Note: Descriptions are shown in the official language in which they were submitted.
~)5534~
,,
HEAT TRANSFER SYSTEM EMPLOYING A ~ ~ :
,:
COANDA EFFECT PRODUCING FAN SHROUD EXIT
, ' . .
SP~CIFICATION
~.:
This invention relates to cooling systems or
internal combustion engines and, more particularly, to a
Coanda effect producing fan shroud exit, involved in the
air handling step of the heat transfer process. -
Reference should be made to my Canadian
appli~i-ation Serial No. 184,880, filed November 2, 1973.
This application is a division of Canadian
Serial No. 220,621, filed February 24, 197S.
A standard mode of removing heat from an internal
combustion engine is to tra~sfer the heat to a liquid, often
1,: ;
water or a mixture thereof, and from therc to a stream of ;
air. The heated air being dispersed out into the atmosphere.
A substantial body of art exists in the provision of means
to transfer the heat from the liquid to the air media. In
standard practice such as associated with a truck, for
example, heated water is passed through a radiator and a
cooling air stream is sucked through the radiator by a fan.
Shroud and shroud exit means are employed to guide the air E~
and improve the efficiency of the fan. Such factors as
shroud exit to fan blade clearance, recirculation of the
same air in the center portions, the generation of fan
noises, and the required horsepower to drive the fan become
critical. To the solutions of these difficulties and problems,
1:
.. ..
. : --1-- , .
~Lq3S~i3~
innumerable patents have been directed. It has been dis- ~
covered that there is a relation between tip clearance,
driving horsepower or fan cfficiency and fan noises. It
is believed at this time that recircu-ation and turbulcnce
in thc tip region of ~he fan are responsible for a majorit~
of the fan generated noises and substantially reduce the
overall efficiency of the fan to move air.
It is therefore an object of this invention to
provide a Coanda effect producing fan shroud means. It is
yet another object of this invention to provide a fan
shroud exit which is capable of creating low pressure
vortices when a s-tream of air is passed thereover.
Another object of this invention is to provide an engine
cooling system wherein fan generated noise and engine horse-
power requirements are reduced. A further object of this
invention is to provide a contoured fan shroud exit having
low pressure vortex creating pockets therein. Moreover,
another object of this invention is to provide a fan shroud
exit means which promotes pressure gradient bending of a
fan generated airstream passing thereover.
In accordance with this invention it has been
discovered that noise generation and horsepower requirements
of a fan assembly can be reduced by the provision of a fan
shroud exit which is capable of pressure gradient deflection
It is believed that by pressure gradient deflecting or tile
achievement of the Coanda effect, fan generated turbulence
and recirculation in the tip regions of the fan are reduced
and that the other results flow therefrom.
If a jet of fluid is introduced adjacent a
curved or flat plate, the jet will l'attach" to the plate
--2--
~5S344
3D
and follow th~ ~late ~ven thou~h the re~ullan~ flow ~ h is
highly divergent from the original direction o~ the jet. '~
This phenomenon is the CDanda effcct named after its discoverer:
Henri Coanda, a Romanian engineer. The Coanda effect, it is
believed, is caused by a stable dynamically formed and
sustained pressure gradient across a jet, which pressure
gradient bends the jet toward an adjacent boùndary or surface. r
For example a jet issuing from a nozzle begins to entrain
ambient fluid into ~he jet "mixing region" if the issuance
of the jet is in the region of a properly designed wall,
adjacent thereto entrained fluid is not easily replaced. On '~
the opposite side of the jet, away from the adjacent wall
entrained fluid is easily replaced by ambient fluid. The
result is the rapid development of a transverse pressure
gradient across the jet and the formation of a "bubble" or
vortex which forms a region of low pressure. It is the
vortex with its low pressure region, a properly designed
adjacent wall, and the pressure of the ambient fluid on the
opposite side of the stream that cause it to bend and thus
follow the contour of the wall. For reasons yet unknown as
the jet flows over the surface it entrains u~ to twenty
times the amount of air in the original jet.
At this time there is much uncertainty as ~o the
nature of the Coanda effect. That is to say the Coanda
effect is not fully understood; however, I have determined
that the provision of a fan with a Coanda effect producing
fan shroud exit causes surprising and unique results.
The object for the invention is attained by a F
vehicle having an engine, and cooliny system of the type
comprising a radiator, and a fan driven by the engine
.,
~L~S5344 ~ .
for drawing air through an air entry side of the radiator
which includes a plurality of radially extending,
circumferentially spaced impeller blades, with each of the
impeller blades having a tip portion having an axial width
Ineasured axially along the rotational axis of the fan
and between a pair of spaced points disposed respectively
on the leading and trailing edges thereof. Those points
disposed on the leading edges ~f the blade tl~ portions
lie substantially in a first plane normal to the rotational
axis of the fan and the points disposed on the trailing
edges of the blade tip portions lie substantiall~ in a
second plane axially spaced a distance from and parallel
to 'che first plane. A fan shroud is connected to an
air exit side of the radiator and encases the fan. The
improved fan shroud for reducing fan generated noisc alld
horsepower requirements of the engine is characterized by the
fan shroud comprising an air intake section, an intermediate
section, and an air discharge section with the air intake
section converging from the air exit side of the radiator
into a duct of circular cross~section. That duct connects
with the intermediate section along a third plane, and
the intermediate section has a cylindrical body extending
axially along the rotational axis of the fan a predetermined
distance from a fourth plane with the air discharge section.
The air discharge section has an expanding bell shape with
an annular lip extending radially along the fourth plane,
with the third and fourth planes being axially spaced and
substantially parallel with respect to each other. The fan is
positioned within the intermediate and air discharge sections,
and an annular step means is connected to at least one of
the shroud sections for creating an area of low pressure for
producing a Coanda effect in the fan generated air stream.
':
~ ~ -4-
~SS3~
In a further embodiment, the invention contempla-tes
a fan shroud struc-ture for use wi-th a rotary, axial flo~
- fan having a plurality of circumferentially spaced,
radially extending impeller blades, with the blades having
an effective axial width (AW) measured axially along the
rotational axis of the ~an between a first plane alld a secolld
plane and with the planes being axially spaced and parallel
with respect to each other and disposed substantially
normal to the rota-tional axis of the fan. The first ancl
second planes extend radially, respectively through points
on the leading edges of the blades at the radial tip portions
thereof and through points on the trailing edges of the blades
at the radial tip portions thereof. The combination, including
the fan, comprises a generally cylindrical axially extending
throat section encircling the Ean, an annular generally radially
extending flat portion which is r.adially spaced outwardly and
axially from one axial end of the throat section, and an
annular intermediate section extending between the one axial
end of the throat section and the radial flat portion, with
the throat section, intermediate section, and the radial flat ~ .
portion being effective to produce a low pressure region
between the air stream flowing over the surface thereof and
such surface when the fan is in operation. An annular
supplementary low pressure vortex creating means is formed .in the throat section, intermediate section and radial flat
portion of the fan shroud structure whereb~ an additional .
low pressure region is generated between the air stream
flowing over the surface of the fan shroud structure and such
fan shroud structure surface when the fan is in operation.
Other objects and advantages of the invention will
become apparent upon reading the followiny detailed
-4a-
~5534~
description and upon reference to the drawings, in which:
FIGURE l is a side view of a tractor showing
one embodimcnt of the invention; and
FI(,URE 2 is a partially broken away side sectional
view of the radiator fan shroud and fan shroud exit which
forms a region of low pressure; and
FIG~RES 3 and 4 are additional embodiments which
produce the low pressure vortex necessary to achieve pressure
gradient bending of the associated fan generated airstream.
While the invention will be described in connection
with preferred embodiments, it is understood that it is ~-
not intended to limit the invention to that embodiment. On r~
the contrary, it is intended to cover all alternatives, ;
modifications and equivalents as may be included within the
spirit and scope of the invention as defined by the appended
claims. r
Referring now to the drawings and, more particularly,~
to Figure l wherein is shown an e~ibodiment of the invention
herein disclosed. A conventional water-cooled heat producing
internal combustion engine means 10 carried forwardly on
longitudinally extending parallel support means 12 of
vehicle means 14, as shown herein vehicle means 19 is a
tractor; however as will hereafter become more apparent
this invention can be employed with any type of vehicle
having a heat generating internal combustion engine or
any portable or stationary device requiring an air moving
fan and fan shroud exit means. Forwardly mounted is a ~-
water cooling radiator or heat exchanger means 16 employed
' to dissipate engine generated heat to an air media. Water
flows between the water jacket associated with the engine
, ~not shown) and the heat exchanger through a series of
'
:
1~5534'~
fluid communicating means 18 and 20. ~leat from the engine
being absorbed into the wa-ter media or as often the case 3.
a mixture of water and other heat carrying fluids such as r
anti-freeze, etc., and passed through the heat exchanger~ F
The heat is then transferred to a fan generated air stream
which in turn is expelled out from the shroud exit as it
will be hereafter more fully disclosed~
Located adjacent the forward end of engine means
10 is a fan shat means Z6 whereby power is delivered to
drive fan means 29. As is apparent, the particular mode
whereby power is transferred to the fan and its particular
location in regard to the engine means is no-t critical, and
any desired location would be satisfactory and any means of
powering could be employed. The fan means 29 herein
depicted is a rotatable suction fan positioned opposite ~ -
radiator means 16 which normally creates a flow o air or,
more particularly, moves a stream of cooling air through r!
the radiator with a subsequent discharge thereof through ,
the air exit side 36 into fan exit shroud means 32. The fan
generated air stream is guided or directed from the radiator
to the fan by means of an air intake section 34. The particu-
lar shape of the forward air intake section 34 thereof is
dependent upon the shape and design of the air exit side 36
o the radiator. The nature o the connection between the
air intake section 34 and the air exit side 36 depends
upon the particular characteristics of the assembly. That '
is, some connections being provided with air gaps, others
are made flexible while in still other situations the
entire area between the two elements is sealed over the
entire periphery of the enclosure. In the preferred form
~, .
.
- 6 -
lC~S5344
of this invention the entire periphery of the rear area
is substantially sealed ayainst the passage of air from any
other direction except through the radiator. From the air
exit side 36 of the radiator, the air intake section of the
shroud means 32 (be it a tapered transition as shown or a
box type shroud) converges rearwardly through a circular -
section 38 and connects to a cylindrical intermediate ~-
section 46 which extends axially for a dis~ance CF.
The critical feature of a Coanda effect producing
shroud is its ability to form a bubble, vortex, or a region
of low pressure adjacent the surface parallel to ~hich it
is desired to bend the air stream. Fan means 29 includes _ -
a plurality of fan blade means 40 (only one as shown here)
as is well known in the art. The fan blade means 40 can be
divided into the end or tip region 42, the hub region 44 and
a middle region 43. At this time,it is believed that with ;,
a standard venturi type shroud and fan arrangements substantial ~1 ~
turbulence is created in the tip region 42 such that noise -
pollution is created and the air moving ability of that
region is substantially impaired. In the hub regions ;
difficulties with the drawing in of air from the rear with
subsequent recirculation substantially impairs the air
moving abilities of that region. As a result only the middle
region of the fan is performing an efficient air moving job.
It is believed at this time for reasons unknown that the
provision of a Coanda generating fan shroud exit generally
surrounding the fan blade somehow reduces turbulence and
improves the overall air moving efficiency of the blade.
The improved efficiency, thaL is, the lower
horsepower requirement to achieve a given cooling rate and
- 7
.
~5s34~
the reduced noise generated in the ti~ recJions result from
the employment of the Coanda gerleratin~ fc~n shroud exit. It
is known from experimentation with a hic7h s~eed ~ir jet
issuing from a nozzle adjacent a Coanda e~fect producing
surface that up to twenty times the volume of air in the jet
will be entrained thereby, from the ambient air mass that is
on the side of the jet opposite the surface. It may be that r
this entrainment phenomenon is helpin~ to pull additional
air through the fan blade. As air passes through the blade
it is immediately entraincd by -the strcam adjacent the
Coanda effect producing shroud exit. ;~
It has been determined by experimentation that a
vortex forms a region of low pressure which can be created
when a high speed air jet is directed over a properly designed
curved surface. See for example my Canadian application
Serial Number 184,880. It has also been determined that the
low pressure regions can be created by a step or groove in
the adjacent surface toward which the airstream is bent. In .
an article entitled "Applications of the Coanda Effect" by
Imants Reba, Scientific American, June 1966, the provision
of steps near the jet exit to generate the Coanda effect is
demonstrated. It should also be noted that the author
admits that the Coanda effect is not fully understood and
the simple provision of a step will probably not suffice to ?: :
create a Coanda efect. In Figures 2, 3, and 4,it is
believed that the annular ste~ or groove means 50 which is
provided in the shroud 32 produces the vortices shown
by air stream arrows. It must also be understood that l ~
the position of the fan blade assembly with regard to the ;~ -
intermediate and air discharge sections 46, 48 of the fan
shroud 32 contributes the formation of the Coanda effect.
The embodiments as shown in Figures 2, 3, and 4
- 8 -
1 !:
., ` . . :. ,: . . ,
~0553~4
combine smooth curved surfaces and indentations to achieve
the Coanda effect in combination with the fan blade. That
is, a fan shroud exit means capc~ble of producing the Coanda _~
effect will be one having a low pressure vorte~ creating
means such that when an air stream i5 passed thereover the
ambient pressure on the side of the stream away from the -
shroud stream causes it to deviate and "follow" the surface
of the shroud. Generallysituated within the shroud is the ~¦
airstream generating fan means.
With reference to Figures 1 and 2 there is shown
an air 'ntake section 34 extending rearwardly from the
rear or air exit side 36 of the radiator 16. The shroud
means 32 is a Coanda efect producing shroud exit means.
Included in the fan shroud means is a cylindrical inter-
~,
mediate section 46, which extends a distance CF that cor~
responds to one-third the axial width AW of the fan 29 when ~ ,
viewed transverse to the axis of the fan, and an air
discharge section 48 having an expanding bell shape with an l
annular lip 58 extending radially along a second plane. The
low pressure forming vortex means 50 takes the form here of
a step or an annular ring or groove 52 between the two
mentioned sections. Generally centrally located between the
two sections 46 and 48 is fan means 29. It should be noted
that throat section means 46 is substantially sealed to the
air intake section 34 and in the preferred embodiment forms '~
a complete circle around the fan means. At an axial
distance CF from the front edge of the intermdeiate section
46, an annular step means 50 forms the low pressure vortex
forming means. Carried at the periphery of the annular ring
42, which forms the groove or step 50, is the bell-like ,~
air discharge section 48. The air discharge section 48
.
11~)5534~
generally expands into a bell shape 28 in the direction in
which it is desirous of directing the exit alrstream passing
thereover. The genexating radius R of the bell portion or
the quarter-annular torus 28 corresponds to two-thirds
of the projected axial width AW of the fan 29.
For optimum results to be achieved a front or
first vertically extending plane passes or extends through
the leading edge means 54 of fan means 29 and also inter- r
sects the connection of the circular portion 38 of the air
intake section 34 and the intermediate cylindrical section
or throat means 46. Also a trailing or second vertically
extending plane or a rear parallel plane passes or extends ;
through the trailing edge 56 and forms the bo-mdary of the
rearward expansion of the annular lip 58 of the bell shaped
air discharge section means 48. The annular lip portion !
58 is located on the second vertical plane and extends
,
radially RF from a point of tangency with the smooth curved r
bell portion28 to a distance corresponding to one-third
of the projected axial width AW of the fan means 29. It
should be understood, however, that these respective rela- i,
tions can vary up to plus or minus twelve percent of the ' `
axial width or AW of the fan blade. The axial ~idth or AW ~;~
being the shortest axially extending distance between the
front and rear or first and second vertical parallel planes
when viewed transverse to the axis of the fan means 29.
The particular embodiment of the intermediate
and air discharge sections 46, 48 shown in Figure 3 again
has the leading and trailing edges 54, 56 of the fan means
29 located between the first and second vertical parallel
planes within the stated plus or minus twelve percent
ranges or tolerances. However, the leading ed~e of the
-- 10 --
~55344
expanding bell portion 28 of -the air discharge section 48 ~ '~
ls now secured directly to the trailing edge of the
cylindrical intermediate section 46 at an axial distance
CF from the first vertical plane while the low pressure
vortex creating means or annular ring 50 is connected the
annular lip 58 and extends axially inwardly towards the
radiator 16 and terminates in a radially extending annular
flange 60. ~s shown the low pressure vortex creating
means 50 is again in the form of a step. ~he particular
embodiment shown in ~igure 4, the low pressure vorte~
creating means 50 takes the form of a bend located in the
curve of the bell portion 28 of the air discharge section.
As previously stated applicant does not believe a unique
design necessary to produce the low pressure vortex. In
regard to the location of the low pressure vorte~ creating
means or the numbers th~reof, applicant believes this will
or may vary from one particular design to another. However,
the exit shroud means must be designed and provided with
sufficient low pressure vortex means, a curve surface ~o `-
direct the alr stream in the desired direction and a fan
generally located thereln.
Thus it is apparent that there has been provided,
in accordance with the invention, a heat transfer system
that fully satisfies the objects, aims, and advantages set
forth above. While the invention has been described in
conjunction with~specific embodiments thereof, it is evident
that many alternatives, modifications and variations will be
apparent to those skilled in the art in light of the
foregoing description. ~ccordingly, it is intended to embrace
all such alternatives, modifications and variations as fall
within the spirit and broad scope of the appended claims.
,1 .
, . _ , . .
