1. Field of the Invention
This invention relates to a fan wheel which may be utilized in an air handling box of a building, for instance, in order to generate an air flow in the ventilation system of the building, for instance.
2. Description of Prior Art
Previously there is known a fan wheel having a first and second end plate arranged at a distance from each other and blades which are attached between the end plates. An opening in the first end plate allows inflow into the fan wheel, and the first and second end plates together with outer edges of the blades delimit openings allowing outflow from the fan wheel.
A problem relating to a fan wheel of this kind is that the performance is far from optimal once the fan wheel is mounted in an air handling box. In practice the air flowing out from the fan wheel in a radial direction needs to be redirected in the axial direction, which has turned out to be problematic.
Attempts have been made to minimize the problems relating to the redirection of the air flow by increasing the size of the air handling box in order to reserve more space for redirecting the air flow in an efficient way, or by using flow guiding plates inside the box. However, such attempts have caused other problems as the space available for an air handling box is in practice limited. Therefore the air handling box should preferably be as small as possible.
An object of the present invention is to provide solution improving the performance and properties of a fan wheel. This and other objects of the invention can be achieved with the solution defined in independent claims 1 and 13.
The possibility of providing the fan wheel with end plates having an outer portion providing a diffusion space and which direct the outflow in an optimal direction from the fan wheel in combination with profiled blades that are inclined in relation to the rotation axis leads to a construction which in practical tests has turned out to have excellent properties.
Preferred embodiments of the invention are disclosed in the dependent claims.
In the following the present invention will be described in closer detail by way of example and with reference to the attached drawings, in which
The illustrated fan wheel 1 is a mixed-flow fan wheel comprising a first end plate 2 and a second end plate 3 arranged at a mutual distance from each other. A mixed-flow fan wheel refers to a fan wheel, where the air flowing out from the fan wheel is not entirely radially directed and not entirely axially directed but instead somewhere between the radial and axial direction. The angle of direction to the rotation axis of the air flowing out from the fan wheel is typically 20° to 70°. The first end plate 2 has an opening 4 which allows inflow into the fan wheel. Blades 5 are arranged between the first 2 and the second 3 end plate. The blades 5 are joined to the first and the second end plate in such a way that the blades 5 together with the first 2 and second 3 end plate limit openings 6 allowing outflow from the fan wheel while the fan wheel is rotated as illustrated by arrow 7 around the rotation axis 9.
The outer (trailing) edges 8 of the blades 5 are inclined in relation to the rotation axis 9 such that the distance between the outer edges 8 and the rotation axis 9 is bigger at the first end plate 2 than at the second end plate 3. As illustrated in
b to 4e illustrate in more detail the inclination of the blade. The above mentioned angle of direction α is accomplished by inclining the blade 5 as illustrated in
The first 2 and second 3 end plate have outer portions 11 and 12 which protrude radially outward beyond the outer edges 8 of the blades 5 such that an outwardly open diffusion space is delimited by the outer portions 11 and 12 and the blades 5. As can be seen from the figures, the outer portions 11 and 12 need not to be exactly radially oriented, in which case they would extend perpendicularly outwards from the rotation axis 9, but instead they may be inclined in relation to the rotation axis. However, when measured perpendicularly from the rotation axis, the outermost parts of the outer portions 11 and 12 are located at a greater distance from the rotation axis than the outermost parts of the blades. In praxis the diffusion space has a generally annular shape. This diffusion space may have a width W which increases outwardly. One alternative is to utilize end plates having straight outer portions 11 and 12 which are inclined in relation to each other with an angle β. This angle β may be 16° to 22°, most preferably 19°. Alternatively the outer portions 11 and 12 may be curved instead of being straight. Additionally, it should be observed that an outwardly widening diffusion space may not be necessary in all embodiments.
As best seen in
The pressure range for which the fan wheel in the embodiment of
where
Δp is the pressure increase for the fan (Pa).
The values given above have been specified by way of example based on practical tests which have indicated that a 4% increase in efficiency for a fan wheel in an air handling box may be achieved, while the sound power level of the fan can be kept low. Therefore, also combinations of these values with other values are possible.
The illustrated blade 5 is profiled to have a constant cross-sectional shape along the profile where the thickness 13 of the blade 5 varies between the outer edge 8 of the blade and the inner edge 14 of the blade. As can be seen from
In the illustrated example, the outer edge 8 of the blade 5 is parallel with the inner edge 14 of the blade over the entire width of the blade.
In
The fan wheel and the blades as illustrated in
One alternative to manufacture the fan wheel is to manufacture the first end plate 2 and the second end plate 3 by cutting from an aluminum plate, for instance. The opening 4 may be cut through the material of the first end plate 2, and after this the first and second end plate may be bent to have their correct shapes by deep drawing, for instance.
The blade 5 may be manufactured by extrusion of aluminum in order to obtain an elongated profile bar having the thickness varying as illustrated in
Once the blades 5 have been manufactured (and possibly slightly machined, if necessary) the profiled blades 5 are arranged in a position as illustrated in
The above solution for producing a fan wheel results in a fan wheel with a very good performance, without any need for twisting the blades. Instead the profiled shape of the blades illustrated in
The walls 18 of the air handling box 17, which are air tight, separate the fan wheel 1 from the surrounding environment. An inlet opening 19 in a front wall of the air handling box allows air to enter an inlet cone 21 which is arranged to conduct air 20 from the inlet opening 19 to the opening 4 in the first end plate 2 of the fan wheel 1.
In
In practice the efficiency of the fan wheel depends at least partially on how heavily the air flow 23 collides with the side walls of the air handing box, which causes disturbance in the flow. The illustrated construction, as explained in connection with the previous embodiments, minimizes losses by efficiently directing the air flow 23 as illustrated in
In
In the illustrated example the outer (trailing) edges 8′ include three sections 26′, 27′ and 29′.
At a location between the first straight section 26′ and the second straight section 27′ there is a third section 29′, where the outer edges extend in a different direction, such that they are not parallel with the edges of the first section 26′, the second section 27′ or the inner edges of the blades.
An advantage obtained with the illustrated step is that speed of the air exiting the fan wheel 1′ at different distances as measured from the first end plate 2 (for instance) along the rotation axis 9 can be efficiently controlled.
It is to be understood that the above description and the accompanying figures are only intended to illustrate the present invention. It will be obvious to a person skilled in the art that the invention can be varied and modified without departing from the scope of the invention.
Number | Date | Country | Kind |
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20145618 | Jun 2014 | FI | national |