Information
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Patent Grant
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6644038
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Patent Number
6,644,038
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Date Filed
Friday, November 22, 200221 years ago
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Date Issued
Tuesday, November 11, 200320 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
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CPC
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US Classifications
Field of Search
US
- 062 6
- 062 2592
- 062 335
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International Classifications
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Abstract
A pulse tube refrigeration system wherein the pulse tube working gas is cooled to a defined first stage temperature and is brought to a defined second stage temperature by operation of a regenerator and pulse tube, which are in flow communication through a cold heat exchanger, prior to providing refrigeration to a high temperature superconductor.
Description
TECHNICAL FIELD
This invention relates generally to pulse tube refrigeration which may be used for a high temperature superconductivity application.
BACKGROUND ART
Superconductivity is the phenomenon wherein certain metals, alloys and compounds lose electrical resistance so that they have infinite electrical conductivity. Until recently, superconductivity was observed only at extremely low temperatures just slightly above absolute zero. Maintaining superconductors at such low temperatures is very expensive, typically requiring the use of liquid helium, thus limiting the commercial applications for this technology.
Recently a number of materials have been discovered which exhibit superconductivity at higher temperatures, such as in the range from 15 to 75 K. While such materials may be kept at their superconducting temperatures using liquid helium or very cold helium vapor, such a refrigeration scheme is quite costly. Unfortunately liquid nitrogen, a relatively low cost way to provide cryogenic refrigeration, cannot effectively provide refrigeration to get down to the superconducting temperatures of most high temperature superconductors.
An electric transmission cable made of high temperature superconducting materials offers significant benefits for the transmission of large amounts of electricity with very little loss. High temperature superconducting material performance generally improves roughly an order of magnitude at temperatures of about 30 to 60 K from that at temperatures around 80 K which is achieved using liquid nitrogen.
A recent significant advancement in the field of generating refrigeration is the pulse tube system wherein pulse energy is converted to refrigeration using an oscillating gas. Such refrigeration could be used for high temperature superconductivity applications. However, it is presently quite costly to generate refrigeration for use at the more efficient high temperature superconductivity temperatures using known pulse tube systems thus negating the performance improvement seen at the lower temperatures.
Accordingly, it is an object of this invention to provide an improved pulse tube refrigeration system which can provide refrigeration at temperatures which are conducive to good high temperature superconductivity performance.
SUMMARY OF THE INVENTION
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for providing refrigeration for high temperature superconductivity comprising:
(A) generating an oscillating pulse tube working gas, and cooling the oscillating pulse tube working gas to a first stage temperature within the range of from 50 to 150 K;
(B) cooling the oscillating pulse tube working gas to a second stage temperature within the range of from 4 to 70 K by direct heat exchange with cold regenerator media to produce cold pulse tube gas;
(C) expanding the cold pulse tube working gas in a pulse tube to generate refrigeration for cooling regenerator media; and
(D) providing refrigeration from the cold pulse tube working gas for high temperature super-conductivity.
Another aspect of the invention is:
Apparatus for providing refrigeration for high temperature superconductivity comprising:
(A) a pulse generator for generating oscillating pulse tube working gas, a first stage heat exchanger, means for passing oscillating pulse tube working gas to the first stage heat exchanger, and means for passing refrigeration to the first stage heat exchanger;
(B) a regenerator and means for passing oscillating pulse tube working gas to the regenerator;
(C) a pulse tube in flow communication with the regenerator, said flow communication including a second stage heat exchanger; and
(D) means for providing high temperature superconductivity media to the second stage heat exchanger.
As used herein the term “pulse” means energy which causes a mass of gas to go through sequentially high and low pressure levels in a cyclic manner, i.e. to oscillate.
As used herein the term “high temperature superconductivity media” means fluid or other heat transfer media which directly or indirectly provides refrigeration to high temperature superconductor material.
As used herein the term “regenerator” means a thermal device in the form of porous distributed mass or media, such as spheres, stacked screens, perforated metal sheets and the like, with good thermal capacity to cool incoming warm gas and warm returning cold gas via direct heat transfer with the porous distributed mass.
As used herein the term “indirect heat exchange” means the bringing of fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the term “direct heat exchange” means the transfer of refrigeration through contact of cooling and heating entities.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a representation of one embodiment of the multistage pulse tube refrigeration system of this invention.
FIG. 2
is a representational diagram of the invention showing an embodiment wherein refrigerant fluid for the first stage heat exchanger is provided from a refrigeration system to forecool a pulse tube refrigerator, which then provides refrigeration to cool a high temperature superconductor system.
FIG. 3
is a representational diagram of the invention showing an embodiment wherein the refrigerator or the first stage heat exchanger is provided from a first refrigeration system which assists the pulse tube refrigeration system in providing refrigeration to the high temperature superconductivity system. The first refrigerator also provides refrigeration for a second heat exchanger which in turn supplies refrigeration for the superconductor at a higher temperature.
DETAILED DESCRIPTION
The invention will be described in detail with reference to the Drawings. Referring now to
FIG. 1
, the multistage pulse tube refrigeration system
21
comprises warm regenerator
32
, cold regenerator
33
, pulse tube
34
, first stage heat exchanger
22
and second stage heat exchanger
23
. The regenerators contain pulse tube working gas which may be helium, hydrogen, neon, nitrogen, a mixture of helium and neon, a mixture of neon and nitrogen, or a mixture of helium and hydrogen. Pure helium is the preferred pulse tube working gas.
A pulse, i.e. a compressive force, is applied to the hot end of regenerator
32
by means of pulse generator
30
thereby generating an oscillating pulse tube working gas and initiating the first part of the pulse tube sequence. Preferably, as illustrated in
FIG. 1
, the pulse is provided by a piston which compresses a reservoir of pulse tube gas in flow communication with regenerator
32
. Another preferred means of applying the pulse to the regenerator is by the use of a thermoacoustic driver which applies sound energy to the gas within the regenerator. Yet another way for applying the pulse is by means of a linear motor/compressor arrangement. Yet another means to apply a pulse is by means of a loudspeaker. The pulse serves to compress the pulse tube gas producing hot compressed pulse tube gas at the hot end of the regenerator
32
. The hot pulse tube gas is cooled, preferably by indirect heat exchange with heat transfer fluid
40
in heat exchanger
31
, to produce warmed heat transfer fluid in stream
41
and to cool the compressed pulse tube gas of the heat of compression. Examples of fluids useful as the heat transfer fluid
40
,
41
in the practice of this invention include water, air, ethylene glycol and the like.
Regenerators
32
and
33
contain regenerator or heat transfer media. Examples of suitable heat transfer media in the practice of this invention include steel balls, wire mesh, high density honeycomb structures, expanded metals, lead balls, copper and its alloys, complexes of rare earth element(s) and transition metals.
The pulsing or oscillating pulse tube working gas is cooled in warm regenerator
32
and then is cooled to a first stage temperature within the range of from 50 to 150 K. This cooling, i.e. the provision of refrigeration, may be by any effective means such as conduction cooling. The embodiment of the invention illustrated in
FIG. 1
is a preferred embodiment wherein the oscillating pulse tube working gas is passed to first stage heat exchanger
22
wherein it is cooled by indirect heat exchange with refrigerant fluid to a first stage temperature within the range of from 50 to 150 K. In the embodiment of the invention illustrated in
FIG. 1
, the first stage heat exchanger
22
is shown as being within the housing which holds regenerators
32
and
33
. First stage heat exchanger
22
may also be positioned outside of this housing. The refrigerant fluid is provided to first stage heat exchanger
22
in stream
60
and is withdrawn from first stage heat exchanger
22
in stream
61
. The refrigerant fluid may be a liquid cryogen such as liquid nitrogen or may be another fluid containing refrigeration generated by a refrigeration system such as a mixed gas refrigeration system, a magnetic refrigeration system or a refrigeration cycle which employs turboexpansion of a working fluid. Heat exchanger
22
can also be cooled by conduction.
The resulting cooled oscillating pulse tube working gas is then passed through cold regenerator
33
wherein it is cooled to a second stage temperature within the range of from 4 to 70 K by direct heat exchange with cold regenerator media to produce cold pulse tube working gas.
Pulse tube
34
and regenerator
33
are in flow communication. The flow communication includes cold or second stage heat exchanger
23
. The cold pulse tube working gas passes in line
42
to second stage heat exchanger
23
and in line
43
from second stage heat exchanger
23
to the cold end
62
of pulse tube
34
. Within second stage heat exchanger
23
the cold pulse tube working gas is warmed by indirect heat exchange with high temperature superconductivity media thereby providing refrigeration to the high temperature superconductivity media for provision to a high temperature superconductor. The high temperature superconductivity media could be a solid block transmitting heat to heat exchanger
23
from the cooled superconductor system. In the embodiment of the invention illustrated in
FIG. 1
, the high temperature superconductivity media is a fluid passed to second stage heat exchanger
23
in line
64
and withdrawn from second stage heat exchanger
23
in line
63
in a cooled, i.e. refrigerated, condition. In this case the high temperature superconductivity media could comprise nitrogen, neon, hydrogen, helium and mixtures of one or more of such species with one or more of argon, oxygen and carbon tetrafluoride. A particularly preferred high temperature superconductivity media is a fluid comprising at least
3
mole percent neon.
The pulse tube working gas is passed from the regenerator
33
to pulse tube
34
at the cold end
62
. As the pulse tube working gas passes into pulse tube
34
at the cold end
62
it compresses gas in the pulse tube and forces some of the gas through heat exchanger
65
and orifice
36
into the reservoir
37
. When the piston moves backward in
30
or in the low pressure point of the compressive pulse, the pulse tube working gas expands and generates a gas pressure wave which flows toward the warm end
65
of pulse
34
and compresses the gas within the pulse tube thereby heating it.
Cooling fluid
44
is passed to heat exchanger
35
wherein it is warmed or vaporized by indirect heat exchange with the pulse tube working gas, thus serving as a heat sink to cool the pulse tube working gas. Resulting warmed or vaporized cooling fluid is withdrawn from heat exchanger
35
in stream
45
. Preferably cooling fluid
44
is water, air, ethylene glycol or the like.
Attached to the warm end
65
of pulse tube
34
is a line
46
having orifice
36
leading through line
47
to reservoir
37
. The compression wave of the pulse tube working gas contacts the warm end wall of the pulse tube and proceeds back in the second part of the pulse tube sequence. Orifice
36
and reservoir
37
are employed to maintain the pressure and flow waves in phase so that the pulse tube generates net refrigeration during the expansion and the compression cycles in the cold end
62
of pulse tube
34
. Other means for maintaining the pressure and flow waves in phase which may be used in the practice of this invention include inertance tube and orifice, expander, linear alternator, bellows arrangements, and a work recovery line with a mass flux suppressor. In the expansion sequence, the pulse tube working gas expands to produce cold pulse tube working gas at the cold end
62
of the pulse tube
34
. The expanded gas reverses its direction such that it flows from the pulse tube toward regenerator
33
. The relatively higher pressure gas in the reservoir flows through valve
36
to the warm end of the pulse tube
34
.
The expanded pulse tube working gas emerging from heat exchanger
23
is passed in line
42
to regenerator
33
wherein it directly contacts the heat transfer media within the regenerator to produce the aforesaid cold heat transfer media, thereby completing the second part of the pulse tube refrigerant sequence and putting the regenerator into condition for the first part of a subsequent pulse tube refrigeration sequence.
FIGS. 2 and 3
illustrate in simplified representational form two arrangements which may employ the multistage pulse tube refrigeration system of this invention integrated with a higher temperature refrigeration system to provide refrigeration for a high temperature superconductivity application. The numerals in
FIGS. 2 and 3
are the same as those of
FIG. 1
for the common elements.
Referring now to
FIG. 2
, higher level refrigeration system
20
, for example a mixed gas refrigeration system, produces refrigerant fluid
60
for the first stage cooling in heat exchanger
22
or cools heat exchanger
22
by conductive means. In this embodiment the pulse tube working gas is provided to first stage heat exchanger
22
in line
66
and then passed to the regenerator from heat exchanger
22
in line
67
. The refrigerated high temperature superconductivity media in line
64
is provided to high temperature superconductor
11
to maintain superconductivity temperatures generally within the range of from 4 to 70 K and typically within the range of from 30 to 50 K.
FIG. 3
illustrates an arrangement similar to that of
FIG. 2
with the added provision of refrigeration from the high temperature refrigeration system
20
to second high temperature superconductivity application
12
which may be a separate entity from application
11
or may be integrated into a single superconducting apparatus
10
which receives refrigeration at two temperature levels. In the embodiment illustrated in
FIG. 3
, refrigerant fluid from refrigeration system
20
is passed in line
68
to heat exchanger
24
wherein it is warmed to provide refrigeration to fluid
69
. The warmed refrigerant fluid is returned to refrigeration system
20
in line
70
, and the refrigerated fluid
71
is passed to high temperature superconductivity application
12
wherein it provides refrigeration at a higher temperature than is provided to superconductor
11
, typically at about 80 K.
Although the invention has been described in detail with reference to certain preferred embodiments, those skilled in the art will recognize that there are other embodiments of the invention within the spirit and the scope of the claims. For example, there could be employed more than one upstream cooling step or stage prior to the final stage which in the embodiment illustrated in
FIG. 1
is the second stage.
Claims
- 1. A method for providing refrigeration for high temperature superconductivity comprising:(A) generating an oscillating pulse tube working gas, and cooling the oscillating pulse tube working gas to a first stage temperature within the range of from 50 to 150 K by indirect heat exchange with refrigerant fluid from a refrigeration system; (B) cooling the oscillating pulse tube working gas to a second stage temperature within the range of from 4 to 70 K by direct heat exchange with cold regenerator media to produce cold pulse tube gas; (C) expanding the cold pulse tube working gas in a pulse tube to generate refrigeration for cooling regenerator media; and (D) providing refrigeration from the cold pulse tube working gas for high temperature superconductivity, and wherein the refrigeration system provides refrigeration for another high temperature superconductivity application at a higher temperature than that provided by the cold pulse tube working gas.
- 2. The method of claim 1 wherein the refrigerant fluid is a liquid cryogen.
- 3. The method of claim 1 wherein cold pulse tube working gas provides refrigeration for high temperature superconductivity by cooling high temperature superconductivity media which is provided to a high temperature superconductor and wherein the high temperature superconductivity media is a fluid which comprises at least 3 mole percent neon.
- 4. The method of claim 1 wherein the oscillating pulse tube working gas is cooled to the first stage temperature by indirect conductive heat exchange means.
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