Regenerator

Abstract

Regenerators for Stirling engines and Vuilleumier heat pumps are difficult to reliably manufacture. A regenerator is disclosed in which edges of the regenerator wire meshes are coated with a stabilizing material. The regenerator wire meshes are then sufficiently stable to be machined to the dimensions of the housing. In some embodiments, the material on the outer surface of the edges of the regenerator is relatively thermally insulating to limit heat transfer to the housing.

Claims

1. A regenerator, comprising: a plurality of wire mesh layers forming a three-dimensional volume wherein each layer has a substantially similar cross-sectional shape and the plurality of wire mesh layers lying in mutually parallel planes; and a material applied to sides of the regenerator, the sides being perpendicular to the mutually parallel planes of the wire mesh layers wherein: the sides are machined to a desired shape and surface finish; and the wire mesh layers comprise at least one of: a woven fabric of wires; a random, substantially planar layer of wires; and a planar, non-woven, regular pattern of wires.

2. The regenerator of claim 1 wherein the material is added via one of: plasma spraying and thermal spraying.

3. The regenerator of claim 1 wherein: the material applied to the sides is one of a liquid paste and a powder: the liquid paste is one of: a liquid metal that is liquid due to being at high temperature and a braze paste that includes metallic particles and a solvent with the solvent driven off via heating the regenerator; and the powder forms a solid when cooled after heating to a predetermined temperature.

4. The regenerator of claim 1 wherein the material is applied by an electrochemical plating process.

5. The regenerator of claim 1 wherein the material is a relative thermal insulator having a thermal conductivity less than about 30 W/m-K.

6. The regenerator of claim 1, further comprising: a coating applied to the material on the sides of the regenerator, the coating having a thermal conductivity much lower than the thermal conductivity of the material on the sides of the regenerator.

7. A regenerator, comprising: a plurality of wire mesh layers forming a three-dimensional volume wherein each layer has a substantially similar cross-sectional shape and the plurality of wire mesh layers lying in mutually parallel planes; and a liquefied material applied to sides of the regenerator wherein the sides are perpendicular to the mutually parallel planes of the wire mesh layers; and the liquefied material become solid when cooled wherein the wire mesh layers comprise at least one of: a woven fabric of wires; a random, substantially planar layer of wires; and a planar, non-woven, regular pattern of wires.

8. The regenerator of claim 7 wherein material applied to the sides are machined so that the regenerator has predetermined dimensions.

9. The regenerator of claim 7 wherein the material applied to the sides has a thermal conductivity lower than the wire mesh material.

10. A process for fabricating a regenerator, comprising: applying a solid material to sides of the regenerator, the regenerator being comprised of a plurality of layers of wire mesh wherein the layers of wire mesh lie in mutually parallel planes; and the sides of the regenerator are perpendicular to the mutually parallel planes of the wire meshes.

11. The process of claim 10, further comprising: stacking a plurality of wire mesh layers, the wire mesh layers having at least one of layers of organized wires, layers of woven mesh, and layers of random wires; compressing the plurality of wire mesh layers; sintering the plurality of wire mesh layers; and cutting the plurality of layers of wire mesh to a desired shape.

12. The process of claim 10 wherein the applying a solid material comprises: heating up a solder-like material to a liquid state; rolling the regenerator in the liquid solder-like material; and allowing the regenerator to cool.

13. The process of claim 10 wherein applying a solid material comprises spraying on the material via one of a plasma process and a thermal process.

14. The process of claim 10 wherein applying a solid material comprises: placing a powder on the sides; heating the regenerator so that the powder material adheres to the sides; and allowing the regenerator to cool.

15. The process of claim 10 wherein applying a solid material comprises: applying a brazing material that includes metallic components and a solvent; heating the regenerator to drive off the solvent; and cooling the regenerator to harden remaining brazing material.

16. The process of claim 10, further comprising: applying a thermally-insulating coating onto the solid material on the sides of the regenerator.

17. The process of claim 10 wherein the sides comprise at least an outer side and an inner side.

18. The process of claim 10, further comprising: installing a thermally-insulating sleeve over the regenerator; and inserting the regenerator into the housing.

19. The process of claim 10, further comprising: machining the sides to a predetermined shape to thereby allow the regenerator to be inserted into the housing.

20. The process of claim 11, further comprising: cutting the plurality of wire mesh layers to a rectangular shape prior to stacking the plurality of wire mesh layers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is an illustration of a prior art regenerator;

[0024] FIG. 2 is an illustration of a regenerator according to an embodiment of the disclosure;

[0025] FIG. 3 is an illustration of a regenerator to be inserted into a housing; and

[0026] FIG. 4 is a flowchart showing one embodiment of a process by which a regenerator is fabricated.

DETAILED DESCRIPTION

[0027] As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated.

[0028] In FIG. 2, a regenerator 132 is shown which has vertical wires 104 and horizontal wires 106. Regenerator 132 is annular and has a cylindrical opening 108. Sides 120 and 122 of regenerator 132 that are parallel to the general direction of flow 130 of gases, are coated. That is, the spikey ends of meshes 102 are covered in material. The general direction of flow 130 is perpendicular to a plane 134 in which mesh 102 sits. In one embodiment, sides 120 and 122 are covered by thermal or plasma spraying. Such material stabilizes the ends of meshes 102 making it more robust for further processing. After spraying sides 120 and 122 of regenerator 132, sides 120 and 122 can be machined to the dimensions of the housing and to provide the desired surface finish. Regenerator 132 is a collection of annularly-shaped meshes forming a 3-dimensional shape that has an inner diameter and an outer diameter. Wire meshes 102 lie in mutually parallel planes 134, respectively. The shape of regenerator 132 in FIG. 2 is one non-limiting example. Alternatively, regenerator 132 could be sectioned into multiple arcs, a parallelepiped, a solid cylinder, or any suitable shape that fits into the space designed into the housing.

[0029] The layers of mesh visible in FIG. 2 have a rectilinear appearance, which could be due to the wires placed like that or woven. Other alternatives exist, including a random arrangement of wires and other regular or repeating patterns of wires with or without weaving, or any other suitable arrangement.

[0030] In an alternative embodiment, sides 120 and 122 of regenerator 132 are costed with a liquid solder or a braze paste. The braze paste has an organic solvent and metal. Regenerator 132 is heated thereby releasing the solvent and melting the metal. When cooled the metal solidifies to hold edges of mesh layers 102 into place. In yet another alternative, a powder coating is applied that when heated melts and fuses the tips of the cut mesh material.

[0031] A desired characteristic of a regenerator is that energy transfer within the regenerator is primarily in plane 134 and much less so in the direction of flow 130. Furthermore, energy transfer into the regenerator's housing is undesirable. Thus, a material with a low thermal conductivity on the outer surfaces of the sides is desirable. Such material may be titanium, stainless steel, or metallic oxides such as aluminum oxide or zirconium oxide. In some embodiments, a very thin metal layer is applied, a metal that has high strength to stabilize the meshes, then followed by a layer of a material of low thermal conductivity.

[0032] In one embodiment, a thin insulating sleeve 136 is slid over regenerator 132 as shown in FIG. 2. Alternatively, sleeve 136 is placed into the housing prior to regenerator 132 being slid into the housing. In such embodiment, sleeve 136 is slid into the housing prior to sliding regenerator 132 into the housing. Alternatively, the insulating material is sprayed into the housing prior to regenerator 132 being slid therein. If material on sides 120 and 122 that is used to secure the edges of the meshes is sufficiently insulating, such sleeve 136 may be obviated.

[0033] In FIG. 3, regenerator 140 fabricated of multiple meshes 144, of a different arrangement than meshes in FIGS. 1 and 2, is slid into an open annular region 148 in a housing 142 that has an interior cylinder 146 in which a displacer or piston may reciprocate.

[0034] One embodiment of a process by which a regenerator is fabricated is shown in FIG. 4. The mesh layers are cut out to the desired shape and then stacked in block 150. In some embodiments, the mesh material come in a roll and rectangular pieces are cut out the bulk material. In embodiments where the material is fabricated into a desired starting geometry, the process in block 150 is eliminated. In block 152, the stack of mesh layers is pressed and then sintered. In block 154, the sintered stack of mesh layers is cut to a desired shape. In block 156, material is added to outer sides of the regenerator. Various options, e.g., plasma spraying, braze paste, are discussed in more detail above. The sides are the outer surfaces which are roughly parallel to the direction of flow, which is roughly perpendicular to the planes of the individual meshes. Depending on the geometry, there may also be inner sides, such as the inside of an annulus. In that case, the material is provided to the inners sides as well. Optionally, an insulating layer is added to outer surfaces of the regenerator in block 158. In other embodiments, an insulating layer is not provided because the material added in block 156 is sufficiently insulating. In block 6-8, the sides are machined so that they fit into the housing and have the desired surface finish. The regenerator is installed into the housing in block 162. As described above, if the system has a separate insulating sleeve, that can be applied to the regenerator prior to installation into the housing or installed into the housing before the housing receives the regenerator.

[0035] As described above, the material supplied to the sides is optionally: plasma sprayed, thermally sprayed, electroplated coated with a liquid solder, coated with a braze paste, or provided by any suitable method for adding material. In the case of the braze paste, the regenerator is heated to liberate the organic solvent. The list of materials that can be thermally sprayed is extensive. Furthermore, materials that can be applied via other processes contemplated herein is also extensive. A few examples are provided above; a comprehensive list is not included.

[0036] While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.