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Claims  |
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I claim:
1. A plate-fin heat exchanger adapted for use in ocean thermal energy
conversion systems, the heat exchanger comprising:
a plurality of elongated metal plate-fin panels arranged in parallel spaced
apart relation, each panel having two rectangular side walls with flat
exterior surfaces and a plurality of longitudinally extending fins
connecting the interior surfaces of said side walls together in spaced
apart relation, said fins creating a plurality of longitudinally
extending, laterally spaced, internal passages between the two side walls;
first and second header chambers disposed at opposite ends of the plate-fin
panels, each header chamber including a headering plate having a plurality
of parallel slotted apertures, and the corresponding end of each plate-fin
panel being inserted through a corresponding one of said slotted apertures
and being fastened thereto, whereby the plurality of panels are maintained
in said parallel closely-spaced relation;
rigid support members extending between the first and second header
chambers;
means for dislodging accumulated foreign matter from at least a localized
portion of the exterior surface of each panel side wall; and
means mounted on said support members and connected to said dislodging
means for moving said dislodging means to traverse the exposed exterior
surface of each panel side wall between the header plates of said header
chambers, wherein the thickness of and spacing between the side walls of
each plate-fin panel are very small compared with the length of the panel,
such that the panel could buckle even without the application of external
load if unsupported with its longitudinal dimension approximately
vertical, and said rigid support members exert an axially outward force
against each header plate, whereby each plate-fin panel is maintained in
tension in its longitudinal dimension to prevent buckling of said panel.
2. A heat exchanger according to claim 1 wherein each plate-fin panel
comprises a plurality of plank-like members positioned edge-to-edge, each
plank edge having interengagement means for keying said edge to mating
interengagement means of an adjacent panel.
3. A heat exchanger according to claim 2 wherein said interengagement means
comprises a tongue formed on an edge of one plank-like member and a mating
groove formed in the contiguous edge of an adjacent panel.
4. A heat exchanger according to claim 1 wherein at least part of the
exterior surface of each panel comprises a layer of heat conductive
material which is resistant to corrosion and biological fouling.
5. A heat exchanger according to claim 4 wherein said exterior layer
terminates at a location spaced from each end of each panel, said heat
exchanger further comprising a resin layer contiguous to each header plate
and covering the terminal location of said exterior layer for preventing
electrolytic corrosion between said exterior layer and the underlying
material of the panel side walls.
6. A heat exchanger according to claim 1 wherein the side walls and fins of
each panel comprise an aluminum extrusion.
7. A heat exchanger according to claim 6 wherein the exterior surface of
each panel comprises a layer of Cu-Ni cladding soldered to said aluminum
extrusion.
8. A heat exchanger according to claim 6 wherein the exterior surface of
each panel comprises a layer of Cu-Ni cladding brazed to said aluminum
extrusion.
9. A heat exchanger according to claim 6 wherein the exterior surface of
each panel comprises a layer of Cu-Ni cladding glued to said aluminum
extrusion.
10. A heat exchanger according to claim 9 wherein the glue comprises a
thermosetting epoxy resin loaded with aluminum powder to provide good heat
conduction.
11. A heat exchanger according to claim 9 wherein the glue comprises a
pressure and heat activated adhesive including approximately 65 percent by
volume of aluminum powder.
12. A heat exchanger according to claim 1 wherein each panel comprises a
flat rolled plate forming each side wall, a corrugated sheet metal core
forming said plurality of fins, and means for fastening said core to said
side walls.
13. A heat exchanger according to claim 12 wherein said corrugated sheet
metal core has right angle bends.
14. A heat exchanger according to claim 12 wherein said fastening means
comprises soft solder.
15. A heat exchanger according to claim 12 wherein said fastening means
comprises brazing metal.
16. A heat exchanger according to claim 12 wherein said flat rolled side
walls comprise Cu-Ni clad steel plates.
17. A heat exchanger according to claim 16 wherein the Cu-Ni cladding of
said side wall plates comprises two layers of cladding, the outer layer
being anodic to the inner layer.
18. A heat exchanger according to claim 12 wherein said flat rolled side
walls comprise tin-plated steel plates.
19. A heat exchanger according to claim 12 wherein said flat rolled side
walls comprise Cu-Ni plates.
20. A heat exchanger according to claim 12 wherein said core comprises a
corrugated steel sheet.
21. A heat exchanger according to claim 12 or 14 wherein the internal
passageways are coated with a layer of pure iron.
22. A heat exchanger according to claim 12 or 14 wherein the internal
passageways are coated with a layer of nickel.
23. A heat exchanger according to claim 12 wherein said core comprises a
corrugated tin-plated steel sheet.
24. A heat exchanger according to claim 1 wherein said rigid support
members being fastened to opposite sides of the first and second header
chambers parallel to said plurality of panels.
25. A heat exchanger according to claim 24 wherein said rigid support
members are made of epoxy resin reinforced with glass fibers.
26. A heat exchanger according to claim 1 wherein said first header chamber
comprises a grating parallel to and spaced from the headering plate, mesh
pads positioned in the openings of said grating, and an opening on the
other side of the grating from the headering plate, whereby fluid passing
through the internal passageways and said opening will traverse said mesh
pads.
27. A heat exchanger according to claim 1 wherein said one header chamber
comprises an opening for fluid spaced from the headering plate and a
spiral passageway between the headering plate and the opening, such that
fluid passing through the internal passageways of the panels and the
opening will traverse the spiral passageway.
28. A heat exchanger according to claim 1 wherein said means for dislodging
accumulated foreign matter comprises double-tufted brushes positioned in
the spaces between adjacent plate-fin panels, with the tufts of each brush
in wiping contact with the exterior surfaces of adjacent side walls of
corresponding pairs of said panels.
29. A heat exchanger according to claim 28 wherein said means for moving
the dislodging means comprises:
a pair of shafts extending adjacent to the opposite longitudinal edges of
said plurality of plate-fin panels, the axes of the shafts being
perpendicular to the planes of the panels;
means for supporting said shafts for rotation about their longitudinal axes
and for translation in a plane parallel to the longitudinal edges of said
panels;
a plurality of spaced driving wheels fastened coaxially to one of said
shafts, each driving wheel being aligned with the space between a
corresponding pair of plate-fin panels;
a corresponding plurality of wheels mounted on the other shaft;
an endless flexible carrier means trained around each driving wheel and the
corresponding wheel on the other shaft;
means for fastening a plurality of said doubletufted brushes to said
carrier means;
means for translating said pair of shafts in unison parallel to the
longitudinal edges of said panels; and
means for rotatably driving said one shaft at any longitudinal position of
said shafts.
30. A heat exchanger according to claim 29 wherein said means for
supporting said shafts for rotation about their longitudinal axes
comprises roller means rotatably mounted on each of said pair of shafts
between at least two pairs of the driving and of the driven wheels,
respectively, each roller means bearing against a longitudinal edge of a
corresponding plate-fin panel.
31. A heat exchanger according to claim 30 wherein the means for
translating said pair of shafts in unison parallel to the longitudinal
edges of said panels comprises:
endless flexible carrier means extending parallel and adjacent to the
opposite longitudinal edges of said plate-fin panels;
means for attaching each end of each of the pairs of shafts to a
corresponding one of the longitudinal endless flexible carrier means for
longitudinal movement thereby; and
means for driving all of said longitudinal endless flexible carrier means
in synchronism.
32. A heat exchanger according to claim 1 wherein said means for dislodging
accumulated foreign matter comprises a pair of support members extending
adjacent to opposite longitudinal edges of said plurality of plate-fin
panels, the axes of said members being perpendicular to the planes of the
panels, and elongated hollow bars positioned in the spaces between each
pair of adjacent plate-fin panels, each bar extending from one of the pair
of support members adjacent one longitudinal edge of a panel to the other
support member adjacent the opposite longitudinal edge of the panel and
having opposed rows of spray orifices facing the exterior surfaces of the
adjacent side walls of corresponding pairs of said panels, and means for
delivering liquid under pressure to said hollow bars for jetting from said
spray orifices against the adjacent panel surfaces.
33. A heat exchanger according to claim 32 wherein said means for moving
the dislodging means comprises means for translating said elongated
support members in unison parallel to the longitudinal edges of said
panels.
34. A heat exchanger according to claim 33 wherein said means for
translating said elongated support bars in unison parallel to the
longitudinal edges of said panels comprises:
endless flexible carrier means extending parallel and adjacent to the
opposite longitudinal edges of said plate-fin panels;
means for attaching each end of each of the pair of support bars to a
corresponding one of the longitudinal endless flexible carrier means for
longitudinal movement thereby; and
means for driving all of said longitudinal endless flexible carrier means
in synchronism. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to heat exchangers of the plate-fin type,
particularly to large heat exchangers of this type adapted for use in
ocean thermal energy conversion (OTEC) systems, and to plate-fin panels
for use in such heat exchangers.
2. Background Art
Serious study of the possibilities of converting the potential energy
represented by the difference in temperature between warm surface water
and cold deep water in the ocean into useful form began at least fifty
years ago with the researches of Georges Claude (see U.S. Pat. No.
2,006,985). Although the thermal energy available from ocean sources is
essentially unlimited, the relatively low temperatures and small
temperature differences involved result in very low plant thermal
efficiencies, so that OTEC systems up to now have been uneconomic in
comparison with fossil fuel plants. The dramatic increase in the cost of
fossil fuels in recent years, however, has led in the cost of fossil fuels
in recent years, however, has led to reconsideration of the economics of
ocean thermal energy conversion.
Because of the small differences in temperature between the thermal source
and thermal sink of an OTEC plant, and also because of the corrosive
nature of, and marine organisms present in, the seawater medium, the
effectiveness of the heat exchangers is a major factor in the efficiency
and cost-effectiveness of an OTEC systems. Although conventional shell and
tube exchangers have been proposed for OTEC plants, this type of exchanger
presents serious drawbacks because of the difficulty of maintaining the
seawater-side heat transfer surfaces free of fouling by algae and other
marine organisms.
U.S. Pat. No. 4,055,145 issued on Oct. 25, 1977 to D. Mager and W. E.
Heronemus and U.S. Pat. No. 4,062,189 issued on Dec. 13, 1977 to D. Mager,
W. E. Heronemus, and P. M. J. Woodhead describe the use of plate-fin heat
exchangers as evaporators and condensers for a closed-loop working fluid,
such as ammonia, in an OTEC power generating plant. Based on an analytical
study directed by the present inventor at the University of Massachusetts,
and presented in a report entitled "Detailed Analytical Model of Rankine
Cycle and Heat Exchangers for Ocean Thermal Difference Power Plants" under
a grant, No. GI-34979, from the National Science Foundation, vertically
arranged parallel plate-fin exchangers would permit maximum possible
transfer of thermal energy between seawater flowing horizontally between
spaced apart plate-fin units and working fluid flowing vertically within
each unit. The above-mentioned U.S. Pat. No. 4,062,189, which is directed
to a method of preventing the accumulation of micro-organisms in OTEC
systems by alternating warm and cold seawater flow through the heat
exchangers, also mentions that plate-fin heat exchangers are adapted for
cleaning by brushing or scraping the flat plate-fin panel surfaces.
Further analytical and experimental studies have demonstrated the
feasibility of the plate-fin heat exchanger concept presented in the
above-mentioned Pat. Nos. 4,055,145 and 4,062,189; they have also
demonstrated the necessity of having all surfaces exposed to seawater made
of corrosion resistant material and the importance of maintaining these
surfaces free of even minor amounts of biological fouling to avoid loss of
heat transfer effectiveness. Copper-nickel alloys are well known for their
resistance to corrosion by seawater, and also for their resistance to
bio-fouling. Heat exchangers made exclusively of such alloys, however,
would be very expensive, making an OTEC plant difficult to justify on an
economic basis. In addition, these corrosion-resistant alloys have
relatively low heat conductivities; so that the temperature drop across
the heat exchanger surfaces can be a significant percentage of the
available thermal difference in such a plant.
Among metals having a high heat conductivity, aluminum has long been used
for evaporators in refrigerator freezing units and in automotive
radiators, as well as for small heat exchangers in other types of service,
because of its relatively low cost, light weight, and capability of being
extruded into tubular elements of complex cross section, including
multi-tubular members. Examples of such elements are shown in U.S. Pat.
Nos. 2,190,494; 2,212,912; 2,415,243; 3,416,600; 3,486,489; 3,662,582;
3,668,757; 3,920,069; and 4,043,015.
Aluminum heat exchanger tubes are typically assembled in groups and
attached to headers by soldering, brazing, welding, or use of adhesives
(U.S. Pat. No. 3,416,600). Alternatively, or in addition, nonmetallic
sealant layers, such as synthetic resins or natural or synthetic rubber
may be used (U.S. Pat. Nos. 2,303,416; 2,385,542; 3,633,660; and
3,993,126).
Although aluminum has excellent heat transfer properties, it is easily
corroded by seawater unless it can be suitably protected. Combining
dissimilar metals to take advantage of respective characteristics such as
high thermal conductivity and resistance to corrosion and bio-fouling is
difficult, however, because of the danger of electrolytic corrosion if the
different metals are exposed to seawater.
In addition to the problems of effective heat transfer, corrosion, and
biological fouling which they share in common with other types of heat
exchangers, plate-fin exchangers present unique structural problems. For
effective thermal operation, the plate-fin panels should be thin and
closely spaced, yet have a large surface area. This means that the
plate-fin panels are very flexible, but intermediate supports can
interfere with optimum flow of fluid past the exterior surfaces of the
panels, as well as provide growth sites for bio-organisms. Also the flat
thin panel configuration presents headering problems compared with
conventional shell-and-tube exchangers, in which the tubes are rolled into
the headers.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide plate-fin panel
components for a heat exchanger, particularly for use in ocean thermal
energy conversion systems, having both high heat conductivity and high
resistance to corrosion.
Another object of the invention is to provide plate-fin panel components
for a heat exchanger of the type described which are simple to fabricate
and assemble.
It is another object of the invention to provide plate-fin panels for a
heat exchanger, the panels having metal cores of high thermal conductivity
and jackets of a different metal with high resistance to corrosion and
bio-fouling.
Still another object of the invention is to provide a heat exchanger
incorporating plate-fin panels of the type described designed for maximum
protection against electrolytic corrosion of the panels and equipped with
means for dislodging accumulated foreign matter from the heat exchanger
surfaces contacted by seawater.
Another object of the invention is to provide a heat exchanger
incorporating plate-fin panels of the type described above which can be
readily assembled into groups of exchangers and disassembled from such
groups for repair.
These and other objects are achieved by a plate-fin panel for a heat
exchanger comprising:
a plurality of elongated thin rectangular parallelepipedal metallic
members, each member having flat parallel exterior side surfaces and a
plurality of passageways extending parallel to the longitudinal axis of
the member, said members being arranged in a row with their respective
exterior side surfaces aligned in two parallel planes;
means for providing tongue and groove interlocking engagement between
adjacent edges of adjacent members; and
elongated strip means of corrosion resistant material sealingly fastened to
the longitudinal edges of the plate-fin panel.
The core of each panel member may be made as a single aluminum extrusion or
as an assembly of several "plank-like" extrusions having interengagement
means such as tongue-and-groove edges. The aluminum core is encased by two
flanged sheet metal jackets of material which is resistant to seawater
corrosion and biological fouling, such as a Cu-Ni, soldered, brazed, or
glued to the faces of the aluminum extrusions.
Alternatively, each plate-fin panel may comprise a flat rolled plate
forming each side wall and a corrugated sheet metal core forming the
plurality of internal fins, the core being fastened to the side walls by
soft solder or brazing metal. The side walls may be Cu-Ni sheets, or they
may be steel or tin-plated steel sheets, the exterior surfaces of which
are clad with Cu-Ni. The corrugated sheet metal core may be a steel sheet,
which may be bare or plated with tin, and the internal passages in
addition may be coated with a layer of pure iron or nickel.
The plate-fin heat exchanger of the invention comprises:
a plurality of elongated metal plate-fin panels arranged in parallel spaced
apart relation, each panel having two rectangular side walls with flat
exterior surfaces and a plurality of longitudinally extending fins
connecting the interior surfaces of said side walls together in spaced
apart relation, said fins creating a plurality of longitudinally
extending, laterally spaced, internal passages between the two side walls;
first and second header chambers disposed at opposite ends of the plate-fin
panels, each header chamber including a headering plate having a plurality
of parallel slotted apertures, and the corresponding end of each plate-fin
panel being inserted through a corresponding one of said slotted apertures
and being fastened thereto, whereby the plurality of panels are maintained
in said parallel closely-spaced relation;
rigid support members extending between the first and second header
chambers;
means for dislodging accumulated foreign matter from at least a localized
portion of the exterior surface of each panel side wall; and
means mounted on said support members and connected to said dislodging
means for moving said dislodging means to traverse the exposed exterior
surface of each panel side wall between the header plates of said header
chambers.
For optimum heat transfer effectiveness the thickness of and spacing
between the side walls of each plate-fin panel desirably are very small
compared with the length of the panel, such that the panel could buckle,
even without the application of external load, if unsupported with its
longitudinal dimension approximately vertical; so preferably said rigid
support members exert an axially outward force against each header plate,
whereby each plate-fin panel is maintained in tension in its longitudinal
dimension to prevent buckling of said panel.
A preferred embodiment of the means for dislodging accumulated foreign
matter from the seawater-exposed surfaces of the plate-fin panels
comprises double-tufted brushes positioned in the spaces between adjacent
plate-fin panels, with the tufts of each brush in wiping contact with the
exterior surfaces of adjacent side walls of corresponding pairs of the
panels. The brushes are mounted on suitable drive means for moving them
across the entire exposed surfaces of each pair of panels for scrubbing
off bio-organisms and other deposited material to maintain optimum heat
transfer effectiveness of the heat exchangers. In an alternative
embodiment, water jetting bars are substituted for the brushes.
These and other features of the invention, and their resulting advantages,
will become more apparent from the following detailed description of the
preferred embodiments of the invention, taken with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are perspective views showing two stages of assembly of one
embodiment of a plate-fin heat exchanger panel.
FIG. 3 is a partial longitudinal section of the panel of FIGS. 1 and 2
taken in the direction of arrows 3--3 in FIG. 2.
FIG. 4 is a partial transverse section of the panel of FIGS. 1 and 2 taken
in the direction of arrows 4--4 in FIG. 3.
FIGS. 5-7 are cross sections of extruded aluminum panel elements having
different numbers and sizes of holes.
FIGS. 8-16 are partial transverse sections of alternative internal passage
profiles for extruded heat exchanger panels.
FIG. 17 is a transverse section of an alternative embodiment of a plate-fin
heat exchanger panel.
FIG. 18 is an elevation view, in section, of a heat exchanger using
plate-fin panels.
FIG. 19 is a plan view of the upper header of the heat exchanger taken in
the direction of arrows 19--19 in FIG. 18.
FIG. 20 is a plan view of the upper header chamber of the heat exchanger
taken in the direction of arrows 20--20 in FIG. 18.
FIG. 21 is an elevation view, in section, of one form of upper headering
chamber.
FIG. 22 is a partial section view taken in the direction of arrows 22--22
in FIG. 21.
FIG. 23 is a perspective view of another form of upper headering chamber.
FIG. 24 is an elevation view, in cross section, of the headering chamber of
FIG. 23.
FIG. 26 is a perspective view of a panel surface brushing unit.
FIG. 27 is a plan view, partly in section, of the support structure and
drive means for the brush units of a heat exchanger assembly taken in the
direction of arrows 27--27 in FIG. 26.
FIG. 28 is an elevation view, partly in section, of the brush unit drive
means of FIG. 27.
FIG. 29 is a perspective view of alternative water jetting bars and drive
mechanism for dislodging foreign matter from the panel surfaces.
FIG. 30 is a partial plan section view of the water jetting bar and drive
mechanism taken in the direction of arrows 30--30 in FIG. 29.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to FIGS. 1-4, one embodiment of a plate-fin panel member 1
includes one or more elongated plank-like aluminum extrusions 2,
preferably encased in sheet metal jackets 3 having a corrosion resistant
outer surface of a material such as Cu-Ni.
Each extruded aluminum core element is in the form of an elongated thin
rectangular parallelepiped having flat parallel side surfaces 4 and
longitudinal edges, of which one is formed with a tongue 5 and the other
with a groove 6, so that adjacent ones of the extruded elements can be
fitted together in tongue and groove fashion. Each aluminum extrusion 2
also includes a plurality of longitudinally extending holes 7, such that
the element in cross section is in the form of two parallel plates 8
defined by the side surfaces 4, joined by a plurality of fins 9 defined by
the material remaining between adjacent holes.
The plate-fin panel member is assembled by first interlocking the necessary
number of extruded aluminum elements 2 together in tongue and groove
fashion and then applying flanged plates 3 to each side surface of the
resulting panel, as shown in FIGS. 1 and 2, so that the flanges of the two
metal jackets abut to form a longitudinal rib or tongue 10 along each
longitudinal edge of the panel member. The jackets are attached to the
core elements to provide both good physical and thermal contact,
preferably by soft solder, by brazing, or by an adhesive. If assembly is
by brazing, either vacuum oven fluxless brazing or induction heated fluxed
brazing processes can be used. In the latter case, flux gathering passages
can be provided in the exterior surface of the core. The adhesive may be a
synthetic resin or other type of adhesive. Two preferred materials are an
epoxy thermoset catalyzed heat cure adhesive heavily loaded with finely
ground metal powder (e.g., silver or aluminum), such as that sold by
TRA-CON, of Medford, Mass. under the name "Tra-Bond BB 2143", or a
pressure-and-heat activated, pressure-sensitive adhesive film loaded with
approximately 65% by volume of finely ground aluminum powder to provide
high thermal conductivity across the adhesive layer. Alternatively, a
lead-foil or aluminum-foil based pressure and heat sensitive adhesive film
of high thermal conductivity can be used.
Preferably, the adhesive film is coated directly on | | |
