U.S. patent application number 11/714402 was filed with the patent office on 2008-09-11 for fan with heat dissipating outlet guide vanes.
This patent application is currently assigned to Xcelaero Corporation. Invention is credited to Chellappa Balan, Ralph James Carl, John Decker.
Application Number | 20080219836 11/714402 |
Document ID | / |
Family ID | 39738589 |
Filed Date | 2008-09-11 |
United States Patent
Application |
20080219836 |
Kind Code |
A1 |
Decker; John ; et
al. |
September 11, 2008 |
Fan with heat dissipating outlet guide vanes
Abstract
A method for designing a fan having a motor which drives an
impeller comprises providing an outlet guide vane assembly which
includes a hub and a plurality of guide vanes that extend radially
outwardly from the hub, attaching the hub to the motor, determining
an approximate amount of heat which is generated by the motor
during operation of the fan, determining an approximate surface
area which is required to dissipate the heat into a surrounding air
stream, and configuring the guide vanes to comprise a total surface
area which is approximately equal to the required surface area. In
this manner, the heat generated by the motor during operation of
the fan can be dissipated by the guide vanes.
Inventors: |
Decker; John; (Cypress,
TX) ; Balan; Chellappa; (Niskayuna, NY) ;
Carl; Ralph James; (Clifton Park, NY) |
Correspondence
Address: |
Henry C. Query, Jr.
504 S. Pierce Avenue
Wheaton
IL
60187
US
|
Assignee: |
Xcelaero Corporation
San Luis Obispo
CA
|
Family ID: |
39738589 |
Appl. No.: |
11/714402 |
Filed: |
March 5, 2007 |
Current U.S.
Class: |
415/177 ;
29/889.3 |
Current CPC
Class: |
F04D 25/06 20130101;
F04D 25/082 20130101; F04D 29/542 20130101; F04D 29/5853 20130101;
F04D 29/5806 20130101; Y10T 29/49327 20150115 |
Class at
Publication: |
415/177 ;
29/889.3 |
International
Class: |
F04D 29/64 20060101
F04D029/64 |
Claims
1. A method for designing a fan which includes a motor that drives
an impeller, the method comprising: providing an outlet guide vane
assembly which includes a hub and a plurality of guide vanes which
extend radially outwardly from the hub; attaching the hub to the
motor; determining an approximate amount of heat which is generated
by the motor during operation of the fan; determining an
approximate surface area which is required to dissipate a
substantial amount of the heat into a surrounding air stream; and
configuring the guide vanes to comprise a total surface area which
is approximately equal to the required surface area; wherein the
heat generated by the motor during operation of the fan can be
dissipated by the guide vanes into the surrounding air stream.
2. The method of claim 1, wherein the step of determining the
required surface area comprises determining a film coefficient for
the guide vanes.
3. The method of claim 1, wherein the step of configuring the guide
vanes comprises: designating a plurality a radially spaced airfoil
segments for each guide vane, each of which comprises a chord, an
area and a perimeter length; determining the chord, area and
perimeter length of each airfoil segment which will result in the
guide vanes comprising a total surface area which is approximately
equal to the surface area required to dissipate the heat.
4. The method of claim 3, further comprising adjusting the chord,
area and perimeter length of each airfoil segment to decrease the
effective thermal resistance of the heat transfer path through the
guide vanes.
5. The method of claim 3, further comprising adjusting the chord,
area and perimeter length of each airfoil segment to decrease the
effective thermal resistance of the heat transfer path between the
guide vanes and a surrounding air stream.
6. The method of claim 3, wherein the plurality of airfoil segments
comprises a first airfoil segment which is located closest to the
hub, an n.sup.th airfoil segment which is located farthest from the
hub and a number of additional airfoil segments which are located
between the first and the n.sup.th airfoil segments, and wherein
the method further comprises making at least one of the chord, the
area and the perimeter length of the first airfoil segment greater
than the chord, the area or the perimeter length of the n.sup.th
airfoil.
7. The method of claim 6, further comprising making the chord, the
area and the perimeter length of the first airfoil segment greater
than the chord, the area and the perimeter length of the n.sup.th
airfoil segment.
8. The method of claim 6, further comprising making at least one of
the chord, the area and the perimeter length of the first airfoil
segment greater than the chord, the area or the perimeter length of
the remaining airfoil segments.
9. The method of claim 6, further comprising making the chord, the
area and the perimeter length of the first airfoil segment greater
than the chord, the area and the perimeter length of the remaining
airfoil segments.
10. The method of claim 1, wherein the step of attaching the hub to
the motor comprises: providing a housing for the motor; and forming
the hub integrally with the housing.
11. The method of claim 10, further comprising forming the motor
housing and the outlet guide vane assembly as an integral unit from
a single piece of a heat conducting material.
12. A fan which comprises: an outlet guide vane assembly which
includes a hub and a plurality of guide vanes which extend radially
outwardly from the hub; and a motor which includes a housing that
is connected to or formed integrally with the hub and which during
operation of the fan generates heat; wherein the guide vanes
together comprise a total surface area which is approximately equal
to a surface area which is required to dissipate a substantial
amount of the heat into a surrounding air stream.
13. The fan of claim 12, wherein each of the guide vanes comprises
a plurality a radially spaced airfoil segments, each of which
includes a chord, an area and a perimeter length.
14. The fan of claim 13, wherein the plurality airfoil segments
comprises a first airfoil segment which is located closest to the
hub, an n.sup.th airfoil segment which is located farthest from the
hub and a number of additional airfoil segments which are located
between the first and the n.sup.th airfoil segments.
15. The fan of claim 14, wherein at least one of the chord, the
area and the perimeter length of the first airfoil segment is
greater than the chord, the area or the perimeter length of the
n.sup.th airfoil segment.
16. The fan of claim 14, wherein the chord, the area and the
perimeter length of the first airfoil segment are greater than the
chord, the area and the perimeter length of the n.sup.th airfoil
segment.
17. The fan of claim 14, wherein at least one of the chord, the
area and the perimeter length of the first airfoil segment is
greater than the chord, the area or the perimeter length of the
remaining airfoil segments.
18. The fan of claim 14, wherein the chord, the area and the
perimeter length of the first airfoil segment is greater than the
chord, the area and the perimeter length of the remaining airfoil
segments.
19. The fan of claim 14, wherein the distance between successive
segments is generally constant.
20. The fan of claim 19, wherein relationship between at least one
of the chords, the areas and the perimeter lengths of the airfoil
segments is non-linear.
21. The fan of claim 19, wherein the relationships between the
chords, the areas and the perimeter lengths of the airfoils
segments are non-linear.
22. The fan of claim 12, wherein the motor comprises a stator which
forms an interference fit with the housing.
23. The fan of claim 12, further comprising a number of radially
extending cooling fins which are attached to or formed integrally
with the motor housing.
24. A fan which comprises: an outlet guide vane assembly which
includes a hub and a plurality of guide vanes which extend radially
outwardly from the hub; and a motor which includes a housing that
is connected to or formed integrally with the hub and which during
operation of the fan generates heat; wherein each of the guide
vanes comprises a plurality a radially spaced airfoil segments,
each of which includes a chord, an area and a perimeter length.
wherein the plurality airfoil segments comprises a first airfoil
segment which is located closest to the hub, an n.sup.th airfoil
segment which is located farthest from the hub and a number of
additional airfoil segments which are located between the first and
the n.sup.th airfoil segments. wherein at least one of the chord,
the area and the perimeter length of the first airfoil segment is
greater than the chord, the area or the perimeter length of the
n.sup.th airfoil segment.
25. The fan of claim 24, wherein the chord, the area and the
perimeter length of the first airfoil segment are greater than the
chord, the area and the perimeter length of the n.sup.th airfoil
segment.
26. The fan of claim 24, wherein at least one of the chord, the
area and the perimeter length of the first airfoil segment is
greater than the chord, the area or the perimeter length of the
remaining airfoil segments.
27. The fan of claim 24, wherein the chord, the area and the
perimeter length of the first airfoil segment is greater than the
chord, the area and the perimeter length of the remaining airfoil
segments.
28. The fan of claim 24, wherein the distance between successive
segments is generally constant.
29. The fan of claim 28, wherein relationship between at least one
of the chords, the areas and the perimeter lengths of the airfoil
segments is non-linear.
30. The fan of claim 19, wherein the relationships between the
chords, the areas and the perimeter lengths of the airfoils
segments are non-linear.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an air mover which
comprises a motor-driven impeller and an outlet guide vane assembly
for de-swirling the air stream generated by the impeller. More
particularly, the invention relates to such an air mover which
comprises an outlet guide vane assembly that is designed to
dissipate the heat generated by the motor.
[0002] Typical air movers, such as fans, include an impeller which
is driven by a motor. This motor, be it electrically or otherwise
powered, will necessarily produce heat during operation of the air
mover. Moreover, the size, weight and life of the air mover is
determined to a large extent by its operating temperature.
Therefore, the desirability exists to dissipate the heat generated
by the motor.
[0003] In high flow axial fans, the motor is often positioned in
the core of the fan. In addition, many of these fans require the
motor to be closed to the external environment. Therefore, the only
path through which the heat generated by the motor may be
dissipated is typically through the air stream which flows over the
motor. Moreover, although motors may be liquid cooled, fans which
include such motors are relatively more complex and intrinsically
less reliable than air cooled fans.
SUMMARY OF THE INVENTION
[0004] In accordance with the present invention, these and other
disadvantages in the prior art are addressed by providing a method
for designing a fan which is capable of dissipating the heat
generated by the motor into the surrounding air stream. The method
comprises the steps of providing an outlet guide vane assembly
which includes a hub and a plurality of guide vanes which extend
radially outwardly from the hub, attaching the hub to the motor,
determining an approximate amount of heat which is generated by the
motor during operation of the fan, determining an approximate
surface area which is required to dissipate the heat into the
surrounding air stream, and configuring the guide vanes to comprise
a total surface area which is approximately equal to the required
surface area. In this manner, the heat generated by the motor
during operation of the fan can be dissipated by the guide vanes
into the surrounding air stream.
[0005] In one embodiment of the invention, the step of configuring
the guide vanes comprises designating a plurality a radially spaced
airfoil segments for each guide vane, each of which comprises a
chord, an area and a perimeter length, and then determining the
chord, area and perimeter length of each airfoil segment which will
result in the guide vanes comprising a total surface area which is
approximately equal to the surface area required to dissipate the
heat. The method may also comprise the step of adjusting the chord,
area and perimeter length of each airfoil segment to decrease the
effective thermal resistance of the heat transfer path through the
guide vanes. In addition, the method may comprise the step of
adjusting the chord, area and perimeter length of each airfoil
segment to decrease the effective thermal resistance of the heat
transfer path between the guide vanes and a surrounding air
stream.
[0006] In accordance with another aspect of the invention, the
plurality of airfoil segments comprises a first airfoil segment
which is located closest to the hub, an n.sup.th airfoil segment
which is located farthest from the hub and a number of additional
airfoil segments which are located between the first and the
n.sup.th airfoil segments. In addition, the method further
comprises the step of making at least one of the chord, the area
and the perimeter length of the first airfoil segment greater than
the chord, the area or the perimeter length of the n.sup.th airfoil
segment. Moreover, the method may comprise the step of making at
least one of the chord, the area and the perimeter length of the
first airfoil segment greater than the chord, the area or the
perimeter length of the remaining airfoil segments.
[0007] In accordance with yet another aspect of the invention, the
step of attaching the hub to the motor comprises providing a
housing for the motor and forming the hub integrally with the
housing. The method may further comprise the step of forming the
motor housing and the outlet guide vane assembly as an integral
unit from a single piece of a heat conducting material.
[0008] The present invention also provides a fan which is adapted
to dissipate the heat which is generated by its motor during
operation of the fan. The fan comprises an outlet guide vane
assembly which includes a hub and a plurality of guide vanes which
extend radially outwardly from the hub. In addition, the motor
includes a housing which is connected to or formed integrally with
the hub. Moreover, the guide vanes together comprise a total
surface area which is approximately equal to the surface area which
is required to dissipate a substantial amount of the heat generated
by the motor into the surrounding air stream.
[0009] In accordance with one aspect of this invention, each of the
guide vanes comprises a plurality a radially spaced airfoil
segments, each of which includes a chord, an area and a perimeter
length. Additionally, the plurality of airfoil segments comprises a
first airfoil segment which is located closest to the hub, an
n.sup.th airfoil segment which is located farthest from the hub and
a number of additional airfoil segments which are located between
the first and the n.sup.th airfoil segments. Furthermore, at least
one of the chord, the area and the perimeter length of the first
airfoil segment may be greater than the chord, the area or the
perimeter length of the n.sup.th airfoil segment. In addition, at
least one of the chord, the area and the perimeter length of the
first airfoil segment may be greater than the chord, the area or
the perimeter length of the remaining airfoil segments.
[0010] Thus, the present invention provides an effective means for
dissipating the heat generated by the motor during operation of the
fan. Consequently, the fan can be equipped with a smaller and more
efficient motor. Moreover, since the heat generated by the motor is
dissipated through the pre-existing outlet guide vane assembly, the
fan does not need to be equipped with additional cooling
components.
[0011] These and other objects and advantages of the present
invention will be made apparent from the following detailed
description, with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a cross sectional view of an exemplary embodiment
of the fan of the present invention;
[0013] FIG. 2 is an exploded perspective view of the fan shown in
FIG. 1;
[0014] FIG. 3 is a schematic representation of an exemplary airfoil
which is used to illustrate certain features of the present
invention; and
[0015] FIG. 4 is a representation of a succession of radially
spaced airfoil segments of a guide vane component of the fan of
FIG. 1, with Airfoil Segment 1 being closest to the root of the
guide vane and Airfoil Segment 8 being closest to the tip of the
guide vane;
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present invention is applicable to a variety of air
movers. However, for purposes of brevity it will be described in
the context of an exemplary vane-axial cooling fan. Nevertheless,
the person of ordinary skill in the art will readily appreciate how
the teachings of the present invention can be applied to other
types of air movers. Therefore, the following description should
not be construed to limit the scope of the present invention in any
manner.
[0017] Referring to FIGS. 1 and 2, the cooling fan of the present
invention, which is indicated generally by reference number 10,
includes an impeller 12 which is mounted on a shaft 14 that is
driven by a motor 16. The motor 16 includes a motor housing 18
which is connected to a fan housing 20 by an outlet guide vane
assembly 22.
[0018] The impeller 12 comprises an impeller hub 24 and a number of
fan blades 26 which are connected to or formed integrally with the
impeller hub. The impeller hub 24 includes an axial bore 28 through
which the shaft 14 extends, and the shaft is secured to the
impeller hub 12 by a pair of counteracting nuts 30a, 30b. The
impeller hub 12 may include a nose cone 32, which in this case is
connected to the shaft 14 by a screw 34.
[0019] The motor 16 may comprise a totally enclosed air-over cooled
("TEAOC") brushless DC motor which includes a rotor 36 and a stator
38. The rotor 36 is attached to or formed integrally with the shaft
14, and the stator 38 is mounted in a cylindrical recess 40 that is
formed in the motor housing 18. As is known in the art, the stator
38 includes a stack of laminations and a number of windings which,
when energized by an electric current, create a magnetic field
which causes the rotor 36 to spin.
[0020] The shaft 14 is rotationally supported in a front bearing 42
and a rear bearing 44, both of which may be, e.g., metal ball
bearings. The front bearing 42 is mounted in an aperture 46 in the
motor housing 18 and is held in place by a retaining ring 48. The
rear bearing 44 is mounted in a collar 50 which is attached to or
formed integrally with a tail cone 52 that is connected to the
motor housing by, e.g., a number of screws 54. The shaft 14 is
retained axially relative to the motor housing 18 by the front
bearing 42.
[0021] Referring still to FIGS. 1 and 2, the outlet guide vane
assembly 22 comprises a hub 64 which is attached to or formed
integrally with the motor housing 18, an outer ring 66 which is
secured to the fan housing 20, and a plurality of guide vanes 68
which extend radially between the hub and the outer ring. Each
guide vane 68 comprises a root, which is the radially innermost
portion of the guide vane, and a tip, which is the radially
outermost portion of the guide vane. In addition, each guide vane
68 may comprises a radial stack of a number of individual airfoil
segments, each of which represents a cross section of the guide
vane at a specific radial distance from its root.
[0022] Referring to FIG. 3, an exemplary airfoil segment 70
includes a leading edge 72 and a trailing edge 74. Each airfoil
segment 70 is oriented such that the air stream, which is
represented by the lines with multiple arrowheads, meets the
airfoil segment 70 at the leading edge 72 and departs the airfoil
segment at the trailing edge 74. Each airfoil segment 70 also
comprises a chord C, an area A and a perimeter P. The chord C is
the straight line distance between the leading and trailing edges
72, 74, and the area A is the cross sectional area of the guide
vane 68 at the radial location of the airfoil segment 70.
[0023] Referring again to FIGS. 1 and 2, the fan housing 20
includes an inlet shroud 76 and an outlet shroud 78. The inlet and
outlet shrouds 76, 78 comprise respective first and second annular
rims 80, 82 which together define a cylindrical recess within which
the outer ring 66 of the outlet guide vane assembly 22 is
positioned. The inlet and outlet shrouds 76, 78 are secured to the
outlet guide vane assembly 22 by a number of screws (not shown),
which extend through corresponding bores 84 in the first and second
rims 80, 82 and into matching holes 86 in the outer ring 66. The
inlet and outlet shrouds 76, 78 may also comprise one or more
radial lips 88 to enable the fan housing 20, and thus the cooling
fan 10, to be mounted to an associated structure.
[0024] In operation of the cooling fan 10, the motor 16 spins the
impeller 12 to draw air into the inlet shroud 76 and through the
fan housing 20. The spinning impeller 12 imparts a significant
degree of swirl to the air stream. As the air stream passes through
the outlet guide vane assembly 22, however, the guide vanes 68
remove this swirl by reorienting the air stream into a
substantially axial direction. Thus, an important function of the
outlet guide vane assembly 22 is to de-swirl, or straighten, the
air stream prior to its exiting the outlet shroud 78. Another
function of the outlet guide vane assembly 22 is to physically
support the motor 16 within the fan housing 20.
[0025] However, in accordance with the present invention, the
outlet guide vane assembly 22 is designed to not only de-swirl the
air stream generated by the impeller 12 and support the motor 16
within the fan housing 20, but also to dissipate the heat produced
by the motor 16. This is accomplished in an effective manner by
conducting the heat through the motor housing 18 to the guide vanes
68, where it can then be readily dissipated into the air stream
flowing through the cooling fan 10.
[0026] In accordance with one aspect of the invention, the cooling
fan 10 is designed to minimize the effective thermal resistance of
the heat transfer path between the motor 16 and the guide vanes 68.
In this embodiment, the stator 38 is ideally mounted in the recess
40 in the motor housing 18 using an interference fit, such as a
press fit. Also, both the motor housing 18 and the outlet guide
vane assembly 22 are made from a heat conductive material, such as
aluminum. Optimally, the motor housing 18 and the outlet guide vane
assembly 22 are constructed from a single block of material using
known techniques, such as machining, casting or pressing.
Consequently, the heat generated by the motor 16 during operation
of the cooling fan 10 will be readily conducted through the motor
housing 18 and into the guide vanes 68.
[0027] In accordance with another aspect of the invention, the
guide vanes 68 are designed to minimize the effective thermal
resistance of the heat transfer path between the guide vanes 68 and
the air stream flowing through the cooling fan 10. In particular,
the present invention defines a process to determine the optimum
number and configuration of guide vanes 68 which will achieve these
functions without interfering with the ability of the guide vanes
to de-swirl the air stream generated by the impeller 12 or support
the motor 16 within the fan housing 20.
[0028] The design of the outlet guide vane assembly 22 is largely
dependent upon the velocity and pressure of the air stream which
the cooling fan 10 is required to deliver for a particular cooling
application. These factors will define the inside and outside
boundaries of the flow path through the cooling fan 10, which in
turn will define the inner and outer radial extents of the guide
vanes 68.
[0029] In accordance with the present invention, the design of the
outlet guide vane assembly 22 is also dependent upon the amount of
heat generated by the motor 16. The amount of heat generated by the
motor 16 is determined by first calculating the amount of power
which the motor will need to generate in order to deliver the
required air stream. The rated efficiency of the motor 16 is then
applied to this power value to compute the total motor losses,
which are a fairly reasonable estimate of the heat generated by the
motor during operation of the cooling fan 10.
[0030] Once the amount of heat generated by the motor 16 is
determined, the total surface area of the guide vanes 68 required
to dissipate a substantial amount of this heat into the surrounding
air stream may be determined. In the context of the present
invention, a "substantial amount" of the heat may comprise greater
than about 50% of the heat, more preferably greater than about 60%
of the heat, and most preferably greater than about 70% of the
heat. First, based on the velocity and temperature of the air
stream, an estimate can be made of the film coefficient for the
guide vanes 68. This film coefficient is then used to estimate the
total surface area of the guide vanes 68 which is required to
dissipate the heat generated by the motor 16. In this regard, both
the film coefficient and the total surface area of the guide vanes
68 may be determined using known heat transfer equations applicable
to the process of forced convection.
[0031] The length and total surface area of the guide vanes 68 will
provide a basis for an initial determination of the number of guide
vanes and the chord C, area A and perimeter length L of each of a
pre-selected number of airfoil segments 70 for each guide vane.
Other factors which may be considered in determining these values
may include the desired or required vane-blade ratio for the
cooling fan 10 (i.e., the ratio of the number of guide vanes to the
number of impeller blades, which has important acoustic
implications), the desired or required chord solidity for the
outlet guide vane assembly (i.e., the chord of the guide vanes
multiplied by the number of guide vanes divided by the outer
circumference of the circle joining the tips of the guide vanes),
the desired or required aspect ratio for the outlet guide vane
assembly (i.e., the ratio of the height of the guide vanes to the
chord of the guide vanes), the desired or required static pressure
rise of the air flowing through the outlet guide vane assembly, the
desired or required Reynolds number of the air flowing over the
guide vanes, and the ability of the guide vanes to support the
motor 16.
[0032] After the number of guide vanes 68 and the chord C, area A
and perimeter length L of the airfoil segments 70 are determined,
the configuration of the airfoil segments 70 may be adjusted to
minimize the effective thermal resistance of the heat transfer
paths through the guide vanes 68 and between the guide vanes and
the surrounding air. For example, since the heat flux through the
outlet guide vane assembly 22 is greatest at the hub 64, increasing
the area A of the airfoil segment 70 closest to the hub will
decrease the effective thermal resistance of the heat transfer path
from the motor housing 18 into the hub and from the hub into the
guide vane 68. In addition, increasing the area A of all the
airfoil segments 70 will increase the perimeter P of the airfoils
segments and, consequently, the entire surface area of the guide
vanes 68, which will accordingly decrease the effective thermal
resistance of the heat transfer path between the guide vanes and
the surrounding air stream. However, since the total surface area
of the guide vanes 68 should be minimized in order to minimize
frictional losses, increasing the area A of the airfoil segment 70
closest to the hub 64 will require that the area A of the other
airfoil segments be reduced.
[0033] Once these adjustments are made, the number and
configuration of the guide vanes 68 may be further modified to both
optimize the heat dissipation capacity of the guide vanes and
provide a desired degree of de-swirling of the air stream generated
by the impeller 12. Factors to consider in making these
modifications may include the desired or required values for the
vane-blade ratio, chord solidity, aspect ratio, static pressure
rise and Reynolds number. Moreover, further changes in the number
and configuration of the guide vanes 68 may be made by modeling the
cooling fan using available computer modeling programs and noting
the effects which these changes have on the ability of the guide
vanes 68 to dissipate the heat generated by the motor 16 and
de-swirl the air stream generated by the impeller 12.
[0034] Several iterations of the above-described process may be
required to achieve an optimum number and configuration of guide
vanes 68. For example, while increasing the area A of the airfoil
segments 70 will improve both the conduction of heat through the
guide vanes 68 and the convection of this heat from the guide vanes
to the surrounding air stream, at some point the airfoil segments
may become so thick that the air flow may separate from the guide
vanes. To avoid this problem, the chords C of the airfoil segments
70 can be made longer to increase both the perimeter P and the area
A without increasing the thickness of the airfoil. Unfortunately,
increasing the chord C also increases the drag coefficient of the
airfoil. Thus, the longer the chord C, the less efficient the
cooling fan 10 will become and the more power the motor 16 will
have to generate to produce the required air stream. Moreover, more
motor power implies more motor losses, which results in additional
heat that must be dissipated. Therefore, an optimal chord length C
exists which is sufficiently long to enable the heat to be
dissipated through convection, but not so long as to create
excessive drag losses.
[0035] The principles of the present invention will be further
elucidated in the context of an exemplary cooling fan 10. In this
example, the inlet temperature of the cooling fan 10 is taken to be
15.degree. C., and the cooling fan comprises a 28 kW motor 16 with
an efficiency of 96%. Thus, during operation of the cooling fan 10
the motor 16 will generate about 1.12 kW of heat. Also, the outlet
guide vane assembly 22 was chosen to include 31 guide vanes 68, and
the outer radius of the motor housing 18 and the inner radius of
the fan housing 20 are assumed to be about 5.2 inches and 8 inches,
respectively. Therefore, the radial length of each guide vane 68
will be approximately 2.8 inches.
[0036] In determining the optimum configuration of the guide vanes
68 for dissipating the maximum amount of heat from the motor 16,
each guide vane was selected to comprise eight airfoil segments 70.
Referring to FIG. 4, the airfoil segments 70 for a single guide
vane 68 are shown successively from bottom to top, with the first
airfoil segment 70 being closest to the root of the guide vane and
the eighth airfoil segment being closest to the tip of the guide
vane. Table 1 below sets forth the radial location of each airfoil
70, as measured from the axial centerline of the cooling fan 10,
and the optimum perimeter length L, area A and chord C of each
airfoil which were determined to dissipate a maximum amount of heat
generated by the motor 16.
TABLE-US-00001 TABLE 1 Radial Height Perimeter Length L Area A
Chord C Airfoil No. (in.) (in.) (in.sup.2) (in.) 1 5.51 7.47 0.84
3.30 2 5.82 7.13 0.75 3.10 3 6.13 6.67 0.66 2.90 4 6.44 6.18 0.60
2.80 5 6.76 5.75 0.56 2.70 6 7.07 5.43 0.53 2.60 7 7.38 5.17 0.51
2.40 8 7.69 4.94 0.47 2.30
[0037] From Table 1 we can see that the optimum configuration for
the guide vanes 68 exists when the perimeter length L, area A and
chord C of the first air foil 70 are each greater than the values
for any other airfoil, and when the perimeter length L, area A and
chord C for the eighth air foil are each smaller than the values
for any other airfoil. More specifically, as the height of each
airfoil 70 from the root of the guide vane 68 increases, the
perimeter length L, area A and chord C all decrease. Moreover,
although the increase in height from the first airfoil to the
eighth airfoil is generally linear, the decrease in the perimeter
length L, area A and chord C from the first airfoil to the eighth
airfoil are all non-linear. However, the amounts by which the
perimeter length L, area A and chord C increase from the first
airfoil to the eighth airfoil are not necessarily equal.
[0038] It should be noted, however, that while the configuration
represented by Table 1 optimizes the amount of heat which the guide
vanes 68 are able to dissipate in this particular cooling fan 10,
other fan designs comprising different parameters may require that
the guide vanes be configured differently. Therefore, the above
example and the conclusions drawn therefrom should not be
considered as limiting the scope of the present invention.
[0039] Referring again to FIG. 1, the cooling fan 10 may optionally
comprise a number of radially extending cooling fins 90 to provide
an additional means for dissipating the heat generated by the motor
16. The cooling fins 90 may be made of a suitable heat conductive
material, such as aluminum, and may be attached to or formed
integrally with the motor housing 18. In this manner, the heat
generated by the motor will be conducted through the motor housing
18 and into the cooling fins 90, and then dissipated into the air
steam flowing through the fan housing 20.
[0040] It should be recognized that, while the present invention
has been described in relation to the preferred embodiments
thereof, those skilled in the art may develop a wide variation of
structural and operational details without departing from the
principles of the invention. Therefore, the appended claims are to
be construed to cover all equivalents falling within the true scope
and spirit of the invention.
* * * * *