WO2017202871A1

WO2017202871A1 - Axial flow fan with divergent and convergent flow duct

Info

Publication number: WO2017202871A1
Application number: PCT/EP2017/062471
Authority: WO
Inventors: Ian Conway; Jody Brown
Original assignee: Vent-Axia Group Limited
Priority date: 2016-05-23
Filing date: 2017-05-23
Publication date: 2017-11-30
Also published as: GB2550588B; GB2550588A; GB201609057D0

Abstract

An extractor fan, comprising a housing which includes an inlet through which a flow of air is drawn and an outlet from which a flow of air is expelled, a duct which defines a flow channel which fluidly connects the inlet to the outlet, and an impeller which is located within the flow channel to draw air from the inlet through the outlet, wherein the flow channel comprises a first channel section which has first and second ends and flares or tapers radially outwardly from the one end at the inlet and a second channel section which has first and second ends and flares or tapers radially inwardly to the outlet.

Description

AXIAL FLOW FAN WITH DIVERGENT AND CONVERGENT FLOW DUCT

The present invention relates to extractor fans, especially extractor fans which are capable of high flow rates with reduced noise.

Various extractor fans exist, and it is an aim of the present invention to provide for extractor fans with increased efficiency, in particular in providing for high flow rates, and especially in providing for reduced noise.

In one aspect the present invention provides an extractor fan, comprising a housing which includes an inlet through which a flow of air is drawn and an outlet from which a flow of air is expelled, a duct which defines a flow channel which fluidly connects the inlet to the outlet, and an impeller which is located within the flow channel to draw air from the inlet through the outlet, wherein the flow channel comprises a first channel section which has first and second ends and flares or tapers radially outwardly from the one end at the inlet and a second channel section which has first and second ends and flares or tapers radially inwardly to the outlet.

In another aspect the present invention provides an extractor fan, comprising a housing which includes an inlet through which a flow of air is drawn and an outlet from which a flow of air is expelled, a duct which defines a flow channel which fluidly connects the inlet to the outlet, an impeller which is located within the flow channel to draw air from the inlet through the outlet, and a flow guide which is disposed downstream of the impeller to confer directionality, optionally linearity, to a flow developed by the impeller, wherein the flow guide comprises a hub which has a leading edge and a trailing edge and comprises an annular member, which includes a plurality of apertures therein which allow for a radial flow of air in relation to the flow axis, and a plurality of blades which extend radially from the hub.

In a further aspect the present invention provides a grille for an extractor fan, comprising an air flow guide which comprises a plurality of guide elements which extend in spaced relation, wherein the guide elements comprise a plurality of first guide elements, which have a first length in the direction of the flow axis, and a plurality of second guide elements, which have a second length in the direction of the flow axis which is shorter than the first length of the first guide elements.

Preferred embodiments of the present invention will now be described hereinbelow by way of example only with reference to the accompanying drawings, in which :

Figure 1 illustrates a front perspective view of an extractor fan in accordance with one embodiment of the present invention;

Figure 2 illustrates a front perspective view of the extractor fan of Figure 1, with the front cover removed;

Figure 3 illustrates a longitudinal sectional view (along section I-I in Figure 1) of the extractor fan of Figure 1;

Figure 4 illustrates a perspective view of the impeller of the motorized impeller of the extractor fan of Figure 1;

Figure 5 illustrates a front view of the impeller of Figure 4;

Figure 6 illustrates a rear view of the impeller of Figure 4;

Figure 7 illustrates a side view of the impeller of Figure 4;

Figure 8 illustrates a perspective view of the flow guide of the extractor fan of Figure 1;

Figure 9 illustrates a front view of the impeller of Figure 8; Figure 10 illustrates a rear view of the impeller of Figure 8; and

Figure 11 illustrates a side view of the impeller of Figure 8.

The extractor fan comprises a housing 3 which includes an inlet 5 through which a flow of air is drawn and an outlet 7 from which a flow of air is expelled.

In this embodiment the housing 3 comprises a first, front housing part 11, which includes the inlet 5, and a rear housing part 15, which includes the outlet 7 and is fixed to a building structure, such as a wall.

In this embodiment the front housing part 11 includes an air flow guide 21 which is in registration with the inlet 5 an acts to regulate the air flow at the inlet 5.

In this embodiment the air flow guide 21 comprises a plurality of guide elements 23a, b which extend in spaced relation, substantially parallel to the flow axis X of the fan.

In this embodiment the guide elements 23a, b define a multi-element spiral which extends from a hub 25 at a central region on the flow axis X of the fan.

In this embodiment the guide elements 23, b comprise a plurality of first guide elements 23a, which have a first length II in the direction of the flow axis X, and a plurality of second guide elements 23b, which have a second length 12 in the direction of the flow axis X which is shorter than the first length II of the first guide elements 23a.

In this embodiment the length II of the first guide elements 23a is at least 1.2 times the length 12 of the second guide elements 23b.

In this embodiment the length II of the first guide elements 23a is at least 1.5 times the length 12 of at least ones of the second guide elements 23b. In one embodiment the length II of the first guide elements 23a is at least 2 times the length 12 of at least ones of the second guide elements 23b.

In this embodiment the second guide elements 23b have at least two different lengths 12', 12".

The fan further comprises a duct 29 which defines a flow channel 31 which fluidly connects the inlet 5 to the outlet 7, and a motorized impeller 35 which is located within the flow channel 31 to draw air from the inlet 5 through the outlet 7.

In this embodiment the duct 29 comprises a first duct part 37 which is fluidly connected to the inlet 5 and a second duct part 39 which is fluidly connected to the outlet 7.

In this embodiment the first duct part 37 includes at least one, here a plurality of engagement elements 41, and the second duct part 39 includes at least one, here a plurality of engagement elements 43, and the engagement elements 41, 43 interengage to define the duct 37.

In this embodiment the engagement elements 41, 43 comprise detents, with at least ones of the engagement elements 41, 43, here the second engagement elements 43, being formed as a resilient clip.

In this embodiment the flow channel 31 comprises a first channel section 47 which has first and second ends 51, 53 and flares or tapers radially outwardly from the one end 51 at the inlet 5 and a second channel section 55 which has first and second ends 57, 59 and flares or tapers radially inwardly to the outlet 7.

In this embodiment the first channel section 47 comprises a frusto-conical section. In this embodiment the second channel section 55 comprises a frusto-conical section.

In this embodiment the first and second channel sections 47, 55 have axial lengths 13, 14, and the adjacent ends 53, 57 of the first and second channel sections 47, 55 are separated by a distance d which is less than the axial lengths 13, 14 of either of the first and second channel sections 47, 55.

In one embodiment the distance d between the adjacent ends 53, 57 of the first and second channel sections 47, 55 is less than half the axial lengths 13, 14 of either of the first and second channel sections 47, 55.

In one embodiment the distance d between the adjacent ends 53, 57 of the first and second channel sections 47, 55 is less than one third of the axial lengths 13, 14 of either of the first and second channel sections 47, 55.

In one embodiment the distance d between the adjacent ends 53, 57 of the first and second channel sections 47, 55 is less than one quarter of the axial lengths 13, 14 of either of the first and second channel sections 47, 55.

In this embodiment the axial length 13 of the first channel section 47 is greater than the axial length 14 of the second channel section 55.

In this embodiment the embodiment the motorized impeller assembly 35 comprises an impeller 61 and a drive motor 63 which is operative to drive the impeller 61.

In this embodiment the impeller 61 is disposed substantially within a region which is defined by the first channel section 47 of the flow channel 31.

In this embodiment the impeller 61 is an axial impeller. In this embodiment the impeller 61 comprises a hub 65 and a plurality of blades 67 which extend radially from the hub 65.

In this embodiment the impeller 61 comprises five blades 67.

In one embodiment the impeller 61 comprises not more than six blades 67.

In this embodiment the blades 67 are forward curved in relation to the flow axis X of the fan.

In this embodiment the blades 67 have a generally rectangular form.

In this embodiment the blades 67 have an inner edge 71, which is connected to the hub 65, an outer edge 73, which extends adjacent a surface defined by the first channel section 47 and has a leading end 73a and a trailing end 73b, a leading edge 75, and a trailing edge 77.

In this embodiment the trailing edge 77 comprises a first, radially-inner section 81, which extends substantially perpendicular to the flow axis X, and a second, radially-outer section 83, which is inclined or tapered in an upstream direction towards the inlet 5.

In this embodiment the inner section 81 has a projected radial length 15 and the outer section 83 has a projected radial length 16, and the length 15 of the inner section 81 is greater than the length 16 of the outer section 83.

In this embodiment the inner section 81 has a notch 91, here a single notch, which has a length 17 at the trailing edge 77 and extends towards the leading edge 75 by a distance h.

In this embodiment the length 17 is greater than half of the length 15 of the first section 81 of the trailing edge 77. In this embodiment the notch 91 is V-shaped.

In this embodiment the notch 91 with a first, inner edge section 93 and a second, outer edge section 95.

In this embodiment the inner edge section 93 is a linear edge.

In this embodiment the outer edge section 95 is a linear edge.

In this embodiment the inner edge section 93 has a length 18 and the outer edge section 95 has a length 19, and the length 18 of the inner edge section 93 is greater than the length 19 of the outer edge section 95.

In this embodiment the length 18 of the inner edge section 93 is at least 1.5 times longer than the length 19 of the outer edge section 95.

In this embodiment the length 18 of the inner edge section 93 is at least 1.2 times longer than the length 19 of the outer edge section 95.

In this embodiment the inner and outer edge sections 93, 95 of the notch 91 enclose an angle of substantially 90 degrees.

In one alternative embodiment the inner and outer edge sections 93, 95 of the notch 91 could enclose an angle of greater than 90 degrees.

In another alternative embodiment the inner and outer edge sections 93, 95 of the notch 91 could enclose an angle of less than 90 degrees.

In this embodiment the hub 65 includes a support 101 to which the blades 67 are attached, and the support 101 is formed so as to have sufficient flexibility that, with increasing rotational speed of the impeller 61, the trailing ends 73b of the outer edges 73 of the blades 67 splay progressively outwardly in relation to the leading ends 73a of the outer edges 73 of the blades 67, such that the space between the outer edges 73 of the blades 67 and the first channel section 47 of the flow channel 31 is progressively closed to provide for a predetermined, minimum spacing at a given, maximum rotational speed.

In this embodiment the support 101 is formed so as to have flexibility, which allows the trailing ends of the blades 67 to splay outwardly.

In this embodiment the support 101 is formed as an annular member, here as a collar, to which the blades 67 are attached at spaced intervals.

In an alternative embodiment the support 101 could be formed as a plurality of separate members to each of which is attached a respective one of the blades 67.

With this arrangement, at lower speeds, at which the fan would operate for longer durations, the spacing between the outer edges 73 of the blades 67 and the first channel section 47 of the flow channel 31 is greater, allowing for quieter operation, albeit at reduced efficiency, and at higher speeds, at which the fan would usually operate for short durations, the spacing between the outer edges 73 of the blades 67 and the first channel section 47 of the flow channel 31 is reduced, allowing for increasing efficiency, albeit at increased noise, which is acceptable for the shorter durations.

In this embodiment the fan further comprises a flow guide 121 which is disposed downstream, here juxtaposed, of the impeller 61, and confers linearity to the flow developed by the impeller 61.

In this embodiment the flow guide 121 is disposed substantially within a region which is defined by the second channel section 49 of the flow channel 31.

In this embodiment the flow guide 121 comprises a fixed, static structure. In this embodiment the flow guide 121 comprises a hub 125 which has a leading edge 126a and a trailing edge 126b, and a plurality of blades 127 which extend radially from the hub 125.

In this embodiment the hub 125 comprises an annular member 128, here in the form of a collar, which includes a plurality of apertures 129 therein, which allow for a radial flow of air in relation to the flow axis X of the fan. The present inventors have recognized surprisingly that a linear flow of air can still be achieved from the flow guide 121 notwithstanding the provision of the radial-flow apertures 129, which allow for an increased air flow.

In this embodiment the apertures 129 are disposed intermediate respective ones of the adjacent blades 127.

In this embodiment the apertures 129 are disposed at the trailing edge 126b of the hub 125, here opening to the trailing edge 126b of the hub 125.

In this embodiment the flow guide 121 comprises eight blades 127.

In one embodiment the flow guide 121 comprises not more than ten blades 127.

In this embodiment the number of blades 127 on the flow guide 121 is greater than the number of blades 127 on the impeller 61.

In this embodiment the blades 67 are curved, here backward curved in relation to the flow axis X of the fan.

In this embodiment the blades 127 have a generally rectangular form.

In this embodiment the blades 127 have an inner edge 131, which is connected to the hub 125, an outer edge 133, which extends adjacent a surface defined by the second channel section 49, a leading edge 135, and a trailing edge 137.

In this embodiment the leading edge 135 is a linear edge.

In this embodiment the leading edges 135 of the blades 127 are located on substantially a common plane, which is orthogonal to the flow axis X of the fan.

In this embodiment the leading edges 135 of the blades 127 are disposed adjacent, here juxtaposed, to the trailing edges 77 of the blades 67 of the impeller 61.

Finally, it will be understood that the present invention has been described in its preferred embodiments and can be modified in many different ways without departing from the scope of the appended claims.

Claims

1. An extractor fan, comprising a housing which includes an inlet through which a flow of air is drawn and an outlet from which a flow of air is expelled, a duct which defines a flow channel which fluidly connects the inlet to the outlet, and an impeller which is located within the flow channel to draw air from the inlet through the outlet, wherein the flow channel comprises a first channel section which has first and second ends and flares or tapers radially outwardly from the one end at the inlet and a second channel section which has first and second ends and flares or tapers radially inwardly to the outlet.

2. The extractor fan of claim 1, wherein the duct comprises a first duct part which is fluidly connected to the inlet and a second duct part which is fluidly connected to the outlet.

3. The extractor fan of claim 1 or 2, further comprising an air flow guide which is in registration with the inlet and acts to regulate the air flow at the inlet, wherein the air flow guide comprises a plurality of guide elements which extend in spaced relation, optionally substantially parallel to the flow axis.

4. The extractor fan of claim 3, wherein the guide elements define a multielement spiral which extends from a hub at a central region on the flow axis.

5. The extractor fan of claim 3 or 4, wherein the guide elements comprise a plurality of first guide elements, which have a first length in the direction of the flow axis, and a plurality of second guide elements, which have a second length in the direction of the flow axis which is shorter than the first length of the first guide elements.

6. The extractor fan of claim 5, wherein the length of the first guide elements is at least 1.2 times the length of the second guide elements.

7. The extractor fan of claim 5, wherein the length of the first guide elements is at least 1.5 times the length of at least ones of the second guide elements.

8. The extractor fan of any of claims 1 to 7, wherein the first channel section comprises a frusto-conical section .

9. The extractor fan of any of claims 1 to 8, wherein the second channel section comprises a frusto-conical section .

10. The extractor fan of any of claims 1 to 9, wherein the first and second channel sections have axial lengths, and adjacent ends of the first and second channel sections are separated by a distance which is less than the axial length of either of the first and second channel sections.

11. The extractor fan of claim 10, wherein the distance between the adjacent ends of the first and second channel sections is less than one half the axial length of either of the first and second channel sections.

12. The extractor fan of claim 10, wherein the distance between the adjacent ends of the first and second channel sections is less than one third the axial length of either of the first and second channel sections.

13. The extractor fan of claim 10, wherein the distance between the adjacent ends of the first and second channel sections is less than one quarter the axial length of either of the first and second channel sections.

14. The extractor fan of any of claims 10 to 13, wherein the axial length of the first channel section is greater than the axial length of the second channel section.

15. The extractor fan of any of claims 1 to 14, wherein the impeller is disposed substantially within a region which is defined by the first channel section of the flow channel.

16. The extractor fan of any of claims 1 to 15, wherein the impeller is an axial impeller.

17. The extractor fan of any of claims 1 to 16, wherein the impeller comprises a plurality of blades.

18. The extractor fan of claim 17, wherein the impeller comprises not more than six blades.

19. The extractor fan of claim 17 or 18, wherein the blades are forward curved in relation to the flow axis.

20. The extractor fan of any of claims 17 to 19, wherein the blades have a generally rectangular form.

21. The extractor fan of any of claims 17 to 20, wherein the blades have an inner edge, an outer edge, which extends adjacent a surface defined by the first channel section and has a leading end and a trailing end, a leading edge, and a trailing edge.

22. The extractor fan of claim 21, wherein the trailing edge comprises a first, radially-inner section, which extends substantially perpendicular to the flow axis, and a second, radially-outer section, which is inclined or tapered in an upstream direction towards the inlet.

23. The extractor fan of claim 22, wherein the radially-inner section has a projected radial length and the radially-outer section has a projected radial length, and the length of the radially-inner section is greater than the length of the radially-outer section.

24. The extractor fan of claim 22 or 23, wherein the radially inner section includes a notch, optionally a single notch, which has a length at the trailing edge and extends towards the leading edge by a distance.

25. The extractor fan of claim 24, wherein the length of the notch is greater than half of the length of the radially-inner section of the trailing edge.

26. The extractor fan of claim 24 or 25, wherein the notch is V-shaped.

27. The extractor fan of any of claims 24 to 26, wherein the notch has a first, inner edge section and a second, outer edge section.

28. The extractor fan of claim 27, wherein the inner edge section of the notch is a linear edge.

29. The extractor fan of claim 27 or 28, wherein the outer edge section of the notch is a linear edge.

30. The extractor fan of any of claims 27 to 29, wherein the inner edge section has a length and the outer edge section has a length, and the length of the inner edge section is greater than the length of the outer edge section.

31. The extractor fan of claim 30, wherein the length of the inner edge section is at least 1.5 times longer than the length of the outer edge section.

32. The extractor fan of claim 30, wherein the length of the inner edge section is at least 1.75 times longer than the length of the outer edge section.

33. The extractor fan of any of claims 27 to 32, wherein the inner and outer edge sections of the notch enclose an angle of about 90 degrees.

34. The extractor fan of any of claims 27 to 32, wherein the inner and outer edge sections of the notch enclose an angle of greater than 90 degrees.

35. The extractor fan of any of claims 27 to 32, wherein the inner and outer edge sections of the notch enclose an angle of less than 90 degrees.

36. The extractor fan of any of claims 17 to 35, wherein the impeller comprises a hub to which the blades are attached.

37. The extractor fan of claim 36, wherein the hub includes a support to which the blades are attached, and the support is formed such that, with increasing rotational speed of the impeller, the trailing ends of the outer edges of the blades splay progressively outwardly in relation to the leading ends of the outer edges of the blades, whereby a space between the outer edges of the blades and the first channel section of the flow channel is progressively closed to provide for a predetermined minimum spacing at a predetermined maximum rotational speed.

38. The extractor fan of claim 37, wherein the support is formed so as to have flexibility, which allows the trailing ends of the blades to splay outwardly.

39. The extractor fan of claim 37 or 38, wherein the support is formed as an annular member, optionally as a collar, to which the blades are attached at spaced intervals.

40. The extractor fan of claim 37 or 38, wherein the support is formed as a plurality of separate members to each of which is attached a respective one of the blades.

41. The extractor fan of any of claims 1 to 40, further comprising a flow guide which is disposed downstream, optionally juxtaposed, of the impeller to confer directionality, optionally linearity, to the flow developed by the impeller.

42. The extractor fan of claim 41, wherein the flow guide is disposed substantially within a region which is defined by the second channel section of the flow channel.

43. The extractor fan of claim 41 or 42, wherein the flow guide comprises a fixed, static structure.

44. The extractor fan of any of claims 41 to 43, wherein the flow guide comprises a hub which has a leading edge and a trailing edge, and a plurality of blades which extend radially from the hub.

45. The extractor fan of claim 44, wherein the hub comprises an annular member, optionally in the form of a collar, which includes a plurality of apertures therein, which allow for a radial flow of air in relation to the flow axis.

46. The extractor fan of claim 45, wherein the apertures in the hub are disposed intermediate respective ones of the adjacent blades.

47. The extractor fan of claim 45 or 46, wherein the apertures are disposed at the trailing edge of the hub, optionally opening to the trailing edge of the hub.

48. The extractor fan of any of claims 44 to 47, wherein the flow guide comprises not more than ten blades.

49. The extractor fan of any of claims 41 to 48, wherein the number of blades on the flow guide is greater than the number of blades on the impeller.

50. The extractor fan of any of claims 41 to 49, wherein the blades on the flow guide are curved, optionally backward curved in relation to the flow axis.

51. The extractor fan of any of claims 41 to 50, wherein the blades on the flow guide have a generally rectangular form.

52. The extractor fan of any of claims 41 to 51, wherein the blades on the flow guide have an inner edge, which is connected to the hub, an outer edge, which extends adjacent a surface defined by the second channel section, a leading edge, and a trailing edge.

53. The extractor fan of claim 52, wherein the leading edge of the blades on the flow guide is a linear edge.

54. The extractor fan of claim 53, wherein the leading edges of the blades on the flow guide are located on substantially a common plane, optionally orthogonal to the flow axis.

55. The extractor fan of claim 54, wherein the leading edges of the blades on the flow guide are disposed adjacent, here juxtaposed, to the trailing edges of the blades of the impeller.

56. An impeller for an extractor fan, comprising a plurality of blades which each have a leading edge and a trailing edge, wherein the trailing edge include a notch, optionally a single notch, which has a length along the trailing edge and extends by a distance towards the leading edge.

57. The impeller of claim 56, wherein the trailing edge comprises a first, radially-inner section, which extends substantially perpendicular to the flow axis, and a second, radially-outer section, which is inclined or tapered in a direction towards the leading edge.

58. The impeller of claim 57, wherein the radially-inner section has a projected radial length and the radially-outer section has a projected radial length, and the length of the radially-inner section is greater than the length of the radially-outer section.

59. The impeller of claim 57 or 58, wherein the notch is disposed in the radially-inner section.

60. The impeller of claim 59, wherein the length of the notch is greater than half of the length of the radially-inner section of the trailing edge.

61. The impeller of any of claims 57 to 60, wherein the notch is V-shaped.

62. The impeller of any of claims 57 to 61, wherein the notch has a first, inner edge section and a second, outer edge section.

63. The impeller of claim 62, wherein the inner edge section of the notch is a linear edge.

64. The impeller of claim 62 or 63, wherein the outer edge section of the notch is a linear edge.

65. The impeller of any of claims 62 to 64, wherein the inner edge section has a length and the outer edge section has a length, and the length of the inner edge section is greater than the length of the outer edge section.

66. The impeller of claim 65, wherein the length of the inner edge section is at least 1.5 times longer than the length of the outer edge section.

67. The impeller of claim 65, wherein the length of the inner edge section is at least 1.75 times longer than the length of the outer edge section.

68. The impeller of any of claims 62 to 67, wherein the inner and outer edge sections of the notch enclose an angle of about 90 degrees.

69. The impeller of any of claims 62 to 67, wherein the inner and outer edge sections of the notch enclose an angle of greater than 90 degrees.

70. The impeller of any of claims 62 to 67, wherein the inner and outer edge sections of the notch enclose an angle of less than 90 degrees.

71. The impeller of any of claims 56 to 70, wherein the impeller comprises a hub to which the blades are attached.

72. The impeller of claim 71, wherein the hub includes a support to which the blades are attached, and the support is formed such that, with increasing rotational speed of the impeller, the trailing ends of the outer edges of the blades splay progressively outwardly in relation to the leading ends of the outer edges of the blades.

73. The impeller of claim 72, wherein the support is formed so as to have flexibility, which allows the trailing ends of the blades to splay outwardly.

74. The impeller of claim 72 or 73, wherein the support is formed as an annular member, optionally as a collar, to which the blades are attached at spaced intervals.

75. The impeller of claim 72 or 73, wherein the support is formed as a plurality of separate members to each of which is attached a respective one of the blades.

76. An extractor fan, comprising a housing which includes an inlet through which a flow of air is drawn and an outlet from which a flow of air is expelled, a duct which defines a flow channel which fluidly connects the inlet to the outlet, an impeller which is located within the flow channel to draw air from the inlet through the outlet, and a flow guide which is disposed downstream of the impeller to confer directionality, optionally linearity, to a flow developed by the impeller, wherein the flow guide comprises a hub which has a leading edge and a trailing edge and comprises an annular member, which includes a plurality of apertures therein which allow for a radial flow of air in relation to the flow axis, and a plurality of blades which extend radially from the hub.

77. The extractor fan of claim 76, wherein the hub has the form of a collar.

78. The extractor fan of claim 76 or 77, wherein the flow guide is juxtaposed the impeller.

79. The extractor fan of any of claims 76 to 78, wherein the flow guide comprises a fixed, static structure.

80. The extractor fan of any of claims 76 to 79, wherein the apertures in the hub are disposed intermediate respective ones of the adjacent blades.

81. The extractor fan of any of claims 76 to 80, wherein the apertures are disposed at the trailing edge of the hub, optionally opening to the trailing edge of the hub.

82. The extractor fan of any of claims 76 to 81, wherein the flow guide comprises not more than ten blades.

83. The extractor fan of any of claims 76 to 82, wherein the number of blades on the flow guide is greater than the number of blades on the impeller.

84. The extractor fan of any of claims 76 to 83, wherein the blades on the flow guide are curved, here backward curved in relation to the flow axis.

85. The extractor fan of any of claims 76 to 84, wherein the blades on the flow guide have a generally rectangular form.

86. The extractor fan of any of claims 76 to 85, wherein the blades on the flow guide have a leading edge, and a trailing edge.

87. The extractor fan of claim 86, wherein the leading edge of the blades on the flow guide is a linear edge.

88. The extractor fan of claim 87, wherein the leading edges of the blades on the flow guide are located on substantially a common plane, optionally orthogonal to the flow axis.

89. The extractor fan of claim 88, wherein the leading edges of the blades on the flow guide are disposed adjacent, here juxtaposed, to the trailing edges of the blades of the impeller.

90. A grille for an extractor fan, comprising an air flow guide which comprises a plurality of guide elements which extend in spaced relation, wherein the guide elements comprise a plurality of first guide elements, which have a first length in the direction of the flow axis, and a plurality of second guide elements, which have a second length in the direction of the flow axis which is shorter than the first length of the first guide elements.

91. The grille of claim 90, wherein the guide elements extend substantially parallel to the flow axis.

92. The grille of claim 90 or 91, wherein the grille is an inlet grille.

93. The grille of any of claim 90 to 92, wherein the guide elements define a multi-element spiral which extends from a hub at a central region.

94. The grille of claim 93, wherein the length of the first guide elements is at least 1.2 times the length of the second guide elements.

95. The grille of claim 93, wherein the length of the first guide elements is at least 1.5 times the length of at least ones of the second guide elements.

96. The grille of claim 93, wherein the length of the first guide elements is at least 2 times the length of at least ones of the second guide elements.