Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/26—Rotors specially for elastic fluids
  • F04D29/28—Rotors specially for elastic fluids for centrifugal or helico-centrifugal pumps for radial-flow or helico-centrifugal pumps
  • F04D29/281—Rotors specially for elastic fluids for centrifugal or helico-centrifugal pumps for radial-flow or helico-centrifugal pumps for fans or blowers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/26—Rotors specially for elastic fluids
  • F04D29/28—Rotors specially for elastic fluids for centrifugal or helico-centrifugal pumps for radial-flow or helico-centrifugal pumps
  • F04D29/30—Vanes

Definitions

• the present invention relates to an improved impeller for a fan, in particular to an impeller for a ventilation fan or blower, more particularly for a fan for use in domestic and/or commercial applications, for use mainly in a duct or airway or in a wall of a building.
• the present invention further relates to a fan comprising such an impeller.
• the present invention provides an impeller for a fan, which impeller comprises a hub and one or more blades, wherein at least one blade has: a radially inner portion which is aerofoil in section; and, a centrifugal accelerator portion which extends radially outwardly from the aerofoil portion, wherein the aerofoil portion has a greater angle of attack than the accelerator portion.
• the angle of attack defines the angle between the front of the blade and the direction of motion of the blade.
• the impeller according to the present invention has part aerofoil and part centrifugal fan characteristics, thus drawing air towards the centre of the fan to a greater extent than conventional impellers. This provides a more even flow profile of air entering the fan, avoiding turbulence towards the centre and the resulting high velocity regions towards the perimeter of the fan inlet.
• the aerofoil portion operates in the manner of an axial impeller, whilst the accelerator section forces the air outward in a radial direction such that the axial and radial elements are both included in a 'combined' flow impeller according to the present invention.
• the radially inner, or aerofoil portion is helicoidal in shape.
• the helicoidal axial section at the root of the impeller imparts a substantially radial force upon the air entering the fan, forcing the air radially outward.
• the air is forced outward to the long path lateral accelerator portion.
• the curvature of the blade increases towards the axis of rotation or centre of the impeller.
• the angle of the blade to the axis of rotation of the impeller is greatest at the central portion.
• the angle of attack of the blade is greatest at the accelerator portion.
• the angle of attack of the blade is reduced in the aerofoil portion and typically the angle of attack is smallest at the radially innermost edge of the blade.
• the orientation of the blade tends towards a outermost edge which is substabtially parallel to the axis of rotation of the blade.
• the outermost edge does not achieve a straight line but retains a slight curvature.
• the curvature of the centrifugal accelerator portion is substantially constant such that the blade is substantially symmetrical at its outermost edge.
• the orientation of the blade towards the outermost edge is particularly advantageous since the centrifugal accelerator portion takes a scoop or paddle- like shape so as to generate substantially radial, as opposed to tangential, flow from the impeller.
• the pressure drop over the accelerator portion is greater than the pressure drop over the aerofoil portion of the blade.
• the long path accelerator portion is particularly advantageous since it obviates air turbulence and imparts energy to the air in order to generate a pressure gradient in a novel manner.
• angle of attack is minimal at the centre, where the speed of the blade is minimal, and increases towards the outermost edge, where the speed is greatest. This promotes an even inlet flow profile over the whole of the impeller inlet.
• the leading edge of the blade is substantially straight.
• the leading edge is substantially tangential to a hub portion of the impeller.
• the impeller preferably comprises 5 or 7 blades, each of which has an aerofoil helicoidal central portion which extends laterally into a centrifugal accelerator portion.
• the present invention further provides a fan comprising an impeller and a housing in which the impeller is mounted for rotation, which impeller comprises one or more blades, wherein the blade or at least one of the blades has an aerofoil helicoidal central portion which extends laterally into a centrifugal accelerator portion.
• the impeller is mounted within a volute formed within the housing.
• angle of attack refers to the angle between the blade and the direction of motion of the blade.
• the angle of attack for a particular blade section may be measured as the angle between the blade centerline and the direction of motion at the leading edge of the blade.
• the direction of motion is generally approximately perpendicular to the axis of rotation.
• Figure 1 is a side view of a conventional centrifugal fan, showing the inlet velocity pattern
• Figure 2 is a plan view of the fan of Figure 1 , showing the air discharge pattern
• Figure 3 is an isometric view of an embodiment of an impeller according to the present invention.
• Figure 4 is a plan view from above of the impeller of figure 3;
• Figure 5 is a side view of a fan according to Figure 3;
• Figure 6 is a side view of a generic fan according to the present invention.
• FIG 7 is a plan view of the fan of Figure 6.
• a conventional centrifugal fan shown generally at 10 comprises an impeller 2 having a diameter D 1 and housed in a housing 4.
• the impeller 2 is driven by a motor 6.
• the inlet diameter D 2 of the impeller 2 is less than the diameter D 1 of the impeller 2.
• the maximum air volume is 400 litres/second which equates to an average inlet velocity of 8.8m/s.
• the area of the housing 4 on the inlet side of the impeller includes a central low velocity and low turbulence area 8 surrounded by a high velocity area 12.
• the velocity in the low velocity area 8 is of the order of 6.5m/s and in the high velocity area 12, the velocity is of the order of 11 m/s.
• the impeller 2 is driven by a motor 6 which is located at the axis of rotation of the impeller 2.
• a curved internal wall 14 is located within the housing 4 and defines a volute 16 in which the impeller 2 is mounted for rotation.
• the curved internal wall 14 forms at one end a close throat plate 18.
• Arrows A 1 and A 2 show the air discharge pattern schematically. As can be seen from the arrows A 1 and A 2 , the air discharge pattern is curved as a result of the swirl which is imparted to the flow by the impeller baldes.
• the discharge has a high inertia, of the order of 15-20m/s for the fan dimensions described above.
• an impeller shown generally at 20 comprises a plurality of blades, 22, 24, 26, 28, 30, 32, 34 spaced equiangularly about a hub portion 36.
• the hub 36 has a curved circumferential surface 35 which terminates at peripheral rim 37.
• the direction of rotation of the impeller is indicated by the arrow 38.
• Each of the blades 22, 24, 26, 28, 30, 32, 34 comprises a leading edge 40 which extends along an aerofoil portion 39 and a lateral air accelerator portion 42.
• the outermost edge 41 is substantially perpendicular to the leading edge 40 and trailing edge 40'.
• the blade is twisted such that the outermost portion of each blade tends towards an orientation which is substantially parallel to the axis of rotation of the impeller.
• the angle of curvature of the blade is also reduced along the length of the blade with distance from the axis of rotation.
• the innermost section of the leading edge defines the aerofoil portion 39 with the air accelerator portion 42 extending radially therefrom.
• Figure 4 shows the impeller 20 of Figure 3 from above. It can be seen that the depth of each blade in a circumferential direction is greatest adjacent the hub and diminishes towards the outermost edge 41. That is to say that the thickness of the blade reduces with distance from the hub 36 when viewed from above. This tapering of the blade is due to the blade twisting such that a greater surface area of the blade is presented to the airflow towards the hub of the impeller than towards the periphery, at which the blade is angled away from the airflow.
• each blade forms a substantially straight line, extending tangentially from the hub.
• the trailing edge 40' of the blade in the accelerator portion is radially aligned with the axis of rotation 45.
• the impeller blades extend radially outwardly from the curved outer circumferential surface 35.
• the depth of the blades in the axial direction is smallest at the innermost point of the blade and increases with distance from the axis of rotation by virtue of the curved shape of hub surface 35.
• each blade follows the curvature of the hub.
• the blades extend outwardly of the outermost rim of the hub portion.
• the axial depth of the blade in the acceleration portion 42, between the outer rim of the hub and the outermost edge 41 of the blade is substantially constant, although each blade is preferably slightly tapered towards the axis of rotation.
• the combination of the aerofoil inner blade section and the accelerator section extending radially outwardly therefrom has the effect of turning the air through substantially 90° as it passes through the fan.
• the impeller 20 has diameter D 3 and is located within a housing 44 having an inlet ring 47.
• the impeller 20 is driven by a motor 46.
• the inlet diameter D 4 of the impeller 20 is less than the diameter D 3 of the impeller 20.
• the maximum inlet volume is 400 litres/second which equates to 6.49 m/s.
• the inlet velocity is substantially the same across the whole area of D 4 on the inlet side of the impeller.
• the height of the impeller H 1 is approximately 50mm
• the height of the fan, including inlet ring, H 2 is approximately 80mm
• the total height of the cavity or ducting in which the fan is located, H 3 is approximately 150mm.
• the fan can operate effectively with a clearance of only 70mm to provide an airflow of approximately 500l/s. This is in contrast to a conventional fan which would require a cavity of typically 250mm height in order to achieve a similar flow rate.
• the air is drawn into the centre of the impeller by the aerofoil elements 40 of the impeller blades 22, 24, 26, 28, 30, 32 and 34. This prevents the generation of a flow profile as shown in figure 1 and causes air to be drawn substantially evenly over the inlet diameter D 2 .
• the exact curvature of the blade and the geometry of the aerofoil portion can be altered to achieve the desired flow profile for optimal performance.
• the lines L 1 and L 2 are parallel to the axis of rotation of the impeller.
• the angle made between the blade 24 and the lines L 1 and L 2 are shown at ⁇ and ⁇ respectively.
• the angle ⁇ represents the angle made between the leading edge of the aerofoil portion 39 and the axis of rotation, whilst the angle ⁇ is between the leading edge of the acceleration portion and the axis of rotation.
• the angle ⁇ may be between 45° and 90°, whilst the angle ⁇ is between 0° and 30°.
• the angle of attack defines the acute angle between the blade and its direction of movement.
• the lines L 1 and L 2 are perpendicular to the direction of rotation of the blades.
• the angle of attack of the blade at the aerofoil portion can be defined as 90° - ⁇ and the angle of attack at the accelerator portion can be defined as 90° - ⁇ . Therefore the angle of attack at the aerofoil section may be between 0 and 45° , whereas the angle of attack for the accelerator portion may be between 60 and 90°.
• angle of attack varies with distance along the leading edge from the hub.
• the angle of attack varies constantly along the length of the blade by virtue of the twisting of the blade about its leading edge.
• angle of attack will be minimal at the innermost point of the blade and maximal at the outermost edge 41.
• the angle of attack may vary from 0 to 90° over the length of the blade.
• the skew of the blade varies along its length.
• the curvature of the blade is greatest in the vicinity of the leading edge within the aerofoil portion and reduces towards the trailing edge.
• the curvature of the blade in the acceleration portion is substantially constant between the leading and trailing edges.
• the blade is substantially symmetrical about the mid point of the blade, although the blade may be curved slightly forward as shown in figure 4.
• the aerofoil section of the blade is highly asymmetrical.
• the impeller 20 is driven by motor 46 which is located at the axis of rotation 45 of the impeller 20.
• the motor is of external rotor type and is disposed within the hub portion so as to provide a compact design.
• a curved internal wall 48 is located within the housing 44 and defines a volute 50 in which the impeller 20 is mounted for rotation. It can be seen that throat 49 is retracted when compared with the throat plate 18 of figure 1 so as to define an open passageway for air leaving the housing 44.
• Arrows B 1 and B 2 show the air discharge pattern schematically. As can be seen from the arrows B 1 and B 2 , the air discharge pattern is straight. The discharge has a low inertia, of the order of 11m/s maximum for the fan dimensions described above.
• the principle of operation of the fan of Figures 3 to 7 is as follows. Conventional centrifugal fan inlet characteristics produce high velocity patterns at the outer edges and high turbulence at the centre as is shown in Figure 1.
• the design of the impeller 20 of Figures 3 to 5 has an aerofoil helicoidal central portion running laterally into a centrifugal accelerator portion, so that the air velocity is even across the entire inlet area providing a low inertia air entry. This also enables a larger inlet to impeller diameter ratio than is possible with the conventional impeller of Figures 1 and 2, thus substantially reducing inlet losses and noise and allowing a much closer than normal inlet clearance.
• the volute design is also modified relative to the volute of a conventional fan to allow, due to the impeller design, lower air discharge velocity than with a conventional fan.
• the impeller uses a long path accelerator to impart kinetic energy to the air providing increased lateral flow and obviating the need for a close throat plate on the discharge. All of the foregoing enable a very much narrower fan than would usually be expected to achieve the airflows, static pressures and noise levels attained.
• the lower velocity of the air leaving the blades with reduced swirl allows a fan of reduced depth according to the present invention to match or exceed the flow rate of a conventional fan since a more even flow into and from the fan can be achieved over wider ducting. This is in spite of the reduced depth of the ducting.
• the fan shown in Figures 3 to 7 has an aerofoil section to bring the air into the centre part of the impeller, effectively creating an axial portion. Since the fan has combined flow, the long path accelerator accelerates the air flow.
• the motor for the fan is preferably a four pole motor running at 50 Hz, so that the fan is rotating at approximately 1500 rpm.
• two pole motors may be preferred for smaller diameter impellers.
• the fan according to the invention must have an odd number of blades, for example, 5 or 7.
• An even number of blades leads to noise problems due to the blade passage frequencies which would be generated.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Structures Of Non-Positive Displacement Pumps (AREA)
• Motorcycle And Bicycle Frame (AREA)
• Motor Or Generator Cooling System (AREA)
• Toys (AREA)

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Cited By (1)

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• 2006
  • 2006-01-25 GB GBGB0601449.2A patent/GB0601449D0/en not_active Ceased
• 2007
  • 2007-01-19 AT AT07704934T patent/ATE433054T1/de not_active IP Right Cessation
  • 2007-01-19 DE DE602007001234T patent/DE602007001234D1/de active Active
  • 2007-01-19 EP EP07704934A patent/EP1979623B1/de not_active Not-in-force
  • 2007-01-19 ES ES07704934T patent/ES2327291T3/es active Active
  • 2007-01-19 US US12/161,678 patent/US20100189557A1/en not_active Abandoned
  • 2007-01-19 NZ NZ569987A patent/NZ569987A/en not_active IP Right Cessation
  • 2007-01-19 WO PCT/GB2007/000152 patent/WO2007085798A1/en not_active Ceased
  • 2007-01-19 CN CN2007800104155A patent/CN101410627B/zh not_active Expired - Fee Related
  • 2007-01-19 AU AU2007209185A patent/AU2007209185B2/en not_active Ceased
• 2008
  • 2008-07-24 ZA ZA200806463A patent/ZA200806463B/xx unknown

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