U.S. patent application number 13/551938 was filed with the patent office on 2013-01-24 for system and method for reverse degradation of a magnetocaloric material.
The applicant listed for this patent is Steven A. JACOBS, Carl B. ZIMM. Invention is credited to Steven A. JACOBS, Carl B. ZIMM.
Application Number | 20130019610 13/551938 |
Document ID | / |
Family ID | 47554784 |
Filed Date | 2013-01-24 |
United States Patent
Application |
20130019610 |
Kind Code |
A1 |
ZIMM; Carl B. ; et
al. |
January 24, 2013 |
SYSTEM AND METHOD FOR REVERSE DEGRADATION OF A MAGNETOCALORIC
MATERIAL
Abstract
A method includes identifying at least partial degradation of a
magnetocaloric material in a magnetic cooling system, wherein the
magnetiocaloric material has a Curie temperature. The method also
includes regenerating the magnetocaloric material by maintaining
the magnetocaloric material at a regenerating temperature, wherein
the regenerating temperature is different from the Curie
temperature of the magnetocaloric material.
Inventors: |
ZIMM; Carl B.; (Madison,
WI) ; JACOBS; Steven A.; (Madison, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ZIMM; Carl B.
JACOBS; Steven A. |
Madison
Madison |
WI
WI |
US
US |
|
|
Family ID: |
47554784 |
Appl. No.: |
13/551938 |
Filed: |
July 18, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61509381 |
Jul 19, 2011 |
|
|
|
Current U.S.
Class: |
62/3.1 |
Current CPC
Class: |
Y02B 30/00 20130101;
F25B 2321/002 20130101; F25B 21/00 20130101; H01F 1/012 20130101;
Y02B 30/66 20130101; F25B 2321/0022 20130101 |
Class at
Publication: |
62/3.1 |
International
Class: |
F25B 21/00 20060101
F25B021/00 |
Claims
1. A method comprising: identifying at least partial degradation of
a magnetocaloric material in a magnetic cooling system, wherein the
magnetiocaloric material has a Curie temperature; and regenerating
the magnetocaloric material by maintaining the magnetocaloric
material at a regenerating temperature, wherein the regenerating
temperature is different from the Curie temperature of the
magnetocaloric material.
2. The method of claim 1, wherein the regenerating temperature
differs from the Curie temperature by at least five degrees
Celcius.
3. The method of claim 1, wherein the regenerating temperature
differs from the Curie temperature by at least ten degrees
Celcius.
4. The method of claim 1, wherein the magnetocaloric material
includes hydrogen, wherein the regenerating temperature is below a
maximum temperature, and wherein the maximum temperature is a
temperature at which at least a portion of the hydrogen will begin
to leave the magnetocaloric material.
5. The method of claim 1, wherein the magnetocaloric material
comprises RE(TM.sub.xSi.sub.y).sub.13H.sub.z, where RE is a rare
earth element and TM is a transition metal.
6. The method of claim 1, further comprising suspending an active
magnetic regenerator cycle of the magnetic cooling system while the
magnetocaloric material is maintained at the regenerating
temperature.
7. The method of claim 1, further comprising: removing the
magnetocaloric material from the magnetic cooling system such that
the magnetocaloric material is maintained at the regenerating
temperature remote from the magnetic cooling system; and replacing
the magnetocaloric material with a regenerated magnetocaloric
material.
8. The method of claim 1, wherein regenerating comprises reversing
age splitting of the magnetocaloric material.
9. A method comprising: forming at least one bed of a magnetic
cooling system, wherein the at least one bed includes a
magnetocaloric material, wherein the magnetocaloric material has a
Curie temperature, and wherein a heat transfer fluid is configured
to transfer heat to or from the magnetocaloric material in the at
least one bed; forming at least one valve of the magnetic cooling
system to control a flow of the heat transfer fluid through the at
least one bed and either a heater or a heat exchanger, wherein flow
of the heat transfer fluid between the at least one bed and the
heater regenerates the magnetocaloric material by maintaining the
magnetocaloric material at a regenerating temperature, and wherein
the regenerating temperature is different from the Curie
temperature of the magnetocaloric material.
10. The method of claim 9, wherein flow of the heat transfer fluid
between the at least one bed and the heat exchanger cools the
magnetocaloric material.
11. The method of claim 9, wherein the at least one bed comprises a
plurality of layers, wherein each layer of the at least one bed
includes a distinct magnetocaloric material having a distinct Curie
temperature, and wherein the distinct Curie temperature of the
distinct magentocaloric material in a given layer is an average
temperature of the given layer during an active magnetic
regenerator cycle.
12. An apparatus comprising: a heat transfer fluid; a bed
comprising a magnetocaloric material that has a Curie temperature,
wherein the bed is configured to allow the heat transfer fluid to
transfer heat to or from the magnetocaloric material; and a heater
configured to maintain the magnetocaloric material at a
regenerating temperature for an amount of time to regenerate the
magnetocaloric material, wherein the regenerating temperature is
different from the Curie temperature of the magnetocaloric
material.
13. The apparatus of claim 12, wherein the heater is configured to
heat the bed via the heat transfer fluid.
14. The apparatus of claim 12, wherein the regenerating temperature
is greater than the Curie temperature.
15. The apparatus of claim 12, wherein the bed comprises a
plurality of magnetocaloric materials having distinct Curie
temperatures, and wherein the regenerating temperature is greater
than a largest of the distinct Curie temperatures.
16. The apparatus of claim 12, wherein the heater is remote from
the bed, and wherein the bed is configured to be temporarily
removed from the apparatus for regeneration by the heater.
17. A heat transfer system comprising: a first subsystem
comprising: a first heat transfer fluid; a first bed having a first
magnetocaloric material, wherein the first magnetocaloric material
has a first Curie temperature; and a first valve configured to
control whether the first subsystem operates in regeneration mode
or cooling mode; and a second subsystem comprising: a second heat
transfer fluid; a second bed having a second magnetocaloric
material, wherein the second magnetocaloric material has a second
Curie temperature; and a second valve configured to control whether
the second subsystem operates in regeneration mode or cooling
mode.
18. The heat transfer system of claim 17, wherein: the first valve
is configured to control the first subsystem to operate in the
cooling mode and the second valve is configured to control the
second subsystem to operate in the regenerating mode during a first
period of time; and the first valve is configured to control the
first subsystem to operate in the regenerating mode and the second
valve is configured to control the second subsystem to operate in
the cooling mode during a second period of time.
19. The heat transfer system of claim 17, wherein the first valve
is configured to control the first subsystem to operate in the
cooling mode and the second valve is configured to control the
second subsystem to operate in the cooling mode during a given
period of time.
20. The heat transfer system of claim 17, wherein: the first bed
comprises a first plurality of layers, wherein each layer of the
first bed includes a distinct magnetocaloric material having a
distinct Curie temperature, and wherein the first subsystem
comprises a cold stage such that the distinct Curie temperatures of
the distinct magnetocaloric materials in the first plurality of
layers are in a range between T.sub.c and T.sub.m; and the second
bed comprises a second plurality of layers, wherein each layer of
the second bed includes a distinct magnetocaloric material having a
distinct Curie temperature, and wherein the second subsystem
comprises a hot stage such that the distinct Curie temperatures of
the distinct magnetocaloric materials in the second plurality of
layers are in a range between T.sub.m and T.sub.h, wherein
T.sub.h>T.sub.m>T.sub.c.
21. The heat transfer system of claim 20, wherein the first heat
transfer fluid is at a temperature of T.sub.c when the cold stage
operates in the cooling mode, and wherein at least one of the first
valve and the second valve direct the first heat transfer fluid at
the temperature of T.sub.c through the hot stage to regenerate the
hot stage.
22. The heat transfer system of claim 20, wherein the second heat
transfer fluid is at a temperature of T.sub.h when the hot stage
operates in the cooling mode, and wherein at least one of the first
valve and the second valve direct the second heat transfer fluid at
the temperature of T.sub.h through the cold stage to regenerate the
cold stage.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional Patent
Application No. 61/509,381 filed Jul. 19, 2011, the entire
disclosure of which is hereby incorporated by reference in its
entirety.
BACKGROUND
[0002] The following description is provided to assist the
understanding of the reader. None of the information provided or
references cited is admitted to be prior art.
[0003] The strong interaction of a ferromagnetic material, such as
iron, with an applied magnetic field derives from the ability of
the atomic spins in the material structure to coherently align
themselves with the applied field. Above a certain temperature,
which is characteristic of the magnetic material and called the
Curie temperature, thermal agitation prevents this coherent spin
alignment, and the interaction with the applied field becomes much
weaker. Above the Curie temperature, the material is paramagnetic,
rather than ferromagnetic. Near the Curie temperature, the coherent
alignment of atomic spins in an applied field results in a decrease
in the magnetic entropy of the material. If the material is
thermally isolated, so that its total entropy is conserved, this
decrease in its magnetic entropy is compensated by an increase in
its thermal entropy, and its temperature rises. This rise in
temperature upon exposure to a magnetic field is known as the
magnetocaloric effect. When the applied field is removed, the
magnetic entropy rises and the thermal entropy decreases, lowering
the temperature of the material.
SUMMARY
[0004] An illustrative method includes identifying at least partial
degradation of a magnetocaloric material in a magnetic cooling
system, wherein the magnetiocaloric material has a Curie
temperature. The method also includes regenerating the
magnetocaloric material by maintaining the magnetocaloric material
at a regenerating temperature, wherein the regenerating temperature
is different from the Curie temperature of the magnetocaloric
material.
[0005] Another illustrative method includes forming at least one
bed of a magnetic cooling system, wherein the at least one bed
includes a magnetocaloric material, wherein the magnetocaloric
material has a Curie temperature, and wherein a heat transfer fluid
is configured to transfer heat to or from the magnetocaloric
material in the at least one bed. The method also includes forming
at least one valve of the magnetic cooling system to control a flow
of the heat transfer fluid through the at least one bed and either
a heater or a heat exchanger, wherein flow of the heat transfer
fluid between the at least one bed and the heater regenerates the
magnetocaloric material by maintaining the magnetocaloric material
at a regenerating temperature, and wherein the regenerating
temperature is different from the Curie temperature of the
magnetocaloric material.
[0006] An illustrative apparatus includes a heat transfer fluid and
a bed comprising a magnetocaloric material that has a Curie
temperature. The bed is configured to allow the heat transfer fluid
to transfer heat to or from the magnetocaloric material. The
apparatus also includes a heater configured to maintain the
magnetocaloric material at a regenerating temperature for an amount
of time to regenerate the magnetocaloric material, wherein the
regenerating temperature is different from the Curie temperature of
the magnetocaloric material.
[0007] An illustrative system includes a first subsystem and a
second subsystem. The first subsystem includes a first heat
transfer fluid and a first bed having a first magnetocaloric
material, wherein the first magnetocaloric material has a first
Curie temperature. The first subsystem also includes a first valve
configured to control whether the first subsystem operates in
regeneration mode or cooling mode. The second subsystem includes a
second heat transfer fluid and a second bed having a second
magnetocaloric material, wherein the second magnetocaloric material
has a second Curie temperature. The second subsystem also includes
a second valve configured to control whether the second subsystem
operates in regeneration mode or cooling mode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The foregoing and other features of the present disclosure
will become more fully apparent from the following description and
appended claims, taken in conjunction with the accompanying
drawings. Understanding that these drawings depict only several
embodiments in accordance with the disclosure and are, therefore,
not to be considered limiting of its scope, the disclosure will be
described with additional specificity and detail through use of the
accompanying drawings.
[0009] FIG. 1 is a diagram illustrating the magnetocaloric effect
in gadolinium (Gd) in accordance with an illustrative
embodiment.
[0010] FIG. 2 is a diagram illustrating stages of an active
magnetic regenerator cycle in accordance with an illustrative
embodiment.
[0011] FIG. 3 illustrates a comparison between the isothermal
entropy change in a 1.0 Tesla field (left panel) and heat capacity
(right panel) of LaFeSiH and Gd in accordance with an illustrative
embodiment.
[0012] FIG. 4 illustrates minimum and maximum fluid temperatures
over the refrigeration cycle as functions of position in a magnetic
refrigeration bed in accordance with an illustrative
embodiment.
[0013] FIG. 5 is a diagram illustrating the performance of a
magnetic refrigeration prototype with 5-layer LaFeSiH beds as
compared to a magnetic refrigeration prototype with single-layer Gd
beds in accordance with an illustrative embodiment.
[0014] FIG. 6 illustrates a differential scanning calorimetry (DSC)
trace of a pristine sample of LaFeSiH in accordance with an
illustrative embodiment.
[0015] FIG. 7 presents the DSC trace of the same material in FIG. 6
after being held close to its Curie temperature for over one year
in accordance with an illustrative embodiment.
[0016] FIG. 8 is a diagram illustrating the recovery of age-split
LaFeSiH by exposure to elevated temperatures in accordance with an
illustrative embodiment.
[0017] FIG. 9 is a diagram illustrating the recovery of age-split
LaFeSiH by exposure to lowered temperature in accordance with an
illustrative embodiment.
[0018] FIG. 10 is a diagram of an active magnetic regenerator type
refrigerator operating in cooling mode in accordance with an
illustrative embodiment.
[0019] FIG. 11 is a diagram of an active magnetic regenerator type
refrigerator operating in recovery mode in accordance with an
illustrative embodiment.
[0020] FIG. 12 is a diagram of an active magnetic regenerator
cooling system with two dual stage subsystems in accordance with a
first illustrative embodiment.
[0021] FIG. 13 is a diagram of an active magnetic regenerator
cooling system with two dual stage subsystems in accordance with a
second illustrative embodiment.
DETAILED DESCRIPTION
[0022] In the following detailed description, reference is made to
the accompanying drawings, which form a part hereof. In the
drawings, similar symbols typically identify similar components,
unless context dictates otherwise. The illustrative embodiments
described in the detailed description, drawings, and claims are not
meant to be limiting. Other embodiments may be utilized, and other
changes may be made, without departing from the spirit or scope of
the subject matter presented here. It will be readily understood
that the aspects of the present disclosure, as generally described
herein, and illustrated in the figures, can be arranged,
substituted, combined, and designed in a wide variety of different
configurations, all of which are explicitly contemplated and make
part of this disclosure.
[0023] A magnetic refrigerator (MR) uses the magnetocaloric effect
to pump heat out of a colder system and exhaust that heat to a
warmer environment. The magnetocaloric effect refers to the rise in
temperature of a material upon exposure to a magnetic field. When
the applied field is removed, the magnetic entropy rises and the
thermal entropy decreases, lowering the temperature of the
material. This temperature change is shown in FIG. 1 for gadolinium
(Gd), which is a magnetocaloric material with a Curie temperature
of about 60.degree. F. With this material initially at a
temperature of 60.degree. F., application of a 2-Tesla field, for
example, will cause a temperature rise of 10.degree. F. The
temperature change increases as the strength of the applied field
is increased.
[0024] Modern room-temperature MR systems may employ an Active
Magnetic Regenerator (AMR) cycle to perform cooling. An early
implementation of the AMR cycle can be found in U.S. Pat. No.
4,332,135, the entire disclosure of which is incorporated herein by
reference. In one embodiment, the AMR cycle has four stages, as
shown schematically in FIG. 2. The MR system in FIG. 2 includes a
porous bed of magnetocaloric material (MCM) and a heat transfer
fluid, which exchanges heat with the MCM as it flows through the
bed. In the figure, the left side of the bed is the cold side,
while the hot side is on the right. In alternative embodiments, the
hot and cold sides can be reversed. The timing and direction
(hot-to-cold or cold-to-hot) of the fluid flow is coordinated with
the application and removal of a magnetic field.
[0025] In the first stage of the cycle ("magnetization"), while the
fluid in the bed is stagnant, a magnetic field is applied to the
MCM, causing it to heat. In the second stage of the cycle
("cold-to-hot-flow"), the magnetic field over the bed is
maintained, and fluid at a fixed temperature T.sub.Ci (the cold
inlet temperature) is pumped through the bed from the cold side to
the hot side. This fluid pulls heat from each section of the bed,
cooling the bed and warming the fluid as it passes to the next
section of the bed, where the process continues at a higher
temperature. The fluid eventually reaches the temperature T.sub.Ho
(the hot outlet temperature), where it exits the bed. Typically,
this fluid is circulated through a hot side heat exchanger, where
it exhausts its heat to the ambient environment. In the third stage
("demagnetization"), the fluid flow is terminated and the magnetic
field is removed. This causes the bed to cool further. In the final
stage of the cycle ("hot-to-cold-flow"), fluid at a fixed
temperature T.sub.Hi (the hot inlet temperature) is pumped through
the bed from the hot side to the cold side in the continued absence
of the magnetic field. The fluid is cooled as it passes through
each section of the bed, reaching a temperature T.sub.Co (the cold
outlet temperature) which is the coldest temperature reached by the
fluid in the cycle. Typically, this colder fluid is circulated
through a cold side heat exchanger, where it picks up heat from the
refrigerated system, allowing this system to maintain its cold
temperature.
[0026] The time that it takes to complete execution of the four
stages of the AMR cycle is called the cycle time, and its inverse
is known as the cycle frequency. The "temperature span" of the MR
system is defined as T.sub.Hi-T.sub.Ci, which is the difference in
the inlet fluid temperatures. The AMR cycle is analogous to a
simple vapor compression cycle, where gas compression (which causes
the gas to heat) plays the role of magnetization, and where free
expansion of the gas (which drops the gas temperature) plays the
role of demagnetization. Although FIG. 2 illustrates the operation
of a single-bed MR system, in alternative embodiments, multiple
beds, each undergoing the same AMR cycle, may be combined in a
single system to increase the cooling power, reduce the system
size, or otherwise improve the implementation of the AMR cycle.
[0027] Typically, a magnetic field of 1-2 Tesla is utilized to
effectively exploit the magnetocaloric effect for refrigeration.
This field is usually provided by an assembly of powerful NdFeB
magnets. The remanent magnetization of the highest grade of NdFeB
magnets is about 1.5 Tesla. The use of a stronger field than this
would improve MR performance, but to achieve fields in excess of
the remanent magnetization, a large (and potentially prohibitive)
increase in magnet size and weight is required. Thus, 1.5 Tesla is
the field strength that provides a roughly optimum balance between
MR system size and performance. As permanent magnet technology
improves, magnets with remanent magnetizations greater than 1.5
Tesla may be obtained. In this case, the optimum field strength of
an MR system will increase accordingly.
[0028] The permanent magnet assembly is generally the most
expensive component in the MR. To make the best use of this
expensive resource, the magnetocaloric material used in the MR
should possess the strongest possible magnetocaloric effect. This
material should also avoid the use of any toxic, reactive, or rare
(and therefore expensive) constituents. The former consideration
rules out the commercial use of Gd, for example, which is nontoxic,
inert, and inexpensive but has a weak magnetocaloric effect. MR
systems employing Gd, or other materials of comparable
magnetocaloric strength, would be too large for commercial utility.
Lanthanum iron silicon hydride (LaFeSiH) is one of the most
promising magnetocaloric materials for use in commercial MR
systems. A description of LaFeSiH can be found in an article by
Fujita et al. titled "Itinerant-electron metamagnetic transition
and large magnetocaloric effects in La(Fe.sub.xSi.sub.1-x).sub.13
compounds and their hydrides," Physical Review B 67 (2003), the
entire disclosure of which is incorporated by reference herein.
This material has a strong magnetocaloric effect. FIG. 3, for
example, shows the two most important measures of magnetocaloric
strength, the isothermal entropy change (left panel) in a 1.0 Tesla
field and heat capacity (right panel) of LaFeSiH. For comparison,
the same properties for Gd are also shown. Because of its greatly
enhanced magnetocaloric strength, MR systems employing LaFeSiH can
be much more compact than a system employing Gd. Although LaFeSiH
has the rare earth metal La (Lanthanum) as a constituent, it
remains inexpensive as La is one of the most abundant of these
elements.
[0029] In most cooling applications, the temperature span will be
substantial, typically about 30.degree. C. (54.degree. F.) or
larger. Although the overall span supported by an MR system may be
large, the temperature within a given axial section of a bed in the
system will remain within a relatively narrow range over the
refrigeration cycle. FIG. 4, for example, shows the theoretical
minimum and maximum fluid temperatures over the refrigeration cycle
as a function of axial position in the bed for a particular MR
system designed as a residential air conditioner. For this case,
although the overall temperature span is 37.degree. C., each axial
position in the bed experiences a temperature variation of only
.+-.2.degree. C. around its mean value. If the bed is composed of a
single magnetocaloric material, some regions of it will therefore
be at temperatures away from its Curie temperature. These regions
of the bed will undergo little entropy change and will have low
heat capacity (see FIG. 3). These regions will behave more like
passive regenerators and will contribute little to the cooling
power of the system. This inefficient use of bed volume can be
circumvented through the use of layered beds, which greatly enhance
the performance of a MR system. In a layered bed, each layer
contains a magnetocaloric material with Curie temperature matched
to the average temperature of that layer over the cycle. By
choosing the Curie temperatures of the layer materials in this
manner, every layer will have a strong entropy change during the
cycle and a large heat capacity. All layers will therefore
contribute actively during the refrigeration cycle, greatly
improving the overall performance of the system. In addition to
having a strong magnetocaloric effect, the Curie temperature of
LaFeSiH can be easily controlled between .+-.60.degree. C. (the
range of interest for room temperature MR systems) by varying the
hydrogen (H) content, making it ideal for use in a layered bed.
[0030] The advantages associated with the use of layered beds of
LaFeSiH are demonstrated in FIG. 5, which shows the measured
cooling power of a prototype MR system as a function of temperature
span with beds formed from 5 layers of LaFeSiH. In alternative
embodiments, fewer or more layers may be used. For comparison, the
figure also shows the performance of identical beds with a single
layer of Gd under the same operating conditions. At a temperature
span of 13.degree. C., for example, the layered LaFeSiH beds
provide over three times the cooling power of the Gd beds.
[0031] Although LaFeSiH appears to be an ideal material for use in
a MR, its properties are not stable. This material has been shown
to undergo a gradual deterioration of its magnetocaloric strength
when it is stored at a temperature very close to its Curie point,
as described in an article by A. Barcza et al. entitled "Stability
and magnetocaloric properties of sintered
La(Fe,Mn,Si).sub.13H.sub.z alloys", presented at the IEEE
International Magnetics Conference (Taipei, Taiwan) 2011, session
ED-07 (hereinafter "A. Barcza et al."), the entire disclosure of
which is incorporated by reference herein. This deterioration is
most readily observed in Differential Scanning calorimetry (DSC).
FIG. 6 illustrates the DSC trace of a pristine sample of LaFeSiH,
which has a single, sharp peak. The figure also illustrates the
width of the peak in the DSC trace. For comparison, FIG. 7 shows
the DSC trace of the same sample after it has been kept close to
its Curie temperature for over one year. When kept at a temperature
close to its Curie temperature, the DSC trace shows that the
ferromagnetic to paramagnetic phase change broadens in width and
declines in height. Eventually, the initially large and sharp
transition of this material will split into two broad, shallow
peaks ("age-splitting"), as illustrated in FIG. 7 and in A. Barcza
et al. The age-splitting of the DSC trace is accompanied by a
reduction in the entropy change of the material, as measured by
magnetometry and as also illustrated in A. Barcza et al. The rate
at which the splitting occurs depends on temperature. For LaFeSiH
with a 2.degree. C. curie point stored at 2.degree. C., significant
broadening of the peak takes about 10 days, and a split peak takes
about 60 days to form. For LaFeSiH material with a 20.degree. C.
curie point stored at 20.degree. C., a split peak develops in about
10 days. For material with a 32.degree. C. curie point stored at
32.degree. C., a split peak develops in about 5 days.
[0032] The ageing process for LaFeSiH appears to not depend on the
synthesis method, as long as the hydrogen content is less than 1.5
per formula unit. The age-splitting process was seen in material
that was arc melted, then annealed for several weeks to form the
1-13 phase, then hydrided. The age-splitting process was also seen
in material that was rapidly solidified by melt spinning or
atomization, and then annealed for a few hours or less to form the
1-13 phase, and then hydrided. The ageing process was seen in
different samples of LaFeSiH with slightly different compositions,
such as La.sub.1.29(Fe.sub.0.88Si.sub.0.12).sub.13H.sub.y and
La.sub.1.2(Fe.sub.0.888Si.sub.0.112).sub.13H.sub.y. The ageing
process was also seen in a sample of
Pr.sub.0.6La.sub.0.6(Fe.sub.0.888Si.sub.0.112).sub.13H.sub.y, where
Pr was substituted for some of the La to increase the
magnetocaloric strength. Thus, the age-splitting process will
generally occur in magnetocaloric materials of the form
RE(TM.sub.xSi.sub.1-x).sub.13H.sub.y material (where RE represents
a rare earth element such as La, Ce, Pr, or Nd, and TM represents a
transition metal such as Fe, Cr, Mn, or Ni, x<0.15, and
y<1.5). In an illustrative embodiment, the value of y can be
between approximately 0.8 and 1.5. Alternatively, a different range
of y values may be used. As discussed herein, different values of y
can be used to generate magnetocaloric materials having different
Curie temperatures.
[0033] When used in an MR system, the magnetocaloric material will
inevitably be exposed to temperatures close to its Curie
temperature. Indeed, in a layered bed, the material in a layer is
selected to have a Curie temperature equal to the average
temperature seen by that layer during the MR cycle. Thus, if
partially hydrogenated LaFeSiH, or more generally
RE(TM.sub.xSi.sub.1-x).sub.13H.sub.y, is used in an MR system, its
magnetocaloric properties will degrade over time. In spite of its
significant advantages over other magnetocaloric materials, this
degradation in the magnetocaloric properties of partially
hydrogenated RE(TM.sub.xSi.sub.1-x).sub.13H.sub.y material could
potentially preclude its use in a commercial MR system.
[0034] Applicants have discovered that when degraded
RE(TMxSi.sub.1-x).sub.13H.sub.y material is subsequently held at a
temperature away from (e.g., either a higher or a lower
temperature) its Curie point, the degradation process reverses and
eventually the properties of the material return to their initial
condition. Moreover, Applicants have found that the recovery of the
material proceeds more quickly at higher temperatures, as shown in
FIG. 8. Material (i.e., LaFeSiH) with a Curie temperature of
26.7.degree. C. was allowed to age-split by storage at this
temperature for over one year, until the width of the magnetic
transition as measured by DSC reached 14.degree. C. The original
magnetic transmission as measured by DSC was 2.1.degree. C. The
degraded material was then exposed to different temperatures as
shown in the figure (i.e., 38.5.degree. C., 44.degree. C.,
60.degree. C., and 100.degree. C.). Exposure at 44.degree. C. for
about 6 days was sufficient to completely restore the material to
its initial condition, and exposure at 60.degree. C. for about 3
days was sufficient to completely restore the material to its
initial condition. Exposure at 100.degree. C. for less than 1 day
was sufficient to obtain complete reversal of age-splitting.
Applicants have also found that age-splitting degradation of
Pr.sub.0.5La.sub.0.5(Fe.sub.1-xSi.sub.x).sub.13H.sub.y is also
completely reversible by this heat treatment. Recovery of the
original sharp magnetic transition of age-split LaFeSiH is also
obtained by exposure to lowered temperature, although the process
proceeds more slowly, as shown in FIG. 9. The LaFeSiH material
initially had a 1.2.degree. C. wide magnetic transition, that had
been widened to 4.4.degree. C. after a 6 day hold near its
37.degree. C. Curie point. Recovery was obtained by holding the
material at 5.degree. C. Recovery was complete after 100 days. In
an illustrative embodiment, the regenerating temperature used to
recover the magnetocaloric material can be less than a maximum
temperature at which hydrogen may begin to leave the magnetocaloric
material. The maximum temperature is approximately 180.degree.
C.
[0035] Because the age-splitting degradation can be completely
reversed in a relatively simple manner,
RE(TM.sub.xSi.sub.1-x).sub.13H.sub.y materials can be used in
suitably modified MR systems, which forms the basis of the subject
matter described herein. In the usual mode of operation of an MR
system with layered beds of magnetocaloric material, the material
layers will remain close to their respective Curie temperatures,
which will cause deterioration of the magnetocaloric material. In
addition, when the system is not operating, the portion of the
magnetocaloric material with Curie point near ambient temperature
may also deteriorate. As such, Applicants have developed a modified
MR system that is configured to hold the layers of magnetocaloric
material at a temperature that differs from the Curie temperature
of the magnetocaloric material to reverse whatever age-splitting
degradation may have occurred and to recover their full
magnetocaloric effect. The temperature at which the magnetocaloric
material is held, which can be higher or lower than the Curie
temperature of the magnetocaloric material, can differ from the
Curie temperature by 10.degree. C., 25.degree. C., 50.degree. C.,
100.degree. C., etc. depending on the desired rate of recovery, the
system capacity, etc. In an illustrative embodiment, temperature at
which the magnetocaloric material is held can differ from the Curie
temperature by approximately 10.degree. C.
[0036] In one illustrative embodiment, an MR system employs
RE(TM.sub.xSi.sub.1-x).sub.13H.sub.y as the magnetocaloric material
and has a heating element plumbed into the flow system. When the MR
system would otherwise be idle (e.g., a residential air conditioner
at night), the heating element can be activated. The MR system
would then circulate heated fluid through the magnetocaloric
material, completely reversing any age-splitting that may have
occurred since the last high-temperature treatment.
[0037] In the particular case of a MR system that normally absorbs
heat at a cold heat exchanger (CHEX) and exhausts heat at a hot
heat exchanger (HHEX), a heater can be plumbed in parallel with the
cold heat exchanger. In normal cooling mode, flow is directed
through the CHEX and the HHEX, as shown in FIG. 10. As illustrated
in FIG. 10, an AMR type refrigerator is operating in cooling mode,
including one or more demagnetized beds providing cooling to a cold
heat exchanger in thermal contact with the load to be cooled. One
or more magnetized beds are rejecting heat to a hot heat exchanger.
In one embodiment, each bed comprises layers of RE(TMxSi1-x)13Hy
with Curie points approximately ranging from Tc to Th, where
Th>Tc.
[0038] FIG. 11 illustrates an AMR type refrigerator operating in
recovery mode. In one embodiment, a heater in series with the beds
heats the beds to more than 10 C above the highest Curie point of
the material in the beds, and the heat exchangers are bypassed.
When the recovery mode is started, a valve switches flow away from
the cold heat exchanger and redirects the flow to the heater, as
shown in FIG. 11 and discussed in more detail below. A second valve
may be added to switch flow away from the hot heat exchanger when
in recovery mode (also see FIG. 11). These two valves thermally
isolate the MR system so it may be heated to a temperature
approximately 10.degree. C. higher than the Curie point of all
magnetocaloric materials in the system using a relatively small
amount of heater power. If either the magnet motion or fluid flow
reversal is suspended during the recovery mode, operation of the
AMR cycle is suspended, which reduces the amount of heater power
required to stay in recovery mode. Because magnet motion and fluid
flow reversal utilize additional electrical power, suspending these
operations also reduces the amount of power consumed by the system
while in recovery mode.
[0039] In an alternative embodiment, in addition to having a
heating element, a cooling system can include two independent MR
subsystems. The first MR subsystem can provide cooling as in FIG.
10, while simultaneously the beds of the second subsystem undergo
heat treatment as in FIG. 11, to reverse age-splitting. After a
certain duration under these operating conditions (e.g., 1 hour, 2
hours, 4 hours, 12 hours, etc.), the MR subsystems can be switched,
with the second subsystem providing cooling, and the first
subsystem undergoing heat treatment. Under periods of peak cooling
demand, both MR subsystems could provide cooling power. In another
alternative embodiment, the system can incorporate more than two
subsystems, with some subsystems providing cooling power while the
remaining subsystems undergo heat treatment.
[0040] In another alternative embodiment, the cooling system can
have two stages, with each stage containing layered AMR beds. The
cold stage can have Curie temperatures ranging from T.sub.c to
T.sub.m, while the hot stage can have Curie temperatures ranging
from T.sub.m to T.sub.h, where T.sub.h>T.sub.m>T.sub.c. In an
air conditioner implementation, T.sub.c may have a value of
10.degree. C., T.sub.m may have a value of 25.degree. C., and
T.sub.h may have a value of 40.degree. C. In alternative
embodiments and/or implementations, different temperature values
may be used. When recovery of the hot stage magnetocaloric material
is desired, the cold stage can operate in cooling mode, generating
a cold outlet fluid stream with temperature near T.sub.c. This cold
fluid, instead of flowing through the cold side heat exchanger, can
be directed through the hot stage to bring the hot stage
temperature near T.sub.c. Because T.sub.c is well below all Curie
temperatures in the hot stage, exposure to this temperature would
reverse any age-splitting in the hot stage. Similarly, when
recovery of the cold stage magnetocaloric material is desired, the
hot stage can operate in cooling mode and can therefore generate a
hot outlet fluid stream with a temperature near T.sub.h. This hot
fluid, instead of flowing through the hot side heat exchanger, can
be directed through the cold stage, bringing its temperature to
approximately T.sub.h. Because this temperature is well above all
Curie temperatures in the cold stage, exposure to this temperature
would reverse any age-splitting of the cold stage material.
[0041] In another alternative embodiment, the system can include
two independent MR subsystems, with each subsystem having two
stages, a hot stage and a cold stage as in the above-described
embodiment. When maximum cooling power is desired, both subsystems
can be run in parallel, with each providing cooling, as shown in
FIG. 12. In FIG. 12, the stages connected to the pump and hot HEX
have LaFeSiH as the magnetocaloric material with Curie points
ranging from Th to Tm. The stages connected to the cold HEX have
LaFeSiH MCM with Curie points ranging from Tm to Tc. In an
illustrative embodiment, the MCM with Curie point at Tm is at the
end of the bed that is connected to another bed. When less cooling
power is needed, one subsystem could be run in cooling mode, while
the other subsystem could be run in recovery mode to restore the
performance of its magnetocaloric material as shown in FIG. 13. In
this figure, the lower subsystem is providing cooling power, while
the upper subsystem is in recovery mode. At least a portion of the
cold outlet fluid stream emerging from the demagnetized beds of the
lower subsystem is diverted into the hot stage beds of the upper
subsystem. Simultaneously, part of the hot outlet fluid stream of
the magnetized beds of the lower subsystem is diverted to the cold
stage beds of the upper subsystem. This embodiment can also be
modified to incorporate more than two subsystems, with some
subsystems providing cooling power while the remaining subsystems
undergo heat treatment. Each subsystem in this generalized case
could have two stages as described above.
[0042] In another alternative embodiment, the possibly multiple
beds of a magnetic refrigeration system can be designed to be
easily removable and replaceable from the system. Beds that have
been degraded from age-splitting can then be removed and replaced
with pristine beds. In a separate device that can be physically
remote from the magnetic refrigeration system, the degraded beds
can be returned to pristine condition through exposure to
temperatures sufficiently far from the Curie temperatures of all
the layers they contain. This device, for example, could be a
simple flow loop with a heater, capable of circulating fluid at an
elevated temperature through the degraded beds, or an oven for
holding the beds at an elevated temperature. Once restored to
pristine condition, these beds can then be re-installed in the
magnetic refrigeration system.
[0043] Any of the operations described herein can be performed by a
computing system that includes a processor, a memory, a
transmitter, a receiver, a display, a user interface, and/or any
other computer components known to those of skill in the art. Any
type of computing system known to those of skill in the art may be
used. In one embodiment, any of the operations described herein can
be coded into instructions that are stored on a computer-readable
medium. A computing system can be utilized to execute the
instructions such that the operations are performed.
EXAMPLES
[0044] To verify the effect on magnetic refrigerator performance of
the age-splitting degradation, and to verify that elevated
temperature treatment was effective at reversing this degradation,
the beds of a magnetic refrigerator were packed with five layers of
La(Fe.sub.0.885Si.sub.0.115)H.sub.y material, with each layer
having a different value of y and therefore a different Curie
point. The Curie points of the layers were initially 8.degree. C.,
11.degree. C., 15.degree. C., 18.degree. C. and 21.degree. C. The
machine was tested under a standard set of operating conditions,
where the cycle frequency was 3.33 Hz, the flow rate was 6 lit/min,
the hot inlet temperature was 25.degree. C., and the cooling load,
provided by an electrical heater, was 400 watts. Before operation
as a MR, the LaFeSiH in the beds was suffused with 35.degree. C.
aqueous fluid for 80 hours to bring the material to its initial
state. The temperature span of the machine with pristine material
under the standard operating conditions was found to be
13.4.degree. C. The machine was then left in a non-operating state
at an ambient temperature of 22.degree. C. for ten days. In this
state, the materials with Curie temperatures of 18.degree. C. and
21.degree. C. would be expected to undergo age-splitting
degradation, and indeed, the temperature span of the machine after
this 10-day treatment under the standard operating conditions
dropped to only 2.9.degree. C. The LaFeSiH MCM was then suffused
with 50.degree. C. aqueous fluid for 19 hours to bring the material
to its initial state, and then the temperature span of the machine
in AMR mode at the standard condition of a cooling load of 400
watts and a hot inlet temperature of 25.degree. C. was measured to
be 13.2.degree. C. Thus bringing the LeFeSiH MCM to a temperature
more than 10.degree. C. above the Curie point of the material for
19 hours was able to restore the performance of the MCM after a
substantial reduction in performance that occurred when the MCM was
kept close to its Curie point for ten days.
[0045] The herein described subject matter sometimes illustrates
different components contained within, or connected with, different
other components. It is to be understood that such depicted
architectures are merely exemplary, and that in fact many other
architectures can be implemented which achieve the same
functionality. In a conceptual sense, any arrangement of components
to achieve the same functionality is effectively "associated" such
that the desired functionality is achieved. Hence, any two
components herein combined to achieve a particular functionality
can be seen as "associated with" each other such that the desired
functionality is achieved, irrespective of architectures or
intermedial components. Likewise, any two components so associated
can also be viewed as being "operably connected", or "operably
coupled", to each other to achieve the desired functionality, and
any two components capable of being so associated can also be
viewed as being "operably couplable", to each other to achieve the
desired functionality. Specific examples of operably couplable
include but are not limited to physically mateable and/or
physically interacting components and/or wirelessly interactable
and/or wirelessly interacting components and/or logically
interacting and/or logically interactable components.
[0046] With respect to the use of substantially any plural and/or
singular terms herein, those having skill in the art can translate
from the plural to the singular and/or from the singular to the
plural as is appropriate to the context and/or application. The
various singular/plural permutations may be expressly set forth
herein for sake of clarity.
[0047] It will be understood by those within the art that, in
general, terms used herein, and especially in the appended claims
(e.g., bodies of the appended claims) are generally intended as
"open" terms (e.g., the term "including" should be interpreted as
"including but not limited to," the term "having" should be
interpreted as "having at least," the term "includes" should be
interpreted as "includes but is not limited to," etc.). It will be
further understood by those within the art that if a specific
number of an introduced claim recitation is intended, such an
intent will be explicitly recited in the claim, and in the absence
of such recitation no such intent is present. For example, as an
aid to understanding, the following appended claims may contain
usage of the introductory phrases "at least one" and "one or more"
to introduce claim recitations. However, the use of such phrases
should not be construed to imply that the introduction of a claim
recitation by the indefinite articles "a" or "an" limits any
particular claim containing such introduced claim recitation to
inventions containing only one such recitation, even when the same
claim includes the introductory phrases "one or more" or "at least
one" and indefinite articles such as "a" or "an" (e.g., "a" and/or
"an" should typically be interpreted to mean "at least one" or "one
or more"); the same holds true for the use of definite articles
used to introduce claim recitations. In addition, even if a
specific number of an introduced claim recitation is explicitly
recited, those skilled in the art will recognize that such
recitation should typically be interpreted to mean at least the
recited number (e.g., the bare recitation of "two recitations,"
without other modifiers, typically means at least two recitations,
or two or more recitations). Furthermore, in those instances where
a convention analogous to "at least one of A, B, and C, etc." is
used, in general such a construction is intended in the sense one
having skill in the art would understand the convention (e.g., "a
system having at least one of A, B, and C" would include but not be
limited to systems that have A alone, B alone, C alone, A and B
together, A and C together, B and C together, and/or A, B, and C
together, etc.). In those instances where a convention analogous to
"at least one of A, B, or C, etc." is used, in general such a
construction is intended in the sense one having skill in the art
would understand the convention (e.g., "a system having at least
one of A, B, or C" would include but not be limited to systems that
have A alone, B alone, C alone, A and B together, A and C together,
B and C together, and/or A, B, and C together, etc.). It will be
further understood by those within the art that virtually any
disjunctive word and/or phrase presenting two or more alternative
terms, whether in the description, claims, or drawings, should be
understood to contemplate the possibilities of including one of the
terms, either of the terms, or both terms. For example, the phrase
"A or B" will be understood to include the possibilities of "A" or
"B" or "A and B."
[0048] The foregoing description of illustrative embodiments has
been presented for purposes of illustration and of description. It
is not intended to be exhaustive or limiting with respect to the
precise form disclosed, and modifications and variations are
possible in light of the above teachings or may be acquired from
practice of the disclosed embodiments. It is intended that the
scope of the invention be defined by the claims appended hereto and
their equivalents.
* * * * *