GB2484696A

GB2484696A - A fan assembly comprising a nozzle with a Coanda surface and masks for directing air flow

Info

Publication number: GB2484696A
Application number: GB1017707.9A
Authority: GB
Inventors: Timothy Nicholas Stickney
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2010-10-20
Filing date: 2010-10-20
Publication date: 2012-04-25
Also published as: GB201017707D0

Abstract

A fan assembly comprises a nozzle 16 includes a mouth 18 for emitting a primary air flow and a Coanda surface 72. To allow a user to adjust at least one parameter, for example at least one of the profile, orientation and the direction, of the airflow, the fan assembly comprises a mask 100 which is locatable at least partially within the bore of the nozzle. The fan assembly may be provided with a set of such masks.

Description

A FAN ASSEMBLY

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.

I

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a fan assembly comprising a nozzle and means for creating an air flow through the nozzle, the nozzle comprising an interior passage, a mouth for receiving the air flow from the interior passage, and a Coanda surface located adjacent the mouth and over which the mouth is arranged to direct the air flow. The fan assembly comprises a removable mask for covering at least part of the 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 entrained with the air emitted from the mouth.

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 mouth of 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 mouth of the nozzle and, by displacement, from other regions around the fan assembly.

The primary air flow directed over the Coanda surface combined with the entrained secondary air flow equates to a combined, or total, air flow emitted or projected forward from the nozzle.

The positioning of the mask over at least part of the Coanda surface allows a user to adjust at least one parameter of the combined air flow. 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 litres per second), and velocity of the combined air flow. Thus, through location of the mask over at least part of the Coanda surface, 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 mask 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 mask may change the orientation of the air flow to provide a relatively wide air flow for cooling a number of users.

The mask may be moveable relative to the Coanda surface to allow a user to change rapidly, for example, the direction in which the combined air flow is projected forward from the fan assembly. The mask may be slidable over or along the Coanda surface, or rotatable relative to the Coanda surface. The nozzle may include means for guiding the movement of the mask relative to the Coanda surface.

The mask may have any shape suitable for changing the air flow in a desired manner.

For example, the mask may comprise one or more sections which are locatable over the Coanda surface to deflect the combined air flow in a particular direction, for example towards or away from a person located to one side of the fan assembly. In one embodiment, the mask comprises a plurality of sections which are locatable simultaneously over the Coanda surface. These sections may have substantially the same shape, or they may have different shapes.

Preferably, the Coanda surface extends about an axis. In a preferred embodiment the Coanda surface is generally annular in shape, and defines, at least in part, a bore through which the secondary air flow from outside the fan assembly is drawn by the primary air flow emitted from the mouth. The mask is preferably in the form of an insert which is at least partially insertable into the bore of the nozzle so as to cover at least part of the Coanda surface. The mouth of the nozzle may be located towards the rear of the nozzle, and arranged to emit the primary air flow through the bore of the nozzle.

The mask may be located partially within the bore of the nozzle, for example so that part of the mask protrudes forwardly from the front end of the nozzle to guide part or all of the combined air flow in a particular direction. Altematively, it may be located substantially fully within the bore of the nozzle. The bore of the nozzle preferably tapers outwardly towards the front end of the nozzle, and so the mask is preferably inserted into the bore through the front end of the nozzle. The mask may be annular in shape. The mask may comprise a rim which is locatable over the front edge of the nozzle to retain the mask within the bore of the nozzle.

The Coanda surface may comprise a diffuser portion inclined to the axis. The diffuser portion is preferably inclined to the axis by an angle in the range from 5 to 35°, and in a preferred embodiment is around 28°. The mask is preferably configured to cover at least part of the diffuser portion of the Coanda surface. The diffuser portion is preferably generally annular in shape, and so the mask may comprise an annular section which is located over at least part of the diffuser portion.

The mask preferably comprises a second diffuser portion which, when the mask is located over the diffuser portion of the Coanda surface, is inclined to the axis, the inclination of the second diffuser portion to the axis being different from that of the diffuser portion of the Coanda surface. In this case, the location of the mask over the Coanda surface can also change the flow rate and the velocity of the combined air flow.

For example where the inclination of the diffuser portion of the mask is shallower than the inclination of the diffuser portion of the Coanda surface to the axis, the flow rate of the combined air flow will decrease when the mask is located over the Coanda surface, but the velocity of the combined air flow will increase.

Substantially all of the diffuser portion of the mask may be inclined to the axis by the same amount, and so the diffuser portion of the mask may have a shape which is cylindrical or frusto-conical. The angle of inclination may be in the range from -15 to 35°. Alternatively, the angle of inclination may vary about the axis. Through varying the angle of inclination about the axis, the air current generated by the fan assembly may have a non-cylindrical or a non-frusto-conical profile when the mask is located over the Coanda surface. The angle of inclination may vary about the axis between at least one maximum value and at least one minimum value. Preferably, the angle of inclination varies about the axis between a plurality of maximum values and a plurality of minimum values. In one embodiment the angle varies about the axis between six maximum values and six minimum values. The maximum values and the minimum values are preferably regularly spaced about the axis. The minimum value may be in the range from -15° to 15°, whereas the maximum value may be in the range from 20 to 35°. In a preferred embodiment the maximum value is at least twice the minimum value. The inclination of the diffuser portion of the mask to the axis may vary continuously or discontinuously about the axis.

The second diffuser portion may be generally annular in shape, and so may define a bore through which, when the mask is located over the Coanda surface, the secondary air flow from outside the fan assembly is drawn by the primary air flow emitted from the mouth. When the mask is located over the Coanda surface, the bore of the mask is preferably substantially co-axial with the bore of the nozzle. The mouth of the nozzle is preferably arranged to direct the primary air flow through the bore of the mask.

Alternatively, the second diffuser portion may comprise a plurality of interconnected sections which are locatable simultaneously over the Coanda surface. These sections may have substantially the same shape, or they may have different shapes. The sections may be wedge-shaped, tapering towards the rear end of the nozzle. The sections may be arranged about the axis. The sections may be regularly or irregularly spaced about the axis.

The fan assembly may comprise a set of masks which are interchangeably locatable over the Coanda surface, and so in a second aspect the present invention provides a fan assembly comprising a nozzle and means for creating a primary air flow through the nozzle, the nozzle comprising an interior passage, a mouth for receiving the air flow from the interior passage, and a Coanda surface located adjacent the mouth and over which the mouth is arranged to direct the air flow, characterised in that the fan assembly comprises a plurality of masks locatable interchangeably over at least part of the Coanda surface, each mask having a different respective profile. For example, as discussed above one of the masks may comprise a plurality of interconnected sections, whereas another one of the mask may comprise a bore through which the secondary air flow is drawn by the emission of the primary air flow from the mouth of the nozzle.

The mouth preferably extends about the Coanda surface. The mouth is preferably continuous about the Coanda surface, and may be substantially circular in shape.

Preferably, the mouth has one or more outlets, and the spacing between opposing surfaces of the nozzle at the outlet(s) of the mouth is preferably in the range from 0.5 mm to 5 mm. The mouth is preferably in the form of a slot.

The nozzle is preferably mounted on a base housing said means for creating an air flow.

In the preferred fan assembly the means for creating an air flow through the nozzle comprises an impeller driven by a motor.

In a third aspect the present invention provides a removable mask for a fan assembly comprising a nozzle having an interior passage, a mouth for receiving the air flow from the interior passage, and a Coanda surface located adjacent the mouth and over which the mouth is arranged to direct the air flow, the mask being arranged to cover at least part of the Coanda surface.

The mask may have a different colour to the nozzle of the fan assembly, and/or may be formed from a different material to the nozzle of the fan assembly.

Features described above in connection with the first aspect of the invention are equally applicable to the second and third 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: Figure 1 is a front perspective view, from above, of a fan assembly; Figure 2 is a side sectional view through the fan assembly; Figure 3 is a front perspective view, from above, of a mask for the fan assembly; Figure 4 is a front perspective view, from above, of the fan assembly with the mask located on the nozzle; Figure 5 is a side view of the fan assembly of Figure 4; Figure 6 is a top view of the fan assembly of Figure 4; Figure 7 is a front view of the fan assembly of Figure 4; Figure 8 is a side sectional view taken along line A-A in Figure 7; Figure 9 is a front perspective view, from above, of a second mask for the fan assembly; Figure 10 is a front perspective view, from above, of the fan assembly with the second mask located on the nozzle; Figure 11 is a front perspective view, from above, of a third mask for the fan assembly; and Figure 12 is a front perspective view, from above, of the fan assembly with the third mask located on the nozzle.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 is an external view of a 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 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 tihed 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.

Figure 2 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 Figure 1, the nozzle 16 has an annular shape, extending about a central S axis X to define a bore 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 bore 70. The mouth 18 surrounds the bore 70. In this example, the nozzle 16 defines a generally circular bore 70 extending along 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 S 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 moulded 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 Figure 2, 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.

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 litres 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 bore 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 bore 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.

With reference now also to Figures 3 to 8, the fan assembly 10 includes a first example of a mask 100 which is removably locatable over the Coanda surface 72 of the nozzle to change at least one parameter of the combined air flow. The mask 100 is in the form of an insert which is insertable into the bore 70 of the nozzle 16 to cover at least part of the Coanda surface 72 of the nozzle 16. As the diffuser portion 74 of the Coanda surface 72, and thus the bore 70, tapers outwardly towards the open front end 96 of the bore 70, the mask 100 is inserted into the bore 70 of the nozzle 16 through the open front end 96 of the bore 70. The mask 100 includes an outer annular rim 102 which is locatable over the front end 96 of the bore 70, and which surrounds the outer surface of the front casing section 76 of the nozzle 16 when the mask 100 is located on the nozzle 16. In this example the mask 100 is retained on the nozzle 16 through an interference fit between the nozzle 16 and the mask 100, but the nozzle 16 may be provided with means for removably securing the mask 100 to the nozzle 16. For example, a movable catch may be located on the outer surface of the front casing section 76 of the nozzle 16 to retain the mask 100 on the nozzle 16. As another example, the mask 100 may be attracted magnetically to the nozzle 16. As a further example, the mask 100 may be frictionally coupled to the nozzle 16.

To remove the mask 100, the user may simply pull the mask 100 from the nozzle 16.

The mask 100 is generally annular in shape. The mask 100 comprises a generally circular front end 104 and a generally circular rear end 106, and an annular outer surface 108 and an annular inner surface 110 which each extend between the front end 104 and the rear end 106 of the mask 100. Each of the outer surface 108 and the inner surface 110 of the mask 100 extend about an axis Y, which, with reference to Figure 2, is substantially co-linear with the axis X of the nozzle 16 when the mask 100 is inserted into the bore 70 of the nozzle 16. The outer surface 108 of the mask 100 has generally the same size and shape as the diffuser portion 74 of the Coanda surface. In particular, the angle of inclination of the outer surface 108 to the axis Y is substantially the same as the angle of inclination of the diffuser portion 74 of the Coanda surface 72 to the axis X, Consequently, and as shown in Figure 8, when the mask 100 is inserted into the bore 70 of the nozzle 16 the diffuser portion 74 of the Coanda surface 72 is fully covered by the mask 100, but the mouth 18 of the nozzle 16 remains fully exposed.

Thus, when the mask 100 is inserted into the bore 70 the primary air flow emitted from the nozzle 16 is directed over the rear section 73 of the Coanda surface 72, as indicated in Figure 8, and over the inner surface 110 of the mask 100. As mentioned above, the inner surface 110 of the mask 100 is annular in shape, and so defines a bore 112 passing through the mask 100 between the front end 104 and the rear end 106 of the mask 100, and through which a secondary air flow from outside the fan assembly 10 is drawn by the primary air flow emirted from the mouth 18.

The inner surface 110 of the mask 100 thus provides a diffuser surface for guiding the combined air flow generated by the fan assembly 10 in a desired direction. The angle of inclination of the inner surface 110 to the axis Y is different from the angle of inclination of the diffuser portion 74 of the Coanda surface 72 to the axis X, and so the result of inserting the mask 100 into the bore 70 of the nozzle 16 is that a number of parameters of the combined air flow are changed. In this example, the angle of inclination of the inner surface 110 to the axis Y is shallower than the angle of inclination of the diffuser portion 74 of the Coanda surface 72 to the axis X, and so the radial thickness of the mask 100 decreases towards the rear end 106 of the mask 100. In this example the angle of inclination of the inner surface 110 to the axis Y is around 100, and so the insertion of the mask 100 into the bore 70 of the nozzle 16 serves to constrict the profile of the combined air flow produced by the fan assembly 10. This can provide a combined air flow which is focussed towards a user located in front of the fan assembly 10. The shallower diffuser portion provided by the mask 100 also serves to increase the velocity of the combined air flow, and to decrease the flow rate of the combined air flow.

Figures 9 and 10 illustrate a second example of a mask 120 which is removably locatable over the Coanda surface 72 of the nozzle to change at least one parameter of the combined air flow. Similar to the mask 100, the mask 120 is also in the form of an insert which is insertable into the bore 70 of the nozzle 16 to cover at least part of the Coanda surface 72 of the nozzle 16. The mask 120 also includes an outer annular rim 122 which is locatable over the front end 96 of the bore 70, and which surrounds the outer surface of the front casing section 76 of the nozzle 16 when the mask 100 is located on the nozzle 16. However, this mask 120 varies from the mask 100 insofar as the front end 124, rear end 126, outer surface 128 and inner surface 130 of the mask 120 are not continuous. Instead, the mask 120 comprises a plurality of sections 132 which are connected by the annular rim 122, and which are located about, and generally regularly spaced about, the axis Y of the mask 120. In this example, the mask 120 comprises six sections 130 regularly spaced about the mask 120. Each section 132 is generally wedge-shaped. The outer surfaces 128 each taper towards the axis Y with the same angle of inclination as that between the diffuser portion 74 of the Coanda surface 72 and the axis X so that, when the mask 120 is located on the nozzle 16, the sections 132 of the mask 120 partially cover the diffuser portion 74 of the Coanda surface 72.

Similar to the inner surface 110 of the mask 100, the angle of inclination of the inner surfaces 130 to the axis Y is shallower than the angle of inclination of the diffuser portion 74 of the Coanda surface 72 to the axis X, and so the radial thickness of the sections 132 decreases towards the rear ends 126 of the sections 130. In this example the angle of inclination of the inner surfaces 130 to the axis Y is also around 10°.

Thus, as illustrated in Figure 9, when the mask 120 is inserted into the nozzle 16 through the open front end 96 of the bore 70, the bore 134 of the nozzle 16 is defined both by the uncovered sections of the diffuser portion 74 of the Coanda surface 72, and by the inner surfaces 130 of the mask 120. The bore 134 of the nozzle 126 thus has a stepped profile, in which the angle of inclination of the bore 134 to the axis X varies between a plurality of maximum values, in this example each at around 28°, and a plurality of minimum values, in this example each at around 10°. This variation in the profile of the bore 134 of the nozzle 16 causes the combined air flow to have a non-circular, or non-frusto-conical, profile which is only partially focussed towards the user due to the discontinuities in the mask 120.

In this second example, the insertion of the mask 120 into the nozzle 16 results in the bore 134 of the nozzle 16 adopting a stepped profile. Figures 11 and 12 illustrate a third example of a mask 140. This mask 140 is similar to the mask 100. The mask 140 is also in the form of an insert which is insertable into the bore 70 of the nozzle 16 to cover at least part of the Coanda surface 72 of the nozzle 16. The mask 140 also includes an outer annular rim 142 which is locatable over the front end 96 of the bore 70, and which surrounds the outer surface of the front casing section 76 of the nozzle 16 when the mask 100 is located on the nozzle 16. The mask 140 also has a continuous front end 144, and a circular rear end 146, an annular outer surface 148 and an annular inner surface 150 which defines a bore 152. The outer surface 148 of the mask 140 is identical to the outer surface 108 of the mask 100. However, the inner surface 150 of the mask 140 differs from the inner surface 110 of the mask 100 insofar as the angle of inclination of the inner surface 150 to the axis Y of the mask 140 varies about the axis Y. This angle of inclination varies between a plurality of maximum values and a plurality of minimum values which are regularly spaced about the axis Y. The inner surface 150 is shaped so as to vary the angle of inclination gradually about the axis Y between the maximum and minimum values.

Thus, when the mask 140 is inserted into the bore 70 of the nozzle 16, the inner surface of the mask 140 also provides a diffuser surface for guiding the combined air flow generated by the fan assembly 10 so as to adopt a non-circular or non-frusto-conical profile. Similar also to the mask 120, the mask 140 is rotatable relative to the nozzle 16 to change the orientation of the combined air flow generated by the fan assembly.

Claims

CLAIMS1. A fan assembly comprising a nozzle and means for creating an air flow through the nozzle, the nozzle comprising an interior passage, a mouth for receiving the air flow from the interior passage, and a Coanda surface located adjacent the mouth and over which the mouth is arranged to direct the air flow; characterised in that the fan assembly comprises a removable mask for covering at least part of the Coanda surface.
2. A fan assembly as claimed in claim 1, wherein the Coanda surface extends about an axis.
3. A fan assembly as claimed in claim 2, wherein the Coanda surface is generally annular in shape.
4. A fan assembly as claimed in claim 2 or claim 3, wherein the Coanda surface comprises a diffuser portion inclined to the axis.
5. A fan assembly as claimed in claim 4, wherein the mask is configured to cover at least part of the diffuser portion.
6. A fan assembly as claimed in claim 5, wherein the mask comprises a second diffuser portion which, when the mask is located over the diffuser portion of the Coanda surface, is inclined to the axis, the inclination of the second diffuser portion to the axis being different from that of the diffuser portion of the Coanda surface.
7. A fan assembly as claimed in claim 6, wherein the inclination of the second diffuser portion varies about the axis.
8. A fan assembly as claimed in claim 6 or claim 7, wherein the inclination of the second diffuser portion varies continuously about the axis.
9. A fan assembly as claimed in any of claims 6 to 8, wherein the second diffuser portion is generally annular in shape.
10. A fan assembly as claimed in any of claims 6 to 8, wherein the second diffuser portion comprises a plurality of interconnected sections.
11. A fan assembly as claimed in claim 10, wherein the sections have substantially the same shape.
12. A fan assembly as claimed in claim 10 or claim 11, wherein the sections are arranged about the axis.
13. A fan assembly as claimed in claim 12, wherein the sections are regularly spaced about the axis.
14. A fan assembly as claimed in any preceding claim, wherein the mask tapers towards a rear end thereof
15. A fan assembly as claimed in any preceding claim, wherein the mask comprises a rim which is locatable over a front end of the nozzle.
16. A fan assembly as claimed in any preceding claim, wherein the mouth is annular in shape.
17. A fan assembly as claimed in any preceding claim, wherein the mouth is substantially circular in shape.
18. A fan assembly as claimed in any preceding claim, wherein the mouth is in the form of a slot.