heat transfer fluid

Abstract

The electrical device includes at least one electrical component in thermal contact with a heat transfer fluid, the heat transfer fluid comprising greater than 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 at least one ester having a carbon number less than 17.

Description

[Technical Field]

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

[0002] The present invention is particularly, but not exclusively, applicable to heat transfer fluids for use in environments where exposure to electricity and low temperatures may be present.

[0003] Although the invention will be described below with reference to batteries, the invention has a wider range of application, for example heat transfer fluids are used in transformers.

[0004] "Lithium plating" is a problem that can occur during charging of lithium-ion batteries. Lithium plating is the deposition of lithium on the anode surface rather than the desired intercalation of lithium into the anode material. It occurs when lithium is deposited more rapidly than it can be intercalated into the anode, and therefore depends on both the charge rate and the kinetics of lithium intercalation into the anode material.

[0005] Lithium plating is exacerbated by operating the battery at low temperatures, which leads to reduced ionic diffusion and electrolyte conductivity, increased resistance, and slower kinetics of lithium intercalation into the anode material. Lithium plating reduces battery capacity and, in extreme cases, can cause short circuits.

[0006] Due to the increased internal resistance of batteries and the slowdown of electrochemical reactions at sub-zero temperatures, it is necessary to limit the input current during battery charging, which can result in very long charging times for battery systems with cell temperatures below 0°C.

[0007] To address this, it is beneficial to pre-heat the battery cells during periods of low ambient temperature to reach a more optimal temperature and achieve an adequate fast charge rate.

[0008] The use of an immersion cooling system provides excellent heat transfer between the preheating device and the battery cells. However, the viscosity of some conventional heat transfer fluids at sub-freezing temperatures hinders heat transfer due to excessive pressure drop within the system and slower fluid flow compared to higher temperatures. Circulating fluids at higher viscosities than experienced at low temperatures also requires extra energy from the pumping system, and the pumps may need to be larger to compensate.

[0009] A variety of heat transfer fluids are known, including hydrocarbons, fluorinated hydrocarbons, esters, and water / glycol mixtures. Water / glycol mixtures must be kept separate from active electrical components, providing an additional thermal barrier between the components and the heat transfer fluid. Such water / glycol mixtures have a viscosity of 100 mm at -40°C. 2 Kinematic viscosities in the range of / s can be achieved (see https: / / detector-cooling.web.cern.ch / data / Table%208-3-1.htm). Hydrocarbons and fluorinated hydrocarbons have a poor reputation for biodegradability. Esters are biodegradable to varying degrees and are known to offer good dielectric properties. Esters that have been proposed for heat transfer fluids include diesters, but their viscosities at, for example, -40°C (approximately 233°K) are too high to offer performance comparable to water / glycol mixtures or fluorinated hydrocarbons.

[0010] U.S. Patent Application Publication No. 2012 / 283162 proposes the use of an oleyl ester having a total of 23 or more terminal methyl groups, methylene groups, and ether groups in the main chain as a base oil for cooling electric motors.

[0011] US Patent Application Publication No. 2022 / 0131205 proposes the use of esters in cooling compositions for, inter alia, cooling batteries and / or power electronics in electric or hybrid vehicles. The only monoester exemplified has 18 carbons and has a viscosity of 55.8 mmHg at -25°C. 2 The polymer is a highly branched 3,5,5-trimethylhexyl 3,5,5-trimethylhexanoate disclosed as having a viscosity of 1000 .mu.m / s.

[0012] WO 2010 / 116234 discloses a fluid heat exchange medium comprising 90% or more by volume of 2-ethylhexyl caprylic acid ester (2-ethylhexyl octanoate), allowing for the presence of other esters of C6-C8 fatty acids with 2-ethylhexanol. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram of an apparatus illustrating an embodiment of the claimed invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The heat transfer fluids used in the present invention provide heat transfer properties comparable to fluorinated hydrocarbons, much lower viscosities than diesters and commonly used hydrocarbons, and are biodegradable. Furthermore, the raw materials for the esters described herein are preferably available from biological sources, providing environmental benefits for their production and use.

[0015] Accordingly, the present invention provides an electrical device including at least one electrical component in thermal contact with a heat transfer fluid, wherein the heat transfer fluid comprises greater than 95% by weight of the fluid of at least one ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol, wherein the at least one ester has a carbon number less than 17; and the heat transfer fluid does not contain greater than 80% by weight of 2-ethylhexyl octanoate. Optionally, the at least one ester may contain less than 60% by weight of 2-ethylhexyl octanoate, less than 40% by weight of 2-ethylhexyl octanoate, less than 20% by weight of 2-ethylhexyl octanoate, less than 10% by weight of 2-ethylhexyl octanoate, or less than 1% by weight of 2-ethylhexyl octanoate. The at least one ester may be essentially free of 2-ethylhexyl octanoate. The C5-C9 monocarboxylic acid is optionally an acyclic monocarboxylic acid, such as a straight-chain monocarboxylic acid or a branched-chain monocarboxylic acid.

[0016] The C5 to C9 monocarboxylic acid may include, by way of non-limiting example, any of pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, 2-ethylhexanoic acid, or 3,5,5-trimethylhexanoic acid.

[0017] The C5-C9 monoalcohol is optionally an acyclic monoalcohol, such as a straight-chain monoalcohol or a branched-chain monoalcohol, and may be a primary, secondary, or tertiary alcohol. If the C5-C9 monoalcohol is branched, it may contain only methyl branches.

[0018] The C5 to C9 monoalcohol may include, by way of non-limiting example, 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.

[0019] The electrical device may include a heat source in thermal contact with a heat transfer fluid, allowing heat to be transferred from the heat source to at least one electrical component by the heat transfer fluid.

[0020] The electrical device may include a heat sink in thermal contact with a heat transfer fluid, allowing heat to be transferred from the at least one electrical component to the heat sink by the heat transfer fluid.

[0021] At least one electrical component may be immersed in the heat transfer fluid.

[0022] The apparatus may be configured to supply 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.

[0023] The at least one electrical component can include a battery, which can be a lithium ion battery, a lithium metal battery, or any other battery.

[0024] The heat transfer fluid in the device can comprise greater than 95% by weight of the fluid of one ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol, and the one ester can be the only ester present. Some or each of the at least one ester in the heat transfer fluid optionally has a carbon number of 16 or less, or 15 or less. Some or each of the at least one ester in the heat transfer fluid optionally has a carbon number of 11 or more, or 12 or more, or 13 or more, or 14 or more.

[0025] The heat transfer fluid in the equipment may include one or more components selected from the group of antioxidants, metal deactivators, friction modifiers, corrosion inhibitors, antifoam additives, detergents, extreme pressure additives, antiwear additives, and thermally conductive particles.

[0026] A method for operating an electrical device includes transferring heat from a heat transfer fluid to at least one electrical component and operating the electrical component upon exceeding a threshold temperature.

[0027] Certain heat transfer fluids are claimed, greater than 95% by weight of at least one ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol, the at least one ester having fewer than 17 carbon atoms; at least one functional additive selected from the group consisting of antioxidants, metal deactivators, friction modifiers, corrosion inhibitors, antifoam additives, detergents, extreme pressure additives, and antiwear additives; Includes:

[0028] Functional additives include: 0.1% by weight or more of the fluid of an antioxidant; At least 0.001% by weight of the fluid of a metal deactivator and optionally the functional additive may comprise 0.1 to 1.0 weight percent of the fluid of an antioxidant; 0.001 to 0.05% by weight of the fluid of a metal deactivator may include:

[0029] Further features of the present invention will become apparent from the appended claims and the following description, which are intended to illustrate, but not limit, the scope of the claimed invention. Please refer to Figure 1, which shows a schematic diagram of an apparatus illustrating an embodiment of the claimed invention.

[0030] 1, a device 1 contains several electrical components 2 (e.g., batteries) that are immersed in, and thus in thermal contact with, a heat transfer fluid 3 that fills the device. The device comprises a heat source 4 and a heat sink 5.

[0031] A heat source 4 can supply heat to the heat transfer fluid 3 and thereby to the electrical component 2. The heat source can be any convenient heat source, for example an electric heater or a heat exchanger with a heating circuit carrying the same or a different heat transfer fluid.

[0032] The heat sink 5 may absorb heat from the heat transfer fluid 3 and remove the heat from the equipment. Heat may be removed in any convenient way, for example by radiation to the surroundings, by heat exchange with a cooling circuit carrying the same or a different heat transfer fluid.

[0033] The equipment 1 is shown as a closed unit in which the movement of the heat transfer fluid is by convection, although a pumping system would normally be required.

[0034] The heat transfer fluid is thus capable of transferring heat to and from a piece of electrical equipment.

[0035] 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 within the device and supply heat as needed to raise the electrical component to the threshold temperature.

[0036] For batteries, having a dielectric fluid with very low viscosity at -40°C allows for more effective transfer of heat from the pre-heating device to the battery cells, lower energy demands from the pump, and the ability to specify smaller, lighter pumping equipment. This would accelerate pre-heating of the battery system, allowing fast-charging current to be applied sooner and making battery charging more efficient overall. This could significantly reduce fast-charging times under low ambient temperature conditions, providing significant benefits to consumers.

[0037] Potential applications include, but are not limited to: Batteries in vehicles (including, but not limited to, land vehicles, aircraft and ships) Stationary battery storage, e.g. batteries for storing renewable energy. The storage units are usually charged with excess energy at night when it is cold, so the batteries may need to be pre-heated. Non-battery applications requiring low viscosity dielectric heat transfer fluids.

[0038] Performance as a heat transfer fluid depends on many factors, and the Mouromtseff number (Mo) can be used as an indicator of a fluid's heat transfer ability.

[0039]

number

[0040] where ρ is the density, k is the thermal conductivity, Cp is the specific heat, and μ is the kinematic viscosity of the heat transfer fluid. The exponents a, b, d, and e are system dependent and vary depending on whether there is turbulent or laminar flow, but for a defined system they provide a means of comparison between heat transfer fluids. The higher the Mo number, the better the heat transfer capability of the fluid in that system.

[0041] Notably, the denominator is a function of dynamic viscosity, which is expected to vary more with temperature than other factors (over a short temperature range and in the absence of phase change).

[0042] Table 1 below shows: monoesters according to the invention (shown in part 1 of the table), monoesters not according to the invention, diesters not according to the invention, and Known non-ester heat transfer fluids The graph shows the properties of various fluids, including

[0043] The properties shown [indicating units and methods used] are as follows: Carbon number (in the case of esters) Density at 20°C [kg / dm 3 -ISO 3675] Specific heat at 20°C [J / kg K-ASTM D2766] Thermal conductivity (40℃) [W / mK-ASTM D7896] Kinematic viscosity at 40°C [mm 2 / s-ISO 3104] Kinematic viscosity at -30°C [mm 2 / s-ISO 3104] Kinematic viscosity at -40°C [mm 2 / s-ISO 3104] ·Pour point [℃-ISO 3016] ·Flash point [℃-ISO 2719]

[0044] If a value is indicated with an asterisk *, the value is estimated or from commercial product data.

[0045] [Table 1]

[0046] [Table 2]

[0047] It can be seen that the C5-C9 / C5-C9 monoesters of the present invention having less than 17 carbon atoms exhibit much lower viscosity at -40°C than diesters, poly-alphaolefins or monoesters of C17 or higher.

[0048] The claimed esters are prepared by dissolving in a water / glycol mixture (100 mm 2 It is a dielectric material that has a viscosity lower than or equal to that of a water / glycol mixture, but allows for direct contact with electrical components. Additionally, having a viscosity lower than or equal to that of a water / glycol mixture allows for the use of pumps with similar pumping capacity, rather than requiring a higher rated pump.

[0049] The claimed esters have higher viscosities than the exemplified fluorinated materials, but have higher thermal conductivity and specific heat (which is beneficial for heat transfer as seen from the Mouromtseff number equation above), are biodegradable and therefore environmentally safer, and furthermore, the alcohols and acids from which the esters are made are available from renewable sources.

[0050] If the carbon number is less than 14, the flash point will be low, so depending on the application, a carbon number of 14 or more may be preferable.

[0051] The above demonstrates the utility of the claimed esters as heat transfer fluids.

[0052] Advantageously, the ester has the formula R1COOR2, where R1 and R2 are each hydrocarbon moieties which may be the same or different. Aliphatic moieties are preferred over aromatic moieties, and acyclic moieties are preferred over cyclic moieties. Unsubstituted aliphatic moieties are preferred over substituted aliphatic moieties. The aliphatic moieties may be saturated or unsaturated.

[0053] In environments where heat transfer fluids are used, it may be necessary to provide additives to protect the fluid or parts that come into contact with the fluid.

[0054] The additives may include any of antioxidants, metal deactivators, friction modifiers, corrosion inhibitors, anti-foam additives, thermally conductive particles, or combinations thereof.

[0055] Antioxidants limit the degradation of esters. Antioxidants include, but are not limited to: Phenolic antioxidants, such as 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. Aromatic amines, such as phenyl-alpha-naphthylamines and alkylated diphenylamines

[0056] Metal deactivators limit the decomposition of the ester or attack on the components, and include, but are not limited to, triazole-based deactivators such as Irgamet® 30, Irgamet® 39, Irgamet® BTZ, and Irgamet® TTZ (commercially available from BASF).

[0057] Friction modifiers limit surface effects caused by surfaces in contact with the heat transfer fluid. Friction modifiers include, but are not limited to, high hydroxyl esters, boron derivatives, cyclic and acyclic amides.

[0058] Corrosion inhibitors limit corrosion of surfaces in contact with the heat transfer fluid and include, but are not limited to, dimercaptothiazoles, mercaptobenzothiazoles, triazoles, imidazoles, alkylamines, amine phosphates, and sulfonates.

[0059] Antifoam additives limit foaming in the heat transfer fluid and include, but are not limited to, polyacrylates and alcohols.

[0060] Detergents limit the separation of components in the heat transfer fluid or aid in the suspension of any particulate matter. Detergents include, but are not limited to, phosphate esters, sulfonates, phenates, and salicylates.

[0061] Some applications may require extreme pressure additives, including, but not limited to, graphite, carbon-based nanomaterials, molybdenum disulfide, sulfurized olefins, and dithiocarbamates.

[0062] In some applications, anti-wear additives may be required to prevent mechanical damage to surfaces that the heat transfer fluid contacts. Anti-wear additives include, but are not limited to, metal alkylthiophosphates, ashless dithiophosphates, ashless phosphorothioates, ashless thiophosphates, amine phosphates, triaryl phosphates, high hydroxyl esters, sulfurized esters, cyclic and acyclic amides, dimer acids, and boron derivatives.

[0063] In some systems, heat transfer can be improved by including thermally conductive particles in the heat transfer fluid, including, but not limited to, graphite, carbon-based nanomaterials, and boron nitride.

[0064] Esters are commonly known compounds and can be prepared by any suitable method suitable for preparing esters.

[0065] In a laboratory setting, 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 under nitrogen and held there for 4 hours, with water being collected in the Dean-Stark trap. Excess alcohol or carboxylic acid can then be removed using reduced pressure fractional distillation.

[0066] Modifications and variations to the above disclosure will be obvious to those skilled in the art and still fall within the scope of the appended claims.

Claims

1. 1. An electrical device comprising at least one electrical component in thermal contact with a heat transfer fluid, wherein the heat transfer fluid comprises greater than 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 at least one ester having a carbon number less than 17, and the heat transfer fluid does not contain greater 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, enabling heat to be transferred from the heat source to the at least one electrical component by the heat transfer fluid.

3. 3. The electrical device of claim 1, further comprising a heat sink in thermal contact with the heat transfer fluid, allowing heat to be transferred from the at least one electrical component to the heat sink by the heat transfer fluid.

4. An 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. 5. The electrical appliance of claim 1, wherein the appliance is configured to supply 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 according to any one of claims 1 to 5, wherein the at least one electrical component comprises a battery.

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

8. 8. The electrical machine of claim 1, wherein the heat transfer fluid comprises more than 95% by weight of the fluid of an ester of one of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol.

9. 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 at least one ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol is selected from the group consisting of: C5-C9 monocarboxylic acids are acyclic monocarboxylic acids C5 to C9 monocarboxylic acids are straight-chain monocarboxylic acids C5-C9 monocarboxylic acids are branched chain monocarboxylic acids C5-C9 monoalcohols are acyclic monoalcohols C5 to C9 monoalcohols are straight-chain monoalcohols C5-C9 monoalcohols are branched chain monoalcohols - C5 to C9 monoalcohols are primary monoalcohols - C5 to C9 monoalcohols are secondary monoalcohols - C5 to C9 monoalcohols are tertiary monoalcohols An electrical device according to any one of claims 1 to 9, comprising one or more of the following features:

11. 11. The electrical device of claim 1, wherein the ester comprises 2-octyl pentanoate, 2-octyl hexanoate, 2-octyl heptanoate, 2-hexyl nonanoate, isononyl hexanoate, 7-methyloctanyl hexanoate, 2-ethylhexyl heptanoate, 2-octyloctanoate, 2-ethylhexyl 2-ethylhexanoate, or a mixture thereof.

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

13. 13. The electrical device of claim 1, wherein the heat transfer fluid comprises at least one functional additive selected from the group consisting of antioxidants, metal deactivators, friction modifiers, corrosion inhibitors, antifoam additives, detergents, extreme pressure additives, antiwear additives, and thermally conductive particles.

14. 14. A method of operating an electrical device according to any one of claims 1 to 13, comprising transferring heat from the heat transfer fluid to the at least one electrical component, and operating the at least one electrical component upon exceeding a threshold temperature.

15. A heat transfer fluid comprising: greater than 95% by weight of at least one ester of a C5 to C9 monocarboxylic acid and a C5 to C9 secondary monoalcohol, wherein the at least one ester has fewer than 17 carbon atoms; at least one functional additive selected from the group consisting of antioxidants, metal deactivators, friction modifiers, corrosion inhibitors, antifoam additives, detergents, extreme pressure additives, and antiwear additives; Including, A heat transfer fluid, wherein the heat transfer fluid does not contain more than 80% by weight of 2-ethylhexyl octanoate.

16. The functional additive is 0.1% by weight or more of an antioxidant in said fluid 0.001% or more of a metal deactivator in said fluid Including, Optionally, the functional additive comprises: 0.1 to 1.0% by weight of said fluid of an antioxidant 0.001 to 0.05% by weight of said fluid of a metal deactivator The heat transfer fluid of claim 15 comprising:

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

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

19. The at least one ester of a C5 to C9 monocarboxylic acid and a C5 to C9 monoalcohol is selected from the group consisting of: C5-C9 monocarboxylic acids are acyclic monocarboxylic acids C5 to C9 monocarboxylic acids are straight-chain monocarboxylic acids C5-C9 monocarboxylic acids are branched chain monocarboxylic acids C5-C9 monoalcohols are acyclic monoalcohols C5 to C9 monoalcohols are straight-chain monoalcohols C5-C9 monoalcohols are branched chain monoalcohols - C5 to C9 monoalcohols are primary monoalcohols - C5 to C9 monoalcohols are secondary monoalcohols - C5 to C9 monoalcohols are tertiary monoalcohols A heat transfer fluid according to any one of claims 15 to 18, comprising one or more of the following features:

20. 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-methyloctanyl hexanoate, 2-ethylhexyl heptanoate, 2-octyloctanoate, 2-ethylhexyl 2-ethylhexanoate, or mixtures thereof.

21. 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. 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. 1. Use of a heat transfer fluid for delivering heat to at least one electrical component at a temperature between 0°C and -40°C, optionally between -30°C and -40°C, wherein the heat transfer fluid comprises greater than 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 at least one ester having a carbon number less than 17, and the heat transfer fluid does not comprise greater than 80% by weight of 2-ethylhexyl octanoate.

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