U.S. patent application number 12/526199 was filed with the patent office on 2012-02-23 for article for magnetic heat exchange and method for manufacturing an article for magnetic heat exchange.
This patent application is currently assigned to Vacuumschmelze GmbH & Co. KG. Invention is credited to Matthias Katter, Georg Werner Reppel.
Application Number | 20120043066 12/526199 |
Document ID | / |
Family ID | 41008655 |
Filed Date | 2012-02-23 |
United States Patent
Application |
20120043066 |
Kind Code |
A9 |
Reppel; Georg Werner ; et
al. |
February 23, 2012 |
Article for Magnetic Heat Exchange and Method for Manufacturing an
Article for Magnetic Heat Exchange
Abstract
An article (1) for magnetic heat exchange extends in a first
direction (3) and in a second direction (5) generally axially
perpendicular to said first direction (3). The article (1)
comprises at least one magnetocalorically active phase (2). The
average thermal conductivity of the article (1) is anisotropic.
Inventors: |
Reppel; Georg Werner;
(Hammersbach, DE) ; Katter; Matthias; (Alzenau,
DE) |
Assignee: |
Vacuumschmelze GmbH & Co.
KG
Hanau
DE
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20110048690 A1 |
March 3, 2011 |
|
|
Family ID: |
41008655 |
Appl. No.: |
12/526199 |
Filed: |
May 16, 2008 |
PCT Filed: |
May 16, 2008 |
PCT NO: |
PCT/IB08/51937 PCKC 00 |
371 Date: |
August 6, 2009 |
Current U.S.
Class: |
165/185;
29/890.03 |
Current CPC
Class: |
F25B 21/00 20130101;
Y02B 30/66 20130101; Y02B 30/00 20130101; F25B 2321/002 20130101;
Y10T 29/4935 20150115; H01F 1/012 20130101 |
Class at
Publication: |
165/185;
29/890.03 |
International
Class: |
F28F 7/00 20060101
F28F007/00; B21D 53/02 20060101 B21D053/02 |
Claims
1. An article for magnetic heat exchange, the comprising: at least
one magnetocalorically active phase, wherein the article extends in
a first direction and in a second direction generally perpendicular
to the first direction, and wherein the average thermal
conductivity of the article is anisotropic such that the average
thermal conductivity in the first direction differs from the
average thermal conductivity in the second direction.
2. The article according to claim 1, wherein the average thermal
conductivity in the first direction is less than the average
thermal conductivity of the article in the second direction.
3. The article according to claim 1 wherein the first direction
corresponds to the thickness of the article, and the second
direction corresponds to a direction in a plane of a lateral area
extending generally perpendicular to the first direction, and
wherein the average thermal conductivity measured over the
thickness of the article is less than the average thermal
conductivity measured in a direction in the plane of a lateral area
of the article.
4. The article according to claim 1, further comprising: a
magnetocalorically passive phase having a thermal conductivity
which is greater than a thermal conductivity of the
magnetocalorically active phase.
5. The article according to claim 4, wherein the magnetocalorically
passive phase comprises a plurality of grains having, on average, a
preferred orientation.
6. The article according to claim 5, wherein the plurality of
grains of the magnetocalorically passive phase comprise an elongate
form having a long direction, and a short direction generally
perpendicular to the long direction.
7. The article according to claim 5, wherein at least some of the
plurality of grains of the magnetocalorically passive phase are
arranged in the article with a preferred texture.
8. The article according to claim 6, wherein the plurality of
grains of the magnetocalorically passive phase are arranged in the
article so that on average their long direction extends generally
perpendicular to the first direction of the article.
9. The article according to claim 5, wherein the plurality of
grains of the magnetocalorically passive phase are arranged in the
article so that on average their short direction extends generally
parallel to the first direction of the article.
10. The article according to claim 1, wherein the
magnetocalorically active phase comprises a plurality of grains
arranged in the article with, on average, a preferred
orientation.
11. The article according to claim 10, wherein the plurality of
grains of the magnetocalorically active phase have, on average, a
preferred texture.
12. The article according to claim 10, wherein the
magnetocalorically active phase comprises a plurality of grains,
each having an elongate form with a long direction and a short
direction generally perpendicular to the long direction.
13. The article according to claim 12, wherein the grains of the
magnetocalorically active phase are arranged in the article so that
on average the long direction of the grains extends generally
perpendicular to the first direction of the article.
14. The article according to claim 13, wherein the grains of the
magnetocalorically active phase are arranged in the article so that
on average the short direction of the grains extends generally
parallel to the first direction of the article.
15. The article according to claim 10, wherein the grains of the
magnetocalorically active phase comprise a corrosion protection
coating disposed thereon.
16. The article according to claim 15, wherein the corrosion
protection coating comprises a metal, an alloy, a polymer, a
ceramic, or an inorganic compound.
17. The article according to claim 15, wherein the corrosion
protection coating comprises Al, Cu, Sn, or a phosphate.
18. The article according to one claim 4, wherein the
magnetocalorically active phase is disposed in a plurality of first
layers interleaved with a plurality of second layers containing the
magnetocalorically passive phase.
19. The article according to claim 1, wherein the
magnetocalorically active phase comprises at least one first layer
having a first density, and at least one second layer having a
second density, wherein the first density is greater than the
second density.
20. The article according to claim 19, wherein the at least one
first layer has a first average porosity and the at least one
second layer has a second average porosity, wherein the second
average porosity is greater than the first average porosity.
21. The article according to claim 18, wherein the at least one
first layer and the at least one second layer are arranged in a
stack, wherein adjacent layers are in physical contact with one
another.
22. The article according to claim 18, wherein the first layers and
the second layers each have a thickness extending generally
parallel to the first direction of the article and a lateral area
extending generally in the second direction of the article.
23. The article according to claim 1, wherein the article comprises
two or more active portions arranged along the first direction,
each portion comprising a magnetocalorically active phase having a
different Curie temperature T.sub.c.
24. The article according to claim 23, wherein the T.sub.c of the
active portions increases in the first direction of the
article.
25. The article according to claim 1, further comprising: at least
one thermal barrier having a thermal conductivity which is less
than the thermal conductivity of the magnetocalorically active
phase.
26. The article according to claim 25, wherein a plurality of
thermal barriers are arranged at intervals along the first
direction of the article.
27. The article according to claim 23, and further comprising a
thermal barrier having a thermal conductivity which is less than
the thermal conductivity of the magnetocalorically active phase,
that is arranged between adjacent active portions.
28. The article according to claim 1, wherein the
magnetocalorically active phase comprises one or more of Gd, a
La(Fe.sub.1-bSi.sub.b).sub.13-based phase, a Gd.sub.5(Si,
Ge).sub.4-based phase, a Mn(As, Sb)-based phase, a MnFe(P,
As)-based phase, a Tb--Gd-based phase, a (La, Ca, Pr, Nd,
Sr)MnO.sub.3-based phase, a Co--Mn--(Si, Ge)-based phase and a
Pr.sub.2(Fe, Co).sub.17-based phase.
29. The article according to claim 4, wherein the
magnetocalorically passive phase comprises one or more of the
elements, Al, Cu, Ti, Mg, Zn, Sn, Bi or Pb.
30. The article according to claim 4, wherein the
magnetocalorically passive phase comprises a soft magnetic
material.
31. The article according to claim 30, wherein the soft magnetic
material comprises one or more of Fe, FeSi, Co, or Ni.
32. The article according to claim 1, further comprising at least
one channel in a surface of the article.
33. The article according to claim 32, wherein the channel is
adapted to direct the flow of a heat exchange medium.
34. The article according to claim 1, further comprising an outer
protective coating.
35. The article according to claim 34, wherein the outer protective
coating comprises a polymer or a metal or an alloy.
36. A heat exchanger, comprising the article according to claim
1.
37. A refrigeration system, comprising the heat exchanger according
to claim 36.
38. An industrial, commercial, or domestic freezer comprising the
refrigeration system according to claim 37.
39. A method of manufacturing an article according to claim 4,
comprising: providing a magnetocalorically active phase or a
precursor of a magnetocalorically active phase, providing a
magnetocalorically passive phase comprising a plurality of
particles, assembling the magnetocalorically active phase or the
precursor of a magnetocalorically active phase and the
magnetocalorically passive phase, compacting the magnetocalorically
active phase or the precursor of a magnetocalorically active phase
and the magnetocalorically passive phase to form an article having
an average preferred orientation of at least the plurality of
grains of the magnetocalorically passive phase in the article.
40. The method according to claim 39, wherein the compacting
comprises inducing a preferred orientation of at least the grains
of the magnetocalorically passive phase.
41. The method according to claim 39 wherein the compacting
comprises inducing a preferred orientation of at least the grains
of the magnetocalorically active phase.
42. The method according to claim 39, wherein the average preferred
orientation of at least the plurality of grains of the
magnetocalorically passive phase or at least the plurality of
grains of the magnetocalorically active phase, or both, is produced
at least in part by applying a magnetic field to the
magnetocalorically passive phase or to the magnetocalorically
active phase or to both.
43. The method according to claim 42, wherein the magnetic field is
applied before the compacting.
44. The method according to claim 42, wherein the magnetic field is
applied at a temperature less than the Curie Temperature of the
magnetocalorically active phase.
45. The method according to claim 39, wherein the particles of the
magnetocalorically passive phase have on average anisotropic
dimensions and the compaction is carried out so that the grains of
the magnetocalorically passive phase are on average orientated such
that the grains have a long direction perpendicular to the first
direction of the article.
46. The method according to claim 39, wherein the average preferred
orientation of at least the plurality of grains of the
magnetocalorically passive phase is produced at least in part by
mechanical deforming the article after the compacting.
47. The method according to claim 46, wherein the mechanical
deforming comprises one of more of rolling, swaging, drawing or
extruding.
48. The method according to claim 39 wherein the assembling of the
magnetocalorically active phase and the magnetocalorically passive
phase comprises intimately mixing the magnetocalorically active
phase and the magnetocalorically passive phase with one
another.
49. The method according to claim 39 wherein the assembling of the
magnetocalorically active phase and the magnetocalorically passive
phase comprises alternately arranging layers consisting essentially
of the magnetocalorically active phase and layers consisting
essentially of the magnetocalorically passive phase.
50. The method according to claim 39 wherein the compacting of the
magnetocalorically active phase and the magnetocalorically passive
phase comprises rolling or pressing.
51. The method according to claim 42, wherein the applying of the
magnetic field during compaction magnetically orientates the grains
of the magnetocalorically passive phase so that on average the
grains have a long direction that is oriented generally
perpendicular to the first direction of the article.
52. The method according to claim 42, wherein the applying of the
magnetic field during compaction magnetically orientates the grains
of the magnetocalorically active phase so that on average the
grains have a long direction that is oriented generally
perpendicular to the first direction of the article.
53. A method of manufacturing an article for magnetic heat
exchange, comprising: providing at least one first plate consisting
essentially of a magnetocalorically active phase and having a first
density, providing at least one second plate consisting essentially
of a magnetocalorically active phase and having a second density,
the first density of the first plate being greater than the second
density of the second plate, arranging the first plate and the
second plate in a stack.
54. The method according to claim 53, wherein the first plate and
the second plate are arranged so that they are in physical contact
with one another.
55. The method according to claim 53, wherein the first plate has a
first porosity and the second plate has a second porosity, the
second porosity being greater than the first porosity.
56. The method according to claim 53, wherein the providing of the
at least one first plate comprises compacting particles of a
magnetocalorically active phase or particles of a precursor of a
magnetocalorically active phase.
57. The method according to claim 56, wherein the providing of the
at least one second plate comprises compacting particles of a
magnetocalorically active phase or particles of a precursor of a
magnetocalorically active phase.
58. The method according to claim 57, wherein the compacting is
conducted so as to produce a lower porosity in the first plate than
in the second plate.
59. The method according to claim 58, wherein the providing of at
least one first plate and the providing of at least one second
plate comprises providing a plurality of first plates and a
plurality of second plates which are interleaved with one another
in a stacking direction of the article.
60. The method according to claim 39, further comprising adding one
or more of a lubricant, an organic binder or a dispersant to the
assembled magnetocalorically active phase or the magnetocalorically
passive phase or both.
61. The method according to claim 39, further comprising heating
the article during the compacting.
62. The method according to claim 61, wherein the heating forms a
magnetocalorically active phase from the precursor.
63. The method according to claim 39, further comprising applying
an outer protective coating to the article.
64. The method according to claim 63, wherein applying the outer
protective coating comprises dipping, spraying or
electro-deposition.
65. A climate control device comprising the heat exchanger
according to claim 36.
66. An air conditioning system comprising the climate control
device according to claim 65.
Description
BACKGROUND
[0001] 1. Field
[0002] Disclosed herein is an article for magnetic heat exchange
and methods for manufacturing an article for magnetic heat
exchange.
[0003] 2. Description of Related Art
[0004] The magnetocaloric effect describes the adiabatic conversion
of a magnetically induced entropy change to the evolution or
absorption of heat. By applying a magnetic field to a
magnetocaloric material, an entropy change can be induced which
results in the evolution or absorption of heat. This effect can be
harnessed to provide refrigeration and/or heating.
[0005] In recent years, materials such as
La(Fe.sub.1-aSi.sub.a).sub.13, Gd.sub.5(Si, Ge).sub.4, Mn (As, Sb)
and MnFe(P, As) have been developed which have a Curie Temperature,
T.sub.c, at or near room temperature. The Curie Temperature
translates to the operating temperature of the material in a
magnetic heat exchange system. Consequently, these materials are
suitable for use in applications such as building climate control,
domestic and industrial refrigerators and freezers as well as
automotive climate control.
[0006] Magnetic heat exchange technology has the advantage that
magnetic heat exchangers are, in principle, more energy efficient
than gas compression/expansion cycle systems. Furthermore, magnetic
heat exchangers are environmentally friendly as chemicals such as
chlorofluorocarbons (CFC) which are thought to contribute to the
depletion of ozone levels are not used.
[0007] Consequently, magnetic heat exchanger systems are being
developed in order to practically realise the advantages provided
by the newly developed magnetocaloric materials. Magnetic heat
exchangers, such as that disclosed in U.S. Pat. No. 6,676,772,
typically include a pumped recirculation system, a heat exchange
medium such as a fluid coolant, a chamber packed with particles of
a magnetic refrigerant working material which displays the
magnetocaloric effect and a means for applying a magnetic field to
the chamber.
[0008] However, further improvements are desirable to enable a more
extensive application of magnetic heat exchange technology.
SUMMARY
[0009] Disclosed herein are embodiments of an article for magnetic
heat exchange which can be reliably and cost effectively
manufactured. Also disclosed herein are embodiments of methods by
which the article may be produced.
[0010] A particular embodiment relates to an article for magnetic
heat exchange. The article extends in a first direction and in a
second direction generally axially perpendicular to said first
direction and comprises at least one magnetocalorically active
phase. The average thermal conductivity of the article is
anisotropic.
[0011] The article may be used as the magnetic refrigerant or
magnetic working medium of a magnetic heat exchange system.
Providing the article with an anisotropic average thermal
conductivity has the advantage that heat generated within the
article due to the magnetocaloric effect can be conducted to the
surface of the article anisotropically. The heat exchange between
the article and a cooling or heat exchange medium which surrounds
the article may be anisotropic as well. As used herein, the terms
"coolant" or "coolant medium" and "heat exchange medium," are used
interchangeably irrespective of whether the article is used to
supply heat to, or remove heat from, the heat exchange medium or
working fluid.
[0012] The article may be arranged in the magnetic heat exchange
system so that the most efficient thermal transfer occurs in
directions perpendicular to the direction of coolant medium flow
and so that the least efficient thermal transfer occurs in the
direction of the coolant medium flow. This arrangement enables a
more efficient heat exchange. Heat generated by the magnetocaloric
effect within the article can be conducted efficiently in
directions perpendicular to the coolant medium flow to the surface
of the article where the heat is transferred to the coolant and
carried by the coolant medium away from the article in the coolant
flow direction.
[0013] The poorer thermal conductivity of the article in the
direction of the coolant flow hinders the transfer of the heat
initially conducted away from the article back into the article and
in the opposite direction to the coolant medium flow. Overall, the
cooling efficiency of the article for magnetic heat exchange is
improved by providing the article with an anisotropic average
thermal conductivity.
BRIEF DESCRIPTION OF DRAWINGS
[0014] Embodiments disclosed herein will now be explained with
reference to the accompanying drawings, which are intended to
illustrate, but not limit, the scope of the appended claims.
[0015] FIG. 1 is a schematic diagram that illustrates a side view
of an embodiment of an article for magnetic heat exchange,
[0016] FIG. 2 is a schematic diagram that illustrates a
cross-sectional view of the article of FIG. 1,
[0017] FIG. 3 is a schematic diagram that illustrates a
cross-sectional view of an article for magnetic heat exchange
having a microstructure according to a first embodiment disclosed
herein,
[0018] FIG. 4 is a schematic diagram that illustrates a
cross-sectional view of an article for magnetic heat exchange
having a microstructure according to a second embodiment disclosed
herein,
[0019] FIG. 5 is a schematic diagram that illustrates a
cross-sectional view of an article for magnetic heat exchange
having a microstructure according to a third embodiment disclosed
herein,
[0020] FIG. 6 is a schematic diagram that illustrates a
cross-sectional view of an article for magnetic heat exchange
having a microstructure according to a fourth embodiment disclosed
herein, and
[0021] FIG. 7 is a schematic diagram that illustrates a
cross-sectional view of an article for magnetic heat exchange
having a microstructure according to a fifth embodiment disclosed
herein.
DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0022] A magnetocalorically active material is defined herein as a
material which undergoes a change in entropy when it is subjected
to a magnetic field. The entropy change may be the result of a
change from ferromagnetic to paramagnetic behaviour, for example.
The magnetocalorically active material may exhibit, in only a part
of a temperature region, an inflection point at which the sign of
the second derivative of magnetization with respect to an applied
magnetic field changes from positive to negative.
[0023] A magnetocalorically passive material is defined herein as a
material which exhibits no significant change in entropy when it is
subjected to a magnetic field.
[0024] In an embodiment, the average thermal conductivity of the
article in the first direction is less than the average thermal
conductivity of the article in the second direction. In operation,
the article is arranged with the first direction generally parallel
to the coolant medium flow to produce the most efficient heat
transfer.
[0025] In an embodiment, the article comprises a first length
extending in said first direction and a cross-sectional area
extending in said second direction, the cross-sectional area having
a second length. The average thermal conductivity measured over the
first length of the article is less than the average thermal
conductivity measured over the second length of the article and,
therefore, in the plane of the cross-sectional area. Again, in
operation the first length of the article is arranged generally
parallel and the second direction generally perpendicular to the
flow direction of the coolant medium.
[0026] The anisotropy in the average thermal conductivity of the
article can be provided in a number of ways. For example, in some
embodiments, the article further comprises a magnetocalorically
passive phase having a thermal conductivity which is greater than
the thermal conductivity of the magnetocalorically active
phase.
[0027] The anisotropic average thermal conductivity of the article
may be produced by various arrangements of the magnetocalorically
active phase and the magnetocalorically passive phase within the
article. The thermal conductivity anisotropy may be produced at a
microscopic level, (i.e., by microscopic anisotropy), that is, the
arrangement of the individual grains or particles of the
magnetocalorically passive phase and/or magnetocalorically active
phase which results in anisotropy in thermal conductivity.
Alternatively, the thermal conductivity anisotropy may be produced
macroscopically, that is, due to arrangements of members consisting
essentially of one of the magnetocalorically active and passive
phases.
[0028] In an embodiment, the magnetocalorically passive phase
comprises a plurality of grains having, on average, a preferred
orientation. Preferred orientation is used to describe an
anisotropic arrangement and/or distribution of grains within the
article. For example, even in embodiments where the individual
grains may be generally spherical in shape and, therefore,
individually have no preferred orientation. However, the spherical
grains may be aligned in one or more rows or in a matrix of rows
and columns and, therefore, have a preferred, i.e. physically
anisotropic, arrangement within the article.
[0029] This anisotropic arrangement provides an article with an
average anisotropic thermal conductivity in the case that the
thermal conductivity of the magnetocalorically passive phase is
different from thermal conductivity of the magnetocalorically
active phase even if the magnetocalorically active phase is
randomly arranged within the article. If the thermal conductivity
of the magnetocalorically passive phase is greater than the thermal
conductivity of the magnetocalorically active phase, then the
average thermal conductivity of the article in the long direction
of the row or in the plane of the matrix of the grains of the
magnetocalorically passive phase is greater than that in directions
perpendicular to the long direction of the row or in the plane of
the matrix of the grains of the magnetocalorically passive phase.
The article as a whole then has an anisotropic average thermal
conductivity.
[0030] In an embodiment, the magnetocalorically passive phase
comprises a plurality of grains, each having an elongate form with
a long direction and at least one short direction generally
perpendicular to the long direction.
[0031] To produce thermal anisotropy at a microscopic level, the
grains of the magnetocalorically passive phase may be arranged in
the article with a preferred orientation and/or a preferred
texture.
[0032] "Preferred orientation" is a term used to describe the
physical arrangement of the grains within the article. "Preferred
texture" is a term used to describe grains which are arranged
within the article such that they have, on average, a preferred
crystallographic orientation. It is, therefore, possible that the
grains have both a preferred orientation and a preferred
texture.
[0033] In the case of grains having an elongate form arranged with
a preferred texture, the average thermal conductivity of the
article in the long direction of the grains is higher than the
average thermal conductivity of the article in the short direction
of the grains.
[0034] A thermally anisotropic article may be provided by arranging
the plurality of elongate grains of the magnetocalorically passive
phase in the article so that on average their long direction
extends generally perpendicular to the first direction of the
article. The plurality of elongate grains of the magnetocalorically
passive phase may be arranged in the article so that on average
their short direction extends generally parallel to the first
direction of the article. These arrangements provide an article
with an average thermal conductivity which is higher in directions
perpendicular to the first direction and lower in directions
parallel to the first direction.
[0035] In operation, the article is arranged so that the long
direction of the grains is orientated generally perpendicular to
the coolant medium flow direction and the short direction of the
grains is orientated generally parallel to the coolant medium flow.
This arrangement discourages heat flow through the article in
directions opposite to the coolant medium flow.
[0036] In an embodiment, the magnetocalorically active phase
comprises a plurality of grains arranged in the article with, on
average, a preferred orientation. In this case, the term "preferred
orientation" is again used to denote an anisotropic arrangement of
grains within the article.
[0037] In a further embodiment, the magnetocalorically active phase
comprises a plurality of grains arranged in the article with a
preferred texture and, in a further embodiment, also with a
preferred orientation. In an embodiment, the magnetocalorically
active phase comprises a plurality of grains, each having an
elongate form with a long direction and at least one short
direction generally perpendicular to the long direction. The grains
may be fibre-like or plate-like, for example.
[0038] To produce an article with thermal anisotropy at the
microscopic level, the grains of the magnetocalorically active
phase may be arranged in the article so that on average the long
direction of the grains extends generally perpendicular to the
first length of the article. The grains of the magnetocalorically
active phase may also be arranged in the article so that on average
the short direction of the grains extends generally parallel to the
first length of the article.
[0039] This arrangement provides an article with an average thermal
conductivity which is higher in directions of the article parallel
to the long direction of the grains and with an average thermal
conductivity which is lower in the short direction of the
grains.
[0040] In some embodiments, both the magnetocalorically passive
phase and the magnetocalorically active phase are arranged within
the article with a preferred orientation and/or preferred texture.
The grains of the two phases may be intimately mixed so as to
provide thermal anisotropy at a microscopic level.
[0041] In other embodiments, only the magnetocalorically active
phase has a preferred orientation and/or texture or elongate grains
to provide an article with an anisotropic average thermal
conductivity. The article may comprise a magnetocalorically passive
phase which has no preferred texture. The magnetocalorically active
phase may be distributed with a preferred orientation and/or
texture among the grains of the magnetocalorically passive phase.
Alternatively, the magnetocalorically active phase may be
distributed without a preferred orientation and/or texture among
grains of the magnetocalorically passive phase having a preferred
orientation and/or texture. The magnetocalorically passive phase
may provide a matrix in which the grains of the magnetocalorically
active phase are arranged. In such an embodiment, the article can
be described as a composite.
[0042] An article for magnetic heat exchange may also be provided
with an anisotropic average thermal conductivity by arranging
materials of different thermal conductivity at a macroscopic level.
In an embodiment, the article comprises a plurality of first layers
consisting essentially of the magnetocalorically active phase
interleaved with a plurality of second layers consisting
essentially of the magnetocalorically passive phase.
[0043] In another embodiment, the article comprises only
magnetocalorically active phases and no substantial portion of
magnetocalorically passive phases. In this sense, phase is used to
denote a solid body and exclude gases and air. The term "no
substantial portion" is defined as less than 10 vol %.
[0044] In this embodiment, an average anisotropic thermal
conductivity is achieved by an anisotropic distribution of the
density of the article. In particular, the density of the article
varies macroscopically. This is provided in one embodiment by at
least one first layer consisting essentially of a
magnetocalorically active phase and having a first density and at
least one second layer consisting essentially of the
magnetocalorically active phase and having a second density, the
first density being greater than the second density.
[0045] The first layer with the greater density has a greater
thermal conductivity than the second layer with a lower density.
Therefore, the average thermal conductivity of the article in
directions perpendicular to the plane of the layers is lower than
the average thermal conductivity of the article in directions
parallel to the plane of the layers. The article, therefore, has an
anisotropic average thermal conductivity.
[0046] The density of the at least one first layer and the at least
one second layer may be adjusted to the desired average value by
controlling the porosity of the respective layer. The at least one
first layer may comprise a first average porosity and the at least
one second layer may comprise a second average porosity, the second
average porosity is greater than the first average porosity. This
provides a first layer with a greater density than the second layer
and an article with an anisotropic average thermal
conductivity.
[0047] In a further embodiment, the at least one first layer and
the at least one second layer are arranged in a stack, wherein
adjacent layers are in physical contact with one another. The
adjacent layers may be connected to their immediate neighbour by a
layer of an adhesive material or be directly connected to each
other by sintering of material of the adjacent layers, for
example.
[0048] The first layers and the second layers have a thickness
which extends generally parallel to the first direction of the
article and a plane of a lateral area extending generally in the
second direction of the article (e.g., perpendicularly to the first
direction of the article). Each layer is built up from a plurality
of layers of grains or particles of the respective phase.
[0049] In operation, the article is arranged so that the
cross-sectional or lateral area of the layers extends in a planar
fashion in directions that are generally perpendicular to the
coolant flow direction and the thickness of the layers extends
generally parallel to the coolant flow direction. The thermal
conductivity of the magnetocalorically passive phase is,
preferably, greater than the thermal conductivity of the
magnetocalorically active phase in this arrangement of the article
in order that the average thermal conductivity of the article in
the coolant flow direction is less than the average thermal
conductivity of the article in directions perpendicular to the
coolant flow direction.
[0050] In another embodiment, the article comprises a plurality of
active layers, each active layer comprising a magnetocalorically
active material having a T.sub.c which is different from the
T.sub.c of the magnetocalorically active material in an adjacent
layer. In a further embodiment, the magnetocalorically active
material of each of the layers is selected, along with the order in
which the materials are arranged, in order that the T.sub.c
progressively increases from one end of the article to the
other.
[0051] The use of articles comprising a plurality of
magnetocalorically active materials having different T.sub.c's, has
the advantage that the operating range of the heat exchanger in
which the article is used is increased. The Curie temperature
T.sub.c translates to the operating temperature and, since a range
of T.sub.c's are provided, the operating range of the heat
exchanger is increased. This enables the heat exchanger to provide
cooling and/or heating over a wider operating temperature range and
to provide cooling and/heating from a starting temperature to a
smaller/larger lowermost/uppermost temperature, respectively, than
that possible using magnetocalorically active material having a
single T.sub.c.
[0052] In a further embodiment, the article further comprises at
least one thermal barrier comprising a thermal conductivity which
is less than the thermal conductivity of the magnetocalorically
active phase.
[0053] The thermal barrier hinders thermal transfer from the region
of the article on one side to the region of the article on the
other side of the thermal barrier. The thermal barrier can be
arranged so that thermal transfer in the direction of the coolant
medium flow is hindered, thus further improving the efficiency of
the magnetic heat exchange.
[0054] In a further embodiment, the article comprises a plurality
of thermal barriers arranged at intervals along the first direction
of the article. If a plurality of portions with differing T, are
provided, the thermal barrier may be arranged between adjacent
portions.
[0055] The magnetocalorically active phase may be one or more of
Gd, a La(Fe.sub.1-bSi.sub.b).sub.13-based phase, a Gd.sub.5(Si,
Ge).sub.4-based phase, a Mn(As, Sb)-based phase, a MnFe(P,
As)-based phase, a Tb--Gd-based phase, a (La, Ca, Pr, Nd,
Sr)MnO.sub.2-based phase, a Co--Mn--(Si, Ge)-based phase and a
Pr.sub.2(Fe, Co).sub.17-based phase. These basic compositions may
further comprise further chemical elements which may substitute
partially or in full for the listed elements. These phases may also
comprise elements which are accommodated at least in part
interstitially within the crystal structure, for example, hydrogen.
These phases may also include impurity elements and small amounts
of elements such as oxygen.
[0056] In a further embodiment, the grains of the
magnetocalorically active phase comprise a corrosion protection
coating. This corrosion protection coating may comprise one or more
metals, alloy, polymers, ceramics or inorganic compounds. The metal
may be Al, Cu or Sn and the alloy may comprise one or more of Al,
Cu and Sn. An inorganic corrosion protection coating may be
provided by a phosphate, for example a zinc phosphate. The
corrosion protection coating may be applied to increase the working
life of the magnetocalorically active phase since the corrosion and
degradation of the magnetocalorically active material into
non-magnetocalorically active phases is at least slowed, or even
prevented entirely, over the working lifetime of the
magnetocalorically active material, due to the corrosion protection
coating.
[0057] The article may further comprise an effective porosity. The
term "effective porosity" is used herein to describe a porosity of
the article which has a measurable effect on the efficiency of the
magnetic heat exchange.
[0058] The effective porosity comprises at least one channel within
the body of the article which extends from a first side of the
article to a second side of the article. The porosity may be in the
range of 10 vol. % to 60 vol. % based upon the total volume of the
article.
[0059] The effective porosity may be provided in the form of a
series of interconnected channels in flow communication with each
other forming a hollow network of skeleton type structure within
the body of the article. The heat exchange fluid or coolant can
then flow through the hollow network from one side of the article
to the other.
[0060] The effective porosity may be provided by loosely compacting
the powder from which the article or a portion thereof is formed,
or by loosely compacting the powder followed by sintering, to form
in each case a body with a density of less than 100% such that the
unoccupied volume provides an interconnected hollow network though
which the heat exchange medium can flow.
[0061] These embodiments of a article having an effective porosity
have the additional advantage that the surface area of the article
is increased. The coolant is in contact with inner surfaces, that
is the surfaces of the interconnected channels that provide the
effective porosity, and which are positioned within the body of the
article, as well as with the overall outer surface of the article.
Thus, the contact area between the article and the heat exchange
fluid is increased. Consequently, the efficiency of the magnetic
heat exchange may be further increased.
[0062] The article may further comprise at least one channel
different from the interconnected channels that provide effective
porosity. The channel may be provided in the form of a through-hole
which is surrounded by the article or may be provided in the form
of a channel in an outer surface of the article. One or more
channels have the advantage of increasing the surface area of the
article which can further improve the heat exchange efficiency
between the article and the coolant. The channel may be formed by
extrusion or profile rolling, for example.
[0063] In a further embodiment, the channel can be adapted to
direct the flow of the coolant. The position of the channel is
determined by the design of the heat exchange system in which the
article is to operate. The channel may be adapted to direct the
flow of the coolant with reduced or, optimally, minimum turbulence
in order to increase the efficiency of the heat exchange.
[0064] The article may be a component of a heat exchanger, a
cooling system, an air conditioning unit for a building or a
vehicle, in particular an automobile, or a climate control device
for a building or an automobile. The climate control device may be
used as a heater in winter and as a cooler in summer by reversing
the direction of the fluid coolant or heat exchanger medium. This
is particularly advantageous for automobiles and other vehicles as
the space available within the chassis for accommodating the
climate control system is limited by the design of the vehicle.
[0065] The article may also comprise an outer protective coating.
The outer protective coating may comprise a metal, an alloy or a
polymer. The material of the outer protective coating may be chosen
so as to be chemically, as well as mechanically, stable during the
lifetime operation of the article in the heat exchange medium. If
the coating is applied to the finished article, it is not subjected
to higher temperatures, for example during sintering, or working of
the article. In this case, a polymer with a relatively low
decomposition temperature or melting temperature may be used.
[0066] The heat exchange medium or working fluid used to exchange
heat with the article may comprise ethanol or glycol, mixtures of
water, ethanol or glycol or an alternative material with a high
thermal conductivity in order to increase the efficiency of the
heat exchange between the heat exchange medium and the article. In
some circumstances, the heat exchange medium may be corrosive to
the magnetocalorically active material and/or the
magnetocalorically passive material of the matrix. Therefore, an
additional outer protective coating may be used to provide
additional protection.
[0067] The article according to one of these embodiments may be
used as a component of a heat exchanger, a refrigeration system, a
climate control device, an air-conditioning unit, or an industrial,
commercial or domestic freezer. The article is arranged so that the
first direction of the article is arranged generally parallel to
the direction of heat flow during operation.
[0068] The invention also provides methods of manufacturing an
article for magnetic heat exchange. In an embodiment, a
magnetocalorically active phase is provided and a
magnetocalorically passive phase comprising a plurality of
particles are provided. The magnetocalorically active phase and the
magnetocalorically passive phase are assembled and compacted to
form an article. A preferred orientation, that is, a preferred
physical arrangement, of at least a plurality of grains of the
magnetocalorically passive phase, on average, is produced.
[0069] In an embodiment, a precursor of a magnetocalorically active
phase is provided and a magnetocalorically passive phase comprising
a plurality of particles are provided. The precursor of the
magnetocalorically active phase and the magnetocaloritally passive
phase are assembled and compacted to form an article. A preferred
orientation of the plurality of grains of the magnetocalorically
passive phase is produced. In this embodiment, the article is
reaction sintered, wherein the magnetocalorically active phase
forms from the precursor.
[0070] The article is provided with an anisotropic thermal
conductivity due to the preferred orientation of the
magnetocalorically passive phase since the thermal conductivity of
the plurality of grains of the magnetocalorically passive phase is
higher in the longer direction of the grains than in the shorter
direction. As previously discussed, the grains may also have, on
average, a preferred texture of crystallographic orientation.
[0071] The preferred orientation may be produced at least in part
by the compaction process or may be produced in part or entirely in
a separate method step which may take place before or after
compaction.
[0072] In an embodiment, the compaction is carried out so as to
induce preferred orientation of at least the grains of the
magnetocalorically passive phase and/or at least the grains of the
magnetocalorically active phase
[0073] In an embodiment, the average preferred orientation of at
least the plurality of grains of the magnetocalorically passive
phase is produced at least in part by applying a magnetic field.
This method may be used when the magnetocalorically passive phase
is ferromagnetic, for example, comprises Fe or FeSi.
[0074] A magnetic field may also be used to provide a preferred
orientation of particles of the magnetocalorically active phase if
the magnetocalorically active phase is in the ferromagnetic state.
If the magnetocalorically active phase is ferromagnetic at
temperatures below its Curie Temperature, the magnetic field may be
applied at a temperature below the Curie temperature of the
magnetocalorically active phase in order to magnetically align the
particles so that at least some of the particles have the preferred
orientation.
[0075] The magnetic field may be applied before the compaction is
carried out so as to provide a preferred orientation of the
particles of the magnetocalorically passive phase and/or
magnetocalorically active phase. This preferred orientation is
maintained during compaction and in the compacted article.
[0076] The compaction may be carried out so as to induce a
preferred texture in at least the magnetocalorically passive phase.
If the particles of the magnetocalorically passive phase have
anisotropic dimensions, the compaction may be carried out by
arranging the compaction direction so that it is generally
perpendicular to the long direction of the grains, or, in the case
of plate-like grains, generally perpendicular to the plane of the
plate. A degree of preferred orientation may also be provided by
shaking the powder in directions perpendicular to the compaction
direction before the compaction is carried out. This encourages
plate-like grains to take on a stratified structure before
compaction.
[0077] The compaction is carried out so that the grains of the
magnetocalorically passive phase are on average orientated with
their long direction perpendicular to the first direction of the
article. This produces an article with a higher average thermal
conductivity in directions perpendicular to the first direction and
a lower average thermal conductivity in the first direction.
[0078] In an embodiment, the average preferred orientation of at
least the plurality of grains of the magnetocalorically passive
phase and/or of the magnetocalorically active phase is produced at
least in part by mechanical deformation of the article after the
compaction. The mechanical deformation may be carried out by one of
more of rolling, swaging, drawing and extruding.
[0079] In an embodiment, the magnetocalorically active phase and
the magnetocalorically passive phase are assembled by intimately
mixing the magnetocalorically active phase and the
magnetocalorically passive phase with one another. This method
produces an article with an anisotropic thermal conductivity
produced on a microscopic scale.
[0080] In a further embodiment, the magnetocalorically active phase
and the magnetocalorically passive phase are assembled by
alternately arranging layers consisting essentially of the
magnetocalorically active phase interleaved with layers consisting
essentially of the magnetocalorically passive phase. This method
produces an article with an anisotropic average thermal
conductivity on a macroscopic scale.
[0081] In an embodiment, additionally one or more of a lubricant,
an organic binder and a dispersant are added to the assembled
magnetocalorically active phase and magnetocalorically passive
phase. These additives can help to increase the density of the
article.
[0082] The assembled magnetocalorically active phase and
magnetocalorically passive phase may be compacted by one or more of
rolling and pressing. Rolling may be used to produced a long length
article in which the thermal conductivity in directions along the
length of the article and across its breadth is greater than the
thermal conductivity in a direction across its thickness. Such
articles can be arranged in a laminated stack. Pressing may be used
to produce an article in which the thermal conductivity is greater
across the breadth of the article than along its length as the long
direction of the magnetocalorically passive phase are orientated
generally perpendicularly to the length of the article.
[0083] In a further embodiment, the article is heated during
compaction. A heat treatment may be used to further compact the
article as well as sinter the grains together. If precursor is
used, the heat treatment is carried out under conditions selected
so that the magnetocalorically active phase is formed from the
precursor.
[0084] A heat treatment during compaction may also be used to
further increase the degree of texture of the grains due to
reorientation of the grains as well as grain growth in a preferred
direction, advantageously the long direction of the grains.
[0085] In a further embodiment, a magnetic field is applied during
compaction so as to magnetically orientate the grains of the
magnetocalorically passive phase and/or active phase so that on
average their long direction is oriented generally perpendicular to
the first direction of the article. Heat may also be applied at the
same time. This method may be used when the magnetocalorically
passive phase comprises a soft magnetic material such as Fe or FeSi
or when the magnetocalorically active phase has already formed and
is ferromagnetic during the pressing process.
[0086] A method of manufacturing an article without a
magnetocalorically passive phase and with an average anisotropic
thermal conductivity is also provided. In this method, at least one
first plate consisting essentially of a magnetocalorically active
phase and having a first density and at least one second plate
consisting essentially of a magnetocalorically active phase and
having a second density is provided. The first density of the first
plate is greater than the second density of the second plate. The
first plate and the second plate are arranged in a stack to provide
an article for magnetic heat exchange.
[0087] The first and the second plates have differing average
thermal conductivities due to their differing densities. A higher
density provides a higher average thermal conductivity. Therefore
the average thermal conductivity in the stack direction, that is
perpendicular to the plane of the plates is lower than the average
thermal conductivity in the plane of the plates.
[0088] In an embodiment, the first plate and the second plate are
arranged so that they are in physical contact with one another.
[0089] In a further embodiment, the first plate comprises a first
porosity and the second plate comprises a second porosity, the
second porosity being greater than the first porosity. This
provides a first plate with a greater density than the second
plate.
[0090] The first plate and/or the second plate may be produced by
compacting particles of a magnetocalorically active phase or
precursor of a magnetocalorically active phase.
[0091] The conditions of the compaction are adjusted so as to
produce a lower porosity in the first plate than in the second
plate. For example, the compaction pressure and, if used,
temperature, can be increased to lower the porosity and increase
the density of the plate. Conversely, the compaction pressure and,
if used, temperature, can be decreased to increase the porosity and
decrease the density of the plate.
[0092] In a further embodiment, a plurality of first plates and a
plurality of second plates are provided. The plurality of first
plates and the plurality of second plates are interleaved with one
another in a stacking direction of the article. The article
produced has a multi-layer or stratified structure.
[0093] In a particular embodiment, after the article is compacted
or after the article has been produced, an outer protective coating
may be applied to the article. The outer protective coating may be
for example, applied by dipping, spraying or
electro-deposition.
[0094] FIG. 1 illustrates a side view of an article 1 for magnetic
heat exchange which comprises a magnetocalorically active phase 2
which, in this particular embodiment, consists essentially of a
La(Fe.sub.1-a-bCo.sub.aSi.sub.b).sub.13-based phase with a Curie
Temperature, T.sub.c, of 20.degree. C. The article 1 provides the
magnetic refrigerant working component of a non-illustrated
magnetic heat exchange system which further includes a pumped
recirculation system, a heat exchange medium, such as a fluid
coolant, and means for applying a magnetic field to the
chamber.
[0095] The article 1 has a first length 1 and a second length b
extending generally perpendicularly to the first length 1. The
direction of the coolant flow is indicated in FIG. 1 by the arrows
3. Depending on whether the heat exchange system is used to provide
refrigeration or to provide heating, the coolant may flow in two
opposing directions. In operation, the first length 1 of the
article 1 is arranged so that it extends in the coolant flow
direction 3 and the second length b is arranged so that it extends
generally perpendicularly to the coolant flow direction 3. In the
view illustrated in FIG. 1, the coolant direction is from top to
bottom. The article 1 is also provided with a plurality of channels
4 in its outer surface which extend in the direction of the coolant
flow 3 and increase the surface area of the article 1 so as to
improve the effectiveness of the heat transfer from the article 1
to the coolant.
[0096] According to the invention, the article 1 has an anisotropic
average thermal conductivity. In particular, the average thermal
conductivity of the article in the direction of the coolant flow 3
is lower than the average thermal conductivity of the article 1 in
directions perpendicular to the coolant flow 3, indicated by the
arrows 5, in which the second length b of the article 1
extends.
[0097] This arrangement enables the magnetically induced heat
produced by the magnetocalorically active phase 2 within the
article 1 to be conducted efficiently to the outer surfaces 6 of
the article 1 in the direction of the arrows 5 and from there to
the coolant while at the same time preventing conduction of the
magnetically induced heat within the article in directions opposing
the coolant flow direction 3. This prevents a type of internal
short circuit within the article 1 in which heat carried from the
cold end 7 to the hot end 8 by the coolant is simply conducted back
to the cold end 7 by the article 1 itself.
[0098] FIG. 2 illustrates a cross-sectional view of the article 1
of FIG. 1. The cross-sectional view of FIG. 2 illustrates that the
article 1 has a layered structure and comprises three active
portions 9, 10, 11, each comprising a magnetocalorically active
phase 2. Each of the three active portions 9, 10, 11 comprises a
magnetocalorically active phase having a different T.sub.c such
that the T.sub.c of each active portion increases in the direction
of coolant flow 3. Each active portion 9, 10, 11 is separated from
its neighbour by a thermal barrier 12 which further prevents
thermal conductivity between adjacent portions 9, 10, 11 of the
article 1.
[0099] Each portion 9, 10, 11 further comprises a
magnetocalorically passive phase 13 which has a greater thermal
conductivity than the thermal conductivity of the
magnetocalorically active phase 2. The anisotropic average thermal
conductivity of the article 1 is provided by providing the grains
14 of the magnetocalorically passive phase 13 in a layered type
arrangement. The layered arrangement may be provided
microscopically, as illustrated in FIGS. 3 and 5, or
macroscopically, as illustrated in FIGS. 2 and 4. Arrangements
including a combination of both microscopic and microscopic
layering may also be used.
[0100] In the embodiment illustrated in FIG. 3, the
magnetocalorically passive phase 13 comprises a plurality of grains
14 having a general plate-like form and for illustrative purposes
only illustrated in the drawing as black shaded, filled rectangular
plates. The plate-like grains 14 have a long direction 15 and a
short direction 16 which is arranged generally perpendicularly to
the long direction 15. The plate-like grains 14 are arranged within
the article 1 such that on average the long direction 15 extends in
directions parallel to the second length b of the article 1 and
generally perpendicular to the coolant flow direction 3. The short
direction 16 of the grains 14 extends on average generally parallel
to the first length 1 of the article and parallel to the coolant
flow direction 3.
[0101] The plurality of grains 14 of the magnetocalorically passive
phase 13 are arranged within the article such that they have a
preferred orientation and/or preferred texture. Preferred
orientation is used to denote the physical arrangement of the
grains and preferred texture is used to denote the crystallographic
orientation of the grains. Due to this preferred orientation and/or
texture, the average thermal conductivity of the article 1 in
directions perpendicular to the coolant flow direction 3 is higher
than the average thermal conductivity of the article 1 in
directions parallel to the coolant flow direction 3.
[0102] The grains 17 of the magnetocalorically active phase 2 are,
in this embodiment, generally isotropic in comparison to the grains
14 of the magnetocalorically passive phase 13 and for illustrative
purposes only are illustrated in the drawing as open, white areas
of variable outline. The grains 17 of the magnetocalorically active
phase 2 are illustrated in FIG. 3 as distributed among the grains
14 of the magnetocalorically passive phase 13 and forming a matrix
therefore. Alternatively, the magnetocalorically passive phase 13
may provide the matrix of the article 1 and act as a binder for the
grains 17 of the magnetocalorically active phase 2. The embodiment
illustrated in FIG. 3 provides an article 1 comprising anisotropic
average thermal conductivity due to the distribution of the grains
14 of the magnetocalorically passive phase 13 on the microscopic
scale.
[0103] In the second embodiment illustrated in FIG. 4, the grains
14 of the magnetocalorically passive phase 13 also have a generally
plate-like form. The grains 14 are also arranged in the article 1
with a preferred orientation such that their long direction 15
extends in directions generally parallel to the second length b of
the article 1 and in directions generally perpendicular to the
coolant flow direction 3.
[0104] In the second embodiment of FIG. 4, as in the embodiment of
FIG. 2, the anisotropic thermal conductivity of the article 1 is
provided by a layered structure in which layers 18 consisting
essentially of a magnetocalorically active phase 2 are interleaved
with layers 19 consisting essentially of a magnetocalorically
passive phase 13. In the embodiment illustrated in FIG. 4, the
anisotropic average thermal conductivity of the article 1 is
provided macroscopically.
[0105] A single layer 19 of a magnetocalorically passive phase 13
sandwiched between two layers 18 of magnetocalorically active phase
2 are illustrated in FIG. 4, although any number of layers can be
provided. The stacked arrangement of layers 18, 19 is built up in
the direction of the first length 1 of the article 1.
[0106] The magnetocalorically passive phase 13 may be a metal and
in some embodiments, is magnetic. A magnetic magnetocalorically
passive phase 13 has the advantage that the grains 14 can be
aligned magnetically to produce the preferred orientation.
[0107] The article 1 may also comprise an outer coating 20 in order
to protect the article 1 and, in particular, the magnetocalorically
active phase 2, from corrosion by the environment and, in
particular, by the coolant.
[0108] The article 1 of FIG. 3 may be fabricated by intimately
mixing a powder of a magnetocalorically active phase 2 and a powder
of a magnetocalorically passive phase 13 and compacting the
resulting mixture. The preferred orientation of the grains 14 of
the magnetocalorically passive phase 13 may occur at least partly
as a result of settling of the powder in the mould in which the
powder mixture is compacted. The preferred orientation of the
grains 14 may also be induced by the compaction process. The
direction of pressure exerted during the compaction process is
generally perpendicular to the long direction 16 of the plate-like
grains 14 so that the plate-like grains 14 are encouraged to lie
with their long direction perpendicular to the direction of
compaction. Furthermore, the plate-like grains 14 may slide over
one another so increasing the degree of preferred orientation.
[0109] The degree of preferred orientation and/or texture may also
be increased by applying heat during the compaction process. The
heat may encourage sintering of the grains which, given a preferred
growth direction, can further increase the anisotropy of the
plate-like grains and the degree of preferred orientation.
[0110] The preferred orientation of the grains may also be at least
in part produced by alignment processes which take place before or
after compaction. The preferred orientation may also be achieved
substantially separate from the compaction process.
[0111] In a further embodiment, the magnetocalorically passive
phase may be provided by a magnetic material and a magnetic field
applied so as to induce preferred orientation in the desired
direction within the article 1. The magnetic field may be applied
before and/or during compaction. Furthermore, a heat treatment may
also be applied at the same time as the magnetic field.
[0112] The article 1 may also be fabricated by reaction sintering.
In this embodiment, precursor of the magnetocalorically active
phase is provided. The precursor consists of non-magnetocalorically
active phases in amounts to produce the magnetocalorically active
phase when they react with one another. The precursor may be
intimately mixed with the magnetocalorically passive phase to
produce an anisotropically thermally conductive article at a
microscopic scale. The precursor of the magnetocalorically active
phase may also be provided as a discreet layer or layers within a
macroscopically layered arrangement similar to that illustrated in
FIG. 4. After or during compaction, the article is heated so as to
reaction sinter the precursor and form the magnetocalorically
active phase.
[0113] The preferred orientation of the magnetocalorically passive
phase may also be achieved by other methods known in the art. For
example, the magnetocalorically passive phase could be subjected to
a rolling treatment or may be provided as a thin layer with a
preferred orientation.
[0114] If an outer coating is provided, the coating may be applied
to the article after compaction and any heat treatment process. The
coating may be applied by e.g., dipping, spraying or
electroplating.
[0115] In a further embodiment, illustrated in FIG. 5, the
magnetocalorically active phase 2 also comprises grains 21 having
an elongate form. For illustrative purposes only, the grains 21 of
the magnetocalorically active phase 2 are shaded black and the
grains 14 of the magnetocalorically passive phase 13 are left
unshaded. In this embodiment, the magnetocalorically active phase 2
is also arranged in the article 1 with a preferred orientation such
that the long direction 22 of the grains 21 extends in directions
generally perpendicular to the coolant flow direction 3 and the
short direction 23 of the grains 21 extends in the direction of the
coolant flow 3.
[0116] FIG. 6 illustrates an embodiment of an article 1 for use as
the working component of a magnetic heat exchange system according
to a fourth embodiment.
[0117] The article 1 of the fourth embodiment comprises a plurality
of grains 17 of a magnetocalorically active phase 2 and a plurality
of grains 14 of a magnetocalorically passive phase 13. For
illustrative purposes only, the grains 17 are unshaded and the
grains 14 are shaded black. On average, each of the grains 14
and/or 17 has a shape which is generally isotropic (e.g., generally
spherical). In this embodiment, the article 1 has anisotropic
thermal conductivity due to the preferred orientation of the
isotropically-shaped grains 14 of the magnetocalorically passive
phase 13.
[0118] The generally spherical grains 14 of the magnetocalorically
passive phase 13 comprises a ferromagnetic material, in this case
iron. The grains 14 are arranged in a plurality of rows or chains
24 having a long direction which extends in directions generally
parallel to the second direction 5 and perpendicular to the coolant
flow direction 3 of the article 1. The chains 24 are arranged in a
series of layers arranged one above the other in the stack
direction 28 which is parallel to the coolant flow direction 3. The
grains 17 of the magnetocalorically active phase 2 are arranged
between the chains 24 of the magnetocalorically passive phase 13
and also have a degree of preferred orientation. The preferred
orientation of the magnetocalorically active phase 2 is produced as
a result of the pre-formation of a preferred orientation in the
magnetocalorically passive phase 13.
[0119] The thermal conductivity of the magnetocalorically passive
phase 13 is greater than the thermal conductivity of the
magnetocalorically active phase 2. The article 1, therefore, has on
average an anisotropic thermal conductivity. In particular, the
thermal conductivity of the article 1 is greater in the second
direction 5 than in the coolant flow direction 3.
[0120] The article 1 of the fourth embodiment illustrated in FIG. 6
is fabricated by intimately mixing particles of the
magnetocalorically active phase 2 and particles of the
magnetocalorically passive phase 13 and placing these in a
compaction vessel such as a die. A magnetic field is applied in the
second direction 5 which causes the ferromagnetic particles of the
magnetocalorically passive phase 13 to align themselves in the
direction of the applied magnetic field to create the plurality of
chains 24.
[0121] The preferred orientation of the grains 17 of the
magnetocalorically active phase 2 occurs due to the restriction of
the movement of the particles of the magnetocalorically active
phase 2 within the article 1 due to the pre-formation of the
aligned chains 24 of the particles of the magnetocalorically
passive phase 13.
[0122] In a further embodiment, the magnetocalorically active phase
2 is ferromagnetic at temperatures below its Curie temperature.
Therefore, if the magnetic field is applied to the powder mixture
at temperatures below the Curie temperature of the
magnetocalorically active phase 2, a preferred orientation of the
particles of the magnetocalorically active phase 2 in the direction
of the applied magnetic field can also be achieved.
[0123] FIG. 7 illustrates an article 1' for use as the working
component of a magnetic heat exchange system according to a fifth
embodiment.
[0124] The article 1' of the fifth embodiment consists essentially
of one or more magnetocalorically active phases 2. For purposes of
illustration, these phases are depicted as unshaded areas. The
article 1' of the fifth embodiment is free from magnetocalorically
passive phases. The anisotropic average thermal conductivity of the
article 1' is provided, in this embodiment, by an anisotropic
distribution of the density of the article 1' and, in particular,
and anisotropic distribution of the porosity of the article 1'.
[0125] The article 1' of the fifth embodiment includes a plurality
of layers of which five are illustrated in FIG. 7. Three first
layers 25 have a relatively low porosity and two second layers 26,
which are arranged between adjacent first layers 25, include a
higher degree of porosity than that of the first layers 25. In the
illustration of FIG. 7, the pores 27 are indicated by the black
shaded regions.
[0126] The pores have a lower thermal conductivity than the
magnetocalorically active phase 2. Therefore, the second layers 26
have a lower average thermal conductivity than the first layers 25.
This provides an article 1' with an average thermal conductivity
measured from end to end of the article in the coolant flow
direction 3 which is less than the average thermal conductivity
measured from the side face to side face of the article 1' in the
second direction 5.
[0127] The multilayer or laminated article 1' of the fifth
embodiment may be fabricated by stacking a plurality of layers of
differing densities or porosities together. In particular, layers
25 having a higher density are interleaved with layers 26 having a
lower density. The layers 25, 26 are stacked directly on top of one
another in the stack direction 28 so that each layer is in physical
contact with its immediate neighboring layer. The layers 25, 26 may
be fixedly attached to their neighbour by an adhesive.
[0128] The article 1' of the fifth embodiment may be fabricated by
first fabricating a plurality of first layers 25 in the form of
plates or foils having a first density. A plurality of second
layers 26 in the form of plates or foils may be fabricated having a
second density which is lower than the first density.
[0129] The first layers 25 and second layers 26 are stacked
alternately on top of one another joining each layer 25, 26 to the
underlying one to produce article 1'.
[0130] The plates or foils which form layers 25, 26 may be
fabricated by compacting particles of a magnetocalorically active
phase which then form grains of magnetocalorically active phase 2.
The density of the plates and foils can be adjusted by adjusting
the compaction conditions. For example, the compaction pressure
and, if a heat treatment is used, the temperature and time of the
heat treatment may be increased to achieve a higher density in the
plate or foil.
[0131] The article 1' of the fifth embodiment may also further
comprise an outer protective coating, thermal barrier layers, a
corrosion protection coating covering the grains of the
magnetocalorically active phase as described in connection with the
previous embodiments.
[0132] The invention having been described with reference to
certain specific embodiments, it will be understood that these
specific embodiments are provided in order to illustrate, and not
limit, the scope of the appended claims.
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