U.S. patent application number 13/298703 was filed with the patent office on 2012-05-24 for heat exchanger.
This patent application is currently assigned to Danfoss A/S. Invention is credited to Lars Persson.
Application Number | 20120125578 13/298703 |
Document ID | / |
Family ID | 45062783 |
Filed Date | 2012-05-24 |
United States Patent
Application |
20120125578 |
Kind Code |
A1 |
Persson; Lars |
May 24, 2012 |
HEAT EXCHANGER
Abstract
The invention relates to a plate heat exchanger (9) with a
plurality of heat exchanger plates (1, 13), each comprising at
least one section showing indentations (2, 3, 14, 15), intended to
be placed against corresponding indentations (2, 3, 14, 15) of a
heat exchanger plate (1, 13) of a corresponding design. The heat
exchanger (9) has a first type of indentations (2, 14) and a second
type of indentations (3, 15), wherein the number of said first type
of indentations (2, 14) and said second type of indentations (3,
15) are differing.
Inventors: |
Persson; Lars; (Guiyang,
CN) |
Assignee: |
Danfoss A/S
Nordborg
DK
|
Family ID: |
45062783 |
Appl. No.: |
13/298703 |
Filed: |
November 17, 2011 |
Current U.S.
Class: |
165/133 ;
165/170 |
Current CPC
Class: |
F28D 9/0093 20130101;
F28F 13/18 20130101; F28F 3/08 20130101; F28D 9/0031 20130101; F28F
2215/04 20130101; F24S 20/20 20180501; F28F 3/044 20130101; F28D
9/005 20130101; F24S 25/10 20180501; F28F 13/12 20130101 |
Class at
Publication: |
165/133 ;
165/170 |
International
Class: |
F28F 13/18 20060101
F28F013/18; F28F 3/08 20060101 F28F003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 2010 |
DK |
PA 2010 01048 |
Claims
1. A plate heat exchanger, comprising at least one heat exchanger
plate, preferably a plurality of heat exchanger plates, wherein at
least one of said exchanger plates comprises at least one section
showing indentations, intended to be placed against corresponding
indentations of a heat exchanger plate of a corresponding design,
wherein at least a first type of indentations and at least a second
type of indentations, wherein the number of said first type of
indentations and said second type of indentations are
differing.
2. The plate heat exchanger according to claim 1, wherein said
first type of indentations and said second type of indentations are
of a different design and/or of a different size.
3. The plate heat exchanger according to claim 1, wherein said
first type of indentations and said second type of indentations are
of a different shape.
4. The plate heat exchanger according to claim 1, wherein said
first type of indentations and said second type of indentations
show essentially the same shape.
5. The plate heat exchanger according to claim 1, wherein at least
said first type of indentations and/or at least said second type of
indentations show at least partially an elliptical shape, a
circular shape, a teardrop-like shape, a polygonal shape and/or a
symmetric polygonal shape.
6. The plate heat exchanger according to wherein the number and/or
the arrangement of at least said first type of indentations and/or
at least said second type of indentations corresponds to the shape
of at least said first type of indentations and/or at least said
second type of indentations.
7. The plate heat exchanger according to claim 1, wherein at least
said first type of indentations and/or at least said second type of
indentations are designed, at least in part, with an essentially
flat top and/or bottom surface area.
8. The plate heat exchanger according to claim 1, wherein at least
said first type of indentations and/or at least said second type of
indentations are arranged, at least in part, along straight lines
(A, B, C, D), wherein said lines (A, B, C, D) are preferably
arranged with an angle relative to a side edge of the corresponding
heat exchanger plate.
9. The plate heat exchanger according to claim 1, wherein at least
said first type of indentations and/or at least said second type of
indentations are arranged, at least in part, in such a way, that at
least sectionally at least one of the circulating fluids has to
follow a curved fluid path.
10. The plate heat exchanger according to claim 1, wherein at least
said first type of indentations and/or at least said second type of
indentations are arranged, at least in part, in such a way, that at
least sectionally at least one straight conduit for at least one of
the circulating fluids is formed.
11. The plate heat exchanger according to claim 1, wherein at least
said first type of indentations and/or at least said second type of
indentations are arranged, at least in part, in such a way that at
least sectionally at least one conduit for at least one of the
circulating fluids is arranged in parallel to at least one of the
side edges of the corresponding heat exchanger plate.
12. The plate heat exchanger according to claim 1, wherein at least
one of said heat exchanger plates is formed, at least partially, of
a metal plate and/or a metal alloy plate, wherein said plate
preferably comprises, at least sectionally, a coating made out of
an adhesive material, preferably made out of a soldering
material.
13. A heat exchanger plate comprising at least one section showing
indentations, intended to be placed against corresponding
indentations of a heat exchanger plate of a corresponding design,
wherein at least a first type of indentations and at least a second
type of indentations, wherein said first type of indentations and
said second type of indentations, wherein the number of said first
type of indentations and said second type of indentations are
differing.
14. The plate heat exchanger according to claim 9, wherein at least
said first type of indentations and/or at least said second type of
indentations are arranged, at least in part, in such a way that at
least sectionally at least one conduit for at least one of the
circulating fluids is arranged in parallel to at least one of the
side edges of the corresponding heat exchanger plate.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] Applicant hereby claims foreign priority benefits under
U.S.C. .sctn.119 from Danish Patent Application No. PA 2010 01048
filed on Nov. 19, 2010, the contents of which are incorporated by
reference herein. Applicant also cross-references this application
to an application internal reference 10 01 690 (Attorney Docket No.
6495-0508) filed on the same day herewith, the contents of which
are incorporated by reference herein.
TECHNICAL FIELD
[0002] The invention relates to a plate heat exchanger, comprising
at least one heat exchanger plate (preferably a plurality of heat
exchanger plates) wherein at least one of said exchanger plates
comprises at least one section showing indentations, intended to be
placed against corresponding indentations of a heat exchanger plate
of a corresponding design. Furthermore, the invention relates to a
heat exchanger plate, comprising at least one section showing
indentations, intended to be placed against corresponding
indentations of a heat exchanger plate of a corresponding
design.
BACKGROUND OF THE INVENTION
[0003] Modern heat exchangers of the plate heat exchanger type are
often provided with plates having a so-called herringbone pattern,
i.e. a pattern which has indentations consisting of straight ridges
and valleys. The ridges and valleys change their respective
direction in the centre, producing the pattern that resembles a
herringbone. In a stacked heat exchanger pack, alternate plates are
turned by 180.degree. so that the indentations cross one another.
The thus stacked heat exchanger plates are brazed together, thus
forming a compact and mechanically stable heat exchanger pack.
Using the herringbone pattern of the heat exchanger plates, the
resulting heat exchanger pack comprises a pattern of fluid channels
through which the respective two fluids can flow and exchange their
thermal energy.
[0004] When a heat exchanger pack of the afore-described type is
exposed to pressure (in particular fluid pressure) and heat, the
plates distort, causing a bending moment in the plates. In order to
withstand high pressures, relatively thick metal sheets are used,
e.g. with a thickness of 0.4 mm.
[0005] When such metal plates are pressed into the herringbone
pattern, an unfavourable material flow takes place. If the press
tool is not very accurately manufactured, cracks can appear in the
plates. The relatively thick plates also require a high pressure in
the press tool.
[0006] In a fully brazed heat exchanger, the joints are typically
brazed with copper or a copper alloy solder placed between the
plates. The copper (alloy) solder is frequently introduced as a
coating of the metal sheets. The solder material collects at the
crossing points of the indentations. The surface area and strength
of the solderings are therefore quite small.
[0007] A fluid which is made to flow through a heat exchanger with
a herringbone pattern is forced to flow over the ridges and down
into the valleys. There are no unbroken straight flow-lines. At the
leading edge of the ridges the flow rate is high, whereas the flow
rate of the fluid is low behind the ridges (i.e. in the valleys).
This variation in flow rate is very large. In the heat exchanger
the heat transfer rate is high where the flow rate is high, but the
heat transfer rate is low where the flow rate is low. A smaller
variation in flow rate as it is the case in heat exchangers with a
herringbone pattern is hence favourable.
[0008] When the flowing fluid contains two phases, i.e. the fluid
is a mixture of a gas and a liquid, the recurring changes of
direction at the ridges and valleys will have the effect that the
gas forces the liquid away from contact with the plates. This
reduction in wetting of the heat exchanger plates' surfaces also
reduces the heat transfer rate.
[0009] The shape of the channels through a heat exchanger of the
herringbone design also gives rise to a high pressure drop in the
fluid as it passes through the heat exchanger. This pressure drop
is proportional to the work done in forcing the fluid through the
heat exchanger. A high pressure drop thus means high (mechanical)
power consumption.
[0010] A heat exchanger trying to solve at least some of these
problems is known from the document US 2007/0261829 A1. In this
document it is suggested to provide a pattern on a heat exchanger
plate that comprises indentations in the form of bulges and
hollows, and between which channels are formed, passing through the
heat exchanger. The shape of the thus formed channels gives rise to
a moderate variation in flow rate through the heat exchanger,
thereby resulting in a higher heat transfer rate. The thus formed
heat exchanger plates are stacked together in a way that an upper
plate is turned so that its downward-pointing hollows (bottoms)
abut against the upward-pointing tops of a lower plate. The upper
and lower plates are brazed together by forming solderings where
the heat exchanger plates touch each other. However, it has been
found, that these plates are prone to break in the side walls of
the bulges during operation of the heat exchanger. Obviously, this
seriously adversely affects the lifetime of the heat exchanger.
SUMMARY OF THE INVENTION
[0011] It is the object of the present invention to provide a plate
heat exchanger that has improved characteristics over plate heat
exchangers, known in the state of the art. It is another object of
the present invention to provide a heat exchanger plate, in
particular a heat exchanger plate for building a plate heat
exchanger that has improved characteristics over heat exchanger
plates, known in the state of the art.
[0012] It is suggested to design a plate heat exchanger, comprising
at least one heat exchanger plate, preferably a plurality of heat
exchanger plates, wherein at least one of said heat exchanger
plates comprises at least one section showing indentations and
wherein said indentations are intended to be placed against
corresponding indentations of a heat exchanger plate of a
corresponding design in a way that at least a first type of
indentations and at least a second type of indentations are
provided, wherein the number of said first type of indentations and
said second type of indentations are differing. The expression
"number of indentations" can be understood in a broad way. In
particular, the "different number of indentations" can relate to
the overall number of the respective indentations on the respective
heat exchanger plate and/or to a certain part of the heat exchanger
plate's surface. In some respect, the different number of
indentations can thus be seen as a density of indentations,
expressed as, for example, the number of the respective type of
indentations per unit area. As already mentioned, the "number of
indentations" can relate to only a certain part of the heat
exchanger plate, wherein the "part" usually has to have a certain
size, in particular has to be chosen in a way that summing up and
averaging the number of indentations per unit area will lead to a
more or less stable number, if the size of the area is changed by a
certain amount. In particular, it is possible to choose a somewhat
advantageous surface part of the heat exchanger plate when looking
for the number (and/or the density) of indentations. For example,
it is not unusual for a heat exchanger plates to deviate from a
"standard pattern" in the vicinity of the fluid inlet and/or the
fluid outlet. If such "non-standard" areas are not considered, the
respective numbers will usually improve in quality. The "different
number" can be essentially any deviation from a ratio of one. In
particular, the ratio can be .gtoreq.1.05, .gtoreq.1.1,
.gtoreq.1.2, .gtoreq.1.3, .gtoreq.1.4, .gtoreq.1.5, .gtoreq.1.6,
.gtoreq.1.6, .gtoreq.1.75, .gtoreq.2, .gtoreq.2.25, .gtoreq.2.5,
.gtoreq.2.75, .gtoreq.3, .gtoreq.3.25, .gtoreq.3.5, .gtoreq.3.75,
.gtoreq.4, .gtoreq.4.25, .gtoreq.4.5, .gtoreq.4.75 and/or
.gtoreq.5. Preferentially, a natural number is chosen for the
ratio. Of course, the reciprocals of the suggested values can be
used as well. When it comes to distinguishing the first type of
indentations from the second type of indentations (and presumably
even a third, fourth, fifth or even more different types of
indentations), essentially every possibility on how to distinguish
those types can be encompassed. For example, the types can be
distinguished by size, surface area, shape (for example parallel to
the heat exchanger plate's surface and/or perpendicular to the heat
exchanger plate's surface), material, surface coating, surface
treatment, heat exchanger plate's thickness at or near the
indentation's position, direction of the indentation (for example
upward and/or downward and/or tilted), angular positioning of the
respective indentation and so on. Combinations of two or more of
the mentioned features are possible as well, of course.
Furthermore, when talking about an "indentation", this does not
necessarily mean that the respective section of the heat exchanger
plate has been actively shaped. Instead, it is also possible that
an indentation has been formed by actively shaping (for example by
pressing or the like) of areas, being close to the respective
indentation. Furthermore, the expression "indentation" can be
understood in a very broad way, as well. As an example, an
indentation can be a protrusion, a recess, a groove, a bulge, a
hollow, a land, a web or the like. As it is usual with heat
exchanger plates for plate heat exchangers, two plates,
neighbouring each other, can be of an alternating, corresponding
design. In other words, it is possible that a plate heat exchanger
mainly consists of two differently arranged heat exchanger plates,
having a corresponding design of indentations (wherein an
indentation, going upward will contact a corresponding indentation
from the corresponding heat exchanger plate that is going downward.
Although it is in principle possible that two differently designed
heat exchanger plates (or even more) are manufactured for building
such a plate heat exchanger, for example, normally only a single
heat exchanger plate is designed and manufactured, wherein the
aforementioned two different "designs" of heat exchanger plates are
achieved by turning every second plate in the stack of heat
exchanger plates by 180.degree.. Of course, the uppermost, as well
as the lowermost plate has usually a different design for
effectively closing the heat exchanger block. Typically essentially
flat metal sheets can be used for this. After the stack of heat
exchanger plates (and possibly other components) has been put
together, the "raw" plate heat exchanger arrangement will usually
be sent through a tunnel furnace to braze/solder the respective
components together, to form a compact and mechanically stable
block. Of course, it is possible that the plate heat exchanger will
(essentially) show only the aforementioned two different types of
indentations. However, it is also possible that a third, a fourth,
a fifth or even more different types of indentations are provided
as well. The presently suggested plate heat exchanger has to have
(like any heat exchanger) two separate sets of fluid channels that
are fluidly separated from each other. This is, because the thermal
energy has to be transferred from one fluid to the other. In rare
cases, more fluids, and hence more separated fluid channels, are
used within a single heat exchanger. Usually, the two (or even
more) fluids show different characteristics. For example, the two
different fluids can have a different state of matter (for example,
one fluid is a liquid, while another fluid is a gas). Also, one or
both fluids can be a mixture of a gas and a liquid, with a varying
gas to liquid ratio. Furthermore, the two different fluids will
normally have a different temperature (at least at the entrance
port of the stack type heat exchanger) and/or a different pressure.
Even more, the different fluids can have a different viscosity, a
different density, a different thermal capacity and so on. By using
a different number (density) for different types of indentations,
it is very easy to provide a mechanical stability that is different
for the two different fluid channels, containing the two different
fluids. This way, the mechanical stability of the plate heat
exchanger can remain at the same level or can be even increased,
while the overall dimension of the stack type heat exchanger can be
reduced. For example, if the first type of indentations is
"responsible" for the connection with the "upper" heat exchanger
plate, while the second type of indentations is "responsible" for
the connection with the "lower" heat exchanger plate, by choosing a
different number of first and second type of indentations, the
mechanical stability between the "middle" and "upper" plate on the
one hand and between the "middle" and "lower" plate on the other
hand can be adapted to the fluid pressure of the respective fluid,
flowing in the respective channels, that is to be expected.
Furthermore, using the proposed design, it is very easy to generate
two different types of fluid channels for the two different fluids.
As an example, the two different fluid channels can differ in cross
section (in particular shape and/or size), the curvature of the
respective fluid channel, the number of "obstacles" (that are
generating vortices, for example) and/or in different ways. This
way, an advantageous heat exchanger can be achieved. For example,
the overall size of the resulting heat exchanger and/or the
lifetime of the resulting heat exchanger and/or the resulting heat
exchanger's effectiveness can be enhanced.
[0013] In particular, it is possible that the plate heat exchanger
is designed in a way that said first type of indentations and said
second type of indentations are of a different design and/or of a
different size. Using such a design, it is particularly simple to
provide different strength of the respective connections (for
example to take into account different pressures of the respective
fluids) and/or to adapt the sizes and/or the characteristics of the
fluid channels, being formed between the respective connections, to
the particular necessities of the respective fluid. The expression
"different design" can be understood in a broad way. The "different
design" cannot only relate to the size and/or the shape of the
respective indentation (especially when looking from above and/or
from below onto the respective heat exchanger plate). For example,
the different design (in particular the size and/or the shape) can
relate to a cross-sectional view onto the respective structure, as
well. Furthermore, even more different "designs" can be encompassed
by this suggestion, for example a different thickness of the
respective heat exchanger plate in the respective section, a
different material, a different material coating, a different
surface treatment and/or the like.
[0014] It can prove to be advantageous, if the plate heat exchanger
is designed in a way that said first type of indentations and said
second type of indentations are of a different shape. The "shape"
of the respective indentation can be in particular the shape, when
seen from above and/or from below onto the respective heat
exchanger plate. Using a different shape for the different types of
indentations can be particularly useful if by choosing a different
shape, the respective connections and/or the resulting fluid
channels are particularly well suited for the characteristics of
the respective fluid involved. As an example, by using a first
shape for the first type of indentations, a very low fluid
resistance can be achieved for the first fluid, used within the
heat exchanger. By using a different shape for the second type of
indentations, however, a higher fluid resistance can be achieved
for the second fluid involved. Such a higher fluid resistance is
introducing additional turbulence. Such additional turbulence can
increase the possible heat transfer rate from the respective fluid
to the channel wall and finally to the other fluid, thus utilising
the higher resistance for increased heat transfer, thus increasing
the performance of the resulting heat exchanger. In particular if a
third, fourth (or even more) type of indentations is present, a
mixture of "same shapes" and "different shapes" can prove to be
useful, as well. Also, it is possible to realise combination
effects by choosing an appropriate combination of number of
indentations and shape of indentations.
[0015] However, it can also be of advantage, if the plate heat
exchanger is designed in a way that said first type of indentations
and said second type of indentations show essentially the same
shape. Using the same shape can be particularly advantageous, if
the respective shape has certain (advantageous) characteristics,
for example a particularly low fluid resistance, a particularly
high mechanical strength, a particularly advantageous ratio of
surface area to the length of the surrounding edge or the like.
[0016] In particular, it is possible to design the plate heat
exchanger in a way that at least said first type of indentations
and/or at least said second type of indentations show at least
partially an elliptical shape, a circular shape, a teardrop-like
shape, a polygonal shape and/or a symmetric polygonal shape. These
shapes have proven to be particularly advantageous during first
experiments. In particular, an elliptical shape and/or a circular
shape usually result in a particularly high mechanical strength, a
particular long lifetime of the resulting connection and/or a
particularly large connection area, when compared to the bordering
line of this connection area, combined with the relatively low
fluid flow resistance. A teardrop-like shape will usually result in
a particularly low fluid flow resistance, thus reducing mechanical
energy losses. A polygonal shape and/or a symmetric polygonal shape
will usually result in an introduction of (slight to moderate)
additional turbulence, which can improve the heat transfer
efficiency. By a symmetric polygonal shape, usually a shape is
meant, in which the majority or even all of the sides of the
polygon show essentially the same length.
[0017] Another preferred embodiment of a plate heat exchanger can
be achieved if the number and/or the arrangement of at least said
first type of indentations and/or at least said second type of
indentations corresponds to the shape of at least said first type
of indentations and/or at least said second type of indentations.
By using such symmetries, a particularly strong heat exchanger with
a long lifetime can be achieved, because mechanical stresses that
are occurring are distributed comparatively homogeneously.
Furthermore, using such symmetries, usually the resulting fluid
flow patterns are advantageous, such decreasing fluid flow
resistance and/or increasing heat transfer performance.
[0018] Another preferred design of the plate heat exchanger can be
achieved if at least said first type of indentations and/or at
least said second type of indentations are designed, at least in
part, with an essentially flat top and/or bottom surface area.
Having such a flat surface area, the strength of the resulting
connection with the corresponding indentation of the neighbouring
heat exchanger plate can be particularly strong, while soldering
material (for example copper solder and/or copper alloy solder) can
be saved.
[0019] Yet another preferred embodiment of the plate heat exchanger
can be achieved if at least said first type of indentations and/or
at least said second type of indentations are arranged, at least in
part, along straight lines, wherein said straight lines are
preferably arranged at an angle relative to a side edge of the
corresponding heat exchanger plate. Using such an arrangement for
the indentations, a simple, yet very efficient design of the heat
exchanger plates can be achieved. In particular, it is possible
that for building a complete plate heat exchanger, essentially only
a single type of indented heat exchanger plate has to be used,
whereas every second plate in the stack of heat exchanger plates is
turned by 180.degree. with respect to the respective neighbouring
heat exchanger plates. This way, manufacturing tools and storage
room can be saved, thus lowering production cost. The straight
lines are preferably arranged at an angle of approximately
45.degree. with respect to the corresponding side edge of the
corresponding heat exchanger plate. However, certain variations
around this preferred angle are possible. For example, the interval
of possible angles can start at 30.degree., 35.degree., 40.degree.,
42.degree., 43.degree. and/or 44.degree. and end at 46.degree.,
47.degree., 48.degree., 50.degree., 55.degree. and/or 60.degree..
But the present invention in its broadest embodiment is not limited
to any such angle.
[0020] Yet another preferred embodiment of a plate heat exchanger
can be achieved if at least said first type of indentations and/or
at least said second type of indentations are arranged, at least in
part, in such a way that at least sectionally at least one of the
circulating fluids has to follow a curved fluid path. This way, it
is usually possible to increase the heat transfer rate of the
respective fluid, thus increasing the performance of the heat
exchanger.
[0021] Additionally or alternatively it is possible to design the
plate heat exchanger in a way that at least said first type of
indentations and/or at least said second type of indentations are
arranged, at least in part, in such a way that at least sectionally
at least one straight conduit for at least one of the circulating
fluids is formed. By this design, the fluid flow resistivity can
usually be decreased. This way, mechanical energy can be saved.
This design is particularly useful with fluids, showing a
particularly high and/or low viscosity and/or in combination with a
design of the plate heat exchanger in which turbulence is generated
by different means.
[0022] Furthermore it is suggested to design the plate heat
exchanger in a way that at least said first type of indentations
and/or at least said second type of indentations are arranged, at
least in part, in such a way that at least sectionally at least one
conduit for at least one of the circulating fluids is arranged in
parallel to at least one of the side edges of the corresponding
heat exchanger plate. This way, usually a particularly advantageous
fluid flow between the fluid inlet duct and the fluid outlet duct
of the respective fluid channel can be achieved.
[0023] Another particularly preferred embodiment of the plate heat
exchanger can be achieved if at least one of said heat exchanger
plates is formed, at least partially, of a metal plate and/or a
metal alloy plate, wherein said plate preferably comprises, at
least sectionally, a coating made out of an adhesive material,
preferably made out of a soldering material. The metal plate can
be, for example, made out of aluminum, an aluminum alloy, iron,
copper, an iron alloy (for example steel), a copper alloy or the
like. As an adhesive material, it is possible that a glue or the
like is used. Of course, it is also possible that a soldering
material (or brazing material) like copper or a copper alloy is
used. It is to be noted that this suggested feature may be
prosecuted in connection with the preamble of originally filed
claim 1.
[0024] Furthermore, it is suggested that a heat exchanger plate,
comprising at least one section showing indentations, that are
intended to be placed against corresponding indentations of a heat
exchanger plate of a corresponding design, is designed in a way
that at least a first type of indentations and at least a second
type of indentations are provided, wherein the number of said first
type of indentations and said second type of indentations are
differing. Such a heat exchanger plate is particularly useful for
manufacturing a plate heat exchanger of the above described type.
Furthermore, the suggested heat exchanger plate can show the same
features and advantages, as already described in connection with
the stack type heat exchanger, at least in analogy. Furthermore,
the heat exchanger plate can be modified in the aforementioned
sense, at least in analogy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The present invention and its advantages will become more
apparent, when looking at the following description of possible
embodiments of the invention, which will be described with
reference to the accompanying figures, which are showing:
[0026] FIG. 1: a first embodiment of a heat exchanger plate for a
plate heat exchanger in a schematic view from above;
[0027] FIG. 2: the heat exchanger plate of FIG. 1 in a schematic
view from the side;
[0028] FIG. 3: a plurality of heat exchanger plates according to
the embodiment of FIGS. 1 and 2, stacked together, in a schematic
view from the side;
[0029] FIG. 4: a typical embodiment of a plate heat exchanger in a
schematic perspective view;
[0030] FIG. 5: a second embodiment of a heat exchanger plate for a
plate heat exchanger in a schematic view from above;
[0031] FIG. 6: the heat exchanger plate of FIG. 5 in a schematic
view from the side;
[0032] FIG. 7: a plurality of heat exchanger plates according to
the embodiment of FIGS. 5 and 6, stacked together, in a schematic
view from the side; and
[0033] FIG. 8: typical flow paths for the fluids within a plate
heat exchanger using heat exchanger plates according to the
embodiment of FIGS. 5 to 7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] Plate heat exchangers (9), such as the typical embodiment,
shown in FIG. 4, are well-known devices for the transfer of heat
between two different fluids. Plate heat exchangers (9) are used in
many different applications, for example in the automotive
industry, for cooling and heating of buildings and so on.
[0035] A plate heat exchanger (9) comprises a plurality of heat
exchanger plates (1, 13) that are stacked over each other. The
individual heat exchanger plates (1, 13) are designed with a
pattern of indentations (2, 3, 14, 15), typically designed as
bulges and hollows and/or as ridges and valleys (the latter one in
particular in combination with the herringbone design). On the very
top and the very bottom of the plate heat exchanger (9), flat metal
sheets (16) are provided for retaining the fluids within the plate
heat exchanger (9). Furthermore, connections (11, 12) for inlet
(11) and outlet (12) of two fluids are provided as well.
[0036] The stack of heat exchanger plates (1, 13) is usually
manufactured by loosely arranging the heat exchanger plates (1, 13)
over each other and joining them together by soldering to form a
mechanically stable integral unit.
[0037] Because of the pattern of indentations (2, 3, 14, 15) on the
heat exchanger plates (1, 13), separate channels for the two
fluids, are formed by the soldering process, wherein the separate
channels are fluidly separated from each other. Typically, the two
fluids circulate in a counterflow between alternate pairs of heat
exchanger plates (1, 13). This technology as such is generally
known.
[0038] FIG. 1 is a plan view onto a first possible embodiment of a
heat exchanger plate (1), showing a distinct pattern of
indentations (2, 3). As can be seen from FIG. 1, the depicted heat
exchanger plate (1) is provided with a pattern of first bulges (2)
and second bulges (3), and not with the currently widely used
herringbone pattern. Furthermore, circular ports (17) are provided
near the four corners of the heat exchanger plate (1). These
circular ports (17) are the typical connections for the inlet (11)
and outlet (12) of two different fluids into and out of the plate
heat exchanger (9). Within the heat exchanger plate (1), shown in
FIG. 1, a square is drawn with a dashed line. The respective
surface part of the heat exchanger plate (1) is shown on the right
side of FIG. 1 at an enlarged scale. Thanks to the enlarged scale,
the pattern of first bulges (2) and second bulges (3) of the heat
exchanger plate (1) is clearly visible. Both first bulges (2) and
second bulges (3) are raised by a given height relative to a
reference plate (18) in opposite directions. The flanks of the
bulges (2, 3) have an edge angle of approximately 45 degrees. This
deformation can be easily done by pressing techniques. In contrast
to the herringbone pattern, the pattern of bulges (2, 3) of the
present heat exchanger plate (1) is well suited to the pressing
process, since the necessary deformation of the plate sheets is
comparatively small. This way, the risk of cracks appearing in the
heat exchanger plate (1) can be significantly reduced.
[0039] The first bulges (2) and second bulges (3) constitute a
first pattern consisting of the first bulges (2), and a second
pattern consisting of the second bulges (3). In the present
embodiment of a heat exchanger plate (1), first bulges (2) and
second bulges (3) have substantially flat first tops (4) and flat
second tops (5) with a corresponding first surface area and second
surface area, respectively. As can be seen from FIG. 1, the surface
area of each individual first top (4) of the first bulges (2) is
smaller as compared to the surface area of each individual second
top (5) of the second bulges (3). Since the number of first bulges
(2) and second bulges (3) is essentially the same, the overall
surface area of the first tops (4) of the first bulges (2) is
likewise smaller as compared to the overall surface area of the
second tops (5) of the second bulges (3).
[0040] When a heat exchanger (9) is made from a plurality of heat
exchanger plates (1), the heat exchanger plates (1) are connected
such that e.g. the first surface areas (4) of one plate (1) are
fixedly connected (soldered, brazed, glued) to the first surface
areas (4) of a lower plate (1), and in the same manner, the second
surface areas (5) of the one plate (1) are fixedly collected
(soldered, brazed, glued) to the second surface areas (5) of an
upper plate (1) (see, for example, FIG. 3). Due to the
comparatively large surface areas of the first surface areas (4)
and the second surface areas (5), relatively strong connections are
made in the present embodiment. The connections by material
engagement (10) are indicated in FIG. 3 between two neighbouring
first surface areas (4) and two neighbouring second surface areas
(5), respectively. The connection by material engagement (10) can
be established by any process known in the art, such as brazing,
soldering, glueing etc.
[0041] In operation, the heat exchanger (9) is filled with
pressurised fluids (wherein the pressure of the two fluids involved
can differ) which tends to force the heat exchanger plates (1)
apart. The heat exchanger plates (1) can also expand due to
increased temperatures, introduced by the fluids. Because of the
pattern of first and second bulges (2, 3), all stresses generated
in the plate material are directed essentially in the direction of
the plate's material, and hence no or only small bending moments
are created. The absence of such bending moments increases the
strength and the lifetime of the structure. The strength of the
heat exchanger (9) is also increased by the comparatively large
contacting areas (10) between the first and second bulges (2, 3).
Because of this improved strength, thinner sheet metal can be used
for the heat exchanger plates (1). Alternatively, the sheet metal
with the usual thickness of 0.4 mm can be used, giving the heat
exchanger (9) a bursting pressure of 600 bar compared with 200 bar
for a standard heat exchanger with a herringbone pattern and the
same metal sheet thickness.
[0042] FIG. 2 shows a profile view of the first (2) and second (3)
bulges along lines A and B, represented by a dashed and solid line,
respectively.
[0043] The heat exchanger (9) according to the present invention
also offers the possibility that the opposite sides may be adapted
to different pressures of the fluids as it may often be
desired.
[0044] By shaping the first (2) and second (3) bulges in way that
they have different surface areas (first (4) and second (5) surface
area), it is first of all possible that the flow characteristics
(which have an influence on the pressure drops of the fluids) can
be made different at the two sides of each of the plates (1) and
hence can be made different for the two fluids involved.
Furthermore, due to the different size the contact zones (4, 5) of
two adjacent plates (1) (where the contact zones (4, 5) are
connected by material engagement (10)) it is possible to design the
final heat exchanger (9) in a way that it can have a higher
pressure resistance towards one fluid, as compared towards the
other fluid.
[0045] Therefore it is possible to design the resulting heat
exchangers (9) according to the specific requirements. In
particular, the sizes (both absolute and relative) and
distributions of the first (2) and second (3) bulges may be
designed in such a way that specific flow rates and/or pressure
drops can be obtained. At the same time the contact zones (4, 5) of
the heat exchanger plates (1) can be dimensioned according to the
required strength.
[0046] In the illustrated first embodiment, the surface areas of
both the first bulges (2) and the second bulges (3) show an oval
shape with the elongated diameter (i.e. the main axis of the
ellipse) pointing substantially in the direction of the fluid flow.
This way, the cross-section in the direction of the fluid flow is
minimised and hence the fluid flow resistance of the fluid (and
consequently the pressure loss in the fluid) can be reduced.
[0047] First experiments indicate that forming the flat tops (4)
and (5) with an elliptical shape is superior to forming them with
circular shapes. There is some indication that circular shapes are
prone to cracks in the side walls of the first (2) and/or second
(3) bulges. While the strength of the connection by material
engagement (10) between neighbouring heat exchanger plates (1)
depends highly on the surface areas of the flat tops (4) and (5),
the load capacity of the walls depends strongly on the
circumferential length and the thickness of the plate sheet. If the
thickness of the plates were to be changed in order to obtain a
similar strength of the walls and the connections (10), the heat
exchanging effectiveness of the heat exchanger (9) would be
adversely affected. Using an elliptic shape for the first (2)
and/or the second (3) bulges the circumferential length can be
easily increased with constant plate sheet thickness and/or surface
area of the connections (10).
[0048] As a matter of completeness, it should be mentioned that
according to alternative embodiments any other suitable shape for
the first (2) and/or the second (3) bulges is possible as well. In
particular, by using different shapes, it is likewise possible to
increase the circumferential lengths without increasing the surface
area of the connections (10).
[0049] In FIG. 3 a plurality of heat exchanger plates (1) that are
connected to each other using connections by material engagement
(10) are shown in a view from the side. The direction of the view
is parallel to the lines A and B of FIG. 1. It can be seen that
channels (6, 7) with two different cross-sections are formed. The
larger channels (6) are formed by the heat exchanger plates (1)
between the first bulges (2) with the first tops (4), showing the
smaller surface areas. Of course, the connections between the
(smaller) first tops (4) will yield a weaker connection as compared
to the connections between the (larger) second tops (5).
Furthermore, between the second bulges (3), smaller second channels
(7) are formed. However, these smaller second channels (7) are
suitable for higher pressurised fluid due to the stronger
mechanical connections (10) between the (larger) second tops
(5).
[0050] According to the embodiment of the heat exchanger plate (1)
that is shown in FIGS. 1 to 3, first (2) and second (3) bulges are
placed symmetrically in a rectangular grid, with first (2) and
second (3) bulges on every other grid point. Thus, they are located
alternating each other along a number of parallel lines, the
distance between first (2) and second (3) bulges being equal and
the distance between such parallel lines being equal. The channels
(6, 7) that are formed for the fluids will then follow an
essentially zig-zag line. In other words, the respective fluid is
not forced to flow over ridges and valleys as in the herringbone
pattern. Instead, it will only encounter the rounded, "pillar-like"
constrictions (in form of first (2) and second (3) bulges) at the
connecting points (10) between the stacked heat exchanger plates
(9).
[0051] Naturally, first (2) and second (3) bulges will still cause
a certain amount of variation in fluid flow rate and direction and
some turbulence in the fluid. However, it is known that it is
usually not desirable to eliminate turbulence completely, because
usually laminar fluid flow gives poorer heat transfer rate. With
the proposed pattern of bulges (2, 3) slight to moderate fluid flow
rate variation in the fluid is obtained. Thus a lower pressure drop
across the heat exchanger (9) per heat transfer unit is obtained
for a given average fluid flow rate of the fluid. The mechanical
power required to force a fluid through the heat exchanger (9) per
heat transfer unit is therefore also lowered, in particular when
compared to a heat exchanger with a herringbone pattern.
[0052] For improved fluid flow characteristics, the first (4) and
second (5) flat top areas are presently positioned such that their
longest diameters (main axis of the ellipse) substantially extend
in a direction parallel to the direction of fluid flow in the heat
exchanger (9). The direction of flow in the heat exchanger may be
defined as the local main flow direction of the fluid, when
averaged over a plurality of bulges (2, 3).
[0053] However, they could also be positioned with their longest
diameter arranged with any angle relative to the direction of fluid
flow in the heat exchanger (9), and may even show varying angles
over the surface of the heat exchanger plates (1). Also, the sizes
and/or shapes of the first top (4) and/or second top (5) areas may
change over the surface of the heat exchanger plate (1), thus
changing individual and/or relative flow and pressure
characteristics locally.
[0054] A particular relevant embodiment for this is if the angles
of the longest diameters are changing from substantially
perpendicular to parallel relative to the direct connecting line
between fluid inlet (11) and fluid outlet (12). Such an arrangement
will assist the fluids entering through the fluid inlet (11) in
distributing over the whole width of the heat exchanger plates (1),
and again, will assist the fluids coming from the sides of the heat
exchanger plates (1) to be directed to the fluid outlet (12).
[0055] As shown in FIG. 3, first (6) and second (7) channels,
especially the respective centres of first (6) and second (7)
channels, have a gap (8) with a straight, essentially undisturbed
fluid flow path.
[0056] When looking at a second channel (7), for example, the fluid
does not need to change its direction because of the proximity to
the upper first tops (4). Still, the fluid is affected to some
extent by the proximity of the left and right second tops (5). If a
heat exchanger (9) with channels (7) of this type is used with a
two-phased fluid, i.e. a fluid that is a mixture of both gas and
liquid, the gas phase tends to flow along said gap (8) in the
centre of the second channel (7). This means that the gas can flow
through the heat exchanger (9) without compromising the wetting of
the walls of the heat exchanger plates (1) by the liquid phase of
the fluid. This provides better heat transfer. The same applies to
the first channels (6) in analogy.
[0057] In some operational cases, nuclear boiling can also occur
instead of surface evaporation along the walls of the heat
exchanger plates (1). Such nuclear boiling will occur especially in
hollows, where the fluid flow rate is significantly reduced. Such
nuclear boiling will further improve the heat transfer rate.
[0058] In an alternative embodiment (not shown), the first (2) and
second (3) bulges are located symmetrically in a grid, but unlike
the embodiment of a heat exchanger plate (1) as shown in FIGS. 1 to
3, the grid is arranged so that the channels (6, 7) formed are
parallel with the edges of the heat exchanger plate (1). This
arrangement usually results in a lower pressure drop but also a
lower heat transfer rate, because the tops (4, 5) obscure one
another.
[0059] However, the arrangement can be modified in essentially any
way. In particular, the pattern does not need to be symmetrical
over the whole plate. This way, different arrangements can be used
to direct the flow of fluid in the desired way and to control
turbulence and pressure drop.
[0060] Furthermore, it is not necessary that the pattern of first
(2) and second (3) bulges (and presumably even more different types
of bulges; not shown) covers essentially the whole of the heat
exchanger plate (1). The pattern can be combined with deflecting
barriers and baffles, with completely flat surfaces, and also with
conventional herringbone patterns if this is required for whatever
reason.
[0061] FIG. 5 is a plan view of a second possible embodiment of a
heat exchanger plate (13). Such a heat exchanger plate (13) can be
used for manufacturing plate heat exchanger (9), as shown in FIG.
4. The present second embodiment is somewhat similar to the first
embodiment of a heat exchanger plate (1), as shown in FIGS. 1 to 3.
However, the arrangement, number and shape of the first (14) and
second bulges (15) are different.
[0062] In the presently shown second embodiment of a heat exchanger
plate (13), the first bulges (14) have an essentially hexagonal
shape, while the second bulges (15) have an essentially triangular
shape. Similar to the first embodiment of the exchanger plate (1),
both first (14) and second (15) bulges of the presently shown heat
exchanger plate (13) have first tops (19) and second tops (20) with
an essentially flat top surface, respectively. It can be seen from
FIG. 5 that the surface area of a single first top (20) (first
bulge (15)) is larger than the surface area of a single second top
(19) (second bulge (14)).
[0063] The arrangement of the first (14) and second (15) bulges
relative to each other is chosen to reflect the individual shapes
of the first (14) and second (15) bulges. Since the first bulges
(14) are shaped in form of a hexagon, the second bulges (15) are
likewise arranged in a hexagonal formation (22) around a central
first bulge (14). Therefore, there are six second bulges (15)
arranged around each first bulge (14). Similarly, since the second
bulges (15) are shaped in form of a triangle, the first bulges (14)
are arranged in a triangular formation (21) around a central second
bulge (15). Therefore, there are three first bulges (14) arranged
around each second bulge (15).
[0064] In the presently shown embodiment, the arrangement of first
(14) and second (15) bulges is done in a way that a corner of the
hexagonally shaped first bulge (14) is pointing towards a
triangularly shaped second bulge (15). Contrary to this, a straight
line of the triangularly shaped second bulge (15) is "pointing"
towards a hexagonally shaped first bulge (14). To achieve this
arrangement, the second bulges (15) are positioned in a way that
the second bulges (15) change direction along a line (C), as seen
in FIG. 5. First experiments have shown that this particular
arrangement reduces mechanical stresses in the metal sheet of the
heat exchanger plate (13) when at least one of the fluids is
changing pressure and/or temperature. Therefore, the lifetime of
the resulting heat exchanger (9) can usually be enhanced.
Furthermore, the suggested arrangement of first (14) and second
(15) bulges have shown a comparatively good heat transfer rate with
relatively low mechanical energy losses (pressure drop of the
fluids) in first experiments.
[0065] However, a different arrangement of first (14) and second
(15) bulges and/or a different alignment of first (14) and second
(15) bulges can be advantageous with different fluids and/or fluid
characteristics. In particular, by choosing an appropriate
arrangement and/or alignment of first (14) and second (15) bulges,
the resulting heat exchanger (9), manufactured from the presently
suggested heat exchanger plates (13) can be adapted to the actual
requirements.
[0066] FIG. 6 shows a profile view of the first (14) and second
(15) bulges along lines (C) and (D), represented by a dashed and a
non-broken line, respectively. By introducing a different number
and/or shape and/or size of first (14) and second (15) bulges,
different flow and/or pressure characteristics can be obtained on
the opposite sides of a heat exchanger plate (13). This is due to
the different number, shape and size of the "obstacles", seen by
the fluid on its way through the heat exchanger (9).
[0067] It shall be noted, that the figure is highly illustrative
showing the profiles as straight lines, this typically will not be
the case. The illustrated `straight` lines usually will be curved,
and the profile will in real life typically comprise no
`corners`.
[0068] In FIG. 7, an arrangement of several heat exchanger plates
(13) that are stacked over each other and connected to each other
by means of material engagement (23) are shown. The depicted view
is onto the side of such a stack of heat exchanger plates (13). The
direction of the view is chosen to be parallel to the lines (C) and
(D) of FIG. 5. Hence FIG. 7 is illustrating "two levels" of a heat
exchanger (9). It can be seen from FIG. 7 that, according to the
presently described second embodiment, the larger first channels
(24) are located between the less numerous second bulges (15).
Likewise, the smaller second channels (25) are located between the
first bulges (14) that are larger in number than the second bulges
(15).
[0069] It should be noted that the overall strength of the
connection between two heat exchanger plates (13) is not only
determined by the surface area of the first tops (19) and/or second
tops (20) of the first bulges (14) and the second bulges (15),
respectively, but also by the (relative) number of first bulges
(14) and/or second bulges (15). Therefore, it is possible to obtain
a higher strength of the overall connection between two neighboring
heat exchanger plates (13) through the (smaller) second flat tops
(20) in comparison to the overall connection through the first flat
tops (15), simply by increasing the number of second flat tops
(20). Of course, the overall connection strength through the first
flat tops (15) can be increased by this method as well.
[0070] By such an adaption of the overall mechanical connection
strength, it is possible to optimise the resulting heat exchanger
(9) with respect to the maximum fluid pressures and/or the maximum
fluid temperatures occurring in the specific design. This way, it
is usually possible to optimize the heat exchanger's effectivity,
the size of the resulting heat exchanger (9) and to lower the
manufacturing costs.
[0071] As it has been described in connection with the first
embodiment of a heat exchanger plate (1) shown in FIGS. 1 to 3,
designing first bulges (14) and/or second bulges (15) with a shape,
being different from the circular shape (in the presently shown
example triangular and hexagonal shapes are used), it is possible
to elongate the circumferential length of the edge lines of the
flat tops (19, 20), without increasing the size of the respective
surface area. As already described, this will result in a design
that is less prone to mechanical failure due to pressure
differences and/or temperature differences. Therefore, the lifetime
of the resulting heat exchanger (9) can usually be increased.
[0072] Even with respect to the presently shown second embodiment
of a heat exchanger plate (13), it is possible that any other
suitable shape, number and/or size can be used for the first bulges
(14) and/or the second bulges (15).
[0073] Similar to the already described first embodiment of a heat
exchanger plate (1), in the presently suggested second embodiment
of a heat exchanger plate (13) the first channels (24) and second
channels (25) may gaps (26) with a straight, essentially
undisturbed fluid flow, also called `lines of sight`. If such
`lines of sight` exists and their extension will be highly
depending on the exact designs of the heat exchanger plate (1) with
first (14) and second (15) bulges, such as their relative distance
in relation to the extension and size of their flat tops (19, 20).
Similar `lines of sight` may exist in the embodiment of e.g. FIG.
3. Here, when looking at the first channel (24), the fluid does not
need to change direction because of the proximity to the first tops
(19), but is affected only to some extent by the second tops (20).
(And likewise when looking at the second channel (25).) If a heat
exchanger (9) with channels (24, 25) of this type is used with a
two-phased fluid, the gas phase tends to flow along said gap (26)
in the centre of the first channel (24) or second channel (25).
Therefore, the gas phase flows through the heat exchanger (9)
without compromising the wetting of the heat exchanger plates (13)
by the liquid phase. This provides better heat transfer.
[0074] Of course, even with respect to the second embodiment of a
heat exchanger plate (13) (or even in connection with different
designs of a heat exchanger plates), in some operational cases
nuclear boiling can occur instead of surface evaporation,
especially in hollows, where the fluid flow rate is significantly
lowered. This can further improve the heat transfer rate.
[0075] A further aspect of the suggested heat exchanger plates (1,
13), in particular with respect to the second embodiment of a heat
exchanger plate (13) is that flow characteristics will be highly
different in relation to the direction of fluid flow relative to
the pattern of first bulges (2, 14) and the second bulges (3,
15).
[0076] FIG. 8A shows the paths (27a, 28a) defined in the overall
direction of fluid flow, where the dashed curvy line (28a)
illustrates a fluid flow path on the side of the heat exchanger
plate (13) defined by the first bulges (14) (which are seen as
protrusions, while the second bulges (14) are seen as hollows). The
unbroken curvy line (27a) illustrates in the same manner a fluid
flow path seen on the other side of the heat exchanger plate (13)
that is defined by the second bulges (15). Both flow paths (27a)
and (28a) are repeatedly changing their respective direction of
fluid flow (similar to some form of a zig-zag) due to deflection at
the first bulges (14) and the second bulges (15) along the heat
exchanger plate (13), respectively.
[0077] In a fluid flow direction orthogonal to the overall
direction of fluid flow the fluid flow will not see the same
obstructions in that the first and second bulges (14, 15) are
arranged nicely along lines (C) and (D) (see FIG. 5), thus leaving
undisturbed `higways` (27b) and (28b) of fluid flow paths for the
fluid flows, being substantially without obstructions (see FIG.
8B). At least, the paths (27b) and (28b) may be such that their
resistance to flow is lower than in other flow directions.
[0078] Such undisturbed `higways` (27b, 28b) have the benefit of a
better distribution of the fluid flow over the heat exchanger plate
(13) (and therefore over the completed heat exchanger (9)), so that
the flow resistance will be lower in a fluid flow direction
orthogonal to the overall direction of fluid flow (the overall
direction of fluid flow corresponds to the direction of fluid flow
parallel to the "long" sides of the heat exchanger plate (13)). By
having a lower fluid flow resistance in a direction, being
different from the direction leading from an inlet (11) to an
outlet (12), the fluid will be better distributed over the heat
exchanger plate (13) as a whole.
[0079] Other modifications, previously described with respect to
the first embodiment of a heat exchanger plate (1), can also be
employed for the presently described second embodiment of a heat
exchanger plate (13) (or any other modification of a heat exchanger
plate), at least in analogy.
[0080] Additional information can be taken from the application,
filed by the same applicant at the same patent office on the same
day under the internal reference number 10 01 690 (Attorney Docket
No. 6495-0508). The contents of this other application is
incorporated by reference into the present application.
[0081] While the present invention has been illustrated and
described with respect to a particular embodiment thereof, it
should be appreciated by those of ordinary skill in the art that
various modifications to this invention may be made without
departing from the spirit and scope of the present.
* * * * *