U.S. patent application number 10/580267 was filed with the patent office on 2007-06-28 for heat exchanger plate and plate heat exchanger comprising such plates.
This patent application is currently assigned to Eco Lean Research & Development A/S. Invention is credited to Hans Rausing.
Application Number | 20070144711 10/580267 |
Document ID | / |
Family ID | 38192255 |
Filed Date | 2007-06-28 |
United States Patent
Application |
20070144711 |
Kind Code |
A1 |
Rausing; Hans |
June 28, 2007 |
Heat exchanger plate and plate heat exchanger comprising such
plates
Abstract
The invention relates a heat exchanger plate (1) comprising a
number of turbulence-promoting protuberances (4) that project from
the plane (3) of the heat exchanger plate. The protuberances (4)
have a surface profile (6) for promoting break-up of laminar
boundary layers. The invention also relates to a plate heat
exchanger comprising such heat exchanger plates (1).
Inventors: |
Rausing; Hans; (East Sussex,
GB) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Eco Lean Research & Development
A/S
Holbergsgade 14, 2 sal tv
Copenhagen
DK
DK-1057
|
Family ID: |
38192255 |
Appl. No.: |
10/580267 |
Filed: |
November 19, 2004 |
PCT Filed: |
November 19, 2004 |
PCT NO: |
PCT/SE04/01694 |
371 Date: |
May 25, 2006 |
Current U.S.
Class: |
165/109.1 ;
165/166 |
Current CPC
Class: |
F28F 3/044 20130101;
F28F 13/02 20130101; F28D 9/0031 20130101; F28F 13/12 20130101 |
Class at
Publication: |
165/109.1 ;
165/166 |
International
Class: |
F28F 13/12 20060101
F28F013/12 |
Claims
1. A heat exchanger plate (1) comprising a number of
turbulence-promoting protuberances (4) which project from the plane
(3) of the heat exchanger plate, characterised in that the
protuberances (4) have a surface profile (6) for promoting break-up
of laminar boundary layers, and the surface profile (6) consists of
spherical or ellipsoid segments.
2. A heat exchanger plate (1) as claimed in claim 1, which together
with a plurality of identical heat exchanger plates (1) is
stackable in such a manner that the protuberances (4) in a first
heat exchanger plate (1) are partially accommodated in the
protuberances (4) in a second heat exchanger plate (1).
3. A heat exchanger plate (1) as claimed in claim 1, in which the
protuberances (4) are symmetrically arranged.
4. A heat exchanger plate (1) as claimed in claim 1, in which the
surface profile (6) has a profile depth that is considerably
smaller than the depth of the protuberances (4).
5. A heat exchanger plate (1) as claimed in claim 1, in which the
surface profile (6) is concavely or convexly arranged relative to
the protuberances (4).
6. A heat exchanger plate (1) as claimed in claim 1, in which the
geometric transition between the plane (3) of the heat exchanger
plate (1) and the protuberances (4) is provided with a radius.
7. A heat exchanger plate (1) as claimed in claim 1, in which the
surface profile (6) together with the protuberances (4) forms a
golf-ball-like structure.
8. A plate heat exchanger comprising heat exchanger plates (1) with
turbulence-promoting protuberances (4) which are arranged in each
heat exchanger plate (1), characterised in that each protuberance
(4) has a surface profile (6) for promoting break-up of laminar
boundary layers, said surface profile (6) consisting of spherical
or ellipsoid segments.
9. A plate heat exchanger as claimed in claim 8, in which the heat
exchanger plates (1) are arranged so that the protuberances (4) in
a first heat exchanger plate (1) in connection with stacking are
partially accommodated in the protuberances (4) in a second heat
exchanger plate (1).
10. A plate heat exchanger as claimed in claim 8, in which the heat
exchanger plates (1) are arranged in pairs with a first (10) pair
of plates and a second (10') pair of plates adjoining the first, in
which pairs of plates (10, 10') a first (1A) and a second (1B)
plate are arranged with the protuberances (4) directed away from
each other and in which pairs of plates a gap is arranged between
the first (1A) and the second (1B) plate.
11. A plate heat exchanger as claimed in claim 8, in which the
protuberances (4) in each heat exchanger plate (1) are
symmetrically arranged.
12. A plate heat exchanger as claimed in claim 8, in which the
surface profile (6) has a profile depth which is considerably
smaller than the depth of the protuberances (4).
13. A plate heat exchanger as claimed in claim 8, in which the
surface profile (6) of each protuberance (4) is concavely or
convexly arranged relative to the protuberance (4).
14. A plate heat exchanger as claimed in claim 8, in which the
protuberances (4) together with the surface profile (6) form a
golf-ball-like structure.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a heat exchanger plate
comprising a number of turbulence-promoting protuberances which
project from the plane of the heat exchanger plate. The invention
also relates to a plate heat exchanger comprising such plates.
BACKGROUND ART
[0002] Plate heat exchangers are frequently used in the food
industry for, for instance, processes for heat treatment of milk
and juice. In its simplest embodiment, a plate heat exchanger
comprises a number of corrugated plates with intermediate packings.
The plates are pressed together in a stand with tube connections
for inlet and outlet of two fluids, i.e. the fluid that is to be
tempered and the fluid that is used for tempering. The two fluids
are made to flow on both sides of the plates so that one fluid
flows between every second pair of plates and the other fluid flows
between the adjoining pair of plates. The number of plates and
their size depend, among other things, on flow velocity, physical
properties of the fluids, pressure drop and inlet and outlet
temperature of the fluids.
[0003] The corrugation of the plates generates a turbulent flow
through the major part of the gap cross-section between two plates
and also a large specific surface, which causes a high heat
transfer capacity. A very large number of documents are to be found
in the field, which demonstrates an intensive development of
different corrugations.
[0004] The document U.S. Pat. No. 4,569,391 discloses, for example,
a plate heat exchanger, in which each plate is provided with
hemispherical protuberances. The protuberances in a first plate are
arranged to abut, with their convex circumferential surface,
between the protuberances in a second adjoining plate.
[0005] Another variant is disclosed in U.S. Pat. No. 2,306,526.
This document discloses a plate heat exchanger, in which a first
plate with hemispherical protuberances is arranged to abut against
a second plate with corresponding protuberances in such a manner
that the protuberances in the first and the second plate are
oriented in diametrically opposite directions.
[0006] A third document U.S. Pat. No. 2,281,754 discloses a plate
heat exchanger, in which the plates comprise hemispherical
protuberances. The plates are arranged relative to each other so
that the protuberances in a first plate abut against a flat portion
on the rear side of a second plate.
[0007] A common feature of these solutions is that the plates
comprise hemispherical protuberances for generating a turbulent
flow through the major part of the gap cross-section between two
adjoining plates. However, it is desirable to achieve a further
improvement of the heat transfer capacity.
OBJECTS OF THE PRESENT INVENTION
[0008] The object of the present invention is to provide a further
development of, and an alternative solution to, the previously
known geometries of heat exchanger plates.
[0009] Another object is to obtain heat exchanger plates which
contribute to increased turbulence and promote the break-up of
laminar boundary layers.
[0010] A further object of the invention is to provide an increased
specific surface of heat exchanger plates.
[0011] Yet another object of the invention is to provide a plate
heat exchanger with improved heat transfer properties.
SUMMARY OF THE INVENTION
[0012] To achieve the above-mentioned and further objects not
mentioned, which will appear from the following description, the
present invention concerns a heat exchanger plate having the
features defined in claim 1. The invention also concerns according
to claim 9 a plate heat exchanger comprising such heat exchanger
plates.
[0013] More specifically, a heat exchanger plate comprising a
number of turbulence-promoting protuberances which project from the
plane of the heat exchanger plate is provided. The heat exchanger
plate is characterised in that the protuberances have a surface
profile for promoting break-up of laminar boundary layers, and that
the surface profile consists of spherical or ellipsoid
segments.
[0014] In hydrodynamics, the term "laminar boundary layer" is often
used. The term relates in general, and in this application, to that
part of a flowing volume of fluid which flows so close to a
boundary surface that the viscous force dominates over the other
forces. The thus low flow velocity implies that this part of the
fluid volume next to the boundary surface flows in a laminar
manner, while the remaining part of the fluid volume flows in a
turbulent manner. With plate heat exchangers, such laminar boundary
layers thus arise along the surfaces of the heat exchanger plates
which together build up a plate heat exchanger. The surface
profile, used in the invention, of the circumferential surfaces of
the protuberances thus creates a "surface roughness" which promotes
break-up of the laminar boundary layers. In other words, the
break-up promotes the production of a turbulent flow in the fluid
volume through all of, or the major part of, a gap cross-section
defined by two heat exchanger plates. The fluid volume through all
of, or the major part of, the gap cross-section flowing turbulently
results in very efficient mixing of the fluid and, thus, efficient
tempering of the fluid to be tempered and also efficient heat
transfer from/to the fluid that is used for tempering. The fact
that the surface profile consists of spherical or ellipsoid
segments contributes to the heat exchanger plate not having any
sharp edges or corners than can create dead spaces which
conventional cleaning methods cannot reach. This is very important
from the aspects of food hygiene since dead spaces may cause
undesirable growth of bacteria and other organisms. The soft
geometry is also favourable from the aspect of forming
technology.
[0015] It should be appreciated that, depending on how the
respective heat exchanger plates are made, the front and rear side
thereof will have different profiles. A pressed heat exchanger
plate has, for instance, one side with a concave profile and one
side with a convex profile. The flow pattern of the fluids will
thus be different on the two sides. Which fluid is in contact with
which side of the heat exchanger plate will be determined from case
to case, as will also the geometry and profile depth of the
protuberances and the surface profile respectively.
[0016] The surface profile also increases the specific surface,
which further favours the tempering of the fluid that is to be
tempered, and also favours the heat transfer to/from the fluid that
is used for tempering.
[0017] By specific surface is meant each of the surfaces which in
operation are exposed to the fluids flowing through the plate heat
exchanger. The front and rear sides of the heat exchanger plate
thus have their specific surface. The increased turbulence in
combination with the increased specific surfaces increases the
total heat transfer capacity of the plate heat exchanger, which
enables more rapid flows and, thus, a higher production
capacity.
[0018] In a preferred embodiment, the heat exchanger plate is,
together with a plurality of identical heat exchanger plates,
stackable in such a manner that the protuberances in a first heat
exchanger plate are partially accommodated in the protuberances in
a second heat exchanger plate. It is also preferred for the
protuberances to be symmetrically arranged. By the heat exchanger
plates thus being stackable, it is possible to ensure, by means of
conventional packings and spacers, a desirable gap width and a
desirable gap cross-section between the plates. Moreover, a compact
and space-saving plate heat exchanger is obtained.
[0019] In another preferred embodiment, the surface profile has a
profile depth that is considerably smaller than the depth of the
protuberances. Thus the surface profile should be so fine that, in
contrast to the protuberances, it is capable of breaking up and
possibly eliminating the laminar boundary layers next to the heat
exchanger plates. The thickness of the laminar boundary layer is
unique for each design of the heat exchanger plate, and therefore
the heat exchanger plate is adjusted to the fluid to be tempered or
to the fluid that is used for tempering, and therefore no
dimensions or ratios of the profile depth of the surface profile to
the depth of the protuberance can be given. Examples of important
parameters are the velocity and viscosity of the fluids.
[0020] In yet another preferred embodiment, the surface profile is
concavely or convexly arranged relative to the protuberances.
[0021] It is also preferred that the geometric transition between
the plane of the heat exchanger plate and the protuberances be
provided with a radius, and that the surface profile, as mentioned
above, consist of spherical or ellipsoid segments. The surface
profile, in combination with the protuberances, can thus in these
preferred embodiments be said to form a golf-ball-like structure.
Owing to the radius in combination with the spherical or ellipsoid
shape, the heat exchanger plate does not have any sharp edges or
corners which can create dead spaces which conventional cleaning
methods cannot reach. This is very important from the aspects of
food hygiene, since dead spaces may cause undesirable growth of
bacteria and other organisms. The soft geometry is also favourable
from the aspect of forming technology.
[0022] According to another aspect, the invention relates to a
plate heat exchanger comprising heat exchanger plates with
turbulence-promoting protuberances arranged in each heat exchanger
plate. The plate heat exchanger is characterised in that each
protuberance has a surface profile for promoting break-up of
laminar boundary layers, and that said surface profile consists of
spherical or ellipsoid segments.
[0023] The plates can be arranged in various ways in the plate heat
exchanger. For example, the heat exchanger plates can be arranged
so that the protuberances in a first heat exchanger plate in
connection with stacking are partially accommodated in the
protuberances in a second heat exchanger plate. The heat exchanger
plates can, for instance, also be arranged in pairs with a first
pair of plates and a second pair of plates adjoining the first, in
which pairs of plates a first and a second plate are arranged with
the protuberances directed away from each other and in which pairs
of plates a gap is arranged between the first and the second plate.
The latter variant allows that the two fluids used in the plate
heat exchanger can be arranged to flow through different gap
cross-sections and, thus, obtain different flow patterns.
DESCRIPTION OF DRAWINGS
[0024] The invention will in the following be described in more
detail by way of example and with reference to the accompanying
drawings which illustrate a currently preferred embodiment.
[0025] FIG. 1 is schematic view of an embodiment of a plate
according to the invention.
[0026] FIGS. 2a and 2b show two examples of stacking of plates in a
plate heat exchanger.
[0027] FIG. 3 shows a partial enlargement of a protuberance in the
plate according to FIG. 1.
TECHNICAL DESCRIPTION
[0028] With reference to FIG. 1, a part of a heat exchanger plate
1, henceforth referred to as plate, according to the present
invention is schematically shown for use in a plate heat exchanger
(not shown). The plate 1 comprises in a conventional manner a plate
element 2 with a plurality of protuberances 4 projecting from the
plane 3 of the plate. In the embodiment illustrated, the
protuberances 4 have the shape of spherical segments. It should,
however, be appreciated that also other geometries of the
protuberances are conceivable. The main purpose of the
protuberances 4 is that they should promote a turbulent flow of a
fluid flowing through a gap defined by two adjoining plates 1.
[0029] Depending on how the plates 1 are intended to be stacked to
form a plate heat exchanger, the protuberances 4 of the plates 1
can be oriented in various ways, which is best appreciated by a
person skilled in the art, and thus create different gap
cross-sections X, Y, see FIGS. 2a and 2b.
[0030] A highly space-saving plate heat exchanger is obtained, for
instance, if the protuberances 4 are symmetrically arranged and
designed in such a manner that the protuberances 4 in a first plate
1A are partially accommodated in the recesses 4' formed by the
protuberances 4 in a second plate 1B, see FIG. 2a. Between the two
plates 1A and 1B a gap is formed, through which the fluids used in
the plate heat exchanger can flow. The fluids used in the plate
heat exchanger will thus flow through identical, or essentially
identical, gap cross-sections X, Y.
[0031] The plates 1 can also be stacked in such a manner that the
heat exchanger plates 1 are arranged in pairs with a first pair of
plates 10 and a second pair of plates 10' adjoining the first, in
which pairs of plates 10, 10' a first 1A and a second 1B plate are
arranged with the protuberances 4 directed away from each other,
see FIG. 2b. A gap is arranged between the first 1A and the second
1B plate in each pair of plates 10, 10', and between the respective
pairs of plates. The gaps form the passages with gap cross-sections
X, Y, through which the fluids used in the plate heat exchanger can
flow. As a result, the two fluids used in the plate heat exchanger
will in this variant flow through different gap cross-sections X,
Y.
[0032] It should be appreciated that the plates 1 can be stacked in
an infinite number of ways, and that the invention should not be
limited by on which side of the protuberances 4 the fluids used in
the plate heat exchanger flow. It should also be appreciated that
the different plates need not have the same geometry of their
protuberances.
[0033] With reference to FIG. 3, the geometric transition 5 between
the plane 3 of the plate 1 and the respective protuberances 4 is
arranged with a radius or with a geometry which is soft in some
other manner. A soft geometric transition is most important from
the aspect of hygiene since plate heat exchangers when used in the
food industry require frequent and very careful cleaning. Any sharp
geometric transitions may create dead spaces which can form growth
zones for bacteria and other organisms. However, it will be
appreciated that soft geometric transitions also reduce the flow
resistance, which is detrimental to an increased turbulence.
[0034] The protuberances 4 may consist of isolated zones, such as
spherical or ellipsoid segments, but may also consist of wholly or
partly continuous zones in the form of, for example, waves or
grooves, i.e. a somehow corrugated surface.
[0035] The protuberances 4 are suitably formed by pressing, thus
allowing the protuberances to create cup-shaped bulges. One side of
the plate 1 will thus have protuberances 4 while the other side
will have corresponding recesses 4'.
[0036] The protuberances 4 are provided with a surface profile 6
which is shown more distinctly in FIG. 3. The main purpose of the
surface profile is to further facilitate and promote the break-up
of the laminar boundary layers next to the plates and, thus,
promote or enforce a turbulent flow through all of, or the major
part of, the gap cross-sections X, Y.
[0037] In its simplest embodiment, the surface profile 6 consists
of a number of spherical or ellipsoid segments in the
circumferential surface 7 of the protuberance 4. However, it will
be appreciated that also other geometries are possible, such as
crosses, stars or other prismatic geometries. The number of
possible geometries is infinite as a person skilled in the art will
realise. The surface profile 6 can thus be concave as well as
convex relative to the protuberance 4, or be alternately concave
and convex. If the surface profile 6 is concavely arranged, it may
be compared to the surface of a golf ball, i.e. the circumferential
surface 7 of the protuberance 4 is pitted. If the surface profile 6
is convexly arranged, the circumferential surface 7 of the
protuberance 4 can be compared to a granular or "wart-like"
surface. Of course, it will be appreciated that by the plate 1
preferably being formed by pressing, one side will obtain a concave
surface profile while the other side will correspondingly obtain a
convex surface profile. The invention should not be limited by
which side faces the fluid that is to be tempered.
[0038] The surface profile 6 is formed, as are also the
protuberances 4, most easily by pressing, but it may also consist
of a surface which is, for instance, etched, or of a profiled
laminate. In the latter cases, the "rear side" will be perfectly
smooth.
[0039] The protuberances 4, together with the surface profile 6,
promote not only a turbulent flow by break-up of the laminar
boundary layers, but also increase the specific surfaces, i.e. the
surfaces exposed to the fluids transported in the plate heat
exchanger. The larger specific surface, the higher heat
transfer.
[0040] The surface profile 6 has a profile depth which is
considerably smaller than the depth of the protuberances 4.
However, it will be appreciated that the selection of profile
depth, profile tightness and orientation depends on factors such as
the physical properties of the fluids transported in the plate heat
exchanger, for instance rheology and viscosity, the desired degree
of turbulence, pressure drop and flow rate. These are factors that
are specific to the situation in which the plate heat exchanger is
intended to operate. Thus the surface profile must be adjusted to
each situation so as to be capable of promoting break-up of the
laminar boundary layers and, thus, provide or promote a laminar
flow through the entire gap cross-section.
[0041] The material of the plates 1 should be a material that is
corrosion resistant and suitable for the food industry and that has
high thermal conductivity. The selected thickness of the material
should be relatively thin for increased heat transfer.
[0042] The present invention also relates to a plate heat exchanger
(not shown), which is made up of a required number of plates 1
designed as described above. The number of plates 1 depends on,
inter alia, the capacity of the plate heat exchanger and will here
not be described in detail. The plates 1 can be stacked in various
ways, two of which are exemplified in the description with
reference to FIGS. 2a and 2b. Depending on how the plates 1 are
stacked, different gap cross-sections X, Y are obtained, and thus
different flow patterns for the fluids intended for the plate heat
exchanger. The number of stacking options is large and should not
limit the invention.
[0043] By means of packings, beads, spacers or the like, a
predetermined gap width and a predetermined gap cross-section X, Y
between adjoining plates for passage of the intended fluids are
ensured.
[0044] As an example of the fluid to be tempered mention can be
made of milk, juice, soup or puree. As an example of the fluid that
is used for tempering, water can be mentioned.
[0045] To sum up, the present invention thus comprises plates 1 for
use in a plate heat exchanger, and also a plate heat exchanger
using such plates. The plates 1 comprise a number of
turbulence-generating protuberances 4. The protuberances 4 have a
surface profile 6 which promotes break-up of the laminar boundary
layers next to the surfaces of the plates 1. The profile depth of
the surface profile 6 is adjusted to the intended operating
conditions of the plate heat exchanger, but should be considerably
smaller than the depth of the protuberance 4 and illustratively
form a golf-ball-like structure. The surface profile 6 can be
concave as well as convex relative to the protuberance 4. The plate
1, the protuberances 4 and their surface profile 6 together form a
surface without sharp geometric transitions which is easy to clean
and which thus prevents undesirable growth of bacteria.
[0046] The protuberances 4 in combination with the surface profile
form a large specific surface, which promotes the heat transfer
between the fluids that are transported in the plate heat
exchanger. Moreover, the surface profile enhances the turbulence by
promoting the break-up of the laminar boundary layers next to the
surfaces of the plates, which further promotes the heat
transfer.
[0047] It will be appreciated that the present invention is not
limited to the shown and described embodiments of the plates and a
plate heat exchanger made from the same. The inventive idea can,
for example, with minor amendments, be applied to other types of
heat exchangers, for instance to tubular heat exchangers in which
the tubes included are provided with protuberances which have a
surface profile to promote break-up of laminar boundary layers.
Several modifications and variants are thus conceivable, and
consequently the invention is defined exclusively by the appended
claims.
* * * * *