U.S. patent application number 10/545889 was filed with the patent office on 2006-11-02 for flat pipe comprising a return bend section and a heat exchanger constructed therewith.
This patent application is currently assigned to BEHR GmbH & CO. KG. Invention is credited to Walter Demuth, Wolfgang Geiger, Martin Kotsch, Michael Kranich, Karl-Heinz Staffa, Christoph Walter.
Application Number | 20060243432 10/545889 |
Document ID | / |
Family ID | 32747996 |
Filed Date | 2006-11-02 |
United States Patent
Application |
20060243432 |
Kind Code |
A1 |
Demuth; Walter ; et
al. |
November 2, 2006 |
Flat pipe comprising a return bend section and a heat exchanger
constructed therewith
Abstract
The invention related to a flat tube (1) comprising a return
bend section (3), inside of which the flat tube (1) is bent back in
such a manner that both planar tube sections (2a, 2b) thereof,
which are connect to the return bend section, extend in a
longitudinal direction with opposite flow-through directions (4a,
4b) and with longitudinal axes (5a, 5b) that are offset with regard
to one another at least in the transverse direction (y). The
invention provides that the return bend section (3) is formed in
such a manner that a main bending axis (A) extends parallel to the
flat tube to be plane and at a predeterminable angle to the tube
longitudinal extension, whereby the flat tube plane is determined
by the longitudinal and width extension of the flat tube (1).
Inventors: |
Demuth; Walter; (Gerlingen,
DE) ; Geiger; Wolfgang; (Ludwigsburg, DE) ;
Kotsch; Martin; (Ludwigsburg, DE) ; Kranich;
Michael; (Besigheim, DE) ; Staffa; Karl-Heinz;
(Stuttgart, DE) ; Walter; Christoph; (Stuttgart,
DE) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
BEHR GmbH & CO. KG
|
Family ID: |
32747996 |
Appl. No.: |
10/545889 |
Filed: |
February 11, 2004 |
PCT Filed: |
February 11, 2004 |
PCT NO: |
PCT/EP04/01257 |
371 Date: |
November 17, 2005 |
Current U.S.
Class: |
165/176 ;
165/177 |
Current CPC
Class: |
F28D 1/0478 20130101;
F28D 1/0476 20130101; F28D 2021/0073 20130101 |
Class at
Publication: |
165/176 ;
165/177 |
International
Class: |
F28D 7/06 20060101
F28D007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 18, 2003 |
DE |
103 06 848.1 |
Claims
1. A flat tube with a return bend section (3), in which the flat
tube (1) is bent around in such a way that its two planar tube
sections (2a, 2b) adjoining it run in the longitudinal direction
with opposite throughflow directions (4a, 4b) and with longitudinal
axes (5a, 5b) offset relative to one another at least in the
transverse direction (y), characterized in that the return bend
section (3) is formed in such a way that a main bend axis (A) runs
parallel to the flat tube plane and at a predeterminable angle with
respect to the tube longitudinal extent, the flat tube plane being
determined by the extent of the flat tube (1) in terms of length
and of width.
2. The flat tube as claimed in claim 1, further characterized in
that the predeterminable angle is 90.degree..
3. The flat tube as claimed in claim 1, further characterized in
that the flat tube (1) is displaced by the amount of a distance
(s), parallel to the tube extent, in the flat tube plane in the
region of the return bend section (3).
4. The flat tube as claimed in claim 1, characterized in that the
tube sections (2a, 2b) merge into the return bend section (3) at a
predeterminable angle (.alpha.).
5. The flat tube as claimed in either claim 1, characterized in
that the angle (a) and/or the distance (s) are/is achieved by means
of at least one bending operation about at least one bend axis (B)
which runs perpendicularly with respect to the flat tube plane.
6. The flat tube as claimed in claim 5, further characterized in
that the displacement of the flat tube (1) is achieved by means of
two bending operations about two bend axes (B1, B2) which are
carried out before or after the main bending operation about the
first bend axis (A), the first bend axis (A) running in the middle
of an offset region (U).
7. The flat tube as claimed in claim 1, further characterized in
that the two planar tube sections (2a, 2b) adjoining the return
bend section (3) are arranged, with a spacing (d), perpendicularly
to the stacked direction (z) in planes parallel to one another.
8. The flat tube as claimed in claim 1, further characterized in
that, in a further forming step, the return bend section (3) is
formed in such a way that the two tube legs (2a, 2b) lie next to
one another and parallel, with the spacing (d), in the same
plane.
9. The flat tube as claimed in claim 7, further characterized in
that the return bend section (3) is formed symmetrically or
asymmetrically.
10. The flat tube as claimed in claim 1, characterized in that the
spacing (d) in the transverse direction (y) is between 0.2 mm and
20 mm.
11. The flat tube as claimed in one of the preceding claims claim
1, characterized in that, by means of the return bend section (3),
an air-facing side of the flat tube section (2a) becomes an
air-facing side of the flat tube section (2b) and a side of the
flat tube section (2a) facing away from the air becomes a side of
the flat tube section (2b) facing away from the air.
12. The flat tube as claimed in claim 1, characterized in that, by
means of the return bend section (3), a tube underside of the tube
section (2a) becomes the tube top side of the tube section (2b) and
a tube top side of the tube section (2a) becomes the tube underside
of the tube section (2b).
13. A flat tube heat exchanger for a motor vehicle air conditioning
system, with a tube block (9) having one or more flat tubes (1) as
claimed in claim 1, which are stacked one above the other in a
stack direction (z).
14. The flat tube heat exchanger as claimed in claim 13,
characterized in that collecting ducts (7) which run along the
stack direction (z) and into which the flat tubes (1) issue in each
case at one end (6) are arranged laterally on the tube block
(9).
15. The flat tube heat exchanger as claimed in claim 13,
characterized in that at least one of the two tube sections (2a,
2b) connected to one another via the return bend section (3) forms
a tube serpentine (12) wound in the stack direction (z).
16. The flat tube heat exchanger as claimed in claim 13,
characterized in that the two flat tube ends (6) lie on the same or
on opposite sides, and at least one of the two tube ends (6a, 6b)
is twisted at an angle of between 0.degree. and 90.degree..
17. A gas cooler with a flat tube heat exchanger (10) as claimed in
claim 13.
18. An evaporator with a flat tube heat exchanger (10) as claimed
in claim 13.
Description
[0001] The invention relates to a flat tube according to the
preamble of claim 1 and to a heat exchanger constructed
therewith.
[0002] A generic flat tube comprising a return bend section and a
heat exchanger comprising a tube block constructed from this type
of flat tube are described in the laid-open publication DE 198 30
863 A1. To produce, there, the flat tube comprising a return bend
section, the flat tube is bent around in such a way that its two
planar tube sections adjoining it run in a longitudinal direction
with opposite throughflow directions and with longitudinal axes
offset relative to one another at least in the transverse
direction.
[0003] The laid-open publication EP 0 659 500 A1 likewise describes
a flat tube comprising a return bend section and a heat exchanger
comprising a tube block constructed from this type of flat tube. To
produce the flat tube there, a rectilinear flat tube blank is first
bent out of the flat tube plane in a U-shaped manner, until the
flat tube legs run parallel to one another, after which the latter
are twisted in each case at 90.degree. with respect to the U-bend
region. The flat tube thereby occurring thus possesses two planar
tube sections which lie in one plane and the issue ends of which
lie on the same side opposite to the return bend section. The angle
which the flat tube transverse axis forms along the return bend
section with the plane in which the rectilinear tube legs lie first
increases, over one twist region, from zero to the value of
90.degree. present at the head end of the return bend section, in
order then to decrease to 0.degree. again over the other twist
region. What is considered to be a disadvantage in the return bend
section described is that the extent of the flat tube perpendicular
to the plane of the planar tube legs in the head region of the
return bend section always corresponds to a flat tube width and
therefore cannot be reduced as required, so that the dimensions of
the associated heat exchanger tube block cannot be influenced in
the direction perpendicular to the plane of the rectilinear flat
tube legs.
[0004] The object of the invention is to provide a flat tube
comprising a return bend section, which flat tube can be produced
relatively simply and is suitable for the construction of highly
pressure-resistant heat exchangers having a small overall space,
and to specify a heat exchanger constructed from such flat
tubes.
[0005] According to the invention, this object is achieved, with
regard to the flat tube, by means of the features of patent claim 1
and, with regard to a heat exchanger, by means of the features of
patent claims 13, 17 or 18.
[0006] The dependent patent claims relate to advantageous
refinements and developments of the invention.
[0007] The main idea of the invention is to design a return bend
section in such a way that a main bend axis runs parallel to the
flat tube plane and at a predeterminable angle with respect to the
tube longitudinal extent, the flat tube plane being determined by
the extent of the flat tube in terms of length and of width. In an
advantageous embodiment, the predeterminable angle amounts to
90.degree., that is to say the main bend axis then runs
perpendicularly with respect to the tube longitudinal extent.
[0008] The flat tube according to the invention, during the forming
operation, is displaced by the amount of a distance s, parallel to
the tube extent, in the flat tube plane in the region of the return
bend section, the distance s being composed of a flat tube width b
and of a desired spacing d between the flat tube sections after the
forming operation.
[0009] In the flat tube according to the invention, an angle
.alpha. with which the flat tube sections merge into the return
bend section can be selected freely during the forming of the flat
tubes and, in an advantageous embodiment of the invention, lies in
the range of 13.degree.<.alpha.<67.degree..
[0010] In an advantageous embodiment of the flat tube according to
the invention, the angle .alpha. and/or the distance s are/is
achieved by means of at least one bending operation about at least
one bend axis (B) which runs perpendicularly with respect to the
flat tube plane.
[0011] In a particularly advantageous embodiment of the flat tube
according to the invention, the displacement of the flat tube is
achieved by means of two bending operations about two bend axes
which are carried out before or after the main bending operation
about the first bend axis, the first bend axis running in the
middle of the offset region, the offset region being approximately
twice as long as the return bend section. This applies particularly
when a main bending operation is carried out about a main bend axis
which runs perpendicularly with respect to the tube extent.
[0012] In the hitherto described flat tube according to the
invention, after the forming operation the two planar tube sections
adjoining the return bend section are arranged so as to lie
perpendicularly with respect to the stack direction z in parallel
planes offset laterally in relation to one another, preferably with
the spacing d in the transverse direction y of between 0.2 mm and
20 mm. If flat tubes bent around once in this way are used, when
the direction of the offset is changed at each deflection a tube
block in a serpentine type of construction, in which the
serpentines run so as to be offset laterally, can be formed. The
tube block thus formed has a depth of double the flat tube width
plus said spacing d between the planar tube sections. With flat
tubes bent around more than once, offset, in the same direction,
the tube block depth per return bend section increases by the
amount of the flat tube width plus said transverse spacing d
between the planar tube sections. As a result of the transverse
spacing, corresponding gaps between the flat tube sections are
formed in a tube block constructed by means of such flat tubes,
thus making it easier for condensation water to be separated, for
example when the tube block is employed in an evaporator of a motor
vehicle air conditioning system.
[0013] In order to ensure that the flat tubes lie in a common
plane, in a further forming step the return bend section is formed
in such a way that the two tube sections lie next to one another
and parallel, at the spacing d, in a common plane. This may take
place by means of a symmetrical or asymmetric forming of the return
bend section.
[0014] As a result of the change between the return bend sections,
in which the flat tube sections lie in the same plane, designated
below as first return bend sections, and the return bend sections,
in which the flat tubes lie in different planes, designated below
as second return bend sections, a tube block in a serpentine type
of construction can be implemented, the depth of which is dependent
on the number of first return bend sections formed one behind the
other. As a result of a constant change of first and second return
bend sections in which the offset is likewise formed in the
opposite direction, for example, a tube block in a serpentine type
of construction, with a depth of double the flat tube width plus
said spacing d between the planar tube sections, can be
implemented, in which a thermal control medium, for example a
refrigerant or a coolant, first flows through the flat tube
sections which lie in a common plane and then flows through the
flat tube sections which lie in the next common plane in the stack
direction or opposite to the stack direction.
[0015] However, it is, moreover, also possible to achieve a
serpentine form of construction in that a number of second return
bend sections are designed without a lateral offset, designated
below as third return bend sections, for example in the stack
direction, and in that, subsequently, a first return bend section
is formed which is followed by a number of second return bend
sections. A second return bend section may, of course, also be
arranged instead of the first return bend section. In such a tube
block, first, the thermal control medium flows through all the flat
tube sections which lie one above the other in a front region, that
is to say in a region facing the air, and, subsequently, after a
first or a second return bend section, flows through all the flat
tube sections lying in a rear region, and the order of the
throughflow may also be opposite, that is to say the thermal
control medium flows first through the rear region and then through
the front region, and, depending on the application, the
throughflow may take place from the top downward or from the bottom
upward.
[0016] In an alternative procedure for the configuration of the
return bend section, the main bending operation about the main bend
axis is carried out at a predeterminable angle with respect to the
tube longitudinal extent, the predeterminable angle corresponding
essentially to the angle .alpha. with which the flat tube sections
merge in to the return bend section.
[0017] After the main bending operation, the two flat tube sections
lie in two planes parallel to one another, the two flat tube
sections forming an angle having a value of 2a. In order to obtain
parallel tube legs, the two tube legs are in each case formed, by
means of a further bending operation about a bend axis running
perpendicularly with respect to the flat tube plane, in such a way
that they merge into the return bend section in each case at the
angle .alpha.. The procedure described gives rise in another way to
the required flat tube offset already described.
[0018] The further forming steps are carried out in a similar way
to those already described, in order to ensure that the two flat
tube sections lie next to one another and parallel, at the spacing
d, in a common plane. As already stated, this may take place by
means of a symmetrical or asymmetric forming of the return bend
section.
[0019] In principle, however, it is also possible to reverse the
order of the forming steps and first form the two tube sections by
means of a symmetrical or asymmetric forming of the return bend
section, in such a way that they lie in a common plane and form the
angle 2.alpha., and subsequently to carry out the two bending
operations described above, in order to ensure that the two tube
sections lie parallel and next to one another, at their spacing d,
in the common plane.
[0020] Overall, what is achieved by means of the configuration
according to the invention of the return bend section is that its
extent in the stack direction can be kept markedly smaller than the
flat tube width. Accordingly, the interspaces between adjacent flat
tubes in the stack-shaped construction of a tube block from these
flat tubes do not need to be as large as or are kept no larger than
the flat tube width, but, instead, may be markedly narrower, this
being conducive to the production of a compact and
pressure-resistant heat exchanger. Moreover, the return bend
section can be implemented by means of relatively simple tube
bending operations. The flat tube may in this case be bent around
in this way once or more than once, its depth extent, that is to
say its extent in the transverse direction, as defined above,
increasing with each bend when the lateral offset always takes
place in the same direction. As a result, it is possible, by means
of relatively narrow pressure-resistant flat tubes, to form a tube
block of any desired depth, that is to say extending in the
transverse direction, this transverse or depth direction normally
being that direction in which a medium to be cooled or to be heated
is conducted through the heat exchanger past the flat tube surfaces
on the outside. In this case, mostly, additional heat conduction
means between the tube block sections succeeding one another in the
stack direction are provided in order to improve the heat
transmission. Since, as stated, the tube interspaces can be kept
very narrow, correspondingly low heat-conducting corrugated ribs
can also be used, thus likewise improving the compactness and
stability of a tube/rib block thus formed.
[0021] To produce a flat tube heat exchanger for motor air
conditioning systems, a plurality of flat tubes according to the
invention are stacked one above the other in a stack direction z in
order to form a tube block. The flat tubes issue in each case at
one end into at least one collecting duct arranged laterally and
running in the stack direction of the tube block, and at least one
of the two tube sections connected to one another via the return
bend section may form a tube serpentine coiled in the stack
direction z, while the two flat tube ends lie on the same or on
opposite sides, and at least one of the two tube ends may be
twisted at an angle of between 0.degree. and 90.degree..
[0022] By the flat tubes being designed according to the invention
with a 180.degree. deflection in the flow direction, it is possible
to implement a smaller overall space for the heat exchangers, such
as, for example, a gas cooler or an evaporator, since narrower
spacings in the stack direction and/or between the tubes can be
implemented. Moreover, a springing open of the flat tube legs is
virtually avoided. A further advantage is that the heat exchangers
constructed with the flat tubes according to the invention have a
more rigid design with narrower tolerances.
[0023] In the present gas cooler variant, the refrigerant is routed
in a flat tube in cross countercurrent to the air. At the opposite
block end, a deflection through 180.degree. takes place, that is to
say the flat tube runs back in the same plane as on the outward
path, but so as to be offset laterally by the amount of distance s,
so that the outgoing section of the flat tube is distanced from the
returning section by the amount of a spacing d. The two flat tube
sections lie in the same plane which is defined by the extent of
the flat tubes in terms of length and of width in their straight
sections. Forming is carried out preferably in three steps. In the
first step, the flat tube undergoes a lateral offset from the
stretched state. The amount of the offset s corresponds to the sum
of the flat tube width b and spacing d. Subsequently, bending takes
place with a radius r about a main bending axis A parallel to the
flat tube plane and perpendicularly with respect to the tube
extent, r being the inner radius of the bend. The main bend axis A
lies approximately in the middle of the offset region. The sections
of the flat tube subsequently lie parallel to one another in
different planes. In a third step, the return bend section is
formed in such a way that the flat tube sections lie in a common
plane again. The formed return bend section may either lie
completely below or above with respect to the common flat tube
plane or lie symmetrically with respect to this common plane.
Moreover, any desired asymmetric positions of the return bend
section in relation to the common plane are possible. Alternatively
to the forming order described, the forming steps may also be
interchanged.
[0024] For the offset of the flat tube in the plane, the following
geometric relations can be set up: the angle .alpha. at which the
flat tube runs in the offset region, contrary to the original tube
extent, is obtained from .alpha.=arctan (b+d/U). With b: flat tube
width, d: distance between the flat tubes, U: offset region.
[0025] For the offset region U, the following estimation: U=2.PI.r
is obtained, r being the inner radius of the 180.degree. bend. The
following applies to the maximum inner radius r:
(h.sub.r-d.sub.FR)/2, h.sub.r being a rib height and d.sub.FR being
a flat tube thickness. The flat tube thickness d.sub.FR seems to be
an appropriate lower limit value for r min. According to these
formulae, an appropriate value for .alpha. lies within the limits
13.degree.<.alpha. 67.degree..
[0026] In an advantageous embodiment, the flat tube according to
the invention forms a serpentine flat tube, in that at least one of
the two flat tube sections connected via a return bend section is
bent in a stack direction to form a tube serpentine, that is to say
consists of third return bend sections succeeding one another in
the stack direction and having the corresponding planar tube
sections. By means of flat tubes thus configured, a serpentine heat
exchanger, as it is known, can be constructed with any desired
number of serpentine block parts succeeding one another in the
depth direction.
[0027] In a further embodiment of the flat tube according to the
invention, the issue ends lie on the same or on opposite sides, at
least one end, preferably both ends, being twisted with respect to
the adjacent middle region. As a result of this twisting, the flat
tube transverse axis is rotated in the direction of the issue end
toward the stack direction, so that the extent of the flat tube
ends in the transverse direction can be kept smaller than the flat
tube width. Twisting takes place at most through 90.degree., so
that then, with the planar tube sections running perpendicularly
with respect to the stack direction, the tube ends lie parallel to
the stack direction and their extent in the transverse direction is
only as large as the flat tube thickness. This makes it possible to
have an arrangement, comparatively narrow in the depth direction of
a tube block constructed therewith, of associated collecting and
distributing ducts extending on the respective tube block sides in
the stack direction.
[0028] A heat exchanger is characterized by the use of one or more
of the flat tubes according to the invention in the construction of
a corresponding tube block, with the abovementioned properties and
advantages of such a tube block construction. In particular, in
this way, a compact and highly pressure-resistant evaporator with
relatively low weight, a small inner volume and good condensation
water separation can be implemented for an air conditioning system
of a motor vehicle, preferably multichamber flat tubes being
employed. The heat exchanger can be implemented both in a
single-layer type of construction, in which the flat tube sections
between two return bend sections or between a return bend section
and a flat tube end consist of a planar rectilinear tube section,
or in a serpentine type of construction, in which these flat tube
sections are bent to form a tube coil.
[0029] In a developed heat exchanger, the tube ends of the flat
tubes used and consequently also the associated collecting and
distributing ducts, designated uniformly below as collecting ducts
for the sake of simplicity, are located on opposite tube block
sides. The connecting ducts may then be formed in each case by a
header box or header tube which run on the respective tube block
side along the stack direction, also designated as the vertical
block direction, and which serve for supplying or discharging the
thermal control medium conducted through the tube interior to or
from the individual flat tubes.
[0030] In an alternative development of the invention, the flat
tubes all issue on the same tube block side. Owing to the
configuration of the flat tubes, the two tube ends of each flat
tube are in this case offset in relation to one another in the
block depth direction, so that they can be assigned two collecting
ducts lying correspondingly next to one another in the block depth
direction. Accordingly, the supply and discharge of the thermal
control medium conducted through the tube interior take place on
the same heat exchanger side.
[0031] In a further refinement of this heat exchanger type with two
collecting ducts lying next to one another on the same tube block
side, there is provision for these collecting ducts to be formed by
two separate header tubes or header boxes, designated uniformly
below as header tubes for the sake of simplicity, or by one common
header tube. The latter can be implemented in that an initially
uniform header tube interior is divided off by means of a
longitudinal partition into the two collecting ducts, or in that
the header tube is manufactured as an extruded tube profile with
two separate hollow chambers forming the collecting ducts.
[0032] In a developed heat exchanger, at least one of the two
header tubes or at least one of the two hollow chambers of a
longitudinally divided header tube is subdivided by means of
transverse partitions into a plurality of collecting ducts
separated from one another in the vertical block direction. As a
result, a grouped serial throughflow of the flat tubes in the tube
block is achieved, in that the thermal control medium supplied to
the tube block via a first collecting duct of the transversely
divided header tube or of the transversely divided hollow chamber
is first fed only into the part of all the flat tubes which issues
there. The collecting ducts into which this part of the flat tubes
issues with the other tube end then functions as a deflecting duct,
in which the thermal control medium is deflected from the flat
tubes issuing there into a further part of all the flat tubes which
likewise issues there with one end. The number and position of the
transverse partitions determine the division of the flat tubes into
successive-throughflow groups of parallel-throughflow flat
tubes.
[0033] In a flat tube produced according to the invention, the
arrangement of the flat tubes with regard to an air stream remains
unchanged despite the return bend section, that is to say a flat
tube side facing the air continues to face the air even after the
return bend section and a flat tube side facing away from the air
continues to face away from the air even after the return bend
section.
[0034] In contrast to this, a position of the tube underside or
tube top side is changed by means of the return bend section, that
is to say the tube underside of the flat tube becomes a tube top
side of the flat tube and a tube top side of the flat tube becomes
the tube underside of the flat tube.
[0035] Advantageous embodiments of the invention are illustrated in
the drawings and are described below. In the drawings:
[0036] FIG. 1 shows a top view of a flat tube with a return bend
section and with twisted tube ends,
[0037] FIG. 2a shows a side view, along the arrow I in FIG. 1, of a
flat tube with a secondary return bend section;
[0038] FIGS. 2b to 2d shows side views, along the arrow I of FIG.
1, of flat tubes with differently designed first return bend
sections;
[0039] FIG. 3a shows a top view of a flat tube before a bending
operation about a main bend axis A;
[0040] FIG. 3b shows a top view of a flat tube after a bending
operation about a main bend axis A;
[0041] FIG. 4 shows a side view of a detail of a tube/rib block of
a heat exchanger, said tube/rib block being constructed from flat
tubes according to FIGS. 1 and 2;
[0042] FIG. 5 shows a side view of a detail of a tube/rib block of
a heat exchanger with serpentine-shaped flat tubes.
[0043] The flat tube 1 shown in the top view in FIG. 1 is
manufactured in one piece from a rectilinear multi chamber profile,
using suitable bending operations. It contains two planar
rectilinear tube sections 2a, 2b which are connected to one another
via a return bend section 3 and which have opposite throughflow
directions for a thermal control medium, for example a refrigerant
of a motor vehicle air conditioning system, conducted through the
plurality of parallel chambers inside the flat tube 1. One of the
two possible flow profiles is illustrated in FIG. 1 by
corresponding flow arrows 4a, 4b. The longitudinal axes 5a, 5b,
running parallel to the throughflow directions 4a, 4b, of the two
planar rectilinear tube sections 2a, 2b define a longitudinal
direction x and are offset relative to one another in a transverse
direction y perpendicular thereto. As is evident particularly from
the side views of FIG. 2b to 2c, the two planar tube sections 2a,
2b lie with a first return bend section 3 in a common x-y plane
perpendicular to a stack direction z in which a plurality of such
flat tubes are stacked one on the other to form a heat exchanger
tube block, as explained in more detail below with reference to
FIG. 4 and 5. For greater clarity, in each case the corresponding
coordinate axes x, y, z are depicted in FIG. 1 to 5. The return
bend section 3 is obtained in that the initial rectilinear flat
tube profile of a desired width b is displaced by the amount of a
distance s, parallel to the tube extent, in the flat tube plane in
the region of an offset region U, as illustrated in FIG. 3a, said
distance being composed of the tube width b and of the desired
spacing d. The displacement or offset may in this case take place
in a positive y-direction or, opposite, in a negative y-direction.
The transition between the flat tube sections 2a, 2b and return
bend section 3 takes place at a predeterminable angle .alpha.. The
angle .alpha. and/or the distance s are/is in this case achieved by
means of at least one bending operation about at least one bend
axis B1, B2 running perpendicularly with respect to the flat tube
plane. Preferably, the described offset by the amount of the
distance s is achieved by means of two bending operations about the
bend axes B1 and B2 illustrated in FIG. 3a, these two bending
operations preferably being carried out before the bending
operation about the main bend axis A. In the exemplary embodiment
illustrated, the main bend axis A runs in the middle of the offset
region U, the offset region U being approximately twice as long as
the return bend section 3.
[0044] The two rectilinear tube sections 2a, 2b of the flat tube 1
are obtained in a way described. After the offset of the flat tube
1 and the main bending operation, the two rectilinear tube sections
2a, 2b lie, as illustrated in FIG. 2a, offset in planes parallel to
one another, with a selectable spacing 2r in the z-direction and
the selectable spacing d in the y-direction, the following applying
to the maximum inner radius r: (h.sub.r-d.sub.FR)/2, h.sub.r being
the rib height and d.sub.FR being the flat tube thickness, thus
resulting in the flat tube thickness d.sub.FR as an appropriate
lower limit value for r. According to these formulae, an
appropriate value for the angle .alpha. lies within the limits
13.degree..ltoreq..alpha..ltoreq.67.degree.. The selectable spacing
is preferably between about 0.2 mm and 20 mm, while the flat tube
width b is typically between one and a few centimeters.
[0045] While the rectilinear tube sections 2a, 2b are connected to
one another on one side via the return bend section 3, they both
run out on the opposite side in the form of twisted tube ends 6a,
6b. Twisting takes place about the respective longitudinal midaxis
5a, 5b, alternatively also about a longitudinal axis parallel
thereto, that is to say with a transverse offset with respect to
the longitudinal mid axis of any desired angle between 0.degree.
and 90.degree., the twist angle being approximately 90.degree. in
the instance shown.
[0046] It becomes clear from FIG. 2 that, because of the depicted
formation of the return bend section 3, the height c of the return
bend section 3 and consequently the extent in the stack direction z
are small and can be selected as a function of the bend radius. In
particular, this height c of the return bend section 3 remains
markedly smaller than the flat tube width c. As a result, a
plurality of such flat tubes can be layered one above the other in
a heat exchanger tube block with a stack height which can be kept
markedly smaller than the flat tube width, as the heat exchanger
examples described below show. A further modification of the flat
tube of FIG. 1 and 2 may be that, as shown in FIG. 2a, the two
planar tube sections 2a, 2b lie in two x-y planes offset in
relation to one another. In this case, the transverse direction y
is defined in that it is perpendicular both to the longitudinal
direction x of the rectilinear tube sections and to the tube block
stack direction z.
[0047] FIG. 3b shows an alternative possibility for the
configuration of a return bend section 3 after the main bending
operation. As is evident from FIG. 3b, here, first the main bending
operation about the bend axis A is carried out, before the offset
is implemented by means of further bending operations about a bend
axis B3. The main bend axis A in this case runs at the
predeterminable angle .alpha. within the limits
13.degree..ltoreq..alpha..ltoreq.67.degree. with respect to the
tube longitudinal extent. After the main bending operation, the two
tube sections are in each case bent inward about the bend axis 3
according to the arrows. According to the illustration in FIG. 3b,
the spacing d between the flat tubes is implemented by means of a
boundary, in the example illustrated is implemented by means of a
boundary strip having the width d, in the example illustrated the
bend axis B3 being implemented by means of an upper end of the
boundary strip. The flat tube sections 2a and 2b illustrated lie in
different parallel planes and form an angle of 2a. After the
additional bending operations, the two flat tube sections 2a and 2b
lie parallel to one another in the different parallel planes, as
illustrated in FIG. 2a, so that the further forming steps already
described can be carried out, in order to ensure that the two flat
tube sections 2a, 2b lie parallel, with the spacing d, in a common
plane (see FIG. 2b to 2c).
[0048] FIG. 4 and 5 show an application for the flat tube type of
FIG. 1 and 2 in the form of a tube/rib block 9 of an evaporator 10,
such as can be used, in particular, in motor vehicle air
conditioning systems. It goes without saying that the heat
exchanger, a detail of which is shown, can also be used, depending
on its design, for any other desired heat transmission purposes,
for example as a gas cooler. As is evident from FIG. 4, this
evaporator 10 contains, between two end cover plates 11, 12, a
stack of a plurality of flat tubes 1 according to FIG. 1 and 2 with
intermediate heat-conductive corrugated ribs 8. The height of the
heat-conducting ribs 8 corresponds approximately to the height c of
the flat tube return bend sections 3 and is consequently markedly
smaller than the flat tube width b.
[0049] Using the flat tube 1 of FIG. 1 and 2, a tube/rib block 9
with a structure which is two-part in depth, that is to say in the
y-direction, is formed, in each of the two block parts in each case
the tube sections with the same throughflow direction lying one
above the other in the stack direction z. Between the two block
parts is formed a gap corresponding to the spacing d of the two
rectilinear tube sections 2a, 2b of each flat tube 1. In the
exemplary embodiment illustrated, the corrugated ribs 8 extend in
one part over the entire flat tube depth and consequently also over
this gap, and can, if required, project on both sides, that is to
say on the front side and on the rear side of the block. It is also
possible, however, to use multipart, in particular two-part
corrugated ribs 8. The block front side is in this case defined in
that it faces the flow of a second thermal control medium, for
example supply air to be cooled for a vehicle interior, conducted
over the evaporator surfaces on the outside, in the tube transverse
direction y, that is to say in the block depth direction.
[0050] The transverse extent of the flat tube issue ends is smaller
than the flat tube width b on account of their twisting. This makes
it easier to connect two associated collecting ducts, not shown in
FIG. 4, which may be formed in each case by a header box or header
tube, of which the transverse extent in the y-direction does not
need to be any greater than the flat tube width b and, in the case
of a twist angle of the flat tube ends of approximately 90.degree.,
even needs in its diameter to be only slightly greater than the
flat tube thickness. It is therefore easily possible to arrange two
header tubes so as to run next to one another in the stack
direction z in the respective tube block side, in order in each
case to receive one of the two ends of each flat tube 1.
Alternatively, a common header tube may be provided for both stack
rows of tube ends 6a, 6b, said common header tube being subdivided
into the two required separate collecting ducts by means of a
longitudinal partition.
[0051] It is shown that the evaporator 10 can be implemented in a
compact form of construction and in a highly pressure-resistant way
by means of the tube/rib block 9 thus formed and at the same time
has a high heat transmission efficiency. By the flat tubes being
bent around to form two tube sections 2a, 2b offset in the block
depth, it is possible, by means of relatively narrow flat tubes, to
achieve a heat transmission capacity for which nonbent flat tubes
having approximately double the width would otherwise be required.
What is achieved at the same time by means of the once-only flat
tube deflection is that the thermal control medium routed through
the tube interior can be supplied and discharged from one and the
same tube block side, this being advantageous in many
applications.
[0052] FIG. 5 shows an exemplary embodiment in a serpentine type of
construction. The view of a detail in FIG. 5 shows in this case a
plurality of serpentine flat tubes 13 which are stacked one above
the other in any desired number to form the serpentine tube block
there. The serpentine flat tube 13 used for this purpose is largely
structurally identical to that of FIG. 1 and 2, with the exception
that each of the two sides of the return bend section 3 identical
to that of FIG. 1 and 2 has adjoining it not simply a rectilinear
single-layer tube section, but a tube coil section 12 which is
multiply coiled in a serpentine-shaped manner the latter thus again
being located opposite one another, offset by the amount of a
corresponding gap in the block depth direction. As is customary,
the serpentine windings 12 of the respective tube coil section 13
are formed by the flat tube being bent at the respective point
around the tube transverse axis there at an angle of 180.degree..
Between the individual tube coil windings 13 and between successive
serpentine flat tubes 12, heat-conductive corrugated ribs 8 are
introduced, with optional projection, continuously from the block
front side as far as the block rear side. It goes without saying
that, here, as also in the example of FIG. 4 and 5, a corrugated
rib row may in each case be provided, instead, for each of the two
tube block rows offset in the block depth direction, in which case
the gap between the two block rows may also remain free. Instead of
this division by half with two corrugated ribs of identical width,
of course, any other desired number of corrugated ribs and/or
corrugated ribs of different depth may be employed over the tube
block depth in each corrugated rib layer, for example first
corrugated rib extending over two thirds of the tube block depth
and a second corrugated rib extending over the remaining third of
the tube block depth. In either case, the gap is conducive to the
separation of condensation water in the evaporator.
[0053] As can be seen from FIG. 4 and 5, in this example, too, the
height of the heat-conducting ribs 8 and consequently the stack
spacing of adjacent rectilinear flat tube sections, both within a
serpentine flat tube 13 and between two adjacent serpentine flat
tubes 13, correspond approximately to the height c of the return
bend section 3' which is markedly smaller than the flat tube width
b. The 90.degree. twisting, selected in this case, of the flat tube
ends 6, again issuing on the same block side, does not conflict
with this low stack height, since the serpentine flat tubes 13,
because of their tube coil sections 12, have, overall, in each case
a height in the stack direction z which is greater than the flat
tube width. As mentioned, the twisting of the ends 6 through
90.degree. at right angles makes it possible to use particularly
narrow collecting ducts or header tubes forming these. FIG. 5
illustrates such a front-side header tube 7, into which the front
row of flat tube ends 6 issues. Moreover, as illustrated in FIG. 5,
the serpentine flat tubes 13 may be combined with the flat tube 1
of FIG. 1 and 2.
[0054] Numerous further alternatives for the two flat tube
configurations shown are possible. Thus, the flat tube may have two
or more return bend sections and corresponding deflections.
[0055] Moreover, the serpentine flat tube 13 of FIG. 5 may be
modified to the effect that, by means of at least one further
serpentine winding in one and/or other serpentine tube section, the
respective flat tube end 6 comes to lie on the block side located
opposite the return bend section 3. In a further embodiment, a
serpentine flat tube 13 of the type in FIG. 5, but with one or more
additional return bend sections 3, may be provided, in order
thereby to construct, for a serpentine heat exchanger, a tube block
which is at least three-part in the block depth direction.
Depending on the application, the flat tube ends 6 may even be left
untwisted.
[0056] In those exemplary embodiments in which the flat tube ends 6
issue on the same block side, it is possible, instead of two header
tubes 7 or one common header tube into which a longitudinal
partition is introduced separately during production, to use a
two-chamber header tube which even at the manufacturing stage has
two separate hollow chambers running longitudinally. Said header
tube is manufactured from extruded profile and integrally contains
two longitudinal chambers which are separate from one another and
which form the collecting ducts for the respective heat exchanger.
For this purpose, as in the other header tube versions, suitable
circumferential slots are to be introduced into the header tube 7,
the flat tube ends 6 being inserted sealingly into said slots.
[0057] Moreover, depending on the type of heat exchanger, header
tubes may be used which, by means of corresponding transverse
walls, contain a plurality of collecting ducts separated from one
another in the vertical block direction z. As a result, the flat
tubes are combined in the tube block in a plurality of groups in
such a way that the tubes of a group have a parallel throughflow
and the various tube groups have a serial throughflow. A thermal
control medium supplied flows from an inlet-side collecting duct
into the group of flat tubes issuing there and then passes at their
other end into a collecting duct which functions as a deflection
space and into which, in addition to this first group, a second
flat tube group issues, into which the thermal control medium is
then deflected. By an appropriate positioning of the transverse
walls, this may be continued in any desired way, in one or both
header tubes, as far as an outlet-side collecting duct, via which
the thermal control medium then leaves the tube block.
[0058] The above description of various exemplary embodiments shows
that, by means of the flat tubes according to the invention, highly
compact pressure-resistant flat tube blocks can be produced in a
single-layer type of construction or serpentine type of
construction with a high heat transmission capacity. Heat
exchangers produced therewith are also suitable, for example, for
CO2 air conditioning systems operating at comparatively high
pressure, such as come under consideration increasingly for motor
vehicles.
* * * * *