Method for manufacturing a cold plate, cold plate and two-phase heat exchanger

Abstract

The application discloses a preparation method of a cold plate, the cold plate and a two-phase heat exchanger. The preparation method comprises the following steps: step 100, pretreating a copper bottom plate; step 200, filling copper powder, a copper powder mixture or a copper mesh assembly into a cavity of a graphite mold plate; step 300, assembling the copper bottom plate and the graphite mold plate to form a sintering mold in a closed mold state; step 400, sintering the sintering mold in sections to form a micro-porous structure connected to the copper bottom plate; and step 500, demolding and cleaning the micro-porous structure, so that the cold plate composed of the micro-porous structure and the copper bottom plate is obtained. The cold plate is prepared by the above preparation method. The two-phase heat exchanger comprises the cold plate and has a heat exchange cavity. The micro-porous structure is located in the heat exchange cavity. The application provides sufficient activation core sites for the boiling of a working medium, so that the heat exchange coefficient is effectively improved, and the local dryout phenomenon is relieved.

Description

Technical Field

[0001] This invention relates to the field of heat dissipation, and in particular to a method for preparing a cold plate, the cold plate itself, and a two-phase heat exchanger. Background Technology

[0002] With the rapid development of information technology and artificial intelligence, the thermal design power (TDP) of data center server chips is continuously breaking through traditional limits and climbing ever higher. This trend has made air-cooled heat sinks, which previously relied mainly on air as a medium, ineffective in handling the huge heat load generated by the chips, forcing the industry to turn its attention to more efficient solutions. Against this backdrop, liquid cooling technology, with its superior heat transfer performance and medium heat capacity advantages, has quickly become the preferred heat dissipation solution for most high-density computing companies. However, traditional single-phase liquid cooling solutions also face inherent bottlenecks. Their heat dissipation limit is roughly below 800W, mainly limited by pipe flow rate, system pumping power, and the resulting system pressure. To break through this heat dissipation ceiling, two-phase boiling heat transfer technology, which has higher energy efficiency and heat dissipation density, has come into focus.

[0003] Boiling heat transfer, by utilizing the characteristic of the working fluid absorbing a large amount of heat during phase change, can achieve efficient and compact heat exchange. This makes it an effective means to address current high heat flux density heat dissipation requirements. In specific implementations, flow boiling heat transfer is achieved in a microchannel structure, and its heat transfer coefficient is much higher than that of single-phase heat transfer.

[0004] However, existing microchannels still face key challenges in practical applications: due to the limited number of surface activation sites, they exhibit low heat transfer coefficients and are prone to localized drying in areas of concentrated heat load. These challenges make it difficult to meet the ever-increasing heat dissipation demands of chips by relying solely on traditional microchannel structures. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a method for preparing a cold plate, a cold plate and a two-phase heat exchanger, which has the advantage of providing sufficient activation core sites for the boiling of the working fluid.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a cold plate includes the following steps:

[0008] Step 100: Pre-treatment of the copper base plate;

[0009] Step 200: Fill the cavity of the graphite template with copper powder, copper powder mixture or copper mesh assembly;

[0010] Step 300: Assemble the copper base plate and the graphite template to form a sintering mold in a closed state;

[0011] Step 400: The sintering mold is sintered in sections to form a microporous structure connected to the copper base plate;

[0012] Step 500: Demold and clean the microporous structure, which together with the copper base plate constitute a cold plate.

[0013] By adopting the above technical solution, a microporous structure with a specific porosity can be directly formed on the copper base plate. This microporous structure is tightly bonded to the copper base plate, effectively improving the heat exchange performance of the cold plate. Specifically, the pretreatment in step 100 ensures the cleanliness and activity of the copper substrate surface, providing a good foundation for the subsequent bonding of the microporous structure. In step 200, copper powder, copper powder mixtures, or copper mesh components are selected for filling according to different microporous structure designs, making the morphology and performance of the microporous structure adjustable. The segmented sintering process in step 400, by precisely controlling the heating rate, sintering temperature, and holding time, and using inert gas as a protective gas, can prevent copper oxidation at high temperatures, while ensuring the sintering quality of the microporous structure and the precise control of porosity within the range of 30%-50%. This porosity range of the microporous structure can significantly increase the heat transfer area, providing sufficient activation core sites for the boiling of the working fluid, thereby effectively improving the heat transfer coefficient and alleviating the local drying phenomenon. Finally, after demolding and cleaning in step 500, the microporous structure and the copper substrate together constitute a cold plate, giving the cold plate excellent overall heat dissipation performance, which can meet the heat dissipation requirements of high heat flux density chips.

[0014] Optionally, the copper base plate is formed into several parallel fins by CNC machining; microchannels are formed between adjacent fins; the microporous structure includes several first porous layers; the first porous layers correspond one-to-one with the microchannels and the first porous layers cover the side walls and bottom walls of the corresponding microchannels; the porosity of the first porous layers is 30%; in step 200, 100-micron dendritic electrolytic copper powder is used to fill the cavity.

[0015] By employing the above technical solution, parallel fins and microchannels between adjacent fins are fabricated on a copper base plate. A first porous layer with a porosity of 30% is then covered on the side and bottom walls of these microchannels, forming a composite structure. In this structure, the microchannels provide pathways for the flow of the working fluid, while the first porous layer covering its inner walls utilizes its 30% porosity to provide abundant activation nuclei for fluid boiling while ensuring structural strength. The cavity is filled with 100-micron dendritic electrolytic copper powder. Due to the large specific surface area and good packing characteristics of the dendritic copper powder, it forms a uniformly distributed and well-connected pore structure after sintering. This results in a tighter bond between the first porous layer and the fins and walls of the microchannels on the copper base plate, effectively reducing contact thermal resistance and improving the efficiency of heat transfer from the copper base plate to the microporous structure, thereby enhancing the overall heat exchange effect of the cold plate.

[0016] Optionally, the microporous structure includes a plurality of parallel porous fins with a porosity of 40%; in step 200, a copper powder mixture of uniformly mixed 100-micron dendritic electrolytic copper powder and 30% by volume pore-forming agent is used to fill the cavity.

[0017] By adopting the above technical solution, a microporous structure composed of several parallel porous fins was designed. The 40% porosity allows the porous fins to possess both structural support and abundant internal pores. This porous structure not only increases the contact area with the working fluid but also forms complex flow channels within the fins, promoting the flow and phase change of the working fluid. In step 200, a mixture of 100-micron dendritic electrolytic copper powder and 30% volume fraction pore-forming agent is used to fill the cavity. The high specific surface area of ​​the dendritic copper powder facilitates sintering bonding between particles, while the pore-forming agent decomposes during sintering, leaving additional pores in the copper powder skeleton, precisely controlling the porosity of the porous fins to 40%. This porous fin structure significantly improves the heat dissipation area and boiling heat transfer efficiency of the cold plate. The parallel arrangement also facilitates the uniform distribution of the working fluid within the cold plate, avoiding localized heat accumulation and further optimizing the heat dissipation performance of the cold plate.

[0018] Optionally, the microporous structure is a second porous layer covering the copper substrate; the porosity of the second porous layer is 50%; in step 200, a copper powder mixture or a copper mesh assembly is used to fill the cavity.

[0019] By adopting the above technical solution, a microporous structure is designed as a second porous layer covering the copper base plate. Its high porosity of 50% creates a large number of interconnected pore networks within, significantly increasing the heat transfer surface area and providing abundant activation nuclei for the boiling of the working fluid, thus significantly improving the boiling heat transfer coefficient. In step 200, a copper powder mixture or copper mesh assembly is used to fill the cavity, providing a flexible option for the preparation of the second porous layer. This second porous layer structure, combined with the copper base plate, enables the cold plate to possess excellent temperature uniformity and heat transfer capacity, making it particularly suitable for heat dissipation needs in areas with high heat flux density.

[0020] Optionally, step 200 uses a copper powder mixture of uniformly mixed 100-micron dendritic electrolytic copper powder and 50% by volume of a pore-forming agent.

[0021] By employing the aforementioned technical solution, using a uniform mixture of 100-micron dendritic electrolytic copper powder and a 50% volume fraction pore-forming agent as the filling material, a high porosity design of 50% for the second porous layer can be precisely achieved. During sintering, the 50% volume fraction pore-forming agent, through volatilization or decomposition, forms numerous regular and interconnected pores between the copper powder particles. Combined with the inherent branched structure and stacking characteristics of the dendritic electrolytic copper powder itself, this results in a uniform pore distribution, suitable pore size, and good connectivity within the final second porous layer. This high porosity structure not only significantly increases the contact area between the working fluid and the porous layer, but more importantly, it provides ample space and channels for the penetration of the working fluid, the formation of vaporization nuclei, and the escape of steam, thereby further enhancing the boiling heat transfer effect and effectively improving the heat dissipation capacity of the cold plate under high heat flux density conditions.

[0022] Optionally, the copper mesh assembly uses several layers of stacked copper mesh, the pore size of the copper mesh increasing sequentially along the direction away from the copper base plate, or the pore size of the copper mesh closest to the copper base plate is smaller than the pore size of the other copper meshes and the pore size of the other copper meshes is the same.

[0023] By adopting the above technical solution, the copper mesh assembly uses several layers of stacked copper mesh, and the pore size of each layer of copper mesh is differentiated to form a gradient pore structure. As the pore size of the copper mesh increases sequentially away from the copper base plate, this gradually loosening structure from bottom to top can guide the working fluid to form an orderly flow and phase change process within the porous layer. The finer pore layer near the copper base plate can quickly absorb heat and promote bubble nucleation, while the gradually increasing pore size provides a smoother channel for the rise and escape of steam, effectively reducing steam blockage and improving the circulation efficiency of the working fluid. In another design, the pore size of the copper mesh closest to the copper base plate is smaller than that of the other copper meshes, and the pore size of the other copper meshes is the same. This structure allows the fine copper mesh at the bottom to efficiently absorb heat from the copper base plate and generate initial bubbles, while the upper copper mesh layer with larger and more uniform pores serves as the main flow area for steam, ensuring both high efficiency in heat transfer and providing a stable channel for steam collection and discharge. This gradient or layered pore design can fully utilize the excellent thermal conductivity and structural stability of the copper mesh material itself. At the same time, through the orderly control of the pores, the heat exchange performance and working fluid flow characteristics of the microporous structure are further optimized, thereby improving the overall heat dissipation effect of the cold plate.

[0024] Optionally, the segmented sintering in step 400 adopts a two-stage heating method, using an inert gas as a protective gas, heating to 800°C at a rate of 5-8°C / min, holding for 30 min, and then continuing to heat to 965°C at a rate of 5-8°C / min, holding for 90 min.

[0025] By adopting the above technical solution, the segmented sintering employs a two-stage heating process with an inert gas as a protective gas, enabling precise control of the sintering process of the microporous structure and ensuring its stable performance. Specifically, the temperature is increased to 800℃ at a rate of 5-8℃ / min and held for 30min. This stage is mainly to gradually remove volatile impurities and pore-forming agents (if used) from the copper powder or copper powder mixture, avoiding the destruction of the integrity of the porous structure due to the rapid volatilization of impurities caused by excessively rapid heating. At the same time, the holding at a lower temperature helps to initially form neck connections between copper powder particles, laying the foundation for densification at higher temperatures. Subsequently, the temperature is increased to 965℃ (close to the melting point of copper, which can effectively promote the diffusion of copper atoms) at a rate of 5-8℃ / min and held for 90min. This stage is crucial for achieving sufficient diffusion welding between copper powder particles and improving the density and mechanical strength of the microporous structure. Through prolonged high-temperature insulation, the contact area between copper powder particles increases, forming a strong metallurgical bond. This ensures sufficient bonding strength and overall stability between the microporous structure and the copper substrate, as well as the structure itself. The protection with an inert gas (such as nitrogen) effectively prevents copper oxidation at high temperatures, avoiding adverse effects of oxidation products on the porosity, thermal conductivity, and bonding strength of the microporous structure. This ensures that the final microporous structure possesses the designed porosity, good thermal conductivity, and structural integrity.

[0026] Optionally, the copper powder filling in step 200 can be carried out in multiple stages, and vibration compaction is required after each filling of copper powder.

[0027] By employing the above-mentioned technical solution, multiple filling operations are performed during the copper powder filling process, coupled with vibration compaction after each filling, which effectively improves the bulk density and uniformity of the copper powder. If a large amount of copper powder is filled at once, gravity can cause the lower part of the copper powder to accumulate densely while the upper part becomes loose, resulting in uneven porosity distribution in the microporous structure after sintering and affecting the stability of heat transfer performance. However, by filling in multiple stages, with an appropriate amount of copper powder added each time, vibration is used to rearrange the copper powder particles, filling the gaps between them, reducing voids and loose areas between particles, and ensuring that the copper powder can be uniformly and densely packed within the cavity. This operation provides a uniform green body foundation for the subsequent segmented sintering process, helping to form a uniformly distributed and well-connected pore network throughout the microporous structure. This ensures that the porosity of the microporous structure can be precisely controlled within the target range, improving the consistency and reliability of the cold-rolled plate products.

[0028] On the other hand, a cold plate is made by the above-mentioned preparation method.

[0029] By adopting the above technical solution, the cold plate possesses a core heat dissipation unit composed of a copper base plate and a microporous structure. The microporous structure is directly formed on the copper base plate using the aforementioned preparation method, and its porosity can be precisely controlled between 30% and 50% according to actual heat dissipation requirements. This structural design allows the cold plate to significantly enhance the boiling heat transfer effect of the working fluid during application, thanks to the abundant activation core sites within the microporous structure. Whether it's the first porous layer covering the walls of the microchannels, the parallel porous fins, or the second porous layer directly covering the copper base plate, all effectively increase the heat transfer area, promote the generation, growth, and detachment of bubbles, thereby significantly improving the heat transfer coefficient. Simultaneously, the reasonable porosity design balances structural strength and working fluid flow characteristics, effectively alleviating localized drying phenomena and ensuring that the cold plate maintains efficient, stable, and uniform heat dissipation performance even under high heat flux density conditions. This makes it particularly suitable for scenarios with stringent heat dissipation requirements, such as data center server chips, providing a practical technical approach to overcome the bottlenecks of traditional heat dissipation solutions.

[0030] On the other hand, the two-phase heat exchanger includes the aforementioned cold plate and has a heat exchange cavity; the inlet end and outlet end of the heat exchange cavity are respectively provided with liquid collection cavities; the microporous structure is located inside the heat exchange cavity and between the two liquid collection cavities.

[0031] By adopting the above technical solution, the cold plate is used as the core component of the two-phase heat exchanger, placing the microporous structure directly in the core region where the working fluid undergoes phase change. This fully leverages the advantages of the microporous structure in enhancing boiling heat transfer. When the working fluid enters the heat exchange chamber and comes into contact with the microporous structure of the cold plate, the numerous vaporization nuclei provided by the microporous structure rapidly induce boiling. During the phase change, the working fluid absorbs a large amount of latent heat to generate bubbles. These bubbles then grow rapidly within the pore network and detach from the wall, efficiently carrying away heat. The coordinated design of the cold plate and the heat exchange chamber ensures orderly flow of the working fluid within the chamber and sufficient contact with the microporous structure. Simultaneously, the liquid collection chamber before entering the channel significantly reduces the fluid dynamic pressure, making the inlet static pressure of each parallel microchannel nearly uniform. The abrupt expansion at the outlet provides a low-resistance escape path for steam, thereby suppressing reverse flow. Furthermore, the integrated structure of the cold plate reduces the contact thermal resistance inside the heat exchanger, improving overall heat transfer efficiency. This two-phase heat exchanger, which includes a cold plate with a specific microporous structure, can significantly improve its heat exchange capacity and operational stability under high heat flux density conditions. It can be widely used in electronic equipment, energy systems and other fields that require efficient heat dissipation, providing strong technical support for solving the heat dissipation problem of high-power devices. Attached Figure Description

[0032] Figure 1 This is an exploded structural diagram of the two-phase heat exchanger of the present invention.

[0033] Figure 2This is a cross-sectional structural diagram of the two-phase heat exchanger of the present invention.

[0034] Figure 3 This is a schematic diagram of the microporous structure of the present invention.

[0035] Figure 4 This is a schematic diagram of the microporous structure of the present invention.

[0036] Figure 5 This is a schematic diagram of the microporous structure of the present invention.

[0037] Figure 6 This is an exploded structural diagram of the copper base plate, graphite template, and clamping assembly of the present invention.

[0038] Figure 7 This is a schematic diagram of the segmented sintering curve of the present invention.

[0039] Figure 8 This is an electron microscope image of the porous fins of the present invention.

[0040] Figure 9 This is an electron microscope image of the second porous layer of the present invention.

[0041] Figure 10 This is a schematic diagram of the structure of the copper partition in another embodiment of the present invention.

[0042] Figure 11 This is a cross-sectional structural diagram of the copper partition in another embodiment of the present invention.

[0043] Figure 12 This is a top view of the copper partition in another embodiment of the present invention.

[0044] Figure 13 This is a cross-sectional structural diagram of the copper partition in another embodiment of the present invention.

[0045] Explanation of reference numerals in the attached figures:

[0046] 10. Copper base plate; 11. Fins;

[0047] 20. Microporous structure; 21. First porous layer; 22. Porous fins; 23. Second porous layer;

[0048] 30. First sealing ring;

[0049] 40. Copper partition; 400. Heat exchange chamber; 401. Liquid collection chamber; 402. Cavity hole; 403. Flow guide channel; 411. First end; 412. Second end;

[0050] 50. Second sealing ring;

[0051] 60. Quartz glass;

[0052] 70. Third sealing ring;

[0053] 80. Cover plate; 800. Glass mounting slot; 801. Observation window;

[0054] 90. Graphite template; 91. Mold closing bolt; 92. Mold closing nut. Detailed Implementation

[0055] The following is in conjunction with the appendix Figures 1-13 The present invention will be described in further detail below.

[0056] Example 1: A two-phase heat exchanger is disclosed, with reference to... Figure 1 and Figure 2 The system includes a cold plate, a first sealing ring 30, a copper partition 40, a second sealing ring 50, and a cover plate 80. The cold plate includes a copper base plate 10 and a microporous structure 20 disposed on the copper base plate 10. The cold plate is made of T2 copper. The microporous structure 20 is formed on the copper base plate 10 by sintering. The copper base plate 10, the copper partition 40, and the cover plate 80 are connected as a whole by several bolts. The first sealing ring 30 is located between the copper base plate 10 and the copper partition 40. The second sealing ring 50 is located between the copper partition 40 and the cover plate 80. At this time, a vertically penetrating rectangular cavity 402 is opened in the middle of the copper partition 40 to form the heat exchange cavity 400 of the two-phase heat exchanger. The inlet and outlet ends of the heat exchange cavity 400 are respectively provided with liquid collection cavities 401. The microporous structure 20 is located inside the heat exchange chamber 400 and between the two liquid collection chambers 401; the cover plate 80 has an inlet and an outlet formed on it; the inlet and outlet are respectively connected to the two ends of the heat exchange chamber 400; in order to facilitate observation of the internal condition of the two-phase heat exchanger, the upper part of the middle of the cover plate 80 has an observation window 801 formed on it, and the lower part has a glass placement groove 800 formed on it; the glass placement groove 800 and the observation window 801 are connected, and the size of the glass placement groove 800 is larger than the size of the observation window 801; a quartz glass 60 is placed inside the glass placement groove 800; a third sealing ring 70 is provided between the quartz glass 60 and the top wall of the glass placement groove 800; the bottom of the quartz glass 60 abuts against the top surface of the copper partition 40 and presses against the second sealing ring 50.

[0057] The microporous structure 20 has various forms, resulting in a variety of cold plates with different structures, which will be explained in detail below:

[0058] The first structure of the microporous structure 20, referenced Figure 3One end face of the copper base plate 10 is formed with several parallel fins 11 by CNC machining. Microchannels are formed between adjacent fins 11. The width of the microchannels is 1 mm, the width of the fins 11 is 0.4 mm, and the height of the fins 11 is 2.4 mm. The microporous structure 20 includes several first porous layers 21. The first porous layers 21 correspond one-to-one with the microchannels and cover the side walls and bottom walls of the corresponding microchannels. The thickness of the first porous layers 21 is 0.3 mm. 100-micron dendritic electrolytic copper powder is used without the addition of pore-forming agents, and the target porosity is 30%. This structure selectively sintersperses a 0.3mm porous layer of copper powder on both sides and the bottom wall of fin 11, while retaining a dense copper surface at the top. This design is based on an optimized integration of boiling heat transfer and bubble dynamics: the porous region provides high-density nucleation sites and enhances capillary replenishment, significantly reducing ONB (Onset of Nucleate Boiling) and increasing the heat transfer coefficient through thin liquid film evaporation. Simultaneously, its fine bubble generation characteristics prevent gas clogging. The dense, smooth surface at the top serves as a low-resistance vapor escape path, guiding bubbles to coalesce and float upwards into the open gaps above, forming a type I laminar flow of "liquid in the channel, vapor in the gap," effectively suppressing flow reversal and pressure oscillations. This design achieves a synergistic effect of enhanced nucleate boiling and rapid vapor removal. While utilizing the high CHF (Critical Heat Flux) advantage of the porous structure, it reduces the two-phase frictional pressure drop, ultimately achieving a balance between enhanced heat transfer, flow stability, and lower pump power consumption.

[0059] Furthermore, the gap between the first porous layer 21 covering the sidewalls of adjacent fins 11 is set as a channel gap with a width of 0.4 mm. At a certain mass flow rate, if the channel gap is too small, the steam discharge resistance increases, making it impossible to suppress the reverse flow in the channel; if the channel gap is too large, it not only weakens the capillary constraint of the sidewall on the liquid, resulting in a lack of liquid adhesion on the upper wall of the fin, but also causes rewetting delay due to an excessively long recirculation path. The design of a channel gap width of 0.4 mm ensures sufficient capillary pressure gradient to drive efficient liquid recirculation and maintains the stability of the liquid film under high heat flux density.

[0060] The second structure of microporous structure 20, see reference. Figure 4 The microporous structure 20 includes several parallel porous fins 22, with microchannels formed between adjacent porous fins 22. The width of the microchannels is 1 mm, the width of the porous fins 22 is 0.4 mm, and the height of the porous fins 22 is 2.4 mm. It uses a mixture of 100-micron dendritic electrolytic copper powder and 30% by volume sodium carbonate pore-forming agent, with a target porosity of 40%. For details on the surface structure of the porous fins 22, please refer to [reference needed]. Figure 8 .

[0061] The third structure of microporous structure 20, see reference. Figure 5 The microporous structure 20 is a second porous layer 23 covering the copper substrate, and the thickness of the second porous layer 23 is 0.3 mm. The second porous layer 23 can be a mixture of 100-micron dendritic electrolytic copper powder and 50% by volume sodium carbonate pore-forming agent, or it can be a three-layer copper mesh. The specific surface structure of the second porous layer 23 is described in [reference needed]. Figure 9 .

[0062] When the second porous layer 23 can be made of a mixture of 100-micron dendritic electrolytic copper powder and 50% by volume sodium carbonate pore-forming agent, the target porosity is 50%. When three layers of copper mesh are stacked, the bottom layer (near the copper base plate 10) is a 200-mesh copper mesh (81μm pore size), and the middle and upper two layers are 100-mesh copper meshes (200μm pore size), forming a dual characteristic pore size. This design implements the core principle of "strong liquid pumping at the bottom and smooth steam exhaust at the top." The small pores at the bottom provide strong capillary force, ensuring efficient liquid delivery to the heating wall surface that needs cooling the most. The uniform large pores in the middle and upper layers provide a low-resistance escape channel for steam. This has solved the most critical contradiction in boiling heat dissipation, so its CHF and overall heat dissipation efficiency can reach a very high level. At the same time, the manufacturing process is simple and the cost is low.

[0063] In other embodiments, the pore sizes of the three copper mesh layers are different, with the pore size increasing sequentially along the direction away from the copper base plate 10. For example, the pore sizes of the three copper mesh layers along the direction away from the copper base plate 10 are 81 μm, 200 μm, and 350 μm, respectively. The innermost copper mesh layer (closely attached to the copper base plate 10, with the smallest pore size) provides the strongest capillary suction force, acting like a pump to continuously and stably transport the liquid working fluid from the edge of the cold plate or the liquid storage area to the hottest and most easily dried-out heating wall surface. The middle copper mesh layer (with moderate pore size) serves as the main boiling generation zone, providing numerous nucleation points to promote bubble generation and providing a transmission channel for the gas-liquid two-phase flow, achieving a dynamic balance between liquid replenishment and steam rise. The outermost copper mesh layer (with the largest pore size) provides a low-flow-resistance main channel for the large amount of steam generated, allowing it to be quickly carried away from the heating area, preventing steam accumulation and the formation of an insulating film, which would hinder liquid recirculation and cause overheating. Compared to the dual-pore design, this gradient design provides a more natural and less resistant liquid transport path, which is especially beneficial for the uniform distribution of liquid under large-size cold plates. In addition, it provides a "gradually expanding" flow channel for steam, which can more effectively prevent steam accumulation, especially when approaching the CHF limit, it is more stable. The overall heat transfer performance is slightly better, the temperature uniformity is better, and the reliability of the system is improved.

[0064] The above three structures use a certain volume fraction of sodium carbonate pore-forming agent, but it can be adjusted according to the porosity of the microporous structure 20 (porosity is 30%-50%). Specifically, 20%-50% volume fraction of sodium carbonate pore-forming agent is added to copper powder. The diameter distribution range of sodium carbonate powder particles is 40-50 micrometers. The sodium carbonate powder and copper powder are thoroughly mixed beforehand and stirred to achieve uniform dispersion.

[0065] Example 2: A method for preparing a cold plate is disclosed, comprising the following steps:

[0066] Step 100: Perform pretreatment on the copper base plate 10;

[0067] Step 200: Fill the cavity of the graphite template 90 with copper powder, copper powder mixture or copper mesh assembly;

[0068] Step 300: Assemble the copper base plate 10 and the graphite template 90 to form a sintering mold in the closed state; the graphite template 90 is made of graphite because graphite has mild properties, high temperature resistance, dimensional stability, good thermal shock resistance, and does not stick to the cold plate.

[0069] Step 400: The sintering mold is sintered in sections to form a microporous structure 20 connected to the copper base plate 10. The porosity of the microporous structure 20 is 30%-50%.

[0070] Step 500: Demold and clean the microporous structure 20 to obtain a cold plate composed of the microporous structure 20 and the copper base plate 10.

[0071] Specifically, step 100 involves: using 1500-grit and 2000-grit sandpaper to successively polish the surface of the copper base plate 10 near the heat exchange chamber 400 to remove the surface oxide layer, grease, and impurities; immersing the polished copper base plate 10 in a 75% ethanol solution for ultrasonic cleaning for 5 minutes to remove residual debris and oil; and drying the cleaned copper base plate 10 in a 60℃ oven for 30 minutes to obtain a clean copper base plate 10. If the copper base plate 10 requires CNC machining, the CNC machining is performed before step 100.

[0072] Step 200 specifically involves the following: The cavities of the graphite templates for different microporous structures 20 vary. Next, the graphite template is inverted so that the openings of the cavities face upwards, and then the cavities are filled with the appropriate materials. Different materials require different filling methods, which will be explained in detail below:

[0073] (1) The filling material is 100-micron dendritic electrolytic copper powder. Without the addition of a pore-forming agent, it is filled into the cavity in 3 times. After each filling, it is placed on a vibration table and vibrated for 4 minutes. Finally, the copper powder surface is scraped flat with a scraper to ensure that the copper powder is densely filled and evenly distributed.

[0074] (2) When the filling material is a mixture of 100-micron dendritic electrolytic copper powder and 30% volume fraction sodium carbonate pore-forming agent, the copper powder and pore-forming agent are stirred for 15 minutes in advance to ensure uniform dispersion. The filling is done in 4 batches. After each filling, the filling is placed on a vibration table and vibrated for 5 minutes. Finally, the surface of the copper powder is scraped flat with a scraper to ensure that the copper powder is densely filled and evenly distributed.

[0075] (3) When the filling material is a mixture of 100-micron dendritic electrolytic copper powder and 50% volume fraction sodium carbonate pore-forming agent, the copper powder and pore-forming agent are mixed evenly and then filled into the cavity in 5 batches. After each filling, the cavity is placed on a vibration table and vibrated for 5 minutes. Finally, the surface of the copper powder is scraped flat with a scraper to ensure that the copper powder is filled densely and evenly.

[0076] (4) When filling the copper mesh assembly consisting of multiple layers of copper mesh, the copper mesh needs to be cut with a laser first, ultrasonically cleaned with 75% ethanol for 5 minutes, dried and set aside, and then the multiple layers of copper mesh are embedded into the cavity in sequence.

[0077] Step 300 specifically refers to: Figure 6 A copper base plate 10 is placed on an inverted graphite template 90 to cover the cavity opening of the graphite template 90. Then, several clamping bolts 91 and several clamping nuts 92 are used to ensure the copper base plate 10 is tightly pressed against the graphite template 90, thus forming a sintering mold in the closed state. At this point, the clamping bolts 91 and clamping nuts 92 serve as clamping components. To improve mold closing accuracy, several guide posts can be set on the copper base plate 10, and guide holes that mate with the guide posts are machined on the graphite template 90. The cooperation between the guide posts and guide holes improves mold closing accuracy. Additionally, the guide posts on the copper base plate 10 can also achieve assembly positioning of the two-phase heat exchanger. For ease of operation, wing nuts are used for the clamping nuts.

[0078] Step 400 specifically involves placing the sintering mold in its closed state into a sintering furnace. The sintering furnace is a tubular furnace with a two-stage heating process. The furnace is filled with inert gas for protection. During sintering, the temperature is increased to 800℃ at a rate of 5-8℃ / min and held for 30 minutes. Then, the temperature is increased to 965℃ at a rate of 5-8℃ / min and held for 90 minutes to promote the melting between copper powder particles or between copper meshes and the solid-state metallurgical bonding between the copper powder or copper mesh and the copper base plate. Nitrogen can be used as the inert gas. The nitrogen is evenly distributed through an annular gas distribution pipe to prevent the copper powder from oxidizing. Three sets of temperature measuring points (left, middle, and right) are set in the sintering furnace to monitor the temperature distribution in real time and ensure that the temperature difference in the sintering furnace is ≤±5℃.

[0079] Step 500 is as follows: After sintering, the heating device is turned off, and the sintering furnace is allowed to cool naturally to room temperature. First, the clamping components are loosened, and the graphite template 90 is guided to move slightly in the vertical direction through the guide column. Then, the copper base plate 10 is slowly shaken to use the low adhesion characteristics of graphite and copper to separate the graphite template 90 from the microporous structure 20. Since graphite is relatively brittle, an elastic buffer sleeve is fitted over the guide column to absorb the demolding impact force in order to prevent the graphite template 90 from breaking. Next, the graphite debris and unsintered copper powder remaining on the surface of the sintered microporous structure 20 are removed by blowing with compressed air and wiping with ethanol to ensure that there are no impurities on the surface of the microporous structure 20. The finished cold plate is thus obtained.

[0080] If a two-phase heat exchanger needs to be assembled later, the sealing surfaces of the copper partition 40, quartz glass 60, and cover plate 80 must first be polished and cleaned to ensure that the surfaces are flat and free of burrs. Then, the first sealing ring 30 is installed on the copper base plate 10 in sequence, the second sealing ring 50 is installed after the copper partition 40 is attached, the quartz glass 60 is placed and the third sealing ring 70 is installed, and the cover plate 80 is covered. Finally, bolts are passed through the cover plate 80, copper partition 40 and copper base plate 10 to ensure that the pressure on each sealing surface is consistent and there is no leakage of working fluid.

[0081] In other embodiments, reference is made to Figures 10-13 A plurality of guide columns 41 are formed on the side wall of the inlet end of the heat exchange cavity 400, located in cavity 402. The direction of the guide columns 41 is the same as the flow direction of the working fluid in the heat exchange cavity 400. A guide channel 403 is formed between adjacent guide columns 41. The outlet of the guide channel 403 along the direction of the guide columns 41 is directly opposite the front end of the microporous structure 20. The end of the guide column 41 connected to the side wall of cavity 402 is the first end 411, and the other end is the second end 412. The cross-sections of the first end 411 and the second end 412 are both isosceles triangles. The bases of the two isosceles triangles are on the same horizontal plane, the planes of symmetry are coplanar, and the heights are equal. The base length of the cross-section of the first end 411 is greater than the base length of the cross-section of the second end 412. Thus, the guide channel 403 flows from top to bottom. The flow channel gradually narrows and gradually widens along the flow direction of the working fluid in the heat exchange cavity 400. As the working fluid flows from the top (large cross-section) to the bottom (small cross-section) of the heat exchange cavity, the cross-sectional area of ​​the flow channel gradually decreases. This contraction effect generates a pressure gradient perpendicular to the mainstream direction, forcing the working fluid to replenish the bottom region of the microporous structure 20. Meanwhile, the flow guide channel 403 gradually widens along the flow direction of the working fluid in the heat exchange cavity 400, increasing the contact range between the working fluid and the front end of the microporous structure 20. In addition, the presence of the flow guide column 41 reduces the space of the liquid collection chamber 401 at the inlet end of the heat exchange cavity 400, making the space of the liquid collection chamber 401 at the inlet end of the heat exchange cavity 400 smaller than that at the outlet end of the heat exchange cavity 400, thus further suppressing the reverse flow phenomenon.

[0082] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a cold plate, characterized in that: Includes the following steps: Step 100: Perform pretreatment on the copper base plate (10); Step 200: Fill the cavity of the graphite template (90) with copper powder, copper powder mixture or copper mesh assembly; Step 300: Assemble the copper base plate (10) and the graphite template (90) to form a sintering mold in a closed state; Step 400: The sintering mold is sintered in sections to form a microporous structure (20) connected to the copper base plate (10). Step 500: Demold and clean the microporous structure (20) to obtain a cold plate composed of the microporous structure (20) and the copper base plate (10).

2. The method for preparing a cold plate according to claim 1, characterized in that: The copper base plate (10) is formed into several parallel fins (11) by CNC machining; a micro channel is formed between adjacent fins (11); the micro porous structure (20) includes several first porous layers (21); the first porous layer (21) corresponds one-to-one with the micro channel and the first porous layer (21) covers the side walls and bottom wall of the corresponding micro channel; the porosity of the first porous layer (21) is 30%; in step 200, 100-micron dendritic electrolytic copper powder is used to fill the cavity.

3. The method for preparing a cold plate according to claim 1, characterized in that: The microporous structure (20) includes several parallel porous fins (22), the porosity of which is 40%. In step 200, a copper powder mixture of 100-micron dendritic electrolytic copper powder and 30% volume fraction of pore-forming agent is used to fill the cavity.

4. The method for preparing a cold plate according to claim 1, characterized in that: The microporous structure (20) is a second porous layer (23) covering the copper base plate (10); the porosity of the second porous layer (23) is 50%; in step 200, a copper powder mixture or a copper mesh assembly is used to fill the cavity.

5. The method for preparing a cold plate according to claim 4, characterized in that: In step 200, a copper powder mixture consisting of uniformly mixed 100-micron dendritic electrolytic copper powder and 50% by volume pore-forming agent is used.

6. The method for preparing a cold plate according to claim 4, characterized in that: The copper mesh assembly uses several layers of stacked copper mesh. The pore size of the copper mesh increases sequentially along the direction away from the copper base plate (10), or the pore size of the copper mesh closest to the copper base plate (10) is smaller than the pore size of the other copper meshes and the pore size of the other copper meshes is the same.

7. The method for preparing a cold plate according to claim 1, characterized in that: The segmented sintering in step 400 adopts a two-stage heating method, using an inert gas as a protective gas, heating to 800°C at a rate of 5-8°C / min, holding for 30 min, and then continuing to heat to 965°C at a rate of 5-8°C / min, holding for 90 min.

8. The method for preparing a cold plate according to claim 1, characterized in that: In step 200, the copper powder filling is carried out in multiple stages, and vibration compaction is required after each filling.

9. A cold-rolled steel plate, characterized in that: It is prepared by any one of the preparation methods described in claims 1-8.

10. A two-phase heat exchanger, characterized in that: The device includes the cold plate as described in claim 9 and has a heat exchange cavity (400); the inlet and outlet ends of the heat exchange cavity (400) are respectively provided with liquid collection cavities (401); the microporous structure (20) is located inside the heat exchange cavity (400) and between the two liquid collection cavities (401).

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