Field of the Invention

[0001] The present invention relates to a fan unit, and in particular a fan unit for providing focused airflow towards a desired target.

[0002] It will be appreciated that the invention has particular application to personal cooling fans, and it will be convenient to describe the invention herein in this exemplary context.

However, the fan may equally be used in other applications in which a concentrated or focussed airflow is desirable.

Background of the Invention

[0003] Fans that use the rotational motion of fan blades to create a pressure difference resulting in air movement are known. The resultant airflow may be used for example, to cool targets by assisting heat transfer. The heat transfer effect achieved is influenced by the velocity of airflow the target experiences. It is desirable that the greatest percentage of input power possible be converted to creating high velocity airflow directed at the target.

[0004] In axial fans, rotation of an axial fan invokes a pressure differential across the fans axial length thereby accelerating the air to induce an axial air flow. While the velocity of the air is predominantly in an axial direction with respect to the axis of rotation of the fan, the

consequence of rotational motion of the fan is a tangential vector to the airflow expelled the fan. In combination, the axial and tangential velocity vectors create a helical or corkscrew pattern in the air stream generated by the fan. The tangential flow vector further comprises an outward radial component thereby imparting the generated airflow stream with an inherent divergence.

In traditional fan design, divergence of the airflow has been seen as an advantage since it results in an increasing effective cross-sectional area of the stream allowing the fan to cool a larger area.

[0005] However, the diverging stream also tends to dissipate energy and the average flow velocity with increasing displacement from the fan unit and thus the effective airflow trajectory length, considered as the length ahead of the fan at which the flow field has some reference velocity is also reduced. This limits the cooling for objects at distance from the fan. [0006] Furthermore, since fans cool by creating air flow to assist heat transfer, airflow at the periphery of the widening flow region may not be passing over the target object and hence does not contribute to cooling.

[0007] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

Summary of the Invention

[0008] In a first aspect the present invention relates to a fan unit, including:

a fan housing;

an elongate cylindrical duct within said housing, said duct extending along a longitudinal duct axis between an air intake and an air outlet disposed respectively at opposite ends of the duct;

a motor having an output shaft;

an air moving axial fan connected to the motor output shaft and located within the duct between the air intake and the air outlet, said axial fan for rotation about a fan rotation axis to produce an airstream through the duct from the air intake to the air outlet and wherein the airstream exiting the axial fan comprises an axial component and a tangential component;

an airflow straightener disposed within the duct between the axial fan and the air outlet, said airflow straightener having a longitudinal airflow straightener axis and a circumferential array of guide vanes, each vane extending within the duct in an outward radial direction from a vane base to a vane tip and in an axial direction from a leading edge to a downstream trailing edge; said vanes forming a circumferential array of air straightening conduits, wherein said airflow straightener is adapted to receive and modify the airstream from the axial fan such that the airstream expelled from the fan unit is substantially unidirectional and colinear with the airflow straightener axis.

[0009] Preferably, a cylindrical cowling is disposed centrally within the duct forming an annular channel.

[0010] Preferably, the motor is located within the cylindrical cowling. [0011] Preferably, each guide vane comprises a first portion extending longitudinally through a first section and wherein the first portion of each guide vane is at a longitudinal vane angle Q with respect to the longitudinal airflow straightener axis.

[0012] Suitably, the first portion of each guide vane is curved in the longitudinal direction such that the longitudinal vane angle Q is measured between a tangent to the vane and the longitudinal duct axis.

[0013] Preferably, the longitudinal vane angle Q of each vane at the respective leading edge is an entrance angle 0 _e and wherein the longitudinal vane angle Q decreases with increased

displacement downstream the respective leading edge.

[0014] Preferably, the longitudinal vane angle Q of each vane decreases longitudinally to zero.

[0015] Preferably, the first portion of vanes are curved in the longitudinal direction by constant radius of curvature.

[0016] Preferably, the entrance angle 0 _e of each vane varies from the vane base to the vane tip.

[0017] Preferably, the entrance angle 0 _e is selected to be substantially aligned with the angle of the airstream entering the airflow straightener at the airflow straightener inlet.

[0018] Preferably, an incidence angle i measured between the entrance angle 0 _e and the angle of the airstream entering the airflow straightener is selected to be less than 15°, more preferably less than 10° across at least 60 % of the cross-sectional area of the airflow straightener inlet, more preferably across at least 75 % of the cross-sectional area of the airflow straightener inlet, most preferably across at least 90 % of the cross-sectional area of the airflow straightener inlet.

[0019] Preferably, the entrance angle 0 _e is between 10° and 50°, preferably between 25° and 40°, most preferably around 35°.

[0020] Preferably, the airflow straightener inlet is immediately downstream or closely spaced to the exit of the axial fan such that the airstream leaving the axial fan is passed directly into the airflow straightener. [0021] Preferably, the airflow straightener axis is aligned with the longitudinal axis of the duct.

[0022] Preferably, the motor shaft and axial fan rotation axis are coincident and aligned with longitudinal axis of duct.

[0023] Preferably, the airflow straightener includes between 12 and 20 straightening vanes in a single circumferential array, dividing the channel into a corresponding number of conduits.

[0024] Preferably, the cylindrical cowling includes a portion of increased diameter providing a venturi.

[0025] Preferably, the leading edge of each vane is curved from base to tip.

[0026] Preferably, the leading edge of each vane is further radially advanced at the base than the tip in the direction of rotation of the fan.

[0027] Preferably, the respective base of each vane is attached to an outer surface of the cowling.

[0028] Preferably, the airflow straightener includes second section disposed downstream of the first section, and wherein each guide vane comprises first and second portions extending longitudinally through the first and second sections respectively and wherein the first portion of each guide vane is at a longitudinal vane angle Q with respect to the longitudinal airflow straightener axis and the second portion of each guide vane is parallel to the longitudinal airflow straightener axis.

[0029] Preferably, the axial length of the first section of the airflow straightener is selected to be around (±50%) of the circumferential spacing between adjacent straightening vanes, measured mid-way between the cowling and outer duct wall.

[0030] In a second aspect the present invention relates to a personal fan unit, including:

a fan housing;

an elongate cylindrical duct within said housing, said duct extending along a longitudinal duct axis between an air intake and an air outlet disposed respectively at opposite ends of the duct;

a motor having an output shaft; an air moving axial fan connected to the motor output shaft and located within the duct between the air intake and the air outlet, said axial fan for rotation about a fan rotation axis to produce an airstream through the duct from the air intake to the air outlet and wherein the airstream exiting the axial fan comprises an axial component and a tangential component;

an airflow straightener disposed within the duct between the axial fan and the air outlet, said airflow straightener having a longitudinal airflow straightener axis and a circumferential array of guide vanes, each vane extending within the duct in an outward radial direction from a vane base to a vane tip and in an axial direction from a leading edge to a downstream trailing edge; said vanes forming a circumferential array of air straightening conduits.

[0031] In another aspect the present invention relates to a personal fan unit, including:

a housing;

an elongate cylindrical duct within said housing, said duct extending along a longitudinal duct axis between an air intake and an air outlet disposed respectively at opposite ends of the duct;

a cylindrical cowling disposed within the duct forming an annular channel ;

a motor having an output shaft, mounted within the cowling;

an air moving axial fan located within the duct between the air intake and the air outlet, said axially fan connected to the motor output shaft for rotation about a fan rotation axis to produce an airstream through the duct from air intake to air outlet and wherein the airstream exiting the axial fan has a helical flow pattern;

an airflow straightener disposed within the annular channel between the axial fan and the air outlet, said airflow straightener comprising a longitudinal airflow straightener axis, an airflow straightener inlet and a circumferential array of guide vanes, each vane extending within the duct radially outward from a respective vane base to a vane tip and longitudinally from a leading edge at the airflow straightener inlet to a trailing edge towards the air outlet; said vanes forming a circumferential array of air straightening conduits, wherein said airflow straightener is adapted to receive and modify the airstream from the axial fan such that the airstream expelled from the fan unit is substantially parallel to the longitudinal airflow straightener axis.

[0032] Preferably, the airflow straightener includes first section disposed upstream of a second section, and wherein each vane is curved in the longitudinal direction through the first section of the airflow straightener and run parallel to the airflow straightener axis through the second section of the airflow straightener and wherein the leading edge of each vane is configured to correspond to the helical flow created by the fan.

[0033] Preferably, each guide vane comprises first and second portions extending longitudinally through the first and second sections respectively and wherein the first portion of each guide vane is at a longitudinal vane angle Q with respect to the longitudinal airflow straightener axis. It will be appreciated that any discussion herein of airflow behaviour including airflow vectors and the like are intended to be indicative of average airflow patterns. That is to say, it is

acknowledged that airflows can and usually do simultaneously include both laminar and turbulent flow patterns particularly considering the influence of factors such as boundary layers, entrainment and the like. However, it will be likewise appreciated that discussion of flow characteristics can be summarised to a portrayal of general or predominant flow patterns and behaviours in order to illustrate the invention.

[0034] Avoiding the divergence of the flow field by generating airflow with a reduced swirl component and more focused,“straight” flow would have numerous benefits. It would increase the airflow velocity within the flow region, resulting in greater cooling, and accordingly increase trajectory length, allowing objects further away to receive the same effective cooling. Focused flow may therefore achieve an equivalent cooling effect at a greater distance from the fan using the similar power as a divergent fan, or, achieve increased cooling at the same distance for the similar power as compared to a divergent fan, or, achieve the same cooling at the same distance using less power when compared to a divergent fan.

Brief Description of the Drawings

[0035] For a more complete understanding of the invention and the advantages thereof, exemplary embodiments of the invention will be explained in more detail in the following detailed description with reference to the accompanying drawings, in which like reference signs designate like parts, and in which:

[0036] Fig. 1 is a perspective view of a fan unit according to an embodiment of the invention;

[0037] Fig. 2 is a side view of the fan unit shown in Fig. 1; [0038] Fig. 3 is a rear end view of the fan unit shown in Fig. 2;

[0039] Fig. 4 is a front end view of the fan unit shown in Fig. 2;

[0040] Fig. 5 is part sectional perspective view taken along the section plane A-A of Fig. 3;

[0041] Fig. 6 is part sectional side view taken along the section plane B-B of Fig. 4

[0042] Fig. 7 is full sectional side view taken along the section plane C-C of Fig. 4;

[0043] Fig 8 is a front perspective view of an airflow straightener and motor housing of the fan unit shown in Fig. 1;

[0044] Fig. 9 is a rear perspective view of the airflow straightener and motor housing of Fig. 7;

[0045] Fig. 10 is a rear end view of the airflow straightener and motor housing shown in Fig. 7;

[0046] Fig. 11 is a sectional side view taken along the section plane D-D of Fig. 10;

[0047] Fig. 12 is a sectional side view taken along the section plane E-E of Fig. 10;

[0048] Fig. 13 is a sectional side view taken along the section plane F-F of Fig. 10;

[0049] Fig. 14 15 is a schematic view displaying the geometry of the airflow straightener vanes in accordance with an embodiment of the invention;

[0050] Fig. 15 is a perspective view of a fan unit according to another embodiment of the invention;

[0051] Fig. 16 is a perspective view of a straightening grill according to yet another embodiment of the invention; and

[0052] Fig. 17 is a perspective view of a housing in accordance with another embodiment of the invention. [0053] The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate particular embodiments of the invention and together with the description serve to explain the principles of the invention. Other embodiments of the invention and many of the attendant advantages of the invention will be readily appreciated as they become better understood with reference to the following detailed description.

[0054] It will be appreciated that common and/or well understood elements that may be useful or necessary in a commercially feasible embodiment are not necessarily depicted in order to facilitate a more abstracted view of the embodiments. The elements of the drawings are not necessarily illustrated to scale relative to each other. It will also be understood that certain actions and/or steps in an embodiment of a method may be described or depicted in a particular order of occurrences while those skilled in the art will understand that such specificity with respect to sequence is not actually required.

Preferred Embodiments of the Invention

[0055] Referring to the drawings, a fan unit 1 is illustrated. The unit 1 is suitable for personal cooling and includes a housing 10 and an elongate cylindrical duct 11 of diameter D and length L defined by duct wall 12 and extending along longitudinal axis X between an air intake 13 and an air outlet 14, respectively disposed at opposite ends of the duct 11. A cylindrical cowling 15 is positioned coaxially within the duct 11 and extends at least partially along the length L of the duct. The cowling and duct together form an annular channel 16 within the duct 11 having a length 1, an inner diameter d and outer diameter D. A motor 20 is mounted within the cowling for driving an air moving axial fan 30 to draw air into the duct through the channel 16 and expel the air from the outlet. The airflow is schematically represented by arrows F in the Figures.

[0056] While the housing 10, duct 11 and cowling 15 are shown with a circular cross-section and will be described herein with reference to their diameters, it will be appreciated that either or both may have near circular and/or non-circular cross-sections without departing from the scope of the invention. Furthermore, the either or both diameters D of the duct and d of the cowling may vary along the length of the longitudinal axis as will be described below. [0057] Indicative dimension for the diameters D and d and lengths L and 1 are between 150 and 200mm; 70 and 120mm; 200 and 350 mm; and 100 and 200 mm respectively however the fan unit is not necessarily limited to these dimensions. In the embodiment shown in the drawings, the diameter D is 160 mm; the diameter d ranges from 72 to 102 and lengths L and 1 are 320mm and 145 mm respectively. It will be appreciated that the diameter D of the duct 11 is greater than the diameter d of the cowling.

[0058] The motor 20 includes a rotating output shaft 23 having a shaft axis Y. The fan 30 is configured for rotation about a fan rotation axis Z and includes a central hub 32 and a circumferential array of air moving blades 33 extending generally radially from the hub 32. The fan 30 is mounted by means of the hub 32 to the shaft 23 of the motor for rotation of the fan about the fan rotation axis. In this embodiment, the axes of the duct 11 and cowling X, the motor shaft axis Y and the fan axis Z are aligned and coincident.

[0059] Upon rotation by the motor 20, the fan blades 33 act on air to move it generally parallel to the rotation axis from a first side of the fan (the fan entry) to an opposite side (the fan exit). When located within duct 11, movement of air through the fan creates a pressure differential within the duct 11 which draws air into the intake 13, through the channel 16 and discharges it from the outlet 14 as a continuous stream as indicated by arrows F. Accordingly, herein, from a reference position the terms“upstream” and“downstream” are used to denote locations toward the intake 13 and outlet 14 respectively.

[0060] While the airflow through the fan 30 is predominantly aligned with respect to the fan rotation axis, the rotating motion of the fan also imparts a tangential vector component to the airflow at the fan exit which tends to increase with increasing radial displacement. The combination of the tangential and axial flow vectors results in air being discharged from the exit of the fan at a small displacement angle or fan airflow exit angle a with respect to the fan axis Z. Again the fan airflow exit angle a tends to be smaller towards the center and increase with increasing radial displacement from the axis of rotation. In any event however, this fan exit angle a gives rise to a resultant helical or corkscrewing pattern of airflow generated by the fan and left unchecked contributes to the aforementioned divergence of the airflow stream.

[0061] Accordingly, the fan unit 1 of the invention incorporates an airflow straightener 40 downstream of the fan 30 to remove or reduce swirl and/ or other turbulence in the airflow such that air expelled from the fan unit is predominantly unidirectional and aligned along a common axis being the axis of the airflow straightener. Preferably the airflow straightener axis is aligned with the longitudinal axis X of the duct. With reference to Fig. 10, the airflow straightener 40 includes a circumferential array of guide vanes 41 each vane extending within the duct in an outward radial direction from a base to a tip and in an axial direction from a leading edge 42 adjacent the fan 30 to a downstream trailing toward the fan outlet. The guide vanes 41 together circumferentially divide the annular channel 16 into a circumferential array of airflow

straightening conduits 44 extending from the fan along the longitudinal axis of the channel toward the outlet 14. The housing 10 comprises a relatively thin walled cylindrical tube body, the inner facing wall 12 of which defines the duct 11. A support 18 is connected to the body for supporting the fan unit 1. The support 18 maybe integrally formed with the body or attached thereto. Typically, the support 18 includes a stand or bracket (not shown) for supporting the fan unit 1 and allowing it to be positioned and orientated as required by the user, for instance, towards a target to be cooled. The stand also may be used for concealing electrical conduits providing power and/or control to the fan.

[0063] In some embodiments, portions of the inner facing surface wall 12 of the tube includes or is formed of sound and/or noise absorbing or abating paneling such as honeycomb paneling. Perforations 19, preferably in an evenly spaced grid pattern through the wall provide

communication between the honeycomb panel potions and interior of the duct.

[0064] In other embodiments, the trailing edge of the tube at the outlet 14 is shaped to tailor the aero-acoustic profiles of the air stream expelled from the outlet 14. In one such embodiment (shown in Fig 17) the peripheral trailing edge of the tube is patterned as a formation of waves or chevrons to broaden the region of flow mixing between the airstream and stagnant air, advantageously resulting in less chaotic mixing and a reduced aero-acoustics noise profile.

[0065] The fan 30 also effects on the performance of the fan unit including acoustics. In this embodiment, the axial fan 30 includes five evenly spaced, highly pitched, radial blades 33 mounted to the central hub 32. Each blade is swept backward with respect to the direction of fan rotation such that the fan is configured for unidirectional rotation (in this case clockwise about the rotation axis Z when viewed from Fig 4). As noted, the fan 30 is mounted within the duct 11 such that its rotation axis Z is aligned and coincident with the longitudinal axis X of duct. [0066] Typically, the diameter of the fan 30 is selected to minimise clearance between the inner surface 12 of the duct 11 and the blade tip. This clearance is defined by manufacturing tolerances but may be between 1-7 mm and preferably between 2 and 4 mm. The fan may be configured for a variable operational speed range - for instance between 1500 rpm and 3500 rpm. hi this this embodiment for example, the fan has an operational speed range of between 2000 rpm and 3150 rpm and a diameter of 156 mm.

[0067] It will be appreciated that other fan designs may be selected to optimize aerodynamics, air moving efficiency and noise performance based on motor output torque and speed, fan dimensions and target airflow velocity range. For instance, in some embodiments each fan blade 32 may include sharp planar or perpendicular comers at the blade tip to disrupt tip vortices and assist with noise suppression. In still further embodiments the tips of adjacent blades are joined so as to form a surrounding circumferential fan ring which adds stiffness and strength to the fan and particularly the fan blades.

[0068] With reference to the sectional view of Fig 6, longitudinally, the fan 30 is positioned in the upstream half of the duct 11, closer to the inlet 13 than the outlet 14. This reduces the distance from the inlet 13 to the fan 30 advantageously reducing resistance for the air drawn into the inlet to reach the fan blades whilst also providing space downstream for locating the motor within the duct.

[0069] As best seen in Fig. 7, the central hub 32 of the fan is cylindrical with a diameter generally equivalent to the outer diameter d of the cowling 15, thereby effectively extending the annular channel 16 into the region of the fan and so that the annular cross-sectional swept by the fan blades generally corresponds with the annular cross-sectional of the annular channel 16 adjacent the fan. In this way the motor torque required to turn the blades at a given RPM is reduced thereby allowing an increased operating RPM at a given power. That is to say, since available motor power moves air through a smaller volume relative to a non-channelled fan, the air velocity in the channelled region is comparatively higher.

[0070] In other embodiments the hub 32 may be tapered or conical, particularly to follow the profile of the cowling 15 and providing a reduced diameter at the upstream or leading tip. In still further embodiments, the diameter of the hub 32 may be substantially less than the diameter of the cowling. In such cases the area swept by the fan blades may be greater than the cross- sectional area of the annular channel adjacent the fan.

[0071 ] The motor 20 may be either an AC or DC type electric motor configured for connection with an electrical supply, typically but not necessarily a mains supply. For instance, in some

embodiments the motor may be configured for connection to a battery or auxiliary power unit. The unit further includes circuitry including a user control interface to control the fan unit. For instance, to activate and control the fan, the fan speed and/or electrical power sent to the motor. The control interface may be located on the fan housing, on the fan stand and/or via a remote control, either wired or wireless.

[0072] The motor 20 is located within the cowling 15 such that the axis Y of the motor shaft 23 is aligned and coincident with the longitudinal axis X of duct 11. The cowling 15 is provided with motor support formations for attaching and supporting motor 30. As seen in Fig 9, the motor is connected to a bulkhead 24 of the cowling by means of threaded connectors received in apertures 25. Accordingly, the cowling is configured with sufficient structural strength to support the motor and fan and functions not only as an aerodynamic cowling but also as a motor housing and support. In other embodiments however, the motor 20 may be supported on a motor frame or housing and the cowling may be provided as a lightweight fairing requiring additional support.

[0073] In still further embodiments the motor 20 may be positioned external the duct, for instance, external the duct located in the housing and connected to the axial fan via a drive shaft or drive train. In such cases the central cowling may be of reduced length and / or diameter or generally non-existent such that the duct forms the channel 16 which is cylindrical rather than annular in crossection.

[0074] The motor is selected based upon parameters such as fan unit size, intended air output velocity and volume, power consumption and torque requirements to provide optimum RPM for the fan. In this embodiment for instance, the motor 20 is rated for a variable output of 30W-60W at a torque of 0.1 N.m -0.2 N.m.

[0075] The cowling 15 extends longitudinally from leading end 50 at a position immediately adjacent the fan 30, along the length of duct 11 to protrude from the outlet 14 at trailing end 51. Furthermore, with reference to Fig. 11 in this embodiment, the diameter d of the cowling 15 varies along the axial length. Beginning at the leading end 50 immediately adjacent the fan 30, the diameter of the cowling gradually increases from diameter di to a maximum of d2 upstream of the duct 11 outlet, before tapering to d ₃ at the trailing end 51, where d2>d3>di. In this way, the cowling 15 is provided with a bulbous shape which, since the diameter D of the duct forming the outer diameter of the annular channel remains relatively constant, effectively reduces the cross-sectional area of the annular channel 16 toward the outlet 14. The reduction of cross- sectional area in the channel adjacent the bulbous portion creates a venturi such that the velocity of the airflow moving through the channel 16 is increased before exiting the fan unit thereby enhancing the effective airflow trajectory length.

[0076] Furthermore, in some embodiments, air passageways (not shown) are provided from outside the housing through the tube and into the duct 11 exiting adjacent the bulbous portion so as to feed air through the housing and into the annular channel. The air is drawn in by the low pressure, and thereby advantageously increasing the flow output of the fan.

[0077] In some embodiments, the cowling may be provided with other shapes and profiles to tailor or enhance performance. For instance, Fig. 15 displays a fan unit whereby cowling diameter d is held relatively constant along its length thereby providing an annular channel of generally uniform cross-sectional profile. Furthermore, the cowling may terminate inside the duct or in line with the trailing edge of the duct.

[0078] In some embodiments space within the cowling downstream of the motor 20 are utilized to aid in lowering the aero-acoustic profile of the fan unit by providing resonant cavities to provide passive noise control. Perforations through the cowling provide a fluid communication into the cavities enabling acoustic tuning to remove or alter undesirable sound frequencies. Such cavities, where equipped are may be disposed within the cowling downstream of the motor.

[0079] Since the motor 20 and cowling 15 are positioned within and suspended from the duct walls 12, they require a supporting formation. In some embodiments, the motor and cowling may be held by dedicated supporting member/s anchored to the housing for instance, in the form of a post support/s, or a plurality of radial spokes. However, in this embodiment, as can be seen in the figures, the radial guide vanes 41 of the airflow straightener 40 serve also to connect and suspend the cowling and motor centrally within the duct 11 to the inner wall 12 of the tube body. [0080] In this regard, the airflow straightener 40 and cowling 15 form a component or assembly adapted to be inserted into and fixed within the duct 11. In this embodiment, as shown in Figs. 8 and 9, the insert is a single integral component molded from a plastics material.

[0081] As can be seen, particularly in Fig. 6, the insert includes a cylindrical peripheral sleeve 52 which fits closely inside the duct 11 forming a portion of the channel wall. The sleeve 52 includes an outer facing surface which may engage the housing or inner wall 12 of the duct 11 and an inner facing surface which forms a portion of the annular channel 16 wall. The sleeve 52 and the cowling 15 are connected by the radial airflow straightener vanes 41, each vane extending from a respective vane base connected to the cowling 15 to a vane tip connected to the cylindrical peripheral sleeve 52. Pairs of adjacent airflow straightener vanes 41 together with the cowling and sleeve define lateral walls of respective airflow straightener conduits 44.

[0082] As noted, the airflow straightener 40 is positioned downstream of the fan to remove or reduce swirl in the airflow produced by the fan such that air expelled from the fan unit is predominantly unidirectional and aligned with the longitudinal axis X of the duct. In this embodiment an airflow straightener inlet is immediately or closely space to the exit of the impeller such that the airstream leaving the impeller is passed directly into the airflow

straightener.

[0083] Accordingly, at the airflow straightener inlet, the leading part of each straightener vane is angled with respect to the fan axis so that the airstream exiting the fan meets each vane at an optimum angle in order to minimize turbulence and disruption of the airstream. From the leading edge, a first portion of each airflow straightener vane is curved to smoothly alter the airstream’ s trajectory in the longitudinal direction, in particular reducing tangential vector components, and guide the airstream into a longer second section of the straightener where the straightening vanes and conduits are straight so as to confine the airstream to a linear path and encourage laminar flow.

[0084] Longitudinally, the airflow straightener 40 may be divided into a first section 45 at an upstream end whereby the vanes 41 are curved, and a second section 46 downstream of the first section within which the vanes 41 are straight. Correspondingly, each vane and conduit includes a first portion and a second portion each portion being curved and straight respectively. It will be appreciated that each of the first and second sections of the airflow straightener define corresponding curved and straight portions of each of the straightening conduits 44. With reference to cross-sections E-E and F-F shown in Figs 12 and 13, the first and second sections (45 & 46) can be seen to extend along respective lengths (lc ¹ & lc ² ) of the length, l _c of the airflow straightener. The first section has a longitudinal axis W ¹ while the second section has a longitudinal axis W ² . In this embodiment axis W ¹ and axis W ² are aligned to be parallel with a common straightener axis W.

[0085] The first portion 45, of each guide vane 41 is inclined at a longitudinal vane angle Q with respect to the longitudinal axis W of the airflow straightener whereby the angle Q at a point on the vane is the angle between a radial plane RP parallel to the longitudinal axis W passing through the point and a tangent line t to the guide vane at that point on a plane orthogonal to the radial plane RP and parallel to the longitudinal axis W. As seen in Fig. 12, the longitudinal vane angle Q is at a maximum at the leading edge of each vane where the angle Q between the tangent t _e of the vane and the W axis is the longitudinal vane entrance angle 0 _e. With increasing longitudinal displacement from the respective leading edge 42, the angle Q decreases to zero thereby proving curvature to the vanes. The vanes may have a constant or variable radius of curvature. However, the point at which the angle Q reaches zero degrees marks a point of transition from the first curved portion 45 to the second straight portion 46. Downstream of this transition point, to the trailing edge 43, each guide vane 41 and the corresponding conduits 44, run parallel to the axis W.

[0086] In one embodiment, the vane entrance angle 0 _e is selected to be aligned with the angle of the airflow entering the airflow straightener referred to herein as the airstream entry angle a'. Any difference between the entrance angle 0 _e of each vane and the angle a' of the airflow entering the airflow straightener is the incidence angle i, and is preferably minimised across the operating envelope of the fan unit.

[0087] It will be appreciated that the airstream entry angle a' is largely dictated by the airstream produced by the axial fan. In this embodiment, since the fan axis Z and the flow straighter axis W are aligned and coincident, and the airflow straightener inlet is immediately downstream the axial fan exit, any difference between the angle a' of the airflow entering the airflow straightener and fan exit angle a is negligible. [0088] The fan exit angle a and therefore angle a' may vary across the radial face of the fan exit, typically with increasing radial displacement. Therefore, while in some embodiments the entrance angle 0 _e of each vane is generally constant along the radial length of each vane, more commonly, in other embodiments the vanes exhibit some“twist” in the radial direction such that the entrance angle 0 _e of each vane varies along the radial length of the vane from base to tip, preferably to correspond to the expected angle a' at a given radial displacement.

[0089] Accordingly, in one embodiment, the incidence angle i (difference between the entrance angle 0 _e of each vane and airstream entrance angle a') of each vane is selected to be less than 10°, more preferably less than 5° across at least 60 % of the cross-sectional area of the airflow straightener inlet, more preferably across at least 75 % of the cross-sectional area of the airflow straightener inlet, most preferably across at least 90 % of the cross-sectional area of the airflow straightener inlet.

[0090] Furthermore, however, the fan exit angle a may also vary with varying fan speed.

Accordingly, in another embodiment, the incidence angle i of each vane is selected to be less than 15°, more preferably less than 10° across at least 60 % of the cross-sectional area of the airflow straightener inlet, more preferably across at least 75 % of the cross-sectional area of the flow straightener inlet, most preferably across at least 90 % of the cross-sectional area of the airflow straightener inlet.

[0091] As noted, in this embodiment axis W ¹ and axis W ² are aligned and coincident with the common straightener axis W. However, in other embodiments the axis W ¹ and axis W ² may be set at a shallow angle with respect to one another such that the straightener aligns the airflow along an axis at an angle not parallel to the fan axis Z.

[0092] It will be appreciated that together, the vanes within the first section 45 of the

straightener 40 adjacent the fan define a longitudinal helical formation which corresponds to the helical pattern of airflow produced by the fan 30. As such, the helical airflow stream enters the straightening conduits 44 with minimal disruption and energy loss and is guided by the gradual and smooth transition of the vanes and conduits to a substantially laminar flow without overtly reducing its energy and speed or introducing turbulence. Advantageously the substantially laminar flow produced leads to lower divergence of the air stream leaving the fan unit. [0093] With reference to Fig. 10, the airflow straightener includes twenty straightening vanes 41 in a single circumferential array, dividing the annular channel into twenty corresponding conduits 44. However, in other embodiments the number of straightening vanes maybe selected based on operational parameters and dimensions of the fan unit. Furthermore, in some embodiments, the airflow straightener may be configured to have two or more concentric layers of straightening vanes each layer separated by a longitudinally extending cylindrical tube. Each layer may have a different number of straightening vanes, with the vanes in each layer set at different entrance angles Q.

[0094] The axial length of each of the first 45 and second 46 sections (b ¹ & l _c ² respectively) of the straightener 40 are selected to optimize air airflow straightening, while reducing drag and/or energy loss and balancing the overall size of the fan unit. As such generally each is selected dependent on parameters such as duct diameter, blade design, motor speed and torque, flow velocity range etc. Preferably the radius of curvature of the vanes in the first section is minimized which allows for a shorter length of the first section b ¹ and a more compact fan unit. However increasing vane curvature may lead to flow separation whereby the airflow detaches from the vane wall thereby introducing unwanted turbulence.

[0095] In one embodiment the length b ¹ of the first section of the straightener is selected to be dependent on the circumferential spacing of the vanes thereby defining proportional range between channel width measured circumferentially and channel length. For instance, the length b ¹ of the first section of the straightener is selected to be around (±50%) of the circumferential spacing between adjacent straightening vanes, measured mid-way between the cowling and outer duct wall. By way of example, with reference to Fig. 10, if the circumferential spacing s between adjacent straightening vanes of the embodiment of the invention is 17 mm, the length of the first section of the straightener is between around 8.5 and 25.5mm.

[0096] The length b ² of the second section of the straightener is selected to enhance laminar flow of the airstream, and in this regard, the effectiveness of the straightener is somewhat improved by extending the length of the conduits. Accordingly, in embodiments of the invention, the length b ² of the second section is at least greater than the duct diameter D. However, it should be noted beyond a certain length there is little advantage to increasing the length of the second section. In addition, the length of the second section tends to contribute substantially to the overall length of the fan unit and therefore must be considered with respect to form factor. Thus in some embodiments, the second section may be of reduced length or even omitted to increase compactness of the fan unit such that the flow straightener comprises vanes with only a generally curved longitudinal profile which guide the airstream from the fan substantially unidirectional and/or colinear with the airflow straightener axis.

[0097] Typically, in the first section, the vanes are configured to each have an entrance angle 0 _e of between 10° and 50°, and preferably between 20° and 40°, and may extend over a length k ¹ of 15-45 mm while the second section may extend over length l _c ² of 15-150mm. For instance, in the embodiment shown in Figs 12 and 13, the entrance angle 0 _e of the first portion is around 35° and the first portion extends 20 mm longitudinally while the second portion measures 100mm in length.

[0098] The above defines the shape of the straightener vanes in the longitudinal plane however with reference to the Figures and particularly the end views of Figs. 4 & 10, it can be seen that the vanes are curved in the lateral plane, orthogonal to the longitudinal axis. As seen in Fig. 10, each vane radiates outwardly from the base at the cowling towards the tip at the outer duct wall. In some embodiments each vane follows a linear radial from the axis A, tracking the shortest distance between the cowling and the duct. However preferably, the base of each vane is further advanced than the tip in the direction of rotation of the fan. That is to say, the base and tip lie on respective first and second radials respectively extending from the axis A and separated by an included angle of less than around 40° and wherein the first radial leads the second radial in the direction of rotation. Furthermore, as shown in the figures, notwithstanding the curve of each vane in the first portion on the respective axial plane, each vane follows an arc from the root to the tip of decreasing radius.

[0099] Geometrically, the arc can be described with reference to schematic illustration Fig. 14 depicting a plane orthogonal to the longitudinal axis A. A radial drawn on the plane to pass through a larger circle of diameter D representing the diameter of the duct (outer diameter of the annular channel) and a smaller concentric circle of diameter d representing the diameter of the cowling (inner diameter of the annular channel). A curve defining the arc of the vane can be drawn from a point p ¹ on the smaller circle to a point p ² on the larger circle p ¹ and p ² lie on respective first and second radials (r ¹ and r ² ) separated by an included angle of between 0° and no more than 40°. [0100] The curve is either monotonic linear or monotonic curvilinear. If the points p ¹ and p ² deviate from a straight line passing through the center of the circles, p ¹ should be situated further in the direction of the motor operation than p ² . For instance, if the motor/fan rotation is viewed by an observer at the outlet of the tube, and appears clockwise, then p ¹ should be situated further clockwise than p ² . In the curvilinear case, the point on the curve which intersects with a concentric circle at a radius that is the average of the inner and outer circles should be offset further clockwise than p ¹ (assuming clockwise rotation viewed from outlet).

[0101] The thickness of each vane is minimized taking into account manufacturing constraints (e.g. minimum thickness for injection molding of plastic) material strength and the like. For instance, preferably, the airflow straightener vanes are made of injection molded plastic and have an average thickness of around 1 - 2.5mm.

[0102] For safety, access to the fan from the intake and outlet is prevented. Typically, the shape and axial length of the straightener vanes combined with the spacing of the fan from the outlet, means that the straightener itself serves as a safety guard preventing access to the motor from the outlet end. However, in some jurisdictions, safety design regulations may require the inclusion of a mesh grill over the outlet.

[0103] At the intake end of the fan unit, the rotating fan is closer to the inlet and therefore, a grill 60 or safety guard is employed.

[0104] Advantageously, the geometry of the straightener and straightener vanes is selected to reduce energy loss by eliminating sharp angles and reducing collision of the airflow.

Furthermore, by configuring the first section of the airflow straightener to correspond to the helical flow created by the fan minimizes turbulence in the transition to the straightening conduits. In addition, the tubular shape of the housing, relative to other cambered straightener s, provides a longer region for gentle redirection in the swept area, and a longer area for streamlining in the straight section. This reduces energy loss and increases the extent of the flows path which is axial after leaving the straightener. The straighteners can extend from the motor face (or their desired starting point) until all the way to the outlet, or part of that distance. These also serve to remove vortices and turbulence, reducing noise. [0105] In alternative embodiments, straighteners, consisting of grill having a“twisted blade” type pattern as shown in Fig 16. Along one of the lateral axes perpendicular to the blades, focused straightening effect is provided while along on a generally orthogonal lateral axes, the blade provide little to no straightening such that the flow is dispersed.

[0106] Although specific embodiments of the invention are illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternative and/or equivalent implementations exist. It should be appreciated that the exemplary embodiment or exemplary embodiments are examples only and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

[0107] It will also be appreciated that in this document the terms "comprise", "comprising", "include", "including", "contain", "containing", "have", "having", and any variations thereof, are intended to be understood in an inclusive (i.e. non-exclusive) sense, such that the process, method, device, apparatus or system described herein is not limited to those features or parts or elements or steps recited but may include other elements, features, parts or steps not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, the terms "a" and "an" used herein are intended to be understood as meaning one or more unless explicitly stated otherwise. Moreover, the terms "primary", "secondary", etc. are used merely as labels, and are not intended to impose numerical requirements on or to establish a certain ranking of importance of their objects.