Two-phase liquid cooling system based on nanoparticle deposition boiling enhancement mechanism

Abstract

The invention relates to a two-phase liquid cooling system based on a nanoparticle deposition boiling enhancement mechanism. The two-phase liquid cooling system comprises an external cooling unit, an immersion cooling cabinet, a cooling water distribution unit, a nanofluid distribution unit and a coolant distribution unit, the immersion cooling cabinet, the nanofluid distribution unit and the coolant distribution unit are all arranged in the cabinet area; the data center machine room is formed by connecting multiple cabinets in parallel. Compared with the prior art, through a simple and low-cost nano-particle self-assembly mode, the boiling capacity is improved, and meanwhile the improvement cost is reduced; a non-homogeneous wettability surface is prepared according to a self boiling mechanism, so that the energy utilization efficiency of the two-phase liquid cooling system is effectively improved; the deposition strength of the nanoparticles is controlled through the difference of the heat conduction materials, so that the boiling surface is selectively enhanced, the pool boiling effect is effectively improved, and the efficiency of a cooling system is improved.

Description

Technical Field

[0001] The invention relates to the technical field of data center cooling, and in particular to a two-phase liquid cooling system based on a nanoparticle deposition boiling enhancement mechanism. Background Art

[0002] According to the "Electricity Report 2024" released by the International Energy Agency (IEA), with the advent of the big data era and the rapid development of AI technology, the global data center power demand will rise from 460TWh in 2022 to 620-1050TWh in 2026. According to the "Electricity Report 2024" released by the International Energy Agency (IEA). In 2025, my country's data center power consumption will exceed 400 billion kWh, accounting for about 4% of the national power consumption, and the power consumption of data center cooling systems accounts for more than 35% of the total power consumption. The cooling methods of data centers are mainly divided into air cooling and liquid cooling. The more common and mature ones are air cooling technology and single-phase liquid cooling technology (mainly single-phase cold plate cooling). However, with the advent of the big data era, the load and heat flux density on the chip side have increased year by year since 2001. The heat exchange coefficient of the conventional air cooling system has been difficult to meet the high-power and high-heat flow chip side heat dissipation. New high-efficiency liquid cooling technology suitable for high-power electronic devices is gradually replacing air cooling and covering the international market. Immersion cooling has been steadily growing in data center cooling in recent years due to its high heat transfer efficiency and stable and safe cooling mode. However, since the cabinet side and chip side of the data center have a smaller space than the outdoor cooling unit side (such as cooling towers, compression cooling units), high-power cabinets and chips need to improve the instantaneous heat transfer capacity as much as possible within the limited space. Therefore, two-phase liquid cooling technology involving phase change of the working fluid has greater application potential.

[0003] In summary, choosing an energy-saving and efficient cooling system and appropriate cooling system optimization methods can improve the cooling capacity of data centers and reduce energy consumption, which is of great significance.

[0004] In the current research on two-phase immersion cooling, there are two very important evaluation parameters, namely, critical heat flux (CHF) and heat transfer coefficient (HTC). At present, the research on pool boiling enhancement mechanism usually requires complex modification and preparation of the heat source surface, such as laser etching, vapor deposition, spraying, sintering, CNC machine tool processing, etc., to change the parameters such as wettability, roughness, capillary core pulling ability of the boiling surface, affect the bubble nucleation rate, detachment diameter and liquid phase replenishment ability, etc., so as to effectively enhance CHF and HTC. However, these methods are costly and the preparation process is relatively complicated, which is not suitable for large-scale production. Therefore, it is very important to choose a suitable and low-cost pool boiling enhancement method to improve the two-phase cooling system of data center cooling. The specific problems of two-phase immersion cooling in data centers are as follows: (1) The placement of servers in two-phase immersion liquid cooling in data centers is relatively complex, usually involving multiple angles, but most of the intellectual property rights for pool boiling mechanism only analyze the bubble rising mechanism of horizontal heat sources. (2) In data center cabinets, due to the angle sensitivity of the two-phase immersion cooling system, the horizontal placement of the server is not conducive to the detachment and rise of the bubbles. If a special guide structure is used for guidance, the system complexity will increase. (3) The vertical placement of the server is conducive to the detachment and rise of the bubbles, but from the perspective of the pool boiling mechanism, compared with the horizontal heat source, the vertical heat source has a more concentrated gas phase and the gas and liquid phases are easy to separate, but under the influence of gravity, the liquid phase is difficult to replenish. (4) The vertical heat source itself has a boiling gradient, and there are currently few existing technologies for pool boiling enhancement that are suitable for vertical heat sources. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art such as high cost and low energy efficiency and to provide a two-phase liquid cooling system based on the boiling enhancement mechanism of nanoparticle deposition. The system can improve the boiling capacity while reducing the improvement cost through a simple and inexpensive nanoparticle self-assembly form; prepare a non-uniform wettability surface according to its own boiling mechanism to effectively improve the energy utilization efficiency of the two-phase liquid cooling system; control the strength of nanoparticle deposition through differences in thermal conductive materials, thereby selectively enhancing the boiling surface, effectively improving the pool boiling effect, and thus improving the efficiency of the cooling system.

[0006] The present invention provides a two-phase liquid cooling system based on the nanoparticle deposition boiling enhancement mechanism, comprising: an external cooling unit, an immersion cooling cabinet, a cooling water distribution unit, a nanofluid distribution unit and a coolant distribution unit; the immersion cooling cabinet, the nanofluid distribution unit and the coolant distribution unit are all arranged in a cabinet area; a data center computer room is a multi-cabinet parallel connection;

[0007] The system includes two operating modes: the nanoparticle self-deposition boiling enhancement stage before cooling and the actual cooling stage; in the boiling enhancement stage, the nanofluid distribution pipeline sends the nanofluid in the nanofluid distribution unit into the immersion cooling cabinet. In this stage, although the cooling capacity of the nanofluid is slightly weaker than that of the low-boiling-point coolant (such as electronic fluoride liquid), it can still bear a certain cooling capacity. At this time, the server in the immersion cooling cabinet is working normally. When the server generates heat, the nanofluid reaches the saturation point and begins to boil. At this time, the high thermal conductivity nanoparticles in the nanofluid will naturally deposit on the boiling surface. The deposition of nanoparticles on the boiling surface will increase the nucleation points of the bubbles and enhance the thermal conductivity of the hot surface. Reduce the bubble detachment diameter and increase the bubble detachment frequency, enhance the pool boiling efficiency, that is, the cooling efficiency of the immersion cooling system. The rising bubbles bring heat to the heat exchanger on the top of the immersion cooling cabinet. The cooling water distribution unit sends the low-temperature cooling water to the top heat exchanger through the cooling water supply pipeline. The bubbles condense at the top heat exchanger and bring heat to the cooling water. The cooling water then flows into the side wall heat exchanger (the purpose of the side wall heat exchanger here is to facilitate the integration of cooling water, and it can also take away a small amount of heat from the side wall of the immersion cooling cabinet). Finally, it is sent to the cooling water distribution unit through the cooling water return pipeline. The cooling water distribution unit brings the heat to the external cooling unit through the cooling water heat exchange pipeline. The external cooling unit cools the return water and then sends it back to the cooling water distribution unit to complete the cycle.

[0008] However, in the boiling enhancement stage, since the cooling capacity of the nanofluid is lower than that of the traditional boiling coolant, and as the nanoparticles are deposited on the surface of the heat source for a long time, the bubble nucleation holes will be blocked, and the excessively thick nanoparticle layer will also increase the thermal resistance of the hot surface and deteriorate the heat transfer. Therefore, after determining the optimal deposition time and deposition concentration and other parameters through appropriate experiments. When the actual deposition reaches this parameter, the nanofluid needs to be extracted and replaced with a conventional coolant. At this time, the nanoparticles deposited on the surface of the heat source can still enhance the pool boiling capacity. In the actual cooling stage, after the actual deposition of the nanoparticles reaches the set parameters, the nanofluid is extracted and replaced with a conventional coolant. At this time, the nanoparticles deposited on the surface of the heat source can still enhance the pool boiling capacity; the coolant distribution unit sends the low-boiling point coolant into the immersion cooling cabinet through the coolant distribution pipeline, and the specific cooling process is similar to the enhancement stage. The enhanced hot surface generates heat, causing the coolant in the immersion cooling cabinet to boil. The rising bubbles bring heat to the heat exchanger on the top of the immersion cooling cabinet. The cooling water distribution unit sends low-temperature cooling water to the top heat exchanger through the cooling water supply pipeline. The bubbles condense at the top heat exchanger and bring heat to the cooling water. The cooling water then flows into the side wall heat exchanger and is finally sent to the cooling water distribution unit through the cooling water return pipeline. The cooling water distribution unit brings heat to the external cooling unit through the cooling water heat exchange pipeline. The external cooling unit cools the return water and then sends it back to the cooling water distribution unit to complete the cycle.

[0009] Since nanoparticles are more likely to deposit on the boiling heat source wall, even under the boiling disturbance of the coolant, the nanoparticles on the enhanced wall surface may re-suspend. However, most of the re-suspended nanoparticles will be re-deposited on the heat source surface under the action of boiling, and a small part will be dispersed in the coolant and the wall of the immersion cooling cabinet. Therefore, one nanoparticle deposition enhancement can usually ensure a longer strengthening effect. It is unlikely that the increase of nanoparticle impurities in the coolant due to frequent enhancement will affect the physical properties of the working fluid.

[0010] Furthermore, the heat source of the system is the heat generated by the computing process of the server. Multiple servers are integrated and immersed in the immersion cooling cabinet. The heat generated by the server is taken away through the side wall heat exchanger, and the final heat load is consumed by the external cooling unit.

[0011] Furthermore, the immersion cooling cabinet is provided with: a server, a chip; a two-phase liquid cooling unit includes: a condenser, a heat exchanger, a cooling water distribution unit, a nanofluid distribution unit and a coolant distribution unit;

[0012] During the boiling enhancement stage, the coolant in the immersion cooling cabinet is drained by the coolant return pipeline, the nanofluid supply pipeline is opened, and the nanofluid is supplied. When the liquid level immerses the server to a certain height, the supply is stopped and the nanofluid supply pipeline is closed. At this time, the server starts to work and generate heat. After the temperature reaches the saturation temperature of the nanofluid, it begins to boil, and the nanoparticles in the nanofluid are deposited on the boiling surface. At this time, the heat flux density of the chip is large and the boiling intensity is also large. Therefore, the nanoparticles tend to be deposited on the chip surface, improving its heat dissipation capacity. Bubbles are generated through the boiling process, and the bubbles rise and take away the heat, and bring the heat to the condenser through the condensation process. The heat exchanger continuously passes cooling water into the condenser to take away the condensation heat, and weak cooling in the boiling enhancement stage is achieved through the condenser heat exchange pipeline and the boiling working medium.

[0013] Furthermore, during the actual cooling stage, the nanofluid return pipeline is opened to extract the nanofluid in the immersion cooling cabinet, and then the nanofluid return pipeline is closed, the coolant supply pipeline is opened, and the coolant in the coolant distribution unit is sent into the immersion cooling cabinet. When the coolant immerses the server to a certain height, the pipeline is closed; at this time, the server starts to work and generate heat, and after the temperature reaches the saturation temperature of the coolant, it begins to boil; bubbles are generated through the boiling process, and the bubbles rise and take away the heat, and bring the heat to the condenser through the condensation process, and the heat exchanger continuously passes cooling water into the condenser to take away the condensation heat, thereby realizing enhanced cooling in the actual boiling stage.

[0014] Furthermore, for the chip surface of the vertical server, the core idea of ​​improving its boiling heat transfer is to resist the downward gravity and improve the liquid phase replenishment capacity of the boiling surface while ensuring the easy separation of gas and liquid phases. A layer of thermal conductive material is etched on the chip surface to enhance heat exchange and prevent the chip from directly contacting the working fluid and causing a short circuit.

[0015] Furthermore, after etching the thermal conductive material on the chip surface, micro-grooves are prepared on the surface of the thermal conductive material by laser etching, physical / chemical vapor deposition, etc. to enhance the capillary wicking ability of the surface of the thermal conductive material, thereby enhancing the liquid phase wetting ability and liquid replenishment ability of the boiling surface.

[0016] The chip itself has a certain boiling gradient. This is because the near-wall rise of the bubbles at the lower end of the chip will bring heat to the upper end of the chip. There is a heat superposition process, that is, there is a strong boiling zone at the upper end of the chip, and the lower end is a weak boiling zone. During the deposition of nanoparticles, nanoparticles tend to be deposited in the strong boiling zone. The more nanoparticles are deposited, the more bubble nucleation holes are formed. Therefore, the bubble detachment frequency at the upper end of the chip can be significantly improved, and the heat can be taken away faster. This also corresponds to the phenomenon that there are more bubbles in the strong boiling zone and it is more difficult to detach. The air film at the upper end is more difficult to form, which delays CHF. In the weak boiling zone at the lower end, the liquid phase is easier to replenish due to the relatively small amount of nanoparticle deposition. The liquid phase replenished from the lower end, under the action of the micro-grooves, quickly infiltrates into the upper end surface, replenishes the upper end, and once again enhances CHF. HTC can also be enhanced due to the deposition of nanoparticles. Therefore, the heat dissipation capacity of the chip is enhanced.

[0017] Furthermore, since the thermal conductive material is close to the chip surface and its thermal conductivity is much higher than that of the nanofluid, the heat first accumulates on the wall of the thermal conductive material and then transfers to the nanofluid. Therefore, the heat of the wall is higher than that of the nanofluid in the microchannel. At this time, the nanoparticles in the cold nanofluid are preferentially deposited on the hot wall. Therefore, the wettability of the wall is improved, and the working fluid is more inclined to "climb" to the wall, thereby improving the capillary wicking ability of the boiling surface.

[0018] Furthermore, the hydrophobic nanoparticles that have not been hydrophilically modified have a higher affinity with the gas phase, that is, during the process of bubble generation, they tend to gather in a circle on the surface of the bubbles rather than near the thermal conductive material. Since the server is arranged vertically at this moment, the influence of gravity may cause the nanoparticles to produce a certain deviation while the bubbles rise and they themselves deposit downward, rather than falling vertically, which inevitably causes uneven deposition shape and deposition density. The hydrophilic nanoparticles that have been hydrophilically modified tend to gather near the liquid microlayer due to the presence of a thin liquid microlayer underneath when the bubbles are generated, and their deposition distance becomes shorter. Therefore, compared with the hydrophobic nanoparticles, the deposition of hydrophilic nanoparticles on the thermal conductive material is more regular and stable.

[0019] Applying the nanoparticle self-deposition method in the two-phase liquid cooling system of the data center can effectively enhance the surface wettability through the deposition of nanoparticles in the nanofluid on the boiling surface without changing the server layout in the cabinet, thereby improving the system's boiling heat transfer capacity, enhancing cooling efficiency, and greatly reducing system improvement costs.

[0020] The system's nanoparticle vertical deposition pattern can adaptively deposit nanoparticles according to the different boiling intensities in the height direction of the vertical server layout to form a gradient wettability surface. It focuses on enhancing the wettability and roughness on the upper end of the server, thereby enhancing the capillary core extraction ability and bubble nucleation points. The lower end of the server serves as a liquid phase replenishment passage to replenish the heat source surface, thereby enhancing the gas-liquid phase separation ability. The gradient wettability surface can also enhance the capillary core extraction ability in the height direction and enhance the liquid phase wetting ability of the chip surface. The vertical deposition pattern can enhance the gas-liquid phase separation ability while improving the liquid phase replenishment and wetting ability, thereby effectively improving HTC and CHF, and thus improving the efficiency of the cooling system.

[0021] In view of the vertical server layout, it is proposed to adhere the micro-groove thermal conductive material to the chip surface to enhance the liquid phase infiltration ability of the thermal conductive material, thereby enhancing the liquid replenishment ability and improving CHF. Nanoparticle self-deposition is combined with the micro-groove modified surface. Due to the boiling deposition mechanism of nanoparticles, they are more easily deposited on the micro-groove wall, further enhancing the capillary wicking and liquid infiltration ability, which is more suitable for the boiling heat exchange of vertical servers.

[0022] For the vertical server layout, a hydrophilic modified nanoparticle deposition method is proposed. Hydrophilic nanoparticles will gather on the hot wall surface when boiling, while hydrophobic nanoparticles will gather around the bubbles. Since the gravity direction is different from horizontal deposition, the deposition of hydrophilic modified nanoparticles is more regular and the targeting is more accurate, which is in line with the vertical server layout.

[0023] The difference in surface boiling intensity caused by the difference in thermal conductivity of different materials is used to cause the difference in the deposition of nanoparticles, thereby selectively enhancing the hydrophilic and hydrophobic capabilities of the boiling surface, thereby enhancing the pool boiling effect.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) It is possible to improve boiling capacity and reduce improvement costs through simple and low-cost nanoparticle self-assembly.

[0026] (2) It can prepare a non-uniform wettability surface based on its own boiling mechanism, effectively improving the energy utilization efficiency of the two-phase liquid cooling system;

[0027] (3) The strength of nanoparticle deposition can be controlled by differences in thermal conductive materials, thereby selectively enhancing the boiling surface, effectively improving the pool boiling effect, and thus improving the efficiency of the cooling system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of a two-phase liquid cooling system based on the boiling enhancement mechanism of nanoparticle deposition;

[0029] Figure 2 Schematic diagram of a two-phase liquid cooling unit based on the nanoparticle deposition boiling enhancement mechanism;

[0030] Figure 3 Schematic diagram of the boiling enhancement mechanism of inhomogeneous surface of nanoparticle deposition;

[0031] Figure 4 Schematic diagram of the nanoparticle deposition mechanism in the microgroove structure;

[0032] Figure 5 Schematic diagram of the deposition mechanism of hydrophilic and hydrophobic nanoparticles;

[0033] Figure 6 Schematic diagram of an example of hydrophilic modification of nanoparticles (hydroxyl-modified multi-walled carbon nanotubes);

[0034] Figure 7 Schematic diagram of the boiling enhancement mechanism of amphiphilic nano-enhanced surface;

[0035] Figure 8 Schematic diagram of a nanoparticle deposition enhanced two-phase liquid cooling unit for a horizontal server arrangement;

[0036] Fig. 9 for Figure 8 Schematic diagram of the nanoparticle deposition mechanism.

[0037] Figure numerals: 1. Immersion cooling cabinet; 2. Side wall heat exchanger; 3. Cooling water distribution unit; 4. Nanofluid distribution unit; 5. Coolant distribution unit; 6. External cooling unit; 7. Cooling water supply pipeline; 8. Condenser heat exchange pipeline; 9. Cooling water return pipeline; 10. Cabinet area; 11. Data center computer room; 12. Coolant distribution pipeline; 13. Nanofluid distribution pipeline; 14. Cooling water heat exchange pipeline; 15. Server; 16. Chip; 17. Boiling working medium; 18. Condenser; 19. Heat exchanger; 20. Nanofluid supply pipeline; 21. Nanofluid return pipeline; 22. Coolant supply pipeline; 23. Coolant return pipeline; 24. Bubbles; 25. Boiling process; 26. Condensation process; 27. Conducting Thermal materials; 28. Microchannels; 29. ​​Heat superposition process; 30. Nanoparticles; 31. Nanoparticle deposition process; 32. Strong boiling zone; 33. Weak boiling zone; 34. Nanofluids; 30. Nanoparticles; 35. Hot wall; 36. Cold nanofluids; 37. Hydrophobic nanoparticles; 38. Hydrophilic nanoparticles; 39. Liquid microlayers; 40. Multi-walled carbon nanotubes; 41. Na2ZnO2-modified multi-walled carbon nanotubes; 42. Multi-walled carbon nanotubes after hydrolysis reaction; 43. Hydroxyl-modified multi-walled carbon nanotubes; 44. High thermal conductivity materials; 45. Low thermal conductivity materials; 46. Gas phase; 47. Liquid phase; 48. Strong particle deposition; 49. Weak particle deposition; 50. Boiling process; 51. Condensation process; 52. Nanoparticle deposition process. DETAILED DESCRIPTION

[0038] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms and other features not clearly described in this technical solution are all considered to be common technical features disclosed in the prior art.

[0039] Example 1

[0040] This embodiment provides a two-phase liquid cooling system based on the nanoparticle deposition boiling enhancement mechanism. Figure 1 , 2 As shown, it includes: an external cooling unit 6, an immersion cooling cabinet 1, a cooling water distribution unit 3, a nanofluid distribution unit 4 and a coolant distribution unit 5; the immersion cooling cabinet 1, the nanofluid distribution unit 4 and the coolant distribution unit 5 are all arranged in the cabinet area 10; the data center room 11 is a multi-cabinet parallel connection;

[0041] The system includes two operation modes: the self-deposition boiling enhancement stage of the nanoparticles 30 before cooling and the actual cooling stage; in the boiling enhancement stage, the nanofluid distribution pipeline 13 delivers the nanofluid 34 in the nanofluid distribution unit 4 into the immersion cooling cabinet 1. In this stage, although the cooling capacity of the nanofluid 34 is slightly weaker than that of the low-boiling-point coolant (such as electronic fluoride liquid), it can still bear a certain cooling capacity. At this time, the server in the immersion cooling cabinet 1 is working normally. When the server 15 generates heat, the nanofluid 34 reaches the saturation point and begins to boil. At this time, the high thermal conductivity nanoparticles 30 in the nanofluid 34 will naturally deposit on the boiling surface. The deposition of nanoparticles 30 on the boiling surface will increase the nucleation point of the bubble and enhance the thermal conductivity of the hot surface. Reduce the bubble detachment diameter and increase the bubble detachment frequency, enhance the pool boiling efficiency, that is, the cooling efficiency of the immersion cooling system. The rising bubbles bring heat to the heat exchanger 19 on the top of the immersion cooling cabinet 1, and the cooling water distribution unit 3 sends the low-temperature cooling water to the top heat exchanger 19 through the cooling water supply pipeline 7. The bubbles condense at the top heat exchanger 19 and bring heat to the cooling water. The cooling water then flows into the side wall heat exchanger 2 (the purpose of the side wall heat exchanger 2 here is to facilitate the integration of cooling water, and it can also take away a small amount of heat from the side wall of the immersion cooling cabinet 1), and is finally sent to the cooling water distribution unit 3 through the cooling water return pipeline 9. The cooling water distribution unit 3 brings heat to the external cooling unit 6 through the cooling water heat exchange pipeline 14. The external cooling unit 6 cools the return water and then sends it back to the cooling water distribution unit 3 to complete the cycle.

[0042] However, in the boiling enhancement stage, since the cooling capacity of the nanofluid 34 is lower than that of the traditional boiling coolant, and with the long-term deposition of the nanoparticles 30 on the surface of the heat source, the bubble nucleation holes will be blocked, and the overly thick layer of nanoparticles 30 will also increase the thermal resistance of the hot surface, deteriorating the heat transfer. Therefore, after determining the optimal deposition time and deposition concentration and other parameters through appropriate experiments. When the actual deposition reaches this parameter, the nanofluid 34 needs to be extracted and replaced by a conventional coolant. At this time, the nanoparticles 30 deposited on the surface of the heat source can still have an enhanced effect on the pool boiling ability. In the actual cooling stage, after the actual deposition of the nanoparticles 30 reaches the set parameters, the nanofluid 34 is extracted and replaced by a conventional coolant. At this time, the nanoparticles 30 deposited on the surface of the heat source can still have an enhanced effect on the pool boiling ability; the coolant distribution unit 5 sends the low-boiling point coolant into the immersion cooling cabinet 1 through the coolant distribution pipeline 12, and the specific cooling process is similar to the enhancement stage. The enhanced hot surface generates heat, causing the coolant in the immersion cooling cabinet 1 to boil, and the rising bubbles bring heat to the heat exchanger 19 on the top of the immersion cooling cabinet 1. The cooling water distribution unit 3 sends the low-temperature cooling water to the top heat exchanger 19 through the cooling water supply pipeline 7. The bubbles condense at the top heat exchanger 19 and bring heat to the cooling water. The cooling water then flows into the side wall heat exchanger 2 and is finally sent to the cooling water distribution unit 3 through the cooling water return pipeline 9. The cooling water distribution unit 3 brings heat to the external cooling unit 6 through the cooling water heat exchange pipeline 14. The external cooling unit 6 cools the return water and then sends it back to the cooling water distribution unit 3 to complete the cycle.

[0043] Since the nanoparticles 30 are more likely to deposit on the boiling heat source wall, even under the boiling disturbance of the coolant, the nanoparticles 30 on the surface of the strengthening wall may be re-suspended. However, most of the re-suspended nanoparticles 30 will also be re-deposited on the heat source surface under the action of boiling, and a small part will be dispersed in the coolant and the wall of the immersion cooling cabinet 1. Therefore, one deposition strengthening of the nanoparticles 30 can usually ensure a long-term strengthening effect. It is less likely that the increase of impurities in the nanoparticles 30 in the coolant caused by frequent strengthening will affect the physical properties of the working fluid.

[0044] In a specific embodiment, the heat source of the system is the heat generated by the computing process of the server 15. Multiple servers 15 are integrated and immersed in the immersion cooling cabinet 1. The heat generated by the server 15 is taken away by the side wall heat exchanger 2, and the final heat load is consumed by the external cooling unit 6.

[0045] In a specific embodiment, the immersion cooling cabinet 1 is provided with: a server 15, a chip 16; a two-phase liquid cooling unit includes: a condenser 18, a heat exchanger 19, a cooling water distribution unit 3, a nanofluid distribution unit 4 and a coolant distribution unit 5;

[0046] In the boiling enhancement stage, the coolant in the immersion cooling cabinet 1 is drained by the coolant return line 23, the nanofluid supply line 20 is opened, and the nanofluid 34 is supplied. When the liquid level immerses the server 15 to a certain height, the supply is stopped and the nanofluid supply line 20 is closed; at this time, the server 15 starts to work and generates heat. After the temperature reaches the saturation temperature of the nanofluid 34, it starts to boil, and the nanoparticles in the nanofluid 34 are deposited on the boiling surface. At this time, the heat flux density of the chip 16 is large and the boiling intensity is also large, so the nanoparticles are more inclined to be deposited on the surface of the chip 16, improving its heat dissipation capacity; bubbles 24 are generated through the boiling process 25, and the bubbles 24 rise and take away the heat, and bring the heat to the condenser 18 through the condensation process 26. The heat exchanger 19 continuously introduces cooling water into the condenser 18 to take away the condensation heat, and the weak cooling in the boiling enhancement stage is realized through the condenser heat exchange line 8 and the boiling working medium 17.

[0047] In a specific embodiment, during the actual cooling stage, the nanofluid return pipeline 21 is opened to extract the nanofluid 34 in the immersion cooling cabinet 1, and then the nanofluid return pipeline 21 is closed, the coolant supply pipeline 22 is opened, and the coolant in the coolant distribution unit 5 is sent into the immersion cooling cabinet 1. When the coolant immerses the server 15 to a certain height, the pipeline is closed; at this time, the server 15 starts to work and generates heat, and after the temperature reaches the saturation temperature of the coolant, it starts to boil; bubbles 24 are generated through the boiling process 25, and the bubbles 24 rise and take away the heat, and bring the heat to the condenser 18 through the condensation process 26, and the heat exchanger 19 continuously passes cooling water into the condenser 18 to take away the condensation heat, thereby realizing enhanced cooling in the actual boiling stage.

[0048] In a specific embodiment, the core idea of ​​improving boiling heat transfer on the chip surface of a vertical server is to resist downward gravity and improve the liquid phase replenishment capacity of the boiling surface while ensuring that the gas and liquid phases are easily separated. A layer of heat-conducting material 27 is etched on the surface of the chip 16 to enhance heat exchange and prevent the chip 16 from directly contacting the working medium and causing a short circuit.

[0049] In a specific embodiment, after the thermal conductive material 27 is etched on the surface of the chip 16, micro-grooves 28 are prepared on the surface of the thermal conductive material 27 by laser etching, physical / chemical vapor deposition, etc., to enhance the capillary wicking ability of the surface of the thermal conductive material 27, so as to enhance the liquid phase wetting ability and liquid replenishment ability of the boiling surface.

[0050] like Figure 3As shown, the chip 16 itself has a certain boiling gradient. This is because the near-wall rise of the bubbles at the lower end of the chip 16 will bring heat to the upper end of the chip 16. There is a heat superposition process 29, that is, there is a strong boiling zone 32 at the upper end of the chip 16, and a weak boiling zone 33 at the lower end. In the nanoparticle deposition process 31, the nanoparticles 30 are more inclined to be deposited in the strong boiling zone 32. The more nanoparticles 30 are deposited, the more bubble nucleation holes are formed. Therefore, the bubble detachment frequency at the upper end of the chip 16 can be significantly improved, and the heat is taken away faster. This also corresponds to the phenomenon that there are more bubbles in the strong boiling zone 32 and it is difficult to detach. The upper air film is more difficult to form, which delays CHF. In the weak boiling zone 33 at the lower end, since the deposition of nanoparticles 30 is relatively small, the liquid phase is easier to replenish. Under the action of the micro-grooves 28, the liquid phase replenished from the lower end quickly infiltrates the upper end surface, replenishes the upper end, and once again enhances CHF. HTC can also be enhanced due to the deposition of nanoparticles 30. Therefore, the heat dissipation capability of the chip 16 is enhanced.

[0051] like Figure 4 As shown, in a specific embodiment, since the heat conductive material 27 is close to the chip surface and its thermal conductivity is much higher than that of the nanofluid 34, the heat first accumulates on the wall of the heat conductive material 27 and then is transferred to the nanofluid 34. Therefore, the heat of the wall is higher than that of the nanofluid 34 in the microchannel 28. At this time, the nanoparticles 30 in the cold nanofluid 36 are preferentially deposited on the hot wall 35. Therefore, the wettability of the wall is improved, and the working fluid is more inclined to "climb" to the wall, thereby improving the capillary wicking ability of the boiling surface.

[0052] like Figure 5 As shown, in a specific embodiment, the hydrophobic nanoparticles 37 that have not been hydrophilically modified have a higher affinity with the gas phase, that is, during the generation of the bubbles 24, they tend to gather in a circle on the surface of the bubbles 24 rather than near the thermal conductive material 5. Since the server is arranged vertically at this moment, the influence of gravity may cause the nanoparticles to produce a certain deviation while the bubbles rise and they themselves are deposited downward, rather than falling vertically, which inevitably causes uneven deposition shape and deposition density. The hydrophilic nanoparticles 38 that have been hydrophilically modified tend to gather near the liquid microlayer 39 due to the presence of a thin liquid microlayer 39 underneath when the bubbles are generated, and their deposition distance becomes shorter. Therefore, compared with the hydrophobic nanoparticles 37, the deposition of the hydrophilic nanoparticles 38 on the thermal conductive material 27 is more regular and stable.

[0053] like Figure 6 As shown, in a specific embodiment, when the nanoparticles 30 are multi-walled carbon nanotubes 40, due to their porous long-chain structure, they can increase the nucleation holes and heat transfer of bubbles, thereby improving the pool boiling effect.

[0054] Under the action of Na2ZnO2, the multi-walled carbon nanotubes 40 generate Na2ZnO2-modified multi-walled carbon nanotubes 41, and undergo two-step hydrolysis reactions to form multi-walled carbon nanotubes 42 after hydrolysis reactions, and finally form hydroxyl-modified multi-walled carbon nanotubes 43.

[0055] Figure 7 This is a biphilic nano-enhanced surface boiling enhancement mechanism. A high thermal conductivity material 44 is coated on one end of the chip 16 surface, and a low thermal conductivity material 45 is coated on the other end. Since the boiling strength of the bubbles 24 on the surfaces of different thermally conductive materials is different, the deposition strength of the nanoparticles 30 is also different. More nanoparticles 30 are deposited at the high thermally conductive material 44, so the enhanced bubble detachment effect is better, and the gas phase 46 is easy to rise from here. Fewer nanoparticles 30 are deposited at the low thermally conductive material 45, so the liquid phase 47 is easier to replenish from here. The gradient deposition of nanoparticles 30 is caused by different thermally conductive materials, and the difference in surface wettability is enhanced by controlling the thermal conductivity of the material, thereby enhancing the heat dissipation capacity of the vertical server and improving the cooling capacity of the two-phase immersion cooling system.

[0056] Figure 8 The invention is a two-phase liquid cooling unit based on nanoparticle deposition enhancement when the server is arranged horizontally. Since the horizontal server arrangement is still the conventional arrangement in most data centers, this embodiment proposes a nanoparticle deposition optimization method for horizontal heat sources. The immersion cooling cabinet 1 is provided with: a server 15, a chip 16; the two-phase liquid cooling unit includes: a condenser 18, a heat exchanger 19, a cooling water distribution unit 3, a nanofluid distribution unit 4 and a coolant distribution unit 5;

[0057] Under the horizontal server arrangement, the server 15 needs to shorten its own size to avoid the accumulation of bubbles on the back plate of the server 15 and improve the gas phase rising path. Therefore, the server 15 is designed in two sections. During the boiling enhancement stage, the coolant in the immersion cooling cabinet 1 is drained by the coolant return line 23, the nanofluid supply line 20 is opened, and the nanofluid 34 is supplied. When the liquid level immerses the server 15 to a certain height, the liquid supply is stopped and the nanofluid supply line 20 is closed. At this time, the server 15 starts to work and generate heat. After the temperature reaches the saturation temperature of the nanofluid 34, it begins to boil. The nanoparticles in the nanofluid 34 are deposited on the boiling surface. At this time, the heat flux density of the chip 16 is large and the boiling intensity is also large. Therefore, the nanoparticles are more inclined to be deposited on the surface of the chip 16, improving its heat dissipation capacity. Bubbles 24 are generated through the boiling process 25. The bubbles 24 rise and take away the heat, and bring the heat to the condenser 18 through the condensation process 26. The heat exchanger 19 continuously passes cooling water into the condenser 18 to take away the condensation heat, realizing weak cooling in the boiling enhancement stage.

[0058] During the actual cooling stage, the nanofluid return line 21 is opened to extract the nanofluid 34 in the immersion cooling cabinet 1, and then the nanofluid return line 21 is closed, the coolant supply line 22 is opened, and the coolant in the coolant distribution unit 5 is sent into the immersion cooling cabinet 1. When the coolant immerses the server 15 to a certain height, the line is closed. At this time, the server 15 starts to work and generate heat. After the temperature reaches the saturation temperature of the coolant, it begins to boil. Bubbles 24 are generated through the boiling process 25. The bubbles 24 rise and take away the heat, and bring the heat to the condenser 18 through the condensation process 26. The heat exchanger 19 continuously passes cooling water into the condenser 18 to take away the condensation heat, thereby achieving enhanced cooling in the actual boiling stage.

[0059] Fig. 9 It is a nanoparticle deposition mechanism, in which the surface of the chip 1 is coated with a high thermal conductivity material 27, and a microchannel structure based on a low thermal conductivity material 45 is prepared above the high thermal conductivity material 27 by a physical / chemical deposition method. The boiling gas phase and liquid phase caused by the horizontal heat source are mixed more evenly, and the rising path of the gas phase and the replenishment path of the liquid phase will block each other. The gas and liquid phases are separated by designing a differential thermal conductive material surface. Heat is preferentially gathered in the high thermal conductivity material 27 with a higher temperature, and the gas phase 46 also rises from here. The low thermal conductivity material 45 is used to replenish the liquid phase 47, and the replenished liquid is transported to the high thermal conductivity area for liquid phase replenishment. The nanoparticle deposition enhancement mechanism proposed here is that the nanoparticles 30 also tend to be deposited near the high thermal conductivity material 27, thereby further enhancing its bubble nucleation and detachment capabilities, while the area of ​​the low thermal conductivity material 45 with less deposition, due to the low particle density, the enhancement of wettability is greater than the enhancement of bubble nucleation ability, so it can better enhance the replenishment of the liquid phase here. This improves the two-phase immersion cooling capabilities of horizontal server arrangements and increases system cooling efficiency.

[0060] Components not described in detail in this embodiment are all existing components that can be purchased through public channels.

[0061] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A two-phase liquid cooling system based on nanoparticle deposition boiling enhancement mechanism, characterized in that: include: An external cooling unit (6), an immersion cooling cabinet (1), a cooling water distribution unit (3), a nanofluid distribution unit (4) and a coolant distribution unit (5); the immersion cooling cabinet (1), the nanofluid distribution unit (4) and the coolant distribution unit (5) are all arranged in a cabinet area (10); the data center computer room (11) is a multi-cabinet parallel connection; The system includes two operation modes: a self-deposition boiling enhancement stage of nanoparticles (30) before cooling and an actual cooling stage; in the boiling enhancement stage, a nanofluid distribution pipeline (13) delivers a nanofluid (34) in a nanofluid distribution unit (4) into an immersion cooling cabinet (1), and when a server (15) generates heat, the nanofluid (34) reaches a saturation point and begins to boil, and bubbles rise to bring heat to a heat exchanger (19) at the top of the immersion cooling cabinet (1), and the cooling water distribution unit (3) transfers the low temperature The cooling water is sent to the top heat exchanger (19) through the cooling water supply pipeline (7), and the bubbles are condensed at the top heat exchanger (19), bringing heat to the cooling water. The cooling water then flows into the side wall heat exchanger (2), and finally sent to the cooling water distribution unit (3) through the cooling water return pipeline (9). The cooling water distribution unit (3) brings heat to the external cooling unit (6) through the cooling water heat exchange pipeline (14). The external cooling unit (6) cools the return water and then sends it back to the cooling water distribution unit (3) to complete the cycle; In the actual cooling stage, after the actual deposition of the nanoparticles (30) reaches the set parameters, the nanofluid (34) is extracted and replaced by a conventional coolant. At this time, the nanoparticles (30) deposited on the surface of the heat source can still enhance the pool boiling capacity; the coolant distribution unit (5) sends the low-boiling point coolant into the immersion cooling cabinet (1) through the coolant distribution pipeline (12). The enhanced hot surface generates heat, causing the coolant in the immersion cooling cabinet (1) to boil, and the bubbles rise to bring the heat to the heat exchanger ( 19), the cooling water distribution unit (3) delivers low-temperature cooling water to the top heat exchanger (19) through the cooling water supply pipeline (7), the bubbles condense at the top heat exchanger (19), bringing heat to the cooling water, and the cooling water then flows into the side wall heat exchanger (2), and finally is delivered to the cooling water distribution unit (3) through the cooling water return pipeline (9), the cooling water distribution unit (3) delivers heat to the external cooling unit (6) through the cooling water heat exchange pipeline (14), the external cooling unit (6) cools the return water and then sends it back to the cooling water distribution unit (3) to complete the cycle.

2. A two-phase liquid cooling system based on nanoparticle deposition boiling enhancement mechanism according to claim 1, characterized in that: The heat source of the system is the heat generated by the computing process of the server (15). Multiple servers (15) are integrated and immersed in the immersion cooling cabinet (1). The heat generated by the server (15) is taken away through the side wall heat exchanger (2), and the final heat load is consumed by the external cooling unit (6).

3. A two-phase liquid cooling system based on nanoparticle deposition boiling enhancement mechanism according to claim 1, characterized in that: The immersion cooling cabinet (1) is provided with: a server (15) and a chip (16); the two-phase liquid cooling unit comprises: a condenser (18), a heat exchanger (19), a cooling water distribution unit (3), a nanofluid distribution unit (4) and a coolant distribution unit (5); In the boiling enhancement stage, the coolant in the immersion cooling cabinet (1) is drained by the coolant return pipe (23), the nanofluid supply pipe (20) is opened, and the nanofluid (34) is supplied. When the liquid level immerses the server (15) to a certain height, the supply is stopped and the nanofluid supply pipe (20) is closed; at this time, the server (15) starts to work and generates heat. After the temperature reaches the saturation temperature of the nanofluid (34), boiling begins, and the nanoparticles in the nanofluid (34) are deposited on the boiling surface; bubbles (24) are generated through the boiling process (25), and the bubbles (24) rise and take away the heat, and bring the heat to the condenser (18) through the condensation process (26); the heat exchanger (19) continuously passes cooling water into the condenser (18) to take away the condensation heat, thereby achieving weak cooling in the boiling enhancement stage.

4. A two-phase liquid cooling system based on nanoparticle deposition boiling enhancement mechanism according to claim 3, characterized in that: During the actual cooling stage, the nanofluid return pipeline (21) is opened to extract the nanofluid (34) in the immersion cooling cabinet (1), and then the nanofluid return pipeline (21) is closed, the coolant supply pipeline (22) is opened, and the coolant in the coolant distribution unit (5) is sent into the immersion cooling cabinet (1). When the coolant immerses the server (15) to a certain height, the pipeline is closed; at this time, the server (15) starts to work and generates heat, and after the temperature reaches the saturation temperature of the coolant, it starts to boil; bubbles (24) are generated through the boiling process (25), and the bubbles (24) rise to take away the heat, and bring the heat to the condenser (18) through the condensation process (26); the heat exchanger (19) continuously passes cooling water into the condenser (18) to take away the condensation heat, thereby achieving enhanced cooling in the actual boiling stage.

5. The two-phase liquid cooling system based on nanoparticle deposition boiling enhancement mechanism according to claim 3, characterized in that: A layer of heat-conducting material (27) is etched on the surface of the chip (16) to enhance heat exchange and also to prevent the chip (16) from directly contacting the working fluid and causing a short circuit.

6. A two-phase liquid cooling system based on nanoparticle deposition boiling enhancement mechanism according to claim 1, characterized in that: After the heat-conducting material (27) is etched on the surface of the chip (16), micro-grooves (28) are prepared on the surface of the heat-conducting material (27) to enhance the capillary wicking ability of the surface of the heat-conducting material (27) so as to enhance the liquid phase wetting ability and liquid replenishing ability of the boiling surface.

7. The two-phase liquid cooling system based on nanoparticle deposition boiling enhancement mechanism according to claim 1, characterized in that: Heat first accumulates on the wall of the heat-conducting material (27) and then is transferred to the nanofluid (34). Therefore, the heat of the wall is higher than that of the nanofluid (34) in the microchannel (28). At this time, the nanoparticles (30) in the cold nanofluid (36) are preferentially deposited on the hot wall (35).

8. The two-phase liquid cooling system based on nanoparticle deposition boiling enhancement mechanism according to claim 1, characterized in that: The hydrophobic nanoparticles (37) that have not been hydrophilically modified have a higher affinity with the gas phase, that is, during the generation of the bubbles (24), they are more inclined to gather in a circle on the surface of the bubbles (24); the hydrophilic nanoparticles (38) that have been hydrophilically modified are more inclined to gather near the liquid microlayer (39) due to the presence of a thin liquid microlayer (39) underneath when the bubbles are generated, and their deposition path becomes shorter. Therefore, compared with the hydrophobic nanoparticles (37), the deposition of the hydrophilic nanoparticles (38) on the thermal conductive material (27) is more regular and stable.

9. The two-phase liquid cooling system based on nanoparticle deposition boiling enhancement mechanism according to claim 1, characterized in that: When the nanoparticles (30) are multi-walled carbon nanotubes (40), since they have a porous long-chain structure, they can increase the nucleation holes and heat transfer of bubbles, thereby improving the pool boiling effect.

10. A two-phase liquid cooling system based on nanoparticle deposition boiling enhancement mechanism according to claim 9, characterized in that: The multi-walled carbon nanotubes (40) are subjected to the action of Na2ZnO2 to generate Na2ZnO2-modified multi-walled carbon nanotubes (41), which are subjected to two-step hydrolysis reactions to form multi-walled carbon nanotubes (42) after hydrolysis reactions, and finally form hydroxyl-modified multi-walled carbon nanotubes (43).

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