Note: Descriptions are shown in the official language in which they were submitted.
This application i~a4~1el~sSon of Canadian Serial
No. 213,118, filed November 6, 1974.
RECIRCULATION BARRIER FOR A HEAT TRANSFER SYSTEM
SPECIFIC~,TION
This invention relates to a cooling assembly and more
; particularly to a fan shroud, a contoured fan shroud exit
section and a fan loca-ted therein which has an air obs-truction
barrier therebehind. Reference should be made -to my copending
Canadian applications Serial Numbers 184,3~0 and 184,381,
both filed November 2, 1973.
Most vehicles in general used today are driven by
internal combustion engines. These engines being heat produc-
ing are for the most part water cooled, that is, the engine is
jacketed for circulation of water which takes up the heat
and subsequently transfers it to the atmosphere. The radiator
is used for cooling the liquid circulating through the engine
by dissipating the heat to an air stream. The air flowing
through the radiator absorbs the heat and carries it out into
the atmosphere. Different types of fan systems are used to
achieve the necessary air velocity through the radiator.
That is, some fan assemblies draw air from the atmosphere
through the radiator and back over the engine thereafter
exiting to the atmosphere. This type of fan is known as an
axial flow suction fan, drawing air axially through the radi-
ator and discharging it into the engine compartment. Other
fans work in the reversed manner, that is, they draw air from
the engine compartment wherefrom it is blown forwardly through
the radiator to achieve the necessary radiator cooling.
Under optimum conditions it is believed prior art fans
norMally employ only about 1/3 of the length of the fan blade
for the movement of air through the heat exchanger. The outer
1/3 of the blade length or tip regions, pulls in air from
behind the shroud and recirculates it. The inner 1/3 or, hub
region, pulls in air from the rear which it thereafter dis-
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charges rearwardly. As a result of these conditions only
about the middle 1/3 of the fan blade is effective in moving
a cooling stream of air past the heat exchanger.
It has been shown, see copending Canadian application
Serial Number 184,880, that a contoured shroud exit reduces
horsepower requirements and generated noise and hampers the
recirculation of air in the tip regions of the fan blade
because of the radial air discharge pattern generated thereby.
Employment of Ihe contoured shroud exit thus increases the
amount of the fan blade which is effective for moving air
past the heat exchanger means.
It is therefore an object of this invention to provide
an air barrier means to prevent the drawing in and recirculat-
ion of air from behind the fan blade. Still another object
of this invention is to provide an air barrier means which
does not interere with the flow of air in the tip regions of
the fan blade. ~et another object of this invention is to
provide an air barrier means which functions as a safety
guard. Another object of this invention is to provide a
2~ cooling assembly wherein a majority of the length of fan
blade is functioning to move air each past the heat exchanger.
The invention thus contemplates a heat exchange
apparatus which comprises a heat exchange means having front
and rear faces, a shroud means including a forward section
having forwardmost edge means arranged to encircle the rear
face of the heat exchange means, and a rear exit shroud means
having forwardmost edge means joined to rearwardmost edge means
of the forward section. The exit shroud means includes, in
successive sections, a generally cylindrical, axially extending
throat section, an annular, radial curved section, and an
annular, generally radially extending flat portion- A rotatable
axial flow, suction-type fan encircled by the rear exit shroud
means has a plurality of circumferentially spaced impeller blades
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extending radially from a hub with each of the impeller blades
having an effective axial width (AW) measured axially along the
rotational axis of the fan between a first plane and a second
plane. Those planes are axially spaced and parallel with respect
to each other and disposed substantially normal to the rotational
axis of the fan with the first and second planes extending radial-
ly, respectively, through-points on the leading edges of the ;
impeller blades at the radial tip regions thereof and through
points on the trailing edges of the impeller blades at the radial r
lO- tip portions thereof. The second plane is substantially coincid-
ent with the plane containing the annular, generally radially
extending flat portion of the exit shroud means, and the following
relationships exist: RF = AW/3 plus or minus 12 percent of AW,
CF = AW/3 plus or minus 12 percent of AW, and R = 2AW/3 plus or
minus 12 percent of AW, and R = 2AW/3 plus or minus 12 percent of
AW where RF is the radial length of the radially extending flat
portion, CF is the axial length of the cylindrical throat section,
and R is the radius of curvature of the radial curved section.
An air recirculation barrier means is axially spaced rearwardly
of the second plane a predetermined distance less than one half
of the diameter of the fan for obstructing axial flow of air in
a forward direction from the region axially rearwardly of the fan
hub when the fan is rotated.
In accordance with the preferred embodiment of this inven-
tion a vehicle is provided having a liquid cooled internal com- ,~
bustion engine and a radiator cooling system for dissipating the
heat produced. The radiator cooling system includes a standard r
radiator, an axial flow fan facing the radiator and having a
plurality of angular blades whereby air is drawn rearwardly
through the radiator. A shroud rearwardly extends from the back
face of the radiator to channel air through the radiator and
hamper the fan from drawing air which has not passed through or
at least come in contact with the perforated heat exchanging
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surfaces of the radiator. For the most part the shroud encloses
the entire perforated heat exchanging rear area of the radiator.
A fan shroud exit means is also provided having secured to the
backwardly extending portion of the fan shroud and extending
rearwardly thereof as well as outwardly. The particular contour
of this exit section in combination with an axial flow fan
located therein, allows the air stream to be converged and directed
generally radially away from the engine compartment. Situated
behind the fan is an air barrier means which in combination with
the shroud exit section forces the fan to draw air through the
radiator. As is apparent this invention is also applicable to
a stationary engine where it is desired to achieve a high degree
of performance from the fan blades.
Other objects and advantages of the invention will become
apparent upon reading the following detailed description and
upon reference to the drawings, in which;
FIGURE 1 is a side elevation of an internal combustion
engine showing the combination of my invention with a contoured
shroud exit section attached to a vehicle;
FIGURE 2 is a fragmentary vertical section showing the
relationship of the fan, the contoured exit section, and the
air flow pattern without an air barrier; and
FIGURE 3 is a fragmentary vertical section showing the
air flow pattern with an air barrier.
While the invention will be described in connection with
a preferred embodiment, it will be understood that it is not
intended to limit the invention to that embodiment- On the
contrary, it is intended to cover all alternatives, modifications
and equivalents as may be included within the spirit and scope
of this invention as defined by the appended claims.
Turning first to Figure 1 there is shown a conventional water
cooled heat producing internal combustion engine means 10 forwardly
carried on longitudinally extend:ing parallel support means 12
of vehicle means 14.
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As shown herein vehicle means 14 is a tractor, however,
as will hereafter become more apparent th;s invention
can be applied to any type of vehicle employing a heat
generating internal combustion engine or any other portable
or stationary device requiring an air moving fan. For-
wardly mounted is a water cooling radiator means 16
employed to dissipate the engine generated heat. Water
flows between the water jacket on the engine (not shown)
and the radiator through a series of fluid communicating
means 18 and 20. In this particular embodiment sheet
metal means 22 encircles engine means 10 thereby forming
the engine compartment area means 24.
Carried at the forward end of engine means 10
is a fan shaft means 26 whereby power is delivered to
drive fan means 28 (Figure 2). As is apparent, the
particular mode whereby power is transmitted thereto
is not critical and belts and pulleys could also be
employed. As employed here, fan means 28 is a rotatable
suction fan positioned opposite the radiator means 16,
and normally creating a flow of air or drawing in a
stream of cooling air rearwardly through the radiator
with a subsequent axial discharge thereof. This axial
flow of air is directed to the fan means by a shroud
~ means 30. The particular shape of the forward section
32 is dependent upon the shape and design of the perforated
heat exchanging design of the radiator. The nature of
the connection between the leading edge of 32 and the
rear face 3~ of the radiator will be dependent upon the
particular characteristics of these components, that is,
some connections being provided with air gaps while others
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are substantially sealed over the entire circumference
of the enclosure. In the preferred form of this inven- -
tion the entire perforated area is substantially sealed
against the passage of air from any other direction
except through the radiator. From the forward edges the
shroud means 30 (be it a taper transition as shown or a
box type~ converges rearwardly to a circular rear section
36. An air barrier means 31 is positioned rearwardly
of the shroud exit section 38 as will be more fully
hereafter discussed.
Referring now to Figure 2 wherein is more
clearly shown a shroud exit means 38 extending rearwardly
and outwardly from shroud edge 36. The connection between
the shroud and the shroud exit can be achieved by any
suitable means, however, it is desirable that such con-
nection be relatively free of gaps or spaces which would
allow the passage of air. Exit shroud means 38 includes
a tubular means 40, an arcuated means portion 42 and a
flat flange portion means 44. For the most part tubular
means portion 40 forms the leading edge of the shroud
exit means while arcuated means portion 42 still extend-
ing generally rearwardly simultaneously extends outwardly
around an arc the reference point of which is defined
- as point 46. That is, arcuated section 42 has a general
bell-shaped appearance being a section of a transition
surface or some approximation thereof. In the preferred
embodiment arcuated section 42 is a section of a constant
radius arch. Flat flange portion 44 forms the trailing
edge of exit shroud means 38 and has a major plane per-
pendicular to that of tubular section 40. For purposes
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of simplicity, tubular means 40 will be hereafter referred to as
the cylindrical throat means, arcuated portion 42 will be referred
to as the radial expanding means and flat flange portion 44 will
be referred to as radial flat means. Overall the entire fan shroud
exit means 38 has a horn-like configuration.
The fan means 28 is rotatingly carried adjacent said radiator
means and operable to establish a flow of cooling air therethrough.
Fan means 28 includes a plurality of fan blade means 48 (only
one shown) as is well known in the art. As shown in Figure 2
fan means 28 is surrounded by said contoured fan shroud exit
section 38. The enclosure of the fan means 28 within shroud
means 30 is such that a front plane struck out by the leading
edge 50 is coextensive and passes through the leading section of
throat means 40 and a rear plane struck out by trailing edge
52 is about coextensive and parallel with said radial flat portion
44. It should be noted, however, that there is a plus or minus
error factor involved in both of these values of about 12 percent
oE AW. That is, the respective planes formed by the blade means
can be within about 12 percent of optimum and still function
satisactorily within the scope of this invention. Thus, within
this range the deflected air stream will still be substan-tially
radial. And generally about the outer two/thirds of the blade
means is efficiently moving air through the radiator means.
While a beneficial effect is achieved by spacing the fan blades
48 with respect to the contoured shroud means 38 within the
- aforementioned range, it has been determined that best results are
obtained when the front or first vertical plane struck out by the
leading edges 50 of the fan blades 48 pass through the juncture
or merger between the entrance shroud means 32 and the cylindrical
3n exit shroud section 40. Even more determinative on the result is
the relationship between the so-called rear plane struck out by the
trailing edges 52 of the fan blades 48 and the radial flat flange
shroud portion 44. Best overall performance is achieved when
the rear or second vertical plane and the radial flat flange
shroud portion or section 44 lie in the same plane.
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The fol.lowing rela-tionship exists between these
parameters: RF = AW/3, CF = AW/3, and R = 2A~/3 where
RF is the length of the radial flat portion 44, CF is
the length of the cylindrical throat section 40 and
R is a radius of the radial expanding section 42 or
distance from the reference point to the transition
surface and AW is the projected axial width of fan 28.
The amount or relation of the fan means 28 -to
the exit section means 38 is most conveniently expressed
in terms of the amount of the fan which is exposed past
the end of the shroud or projects rearwardly thereof
(XE). It has been found that XE equal to zero gives
optimum resul-ts; however, reasonable resul-ts can be
achieved by having XE about equal to plus or minus 12
percent of AW. That is, as explained previously when
the plane swept out by the rear edge is coextensive with
the surface of the radial flat or within -the tolerance
set forth. By changing the orientation of the fan with
respect to the fan exit section it is also possible to
direct the air stream, straight back, at an angle off
radial, etc., depending on preference and need.
Considering the air flow patterns shown in
E`igure 2 it is necessary to cut off the air flow, figura-
tively shown as number 51, without the interruption of the
generally radially flow pattern shown as number 53. As
was previously stated the drawing of air in the hub
region has a substantial detrimental effect on the eficiency of
the fan. However, if a barrier is employed it should
be positioned to cut off hub recirculation and not
disrupt the flow pattern in the tip regions.
Referring to Figure 1 and 3, an air recirculation
barrier means 31 is shown positioned behind the fan blade
means 28. As shown in Figure 1 barrier means 31 is in
the form of a flat disk which
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has an overall diameter abou-t equal to that of the periphery
of flange 44 of the shroud exit section 38. The barrier means
is secured to frame means 12 by any suitable mode with a
properly located opening for the fan drive shaft means 26.
It should be noted, however, barrier means or disk 31 could be
mounted to the drive shaft 26 or in fact front portion means
37 of engine means 10 could be positioned and modified to
perform the necessary function of preventing the recirculation
of air in the hub region.
It has been determined that optimum performance
of the cooling assembly so described can be achieved when
barrier means 31 is positioned on a third vertical plane rear-
wardly of the second plane containing the trailing edge means
52 of fan means 28, a distance corresponding to about 15
percent of the diameter of the circle generated by the tips
of the fan means 28, which is an axial distance less than
one-half of the diameter of the generated circle. The diameter
of the barrier need only be substantially equal to that of
the periphery of flange 44 in order to prevent the drawing in
of air from the rearward areas into the hub portion.
The location of such a barrier means on a third plane
which is generally opposite and parallel with the second plane
containing the trailing edge of fan means 28 has been found
to effectively retard hub recirculation without detrimentally
effecting air flow patterns in the tip regions. This result
is shown in Figure 3 by the air flow pattern as characterized
by the number 39.
The barrier means 31 also serves as a safety guard
for preventing accidental entry of hands etc. into the area
adjacent fan means 28.
Thus it is apparent that there has been provided
in accordance with the invention a shroud exit means that
fully satisfies the objects, aims, and advantages set
forth above. While the invention has been described in
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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 fore~oin~ description. ~ccordingly, it
is int~nded to emhrace all such alternatives, modifica-
tions, and variations as fall within the spirit and
broad scope of the appended claims.
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