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Title:
AXIAL FLOW FAN WITH OPTIMISED BLADE TWIST CLOSE TO THE IMPELLER HUB
Document Type and Number:
WIPO Patent Application WO/2018/036598
Kind Code:
A1
Abstract:
Disclosed is an axial flow fan comprising a hub rotatable about an axis; an annular shroud extending concentric with said axis in a radial distance from said hub; a plurality of fan blades connected at a root end to said hub and having a free tip end extending radially towards said shroud, and a fan driver coupled to said hub and arranged for driving the rotation of said hub around the axis.

Inventors:
DYBDAHL, Jens (Møllebakken 9, Gludsted, 7361 Ejstrupholm, 7361, DK)
Application Number:
DK2017/050272
Publication Date:
March 01, 2018
Filing Date:
August 22, 2017
Export Citation:
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Assignee:
DACS A/S (Falkevej 18, 8766 Nørre Snede, 8766, DK)
International Classes:
F04D29/38
Domestic Patent References:
WO2015090318A12015-06-25
Foreign References:
US20040165986A12004-08-26
Attorney, Agent or Firm:
ZACCO DENMARK A/S (Arne Jacobsens Allé 15, 2300 København S, 2300, DK)
Download PDF:
Claims:
ims

An axial flow fan (1) comprising:

- a hub (3) rotatable about an axis (4);

- an annular shroud (6) extending concentric with said axis (4) in a radial distance from said hub (3);

- a plurality of fan blades (2) connected at a root end (1 1) to said hub (3) and having a free tip end (7) extending radially towards said shroud (6),

- a fan driver coupled to said hub and arranged for driving the rotation of said hub around the axis,

wherein for R being the radial distance from said axis (4) to the free tip end (7) of the blade and r being the radial distance from said axis (4), the plurality of fan blades (2) each comprises a root area extending from a radial positon of r/R=0.17 to a radial positon of r/R=0.34, the root area having a root angle AQmot extending between the chord of the blade at any radial position in the root area and the chord at the radial position of r/R=0.34, wherein ΔΘΓ00ι substantially follows a curve define 2. An axial flow fan according to claim 1 , wherein the plurality of fan blades each comprises a middle area extending from the radial positon of r/R=0.34 to the radial position of r/R=0.72, the middle area having a middle angle A9midd|e extending between the chord of the blade at any radial position in the middle area and the chord at the radial position of r/R=0.72, wherein Aemiddte substantially follows a curve defined as:

3. An axial flow fan according to claim 1 or 2, wherein the plurality of fan blades each comprises a tip area extending from the radial positon of r/R=0.72 to the tip of the free tip end at r/R=1 , the tip area having a tip angle Δθ(ίρ extending between the chord of the blade at any radial position in the tip area and the chord at the radial position of r/R=1 , wherein Δθ(ίρ substantially follows a curve defined as:

An axial flow fan according to any of the preceding claims, wherein the angle Θ between a plane of rotation of the blades and the chord of the blade at the radial position of r/R=0.34 is in the range of 20° to 40°, preferably in the range of 25 to 35°, such as substantially 31.9°.

5. An axial flow fan according to any preceding claim, wherein:

- the angle AQmot deviates less than 4°, preferably less than 3°, more

preferably less than 2°, even more preferably less than 1 ° from the curve defined by the equation within the root area; and/or

- the angle A0middie deviates less than 4°, preferably less than 3°, more preferably less than 2°, even more preferably less than 1 ° from the curve defined by the equation within the middle area; and/or

- the angle Δθ(ίρ deviates less than 4°, preferably less than 3°, more

preferably less than 2°, even more preferably less than 1 ° from the curve defined by the equation within the tip area.

An axial flow fan according to any preceding claim, wherein R is in the range of 500 to 900 millimetres.

An axial flow fan according to any preceding claim, wherein the chord increases in the root area from the hub towards the radial position of r/R=0.34, flattens out until the radial position of r/R=0.40 and decreases towards the tip of the blade at the radial position of r/R=1 . 8. An axial flow fan according to any preceding claim, wherein the inner radius of the annular shroud is in the range of 600 to 1500 millimetres.

9. An axial flow fan according to any preceding claim, wherein the radius {Rhub) of the hub is in the range of 50 to 150 millimetres.

An axial flow fan according to any preceding claim comprising a diffuser (10) arranged concentric with said axis (4) at a downstream position of the annular shroud (6).

An axial flow fan according to claim 10, wherein the diffuser (10) has a conical shape with a diffusion angle in the range of 2 to 15° to the axis (4) of rotation of the rotor, preferably in the range of 6 to 10°.

An axial flow fan according to any preceding claim comprising an inlet part (9) provided with a bellmouth arranged concentric with said axis (4) at an upstream position of the annular shroud (6).

An axial flow fan according to any preceding claim, wherein the hub (3) comprises

a seating part (16) allowing the blades (2) to be arranged in a plurality of blade pitch angles, and

blade locking part (18) for locking the blade pitch angle of the at least one blade (2) into a specific blade pitch angle,

wherein said locking part (18, 18a, 18b, 18c) is designed to lock said blade (2) into one specific blade pitch angle only.

An axial flow fan according to claim 13, comprising one locking part (18, 18a, 18b, 18c) for each of the blades (2).

15. An axial flow fan according to claim 13 or 14, wherein the blades (2) each

comprises a recess cooperating with a corresponding pin (20, 20a, 20b, 20c) of the locking part (18, 18a, 18b, 18c).

Description:
AXIAL FLOW FAN WITH OPTIMISED BLADE TWIST CLOSE TO THE IMPELLER HUB

The invention relates to an axial flow fan with an improved wing design. Background

Axial flow fans are well known in the art and many different designs have been proposed and manufactured in order to improve the performance of the fan, in particular with respect to generation of noise and improved power efficiency. It is an object of the present invention to provide an improved fan design to improve the efficiency of the fan.

Description of the invention

Disclosed herein is an axial flow fan comprising a hub rotatable about an axis; an annular shroud extending concentric with said axis in a radial distance from said hub; a plurality of fan blades connected at a root end to said hub and having a free tip end extending radially towards said shroud, and a fan driver coupled to said hub and arranged for driving the rotation of said hub around the axis.

For R being the radial distance from said axis to the free tip end of the blade and r being the radial distance from said axis, the plurality of fan blades each comprises a root area extending from a radial positon of r/R=0.17 to a radial positon of r/R=0.34, the root area having a root angle AQ rool extending between the chord of the blade at any radial position in the root area and the chord at the radial position of r/R=0.34, wherein ΔΘ Γ00 ι substantially follows a curve defined as:

WO 2015/090318 also discloses an example of an axial flow fan with a number of the wings designed for reducing the power consumption by gradually angling the wings. The chord angle in WO 2015/090318 is significantly steeper than the chord angle obtained with the above axial flow fan, which has shown to introduce an improved efficiency of 15% in terms of improved energy efficiency. The blades normally have a steeper chord angle Θ at the region near the hub and tends to drive the core of the flow right after the rotor in a so-called forced vortex, which appear to improve the efficiency of the fan. The region directly next to the hub, i.e. between the hub and the radial distance of r/R=0.17, the angle may also be adequately described by the above equation. The deviation between the measured angle value and AQ mo t will however normally be larger than the deviation in the root area, where r/R=0.17-0.34. By substantially is meant a deviation of up to 5°.

In one or more embodiments, the angle ΔΘ Γ00 ι deviates less than 4° from the curve defined by the equation within the root area.

In one or more embodiments, the angle ΔΘ Γ00 ι deviates less than 3° from the curve defined by the equation within the root area. In one or more embodiments, the angle ΔΘ Γ00 ι deviates less than 2° from the curve defined by the equation within the root area.

In one or more embodiments, the angle ΔΘ Γ00 ι deviates less than 1 ° from the curve defined by the equation within the root area.

The angle ΔΘ Γ00 ι may also deviate less than 4° from the curve defined by the equation within the root area for r/R values up to r/R=0.47.

In one or more embodiments the plurality of fan blades each comprises a middle area extending from the radial positon of r/R=0.34 to the radial position of r/R=0.72, the middle area having a middle angle Ae midd i e extending between the chord of the blade at any radial position in the middle area and the chord at the radial position of r/R=0.72, wherein Ae midd i e substantially follows a curve defined as: By substantially is meant a deviation of up to 5°. In one or more embodiments, the angle A9 midd | e deviates less than 4° from the curve defined by the equation within the middle area. In one or more embodiments, the angle A9 midd | e deviates less than 3° from the curve defined by the equation within the middle area.

In one or more embodiments, the angle A9 midd i e deviates less than 2° from the curve defined by the equation within the middle area.

In one or more embodiments, the angle A9 midd i e deviates less than 1 ° from the curve defined by the equation within the middle area.

The angle A9 midd i e may also deviate less than 4° from the curve defined by the equation within the middle area for r/R values lying outside the middle area. In one or more embodiments, the angle Ae middte deviates less than 4° from the curve defined by the equation within the middle area for r/R=0.23-1. Thus there is a 'root- middle' area for values between r/R=0.23 and r/R=0.47, where the root area and the middle area overlaps and where the angle ΔΘ continuously changes from the description given for the root area and that of the middle area.

In one or more embodiments, the plurality of fan blades each comprises a tip area extending from the radial positon of r/R=0.72 to the tip of the free tip end at r/R=1 , the tip area having a tip angle Δθ (ίρ extending between the chord of the blade at any radial position in the tip area and the chord at the radial position of r/R=1 , wherein Δθ ( ,ρ substantially follows a curve defined as:

By substantially is meant a deviation of up to 5°. In one or more embodiments, the angle Δθ (ίρ deviates less than 4° from the curve defined by the equation within the tip area. In one or more embodiments, the angle Δθ (ίρ deviates less than 3° from the curve defined by the equation within the tip area.

In one or more embodiments, the angle Δθ (ίρ deviates less than 2° from the curve defined by the equation within the tip area.

In one or more embodiments, the angle Δθ (ίρ deviates less than 1 ° from the curve defined by the equation within the tip area. The angle Δθ (ίρ may also deviate less than 4° from the curve defined by the equation within the tip area for r/R values lying outside the tip area. In one or more embodiments, the angle Δθ (ίρ deviates less than 4° from the curve defined by the equation within the tip area for r/R=0.51 -0.72. Thus, there is a 'middle-tip' area for values between r/R=0.51 and r/R=1 , where the middle area and the tip area overlaps and where the angle ΔΘ continuously changes from the description given for the middle area and that of the tip area.

In one or more embodiments, the angle Θ between a plane of rotation of the blades and the chord of the blade at the radial position of r/R=0.34 is in the range of 20° to 40°, preferably in the range of 25 to 35°, such as substantially 31 .9°.

In one or more embodiments, R is in the range of 500 to 900 millimetres, such as 600 to 800 millimetres, or such as 650 to 750 millimetres. In one or more embodiments, the chord increases in the root area from the hub towards the radial position of r/R=0.34, flattens out until the radial position of r/R=0.40 and decreases towards the tip of the blade at the radial position of r/R=1.

In one or more embodiments, the inner radius of the annular shroud is in the range of 600 to 1500 millimetres, such as 700 to 1300 millimetres, or such as 800 to 900 millimetres. The inner radius of the annular shroud is normally smaller than R.

In one or more embodiments, the radius (R hub ) of the hub is in the range of 50 to 150 millimetres, such as 60 to 120 millimetres, or such as 70 to 80 millimetres. The fan may further comprise a diffuser arranged concentric with said axis at a downstream position of the annular shroud. In one or more embodiments, the diffuser has a conical shape with a diffusion angle in the range of 2 to 15° to the axisof rotation of the rotor, preferably in the range of 6 to 10°.

The fan may also further comprise an inlet part provided with a bellmouth arranged concentric with said axis at an upstream position of the annular shroud.

In one or more embodiments, the hub comprises a seating part allowing the blades to be arranged in a plurality of blade pitch angles, and blade locking part for locking the blade pitch angle of the at least one blade into a specific blade pitch angle, wherein said locking part is designed to lock said blade into one specific blade pitch angle only.

In one or more embodiments, there is one locking part for each of the blades. In one or more embodiments, the blades each comprises a recess cooperating with a corresponding pin of the locking part.

Brief description of the drawings

Figure 1 shows a perspective view of a hub part, three blades and three locking parts for an axial flow fan according to an aspect of the present invention.

Figure 2 shows a longitudinal schematic cross-section of an axial flow fan according to an aspect of the present invention. Figure 3 shows a blade of an axial flow fan according to the invention.

Figure 4 illustrates a cross-section of a blade together with the flow direction, the direction of blade movement and the angle Θ between the blade chord and the direction of movement. Figure 5 shows a blade of an axial flow fan according to the invention, where the blade is connected to a hub. Figure 6 illustrates a number of cross-sections of the blade in figure 5.

Figure 7 shows three different designs of the locking parts shown in the embodiment of the fan in figure 1. Description of preferred embodiments

An axial flow fan 1 according to an embodiment of the invention is shown in figures 1 and 2, where figure 1 shows a perspective view of an axial flow fan 1 and figure 2 shows a longitudinal schematic cross-section of an axial flow fan 1. The fan 1 comprises a hub 3 where to a plurality of fan blades 2 are connected at the root end 1 1 of the blades 2. The free tip end 7 of the blades 2 extend radially towards the shroud 6 as shown in figure 2. The fan 1 in figure 1 has three blades 2, but may as well be equipped with any convenient number of blades 2. It is generally preferred that the rotor 5 of the fan comprises from 3 to 6 blades.

The fan has a fan driver (not shown) coupled to the hub 3 and arranged for driving the rotation of the hub 3 around the axis 4 shown in figure 2. The fan driver may be arranged in the hub 3 or next to the hub 3 and be connected thereto by means of a drive arrangement, e.g. a belt drive (not shown).

The hub 3 and the blades 2 form a rotor 5, which is rotated about an axis 4 (see figure 2) by means of the fan driver, e.g. a motor. The rotor 5 is arranged inside the cylindrical shroud 6 which is concentric arranged about the axis 4 so there is a clearance between the tip 7 of the blades 2 and the shroud 6. The rotation of the rotor 5 drives a flow of air axially through the fan 1 in the direction of the arrow A as shown in figure 2. The flow path through the fan 1 is illustrated by streamlines 8 indicated in figure 2. The shroud 6 is preceded by an inlet part 9 arranged upstream of the shroud, i.e. in the direction against the driven flow A, where the inlet part 9 also is concentric with the axis 4 and comprises a bellmouth to smoothen the flow at the inlet part 9 in order to avoid separation of the flow.

The passage of the air flow through the rotor 5 causes a pressure increase which is further increased by regained part of the kinetic energy present in of the air flow immediately after the rotor due to the axial velocity component by means of a diffuser 10 arranged downstream of the shroud 6 and concentric with the axis 4. The diffuser 10 has a conical shape with an diffusion angle of 8.5° to the centre line, i.e. to the axis 4 of rotation of the rotor 5. The blades 2 are attached by their root end 11 to the hub 3, preferably in a manner discussed later.

A single blade 2 of the fan 1 is shown in figure 3 where the axis 4 of rotation of the rotor 5 is indicated, the distance R from the axis 4 and to the tip end 7 of the blade 2 and an indication of the radial position of r/R=0.34, i.e. where the distance r from the axis 4 is 0.34 times the radial position R of the blade tip end 7.

A cross section of a fan blade 2 is shown in figure 4 with indication of the leading edge 12 of the blade 2 as well as the trailing edge 13 of the blade 2. The chord line 14 is extending between the leading edge 12 and the trailing edge 13, and the length of the chord of the blade 2 is defined by the distance between the leading edge 12 and the trailing edge 13. The blade 2 is moved in the direction indicated as M on figure 4 due to the rotation of the rotor 5 of the fan 1 during operation thereof.

The angle Θ between the chord line 14 and the direction of movement M is indicated on figure 4 together with the direction A of the incoming air flow. The direction A is depicted as being perpendicular to the direction M of movement which is generally the case for an axial flow fan 1.

Figure 5 shows a blade 2 according to the invention connected to by the root end 1 1 to a hub 3. A number of cross sectional cut from the first cross sectional cut A-A starts at the root end 11 to the last cross sectional cut 40-40 at the tip end 7 of the blade 2 are marked in figure 5. The cross sectional cuts are evenly distributed over the length of the blade 2.

Figure 6 shows selected examples of the cross sectional cuts of the blade 2 shown in figure 5. The angle Θ between the chord line 14 and the direction of movement M are listed in the cross sectional cuts in figure 6 along with a value of the chord length. Table 1 lists the values for the chord length, the angle Θ between the chord line 14 and the direction of movement M, the radial distance r at the different cross sectional cuts of the blade 2 shown in figure 5.

Table 1 also shows the values of angle Θ calculated using equations 1-3 given

where for R is the radial distance from the axis 4 to the free tip end 7 of the blade 2 and r is the radial distance from the axis.

Table 1

Θ Dev. Θ Dev. Dev. Θ

Cut r/R r Θ Chord

Eq. 1 Eq. 1 Eq. 2 Eq. 2 Eq. 3 Eq. 3

[-] [-] [m] Π [m] Π Π Π Π Π Π

A 0,1 00 0,072 52,70 0, 122 55,73 -3, 03 65,58 -12,88 39,67 13,03

B 0,1 14 0,082 51 ,14 0, 127 52,89 -1, 75 62,61 -11,47 36,93 14,21

C 0,127 0,092 49,40 0, 135 50,37 -0, 97 59,78 -10,38 34,63 14, 77

D 0,141 0, 102 47,75 0, 138 48,12 -0,37 57,09 -9,34 32,68 15,07

E 0,1 55 0, 1 12 46,04 0, 138 46,12 -0, 08 54,55 -8,51 31 ,02 15,02

F 0,169 0, 122 44,61 0, 139 44,33 0,28 52,15 -7,54 29,59 15,02

G 0,1 83 0, 132 43,15 0, 142 42,72 0,43 49,89 -6, 74 28,33 14,82 H 0,197 0,142 41,76 0,146 41,27 0,49 47,75 -5,99 27,23 14,53

1 0,211 0,152 40,48 0,151 39,95 0,53 45,75 -5,27 26,26 14,22

J 0,224 0,162 39,19 0,157 38,75 0,44 43,87 -4,68 25,39 13,80

K 0,238 0,172 38,11 0,163 37,65 0,46 42,10 -3,99 24,62 13,49

L 0,252 0,182 37,11 0,170 36,65 0,46 40,43 -3,32 23,92 13,19

M 0,266 0,192 36,17 0,176 35,73 0,44 38,87 -2,70 23,29 12,88

N 0,280 0,202 35,21 0,183 34,88 0,33 37,40 -2,19 22,71 12,50

O 0,294 0,212 34,34 0,189 34,10 0,24 36,02 -1,68 22,19 12,15

P 0,307 0,222 33,49 0,194 33,38 0,11 34,72 -1,23 21,70 11,79

Q 0,321 0,232 32,66 0,199 32,70 -0,04 33,49 -0,83 21,26 11,40

R 0,335 0,242 31,85 0,203 32,07 -0,22 32,33 -0,48 20,85 11,00

S 0,349 0,252 31,06 0,205 31,49 -0,43 31,24 -0,18 20,47 10,59

T 0,363 0,262 30,30 0,207 30,94 -0,64 30,21 0,09 20,12 10,18 u 0,377 0,272 29,53 0,207 30,43 -0,90 29,23 0,30 19,80 9,73

V 0,391 0,282 28,81 0,206 29,95 -1,14 28,31 0,50 19,49 9,32 w 0,404 0,292 27,95 0,204 29,50 -1,55 27,43 0,52 19,21 8,74

X 0,418 0,302 27,17 0,202 29,07 -1,90 26,60 0,57 18,94 8,23

Y 0,432 0,312 26,31 0,199 28,67 -2,36 25,82 0,49 18,69 7,62 z 0,446 0,322 25,38 0,196 28,29 -2,91 25,07 0,31 18,46 6,92

1 0,460 0,332 24,50 0,193 27,93 -3,43 24,36 0,14 18,23 6,27

2 0,474 0,342 23,66 0,190 27,59 -3,93 23,68 -0,02 18,02 5,64

3 0,488 0,352 22,87 0,187 27,27 -4,40 23,04 -0,17 17,83 5,04

4 0,501 0,362 22,12 0,185 26,96 -4,84 22,42 -0,30 17,64 4,48

5 0,515 0,372 21,42 0,183 26,67 -5,25 21,83 -0,41 17,46 3,96

6 0,529 0,382 20,78 0,181 26,39 -5,61 21,27 -0,49 17,29 3,49

7 0,543 0,392 20,20 0,179 26,12 -5,92 20,73 -0,53 17,13 3,07

8 0,557 0,402 19,66 0,176 25,87 -6,21 20,22 -0,56 16,98 2,68

9 0,571 0,412 19,17 0,174 25,63 -6,46 19,73 -0,56 16,83 2,34

10 0,584 0,422 18,71 0,172 25,40 -6,69 19,26 -0,55 16,69 2,02

11 0,598 0,432 18,24 0,170 25,18 -6,94 18,81 -0,57 16,56 1,68

12 0,612 0,442 17,85 0,167 24,96 -7,11 18,37 -0,52 16,43 1,42

13 0,626 0,452 17,50 0,165 24,76 -7,26 17,96 -0,46 16,31 1,19

14 0,640 0,462 17,17 0,163 24,57 -7,40 17,56 -0,39 16,20 0,97

15 0,654 0,472 16,87 0,160 24,38 -7,51 17,17 -0,30 16,09 0,78

16 0,668 0,482 16,60 0,158 24,20 -7,60 16,80 -0,20 15,98 0,62

17 0,681 0,492 16,35 0,156 24,02 -7,67 16,44 -0,09 15,88 0,47

18 0,695 0,502 16,11 0,154 23,86 -7,75 16,10 0,01 15,78 0,33

19 0,709 0,512 15,96 0,151 23,70 -7,74 15,77 0,19 15,68 0,28 20 0,723 0,522 15,70 0,149 23,54 -7,84 15,45 0,25 15,59 0,11

21 0,737 0,532 15,57 0,147 23,39 -7,82 15,14 0,43 15,50 0,07

22 0,751 0,542 15,40 0,144 23,25 -7,85 14,84 0,56 15,42 -0,02

23 0,765 0,552 15,24 0,142 23,11 -7,87 14,55 0,69 15,34 -0,10

24 0,778 0,562 15,10 0,140 22,97 -7,87 14,27 0,83 15,26 -0,16

25 0,792 0,572 14,97 0,138 22,84 -7,87 14,00 0,97 15,18 -0,21

26 0,806 0,582 14,86 0,135 22,72 -7,86 13,74 1,12 15,11 -0,25

27 0,820 0,592 14,75 0,133 22,59 -7,84 13,49 1,26 15,04 -0,29

28 0,834 0,602 14,86 0,130 22,48 -7,62 13,25 1,61 14,97 -0,11

29 0,848 0,612 14,59 0,128 22,36 -7,77 13,01 1,58 14,90 -0,31

30 0,861 0,622 14,54 0,126 22,25 -7,71 12,78 1, 76 14,84 -0,30

31 0,875 0,632 14,50 0,124 22,14 -7,64 12,56 1,94 14,77 -0,27

32 0,889 0,642 14,47 0,121 22,04 -7,57 12,34 2,13 14,71 -0,24

33 0,903 0,652 14,45 0,119 21,94 -7,49 12,13 2,32 14,65 -0,20

34 0,917 0,662 14,42 0,117 21,84 -7,42 11,92 2,50 14,60 -0,18

35 0,931 0,672 14,45 0,115 21,74 -7,29 11,73 2,72 14,54 -0,09

36 0,945 0,682 14,50 0,113 21,65 -7,15 11,53 2,97 14,49 0,01

37 0,958 0,692 14,50 0,110 21,56 -7,06 11,35 3,15 14,44 0,06

38 0,972 0,702 14,59 0,108 21,47 -6,88 11,16 3,43 14,38 0,21

39 0,986 0,712 14,64 0,106 21,39 -6,75 10,99 3,65 14,33 0,31

40 1,000 0,722 14,75 0,105 21,30 -6,55 10,81 3,94 14,29 0,46

The first column of the table is the cross-sectional cut as seen in figure 5, the next four columns provide the parameters of the blade 2 as found by standard design tools, and the last six columns are the chord angles Θ found by means of Eq.1 , Eq. 2 and Eq.3, and the respective deviations between the calculated angles using Eq. 1, Eq.2 and Eq.3 and the measured angle.

Table 1 shows that the deviation between the measured chord angle Θ and the one calculated with the use of Eq.1 is less than 1° at relative radial positions between r/R=0.13 and r/R=0.38. Close to the blade root, the deviation increases however still maintaining a value of less than 3.5° using Eq.1.

Table 1 also shows that the deviation between the measured chord angle Θ and the one calculated with the use of Eq.2 is less than 1° at relative radial positions between r/R=0.32 and r/R=0.79 and less than 4° at relative radial position between r/R=0.24 and r/R=1 when using Eq. 2.

Table 1 further shows that the deviation between the measured chord angle Θ and the one calculated with the use of Eq. 3 is less than 1 ° at relative radial positions from r/R=0.65 to r/R=1 and less than 4° at relative radial positions above r/R=0.51 when using Eq. 3.

Extensive testing of the blades of fans designed according to the design principles has revealed that a change of pitch angle of the blade to adjust a fan designed for one nominal set of operational conditions to a different set of operational conditions, mainly a different flow rate through the fan and a different rotational speed n of the fan to a large extent preserve the advantages of the fan design, i.e. an improved overall efficiency of the fan as compared to traditionally designed fans, for which reason an axial fan having blades following the design principles generally have shown to exhibit the advantages, even though the blades are turned to another pitch and the fan is operated with other operational conditions than the original nominal set of operational conditions. These advantages have been apparent at pitch angles deviating at least about 10° from the designed pitch angle and are increasing for pitch angles deviating in the range of 5° from the designed pitch angle of the blade 2.

The assembly in figure 1 also show a seating part 16 of the hub 3, three blades 2 and three locking parts 18 for an axial flow fan according to an aspect of the present invention. The blades 2 are at the root end 11 equipped with a projection 15 that allows the individual blade 2 to be seated in a blade seating opening 17 of the seating part 16 at any pitch angle of the blade 2 as desired, the projections 15 being rotatable in the U-shaped seating openings 17. The blade root protections 15 being equipped with a recess (not visible) designed for cooperating with a pin 20 having a rectangular cross-section, the pin 20 being extending from the body of a locking part 18 which is suited to the inserted into the blade seating opening 17 when the blade root projection 15 is in place so as to lock the pitch angle of the blade 2 to a specific blade pitch angle defined by the locking part 18. In figure 7 is shown three different locking parts 18a, 18b, 18c where the pin 20a, 20b, 20c are arranged at different positions to define different pitch angles of the blade 2. The locking parts 18a, 18b, 18c are provided with side tracks 19 to accommodate the edges of the blade seating opening 17 of the seating part 16 of the hub 3.

By providing a fan 1 with such system of a seating part 16, blades 2 provided with a recess in the blade root projection 15 and locking parts 18a, 18b, 18c defining one specific pitch angle of the blade 2, any possible erroneous re-assembly of the hub 3 after repair of the fan 1 resulting in erroneous blade pitch may be avoided.

List of reference numerals

1 Axial flow fan

2 Blade

3 Hub

4 Axis of rotation of the rotor

5 Rotor

6 Shroud

7 Blade tip

8 Streamlines of air flow through fan

9 Inlet part

10 Diffuser

11 Root end of blade

12 Leading edge of blade

13 Trailing edge of blade

14 Chord line

15 Blade root projection

16 Seating part of hub

17 Blade seating opening

18, 18a, 18b, 18c Locking part

19 Side tracks

20, 20a, 20b, 20c Pin

Direction of incoming air flow before the rotor

Direction of movement of the blade Distance from axis of rotation to a radial position of the rotor Distance from axis of rotation to tip end of blade

Radius of the hub

Angle between the blade chord and the direction of movement Angle between the chord of the blade and the blade chord at a predetermined radial position, e.g. of r/R = 0.34

Angle between the chord of the blade and the blade chord at a predetermined radial position at r/R = 0.34 in the root area between r/R=0.17-0.34

Angle between the chord of the blade and the blade chord at a predetermined radial position at r/R = 0.72 in the middle area between r/R=0.34-0.72

Angle between the chord of the blade and the blade chord at a predetermined radial position at r/R = 0.72 in the tip area between r/R=0.72-1.