Shaped tube with elliptical cross-section for tubular heat exchangers and a method for their manufacture

A shaped tube with an elliptical cross-section with a multichamber design for tubular heat exchangers is provided with at least two cross ribs passing through an interior space of the tube at a distance from one another. A method for making this tube provides for bending an endless metal strip into two semifinished products with congruent profiles. Each profile has the shape of an isosceles triangle with rounded vertices and an elongated leg. The semifinished products are then placed against one another so that the free end of the elongated leg of one semifinished product abut the triangle base edge of the other semifinished product.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to a shaped tube with an elliptical or 
lancet-shaped cross section for tubular heat exchangers, manufactured from 
thin-walled sheet metal. 
A tube of this general type is shown in German Unexamined Patent 
Application No. 33 27 660, this tube being divided into two chambers by a 
cross rib running centrally in the direction of the minor ellipse axis 
(two-chamber profile). In the shaped tubes manufactured from thin-walled 
sheet metal, such a cross rib serves both to stiffen the tube to prevent 
the slightly convex tube walls from flattening out and to increase the 
degree of heat exchange. It has been found that the efficiency of such a 
tubular heat exchanger can be increased by using in the matrix, shaped 
tubes with especially slender lancet cross sections. 
An objective of the present invention therefore is to provide a shaped tube 
with an elliptical or lancet-shaped cross-section which has a slender 
contour and is able to withstand high internal pressure, permits a high 
degree of heat exchange, and can therefore bring about the smallest 
possible flow losses inside. 
This and other objectives are achieved by the present invention by 
providing a shaped tube with an elliptical or lancet-shaped cross-section 
with at least two cross ribs passing through the interior at a distance 
from one another parallel to the minor ellipse axis. 
Subdivision of the shaped tube according to the invention into at least 
three chambers offers a considerable improvement of flow and heat exchange 
conditions over a two-chamber profile. Particularly in the case of shaped 
tubes with larger cross sections for heat exchangers with larger 
dimensions, by using the multichamber design, equally thin sheet metal can 
be used as for small shaped tubes in the two-chamber design without 
thereby unacceptably reducing resistance to flattening out. 
The present invention also relates to a method for manufacturing shaped 
tubes with elliptical or lancet-shaped cross sections for tubular heat 
exchangers with at least two cross ribs passing through the interior space 
at a distance from one another in the direction of the minor ellipse axis 
by bending endless metal strips and then fitting the free edges together. 
A method of this general kind has been disclosed for a two-chamber profile 
by the above-mentioned German Published Unexamined Patent Application No. 
33 27 660. 
An object of the present invention is to provide a method suitable for 
making multichamber shapes which, while taking into account the very thin 
walls to be processed, both guarantees high dimensional accuracy of the 
shaped tubes produced and also is adjustable in terms of the number of 
desired chambers, while also allowing high production levels. 
This and other objects are achieved according to the present invention by 
bending an endless metal strip into two semifinished products with 
congruent profiles. Each said profile has the shape of an isosceles 
triangle with rounded vertices and with one leg extended beyond the base. 
The semifinished products are then placed against one another so that each 
free end of an elongated leg abuts the base edge of the other semifinished 
product. 
The method according to the invention provides a tube that has a slender 
contour, is able to withstand a high internal pressure, and permits a high 
degree of heat exchange. It also ensures a low engineering cost since the 
construction from two congruent semifinished products means that only one 
relatively simple profile need be bent. 
A further preferred embodiment of this method according to the present 
invention provides the manufacture of shaped tubes with more than two 
(2+n) cross ribs. In this method, n intermediate parts with rectangular Z 
contours and free legs are interposed between the two semifinished 
products. In this way, multichamber lancet profiles with a maximum of two 
differently-bent shaped semifinished products can be assembled, with the 
manufacturing cost being kept low. 
According to one preferred embodiment of the method according to the 
present invention, the semifinished product is bent, with the initially 
flat metal strip first being shaped into a right-angled Z shape with two 
free legs. Then the longer of the free legs is bent at approximately half 
the length of the longer leg by more than 90.degree. so that its end edge 
abuts the base edge formed by the Z rib and the shorter free leg. This 
type of bending of the semifinished product is especially advantageous in 
view of the subsequent fitting together, since the edges to be fitted 
together are in the areas of flat or slightly convex surfaces and are 
therefore especially easily accessible. 
Alternatively to the above-described bending of the semifinished products, 
according to another preferred embodiment of the invention, a semifinished 
product is shaped by first bending the initially flat metal strip into a 
right-angled profile with a shorter leg that has the same length as the 
cross rib and a longer leg. The longer leg is then bent for more than 
90.degree. around a point which is less than half the length of the leg 
from the right-angled vertex, until it abuts the free end of the shorter 
leg. This type of bending of the semifinished product has the advantage 
that the flat metal strip is subjected to bending in one direction only. 
Preferably, the distance of the bending point from the right-angled vertex 
is about one-third of the length of the longer leg, so that the lengths of 
the three chambers of the finished shaped tube are about the same. 
Especially with respect to a fitting together of the free edges by welding, 
it is advantageous for the free legs of the semifinished products and the 
intermediate parts to have end edges bent outward, as provided by certain 
preferred embodiments of the method according to the present invention. 
Although the method according to the present invention can be worked so 
that the triangular hollow shapes of the two semifinished products can 
initially be sealed, and then the semifinished products can be joined to 
one another or with interposition of intermediate parts, it is 
advantageous for sealing each semifinished product as well as the fitting 
together of the semifinished products with one another or with the 
intermediate parts to take place in the same work process. This 
considerably facilitates the manufacture of endless shaped tubes. 
Other objects, advantages and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
In FIG. 1, three shaped tubes r of a tubular heat exchanger matrix are 
shown in their staggered arrangement, one of them in cross section and the 
other two only in outline. The elliptical shaped tubes shown in 
cross-section have two cross ribs q traversing the inner space at a 
distance from one another parallel to the minor ellipse axis k. This 
produces two roughly triangular hollow chambers at both ends of an 
approximately rectangular hollow chamber. It is evident from FIG. 1 that 
the so-called three-chamber profile shown already has a shape of a very 
slender ellipse, whose wall parts are correspondingly slightly convex. 
Accordingly, in contemplated embodiments having multichamber profiles 
which have 2+n cross ribs, even more slender tube contours are produced. 
The diagram in FIG. 2 shows a first type of manufacture according to the 
invention for a shaped tube according to FIG. 1. According to the drawing, 
by bending endless metal strip, the two semifinished products 2, 3 which 
have a congruent profile are formed. Each of these semifinished products 
2, 3 has roughly the shape of an isosceles triangle with rounded vertices 
and with one leg 23 or 33 extended beyond the bases 20, 30. These 
semifinished products 2, 3 are placed against one another so that free 
ends 22, 32 of elongated legs 23, 33 each abut the base edge 25, 35 of the 
other semifinished product. The junctions at edges 25, 26, 35, 36 shown in 
FIG. 2 still as open gaps are sealed by welding or soldering. 
The bending of the semifinished products 2, 3 shown in FIG. 2, as indicated 
in FIG. 4, is performed such that the originally flat metal strip is first 
shaped into a right-angled Z contour with free legs, 21, 23. The longer of 
the free legs 21 is then bent further at approximately half the length of 
the leg 21 so that its end edge 24 abuts base edge 26. Solid lines show 
the right-angled Z contour while the bending of the longer leg 21 is 
indicated by the dashed line. 
FIGS. 3 and 5 show a second method of manufacturing an elliptical shaped 
tube according to the embodiment of FIG. 1. Similar parts have been given 
similar reference numerals in FIGS. 2-5. As in the case of the first 
method of manufacture shown in FIG. 2, once again two semifinished 
products 2, 3 with congruent profiles are bent and placed against one 
another so that the complete profile of the tube according to FIG. 1 
results. In contrast to the method of manufacture shown in FIGS. 2 and 4 
however, a semifinished product 2', 3' is so shaped that the originally 
flat metal strip is first bent into a right angle profile with one shorter 
leg 20' which has the length of cross rib q of the shaped tube and a 
longer leg 21'. Longer leg 21' is then bent around a point which lies less 
than half the length of the leg from right-angled vertex 25' until leg 21' 
abuts the free end of shorter leg 20'. The movement of the end edge of 
longer leg 21' is represented in FIG. 5 by a dashed line and arrow. 
Preferably, the point at which longer leg 21' is bent is approximately 
one-third of the total length of the leg. Thus, in the finished profile 
tube, the middle rectangular chamber is approximately the same length as 
the two outer triangular chambers. 
FIG. 6 shows the manufacture of an elliptical shaped tube with four 
chambers. The overall contour of this shaped tube is formed by two 
congruent semifinished products 2, 3 described above and an intermediate 
part I, which has a right-angled Z contour with free legs 11, 13. The Z 
rib of intermediate part 1 is represented by reference numeral 10. The 
other reference numbers are the same as in FIG. 2. The finished shaped 
tube results as described above from the welding or soldering of the 
joining gaps. Shaped tubes of even greater length in the direction of 
major ellipse axis g are produced by inserting a plurality of intermediate 
parts 1 in similar fashion between the two semifinished products 2 and 3. 
The embodiment shown in FIG. 7 of the semifinished products joined to form 
the contours of the tube differs from the embodiment shown in FIG. 6 only 
in that the free legs of semifinished products 2, 3 and intermediate part 
1 to be joined together have outwardly bent end edges 27. This type of 
contour has proven to be especially advantageous for performing the 
welding. 
It should be noted that the figures contain considerably enlarged 
representation of the shaped tubes to be manufactured. In certain 
preferred embodiments, the extent of the elliptical cross-sectional shape 
is about 10 mm in the direction of the major ellipse axis and about 3 mm 
in the direction of the minor ellipse axis, and the wall thickness of the 
sheet metal used is between 0.2 and 0.4 mm. 
From the preceding description of the preferred embodiments, it is evident 
that the objects of the invention are attained, and although the invention 
has been described and illustrated in detail, it is to be clearly 
understood that the same is by way of illustration and example only and is 
not to be taken by way of limitation. The spirit and scope of the 
invention are to be limited only by the terms of the appended claims.