U.S. patent number 3,662,582 [Application Number 05/038,132] was granted by the patent office on 1972-05-16 for heat-exchange tubing and method of making it.
This patent grant is currently assigned to Noranda Metal Industries Inc.. Invention is credited to Fred W. French.
United States Patent |
3,662,582 |
French |
May 16, 1972 |
HEAT-EXCHANGE TUBING AND METHOD OF MAKING IT
Abstract
Heat-exchange tubing with a peripheral wall of oblong
cross-section, and inner fins on the wall of which the fins on
either of two opposite flat wall sections extend with their tips at
least to the level of the tips of the fins on the other flat wall
section, and a method of forming the tubing from a round inner-fin
tube blank, involving partially flattening the round blank into the
tubing with its peripheral wall of oblong cross-section.
Inventors: |
French; Fred W. (Morris,
CT) |
Assignee: |
Noranda Metal Industries Inc.
(N/A)
|
Family
ID: |
27184145 |
Appl.
No.: |
05/038,132 |
Filed: |
May 18, 1970 |
Current U.S.
Class: |
72/370.17;
29/890.046; 165/177 |
Current CPC
Class: |
F28F
1/42 (20130101); B21C 37/207 (20130101); F28F
1/424 (20130101); B21C 37/20 (20130101); F28F
1/40 (20130101); F28F 1/022 (20130101); F28F
1/422 (20130101); B21C 37/202 (20130101); F28F
1/02 (20130101); F28D 7/024 (20130101); F28F
1/025 (20130101); B21C 37/15 (20130101); G11C
7/1048 (20130101); Y10T 29/49378 (20150115) |
Current International
Class: |
F28F
1/40 (20060101); G11C 7/10 (20060101); F28F
1/02 (20060101); F28F 1/42 (20060101); F28D
7/02 (20060101); F28D 7/00 (20060101); F28F
1/10 (20060101); B21C 37/20 (20060101); B21C
37/15 (20060101); B21d 053/06 () |
Field of
Search: |
;72/256,367
;29/157.3A,157.3AH,157.3B ;113/118A,118B ;165/177,179 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Larson; Lowell A.
Claims
I claim:
1. Method of forming longitudinal heat-exchange tubing, which
comprises providing a round metal tube blank having an axis, a
peripheral wall about said axis, and longitudinal inner-fins on
said wall, with said fins being of equal height and spaced from
said axis; and forming the entire interior of the blank into
individual flow channels of a depth within the height of the fins,
by partially flattening the blank from two opposite sides into
oblong cross-section with two opposite flat parallel wall sections
at a spacing at which the fins on one flat wall section extend with
their tips at least to the level of the tips of the fins on the
other flat wall section.
2. Method of forming longitudinal heat-exchange tubing as in claim
1, in which the fins on the peripheral wall of the round tube blank
extend helically thereof at the same helix angle, whereby in said
partial flattening of the blank the fins on said flat wall sections
are extended straight and are inclined to and cross each other.
3. Method of forming longitudinal heat-exchange tubing as in claim
2, in which the blank is partially flattened until the fins on
either flat wall section extend with their tips beyond the level of
the tips of the fins on the other flat wall section but are spaced
from the latter, and metal of the fins on the flat wall sections,
respectively, is displaced at their crossings for interpress of the
fins at their crossings into interlock with each other.
4. Method of forming longitudinal heat-exchange tubing as in claim
1, in which the tubing is subsequently bent into curved extension
longitudinally thereof.
5. Method of forming longitudinal heat-exchange tubing as in claim
1, in which the flat wall sections are subsequently bent into
transversely-curved parallel disposition.
6. Method of forming longitudinal heat-exchange tubing as in claim
1, in which the tubing is subsequently bent longitudinally into
successive helical turns.
7. Longitudinal heat-exchange tubing as in claim 2, in which the
fins on the respective flat wall sections are brazed together at
their crossings.
8. Method of forming longitudinal heat-exchange tubing as in claim
2, which further comprises, in the course of partially flattening
the blank and before the fins on one flat wall section extend with
their tips to the level of the tips of the fins on the other flat
wall section, inserting between the tips of the fins on said flat
wall sections, respectively, a longitudinal metal brazing strip;
and subsequent to the partial flattening of the blank heating the
tubing to melt said strip and thereby braze the fins together at
their crossings.
Description
This invention relates to heat-exchange tubing in general, and to
finned heat-exchange tubing in particular.
The type of heat-exchange tubing with which the present invention
is concerned is provided with inwardly extending fins, or so-called
"inner" fins, on its peripheral wall. Tubing of this type is well
known for its heat-exchange properties which vary from good to
excellent, depending on the inner-fin pattern and size, the
particular heat-exchange application, and other factors. However,
even this type of tubing does not lend itself to certain exacting
heat-exchange requirements for various applications. There are
several reasons for this, and chief among them is that
heat-exchange of the fins and also peripheral wall of such tubing
with fluid passing through the latter is inadequate for certain
purposes regardless of the height and number of the fins.
It is the primary object of the present invention to provide
heat-exchange tubing of this type which meets many exacting
heat-exchange requirements that cannot be met by the aforementioned
known inner-fin tubing.
It is another object of the present invention to provide
heat-exchange tubing of this type of which the peripheral wall and
the inner fins are arranged to divide the entire interior of the
tubing into individual flow channels of a number, depth and width
to best meet specified heat-exchange requirements as well as other
requirements, such as a specified volumetric flow rate of a fluid
through the tubing, or to keep pressure drop of the fluid in the
tubing within specified limits, for example.
It is a further object of the present invention to provide
heat-exchange tubing of this type the interior of which is divided
into flow channels for meeting various specific, including
heat-exchange, requirements as aforementioned, by making the
peripheral wall generally oblong in cross-section, with the same
providing two opposite flat wall sections and opposite return wall
sections which join the flat wall sections, and the fins on either
flat wall section extend with their tips at least to the level of
the tips of the inner fins on the other flat wall section. It is
thus within the wide parameters of oblong cross-section of the
peripheral wall and the number, height and spacing of the fins,
that a great variety of heat-exchange tubing for many different
applications may be fashioned.
Another object of the present invention is to devise a method of
forming heat-exchange tubing of this type, which comprises
providing a round inner-fin tube blank, and partially flattening
the blank into the aforementioned oblong cross-section of its
peripheral wall at which the fins on either one of the then
opposite flat wall sections extend with their tips at least to the
level of the tips of the fins on the other flat wall section. In
thus forming the heat-exchange tubing, which may aptly be termed
"flat" tubing, the number, height, spacing and direction of the
fins therein may be selected from the wide variety of fin patterns
and sizes which may readily be formed in round tubular blanks
according to different known methods, but which could hardly, and
never practically, be formed in flat tubing. Moreover, extreme
simplicity characterizes the reformation of a round inner-fin tube
blank into flat tubing of this kind in accordance with the present
method, as by passing the round blank between rotary companion
rolls or drawing the same through a die, all in a single pass, for
example. Moreover, reformation in this fashion of a round tube
blank particularly with helical inner fins into flat tubing of this
type brings the fins into an entirely new and extremely effective
cooperative relation, in that the then-straight fins on the
respective flat wall sections abut and are inclined to and cross
each other, with the result that these fins sharply divide and
divert into different directions at each cross-section of the
tubing much of the fluid flowing through the entirely finned
passage in the tubing.
A further object of the present invention is to provide flat tubing
of this type whose heat-exchange with a fluid passing therethrough
is further enhanced, in that in the aforementioned partial
flattening of a round inner-fin tube blank into the flat tubing,
the flat opposite wall sections are spaced apart a distance at
which the fins on either flat wall section extend with their tips
beyond the level of the tips of the fins on the opposite flat wall
section but remain spaced from the latter. With this arrangement,
the path of fluid through the tubing is even more tortuous past the
fins therein especially where the fins on the opposite flat wall
sections cross each other, involving additional diversion of fluid
within the channels between successive fins over the tips of
opposite fins projecting within the confines of the channels.
Further, where the fins on the opposite flat wall sections are
inclined to and cross each other, the fins will over the extent of
their interpress at their crossings readily give way in denting and
there interlock without distorting the fin pattern.
It is another object of the present invention to provide
heat-exchange tubing of this type which, if desired, may have
graduated heat-exchange properties over different lengths or from
one end to the other end, by simply partially flattening a round
inner-fin tube blank to different extents so that the sets of inner
fins on the respective flat opposite wall sections vary in their
relative projection from level at their tips to
interprojection.
It is a further object of the present invention to form
heat-exchange tubing of this type according to the aforementioned
method, and which is subsequently further deformed in
cross-sectionally or longitudinally curved fashion, thereby to
reenforce the tubing against spread-apart of their opposite flat
wall sections under pressure from fluid passing through the
tubing.
Another object of the present invention is to provide heat-exchange
tubing of this type which for any, and even exceptional, length
and, hence, heat-exchange capacity, may be of very condensed
lengthwise construction, by lengthwise bending the tubing into more
or less closely adjacent, successive helical turns, as around a
cylindrical mandrel, for instance.
It is another object of the present invention to provide
heat-exchange tubing of this type which is formed, according to the
aforementioned method, from a round tube blank with inner and outer
fins, so that the tubing has by virtue of the additional outer fins
further enhanced heat-exchange properties. The outer fins on the
round tube blank may longitudinally extend parallel to, or
helically about, the tube axis, with neither axial nor helical
outer fins interfering with orderly partial flattening of the blank
on providing for suitable clearance of the outer fins in the
blank-flattening tooling.
Further objects and advantages will appear to those skilled in the
art from the following, considered in conjunction with the
accompanying drawings.
In the accompanying drawings, in which certain modes of carrying
out the present invention are shown for illustrative purposes:
FIG. 1 is a plan view of heat-exchange tubing embodying the
invention;
FIGS. 2 and 3 are sections through the tubing taken on the lines
2--2 and 3--3, respectively, in FIGS. 1 and 2;
FIG. 4 is a cross-section through a round inner-fin tube blank from
which the tubing of FIGS. 1 to 3 is fashioned;
FIG. 5 is a section through the tube blank on the line 5--5 in FIG.
4;
FIG. 6 is a cross-section through heat-exchange tubing embodying
the invention in a modified manner;
FIG. 7 is a section through the modified tubing substantially along
the line 7--7 in FIG. 6;
FIG. 8 is an enlarged section through part of the modified tubing
substantially along the line 8--8 of FIG. 7;
FIG. 9 is a cross-section through heat-exchange tubing embodying
the invention in another modified manner;
FIG. 10 is a section through the modified tubing of FIG. 9 along
the line 10--10 thereof;
FIG. 11 is a cross-section through heat-exchange tubing embodying
the invention in a further modified manner;
FIG. 12 demonstrates a step in the formation of heat-exchange
tubing according to a method which also embodies the invention;
FIG. 13 demonstrates a modified step in the formation of
heat-exchange tubing according to a method of the invention;
FIG. 14 is a cross-section through heat-exchange tubing of still
another modification;
FIG. 15 is a side view, partly in section, of a heat exchanger
embodying the featured tubing;
FIG. 16 is a section through the heat-exchanger along the line
16--16 in FIG. 15;
FIG. 17 is a side view, partly in section, of a modified
heat-exchanger embodying the featured tubing;
FIG. 18 is a view of the featured heat exchange tubing with a
longitudinal twist;
FIG. 19 is a section through the featured heat-exchange tubing
which is also cross-sectionally curved;
FIG. 20 is a perspective view of the featured heat-exchange tubing
which is also bent longitudinally into successive helical
turns;
FIG. 21 is a cross-section through heat-exchange tubing embodying
the invention in a further modified manner;
FIG. 22 is a cross-section through a round finned tube blank from
which the heat-exchange tubing of FIG. 21 is fashioned; and
FIG. 23 is a cross-section through heat-exchange tubing embodying
the invention in a still further modified manner.
Referring to the drawings, and more particularly to FIGS. 1 to 3
thereof, the reference numeral 10 designates heat-exchange tubing
having a peripheral metal wall 12 of oblong cross-section and a
multitude of metal fins 14 with tips 16. The peripheral wall 12
provides two flat opposite, and preferably parallel, wall sections
18, and opposite return wall sections 20 which join the flat wall
sections 18, with the flat wall sections 18 constituting in this
instance a far predominant part of the wall 12. The fins 14, which
project inwardly from the wall 12 and are preferably formed
integrally therewith, are of the same height which is such that the
fins on either flat wall section 18 extend with their tips 16 to
the level of the tips of the fins on the opposite flat wall section
(FIG. 2), so that the entire interior of the flat tubing is within
reach of the fins. Successive fins 14 on the wall 12 are preferably
equally spaced, and the fins on either flat wall section 18 extend
parallel to each other and at an inclination to the longitudinal
axis x of the tubing, with the fins on the respective wall sections
18 being also inclined to and crossing each other (FIG. 3).
With the interior of the flat tubing being within full reach of the
fins 14, the entire passage through the tubing is divided into
individual flow channels 22, which makes for good heat-exchange
between a fluid passing through the tubing and the fins 14 as well
as peripheral wall 12 of the tubing. Heat-exchange between such
fluid and the fins and peripheral wall of the tubing is even
enhanced by the inclination to each other of the channels 22 on the
opposite flat wall sections 18 (FIG. 3), in that they sharply
divide and divert into different channels much of the fluid passing
therein at each cross-section of the tubing.
The "flat" metal tubing 10 is advantageously formed from a round
inner-fin tube blank 24 (FIGS. 4 and 5) in accordance with an
exceedingly simple method. For reasons more fully apparent
hereinafter, the peripheral wall of the blank 24 is of the same
thickness and peripheral extent as the wall 12 of the flat tubing
10, and the fins of the blank are of the same height and thickness,
and also spaced, as the fins 14 of the tubing, wherefore the
peripheral wall and fins of the blank are appropriately designated
by the reference numerals 12 and 14, respectively, i.e., the same
as their counterparts of the flat tubing. Further, the fins 14 on
the round wall 12 of the blank 24 extend longitudinally helically
at the same helix angle throughout (FIG. 5).
The inner-fin tube blank 24 itself may be formed in any known
manner, including brazing or otherwise joining inserted fins to the
round wall of the blank, but preferably by displacement, according
to different known methods, of metal from the wall of the blank
into grooves on a mandrel therein to form the fins 14 integral with
the wall. One such method is disclosed in my prior U.S. Pat. No.
3,422,518, dated Jan. 21, 1969, with this method involving
externally swaging a cylindrical tube blank against a grooved
mandrel therein in a single pass of the blank over and beyond the
mandrel, whereby metal from the blank wall is displaced into the
mandrel grooves to form the fins. This method is preferred, not
only because the same is highly efficient and readily lends itself
to the formation of an inner-fin tube blank of most any desired fin
pattern and size, but also because the swaging of the blank over
the mandrel entails quite extensive elongation of the blank. Such
extensive elongation of the blank and the formation of the fins
exclusively by metal from the blank wall entail a considerable
reduction of the wall thickness of the finished inner-fin tube
blank, which is highly advantageous in point of heat-exchange of
the tube wall, and hence also entire tube, with a surrounding
temperature-modifying medium, such as a coolant, for example.
The method of forming the inner-fin tube blank 24 into the flat
tubing 10 simply involves partially flattening the blank to form
opposite peripheral wall portions thereof into the flat parallel
wall sections 18, which concludes the formation of the flat tubing
10. Such partial flattening of the round blank 24 may be achieved
in any suitable manner, as by passing the blank between rotary
companion rolls 30 and 32 in the direction of the arrow 34 (FIG.
12), or by drawing the blank through a die 36 in the direction of
the arrow 38 (FIG. 13).
It follows from the preceding that the peripheral wall 12 of the
flat tubing 10 is indeed the same wall 12 of the blank 24 which
remains of the same thickness and peripheral extent. It is now also
apparent that the fins 14 of the blank 24 and of the flat tubing 10
are indeed the same and retain their height and thickness as well
as their spacing from each other. Further, in the course of
partially flattening the round blank 24, the helically extending
fins 14 will over the extent of the flat wall sections 18 of the
tubing be extended into straight disposition (FIG. 3).
To bring the fins 14 for all practical purposes within full reach
of the interior of the flat tubing 10, the fins in the round tube
blank must obviously be spaced some distance from the axis of the
blank. In this connection, it has been found that for a given
inside diameter of the blank, the fin height may vary widely from
less than the thickness of the peripheral blank wall to many times
such wall thickness, with the fins of any height within this wide
range being adequately spaced from the axis of the blank for its
formation into flat tubing in which the fins are within full reach
of the interior of the tubing. Within this wide range of fin
height, and with available round inner-fin tube blanks of many
different fin patterns and sizes, it is possible to obtain widely
different flat inner-fin tubing which not only has good
heat-exchange properties, but also meets other requirements, such
as a specified volumetric flow rate of fluid through the tubing, or
to keep pressure drop of passing fluid in the tubing within
prescribed limits, for example. Thus, the number of fins, also
their height within the above wide range, and the peripheral extent
of the wall, of flat tubing may vary widely to meet many different,
including heat-exchange, requirements. Insofar as the height of the
fins is concerned, the same is for many, but not all, applications
greater than the thickness of the peripheral wall of the
tubing.
Reference is now had to FIGS. 6 and 7 which show flat inner-fin
tubing 10a that basically differs from the described tubing 10 in
that the fins 14a on either flat wall section 18a extend with their
tips 16a beyond the level of the tips of the fins on the opposite
flat wall section but remain spaced from the latter. The flat
tubing 10a may otherwise be like the tubing 10 and, hence, formed
from the same round inner-fin tube blank 24 (FIGS. 4 and 5), with
the tubing 10a being formed by the same method as the tube 10,
except that the round blank is partially flattened to an extent at
which the fins on the opposite flat wall sections interproject. In
thus partially flattening the round blank, the fins 14a on the
opposite flat wall sections 18a are at, and over the extent of,
their crossings 40 interpressed and thereby interlocked due to
mutual denting of the fins thereat as at 42 (FIG. 8). Thus, due to
the mutual denting of the fins at their crossings in consequence of
partially flattening the round blank to the extent of part-way
interprojecting the fins on the opposite flat wall sections, the
fin pattern as such remains intact and is not distorted (FIG. 7).
Owing to the part-way interprojection of the fins in this tubing,
the fluid path therethrough is quite tortuous in any event, and may
even vary considerably with different degrees of interprojection of
the fins. Different interprojection of the fins is thus another
tool toward achieving good heat-exchange and meeting other widely
varying requirements, such as volumetric flow rate of a fluid
passing through the tubing, or to keep pressure drop of the passing
fluid within prescribed limits.
Reference is now had to FIGS. 9 and 10 which show flat
heat-exchange tubing 10b that is formed from a round inner-fin tube
blank (not shown) in which the fins extend parallel to the axis of
the blank. Thus, in partially flattening the round blank in
accordance with the present method, all the fins 14b in the flat
tubing extend parallel to the longitudinal axis xb. In this
exemplary flat tubing, the fins 14b on the opposite flat wall
sections 18b interproject to some extent, though it is entirely
obvious that by different partial flattening of the blank the fins
on the flat opposite wall sections 18b may interproject to a
different extent, or the tips of the fins on either flat wall
section 18b may with their tips extend to the level of the tips of
the fins on the other flat wall section 18b.
In the case of flat tubing in which the fins extend parallel to the
longitudinal axis of the tubing, as in FIGS. 9 and 10, it is also
feasible partially to flatten the round inner-fin tube blank to the
extent where the fins on either flat wall section extend with their
tips to the opposite flat wall section, with such heat-exchange
tubing 10c being shown in FIG. 11. In this tubing 10c, successive
fins 14c divide the interior of the tubing into flow channels 22c
which, in contrast to those in the described tubing 10, 10a and
10b, are closed to each other.
In the described flat heat-exchange tubing 10 to 10c, the two
opposite flat wall sections constitute the predominant part of the
peripheral wall of the tubing. While this is preferred for exacting
heat-exchange and also other requirements of many applications,
such as cooling the transmission oil of automotive vehicles, just
to mention one such application, the advantages of having the fins
within full reach of the interior of flat tubing are secured even
where the two flat opposite wall sections do not constitute a
predominant part, or even constitute less than one-half, of the
peripheral wall of the tubing. Thus, FIG. 14 shows flat
heat-exchange tubing 10d of which the flat opposite wall sections
18d constitute less than one-half of the peripheral wall 12d of the
tubing, with the round inner-fin tube blank (not shown) from which
the tubing is fashioned being, in accordance with the present
method, partially flattened to an exemplary extent at which the
fins 14d on either flat wall section 18d extend with their tips to
the level of the tips of the fins on the other flat wall section
18d. Further, the indicated fin height for the also indicated
peripheral extent and thickness of the wall of the tubing obviously
falls within the aforementioned fin-height range within which the
fins in flat tubing are brought within full reach of the interior
of the tubing.
Reference is now had to FIGS. 15 and 16 which show a heat-exchange
unit 50 using a length of piece 52 of the featured flat inner-fin
tubing, for example a piece of the flat tube 10a of FIGS. 6 and 7.
The opposite ends 54 and 56 of the tube piece 52 are in
communication with the interior of casings 58 and 60, with the tube
ends 54 and 56 being fitted in, and conveniently brazed to, slots
62 in the respective casings 58 and 60. The casings 58 and 60 have
tapped holes 64 and 66 for connection with conduits through which
to lead a fluid, liquid or gas, to and from the unit 50 for
temperature modification, such as cooling, for instance.
While in the described heat-exchange unit 50 the end casings 58 and
60 and their slots 62 are rectangular in section (FIG. 16), FIG. 17
shows a heat-exchange unit 70 of which the end casings 72 and 74
are circular in section. To this end, the length or piece 76 of
featured inner-fin tubing is, in its formation from a round
inner-fin tube blank, partially flattened only over its
longitudinal extent l so that opposite end lengths 78 and 80 of the
tubing remain cylindrical, and these cylindrical end lengths 78 and
80 are connected with the casings 72 and 74.
In many heat-exchange applications, the fluid passing through the
featured flat inner-fin tubing is under operating pressure which
may be sufficiently high to "open" the tubing by forcing the
opposite flat sections of the peripheral wall more or less apart,
such as the flat wall sections 18 to 18c of the described tubing 10
to 10c, for example, and thereby greatly reducing the heat-exchange
capacity of the tubing, if not rendering the tubing unfit for
further use in a particular heat-exchange application. Opening of
the tubing in this fashion and from this cause is in many cases
prevented by additionally curving the same longitudinally, or
transversely, or both, and thereby reenforcing the tubing against
such opening. Thus, a length 90 of the featured flat inner-fin
tubing may be twisted about its longitudinal axis x (FIG. 18),
whereby the tubing becomes curved, longitudinally as well as
transversely, over its lengthwise extent, and is thereby reenforced
against opening under internal pressure. The tube length 90 may be
twisted by forcing the same through a correspondingly twisting
opening in a die 92.
FIG. 19 shows a piece 94 of the featured flat inner-fin tubing
which is transversely curved for reenforcement against opening
under internal pressure. The initially flat tube piece 94 may to
this end be drawn through a die 96 with an opening of the outline
of the curved tubing.
FIG. 20 shows a piece 98 of the featured flat inner-fin tubing
which is longitudinally curved for reenforcement against opening
under internal pressure. This is achieved in this instance by
bending the flat tubing around a cylindrical arbor 100. The
exemplary tube piece 98 is of quite extensive length with
correspondingly large heat-exchange capacity, and in order greatly
to reduce the lengthwise expanse of the longitudinally curved
tubing, the tubing is bent around the arbor 100 in successive and
more or less closely adjacent helical turns 102.
While the flat heat-exchange tubing described so far has only
inner-fins, such flat tubing may have both, inner and outer fins.
Thus, FIG. 21 shows flat heat-exchange tubing 104 which has inner
and outer fins 106 and 108. The tubing 104 is, in accordance with
the present method, formed from the round inner-and outer-fin tube
blank 110 (FIG. 22). The outer fins 108 extend in this instance
parallel to the axis of the blank, but they may also extend
helically, with the partial flattening of the round tube blank into
the flat tubing being in either case entirely feasible on providing
companion flattening rolls, for example, with suitable slots for
clearing the outer fins.
Reference is now had to FIG. 23 which shows flat heat-exchange
tubing 10e that may be like the tubing 10 of FIG. 2, except that
there is interposed between the tips 16e of the fins 14e on the
opposite flat wall sections 18e a longitudinal strip 112 of any
suitable brazing material. One of these strip materials, which is
commercially available, is known to the trade as SIL-FOS and
manufactured by Handy and Harman. The brazing strip 112 is inserted
in the course of flattening the initially round inner-fin tube
blank into the flat tubing 10e, with the strip 112, which is shown
of exaggerated thickness for clarity's sake, being engaged by the
tips of the fins. The flat tubing 10e is then heated, as in a
furnace 114, for example, to melt the brazing strip 112 and brace
the fins together at their crossing tips, with the excess brazing
material spreading over nearby portions of the fins. The tubing
10e, being thus brazed together at the crossing tips of the fins,
will not open under operational, including particularly high,
internal fluid pressures. Brazing of flat tubing at the crossing
tips of the fins is indicated where higher internal operational
fluid pressures are involved, and especially for applications of
such tubing which require that the same remains flat and is not to
be curved for reenforcement against opening under internal fluid
pressure. Of course, brazing of flat tubing in this manner applies
as fully for tubing in which the inner-fins become interpressed in
the course of flattening the initially round inner-fin tube blank
into the flat tubing, as in FIG. 6, for example.
* * * * *