A continuous refrigeration system and method using a mixture of helium-3 and helium-4 with very low concentration and without phase separation

Abstract

The present application relates to the field of refrigeration equipment, and more particularly to a phase separation-free continuous refrigeration system and method using a mixture of extremely low concentration of helium-3 and helium-4 as refrigerant. The system comprises a pre-cooling machine, a first-stage heat exchanger, a second-stage heat exchanger, a third-stage heat exchanger, a 1K pool, a distillation chamber, a first-stage cold plate, a second-stage cold plate, a third-stage cold plate, a fourth-stage cold plate, a first circulation pipeline, a second circulation pipeline, a first gas pipeline, and a second gas pipeline. The first gas pipeline is connected to an external helium-4 gas source, and the second gas pipeline is connected to an external mixture of helium-3 and helium-4. The system uses a mixture of helium-3 and helium-4 as refrigerant. The mixture has a saturated vapor pressure in the low-temperature region that is significantly higher than that of pure helium-4 and approaches that of pure helium-3 without phase separation. By using three-stage cooling, the system achieves a base temperature of 462 mK and a refrigeration power of 1 mW at 533 mK and 2 mW at 585 mK, with a helium-3 consumption of only 0.9 L.

Description

Technical Field

[0001] This invention relates to the field of refrigeration equipment, and in particular to a phase-separation-free continuous refrigeration system and refrigeration method using a mixture of extremely low concentrations of helium-3 and helium-4 as the working fluid. Background Technology

[0002] Vacuum-reduced evaporative refrigeration is a refrigeration technology used to achieve low and even extremely low temperature environments, widely applied in materials science, condensed matter physics experiments, and other fields. It is based on the endothermic evaporation process of a liquid working fluid under reduced pressure, achieving a temperature decrease. Currently, systems based on the principle of vacuum evaporation for extremely low temperature refrigeration mainly fall into two categories: helium-3 / helium-4 evaporative refrigeration systems and helium-3 / helium-4 adsorption refrigeration systems. Both are based on the characteristic that the saturated vapor pressure of helium-3 and helium-4 changes with temperature, and can achieve low-temperature environments in the range of 0.3-1.5 K.

[0003] Adsorption refrigeration technology utilizes the physical adsorption of helium by an adsorbent under low-temperature conditions, creating a decompression-evaporation-like effect to achieve cryogenic temperatures. However, this technology relies on the periodic regeneration of the adsorbent, making it difficult to achieve a continuous and stable refrigeration process. In contrast, helium-3 / helium-4 evaporative refrigeration systems use external pumps to continuously evacuate the cryogenic liquid, maintaining a stable evaporation process and achieving continuous, controllable, and highly reliable refrigeration operation. Therefore, helium-3 / helium-4 evaporative refrigeration technology has become the most mainstream and widely used refrigeration solution in the 0.3–1.5K temperature range.

[0004] In evaporative refrigeration systems using helium-4 as the working fluid, the saturated vapor pressure of helium-4 decreases sharply with decreasing temperature, reaching a minimum temperature of only about 0.8 K. To overcome this lower temperature limit, helium-3, an isotope of helium-4, must be used as the working fluid. Under the same temperature conditions, the saturated vapor pressure of helium-3 is about two orders of magnitude higher than that of helium-4; therefore, the minimum temperature that can be reached using helium-3 for evaporative refrigeration is 0.3 K. However, this requires the consumption of a large amount of helium-3, which is a scarce and expensive strategic resource. The large-scale use of helium-3 significantly increases system costs and application barriers, making it difficult to meet the comprehensive requirements of high reliability, low cost, and continuous operation capability in practical applications.

[0005] To reduce helium-3 consumption while achieving cryogenic performance close to that of helium-3 evaporative cooling, researchers have proposed a refrigeration system based on the phase separation mechanism of a helium-3-helium-4 mixed solution. The principle is based on the phase separation characteristics of the helium-3-helium-4 mixed solution under extremely low temperatures: the helium-rich phase floats on the upper layer, and by pumping it out, a lower temperature than that achieved with pure helium-4 evaporative cooling can be obtained. However, this approach still has significant limitations: the required helium-3 concentration remains relatively high, and the system's lowest temperature can only reach approximately 600 mK. Therefore, in practical applications, existing refrigeration systems based on phase separation mechanisms still struggle to simultaneously meet the three key performance indicators of low helium-3 consumption, low base temperature, and high cooling power.

[0006] Therefore, existing technologies need to be improved. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a phase-separation-free continuous refrigeration system and refrigeration method using a mixture of helium-3 and helium-4 with extremely low concentrations, aiming to solve the problems of high helium-3 consumption, high base temperature and difficulty in achieving refrigeration power in existing phase separation-based refrigeration systems in practical applications.

[0008] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a phase-separation continuous refrigeration system employing a mixture of extremely low concentrations of helium-3 and helium-4 as the working fluid, comprising: Precooler, first-stage heat exchanger, second-stage heat exchanger, third-stage heat exchanger, 1K tank, distillation chamber, first-stage cold plate, second-stage cold plate, third-stage cold plate, fourth-stage cold plate, circulation pipeline one, circulation pipeline two, first gas pipe, second gas pipe. The third-stage heat exchanger is located above the 1K pool; the second circulation pipeline is located above the 1K pool and connected to the inside of the 1K pool; the first circulation pipeline is located above the distillation chamber and connected to the inside of the distillation chamber; the first gas pipe is connected to an external helium-4 gas source; the second gas pipe is connected to an external helium-3 and helium-4 mixed working fluid source. The first-stage and second-stage cold plates are spaced apart on the low-temperature cavity of the precooler, the third-stage cold plate is located at the bottom of the 1K pool, and the fourth-stage cold plate is located at the bottom of the distillation chamber. The first gas pipe passes through the first stage heat exchanger, then extends to and passes through the precooler, then extends to and passes through the third stage heat exchanger, and then connects to the 1K pool. The second gas pipe passes through the second-stage heat exchanger, then extends to and passes through the precooler, then extends to and passes through the 1K pool, and then connects to the distillation chamber.

[0009] Optionally, a first heat switch is provided between the secondary and tertiary cold plates.

[0010] Optionally, a second heat switch is provided between the secondary and quaternary cold plates.

[0011] Optionally, a flow resistance is provided at the location of the first air pipe connected to the 1K pool.

[0012] Optionally, a flow resistance 2 is provided at the location of the second gas pipe connected to the distillation chamber.

[0013] Optionally, the precooling machine is a pulse tube refrigerator, a GM refrigerator, or a liquid helium bath.

[0014] Optionally, the first thermal switch and the second thermal switch may be air-gap thermal switches, mechanical thermal switches, superconducting thermal switches or magnetoresistive thermal switches.

[0015] Optionally, the molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid is 1%-20%.

[0016] Optionally, the molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid is 1%-6.4%.

[0017] Optionally, the molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid is 3.7%.

[0018] Secondly, the present invention provides a phase-separation continuous refrigeration method using a mixture of extremely low concentrations of helium-3 and helium-4 as the working fluid, comprising the following sequential steps: Pre-cooling: Start the pre-cooling machine and maintain it for 11-13 hours; 1K refrigeration cycle: Helium-4 gas is introduced into the first gas pipe, and the precooler is kept on. The introduced helium-4 gas passes through the first heat exchanger through the first gas pipe, then extends to the precooler and passes through the precooler, then extends to the third heat exchanger and passes through the third heat exchanger, and then liquefies and flows into the 1K pool; the 1K pool is depressurized and evaporated through the second circulation pipe until the temperature stabilizes. Helium-3 and Helium-4 Evaporative Refrigeration: A mixture of helium-3 and helium-4 working fluid is introduced into the second gas pipe, allowing it to pass through the second-stage heat exchanger, then extend to and pass through the precooler, then extend to and pass through the 1K pool, and finally liquefy and flow into the distillation chamber. The mixture is then subjected to reduced pressure evaporation in a pair of distillation chambers through a circulation pipeline until a stable temperature is reached, thus completing the phase-free continuous refrigeration using a mixture of extremely low concentrations of helium-3 and helium-4 working fluid.

[0019] Beneficial Effects: This invention provides a continuous refrigeration system and method using a mixture of helium-3 and helium-4 with extremely low concentrations as the refrigerant. The system utilizes this mixture, especially at extremely low concentrations, which exhibits a significantly higher saturated vapor pressure than pure helium-4 but close to that of pure helium-3 in the low-temperature region without phase separation. By employing a three-stage cooling system—including a first-stage precooler, a second-stage helium-4 evaporative refrigeration, and a third-stage helium-3 and helium-4 evaporative refrigeration—continuous and stable refrigeration below 500 mK is achieved. The system performance reaches a base temperature of 462 mK and refrigeration power of 1 mW at 533 mK and 2 mW at 585 mK, with a helium-3 consumption of only 0.9 L. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the phase-separation continuous refrigeration system using a mixture of extremely low concentrations of helium-3 and helium-4 as the working fluid in Embodiment 1 of the present invention.

[0021] Figure 2 Schematic diagram of the evaporative cooling principle of a mixed working fluid of 3.7% concentrated helium-3 and helium-4.

[0022] Figure 3 This is a phase diagram of a mixture of helium-3 and helium-4 working fluids. Detailed Implementation

[0023] This invention provides a phase-separation continuous refrigeration system and method using a mixture of helium-3 and helium-4 with extremely low concentrations. To enable those skilled in the art to better understand this invention, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] Due to manufacturing techniques and / or tolerances, variations in the shapes shown in the accompanying drawings may occur. Therefore, the examples described herein are not limited to the specific shapes shown in the drawings, but include changes in shape that may occur during manufacturing. The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all contents, operations, or steps, nor do they necessarily need to be performed in the order described. For example, some operations or steps may be broken down, combined, or partially merged, so the actual order of execution may change depending on the specific circumstances.

[0025] As used herein, the term “and / or” includes any one of the relevant items listed and any combination of any two or more items.

[0026] Although terms such as “first,” “second,” and “third” may be used herein to describe individual components, assemblies, regions, layers, or parts, these components, assemblies, regions, layers, or parts are not limited by these terms. Rather, these terms are used only to distinguish one component, assembly, region, layer, or part from another. Therefore, without departing from the teachings of the examples described herein, the first component, assembly, region, layer, or part referred to as the second component, assembly, region, layer, or part may also be referred to as the second component, assembly, region, layer, or part.

[0027] For ease of description, spatial relation terms such as “above,” “upper,” “below,” and “lower” are used herein to describe the relationship between one element and another, as shown in the accompanying drawings. Such spatial relation terms are intended to include not only the orientation depicted in the drawings but also different orientations of the device during use or operation. For example, if the device in the drawings is flipped, an element described as being “above” or “upper” relative to another element will subsequently be “below” or “lower” relative to that other element. Therefore, the term “above” includes both “above” and “below” orientations depending on the spatial orientation of the device. The device may also be positioned in other ways, and the spatial relation terms used herein will be interpreted accordingly.

[0028] The terminology used herein is for the purpose of describing various examples only and is not intended to limit this disclosure. Unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. The terms “comprising,” “including,” and “having” enumerate the stated features, quantities, operations, components, elements, and / or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, operations, components, elements, and / or combinations thereof.

[0029] This embodiment provides a phase-separation continuous refrigeration system using a mixture of extremely low concentrations of helium-3 and helium-4 as the working fluid, such as... Figure 1 As shown, it includes: Precooler 1, First-stage heat exchanger 2, Second-stage heat exchanger 3, Third-stage heat exchanger 4, 1K tank 5, Distillation chamber 8, First-stage cold plate 11, Second-stage cold plate 12, Third-stage cold plate 13, Fourth-stage cold plate 14, Circulation pipeline 1 15, Circulation pipeline 2 16, First gas pipe 17, Second gas pipe 18, The third-stage heat exchanger 4 is located above the 1K pool 5; the second circulation pipe 16 is located on the 1K pool 5 and connected to the inside of the 1K pool 5; the first circulation pipe 15 is located on the distillation chamber 8 and connected to the inside of the distillation chamber 8; the first gas pipe 17 is connected to an external helium-4 gas source; the second gas pipe 18 is connected to an external helium-3 and helium-4 mixed working fluid source. The first-stage cold plate 11 and the second-stage cold plate 12 are spaced apart on the low-temperature cavity of the precooler 1, the third-stage cold plate 13 is located at the bottom of the 1K pool 5, and the fourth-stage cold plate 14 is located at the bottom of the distillation chamber 8. The first gas pipe 17 passes through the first stage heat exchanger 2, then extends to and passes through the precooler 1, then extends to and passes through the third stage heat exchanger 4, and then communicates with the 1K pool 5. The second gas pipe 18 passes through the second stage heat exchanger 3, then extends to and passes through the precooler 1, then extends to and passes through the 1K pool 5, and then communicates with the distillation chamber 8.

[0030] In this embodiment, the primary cold plate 11 receives the initial cooling capacity of the precooler 1, isolates room temperature radiative heat leakage, and provides overall precooling. The secondary cold plate 12 collects the terminal cooling capacity of the precooler 1, providing a stable reference cold source for the system. The tertiary cold plate is installed at the bottom of the 1K pool, adhering to the pressure-bearing heat exchange surface of the pool body, balancing the overall wall temperature of the 1K pool, eliminating local temperature differences caused by the evaporation of helium-4, maintaining a constant temperature zone in the 1K pool, and ensuring stable evaporative cooling conditions. Simultaneously, it isolates the upward reverse heat leakage from the 1K pool and provides pre-cooling for the distillation chamber and connecting pipelines, mitigating thermal disturbances at the distillation station. The quaternary cold plate is installed at the bottom of the distillation chamber, serving as the system's terminal low-temperature homogenizing component. It precisely maintains a constant low-temperature environment inside the distillation chamber, balances the heat exchange temperature of the inner wall of the chamber, ensures stable gas-liquid separation and low-temperature distillation purification of the mixed working fluid within the chamber, avoids working fluid separation failures caused by temperature difference disturbances, and ensures the purity and operational stability of the entire ultra-low temperature working fluid cycle.

[0031] This embodiment employs a multi-stage refrigeration strategy, optimizing the refrigeration cycle and working fluid to achieve ultra-low temperature ranges. By using a helium-3 and helium-4 mixed working fluid, especially an extremely low concentration of helium-3 and helium-4 mixed working fluid, a base temperature of 462 mK can be achieved with a helium-3 consumption of only 0.9 L, and refrigeration power of 1 mW and 2 mW can be provided at 533 mK and 585 mK, respectively. Therefore, this invention significantly reduces helium-3 consumption while ensuring a lower base temperature, such as <500 mK, and a higher refrigeration power, achieving a balance between low resource consumption and high refrigeration performance. The system has continuous operation capability and is suitable for multiple fields such as quantum computing, condensed matter physics experiments, and cryogenic electronics.

[0032] Evaporative refrigeration relies on the gas-liquid phase change process of the liquid working fluid under low-pressure conditions, achieving a temperature decrease by absorbing the latent heat of vaporization. For a mixture of helium-3 and helium-4 working fluids, its saturated vapor pressure depends not only on the temperature but also on the concentration of helium-3 in the mixture. Figure 2 The characteristic curves of the saturated vapor pressure of a helium-3 and helium-4 mixture with a helium-3 concentration of 3.7% as a function of temperature are shown. Figure 2As shown, as the temperature decreases, the saturated vapor pressure of this low-concentration mixed solution gradually exceeds that of pure helium-4 and approaches the saturated vapor pressure characteristics of pure helium-3. Based on this physical property, when a suitable pump set is used to continuously evacuate the distillation chamber, the lowest temperature that this mixed working fluid can reach is far below the limiting temperature of pure helium-4 evaporative cooling, approximately 800 mK, and is expected to approach the lowest temperature of pure helium-3 evaporative cooling, approximately 300 mK. Simultaneously, the mixed solution remains in a mixed state within the operating temperature range, and phase separation does not occur. Figure 3 The green area is shown.

[0033] Based on this, the system in this embodiment can significantly reduce the amount of helium-3 used through the coordinated operation of multi-stage refrigeration technology, while achieving a lower base temperature and a larger refrigeration power. The system adopts a three-stage refrigeration strategy, including: a pre-cooling stage, a 1K refrigeration cycle stage, and a helium-3 and helium-4 evaporative refrigeration stage.

[0034] The pre-cooling stage and the 1K refrigeration cycle stage consist of a pre-cooler, such as a pulse tube refrigerator, and a helium-4 evaporative refrigeration cycle, providing a pre-cooling temperature of approximately 1K for the helium-3 and helium-4 evaporative refrigeration stages. The helium-3 and helium-4 evaporative refrigeration cycle includes distillation chamber 8, circulation pipeline 15, and the second gas pipe 18. The lowest temperature of the final system is achieved at distillation chamber 8.

[0035] In one specific implementation, such as Figure 1 As shown, a first thermal switch 6 is provided between the secondary cold plate 12 and the tertiary cold plate 13.

[0036] It should be noted that this embodiment is designed to enable controllable opening and closing of the heat conduction path between the secondary cold plate and the tertiary cold plate at the bottom of the 1K pool, adapting to the system's segmented cooling operation logic. During the pre-cooling stage of the entire system, the first thermal switch is activated by gas, efficiently transferring the cooling energy from the secondary cold plate to the tertiary cold plate, rapidly cooling the 1K pool and the downstream distillation chamber structure, significantly shortening the overall pre-cooling time of the system. After the system reaches the rated ultra-low temperature operating condition, the first thermal switch is deactivated, isolating the parasitic heat leakage from the secondary cold plate to the tertiary cold plate in the 1K temperature zone, preventing heat from the upper temperature zone from interfering with the steady-state evaporative cooling of the 1K pool, ensuring the constant temperature operation of the 1K pool, and simultaneously protecting the low-temperature environment of the downstream distillation chamber from temperature rise disturbances.

[0037] In one specific embodiment, a second thermal switch 7 is provided between the secondary cold plate 12 and the quaternary cold plate 14.

[0038] It should be noted that, in order to achieve controllable switching of the heat conduction path between the secondary cold plate and the fourth-stage cold plate at the bottom of the distillation chamber, the second thermal switch is simultaneously turned on during the pre-cooling stage. The cooling capacity of the secondary cold plate is directly used to rapidly pre-cool the terminal distillation chamber and the fourth-stage cold plate, avoiding the problem of slow cooling of the distillation chamber caused by relying solely on the cooling of the tertiary cold plate. When the system is operating at normal low temperature, the second thermal switch is turned off, completely isolating the heat from the secondary cold plate from being directly conducted to the terminal distillation chamber, preventing cross-stage high-temperature heat leakage, maximizing the protection of the ultra-low constant temperature environment of the distillation chamber, ensuring that the distillation of the mixed working fluid and the gas-liquid separation are not affected by the upper temperature zone, and improving the low-temperature stability of the system.

[0039] In one specific embodiment, a flow resistance 9-1 is provided at the position of the first air pipe 17 connected to the 1K pool 5.

[0040] It should be noted that the flow resistance 9-1 in this embodiment has the effects of throttling and depressurizing the helium-4 gas flowing through the first gas pipe 17, as well as stagnant heat exchange. This reduces the pressure and flow rate of the medium inside the pipe, prolongs the low-temperature heat exchange time of helium-4, and relies on the low-temperature environment provided by the secondary cold plate to assist in completing the Joule-Thomson throttling phase change, ensuring that the helium-4 gas in the pipe is fully liquefied, supplying a sufficient amount of stable liquid helium-4 to the 1K pool 5, and ensuring continuous and stable evaporative cooling of the 1K pool.

[0041] In one specific embodiment, a flow resistance 9-2 is provided at the location of the second gas pipe 18 connected to the distillation chamber 8.

[0042] It should be noted that the flow resistance 2 9-2 in this embodiment plays a role in throttling and depressurizing the helium-3 and helium-4 mixed working fluid flowing through the second gas pipe 18, and in slow-speed stagnant heat exchange. By utilizing the low-temperature cooling capacity of the system, the Joule-Thomson throttling phase change is completed, reducing the flow rate and pressure of the mixed working fluid, promoting the full liquefaction of the helium-3 and helium-4 mixed working fluid inside the pipeline, and facilitating the low-temperature gas-liquid stratification, separation and purification of the two helium working fluids inside the distillation chamber, thus ensuring the orderly progress of the mixed working fluid distillation and separation operation.

[0043] In some embodiments, the precooling machine 1 is a pulse tube refrigerator, a GM refrigerator, or a liquid helium bath.

[0044] In some embodiments, the first thermal switch 6 and the second thermal switch 7 may be air-gap thermal switches, mechanical thermal switches, superconducting thermal switches or magnetoresistive thermal switches.

[0045] In some embodiments, the molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid is 1%-20%, and its concentration can be 1%, 5%, 10%, 20%, or other concentrations within this range. Any concentration within this range can achieve the effects of the present invention.

[0046] In some embodiments, the molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid is 1%-6.4%, and its concentration can be 1%, 2%, 3%, 6%, or other concentrations within the range. Any concentration within the range can achieve the effects of this invention.

[0047] In one embodiment, the molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid is 3.7%.

[0048] This embodiment also provides a phase-separation continuous refrigeration method using a mixture of extremely low concentrations of helium-3 and helium-4 as the working fluid, comprising the following sequential steps: Precooling: Start precooler 1 and maintain it for 11-13 hours; 1K refrigeration cycle: Helium-4 gas is introduced into the first gas pipe 17, and the precooler 1 is kept on. The introduced helium-4 gas passes through the first heat exchanger 2 through the first gas pipe 17, then extends to the precooler 1 and passes through the precooler 1, then extends to the third heat exchanger 4 and passes through the third heat exchanger 4, and then flows into the 1K pool 5 in a liquefied manner; the pressure of the 1K pool 5 is reduced from the second circulation pipe 16 until the temperature stabilizes. Helium-3 and Helium-4 Evaporation Refrigeration: A mixture of helium-3 and helium-4 working fluid is introduced into the second gas pipe 18, allowing the mixture to pass through the second-stage heat exchanger 3, then extend to and pass through the precooler 1, then extend to and pass through the 1K pool 5, and finally liquefy and flow into the distillation chamber 8. The distillation chamber 8 is then subjected to depressurized evaporation through the circulation pipe 15 until the temperature stabilizes, thus completing the phaseless separation continuous refrigeration using a mixture of extremely low concentrations of helium-3 and helium-4 working fluid.

[0049] In this embodiment, a precooler 1 is used to precool the system, so that the first-stage cold plate 11 of the system is stably below 40K and the second-stage cold plate 12 is stably below 4K; then a 1K refrigeration cycle is performed to lower the system temperature and stabilize it at about 1.2K; finally, helium-3 and helium-4 evaporative cooling are used to lower the system temperature and stabilize it at below 500mK.

[0050] The present invention will be further described below through specific embodiments.

[0051] Example 1 like Figure 1 As shown, this embodiment of a phase-separation continuous refrigeration system using a mixture of extremely low concentrations of helium-3 and helium-4 as the working fluid includes: Precooler 1, First-stage heat exchanger 2, Second-stage heat exchanger 3, Third-stage heat exchanger 4, 1K tank 5, Distillation chamber 8, First-stage cold plate 11, Second-stage cold plate 12, Third-stage cold plate 13, Fourth-stage cold plate 14 (diameter 300mm, thickness 6mm), Circulation pipeline 1 15, Circulation pipeline 2 16, First gas pipe 17, Second gas pipe 18, The third-stage heat exchanger 4 is located above the 1K pool 5; the second circulation pipe 16 is located on the 1K pool 5 and connected to the inside of the 1K pool 5; the first circulation pipe 15 is located on the distillation chamber 8 and connected to the inside of the distillation chamber 8; the first gas pipe 17 is connected to an external helium-4 gas source; the second gas pipe 18 is connected to an external helium-3 and helium-4 mixed working fluid source. The first-stage cold plate 11 and the second-stage cold plate 12 are spaced apart on the low-temperature cavity of the precooler 1, the third-stage cold plate 13 is located at the bottom of the 1K pool 5, and the fourth-stage cold plate 14 is located at the bottom of the distillation chamber 8. The first gas pipe 17 passes through the first stage heat exchanger 2, then extends to and passes through the precooler 1, then extends to and passes through the third stage heat exchanger 4, and then communicates with the 1K pool 5. The second gas pipe 18 passes through the second stage heat exchanger 3, then extends to and passes through the precooler 1, then extends to and passes through the 1K pool 5, and then communicates with the distillation chamber 8.

[0052] The precooling machine 1 is a pulse tube refrigerator.

[0053] In this embodiment, a first thermal switch 6 is provided between the secondary cold plate 12 and the tertiary cold plate 13.

[0054] A second heat switch 7 is provided between the secondary cold plate 12 and the quaternary cold plate 14.

[0055] A flow resistance 9-1 is provided at the position of the first air pipe 17 connected to the 1K pool 5.

[0056] A flow resistance 29-2 is provided at the position of the second gas pipe 18 connected to the distillation chamber 8.

[0057] The first thermal switch 6 and the second thermal switch 7 can be air gap type thermal switches.

[0058] The molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid is 3.7%.

[0059] This embodiment describes a phase-separation continuous refrigeration method using a mixture of extremely low concentrations of helium-3 and helium-4 as the working fluid, comprising the following sequential steps: Precooling: Start precooler 1 and maintain it for 11-13 hours; 1K refrigeration cycle: Helium-4 gas is introduced into the first gas pipe 17, and the precooler 1 is kept on. The introduced helium-4 gas passes through the first heat exchanger 2 through the first gas pipe 17, then extends to and passes through the precooler 1, then extends to and passes through the third heat exchanger 4, and then flows into the 1K pool 5 after liquefaction. The 1K pool 5 is subjected to depressurization evaporation through the second circulation pipe 16 for about 5-10 minutes until the temperature stabilizes. Helium-3 and Helium-4 Evaporation Refrigeration: A mixture of helium-3 and helium-4 working fluid is introduced into the second gas pipe 18, allowing the mixture to pass through the second-stage heat exchanger 3, then extend to and pass through the precooler 1, then extend to and pass through the 1K pool 5, and finally liquefy and flow into the distillation chamber 8. The distillation chamber 8 is then subjected to depressurized evaporation through the circulation pipe 15 for about 10-20 minutes until the temperature stabilizes, thus completing the phase-free separation continuous refrigeration using a mixture of extremely low concentrations of helium-3 and helium-4 working fluid.

[0060] Using the system and method of this embodiment, the system performance reaches a base temperature of 462mK and a cooling power of 1mW@533mK and 2mW@585mK, with a helium-3 consumption of only 0.9L.

[0061] Example 2 Unlike Example 1, the molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid in this example is 6.4%.

[0062] Example 3 Unlike Example 1, the molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid in this example is 1%.

[0063] Example 4 Unlike Example 1, the molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid in this example is 10%.

[0064] Example 5 Unlike Example 1, the molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid in this example is 15%.

[0065] Example 6 Unlike Example 1, the molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid in this example is 20%.

[0066] The above embodiments 2-6 can also achieve the same system performance as embodiment 1 of the present invention.

[0067] In summary, this embodiment provides a phase-separation-free continuous refrigeration system and method using a mixture of helium-3 and helium-4 with extremely low concentrations. This embodiment utilizes the helium-3 and helium-4 mixture as the refrigerant, taking advantage of its characteristic that, in the low-temperature region, the saturated vapor pressure of this helium-3 and helium-4 mixture is significantly higher than that of pure helium-4 but approaches that of pure helium-3, without phase separation. By employing a three-stage cooling system—including a first-stage precooler, a second-stage helium-4 evaporative refrigeration, and a third-stage helium-3 and helium-4 evaporative refrigeration—continuous and stable refrigeration below 500 mK is achieved. The system performance can reach a base temperature of 462 mK and refrigeration power of 1 mW at 533 mK and 2 mW at 585 mK, with a helium-3 consumption of only 0.9 L.

[0068] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A phase-separation continuous refrigeration system employing a mixture of extremely low concentrations of helium-3 and helium-4 as the working fluid, characterized in that, include: Precooler (1), first stage heat exchanger (2), second stage heat exchanger (3), third stage heat exchanger (4), 1K pool (5), distillation chamber (8), first stage cold plate (11), second stage cold plate (12), third stage cold plate (13), fourth stage cold plate (14), circulation pipeline one (15), circulation pipeline two (16), first gas pipe (17), second gas pipe (18). The third-stage heat exchanger (4) is located above the 1K pool (5); the second circulation pipe (16) is located on the 1K pool (5) and connected to the inside of the 1K pool (5); the first circulation pipe (15) is located on the distillation chamber (8) and connected to the inside of the distillation chamber (8); the first gas pipe (17) is connected to an external helium-4 gas source; the second gas pipe (18) is connected to an external helium-3 and helium-4 mixed working fluid source; The first-stage cold plate (11) and the second-stage cold plate (12) are spaced apart on the low-temperature cavity of the precooler (1), the third-stage cold plate (13) is located at the bottom of the 1K pool (5), and the fourth-stage cold plate (14) is located at the bottom of the distillation chamber (8). The first gas pipe (17) passes through the first stage heat exchanger (2), then extends to and passes through the precooler (1), then extends to and passes through the third stage heat exchanger (4), and then connects to the 1K pool (5); The second gas pipe (18) passes through the second stage heat exchanger (3), then extends to and passes through the precooler (1), then extends to and passes through the 1K pool (5), and then communicates with the distillation chamber (8).

2. The phase-separation continuous refrigeration system using a mixture of extremely low concentrations of helium-3 and helium-4 as described in claim 1, characterized in that, A first thermal switch (6) is provided between the secondary cold plate (12) and the tertiary cold plate (13); a second thermal switch (7) is provided between the secondary cold plate (12) and the quaternary cold plate (14).

3. The phase-separation continuous refrigeration system using a mixture of extremely low concentrations of helium-3 and helium-4 as described in claim 1, characterized in that, A flow resistance 1 (9-1) is provided at the position of the first air pipe (17) connected to the 1K pool (5).

4. A phase-separation continuous refrigeration system using a mixture of extremely low concentrations of helium-3 and helium-4 as a working fluid according to claim 1, characterized in that, A flow resistance 2 (9-2) is provided at the position of the second gas pipe (18) connected to the distillation chamber (8).

5. A phase-separation continuous refrigeration system using a mixture of extremely low concentrations of helium-3 and helium-4 as a working fluid according to claim 1, characterized in that, The precooler (1) is a pulse tube refrigerator, a GM refrigerator, or a liquid helium bath.

6. A phase-separation continuous refrigeration system using a mixture of extremely low concentrations of helium-3 and helium-4 as a working fluid according to claim 2, characterized in that, The first thermal switch (6) and the second thermal switch (7) can be air gap thermal switches, mechanical thermal switches, superconducting thermal switches or magnetoresistive thermal switches.

7. A phase-separation continuous refrigeration system using a mixture of extremely low concentrations of helium-3 and helium-4 as a working fluid according to claim 1, characterized in that, The molar concentration of helium-3 in the helium-3 and helium-4 mixed working medium is 1%-20%.

8. A phase-separation continuous refrigeration system using a mixture of extremely low concentrations of helium-3 and helium-4 as a working fluid according to claim 7, characterized in that, The molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid is 1%-6.4%.

9. A phase-separation continuous refrigeration system using a mixture of extremely low concentrations of helium-3 and helium-4 as a working fluid, as described in claim 8, is characterized in that... The molar concentration of helium-3 in the helium-3 and helium-4 mixed working fluid is 3.7%.

10. A continuous refrigeration method without phase separation using a mixture of extremely low concentrations of helium-3 and helium-4 as the working fluid, characterized in that, The phase-separation continuous refrigeration system using a mixture of helium-3 and helium-4 with extremely low concentrations as described in any one of claims 1-9 comprises the following sequential steps: 1) Start the precooler (1) and keep it running for 11-13 hours to make the first-stage cold plate (11) stably reach below 40K and the second-stage cold plate (12) stably reach below 4K; 2) Introduce helium-4 gas into the first gas pipe (17), keep the precooler (1) on, and let the introduced helium-4 gas pass through the first heat exchanger (2) through the first gas pipe (17), then extend to the precooler (1) and pass through the precooler (1), then extend to the third heat exchanger (4) and pass through the third heat exchanger (4), and then liquefy and flow into the 1K pool (5); reduce the pressure and evaporate the 1K pool (5) through the second circulation pipe (16) until the temperature stabilizes; 3) Introduce a mixture of helium-3 and helium-4 working fluid into the second gas pipe (18), so that the mixture of helium-3 and helium-4 working fluid passes through the second heat exchanger (3) through the second gas pipe (18), then extends to the precooler (1) and passes through the precooler (1), then extends to the 1K pool (5) and passes through the 1K pool (5), and then flows into the distillation chamber (8) through the circulation pipeline (15) to reduce the pressure and evaporate the distillation chamber (8) until the temperature stabilizes, thus completing the phase-free separation continuous refrigeration using a mixture of helium-3 and helium-4 working fluid with extremely low concentration.

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