U.S. patent application number 10/694769 was filed with the patent office on 2004-09-23 for magnetocaloric refrigeration device.
Invention is credited to Chiang, Hsu-Cheng, Hu, Yie-Zu Robert, Yang, Bing-Chwen.
Application Number | 20040182086 10/694769 |
Document ID | / |
Family ID | 32734822 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040182086 |
Kind Code |
A1 |
Chiang, Hsu-Cheng ; et
al. |
September 23, 2004 |
Magnetocaloric refrigeration device
Abstract
A magnetocaloric refrigeration device, placed in a controllable
magnetic field, includes a heat release/absorption module. The heat
release/absorption module includes a magnetocaloric working unit
and at least one heat pipe. The magnetocaloric working unit is made
of a magnetocaloric material. The temperature of the unit changes
as the magnetic field is applied or removed. The heat pipe includes
evaporation and condensation portions respectively extending from
top and bottom of the magnetocaloric working unit. When a magnetic
field is applied to the magnetocaloric working unit to absorb heat,
the lower condensation portion of the heat pipe transfers heat
upward to the magnetocaloric working unit. When the magnetic field
is removed from the magnetocaloric working unit to release heat,
the heat from the magnetocaloric working unit is transferred to the
outside through the upper heat release portion. The magnetocaloric
refrigeration device has advantages of simple structure, low
production cost, and small size.
Inventors: |
Chiang, Hsu-Cheng; (Hsinchu
Hsien, TW) ; Yang, Bing-Chwen; (Hsinchu Hsien,
TW) ; Hu, Yie-Zu Robert; (Hsinchu Hsien, TW) |
Correspondence
Address: |
RABIN & BERDO, P.C.
Suite 500
1101 14th Street, N.W.
Washington
DC
20005
US
|
Family ID: |
32734822 |
Appl. No.: |
10/694769 |
Filed: |
October 29, 2003 |
Current U.S.
Class: |
62/3.1 |
Current CPC
Class: |
Y02B 30/00 20130101;
F25B 2321/0021 20130101; F25B 23/006 20130101; Y02B 30/66 20130101;
F28D 15/02 20130101; F25B 21/00 20130101; F25B 25/00 20130101 |
Class at
Publication: |
062/003.1 |
International
Class: |
F25B 021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 20, 2003 |
TW |
092204351 |
Claims
What is claimed is:
1. A magnetocaloric refrigeration device for use in a controllable
magnetic field, comprising a heat release/absorption module,
wherein the heat release/absorption module comprising: a
magnetocaloric working unit made of a magnetocaloric material,
wherein the temperature of the magnetocaloric working unit changes
as the magnetic field is alternately applied and removed; and at
least one heat pipe having an evaporation portion and a
condensation portion, wherein at least one of the evaporation and
condensation portions is connected to the magnetocaloric working
unit such that heat is transferred from the evaporation portion to
the condensation portion by a working medium contained in the heat
pipe responsive to the temperature change of the magnetocaloric
working unit.
2. The magnetocaloric refrigeration device of claim 1, wherein the
heat pipe is a one-way heat transfer element.
3. The magnetocaloric refrigeration device of claim 1, wherein the
heat pipe is attached to an external surface of the magnetocaloric
working unit.
4. The magnetocaloric refrigeration device of claim 1, wherein the
heat pipe is inserted in the magnetocaloric working unit.
5. The magnetocaloric refrigeration device of claim 1, wherein if
the heat release/absorption module has only one heat pipe, the
evaporation and condensation portions of the heat pipe are both
connected to the heat release/absorption module for heat release
and heat absorption.
6. The magnetocaloric refrigeration device of claim 5, wherein the
condensation portion of the heat pipe has an externally exposed
heat release extension formed through a top of the magnetocaloric
working unit, and the evaporation portion thereof has an externally
exposed beat absorption extension formed through a bottom of the
magnetocaloric working unit.
7. The magnetocaloric refrigeration device of claim 1, wherein if
the heat release/absorption module has at least two heat pipes, the
heat pipes are respectively a heat releasing pipe mounted on the
magnetocaloric working unit via the evaporation portion thereof,
and a heat absorbing pipe mounted on the magnetocaloric working
unit via the condensation portion thereof.
8. The magnetocaloric refrigeration device of claim 7, wherein the
condensation portion of the heat releasing pipe has an externally
exposed heat release extension formed through a top of the
magnetocaloric working unit, and the evaporation portion of the
heat absorbing pipe has an externally exposed heat absorption
extension formed through a bottom of the magnetocaloric working
unit.
9. The magnetocaloric refrigeration device of claim 1, wherein the
heat release extensions of the heat releasing pipes are spaced from
or communicative with each other.
10. The magnetocaloric refrigeration device of claim 1, wherein the
heat absorption extensions of the heat absorbing pipes are spaced
from or communicative with each other.
11. The magnetocaloric refrigeration device of claim 1, wherein a
wick structure is formed on an inner wall of the heat pipe.
12. The magnetocaloric refrigeration device of claim 1, wherein an
inner wall of the heat pipe is bare and featureless.
13. The magnetocaloric refrigeration device of claim 1, wherein the
magnetocaloric material is composed of Gd, Si and Ge in a relation
of Gd.sub.5(Si.sub.xGe.sub.1-x).sub.4.
14. The magnetocaloric refrigeration device of claim 1, wherein the
magnetocaloric working unit is filled with powders of the
magnetocaloric material.
15. The magnetocaloric refrigeration device of claim 1, wherein the
magnetocaloric working unit is made of an alloy film formed from a
deposition of the magnetocaloric material.
16. The magnetocaloric refrigeration device of claim 1, wherein a
plurality of resin layers are formed in the magnetocaloric working
unit for partitioning the magnetocaloric material.
17. The magnetocaloric refrigeration device of claim 1, wherein the
controllable magnetic field is formed by a stationary electromagnet
that alternately magnetizes and demagnetizes.
18. The magnetocaloric refrigeration device of claim 1, wherein the
controllable magnetic field is formed by a stationary
superconductive magnet that alternately magnetizes and
demagnetizes.
19. The magnetocaloric refrigeration device of claim 1, wherein the
controllable magnetic field is formed by a movable permanent
magnet.
20. The magnetocaloric refrigeration device of claim 1, further
comprising a heat exchanger through which the working medium
transfers the heat so as to form a magnetic refrigerator.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a magnetocaloric device, and more
particularly, to a magnetocaloric device having a simplified
structure, high performance, and economical manufacturing.
BACKGROUND OF THE INVENTION
[0002] A magnetocaloric effect (MCE) is caused from the
magnetization/demagnetization of a ferromagnetic material such as a
transition metal or a Lanthanide-series rare earth element.
Specifically, electrons inside the material self-spin when
subjected to an external magnetic field and are arranged in a
regular way, which causes the reduction of a magnetic entropy of
the material, resulting in an exothermal phenomenon due to the
reduced randomness of the magnetic dipole arrangements. At this
time, the temperature of the material increases. Similarly, when
the magnetic field is removed, the magnetic dipoles in the
ferromagnetic material are irregularly arranged, which increases
the randomness of the dipole arrangements, absorbing thermal
energy. At this time, the temperature of the material drops. FIG. 9
illustrates the process of the heat release and absorption known in
the art.
[0003] To reduce the greenhouse effect caused by the discharge of a
cooling medium (such as CFC used in most refrigerators) into the
environment, and to eliminate noise generated by the compressor
used in conventional cooling equipment, the magnetocaloric effect
is usually implemented to replace the traditional gas-cycle in the
conventional gas-compression type refrigerator. FIG. 10 is a
schematic view that compares the conventional gas cycle 2 with the
magnetocaloric cycle 4, illustrating the relationships respectively
between pressure and the magnetic field, and the gas volume and the
magnetization. In the gas cycle 2, the distribution of gas
molecules is changed due to gas compression and expansion, which
reduces the entropy of the gas. Specifically, the gas compression
of step a) through step b) results in an exothermic effect and an
increase in temperature. The gas expansion of step c) through step
d) results in an endothermic effect and a decrease in temperature.
In the magnetocaloric cycle 4 including two isothermal and
isomagnetic field stages, an external magnetic field is applied to
change the spin orientation of electrons inside the magnetic
material and, thereby, reduce its entropy. At step A) through step
B), when a magnetic field is applied to orderly arrange the dipoles
inside the material, the temperature of the material increases,
similar to the gas cycle stage where the gas is compressed.
Conversely, at step C) through step D) where the magnetic field has
been removed, the dipoles inside the material are irregularly
arranged and thereby the temperature of the material drops, which
draws ambient heat into the material. Although the two techniques
have similarities, the reversibility of the dipole arrangements in
the magnetocaloric cycle 4 is much greater than the reversibility
of present levels in the gas cycle 2. The change in the dipole
arrangement within the magnetocaloric cycle 4 is achieved through
applying and removing the magnetic field. This superior
characteristic of the magnetocaloric material allows a higher
energy efficiency for the magnetocaloric cycle compared to gas
cycle used in the conventional compression type refrigeration. An
intensity of only a little more than 5 Tesla (for a normal
superconductive magnet) is required to achieve more than 50-60% of
an ideal Carnot cycle. Furthermore, the temperature change in the
magnetocaloric material is more uniform than that in the gas of the
conventional compression type refrigerator.
[0004] Although refrigeration magnetocaloric has advantages such as
high energy efficiency and low environmental pollution due to the
lack of any cooling medium, its design and manufacture have some
disadvantages. It is difficult to quickly move the magnetocaloric
material in and out of the high-intensity magnetic field to
dissipate the high thermal energy absorbed by the magnetocaloric
material. Furthermore, the design of the heat exchange mechanism is
critical to achieve the highest heat transfer efficiency in a
magnetocaloric refrigerator. For example, a heat transfer fluid
having a large contact area with the magnetocaloric material may be
used and contained inside the refrigerator. Alternately, a heat
exchanger with a large heat dissipation area may be mounted in the
refrigerator. Therefore, in order to optimize the magnetocaloric
refrigerator, a magnetocaloric movement/rotation member, a magnetic
field generating device, a heat transfer pipe and valve, and one or
more heat exchangers have to be appropriately chosen, increasing
the complexity of the construction as well as the manufacturing
cost, and making it difficult to reduce the size of the device.
Furthermore, the aggregation of all the constituent pieces (valves,
etc.) may produce more noise and unstable operation than a
conventional design, which presents serious obstacles in the
development of this type of refrigerator.
[0005] The above disadvantages have been observed in practice with
commercially available magnetocaloric refrigerators. Referring to
FIG. 11, a rotary magnetocaloric refrigerator 70 is provided with a
superconductive magnet 71. A rotation disk 73 made of the
magnetocaloric material is controlled via a motor 72. Two fluid
channels 74 are oppositely disposed along the periphery of rotation
disk. As the rotation disk 73 moves in and out of the magnetic
field while rotating, the increase and decrease of the temperature
of the rotation disk 73 is caused by the magnetocaloric effect of
the magnetocaloric material. The heat transfer fluid 75 is charged
in the fluid channel 74 through a valve for heat exchange to induce
refrigeration. The flow of the heat transfer fluid is controlled
via appropriately setting the rotation speed of the rotation disk
73, for example, 10 rpm. However, the assembly of these
constituting pieces and valves is complex and uneconomical.
Furthermore, mechanical wear and operation noises are unavoidable
problems.
[0006] In FIG. 12, a movable magnetocaloric refrigerator 80,
manufactured by the TOSHIBA company, Japan, also exhibits the above
problems. In this design, a linearly transverse reciprocating
device 85 made of a movable permanent magnet 81 is located adjacent
to a magnetocaloric working unit 82. As the linearly transverse
reciprocating device 85 moves, the temperature in the
magnetocaloric working unit 82 increases. Then, a heat transfer
medium 84 is charged in under the precise control of a valve 83 for
heat exchange. However, the conveyance of the heat transfer medium
84 and the operation of the valve 83 may result in energy loss,
increasing the load. The linearly transverse reciprocating device
85 and the vale 83 not only tend to create the same drawbacks of
the rotary magnetocaloric refrigerator 70, but they also reduce
heat transfer efficiency and stability of the refrigeration
system.
[0007] Therefore, there is a need to provide a magnetocaloric
refrigeration device that overcomes the problems of the prior art,
has a simplified and smaller structure, and is more economical to
manufacture.
SUMMARY OF THE INVENTION
[0008] It is a primary object of the invention to provide a
magnetocaloric refrigeration device that has high heat transfer
efficiency.
[0009] It is another object of the invention to provide a
magnetocaloric refrigeration device that has a simple
structure.
[0010] It is another object of the invention to provide a
magnetocaloric refrigeration device that is economical to
manufacture.
[0011] It is another object of the invention to provide a
magnetocaloric refrigeration device that can be used in a compact
system.
[0012] Finally, it is another object of the invention to provide a
magnetocaloric refrigeration device that can be used in a magnetic
refrigerator, does not need valves and reciprocating devices.
[0013] To achieve the above and other objectives, the
magnetocaloric refrigeration device of the invention placed in a
controllable magnetic field comprises a heat release/absorption
module, at least one first heat pipe and at least one second heat
pipe. The heat/absorption module comprises a magnetocaloric working
unit made of a magnetocaloric material. The temperature of the unit
changes as a magnetic field is applied or removed to release or
absorb heat respectively. The first heat pipe includes a first
evaporation portion and a first condensation portion. The first
condensation portion is connected on the magnetocaloric working
unit and the first evaporation portion extends from a bottom of the
magnetocaloric working unit. The second heat pipe has a second
evaporation portion and a second condensation portion. The second
evaporation portion is connected on the magnetocaloric working
unit, and the second condensation portion extends from a top of the
magnetocaloric working unit. When the controllable magnetic field
is removed to allow heat absorption of the magnetocaloric working
unit, the heat is subsequently transferred upward to the
magnetocaloric working unit through the first evaporation portion
and the first condensation portion via flow of a working medium
through the first heat pipe. When the controllable magnetic field
is applied on the magnetocaloric working unit to release heat, the
heat is transferred to the second evaporation portion of the second
heat pipe, and further to the outside through the second
condensation portion via flowing of the working medium. Thereby, a
magnetocaloric refrigeration system is accomplished.
[0014] The magnetocaloric material is composed of Gd, Si, and Ge in
a relation of Gd.sub.5(SixGe.sub.1-x).sub.4. The magnetocaloric
material may be packed in a powder form in the magnetocaloric
working unit. Alternatively, the magnetocaloric material may be
deposited to form an alloy film for production of the
magnetocaloric working unit.
[0015] The heat pipes are mounted on the magnetocaloric working
unit. Heat absorption/release is achieved through the
magnetization/demagnetization of the magnetocaloric material, using
highly efficient heat-transfer pipes as a heat transfer mechanism.
The flow of the working medium carries away heat to be dissipated.
This system eliminates the need for highly polluting cooling
mediums, such as those used in conventional gas-cycle compressors,
and further reduces mechanical vibration, wear, and operating
noise.
[0016] Furthermore, a plurality of magnetocaloric refrigeration
devices can be ganged together to make a refrigeration system, in
which a heat-exchanging medium flows through the heat
release/absorption extensions of each heat pipe. The magnetocaloric
refrigeration device can be used to construct a magnetic
refrigerator without the need of any of the gears or valves that
are necessary for a conventional refrigerator. Therefore, the
operation stability and refrigeration effect of the whole system
are improved.
[0017] To provide a further understanding of the invention, the
following detailed description illustrates embodiments and examples
of the invention, this detailed description being provided only for
illustration of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The drawings included herein provide a further understanding
of the invention. A brief introduction of the drawings is as
follows:
[0019] FIG. 1 is a side view of a magnetocaloric refrigeration
device according to a first embodiment of the invention;
[0020] FIG. 2 is a side view of a magnetocaloric refrigeration
device according to a second embodiment of the invention;
[0021] FIG. 3A and FIG. 3B are schematic views of a magnetocaloric
refrigeration device according to a third embodiment of the
invention;
[0022] FIG. 4A and FIG. 4B are schematic views of a magnetocaloric
refrigeration device according to a fourth embodiment of the
invention;
[0023] FIG. 5 is a schematic view of a magnetocaloric refrigeration
device according to a fifth embodiment of the invention;
[0024] FIG. 6 is a schematic view of a magnetic refrigerator
assembled with a magnetocaloric refrigeration device having a
permanent magnet according to one embodiment of the invention;
[0025] FIG. 7 is a schematic view of a magnetic refrigerator
assembled with a magnetocaloric refrigeration device having an
electromagnet according to one embodiment of the invention;
[0026] FIG. 8 is a schematic view of a magnetic refrigerator
assembled with a multi-layered magnetocaloric refrigeration device
according to one embodiment of the invention;
[0027] FIG. 9 (PRIOR ART) is a schematic view illustrating the
process of heat release and absorption used by an embodiment of the
invention;
[0028] FIG. 10 (PRIOR ART) is a schematic view that compares the
conventional gas cycle with the magnetocaloric cycle;
[0029] FIG. 11 (PRIOR ART) is a schematic view of a conventional
rotary magnetic refrigerator; and
[0030] FIG. 12 (PRIOR ART) is a schematic view of a conventional
magnetic refrigerator having a movable magnet.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0031] Wherever possible in the following description, like
reference numerals will refer to like elements and parts unless
otherwise noted.
[0032] Referring to FIG. 1, a magnetocaloric refrigeration device 1
includes a magnetocaloric working unit 10 made of a material that
has a magnetocaloric effect (hereafter referred to as a magnetic
material). One-way heat transfer elements 20 are mounted on two
opposite surfaces of the magnetocaloric working unit 10. One of the
heat transfer elements 20 protrudes from a top of the
magnetocaloric working unit 10, while the other heat transfer
element 20 oppositely protrudes from a bottom of the magnetocaloric
working unit 10. A working medium 21 fills each one-way heat
transfer element 20. The heat transfer elements 20 respectively
provided with the working medium 21 therein are placed in a
metallic container 30. Thereby, the magnetocaloric working unit 10
is subjected to a controllable periodic magnetic field 5.
[0033] The magnetocaloric working unit 10 is made of a
magnetocaloric material 11, such as an alloy of Gd, Si, and Ge at a
composition ratio of Gd.sub.5(SixGe.sub.1-x).sub.4, wherein x is
optionally selected in order to adjust the magnetocaloric intensity
of the alloy 11. Different composition of the alloy 11 influence
the temperature range due to the change of its interior phase.
Methods for forming the magnetocaloric working unit 10 include the
use of the alloy 11 packed in a powder form according to a specific
shape, and a film formation by a nanometer process. The
magnetocaloric working unit requires a material that has the
optimal magnetocaloric effect among the magnetocaloric materials
known in the art. However, the magnetocaloric material suitable for
the invention is not limited to any specific material. Other
compounds such as GdNi, Gd.sub.5(Si.sub.2),
Gd.sub.3Ga.sub.5O.sub.12, GdPd, and the like may also be adequate
to form the magnetocaloric working unit 10.
[0034] The magnetocaloric working unit 10 is placed in the
controllable magnetic field 5 with a working surface 10a of the
magnetocaloric working unit 10 parallel to the magnetic field 5 to
receive a maximal magnetic effect, i.e. highest magnetic flux
(density) through the working surface 10a to obtain the highest
heat transfer efficiency. Furthermore, as shown in FIG. 1, a
sublevel 12 is mounted at a constant interval in the magnetocaloric
working unit 10. The sublevel 12 is made of, for example, a
resin.
[0035] In this embodiment of the invention, the one-way heat
transfer elements 20, as shown in FIG. 1, are hollow closed heat
pipes 25a, 25b. The heat is transferred upwardly to the working
medium 21 in a bottom or on an inner wall of a bottom of the heat
pipes 25a, 25b due to high specific heat and siphon/capillary
attraction. The inner walls of the heat pipes 25a, 25b respectively
have wick structures at their lower sections, which enable one-way
heat transfer preventing reverse heat transfer. At the upper
sections, the inner walls are bare/featureless while the outer
walls are provided with a plurality of fins (not shown) to increase
the heat-transfer efficiency. According to another example, the
heat pipes 25a, 25b may have bare inner walls along the whole
section, or inner walls provided with a porous structure 23, which
also achieves heat transfer.
[0036] The heat pipe can be made of copper, stainless steel, or
tungsten, and the like. The working medium 21 can be among other
things, water, silver solution, acetone, liquid nitrogen or
ethanol. The working medium 21 is selected based on the heat
transfer property needed by the refrigeration requirement. For
example, if the working medium 21 is used at a normal temperature,
then the working medium 21 can be water or ethanol. If the working
medium is used at a temperature lower than the freezing point of
water, then it may be liquid nitrogen. Different pipes may be
packed with different mediums 21 therein or the same, as long as
the working medium 21 can evaporate in the presence of heat as the
magnetocaloric material magnetizes/demagnetizes.
[0037] The heat pipes 25a, 25b respectively mounted to the opposite
sides of the magnetocaloric working unit 10 are located at
different levels to respectively serve as a heat sink and a heat
absorber. As illustrated, the heat pipe 25a is provided with an
externally exposed heat release extension 22a protruding from a top
of the magnetocaloric working unit 10. The heat pipe 25b is
provided with an externally exposed heat absorption extension 22b
protruding from a bottom of the magnetocaloric working unit 10.
Thereby, the heat pipes 25a, 25b respectively dissipate heat from
the magnetocaloric working unit 10 and absorb heat from an ambient
environment as the magnetic field 5 is applied or removed. The
exposed extensions 22a, 22b of the heat pipes 25a, 25b have a
certain extension length so that for each pipe, there is a
temperature difference respectively between the externally exposed
extension and the pipe to increase the heat-exchange efficiency
when the magnetocaloric working unit 10 operates.
[0038] The principle of operation of the magnetocaloric
refrigeration device 1 is described hereafter. The magnetocaloric
working unit 10 is subjected to the controllable periodic magnetic
field 5. When the magnetocaloric working unit 10 moves in the
magnetic field 5, the portion of each pipe that releases heat
caused by the magnetocaloric effect is referred to as an
evaporation portion "a". The portion of each pipe that absorbs the
heat as the magnetocaloric working unit 10 moves out of the
magnetic field 5 is referred to as a condensation portion "b". The
control and frequency of the periodic magnetic field 5 are
determined according to the device design. For example, a
stationary electromagnet or superconductive magnet that alternately
magnetizes and demagnetizes may be used. Alternatively, a
back-and-forth movement/rotation member with a permanent magnet may
be used to periodically pass through a fixed permanent magnet. In
this case, the unit 10 is mounted on the back-and-forth
movement/rotation member to pass through the periodic magnetic
field 5. Therefore, when the magnetic field 5 magnetizes the
magnetocaloric working unit 10, the entropy of the magnetocaloric
material 11 changes to generate heat absorbed by the heat pipes
25a, 25b. The liquid working medium 21 in the evaporation portion
"a" of the heat pipe 25a (either the bottom of the pipe or the wick
structure 23) evaporates producing cooling while the temperature at
the upper section of the heat pipe 25b increases. The evaporated
working medium travels through the heat pipe 25a to the
condensation portion "b" of the externally exposed heat releasing
extension 22a. Optionally, receiver equipment may be externally
mounted on a top of the magnetocaloric refrigeration device 1 to
accelerate the conveyance of the evaporated working medium 21.
After the medium travels to the condensation portion "b" to release
the heat or transmit the heat to the receiver equipment, the
temperature of the working medium 21 progressively decreases until
the working medium 21 condenses due to the external exposure of the
condensation portion "b" away from the magnetocaloric working unit
10. The condensed working medium 21 becomes liquid and flows back
to the evaporation portion "a" along the bare inner walls of the
condensation portion "b". That is, the condensed working medium 21
flows down to the bottom of the heat pipe 25a or adheres on the
wick structure 23 at the upper section. Then, a new cycle of
evaporation/condensation begins. On the other hand, the working
medium 21 at the evaporation portion "a" of the bottom 22b of the
heat pipe 25b, which downwardly protrudes from the magnetocaloric
working unit 10, does not evaporate immediately after the magnetic
field 5 is applied. After the magnetic field 5 is removed and the
magnetocaloric working unit 10 suddenly cools down, the working
medium 21 at the evaporation portion "a" at the bottom 22b of the
heat pipe 25b absorbs heat released from the refrigeration load and
consequently evaporates. The evaporated working medium 21 travels
upwardly in the heat pipe 25b. A decrease in the temperature of the
magnetocaloric working unit 10 draws the ambient heat (for example
from the receiver equipment externally mounted on the bottom of the
refrigeration device 1) and the heat from the working medium 21
toward the magnetocaloric working unit 10 to achieve refrigeration.
The working medium 21 condenses at the condensation portion "b" and
loses its thermal energy. The condensed working medium 21 flows
down along the inner wall of the heat pipe 25b until it reaches the
evaporation portion "a" at the bottom of the heat pipe 25b. Then,
another exothermal/endothermic cycle ensues, again involving
evaporation/condensation of the working medium 21. In the one-way
heat transfer mechanism of the invention, the magnetocaloric
working unit 10 absorbs heat from heat pipe 25b and releases heat
to the outside through heat pipe 25a.
[0039] In this one-way heat transfer mechanism, the heat pipes 25a,
25b located at different levels and mounted with external
extensions respectively operate as a heat release means and a heat
absorption means. The working medium at the top and the bottom of
the magnetocaloric refrigeration device 1 evaporates quickly and
thus has high heating/refrigeration performance. The magnetocaloric
refrigeration device 1 can be used in or mounted on a refrigeration
system, according to the user's requirements. For example, by
flowing the working medium 21 through the top and the bottom of the
magnetocaloric refrigeration device 1, heat dissipation and cooling
can be achieved at the same time. A plurality of fins are further
mounted on the top and bottom of the magnetocaloric refrigeration
device 1 to increase surface area for heat dissipation.
Alternatively, if the working medium or a valve is not provided,
the magnetocaloric refrigeration device 1 can be provided with a
cooling or heating receiver system. For example, an external
cooling receiver system is connected to the bottom of the
magnetocaloric refrigeration device 1 for further heat dissipation.
The magnetocaloric refrigeration device 1 of the invention has a
small structure, which facilitates mounting inside the heat
dissipation assembly of an electronic device.
[0040] The implementation of the invention is not limited to the
above embodiment. For example, the number and the locations of the
one-way heat transfer units 20 are based on the design
requirements. For example, the one-way heat transfer unit 20 may be
mounted on a single side of the magnetocaloric working unit 10. In
a second embodiment of the invention as illustrated, the pipes 25
release and absorb heat when the magnetic field 5 respectively is
applied and removed. That is, when the temperature of the
magnetocaloric working unit 10 increases, the working medium 21,
adhered on the wick structure 23 and wetting a middle section of
the heat pipes 25 due to siphon/capillary attraction, evaporates
and thereby carries heat out of the heat pipes 25 from the tops of
the heat pipes 25. On the other hand, when the temperature of the
magnetocaloric working unit 10 decreases, the working medium 21
serves as a heat absorber to carry heat from the bottoms of the
heat pipes 25 to the magnetocaloric working unit 10. The heat pipes
25, as illustrated, protrude from the top and bottom of the
magnetocaloric working unit 10 to provide improved heat release and
absorption performance. The externally exposed heat release
extension 22a at the top of the magnetocaloric working unit 10
serves as the condensation portion "b" for heat release, while the
externally exposed heat absorbing extension 22b at the bottom of
the magnetocaloric working unit 10 serves as the evaporation
portion "a" for heat absorption. The middle section of the
magnetocaloric working unit 10 contacting the heat pipes 25
respectively serves as the evaporation portion "a" when heat is
released from the magnetocaloric refrigeration device, and as the
condensation portion "b" when heat is absorbed by the
magnetocaloric working unit 10. In this embodiment, the heat pipes
25 operate to release and absorb heat in the same cycle, which may
cause high heat loading.
[0041] In another embodiment of the invention, a plurality of
magnetocaloric refrigeration devices 1 are assembled together to
achieve improved heat efficiency by means of a large number of
magnetocaloric working units 10 and heat pipes 25. FIG. 3A is a
perspective view of a heat transfer structure according to a third
embodiment of the invention. FIG. 3B is a side view of a
magnetocaloric refrigeration device from an angle of view taken
along line A-A. Referring to FIG. 3A and FIG. 3B, four heat pipes
25 protrude from the top of the magnetocaloric refrigeration device
1, and another set of four heat pipes 25 protrude from the bottom
of the magnetocaloric refrigeration device 1. Heat release and
absorption are conducted according to the same way as described
above.
[0042] FIG. 4A is a perspective view of a heat transfer structure
according to a fourth embodiment of the invention. FIG. 4B is a
side view of a magnetocaloric refrigeration device from an angle of
view taken along line B-B. Heat is conveyed from the evaporated
working medium 21 in the heat pipes 25 to a top connecting space
29a. A bottom connecting space 29b is further formed in the
magnetocaloric refrigeration device 1, having a smooth heat
releasing surface 28a and a smooth heat absorbing surface 28b. The
smooth heat absorbing surface 28b is connected to the cooling
receiver device such as a heat sink of a semiconductor device. A
weak magnetic field is externally applied to the magnetocaloric
refrigeration device to further increase the heat-transfer
efficiency.
[0043] In the magnetocaloric refrigeration device 1 of the
invention, the one-way heat transfer unit 20 mounted inside or on
the magnetocaloric working unit 10 is not limited to the above heat
pipes 25. Any heat transfer member that has heat transfer
properties and conveys the working medium 21 can be used in the
invention. FIG. 5 illustrates a magnetocaloric refrigeration device
according to a fifth embodiment of the invention. As shown, a
plurality of heat pipes 26 can be used to conduct heat to and from
the magnetocaloric working unit 10. The heat pipes 26 are arranged
alternately on and protrude from the top and bottom of the
magnetocaloric refrigeration device 1. The working medium 21 (not
shown in FIG. 5) is contained in the bottom of the heat pipes 26
and conveyed by siphon/capillary attraction along the heat pipe 26.
Heat release and absorption are achieved by applying a periodic
magnetic field 5. A wick structure 23 (not shown in FIG. 5) is also
formed on the inner walls of the bottoms of the heat pipes 26, and
is wetted by the working medium 21 to increase surface area for
heat transfer. The externally exposed heat extensions of the heat
pipe 26 can further connect with one another to form a heat space
having a structure similar to that shown in FIG. 4A and FIG. 4B.
The one-way heat transfer member is not limited to the heat pipe 25
and the heat pipe 26 described above. Any type of heat transfer
member can be used, as long as its shape does not adversely affect
the heat-transfer efficiency.
[0044] The invention can be applied in any type of heat circulation
system, such as a magnetic refrigerator 3 as shown in FIG. 6. As
illustrated, a plurality of magetocaloric refrigeration devices 1
are arranged in series. One or more moving members 9 generating a
magnetic field 5 of about 1 Tesla, are mounted adjacent to the
devices 1. The moving members 9 are permanent magnets 8, and move
along the magnetocaloric refrigeration devices 1 at a predetermined
speed to generate periodic magnetic fields 5. The heat pipes 25 are
respectively provided with a heat exchanger and at least one fin
50. A working medium 51 flows through the heat exchanger to provide
a refrigeration effect similar to the prior art. Since the
construction of the system is simple, control of the moving members
9 is easily achieved. Furthermore, no additional valve is needed to
switch the working medium 51, which greatly improves over on the
conventional magnetocaloric refrigeration system.
[0045] In another embodiment of the invention, the external
magnetic field 5 is generated in a manner different from the above
description. A plurality of equally spaced electromagnets 7 are
mounted near one side of the series-arranged magnetocaloric
refrigeration devices 1. A controller alternately
magnetizes/demagnetizes the electromagnets 7 at a constant rate to
respectively produce a magnetized electromagnet 7a and a
demagnetized electromagnet 7b, which provides the same effect as
the above movable permanent magnet 8. A magnetic field 5 is applied
to the magnetocaloric working unit 10 of the magnetocaloric
refrigeration device 1. The magnetic refrigerator 3 experiences a
higher magnetic field 5 than that of the prior art and therefore
provides higher refrigeration efficiency than in the prior art.
Furthermore, all the constituting elements of the device 1 are
controlled electromagnetically (instead of by traditional
mechanical control). Thereby, mechanical wear and noise can be
eliminated, while operating stability and processibility of the
whole device is increased.
[0046] Aside the above construction of magnetic refrigerator 3,
magnetocaloric refrigeration devices 1 can be arranged according to
other assembly schemes. For example, the magnetocaloric
refrigeration devices 1 may be stacked up to form a multi-layered
refrigeration system 6, as shown in FIG. 8. The magnetocaloric
material 11 is used in different ratios in order to tolerate a
temperature range larger than that of the prior art. In system 6, a
lower layer is made of an alloy of Gd.sub.5(SixG.sub.1-x).sub.4 and
an upper layer is made of
Gd.sub.5(Si.sub.1.985Ge.sub.1.985Ga.sub.0.03). The heat from the
medium to be cooled down is subsequently transferred outward
through the lower and upper layers. Heat at temperatures between,
for example, 3.degree. C. and 37.degree. C., is transferred through
the multi-layers. The working medium 21 can be varied according to
the material 11 of the heat pipe 25. The arrangement and number of
the material layers as well as the alloy composition ratio and type
of the working medium can be appropriately chosen to obtain optimal
heat-transfer efficiency depending on the system requirements.
[0047] The configuration of the magnetocaloric working unit 10 and
the one-way heat transfer member 20, and the way to generate the
magnetic field 5, are not limited to the above description. The
application of the invention includes, but is not limited to, a
magnet refrigerator 3, a refrigeration circulation system, an
electronic heat dissipation system, a microfluid system, and the
production of low-temperature liquid nitrogen used in a fuel
battery.
[0048] The magnetocaloric refrigeration device of the invention has
advantages such as high heat-transfer efficiency, a simplified and
smaller structure, a low production cost, low environmental
pollution, stable operation and low energy-consumption. If the
invention is implemented in a magnetocaloric refrigerator, the
gears and valves that were necessary in the conventional
refrigerator are eliminated, which thus reduces mechanical wear and
noise produced during operation of the system, and increases the
operation stability.
[0049] It should be apparent to those skilled in the art that the
above description is only illustrative of specific embodiments and
examples of the invention. The invention should therefore cover
various modifications and variations made to the herein-described
structure and operation of the invention, provided they fall within
the scope of the invention as defined in the following appended
claims.
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