A two-stage regenerator for a cryogenic refrigerator

Abstract

This invention discloses a secondary regenerator for a cryogenic refrigerator and a cryogenic refrigerator containing the regenerator. The secondary regenerator is divided into four sections and filled with four spherical cold storage materials: zinc alloy, bismuth alloy, holmium copper, and gadolinium sulfide, with volume percentages of 19%-23%, 27%-31%, 25%, and 25%, respectively. The total filling length is increased by 10%-32%, and the length-to-diameter ratio is between 5 and 6. Without changing the overall installation dimensions of the cryogenic refrigerator, it can significantly improve the cooling capacity of the primary and secondary stages. It is suitable for GM or pulse tube refrigerators and can provide stable cooling support for experimental and production scenarios with high requirements for the low-temperature environment of the preceding stage.

Description

Technical Field

[0001] This invention relates to the field of refrigeration, further to the field of cryogenic refrigerators, and more specifically to a two-stage regenerator for a cryogenic refrigerator. Background Technology

[0002] Cryogenic refrigerators are closed-loop refrigerators that can provide cooling at extremely low temperatures. They have only been developed in recent decades, and with the advancements in cryogenic physics, electronics, and aerospace technology, cryogenic refrigerators have gained a crucial position in medium-sized, small-scale, and especially micro-scale cryogenic refrigeration technologies. Among the most important are pulse tube refrigerators and GM refrigerators, both typical refrigerators operating in the liquid helium temperature range. They have wide applications in condensed matter physics, quantum computing, communications, medicine, power, energy, scientific instruments, and aerospace, such as in magnetic resonance imaging (MRI), dilution refrigerators, particle accelerators, and astronomical telescopes.

[0003] Taking the GM (Gifford-McMahon) refrigerator as an example, it is manufactured based on the GM cycle principle and mainly consists of a motor, cylinder, piston, regenerator, and cold-end heat exchanger. It achieves refrigeration by utilizing the charging and discharging process of high and low-pressure helium gas within a closed pulse tube. During operation, in the intake phase, high-pressure gas enters the expansion chamber after heat exchange with the regenerator. The piston then moves upward to a designated position. Once the expansion chamber is filled with high-pressure gas, the intake ends, and the rotary valve switches the gas passage to the low-pressure circuit. The high-pressure gas in the expansion chamber then expands into the low-pressure circuit, exchanges heat with the regenerator again, and flows out of the refrigerator. Simultaneously, the cooling energy is transferred to the object being cooled through the cold-end heat exchanger. Subsequently, the piston moves towards the bottom of the cylinder to expel the remaining helium gas in the expansion chamber, completing one refrigeration cycle. This continuous switching between high and low pressures for continuous Simon expansion, with the regenerator constantly accumulating cooling energy, results in a sustained cooling effect for the GM refrigerator.

[0004] Two-stage GM refrigerators are available in models such as 408, 412, 415, and 418, depending on the second-stage cooling capacity. The "4" represents the minimum cooling temperature of the second stage, and the following numbers correspond to the second-stage cooling capacity. For example, "418" represents a refrigerator with a second-stage cooling capacity of 1.8W@4.2K. Currently, the 418-type two-stage GM refrigerator has a significant drawback: while increasing the second-stage cooling capacity, the first-stage cooling capacity remains relatively low, typically only 42W@45K (i.e., 42W of cooling capacity at 45K). This poses a challenge for experiments and production scenarios that require higher pre-stage low-temperature environments, impacting experimental and production efficiency. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems mentioned in the background section, thereby providing a two-stage regenerator for a cryogenic refrigerator and a cryogenic refrigerator with the two-stage regenerator, which can simultaneously increase the cooling capacity of the first and second stages, especially providing stable and reliable high-capacity cooling support for various experimental and production scenarios with higher requirements for the low-temperature environment of the preceding stage. The specific invention details are as follows:

[0006] A secondary regenerator for a cryogenic refrigeration unit adopts a cylindrical structure and includes four different sections. The first section is filled with zinc alloy, the second section is filled with bismuth alloy, and the third and fourth sections are filled with holmium copper and gadolinium sulfide, respectively. The volume of the different cold storage materials filled in the four sections accounts for 19%-23%, 27%-31%, 25%, and 25% of the total volume of cold storage materials filled in the secondary regenerator, respectively. The first section is close to the hot end of the secondary regenerator. The first section and the second section together constitute a high-temperature section, the third section constitutes a medium-temperature section, and the fourth section constitutes a low-temperature section.

[0007] Furthermore, the ratio of the length to the diameter of the total packing volume of the cold storage packing in the secondary regenerator is between 5 and 6.

[0008] Furthermore, the overall length of the total filling volume of the cold storage material in the secondary regenerator is increased by 10%-32%.

[0009] Furthermore, the secondary regenerator is equipped with multiple support structures to fix the loaded cold storage material and prevent the cold storage material from shifting or accumulating due to vibration during long-term operation.

[0010] Furthermore, the plurality of support structures are porous partitions or sieves.

[0011] Furthermore, the two ends of the secondary regenerator are equipped with airflow distribution devices to ensure that helium flows uniformly through the packed cold storage material during the alternating flow process.

[0012] Furthermore, the airflow distribution device is a multi-layered guide net, which further optimizes the uniformity of helium flow through multi-layer superposition design.

[0013] Furthermore, all four types of cold storage materials are spherical cold storage materials, which increases the heat exchange area while improving the helium gas throughput.

[0014] The present invention further provides a cryogenic refrigeration machine, including the two-stage regenerator as described above.

[0015] Furthermore, the cryogenic refrigerator is a GM refrigerator or a pulse tube refrigerator.

[0016] Based on the above-mentioned invention, compared with the prior art, the secondary regenerator of this invention uses four spherical cold storage materials—zinc alloy, bismuth alloy, holmium copper, and gadolinium oxysulfide—filled in four sections, with volume percentages of 19%-23%, 27%-31%, 25%, and 25% respectively. The total filling length is increased by 10%-32%, and the length-to-diameter ratio is between 5 and 6. Without changing the overall installation dimensions of the cryogenic refrigerator, it can significantly improve the cooling capacity of the first and second stages. It is suitable for GM or pulse tube refrigerators and can provide stable cooling support for experimental and production scenarios with high requirements for the pre-stage cryogenic environment. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the operation of a cryogenic refrigeration system;

[0019] Figure 2 This is a schematic diagram of the structure of a traditional two-stage regenerator in a cryogenic refrigeration unit.

[0020] Figure 3 This is a graph showing the relationship between the acoustic power of a secondary regenerator and the specific heat capacity of some common cold storage materials.

[0021] Figure 4 PV diagram of the first-stage regenerator of the GM chiller;

[0022] Figure 5 This is a schematic diagram of the loading structure of the secondary regenerator of the present invention.

[0023] Figure reference numerals: 1-Compressor pump; 2-Plate heat exchanger; 3-Oil separator; 4-Adsorber; 5-Cold head; 6-Gas tank; 11-High temperature section; 12-Medium temperature section; 13-Low temperature section; 21-First section; 22-Second section; 23-Third section; 24-Fourth section. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. It is obvious that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] Figure 1This is a schematic diagram of the operation of a cryogenic refrigeration system. The cryogenic refrigeration system can be a GM refrigeration system or a pulse tube refrigeration system. The high-pressure, high-temperature helium gas is sequentially delivered to the plate heat exchanger 2, oil separator 3 and adsorber 4 in the helium compressor through the compressor pump 1. It is then transformed into high-pressure, room-temperature, clean helium gas, which is then delivered to the cold head 5. In the cold head 5, adiabatic expansion is completed, and the temperature is cooled during the adiabatic expansion process. Then, it returns to the compressor pump 1 in the helium compressor through the gas storage tank 6, completing one cycle.

[0026] Traditional cryogenic refrigerators typically employ a cylindrical secondary regenerator with internal support structures (such as perforated baffles or sieves) spaced 10-20 mm apart. These baffles secure the stored cryogenic material and prevent displacement or accumulation due to vibration during long-term operation. Both ends are equipped with airflow distribution devices (such as multi-layered guide nets), often using 100-200 mesh stainless steel wire mesh. This multi-layered design further optimizes airflow uniformity, ensuring a uniform flow of helium through the stored cryogenic material during alternating flow. The secondary regenerator is usually made of 304 or 316 stainless steel, which maintains good mechanical strength and corrosion resistance even at liquid helium temperatures (4.2K), effectively preventing structural failure due to cryogenic embrittlement and ensuring structural stability at low temperatures.

[0027] The secondary regenerator is primarily filled with low-temperature, high-specific-heat-capacity magnetic cold storage materials, supplemented by metal wire mesh to enhance heat exchange. Generally speaking, such as... Figure 2 As shown, the secondary regenerator typically consists of three sections: a high-temperature section 11, a medium-temperature section 12, and a low-temperature section 13. The most common cold storage materials filled in each section are shown in Table 1.

[0028] Table 1: The most common cold storage materials used in each section of the secondary regenerator

[0029]

[0030] Taking a two-stage GM refrigerator as an example, the two-stage regenerator achieves refrigeration through the following process: High-pressure helium gas enters the hot end of the two-stage regenerator from the first-stage cooling platform. As it flows through the two-stage regenerator, the heat is absorbed by the internal cold storage material, and the temperature decreases step by step; Low-temperature helium gas enters the expansion space, generating a refrigeration effect; The returning low-pressure helium gas flows from the cold end to the hot end through the two-stage regenerator, absorbing the heat from the internal cold storage material, causing the cold storage material to return to its initial state. This process is carried out with the periodic reciprocating motion of the displacement device, thereby achieving continuous refrigeration.

[0031] Due to the real gas properties of helium, the temperature distribution of the second-stage regenerator in a two-stage GM refrigerator or pulse tube refrigerator is non-linear. Although the properties of helium cannot be changed, the total loss caused by the real gas properties can be reduced by altering the temperature distribution of the second-stage regenerator. The temperature distribution of the second-stage regenerator is affected not only by the type and proportion of the regenerator filler but also by the size of the second-stage regenerator, especially by the ratio of the length to the diameter of the total filler volume. A traditional second-stage regenerator, for example, has a filler volume of 160 mm in length and 34 mm in diameter, resulting in a length-to-diameter ratio of approximately 4.7. Regarding the filler material, typically the high-temperature section 11 is filled with 35% lead (Pb) balls, the intermediate-temperature section 12 with 40% holmium copper (HoCu2), and the low-temperature section 13 with 25% gadolinium oxide (GOS) balls. The filler proportion here refers to the ratio of the volume of each filler material to the total filler volume.

[0032] This invention, based on a traditional two-stage regenerator, increases the length of the two-stage regenerator, thereby increasing the filling height and ultimately increasing the total filling volume of the cold storage material. While maintaining the same diameter of the total filling volume, it increases the length-to-diameter ratio of the total filling volume of the cold storage material. Furthermore, by filling with a zinc (Zn) alloy and a bismuth (Bi) alloy in a specific ratio, the zinc and bismuth alloys exhibit approximately 20% lower specific heat capacity near 4K compared to lead alloys.

[0033] Specifically, for the secondary regenerator itself, to achieve the highest coefficient of performance (COP), the acoustic power loss due to limited heat capacity must be considered. In an ideal secondary regenerator, when the solid heat capacity and gas thermal contact completely suppress temperature oscillations, the acoustic power is proportional to 1 / ρ (where ρ is the gas density of helium). However, limited by the actual heat capacity of the secondary regenerator, temperature oscillations cause the acoustic power attenuation from the hot end to the cold end to be less than 1 / ρ. An extreme case to intuitively understand this phenomenon is when the heat capacity of the secondary regenerator approaches zero and the temperature oscillation reaches an adiabatic value; in this case, the secondary regenerator acts as an ideal buffer tube, and there is no acoustic power loss between the hot and cold ends. According to the pulse tube effect, the acoustic power of the secondary regenerator will increase, thus increasing the secondary cooling capacity. The relationship between the acoustic power of the secondary regenerator and the specific heat capacity of some common cold storage materials is as follows... Figure 3 As shown.

[0034] In addition, according to Figure 4As shown in the PV diagram of the first-stage regenerator of the GM refrigeration unit, the design of this invention also has a significant impact on the first-stage regenerator. This is because the zinc alloy and bismuth alloy of the second-stage regenerator have lower specific heat capacity near 4K compared to the lead alloy. The pressure in the expansion volume decreases more slowly when approaching high pressure and rises more slowly when approaching low pressure. Therefore, the phase shift between pressure and expansion volume is increased, which increases the PV power of the first-stage regenerator and thus increases the first-stage cooling capacity.

[0035] Based on the above analysis, this invention improves the secondary regenerator of a cryogenic refrigerator, designing a completely new secondary regenerator based on the conventional standard cryogenic refrigerator's secondary regenerator. Specifically, as follows... Figure 5 As shown, the new two-stage cryogenic refrigerator's secondary regenerator comprises four sections, incorporating new cold storage materials of zinc alloy and bismuth alloy in proportion. The entire unit is filled with a combination of cold storage materials consisting of zinc alloy, bismuth alloy, holmium copper, and gadolinium oxysulfide balls. Specifically, the first section 21 is filled with zinc alloy, accounting for 19%-23% of the total cold storage material volume in the secondary regenerator; the second section 22 is filled with bismuth alloy, accounting for 27%-31% of the total cold storage material volume; the third section 23 and the fourth section 24 are filled with holmium copper and gadolinium oxysulfide balls, respectively, accounting for 25% and 25% of the total cold storage material volume. The first section 21 is located closest to the hot end of the secondary regenerator, and together with the second section 22, they constitute the high-temperature section of the secondary regenerator. The third section 23 constitutes the medium-temperature section, and the fourth section 24 constitutes the low-temperature section.

[0036] Furthermore, based on improvements to the section distribution and the type of cold storage material used in the secondary regenerator, the diameter of the total volume of cold storage material in the secondary regenerator is kept constant while the length of the total volume is increased by 10%-32%, thereby achieving a length-to-diameter ratio between 5 and 6 for the total volume of cold storage material in the secondary regenerator. For example, in the aforementioned conventional secondary regenerator, the length of the total volume of cold storage material is 160 mm, and the diameter is 34 mm, resulting in a ratio of 4.71. Based on this, increasing the length of the total volume of cold storage material by 10% to 176 mm while keeping the diameter unchanged at 34 mm yields a calculated length-to-diameter ratio of 5.18.

[0037] For those skilled in the art, the ratio of the length to the diameter of the total filling volume of the cold storage material in the secondary regenerator of a traditional cryogenic refrigerator is usually less than 5. This invention breaks free from the constraints of traditional design by innovatively increasing the length of the total filling volume of the cold storage material, thereby improving the ratio of the length to the diameter of the total filling volume to between 5 and 6. This significantly improves the cooling capacity of the cryogenic refrigerator, especially the primary cooling capacity, which is often overlooked in traditional cryogenic refrigerators.

[0038] Of course, the neglect of primary cooling capacity is mainly due to the limitations of cryogenic refrigerator applications. Traditional applications mostly focus on the magnitude of secondary cooling capacity, with primary cooling capacity often only used for thermal shielding. In pursuit of secondary cooling capacity, primary cooling capacity is easily overlooked. However, with the continuous expansion of cryogenic refrigerator applications, the role of primary cooling capacity is becoming increasingly important and valued in more and more experimental and production scenarios, such as quantum computing devices and magneto-optical measurement devices. Therefore, to address this newly emerging technical problem, this invention proposes a technical solution to significantly improve primary cooling capacity, while also improving secondary cooling capacity to a certain extent.

[0039] Based on the above improvements, this invention can significantly increase the primary and secondary cooling capacities of a secondary cryogenic refrigerator without substantially increasing the cost or altering the overall installation dimensions. Specifically, it can significantly increase the primary cooling capacity of the secondary cryogenic refrigerator by approximately 20%-30%. For example, the primary cooling capacity of the GM418 is increased from 42W@45K to 53W@43K, and the primary cooling capacity of the GM421 is increased from 35W@45K to 45W@45K. By increasing the primary cooling capacity, stable and reliable high-capacity cooling support is provided for experimental and production scenarios with higher requirements for various pre-stage cryogenic environments (i.e., cooling using the primary cold head of the cryogenic refrigerator).

[0040] Simultaneously, while increasing the primary cooling capacity of the two-stage cryogenic refrigerator, its secondary cooling capacity is also increased by approximately 10-20%. For example, the secondary cooling capacity of the GM418 increases from 1.8W@4.2K to 2.0W@4.2K, and the secondary cooling capacity of the GM421 increases from 2.1W@4.2K to 2.5W@4.2K. Furthermore, while significantly increasing the primary and secondary cooling capacities, the overall assembly dimensions of the cryogenic refrigerator change only slightly; only the length of the secondary regenerator needs adjustment. Therefore, it can be directly replaced with existing standard cryogenic refrigerators, improving efficiency.

[0041] The foregoing has provided a detailed description of the secondary regenerator of the cryogenic refrigeration machine provided by this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are merely for the purpose of helping to understand the method and core ideas of this invention. For those skilled in the art, the technical solutions of this invention are not limited to the solutions defined in the specific embodiments. Technical solutions formed by other modifications that can be obviously implemented based on ordinary technical knowledge in the art are all within the protection scope of this invention.

Claims

1. A secondary regenerator for a cryogenic refrigeration unit, comprising a cylindrical structure and four distinct sections: a first section filled with a zinc alloy, a second section filled with a bismuth alloy, and a third and fourth section filled with holmium copper and gadolinium sulfide, respectively. The volume ratios of the different cryogenic storage materials in the four sections to the total volume of the cryogenic storage materials in the secondary regenerator are 19%-23%, 27%-31%, 25%, and 25%, respectively. The first section is close to the hot end of the secondary regenerator. The first section and the second section together constitute the high-temperature section, the third section constitutes the medium-temperature section, and the fourth section constitutes the low-temperature section. While keeping the diameter of the total filling volume of the cold storage material in the secondary regenerator unchanged, the length of the total filling volume of the cold storage material is increased by 10%-32%, so that the ratio of the length to the diameter of the total filling volume of the cold storage material in the secondary regenerator is between 5 and 6.

2. The secondary regenerator of the cryogenic refrigeration machine as described in claim 1, characterized in that: The secondary regenerator has multiple support structures inside to fix the filled cold storage material and prevent the cold storage material from shifting or accumulating due to vibration during long-term operation.

3. The secondary regenerator of the cryogenic refrigeration machine as described in claim 2, characterized in that: The multiple support structures are porous partitions or sieves.

4. The secondary regenerator of the cryogenic refrigeration machine as described in claim 1, characterized in that: The two ends of the secondary regenerator are equipped with airflow distribution devices to ensure that helium flows evenly through the packed cold storage material during the alternating flow process.

5. The secondary regenerator of the cryogenic refrigeration machine as described in claim 4, characterized in that: The airflow distribution device is a multi-layer guide net, which further optimizes the uniformity of helium flow through multi-layer superposition design.

6. The secondary regenerator of the cryogenic refrigerator as described in any one of claims 1-5, characterized in that: All four types of cold storage materials are spherical cold storage materials, which can increase the heat exchange area and the helium gas throughput.

7. A cryogenic refrigerator, comprising a secondary regenerator of the cryogenic refrigerator as described in any one of claims 1-6.

8. The cryogenic refrigerator as described in claim 7, characterized in that: The low-temperature refrigeration unit is either a GM refrigeration unit or a pulse tube refrigeration unit.

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