This disclosure relates to heat exchangers in general, and, more particularly, to heat exchangers employing fins made from a heat conducting foam material.
Heat exchangers are used in many different types of systems for transferring heat between fluids in single phase, binary or two-phase applications. Many different types of heat exchangers are known including plate-fin, plate-frame, and shell-and-tube heat exchangers. In plate-fin heat exchangers, a first fluid or gas is passed on one side of the plate and a second fluid or gas is passed on another side of the plate. The first fluid and/or the second fluid flow along channels between fins mounted on one side of the plate, and heat energy is transferred between the first fluid and second fluid through the fins and the plate. Materials such as titanium, high alloy steel, copper and aluminum are typically used for the plates, frames, and fins.
This description relates to heat exchangers that employ fins made of a heat conducting foam material to enhance heat transfer. The foam fins can be used in any type of heat exchanger including, but not limited to, a plate-fin heat exchanger, a plate-frame heat exchanger or a shell-and-tube heat exchanger. The heat exchangers employing foam fins described herein are highly efficient, inexpensive to build, and corrosion resistant. The described heat exchangers can be used in a variety of applications, including but not limited to, low thermal driving force applications, power generation applications, and non-power generation applications such as refrigeration and cryogenics. The fins can be made from any thermally conductive foam material including, but not limited to, graphite foam or metal foam. In addition, the fins can be a combination of graphite foam fins, metal foam fins, and/or metal (for example aluminum) fins.
In one embodiment, a heat exchange unit includes first and second opposing plates that include surfaces that face each other, and a plurality of fins are disposed between the first and second opposing plates. Each fin has a first end connected to and in thermal contact with the surface of the first plate and a second end connected to and in thermal contact with the surface of the second plate. The fins define a plurality of fluid paths that extend generally from the second end to the first end, and the fins include graphite foam or metal foam. The first and second plates are made of a thermally conductive material, for example metal, and the fins may comprise, consist essentially of, or may consist of, graphite foam or metal foam.
In another embodiment, a heat exchange unit includes a plurality of fins disposed on a first major surface of a plate. Each fin has a first end connected to and in thermal contact with the first major surface and a second end spaced from the first major surface. The fins define a plurality of fluid paths that extend generally from the second end to the first end, and the fins include, consist essentially of, or consist of, graphite foam or metal foam.
In another embodiment, a plate-fin heat exchange unit includes a plate or frame that includes first and second opposing major surfaces and first and second opposing ends, and a plurality of enclosed fluid flow channels extending through the frame from the first end to the second end. The enclosed fluid flow channels do not extend through the first and second opposing major surfaces. In addition, the plate-fin heat exchange unit includes a plurality of fins disposed on the first major surface, each fin having a first end connected to and in thermal contact with the first major surface and a second end spaced from the first major surface, the fins defining a plurality of fluid paths that extend generally from the second end to the first end, and the fins include graphite foam or metal foam. The frame may be made of metal, and the fins comprise, consist essentially of, or consist of graphite foam or metal foam.
An embodiment of a plate-fin heat exchanger may also include a housing, a first inlet and a first outlet for a first fluid, a second inlet and a second outlet for a second fluid, and the plate-fin heat exchange unit disposed inside the housing.
The following description describes examples of heat exchangers that employ fins made of graphite foam to enhance heat transfer. The fins can comprise, consist essentially of, or consist of graphite foam or other type of foam material that facilitates heat exchange. The graphite foam fins can be used in any type of heat exchanger including, but not limited to, a plate-fin heat exchanger, a plate-frame heat exchanger or a shell-and-tube heat exchanger.
Although the description focuses on graphite foam fins, the fins can alternatively be made of metal foam. In some embodiment, the fins can be metal fins, such as aluminum fins. In addition, in some embodiments, the heat exchanger and heat exchange units can include a combination of graphite foam fins, metal foam fins and/or metal (such as aluminum) fins.
The fluids described in the examples herein can be liquids or vapors/gases, and one or both of the fluids can retain their phase during heat transfer (e.g. remain a liquid or vapor) or change phase (e.g. liquid turns to vapor; vapor turns to liquid; etc.).
The heat exchanger 100 includes a plate-fin tube bundle 116 disposed inside the housing 102, the tube bundle 116 being made of one or more plate-fin heat exchange units 118. The heat exchange units 118 define fluid paths 120 through which the first fluid 108 can flow, as well as define fluid channels 126 through which the second fluid 114 can flow separated from the first fluid 108.
Each heat exchange unit 118 is constructed of a plurality of fins 122 connected to and in thermal contact with a plate 124. As described in more detail below, each plate 124 comprises a pair of opposing plates separated by side plates and intermediate plates, which together define the fluid channels 126. The fins 122 are suitably mounted on the exterior surface of one of the opposing plates.
The fins 122 can take on any number of configurations depending upon, for example, the application and heat transfer requirements. For example, in the embodiment illustrated in
In
As illustrated in
The channels 126 of each heat exchange unit 118 extend from and through the first facesheet 128 at the second inlet 110 to and through the second facesheet 130 at the second outlet 112. The channels 126 are configured to keep the second fluid 114 fluidically isolated from the first fluid 108 to prevent mixing of the two fluids. However, each heat exchange unit 118 is configured to exchange heat between the fluids 108, 114. For example, if the second fluid 114 is at a higher temperature than the first fluid 108, each heat exchange unit 118 is configured to transfer heat from the second fluid 114 flowing in the channels 126 through the plate 124 and the fins 122 to the first fluid 108 flowing in the fluid paths 120 and in contact with the fins. Likewise, in the case where the first fluid is at a higher temperature than the second fluid 114, heat is transferred from the first fluid via the fins and the plate 124 into the second fluid. As discussed further below with respect to
The extensions 133 of the heat exchange units 118 may be attached to the facesheets 128, 130 by bonding, brazing, welding, and/or other suitable attachment methods. In an embodiment, the extensions 133 and the facesheets 128, 130 are attached by friction stir welding (FSW).
FSW is a known method for joining elements of the same material. Immense friction is provided to the elements such that the immediate vicinity of the joining area is heated to temperatures below the melting point. This softens the adjoining sections, but because the material remains in a solid state, the original material properties are retained. Movement or stirring along the weld line forces the softened material from the elements towards the trailing edge, causing the adjacent regions to fuse, thereby forming a weld. FSW reduces or eliminates galvanic corrosion due to contact between dissimilar metals at end joints. Furthermore, the resultant weld retains the material properties of the material of the joined sections. Further information on FSW is disclosed in U.S. Patent Application Publication Number 2009/0308582, titled Heat Exchanger, filed on Jun. 15, 2009, which is incorporated herein by reference.
The facesheets 128, 130 are formed from the same material as the plates 124 of the heat exchange units 118. Materials suitable for use in forming the plates 124 and the facesheets 128, 130 include, but are not limited to, marine grade aluminum alloys, aluminum alloys, aluminum, titanium, stainless-steel, copper, bronze, plastics, and thermally conductive polymers.
The fins described herein can be made partially or entirely from foam material. In one example, the fins can consist essentially of, or consist of, foam material. The foam material may have closed cells, open cells, coarse porous reticulated structure, and/or combinations thereof. In an embodiment, the foam can be a metal foam material. In an embodiment, the metal foam includes aluminum, copper, bronze or titanium foam. In another embodiment, the foam can be graphite foam. In an embodiment, the fins do not include metals, for example aluminum, titanium, copper or bronze. In an embodiment, the fins are made only of graphite foam having an open porous structure. In addition, in some embodiments, the heat exchanger and heat exchange units can include a combination of graphite foam fins, metal foam fins and/or metal (such as aluminum) fins.
As shown in
The tube bundle 116 is formed from a plurality of the heat exchange units 118 stacked together. When the heat exchange units are stacked, the channels 126 defined by the plates 124 form an array of fluid channels for the fluid 114 to flow through the tube bundle 116 from the inlet 110 to the outlet 112. Also, the fluid paths 120 for the fluid 108 are defined between the fins 122 and the plates 124. As evident from
The fins 122 of the heat exchange units 118 shown in
In
The plate 150 will be described with reference to
The fins 170 are disposed on an outward facing, first major surface 172 of the plate 152, with each fin 170 having a first end connected to and in thermal contact with the surface 172 of the plate 152. Each fin 170 also has a second end spaced from the surface 172. Fluid paths are defined by the fins and the surface 172 extending generally from the second end of the fins to the first ends of the fins.
In
An “X”-degree cross corrugated diamond-shaped configuration is used herein to mean, when viewed from the top perspective, a configuration wherein a first straight portion of the fins and a second straight portion of the fins is provided in a crisscross configuration forming substantially diamond-shaped holes. The numerical value for X indicates the vertical angle at an intersection of the first and the second straight portions, when the fins are viewed from the top. The value for X can range anywhere from about zero degrees to less than about 90 degrees.
Other arrangements of fins are possible as discussed below in
The tube bundle 200 can be used by itself in the shell or arranged with other tube bundles in the shell. Also, other configurations of tube bundles are possible. For example,
The baffles 304 comprise plates that help to support the bundle 302 with the shell, and to create a desired flow pattern of the fluid within the shell. Any type or configuration of baffling can be used to achieve any desired flow pattern. The baffles 304 can be made of any material suitable for accomplishing the tasks of the baffles 304, for example aluminum.
In the illustrated embodiment, the baffles 304 are substantially semicircular in shape and include an outer edge 306 that matches the interior surface of the shell to prevent or minimize the flow of fluid between the outer edge 306 and the shell. The baffles 304 also include slots 308 that allow the various parts of the tube bundle to be inserted through the slots during installation.
In
The foam fins described herein are not limited to being secured to plates that define flow channels.
The diamond-shaped fins 352 have a diamond shaped end surface 356, when viewed from the top perspective, which is substantially flat for stacking and for making contact with another surface, for example the surface of the plate of another heat exchange unit 350. The fins 352 are disposed on a major surface 358 of the plate 354, with each fin 352 having a first end 360 connected to and in thermal contact with the surface 358 of the plate 354. Each fin 352 has a second end 362 spaced from the surface 358 of the plate 354, where the end 362 defines the end surface 356. Fluid flow paths 364 are defined by the fins 352 and the plate 354.
As would be apparent to a person of ordinary skill in the art, the aspect ratio (i.e. the ratio of the longer dimension of the end surface 356 to its shorter dimension), the height, the width, the spacing and other dimensional parameters of the fins 352 can be varied depending in part upon the application and the desired heat transfer characteristics.
The plates in the illustrated embodiments have been rectangular or square plates. However, the fins can be used with plates of any shape, including but not limited to circular, elliptical, triangular, diamond, or any combination thereof, with the fins disposed on a plate (similar to
The configuration of the fins, when viewed from the top, does not necessarily define the direction of fluid flow. When viewing
One skilled in the art would understand that the various fin configurations described herein may be used in combination with each other and in any of the heat exchange units described herein, based on factors such as the flow regime, area and flow paths within the heat exchanger, as well as the application of the heat exchanger.
The heat exchangers described herein can be employed in any number of applications, including but not limited to, low thermal driving force applications such as Ocean Thermal Energy Conversion, power generation applications, and non-power generation applications such as refrigeration and cryogenics.
All of the heat exchangers described herein operate as follows. A first fluid flows past and is in contact with the fins on the fin side of the plate. Simultaneously, a second fluid is present on the opposite side of the plate. The second fluid can flow primarily counter to the first fluid, in the same direction as the first fluid, in a cross-flow direction relative to the flow direction of the first fluid, or any angle thereto. The first and second fluids are at different temperatures and therefore heat is exchanged between the first and second fluids. Depending upon the application, the first fluid can be at a higher temperature than the second fluid, in which case heat is transferred from the first fluid to the second fluid via the fins and the plate. Alternatively, the second fluid can be at a higher temperature than the first fluid, in which case heat is transferred from the second fluid to the first fluid via the plate and fins.
The examples disclosed in this application are to be considered in all respects as illustrative and not limitative. The scope of the invention is indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.
This application claims the benefit of U.S. Provisional Applicant Ser. No. 61/439,562, filed on Feb. 4, 2011, the entire contents of which are incorporated herein by reference.
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