FIELD OF INVENTION:
The disclosed invention relates to the automobile industry and specifically to the cooling section of the automobiles. This invention discloses the noise reduction mechanism incorporated in electric motor driven radiator fan, which is an axial flow fan, of electric vehicles. This is also applicable to crankshaft driven fans such as used in internal combustion engines and hydrostatic drive fans.
BACKGROUND OF THE INVENTION:
Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. Most radiators are constructed to function in automobiles, buildings, and electronics. The radiator, that being located behind the front grille of a commercial vehicle, passes the hot radiator fluid or coolant through metal “fins” which disperse the heat. As the coolant passes through the radiator it is cooled by an axial flow fan. Maintaining the radiator is important for keeping the vehicle in good working condition.
Axial flow fan is the most widely used fan for cooling purposes in electric vehicle (EV) and in internal combustion engine (ICE) vehicles. In EV a radiator fan exchanges heat from motor, motor controller, HVAC compressor and battery etc. In ICE vehicles a radiator fan exchanges heat in the engine. When an engine is running, it produces heat, and that heat dissipates so that the engine does not become too hot and overheat. The cooling fans are part of the cooling system and their design helps to maintain and cool the temperature in the engine. The cooling fans, with multiple blades, spin rapidly to provide cooler air to pass through the radiator.
The radiator fans do not work alone. They are part of a larger overall cooling system in the vehicle. All the parts should be working correctly for the fan to be able to do its mechanism and cool the engine. Different kinds of radiator fans exist, and they all work slightly differently.
The radiator fans are situated between the radiator and the engine, although some radiator fans are located at the front of the radiator. Many of the fans are electric. The electric

radiator fans mounted in the front of the radiator are known as pusher fans. Those located at the rear of the radiator are called puller fans. The pusher fans receive air that comes in through the grill area and then they push that cooler air over the radiator. The puller fans pull the air from the grill, drawing it over the radiator.
Engine cooling fans have long been recognized as one of the major noise sources in a vehicle. As the engine and other vehicle components are made quieter, the need to reduce fan noise has become more and more urgent. To reduce fan noise in a cost-effective manner, it is necessary to incorporate the component of noise reduction into an early design stage without degradation of the aerodynamic performance of the fan.
In case of internal combustion engine vehicle, most of the times the engine is louder than the fan. Hence, least importance is given to the fan noise. Whereas in case of electric vehicles, the fan noise becomes predominant because of the absence of engine noise and can be perceived easily. The radiator fan noise is heard inside the cabin as well as exterior to the vehicle. Hence there is a need for the fan noise reduction.
An axial radiator fan is a type of fan that causes air to flow through it in an axial direction, parallel to the shaft about which the blades rotate. The flow is axial at entry and exit. The fan is designed to produce a pressure difference, and hence force, to cause a flow through the fan. Factors which determine the performance of the fan include the construction of blades, sturdily of blades, number and shape of the blades.
The axial flow fan such as electric motor driven fan includes several blades each having a base attached to a central hub that is driven by an electric motor. The blades extend radially outward from the central hub. A shroud is placed circumferentially around the blade tips with finite clearance. Several support struts extend from the motor to the fan shroud to provide structural support and to keep the motor in centre to the shroud.
The fan noise is classified into discrete frequency noise and broadband noise. When the fan rotates during operation, the fan blades produce variations in air pressure. The pressure pulsations in the surrounding air results in a discrete frequency tone being generated that is equal to number of blades multiplied by the fan speed in revolutions per second. This is called the blade passing frequency (BPF). These tones are enhanced by the obstructions

located in the air stream such as motor support struts. The presence of the shroud and support housing has a very powerful impact on the acoustics of the axial flow fan. The blade interaction with the disturbances caused by these support struts generate sound at frequencies that are multiples of fan speed (multiples of BPF) thereby producing discrete frequency noise.
Broadband noise is related to random force fluctuations on the blade, which are generated by the interaction of blade surfaces with the turbulent flow. Heat exchangers/radiators installed upstream of a fan would be typical sources of such turbulence in the incident airflow. Tip clearance is also a source of broadband noise. The pressure imbalance at the tip of the fan blades causes roll-up of a tip vortex, which is shed downstream of the blade. The unsteady tip vortex interacts with both the trailing edge from which it is shed, and the leading edge of the following blade causing broadband noise to be generated. Another source of broadband noise is the vortex shedding at the trailing edge of a fan blade. Hence the reduction in the broadband noise decreases the overall noise to a great extent and improves the passenger comfort.
SUMMARY OF THE INVENTION:
It is an object of the invention to provide an automotive cooling system that generates less noise than the conventional cooling system. Another object of the present invention is to provide an automotive radiator system which should not cause any disturbances to flow of air thereby reducing the noise in the cooling system.
In one embodiment of the present invention, the broadband noise is reduced with the constructional structure of flat inner cone (IC) and outer cone (OC) concept. These plain cones are placed on the downstream (pressure) side of the fan. The inner cone’s minor diameter side is fixed to the motor and the major diameter side is closed and kept towards the fan downstream side. The outer cone’s minor diameter side is fixed to the fan shroud and the major diameter side is kept open towards the fan downstream side. Sound generated from the fan is radiated in all directions around the fan. Part of the sound radiation is reflected between the inner cone’s outer surface and the outer cone’s inner surface resulting in energy loss and hence noise reduction on the downstream side.

In another embodiment of the present invention, the cones are made with a perforated sheet and acoustic material such as polyurethane foam (PUF) or ceramic wool that is swathed as lining on the inner surface of the inner cone and on the outer surface of the outer cone. The reflected sound between the inner and outer cones penetrate through these perforations and gets absorbed by the acoustic material resulting in further noise reduction.
In another embodiment of the present invention, micro-perforated panel (MPP) backed with air cavity is incorporated as the cones for the sound absorption. The two types of micro perforated panels are Circular holed MPP and Slit holed MPP. MPP is formed by a panel with sub-millimetre diameter/width of perforation and backed with air cavity. The sound absorption is based on Helmholtz resonator principle and the performance depends on perforation diameter/width, air cavity depth, pitch of perforation, and panel thickness. The MPP sound absorption performance is limited to narrowband frequencies. The noise at blade passing frequencies falling in the low frequency region can also be attenuated with this arrangement. One advantage with this kind of arrangement is, the frequency range of sound absorption can be tuned as per the requirement.
PRIOR ARTS:
The following applications also endures to find a solution to compact the noise problem in a different approach.
US4692091A teaches a fan assembly provides for the compact and efficient movement of ambient air in areas requiring very low noise generation. In this new configuration, stationary turning vanes are placed at the air inlet followed by a sound cell, axial discharge fan and short axial (vaned) diffuser splitter sections. The stationary turning vanes induce a predetermined air rotation which provides a smooth rotating air flow into the rotating fan blades. The stationary turning vanes also block radiated noise from discharge through the air inlet and support the fan motor. The fan blades impart an opposite rotational momentum just sufficient to obtain an axial or nearly axial velocity discharge increment. The resulting axial fan discharge velocity is slowed in the short diffuser sections where diffuser vanes also block rear noise radiation. The slowed but pressurized air can now enter into an air distribution system with significantly reduced fan generated noise. Further noise reductions

can be provided by inlet sound baffles, outlet acoustic diffuser splitters, and acoustic absorption materials in the inlet and short, rear axial diffuser short sections.
US6896095B2 teaches a system and method to significantly reduce noise associated with air-moving devices such as an axial flow fan using a fan shroud and barrel combination with built in silencers such as Helmholtz resonators. The invention can be applied to a variety of applications such as a thermal management system for a fuel cell powered vehicle. The resonator can be a hollow cavity in networks attached to an outer or inner barrel or shroud and tuned to reduce noise at predetermined noise frequency ranges within the airflow. The invention can also attach stator members on the inner surface of the outer barrel to further reduce noise. Additional sound absorbing material, such as steel wool, can be disposed within the resonator cavity.
US6112850A teaches an acoustic silencer nozzle for ventilation and exhaust fans. The nozzle provides at least two converging exhaust paths, each of which extend through an area that is adjacent acoustically absorbing media or resonating chambers. In this manner, the noise is reduced at the nozzle or outlet portion and provides a tight plume of high velocity discharge flow. Preferably, the nozzle has at least one opening that allows for ambient atmospheric air to mix with the exhaust gases at the outlet of the nozzle.
US6454527B2 teaches about Porous damping material that is attached to an entire inner circumference of the fan shroud opposing to an end of a fan and is exposed to opposing space without using conventional perforated metal. Accordingly, jet noise caused by strong swirl between the fan and the fan shroud can be damped by the damping material and impulsive sound scarcely occurs. Thus, both impulsive sound and the jet noise can be effectively damped, thereby securely reducing noise. The pours member constituting the porous damping material is a die-molding product made by a die having a cavity.
BRIEF DESCRIPTION OF THE DRAWINGS:
The present invention will be understood more fully from the detailed description given here below and from the accompanying drawing of the preferred embodiments of the present invention, which, however, should not be taken as limitative to the invention but for explanation and illustration only.

In the drawings:
Figure 1 shows the front view of the conventional fan.
Figure 2 shows the rear view of the conventional fan.
Figure 3 shows isometric view of the conventional fan.
Figure 4 shows the arrangement of plain inner cone and outer cone in isometric view on the downstream side.
Figure 5 shows the arrangement of plain flat inner cone and outer cone in front view.
Figure 6 shows the sectional view A-A and principle of operation with plain flat inner cone and outer cone arrangement.
Figure 7 shows fan assembly made of perforated cones with acoustic material in isometric view.
Figure 8 shows fan assembly made of perforated cones with acoustic material in front view.
Figure 9 shows sectional view B-B of the fan assembly made of perforated cones with acoustic material.
Figure 9A shows fan assembly made of perforated cone with acoustic material and air gap.
Figure 10 shows the types of micro-perforated panel which are used for making the inner cone and outer cone of the fan assembly.
Figure 11 shows the fan assembly with inner and outer cone arrangement with micro-perforated panel with air cavity.
Figure 12 shows another variation of the fan assembly with inner and outer cone arrangement with micro-perforated panel with backing air cavity.

Figure 12A shows another variation of the fan assembly with inner and outer cone arrangement with micro-perforated panel with backing cavity partitions
Figure 13 shows the comparison chart of the noise value between the conventional and disclosed fan with plain inner and outer cone arrangement.
Figure 14 shows the comparison chart of the noise value between the conventional and disclosed fan with perforated inner cone and outer cone with acoustic materials.
Figure 15 shows the comparison chart of the noise value between the conventional and disclosed fan with MPP inner cone and outer cone with backing air cavity.
DETAILED DESCRIPTION OF THE PRESENT INVENTION:
The axial flow fan (1) such as electric motor driven fan includes multiple blades (3) each having a base attached to a central hub (2a) that is driven by an electric motor (2). The central hub is the portion that acts as a casing for the motor (2). The fan blade is further identified as root region (3a) and tip region (3b), The blades (3) extend radially outward from the central hub (2a). Blades (3) can be attached to hub (2a) at blade attachment surface (3c) by various methods. In the preferred embodiment, blades (3) are formed via an injection moulding process. In an alternate embodiment of the present invention, blades (3) are ultrasonically bonded to the hub (2a). Each blade (3) is positioned on hub (2a) such that the blade’s root region (3a) fits into a groove formed at blade attachment surface (3c) of hub (2a). An ultrasonic horn creates a bond between the blade (3) and the hub (2a) at various locations, thereby bonding each blade (3) to hub (2a).A shroud (4) is placed circumferentially around the hub (2a) and blade tips (3b) with finite clearance. The shroud (4) according to the present invention protects the blades (3) and provides substantially closed airflow channel between the fan (1) and the heat exchanger. The shroud (4) is provided with multiple provisions of locking mechanisms enabling the shroud (4) and the entire arrangement to be secured.
Struts (2b) extending from the shroud (4) to the motor (2) support the entire assembly. The struts (2b) are arranged symmetrically or asymmetrically at both sides. The asymmetrically designed support struts allow free flow of air without any noise and

disturbance. The number of struts (2b) can be increased and decreased based upon the size of the entire assembly and rigidity required.
In one embodiment of the present invention several support struts (2b) being asymmetrically placed extend from the motor (2) to the shroud (4) to provide structural support, to keep the motor (2) in centre to the shroud (4) and to reduce the noise.
Similarly, while struts (2b) of large cross-section can reduce torsional vibration, they cause pressure loss and noise. The large cross-sectional profile area blocks airflow. This blockage causes a pressure loss, which is counter-productive, because the primary purpose of the fan is to provide an increase in pressure, which induces airflow from the high-pressure region to the low-pressure region so to maintain and cool the temperature at the specified region. Therefore, to avoid the demerits of large cross-section support struts (2b), the asymmetrical support struts or symmetrical support struts incorporated in the fan assembly is of small cross section with high strength materials without increase in the torsional vibration.
Inner cone (5) and outer cone (6) have been incorporated in the fan assembly (1). The inner cone (5) has minor diameter side (d1) and major diameter side (d2). The outer cone (6) has minor diameter side (d3) and major diameter side ( d4). Provisions are made in the minor diameter side (d1) of the cone for securing the inner cone (5) to motor (2) of the fan assembly. The outer cone’s minor diameter side (d3) is secured to the shroud (4) and the major diameter side (d4) is left open. The inner cone’s major diameter side is closed and kept towards the fan downstream side. The inner cone’s major diameter shall be decided by considering the fact that the maximum sound generated from the fan should interfere with the inner cone and then the outer cone before passing the downstream side. The size and angle of the inner cone (5) and outer cone (6) is determined based upon the number of times the generated sound interferes with the cones. In one embodiment of the disclosed invention, the inner cone and the outer cone are defined at an angle of 115° and 95° respectively w.r.t motor surface (2c), and the inner cone’s major diameter is 85% of fan dia. & outer cone’s major dia. is 125% of fan dia., the length of the cones are approximately 14cm for the maximum sound reflections and cancellations without effecting the fan performance. The reduction in noise level is directly proportional to the number of times the generated sound interferes with the inner cones and outer cones. i.e. If the inner and outer cones (5, 6) are designed in such a way

for maximum interference with generated sound then substantial reduction in noise level can be achieved.
Another explanation for the noise reduction with inner and outer cone arrangement is the acoustic impedance mismatch between sound source (fan) and load (outside air). The acoustic impedance is the product of the medium’s (air in this case) sound speed and density. The smaller air space provides more acoustic impedance than the larger space. The more the acoustic impedance, the lesser the sound transmission into the air. By starting with a larger space between inner and outer cone (the minor diameter side of the inner cone and outer cone), and gradually working up to a smaller space (the major diameter side of the inner cone and outer cone), slow transition from a low impedance to a high impedance occurs, thereby reducing the sound radiation to the outside air.
In figures 7 and 8 the inner cone (5) and outer cone (6) are made with a perforated sheet and acoustic material (7) such as polyurethane foam (PUF) or ceramic wool is given as lining on the inner surface (5i) of the inner cone (5) and on the outer surface (6o) of the outer cone (6). The said acoustic materials absorb the energy of the sound waves impinging on it and minimizes the transmission of noise. These acoustic materials can be easily glued to the inner and outer cones (5, 6). The reflected sound between the inner and outer cones (5, 6) penetrate through the perforations (8) and gets absorbed by the acoustic material resulting in further noise reduction.
In another embodiment of the invention as shown in figure 9A, after lining the perforated sheet with acoustic material, an air gap is provided between the lining and rigid wall to improve the low frequency performance of the cones.
In figure 10, two types of micro perforated panels (9) are illustrated that being used as cones in other embodiments of the invention. Microperforated panels (MPP) are acoustic absorbers that are reclaimable, non-combustible, and environmentally friendly. Sound is attenuated due to viscous friction in the submillimetre size pores. The panels are typically spaced from a hard surface and are most effective when the acoustic particle velocity is a maximum in the pores. For ordinary perforates such as those used in mufflers and silencers, hole diameters are on the order of millimetres or even centimetres and have little acoustic resistance. MPP absorbers have pore diameters that are submillimetre in size. Due to the

small pores, MPP absorbers provide acoustic resistance, which enhances sound attenuation. Compared to traditional sound-absorbing materials, MPP absorbers are unique, because they are reclaimable, cleanable, non-combustible, rugged, fibre free, and light weight.
In figure 11, the micro-perforated panel (MPP) backed with air cavity (10) is used as cones for the sound absorption. Figure 12 shows another variation of this arrangement. The first type being incorporated in the embodiment of the invention is the circular holed micro perforated panels and the second type being the slit holed micro perforated panels. The sound absorption is based on Helmholtz resonator principle and the performance depends on perforation diameter, air cavity depth, pitch of perforation, and panel thickness. The MPP sound absorption performance is limited to narrowband frequencies. The noise at blade passing frequencies falling in the low frequency region can also be attenuated with this arrangement. If we want to achieve the same low frequency performance with porous sound absorbing materials such as PUF and ceramic wool, the thickness of these materials should be of the order of 1/8th of the wavelength of sound. Another advantage with this kind of arrangement is, the frequency range of sound absorption can be tuned as per the requirement.
In another embodiment of the invention as shown in Figure 12A, the inner cone and outer cone are portioned horizontally. Such horizontal partition of the cones will improve the acoustic performance of the MPP when grazing flow (flow that is parallel to the MPP surface) is present. Partitioning disrupts wave propagation behind the MPP and forces it to behave like a locally reacting absorber
The comparison of the noise between conventional and disclosed fan with plain inner and outer cone (5, 6) arrangement is shown in Fig.13. A noise reduction of 0.8dB(A) on the fan downstream side is witnessed.
Fig. 14 shows the comparison of 1/3rd octave spectrum at maximum noise of the conventional and disclosed (perforated inner cone and outer cone with acoustic materials) fans. The disclosed fan resulted in an overall noise reduction of 3.4dB(A) on the fan downstream side and the noise reduction is seen in the frequency range of 1-8kHz.
Fig. 15 shows the comparison of 1/3rd octave spectrum at maximum noise of the conventional and disclosed (MPP cones with backing cavity) fans. The disclosed fan resulted

in an overall noise reduction of 4dB(A) on the fan downstream side and the noise reduction is seen in the frequency range of 0.63-8kHz.
EMBODIMENTS:
Embodiment 1: A fan assembly comprising an axial flow fan, said fan having a hub portion and a plurality of fan blades, each fan blade having a root region and a tip region, the root regions of each fan blade being secured to the hub portion, a motor secured at the centre of the fan assembly powering the fan blades, a shroud encompassing the fan blades characterized in that an inner cone secured to the motor and an outer cone secured to the shroud.
Embodiment 2: A fan assembly comprising an axial flow fan, said fan having a hub portion and a plurality of fan blades, each fan blade having a root region and a tip region, the root regions of each fan blade being secured to the hub portion, a motor secured at the centre of the fan assembly powering the fan blades, a shroud encompassing the fan blades characterized in that an inner cone secured to the motor and an outer cone secured to the shroud, wherein the inner cone and the outer cone are defined at an angle of 115° and 95° w.r.t motor surface respectively for the sound reflections and cancellations.
Embodiment 3: A fan assembly comprising an axial flow fan, said fan having a hub portion and a plurality of fan blades, each fan blade having a root region and a tip region, the root regions of each fan blade being secured to the hub portion, a motor secured at the centre of the fan assembly powering the fan blades, a shroud encompassing the fan blades characterized in that an inner cone secured to the motor and an outer cone secured to the shroud, the inner cone and the outer cone are made from standard materials such as aluminium sheets, GI sheet, MS sheet, FRP, polypropylene (plastics).
Embodiment 4: A fan assembly comprising an axial flow fan, said fan having a hub portion and a plurality of fan blades, each fan blade having a root region and a tip region, the root regions of each fan blade being secured to the hub portion, a motor secured at the centre of the fan assembly powering the fan blades, a shroud encompassing the fan blades characterized in that an inner cone secured to the motor and an outer cone secured to the shroud, the inner cone and the outer cone are made with perforated sheet.

Embodiment 5: A fan assembly comprising an axial flow fan, said fan having a hub portion and a plurality of fan blades, each fan blade having a root region and a tip region, the root regions of each fan blade being secured to the hub portion, a motor secured at the centre of the fan assembly powering the fan blades, a shroud encompassing the fan blades characterized in that an inner cone secured to the motor and an outer cone secured to the shroud, the inner cone and outer cone are made with acoustic material.
Embodiment 6: A fan assembly comprising an axial flow fan, said fan having a hub portion and a plurality of fan blades, each fan blade having a root region and a tip region, the root regions of each fan blade being secured to the hub portion, a motor secured at the centre of the fan assembly powering the fan blades, a shroud encompassing the fan blades characterized in that an inner cone secured to the motor and an outer cone secured to the shroud, the inner cone and outer are made with perforated sheet and acoustic material.
Embodiment 7: A fan assembly comprising an axial flow fan, said fan having a hub portion and a plurality of fan blades, each fan blade having a root region and a tip region, the root regions of each fan blade being secured to the hub portion, a motor secured at the centre of the fan assembly powering the fan blades, a shroud encompassing the fan blades characterized in that an inner cone secured to the motor and an outer cone secured to the shroud, the inner cone and outer are made with perforated sheet and acoustic material wherein the acoustic material is provided as lining on inner surface of the inner cone and on outer surface of the outer cone.
Embodiment 8: A fan assembly comprising an axial flow fan, said fan having a hub portion and a plurality of fan blades, each fan blade having a root region and a tip region, the root regions of each fan blade being secured to the hub portion, a motor secured at the centre of the fan assembly powering the fan blades, a shroud encompassing the fan blades characterized in that an inner cone secured to the motor and an outer cone secured to the shroud, wherein the acoustic material is provided as lining on inner surface of the inner cone and on outer surface of the outer cone.
Embodiment 9: A fan assembly comprising an axial flow fan, said fan having a hub portion and a plurality of fan blades, each fan blade having a root region and a tip region, the root regions of each fan blade being secured to the hub portion, a motor secured at the centre of

the fan assembly powering the fan blades, a shroud encompassing the fan blades characterized in that an inner cone secured to the motor and an outer cone secured to the shroud, the inner cone and outer cone are made with micro-perforated panel backed with air cavity.
Embodiment 10: A fan assembly comprising an axial flow fan, said fan having a hub portion and a plurality of fan blades, each fan blade having a root region and a tip region, the root regions of each fan blade being secured to the hub portion, a motor secured at the centre of the fan assembly powering the fan blades, a shroud encompassing the fan blades characterized in that an inner cone secured to the motor and an outer cone secured to the shroud wherein the inner cone and the outer cone are horizontally partitioned
Embodiment 11: A fan assembly comprising an axial flow fan, said fan having a hub portion and a plurality of fan blades, each fan blade having a root region and a tip region, the root regions of each fan blade being secured to the hub portion, a motor secured at the centre of the fan assembly powering the fan blades, a shroud encompassing the fan blades characterized in that an inner cone secured to the motor and an outer cone secured to the shroud, the inner cone and outer cone are made with micro-perforated panel with air cavity and the micro-perforated panel are circular holed or slit holed.
LIST OF REFERENCE NUMERALS:
Fan assembly – (1)
Motor – (2)
Hub portion - ( 2a)
Support struts - (2b)
Motor surface - (2c)
Plurality of Fan blade/ fan blade – (3)
Fan blade root region – (3a)
Fan blade tip region – (3b)
Blade attachment surface - (3c)
Shroud – (4)
Inner cone – (5)
Inner cone’s inner surface - (5i)

Inner cone’s outer surface - (5o)
Smaller diameter area of inner cone - (d1)
Maximum diameter area of inner cone - (d2)
Outer cone - (6)
Outer cone’s inner surface - (6i)
Outer cone’s outer surface - (6o)
Smaller diameter area of outer cone - (d3)
Maximum diameter area of outer cone - (d4)
Acoustic material - (7)
Perforations - (8)
Micro-perforated panel - (9)
Air cavity - (10)
Rigid wall - (11)
Rigid partition - (12)
The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for the purpose of illustration only and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

We claim:
1. A fan assembly comprising an axial flow fan (1), said fan having a hub portion (2a) and a plurality of fan blades (3), each fan blade having a root region (3a) and a tip region (3b), the root regions (3a) of each fan blade (3) being secured to blade attachment surface (3c) at the hub portion (2a), a motor (2) secured at the centre of the fan assembly powering the fan blades (3), a shroud (4) encompassing the fan blades (3) characterized in that an inner cone (5) secured to the motor (2) and an outer cone (6) secured to the shroud.
2. The fan assembly as claimed in claim 1, wherein the inner cone (5) and the outer cone (6) are defined at an angle about 115° and 95° respectively with respect to motor surface (2c) for the sound reflections and cancellations.
3. The fan assembly as claimed in claim 1, wherein the inner cone (5) and the outer cone (6) are made from standard materials such as aluminium sheets, GI sheet, MS sheet, FRP, polypropylene.
4. The fan assembly as claimed in claim 1, wherein the inner cone (5) and the outer cone (6) are made with perforated sheet (8).
5. The fan assembly as claimed in claim 1, wherein the inner cone (5) and outer cone (6) are made with acoustic material (7).
6. The fan assembly as claimed in claim 1, wherein the inner cone (5) and outer cone (6) are made with perforated sheet (8) and acoustic material (7).
7. The fan assembly as claimed in claim 6, wherein the acoustic material (7) is provided as lining on inner surface (5i) of the inner cone (5) and on outer surface (6o) of the outer cone (6).
8. The fan assembly as claimed in claim 1, wherein the acoustic material (7) and air cavity (10) is provided between the perforated sheet (8) and rigid wall (11) of the inner cone (5) and outer cone (6).

9. The fan assembly as claimed in claim 1, wherein the inner cone (5) and the outer cone (6) are made with micro-perforated panel (9) with the air cavity (10).
10. The fan assembly as claimed in claim 9, wherein the inner cone (5) and the outer cone (6) are horizontally partitioned with rigid partitions(12).
11. The fan assembly as claimed in claim 9, wherein the micro-perforated panel (9) are circular holed.
12. The fan assembly as claimed in claim 9, wherein the micro-perforated panel (9) are slit holed.