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Patent Searching and Data


Title:
A CENTRIFUGAL FAN
Document Type and Number:
WIPO Patent Application WO/2010/018607
Kind Code:
A1
Abstract:
There is described a centrifugal fan comprising a radial impeller (2) and a manifold (4) for receiving the impeller, with at least one intake cross- section (5) and at least one outlet cross-section (6) for the flow which is produced by the impeller, the impelier (2) being provided so as to be moved in rotation about an axis of rotation (X), the intake cross-section (5) and the outlet cross-section (6) being provided near the axis of rotation and in a position remote from that axis, respectively. The impeller (2) comprises a plurality of substantially radial blades (3) which extend in an axial direction between a disc (7) and a counter-disc (8) which are fixedly joined to the blades and which define, together with the blades, corresponding conduits (9) which extend between the intake and outlet cross-sections, the counter-disc (8) extending between those cross- sections (5, 6) with spacing from a wall (11) of the manifold (4) facing it, and wherein the counter-disc (8) is provided with at least one through-hole (15) through the counter-disc so as to place each conduit (9) of the impeller (2) in fluid communication with the spatial region (13) defined between the counter-disc (8) and the wall (11) of the manifold facing it.

Inventors:
RANALLI ANTONIO (IT)
TANONI FRANCESCO (IT)
Application Number:
PCT/IT2009/000367
Publication Date:
February 18, 2010
Filing Date:
August 05, 2009
Export Citation:
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Assignee:
LN 2 SRL SOCIO UNICO (IT)
RANALLI ANTONIO (IT)
TANONI FRANCESCO (IT)
International Classes:
F04D29/28; F04D27/02
Foreign References:
FR1528797A1968-06-14
DE2357305A11975-05-22
DE2550481A11977-05-18
US5628616A1997-05-13
Attorney, Agent or Firm:
FABRIS, Stefano et al. (Piazzetta Cappellato Pedrocchi 18, Padova, IT)
Download PDF:
Claims:
CLAIMS

1. A centrifugal fan comprising a radial impeller (2) and a manifold (4) for receiving that impeller, with at least one intake cross-section (5) and at least one outlet cross-section (6) for the flow which is produced by the impeiier, the impeller (2) being provided so as to be moved in rotation about an axis of rotation (X), the intake cross-section (5) and the outlet cross-section (6) being provided near the axis of rotation and in a position remote from the axis of rotation, respectively, the impeller comprising a plurality of substantially radial blades (3) which extend in an axial direction between a disc (7) and a counter-disc (8) which are fixedly joined to the blades and which define, together with the blades- (3), corresponding conduits (9) which extend between the intake and outlet cross-sections (5, 6), the counter-disc (8) extending between the cross-sections with spacing from a wall (11) of the manifold (4) facing it, characterized in that the counter-disc (8) is provided with at least one through-hole (15) through the counter-disc so as to place each conduit (9) of the impeller in fluid communication with the spatial region (13) defined between the counter- disc (8) and the wall (11) of the manifold facing it.

2. A fan according to claim 1, wherein the hole (15) extends along a circumferential profile which is concentric relative to the axis (X).

3. A fan according to claim 2, wherein the hole (15) is a slot-like hole which extends without any gap along the circumferential profile, defining a first portion (8a) and a second portion (8b) of a counter-disc (8) which are mutually separate and distinct. 4. A fan according to claim 3, wherein the slot-like hole (15) has an annular formation and is delimited by a pair of concentric annular edges (16a, 16b) which belong to the first portion and second portion (8a, 8b) of the counter-disc, respectively, with mutual spacing.

5. A fan according to claim 4, wherein, with the relationship between the distance (t) measured perpendicuiariy relative to the axiai direction between the edges of the profiles of the portions (8a, 8b) of the counter- disc (8) and the outside radius (R9) of the fan being indicated as the first relationship, and the relationship between the radial distance (Rt) from the axis of the annular edge (16b) nearest the axis (X) and the outside radius (Rg) of the fan (2) being indicated as the second relationship, the first and second relationships are selected in the following value intervals:

0.01 < t/Rg < 0.25 0.4 ≤ Rt/Rg < 0.99

6. A fan according to any one of the preceding claims, comprising a member having an annular profile (20) arranged in a position facing and concentric relative to the hole (15), the profile being positioned at a predetermined distance from the hole (15), in the axial direction, so as to define a first passage and a second passage for the flow which passes through the hole (15) downstream of the counter-disc (8) with respect to the direction of flow.

Description:
A centrifugal fan

Technical Field

The present invention relates to a centrifugal fan having the features set out in the preamble of main claim 1. Technological Background

Centrifugal fans of the above-mentioned type are well known for being used in pre-mixing air/gas mixtures for burners of heating devices. They are typically provided with a bladed impeller which is housed in a manifold which is, for example, helical, and inside which the impeller is rotatably supported so as to be driven about an axis of rotation. Typically, the intake cross-section is formed laterally in the manifold , and is constructed in the form of an opening which is coaxial with the axis of the impeller. The outlet cross-section of the impeller is connected to the helical volute of the manifold so as to impart to the radial flow which is generated by the impeller a main tangential component as far as the outlet cross- section of the manifold.

A typical structural form of a centrifugal fan makes provision for the set of blades to extend, in the axial direction, between a base disc, which carries a hub for connection to the shaft of the impeller, and a counter-disc which extends between the intake cross-section and outlet cross-section of the impeller. Those discs define, together with the blades of the impeller, bladed conduits with cross-sections of the conduits having profiles of closed contour, those conduits extending between the axially opposing walls of the manifold for receiving the impeller. ' In those configurations of fans, the region between the counter-disc and the wall of the manifold facing it is normally the location for recirculation of fluid which flows from the outlet cross-section into the intake region, with consequent reductions in terms of performance and effectiveness of the fan. On the other hand, the above-mentioned region is provided so as to bring about, aibeit minimai, spacing between the fan and the manifold, which are in relative movement during the operation of the fan. Any interposition of sliding type sealing means between the impeller and the counter-disc would not be an acceptable solution because of the reduction in effectiveness which it would involve owing to the occurrences of friction in addition to the wear which would occur between the parts in contact. Statement of the Invention

A main object of the invention is to provide a fan which is structurally and operationally configured to overcome the limits set out with reference to the prior art mentioned.

This object is achieved by the invention by means of a fan which is constructed in accordance with the appended claims. Brief Description of the Drawings

Further features and advantages of the invention will be better appreciated from the following detailed description of one preferred embodiment thereof which is illustrated by way of non-limiting example with reference to the appended drawings, in which :

Figure 1 is a perspective view of a fan constructed in accordance with the invention, - Figure 2 is an axially sectioned view of part of the fan of Figure 1, Figure 3 is a view corresponding to that of Figure 2 of a fan constructed in accordance with the prior art,

Figure 4 is an axially sectioned view of a detail of part of the fan of the preceding Figures, - - Figure 5 is a view corresponding to that of Figure 4, in a construction variant of the invention. Preferred Embodiment of the Invention

With reference to the Figures mentioned, a centrifugal fan is generally designated 1 and comprises an impeller 2 which has a set of blades having a plurality of blades 3 which extend substantially radially and a manifold 4 for receiving the impeller.

There are defined in the impeller of the fan an intake cross-section 5 and an outlet cross-section 6 which are arranged at the intake profile and outlet profile of the blades 3, respectively. The impeller 2 can be rotated about an axis of rotation X, for example, by means of a motor which is not illustrated, to the driving shaft of which (also not illustrated) there is provision for the impeller 2 to be securely attached.

The intake cross-section 5 is advantageously constructed in the form of a circular opening 5a of the manifold, which is coaxial with the axis X, as illustrated in Figure 1, and the outlet cross-section 6 is constructed as an opening 6a which extends circumferentially at the outer diameter of the impeller 2. The measurement of the outer radius of the impeller is designated R 9 (Figure 4). The set of blades formed by the blades 3 extends parallel with the axial direction from a first disc 7 until it terminates at a second opposing counter-disc 8. Each pair of adjacent blades 3 defines, together with the disc 7 and the counter-disc 8, a bladed conduit 9 which extends between the intake cross-section 5 and outlet cross-section 6 and in which the fluid processed by the fan is conveyed in the direction of the outlet cross- section.

The disc 7 radially extends, with respect to the axis X, with spacing from a first wall 10 of the manifold 4. At the opposite side, the counter-disc 8 also extends substantially parallel with and spaced-apart from a second wall 11 of the manifold, as clearly shown in Figure 2.

There remain formed spatial regions which are designated 12 and 13 between the discs 7, 8 and the corresponding walls 10, 11 facing them, respectively.

Advantageously, the counter-disc 8 and the wall 11 facing it have a surface profile of conical extent having a main axis X, as illustrated in the axial section of Figure 2.

According to a main feature of the invention, the counter-disc 8 is provided with a slot-like hole which has a circumferential profile concentric with the axis X and which is designated 15. The hole 15 extends through the thickness of the counter-disc 8 so as to define a passage for fluid communication between each bladed conduit 9 and the spatial region 13 which is external with respect to the conduit and which is delimited by the wall 11.

The counter-disc 8 is divided by the hole 15, which extends without any gap, into two separate portions designated 8a, 8b. In greater detail, the slot-like hole 15 is of annular construction and is delimited by a pair of concentric annular edges 16a, 16b which belong to the first and the second portion 8a, 8b of the counter-disc, respectively, in a mutual spaced-apart relationship. With reference to Figure 2, the recirculation of fluid which is brought about owing to the provision of the slot-like hole 15 is indicated with the arrows A, which recirculation limits the "by-pass" which is normally found in impellers having a closed counter-disc (which is continuous), an example of which is shown in Figure 3, in which the flow is indicated with the arrows B..

In Figure 2, the arrows B' indicate a residual by-pass flow which occurs in the impellers according to the invention, wherein there is produced, owing to the slot-like hole 15, a type of aerodynamic sealing which is produced in the alternative to contact type sealing. With reference to Figure 4, there being designated t the distance measured in an axial direction between the edges of the profiles of the portions 8a, 8b of the counter-disc 8 defining the hole 15 and R t the radial distance of the edge 16b which defines the radial positioning of the hole 15 with respect to the counter-disc 8, the dimensional relationships t/R g and Rt/Rg are selected in the following preferred value intervals:

0.01 < t/R g < 0.25

Figure 5 illustrates a construction variant of the invention, in which details similar to those of the preceding example are referred to with the same reference numerals.

That variant differs principally in that there is provision, in the spatial region 13, in a position facing the hole 15, for a body having an annular profile which is designated 20 and which is fixedly joined to the stationary wall 11 of the manifold 4. That profile is formed so as to have a quadrilateral cross-section and is positioned with predetermined spacing from the passage which is defined by the slot-like hole 15 in the counter- disc 8, as clearly shown in the corresponding Figure. The symbol s designates the distance, measured perpendicularly relative to the generating line of the conical profile of the counter-disc 8, between the counter-disc itself and the profile 20. The dimension of the cross-section of the profile 20 measured radially with respect to the axis X is designated t 2 . The measurement of the radial dimension of the opening 20a formed between the edge 16b and the facing edge of the profile 20 is designated ti.

The measurement of the radial dimension of the opening 20b which is formed between the edge 16a and the corresponding facing edge of the profile 20 is designated t 3 . The radial distance from the axis X of the edge 16b of the hole 15 is designated R tl , which distance identifies the radial positioning of the slot-like hole in the counter-disc 8.

The preferred values of the following dimensional relationships are:

0.005 < ti/R g < 0.25, with i = 1, 2, 3

0.4 < R t i/R g < 0.98, with i = 1, 2, 3

The invention thereby achieves the object set out and provides a number of advantages over known solutions.

It will further be appreciated that the slot-like hole provided in the cqunter-disc is also advantageous during balancing because it acts as a means for engaging any balancing masses which may have to be positioned on the impeller during such a step.

A main advantage consists in that, with the fan according to the invention, it is possible to obtain aerodynamic type sealing in contrast to the recirculation of fluids which occurs between the intake cross-section and outlet cross-section in fans of conventional type. Such sealing advantageously limits the by-pass effect which is typically found in impeller structures with manifolds having counter-discs of a closed type in the radial direction, that is to say, which extend continuously between the intake cross-section and outlet cross-section of the fan. In other words, the invention achieves an overall increase in the performance and effectiveness with respect to solutions of the conventional type.