Radial fan

Abstract

A radial fan that includes a fan wheel, which can be rotated about an axis and which comprises a base plate and airfoils protruding from the base plate, wherein the airfoils each comprise an upstream edge in a first spacing (r1) from the axis and a downstream edge in a second spacing (r2) from the axis, and an end wall, which together with the base plate, delimits a flow channel in which the airfoils engage. The cross-sectional area (A) of the flow channel between the upstream edge and the downstream edge passes through a maximum in a third spacing (r3) from the axis. The difference between a fourth spacing (r4) and a fifth spacing (r5), at which the cross-sectional area (A) in each case assumes nearest adjacent minima to the maximum, is at least half of the difference (r2−r1) between the first and the second spacing.

Claims

1. A radial fan with a fan wheel which can be rotated about an axis and which comprises a base plate and airfoils protruding from the base plate, wherein the airfoils each comprise an upstream edge in a first spacing (r1) from the axis and a downstream edge in a second spacing (r2) from the axis, and with an end wall which together with the base plate delimits a flow channel in which the airfoils engage, wherein a cross-sectional area (A) of the flow channel between the upstream edge and the downstream edge passes through a maximum in a third spacing (r3) from the axis and in that a difference between a fourth spacing (r4) and a fifth spacing (r5), at which the cross-sectional area (A) in each case assumes nearest adjacent minima to the maximum, is at least half of the difference (r2−r1) between the first and the second spacing; wherein the fourth spacing (r4) is greater than the second spacing (r2), and a difference (r4−r2) between the fourth spacing and the second spacing is smaller than a difference (r4−r3) between the third spacing and the fourth spacing.

2. The radial fan according to claim 1, wherein the cross-sectional area (A) at the fourth spacing (r4) is at least 4% smaller than at the third spacing (r3).

3. The radial fan according to claim 2, wherein the cross-sectional area (A) is calculated as a product of a spacing (r) from the axis and the axial distance between the end wall and base plate measured in this spacing (r).

4. The radial fan according to claim 1, wherein the fifth spacing (r5) is smaller than the third spacing (r3), and a difference (r3−r5) between the third spacing and the fifth spacing is at least one fourth of a difference between the first and the second spacing (r2−r1).

5. The radial fan according to claim 4, wherein the cross-sectional area (A) at the fifth spacing (r5) is smaller than at the fourth spacing (r4).

6. The radial fan according to claim 5, wherein the cross-sectional area (A) at the fifth spacing (r5) is at least 8% less than the cross-sectional area (A) at the third spacing (r3).

7. The radial fan according to claim 6, wherein the cross-sectional area (A) is calculated as a product of a spacing (r) from the axis and the axial distance between the end wall and base plate measured in this spacing (r).

8. The radial fan according to claim 5, wherein the cross-sectional area (A) is calculated as a product of a spacing (r) from the axis and the axial distance between the end wall and base plate measured in this spacing (r).

9. The radial fan according to claim 4, wherein the cross-sectional area (A) at the fifth spacing (r5) is at least 8% less than the cross-sectional area (A) at the third spacing (r3).

10. The radial fan according to claim 9, wherein the cross-sectional area (A) is calculated as a product of a spacing (r) from the axis and the axial distance between the end wall and base plate measured in this spacing (r).

11. The radial fan according to claim 1, wherein a radius of curvature (R1) of the end wall in a radial section between the first and the second spacing (r1, r2) is no smaller than one fourth of the first spacing (r1).

12. The radial fan according to claim 11, wherein the end wall has a concave surface region in the third spacing (r3) from the axis, which is concave in the radial section.

13. The radial fan according to claim 1, wherein the end wall has a concave surface region in the third spacing (r3) from the axis, which is concave in radial section.

14. The radial fan according to claim 13, wherein the concave surface region in the radial section has a radius of curvature (R2) which is greater than the first spacing (r1).

15. The radial fan according to claim 14, wherein, in the third spacing (r3) from the axis, the airfoils each comprise a protrusion opposite the concave surface region.

16. The radial fan according to claim 15, wherein the cross-sectional area (A) is calculated as a product of a spacing (r) from the axis and the axial distance between the end wall and base plate measured in this spacing (r).

17. The radial fan according to claim 13, wherein in the third spacing (r3) from the axis, the airfoils each comprise a protrusion opposite the concave surface region.

18. The radial fan according to claim 1, wherein the cross-sectional area (A) is calculated as a product of a spacing (r) from the axis and the axial distance between the end wall and base plate measured in this spacing (r).

19. The radial fan according to claim 1, wherein the fifth spacing (r5) is smaller than the third spacing (r3), and a difference (r3−r5) between the third spacing and the fifth spacing is at least one fourth of a difference between the first and the second spacing (r2−r1).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Additional features and advantages of the invention result from the following description of embodiment examples in reference to the appended figures, in which:

(2) FIG. 1 shows a radial section through a radial fan according to the invention;

(3) FIG. 2 shows an axial section through a fan chamber of the radial fan of FIG. 1;

(4) FIG. 3 shows an enlarged radial section through a fan wheel and an end wall of the radial fan from FIG. 1; and

(5) FIG. 4 shows measurement curves of the pressure increase and of the efficiency of the radial fan according to the invention and of a conventional fan.

DETAILED DESCRIPTION

(6) Referring to FIG. 1 a radial fan is shown according to the present disclosure in section along a rotation axis 1 of its fan wheel 2. One can see shaft 3, rotor 4 and stator 5 of an electric motor 6 as well as a circuit board 7, which supports an inverter for supplying the motor 6, enclosed in an inner housing 8. The inner housing 8 comprises a container 9 which receives the motor 6 and the circuit board 7, and a cover 10 which closes the container 9 and through the central opening of which the shaft 3 protrudes.

(7) An outer housing 11 comprises a bottom plate 12, an outer wall 13, an annular partition 14, and an end wall 15. The bottom plate 12 is connected by the outer wall 13 via an elastic buffer ring 16 to a second outer container, which receives the inner container 9 forming a cooling air channel 17 extending annularly around the inner container 9 and the motor 6.

(8) The outer wall 13, on its inner side, comprises two shoulders 18, 19, where the diameter thereof decreases in each case toward the bottom plate 12. The partition 14 is inserted into the hollow space surrounded by the outer wall 13 so that an edge of the partition 14 lies on the shoulder 18 close to the bottom. In this position, the outer wall 13 and the partition 14 together form a blowing air channel 20, the bottom of which is formed by the shoulder 19.

(9) As can be seen in FIG. 2, which shows a section through the radial fan along a sectional plane designated by II-II in FIG. 1, the blowing air channel 20 extends with gradually increasing cross section around the shaft 1 and transitions after a rotation about the axis 1 into a tangentially branching off outlet channel 21. At the transition from the blowing air channel 20 to the outlet channel 21, at the bottom of the blowing air channel 20 between the outer wall 13 and the partition 14, a passage 22 is hollowed, which connects the blowing air channel 20 to the cooling air channel 17.

(10) As again shown in FIG. 1, the cover 10 of the inner housing 8 engages in a central opening of the partition 14. Between the cover 10 and the partition 14, an additional elastic buffer ring 23 extends. The inner housing 8 is oscillation-damped by the buffer rings 16, 23 opposite the outer wall 13, so that oscillations of the motor 6 are transmitted only to a slight extent as impact sound to the environment.

(11) On the edge of the outer wall 13 facing away from the bottom plate 12, the end wall 15 is latched to the outer wall 13 with the help of catches 24 (see FIG. 2, 3), which enclose protrusions of the outer wall 13. The end wall 15 together with the outer wall 13, the partition 14 and the cover 10, delimits a wheel chamber 25. The wheel chamber 25 accommodates the fan wheel 2 stuck on an end of the shaft 3. As a result of the rotation thereof, air is suctioned into the wheel chamber 25 via a central inlet opening 26 of the end wall 15 in a manner which is known per se, is driven radially outward into the blowing air channel 20 and is released again to the outside via the outlet channel 21 thereof.

(12) The partition 14 has one or more openings 27 which communicate with the cooling air channel 17 and which are adjacent to the end of the blowing air channel 20 facing away from the outlet channel 21. These openings 27 are hidden in the representation of FIG. 2 by the fan wheel 2 and are therefore represented by a dashed line. The rotation of the fan wheel 2 generates a higher pressure in front of the passage 22 than at the openings 27, so that air enters the cooling air channel 17 via the passage 22, absorbs waste heat of the motor 6 there, and then returns via the openings 27 into the wheel chamber 25. A radial wall 28 between the container 9 and the outer wall 13 sections the cooling air channel 17 and forces the suctioned air to almost completely circumnavigate the container 9 on the way from the passage 22 to the openings 27.

(13) The fan wheel 2 comprises a base plate 29 which together with the end wall 15 delimits a flow channel 30, in which the air is driven radially outward by the rotation of the fan wheel 2, and a plurality of airfoils 31 which protrude from a surface of the base plate 29 facing the end wall 15 into the flow channel 30. The airfoils 31 are in the shape of ribs which extend substantially in radial direction in each case from a radially inner upstream edge 32 to a downstream edge 33 and comprise an elongate vertex edge 34 lying opposite the end wall 15 at a small distance. The upstream edges 32 and the downstream edges 33 of the airfoils 31 lie on circles around the axis 1 with radii r1, r2. The surface of the base plate 29, in an annular region 35 between the two circles, has approximately the shape of a rotation hyperboloid centered on the axis 1.

(14) If, in this region 35, the cross-sectional area of the flow channel 30 run through by the air were constant, then the air could flow radially outward in this flow channel 30 at constant speed. To be exact, one would have to select a surface as cross-sectional area to which the flow direction of the air is perpendicular at all points. Finding such a surface requires complex simulations. By approximation, it could be replaced by a conical surface which intersects the mutually facing surfaces of the base plate 29 and of the end wall 15 at the same angle. Since, in the case considered here, the opening angle of such a cone between r1 and r2 does not substantially change, and since what matters here is not an absolute cross-sectional area but only their ratio with respect to one another, an additional simplification can be made, and the cone can be replaced by a cylindrical surface, i.e., one uses, as measure for the cross-sectional area, the product of the distance between the base plate 29 and the end wall 15, measured in the direction of the axis 1, and a spacing r of the measurement site from the axis 1.

(15) A course of the end wall 15, which would meet the requirements of a constant cross-sectional area, is drawn as a dashed contour 36 in the enlarged section of FIG. 3. As one can see, this contour 36 separates tangentially from the actual surface of the end wall 15 at a point 37 in order to extend first up to a point 38 through the material of the end wall 15; from the point 38, it runs through the flow channel 30 until it meets a point 39 again on the surface of the end wall 15. Accordingly, the cross-sectional area of the flow channel 30 is smaller between the points 37 and 38 and greater between the points 38, 39 than at the points 37, 38, 39.

(16) A diagram in the lower right corner of FIG. 3 quantitatively shows the cross-sectional area A of the flow channel 30 as a function of the spacing r from the axis 1, wherein the cross-sectional area at spacing r2 of the downstream edges 33 is arbitrarily set equal to 1. Starting from an initial value close to 1 at small spacings close to r1, the area A first decreases to a minimum at r5, and then reaches a maximum at r3 and from there it again approaches a minimum, a spacing r4 of which here is in agreement with the spacing r2 of the downstream edges 33. The spacing r4−r5 between the two minima here corresponds to approximately two thirds of the spacing r2−r1 between the edges 33, 32. The cross-section decrease from r3 to r4 is considerably more gradual than the increase from r5 to r3, so that, although the difference of the cross-sectional areas between r5 and r3 is greater than between r3 and r4, the spacing r3−r5 is clearly smaller than r4−r3.

(17) At the level of the maximum of the cross-sectional area at r3, the end wall 24, between surface regions 40, 42 which have convex curvature in the radial section, has a concavely curved surface region 41. The radius of curvature of the entire end wall 24 should not be too small, in order to avoid an abrupt deflection of the air and vortex build-up. The smallest value R1 of the radius of curvature is here achieved at spacing r5; R1>0.5 r1 applies. The minimum radius of curvature R2 of the concave region 41 is even larger; for it R2>r1 applies. Opposite the surface region 41, protrusions 43 of the airfoils 31 are located, so that the width of a gap between the vertex edges 34 of the airfoils 31 and the end wall 24 remains substantially constant over the entire length of the vertex edges 34.

(18) FIG. 4 shows measurement curves Δp, Δp′ of the pressure increase and η, η′ of the efficiency as a function of the volume flow for a radial fan according to the invention, the end wall 15 of which, as shown in FIG. 3, has differently curved surface regions 40, 41, 42, and for a radial fan of equal dimensions with hyperboloid end wall and constant cross section of the flow channel. According to curve η′, the conventional radial fan reaches its optimal efficiency of approximately 21% at a volume flow of approximately 270 L/min. At identical volume flow, the efficiency of the fan according to the invention according to curve η is more than 30%, and thus the maximum efficiency is still not reached. At lower volume flows up to and including the efficiency optimum, by means of the fan according to the invention, considerably greater pressure increases can also be achieved, as can be seen in the curves Δp, Δp′.

(19) TABLE-US-00001 List of reference numerals 1 Rotation axis 2 Fan wheel 3 Shaft 4 Rotor 5 Stator 6 Electric motor 7 Circuit board 8 Inner housing 9 Container 10 Cover 11 Outer housing 12 Bottom plate 13 Outer wall 14 Partition 15 End wall 16 Buffer ring 17 Cooling air channel 18 Shoulder 19 Shoulder 20 Blowing air channel 21 Outlet channel 22 Passage 23 Buffer ring 25 Catch 26 Wheel chamber 27 Inlet opening 27 Opening 28 Radial wall 29 Base plate 30 Flow channel 31 Airfoil 32 Upstream edge 33 Downstream edge 34 Vertex edge 35 Region 36 Contour 37 Point 38 Point 39 Point 40 Surface region 41 Surface region 42 Surface region 43 Protrusion