Note: Descriptions are shown in the official language in which they were submitted.
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STACKED-TUBE HEAT EXCHANGER
FIELD OF THE INVENTION
The invention relates to heat exchangers, and particularly to heat exchangers
including a stack of spaced-apart tubes and/or plate pairs which define flow
passages for first and second fluids.
BACKGROUND OF THE INVENTION
Heat exchangers are commonly constructed from stacks or bundles of spaced-
apart flat tubes, in which the interiors of the tubes define flow passages for
a first
fluid and in which spaces between adjacent tubes define flow passages for a
second fluid. The flat tubes may comprise pairs of flat plates joined together
at
their margins.
The ends of the tubes in the stack or bundle are usually retained by a
perforated
header or tube sheet and the spaces between the plates may be at least
partially
enclosed by a housing. Examples of exhaust gas heat exchangers of this type
are shown in U.S. Patent No. 6,293,337 (Strahle et al.) and in U.S. Patent No.
6,269,870 (Banzhaf et al.).
It is also known to construct heat exchangers comprising bundles of spaced-
apart flat tubes in which the need for a perforated header is eliminated. An
example of a heat exchanger having this type of construction is described in
U.S.
Patent No. 6,321,835 (Damsohn et al.). In this patent, the ends of the heat
exchanger tubes are expanded in width and height relative to the central
portions
of the tubes. The tube ends are sealed directly to one another and to the
housing, thereby eliminating the need for a perforated header.
There remains a need to provide stacked-tube heat exchangers of simplified,
reliable construction and to improve and simplify processes for manufacturing
such heat exchangers.
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SUMMARY OF THE INVENTION
In one aspect, the present invention provides a heat exchanger for heat
transfer
between a first fluid and a second fluid. The heat exchanger comprises: (a) a
core comprising a stack of tubes, each of the tubes having a top wall, a
bottom
wall, side walls connecting the top and bottom walls, a hollow interior
enclosed
by the top, bottom and side walls, and inlet and outlet openings for the first
fluid,
wherein each of the tubes has a pair of end portions spaced apart along a
longitudinal axis and a central portion located between the end portions, the
end
portions of adjacent tubes in the stack being sealed to one another along
their
top and bottom walls, wherein the end portions are greater in height than the
central portions of the tubes such that the central portions of adjacent tubes
in
the stack are spaced from one another; (b) a plurality of first fluid flow
passages,
each of which comprises the hollow interior of one of the tubes and extends
longitudinally from the first fluid inlet opening to the first fluid outlet
opening; (c) a
plurality of second fluid flow passages, each of which comprises the space
between the central portions of an adjacent pair of the tubes, each of the
second
fluid flow passages having a pair of longitudinally-spaced ends and a pair of
transversely spaced sides, each of the second fluid flow passages being sealed
along its ends by the end portions of the adjacent pair of tubes; and (d) a
pair of
side plates covering the transversely spaced sides of the second fluid flow
passages, the side plates engaging the side walls of the tubes in the stack
and
being sealed to the tube side walls in the end portions of the tubes, wherein
an
inlet manifold is provided in one of the side plates and an outlet manifold is
provided in one of the side plates, each of the manifolds communicating with
each of the second fluid flow passages.
In another aspect, the present invention provides a method for manufacturing a
heat exchanger according to the invention. The method comprises: (a) stacking
the tubes to form the core; (b) attaching the U-shaped side plates to opposite
sides of the core with one of the longitudinally-extending edges of each side
plate
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engaging the top wall of the uppermost tube in the core and the other edge of
each side plate engaging the bottom wall of the lowermost tube in the core,
wherein the edges of the side plates frictionally engage the uppermost and
lowermost tubes to retain the tubes in position in the core; and (c) heating
the
core with the attached side plates for a time and at a temperature sufficient
to
seal the end portions of adjacent tubes together, to seal the longitudinally-
extending edges of the side plates to the uppermost and lowermost tubes in the
core, and to seal the side plates to the tube side walls in the end portions
of the
tubes and to tubes to one another and to the side plates.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described, by way of example only, with reference to
the accompanying drawings in which:
Figure 1 is a perspective view of a heat exchanger according to a first
preferred
embodiment of the invention;
Figure 2 is an exploded perspective view of the heat exchanger of Figure 1;
Figure 3 is a cross section along the line 3-3' of Figure 1;
Figure 4A is a close-up of area B of Figure 3;
Figure 4B is a close-up of area B of Figure 3 according to a variant of the
first
preferred embodiment;
Figure 4C is a close-up of area B of Figure 3 according to another variant of
the
first preferred embodiment;
Figure 5 is a front elevation view of the heat exchanger of Figure 1, with the
end
caps removed;
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Figure 6 is a front elevation view of one of the tubes making up the heat
exchanger of Figure 1;
Figure 7 is a front elevation view of an alternate tube construction for use
in a
heat exchanger according to the invention;
Figure 8 is a perspective view of a heat exchanger according to a second
preferred embodiment of the invention;
Figure 9 is an exploded perspective view of the heat exchanger of Figure 8;
Figure 10 is a perspective view of a heat exchanger according to a third
preferred
embodiment of the invention;
Figure 11 is an exploded perspective view of the heat exchanger of Figure 10;
Figure 12 is an exploded perspective view of a heat exchanger according to a
fourth preferred embodiment of the invention;
Figure 13 is a close-up of area C of Figure 5;
Figure 14 is a close-up of a portion of a heat exchanger according to a fifth
preferred embodiment of the invention;
Figure 15 is a perspective view of one,plate pair of a heat exchanger
according
to a sixth preferred embodiment of the invention;
Figure 16 is an exploded perspective view of a heat exchanger according to a
seventh preferred embodiment of the invention; and
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Figure 17 is a perspective view of the heat exchanger of Figure 16.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Heat exchangers according to the invention are suited for use as exhaust gas
coolers for vehicular applications in which hot exhaust gases are cooled by a
liquid coolant, for example to cool or prevent overheating of the catalyst in
a
catalytic converter andlor to provide supplementary cabin heating. It will,
however, be appreciated that the heat exchangers described herein can be
applied to a number of different uses other than the cooling of exhaust gases.
For example, heat exchangers according to the invention can be used for
reformer-based fuel processors.
A first preferred heat exchanger 10 is illustrated in Figures 1 to 5. Heat
exchanger 10 comprises a core 11 (Figs. 2, 3 and 5) comprising a stack of open-
ended tubes 12, each of which has a top wall 14, an opposed bottom wall 16 and
a pair of opposed side walls 18, 20. The tubes 12 each have a pair of end
portions 22, 24 spaced apart along longitudinal axis A and a central portion
26
located between the end portions 22, 24. The central portions 26 of adjacent
tubes 12 are spaced apart while the end portions 22, 24 of adjacent tubes 12
are
sealed to one another along their top and bottom walls 14, 16.
In heat exchanger 10, the tubes 12 have a rectangular cross-section when
viewed in a transverse plane, with the top and bottom walls 14,16 being
substantially flat and parallel to one another and with the side walls 18,20
being
substantially flat and parallel to one another. It will, however, be
appreciated that
fhe tubes 12 may be of other suitable shapes, preferably having substantially
flat
top and bottom walls 14,16. For example, the cross sections of tubes 12 may be
shaped as elongate hexagons or as elongate ovals in which the side walls 18,
20
are multi-faceted or rounded. However, it is preferred that the tubes 12 have
an
elongate rectangular cross sectional shape, as shown in the drawings, so as to
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simplify the shapes of other components of the heat exchanger, which are
described below.
The tubes 12 in heat exchanger 10 are of constant width and have end portions
22, 24 which are expanded in the vertical direction so that the end portions
22,
24 have a height which is greater than a height of the central portions 26 of
tubes
12. This permits the central portions 26 of the tubes 12 to be spaced apart
while
the end portions 22, 24 of adjacent tubes 12 may be sealed directly to one
another without the need for a perforated header or tube sheet. It will be
appreciated that the width of the tubes is not necessarily constant throughout
their length.
Heat exchanger 10 includes fluid flow passages for heat exchange between a
first fluid and a second fluid, which may be either liquid or gaseous. A
plurality of
first fluid flow passages 30 is defined by the hollow interiors of tubes 12.
Each of
the first fluid flow passages 30 extends longitudinally from one open end 34
to
another open end 36 of a tube 12. Where heat exchanger 10 comprises an
exhaust gas cooler, the first fluid is preferably a hot engine exhaust gas.
A plurality of second fluid flow passages 38 is defined by the spaces between
the
central portions 26 of adjacent tubes 12. Each of the second fluid flow
passages
38 has a pair of IongitudinaUy-spaced ends 40 and a pair of transversely
spaced
sides 42. As shown in Figure 3, the second fluid flow passages 38 are sealed
along their ends 40 by the sealed end portions 22, 24 of the adjacent tubes 12
between which they are formed.
The heat exchanger 10 further comprises a housing 44 which covers the top,
bottom and sides of the core 11. The housing 44 is open-ended, has a
rectangular transverse cross section and comprises a pair of side plates 46,
48
and a pair of end plates 50, 52. As shown in the drawings, the housing 44 may
comprise a pre-formed rectangular casing made from a drawn pipe which is
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formed into a rectangular shape, or from sheet metal which is stamped or
folded
into a rectangular shape and joined along a seam by welding or brazing.
Although the housing 44 is shown in the drawings as having a rectangular
shape,
it will be appreciated that it may have any other suitable shape, depending on
the
shape of the core 11.
The side plates 46, 48 of housing 44 substantially enclose the sides 42 of the
second fluid flow passages 38 and may preferably engage the side walls 18, 20
of the tubes 12, thereby substantially preventing bypass flow between the tube
side walls 18, 20 and the side plates 46, 48. In the preferred heat exchanger
10,
the side plate 46 is provided with an inlet opening 54 which is formed in a
raised
inlet manifold 56. The manifold 56 comprises a raised portion of side plate 46
which extends throughout substantially the entire height of the side plate 46
so
as to permit flow communication between the inlet opening 54 and each of the
second fluid flow passages 38. The other side plate 48 is provided with an
outlet
opening 58 and an outlet manifold 60 substantially identical to the inlet
opening
and manifold 54, 56 described above. Although heat exchanger 10 has inlet and
outlet openings 54,58 and the associated manifolds 56, 60 formed in opposite
side plates 46,48 of housing 44, they may instead be provided in the same side
plate 46 or 48. Furthermore, where the openings 54, 58 are provided in
opposite
side plates 46, 48, it will be appreciated that they are not necessarily
offset from
one another. Rather, the openings 54, 58 may be located directly opposite to
one another, as will be discussed below in more detail.
The end plates 50, 52 extend between and are connected to the side plates 46,
48. As shown in Figure 3, an additional second fluid flow passage 62 is formed
between the top end plate 50 and the top wall 14 of the uppermost tube 12 of
core 11, and an additional fluid flow passage 64 is formed between the bottom
end plate 52 and the bottom wall 16 of the lowermost tube 12 of core 11. These
passages 62, 64 are also in communication with the inlet and outlet openings
54,
58 through manifolds 56, 60.
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Referring now to Figures 3 and 4, it will be seen that the longitudinally-
spaced
ends of housing 44 are sealed to the end portions of the tubes 12 in the core
11,
thereby sealing the ends of the second fluid flow passages 38, 62, 64.
Specifically, as shown in Figure 3, it will be seen that the ends of top end
plate 50
overlap with and sealingly engage the end portions 22, 24 of uppermost tube 12
and the ends of bottom end plate 52 overlap with and sealingly engage the end
portions 22, 24 of the lowermost tube 12. Similarly, as shown in Figure 5, the
side plates 46, 48 of housing 44 sealingly engage the side walls 18, 20 of
tubes
12, at least along their end portions 22, 24, throughout the height of the
core 11.
The heat exchanger 10 preferably also comprises a pair of end fittings 68
which,
in the first preferred embodiment, are identical to each other. Fittings 68
form an
inlet and outlet for the first fluid and are in flow communication with the
first fluid
flow passages 30 at the ends 34, 36 of tubes 12. Each of the end fittings 68
has
a longitudinally-extending flange 70 which is of substantially square or
rectangular shape. The flange 70 fits over and is sealed to the end portions
22,
24 of the stacked tubes 12 or, as described below in greater detail, may
overlap
the ends of housing 44.
There are various methods by which the heat exchanger 10 may be assembled.
According to one method, the tubes 12 comprising the core 11 are brazed
together and the core 11 is then slid as a unit into a pre-formed housing 44,
with
the walls 46, 48, 50 and 52 overlapping the ends 22, 24 of the tubes 12. The
end
fittings 68 are then slid over the ends of the core 11, with a small gap 72
being
provided between the flange 70 and the housing 44, as shown in the close-up of
Figure 4A. The provision of gap 72 is advantageous where the fittings 68,
housing 44 and core 11 are simultaneously brazed or welded together. The gap
72 is filled by a filler metal during brazing or welding, and the filler metal
is drawn
into the gaps between the tubes 12, the housing 44 and the end fittings 68 by
capillary flow, thereby ensuring a leak-proof seal. Alternatively, the flanges
70 of
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fittings 68 may overlap the ends of the housing 44, as shown in the close-up
of
Figure 4B.
In other assembly methods, the housing 44 may be formed from a sheet of metal
which is wrapped around the core 11, held in tension and then fastened
together
by welding, mechanical fasteners or staking. In this type of assembly method,
the end fittings 68 can be applied to the core either before or after the
housing
44. For example, the end fittings 68 may first be applied over the ends of an
unbrazed core 11, whereby frictional engagement between the flanges 70 of the
end fittings 68 and the tubes 12 is sufficient to hold the core together
during
brazing. This reduces or eliminates the need for additional fixturing means to
keep the tubes 12 from shifting their relative positions in the tube stack
prior to
brazing. Accordingly, the end fittings 68 provide "self-fixturing" during
assembly
of the heat exchanger and simplify the manufacturing process. The fittings 68
and core 11 are then brazed together. The housing 44 is subsequently wrapped
around the core 11 and may either overlap the flanges 70 of the end fittings
68,
as shown in the close-up of Figure 4C or be spaced from the fittings as in
Figure
4A. The housing 44 is then welded to the flanges 70 and to the underlying
tubes
12.
As shown in Figure 3, the central portions 26 of tubes 12 are preferably
provided
with upstanding protrusions 77 in one or both of their top and bottom walls
14,
16. In all but the uppermost and lowermost tubes 12, the upper surfaces 79 of
protrusions 77 engage the top or bottom wall 14, 16 or a protrusion 77 of an
adjacent tube 12. The protrusions 77 in the top wall 14 of the uppermost tube
12
preferably engage the end wall 50 of housing 44 and the protrusions 77 in the
bottom wall 16 of the lowermost tube preferably engage the end wall 52 of
housing 44. It will be appreciated that protrusions 77 assist in maintaining
the
spaces between the central portions 26 of adjacent tubes 12 by providing
support
between the top and bottom walls 14, 16, thereby enhancing the strength of the
heat exchanger 10.
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1~
In the first preferred embodiment, the protrusions 77 are in the form of
spaced
dimples having a truncated cone shape, the upper surfaces 79 of the
protrusions
being flat. Preferably, both the top and bottom walls 14, 16 are provided with
protrusions 77 arranged in the same pattern so that the upper surfaces 79 of
the
protrusions 77 of adjacent tubes 12 engage one another as shown in Figure 3.
It
will be appreciated that the tubes 12 may be provided with protrusions 77
other
than, or in addition to, dimples 77. For example, the tubes could be provided
with spaced, angled ribs provided in their top and/or bottom walls 14, 16.
The heat exchanger 10 preferably also comprises turbulence-enhancing inserts
provided in one or more of the first fluid flow passages 30, preferably in all
the
first fluid flow passages 30. As shown in Figure 5, the turbulence-enhancing
inserts comprise a plurality of con-ugated fins 80, each of which comprises a
plurality of longitudinally-extending fin walls 82 having a height
substantially
equal to the height of the first fluid flow passages 30 in the central
portions 26 of
tubes 12. The fin walls 82 are connected by top and bottom walls 83, 84 which
are in heat exchange contact with the top and bottom walls 14, 16,
respectively,
of tubes 12. In order to maximize contact between the fins 80 and tubes 12,
the
top and bottom walls 83, 84 of fins 80 may preferably be flat, although this
is not
necessary.
In order to simplify the manufacturing process and reduce cost, it is
preferred that
each of the tubes 12 is comprised of a pair of plates, which in the first
preferred
embodiment, are identified as upper plate 88 and lower plate 90 (Figures 5 and
6). Each of the plates have a pair of longitudinally-extending side portions
along
which the plates 88, 90 are sealed together. In the first preferred
embodiment,
the plates 88, 90 are generally U-shaped, with the upper plate 88 having a
pair of
identical side portions 92 joined by a substantially flat middle portion 96,
and the
lower plate 90 has a pair of identical side portions 94 joined by a
substantially flat
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11
middle portion 98. The angle between middle portions 96, 98 and respective
side portions 92, 94 is about 90 degrees.
In order to provide good sealing contact between the plates 88, 90, the side
portions 92, 94 of the plates 88, 90 are preferably in nested relation. This
is
shown in Figures 5 and 6, from which it can be seen that the shorter side
portions 92 of the upper plate 88 are completely nested inside (i.e. between)
the
relatively longer side portions 94 of lower plate 90, thereby providing good
contact for a braze joint between the side portions 92, 94. It can also be
seen
from the end view of Figure 5 that the side portions 94 of lower plate 90 are
sufficiently long to extend up to the top wall 14 of tube 12 in the end
portions 22,
24 thereof, and preferably into contact with the bottom wall 16 of an upwardly
adjacent tube 12. As shown in Figure 5 and 13, this minimizes the size of the
gaps 100 formed between the side walls 18, 20 of adjacent tubes 12, thereby
ensuring that a well sealed braze joint will be formed between the side walls
of
tubes 12 and the side plates 44.
In the tube 12 shown in Figure 6, the corrugated fin 80 also serves as a
spacer to
maintain the desired degree of nesting between plates 88, 90 and the height of
first fluid flow passages 30.
It will be appreciated that the construction of the tubes for heat exchangers
according to the invention may vary from that shown in Figures 1 to 6. Figure
7
shows an alternate construction for a heat exchanger tube 102 which, except
for
the details of its construction described below, is preferably identical to
tube 12.
The tube 102 comprises a pair of identical U-shaped plates 104 having a pair
of
side portions 106, 108 joined by a middle portion 110. The side portions 106,
108 are of different lengths, with side portion 106 being higher than side
portion
108. When two plates 104 are brought together in nested engagement as shown
in Figure 6, the higher side portions 106 are on the outside of the shorter
side
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12
portions 108. As in tube 12, a corrugated fin 80 is preferably provided for
turbulence and to maintain the spacing between the plates 104.
A second preferred heat exchanger 120 according to the invention is now
described with reference to Figures 8 and 9. Heat exchanger 120 includes a
core 11 and end fittings 68 which are identical to those of heat exchanger 10
described above. Heat exchanger 120 differs from heat exchanger 10 in that it
does not include a housing 44, but rather utilizes a pair of side plates 122,
124
to seal the sides of the second fluid flow passages 38. Side plate 122 is
provided
with an inlet opening 126 and an inlet manifold 128 and side plate 124 is
provided with an outlet opening 130 and an outlet manifold 132, which are
preferably identical to the inlet and outlet openings and manifolds of heat
exchanger 10 described above. It will be appreciated that both the inlet and
outlet openings 126, 130 and the associated manifolds 128,132 may instead be
provided side-by-side in one of the plates 122 or 124. Where the inlet and
outlet
openings 126, 130 are provided in opposite side plates 122, 124, they are not
necessarily offset from one another, but rather may be directly opposite one
another as described below in more detail.
Each side plate 122,124 is sealed to the side walls 18, 20 of the tubes 12
along
one side of the core 11, at least in the end portions 22,24 of the tubes 12.
The
side plates 122,124 are preferably U-shaped, having angled flanges which are
sealed to the central portions 26 of the uppermost and lowermost tubes 12 in
the
core 11, thereby sealing the sides of the second fluid flow passages 38. The
flanges preferably terminate short of the end portions 22, 24 of tubes 12. As
shown in Figures 8 and 9, side plate 122 is provided with flanges 134, 136 and
side plate 124 is provided with flanges 138, 140. One flange 134 of plate 122
is
sealed to the top wall 14 of the uppermost tube12 and, although not visible in
the
drawings, the other flange 136 is sealed to the bottom wall 16 of the
lowermost
tube 12. Similarly, the flanges 138,140 of the other plate 124 are sealed to
the
uppermost and lowermost tubes 12, respectively.
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13
Preferably, during assembly of the heat exchanger 10, the angled flanges of
plates 122,124 frictionally engage the uppermost and lowermost tubes 12,
thereby reducing or eliminating the need for additional fixturing means to
keep
the tubes 12 from shifting their relative positions in the core 11 prior to
brazing.
Accordingly, the side plates 122,124 provide "self-fixturing" during assembly
of
the heat exchanger and simplify the manufacturing process.
Figures 10 and 11 illustrate a third preferred heat exchanger 150 according to
the
invention. Heat exchanger 150 includes a core comprising a stack of tubes 152
which are similar to tubes 12 in that each has a top wall 154, an opposed
bottom
wall 156 and a pair of side walls 158, 160. The tubes 152 each have a pair of
longitudinally spaced end portions 162, 164 and a central portion 166 located
between the end portions 162, 164. The end portions 162, 164 of the tubes have
a vertical height greater than a height of the central portion, with a raised
shoulder 167 being provided between the central portion 166 and the end
portions 162, 164. Accordingly, the central portions 166 of adjacent tubes 152
are spaced apart and the end portions 162, 164 of adjacent tubes 152 are
sealed
to one another along their top and bottom walls 154, 156.
The most significant difference between tubes 152 and tubes 12 is that the
tubes
152 are not open-ended. Rather, the side walls 158, 160 of tube 152 form part
of
a continuous perimeter wall which seals the periphery of tube 152. Further, in
all
but the uppermost and lowermost tubes 152, the end portion 162 is provided
with
aligned openings 168 extending through both the top and bottom walls 154, 156
and the opposite end portion 164 is provided with aligned openings 170
extending through both the top and bottom walls 154, 156. In Figure 11, the
uppermost tube is labeled 152' and the lowermost tube is labeled 152". In the
uppermost tube 152', the end portion 162 is provided with a connection flange
172 which communicates with the aligned openings 168 and the opposite end
portion 164 is provided with an opening 170 only in its bottom wall 156. There
is
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1
no opening 170 in the top wall 154; it is either missing entirely or plugged.
Similarly, the end portion 164 of lowermost tube 152" is provided with a
connection flange 172 and, although not seen in the drawings, the opposite end
portion 162 is provided with an opening only in its upper wall 154. There is
no
opening 168 in the bottom wall 156; it is either missing entirely or plugged.
Therefore, the first fluid, which may preferably comprise a hot exhaust gas,
enters the heat exchanger 150 through one of the connection flanges 172, flows
through the interiors of the tubes 152 and exits the heat exchanger 150
through
the other connection flange 172. The aligned openings 168 and 170 of tubes
152 provide integrally formed inlet and outlet manifolds and eliminate the
need
for end fittings as in the first and second embodiments.
Like tubes 12 described above, tubes 152 preferably also have a rectangular
cross section and the top and bottom walls 154, 156 are preferably also
provided
with protrusions 174 which may be in the form of truncated conical dimples. It
will be appreciated that the tubes 152 may be provided with protrusions other
than, or in addition to, dimples 174. For example, the tubes 152 could be
provided with spaced, angled ribs provided in their top and/or bottom walls
154,
156. As shown in Fig. 11, the top wall 154 of uppermost plate 152' may
preferably be free of protrusions 174 since they would serve no purpose in
heat
exchanger 150. The bottom wall 156 of lowermost plate 152" may similarly be
free of protrusions 174.
Although not shown in Figures 10 and 11, the interiors of the first fluid flow
passages may preferably be provided with corrugated fins which may be
identical
to fins 80 described above.
A plurality of second fluid flow passages 176 are defined by the spaces
between
the central portions 166 of adjacent tubes 152. Each second fluid flow passage
176 has a pair of longitudinally spaced ends 178 and a pair of transversely
spaced sides 180. As shown in Figure 11, the second fluid flow passages 176
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are sealed at their ends 178 by the sealed end portions 162, 164 of the
adjacent
tubes 152 between which they are formed.
Heat exchanger 150 further comprises a pair of side plates 182, 184 which seal
the sides 180 of the second fluid flow passages 176. Each of the side plates
182, 184 has a pair of longitudinally-spaced ends 186 and a pair of
flanges188.
In the preferred heat exchanger 150, the side plate 182 is provided with both
the
second fluid inlet and outlet openings 190, 192 while the side plate 184 (of
which
only one flange is visible in Figure 10) does not have an inlet or outlet for
the
second fluid. It will be appreciated that the second fluid inlet and outlet
openings
190,192 could instead be provided in opposite side plates 182,184 and may
either be offset or directly opposite one another. The second fluid inlet and
outlet
openings 190, 192 are also shown in Figures 10 and 11 as being provided with
inlet and outlet fittings 194, 196 respectively.
Each side plate 182, 184 is sealed to the side walls 158, 160 of the tubes 152
along one side of the core 11, at least near its ends. Furthermore, the
flanges
188 of each side plate 182, 184 are sealed to an uppermost tube 152 in the
stack
and to the lowermost tube 152 in the stack. Therefore, the side plates 182,
184
seal the sides 180 of the second fluid flow passages 176 as in heat exchanger
120 described above.
The side plates 182, 184 are preferably U-shaped, with the flanges 188 being
angled relative to the plate side wall 198. The angle between the edges 188
and
the plate side wall is preferably about 90 degrees. As with plates 44
described
above, the flanges 188 of plates 182, 184 preferably frictionally engage the
uppermost and lowermost tubes 152', 152" during assembly, thereby reducing or
preferably eliminating the need for additional fixturing means to keep the
tubes
152 from shifting their relative positions in the core prior to brazing.
Rather than
using side plates 182,184, it will be appreciated that the heat exchanger 150
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16
could instead be provided with a housing similar or identical to housing 44
described above.
As shown in Figure 11, each of the tubes 152 is preferably comprised of a pair
of
plates, an upper plate 200 and a lower plate 202. Upper plate 200 comprises a
substantially flat middle portion 204 a continuous peripheral flange 206 and
lower
plate 202 similarly comprises a middle portion 208 and a continuous peripheral
flange 210. One of the flanges 206, 210 nests within the other flange as
described above with reference to heat exchanger 10.
Figure 12 illustrates a heat exchanger 250 according to a fourth preferred
embodiment of the invention. Heat exchanger 250 is a hybrid of the second and
third embodiments in that the tubes 252 of heat exchanger 250 have first end
portions 254 which are open-ended as in heat exchanger 10 and second end
portions 256 which form an integral manifold as in heat exchanger 150. The
other components of heat exchanger 250, namely connecting flange 172, side
plates 182,184 and end fitting 68, are as described above.
A further preferred feature of the invention is now described below with
reference
to Figures 13 and 14. Figure 13 is a close-up of area C of Figure 5. In order
to
provide a seal between the tubes 12 and the side plates 46,48 of housing 44,
it is
necessary to completely fill all the gaps between the tubes 12 and the side
plates
46,48 with filler metal. As shown in Figure 13, there is an approximately
triangular-shaped gap 100 at the point where two tubes 12 abut the side plates
46,48 (only side plate 48 is shown in Figure 13). If this gap 100 is too
large, filler
metal will not reliably be drawn into the gap by capillary flow. In order to
prQVide
more reliable sealing, it may be preferred to modify the tubes 12 and the side
plates 46,48 as shown in Figure 14 so as to provide a narrower gap 262 which
will be more readily filled. Firstly, according to the modified structure of
Figure
14, the shapes of the plates 88,90 making up tubes 12 are somewhat modified to
have slightly more rounded edges 264,266 and the height of the side portions
94
CA 02503424 2005-04-O1
17
of lower plates 90 are somewhat reduced. Secondly, the side plates 46,48 (only
plate 48 is visible in the close-up of Figure 14) are formed with ribs 268, at
least
near the ends of the side plates 46,48. These ribs 268 extend into the area
between adjacent tubes 12 so as to provide a relatively narrow gap 262.
Figure 15 illustrates a pair of plates 88' and 90' of a heat exchanger
according to
a sixth preferred embodiment of the invention. Plates 88' and 90' together
define
a heat exchanger tube 12' which is substantially identical to tubes 12 of heat
exchanger 10 described above except that the upper surface 14' of tube 12' is
provided with an elongate, upstanding rib 270 extending longitudinally from
one
end portion 22' and along the central portion 26' of tube 12'. The rib 270 has
a
height which is substantially the same as that of the end portion 22' and has
one
end 272 which preferably forms a smooth transition with the end portion 22' of
tube 12'. The other end 274 of rib 270 is spaced from the other end portion
24'
of tube 12'. Similarly, the lower surface 16' of tube 12' is provided with an
elongate, depressed rib 276 extending longitudinally from end portion 22'. The
rib 276 has a height which is substantially the same as that of end portion
22',
has one end 278 which preferably forms a smooth transition with the end
portion
22' of tube 12' and an opposite end 280 spaced from the other end portion 22'.
The same effect will be produced by providing only one of the upper surface
14'
or the lower surface 16' of tube 12' with a rib which has a height equal to
the
height of the second fluid flow passage 38 between adjacent tubes 12'.
When a core 11' (not shown) is formed by stacking tubes 12', the ribs 270, 276
of
adjacent tubes 12' engage one another, thereby forming a barrier against
transverse flow of the second fluid directly across the core. Rather, the
second
fluid must flow around the flow barrier formed by ribs 270, 276 and pass
through
a gap between the ends 274, 280 of ribs 270, 276 and the end portions 24' of
the
adjacent tubes 12'. In this embodiment, it may be advantageous to locate the
second fluid inlet and outlet openings (not shown) of the side plates (not
shown)
directly across the core 11' from one another, and adjacent the ends 22' of
tubes
CA 02503424 2005-04-O1
Ig
12', so as to maximize the length of the flow path followed by the second heat
exchange fluid. The flow between an inlet and outlet situated in these
positions
is indicated by the arrows in Figure 15. It will be appreciated that ribs may
instead be provided in the tube interiors to lengthen the flow path of the
first fluid
in a similar manner.
A heat exchanger 300 according to a seventh preferred embodiment of the
invention is now described below with reference to Figures 16 and 17. Heat
exchanger 300 includes a core 11 and a pair of end fittings 68 which are shown
as being identical to those of heat exchangers 10 and 120 described above.
Heat exchanger 300 further comprises a pair of side plates 122', 124' which
are
similar to side plates 122, 124 of heat exchanger 120 and are therefore
described using like reference numerals.
The side plates 122', 124' seal the sides of the second fluid flow passages
38.
Side plate 122' is provided with an inlet opening 126' and a raised inlet
manifold
128' and side plate 124' is provided with an outlet opening 130' and a raised
outlet manifold 132'.
Heat exchanger 300 further comprises a pair of end plates 302, 304 which, in
the
preferred embodiment of Figures 16 and 17, are flat and rectangular. The end
plates are of a length sufficient to overlap with and sealingly engage the end
portions 22, 24 of the uppermost and lowermost tubes 12 of the core 11. The
end plates 302, 304 preferably are of substantially the same width as the core
11. Therefore, additional second fluid flow passages are formed between the
end plates 302, 304 and the core 11, in an identical manner as described above
with reference to the end plates 50, 52 of heat exchanger 10.
Each side plate 122', 124' overlaps and is sealed to sides of the core 11 in
the
manner described above with reference to heat exchanger 150. The side plates
122',124' are preferably U-shaped, having angled flanges which are sealed to
the
CA 02503424 2005-04-O1
19
end plates 302, 304, thereby sealing the sides of the second fluid flow
passages
38. The flanges preferably extend the full length of the end plates 302, 304.
As
shown in Figures 16 and 17, side plate 122' is provided with flanges 134',
136'
and side plate 124' is provided with flanges 138', 140'. One flange 134' of
plate
122' is sealed to the upper end plate 302 the other flange 136' is sealed to
the
lower end plate 304. Similarly, the flanges 138',140' of the other plate 124'
are
sealed to the upper and lower end plates 302, 304, respectively.
Preferably, during assembly of the heat exchanger 300, the angled flanges
134',
136', 138', 140' of plates 122',124' frictionally engage the end plates 302,
304,
thereby reducing or eliminating the need for additional fixturing means to
keep
the end plates 302, 304 and the tubes 12 of core 11 from shifting their
relative
positions prior to being joined, for example by brazing. Accordingly, the side
plates 122',124' provide "self-fixturing" during assembly of the heat
exchanger
and simplify the manufacturing process.
The heat exchanger 300 is shown in its assembled state in Figure 17. As shown,
the flanges 70 of end fittings 68 may preferably be spaced from the side
plates
122', 124' and the end plates 302, 304 in the manner described above with
reference to Figure 4A. Alternatively, the end plates 302, 304 may be
overlapped by the fittings 68 in the manner shown in Figure 4B, in which case
it
may be preferred to use side plates 122, 124 identical to those of heat
exchanger
150 in which the flanges 134, 136, 138, 140 which terminate short of the ends
of
the plates 122, 124 such that the flanges are not overlapped by the fittings
68.
Alternatively, the end plates 302, 304 may overlap the fittings 68 in the
manner
shown in Figure 4C.
Although the invention has been described in connection with certain preferred
embodiments, it is not limited thereto. Rather, the invention includes within
its
scope all embodiments which may fall within the scope of the following claims.
