Impellers, mixed flow fans and air conditioners

Abstract

The present invention discloses an impeller, a mixed flow fan and an air conditioner. The impeller includes a hub, a wheel cover and a plurality of blades, which are connected between the outer surface of the hub and the inner surface of the wheel cover and include a leading edge located on the side of the air inlet end. On a transverse projection plane perpendicular to the axis, the projection of the contour line of the leading edge has a first intersection point intersecting with the projection of the hub and a second intersection point intersecting with the projection of the wheel cover, and the projection of the contour line of the leading edge is a concave curve connecting the first intersection point and the second intersection point. The leading edge of the blade of the impeller of the present invention is roughly concave, so compared with a planar leading edge, when the total air inlet area of ​​the impeller is the same, the air inlet area of ​​the flow channel between adjacent blades is increased, thereby improving the air inlet smoothness.

Description

Technical Field

[0001] The present invention relates to the technical field of fans, and in particular to an impeller, a mixed flow fan and an air conditioner. Background Art

[0002] The air duct system is one of the components of the air conditioner that is used to accelerate the heat exchange of the air in the air conditioner's working area. In the air duct system of the air conditioner, the designer selects and matches the appropriate fan according to the actual needs corresponding to the different models and specifications of the air conditioner to meet the working quality and comfort of the air conditioner.

[0003] In order to meet the air volume and pressure head indicators of the air conditioner, the air duct system of the air conditioner in the related art adopts a mixed flow fan. Designers found that the blades of the mixed flow fan in the related art are flat, which makes the flow channel area between adjacent blades small and thus affects the air intake smoothness. Summary of the invention

[0004] The object of the present invention is to provide an impeller, a mixed flow fan and an air conditioner to optimize the air intake conditions of the fan.

[0005] A first aspect of the present invention provides an impeller, comprising:

[0006] The wheel cover comprises an inner cavity which penetrates along the axis, and the inner cavity has an air inlet end and an air outlet end which are arranged oppositely;

[0007] a wheel hub disposed in the wheel cover; and

[0008] A plurality of blades are connected between the outer surface of the hub and the inner surface of the wheel cover, and the blades include a leading edge located on the side of the wind inlet end. On a transverse projection plane perpendicular to the axis, a projection of a contour line of the leading edge has a first intersection point intersecting with the projection of the hub and a second intersection point intersecting with the projection of the wheel cover, and the projection of the contour line of the leading edge is a concave curve connecting the first intersection point and the second intersection point.

[0009] In some embodiments, the concave curve is oriented opposite to the direction of rotation of the impeller.

[0010] In some embodiments, the concave curve comprises a lobe line.

[0011] In some embodiments, the angle between the tangent of the concave curve at the first intersection and the tangent of the projection of the wheel hub at the first intersection is in the range of [20°, 150°]; and / or, the angle between the tangent of the concave curve at the second intersection and the tangent of the projection of the wheel cover at the second intersection is in the range of [20°, 150°].

[0012] In some embodiments, the angle between the tangent of the concave curve at the first intersection and the tangent of the projection of the wheel hub at the first intersection is 70°; and / or, the angle between the tangent of the concave curve at the second intersection and the tangent of the projection of the wheel cover at the second intersection is 78.5°.

[0013] In some embodiments, a line connecting the first intersection point and the second intersection point forms a chord line, and a length of the chord line is in the range of [40 mm, 55 mm].

[0014] In some embodiments, the length of the string is 48 mm.

[0015] In some embodiments, a line connecting the first intersection point and the second intersection point forms a chord line, and a distance between a maximum bending point of the concave curve and the chord line ranges from [2 mm, 12 mm].

[0016] In some embodiments, the distance from the maximum bending point of the concave curve to the chord line is 2.4 mm.

[0017] In some embodiments, a line connecting the first intersection point and the second intersection point forms a chord line, and a distance between a projection of a maximum bending point of the concave curve on the chord line and the first intersection point is 20%-85% of the chord length.

[0018] In some embodiments, on the longitudinal projection plane passing through the axis, the projection of the contour line of the leading edge is an inclined line, and in the extension direction from the radial inside to the radial outside, the distance between the inclined line and the transverse reference line gradually increases, and the transverse reference line is perpendicular to the axis and passes through the radial inner end point of the inclined line.

[0019] In some embodiments, the maximum distance between the inclined line and the lateral reference line is in the range of [0 mm, 15 mm].

[0020] In some embodiments, the blade includes a blade root connected to the hub and extending along the outer surface of the hub, and an outer edge opposite to the blade root, and the projection of the contour line of the outer edge on the longitudinal projection plane passing through the axis is a variable inclination curve, and in the direction from the air inlet end to the air outlet end, the angle between the tangent of the variable inclination curve and the longitudinal reference line gradually increases, and the longitudinal reference line is parallel to the axis.

[0021] In some embodiments, the outer edge is an S-shaped curve.

[0022] In some embodiments, the blade comprises a trailing edge opposite to the leading edge, the trailing edge is a concave arc line, and the concave arc line is concave toward the outer side of the blade.

[0023] In some embodiments, the number of blades is between 6 and 20.

[0024] A second aspect of the present invention provides a mixed flow fan, comprising an impeller as provided in any one of the first aspects of the present invention.

[0025] A third aspect of the present invention provides an air conditioner, comprising the mixed flow fan provided by the second aspect of the present invention.

[0026] Based on the technical solution provided by the present invention, the impeller includes a hub, a wheel cover and a plurality of blades, which are connected between the outer surface of the hub and the inner surface of the wheel cover and include a leading edge located on one side of the air inlet end. On a transverse projection plane perpendicular to the axis, the projection of the contour line of the leading edge has a first intersection point intersecting with the projection of the hub and a second intersection point intersecting with the projection of the wheel cover, and the projection of the contour line of the leading edge is a concave curve connecting the first intersection point and the second intersection point. The shape of the leading edge of the blade of the impeller of the present invention is roughly concave, so compared with the planar leading edge, under the condition that the total air inlet area of ​​the impeller is the same, the air inlet area of ​​the flow channel between adjacent blades is increased, thereby improving the air inlet smoothness; and the improvement of the air inlet smoothness will also reduce its air inlet resistance accordingly. When the direction of the air inlet airflow is not concentrated, the setting of the leading edge concave surface allows more airflows in different directions to enter the impeller to avoid direct impact of the airflow on the blades, thereby reducing noise. Moreover, the setting of the leading edge concave surface can rectify the airflows in different directions, so that the velocity distribution of the airflow is more uniform.

[0027] Further features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0029] Figure 1 is a schematic diagram of the three-dimensional structure of an impeller according to an embodiment of the present invention;

[0030] Figure 2 for Figure 1 The schematic diagram of the cross-sectional structure of the impeller shown;

[0031] Figure 3 for Figure 2 A partial enlarged structural schematic diagram of an impeller shown;

[0032] Figure 4 for Figure 1 The structure diagram of the impeller shown is after the wheel cover is removed;

[0033] Figure 5 for Figure 4 A schematic diagram of the three-dimensional structure of one of the leaves;

[0034] Figure 6 for Figure 1The schematic diagram of the top view of the impeller shown;

[0035] Figure 7 for Figure 6 A partial enlarged structural schematic diagram of the impeller in FIG.

[0036] Figure 8 for Figure 1 The bottom view of the impeller is shown;

[0037] Figures 9 to 11 for Figure 4 A schematic diagram of the projection structure of another blade on the longitudinal projection plane;

[0038] Fig.12 A velocity vector diagram in the inlet flow passage of a mixed flow fan in the related art;

[0039] Fig.13 FIG. 1 is a velocity vector diagram in the inlet flow passage of a mixed flow fan according to an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0042] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" may include both "above" and "below". The device may also be positioned in other different ways, and the spatially relative descriptions used here are interpreted accordingly.

[0043] like Figure 1 As shown, the impeller of this embodiment includes:

[0044] The wheel cover 3 includes an inner cavity extending along the axis L, and the inner cavity has an air inlet end and an air outlet end which are arranged opposite to each other;

[0045] A wheel hub 1 is disposed in a wheel cover 3; and

[0046] A plurality of blades 2 are connected between the outer surface of the hub 1 and the inner surface of the wheel cover 3, and the blades 2 include a leading edge 21 located on the wind inlet side. On a transverse projection plane perpendicular to the axis L, a projection of a contour line of the leading edge 21 has a first intersection point E intersecting with the projection of the hub 1 and a second intersection point F intersecting with the projection of the wheel cover 3. The projection of the contour line of the leading edge 21 is a concave curve connecting the first intersection point E and the second intersection point F.

[0047] like Figure 6 and Figure 7 As shown, in the top view of the impeller, the leading edge 21 of this embodiment has a first intersection E intersecting with the hub 1 and a second intersection F intersecting with the wheel cover 3. At this time, the leading edge 21 is a concave curve connecting the first intersection E and the second intersection F. That is to say, looking down at the impeller from above, the shape of the leading edge 21 of its blade 2 is roughly concave. Then, compared with the planar leading edge, when the total air intake area of ​​the impeller is the same, the air intake area of ​​the flow channel between adjacent blades 2 is increased to improve the air intake smoothness; and the improvement of air intake smoothness will also reduce its air intake resistance accordingly. When the direction of the intake air flow is not concentrated, the setting of the leading edge concave surface allows more airflows in different directions to enter the impeller to avoid direct impact of the airflow on the blades, thereby reducing noise. Moreover, the setting of the leading edge concave surface can rectify the airflows in different directions, making the velocity distribution of the airflow more uniform.

[0048] It should be noted that the transverse projection surface of the embodiment of the present invention is perpendicular to the axis L of the impeller. The longitudinal projection surface of the embodiment of the present invention needs to pass through the axis L of the impeller. And for any blade, the longitudinal projection surface refers to the longitudinal projection surface of the blade facing the direction of the axis L. For example, Figure 4 The longitudinal projection plane corresponding to the blade located in the front side of the hub 1 and in the middle of each blade 2 is the longitudinal projection plane parallel to the paper surface. In other words, the position of the longitudinal projection plane is different for different blades. The longitudinal reference line of the embodiment of the present invention is located in the longitudinal projection plane and is parallel to the axis L, and the transverse reference line is perpendicular to the axis L.

[0049] like Figure 2 As shown, the internal flow channel of the mixed flow fan of this embodiment is special, so that the airflow flows in along the impeller axis L and then flows out obliquely. The design of the leading edge concave surface of the blade of this embodiment is also conducive to the airflow flowing out along such an oblique flow channel after entering the impeller.

[0050] Specifically, in the longitudinal projection plane, the impeller flow channel of the present embodiment is roughly a flow channel curve M1M2, and the angle α between the tangent of the flow channel curve M1M2 at the air inlet end and the longitudinal reference line is in the range of [0, 30°], and the angle β between the tangent at the air outlet end and the transverse reference line is in the range of [0, 80°].

[0051] Optionally, an angle α between a tangent line of the flow channel curve M1M2 at the air inlet end and the longitudinal reference line is 10 degrees, and an angle β between a tangent line of the flow channel curve M1M2 at the air outlet end and the transverse reference line is 40 degrees.

[0052] In this embodiment, the direction of the concave curve is opposite to the rotation direction of the impeller. This arrangement allows the airflow entering the impeller to rotate under the wrapping of the blades 2, which is more conducive to rectifying the airflow and further improving the uniformity of the airflow velocity distribution.

[0053] Specifically, the concave curve of this embodiment includes a lobe line. For example, the lobe line trajectory can be obtained by using the following equation.

[0054] x=p*m1*k*t / n1+t 3 ;

[0055] y=m1*k*t 2 / n2+t 3 ;

[0056] Among them, k is a parameter used to adjust the chord length of the concave curve; p=±1 is used to adjust the direction of the concave curve; the value range of t is; m1, n1, and n2 are used to adjust the curvature of the concave curve.

[0057] In this embodiment, if Figure 5 and Figure 6As shown, the angle a between the tangent of the concave curve at the first intersection E and the tangent of the projection of the wheel hub 1 at the first intersection E is in the range of [20°, 150°], preferably, the angle a is 70°. The angle b between the tangent of the concave curve at the second intersection F and the tangent of the projection of the wheel cover 3 at the second intersection F is in the range of [20°, 150°], preferably, the angle b is 78.5°.

[0058] In this embodiment, the distance between the projection of the maximum bending point O of the concave curve on the chord connecting the first intersection point E and the second intersection point F and the first intersection point E is 20%-85% of the chord length. The maximum bending point O here refers to the point on the concave curve with the largest distance from the chord.

[0059] In this embodiment, the distance c between the maximum bending line O and the chord line ranges from [2 mm to 12 mm]. Preferably, the distance c between the maximum bending line O and the chord line is 2.4 mm.

[0060] like Figure 3 As shown, the projection of the leading edge 21 on the longitudinal projection plane is an inclined line, and the vertical distance between the inclined line and the transverse reference line gradually increases in the extension direction from the radial inner side to the radial outer side. The transverse reference line here refers to a transverse reference line passing through the radial inner end point of the inclined line and perpendicular to the axis. Preferably, the maximum vertical distance h between the inclined line and the transverse reference line is in the range of [0, 15 mm]. More preferably, h is 6.7 mm.

[0061] Figures 9 to 11 It is the projection of a single blade on the longitudinal projection plane.

[0062] like Fig.10 As shown, the blade 2 includes a blade root 24 connected to the outer surface of the hub 1 and extending along the outer surface of the hub 1, and a blade outer edge 22 opposite to the blade root 24. The projection of the contour line of the blade outer edge 22 on the longitudinal projection plane passing through the axis L is a variable inclination curve, and the angle between the tangent line of the variable inclination curve and the longitudinal reference line gradually increases in the direction from the air inlet end to the air outlet end.

[0063] The projection of the blade outer edge 22 on the longitudinal projection plane is a variable inclination curve, and the angle between the tangent of the variable inclination curve and the longitudinal reference line gradually increases, so that the blade of this embodiment gradually guides the airflow in the flow channel to avoid a large pressure gradient and reduce flow losses.

[0064] In some embodiments, Fig.10As shown, the variable inclination curve includes a first endpoint B located at the air inlet side and a second endpoint C located at the air outlet side, wherein the inlet angle d between the tangent line of the variable inclination curve at the first endpoint B and the longitudinal reference line is in the range of [20°, 85°]. The outlet angle g between the tangent line of the variable inclination curve at the second endpoint C and the longitudinal reference line is in the range of [10°, 70°].

[0065] Optionally, through experiments, when the inlet angle d is set to 50° and the outlet angle g is set to 57.7°, the flow loss of the airflow is minimal.

[0066] In this embodiment, if Fig.10 As shown, the variable inclination curve is a first S-shaped curve. Specifically, the first S-shaped curve of this embodiment has an inflection point and includes a first curve segment and a second curve segment respectively located on both sides of the inflection point, and the ratio between the curvature radius R1 of the first curve segment and the curvature radius R2 of the second curve segment is in the range of [0.2, 5].

[0067] Optionally, experiments have shown that when the curvature radius R1 of the first curve segment is set to 125 mm and the curvature radius R2 of the second curve segment is set to 38 mm, the flow loss of the airflow is minimal.

[0068] like Fig.11 As shown, in this embodiment, the projection of the blade root 24 on the longitudinal projection plane is a second S-shaped curve.

[0069] Specifically, the second S-shaped curve includes a third endpoint A located at the air inlet side and a fourth endpoint D located at the air outlet side, wherein the inlet angle m between the tangent line of the second S-shaped curve at the third endpoint A and the transverse reference line is in the range of [65°, 120°]; the outlet angle n between the tangent line of the root S-shaped line at the fourth endpoint D and the transverse reference line is in the range of [10°, 65°]. The transverse reference line here is not an absolute transverse reference line either, but is located in the longitudinal projection plane passing through the axis L and is perpendicular to the axis L.

[0070] Optionally, an entrance angle m between a tangent line of the second S-shaped curve at the third endpoint A and the transverse reference line is 91°, and an entrance angle n between a tangent line of the second S-shaped curve at the fourth endpoint D and the transverse reference line is 24°.

[0071] The second S-shaped curve of this embodiment has an inflection point and includes a first curve segment and a second curve segment respectively located on both sides of the inflection point, and the ratio between the curvature radius R4 of the first curve segment and the curvature radius R3 of the second curve segment is in the range of [0, 3.5].

[0072] Furthermore, the blade 2 of this embodiment further includes a trailing edge 23 located at one side of the wind outlet end. Fig. 9As shown in FIG. 1 , the projection of the trailing edge 23 on the longitudinal projection plane is a concave arc line. And the concave arc line is concave toward the outer side of the blade, where the outer side of the blade refers to the direction away from the blade body. In other words, Figure 6 As shown, when looking up at the impeller from below, the trailing edge 23 of the blade 2 is generally concave in shape to prevent the airflow from forming vortices when it is discharged, thereby optimizing the airflow.

[0073] In practical application, the projection length of the trailing edge chord length CD on the longitudinal projection plane is in the range of [10, 30 mm], the angle e between the tangent line at the trailing edge point C and the chord length is in the range of [10°, 50°], and the angle f between the tangent line at the point D and the chord length is [10°, 50°]. Preferably, in this embodiment, the projection length of the trailing edge chord length CD on the longitudinal projection plane is 19 mm, the angle e between the tangent line at the trailing edge point C and the chord length is 31°, and the angle f between the tangent line at the point D and the chord length is 31.5°.

[0074] The impeller of the mixed flow fan is applied to an air conditioner, and the optimal range of the number of impeller blades is controlled within 6-20 according to the structure of the air conditioner housing.

[0075] A simulation experiment was conducted on the mixed flow fan of this embodiment, and compared with the simulation of the mixed flow fan before optimization. The experimental data are shown in the following table. During the simulation experiment, the noise measurement point was 0.5m from the fan outlet.

[0076]

[0077] From the simulation data, we can see that when the air volume is similar, the fan speed is significantly reduced after optimization, the noise value is reduced under the same air volume, the operating efficiency and pressure head are improved, and the fan aerodynamic performance and wind noise level are significantly improved. Fig.12 and Fig.13 It can also be found from the comparison of the velocity vector diagram that after optimization, the direction of the airflow entering along the guide ring has changed significantly, the airflow has shifted to the middle of the flow channel, and through the intake rectification, the flow velocity distribution has become more uniform and the velocity gradient has been significantly reduced.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. An impeller of a mixed flow fan, characterized in that: include: The wheel cover (3) comprises an inner cavity extending through the axis, and the inner cavity has an air inlet end and an air outlet end which are arranged opposite to each other; A wheel hub (1) is arranged inside the wheel cover (3); as well as A plurality of blades (2) connected between the outer surface of the hub (1) and the inner surface of the wheel cover (3), and the blades (2) include a leading edge (21) located on the side of the air inlet end, and on a transverse projection plane perpendicular to the axis, a projection of a contour line of the leading edge (21) has a first intersection point (E) intersecting with a projection of the hub (1) and a second intersection point (F) intersecting with a projection of the wheel cover (3), and the projection of the contour line of the leading edge (21) is a concave curve connecting the first intersection point (E) and the second intersection point (F); A line connecting the first intersection point (E) and the second intersection point (F) forms a chord line, and a distance (c) between the maximum bending point (O) of the concave curve and the chord line ranges from [2 mm, 12 mm]; The line connecting the first intersection point (E) and the second intersection point (F) forms a chord line, and the distance between the projection of the maximum bending point (O) of the concave curve on the chord line and the first intersection point (E) is 20%-85% of the chord length.

2. The impeller according to claim 1, characterized in that: The direction of the concave curve is opposite to the rotation direction of the impeller.

3. The impeller according to claim 1, characterized in that: The concave curve comprises a lobe line.

4. The impeller according to claim 1, characterized in that: The range of the angle (a) between the tangent of the concave curve at the first intersection point (E) and the tangent of the projection of the wheel hub (1) at the first intersection point (E) is [20°, 150°]; and / or the range of the angle (b) between the tangent of the concave curve at the second intersection point (F) and the tangent of the projection of the wheel cover (3) at the second intersection point (F) is [20°, 150°].

5. The impeller according to claim 4, characterized in that: The angle (a) between the tangent of the concave curve at the first intersection point (E) and the tangent of the projection of the wheel hub (1) at the first intersection point (E) is 70°; and / or the angle (b) between the tangent of the concave curve at the second intersection point (F) and the tangent of the projection of the wheel cover (3) at the second intersection point (F) is 78.5°.

6. The impeller according to claim 1, characterized in that A line connecting the first intersection point (E) and the second intersection point (F) forms a chord line, and a length of the chord line ranges from [40 mm to 55 mm].

7. The impeller according to claim 6, characterized in that The length of the string is 48 mm.

8. The impeller according to claim 1, characterized in that The distance (c) between the maximum bending point (O) of the concave curve and the chord line is 2.4 mm.

9. The impeller according to any one of claims 1 to 8, characterized in that On a longitudinal projection plane passing through the axis, the projection of the contour line of the leading edge (21) is an inclined line, and in the extension direction from the radial inner side to the radial outer side, the distance between the inclined line and a transverse reference line gradually increases, and the transverse reference line is perpendicular to the axis and passes through the radial inner end point of the inclined line.

10. The impeller according to claim 9, characterized in that The maximum distance (h) between the inclined line and the transverse reference line is in the range of [0 mm, 15 mm].

11. The impeller according to any one of claims 1 to 8, characterized in that The blade (2) comprises a blade root (24) connected to the hub (1) and extending along the outer surface of the hub (1), and an outer edge (22) opposite to the blade root (24), wherein a projection of a contour line of the outer edge (22) on a longitudinal projection plane passing through the axis (L) is a variable inclination curve, and in a direction from the air inlet end to the air outlet end, an angle between a tangent line of the variable inclination curve and a longitudinal reference line gradually increases, and the longitudinal reference line is parallel to the axis (L).

12. The impeller according to claim 11, characterized in that The outer edge (22) is an S-shaped curve.

13. The impeller according to any one of claims 1 to 8, characterized in that The blade (2) comprises a trailing edge (23) opposite to the leading edge (21); the trailing edge (23) is an inwardly concave arc line, and the inwardly concave arc line is concave toward the outer side of the blade (2).

14. The impeller according to claim 1, characterized in that The number of the blades (2) is 6 to 20.

15. A mixed flow fan, characterized in that: Comprising an impeller as claimed in any one of claims 1 to 14.

16. An air conditioner, characterized in that: Comprising the mixed flow fan as claimed in claim 15.

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