Abstract:
A fan assembly includes a nozzle and a system for creating a primary air flow through the nozzle. The nozzle includes an outlet for emitting the primary air flow, and defines an opening through which a secondary air flow from outside the fan assembly is drawn by the primary air flow emitted from the outlet. To allow a parameter of an air flow, formed from the combination of the primary and secondary air flows, to be adjusted by a user, the nozzle has an adjustable configuration.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of United Kingdom Application No. 1017551.1 filed Oct. 18, 2010, and United Kingdom Application No. 1105687.6, filed Apr. 4, 2011, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a fan assembly. Particularly, but not exclusively, the present invention relates to a floor or table-top fan assembly, such as a desk, tower or pedestal fan. 
     BACKGROUND OF THE INVENTION 
     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 generally 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. 
     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 mouth through which the primary air flow is emitted from the fan. The nozzle defines an 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. The nozzle includes a Coanda surface over which the mouth is arranged to direct the primary air flow. The Coanda surface extends symmetrically about the central axis of the opening so that the air flow generated by the fan assembly is in the form of an annular jet having a cylindrical or frusto-conical profile. 
     SUMMARY OF THE INVENTION 
     In a first aspect the present invention provides a fan assembly comprising a nozzle and a system for creating a primary air flow through the nozzle. The nozzle comprises at least one outlet for emitting the primary air flow, and defines an opening through which a secondary air flow from outside the fan assembly is drawn by the primary air flow emitted from the at least one outlet. To allow at least one parameter of an air flow, formed from the combination of the primary and secondary air flows, to be adjusted by a user, the nozzle has an adjustable configuration. 
     The at least one parameter of the combined air flow may comprise at least one of the profile, orientation, direction, flow rate (as measured, for example, in liters per second), and velocity of the combined air flow. Thus, through adjusting the configuration of the nozzle a user may adjust the direction in which the combined air flow is projected forward from the fan assembly, for example to angle the air flow towards or away from a person in the vicinity of the fan assembly. Alternatively, or additionally, the user may expand or restrict the profile of the combined air flow to increase or decrease the number of users within the path of the air flow. As another alternative the user may change the orientation of the air flow, for example through the rotation of a relatively narrow air flow to provide a relatively wide air flow for cooling a number of users. 
     The nozzle may be adjustable to adopt one of a number of discrete configurations. The nozzle may be locked in a selected configuration so that the configuration of the nozzle cannot be adjusted later by a user. However, it is preferred that the nozzle may be releasable or otherwise moveable from a selected configuration to allow a user to adjust the configuration of the nozzle as required during the use of the fan assembly. 
     The configuration of the nozzle may be adjusted manually by the user, or it may be adjusted automatically by an automated mechanism of the fan assembly, for example in response to a user operation of a user interface of the fan assembly. This user interface may be located on a body of the fan assembly, or it may be provided by a remote control connected wirelessly to the fan assembly. 
     The configuration of the nozzle may be adjusted by altering the position, shape or state of at least one part of the nozzle. This part of the nozzle may be rotated, translated, pivoted, extended, retracted, expanded, contracted, slid or otherwise moved relative to another part of the nozzle to adjust the configuration of the nozzle. 
     For example, the size and shape of the opening may be fixed, and so a part of the nozzle may be moved relative to the opening to adjust the configuration of the nozzle. Alternatively, or additionally, the size and shape of the at least one outlet may be fixed, and so a part of the nozzle may be moved relative to the at least one outlet to adjust the configuration of the nozzle. This moveable part of the nozzle may be located upstream or downstream of the at least one outlet, but in a preferred embodiment the moveable part of the nozzle is located downstream of the at least one outlet. 
     The nozzle may comprise a first part, and a second part which is moveable relative to the first part, thereby adjusting the configuration of the nozzle. As mentioned above, this second part of the nozzle may be moveable relative to the opening, which may remain in a fixed configuration as the second part of the nozzle is moved relative thereto. Alternatively, or additionally, this second part of the nozzle may be moveable relative to the at least one outlet, which may remain in a fixed configuration as the second part of the nozzle is moved relative thereto. 
     The second part of the nozzle preferably comprises a flow guiding member. The flow guiding member may be selectively exposed to at least the primary air flow to vary said at least one parameter of the combined air flow. Alternatively, or additionally, at least one of the position and the orientation of the flow guiding member relative to the opening or the at least one air outlet may be adjusted to vary said at least one parameter of the combined air flow. 
     The second part of the nozzle is preferably rotatable relative to the first part of the nozzle. Alternatively, or additionally, the second part of the nozzle may be slidably moveable relative to the first part of the nozzle. 
     The second part of the nozzle may be mounted on an external surface of the nozzle. The second part of the nozzle may be moved over this external surface to vary the configuration of the nozzle. 
     The second part of the nozzle may be moveable relative to the first part of the nozzle between a stowed position and at least one deployed position, for example, to vary a parameter of the combined air flow generated by the fan assembly. In the stowed position the first part of the nozzle may be shielded from the air flow, whereas in each of the deployed positions the first part of the nozzle may be exposed to the combined air flow to adjust a parameter of the air flow generated by the fan assembly by a respective different amount. For example, in each of the deployed positions the second part of the nozzle may be exposed to the air flow by a respective different amount. 
     The second part of the nozzle may be moveable between a first position in which the combined air flow generated by the fan assembly has a first parameter, for example a first orientation, a first shape or a first direction, and a second position in which the combined air flow generated by the fan assembly has a second parameter, for example a second orientation, a second shape or a second direction, which is different from the first parameter. In each position, the second part of the nozzle may be exposed to the primary air flow. 
     The first part of the nozzle may be located downstream from the at least one outlet. The first part of the nozzle is preferably maintained in a fixed position relative to the at least one outlet as the second part of the nozzle is moved between the stowed position and the at least one deployed position. In the at least one deployed position, the second part of the nozzle is preferably located downstream from the first part of the nozzle. 
     The first part of the nozzle preferably comprises a surface over which the at least one outlet is arranged to direct the air flow. Preferably, the surface over which the at least one outlet is arranged to direct the air flow comprises a Coanda surface. A Coanda surface is a known type of surface over which fluid flow exiting an output orifice close to the surface exhibits the Coanda effect. The fluid tends to flow over the surface closely, almost ‘clinging to’ or ‘hugging’ the surface. The Coanda effect is already a proven, well documented method of entrainment in which a primary air flow is directed over a Coanda surface. A description of the features of a Coanda surface, and the effect of fluid flow over a Coanda surface, can be found in articles such as Reba, Scientific American, Volume 214, June 1966 pages 84 to 92. Through use of a Coanda surface, an increased amount of air from outside the fan assembly is drawn through the opening by the air emitted from the at least one outlet. 
     In a preferred embodiment an air flow is created through the nozzle of the fan assembly. In the following description this air flow will be referred to as the primary air flow. The primary air flow is emitted from the nozzle and preferably passes over a Coanda surface. The primary air flow entrains air surrounding the nozzle, which acts as an air amplifier to supply both the primary air flow and the entrained air to the user. The entrained air will be referred to here as a secondary air flow. The secondary air flow is drawn from the room space, region or external environment surrounding the nozzle and, by displacement, from other regions around the fan assembly, and passes predominantly through the opening defined by the nozzle. The primary air flow directed over the Coanda surface combined with the entrained secondary air flow equates to a total air flow emitted or projected forward from the opening defined by the nozzle. 
     The surface over which the primary air flow is directed preferably comprises a diffuser portion downstream from the at least one outlet. The diffuser portion may thus form part of a Coanda surface. The diffuser portion preferably extends about an axis, and preferably tapers towards or away from the axis. 
     The surface of the nozzle may also include a guide portion located downstream of the diffuser portion and angled thereto for channelling the combined air flow generated by the fan assembly. The guide portion is preferably tapered inwardly, that is, towards the axis, relative to the diffuser portion. The guide portion may itself taper towards or away from the axis. For example, the diffuser portion may taper away from the axis, and the guide portion may taper towards the axis. Alternatively, the diffuser portion may taper away from the axis, and the guide portion may be substantially cylindrical. 
     The surface of the nozzle may comprise a cutaway portion, with the second part of the nozzle being moveable to at least partially cover the cutaway portion. The surface may comprise a plurality of cutaway portions, with the second part of the nozzle being moveable to at least partially cover at least one of the cutaway portions. For example, the second part of the nozzle may be moveable relative to the surface to cover a selected one of the cutaway portions by a desired amount. Alternatively, the second part of the nozzle may be moveable to cover simultaneously each of the cutaway portions by a desired amount. 
     The cutaway portions may be regularly or irregularly spaced about the nozzle. The cutaway portions are preferably arranged in an annular array. The cutaway portions may have the same or different sizes and/or shapes. The, or each, cutaway portion may have any desired shape. In a preferred embodiment the, or each, cutaway portion has a shape which is generally arcuate, but the, or each, cutaway portion may be circular, oval, polygonal or irregular. 
     The, or each, cutaway portion may be located in the diffuser portion of the surface, or in the guide portion of the surface. The, or each, cutaway portion is preferably located at or towards a front edge of the nozzle. For example, the nozzle may comprise cutaway portions located on opposite sides of the guide portion. These cutaway portions may be located at side extremities of the nozzle, and/or at upper and lower extremities of the nozzle. 
     The second part of the nozzle may be generally annular in shape, and rotated relative to the Coanda surface by the user. This can allow one or more of the cutaway portions to be selectively covered. The inner surface of the second part of the nozzle preferably has substantially the same shape as the inner surface of the guide portion. 
     As an alternative to arranging the second part of the nozzle to cover cutaway portions of the surface of the nozzle, the second part of the nozzle may be moveable between a stowed position and at least one deployed position in which the second part of the nozzle is located downstream from the surface of the nozzle. In its stowed position, the second part of the nozzle may extend about the surface so that it is shielded from the combined air flow. As mentioned above, the second part of the nozzle may be located on an external surface of the nozzle, but alternatively the second part of the nozzle may be located within the nozzle when in its stowed position. The second part of the nozzle may then be pulled from the nozzle to move it from its stowed position to a deployed position. For example, a front part of the nozzle may comprise a slot from which the second part of the nozzle is pulled to withdraw the second part from the nozzle and into one of its deployed positions. A tab or other graspable member may be located on the second part to facilitate its withdrawal from the stowed position. 
     The second part of the nozzle may comprise a guide surface for changing the profile of the combined air flow. The guide surface may have a similar configuration to the guide portion discussed above. The guide surface may have a cylindrical or a frusto-conical shape. The guide surface preferably tapers inwardly relative to the surface of the nozzle. In the deployed position, the guide surface may converge inwardly in a direction extending away from the surface in order to focus the combined air flow towards a user located in front of the fan assembly. 
     As mentioned above, the second part of the nozzle is preferably generally annular in shape, and may be in the form of a hoop which is moveable relative to the other parts of the nozzle. 
     The nozzle is preferably in the form of a loop extending about the opening. 
     The nozzle may have a single outlet from which the primary air flow is emitted. Alternatively, the nozzle may comprise a plurality of outlets each for emitting a respective portion of the primary air flow. In this case, the outlets are preferably spaced about the opening. The nozzle preferably comprises a mouth for receiving the primary air flow, and for conveying the primary air flow to the outlet(s). The mouth preferably extends about the opening, more preferably continuously about the opening. 
     The spacing between opposing surfaces of the nozzle at the outlet(s) is preferably in the range from 0.5 mm to 5 mm. The nozzle preferably comprises an interior passage which extends about the opening, preferably continuously about the opening so that the opening is an enclosed opening which is surrounded by the interior passage. 
     The nozzle is preferably mounted on a base housing said system for creating an air flow. In the preferred fan assembly the system for creating an air flow through the nozzle comprises an impeller driven by a motor. 
     In a second aspect the present invention provides a fan assembly comprising a nozzle and a system for creating an air flow through the nozzle, the nozzle comprising an interior passage, at least one outlet for receiving at least a portion of the air flow from the interior passage, and a surface located adjacent said at least one outlet and over which said at least one outlet is arranged to direct said at least a portion of the air flow, characterized in that the nozzle has an adjustable configuration. 
     In a third aspect, the present invention provides a nozzle for a fan assembly, the nozzle comprising at least one outlet for emitting a primary air flow, and defining an opening through which a secondary air flow from outside the fan assembly is drawn by the primary air flow emitted from the at least one outlet, the nozzle comprising a first part and a second part which is moveable relative to the first part. The first part of the nozzle may be located upstream or downstream from the at least one outlet. The second part is preferably moveable relative to the first part between a stowed position in which it is shielded from the air flow and a deployed position in which it may be located downstream from the first part. Each part of the nozzle may comprise a surface over which the air flow is directed by said at least one outlet. 
     In a fourth aspect, the present invention provides a nozzle for a fan assembly, the nozzle comprising an interior passage, at least one outlet for receiving at least a portion of the air flow from the interior passage, and a surface located adjacent said at least one air outlet and over which said at least one outlet is arranged to direct said at least a portion of the air flow, characterized in that the nozzle has an adjustable configuration. The nozzle preferably comprises a moveable part which is moveable between a stowed position in which it is shielded from the air flow and a deployed position in which it is located downstream from the surface. 
     Features described above in connection with the first aspect of the invention are equally applicable to each of the second to fourth aspects of the invention, and vice versa. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred features of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a front perspective view, from above, of a first fan assembly, with a nozzle of the fan assembly in a first configuration; 
         FIG. 2  is a left side view of the first fan assembly; 
         FIG. 3  is a top view of the first fan assembly; 
         FIG. 4  is a front view of the first fan assembly; 
         FIG. 5  is a side sectional view of the first fan assembly, taken along line A-A in  FIG. 4 ; 
         FIG. 6  is a front perspective view, from above, of the first fan assembly, with the nozzle in a second configuration; 
         FIG. 7  is a front perspective view, from above, of the first fan assembly, with the nozzle in a third configuration; 
         FIG. 8  is a front perspective view, from above, of a second fan assembly, with a nozzle of the fan assembly in a first configuration; 
         FIG. 9  is a front perspective view, from above, of the second fan assembly, with the nozzle in a second configuration; 
         FIG. 10  is a front perspective view, from above, of a third fan assembly, with a nozzle of the fan assembly in a first configuration; 
         FIG. 11  is a front view of the third fan assembly; 
         FIG. 12  is a side sectional view of the third fan assembly, taken along line A-A in  FIG. 11 ; 
         FIG. 13  is a front perspective view, from above, of the third fan assembly, with the nozzle in a second configuration; 
         FIG. 14  is a front perspective view, from above, of a fourth fan assembly, with a nozzle of the fan assembly in a first configuration; 
         FIG. 15  is a front view of the fourth fan assembly; 
         FIG. 16  is a side sectional view of the fourth fan assembly, taken along line A-A in  FIG. 15 ; and 
         FIG. 17  is a front perspective view, from above, of the fourth fan assembly, with the nozzle in a second configuration. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 to 4  are external views of a first fan assembly  10 . The fan assembly  10  comprises a body  12  comprising an air inlet  14  through which a primary air flow enters the fan assembly  10 , and a nozzle  16  in the form of an annular casing mounted on the body  12 , and which comprises a mouth  18  having at least one outlet for emitting the primary air flow from the fan assembly  10 . 
     The body  12  comprises a substantially cylindrical main body section  20  mounted on a substantially cylindrical lower body section  22 . The main body section  20  and the lower body section  22  preferably have substantially the same external diameter so that the external surface of the upper body section  20  is substantially flush with the external surface of the lower body section  22 . In this embodiment the body  12  has a height in the range from 100 to 300 mm, and a diameter in the range from 100 to 200 mm. 
     The main body section  20  comprises the air inlet  14  through which the primary air flow enters the fan assembly  10 . In this embodiment the air inlet  14  comprises an array of apertures formed in the main body section  20 . Alternatively, the air inlet  14  may comprise one or more grilles or meshes mounted within windows formed in the main body section  20 . The main body section  20  is open at the upper end (as illustrated) thereof to provide an air outlet  23  through which the primary air flow is exhausted from the body  12 . 
     The main body section  20  may be tilted relative to the lower body section  22  to adjust the direction in which the primary air flow is emitted from the fan assembly  10 . For example, the upper surface of the lower body section  22  and the lower surface of the main body section  20  may be provided with interconnecting features which allow the main body section  20  to move relative to the lower body section  22  while preventing the main body section  20  from being lifted from the lower body section  22 . For example, the lower body section  22  and the main body section  20  may comprise interlocking L-shaped members. 
     The lower body section  22  comprises a user interface of the fan assembly  10 . The user interface comprises a plurality of user-operable buttons  24 ,  26 , a dial  28  for enabling a user to control various functions of the fan assembly  10 , and user interface control circuit  30  connected to the buttons  24 ,  26  and the dial  28 . The lower body section  22  is mounted on a base  32  for engaging a surface on which the fan assembly  10  is located. 
       FIG. 5  illustrates a sectional view through the body fan assembly. The lower body section  22  houses a main control circuit, indicated generally at  34 , connected to the user interface control circuit  30 . In response to operation of the buttons  24 ,  26  and the dial  28 , the user interface control circuit  30  is arranged to transmit appropriate signals to the main control circuit  34  to control various operations of the fan assembly  10 . 
     The lower body section  22  also houses a mechanism, indicated generally at  36 , for oscillating the lower body section  22  relative to the base  32 . The operation of the oscillating mechanism  36  is controlled by the main control circuit  34  in response to the user operation of the button  26 . The range of each oscillation cycle of the lower body section  22  relative to the base  32  is preferably between 60° and 120°, and in this embodiment is around 80°. In this embodiment, the oscillating mechanism  36  is arranged to perform around 3 to 5 oscillation cycles per minute. A mains power cable  38  for supplying electrical power to the fan assembly  10  extends through an aperture formed in the base  32 . The cable  38  is connected to a plug (not shown) for connection to a mains power supply. 
     The main body section  20  houses an impeller  40  for drawing the primary air flow through the air inlet  14  and into the body  12 . Preferably, the impeller  40  is in the form of a mixed flow impeller. The impeller  40  is connected to a rotary shaft  42  extending outwardly from a motor  44 . In this embodiment, the motor  44  is a DC brushless motor having a speed which is variable by the main control circuit  34  in response to user manipulation of the dial  28 . The maximum speed of the motor  44  is preferably in the range from 5,000 to 10,000 rpm. The motor  44  is housed within a motor bucket comprising an upper portion  46  connected to a lower portion  48 . The upper portion  46  of the motor bucket comprises a diffuser  50  in the form of a stationary disc having spiral blades. 
     The motor bucket is located within, and mounted on, a generally frusto-conical impeller housing  52 . The impeller housing  52  is, in turn, mounted on a plurality of angularly spaced supports  54 , in this example three supports, located within and connected to the main body section  20  of the base  12 . The impeller  40  and the impeller housing  52  are shaped so that the impeller  40  is in close proximity to, but does not contact, the inner surface of the impeller housing  52 . A substantially annular inlet member  56  is connected to the bottom of the impeller housing  52  for guiding the primary air flow into the impeller housing  52 . An electrical cable  58  passes from the main control circuit  34  to the motor  44  through apertures formed in the main body section  20  and the lower body section  22  of the body  12 , and in the impeller housing  52  and the motor bucket. 
     Preferably, the body  12  includes silencing foam for reducing noise emissions from the body  12 . In this embodiment, the main body section  20  of the body  12  comprises a first foam member  60  located beneath the air inlet  14 , and a second annular foam member  62  located within the motor bucket. 
     A flexible sealing member  64  is mounted on the impeller housing  52 . The flexible sealing member prevents air from passing around the outer surface of the impeller housing  52  to the inlet member  56 . The sealing member  64  preferably comprises an annular lip seal, preferably formed from rubber. The sealing member  64  further comprises a guide portion in the form of a grommet for guiding the electrical cable  58  to the motor  44 . 
     Returning to  FIGS. 1 to 4 , the nozzle  16  has an annular shape, extending about a central axis X to define an opening  70 . The mouth  18  is located towards the rear of the nozzle  16 , and is arranged to emit the primary air flow towards the front of the fan assembly  10 , through the opening  70 . The mouth  18  surrounds the opening  70 . In this example, the nozzle  16  defines a generally circular opening  70  located in a plane which is generally orthogonal to the central axis X. The innermost, external surface of the nozzle  16  comprises a Coanda surface  72  located adjacent the mouth  18 , and over which the mouth  18  is arranged to direct the air emitted from the fan assembly  10 . The Coanda surface  72  comprises a diffuser portion  74  tapering away from the central axis X. In this example, the diffuser portion  74  is in the form of a generally frusto-conical surface extending about the axis X, and which is inclined to the axis X at an angle in the range from 5 to 35°, and in this example is around 28°. 
     The nozzle  16  comprises an annular front casing section  76  connected to and extending about an annular rear casing section  78 . The annular sections  76 ,  78  of the nozzle  16  extend about the central axis X. Each of these sections may be formed from a plurality of connected parts, but in this embodiment each of the front casing section  76  and the rear casing section  78  is formed from a respective, single molded part. The rear casing section  78  comprises a base  80  which is connected to the open upper end of the main body section  20  of the body  12 , and which has an open lower end for receiving the primary air flow from the body  12 . 
     With reference also to  FIG. 5 , during assembly, the front end  82  of the rear casing section  78  is inserted into a slot  84  located in the front casing section  76 . Each of the front end  82  and the slot  84  is generally cylindrical. The casing sections  76 ,  78  may be connected together using an adhesive introduced to the slot  84 . 
     The front casing section  76  defines the Coanda surface  72  of the nozzle  16 . The front casing section  76  and the rear casing section  78  together define an annular interior passage  88  for conveying the primary air flow to the mouth  18 . The interior passage  88  extends about the axis X, and is bounded by the internal surface  90  of the front casing section  76  and the internal surface  92  of the rear casing section  78 . The base  80  of the front casing section  76  is shaped to convey the primary air flow into the interior passage  88  of the nozzle  16 . 
     The mouth  18  is defined by overlapping, or facing, portions of the internal surface  92  of the rear casing section  78  and the external surface  94  of the front casing section  76 , respectively. The mouth  18  preferably comprises an air outlet in the form of an annular slot. The slot is preferably generally circular in shape, and preferably has a relatively constant width in the range from 0.5 to 5 mm. In this example the air outlet has a width of around 1 mm. Spacers may be spaced about the mouth  18  for urging apart the overlapping portions of the front casing section  76  and the rear casing section  78  to control the width of the air outlet of the mouth  18 . These spacers may be integral with either the front casing section  76  or the rear casing section  78 . The mouth  18  is shaped to direct the primary air flow over the external surface  94  of the front casing section  76 . 
     The external surface of the nozzle  16  also comprises a guide portion  96  located downstream from the diffuser portion  74  and angled thereto. The guide portion  96  similarly extends about the axis X. The guide portion  96  may be inclined to the axis X by an angle in the range from −30 to 30°, but in this example the guide portion  96  is generally cylindrical and is centered on the axis X. The depth of the guide portion  96 , as measured along the axis X, is preferably in the range from 20 to 80% of the depth of the diffuser portion  74 , and in this example is around 60%. 
     The guide portion  96  comprises a first section  98  which is connected to, and preferably integral with, the diffuser portion  74  of the Coanda surface  72 , and a second section  100  which is moveable relative to the first section  98  to adjust a parameter of the air flow generated by the fan assembly  10 . In this example, the first section  98  of the guide portion  96  of the nozzle  16  comprises an upper portion  102  and a lower portion  104 . Each of the upper portion  102  and the lower portion  104  is in the form of a partially cylindrical surface centered on the axis X, and which extends about the axis X by an angle which is preferably in the range from 30 to 150°, and in this example is around 120°. The upper and lower portions  102 ,  104  are separated by a pair of cutaway portions  106 ,  108  of the first section  98 . In this example each cutaway portion  106 ,  108  is located at a respective side of the first section  98 , and extends from the front edge  110  of the first section  98  to the substantially circular front edge  112  of the diffuser portion  74 . The cutaway portions  106 ,  108  have generally the same size and shape, and in this example each extend around 60° about the axis X. 
     The second section  100  of the guide portion  96  is generally annular in shape, and is mounted on the external surface of the nozzle  16  so as to extend about the first section  98  of the guide portion  96 . The second section  100  has a generally cylindrical curvature, and is also centered on the axis X. The front edge  114  of the second section  100  is substantially co-planar with the front edge  110  of the first section  98 , whereas the substantially circular rear edge  116  is located rearwardly of the first section  96  so as to surround the diffuser portion  74  of the Coanda surface  72 . 
     The depth of the second section  100  of the guide portion  96 , as measured along the axis X, varies about the axis X. The second section  100  comprises two forwardly extending portions  118 ,  120  which are connected by arcuate connectors  122 ,  124 . The forwardly extending portions  118 ,  120  of the second section  100  have generally the same size and shape as the upper and lower portions  102 ,  104  of the front section  98 . The connectors  122 ,  124  are relatively narrow, and are located behind the front edge  112  of the diffuser portion  74  of the Coanda surface  72  so that these connectors  122 ,  124  are not exposed to the air flow generated by the fan assembly  10 . 
     As mentioned above, the second section  100  of the guide portion  96  is moveable relative to the first section  98  of the guide portion  96 . In this example, the second section  100  is located about the first section  98  so as to be rotatable about the axis X. The second section  100  comprises a pair of tabs  126  which extend radially outwardly to allow a user to grip the tabs to rotate the second section  100  relative to the first section  98 . In this example, the second section  100  slides over the first section  98  as it is moved relative thereto. The inner surface of the second section  100  may comprise a radially inwardly extending ridge, which may extend partially or fully about the axis X, which is received within an annular groove formed on the outer surface of the front casing section  76  and which guides the movement of the second section  100  relative to the first section  98 . 
     To operate the fan assembly  10  the user the user presses button  24  of the user interface. The user interface control circuit  30  communicates this action to the main control circuit  34 , in response to which the main control circuit  34  activates the motor  44  to rotate the impeller  40 . The rotation of the impeller  40  causes a primary air flow to be drawn into the body  12  through the air inlet  14 . The user may control the speed of the motor  44 , and therefore the rate at which air is drawn into the body  12  through the air inlet  14 , by manipulating the dial  28  of the user interface. Depending on the speed of the motor  44 , the primary air flow generated by the impeller  40  may be between 10 and 30 liters per second. The primary air flow passes sequentially through the impeller housing  52  and the air outlet  23  at the open upper end of the main body portion  20  to enter the interior passage  88  of the nozzle  16 . The pressure of the primary air flow at the air outlet  23  of the body  12  may be at least 150 Pa, and is preferably in the range from 250 to 1.5 kPa. 
     Within the interior passage  88  of the nozzle  16 , the primary air flow is divided into two air streams which pass in opposite directions around the opening  70  of the nozzle  16 . As the air streams pass through the interior passage  70 , air is emitted through the mouth  18 . The primary air flow emitted from the mouth  18  is directed over the Coanda surface  72  of the nozzle  16 , 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 through the central opening  70  of the nozzle  16 , where it combines with the primary air flow to produce a combined, or total, air flow, or air current, projected forward from the nozzle  16 . 
     As part of the nozzle  16 , in this example the second section  100  of the guide portion  96  of the nozzle  16 , is moveable relative to the remainder of the nozzle  16 , the nozzle  16  may adopt one of a number of different configurations.  FIGS. 1 to 5  illustrate the nozzle  16  in a first configuration, in which the second section  100  of the guide portion  96  is in a stowed position relative to the other parts of the nozzle  16 . In this stowed position the forwardly extending portions  118 ,  120  of the second section  100  are located radially behind the upper and lower portions  102 ,  104  of the front section  98  so that the second section  100  is substantially fully shielded from the air flow. This allows part of the combined air flow to pass through the cutaway portions  106 ,  108  of the first section  96  without being channelled or focussed towards the axis X by the guide portion  96  of the nozzle  16 . 
     As the angle of the diffuser portion  74  of the Coanda surface  72  is relatively wide, in this example around 28°, the profile of the combined air flow projected forward from the fan assembly  10  will be relatively wide. However, in view of the partial guiding of the combined air flow towards the axis X, the profile of the air current generated by the fan assembly  10  is non-circular. The profile is generally oval, with the height of the profile being smaller than the width of the profile. This flattening, or widening, of the profile of the air current in this nozzle configuration can make the fan assembly  10  particularly suitable for use as a desk fan in a room, office or other environment to deliver a cooling air current simultaneously to a number of users in proximity to the fan assembly  10 . 
     By gripping the tabs  126  of the second section  100  of the guide portion  96 , a user may rotate the second section  100  relative to the first section  98  to change the configuration of the nozzle  16 .  FIG. 6  illustrates the fan assembly  10  in a second configuration in which the second section  100  is in a partially deployed position relative to the other parts of the nozzle  16  following a partial rotation of the second section  100  about the first section  98 . In this partially deployed position, the forwardly extending portions  118 ,  120  of the second section  100  partially cover the cutaway portions  106 ,  108  of the first section  96 , changing the profile of the combined air and increasing the proportion of the combined air flow which is channelled towards a user located in front of the fan assembly  10 . 
       FIG. 7  illustrates the fan assembly  10  in a third configuration in which the second section  100  is in a fully deployed position relative to the other parts of the nozzle  16  following a further partial rotation of the second section  100  about the first section  98 . In this fully deployed position, the forwardly extending portions  118 ,  120  of the second section  100  cover fully the cutaway portions  106 ,  108  of the first section  96 , again changing the profile of the combined air so that all of the combined air flow is channelled towards a user located in front of the fan assembly  10 . The upper and lower portions  102 ,  104  of the front section  98  and the forwardly extending portions  118 ,  120  of the second section  100  provide a substantially continuous, substantially cylindrical guide surface for channelling the combined air flow towards the user, and so the profile of the combined air flow, in this nozzle configuration, is generally circular. This focussing of the profile of the air flow can make the fan assembly  10  particularly suitable for use as a desk fan in a room, office or other environment to deliver a cooling air current to a single user in proximity to the fan assembly  10 . 
     The movement of the nozzle  16  between these configurations also varies the flow rate and the velocity of the combined air flow generated by the fan assembly  10 . When the second section  100  is in the stowed position, the combined air flow has a relatively high flow rate but a relatively low velocity. When the second section  100  is in the fully deployed position, the combined air flow has a relatively low flow rate but a relatively high velocity. 
     As an alternative to locating the portions  102 ,  104  of the front section  98  at the upper and lower extremities of the guide portion  96 , these portions may be located at the side extremities of the guide portion  96 . Thus, when the second section  100  is in its stowed position, the height of the profile of the air current may be greater than the width of the profile. This stretching of the profile of the air current in a vertical direction can make the fan assembly particularly suitable for use as a floor standing tower or pedestal fan. 
     In the fan assembly  10 , the second section  100  is arranged to cover simultaneously both of the cutaway portions  106 ,  108  when in its fully deployed position.  FIGS. 8 and 9  illustrate a second fan assembly  10 ′, which differs from the fan assembly  10  in that the forwardly extending portion  120  has been omitted from the second section  100  of the guide portion  96 . In view of this, the second section  100  is moveable from a stowed position in which, similar to the fan assembly  10 , air can flow through both of the cutaway portions  106 ,  108  of the first section  98 , to one of a first fully deployed position and a second fully deployed position. In the first fully deployed position, illustrated in  FIG. 8 , only the cutaway portion  108  is covered fully by the second section  100  whereas in the second fully deployed position, illustrated in  FIG. 9 , only the cutaway portion  106  is covered fully by the second section  100 . The movement of the second section  100  between these fully deployed positions thus not only changes the profile of the combined air flow, but also changes the direction and the orientation of the combined air flow. 
     In this example, the change in the orientation of the combined air flow between the first and second fully deployed positions is around 180°. Thus, the movement of the nozzle  16  between these two configurations, in which the second section  100  is in the first fully deployed position and the second fully deployed position respectively, can produce an effect which is similar to that produced by oscillating the lower body section  22  relative to the base  32 , that is, a sweeping of the combined air flow over an arc during the use of the fan assembly  10 ′. Mechanizing the movement of the second section  100  relative to the first section  98  can thus provide an alternative means of sweeping the combined air flow over an arc. 
       FIGS. 10 to 13  illustrate a third fan assembly  200 . The fan assembly  200  comprises a body  12  comprising an air inlet  14  through which a primary air flow enters the fan assembly  200 . The base  12  of the fan assembly  200  is the same as that of the first fan assembly  10 . The fan assembly  200  further comprises a nozzle  202  in the form of an annular casing mounted on the body  12 , and which comprises a mouth  204  having at least one outlet for emitting the primary air flow from the fan assembly  10 . Similar to the nozzle  16 , the nozzle  202  has an annular shape, extending about a central axis X to define an opening  206 . The mouth  204  is located towards the rear of the nozzle  202 , and is arranged to emit the primary air flow towards the front of the fan assembly  200 , through the opening  206 . The mouth  204  surrounds the opening  206 . In this example, the nozzle  202  defines a generally circular opening  206  located in a plane which is generally orthogonal to the central axis X. The innermost, external surface of the nozzle  202  comprises a Coanda surface  208  located adjacent the mouth  204 , and over which the mouth  204  is arranged to direct the air emitted from the nozzle  16 . The Coanda surface  208  comprises a diffuser portion  210  tapering away from the central axis X. In this example, the diffuser portion  210  is in the form of a generally frusto-conical surface extending about the axis X, and which is inclined to the axis X at an angle in the range from 5 to 35°, and in this example is around 20°. 
     The nozzle  202  comprises an annular front casing section  212  connected to and extending about an annular rear casing section  214 . The annular sections  212 ,  214  of the nozzle  202  extend about the central axis X. Each of these sections may be formed from a plurality of connected parts, but in this embodiment each of the front casing section  212  and the rear casing section  214  is formed from a respective, single molded part. The rear casing section  214  comprises a base  216  which is connected to the open upper end of the main body section  20  of the body  12 , and which has an open lower end for receiving the primary air flow from the body  12 . As with the nozzle  16  of the fan assembly  10 , during assembly the front end of the rear casing section  214  is inserted into a slot located in the front casing section  212 . The casing sections  212 ,  214  may be connected together using an adhesive introduced to the slot. 
     The front casing section  212  defines the Coanda surface  208  of the nozzle  202 . The front casing section  212  and the rear casing section  214  together define an annular interior passage  218  for conveying the primary air flow to the mouth  204 . The interior passage  218  extends about the axis X, and is bounded by the internal surface  220  of the front casing section  212  and the internal surface  222  of the rear casing section  214 . The base  216  of the front casing section  212  is shaped to convey the primary air flow into the interior passage  218  of the nozzle  202 . 
     The mouth  204  is defined by overlapping, or facing, portions of the internal surface  222  of the rear casing section  214  and the external surface  224  of the front casing section  212 , respectively. The mouth  204  preferably comprises an air outlet in the form of an annular slot. The air outlet is preferably generally circular in shape, and preferably has a relatively constant width in the range from 0.5 to 5 mm. In this example the air outlet has a width of around 1 mm. Spacers may be spaced about the mouth  204  for urging apart the overlapping portions of the front casing section  212  and the rear casing section  214  to control the width of the air outlet of the mouth  204 . These spacers may be integral with either the front casing section  212  or the rear casing section  214 . The mouth  204  is shaped to direct the primary air flow over the external surface  224  of the front casing section  212 . 
     The nozzle  202  further comprises a guide surface  226 . The guide surface  226  extends about the axis X, and is angled relative to the diffuser portion  210  of the Coanda surface  208 . The guide surface  226  may be inclined to the axis X by an angle in the range from −30 to 30°, but in this example the guide surface  226  is generally cylindrical and is centered on the axis X. The depth of the guide surface  226 , as measured along the axis X, is preferably in the range from 20 to 80% of the depth of the diffuser portion  210 , and in this example is around 50%. 
     The guide surface  226  is moveable relative to the diffuser portion  210  of the Coanda surface  208  to adjust a parameter of the air flow generated by the fan assembly  10 . In this fan assembly  200 , the guide surface  226  is mounted on the external surface of the nozzle  202  so as to be rotatable about the axis X. The guide surface  226  comprises a pair of tabs  228  which extend radially outwardly from the outer surface of the guide surface  226  to allow a user to grip the tabs  228  to rotate the guide surface  226  relative to the diffuser portion  210 . In this example, the guide surface  226  slides over the outer surface of the nozzle  16  as it is moved by the user. 
     The inner surface of the guide surface  226  comprises a plurality of helical grooves  230  which each receive a respective helical ridge  232  which extends outwardly from the outer surface of the nozzle. The engagement between the groves  230  and the ridges  232  guides the movement of the guide surface  226  relative to the diffuser portion  210  so that as the guide surface  226  is rotated relative to the nozzle  202 , it moves along the axis X. 
     As an alternative to providing helical grooves  230  and ridges  232 , the grooves  230  and ridges  232  may each extend substantially parallel to the axis X. In this case, the guide surface  226  may be pulled over the external surface of the nozzle  202  to move the guide surface  226  relative to the diffuser portion  210 . 
     The guide surface  226  is moveable relative to the diffuser portion  210  between a stowed position and a deployed position to adjust the configuration of the nozzle  202 .  FIGS. 10 to 12  illustrate the fan assembly  200  in a first configuration, in which the guide surface  226  is in its stowed position. In this position, the guide surface  226  is located substantially fully about the outer surface of the nozzle  202  so that it is shielded from the primary air flow emitted from the air outlet of the nozzle  202  during use of the fan assembly  200 . In this configuration of the nozzle  202 , the portion of the combined air flow which passes through the opening  206  of the nozzle  202  is not channelled or focussed towards the axis X by the guide surface  226  of the nozzle  16 , and so the air combined flow has a relatively wide profile. In this configuration, the fan assembly  200  is particularly suitable for use as a desk fan in a room, office or other environment to deliver a cooling air current simultaneously to a number of users in proximity to the fan assembly  200 . When the guide surface  226  is in the stowed position, the combined air flow generated by the fan assembly  200  has a relatively high flow rate but a relatively low velocity. 
     By gripping the tabs  228  of the guide surface  226 , a user may rotate the guide surface  226  to move the guide surface  226  along the axis X, and thereby change the configuration of the nozzle  202 .  FIG. 13  illustrates the fan assembly  200  in a second configuration, in which the guide surface  226  is in a deployed position. In this deployed position, the guide surface  226  is located downstream from the diffuser portion  210  of the Coanda surface  208 . During use of the fan assembly  200 , the portion of the combined air flow which passes through the opening  206  of the nozzle  202  is now channelled or focussed towards the axis X by the guide surface  226  of the nozzle  202 , and so the combined air flow now has a relatively narrow profile. This focussing of the profile of the air flow can make the fan assembly  200  particularly suitable for use as a desk fan in a room, office or other environment to deliver a cooling air current to a single user in proximity to the fan assembly  200 . When the guide surface  226  is in the fully deployed position, the combined air flow has a relatively low flow rate but a relatively high velocity. 
       FIGS. 14 to 17  illustrate a fourth fan assembly  300 . Again, the fan assembly  300  comprises a body  12  comprising an air inlet  14  through which a primary air flow enters the fan assembly  300 . The base  12  of the fan assembly  300  is the same as that of the first fan assembly  10 . The fan assembly  300  further comprises a nozzle  302  in the form of an annular casing mounted on the body  12 , and which comprises a mouth  304  having at least one outlet for emitting the primary air flow from the fan assembly  10 . Similar to the nozzle  16 , the nozzle  302  has an annular shape, extending about a central axis X to define an opening  306 . The mouth  304  is located towards the rear of the nozzle  302 , and is arranged to emit the primary air flow towards the front of the fan assembly  300 , through the opening  306 . Again, the mouth  304  surrounds the opening  306 . In this example, the nozzle  302  defines a generally circular opening  306  located in a plane which is generally orthogonal to the central axis X. 
     The innermost, external surface of the nozzle  302  comprises a Coanda surface  308  located adjacent the mouth  304 , and over which the mouth  304  is arranged to direct the air emitted from the nozzle  16 . The Coanda surface  308  comprises a diffuser portion  310  tapering away from the central axis X. In this example, the diffuser portion  310  is in the form of a generally frusto-conical surface extending about the axis X, and which is inclined to the axis X at an angle in the range from 5 to 35°, and in this example is around 20°. 
     The nozzle  302  comprises an annular front casing section  312  connected to an annular rear casing section  314 . The annular sections  312 ,  314  of the nozzle  302  extend about the central axis X. Each of these sections may be formed from a single component or a plurality of connected parts. In this embodiment, the front casing section  312  is integral with the rear casing section  314 . The rear casing section  314  comprises a base  316  which is connected to the open upper end of the main body section  20  of the body  12 , and which has an open lower end for receiving the primary air flow from the body  12 . The front casing section  312  defines the Coanda surface  308  of the nozzle  302 . The front casing section  312  and the rear casing section  314  together define an annular interior passage  318  for conveying the primary air flow to the mouth  304 . The interior passage  318  extends about the axis X, and is bounded by the internal surface  320  of the front casing section  312  and the internal surface  322  of the rear casing section  314 . The base  316  of the front casing section  312  is shaped to convey the primary air flow into the interior passage  318  of the nozzle  302 . 
     The mouth  304  is defined by overlapping, or facing, portions of the internal surface  322  of the rear casing section  314  and the external surface  324  of the front casing section  312 , respectively. The mouth  304  is shaped to direct the primary air flow over the external surface  324  of the front casing section  312 . The mouth  304  preferably comprises an air outlet in the form of an annular slot. The air outlet is preferably generally circular in shape, and preferably has a relatively constant width in the range from 0.5 to 5 mm. In this example the air outlet has a width of around 1 mm. Where the front casing section  312  and the rear casing section  314  are formed from separate components, spacers may be spaced about the mouth  304  for urging apart the overlapping portions of the front casing section  312  and the rear casing section  314  to control the width of the air outlet of the mouth  304 . These spacers may be integral with either the front casing section  312  or the rear casing section  314 . Where the front casing section  312  is integral with the rear casing section  314 , the nozzle  302  may be formed with a series of fins which are spaced about, and extend across, the mouth  304  between the internal surface  322  of the rear casing section  314  and the external surface  324  of the front casing section  312 . 
     The nozzle  302  further comprises a guide surface  326 . The guide surface  326  extends about the axis X, and is centered on the axis X. The guide surface  326  is angled relative to the diffuser portion  310  of the Coanda surface  308 . In this fan assembly  300 , the guide surface  326  converges inwardly towards the axis X, and is inclined to the axis X by an angle of around 15°. The depth of the guide surface  326 , as measured along the axis X, is preferably in the range from 20 to 80% of the depth of the diffuser portion  310 , and in this example is around 30%. 
     The nozzle  302  further comprises an annular outer casing section  328  which extends about the front portion of the external surface  324  of the front casing section  312 . An annular housing  330  is defined between the front casing section  312  and the outer casing section  328 . The housing  330  has an opening in the form of an annular slot  332  which is located at the front of the nozzle  302 . 
     The guide surface  326  is moveable relative to the diffuser portion  310  between a stowed position and a deployed position to adjust the configuration of the nozzle  302 .  FIGS. 14 to 16  illustrate the fan assembly  300  in a first configuration, in which the guide surface  326  is in its stowed position. In this position, the guide surface  326  is located substantially fully within the housing  330  so that it is shielded from the primary air flow emitted from the air outlet of the nozzle  302  during use of the fan assembly  300 . In this configuration of the nozzle  302 , the portion of the combined air flow which passes through the opening  306  of the nozzle  302  is not channelled or focussed towards the axis X by the guide surface  326  of the nozzle  16 , and so the air combined flow has a relatively wide profile. In this configuration, the fan assembly  300  is particularly suitable for use as a desk fan in a room, office or other environment to deliver a cooling air current simultaneously to a number of users in proximity to the fan assembly  300 . 
     When the guide surface  326  is in the stowed position, the combined air flow generated by the fan assembly  300  has a relatively high flow rate but a relatively low velocity. 
     The guide surface  326  comprises a tab  334  which extends forwardly from the front of the guide surface  326  so as to protrude from the housing  330  when the guide surface  326  is in its stowed position. To move the guide surface  326  from its stowed position, the user grips the tab  334  and rotates the guide surface  326  relative to the diffuser portion  310  in a clockwise direction as viewed in  FIG. 15 . The slot  332  has a locally enlarged region  332   a  for receiving the tab  334  as the guide surface  326  is rotated. The guide surface  326  and the external surface  324  of the front section  312  of the nozzle  302  are preferably configured so that as the guide surface  326  slides relative to the external surface  324  of the front section  314  with rotation relative to the nozzle  302 , the guide surface  326  moves forwardly along the axis X. As with the nozzle  202 , co-operating grooves and ridges may be formed on the guide surface  326  and the external surface  324  of the front section  312  of the nozzle  302  to guide the movement of the guide surface  326  as it is rotated relative to the nozzle  302 . 
     Alternatively, the guide surface  326  may be pulled over the external surface of the nozzle  302  to move the guide surface  326  from its stowed position. 
     By moving the guide surface  326  along the axis X, the user changes the configuration of the nozzle  302 .  FIG. 17  illustrates the fan assembly  300  in a second configuration, in which the guide surface  326  is in a deployed position. In this deployed position, the guide surface  326  is located downstream from the diffuser portion  310  of the Coanda surface  308 , the guide surface  326  converging inwardly towards the axis X from the diffuser portion  310  of the Coanda surface  308 . During use of the fan assembly  300 , the portion of the combined air flow which passes through the opening  306  of the nozzle  302  is now channelled or focussed towards the axis X by the guide surface  326  of the nozzle  302 , and so the combined air flow now has a relatively narrow profile. This focussing of the profile of the air flow can make the fan assembly  300  particularly suitable for use as a desk fan in a room, office or other environment to deliver a cooling air current to a single user in proximity to the fan assembly  300 . When the guide surface  326  is in the fully deployed position, the combined air flow has a relatively low flow rate but a relatively high velocity.