Centrifugal fan, particularly for extractor hoods and fume extractors

Abstract

 A centrifugal fan comprises a casing (2) having a helical external profile, defined by a pair of half-shells (2a, 2b) capable of being coupled to each other, a fan wheel (3) mounted in the casing (2) and capable of being driven in rotation about a first axis (X), there being defined in the casing (2) a lateral suction aperture (6), coaxial with the first axis (X), and a tangential delivery aperture (5), coaxial with a second axis (Y) directed tangentially to the fan wheel (3), inside the casing (2) a pressure chamber (7) being defined having a volume formed between the fan wheel (3) and the inner helical profile (3b) of the casing (2). The fan further comprises a flow separator (8) arranged at the zone (M) having the smallest radial distance between the fan wheel (3) and the inner profile (3b) of the casing (2), the flow separator (8) being defined conjointly by a pair of appendages (9), each formed in the respective casing half-shell (2a, 2b), the projection of each of the appendages (9), in a first plane (Q) perpendicular to the first axis (X), extending substantially along an arc of circumference (B), extending in prolongation of the inner helical profile (3b) of the casing (2) and also protruding into the pressure chamber (7) behind the delivery aperture (5). The free edge (10) of at least one of the appendages (9) of the flow separator (8) has, in the lateral projection in a second plane (W) perpendicular to the second axis (Y), at least a first and a second curved section (10a, 10b), in prolongation of each other, having radii of curvature (R1, R2) of opposite sign and defining a point of flexion (F) in the connection zone, the section (10a) closest to the median plane (P) of coupling of the casing half-shells (2a, 2b) having a convex curvature with respective radius of curvature (R1) centred in the part of the second plane (W) of projection containing the second axis (Y).

Description

[0001] The present invention relates to a centrifugal fan having the characteristics mentioned in the preamble of main claim 1.

[0002] The invention is placed particularly, but not exclusively, in the technical field of centrifugal fans designed for applications in extractor hoods or fume extraction devices.

[0003] In the specific field of reference, fans of the aforesaid type, as is well known, are used as suction devices for vapours, combustion fumes, exhaust gases, or in all those applications in which provision is made for the extraction and conveying, in general, of gaseous mixtures. Typical embodiments provide for the use of centrifugal fans with helical casing having a cylindrical drum type fan wheel and axially extending blades. The casings of these fans are further provided with a lateral suction aperture and a tangential delivery aperture, between which extends a pressure chamber following a helical course and the volume of which is defined between the casing and the fan wheel.

[0004] In fans of the aforesaid type it is known to provide inside the pressure chamber, in the zone behind the delivery aperture, a flow separator, typically comprising an appendage standing up in the casing at the zone having a lesser radial distance between the fan wheel and the helical profile of the casing, in which zone the emerging delivery flow (directed tangentially) runs close to the flow introduced by suction in the fan wheel (at the smaller cross-section of the helical chamber of the fan). An example of a fan comprising a similar flow separator device is known from European Patent Application No. 1462658.

[0005] Such separators, although on the one hand they make it possible to improve the characteristics of separation and exchange of the gaseous fluids treated by the fan, on the other hand they give rise to noisy operation, in particular generated by the passage of the blades in the region of the separator. The endeavour to reconcile both these aspects, opposed to each other, has caused the prior art to propose compromise solutions, one of which is described in the European Application mentioned above, in which the separator is configured as a tongue extending partly into the pressure chamber and having a profile of the edge of said tongue comprising a double consecutive ramp spaced by a step formation.

[0006] The principal aim of the invention is that of providing a centrifugal fan equipped with a flow separator of the aforesaid type, which makes it possible to improve, with respect to known solutions, the overall output, guaranteeing an adequate capacity of separation of the fluids, and at the same time minimising the noise produced by the separator, for the purpose of improved overall efficiency.

[0007] This aim is achieved by the invention by means of a centrifugal fan produced in accordance with the following claims.

[0008] Further characteristics and advantages of the invention will become clearer from the following detailed description of a preferred exemplary embodiment thereof, illustrated by way of non-limiting example with reference to the appended drawings, in which:

• Figure 1 is a partial perspective view of a centrifugal fan produced according to the invention.
• Figure 2 is a perspective view of a detail of the fan of Figure 1,
• Figure 3 is a perspective view of a further detail of the fan of Figure 1,
• Figure 4 is a diagrammatic plan view of the detail of Figure 2,
• Figure 5 is a diagrammatic view in front elevation of the detail of Figure 2,
• Figure 6 is a further perspective view of a detail of the fan according to the invention.

[0009] With reference to the figures listed, the reference 1 designates a centrifugal fan, particularly designed for use in extractor hoods or fume extraction devices, and produced according to the present invention.

[0010] The fan 1 comprises a casing 2 with helical external profile, and which is defined by two casing half-shells 2a, 2b capable of being removably coupled to each other, at a plane of junction, indicated diagrammatically by P in the drawings. The two casing half-shells are configured with substantial mirror-image symmetry with respect to the junction plane P, as shown in the assembled state in Figure 3, except for the lateral suction aperture provided on only one of the two casing half-shells.

[0011] In the casing 2 there is housed a cylindrical drum type fan wheel 3 provided with axially extending blades 4, the fan wheel being capable of being driven in rotation about an axis X. Also defined in the casing is a tangential delivery aperture 5, coaxial with an axis, indicated by Y, directed tangentially to the fan wheel, and a second, lateral suction aperture 6, coaxial with the axis X.

[0012] The reference 7 indicates a pressure chamber defined within the casing, along the helical course of same, and the volume of which is formed between the drum of the fan wheel 3 and the inner surface profile 3b of the casing itself.

[0013] The fan also comprises a flow separator device, indicated as a whole by 8, which is arranged at the zone having the smallest radial distance between the fan wheel 3 and the inner surface profile 3b of the casing. This zone is indicated by M in the drawings.

[0014] In more detail, the flow separator 8 is defined conjointly by a pair of appendages 9, each formed in the respective casing half-shell 2a, 2b, and being also preferably produced with mirror-image symmetry with respect to the median plane P of junction of the half-shells, as shown in Figure 3. By reason of this symmetry, only one of the appendages 9 defining the flow separator, that relating to the casing half-shell 2a, will be described in detail hereinafter, it being understood that the other appendage, where not otherwise specified, is structurally identical and also symmetrical in mirror image to the plane P.

[0015] For the description of the separator 8, particular reference will be made hereinafter to Figures 4 and 5, the drawing planes of which, indicated respectively by Q and W, are to be regarded respectively as the lateral planes of projection of the half-shell 2a respectively perpendicular to the axis X (Figure 4) and to the axis Y (Figure 5).

[0016] The projection of the appendage 9 in the plane Q of Figure 4 extends substantially along an arc B of circumference, extending in prolongation of the inner helical profile 3b of the casing and also protruding into the pressure chamber behind the delivery aperture 5. The appendage is preferably produced integrally with the corresponding casing half-shell and has a free edge 10, at its free end opposed to the casing wall, the profile of which is also clearly illustrated in the lateral projection of the plane W of Figure 5. In that plane of projection, according to a principal characteristic of the invention, the profile of the free edge 10 of the appendage 9 comprises at least a first and a second curved section 10a, 10b, in prolongation of each other, having respective radii of curvature R1, R2 of opposite sign and also defining a point of flexion F in the connection zone. Moreover, the section 10a, that closest to the median plane P of coupling of the casing half-shells, has a convex curvature, the radius of curvature R1 of which is centred in the part of the plane of projection W of Figure 5 containing the axis Y. For the location of the point of flexion F in the plane of projection of Figure 5, it is convenient to refer to a two-dimensional system of reference to orthogonal axes that is contained in the plane of projection and centred on the point of intersection between the plane W and the axis Y, with the axis of the abscissae x perpendicular to the median plane P and axis of the ordinates y parallel to the plane P itself. With respect to this system of reference, the point of flexion has coordinates (x, y) such that the ratio (x/D) between the abscissa and the outside diameter of the fan wheel, this diameter being indicated by D, is selected to have a value ranging between 0.04 and 0.185, and the ratio (y/D) between the ordinate and the fan wheel outside diameter D is between 0.04 and 1.11.

[0017] With reference to Figure 5, the radius of curvature R1 of the first section 10a is selected to have a value such that the ratio between the radius R1 and the fan wheel outside diameter D is between 1.11 and 0.04, and also preferably equal to around 0.085.

[0018] The radius of curvature R2 of the second section 10b is selected to have a value such that the ratio between the radius R2 and the fan wheel outside diameter D is between 0.04 and 1.11, and also preferably equal to around 0.16.

[0019] Moreover, the sections 10a, 10b may conveniently be extended, in the plane of projection W, so as to terminate respectively on the median plane P and on the semicircular bottom of the delivery aperture. Alternatively, provision is made for those sections to be in turn connected, on the opposite side from the flexion zone, with further sections of the free edge 10, as illustrated in Figure 5.

[0020] In particular, provision is made for the curved section 10a to be extended, on the opposite side from the flexion F, in a third section 10c, substantially rectilinear and also extending as far as the median plane P, and for the curved section 10b to be extended in a corresponding manner in a fourth, curved section 10d.

[0021] The rectilinear section 10c is moreover inclined, in the plane of projection W, with respect to the perpendicular to the median plane P, with definition of an angle of inclination A having a value conveniently between 0° and 45°.

[0022] The fourth section 10d has a radius of curvature, indicated by R4, of the same direction as the radius of curvature R2 of the section 10b. The radius of curvature R4 is moreover conveniently selected to have a value such that the ratio (R4/D) between the radius of curvature itself and the outside diameter of the fan wheel is between 0.04 and 1.11.

[0023] Returning to the plane of projection Q of Figure 4, reference will be made hereinafter to a two-dimensional system of reference to orthogonal axes that is contained in the plane W and centred in the point of intersection between the plane W and the axis X, with the axis of the abscissae x' directed parallel to the axis Y. With respect to this system of reference, the point S in which is centred the radius of curvature R' of the arc of circumference which identifies the curved course of the appendage 9 in the plane of projection Q, has coordinates (x',y') such that the ratio (x'/D) between its abscissa and the outside diameter D of the fan wheel is selected to have a value of between 0 and 0.5., and the ratio (y'/D) between the ordinate and the outside diameter D of the fan wheel has a value of between 0 and 0.5.

[0024] The radius of curvature R' of the arc B is moreover conveniently selected to have a value such that the ratio (R'/D) between same and the diameter D of the fan wheel is between 0.15 and 0.6, and also preferably equal to around 0.3.

[0025] As to the circumferential length of the arc B, the angle E subtended by that arc is selected to have a value of between 15° and 90°, preferably equal to 35°.

[0026] Provision is also made for the arc B of development of the appendage in the plane Q to extend, in the rectilinear zone M, (with values of the ratio M'/D between 0 and 0.3, where M' is the distance indicated in Figure 4) starting from the initial point of the volute.

[0027] According to a further characteristic of the invention, provision is made for the helical surface profile of the fan wheel, with reference to its projection in the plane Q of Figure 4, to be connected behind the delivery aperture with a fifth and sixth curved section 12a, 12b, having radii of curvature R5, R6 of opposite sign and defining a point of flexion F' in the connection zone. In particular, provision is made for the section 12b, that closest to the delivery aperture, to have a convex curvature with a radius of curvature centred in the plane of projection on the opposite side from the axis X with respect to the section itself.

[0028] The point of flexion F' is further located, with respect to the system of coordinates x',y', defined above, with respective coordinates such that the ratio (x"/D) between its abscissa and the diameter D of the fan wheel is between 0 and 0.95, and the ratio (y"/D) between its ordinate and the diameter D is between 0.4 and 1.4. The radius of curvature R5 of the fifth section 12a is conveniently selected moreover to have a value such that the ratio R5/D between said radius and the diameter of the fan wheel is between 0 and 9.5.

[0029] The radius of curvature R6 of the sixth section 12b is conveniently selected moreover to have a value such that the ratio R6/D between said radius and the diameter of the fan wheel is between 0 and 5.

[0030] With reference to Figure 6, the reference 15 indicates diagrammatically a pressure intake, for example produced in the form of an aperture or through-hole provided in the body of one of the appendages 9 defining the flow separator 8. The aperture 15, advantageously provided integrally with the separator 8, is provided behind the delivery aperture 5 of the fan and may conveniently be used for housing a pressure sensor, for example intended for determining the rate of flow delivered by the fan or to give the signal to a pressure switch, without interfering noticeably with the flow and therefore without altering the performance of the appliance.

Claims

1. A centrifugal fan comprising:

- a casing (2) with helical external profile, defined by a pair of half-shells (2a, 2b) capable of being coupled to each other,

- a fan wheel (3) mounted in the casing (2) and capable of being driven in rotation about a first axis (X), there being defined in the casing (2) a lateral suction aperture (6), coaxial with said first axis (X), and a tangential delivery aperture (5), coaxial with a second axis (Y) directed tangentially to the fan wheel (3),

- inside the casing (2), a pressure chamber (7) being defined having a volume formed between the fan wheel (3) and the inner helical profile (3b) of the casing (2),

- the fan further comprising a flow separator (8) arranged at the zone (M) having the smallest radial distance between the fan wheel (3) and the inner profile (3b) of the casing, said flow separator (8) being defined conjointly by a pair of appendages (9), each formed in the respective casing half-shell (2a, 2b), the projection of each of said appendages (9), in a first plane (Q) perpendicular to said first axis (X), extending substantially along an arc of circumference (B), extending in prolongation of the inner helical profile (3b) of the casing (2) and also protruding into the pressure chamber behind the delivery aperture (5),

characterized in that the free edge (10) of at least one of said appendages (9) of the flow separator (8) has, in the lateral projection in a second plane (W) perpendicular to said second axis (Y), at least a first and a second curved section (10a, 10b), in prolongation of each other, having radii of curvature (R1, R2) of opposite sign and defining a point of flexion (F) in the connection zone, the section (10a) closest to the median plane (P) of coupling of the casing half-shells (2a, 2b) having a convex curvature with a respective radius (R1) of curvature centred in the part of the second plane (W) of projection containing said second axis (Y).

2. A fan according to claim 1, wherein, with respect to a first two-dimensional system of reference to orthogonal axes (x, y) that is contained in said second plane (W) and centred in the point of intersection between said second plane (W) and said second axis (Y), with the axis of the abscissae (x) perpendicular to the median plane (P) and axis of the ordinates (y) parallel to the median plane, the point of flexion (F) has coordinates such that the ratio (x/D) between the abscissa (x) and the outside diameter (D) of the fan wheel (3) is between 0.04 and 0.185, and the ratio (y/D) between the ordinate (y) and the outside diameter (D) of the fan wheel (3) is between 0.04 and 1.11.

3. A fan according to claim 1 or claim 2, wherein said radius of curvature (R1) of the first section (10a) is selected to have a value such that the ratio between said radius (R1) and the outside diameter (D) of the fan wheel (3) is between 0.04 and 1.11.

4. A fan according to any one of the preceding claims, wherein said radius of curvature (R2) of the second section (10b) is selected to have a value such that the ratio between said radius of curvature (R2) and the outside diameter (D) of the fan wheel (3) is between 0.04 and 1.11.

5. A fan according to any one of the preceding claims, wherein, in the second plane (W) of projection, said first curved section (10a) is extended, on the opposite side from the point of flexion (F), in a third rectilinear section (10c) extending as far as the median plane (P) of coupling of the casing half-shells (2a, 2b).

6. A fan according to claim 5, wherein said third rectilinear section (10c) is inclined with respect to the perpendicular to the median plane (P) of coupling of the half-shells (2a, 2b), with definition of an angle of between 0° and 45°.

7. A fan according to any one of the preceding claims, wherein, in the second plane (W) of projection, said second curved section (10b) is extended, on the opposite side from the point of flexion (F), in a fourth curved section (10d).

8. A fan according to claim 7, wherein said fourth curved section (10d) has a radius of curvature (R4) in the same direction as the radius of curvature (R2) of the second section (10b).

9. A fan according to claim 7 or claim 8, wherein the radius of curvature (R4) of the fourth section (10d) is selected to have a value such that the ratio between said radius of curvature (R4) and the outside diameter (D) of the fan wheel (3) is between 0.04 and 1.11.

10. A fan according to one or more of the preceding claims, wherein the appendages (9) in each respective casing half-shell (2a, 2b) conjointly defining said separator (8) are symmetrical in mirror-image with respect to the median plane (P) of coupling of the corresponding casing half-shells (2a, 2b).

11. A fan according to one or more of the preceding claims, wherein, with respect to a second two-dimensional system of reference to orthogonal axes (x', y') that is contained in said first plane (Q) of projection and is centred in the point of intersection between said first plane (Q) and said first axis (X), with the axis of the abscissae (x') parallel to said second axis (Y), the point (S) in which the radius of curvature (R') of said arc of circumference (B) is centred has coordinates such that the ratio (x'/D) between its abscissa and the outside diameter (D) of the fan wheel (3) is between 0 and 0.5, and the ratio (y'/D) between its ordinate and the outside diameter (D) of the fan wheel (3) is between 0 and 0.5, said centre (S) of curvature being arranged on the opposite side from said arc (B) with respect to a plane containing said first axis (X) and perpendicular to said second axis (Y).

12. A fan according to claim 11, wherein the angle (E) of the circumferential development of said arc (B) is between 15° and 90°.

13. A fan according to one or more of the preceding claims, wherein the projection in the first plane (Q) of the helical profile of the casing, on the opposite side from the separator (8), is connected, behind the delivery aperture (5), with a fifth and sixth curved section (12a, 12b), having radii of curvature (R5, R6) of opposite sign and defining a point of flexion (F') in the connection zone, the sixth section (12b), closest to the delivery aperture (5), having a convex curvature with respective radius of curvature (R6) centred in the first plane of projection (Q) on the opposite side from the first axis (X) with respect to said curved section (12b).

14. A fan according to claim 11, wherein with respect to said second system of reference to orthogonal axes (x', y') that is contained in the first plane (Q) of projection, the second point of flexion (F') has coordinates (x", y") such that the ratio (x"/D) between its abscissa and the outside diameter (D) of the fan wheel (3) is between 0 and 0.95, and the ratio (y"/D) between its ordinate and the outside diameter (D) of the fan wheel (3) is between 0.4 and 1.4.

15. A fan according to claim 13, wherein the radius of curvature (R6) of the sixth section (12b) is selected to have a value such that the ratio between said radius of curvature (R6) and the outside diameter (D) of the fan wheel (3) is between 0 and 5.

16. A fan according to claim 13, wherein the radius of curvature (R5) of the fifth section (12a) is selected to have a value such that the ratio between said radius (R5) of curvature and the outside diameter (D) of the fan wheel (3) is between 0 and 9.5.

17. A fan according to one or more of the preceding claims, comprising an aperture (15) in at least one of said appendages (9), constituting a pressure intake for the fan or a seat for housing a pressure sensing means.

18. A fan according to claim 17, wherein said aperture (15) is provided integrally with the corresponding appendage (9) of the flow separator (8).

Drawing