Spiral multi-stage powder sintered heat exchanger for dilution refrigerator and manufacturing method thereof

Abstract

The present application relates to refrigeration and cryogenics, and particularly relates to a spiral multi-stage powder sintered heat exchanger for a dilution refrigerator, comprising a plurality of heat exchange units. The heat exchange units are coaxially stacked in series. Each heat exchange unit has a planar spiral structure and has two spiral main flow channels arranged independently and in full counter flow. The two spiral main flow channels of adjacent heat exchange units are connected by connecting pipes. The present application also relates to a manufacturing method, comprising processing a shell, processing a heat-conducting partition, sealing and welding the shell and the heat-conducting partition after alignment to form a heat exchange unit, and stacking the heat exchange units coaxially in series. The present application can greatly improve the radial space utilization and prolong the effective heat exchange travel of the working medium through the spiral main flow channel design, effectively solve the straight-through flow problem, and increase the heat exchange area through the porous metal powder sintered block. In combination with the multi-stage series structure, the axial heat conduction is inhibited, which has a positive significance for the performance improvement and production of the dilution refrigerator.

Description

Technical Field

[0001] This invention relates to refrigeration and cryogenic engineering, and in particular to a spiral multi-stage powder sintering heat exchanger for a dilution refrigeration machine and its manufacturing method. Background Technology

[0002] Dilution refrigerators primarily serve cutting-edge scientific and engineering fields such as superconducting quantum computing, fundamental research in condensed matter physics, and deep space exploration, providing these fields with a continuously sustainable mK-level cryogenic environment. The powder-sintered heat exchanger is the core component of the dilution unit of the dilution refrigerator. Its core function is to address the critical challenge of declining heat exchange efficiency in conventional heat exchangers at mK-level cryogenic temperatures due to the sharp increase in Carpicar thermal resistance. Through the porous structure formed by sintering metal powder, the contact area between the liquid helium working fluid and the heat exchange substrate is increased by several orders of magnitude. The working mechanism of the powder-sintered heat exchanger is to utilize the recovered cooling capacity of the upward-flowing dilute-phase fluid to deeply pre-cool the downward-flowing dense-phase fluid, thereby significantly reducing the cooling load on the final mixing chamber. It is a key component that determines the ultimate cooling temperature, cooling power, and long-term continuous operational stability of the dilution refrigerator.

[0003] Ideally, powder sintering heat exchangers need to achieve the following four functions:

[0004] First, efficient countercurrent heat exchange. By combining a long-range effective flow path with the ultra-large heat exchange area of ​​powder sintering, the Carpi Chau thermal resistance of the solid-liquid interface at extremely low temperatures is significantly reduced, achieving near-ideal countercurrent heat exchange between the downward-flowing dense helium-3 and the upward-flowing dilute helium-3 / helium-4 solution. The dense helium-3 entering the mixing chamber is pre-cooled to near the operating temperature of the mixing chamber, maximizing the release of the enthalpy difference cooling capacity of the dilution process;

[0005] Second, parasitic heat leakage prevention. Under extremely low temperature conditions in the mK range, it is necessary to suppress various parasitic heat loads such as heat dissipation from fluid viscosity and heat leakage through axial conduction of solid tube walls to the greatest extent possible, so as to avoid irreversible loss of the effective cooling capacity of the dilution refrigeration cycle, thereby providing a core guarantee for the dilution refrigeration machine to achieve a lower ultimate base temperature;

[0006] Third, high-reliability sealing performance. The helium-3 working fluid used in the dilution refrigerator is expensive, which places extremely high demands on the sealing performance of the powder sintered heat exchanger. This requires the heat exchange components themselves to minimize the moving connection structure, while possessing high-strength and high-reliability sealing capabilities.

[0007] Fourth, high space utilization. The installation space of the dilution refrigerator, especially the radial dimension and vertical installation height of the cold plate, is strictly limited by the overall cavity structure. Moreover, with the further development of refrigeration requirements, the cold platform needs to reserve more available space for core loads such as quantum chips and detection devices. This requires the powder sintering heat exchanger to achieve the optimal match between heat exchange performance and structural volume within the limited geometric boundaries.

[0008] Currently, most powder sintered heat exchangers employ straight or annular flow channel structures, which suffer from uneven working fluid velocity distribution within the channel, short effective counter-current heat exchange path, and insufficient contact between hot and cold fluids. This limits heat exchange efficiency improvement under extremely low temperatures and low Reynolds numbers. Furthermore, the flow channel length is constrained by installation space, resulting in low space utilization and an inability to maximize the effective heat exchange path within a limited radial dimension, making it difficult to balance heat exchange efficiency with the need for miniaturization. Therefore, it is clearly insufficient to meet the core functions required of powder sintered heat exchangers. Summary of the Invention

[0009] The purpose of this invention is to provide a spiral multi-stage powder sintered heat exchanger for a dilution refrigerator and its manufacturing method, which mainly solves the problems existing in the prior art. It maximizes the effective heat exchange stroke within a limited space through the Archimedean spiral continuous flow channel design; it forces the concentrated and dilute phase working fluids to flow along the entire spiral flow channel, eliminating the problem of the working fluid passing through the shortest path in the disc-shaped flow channel, and ensuring that most of the sintered porous medium participates in heat exchange; at the same time, it significantly increases the heat exchange specific surface area through porous metal powder sintered blocks, and suppresses axial heat conduction by combining a multi-stage series structure, thereby significantly enhancing the countercurrent heat exchange effect at extremely low temperatures.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is to provide a spiral multi-stage powder sintering heat exchanger for a dilution refrigeration machine, characterized in that it includes multiple heat exchange units; the heat exchange units are coaxially stacked and connected in series; each heat exchange unit has a planar spiral structure and has two independent spiral main channels arranged in countercurrent throughout; the two spiral main channels of adjacent heat exchange units are respectively connected by connecting pipes.

[0011] Furthermore, the helix of the planar spiral structure is an equidistant spiral.

[0012] Furthermore, the heat exchange unit includes a first shell, a second shell, and a heat-conducting partition; the heat-conducting partition is sandwiched between the first shell and the second shell; flow channels are respectively formed on the first shell and the second shell; the two flow channels rotate in opposite directions and have opposite openings, respectively forming two independent spiral main channels with the heat-conducting partition.

[0013] Furthermore, a first ear plate and a second ear plate that extend continuously are respectively provided on the outer periphery of the first housing and the second housing; the first ear plate and the second ear plate are fully fitted with the corresponding surfaces of the heat-conducting partition and are sealed and fixed by full-circumferential welding.

[0014] Furthermore, countersunk holes for installing connecting pipes are respectively provided on the first housing and the second housing; a sealing ring is provided at the position where the connecting pipe passes through the heat-conducting partition to achieve fluid isolation between the two spiral main channels.

[0015] Furthermore, a guide channel is provided below the counterbore along the direction of the flow channel groove; the cross-section of the guide channel is semi-circular.

[0016] Furthermore, the spiral main channel is filled with a porous thermally conductive sintered block.

[0017] The present invention also discloses a method for manufacturing the above-mentioned spiral multi-stage powder sintered heat exchanger for a dilution refrigerator, characterized by comprising the following steps:

[0018] Step S100: Machining the first housing and the second housing, machining planar spiral flow channel grooves on the surfaces of the first housing and the second housing;

[0019] Step S200: Process the heat-conducting baffle so that its shape matches the contour of the flow channel groove;

[0020] Step S300: The heat-conducting partition is clamped between the first housing and the second housing, aligned and then sealed and welded to form a heat exchange unit;

[0021] In step S400, multiple heat exchange units are coaxially stacked and connected in series, and the connecting pipes are installed to connect the spiral main channels corresponding to adjacent heat exchange units.

[0022] Furthermore, between step S200 and step S300, the following step is also included:

[0023] Step S250: In the corresponding area on the surface of the thermally conductive partition, a porous thermally conductive sintered block is formed by powder sintering.

[0024] Furthermore, in step S200, the surface of the heat-conducting partition is mirror-polished; in step S300, the sealing welding adopts a low heat input welding process, and the heat input is controlled through the welding process to avoid deformation of the heat-conducting partition and performance degradation of the porous heat-conducting sintered block.

[0025] In view of the above technical features, the present invention provides a spiral multi-stage powder sintering heat exchanger for a dilution refrigerator and its manufacturing method, which, compared with the prior art, has the following significant advantages:

[0026] 1. This invention adopts an Archimedes spiral continuous single spiral groove structure, which forces the concentrated and dilute working fluids to flow along the entire spiral channel, effectively solving the problem of direct flow of the working fluid and significantly extending the effective heat exchange path. At the same time, this structure can continuously extend the channel length within the same radial dimension by adjusting the number of spiral turns, and the radial space utilization rate is greatly improved compared with the traditional structure.

[0027] 2. The present invention, in conjunction with the high specific surface area porous medium formed by sintering nano-sized silver powder, significantly reduces the Carpicar thermal resistance in the millikelvin temperature range and significantly enhances the countercurrent heat transfer effect under extremely low temperature conditions.

[0028] 3. Based on the flow rate and viscosity characteristics of the concentrated and dilute working fluids, the present invention designs the volume of the dilute phase flow channel to be larger than that of the concentrated phase flow channel, thereby reducing local stagnation and viscous heat dissipation. At the same time, the flow resistance is effectively reduced through the design of the guide channel.

[0029] 4. In this invention, adjacent heat exchange units are coaxially connected by short straight pipes, avoiding the complex external piping layout of traditional multi-stage structures. At the same time, the double sealing design of continuous lug welding around the circumference and indium metal sealing rings at the pipe through holes reduces the risk of leakage and cross-contamination of helium-3 working fluid. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of a preferred embodiment of the spiral multi-stage powder sintering heat exchanger for a dilution refrigeration machine according to the present invention.

[0031] Figure 2 This is a partial cross-sectional view of a heat exchange unit in a preferred embodiment of the spiral multi-stage powder sintering heat exchanger for a dilution refrigeration machine according to the present invention.

[0032] Figure 3 This is a front view of the first shell in a preferred embodiment of the spiral multi-stage powder sintering heat exchanger for a dilution refrigerator according to the present invention.

[0033] Figure 4 This is a schematic diagram of the reverse side structure of the first shell in a preferred embodiment of the spiral multi-stage powder sintering heat exchanger for a dilution refrigerator of the present invention.

[0034] Figure 5 This is a front view of the second shell in a preferred embodiment of the spiral multi-stage powder sintering heat exchanger for a dilution refrigeration machine according to the present invention.

[0035] Figure 6 This is a schematic diagram of the reverse side structure of the second shell in a preferred embodiment of the spiral multi-stage powder sintering heat exchanger for a dilution refrigerator of the present invention.

[0036] Figure 7This is a schematic diagram of the structure of the heat-conducting baffle in the heat exchange unit of a preferred embodiment of the spiral multi-stage powder sintering heat exchanger for a dilution refrigeration machine of the present invention.

[0037] Figure 8 This is a schematic diagram of the working fluid flow in a preferred embodiment of the spiral multi-stage powder sintering heat exchanger for a dilution refrigerator according to the present invention;

[0038] Figure 9 This is a flowchart of a preferred embodiment of the manufacturing method of a spiral multi-stage powder sintering heat exchanger for a dilution refrigeration machine according to the present invention.

[0039] In the diagram: 10 - First heat exchange unit, 20 - Second heat exchange unit, 30 - Third heat exchange unit;

[0040] 11-First shell, 12-Second shell, 13-Heat-conducting baffle, 14-Dense phase inlet pipe, 15-Dilute phase outlet pipe, 16-Dense phase connecting pipe, 17-Dilute phase connecting pipe, 18-Dense phase outlet pipe, 19-Dilute phase inlet pipe;

[0041] 111-First ear plate, 112-First large countersunk hole, 113-First small countersunk hole, 114-First guide channel, 115-First sintered block;

[0042] 121 - Second ear plate, 122 - Second large countersunk hole, 123 - Second small countersunk hole, 124 - Second guide channel, 125 - Second sintered block. Detailed Implementation

[0043] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0044] Please see Figures 1 to 8 This invention discloses a spiral multi-stage powder sintering heat exchanger for a dilution refrigeration machine. As shown in the figure, in a preferred embodiment, it consists of multiple heat exchange units coaxially stacked and connected in series. In this embodiment, there is a total of three-stage series structure, including a first heat exchange unit 10, a second heat exchange unit 20, and a third heat exchange unit 30. In other embodiments, the number of heat exchange units is not limited to this, and can be set to two, four, or more stages according to actual refrigeration requirements.

[0045] The first heat exchange unit 10, the second heat exchange unit 20, and the third heat exchange unit 30 are arranged in a stacked manner along the same vertical axis from top to bottom (or from bottom to top). Adjacent heat exchange units are connected by connecting pipes. Specifically, the first heat exchange unit 10 and the second heat exchange unit 20, and the second heat exchange unit 20 and the third heat exchange unit 30, are respectively connected by a helium-3 concentrated phase connecting pipe 16 and a helium-3 dilute phase connecting pipe 17. The diameter of the dilute phase connecting pipe 17 is larger than the diameter of the concentrated phase connecting pipe 16 to accommodate the larger flow rate of the dilute phase working fluid. Similarly, the diameter of the helium-3 dilute phase outlet pipe 15 is larger than the diameter of the helium-3 concentrated phase inlet pipe 14.

[0046] The basic structure of each heat exchange unit is the same, the only difference being that the positions of the countersunk holes in the upper and lower shells are opposite. The following is a detailed description using the first heat exchange unit 10 as an example. The first heat exchange unit 10 includes a first shell 11, a second shell 12, and a heat-conducting partition 13 sandwiched between the two.

[0047] Both the first housing 11 and the second housing 12 are made of a low thermal conductivity, high strength material, with a base plate thickness of 1.5 to 3 mm. On the inner surface of the housing (i.e., the side opposite to the heat-conducting partition 13), a continuous single-spiral downward groove in a planar spiral shape is milled. In this embodiment, the spiral groove is preferably an Archimedean spiral with a pitch of 25 to 30 mm and 2 to 4 turns. The spiral groove has a rectangular cross-section with a side distance of 1.5 to 3 mm, a groove depth of 4 to 6 mm, a groove width of 8 to 10 mm, and a machining tolerance controlled within ±0.01 mm. The spiral grooves of the first housing 11 and the second housing 12 have opposite spiral directions (for example, if the first housing 11 is a clockwise spiral, then the second housing 12 is a counterclockwise spiral), with opposite openings and coaxially symmetrical arrangement. On the outer periphery of the spiral groove, a continuously extending first ear plate 111 and a second ear plate 121 are respectively provided. The ear plate has a width of 3 to 5 mm and a thickness of 0.5 to 1 mm.

[0048] Along the central helical line 6 mm from the end of the spiral groove of the first shell 11, a first large countersunk hole 112 and a first small countersunk hole 113 are sequentially arranged, with a distance of 5 mm between the two countersunk holes. The diameter of the first small countersunk hole 113 is 2 to 3 mm, and it is used to install a smaller diameter helium-3 concentrated phase inlet pipe 14. The diameter of the first large countersunk hole 112 is 3 to 4 mm, and it is used to install a larger diameter helium-3 dilute phase outlet pipe 15. Below the countersunk holes, along the direction of the spiral groove, a first guide channel 114 with a semi-circular cross-section is formed, and the diameter of the guide channel is 0.5 to 1 mm.

[0049] Along the central helical line 6 mm from the starting point of the helical groove of the second shell 12, a second large countersunk hole 122 and a second small countersunk hole 123 are sequentially arranged, with a distance of 5 mm between the two countersunk holes. The diameter of the second small countersunk hole 123 is 2 to 3 mm, and it is used to install a thinner helium-3 concentrated phase connection pipe 16. The diameter of the second large countersunk hole 122 is 3 to 4 mm, and it is used to install a thicker helium-3 dilute phase connection pipe 17. Below the countersunk holes, along the direction of the helical groove, a second guide channel 124 with a semi-circular cross-section is opened, and the diameter of the guide channel is 0.5 to 1 mm.

[0050] The thermally conductive baffle 13 is made of a thin sheet of high thermal conductivity oxygen-free copper, with a thickness of 0.2 to 0.4 mm. The shape of the thermally conductive baffle 13 perfectly matches the contour of the spiral grooves of the upper and lower shells, forming a continuous spiral sheet. The surface of the thermally conductive baffle 13 is mirror-polished, with a flatness controlled within ±0.01 mm and a surface roughness Ra≤0.4μm. Through-holes are provided at the locations where the pipes pass through the thermally conductive baffle 13, allowing the helium-3 concentrated phase connection pipe 16 and the helium-3 dilute phase connection pipe 17 to pass through in an isolated and sealed manner.

[0051] The spiral grooves of the first shell 11 and the upper surface of the thermally conductive baffle 13 enclose a closed first spiral main channel (for the flow of the concentrated helium-3 phase), and the spiral grooves of the second shell 12 and the lower surface of the thermally conductive baffle 13 enclose a closed second spiral main channel (for the flow of the dilute helium-3 phase). The two main channels are independent of each other and are arranged coaxially and counter-currently throughout. The volume of the second spiral main channel is larger than that of the first spiral main channel to accommodate the larger flow rate and lower viscosity of the dilute working fluid (helium-3 / helium-4 mixed solution), reducing local stagnation and viscous heat dissipation.

[0052] The shapes of the first sintered block 115 and the second sintered block 125 are consistent with the contours of the corresponding spiral grooves, respectively filling all areas within the first and second spiral main channels except for the space occupied by the pipes. The bottom surface of the first sintered block 115 and the top surface of the second sintered block 125 are in close contact with the corresponding surfaces of the heat-conducting partition 13. The sintered blocks are formed by sintering high-purity silver powder with a particle size of 50 to 150 nm, and the specific surface area of ​​the porous body after sintering is controlled at 2.5 to 4 m² / g. The porous structure formed by sintering silver powder can significantly increase the solid-liquid heat transfer contact area and effectively reduce the Carpicar thermal resistance in the millikelvin temperature range.

[0053] The first housing 11 and the second housing 12, with the cooperation of the first lug 111 and the second lug 121, clamp the heat-conducting partition 13 to form a whole. Specifically, the first lug 111 and the second lug 121 are fully fitted to the upper and lower surfaces of the heat-conducting partition 13, respectively, and are sealed and fixed by full-circumference welding to form a complete first heat exchange unit 10. The helium-3 concentrated phase connection pipe 16 passes through the heat-conducting partition 13 and the second housing 12 and communicates with the first spiral main flow channel. The helium-3 dilute phase outlet pipe 15 passes through the heat-conducting partition 13 and the first housing 11 and communicates with the second spiral main flow channel. An indium metal sealing ring is provided between the pipe and the through hole of the heat-conducting partition 13 to achieve fluid isolation between the first spiral main flow channel and the second spiral main flow channel.

[0054] The following describes the multi-stage series structure of multiple heat exchange units. The second heat exchange unit 20 has the opposite opening positions of the upper and lower shell countersunk holes to the first heat exchange unit 10 (i.e., the dense phase inlet and dilute phase outlet of the second heat exchange unit 20 are located below, so as to connect with the outlet of the first heat exchange unit 10). The third heat exchange unit 30 has the same structure as the first heat exchange unit 10. Multiple heat exchange units are arranged coaxially stacked, with the overlap of the spiral central axes of adjacent heat exchange units ≤0.02 mm, to ensure precise alignment of the flow channels at each stage. The first spiral main flow channels of adjacent heat exchange units are coaxially connected through a helium-3 dense phase connecting pipe 16, forming a dense phase flow channel. The second spiral main flow channels of adjacent heat exchange units are coaxially connected through a helium-3 dilute phase connecting pipe 17, forming a dilute phase flow channel. The two channels are independent of each other, forming a multi-stage series heat exchange structure with counter-current flow throughout.

[0055] Please see Figure 8 In operation, the concentrated helium-3 phase flows downwards, following the following path: it enters the first spiral main channel of the first heat exchange unit 10 from the helium-3 concentrated phase inlet pipe 14, flows inwards along the spiral path, exchanges heat with the first sintered block 115 and the thermally conductive partition 13, then enters the first spiral main channel of the second heat exchange unit 20 through the helium-3 concentrated phase connecting pipe 16, and so on, finally flowing out from the helium-3 concentrated phase outlet pipe 18 and entering the mixing chamber to participate in the dilution refrigeration cycle. The dilute helium-3 phase, on the other hand, flows upwards, following the following path: after exiting the mixing chamber, it enters the second spiral main channel of the third heat exchange unit 30 from the helium-3 dilute phase inlet pipe 19, flows inwards along the spiral path, exchanges heat with the second sintered block 125 and the thermally conductive partition 13, then enters the second spiral main channel of the second heat exchange unit 20 and the first heat exchange unit 10 sequentially through the helium-3 dilute phase connecting pipe 17, finally flowing out from the helium-3 dilute phase outlet pipe 15, completing the counter-current heat exchange cycle.

[0056] Through the aforementioned spiral multi-stage series structure, the dense and dilute working fluids achieve sufficient heat exchange over a long stroke and large area in each heat exchange unit, effectively reducing the temperature of the dense phase entering the mixing chamber and improving the overall refrigeration efficiency of the dilution refrigerator.

[0057] Please see Figure 9 The present invention also discloses a method for manufacturing the above-mentioned spiral multistage heat exchanger, a preferred embodiment of which includes the following steps:

[0058] Step S100: Shell machining.

[0059] First, the first and second housings are machined using a low thermal conductivity, high strength material. A continuous single-helix recessed groove in a planar spiral shape is milled onto one side surface of the housing. In this embodiment, the spiral groove is preferably an Archimedean spiral with a pitch of 25 to 30 mm and 2 to 4 turns. The spiral groove has a rectangular cross-section with a side distance of 1.5 to 3 mm, a groove depth of 4 to 6 mm, and a groove width of 8 to 10 mm, with machining tolerances controlled within ±0.01 mm. The spiral grooves of the first and second housings rotate in opposite directions, and the cross-sectional area of ​​the second spiral groove is larger than that of the first spiral groove.

[0060] Then, continuously extending ear plates are machined on the outer periphery of the spiral groove, with a width of 3 to 5 mm and a thickness of 0.5 to 1 mm.

[0061] Finally, on the other side surface of the shell, large and small countersunk holes are sequentially machined along the central helical line 5 to 12 mm from the end or beginning of the helical groove. The diameter of the large countersunk hole is 3 to 4 mm, and the diameter of the small countersunk hole is 2 to 3 mm. The coaxiality tolerance of the corresponding countersunk holes on the upper and lower shells is ≤0.01 mm. The small countersunk hole is used to install smaller diameter helium-3 dense phase pipes, and the large countersunk hole is used to install larger diameter helium-3 dilute phase pipes. Below the countersunk holes, semi-circular cross-section guide channels are machined along the direction of the helical groove, with a diameter of 0.5 to 1 mm for each channel.

[0062] Step S200: Process the heat-conducting partition.

[0063] The heat-conducting baffle is fabricated from high thermal conductivity oxygen-free copper sheets, with a thickness of 0.2 to 0.4 mm. The baffle shape is cut to perfectly match the spiral groove contour, ensuring a burr-free and deformation-free cut surface. Then, the baffle surface is mirror-polished, with flatness controlled within ±0.01 mm and surface roughness Ra≤0.4 μm. Finally, through holes are machined in the heat-conducting baffle at the locations where the pipes pass through.

[0064] Step S250: Powder is sintered to form a porous block.

[0065] A sintering slurry was prepared using high-purity silver powder with a particle size of 50 to 150 nm. The slurry was uniformly coated on the upper and lower surfaces of the heat-conducting partition in the area corresponding to the spiral channel, with the coating thickness consistent with the spiral groove depth (4 to 6 mm).

[0066] The coated thermally conductive separator is placed in a sintering mold and positioned, and then sintered under a protective atmosphere (such as argon or nitrogen). The sintering temperature is 500 to 600 °C, and the holding time is 2 to 4 h. After sintering, the specific surface area of ​​the porous body is controlled at 2.5 to 4 m² / g, and the dimensional tolerance is ±0.01 mm.

[0067] Step S300: Assemble the heat exchange unit.

[0068] The sintered heat-conducting partition is clamped between the first and second shells, ensuring complete alignment of the spiral groove with the sintered block contour and tight contact between the ear plate and the corresponding surface of the heat-conducting partition. A sealing weld is then performed around the circumference of the contact surface between the ear plate and the heat-conducting partition to form a complete heat exchange unit. The welding process employs low-heat-input welding techniques (such as laser welding or micro-beam plasma welding), strictly controlling the welding heat input to avoid deformation of the heat-conducting partition and performance degradation of the sintered block. Precise alignment of the countersunk holes, guide channels, and the inlet / outlet of the spiral main channel must be ensured during welding.

[0069] Step S400: Multi-stage series connection.

[0070] Multiple heat exchange units are arranged coaxially in layers according to the design number of stages, with the overlap of the spiral center axes of adjacent heat exchange units ≤0.02 mm.

[0071] The helium-3 concentrated phase outlet of the previous heat exchange unit and the helium-3 concentrated phase inlet of the next heat exchange unit are coaxially welded together via a helium-3 concentrated phase connecting pipe. The helium-3 dilute phase inlet of the previous heat exchange unit and the helium-3 dilute phase outlet of the next heat exchange unit are coaxially welded together via a helium-3 dilute phase connecting pipe.

[0072] An indium metal sealing ring is installed at the point where the pipe passes through the heat-conducting baffle to ensure complete isolation between the two flow channels, forming a multi-stage series flow channel with full counterflow.

[0073] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A spiral multi-stage powder sintering heat exchanger for a dilution refrigeration machine, characterized in that, It includes multiple heat exchange units; the heat exchange units are coaxially stacked and connected in series; each heat exchange unit has a planar spiral structure and has two independent spiral main channels arranged in countercurrent throughout; the two spiral main channels of adjacent heat exchange units are connected to each other through connecting pipes.

2. The spiral multi-stage powder sintering heat exchanger for a dilution refrigerator according to claim 1, characterized in that, The helix of the planar spiral structure is an equidistant spiral.

3. The spiral multi-stage powder sintering heat exchanger for a dilution refrigerator according to claim 1, characterized in that, The heat exchange unit includes a first shell, a second shell, and a heat-conducting partition; the heat-conducting partition is sandwiched between the first shell and the second shell; flow channels are respectively formed on the first shell and the second shell; the two flow channels rotate in opposite directions and have opposite openings, respectively forming two independent spiral main channels with the heat-conducting partition.

4. The spiral multi-stage powder sintering heat exchanger for a dilution refrigerator according to claim 3, characterized in that, On the outer periphery of the first housing and the second housing, a first ear plate and a second ear plate that extend continuously are respectively provided; the first ear plate and the second ear plate are fully fitted with the corresponding surfaces of the heat-conducting partition and are sealed and fixed by full-circumferential welding.

5. The spiral multi-stage powder sintering heat exchanger for a dilution refrigerator according to claim 3, characterized in that, Countersunk holes for installing connecting pipes are provided on the first housing and the second housing, respectively; a sealing ring is provided at the position where the connecting pipe passes through the heat-conducting partition to achieve fluid isolation between the two spiral main channels.

6. The spiral multi-stage powder sintering heat exchanger for a dilution refrigerator according to claim 5, characterized in that, Below the counterbore, a guide channel is provided along the direction of the flow channel groove; the cross-section of the guide channel is semi-circular.

7. The spiral multi-stage powder sintering heat exchanger for a dilution refrigerator according to claim 1, characterized in that, The spiral main channel is filled with a porous thermally conductive sintered block.

8. A method for manufacturing a spiral multi-stage powder sintered heat exchanger for a dilution refrigerator as described in claim 1, characterized in that, Includes the following steps: Step S100: Machining the first housing and the second housing, machining planar spiral flow channel grooves on the surfaces of the first housing and the second housing; Step S200: Process the heat-conducting baffle so that its shape matches the contour of the flow channel groove; Step S300: The heat-conducting partition is clamped between the first housing and the second housing, aligned and then sealed and welded to form a heat exchange unit; In step S400, multiple heat exchange units are coaxially stacked and connected in series, and the connecting pipes are installed to connect the spiral main channels corresponding to adjacent heat exchange units.

9. The method for manufacturing a spiral multi-stage powder sintered heat exchanger for a dilution refrigerator according to claim 8, characterized in that, Between step S200 and step S300, the following step is also included: Step S250: In the corresponding area on the surface of the thermally conductive partition, a porous thermally conductive sintered block is formed by powder sintering.

10. The method for manufacturing a spiral multi-stage powder sintered heat exchanger for a dilution refrigerator according to claim 8, characterized in that, In step S200, the surface of the heat-conducting partition is mirror-polished; in step S300, the sealing welding adopts a low heat input welding process, and the heat input is controlled by the welding process to avoid deformation of the heat-conducting partition and performance degradation of the porous heat-conducting sintered block.

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