Patent Abstract:
A fan assembly for creating an air current includes a bladeless fan assembly including a nozzle and a device for creating an air flow through the nozzle. The nozzle includes an interior passage and a mouth receiving the air flow from the interior passage. A Coanda surface located adjacent the mouth and over which the mouth is arranged to direct the air flow. The fan provides an arrangement producing an air current and a flow of cooling air created without requiring a bladed fan, that is, the air flow is created by a bladeless fan.

Full Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of United Kingdom Application Nos. 0717155.6, 0717148.1, 0717151.5 and 0717154.9, all filed Sep. 4, 2007, the contents of which prior applications are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a fan appliance. Particularly, but not exclusively, the present invention relates to a domestic fan, such as a desk fan, for creating air circulation and air current in a room, in an office or other domestic environment. 
       BACKGROUND OF THE INVENTION 
       [0003]    A number of types of domestic fan are known. It is common for a conventional fan to include a single set of blades or vanes mounted for rotation about an axis, and driving apparatus mounted about the axis for rotating the set of blades. Domestic fans are available in a variety of sizes and diameters, for example, a ceiling fan can be at least 1 m in diameter and is usually mounted in a suspended manner from the ceiling and positioned to provide a downward flow of air and cooling throughout a room. 
         [0004]    Desk fans, on the other hand, are often around 30 cm in diameter and are usually free standing and portable. In standard desk fan arrangements the single set of blades is positioned close to the user and the rotation of the fan blades provides a forward flow of air current in a room or into a part of a room, and towards the user. Other types of fan can be attached to the floor or mounted on a wall. The movement and circulation of the air creates a so called ‘wind chill’ or breeze and, as a result, the user experiences a cooling effect as heat is dissipated through convection and evaporation. Fans such as that disclosed in USD 103,476 are suitable for standing on a desk or a table. U.S. Pat. No. 2,620,127 discloses a dual purpose fan suitable for use either mounted in a window or as a portable desk fan. 
         [0005]    In a domestic environment it is desirable for appliances to be as small and compact as possible. U.S. Pat. No. 1,767,060 describes a desk fan with an oscillating function that aims to provide an air circulation equivalent to two or more prior art fans. In a domestic environment it is undesirable for parts to project from the appliance, or for the user to be able to touch any moving parts of the fan, such as the blades. USD 103,476 includes a cage around the blades. Other types of fan or circulator are described in U.S. Pat. No. 2,488,467, U.S. Pat. No. 2,433,795 and JP 56-167897. The fan of U.S. Pat. No. 2,433,795 has spiral slots in a rotating shroud instead of fan blades. 
         [0006]    Some of the above prior art arrangements have safety features such as a cage or shroud around the blades to protect a user from injuring himself on the moving parts of the fan. However, caged blade parts can be difficult to clean and the movement of blades through air can be noisy and disruptive in a home or office environment. 
         [0007]    A disadvantage of certain of the prior art arrangements is that the air flow produced by the fan is not felt uniformly by the user due to variations across the blade surface or across the outward facing surface of the fan. Uneven or ‘choppy’ air flow can be felt as a series of pulses or blasts of air. A further disadvantage is that the cooling effect created by the fan diminishes with distance from the user. This means the fan must be placed in close proximity to the user in order for the user to receive the benefit of the fan. 
         [0008]    Locating fans such as those described above close to a user is not always possible as the bulky shape and structure mean that the fan occupies a significant amount of the user&#39;s work space area. In the particular case of a fan placed on, or close to, a desk the fan body reduces the area available for paperwork, a computer or other office equipment. 
         [0009]    The shape and structure of a fan at a desk not only reduces the working area available to a user but can block natural light (or light from artificial sources) from reaching the desk area. A well lit desk area is desirable for close work and for reading. In addition, a well lit area can reduce eye strain and the related health problems that may result from prolonged periods working in reduced light levels. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention seeks to provide an improved fan assembly which obviates disadvantages of the prior art. It is an object of the present invention to provide a fan assembly which, in use, generates air flow at an even rate over the emission output area of the fan. It is another object to provide an improved fan assembly whereby a user at a distance from the fan feels an improved air flow and cooling effect in comparison to prior art fans. 
         [0011]    According to the invention, there is provided a bladeless fan assembly for creating an air current, the 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. 
         [0012]    Advantageously, by this arrangement an air current is generated and a cooling effect is created without requiring a bladed fan. The bladeless arrangement leads to lower noise emissions due to the absence of the sound of a fan blade moving through the air, and a reduction in moving parts and complexity. 
         [0013]    In the following description of fans and, in particular a fan of the preferred embodiment, the term ‘bladeless’ is used to describe apparatus in which air flow is emitted or projected forwards from the fan assembly without the use of blades. By this definition a bladeless fan assembly can be considered to have an output area or emission zone absent blades or vanes from which the air flow is released or emitted in a direction appropriate for the user. A bladeless fan assembly may be supplied with a primary source of air from a variety of sources or generating means such as pumps, generators, motors or other fluid transfer devices, which include rotating devices such as a motor rotor and a bladed impeller for generating air flow. The supply of air generated by the motor causes a flow of air to pass from the room space or environment outside the fan assembly through the interior passage to the nozzle and then out through the mouth. 
         [0014]    Hence, the description of a fan assembly as bladeless is not intended to extend to the description of the power source and components such as motors that are required for secondary fan functions. Examples of secondary fan functions can include lighting, adjustment and oscillation of the fan. 
         [0015]    The bladeless fan assembly achieves the output and cooling effect described above with a nozzle which includes a Coanda surface to provide an amplifying region utilising the Coanda effect. 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 whereby a primary air flow is directed over the 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 1963 pages 84 to 92. 
         [0016]    Preferably the nozzle defines an opening through which air from outside the fan assembly is drawn by the air flow directed over the Coanda surface. Air from the external environment is drawn through the opening by the air flow directed over the Coanda surface. Advantageously, by this arrangement the assembly can be produced and manufactured with a reduced number of parts than those required in prior art fans. This reduces manufacturing cost and complexity. 
         [0017]    In the present invention an air flow is created through the nozzle of the fan assembly. In the following description this air flow will be referred to as primary air flow. The primary air flow exits the nozzle via the mouth and passes over the Coanda surface. The primary air flow entrains the air surrounding the mouth of 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 secondary air flow entrained by the air amplifier gives a total air flow emitted or projected forward to a user from the opening defined by the nozzle. The total air flow is sufficient for the fan assembly to create an air current suitable for cooling. 
         [0018]    The air current delivered by the fan assembly to the user has the benefit of being an air flow with low turbulence and with a more linear air flow profile than that provided by other prior art devices. Linear air flow with low turbulence travels efficiently out from the point of emission and loses less energy and less velocity to turbulence than the air flow generated by prior art fans. An advantage for a user is that the cooling effect can be felt even at a distance and the overall efficiency of the fan increases. This means that the user can choose to site the fan some distance from a work area or desk and still be able to feel the cooling benefit of the fan. 
         [0019]    Advantageously, the assembly results in the entrainment of air surrounding the mouth of the nozzle such that the primary air flow is amplified by at least 15%, whilst a smooth overall output is maintained. The entrainment and amplification features of the fan assembly result in a fan with a higher efficiency than prior art devices. The air current emitted from the opening defined by the nozzle has an approximately flat velocity profile across the diameter of the nozzle. Overall the flow rate and profile can be described as plug flow with some regions having a laminar or partial laminar flow. 
         [0020]    Preferably the nozzle comprises a loop. The shape of the nozzle is not constrained by the requirement to include space for a bladed fan. In a preferred embodiment the nozzle is annular. By providing an annular nozzle the fan can potentially reach a broad area. In a further preferred embodiment the nozzle is at least partially circular. This arrangement can provide a variety of design options for the fan, increasing the choice available to a user or customer. 
         [0021]    Preferably, the interior passage is continuous. This allows smooth, unimpeded air flow within the nozzle and reduces frictional losses and noise. In this arrangement the nozzle can be manufactured as a single piece, reducing the complexity of the fan assembly and thereby reducing manufacturing costs. 
         [0022]    It is preferred that the mouth is substantially annular. By providing a substantially annular mouth the total air flow can be emitted towards a user over a broad area. Advantageously, an illumination source in the room or at the desk fan location or natural light can reach the user through the central opening. 
         [0023]    Preferably, the mouth is concentric with the interior passage. This arrangement will be visually appealing and the concentric location of the mouth with the passage facilitates manufacture. Preferably, the Coanda surface extends symmetrically about an axis. More preferably, the angle subtended between the Coanda surface and the axis is in the range from 7° to 20°, preferably around 15°. This provides an efficient primary air flow over the Coanda surface and leads to maximum air entrainment and secondary air flow. 
         [0024]    Preferably the nozzle extends by a distance of at least 5 cm in the direction of the axis. Preferably the nozzle extends about the axis in the shape of a loop and preferably by a distance in the range from 30 cm to 180 cm. This provides options for emission of air over a range of different output areas and opening sizes, such as may be suitable for cooling the upper body and face of a user when working at a desk, for example. In the preferred embodiment the nozzle comprises a diffuser located downstream of the Coanda surface. An angular arrangement of the diffuser surface and an aerofoil-type shaping of the nozzle and diffuser surface can enhance the amplification properties of the fan assembly whilst minimising noise and frictional losses. 
         [0025]    In a preferred arrangement the nozzle comprises at least one wall defining the interior passage and the mouth, and the at least one wall comprises opposing surfaces defining the mouth. Preferably, the mouth has an outlet, and the spacing between the opposing surfaces at the outlet of the mouth is in the range from 1 mm to 5 mm, more preferably around 1.3 mm. By this arrangement a nozzle can be provided with the desired flow properties to guide the primary air flow over the Coanda surface and provide a relatively uniform, or close to uniform, total air flow reaching the user. 
         [0026]    In the preferred fan arrangement the means for creating an air flow through the nozzle comprises an impeller driven by a motor. This arrangement provides a fan with efficient air flow generation. More preferably the means for creating an air flow comprises a DC brushless motor and a mixed flow impeller. This arrangement reduces frictional losses from motor brushes and also reduces carbon debris from the brushes in a traditional motor. Reducing carbon debris and emissions is advantageous in a clean or pollutant sensitive environment such as a hospital or around those with allergies. 
         [0027]    The nozzle may be rotatable or pivotable relative to a base portion, or other portion, of the fan assembly. This enables the nozzle to be directed towards or away from a user as required. The fan assembly may be desk, floor, wall or ceiling mountable. This can increase the portion of a room over which the user experiences cooling. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    An embodiment of the invention will now be described with reference to the accompanying drawings, in which: 
           [0029]      FIG. 1  is a front view of a fan assembly; 
           [0030]      FIG. 2  is a perspective view of a portion of the fan assembly of  FIG. 1 ; 
           [0031]      FIG. 3  is a side sectional view through a portion of the fan assembly of  FIG. 1  taken at line A-A; 
           [0032]      FIG. 4  is an enlarged side sectional detail of a portion of the fan assembly of  FIG. 1 ; and 
           [0033]      FIG. 5  is a sectional view of the fan assembly taken along line B-B of  FIG. 3  and viewed from direction F of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]      FIG. 1  shows an example of a fan assembly  100  viewed from the front of the device. The fan assembly  100  comprises an annular nozzle  1  defining a central opening  2 . With reference also to  FIGS. 2 and 3 , nozzle  1  comprises an interior passage  10 , a mouth  12  and a Coanda surface  14  adjacent the mouth  12 . The Coanda surface  14  is arranged so that a primary air flow exiting the mouth  12  and directed over the Coanda surface  14  is amplified by the Coanda effect. The nozzle  1  is connected to, and supported by, a base  16  having an outer casing  18 . The base  16  includes a plurality of selection buttons  20  accessible through the outer casing  18  and through which the fan assembly  100  can be operated. 
         [0035]      FIGS. 3 ,  4  and  5  show further specific details of the fan assembly  100 . A motor  22  for creating an air flow through the nozzle  1  is located inside the base  16 . The base  16  further comprises an air inlet  24  formed in the outer casing  18 . A motor housing  26  is located inside the base  16 . The motor  22  is supported by the motor housing  26  and held in a secure position by a rubber mount or seal member  28 . 
         [0036]    In the illustrated embodiment, the motor  22  is a DC brushless motor. An impeller  30  is connected to a rotary shaft extending outwardly from the motor  22 , and a diffuser  32  is positioned downstream of the impeller  30 . The diffuser  32  comprises a fixed, stationary disc having spiral blades. 
         [0037]    An inlet  34  to the impeller  30  communicates with the air inlet  24  formed in the outer casing  18  of the base  16 . The outlet  36  of the diffuser  32  and the exhaust from the impeller  30  communicate with hollow passageway portions or ducts located inside the base  16  in order to establish air flow from the impeller  30  to the interior passage  10  of the nozzle  1 . The motor  22  is connected to an electrical connection and power supply and is controlled by a controller (not shown). Communication between the controller and the plurality of selection buttons  20  enable a user to operate the fan assembly  100 . 
         [0038]    The features of the nozzle  1  will now be described with reference to  FIGS. 3 and 4 . The shape of the nozzle  1  is annular. In this embodiment the nozzle  1  has a diameter of around 350 mm, but the nozzle may have any desired diameter, for example around 300 mm. The interior passage  10  is annular and is formed as a continuous loop or duct within the nozzle  1 . The nozzle  1  is formed from at least one wall defining the interior passage  10  and the mouth  12 . In this embodiment the nozzle  1  comprises an inner wall  38  and an outer wall  40 . In the illustrated embodiment the walls  38 ,  40  are arranged in a looped or folded shape such that the inner wall  38  and outer wall  40  approach one another. The inner wall  38  and the outer wall  40  together define the mouth  12 , and the mouth  12  extends about the axis X. The mouth  12  comprises a tapered region  42  narrowing to an outlet  44 . The outlet  44  comprises a gap or spacing formed between the inner wall  38  of the nozzle  1  and the outer wall  40  of the nozzle  1 . The spacing between the opposing surfaces of the walls  38 ,  40  at the outlet  44  of the mouth  12  is chosen to be in the range from 1 mm to 5 mm. The choice of spacing will depend on the desired performance characteristics of the fan. In this embodiment the outlet  44  is around 1.3 mm wide, and the mouth  12  and the outlet  44  are concentric with the interior passage  10 . 
         [0039]    The mouth  12  is adjacent the Coanda surface  14 . The nozzle  1  further comprises a diffuser portion located downstream of the Coanda surface. The diffuser portion includes a diffuser surface  46  to further assist the flow of air current delivered or output from the fan assembly  100 . In the example illustrated in  FIG. 3  the mouth  12  and the overall arrangement of the nozzle  1  is such that the angle subtended between the Coanda surface  14  and the axis X is around 15°. The angle is chosen for efficient air flow over the Coanda surface  14 . The base  16  and the nozzle  1  have a depth in the direction of the axis X. The nozzle  1  extends by a distance of around 5 cm in the direction of the axis. The diffuser surface  46  and the overall profile of the nozzle  1  are based on an aerofoil shape, and in the example shown the diffuser portion extends by a distance of around two thirds the overall depth of the nozzle  1 . 
         [0040]    The fan assembly  100  described above operates in the following manner. When a user makes a suitable selection from the plurality of buttons  20  to operate or activate the fan assembly  100 , a signal or other communication is sent to drive the motor  22 . The motor  22  is thus activated and air is drawn into the fan assembly  100  via the air inlet  24 . In the preferred embodiment air is drawn in at a rate of approximately 20 to 30 litres per second, preferably around 27 l/s (litres per second). The air passes through the outer casing  18  and along the route illustrated by arrow F of  FIG. 3  to the inlet  34  of the impeller  30 . The air flow leaving the outlet  36  of the diffuser  32  and the exhaust of the impeller  30  is divided into two air flows that proceed in opposite directions through the interior passage  10 . The air flow is constricted as it enters the mouth  12  and is further constricted at the outlet  44  of the mouth  12 . The air flow exits through the outlet  44  as a primary air flow. 
         [0041]    The output and emission of the primary air flow creates a low pressure area at the air inlet  24  with the effect of drawing additional air into the fan assembly  100 . The operation of the fan assembly  100  induces high air flow through the nozzle  1  and out through the opening  2 . The primary air flow is directed over the Coanda surface  14  and the diffuser surface  46 , and is amplified by the Coanda effect. A secondary air flow is generated by entrainment of air from the external environment, specifically from the region around the outlet  44  and from around the outer edge of the nozzle  1 . A portion of the secondary air flow entrained by the primary air flow may also be guided over the diffuser surface  46 . This secondary air flow passes through the opening  2 , where it combines with the primary air flow to produce a total air flow projected forward from the fan assembly  100  in the region of 500 to 700 l/s. 
         [0042]    The combination of entrainment and amplification results in a total air flow from the opening  2  of the fan assembly  100  that is greater than the air flow output from a fan assembly without such a Coanda or amplification surface adjacent the emission area. 
         [0043]    The amplification and laminar type of air flow produced results in a sustained flow of air being directed towards a user from the nozzle  1 . The flow rate at a distance of up to 3 nozzle diameters (i.e. around 1000 to 1200 mm) from a user is around 400 to 500 l/s. The total air flow has a velocity of around 3 to 4 m/s (metres per second). Higher velocities are achievable by reducing the angle subtended between the Coanda surface  14  and the axis X. A smaller angle results in the total air flow being emitted in a more focussed and directed manner. This type of air flow tends to be emitted at a higher velocity but with a reduced mass flow rate. Conversely, greater mass flow can be achieved by increasing the angle between the Coanda surface and the axis. In this case the velocity of the emitted air flow is reduced but the mass flow generated increases. Thus the performance of the fan assembly can be altered by altering the angle subtended between the Coanda surface and the axis X. 
         [0044]    The invention is not limited to the detailed description given above. Variations will be apparent to the person skilled in the art. For example, the fan could be of a different height or diameter. The fan need not be located on a desk, but could be free standing, wall mounted or ceiling mounted. The fan shape could be adapted to suit any kind of situation or location where a cooling flow of air is desired. A portable fan could have a smaller nozzle, say 5 cm in diameter. The means for creating an air flow through the nozzle can be a motor or other air emitting device, such as any air blower or vacuum source that can be used so that the fan assembly can create an air current in a room. Examples include a motor such as an AC induction motor or types of DC brushless motor, but may also comprise any suitable air movement or air transport device such as a pump or other means of providing directed fluid flow to generate and create an air flow. Features of a motor may include a diffuser or a secondary diffuser located downstream of the motor to recover some of the static pressure lost in the motor housing and through the motor. 
         [0045]    The outlet of the mouth may be modified. The outlet of the mouth may be widened or narrowed to a variety of spacings to maximise air flow. The Coanda effect may be made to occur over a number of different surfaces, or a number of internal or external designs may be used in combination to achieve the flow and entrainment required. 
         [0046]    Other shapes of nozzle are envisaged. For example, a nozzle comprising an oval, or ‘racetrack’ shape, a single strip or line, or block shape could be used. The fan assembly provides access to the central part of the fan as there are no blades. This means that additional features such as lighting or a clock or LCD display could be provided in the opening defined by the nozzle. 
         [0047]    Other features could include a pivotable or tiltable base for ease of movement and adjustment of the position of the nozzle for the user.

Technology Classification (CPC): 5