In-line configured circulating cryogenic cooler system

Abstract

A circulation loop that transports refrigeration to a remote location is connected in series between a Gifford-McMahon (GM) or GM type pulse tube cold head and the compressor. High pressure gas from the compressor can flow through a remote heat station before returning to the cold head, or low pressure gas can flow from the cold head to a remote heat station before returning to the compressor. A first portion of the gas, which can include all of the gas at ambient temperature, enters a counterflow heat exchanger, is cooled by the cold head, flows to a remote load, and then returns to ambient temperature as it flows through the counterflow heat exchanger. The high or low pressure line can have a circulation control valve that redirects a second portion of the gas to flow directly between the cold head and the compressor. A controller adjusts the circulation control valve to optimize cooling of the remote load.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 63 / 226,851, filed Jul. 29, 2021, the entire disclosure of which is hereby incorporated by reference herein.

[0002] The present invention relates to the cooling of a load remote from a Gifford - McMahon (GM) or GM - type pulse tube cold head (expander).

Background Art

[0003] Valve-equipped regenerative cycle cryogenic refrigerators (cryocoolers), such as Gifford-McMahon (GM) or pulse tube cryocoolers, are well-known for providing cryogenic refrigeration at refrigeration loads of less than 1 kW due to their relative efficiency, small size, and relatively low cost. These cryocoolers are defined by having a compressor that provides high-pressure gas to a cold head and receives low-pressure gas from the cold head, and a cold head that includes a valve that circulates gas to a reciprocating displacer that transfers gas through a regenerator in warm and cold displaced volumes. A drawback of this type of cryocooler is that the refrigeration provided is only available at the cold surface located at the cold head. Unlike Brayton cycle expanders that can discharge low-temperature gas at low pressure and circulate it to a remote load, these regenerative expanders return the low-pressure gas at room temperature. To address this drawback, a system has been developed that combines a regenerative cycle cryocooler with a fluid-containing loop that transfers refrigeration by circulating a cooling fluid from the cold surface of the cold head to a location remote from the cold head. When cooling over a wide temperature range is required, or when the nature of the object to be cooled prevents cooling by a liquid or a phase change from a liquid to a gas, a gas is used as the fluid in such a loop. In this case, refrigeration is transferred by the sensible heat of the gas, where the temperature decreases (is cooled) in one part of the loop and increases (warms up) in another part of the loop.

[0004] Two types of circulation loops that use gas as the circulating fluid are described. One type with a cryogenic circulator has an all-cryogenic circulation loop and includes a mechanism for moving a cooling fluid through the loop. The other type with a warm circulator has a portion of the loop that includes a cryogenic cold head and a remote load, and a portion that includes a mechanism for moving a fluid at a warm temperature (e.g., above room temperature). A heat transfer heat exchanger is disposed within the loop and between the two portions to enable the cooling portion of the loop to operate at a temperature significantly lower than the temperature of the circulator. The heat transfer heat exchanger cools the fluid coming from the circulator and warms the fluid returning to the circulator.

[0005] Examples of systems with cryogenic circulators are described in U.S. Patent No. 6,347,522, British Patent 2,433,581, and numerous technical papers such as Cryogenic Cooler 18, Kim et al., "Cryogenic Thermal Studies on Cryocooler-Based Helium Circulation Systems for Gas Cooled Superconducting Power Devices". U.S. Patent No. 10,704,809 describes a system that includes a GM expander having means for using a cryogenic circulator to cool or warm a cryogenic circulator and a remote load. In these systems, the circulation loop is separated from the cryogenic cooler, such that the circulation loop and the cryogenic cooler do not share or exchange fluids. A variation of the system that includes a cooling circulation mechanism that shares or exchanges fluids with the cryogenic cooler is described in Cryogenic Cooler 16, Maddocks et al., "Performance Test of Pulse Tube Cooler with Integrated Circulator". In this variation, the circulating fluid originates within the cryogenic surface of the cryogenic cooler, is discharged within the cryogenic surface, and is moved by a pressure swing within the cryogenic cooler that is rectified to a direct current by a check valve.

[0006] Examples of systems with warm circulators are described in U.S. Patent No. 5,889,456, U.S. Patent No. 9,612,062, and the technical paper "Remote Helium Cooling Loops for Laboratory Applications" by Cryocooler 17, Trollier, et al. U.S. Patent No. 7,003,977 describes a circulation system having a refrigeration component that can have either a warm or a cryogenic circulator. In these examples, the cryocooler and the circulation loop are separated as described above. Examples of systems with warm circulators in which the circulation loop and the cryocooler share and exchange fluid are described in U.S. Patent No. 7,474,099 and the technical paper "Remote Cooling with the HEC COOLER" by Cryocooler 15, Michaelian, et al. U.S. Patent Application Publication No. 2021 / 0025624 describes using an ejector to circulate a portion of the compressor flow to increase the cryogenic flow of a remote load. In these examples, one compressor is used for both the cold head and a circulation loop arranged in parallel with the cold head. An example of a system with a warm circulator in which the cryocooler is exchanged with a heat exchanger cooled by a consumable cryogenic fluid is described in U.S. Patent No. 6,923,009.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] These prior disclosures do not teach, and what is disclosed in the present invention is a system in which a circulation loop and a cryocooler share and exchange fluid, and the circulation loop is arranged in a flow series with the warm intake or exhaust of the cold head of the cryocooler.

MEANS FOR SOLVING THE PROBLEMS

[0008] The circulation loop for transferring refrigeration to a remote location is connected in series between a GM or GM-type pulse tube cold head and a compressor. Some or all of the gas flowing between the compressor and the cold head is redirected to be cooled by the cold head and then cools the remote load before rejoining the portion of the gas flowing directly to or from the cold head. The high-pressure gas from the compressor can flow through the remote heat station before returning to the cold head (expander), or the low-pressure gas can flow from the cold head to the remote heat station before returning to the compressor. The circulating gas flows through a counterflow heat exchanger disposed between lines at ambient temperature connected to the cold head and the compressor, and through the low-temperature surface or surfaces of the cold head and the remote load. The line through which the gas flowing directly to or from the compressor passes has a circulation control valve that controls the pressure drop that redirects the flow toward the circulation loop and drives the flow through the circulation loop. A control device having inputs from various sensors adjusts the circulation control valve to optimize the cooling of the load. The gas circulating through the load is referred to as the first portion, and the remainder of the gas flowing directly between the compressor and the cold head is referred to as the second portion.

[0009] The circulation loop can include elements such as isolation valves, adsorbents, inlets and outlets, bayonets and vacuum jacket transfer lines, and heaters to support the function of cooling the remote load to cryogenic temperatures and warming it to room temperature.

[0010] These advantages and other advantages are achieved, for example, by a cryogenic refrigeration system that circulates gas to a remote load. The cryogenic refrigeration system includes a compressor that compresses gas from low pressure to high pressure, and at least one Gifford-McMahon (GM) or GM-type pulse tube cold head that receives the gas from the compressor in a high-pressure line at ambient temperature and returns the gas into a low-pressure line to generate refrigeration on one or more low-temperature surfaces of a GM or GM-type pulse tube, and a circulation loop through which all or part of the gas in one of the high-pressure and low-pressure lines flows. The circulation loop transfers refrigeration from the one or more low-temperature surfaces to a remote load. These advantages and other advantages are achieved, for example, by a method of adjusting a circulation control valve to control cooling of a remote load.

[0011] The drawings, which are not intended to be limiting and are for illustrative purposes only, depict one or more embodiments in accordance with the present invention. In the drawings, like reference numerals refer to the same or similar elements.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

[0013] In this section, some embodiments of the present invention will be described in more detail with reference to the accompanying drawings showing preferred embodiments of the present invention. However, the present invention can be embodied in many different forms and should not be construed as limited to the embodiments disclosed herein. That is, these embodiments are provided for the purpose of conveying the scope of the present invention to those skilled in the art so that the disclosure will be complete and thorough. In the drawings, the same or similar parts are denoted by the same reference numerals and the description is usually not repeated.

[0014] Embodiments provide a system that cools a load that is remotely located and operates at cryogenic temperatures from a Gifford-McMahon (GM) or GM-type pulse tube cold head (expander) by circulating helium. Referring to FIG. 1, a cryogenic refrigeration system 100 that provides refrigeration to a remote load 80 is illustrated by arranging a circulation loop in series with a cold head 40. In particular, a compressor 20 provides a high-pressure helium stream at ambient temperature (room temperature), and the helium stream flows directly through line 10 into the warm end of the cold head (expander) 40. The cold head 40 operates to receive the high-pressure helium gas, expand the gas to provide refrigeration to the low-temperature surface 42, and exhaust the gas into line 13 at a first low pressure P1' and a temperature close to ambient temperature (room temperature). Some or all of the helium stream exhausted from the cold head 40 flows into the circulation loop through line 14, and the remaining helium stream returns to the compressor 20 through the circulation control valve 90 and line 12 of the return pressure P1. The circulation loop arranged in series with the cold head is part of the system that includes the flow entering line 14 and exiting line 16.

[0015] The helium entering the circulation loop through line 14 flows through the supply side of the heat transfer heat exchanger 60 and is cooled by the counter helium flow to a temperature close to the low operating temperature of the circulation loop. The helium flows from the supply side of the heat transfer heat exchanger 60 to the heat exchanger 44 and is further cooled by the refrigeration provided at the low temperature surface 42 of the cold head 40. Thereafter, the circulating helium flows through line 15 to the heat exchanger 72 to cool the remote load 80. The helium then returns through the heat exchanger 60, cools the supply side helium, and then merges into line 12 through line 16 and returns to the compressor 20 at pressure P1. Lines 14 and 16 pass through the warm flange 21, and the warm flange 21 separates the components operating at room temperature from the cryogenic components isolated by the vacuum 22. Most GM and GM type pulse tube cryocoolers are designed to operate at ambient temperatures between 10°C and 40°C, although some can be designed to operate outside this range.

[0016] The pressures of helium in lines 10 and 12 in the compressor are usually in the ranges of 2 - 3 MPa and 0.5 - 1 MPa respectively. When the system is at the operating temperature, the pressure difference across the circulation control valve 90 is usually about 0.1 MPa, but it becomes higher during cooling or heating. The circulation control valve 90 adjusts the pressure drop dP between the pressure P1 in line 12 in the compressor 20 and the pressure P1’ (P1 + dP) in line 13 at the outlet of the cold head. When the pressure drop increases, the flow rate through the circulation loop increases, and the cooling rate of the cold head 40 decreases. The advantage of active control can be seen when using a cryogenic refrigeration system to cool a remote load from room temperature. When the remote load 80 is warm (close to room temperature), the pressure loss in the circulation loop is relatively high. This is because the gas has a lower density and higher viscosity than at low temperatures. The refrigeration efficiency is also relatively high. This is because the heat loss in the cold head 40 is low. By reducing the flow rate through the circulation control valve 90, the flow rate through the circulation loop increases, and the temperature difference dT between the low-temperature surface 42 at temperature T1 and the remote load 80 at temperature T1 + dT is minimized. The first part of the circulating gas is cooled at the low-temperature surface 42, and the refrigeration is transferred to the remote load 80, which warms up. Temperature sensors 42a and 80a measure the temperature at these two positions respectively.

[0017] By actively controlling the circulation using the circulation control valve 90, the flow rate through the circulation loop and the flow rate through the cold head 40 are optimized for a given set of operating conditions. Measurements of flow rate, temperature, pressure, differential pressure, or combinations thereof are used to inform the flow rate control decision of the circulation control valve 90.

[0018] A preferred method is to use a control device (not shown) that adjusts the circulation control valve 90 to minimize the temperature difference between sensors 42a and 80a. The position and type of the sensors are not limited to the temperature sensors 42a and 80a shown in FIG. 1, and can be any position and type of sensor that can effectively detect the pressure, temperature, and / or flow rate of the gas in the circulation loop. The amount of some gas flowing through the circulation loop is determined to minimize the temperature of the remote load 80 or to maximize the cooling rate at which the remote load 80 is cooled.

[0019] FIG. 2 shows a cryogenic refrigeration system 200 that is different from the cryogenic refrigeration system 100 in that high-pressure gas is circulated from the compressor 20 to the remote load 80 before entering the cold head 40. Low-pressure gas returns directly from the cold head 40 to the compressor 20 through line 12. The cryogenic refrigeration system 200 can also have the circulation control valve 90 shown in FIG. 1, but FIG. 2 shows that all of the flow from the compressor 20 is circulated. Whether the gas is circulated at high pressure or low pressure, the cryogenic refrigeration system can have the circulation control valve 90 as shown in the cryogenic refrigeration system 100 (see also FIG. 4), or can not include the circulation control valve 90 as shown in the cryogenic refrigeration system 200. The gas exits the compressor 20 through line 10 at pressure Ph, returns to the cold head 40 through line 11 at pressure Ph', and the pressure difference dP is the pressure drop in the circulation loop. The circulation loop is typically designed to have a pressure drop dP that is less than about 10% of Ph - P1.

[0020] An example is given of cooling a load at 80K using a GM refrigerator that produces 600W of cooling at 80K, but at temperatures below 80K with a pressure of 2.0 / 0.8MPa and a flow rate of 10g / s at the cold surface 42, about 10W / K less is produced. The circulation loop is preferably designed to have a pressure drop lower than 0.1MPa and a high heat exchanger efficiency, for example.

[0021] Figure 3 shows a graph of the cooling available at 80 K for the remote load 80 as a function of the circulation rate at heat exchanger efficiencies of 98.5% and 99%. Circulating the gas to cool the remote load 80 at 80 K requires that the gas be cooled below 80 K. Figure 3 also shows the temperature of the cryogenic surface 42, assuming that the gas has been cooled to that temperature. At a circulation flow rate of 6 g / s and a heat exchanger 60 efficiency of 98.5%, assuming no losses outside the heat exchanger 60, up to 375 W of cooling is available at the remote load 80. The two main causes of the losses are 105 W in the heat exchanger and a 120 W reduction in cooling capacity, because the expander 40 is operating at 68 K. At a heat exchanger efficiency of 99%, the optimum circulation flow rate is approximately 8 g / s. The heat exchanger loss is 94 W, the expander 40 operates at 70.2 K, and with a 98 W reduction in cooling capacity, 408 W remains available for cooling the remote load 80. If the circulation control valve 90 is closed and all of the flow passes through the circulation loop, 404 W of cooling is available at the remote load 80. The designer can also choose to eliminate the circulation control valve 90 and circulate all of the flow.

[0022] The flow rate that minimizes the temperature difference between the cryogenic surface 42 and the remote load 80 in the foregoing example can be obtained using a control device (not shown) that adjusts the flow rate circulated using the circulation control valve 90.

[0023] Figure 4 shows a cryogenic refrigeration system 250 having a two-pass circulation loop between the circulation control valve 90 and the cryogenic surface 42 and the remote load 80. The cryogenic refrigeration system 250 includes a first-pass heat exchanger 44a and 72a connected by line 15a, and a second-pass heat exchanger 44b and 72b connected by lines 15b and return line 17. Figure 5 shows a graph of the cooling available from the system 250 for a heat exchanger 60 having an efficiency of 99% under the same assumptions as in Figure 3. The optimum circulation flow rate is near 6 g / s, the heat exchanger loss is 71 W, the expander is at 72.7 K so the reduction in cooling capacity is 73 W, and 457 W remains available for cooling the remote load 80.

[0024] FIG. 6 shows a schematic diagram of a cryogenic refrigeration system 300 that shows how a basic circulation system can be adapted to different applications. The circulation loop is shown as high pressure, as in system 200, but similarly, the above adaptation can also be applied to system 100 that circulates gas at low pressure.

[0025] Many applications require warming the load as part of maintenance or the process. Some GM and GM-type pulse tubes can "run backwards" and can generate heating rather than cooling. In these cases, no changes are needed to systems 100 and 200. In cold heads that cannot run backwards, the gas in line 15 and then the heater 54 that heats the remote load 80 require the gas to be circulated around the cold head. The bypass valve 94 allows the gas to be circulated even while the cold head 40 is blocked off.

[0026] It is common for the cryogenic components of a cryogenic refrigerator to be housed within their own vacuum housing 62 and for gas to be circulated to the remote load 80 through vacuum break (or jacket) transfer lines 74a and 74b. The transfer lines can be removably connected using bayonets 70a and 70b or can share the common vacuum 22 of the refrigerator. The remote load 80 can be cooled by flowing gas through the remote load or by the heat exchanger 72. One concern with cooling the remote load 80 by circulating gas through the remote load is keeping the gas clean. The isolation valves 68a and 68b, when closed, allow the gas within the refrigerator to be kept clean while connected to the remote load 80. After being connected to the remote load, the circuit needs to be cleaned. This is usually accomplished by filling and evacuating the lines through valves 64a and 64b. An adsorber 52 can be added to line 15 to assist in keeping the gas clean. When the system is cooled, gas is added through valve 64a or 64b.

[0027] System 300 includes a buffer volume 96 between the circulation control valve 90 and the cold head 40. The buffer volume 96 serves to smooth the flow entering the cold head. In the case of System 200, it is added to line 11. Options not previously described or illustrated include using one or more cold heads, operating one or more compressors arranged in parallel, using a multi-stage cold head having two or more cryogenic surfaces to circulate gas at different temperatures to a remote load, operating the cold heads at different speeds, adding a gas storage system that enables adding gas to or removing gas from the system, or using other gases such as neon, argon, or nitrogen.

[0028] The terms and descriptions used herein are for illustrative purposes only and are not intended to limit the invention. It will be apparent to those skilled in the art that many modifications are possible within the spirit and scope of the present invention and the embodiments described herein.

Description of Reference Numerals

[0029] 10 Line 11 Line 12 Line 13 Line 14 Line 15 Line 15a Line 15b Line 16 Line 17 Return Line 20 Compressor 21 Flange 22 Vacuum 40 Cold Head, Expander 42 Cryogenic Surface 44 Heat Exchanger 44a Heat Exchanger 44b Heat Exchanger 52 Adsorber 54 Heater 60 Heat Exchanger 62 Vacuum Housing 64a Valve 64b valve 68a isolation valve 68b isolation valve 70a bayonet 70b bayonet 72 heat exchanger 72a heat exchanger 72b heat exchanger 74a transfer line 74b transfer line 80 remote load 90 circulation control valve 94 bypass valve 96 buffer volume 100 cryogenic refrigeration system 200 cryogenic refrigeration system 250 cryogenic refrigeration system 300 cryogenic refrigeration system

Claims

1. A cryogenic refrigeration system for circulating gas to a remote load, wherein the cryogenic refrigeration system comprises: a compressor for compressing gas from low pressure to high pressure; at least one Gifford-McMahon (GM) or GM-type pulse tube cold head that receives all of the gas at ambient temperature from the compressor in a high-pressure first line and returns all of the gas at a temperature close to ambient temperature into a low-pressure second line to generate refrigeration on one or more low-temperature surfaces of a GM or GM-type pulse tube; a circulation loop for transferring refrigeration from the one or more low-temperature surfaces of the GM or GM-type pulse tube to the remote load; comprising the circulation loop is i) connected to the second line, and all or part of the gas from the second line flows through the circulation loop to transfer the refrigeration to the remote load and then returns to the second line, or ii) connected to the first line, and all or part of the gas from the first line flows through the circulation loop to transfer the refrigeration to the remote load and then returns to the first line, A cryogenic refrigeration system characterized in that it is configured as described above.

2. The cryogenic refrigeration system according to claim 1, wherein one of the first line and the second line has a circulation control valve controlled by a control device connected to a sensor.

3. The cryogenic refrigeration system according to claim 1, further comprising a heat transfer type heat exchanger in the circulation loop located between the ambient temperature and the temperature of the one or more low-temperature surfaces.

4. The cryogenic refrigeration system according to claim 3, further comprising an isolation valve for isolating the line connected to the remote load from other parts of the system.

5. The cryogenic refrigeration system according to claim 4, further comprising one or more ports configured to add or remove gas in the line connected to the remote load.

6. The cryogenic refrigeration system according to claim 1 or 2, wherein the circulation loop further comprises a second path for returning the circulating gas from the remote load to the one or more low-temperature surfaces and then back to the remote load.

7. The cryogenic refrigeration system according to claim 1 or 2, wherein the cold head has two low-temperature surfaces at different temperatures.

8. The cryogenic refrigeration system according to claim 1 or 2, characterized in that the gas is one or more gases selected from the group consisting of helium, neon, nitrogen, and argon.

9. The cryogenic refrigeration system according to claim 1 or 2, further comprising one or more buffer volumes communicating with the cold head to smooth gas flow pulsations.

10. The cryogenic refrigeration system according to claim 1 or 2, further comprising a bayonet connection between the remote load and the one or more cryogenic surfaces.

11. The cryogenic refrigeration system according to claim 1 or 2, further comprising a vacuum jacket transfer line between the remote load and the one or more cryogenic surfaces.

12. A method of cooling a remote load by using a cryogenic refrigeration system that circulates a gas to the remote load, the cryogenic refrigeration system comprising: a compressor that compresses the gas from low pressure to high pressure; at least one GM or GM-type pulse tube cold head that receives all of the gas at ambient temperature from the compressor in a high-pressure first line and returns all of the gas at a temperature close to ambient temperature into a low-pressure second line to generate refrigeration at at least one cryogenic surface of the GM or GM-type pulse tube; a circulation loop that transfers refrigeration from the one or more cryogenic surfaces of the GM or GM-type pulse tube to the remote load; comprising the circulation loop is i) connected only to the second line, and all or part of the gas from the second line flows through the circulation loop to transfer the refrigeration to the remote load and then returns to the second line, or ii) connected only to the first line, and all or part of the gas from the first line flows through the circulation loop to transfer the refrigeration to the remote load and then returns to the first line, configured such that one of the first line and the second line has a circulation control valve that redirects a first portion of the gas to flow through the circulation loop to transfer the refrigeration from the cryogenic surface to the remote load, the method comprising adjusting the circulation control valve to control the cooling of the remote load.

13. The method according to claim 12, characterized in that the amount of the first part of the gas is determined based on at least one of the measured pressure, temperature, or flow rate in the first line and the second line.

14. The method according to claim 12 or 13, characterized in that the amount of the first part of the gas is determined to minimize the temperature of the remote load.

15. The method according to claim 12 or 13, characterized in that the amount of the first part of the gas is determined to maximize the cooling rate for cooling the remote load.

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