Thermal Management System

Abstract

The present invention provides a thermal management system, comprising: a housing having an interior space; a heat generating component disposed within the interior space; A heat exchanger; a working fluid liquid disposed within the interior space such that the heat-generating components are in contact with the working fluid; The thermal management system is configured to maintain a constant, cyclical flow of the working fluid across one or more heat-generating components, to a heat exchanger, and then back to the heat-generating components. The present invention also provides a method of thermal management of a heat generating component comprising the steps of at least partially immersing the heat generating component in a working fluid and using the working fluid to transfer heat from the heat generating component in a constant cyclic flow of the working fluid across one or more heat generating components, to a heat exchanger and then back to the heat generating component, wherein the working fluid comprises a Fischer-Tropsch derived base fluid, an antioxidant additive, and an antistatic additive. The present invention also provides the use of a Fischer-Tropsch derived base fluid in a working fluid in contact with a heat generating component in a thermal management system to improve the anti-aging properties of the working fluid, wherein the working fluid also comprises an antioxidant additive and an anti-static additive.

Description

[Technical Field]

[0001] The present invention relates to thermal management systems, methods of thermal management for heat-generating components, and the use of Fischer-Tropsch derived base fluids in thermal management systems and in working fluids in contact with heat-generating components. [Background technology]

[0002] New technologies are being sought to provide more energy efficient, lower CO2 solutions across various industries. The present invention relates to many possible efficiencies that promote lower energy requirements and lower CO2 emissions. First, it relates to electric vehicle technology. Second, the present invention is also applicable to thermal management of IT equipment such as servers. However, the invention described herein is not inherently limited by the technology to which it may be applied. The present invention is applicable to any heat-generating electrical technology.

[0003] By 2040, up to 50% of all new passenger vehicle sales are expected to be electric vehicles. This includes battery electric vehicles (BEVs) and fuel cell electric vehicles (FCEVs) hybrid electric vehicles (HEVs). Hybrid electric vehicles contain a battery combined with a conventional combustion engine or a fuel cell. Fuel cell electric vehicles also require batteries for buffering and temporary storage of electrical energy.

[0004] Current battery technology relies on lithium-ion batteries, which are likely to remain the dominant battery technology for at least the next 15 years. While slow charging at home or at the destination will likely become the dominant mode of charging, many customers who want to drive longer distances will require high-performance fast charging (HPC) while on the go. To improve and shorten the charging process, voltage, current, or both must be increased simultaneously. Higher currents also increase the excess heat generated. The level of excess heat can be very high, potentially reaching 20 kWh or more. Effective thermal management is required to control temperature uniformity within the cell pack to prevent irreversible degradation of the battery cells.

[0005] Within an electric vehicle, other components also require thermal management, particularly cooling. Heat is generated by both the electric motor and the inverter during use. A method of thermal management that can be applied to each of these components, and preferably to the circuitry incorporating all of these components (including the battery), would be most desirable.

[0006] Fuel cell powered electrical systems also generate significant waste heat during operation (approximately 50% of the energy is generated as waste heat) that needs to be removed. Thermal management of components poses challenges across other industries as well. Thermal management of IT components, especially servers, also poses many challenges. Air cooling of these components requires high energy usage and expensive cooling infrastructure. A simpler, more energy-efficient system for thermal management of these electronic components would be highly desirable.

[0007] Most cooling systems have historically used air passing over the heat source to manage excess heat. However, such systems have limited thermal capacity and cannot manage the heat generated within electrical devices subjected to process strains, such as HPC. The infrastructure involved in air cooling systems can also be complex and expensive, with many moving parts to maintain.

[0008] More advanced thermal management systems have been developed that use traditional water / glycol mixtures as heat transfer fluids. Battery blocks containing many individual battery cells can be effectively cooled by water / glycol mixtures. This is more efficient than air cooling and is therefore becoming the dominant thermal management technology for use in currently sold electric vehicles. US2009 / 0023056, US2010 / 0025006, and US2011 / 021356, all in the name of Tesla Motors Inc., describe pipe systems in which approximately 11% of the cell surface is in direct contact with pipes containing the coolant. In these indirect thermal management systems, heat must pass through the pipe material, which is then transferred to the glycol / water. This limits the overall effectiveness of this heat transfer design.

[0009] Phase change materials (PCMs) are also utilized in some systems and are an effective means of absorbing heat as they change from a solid to a liquid state. PCMs are limited to select melting temperatures and are not well suited for thermal management. At high ambient temperatures, the PCM may melt without any excess heat from heat-generating components being able to dissipate.

[0010] Under HPC conditions, if these systems cannot effectively control cell temperature and uniformity, the battery management system (BMS) in the vehicle will limit the current to protect the battery. This can very significantly slow the charging process and limit fast charging capabilities. Other systems may simply overheat or be subject to safety shutdown in high temperature conditions.

[0011] Direct liquid cooling with novel thermal management systems is generally designed with heat-generating components immersed in a liquid coolant, and can help control the temperature of each component more effectively because the fluid is in direct contact with the cell surface. Such systems are described, for example, in US 2017 / 0279172. To prevent short circuits, this requires a fluid with very good dielectric properties. Suitable fluids also require low viscosity to aid in pumping, as well as high thermal conductivity and heat capacity. It has already been demonstrated that immersion thermal management can help increase the power and energy density ratios and significantly improve cell durability.

[0012] Hydrofluorinated ethers have been demonstrated as suitable fluids for immersion heat management (e.g., in WO2018 / 224908). Although these fluids mitigate the risk of flammability, they pose several technical challenges for application, such as their low boiling point, high pressure due to their high density, and the resulting challenges in material compatibility. Summary of the Invention [Problem to be solved by the invention]

[0013] The development of improved methods and suitable working fluids for direct thermal management of electrical systems remains an ongoing challenge. Such working fluids require excellent material compatibility, thermodynamic properties, and low flammability. For practical purposes, cost and weight considerations must also be taken into account. The dielectric properties of these working fluids must be maintained over time. It is important that the fluid have a low conductivity level that can be maintained as the fluid ages to prevent short circuits and / or damage to heat-generating components. It is also desirable to avoid electrostatic charging of the working fluid during use, for example, when pumping at high flow rates. [Means for solving the problem]

[0014] The present invention provides 1. A thermal management system comprising: a housing having an interior space; a heat generating component disposed within the interior space; A heat exchanger; a working fluid liquid disposed within the interior space such that the heat-generating components are in contact with the working fluid; The thermal management system is configured to maintain a constant, cyclical flow of the working fluid across one or more heat-generating components, to a heat exchanger, and then back to the heat-generating components.

[0015] The present invention also provides a method of thermal management of a heat generating component comprising the steps of at least partially immersing the heat generating component in a working fluid and transferring heat from the heat generating component using the working fluid in a constant cyclical flow of the working fluid across one or more heat generating components, to a heat exchanger and then back to the heat generating component, wherein the working fluid comprises a Fischer-Tropsch derived base fluid, an antioxidant additive, and an antistatic additive.

[0016] The present invention also provides the use of a Fischer-Tropsch derived base fluid in a working fluid in contact with a heat generating component in a thermal management system to improve the anti-aging properties of the working fluid, wherein the working fluid also comprises an antioxidant additive and an anti-static additive.

[0017] The inventors have surprisingly found that a highly efficient system and method can be provided for immersion thermal management of heat generating components, wherein the heat generating components are in direct contact with a working fluid, the working fluid comprising a Fischer-Tropsch derived base fluid, an antioxidant additive, and an antistatic additive. [Brief explanation of the drawings]

[0018] [Figure 1] 1 shows a simplified circuit for the thermal management system of the present invention. [Figure 2]1 is a diagram of a battery including multiple cells in a thermal management system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] The heat-generating components are preferably electrical elements. Typical electrical elements that can benefit from the systems and methods described herein include computer servers, batteries, inverters, electric motors, and fuel cells, or any combination thereof.

[0020] One or more heat-generating components may be cooled within the thermal management system of the present invention. The thermal management system of the present invention includes a housing having an interior space, a heat-generating component disposed within the interior space, and a working fluid liquid disposed within the interior space such that the heat-generating component is in contact with the working fluid. The heat-generating component may be partially immersed or fully immersed in the working fluid.

[0021] The thermal management system is constructed so that a constant cyclical flow of working fluid is maintained across one or more heat-generating components, to a heat exchanger, and then back to the heat-generating components.

[0022] The heat exchanger may be located internally or externally to the housing. The thermal management system may include a fluid circuit including a pump and a heat exchanger, in which the pump operates to move working fluid from the heat-generating component to and from the heat exchanger.

[0023] Heat is transferred from the heat-generating component to the working fluid. The working fluid can then be pumped away from the heat-generating component to a heat exchanger. Heat can then be transferred from the working component through the heat exchanger. The working fluid can then be returned to the heat-generating component.

[0024] The thermal management system not only functions to remove heat from heat-generating components disposed therein, but may also be suitable for providing heat to the heat-generating components at certain times during the functioning of the components, such as during start-up or operation in cold environments. In this embodiment of the invention, a source of heat is contained within the thermal management system. Such a source of heat may include an internal heat source or an external heat source. A control mechanism is also included within the thermal management system to enable switching between cooling and heating embodiments of the system.

[0025] A suitable internal heat source may involve a battery with a load to form a heat generating circuit. Suitable external heat sources include heat pumps, phase change materials that can release heat upon changing phase, electric heaters, and heaters that burn ethanol, bioethanol, or other fuels.

[0026] The working fluid comprises a Fischer-Tropsch derived base fluid and an antioxidant additive. Preferably, the working fluid also comprises an antistatic additive. Fischer-Tropsch derived base fluids are known in the art. The term "Fischer-Tropsch derived" means that the base fluid is a synthesis product of, or is derived from, a Fischer-Tropsch process.

[0027] Fischer-Tropsch derived base fluids are often classified by the starting material in the Fischer-Tropsch process, i.e., "X-to-liquid" or "XTL," where X represents the starting material. Biomass-to-liquid (BTL), coal-to-liquid (CTL), gas-to-liquid (GTL), and power-to-liquid (PTL) processes are some examples of Fischer-Tropsch processes that produce base fluids. Preferably, the Fischer-Tropsch derived base fluid is a GTL (Gas-To-Liquid) base fluid.

[0028] Suitable Fischer-Tropsch derived base fluids, including oils, that may be conveniently used in Fischer-Tropsch derived working fluids are, for example, those described in EP0776959, EP0668342, WO97021788, WO0015736, WO0014188, WO0014187, WO0014183, WO0014179, WO0008115, WO9941332, EP1029029, WO0118156 and WO0157166.

[0029] The Fischer-Tropsch derived base fluid for use in the present invention preferably has a viscosity of up to 4mm at 100°C. 2 / sec. Particularly preferred Fischer-Tropsch derived base fluids for use in the working fluids herein are Fischer-Tropsch derived base oils having a kinematic viscosity in the range of 2 to 4 mm2 / s at 100°C, such as GTL3 (approximately 3 mm2 / s at 100°C). 2 / sec).

[0030] Another particularly preferred Fischer-Tropsch derived base fluid for use in the working fluids herein is a Fischer-Tropsch derived base fluid produced from a gas oil stream from a GTL process, preferably a dewaxed gas oil stream, the fluid having a viscosity of from 2.0 to 11 mmHg at 40°C. 2 Preferably, the Fischer-Tropsch derived base fluid produced from a gas oil stream has a kinematic viscosity in the range of at least 2.1 mm / s at 40°C. 2 / sec, more preferably at least 2.2 mm 2 Preferably, the fluid has a kinematic viscosity of at most 10.0 mm / s at 40°C. 2 / sec, preferably up to 7.0mm 2 / sec, most preferably up to 6.0mm 2 / sec.

[0031] In one embodiment of the present invention, the working fluid comprises a mixture of two or more Fischer-Tropsch derived base fluids. For example, the working fluid may comprise both a Fischer-Tropsch derived base oil having a kinematic viscosity at 100°C in the range of 2 to 4 mm2 / s and a Fischer-Tropsch derived base fluid produced from a light oil stream.

[0032] The total amount of Fischer-Tropsch derived base fluid incorporated into the working fluid is preferably in the range of 60.0 to 99.9 wt.%. Other components in the working fluid may include one or more additional base oils, including mineral oils and synthetic oils. Mineral oils include liquid petroleum oils and solvent- or acid-treated mineral oils of the paraffinic, naphthenic, or mixed paraffinic / naphthenic types, which may be further refined by hydrofinishing processes and / or dewaxing. Synthetic oils include hydrocarbon oils such as olefin oligomers (including polyalphaolefin base oils; PAOs), dibasic acid esters, polyol esters, polyalkylene glycols (PAGs), alkylbenzenes, alkylnaphthalenes, and dewaxed waxy isomerates.

[0033] In a preferred embodiment, the working fluid comprises one or more additional base oils selected from alkylbenzenes, alkylnaphthalenes, and mixtures thereof. When present, the one or more additional base oils selected from alkylbenzenes, alkylnaphthalenes, and mixtures thereof are present in an amount of 35 wt.% or less, based on the total weight of the working fluid. Preferably, the one or more additional base oils selected from alkylbenzenes, alkylnaphthalenes, and mixtures thereof are present in an amount ranging from 1 to 30 wt.%, based on the total weight of the working fluid.

[0034] The working fluid preferably has a pour point, measured in accordance with ISO 3016, of -40°C or less, more preferably -50°C or less. The working fluid also preferably has a flash point according to ASTM D93 of at least 100°C, more preferably at least 110°C, most preferably at least 120°C, and preferably at most 240°C.

[0035] The working fluid preferably has a viscosity of at least 2.0 mmHg at 40°C measured in accordance with ISO 3104. 2 / sec, more preferably at least 2.1 mm 2 / sec, most preferably at least 2.2 mm 2 The working fluid preferably has a kinematic viscosity of up to 22.0 mm / s at 40°C. 2 / sec, preferably up to 11.0mm 2 / sec, most preferably up to 10.0 mm 2 / sec.

[0036] The thermal conductivity of the working fluid at 20°C is preferably at least 0.135 w / mK, measured according to ASTM D7896. The specific heat capacity of the working fluid at 20° C. according to ASTM D1269 is preferably at least 1.9 kJ / kg*K, more preferably at least 2.0 kJ / kg*K.

[0037] The antioxidant additives are preferably hindered phenol antioxidant additives, sterically hindered mono-, di- and trihydric phenols, sterically hindered di-, tri- and polynuclear phenols. Sterically hindered phenol antioxidants of particular interest are 2,6-di-tert-butylphenol (available from BASF under the trade name "IRGANOX™ L 140"), di-tert-butylated hydroxytoluene ("BHT"), methylene-4,4'-bis-(2,6-tert-butylphenol), 2,2'-methylenebis-(4,6-di-tert-butylphenol), 1,6-hexamethylene-bis-(3,5-di-tert-butyl-hydroxyhydrocinnamate) (available from BASF under the trade name "IRGANOX™ L109"), ((3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl)methyl)thio)acetic acid, C 10 ~C 14isoalkyl esters (available from BASF under the trade name "IRGANOX™ L118"), 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, C7-C9 alkyl esters (available from BASF under the trade name "IRGANOX™ L135"), tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionyloxymethyl)methane (available from BASF under the trade name "IRGANOX™ 1010"), thiodiethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate) (available from BASF under the trade name "IRGANOX™ 1035"), octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate (available from BASF under the trade name "IRGANOX™ 1076"), 2,5-di-tert-butylhydroquinone, and mixtures thereof.

[0038] Particularly preferred antioxidants for use herein are di-tert-butylated hydroxytoluene ("BHT") and C7-C9 alkyl ester of 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid (available from BASF under the trade name "IRGANOX™ L135").

[0039] In one embodiment of the present invention, two or more antioxidant additives may be present in the working fluid. Optionally, additional amine antioxidants, such as alkylated or styrenated diphenylamines, may be added to the working fluid.

[0040] Examples of amine antioxidants include aromatic amine antioxidants, such as N,N'-di-isopropyl-p-phenylenediamine, N,N'-di-sec-butyl-p-phenylenediamine, N,N'-bis(1,4-dimethyl-pentyl)-p-phenylenediamine, N,N'-bis(1-ethyl-3-methyl-pentyl)-p-phenylene-diamine, N,N'-bis(1-methyl-heptyl)-p-phenylenediamine, N,N'-dicyclohexyl-p-phenylene-diamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di(naphthyl-2 -)-p-Phenylenediamine, N-Isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-(1-methylheptyl)-N'-phenyl-p-phenylenediamine, N'-Cyclohexyl-N'-phenyl-p-phenylenediamine, 4-(p-toluene-sulfamido)diphenylamine, N,N'-Dimethyl-N,N'-di-sec-butyl-p-phenylenediamine, Diphenylamine, N-Allyldiphenylamine, 4-Isopropoxydiphenylamine, N -phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, octylated diphenylamines such as p,p'-di-tert-octyldiphenylamine, 4-n-butylaminophenol, 4-butyrylaminophenol, 4-nonanoylaminophenol, 4-dodecanoylaminophenol, 4-octadecanoylaminophenol, di(4-methoxyphenyl)amine, 2,6-di-tert-butyl-4-dimethylaminomethylphenol, 2,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, N,N,N ',N'-tetramethyl-4,4'-diaminodiphenylmethane, 1,2-di(phenylamino)ethane, 1,2-di[(2-methylphenyl)amino]ethane, 1,3-di(phenylamino)propane, (o-tolyl)biguanide, di[4-(1',3'-dimethylbutyl)phenyl]amine, alkylated phenylalphanaphthylamines such as tert-octylated N-phenyl-1-naphthylamine, mixtures of mono- and dialkylated tert-butyl- / tert-octyldiphenylamine, 2,3-dihydro-3,3-dimethyl-4H-1,Possible amine antioxidants are 4-benzothiazine, phenothiazine, N-allylphenothiazine, tert-octylated phenothiazine, 3,7-di-tert-octylphenothiazine, and also compounds according to formulas VIII and IX of EP 1054052, which compounds are also described in US Pat. No. 4,824,601.

[0041] The total amount of the one or more antioxidant additives present in the working fluid is preferably at least 0.1 wt. %, more preferably at least 0.15 wt. %, and preferably at most 3.0 wt. %, more preferably at most 2.0 wt. %, based on the total weight of the working fluid.

[0042] Antistatic additives for use herein are preferably selected from those containing alkyl-substituted naphthalene sulfonic acids, benzotriazoles and substituted benzotriazoles.

[0043] Substituted benzotriazole compounds for use herein can be represented by formula (I):

[0044] [ka]

[0045] In the formula, R 4 is hydrogen or a group represented by the formula (II)

[0046] [ka]

[0047] or a group represented by formula (III):

[0048] [ka]

[0049] During the ceremony, c is 0, 1, 2 or 3; R1 and R 2 are hydrogen or the same or different straight or branched chain alkyl groups of 1 to 18 carbon atoms, preferably branched chain alkyl groups of 1 to 12 carbon atoms, and R 3 is a linear or branched chain C 1~4 is an alkyl group, preferably R 3 is methyl or ethyl, C is 1 or 2, and R 5 is a methylene or ethylene group, and R 6 and R 7 are the same or different alkyl groups of 3 to 15 carbon atoms, preferably 4 to 9 carbon atoms.

[0050] Preferred compounds are 1-[bis(2-ethylhexyl)aminomethyl]benzotriazole, methylbenzotriazole, dimethylbenzotriazole, ethylbenzotriazole, ethylmethylbenzotriazole, diethylbenzotriazole, and mixtures thereof. Other preferred compounds include (N-bis(2-ethylhexyl)-aminomethyl-tolutriazole, unsubstituted benzotriazole, and 5-methyl-1H-benzotriazole.

[0051] Preferred alkyl-substituted naphthalene sulfonic acids include di-C8-C10, branched, C9-rich, alkyl naphthalene sulfonic acids, such as those commercially available as "Stadis 450" from Innospec.

[0052] The content of the antistatic additive in the working fluid herein is preferably greater than 0.5 mg / kg, more preferably greater than 1 mg / kg, based on the total weight of the working fluid. The practical upper limit may vary depending on the particular application of the lubricating composition. This concentration may be up to 3 wt. % based on the total weight of the working fluid, but preferably ranges from 1 mg / kg to 1 wt. %. However, such compounds may be advantageously used at concentrations less than 1000 mg / kg, more preferably less than 300 mg / kg, based on the total weight of the working fluid.

[0053] It has also been surprisingly found that the use of a Fischer-Tropsch derived base fluid in a working fluid in contact with heat-generating components in a thermal management system, which also contains antioxidants and antistatic additives, provides the working fluid with improved anti-aging properties. "Anti-aging properties" herein means that at least one property selected from electrical conductivity (measured in accordance with IEC 60247), appearance and sludge formation (measured in accordance with visual evaluation), dielectric constant (measured in accordance with IEC 60247), and discoloration (measured in accordance with ISO 2049) at 24 and / or 90°C is maintained at a suitable level over time. Preferably, the use of a Fischer-Tropsch derived base fluid in a working fluid in contact with heat-generating components in a thermal management system, which also contains antioxidants and antistatic additives, provides the working fluid with improved conductivity levels over time. [Detailed description of the drawings]

[0054] Figure 1 shows a fluid circuit suitable for the thermal management system of the present invention. In Figure 1, a heat-generating component (1) is located within a housing (2). A flow of working fluid (3) passes through the interior space of the housing (1) and then through connecting piping (4) to one or more heat exchangers (5). In this embodiment, the flow is maintained by a pump (6).

[0055] Figure 2 is a diagram of a battery including multiple cells in a thermal management system according to the present invention. In this embodiment, multiple pouch cells (7) are disposed within a housing (not shown). The flow of working fluid across and between the pouch cells (7) is indicated by arrows (8).

[0056] The invention will now be further illustrated by the following non-limiting examples. [Example]

[0057] Six blends of hydraulic fluid formulations were produced according to the components listed in Table 2. The base oils used were an API Group I base oil commercially available from Shell as HVI60, and a Fischer-Tropsch derived base oil commercially available from Shell as GTL 3. The characteristics of the base oils are shown in Table 1.

[0058] [Table 1]

[0059] The antioxidant additive used in the examples was di-tert-butylated hydroxytoluene (BHT), and the antistatic additive was, for example, Innospec's Stadis 450. Stadis 450 is indicated to contain 10-25% di-C8-C10, branched, C9-rich, alkyl naphthalene sulfonic acid.

[0060] The working fluids (900 mL per fluid) were placed in separate 1000 mL beakers. A copper and steel coil was also placed in each beaker. Such coils were of the type used in the ASTM D493 oxidation stability test method, but were half the normal size.

[0061] To prepare the coils of copper and steel wire, a 112 mm length of low-metallic steel wire having a diameter of 1.59 mm and an electrolytic copper wire also 112 mm long but having a diameter of 1.63 mm were placed next to each other. The wires were then twisted into a coil before being used for testing.

[0062] The beaker containing the oil sample and coil was then kept in an oven (with ventilation) at 120° C. The beaker was uncovered. At each of the times shown in Table 2 below, 125 mL oil samples were taken and tested. Electrical conductivity was tested according to IEC 60247. Appearance was tested by visual assessment. Sample color was tested according to ISO 2049.

[0063] These examples, representative of the use of working fluids in thermal management systems, clearly demonstrate that working fluids containing Fischer-Tropsch derived base fluids (Blends 1-3) have and maintain better conductivity and appearance characteristics over time when compared to working fluids containing API Group I base oils (Blends 4-6). These characteristics are further improved by the addition of an antioxidant additive (Blend 2). Blend 2 demonstrates the maintenance of electrical conductivity at low levels as well as good appearance and color characteristics. The further addition of an antistatic additive to working fluids containing Fischer-Tropsch derived base fluids and antioxidant additives maintains the electrical conductivity of the fluids over time at excellent levels that prevent static buildup and short circuits. These improvements are not seen in comparable blends of working fluids containing API Group I base oils (Blends 4 and 5).

[0064] [Table 2]

Claims

1. 1. A thermal management system comprising: a housing having an interior space; a heat generating electrical element disposed within the interior space; A heat exchanger; a working fluid liquid disposed within the interior space such that the heat generating electrical element is in direct contact with the working fluid and the heat generating electrical element is partially or completely immersed in the working fluid; the working fluid comprises a Fischer-Tropsch derived base fluid, an antioxidant additive, and an antistatic additive; the antistatic additive is selected from the group consisting of alkyl-substituted naphthalene sulfonic acids, alkylated benzotriazoles, and benzotriazoles; The thermal management system is constructed to maintain a constant cyclical flow of working fluid across the one or more heat-generating electrical elements, toward the heat exchanger, and then back to the heat-generating electrical elements.

2. The thermal management system of claim 1 , wherein the antioxidant additive comprises a hindered phenol.

3. The antioxidant additive is selected from the group consisting of 2,6-di-tert-butylphenol, di-tert-butylated hydroxytoluene, methylene-4,4'-bis-(2,6-tert-butylphenol), 2,2'-methylenebis-(4,6-di-tert-butylphenol), 1,6-hexamethylene-bis-(3,5-di-tert-butyl-hydroxyhydrocinnamate), ((3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl)methyl)thio)acetic acid, C10 to C14 isoalkyl esters, 3,5-di 3. The thermal management system of claim 2, wherein the at least one hydroxypropyl methyl group is selected from the group consisting of 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, C7 to C9 alkyl esters, tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionyloxymethyl)methane, thiodiethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate, octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, 2,5-di-tert-butylhydroquinone, and mixtures thereof.

4. The thermal management system of any one of claims 1 to 3, further comprising a pump, the pump configured to move the working fluid to and from the heat exchanger.

5. The thermal management system of any one of claims 1 to 4, wherein the heat generating electrical element comprises a server.

6. The thermal management system according to any one of claims 1 to 4, wherein the heat generating electrical element is a battery.

7. The thermal management system of any one of claims 1 to 3, wherein the heat-generating electrical element is one or more of a battery, an e-motor, and an inverter in an electric vehicle.

8. 1. A method of thermal management of heat-generating electric elements, comprising: at least partially immersing a heat-generating electric element in direct contact with a working fluid; and transferring heat from the heat-generating electric element using the working fluid in a constant cyclical flow of the working fluid across the one or more heat-generating electric elements, to a heat exchanger, and then back to the heat-generating electric elements, wherein the working fluid comprises a Fischer-Tropsch derived base fluid, an antioxidant additive, and an antistatic additive; The method wherein the antistatic additive is selected from the group consisting of alkyl-substituted naphthalene sulfonic acids, alkylated benzotriazoles, and benzotriazoles.

9. 9. The method of claim 8, wherein the method includes pumping the working fluid through a heat exchanger, transferring heat from the working fluid, and returning the working fluid to the heat-generating electrical element.

10. 10. The method of claim 8 or 9, wherein the antioxidant additive is a hindered phenol.

11. The method of claim 8, wherein the antioxidant additive is 2,6-di-tert-butyl-4-methylphenol.

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