DESCRIPTION

Technical field

The present invention relates to a sound-reducing panel, configured for application to an axial fan apparatus to reduce a noise from the impeller of the axial fan.

In general, the present invention finds application in the fields of ventilation, air conditioning, de-humidification, cooling or heating, and in any technical field where apparatuses including fans, in particular axial type fans, are present.

Prior art

Fans, i.e. air circulation pumps, are sources of noise when in operation. In fact, the impeller of a rotating fan propagates an acoustic field, due among other things to the interaction of the fan blades with the air and to the noise of the electric motor used to turn the impeller blades. This acoustic field generated by the fan is clearly undesirable and therefore represents noise that propagates into the environment.

There is a wide range of apparatuses that incorporate a fan for their operation; they include machinery such as heat pumps, air conditioners, ventilation systems.

Document US6880813 (B2) relates to a sound-attenuating apparatus to be mounted on a heat exchanger such as a cooling tower, having a vertical attenuator housing with perforated internal walls to define an air passage.

Document JPH0571767 (A) relates to a multilayer fan casing having arbitrary shapes, adapted to cancel sound waves by interference, for the reduction of the noise generated by an external fan unit. Document CN 106014924 (A) relates to a box-shaped element for an air pump, adapted to eliminate noise and dissipate heat; the box-shaped element comprises sound-absorbing material at the internal walls.

Document US5473123 (A) relates to a combined air duct apparatus with silencer, which can be connected to a fan unit; a resonator chamber for reducing the noise generated by the fan unit extends around or adjacent to the inlet or outlet which is connected to the fan unit. Part of the chamber includes peripheral walls with a plurality of holes and facing onto the air flow passages. A non-perforated diffuser plate provides uniform air distribution at the outlet.

Document US20050191 169 (Al) relates to a silencer for a ventilation system, for example for an air intake system in a gas turbine, comprising a body with several sections.

Document US4330047 (A) relates to a sound-attenuating ventilation louver to allow gaseous flows to pass into and out of a chamber while minimizing the noise; the louver includes a plurality of profiled slats each in the form of an aerodynamically- shaped blade, each slat including a solid portion made of a sound-absorbent material and a hollow portion defined by a thin wall of rigid material; the hollow portion of each slat is subdivided into a plurality of chambers communicating with the atmosphere through ports and acting as resonators.

Document W02008 106526 (Al) relates to a noise reducing air handler including a plenum, a fan and a conditioning apparatus; the air handler further includes a sound-attenuating panel to interact with a flow of air in the plenum to attenuate sound.

However, known solutions are not fully effective in acoustically attenuating the acoustic field or noise generated by a fan, particularly in the case of an axial fan.

Summary of the invention An object of the present invention is to overcome drawbacks of the prior art.

A particular object of the present invention is to more effectively attenuate an acoustic field or noise generated by a fan apparatus, in particular an axial fan.

A further particular object of the present invention is to present a noise reduction system that is compact.

A further particular object of the present invention is to enable a better regulation of the air flow exiting from a fan, in particular an axial fan.

A further particular object of the present invention is to present a solution that is suitable for application on existing fan apparatuses, such as heat pumps, air conditioning and air circulation systems.

These and other objects are achieved by means of a sound-reducing panel according to the attached claims, which form an integral part of this description.

An idea underlying the present invention is to provide a sound-reducing panel for an axial fan apparatus, comprising a planar main body comprising: a sound-reducing surface configured to face towards a fan outlet of the axial fan apparatus; at least one perimetric acoustic resonator at at least one outer edge of said sound-reducing surface.

Advantageously, by means of the sound-reducing panel of the present invention it becomes possible to attenuate a sound field or a noise generated by an axial fan apparatus.

The at least one acoustic resonator comprises at least one internal cavity to the planar main body, and further comprises at least one inlet slit open towards the at least one internal cavity at a plane of the sound-reducing surface, in particular providing at least one resonator of lambda/4 or Helmholtz type. Thus, advantageously, the resonator of the lambda/4 or Helmholtz type enables a sound field or noise generated by the axial fan apparatus to be attenuated more effectively, while at the same time providing a sound-reducing panel that is compact in size.

In a preferred embodiment, the sound-reducing surface further comprises at least a first perforated portion, comprising a first plurality of holes or slits distributed therein, which contributes to a further attenuation of the sound field or noise generated by the axial fan apparatus.

In a preferred embodiment, the sound-reducing surface further comprises a non-planar element protruding from the sound-reducing surface, for example a bell-shaped element, configured at the fan outlet to fluid-dynamically interact with an air flow exiting from the axial fan apparatus.

Advantageously, this non-planar element contributes to a better regulation of the air flow exiting from the axial fan, with beneficial effects also on the overall reduction of the sound field or noise.

The sound-reducing panel according to the present invention further comprises a fixing system, configured to apply and position the sound- reducing surface at and at a predetermined distance from an axial fan apparatus.

Advantageously, the sound-reducing panel according to the present invention is particularly effective when applied to axial fan apparatuses, also pre-existing ones, such as heat pumps, air conditioning and air circulation systems and in general in all industrial machinery and/or household appliances in which an axial fan is present.

The present invention also relates to an axial fan apparatus comprising a sound-reducing panel. Further features and advantages will become more apparent from the following detailed description of preferred, non-limiting forms of embodiment of the present invention and dependent claims outlining preferred, particularly advantageous embodiments of the invention.

Brief description of the drawings

The invention is illustrated by reference to the following figures, provided by way of non-limiting example, wherein:

Figure 1 illustrates a front view of an example of an axial fan apparatus.

Figure 2 illustrates an upper view of the axial fan apparatus from Figure 1.

Figure 3 illustrates an upper view of the axial fan apparatus of Figure 2, to which an example of a sound-reducing panel according to the present invention is applied.

Figure 4 illustrates a side view of Figure 3, including the example of a sound-reducing panel according to the present invention.

Figure 5 illustrates a front view of a first embodiment of a sound- reducing panel according to the present invention.

Figure 6 illustrates an upper section view of the first embodiment of a sound-reducing panel according to the present invention.

Figure 7 illustrates a side section view of the first embodiment of a sound-reducing panel according to the present invention.

Figure 8 illustrates a front view of a second embodiment of a sound-reducing panel according to the present invention.

Figure 9 illustrates an upper section view of the second embodiment of a sound-reducing panel according to the present invention.

Figure 10 illustrates a side section view of the second embodiment of a sound-reducing panel according to the present invention.

Figure 11 illustrates a front view of a third embodiment of a sound- reducing panel according to the present invention.

Figure 12 illustrates a perspective view of the third embodiment of a sound-reducing panel according to the present invention, applied to an axial fan apparatus.

Figure 13 illustrates an upper view of a fourth embodiment of a sound-reducing panel according to the present invention, applied to an axial fan apparatus.

Figure 14 illustrates a front view of a fifth embodiment of a sound- reducing panel according to the present invention.

Figure 15 illustrates an upper section view of the fifth embodiment of a sound-reducing panel according to the present invention.

Figure 16 illustrates a perspective view of the fifth embodiment of a sound-reducing panel according to the present invention, applied to an axial fan apparatus.

Figure 17 illustrates a perspective view of a sixth embodiment of a sound-reducing panel according to the present invention.

Figure 18 illustrates a front view of a seventh embodiment of a sound-reducing panel according to the present invention.

In the different figures, similar elements will be identified by similar reference numbers.

Furthermore, in the figures, where there are several analogous elements, only one of them will be indicated by a reference number for the sake of clarity; the other analogous elements, even if not indicated by a reference number, will be included by analogy.

Detailed description

Figure 1 illustrates a front view of an example of an axial fan apparatus 10.

Such an axial fan apparatus 10 represents an example of machinery to which the present invention is applicable, as it will be explained below. In general, the present invention is of considerable applicability for machinery such as heat pumps and air conditioners, ventilation systems and devices in general comprising axial fans.

The axial fan apparatus 10 has a fan outlet 11 downstream of the fan 12 itself, from which the air flow generated by the fan 12 is dispersed into the environment. The outlet 11 constitutes a preferential propagation route for the noise produced both by fan 12 and by aerodynamic phenomena associated with the air flow, with emission propagating into the environment from the outlet 11.

Furthermore, the axial fan apparatus 10 may comprise additional noise sources such as, for example, an electric motor or a compressor 13, internal to its casing. Figure 2 illustrates an upper view of the axial fan apparatus 10.

The axial fan 12 provides creation of an air flow of non-homogeneous speed 14, with minimum speed at the central part of the fan 12 and maximum speed at the radial ends of the fan 12. This non- homogeneous air speed profile 14 is the cause of aerodynamic phenomena and turbulence that increase the acoustic emission of the axial fan apparatus 10.

Figure 3 illustrates an upper view of the axial fan apparatus 10, to which an example of a sound-reducing panel 100 according to the present invention is applied.

The sound-reducing panel according to the present invention is in fact configured to reduce the noise generated by the axial fan 12 propagated to the surrounding environment.

In general, the sound-reducing panel 100 comprises a planar main body

101, applied to the axial fan apparatus 10, in particular perpendicular to the direction of exit of the air flow coming from the fan 12 and coming from the outlet 11.

The planar main body 101 comprises a sound-reducing surface 102, configured to face towards the fan outlet 11 of the axial fan apparatus 10.

The planar main body 101 comprises at least one perimetric acoustic resonator 103 at at least one outer edge of the sound-reducing surface

102.

It should be noted that the perimetric acoustic resonator 103, which will be further described, is not placed in the immediate vicinity of the air flow exiting the fan outlet 11, as a turbulent grazing flow is established in this area, which may constitute a disturbance to the air flow and lead to increased turbulence and creation of unwanted secondary acoustic sources.

According to the present invention, advantageously, the at least one perimetric acoustic resonator 103 is placed at an outer edge of the sound-reducing surface 102, thus sufficiently far away from the turbulent area at the fan outlet 11.

In particular, the overall dimensions of the planar main body 101 may substantially correspond to the overall dimensions of a face of the axial fan apparatus 10.

Figure 4 illustrates a side view of the axial fan apparatus 10 and of the example of sound-reducing panel 100 according to the present invention.

The sound-reducing panel 100 comprises a fixing system 104 configured to position a sound-reducing surface 102 of the panel, which will be further described, at a predetermined distance from the axial fan apparatus 10.

In the preferred example of application of the sound-reducing panel 100 to a machinery such as a heat pump or air conditioner, the sound- reducing panel 100 may be anchored through anchoring elements 104, preferably angular ones, to the base supports of the machinery 10 of which the axial fan 12 is a part.

Figure 5 illustrates in greater detail a front view of a first embodiment of the planar main body 101 of a sound-reducing panel 100 according to the present invention.

The at least one acoustic resonator 103 placed at at least one outer edge of the sound-reducing surface 102, comprises at least one internal cavity 105 to the main planar body 101.

The at least one acoustic resonator 103 further comprises at least one inlet slit 106 open towards the at least one internal cavity 105, at a plane of the sound-reducing surface 102.

Thus, the acoustic resonator 103 comprising the internal cavity 105 and the inlet slit 106, provides a resonator of the lambda/4 or Helmholtz type.

In preferred embodiments, the planar main body 101 is rectangular or squared-shaped, comprising two perimetric acoustic resonators 103 on outer edges of opposite sides of the sound-reducing panel.

Figure 6 illustrates an upper section view of the first embodiment of the planar main body 101. In this view, the at least one internal cavity 105 to the planar main body 101, and the inlet slit 106 open towards the at least one internal cavity 105 at a plane of the sound-reducing surface 102 can be viewed.

The at least one inlet slit 106, when the sound-reducing panel is installed on the axial fan apparatus 10, is located at a predetermined distance from the fan outlet 11, on a plane perpendicular to a rotation axis of an axial fan 12 having the fan outlet 11. In fact, the fan outlet 11, as will be further described, is located in a central area of the sound-reducing surface 102.

Figure 7 illustrates a side section view of the first embodiment of the planar main body 101.

Since this embodiment provides for only two perimetric acoustic resonators 103 on outer edges that are lateral and opposite, no internal cavities 105 are visible in this meridian section.

Figure 8 illustrates a front view of a second embodiment of the planar main body 201 of a sound-reducing panel 100 according to the present invention.

The at least one acoustic resonator 203 placed at at least one outer edge of the sound-reducing surface 102, comprises at least one internal cavity 205 to the main planar body 201.

The at least one acoustic resonator 203 further comprises at least one inlet slit 206 open towards the at least one internal cavity 205, at a plane of the sound-reducing surface 102.

Thus, the acoustic resonator 203 comprising the internal cavity 205 and the inlet slit 206, provides a resonator of the lambda/4 or Helmholtz type.

In preferred embodiments, the main planar 201 body is rectangular or squared-shaped, comprising four perimetric acoustic resonators 203 on all four outer edges.

Figure 9 illustrates an upper section view of the second embodiment of the main planar body 201.

In this view, the at least one internal cavity 205 to the planar main body 201, and the inlet slit 206 open towards the at least one internal cavity 205 at a plane of the sound-reducing surface 102 can be viewed.

The at least one inlet slit 206, when the sound-reducing panel is installed on the axial fan apparatus 10, is located at a predetermined distance from the fan outlet 11, on a plane perpendicular to a rotation axis of an axial fan 12 having the fan outlet 11. In fact, the fan outlet 11, as will be further described, is located in a central area of the sound-reducing surface 102.

Figure 10 illustrates a side section view of the second embodiment of a sound-reducing panel according to the present invention.

Since this embodiment comprises four perimetric acoustic resonators 203 on all the outer edges, also in this view, the at least one internal cavity 205 at the main planar body 201, and the inlet slit 206 open towards the at least one internal cavity 205, at a plane of the sound- reducing surface 102, can be viewed.

Figure 11 illustrates in greater detail a front view of a third embodiment of the planar main body 301 of a sound-reducing panel 100 according to the present invention.

The planar main body 301 comprises the at least one acoustic resonator 103 placed at the at least one outer edge of the sound-reducing surface 102, the at least one internal cavity (not visible in the figure) and the at least one inlet slit 106, which are analogous to what has already been described.

The planar main body 301 further comprises a sound-reducing surface 102 further comprising at least a first perforated portion 307. The first perforated portion 307 comprises a first plurality of holes or slits, distributed on the sound-reducing surface 102.

The plurality of holes or slits may be periodically or randomly distributed on the sound-reducing surface 102.

Each perforation of the holes or slits, projected onto the plane of the sound-reducing surface 102, identifies a concave or convex shape. Preferably the shape of such projections of holes or slits is circular or elongated.

Figure 12 illustrates a perspective view of the third embodiment of the planar main body 301 of a sound-reducing panel 100 according to the present invention, applied to an axial fan apparatus 10.

It is understood that the planar main body 301, applied to the apparatus 10, is perpendicular to a rotation axis of the axial fan 12 (not visible in the figure) having the fan outlet 11 (not visible in the figure) .

It is also understood that the first plurality of holes or slits extend in depth inside the planar main body 301, at least partially perpendicular to the sound-reducing surface 102.

In this way, the sound-reducing panel 100 is positioned downstream of the air flow of the fan 12 and invested by the flow exiting from the fan outlet 12 of the machinery 10 (or also of a ventilation duct associated with the fan itself).

The sound-reducing panel 100 thus provides multiple effects for noise reduction:

- the acoustic resonators 103 provide sound absorption and/or insulation at specific frequency ranges that are characteristic of the resonator;

- the planar main body 301 provides broadband isolation of the radiated sound emission in the direction of the air flow, being an obstacle to the free propagation thereof;

- the addition of the first perforated portion 307, preferably with an air cavity behind it which will be further described, allows sound absorption to be provided at specific frequency ranges;

- in the case where the sound-reducing panel 100 is applied to a machinery 10 having other sources of acoustic emission, such as the compressor 13 of a heat pump or an air conditioner, the use of non- homogeneously distributed perforations in the first perforated portion 307, may be effective for the absorption at the characteristic frequencies of the fan 13 and of the other acoustic sources.

Figure 13 illustrates an upper view of a fourth embodiment of the planar main body 401, applied to an axial fan apparatus 10.

The planar main body 401 comprises the at least one acoustic resonator 103 placed at at least one outer edge of the sound-reducing surface 102.

The sound-reducing surface 102 further comprises a non-planar element 408 protruding from the sound-reducing surface 102.

The non-planar element 408 is configured at the fan outlet 11 to fluid- dynamically interact with an air flow exiting from the axial fan apparatus 10. The non-planar element 408 is substantially bell-shaped, with an apex at a centre of the fan outlet 11.

The presence of the non-planar element 408 offers a guide to the air flow, which is slowed down and gradually deflected towards a direction perpendicular to the rotation axis of the fan 12, reducing turbulence and therefore acoustic propagation. The air flow is regulated and conveyed towards the perimetric acoustic resonators 103, preventing the resonators 103 from disturbing the air flow, thus avoiding an increased turbulence and the creation of unwanted secondary sound sources.

Figure 14 illustrates a front view of a fifth embodiment of the planar main body 501 of a sound-reducing panel 100 according to the present invention.

In this embodiment, the sound-reducing surface 102 further comprises a protruding non-planar element 408, which is analogous to what is described.

The sound-reducing surface 102 further comprises at least a first perforated portion 307, comprising a first plurality of holes or slits distributed on the sound-reducing surface 103.

In this embodiment, the planar element 408 is also affected by the first plurality of holes or slits of the first perforated portion 307.

Figure 15 illustrates an upper section view of the planar main body 501.

Again, it can be also understood that the first plurality of holes or slits extend in depth inside the main planar body 501, at least partially perpendicular to the sound-reducing surface 102, and internally also to the planar element 408.

The holes or slits of the first perforated portion 307 are passing through a first portion of the sound-reducing surface 102, and the planar main body 501 further comprises a closing planar element 509, parallel to the sound-reducing surface 102 and configured to define a rear cavity 510.

The rear cavity 510 is therefore in iluidic communication with the at least one first perforated portion 307, and its presence allows for additional sound absorption to be provided at specific frequency ranges.

Preferably, the planar closing element 509 of the rear cavity 510 defines a thickness of the planar main body 501 which is analogous to a second thickness of the at least one perimetric acoustic resonator 103, to the advantage of the overall compactness of the sound-reducing panel 100.

Figure 16 illustrates a perspective view of the fifth embodiment of the planar main body 501 of a sound-reducing panel 100 according to the present invention, applied to an axial fan apparatus 10.

It is understood that the non-planar element 408 is substantially bell shaped, with an apex at a centre of the fan outlet 11.

Figure 17 illustrates a perspective view of a sixth embodiment of a planar main body 601 of a sound-reducing panel 100 according to the present invention.

The main planar body 601 comprises the sound-reducing surface 102, the at least one acoustic resonator 103, the first perforated portion 307, the non-planar element 408 which are analogous to what has already been described.

In this embodiment, the sound-reducing surface 102 further comprises at least a second perforated portion 611 comprising a second plurality of holes or slits distributed on the sound-reducing surface 102.

The second plurality of holes or slits 611 has dimensions and/or distribution different from the first plurality of holes or slits 307, representing a further acoustic tuning element of the sound-reducing panel 100. The expedient of having both a first and a second plurality of holes or slits on the sound-reducing surface 102 different from each other is particularly effective if there are additional sound sources (for example, an electric motor or a compressor 13) in the axial fan apparatus 10.

Figure 18 illustrates a front view of a seventh embodiment of a planar main body 701 of a sound-reducing panel 100 according to the present invention.

The planar main body 701 comprises the sound-reducing surface 102, the at least one acoustic resonator 103, the first perforated portion 307 and the second perforated portion 611, which are analogous to what has already been described.

In this sense, the main planar body 701 corresponds to the main planar body 601 with the exception of the non-planar element 408, which is absent in this embodiment.

Industrial applicability

Advantageously, the sound-reducing panel of the present invention enables a sound field or noise generated by an axial fan apparatus to be attenuated. Therefore, the sound-reducing panel according to the present invention is particularly effective in application to axial fan apparatuses, such as heat pumps, air conditioning and air circulation systems and in general in all industrial machinery and/or household appliances in which an axial fan is present.

In general, the sound-reducing panel of the present invention may be an original equipment of an axial fan apparatus, or an accessory thereof which may also be integrated at a later time into a pre-existing machinery.

In view of the description given here, the person skilled in the art may devise further modifications and variants in order to meet contingent and specific requirements.

For example, the sound-reducing panel may be smaller or larger than one face of the axial fan apparatus.

In addition, it is possible for the sound-reducing panel to have a shape other than rectangular or square, for example being circular around the fan outlet.

In addition, instead of providing a fixing system, the sound-reducing panel could be directly integrated into the aesthetic cover of an axial fan apparatus.

Again, the sound-reducing panel could comprise more than one perimetric acoustic resonator, for example a double acoustic resonator frame or even two or more acoustic resonators in series. A single internal cavity of a perimetric acoustic resonator may comprise more than one inlet slit.

It is also clear that, where there are no obvious technical incompatibilities to those skilled in the art, the configurations of specific elements described with reference to certain embodiments, can be used in other embodiments described herein.

The embodiments described here are therefore intended to be illustrative and non-limiting examples of the invention.