Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a plate heat
exchanger for heat exchange between media, of which at
least one medium passes through the heat exchanger from an ~ -
inlet passage to an outlet passage without changing its
condition from liquid to gas or vice versa on passing.
More particularly, the invention relates to plate heat
exchangers in which the passages are formed by holes in
the plates that are aligned when the plates are assembled.
One problem of prior heat exchangers of this kind
is that the said inlet and outlet passag~s present a
relatively large flow resistance to the media exchanging
heat.
It is an object of the present invention to reduce
this flow resistance without change of size of the
exchanger or of its plates and without substantial change
in heat exchanging properties. It has surprisingly been
discovered that this object can be fulfilled according to
this invention by the plates of the heat exchanger being
formed such that the area of the outlet passage for at least
one medium is substantially larger than the inlet passage
for the same medium. In other words, redistribution of the
cross-sectional areas of the inlet and outlet passages
whilst maintaining the total cross-sectional area of the
two passages unchanged and the size of the heat exchange
areas of the plates likewise unchanged, the pressure drop
over the heat exchanger decreases by up to 25%, without the
heat exchanging properties of the heat exchanger being
substantially changed.
According to a preferred embodiment of the
invention, the inlet passage and the outlet passage each
have cross-sectional areas which are respectively
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substantially constant along the lengths of the respective
passages. By this means all the heat exchange plates may
have inlet holes of the same size and outlet holes of the
same size, which is an advantage in the manufacturing of the
heat exchange plates.
According to one embodiment of the invention the
outlet passage is divided up into at least two channels
whereby it becomes possible to make the heat exchange plates
with holes which are of the same size which is advantageous
in the production of the plates.
In the prior art,U.S. patent 3,117,624 discloses
a plate heat exchanger having a plurality of heat exchange
plates with outlet holes which are larger than the inlet
holes. However, this difference in size of the holes was
due to the fact that the condition of the medium changed
by vaporization from a liquid to a gas, between the heat
exchange plates, the medium quite naturally requiring wider
channels for the flow in gaseous state than in liquid state.
This patent did not perceive that a heat exchanger in which
the condition of the medium did not change between liquid
and gas could be improved without loss of capacity or
increase in size or increase in cost.
In the drawing, Figure 1 shows a longitudinal
sectional view through a plate heat exchanger of a known
structure.
Figure 2 shows a ~ngitudinal sectional view taken
along line II-II of Figure 3, through a heat exchanger
according to one form of the invention.
Figure 3 is an elevation view of a heat exchange
plate viewed along line III-III in Figure 2.
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Figure 4 is a graph showing how the pressure drop
in the heat exchanger of this invention varies with the
ratio between the cross-sectional areas of an outlet
passage and an inlet passage.
Figure 5 is a diagrammatic exploded perspective
view of another embodiment of the heat exchange plates ;
according to this invention.
Figure 6 is a view similar to Figure 5 of a further
embodiment of heat exchange plates according to this
invention with six holes.
Referring to the drawings, the invention illustrated
in Figures 2 and 3 may be compared with a prior art con-
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struction shown in Figure 1 wherein like parts are dex;i~ff~*
by like reference numerals.
The heat exchanger according to this invention
comprises a plurality of parallel heat exchange plates 1
which are arranged between two end elements 2 and 3 which
may be in the form of plates. The heat exchange plates 1
which may be of flat rectangular shape as shown in Figure 3,
or of other suitable desired shape, are spaced apart by
sealing and separating members 12 which may be of irregular
shape as shown in Figure 3 or of other shape suitable to
enable them to form the periphery of individual heat
; transfer passages or chambers.
In Figure 3 the heat exchange plate 1 which may be
considered to be the one located at the left end of the
assembly in Figure 1, is seen in front of the end-plate 2.
In front of the heat exchange plate is a spacing and sealing
member 12.
Each heat exchange plate has four holes through it
adjacent its corners which when assembled in alignment
provide inlet passages and outlet passages for the heat
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transfer media. Two holes 8A at one side are of smaller
diameter than the two holes lOA at the other side.
When the heat exchange plates 1 and separator
members 12 are assembled as in Figure 2 they confine a
plurality of first heat exchange chambers 4 and a number of
second heat exchange chambers 5.
Through the chambers 4 a first medium flows, while
a second medium flows through the chambers 5. Each heat
exchange plate forms a common wall between adjacent heat
exchange chambers whereby the heat transfer between the
media in adjacent chambers 4 and 5 takes place through the
common heat exchange plates.
The first medium is introduced into the heat
exchanger through an inlet conduit 6 and a convergent
15 fitting 15. The fitting 15 is affixed to the end-plate 2
around an opening in the end-plate which opens into an
inlet passage 7a by which the medium is distributed to the
first heat-exchange chambers 4.
The inlet passage 7A is formed by the small inlet
holes 8A in the top of the heat exchange plates and along
its length is of substantially uniform cross sectional area.
When the first medium has passed through the
chambers 4 it is collected in an outlet passage 9A which is
formed by large outlet holes lOA through the bottom of the
heat exchange plates. This passage is of substantially
uniform cross-section along its length.
Between the second and third heat exchange plates,
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reading from left to right in Figure 2 (and likewise between
the 4th and 5th, 6th and 7th, et sequi) sealing means is
provided around the passage 7A and the passage 9A, dimension-
ed in each instance so that the cross sectional area of the
passages 7A and 9A between the holes in one heat transfer
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plate and the next, is maintained uniform. This sealing
means may be made integral with the separator member 12.
It allows distribution of the medium only to alternate
chambers.
The second medium flows in an analogous way through
an inlet conduit, an inlet passage, heat exchange chambers
5, an outlet passage and outlet conduit, of which only the
chambers 5 are shown in Figure 2. In the case of the second
medium, the inlet is at the bottom through small passages
and the outlet at the top through large passages. The same
form of separating means 12 can be used for providing the
chambers 5, by inverting the separators end-over-end.
In the prior art of Figure 1, the inlet passage 7
and the ou~let passage 9 are of the same cross-sectional
area; and because the medium was not intended to change its
state but was intended to remain always in a liquid state,
the flow resistance of the medium was relatively large.
In the present invention, as shown in Figures 2 and
3, the outlet passage 9A and each outlet hole lOA have a
cross-sectional area that is substantially larger than the
cross-sectional area of inlet passage 7A and each inlet
hole 8A. At the same time the sum of cross-sectional areas
of the inlet and outlet passages 7A and 9A is kept substan-
tially unchanged. As a result of observing these para-
meters, the pressure drop of the medium will decrease
during its flow through the heat exchanger while the heat
exchange area of the plates 1 is maintained the same as
heretofore. In consequence, improved and more efficient
operation of the heat exchanger is attained.
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Figure 4 is a graph where A2 is the cross-
sectional area of the outlet passage 9A, and Al is the
- cross-sectional area of the inlet passage 7A, and C is a
constant. Figure 4 shows how the pressure drop,~ p, can
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vary, when the ratio A2 is changed.
Al A
~p decreases by about 25% when 2 increases to about
1.8.
At A2 = 2.8 ~p has again increased to the same value
as at A2 = 1. In other words, Fig. 4 shows that A2 should be
larger than Al but less than 2.8~Al, in order to obtain a sig-
nificant reduction in the pressure drop, the latter being reduced
the greatest amount when A2 is about 1.8 Al.
Furthermore, in the graph of Figure 4 the condition
Al ~ A2 = C applies, and the flow of the medium through the heat
exchanger is not changed.
In prior art heat exchangers, for example, see Figure
1, a special convergent connecting pipe fitting 15 at the inlet
to the exchanger and a special divergent connecting fitting at
the outlet from the exchanger were often required. The purpose
of the fittings 15 and 16 was to accomplish a smooth transition
between inlet and outlet conduits 6 and 11, respectively. The
conduits usually are dimensioned for a flow velocity of 2-4 m/s,
while the connections of the heat exchanger usually are dimen-
sioned for a higher flow velocity, namely 5-8 m/s. ~y the inven-
tion the outlet passage of the heat exchanger is better adapted
to the diameter of the outlet conduit; and in many cases a
special connecting fitting between the conduit 11 and the heat
exchanger can be avoided (see Figure 2).
The plates of the heat exchanger may have different
~orms.
In Figure 5 wherein equivalent parts have the same
reference numerals as in Figures 2 and 3, the small inlet holes
8A and the large outlet holes lOA are located in diagonally
opposite corners. The upper small holes 8A form the inlet pas-
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sage for the first medium and distribute the first medium to the
heat exchange chambers 4 as shown by
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the broken lines and arrows 13. The lower large holes lOA ,
form the outlet passage for the first medium.
In equivalent manner the lower small holes 8A form
the inlet passage for the second medium and distribute the
second medium to the heat exchange chambers 5 as shown by
the broken lines and arrows 14. The upper large holes lOA
form the outlet passage for the second medium.
The separating and sealing members 12 form the
; peripheries of the chambers 4 and 5 in the same way as
before; and sealing meanis between the holes in adjacent
plates to complete the inlet and outlet passages,
respectively, is provided in equivalent fashion, as before.
In Figure 6 an embodiment is shown in which each
plate has six holes, three adjacent the top edge and three
adjacent the bottom edge. All the holes are of the same
size but one hole at the top and one at the bottom are used
as inlet holes and two at the bottom and two at the top are
used as outlet holes. In the particular illustration of
Figure 6 the middle hole at the top and the middle hole at
the bottom are used as inlet holes. The separating and
sealing members which define the chambers 4 for the first
medium exclude the lower middle inlet hole and two upper
outer outlet holes; and similarly the sealing members
which define chambers 5 for the second medium exclude the
upper middle inlet hole and two lower outer outlet holes.
By the Figure 6 arrangement there is one inlet
passage or channel for each medium and two outlet passages
or channels for each medium. Thus the cross-sectional
area of the outlet is twice the size of the inlet area.
In all the arrangements illustrated, decreased
pressure drops result for both the first and the second
heat exchange mediums.
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Without departing from the invention, the outlet
area for the first media can be larger than the inlet area,
whether one or more holes or channels are provided for the
; outlet, while the inlet area or holes for the second media
` 5 can be substantially larger than the outlet area or holes.
Such an arrangement would be employed if the second medium
enters the heat exchanger in a gaseous state and then
condenses and leaves the exchanger in a liquid state.
Many modifications of the invention will occur to
those skilled in the art. Therefore, the invention is not
limited to the specific embodiments illustrated and
described.
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