Coolant for immersion cooling systems

Abstract

To provide a cooling liquid for an immersion cooling system in which the influence on an electronic device to be immersed is further suppressed.SOLUTION: A cooling liquid for a liquid immersion cooling system is contained in a liquid immersion tank of a liquid immersion cooling system as a cooling liquid. The cooling liquid contains a hydrocarbon oil and one or more antioxidants selected from the group consisting of amine-based antioxidants and phenol-based antioxidants. The hydrocarbon oil is contained in an amount of 50 mass% or more with respect to the total amount of the cooling liquid for an immersion cooling system. A 5% distillation temperature of the cooling liquid for an immersion cooling system is 320°C or higher, a %CN is 30.0 or less, and a kinematic viscosity at 40°C is 11.5 mm2 / s or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a coolant for an immersion cooling system. This application claims priority based on Japanese Patent Application No. 2022-113248, filed in Japan on July 14, 2022, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] With the rapid increase in the volume of data transmitted and received, the load on supercomputers and data servers is increasing, and the amount of heat generated by these electronic devices is also increasing. Until now, air cooling has been the mainstream method for cooling these electronic devices, but because air cooling has limitations in cooling efficiency, liquid immersion cooling, which offers higher cooling efficiency, is attracting attention.

[0003] Figure 1 shows a basic example of the configuration of a liquid immersion cooling system. The immersion cooling system 10 comprises an immersion tank 1, a heat exchanger 3, a pump 5, and a cooling device 7. The immersion tank 1 is filled with a coolant for the immersion cooling system. The electronic equipment is cooled in the immersion tank 1. The coolant for the immersion cooling system, heated by the waste heat from the electronic equipment, is pumped up by the pump 5 and heat-exchanged with chilled water produced by the cooling device 7 in the heat exchanger 3. The coolant for the immersion cooling system, cooled by the heat exchange, is then circulated back into the immersion tank 1. By using the liquid immersion cooling system 10, it is possible to maintain a constant, safe temperature even when electronic equipment is used continuously under high load conditions.

[0004] Specifically, as an immersion cooling system, Patent Document 1 discloses an apparatus comprising (a) an electronic hardware device and (b) a liquid cooling medium. The liquid cooling medium is disclosed to be (i) a mixture of a synthetic ester and a saturated medium-chain triglyceride, wherein the synthetic ester has a viscosity of 28 to 38 cSt at 40°C as determined according to ASTM D445, or (ii) a polyalkylene glycol, wherein if the liquid cooling medium contains a polyalkylene glycol, the polyalkylene glycol constitutes at least 70% by weight of the liquid cooling medium. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6282289 [Overview of the project] [Problems that the invention aims to solve]

[0006] For immersion cooling systems, it is important that the coolant does not affect the electronic equipment being immersed. Specifically, this means suppressing swelling of the insulating material of the electronic equipment and the leaching of metals from the electronic equipment. While the liquid coolant described in Patent Document 1 takes into account the balance between flash point and viscosity, its effect on the electronic equipment being immersed has not been considered. The ester contained in the liquid coolant in Patent Document 1 can hydrolyze to produce acid, which may pose a problem as it could lead to the leaching of metals from the electronic equipment. Furthermore, from the perspective of maintaining high visibility within the immersion cooling system, the coolant used in the immersion cooling system must also have high light resistance.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a coolant for an immersion cooling system that has high light resistance and further suppresses the impact on electronic equipment to be immersed. [Means for solving the problem]

[0008] To solve the above problems, the present invention employs the following configuration. [1] A coolant for an immersion cooling system, which is filled as a coolant in the immersion tank of an immersion cooling system, containing hydrocarbon oil in an amount of 50% by mass or more relative to the total amount of the coolant for the immersion cooling system, and not containing an amine-based antioxidant, or if it further contains the amine-based antioxidant, the content of the amine-based antioxidant is less than 0.01% by mass relative to the total amount of the coolant for the immersion cooling system, and the 5% distillation temperature is 320°C or higher, and %C N The coefficient of viscosity is 30.0 or less, and the kinematic viscosity at 40°C is 11.5 mm³. 2 A coolant for immersion cooling systems with a temperature of / s or higher. [2] A coolant for an immersion cooling system according to [1], wherein the 95% distillation temperature is 430°C or higher. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a coolant for an immersion cooling system that has high light resistance and further suppresses the impact on electronic equipment that is immersed in it. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of a liquid immersion cooling system. [Modes for carrying out the invention]

[0011] (Coolant for immersion cooling systems) The coolant for the immersion cooling system in this embodiment is a coolant for the immersion cooling system that is filled as a coolant into the immersion tank of the immersion cooling system. The coolant for the immersion cooling system of this embodiment is used to cool electronic equipment. Examples of such electronic devices include computer servers, server motherboards, microprocessors, capacitors, and other heat-generating electronic devices.

[0012] The coolant for the immersion cooling system of this embodiment contains hydrocarbon oil in an amount of 50% by mass or more relative to the total volume of the coolant for the immersion cooling system, and has a 5% distillation temperature of 320°C or higher, and %CN is 30.0 or less, and the kinematic viscosity at 40°C is 11.5 mm 2 / s or more.

[0013] In the present embodiment, the coolant for an immersion cooling system has a kinematic viscosity at 40°C of 11.5 mm 2 / s or more, preferably 15.0 mm 2 / s or more, more preferably 20.0 mm 2 / s or more, still more preferably 25.0 mm 2 / s or more. Furthermore, in the present embodiment, the coolant for an immersion cooling system preferably has a kinematic viscosity at 40°C of 70.0 mm 2 / s or less, more preferably 60.0 mm 2 / s or less, still more preferably 50.0 mm 2 / s or less.

[0014] In the present embodiment, since the coolant for an immersion cooling system has a kinematic viscosity at 40°C of 11.5 mm 2 / s or more, swelling of the insulating material of electronic devices can be suppressed. This is presumed to result from the fact that high-viscosity components (e.g., compounds with long carbon chains) are less likely to be incorporated into resins such as insulating materials of electronic devices. When the kinematic viscosity at 40°C of the coolant for an immersion cooling system of the present embodiment is not less than the above-mentioned preferable lower limit, swelling of the insulating material of electronic devices can be further suppressed. When the kinematic viscosity at 40°C of the coolant for an immersion cooling system of the present embodiment is not more than the above-mentioned preferable upper limit, the fluidity of the coolant for an immersion cooling system of the present embodiment is improved, and circulation is facilitated, so that the cooling performance is improved. Furthermore, the load on the pump that delivers the coolant in the immersion cooling system can be further reduced.

[0015] For example, in the present embodiment, the coolant for an immersion cooling system preferably has a kinematic viscosity at 40°C of 11.5 mm 2 / s or more and 70.0 mm 2 / s or less, 15.0 mm 2 / s or more and 60.0 mm 2It is more preferable that the value be less than or equal to / s, and 20.0 mm 2 / s or more 60.0mm 2 It is even more preferable that the speed be less than or equal to 25.0 mm 2 / s or more 50.0mm 2 It is especially preferable that the time is less than or equal to / s.

[0016] The coolant for the immersion cooling system in this embodiment has a kinematic viscosity of 3.5 mm at 80°C. 2 / s or more 30.0mm 2 Preferably, it is less than or equal to / s, and 4.5 mm 2 / s or more 27.5mm 2 It is more preferable that the value be less than or equal to / s, and 5.5 mm 2 / s or more 25.0mm 2 It is even more preferable that the time is less than or equal to / s.

[0017] The coolant for the immersion cooling system in this embodiment has a kinematic viscosity of 2.5 mm at 100°C. 2 / s or more 20.0mm 2 It is preferable that the value be less than or equal to / s, and 3.0 mm 2 / s or more 17.5mm 2 It is more preferable that the value be less than or equal to / s, and 3.5 mm 2 / s or more 15.0mm 2 It is even more preferable that the time is less than or equal to / s.

[0018] In this specification, the kinematic viscosity at 40°C, 80°C, and 100°C refers to the kinematic viscosity at 40°C, 80°C, and 100°C measured in accordance with JIS K2283:2000.

[0019] The 5% distillation temperature of the coolant for the immersion cooling system in this embodiment is 320°C or higher, preferably 330°C or higher, more preferably 350°C or higher, and even more preferably 370°C or higher. Furthermore, the 5% distillation temperature of the coolant for the immersion cooling system is preferably 600°C or lower, more preferably 550°C or lower, and even more preferably 520°C or lower.

[0020] By ensuring that the 5% distillation temperature of the coolant for the immersion cooling system is 320°C or higher, swelling of the insulating material of electronic equipment can be suppressed. This is presumed to be because high-boiling-point components are less likely to be incorporated into resins such as the insulating material of electronic equipment. If the 5% distillation temperature of the coolant for the immersion cooling system is above the above preferred lower limit, swelling of the insulating material of electronic equipment can be further suppressed. If the 5% distillation temperature of the coolant for the immersion cooling system is below the above preferred upper limit, the fluidity of the coolant improves, making it easier to circulate, and thus improving cooling performance. In addition, the load on the pump that delivers the coolant in the immersion cooling system can be reduced.

[0021] For example, the 5% distillation temperature of the coolant for the immersion cooling system in this embodiment is preferably 320°C or higher and 600°C or lower, more preferably 330°C or higher and 550°C or lower, even more preferably 350°C or higher and 550°C or lower, and particularly preferably 370°C or higher and 520°C or lower.

[0022] The 95% distillation temperature of the coolant for the immersion cooling system in this embodiment is preferably 430°C or higher, more preferably 450°C or higher, and even more preferably 500°C or higher. Furthermore, the 95% distillation temperature of the coolant for the immersion cooling system is preferably 800°C or lower, more preferably 750°C or lower, and even more preferably 700°C or lower.

[0023] If the 95% distillation temperature of the coolant for the immersion cooling system is above the above preferred lower limit, swelling of the insulating material of electronic equipment can be further suppressed. If the 95% distillation temperature of the coolant for the immersion cooling system is below the above preferred upper limit, the fluidity of the coolant improves, making it easier to circulate, and thus improving cooling performance. In addition, the load on the pump that delivers the coolant in the immersion cooling system can be reduced.

[0024] For example, the 95% distillation temperature of the coolant for the immersion cooling system in this embodiment is preferably 430°C to 800°C, more preferably 450°C to 750°C, and even more preferably 500°C to 700°C.

[0025] For example, among the above, the coolant for the immersion cooling system of this embodiment preferably has a 5% distillation temperature of 320°C to 600°C and a 95% distillation temperature of 430°C to 800°C, more preferably has a 5% distillation temperature of 330°C to 550°C and a 95% distillation temperature of 450°C to 750°C, even more preferably has a 5% distillation temperature of 350°C to 550°C and a 95% distillation temperature of 450°C to 750°C, and particularly preferably has a 5% distillation temperature of 370°C to 520°C and a 95% distillation temperature of 500°C to 700°C. If the 5% distillation temperature and the 95% distillation temperature of the coolant for the immersion cooling system in this embodiment are within the above preferred range, the cooling performance can be improved while further suppressing the swelling of the insulating material of the electronic equipment.

[0026] In this specification, the 5% distillation temperature and the 95% distillation temperature refer to values ​​obtained by gas chromatography distillation in accordance with JIS K2254:2018.

[0027] The measurement conditions for gas chromatography distillation in this specification are as follows: (1) When the endpoint (100% distillation temperature) is 600°C or higher Equipment: Shimadzu Corporation GC-2030 Column: UA-1HT (30m × 0.5mm I.D. × 0.10μm) Carrier gas: Helium 15 mL / min Detector: FID Detector temperature: 400℃ Inlet temperature: PTV 40~380℃ Column temperature: 40-380°C (6 min) Heating rate: 10℃ / min Injection volume: 0.5 μL (carbon disulfide solution) (2) When the endpoint (100% distillation temperature) is less than 600°C Equipment: Shimadzu Corporation GC-2010plus Column: UA-1HT (30m × 0.5mm I.D. × 0.10μm) Carrier gas: Helium 15 mL / min Detector: FID Detector temperature: 360℃ Inlet temperature: PTV 40~380℃ Column temperature: 40-350°C (6 min) Heating rate: 10℃ / min Injection volume: 0.5 μL (carbon disulfide solution)

[0028] %C of the coolant for the immersion cooling system of this embodiment N It is 30.0 or less, preferably 27.5 or less, and more preferably 25.0 or less. Also, the %C of the coolant for immersion cooling systems N It is preferably 0.5 or higher, more preferably 1.5 or higher, and even more preferably 2.5 or higher.

[0029] %C of coolant for immersion cooling systems N If the value is 30.0 or less, swelling of the insulating material in electronic equipment can be suppressed. If it is below the preferred upper limit value mentioned above, swelling of the insulating material in electronic equipment can be suppressed even further. %C of coolant for immersion cooling systems N If the value is above the preferred lower limit mentioned above, the solubility of the additive will improve.

[0030] For example, the %C of the coolant for the immersion cooling system of this embodiment N It is preferably 0.5 or more and 30.0 or less, more preferably 1.5 or more and 27.5 or less, and even more preferably 2.5 or more and 25.0 or less.

[0031] %C of the coolant for the immersion cooling system of this embodiment PIt is preferably 99.5 or less, more preferably 98.5 or less, and even more preferably 97.5 or less. Also, the %C of the coolant for immersion cooling systems P It is preferably 70.0 or higher, more preferably 72.5 or higher, and even more preferably 75.0 or higher.

[0032] %C of coolant for immersion cooling systems P If the value is below the above preferred upper limit, the solubility of the additive will be further improved. %C of coolant for immersion cooling systems P If the value is above the above preferred lower limit, swelling of the insulating material of electronic equipment can be further suppressed.

[0033] For example, the %C of the coolant for the immersion cooling system of this embodiment P Preferably, it is 70.0 to 99.5, more preferably 72.5 to 98.5, and even more preferably 75.0 to 97.5.

[0034] %C of the coolant for the immersion cooling system of this embodiment A It is preferably 5.0 or less, more preferably 3.0 or less, and even more preferably 0.

[0035] %C of coolant for immersion cooling systems A If it is below the above-mentioned preferred upper limit, it will have less impact on electronic devices.

[0036] In this specification, %C N , %C P and %C A These are determined by methods (ndM ring analysis) in accordance with ASTM D 3238-85. %C N This represents the percentage (mass ratio) of the number of naphthenic carbon atoms relative to the total number of carbon atoms. P This represents the percentage (mass ratio) of the number of carbon atoms in paraffin to the total number of carbon atoms. AThis represents the percentage of aromatic carbon atoms relative to the total number of carbon atoms. The above %C N , %C P and %C A The preferred range is based on the value obtained by the above method, and even for mineral oil-based base oils that do not contain naphthenes, the %C obtained by the above method is also applicable. N This can represent a value greater than 0.

[0037] <Hydrogen oils> The coolant for the immersion cooling system of this embodiment includes a hydrocarbon oil. Examples of hydrocarbon oils include aliphatic saturated hydrocarbon oils, aliphatic unsaturated hydrocarbon oils (olefinic hydrocarbons), alicyclic hydrocarbon oils (naphthenic hydrocarbons), and aromatic hydrocarbon oils. The aliphatic saturated hydrocarbon oil may be a straight-chain saturated hydrocarbon oil (normal paraffinic hydrocarbon) or a branched-chain saturated hydrocarbon oil (isoparaffinic hydrocarbon). Specifically, examples of hydrocarbon oils in the coolant for the immersion cooling system of this embodiment include mineral oil and synthetic oil.

[0038] Mineral oil As the mineral oil, distillate obtained by atmospheric distillation of crude oil can be used. In addition, lubricating oil fractions obtained by further vacuum distillation of this distillate and then refined through various refining processes can also be used. The refining process can be a combination of various methods, including hydrogenation, solvent extraction, solvent dewaxing, hydrogenation dewaxing, sulfuric acid washing, and clay treatment. By combining these refining processes in an appropriate order, mineral oil can be obtained. Mineral oil also includes wax isomerized oil. Wax isomerized oil is a hydrocarbon obtained by hydrocracking and hydroisomerizing GTL wax or CTL wax synthesized by the Fischer-Tropsch process (FT process), or slack wax obtained by solvent dewaxing, to obtain a lubricating oil fraction. GTL wax is a wax synthesized using natural gas as a raw material by the FT process, and CTL wax is a wax synthesized using coal as a raw material by the FT process. Hydrocarbons obtained by hydrocracking and isomerizing these waxes to obtain a lubricating oil fraction are generally called GTL or CTL. As the mineral oil, a mixture of several refined oils with different properties obtained by subjecting different crude oils or distillates to different refining processes, as well as a mixture with GTL, etc., may be used.

[0039] As for the mineral oil, you can use base oils of API Group I (hereinafter referred to as "API Group I base oil"), Group II (hereinafter referred to as "API Group II base oil"), or Group III (hereinafter referred to as "API Group III base oil"), or a mixture thereof. API Group I base oils are mineral oil-based base oils having a sulfur content of more than 0.03% by mass and / or a saturation content of less than 90% by mass, and a viscosity index of 80 or more and less than 120. API Group II base oils are mineral oil-based base oils with a sulfur content of 0.03% by mass or less, a saturation content of 90% by mass or more, and a viscosity index of 80 or more and less than 120. API Group III base oils are mineral oil-based base oils with a sulfur content of 0.03% by mass or less, a saturation content of 90% by mass or more, and a viscosity index of 120 or higher.

[0040] The hydrocarbon oil may consist of one type of mineral oil, or it may be a mixed base oil containing two or more types of mineral oil. In the case of a mixed base oil containing two or more types of mineral oil, the API classifications of those mineral oils may be the same or they may be different from one another. In this embodiment, the mineral oil used in the immersion cooling system preferably contains an API group III base oil, from the viewpoint of further suppressing the impact on electronic equipment.

[0041] ≪Synthetic oil≫ Examples of synthetic oils include polyolefins and alkylbenzenes.

[0042] • Polyolefins Examples of polyolefins include homopolymers or copolymers of olefin monomers having 2 to 16 carbon atoms, preferably 2 to 12 carbon atoms, and hydrides of these polymers. The olefin monomer may be any of α-olefins, internal olefins, linear olefins, or branched olefins. Specific examples of such olefin monomers include ethylene, propylene, 1-butene, 2-butene, isobutene, pentene, hexene, heptene, octene, nonene, decene, undecene, dodecene, tridecene, tetradecene, pentadecene, hexadecene, and mixtures thereof. Among the polyolefins listed above, poly-α-olefin (PAO) is preferred from the viewpoint of viscosity characteristics and oxidation stability.

[0043] The above polyolefins can be produced by known methods. For example, they can be produced by a catalyst-free thermal reaction, or by homopolymerizing or copolymerizing the above olefins using known catalysts such as organic peroxide catalysts such as benzoyl peroxide; Friedel-Crafts type catalysts such as aluminum chloride, aluminum chloride-polyhydric alcohol systems, aluminum chloride-titanium tetrachloride systems, aluminum chloride-alkyltin halide systems, and boron fluoride; Ziegler type catalysts such as organic aluminum chloride-titanium tetrachloride systems and organic aluminum chloride-titanium tetrachloride systems; metallocene type catalysts such as aluminoxane-zirconocene systems and ionic compound-zirconocene systems; and Lewis acid complex type catalysts such as aluminum chloride-base systems and boron fluoride-base systems.

[0044] • Alkylbenzene Preferably, the alkylbenzene has 1 to 4 alkyl groups with 1 to 40 carbon atoms in its molecule. The alkyl groups of the alkylbenzene may be linear or branched, but branched alkyl groups are preferred in terms of stability and viscosity properties, and branched alkyl groups derived from olefin oligomers such as propylene, butene, and isobutylene are more preferred because they are readily available.

[0045] In this embodiment, among the above, alkylbenzenes having one or two alkyl groups, i.e., monoalkylbenzenes, dialkylbenzenes, or mixtures thereof, are most preferred in terms of stability and availability. Furthermore, the alkylbenzene may be not only alkylbenzenes with a single structure, but also mixtures of alkylbenzenes having different structures.

[0046] The alkylbenzenes described above can be produced by known methods. For example, they can be produced using aromatic compounds as raw materials, along with alkylating agents and alkylation catalysts. Here, examples of aromatic compounds used as raw materials include benzene, toluene, xylene, ethylbenzene, methylethylbenzene, diethylbenzene, and mixtures thereof. Examples of alkylating agents include: linear or branched olefins with 6 to 40 carbon atoms obtained by polymerization of lower monoolefins such as ethylene, propylene, butene, and isobutylene, preferably propylene; linear or branched olefins with 6 to 40 carbon atoms obtained by thermal decomposition of waxes, heavy oils, petroleum fractions, polyethylene, polypropylene, etc.; linear olefins with 9 to 40 carbon atoms obtained by separating n-paraffin from petroleum fractions such as kerosene and light oil and olefinizing it with a catalyst; and mixtures thereof. Examples of alkylation catalysts used in alkylation include Friedel-Crafts type catalysts such as aluminum chloride and zinc chloride; and known catalysts such as acidic catalysts such as sulfuric acid, phosphoric acid, silicatungstic acid, hydrofluoric acid, and activated clay.

[0047] The hydrocarbon oil in the coolant for the immersion cooling system of this embodiment may include a hydrocarbon oil having biomass-derived carbon. Examples of hydrocarbon oils containing carbon derived from biomass include base oils synthesized from vegetable oils such as palm oil, coconut oil, soybean oil, rapeseed oil, and mixtures thereof.

[0048] Examples of commercially available hydrocarbon oils containing biomass-derived carbon include SynNova. TM 4 Base Oil (Novvi), and SynNova TM Examples include 9. Base Oil (manufactured by Novvi).

[0049] The hydrocarbon oil in the coolant for the immersion cooling system of this embodiment may be mineral oil only, synthetic oil only, or a mixture of mineral oil and synthetic oil. Among these, API group III base oil or poly-α-olefin is preferred.

[0050] In this embodiment, the 5% distillation temperature of the hydrocarbon oil in the immersion cooling system is preferably 320°C or higher, more preferably 330°C or higher, and even more preferably 350°C or higher. Furthermore, the 5% distillation temperature of the hydrocarbon oil is preferably 600°C or lower, more preferably 550°C or lower, and even more preferably 520°C or lower.

[0051] If the 5% distillation temperature of the hydrocarbon oil is above the above preferred lower limit, swelling of the insulating material of electronic equipment can be further suppressed. If the 5% distillation temperature of the hydrocarbon oil is below the above preferred upper limit, the fluidity of the coolant for the immersion cooling system in this embodiment improves, making it easier to circulate and thus improving the cooling performance. In addition, the load on the pump that delivers the coolant in the immersion cooling system can be reduced.

[0052] For example, the 5% distillation temperature of the hydrocarbon oil in the coolant for the immersion cooling system of this embodiment is preferably 320°C or higher and 600°C or lower, more preferably 330°C or higher and 550°C or lower, and even more preferably 350°C or higher and 520°C or lower.

[0053] In the coolant for the immersion cooling system of this embodiment, the 95% hydrocarbon oil distillation temperature of the hydrocarbon oil is preferably 430°C or higher, more preferably 450°C or higher, and even more preferably 500°C or higher. Furthermore, the 95% distillation temperature of the hydrocarbon oil is preferably 800°C or lower, more preferably 750°C or lower, and even more preferably 700°C or lower.

[0054] If the 95% distillation temperature of the hydrocarbon oil is above the above preferred lower limit, swelling of the insulating material of electronic equipment can be further suppressed. If the 95% distillation temperature of the hydrocarbon oil is below the above preferred upper limit, the fluidity of the coolant for the immersion cooling system in this embodiment improves, making it easier to circulate and thus improving the cooling performance. In addition, the load on the pump that delivers the coolant in the immersion cooling system can be reduced.

[0055] For example, the 95% distillation temperature of the hydrocarbon oil in the coolant for the immersion cooling system of this embodiment is preferably 430°C to 800°C, more preferably 450°C to 750°C, and even more preferably 500°C to 700°C.

[0056] For example, among the above, the hydrocarbon oil in the coolant for the immersion cooling system of this embodiment preferably has a 5% distillation temperature of 320°C to 600°C and a 95% distillation temperature of 430°C to 800°C, more preferably has a 5% distillation temperature of 330°C to 550°C and a 95% distillation temperature of 450°C to 750°C, and even more preferably has a 5% distillation temperature of 350°C to 550°C and a 95% distillation temperature of 500°C to 700°C. If the 5% distillation temperature and the 95% distillation temperature of the hydrocarbon oil in the immersion cooling system of this embodiment are within the above preferred range, the cooling performance can be improved while further suppressing the swelling of the insulating material of the electronic equipment.

[0057] In the cooling fluid for the immersion cooling system of this embodiment, one type of hydrocarbon oil may be used alone, or two or more types may be used in combination. If the coolant for the immersion cooling system of this embodiment contains two or more hydrocarbon oils, the above-mentioned "5% distillation temperature" and "95% distillation temperature" refer to values ​​obtained from gas chromatographic distillation measured for a mixture of two or more hydrocarbon oils.

[0058] The hydrocarbon oil content in the coolant for the immersion cooling system of this embodiment is 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 100% by mass, based on the total amount of coolant for the immersion cooling system.

[0059] If the hydrocarbon oil content in the coolant for the immersion cooling system of this embodiment is above the above preferred lower limit, the impact on electronic equipment can be further suppressed.

[0060] The coolant for the immersion cooling system of this embodiment contains the hydrocarbon oil described above and substantially does not contain amine-based antioxidants. Here, "substantially free of amine-based antioxidants" has the following two meanings: (i) Does not contain amine-based antioxidants. (ii) If an amine-based antioxidant is included, the total amount of amine-based antioxidants shall be less than 0.01% by mass of the total amount of coolant for the immersion cooling system.

[0061] Coolants for immersion cooling systems have good light resistance because they contain virtually no amine-based antioxidants. Light resistance of coolants is not a particular problem in other applications. However, when using an immersion cooling system, electronic equipment must be immersed in the coolant and observed while immersed in the coolant during maintenance. Therefore, maintaining transparency is important for immersion cooling systems. The coolant for immersion cooling systems contains virtually no amine-based antioxidants. Therefore, it exhibits good light resistance, maintains transparency easily, and improves the maintainability of electronic equipment immersed in the coolant.

[0062] • Amine-based antioxidants Examples of amine-based antioxidants include aromatic amine-based antioxidants and hindered amine-based antioxidants. Examples of aromatic amine antioxidants include primary aromatic amine compounds such as alkylated α-naphthylamine; and secondary aromatic amine compounds such as alkylated diphenylamine, phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, and phenyl-β-naphthylamine.

[0063] Examples of hindered amine antioxidants include compounds having a 2,2,6,6-tetraalkylpiperidine skeleton (2,2,6,6-tetraalkylpiperidine derivatives). Examples of 2,2,6,6-tetraalkylpiperidine derivatives include those having a substituent at the 4-position. Alternatively, two 2,2,6,6-tetraalkylpiperidine skeletons may be bonded via their respective 4-position substituents. Furthermore, the N-position of the 2,2,6,6-tetraalkylpiperidine skeleton may be unsubstituted, or it may be substituted with an alkyl group having 1 to 4 carbon atoms. The 2,2,6,6-tetraalkylpiperidine skeleton is, for example, the 2,2,6,6-tetramethylpiperidine skeleton.

[0064] The substituent at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton is an acyloxy group (R 1 COO-), alkoxy group (R 1 O-), alkylamino group (R 1 NH-), acylamino group (R 1 Examples include CONH-). R 1 These are, for example, hydrocarbon groups with 1 to 30 carbon atoms. Examples of hydrocarbon groups include alkyl groups, alkenyl groups, cycloalkyl groups, alkylcycloalkyl groups, aryl groups, alkylaryl groups, and arylalkyl groups.

[0065] When two 2,2,6,6-tetraalkylpiperidine skeletons are bonded via substituents at their respective 4-positions, the substituents include hydrocarbylenebis(carbonyloxy) groups (-OOC-R 2 -COO-), hydrocarbylenediamino group (-HN-R 2 -NH-), hydrocarbylenebis(carbonylamino) group (-HNCO-R 2 Examples include -CONH-) and R 2 For example, this is a hydrocarbylene group having 1 to 30 carbon atoms.

[0066] An acyloxy group can be used as a substituent at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton. Examples of compounds having an acyloxy group at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton include esters of 2,2,6,6-tetramethyl-4-piperidinol and carboxylic acids. Examples of such carboxylic acids include linear or branched aliphatic carboxylic acids having 8 to 20 carbon atoms.

[0067] The hydrocarbon oil content in the coolant for the immersion cooling system is preferably 99.9% by mass or more, and may be 100% by mass, based on the total amount of coolant for the immersion cooling system.

[0068] The coolant for the immersion cooling system in one embodiment is a coolant for the immersion cooling system consisting solely of the hydrocarbon oil described above.

[0069] The content of amine-based antioxidants in the coolant for the immersion cooling system is less than 0.01% by mass, preferably less than 0.001% by mass, and more preferably no amine-based antioxidants are present, based on the total amount of coolant for the immersion cooling system.

[0070] The coolant for the immersion cooling system may contain optional components. If the coolant for the immersion cooling system contains optional components, it is preferable that the content of the optional components be 0.1% by mass or less relative to the total amount of the coolant for the immersion cooling system.

[0071] <Optional ingredients> The coolant for the immersion cooling system of this embodiment may contain optional components other than the hydrocarbon oil described above. Examples of such optional components include antioxidants other than amine-based antioxidants, metal deactivators, rust inhibitors, defoamers, metal-based detergents, anti-wear agents, viscosity index improvers, pour point depressants, mist inhibitors, and deemulsifiers.

[0072] <<Other antioxidants>> Other antioxidants include, specifically, peroxide decomposing agents such as phenolic antioxidants, sulfur-based antioxidants, and sulfur-phosphorus-based antioxidants.

[0073] ≪Metal deactivator≫ Examples of metal deactivators include benzotriazole compounds, toltriazole compounds, thiadiazole compounds, and imidazole compounds.

[0074] Antifoaming agent Examples of defoaming agents include silicone-based defoaming agents.

[0075] Viscosity index improvers Examples of viscosity index improvers include non-dispersible or dispersed poly(meth)acrylate-based viscosity index improvers, non-dispersible or dispersed olefin-(meth)acrylate copolymer-based viscosity index improvers, styrene-maleic anhydride copolymer-based viscosity index improvers, and mixtures thereof.

[0076] ≪Pour point depressants≫ Examples of pour point depressants include polymethacrylate-based polymers that are compatible with the hydrocarbon oils mentioned above.

[0077] ≪Mist Prevention Agent≫ Examples of mist suppressants include ethylene-propylene copolymers, polymethacrylates, polyisobutylenes, and polybutenes. The average molecular weight of these compounds used as mist suppressants is typically between 10,000 and 8,000,000.

[0078] The coolant for the immersion cooling system in this embodiment preferably has an acid value of 0.1 mg KOH / g or less, and more preferably 0.05 mg KOH / g or less. If the acid value of the coolant for the immersion cooling system in this embodiment is below the above preferred upper limit, the corrosion prevention effect on the metal used in the immersed electronic equipment is further improved. Acid value refers to the total acid value measured in accordance with JIS K 2501 "Petroleum products and lubricating oils - Neutralization value test method". [Examples]

[0079] The effects of the present invention will be described in detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0080] <Formulation of coolant for immersion cooling systems> Cooling fluids for immersion cooling systems were prepared using the formulation ratios shown in Tables 1 to 6 for Examples 1 to 13, as well as for Comparative Examples 1 and 2. The values ​​in Tables 1 to 6 represent mass percentages based on the total volume of the immersion cooling system cooling fluid.

[0081] The details of each component contained in the coolant for liquid immersion cooling are shown below. <Carbonized Hydrogen Oil> (A-1): Soybean oil (40℃ dynamic viscosity: 44.9mm 2 / s, 5% retention temperature: 412℃, 95% retention temperature: 554℃, %C P 80.4, %C N 19.6、%C A :0) (A-2): ポリ-α-オレフィン (40℃ kinematic viscosity: 45.8mm 2 / s, 5% retention temperature: 463℃, 95% retention temperature: 581℃, %C P 91.6、%C N 8.4、%C A :0) (A-3): ポリ-α-オレフィン (40℃ dynamic viscosity: 48.0mm 2 / s, 5% retention temperature: 426℃, 95% retention temperature: 593℃, %C P 90.9, %C N 9.1、%C A :0) (A-4): ポリ-α-オレフィン (40℃ kinematic viscosity: 17.4mm 2 / s, 5% retention temperature: 412℃, 95% retention temperature: 487℃, %C P 91.4、%C N 8.6、%C A :0) (A-5): Methyl iron oil (kinematic viscosity at 40℃: 8.7 mm) 2 / s, 5% retention temperature: 271℃, 95% retention temperature: 418℃, %C P 65.3, %C N 34.7, %C A :0) (A-6): Yarn oil (kinematic viscosity at 40℃: 37.8 mm) 2 / s, 5% retention temperature: 377℃, 95% retention temperature: 520℃, %C P 71.0、%C N 29.0, %C A :0) (A-7): 100% plant-derived carbonized hydrogen oil (product name "SynNova 4 TM Base Oil, manufactured by Novvi, dynamic viscosity at 40°C: 19.7 mm 2 / s, 5% distillation temperature: 425°C, 95% distillation temperature: 461°C, %C P : 93.1, %C N : 6.9, %C A : 0) (A-8): Mineral oil (kinematic viscosity at 40°C: 34.8 mm 2 / s, 5% distillation temperature: 413°C, 95% distillation temperature: 528°C, %C P : 84.3, %C N : 15.7, %C A : 0)

[0082] (a-1): Mineral oil (kinematic viscosity at 40°C: 54.8 mm 2 / s, 5% distillation temperature: 319°C, 95% distillation temperature: 438°C, %C P : 38.3, %C N : 49.6, %C A : 12.2) (a-2): Poly-α-olefin (kinematic viscosity at 40°C: 5.0 mm 2 / s, 5% distillation temperature: 308°C, 95% distillation temperature: 332°C, %C P : 85.5, %C N : 12.5, %C A : 2) (a-3): Ester oil (a 78:22 mixed oil of the trade name "UNISTAR (registered trademark) H-281R" and the trade name "UNISTAR (registered trademark) H-381R", both manufactured by NOF Corporation) (kinematic viscosity at 40°C: 28.6 mm 2 / s, 5% distillation temperature: 408°C, 95% distillation temperature: 615°C, %C P : 31.6, %C N : 68.4, %C A : 0)

[0083] <Antioxidant> (B-1): Phenolic antioxidant (compound name: octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (b-1): Amine-based antioxidant (compound name: monobutylphenyl monooctylphenylamine) (b-2): Amine-based antioxidant (compound name: N-dodecylphenyl-1-naphthylamine)

[0084] [Assessment of impact on electronic devices] 50 mL of the immersion cooling system coolant for each example was added to a 100 mL beaker, and two capacitors (AVX, SCCR20B335PRBLE) with their insulation stripped and terminals cut were immersed in the beaker. The length (mm) of the swelling and elongation of the insulating material of the capacitors after immersion at 80°C for one week was measured to evaluate the effect on electronic equipment (swelling ability). The average values ​​of the measured lengths and the results evaluated according to the following criteria are shown in Tables 1 to 6. ≪Immersion Test Judgment Criteria≫ A: The length of the capacitor's insulating material that has swollen and stretched is less than 0.29 mm. B: The length of the capacitor's insulating material that has swollen and stretched is between 0.29 mm and 0.39 mm. C: The length of the capacitor's insulating material that has swollen and stretched is 0.39 mm or more.

[0085] [Evaluation of kinematic viscosity] Tables 1-6 show the kinematic viscosity of immersion cooling fluids for various examples at 40°C, 80°C, and 100°C, measured in accordance with JIS K2283:2000.

[0086] [Evaluation of distillation properties] Tables 1-6 show the 5% and 95% distillation temperatures of the coolant for each example of an immersion cooling system, measured under the following conditions in accordance with JIS K2254:2018. <Measurement Conditions> (1) When the endpoint (100% distillation temperature) is 600°C or higher Equipment: Shimadzu Corporation GC-2030 Column: UA-1HT (30m × 0.5mm I.D. × 0.10μm) Carrier gas: Helium 15 mL / min Detector: FID Detector temperature: 400℃ Inlet temperature: PTV 40~380℃ Column temperature: 40-380°C (6 min) Heating rate: 10℃ / min Injection volume: 0.5 μL (carbon disulfide solution) (2) When the endpoint (100% distillation temperature) is less than 600°C Equipment: Shimadzu Corporation GC-2010plus Column: UA-1HT (30m × 0.5mm I.D. × 0.10μm) Carrier gas: Helium 15 mL / min Detector: FID Detector temperature: 360℃ Inlet temperature: PTV 40~380℃ Column temperature: 40-350°C (6 min) Heating rate: 10℃ / min Injection volume: 0.5 μL (carbon disulfide solution)

[0087] [Evaluation of Acid Value] Tables 1-6 show the acid values ​​of the coolants for each example of immersion cooling systems, measured in accordance with JIS K2501:2003. From the perspective of further suppressing metal leaching, a value of 0.1 or less was deemed acceptable.

[0088] [Evaluation of lightfastness] 80 mL of the immersion cooling system coolant for each example was sealed in a 100 mL screw-top bottle, left to stand by a window for 4 days, and then the color was observed in accordance with JIS K2580.

[0089] [Table 1]

[0090] [Table 2]

[0091] [Table 3]

[0092] [Table 4]

[0093] [Table 5]

[0094] [Table 6]

[0095] As shown in Tables 1-6, it was confirmed that the coolant for the immersion cooling system in the example achieved both light resistance and an effect of suppressing the impact on the immersed electronic equipment, compared to the coolant for the immersion cooling system in the comparative example.

[0096] 5% distillation temperature is 320°C or higher, %C N The coefficient of viscosity is 30.0 or less, and the kinematic viscosity at 40°C is 11.5 mm³. 2 The coolant for the immersion cooling system in the example having a 5% distillation temperature of less than 320°C and %C N Comparative Example 1 had a value greater than 30.0, and the 5% distillation temperature was less than 320°C, with a kinematic viscosity of 11.5 mm³ at 40°C. 2 Compared to the coolant for the immersion cooling system in Comparative Example 4, which was less than / s, swelling of the capacitor's insulating material was suppressed. Therefore, it was confirmed that the coolant used in the immersion cooling system of the example had a more suppressed effect on the electronic equipment being immersed. The coolant used in Comparative Example 5 for the immersion cooling system had a high acid value because it used ester oil instead of hydrocarbon oil. Therefore, it is presumed that the coolant for the immersion cooling system in Comparative Example 5 is more likely to dissolve metals from electronic equipment compared to the coolant for the immersion cooling system in the Example. [Explanation of Symbols]

[0097] 10: Immersion cooling system, 1: Immersion tank, 3: Heat exchanger, 5: Pump, 7: Cooling device

Claims

1. A coolant for an immersion cooling system, which is filled as a coolant in the immersion tank of the immersion cooling system, and which is a coolant for an immersion cooling system that comes into direct contact with the insulating material of electronic equipment containing insulating material in the immersion cooling system. The coolant for the immersion cooling system contains hydrocarbon oil in an amount of 50% by mass or more relative to the total amount of coolant for the immersion cooling system, and does not contain an amine-based antioxidant, or if it further contains the amine-based antioxidant, the amount of the amine-based antioxidant is less than 0.01% by mass relative to the total amount of coolant for the immersion cooling system. The 5% distillation temperature is 320°C or higher, and the %CN content is 30.0 or less. The kinematic viscosity at 40°C is 11.5 mmHg. ２ A coolant for immersion cooling systems with a temperature of 1 / s or higher.

2. A coolant for an immersion cooling system, which is used in an immersion cooling system, comprising an immersion tank for cooling electronic equipment, a heat exchanger for cooling the immersion cooling system coolant, and a pump for circulating the immersion cooling system coolant between the immersion tank and the heat exchanger. The coolant for the immersion cooling system contains hydrocarbon oil in an amount of 50% by mass or more relative to the total amount of coolant for the immersion cooling system, and does not contain an amine-based antioxidant, or if it further contains the amine-based antioxidant, the amount of the amine-based antioxidant is less than 0.01% by mass relative to the total amount of coolant for the immersion cooling system. The 5% distillation temperature is 320°C or higher, and the %CN content is 30.0 or less. The kinematic viscosity at 40°C is 11.5 mmHg. ２ A coolant for immersion cooling systems with a temperature of 1 / s or higher.

3. The coolant for the immersion cooling system according to claim 1 or 2, wherein the electronic device is a computer server, a server motherboard, or a microprocessor.

4. %C Ｎ A coolant for an immersion cooling system according to claim 1 or 2, wherein the coefficient is 0.5 or more and 30.0 or less.

5. The kinematic viscosity at 40°C is 25 mm². ２ A coolant for an immersion cooling system according to claim 1 or 2, wherein the coolant is 1 / s or more.

6. The coolant for an immersion cooling system according to claim 1 or 2, wherein the hydrocarbon oil is a poly-α-olefin.

7. The coolant for an immersion cooling system according to claim 1 or 2, wherein the hydrocarbon oil is a hydrocarbon oil having carbon derived from biomass.

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