U.S. patent application number 13/062368 was filed with the patent office on 2011-09-15 for extraction fan and rotor.
This patent application is currently assigned to HUNTER PACIFIC INTERNATIONAL PTY LTD. Invention is credited to Philip Cedric Allen, Liam Peter Keene, David Glen Stocks.
Application Number | 20110223029 13/062368 |
Document ID | / |
Family ID | 42004721 |
Filed Date | 2011-09-15 |
United States Patent
Application |
20110223029 |
Kind Code |
A1 |
Allen; Philip Cedric ; et
al. |
September 15, 2011 |
EXTRACTION FAN AND ROTOR
Abstract
An extraction fan rotor including a hub and a plurality of vanes
extending radially therefrom, wherein said vanes have an aerofoil
profile in cross-section.
Inventors: |
Allen; Philip Cedric; (New
South Wales, AU) ; Stocks; David Glen; (New South
Wales, AU) ; Keene; Liam Peter; (New South Wales,
AU) |
Assignee: |
HUNTER PACIFIC INTERNATIONAL PTY
LTD
Dural
AU
|
Family ID: |
42004721 |
Appl. No.: |
13/062368 |
Filed: |
September 11, 2009 |
PCT Filed: |
September 11, 2009 |
PCT NO: |
PCT/AU2009/001192 |
371 Date: |
May 26, 2011 |
Current U.S.
Class: |
416/223R |
Current CPC
Class: |
F04D 29/384 20130101;
F04D 29/329 20130101 |
Class at
Publication: |
416/223.R |
International
Class: |
F01D 5/14 20060101
F01D005/14 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 2008 |
AU |
2008904736 |
Claims
1. An extraction fan rotor, said rotor including a hub and a
plurality of vanes extending radially therefrom, wherein said vanes
have an aerofoil profile in cross-section.
2. The extraction fan rotor of claim 1, wherein said aerofoil
corresponds to a Selig aerofoil profile.
3. The extraction fan rotor of claim 2, wherein said aerofoil
corresponds to a Selig SG6043 aerofoil profile.
4. The extraction fan rotor of claim 1, wherein the angle of attack
of the vane increases with distance from the center of the
rotor.
5. The extraction fan rotor of claim 1, wherein the hub has a
hemispherical profile.
6. The extraction fan rotor of claim 5, wherein the leading edges
of the vanes are coplanar with the apex of the hemispherical
profile of the hub.
7. An extraction fan comprising a rotor, said rotor including a hub
and a plurality of vanes radially extending therefrom, wherein said
vanes have an aerofoil profile in cross section.
8. The extraction fan of claim 7, said fan including a stator,
wherein said stator includes a core and a plurality of vanes
extending radially therefrom.
9. The extraction fan of claim 8, wherein a cross sectional profile
of said hub is approximately parabolic, and is operably arranged
such that the diameter of said hub decreases in the direction of
air flow.
10. (canceled)
11. (canceled)
12. The extraction fan rotor of claim 2, wherein the angle of
attack of the vane increases with distance from the center of the
rotor.
13. The extraction fan rotor of claim 3, wherein the angle of
attack of the vane increases with distance from the center of the
rotor.
14. The extraction fan rotor of claim 2, wherein the hub has a
hemispherical profile.
15. The extraction fan rotor of claim 3, wherein the hub has a
hemispherical profile.
16. The extraction fan of claim 7, wherein said aerofoil
corresponds to a Selig aerofoil profile.
17. The extraction fan of claim 7, wherein said aerofoil
corresponds to a Selig SG6043 aerofoil profile.
18. The extraction fan of claim 7, wherein the angle of attack of
the vane increases with distance from the center of the rotor.
19. The extraction fan of claim 7, wherein the hub has a
hemispherical profile.
Description
FIELD OF THE INVENTION
[0001] The invention relates to the field of design and manufacture
of extraction fans for domestic or commercial applications. In
particular, the invention relates to an improved rotor blade
configuration.
BACKGROUND OF THE INVENTION
[0002] Air extraction fans are used in a number of domestic and
commercial applications, such as in extracting poisonous gases from
fume hoods, or, most commonly, extracting odours and vapour from
kitchens, bathrooms and the like.
[0003] Typically, these fans are mounted inside a duct and include
a rotor, which is designed to impart mechanical energy to air
inside the duct to impel air flow through the duct away from the
room; and a stator downstream of the rotor which is designed to aid
smooth airflow through the duct.
[0004] However, many existing designs are not particularly
efficient in performing this task. Testing of many prior art
designs reveals that domestic kitchen extraction fans are
particularly inefficient in moving air through the duct. Very few
designs actually maintain significant operational downstream
pressure, or suction at the duct inlet, often doing little more
than internally agitate the air. Often the fan does little more
than suck in some air, agitate it, actually blow it back out of the
inlet and then re-extract it again--effectively setting up a
recycling stream wherein only a small portion of the agitated air
is actually impelled through the duct.
[0005] Accordingly, it is an object of the invention to provide an
extraction fan that efficiently meets the objective of such
devices, by causing a substantially greater proportion of the air
to be extracted from the source room and impelled away from the
room to its target destination.
SUMMARY OF THE INVENTION
[0006] According to a first aspect of the invention, there is
provided an extraction fan rotor, said rotor including a hub and a
plurality of vanes extending radially therefrom, wherein said vanes
have an aerofoil profile in cross-section.
[0007] The new and inventive use of an aerofoil profile for the
vanes of an extraction fan provides a number of functional
advantages. These include a significantly greater transfer of
mechanical energy from the rotor to the air mass, thereby
generating greater pressure and less noise. This is due mainly to
the ability of a true aerofoil to maintain linear flow of air at
the boundary layer along the vast majority of its surface.
[0008] Preferably, the profile of said aerofoil corresponds to a
Selig SG6043 aerofoil profile.
[0009] Advantageously, the vanes are configured such that the angle
of attack of the vanes increases with distance from the centre of
the rotor. This appears to resemble a `twisting` of the vane when
viewed in a direction from the end of the vane toward the hub. This
accounts for a different linear speed at each point of the vane and
significantly improves the efficiency of the rotor.
[0010] The extraction fan rotor of any preceding claim, wherein the
hub has a substantially hemispherical profile. This profile
provides particularly good performance, and in particular, where
the leading edges of the vanes are coplanar with the apex of the
hemispherical profile of the hub.
[0011] According to another aspect of the invention, there is
provided an extraction fan, said fan including a rotor according
with that described above. It is advantageous if the rotor is
couples with a downstream stator, wherein said stator includes a
core and a plurality of vanes extending radially therefrom, and
which make operative connection with the inner wall of a duct, in
which the rotor and stator are housed.
[0012] Preferably, the cross-sectional profile of said hub is
approximately parabolic, and is operably arranged such that the
diameter of said hub decreases in the direction of air flow. This
profile has been found by the inventors to enhance the ability of
the extraction fan to impart energy to the movement of air through
the duct. It is thought that the parabolic curvature of the stator
helps to reduce turbulence in the air flowing through said
duct.
[0013] Now will be described, with by way of a specific,
non-limiting example, a preferred embodiment of the invention.
BRIEF DESCRIPTION OF THE FIGURES
[0014] FIG. 1a is an end-on view of a rotor for an air extraction
fan according to the invention.
[0015] FIG. 1b is an end-on view of a rotor for an air extraction
fan typical of the prior art.
[0016] FIG. 2a is a side view of a rotor for an air extraction fan
according to the invention.
[0017] FIG. 2b is a side view of a rotor for an air extraction fan
typical of the prior art.
[0018] FIG. 3a is a detail view of a single vane of the rotor of
FIG. 2a.
[0019] FIG. 3b is a scale representation of the cross-sectional
profile of the vane of FIG. 3a.
[0020] FIG. 4 is a computer generated fluid dynamic model of
turbulence generated by simple inclined plane rotor blade, typical
of the prior art.
[0021] FIG. 5 is a computer generated representation of modelled
flow path lines for a conventional inclined plane rotor vane,
typical of the prior art.
[0022] FIG. 6 is a computer generated representation of modelled
flow path lines for a rotor for an air extraction fan according to
the invention.
[0023] FIG. 7a is an isometric view cut-away view of a stator
according to the invention mounted in a duct.
[0024] FIG. 7b is an isometric view cut-away view of a stator
typical of the prior art mounted in a duct.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] The invention provides an improved air extraction fan rotor
which alleviates the problems of the prior art principally via a
superior vane profile design, and which also features an improved
hub and vane configuration.
[0026] The invention further provides an improved air extraction
fan which incorporates said rotor and which advantageously further
includes an improved stator design.
[0027] Turning to FIGS. 1a and 1b, there are contrasted a rotor 1
according to the invention and a rotor 1' typical of the prior art.
Both rotors feature a central hub (5, 5'), from which extend
radially a plurality of vanes (10, 10'). It will be noted from
these views that the hub 5 of the inventive rotor 1 is
hemispherical in profile, and that the vanes 10 of the inventive
rotor 1 are arranged such that their leading edges 15 are
substantially coplanar with the centre of the hub 5, which
represents the apex of said hemisphere.
[0028] FIGS. 2a and 2b show a side elevation of the rotors of FIGS.
1a and 1b, respectively. Most notable in FIG. 2b is the profile of
the vanes 10': they are curved and have a substantially consistent
thickness. Other typical prior art vanes have a flat profile and
are also of substantially consistent thickness. This is one of the
main causes of aerodynamic inefficiency amongst prior art vane
designs.
[0029] This is illustrated in FIG. 4, which is a computer-modelled
representation of the turbulence that results from rapid air flow
over an `inclined plane` vane. It will be noted from the figure
that very substantial turbulent air flow is produced. The principal
disadvantages of conventional inclined plane rotor vanes using is
turbulence-induced cavitation and substantial form drag. Turbulence
prevents the rotor vane from effectively transferring air across
its entire span, and form drag increases the energy required to
move a parcel of air from one side of the rotor vane to the
other.
[0030] This effect is further illustrated in FIG. 5. This is a
representation of computer-modelled flow path lines 20 for air
moving across a conventional inclined plane rotor vane 25 showing
that boundary layer separation commences close to the leading edge
30 of the vane 25. Boundary-layer separation is where the layer of
air flowing at the boundary between air and the vane surface 35
(known as the boundary layer) actually separates from the vane
surface, creating a region of vacuum 140. This vacuum region 140
then tends to distort the flow of the layers of air nearest to it,
which initiates turbulent air flow.
[0031] By contrast, it will be noted from FIG. 2a that the
inventive rotor 1 has vanes 10 that have a profile that corresponds
to an aerofoil, in this illustration a preferred Selig SG6043
aerofoil. This profile is illustrated in greater detail in FIG. 3b.
The profile is asymmetrical between the upper surface 40 and lower
surface 45, and is thicker toward the leading edge 50, whilst
thinning toward the trailing edge 55.
[0032] The inventive rotor vane has been designed to minimise
turbulence. As illustrated in the representation of
computer-modelled flow path lines in FIG. 6, air is drawn along the
profile of the vane 60 and the varying cross section of the
aerofoil reduces and/or delays separation of the boundary layer 65.
Delaying separation of the boundary layer 65 tends to significantly
reduce, or eliminate, the onset of turbulent airflow, which makes
more efficient use of the energy delivered by the motor to the
rotor.
[0033] As illustrated in FIG. 2a and shown in greater detail in
FIG. 3a, the inventive vane 10 also appears to incorporate a
`twist`, in that the angle of attack A (i.e. the angle at which the
leading edge 50 of the vane strikes the air, relative to the
direction of air flow) of the vane 10 becomes greater with distance
from the hub 5. This is in recognition of the fact that the
relative instantaneous linear air speed at any point along the
leading edge of the vane will be greater with distance from the
centre of the hub. The change in angle of attack at different
speeds assists in reducing the likelihood of creating turbulent
flow across the vane surface.
[0034] Turning to FIGS. 7a and 7b, there is illustrated a cutaway
view of an extraction fan (100, 100') according to the invention
and according to the prior art respectively. Both views are shown
with the rotor removed. Both fans feature a duct (105, 105'), which
houses a stator assembly (110, 110'). The stator assembly in each
case is made up of a central core (115, 115') which is attached to
the inner surface of the duct (105, 105') by a plurality of vanes
(120, 120'). Air flows through the duct in the direction of arrows
B and B'.
[0035] However, the crucial difference is the particular profile of
the core 115 in FIG. 7a. The core 115 is substantially elongated by
comparison with the prior art 115'. The cross-sectional profile of
the core 115 is approximately parabolic. This is illustrated in
greater detail in FIG. 8. This design has been determined to
provide the least turbulent air flow through the duct 105,
especially by comparison with the approximately hemispherical prior
art core 115'.
[0036] It will be appreciated by those skilled in the art that the
foregoing is merely one way in which the invention may be embodied.
It will be understood by those skilled in the art that other
embodiments may be conceived of which, while differing in some
aspects, nevertheless fall within the scope of the invention and
the claims appended hereto.
* * * * *