U.S. patent application number 11/632582 was filed with the patent office on 2008-02-07 for plate heat exchanger.
This patent application is currently assigned to SWEP INTERNATIONAL AB. Invention is credited to Peter Nilsson.
Application Number | 20080029257 11/632582 |
Document ID | / |
Family ID | 34926346 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080029257 |
Kind Code |
A1 |
Nilsson; Peter |
February 7, 2008 |
Plate Heat Exchanger
Abstract
A plate heat exchanger comprising separate flow paths for two
flows of fluid said paths having different pressure drops at equal
mass flows may according to the invention be designed economically
by stacking pairs of two plates (4, 5) provided with pressed
patterns, at least one of the plates (4) in a pair (4, 5) being
provided with at least two different press depths (D.sub.1,
D.sub.2), the smaller (D.sub.2) being at least 40% of the greater
(D.sub.1).
Inventors: |
Nilsson; Peter; (Landskrona,
SE) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
SWEP INTERNATIONAL AB
Box 105
Landskrona
SE
S-261 22
|
Family ID: |
34926346 |
Appl. No.: |
11/632582 |
Filed: |
July 7, 2005 |
PCT Filed: |
July 7, 2005 |
PCT NO: |
PCT/EP05/07329 |
371 Date: |
January 16, 2007 |
Current U.S.
Class: |
165/167 |
Current CPC
Class: |
F28F 3/04 20130101; F28D
9/005 20130101 |
Class at
Publication: |
165/167 |
International
Class: |
F28D 9/00 20060101
F28D009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 28, 2004 |
EP |
04020494.3 |
Claims
1. A plate heat exchanger comprising at least two separate flow
paths for primary and secondary fluids to exchange heat, the said
flow paths being substantial defined by permanently interconnected
heat exchanger plates provided with a herring bone pattern of
ridges and depressions and offering different pressure drops at
equal mass flows of the two fluids, wherein the depressions in at
least some pairs of plates defining the flow path having the lower
pressure drop at least partly are alternatively of two different
press depths (D.sub.1, D.sub.2) measure from the plan define by the
tops of the ridges of the herring bone patter the heat exchanger
plate, the smaller (D.sub.2) being located between two tops of the
herring bone patter and being at least 40% of the greater
(D.sub.1), and thereby that the tops of the ridges engaging the
tops of a neighboring plate to define a flow channel having high
pressure drop substantially contact each other along points defined
by crossing lines.
Description
[0001] The present invention relates to a plate heat exchanger
comprising at least two separate flow paths for primary and
secondary fluids to exchange heat, the said two flow paths being
substantially defined by permanently interconnected heat exchanger
plates provided with a herring bone pattern of ridges and
depressions and offering different pressure drops at equal mass
flows of the two fluids.
[0002] Many heat exchangers of the above type are used for heating
tap water by means of hot water also used for heating dwelling
houses. The inlet temperature of the heating water may be e.g.
75.degree. C., and the outlet temperature thereof may be about
60.degree. C. The inlet temperature of the tap water may be about
10.degree. C. and the outlet temperature thereof may be 55.degree.
C. This indicates that the mass flow of the heating water must be
2.5 times the mass flow of the tap water. Therefore, it is
economical to make the cross section of the flow path for the
heating water wider than that of the tap water. E.g. by making the
tops of the herring bone pattern flat--and thus wider--while the
bottoms are unaltered this may be obtained.
[0003] Although this making the heat exchanger "asymmetric" is an
improvement it is still an object to further increase the
efficiency of the exchanger--i.e. to increase the heat transmission
between the heat exchanging fluids without increasing the weight of
the plate heat exchanger.
[0004] The Japanese Patent Application No. 11173771 A published
Jul. 2, 1999 discloses a plate heat exchanger having different
pressure drops in the flow paths in case of equal mass flows.
[0005] This is done by increasing the pitch--i. e. the distance
between the contacts of adjacent ridges in the herringbone pattern.
This known device is adapted to exchange heat between water and a
cooling fluid the water flowing through the flow path having the
smaller pressure drop. By making small depressions in parts of
plates forming the water channels it is obtained that freezing of
water will not cause damage to the plate heat exchanger. However,
the areas of contact between plates will thus be relatively great
and lost for the heat exchange between the fluids. The small
depressions in the channels guiding the water flow will cause
corresponding very narrow flow channels in the flow path for the
cooling fluid. The areas of contact between adjacent plates are not
rigidly interconnected in order to increase the elasticity of the
plate heat exchanger, but the mechanical strength of the exchanger
will be rather poor making the exchanger unsuitable for high
pressure fluids.
[0006] The Japanese Patent Application No. 11281283 A also
discloses a heat exchanger in which the pressure drops of two heat
exchanging fluids are different in case of equal mass flows.
According to the embodiment in FIG. 5 of said disclosure the flow
paths forming a herring bone pattern comprise channels having
greater cross sectional flow area provided with two small secondary
depressions in the channels of greater cross section. This involves
that the flow path having a total relatively high pressure drop
will consist of parts causing very different pressure drops. This
is an uneconomical way of using the material in the exchanger for
exchanging heat. Also--as the pitch will increase with increasing
numbers of the secondary depressions--the mechanical strength of
the exchanger will decrease due to the smaller numbers of contact
points at which the plates could be rigidly connected.
[0007] The object of the present invention is to design an
"asymmetric" plate heat exchanger in which the material of the
plates is used in a more economic way and thus in which the
efficiency is improved while maintaining a high mechanical strength
of the exchanger
[0008] According to the present invention this is obtained thereby
that the depressions in at least some pairs of plates defining the
flow path having the lower pressure drop at least partly are
alternatively of two different press depths measured from the plan
defined by the tops of the ridges of the herring bone pattern of
the heat exchanger plate, the smaller being located between two
tops of the herring bone pattern and being at least 40% of the
greater, and thereby that the tops of the ridges engaging the tops
of a neighboring plate to define a flow channel having high
pressure drop substantially contact each other along points defined
by crossing lines.
[0009] The invention will be described in more detail with
reference to the accompanying drawings in which:
[0010] FIG. 1 is a plan view of plate in one known type of a plate
heat exchanger.
[0011] FIG. 2 schematically shows the crossing patterns of two
plates according to FIG. 1 placed on each other--after one of them
has been turned in its plan.
[0012] FIG. 3 is a section along the line A-A in FIG. 1.
[0013] FIG. 4 is a section along the line B-B in FIG. 2 in a stack
of four plates according to FIG. 1.
[0014] FIG. 5 is a section corresponding to FIG. 4, but through a
known "asymmetric" plate heat exchanger.
[0015] FIG. 6 is a section corresponding to those of FIGS. 4 and 5,
but through a plate heat exchanger according to the Japanese Patent
Application No. 11173771 A.
[0016] FIG. 7 is a section corresponding to FIG. 6, but through a
plate heat exchanger according to the Japanese Patent application
No. 11281283 A.
[0017] FIG. 8 shows a section corresponding to those shown in FIGS.
4-7 through two neighboring plates of a heat exchanger according to
the present invention--the plates being drawn apart.
[0018] FIG. 9 is a section through four plates in heat exchanger
according to the present invention.
[0019] FIGS. 10-12 show alternative embodiments of the
invention.
[0020] FIG. 1 is a plan view of a plate 1 of a known and widely
used plate heat exchanger provided with a herring bone pattern of
ridges 2 and depressions 3. In the exchanger a stack of plates of
this type is formed after turning each other plate in the stack in
its plane. FIG. 2 illustrates how the ridges and depressions then
will cross each other.
[0021] FIG. 3--which is a section along the line A-A in FIG.
1--illustrates the pitch P and the press depth D both values being
of importance for characterising the plate heat exchanger.
[0022] FIG. 4 is a section along the line B-B of FIG. 2 through
four plates in a heat exchanger according to the FIGS. 1-3. The two
flows of heat exchanging fluids limited by the plates are shown by
different hatching. It will be understood that the two flow paths
are offering equal pressure drops at equal mass flows.
[0023] By increasing the pitch P and making the tops 2 of the
ridges flat the flow path of one of the fluids will obtain a
greater cross section than the flow path of the other fluid.
[0024] However, as shown in FIG. 5 the contact areas between the
heat exchanger plates will be much larger. These areas cannot be
used for heat exchange between the two flows of fluids.
[0025] FIG. 6 shows a prior art plate heat exchanger according to
the Japanese Patent Application No. 11173771 which shows a plate
heat exchanger of the "asymmetric" type in which the pairs of
plates limiting the flow path having the greater cross sectional
area are provided with depressions of less depths D.sub.2 than the
press depths D.sub.1 of tops of the ridges of the herring bone
pattern. This has been done in order to make the plate heat
exchanger more resistant against damage caused by ice formations.
The plan contact areas between the plates and not used for heat
exchange are still existing in this embodiment.
[0026] Another proposal for manufacturing an "asymmetric" plate
heat exchanger has been described in the Japanese Patent
Application No. 11281283 A. Here the contact areas between the
plates of the exchanger has been established by replacing the plan
contact areas by areas containing small depressions. This has been
shown in FIG. 7 and it will be understood that the flow path having
the greater pressure drop will consist of channels of large cross
section and at least the double number of much smaller cross
sections. This design is detrimental to the heat transfer in the
narrow channels because of the much lower flow rate than in the
flow channels having wider cross sections.
[0027] FIG. 8 shows a section corresponding to the sections shown
in FIGS. 4-7 through two heat exchanger plates according to the
present invention. A primary press depth press depth--i. e. the
distance between the plan defined by the tops of the ridges and the
lowest plan defined by bottoms of ridges--has been indicated as
D.sub.1. A secondary press depth defined as the distance between
the plan of the tops of the ridges of the herring bone pattern and
a plan of the bottom of minor depressions has been designated by
D.sub.2. The pitch of the herringbone pattern has been indicated by
P.
[0028] The herring bone patterns of the two plates 4 and 5 shown in
FIG. 8 are mirror images of each other and thus two tools are used
for the pressing of the plates. Also each other of the plates
should be turned 180 degrees in its plan relative the adjacent
plates in the stack in order to obtain the crossing herring bone
patterns. FIG. 9 is a section through four plates 4, 5, 6 and 7 of
the types shown in FIG. 8 and corresponding to the sections C-C
shown in FIGS. 4-7. The three channels formed for the flows
exchanging heat are shown by two different hatchings. It will be
understood from FIG. 9 that the resistance for the flow limited by
the plates 5 and 6 is higher than the resistance for the flow
limited by the plates 4 and 5 or 6 and 7. However, the contact
areas between the plates are kept at a minimum, but the number of
contacts at which the plates are interconnected by soldering is
substantial and will give mechanical strength to the heat
exchanger. It is essential to maintain a substantial mass flow of
fluid through the cross sections designed by 8 in FIG. 9. The mass
flow through the area 8 is nearly proportional to its cross
sectional area and this is in turn mainly dependant on the
magnitude of the press depth D.sub.2. A small press depth
D.sub.2--e.g. as shown in FIG. 7--will make the areas 8 small and
may almost block passage of fluid. A small secondary press depth
will the have nearly the same effect as the large contact areas
between the ridges of the herring bone pattern shown in FIG. 5.
[0029] It has been found that the secondary press depth D.sub.2
should be at least 40 percent of the press depth
D.sub.1--preferably about 50 percent thereof.
[0030] FIG. 10 is a section corresponding to that of FIG. 9, but in
which only the plate 4 in a pair of plates 4, 5 has two different
press depths. The other plate in the pair--designated by 5--is of
conventional shape having only one press depth. The two plates 4, 5
according to FIG. 10 have not patterns which are mirror images of
each other and may be designed so that a turning of a plate will
not be necessary in order to obtain crossing of the contacting
ridges.
[0031] According to the embodiment of FIG. 11 the secondary press
depth D.sub.2 of the plate 5 is greater than the secondary press
depth D.sub.3 of the plate 6.
[0032] FIG. 12 shows an embodiment in which the plate 4 has two
different secondary press depths. The press depth D.sub.2 is used
in one area of the plate and the press depth D.sub.4 in another
area of the plate.
[0033] It will be understood that a heat exchanger according to the
present invention may comprise other combinations of pairs of
plates than those described above. E.g. some pairs may be of the
known type shown in FIG. 4 providing equal pressure drops in the
flow channels for the heat exchanging media--in case of equal mass
flows.
* * * * *