Refrigeration – Gas compression – heat regeneration and expansion – e.g.,...
Reexamination Certificate
2000-04-03
2001-10-23
Capossela, Ronald (Department: 3744)
Refrigeration
Gas compression, heat regeneration and expansion, e.g.,...
C062S051100, C062S383000
Reexamination Certificate
active
06305174
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to self-triggering cryogenic heat flow or heat flux switches that are used particularly with cooling systems that require a redundant operation.
BACKGROUND INFORMATION
In satellite communications technology, maintenance-free refrigerator-cooled electronic systems (antennas, high temperature superconducting filters, amplifiers) are already being used and will be used increasingly in the future. Such systems must be constructed to provide a service life of several years. The refrigerators are subject to wear in operation and, therefore, in order to avoid a system failure, at least one other refrigerator must be provided as a redundancy. During operation, this redundant refrigerator must be thermally isolated from the end use device or application, since it otherwise acts as a parasitic heat bridge, and must be thermally coupled with the application when the primary cooling refrigerator fails. At the same time, the defective primary refrigerator must be thermally isolated from the end use device or application. The switch-over to the redundant refrigerator must occur as quickly as possible so that the end use device or application does not heat up excessively in the meantime and possibly have to be temporarily taken out of operation. For this reason it is advantageous to cool down the redundant cooler or refrigerator in a no-load condition and only then connect it to the end use device or application as soon as its cold head temperature is lower than the temperature of the application.
In order to solve this problem, various conventional devices have been used, such as active electromechanically or pneumatically operated heat switches, self-triggering uni-directional cryogenic heat exchanger tubes or heat pipes (U.S. Pat. No. 4,673,030), or gas gap heat flow switches that are pumped by cryosorption (U.S. Pat. No. 4,771,823).
The active mechanical systems have provided the best solution functionally to date. They are, however costly to manufacture, require additional control electronics, and themselves carry a significant risk of failure.
Uni-directional cryogenic heat pipes are still the subject of intensive development. They are very costly to manufacture, as either high pressure engineering or cryo-engineering is required to fill them with the working medium. At ambient temperature they are subject to a high internal pressure, which requires great tube wall thicknesses. Consequently, these heat pipes have a poor switching ratio and are still perceptible as parasitic heat bridges even after isolation or separation of the heat contact.
In contrast, it is substantially less costly to manufacture gas gap heat flow switches that are pumped by cryosorption. These switches are also self-actuating without an additional control. In order to switch over to the redundant refrigerator, however, the application and the failed refrigerator must be heated to the extent that the cryosorption pump desorbs sufficient gas to close the heat flow switch of the redundant refrigerator. A high-temperature superconducting application would have to be taken out of operation to do this.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a self-triggering cryogenic heat flow switch that has the simplest possible construction while providing a reliable maintenance-free mode of operation, and ensuring thereby a self-switching connection between a heat sink and an end use device or application to be cooled.
The above object of the invention has been achieved in a cryogenic cooling arrangement including a selectively actuatable heat sink, an end use application which is to be cooled, and a cryogenic heat flow switch selectively coupling the end use application with the heat sink for heat transfer therebetween. According to the invention, the heat flow switch is a self-triggering cryogenic heat flow switch comprising an outer hollow cylinder that has an inner perimeter surface and that is connected to the heat sink, an inner body that has an outer perimeter surface arranged coaxially relative to and at least partly within the inner perimeter surface of the outer hollow cylinder and that is connected to the end use application which is to be cooled, and a plurality of spacers arranged radially between the outer perimeter surface of the inner body and the inner perimeter surface of the outer hollow cylinder. The outer hollow cylinder has a linear thermal expansion coefficient greater than that of the inner body. A concentric annular gap is formed between the outer perimeter surface of the inner body and the inner perimeter surface of the outer hollow cylinder and is maintained by the spacers when the heat sink is not actuated. This concentric annular gap is closed and the inner perimeter surface of the outer hollow cylinder comes into contact with the outer perimeter surface of the inner body when the heat sink is actuated.
The heat flow switch according to the invention functions according to the principle of thermal expansion. With reference to the starting temperature T. and the linear dimensions at this starting temperature, the heat flow switch has a switch-on point Te and a switch-off point Ta. These points are defined by the following relationships:
D
(
1
+
∫
To
Te
α
D
(
T
)
ⅆ
T
)
-
d
=
0
D
(
1
+
∫
To
Ta
α
D
(
T
)
ⅆ
T
)
-
d
(
1
+
∫
To
Ta
α
d
(
T
)
ⅆ
T
)
=
0
The heat sink is connected to the outer hollow cylinder of the heat flow switch. The device or application to be cooled is connected to the inner solid or hollow cylinder of the heat flow switch. While cooling, the outer hollow cylinder contracts until, at the switch-on point, its inner diameter reaches the outer diameter of the still warm inner solid or hollow cylinder. A heat transfer is established, whereby the inner solid or hollow cylinder and the outer hollow cylinder continue to cool together to a temperature below the switch-off point. The compressive strain between the two parts provides a reliable heat contact with low heat transfer resistance.
The heat contact opens when the outer hollow cylinder heats up above the switch-off point. The device or application to be cooled is thermally decoupled from the heat sink as the heat sink continues to heat up.
These heat flow switches can be constructed with great precision with the aid of the above mentioned relationships once the temperature dependency of the linear thermal expansion coefficients of the materials selected for use have been dilatometrically ascertained. If the diameters D and d are freely selectable, the switch-on point and the switch-off point of the heat flow switch can be freely selected in broad ranges. If one of the diameters is predefined, then either the switch-on point or the switch-off point can be freely selected.
REFERENCES:
patent: 3225820 (1965-12-01), Riordan
patent: 3306075 (1967-02-01), Cowans
patent: 3362467 (1968-01-01), Kummerer
patent: 3430455 (1969-03-01), Stuart et al.
patent: 3519067 (1970-07-01), Schmidt
patent: 3531752 (1970-09-01), Gourley
patent: 3807188 (1974-04-01), Lagodmos
patent: 4673030 (1987-06-01), Basiulis
patent: 4770004 (1988-09-01), Lagodmos
patent: 4771823 (1988-09-01), Chan
patent: 5379601 (1995-01-01), Gillett
patent: 5682751 (1997-11-01), Langhorn et al.
patent: 5842348 (1998-12-01), Kaneko et al.
patent: 2115771 (1972-10-01), None
patent: 3017252 (1981-11-01), None
patent: 4126227 (1993-02-01), None
patent: 4224449 (1994-02-01), None
patent: 4320505 (1994-12-01), None
patent: 1518726 (1968-03-01), None
patent: 56-65216 (1981-06-01), None
Binneberg Armin
Kaiser Gunter
Capossela Ronald
Fasse W. F.
Fasse W. G.
Institut fuer Luft- und Kaeltetechnik Gemeinnuetzige Gesellschaf
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