Refrigerant composition and cooling system

Abstract

The present invention provides a refrigerant composition and a cooling system capable of achieving excellent cooling efficiency when used for a liquid-cooling type cooling device provided with a heat exchange unit having a narrow flow path. A refrigerant composition according to the present invention comprises a refrigerant and a nanomaterial. When the viscosity of the refrigerant composition at a shear rate of 10 s-1 at 25°C is defined as viscosity η10, when the viscosity of the refrigerant composition at a shear rate of 1000 s-1 at 25°C is defined as viscosity η1000, and when the viscosity of the refrigerant composition at a shear rate of 5000 s-1 at 25°C is defined as viscosity η5000, the viscosity η1000 is the smallest among the viscosity η10, the viscosity η1000, and the viscosity η5000.

Description

Refrigerant compositions, cooling systems 【0001】 This invention relates to a refrigerant composition and a cooling system. 【0002】 A server has heat-generating components such as a GPU (Graphics Processing Unit) and a CPU (Central Processing Unit). Various methods have been proposed for cooling the heat-generating components within a server. For example, Patent Document 1 discloses a cooling system that includes a cold plate using a refrigerant composition, which is a liquid heat-transporting fluid. 【0003】 Japanese Patent Publication No. 2024-039232 【0004】 In recent years, there has been a growing demand for even greater cooling efficiency in cooling systems. In particular, due to the miniaturization of devices, the flow paths of refrigerant compositions are becoming increasingly narrower, and there is a need for improved cooling efficiency in liquid-cooled cooling systems that include cold plates with narrow flow paths and heat exchange parts such as silicon semiconductor chips with built-in narrow flow paths. The present inventors investigated the cooling efficiency of a cooling system using conventionally known refrigerant compositions disclosed in Patent Document 1 and other documents, and found that it did not reach the level required today, and that further improvements were necessary. 【0005】 In view of the above circumstances, the present invention aims to provide a refrigerant composition that can achieve excellent cooling efficiency when applied to a liquid-cooled cooling device equipped with a heat exchange section having a narrow flow path. Furthermore, the present invention also aims to provide a cooling system. 【0006】 The inventors have found that the above problems can be solved by the following configuration. 【0007】 (1) A refrigerant composition comprising a refrigerant and a nanomaterial, wherein the shear rate at 25°C is 10s. －１ The viscosity of the refrigerant composition is set to viscosity η10, and the shear rate at 25°C is 1000 s. －１ The viscosity of the refrigerant composition is set to viscosity η 1000, and the shear rate at 25°C is 5000 s. －１(1) A refrigerant composition in which, when the viscosity of the refrigerant composition is set to viscosity η5000, the viscosity η1000 is the smallest among viscosity η10, viscosity η1000, and viscosity η5000. (2) The refrigerant composition according to (1), wherein the nanomaterial is fibrous or plate-shaped. (3) The refrigerant composition according to (1) or (2), wherein the nanomaterial comprises a material selected from the group consisting of carbon nanomaterials, metal nanomaterials, and boron nitride nanomaterials. (4) The refrigerant composition according to any one of (1) to (3), wherein the nanomaterial comprises carbon nanotubes. (5) The refrigerant composition according to any one of (1) to (4), wherein the refrigerant composition comprises aggregates of nanomaterials. (6) The refrigerant composition according to any one of (1) to (5), wherein the refrigerant is selected from the group consisting of water, alcohol-based solvents, glycol-based solvents, and glycol ether-based solvents. (7) A cooling system comprising the refrigerant composition according to any one of (1) to (6). 【0008】 According to the present invention, a refrigerant composition can be provided that can achieve excellent cooling efficiency when applied to a liquid-cooled cooling device equipped with a heat exchange section having a narrow flow path. Furthermore, according to the present invention, a cooling system can be provided. 【0009】 This figure shows one embodiment of the cooling system of the present invention. 【0010】 The present invention will now be described in detail. The following descriptions of constituent elements may be based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In this specification, numerical ranges expressed using "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits. 【0011】The refrigerant composition of the present invention is characterized by containing nanomaterials and exhibiting predetermined viscosity characteristics. The predetermined viscosity characteristics refer to the fact that viscosity η1000, described later, is lower than viscosity η10 and viscosity η5000. When the refrigerant composition flows through a narrow channel arranged in a heat exchange section such as a cold plate, the refrigerant composition flows efficiently in the center of the channel, but its flow is slow near the channel walls. If nanomaterials are included in the slow-flowing region of the refrigerant composition near the channel walls, heat is more easily transferred from the channel walls to the refrigerant composition, resulting in improved cooling efficiency in the cooling system. Furthermore, as mentioned above, when the refrigerant composition flows through a narrow channel, it flows more easily in the center of the channel compared to near the channel walls, and shear stress is applied to the refrigerant composition. From the viewpoint of cooling efficiency, it is desirable for the refrigerant composition to flow smoothly. The inventors have found that when the refrigerant composition exhibits predetermined viscosity characteristics when flowing through a narrow channel, the refrigerant composition flows more easily in the center of the channel, resulting in improved cooling efficiency in the cooling system. The exact reasons why the refrigerant composition flows more easily are unknown, but the following is speculated. First, when the refrigerant composition flows from the refrigerant supply channel into the narrow channel within the heat exchange section, the shear force on the refrigerant composition increases. In this case, if the refrigerant composition of the present invention has a reduced viscosity η, it becomes easier for the refrigerant composition to enter the narrow channel from the refrigerant supply channel, and as a result, the flow of the refrigerant composition in the center of the channel becomes smoother. Furthermore, as mentioned above, when the refrigerant composition flows through a narrow channel, there is a region near the wall of the channel where the flow of the refrigerant composition is slow. On the other hand, by including nanomaterials in the refrigerant composition, the thickness of the above region is reduced, which in turn reduces pressure loss, increases the amount of refrigerant composition that flows, and improves cooling efficiency. 【0012】 The refrigerant composition of the present invention comprises a refrigerant and a nanomaterial, and has a shear rate of 10 s at 25°C. －１ The viscosity of the refrigerant composition is set to viscosity η10, and the shear rate at 25°C is 1000 s. －１ The viscosity of the refrigerant composition is set to viscosity η 1000, and the shear rate at 25°C is 5000 s.－１ When the viscosity of the refrigerant composition is set to viscosity η5000, viscosity η1000 is the smallest among viscosity η10, viscosity η1000, and viscosity η5000. The materials contained in the refrigerant composition and their properties are described in detail below. 【0013】 <Refrigerant> The refrigerant composition of the present invention contains a refrigerant. The type of refrigerant is not particularly limited, and known refrigerants can be used. Examples of refrigerants include water and organic solvents. Water and organic solvents may be used in combination. The type of organic solvent is not particularly limited, and known organic solvents can be used, such as alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, amide-based solvents, ester-based solvents, and halogen-based solvents. These solvents may be used in combination. Among these, alcohol-based solvents, glycol-based solvents, or glycol ether-based solvents are preferred because they provide superior cooling efficiency to the cooling system to which the refrigerant composition of the present invention is applied (hereinafter also simply referred to as "the superior effect of the present invention"). Ultrapure water can also be used as the water. Ultrapure water used in the present invention refers to highly purified water in which impurities such as ions, fine particles, organic matter, and microorganisms are suppressed to extremely low concentrations. Because ultrapure water has very low electrical conductivity and high homogeneity, when used as a refrigerant, it has the characteristic of contributing to the stabilization and improvement of thermal conductivity and the avoidance of electronic equipment failure in the event of liquid leakage. The electrical conductivity of ultrapure water should ideally be 15 MΩcm or higher. The production of ultrapure water involves a combination of multiple processes, including ion exchange resin treatment, reverse osmosis membrane filtration, ultrafine filtration, and ultraviolet sterilization, to thoroughly remove impurities. 【0014】 Examples of alcoholic solvents include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, and octanol. 【0015】 Examples of glycol-based solvents include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol. 【0016】 Examples of glycol ether solvents include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether. 【0017】 The refrigerant is preferably selected from the group consisting of water, alcohol-based solvents, glycol-based solvents, and glycol ether-based solvents, and preferably contains water and a solvent selected from the group consisting of alcohol-based solvents, glycol-based solvents, and glycol ether-based solvents (hereinafter also referred to as "specific solvent"). When the refrigerant contains water and the specific solvent, the content of the specific solvent is preferably 5 to 45% by mass, and more preferably 15 to 35% by mass, based on the total mass of the refrigerant. 【0018】 The refrigerant content is not particularly limited, but in terms of achieving superior effects of the present invention, it is preferably 80.00% by mass or more and less than 100% by mass, more preferably 90.00% to 99.99% by mass, and even more preferably 95.00% to 99.95% by mass, relative to the total mass of the refrigerant composition. 【0019】<Nanomaterials> The refrigerant composition of the present invention contains nanomaterials. Nanomaterials mean materials whose size in at least one one-dimensional direction in three-dimensional space is in the nanosize range (0.1 to 100 nm). The shape of the nanomaterials is not particularly limited and includes, for example, fibrous, plate-like, and particulate shapes. Fibrous means a shape that extends in one direction and whose maximum length is five times or more the maximum length of the cross section perpendicular to the length direction. Plate-like means that there is at least one pair of opposing faces and the length between the faces (i.e., thickness) is shorter than the length in the direction parallel to the faces (for example, the length and width if the face is roughly rectangular, or the diameter if the face is roughly circular). Particulate means a shape in which the ratio of the maximum diameter to the minimum diameter of the particles (maximum diameter / minimum diameter) is less than 5. As for the shape of the nanomaterials, fibrous or plate-like shapes are preferred in that they provide superior effects of the present invention. 【0020】 When the nanomaterial is in the form of a flat plate, the shape of the surface is not particularly limited and examples include polygonal shapes such as triangular and hexagonal shapes, as well as circular shapes. Among these, polygonal shapes with hexagons or more, or circular shapes are preferred, and hexagonal shapes or circular shapes are more preferred. In this specification, a circular shape means a shape in which, when the irregularities of the nanomaterial that are 10% or less of the average equivalent diameter of the circle are ignored, the number of sides on the main surface having a length of 50% or more of the average equivalent diameter of the circle is 0 per nanomaterial. In this specification, a hexagonal shape means a shape in which, when the irregularities of the nanomaterial that are 10% or less of the average equivalent diameter of the circle are ignored, the number of sides on the main surface having a length of 20% or more of the average equivalent diameter of the circle is 6 per nanomaterial. The hexagonal nanomaterial may have acute or obtuse angles in its hexagonal shape. 【0021】The materials constituting the nanomaterial are not particularly limited and may be organic or inorganic. The nanomaterial may, for example, contain carbon atoms, metal atoms, or boron nitride. If the material contains metal atoms, the nanomaterial may be composed of, for example, a metal or a metal oxide. As for the nanomaterial, carbon nanomaterials, metal nanomaterials, or boron nitride nanomaterials are preferred in that they exhibit superior effects of the present invention. Carbon nanomaterials refer to materials that are mainly composed of carbon atoms and structured at the nanoscale. Examples of carbon nanomaterials include carbon nanotubes, graphite, graphene, graphene oxide, carbon nanohorns, and fullerenes. Metal nanomaterials refer to materials that are composed of metal and structured at the nanoscale. Examples of metal atoms constituting metal nanomaterials include noble metal atoms, with silver, gold, aluminum, copper, rhodium, nickel, or platinum being preferred, and silver being more preferred. Boron nitride nanomaterials refer to materials that are composed of boron nitride and structured at the nanoscale. 【0022】 In the refrigerant composition of the present invention, the particle size (D50) of the nanomaterial is not particularly limited, but 0.03 to 1000 nm is preferred, and 0.05 to 150 nm is more preferred, in terms of achieving superior effects of the present invention. A method for measuring the particle size (D50) of the nanomaterial is to determine it by calculation using the laser scattering method. 【0023】In the refrigerant composition of the present invention, the nanomaterials may be aggregated. That is, the refrigerant composition of this invention may contain aggregates of nanomaterials. When the refrigerant composition contains the above aggregates, the thickness of the slow-flow region of the refrigerant composition near the wall of the flow path becomes thinner, resulting in an effect that lowers the viscosity of the refrigerant composition, increases the flow rate of the refrigerant composition, and improves the cooling effect. The diameter of the above aggregates is not particularly limited, but is preferably 1.0 to 140 μm, more preferably 1.5 to 70 μm, and even more preferably 2.0 to 50 μm. A method for measuring the diameter of the aggregates is to calculate it using the laser scattering method. The shape of the above aggregates is not particularly limited and may be spherical or irregular in shape. A method for preparing the above aggregates of nanomaterials is to adjust the type and content of the components used in the refrigerant composition of the present invention, and a method of letting the refrigerant composition of the present invention stand for a predetermined period of time. In cases where the mixture is in a metastable state immediately after preparation and then transitions to a stable state after some time, a method of letting it stand for a predetermined period of time to age it is preferably used as it can further enhance the effects of the present invention. 【0024】 The content of nanomaterials is not particularly limited, but in terms of superior effects of the present invention, it is preferably 0.001 to 10% by mass, more preferably 0.01 to 5.0% by mass, even more preferably 0.05 to 1.5% by mass, and most preferably 0.05 to 1.0% by mass, relative to the total mass of the refrigerant composition. More specifically, the content of nanomaterials is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.05% by mass, preferably 10% by mass or less, more preferably 5.0% by mass or less, even more preferably 1.5% by mass or less, even more preferably 1.0% by mass or less, even more preferably 0.25% by mass or less, even more preferably 0.20% by mass or less, and most preferably 0.15% by mass or less, relative to the total mass of the refrigerant composition. A combination of the above content ranges is preferably 0.01 to 0.25% by mass, more preferably 0.05 to 0.20% by mass, and even more preferably 0.05 to 0.15% by mass. 【0025】The refrigerant composition may contain materials other than the refrigerant and nanomaterials described above. Examples of other materials include dispersants, corrosion inhibitors, defoamers, and rust inhibitors. 【0026】 <Dispersant> The dispersant is not particularly limited as long as it is a compound that has the function of improving the dispersibility of nanomaterials, and known materials can be used. More specifically, examples of dispersants include polymeric dispersants and surfactants, with polymeric dispersants being preferred. Examples of polymeric dispersants include cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethylcellulose, ethyl hydroxyethylcellulose, nitrocellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropyl methylcellulose, carboxymethylcellulose, etc.), polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, hydrogenated nitrile butadiene rubber, starch, gelatin, polycarboxylic acid or its salts, and polystyrene sulfonic acid or its salts. The surfactant may be anionic surfactant, cationic surfactant, nonionic surfactant, or amphoteric surfactant. 【0027】 The amount of dispersant is not particularly limited, but in terms of achieving superior effects of the present invention, it is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass, and even more preferably 5 to 15 parts by mass, per 100 parts by mass of nanomaterial in the refrigerant composition. 【0028】 <Corrosion Inhibitors> Known corrosion inhibitors can be used as corrosion inhibitors, and metal corrosion inhibitors that prevent metal corrosion are particularly preferred. Examples of corrosion inhibitors include benzotriazole compounds, higher carboxylic acids, phosphate ester compounds, epoxy compounds, alkanethiol compounds, and Cu-based materials. Examples of Cu-based materials include Cu itself, copper oxide, copper hydroxide, brass, and bronze. 【0029】<Antifoaming agent> As the antifoaming agent, known antifoaming agents can be used. Examples of the antifoaming agent include silicone compounds and polymethacrylate compounds. 【0030】 <Rust inhibitor> As the rust inhibitor, known rust inhibitors can be used. Examples of the rust inhibitor include benzotriazole compounds and Si ethers. The Si ether is a compound in which an -OR group is directly bonded to silicon. For example, Si-(OR) ４ can be mentioned. R represents a substituent. Examples of the substituent include a hydrocarbon group and a halogenated hydrocarbon group in which a hydrogen atom of the hydrocarbon group is substituted with a halogen atom. 【0031】 Also, in the refrigerant composition, it is desirable to prevent the incorporation of metal ions (such as Fe and Cu) that promote oxidation and deterioration. Therefore, in order to stabilize trace amounts of metal ions incorporated in the flow path, metal ion sequestering agents (chelating agents) such as EDTA (ethylenediaminetetraacetic acid) and citrate may be included in the refrigerant composition. Further, the refrigerant composition may contain an organosilanease (silane coupling agent), a silicone oil such as polydimethylsiloxane (PDMS), and a high molecular weight silicon compound. These additives can function as protectants for the interface. Also, these additives can contribute to maintaining the stability of the refrigerant, hydrophobizing the silicon surface within the semiconductor chip, and forming a protective layer on the silicon surface. 【0032】 The total mass of the refrigerant and the nanomaterial in the refrigerant composition is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more with respect to the total mass of the refrigerant composition. The above content may be 100% by mass. 【0033】 <Properties> In the refrigerant composition of the present invention, the viscosity of the refrigerant composition at a shear rate of 10 s －１ at 25°C is defined as viscosity η10, and the viscosity of the refrigerant composition at a shear rate of 1000 s －１ at 25°C is defined as viscosity η1000, and the shear rate of 500*0 s －１When the viscosity of the refrigerant composition is set to viscosity η5000, viscosity η1000 is the smallest among viscosity η10, viscosity η1000, and viscosity η5000. The difference between viscosity η1000 and viscosity η10 (viscosity η10 - viscosity η1000) is not particularly limited, but in terms of achieving better effects of the present invention, it is preferably 0.5 mPa·s or more, more preferably 1.5 mPa·s or more, and even more preferably 2.5 mPa·s or more. The upper limit of the above difference is not particularly limited, but it is often 10 mPa·s or less. The difference between viscosity η1000 and viscosity η5000 (viscosity η5000 - viscosity η1000) is not particularly limited, but in terms of achieving better effects of the present invention, it is preferably 0.5 mPa·s or more, more preferably 1.0 mPa·s or more, and even more preferably 1.5 mPa·s or more. The upper limit of the above difference is not particularly limited, but it is often 10 mPa·s or less. 【0034】 The viscosity η1000 is not particularly limited as long as it is smaller than viscosity η10 and viscosity η5000, but in terms of achieving better effects of the present invention, it is preferably 10 mPa·s or less, more preferably 5.0 mPa·s or less, and even more preferably 2.0 mPa·s or less. The lower limit of viscosity η1000 is not particularly limited, but it is often 0.1 mPa·s or more, and more often 0.3 mPa·s or more. However, in this specification, if the viscosity η1000 is too low to be measured by the measurement method described later, the viscosity η1000 shall be set to 0.1 mPa·s, which is the measurement limit of the apparatus. The viscosity η10 is not particularly limited as long as it satisfies the above-mentioned relationship with viscosity η1000 and viscosity η5000, but in terms of achieving better effects of the present invention, it is preferably 1.0 to 200 mPa·s, more preferably 1.0 to 50 mPa·s, and even more preferably 1.0 to 10 mPa·s. The viscosity η5000 value is not particularly limited as long as it satisfies the above-mentioned relationship with viscosity η1000 and viscosity η10, but in terms of superior effects of the present invention, 1.0 to 100 mPa·s is preferred, 1.0 to 50 mPa·s is more preferred, and 1.0 to 20 mPa·s is even more preferred. 【0035】The method for adjusting the magnitudes of the viscosity values ​​η10, η1000, and η5000 described above is not particularly limited, and the viscosity of the refrigerant composition of the present invention can be adjusted by adjusting the type and content of the components used in the refrigerant composition of the present invention. For example, the viscosity of the refrigerant composition of the present invention can be adjusted by selecting the type of nanomaterial used. The viscosity of the refrigerant composition of the present invention can also be adjusted by whether or not a dispersant is used, and by the type of dispersant. Furthermore, the viscosity of the refrigerant composition of the present invention can also be adjusted by the manufacturing method used to produce the nanomaterial. For example, the viscosity of the refrigerant composition of the present invention can be adjusted by adjusting the mixing process between the refrigerant and the nanomaterial. Adjustments to the mixing process include, for example, adjusting the stirring speed during mixing and adjusting the mixing time. 【0036】 For measuring viscosity η10 and viscosity η1000, a coaxial double-cylinder rheometer (ONRH rheometer, probe (inner cylinder) made of SUS, outer glass cylinder rotates, gap between outer and inner cylinder is 1 mm, manufactured by Daisai Giken Co., Ltd.) was used at a liquid temperature of 25°C, with a shear rate of 1000 to 0.1 s. －１ A method for measuring viscosity η10 and viscosity η1000 is performed by changing the range within the specified parameters. More specifically, viscosity η10 and viscosity η1000 are measured using a coaxial double-cylinder rheometer ONRH-1 manufactured by Daisai Giken Co., Ltd. This rheometer employs a glass outer cylinder, which has advantages such as allowing confirmation of the liquid state and minimizing the exposure of the sample to the outside air. As mentioned above, the inner cylinder is made of stainless steel, and the distance between the outer and inner cylinders is 1 mm. The measurement is performed using a water jacket at a liquid temperature of 25°C for 0.1 to 1000 s. －１ During this time, the shear rate was changed by repeating the acceleration / deceleration process three times, and the viscosity was measured. The average value of the second and third measurements was taken as η10 and viscosity η1000. Furthermore, for the measurement of viscosity η5000, a cone-plate rheometer (MCR301 rheometer, cone plate model number CP50-1 (diameter 50 mm, cone angle 1 degree) was used, the cone plate rotates, both the rheometer and cone plate manufactured by Anton Paar) was used at a liquid temperature of 25°C, with a shear rate of 5000 to 2000 s. －１The method for measuring viscosity η5000 will be implemented by changing the value within the specified range. More specifically, viscosity η5000 will be measured using an Anton Paar MCR301 rheometer. A cone plate: CP50-1 (diameter 50 mm, cone angle 1 degree) will be used for the measurement, and the measurement will be performed at a liquid temperature of 25°C. The measurement will first involve setting the shear rate to 5000 s. －１ Increase it to that point, and then increase the shear rate to 2000 s －１ Gradually decelerate until 2000s －１ If it drops to that point, then 5000s again. －１ It accelerates to 5000s －１ The viscosity at that time is measured by repeating the deceleration / acceleration operation twice, and the two 5000s obtained from the two deceleration / acceleration operations are measured. －１ Let the average viscosity value at that time be defined as viscosity η 5000. 【0037】 When a semiconductor chip and a refrigerant composition come into contact, such as when the refrigerant composition is flowed through a channel embedded in a semiconductor chip, it is desirable to maintain the pH of the refrigerant composition at neutral, weakly acidic, or weakly alkaline, because the semiconductor materials silicon (Si) and silicon oxide film (SiO2) are easily dissolved in strongly acidic or strongly alkaline environments. Here, neutral means a pH in the range of greater than 6.0 and less than 8.0, weakly acidic means a pH in the range of 4.5 to 6.0, and weakly alkaline means a pH in the range of 8.0 to 9.5. Alternatively, pH buffering agents such as boric acid and phosphate compounds may be added to the refrigerant composition to maintain a pH near neutral. 【0038】<Cooling System> The refrigerant composition of the present invention is suitably used as a heat transfer medium in a cooling system. In the cooling system of the present invention, the configuration is not particularly limited as long as the refrigerant composition of the present invention is used. Figure 1 shows one embodiment of the cooling system of the present invention. The cooling system 10 shown in Figure 1 has a cold plate 12, a refrigerant composition supply passage 14, a refrigerant composition discharge passage 16, and a cooling unit 18. A heating element (not shown) is placed on the cold plate 12 of the cooling system 10, so that heat exchange occurs between the refrigerant composition of the present invention flowing through the cold plate 12 and the heating element, and the heating element is cooled. Each component will be described in detail below. 【0039】 The cold plate 12 contains a channel through which the refrigerant composition of the present invention flows. The shape of the channel is not particularly limited, and known channel shapes can be used. In addition, multiple fins may be arranged inside the channel, and the shape of the fins is not particularly limited. As described above, a heating element is placed on the cold plate 12 directly or via another component, and the refrigerant composition flowing through the channel receives heat from the heating element, thereby performing heat exchange. 【0040】 The refrigerant composition supply passage 14 is connected to the cold plate 12, and the refrigerant composition of the present invention is supplied to the cold plate 12 through the refrigerant composition supply passage 14. More specifically, the refrigerant composition supply passage 14 is in communication with the flow path within the cold plate 12. The refrigerant composition discharge passage 16 is connected to the cold plate 12, and the refrigerant composition that has passed through the cold plate 12 is discharged through the refrigerant composition discharge passage 16. More specifically, the refrigerant composition discharge passage 16 is in communication with the flow path within the cold plate 12. The cooling unit 18 cools the refrigerant composition of the present invention that has passed through the refrigerant composition discharge passage 16 and introduces it into the refrigerant composition supply passage 14. The configuration of the cooling unit 18 is not particularly limited, and a known configuration may be adopted. The cooling unit 18 houses, for example, a cooler and a pump. The cooler is a device that cools the refrigerant composition from the refrigerant composition discharge passage 16. The pump pumps the refrigerant composition cooled by the cooler toward the refrigerant composition supply passage 14. 【0041】The circulation of the refrigerant composition within the above-mentioned cooling system is described below. First, the refrigerant composition of the present invention is pumped by a pump (not shown) in the cooling unit 18 and supplied to the refrigerant composition supply passage 14. Next, the pumped refrigerant composition of the present invention is supplied to the cold plate 12 via the refrigerant composition supply passage 14. A heating element (not shown) is placed on the cold plate 12, and heat exchange takes place between the refrigerant composition of the present invention flowing through the flow path in the cold plate 12 and the heating element. As a result, the heating element is cooled and the refrigerant composition of the present invention is heated. The heated refrigerant composition of the present invention is supplied to the refrigerant composition discharge passage 16 and returned to the cooling unit 18 through the refrigerant composition discharge passage 16. In the cooling unit 18, the refrigerant composition of the present invention is cooled by a cooler (not shown), and the cooled refrigerant composition is pumped again and supplied to the refrigerant composition supply passage 14. Normally, when comparing the refrigerant composition supply passage 14 with the flow path in the cold plate 12, the flow path in the cold plate 12 is narrower, and as described above, the refrigerant composition of the present invention is subjected to shearing within this flow path. 【0042】 Although the above description details an embodiment using a cold plate in the cooling system, the cooling system of the present invention is not limited to the above embodiment, as long as the refrigerant composition of the present invention is used. In particular, the refrigerant composition of the present invention may be applied to other heat exchange parts other than a cold plate. For example, a cooling system may be provided in which a flow path for the refrigerant composition is arranged within an electronic component including a heat-generating element, and the refrigerant composition of the present invention flows through this flow path to cool the heat-generating element. 【0043】A preferred application of the cooling system of the present invention is a direct liquid cooling system. This method involves forming fine channels for circulating a coolant on or inside a semiconductor chip, thereby directly cooling the semiconductor chip with a liquid. Using the coolant composition of the present invention as the coolant in a direct liquid cooling system can reduce pressure loss and increase cooling efficiency. For more details on configurations using the coolant composition in a direct liquid cooling system, see, for example, “Integrated Microfluidic Cooling and Interconnects for 2D and 3D Chips,” IEEE Transactions on Advanced Packaging (Volume: 33, Issue: 1, February 2010) (https: / / ieeexplore.ieee.org / abstract / document / 5423273). 【0044】 Another type of direct liquid cooling system uses pin-fin shaped fine channels for circulating a coolant over a semiconductor chip. Using the coolant composition of the present invention in this system can reduce pressure loss and improve cooling efficiency. For more details on using the coolant composition in a pin-fin type direct liquid cooling system, see, for example, “Integrated Silicon Microfluidic Cooling of a High-Power Overclocked CPU for Efficient Thermal Management,” IEEE Access (Volume: 10, Page(s): 59259 - 59269) (https: / / ieeexplore.ieee.org / document / 9785822). 【0045】Another application of the liquid-cooled cooling system equipped with a heat exchange section having a narrow flow path is lithium-ion batteries. When the refrigerant composition of the present invention is used in a lithium-ion battery, heat can be efficiently removed from the heat-generating parts inside the battery, thereby improving the battery's temperature control performance and contributing to the suppression of degradation due to overheating and improved safety. Furthermore, the refrigerant based on ultrapure water has high electrical insulation properties, which can reduce the risk of short circuits in narrow flow paths and complex cooling channels. As a result, stable cooling performance can be maintained for a long period in lithium-ion battery cooling systems, contributing to extending battery life and optimizing performance. 【0046】 The features of the present invention will be described in more detail below with reference to examples and comparative examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. 【0047】 <Example 1> First, an aqueous dispersion of MWCNTs (multiwalled carbon nanotubes) was prepared. Specifically, an aqueous dispersion was prepared by mixing water, a dispersant, and MWCNTs using the micro-slurry jet erosion (MS E) method. NanoCyl NC7000 was used as the MWCNT. The MWCNT content was 2% by mass relative to the total mass of the dispersion. Polyvinylpyrrolidone (PVP, manufactured by Nippon Shokubai Co., Ltd.) was used as the dispersant. The mass ratio of the dispersant content to the total mass of MWCNTs (mass of dispersant / mass of MWCNTs) was 0.1. 【0048】A mixed solvent of propylene glycol and water was prepared as a refrigerant, and refrigerant composition 1 was manufactured by mixing the mixed solvent with the MWCNT aqueous dispersion prepared above in a predetermined ratio using a low-frequency resonant acoustic mixer. The solvent in refrigerant composition 1 contained water and propylene glycol. The propylene glycol content in the solvent of refrigerant composition 1 was 25% by mass relative to the total mass of the solvent in refrigerant composition 1. The water content in the solvent of refrigerant composition 1 was 75% by mass relative to the total mass of the solvent in refrigerant composition 1. The mixing using the low-frequency resonant acoustic mixer was carried out at 90G for 5 minutes. The carbon nanotube content in the obtained refrigerant composition 1 was 0.1% by mass relative to the total mass of refrigerant composition 1. Carbon nanotubes are carbon nanomaterials and have a fibrous shape. 【0049】 <Comparative Examples 1 and 2> Refrigerant compositions C1 and C2 were prepared in the same manner as in Example 1, except that the carbon nanonanotube content in the refrigerant composition was changed to the values ​​shown in the table below. 【0050】 <Example 2> A refrigerant composition was prepared according to the same procedure as in Example 1, except that the liquid from Example 1 was allowed to stand at room temperature for the number of days shown in the table. After the specified number of days had elapsed, the mixture was shaken for 30 seconds using a shaker (IKA VORTEX3 shaker; https: / / www.ika.com / ja / Products-LabEq / Shakers-pg179 / VORTEX-3-3340000 / ) before use. 【0051】 <Examples 3-4 and Comparative Examples 2-3> Refrigerant compositions were prepared in the same manner as in Example 1, except that the carbon nanonanotube content in the refrigerant composition was changed to the values ​​shown in the table below. 【0052】 <Comparative Examples 4-5> Except for changing the mixing time using a low-frequency resonant acoustic mixer in the mixing of the mixed solvents to the values ​​shown in the table below, the refrigerant compositions were manufactured according to the same procedure as in Example 1. 【0053】<Example 5> A refrigerant hydrophobic material was produced in the same procedure as in Example 1, except that an AgNW (silver nanowire) aqueous standard ink (CHEMIPAZ Corporation) was used instead of an MWCNT (multilayer carbon nanotube) aqueous dispersion, and the amount used was adjusted to achieve the AgNW content shown in the table below. 【0054】 <Example 6> A refrigerant composition was prepared in the same procedure as in Example 1, except that a water dispersion of NanoBorNT-80 (Philgen Co., Ltd.), an aqueous solution containing boron nitride nanotubes, was used instead of an aqueous dispersion of MWCNT (multiwall carbon nanotubes), and the amount used was adjusted to achieve the boron nitride nanotube content shown in the table below. 【0055】 <Viscosity Measurement> A coaxial double-cylinder rheometer (ONRH rheometer, probe made of SUS, outer glass cylinder rotates, gap between outer and inner cylinder is 1 mm, manufactured by Daisai Giken Co., Ltd.) was used at a liquid temperature of 25°C, with a shear rate of 1000 to 0.1 s. －１ The viscosity (viscosity η10 and viscosity η1000) of the refrigerant compositions obtained in each example and comparative example was measured by changing the viscosity within the specified range. As described above, the measurement was performed using a water jacket at a liquid temperature of 25°C for 0.1 to 1000 s. －１ During this time, the shear rate was changed by repeating the acceleration / deceleration process three times, and the viscosity was measured. The average of the second and third measurements was taken as the above-mentioned η10 and viscosity η1000. In addition, a cone-plate rheometer (MCR301 rheometer, cone plate model number CP50-1 (diameter 50 mm, cone angle 1 degree) was used, the cone plate rotates, both the rheometer and cone plate manufactured by Anton Paar) was used, and the shear rate was set from 5000 to 2000 s at a liquid temperature of 25°C. －１ The viscosity (viscosity η 5000) of the refrigerant compositions obtained in each example and comparative example was measured by changing the viscosity within the specified range. More specifically, the measurement was performed by first setting the shear rate to 5000 s. －１ Increase it to that point, and then increase the shear rate to 2000 s －１ Gradually decelerate until 2000s －１ If it drops to that point, then 5000s again. －１ It accelerates to 5000s －１The viscosity at that time is measured by repeating the deceleration / acceleration operation twice, and the two 5000s obtained from the two deceleration / acceleration operations are measured. －１ The average viscosity value was defined as viscosity η 5000. The results are summarized in the table below. 【0056】 <Particle Size Measurement> The particle size (D50) of the nanomaterials in the refrigerant compositions obtained in each example and comparative example was measured using the LA960 (laser scattering method, Horiba, Ltd.). A 405 nm LED light was used as the laser beam. A fitting model was created using monodisperse silica (spherical) of known diameter, which is a standard material, to obtain the desired particle size, and this model was also applied to the refrigerant compositions. 【0057】 <Measurement of aggregate size> The size of aggregates in the refrigerant composition was measured using the same measurement method as in <Particle size measurement> above, except that both 650 nm LED light and 405 nm LED light were irradiated as laser light. 【0058】 <Cooling Efficiency Evaluation> To measure the cooling efficiency, a cooling jacket was fabricated as described in Fig. 1 of the paper "Development of a Forced Flow Boiling Cooling Jacket for Narrow Channels in Electronic Equipment" (Kyushu University, AIST, SOHKi, Utsunomiya University) presented at the Japan Society of Mechanical Engineers Thermal Engineering Conference 2010. The dimensions were 60 mm in depth, 42 mm in width, and 12 mm in height. The inlet and outlet for the refrigerant composition were located on one side of the jacket. Inside the jacket, a copper heat transfer surface (30 mm x 30 mm) was placed with continuously machined V-shaped grooves (apex angle 90 degrees, pitch 1 mm), so that the liquid would flow from the longitudinal direction of the V-shaped grooves corresponding to the narrow channel. An aluminum heat transfer block simulating a GPU was placed in close contact with the aforementioned copper heat transfer surface. A pipe with an inner diameter of 6.5 mm was used to connect to the cooling jacket, and the flow rate was adjusted to 1 L / min. The refrigerant compositions obtained in each example and comparative example were supplied. The temperature of the refrigerant composition at the inlet was 25°C. The thermocouple's indicated temperature was set to 90°C. 【0059】The temperature of the cooling jacket was measured using an infrared thermograph (FLIR SC5000, manufactured by FLIR Systems Japan). After supplying each refrigerant composition, the cooling efficiency was evaluated after waiting for the temperature of the cooling jacket to stabilize. The in-plane average temperature of the cooling jacket was calculated, and a value of 100 was assigned to an in-plane average temperature of 25°C, and 100 to an in-plane average temperature of 60°C. Temperatures in between were divided equally, and the cooling efficiency was evaluated in the following order from highest to lowest: AA = 800 to 1000, A = 400 to less than 800, B = 300 to less than 400, C = 200 to less than 300, D = 100 to less than 200. 【0060】 In Table 1, the "CNT amount (mass%)" column represents the carbon nanotube content (mass%) relative to the total mass of the refrigerant composition. "-" in Comparative Example 1 indicates that no carbon nanotubes are present. In Table 1, the "Ag-NW amount (mass%)" column represents the silver nanowire content (mass%) relative to the total mass of the refrigerant composition. In Table 1, the "BN-NW amount (mass%)" column represents the boron nitride nanowire content (mass%) relative to the total mass of the refrigerant composition. In Table 1, the "Dispersion time" column represents the mixing time using a low-frequency resonant acoustic mixer. In Table 1, the "Time elapsed after adjustment" column indicates how many days after manufacturing the refrigerant composition the various measurements were performed. In Table 1, the "Particle size (μm)" column represents the measurement results of the <Particle size measurement> above. In Table 1, the "Agglomerate diameter (μm)" column represents the measurement results of the <Agglomerate size measurement>. In Table 1, the "Viscosity η 10 (mPa·s)" column represents the shear rate of 10s at 25°C. －１ This represents the viscosity of the refrigerant composition at 25°C. In Table 1, the column "Viscosity η 1000 (mPa·s)" represents the shear rate at 1000 s at 25°C. －１ This represents the viscosity of the refrigerant composition at 25°C. In Table 1, the column "Viscosity η 5000 (mPa·s)" represents the shear rate at 5000 s at 25°C. －１ This represents the viscosity of the refrigerant composition. 【0061】 【0062】 As shown in Table 1 above, the refrigerant composition of the present invention was confirmed to exhibit the desired effects. 【0063】10 Cooling system 12 Cold plate 14 Refrigerant composition supply passage 16 Refrigerant composition discharge passage 18 Cooling section

Claims

1. A refrigerant composition comprising a refrigerant and a nanomaterial, wherein the shear rate at 25°C is 10 s. －１ The viscosity of the refrigerant composition is set to viscosity η10, and the shear rate at 25°C is 1000 s. －１ The viscosity of the refrigerant composition is set to viscosity η 1000, and the shear rate at 25°C is 5000 s. －１ A refrigerant composition in which, when the viscosity of the refrigerant composition is set to viscosity η5000, the viscosity η1000 is the smallest among viscosity η10, viscosity η1000, and viscosity η5000.

2. The refrigerant composition according to claim 1, wherein the nanomaterial is fibrous or plate-shaped.

3. The refrigerant composition according to claim 1, wherein the nanomaterial comprises a material selected from the group consisting of carbon nanomaterials, metal nanomaterials, and boron nitride nanomaterials.

4. The refrigerant composition according to claim 1, wherein the nanomaterial includes carbon nanotubes.

5. The refrigerant composition according to claim 1, wherein the refrigerant composition comprises aggregates of the nanomaterial.

6. The refrigerant composition according to claim 1, wherein the refrigerant is selected from the group consisting of water, alcohol-based solvents, glycol-based solvents, and glycol ether-based solvents.

7. A cooling system comprising the refrigerant composition according to any one of claims 1 to 6.

Images