Centrifugal electric fan with forward-bladed rotor

Abstract

A centrifugal electric fan (100) comprises a scroll (S), a baffle (9) arranged in the scroll at the outlet (5), an electric motor (6) having a drive shaft (60), and a rotor (7) keyed to the drive shaft (60) and arranged in the scroll (S); the scroll (S) comprises two half-bodies (1); each half-body (1) has a side edge (11) that defines a perimeter (B) in the shape of an evolute that continues with the baffle (9); the geometry of the perimeter (B) is defined by means of dimensional ratios between the radius (R0) of the rotor and the radii (R1, R2, R3, R4, R5) of sections shaped like an arc of a circle of the evolute-shaped perimeter.

Description

[0001] The present invention relates to a centrifugal electric fan with forward-bladed rotor, particularly for extractor hoods for domestic use.

[0002] EP3211242A1, US2002131861A1 and WO8302646A1 disclose centrifugal electric fans. Such a type of electric fan has a casing, which is defined as "scroll", wherein a rotor driven by an electric motor is mounted. The air is sucked from inlets and is ejected from an outlet of the electric fan. Since such electric fans have no baffle at the outlet, the airflow is turbulently conveyed towards the outlet, resulting in a loss in the fluid dynamic efficiency of the electric fan.

[0003] The purpose of the present invention is to eliminate the drawbacks of the prior art by providing an electric fan that is capable of maximizing its fluid dynamic efficiency.

[0004] Another purpose is to provide such an electric fan that is efficient, reliable, versatile, and space-saving.

[0005] These purposes are achieved in accordance with the invention with the features of the appended independent claim 1.

[0006] Advantageous achievements of the invention appear from the dependent claims.

[0007] The centrifugal electric fan according to the invention is defined by claim 1. The optimization design of the air intake in the electric fan refers only to the geometric shape of the scroll and of the baffle.

[0008] In order to evaluate the aerodynamic performance of the electric fan according to the invention, numerous experimental tests were carried out by the applicant, using the same electric motor and the same rotor with different geometric shapes of the profile of the scroll and of the baffle. In such a way, it was possible to study and analyze the different configurations of the scroll and of the baffle, identifying the improvements needed to optimize the aerodynamic efficiency of the electric fan.

[0009] For such a purpose, a research study aimed at improving the aerodynamic process of the air intake was undertaken. In order to increase the efficiency of the aerodynamic process, the issue related to the analysis of the airflows exiting the electric fan was examined, with a detailed analysis of the contributions of the resulting airflow vector and of all the other vector components of the airflow.

[0010] With reference to the modification made to optimize the aerodynamics of the electric fan, a special baffle was provided at the outlet of the electric fan that continues the evolute-shaped profile of the scroll. Such a baffle was properly designed and realized by taking into consideration the relative directions of the airflow vector coming out of the electric fan. As a matter of fact, if not properly designed, such a baffle would create an obstruction for the exiting airflow, worsening the fluid dynamic efficiency, without bringing any improvement.

[0011] Therefore, in order to obtain the hypothesized improvements, the various vectorial components of the airflow vector were examined. The empirical tests carried out directly on the various prototypes of the scroll made it possible to identify the correct configuration and dimension of the baffle to be used in order to achieve the hypothesized improvements.

[0012] As a result of the aerodynamic and aeraulic studies carried out on various prototypes of the scroll, the applicant identified a solution that is capable of increasing the efficiency of such a type of the electric fans available on the market by about 10 %.

[0013] The innovation mainly refers to the realization of a special internal geometry of the scroll of the fan and of the baffle. The geometries of the arcs of a circle used for the geometric construction of the profile of the half-bodies of the scroll and of the profile of the baffle and the respective coordinates of the centers of the arcs of a circle will be indicated hereinafter in detail.

[0014] The scroll terminates in the baffle, which represents the geometric part that most affects the improvement of the aeraulic efficiency.

[0015] Although centrifugal electric fans with a baffle are known, up to now, none of them has achieved the aerodynamic efficiency obtained by the electric fan according to the invention. Such a result can be demonstrated by comparing the performance obtained with the same rotor and the same electric motor by the electric fans available on the market with the values measured by the electro fan according to the invention.

[0016] Thus, it can be said that the provision of the baffle is of strategic importance for the improvement of the aeraulic efficiency. Nevertheless, a generic arrangement of such a baffle does not guarantee a clear improvement in the aerodynamic performance of the electric fan; on the contrary, if it is not placed and sized correctly, the baffle could represent an obstacle to the exit of the airflow.

[0017] Therefore, the innovation brought by the electric fan according to the invention lies precisely in the accurate construction of the entire scroll and especially of the baffle.

[0018] Further features of the invention will appear clearer from the following detailed description, which refers to a purely illustrative and therefore non-limiting embodiment, illustrated in the attached drawings, wherein: Figs. 1 and 2 are two perspective views of a centrifugal electric fan according to the invention seen from different angles; Fig. 3 is a perspective view of the centrifugal electric fan according to the invention, wherein a half-body of the scroll has been removed; Fig. 4 is a top view of a half-body of the scroll with the rotor of the centrifugal electric fan according to the invention; Fig. 5A is the same view as Fig. 4, wherein the centers and the radii of curvature of the evolute-shaped profile of the half-body of the scroll of the centrifugal electric fan according to the invention are shown; Fig. 5B is the same view as Fig. 4, wherein the angles at the center of the arcs of a circle of the evolute-shaped profile of the half-body of the scroll of the centrifugal electric fan according to the invention are shown; Fig. 6 is a diagrammatic view illustrating the evolute-shaped perimeter of the half-body, the circular perimeter of the rotor, the junction points of five portions shaped like an arc of a circle of the evolute and the angles at the center subtended at the junction points; Fig. 7 is a table illustrating the performance values obtained in an experimental test by the electric fan according to the invention; and Fig. 8 is a table illustrating the performance values obtained in an experimental test by an electric fan according to the prior art.

[0019] With the aid of the figures, a centrifugal electric fan according to the invention is described, which is comprehensively indicated with reference numeral 100.

[0020] With reference to Figs. 1 and 2, the centrifugal electric fan (100) comprises a box-shaped casing, commonly referred to as scroll (S).

[0021] The scroll (S) has at least one inlet (3) for the intake of air and one outlet (5) for the exit of air. The inlet (3) has an axis (A1) and the outlet (5) has an axis (A2) orthogonal and skewed to the axis (A1) of the inlet (3).

[0022] Generally, the scroll (S) has two inlets (3) arranged on opposite sides of the scroll and having the same axis (A1).

[0023] Referring to Fig. 3, the centrifugal electric fan (100) comprises an electric motor (6) arranged in the scroll (S). The electric motor (6) has a drive shaft (60) having the same axis (A1) as the inlets (3).

[0024] A rotor (7) is keyed to the drive shaft (60) and is arranged in the scroll (S) around the electric motor (60). The rotor (7) is a centrifugal rotor.

[0025] The rotor (7) comprising a support plate wherein the drive shaft (60) is centrally keyed in such a way that the drive shaft is orthogonal relative to the support plate of the rotor. A plurality of blades (70) protrudes from the support plate of the rotor. The blades (70) of the rotor are forward blades, that is, blades having a forward curvature with respect to the direction of rotation of the rotor.

[0026] Thus, a rotation of the rotor (7) causes an intake of air from the inlets (3) and a delivery of air from the outlet (5).

[0027] A baffle (9) is arranged inside the scroll (S), opposite the outlet (5) to convey the air towards the outlet (5).

[0028] The scroll (S) comprises two substantially identical half-bodies (1). The two half-bodies (1) are concave in shape and are coupled together to define a compartment wherein the rotor (7) driven by the electric motor (6) is arranged. The half-bodies (1) can be made of aluminum or plastic.

[0029] Referring to Fig. 4, the half-body (1) has a plate-shaped back wall (10) with an evolute-shaped perimeter. The half-body (1) has a side edge (11) that rises from the back wall (10) following the evolute-shaped perimeter of the back wall.

[0030] The inlet (3) is centrally formed in the back wall (10) of the half-body (1).

[0031] The half-body (1) has a semicylindrical duct (12) that is coupled with a corresponding semicylindrical duct of another half-body to form the outlet (5), which is cylindrical in shape, with a diameter (D) substantially identical to the diameter of the rotor (7). For illustrative purposes, the diameter (D) of the outlet may be 140-155 mm.

[0032] As shown in Fig. 4, the outlet (5) of the scroll has an axis (A2) orthogonal and skewed to the axis (A1) of the inlet (3) of the scroll.

[0033] The baffle (9) is arranged in the half-body (1) opposite the outlet (5) so as to continue the side edge (11) of the half-body with an evolute-shaped profile. The baffle (9) extends for about half of the diameter of the outlet (5). So, the baffle (9) has one end (90) that ends near the axis (A2) of the outlet. The end (90) of the baffle terminates at a cut-out point (B7).

[0034] Fig. 5 illustrates the center P0 of the rotor that coincides with the axis (A1) of the inlet, the radius R0 of the rotor, and five centers (P1, P2, P3, P4, P5) and five respective radii of curvature (R1, R2, R3, R4, R5) for the construction of an evolute-shaped profile of the half-body (1) of the scroll and of the baffle (9).

[0035] Fig. 6 illustrates a circumference (C) of the rotor (7) and an evolute-shaped perimeter (B) defined by the side edge (11) of the half-body and by the baffle (9).

[0036] Hereafter, all dimensional references are understood with a tolerance of ± 5%.

[0037] The circumference (C) is tangent to the outermost edges of the blades (70) of the rotor. The circumference (C) has a center (P0) on the axis (A1) of the drive shaft (60) coincident with the axis of the inlet (3) of the half-body (1). The circumference (C) of the rotor has a radius (R0) of 73.5 mm, that is, the rotor (7) has a diameter of 147 mm.

[0038] Two Cartesian axes (X, Y) passing through the center (P0) of the circumference of the rotor were drawn, wherein the x-axis (X) is parallel to the axis (A2) of the outlet (5) and the y-axis (Y) is orthogonal to the axis (A2) of the outlet.

[0039] The evolute-shaped section of the perimeter (B) of the half-body and of the baffle (9) goes from an initial point (B1), which is near where the x-axis (Y) intersects the perimeter (B), to an end point (B6), which is near the end (90) of the baffle. The baffle (9) continues from the end point (B6) of the evolute to the cut-out point (B7).

[0040] The perimeter of the semi-cylindrical duct (12) defining the outlet (5) is defined by two straight lines (12a, 12b) parallel to each other. The first straight line (12a) of the semi-cylindrical duct perimeter is connected to the initial point B1 of the evolute.

[0041] The evolute-shaped section of the perimeter (B) going from the initial point (B1) to the end point (B6) is obtained by means of five sections shaped like an arc of a circle having different radii and different centers.

[0042] A first section shaped like an arc of a circle goes from the initial point (B1) to a second point (B2), has a center P1 in the first quadrant of the Cartesian axes and a radius R1 of 123.5 mm. The arc of a circle (B1-B2) is subtended by an angle (α1) of about 42°-47°.

[0043] A second section shaped like an arc of a circle goes from the second point (B2) to a third point (B3), has a center P2 in the fourth quadrant of the Cartesian axes and a radius R2 of 109 mm. The arc of a circle (B2-B3) is subtended by an angle (α2) of about 95°-100°.

[0044] A third section shaped like an arc of a circle goes from the third point (B3) to a fourth point (B4), has a center P3 in the third quadrant of the Cartesian axes and a radius R3 of 92 mm. The arc of a circle (B3-B4) is subtended by an angle (α3) of about 64°-69°.

[0045] A fourth section shaped like an arc of a circle goes from the fourth point (B4) to a fifth point (B5) that lies in the middle of the baffle (9); the fourth section shaped like an arc of a circle (B4-B5) has a center P4 in the third quadrant of the Cartesian axes and a radius R4 of 82.5 mm. The arc of a circle (B4-B5) is subtended by an angle (α4) of about 72°-77°.

[0046] A fifth section shaped like an arc of a circle goes from the fifth point (B5) to a sixth point (B6), has a center P5 in the third quadrant of the Cartesian axes, near the circumference (C) and a radius R5 of 150.5 mm. The arc of a circle (B5-B6) is subtended by an angle (α5) of about 7°-12°.

[0047] A straight end section (91), and not a section shaped like an arc of a circle, is provided between the sixth point (B6) and the end cut-out point (B7) of the baffle. The end section (91) of the baffle has a length of about 35-40 mm and an inclination of about 75°-80° with respect to the x-axis.

[0048] The first arc of a circle (B1-B2) at the initial point (B1) is tangent to the first straight line (12a) of the outlet.

[0049] The first arc of a circle (B1-B2) and the second arc of a circle (B2-B3) have the same tangent at the junction point B2.

[0050] The second arc of a circle (B2-B3) and the third arc of a circle (B3-B4) have the same tangent at the junction point B3.

[0051] The third arc of a circle (B3-B4) and the fourth arc of a circle (B4-B5) have the same tangent at the junction point B4.

[0052] The fourth arc of a circle (B4-B5) and the fifth arc of a circle (B5-B6) have the same tangent at the junction point B5.

[0053] The fifth arc of a circle (B5-B6) is tangent to the end section (B6-B7) of the baffle at the junction point B6.

[0054] Following is a table with the Cartesian coordinates of the various points of the scroll profile of the semi-body expressed in millimeters. Table 1POINTSDESCRIPTIONCOORDINATESP0Rotor center(0, 0)P1Center of first arc with radius R1(17.00; 1.33)P2Center of second arc with radius R2(7.06; 11.89)P3Center of third arc with radius R3(-4.04; -1.52)P4Center of fourth arc with radius R4(0; -9.67)P5Center of fifth arc with radius R5(-66.36; -22.01)B6Evolute end point(74.46; 29.65)B7Baffle cut-out point(74,75; 48,19)

[0055] According to the invention, the geometry of the evolute-shaped profile of the scroll and of the baffle and the dimensions of the scroll are such to ensure the following dimensional ratios between the radii of curvature of the sections shaped like an arc of a circle of the evolute and the radius of the rotor: Rp 1 = R 1 / R 0 = 1.68 Rp 2 = R 2 / R 0 = 1.48 Rp 3 = R 3 / R 0 = 1.25 Rp 4 = R 4 / R 0 = 1.12 Rp 5 = R 5 / R 0 = 2.04

[0056] In addition, it should be considered that the baffle (9) has an end section (91) extending between the points B6 and B7, which is basically straight, has a length of about 35-40 mm and an inclination of about 75°-80° with respect to the x-axis.

[0057] The applicant carried out comparative tests between an electric fan according to the invention and an electric fan according to the prior art that is commonly found on the market. The tests were done using the same rotor and the same motor.

[0058] Fig. 7 illustrates the results obtained with the electric fan according to the invention. Fig. 8 illustrates the results obtained with the electric fan according to the prior art.

[0059] As it can be seen from the results obtained, the electric fan according to the invention showed an efficiency higher by about 10 percentage points than the electric fan of the prior art.

[0060] The electric fan of the prior art showed a maximum fluid dynamic efficiency (FDE) of 36.1%, whereas the fan according to the invention showed a maximum FDE of 40%.

[0061] Having used the same electric motor and the same rotor in both tests, it can be seen that the improvement depends solely and exclusively on the special geometry of the scroll and of the baffle of the electric fan according to the invention.

[0062] In particular, the special geometry of the baffle (9) conveys the airflow exiting the electric fan in a direction perpendicular to the exit plane of the airflow defined by the outlet (5). the following normalized values were considered: The following normalized values were considered to properly compare the measured values of volumetric flow rate, static pressure and active electric power: Ambient Temperature: 20 [°C] Atmospheric Pressure: 1013.25 [mBar] Relative Humidity: 50 [%]

[0063] Therefore, from the analysis of the reported data, it can be concluded that the increase in the active electric power obtained with the centrifugal electric fan (100) according to the invention is caused by an increase in the static pressure and in the volumetric flow rate. The increase in the values of static pressure and volumetric flow rate of the airflow allows a maximum FDE increase of 3.9% and an overall FDE increase of about 10% compared to a fan of the prior art.

[0064] The increase in the aerodynamic parameters is due to the provision of the baffle (9) with the particular configuration described above. In fact, a generic position of the baffle would cause an obstruction for the airflow exiting the fan; for such a reason, it was necessary and essential to design and prototype a particular geometry of the scroll and of the baffle, taking into account the existing ratios between the radius (R0) of the rotor and the radii (R1, R2, R3, R4, R5) of the arcs of a circle used for the construction of the evolute-shaped profile of the scroll and of the baffle.

[0065] Equivalent variations and modifications may be made to the present embodiment of the invention, within the scope of a person skilled in the art, but still within the scope of the invention as expressed by the appended claims.

Claims

1. Centrifugal electric fan (100) comprising: - a scroll (S) having at least one inlet (3, 4) with axis (A1) and an outlet (5) with axis (A2), said axis (A2) being skew to the axis (A1) of the inlet, - a baffle (9) arranged in the scroll opposite the outlet (5), - an electric motor (6) arranged in the scroll (S) and having a drive shaft (60) with an axis that is coincident with the axis (A1) of the inlet, and - a rotor (7) keyed to the drive shaft (60) and arranged in the scroll (S); the rotor having a center (P0) on the axis (A1) of the inlet and a radius (R0), wherein said scroll (S) comprises two half-bodies (1) having a concave shape, which are coupled to each other so as to define a compartment; each half-body (1) having a plate-shaped back wall (10) with a side edge (11) so as to define a perimeter (B) in the shape of an evolute that continues with said baffle (9), wherein when drawing two Cartesian axes (X, Y) passing through the center (P0) of the rotor, the x-axis (X) is parallel to the axis (A2) of the outlet and the y-axis (Y) is orthogonal to the axis (A2) of the outlet, characterised in that said perimeter (B) in the shape of an evolute is being obtained by means of five sections shaped like an arc of a circle: - a first section shaped like an arc of a circle subtended by an angle (α1) of 42°-47° from an initial point (B1) to a second point (B2), having a center P1 and a radius R1; - a second section shaped like an arc of a circle subtended by an angle (α2) of 95°-100° from the second point (B2) to a third point (B3), having a center P2 and a radius R2; - a third section shaped like an arc of a circle subtended by an angle (α3) of 64°-69° from the third point (B3) to a fourth point (B4), having a center P3 and a radius R3; - a fourth section shaped like an arc of a circle subtended by an angle (α4) of 72°-77° from the fourth point (B4) to a fifth point (B5), having a center P4 and a radius R4; and - a fifth section shaped like an arc of a circle subtended by an angle (α5) of 7°-12° from the fifth point (B5) to a sixth point corresponding with an end point (B6) of the evolute, having a center P5 and a radius R5 said baffle having a straight end section (91) between the end point (B6) of the evolute and a cut-out point (B7) of the baffle, so that the baffle extends for about half the diameter of said outlet (5), wherein the center of the rotor (P0), the centers (P1. P2, P3, P4, P5) of the sections shaped like an arc of a circle, the end point (B6) and the cut-out point (B7) have the coordinates shown in the following table, expressed in millimeters with a tolerance of ± 5%; POINTSDESCRIPTIONCOORDINATESP0Rotor center(0, 0)P1Center of first arc with radius R1(17.00.; 1.33)P2Center of second arc with radius R2(7.06; 11.89)P3Center of third arc with radius R3(-4.04; -1.52)P4Center of fourth arc with radius R4(0; -9.67)P5Center of fifth arc with radius R5(-66.36; -22.01)B6Evolute end point(74.46; 29.65)B7Baffle cut-out point(74.75; 48.19) the following ratios between the radius (R0) of the rotor and the radii of curvature (R1, R2, R3, R4, R5) of the sections shaped like an arc of a circle of the evolute being defined, with a tolerance of ± 5%: Rp 1 = R 1 / R 0 = 1.68 Rp 2 = R 2 / R 0 = 1.48 Rp 3 = R 3 / R 0 = 1.25 Rp 4 = R 4 / R 0 = 1.12 Rp 5 = R 5 / R 0 = 2.

042. The centrifugal electric fan (100) according to claim 1, wherein the rotor (7) has a radius (R0) of 73.5 mm, with a tolerance of ± 5%.

3. The centrifugal electric fan (100) according to claim 1 or 2, wherein the radii of curvature (R1, R2, R3, R4, R5) of the sections shaped like an arc of a circle of the evolute have the following values with a tolerance of ± 5%: R 1 = 123.5 mm R 2 = 109 mm R 3 = 92 mm R 4 = 82.5 mm R 5 = 150.5 mm4. The centrifugal electric fan (100) according to any one of the preceding claims, wherein said end section (91) of the baffle has a length of 35-40 mm and an inclination of 75°-80° with respect to the x-axis.

5. The centrifugal electric fan (100) according to any one of the preceding claims, wherein said rotor (7) is a forward-bladed rotor.

6. The centrifugal electric fan (100) according to any one of the preceding claims, wherein said outlet (5) has a diameter that is substantially equal to the diameter of the rotor (7).

7. The centrifugal electric fan (100) according to any one of the preceding claims, wherein the baffle (9) extends for about half the diameter of the outlet (5).

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