Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02632382 2008-05-28
HEAT EXCHANGER
Field of the Invention
The invention relates to heat exchangers and, more particularly, to a method
for
manufacturing heat exchangers such as radiators, oil coolers, air-to-air heat
exchangers (charge air coolers "CAC"),compressors, fuel coolers, conditioned
air
units, and the like.
Description of the Prior Art
Radiators are heat exchangers that are used to reject heat from the coolarit
of an
internal combustion engine to the ambient. The engine coolant is typically
circulated
through coolant passages in the engine block to the so-called liquid side of
the
radiator where it is cooled and then returned to the engine block. Cooling
occurs by
forcing ambient air through the radiator core.
The thermal efficiency of an engine typically increases as its operating
temperature
is increased. Consequently, it is desirable to raise the operating temperature
of the
engine as much as possible to maximize efficiency. The operating temperature
can
hardly be raised to the point where the coolant within cooling passages in the
engine
begins to vaporize.
Consequently, if engines are to be operated at higher temperatures, it is
necessary
that the boiling point of the coolant being employed be raised. This can be
done by
increasing system pressure. At the same time, it becomes necessary to increase
the
strength of the radiator / heat exchanger so that the same can operate at the
increased pressure.
Oil coolers are heat exchangers wherein heat dissipation occurs through oil.
Oil
viscosity increases in cold temperature. Thus, when operating in relatively
cold
conditions or when the motor associated with the oil cooler is cold, the oil
cooler
must sustain high pressure.
Finally, radiators and charge air coolers have a longer operating life if they
can
support higher pressure when operating in high vibrating environment.
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BRIEF SUMMARY OF THE INVENTION
It is therefore an aim of the present invention to address the above mentioned
issues.
According to a general aspect, there is provided a heat exchanger comprising:
a
core portion including a plurality of heat exchanger tubes and fins disposed
alternatively; and at least one substantially straight header plate having a
plurality of
insertion slots extending therethrough for receiving a respective end of the
heat
exchanger tubes therein, the core portion and the at least one header plate
being
brazeable together.
According to another general aspect, there is provided a heat exchanger
comprising:
a core portion including a plurality of heat exchanger tubes; at least one
substantially
straight header plate having a plurality of insertion slots defined therein
for receiving
a respective end of the heat exchanger tubes therein, the core portion ancl
the at
least one header plate being brazeable together; and at least one tank cover
securable to the at least one header plate and defining a tank cavity with the
at least
one header plate when secured thereto, the heat exchanger tubes being in fluid
communication with the tank cavity.
According to still another general aspect, there is provided a method for
manufacturing a heat exchanger comprising: inserting a respective end of a
plurality
of heat exchanger tubes in a respective insertion slot extending through a
substantially straight header plate to define a heat exchanger tube and header
plate
assembly; and brazing the heat exchanger tube and header plate assembly.
According to a further general aspect, there is provided a heat exchanger
header
comprising: a brazeable substantially straight header plate having an inner
surface,
an outer surface opposed to the inner surface, a plurality of tube insertion
slots
extending throughout the header plate and extending in a longitudinal
succession;
and a tank cover having peripheral edges secured to the outer surface of the
header
plate, proximate to external edges of the header plate, and defining a tank
cavity with
the header plate, the tube insertion slots being in fluid communication with
the tank
cavity.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of a heat exchanger in accordance with an
embodiment;
Fig. 2 is a sectional view taken along cross-section lines 2-2 of Fig. 1 of
the heat
exchanger;
Fig. 3 is a perspective view of a core portion and two header plates of the
heat
exchanger shown in Fig. 1;
Fig. 4 includes Fig. 4a and Fig. 4b, Fig. 4a is a top plan view of the core
portion and
one of the header plates shown in Fig. 3 and Fig. 4b is an enlargeci view,
fragmented, of heat exchanger tubes inserted in cavities defined in one of the
header
plates;
Fig. 5 is a perspective view, partly sectioned and fragmented, of the heat
exchanger
shown in Fig. 1; and
Fig. 6 is a flow chart illustrating a method for manufacturing the heat
exchanger
shown in Fig. 1.
It will be noted that throughout the appended drawings, like features are
identified by
like reference numerals.
DETAILED DESCRIPTION
Figs. 1 and 2 show a heat exchanger 10 having a housing 12 covering a core
portion
14 and extending between a pair of hollow headers 16 disposed in parallel with
each
other. Fluid inlet and outlet connectors 18 are mounted to the headers 16 and
are in
fluid communication with a tank cavity 20 defined in the hollow headers 16, as
will be
described in more details below.
The housing 12 includes two opposed and spaced-apart side plates 24 having an
edge secured to headers 16.
Figs. 2 and 3 show an internal view of the heat exchanger 10. The core portion
14
includes a plurality of heat exchanger flat tubes 26 disposed in parallel with
their
opposite sides in fluid communication with the hollow headers 16. Corrugated
fins 28
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are disposed between adjacent heat exchanger tubes 26 and outside the
outermost
heat exchanger tubes 26. The side plates 24, defining a portion of the housing
12,
are disposed outside the outermost corrugated fins 28.
The heat exchanger tubes 26 are hollow extruded articles defining an inner
channel
30 with an obround cross-section. The inner channel 30 is in fluid
communication
with the tank cavities 20. The inner channel 30 can be divided into a
plurality of
passages with partition walls (not shown), also called micro-channel tubes,
extending longitudinally therein to reinforce the tubes 26.
Each header 16 includes a substantially straight rectangular header plate 32
having
an inner surface 34 and an opposed outer surface 36. The substantially
straight
header plates 32 do not include upwardly extending peripheral edges like in
prior art
heat exchangers. The inner surfaces 34 of both headers 16 face one another
when
the heat exchanger 10 is assembled. A plurality of tube insertion slots 38
extend
throughout the header plates 32 in a longitudinal succession as shown in Fig.
4a.
The insertion slots 38 are defined to receive therein an end of one heat
exchanger
tube 26. Fig. 4b shows that the outer surface of the heat exchanger tubes 26,
proximate to an end thereof, is juxtaposed to the inner surface of the
insertion slots
38. Thus, the external size of the heat exchanger tubes 26 is slightly smaller
than the
size of the insertion slots 38. In an embodiment, the insertion slots 38 in
header plate
32 are created by machining.
Figs. 2 and 5 show that each header 16 also includes a tank cover 40 having an
upper wall 42, two opposed and spaced-apart lateral walls 44, and two opposed
and
spaced-apart side walls 46, extending between the lateral walls 44. The
lateral walls
44 and the side walls 46 have peripheral edges 48 secured to the outer surface
36 of
the header plate 32, proximate to external edges 50 of the header plate 32.
For
example and without being limitative, the peripheral edges 48 of the tank
cover 40
can be welded to the header plate 32. In the embodiment shown, the side walls
46
are recessed internally from the external edges 50 of the header plate 32. The
tank
cover 40 and the header plate 32 define the tank cavity 20 when secured
together.
In an alternative embodiment (not shown), the peripheral edges 48 of the tank
cover
can be welded to the lateral walls of the heater plate 32, i.e. the walls
extending
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between the inner surface 34 and the outer surface 36. In another alternative
embodiment (not shown), the outer surface 36 of the heater plate 32 can
include a
peripheral recess section in which the peripheral edges 48 of the tank cover
40 are
inserted and secured. The peripheral recess section can be machined in the
header
plate 32. In another alternative embodiment (not shown), both the edges of the
header plate 32 and the peripheral edges 48 of the tank cover 40 can be
beveled
edges which are matingly engaged when securing the tank cover 40 to the header
plate 32.
The tank cavity 20 is in fluid communication with the inner channels 30 of the
heat
exchanger tubes 26 inserted in the tube insertion slots 38 and with the fluid
irilet and
outlet connectors 18.
In the embodiment described above, the heat exchanger is a single tube pass
heat
exchanger wherein the fluid enters the heat exchanger at one end, flows once
in the
tubes, and exits at the opposed heat exchanger end. In alternative
embodiments, the
heat exchanger can be a multiple tube pass heat exchanger such as and without
being limitative a double tube pass or a triple tube pass heat exchanger. For
example and without being limitative, in a double tube pass heat exchanger,
the fluid
enters the heat exchanger at a first end, flows twice in the tubes, and exits
at the first
end. Similarly, in a triple tube pass heat exchanger, the fluid enters the
heat
exchanger at a first end, flows thrice in the tubes, and exits at the opposed
heat
exchanger end. In multiple tube pass heat exchangers, at least one of the tank
covers includes a partition wall which separated the tank cavity into
separated
chambers. It is appreciated that the heat exchanger can include more than
three
passes.
Referring now to Fig. 6, for manufacturing a heat exchanger, the core portiori
is first
assembled to the header plates 70. The heat exchanger tubes and the corrugated
fins are stacked alternatively and the opposite ends of the heat exchanger
tubes are
inserted in the corresponding insertion slots defined in the header plates to
form a
provisional assembly, as shown in Fig. 3. The edges of the heat exchanger
tubes
extend substantially flush with the outer face of the header plate in which
they are
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inserted. Furthermore, side plates are assembled to the core portion. Then,
this
provisional assembly is integrally brazed in a furnace 72.
The brazing step is carried out in a controlled environment in an atmosphere
of inert
gas such as nitrogen, for instance, during 10 to 20 minutes and, in an
alternative
embodiment, during 12 to 18 minutes. The temperature in the furnace ranges
between approximately 1000 and 1200 F (approximately 530 and 650 C',). It is
appreciated that the brazing conditions (temperature, atmosphere, time, etc.)
can
vary in accordance with the heat exchanger size and materials.
More particularly, in an embodiment, prior to the brazing step, a brazing flux
is
deposited on the provisional assembly through electromagnetism. The use of
these
fluxing agents with aluminum heat exchangers promotes the dissociation and
disruption of the native aluminum oxide (AI203). Then, the provisional
assembly is
introduced in a controlled environment where vacuum is created. Nitrcigen is
introduced and the temperature in the controlled environment is increased to
approximately 400-450 F (approximately 200 and 230 C) for a pre-heating
step.
Following the pre-heating step, the provisional assembly is brazed as
mentioned
above. The brazed assembly is then cooled in the controlled environment, under
nitrogen, wherein the temperature is lowered to approximately 400 F. Finally,
the
brazed assembly is removed from the controlled environment and cooled to
ambient
temperature under forced air convection.
Then, the tank covers are mounted to a respective header plate and secured
thereto
74. In an embodiment, the peripheral edges of the tank covers are secured to
the
outer face of the header plate, proximate to external edges of the header
plate, to
define the tank cavity. The peripheral edges can be welded to the header plate
for
securing the tank covers.
Finally, the side plates are sawed to create dilatation joints 54 (Fig. 1)
therein 76. It is
appreciated that, in an alternative embodiment, the dilatation joints can be
sawed
before securing the tank cover to the brazed assembly.
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In an alternative embodiment, the provisional assembly can include tank
covers. The
tank covers are thus secured by brazing simultaneously with the other
components.
They can also be welded to the header plates prior to the brazing step.
The heat exchanger tubes, the corrugated fins, and the headers 16 are made of
an
aluminum alloy adapted for heat exchanger applications. For example and
without
being limitative, they can be made of AA 3003. The heat exchanger tubes, the
corrugated fins, and the header plates include a surface clad. For example and
without being limitative, the clad material can be 4000 series aluminum. It is
appreciated that, in alternative embodiments, other aluminum alloys adapted
for heat
exchanger and brazing applications can be used.
The header plates can either have a clad on both sides or on only one side,
either
the inner surface or the outer surface. Similarly, the corrugated fins can
have a clad
on both sides or on only one side. The outer surface of the heat exchanger
tubes
includes the clad material. The clad material can represent between 2 and 15 %
of
the heat exchanger component thickness. In an alternative embodiment, the clad
material can represent between 5 and 10 % of the heat exchanger corriponent
thickness.
In a non-limitative embodiment, the header plates are rectangular with a
length
ranging between 75 and 1020 millimeters (mm) (2.95 and 40.0 inches), a width
ranging between 12.7 and 180 mm (0.5 and 7.0 inches), and a thickness ranging
between 2.0 and 12.7 mm (0.08 and 0.5 inch). In an alternative embodiment, the
header plates have a length ranging between 100 and 950 mm (4 and 37.5
inches),
a width ranging between 19 and 170 mm (0.75 and 6.75 inches), and a thickness
ranging between 2.5 and 10 mm (0.1 and 0.4 inch).
In an embodiment, the heat exchanger tubes have a cross section length (major
diameter) ranging between 19 and 120 mm (0.75 and 4.8 inches) and a cross-
section width (minor diameter) ranging between 2 and 12 mm (0.08 and 0.5
inch). In
an alternative embodiment, the heat exchanger tubes have a cross section
length
ranging between 25 and 80 mm (1.0 and 3.15 inches) and a cross-section width
ranging between 3.7 and 7 mm (0.15 and 0.28 inch).
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In an embodiment, the thickness of the heat exchanger tube wall ranges between
0.1 and 3.6 mm (0.004 and 0.14 inch) and in an alternative embodiment, the
thickness of the heat exchanger wall ranges between 0.2 and 3.2 mm (0.008 and
0.125 inch). In an embodiment, the thickness of the heat exchanger tube wall
can
vary along the tube length.
In an embodiment, the distance between the external edges of the header plate
and
the outermost heat exchanger tubes ranges between 1.3 and 3.2 mm (0.05 and
0.125 inch). In an alternative embodiment, this distance ranges between 1.3
and 6.4
mm (0.05 and 0.25 inch).
As mentioned above, the thickness of the header plates ranges between 2.0 and
12.7 mm (0.08 and 0.50 inch). In comparison with the headers of prior art heat
exchangers, the header plate is thicker, providing an increased stiffness to
the
resulting heat exchanger and a stronger physical bond between the heat
exchanger
tubes and the header plate since brazing occurs on a larger surface area. The
resulting header plate and tube exchanger assembly can thus support higher
pressure.
Moreover, the outermost heat exchanger tubes are mounted proximate to the
external edge of the header plate since the header plate is substantially
straight.
Thus, the moment arm between the junction of the exchanger tubes and the
header
plate and the external edges of the header plate is reduced. The resultirig
heat
exchangers have improved mechanical properties, such as higher pressure
resistance, stiffness, vibration resistance, and impact strength,
comparatively to prior
art heat exchangers.
Comparatively, to prior art heat exchangers wherein the tank cover is mounted
inwardly of the header plates having turn up edges, the heat exchanger has a
higher
burst pressure strength. For example, in an embodiment, the heat exchanger
withstood 1825 psi comparatively to 580 psi for the prior art heat exchanger.
Moreover, the heat exchanger did not show any cracking comparatively to the
prior
art heat exchanger which showed cracking at 300 psi.
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It is appreciated that the heat exchangers described above can be used in
radiators,
compressors, fuel coolers, conditioned air units, air-to-air heat exchangers
(charge
air coolers), oil coolers, and the like.
It can be used in new products (OEM) or replacement products.
The embodiments of the invention described above are intended to be exemplary
only. For example, the shape of the heat exchanger tubes can vary and the
shape
of the insertion slots can vary accordingly. Furthermore and without being
limitative,
the shape of the headers can vary. The position of fluid inlet and outlet
connectors
can be modified from the one described above in reference to Fig. 1, which is
typically associated with oil coolers. For example and without being
limitative, for
radiators and charge air coolers, the fluid inlet and outlet connectors can be
centrally
mounted to a respective hollow header.
The scope of the invention is therefore intended to be limited solely by the
scope of
the appended claims.
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