Heat transfer fluid

Abstract

The electrical device comprises at least one electrical element in thermal contact with a heat transfer fluid comprising gt, in weight percent of fluid; 95% of at least one ester of a C5 to C9 monocarboxylic acid with a C5 to C9 monoalcohol, the ester having a carbon number of less than 17.

Description

[0001] The present invention relates to heat transfer fluids for transferring heat from one location to another, electrical equipment comprising such heat transfer fluids and methods of using such heat transfer fluids in electrical equipment.

[0002] The present invention is particularly well suited for use with heat transfer fluids used in environments where electrical exposure may occur and cryogenic temperatures may exist, although its application is not limited thereto.

[0003] The invention is described below with reference to a battery, but has wider applicability. For example, the heat transfer fluid is used in a transformer.

[0004] "Lithium plating" is a problem that can occur during the charging of lithium-ion battery packs. Lithium plating refers to the deposition of lithium on the surface of the anode, rather than the lithium being ideally intercalated into the anode material. This occurs when the rate at which lithium is deposited is faster than it can be intercalated into the anode, so it depends on the charge rate and the kinetics of lithium intercalation into the anode material.

[0005] Lithium plating is exacerbated by operating the battery pack at low temperatures, as low temperatures lead to reduced ion diffusion and electrolyte conductivity, increased resistance, and slower kinetics of lithium insertion into the anode material. Lithium plating can lead to reduced battery pack capacity and, in extreme cases, short circuits.

[0006] Since the internal resistance of the battery (cell) increases and the electrochemical reaction slows down at sub-zero temperatures, it is necessary to limit the input current during battery pack charging. This in turn causes the battery pack system to take a very long time to charge when the battery temperature is below 0°C.

[0007] To counteract this, it is beneficial to preheat the battery cells in cold ambient temperatures to reach a more suitable temperature and achieve a suitable fast charging rate.

[0008] Using an immersion cooling system provides good heat transfer between the preheating device and the battery cells. However, the viscosity of some traditional heat transfer fluids at sub-zero temperatures compared to higher temperatures causes excessive pressure drop in the system, slowing the flow of the fluid, which hinders heat transfer. The pumping system also requires additional energy to circulate the fluid, which has a higher viscosity at low temperatures, and the pump may need to be oversized to compensate.

[0009] A variety of heat transfer fluids are known including, for example, hydrocarbons, fluorinated hydrocarbons, esters, and water / glycol mixtures.

[0010] The water / glycol mixture needs to be isolated from the operating electrical components, which creates a thermal barrier between the components and the heat transfer fluid. This water / glycol mixture has a kinematic viscosity of up to 100 mm at -40°C. 2 / s (see https: / / detector-cooling.web.cern.ch / data / Table%208-3-1.htm).

[0011] Hydrocarbons and fluorinated hydrocarbons have a poor reputation when it comes to biodegradability.

[0012] Esters are known to be biodegradable to varying degrees and to provide good dielectric properties. Esters proposed to date for use in heat transfer fluids include diesters, but their viscosity at, for example, -40°C (about 233K) is too high to provide comparable performance to water / glycol mixtures or fluorinated hydrocarbons.

[0013] US 2012 / 283162 A1 proposes using an oil ester having a total of 23 or more terminal methyl, methylene and ether groups in the main chain as a base oil for cooling electric motors.

[0014] US2022 / 0131205A1 proposes the use of esters in cooling compositions for cooling battery packs and / or power electronics of electric or hybrid vehicles, etc. The only exemplified monoester is highly branched 3,5,5-trimethylhexyl 3,5,5-trimethylhexanoate having 18 carbon atoms, and its viscosity at -25°C is disclosed to be 55.8 mm 2 / s.

[0015] WO2010 / 116234 discloses a liquid heat exchange medium comprising 90% by volume or more of 2-ethylhexyl caprylate (2-ethylhexyl octanoate), and allowing for the presence of other esters of C6 to C8 fatty acids with 2-ethylhexanol.

[0016] The heat transfer fluid used in the present invention provides heat transfer performance comparable to that of fluorinated hydrocarbons, has a viscosity much lower than that of diesters and conventional hydrocarbons, and is biodegradable. In addition, the raw materials for the esters described herein are preferably obtained from biological sources, thereby providing environmental benefits during their manufacture and use.

[0017] Therefore, the present invention provides an electrical device comprising at least one electrical component in thermal contact with a heat transfer fluid, wherein the heat transfer fluid comprises >95% by weight of the fluid of an ester of at least one C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol, the carbon number of the ester being less than 17, and the heat transfer fluid comprises no more than 80% by weight of 2-ethylhexyl octanoate.

[0018] Alternatively, at least one ester may include less than 60 wt% 2-ethylhexyl octanoate, less than 40 wt% 2-ethylhexyl octanoate, less than 20 wt% 2-ethylhexyl octanoate, less than 10 wt% 2-ethylhexyl octanoate, or less than 1 wt% 2-ethylhexyl octanoate. At least one ester may be substantially free of 2-ethylhexyl octanoate.

[0019] The C5 to C9 monocarboxylic acid may optionally be an acyclic monocarboxylic acid, such as a linear monocarboxylic acid or a branched monocarboxylic acid.

[0020] As non-limiting examples, the C5 to C9 monocarboxylic acid may include any one of pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, 2-ethylhexanoic acid, or 3,5,5-trimethylhexanoic acid.

[0021] The C5 to C9 monoalcohol is optionally an acyclic monoalcohol, such as a linear monoalcohol or a branched monoalcohol, and may be a primary, secondary or tertiary alcohol. When branched, the C5 to C9 monoalcohol may contain only methyl branches.

[0022] As non-limiting examples, the C5 to C9 monohydric alcohols may include any of 2-pentanol, 3-pentanol, 2-hexanol, 3-hexanol, 2-heptanol, 3-heptanol, 4-heptanol, 2-octanol, 3-octanol, 4-octanol, 2-nonanol, 3-nonanol, 4-nonanol, 5-nonanol, isononanol, 7-methyloctan-1-ol, 2-ethylhexanol, or 3,5,5-trimethyl-1-hexanol.

[0023] The electrical device may include a heat source in thermal contact with a heat transfer fluid such that heat is transferred from the heat source to the at least one electrical component through the heat transfer fluid.

[0024] The electrical device may include a heat sink in thermal contact with the heat transfer fluid such that heat is transferred from the at least one electrical component to the heat sink via the heat transfer fluid.

[0025] At least one electrical component may be immersed in the heat transfer fluid.

[0026] The device may be configured to provide heat to the at least one electrical component when the at least one electrical component is below a first temperature and to remove heat from the at least one electrical component when the at least one electrical component is above a second temperature.

[0027] The at least one electrical component may include a battery, which may be a lithium-ion battery, a lithium metal battery, or any other battery.

[0028] The heat transfer fluid in the apparatus comprises>95% by weight of the fluid of an ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol, and the one ester may be the only ester present. The carbon number of some or each of the at least one ester in the heat transfer fluid is optionally 16 or less, or 15 or less. The carbon number of some or each of the at least one ester in the heat transfer fluid is 11 or more, or 12 or more, or 13 or more, or 14 or more.

[0029] The heat transfer fluid in the device may include one or more of the following components: antioxidants, metal passivators, friction modifiers, corrosion inhibitors, defoamers, detergents, extreme pressure additives, anti-wear additives, and thermally conductive particles.

[0030] A method of operating an electrical device includes transferring heat from a heat transfer fluid to at least one electrical component and operating the electrical component when a threshold temperature is exceeded.

[0031] The specific heat transfer fluid claimed includes the following components by weight percentage:

[0032] >95% of at least one ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol, the ester having a carbon number of less than 17, and at least one functional additive selected from antioxidants, metal passivators, friction modifiers, corrosion inhibitors, defoamers, detergents, extreme pressure additives, and antiwear additives.

[0033] The functional additives include the following components in weight percentage of the fluid:

[0034] ≥ 0.1% antioxidant,

[0035] ≥0.001% metal passivator.

[0036] Optionally, the functional additive includes the following components in weight percentage of the fluid:

[0037] 0.1% to 1.0% antioxidants,

[0038] 0.001% to 0.05% metal passivator.

[0039] Other features of the present invention will be apparent from the appended claims and the following description, which illustrates by way of example but not by way of limitation the scope of the claimed invention. Figure 1 , which schematically illustrates a device embodying aspects of the invention as claimed.

[0040] exist Figure 1 In the embodiment, a device 1 contains a plurality of electrical components 2 (eg, battery packs), which are immersed in a heat transfer fluid 3 filling the device so as to be in thermal contact with the heat transfer fluid 3. The device includes a heat source 4 and a heat sink 5.

[0041] A heat source 4 can provide heat to the heat transfer fluid 3 and thereby to the electrical component 2. The heat source can be any convenient source, such as an electric heater or a heat exchanger with a heating circuit which can carry the same or a different heat transfer fluid.

[0042] The heat sink 5 may absorb heat from the heat transfer fluid 3 to remove heat from the device. The heat may be removed in any convenient manner, such as by radiation to the environment, by heat exchange with a cooling circuit carrying the same or a different heat transfer fluid.

[0043] The apparatus 1 is shown as a closed unit and movement of the heat transfer fluid is achieved by convection, but would normally require a pumping system.

[0044] Thus, the heat transfer fluid is able to transfer heat to one part of the electrical device or to transfer heat from another part of the electrical device.

[0045] The device may be configured to transfer heat to the electrical component when the temperature of the portion is below a threshold temperature. For example, a temperature sensor may be used to detect the temperature in the device and provide heat as needed to raise the electrical component to a threshold temperature.

[0046] For battery packs, using a dielectric fluid with a very low viscosity at -40°C can more efficiently transfer heat from the preheating equipment to the battery cells, reducing the energy requirements of the pump and enabling the specification of smaller, lighter pumping equipment. This will speed up the preheating of the battery pack system and allow the fast charge current to be applied more quickly while making the battery pack charging more efficient overall. This in turn has the potential to significantly reduce fast charge times in low temperature environments, providing significant advantages to consumers.

[0047] Potential applications include but are not limited to:

[0048] Battery packs in vehicles (including but not limited to land, air and sea vehicles);

[0049] Stationary battery storage, such as those used to store renewable energy. Storage units are typically charged with surplus energy at night when it is cooler, so the battery may need to be preheated;

[0050] Non-battery applications requiring low viscosity dielectric heat transfer fluids.

[0051] The performance of a heat transfer fluid depends on many factors, and the Mouromtseff number (Mo) can reflect the heat transfer ability of the fluid.

[0052]

[0053] Where ρ is density, k is thermal conductivity, Cp is the specific heat and μ is the dynamic viscosity of the heat transfer fluid.

[0054] The exponents a, b, d, and e are system dependent and vary according to whether the flow is turbulent or laminar; but provide a means of comparison between heat transfer fluids for a defined system. The higher the Mo value, the better the heat transfer capability of the fluid in that system.

[0055] It is worth noting that the denominator is a function of dynamic viscosity, which (in the absence of any phase change over a short temperature range) varies more with temperature than any other factor.

[0056] Table 1 below shows the properties of a range of fluids, including:

[0057] • Monoesters of the present invention (shown in part 1 of the table);

[0058] Monoesters not in accordance with the invention;

[0059] Diesters not in accordance with the invention; and

[0060] • Known non-ester heat transfer fluids.

[0061] The properties shown [including units and methods used] are:

[0062] Carbon number (for esters)

[0063] Density at 20℃ [kg / dm 3 -ISO 3675]

[0064] Specific heat at 20℃ [J / kg K-ASTM D2766]

[0065] Thermal conductivity at 40°C [W / mK-ASTM D7896]

[0066] Kinematic viscosity at 40℃ [mm 2 / s-ISO 3104]

[0067] Kinematic viscosity at -30℃ [mm 2 / s-ISO 3104]

[0068] Kinematic viscosity at -40℃ [mm 2 / s-ISO 3104]

[0069] Pour point [℃-ISO 3016]

[0070] Flash point [℃-ISO 2719]

[0071] Values ​​marked with an asterisk* are estimates or are derived from commercial product data.

[0072]

[0073]

[0074]

[0075] Isononanol from Evonik - the main isomer is 7-methyloctanol

[0076] The main isomer is 3,5,5-trimethylhexanoic acid

[0077] It can be seen that the viscosity of the C5 to C9 / C5 to C9 monoesters with a carbon number less than 17 at -40°C is much lower than that of diesters, poly-α-olefins or monoesters of C17 and above.

[0078] Although the claimed esters have a higher 2 / s) lower or comparable viscosity, but they are dielectric materials that allow direct contact with electrical components. In addition, having a lower or comparable viscosity than a water / ethylene glycol mixture enables the use of pumps with similar pumping power without the need for a higher rated power pump.

[0079] Although the claimed esters have higher viscosities than the exemplified fluorinated materials, they have higher thermal conductivity and specific heat (which facilitates heat transfer as can be seen from the Mouromtseff number equation given above); are safer for the environment and are biodegradable; and, in addition, the alcohols and acids from which the esters are prepared can be obtained from renewable resources.

[0080] As the carbon number drops below 14, the flash point decreases, so in some applications, a carbon number of 14 or higher may be preferred.

[0081] The foregoing illustrates the use of the claimed esters as heat transfer fluids.

[0082] Advantageously, the ester has a molecular formula of R1COOR2, wherein R1 and R2 are each a hydrocarbon group, which may be the same or different. Aliphatic groups are preferred over aromatic groups, and acyclic groups are preferred over cyclic groups. Unsubstituted aliphatic groups are preferred over substituted aliphatic groups. Aliphatic groups may be saturated or unsaturated.

[0083] The environment in which the heat transfer fluid is used may require the provision of additives to protect the fluid or components in contact with it.

[0084] The additives may include any of antioxidants, metal deactivators, friction modifiers, corrosion inhibitors, defoamers, thermally conductive particles, or combinations thereof.

[0085] Antioxidants limit the degradation of the esters. Antioxidants may include, but are not limited to:

[0086] Phenolic antioxidants, for example 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butylphenol, 4,4'-methylenebis(2,6-di-tert-butylphenol), pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and butylated hydroxyanisole;

[0087] Aromatic amines, such as phenyl-alpha-naphthylamine and alkylated diphenylamines.

[0088] The metal deactivator limits the degradation of the ester or the corrosion of the component. The metal deactivator may include but is not limited to triazole deactivators, such as and (Commercially available from BASF).

[0089] Friction modifiers limit the surface effects of surfaces in contact with the heat transfer fluid. Friction modifiers may include, but are not limited to: high hydroxyl esters, boron derivatives, cyclic and acyclic amides.

[0090] The corrosion inhibitors limit corrosion of surfaces in contact with the heat transfer fluid. Corrosion inhibitors may include, but are not limited to, dimercaptothiazoles, mercaptobenzothiazoles, triazoles, imidazoles, alkylamines, phosphate amines, and sulfonates.

[0091] Defoamers limit foaming of the heat transfer fluid. Defoamers may include, but are not limited to: polyacrylates and alcohols.

[0092] Detergents may limit separation of components in the heat transfer fluid or help to suspend any particulate matter. Detergents may include, but are not limited to: phosphates, sulfonates, phenates, and salicylates.

[0093] Extreme pressure additives may be required in some applications. Extreme pressure additives may include, but are not limited to, graphite, carbon-based nanomaterials, molybdenum disulfide, olefin sulfides, and dithiocarbamates.

[0094] Antiwear additives may be required in some applications to prevent mechanical damage to surfaces contacted by the heat transfer fluid. Antiwear additives include, but are not limited to, metal alkylthiophosphates, ashless dithiophosphates, ashless phosphorothioates, ashless thiophosphates, phosphate amines, triaryl phosphates, high hydroxy esters, sulfided esters, cyclic and acyclic amides, dimer acids, and boron derivatives.

[0095] In some systems, heat transfer can be improved by including thermally conductive particles in the heat transfer fluid. Thermally conductive particles can include, but are not limited to, graphite, carbon-based nanomaterials, and boron nitride.

[0096] Esters are common chemical compounds and can be produced by any suitable process for producing esters.

[0097] On a laboratory scale, the alcohol and carboxylic acid (1 equivalent) can be added to a round bottom flask equipped with a Dean-Stark trap and a condenser. The reaction mixture can be heated to 240°C for 4 hours under nitrogen and water can be collected in the Dean-Stark trap. Any excess alcohol or carboxylic acid can then be removed by fractional distillation under reduced pressure.

[0098] Modifications and variations to the above disclosure may be apparent to those skilled in the art and still fall within the scope of the appended claims.

Claims

1. An electrical device comprising at least one electrical component in thermal contact with a heat transfer fluid, wherein the heat transfer fluid comprises >95% by weight of at least one ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol, the ester having a carbon number of less than 17, and the heat transfer fluid comprises no more than 80% by weight of 2-ethylhexyl octanoate.

2. The electrical device of claim 1, further comprising a heat source in thermal contact with the heat transfer fluid such that heat is transferred from the heat source to the at least one electrical component through the heat transfer fluid.

3. The electrical device according to claim 1 or 2, further comprising a heat sink in thermal contact with the heat transfer fluid, so that heat is transferred from the at least one electrical component to the heat sink through the heat transfer fluid.

4. The electrical device according to any one of claims 1 to 3, wherein the at least one electrical component is immersed in the heat transfer fluid.

5. The electrical device of any one of claims 1 to 4, wherein the electrical device is configured to provide heat to the at least one electrical component when the at least one electrical component is below a first temperature, and to remove heat from the at least one electrical component when the at least one electrical component is above a second temperature.

6. The electrical device of any one of claims 1 to 5, wherein the at least one electrical component comprises a battery pack.

7. The electrical device of claim 6, wherein the battery pack is a lithium-ion battery pack.

8. An electrical device according to any one of claims 1 to 7, wherein the heat transfer fluid comprises >95% by weight of the fluid of an ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol.

9. The electrical device of claim 8, wherein the one ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol is the only ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol present in the heat transfer fluid.

10. The electrical device of any one of claims 1 to 9, wherein the at least one ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol comprises one or more of the following features: The C5 to C9 monocarboxylic acid is an acyclic monocarboxylic acid, The C5 to C9 monocarboxylic acid is a straight-chain monocarboxylic acid, The C5 to C9 monocarboxylic acid is a branched monocarboxylic acid, The C5 to C9 monohydric alcohol is an acyclic monohydric alcohol, The C5 to C9 monohydric alcohol is a straight chain monohydric alcohol, The C5 to C9 monohydric alcohol is a branched monohydric alcohol, The C5 to C9 monohydric alcohol is a primary monohydric alcohol, The C5 to C9 monohydric alcohol is a secondary monohydric alcohol, The C5 to C9 monohydric alcohol is a tertiary monohydric alcohol.

11. The electrical device according to any one of claims 1 to 10, wherein the ester comprises: 2-octyl pentanoate, 2-octyl hexanoate, 2-octyl heptanoate, 2-hexyl nonanoate, isononyl hexanoate, 7-methyloctyl hexanoate, 2-ethylhexyl heptanoate, 2-octyl octanoate, 2-ethylhexyl-2-ethylhexanoate or a mixture thereof.

12. An electrical device according to any one of claims 1 to 11, wherein the carbon number is 13 or more, optionally 14 or more.

13. The electrical device according to any one of claims 1 to 12, wherein the heat transfer fluid comprises at least one functional additive selected from antioxidants, metal passivators, friction modifiers, corrosion inhibitors, defoamers, detergents, extreme pressure additives, anti-wear additives and thermally conductive particles.

14. A method of operating an electrical device as claimed in any preceding claim, comprising transferring heat from the heat transfer fluid to the at least one electrical component and operating the at least one electrical component when a threshold temperature is exceeded.

15. A heat transfer fluid comprising the following components in weight percentage: >95% of at least one ester of a C5 to C9 monocarboxylic acid and a C5 to C9 secondary monoalcohol, the ester having a carbon number of less than 17, the heat transfer fluid comprising no more than 80% by weight of 2-ethylhexyl octanoate; and At least one functional additive selected from antioxidants, metal deactivators, friction modifiers, corrosion inhibitors, defoamers, detergents, extreme pressure additives and anti-wear additives.

16. The heat transfer fluid of claim 15, wherein the functional additive comprises the following components by weight percentage of the fluid: ≥ 0.1% antioxidant, ≥0.001% metal passivator; Optionally, the functional additive comprises the following components in weight percentage of the fluid: 0.1% to 1.0% antioxidants, 0.001% to 0.05% metal passivator.

17. The heat transfer fluid of any one of claims 15 to 16, wherein the heat transfer fluid comprises >95% of an ester of a C5 to C9 linear monocarboxylic acid and a C5 to C9 linear secondary monoalcohol.

18. The heat transfer fluid of claim 17, wherein the one ester of a C5 to C9 straight chain monocarboxylic acid and a C5 to C9 straight chain secondary monoalcohol is the only ester of a C5 to C9 straight chain monocarboxylic acid and a C5 to C9 straight chain secondary monoalcohol present.

19. The heat transfer fluid of any one of claims 15 to 18, wherein the at least one ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol comprises one or more of the following features: The C5 to C9 monocarboxylic acid is an acyclic monocarboxylic acid, The C5 to C9 monocarboxylic acid is a straight-chain monocarboxylic acid, The C5 to C9 monocarboxylic acid is a branched monocarboxylic acid, The C5 to C9 monohydric alcohol is an acyclic monohydric alcohol, The C5 to C9 monohydric alcohol is a straight chain monohydric alcohol, The C5 to C9 monohydric alcohol is a branched monohydric alcohol, The C5 to C9 monohydric alcohol is a primary monohydric alcohol, The C5 to C9 monohydric alcohol is a secondary monohydric alcohol, The C5 to C9 monohydric alcohol is a tertiary monohydric alcohol.

20. The heat transfer fluid of any one of claims 15 to 19, wherein the ester comprises: 2-octyl pentanoate, 2-octyl hexanoate, 2-octyl heptanoate, 2-hexyl nonanoate, isononyl hexanoate, 7-methyloctyl hexanoate, 2-ethylhexyl heptanoate, 2-octyl octanoate, 2-ethylhexyl-2-ethylhexanoate or a mixture thereof.

21. A heat transfer fluid according to any one of claims 15 to 20, wherein the carbon number is 13 or more, optionally 14 or more.

22. The heat transfer fluid according to any one of claims 15 to 21, wherein the C6 to C9 straight chain monocarboxylic acid is heptanoic acid and the C6 to C9 straight chain secondary monoalcohol is 2-octanol.

23. Use of a heat transfer fluid to transfer heat to at least one electrical component at a temperature of 0°C to -40°C, optionally -30°C to -40°C, the heat transfer fluid comprising >95% by weight of the fluid of at least one ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol, the ester having a carbon number of less than 17, the heat transfer fluid comprising no more than 80% by weight of 2-ethylhexyl octanoate.

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