Note: Descriptions are shown in the official language in which they were submitted.
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PLATE-TYPE HEAT EXCHANGER WITH DISTRIBUTION ZONE
Technical Field
This invention relates to heat exchangers and methods for their
manufacture. In particular it relates to "compact" heat exchangers
5 which are characterised by high "area density". This means that they
have a high ratio of heat transfer surface to heat exchange volume.
Rack~round Art
Booklet No. 89 in the Good Practice Guide Series published by
the Energy Efficiency Office of the Department of Environment of the
10 IJK Government in 1994 describes and illustrates the various types of
compact heat exchanger available in the United Kingdom at that date
and contains notes on proposals for future developments. Guide No. 89
which may be obtained from the Energy Efficiency ~nquiries Bureau
(telephone number 44-I235-436-747) is hereby incorporated by
15 reference into this document.
Because of the wide variety of heat exchangers and the
differences in their construction, their classification is complex. Once
the tube and shell type construction is separated out, there remain a
variety of stacked plate, brazed plate, plate-fin, polymer film, porous
20 matrix and other devices. The present invention could be considered to
have features common to the stacked plate type of configuration or to
the plate-fin confi1guration depending upon the characteristics used in
categorisation.
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The invention has its most important application in compact heat
exchangers having an area density greater than 700m2/m3 when
referring to the gas side of a gas/liqu;d heat exchanger.
Recent developments in compact heat exchanger technology have
5 resulted in significant improvements in area density and in the precision
of manu~acture of such heat exchangers such that there is high
constructional integrity and thus much less chance of interaction
between fluids flowing on the different sides of the heat exchanger.
Developments such as the printed circuit heat exchanger e.g. that
illustrated in US patent 4,665,975 (the passage of which entitled
"Background of the Invention" is hereby incorporated by way of
reference) have resulted in substantial improvements in heat exchanger
design. Proposals such as that illustrated in GB 2 25 l 679, which
illustrates a form o~perforated plate technology, may lead to extremely
15 compact designs with very high efficiency.
These existing designs focus on the manufacture of standard
plates which can be bonded together e.g. by vacuum brazing or
diffusion bonding to create passageways between the plates through
which the fluids pass. Heat exchange takes place through the plates
20 themselves with a fluid flowing in an adjacent set of passageways,
typically in a direction different from that in which the original fluid is
~lowing. Secondary heat exchange surface may extend between such
plates.
In designing a heat exchanger it is theoretically the case that for
25 optimum results the incoming fluid should be distributed uniformally
=
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across the full width of the entry to the heat exchanger. This creates
particular difficulties when a fluid is required to enter a heat exchanger
via an oblique or side entry at the end of the heat exchanger. The heat
exchanger designer in such cases tries to create an environment in what
5 is called the "distribution zone" in US 43665,975 which prevents an
otherwise inevitable disproportionally high flow down the easiest (i.e.
lowest pressure drop) passage through the heat exchanger.
The optimum manufacturing requirement, however, is that the
plates and other components of a heat exchanger should be as uniform
10 as possible, and straightforward to produce from standard machinery or
standard components. Design features r~lnnin~; in straight lines i.e.
rectilinear, or on f1xed radii are particularly desirable. This simplifies
assembly and it is much cheaper to produce only a limited number of
components than a huge variety. The designer is therefore constrained
15 in his efforts to design a "distribution zone" which has a means of
progressively adjusting the flow restrictions and hence the pressure drop
as the fluid passes through a distribution zone. Flow restrictions
associated with any particular movement of fluid through the
distribution zone should ideally be decreased as the distance from the
20 entry to the distribution zone increases.
~ :t is an object of the invention to provide a compact plate-t~pe
heat exchanger having a plurality of plates arranged in face-to-face
- relationship and bonded together, which has progressively changing
flow restrictions within the distribution zone enabling a more uniform
2~ distribution of flow across the full width of the heat exchanger.
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nisclosure of Jnvention
According to one aspect of the invention, we provide a heat
exchanger comprising a plurality of plates bonded face-to-face one to
the other, said plates having on their faces a plurality of upstanding fins
5 defining therebetween passages for fluid flow, said heat exchanger
having a main heat exchange zone arld a distribution zone between the
entry to the heat exchanger and the main heat exchanger zone, said
plates similarly having a main heat exchanger zone and a distribution
zone, there being upstanding fins in both said zones of said plates, said
10 upstanding fins in the distribution zone of the plates comprising a
plurality of discrete projections along the direction of ~luid flow,
characterised in that said discrete projections include amongst them a
plurality of projections which are aligned differently from adjacent
projections along the direction of fluid flow.
The projections are typically created by photochemically or
electrochemically etching (or by any other appropria~e method) a
network of discreet upstanding fins on one or both sides of said plates.
The ~luid passageways through the distribution zone are
preferably interconnected, the interconnection being provided by spaces
20 between said fins. At the extreme edges of the plates, side bars are
typically created from unetched metal. The fins may be of variable
length in the direction of fluid flow and offset at different angles to the
overall flow direction of fluid through the heat exchange zone. The fins
may comprise both rectilinear and curved projections. The fins may be
25 straight-sided7 curved or aerofoil-shaped or a combination of each.
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Where there are fins on both sides of the plates, the fins on one plate
may register with identically configured f~ms on an adjacent plate and
are joined together by e.g. brazing or diffusion bonding, or by the use of
adhesives.
The fin configuration etched onto one side of a particular plate
may be identical to or different from that etched on an adjacent plate, or
where a plate is etched on both sides, onto the other side of the same
plate. Plane metal sheets may be used as separator plates with two or
more finned plates to form one discrete ilow layer for a single fluid.
The designer of the distribution zone can vary the length of fins,
the distance between them, (both along the flow direction and laterally
of it), and the density oi~ fins in a particular area of the distribution zone
in the direction of fluid flow.
The discrete projections, or fins, at the entry to the distribution
zone may be positioned and angled such as to create a higher flow
resistance to fluid which traverses a shorter path through the heat
exchanger.
Brief nescriptio~ of nraw;n~;s
An embodiment of the invention will now be described, by way of
example only, with reference to the accompanying drawings in which;
Figure 1 is a schematic plan view showing a cross-section of a
heat exchanger in accordance with the invention;
Figure 2 is a cut-away view of part of the heat exchanger of
Figure 1;
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Figure 2A is a cut-away view of part of an alternative heat
exchanger;
l~igure 3 is a cross-section illustrating a principle of construction
of the heat exchanger of Figure 2;
Figure 3A is a cross-section (similar to that of Figure 3)
illustrating a principle of construction of the heat exchanger of Figure
2A; and
Figure 4 is a schematic view, similar to Fi~sure 1, illustrating
certain of the design characteristics of the heat exchangers according to
the invention.
Best Msde for (~arryins~ Out ~he ~nvention
A heat exchanger 10 (see Figure 1 ) has a main heat exchange
zone 11 connected with a distribution zone 1 at its entry end. Heat
exchanger 10 comprises a series of thin plates aligned parallel to one
another, some of which are planar 14 and some of which 15 have a
plurality of discrete projections or fns 16 and 17 extending towards
plate l S. It is a plate of the type l S (with projections or fins 16) which
is seen in Figures 1, 2, ~A and 4.
Plate 15 has fins 16 which extend parallel to one another along
2û the line of flow (shown by arrow 18) through the main heat exchange
zone. Within the distribution zone 12, the distributor fms 17 may have
some which are parallel to others but their alignment and location is
determined by factors which will be described later in this document.
Both types of fm 16 and 17 are photochemically or
electrochemically etched from a sheet of parent metal e.g. stainless steel
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as are upstanding side bars or spacers 19 which are of the same height as
the fins 16, 17. Fins 16, 17 and side bars 19 or spacers are etched on
either both sides (Figure 2) or one side only (Figure 2A~ of plates 15.
When both sides of a plate are etched, the fins are coincident with one
5 another, such that they will register identically with fins 16, 17 and side
bars 19 on adjacent plates 15 as seen in Figure 3. When etched on one
side only, plate 15 may be stacked or shown in Figure 3A.
The side bars or spacers 19 extend around the periphery of plate
1 5 except for portions where an entry 20 and an exit 21 to the heat
10 exchanger 10 are provicled. The entry 20 is a side entry into the
distribution zone 12 of heat exchanger 10 such that fluid passing
through the heat exchanger 10 can enter at right angles to the direction
of fluid flow through the main heat exchange zone 1 1. The exit 21 is
similarly treated to permit fluid to exit at right angles to the flow
15 through the main heat exchange zone 1 1. Fins 16, 17 are shown only in
the portion of heat exchanger 10 adjacent entry 20, but in practice they
extend throughout the heat exchanger. The junction between the
distribution zone 12 and the main heat exchange zone 1 1 extends across
the heat exchanger from the side 22 of entry 20 away from the end of
20 the heat exchanger. The junction between the main heat exchange zone
11 and the exit distribution zone is shown by dashed line 23 in Figure 1.
Side entry and exit configurations enable heat exchangers to be provided
with multi-stream capability.
Plates 14 and plates 15 which are etched on both sides are
25 arranged in a stack, part of which is seen in Figure 3. A pair of etched
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plates 15 are arranged with their fins 16 and side bars 19 registered
(Figure 3 illustrates a fin configuration in the main heat exchange zone
I 1). Planar plates (side plates 14) are added to provide a sandwich, or
flow layer 30 which has enclosed passageways 30, all of which will
5 carry the same fluid. An adjacent flow layer (not shown) can be built up
parallel to that shown in Figure 3 and registering with its side bars 19.
A different fluid will flow through the adjacent flow layer, and it may be
that the fin pattern and distribution in adjacent flow layers may be
different according to the fluid characteristics. The number of plates 15
10 malcing up a single flow layer may also be more than two. Typically the
entry and exit to the heat exchanger for different fluids are arranged to
be from different sides of the heat exchanger, and this may be achieved
by etching the entry and exit through the side bars 19 in different
positions.
An alternative build up of plates which are etched only on one
side is shown in Figure 3A.
The separation of the fins 17 in the distribution zones 12 (both
along the overall flow direction and laterally of it) is generally not
uniform, even at entry 20. The flow passageways in the distribution
20 zones 12 which are created by the fins 17 are able to interact with each
other by way of the spacings along the flow direction.
Fins 16, 17 may be positioned anywhere on the surface of plate 15
where it is desired. As illustrated in this example, in the heat exchange
zone 1 I the fins 16 are arranged in rows in a regular pattern with
25 alternate rows offset relative to each other i.e. the leading edge of each
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fin 16 in one row trails (or leads) the le~-lin~; edge of each fin 16 in an
adjacent row. The pitch of fins 16 may be such that the gap between
fins along the flow direction is greater than the fin length. Each offset
fin may then be more than a fin length behind the leading edge of a fin
5 in an adjacent row. In the distribution zone 12, the fins 17 are arranged
in lines which will curve towards the heat exchange zone 11. Alternate
lines of fins 17 are then offset from one another in a similar way to the
rows of fins 16 in the heat exchange zone 1 1. The offset fins, or some
of them, may be angled differently from adjacent fins 17. The length of
10 the fins 17 may be different at different positions in the distribution zone
12 e.g. the length may be greater as the flow approaches the heat
exchange zone 1 1. 7'he pitch o~fins 17 may also change along their line
through the distribution zoMe 12.
There may be supplementary fins 53, 54, SS within the
15 distribution zone 12 which do not form part of lines of fins 17, along the
flow direction, whether offset or otherwise. These supplementary fins
53, 54, 55 are used to give a local higher fin density and to make small
adjustments to the flow patterns to enhance even distribution of fluid
across the whole of the heat exchange zone 1 1. Fins may be curved 40,
20 aerofoil 41 or straight and they may be set at a variety of angles to the
flLuid flow.
A typical distribution side entry (see ~igure 4) could be designed
such that the pitch and angle of fins 17 which are encountered by the
fluid entering adjacent the point of entry 20 furthest from side 22, are
25 such as to create a lower resistance to flow than the fins 17 (which are
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differently pitched and angled) encountered by fluid entering the
distribution zone l 2 closer to side 22 of entry 20. In this way a higher
flow resistance may be created to fluid which takes a shorter path (e.g.
arrow 5 l - see Figure 4) than that which takes a longer path (e.g. arrow
5 52 - see Figure 4) through the heat exchanger lO.
