EP2058525B1

EP2058525B1 - Impeller for a radial fan and radial fan

Info

Publication number: EP2058525B1
Application number: EP07425710A
Authority: EP
Inventors: Maurizio Achille Abate; Mauro Castello
Original assignee: Elica SpA
Current assignee: Elica SpA
Priority date: 2007-11-12
Filing date: 2007-11-12
Publication date: 2010-04-28
Anticipated expiration: 2027-11-12
Also published as: EP2058525A1; ATE466195T1; RU2008144614A; RU2492363C2; DE602007006209D1

Abstract

An impeller (2) for a radial fan (1) adapted to rotate about a rotation axis (A) comprises a plurality of main blades (25) that are sequentially arranged about such rotation axis (A), and having radially innermost inlet ends (32) and radially outermost outlet ends (33). Each of the main blades (25) comprises a concave main blade first surface (26) and a convex main blade second surface (27) opposite the main blade first surface (26) and facing the main blade first surface of the successive main blade. The main blade first surfaces (26) define main blade arcs (PP) which comprise a first (PP1), a second (PP2), a third (PP3), and a fourth (PP4) main blade circle arcs that are radially arranged from the inside to the outside of the impeller (2), and having a first (R1), a second (R2), a third (R3), and a fourth (R4) main blade radii of curvature, respectively. The main blade radii of curvature (R1, R2, R3, R4) have ratios in the following ranges: R2/R1=1-1.1; R3/R1=1.1-1.2; R4/R1=1.2-1.5.

Description

The objects of the present invention are an impeller for a radial fan and a radial fan provided with such impeller.
Radial fans, in particular fans intended to transfer air and/or gas (frequently in the form of a mixture thereof) to boilers, such as, for example, condensation boilers, comprise a housing provided with a suction port and a air exhausting port. Inside the housing, an impeller is provided which is able to rotate about a rotation axis. The air enters the housing through the suction port in the axial direction, it passes through the impeller, and it is discharged therefrom in the radial direction in a spiral portion of the housing, from where the air reaches the exhausting port. In order to convey the air according to said path, the impeller is provided with a plurality of blades arranged about the rotation axis of the impeller having an arch-shaped profile in the transversal direction to the rotation axis.
Radial fans should be capable of providing suitable lifts in well-defined capacity intervals (so-called "working curves") in order to ensure the proper functioning, for example, of the condensation boiler which they are connected to.
A further particularly felt need, which the research in the field of radial fans devotes considerable efforts to, is to achieve dimension decrements without a performance worsening. In other terms, it is particularly desirable for the radial fans to be capable of achieving efficient working curves, while keeping overall dimensions at not unduly high level.
A further most felt need is that the energy consumption associated with the impeller operation, which is usually actuated by an electric motor, is reduced.
In order to achieve the above-mentioned objects, a number of solutions for radial fans have been proposed, in particular, several conformations of the impeller blades, as well as the housings adapted to receive these latter, have been proposed. Some examples are given in WO 2006/013067 A2 and EP 1 744 060 A2 , in which impellers for radial fans and radial fans in which some of the components have peculiar and advantageous geometric features are disclosed. The document WO 02 16777 , which is considered the closest prior art to the subject-matter of claim 1, discloses the features of the preamble of the claim.
The object of the present invention is to provide an impeller for a radial fan and a radial fan which allow obtaining efficient lift-capacity curves, in particular which are suitable for the operation of condensation boilers, such as not to require undue power consumption for the impeller actuation and which, in the whole, have reduced dimensions.
These and other objects are achieved by an impeller for a radial fan according to claim 1 and a radial fan according to claim 24.
In order to better understand the invention and appreciate the advantages thereof, some non-limiting exemplary embodiments thereof will be described with reference to the annexed Figures, in which:
Fig. 1 is an exploded perspective view of a radial fan according to the invention;
Fig. 2 is a perspective view of an impeller according to the invention;
Fig. 3 is a perspective view from a different angle of the impeller in Fig. 2;
Fig. 4 is a side view of the impeller in Fig. 2;
Fig. 5 is an enlarged view of the detail A of the impeller in Fig. 4;
Fig. 6 is an enlarged view of the detail B of the impeller in Fig. 4;
Fig. 7 is a further side view of the impeller in Fig. 2;
Fig. 8 a further side view of the impeller in Fig. 2;
Fig. 9 is a sectional view, according to the IX-IX line, of the impeller in Fig. 8;
Fig. 10 is a perspective view of a component of the radial fan in Fig. 1;
Fig. 11 is a further perspective view of the component in Fig. 10;
Fig. 12 is a side view of the component in Fig. 10;
Fig. 13 is a sectional view, according to the XIII-XIII line, of the component in Fig. 12;
Fig. 14 is a further side view of the component in Fig. 10;
Fig. 15 is a further side view of the component in Fig. 10;
Fig. 16 is a sectional view, according to the XVI-XVI line, of the component in Fig. 15;
Fig. 17 is a perspective view of a further component of the radial fan in Fig. 1;
Fig. 18 is a further perspective view of the component in Fig. 17;
Fig. 19 is a side view of the component in Fig. 17;
Fig. 20 is a further side view of the component in Fig. 17;
Fig. 21 is a sectional view, according to the XXI-XXI line, of the component in Fig. 20;
Fig. 22 is a further side view of the component in Fig. 17;
Fig. 23 is an exploded, perspective view of an impeller according to a further embodiment of the invention;
Fig. 24 is a perspective view of an impeller according to a further embodiment of the invention.
With reference to the Figures, a radial fan is indicated by the reference numeral 1. The fan 1 is, for example, adapted to convey air and/or gas (also as a mixture thereof) towards a burner, a boiler, or a general heating system. The fan 1 is particularly adapted to the conveyance of air and/or gas towards a condensation boiler.
The fan 1 comprises an impeller 2 able to rotate about a rotation axis A, in particular inside a fan housing 3. In the present specification, and in the annexed Figures, the terms "axial" and "radial" refer to the rotation axis A of the impeller 2, unless otherwise noted.
The housing 3 preferably comprises two mutually connectable, separate parts, for example a half-shell 4 which defines an impeller space 6 adapted to receive the impeller 2 therein, and a lid 5 adapted to close the impeller space 6. The half-shell 4 and the lid 5 can be mutually connected, for example, through threaded couplers 7. The lid 5 can further comprise a projecting portion 5' (Figures 18-19) adapted to shape-fit into the impeller space 6 defined by the half-shell 4, which advantageously is essentially complementary thereto.
The lid 5 is adapted to support a preferably electric motor 8 intended to rotate the impeller 2 through a shaft 9 thereof which, in the assembled fan 1 condition, is coaxial to the rotation axis A. The motor 8 can be connected to the lid 5 through an intermediate support 10 prearranged for the connection to the lid 5, for example through screws 11 to be inserted in corresponding screw seats 12 of the lid 2. Preferably, the screw seats 12 are arranged at constant angular distances along a circumference. For example, the screw seats 12 can be in a number of three and spaced at 120° apart one to the other. In order to make the coupling between screws 11 and screw seats 12 possible, the intermediate support 10 can be provided with as many radial brackets 15 correspondingly distributed to the screw seats 12 of the lid 10.
In order to minimize the vibrations transfer between the motor 8 and the lid 5, the fan 1 can comprise vibration dampening means. According to a possible embodiment, such vibration dampening means comprise first dampeners 13 adapted to act between the intermediate support 10 and the lid 5, for example rubber members provided with an opening passing through the bore for the screws 11, so as to dampen the vibrations parallel to the rotation axis A. Alternatively, or in addition to the first dampeners 13, the fan 1 can further comprise second dampeners 14, acting between the intermediate support 10 and the lid 5, thus oriented and shaped so as to dampen the vibrations which, from the motor 8, transfer to the housing 3 along radial directions. The second dampeners 14, for example, rubber members, can be inserted in support brackets 16 formed by or connected to the lid 5, and preferably arranged along a circumference which is inside the circumference along which the screw seats 12 are arranged. Still more preferably, such support brackets 16 are in a number of three and arranged at 120° one to the other. The second dampeners 14 can, for example, be laterally contacted to the intermediate support 10, so as to act in the radial direction between the latter and the support brackets 16.
In order to ensure the motor 8 a protection during the fan 1 functioning, the latter can comprise a covering member 17 which is connectable to the lid 5, for example, through screws 18. Such covering member 17 is preferably cup-shaped, so as to make the motor 8 not accessible, once the fan 1 is assembled. The covering member 17 can act so as to protect both the motor 8 and one or more further auxiliary members 48, such as, for example, control logic circuits for the motor 8.
Advantageously, in order to allow the passage of the motor 8 shaft 9 through the lid 5 and its connection to the impeller 2 housed in the impeller space 6, the lid 5 comprises a through opening 19.
With further advantage, the fan 1 comprises an air and/or gas suction port 20 and exhausting port 21.
According to a possible embodiment, the suction port 20 and the exhausting port 21 are formed in the half-shell 4 (Figures 1 and 10-16). In particular, the suction port 20 is preferably laterally arranged on the half-shell 4 and it is so shaped that the entering air and/or gas enter the impeller space 6 and reach the impeller 2 along an essentially axial direction. The exhausting port 21 is preferably formed at an end 23 of an exhausting portion 22 of the half-shell 4 which extends in a direction which is essentially tangential to the housing 3, so that air and/or gas discharged by the impeller 2 may circulate in the impeller space 6 according to essentially tangential flow lines, and are discharged by the fan 1 through the exhausting port 21 without being subjected to undue deviations of their motion.
At the end 23 of the exhausting portion 22, a flange 24 can be provided, adapted to connect the fan 1 to outer support members (not shown in the Figures), for example, through threaded couplers.
In order to ensure the air and/or gas motion in the fan 1, the impeller 2 comprises a plurality of main blades 25 sequentially arranged about the rotation axis A (Figures 2-9). Each of such main blades 25 has a radially innermost inlet end 32 and a radially outermost outlet end 33. The inlet end 32 has the function of sucking and entrapping the air and/or gas coming from the suction port 20 in the axial direction, and the outlet end 34 has the function of guiding the air and/or gas discharged by the impeller 2 to the impeller space 6 of the housing 3.
Each of the main blades 25 comprises a concave main blade first surface 26 and a convex main blade second surface 27 opposite the main blade first surface 26. In this way, each of the main blades 25 has an essentially arc-shape. Furthermore, the main blade second surface 27 of each of the main blades 25 is facing the main blade first surface 26 of the next main blade. In this way, a flow passage 28 for air and/or gas conveyance between a radially inner position and a radially outer position of the impeller 1 is formed between two successive main blades of a pair of main blades. In particular, in the assembled condition of the fan 1, the impeller 2, rotating under the effect of the actuation by the motor 8, sucks the air and/or gas from the suction port 20 of the housing 3, coaxial to the impeller 2, and conveys them under the effect of the impeller rotation into the flow passages 28 defined by the main blades 25, finally radially discharging them outside the impeller 2 in the impeller space 6.
The main blades 25 are shaped so as to optimize the inner fluid dynamics of the impeller, hence the overall performance of the fan 1.
In fact, the main blade first surfaces 26 of the main blades 25 are so shaped as to define main blade arcs PP which comprise a main blade first circle arc PP1, a main blade second circle arc PP2, a main blade third circle arc PP3, and a main blade fourth circle arc PP4, radially arranged from the inside to the outside of the impeller 2 (Fig. 5). Each of such circle arcs PP1, PP2, PP3, PP4 has its own radius of curvature, in particular the first circle arc PP1 has a first radius of curvature R1, the second circle arc PP2 has a second radius of curvature R2, the third circle arc PP3 has a third radius of curvature R3, and the fourth circle arc PP4 has a fourth radius of curvature R4. Advantageously, the main blade radii of curvature have ratios in the following ranges:

R2/R1=1-1.1; R3/R1=1.1-1.2; R4/R1=1.2-1.5

Preferably, the above-mentioned ratios between the main blade radii of curvature have approximately the following ratios, ranging within the previously noted intervals:

R2/R1=1.06; R3/R1=1.15; R4 /R1=1.37.

Of course, such preferred ratios can undergo slight deviations, for example associated to working tolerances. Furthermore, evaluating the above-mentioned size ratios, it is of course necessary to take into account the expected rounding off of the decimal numerals. Such remark can be also extended to the dimensional ratios and/or the dimensions which will be described and claimed herein below, therefore it will not be repeated each time.
The main blade arcs PP are advantageously without discontinuity points. In other terms, in the intersection points between successive circle arcs of the same main blade arc PP, the adjacent circle arcs have the same slope or, in mathematical terms, have the same first derivative.
In accordance with an embodiment, the impeller 2 comprises a plurality of auxiliary blades 29 preferably having an extension which is smaller than the main blades 25 extension, also arranged about the impeller 2 rotation axis. The auxiliary blades 29 are individually or in groups arranged between a first and a second main blades of a pair of main blades 25. Preferably, the main blades 25 and the auxiliary blades 29 are alternating one to the others, so that in each of the flow passages 28 a single one of the auxiliary blades 29 is provided for.
Each of the auxiliary blades 29 has a radially inner inlet end 34 and a radially outer outlet end 35.
Furthermore, each of the auxiliary blades 29 comprises a concave auxiliary blade first surface 30 and a convex auxiliary blade second surface 31, opposite the auxiliary blade first surface 30 of the same auxiliary blade 29 (Fig. 6). The auxiliary blade first surface 30 of each of the auxiliary blades 29 is facing the main blade second surface 27 of a first one of the main blades 25 between which the auxiliary blade 29 is arranged, and the auxiliary blade second surface 31 of each of the auxiliary blades 29 is facing the main blade first surface 26 of a second one of the main blades 25 between which the auxiliary blade 29 is arranged.
The auxiliary blade first surfaces 30 of each of the auxiliary blades 29 define auxiliary blade arcs PS which comprise a first circle arc PS1, a second circle arc PS2, and a third circle arc PS3, radially arranged from the inside to the outside of the impeller 2. Each of such auxiliary blade circle arcs PS1, PS2, PS3 has its own radius of curvature, in particular the first circle arc PS1 has a first radius of curvature r1, the second circle arc PS2 has a second radius of curvature r2, and the third circle arc PS3 has a third radius of curvature r3. The auxiliary blade radii of curvature have ratios which are advantageously in the following ranges:

r2/r1=1.06-1.15; r3/r1=1.05-1.1.

Preferably, the auxiliary blade radii of curvature have the following dimensional ratios, ranging within the above-mentioned intervals:

r2/r1=1.11; r3/r1=1.08.

Advantageously, the auxiliary blade arcs PS also are without discontinuity points. In this way, the air and/or gas turbulences are reduced when passing through the flow passages 28; in addition, in this way the overall head losses in the fan 1 during its functioning are also reduced.
The main blades 25 and the auxiliary blades 29 have mutual dimensional ratios specifically designed in order to achieve a high overall performance for the fan 1. In particular, advantageously, the first auxiliary blade radius of curvature r1 and the first main blade radius curvature R1 have a ratio r1/R1 ranging within 1.2-1.3. Preferably, such ratio r1/R1 is equal to about 1.25. Of course, as those skilled in the art will appreciate, after the dimensional ratio between the first auxiliary blade radius of curvature r1 and the first main blade radius of curvature R1 has been known, and also knowing the respective dimensional ratios between the circle arcs of the main blade arcs PP and between the circle arcs of the auxiliary blade arcs PS, it is possible to determinate the overall dimensional ratios of the main blade arcs PP and the auxiliary blade arcs PS.
The main blades 25 have a main blade thickness s_pp defined between the main blade first surface 26 and the main blade second surface 27, and the auxiliary blades 29 have an auxiliary blade thickness s_ps defined between the auxiliary blade first surface 30 and the auxiliary blade second surface 31 (Figures 5 and 6). Advantageously, the first main blade radius R1 and the main blade thickness s_pp have a ratio R1/s_pp ranging within 18-21, preferably equal to about 19.5. Furthermore, advantageously, the first main blade radius r1 and the auxiliary blade thickness s_ps have a ratio r1/s_ps ranging within 23-26, preferably equal to about 24.32. According to a possible embodiment, the main blade thickness s_pp and the auxiliary blade thickness s_ps are constant and essentially equal one to the other, so as to simplify the impeller 2 working operations. It shall be noted that the main blades and/or auxiliary blades thicknesses are evaluated in one of their axial ends. Due to the working operations of the impeller, the blades can have a gradually variable thickness between such two axial ends (for example, in order to make their detachment from the moulds easier). In such a case, the smallest thicknesses of the blades are taken as main blade s_pp and auxiliary blade s_ps thicknesses.
In order to ensure an efficient air and/or gas conveyance through the impeller 2, as well as reduced power consumptions by the motor 8 actuating the impeller 2, it is important that the blades, as well as the above-described shape, also have a suitable spatial arrangement inside the impeller, as well as a suitable orientation at the inlet and outlet ends thereof, where the air and/or gas are respectively suctioned and discharged.
With reference to the main blades (Fig. 8), at the outlet end 33 it is possible to draw a straight line T_outpp which is tangential to the main blade arc PP, and a further radial straight line R_outpp which connects such outlet end 33 to the impeller center, that is to the rotation axis A. Such two straight lines, T_outpp and R_outpp, define a main blade exiting angle β_outpp which, advantageously, ranges between 45° and 55°, and which is preferably equal to about 50.4°.
At the inlet end 32 of the main blade 25 it is also possible to draw a straight line T_inpp which is tangential to the main blade arc PP, and a further radial straight line R_inpp which connects such inlet end 32 to the rotation axis A. Such two straight lines, T_inpp and R_inpp, individuate a main blade entering angle β_inpp which, advantageously, ranges between 0° and 15°, and which is preferably equal to about 12.9°.
The above-mentioned straight lines, R_outpp and R_inpp, passing through the rotation axis A and, respectively, through the inlet end 32 and the outlet end 33 of the main blade 25, form a main blade enclosing angle θ_pp one to the other, which advantageously ranges between 15° and 25°, and which is preferably equal to about 22.8°.
not, with reference to the auxiliary blades 29, through geometric constructions which are completely similar to those described for the main blades 25, it is possible to individuate an auxiliary blade exiting angle β_outps, an auxiliary blade entering angle β_inps, and an auxiliary blade enclosing angle θ_ps (Fig. 4).
The auxiliary blade exiting angle β_outps can range between 45° and 55°, and it is preferably equal to about 50.7°.
The auxiliary blade entering angle β_inps can range between 25° and 35°, and it is preferably equal to about 30.1°.
The auxiliary blade enclosing angle θ_ps can range between 15° and 20°, and it is preferably equal to about 17.8°.
Advantageously, the outlet ends 33 of the main blades 25 are arranged so as to define an impeller outer circumference which essentially delimits the maximum radial dimensions of the impeller. Furthermore, advantageously, the inlet ends 32 of the main blades 25 are arranged so as to define a main blades inner circumference. The impeller outer circumference and the main blades inner circumference have an impeller diameter D_max and a main blades inner diameter d_ipp (Fig. 8), respectively, which, advantageously, have a dimensional ratio D_max/d_ipp ranging within 2-3.5, and which is preferably equal to about 2.78.
At the impeller outer circumference, the impeller 2 has an impeller axial height h_ext (Fig. 7). According to a possible embodiment, the impeller diameter D_max and the impeller axial height h_ext have a ratio D_max/h_ext ranging within 6-9, and which is preferably equal to about 7.37.
Advantageously, the outlet ends 35 of the auxiliary blades are also arranged along the impeller outer circumference (Fig. 4). Furthermore, the inlet ends 34 thereof are arranged so as to define an auxiliary blades inner circumference with an auxiliary blades inner diameter d_ips. Advantageously, the impeller diameter D_max and the auxiliary blades inner diameter d_ips have a ratio D_max/d_ips ranging within 1.2-1.6, preferably equal to about 1.43.
In accordance with an embodiment, the impeller diameter D_max and the first main blade radius of curvature R1 have a ratio D_max/R1 ranging within 4-5, preferably equal to 4.4.
The impeller 2 provided with the blades having the previously-described features can be constructively produced according to different conformations.
In accordance with an embodiment (Fig. 23), the impeller 2 comprises a first 36 and a second 37 separate and connectable support members. The first support member 36 is intended to be connected to the motor 8 shaft 9 for the impeller 2 actuation. The second support member 37 is located opposite the first support member 36 and comprises an opening 38 which is designed, once the fan is assembled, to be arranged in a position which corresponds to the suction port 20 of the housing 3, so as to axially suck the air and/or gas from outside the fan during the impeller 2 rotational movement. The first 36 and the second 37 support members enclose, on two axially opposing sides, the flow passages 28 defined by the blades, thereby forcing the air and/or gas to pass therein. The main and/or auxiliary blades can be made in a single piece with the second support member 37 (as shown in Fig. 23). Alternatively, the blades can be made in a single piece with the first support member 36 (such solution is not shown in the Figures).
In accordance with a further embodiment, the first support member 36, the second support member 37, and the main 25 and/or second 29 blades are mutually separate and connectable (in this regard, reference is to be made, for example, to Fig. 24, in which an impeller 2 is shown provided only with main blades 25). For example, the first 36 and the second 37 support members can comprise connection seats 39 intended to receive connection means which are either connectable to the blades or formed in a single piece therewith.
In accordance with a further embodiment, the first support member 36, the second support member 37, and the main and/or second blades are made as one piece (Figures 2-9), for example by means of a moulding process.
In order to make the single-piece moulding operation of the impeller 2 possible, the first support member 36 and the second support member 37 advantageously have essentially complementary shapes. Furthermore, the first support member 36 and the second support member 37 are arranged so that the projection of the first support member 36 on the second support member 37 along the impeller A rotation axis is correspondent or inner to the air and/or gas opening 38 of the second support member 37. For example, the second support member 37 may be of a ring shape, the air and/or gas passage opening 38 having a circular shape, and the first support member 36 may be of a circular shape having dimensions which are equal to or smaller (preferably slightly smaller) than those of the opening 38.
Advantageously, in order to ensure an easy extraction of the impeller 2 from the moulds, suitable rakes are provided for one or more of the members which extend according to the rotation axis A. In particular, for the main and auxiliary blades, a rake angle δ is provided which ranges between 4 and 9°, preferably it is equal to 7° at the outlet ends 33 and 35 thereof, respectively (in this regard, see, for example, Fig. 9). Preferably, the rake angle δ is so arranged that the impeller 2 radial dimensions are bigger on the first support member 36 side than on the second support member 37 side.
Advantageously, the first support member 36 and the second support member 37 are mutually connected through the main blades 25 (Fig. 3). The latter have their inlet ends 32 on the first support member 36 and comprise connection portions 40 in which the height thereof (in the impeller axial direction) gradually increases, from such inlet ends 32, radially towards the outside, until reaching the peak value at the second support member 37. Starting from the radial position corresponding to the second support member 37, the main blades 25 radially extend to the outside along the second support member 37 to the outlet ends 33 thereof (Fig. 2). Preferably, the outlet ends 33 of the main blades 25, which define the impeller circumference with diameter D_max, radially protrude in relation to the second support member 37, so as to suck air and/or gas possibly entrapped between the impeller 2 and the housing 3 during the fan 1 functioning (Fig. 3).
In order to provide the impeller 2 with a suitable overall stiffness, a stiffening ring 41 can be provided on the impeller 2, also preferably made in a single piece with the impeller 2, connecting the outlet ends 33 of the main blades 25. Preferably, the stiffening ring 41 is located on the first support member 36 side.
In order to allow the connection of the impeller 2 to the motor 8, the first support member 36 advantageously comprises a tubular portion 42 adapted to receive the motor 8 shaft 9 and which preferably extends parallel to the impeller rotation axis A. The shaft 9 can be connected to the tubular portion 42 through locking means (not shown in the Figures) adapted to integrally connect rotationally and translationally the latter along the rotation axis A.
Advantageously, the first support member 36 of the impeller 2 comprises stiffening members adapted to oppose the impeller strains. For example, the first support member 36 can comprise one or more ribs 43 which radially extend starting from the tubular portion 42. Preferably, the ribs 43 are in a number of four and, still more preferably, are crosswise arranged and mutually spaced apart of about 90° (see, for example, Fig. 4).
In accordance with an embodiment, the auxiliary blades 29 extend on the second support member 37 and, still more preferably, are also radially projecting to the outside of the latter, as the main blades 25 are, so as to co-operate in the suction of residual air and/or gas in the gap between the impeller 2 and the housing 3. Furthermore, the auxiliary blades inner circumference, along which the inlet ends 34 of the auxiliary blades 29 are arranged, is preferably located internally to the second support member 37, in a concentric manner thereto (Fig. 4).
The impeller 2, in the single piece configuration, is preferably made of a plastic material.
In order to ensure an efficient overall functioning of the fan 1 when it is assembled, the impeller space 6 preferably has a configuration designed for coupling with the impeller 2 according to one or more of the embodiments described above.
The impeller space 6 of the housing 3 has, in the axial direction, a housing axial height H_all (Fig. 13) which, advantageously, has a ratio to the impeller axial height h_ext ranging within H_all/h_ex = 1.2-1.3. Such ratio is preferably equal to about H_all/_hex = 1.24.
Furthermore, the impeller space 6 of the housing 3, transversally to the height H_all thereof, therefore transversally to the impeller A rotation axis, has a transversal profile which comprises a main length 45 advantageously shaped as a plurality of successive housing circle arcs (Fig. 12). The impeller space 6 transversal profile can further comprise an exhausting length 46, in which the housing 3 extends in the exhausting portion 22, individuated by a reference angle α.
In accordance with an embodiment, the main length 45 comprises four of the above-mentioned successive housing circle arcs, in particular a first CC1, a second CC2, a third CC3, and a fourth CC4 housing circle arcs having a first RC1, a second RC2, a third RC3, and a fourth RC4 housing radii of curvature, respectively. Such housing circle arcs are arranged, preferably starting from the exhausting length 46, with a direction opposite to the rotation of the impeller 2 (in particular, with reference to the Fig. 12, the housing circle arcs are arranged counter-clockwise, while the impeller is intended to rotate clockwise).
Advantageously, such housing radii of curvature have ratios in the following ranges:

RC1/RC2 = 1.04-1.075; RC1/RC3 = 1.075-1.15; RC1/RC4=1.2-1.4.

Preferably, the above-mentioned ratios between the housing radii of curvature are approximately equal to:

RC1/RC2 = 1.06; RC1/RC3 = 1.09; RC1/RC4=1.29.

In accordance with an embodiment, the first housing radius of curvature RC1 and the impeller diameter D_max have a ratio in the following range: D_max/RC1= 1.5-1.8. Preferably, such ratio D_max/RC1 is equal to about 1.63.
The housing circle arcs are advantageously connected so that the main length 45 of the impeller space 6 transversal profile is essentially without discontinuity points.
The exhausting length 46 may have a width α ranging between 60° and 80°, preferably equal to about 70°.
Advantageously, the housing 3 comprises a conveyance tongue 47 adapted to convey air and/or gas exhausted by the impeller 2 towards the exhausting portion 22 and, therefrom, to the exhausting port 21 (Figures 10-16). Such conveyance tongue 47, preferably cantilevered formed in a single piece with the half-shell 4 of the housing 3, is located in the impeller space 6 at the exhausting length 46.
The conveyance tongue 47 advantageously extends along a tongue axis L which comprises an essentially rectilinear length, and which may optionally have slight curvatures at the two conveyance tongue ends, so as to partially enclose the impeller 2.
Furthermore, advantageously, the conveyance tongue 47 has a gradually increasing section along the tongue extension axis L towards the exhausting port 21, so as to force the air and/or gas discharged by the impeller to run a circumferential path along all the impeller space, before reaching the exhausting portion 22. According to a possible embodiment, such gradually increase of the conveyance tongue 47 section takes place in such a way that, proceeding along the tongue L extension axis towards the exhausting port 21, the conveyance tongue 47 width parallel to the rotation axis A increases towards the inner part of the impeller space 6 (Fig. 13).
The housing 3, in particular the half-shell 4 and the lid 5, are preferably made in aluminium or an aluminium alloy.
A possible embodiment of an impeller according to the invention, and a possible embodiment of a housing suitable to be coupled with such impeller will be now described, with reference in particular to the previously described features and geometric sizes.
According to such embodiment, the impeller 2 is provided with seventeen main blades 25 and seventeen auxiliary blades 29. The auxiliary blades 25 and the auxiliary blades 29 are alternatively arranged about the impeller rotation axis A. The impeller circumference has an impeller diameter D_max equal to about 120 mm, along which the outlet ends 33 and 35 of the main blades 25 and the auxiliary blades 29 are arranged, respectively. The impeller 2 further has an axial height h_ext at the impeller circumference equal to about 16.28 mm.
The inlet end 32 of the main blades 25 are arranged according to a main blades inner circumference having a diameter d_ipp of about 43.2 mm. The four main blade circle arcs PP1, PP2, PP3, and PP4 have radii of curvature R1 equal to about 27.3 mm, R2 equal to about 29 mm, R3 equal to about 31.5 mm, and R4 equal to about 37.5 mm, respectively, and are mutually connected without discontinuity in the main blade arc PP profile.
The main blades 25 have a main blade enclosing angle θ_pp equal to about 22.8°, a main blade entering angle β_inpp equal to about 12.9°, and a main blade exiting angle β_outpp equal to about 50.4°.
The main blades 25 further have a thickness s_pp essentially constant and equal to about 1.4 mm (to the axial end with smallest thickness).
The inlet ends 34 of the auxiliary blades 29 are arranged according to an auxiliary blades inner circumference having a diameter d_ips of about 84 mm. The three auxiliary blade circle arcs PS1, PS2, and PS3 have radii of curvature r1 equal to about 34.05 mm, r2 equal to about 37.8 mm, and r3 equal to about 36.75 mm, respectively, and are mutually connected without discontinuity in the auxiliary blade arc PS profile.
The auxiliary blades 29 have an enclosing angle of auxiliary blade θ_pa equal to about 17.8°, an auxiliary blade entering angle β_inps equal to about 30.1°, and an auxiliary blade exiting angle β_outps equal to about 50.7°.
The auxiliary blades further have a thickness s_ps essentially constant and equal to about 1.4 mm (at the axial end with smallest thickness).
A housing 3 adapted to be coupled with an impeller of this kind has the impeller space 6 with an axial height H_all of about 20.28 mm. The impeller space transversal profile is so divided:

the exhausting length 46 has an angular extension α equal to about 70°;

the main length 45 has an extension of 290°.

The four housing circle arcs have the following radii of curvature:

RC1= 74.1 mm; RC2=69.9 mm; RC3= 68.2 mm; RC4 = 57.6 mm.

It has been evaluated that the thus-shaped fan is able to ensure lift values which are high and which do not undergo undue variations when the delivered flow rate capacities vary. Furthermore, it has been verified that the power absorbed by the electric motor for the fan functioning at the working pressure and capacities keeps being at suitably low levels. By way of example, it has been noted, in particular, that:

for capacities of about 49 m³/h, the fan in the described configuration ensures a lift of about 950-1000 Pa for a power at the motor axis of about 35 W;

for capacities of about 35 m³/h, the fan in the described configuration ensures a lift of about 1050-1100 Pa for a power at the motor axis of about 26 W;

for capacities of about 14 m³/h, the fan in the described configuration ensures a lift of about 1150-1200 Pa for a power at the motor axis of about 16.3 W.

The fan overall dimensions, essentially due to the impeller axial and radial dimensions, which dictate the housing axial and radial dimensions, are suitable for the applications which the fans according to the invention are intended to, in particular for air and/or gas supply to condensation boilers.
From the previously-provided description, those skilled in the art shall be able to appreciate how the impeller and fan according to the invention allow obtaining efficient lift-capacity working curves with reduced energetic consumptions for actuating the impeller and reduced overall dimensions.
To the described embodiments of the impeller and the radial fan, those skilled in the art, with the aim of meeting specific, contingent needs, will be able to make a number of adaptations, modifications, or replacements of members with functionally equivalent others, without departing from the scope of the following claims.

Claims

An impeller (2) for a radial fan (1) adapted to rotate about a rotation axis (A), and comprising a plurality of main blades (25) sequentially arranged about said rotation axis (A), and having radially innermost inlet ends (32) and radially outermost outlet ends (33), each of said main blades (25) comprising a concave main blade first surface (26) and a convex main blade second surface (27) opposite said main blade first surface (26) and facing the main blade first surface of the successive main blade, wherein the main blade first surfaces (26) define main blade arcs (PP) comprising a first (PP1), a second (PP2), a third (PP3), and a fourth (PP4) main blade circle arcs that are radially arranged from the inside to the outside of the impeller (2), and having a first (R1), a second (R2), a third (R3), and a fourth (R4) main blade radii of curvature, respectively, characterized in that said main blade radii of curvature (R1, R2, R3, R4) have ratios in the following ranges: R2/R1=1-1.1; R3/R1=1.1-1.2; R4/R1=1.2-1.5.
The impeller (2) according to the preceding claim, comprising a plurality of auxiliary blades (29) individually or in groups arranged about said rotation axis (A) between a first and a second one of said plurality of successive main blades (25), and having radially innermost inlet ends (34) and radially outermost outlet ends (35), wherein each of said auxiliary blades (29) comprises a concave auxiliary blade first surface (30) facing the main blade second surface (27) of said first main blade, and a convex auxiliary blade second surface (31) opposite said auxiliary blade first surface (30) and facing the main blade first surface (26) of said second main blade, wherein the auxiliary blade first surfaces (30) define auxiliary blade arcs (PS) comprising a first (PS1), a second (PS2), and a third (PS3) auxiliary blade circle arcs that are radially arranged from the inside to the outside of the impeller (2), and having a first (r1), a second (r2), and a third (r3) auxiliary blade radii of curvature, respectively, wherein said auxiliary blade radii of curvature (r1, r2, r3) have ratios in the following ranges: r2/r1=1.08-1.15; r3/r1=1.05-1.1.
The impeller (2) according to the preceding claim, wherein said first auxiliary blade radius of curvature (r1) and said first main blade radius of curvature (R1) have a ratio in the following range: r1/R1=1.2-1.3.
The impeller (2) according to any one of the preceding claims, wherein the ratios between said main blade radii of curvature (R1, R2, R3, R4) are approximately equal to the following values: R2/R1=1.06; R3/R1=1.15; R4/R1=1.37.
The impeller (2) according to any of the claims 2 to 4, wherein:
- the ratios between said auxiliary blade radii of curvature (r1,r2,r3) are approximately equal to the following values: r2/r1=1.11; r3/r1=1.08; and

- said first auxiliary blade radius of curvature (r1) and said first main blade radius of curvature (R1) have a ratio approximately equal to: r1/R1= 1.25.
The impeller (2) according to any one of the preceding claims, wherein straight lines (T_outpp) which are tangential to said main blade arcs (PP) at said outlet ends (33) of the main blades (25) form, with radial straight lines (R_outpp) passing through said rotation axis (A) and through said outlet ends (33) of the main blades (25), main blade exiting angles (β_outpp) ranging within 45°-55°.
The impeller (2) according to any one of the preceding claims, wherein straight lines (T_inpp) tangential to said main blade arcs (PP) at said inlet ends (32) of the main blades (25) form, with radial straight lines (R_inpp) passing through said rotation axis (A) and through said inlet ends (32) of the main blades (25), main blade entering angles (β_inpp) ranging within 0-15°.
The impeller (2) according to the claims 6 and 7, wherein said radial straight lines (R_outpp) passing through the outlet ends (33) of the main blades (25) and said radial straight lines (R_inpp) passing through the inlet ends (32) of the main blades (25) form main blade enclosing angles (θ_pp) ranging within 15°-25°.
The impeller (2) according to the preceding claim, wherein:
- said main blade exiting angles (β_outpp) have widths approximately equal to 50.4°;

- said main blade entering angles (β_inpp) have widths approximately equal to 12.9°;

- said main blade enclosing angles (θ_pp) have widths approximately equal to 22.8°.
The impeller (2) according to any of the claims 2 to 9, wherein straight lines tangential to said auxiliary blade arcs (PS) at said outlet ends (35) of the auxiliary blades (29) form, with radial straight lines passing through said rotation axis (A) and through said outlet ends (35) of the auxiliary blades (29), auxiliary blade exiting angles (β_outps) ranging within 45-55°.
The impeller (2) according to any of the claims 2 to 10, wherein straight lines tangential to said auxiliary blade arcs (PS) at said inlet ends (34) of the auxiliary blades (29) form, with radial straight lines passing through said rotation axis (A) and through said inlet ends (34) of the auxiliary blades (29), auxiliary blade entering angles (β_inps) ranging within 25°-35°.
The impeller (2) according to the claims 10 and 11, wherein said radial straight lines passing through the outlet ends (35) of the auxiliary blades (29), and said radial straight lines passing through the inlet ends (34) of the auxiliary blades (29) form auxiliary blade enclosing angles (θ_ps) ranging within 15°-20°.
The impeller (2) according to the preceding claim, wherein:
- said auxiliary blade exiting angles (β_outps) have widths approximately equal to 50.7°;

- said auxiliary blade entering angles (β_inps) have widths approximately equal to 30.1°;

- said main blade enclosing angles (θ_ps) have widths approximately equal to 17.8°.
The impeller (2) according to any one of the preceding claims, wherein said outlet ends (33) of the main blades (25) define an impeller outer circumference having an impeller diameter (D_max), and said inlet ends of the main blades (25) define a main blades inner circumference having a main blades inner diameter (d_ipp), said impeller diameter (D_max) and said main blades inner diameter (d_ipp) having a ratio in the following range: D_max/d_ipp=2-3.5.
The impeller (2) according to the preceding claim, having an impeller axial height (h_ext) at said impeller outer circumference, said impeller diameter (D_max) and said impeller axial height (h_ext) having a ratio in the following range: D_max/h_ext=6-9.
The impeller (2) according to the claim 14 or 15, wherein said outlet ends (35) of the auxiliary blades (29) are arranged along said impeller outer circumference, and said inlet ends (34) of the auxiliary blades (29) define an auxiliary blades inner circumference having an auxiliary blades inner diameter (d_ips), said impeller diameter (D_max) and said auxiliary blades inner diameter (d_ips) having a ratio in the following range: D_max/d_ips=1.2-1.6.
The impeller (2) according to the preceding claim, wherein:
- said impeller diameter (D_max) and said impeller axial height (h_ext) have a ratio approximately equal to D_max/hext=7.37;

- said impeller diameter (D_max) and said main blades inner diameter (d_ipp) have a ratio approximately equal to D_max/d_ipp = 2.78;

- said impeller diameter (D_max) and said auxiliary blades inner diameter (dips) have a ratio approximately equal to D_max/d_ips=1.43;
The impeller (2) according to any of the claims 14 to 17, wherein said impeller diameter (D_max) and said first main blade radius of curvature (R1) have a ratio in the following range: D_max/R1=4-5.
The impeller (2) according to the preceding claim, wherein said impeller diameter (D_max) and said first main blades radius of curvature (R1) have a ratio approximately equal to the following value: D_max/R1=4.4.
The impeller (2) according to any one of the preceding claims, wherein said main blades (25) have a main blade thickness (s_pp) defined between said main blade first surface (26) and said main blade second surface (27), said first main blade radius of curvature (R1) and said main blade thickness (s_pp) having a ratio in the following range: R1/spp=18-21.
The impeller (2) according to the preceding claim, wherein said first main blade radius of curvature (R1) and said main blade thickness (spp) have a ratio approximately equal to R1/spp=19.5.
The impeller (2) according to claim 20 or 21, wherein said auxiliary blades (29) have an auxiliary blade thickness (s_ps) defined between said auxiliary blade first surface (30) and said auxiliary blade second surface (31), said main blade thickness (s_pp) and said auxiliary blade thickness (s_ps) being approximately constant and essentially equal one to the other.
The impeller (2) according to any one of the preceding claims, wherein said main blade radii of curvature have about the following values: R1=27.3 mm; R2=29 mm; R3=31.5 mm; R4=37.5 mm.
A radial fan (1) comprising a housing (3) which defines an impeller space (6) adapted to receive an impeller (2) according to any one of the preceding claims.
The radial fan (1) according to the preceding claim when dependant from claim 15, wherein said impeller space (6) of the housing (3) has a housing axial height (H_all) , said housing axial height (H_all) and said impeller axial height (h_ext) having a ratio in the following range: H_all/h_ext = 1.2-1.3.
The radial fan (1) according to the preceding claim, wherein said housing axial height (H_all) and said impeller axial height (h_ext) have a ratio approximately equal to: H_all/h_ext = 1.24.
The radial fan (1) according to any of the claims 24 to 26, wherein said impeller space (6) has, transversally to said rotation axis (A) of the impeller (2), a transversal profile comprising a main length (45) shaped as a plurality of successive circle arcs.
The radial fan (1) according to the preceding claim, wherein said impeller space (6) transversal profile further comprises an exhausting length (46), at an exhausting portion (22) projecting from the housing (3), which comprises an exhausting port (21) for an air and/or gas exit arranged in fluid connection with said impeller space (6).
The radial fan (1) according to the preceding claim, wherein said main length (45) comprises a first (CC1), a second (CC2), a third (CC3), and a fourth (CC4) housing circle arcs of said plurality of housing successive circle arcs arranged starting from said exhausting length (46) having a direction which is opposite the rotation direction of the impeller (2), said housing circle arcs (CC1, CC2, CC3, CC4) having a first (RC1), a second (RC2), a third (RC3), and a fourth (RC4) housing radii of curvature, respectively, wherein said housing radii of curvature (RC1, RC2, RC3, RC4) have ratios in the following ranges: RC1/RC2=1.04-1.075; RC1/RC3= 1.075-1.15; RC1/RC4=1.2-1.4.
The radial fan (1) according to the preceding claim, wherein said housing radii of curvature (RC1, RC2, RC3, RC4) have the following ratios: RC1/RC2=1.06; RC1/RC3= 1.09; RC1/RC4=1.29.
The radial fan (1) according to claim 29 or 30, wherein the impeller diameter (D_max) and said first housing radius of curvature (RC1) have a ratio in the following range: D_max/RC1= 1.5-1.8.
The radial fan (1) according to the preceding claim, wherein said ratio between the impeller diameter (D_max) and the first housing radius of curvature (RC1) is equal to about 1.63.
The radial fan (1) according to any of the claims 29 to 32, wherein said housing radii of curvature (RC1, RC2,RC3,RC4) have about the following values: RC1= 74.1 mm; RC2=69.9 mm; RC3= 68.2 mm; RC4 = 57.6 mm.
The radial fan (1) according to any of the claims 28 to 33, wherein said exhausting length (46) has a width (α) ranging between 60° and 80°.
The radial fan (1) according to any of the claims 28 to 34, wherein said housing (3) further comprises a conveyance tongue (47) located in the impeller space (6) at said exhausting length (46), wherein said conveyance tongue (47) extends according to a tongue axis (L) which comprises an essentially rectilinear length, and has a gradually increasing section towards said exhausting port (21) along said tongue axis (L).