Through-type heat exchanger for heat leakage control between different last cold stages of dilution refrigerator and manufacturing method of through-type heat exchanger

Abstract

The invention discloses a through-type heat exchanger for controlling heat leakage between different last cold stages of a dilution refrigerator and a manufacturing method, and particularly relates to the technical field of refrigeration and low-temperature engineering, the through-type heat exchanger comprises an inlet connecting pipe, an annular upper sealing plate, a heat exchanger shell, an annular lower sealing plate, an outlet connecting pipe and a metal sintering body, an inner wall face fixing step is fixedly arranged on the inner wall of the heat exchanger shell, the inner wall face fixing step is close to an opening in the bottom end of the heat exchanger shell, the metal sintering body is arranged in the heat exchanger shell and is tightly matched with the heat exchanger shell, and the length of the metal sintering body is slightly smaller than that of the heat exchanger shell. By arranging the metal sintering body, the heat exchange area is increased to the maximum extent within the limited volume, the porosity and the specific surface area of the metal sintering body are reasonably set, and therefore stable flowing and diffusion of the helium-3 / helium-4 mixed working medium are achieved.

Description

Technical Field

[0001] The present invention relates to the field of refrigeration and cryogenic engineering technology, and in particular to a through-type heat exchanger for controlling heat leakage between different cold stages in the final stage of a dilution refrigerator and a manufacturing method thereof. Background Art

[0002] Dilution refrigerators utilize the entropy increase effect at the interface between concentrated and dilute helium-3 phases to achieve millikelvin cooling, reaching temperatures as low as 10mK. As a millikelvin cooling technology, dilution refrigerators offer advantages such as continuous and stable operation, extremely low electromagnetic and vibration interference, and large cooling capacity. In recent years, they have become a hot topic in ultra-low temperature research and have found widespread application in fields such as superconducting quantum computing and condensed matter physics. Dilution refrigerators typically consist of a precooling unit, a throttling unit, and a dilution unit, with the final stage typically referring to the millikelvin dilution unit.

[0003] The final stage of a dilution refrigerator typically operates below 100mK. Cooling the extremely low-temperature cold plate requires a through-type heat exchanger between the different cooling stages to achieve heat leakage control, thereby ensuring stable operation of the dilution refrigerator at 100mK and below. Ideally, the through-type heat exchanger at the final stage of the dilution refrigerator, which implements heat leakage control between the different cooling stages, should have the following four functions:

[0004] First, it achieves efficient heat exchange within a limited volume; second, it achieves effective diffusion and flow of the working fluid; third, it reduces the impact of radiation on the final stage temperature; fourth, it has high sealing performance.

[0005] However, conventional dilution refrigerators currently lack a detailed description of the internal structure. In addition, due to spatial layout issues, the internal heat exchange is usually insufficient. In addition, the structural setting makes the piping arrangement more complicated, and therefore cannot meet the above four requirements. Summary of the Invention

[0006] The present invention aims to provide a through-type heat exchanger and a manufacturing method for controlling heat leakage between different cold stages in the final stage of a dilution refrigerator. By providing a metal sintered body, the heat exchange area is maximized within a limited volume. The porosity and specific surface area of the metal sintered body are rationally set, thereby achieving stable flow and diffusion of a helium-3 / helium-4 mixture.

[0007] To achieve the above-mentioned object, the present invention provides the following technical solution: a through-type heat exchanger for controlling heat leakage between different cooling stages in the final stage of a dilution refrigerator, comprising an inlet connecting pipe, an annular upper sealing plate, a heat exchanger shell, an annular lower sealing plate, an outlet connecting pipe, and a metal sintered body, wherein the heat exchanger shell is in the shape of a hollow cylinder;

[0008] The inner wall of the heat exchanger shell is fixedly provided with an inner wall fixed step, and the inner wall fixed step is close to the opening at the bottom end of the heat exchanger shell. The metal sintered body is arranged inside the heat exchanger shell and is tightly matched with the heat exchanger shell. The fitting tolerance between the metal sintered body and the heat exchanger shell is approximately 0.01mm. The length of the metal sintered body is slightly smaller than the length of the heat exchanger shell. The annular upper sealing plate is located above the metal sintered body and is in close contact with the top end of the metal sintered body.

[0009] The upper plane of the annular lower sealing plate contacts the bottom surface of the fixed step of the inner wall surface. The outer diameter of the annular lower sealing plate is the same as the inner diameter of the heat exchanger shell and is tightly matched.

[0010] Furthermore, a circular ring is fixedly provided at the middle part of the outer end of the heat exchanger shell, the circular ring is coaxial with the heat exchanger shell, the outer diameter of the circular ring is 1.5-1.7 times the outer diameter of the cross section of the heat exchanger shell, and the heat exchanger shell is provided with four cold plate mounting holes that pass through the heat exchanger shell, and the cold plate mounting holes are evenly distributed on the heat exchanger shell.

[0011] Furthermore, the bottom end of the inner wall fixed step is 0.3-0.8 mm away from the bottom end of the heat exchanger shell, the bottom end of the metal sintered body contacts the upper end surface of the inner wall fixed step, and the top end of the metal sintered body is 0.1-0.5 mm lower than the top end of the heat exchanger shell.

[0012] Furthermore, the side wall of the annular upper sealing plate is tightly fitted with the inner wall of the heat exchanger shell, and the fitting tolerance between the outer end of the annular upper sealing plate and the inner wall of the heat exchanger shell is controlled at 0.01 mm. The junction of the annular upper sealing plate and the heat exchanger shell is connected by welding, and the welding portion of the annular upper sealing plate and the heat exchanger shell is welding point B.

[0013] Furthermore, the bottom end of the inlet connecting pipe is inserted into the hole at the center of the annular upper sealing plate and maintained in a tight fit, and the intersection of the inlet connecting pipe and the annular upper sealing plate is connected by welding, and the welding position of the inlet connecting pipe and the annular upper sealing plate is welding point A.

[0014] Furthermore, the annular lower sealing plate is clamped on the step formed between the fixed step on the inner wall surface and the inner wall of the heat exchanger shell. The annular lower sealing plate and the heat exchanger shell are connected by welding at the intersection. The welding position of the heat exchanger shell and the annular lower sealing plate is the welding point C. The annular lower sealing plate closes the opening at the bottom end of the heat exchanger shell. The top end of the outlet connecting pipe is inserted into the hole in the center of the annular lower sealing plate and maintained in a tight fit. The connection between the outlet connecting pipe and the annular lower sealing plate is connected by welding. The welding position of the annular lower sealing plate and the outlet connecting pipe is the welding point D.

[0015] The present invention also includes a method for manufacturing the above-mentioned through-type heat exchanger for controlling heat leakage between different cold stages in the final stage of a dilution refrigerator, which comprises the following specific steps:

[0016] Step 1: Use high thermal conductivity material to make the heat exchanger shell. The heat exchanger shell is in direct contact with the cold plate and serves as the main cooling heat exchange surface. The main part of the heat exchanger shell is a hollow cylinder. A circle of rings is machined at the center waist of the hollow cylinder. The ring and the hollow cylinder keep the same axis. The shape of the entire heat exchanger shell remains symmetrical from top to bottom. The outer diameter of the ring is about 1.5 to 1.7 times the outer diameter of the hollow cylinder. To ensure good heat conduction effect, the upper and lower planes of the ring need to ensure flatness of ±0.01mm. Four evenly distributed through holes are machined on the ring of the heat exchanger shell, which are the cold plate mounting holes. The diameter of the cold plate mounting holes is about 1.2 to 1.3 times the outer diameter of the hollow cylinder. The hole diameter is 2 to 3mm and is used to fix the heat exchanger and the cold plate.

[0017] Step 2: Process a circle of raised steps on the lower part of the inner wall of the heat exchanger shell, which is the fixed step on the inner wall. The lower plane is 0.3-0.8mm away from the bottom end of the heat exchanger shell, and the height of the raised step is about 0.2-0.4mm. It is used to limit the metal sintered body to keep it fixed during the welding process;

[0018] Step 3: Use high thermal conductivity metal powder to sinter at high temperature to form a metal sintered body. The powder particle size is controlled between 0.5 and 1.5 μm. The diameter of the metal sintered body is consistent with the inner diameter of the heat exchanger shell and is tightly matched with the inner wall of the heat exchanger shell. The matching tolerance is about 0.01 mm.

[0019] Step 4: Use low thermal conductivity and high strength material to manufacture an annular upper sealing plate with a thickness of 0.8-1.2mm. Place it on top of the metal sintered body and press it tightly. The diameter of the annular upper sealing plate is consistent with that of the metal sintered body. The upper surface of the annular upper sealing plate protrudes 0.4-0.6mm above the upper surface of the heat exchanger shell, forming a circle of grooves. Clean brazing technology is used at welding point B to make the two become one. The annular lower sealing plate is also made of low thermal conductivity and high strength material like the annular upper sealing plate, and its external dimensions are exactly the same. Clean brazing technology is used at welding point C to complete the connection and sealing of the heat exchanger shell and the annular lower sealing plate.

[0020] Step 5: Use low thermal conductivity and high strength material to make the inlet connecting pipe, and connect it at welding point A using high-precision laser welding technology to form an inflow channel for the helium-3 / helium-4 mixture. The material and size of the outlet connecting pipe are exactly the same as those of the inlet connecting pipe. The outlet connecting pipe is tightly matched with the hole in the middle of the annular lower sealing plate to provide a channel for the helium-3 / helium-4 mixture to flow out. At welding point D, high-precision laser welding technology is used to combine the annular lower sealing plate and the outlet connecting pipe into one.

[0021] In the above technical solution, the technical effects and advantages provided by the present invention are:

[0022] 1. By setting up a metal sintered body, the heat exchange area is maximized within a limited volume, and the porosity and specific surface area of the metal sintered body are reasonably set to achieve stable flow and diffusion of the helium-3 / helium-4 mixed working fluid;

[0023] In addition, high thermal conductivity materials are used to effectively utilize the cooling capacity of the He-3 / Helium-4 mixed working fluid, and a symmetrical structure that runs through the cold plate is used to further cool the 100mK cold plate and radiation shield, thereby reducing the radiation impact on the final stage temperature.

[0024] 2. The stable flow of the helium-3 / helium-4 mixed working fluid in the millikelvin temperature range is achieved, the temperature of the final dilution refrigeration stage is further optimized, high-strength clean welding technology is used to process all welding points, the welding process is simplified through structural improvements, and the leakage risk is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments described in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0026] Figure 1 This is the overall appearance structure diagram of the present invention;

[0027] Figure 2 is a cross-sectional view of the present invention;

[0028] Figure 3 This is a structural diagram of the heat exchanger shell and the internal metal sintered body of the present invention;

[0029] Figure 4 A cross-sectional view of the heat exchanger shell and the internal metal sintered body of the present invention;

[0030] Figure 5 This is a structural diagram of the metal sintered body of the present invention.

[0031] Description of reference numerals:

[0032] 1. Inlet connecting pipe; 2. Annular upper sealing plate; 3. Heat exchanger shell; 4. Cold plate mounting hole; 5. Inner wall fixing step; 6. Annular lower sealing plate; 7. Outlet connecting pipe; 8. Welding point A; 9. Welding point B; 10. Welding point C; 11. Welding point D; 12. Metal sintered body. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0034] The present invention provides Figure 1-5 The through-type heat exchanger shown is used for controlling heat leakage between different cooling stages in the final stage of a dilution refrigerator, and includes an inlet connecting pipe 1, an annular upper sealing plate 2, a heat exchanger shell 3, an annular lower sealing plate 6, an outlet connecting pipe 7, and a metal sintered body 12. The heat exchanger shell 3 is hollow cylindrical.

[0035] An inner wall fixing step 5 is fixedly provided on the inner wall of the heat exchanger shell 3. The inner wall fixing step 5 is close to the opening at the bottom end of the heat exchanger shell 3. The metal sintered body 12 is arranged inside the heat exchanger shell 3 and is tightly fitted with the heat exchanger shell 3. The fitting tolerance between the metal sintered body 12 and the heat exchanger shell 3 is approximately 0.01 mm. The length of the metal sintered body 12 is slightly smaller than the length of the heat exchanger shell 3. The annular upper sealing plate 2 is located above the metal sintered body 12 and is in close contact with the top end of the metal sintered body 12.

[0036] The metal sintered body 12 is made by sintering high-temperature metal powder with high thermal conductivity. The powder particle size is controlled between 0.5 and 1.5 μm. The diameter of the metal sintered body 12 is consistent with the inner diameter of the heat exchanger shell 3 and is tightly matched with the inner wall surface of the heat exchanger shell 3 with a fitting tolerance of approximately 0.01 mm. The metal sintered body 12 is a porous medium metal powder sintered body, which maximizes the heat exchange area within a limited volume. Secondly, the porosity and specific surface area of the metal sintered body are reasonably set to achieve stable flow and diffusion of the helium-3 / helium-4 mixed working medium.

[0037] A circular ring is fixedly provided at the middle part of the outer end of the heat exchanger shell 3. The circular ring is coaxial with the heat exchanger shell 3. The outer diameter of the circular ring is 1.5-1.7 times the outer diameter of the cross section of the heat exchanger shell 3. Four cold plate mounting holes 4 are opened on the heat exchanger shell 3 and pass through the heat exchanger shell 3. The cold plate mounting holes 4 are evenly distributed on the heat exchanger shell 3.

[0038] The heat exchanger shell 3 is made of high thermal conductivity material. The heat exchanger shell 3 is in direct contact with the cold plate and serves as the main cooling heat exchange surface. The main part of the heat exchanger shell 3 is a hollow cylinder. A ring is processed at the center waist of the hollow cylinder. The ring and the hollow cylinder keep the same axis. The shape of the entire heat exchanger shell remains symmetrical from top to bottom. The outer diameter of the ring is about 1.5 to 1.7 times the outer diameter of the hollow cylinder. To ensure good heat conduction effect, the upper and lower planes of the ring need to maintain a flatness of ±0.01m m. Four evenly distributed through-holes are machined on the circular ring of the heat exchanger shell 3, namely the cold plate mounting holes 4. The diameter of the cold plate mounting holes 4 is approximately 1.2 to 1.3 times the outer diameter of the hollow cylinder, and the hole diameter is 2 to 3 mm. They are used to fix the heat exchanger and the cold plate. High thermal conductivity materials are used to effectively utilize the cooling capacity of the helium-3 / helium-4 mixed working fluid. A symmetrical structure that runs through the cold plate is used to further cool the 100mK cold plate and radiation shield, thereby reducing the radiation impact on the final stage temperature.

[0039] A circle of raised steps is machined on the lower part of the inner wall of the heat exchanger shell 3, namely the inner wall fixed step 5. The raised height is about 0.2-0.4 mm, which is used to limit the metal sintered body 12 to keep it fixed during the welding process. The bottom end of the inner wall fixed step 5 is 0.3-0.8 mm away from the bottom end of the heat exchanger shell 3. The bottom end of the metal sintered body 12 contacts the upper end surface of the inner wall fixed step 5, and the top of the metal sintered body 12 is 0.1-0.5 mm lower than the top end of the heat exchanger shell 3.

[0040] The side wall of the annular upper sealing plate 2 is tightly fitted with the inner wall of the heat exchanger shell 3. The fitting tolerance between the outer end of the annular upper sealing plate 2 and the inner wall of the heat exchanger shell 3 is controlled within 0.01 mm. The intersection of the annular upper sealing plate 2 and the heat exchanger shell 3 is connected by welding. The welding location of the annular upper sealing plate 2 and the heat exchanger shell 3 is welding point B9.

[0041] The annular upper sealing plate 2 is made of low thermal conductivity and high strength material with a thickness of 0.8 to 1.2 mm. It is placed on top of the metal sintered body 12 and pressed tightly. The diameter of the annular upper sealing plate 2 is consistent with that of the metal sintered body 12. The upper surface of the annular upper sealing plate 2 exceeds the upper surface of the heat exchanger shell 3 by 0.4 to 0.6 mm, forming a circle of grooves. Clean brazing technology is used at the welding point B9 to make the two become one.

[0042] The bottom end of the inlet connecting pipe 1 is inserted into the hole at the center of the annular upper sealing plate 2 and maintained in a tight fit. The intersection of the inlet connecting pipe 1 and the annular upper sealing plate 2 is connected by welding. The welding point between the inlet connecting pipe 1 and the annular upper sealing plate 2 is welding point A8. The inlet connecting pipe 1 is made of low thermal conductivity and high strength material. The connection is made at welding point A8 using high-precision laser welding technology to form an inflow channel for the helium-3 / helium-4 mixture.

[0043] The upper plane of the annular lower sealing plate 6 contacts the bottom surface of the inner wall fixed step 5. The outer diameter of the annular lower sealing plate 6 is the same as the inner diameter of the heat exchanger shell 3 and is tightly fitted. The annular lower sealing plate 6 is stuck on the step formed between the inner wall fixed step 5 and the inner wall of the heat exchanger shell 3. The annular lower sealing plate 6 and the heat exchanger shell 3 are connected by welding at the intersection. The welding position of the heat exchanger shell 3 and the annular lower sealing plate 6 is the welding point C10. The annular lower sealing plate 6 closes the opening at the bottom end of the heat exchanger shell 3. The top end of the outlet pipe 7 is inserted into the hole in the center of the annular lower sealing plate 6 and keeps a tight fit. The outlet connecting pipe 7 and the annular lower sealing plate 6 are connected by welding. The welding point between the annular lower sealing plate 6 and the outlet connecting pipe 7 is welding point D11. The annular lower sealing plate 6, like the annular upper sealing plate 2, is also made of low thermal conductivity and high strength material and has completely identical dimensions. Clean brazing technology is used at welding point C10 to complete the connection and sealing between the heat exchanger shell 3 and the annular lower sealing plate 6. High-strength clean welding technology is used to process all welding points at welding points A8, welding point B9, welding point C10 and welding point D11. The structural improvement simplifies the welding process and significantly reduces the risk of leakage.

[0044] Similarly, the material and dimensions of the outlet connecting pipe 7 are exactly the same as those of the inlet connecting pipe 1. The outlet connecting pipe 7 is tightly fitted with the hole in the middle of the annular lower sealing plate 6, providing a channel for the outflow of the helium-3 / helium-4 mixture. High-precision laser welding technology is used at welding point D11 to integrate the annular lower sealing plate 6 and the outlet connecting pipe 7 into one, thereby achieving stable flow of the helium-3 / helium-4 mixed working medium in the millikelvin temperature range, further optimizing the final stage temperature of the dilution refrigeration, and having very positive significance for the application of dilution refrigerators in special fields such as superconducting quantum computing and condensed matter physics research.

[0045] The above description is merely illustrative of certain exemplary embodiments of the present invention. It goes without saying that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims.

Claims

1. A through-type heat exchanger for controlling heat leakage between different cooling stages in the final stage of a dilution refrigerator, comprising an inlet connecting pipe (1), an annular upper sealing plate (2), a heat exchanger shell (3), an annular lower sealing plate (6), an outlet connecting pipe (7) and a metal sintered body (12), characterized in that: The heat exchanger shell (3) is in the shape of a hollow cylinder; An inner wall fixed step (5) is fixedly provided on the inner wall of the heat exchanger shell (3); the metal sintered body (12) is arranged inside the heat exchanger shell (3) and is tightly fitted with the heat exchanger shell (3); the annular upper sealing plate (2) is located above the metal sintered body (12) and is in close contact with the top of the metal sintered body (12); The upper plane of the annular lower sealing plate (6) contacts the bottom surface of the inner wall fixed step (5), and the outer diameter of the annular lower sealing plate (6) is the same as the inner diameter of the heat exchanger shell (3) to achieve a tight fit.

2. A through-type heat exchanger for controlling heat leakage between different cold stages in the final stage of a dilution refrigerator according to claim 1, characterized in that: A circular ring is fixedly provided at the middle portion of the outer end of the heat exchanger shell (3), the circular ring being coaxial with the heat exchanger shell (3), and four cold plate mounting holes (4) penetrating the heat exchanger shell (3) are provided on the heat exchanger shell (3).

3. The through-type heat exchanger for controlling heat leakage between different cold stages of the final stage of a dilution refrigerator according to claim 1, characterized in that: The bottom end of the inner wall fixed step (5) is 0.3-0.8 mm away from the bottom end of the heat exchanger shell (3), the bottom end of the metal sintered body (12) contacts the upper end surface of the inner wall fixed step (5), and the top end of the metal sintered body (12) is 0.1-0.5 mm lower than the top end of the heat exchanger shell (3).

4. The through-type heat exchanger for controlling heat leakage between different cold stages of the final stage of a dilution refrigerator according to claim 1, characterized in that: The side wall of the annular upper sealing plate (2) is tightly fitted with the inner wall of the heat exchanger shell (3); the fitting tolerance between the outer end of the annular upper sealing plate (2) and the inner wall of the heat exchanger shell (3) is controlled to be 0.01 mm; the intersection of the annular upper sealing plate (2) and the heat exchanger shell (3) is connected by welding; the welding portion of the annular upper sealing plate (2) and the heat exchanger shell (3) is welding point B (9).

5. The through-type heat exchanger for controlling heat leakage between different cold stages of the final stage of a dilution refrigerator according to claim 1, characterized in that: The bottom end of the inlet connecting pipe (1) is inserted into the hole at the center of the annular upper sealing plate (2) and is kept tightly fitted. The intersection of the inlet connecting pipe (1) and the annular upper sealing plate (2) is connected by welding. The welding position of the inlet connecting pipe (1) and the annular upper sealing plate (2) is the welding point A (8).

6. The through-type heat exchanger for controlling heat leakage between different cold stages of the final stage of a dilution refrigerator according to claim 1, characterized in that: The annular lower sealing plate (6) is clamped on the step formed between the inner wall fixed step (5) and the inner wall of the heat exchanger shell (3). The annular lower sealing plate (6) and the heat exchanger shell (3) are connected by welding at the intersection. The welding position of the heat exchanger shell (3) and the annular lower sealing plate (6) is the welding point C (10). The top end of the outlet connecting pipe (7) is inserted into the hole in the center of the annular lower sealing plate (6) and maintained in a tight fit. The connection between the outlet connecting pipe (7) and the annular lower sealing plate (6) is connected by welding. The welding position of the annular lower sealing plate (6) and the outlet connecting pipe (7) is the welding point D (11).

7. A method for manufacturing a through-type heat exchanger for controlling heat leakage between different cold stages in the final stage of a dilution refrigerator according to any one of claims 1 to 6, characterized in that: The specific steps are as follows: Step 1: Use high thermal conductivity material to make a heat exchanger shell (3). The heat exchanger shell (3) is in direct contact with the cold plate and serves as the main cooling heat exchange surface. The main part of the heat exchanger shell (3) is a hollow cylinder. A circle of rings is processed at the central waist position of the hollow cylinder. The rings and the hollow cylinder keep the same axis. The shape of the entire heat exchanger shell remains symmetrical up and down. The outer diameter of the ring is about 1.5 to 1.7 times the outer diameter of the hollow cylinder. To ensure good heat conduction effect, the upper and lower planes of the ring need to ensure flatness of ±0.01mm. Four evenly distributed through holes are processed on the ring of the heat exchanger shell (3), which are the cold plate mounting holes (4). The diameter of the cold plate mounting holes (4) is about 1.2 to 1.3 times the outer diameter of the hollow cylinder. The hole diameter is 2 to 3mm and is used to fix the heat exchanger and the cold plate. Step 2: A raised step is machined on the lower portion of the inner wall of the heat exchanger shell (3), which is the inner wall fixed step (5). The lower plane of the step is 0.3 to 0.8 mm away from the bottom end of the heat exchanger shell (3), and the raised height is about 0.2 to 0.4 mm. The step is used to limit the metal sintered body (12) so that it remains fixed during the welding process. Step 3: Using high thermal conductivity metal powder and sintering at high temperature to form a metal sintered body (12), the powder particle size is controlled between 0.5 and 1.5 μm, the diameter of the metal sintered body (12) is consistent with the inner diameter of the heat exchanger shell (3), and it is tightly matched with the inner wall surface of the heat exchanger shell (3), with a matching tolerance of about 0.01 mm; Step 4: Use low thermal conductivity and high strength material to manufacture an annular upper sealing plate (2) with a thickness of 0.8 to 1.2 mm, place it on the metal sintered body (12) and press it tightly, with the diameter consistent with the metal sintered body (12). The upper surface of the annular upper sealing plate (2) exceeds the upper surface of the heat exchanger shell (3) by 0.4 to 0.6 mm, forming a circle of grooves. Clean brazing technology is used at welding point B (9) to make the two become one. The annular lower sealing plate (6) is also made of low thermal conductivity and high strength material like the annular upper sealing plate (2), and the outer dimensions are completely consistent. Clean brazing technology is used at welding point C (10) to complete the connection and sealing of the heat exchanger shell (3) and the annular lower sealing plate (6); Step 5: The inlet connecting pipe (1) is made of a low thermal conductivity and high strength material, and is connected at welding point A (8) by high-precision laser welding technology to form an inflow channel for the helium-3 / helium-4 mixture. The material and size of the outlet connecting pipe (7) are completely consistent with those of the inlet connecting pipe (1). The outlet connecting pipe (7) and the hole in the middle of the annular lower sealing plate (6) are tightly matched to provide a channel for the helium-3 / helium-4 mixture to flow out. At welding point D (11), high-precision laser welding technology is used to combine the annular lower sealing plate (6) and the outlet connecting pipe (7) into one.

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