Patent Description:
The present invention relates to the field of thermal management fluids for direct cooling. More efficient as well as fast charging battery applications require effective cooling systems to dissipate heat from low to high voltage applications, e.g. 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 arcing. Next to air and indirect cooling, there is direct liquid immersion cooling, which is the most efficient cooling technology. Especially for larger batteries e.g. in electric vehicles there is a high amount of heat generated during charging and discharging processes. The optimum temperature for lithium-ion batteries is <NUM>-<NUM>, any higher temperature would decrease battery performance and longevity, and may lead to battery failures like thermal runaway. This is the reason why there is a need for efficient thermal management fluids.

Currently available cooling fluids are typically hydrocarbon-based cooling fluids with a high amount of C17 or longer branched alkyl chains. For example, <CIT> discloses renewable paraffinic composition comprising a major amount of a mixture of C17 and C18 paraffins. It is also described that the composition should comprise less than 10wt% C16, and preferably less than 5wt% as exemplified in the experimental part, where the compositions comprise a total amount of around 4wt% C16 iso- and n- paraffins and approximately 90wt% or more of a mixture of C17 and C18 iso- and n- paraffins.

<CIT> describes heat transfer fluids with a boiling point from <NUM> to <NUM> and a boiling range below <NUM>, wherein said fluids comprise more than <NUM>% by weight of iso-paraffins and less than <NUM>% naphthene. While this document focuses mainly on specific heat capacity and lubricity properties, it is silent on cold flow properties (pour point and viscosities at low temperatures), which are crucial for a broad temperature range application as thermal management fluid.

These thermal management compositions comprising hydrocarbons with high branched alkyl chains (major amount C17 or longer branched alkyl chains) cause problems, especially in regard to low temperature performance over a broad temperature range of use. Therefore, an object of the present invention was to provide a new thermal management method of cooling an electrical equipment system, wherein the thermal management fluid composition should have a low electrical conductivity, low viscosity, excellent thermal properties over a wide temperature range while maintaining low pour point, high flash point and high auto ignition temperatures.

After thorough investigation, the inventors of the present invention have surprisingly found that hydrogenated branched isoparaffinic oligomers of butene as defined in claim <NUM>, with a predominant amount of hydrogenated branched isoparaffinic oligomers with an alkyl chain of <NUM> carbon atoms, solves the above technical problem and provides, excellent and consistent heat dissipation over a wide temperature range, while having excellent low temperature performance as well as high flash point and auto ignition point.

Therefore, in a first aspect, the present invention relates to a method of cooling an electrical equipment system as defined in claim <NUM>.

For the purpose of better illustrating the advantages and properties of the claimed method of cooling, object of the present invention, one graph is attached as a non-limiting example:
<FIG> is a graph showing heat dissipation performance of different hydrocarbons from -<NUM> to <NUM>. The dielectric fluid composition Comp. HC1 (■) shows a steep increase in Prandtl Number at lower temperatures. The dielectric fluid compositions Comp. HC2 (▲) and HC1 (•) show a similar behavior at high and medium temperature. However, the dielectric fluid composition HC1 has a lower increase in Prandtl number at lower temperatures. The dielectric fluid composition HC2 (◆) shows the lowest Prandtl number with a very low slope over the whole temperature profile.

Thus, the present invention relates to a method of cooling an electrical equipment system by using a dielectric fluid composition comprising a base fluid A) comprises hydrogenated oligomers obtained from the oligomerization of butene,.

In other words, the base fluid A) comprises hydrogenated oligomers obtained from the oligomerization of butene of Formula (I), Formula (II) and Formula (III)
<CHM>.

According to another preferred embodiment, the base fluid A) comprises hydrogenated oligomers obtained from the oligomerization of butene of Formula (I), Formula (II) and Formula (III) and the content of oligomers obtained from the oligomerization of butene of Formula (III) is less than <NUM>% by weight, preferably less than <NUM>% by weight, even more preferably less than <NUM>% by weight, based on the total weight of the base fluid A). Preferably, the base fluid A) consists of hydrogenated oligomers obtained from the oligomerization of butene.

In a preferred embodiment of the invention, the base fluid A), comprising hydrogenated branched isoparaffinic saturated oligomers obtained from the oligomerization of butene and further hydrogenation step, is free of n-paraffins and aromatic components. More preferably, the base fluid A) consists of hydrogenated branched isoparaffinic saturated oligomers obtained from the oligomerization of butene of Formula (I), Formula (II) and Formula (III) and is free of n-paraffins and aromatic components.

In another preferred embodiment of the invention, the base fluid A) comprises, based on the total weight of the base fluid A),.

Yet in another preferred embodiment of the invention, the base fluid A) comprises, based on the total weight of the base fluid A),.

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),.

According to the present invention, it is preferred that the hydrogenated branched isoparaffinic oligomers b) consists of.

The base fluid A) according to the invention is prepared by the oligomerization of butene, in which the oligomerization of butene of Formula (I), Formula (II) and Formula (III) is carried out using a heterogeneous oligomerization catalyst forming an oligomerizate, followed by subsequent distillation in which the oligomers formed during the oligomerization partially separated from the residual oligomerizate. Finally, the distillated oligomers are hydrogenated. The resulting product is the base fluid A). Preferably, the base fluid A) according to the invention is prepared following the example of <CIT>.

According to the invention, the base fluid A) comprises hydrogenated oligomers a), b) and c) obtained from the oligomerization of butene, wherein the hydrogenated oligomers a), b) and c) of the base fluid A) have an iodine value of less than <NUM> iodine / <NUM> of oligomer, preferably less than <NUM> iodine / <NUM> of oligomer, more preferably less than <NUM> iodine / <NUM> of oligomer according to DIN <NUM>. The iodine value is a measure of the relative degree of unsaturation in components, as determined by the uptake of halogen. In the present invention, the iodine value is the mass of iodine in grams that is consumed by <NUM> grams of the hydrogenated oligomers of the base fluid A).

Preferably, the electrical equipment system is selected from the group consisting of electric batteries, electric motors, inverter, electric transformers, electric capacitors, fluid-filled transmission lines, fluid-filled power cables, computers, data servers and power electronics.

In another preferred embodiment of the invention, the method of cooling an electrical equipment system according to the invention is a direct liquid immersion cooling. In a direct liquid immersion cooling, the heat is removed from the system by circulating liquid into direct contact with hot components.

According to a preferred embodiment of the invention, the dielectric fluid composition as defined in claim <NUM> further comprises a base fluid B) selected from the group consisting of polyol esters, monoesters, saturated hydrocarbons, dicarboxylic acid esters, carbonates, ethers, alcohols, amines, amides, or a mixture thereof. In the context of the present invention, component B) is a base fluid, different from the base fluid A) as defined in claim <NUM> and throughout the present specification. Thus, preferably, the dielectric fluid composition comprises the base fluid A) according to the invention as a first base fluid, and the above-indicated component B) as a second base fluid.

Preferably, the amounts of the base fluid A) and the base fluid B) add up to at least <NUM>% by weight, more preferably add up to at least <NUM>% by weight, based on the total weight of the dielectric fluid composition.

Preferably, the dielectric fluid composition may further comprise an additive C) selected from the group consisting of defoamers, seal compatibility agents, antioxidants, yellow metal passivators, rust inhibitors, electrostatic discharge depressants, demulsifiers, dyes or a mixture thereof. The additive compounds C) correspond to typical additives used in thermal management fluids and are described in detail, inter alia, in <NPL>; <NPL>". Preferably, suitable yellow metal passivators are selected from the list consisting of imidazonines, imidazoles, thiazoles, thiadiazoles, triazoles, tolyltriazoles, pyridines, quinolines, morpholines or a mixture thereof.

Preferably, suitable rust inhibitors are selected from the list consisting of sulfonates, carboxylates, alkyl amines, amine carboxylates, amine borates, phosphates or a mixture thereof.

Preferably, suitable electrostatic discharge depressants are selected from the list consisting of ester quats, imidazolium quats, alkoxy alkyl quats, trialkyl monomethyl quats, monoalkyl trimethylquats, diamidoaminequats, benzyl quats, ethoxylated ether amines, ether diamines, fatty alcohols ethoxylates, ether amine oxides, ether amine quats or a mixture thereof.

Preferably, suitable demulsifiers are selected from the list consisting of polyalkoxylated phenols, polyalkoxylated polyols, polyalkoxylated polyamines or a mixture thereof.

Preferably, suitable defoamers are selected from the list consisting of silicone oils, fluorosilicone oils, fluoroalkyl ethers, polyacrylates or a mixture thereof.

Preferably, the seal compatibility agents are selected from the list consisting of adipate-ester, sebacate-ester, neopentylpolyol-ester, sulfolanes.

Preferably, the suitable antioxidants include phenol-based antioxidants and amine-based antioxidants.

In a preferred embodiment, the phenol-based antioxidants are selected from the list consisting of octadecyl-<NUM>-(<NUM>,<NUM>-di-tert-butyl-<NUM>-hydroxyphenyl)propionate; <NUM>,<NUM>' -methylenebis(<NUM>,<NUM>-di-tertbutylphenol); <NUM>,<NUM>' -bis(<NUM>,<NUM>-di-t-butylphenol); <NUM>,<NUM>' -b is(<NUM>-methyl-<NUM>-t-butylphenol); <NUM>,<NUM>' -methylenebis(<NUM>-ethyl-<NUM>-t-butylphenol); <NUM>,<NUM>' -methylenebis( <NUM>-methyl-<NUM>-t-butyl phenol); <NUM>,<NUM>' -butylidenebis(<NUM>-methyl-<NUM>-t-butylphenol); <NUM>,<NUM>'-isopropylidenebis(<NUM>,<NUM>-di-t-butylphenol); <NUM>,<NUM>'-methylenebis(<NUM>-methyl-<NUM>-nonylphenol); <NUM>,<NUM>'-isobutylidenebis(<NUM>,<NUM>-dimethylphenol); <NUM>,<NUM>'-methylenebis(<NUM>-methyl-<NUM>-cyclohexylphenol); <NUM>,<NUM>-di-t-butyl-<NUM>-methylphenol; <NUM>,<NUM>-di-t-butyl-<NUM>-ethyl-phenol; <NUM>,<NUM>-dimethyl-<NUM>-t-butylphenol; <NUM>,<NUM>-di-t-amyl-p-cresol; <NUM>,<NUM>-di-t-butyi-<NUM>-(N,N'-dimethylaminomethylphenol); <NUM>,<NUM>'thiobis(<NUM>-methyl-<NUM>-t-butylphenol); <NUM>,<NUM>'-thiobis(<NUM>-methyl-<NUM>-t-butylphenol); <NUM>,<NUM>'-thiobis(<NUM>-methyl-<NUM>-t-butylphenol); bis(<NUM>-methyl-<NUM>-hydroxy-<NUM>-t-butylbenzyl) sulfide; bis(<NUM>,<NUM>-di-t-butyl-<NUM>-hydroxybenzyl) sulfide; n-octyl-<NUM>-(<NUM>-hydroxy-<NUM>,<NUM>-di-t-butylphenyl)propionate; n-octadecyl-<NUM>-(<NUM>-hydroxy-<NUM>,<NUM>-di-t-butylphenyl)propionate; <NUM>,<NUM>'-thio[diethyl-bis-<NUM>-(<NUM>,<NUM>-di-t-butyl-<NUM>-hydroxyphenyl)propionate], or a mixture thereof. Even more preferred phenol-based antioxidants are bis-phenol-based antioxidants and ester group containing phenol-based antioxidants.

Amine-based antioxidants include, for example, monoalkyldiphenylamines such as monooctyldiphenylamine, monononyldiphenylamine; dialkyldiphenylamines such as <NUM>,<NUM>' - dibutyldiphenylamine, <NUM>,<NUM>'-dipentyldiphenylamine, <NUM>,<NUM>'- dihexyldiphenylamine, <NUM>,<NUM>'-diheptyldiphenylamine, <NUM>,<NUM>'-dioctyldiphenylamine, <NUM>,<NUM>'-dinonyldiphenylamine; polyalkyldiphenylamines such as tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, tetranonyldiphenylamine; naphthylamines, concretely alpha-naphthylamine, phenyl-alpha-naphthylamine and further alkyl-substituted phenyl-alpha-naphthylamines such as butylphenyl-alpha-naphthylamine, pentylphenyl-alpha-naphthylamine, hexylphenyl-alpha-naphthylamine, heptylphenyl-alpha-naphthylamine, octylphenyl-alpha-naphthylamine, nonylphenyl-alpha-naphthylamine. Of those, diphenylamines are preferred to naphthylamines, from the viewpoint of the antioxidation effect thereof.

According to a preferred embodiment of the invention, the dielectric fluid composition according to the invention comprises from <NUM> to <NUM>% by weight of base fluid A), from <NUM> to <NUM>% by weight of base fluid B), and <NUM> to <NUM>% by weight of additive C), based on the total weight of the dielectric fluid composition. More preferably, the total amount of A), B) and C) adds up to at least <NUM>% by weight, more preferably at least <NUM>% by weight, even more preferably <NUM> % by weight, based on the total weight of the dielectric fluid composition according to the invention.

According to a preferred embodiment of the invention, the base fluid A) has a pour point below minus <NUM> (-<NUM>) according to ASTM D5950.

In the present invention, the Prandtl number (Pr) is calculated according to the formula below. The Prandtl number is a dimensionless quantity that puts the viscosity of a fluid in correlation with the thermal conductivity (see <NPL>). The Prandtl number is given as: <MAT> wherein.

As shown in the experimental part below, the inventors of the present invention have surprisingly found out that the base fluid A) of the method according to the invention have all small Prandtl numbers over a wide range of temperatures. It confirms that the base fluids A) according to the invention have high thermal conductivity and low viscosity, which is advantageous for thermal management in electric devices. This means that the dielectric fluids of the invention are capable of efficiently exchanging heat with an electrical device. Indeed, the higher the thermal conductivity, the better the heat transfer capacity. Furthermore, the fluids show great cold flow properties.

According to a preferred embodiment, the base fluid A) of the invention has a Prandtl number below <NUM> at <NUM> and 1013hPa pressure, more preferably, below <NUM> at <NUM> and 1013hPa pressure.

The invention is further illustrated in detail hereinafter with reference to examples and comparative examples, without any intention to limit the scope of the present invention.

The kinematic viscosities of the dielectric fluid compositions were measured at the temperatures indicated in Table1 (namely <NUM>, <NUM> and -<NUM>) and according to ASTM D445.

Specific heat capacity and thermal conductivity were measured at the temperatures indicated in Table <NUM> with the hot wire method according to ASTM D7896-<NUM>.

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

Flash point was measured with a closed-cup Pensky Martin set-up according to ASTM D93.

The electrical conductivity was measured at <NUM> according to ASTM D2624.

Density was measured at the temperatures indicated in Table <NUM> and according to DIN EN ISO <NUM>.

The Auto Ignition Temperature was measured according to DIN <NUM>.

The quantitative analysis of the thermal management fluids components was measured via gas chromatography. The analysis was carried out with a quartz capillary column DB-<NUM><NUM>% Diphenyl / <NUM>% Dimethylpolysiloxan (<NUM> x <NUM> x <NUM>) from Agilent, interfaced with a flame ionization detector. The temperature program was <NUM> for <NUM> which increased to <NUM> for <NUM>. The flow rate was <NUM>/min for <NUM> which was increased to <NUM>/min. The injection temperature is <NUM> and the detector temperature <NUM>. Helium gas was used as a carrier gas and was adjusted to column velocity flow of <NUM>/min.

For the identification of the chromatogram peaks mass spectroscopy was used. The analysis was carried out with a quartz capillary column DB-<NUM><NUM>% Diphenyl / <NUM>% Dimethylpolysiloxan (<NUM> x <NUM> x <NUM>) from Agilent, interfaced with a mass spectrometer. The temperature program was <NUM> for <NUM> which increased to <NUM> for <NUM>. The injection temperature is <NUM> and the carrier flow <NUM>/min.

The degree of hydrogenation of hydrogenated oligomers a), b) and c) obtained from the oligomerization of butene of the base fluid was determined according to DIN <NUM>.

The base fluid HC1 is prepared in the same manner as the example in <CIT>. Butene compounds of Formula (I), (II) and (III) are being oligomerized in the presence of a nickel catalyst. Next, the formed C16-oligomers are separated by distillation and finally hydrogenated.

Analysis of the product shows that the base fluid consists of 64wt% C16 / 34wt% C20 and C24 branched isoparaffinic hydrocarbon / Rest high boiling hydrocarbons (C28 or more branched isoparaffinic hydrocarbons).

The iodine value according to DIN <NUM> of the base fluid HC1 is <NUM> iodine / <NUM> oligomers.

The base fluid HC2 is prepared following the same procedure as for the base fluid HC1. The product obtained by further purification via distillation has the following composition:
Analysis of the product shows that the base fluid consists of 78wt% C16 / 22wt% C20 and C24 branched isoparaffinic hydrocarbon.

The comparative base fluid Comp. HC1 is a distillate comprising iso and n-paraffins with alkyl chains of more than <NUM> carbon atoms (hydrotreated light paraffinic base oil with a KV40 of <NUM> mm2/s).

The comparative base fluid Comp. HC2 corresponds to <NUM>-decene based dimer.

The base fluid examples according to the invention (base fluid A) of claim <NUM>) and the comparative base fluid examples (Comp. HC) are shown in Table <NUM> below with their respective physical properties.

As shown in Table <NUM> above, the C16-enriched hydrocarbon base fluids according to the invention (Examples HC1 and HC2) have very good thermal conductivity properties combined with low viscosity and excellent low temperature performance. In contrast, Comparative Examples Comp. HC1 and Comp. HC2 do not combine all together the above-indicated properties and thus do not perform so efficiently.

Furthermore, although the C16-enriched hydrocarbon base fluid Example HC1 according to the invention shows an acceptable flash point (<NUM>), surprisingly the autoignition point of HC1 is superior to the autoignition point of Comp. HC1 (<NUM> versus <NUM>, respectively). This is of course a big advantage to hinder self-ignition when the electrical system has a malfunction which would cause a thermal runaway.

Table <NUM> below shows the evolution of the Prandtl Index value of some thermal management fluid compositions according to the invention and some comparative thermal management fluids over a wide range of temperature. The slope indicates the efficiency of the Prandtl number over a wide temperature range, the lower the increase the better is the efficiency. The intercept describes the Prandtl number at <NUM>. Again, the lower the Prandtl number the better the heat removal of the electric system. This is also reflected in <FIG> in the present invention.

The comparative thermal management fluid Comp. HC1 shows a sharp increase in the slope at <NUM>, and therefore does not fulfill a steady thermal management effect over a wide range of temperature.

The comparative thermal management fluid composition Comp. HC2 also shows an increase of the Prandtl Index value. Even if the results are better than for the comparative thermal management fluid Comp. HC1, the slope for the base fluid Comp. HC2 is steeper than the slopes of the inventive base fluids HC1 and HC2 according to the invention.

In particular, the inventive base fluid HC2 shows the lowest slope. Indeed, the Prandtl Index value slope should be steady over a wide temperature profile. This is observed by the inventive thermal management fluid compositions according to the invention, where a clear improvement can be observed.

Claim 1:
Method of cooling an electrical equipment system by using a dielectric fluid composition comprising a base fluid A) comprising hydrogenated oligomers obtained from the oligomerization of butene, and wherein the base fluid A) comprises, based on the total weight of the base fluid A),
a) from <NUM> to <NUM>% by weight of hydrogenated branched isoparaffinic oligomers with an alkyl chain of <NUM> carbon atoms,
b) from <NUM> to <NUM>% by weight of hydrogenated branched isoparaffinic oligomers with an alkyl chain of <NUM> carbon atoms or with an alkyl chain of <NUM> carbon atoms or a mixture thereof,
c) from <NUM> to <NUM>% by weight of hydrogenated branched isoparaffinic oligomers with an alkyl chain of more than <NUM> carbon atoms,
and wherein the hydrogenated oligomers a), b) and c) of the base fluid A) have an iodine value of less than <NUM> iodine / <NUM> of oligomer according to DIN <NUM>.