Modular heat exchanger

Abstract

A heat exchanger comprising a plurality of plates that are demountably attached to a frame is disclosed. Each plate comprises a plurality of channels for conveying a primary fluid through the heat exchanger. The frames are arranged in the frame so that spaces between adjacent frame pairs define conduits for conveying a secondary fluid through the heat exchanger. The plates are mounted in the frame so that they can be individually removed from the frame. Further, each of the channels is fluidically connected to input and output ports for the primary fluid by detachable couplings. As a result, heat exchangers in accordance with the present invention are more easily repaired or refurbished than prior-art heat exchangers.

Claims

1. A modular heat exchanger comprising: a heat exchanger core configured for ocean thermal energy conversion comprising: a frame comprising a plurality of spaced-apart seats; a plurality of plate assemblies, each plate assembly comprising: two spaced-apart side panels joined at end portions by supports brazed to the two spaced-apart side panels, each side panel comprising a rigid extrusion of a material substantially resistant to corrosion from exposure to seawater and to a working fluid; and an interposer brazed to at least one spaced-apart side panel of the two spaced-apart side panels to form an internal structure and define at least one channel between the two spaced-apart side panels, wherein each spaced-apart seat of the plurality of spaced-apart seats is configured to receive a corresponding plate assembly of the plurality of plate assemblies and define a plurality of conduits for the seawater, each conduit of the plurality of conduits defined between a corresponding pair of adjacent plate assemblies of the plurality of plate assemblies, wherein the at least one channel is configured to convey the working fluid, and wherein each plate assembly of the plurality of plate assemblies is configured to detachably mount into a respective spaced-apart seat of the plurality of spaced-apart seats; and a plurality of inlet distributors, wherein each inlet distributor is joined to a respective plate assembly of the plurality of plate assemblies by a respective galvanic-corrosion-free joint to place the inlet distributor in fluidic communication with the at least one channel of the respective plate assembly; and an input manifold, fluidically coupled to the plurality of inlet distributors by a respective plurality of detachable couplings, each detachable coupling of the plurality of detachable couplings independently connectable and removable, the input manifold configured to convey the working fluid to each inlet distributor.

2. The modular heat exchanger of claim 1 wherein each detachable coupling of the plurality of detachable couplings comprises one of a click-to-connect connector, a quick-disconnect fluid connector, and a thread-to-connect connector.

3. The modular heat exchanger of claim 1 wherein at least some of the detachable couplings of the plurality of detachable couplings comprise a flexible conduit and two connectors.

4. The modular heat exchanger of claim 1 further comprising a friction-stir-weld joint that joins the input manifold and the frame to one another.

5. The modular heat exchanger of claim 1 further comprising a plurality of clamps, wherein each clamp of the plurality of clamps is configured to secure a corresponding plate assembly of the plurality of plate assemblies to a respective spaced-apart seat of the plurality of spaced-apart seats, and wherein each clamp of the plurality of clamps is independently attachable and removable with respect to each of the other clamps of the plurality of clamps so that each plate assembly of the plurality of plate assemblies is detachably mounted independently from each of the other plate assemblies of the plurality of plate assemblies.

6. The modular heat exchanger of claim 1 further comprising a second galvanic-corrosion-free joint that joins the input manifold and the frame to one another.

7. The modular heat exchanger of claim 1, wherein each conduit of the plurality of conduits is fluidically isolated from each other conduit of the plurality of conduits.

8. The modular heat exchanger of claim 1, wherein the galvanic-corrosion-free joint that joins each inlet distributor of the plurality of inlet distributors to the respective plate assembly of the plurality of plate assemblies comprises a friction-stir-weld joint.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts a schematic diagram of an OTEC power generation system in accordance with an illustrative embodiment of the present invention.

(2) FIG. 2 depicts a schematic diagram of a heat exchanger in accordance with the illustrative embodiment of the present invention.

(3) FIG. 3 depicts a heat exchanger core in accordance with the illustrative embodiment.

(4) FIG. 4 depicts operations of a method suitable for forming heat exchanger 110.

(5) FIG. 5A depicts a front view of an individually removable plate assembly in accordance with the illustrative embodiment of the present invention.

(6) FIG. 5B depicts a side view of an individually removable plate assembly in accordance with the illustrative embodiment of the present invention.

(7) FIG. 6 depicts a schematic drawing of a detachable coupling in accordance with the illustrative embodiment of the present invention.

(8) FIG. 7 depicts a schematic drawing of an input manifold coupled to a heat exchanger core.

(9) FIG. 8 depicts a schematic drawing of an output manifold coupled to a heat exchanger core.

(10) FIG. 9A depicts a schematic drawing of a plate assembly in accordance with a first alternative embodiment of the present invention.

(11) FIG. 9B depicts a schematic drawing of a plate assembly in accordance with a second alternative embodiment of the present invention.

(12) FIG. 9C depicts a schematic drawing of a plate assembly in accordance with a third alternative embodiment of the present invention.

(13) FIG. 9D depicts a schematic drawing of a plate assembly in accordance with a fourth alternative embodiment of the present invention.

DETAILED DESCRIPTION

(14) FIG. 1 depicts a schematic diagram of an OTEC power generation system in accordance with an illustrative embodiment of the present invention. OTEC system 100 comprises turbogenerator 104, closed-loop conduit 106, heat exchanger 110-1, heat exchanger 110-2, pumps 114, 116, and 124, and conduits 120, 122, 128, and 130.

(15) Turbo-generator 104 is a conventional turbine-driven generator. Turbogenerator 104 is mounted on floating platform 102, which is a conventional floating energy-plant platform. Platform 102 is anchored to the ocean floor by mooring line 132 and anchor 134, which is embedded in the ocean floor. In some instances, platform 102 is not anchored to the ocean floor but is allowed to drift. Such a system is sometimes referred to as a “grazing plant.”

(16) In typical operation, pump 114 pumps a primary fluid (i.e., working fluid 108), in liquid form, through closed-loop conduit 106 to heat exchanger 110-1. Ammonia is often used as working fluid 108 in OTEC systems; however, it will be clear to one skilled in the art that any fluid that evaporates at the temperature of the water in surface region 118 and condenses at the temperature of the water in deep water region 126 is suitable for use as working fluid 108 (subject to material compatibility requirements).

(17) Heat exchanger 110-1 and 110-2 are configured for operation as an evaporator and condenser, respectively. One skilled in the art will recognize that the operation of a heat exchanger as evaporator or condenser is dependent upon the manner in which it is configured within system 100. Heat exchanger 110 is described in detail below and with respect to FIG. 2.

(18) In order to enable its operation as an evaporator, pump 116 draws warm secondary fluid (i.e., seawater from surface region 118) into heat exchanger 110-1 via conduit 120. At heat exchanger 110-1 heat from the warm water is absorbed by working fluid 108, which induces working fluid 108 to vaporize. After passing through heat exchanger 110-1, the warm water is ejected back into the body of water via conduit 122. In a typical OTEC deployment, the water is surface region 118 is at a substantially constant temperature of approximately 25 degrees centigrade (subject to weather and sunlight conditions).

(19) The expanding working fluid 108 vapor is forced through turbogenerator 104, thereby driving the turbogenerator to generate electrical energy. The generated electrical energy is provided on output cable 112. Once it has passed through turbogenerator 104, the vaporized working fluid enters heat exchanger 110-2.

(20) At heat exchanger 110-2, pump 124 draws cold secondary fluid (i.e., seawater from deep water region 126) into heat exchanger 110-2 via conduit 128. The cold water travels through heat exchanger 110-2 where it absorbs heat from the vaporized working fluid. As a result, working fluid 108 condenses back into liquid form. After passing through heat exchanger 110-2, the cold water is ejected into the body of water via conduit 130. Typically deep water region 126 is 1000+ meters below the surface of the body of water, at which depth water is at a substantially constant temperature of a few degrees centigrade.

(21) Pump 114 pumps the condensed working fluid 108 back into heat exchanger 110-1 where it is again vaporized; thereby continuing the Rankine cycle that drives turbogenerator 104.

(22) FIG. 2 depicts a schematic diagram of a heat exchanger in accordance with the illustrative embodiment of the present invention. Heat exchanger 110 comprises input manifold 202, detachable couplings 204, heat exchanger core 206, and output manifold 208.

(23) FIG. 3 depicts a heat exchanger core in accordance with the illustrative embodiment. Core 206 is a modular heat exchanger core that comprises frame 302, plate assemblies 304-1 through 304-4, and clamps 314.

(24) FIG. 4 depicts operations of a method suitable for forming heat exchanger 110. FIG. 4 is described herein with continuing reference to FIGS. 1-3 and reference to FIGS. 5-7. Method 400 begins with operation 401, wherein plate assemblies 304-1 through 304-4 are inserted into seats 306-1 through 306-4, respectively. Although the illustrative embodiment comprises four plate assemblies, it will be clear to one skilled in the art, after reading this specification, how to specify, make, and use alternative embodiments of the present invention that comprise any practical number of plate assemblies.

(25) Frame 302 is a rigid frame comprising seats 306-1 through 306-4 (collectively referred to as seats 306) for receiving and locating plate assemblies 304-1 through 304-4 (collectively referred to as plate assemblies 304). Seats 306 locate plate assemblies 304 such that each pair of adjacent plate assemblies defines a conduit for conveying secondary fluid. For example, seats 306-1 and 306-2 locate plate assemblies 304-1 and 304-2 such that these plate assemblies define conduit 308-2. In similar fashion, seats 306-3 and 306-4 locate plate assemblies 304-3 and 304-4 such that these plate assemblies define conduit 308-4. Further, seats 306-1 and 306-4 locate plate assemblies 304-1 and 304-4 away from the sidewalls of frame 302 such that frame 302 and the plate assemblies collectively define conduits 308-1 and 308-5. For clarity, input and output manifolds for secondary fluid are not depicted. It will be clear to one skilled in the art, after reading this specification, how to specify, make, and use input and output manifolds for secondary fluid.

(26) FIGS. 5A and 5B depict front and side views, respectively, of an individually removable plate assembly in accordance with the illustrative embodiment of the present invention. Plate assembly 304 comprises plate 502, distributors 506 and 510, and nipples 508-1 and 508-2.

(27) Plate 502 is a rigid extrusion of aluminum alloy comprising a plurality of internal channels 504. Each of channels 504 is suitable for conveying working fluid 108. Although in the illustrative embodiment plate 502 is aluminum alloy, it will be clear to one skilled in the art, after reading this specification, how to specify, make, and use plates that are made of any material that is substantially corrosive-resistant for working fluid 108. Suitable materials for use in elements of plate assembly 304 include, without limitation, aluminum alloy, aluminum, composite materials, ceramics, and the like.

(28) It will be clear to one skilled in the art, after reading this specification, that heat exchanger 100 can be configured so that channels 504 convey secondary fluid and conduits 308 convey primary fluid.

(29) Distributors 506 and 510 are substantially identical housings of aluminum alloy that are joined to plate 502 with joints 512. Joints 512 are friction-stir welding joints, which are substantially galvanic corrosion-free joints. Distributor 506 receives working fluid 108 from nipple 508-1 and provides it to channels 504. Distributor 510 receives working fluid 108 from channels 504 and provides it to nipple 508-2. Nipples 508-1 and 508-2 are threaded connectors that mate with detachable couplings 204. Nipples 508-1 and 508-2 are also made of the aluminum alloy and are joined to distributors 506 and 510, respectively, with joints 512. Although in the illustrative embodiment, plate 502, distributors 506 and 510, and nipples 508-1 and 508-2 are joined together using friction-stir welding, it will be clear to one skilled in the art, after reading this specification, how to specify, make, and use alternative embodiments of the present invention wherein these elements are joined using a different joining technology that is substantially galvanic corrosion-free.

(30) At operation 402, plate assemblies 304 are secured in seats 306 by clamps 310. Clamps 310 are independently removable. As a result, plate assemblies 304 are demountably attachable with respect to frame 302. For the purposes of this Specification, including the appended claims, the term “demountably attachable” is defined as attachable in a non-permanent manner, such as through the use of a removable fastener (e.g., a screw, clamp, bolt, etc.). Individual plate assemblies 304, therefore, can be independently removed so that each plate assembly can be independently replaced, serviced, or refurbished. In some embodiments, each of plate assemblies 304 is serviceable while heat exchanger 110 is submerged at its operational depth.

(31) Clamps 310 comprise corrosion-resistant plates 312, which are secured to frame 302 by corrosion-resistant screws 314. Clamps 310 are merely representative of a mechanism suitable for securing plate assemblies 304 in seats 306 and one skilled in the art will be able to devise any number of alternative clamping devices that are in accordance with the present invention.

(32) At operation 403, input manifold 202 is fluidically coupled with channels 504 of heat exchanger core 206.

(33) FIG. 6 depicts a schematic drawing of a detachable coupling in accordance with the illustrative embodiment of the present invention. Detachable coupling 204 is a connectorized flexible conduit for fluidically coupling heat exchanger core to input manifold 202 or output manifold 208. By virtue of detachable couplings 204, each of input manifold 202 and output manifold 208 is detachably connectable with respect to the inlet and outlet, respectively, of channels 504. For the purposes of this Specification, including the appended claims, the term “detachably connectable” is defined as connectable in a non-permanent way, such as through a connection that can be readily made and broken. Detachable coupling 204 comprises conduit 602 and connectors 604.

(34) Conduit 602 is a flexible conduit of substantially corrosion-resistant material. In some embodiments, conduit 602 is substantially rigid.

(35) Connectors 604 are threaded connectors that mate with nipples 508 to form a leak-proof seal. In some embodiments, gasket 606 is included in connector 604 to improve the integrity of the leak-proof seal. In some embodiments, connectors 604 and nipples 508 are components other than conventional threaded connectors. Fluidic coupling systems suitable for use in accordance with the present invention include, without limitation: click-to-connect connectors (i.e., snap-ring connectors), such as quick-disconnect fluidic connectors; upchurch connectors; blindmate connectors; thread-to-connect connectors; heparin-lock connectors; and the like. It will be clear to one skilled in the art, after reading this specification, how to specify, make, and use connectors 604 and nipples 508.

(36) In some embodiments, couplings 204 and 208 are made of the same material as the plate, distributors, and nipples to mitigate the effects of galvanic corrosion.

(37) In some embodiments, detachable couplings 204 are bulkhead elements suitable for making direct rigid fluidic connection between input and output manifolds 202 and 208 and plate assemblies 304. Detachable couplings suitable for use in accordance with the present invention include, without limitation, pressure fittings, hydraulic fittings, upchurch connectors, blindmate connectors, rapid-disconnect hydraulic line connectors, and the like. It will be clear to one skilled in the art, after reading this specification, how to specify, make, and use detachable couplings other than flexible conduits and threaded connectors.

(38) FIG. 7 depicts a schematic drawing of an input manifold coupled to a heat exchanger core. Input manifold 202 is a housing of aluminum alloy that is joined to frame 302 using friction-stir welding. Input manifold 202 is fluidically coupled with distributors 506 by detachable couplings 204. Detachable couplings 204 are connected to nipples 508 of input manifold 202 and nipples 508 of plate assemblies 304.

(39) FIG. 8 depicts a schematic drawing of an output manifold coupled to a heat exchanger core. Output manifold 208 is a housing of aluminum alloy that is joined to frame 302 using friction-stir welding. Output manifold 208 is fluidically coupled with distributors 506 by detachable couplings 204. Detachable couplings 204 are connected to nipples 508 of output manifold 208 and nipples 508 of plate assemblies 304. It will be clear to one skilled in the art, after reading this specification, that the material used for input manifold 202 and output manifold 208 can be selected from any material suitable for use in heat exchanger core 206, as discussed above.

(40) FIG. 9A depicts a schematic drawing of a plate assembly in accordance with a first alternative embodiment of the present invention. Plate assembly 900 comprises panel 902 and panel 904. Panels 902 and 904 are extruded panels of aluminum alloy. Each of panels 902 and 904 comprises a plurality of fins 906. Panels 902 and 904 are joined with friction-stir welding such that fins 906 collectively define a plurality of channels 504. In some embodiments, fins 906 do not span the full separation distance between panels 902 and 904; therefore, in such embodiments panels 902 and 904 collectively define a single conduit into which fins 906 partially extend. In some embodiments, panels 902 and 904 comprise a different material that is substantially corrosion-resistant for working fluid 108 and seawater.

(41) FIG. 9B depicts a schematic drawing of a plate assembly in accordance with a second alternative embodiment of the present invention. Plate assembly 908 comprises panel 910, panel 912, fins 914, supports 916, and seals 918. Fins 906 and supports 916 are brazed onto panels 910 and 912 to collectively define channels 504. Since brazed connections are highly susceptible to galvanic corrosion in the presence of seawater, seals 918 are formed between panels 910 and 912 to substantially isolate all brazed connections from exposure to seawater.

(42) FIG. 9C depicts a schematic drawing of a plate assembly in accordance with a third alternative embodiment of the present invention. Plate assembly 920 comprises panel 910, panel 912, interposer 922, supports 916, and seals 918. Interposer 922 and supports 916 are brazed onto panels 910 and 912 to collectively define channels 504. Seals 918 are formed between panels 910 and 912 to substantially isolate all brazed connections from exposure to seawater. Although the third alternative embodiment comprises an interposer having u-shaped regions that partially define channels 504, it will be clear to one skilled in the art, after reading this specification, how to specify, make, and use other alternative embodiments of the present invention that comprise an interposer having regions of any suitable shape.

(43) FIG. 9D depicts a schematic drawing of a plate assembly in accordance with a fourth alternative embodiment of the present invention. Plate assembly 924 comprises panel 910, panel 912, interposer 926, and supports 928. Supports 928 are stand-offs of aluminum alloy. Interposer 926 is bonded to panels 910 and 912. Since supports 928 and panels 910 and 912 are all made of the same material, friction-stir welding is the preferred technique for joining these elements together.

(44) Interposer 926 is an extruded sheet of thermally conductive graphite foam that comprises a plurality of channels 504. Graphite foam provides suitable structural integrity for plate assembly 924. In addition, a typical graphite foam composition has a specific gravity within the range of 0.5-0.7. As a result, graphite foam-based interposer 926 enables heat exchangers that can be lighter than comparable conventional metal-based heat exchangers.

(45) Further, graphite foam has a bulk thermal conductivity of approximately 180 W/M Deg C range. This thermal conductivity is as high as pure bulk aluminum, for example, and much higher than the effective conductivity of most aluminum fin constructions.

(46) Still further, interposer 926 can comprise graphite wall surfaces that are characterized by open pores. This allows evaporation and condensation to occur over a much larger surface area than comparable conventional heat exchangers. As a result, heat exchangers in accordance with the present invention can exhibit reduced volume for a given heat transfer duty, as compared to prior art shell and tube and plate-frame heat exchangers.

(47) Although the fourth alternative embodiment comprises an interposer having square-shaped channels 504, it will be clear to one skilled in the art, after reading this specification, how to specify, make, and use other alternative embodiments of the present invention that comprise an interposer having regions of any suitable shape.

(48) It is to be understood that the disclosure teaches just one example of the illustrative embodiment and that many variations of the invention can easily be devised by those skilled in the art after reading this disclosure and that the scope of the present invention is to be determined by the following claims.