Note: Descriptions are shown in the official language in which they were submitted.
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HEAT EXCHANGER
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001]
This application claims priority to U.S. Serial No. 13/536,287,
filed June 28, 2012, which is a Continuation in Part of U.S. Serial No.
12/874,334, filed September 2, 2010.
The disclosures of these
applications are incorporated by reference as if fully set forth here.
TECHNICAL FIELD
[0002] The present
teachings generally relate to heat exchangers.
More particularly, the present teachings relate to cooling systems for
internal combustion engines.
INTRODUCTION
[0003] This section
provides background information related to the
present disclosure which is not necessarily prior art.
[0004]
Various heat exchangers are used in modern vehicles to
transfer thermal energy from one medium to another for the purpose of
cooling or heating. In
this regard, it is necessary to cool various
components of a motor vehicle to avoid overheating. As one example, a
heat exchanger takes the form of a cooling radiator for an internal
combustion engine.
[0005] A
conventional radiator cools an internal combustion engine by
passing a coolant through the engine block where it is heated. The
coolant is fed into an inlet tank of the radiator which distributes the
coolant
through radiator tubes to an outlet tank. An airflow pulled by a cooling
fan circulates across the radiator using the air to extract heat from the
radiator and transfer it to the atmosphere. The colder coolant is fed back
to the engine and the cycle repeats. The coolant is usually water-based,
with addition of glycol to prevent freezing and other additives to limit
corrosion.
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[0006] As
the coolant circulates through the tubes, it transfers its heat
to the tubes. In turn, the tubes transfer part of the heat to fins that are
positioned between each row of tubes. The purpose of the fins is to
increase the total heat transfer area because the tubes generally do not
provide enough cooling area. Both the tubes and the fins release heat to
the ambient air. The heat released by the tubes is referred to as primary
heat transfer, while the heat released by the fins is referred to as
secondary heat transfer. Primary heat transfer is generally more efficient
than secondary heat transfer because the heat has to travel only from the
coolant to the tube and then to the air, which is a short path. The
secondary heat transfer is generally less efficient because the heat has to
travel from the coolant to the tube, then from the tube to the fin (across an
imperfect brazed joint) and then from the fin to the air, which is a much
longer and restrictive path. Still, it is necessary to supplement the tubes
with the less efficient fins because the tubes do not provide enough heat
exchange area.
[0007]
Because air has a lower heat capacity and density than liquid
coolants, a fairly large volume flow rate must pass through the radiator
core to sufficiently extract heat from the coolant. Radiators have one or
more fans that draw air through the radiator. To save fan power
consumption in vehicles, radiators are often behind the grille at the front
end of a vehicle. Ram air provides a portion of the necessary cooling air
flow.
[0008]
Because of dramatically increased fuel efficiency standards in
Europe, in the United States and most of the world (almost double the fuel
mileage is being targeted), much tougher emission regulations and higher
heat transfer needs due to smaller, higher speed engines with higher
compression and increased use of exhaust gas recirculation, a need for
substantial improvement exists in the automobile industry for heat
exchangers that can provide higher heat transfer, lower weight, smaller
area and ability to absorb a substantially higher heat load.
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SUMMARY
[0009]
This section provides a general summary of the disclosure, and
is not a comprehensive disclosure of its full scope or all of its features.
[0010] In
accordance with one particular aspect, the present teachings
provide a heat exchanger including an inlet tank, an outlet tank, and a
core. The core is positioned between the inlet tank and the outlet tank.
The core includes a plurality of tubes, a set of cooling fins and a plurality
of channels formed between the tubes and the fins. Each tube of the
plurality of tubes provides fluid communication between the inlet tank and
the outlet tank. The set of cooling fins are located between the heat
exchange tubes of the plurality of tubes to increase a heat exchange area.
The plurality of channels is defined by the plurality of tubes and the set of
cooling fins. In a conventional radiator, the airflow crosses the radiator
core in a straight line pattern. In accordance with the present teachings,
the channels of the plurality of channels are operative for directing a flow
of air through the core such that a flow of air enters a front face of the
core in a first direction and exits the core in a different direction. The
change of direction causes air turbulence and direct impingement of the
air upon the core, resulting in a substantially higher heat transfer
efficiency. In certain preferred embodiments, the change of direction is
achieved by tubes made with a non-straight shape, in some cases shaped
like a V, or like a curve, or other non-straight shapes. One of the key
advantages of this approach is that it relies largely on primary heat
exchange rather than secondary heat exchange to increase heat transfer
efficiency.
[0011] In
accordance with another particular aspect, the present
teachings provide a heat exchanger with a core having a first group of air
channels and a second group of air channels. The first group of air
channels is disposed on a first side of an imaginary plane. The second
group of air channels is disposed on a second side of the imaginary
plane. The first and second groups of air channels both converge toward
the imaginary plane as the air channels extend from a front side of the
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heat exchanger to a rear side of the heat exchanger. This convergence
can be used to focus and orient the air exiting the radiator in the direction
of the cooling fan, thus increasing fan efficiency and reducing power
consumption.
[0012] In
accordance with another particular aspect, the present
teachings provide a radiator for a motor vehicle. The radiator includes
first and second header tanks, a plurality of tubes and a plurality of fins.
The plurality of tubes extends between the first and second header tanks
and fluidly connects the first and second header tanks for transferring a
medium to be cooled there between. The plurality of fins defines multiple
groups of air channels that bias the airflow in different directions for
redirecting the airflow in a plurality of predetermined directions. These
predetermined directions may include left, right, up and down, and/or
others in order to orient the airflow in a desired direction, such as toward
the cooling fan, or toward the air exit of the under the hood engine
compartment.
[0013] In
accordance with yet another particular aspect, the present
teachings provide a method of manufacturing a fin for a heat exchanger.
The method includes providing a metal strip, such as aluminum fin stock,
having a width and a length, and stamping the strip to define at least one
hinge axis extending parallel to the length of the metal strip. The method
additionally includes pleating the metal strip to create a plurality of fold
lines perpendicular to the length of the metal strip. The method further
includes bending a first portion of the metal strip relative to a second
portion of the metal strip about a first hinge axis of the at least one hinge
axis.
[0014]
According to still yet another aspect, the present teachings
provide a method of improving the flow of air through a radiator. The
radiator has a plurality of channels defined by a plurality of tubes and a
plurality of fins. The radiator assembly includes a shroud for directing the
air toward a fan assembly, the method comprising:
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[0015]
generally directing a first flow of the air toward the first plane
with a first group of channels, the first plane intersecting a fan drive of
the
fan assembly;
[0016]
generally directing a second flow of the air toward the first plane
with a second group of channels, the channels of the first group
converging relative to the channels of the second group as the channels
of the first and second groups extend from a front side of the radiator to a
rear side of the radiator; and
[0017]
creating turbulence proximate the fan drive with the first and
second groups of generally directed air to thereby break away a boundary
layer of air molecules adjacent to the fan drive. The boundary layer may
be a stationary or low-speed boundary layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The drawings
described herein are for illustrative purposes only
of selected embodiments and not all possible implementations, and are
not intended to limit the scope of the present disclosure.
[0019]
Figure 1 is a front view of a heat exchanger constructed in
accordance with the present teachings.
[0020] Figure 2 is
a simplified top view of the heat exchanger of
Figure 1, the heat exchanger shown operatively associated with an
engine/transmission of a motor vehicle.
[0021]
Figure 3 is a side view of a portion of the core of the heat
exchanger of Figure 1.
[0022] Figure 4 is a front view of the portion of the core of Figure 3.
[0023]
Figure 5 is a simplified front view of another heat exchanger
constructed in accordance with the present teachings.
[0024]
Figure 6 is a simplified top view of the heat exchanger of
Figure 5, the heat exchanger shown operatively associated with an
engine/transmission of a motor vehicle.
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[0025]
Figure 7 is a simplified side view of the heat exchanger of
Figure 5, the heat exchanger again shown operatively associated with an
engine/transmission of a motor vehicle.
[0026]
Figure 8 is a simplified front view of another heat exchanger
constructed in accordance with the present teachings.
[0027]
Figure 9 is a simplified side view of the heat exchanger of
Figure 8, the heat exchanger shown operatively associated with an
engine/transmission of a motor vehicle.
[0028]
Figure 10 is a side view of the metal strip of Figure 1 before
shaping to conform with tubes.
[0029]
Figure 11 is a side view similar to Figure 10, illustrating the fin
after shaping to conform with the tubes.
[0030]
Figure 12 is a side view of another tube in accordance with the
present teachings.
[0031] Figure 13
illustrates the general steps of a method of
manufacturing a fin in accordance with the present teachings.
[0032]
Figure 14 is a top view of a metal strip for making a fin in
accordance with the method of the present teachings.
[0033]
Figure 15 is a top view of the metal strip of Figure 14 after
stamping.
[0034]
Figure 16 is a simplified prior art view illustrating airflow through
a typical heat exchanger.
[0035]
Figure 17 is a simplified view illustrating airflow through a heat
exchanger constructed in accordance with the present teachings to
include angled tubes.
[0036]
Figure 18 is a simplified view similar to Figure 17 illustrating a
"cloud" of air molecules that may form on a front side of the heat
exchanger.
[0037]
Figure 19 is another simplified view illustrating airflow through a
heat exchanger constructed in accordance with the present teachings to
include angled tubes.
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[0038]
Figure 20 is another simplified view illustrating airflow through a
heat exchanger constructed in accordance with the present teachings to
include angled tubes. In the embodiment illustrated, the angling of the
tubes is achieved through a gradual curve shape.
[0039] Figure 21
is a simplified front view of another heat exchanger in
accordance with the present teachings.
[0040]
Figure 22 is a simplified top view of the heat exchanger of
Figure 21.
[0041]
Figure 23 is a simplified front view of another heat exchanger in
accordance with the present teachings.
[0042]
Figure 24 is a simplified top view of the heat exchanger of
Figure 23.
[0043]
Figure 25 is a simplified front view of yet another heat
exchanger in accordance with the present teachings.
[0044] Figure 26 is
a simplified top view of the heat exchanger of
Figure 25.
[0045]
Figure 27 is a front view of still yet another heat exchanger in
accordance with the present teachings.
DETAILED DESCRIPTION OF VARIOUS ASPECTS
[0046]
With initial reference to Figures 1 and 2, a heat exchanger
constructed in accordance with the present teachings is illustrated at
generally identified at reference character 10. In
the embodiment
illustrated, the heat exchanger 10 is illustrated as a radiator for a motor
vehicle. In Figures 2 and 3, the heat exchanger 10 is shown operatively
associated with an engine/transmission 12 of a motor vehicle. It will be
understood that the present teachings are not limited to the exemplary
embodiment(s) shown in the drawings and described herein. In this
regard, the present teachings may be adapted for the cooling of various
media within a motor vehicle. In addition, the present teachings may also
be readily adapted for non-automotive applications. The heat exchanger
may be selected from a including but not limited to a radiator, a
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condenser, an evaporator, an engine oil cooler, and a transmission oil
cooler.
[0047]
Before addressing details of the construction and operation of
the heat exchanger 10 of the present invention, an understanding of the
exemplary use environment shown in the drawings is warranted. It will be
understood that details of the exemplary use environment not specifically
described herein are conventional in both construction and operation.
Figure 2 uses an engine-mounted cooling fan configuration as an
example. This configuration is typically used for trucks. An alternative
configuration would be a radiator-mounted electric fan assembly, which is
typically used in passenger cars. It will be understood that the present
teachings apply to both of these possible configurations.
[0048] A
shroud 14 is positioned between the heat exchanger 10 and
the engine/transmission 12. The shroud 14 functions to collect and direct
air passing through the heat exchanger 10 toward a fan assembly 18.
The shroud 14 conventionally tapers from a front side to a rear side.
[0049]
The fan assembly 18 operates to draw air through the heat
exchanger 10. The fan assembly includes a fan drive 20 driven by a shaft
22 extending from the engine 12. The fan drive 20 holds and drives the
fan24. Conventionally, a significant amount of heat is generated at the
fan drive 20. Also conventionally, air molecules are impinged against the
fan drive 20 and the root of the fan blade hub. This impingement creates
a boundary layer of stagnant air that may impede or constrain the flow of
air 16 through the heat exchanger 10.
[0050] With
continued reference to Figures 1 through 4 of the
drawings, the heat exchanger 10 of the present teachings will be further
detailed. The heat exchanger 10 is illustrated to generally include first and
second tanks 26 and 28 and a core 29. The core 29 includes a plurality of
tubes 30 and a plurality of fins 32. The first tank 26 receives a medium to
be cooled from the engine/transmission 12 in the direction of arrow A.
The medium may be coolant. The medium to be cooled enters the first
tank 26 through an input port 34. The second tank 28 defines an output
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port 36 through which cooled medium is directed to the
engine/transmission 12 in the direction of arrow B.
[0051]
The plurality of tubes 30 extends between the first and second
tanks 26 and 28. The tubes 30 fluidly connect the first and second tanks
26 and 28 for transferring the medium to be cooled there between. In the
embodiment illustrated, the tubes 30 are oriented horizontally between the
vertically oriented header tanks 26 and 28. The tubes are in direct
contact with the coolant and therefore serve as the primary structure for
removing heat from the coolant.
[0052] A fin 32 is
located between each adjacent pair of tubes 30. As
such, the fins 32 each extend in a generally horizontal direction. Each fin
32 cooperates with the adjacent tubes 30 to define a plurality of channels
for directing the flow of air 16 through the heat exchanger 10. The fins 32
are indirectly in contact with the coolant and define secondary structure
for removing heat from the coolant.
[0053] As
will become apparent herein, the fins 32 and tubes 30
cooperate to generally direct the air 16 through the heat exchanger 10
such that a flow of air enters a front face of the core 29 in a first
direction
(i.e., in the direction indicated by the arrow associated with reference
character 16) and is biased in at least a second direction. In the
embodiment illustrated, the airflow may be generally directed toward an
imaginary plane 40. The plane 40 may be parallel to the direction 16. In
the embodiment illustrated, the plane 40 toward which the air 16 is
generally directed is horizontally oriented and intersects the fan drive 20.
Alternatively and as will be addressed further below, the plane 40 toward
which the air 16 is directed may be horizontally oriented.
[0054] As
shown in the front view of Figure 1, the plane 40 generally
bisects a core of the heat exchanger 10 in a horizontal direction. A first
group of channels 42 defined by the plurality of fins 32 and plurality of
tubes 30 are disposed on a first side of the plane 40 (i.e., above the plane
as illustrated in Figure 1). A second group of channels 44 defined by
the plurality of fins 32 and the plurality of tubes 30 are disposed on a
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second, opposite side of the plane 40 (i.e., below the plane 40 as
illustrated in Figure 1).
[0055] With reference
to the simplified side view of Figure 2, the first
and second groups of air channels 42 and 44 both generally converge
toward the first imaginary plane 40 as the air channels 42 and 44 extend
from a front side 46 of the heat exchanger 10 to a rear side 48 of the heat
exchanger 10. As will become apparent, in the embodiment illustrated the
geometry of the tubes 30 serves to generally converge the flow of air
toward the plane 40. In other embodiments (some of which are described
below), the configuration of the fins may generally converge the flow of air
toward a plane.
[0056] As illustrated
in Figure 2, the channels 42 and 44 defined by the
fins 32 and tubes 30 linearly converge toward plane 40. It will be
understood, however, that the channels 42 and 44 may non-linearly
converge in alternative embodiments. In this regard, various other fin
shapes may be used. Any fin shape suitable for generally directing the air
40 toward the plane 40 may be utilized within the scope of the present
teachings.
[0057] As perhaps best
shown in the partial side view of Figure 3, the
tubes 30 may be bent to generally converge the flow of air. As illustrated,
the tubes 30 may include two or more generally planar segments. In the
particular embodiment shown, the tubes 30 include two planar segments.
Fins 32 suitable for use with the bent tubes 30 will be further described
below.
[0058] As the motor
vehicle moves, air 16 enters the front side 46 of
the heat exchanger 10 in a direction generally perpendicular thereto. The
angled channels 42 and 44 function to increase contact between the air
16 and the tubes 30 and further function to generally direct the flow of the
air 16 toward the plane 40. By generally concentrating the air 16 toward
the plane 40 proximate the fan drive 20, turbulence is created to break
away the thermal boundary layer of air molecules adjacent the fan drive
20. As a result,
heat transfer (and thus heat dissipation) at the fan drive
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20 is greatly improved. Fan performance may be improved as turbulent
air is pulled along the roots of the radial flow fan blades.
[0059]
Turning to Figures 5-7, another heat exchanger constructed in
accordance with the present teachings is illustrated and identified at
reference character 10'. The heat exchanger 10' differs from the heat
exchanger 10 in that the flow of air 16 is generally directed toward a first
plane 40' that is vertically oriented and that the geometries of the fins 32
function to generally divert the flow of air 16. Given the similarities
between the heat exchangers 10 and 10', like reference characters will be
used to identify similar elements.
[0060] As
shown in the front view of Figure 5, the plane 40' generally
bisects the core 29 of the heat exchanger 10' in a vertical direction. A first
group of channels 42' defined by the plurality of fins 32 and plurality of
tubes 30 are disposed on a first side of the plane 40' (i.e., to the left of
the
plane 40 as illustrated in Figure 1). A second group of channels 44'
defined by the plurality of fins 32 and the plurality of tubes 30 are
disposed on a second, opposite side of the plane 40' (i.e., to the right as
illustrated in Figure 1).
[0061]
With reference to the simplified top view of Figure 6, the first
and second groups of air channels 42' and 44' both converge toward the
first imaginary plane 40' as the air channels 42 and 44 extend from the
front side 46 of the heat exchanger 10 to the rear side 48 of the heat
exchanger 10. In the embodiment illustrated, the channels 42 and 44
defined by the fins 32 are oriented at common angles relative to the plane
40'. In alternative embodiments, the angles of the channels 42 and 44
may vary. In this regard, the angles of the channels 42 and 44 relative to
the plane 40' may be greater (e.g., more aggressive) as the lateral
distance from the plane 40' increases for purposes of concentrating the
flow of air 16 toward the plane 40'.
[0062] As
illustrated in Figure 6, the channels 42 and 44 defined by the
fins 32 and tubes 30 linearly converge toward plane 40'. As above, it will
again be understood that the channels 42 and 44 may non-linearly
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converge in alternative embodiments.
Any fin shape suitable for
generally directing the air 40' toward the plane 40' may be utilized within
the scope of the present teachings.
[0063] As
the motor vehicle moves, air 16 enters the front side 46 of
the heat exchanger 10 in a direction generally perpendicular thereto. The
angled channels 42 and 44 function to increase contact between the fins
32 and further function to generally direct the flow of the air 16 toward the
plane 40'. By generally concentrating the air 16 toward the plane 40
proximate the fan drive 20, turbulence is created to break away the
thermal boundary layer of air molecules adjacent the fan drive 20.
[0064]
Turning now to Figures 8 and 9, another heat exchanger in
accordance with the present teaching is illustrated and generally identified
at reference character 100. The heat exchanger 100 differs from the heat
exchanger 10 in that the air 16 is generally directed to a point rather than
a plane. Given the similarities between the heat exchanger 10 and the
heat exchanger 100, like reference characters will be used throughout the
views to identify similar elements.
[0065] It
will be understood that to the extent not described herein,
details of the heat exchanger 100 are similar to corresponding details of
the heat exchanger 10. For example, the simplified view of Figure 6
equally applies to the heat exchanger 100.
[0066] As
shown in the front view of Figure 8, the channels defined by
the fins 32 and tubes 30 may be divided into four distinct groups of
channels 102, 104, 106 and 108. These groups of channels 102-108 may
be divided by a first imaginary plane 40 and a second imaginary plane
110.
[0067] As
shown in the front view of Figure 4, the first plane 40
generally bisects the core of the heat exchanger 100 in a horizontal
direction. The second plane 110 generally bisects the core of the heat
exchanger 100 in a vertical direction. A first group of channels 102 is
disposed on a first side of the first plane 40 (i.e., to the left of plane 40
in
Figure 4) and on a first side of the second plane 102 (i.e., above the plane
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110 in Figure 4). A second group of channels 104 is disposed on a
second, opposite side of the first plane 40 (i.e., to the right of plane 40 in
Figure 4) and on the first side of the second plane 102. A third group of
channels 106 is disposed on a first side of the first plane 40 and on a
second side of the second plane 102 (i.e., below the plane 110 in Figure
4). A fourth group of channels 108 is disposed on the second side of the
first plane 40 (i.e., to the right of plane 40 in Figure 4) and on the second
side of the second plane 102.
[0068]
Similar to that shown in the top view of Figure 6 for the heat
exchanger 10', the first, second, third, and fourth groups of channels 102-
108 all converge toward the plane 40 as the channels extend from the
front side 46 of the heat exchanger 100 to the rear side 48 of the heat
exchanger 100.
[0069]
With reference to the simplified side view of Figure 9, the
second and fourth groups of channels 104 and 108 may generally
converge toward the plane 110 as the channels extend from the front side
46 to the rear side 48 of the heat exchanger 100. It will be understood that
the opposite side to that shown in Figure 5 is a mirror image thereof. In
this regard, the channels of the first and third groups of channels 102 and
106 similarly, generally converge toward the plane 110 as the channels
extend from the front side 46 to the rear side 48. Otherwise stated, the
channels 102-108 all converge toward the plane 110 as the channels
extend from the front side 46 to the rear side 48 of the heat exchanger
100.
[0070] As the motor
vehicle moves, air 16 enters the front side 46 of
the heat exchanger 110. The channels function to generally converge the
flow of air 16 both toward the plane 40 and toward the plane 110. As a
result, the flow of air 16 is generally directed to (or converges toward) a
point. This point may be proximate the fan drive 20 for purposes of
breaking away the thermal boundary layer of air molecules adjacent to fan
drive, as discussed above with respect to the heat exchanger 10'.
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[0071]
Reference will now be made to Figures 9 and 10. Where the
tubes 30 are bent as discussed above with respect to the heat exchanger
10, it will be necessary to correspondingly shape the fins 32 between
adjacent tubes 30 for secondary cooling. A side view of one suitable fin 32
is shown in Figure 9 prior to bending. Figure 10 illustrates this fin 32 after
bending.
[0072] In
certain applications, it may be desirable to provide the tubes
30 of the heat exchanger 10 with a more complex shape. For example,
the tubes may define a lead-in having a segment that is generally parallel
with the flow of air into the front of the heat exchanger 10.
[0073]
With reference to Figure 12, another side view of a fin 210 in
accordance with the present teachings is illustrated. This fin 210 may be
used with such an alternative arrangement in which the tubes define a
lead-in. The fin 210 differs from the fin 32 discussed above in that the fin
210 includes three generally planar segments. A method of manufacturing
the fin 210 in accordance with the present teachings will be described
below with reference to Figure 13.
[0074] In
accordance with a first general step 212, a metal strip 214 is
provided having a length I and a width w. The metal strip is illustrated in
Figure 9.
[0075] In
accordance with a second general step 215, the metal strip
214 is stamped or otherwise suitably formed to define at least one hinge
axis extending parallel to the length I of the metal strip 214. In the
embodiment illustrated, the metal strip 214 is stamped to include first and
second hinge axes. In this regard, the metal strip 214 is stamped to
include a row of diamond shaped openings and a row of slots. The
second hinge axis extends through the centers of the diamond shaped
openings and parallel to the first hinge axis.
[0076] In
accordance with a third general step 216, the stamped metal
strip 214 is pleated to define a plurality of fold lines perpendicular to the
length I of the metal strip 214. The step of pleating may be carried out in
a conventional manner with rollers.
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[0077] In
accordance with a fourth general step 218, a first portion 220
of the metal strip 214 is bent relative to a second portion 222 of the metal
strip 214 about the first hinge axis. The reduced material between
adjacent slots facilitates bending of the metal strip 214 about the first
hinge axis. In the embodiment illustrated, a third portion 224 is bent
relative to the second portion 222 about the second hinge axis. Again,
the reduced material between adjacent diamond shaped openings
facilitates bending of the metal strip 214. The openings permit downward
bending of the third portion 224 (as shown in Figure 7).
[0078] It will be
appreciated that the present teachings provide a heat
exchanger with features that can individually or in combination provide a
significant increase in heat transfer performance. Such an increase in
thermal performance can be used to design a heat exchanger with
reduced frontal area, radiator thickness, weight, and cost. Additionally or
alternatively, a smaller fan drive may be utilized and/or a smaller fan may
be used. Smaller components may provide for improved styling flexibility.
[0079]
With general reference to Figures 15-25, various simplified
views are provided to further explain aspects of the present invention.
Like reference characters will be used to refer to previously introduced
elements.
[0080]
The angled tube heat exchanger of the present teachings seeks
to enhance heat exchange by making the airflow through a heat
exchanger non-straight by shaping the tubes 30 in a way that the air paths
through the heat exchanger force the air to impinge on the heat exchange
areas of the heat exchanger (fins and tubes) as opposed to just flow
mostly parallel to these heat exchange areas.
[0081] By
forcing the air to change direction through the non-straight tube
geometry a turbulent flow can be created and a direct impingement of the
air on the heat exchange surfaces is achieved, which leads to a
significantly better heat transfer. It is important, however, to ensure that
the heat exchanger does not become too restrictive to the airflow and that
any pressure drop across the radiator is not too significant. Otherwise, a
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more powerful cooling fan to draw air through the heat exchanger may be
required. Such a more powerful fan would consume more energy, which
is contrary to the target of reducing all parasitic losses in a vehicle to
maximize a heat exchanger fuel efficiency and minimize emissions. The
present teachings provide different tube configurations that increase heat
transfer without unduly increasing pressure drop.
[0082]
Before addressing the present teachings, a comparison analysis of
a typical heat exchanger is warranted. Figure 16 shows that in a
conventional heat exchanger the air molecules 300 have a very low
probability of actually touching the tubes 30. Most of the airflow can go
relatively undisturbed between the tubes 30 and the fins 32 of the core.
This situation creates inefficient heat transfer.
[0083]
Figure 17 shows that by slanting the tubes 30 by a certain angle,
an angled airflow path is created that forces the air molecules 300 to
collide against the tubes 30 and the fins 32 of the channels, destroying
laminar flow boundaries, bouncing around and creating turbulence that
enhances heat transfer. The arrow 302 shows the direction of travel of the
vehicle.
[0084]
Figure 18 illustrates an unintended consequence: a "cloud" 304 of
air molecules forms in front of the vehicle because of air molecules being
bounced back by the movement of the vehicle when they collide against
the radiator. Not all molecules are bounced in an angle toward the inside
of the radiator. Many molecules are just thrown back out of the radiator,
creating the cloud of air molecules 304, which represents an obstacle to
the air getting into the radiator. The vehicle pushes this cloud in front of
it,
which is undesirable because it acts like a brake on the vehicle and also
makes it harder for air to enter the radiator, increasing the pressure drop
across the radiator.
[0085]
Experiments and tests have shown that the right geometry can
partially or completely overcome this obstacle. Figure 19 shows that if the
tubes 30 are designed with a straight portion in the front, the cloud 304
shown in Figure 18 may be reduced or may disappear because the air is
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allowed to enter the radiator before starting to force it to change direction.
The pressure drop and the air resistance are dramatically reduced with
this configuration. This effect is so significant that without it the angled
tube 30 approach may be of very limited practical value for a vehicle
application (it still could work well for stationary applications, but not
necessarily for mobile applications such as a vehicle radiator). Further
experiments showed that the straight portion of the tube (called the lead-
in) has to have a minimum length L for it to work. If L is too short, the
obstacle cloud starts developing again. If L is too long, no cloud develops,
but the heat transfer deteriorates. In certain applications, the length L that
worked best was between 0.2 to 0.4 times the total radiator thickness T. A
good value in many tests tuned out to be 0.3 T.
[0086]
Figure 20 illustrates another tube arrangement in accordance with
the present teachings. As illustrated, tubes 30 are bent in a gradual,
curved shape (as opposed to the abrupt bending of Figure 19). The
resultant pressure drop is further reduced in a substantial way. In certain
applications, the minimum lead-in length L may be approximately 0.1 to
0.4 times the radiator thickness. A good value in many tests turned out to
be 0.2 T.
[0087] Figures 21
and 22 illustrate another embodiment of the present
invention. In this embodiment, all the tubes 30 have the same angle.
Therefore, the airflow is deflected laterally which is desirable in some
situations. In other situations it may be desirable to orient the airflow
toward the center of the cooling fan (instead of a laterally shift of the
airflow). In all those cases, the angled tube heat exchanger allows a
degree of airflow management heretofore not available.
[0088]
Figures 23 and 24 illustrate a radiator in accordance with the
present teachings that has two portions, each with tubes 30 oriented in
opposite directions. Therefore, one portion of the radiator deflects the air
toward the right side, while the other portion deflects the air toward the
left
side. The result is a focused and centered airflow, which can substantially
increase the efficiency of the cooling fan.
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[0089]
Figures 25 and 26 illustrate another radiator in accordance with
the present teachings. In this embodiment, the radiator includes four
sections. Two of the sections center the airflow in horizontal direction,
while the two other sections orient the airflow in vertical direction. The
result is airflow focused on the fan from all directions, which further
increases fan efficiency.
[0090] As
shown in Figure 26, the tube angle does not have to be
constant. This figure shows a variable angle, with the angle almost zero
near the center and becoming much more larger in the periphery. This
variable tube geometry may achieve an even better focusing of the
airflow.
[0091]
Turning finally to Figure 27, another radiator constructed in
accordance with the present teachings is illustrated. As shown, the
radiator has a circular shape to closely match the shape of the cooling
fan. The core of the radiator may be constructed to include any of the
angled tube and/or angled fin constructions discussed above. In a front
view, the inlet and outlet tubes are curved. As a result, the length of the
tubes has a maximum dimension at a horizontal center of the radiator and
decreases in both upper and lower directions.
[0092] The
foregoing description of the embodiments has been provided
for purposes of illustration and description. It is not intended to be
exhaustive or to limit the invention. Individual elements or features of a
particular embodiment are generally not limited to that particular
embodiment, but, where applicable, are interchangeable and can be used
in a selected embodiment, even if not specifically shown or described.
The same may also be varied in many ways. Such variations are not to be
regarded as a departure from the invention, and all such modifications are
intended to be included within the scope of the invention.
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