The magnetocaloric effect is a phenomenon whereby, for appropriately chosen materials (referred to as “magnetocaloric materials”), a change in the temperature of the material can be induced by exposing the material to a changing magnetic field. Specifically, increasing the magnitude of an externally applied magnetic field orders the magnetic moments within the material, increasing the temperature via the magnetocaloric effect. Conversely, decreasing the magnitude of the externally applied magnetic field disorders the magnetic moments within the material, reducing temperature via the magnetocaloric effect.
In one aspect, an apparatus, such as a heat exchanger, is provided. The apparatus can include a first tubular region that is substantially hollow. A second tubular region can be disposed adjacent to the first tubular region. For example, the first and second tubular regions can define respective elongated axes that are substantially parallel, with the first and second tubular regions being, say, juxtaposed. The first and second tubular regions can each have a dimension less than or equal to about 100 μm, and/or can each have an aspect ratio of at least five.
The first and second tubular regions can respectively include pluralities of first and second tubular regions tubular regions, with at least one first tubular region being adjacent to at least one second tubular region. In some embodiments, the first and second tubular regions may be arranged so as to form an array, for example, of alternating first and second tubular regions. In some embodiments, the first and second tubular regions can be disposed within a major passage defined by a major tubular structure. In other embodiments, the first and second tubular regions may be incorporated into a unitary structure.
The apparatus may include a first tubular structure that defines a first passage, with the first tubular region being defined by the first passage. The first tubular structure may include a plurality of first tubular structures that are arranged so as to define therebetween said second tubular region. Alternatively, or additionally, the apparatus may further include a second tubular structure that defines a second passage, with the second tubular region being defined by the second passage. The first and/or second tubular structures can be formed at least partially of copper, silver, aluminum, and/or a thermoplastic.
A first material can be disposed within the second tubular region. The first material can be granular, and may have a strain to failure of less than about 1% at room temperature. For example, the first material can be a magnetocaloric material. A second material may also be disposed within the second tubular region.
Where the first material includes magnetocaloric material, the apparatus may also include a magnetic field generating component configured to vary a magnetic field to which the magnetocaloric material is exposed. A working fluid can be directed through the first tubular region so as to exchange heat with the magnetocaloric material.
In another aspect, a method is provided, the method including providing a first tubular structure that defines a first passage. A sacrificial material can be disposed in the first passage. A second tubular structure can be provided so as to be adjacent to the first tubular structure, with the second tubular structure defining a second passage within which can be disposed a granular material. The first and second tubular structures can then be deformed (e.g., drawn, rolled, and/or swaged) together so as to reduce an external dimension of each of the first and second tubular structures, for example, by at least 50%. The sacrificial material can then be removed from the first passage, for example, through etching, melting, and/or decomposing the sacrificial material.
In some embodiments, a major tubular structure can be provided, the major tubular structure acting to define a major passage. The first and second tubular structures can be disposed within the major passage, and the first and second tubular structures can be deformed together with major tubular structure.
In yet another aspect, an apparatus, such as a heat exchanger, is provided. The apparatus can include a first tubular region with a sacrificial material and, in some cases, a second material, such as another sacrificial material, disposed therein. A second tubular region can be disposed adjacent to the first tubular region, with a first material being disposed in the second tubular region.
In still another aspect, a method is provided, the method including providing a major tubular structure defining a major passage. A first tubular structure can be provided, the first tubular structure that defines a first passage that has disposed therein sacrificial material. A first, granular material can be disposed in an area between the first tubular structure and the major tubular structure. The major and first tubular structures can be deformed together, and the sacrificial material can be removed.
In yet another aspect, a method is provided, the method including providing a plurality of first tubular structures, each of which defines a first passage. A sacrificial material can be disposed in each of the respective first passages. The first tubular structures can be configured so as to enclose therebetween an interstitial space, within which interstitial space can be disposed a first, granular material. The plurality of first tubular structures and the first, granular material can be deformed together, and the sacrificial material can be removed.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Example embodiments of the present invention are described below in detail with reference to the accompanying drawings, where the same reference numerals denote the same parts throughout the drawings. Some of these embodiments may address the above and other needs.
Referring to
The first tubular regions 102 can be substantially hollow so as to define respective passages 106 therealong, while a first material 108 can be disposed within the second tubular regions 104. The first material can be granular, and may be compacted within the second tubular regions 104 so as to substantially fill the second tubular regions. The granular first material 108 may include granules of any shape, including, for example, one or more of spherical, cubic, pyramidal, etc. Regardless of shape, the granules may have diameters less than or equal to about 100 μm, and in some cases less than or equal to about 50 μm. Caps 110 can be provided in order to enclose the first material 108 within the second tubular regions 104. The first material 108 can be relatively brittle, for example, exhibiting a strain to failure of less than about 1% at room temperature. In some embodiments, a multiple materials may be disposed within the second tubular regions 104. For example, a second granular material may be mixed with the granular first material 108. The second material, when included, may also be relatively brittle. In other embodiments, respective second tubular regions 104 may contain different materials.
The first and second tubular regions 102, 104 may have cross sections that are substantially geometrically similar. For example, the first and second tubular regions 102, 104 may define square or rectangular cross sections that are roughly similar to one another in size and shape. However, the first and second tubular regions 102, 104 need not have rectangular cross-sections, and need not have cross-sectional shapes similar to one another. For example, referring to
Referring to
Referring again to
Referring to
In all of the previously described embodiments, the first and second tubular regions have been juxtaposed. Referring to
Referring to
In order to maximize the thermal performance of the magnetic refrigeration system 830, efficient thermal contact may be facilitated between the working fluid 832 in the first tubular region 802 and the magnetocaloric material 808 in the second tubular region 804. In embodiments where each of the adjacent first and second tubular regions is defined by a tubular structure (e.g., as depicted in
In some embodiments, the heat exchanger 800 can be configured such that 50-90% of the overall cross-sectional area of the heat exchanger (i.e., the area of the surface opposing the flow of working fluid 832) is consumed by magnetocaloric material 808. Generally, the operation of the heat exchanger 800 will be enhanced by proportionately higher concentrations of magnetocaloric material in the heat exchanger. In other embodiments, the heat exchanger 800 can be configured such that at least 70% of the overall cross-sectional area of the heat exchanger is consumed by magnetocaloric material 808, with about 25% being consumed by hollow areas for channeling working fluid flow, and another 5% being consumed, for example, by the structures defining the first and second tubular regions 802, 804.
Referring to
The first and second tubular structures 916, 918 can then be deformed together (say, along with the major tubular structure 912) so as to reduce an external dimension of each of the first and second tubular structures (
Following deformation of the first and second tubular structures 916, 918 the sacrificial material 940 can be removed from the first passages 906 to produce a heat series of adjacent tubular structures that either include either granular material 908 or define passages 906 that are hollow (
Once the sacrificial material 940 has been removed from the first tubular structures 916, the first and second tubular structures 916, 918 together may form a heat exchanger 900 with fluid conduits formed integrally therein (i.e., the hollow passages 906). It is noted that the first and second tubular structures 916, 918 may be cut to any desired length (e.g., to a length ranging from about 0.1 mm to a few centimeters). As mentioned, when cutting the first and second tubular structures 916, 918 may, both the sacrificial material 940 and the granular material 908 may be exposed. However, either during the sacrificial material removal process or during ultimate use of the heat exchanger 900, it may be desirable to protect the granular material 908 from exposure to the surrounding environment. In such cases, the ends of the second tubular structures 918 can be covered/protected by chemically inert coatings/barriers.
The above-described process may enable the manufacture of components having relatively complex geometries and formed substantially of brittle materials. Such materials are typically challenging to machine or otherwise shape. By utilizing the brittle materials in granular form and enclosing the granules in another, more ductile material, relatively complex geometries can be formed. It is noted that the first, second, and major tubular structures 912, 916, 918 could, in some embodiments, be replaced by a monolithic structure through which a series of bores may be formed, which bores could then be respectively filled with granular material and sacrificial material. Further, a drawing/swaging process may, in some embodiments, result in a higher density than would otherwise be realizable for structures formed of granular materials. Finally, where the brittle material is a magnetocaloric material, a drawing/swaging process may, in some embodiments, result in a magnetocaloric material with a microstructure consisting of grains that are elongated in the drawing/swaging direction, which aspect may enhance the magnetocaloric properties of the material.
It is noted that the major tubular structure 912 may be excluded in some cases. In such embodiments, the deformation of the first and second tubular structures 916, 918 may act to bind these structures together, either through a physical interlocking of the tubes or due to reactions between or localized melting of the tubes.
In some embodiments, the deformation process may be facilitated through the use of a granular material 908 having granules with generally regular surface profiles, such that the surfaces of the granules lack asperities, protrusions, sharp indentations, etc. (other than nanometer and/or atomic level roughness). For example, this may allow the granules to flow past one another more readily, thereby helping to avoid instances of unusually low density and/or voids therein. In order to produce granules having a sufficiently smooth surface, the granules may be subjected to an isotropic chemical etch, which will tend to preferentially etch more pronounced surface features.
Referring to
Referring again to
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.