U.S. patent application number 13/715514 was filed with the patent office on 2013-06-20 for composite heat exchanger shell and buoyancy system and method.
This patent application is currently assigned to LOCKHEED MARTIN CORPORATION. The applicant listed for this patent is Lockheed Martin Corporation. Invention is credited to Natalie B. LEVINGS, Alan K. MILLER, Nicholas J. NAGURNY.
Application Number | 20130153171 13/715514 |
Document ID | / |
Family ID | 47739467 |
Filed Date | 2013-06-20 |
United States Patent
Application |
20130153171 |
Kind Code |
A1 |
NAGURNY; Nicholas J. ; et
al. |
June 20, 2013 |
COMPOSITE HEAT EXCHANGER SHELL AND BUOYANCY SYSTEM AND METHOD
Abstract
A heat exchanger includes a shell made of a composite material,
and a heat exchanger housed substantially within the shell. The
shell is made of a composite material further comprises planks
positioned in the outer periphery of the shell. The planks, in one
embodiment, are substantially hollow or include substantially
hollow portions. In some embodiments, the planks are formed of
pultruded plastic. The shell of the heat exchanger further includes
layers of fiberglass. The pultruded plastic planks are sandwiched
between at least a first layer of fiberglass and a second layer of
fiberglass. The layers of fiberglass are infused with resin. A
floating portion of an Ocean Thermal Energy System includes shells
made of composite material. The cold seawater intake can also be an
elongated tube of composite material.
Inventors: |
NAGURNY; Nicholas J.;
(Manassas, VA) ; MILLER; Alan K.; (Santa Cruz,
CA) ; LEVINGS; Natalie B.; (North Richland Hills,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lockheed Martin Corporation; |
Bethesda |
MD |
US |
|
|
Assignee: |
LOCKHEED MARTIN CORPORATION
Bethesda
MD
|
Family ID: |
47739467 |
Appl. No.: |
13/715514 |
Filed: |
December 14, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61570733 |
Dec 14, 2011 |
|
|
|
Current U.S.
Class: |
165/67 ; 165/185;
425/112 |
Current CPC
Class: |
F28F 21/084 20130101;
B63B 2035/4486 20130101; Y02E 10/34 20130101; C02F 1/04 20130101;
C02F 2103/08 20130101; F28D 1/022 20130101; F28F 21/067 20130101;
B63B 2035/4473 20130101; F28F 9/007 20130101; F28F 9/00 20130101;
F28F 21/00 20130101; F03G 7/05 20130101; F28F 21/006 20130101; F28F
9/0219 20130101; C02F 2201/008 20130101; Y02E 10/30 20130101 |
Class at
Publication: |
165/67 ; 165/185;
425/112 |
International
Class: |
F28F 9/00 20060101
F28F009/00; F28F 9/007 20060101 F28F009/007 |
Claims
1. A heat exchanger comprising: a shell made of a composite
material; and a heat exchanger housed substantially within the
shell.
2. The heat exchanger of claim 1 wherein the shell of composite
material further comprises planks positioned in the outer periphery
of the shell. The heat exchanger of claim 2 wherein the planks are
substantially hollow.
3. The heat exchanger of claim 2 wherein the planks are formed of
pultruded plastic.
4. The heat exchanger of claim 1 wherein the composite material is
further comprised of: pultruded plastic core planks; and layers of
fiberglass, the pultruded plastic planks sandwiched between at
least a first layer of fiberglass and a second layer of
fiberglass.
5. The heat exchanger of claim 1 wherein the layers of fiberglass
are infused with resin.
6. The heat exchanger of claim 5 wherein the layers of fiberglass
are infused with resin using a Vacuum-Assisted Resin Transfer
Molding (VARTM) process.
7. The heat exchanger of claim 1 wherein the shell further
comprises: a first end; a second end; and at least one metal flange
coupled to one of the first end or second end of the shell.
8. The heat exchanger of claim 7 wherein at least one metal flange
is comprised of: an inner termination ring having inner trap-lock
grooves therein; and an outer termination ring having inner
trap-lock grooves therein.
9. The heat exchanger of claim 1 wherein the shell of composite
material is buoyant.
10. The heat exchanger of claim 1 wherein the shell of composite
material is over 70 meters in length.
11. An apparatus for forming elongated tubes of composite material,
the apparatus comprising: a floating base; a molding region
attached to the base, the molding region including a core ring for
receiving a core material; a fiber supply region for providing a
substantially continuous supply of a fiber to the molding region,
the fiber supply region supplying fiber to an inner region of the
core ring and an outer region of the core ring; and a resin
infusion apparatus for infusing the fiber with resin.
12. The apparatus for forming elongated tubes of composite material
of claim 11 further comprising a core material that is inserted
into the core ring.
13. The apparatus for forming elongated tubes of composite material
of claim 11 further comprising a core material that is inserted
into the core ring, the core material including elongated planks of
plastic.
14. The apparatus for forming elongated tubes of composite material
of claim 11 further comprising a core material that is inserted
into the core ring, the core material including elongated planks of
pultruded plastic having hollow portions therein.
15. The apparatus for forming elongated tubes of composite material
of claim 11 further comprising a vacuum assisted resin infusion
apparatus to apply a vacuum to a portion of the molding
chamber.
16. The apparatus for forming elongated tubes of composite material
of claim 11 wherein the molding process occurs at a site where the
elongated tubes of composite material are used to form a floating
heat exchanger for an Ocean Thermal Energy System.
17. The apparatus for forming elongated tubes of composite material
of claim 11 wherein a plurality of elongated planks are positioned
around the ring core in forming the elongated tubes.
18. The apparatus for forming elongated tubes of composite material
of claim 11 further comprising an apparatus for applying a metal
flange to at least one of the ends of the elongated tube.
19. A floating portion of an Ocean Thermal Energy System
comprising: a platform; a plenum attached to the platform; a cold
seawater intake attached to the plenum; a plurality of heat
exchangers attached to the plenum, the heat exchangers including
pumps for moving the cold seawater from the plenum through the heat
exchangers, wherein the heat exchangers include shells made of
composite material.
20. A floating portion of an Ocean Thermal Energy System of claim
19 wherein the cold seawater intake is an elongated tube of
composite material.
Description
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 61/570,733, filed on Dec. 14, 2011,
which is incorporated by reference herein.
TECHNICAL FIELD
[0002] Various embodiments described herein relate to a composite
heat exchanger shell and buoyancy system and method. The composite
heat exchanger shell and buoyancy system and method is used as part
of a floating Ocean Thermal Energy Conversion ("OTEC") system. It
can also be used in floating thermal desalination plants and in
other marine and land-based applications.
BACKGROUND
[0003] An increase in worldwide population has led to the increase
in demand for fresh water for human consumption and irrigation.
Over 99% of the world's fresh water comes from tapping a
diminishing source of the world's rivers, lakes, and groundwater
locations that are becoming less dependable as some are reaching
maximum capacities. With only 1% of the world's water supply
available for human use in a constantly expanding worldwide
population, clean water is becoming the most important commodity in
water-stressed regions. The increase in demand for fresh water has
been most evident in dry areas where rainwater is scarce and
groundwater sources are drying up such as: the Middle East,
Australia, and the American West and Southwest, to name a few.
[0004] Clean water is necessary for irrigation in arid regions
where occupants rely on importing most of their food because
agriculture is too expensive or not possible. Although clean water
is basic utility in water-rich and developed regions, the arid and
less developed regions of the world do not have access to clean
water.
[0005] Most of the earth's surface, about 71%, is covered with
water. However, most of the water is in saltwater oceans. Of
course, salt water is unfit for human consumption. Water can be
desalinated. The two most common options for water production
include non-thermal/pressure/membrane processes, and thermal
processes. The non-thermal/pressure/membrane processes include
reverse osmosis ("RO"), filtration, sludge, and the like. The
thermal processes include multi-stage flash, multi-effect
distillation, and low-temp thermal desalination. Generally, water
treatment and desalination methods require capital intensive
equipment and facilities that become more expensive in regions that
are arid and underdeveloped.
[0006] Each of the thermal processes includes a heat exchanger
which is generally used to transfer heat from steam or humid air to
cooler seawater. By transferring heat from the steam or humid air,
freshwater condenses onto the heat transfer surfaces of the heat
exchanger. As in the case of OTEC, expensive materials drive up
heat exchanger capital costs and often eliminate the thermal
desalination process from consideration.
[0007] Large heat exchangers are required for Ocean Thermal Energy
Conversion (OTEC) for producing power based on the temperature
difference between deep seawater and seawater near the surface of
the ocean. A closed Rankine cycle using ammonia as the working
fluid is commonly used in OTEC. Warm seawater is used to transfer
heat to the boil liquid ammonia in the evaporator of the Rankine
cycle. The cold seawater is used to remove heat from ammonia gas
during a substantially constant pressure transfer of heat from the
ammonia gas as it condenses in the condenser. Both the evaporator
and the condenser each comprise one or more heat exchangers.
[0008] Expensive corrosion resistant metals are normally required
for these heat exchangers since sea water is corrosive. The ammonia
working fluid is used in the discussed application, but is
incompatible with alloys containing copper, and titanium has been
cited as the baseline material in past studies for OTEC plants but
this idea is not restricted to ammonia as the working fluid. Many
of the heat exchangers employ shell and tube technology; while
others incorporate more compact plate-fin geometries. The expensive
materials drive up the capital expenditure associated with OTEC
heat exchangers to largely restrict locations where plants can be
economically deployed.
[0009] Aluminum tubes or extrusions can be used in the heat
exchangers. However, when a different metal is used as an exposed
end plate or sheet in these heat exchangers a galvanic reaction
causes corrosion concerns. Even with an aluminum tubesheet, the
traditional fusion welding process (MIG or TIG welding) requires a
filler material with a different alloy composition than the base
metal. Fusion welding also results in a heat affected zone, where
the region around the weld joint has a different grain structure
than the surrounding tube or tube sheet material. These negative
impacts from fusion welding can produce accelerated corrosion.
Other joining techniques introduce aluminum alloys with a different
composition than the base metal to weld or braze aluminum tubes or
extrusions to adjacent aluminum plates. This too causes corrosion
problems based on the formation of a galvanic reaction. In many
heat exchangers the aluminum tubes must be isolated from a sheet of
dissimilar material by way of an isolating gasket. Even with the
gasket isolating dissimilar metals from each other, crevices at the
tube end/tube sheet joint can trap chloride ions, resulting in
preferential corrosion. Even if a bundle of aluminum tubes can be
attached to an aluminum sheet without using a different material,
these condensers are generally housed in a structural steel shell.
Aluminum sheets and tubes must be isolated from the steel shell to
prevent or substantially reduce a galvanic corrosion reaction.
[0010] Non-OTEC solutions for production of power are generally
land based where weight of the heat exchangers can be easily
accommodated. However, economical floating OTEC plants typically
require buoyant structures to support the heat exchangers near the
surface of the ocean.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic view of a Rankine cycle that uses
ammonia as a working fluid to generate power, according to an
example embodiment.
[0012] FIG. 2 is a schematic view of a floating portion of a plant,
according to an example embodiment.
[0013] FIG. 3 is a perspective view of the outlet end of the cold
water pipe which has a plurality of shells attached thereto,
according to an example embodiment.
[0014] FIG. 4 is a set of photos showing one or more aluminum tubes
friction stir welded to a tube sheet to form the core of a heat
exchanger, according to one example embodiment.
[0015] FIG. 5 is a set of photos showing one or more multi-hollow
aluminum extrusions friction stir welded (FSW) to a tube sheet,
according to another example embodiment.
[0016] FIG. 6 shows an exploded view of a heat exchanger positioned
within a composite heat exchanger shell, according to another
example embodiment.
[0017] FIG. 7 shows a perspective cutaway view of a composite heat
exchanger shell 640, according to an example embodiment.
[0018] FIG. 8 shows a cutaway view of a flange attached to an end
of a composite heat exchanger shell, according to an example
embodiment.
[0019] FIG. 9 is a side cut-away view of an apparatus for forming a
composite shell on a platform, according to an example
embodiment.
[0020] FIGS. 10A-E depict various portions of the apparatus shown
schematically in FIG. 9.
DETAILED DESCRIPTION
[0021] FIG. 1 is a schematic view of a Rankine cycle that uses
ammonia as a working fluid to generate power, according to an
example embodiment. The Rankine cycle 100 includes an evaporator
110, a turbine 120, a condenser 130, and a pump 140. The evaporator
110, the turbine 120, the condenser 130, and the pump 140 are in
fluid communication with one another. Ammonia in a liquid phase and
a vapor phase is circulated to the various components of the
Rankine cycle 100. Fluid lines join the evaporator 110 to the input
of the turbine 120 and the fluid output of the turbine 120 to the
condenser 130. The fluid output of the condenser 130 is attached to
the pump 140. As mentioned, in this embodiment ammonia is the
working fluid but various other working fluids can be used. Large
flows of warm surface seawater are used to boil the ammonia in
evaporators or evaporator 110. The ammonia vapor drives the turbine
120. Attached to the turbine is a rotor portion generator 122.
Rotating the shaft of the turbine 120 rotates the rotor of a
generator to generate electric power. To complete the cycle, low
pressure ammonia vapor exits the turbine 120 and enters condenser
130 or condensers which are cooled using large flows of cold, deep
ocean water. A pump 140 add pressure to the condensed ammonia
liquid at the output of the pump 140 to match the required input
pressure of the evaporator 110. It should be noted that there may
be more than multiple components of the evaporator 110, the turbine
120, the condenser 130 and the pump 140 in a given OTEC plant.
Other pumps are used to move the warm and cold seawater through the
evaporator 110, and the condenser 130, respectively. An OTEC plant
requires no fuel and has low operating costs (a portion of the
gross generated power is assigned to pump the warm and cold
seawater).
[0022] FIG. 2 is a schematic view of a floating portion of a plant
200, according to an example embodiment. The floating portion of
the plant can be for an OTEC plant or for a desalination plant or
any other plant that would require heat exchangers of this nature.
For the sake of convenience, an OTEC plant will be further detailed
initially. The floating portion 200 includes a ship (barge) 210 and
a floating condenser portion 220. The ship 210 in the OTEC plant
includes the evaporator 110, the turbine 120, and the generator 122
for producing power. The condenser portion 220 includes a buoyancy
section 222, a plenum 224, a platform 226, and a cold water pipe
228. The buoyancy section 222 is a watertight chamber or
substantially watertight chamber that is of sufficient space to
provide a buoyancy force to hold the remaining portions of the
floating condenser portion 220. Lesser weight of the components
results in a smaller chamber. Considerable weight can be saved by
making the heat exchanger 130, 230 from aluminum (as discussed
below) and by making a shell 240 to enclose the heat exchanger out
of a composite material. Of course, the smaller the chamber or
buoyancy section 222, the less material needed and the less cost
associated with the floating condenser portion 222 of the OTEC
plant. Attached to the top of the buoyancy section 222 is a
platform 226. The platform 226 provides routing for cables and
pipes or lines connected between the ship 210 and the condensing
portion 220. The platform 226 also includes a flat surface on which
helicopters can land or on which people can place instruments or
tools. The platform 226 can also serve as an area on which to store
machines and materials for producing some of the parts of the
condensing portion 220. Attached below the buoyancy section 222 is
a plenum 224. The plenum 224 is a pressurized housing containing a
fluid, in this case cold seawater, at a positive pressure. The cold
water pipe 228 is attached to the plenum 224. The pressure in the
plenum 224 is higher than the pressure of the surroundings. The
plenum 224 equalizes the pressure for more even distribution of the
cold seawater, because of irregular supply or demand. The cold
water pipe 228 is in fluid communication with the plenum 224. The
cold water pipe 228 is very long and reaches down well below the
thermocline. The distances can be 300 meters to 1000 meters or
more. The cold water pipe 228 has a length to extend down to water
having a temperature that will condense ammonia vapor within the at
least one condenser 130 (see FIG. 1). The condenser portion 220
also includes at least one condenser 130. The condenser includes at
least one heat exchanger 230 housed within a shell 240. In one
embodiment, the shell 240 also includes an axial pump 250 on the
outlet side of the heat exchanger. The inlet side of the heat
exchanger 230 is positioned near the cold water inlet end 241 of
the shell 240. The cold water inlet end 241 of the shell 240 is in
fluid communication with the plenum 224. The axial pump 250 is
positioned near the cold water outlet end 242 of the shell 240. The
axial pump 250 moves the water through the heat exchanger 230, the
plenum 224 and up the cold water pipe 228.
[0023] FIG. 3 is a perspective view of the outlet end 229 of the
cold water pipe 228 which has a plurality of shells 240 attached
thereto, according to an example embodiment. The buoyancy section
222, the plenum 224, and the platform 226 are not shown in FIG. 3.
As shown, there are a plurality of shells 240 attached near or
proximate the cold water outlet or discharge end 229 of the cold
water pipe 228. In FIG. 3, there are eight shells attached to the
cold water pipe 228. It should be noted that more or even a lesser
number of shells 240 can be attached to the cold water pipe 228.
The shells are positioned around the central cold water pipe 228 in
the embodiment shown. The plurality of shells 240 are attached to a
first structure 340 about midway down the length of the plurality
of shells 240. The plurality of shells 240 are attached to a second
structure 342 near the discharge end 242 of the plurality of shells
240. The first structure 340 and the second structure 342 hold the
shells 240 about the outlet end 229 of the cold water pipe 228. In
one embodiment, each of the shells includes an axial pump 250 and a
heat exchanger 230. The heat exchangers 230 are used to condense
ammonia vapor to a liquid state in an OTEC system.
[0024] In operation, the plurality of axial pumps 250 located in
the plurality of shells 240 essentially pump cold water from the
inlet end of the cold water pipe 228 up from depths of 1000 meters.
The pumps 250 move the cold water into the plenum 224 and through
the heat exchangers 230 in the shells 240. The heat exchangers 230
are used to change ammonia gas to ammonia liquid in an OTEC
system.
[0025] As shown in FIGS. 2 and 3, the condensing portion 220 of the
OTEC plant 200 floats in the water, separate from the ship or barge
210. In order to lower the cost of OTEC solutions, the components
are made of lighter materials. Two of the components, the heat
exchanger 230 and the shell 240 include lighter weight materials
than steel or titanium metals which were used in the past. In the
embodiment shown, the interior (core) of heat exchangers 230 within
the shells are made of aluminum. Incorporating aluminum core
construction within heat exchangers 230 brings substantial
reduction in capital cost. For example, an aluminum heat exchanger
230 is roughly half the heat exchanger cost compared to a heat
exchanger made of titanium. Further weight and cost reductions are
achieved by forming the exteriors shells of heat exchangers 230
from composite materials, as well as the plurality of structural
shells 240 from composite materials rather than steel or other
heavy metal shells. Reductions such as these make OTEC solutions
more cost-competitive in more geographic locations.
[0026] FIG. 4 is a set of photos showing one or more aluminum tubes
friction stir welded (FSW) to a tube sheet, according to one
example embodiment. Aluminum tube and sheet heat exchangers are
fabricated using a friction stir welding (FSW) approach. Using the
FSW approach, a bundle of tubes or extrusions can be joined to an
aluminum tube sheet in such a way that there is a minimal heat
affected zone and no dissimilar metal at the joints. Furthermore,
there are no crevices to act as sites for corrosion initiation in
flowing seawater. With the FSW approach, aluminum heat exchanger
cores can serve as a low cost alternative to titanium and high
alloy stainless steel construction. In addition to this fabrication
technique, the aluminum heat exchangers are provided with graphite
foam or compact aluminum fin heat transfer surfaces to enhanced the
heat transfer capability of the heat exchangers 230.
[0027] FIG. 5 is a set of photos showing one or more multi-hollow
aluminum extrusions 510 friction stir welded (FSW) to a tube sheet,
according to another example embodiment. The aluminum extrusion 510
shown includes graphite foam attached to the multi-hollow extrusion
510. FIG. 5 also includes a cross sectional view of aluminum
seawater passageways 520, 522, 524 which sandwich several layers
530, 532 of graphite foam. The graphite foam enhances the heat
transfer characteristics of the resultant heat exchanger. Other
materials such as metal foams and compact aluminum fins can be used
as alternatives to the graphite foam.
[0028] FIG. 6 shows an exploded view of a heat exchanger 230
positioned within a composite heat exchanger shell 640. The shell
640 is a lightweight, low cost, low pressure, fiber composite shell
for use in OTEC applications, desalination applications, marine
heat exchanger applications, and other applications. Inside the
composite shell 640, one or more aluminum cores or heat exchangers
230 comprising tube bundles or extrusion are installed. In the
embodiment shown, the tubes or extrusions are joined into circular
tube sheets using Friction Stir Welding (FSW). The tube bundles or
extrusions can be plain aluminum. In some embodiments, the tube
bundles or extrusions include graphite foam bonded to the outside
tube or extrusion surfaces. In other embodiments, compact aluminum
fins are bonded or brazed to the extrusions in place of graphite
foam. The graphite foam or bonded/brazed aluminum fins enhances the
thermal transfer characteristics of the heat exchanger 230. Using a
fiberglass or composite shell 640 to enclose a substantially
aluminum heat exchanger core can produce lower thermal energy input
requirements, decreased cost of capital equipment, decreased
buoyancy requirements, and increased resistance to corrosion and
other desirable results. As shown in FIG. 6, the shell 640 also
includes a first pipe flange 810, and a second pipe flange
810'.
[0029] In the marine HX application, seawater (first fluid) flows
axially through the inside of tubes or extrusions. Other corrosive
or non-corrosive fluids can flow through the tubes, depending on
the application. On the shell side of the heat exchanger (ie
outside of the tubes or extrusions), a second fluid absorbs heat
from or rejects heat to the surfaces on outsides of tubes or
extrusions. This shell-side fluid can be a gas, liquid or two-phase
(boiling or condensing). The fluid can be ammonia, water/water
vapor or other liquids and gases depending on the application. The
shell-side fluid enters/exits via side ports, or through co-axial
ports at the ends of HX.
[0030] FIG. 7 shows a perspective cutaway view of a composite heat
exchanger shell 640, according to an example embodiment. The
composite heat exchanger shell 640 includes hollow planks 710. In
one embodiment, the hollow planks 710 are also made of fiberglass
or another composite. In still another embodiment, the planks are
pre-pultruded hollow planks 710. The hollow planks 710 are
surrounded by fabric which is longitudinally continuous so as to
form a substantially continuous inside fabric layer 720 and a
substantially continuous outside fabric layer 722. The fabric
layers 720, 722 are infused with a vinyl ester resin. In short, the
composite heat exchanger shell adopts a tube architecture,
utilizing sandwich wall construction. The pre-pultruded hollow
planks 710 are assembled into core rings. Face sheets of
longitudinally continuous fabric are applied over the assembled
core rings. Face sheet material consists of low-cost glass fibers
with excellent fatigue resistance. The face sheets and the core
planks are joined together, and a vinyl ester resin is infused
using a Vacuum Assisted Resin Transfer Molding (VARTM) process.
[0031] FIG. 8 shows a cutaway view of a flange 810 attached to an
end of a composite heat exchanger shell 640, according to an
example embodiment. The flange includes an inner termination ring
820 and an outer termination ring 830. The inner termination ring
820 includes grooves 822. The outer termination ring 830 includes
grooves 832. The traplock grooves 822, 832 transfer axial tensile
and compression loads from individual fabric plies to the metallic
termination rings 820, 830 which form the flange 810. The inner
termination ring 820 and the outer termination ring 830 are
substantially continuous. The inner termination ring 820 and the
outer termination ring 830 are tied together with bolts, such as
bolts 841, 842, 843, 844. The flange 810 works for moderate
pressure applications (.about.15-300 psi). In another embodiment,
adhesive bonded rings and a circumferential clamp can be used. For
example, in one embodiment, a marlin clamp is used.
[0032] FIG. 9 is a side cut-away view of an apparatus 1200 for
forming a composite shell 640 on a platform, such as platform 1202,
according to an example embodiment. The apparatus 1200 is used to
fabricate composite articles, such as the shell 630 or even a cold
water pipe 228. Apparatus 1200 is generally suitable for
fabricating continuous-fiber composite articles and is uniquely
well suited for fabricating multi-shot, continuous-fiber composite
articles, especially those that are very wide and very tall.
[0033] In the illustrative embodiment, apparatus 1200 is disposed
on floating platform 1202, which, in some embodiments, ultimately
serves as a part of an OTEC plant (see FIG. 2). Apparatus 1200 is
oriented vertically on platform 1202; that is, the axial (as
opposed to radial) direction of a work piece produced via apparatus
1200 is vertically aligned.
[0034] Apparatus 1200 comprises fiber supply region 1206 and
molding region 1212. Fiber supply region 1206 provides a continuous
supply of fiber to the molding region. The fiber used in
continuous-fiber composite materials is typically available in a
variety of forms, including uni-directional tapes of various
widths, plain weave fabric, harness satin fabric, braided fabric,
and stitched fabric. Commonly-used fibers include, without
limitation, fiber glass, commercially available from Owens Corning
Technical fabrics, PPG, AGY and carbon fiber, commercially
available from Zoltek and others. For use in conjunction with the
present invention, the fiber is typically in the form of a fabric,
provided in a convenient width as a function of the intended
cross-sectional shape and size of the article (e.g., 1 to 2 meters
width for a 10-meter diameter pipe, etc.). Such fabrics as
fiberglass are, and as carbon fibers from Zoltek and others.
[0035] Fiber supply region 1206 and molding region 1212 are
environmentally isolatable, collectively, from the other regions of
apparatus 1200. This is illustrated by notional access-way 1207 in
fiber supply region 1206 and a seal at the bottom of molding region
1212. The access-way is required to enable core 1214, discussed
further below, to be inserted into molding region 1212.
[0036] In the illustrative embodiment, fiber in the form of fabric
1210A and 1210B (collectively "fabric 1210") is disposed on
respective rolls 1208A and 1208B (collectively "rolls 1208"). Rolls
1208A and fabric 1210A are disposed radially-outward of rolls 1208B
and fabric 1208B. In the illustrative embodiment, there is no
difference in material type between fabric 1210A and 1210B. In
accordance with the present invention, continuity of fiber is
maintained between fabric 1210 in supply region 1206 and fabric
1210 that has been fed to molding region 1212.
[0037] The inner portions of apparatus 1200, such as inner fabric
rolls 1208B and central inner shell 1213 are stabilized/supported
via vertical central member 1205. The central member is, in turn,
supported by frame 1204.
[0038] In the illustrative embodiment, core 1214 is disposed in
molding region 1212. The core material, which in the illustrative
embodiment is available as a plurality of plank-like segments,
forms a cylindrical shape or ring when assembled and positioned in
molding region 1212. This core ring (cylindrical or otherwise)
establishes the basic shape for the work piece being produced in
molding region 1212. As depicted in FIG. 9, fabric 1210 is disposed
on both sides of core 1214 in preparation for fabricating a work
piece. More particularly, fabric 1210A is disposed between core
1214 and the outer circumference of molding region 1212 and fabric
1210B is disposed between core 1214 and the inner circumference of
molding region 1212. As described in further detail later in this
specification, the process proceeds by compacting fabric 1210 on
both sides of core 1214 against the core, infusing the fabric with
resin, and then curing the resin.
[0039] In the illustrative embodiment, core 1214 is lowered into
molding region 1212 via overhead traveling crane 1203. In some
embodiments, the core comprises hollow planks produced from fiber
and polymer via a pultrusion process, some of which may be
available at a cost per pound which is generally low compared to
other methods of fabricating linear composite shapes, from
pultruders such as Glasforms and Strongwell. Other processes can be
used to produce a structure suitable for use as core 1214. In some
other embodiments, the core can be produced from other materials
(e.g., aluminum, etc.) and exhibit other structural arrangements
(e.g., foam, sealed honeycomb internal arrangement, etc.).
[0040] FIGS. 10A-E depict various portions of the apparatus 900
discussed above. FIG. 10A shows the shear key and core assembly,
FIGS. 10B and 10C show the fabric dispensing and guidance system,
and FIGS. 10D and 10E show the pipe molding region for forming the
composite heat exchanger shell 240, 640.
[0041] Up to this point, a substantially aluminum heat exchanger
230 enclosed within a composite shell 640 has been discussed with
respect to use in an OTEC application. It should be noted that a
substantially aluminum heat exchanger 230 enclosed within a
composite shell 640 can also be used as a condenser for
desalination projects. The desalination projects can be for
removing water from ambient air in humid climates or can be for
desalination projects that remove water that use energy to flash or
boil water off from seawater, such as multi stage flash ("MSF") or
multi effect distillation ("MED"). The desalination projects could
even be conducted in tandem with a project, such as the production
of power, that has waste heat generated. It should be noted that
desalination projects represent another capital intensive market
which can benefit from innovative, low cost heat
exchanger/condenser solutions.
[0042] A heat exchanger includes a shell made of a composite
material, and a heat exchanger housed substantially within the
shell. The shell is made of a composite material further comprises
planks positioned in the outer periphery of the shell. The planks,
in one embodiment, are substantially hollow or include
substantially hollow portions. In some embodiments, the planks are
formed of pultruded plastic. The shell of the heat exchanger
further including layers of fiberglass. The pultruded plastic
planks are sandwiched between at least a first layer of fiberglass
and a second layer of fiberglass. The layers of fiberglass are
infused with resin. In one embodiment, the layers of fiberglass are
infused with resin using a Vacuum-Assisted Resin Transfer Molding
(VARTM) process. In addition, the shells of the heat exchanger
includes a first end and a second end. At least one metal flange is
coupled to one of the first end or second end of the shell. The
metal flange includes an inner termination ring having inner
trap-lock grooves therein, and an outer termination ring having
inner trap-lock grooves therein. The shell of composite material
can be formed to be buoyant. The shells can be long. For example,
the shell can be over 70 meters in length. In some embodiments, the
shells can be over 100 meters in length.
[0043] An apparatus for forming elongated tubes of composite
material includes a floating base, a molding region attached to the
base, a fiber supply region, and a resin infusion apparatus for
infusing the fiber with resin. The molding region including a core
ring for receiving a core material. The fiber supply region
provides a substantially continuous supply of a fiber to the
molding region. The fiber supply region supplies fiber to an inner
region of the core ring and an outer region of the core ring. The
apparatus for forming elongated tubes also includes a supply of a
core material that is inserted into the core ring. A plurality of
elongated planks are positioned around the ring core in forming the
elongated tubes. The core material is inserted into the core ring,
the core material including elongated planks of plastic. In one
embodiment, the core material includes elongated planks of
pultruded plastic having hollow portions therein. A vacuum assisted
resin infusion apparatus can also be added to the apparatus to
apply a vacuum to a portion of the molding chamber. In one
embodiment, The apparatus for forming elongated tubes of composite
material wherein the molding process is performed at a site where
the elongated tubes of composite material are used to form a
floating heat exchanger for an Ocean Thermal Energy System. The
apparatus for forming elongated can also include apparatus for
applying a metal flange to at least one of the ends of the
elongated tube.
[0044] A floating portion of an Ocean Thermal Energy System
includes a platform, a plenum attached to the platform, a cold
seawater intake attached to the plenum, and a plurality of heat
exchangers attached to the plenum. The heat exchangers include
pumps for moving the cold seawater from the plenum through the heat
exchangers. The heat exchangers include shells made of composite
material. The cold seawater intake can also be an elongated tube of
composite material.
[0045] A heat exchanger shell can comprise composite sandwich wall
construction. The wall, in one embodiment, include pultruded
plastic core "planks" sandwiched between layers of fiberglass,
infused with resin. The process used to infuse the fiberglass with
resin can be Vacuum-Assisted Resin Transfer Molding (VARTM). This
type of construction can be used to form The heat exchanger shell
can be produced using a vertical molding apparatus). It is
contemplated that the heat exchanger shell can also be produced
using a horizontal molding apparatus. In one embodiment, the
molding apparatus can be used to form shells on site, such as on a
platform floating in the ocean during construction of an OTEC
system, such as shown in FIG. 2 above. Shells or composite tubes
formed as above can be very long, and continuous structures
measuring up to 100 m or greater in length, and up to 10 m in
diameter.
[0046] Metal flanges can be attached to the ends of the composite
shells or tubes. The metal flanges are ASME Code-compliant metalic
flanges made of aluminum, steel, stainless steel or other metals,
The metal flanges are attached to the ends of the composite shell
using a fiber entrapment approach.
[0047] Condenser Heat Exchangers with composite shell can be made
buoyant in water by adjusting the tube-tube pitch, tube wall
thickness and number of tubes in tube bundle, to form a buoyant
structure. The combined operating weight (dry weight plus water in
tubes and condensing vapor outside of tubes, plus the composite
shell weight) is less than the weight of surrounding water that is
displaced. As a result, the floating portion 200 floats, as shown
in FIG. 2.
[0048] The buoyant composite shell heat exchanger can support other
elements in a floating OTEC or desalination plant, such as a
central cold water pipe/riser (used to pump cold, deep ocean water
to the OTEC plant), or the OTEC platform containing power
generation and transmission equipment.
[0049] The buoyancy of composite shell heat exchanger can be
adjusted in-situ by controlling the level of liquid (i.e. ammonia
or other working fluid) on the outside of heat exchanger tubes
(surrounded the composite shell).
[0050] This has been a detailed description of some exemplary
embodiments of the invention(s) contained within the disclosed
subject matter. Such invention(s) may be referred to, individually
and/or collectively, herein by the term "invention" merely for
convenience and without intending to limit the scope of this
application to any single invention or inventive concept if more
than one is in fact disclosed. The detailed description refers to
the accompanying drawings that form a part hereof and which shows
by way of illustration, but not of limitation, some specific
embodiments of the invention, including a preferred embodiment.
These embodiments are described in sufficient detail to enable
those of ordinary skill in the art to understand and implement the
inventive subject matter. Other embodiments may be utilized and
changes may be made without departing from the scope of the
inventive subject matter. Thus, although specific embodiments have
been illustrated and described herein, any arrangement calculated
to achieve the same purpose may be substituted for the specific
embodiments shown. This disclosure is intended to cover any and all
adaptations or variations of various embodiments. Combinations of
the above embodiments, and other embodiments not specifically
described herein, will be apparent to those of skill in the art
upon reviewing the above description.
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