Suction flow preswirl control bypass structure for blowers

Details Suction flow preswirl control bypass structure for blowers Suction flow preswirl control bypass structure for blowers

1999-06-18

2001-02-20

Ryznic, John E. (Department: 3745)

Rotary kinetic fluid motors or pumps

Working fluid passage or distributing means associated with...

Casing having tangential inlet or outlet

C415S182100

Reexamination Certificate

active

06190125

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates to a by-pass unit for controlling the prerotation of flow in a suction pipe, in more particular, a unit for controlling the prerotation of the air flowing into an impeller of a fan, e.g., of the centrifugal flow type, the axial flow type and the mixed flow type, in order to increase fan efficiency and to reduce fan noise.
PRIOR ART
Various technical ideas have been made to suppress the prerotation of the air flowing into an impeller of a pump and/or a fan. For instance, ‘Designing and Drawing for Centrifugal Flow Pump’ authored by Susumu TERADA, Jun. 15, 1972, 4th edition, (published by Riko Tosho Co. Ltd.,), page 36 and pages 66 to 71, ‘Centrifugal and Axial Flow Fan and Compressor’ authored by Takebumi IKUI, Jul. 30, 1964, 5th edition, (published by Asakura Shoten Co. Ltd.,), pages 222 to 225, and ‘Turbo Fan and Compressor’ authored by Takebumi IKUI and Masahiro INOUE, Aug. 25, 1988, (published by Corona Co. Ltd.,) teach that a flat or cylindrical baffle plate disposed at ‘the region ahead of an impeller’ inside a suction pipe contributes to suppress the prerotation of the suction air flowing into an impeller and that a tapered suction pipe decreases the unfavorable influence based on the prerotation of flow.
A general theory of the generation mechanism of the prerotation of flow is explained as follows: Reverse flow (spiral vortex) induced at ‘the region ahead of an impeller’ inside a suction pipe of a pump and/or a fan with any cause results in generating the prerotation of flow. According to such a prior theory the ideas mentioned above do not provide a concrete structure for rationally controlling the energy based on the tangential velocity of prerotation flow.
According to the ‘2nd Edition Centrifugal and Axial Flow Pumps’ authored by A. J. STEPANOFF, 1957, (published by John Wiley & Sons, Inc.,), pages 38 to 42, and in the ‘Pump and Blower’ authored by A. J. STEPANOFF, translated by Kensaku IMAICHI et al., Nov. 12, 1979, 1st edition, (published by Sangyo Tosho Co. Ltd.,), pages 78 to 101, the mechanism of prerotation of the air flowing into an impeller is explained as follows:
At ‘the region ahead of an impeller’ inside a suction pipe of a pump or a fan the prerotation is generated according to the principle of the least resistance. The rotational direction of prerotation is not always identical to that of a fan impeller because the prerotation is not generated by the fact that the impeller blades directly transmit the force to the air. The prerotation has the tangential velocity with the direction identical to that of the rotation of an impeller under the operation at a capacity smaller than the design normal capacity, on the other hand, it has the tangential velocity with the direction opposite to that of the rotation of an impeller under the operation at a capacity greater than the design normal capacity. It should be noted that the reverse flow (spiral vortex) at ‘the region ahead of an impeller’ inside a suction pipe generates in consequence of the prerotation because the prerotation is not induced by the reverse flow.
The first object of the present invention is to provide a by-pass unit for controlling the prerotation of flow in the suction pipe of a fan, improving the fan efficiency by the decrease of the shaft power of a fan and/or the increase of the pressure rise (head) based on the impeller of a fan, which are accomplished by rationally controlling the energy based on the tangential velocity of the prerotation flow generating at ‘the region ahead of an impeller’ inside a suction pipe of a fan according to the STEPANOFF's theory described above. And the second object is to improve the air flow inside a suction pipe at the region in close vicinity to an impeller, thereby, reducing the fan noise.
THE PRESENT INVENTION
The present invention is applied to the inlet of a fan equipping the suction pipe for introducing suction air into a fan impeller. Referring to
FIG. 1
, it is characterized by that an air chamber
3
forming a closed spatial region is disposed at the outside of ‘the region ahead of an impeller’ of a suction pipe
2
and more than three communicating passages
4
for connecting between the air chamber
3
and the suction pipe
2
is provided along the flowing direction of suction air, enabling to transmit air pressure from the suction pipe
2
to the air chamber
3
and vice versa and to introduce air thereinto through the communicating passages
4
, and forming by-pass routes of the suction pipe
2
by the air chamber
3
and the communicating passages
4
, thereby, generating by-pass flow
5
a
(see
FIG. 8
) in a part of the suction air.
As shown in
FIG. 2
, the air chamber
3
is a box
3
A equipped outside the suction pipe
2
, and the communicating passages
4
are tubes
4
A connecting the suction pipe
2
to the box
3
A. For example, as shown in
FIG. 13
, in the case that a cylindrical closed chamber
3
B is formed on the periphery of ‘the region ahead of an impeller’ of the suction pipe
2
, the holes
4
B punched on the peripheral wall
2
m
of the suction pipe
2
, which partitions off the cylindrical closed chamber
3
B and the suction pipe
2
, are usable as the communicating passages
4
.
Referring to
FIG. 3
, ‘the region ahead of an impeller’ of the suction pipe
2
comprises n cylindrical portions
2
1
,
2
2
, . . . ,
2
n−1
and
2
n
having different inner diameters along the flowing direction of suction air and truncated cone portions
2
a
1
,
2
a
2
, . . . ,
2
a
n−2
and
2
a
n−1
for connecting the cylindrical portions, where a maximum inner diameter is given by d
MAX
and a minimum is by d
MIN
, and the axial length of truncated cone portions are B
i
(when i=1, 2, 3, . . . and n−1), in the case of a centrifugal flow fan
11
(see FIG.
4
(
a
)) not providing a side plate on the side of a suction pipe along the impeller axis
1
a
of the blades
1
A
1
, a point Z
Pa
on the impeller axis corresponding to the entrance end p
a1
of blades is chosen as a reference point when the entrance end p
a1
of blades on the side edge located at the side of a suction pipe of the impeller blades
1
A
1
is closer to the suction pipe than the discharge end p
a2
thereof along the impeller axis
1
a
, the length from the reference point Z
Pa
to the upstream point of the by-pass unit
5
for controlling the prerotation of flow is defined by Z
1
, and the length from the reference point Z
Pa
to the downstream point thereof is by Z
2
, the present invention is characterized by that the positional relation between the by-pass unit
5
for controlling the prerotation of flow and the impeller
1
should fulfil following equations;
Z
1
≦2·d
MAX
+&Sgr;B
i
and
0.03·d
MIN
≦Z
2
<Z
1
,
besides, in the case of d
MAX
>100 mm and d
MIN
>100 mm
0.4·d
MIN
<Z
1
−Z
2
,
and in the case of d
MAX
≦100 mm and/or in the case of d
MAX
>100 mm and d
MIN
≦100 mm
40 mm<Z
1
−Z
2
.
As shown in FIG.
4
(
b
), in the case that a side plate is not provided on the side of suction pipe along the impeller axis
1
a
of the blades
1
A
1
of a centrifugal flow fan
11
and the discharge end p
b2
of blades on the side edge located at the side of a suction pipe of the blades
1
A
1
is closer to the suction pipe than the entrance end p
b1
thereof along the impeller axis
1
a
, the above-mentioned reference point is assigned to the point Z
Pb
on the impeller axis corresponding to the discharge end p
b2
of blades. On the other hand, as shown in FIG.
4
(
c
), in the case that a side plate
1
p
is fixed to the blades
1
A
1
of the centrifugal flow fan
11
on the side of suction pipe, a main plate
1
q
is fixed to the blades on the counter side of suction pipe, and a mouth ring Im is attached to the side plate, the reference point is assigned to the point Z
Pc
on the impeller axis
1
a
corresponding to the most upstream point of the mouth ring
1
m.
The case of an axial flow fan is as follows: As shown in FIG.
5
(
a
)

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