Method for cooling electrical equipment system by using dielectric fluid composition having good heat dissipation over wide temperature range

Abstract

The present invention relates to a method of cooling an electrical equipment system by using a dielectric fluid composition comprising a base fluid comprising a hydrogenated oligomer obtained from oligomerization of butene. The method according to the invention provides good and consistent heat dissipation of the electrical equipment system over a wide temperature range.

Description

Technical Field

[0001] The present invention relates to a method for cooling an electrical equipment system by using a dielectric fluid composition, the dielectric fluid composition comprising a base fluid A), the base fluid A) comprising a hydrogenated oligomer obtained by the oligomerization of butene. The method according to the present invention provides excellent and consistent heat dissipation of the electrical equipment system over a wide temperature range. Background Art

[0002] The present invention relates to the field of thermal management fluids for direct cooling. More efficient and fast-charging battery applications require effective cooling systems to dissipate heat from low-voltage to high-voltage applications, such as pure electric vehicles (EVs), hybrid electric vehicles (HEVs), fuel cell electric vehicles, computers, transformers, capacitors, high-voltage cables, switchgear, and whose function is to provide electrical insulation, suppress corona and arc discharges. In addition to air cooling and indirect cooling, there is also direct liquid immersion cooling, which is the most efficient cooling technology. Especially for larger batteries, such as in electric vehicles, a large amount of heat is generated during charging and discharging. The optimal temperature for lithium-ion batteries is 20 - 40 °C, and any higher temperature will reduce battery performance and lifespan and may lead to battery failures such as thermal runaway. This is why highly efficient thermal management fluids are needed.

[0003] Currently available cooling fluids are typically hydrocarbon-based cooling fluids having a large number of C17 or longer branched alkyl chains. For example, WO2022038313 discloses a renewable alkane composition comprising a major amount of a mixture of C17 and C18 alkanes. As illustrated in the experimental section, it also describes that the composition should contain less than 10 wt% of C16, preferably less than 5 wt%, wherein the composition comprises a mixture of about 4 wt% of C16 isoparaffins and n-paraffins and more than about 90 wt% of C17 and C18 isoparaffins and n-paraffins.

[0004] WO2018078024 describes a heat transfer fluid having a boiling point of 200 to 400 °C and a boiling range of less than 80 °C, wherein the fluid comprises more than 95 wt% of isoparaffins and less than 3% of naphthenes. This document mainly focuses on specific heat capacity and lubricating properties, but it does not mention low-temperature flow properties (pour point and viscosity at low temperatures), which are crucial for wide-temperature-range applications as thermal management fluids.

[0005] These thermal management compositions comprising hydrocarbons having highly branched alkyl chains (a major amount of C17 or longer branched alkyl chains) cause problems, especially in terms of low-temperature performance over a wide operating temperature range. Summary of the Invention

[0006] Accordingly, an object of the present invention is to provide a novel thermal management method for cooling an electrical equipment system, wherein the thermal management fluid composition should have low electrical conductivity, low viscosity, excellent thermal properties in a wide temperature range, while maintaining a low pour point, high flash point and high autoignition temperature. Summary of the Invention

[0008] After thorough research, the inventors of the present invention unexpectedly found that the hydrogenated branched isoparaffin oligomer of butene as defined in claim 1 - which has a major amount of hydrogenated branched isoparaffin oligomers having alkyl chains of 16 carbon atoms - solves the above - mentioned technical problems and provides excellent and consistent heat dissipation in a wide temperature range, while having excellent low - temperature performance as well as high flash point and auto - ignition point.

[0009] Accordingly, in a first aspect, the present invention relates to a method for cooling an electrical equipment system as defined in claim 1. Brief Description of the Drawings

[0010] To better illustrate the advantages and properties of the claimed cooling method and the objects of the present invention, a graph is attached as a non - limiting example:

[0011] Figure 1 is a graph showing the heat dissipation performance of different hydrocarbons from - 15 °C to 40 °C. The dielectric fluid composition Comp.HC1 (■) shows a sharp increase in the Prandtl number at lower temperatures. The dielectric fluid compositions Comp.HC2 (▲) and HC1 (●) show similar behavior at high and medium temperatures. However, the dielectric fluid composition HC1 has a lower increase in the Prandtl number at lower temperatures. The dielectric fluid composition HC2 (◆) shows the lowest Prandtl number with a very low slope throughout the temperature profile. Detailed Description of the Invention

[0013] Accordingly, the present invention relates to a method for cooling an electrical equipment system by using a dielectric fluid composition, said dielectric fluid composition comprising a base fluid A), said base fluid A) comprising a hydrogenated oligomer obtained by oligomerization of butene,

[0014] and wherein said base fluid A) comprises, based on the total weight of the base fluid A),

[0015] a) 50 to 78% by weight of a hydrogenated branched isoparaffin oligomer having an alkyl chain of 16 carbon atoms,

[0016] b) 22 to 50% by weight of a hydrogenated branched isoparaffin oligomer having an alkyl chain of 20 carbon atoms or an alkyl chain of 24 carbon atoms or a mixture thereof,

[0017] c) 0 to 5% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain with more than 28 carbon atoms,

[0018] and wherein the hydrogenated oligomers a), b) and c) of the base fluid A) have an iodine value of less than 3 g iodine / 100 g oligomer according to DIN 14111.

[0019] In other words, the base fluid A) comprises hydrogenated oligomers obtained by the oligomerization of butenes of formula (I), formula (II) and formula (III)

[0020]

[0021] and wherein the base fluid A) comprises, based on the total weight of the base fluid A),

[0022] a) 50 to 78% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain with 16 carbon atoms,

[0023] b) 22 to 50% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain with 20 carbon atoms or an alkyl chain with 24 carbon atoms or a mixture thereof,

[0024] c) 0 to 5% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain with more than 28 carbon atoms,

[0025] and wherein the hydrogenated oligomers a), b) and c) of the base fluid A) have an iodine value of less than 3 g iodine / 100 g oligomer according to DIN 14111.

[0026] According to another preferred embodiment, the base fluid A) comprises hydrogenated oligomers obtained by the oligomerization of butenes of formula (I), formula (II) and formula (III), and based on the total weight of the base fluid A), the content of the oligomers obtained by the oligomerization of butenes of formula (III) is less than 10% by weight, preferably less than 8% by weight, more preferably less than 5% by weight. Preferably, the base fluid A) consists of hydrogenated oligomers obtained from the oligomerization of butenes.

[0027] In a preferred embodiment of the present invention, the base fluid A) comprising hydrogenated branched isoparaffin saturated oligomers obtained by the oligomerization of butenes and a further hydrogenation step does not contain n-alkanes and aromatic components. More preferably, the base fluid A) consists of hydrogenated branched isoparaffin saturated oligomers obtained from the oligomerization of butenes of formula (I), formula (II) and formula (III) and does not contain n-alkanes and aromatic components.

[0028] In another preferred embodiment of the present invention, the base fluid A) comprises, based on the total weight of the base fluid A),

[0029] a) 55 to 78% by weight of a hydrogenated branched isoparaffin oligomer having an alkyl chain of 16 carbon atoms,

[0030] b) 22 to 45% by weight of a hydrogenated branched isoparaffin oligomer having an alkyl chain of 20 carbon atoms or an alkyl chain of 24 carbon atoms or a mixture thereof,

[0031] c) 0 to 5% by weight of a hydrogenated branched isoparaffin oligomer having an alkyl chain of more than 28 carbon atoms.

[0032] In a further preferred embodiment of the present invention, the base fluid A) comprises, based on the total weight of the base fluid A),

[0033] a) 60 to 75% by weight of a hydrogenated branched isoparaffin oligomer having an alkyl chain of 16 carbon atoms,

[0034] b) 25 to 40% by weight of a hydrogenated branched isoparaffin oligomer having an alkyl chain of 20 carbon atoms or an alkyl chain of 24 carbon atoms or a mixture thereof,

[0035] c) 0 to 5% by weight of a hydrogenated branched isoparaffin oligomer having an alkyl chain of more than 28 carbon atoms.

[0036] In an even more preferred embodiment of the present invention, the base fluid A) comprises, based on the total weight of the base fluid A),

[0037] a) 60 to 70% by weight of a hydrogenated branched isoparaffin oligomer having an alkyl chain of 16 carbon atoms,

[0038] b) 30 to 40% by weight of a hydrogenated branched isoparaffin oligomer having an alkyl chain of 20 carbon atoms or an alkyl chain of 24 carbon atoms or a mixture thereof,

[0039] c) 0 to 5% by weight of a hydrogenated branched isoparaffin oligomer having an alkyl chain of more than 28 carbon atoms.

[0040] According to the present invention, preferably, the hydrogenated branched isoparaffin oligomer b) consists of, based on the total weight of the hydrogenated branched isoparaffin oligomer b)

[0041] - 50 to 98% by weight, more preferably 70 to 98% by weight, even more preferably 70 to 80% by weight of a hydrogenated branched isoparaffin oligomer having an alkyl chain of 20 carbon atoms, and

[0042] - 2 to 50% by weight, more preferably 2 to 30% by weight, even more preferably 20 to 30% by weight of a hydrogenated branched isoparaffin oligomer having an alkyl chain of 24 carbon atoms.

[0043] The base fluid A) according to the present invention is prepared by the oligomerization of butene, wherein the oligomerization of butene of formula (I), formula (II) and formula (III) is carried out using a heterogeneous oligomerization catalyst to form an oligomerization product, and then subsequent distillation is carried out, wherein the oligomers formed during the oligomerization are partially separated from the remaining oligomerization product. Finally, the distilled oligomers are hydrogenated. The resulting product is the base fluid A). Preferably, the base fluid A) according to the present invention is prepared according to the examples of DE102004018753.

[0044] According to the present invention, the base fluid A) comprises hydrogenated oligomers a), b) and c) obtained by the oligomerization of butene, wherein the hydrogenated oligomers a), b) and c) of the base fluid A) have an iodine value of less than 3 g iodine / 100 g oligomer according to DIN 14111, preferably less than 2 g iodine / 100 g oligomer, more preferably less than 1.5 g iodine / 100 g oligomer. The iodine value is a measure of the relative unsaturation in the component as determined by the absorption of halogen. In the present invention, the iodine value is the mass of iodine in grams consumed by 100 grams of the hydrogenated oligomers of the base fluid A).

[0045] Preferably, the electrical equipment system is selected from batteries, electric motors, inverters, power transformers, capacitors, fluid-filled transmission lines, fluid-filled power cables, computers, data servers and power electronics.

[0046] In another preferred embodiment of the present invention, the method of cooling the electrical equipment system according to the present invention is direct liquid immersion cooling. In direct liquid immersion cooling, heat is removed from the system by circulating the liquid in direct contact with the hot components.

[0047] According to a preferred embodiment of the present invention, the dielectric fluid composition as defined in claim 1 further comprises a base fluid B) selected from polyol esters, monoesters, saturated hydrocarbons, dicarboxylic esters, carbonates, ethers, alcohols, amines, amides or mixtures thereof. In the context of the present invention, component B) is a base fluid different from the base fluid A) as defined in claim 1 and defined throughout this specification. Thus, preferably, the dielectric fluid composition comprises the base fluid A) according to the present invention as the first base fluid and the above-mentioned component B) as the second base fluid.

[0048] Preferably, based on the total weight of the dielectric fluid composition, the amounts of the base fluid A) and the base fluid B) together are at least 90% by weight, more preferably at least 95% by weight.

[0049] Preferably, the dielectric fluid composition may further comprise an additive C) selected from defoamers, seal compatibilizers, antioxidants, yellow metal passivators, rust inhibitors, electrostatic discharge inhibitors, demulsifiers, dyes, or mixtures thereof. Additive compound C) corresponds to typical additives used in heat transfer fluids and is described in particular detail in T. Mang, W. Dresel (eds.): "Lubricants and Lubrication", Wiley-VCH, Weinheim 2001; R.M. Mortier, S.T. Orszulik (eds.): "Chemistry and Technology of Lubricants". Preferably, suitable yellow metal passivators are selected from imidazonine, imidazole, thiazole, thiadiazole, triazole, tolyltriazole, pyridine, quinoline, morpholine, or mixtures thereof.

[0050] Preferably, suitable rust inhibitors are selected from sulfonates, carboxylates, alkylamines, amine carboxylates, amine borates, phosphates, or mixtures thereof.

[0051] Preferably, suitable electrostatic discharge inhibitors are selected from ester quaternary ammonium salts, imidazole quaternary ammonium salts, alkoxyalkyl quaternary ammonium salts, trialkylmonomethyl quaternary ammonium salts, monoalkyltrimethyl quaternary ammonium salts, diamidoamine quaternary ammonium salts, benzyl quaternary ammonium salts, ethoxylated ether amines, ether diamines, fatty alcohol ethoxylates, ether amine oxides, ether amine quaternary ammonium salts, or mixtures thereof.

[0052] Preferably, suitable demulsifiers are selected from polyalkoxylated phenols, polyalkoxylated polyols, polyalkoxylated polyamines, or mixtures thereof.

[0053] Preferably, suitable defoamers are selected from silicone oils, fluoro silicone oils, fluoroalkyl ethers, polyacrylates, or mixtures thereof.

[0054] Preferably, seal compatibilizers are selected from adipates, sebacates, neopentyl polyol esters, sulfolane.

[0055] Preferably, suitable antioxidants include phenolic antioxidants and amine antioxidants.

[0056] In a preferred embodiment, the phenolic antioxidant is selected from octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; 4,4'-methylenebis(2,6-di-tert-butylphenol); 4,4'-bis(2,6-di-tert-butylphenol); 4,4'-bis(2-methyl-6-tert-butylphenol); 2,2'-methylenebis(4-ethyl-6-tert-butylphenol); 2,2'-methylenebis(4-methyl-6-tert-butylphenol); 4,4'-butylidenebis(3-methyl-6-tert-butylphenol); 4,4'-isopropylidenebis(2,6-di-tert-butylphenol); 2,2'-methylenebis(4-methyl-6-nonylphenol); 2,2'-isobutylidenebis(4,6-dimethylphenol); 2,2'-methylenebis(4-methyl-6-cyclohexylphenol); 2,6-di-tert-butyl-4-methylphenol; 2,6-di-tert-butyl-4-ethylphenol; 2,4-dimethyl-6-tert-butylphenol; 2,6-di-tert-amyl-p-cresol; 2,6-di-tert-butyl-4-(N,N'-dimethylaminomethylphenol); 4,4'-thiobis(2-methyl-6-tert-butylphenol); 4,4'-thiobis(3-methyl-6-tert-butylphenol); 2,2'-thiobis(4-methyl-6-tert-butylphenol); bis(3-methyl-4-hydroxy-5-tert-butylbenzyl)sulfide; bis(3,5-di-tert-butyl-4-hydroxybenzyl)sulfide; n-octadecyl 3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate; n-octadecyl 3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate; 2,2'-thio[diethyl-bis-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] or a mixture thereof. Even more preferred phenolic antioxidants are bisphenolic antioxidants and phenolic antioxidants containing ester groups.

[0057] Amino antioxidants include, for example, monoalkyl diphenylamines such as monooctyl diphenylamine and monononyl diphenylamine; dialkyl diphenylamines such as 4,4'-dibutyl diphenylamine, 4,4'-dipentyl diphenylamine, 4,4'-dihexyl diphenylamine, 4,4'-diheptyl diphenylamine, 4,4'-dioctyl diphenylamine, 4,4'-dinonyl diphenylamine; polyalkyl diphenylamines such as tetrabutyl diphenylamine, tetrahexyl diphenylamine, tetraoctyl diphenylamine, tetranonyl diphenylamine; naphthylamines, specifically α-naphthylamine, phenyl-α-naphthylamine and other alkyl-substituted phenyl-α-naphthylamines such as butylphenyl-α-naphthylamine, pentylphenyl-α-naphthylamine, hexylphenyl-α-naphthylamine, heptylphenyl-α-naphthylamine, octylphenyl-α-naphthylamine, nonylphenyl-α-naphthylamine. Among them, from the perspective of their antioxidant effects, diphenylamine is preferred over naphthylamine.

[0058] According to a preferred embodiment of the present invention, based on the total weight of the dielectric fluid composition, the dielectric fluid composition according to the present invention comprises 2 to 100% by weight of base fluid A), 0 to 98% by weight of base fluid B), and 0 to 10% by weight of additive C). More preferably, based on the total weight of the dielectric fluid composition according to the present invention, the total amount of A), B), and C) is at least 90% by weight, more preferably at least 95% by weight, and even more preferably 100% by weight.

[0059] According to a preferred embodiment of the present invention, base fluid A) has a pour point below -80 °C according to ASTM D5950.

[0060] In the present invention, the Prandtl number (Pr) is calculated according to the following formula. The Prandtl number is a dimensionless quantity that relates the viscosity of a fluid to its thermal conductivity (see Bastian E. Rapp, Microfluidics: Modelling, Mechanics and Mathematics, 2017). The Prandtl number is given as follows:

[0061] Pr = θ / α = momentum diffusivity / thermal diffusivity = (μ / ρ) / (k / (c p ρ)) = c p μ / k

[0062] where

[0063] θ: momentum diffusivity (kinematic viscosity) θ = μ / ρ; SI unit: m 2 / s

[0064] α: thermal diffusivity; SI unit: m 2 / s

[0065] μ: dynamic viscosity; SI unit: Pa·s = N·s / m 2

[0066] k: thermal conductivity; SI unit: W / (m·K)

[0067] c p : specific heat; SI unit: J / (kg·K)

[0068] ρ: density; SI unit: kg / m 3

[0069] As shown in the experimental part below, the inventors of the present invention have unexpectedly found that the base fluid A) of the method according to the present invention has a small Prandtl number over a wide temperature range. This confirms that the base fluid A) according to the present invention has a high thermal conductivity and a low viscosity, which is beneficial for heat management in electrical devices. This means that the dielectric fluid of the present invention can effectively exchange heat with electrical devices. In fact, the higher the thermal conductivity, the better the heat transfer ability. In addition, the fluid exhibits good low-temperature flow properties.

[0070] According to a preferred embodiment, the base fluid A) of the present invention has a Prandtl number below 60, more preferably below 55, at 40 °C and a pressure of 1013 hPa. Detailed Description

[0071] Experimental Part

[0072] The present invention is further illustrated in detail below with reference to examples and comparative examples, without intending to limit the scope of the present invention.

[0073] Abbreviation

[0074] AIT Autoignition temperature according to DIN 51794

[0075] Comp.HC1 Yubase 3 from SK Lubricants, which is a distillate containing isoalkanes and n-alkanes with alkyl chains having more than 20 carbon atoms (hydrotreated light paraffinic base oil with a KV40 of 11.80 mm 2 / s)

[0076] Comp.HC2 PAO 2, corresponding to a dimer based on 1-decene

[0077] Cp Specific heat capacity at the temperatures shown in Table 1 and according to ASTM D7896-19

[0078] Elect.Cond. Electrical conductivity measured at 25 °C according to ASTM D2624

[0079] FP Flash point ASTM D93

[0080] HC1 64 wt% C16 / 34 wt% C20 and C24 hydrogenated branched isoalkanes / remaining high-boiling hydrocarbons (hydrogenated branched isoalkanes above C28)

[0081] HC2 78 wt% C16 / 22 wt% C20 and C24 hydrogenated branched isoalkanes

[0082] KV Kinematic viscosity at the temperatures shown in Table 1 and according to ASTM D445

[0083] The Prandtl number of PN at the temperatures shown in Table 1 and 1013 hPa (1 atm)

[0084] The pour point of PP according to ASTM D5950

[0085] The thermal conductivity of λ at the temperatures shown in Table 1 and according to ASTM D7896-14

[0086] The density of δ at the temperatures shown in Table 1 and according to DIN EN ISO12185 Test method

[0087] The kinematic viscosity of the dielectric fluid composition is measured at the temperatures shown in Table 1 (i.e., 40 °C, 20 °C, and -15 °C) and according to ASTM D445.

[0088] The specific heat capacity and thermal conductivity are measured at the temperatures shown in Table 1 by the hot wire method according to ASTM D7896-19.

[0089] The pour point (PP) is measured according to ASTM D5950.

[0090] The flash point is measured according to ASTM D93 using a closed cup Pensky Martin apparatus.

[0091] The electrical conductivity is measured at 25 °C according to ASTM D2624.

[0092] The density is measured at the temperatures shown in Table 1 and according to DIN ENISO 12185.

[0093] The autoignition temperature is measured according to DIN 51794.

[0094] The quantitative analysis of the components of the thermal management fluid is measured by gas chromatography. Analysis is performed using a quartz capillary column DB-5 5% diphenyl / 95% dimethyl polysiloxane (30 m × 0.25 mm × 0.25 μm) from Agilent connected to a flame ionization detector. The temperature program is 50 °C for 4 minutes, which is increased to 350 °C for 20 minutes. The flow rate is 1.5 mL / min for 34 minutes, which is increased to 2 mL / min. The injection temperature is 280 °C and the detector temperature is 350 °C. Helium is used as the carrier gas and the column flow rate is adjusted to 1.5 mL / min.

[0095] To identify the chromatographic peaks, mass spectrometry was used. Analysis was carried out using a quartz capillary column DB-5 5% diphenyl / 95% dimethyl polysiloxane (30 m × 0.25 mm × 0.25 μm) from Agilent connected to a mass spectrometer. The temperature program was 80 °C for 2 minutes, which was increased to 320 °C for 22 minutes. The injection temperature was 250 °C and the carrier flow rate was 1.1 mL / min.

[0096] The degree of hydrogenation of the hydrogenated oligomers a), b) and c) obtained by oligomerization of butene in the base fluid was determined according to DIN 14111.

[0097] Preparation of base fluid

[0098] The base fluid HC1 was prepared in the same manner as in the examples of DE102004018753. The butene compounds of the formulas (I), (II) and (III) were oligomerized in the presence of a nickel catalyst. Subsequently, the formed C16 oligomers were separated by distillation and finally hydrogenated.

[0099] Analysis of the product showed that the base fluid consisted of 64 wt% C16 / 34 wt% C20 and C24 branched isoparaffins / the remaining high-boiling hydrocarbons (branched isoparaffins above C28).

[0100] The iodine value of the base fluid HC1 according to DIN 14111 was 1.3 g iodine / 100 g oligomer.

[0101] The base fluid HC2 was prepared according to the same procedure as the base fluid HC1. The product obtained by further purification by distillation had the following composition:

[0102] Analysis of the product showed that the base fluid consisted of 78 wt% C16 / 22 wt% C20 and C24 branched isoparaffins.

[0103] The iodine value of the base fluid HC1 according to DIN 14111 was 1.3 g iodine / 100 g oligomer.

[0104] The comparative base fluid Comp.HC1 is a distillate containing isoparaffins and n-paraffins with alkyl chains having more than 20 carbon atoms (a hydrotreated light paraffinic base oil with a KV40 of 11.80 mm 2 / s).

[0105] The comparative base fluid Comp.HC2 corresponds to a dimer based on 1-decene.

[0106] The base fluid examples according to the invention (base fluid A) of claim 1) and the comparative base fluid examples (Comp.HC) together with their respective physical properties are shown in Table 1 below.

[0107] Table 1 :Thermal management properties of the thermal management fluid composition according to the present invention

[0108]

[0109] n.m. Not measured

[0110] As shown in Table 1 above, the C16-rich hydrocarbon base fluids according to the present invention (Examples HC1 and HC2) have very good thermal conductivity properties, as well as low viscosity and excellent low-temperature performance. In contrast, Comparative Examples Comp.HC1 and Comp.HC2 do not combine all of the above properties and are therefore less effective.

[0111] Furthermore, although Example HC1 of the C16-rich hydrocarbon base fluid according to the present invention exhibits an acceptable flash point (124 °C), surprisingly, the autoignition point of HC1 is superior to that of Comp.HC1 (275 °C and 260 °C respectively). This is of course a great advantage in preventing autoignition when the electrical system has a fault that can cause thermal runaway.

[0112] Table 2 below shows the evolution of the Prandtl index values of some thermal management fluid compositions according to the present invention and some comparative thermal management fluids over a wide temperature range. The slope indicates the efficiency of the Prandtl number over a wide temperature range, and the smaller the increase, the better the efficiency. The intercept describes the Prandtl number at 0 °C. Similarly, the lower the Prandtl number, the better the heat removal of the electrical system. This is also reflected in the present invention's Figure 1 ones.

[0113] Table 2 :Evolution of the Prandtl index values of some thermal management fluid compositions over a certain temperature range

[0114] Compound Slope Intercept Comp.HC1 -22.8 933.4 Comp.HC2 -6.6 289.9 HC1 -5.8 251.1 HC2 -2.2 115.5

[0115] The comparative thermal management fluid Comp.HC1 shows a sharp increase in slope at 30 °C and therefore does not achieve a smooth thermal management effect over a wide temperature range.

[0116] The comparative thermal management fluid composition Comp.HC2 also shows an increase in the Prandtl index value. Even though the results are better than those of the comparative thermal management fluid Comp.HC1, the slope of the base fluid Comp.HC2 is still steeper than the slopes of the base fluids HC1 and HC2 according to the present invention.

[0117] In particular, the base fluid HC2 of the present invention shows the lowest slope. In fact, the slope of the Prandtl index value should be smooth over a wide temperature distribution. This is observed in the thermal management fluid compositions according to the present invention, where a significant improvement can be observed.

[0118] The above experimental data show that the C16-rich hydrocarbon base fluid A) according to the present invention has a small and stable Prandtl number over a wide temperature range. This confirms that the dielectric fluid composition according to the present invention has high thermal conductivity and low viscosity over a wide temperature range, which is beneficial for effective circulation and pumpability in electrical equipment for heat dissipation. In addition, the base fluid A) according to the present invention has excellent low-temperature flow properties (a very low pour point value as shown in Table 1).

Claims

1. A method for cooling an electrical equipment system by using a dielectric fluid composition, the dielectric fluid composition comprising a base fluid A), the base fluid A) comprising hydrogenated oligomers obtained by the oligomerization of butene, and wherein the base fluid A) comprises, based on the total weight of the base fluid A), a) 50 to 78% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain of 16 carbon atoms, b) 22 to 50% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain of 20 carbon atoms or an alkyl chain of 24 carbon atoms or a mixture thereof, c) 0 to 5% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain of more than 28 carbon atoms, and wherein the hydrogenated oligomers a), b) and c) of the base fluid A) have an iodine value of less than 3 g iodine / 100 g oligomer according to DIN 14111.

2. The method according to claim 1, wherein the base fluid A) does not contain n-alkanes and aromatic components.

3. The method according to claim 1 or 2, wherein the base fluid A) comprises, based on the total weight of the base fluid A), a) 55 to 78% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain of 16 carbon atoms, b) 22 to 45% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain of 20 carbon atoms or an alkyl chain of 24 carbon atoms or a mixture thereof, c) 0 to 5% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain of more than 28 carbon atoms.

4. The method according to any one of the preceding claims, wherein the hydrogenated oligomers a), b) and c) of the base fluid A) have an iodine value of less than 2 g iodine / 100 g oligomer according to DIN 14111, preferably less than 1.5 g iodine / 100 g oligomer.

5. The method according to any one of the preceding claims, wherein the base fluid A) comprises, based on the total weight of the base fluid A), a) 60 to 75% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain of 16 carbon atoms, b) 25 to 40% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain of 20 carbon atoms or an alkyl chain of 24 carbon atoms or a mixture thereof, c) 0 to 5% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain of more than 28 carbon atoms.

6. The method according to any one of the preceding claims, wherein the base fluid A) comprises, based on the total weight of the base fluid A), a) 60 to 70% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain of 16 carbon atoms, b) 30 to 40% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain of 20 carbon atoms or an alkyl chain of 24 carbon atoms or a mixture thereof, c) 0 to 5% by weight of hydrogenated branched isoparaffin oligomers having an alkyl chain of more than 28 carbon atoms.

7. The process according to any one of the preceding claims, wherein the hydrogenated branched isoparaffin oligomers b) consist of 50 to 98 wt. % of hydrogenated branched isoparaffin oligomers having an alkyl chain of 20 carbon atoms and 2 to 50 wt. % of hydrogenated branched isoparaffin oligomers having an alkyl chain of 24 carbon atoms, based on the total weight of the hydrogenated branched isoparaffin oligomers b).

8. The process according to claim 7, wherein the hydrogenated branched isoparaffin oligomer b) consists of 70 to 98 wt. % of hydrogenated branched isoparaffin oligomers having an alkyl chain of 20 carbon atoms and 2 to 30 wt. % of hydrogenated branched isoparaffin oligomers having an alkyl chain of 24 carbon atoms, based on the total weight of the hydrogenated branched isoparaffin oligomer b).

9. The process according to claim 8, wherein the branched isoparaffin oligomer b) consists of 70 to 80 wt. % of hydrogenated branched isoparaffin oligomers having an alkyl chain of 20 carbon atoms and 20 to 30 wt. % of hydrogenated branched isoparaffin oligomers having an alkyl chain of 24 carbon atoms, based on the total weight of the hydrogenated branched isoparaffin oligomer b).

10. The method of any preceding claim, wherein the electrical equipment system is selected from the group consisting of batteries, electric motors, inverters, power transformers, capacitors, fluid-filled transmission lines, fluid-filled power cables, computers, data servers, and power electronics.

11. A method according to any preceding claim, wherein the method of cooling the electrical equipment system is direct liquid immersion cooling.

12. The method according to any one of the preceding claims, wherein the dielectric fluid composition further comprises a base fluid B) selected from polyol esters, monoesters, saturated hydrocarbons, dicarboxylic acid esters, carbonates, ethers, alcohols, amines, amides or mixtures thereof.

13. The method of any one of the preceding claims, wherein the dielectric fluid composition further comprises an additive C) selected from defoamers, seal compatibilizers, antioxidants, yellow metal passivators, rust inhibitors, electrostatic discharge inhibitors, demulsifiers, dyes or mixtures thereof.

14. The method according to any one of the preceding claims, wherein the dielectric fluid composition comprises 2 to 100 wt. % base fluid A), 0 to 98 wt. % base fluid B) and 0 to 10 wt. % additive C), based on the total weight of the dielectric fluid composition.

15. A method according to any one of the preceding claims, wherein the amounts of A) to C) add up to at least 90 wt%, more preferably at least 95 wt%, even more preferably 100 wt%, based on the total weight of the dielectric fluid composition.

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