U.S. patent application number 12/952726 was filed with the patent office on 2011-06-02 for bell-mouth structure of air blower.
This patent application is currently assigned to SANYO ELECTRIC CO., LTD.. Invention is credited to Abastari, Takayuki Masukawa, Takeshi Nakamura, Hirofumi Yanagi.
Application Number | 20110127019 12/952726 |
Document ID | / |
Family ID | 43660180 |
Filed Date | 2011-06-02 |
United States Patent
Application |
20110127019 |
Kind Code |
A1 |
Abastari; ; et al. |
June 2, 2011 |
BELL-MOUTH STRUCTURE OF AIR BLOWER
Abstract
A bell-mouth structure of an air blower provided around a blade
wheel of an axial-flow air blower for guiding air from an air
suction side of the blade wheel to an air blow-out side including
an air blow-out wall portion that intercommunicates with an air
blow-out opening and extends substantially along an axial direction
of the blade wheel, and a slope wall portion that intercommunicates
with the air blow-out wall portion and slopes to an air suction
opening so as to expand in diameter. When the overall height of the
bell-mouth is represented by H, the height of the slope wall
portion is represented by h and a slope angle of the slope wall
portion is represented by .beta., the bell mouth structure is
configured so as to satisfy 0.33.ltoreq.h/H.ltoreq.0.42 and
60.degree..ltoreq..beta..ltoreq.70.degree..
Inventors: |
Abastari;; (Oura-gun,
JP) ; Masukawa; Takayuki; (Ota-shi, JP) ;
Yanagi; Hirofumi; (Kumagaya-shi, JP) ; Nakamura;
Takeshi; (Oura-gun, JP) |
Assignee: |
SANYO ELECTRIC CO., LTD.
Osaka
JP
|
Family ID: |
43660180 |
Appl. No.: |
12/952726 |
Filed: |
November 23, 2010 |
Current U.S.
Class: |
165/121 ;
415/219.1 |
Current CPC
Class: |
F24F 13/08 20130101;
F24F 13/06 20130101; F04D 29/547 20130101; F24F 1/38 20130101 |
Class at
Publication: |
165/121 ;
415/219.1 |
International
Class: |
F28F 13/00 20060101
F28F013/00; F01D 1/04 20060101 F01D001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 2009 |
JP |
2009-270342 |
Claims
1. A bell-mouth structure of an air blower that is provided around
a blade wheel of an axial-flow air blower and guides air from an
air suction side of the blade wheel to an air blow-out side of the
blade wheel, comprising: an air blow-out wall portion that
intercommunicates with an air blow-out opening and extends
substantially along an axial direction of the blade wheel; and a
slope wall portion that intercommunicates with the air blow-out
wall portion and slopes to an air suction opening so as to expand
in diameter, wherein when the overall height of the bell-mouth is
represented by H, the height of the slope wall portion is
represented by h and a slope angle of the slope wall portion is
represented by .beta., the bell mouth structure is configured so as
to satisfy 0.33.ltoreq.h/H.ltoreq.0.42 and
60.degree..ltoreq..beta..ltoreq.70.degree..
2. The bell mouth structure according to claim 1, wherein when the
diameter of an opening of a connecting portion between the air
blow-out wall portion and the slope wall portion is represented by
D and the diameter of the blade wheel is represented by d,
1.02<D/d<1.03 is satisfied.
3. The bell mouth structure according to claim 1, wherein when the
height from the air suction opening to the position of a blade out
of blades of the blade wheel which is nearest to the air suction
opening is represented by hL, 0.24.ltoreq.hL/h.ltoreq.0.4 is
satisfied.
4. The bell mouth structure according to claim 1, wherein when the
height from the air suction opening to a position of a blade out of
blades of the blade wheel which is nearest to the air blow-out
opening is represented by hZ, 0.875.ltoreq.hZ/H.ltoreq.0.925 is
satisfied.
5. The bell mouth structure according to claim 1, wherein the
axial-flow air blower is a propeller fan.
6. The bell mouth structure according to claim 5, wherein the blade
wheel of the propeller fan is disposed so as to be perfectly
overlapped with the bell mouth in side view.
7. An air conditioner comprising: a heat exchanger; an axial-flow
air blower having a blade wheel for blowing air to the heat
exchanger; and a bell mouth that is provided around the blade wheel
of the air blower and guides air from an air suction side of the
blade wheel to an air blow-out side, wherein the bell mouth has an
air blow-out wall portion that intercommunicates with an air
blow-out opening and extends substantially along an axial direction
of the blade wheel, and a slope wall portion that intercommunicates
with the air blow-out wall portion and slopes to an air suction
opening so as to expand in diameter, and when the overall height of
the bell-mouth is represented by H, the height of the slope wall
portion is represented by h and a slope angle of the slope wall
portion is represented by .beta., the bell mouth is configured so
as to satisfy 0.33.ltoreq.h/H.ltoreq.0.42 and
60.degree..ltoreq..beta..ltoreq.70.degree..
Description
INCORPORATION BY REFERENCE
[0001] The present application claims priority under 35 U.S.C.
.sctn.119 to Japanese Patent Application No. 2009-270342 filed on
Nov. 27, 2009. The content of the application is incorporated
herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a bell-mouth structure of
an air blower used in an air conditioner or the like.
[0004] 2. Description of the Related Art
[0005] An axial-flow air blower such as a propeller fan or the like
has been widely used as an air blower for an air conditioner or the
like, and a bell-mouth for smoothly guiding air from an air suction
side to an air blow-out side and reducing a leakage amount of air
is provided around a blade wheel for blowing air. With respect to
this type of air blower, it has been recently more strongly
required to enhance the performance and reduce the noise, and a
performance enhancing method based on an improvement of the
bell-mouth shape has been proposed (for example, see
JP-A-2004-211971).
[0006] Furthermore, it has been recently required to enhance the
air flow amount of the air blower and reduce the driving force of
the air blower (motor load) from the viewpoint of energy
saving.
SUMMARY OF THE INVENTION
[0007] Therefore, an object of the present invention is to provide
a bell-mouth structure of an air blower that can solve the problem
of the technique described above, and also satisfy reduction of
both of the rotational number and the driving force of the air
blower at the same time with keeping the air flow amount equal.
[0008] In order to attain the above object, according to a first
aspect of the present invention, a bell-mouth structure of an air
blower that is provided around a blade wheel of an axial-flow air
blower and guides air from an air suction side of the blade wheel
to an air blow-out side of the blade wheel has an air blow-out wall
portion that intercommunicates with an air blow-out opening and
extends substantially along an axial direction of the blade wheel,
and a slope wall portion that intercommunicates with the air
blow-out wall portion and slopes to an air suction opening so as to
expand in diameter, wherein when the overall height of the
bell-mouth is represented by H, the height of the slope wall
portion is represented by h and a slope angle of the slope wall
portion is represented by .beta., 0.33.ltoreq.h/H.ltoreq.0.42 and
60.degree..ltoreq..beta..ltoreq.70.degree. are satisfied.
[0009] In this construction, when the diameter of an opening of a
connecting portion between the air blow-out wall portion and the
slope wall portion is represented by D and the diameter of the
blade wheel is represented by d, 1.02<D/d<1.03 may be
satisfied. When the height from the air suction opening to the
position of a blade out of blades of the blade wheel which is
nearest to the air suction opening is represented by hL,
0.24.ltoreq.hL/h.ltoreq.0.4 may be satisfied.
[0010] Furthermore, when the height from the air suction opening to
the position of a blade out of blades of the blade wheel which is
nearest to the air blow-out opening is represented by hZ,
0.875.ltoreq.hZ/H.ltoreq.0.925 may be satisfied. The axial-flow air
blower may be a propeller fan. The blade wheel of the propeller fan
may be disposed so as to be perfectly overlapped with the bell
mouth in side view.
[0011] According to a second aspect of the present invention, an
air conditioner includes an axial-flow air blower having a blade
wheel for blowing air to a heat exchanger and a bell mouth that is
provided around the blade wheel of the air blower and guides air
from an air suction side of the blade wheel to an air blow-out side
of the blade wheel, wherein the bell mouth has an air blow-out wall
portion that intercommunicates with an air blow-out opening and
extends substantially along an axial direction of the blade wheel,
and a slope wall portion that intercommunicates with the air
blow-out wall portion and slopes to an air suction opening so as to
expand in diameter, and when the overall height of the bell-mouth
is represented by H, the height of the slope wall portion is
represented by h and a slope angle of the slope wall portion is
represented by .beta., 0.33.ltoreq.h/H.ltoreq.0.42 and
60.degree..ltoreq..beta..ltoreq.70.degree. are satisfied.
[0012] According to the present invention, the bell mouth is
configured so as to satisfy 0.33.ltoreq.h/H.ltoreq.0.42 and
60.degree..ltoreq..beta..ltoreq.70.degree., whereby the reduction
of the rotational number and the reduction of the driving force of
the air blower can be satisfied at the same time with keeping the
air flow amount equal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a side cross-sectional view of an outdoor unit of
an air conditioner according to a first embodiment of the present
invention;
[0014] FIG. 2 is a top view showing the internal construction of
the outdoor unit;
[0015] FIG. 3A is a side view showing the arrangement relationship
between a bell mouth and a propeller fan, and FIG. 3B is a
partially cross-sectional view of the bell mouth;
[0016] FIG. 4 is a diagram showing the relationship of a height
ratio of a slope wall portion of the bell mouth at the same
operating point, a slope angle of the slope wall portion, the
rotational number of the propeller fan and a motor load;
[0017] FIG. 5 is a diagram showing the relationship of the diameter
ratio between the bell mouth and the propeller fan, the rotational
number of the propeller fan and the motor load;
[0018] FIG. 6 is a diagram showing the height ratio of the height
from an air suction opening till the lower end point of the
propeller fan to the height of the slope wall portion; and
[0019] FIG. 7 is a diagram showing the relationship of the height
ratio of the height from the air suction opening till the upper end
point of the propeller fan to the height of the bell mouth, the
rotational number of the propeller fan and the motor load.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] A preferred embodiment according to the present invention
will be described with reference to the accompanying drawings.
[0021] An air conditioner according to an embodiment comprises an
outdoor unit 10 and an indoor unit (not shown), and makes
refrigerant flow through a refrigerant circuit connected through a
refrigerant pipe to perform cooling operation or heating operation.
The outdoor unit 10 is disposed outdoors to heat-exchange with
outdoor air so that refrigerant is condensed and heat is radiated
to the outdoor air under cooling operation and also refrigerant is
vaporized and take in heat from the outdoor air under heating
operation. UP-and-down and right-and-left directions described
below correspond to directions when the outdoor unit 10 is viewed
from the front side thereof under the state that the outdoor unit
10 is installed.
[0022] FIG. 1 is a side cross-sectional view of the outdoor unit
10, and FIG. 2 is a top view showing the internal construction of
the outdoor unit 10. The outdoor unit 10 has a substantially
rectangular parallelepiped box-shaped unit case (housing) 11, and
the unit case 11 has a bottom plate 12, support poles 14 extending
from the four corners of the bottom plate 12 in the vertical
direction, and a front panel 15 (FIG. 2).
[0023] As shown in FIG. 2, a heat exchanger 21 which is formed so
as to be bent in a substantially U-shape in top view is disposed on
the bottom plate 12, and an air blower (axial-flow air blower) 22
is disposed at the upper side of the heat exchanger 21. The heat
exchanger 21 constitutes side surface portions of the unit case 11,
and it is disposed so as to extend from the left side surface of
the unit case 11 along the back surface and the right side surface
thereof.
[0024] As shown in FIG. 1, the air blower 22 comprises a fan motor
23 disposed above the heat exchanger 21, and a propeller fan (blade
wheel) 24 secured to the shaft of the fan motor 23. Joint members
16 for joining the neighboring support poles 14 at the position
corresponding to the upper end of the heat exchanger 21 are
provided between the neighboring support poles 14, and a pair of
support frames 17 bridged between the joint members 16 are fixed to
the fan motor 23.
[0025] A bell mouth 25 for guiding air at the air suction side of
the propeller fan 24 to the air blow-out side of the propeller fan
24 is provided around the propeller fan 24, and the air blow-out
opening 25A of the bell mouth 25 is covered by a fan guard (not
shown) for preventing a human body or the like from coming into
contact with the propeller fan 24. A face panel (not shown) is
provided around the bell mouth 25 through a heat insulating member
26 such as foamed polystyrene.
[0026] When the propeller fan 24 is rotated by the fan motor 23,
outdoor air is sucked into the unit case 11 from the surrounding of
the outdoor unit 10, specifically, from the left, back and right
sides of the unit case 11 excluding the front side of the unit case
11 as indicated by arrows X in FIG. 1, and discharged to the
outside through an air blow-out opening 25A of the bell mouth 25
which is provided to the top surface portion of the unit case 11.
That is, the outdoor unit 10 is configured as a top blow-out type
for blowing out heat-exchanged air from the top surface.
[0027] A compressor (not shown), an accumulator 31, an oil
separator 32 and a receiver tank 33 which constitute a part of the
refrigerant circuit are provided on the bottom plate 12 in the unit
case 11, and refrigerant circuit constituting parts such as valve
members such as a four-way valve (not shown), an expansion valve
(not shown), etc. are mounted in the unit case 11 so as to be
connected to one another through pipes. One end sides of the pipes
for the refrigerant circuit constituting parts are connected to the
indoor unit through the heat exchanger 21, and the other end sides
of the pipes for the refrigerant circuit constituting parts are
connected to the indoor unit, thereby constructing the refrigerant
circuit in which refrigerant is circulated.
[0028] In this construction, the compressor is disposed at the
front side of the unit case 11, and an electrical component box 34
in which various kinds of electrical component units such as a
control board, etc. for controlling the air conditioner are
arranged is disposed at the upper space of the compressor.
Therefore, by detaching the front panel 15, a worker can easily
perform a maintenance work for parts in the unit case 11. Reference
numeral 35 represents a cover plate which is provided at the upper
side of the compressor and prevents rain drops from directly
impinging against the compressor.
[0029] Next, the construction of the bell mouth will be
described.
[0030] The bell mouth 25 is formed by resin molding and thus it can
be configured to be light in weight and have a desired shape. As
shown in FIG. 3A, the bell mouth 25 is configured in a cylindrical
shape so as to have an air low-out opening 25A and an air suction
opening 25B which is larger in diameter than the air blow-out
opening 25A, and also has an air blow-out wall portion 40 which
intercommunicates with the air blow-out opening 25A and extends
substantially along the axial direction of the propeller fan 24,
and a slope wall portion 41 which intercommunicates with the air
blow-out wall portion 40 and slopes toward the air suction opening
25B so as to gradually increase in diameter.
[0031] The air blow-out wall portion 40 guides air blown out by the
propeller fan 24 to the air blow-out opening 25A, and an angle
.alpha. with respect to the plane of the air blow-out opening 25A
is set to a right angle or an angle which is slightly smaller than
the right angle (in this embodiment, the angle .alpha.=89.degree.).
Furthermore, the upper end portion of the air blow-out wall portion
40 (the end portion at the air blow-out opening side) is outwardly
and annually bent to have a predetermined radius of curvature, and
suppresses resistance to air flow when air is blown out.
[0032] Furthermore, the slope wall portion 41 smoothly feed air in
the unit case 11 into the bell mouth 25 when the propeller fan 24
is operated, and it is integrally joined to the air blow-out wall
portion 40 by a joint portion 42 as shown in FIG. 3B. The slope
wall portion 41 expands outwardly toward the air suction opening
25B, and it is formed so as to be bent annularly at a slope angle
.beta. with respect to the plane of the air suction opening 25B.
Furthermore, the lower end portion (the end portion at the air
suction opening side) 41A of the slope wall portion 41 is bent
outwardly along the plane of the air suction opening 25B.
[0033] The propeller fan 24 has a hub 45 fixed to the motor shaft
of a fan motor 23 (FIG. 1), and plural blades 46 which are
integrally formed on the outer periphery of the hub 45 so as to
have a predetermined blade angle and be spaced from one another at
predetermined intervals. As shown in FIG. 3A, the propeller fan 24
is disposed so as to be perfectly overlapped with the bell mouth 25
in side view. According to this construction, since the bell mouth
25 covers an area where the propeller fan 24 operates, all the air
blown out by the propeller fan 24 can be guided by the bell mouth
25, so that the air blowing amount of the propeller fan 24 can be
enhanced.
[0034] The inventors of this application has performed a simulation
to derive shape factors for the bell mouth 25 which can
simultaneously satisfy both reduction of the rotational number of
the propeller fan 24 and reduction of the load of the fan motor 23
at the same operating point of the air blower 22. Here, the same
operating point of the air blower 22 means an operating condition
that the air flow amount Q (m.sup.3/min) and the static pressure
(mmAq) are equal. In FIGS. 3A and 3B, when the height H of the bell
mouth 25, the height h of the slope wall portion 41, the slope
angle .beta. of the slope wall portion 41, the diameter D of the
bell mouth 25 at the joint portion 42, the diameter d of the
propeller fan 24, the height hZ from the air suction opening 25B to
the upper endpoint (the position nearest to the air blow-out
opening 25A) 46A of the blade 46 of the propeller fan 24, and the
height hL from the air suction opening 25B to the lower end point
(the position nearest to the air suction opening 25B) of the blade
of the propeller fan 24 are introduced as parameters, the inventors
have found how the variation of these shape values act on the
reduction of the rotational number of the propeller 24 and the
reduction of the load of the fan motor 23.
[0035] In FIG. 4, the abscissa axis represents an air suction port
angle, that is, the slope angle .beta. of the slope wall portion 41
of the bell mouth 25, the ordinate axis at the left side represents
a motor load (W) and the ordinate axis at the right side represents
the rotational number (rpm) of the propeller fan 24. When the air
blower 22 is operated under the same condition that the air flow
amount Q is set to (200 m.sup.3/min) and the static pressure is set
to (6 mmA), it is simulated how the rotational number of the
propeller fan 24 and the load of the fan motor 23 vary while each
of the height ratio h/H of the slope wall portion 41 of the bell
mouth 25 and the slope angle .beta. of the slope wall portion 41 is
changed.
[0036] According to this simulation, it has been found that a bell
mouth 25 designed in the neighborhood of the condition that
h/H=0.33 (filled circles, filled rectangles) and the slope angle
.beta.=60.degree. has the minimum rotational number of the
propeller fan 24 and the minimum load of the fan motor 23 and thus
has highest performance.
[0037] In a range where the slope angle .beta. is larger than
70.degree., with respect to all bell mouths satisfying
0.20.ltoreq.h/H.ltoreq.0.67, the motor load and the rotational
number of the propeller fan 24 trend to increase as the slope angle
increases. On the other hand, in a range where the slope angle
.beta. is not more than 70.degree., with respect to a bell mouth
satisfying h/H=0.67, the motor load and the rotational number are
extremely high values.
[0038] When considered from the viewpoint of the motor load, with
respect to bell mouths satisfying h/H-0.20, 0.33, the motor load
has a local minimum point in the neighborhood of the slope angle
.beta. of 60.degree., and the motor load increases even when the
slope angle .beta. is smaller and larger than 60.degree.. Here, the
bell mouth satisfying h/H=0.20 has the remarkably largest value at
the slope angle .beta.=70. With respect to bell mouths satisfying
h/H=0.42, 0.50, the motor load decreases when the slope angle
.beta. ranges from 50.degree. to 60.degree., and it is equal to a
substantially fixed value when the slope angle .beta. ranges from
60.degree. to 70.degree..
[0039] Furthermore, when considered from the viewpoint of the
rotational number, with respect to a bell mouth satisfying
h/H=0.50, it trends to decrease when the slope angle .beta. ranges
from 50.degree. to 70.degree.. With respect to a bell mouth
satisfying h/H=0.42, it decreases when the slope angle .beta.
ranges from 50.degree. to 60.degree., and it is equal to a
substantially fixed value when the slope angle .beta. ranges from
60.degree. to 70.degree.. With respect to a bell mouth satisfying
h/H=0.3, the rotational number has a local minimum point in the
neighborhood of the slope angle .beta. of 60.degree., and the
rotational number increases even when the slope angle .beta. is
smaller and larger than 60.degree.. With respect to a bell mouth
satisfying h/H=0.20, it trends to be substantially constant when
the slope angle .beta. ranges from 50.degree. to 60.degree., but
increase when the slope angle .beta. ranges from 60.degree. to
70.degree..
[0040] In order to reduce the rotational number of the propeller
fan 24 and the load of the fan motor 23, it is found from this
simulation that it is desirable to set 0.33.ltoreq.h/H.ltoreq.0.42
and 60.degree..ltoreq..beta..ltoreq.70.degree..
[0041] As described above, when the bell mouth of this embodiment
is configured to satisfy 0.33.ltoreq.h/H.ltoreq.0.42 and
60.degree..ltoreq..beta..ltoreq.70.degree., it has been found that
the bell mouth of this embodiment can satisfy both the reduction of
the rotational number of the propeller fan 24 and the reduction of
the motor load at the same time with keeping the same air flow
amount.
[0042] FIG. 5 is a diagram showing the relationship of the diameter
ratio (D/d) between the bell mouth 25 and the propeller fan, the
rotational number of the propeller fan and the motor load when the
bell mouth 25 is designed to satisfy h/H=0.33 and the slope angle
.beta.=60.degree..
[0043] As shown in FIG. 5, the motor load and the rotational number
trend to increase as the diameter ratio D/d increases. Therefore,
in order to reduce the motor load and the rotational number, it is
desirable that the value of the diameter ratio D/d is set to be as
small as possible. On the other hand, when the value of the
diameter ratio D/d is reduced, there occurs a risk that the blades
46 of the propeller fan 24 come into contact with the inner surface
of the bell mouth 25. Therefore, from the viewpoint of reducing the
motor load and the rotational number and suppressing the contact
between the propeller fan 24 and the bell mouth 25, it is desirable
from the simulation result that the bell mouth and the propeller
fan are configured in the range of 1.02<D/d<1.03, and further
it is more desirable that the bell mouth and the propeller fan are
configured in the range of 1.0225.ltoreq.D/d.ltoreq.1.0285.
[0044] FIG. 6 is a diagram showing the relationship of the rate
hL/h of the height hL from the air suction opening 25B to the lower
end point of the propeller fan 24 to the height h of the slope wall
portion 41, the rotational number of the propeller fan and the
motor load. It has been found from the simulation result that the
motor load trends to increase as hL/h increases, however, the
rotational number has a local minimum value in the neighborhood of
hL/h=0.24 or hL/h=0.3.
[0045] Accordingly, it is desirable from the simulation result that
the propeller fan 24 is disposed so as to satisfy the range of
0.24.ltoreq.hL/h.ltoreq.0.40, whereby the rotational number of the
propeller fan 24 and the motor load can be further reduced.
[0046] FIG. 7 is a diagram showing the relationship of the rate of
the height hZ from the air suction opening 25B to the upper end
point 46A of the propeller fan 24 to the height H of the bell mouth
25, the rotational number of the propeller fan and the motor load.
It has been found from this simulation result that the motor load
trends to increase as hZ/H increases and the rotational number has
a local minimum value in the neighborhood of hZ/H=0.9.
[0047] Accordingly, it is desirable from this simulation result
that the propeller fan 24 is disposed so as to satisfy the range of
0.866.ltoreq.hZ/H.ltoreq.0.933, and further the propeller fan 24 is
disposed so as to satisfy the range of
0.875.ltoreq.hZ/H.ltoreq.0.925. Accordingly, the rotational number
of the propeller fan 24 and the motor load can be further
reduced.
[0048] As described above, the bell mouth of this embodiment is
configured so as to satisfy 0.33.ltoreq.h/H.ltoreq.0.42 and
60.degree..ltoreq..beta..ltoreq.70.degree., the diameter D of the
opening of the joint portion 42 of the bell mouth 25 is set to
satisfy 1.02<D/d<1.03, and the propeller fan 24 is disposed
in the bell mouth so as to satisfy 0.24.ltoreq.hL/h.ltoreq.0.40 and
0.866.ltoreq.hZ/H.ltoreq.0.933, whereby both the reduction of the
rotational number of the propeller fan 24 and the reduction of the
motor load can be satisfied at the same time with keeping the same
air flow amount.
[0049] According to this embodiment, the propeller fan 24 is
disposed so as to be perfectly overlapped with the bell mouth 25 in
side view. Therefore, the area where the propeller fan 24 operates
is covered by the bell mouth 25, whereby all the air blown by the
propeller fan 24 can be guided by the bell mouth 25, and the air
flow amount of the propeller fan 24 can be enhanced.
* * * * *