U.S. patent application number 09/814508 was filed with the patent office on 2004-09-23 for heat exchanger tube.
Invention is credited to Anders, James, Beamer, Henry Earl, Kent, Scott Edward.
Application Number | 20040182559 09/814508 |
Document ID | / |
Family ID | 25215254 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040182559 |
Kind Code |
A1 |
Kent, Scott Edward ; et
al. |
September 23, 2004 |
HEAT EXCHANGER TUBE
Abstract
A folded heat exchanger tube (10) of the type that is rigidified
with a pair of abutted 90 degree walls (16) extending along the
interior length thereof, so as to join the lower (12) and upper
(14) walls thereof, has a separate inner web member (20) anchored
and fixed inside between a pair of curved, out turned feet (18) on
the abutted walls (16) and the inner surface of the lower wall
(12). A widened and flattened central channel (24) in the web (20)
is engaged by the under surfaces of the curved feet (18), and is
approximately as wide as the total width of the tow feet (18).
Inventors: |
Kent, Scott Edward; (Albion,
NY) ; Anders, James; (Williamsville, NY) ;
Beamer, Henry Earl; (Middleport, NY) |
Correspondence
Address: |
DELPHI TECHNOLOGIES, INC.
M/C 480-410-202
PO BOX 5052
TROY
MI
48007
US
|
Family ID: |
25215254 |
Appl. No.: |
09/814508 |
Filed: |
March 22, 2001 |
Current U.S.
Class: |
165/183 ;
165/177 |
Current CPC
Class: |
B21C 37/225 20130101;
F28F 3/025 20130101; F28D 1/0391 20130101 |
Class at
Publication: |
165/183 ;
165/177 |
International
Class: |
F28F 001/00; F28F
001/14; F28F 001/36 |
Claims
1. A heat exchanger tube (10) comprising an outer shell having a
lower wall (12), a pair of integral upper walls (14) spaced
therefrom, and a pair of abutted walls (16) brazed together that
are integral to and perpendicular to said upper walls (14),
characterized in that, each of said abutted walls (14) has an out
turned foot (18) integral thereto having a curved undersurface and
a predetermined width (F) and, a separate inner web (20) has a
series of corrugations (22) brazed between the inner surfaces of
said lower tube wall (12) and said upper tube walls (14) and a
flattened intermediate channel (24) having a width (C)
substantially equal to twice the width (F) of said out turned foot
(18), with said channel (24) being anchored between, and brazed to,
the curved undersurfaces of said out turned feet (18) and the inner
surface of said lower wall (12), thereby indirectly joining said
upper walls (14) to said lower wall (12) with said abutted walls
(16) as well as dividing said channel (24) into a pair of flow
passages within said tube (10).
2. A heat exchanger tube according to claim 2, further
characterized in that said abutted walls (16) are centrally located
within said tube (10) and said channel (24) is centrally located
within said web (20).
3. A heat exchanger according to claim 1, further characterized in
that said tube lower (12) and upper (14) walls are coated with
braze material on both the inner and outer surfaces thereof.
4. A heat exchanger according to claim 1, further characterized in
that said tube lower (12) and upper (14) walls are coated with
braze material on only the outer surface thereof, and said web (20)
is coated with braze material on both the upper and lower surfaces
thereof.
Description
TECHNICAL FIELD
[0001] This invention relates to heat exchangers in general, and
specifically to a novel construction for a fabricated heat
exchanger tube.
BACKGROUND OF THE INVENTION
[0002] Cross flow automotive heat exchangers, such as radiators,
condensers, and heater cores have, for decades, followed the same
general design of a basic core bordered by two side tanks or header
tanks. The basic core consists of a plurality of parallel flow
tubes, stacked with brazed corrugated air fins between, the ends of
which tubes are brazed leak tight into regularly spaced slots in
the header tanks. The header tanks feed a flow medium into and out
of the tubes, while air is blown across the tubes and air fins in a
perpendicular or "cross" flow direction. Basic flow and heat
transfer formula, also well known for decades, determine the
optimum size of the flow tubes, as well, so that the biggest choice
that a designer has to make is simply the best and most economical
method of manufacturing the tubes. That choice, in turn, is
partially driven by the method of assembling and manufacturing the
core.
[0003] One of the two standard manufacturing methods for the tubes
are the one piece extruded tube, in which a billet of hot metal,
generally aluminum, is forced through a die that gives a constant
cross section to the tube all along its length. Any part, produced
in one, integral piece is generally thought to be more economical
than a multi part piece, but, as noted, other considerations may
apply. Extruded tubes have proven difficult to surface coat with
braze material. Consequently, the surface coating of braze material
necessary to braze all parts of the core together must generally be
applied to the corrugated fin material that contacts the outside of
the extruded, one piece tube. Such braze material is abrasive and
deleterious to the fin forming machinery, and the fin material must
be made thicker and heavier than otherwise needed in order to allow
successful braze material coating. Fabricated, multi piece tubes,
on the other hand, are formed from flat stock that can easily be
coated with braze material first, obviating the need to coat the
fins.
[0004] In the case of tubes that are subjected to a fairly high
internal pressure, it has been the practice to incorporate an
internal strengthening member inside the tube, to act in tension to
hold the walls together. Such members also divide the tube interior
into multiple, smaller passages, with the obvious improvement in
heat transfer that results therefrom. Extruded tubes use simple,
integral dividing and strengthening ribs, which cannot practically
be made as anything but straight, uninterrupted walls. Fabricated
high pressure tubes have far more potential design variations,
since the internal member can be, but need not absolutely be, made
as a separate piece. In addition, the outer shell or walls of the
tube can and has been made in a variety of ways, which are outlined
below.
[0005] The simplest design for a fabricated tube that does not need
internal reinforcement for internal pressure resistance is simply a
folded shell, with a live hinge on one side and a seam on the
other. An example may be seen in U.S. Pat. No. 4,470,452. Adding a
corrugated web on the inside can easily be done before the tube is
folded, as seen in Japanese patent 57-66389, a patent which also
illustrates the equivalence between the extruded and fabricated
tube design. A design that attempts to combine the advantages of
fabricated and extruded designs uses a single piece of metal stock
folded in a general Z shape, with the center of the Z being
corrugated to provide the inner web, and the top and bottom of the
Z folded down over the center corrugation from opposite directions
to form integral outer walls of the tube. An example may be seen in
U.S. Pat. No. 2,757,628. While one piece, such a design is limited
insofar as both the central corrugation and top and bottom walls
must have the same material and thickness, meaning that the
integral internal web may well be thicker and heavier than it would
otherwise have to be. In addition, the internal web will inevitably
be coated with the same braze material as the outer integral walls.
A variation of the Z design bends the two outer walls only half way
down over the width of the tube, into abutment with a single
central wall, giving only two, rather than several, divided
compartments in the tube. An example is shown in U.S. Pat. No.
4,633,056, which also shows that the edges of the outer walls,
where they are brazed to the single central wall, may either be
sharp, or bent over in a curved foot, the latter obviously giving
more surface to surface braze contact, although requiring an extra
bending step in processing.
[0006] Very early on, it was recognized that a simple, strengthened
version of the hollow fabricated tube, divided into n distinct
chambers, could be made with (n-1) separate pieces of metal stock
by bending the separate pieces over with short 90 degree inner
walls welded to one another along the surface, with edges that abut
the inner surface of the tube. As such, the welded inner walls act
as spacers and strengtheners for the tube as a whole. An example
may be seen in UK patent 1,149,923. The simplest version of this
basic design is simply two (n) chambers, with only one (n-1) piece
of metal stock, bent back on itself to the center in a general B
shape, with only two adjacent 90 degree inner walls, centrally
located. While this simple design does not provide particularly
compact flow paths, it is stronger than a single chamber, hollow
tube. With the later common use of braze material coated metal
stock, it was possible to eliminate the separate welding step for
the abutted 90 degree edges, which would naturally braze to one
another as the surface material melted, as shown in published
Japanese Patent Application 63242432A. While the design shown there
uses sharp edged inner walls, it is also known to provide inwardly
bent feet to the otherwise sharp edges. These may be either curved
feet, as taught by U.S. Pat. No. 4,633,056 noted above, or
perpendicular and flattened feet, as shown in U.S. Pat. No.
6,004,461. Compared to sharp edges, the integral, outwardly bent
feet provide more surface in mutual contact between the central
stiffening walls and the opposed inner surface of the tube.
[0007] It is also known to incorporate an integral corrugation
within the basic B tube design, analogous to the integral
corrugation in the simple folded tube of U.S. Pat. No. 2,757,628.
An example may be seen in U.S. Pat. No. 5,441,106, in which the
inwardly bent curved feet described above are, in effect, extended
on out to create two halves of an internal web. Such a design has
the same basic drawbacks as the integral corrugation design shown
in U.S. Pat. No. 2,757,628, in that the inner web and outer walls
must be of the same thickness and material, and will be inevitably
coated with braze material, as well. A common feature of internal
corrugated webs in all fabricated tubes, so far as is known, is
that the corrugations are regular or symmetric. This gives both a
uniform size for all of the flow paths (but for the outboard pair,
which are often inevitably smaller in cross section), and gives a
uniform internal pressure resistance to the tube all across its
width.
SUMMARY OF THE INVENTION
[0008] The invention is a novel tube construction that has the
central strengthening feature of the B tube design described above,
but with divided flow paths provided by a specially designed,
separate inner corrugated web.
[0009] In the preferred embodiment disclosed, the outer shell of
the tube is formed in a general "B" shape, with two 90 degree walls
that abut at the center. Preferably, the edges of the abutting 90
degree walls are curved upwardly, rather than being sharp. Unlike
other fabricated tubes, however, the edges of the 90 degree walls
do not directly contact the inner surface of the tube. Instead, a
corrugated inner web is placed inside the tube as it is folded
down, and is captured between the under surface of the 90 degree
wall edges and the opposed inner surface of the tube. The
corrugated web, rather than being regular and symmetric, has a
widened and flattened central channel that allows it to be captured
without deforming the corrugations to either side. Preferably, both
the inner and outer surfaces of the outer tube are braze coated, so
that the inner web need not be.
[0010] In the braze operation, one side of the web channel brazes
to the undersurface of the 90 degree wall edges, and the other side
of the web channel brazes to the opposed inner surface of the tube,
solidly anchoring and locating the web within the tube. The net
effect is that the abutted 90 degree walls strengthen the tube,
even without direct contact across both sides of the tube. The web
can be formed with any desired thickness, independent of the outer
tube wall thickness and, as noted, need not be braze coated, though
it can be. Small, divided flow paths inside the tube are created
both by the regular corrugations located to either side of the
central web channel, and by the location of the abutted 90 degree
walls within the central web channel. The decoupling of the web and
tube material allows the optimal material to be independently used
for both, but the end result is similar to a one piece extruded
tube in terms of strength and function.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] These and other features of the invention will appear from
the following written description, and from the drawings, in
which:
[0012] FIG. 1 is a perspective view of the end of a preferred
embodiment of a tube made according to the invention;
[0013] FIG. 2 is an end view of a piece of tube stock prior to the
manufacturing operation;
[0014] FIG. 3 is an end view of the tube stock after a first
bending operation;
[0015] FIG. 4 is an end view of the tube stock after a second
bending operation;
[0016] FIG. 5 is an end view of the tube stock after a third
bending operation;
[0017] FIG. 6 is an end view of the tube stock after a fourth
bending operation, and showing the web;
[0018] FIG. 7 is an end view of the tube stock after a fifth
bending operation, and showing the web in place;
[0019] FIG. 8 is an end view of the tube stock after a sixth
bending operation, and showing the web in place and anchored
down.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] Referring first to FIG. 1, an end view of a preferred
embodiment of a tube according to the invention, indicated
generally at 10. Tube 10 is a brazed, fabricated tube, having only
two basic components, one of which is an outer shell formed with
two inner chambers, like the so called "B tube" configuration
described in UK patent 1,149,923 noted above. As such, n=2 (the
number of inner chambers), and only n-1, or one, piece of tube
stock is needed to form the outer shell, in a manner described in
more detail below. Specifically, the outer shell, though unitary,
can be conceptualized as a single, full width lower wall 12 spaced
from a pair of upper walls 14 which preferably, but not
necessarily, are equal in width. Upper walls 14 are integral to a
pair of equal height, abutted 90 degree walls 16, each of which
terminates in a curved, out turned foot 18. The abutted 90 degree
walls 16 form a central seam running the entire length of the outer
shell of tube 10, and form a central strengthening member therefor.
While the coincidental provision of two divided chambers within
tube 10 would provide some heat transfer advantage, by the obvious
expedient of providing a greater ratio of conductive perimeter
surface per enclosed volume, that effect is minimal, for such a
minimal subdivision of the inner volume. The primary advantage of
the abutted 90 degree walls 16, as in the UK patent noted above, is
simply the additional stiffening and strengthening and outer shell,
and the location of the inevitable at least one seam down the
central upper surface of the tube 10, rather than down the side
edge. The end of tube 10 is ultimately brazed into a header slot,
as with any headered cross flow heat exchanger, and it is easier to
control the geometry of the slot-tube end braze interface along the
width of the slot, rather than at the edge of the slot.
[0021] Referring next to FIGS. 1 and 5, the other basic component
of tube 10 is a corrugated inner web, a preferred embodiment of
which is indicated generally at 20. Web 20 would likely be same
basic material as the outer shell of tube 10, or at least similar
enough to prevent a significant galvanic differential. However, web
20 need not be identical to the outer shell of tube 10, since it is
not integral therewith. Therefore, it can be, preferably, thinner,
as shown, and need not be coated with braze material on its outer
surface (though it can be, as described in more detail below).
Specifically, web 20 has a width W1 and is formed with a series of
corrugations 22 which may be, but need not be, generally sinusoidal
and regular in shape, with rounded crests and sloped sides. They
could also be more pointed at the crests, or completely squared off
with vertical sides, if desired. Most significantly, the entire
width of web 20 is not comprised of regular, symmetrical
corrugations, as is conventional. Instead, a widened, intermediate
channel 24 of width C, is formed, which is flattened at the bottom,
and open at the top, for a purpose described below. Preferably, the
channel 24 is also central to the web 20, with an equal number of
regular corrugations 22 located to either side, though, again, it
need not absolutely be centrally located.
[0022] Referring next to FIGS. 2 through 5, the initial steps in
the manufacture of the outer shell of tube 10 are illustrated. A
single, flat piece of flat metal stock S is braze coated on at
least one surface, that which will ultimately comprise the outer
surface of tube 10 and, preferably, on the other surface, as well,
though not necessarily on more than the outer surface. Most likely,
stock S would be pulled from a continuous coil of stock, and run
through a progressive series of rollers, that would continually and
gradually form it into the subsequent shapes illustrated, rather
than being bent incrementally in individual dies. The first step in
the gradual formation of the final shell shape is the bending of
the curved feet 18, each of which has a total width F, shown in
FIG. 3. Next, as shown in FIG. 4, the 90 degree walls 16 are bent
to shape, each with a total height H, which will ultimately
determine the inner height of final tube 10. The two upper walls 14
are partially bent up, leaving the lower wall 12 in the center. As
disclosed, each upper wall 14 is preferably one half the total
outside width W2 of lower wall 12, "upper" and "lower" being terms
of convenience, of course. Before the upper walls 14 are bent too
close together to prevent it, web 20 would be fed in between them
by a suitable apparatus.
[0023] Referring next to FIGS. 6 through 8, after the web 20 is fed
in, the upper walls 14 are bent progressively farther over and,
eventually, the web 20 settles onto the inner surface of lower wall
12. The web width W1 is comparable to the width W2 of lower wall
12, less by approximately twice the wall thickness of stock S, so
as to facilitate the location of web 20 inside of tube 10.
Eventually, the upper walls 14 are bent over far enough to abut,
and the under surfaces of the feet 18 pass by the crests of the two
inner most corrugations 22 and down to engage the upper surface of
web channel 24, anchoring its lower surface to the inner surface of
lower wall 12. The height H of the 90 degree walls 16, added to the
thickness of the material of web 20, is set so as to assure that
the tops and bottoms of the web corrugations 22 make close contact,
without crushing, with the inner surfaces of both the upper walls
14 and the lower wall 12. The total width of the out turned feet 18
is just slightly less than the width C of web channel 24, so as to
assure a close fit into the channel 24 without binding, but still
serving to help positively locate the web 20 accurately within the
interior of tube 10, with a limited side to side play.
[0024] Referring finally to FIGS. 1 and 8, the fully nested and
abutted composite of the bent metal stock S and separate, anchored
inner web 20 are brazed together in a conventional braze oven to
complete tube 10. This is best done as part of an entire core with
tubes 10. As is typical, braze material melted from and near the
interfaces of the abutted component surfaces is drawn by capillary
action into those closely abutted interfaces, later hardening to
create strong bonds. There are several possible combinations for
the braze coating of these contacting surfaces. Both surfaces of
the tube stock S could be coated, and web 20 not at all. Or, only
the outer surface of the tube stock S could be coated, and both
sides of the web 20 coated. When a total core is brazed, clad
material on the air centers could provide what was needed for a
bolted walls 16, so bare tube stock S could be used. Or, all
surfaces could be coated, on both. Any such combination would
provide a supply of melted braze material to the various
interfaces. For example, the under surfaces of the feet 18 would
braze to the upper surface of the flattened channel 24, and the
under surface of channel 24 would braze to the inner surface of
tube lower wall 12, ultimately securing the upper walls 14 to the
lower wall 12. The abutted 90 degree walls alone 16 add a degree of
strengthening to the tube 10, and the presence of the intermediate
bonded corrugations add to that strengthening, depending on the
thickness of the material of web 20. That thickness cannot be
varied in the design shown in U.S. Pat. No. 5,441,106, where the
thickness of outer shell and inner web are inevitably the same. One
of the advantages of decoupling the outer shell from the inner web
is that, for example, a very thin web 20 could be used in a low
pressure tube, where additional strength was not needed. Another
advantage is the ability to not coat the web 20 with the rather
abrasive braze material that tends to wear on the machines that
typically produce corrugations like 22. Regardless of the thickness
and consequent inner pressure resistance potential of web 20, it
serves to subdivide the interior of tube 10 into multiple flow
paths, with the attendant increase in the ratio of conductive
surface area (wetted perimeter) to flow area that improves
efficiency. The location of the abutted 90 degree walls, within the
web channel 24, serves to produce two subdivided flow channels, in
and of itself.
[0025] Variations of the preferred embodiment disclosed could be
made. The width F of the curved feet 18 could be varied, in
absolute terms, but making the width of the feet 18 together
approximately equal to the width of two corrugations 22 serves to
subdivide the channel 24 into two flow paths approximately equal to
the size of the flow paths created by each of the corrugations 22,
and so yields a measure of structural symmetry across the entire
width of tube 10. The degree of curvature of the feet 18 could be
made more or less, but flattened edges, or sharp edges, instead of
a curvature would not be preferred. Such edges would not braze as
well to the upper surface of the channel 24, and would not be as
likely to fold past the adjacent web corrugations 22 without
binding as the upper walls 14 were folded down. As disclosed, the
abutted 90 degree walls are central, and the upper walls 12
consequently of equal width, but they could be shifted to one side
or the other, if desired, especially if the relative width of the
feet 18 and the corrugations 22 noted above were maintained, since
the effect on the inner structural symmetry of the tube 10 would
not be severe. Therefore, it will be understood that it is not
intended to limit the invention to just the embodiment
disclosed.
* * * * *