Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This inven-tion relates to a fan and in par-ticular to an aeration
fan for clrying grain and other bin stored granular material.
In the recent past the aeration of grain in grain bins has
replaced the drying of grain prior to storage. In other words, instead of
drying grain and then depositing the grain in a storage bin i-t has become
common practice to aerate the grain by continuously blowing air through the
grain. Aeration of the grain cools and drys the grain, thereby preventing
spoilage during storage. Normally, aeration is effected by using a 12" to 18"
diameter perforated tube or tubes on the bin floor. The tube extends out-
wardly through the side of the bin to an electric fan.
The three types of fans commonly used in -the aeration of grain are
the axial, the vane axial and the centrifugal fan. The axial is the fan most
commonly used because the axial is the simplest and most economical of the
three types of fan. The axial fan includes a cylindrical casing, which con-
tains a motor and an axial impeller. The axial fan is readily portable. The
disadvantages of the axial fan are its low efficiency and high noise level.
The vane axial fan is the same as the axial fan, excep-t that curved
vanes are provided downstream of the impeller in the direction of air Elow.
The vanes reduce air turbulence caused by the impeller and thus improve Ean
perEormarlce. Of course, the vane a~ial fan is more expensive than the simple
axial fan.
The centrifugal fan is available in high and low speed versions.
1~11 centrifugal fans are more expensive than their axial couterparts.
('entrifugual fans possess the advantage of a low noise level. The high
,peed centrifugal fan uses an impeller having a smaller diameter than that
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of the low speed centriEuyal fan and has the lowest air Elow of all types of
fan. The low speed centrifugal fan is the best perEorming fan available bu-t,
in general, is quite heavy and expensive. A low speed centrifugal fan must be
moved using a tractor or forklift and costs -two or more times as much as an
axial fan of the same size. Another disadvantaye of centrifugal fans is that
motor heat is wasted because the motor is not mounted in the air stream from
the impeller.
The object of the present invention is to solve, at least partially,
most of the problems mentioned above.
Accordingly, the present invention relates to an aeration fan for
drying granular material comprising a cylindrical casing, first motor means
in said casing; first impe}ler means connected to said first motor means for
driving air through said casing from an open inlet end through an open outlet
end of said casing; second motor means in said casing downstream of said first
impeller means in the direction of air flow; and second impeller means connec-
ted to said second motor means for rotation in a direction opposite to the
direction of rot:ation of said first impeller means, said first and second
impeller means including equal blades of opposite pitch and said first and
second impeller means being spaced a short distance apart, whereby the air
Elow through said casing is greater than the total air flow created by said
first and second impsllers individually.
The invention will now be described with reference to the
a~companying drawing, a single figure which is a schematic, longitudinal
sectional view of a preferred embodiment of a fan in accordance with the
present inven-tion.
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With reference to the drawing, the fan of the present invention
which is generally indicated at 1 includes a cylindrical casing 2, which is
open at each end 3 and 4. Air introduced into the inlet end 3 and discharged
-through the outlet end 4. Normally the outlet end 4 of the casing 2 is
connected to a perforated tube (not shown) for aerating a grain bin.
A pair of electric motors 5 and 6 are mounted in the casing 2. The
first motor 5 is on the upstream (in the direction of air flow) side of the
centre of the casing 2, and the motor 6 is on the downstream side of the centre
of the casing. An impeller 7 is mounted on a drive shaft 8 of the motor 5 and
an impeller 9 is mounted in a drive shaft 10 of the motor 6. Thus, the
impellers 7 and 10 oppose each other on elther side of the centre of the
casing 2. The impellers 7 and 9 have an equal number of opposite pitch blades
or vanes ll and 12 respectively.
During operation the impeller 7 rotates in one direction and impell-
er 9 rotates in the opposite direc-tion. Because the blades 11 and 12 have
equal but opposite pitch, air flow is in one direction through the casing 2.
It has been found that this arrangement increases air flow at operating
pressures. The air flow of any fan decreases as the pressure (resistance to
air flow) increases. Air escapes back through the fan blades rather than
beincJ Eorced through the outlet end 4 of the casing 2. In any axial fan, as
the pressure increases air starts to swirl with the impeller. The swirling of
air in the same direction as fan rota-tion has the same effec-t as a reduction
in motor speed. The problem becomes worse as the pressure increases, result-
ing in poor fan performance. With counter-rotating fans or impellers 7 and 9
~hen air begins to swirl in the same direction as the impeller 7, such air is
swirling in the direction opposite to the direction of rotation of the
impeller 9. This has the same effect as increasing the speed of the second
motor 6. Therefore, when two oppositely rota-ting impellers at the proper
distance apart are operated in a single casing, -the normal reduced efficiency
of the first impeller is regained by the second impeller. Two fan arrange-
ments with the impellers rotating in the same direction produce one-third to
one-half the air flow of equivalent two impeller fans of the type described
herein.
In tests involving counter-rotating impellers, it was found that
the impellers should be quite close together (1 to 3 inches apart) for
optimum performance. Counter-rotating fans have been found to perform better
than any of the three types of fan (axial, vane axial or centrifugal) of
equivalent size, with reduced power consumption in some cases. Noise levels
were equal to those of axial or vane axial fans.
The two motor concept has the advantage that one can be s-tarted
after the other, thereby reducing the surge of power normally required to
start one motor.
Moreover, the two impeller fan is relatively inexpensive to produce.
A larger axial fan is required to produce the same air flow as a smaller
~ counter-rotating, -two impeller fan of the type described herein. The main
cost of an axial or coun-ter-rotating fan is the motor. Whereas two small
motors can be used in the fan of the present invention, one large motor is
used in -the axial fan. It has been found that the large motor required to
produce the same air flow as the double impeller fan is more expensive than
the two small motors used in the double impeller fan.
During testing it was found that there is a substantial increase
in air -temperature due to motor heat. The hot air thus produced aids the
grain drying process.
The counter-rotating Eans described in -the foregoing are ~ horse-
power (two motors each of 2 horsepower) with 18 inch diarneter impellers.
In closing it is worth noting that the present inven-tor does not
claim to have invented the concept of the two stage counter-rotating fan.
What the inventor has done is to conceive the idea of using the concept in
a grain aeration fan and, by research, proved that the concept can indeed
be used with advantage in grain aeration.
