Heat transfer fluid

Abstract

The present invention provides a heat transfer fluid comprising: (a) from 10 to 90% by mass of a freezing point depressant, based on the overall mass of the heat transfer fluid; (b) from 90 to 10% by mass of water based on the overall mass of the heat transfer fluid; and (c) from 0.005 to 5% by mass, based on the overall mass of the heat transfer fluid, of a first additive, said first additive being a non-azole, aromatic, heterocyclic additive containing two or more heteroatoms. The present invention also provides a heat transfer system comprising: a housing having an interior space; a heat-generating component disposed within the interior space; and a heat transfer fluid disposed within the interior space such that the heat-generating component is in contact with the heat transfer fluid; wherein the heat transfer fluid comprises: - from 10 to 90% by mass of a freezing point depressant, based on the overall mass of the heat transfer fluid; - from 90 to 10% by mass of water based on the overall mass of the heat transfer fluid; and - from 0.005 to 5% by mass, based on the overall mass of the heat transfer fluid, of a first additive, said first additive being a non-azole, aromatic, heterocyclic additive Further, the present invention provides the use of a heat transfer fluid to reduce copper and aluminum corrosion in a heat transfer system, wherein the heat transfer fluid comprises from 10 to 90% by mass of a freezing point depressant, based on the overall mass of the heat transfer fluid; from 90 to 10% by mass of water based on the overall mass of the heat transfer fluid; and from 0.005 to 5% by mass, based on the overall mass of the heat transfer fluid, of a first additive, said first additive being a non-azole, aromatic, heterocyclic additive.

Description

[0001] HEAT TRANSFER FLUID

[0002] Field of the Invention

[0003] This invention relates to a heat transfer fluid, in particular a heat transfer fluid with low conductivity. Background of the Invention

[0004] Throughout a range of industries, new technologies are being sought in order to provide more energy efficient, lower CO2 solutions. This invention relates to a number of possible efficiencies driving lower energy requirements and lower CO2 emissions. Firstly, it relates to electric vehicle technology. Secondly, the invention is also applicable to the 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 electric technology.

[0005] By 2040, it is expected that up to 50% of all new passenger car sales will be electric vehicles. This includes battery electric vehicles (BEV) , hybrid electric vehicles (HEV) and fuel cell electric vehicles (FCEV) . Hybrid electric vehicles include a battery in combination with conventional combustion engines or fuel cells. Fuel cell electric vehicles also need a battery for buffering and interim storage of electrical energy.

[0006] Current battery technology relies on lithium-ion batteries and it is likely that these will remain the dominant battery technology for at least the next 15 years . While slow charging at home or destination is likely to be the dominant way of charging, high- performance fast-charging (HPC) during a journey will be required by many customers who want to drive longer distances. To improve and shorten the charging process, it is required to increase voltage, current, or both at the same time. A higher current will also increase excess heat generated. The level of excess heat is very high and can reach 20 kWh or higher. Effective thermal management to control temperature uniformity within the cell pack is required to prevent battery cells from irreversible deterioration.

[0007] Within an electric vehicle, other components also require thermal management, especially cooling. Heat is generated by both the electric motor and the inverter in use. A method of thermal management that could be applied to each of these components and preferably a circuit incorporating all of these components (including the battery) would be most desirable.

[0008] Fuel cell powered electrical systems also generate significant waste heat (approximately 50% of the energy is produced as waste heat) in use that needs to be removed during operation.

[0009] The thermal management of components provides challenges across other industries as well. The thermal management of IT components, especially servers, also provides many challenges. Air cooling of these components requires high energy usage and expensive cooling infrastructure. A simpler, more energy efficient system for the thermal management of these electronic components would be highly desirable.

[0010] Most cooling systems historically have used air passed over the source of heat in order to manage excess heat. However, such systems are limited in heat capacity and are not capable of managing the heat produced, for example, in an electrical device subjected to the strains of a process such as HPC. The infrastructure included in an air-cooling system can also be complex, expensive and involve the maintenance of many moving parts. More advanced thermal management systems have been developed in which a conventional water / glycol mixture is used as a heat transfer fluid. A battery block, containing a large number of individual battery cells, may be effectively cooled with a water / glycol mixture. This is rapidly becoming the dominant thermal management technology in use in electric vehicles sold today as it is more efficient than air-cooling.

[0011] Developing improved working fluids for thermally managing electrical systems remains an on-going challenge. Such working fluids require excellent material compatibility, thermodynamic properties and low flammability. It is also important that the fluids have low conductivity levels, which can be maintained as the fluid ages, so as to prevent short circuits and / or damage to the heat-generating component.

[0012] In order to maintain corrosion protection, additives are contained in typical low conductivity heat transfer fluids. Of particular note are the heat transfer fluid formulations described in US2006 / 0219975 which contain one or more azole derivatives as well as orthosilicates in order to provide protection for metals in the heat transfer system.

[0013] Although said azole / silicate systems are well-known for the protection of "yellow" metals, such as copper and brass, they provide less effective protection against corrosion for aluminum, a key component of modern heat transfer systems. Further, over-treating with silicates can actually result in metal corrosion and / or sludge / scale formation in the heat transfer system.

[0014] There remains a need to provide suitable low conductivity heat transfer fluids with improved corrosion protection, particularly for systems containing aluminum. Summary of the Invention

[0015] The present invention provides a heat transfer fluid comprising :

[0016] (a) from 10 to 90% by mass of a freezing point depressant, based on the overall mass of the heat transfer fluid;

[0017] (b) from 90 to 10% by mass of water based on the overall mass of the heat transfer fluid; and

[0018] (c) from 0.005 to 5% by mass, based on the overall mass of the heat transfer fluid, of a first additive, said first additive being a non-azole, aromatic, heterocyclic additive.

[0019] The present invention also provides a heat transfer system comprising: a housing having an interior space; a heat-generating component disposed within the interior space; and a heat transfer fluid disposed within the interior space such that the heat-generating component is in contact with the heat transfer fluid; wherein the heat transfer fluid comprises:

[0020] - from 10 to 90% by mass of a freezing point depressant, based on the overall mass of the heat transfer fluid;

[0021] - from 90 to 10% by mass of water based on the overall mass of the heat transfer fluid; and

[0022] - from 0.005 to 5% by mass, based on the overall mass of the heat transfer fluid, of a first additive, said first additive being a non-azole, aromatic, heterocyclic additive

[0023] Further, the present invention provides the use of a heat transfer fluid to provide improved metal corrosion suppression in a heat transfer system, wherein the heat transfer fluid comprises from 10 to 90% by mass of a freezing point depressant, based on the overall mass of the heat transfer fluid; from 90 to 10% by mass of water based on the overall mass of the heat transfer fluid; and from 0.005 to 5% by mass, based on the overall mass of the heat transfer fluid, of a first additive, said first additive being a non-azole, aromatic, heterocyclic additive .

[0024] Detailed Description of the Invention

[0025] One or more specific embodiments of the present disclosure will be described below. These described embodiments are examples of the presently disclosed techniques . Additionally, in an effort to provide a concise description of these embodiments, not all features of an actual implementation may be described in the specification.

[0026] When introducing elements of various embodiments of the present disclosure, the articles "a," "an," and "the" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to "one embodiment" or "an embodiment" of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0027] In the context of the present invention, in a case where a composition comprises two or more components, these components are to be selected in an overall amount not to exceed 100 mass%.

[0028] The present inventors have surprisingly found that heat transfer fluids comprising non-azole aromatic heterocyclic additives containing two or more heteroatoms provide considerably improved corrosion protection in heat transfer fluid systems.

[0029] The heat transfer fluid comprises a freezing point depressant. Freezing point depressants suitable for use in a heat transfer fluid in accordance with the present teachings include, but are not limited to, alcohols and mixture of alcohols (e.g. , monohydric alcohols, polyhydric alcohols, and mixtures thereof) . Representative alcohols for use as freezing point depressants include but are not limited to methanol, ethanol, propanol, butanol, furfurol, furfuryl alcohol, tetrahydrofurfuryl alcohol, ethoxylated furfuryl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, 1 , 2-propylene glycol (1,2- propanediol) , 1 , 3-propylene glycol (1,3- propanediol) , dipropylene glycol, butylene glycol, glycerol, glycerol- 1,2-dimethyl ether, glycerol- 1,3 -dimethyl ether, monoethylether of glycerol, sorbitol, 1 , 2 , 6-hexanetriol , trimethylopropane , C1-C4 alkoxy alkanols (e.g. , methoxy ethanol) , and / or the like, and combinations thereof. Preferably, the freezing point depressant comprises an alcohol which is selected from the group consisting of ethylene glycol, 1 , 2-propylene glycol, 1 , 3-propanediol, glycerol, and a combination thereof. Most preferably the freezing point depressant is a glycol.

[0030] The concentration of freezing point depressant is between 10 to 90% by mass on the basis of the overall mass of the heat transfer fluid and may vary depending on the application. Preferably, the freezing point depressant is present in an amount of at least 20 mass%, more preferably at least 30 mass%, even more preferably at least 40 mass%, based on the overall mass of the heat transfer fluid. Also the freezing point depressant may be present in an amount of at most 80 mass%, more preferably at most 70 mass%, even more preferably at most 60 mass%, based on the overall mass of the heat transfer fluid.

[0031] The water present in the heat transfer fluid is suitably deionized or distilled water. The concentration of water is between 10 to 90% by mass on the basis of the overall mass of the heat transfer fluid and may vary depending on the application. Preferably, the water is present in an amount of at least 20 mass%, more preferably at least 30 mass%, even more preferably at least 40 mass%, based on the overall mass of the heat transfer fluid. Also, the water may be present in an amount of at most 80 mass%, more preferably at most 70 mass%, even more preferably at most 60 mass%, based on the overall mass of the heat transfer fluid.

[0032] Azoles, by definition, comprise a five-membered aromatic ring said ring containing at least two heteroatoms, at least one of which is nitrogen. Typically, the remaining heteroatoms in an azole are selected from the group consisting of sulfur, nitrogen and oxygen. Thus, the term azoles covers, but is not limited to, imidazoles, oxazoles, thiazoles, isoazoles, isothiazoles and pyrazoles .

[0033] The first additive in the heat transfer fluid of the invention is a non-azole, aromatic, heterocyclic additive. Thus, the first additive does not contain a five-membered aromatic ring containing a nitrogen and a least one further heteroatom.

[0034] The first additive preferably comprises one or more compound selected from (i) compounds containing an optionally substituted six-membered aromatic ring said ring containing two heteroatoms; and (ii) optionally substituted compounds of formula (I) wherein X is selected from 0, S and NH and R is selected from N and CH.

[0035] Wherein the first additive comprises a compound selected from those containing an optionally substituted six-membered aromatic ring said ring containing two heteroatoms, said heteroatoms preferably include at least one and more preferably two nitrogen atoms. Substitution of the six-membered aromatic ring, if present, suitably comprises further aromatic rings. Preferable compounds selected from those containing an optionally substituted six-membered aromatic ring said ring containing two heteroatoms are selected from the list consisting of quinazoline, pyrazine and pyridazine.

[0036] When the first additive comprises an optionally substituted compound of formula (I) , preferably said compound is selected form the list consisting of 7-aza- indoles, benzofuran and benzothiophene.

[0037] Preferably, the heat transfer fluid also comprises one or more azole derivatives. More preferably, said azole derivative is selected from the list consisting of benzimidazole, benzotriazole, tolutriazole and mixtures thereof .

[0038] As well as the first additive and optionally the azole derivative, the heat transfer fluid may contain further additives. Said further additives may be selected from this list including non-ionic surfactants, low conductivity corrosion inhibitors, non-conductive colorants, antifoaming agents or defoamers, biocides, pH- adjusting agents, wetting agents, other non-conductive or low-conductivity corrosion inhibitors, non-ionic dispersants, scale inhibitors, bittering agents, other heat transfer f luid / antif reeze additives, and / or the like, and combinations thereof. If present, the optional one or more additional components should be non-conductive or have low electrical conductivity.

[0039] It is preferred that the heat transfer fluid is substantially free from silicon-containing compounds.

[0040] The invention will now be illustrated by reference to the following, non-limiting, examples. Examples

[0041] A range of heat transfer fluid compositions were blended and tested as set out in Tables 1 and 2.

[0042] Table 1 Table 2 (comparative Examples)

[0043] The Examples were all tested according to a Modified ASTM D1384 (Glassware Corrosion Test) run at 80 °C with an aeration rate at lOOmL / minute for 2 weeks. The electrical conductivity was measured according to ASTM D1125. Metal corrosion rate according to the Electrochemistry Test Platform, measured in millilitres per year (mpy) was also measured . The formulations according to the present invention provide much improved copper, stainless stell and aluminium corrosion protection compared with a simple ethylene glycol / water fluid (reference example) . Aluminium corrosion protection is much improved for the heat transfer fluid of the invention compared with the heat transfer fluids containing azole only and azole / TEOS additives (comparative examples 1 to 5) . Examples 3 and 4 demonstrate exceptional results for the heat transfer fluids of the invention wherein a non-azole, aromatic, heterocyclic additive is used in combination with an azole based additive such as TTZ.

Claims

C L A I M S1. A heat transfer fluid comprising:(a) from 10 to 90% by mass of a freezing point depressant, based on the overall mass of the heat transfer fluid;(b) from 90 to 10% by mass of water based on the overall mass of the heat transfer fluid; and(c) from 0.005 to 5% by mass, based on the overall mass of the heat transfer fluid, of a first additive, said first additive being a non-azole, aromatic, heterocyclic additive.

2. The heat transfer fluid as claimed in Claim 1, wherein the freezing point depressant is a glycol.

3. The heat transfer fluid as claimed in Claim 1 or Claim2, wherein the first additive comprises one or more compound selected from (i) compounds containing an optionally substituted six-membered aromatic ring said ring containing two heteroatoms; and (ii) optionally substituted compounds of formula (I)wherein X is selected from 0, S and NH and R is selected from N and CH.

4. The heat transfer fluid as claimed Claim 3, wherein the first additive comprises a compound selected from those containing an optionally substituted six-membered aromatic ring said ring containing two nitrogen atoms.

5. The heat transfer fluid as claimed in Claim 4, wherein the first additive comprises one or more compound selectedfrom the list consisting of quinazoline, pyrazine and pyridazine .

6. The heat transfer fluid as claimed in Claim 3, wherein the first additive comprises an optionally substituted compound of formula (I) , selected from the list consisting of 7-aza-indoles , benzofuran and benzothiophene7. The heat transfer fluid as claimed in any one of Claim 1 to 6, wherein said heat transfer fluid also comprises one or more azole derivatives, preferably selected from the list consisting of benzimidazole, benzotriazole, tolutriazole and mixtures thereof.

8. A heat transfer system comprising heat transfer system comprising : a housing having an interior space; a heat-generating component disposed within the interior space; and a heat transfer fluid disposed within the interior space such that the heat-generating component is in contact with the heat transfer fluid; wherein the heat transfer fluid comprises:- from 10 to 90% by mass of a freezing point depressant, based on the overall mass of the heat transfer fluid;- from 90 to 10% by mass of water based on the overall mass of the heat transfer fluid; and- from 0.005 to 5% by mass, based on the overall mass of the heat transfer fluid, of a first additive, said first additive being a non-azole, aromatic, heterocyclic additive9. Use of the heat transfer fluid as claimed in any one of Claims 1 to 7 in a heat transfer system to provide improved metal corrosion suppression.

10. Use as claimed in Claim 9 to provide improved copper and aluminum corrosion suppression.

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