Abstract:
Described is a fan assembly comprising a body comprising an inlet, an outlet, and a means for generating an air flow through the body. The fan assembly also comprises a nozzle mountable on the body for receiving the air flow from the body and for emitting the air flow, wherein the body and the nozzle have cooperative inclined surfaces configured to assist alignment of the nozzle on the body.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of United Kingdom Application No. 1502476.3, filed Feb. 13, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a fan. Particularly, but not exclusively, the present invention relates to a floor or table-top fan, such as a desk, tower or pedestal fan. 
       BACKGROUND OF THE INVENTION 
       [0003]    A conventional domestic fan typically includes a set of blades or vanes mounted for rotation about an axis, and drive apparatus for rotating the set of blades to generate an air flow. The movement and circulation of the air flow creates a ‘wind chill’ or breeze and, as a result, the user experiences a cooling effect as heat is dissipated through convection and evaporation. The blades are generated located within a cage which allows an air flow to pass through the housing while preventing users from coming into contact with the rotating blades during use of the fan. 
         [0004]    WO 2009/030879 describes a fan assembly which does not use caged blades to project air from the fan assembly. Instead, the fan assembly comprises a cylindrical base which houses a motor-driven impeller for drawing a primary air flow into the base, and an annular nozzle connected to the base and comprising an annular air outlet through which the primary air flow is emitted from the fan. The nozzle defines a central opening through which air in the local environment of the fan assembly is drawn by the primary air flow emitted from the mouth, amplifying the primary air flow. 
         [0005]    WO 2010/100452 also describes a similar fan assembly. Within the base, the impeller is located within an impeller housing, and the motor for driving the impeller is located within a motor bucket which is mounted on the impeller housing. The impeller housing is supported within the base by a plurality of angularly spaced supports. Each support is, in turn, mounted on a respective support surface extending radially inwardly from the inner surface of the base. In order to provide an air tight seal between the impeller housing and the base, a lip seal is located on an external side surface of the impeller housing for engaging the internal side surface of the base. 
         [0006]    WO 2010/046691 also describes a fan assembly. The fan assembly comprises a cylindrical base which houses a motor-driven impeller for drawing a primary air flow into the base, and an annular nozzle connected to the base and comprising an annular air outlet through which the primary air flow is emitted from the fan. The fan assembly comprises a filter for removing particulates from the air flow. The filter may be provided upstream from motor-driven impeller, in which case particulates are removed from the air flow prior to passing through the impeller. This protects the impeller from debris and dust that may be drawn into the fan assembly and which may damage the fan assembly. Alternatively, the filter may be provided downstream from the motor-driven impeller. In this configuration it is possible to filter and clean the air drawn through the motor-driven impeller, including any exhaust emissions, prior to progression through the elements of the fan assembly and supply to the user. 
       SUMMARY OF THE INVENTION 
       [0007]    Disclosed is an improved fan assembly which overcomes some of the disadvantages of the prior art, or at least provides an alternative fan assembly. In a first aspect, the present invention provides a fan assembly comprising a body comprising means for generating an air flow, a nozzle mountable on the body for receiving the air flow from the body and for emitting the air flow, a nozzle retaining means for releasably retaining the nozzle on the body, the nozzle retaining means having a first configuration in which the nozzle is retained on the body and a second configuration in which the nozzle is released for removal from the body, and a manually actuable member located on the nozzle for effecting movement of the nozzle retaining means from the first configuration to the second configuration. 
         [0008]    The provision of a manually actuable member for effecting movement of the nozzle retaining means from the first configuration to the second configuration allows the nozzle to be rapidly and easily released for removal from the body. By providing the manually actuable member on the nozzle it is possible to release the nozzle from the body and remove it in a single action, as the manually actuable member is lifted off with the nozzle. Once the nozzle has been released it may be pulled away from the body by a user, for example for cleaning or replacement of the nozzle, or for the cleaning or replacement of another component, such as a filter. 
         [0009]    The nozzle retaining means is biased towards the first configuration, such that the nozzle is retained on the body in its normal state. Biasing means is preferably provided for biasing the manually actuable member towards the first position. The biasing means may conveniently be in the form of a compression spring, but other forms of biasing means are also envisaged within the scope of the invention. 
         [0010]    The manually actuable member is preferably moveable from a first position to a second position to effect movement of the nozzle retaining means from the first configuration to the second configuration. The manually actuable member is preferably depressible. The manually actuable member may conveniently take the form of one or more buttons which are located on an exterior surface of the nozzle and may conveniently be pressed by a user. In an embodiment of the invention the nozzle may be provided with two diametrically opposed buttons on a base of the nozzle such that a user may grasp the base of the nozzle in both hands and press the buttons with their thumbs while lifting the nozzle from the base. This configuration provides a particularly easy method of removal. 
         [0011]    The manually actuable member preferably comprises a seal member to prevent air flow generated by the fan assembly from leaking out during use of the fan. The seal member preferably seals against a surface of the nozzle when the manually actuable member is in its first position. 
         [0012]    The nozzle retaining means preferably comprises a detent which is moveable relative to the nozzle and the body to retain the nozzle on the body in the first configuration, and to release the nozzle for removal from the body in the second configuration. The detent of the nozzle retaining means is preferably provided on the nozzle. The detent is preferably moveable from a first position to a second position to release the nozzle for removal from the body. 
         [0013]    Preferably the nozzle retaining means comprises biasing means for biasing the detent towards the first position. The biasing means may conveniently be the same biasing means that biases the nozzle retaining means towards its first configuration. Alternatively, an additional biasing means may be provided. Preferably the detent is pivotably moveable relative to the nozzle and the body. 
         [0014]    In an embodiment of the invention the manually actuable member and the detent may be formed as a single component, with the manually actuable member being provided at one end and the detent being provided at the other. When this member is pivotably mounted on the nozzle manual pressure on the manually actuable member overcomes the biasing force of the biasing member and causes the manually actuable member and the detent to pivot, such that the detent moves to its second position for removal of the nozzle from the body. 
         [0015]    The detent is preferably arranged to engage an outer surface of the body to retain the nozzle on the body. The detent is preferably arranged to engage a recessed portion of the outer surface of the body to retain the nozzle on the body. 
         [0016]    The nozzle preferably defines an opening through which air from outside the fan assembly is drawn by the air emitted from the nozzle. The fan assembly preferably comprises a filter upstream from the air inlets. 
         [0017]    The user experience is improved with a nozzle which is securely held in place, yet may be quickly and easily removed in a single action. It is desirable to provide a nozzle which may be located on the body just as easily, and so in a second aspect the present invention provides a fan assembly comprising a body comprising an inlet, an outlet and means for generating an air flow through the body, and a nozzle mountable on the body for receiving the air flow from the body and for emitting the air flow, wherein the body and the nozzle have cooperative inclined surfaces configured to assist alignment of the nozzle on the body. 
         [0018]    The cooperative inclined surfaces are complementary and configured such that they are able to slide relative to one another when they come into contact and guide the nozzle into the correct position for engagement with the body. The arrangement of the inclined surfaces is such when the body is situated on a surface, such as a floor or table, and the inclined surfaces are caused to slide relative to one another they cause nozzle to rotate relative to the body. This results in a “self twist” docking mechanism for the nozzle on the base which doesn&#39;t rely on a user perfectly aligning the nozzle and the body. 
         [0019]    The inclined surfaces are preferably undulating. The term “undulating” as used herein describes a sinuous, wave-like surface which has a plurality of peaks and troughs. 
         [0020]    Preferably the cooperative inclined surface on the body comprises a top edge of the body. Preferably the cooperative inclined surface on the nozzle comprises a surface located in a channel in a base of the nozzle. 
         [0021]    The body is preferably cylindrical, although elliptical shaped bodies will also be able to function in a similar manner. 
         [0022]    Preferably the nozzle comprises a nozzle retaining means for retaining the nozzle on the body. An outer surface of the body preferably comprises recesses for receiving a portion of the nozzle retaining means. 
         [0023]    The inclined surfaces preferably define opposing pairs of peaks and troughs. The recesses are preferably located on the peaks. The inclined surfaces preferably comprise a pair of diametrically opposed peaks and a pair of diametrically opposed troughs. 
         [0024]    The fan assembly preferably comprises a filter upstream from the air inlet, and so in a third aspect the present invention provides a fan assembly comprising a body comprising an air inlet, an air outlet, and means for generating an air flow through the body, a nozzle removably mounted on the body for receiving the air flow from the body and for emitting the air flow, and a filter surrounding at least a portion of the body upstream from the air inlet, the filter being held captive on the fan assembly between the nozzle and a portion of the body while remaining free to move relative to the body and the nozzle, and wherein the filter is removable from the fan assembly only after removal of the nozzle from the body. 
         [0025]    The filter is securely held in place when the nozzle is mounted on the body, but it is not connected to either the body or the nozzle. The term “connected” as used herein implies some degree of interlocking, or inter-engagement, and does include the fact that the filter is in contact with the body and the nozzle. The filter may be considered to be loose fitting as it is free to move relative to the body and nozzle. The filter may simply be lowered onto the body and then secured in place by the engagement of the nozzle with the base. There is no need to make any connection between the filter and the body, other than lowering the filter into place. This provides a convenient and easy way to fit and remove the filter. 
         [0026]    The body preferably comprises a seat for the supporting the filter. Preferably the seat comprises an upwardly facing surface for supporting the filter. Preferably the seat is substantially orthogonal to a longitudinal axis of the body. 
         [0027]    The body preferably comprises a lower body section and an upper body section and the seat projects outwardly from the upper body section. The means for generating the air flow through the body may conveniently be located within the upper body section, and a control circuit for controlling the means for generating the air flow may conveniently be located within the lower body section. The lower body section preferably also comprises means for rotating the upper body section relative to the lower body section. The means for rotating the upper body preferably comprises an oscillation mechanism for oscillating the upper body back and forth relative to the lower body. 
         [0028]    Preferably the diameter of the lower body section is larger than the diameter of the upper body section. An outer edge of the seat is preferably substantially flush with an outer surface of the lower body section. When the filter is located on the body it preferably rests on the on the seat and an outer surface of the filter is preferably substantially flush with an outer surface of the lower body section. 
         [0029]    The fan assembly preferably further comprises sealing means for forming a seal between the filter and at least the body to define a flow path between a downstream surface of the filter and the air inlet of the body. 
         [0030]    Sealing means is preferably provided for forming a seal between a filter other components of the fan assembly, and so in a fourth aspect the present invention provides a fan assembly comprising a body comprising an air inlet, an air outlet, and means for generating an air flow through the body, a nozzle for receiving the air flow from the body and for emitting the air flow, a filter upstream from the air inlet and having an upstream surface and a downstream surface, a seat on the body having an upwardly facing surface for supporting the filter, and sealing means for forming a seal between the filter and the body to define a flow path between the downstream surface of the filter and the air inlet. 
         [0031]    It is important to ensure that all of the air entering the body has passed through the filter. This facilitates the removal of particulate matter from the air flow entering the body, which is beneficial for both the internal workings of the fan assembly and ensures that the air flow emitted from the nozzle is free from particulate matter. This enables impurities to be removed from the air in the space in which the fan is located. In order to effectively do this it is important to ensure that all of the air entering the body has passed through the filter. This is achieved by providing the sealing means which define a flow path between a downstream surface of the filter and the air inlet of the body. When the fan assembly draws air into the body it is drawn through the filter. 
         [0032]    Preferably the sealing means comprises at least one sealing member provided on the nozzle. Preferably the sealing means comprises at least one sealing member provided on the body. Preferably the sealing means comprises a first sealing member provided on the body and a second sealing member provided on the nozzle. Preferably the sealing means comprises at least one sealing member provided on the filter. More preferably the filter is provided with at least two sealing members. 
         [0033]    The filter is preferably supported on a seat which extends substantially orthogonal to a longitudinal axis of the body. Preferably the upwardly facing surface is inclined downwardly away from a longitudinal axis of the body. A lower seal member is preferably provided adjacent the seat for forming a seal against a bottom surface of the filter. An upper seal member is preferably provided on the nozzle for forming a seal against an upper surface of the filter. The sealing means are preferably annular. 
         [0034]    It is desirable that a filter is provided upstream of the air inlets, and so in a fifth aspect the present invention provides a fan assembly comprising a body comprising an air inlet, an air outlet, and means for generating an air flow through the body, the body having a lower body section and an upper body section capable of rotation relative to the lower body section, a nozzle for receiving the air flow from the body and for emitting the air flow, a filter upstream from the air inlet, and a seat on the upper body section for supporting the filter such that the filter rotates relative to the lower body section when the upper body section is caused to rotate, wherein the seat has an upwardly facing surface for supporting the filter. 
         [0035]    Since the upper body is rotatable relative to the lower body it is advantageous for the filter to be supported by a seat on the upper body section. In order for the filter to function properly it needs to be sealed to the fan assembly in order to define a flow path between a downstream surface of the filter and the air inlet of the body. Preferably the seat is provided with a seal for forming a sealing engagement with the filter. With the filter supported on the upper body section it is able to rotate with the upper body section and the seals are not disturbed. However, if the filter was supported on the lower body section then at least one of its seals would drag against the body when the upper body section was rotated. This is undesirable as it increases the likelihood of air leaking around and bypassing the filter. 
         [0036]    The seat is preferably substantially orthogonal to a longitudinal axis of the upper body section. Preferably the lower body section and upper body section are cylindrical and the seat projects radially from the upper body section. Preferably the diameter of the lower body section is larger than the diameter of the upper body section. Other shapes for the upper and lower body sections are also envisaged, for example, they may be square, rectangular, triangular, or any other regular or irregular shape. It is preferred that the outer edges of the lower body section extend beyond those of the upper body section. 
         [0037]    Preferably the seat projects radially from the upper body section. Preferably an outer edge of the seat is substantially flush with an outer surface of the lower body section. 
         [0038]    The lower body section preferably comprises means for rotating the upper body section relative to the lower body section. Preferably the means for rotating the upper body section comprises an oscillation mechanism. 
         [0039]    The filter is preferably tubular and surrounds at least a portion of the body. Preferably the filter extends 360° around the body. Alternatively, the filter may preferably extend radially around at least a portion of the body. 
         [0040]    When the filter is on the seat an outer surface of the filter is preferably substantially flush with an outer surface of the lower body section. This provides a more aesthetically pleasing product as the filter and lower body section have a sleek profile. It is further preferred that when the nozzle is mounted on the body an outer surface of the filter is substantially flush with an outer surface of a base portion of the nozzle. Again, this helps to integrate the filter into the fan assembly and provides a more visually appealing appearance as the filter and the lower body section form a contiguous outer surface. 
         [0041]    Preferably the seat comprises a first section which extends substantially perpendicular to a longitudinal axis of the upper body section and a second section which is inclined downwardly relative to the longitudinal axis. The filter preferably comprises a plurality of wedge-shaped projections on a lower surface. The wedge-shaped projections are preferably angularly spaced around the periphery of the filter. The wedge-shaped projections preferably taper upwardly and inwardly from an outer edge of the filter towards the longitudinal axis. When the filter is placed onto the body the wedge-shaped projections cooperate with the inclined surface of the seat to centre the filter on the body. The cooperating surfaces of the wedge-shaped projections and the inclined surfaces slide relative to one another such that the filter is effectively able to self-centre on the body in a position substantially parallel to a surface on which a base of the body is situated. 
         [0042]    The filter preferably comprises a filter media comprising a HEPA filter. The filter preferably comprises a filter media comprising an activated carbon cloth filter. The filter media may preferably be pleated in order to increase the available surface area of the filter media. The filter preferably comprises a perforated shroud surrounding a filter media of the filter. The shroud serves to protect the filter media from damage, e.g. during transit, and it also comprises apertures which are sized to prevent larger particles from coming into contact with the filter media. In addition, the shroud provides an attractive outer surface for the filter, which complements the body and nozzle of the fan assembly. 
         [0043]    The fan assembly is preferably provided with a seat for supporting the filter, and so in a sixth aspect the present invention provides a fan assembly comprising a body comprising an air inlet, an air outlet, and means for generating an air flow through the body, a nozzle for receiving the air flow from the body and for emitting the air flow, and a filter upstream from the air inlet, and a seat on the body, the seat comprising an upwardly facing surface for supporting the filter. 
         [0044]    Preferably the seat is substantially orthogonal to a longitudinal axis of the body. 
         [0045]    Preferably the body is cylindrical. Preferably the seat projects radially from the body. Preferably the upwardly facing surface is inclined downwardly away from a longitudinal axis of the body. 
         [0046]    Preferably the seat comprises a first section which projects radially from the body substantially perpendicular to the longitudinal axis and a second section which is inclined downwardly away from the longitudinal axis. Preferably the body comprises a lower body section and an upper body section and the seat projects radially outwardly from the upper body section. 
         [0047]    Preferably the diameter of the lower body section is larger than the diameter of the upper body section. Preferably an outer edge of the seat is substantially flush with an outer surface of the lower body section. When the filter is on the seat an outer surface of the filter is preferably substantially flush with an outer surface of the lower body section. 
         [0048]    The lower body section preferably comprises means for rotating the upper body section relative to the lower body section. Preferably the means for rotating the upper body section comprises an oscillation mechanism. 
         [0049]    The filter preferably comprises a plurality of wedge-shaped projections on a lower surface. The wedge-shaped projections preferably taper upwardly and inwardly from an outer edge of the filter towards the longitudinal axis. The wedge-shaped projections are preferably angularly spaced around the periphery of the filter. When the filter is placed onto the body the wedge-shaped projections cooperate with the inclined surface of the seat to centre the filter on the body. The cooperating surfaces of the wedge-shaped projections and the inclined surfaces slide relative to one another such that the filter is effectively able to self-centre on the body in a position substantially parallel to a surface on which a base of the body is situated. 
         [0050]    In a seventh aspect the invention provides a fan assembly comprising a body comprising an air inlet, an air outlet, and means for generating an air flow through the body, the body comprising a lower body section and an upper body section, the upper body section housing the means for generating the air flow and the lower body section housing a control circuit for controlling the means for generating the air flow, and a nozzle for receiving the air flow from the body and for emitting the air flow, wherein the lower body section comprises an outer wall and an inner wall, the outer wall and inner wall defining an outer cavity surrounding an inner cavity, and wherein the control circuit is located within the inner cavity surrounded by the inner wall. 
         [0051]    Providing the control circuit within an inner cavity of the lower body section provides protection for the various elements of the control circuit against damage caused by the ingress of fluid, e.g. water, into the fan assembly. If fluid comes into contact with the fan assembly, e.g. as a result of a spillage, it is likely to run off the outer surfaces of the fan assembly. However, if the fluid does manage to penetrate into the lower body of the fan assembly it will be collected within the outer cavity where it cannot come into contact with any of the elements of the control circuit. 
         [0052]    Preferably the outer cavity comprises a floor surface located between the outer wall and the inner wall. Preferably the floor surface comprises a plurality of drain holes. The drain holes provide a pathway for fluid to exit the outer cavity, thus preventing the outer cavity from becoming full and overflowing. Preferably the drain holes are angularly spaced about the outer cavity. 
         [0053]    Preferably the floor surface is inclined downwardly from the inner wall towards the outer wall. Preferably the drain holes are located adjacent the outer wall. This arrangement aids drainage by directing any fluid in the outer cavity towards the drain holes. 
         [0054]    Preferably the outer wall and the inner wall are annular. The inner wall is preferably taller the outer wall. Preferably a top edge of the inner wall terminates adjacent a lower surface of the upper body section. 
         [0055]    Preferably a passageway is provided from an inner surface of the inner wall to an outer surface of the outer wall for conveying a power supply cable from the control circuit. A sealing member for sealing the power supply cable to the passageway to prevent the ingress of fluid into the inner cavity is preferably provided. 
         [0056]    Preferably a bottom surface of the body is provided with a plurality of feet for supporting the fan assembly. The feet serve to raise the bottom surface above the surface upon which the fan assembly is being supported, e.g. a floor surface or the surface of a table. This ensures that the outlet from the drain holes does not become blocked by the support surface and fluid is able to flow freely from the outer cavity through the drain holes. 
         [0057]    Preferably a filter is provided surrounding at least a portion of the body upstream from the air inlet. 
         [0058]    The fan assembly preferably comprises means for rotating the upper body relative to the lower body. The means for rotating the upper body preferably comprises an oscillation mechanism. Preferably the means for rotating the upper body section is located within the outer cavity of the lower body section. As with the control circuit, this provides protection for the rotation means from damage caused by the ingress of fluids into the lower body section. 
         [0059]    Features described above in connection with the first aspect of the invention are equally applicable to each of the second to seventh aspects of the invention, and vice versa. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0060]    Preferred features of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0061]      FIG. 1  is a front perspective view of a fan; 
           [0062]      FIG. 2  is a front view of the fan; 
           [0063]      FIG. 3  is a side view of the fan; 
           [0064]      FIG. 4  is a side sectional view through the fan taken along line A-A in  FIG. 2 ; 
           [0065]      FIG. 5 a    is a front sectional view through the fan taken along line B-B in  FIG. 3  with the nozzle engaged on the body,  FIG. 5 b    is a front sectional view through the fan taken along line B-B in  FIG. 3  with the nozzle released from the body; 
           [0066]      FIG. 6  is a front perspective view of the base of the fan; 
           [0067]      FIG. 7  is a side sectional view of the base of the fan; 
           [0068]      FIG. 8  is a front sectional view of the base of the fan; 
           [0069]      FIG. 9  is a perspective view from below of the nozzle removed from the base; 
           [0070]      FIG. 10  is bottom view of the nozzle removed from the base; 
           [0071]      FIG. 11  is a top view of the lower body section of the fan; 
           [0072]      FIG. 12  is a perspective view of the filter removed from the fan; 
           [0073]      FIG. 13  is a perspective view of the filter on the body of the fan; and 
           [0074]      FIG. 14  is a perspective view of the filter from below. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0075]      FIGS. 1 to 3  are external views of a fan  10 , and  FIGS. 4 and 5  show sectional views through lines A-A and B-B of  FIGS. 2 and 3  respectively. In  FIGS. 4 and 5  the top portion of the nozzle has been omitted in order to improve the clarity of the remainder of the fan  10 . In overview, the fan comprises a body  12 , a removable filter  14  mounted on the body  12 , and an annular nozzle  16  mounted on the body  12 . The filter  14  rests on an annular flange  54  extending radially outwardly from the body  12 , and its removal from the body is prevented by the presence of the nozzle  16 . In order to remove the filter  14  from the fan  10  the nozzle  16  must first be removed. 
         [0076]    The annular nozzle  16  has an air outlet  18  for emitting a primary air flow from the fan  10  and defines a bore  19 , or opening, through which air from outside of the fan assembly  10  is drawn by the air emitted from the outlet  18 . The body  12  further comprises a user interface for allowing a user to control the operation of the fan  10 . The user interface comprises a user-operable button  20  to enable a user to operate the fan  10 . The fan  10  may also be provided with a remote control unit for controlling the operation of the fan  10 . The remote control unit may be provided with a plurality of user-operable buttons and may advantageously be mounted on the nozzle  16  when not in use. A variety of mounting mechanisms are envisaged, but in one embodiment the remote control unit may be provide with a magnet for attaching to a corresponding magnet housed within the nozzle  16 . 
         [0077]    The nozzle  16  has an elongate annular shape. The nozzle  16  comprises an outer wall  28  extending about an annular inner wall  30 . In this example, each of the walls  28 ,  30  is formed from a separate component. Each of the walls  28 ,  30  has a front end and a rear end. The rear end of the outer wall  28  curves inwardly towards the rear end of the inner wall  30  to define a rear end of the nozzle  16 . The front end of the inner wall  30  is folded outwardly towards the front end of the outer wall  28  to define a front end of the nozzle  16 . The front end of the outer wall  28  is inserted into a slot located at the front end of the inner wall  30 , and is connected to the inner wall  30  using an adhesive introduced to the slot. The inner wall  30  extends about an axis X to define the bore  19  of the nozzle  16 . 
         [0078]    The inner wall  30  is shaped so that the external surface of the inner wall  30 , that is, the surface that defines the bore  19 , has a number of sections. The external surface of the inner wall  30  has a convex Coanda surface  32  located adjacent the mouth  18  and over which the mouth  18  directs the air emitted from the fan  10 , a diffuser surface  34  located downstream of the Coanda surface  32  and a guide surface  36  located downstream of the diffuser surface  34 . The diffuser surface  34  is arranged to taper away from the central axis X of the opening  19  in such a way so as to assist the flow of air emitted from the fan  10 . A visually appealing tapered surface  38  is located downstream from the guide surface  36 . 
         [0079]    The rear end of the outer wall  28  is shaped to overlap the rear end of the inner wall  30  to define the air outlet  18 , or mouth, of the nozzle  16  between the inner surface of the outer wall  28  and the outer surface of the inner wall  30 . The air outlet  18  is in the form of a slot with a width which is preferably substantially constant about the axis X, and is in the range from 0.5 to 5 mm. The overlapping portions of the outer wall  28  and the inner wall  30  are substantially parallel, and are arranged to direct air over the Coanda surface  32  of the inner wall  30 . 
         [0080]    The outer wall  28  and the inner wall  30  define an interior passage  44  for conveying air to the air outlet  18 . The interior passage  44  extends about the bore  19  of the nozzle  16 . The nozzle  16  further comprises two curved seal members  112  each for forming a seal between the outer wall  28  and the inner wall  30  at the top and bottom curved sections of the nozzle  16 , so that there is substantially no leakage of air from the curved sections of the interior passage  44  of the nozzle  16 . The mouth  18  may thus be considered to comprise two elongate outlets each located on a respective long side of the central opening  19 . 
         [0081]    In order to direct the primary air flow into the mouth  18 , the nozzle  16  comprises a plurality of stationary guide vanes  120  located within the interior passage  44  and each for directing a portion of the air flow towards the mouth  18 . The guide vanes  120  are integral with the internal surface of the outer wall  28  of the nozzle  16 . The guide vanes  120  are curved so that there is no significant loss in the velocity of the air flow as it is directed into the mouth  18 . The guide vanes  120  are substantially vertically aligned and evenly spaced apart to define a plurality of passageways between the guide vanes  120  and through which air is directed into the mouth  18 . The even spacing of the guide vanes  120  provides a substantially even distribution of the air stream along the length of the section of the mouth  18 . 
         [0082]    The guide vanes  120  are preferably shaped so that a portion of each guide vane  120  engages the external surface of the inner wall  30  of the nozzle  16  so as to urge apart the overlapping portions of the internal surface of the outer wall  28  and the external surface of the inner wall  30 . This can assist in maintaining the width of each outlet at a substantially constant level along the length of each section of the mouth  18 . Additional spacers may be provided along the length of each section of the mouth  18 , also for urging apart the overlapping portions of the internal surface of the outer wall  28  and the external surface of the inner wall  30 , to maintain the width of the outlet  18  at the desired level. 
         [0083]    The outer wall  28  comprises a base  40  which is connected to an open upper end of the body  12 , and which has an open lower end which provides an air inlet  42  for receiving the primary air flow from the body  12 . 
         [0084]    The base  40  of the nozzle  16  is provided with a sealing member  130  which extends around the inner periphery of the base  40 . The sealing member  130  is an annular rubber seal and is attached to a support member  132  which is located within the base  40  of the nozzle  16 . The support member  132  is itself annular and surrounds the air inlet  42  and is attached to the base  40  of the nozzle  16 , for example by a plurality of screws. 
         [0085]    As can best be seen in  FIGS. 6 to 8 , the body  12  comprises a substantially cylindrical main body section  50  mounted on a substantially cylindrical lower body section  52 . The main body section  50  and the lower body section  52  are preferably formed from plastics material. The main body section  50  has a smaller external diameter than the lower body section  52  and an annular flange  54  extends radially from a lower portion of the main body section  50  such that the outer edge of the annular flange  54  is substantially flush with the external surface of the lower body section  52 . The annular flange  54  comprises a first portion  54   a  which extends perpendicularly away from the main body section  50 , and a second portion  54   b  which tapers downwardly away from the first portion  54   a . An annular seal  56  is provided around the main body section  50  at the junction of the main body section  50  and the annular flange  54 . The annular seal  56  may conveniently be formed from a rubber material and it is received in an annular groove  58  defined by the first portion  54   a  of the annular flange  54  and an annular rib  60  which extends radially from the main body section  50 . 
         [0086]    The fan  10  comprises a mechanism for releasably retaining the nozzle  16  on the body  12 .  FIG. 5 a    illustrates a first configuration of the mechanism when the nozzle  16  is retained on the body  12 , whereas  FIG. 5 b    illustrates a second configuration of the mechanism when the nozzle  16  is released from the body  12 . The mechanism for releasably retaining the nozzle  16  on the body  12  comprises a pair of detents  200  which are located on diametrically opposed sides of the nozzle  16 . Each detent  200  is pivotably moveable between a deployed position for retaining the nozzle  16  on the body  12 , and a stowed position, in which the nozzle  16  can be removed from the body  12 . Resilient elements  204 , such as compression springs, are located within the nozzle  16  for biasing the detents  200  towards their deployed positions. 
         [0087]    The nozzle  16  comprises two diametrically opposed manually actuable buttons  202  which are operable to move the detents  200  between the deployed position, in which the nozzle  16  is retained on the body, and the stowed position, in which the nozzle  16  can be removed from the body  12 . The buttons  202  are mounted on the nozzle  16  for pivoting movement from a first position, in which the detents  200  are in their deployed position, to a second position, in which the detents  200  are in their stowed position. The first and second positions of the buttons  202  are shown in  FIGS. 5 a  and 5 b    respectively. The buttons  202  are biased into their first position by the resilient elements  204  which are provided behind the buttons  202  and urge them into their first position. The strength of the resilient elements  204  is selected such that the biasing force can be overcome by a user grasping the nozzle  16  and pressing with their fingers. An advantage of providing the buttons  202  on the nozzle  16  is that the nozzle  16  may be quickly and easily released and removed from the body  12  in a single step. A user simply needs to grasp the nozzle  16 , depress the buttons  202  and lift the nozzle  16  away from the base  12 . 
         [0088]    The base  40  of the nozzle  16  comprises two diametrically opposed apertures  206  which have a diameter slightly larger than that of the buttons  202 , such that the buttons  202  can project through the apertures  206 . Rubber seals  208  are provided surrounding the periphery of the buttons  202 , and the seals  208  are urged into sealing engagement with an inner wall of the base  40  surrounding the periphery of the apertures  206  when the buttons  202  are in their first position. This prevents air from flowing out of the apertures  206  during use of the fan  10 . 
         [0089]    As can best be seen in  FIGS. 5 a , 5 b    and  6 , the outer surface of the main body section  50  of the base  12  comprises a pair of diametrically opposed recesses  210 . When the detents  200  are in their deployed position they engage the recesses  210  on the outer surface of the main body section  50  of the base  12  to prevent the nozzle  16  from becoming withdrawn from the body  12 , for example if the fan apparatus  10  is lifted by a user gripping the nozzle  16 . When a user depresses the buttons  202  this moves the detents  200  from their deployed position to their stowed position. In the stowed position the detents  200  are not engaged with the recesses  210 , and the nozzle  16  may be removed from the body  12 . 
         [0090]    Referring now to  FIGS. 6 to 10 , the base  40  of the nozzle  16  and the main body section  50  of the base  12  comprise complementary features which cooperate to facilitate location of the nozzle  16  on the base  12 . The base  40  of the nozzle  16  comprises an annular channel  134  which surrounds the air inlet  42 . The annular channel  134  is defined by an outer annular wall  148  and an inner annular wall  150 . The outer annular wall  148  and inner annular wall  150  depend downwardly from the nozzle  16  and the inner annular wall  150  extends beyond the outer annular  148 , such that it extends into the main body section  50  of the base  12  when the nozzle  16  is located on the base  12 . The annular channel  134  has an undulating profile, such that when viewed from below it has two diametrically opposed low points  136   a,b  and two diametrically opposed high points  138   a,b . The low points  136   a,b  of the annular channel  134  are offset from the high points  138   a,b  such that a line bisecting the low points  136   a,b  is orthogonal to a line bisecting the high points  138   a,b . The low points  136   a,b  of the annular channel  134  are aligned with the buttons  202  on the nozzle  16 . Two ribs  140  extend across the width of the annular channel  134  in a rear half of the nozzle  16  and further serve to aid in the correct fitting of the nozzle  16  on the base  12 , as will be described in more detail below. 
         [0091]    The main body section  50  of the base  12  comprises an outer casing  24  which defines the side walls of the main body section  12 . The main body section  50  is cylindrical and the top edge  26  of the outer casing  24  has an undulating profile, such that it has two diametrically opposed high points  142   a,b  and two diametrically opposed low points  144   a,b . The high points  142   a,b  of the top edge  26  of the outer casing  24  are offset from the low points  144   a,b  of the top edge  26  of the outer casing  24  such that a line bisecting the high points  142   a,b  is orthogonal to a line bisecting the low points  144   a,b . As can best be seen in  FIG. 10 , a locating notch  146  is provided in a rear portion of the outer casing  24  depending downwardly from the top edge  26 . The recesses  210  on the outer surface of the outer casing  24  are adjacent the high points  142   a,b  of the top edge  26 . 
         [0092]    When attaching the nozzle  16  to the base  12  it is important to ensure that nozzle  16  faces in the correct direction. To prevent incorrect attachment of the nozzle  16  to the base  12  the nozzle  16  is provided with ribs  140  which extend across the annular channel  134  in a rear portion of the nozzle  16 . The ribs  140  are arranged to be received in the notch  146  which is provided in a rear portion of the top edge  26  of the outer casing  24  to ensure that the nozzle can only be fitted in the correct orientation. If an attempt is made to attach the nozzle  16  in an incorrect position it will be unsuccessful as the ribs  140  will abut the top edge  26  of the outer casing  24  and prevent further insertion of the nozzle  16  into the base  12 . 
         [0093]    Once care has been taken to ensure that the rear portion of the nozzle  16  is aligned with the rear portion of the base  12  the nozzle  16  be lowered onto the base  12  with the buttons  202  being generally aligned with the detents  200  on the outer surface of the outer casing  24 . The undulating top edge  26  of the outer casing  24  is arranged to be received into the annular channel  134  of the base  40  of the nozzle  16 . The undulating surfaces of the top edge  26  and the annular channel  134  are complementary such that the high points  142   a,b  of the outer casing  24  are received within the low points  136   a,b  of the outer casing. Similarly, the low points  144   a,b  of the outer casing  24  align with the high points  138   a,b  of the annular channel  134 . The complementary nature of the surfaces is such that the undulating top edge  26  of the outer casing  24  is able to slide over the undulating surface of the annular channel  134  until it is received in the correct position. The sliding movement of the top edge  26  relative to the annular channel  134  causes the nozzle  16  to rotate about the longitudinal axis of the nozzle  16  and base  12 . This provides a convenient location mechanism which does not rely on the user precisely aligning the nozzle  16  on the base  12 . 
         [0094]    Referring now to  FIGS. 6 to 8 , the main body section  50  comprises an air inlet  22  in the form of a plurality of apertures formed in the outer casing  24  of the body  12 , and through which a primary air flow is drawn into the body  12  from the external environment. In this embodiment the air inlet  22  comprises an array of apertures formed in the section of the outer casing  24  of the body  12  which is defined by the main body section  50 . Alternatively, the air inlet  22  may comprise one or more grilles or meshes mounted within windows formed in the outer casing  24 . The main body section  50  is open at the upper end (as illustrated) for connection to the base  40  of the nozzle  16 , and to allow the primary air flow to be conveyed from the body  12  to the nozzle  16 . A lower surface of the main body section  50 , located below the air inlet  22 , is lined with noise absorbing material  23 , preferably an acoustic foam material, to suppress noise generated during operation of the fan  10 . 
         [0095]    The lower body section  52  comprises the aforementioned user interface and a control circuit, indicated generally at  62 , for controlling various functions of the fan  10  in response to operation of the user interface. The lower body section  52  also houses a mechanism for oscillating the main body section  50  relative to the lower body section  52 . The operation of the oscillation mechanism is controlled by the control circuit  62  in response to the user&#39;s depression of the appropriate button on the remote control unit. The range of each oscillation cycle of the main body section  50  relative to the lower body section  52  is preferably between 60° and 120°, and the oscillation mechanism is arranged to perform around 3 to 5 oscillation cycles per minute. A mains power cable  64  for supplying electrical power to the fan  10  extends through an aperture formed in the lower body section  52 . 
         [0096]    Referring now to  FIG. 11 , it can be seen that the lower body section  52  comprises an outer wall  53 , which defines the outer cylindrical surface of the lower body section  52  and an inner wall  55 . A first cavity  57  is defined between the outer wall  53  and the inner wall  55 . The inner wall is annular and defines an inner cavity  59  which encloses all of the electrical components of the lower body section  52 , such as the control circuit  62  and oscillation mechanism. The cavity  57  provides protection for the electrical components of the lower body section  52  in the event of water, or other liquid, ingress into the base  12 . If the fan  10  comes into contact with a liquid, e.g. spillage of a beverage, then any water which penetrates the base  12  will be received within the channel  57 , and prevented from entering the inner cavity  59  and coming into contact with the electrical components of the lower base section  52 , such as the control circuit  62 . Drainage holes  41  are provided in a floor surface  43  of the first cavity  57 . The drainage holes  41  provide an outlet to permit any water collected in the first cavity to flow out of the lower base section  52  and onto a surface on which the fan assembly  10  is supported. As can best be seen in  FIG. 8 , the floor surface  43  is inclined outwardly and downwardly away from the longitudinal axis of the lower body section  52  to direct the flow of liquid towards the drainage holes  41 . As can best be seen in  FIGS. 7 and 8 , the lower body section  52  is provided with feet  89  which support the fan assembly on a surface, such as a floor or table. The feet  89  raise the floor surface  43  above the surface on which the fan assembly  10  is supported, to provide a flow path for liquid exiting the drainage holes  41 . A passageway  87  is provided through the first cavity  57  to convey the power supply cable  64  away from the control circuit  62 . The passageway  87  ensures that the power supply cable  64  does not come into contact with liquid in the first cavity  57  and a seal is provided between the passageway  87  and the power supply cable  64  to prevent liquid ingress. 
         [0097]    Turning now to  FIGS. 12-14 , these show the filter  14  according to the present invention. The filter  14  is a tubular, barrel-type filter and comprises a two-layer structure of filter media. Any number of alternative combinations of filter media are envisaged within the scope of the present invention, but filter  14  comprises an outer layer  160  of a pleated HEPA filter surrounding an inner layer  162  of activated carbon cloth. The two layers  160 ,  162  are encapsulated by top and bottom end caps  164 ,  166 , which are annular members with a generally U-shaped cross section. The filter  14  further comprises a perforated shroud  168  in the form of a tubular plastic member which surrounds the filter media and comprises an array of apertures which act as an air inlet  170  of the filter  14  in use of the fan  10 . Alternatively, the air inlet  170  of the shroud  168  may comprise one or more grilles or meshes mounted within windows in the shroud  168 . It will also be clear that alternative patterns of air inlet arrays are envisaged within the scope of the present invention. 
         [0098]    As can best be seen in  FIG. 14 , the shroud  168  is connected to the bottom end cap  166  by means of connecting ring  172 , which is glued to the shroud  168  and bottom end cap  166  to retain them in a spaced relationship. The shroud  168  protects the filter media from damage, for example during transit, and also provides a visually appealing outer surface for the filter  14 , which is in keeping with the overall appearance of the fan  10 . The shroud  168  defines the air inlet  170  for the filter  14  and the array of apertures are sized to prevent larger particles from entering the filter  14  and blocking, or otherwise damaging, the filter media. 
         [0099]    A lower surface  174  of the connecting ring  172  is provided with a plurality of angularly spaced wedge-shaped projections  176 . The wedge-shaped projections  176  are inclined inwardly and upwardly from an outer periphery of the connecting ring  172  towards its longitudinal axis. The filter  14  does not interlock with any other component of the fan  10 , and for this reason it may be considered to be loose fitting. When the filter is located on the base  12  of the fan  10  it rests on the annular flange  54  and the wedge-shaped projections  176  cooperate with the tapered second portion  54   b  of the annular flange  54  to help centre the filter  14  on the base  12 . The wedges  176  slide over the tapered portion  54   b  until the filter  14  is substantially parallel to the surface on which the fan  10  is sitting. When the oscillation mechanism is activated to cause the main body section  50  to oscillate relative to the lower body section  52  the filter  14  moves with the main body section  50 . 
         [0100]    As noted above, when the filter  14  is located on the base  12  of the fan  10  is sits on the annular flange  54 . The annular seal  56  forms a seal against the bottom end cap  166  of the filter  14  to prevent leakage of air between the bottom of the filter  14  and the base  12 . The filter  14  is located upstream from the air inlets  22  of the main body section  50 , such that the air drawn into the main body section  50  by the impeller  80  is filtered prior to entering the main body section  50 . This serves to remove any particles which could potentially cause damage to the fan  10 , and also ensures that the air emitted from the mouth  18  is free from particulates. 
         [0101]    When the nozzle  16  is located on the body  12 , as described above, the sealing member  130  on the base  40  of the nozzle  16  forms a seal against the top end cap  164  of the filter  14  to prevent leakage of air between the top of the filter  14  and the nozzle  16 . The top and bottom seals to the filter  14  define a flow path, such that all air drawn into the main body section  50  by the impeller  80  must pass through the filter  14 . 
         [0102]    Referring back to  FIGS. 7 and 8 , the main body section  50  comprises a duct  70  having a first end defining an air inlet  72  of the duct  70  and a second end located opposite to the first end and defining an air outlet  74  of the duct  70 . The duct  70  is aligned within the main body section  50  so that the longitudinal axis of the duct  70  is collinear with the longitudinal axis of the body  12 , and so that the air inlet  72  is located beneath the air outlet  74 . 
         [0103]    The air inlet  72  is defined by an outwardly flared inlet section  76  of an outer wall  77  of the duct  70 . The inlet section  76  of the outer wall  77  is connected to an impeller housing  78  of the outer wall  77 . The impeller housing  78  extends about an impeller  80  for drawing the primary air flow into the body  12  of the fan  10 . The impeller  80  is a mixed flow impeller. The impeller  80  comprises a generally conical hub  82 , a plurality of impeller blades  84  connected to the hub  82 , and a generally frusto-conical shroud  86  connected to the blades  84  so as to surround the hub  82  and the blades  84 . The blades  84  are preferably integral with the hub  82 , which is preferably formed from plastics material. 
         [0104]    The impeller  80  is connected to a rotary shaft  90  extending outwardly from a motor  92  for driving the impeller  80  to rotate about a rotational axis. The rotational axis is collinear with the longitudinal axis of the duct  70 . In this embodiment, the motor  92  is a DC brushless motor having a speed which is variable by the control circuit  62  in response to user selection. The maximum speed of the motor  92  is preferably in the range from 5,000 to 10,000 rpm. The motor  92  is housed within a motor housing. The outer wall  77  of the duct  70  surrounds the motor housing, which provides an inner wall  95  of the duct  70 . The walls  77 ,  95  of the duct  70  thus define an annular air flow path which extends through the duct  70 . The motor housing comprises a lower section  96  which supports the motor  92 , and an upper section  98  connected to the lower section  96 . The shaft  90  protrudes through an aperture formed in the lower section  96  of the motor housing to allow the impeller  80  to be connected to the shaft  90 . The motor  92  is inserted into the lower section  96  of the motor housing before the upper section  98  is connected to the lower section  96 . 
         [0105]    The lower section  96  of the motor housing is generally frusto-conical in shape, and tapers inwardly in a direction extending towards the air inlet  72  of the duct  70 . The hub  82  of the impeller  80  has a conical inner surface which has a similar shape to that of a contiguous part of the outer surface of the lower section  96  of the motor housing. 
         [0106]    The upper section  98  of the motor housing is generally conical in shape, and tapers inwardly towards the air outlet  74  of the duct  70 . The upper section  98  of the motor housing comprises an annular diffuser  100 . The diffuser  100  comprises a plurality of blades  102  for guiding the air flow towards the air outlet  74  of the duct  70 . The shape of the blades  102  is such that the air flow is also straightened as it passes through the diffuser  100 . The diffuser  100  comprises 11 blades  102 . One of the blades  102  defines a passageway through which a cable passes to the motor  92 . 
         [0107]    The outer wall  77  of the duct  70  comprises a diffuser housing  104  connected to the upper end of the impeller housing  78 , and which extends about the diffuser  100 . The diffuser housing  104  defines the air outlet  74  of the duct  70 . The internal surface of the diffuser housing  104  is provided with grooves which receive the outer edges of the blades  102 . The diffuser housing  104  and the upper section  98  of the motor housing define a diffuser section of the air flow path through the duct  70 . 
         [0108]    The upper section  98  of the motor housing is perforated. The inner surface of the upper section  98  of the motor housing is lined with noise absorbing material, preferably an acoustic foam material, to suppress broadband noise generated during operation of the fan  10 . The noise absorbing material is not shown in the Figures so as to not obscure the perforations in the upper section  98  of the motor housing. 
         [0109]    A retaining ring  124  is provided in an upper portion of the main body section  50  for preventing the motor housing from falling out of the main body section  50 , for example during transit. The retaining ring  124  is provided with four angularly spaced recesses  126 , the top side of which can be seen in  FIG. 6 . Located within each of the recesses  126  is a foam pad. The angularly spaced foam pads are arranged such that when the retaining ring  124  is secured to the main body section  50  the foam pads rest on corresponding angularly spaced members  128  which project outwardly from an outer surface of the diffuser housing  104 . The foam pads reduce the transmission of vibrations from the motor housing  94  to the retaining ring  124 . 
         [0110]    The retaining ring  124  further comprises an annular sealing member  154 . The annular sealing member  154  extends around the periphery of the retaining ring  124  and is trapped between the outer surface of the retaining ring  124  and the inner surface of the main body section  50 . The sealing member  154  has a lip  156  which extends radially inwardly towards the longitudinal axis of the motor housing. The lip  156  is arranged such that when the nozzle  16  is located on the main body section  52  of the base  12  the lip  156  seals against an outer surface of the downwardly depending inner annular wall  150  defining the inner wall of the annular channel  134 . This seal prevents the leakage of air as it passes from the air outlet  74  of main body section  50  and into the air inlet  42  of the nozzle  16 . This ensures that the fan  10  can function even in the absence of the filter  14 . 
         [0111]    Referring to  FIG. 7  band  8 , the impeller housing  78  is mounted on an annular seat  106  located within the main body section  50  of the body  12 . The seat  106  extends radially inwardly from the inner surface of the outer casing  24  so that an upper surface of the seat  106  is substantially orthogonal to the rotational axis Z of the impeller  80 . 
         [0112]    An annular seal  108  is located between the impeller housing  78  and the seat  106 . The annular seal  108  is preferably a foam annular seal, and is preferably formed from a closed cell foam material. The outer diameter of the annular seal  108  is preferably smaller than the inner diameter of the outer casing  24  so that the annular seal  108  is spaced from the inner surface of the outer casing  24 . 
         [0113]    To operate the fan  10  the user presses button  20  of the user interface or a button on the remote control, in response to which the control circuit  62  activates the motor  92  to rotate the impeller  80 . The rotation of the impeller  80  causes a primary air flow to be drawn through the air inlets  170  of the filter  14 , through the two layers  162 ,  164  of filter media, and into the body  12  through the air inlet  22 . Particles are thus removed from the air flow upstream from the air inlets  22  and do not enter the body  12 . The user may control the speed of the motor  92 , and therefore the rate at which air is drawn into the body  12 , by pressing the appropriate buttons on the remote control. 
         [0114]    The rotation of the impeller  80  by the motor  92  generates vibrations which are transferred through the motor housing and the impeller housing  78  towards the seat  106 . The annular seal  108  located between the impeller housing  78  and the seat  106  is compressed under the weight of the duct  70 , the impeller  80 , the motor housing and the motor  92  so that it is in sealing engagement with the upper surface of the seat  106  and the impeller housing  78 . The annular seal  108  thus not only prevents the primary air flow from returning to the air inlet  72  of the duct  70  along a path extending between the inner surface of the outer casing  24  of the main body section  50  and the outer wall  77  of the duct  70 , but also reduces the transmission of these vibrations to the seat  106 , and thus to the body  12  of the fan  10 . 
         [0115]    The air flow entering the body  12  through the air inlet  22  passes to the air inlet  72  of the duct  70 . Within the duct  70 , the primary air flow passes through the impeller housing  78  and the diffuser housing  104  to be emitted from the air outlet  74  of the duct  70  and into the air inlet  42  of the nozzle  16 . 
         [0116]    Within the interior passage  44  of the nozzle  16 , the primary air flow is divided into two air streams which pass in opposite angular directions around the bore  19  of the nozzle  16 . As the air streams pass through the interior passage  44 , air is emitted through the air outlet  18 . The emission of the primary air flow from the air outlet  18  causes a secondary air flow to be generated by the entrainment of air from the external environment, specifically from the region around the nozzle  16 . This secondary air flow combines with the primary air flow to produce a combined, or total, air flow, or air current, projected forward from the nozzle  16 . 
         [0117]    Each of the air streams enters a respective one of the two vertically extending sections of the interior passage  44  of the nozzle  16 , and is conveyed in a substantially vertical direction up through each of these sections of the interior passage  44 . The set of guide vanes  120  located within each of these sections of the interior passage  44  directs the air stream towards the section of the mouth  18  located adjacent that vertically extending section of the interior passage  44 . Each of the guide vanes  120  directs a respective portion of the air stream towards the section of the mouth  18  so that there is a substantially uniform distribution of the air stream along the length of the section of the mouth  18 . The guide vanes  120  are shaped so that each portion of the air stream enters the mouth  18  in a substantially horizontal direction. 
         [0118]    The primary air flow emitted from the mouth  18  is directed over the Coanda surface  34  of the nozzle  14 , causing a secondary air flow to be generated by the entrainment of air from the external environment, specifically from the region around the mouth  18  and from around the rear of the nozzle  16 . This secondary air flow passes predominantly through the central opening  19  of the nozzle  16 , where it combines with the primary air flow to produce a total air flow, or air current, projected forward from the nozzle  16 . 
         [0119]    The even distribution of the primary air flow along the mouth  18  of the nozzle  16  ensures that the air flow passes evenly over the diffuser surface  34 . The diffuser surface  34  causes the mean speed of the air flow to be reduced by moving the air flow through a region of controlled expansion. The relatively shallow angle of the diffuser surface  34  to the central axis X of the opening  19  allows the expansion of the air flow to occur gradually. A harsh or rapid divergence would otherwise cause the air flow to become disrupted, generating vortices in the expansion region. Such vortices can lead to an increase in turbulence and associated noise in the air flow, which can be undesirable, particularly in a domestic product such as a fan. In the absence of the guide vanes  120  most of the primary air flow would tend to leave the fan  10  through the upper part of the mouth  18 , and to leave the mouth  18  upwardly at an acute angle to the central axis of the opening  19 . As a result there would be an uneven distribution of air within the air current generated by the fan  10 . Furthermore, most of the air flow from the fan  10  would not be properly diffused by the diffuser surface  34 , leading to the generation of an air current with much greater turbulence. 
         [0120]    The air flow projected forwards beyond the diffuser surface  34  can tend to continue to diverge. The presence of the guide surface  36  extending substantially parallel to the central axis X of the opening  19  tends to focus the air flow towards the user or into a room. 
         [0121]    The invention is not limited to the detailed description given above. Variations will be apparent to the person skilled in the art. 
         [0122]    For example, the base and the nozzle of the fan may be of a different shape and/or shape. The outlet of the mouth may be modified. For example, the outlet of the mouth may be widened or narrowed to a variety of spacings to maximise air flow. The air flow emitted from the mouth may pass over a surface, such as a Coanda surface, but alternatively the air flow may be emitted through the mouth and projected forward from the fan without passing over an adjacent surface. The Coanda effect may be effected over a number of different surfaces, or a number of internal or external designs may be used in combination to achieve the flow and entrainment required. The diffuser surface may be comprised of a variety of diffuser lengths and structures. The guide surface may be a variety of lengths, and may be arranged at a number of different positions and orientations as required for different fan requirements and different types of fan performance.