternative cyclonic separation apparatus according to the present invention; Figure 4 is a schematic drawing of the test apparatus used to determine the results of the expeπments described below, and Figure 5 is a graph showing a comparison in cyclone noise w ith and without an optimised vortex findei proboscis in place Figure 1 shows cyclonic separation apparatus 10 suitable for use in a cyclonic vacuum cleaner In fact, in this example, the cyclonic separation apparatus consists of two concentπc cyclones 12,14 for sequential cleaning of an airflow The remaining features of the vacuum cleaner (such as the cleaner head or hose, the motor, motor filters, handle, supporting wheels, etc ) are not shown in the drawing because they do not form part of the present invention and will not be descπbed any further heie Indeed, it is only the innermost, high efficiency cyclone 14 which incorporates a voitex finder in this embodiment and therefore it is only the innermost cyclone 14 which is of inteiest in the context of this invention It will, however, be understood that the invention is applicable to cyclonic separation apparatus other than that which is suitable for use in vacuum cleaners and also to cyclonic separation apparatus incorporating only a single cyclone The innermost cyclone 14 comprise a cyclone body 16 which is generally frusto-conical in shape and has a fluid inlet 18 at its upper end and a cone opening 20 at its lower end The cone opening 20 is surrounded by a closed collection chamber 22 in which particles enteπng the cyclone 14 via the fluid inlet 18 and separated from the airflow within the cyclone body 16 are collected. The cyclone body 16 has an upper surface 24 m the centre of which is located a vortex finder 26 The vortex finder is generally tubular in shape and has a lower cylindrical portion 26a which merges into an upper frusto-conical portion 26b which leads out of the cyclone body 16 to an exit conduit The operation of cyclonic separation apparatus of the type descπbed thus far is well known and documented elsewhere and will not be descπbed in any further detail here The invention takes the form of a vortex finder proboscis 30 which is located inside the vortex finder 26 and is shown in position in Figure 1 The proboscis 30 is also shown on an enlarged scale in Figure 2a The proboscis 30 compπses a central elongate member 32 which is cy ndπcal along the majoπty of its length and has hemispheπcal ends 32a, 32b. The hemispherical shaping of the ends 32a,32b reduces the risk of turbulence being introduced to the airflow as a result of the presence of the proboscis 30. The elongate member 32 carries two diametrically opposed tabs 34 which are generally rectangular in shape and extend radially outwardly from the elongate member 32 sufficiently far to abut against the inteπor walls of the vortex finder 26 within the cy ndπcal portion 26a The downstream edges of the tabs 34 have radiussed outer corners to reduce the πsk of turbulence being introduced. Also, notches or grooves 36a are formed in the outer edges of the tabs 34 whilst corresponding tongues or projectιons36b are formed in the inteπor walls of the cy ndπcal portion 26a of the vortex finder 26. The tongues or projections 36b are also diametπcally opposed and are designed and positioned to cooperate with the notches or grooves 36a in the tabs 34 and so hold the proboscis 30 in position in the vortex finder 26. It will be understood that the exact method of holding the proboscis in position is immateπal to the invention and the notches/grooves 36a and tongues/projections 36b can be replaced by any alternative suitable means for reliably holding the proboscis 30 within the vortex finder 26 so that the proboscis 30 will not be dislodged by the likely rate of flow of fluid through the cyclonic separation apparatus, nor subjected to unacceptable vibrations A snap fitting method is regarded as particularly desirable because of its ease of manufacture and ease of use. The length of the proboscis 30 and its positioning are sufficient to ensure that the end 32a of the proboscis 30 furthest from the upper surface 24 lies at a point whose distance below the upper surface 24 is equal to at least twice the smallest diameter of the vortex finder 26. Thus the length of the protrusion of the proboscis 30 beyond the lower end of the vortex finder 26 added to the total length of the vortex finder 26 (below the upper surface 24) must be at least twice the diameter of the vortex finder 26. If this cπteπon is satisfied, the noise reduction achievable is improved. In the embodiment shown in Figure 1, the lowermost point of the proboscis 30 lies below the upper surface 24 at a distance which is equal to approximately 2.58 times the smallest diameter of the vortex finder 26. Specifically, the lowermost point of the proboscis 30 lies 82.5mm below the upper surface 24 and the smallest diameter of the vortex finder 26 is 32mm. Furthermore, the length of the proboscis 30 is 60mm and its diameter is 6mm. The proboscis 30 projects below the lowermost edge of the vortex finder 26 to a distance of 16.5mm. This arrangement succeeds in achieving a reduction in overall sound pressure level (noise) emitted from the whole vacuum cleaner product of 1.5dBA. In order for the proboscis 30 to function well, the cross-section of the proboscis 30 is made circular at any point along its length. The main body of the proboscis 30 is cylindrical, as mentioned above, but the upstream and downstream ends 32a, 32b can take various shapes. In the embodiment shown in Figure 2a, both of the ends 32a, 32b are hemispherical. However, one or other of the ends could be, for example, conical or frusto-conical, although a conical end will be preferable because this will reduce pressure drop and/or energy losses within the apparatus. An alternative proboscis 50 is shown in Figure 2b in which the central portion of the elongate body 52 of the proboscis 50 is again cylindrical and the downstream end 52b is hemispherical, but the upstream end 52a is conical in shape. A further difference between the proboscis 50 shown in Figure 2a and the alternative proboscis shown in Figure 2b is the number of tabs 54 provided on the elongate body 52 for support purposes. In the embodiment shown in Figure 2b, four equiangularly spaced tabs 54 are provided. Corresonding tongues are then provided on the wall of the vortex finder 26 in order to support the proboscis 50 therein. A further alternative embodiment is shown from two different angles in Figure 2c. In the Figure, the proboscis 70 is shown from two different perspective views so that the helical shape of the tabs 74 can clearly be seen. The helical shape is present so that the tabs 74 do not interfere with the rotational motion of the air exiting via the vortex finder. As in the embodiment shown in Figure 2a, the elongate body 72 is generally cylindrical in shape and the upstream end 72a is hemispherical. The downstream end 72b is planar. Each tab 74 is shaped at its distal end so as to include grooves 74a which cooperate with projections moulded into the vortex finder so that the proboscis 70 is held firmly in the correct position in the voitex finder. An alternative configuration of sepaiation apparatus is shown in part in Figure 3 The figure shows only the upper portion of the separation apparatus 80 which, as before, compπses an upstream, low-efficiency cyclone 82 and a downstream, high-efficiency cyclone 84 The low-efficiency cyclone 84 has a cyclone body 86 which has an inlet 88 communicating with the upper end of the cyclone 84 and a cone opening (not shown) at the opposite end thereof suπ-ounded by a collector (also not shown) in the same manner as shown in Figure 1 The cyclone 84 is closed at its upper end by an upper surface 90 from which depends a vortex finder 92 which extends into the interior of the cyclone 84 along a central axis thereof The vortex finder 92 is cylindrical in shape for the majoπty of its length but flares outwaidly at its upper end so as to merge smoothly with the upper surface 90. A proboscis 94 is immovably mounted within the vortex finder 92 and extends from a point above the level of the upper surface 90 πght through the vortex finder 92 so that the proboscis 94 projects beyond the lower edge of the vortex finder 92 The body of the proboscis 94 is generally cy ndπcal with a slight taper towards the upstream end 94b The upstream end 94a is hemispheπcal in shape but its downstream end 94b is merely planar. The proboscis 94 has three equiangularly spaced tabs or flanges 96 which extend outwardly from the upper end of the proboscis 94 to the inner wall of the vortex finder 92. The outermost edges of the tabs or flanges 96 are shaped so as to follow the shape of the inner wall of the vortex finder 92 to assist with correct positioning of the proboscis 94 In this embodiment, the diameter of the proboscis 30 is 10mm and the diameter Dl of the vortex finder 92 is 30.3mm The length LI of the vortex finder is 50mm and the distance L2 between the lower end 94a of the proboscis 94 and the upper surface 90 is 64 4mm. Hence the lowermost point of the proboscis 94 lies below the upper surface 90 at a distance of 2 13 times the (smallest) diameter of the vortex finder 92 The proboscis 94 projects below the vortex finder 92 to a distance of 14 4mm Tests to determine the optimum position of the lowermost end of the proboscis in the apparatus shown in Figure 1 have been cairied out. The test method and apparatus will now be described with reference to Figure 4 of the accompanying drawings. A clear cyclone 100 with a variable-length vortex finder 120 and a variable-length proboscis 140 was mounted in an upright position using appropriate clamps and mounting devices (not shown). The cyclone 100 had a maximum diameter of 140mm and a height of 360mm. Suction was provided to the cyclone 100 by a quiet source connected via a first flexible hose 102 to ensure the minimum of interference from motor noise. A second flexible hose 104 connected to the cyclone inlet 106 took incoming air from a remote chamber (not shown) to avoid interference from the noise associated with air entering the hose opening. At the inlet 106 to the cyclone 100 a flow rate meter 108 was attached to allow the incoming flow rate to be measured accurately. The variable-length vortex finder 120 consisted of a tube 122 of fixed length and fixed diameter connected to the first flexible hose 102 and slidably mounted in the upper plate 110 of the cyclone 100 by means of a sealing and clamping ring 124. In this case, the diameter of the tube was 32mm. By clamping the tube 122 at different positions so that it projected into the cyclone 100 by different amounts, the length S of the vortex finder 120 could be varied. The variable-length proboscis 140 consisted of an elongate member 142 mounted in a knee 126 in the upper end of the vortex finder 120. The elongate member 142 was slidably mounted in the knee 126 by means of a sealing and clamping block 144. Further support was provided to the elongate member 142 by way of two tabs 146 extending from the elongate member 142 to the interior wall of the vortex finder 122. The tabs 146 prevented the elongate member 142 from oscillating during the test procedure. By clamping the elongate member 142 so that it projected beyond the lower end 128 of the tube 122 by different amounts, the length L of the proboscis 140 could be varied. In order to perform the experiment, the vortex finder length S was set to the required value and the end of the elongate member 142 was set flush with the lower end 128 of the tube 122 (ie, L=0). The suction source was activated and the flow rate measured and set to the required level by appropriate adjustment. The proboscis 140 was then moved down in 5mm stages and sound measurements taken at each stage. The optimum length of the proboscis being sought was the length at which the noise level was reduced to a minimum. When an approximate location of the optimum length of the proboscis 140 had been located, 2mm increments in proboscis length L were then used to pinpoint more accurately the optimum length. Having determined the optimum length of the proboscis 140 for a given flowrate and a given vortex finder length S, the flowrate was then varied by adjusting the suction source and the incremental variation of the proboscis length L was repeated to determine the optimum proboscis length for that flowrate. Having determined the optimum proboscis length for each required flowrate and a given vortex finder length, the vortex finder length was then adjusted and a second series of experiments were carried out using the same set of flowrates to produce comparable results. The results obtained are set out below. The optimum length was further defined as being the length of the proboscis at which noise reduction reversed to a slight gain in noise level. The optimum length was therefore seen as a minimum overall sound pressure level, a point where no significant reduction is gained by continuing to extend the proboscis or a point where the tonal quality starts to deteriorate. In particular the fundamental frequency, identified using narrow band analysis, of the vortex precession was considered as being at its minimum at the optimum length. Further tests revealed that, in a cyclone body having diameter of 140mm, a height of 300mm, a vortex finder diameter of 32mm and a vortex finder length of 66mm, the optimum protrusion of the proboscis 30 beyond the lowermost end of the vortex finder is 16.5mm. This gives a distance between the lowermost end of the proboscis 30 and the upper surface 24 of 82.5mm, which is 2.58 times the diameter of the vortex finder 26. Further tests were carried out using apparatus similar to that described above but with replaceable vortex finders having different diameters. In each case, the vortex finder length was 46mm and a fixed flow rate of 271itres/second was used. The proboscis used was similar to that described above but had a diameter of 10mm. A method similar to that described above was used to find the optimum proboscis length for each vortex finder diameter. The results obtained are as follows: This clearly shows that the optimum proboscis length for a given flow rate and a given proboscis diameter decreases generally with the diameter of the vortex finder. The proboscis 30 is preferably made from a plastics material and must be sufficiently rigid not to bend or oscillate when exposed to the flowrates likely to be passed through the separation apparatus. For a proboscis suitable for use in a vacuum cleaner, a suitable material is polypropylene and this allows the proboscis to be moulded simply and economically using any one of a variety of common techniques, for example, injection moulding. Testing and research have shown that, depending upon the specific configuration of the cyclone, optimising the proboscis length can result in a reduction of between 2 and 6 dB of the overall sound pressure level of a cyclone. This is sufficient to achieve an audible difference in the overall noise levels of a domestic vacuum cleaner. Figure 5 illustrates the difference in noise (sound pressure level) produced by the cyclone of a specific vacuum cleaner with and without an optimised proboscis in place. As can clearly be seen, the presence of the proboscis (noise level shown in bold lines) removes a significant tone which is present when the proboscis is absent (noise level shown in dotted lines). The advantages of reducing the noise level of a domestic vacuum cleaner are to improve consumer satisfaction and allow a user to hear other sounds and noises within the environment in which the cleaner is being used. This can improve the safety of the user when using the cleaner.

Claims: Claims: 1. Cyclonic separation apparatus comprising a cyclone body having at least one fluid inlet and a fluid outlet, the fluid outlet being concentric with a longitudinal axis of the cyclone body and comprising a vortex finder projecting from an end surface of the cyclone body into the interior thereof, and a proboscis located partially within the vortex finder and projecting beyond the distal edge thereof so that the distance between the end surface of the cyclone body and the furthermost end of the proboscis is at least twice the smallest diameter of the vortex finder, wherein the cross-sectional area of the proboscis is circular at any point along its length. 2. Cyclonic separation apparatus as claimed in claim 1, wherein the distance between the end surface of the cyclone body and the furthermost end of the proboscis is at least 2.3 times the smallest diameter of the vortex finder. 3. Cyclonic separation apparatus as claimed in claim 2, wherein the distance between the end surface of the cyclone body and the furthermost end of the proboscis is at least 2.5 times the smallest diameter of the vortex finder. 4. Cyclonic separation apparatus as claimed in any one of the preceding claims, wherein the proboscis is generally cylindrical with at least one hemispherical end. 5. Cyclonic separation apparatus as claimed in any one of claims 1 to 3, wherein the proboscis is generally cylindrical with at least one conical end. 6. Cyclonic separation apparatus as claimed in any one of the preceding claims, wherein the diameter of the proboscis is no more than one half.of the smallest diameter of the vortex finder. 7. Cyclonic separation apparatus as claimed in claim 6, wherein the diameter of the proboscis is no more than one third of the smallest diameter of the voitex finder. 8. Cyclonic separation apparatus as claimed in claim 7, wherein the smallest diameter of the vortex finder is substantially 32mm and the diameter of the proboscis is substantially 6mm. 9. Cyclonic separation apparatus as claimed in claim 8, wherein the distance of the furthermost end of the proboscis is between 80mm and 110mm from the end surface of the cyclone body. 10. Cyclonic separation apparatus as claimed in claim 9, wherein the distance of the furthermost end of the proboscis is between 85mm and 95mm from the end surface of the cyclone body. 11. Cyclonic separation apparatus as claimed in claim 7, wherein the smallest diameter of the vortex finder is substantially 30mm and the diameter of the proboscis is substantially 10mm. 12. Cyclonic separation apparatus as claimed in claim 11, wherein the distance of the furthermost end of the proboscis is between 50mm and 90mm from the end surface of the cyclone body. 13. Cyclonic separation apparatus as claimed in claim 12, wherein the distance of the furthermost end of the proboscis is between 60mm and 70mm from the end surface of the cyclone body. 14. Cyclonic separation apparatus as claimed in any one of the preceding claims, wherein the proboscis projects beyond the lower edge of the vortex finder to a distance of at least 10mm. 15. Cyclonic separation apparatus as claimed in claim 14 and any one of claims 11 to 13, wherein the proboscis projects beyond the lower edge of the vortex finder to a distance of substantially 14.4mm. 15. Cyclonic separation apparatus as claimed in claim 14 and any one of claims 8 to 10, wherein the proboscis projects beyond the lower edge of the vortex finder to a distance of substantially 16.5mm. 16. Cyclonic separation apparatus as claimed in any one of the preceding claims, wherein the proboscis is supported in the vortex finder by means of supporting tabs extending as far as the interior wall of the vortex finder. 17. Cyclonic separation apparatus as claimed in claim 16, wherein the tabs are diametrically opposed. 18. Cyclonic separation apparatus as claimed in claim 16 or 17, wherein the tabs comprise helical vanes. 19. Cyclonic separation apparatus as claimed in any one of claims 16 to 18, wherein the tabs and the interior wall of the vortex finder incorporate retaining means for retaining the proboscis in position inside the vortex finder. 20. Cyclonic separation apparatus as claimed in claim 19, wherein the retaining means comprise resilient tongues engageable with corresponding grooves. 21. Cyclonic separation apparatus as claimed in any one of the preceding claims and forming part of a vacuum cleaner. 22. A proboscis for use in cyclonic separation apparatus as claimed in any one of the preceding claims. 23. Cyclonic separation apparatus substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings. 24. A proboscis substantially as hereinbefore described with reference to Figure 2a or 2b of the accompanying drawings.

Inventors: CROGGON JAMES HUGH, CROGGON, JAMES, HUGH
Applicants: CROGGON JAMES HUGH, NOTETRY LTD, CROGGON, JAMES, HUGH, NOTETRY LIMITED
Application year: 1999
Main classification: B04C5
IPC codes: A47L9, B04C5, B04C11