GB2581371A

GB2581371A - Diffuser

Info

Publication number: GB2581371A
Application number: GB1902062.7A
Authority: GB
Inventors: Wright Callum; Mary Jackson Louise; Jie Lam Wei; Leng Lim Boon; Guan Tan Wee; Francois Atkinson Antoine; Phang Lim Wei
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2019-02-14
Filing date: 2019-02-14
Publication date: 2020-08-19
Anticipated expiration: 2039-02-14
Also published as: GB201902062D0; GB2581371B

Abstract

A diffuser comprises an air inlet 2 for receiving an airflow from a hair dryer and an external grille 4 having a plurality of air outlets 6 for emitting at least part of the airflow from the diffuser. First and second internal grilles 12, 10 comprising an array of apertures are located between the at least one air inlet and the external grille. The first internal grille may be arranged with a gap 32 between an edge of the grille and an internal wall 26. The second internal grille may be a friction fit with the internal wall. The grilles preferably comprise planar perforated plates with frustoconical shaped apertures. The diffuser may be provided with a baffle 3 defining an air chamber through which airflow passes.

Description

DIFFUSER

FIELD OF THE INVENTION

The present invention relates to a diffuser for a hair dryer.

BACKGROUND OF THE INVENTION

A diffuser is a known form of attachment for a hair dryer. The diffuser is attached to the airflow outlet end of the hair dryer, and serves to reduce the velocity of the airflow emitted from the hair dryer before it is incident upon the hair of the user. I0

A diffuser generally comprises a baffle and a grille connected to the baffle. The baffle has an air inlet end, an air outlet end which is larger than the air inlet end, and a tapering wall which ex-tends between the air inlet end and the air outlet end. The air inlet end comprises an air inlet for receiving the airflow from the hair dryer. The wall of the I5 baffle defines a diffusing air chamber within which the velocity of the airflow decreases as the cross-section of the air chamber increases. The grille is connected to the air outlet end of the diffuser, and provides air outlets from which air is emitted from the diffuser. A set of projections or prongs are generally upstanding from the grille to contact the hair of the user during hair drying. Each of the projections generally has an air outlet for emitting air into the user's hair.

SUMMARY OF THE INVENTION

The present invention provides a diffuser for attachment to an airflow outlet end of a hair dryer, the diffuser comprising: at least one air inlet for receiving an airflow from a hair dryer; an external grille comprising a plurality of air outlets for emitting at least part of the airflow from the diffuser; a first internal grille comprising an array of apertures; and a second internal grille comprising an array of apertures; wherein the first internal grille and the second internal grille are located between the at least one air inlet and the external grille. The first internal grille serves primarily to promote eveness by way of distribution of the air flow flowing through the diffuser. The second internal grille serves primarily to reduce the velocity of the air flowing through the diffuser. A secondary purpose of the second internal grille is to partially diffuse the air across the width of the diffuser. The combined effect of the first internal grille and the second internal grille is an even distribution of air within the diffuser. A further combined effect of the first internal grille and the second internal grille is a reduction in air turbulence within the diffuser and, thus, a reduction in noise.

The second internal grille may be located between the at least one air inlet and the first internal grille. This ensures that the velocity of the air flow is reduced before impinging on the first internal grille.

The first internal grille may be located between the second internal grille and the external grille. Air is evenly distributed within the diffuser before it is expelled through the external grille.

I5 A distance between a center of an aperture and a center of an adjacent aperture for each aperture in the array of apertures of the second internal grille may be in the range of 200 pm to 600 Rm. This range of distances results in an open area of the second internal grille which impedes effectively the air flow to reduce air flow velocity.

The distance between a center of an aperture and a center of an adjacent aperture for each aperture in the array of apertures of the second internal grille may be approximately 500 pm.

A distance between a center of an aperture and a center of an adjacent aperture for each aperture in the array of apertures of the first internal grille may be in the range of 200 pm to 600 pm. This range of distances results in an open area of the first internal grille which creates a path of least resistance radially outwards. A portion of the impinging air follows said path of least resistance, promoting an even diffusion of air flow.

The distance between a center of an aperture and a center of an adjacent aperture for each aperture in the array of apertures of the first internal grille may be approximately 520 A distance between the first internal grille and the second internal grille may be in the range of 0.1 mm to 4.6 mm. This range of distances ensures minimal turbulence and, thus, minimal noise created by the diffuser in use. The air flow velocity is adequately reduced before the air flow enters the first internal grille and the air flow is adequately diffused before exiting the external grille. I0

One or both of the first internal grille and the second internal grille may be in the form of a perforated plate.

One or both of the first internal grille and the second internal grille may be substantially I5 planar.

Each of the apertures of one or both of the first internal grille and the second internal grille may be circular in cross-section.

Each of the apertures of one or both of the first internal grille and the second internal grille may be frustoconical in shape.

Each aperture of one or both of the first internal grille and the second internal grille may have a diameter in the range of 100 p.m to 300 p.m. In combination with the distance between the center of an aperture and an adjacent aperture for each aperture in the array of apertures, this range of diameters leads to an open area which impedes air flowing through the first internal grille and second internal grille by a desired amount.

Each aperture of the second internal grille may have a diameter of approximately 290 30 pm.

Each aperture of the first internal grille may have a diameter of approximately 260 pm.

Within the array, the apertures of one or both of the first internal grille and the second intern& grille may be evenly distributed.

The second internal grille may be proximate to the diffuser air inlet. The second internal grille is positioned dose to the air inlet such that air is slowed down as soon as possible after entering the diffuser to prevent turbulence in a body of the diffuser.

The second internal grille may have an edge extending around a periphery of the second internal grille. The edge may be friction fit with an internal wall of the diffuser.

The friction fit between the edge of the second internal grille and the internal wall may provide a hermetic seal. This ensures that any liquid that may enter the diffuser does not IS leak into an attached hair dryer housing electrical elements and heating dements, for example as the user is drying their wet hair with the diffuser.

The first internal grille may have an edge extending around a periphery of the first internal grille. The edge of the first internal grille may be spaced apart from the internal wall to form a gap between the edge of the first internal grille and the internal wall. This provides a path of least resistance for the portion of air flow deflected radially outwards by the first internal grille. Said portion of air then escapes through the gap. This leads to an improved even flow exiting the diffuser at the external grille.

The edge of the first internal grille may be secured at a plurality of points to the internal wall. This ensures the first internal grille does not move about within the diffuser, for example, from the force of air passing through it. As a result turbulence and noise within the diffuser is reduced.

The diffuser may comprise a baffle which defines a diffusing air chamber through which the airflow passes from said at least one air inlet to the air outlets, wherein the

S

baffle defines said at least one air inlet and the internal wall of the diffuser and wherein the first internal grille and the second internal grille are located within the air chamber.

The gap between the edge of the first internal grille and the internal wall of the diffuser may be configured to allow partial airflow around the first internal grille.

The gap between the edge of the first internal grille and the internal wall of the diffuser may be in the range of 0.2 to 1.4 mm. The gap between the edge of the first internal grille and the internal wall of the diffuser may be approximately 1.0 mm. I0

The edge of the first internal grille may be secured to the internal wall by connections at the plurality of circumferentially spaced locations.

The first internal grille may be secured to the internal wall at the plurality of I5 circumferentially spaced locations by ultrasonic welding.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure I is a right side, front perspective view of a diffuser; Figure 2 is a left side, rear perspective of the diffuser; Figure 3 is a top view of the diffuser; Figure 4 is a bottom view of the diffuser: Figure 5 is a side view of the diffuser; Figure 6 is a side sectional view taken along line A-A of Figure 5; Figure 7 is an enlarged view of part of an internal grille of the diffuser; Figure 8 is a right side, front exploded view of the diffuser; Figure 9 is a left side, rear exploded view of the diffuser; Figure 10 is a left side, rear perspective view of an example hair dryer with the diffuser connected: Figure l la is a velocity map of fluid exiting an alternative diffuser; and Figure l lb is a velocity map of fluid exiting the diffuser of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figures 1 to 5 are external views of a diffuser 1. The diffuser I comprises an air inlet 2 for receiving an airflow from an airflow outlet end of a hair dryer such as hair dryer 18 shown in Figure 10. With reference to Figures 8 and 9, the diffuser air inlet 2 is generally annular in shape, and is in the form of a slot located at the air inlet end 31 of a baffle 3. The baffle 3 has an air outlet end 33 which is larger than the air inlet end 31, and an outwardly tapering wall 26 extending between the air inlet end 31 and the air outlet end 33. Said tapering wall 26 of the baffle 3 defines an internal wall of the diffuser I. As illustrated in Figure 6, the tapering wall 26 of the baffle 3 defines a diffusing air chamber 27 through which the airflow passes within the diffuser 1.

The baffle 3 comprises an annular air channel which defines the diffuser air inlet 2 and from which the airflow is emitted into the air chamber 27. An external grille 4 is connected to the air outlet end 33 of the baffle 3. The external grille 4 is generally concave in shape. The external grille 4 comprises air outlets 6 from which a first part of the airflow is emitted from the diffuser 1. Each of the air outlets 6 is circular in cross-section. Each of the air outlets 6 may be cylindrical in shape, however, in this I0 embodiment each of the air outlets 6 is frustoconical in shape, tapering inwardly from an internal surface 4a (see Figure 9) of the external grille 4 towards an external surface 4b (see Figure 8) of the external grille 4. At the external surface 4b, each of the air outlets 6 has a diameter which is in the range from 0.5 to 2.5 mm, and in this embodiment is in the range from 1.5 to 1.6 mm. Each of the air outlets 6 has a perimeter on the external surface 4b of the external grille 4 which is sharper than the perimeter of the air outlet 6 on the internal surface 4a of the external grille 4. The perimeter of the air outlet 6 on the internal surface 4a is preferably rounded, and has a curvature with a radius in the range from 0.2 to 0.4 mm.

The air outlets 6 are regularly spaced on the external grille 4 to promote an even, diffused emission of air from the diffuser I. The spacing between neighbouring air outlets is in the range from 0.5 to 2 mm, and in this embodiment is also in the range from 1.5 to 1.6 mm.

The diffuser I also comprises a plurality of projections 8 for contacting the hair of a user, and for emitting a second part of the airflow from the diffuser 1. The projections 8 are upstanding from the external surface 4b of the external grille 4.

Each of the projections 8 comprises an air inlet 5 formed in the external grille 4, an air outlet II, and a bore 7 for conveying air from the projection air inlet 5 to the air outlet 11.

As illustrated in Figure 6, Figure 8 and Figure 9, a first internal grille 12 and a second internal grille 10 are located within the diffuser 1. In the particular embodiment described herein, the second internal grille 10 and the first internal grille 12 are located within the air chamber 27 of the baffle 3. The second internal grille 10 and the first internal grille 12 are spaced from both the diffuser air inlet 2, and the external grille 4. The second internal grille 10 is located between the diffuser air inlet 2 and the first internal grille 12. The first internal grille 12 is located between the second internal grille and the external grille 4.

The second internal grille 10 is in the form of a circular disc or plate which comprises an array of apertures 14 through which the impinging airflow passes. The first internal grille 12 is also in the form of a circular disc or plate which comprises an array of apertures 16.

Each aperture in the array of apertures 14 of the second internal grille 10 has the same size and shape. Each aperture in the array of apertures 16 of the first internal grille 12 has the same size and shape but may have a different size and shape to the apertures in the array of apertures of the second internal grille 10. Each aperture in both arrays of apertures 14, 16 are generally circular in cross-section and cylindrical in shape. Each aperture in the array of apertures 14, 16 have a diameter in the range from 100tim to 300pm. In the particular example described herein, each aperture in the array 14 of apertures of the second internal grille 10 has a diameter of approximately 290pm. Also in the particular example described herein, each aperture in the array 16 of apertures of the first internal grille 12 has a diameter of approximately 260p.m.

In some embodiments, each aperture in the array of apertures 14, 16 tapers inwardly from a first, inlet surface, which faces the diffuser air inlet 2, towards a second, outlet surface which faces the external grille 4. In other words, the apertures in the arrays 14, 16 are generally frustoconical in shape. To reduce noise as air passes through the second internal grille 10 and the first internal grille 12, the perimeter of each aperture in the arrays 14, 16 on the outlet surface of the second internal grille 10 and the first internal grille 12, respectively, may be sharper than the perimeter of the apertures in the arrays 14, 16 on the inlet surface of the second internal grille 10 and the first internal grille 12, respectively.

As shown in Figure 6, the periphery of the second internal grille 10 is supported by a ledge 9 formed on an internal surface of the tapering wall 26 of the baffle 3. The ledge 9 is located closer to the air inlet end 31 than to the air outlet end 33 of the baffle 3.

Preferably, the second internal grille 10 is proximate to the annular air channel in the baffle 3. Air flow through the diffuser 1 is decelerated and evenly diffused proximate to the baffle air inlet end 31 when the second internal grille 10 is positioned close to the diffuser air inlet 2. Furthermore, partial deceleration and diffusion of the air flow is achieved before the air flow enters the first internal grille for further deceleration and diffusion when the second internal grille 10 is positioned dose to the diffuser air inlet 2.

The second internal grille 10 is secured to the internal surface of the tapering wall 26 by a friction fit between an edge 24 of the second internal grille 10 and the internal surface of the tapering wall 26. The friction fit doesn't require any other type of connecting mechanism or welding of parts which may simplify manufacture of the diffuser 1. Furthermore, the friction fit provides a hermetic seal between the edge 24 and the internal surface of the tapering wall 26. This hermetically seals the air outlet end 33 of the baffle from the air inlet end 31. It is desirable that liquid that may ingress through air outlets 6, 11 of diffusor 1 is prevented from egressing into heating elements located in a hair dryer 18 to which the diffuser 1 is attached. The user may contact their hair directly with the diffuser 1 and may angle the hair dryer 18 with attached diffuser 1 against the force of gravity to achieve the desired effect and style, all of which may increase the possibility of liquid leaking into the diffuser 1 and, subsequently, the hair dryer 18. The hermetic seal inside the air chamber 27 of the baffle 3 creates a barrier against °grossing liquid. The result of the addition of the friction fit is that the diffuser 1 does not require drainage channels for receiving liquid which has entered the air chamber 27 of the baffle 3 through the air outlets 6, 11 of the diffuser 1, thus, further simplifying manufacture of the diffuser 1, reducing the dimensions of the diffuser 1 and giving the diffuser 1 an improved aesthetic.

An edge 28 of the first internal grille 12 is spaced apart from the internal surface of the tapering wall 26 of the baffle 3 within the air chamber 27. This provides a gap 32 between the edge 28 of the first internal grille 12 and the tapering wall 26 of the baffle 3. The first internal grille 12 provides a resistive obstacle to air flowing through the diffuser 1. As a result, the first internal grille 12 causes a portion of the air flow impinging on the first internal grille 12 to divert radially outwards within the air chamber 27 towards the tapering wall 26. When the portion of diverted air reaches the edge 28 of the first internal grille 12 it escapes through the gap 32 between the edge 28 of the first internal grille 12 and the tapering wall 26 of the baffle 3.

The gap 32 promotes even diffusion of air across the diffuser 1 leading to a well distributed flow of air through each of the air outlets 6, 11. The greater the effect of impedance that the first internal grille 12 has on the impinging air, the greater the portion of the total air flow that is diverted to the edge 28 and exits through the gap 32. The gap in the example of figure 6 is 1.0nun.

The impedance effect of the first internal grille 12 is inversely proportional to its open area. The open area defines a percentage of surface area of an internal grille that is hollow and that air flow can pass through. Open area of an internal grille is determined by a number of apertures and the size of each of said apertures. A smaller number of apertures in an array increases the impedance. A smaller aperture size also increases the impedance.

in the particular example of Figures 6 and 7, wherein each aperture in the array of apertures 16 of the first internal grille 12 has a diameter of 260pm, the approximate 20 open area is 9%.

Each aperture in the array of apertures 14 of the second internal grille 10 has a diameter of 290pm. The approximate corresponding open area of the second internal grille 10 is 11 ills.

An important parameter of the arrays of the second internal grille 10 and the first internal grille 12 is their pitch. As illustrated by Figure 7, the pitch is the distance 34 from a centre of one aperture in the array of apertures 14, 16 to a centre of its neighbouring aperture. The pitch of the second internal grille 10 and the first internal grille 12 is in the range of 200 pm to 600 pm. In a preferred embodiment, the pitch of the second internal grille 10 is 500 pm and the pitch of the first internal grille 12 is 520 The even diffusion provided by the above described diffuser arrangement is such that the apertures 6 in the external grille 4 can be disposed over an entire surface of said external grille 4. In contrast to the present invention, a diffuser arrangement which has only one internal grille may need to have area on the surface of the external grille where the array of apertures does not extend. Removing the requirement of having sections of the surface of the external grille without apertures reduces noise produced by the diffuser and simplifies manufacture of the external grille 4 in comparison to a diffuser with only one internal grille or without internal grilles.

As hot air flow passes through the diffuser 1, the temperature of the tapering wall 26 of the baffle 3 will rise. To shield the user from the hot tapering wall 26 of the baffle 3, the diffuser I further comprises an external wall 36 which surrounds the baffle 3 and the external grille 4. The external wall 36 is generally frustoconical in shape. The external wall 36 is connected to the air outlet end 33 of the baffle 3 and comprises a plurality of spacers 37 formed on the internal surface of the external wall 36, and which are connected to the baffle 3 during assembly of the diffuser 1.

External components of the diffuser I and the baffle 3 may be formed from a plastics material, in this embodiment glass filled nylon. The external components comprise the external grille 4 and the external wall 36. One or more of the second internal grille 10 and the first internal grille 12 may be formed from a metallic material, in which case the apertures may be formed in the internal grilles 10, 12 by an etching process. Alternatively, one of more of the second internal grille 10 and the first internal grille 12 may be formed from a plastics material, in which case the apertures may be formed during molding of the internal grilles.

To assemble the diffuser 1, the second internal grille 10 is first positioned within the baffle 3. As illustrated in Figures 6, 8 and 9, the second internal grille 10 comprises a central aperture 13 which is slotted around a perimeter of a female connector 17 located on the end of a frustoconical projection 19 of the baffle 3. To create a friction fit the perimeter of the second internal grille 10 is push fit up to the ledge 9 of the baffle 3. The second internal grille 10 has an annular cap 23 circumferentially surrounding its central aperture 13. The annular cap 23 extends axially towards the air outlet end 33 of the diffuser 1.

The first internal grille 12 is then positioned within the baffle 3. The first internal grille 12 also comprises a central aperture 15 with an annular cap 25 circumferentially surrounding said central aperture 15. The aperture 15 is slotted around the perimeter of the female connector 17 until the annular cap 25 abuts the annular cap 23 of the second internal grille 10. The second annular cap 25 extends axially towards the air inlet end 31 of the diffuser 1.

A distance 20 between the second internal grille 10 and the first internal grille 12 is, therefore, determined and maintained by the distance that the annular caps 23, 25 extend in the axial direction. The annular caps 23, 25 may be made of a plastics material, for example, in this embodiment the annular caps 23, 25 are made from glass filled nylon. in a preferred embodiment, the distance 20 between the second internal grille 10 and the first internal grille 12 is in the range of 0.1 mm to 4.6 mm, preferably 4.6mm.

In an alternative example, the first and second annular caps 23, 25 may be formed as a single part.

As shown in Figure 8, the baffle 3 includes connectors 30 which extend radially inwards and are concentrically spaced from the internal surface of the tapering wall 26 of the baffle 3. These connectors 30 may partially overlap with an edge 28 of the internal grille 12 to provide additional support to the internal grille 12. The connectors 30 may be ultrasonically welded to the internal grille 12. The welding may also be induction welding. in another embodiment, the connectors may be secured to the edge 28 by an adhesive.

The baffle 3 is then located within the external wall 36 so that the air outlet end 33 of the baffle 3 rests on the spacers 37 of the external wall 36. The external grille 4 is then positioned on the air outlet end 33 of the baffle 3. As shown in Figure 9, an internal surface of the external grille 4 comprises a male connector 21 which is received by the female connector 17 of the baffle 3 as the external grille 4 is positioned on the air outlet end 33 of the baffle 3. The female connector 17 on the baffle 3 and the male connector 21 on the external grille 4 may include inter-engaging alignment members, for example, a slot (not shown) formed in the perimeter of the female connector 17 for receiving a radial rib (not shown) formed on the male connector 21, which angularly align the external grille 4 with the baffle 3. The connection of the external grille 4 to the baffle 3 sandwiches the annular cap 23 of the second internal grille 10 and the annular cap 25 of the first internal grille 12 between the baffle 3 and the external grille 4, thus, ensuring a tight fit between all the elements within the baffle 3 to prevent turbulence from passing air flow and reducing noise creating by turbulence as a result.

The assembly of the diffuser 1 is completed using ultrasonic welding to secure the external grille 4 to the baffle 3, and to secure the baffle 3 to the external wall 36.

in use, the diffuser I is attached to the airflow outlet end of a hair dryer 18. For example, the diffuser 1 may be attached to the hair dryer 18 by a magnet located at the air inlet end 31 of the baffle 3. An example of a hair dryer 18 and attached diffuser 1 is illustrated in Figure 10. Such a hair dryer 18 is described in W02015/001306, the contents of which are incorporated herein by reference.

Figure 1 la shows a velocity map of air flow exiting an alternative diffuser to the diffuser 1 of the present invention. The alternative diffuser has a single internal grille.

Figure 11b is a velocity map of fluid exiting the diffuser of the present invention. The darker grey regions of the velocity map in Figure I la and Figure I lb represent a higher velocity and lighter grey areas represent a lower velocity of air flow.

As illustrated in Figure I la, an area of very dark grey is present in the centre of the graph within central ring 40. This represents an area 38 of yen' high velocity air flow exiting the alternative diffuser. As illustrated in Figure 11b, there is no equivalent area of very high velocity air flow. This is because the arrangement of diffuser I described above provides an improved eveness in air flow distribution and decelerates air flowing into the diffuser to a greater extent in comparison to the alternative diffuser. I0

Furthermore, in Figure 11a, between central ring 40 and second ring 42 is an area of low velocity and between the second ring 42 and fourth ring 46 is an area of higher velocity. In comparison, the velocity map in Figure l lb has a consistent velocity across the entire velocity map with a slight area of lower velocity between the third ring 54 and fourth I5 ring 56. Thus, the overall velocity distribution in Figure I lb is more uniform than the velocity distribution in Figure I I a.

A more uniform velocity distribution of the air exiting the diffuser will lead to a more even treatment of the hair in contact with the diffuser. This may result in a better user experience and make it easier for the user to create their desired style when using the attachment.

Claims

CLAIMS1. A diffuser for attachment to an airflow outlet end of a hair dryer, the diffuser comprising: at least one air inlet for receiving an airflow from a hair dryer; an external grille comprising a plurality of air outlets for emitting at least part of the airflow from the diffuser; a first internal grille comprising an array of apertures; and a second internal grille comprising an array of apertures; wherein the first internal grille and the second internal grille are located between the at least one air inlet and the external grille.
2. A diffuser according to claim 1, wherein the second internal grille is located between the at least one air inlet and the first internal grille.
3. A diffuser according to claim 2, wherein the first internal grille is located between the second internal grille and the external grille.
4. A diffuser according to any of claim 1 to 3, wherein a distance between a center of an aperture and a center of an adjacent aperture for each aperture in the array of apertures of the second internal grille is in the range of 200 tun to 600 p.m.
5. A diffuser according to claim 4, wherein the distance between a center of an aperture and a center of an adjacent aperture for each aperture in the array of apertures of the second internal grille is approximately 500 p.m.
6. A diffuser according to any preceding claim, wherein a distance between a center of an aperture and a center of an adjacent aperture for each aperture in the array of apertures of the first internal grille is in the range of 200 pm to 600 pm. I0 I5
7. A diffuser according to claim 6, wherein the distance between a center of an aperture and a center of an adjacent aperture for each aperture in the array of apertures of the first internal grille is approximately 520 pm.
8. A diffuser according to any preceding claim, wherein a distance between the first internal grille and the second internal grille is in the range of 0.1 mm to 4.6 mm.
9. A diffuser according to any preceding claim, wherein one or both of the first internal grille and the second internal grille is in the form of a perforated plate.
10. A diffuser according to any preceding claim, wherein one or both of the first internal grille and the second internal grille is substantially planar.
11. A diffuser according to any preceding claim, wherein each of the apertures of one or both of the first internal grille and the second internal grille is circular in cross-section.
12. A diffuser according to any preceding claim, wherein each of the apertures of one or both of the first internal grille and the second internal grille is frnstoconical in 20 shape.
13. A diffuser according to any preceding claim, wherein each aperture of one or both of the first internal grille and the second internal grille has a diameter in the range of 100 pm to 300 pm.
14. A diffuser according to claim 13, wherein each aperture of the second internal grille has a diameter of approximately 290 pm.
15. A diffuser according to claim 13 or claim 14, wherein each aperture of the first internal grille has a diameter of approximately 260 pm.
16. A diffuser according to any preceding claim, wherein, within the array, the apertures of one or both of the first internal grille and the second internal grille are evenly distributed.
17. A diffuser according to any preceding claim, wherein the second internal grille is proximate to the air inlet.
18. A diffuser according to any preceding claim, wherein the second internal grille has an edge extending around a periphery of the second internal grille and wherein the edge is friction fit with an internal wall of the diffuser.
19. A diffuser according to claim 18, wherein the friction fit between the edge of the second internal grille and the internal wall provides a hermetic seal.
I5 20. A diffuser according to any preceding claim, wherein the first internal grille has an edge extending around a periphery of the first internal grille and wherein the edge of the first internal grille is spaced apart from the internal wall to form a gap between the edge of the first internal grille and the internal wall.
21. A diffuser according to claim 20, wherein the edge of the first interal grille is secured at a plurality of points to the internal wall.
22. A diffuser according to any preceding claim, comprising a baffle which defines a diffusing air chamber through which the airflow passes from said at least one air inlet to the air outlets, wherein the baffle defines said at least one air inlet and the internal wall of the diffuser and wherein the first internal grille and the second internal grille are located within the air chamber.