Cryogenic Refrigeration Heat Exchange Systems and Methods

Abstract

Cryocooler systems are provided that include a section of incoming helium gas conduit extending between the first and second stages, this section configured to thermally couple with both the regenerator and the PT tube. Systems are provided that include sections of incoming helium gas conduit extending between the first and second stages that are configured to thermally couple with helium return section. Systems are provided that include a section of the regenerator residing between the first and second stages that houses at least one discrete heat exchanger. Methods for cooling incoming helium gas to the cryocooler are also provided.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 63/764,346 filed Feb. 27, 2025, entitled “Cryogenic Refrigeration Heat Exchange Systems and Methods”, the entirety of which is incorporated by reference herein.

TECHNICAL FIELD

This application generally pertains to the field of cryogenic refrigeration. More particularly, the application pertains to dilution refrigerators or other low-temperature refrigeration systems near 1 Kelvin.

BACKGROUND

Cryogen-free dilution refrigerators or other 1 K and sub-Kelvin refrigerators can be used for cooling quantum computers, quantum sensors, etc. In a cryogen-free dilution refrigerator or a 1K refrigeration system, there is a need to cool helium within a dilution refrigerator loop or a 1 K refrigeration loop efficiently. Presently, quantum computers are scaling up and requiring higher and higher cooling capacities of dilution refrigerators. A large dilution refrigerator may employ 5-9 pulse tube (PT) cryocoolers for higher cooling power. The present disclosure provides systems and methods for cooling helium within these loops.

SUMMARY

Cryocooler systems are provided that include: both a regenerator and PT tube operably configured within the cryocooler system; first and second stages thermally associated with both the regenerator and PT tube; and a section of incoming helium gas conduit extending between the first and second stages, wherein this section is configured to thermally couple with both the regenerator and the PT tube.

Cryocooler systems are also provided that can include: both a regenerator and PT tube operably configured within the cryocooler system; first and second stages thermally associated with both the regenerator and PT tube; a section of return helium gas extending between the first and second stages; and a section of incoming helium gas conduit extending between the first and second stages, wherein this section is configured to thermally couple with helium return section.

Cryocooler systems are also provided that can include: both a regenerator and PT tube operably configured within the cryocooler system; first and second stages thermally associated with both the regenerator and PT tube, a section of the regenerator and a section of the PT tube residing between the first and second stages, the section of the regenerator housing at least one discrete heat exchanger and the section of the PT tube housing at least one discrete heat exchanger; a section of incoming helium gas conduit extending between the first and second stages, wherein this section is configured to thermally couple with the at least one discrete heat exchanger of the section of the regenerator and one discrete heat exchanger of the section of the regenerator.

Methods for cooling incoming helium gas to the cryocooler are provided. The methods can include: supplementally cooling the incoming helium gas using portions of one or more of: the regenerator, the PT tube; the helium gas return conduit; and one or more discrete heat exchangers within the regenerator.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the disclosure are described below with reference to the following accompanying drawings.

FIG. 1 is a schematic of an example of continuous precooling using both second-stage regenerator and second-stage pulse tube (PT) cryocooler tube.

FIG. 2 depicts measured performances of the precooling heat exchangers on the second-stage regenerator and the second-stage PT tube.

FIG. 3 is a schematic of an example of discrete heat exchangers using both the second-stage regenerator and the second-stage PT tube.

FIG. 4 depicts schematics of an example of having a system heat exchanger using the helium return line.

FIG. 5 depicts schematics of an example system using the second-stage regenerator, the second-stage PT tube, and the helium return line.

FIG. 6 depicts schematics of an example system using the helium return line as a first step, and the second-stage regenerator and the second-stage PT tube as a second step.

FIG. 7 depicts a system having heat exchangers inside of the second-stage regenerator.

FIG. 8 depicts a system, which has the heat exchangers, equipped with additional heat exchangers in the regenerator.

DESCRIPTION

This disclosure is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8).

Applicant recognizes that overall system efficiency can be increased by supplementally cooling helium gas in the dilution refrigerator loop or a 1 K refrigeration loop between the 1^st stage temperature of the pulse tube (PT) cryocooler to a temperature near the 2^nd stage. For example, the incoming helium gas when additionally cooled through a heat exchanger after the 1^st stage and before the 2^nd stage can significantly reduce the enthalpy of the helium gas before it exchanges heat with the 2^nd stage; thus it reduces the heat load to the 2^nd stage of the PT cryocooler and increases the overall system efficiency.

The present disclosure provides cryocooler systems and methods that increase overall system efficiency. In particular embodiments, the cryocooler systems and methods utilize portions of the cryocooler system to facilitate reduced enthalpy between stages and/or increase mass flow. Specific implementations of the systems and methods can be used to provide additional cooling to helium gas between 1^st and 2^nd stages using a two-stage PT cryocooler. This additional cooling can be provided by portioning the flow of helium gas after the 1^st stage and merging the portioned flows before the 2^nd stage. In other embodiments cooling can be provided from within discrete portions of the cryocooler as well.

The present disclosure will be described with reference to FIGS. 1-8. Referring first to FIG. 1, FIG. 1 depicts a PT cryocooler system according to an embodiment of the disclosure that is configured as a cryogen-free dilution refrigerator configured as a two-stage PT cryocooler. The application could be a dilution refrigerator or other cryogenic systems using heat exchangers between the 1^st and 2^nd stages, such as a 1 K refrigeration system or helium liquefier, for example.

The system can include a PT cryocooler cold head 1, a first-stage regenerator 2, a first-stage PT tube 9, a second-stage PT tube 3, a first cooling station 4, a second-stage regenerator 5, and a second cooling station 6.

In accordance with example implementations, Helium-3 gas enters the DR loop through an inlet 20, it is first precooled in a heat exchanger 21 thermally attached to first cooling station 4 of PT cold head 1 through a thermal coupling 8. After heat exchanger 21, Helium-3 gas proceeds through portions as heat exchanger 40 thermally engaged with second-stage PT tube 3. In accordance with example implementations, increased mass flow can be achieved by receiving cooling power from second-stage PT tube 3. Accordingly, the conduit of the DR loop can be arranged to extend to heat exchanger 40 before proceeding.

In accordance with at least one implementation, the system can include two heat exchangers arranged to receive gas after heat exchanger 21, one discrete portion as heat exchanger 22 thermally engaged with second-stage regenerator 5 and heat exchanger 40 thermally engaged with second-stage PT tube 3. Accordingly, a section of helium gas conduit post heat exchanger 21 can be portioned into segments, in this embodiment divided into two streams: one flows through heat exchanger 22 thermally engaged with second-stage regenerator 5; another one flows through heat exchanger 40 thermally engaged with second-stage PT tube 3. The multiple streams, in this case two streams, of helium gas can then be merged before engaging with heat exchanger 23 that is cooled to 2^nd stage 6 via thermal coupling 7. Heat exchangers 22 and 40 can also be arranged in series. Accordingly, the helium gas enters the heat exchanger 22, then enters the heat exchanger 40, however, it is contemplated that the gas can enter exchanger 40 then exchanger 22.

In the shown embodiment of FIG. 1, the heat exchangers can include coiled segments of the incoming helium conduit about the regenerator or PT tube. Heat exchangers 22 and/or 40 can be continuous heat exchangers and can be made of capillary tubes, such as stainless-steel tubes or CuNi tubes. They can be soldered, glued, or clamped on the outer surfaces of second-stage regenerator tube 5 and/or PT tube 3, for example.

After the 2^nd stage, the cooled helium enters the PT stage. The helium can pass a heat exchanger 24 then a first impedance 25. The helium is expanded and entirely liquefied in a still heat exchanger 26. From the still heat exchanger 26, the Helium-3 flows through a second impedance 27 to a series of counter-flow heat exchangers 28 into a mixing chamber 29.

In mixing chamber 29, two phases of the ³He-⁴He mixture, the concentrated phase (practically 100% ³He) and the dilute phase (about 6.6% ³He and 93.4% ⁴He), are in equilibrium and separated by a phase boundary. The ³He is diluted as it flows from the concentrated phase through the phase boundary into the dilute phase. The heat necessary for the dilution is the refrigerator's useful cooling power. The ³He then leaves the mixing chamber in the dilute. On its way up, the cold, dilute ³He cools the downward flowing concentrated ³He via the heat exchangers 28 and enters still 30. The ³He in still 30 is pumped through a pumping line 31 by vacuum pumps (not shown) at room temperature to conduit 32. The pumps compress the ³He to the inlet 20, completing the cycle.

Providing cooling power after the 1^st stage and before the 2^nd stage lowers the helium enthalpy between the 1^st stage (~50 K) and the 2^nd stage (~3 K), and/or can greatly reduce the heat load to the 2^nd stage. Accordingly, the 2^nd stage can maintain a desired low temperature of ~3 K and provide a high ³He throughput in the dilution unit which can give high refrigeration capacity. This additional cooling between the temperatures of 50 K and 3 K can increase the ³He throughput for high cooling power and overall efficiency of the dilution refrigerator.

The performances of the heat exchangers on the second-stage regenerator and the second-stage PT tube in a two-stage PT cryocooler were measured and data provided in FIG. 2. In the test of the second-stage regenerator only, the helium gas flows through the heat exchanger on the 1^st stage with the conduit thermally engaged on the second-stage regenerator and proceeds to the heat exchanger on the 2^nd stage.

In the test of the second-stage PT tube only, the helium gas flows through the heat exchanger on the 1^st stage with the conduit thermally engaged on the second-stage PT tube and proceeds to the heat exchanger on the 2^nd stage. During these tests, the 1^st stage was kept at 50 K by a heater.

Having the conduits thermally engaged with the second-stage regenerator can provide a helium flow rate of 2 SLM without affecting the 2^nd stage temperature. Having the conduits thermally engaged with the second-stage PT tube can provide a helium flow rate of 1 SLM without increasing the 2^nd stage temperature. The measured results demonstrate that the precooling capacity can be improved by 50% using the second-stage PT tube without losing the 2^nd stage performance.

Referring next to FIG. 3, an example of discrete heat exchanger configurations 31/32 and 33/34 thermally engaged to second-stage regenerator 5 and second-stage PT tube 3 is depicted. In this embodiment, like numbers refer to like parts for the sake of convenience. These discrete heat exchangers can include a plurality of thermal conductors 31 and 34, respectively, thermally engaged with second-stage regenerator 5 and/or second-stage PT tube 3. Conduits 32 and 33, respectively, are thermally engaged with conductors 31 and 34.

Referring to FIG. 4, an example of using return helium 31 for precooling the incoming helium 20 is depicted. Again, in this embodiment, like numbers refer to like parts for the sake of convenience.

In accordance with the embodiment of FIG. 4, a section of incoming helium 20 can be configured as heat exchanger 41 to provide cooling power between 1^st stage 21 and 2^nd stage 22. Heat exchanger 41 can be arranged to be in thermal engagement with line 31. In accordance with example implementations, exchanger 41 can be inside pumping line 31 and may act as a counterflow heat exchanger. In a variation of this embodiment, heat exchanger 41 can be thermally engaged to the outer surface of the pumping line 31. In accordance with this configuration, the helium gas incoming from the 1^st stage can be precooled by heat exchanger 41 to a temperature less than the 1^st stage and/or close to the 2^nd stage before entering heat exchanger 23, after which the helium gas can continue through the system.

FIG. 5 depicts an additional embodiment combining segments of the section of incoming helium 20 to form additional heat exchangers. While a combination of three heat exchangers 22, 40, and 41 are shown, alternative combinations of these heat exchangers is contemplated, for example 22 and 41 or 40 and 41. In accordance with this implementation, helium gas to be liquefied flows from inlet 20, and is cooled by the heat exchanger 21 which is thermally engaged with the 1^st stage. Then the helium gas can be portioned into multiple segments or streams, in this depiction three streams, and they are divided. For example, one steam flows through heat exchanger 22 thermally engaged with the second-stage regenerator 5; another (second) stream flows through heat exchanger 40 thermally engaged with the second-stage PT tube 3; and yet another (third) stream flows through heat exchanger 41 thermally engaged with pumping line 31. The plurality of streams of helium gas can then be merged before thermally engaging with heat exchanger 23 and cooled down to the temperature of the 2^nd stage, after which the helium gas can continue through the system.

An alternative configuration of the embodiment in FIG. 5 is depicted in FIG. 6. In this configuration, helium gas first flows into heat exchanger 41 which is thermally engaged with pumping line 31. The flow of helium is then portioned (in this case divided) into two streams: one steam flows through heat exchanger 22 which is thermally engaged with the second-stage regenerator 5; and the second stream flows through heat exchanger 40 which is thermally engaged with the second-stage PT tube. After which, these two streams of helium are merged before entering heat exchanger 23 and cooled down to the temperature of the 2^nd stage, after which the helium gas can continue through the system.

Still another embodiment of the disclosure provides one or more heat exchangers within discrete portions of the second-stage regenerator. In accordance with this embodiment, FIG. 7 depicts heat exchangers 51 inside of or housed by second-stage regenerator 5. Heat exchanger 51 can extract cooling capacity from second-stage regenerator 5. The second-stage regenerator 5 in a two-stage PT cryocooler can include multi-layer spherical materials. Heat exchangers 51 can be used for separating different layer of spheres, used to prevent mixing of the different layers, and/or configured to thermally engage an interior portion of second-stage regenerator 5 with an exterior portion or housing of second-stage generator 5. Heat exchangers 51 can be constructed of high thermal conductive materials such as copper or aluminum. The heat exchangers 51 have flow channels with opening size less than the size of the regenerator particle. The 3-D printed part, sintered copper screens, sintered copper power disks, etc. can be dividers and heat exchangers.

In accordance with another configuration, FIG. 8 depicts heat exchangers 51 and heat exchanger 22. In accordance with example implementations, these heat exchangers can be associated complimentary to provide for efficient transfer of cooling power from within second-stage regenerator 5 to helium flowing between 1^st stage 21 and 2^nd stage 23, thereby improving cooling before the helium is thermally engaged with 2^nd stage 23. The use of more or even less than the two shown heat exchangers 51 is contemplated.

In compliance with the statute, embodiments of the invention have been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the entire invention is not limited to the specific features and/or embodiments shown and/or described, since the disclosed embodiments comprise forms of putting the invention into effect.

Claims

1. A cryocooler system configured to cool helium gas between the first and second stages, the system comprising:

both a regenerator and PT tube operably configured within the cryocooler system;

first and second stages thermally associated with both the regenerator and PT tube; and

a section of incoming helium gas conduit extending between the first and second stages, wherein this section is configured to thermally couple with both the regenerator and the PT tube.

2. The system of claim 1 wherein the section of incoming helium gas conduit comprises individual segments of conduit, one of the individual segments being in thermal communication with the regenerator, and another of the individual segments being in thermal communication with the PT tube.

3. The system of claim 2 wherein the one individual segment is coiled about the PT tube, and another individual segment is coiled about the regenerator.

4. The system of claim 2 further comprising thermocouples about each of the regenerator and the PT tube, wherein the one of the individual segments is in thermal communication with the thermocouples about the regenerator, and the other of the individual segments is in thermal communication with the thermocouples about the PT tube.

5. The system of claim 2 wherein the section branches into the segments about the first stage, and the segments merge into the section about the second stage.

6. The system of claim 1 wherein both the regenerator and PT tube define individual sections that extend between the first and second stages, and wherein the section of incoming helium gas thermally couples with the individual sections of the first and second stages in series.

7. A cryocooler system configured to cool helium gas between the first and second stages, the system comprising:

both a regenerator and PT tube operably configured within the cryocooler system;

first and second stages thermally associated with both the regenerator and PT tube;

a section of return helium gas extending between the first and second stages; and

a section of incoming helium gas conduit extending between the first and second stages, wherein this section is configured to thermally couple with helium return section.

8. The system of claim 7 wherein the section of incoming helium gas coils about the section of return helium gas.

9. The system of claim 7 further comprising wherein the section is configured to thermally couple with the PT tube and/or the regenerator.

10. The system of claim 9 wherein the section of incoming helium gas defines individual segments, each of the segments thermally coupling with the section of return helium gas and one or both of the PT tube and/or the regenerator.

11. The system of claim 10 wherein the section branches into segments about the first stage and merges into the section about the second stage.

12. The system of claim 10 wherein the section is configured to provide incoming helium gas about the section of return helium gas and then about one or both of the PT tube and the regenerator.

13. The system of claim 12 wherein the section defines individual segments about the PT tube and the regenerator.

14. A cryocooler system configured to cool helium gas between the first and second stages, the system comprising:

both a regenerator and PT tube operably configured within the cryocooler system;

first and second stages thermally associated with both the regenerator and PT tube, a section of the regenerator residing between the first and second stages, the section of the regenerator housing at least one discrete heat exchanger; and

a section of incoming helium gas conduit extending between the first and second stages, and in thermal communication with the discrete heat exchangers housed within the regenerators.

15. The system of claim 14 wherein the section of incoming helium gas coils about the regenerator.

16. The system of claim 14 wherein a segment of the regenerator extends between the discrete heat exchangers.

17. The system of claim 15 wherein the section of incoming helium gas is in thermal communication with the segment of the regenerator.

18. A method for cooling incoming helium gas between the first stage and the second stage of a cryocooler, the method comprising:

supplementally cooling the incoming helium gas using discrete portions of one or more of: the regenerator and the PT tube; the helium gas return conduit; the helium gas return conduit and the PT tube; the helium gas return conduit, the PT tube and the regenerator; and/or one or more discrete heat exchangers within the regenerator.