U.S. patent application number 14/973190 was filed with the patent office on 2016-09-01 for indoor unit of air conditioner and air conditioner including the same.
The applicant listed for this patent is Hitachi Appliances, Inc.. Invention is credited to Naoyuki FUSHIMI, Taku IWASE, Hideshi OBARA, Daiwa SATO, Hiroyasu YONEYAMA.
Application Number | 20160252259 14/973190 |
Document ID | / |
Family ID | 56798211 |
Filed Date | 2016-09-01 |
United States Patent
Application |
20160252259 |
Kind Code |
A1 |
SATO; Daiwa ; et
al. |
September 1, 2016 |
Indoor Unit of Air Conditioner and Air Conditioner Including the
Same
Abstract
An indoor unit of an air conditioner of the present invention
includes a cabinet; an air inlet through which air is sucked into
the cabinet; a centrifugal fan which blows the air sucked in to the
surrounding portions; and an a heat exchanger which is provided in
the direction of air supply of the centrifugal fan and allows heat
exchange between the air and a refrigerant flowing thereinside, in
which the following equation is satisfied:
0.16.ltoreq.L/D.ltoreq.0.19, where D is an outer diameter of the
centrifugal fan and L is a distance between the centrifugal fan and
the heat exchanger in their closest positions. Thus, a variation in
a velocity distribution created in the heat exchanger can be
suppressed, and the indoor unit of the air conditioner which
achieves an improved energy saving property due to a reduced
pressure loss and an improved heat exchange efficiency of the heat
exchanger can be provided.
Inventors: |
SATO; Daiwa; (Tokyo, JP)
; IWASE; Taku; (Tokyo, JP) ; YONEYAMA;
Hiroyasu; (Tokyo, JP) ; FUSHIMI; Naoyuki;
(Tokyo, JP) ; OBARA; Hideshi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi Appliances, Inc. |
Tokyo |
|
JP |
|
|
Family ID: |
56798211 |
Appl. No.: |
14/973190 |
Filed: |
December 17, 2015 |
Current U.S.
Class: |
165/122 |
Current CPC
Class: |
F24F 1/0059 20130101;
F24F 2013/0616 20130101; F24F 1/0022 20130101; F28F 13/06 20130101;
F24F 1/0047 20190201 |
International
Class: |
F24F 1/00 20060101
F24F001/00; F28F 13/06 20060101 F28F013/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2015 |
JP |
2015-037610 |
Claims
1. An indoor unit of an air conditioner comprising: a cabinet; an
air inlet through which air is sucked into the cabinet; a
centrifugal fan which blows the air sucked in to the surrounding
portions; and an a heat exchanger which is provided in the
direction of air supply of the centrifugal fan and allows heat
exchange between the air and a refrigerant flowing thereinside,
wherein the following equation is satisfied:
0.16.ltoreq.L/D.ltoreq.0.19, where D is an outer diameter of the
centrifugal fan and L is a distance between the centrifugal fan and
the heat exchanger in their closest positions.
2. The indoor unit of the air conditioner according to claim 1,
wherein the following equation is satisfied: 835
mm.ltoreq.W.ltoreq.845 mm, where W is an external dimension of the
cabinet.
3. The indoor unit of the air conditioner according to claim 1,
wherein the outer diameter D of the centrifugal fan satisfies the
following equation: 440 mm.ltoreq.D.ltoreq.470 mm.
4. The indoor unit of the air conditioner according to claim 2,
wherein the outer diameter D of the centrifugal fan satisfies the
following equation: 440 mm.ltoreq.D.ltoreq.470 mm.
5. The indoor unit of the air conditioner according to claim 1,
wherein the following equation is satisfied:
0.3.ltoreq.b2/H.ltoreq.0.5, where b2 is a height of a discharge
port of the centrifugal fan and H is a height of the heat
exchanger.
6. The indoor unit of the air conditioner according to claim 1,
wherein the following equation is satisfied: A/W.sup.2.gtoreq.0.21,
where W is an external dimension of the cabinet, and A is an area
of a region enclosed by an outer peripheral line of the centrifugal
fan, an inner peripheral line of a face through which air flows
into the heat exchanger, and straight lines connecting peripheral
ends of the heat exchanger and a rotational center of the
centrifugal fan in a cross section perpendicular to an axis of
rotation of the centrifugal fan.
7. The indoor unit of the air conditioner according to claim 1,
wherein the following equation is satisfied:
0.52.ltoreq.D/W.ltoreq.0.56, where W is an external dimension of
the cabinet.
8. The indoor unit of the air conditioner according to claim 1,
further comprising a bell mouth which guides the air flowing from
the air inlet to the centrifugal fan, wherein the bell mouth has a
curved surface portion which curves in such a direction that its
opening area expands towards the air inlet, and an inclined plane
having a shape which is inclined in such a direction that its
opening area further expands from the curved surface portion.
9. An air conditioner comprising: the indoor unit according to
claim 1; an outdoor unit; and pipes connecting these.
Description
CLAIM OF PRIORITY
[0001] The present application claims priority from Japanese Patent
application serial No. 2015-037610, filed on Feb. 27, 2015, the
content of which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an indoor unit of an air
conditioner and an air conditioner including the same.
[0004] 2. Description of Related Art
[0005] Japanese Unexamined Patent Application Publication No.
2011-12937 (Patent Document 1) discloses that an indoor unit of an
air conditioner includes a guide member which leads the air fed
from a fan of a heat exchanger to a lower part of the heat
exchanger on a side opposing the fan.
[0006] A heat exchanger arranged in an indoor unit is enlarged in
size for the purpose of improving heat exchange efficiencies and
reducing pressure losses. A height of the heat exchanger is greater
than a height of a discharge port of a centrifugal fan. In
addition, if the centrifugal fan is to be arranged in a limited
space of the indoor unit, the centrifugal fan is inevitably
arranged in an upper part of the heat exchanger. Such an
arrangement creates a variation in a velocity distribution inside
the heat exchanger.
[0007] Accordingly, a guide member which leads the air fed from the
fan to a lower part of the heat exchanger is provided on the side
opposing the fan, as in the constitution described in Patent
Document 1, whereby the variation in the velocity distribution
created in the heat exchanger can be suppressed.
[0008] The means for attaching the guide member around the
centrifugal fan can suppress the variation in the velocity
distribution created in the heat exchanger, but it does not
suppress the generation of the variation itself, and has been
insufficient to achieve further improvement in the efficiency and
energy saving.
[0009] To this end, an objective of the present invention is to
suppress the variation in the velocity distribution created in the
heat exchanger, and to provide the indoor unit of the air
conditioner which achieves an improved energy saving property.
SUMMARY OF THE INVENTION
[0010] In order to achieve the above object, an indoor unit of an
air conditioner of the present invention includes a cabinet; an air
inlet through which air is sucked into the cabinet; a centrifugal
fan which blows the air sucked in to the surrounding portions; and
an a heat exchanger which is provided in the direction of air
supply of the centrifugal fan and allows heat exchange between the
air and a refrigerant flowing thereinside, in which the following
equation is satisfied:
0.16.ltoreq.L/D.ltoreq.0.19,
[0011] where D is an outer diameter of the centrifugal fan and L is
a distance between the centrifugal fan and the heat exchanger in
their closest positions.
[0012] According to the present invention, a variation in a
velocity distribution created in the heat exchanger can be
suppressed, and the indoor unit of the air conditioner which
achieves an improved energy saving property due to a reduced
pressure loss and an improved heat exchange efficiency of the heat
exchanger can be provided. Other objects, constitutions, actions
and effects of the present invention will be described below in the
following Examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a perspective view of an indoor unit of an air
conditioner according to an embodiment of the present
invention;
[0014] FIG. 2 is a cross-sectional view which is perpendicular to
an axis of rotation of a centrifugal fan of the indoor unit of the
air conditioner according to an embodiment of the present
invention;
[0015] FIG. 3 is a cross section of the indoor unit of the air
conditioner shown in FIG. 2 taken along line A-A;
[0016] FIG. 4 is a graph in which a horizontal axis represents L/D,
and a vertical axis represents a standard deviation of a velocity
distribution occurring within a heat exchanger;
[0017] FIG. 5 is a graph in which a horizontal axis represents
b2/H, and a vertical axis represents the standard deviation of the
velocity distribution occurring within the heat exchanger;
[0018] FIG. 6 is a drawing which shows a region between a
centrifugal fan and a heat exchanger;
[0019] FIG. 7 is a cross-sectional view in which the filter, the
bell mouth and the centrifugal fan are enlarged in FIG. 3; and
[0020] FIG. 8 is a cross-sectional view of known filter, bell mouth
and centrifugal fan.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] Examples of the present invention will be described below
with reference to the drawings.
First Embodiment
[0022] FIG. 1 shows a perspective view of an indoor unit of an air
conditioner according to an embodiment of the present invention.
The indoor unit of FIG. 1 is connected with an outdoor unit (not
shown) via a refrigerant pipe, and is a component of the air
conditioner. A compressor is arranged in the outdoor unit. A
refrigerant is compressed by this compressor, and a refrigerating
cycle is formed by circulating the refrigerant through the inside
of the refrigerant pipe. The indoor unit includes a cabinet 1
disposed inside a ceiling and a panel 2 attached to on an indoor
side of the cabinet 1. The panel 2 is provided with a grill 3 for
drawing indoor air in, and four air outlets 4 for blowing the air
sucked in from the grill 3 indoors. Air outlets 5 are each provided
with a louver 4 attached thereto in a manner of being rotationally
driven by a motor for the louver (not shown), which adjusts a
direction of the air blown out. In other words, the panel 2 has an
air inlet through which the air is sucked into the cabinet 1.
[0023] FIG. 2 is a drawing which shows a cross-sectional view of
the indoor unit of FIG. 1 seen toward a direction of an axis of
rotation Z of the fan (FIG. 3). As shown in FIG. 2, the indoor unit
of this Example has a centrifugal fan 10 having backward curved
blades which are disposed in a central portion of the indoor unit
and discharges air in a direction away from the axis of the
rotation Z, and a heat exchanger 11 which is disposed in the
direction of air supply of the centrifugal fan 10 in a manner of
surrounding the centrifugal fan 10 and performs heat exchange
between the air from centrifugal fan 10 and the refrigerant which
flows through thereinside.
[0024] The configuration of the heat exchanger 11 is a polygon such
that it has a curvature at a corner when seen in a cross section
perpendicular to the axis of rotation Z of the centrifugal fan 10,
and has a substantially rectangular shape with a part of the
corners being open. In FIG. 2, the heat exchanger 11 has such a
shape that the centrifugal fan 10 is surrounded by three corner
portions and four straight sides. One of the corners has a straight
line shape shorter than other straight parts, and has such a shape
that the distance between itself and the outer circumference of the
centrifugal fan 10 is shorter than from other corners. Although not
illustrated, in the space provided between this corner and the
cabinet 1, a drain pump for discharging a dew condensation water (a
drain water) generated by the heat exchanger 11 during an air
conditioning operation is disposed.
[0025] FIG. 3 is a drawing which shows a cross section taken along
line A-A in FIG. 2. By rotating the centrifugal fan 10 about the
axis of rotation Z by motor 20 connected to centrifugal fan 10, air
is sucked in through a filter 6 attached to the grill 3. The air
sucked in passes through a bell mouth 12 whose opening portion
gradually contracts towards the centrifugal fan 10, and is blown
out to a radial direction (the direction of the circumference) of
the centrifugal fan 10 by the centrifugal fan 10. The air blown out
passes through the heat exchanger 11, flows out from the heat
exchanger 11, and is then discharged into the room from the air
outlet 5 so that an air current 50 shown in FIG. 3 is formed. When
the air shown by the airflow 50 is blown out from the air outlet 5
into the room, the wind direction is adjusted by the louver 4
attached to the panel 2.
[0026] Heat exchange is performed between air and the refrigerant
flowing through the inside of the heat exchanger 11 in the heat
exchanger 11 during a heating operation or cooling operation,
whereby heating or cooling of indoor air is performed. An
electrical component box 7 accommodating a control board (not
shown) for controlling the behavior of the indoor unit is attached
to a lower part of the bell mouth 12 that is a space between the
filter 6 and bell mouth 12.
[0027] Next, a dimensional relationship between the centrifugal fan
10 and heat exchanger 11 in this Example will be described.
[0028] The outer diameter of the centrifugal fan 10 is D, and the
distance that the centrifugal fan 10 and the heat exchanger 11 is
the closest is defined as L in a cross section perpendicular to the
axis of rotation Z of the centrifugal fan 10 (see FIG. 2). The
ratio L/D is the lowest when the distance between the centrifugal
fan 10 and the heat exchanger 11 in their closest positions is L.
It should be noted that the heat exchanger 11 has four straight
line portions, but the distances L between each of the straight
line portions and the centrifugal fan 10 are approximately the
same.
[0029] Conventionally, a centrifugal fan has been designed to have
a reduced shaft power at the same flow rate by increasing the
diameter of the centrifugal fan 10 as much as possible. The present
invention, however, does not simply aim at providing a larger
diameter, but focuses on the relationship L/D between the outer
diameter D of the centrifugal fan 10 and the distance L between the
centrifugal fan 10 and the heat exchanger 11 for the purpose of
reducing the pressure loss and improving the performance of the
heat exchange cycle of the heat exchanger 11 by reducing a
variation in the flow rate of the air passing through the inside of
the heat exchanger 11.
[0030] FIG. 4 is a graph in which a horizontal axis represents L/D,
and a vertical axis represents a standard deviation indicating the
variation in the flow rate of the air passing through the inside of
the heat exchanger 11. A height b2 of a discharge port of the
centrifugal fan 10 illustrated in FIG. 3 is changed, and the
changes in the standard deviation relative to L/D at different
values of b2 are shown by a solid line and a broken line. The
lowered standard deviation shows that the variation in the flow
rate of the air passing through the inside of the heat exchanger 11
is reduced and the velocity distribution becomes nearly uniform.
When the velocity distribution becomes nearly uniform, the pressure
loss of the heat exchanger 11 is reduced, and the effects in
improving the heat exchange efficiency can be obtained. In a
conventional device, for example, L=54 mm, D=490 mm, and L/D=0.11,
but this graph revealed that the region of L/D in which the
standard deviation becomes low is when
0.16.ltoreq.L/D.ltoreq.0.19.
[0031] Specifically, when the centrifugal fan 10 and the heat
exchanger 11 are too close (L/D is low), the wind velocity of the
closest part between the centrifugal fan 10 and the heat exchanger
11 becomes locally high, and therefore a variation in the velocity
distribution occurs. On the other hand, when the centrifugal fan 10
and the heat exchanger 11 are too far apart (L/D is high), the
outer diameter D of the centrifugal fan 10 becomes too small
relative to the heat exchanger 11, and therefore the number of
revolutions of the centrifugal fan 10 needs to be increased in
order to deliver the same volume of air into the heat exchanger 11.
Since the increased number of revolutions increases the
circumferential speed, the air blowing angle from the centrifugal
fan 10 becomes nearly parallel to the inflow face of the heat
exchanger 11, which adversely affects the velocity distribution.
Considering this, based on FIG. 4, in this Example, the centrifugal
fan 10 and the heat exchanger 11 are so configured to attain
0.16.ltoreq.L/D.ltoreq.0.19. It is further desirable that
0.17.ltoreq.L/D.ltoreq.0.18. This can greatly improve the velocity
distribution and heat exchange efficiency.
[0032] Moreover, in order to change L/D (for example, in order to
increase L/D), there are the following options: reducing the outer
diameter of the centrifugal fan 10; and enlarging the heat
exchanger 11. If the heat exchanger 11 is enlarged, the air outlet
5 between the cabinet 1 and the heat exchanger 11 is narrowed,
which increases the pressure loss and lowers the air blowing
efficiency. Meanwhile, there is an option to maintain the opening
area of the air outlet 5 by also enlarging the cabinet 1 with the
enlargement of the heat exchanger 11. However, it is desirable that
the installation space of the indoor unit (especially in-ceiling
type) is not changed in terms of construction, and that a
conventional size of the cabinet: approximately 840 mm is not
changed. Therefore, it is preferable that the requirement that
0.16.ltoreq.L/D.ltoreq.0.19 is satisfied and further the external
dimension W of the cabinet 1 is designed to satisfy 830
mm.ltoreq.W.ltoreq.850 mm. Moreover, it is preferable that the
outer diameter D of the fan is 440 mm.ltoreq.D.ltoreq.470 mm in
order not to affect the dimensions of the heat exchanger 11 and the
air outlet 5.
Second Embodiment
[0033] FIG. 3 shows the definitions of the height b2 of the
discharge port of the centrifugal fan 10 and the height H of the
heat exchanger 11. In this case, the ratio of the height b2 of the
discharge port of the centrifugal fan 10 to the height H of the
heat exchanger 11 is b2/H. By setting b2/H to an appropriate value,
the efficiency of the centrifugal fan 10 can be further increased
by applying the above first embodiment.
[0034] First, the case where the height H of the heat exchanger 11
is constant, and the height b2 of the discharge port of the
centrifugal fan 10 is changed will be described.
[0035] As the height b2 of the discharge port of the centrifugal
fan 10 is reduced and b2/H is lowered, the width of the passage
composed of a hub face 101 and a shroud face 102 of the centrifugal
fan 10 is reduced, and an increased friction loss within the
centrifugal fan 10 lowers the efficiency of the centrifugal fan
10.
[0036] On the other hand, as the height b2 of the discharge port of
the centrifugal fan 10 is increased and b2/H is increased, the
width of the passage composed of the hub face 101 and the shroud
face 102 is increased, and the friction loss is lowered. The
centrifugal fan 10 is characterized in that it draws air from the
bottom in FIG. 3 in the direction of the axis of rotation Z, and
blows air at an angle which is perpendicular to the axis of
rotation Z or the almost the same angle. Accordingly, it is
desirable that the air sucked in by the centrifugal fan 10 flows
along the shroud face 102. However, when the width of the passage
composed of the hub face 101 and the shroud face 102 increases, the
air sucked in by the centrifugal fan 10 peels off from the shroud
face 102, resulting in a lowered efficiency of the centrifugal fan
10.
[0037] Next, the case where the height b2 of the discharge port of
the centrifugal fan 10 is constant, and the height H of the heat
exchanger 11 is changed will be described. When the height H of the
heat exchanger 11 is decreased and b2/H is increased, a heat
transfer area of the heat exchanger 11 is decreased, resulting in
the lowered heat exchange efficiency.
[0038] On the other hand, when the height H of the heat exchanger
11 is increased, and b2/H is decreased, the heat transfer area of
the heat exchanger 11 is increased, which improves the heat
exchange efficiency, but the height H of the heat exchanger 11
becomes excessively large, and an air blow from the centrifugal fan
10 becomes ununiform. As a result, a variation is created in the
velocity distribution of the air passing through the inside of the
heat exchanger 11, resulting in a lowered heat exchange
efficiency.
[0039] FIG. 5 is a graph in which a horizontal axis represents b2/H
and a vertical axis represents the standard deviation indicating
the variation in the flow rate of the air passing through the
inside of the heat exchanger 11. As in FIG. 4, it means that when
the standard deviation is lowered, the variation in the flow rate
of the air passing through the inside of the heat exchanger 11 is
reduced, and the velocity distribution becomes nearly uniform. This
graph reveals that the region of b2/H in which the standard
deviation becomes low is when 0.3.ltoreq.b2/H.ltoreq.0.5.
[0040] Thus, too high or low a value of b2/H results in a lowered
efficiency of the centrifugal fan 10 and a lowered heat exchange
efficiency of the heat exchanger 11. It is therefore desirable that
0.3.ltoreq.b2/H.ltoreq.0.5. It is even more desirable that
0.35.ltoreq.b2/H.ltoreq.0.45.
Third Embodiment
[0041] FIG. 6 is a drawing which shows a region between the
centrifugal fan and the heat exchanger. In a cross section
perpendicular to the axis of the rotation Z of the centrifugal fan
10 of the centrifugal fan 10, an area enclosed by an outer
periphery of the centrifugal fan 10, an inflow face of the heat
exchanger 11, and a straight lines connecting the peripheral ends
of the heat exchanger 11 with the rotational center of the
centrifugal fan 10 is referred to as a region X, which is indicated
in gray in FIG. 6.
[0042] When the outer diameter D of the centrifugal fan 10 and the
height H of the heat exchanger 11 are the same, and the radial
distance between the centrifugal fan 10 and the heat exchanger 11
becomes longer, that is, when an area A of the region X is
increased, the inflow area of the heat exchanger 11 is increased.
The increase in the inflow area increases the heat transfer area of
the heat exchanger 11, thereby improving the heat exchange
efficiency. Moreover, the pressure loss of the heat exchanger 11
changes depending on the flow rate of the air passing through
thereinside. Accordingly, the increase in the inflow area decreases
the average flow rate of the air passing through the inside of the
heat exchanger 11, whereby the pressure loss of the heat exchanger
11 is reduced, and the shaft power of the centrifugal fan 10 is
reduced.
[0043] According to the above first embodiment, attaining
0.16.ltoreq.L/D.ltoreq.0.19 can suppress the variation in the
velocity distribution of the air passing through the inside of the
heat exchanger 11. This expectedly improves the heat exchange
efficiency and reduces the pressure loss of the heat exchanger 11.
Furthermore, increasing the area A of the region X, that is,
increasing A/W.sup.2 which corresponds to a ratio of the area
calculated from the external dimension W of the cabinet 1 to the
area A of the region X expectedly improves the heat exchange
efficiency and reduces the pressure loss.
[0044] However, as the A/W.sup.2 is increased when
0.16.ltoreq.L/D.ltoreq.0.19, the heat exchanger 11 gradually
expands towards the outside. In such a case, the sufficient opening
area of the air outlet 5 and width of the air outlet passage 8 can
be no longer ensured, and the pressure loss in these is increased,
which prevents the air conditioner from performing its main
function of conditioning the indoor air. Accordingly, it is
desirable that 0.21.ltoreq.A/W.sup.2.ltoreq.0.27.
Fourth Embodiment
[0045] A fourth embodiment which allows obtaining more effects by
applying the above first embodiment will be described.
[0046] According to the above first embodiment, attaining
0.16.ltoreq.L/D.ltoreq.0.19 can suppress the variation in the
velocity distribution of the air passing through the inside of the
heat exchanger 11. However, when the outer diameter D of the
centrifugal fan 10 is changed so that L/D becomes the same, the
dimension of the heat exchanger 11 needs to be changed.
[0047] Regarding a ratio D/W of the outer diameter D of the
centrifugal fan 10 to the external dimension W of the cabinet 1,
lowering D/W reduces the dimension of the heat exchanger 11 which
is defined by D+2L. At the same time, the circumferential length of
the heat exchanger 11 is reduced. And then the heat transfer area
is reduced, and the heat exchange efficiency is deteriorated.
[0048] On the other hand, increasing D/W increases the dimension of
the heat exchanger 11 defined as above, and the heat transfer area
is increased. Although this improves the heat exchange efficiency,
the passage width of the air outlet passage 8 is decreased. And the
area of the air outlet 5 can be no longer sufficiently ensured,
which increases the pressure loss of the air outlet 5. Accordingly,
it is desirable that 0.52.ltoreq.D/W.ltoreq.0.56 to further obtain
effects by applying the above first embodiment.
Fifth Embodiment
[0049] FIG. 8 is a cross-sectional view of the filter 6, a bell
mouth 12a, and the centrifugal fan 10 in the case where this
Example is not applied. The bell mouth 12a is so configured to have
an opening area which is gradually contracting from an inlet
diameter D.sub.b1 to an outlet diameter D.sub.b2 to guide air to
the centrifugal fan 10. When the connection of a face 13 on which
the filter 6 and the bell mouth 12a are parallel as shown in FIG. 8
and the opening portion of the bell mouth 12a is configured by a
single arc, if a height H.sub.b of the bell mouth 12a is not high
enough, the inlet diameter D.sub.b1 of the bell mouth 12a becomes
small, and the area of the face 13 increased. Since the distance
between the filter 6 and the face 13 is shorter than other
portions, the flow rate of the air passing through the region of
the filter 6 overlapping the face 13 becomes lower than the flow
rate of the air passing through the center of the filter 6.
Accordingly, as the area of the face 13 increases, as a flow field
51 shown in FIG. 8, the flow rate of the air passing through the
filter 6 tends to be greater at the center of the filter 6.
[0050] FIG. 7 is a cross-sectional view of the filter 6, a bell
mouth 12, and the centrifugal fan 10 in the case where this Example
is applied. The bell mouth 12 includes an inclined plane 12b having
a constant inclination angle and a face 13. The face 13 is parallel
to the filter 6. That is, the opening portion of the bell mouth 12b
is formed to be cone-shaped (to be a shape of a hollow truncated
cone). This allows the inlet diameter of the bell mouth 12b to be
increased from D.sub.b1 to D.sub.b1' even if the height H.sub.b of
the bell mouth 12 cannot be sufficiently ensured. Also, this allows
the area of the face 13 to be decreased. As a result, as a flow
field 52 shown in FIG. 7, the flow rate of the air passing through
the edge portions of the filter 6 can be increased, and the flow
rate of the air passing through the filter 6 can be nearly uniform
throughout the filter 6, and therefore the pressure loss of the
filter 6 can be reduced.
* * * * *