Auxiliary Cryogenic Cooling Systems Based on Commercial Cryo-Coolers

CROSS-REFERENCES TO RELATED APPLICATIONS

This non-provisional application claims the benefit of an earlier-filed provisional application pursuant to the provisions of 37 C.F.R. §(c). The provisional application was assigned Ser. No. 61/507,725. It was filed on Jul. 13, 2011 and listed the same inventors.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This application is based on work performed at the Center for Advanced Power Systems at the Florida State University. A portion of this work has been funded by the United States Navy.

MICROFICHE APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of heat transfer. More specifically, the invention comprises a device and method for distributing cooling capacity of a prior art cryo-cooler to one or more auxiliary applications needing such cooling capacity.

2. Description of the Related Art

A cryo-cooler is a commercially available device capable of producing extremely low temperatures. Superconducting power system components and other electronic components requiring very low temperatures are entering the marketplace in the fields of defense, aerospace, and power distribution systems. The most common device for achieving cryogenic temperatures in such devices is a cryo-cooler. These are typically gas compression devices such as Stirling cycle engines.

Commercial cryo-coolers operate like residential heat pumps, in that they are generally only “on” or “off.” In other words, they have no throttling capacity. Such systems are often designed with excess cooling capacity in order to provide a suitable engineering margin and to accommodate the occasional “spike” cooling load. They generally run while the application is running. Since there is some degree of excess cooling capacity during most operations, the application will actually be over-cooled without an additional feature. The additional feature is the inclusion of a small heater to controllably raise and stabilize the temperature of the application itself. This is analogous to providing a central air conditioning system sized to overcool a house and then using a controllable space heater to bring the temperature in one room of the house up to a desired level. Obviously this is an inefficient approach.

FIG. 1 shows a prior art cryocooled application 10 in which a cryo-cooler is configured to provide cooling to an experimental application. The cryo-cooler in this example is a helium compressor 14. It feeds very cold helium gas through delivery line 22 to cold head 16. The cold gas provides cooling to experimental application 18 housed in cryostat 12. The gas is returned to the helium pump by return line 24.

Heater 20 is provided to maintain experimental application 18 at a suitable temperature. The heater may assume many forms, with one example being an electrical heater having a variable voltage input. The heater provides a variable amount of heat transfer to the experimental application so that a constant temperature can be maintained (or so that the temperature can be varied in a controlled fashion, if that is desired).

It is typical to provide an individual cryo-cooler for each application requiring cooling, even though some of the applications may be in close proximity. This is tnie because no suitable device capable of sharing cooling capacity between two or more applications presently exists.

Commercial cryo-coolers are heavy and often increase the footprint and weight of the overall application. Providing a cryo-cooler for each cooling application is obviously inefficient. It would therefore be preferable to use a single cryo-cooler to provide cooling for two or more applications. The present invention provides a device and method for accomplishing this goal.

BRIEF SUMMARY OF THE PRESENT INVENTION

The present invention comprises a novel apparatus and method for distributing the cooling capacity provided by a commercial cryo-cooler. The cryo-cooler is connected to a first application housed in a first cryostat. A second application is provided—typically in a second cryostat.

A heat exchanger is added to the first application. Circulating gas lines connect this heat exchanger to the second application contained in the second cryostat. Helium is circulated in the gas lines, with the flow of the helium being regulated so that it may be throttled between a zero flow condition and a maximum flow condition. The circulating helium gas transfers some of the available cooling capacity from the first application to the second application. This circulation regulates the temperature of both applications.

REFERENCE NUMERALS IN THE DRAWINGS

10

cryocooled application

12

cryostat

14

helium compressor

16

cold head

18

experimental application

20

heater

22

delivery line

24

return line

26

tunable helium flow system

28

delivery line

29

return line

30

auxiliary application

32

heat exchanger

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view, showing a prior art cryo-cooler providing cooling to a single experimental application.

FIG. 2 is a schematic view, showing the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows the cryocooled application of FIG. 1 with the addition of a heat transfer apparatus constructed according to the present invention. Heat exchanger 32 is thermally connected to the cooling delivery system providing cooling to experimental application 18. The thermal connection can be achieved via any suitable means. Directly attaching the heat exchanger to the cold head is one suitable approach.

Heat exchanger 32 is then connected to auxiliary application 30 in a second cryostat 12 via a closed loop circulation system. Delivery line 28 carries gas from heat exchanger 32 and return line 29 returns gas from auxiliary application 30. The circulating gas is preferably cold helium.

Tunable helium flow system 26 regulates the flow of the gas circulating between heat exchanger 32 and auxiliary application 30. Tunable helium flow system may comprise many individual components. As an example, a centrifugal pump attached to a variable speed drive can be used to continuously alter the rate of flow in the circulating loop. One or more throttling valves, check valves, and shut-off valves may be included as well.

As those skilled in the art will know, a variable speed drive is able to continuously vary its rotational speed over a range of speeds. The term “continuously” should be understood in this context to include an infinitely variable drive and a drive which is capable of operating at a number of different and discrete speed steps. Some drives deemed “continuously” variable have as few as 4 different speed steps, though it is more common to have 16 or more possible speed steps.

Such a variable speed drive may be used to directly drive a centrifugal pump, or the pump may be driven through a gear-train or other ratio-creating device. In any case, varying the speed of the variable speed drive also varies the speed of the centrifugal pump and thereby varies the flow rate within the circulating loop.

A throttling valve may also be used to continuously vary the flow rate. A throttling valve may be a simple butterfly valve, a needle-and-seat valve, a spring-loaded globe valve, or any other suitable type of valve. The position of the valve may be varied infinitely. Alternatively, it may be possible to place the valve in any number of discrete positions.

Whatever individual components are used, the purpose of tunable helium flow system 26 is to provide a controlled and variable flow rate in the circulating loop connecting heat exchanger 32 to auxiliary application 30. The tunable flow system is thereby able to transmit some of the excess available cooling capacity at experimental application 18 to auxiliary application 30. This regulates the temperature of experimental application 18 without the use of a heater.

Those skilled in the art will appreciate that the inventive system can be applied to two or more auxiliary applications by providing a tunable helium flow system 26 with multiple lines and flow control devices. A single cryo-cooler having considerable capacity could thereby supply two, three, or more applications needing cooling. One could even incorporate a second external heat exchanger configured to “dump” excess cooling capacity in the event that only a small percentage of the current capacity is needed.

Although the preceding description contains significant detail, it should not be construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. Many other embodiments will occur to those knowledgeable in this field. The inventive structure and process could be carried out in many different ways. Thus, the scope of the invention should be fixed by the following claims rather than the examples given.