Abstract:
The invention provides cyclonic separating apparatus comprising a tapering cyclone having a larger end a smaller end, a fluid outlet located at the larger end of the cyclone, the fluid outlet becoming located coaxially with the cyclone, and a tangential offtake conduit communicating with the fluid outlet, wherein the distance between the tangential offtake conduit and the smaller end of the cyclone increases in the downstream direction of the tangential offtake conduit. Preferably, the tengential offtake conduit follows a substantially helical path. This reduces the turbulence created in the tangential offtake conduit and allows kinetic energy of the exiting fluid to be recovered as pressure energy.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The invention relates to cyclonic separating apparatus. Particularly, but not exclusively, the invention relates to cyclonic separating apparatus for use in vacuum cleaners. 
     BACKGROUND OF THE INVENTION 
     Cyclonic separating apparatus in which particulate material is separated from a fluid, usually a gas, by means of high centrifugal forces is known. Such apparatus comprises a tapering cyclone body having a fluid inlet located at the larger end of the cyclone body and arranged to introduce fluid to the interior surface of the cyclone body in a tangential manner. The smaller end of the cyclone body is surrounded by a collector or, alternatively, leads to a particulate material outlet. A fluid outlet in the form of a vortex finder is located centrally of the larger end of the cyclone body. In use, the fluid inlet introduces the fluid with the particulate material entrained therein to the interior of the cyclone body in a tangential manner. The taper of the cyclone body causes the fluid to be accelerated down the length of the cyclone body which causes the particulate matter to be separated from the fluid and to collect in the collector or, if appropriate, to exit the apparatus via the material outlet. The fluid forms a vortex generally along the longitudinal axis of the cyclone body and exits the apparatus via the vortex finder at the centre of the larger end of the cyclone body. 
     When the exiting fluid passes through the vortex finder, it is spinning with a high angular velocity. If the offtake conduit leading from the vortex finder is linear with respect to the vortex finder (ie. the conduit has a central axis which is continuous with the central axis of the vortex finder), then the outgoing fluid will continue to spin as it travels along the conduit but will, eventually, revert to linear flow and the kinetic energy of the fluid flow associated with the spinning movement will be lost, probably in the form of frictional losses. Some attempt has been made to recover some of the kinetic energy of the spinning exiting fluid by utilising tangential offtakes from the vortex finder. The offtake is positioned so as to be tangential to one side of the vortex finder so that the spinning fluid enters the offtake in a linear manner. Examples of tangential offtakes used in conjunction with cyclonic separators are shown and described in the paper entitled “The Use of Tangential Offtakes for Energy Savings in Process Industries” by T. O&#39;Doherty, M. Biffin and N. Syred (Journal of Process Mechanical Enginering, Vol. 206, Page 99ff). The arrangements shown and described in this paper attempt to convert some of the kinetic energy of the fluid flow into pressure energy. However, the pressure recovery is not wholly successful. This is partly due to the fact that the fluid flow exiting the cyclonic separator is still required to follow a path which contains sharp changes in direction. In the paper referred to above, the tangential offtakes are each located within a horizontal plane which requires the axial velocity component of the exiting fluid to be turned through a 90° angle in a short distance. This results in turbulent flow downstream of the vortex finder which leads to energy loss from the fluid. 
     One application of such separators is in vacuum cleaners in which dirt and dust particles are separated from an airflow within the vacuum cleaner so that, when dirty air is drawn into the cleaner, the dirt and dust particles are separated from the airflow and retained for disposal whilst clean air is expelled. Vacuum cleaners of this type are shown and described in various prior published patents, such as EP 0 042 723, EP 0 636 338 and EP 0 134 654. Recovery of a higher proportion of the kinetic energy of the fluid exiting the cyclonic separating apparatus would result in a vacuum cleaner having a higher efficiency and thus a better level of performance. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide cyclonic separating apparatus in which a greater proportion of the kinetic energy of exiting fluid is recoverable. It is a further object of the present invention to provide cyclonic separating apparatus which, when incorporated into a vacuum cleaner, results in the vacuum cleaner performing with a higher efficiency and/or better performance. 
     The invention provides a cyclonic separating apparatus comprising a tapering cyclone having an axis, a larger end and a smaller end, a fluid inlet and a fluid outlet located at the larger end of the cyclone, the fluid outlet being located coaxially with the cyclone, and a tangential offtake conduit communication with the fluid outlet, wherein the distance, measured parallel to the axis, between the tangential offtake and the smaller end of the cyclone increases in the downstream direction of the tangential offtake conduit. Preferably, the tangential offtake conduit follows a substantially helical path downstream of the fluid outlet. Such an arrangement allows the fluid exiting the separating apparatus to be gradually turned through a required angle without imposing sharp changes of direction. This reduces the amount of turbelence induced in the fluid flow by virtue of the direction change and this in turn reduces energy loss through friction. 
     The invention provides cyclonic separating apparatus comprising a tapering cyclone having an axis, a larger end and a smaller end, a fluid inlet and a fluid outlet located at the larger end of the cyclone, the fluid outlet being located coaxially with the cyclone, and a tangential offtake conduit communicating with the fluid outlet, wherein the distance, measured parallel to the axis, between the tangential offtake and the smaller end of the cyclone increases in the downstream direction of the tangential offtake conduit. Preferably, the tangential offtake conduit follows a substantially helical path downstream of the fluid outlet. Such an arrangement allows the fluid exiting the separating apparatus to be gradually turned through a required angle without imposing sharp changes of direction. This reduces the amount of turbulence induced in the fluid flow by virtue of the direction change and this in turn reduces energy loss through friction. 
     The tangential offtake conduit preferably has a central axis which is inclined at an angle of between 35° and 70°, preferably 60°, to the longitudinal axis of the cyclone body. This arrangement turns the exiting fluid through a required angle without significantly increasing the possibility of separation occurring as the fluid passes through the tangential offtake conduit. It also allows the kinetic energy of the spinning fluid to be recovered as pressure energy which in turn results in the provision of a highly efficient system for separation of particles from a fluid. 
     In a preferred embodiment, a centerbody is located in the fluid outlet, which consists of a vortex finder. The tangential offtake conduit then communicates with an annular chamber delimited on the outside by the fluid outlet and on the inside by the centerbody. The arrangement of an annular chamber around the centerbody ensures that all of the exiting air is aligned with the tangential offtake conduit so that the amount of turbulence introduced at the entrance to the tangential offtake conduit is kept to a minimum. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein: 
     FIG. 1 is a side view of a vacuum cleaner incorporating cyclonic separating apparatus according to the invention; 
     FIG. 2 is a view of the vacuum cleaner of FIG. 1 taken along arrow A; 
     FIG. 3 is a partially cut-away view of part of the vacuum cleaner of FIG. 1, including the cyclonic separating apparatus; 
     FIG. 4 is a side view of a tangential offtake conduit and centerbody forming part of cyclonic separating apparatus according to the invention; and 
     FIG. 5 is a plan view of the tangential offtake conduit and centerbody of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Cyclonic separating apparatus according to the invention can be incorporated to good effect in a vacuum cleaner. A vacuum cleaner incorporating cyclonic separating apparatus according to the invention is shown in FIGS. 1 and 2. The vacuum cleaner  10  has a chassis  12  which supports a motor and fan unit  14  and cyclonic separating apparatus  50 . Support wheels  16  are mounted on the chassis  12  towards the rear thereof and a castor wheel  18  is arranged beneath the chassis  12  towards the front thereof to allow the cleaner  10  to be maneouvred across a surface to be cleaned The motor and fan unit  14  is arranged substantially between the support wheels  16  to give the cleaner  10  a high degree of maneouvrability. 
     The cyclonic separating apparatus  50  is designed to effect the separation of dirt and dust particles from an airflow which is drawn into the cleaner  10  by the motor and fan unit  14 . A hose (not shown) carrying a floor tool is connected to an air inlet  20  of the cyclonic separating apparatus  50  so that the dirty airflow can be drawn into the machine. The dirty air passes into the cyclonic separating apparatus  50  which operates in a known manner to extract, initially, larger dirt and fluff and, subsequently, finer dirt and dust particles from the airflow. The airflow from which dirt and dust has been extracted passes out of the cyclonic separating apparatus  50  and then to the motor and fan unit  14  via an offtake conduit  22 . The airflow passes through the fan and around the motor so as to provide a cooling effect in a known manner. Pre- and post-motor filters (not shown) can be provided in housings  24 ,  26  in order to protect the motor and to prevent particulates released from the motor brushes from being released into the atmosphere. The clean air is exhausted to atmosphere via a clean air outlet  28 . 
     A cover portion  30  is hingedly attached to the chassis  12  about a hinge  32  to provide access to the pre-motor filter housing  24  so that the pre-motor filter can be replaced periodically. The cover portion  30  also releases the cyclonic separating apparatus to allow it to be removed from the chassis  12  for emptying purposes as and when necessary. The cover portion  30  includes the offtake conduit  22  and a carrying handle  34 . 
     Having described the basic structure and operation of the vacuum cleaner  10 , the cyclonic separating apparatus  50  will now be described in more detail with reference to FIG.  3 . It will be appreciated that the separating apparatus itself, ie the cyclone arrangement, is known and details can be found in, inter alia, EP 0134 654B. Essentially, the cyclonic separation apparatus  50  comprises an outer cyclone  52  and an inner cyclone  54 . The outer cyclone comprises a generally cylindrical container or bin  56  having a side wall  56   a,  a base  56   b  and a tangential inlet  58 . The inner cyclone  54  comprises a frusto-conical cyclone body  60  depending from an upper surface  62  of the separating apparatus  50  The inner cyclone  54  has a cone opening  64  at the lower end thereof and a tangential inlet  66 . Depending between the side wall  56   a  of the outer cyclone  52  and the inner cyclone body  60  is a shroud  68  which is substantially cylindrical in shape and includes a multiplicity of perforations  70  within a cylindrical band  68   a  of the shroud  68 . The shroud  68  is supported by way of a flange  68   a  extending between the shroud  68  and an upper portion of the outer cyclone  52 . The shroud  68  is also sealed to the outer surface of the cyclone body  60  at the lower end of the shroud  68 . The upper part of the interior of the shroud  68  communicates with the tangential inlet  66 . Below the shroud  68 , a fine dust collector  72  is positioned so that it surrounds the cone opening  64 . The fine dust collector  72  is sealed to the base  56   b  of the container  56  and also to the cyclone body  60  so that a closed collector is formed around the cone opening  64 . A cylindrical vortex finder  74  is positioned centrally of the upper surface  62  so that it extends into the interior of the inner cyclone  54  along the axis of the frusto-conical cyclone body  60 . 
     In use, as will be understood from the prior art, dirty air enters the cyclonic separating apparatus  50  via the tangential inlet  58 . The tangential nature of the inlet  58  forces the incoming air to follow a spiral path in a swirling motion around the interior surface of the container  56  so that larger dirt and fluff particles become separated from the airflow and collect in the lower area of the container  56  on top of the fine dust collector  72 . The airflow moves inwardly towards the upper portion of the fine dust collector  72  and then travels, still swirling, up the outer surface of the shroud  68 . The airflow then travels through the perforations  70  in the shroud  68  and is then introduced to the interior of the inner cyclone  54  via the tangential inlet  66 . The tangential nature of this inlet  66  also forces the airflow to follow another spiral path inside the cyclone body  60 . The frusto-conical shape of the cyclone body  60  causes the velocity of the airflow to increase as it travels down the cyclone body  60  and the high speeds attained by the airflow allow very small particulates of dirt and dust to be separated from the airflow and collected in the fine dust collector  72 . The clean airflow then forms a vortex substantially along the longitudinal axis of the cycone body  60  which exits the inner cyclone  54  by way of the vortex finder  74 . 
     As has been stated, the construction and operation of such separation apparatus is well known and the finer details need not be described any further. The invention lies in the vortex finder  74  and the offtake conduit  22  located immediately downstream of the vortex finder  74 . The invention is therefore applicable to any cyclonic separating apparatus having a frusto-conical cyclone body in which a vortex is created and in which the exiting air is carried out of the apparatus via a vortex finder. 
     As can be seen from FIG. 3, the vortex finder  74  is cylindrical and depends from the upper surface  62  into the inner cyclone  54  by means of an inclined support wall  62   a.  The vortex finder  74  also extends upwardly from the support wall  62   a  so that the vortex finder  74  terminates in a plane level with the upper surface  62 , although this is not critical. Extending along the central axis of the vortex finder  74  is a centerbody  76  which is generally cylindrical but may taper slightly from the upper end towards the lower end. The centerbody  74  has a hemispherical distal end  76   a  which terminates within the vortex finder  74  without extending beyond the lower end thereof. Again, this is not critical. The vortex finder  74  communicates with a chamber  78  located immediately above the vortex finder  74  and at the upstream end of the tangential offtake conduit  22 . The chamber has an arcuate outer wall  80  which has a generally spiral shape so that the chamber  78  communicates with the tangential offtake  22  in the manner of a scroll. 
     The centerbody  76  is formed integrally with a support portion  84  which is shaped so as to fit inside the upper end of the chamber  78  and to abut against the roof of the chamber  78 . The support portion  84  defines the upper boundary of the chamber  78  and also provides support for the centerbody  76 . The shape of the lower surface  86  of the support portion  84  is generally helical to form a scroll with a roughly constant cross-sectional area and is contiguous with the tangential offtake conduit  22 . The tangential offtake conduit  22  communicates with the chamber  78  in a scroll-like manner and then follows a path which increases in distance from the cone opening  64  in the direction of the airflow. The tangential offtake conduit  22  is also slightly arcuate in plan view as can be seen from FIG.  2 . After a predetermined distance, the portion of the tangential offtake conduit  22  ceases to increase in distance from the cone opening  64  and is then directed towards the housing  24  of the pre-motor filter. The tangential offtake conduit  22 , opens into the housing  24  at an inlet  88 . 
     A helical offtake conduit  122  suitable for use in the vacuum cleaner  10  of FIGS. 1 and 2 is shown in isolation in FIGS. 4 and 5. Also shown are the chamber  178  and the centerbody  176  which form part of the same constructional piece. The centerbody  176  projects along an axis  200  which is, in use, coaxial with the axis of the vortex finder  74  shown in FIG. 3. A cylindrical neck  190  surrounds the centerbody  176  and carries a seal  192  which, in use, abuts against the upper lip of the vortex finder  74  to form a seal therewith. The neck  190  opens into the chamber  178  which, as can be seen from FIG. 5, is spiral in shape so as to allow the tangential offtake conduit  122  to communicate with the chamber  178  in a scroll-manner. The tangential offtake conduit  122  then leaves the chamber  178  at an acute angle with respect to the axis  200  of the centerbody. The tangential offtake conduit  122  has a central axis  202  which meets the axis  200  at an angle a which is ideally about 60° but can vary between 35° and 70°. The distance (measured parallel to the axis  200 ) between the tangential offtake conduit  122  and the hemispherical end  176   a  of the centerbody  176  increases with distance along the tangential offtake conduit  122 . The arcuate shape of the tangential offtake conduit  122  can be seen clearly in FIG.  5 . The distal end  122   a  of the conduit  122  is shaped and arranged to communicate directly with the pre-motor filter housing  24  (see FIG.  1 ). A seal can be arranged around the open mouth of the distal end  122   a  of the conduit  122  if desired. 
     When fluid leaves the cyclonic separating apparatus  50  shown in FIG. 3 via the vortex finder  74 , it is spinning with a high angular velocity. The angular velocity is still very high as the fluid flow enters the chamber  78 . However, the scroll-like connection between the tangential offtake conduit  22  and the chamber  78  allows the spinning fluid to enter the offtake conduit  22  in a tangential manner and to progress along the offtake conduit  22  as a linear flow. The helical shape of the lower surface  86  of the support portion  84  guides the spinning fluid into the open end of the tangential offtake conduit  22 . Furthermore, because the tangential offtake conduit  22  is inclined to the axis of the vortex finder  74  and thereby increases in its distance from the cone opening  64  in the downstream direction, the fluid flow is not turned through a sharp 90° bend which means that less turbulence than would otherwise be the case is induced in the flow. The helical formation of the offtake conduit  22  provides a smooth path for the fluid exiting the separating apparatus so that as much as possible of the kinetic energy of the spinning fluid is recovered as pressure energy. This energy recovery results in a higher efficiency of the apparatus overall. 
     It will be appreciated that a helical or inclined tangential offtake can be applied to any situation where separation takes place in a cyclone with a vortex finder providing the outlet for the fluid. The application to a vacuum cleaner is described above but the invention is not to be regarded as limited to such an application. Other applications are envisaged such as other types of separation or filtration system for separating particulates from a fluid, eg. diesel exhaust systems and air conditioning systems.