U.S. patent application number 11/534294 was filed with the patent office on 2007-03-29 for heat exchanger.
This patent application is currently assigned to PIERBURG GMBH. Invention is credited to Uwe Rothuysen, Gunter Thiel, Oliver Thomer, Dieter Thonnessen.
Application Number | 20070068663 11/534294 |
Document ID | / |
Family ID | 37056515 |
Filed Date | 2007-03-29 |
United States Patent
Application |
20070068663 |
Kind Code |
A1 |
Thomer; Oliver ; et
al. |
March 29, 2007 |
HEAT EXCHANGER
Abstract
The invention relates to a heat exchanger with a channel (4)
through which cooling agent flows and a channel (3) through which
fluid to be cooled flows, whereby ribs (6) project into at least
one of the channels (3, 4). According to the invention, these ribs
(6) feature a linear approach edge (11) and a linear flow-off edge
(15), whereby the side walls (12) run continuously between the
approach edge (11) and the flow-off edge (15). By these means it is
achieved that a turbulent boundary layer forms at the ribs, which
boundary layer ends in a turbulent eddy in the area of the flow-off
edge (15). This leads to an increased efficiency of the heat
exchanger and simultaneously to a good homogenization of the fluid.
Moreover, sooting is reliably avoided.
Inventors: |
Thomer; Oliver; (Willich,
DE) ; Rothuysen; Uwe; (Krefeld, DE) ;
Thonnessen; Dieter; (Viersen, DE) ; Thiel;
Gunter; (Korsechenbroich, DE) |
Correspondence
Address: |
GRIFFIN & SZIPL, PC
SUITE PH-1
2300 NINTH STREET, SOUTH
ARLINGTON
VA
22204
US
|
Assignee: |
PIERBURG GMBH
Alfred-Pierburg Str.1
Neuss
DE
|
Family ID: |
37056515 |
Appl. No.: |
11/534294 |
Filed: |
September 22, 2006 |
Current U.S.
Class: |
165/164 |
Current CPC
Class: |
F28D 9/0081 20130101;
F28D 7/106 20130101; F28F 1/02 20130101; F28F 2255/14 20130101;
F28F 1/16 20130101; F28F 2250/102 20130101; F28F 9/24 20130101;
F28D 21/0003 20130101; F28F 13/06 20130101; F28F 13/12
20130101 |
Class at
Publication: |
165/164 |
International
Class: |
F28D 7/02 20060101
F28D007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 16, 2006 |
DE |
20 2006 009 464.4 |
Sep 23, 2005 |
WO |
PCT/EP05/10303 |
Claims
1. A heat exchanger comprising: a channel through which cooling
agent flows; and a channel through which fluid to be cooled flows,
wherein channels are separated from one another by a wall from
which issue ribs extending into at least one of the two channels,
wherein each rib includes one linear approach edge and two linear
flow-off edges, whereby the approach edge and the two flow-off
edges delimit two continuously running side walls of the ribs.
2. A heat exchanger according to claim 1, wherein the ribs extend
along a main flow direction.
3. A heat exchanger according to claim 1, wherein the side walls of
each rib adjacent to the approach edge and the flow-off edges
enclose an angle to one another that is less than or equal to
90.degree..
4. A heat exchanger according to claim 3, wherein in a front area,
the side walls extending from the approach edge of each rib are
arranged essentially wedge-shaped with respect to one another.
5. A heat exchanger according to claim 1, wherein in a front area,
an angle between tangents to the two side walls decreases
continuously in a main flow direction until the side walls run
parallel to one another in a back area.
6. A heat exchanger according to claim 1, wherein the ribs are
arranged in rows adjacent to one another perpendicular to a main
flow direction, whereby the ribs of each row are arranged staggered
with respect to the following row.
7. A heat exchanger according to claim 1, wherein the heat
exchanger is an exhaust gas heat exchanger whose ribs project into
the channel through which fluid to be cooled flows conducting
exhaust gas.
8. A heat exchanger according to claim 2, wherein the side walls of
each rib adjacent to the approach edge and the flow-off edges
enclose an angle to one another that is less than or equal to
90.degree..
9. A heat exchanger according to claim 2, wherein in a front area,
an angle between tangents to the two side walls decreases
continuously in the main flow direction until the side walls run
parallel to one another in a back area.
10. A heat exchanger according to claim 2, wherein the ribs are
arranged in rows adjacent to one another perpendicular to the main
flow direction, whereby the ribs of each row are arranged staggered
with respect to the following row.
11. A heat exchanger according to claim 3, wherein the ribs are
arranged in rows adjacent to one another perpendicular to a main
flow direction, whereby the ribs of each row are arranged staggered
with respect to the following row.
12. A heat exchanger according to claim 4, wherein the ribs are
arranged in rows adjacent to one another perpendicular to a main
flow direction, whereby the ribs of each row are arranged staggered
with respect to the following row.
13. A heat exchanger according to claim 5, wherein the ribs are
arranged in rows adjacent to one another perpendicular to a main
flow direction, whereby the ribs of each row are arranged staggered
with respect to the following row.
Description
[0001] This application claims priority from International Patent
Application No. PCT/EP2005/010303 filed Sep. 23, 2005, and from
German Patent Application No. 20 2006 009 464.4, filed Jun. 16,
2006. The entire disclosures of the above patent applications are
hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The invention relates to a heat exchanger with a channel
through which cooling agent flows and a channel through which fluid
to be cooled flows, which channels are separated from one another
by at least one wall from which issue ribs extending into at least
one of the two channels.
BACKGROUND OF THE INVENTION
[0003] Such heat exchangers are generally known and are described
in a number of Applications. There exist heat exchangers in which
the ribs project only into the channel conducting cooling agent as
well as heat exchangers whose ribs project into the channel through
which the fluid to be cooled flows and heat exchangers with ribs
pointing in both directions. These ribs distinctly improve the heat
transfer between the two fluids. In particular, the ribs increase
the residence time and the dynamic pressure in the corresponding
channel in comparison with embodiments without ribs. In a heat
exchanger used as an exhaust gas heat exchanger in internal
combustion engines, such ribs can also be used in order to prevent
to the greatest extent possible, a sooting or carbon fouling of the
channel through which the exhaust gas flows.
[0004] Thus in DE 10 2004 045 923 A1 heat exchangers are described
whose ribs are shaped in different ways. They project from two
inner walls bordering the channel into the channel conducting the
fluid to be cooled. All these ribs feature an axially symmetrical
shape and are installed at an angle to the main flow direction, at
least over a section. Both the approach area and the flow-off area
of these ribs are embodied with a radius.
[0005] The disadvantage of the above-mentioned embodiments is that
the manufacturing cost is relatively high, since both inner walls
must be embodied with ribs and secondly a high pressure drop is
present due to the relatively large dynamic pressure zone as the
rib is approached.
[0006] An improved efficiency is achieved through the plate heat
exchanger known from U.S. Pat. No. 2,892,618, whose ribs feature
side walls arranged concave to one another, each with an approach
edge and a flow-off edge.
[0007] From GB 892 534 a heat exchanger is known that features ribs
with a straight side wall and a concave side wall. As a result of
the linear approach edge, the dynamic pressure zone of the flow as
it approaches the rib, in which the speed is reduced to zero, is
minimized, so that a lower pressure drop is achieved. Moreover the
continuously running side walls cause the formation of a boundary
layer that is adjacent in the area of the rib, so that heat can be
exchanged over a lengthened cooling zone.
[0008] In all the above-mentioned embodiments, however, a
relatively high susceptibility of the heat exchanger to sooting
arises, in particular during use as an exhaust gas heat exchanger.
The efficiency is also limited by a lack of mixing of the fluid to
be cooled.
[0009] The object of the invention is therefore to develop a heat
exchanger whose ribs are optimized with respect to the flow, so
that the efficiency of the heat exchanger is increased by raising
the heat transfer at the ribs, whereby at the same time the
pressure drop in the heat exchanger is to remain as low as
possible. Moreover it is desirable to achieve the lowest possible
sooting of the ribs, and homogeneity of the fluid to be cooled.
SUMMARY OF THE INVENTION
[0010] This object is achieved in that each rib features one linear
approach edge and two linear flow-off edges, whereby the approach
edge and the two flow-off edges delimit two continuously running
side walls of the rib. Thus the pressure drop is minimized by means
of the single approach edge and boundary layer flows are created
along the entire length of the rib due to the continuous course of
the side walls, and a separation of the boundary layer flows is
prevented, so that the heat transfer is improved. Due to the two
flow-off edges, compared with known embodiments a distinctly
improved intensive mixing transverse to the flow direction is
achieved, so that the homogeneity of the fluid stream is increased,
which in turn results in a temperature exchange and temperature
equilibrium of the entire mass flow. All this increases the
efficiency of the heat exchanger.
[0011] In a preferred embodiment, the ribs extend along the main
flow direction, as a result of which the pressure drop is minimized
and it is ensured that the boundary layer will be adjacent on both
sides of the rib. A low pressure drop is particularly advantageous
when the heat exchanger is used as an exhaust gas heat exchanger in
the low-pressure zone of an internal combustion engine, since in
such a use the pressure drop present is very low.
[0012] In a further form of embodiment of the invention, the side
walls of each rib adjacent to the approach edge and the flow-off
edge enclose an angle to one another that is less than or equal to
90.degree.. This ensures that the pressure drop is sufficiently
small and undesired turbulence and separation along the cooling
zone of each rib are avoided.
[0013] In order to ensure that a boundary layer flow first forms
behind the dynamic pressure point, i.e. behind the approach edge,
in a front area the side walls extending from the approach edge of
each rib are arranged with respect to one another essentially
wedge-shaped.
[0014] In an advantageous alternative embodiment, in a front area
the angle between tangents to the two side walls decreases
continuously in the main flow direction until the side walls run
parallel to one another in a back area. This, too, leads to an
increase in the efficiency, since a separation of the boundary
layers over the course of the rib is avoided in this manner and a
sufficiently long cooling zone is available at the rib.
[0015] In a further form of embodiment of the heat exchanger, the
ribs are arranged in rows adjacent to one another perpendicular to
the main flow direction, whereby the ribs of each row are arranged
staggered with respect to the following row. This prolongs the
residence time of the fluid flowing through the channel and thus in
turn raises the efficiency of the heat exchanger, since a smooth
flow-through of the heat exchanger is avoided to the greatest
possible extent. Moreover the flow-through speed is raised due to
the small cross-sections available for the flow such that a
turbulent flow around the ribs is ensured, as a result of which a
high wall shearing stress and thus a higher heat transfer factor a
is achieved, so that an increase in the cooling performance is
ensured by raising the heat convection.
[0016] Advantageously a heat exchanger of this type is used as an
exhaust gas heat exchanger whose ribs project into the channel
conducting exhaust gas. This is particularly advantageous, since a
carbon fouling due to the flow speeds and turbulence arising is
reliably avoided, whereby at the same time a high efficiency and
thus a low necessary size are achieved, which is particularly
important in automobile manufacture based on the small space
available.
[0017] Thus in comparison with the known prior art, a heat
exchanger is created that requires a smaller space due to an
increase in the efficiency, and is not susceptible to sooting. At
the same time it can be produced cost-effectively using the
die-casting process. The fluid to be cooled leaves the heat
exchanger in a well-homogenized state.
[0018] An embodiment of the heat exchanger according to the
invention is shown in the Figures and is described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 shows a top view of a heat exchanger according to the
invention in sectional view.
[0020] FIG. 2 shows a head-on view of the heat exchanger from FIG.
1 in sectional view.
[0021] FIG. 3 shows a section of the heat exchanger from FIG. 1 in
an enlarged view.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The heat exchanger shown in the drawings, which is
preferably used as an exhaust gas heat exchanger in motor vehicles,
is composed of an outer housing 1 in which an inner housing 2,
which can be produced using the die-casting process, is arranged.
After assembly, a channel through which fluid to be cooled flows,
is formed between the inner housing 2 and the outer housing 1. In
the interior of the inner housing 2, a channel 4 through which
cooling agent flows is arranged whose inflow and outflow connection
pieces are not shown in the drawings and that can be arranged as
desired, depending on the application. The channel 4 through which
cooling agent flows is bounded by walls 5 from which ribs 6 extend
into the channel 3 through which fluid to be cooled flows. The
channel 3 through which fluid to be cooled flows is embodied in
such a way that its entry 7 is arranged at the same head side as
the exit 8, so that the fluid to be cooled is diverted by
180.degree. in a back area 9 of the heat exchanger. Accordingly the
ribs 6 are arranged in this area following the main flow
direction.
[0023] The central rib 10 extends from the entry 7 or exit 8 to a
back area 9 in which the deflection is embodied and whose height is
embodied such that it extends as far as the outer housing 1, by
means of which a crossflow and an overflow is prevented via a short
path from the entry 7 to the exit 8.
[0024] As can be seen in particular in FIG. 1, the ribs 6 seen in
the main flow direction, are arranged respectively in rows adjacent
to one another, whereby as a first row finishes a second row
follows respectively, whose ribs 6 are arranged staggered with
respect to the ribs 6 of the first row. Such an arrangement of the
ribs 6 increases the residence time of the exhaust gas in the heat
exchanger and thus its efficiency, since a straight,
obstruction-free flow-through is no longer possible for the fluid
to be cooled.
[0025] In FIG. 3 a cross-section shape according to the invention
of the ribs 6 can be seen. It features an approach edge 11, which
extends to the end of each rib 6 in the channel 3 linearly from the
wall 5 of the inner housing 2 and can be seen in the Figure only as
a dynamic pressure point. The side walls 12 of the ribs 6 adjacent
to the approach edge 11 are embodied such that the angle between
the two tangents to each side wall 12 of the ribs 6 continuously
decreases in a front area 13 until the enclosed angle is 0.degree.
and thus the two side walls 12 run parallel to one another in a
back area 14. At the end of each rib 6, viewed in the direction of
flow, both side walls 12 end at a flow-off edge 15 respectively, so
that between a back wall 16 of each rib 6 and the side walls 12, a
right angle exists.
[0026] Moreover it would be conceivable to allow the ribs 6 to run
in a wedge shape from the approach edge 11 and subsequently to
allow this wedge shape to change continuously into the parallel
guiding of the side walls 12.
[0027] The heat exchanger is designed so that turbulent boundary
layer flows result at the side walls 12, in which the wall shearing
stress is greater than in laminar flows, so that the heat transfer
factor .alpha. and thus the resulting heat transfer between rib 6
and the fluid to be cooled increases. Accordingly non-continuous
embodiments of the side walls 12 in front of the flow-off edge 15
are to be avoided, since these lead to a separation that would
prevent good heat transfer in the boundary layer. Correspondingly,
the length of the ribs 6 must also be embodied so that a separation
is avoided. Instead, the length is embodied in a defined manner at
the two flow-off edges 15, which in comparison with known
embodiments improve the heat transfer distinctly. This occurs due
to the fact that first the good heat exchange in the boundary layer
at the ribs 15 is utilized and then due to the linear flow-off
edges a distinctly improved fluid exchange is achieved transverse
to the main flow direction. The latter is explained by
Kelvin-Helmholtz instabilities arising behind the flow-off edges
15, i.e. during separation at approximately stepped profiles. These
instabilities occur due to a rolling-up of the shear layers arising
at the flow-off edges. The chief trigger of this rolling-up is a
strong speed gradient at the shear layer. These Kelvin-Helmholtz
instabilities continue and become macroscopically visible as a
broad turbulent eddy. Due to the arrangement according to the
invention of the two flow-off edges at a distance H from one
another, this effect, which occurs at both flow-off edges, which
should feature approximately a right angle to their adjacent walls,
is again distinctly intensified, since a pairing of the two eddies
occurs at the upper and the lower flow-off edge. Due to this
pairing, a turbulent area arises behind the ribs whose extent
transverse to the flow direction is distinctly greater than the
thickness H of the ribs. This turbulent flow produced by the
flow-off edge 15 leads to an excellent homogenization of the
exhaust gas in the heat exchanger.
[0028] In comparison with ribs with only one flow-off edge, the
width of the turbulent area behind each rib 6 is distinctly greater
and thus a distinctly improved thorough mixing is achieved
transverse to the flow direction, since with single flow-off edges
a dead water area forms with small eddies and low thickness. This
is particularly important because the boundary layer flows forming
at the continuous side walls 12 do indeed lengthen the cooling zone
and thus improve the heat transfer, but to a great extent prevent a
fluid exchange due to transverse flows.
[0029] Moreover a high kinetic energy is desired in the rib
boundary layer, as a result of which a separation of the boundary
layer is delayed. The boundary layer flow thus lies against the
cooling rib longer, so that the cooling zone is lengthened. Through
these measures a sooting or carbon fouling of the ribs is reliably
avoided, so that over a long service life, the heat exchanger
features a better efficiency in comparison with other known heat
exchangers.
[0030] It is clear that the design of the rest of the construction
of the heat exchanger can be changed. Both the position of the
channel conducting the cooling agent and the position of the
channel through which fluid to be cooled flows can be modified.
Furthermore ribs embodied in this manner can extend as far as both
or either of the two channels through which fluid flows. The
above-mentioned advantages are achieved both for a liquid and for a
gas.
* * * * *