Radial fan wheel

A radial fan wheel comprising a number of fan blades symmetrically arranged with substantially equal spacing around the rotational shaft of the fan wheel. The blades are mounted between two end plates that are arranged perpendicularly to the shaft and are provided with blade surfaces which are substantially parallel to the shaft and each of which blade extends from one point at a distance from the shaft and substantially arched in the direction outwardly towards the periphery of the wheel. One first end plate is provided with a central air inlet and is shaped with a curve that, in a position radially outwardly from the innermost edges of the blades, substantially arches towards the second end plate and further radially outwardly towards the peripheral edges of the blades. Each blade is so designed in the peripheral segment that the blade extends radially longer outwardly adjacent the first end plate than the second end plate.

FIELD OF THE INVENTION 
The present invention refers to a radial fan wheel comprising a number of 
fan blades symmetrically arranged with substantially equal spacing around 
the rotational shaft of the fan wheel, said blades being mounted between 
two perpendicular to said shaft arranged end plates and being provided 
with surfaces which are substantially parallel with said shaft and each of 
which extends from one point at a distance from said shaft and 
substantially arched in the direction out to the periphery of the wheel, 
wherein one end plate is provided with a central air inlet. 
BACKGROUND OF THE INVENTION 
Fans are used as means for driving air through ventilation systems. 
Efficiency and a low level of noise are requirements upon fans. The most 
common type of fans in the field of ventilation, are double suction radial 
fans. They have a high degree of efficiency but the level of noise 
requires subsequent silencers. A problem with double suction radial fans, 
is that the outlet velocity is high and uneven. This makes it impossible 
to place subsequent silencers immediately in connection to the fan. In 
recent time, chamber fans which is an old design, has come back to the 
market. They have the advantage that they provide a flow having a low and 
fairly even velocity. The fan is compact and a silencer may be placed 
closer to the fan. The lower maximum degree of efficiency for a chamber 
fan is compensated by the lower velocity and the accompanying lower 
pressure losses, so that for high flows, chamber fans obtains higher 
efficiency than double suction radial fans. 
Fans are the cause of low frequency noise which is difficult to muffle. It 
is true that the level of noise in a ventilation system may be reduced by 
the use of silencers. However, this is a space consuming and expensive 
solution of the problem. 
The primary sound source in a chamber fan is the fan wheel, which for 
example generates noise in the frequency range 50-300 Hz. The periphery of 
the fan wheel is preferably symmetrically shaped with blade edges 
extending substantially in parallel with the rotation shaft of the wheel. 
The blades are located between two lateral to said shaft arranged, 
mutually substantially parallel end plates. The generation of noise is 
predominantly caused by turbulence being created when the air is pressed 
radially out of the wheel by the rotation of the blades, and then is 
brought to flow on, e.g. axially, by the design of the chamber walls. 
THE TECHNICAL PROBLEM 
One object of the present invention is therefore to provide a fan wheel 
which reduces the generation of noise in a fan, with preserved efficiency, 
alternatively enabling an increased efficiency with preserved noise level. 
THE SOLUTION 
For this object, the invention is characterized in that the end plate which 
is provided with the air inlet is shaped with a curve extending 
substantially arched from the inlet edge, in the direction toward the 
other end plate and further radially out toward the peripheral edge which 
is curved away from the other end plate, and that each blade is so 
designed in a peripheral segment, that the blade extends radially longer 
adjacent the end plate which is provided with the air inlet than at the 
other end plate. By this design of the fan wheel, a reduced level of noise 
is achieved, without any appreciable reduction of the working capacity of 
the fan.

DESCRIPTION OF AN EMBODIMENT 
The radial fan wheels shown in the figures comprise a number of fan blades 
10 being symmetrically arranged with substantially equal spacing around 
the rotational shaft 11 of the fan wheel. The blades 10 are mounted 
between two perpendicular to said shaft arranged end plates 12, 13 and 
they are provided with blade surfaces which are substantially parallel 
with said shaft. Each blade extends from one point at a distance from said 
shaft and substantially arched in the direction out to the periphery of 
the wheel. 
One of the end plates 12 is provided with a central air inlet 14 and it has 
a larger diameter than the other end plate 13. The end plate 12 is shaped 
with a curve extending substantially arched from the inlet edge 15, in the 
direction toward the other end plate 13 and further radially out toward 
the peripheral edge 16 which is curved away from the other end plate 13. 
By this design of the end plate 12, a zone is created beyond the blades 
10, where the air velocity is equalized, while maintaining the kinetic 
energy, which means that less noise is generated downstream the fan wheel. 
As is illustrated by FIG. 2 and 3, also the peripheral edge 17 of the 
other end plate 13 is curved away from the end plate 12 which is provided 
with the air inlet 14. This curving of the peripheral edge 17 of the other 
end plate 13 contributes to a further equalizing of the air velocity 
downstream the blades, so that the turbulence in this part of the fan is 
reduced. This in FIGS. 2 and 3 shown fan wheel is primarily intended for 
use at a fan unit without fan housing, a so called chamber fan. The fan 
wheel may also be used in a radial fan. 
Each blade 10 is so designed in a peripheral segment, that the blade is 
provided with a larger contact surface at that end plate 12 which is 
provided with the air inlet 14, than at the other end plate 13. For 
example, the peripheral edge 18 of each blade 10 may be straight or curved 
obliquely, so that this edge meets the inside of the end plate 12 on a 
point 19 at a distance from the axis of rotation 11 which is larger than 
the distance between said shaft and the point 20 where the peripheral edge 
18 meets the other end plate 13. The design of the blades means, that air 
that moves between two blades will be accelerated somewhat less if it 
moves along the end plate 13, than if it moves along the end plate 12. By 
this design of the blades, the air will leave the fan wheel with varying 
kinetic energy, which means that pressure pulses are reduced at the 
downstream side of the fan wheel. 
FIG. 4 shows a fan wheel in which the second end plate 13 is completely 
flat. This fan wheel functions in accordance with the invention, with 
reduction of noise while maintaining the working efficiency. The fan wheel 
according to FIG. 4 is primarily intended to be used at a single or double 
suction radial fan, wherein in the latter case two fan wheels are placed 
together with the end gables 13 against each other. 
The design of the fan wheel in accordance with the invention, provides a 
considerable reduction of the sound level in the range 50-300 Hz with 
maintained fan capacity. When using the fan wheel for delivering air to a 
ventilation system, it will be possible to reduce the design length of the 
system, which will make it less space consuming and cheaper to build. 
Because of the reduction in design length and that the need for silencers 
is reduced, also the pressure drop in the system is reduced, so that the 
ventilation capacity increases. This also leads to decreased running costs 
for the system, due to the reduction in power consumption. 
The invention is not limited to the above described embodiments, instead 
more variants are conceivable within the scoop of the following claims. 
For example, the peripheral edges of the blades may be designed in many 
ways, in order to provide varying kinetic energy for the air which leaves 
the fan blades.