Dielectric fluid compositions containing low viscosity monoesters having improved low temperature performance - Patents.com

Abstract

The present invention relates to branched monoesters of formula (I) and to dielectric fluid compositions intended for use as cooling fluids for electrical equipment systems, comprising at least one of these branched monoesters of formula (I). The present invention also relates to a method for cooling electrical equipment systems by use of the dielectric fluid composition according to the invention.

Description

[Technical field]

[0001] TECHNICAL FIELD OF THEINVENTION The present invention relates to branched monoesters of formula (I) and to dielectric fluid compositions intended for use as cooling fluids for electrical equipment systems, comprising at least one of these branched monoesters of formula (I). The present invention also relates to a method for cooling electrical equipment systems by use of the dielectric fluid composition according to the invention.

[0002] 2. Background of the Invention In recent years, energy shortages and environmental issues have had a major impact on technological advances. In the automotive industry, reducing carbon dioxide emissions has become a top priority, and the demand for zero-emission vehicles fueled by renewable energy sources such as pure electric vehicles (EVs), hybrid electric vehicles (HEVs) and fuel cell electric vehicles is gradually increasing and is expected to increase significantly over the next two decades. The energy for such vehicles is supplied and stored in batteries that have a high specific energy density. Various types of batteries are available for EVs and HEVs, such as lithium nickel manganese cobalt oxide, lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt aluminium oxide, lithium manganese oxide and sodium-ion batteries.

[0003] To improve the performance of electric vehicles, large batteries with high current discharge are required. Due to their size and power output, these large batteries generate a lot of heat during rapid charge and discharge cycles at high current levels. Therefore, to prevent battery failure and extend battery life, the battery needs to be thermally managed by cooling or dissipating heat.

[0004] Furthermore, battery performance is temperature dependent: batteries only operate optimally in certain temperature ranges, depending on their type. Proper thermal management can therefore optimize battery performance.

[0005] Dielectric fluid means a fluid intended for use in low to high voltage applications, such as computers, transformers, capacitors, high voltage cables, switchgear, whose functions are to provide electrical insulation, suppress corona and arcing, and act as a coolant to carry and dissipate heat in such electrical applications. Dielectric fluids include, for example, mineral oil-based fluids, natural ester-based fluids, and synthetic ester-based fluids, such as polyol esters.

[0006] Mineral oil-based dielectric fluids have been widely used for a long time because they meet some of the above criteria, however, there is still a need to explore better dielectric fluids with better thermal management properties because pure mineral oil does not dissipate heat efficiently.

[0007] Furthermore, growing environmental awareness has led to an increased interest in so-called green technologies, especially in the automotive industry. Therefore, an ideal dielectric fluid should be biodegradable, non-toxic and renewable. Mineral oil-based dielectric fluids are poorly biodegradable, relatively toxic and have no renewable sources.

[0008] US Patent No. 5,949,017 discloses an electrical transformer containing an electrical insulating fluid comprising a high oleic oil composition as a replacement for mineral oil-based dielectric fluids. However, these dielectric fluids exhibit high viscosity compared to mineral oil, which is disadvantageous for heat dissipation.

[0009] WO 2013 / 159761 discloses a composition comprising an ester of a polyhydric alcohol esterified with a partially unsaturated fatty acid derived from vegetable oil, and its use as a cooling and insulating fluid for transformers. The esters used have a viscosity of about 30 mm. 2 It is a hyperbranched ester that exhibits a KV40 of 1.0001 / s and a pour point of approximately -50°C.

[0010] WO 2015 / 174992, US 2013 / 085090 or EP 3012316 disclose branched monoesters and lubricant compositions containing same, but these documents do not address performance in cooling electrical equipment systems.

[0011] EP 2908317 and EP 3138893 disclose dielectric fluid compositions suitable for use in dielectric fluid compositions, the ester composition comprising an ester of an alcohol and a branched carboxylic acid. Both documents teach the use of an ester composition comprising an ester of a branched carboxylic acid and a polyol.

[0012] GB 2525281 A1 relates to ester dielectric fluid compositions suitable for use in electrical devices (e.g., transformers). The ester comprises (a) one or more alcohols selected from C2 and C3 polyols, such as glycerol or ethylene glycol, and (b) one or more C4 to C6 polyols. 14 The dielectric fluid composition is derived from reaction with carboxylic acids, where at least one of the acids is a branched acid (e.g., 2-ethyl-hexanoic acid). One or more additives such as antioxidants, metal deactivators, or pour point depressants are also present. The dielectric fluid composition has a viscosity of about 16 mm. 2 / s and a pour point of about -60°C.

[0013] A low viscosity of the dielectric fluid is a crucial parameter as it allows for more efficient heat dissipation through more effective circulation, which in turn allows for better cooling of electrical devices. Thus, the viscosity properties of the dielectric fluid play an important role in heat dissipation.

[0014] Accordingly, the present invention aims to provide a novel dielectric fluid composition that has superior performance in cooling electrical equipment systems such as batteries, electric motors, electrical transformers, electrical capacitors, fluid filled electrical transmission lines, fluid filled power cables, computers, data centers and power electronics, etc. The novel dielectric fluid composition should not only have good electrical and thermal properties, but also be low viscosity, non-corrosive and low flammable while maintaining excellent low temperature performance.

[0015] BRIEF SUMMARY OF THE INVETION After extensive research, the inventors of the present invention have surprisingly found that the use of a dielectric fluid composition comprising a branched monoester of formula (I) as defined in the present invention as a heat transfer fluid for batteries and other electrical devices can dramatically improve the cooling performance of the electrical devices, especially at low temperatures. The challenge was to combine improved heat dissipation performance while still maintaining the excellent low temperature properties of the dielectric fluid composition.

[0016] Indeed, developing one dielectric fluid composition possessing these properties would represent a great advantage since it would not require additional pour point depressants.

[0017] According to a first aspect, the present invention relates to a branched monoester of formula (I) as defined in claim 1 and its dependent claims.

[0018] According to a second aspect, the present invention relates to a dielectric fluid composition comprising a monoester of formula (I) according to the invention.

[0019] A third aspect of the present invention is a method of cooling an electrical equipment system by use of a dielectric fluid composition according to the present invention.

[0020] Detailed Description of the Invention Branched monoesters according to the invention The present invention relates to a branched monoester A), which is of formula (I): [ka] [In the formula, R1 is a linear alkyl group having 3 to 13 carbon atoms, R2 and R3 are each a linear alkyl group having 5 carbon atoms.

[0021] Preferably, R1 is a linear alkyl group having 5 to 11 carbon atoms, more preferably 5 to 7 carbon atoms.

[0022] According to the invention, the alkyl groups R2 and R3 are both linear alkyl groups having 5 carbon atoms.

[0023] According to a preferred embodiment of the invention, the branched monoesters A) are selected from 6-undecyl laurate, 6-undecyl hexanoate, 6-undecyl octanoate or mixtures thereof.

[0024] According to the invention, the monoesters A) can be prepared by esterification reaction of alcohols with acids, as described, for example, in EP 2 155 754 B1.

[0025] Preferably, the alcohol may be produced according to the method disclosed in patent application WO 2020 / 104429, which method advantageously has a low CO2 footprint.

[0026] Dielectric fluid composition according to the present invention The present invention also relates to a dielectric fluid composition comprising at least one branched monoester A), said branched monoester A) being of formula (I). [ka] [In the formula, R1 is a linear alkyl group having 3 to 13 carbon atoms, R2 and R3 are each a linear alkyl group having 5 carbon atoms.

[0027] In the context of the present invention, the term "at least" as used herein also means "one or more" or "one branched monoester A) or a mixture thereof".

[0028] All properties and preferences given above for the branched monoesters A) according to the invention apply to the dielectric fluid composition.

[0029] According to a preferred embodiment of the present invention, the dielectric fluid composition comprises a branched monoester A) selected from 6-undecyl laurate, 6-undecyl hexanoate, 6-undecyl octanoate, or mixtures thereof, more preferably selected from 6-undecyl hexanoate, 6-undecyl octanoate, or mixtures thereof.

[0030] As shown in the experimental section below, the dielectric fluid compositions of the present invention have excellent electrical and heat transfer properties, are low flammable, and are non-corrosive. They also have excellent low temperature performance. A further advantage of the dielectric fluid compositions according to the present invention is their low viscosity, which allows for more efficient heat dissipation through more effective circulation (especially thanks to more efficient pumping), which in turn allows for better cooling of electrical devices.

[0031] In accordance with the present invention, the dielectric fluid composition has a melting point of 2 mm at 40° C. according to ASTM D445. 2 / s~12mm 2 It is preferred that the composition has a kinematic viscosity of 100 / s and a flash point according to ASTM D93 greater than 110° C., more preferably greater than 140° C.

[0032] In accordance with the present invention, it is preferred that the dielectric fluid composition have a pour point of less than -70°C (minus 70°C) according to ASTM D5950, and more preferably less than -75°C (minus 75°C) according to ASTM D5950.

[0033] According to a preferred embodiment, the dielectric fluid composition of the present invention has a Prandtl number at 40° C. and 1 atm pressure of less than 90. More preferably, it is less than 60, and even more preferably less than 55, at 40° C. and 1 atm pressure.

[0034] In the present invention, the Prandtl number (Pr) is calculated according to the following formula: The Prandtl number is a dimensionless quantity that correlates the viscosity of a fluid with its thermal conductivity (see Bastian E. Rapp, in Microfluidics: Modelling, Mechanics and Mathematics, 2017). The Prandtl number is given as: Pr=θ / α=momentum diffusivity / thermal diffusivity=(μ / ρ) / (k / (c p ρ))=c p μ / k where θ: Momentum diffusivity (kinetic viscosity) θ=μ / ρ; SI unit: m 2 / s α: Thermal diffusivity; SI unit: m 2 / s μ: dynamic viscosity; SI unit: Pa s=N s / m 2 k: Thermal conductivity; SI unit: W / (m K) c p : specific heat; SI unit: J / (kg K) ρ: Density; SI unit: kg / m 3

[0035] As shown in the experimental section below, the inventors of the present invention have surprisingly found that the monoesters of the present invention and their corresponding dielectric fluid compositions of the present invention all have low Prandtl numbers, which confirms that the dielectric fluid compositions of the present invention have high thermal conductivity and low viscosity, which are advantageous for thermal management in electrical devices.

[0036] In particular, it has been found that all of the dielectric fluid compositions of the present invention advantageously have high thermal conductivity values, which means that the dielectric fluids of the present invention can efficiently exchange heat with electrical devices. In fact, the higher the thermal conductivity, the better the heat transfer capability.

[0037] According to a preferred embodiment of the present invention, the dielectric fluid composition further comprises a base fluid component B) selected from the group consisting of polyol esters, saturated hydrocarbons, dicarboxylic esters, carbonates, ethers, alcohols or mixtures thereof. Preferably, component B) is glycerol trihexanoate, API Group IV synthetic oils (preferably polyalphaolefins), API Group III mineral oils or mixtures thereof. In the context of the present invention, component B) is a base fluid different from the branched monoester A). Thus, preferably, the dielectric fluid composition comprises the branched monoester A) according to the present invention as a first base fluid and the above indicated component B) as a second base fluid.

[0038] Preferably, the amounts of branched monoester A) and base fluid B) total at least 90% by weight, more preferably at least 95% by weight, based on the total weight of the dielectric fluid composition.

[0039] Preferably, the dielectric fluid composition may contain an additive C) selected from the group consisting of antifoaming agents, seal compatibility agents, antioxidants, yellow metal passivators, rust inhibitors, electrostatic discharge suppressants, demulsifiers, dyes or mixtures thereof. The additive compounds C) correspond to typical additives used in thermal management fluids and are described in detail, inter alia, in T. Mang, W. Dresel (eds.): “Lubricants and Lubrication”, Wiley-VCH, Weinheim 2001; RM Mortier, ST Orszulik (eds.): “Chemistry and Technology of Lubricants”. Preferably, suitable yellow metal passivators are selected from the list consisting of imidazolines, imidazoles, thiazoles, thiadiazoles, triazoles, tolyltriazoles, pyrazines, quinolines, morpholines or mixtures thereof.

[0040] Preferably, suitable rust inhibitors are selected from the list consisting of sulfonates, carboxylates, alkylamines, amine carboxylates, amine borates, phosphates or mixtures thereof.

[0041] Preferably, suitable electrostatic discharge inhibitors are selected from the list consisting of ester quats, imidazolium quats, alkoxyalkyl quats, trialkyl monomethyl quats, monoalkyl trimethyl quats, diamidoamine quats, benzyl quats, ethoxylated ether amines, ether diamines, fatty alcohol ethoxylates, ether amine oxides, ether amine quats or mixtures thereof.

[0042] Preferably, the suitable demulsifier is selected from the list consisting of polyalkoxylated phenols, polyalkoxylated polyols, polyalkoxylated polyamines or mixtures thereof.

[0043] Preferably, suitable antifoaming agents are selected from the list consisting of silicone oils, fluorosilicone oils, fluoroalkyl ethers, polyacrylates or mixtures thereof.

[0044] Preferably, the seal compatibility agent is selected from the list consisting of adipates, sebacates, neopentyl polyol-esters, sulfolane.

[0045] Preferably, suitable antioxidants include phenolic antioxidants and aminic antioxidants.

[0046] In a preferred embodiment, the phenolic antioxidant is selected from the group consisting of octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 4,4'-methylenebis(2,6-di-tert-butylphenol), 4,4'-bis(2,6-di-t-butylphenol), 4,4'-bis(2-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 2,2'-methylenebis(4-methyl- 6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol), 4,4'-isopropylidenebis(2,6-di-t-butylphenol), 2,2'-methylenebis(4-methyl-6-nonylphenol), 2,2'-isobutylidenebis(4,6-dimethylphenol), 2,2'-methylenebis(4-methyl-6-cyclohexylphenol), 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-bu 4,4'-thiobis(2-methyl-6-t-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), 2,2'-thiobis(4-methyl-6-t-butylphenol), bis(3-methyl-4-hydroxy-5-t-butyl) benzyl) sulfide, bis(3,5-di-t-butyl-4-hydroxybenzyl) sulfide, n-octyl-3-(4-hydroxy-3,5-di-t-butylphenyl) propionate, n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl) propionate, 2,2'-thio[diethyl-bis-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate], or mixtures thereof. Even more preferred phenolic antioxidants are bisphenolic antioxidants and ester group-containing phenolic antioxidants.

[0047] Examples of the amine-based antioxidants include monoalkyldiphenylamines, such as monooctyldiphenylamine and monononyldiphenylamine; dialkyldiphenylamines, such as 4,4'-dibutyldiphenylamine, 4,4'-dipentyldiphenylamine, 4,4'-dihexyldiphenylamine, 4,4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine and 4,4'-dinonyldiphenylamine; polyalkyldiphenylamines, such as tetrabutyldiphenylamine and tetranonyldiphenylamine; naphthylamine, specifically α-naphthylamine, phenyl-α-naphthylamine and further alkyl-substituted phenyl-α-naphthylamine, such as butylphenyl-α-naphthylamine, pentylphenyl-α-naphthylamine, hexylphenyl-α-naphthylamine, heptylphenyl-α-naphthylamine, octylphenyl-α-naphthylamine, nonylphenyl-α-naphthylamine.Among them, diphenylamine is more preferable than naphthylamine from the viewpoint of antioxidant effect.

[0048] Preferably, the dielectric fluid composition comprises, based on the total weight of the dielectric fluid composition, 2-100 wt % of the branched monoester A), 0-98 wt % of the component B), and 0-5 wt % of the additive C. More preferably, the dielectric fluid composition comprises, based on the total weight of the dielectric fluid composition, 5-100 wt % of the branched monoester A), 0-95 wt % of the component B), and 0-5 wt % of the additive C.

[0049] According to a preferred embodiment, the amounts of A)-C) total at least 90% by weight, more preferably total at least 95% by weight, and even more preferably total 100% by weight, based on the total weight of the dielectric fluid composition.

[0050] According to another preferred embodiment, the dielectric fluid composition of the invention consists of a branched monoester A) of formula (I), and all the properties and preferences given above for said dielectric fluid composition apply to this preferred embodiment.

[0051] Preferably, the dielectric fluid composition of the present invention comprising at least one monoester A) of formula (I) is biodegradable.

[0052] According to another preferred embodiment, the dielectric fluid composition of the present invention comprising at least one branched monoester A) of formula (I) is halogen-free, which means that the dielectric fluid composition does not contain any halogen-containing components.

[0053] Preferably, the dielectric fluid composition is produced using sustainable technologies with a low carbon footprint and is halogen-free.

[0054] Method for cooling an electrical equipment system according to the present invention According to another aspect of the invention, the present invention also relates to a method for cooling an electrical equipment system by use of a dielectric fluid composition as defined herein above.

[0055] Preferably, the electric equipment system is selected from the group consisting of a battery, an electric motor, an electric transformer, an electric capacitor, a fluid filled electric transmission line, a fluid filled power cable, a computer, a data server and power electronics.

[0056] Preferably, the method of cooling an electrical equipment system according to the present invention is direct immersion cooling, in which heat is removed from the system by circulating a liquid in direct contact with the hot components.

[0057] Experimental Department The present invention will be described in more detail below with reference to examples and comparative examples, but they are not intended to limit the scope of the present invention in any way.

[0058] (abbreviation) Cp@40℃: Specific heat capacity measured at 40℃ according to ASTM D7896-14 DPT: Diisopentyl terephthalate Elect.Cond.: Electrical conductivity measured at 25°C according to ASTM D2624 FHE: C12 / 14 fatty alcohol hexanoate FP: Flash point according to ASTM D93 GHE: glycerol trihexanoate KV40: Kinematic viscosity at 40°C according to ASTM D445 OptiCool-A Fluid: PAO ultra-low viscosity dielectric heat transfer fluids containing the hydrodimerization products of 1-decene and 1-dodecene, marketed by DSI Ventures PAO2: 5.10mm 2 Polyalphaolefin with KV40 of 100 / s PN40: Prandtl number at 40℃ and 1013hPa (1atm) PP: Pour point according to ASTM D5950 ULE: 6-undecyl laurate UHE: 6-undecylhexanoate UOE: 6-undecyl octanoate Yubase3: 11.80mm 2 Hydrotreated light paraffin base oil with a KV40 of 1.0 / s Yubase4: 19.20mm 2 Hydrotreated heavy paraffin base oil with a KV40 of 1.0 / s λ@40℃: Thermal conductivity at 40℃ according to ASTM D7896-14

[0059] (Test Method) The kinematic viscosity of the dielectric fluid was measured at 40° C. according to ASTM D445 with no deviation.

[0060] The specific heat capacity and thermal conductivity were measured at 40° C. by the hot wire method according to ASTM D7896-14.

[0061] Pour point (PP) was measured according to ASTM D5950.

[0062] Flash points were measured by the Pensky-Martens closed cup method according to ASTM D93.

[0063] Electrical conductivity was measured at 25° C. according to ASTM D2624.

[0064] Monoesters of the Invention Compared to Prior Art Components Suitable for Use as Dielectric Fluids (Example of the present invention) Synthesis of monoester A1 (ULE) according to the invention In a 4 liter distillation flask equipped with a stir bar, water separator, reflux condenser, dropping funnel and internal thermometer, 482 g (2.8 mol) of 6-undecanol were mixed with 701 g (3.5 mol) of lauric acid and 1.75 g of a 50% aqueous solution of hypophosphorous acid (Sigma Aldrich) (0.4% by weight H3PO2 based on 6-undecanol) and heated to 240 °C with stirring. The course of the reaction was followed by GC analysis. The reaction was terminated 6 hours after the start of boiling. A portion of this batch was removed and placed in a corresponding smaller apparatus in which the water separator was replaced by a distillation bridge. Excess lauric acid was distilled off at high temperature with stirring. Heating was then stopped and the batch was cooled to 80 °C. The batch was further purified by adding water dropwise through the dropping funnel at a pressure of 27-33 hPa (principle of steam distillation). This mixture was stirred with 2% basic aluminum oxide and 2% activated carbon for a further hour at a temperature of 100° C. The product was then separated from the activated carbon and aluminum oxide by filtration.

[0065] Synthesis of monoester A2 (UHE) according to the present invention To synthesize monoester A2 (UHE), 482 g (2.8 mol) of 6-undecanol was mixed with 407 g (3.5 mol) of hexanoic acid, following the same procedure as disclosed above for the synthesis of monoester A1.

[0066] Synthesis of monoester A3 (UOE) according to the present invention To synthesize monoester A3 (UOE), 482 g (2.8 mol) of 6-undecanol was mixed with 505 g (3.5 mol) of octanoic acid, following the same procedure as disclosed above for the synthesis of monoester A1.

[0067] (Comparative Example) FHE, Comparative Example 1 (Comp.1) corresponding to linear C12-C14 monoesters 11.7 kg (100 mol) of hexanoic acid, 13.7 g (0.11% by weight based on hexanoic acid) of tetrabutyl orthotitanate and 15.7 kg (80 mol) of lorol were used as initial charges in a stirred flask with a distillation bridge equipped with a reflux distributor, a stirrer, a dropping funnel and a thermometer and esterified at 200 ° C. At the end of the reaction, the excess acid was removed by distillation at 180 ° C and 3 mbar. The system was then cooled to 80 ° C and neutralized using a 10% strength by weight aqueous NaOH solution. Steam distillation was then carried out at a temperature of 80 ° C and a pressure of 20-5 mbar. The mixture was then dried at this temperature and at 5 mbar. The mixture was stirred with activated carbon at a temperature of 100 ° C. The product was then separated from the activated carbon by filtration.

[0068] Comparative Example 2 (Comp. 2) corresponds to methyl laurate (a methyl ester of a saturated fatty acid).

[0069] Comparative Example 3 (Comp. 3) corresponds to a pure synthetic diester base stock, di-2-ethylhexyl sebacate.

[0070] Comparative Example 4 (Comp. 4) corresponds to di-(isononyl) adipate.

[0071] Comparative Example 5 (Comp. 5) corresponds to Yubase 3 manufactured by SK Lubricants, which is a hydrotreated light paraffinic base oil.

[0072] All the examples and their respective physical properties are shown in Table 1 below.

[0073] (Discussion of Results) The branched monoesters of the present invention (Inventive Examples 1, 2 and 3) have very good heat transfer properties combined with low viscosity and excellent low temperature performance. In contrast, Comparative Examples 1 to 5 do not have all the properties shown above and therefore do not perform as efficiently.

[0074] Comparative Examples 1 and 2 have similar low viscosities as Inventive Examples 2 and 3, but do not have as good low temperature performance (-6°C and +3°C, respectively).

[0075] Comparative Examples 3, 4 and 5 show acceptable low temperature performance (pour point values ​​of -78°C and -51°C, respectively). However, due to their high viscosities, their respective Prandtl numbers, when correlating the viscosity of a fluid with its thermal conductivity as explained above (PN40 of 136.5 and 128.7, respectively), are high and therefore much higher than the inventive monoesters according to the invention. In fact, the branched monoesters A1, A2 and A3 according to the invention all have Prandtl numbers (PN40 at 40°C and 1013 hPa (1 atm)) of less than 85. [Table 1]

[0076] [Dielectric fluid composition] To prepare the dielectric fluid composition, the ingredients listed in Table 2 below were mixed together at room temperature. [Table 2]

[0077] The physical properties of the dielectric fluid formulations listed in Table 2 above are presented in Table 3 below.

[0078] From Table 3 below, it can be seen that the dielectric fluid composition comprising the branched monoester according to the present invention exhibits excellent low temperature properties in combination with a low Prandtl number and low viscosity at 40° C. and 1013 hPa (1 atm), which confirms that the dielectric fluid composition according to the present invention has excellent performance in cooling electrical equipment systems.

[0079] The comparative dielectric fluid Comp.F1 has a high flash point, but poor low temperature performance (only -9°C) and a high viscosity (7.02 mm 2 / s) and a high Prandtl number (PN40 of 83.0).

[0080] The comparative dielectric fluid Comp.F2 has a higher kinematic viscosity (6.50 mm 2 / s) and do not provide as efficient heat dissipation as lower viscosity dielectric fluids due to inefficient circulation and pumping capabilities of the fluid within the electrical system.

[0081] Comparative dielectric fluid Comp. F3 has comparable low temperature performance with a pour point of -75°C, but has a higher viscosity and a higher Prandtl number and therefore does not provide all the advantages of the thermal dielectric fluid compositions of the present invention containing the branched monoesters of the present invention.

[0082] The thermal management results of the dielectric fluid compositions of the present invention confirm that the dielectric fluid compositions containing the branched monomer A) of formula (I) not only exhibit excellent low temperature properties, but also very good electrical cooling performance, as confirmed by the low Prandtl number. This combination of excellent low temperature properties, low viscosity and electrical cooling performance is not found in comparative dielectric fluids. [Table 3]

Claims

1. Branched monoester A), which has the formula (I). 【Chemical 1】 [wherein, R １ is a linear alkyl group having 3 to 13 carbon atoms, R ２ and R ３ are each a linear alkyl group having five carbon atoms.

2. R １ The branched monoester A) according to claim 1, wherein R is a linear alkyl group having 5 to 11 carbon atoms.

3. The branched monoester A) according to claim 1 or 2, wherein the branched monoester A) is selected from 6-undecyl laurate, 6-undecyl hexanoate, 6-undecyl octanoate or a mixture thereof.

4. A dielectric fluid composition comprising the branched monoester A) defined in claim 1, or a mixture thereof.

5. The dielectric fluid composition according to claim 4, wherein the dielectric fluid composition further comprises a base fluid B) selected from the group consisting of polyol esters, saturated hydrocarbons, dicarboxylic acid esters, carbonates, ethers, alcohols or mixtures thereof.

6. The dielectric fluid composition according to claim 4, wherein the dielectric fluid composition comprises an additive C) selected from the group consisting of an antifoaming agent, a seal compatibility agent, an antioxidant, a noble metal passivator, a rust inhibitor, an electrostatic discharge inhibitor, an anti-emulsifier, a dye or a mixture thereof.

7. The dielectric fluid composition according to any one of claims 4 to 6, wherein the dielectric fluid composition comprises 2 to 100% by weight of the branched monoester A), 0 to 98% by weight of the base fluid B), and 0 to 5% by weight of the additive C) based on the total weight of the dielectric fluid composition.

8. The dielectric fluid composition according to claim 7, wherein the amounts of A) to C) total 90% by weight based on the total weight of the dielectric fluid composition.

9. A method of cooling an electrical equipment system by using the dielectric fluid composition defined in any one of claims 4 to 6.

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