Multi-stage box sintering heat exchanger for dilution refrigerator in milliKelvin temperature zone and manufacturing method of multi-stage box sintering heat exchanger

Abstract

The invention belongs to the technical field of refrigeration and low temperature, and discloses a multistage box sintering heat exchanger for a milliKelvin temperature zone dilution refrigerator, which comprises an upper square shell and a lower square shell, and a sealing thin plate is arranged between the upper square shell and the lower square shell. Sinking grooves are formed in the bottom of the upper square shell and the top of the lower square shell, an upper metal powder sintering body is arranged in the sinking groove of the upper square shell, and a lower metal powder sintering body is arranged in the sinking groove of the lower square shell. Through cooperation of the upper square shell, the lower square shell and other structures, high-efficiency heat exchange in the dilution refrigeration sintering heat exchanger can be effectively promoted, stable flowing of a helium-3 working medium in a milliKelvin temperature zone is achieved, the minimum dilution refrigeration temperature is further reduced, and the dilution refrigeration efficiency is improved. And the method has very positive significance in application of the dilution refrigerator in special fields such as superconducting quantum calculation and the like.

Description

Technical Field

[0001] The invention belongs to the field of refrigeration and low temperature technology, and in particular relates to a multi-stage box sintered heat exchanger for a dilution refrigerator in the millikelvin temperature range and a manufacturing method thereof. Background Art

[0002] The millikelvin temperature range dilution refrigerator uses the entropy increase effect of the helium-3 concentrated and dilute phase through the phase interface to obtain the base temperature, and the lowest temperature can reach below 10mK. As a millikelvin temperature range refrigeration technology, the dilution refrigerator has the advantages of continuous and stable operation, extremely low electromagnetic and vibration interference, and large cooling capacity. In recent years, it has become a hot spot in the research of refrigerators in this temperature range, and has been widely used in superconducting quantum computing, condensed matter physics and other fields.

[0003] This invention focuses on the sintered heat exchanger in the millikelvin temperature range of a dilution refrigerator. This is the core heat exchange component that allows the dilution refrigerator to achieve the lowest temperature below 100mK. Ideally, the sintered heat exchanger in a dilution refrigerator should achieve the following three functions:

[0004] Achieving efficient heat transfer within a limited volume is crucial for the final stage of dilution refrigeration, where efficient heat transfer between the concentrated and dilute helium-3 phases is crucial. This process involves heat transfer between different working fluid components, and the inlet and outlet temperature differential is minimal below 100 mK. Therefore, it is necessary to minimize the effects of axial heat transfer under these small temperature differentials while simultaneously increasing the heat transfer area within the limited space.

[0005] To achieve effective diffusion and flow of the working fluid, during the cooling process, the fluids on both sides of the heat exchanger will be completely liquefied from the gas phase. At this time, the driving source is entirely from the concentration difference between the upper and lower cavity components. Therefore, the internal structure of the heat exchanger needs to be designed to allow the fluid to flow smoothly and diffuse completely to complete the heat exchange.

[0006] It has extremely high sealing performance. The dilution refrigerator uses helium-3 as the working fluid, which is expensive and has extremely high requirements for the sealing performance of welding points and joints, especially in the mK temperature range. This requires the heat exchange components themselves to have as few joints as possible and have high-strength sealing performance.

[0007] Currently, the sintered heat exchangers in conventional dilution refrigerators are mainly of an upper and lower structure, which increases the dilute phase flow resistance of helium-3 to a certain extent. In addition, due to the arrangement of the pipelines, it is difficult to ensure sealing, and the internal structure is complicated and the risk of leakage is increased, so it cannot fully meet the above three requirements. Summary of the Invention

[0008] In view of the above-mentioned defects in the prior art, the present invention provides a multi-stage box sintered heat exchanger for a milliKelvin temperature range dilution refrigerator and a manufacturing method thereof.

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution: a multi-stage box sintered heat exchanger for a millikelvin temperature zone dilution refrigerator, comprising an upper square shell and a lower square shell, a sealing thin plate being arranged between the upper square shell and the lower square shell, a sinking groove being provided at the bottom of the upper square shell and a top of the lower square shell, an upper metal powder sintered body being provided in the sinking groove of the upper square shell, and a lower metal powder sintered body being provided in the sinking groove of the lower square shell, four groups of the upper square shell, the lower square shell and the sealing thin plate being arranged, and a helium-3 dense phase inlet pipe and a helium-3 dense phase outlet pipe being fixedly mounted on the top surfaces of the two upper square shells, respectively.

[0010] Preferably, a helium-3 concentrated phase fluid connecting pipe is provided between the top surfaces of the two upper square shells, a helium-3 dilute phase outlet pipe and a helium-3 dilute phase inlet pipe are respectively provided on the bottom surfaces of the two lower square shells, and a helium-3 dilute phase fluid connecting pipe is provided between the two lower square shells.

[0011] Preferably, the upper square shell and the lower square shell are provided with countersunk holes at the center position 5 to 10 mm away from the short side, and the centers of the countersunk holes are kept consistent. A helium-3 dense phase flow channel and a helium-3 dilute phase flow channel are opened below the countersunk holes. The upper square shell and the lower square shell are both made of titanium alloy with an aspect ratio of 5:1, and the sealing sheet is made of copper.

[0012] Preferably, the sealing plate is completely consistent with the length of the upper square shell, the sealing plate is fixedly installed between the upper square shell and the lower square shell, and the upper square shell and the lower square shell are completely consistent in shape and size.

[0013] Preferably, the lengths of the upper metal powder sintered body and the lower metal powder sintered body are consistent with the sinking groove, and the bottom surface of the upper metal powder sintered body and the top surface of the lower metal powder sintered body are both in contact with the sealing sheet.

[0014] Preferably, the upper metal powder sintered body and the lower metal powder sintered body are formed by low-temperature sintering of nano-scale metal powder with high thermal conductivity. The upper metal powder sintered body and the lower metal powder sintered body are composed of porous media with high specific surface area, and the particle size of the sintered powder is controlled between 50 and 200 nm.

[0015] Preferably, the helium-3 dilute phase fluid connecting pipe and the helium-3 dense phase fluid connecting pipe are both in an inverted "C" shape, and the two upper square shells are connected by the helium-3 dense phase fluid connecting pipe, and the two lower square shells are connected by the helium-3 dilute phase fluid connecting pipe.

[0016] Preferably, the helium-3 dense phase flow channel is connected to the helium-3 dense phase inlet pipe, the helium-3 dense phase outlet pipe and the helium-3 dense phase fluid connecting pipe, and the helium-3 dilute phase flow channel is connected to the helium-3 dilute phase outlet pipe, the helium-3 dilute phase inlet pipe and the helium-3 dilute phase fluid connecting pipe, and the helium-3 dense phase flow channel and the helium-3 dilute phase flow channel are opened with a square cross-section.

[0017] Preferably, the cross-sectional area of the helium-3 dense phase flow channel is one quarter of the cross-sectional area of the helium-3 dilute phase flow channel, and the lengths of the helium-3 dense phase flow channel and the helium-3 dilute phase flow channel are the same as the length of the sinking groove.

[0018] A method for manufacturing a multi-stage box sintered heat exchanger for a millikelvin temperature range dilution refrigerator is applied to the multi-stage box sintered heat exchanger for the millikelvin temperature range dilution refrigerator:

[0019] Step 1: The upper and lower square shells are made of low-thermal-conductivity, high-strength metal materials with an aspect ratio of 5:1. Equidistant sunken grooves are machined on each side, with a margin of 3 to 5 mm and a depth of 1.5 to 2 mm. The tolerance is controlled within plus or minus 0.01 mm. A narrow, long, square-section helium-3 concentrated-phase flow channel and a helium-3 dilute-phase flow channel are machined along the flow direction at the center of the sunken surface of the upper and lower square shells, respectively. The length is consistent with the double-sided sunken grooves, and the width and depth are the same, 0.8 to 1.2 mm. The cross-sectional area of the helium-3 concentrated-phase flow channel is usually one-fourth that of the helium-3 dilute-phase flow channel.

[0020] Step 2: Countersinks are machined at the center of the upper and lower square shells at a distance of 5 to 10 mm from the short side. The diameter of the countersink of the upper square shell is 2 to 3.5 mm, and that of the lower square shell is 4 to 6 mm. The tolerance is controlled within plus or minus 0.01 mm. The upper and lower countersinks are kept coaxial, and the distance between the bottom of the countersink and the helium-3 concentrated phase flow channel and the helium-3 dilute phase flow channel is consistent, controlled at 0.8 to 1.2 mm.

[0021] Step 3: The sealing plate is made of high thermal conductivity material, completely consistent with the length and width of the upper square shell, with a thickness of 0.2 to 0.4 mm and a flatness of ±0.01 mm. Clean welding technology is used at the upper and lower joints between the sealing plate and the upper and lower square shells to achieve side sealing of the single-stage box-type heat exchanger and separation of the helium-3 concentrated and dilute phase fluids;

[0022] Step 4: The upper metal powder sintered body is made of nano-scale metal powder with high thermal conductivity and sintered at low temperature. The sintered powder particle size is controlled between 50 and 200 nm, and the specific surface area needs to reach 2.5 to 4 cm2 per gram. Its external dimensions are consistent with the sunken grooves of the upper and lower square shells, and the dimensional tolerance between the two is plus or minus 0.01 mm. The upper and lower metal powder sintered bodies are bonded to both sides of the sealing sheet through sintering technology and formed into one piece through a sintering mold;

[0023] Step 5: Clamp the upper square shell, lower square shell, sealing plate, upper metal powder sintered body, and lower metal powder sintered body into an integral structure to form a single-stage box-type sintered heat exchanger. The box-type sintered heat exchanger consists of 10 single-stage heat exchangers. Weld the upper square shells of the first and fourth stages to the helium-3 dense phase inlet pipe and the helium-3 dense phase outlet pipe along a circumference. Weld the lower square shells of the first and fourth stages to the helium-3 dilute phase outlet pipe and the helium-3 dilute phase inlet pipe along a circumference.

[0024] Step 6: The countersunk holes on the same side of the upper end surface of the square shell of each two-stage heat exchanger are integrated with the helium-3 concentrated phase fluid connecting pipe at the intersection. A total of three helium-3 concentrated phase fluid connecting pipes need to be connected. The countersunk holes on the same side of the lower section of the square shell of each two-stage heat exchanger are integrated with the helium-3 dilute phase fluid connecting pipe at the intersection. A total of three helium-3 dilute phase fluid connecting pipes are welded, thereby connecting the upper and lower flow channels of each stage box-type heat exchanger;

[0025] Step 7: Combine the upper square shell, the sealing thin plate, the upper metal powder sintered body, the helium-3 dense phase fluid connecting pipe and the helium-3 dilute phase fluid connecting pipe into a whole, thereby forming a multi-stage box-type sintered heat exchanger for the millikelvin temperature range dilution refrigerator.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention arranges helium-3 concentrated phase flow channels and helium-3 dilute phase flow channels, designs narrow and long flow channels inside the upper square shell and the lower square shell, and arranges heat exchangers of various stages in parallel, so that the concentrated and dilute phase working media can flow and diffuse stably.

[0028] The present invention arranges a sealing thin plate and an upper metal powder sintered body and other structures. The heat exchanger consists of multiple stages of single sintered heat exchangers. The single sintered heat exchanger uses high specific surface area metal powder sintered blocks inside, thereby maximizing the heat exchange area within a limited volume and maximizing the elimination of the influence of axial heat conduction.

[0029] The present invention can effectively promote high-efficiency heat exchange inside the dilution refrigeration sintered heat exchanger by arranging structures such as the upper square shell and the lower square shell, realize the stable flow of helium-3 working fluid in the millikelvin temperature range, and further reduce the minimum temperature of dilution refrigeration. It has very positive significance for the application of dilution refrigerators in special fields such as superconducting quantum computing. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the structure of the present invention;

[0031] Figure 2 Schematic diagram of the overall structure of the multi-stage box-type sintered heat exchanger of the present invention in multiple sections;

[0032] Figure 3 A three-dimensional diagram of the shell of the single-stage box-type sintered heat exchanger of the present invention;

[0033] Figure 4 It is a cross-sectional view of a single-stage box-type sintered heat exchanger of the present invention;

[0034] Figure 5 This is a three-dimensional schematic diagram of the metal powder sintered body of the present invention.

[0035] In the figure: 1. upper square shell; 2. lower square shell; 3. sealing plate; 4. upper metal powder sintered body; 5. lower metal powder sintered body; 6. helium-3 dense-phase flow channel; 7. helium-3 dilute-phase flow channel; 8. helium-3 dense-phase inlet pipe; 9. helium-3 dense-phase outlet pipe; 10. helium-3 dense-phase fluid connecting pipe; 11. helium-3 dilute-phase outlet pipe; 12. helium-3 dilute-phase inlet pipe; 13. helium-3 dilute-phase fluid connecting pipe. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0037] like Figures 1 to 5 As shown, the present invention provides a multi-stage box sintered heat exchanger for a dilution refrigerator in the millikelvin temperature range, comprising an upper square shell 1 and a lower square shell 2, a sealing thin plate 3 is arranged between the upper square shell 1 and the lower square shell 2, the bottom of the upper square shell 1 and the top of the lower square shell 2 are both provided with a sunken groove, an upper metal powder sintered body 4 is arranged in the sunken groove of the upper square shell 1, and a lower metal powder sintered body 5 is arranged in the sunken groove of the lower square shell 2, four groups of upper square shells 1, lower square shells 2 and sealing thin plates 3 are provided, the top surfaces of the two upper square shells 1 are respectively fixed with a helium-3 dense phase inlet pipe 8 and a helium-3 dense phase outlet pipe 9, a helium-3 dense phase fluid connecting pipe 10 is arranged between the top surfaces of the two upper square shells 1, the bottom surfaces of the two lower square shells 2 are respectively provided with a helium-3 dilute phase outlet pipe 11 and a helium-3 dilute phase inlet pipe 12, and a helium-3 dilute phase fluid connecting pipe 13 is provided between the two lower square shells 2.

[0038] The above scheme is adopted: through the cooperation of the upper square shell 1 and the lower square shell 2, the upper square shell 1 and the lower square shell 2 are long rectangular blocks with the same external dimensions, and the bottom of the upper square shell 1 and the top of the lower square shell 2 are processed with equidistant sunken grooves for placing the upper metal powder sintered body 4 and the lower metal powder sintered body 5. The upper and lower joints between the upper square shell 1 and the lower square shell 2 are cleanly welded to achieve the side sealing of the single-stage box heat exchanger and the separation of the helium-3 concentrated and dilute phase fluids. The upper square shell 1 and the lower square shell 2, the upper metal powder sintered body 4 , the sealing thin plate 3 and the lower metal powder sintered body 5 are clamped in an integrally formed structure, similar to a "sandwich" structure, thereby forming a single-stage box-type sintered heat exchanger. The multi-stage box-type sintered heat exchanger is composed of four single-stage heat exchangers. The heat exchanger is composed of multiple stages of single sintered heat exchangers. The single sintered heat exchanger uses a high specific surface area metal powder sintered block to maximize the heat exchange area within a limited volume and maximize the elimination of the influence of axial heat conduction. The upper square shell 1 of the first and fourth stages, the helium-3 dense phase inlet pipe 8 and the helium- 3 dense phase outlet pipe 9 is welded along the circumference, and the shielding gas clean welding technology is used to weld the lower square shell 2 of the first and fourth stages with the helium-3 dilute phase inlet pipe 12 and the helium-3 dilute phase outlet pipe 11 along the circumference. The countersunk holes on the same side of the upper end face of the square shell 1 of each two-stage heat exchanger and the helium-3 dense phase fluid connecting pipe 10 are combined into one at the intersection by shielding gas clean welding. There are three helium-3 dense phase fluid connecting pipes 10 that need to be connected. Similarly, the countersunk holes on the same side of the lower section of the square shell 2 of each two-stage heat exchanger and the helium-3 dilute phase fluid connecting pipe 13 are combined at the intersection. The joints are combined into one by shielding gas clean welding. There are three helium-3 dilute phase fluid connecting pipes 13 shielding gas clean welding, and all welding points are processed with high-strength clean welding technology. The welding process is simplified through structural improvement, which greatly reduces the risk of helium-3 working fluid leakage. Then, the upper and lower flow channels of each stage of the box-type heat exchanger are connected, and the upper square shell 1, the sealing thin plate 3, the upper metal powder sintered body 4, the helium-3 dense phase fluid connecting pipe 10 and the helium-3 dilute phase fluid connecting pipe 13 are combined into a whole, thereby forming a multi-stage box-type sintered heat exchanger for a dilution refrigerator in the millikelvin temperature range.

[0039] like Figure 1 、 Figure 3 As shown, the upper square shell 1 and the lower square shell 2 are provided with countersunk holes at the center position 5 to 10 mm away from the short side, and the center of the countersunk holes is consistent. A helium-3 concentrated phase flow channel 6 and a helium-3 dilute phase flow channel 7 are opened below the countersunk holes. The sealing plate 3 is exactly the same in length as the upper square shell 1. The sealing plate 3 is fixedly installed between the upper square shell 1 and the lower square shell 2. The upper square shell 1 and the lower square shell 2 are exactly the same in shape and size. The upper square shell 1 and the lower square shell 2 are both made of titanium alloy with an aspect ratio of 5:1. The sealing plate 3 is made of copper.

[0040] The above scheme is adopted: through the cooperation of the upper square shell 1 and the lower square shell 2, the upper square shell 1 and the lower square shell 2 are respectively processed with countersunk holes at the center position 5 to 10 mm away from the short side. The countersunk hole diameter of the upper square shell 1 is about 2 to 3.5 mm, and that of the lower square shell 2 is about 4 to 6 mm. The tolerance is controlled at plus or minus 0.01 mm. The upper and lower countersunk holes are kept coaxial, and the bottom of the countersunk hole is at the same distance from the helium-3 concentrated phase flow channel 6 and the helium-3 dilute phase flow channel 7, which is controlled at 0.8 to 1.2 mm. Through the cooperation of the sealing sheet 3 and the upper square shell 1, the length value of the upper square shell 1 and the sealing sheet 3 are completely consistent, so that the upper square shell 1, the lower square shell 2 and the sealing sheet 3 are welded at the upper and lower seams to complete the sealing between the upper square shell 1 and the lower square shell 2 respectively, and the thickness of the sealing sheet 3 is about It is 0.2 to 0.4mm, and the flatness needs to be controlled within plus or minus 0.01mm to avoid subsequent impact on welding. Through the limitation of the materials of the upper square shell 1 and the lower square shell 2, titanium alloy has very high strength and light weight characteristics, which enables it to maintain good mechanical properties under high temperature and high load environments, and has relatively low thermal conductivity, which makes it have advantages in some applications requiring heat insulation or preventing heat conduction. Equidistant sunken grooves are processed on each side with a margin of 3 to 5mm and a depth of 1.5 to 2mm. The tolerance is controlled within plus or minus 0.01mm. Through the limitation of the material of the sealing sheet 3, the thermal conductivity of copper is very high. It is ideal in applications requiring efficient heat conduction and has good corrosion resistance, especially in a humid environment. It can naturally form a layer of copper oxide protective film to prevent further corrosion.

[0041] like Figure 4 、 Figure 5 As shown, the length values of the upper metal powder sintered body 4 and the lower metal powder sintered body 5 are consistent with the sinking groove, the bottom surface of the upper metal powder sintered body 4 and the top surface of the lower metal powder sintered body 5 are both in contact with the sealing thin plate 3, the upper metal powder sintered body 4 and the lower metal powder sintered body 5 are made of nano-scale metal powder with high thermal conductivity and sintered at low temperature, the upper metal powder sintered body 4 and the lower metal powder sintered body 5 are composed of porous media with high specific surface area, and the particle size of the sintered powder is controlled between 50 and 200 nm.

[0042] The above scheme is adopted: through the design of the upper metal powder sintered body 4 and the lower metal powder sintered body 5, the sintered powder particle size is controlled between 50 and 200 nm, which can better exchange heat between helium-3 concentrated and dilute phase fluids. The upper metal powder sintered body 4 uses high thermal conductivity nano-scale metal powder for low-temperature sintering, which can save energy and reduce the damage of high temperature to the material. Due to the high surface energy of nanoparticles, better inter-particle connection is easy to achieve during the sintering process, resulting in higher density and strength. Low-temperature sintering avoids excessive growth of metal grains at high temperatures, so that the fine structure of the material is maintained, thereby improving the mechanical properties and wear resistance of the material. Low-temperature sintering can significantly reduce energy consumption and reduce the emission of harmful gases. The upper metal powder sintered body 4 and the lower metal powder sintered body 5 are bonded to both sides of the sealing thin plate 3 through sintering technology, and are integrally formed through a sintering mold, thereby achieving sufficient heat exchange between helium-3 concentrated and dilute phase fluids.

[0043] like Figure 1 、 Figure 2 As shown, the helium-3 dense phase flow channel 6 is connected to the helium-3 dense phase inlet pipe 8, the helium-3 dense phase outlet pipe 9 and the helium-3 dense phase fluid connecting pipe 10, and the helium-3 dilute phase flow channel 7 is connected to the helium-3 dilute phase outlet pipe 11, the helium-3 dilute phase inlet pipe 12 and the helium-3 dilute phase fluid connecting pipe 13. The helium-3 dense phase flow channel 6 and the helium-3 dilute phase flow channel 7 are square in cross-section. The cross-sectional area of the helium-3 dense phase flow channel 6 is one-fourth of the cross-sectional area of the helium-3 dilute phase flow channel 7. The length of the helium-3 dense phase flow channel 6 and the helium-3 dilute phase flow channel 7 is the same as the length of the sunken groove. The helium-3 dilute phase fluid connecting pipe 13 and the helium-3 dense phase fluid connecting pipe 10 are both in an inverted "C" shape. The two upper square shells 1 are connected by the helium-3 dense phase fluid connecting pipe 10, and the two lower square shells 2 are connected by the helium-3 dilute phase fluid connecting pipe 13.

[0044] The above scheme is adopted: through the coordination of the helium-3 dense phase flow channel 6 and the helium-3 dilute phase flow channel 7, the helium-3 dense phase flow channel 6 is connected with the helium-3 dense phase inlet pipe 8, the helium-3 dense phase outlet pipe 9 and the helium-3 dense phase fluid connecting pipe 10, and the helium-3 dilute phase flow channel 7 is connected with the helium-3 dilute phase outlet pipe 11, the helium-3 dilute phase inlet pipe 12 and the helium-3 dilute phase fluid connecting pipe 13, so that sufficient heat exchange can be carried out between the upper square shell 1 and the lower square shell 2. The upper square shell 1 and the lower square shell 2 are respectively machined with a narrow and long helium-3 dense phase flow channel 6 and a helium-3 dilute phase flow channel 7 with a square cross-section along the flow direction at the center position of the sinking surface. The length is consistent with the double-sided sinking groove, and the width and depth are the same, which is 0.8 to 1.2 mm. The cross-sectional area of the helium-3 dense phase flow channel 6 is usually one-fourth of the helium-3 dilute phase flow channel 7. Narrow and long helium-3 dense phase flow channels 6 and helium-3 dilute phase flow channels 7 are designed inside the shell 1 and the lower square shell 2, and the heat exchangers of each stage are arranged in parallel, so that the dense and dilute phase working fluids can flow and diffuse stably. Through the design of the helium-3 dense phase fluid connecting pipe 10 and the helium-3 dilute phase fluid connecting pipe 13, the inverted "C" shape of the helium-3 dense phase fluid connecting pipe 10 and the helium-3 dilute phase fluid connecting pipe 13 makes it possible to better connect the four box-type sintered heat exchangers. The upper square shells 1 are connected by the helium-3 dense phase fluid connecting pipe 10 and the two lower square shells 2 are connected by the helium-3 dilute phase fluid connecting pipe 13, so that the upper square shell 1 and the lower square shell 2 can fully exchange heat through the helium-3 dense phase fluid connecting pipe 10 and the helium-3 dilute phase fluid connecting pipe 13.

[0045] The manufacturing method of the multi-stage box sintered heat exchanger for the dilution refrigerator in the milliKelvin temperature range is applied to the multi-stage box sintered heat exchanger for the dilution refrigerator in the milliKelvin temperature range:

[0046] Step 1: The upper square shell 1 and the lower square shell 2 are made of low thermal conductivity and high strength metal material with an aspect ratio of 5:1. Equally spaced sunken grooves are machined on each side with a margin of 3 to 5 mm and a depth of 1.5 to 2 mm. The tolerance is controlled within plus or minus 0.01 mm. The upper square shell 1 and the lower square shell 2 are respectively machined with a narrow and long helium-3 concentrated phase flow channel 6 and a helium-3 dilute phase flow channel 7 with a square cross-section at the center of the sunken surface along the flow direction. The length is consistent with the double-sided sunken grooves, and the width and depth are the same, 0.8 to 1.2 mm. The cross-sectional area of the helium-3 concentrated phase flow channel 6 is generally one-fourth of that of the helium-3 dilute phase flow channel 7.

[0047] Step 2: Countersinks are machined at the center of the upper square shell 1 and the lower square shell 2 at a distance of 5 to 10 mm from the short side. The diameter of the countersink of the upper square shell 1 is 2 to 3.5 mm, and that of the lower square shell 2 is 4 to 6 mm. The tolerance is controlled within plus or minus 0.01 mm. The upper and lower countersinks are kept coaxial, and the distance between the bottom of the countersink and the helium-3 concentrated phase flow channel 6 and the helium-3 dilute phase flow channel 7 is consistent, and is controlled within 0.8 to 1.2 mm.

[0048] Step 3: The sealing plate 3 is made of a high thermal conductivity material, and is completely consistent with the length and width of the upper square shell 1. The thickness is 0.2 to 0.4 mm, and the flatness needs to be controlled within ±0.01 mm. Clean welding technology is used at the upper and lower joints between the sealing plate 3 and the upper square shell 1 and the lower square shell 2 to achieve side sealing of the single-stage box-type heat exchanger and separation of the helium-3 concentrated and dilute phase fluids;

[0049] Step 4: The upper metal powder sintered body 4 is made of nano-scale metal powder with high thermal conductivity and sintered at low temperature. The sintered powder particle size is controlled between 50 and 200 nm, and the specific surface area needs to reach 2.5 to 4 cm2 per gram. Its external dimensions are consistent with the sunken grooves of the upper square shell 1 and the lower square shell 2, and the dimensional tolerance between the two is plus or minus 0.01 mm. The upper metal powder sintered body 4 and the lower metal powder sintered body 5 are bonded to both sides of the sealing sheet 3 through sintering technology and are integrally formed by a sintering mold;

[0050] Step 5: The upper square shell 1, the lower square shell 2, the sealing plate 3, the upper metal powder sintered body 4 and the lower metal powder sintered body 5 are integrally clamped to form a single-stage box-type sintered heat exchanger. The box-type sintered heat exchanger is composed of 10 single-stage heat exchangers. The upper square shells 1 of the first and fourth stages are welded to the helium-3 dense phase inlet pipe 8 and the helium-3 dense phase outlet pipe 9 along a circumference. The lower square shells 2 of the first and fourth stages are welded to the helium-3 dilute phase outlet pipe 11 and the helium-3 dilute phase inlet pipe 12 along a circumference.

[0051] Step 6: The countersunk holes on the same side of the upper end surface of the square shell 1 of each two-stage heat exchanger are integrated with the helium-3 concentrated phase fluid connecting pipe 10 at the intersection. A total of three helium-3 concentrated phase fluid connecting pipes 10 need to be connected. The countersunk holes on the same side of the lower section of the square shell 2 of each two-stage heat exchanger are integrated with the helium-3 dilute phase fluid connecting pipe 13 at the intersection. A total of three helium-3 dilute phase fluid connecting pipes 13 are welded, thereby connecting the upper and lower flow channels of each stage of the box-type heat exchanger;

[0052] Step 7: Combine the upper square shell 1, the sealing thin plate 3, the upper metal powder sintered body 4, the helium-3 dense phase fluid connecting pipe 10 and the helium-3 dilute phase fluid connecting pipe 13 into a whole, thereby forming a multi-stage box-type sintered heat exchanger for a millikelvin temperature range dilution refrigerator.

[0053] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0054] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A multi-stage box sintered heat exchanger for a millikelvin temperature range dilution refrigerator, comprising an upper square shell (1) and a lower square shell (2), characterized in that: A sealing thin plate (3) is provided between the upper square shell (1) and the lower square shell (2); a sinking groove is provided at the bottom of the upper square shell (1) and the top of the lower square shell (2); an upper metal powder sintered body (4) is provided in the sinking groove of the upper square shell (1); a lower metal powder sintered body (5) is provided in the sinking groove of the lower square shell (2); four groups of the upper square shell (1), the lower square shell (2) and the sealing thin plate (3) are provided; and a helium-3 concentrated phase inlet pipe (8) and a helium-3 concentrated phase outlet pipe (9) are fixedly mounted on the top surfaces of the two upper square shells (1), respectively.

2. The multi-stage box sintered heat exchanger for a millikelvin temperature range dilution refrigerator according to claim 1, characterized in that: A helium-3 concentrated phase fluid connecting pipe (10) is provided between the top surfaces of the two upper square shells (1), a helium-3 dilute phase outlet pipe (11) and a helium-3 dilute phase inlet pipe (12) are provided on the bottom surfaces of the two lower square shells (2), and a helium-3 dilute phase fluid connecting pipe (13) is provided between the two lower square shells (2).

3. The multi-stage box sintered heat exchanger for a millikelvin temperature range dilution refrigerator according to claim 1, characterized in that: The upper square shell (1) and the lower square shell (2) are provided with countersunk holes at central positions 5 to 10 mm away from the short sides, and the centers of the countersunk holes are kept consistent. A helium-3 concentrated phase flow channel (6) and a helium-3 dilute phase flow channel (7) are provided below the countersunk holes. The upper square shell (1) and the lower square shell (2) are both made of titanium alloy with an aspect ratio of 5:

1. The sealing thin plate (3) is made of copper.

4. The multi-stage box sintered heat exchanger for a millikelvin temperature range dilution refrigerator according to claim 1, characterized in that: The sealing thin plate (3) is completely consistent with the length of the upper square shell (1), and the sealing thin plate (3) is fixedly installed between the upper square shell (1) and the lower square shell (2). The upper square shell (1) and the lower square shell (2) are completely consistent in shape and size.

5. The multi-stage box sintered heat exchanger for a millikelvin temperature range dilution refrigerator according to claim 1, characterized in that: The lengths of the upper metal powder sintered body (4) and the lower metal powder sintered body (5) are consistent with the sunken groove, and the bottom surface of the upper metal powder sintered body (4) and the top surface of the lower metal powder sintered body (5) are both in contact with the sealing thin plate (3).

6. The multi-stage box sintered heat exchanger for a millikelvin temperature range dilution refrigerator according to claim 1, characterized in that: The upper metal powder sintered body (4) and the lower metal powder sintered body (5) are formed by low-temperature sintering of nano-scale metal powder with high thermal conductivity. The upper metal powder sintered body (4) and the lower metal powder sintered body (5) are composed of porous media with high specific surface area, and the particle size of the sintered powder is controlled between 50 and 200 nm.

7. The multi-stage box sintered heat exchanger for a millikelvin temperature range dilution refrigerator according to claim 2, characterized in that: The helium-3 dilute phase fluid connecting pipe (13) and the helium-3 dense phase fluid connecting pipe (10) are both in an inverted "C" shape, and the two upper square shells (1) are connected by the helium-3 dense phase fluid connecting pipe (10), and the two lower square shells (2) are connected by the helium-3 dilute phase fluid connecting pipe (13).

8. The multi-stage box sintered heat exchanger for a millikelvin temperature range dilution refrigerator according to claim 3, characterized in that: The helium-3 concentrated phase flow channel (6) is connected to the helium-3 concentrated phase inlet pipe (8), the helium-3 concentrated phase outlet pipe (9) and the helium-3 concentrated phase fluid connecting pipe (10), and the helium-3 dilute phase flow channel (7) is connected to the helium-3 dilute phase outlet pipe (11), the helium-3 dilute phase inlet pipe (12) and the helium-3 dilute phase fluid connecting pipe (13). The helium-3 concentrated phase flow channel (6) and the helium-3 dilute phase flow channel (7) are opened with a square cross section.

9. The multi-stage box sintered heat exchanger for a millikelvin temperature range dilution refrigerator according to claim 3, characterized in that: The cross-sectional area of the helium-3 concentrated phase flow channel (6) is one quarter of the cross-sectional area of the helium-3 dilute phase flow channel (7), and the lengths of the helium-3 concentrated phase flow channel (6) and the helium-3 dilute phase flow channel (7) are the same as the length of the sinking groove.

10. A method for manufacturing a multi-stage box sintered heat exchanger for a millikelvin temperature range dilution refrigerator, applicable to the multi-stage box sintered heat exchanger for a millikelvin temperature range dilution refrigerator according to any one of claims 1 to 9, characterized in that: Step 1: The upper square shell (1) and the lower square shell (2) are made of a low thermal conductivity and high strength metal material with an aspect ratio of 5:

1. Equally spaced sunken grooves are machined on each side, with a margin of 3 to 5 mm and a depth of 1.5 to 2 mm. The tolerance is controlled within plus or minus 0.01 mm. The upper square shell (1) and the lower square shell (2) are respectively machined to form a narrow and long helium-3 concentrated phase flow channel (6) and a helium-3 dilute phase flow channel (7) with a square cross-section along the flow direction at the center position of the sunken surface. The length is consistent with the double-sided sunken grooves, and the width and depth are the same, which are 0.8 to 1.2 mm. The cross-sectional area of the helium-3 concentrated phase flow channel (6) is usually one-fourth of that of the helium-3 dilute phase flow channel (7). Step 2: Countersinks are respectively machined at the center positions of the upper square shell (1) and the lower square shell (2) at a distance of 5 to 10 mm from the short side. The diameter of the countersink of the upper square shell (1) is 2 to 3.5 mm, and that of the lower square shell (2) is 4 to 6 mm. The tolerance is controlled within plus or minus 0.01 mm. The upper and lower countersinks are kept coaxial. The distance between the bottom of the countersink and the helium-3 concentrated phase flow channel (6) and the helium-3 dilute phase flow channel (7) is consistent and controlled within 0.8 to 1.2 mm. Step 3: The sealing sheet (3) is made of a high thermal conductivity material, and is completely consistent with the length and width of the upper square shell (1). The thickness is 0.2 to 0.4 mm, and the flatness needs to be controlled within plus or minus 0.01 mm. Clean welding technology is used at the upper and lower joints between the sealing sheet (3) and the upper square shell (1) and the lower square shell (2) to achieve the side sealing of the single-stage box-type heat exchanger and the separation of the helium-3 concentrated and dilute phase fluids; Step 4: The upper metal powder sintered body (4) is formed by sintering nano-scale metal powder with high thermal conductivity at low temperature. The particle size of the sintered powder is controlled between 50 and 200 nm, and the specific surface area needs to reach 2.5 to 4 cm2 per gram. Its external dimensions are consistent with the sunken grooves of the upper square shell (1) and the lower square shell (2), and the dimensional tolerance between the two is plus or minus 0.01 mm. The upper metal powder sintered body (4) and the lower metal powder sintered body (5) are bonded to both sides of the sealing thin plate (3) through sintering technology and are integrally formed through a sintering mold; Step 5: The upper square shell (1), the lower square shell (2), the sealing thin plate (3), the upper metal powder sintered body (4) and the lower metal powder sintered body (5) are integrally formed and clamped to form a single-stage box-type sintered heat exchanger. The box-type sintered heat exchanger is composed of a total of 10 single-stage heat exchangers. The upper square shells (1) of the first and fourth stages are welded to the helium-3 dense phase inlet pipe (8) and the helium-3 dense phase outlet pipe (9) along a circle, and the lower square shells (2) of the first and fourth stages are welded to the helium-3 dilute phase outlet pipe (11) and the helium-3 dilute phase inlet pipe (12) along a circle; Step 6: The countersunk holes on the same side of the upper end surface of the square shell (1) of each two-stage heat exchanger and the helium-3 concentrated phase fluid connecting pipe (10) are combined into one at the intersection, and a total of three helium-3 concentrated phase fluid connecting pipes (10) need to be connected. The countersunk holes on the same side of the lower cross-section of the square shell (2) of each two-stage heat exchanger and the helium-3 dilute phase fluid connecting pipe (13) are combined into one at the intersection, and a total of three helium-3 dilute phase fluid connecting pipes (13) are welded, thereby connecting the upper and lower flow channels of each stage box-type heat exchanger; Step 7: Combine the upper square shell (1), the sealing thin plate (3), the upper metal powder sintered body (4), the helium-3 dense phase fluid connecting pipe (10) and the helium-3 dilute phase fluid connecting pipe (13) into a whole, thereby forming a multi-stage box-type sintered heat exchanger for a millikelvin temperature range dilution refrigerator.

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