Patent Application
20240287371
The present disclosure relates to a heat transfer fluid for immersion cooling of electrical componentry and an immersion cooling system employing the heat transfer fluid. The heat transfer fluid comprises a mixture of phosphate esters, as described herein. The mixture of phosphate esters exhibits favorable properties in a circulating immersion cooling system, such as low flammability, low pour point, high electrical resistivity and low viscosity for pumpability.
Electrical componentry that use, store and/or generate energy or power can generate heat. For example, battery cells, such as lithium-ion batteries, generate large amounts of heat during charging and discharging operations. Traditional cooling systems employ air cooling or indirect liquid cooling. Commonly, water/glycol solutions are used as heat transfer fluids to dissipate heat via indirect cooling. In this cooling technique, the water/glycol coolant flows through channels, such as jackets, around the battery modules or through plates within the battery framework. The water/glycol solutions, however, are highly conductive and must not contact the electrical componentry, such as through leakage, for risk of causing short circuits, which can lead to heat propagation and thermal runaway. In addition, questions remain whether indirect cooling systems can adequately and efficiently remove heat under the increasing demands for high loading (fast charging), high capacity batteries.
Cooling by immersing electrical componentry into a coolant is a promising alternative to traditional cooling systems. For example, US 2018/0233791 A1 discloses a battery pack system to inhibit thermal runaway wherein a battery module is at least partially immersed in a coolant in a battery box. The coolant may be pumped out of the battery box, through a heat exchanger, and back into the battery box. As the coolant, trimethyl phosphate and tripropyl phosphate are mentioned, among other chemistries. However, as shown in the present application, a trimethyl phosphate fluid or tripropyl phosphate fluid exhibits a low direct-current (DC) resistivity, and each exhibits a low flash point such that the flammability of each fluid renders it unsuitable.
A need exists for the development of heat transfer fluids, particularly for immersion cooling systems, having low flammability, low pour point, high electrical resistivity and low viscosity. To fulfill this need, new heat transfer fluids are disclosed herein comprising certain mixtures of phosphate esters. Also disclosed is an immersion cooling system using the presently disclosed heat transfer fluids.
In accordance with the present disclosure, a heat transfer fluid for immersion cooling of electrical componentry comprises
Also disclosed is an immersion cooling system comprising electrical componentry, a heat transfer fluid of the present disclosure, and a reservoir, wherein the electrical componentry is at least partially immersed in the heat transfer fluid within the reservoir, and a circulating system capable of circulating the heat transfer fluid out of the reservoir, through a circulating pipeline of the circulating system, and back into the reservoir.
The present disclosure also includes a method of cooling electrical componentry comprising at least partially immersing electrical componentry in a heat transfer fluid of the present disclosure within a reservoir, and circulating the heat transfer fluid out of the reservoir, through a circulating pipeline of a circulation system, and back into the reservoir.
The heat transfer fluid, system and method of the present disclosure are suitable for cooling a wide variety of electrical componentry, and particularly in the cooling of battery systems.
The preceding summary is not intended to restrict in any way the scope of the claimed invention. In addition, it is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
Unless otherwise specified, the word “a” or “an” in this application means “one or more than one”.
A heat transfer fluid for immersion cooling of electrical componentry comprises
The ratio by weight of the phosphate ester component (a) to the phosphate ester component (b) in the heat transfer fluid often ranges from 40:1 to 1:40, often 39:1 to 1:39, such as 35:1 to 1:35, 30:1 to 1:30, 25:1 to 1:25, 20:1 to 1:20, 12:1 to 1:12, 10:1 to 1:10, 8:1 to 1:8, 5:1 to 1:5 or 3:1 to 1:3.
While the heat transfer fluid may contain phosphate esters other than those of formulas (I) and (II), the phosphate ester components (a) and (b) typically collectively make up more than 50% by weight based on the total weight of all phosphate esters in the heat transfer fluid, e.g., at least 60%, at least 70%, at least 80%, at least 90%, at least 95% or at least 99% by weight of all phosphate esters in the heat transfer fluid.
In formula (I) of phosphate ester component (a), each R may, but need not, be the same.
In formula (II) of phosphate ester component (b), each R′ may, but need not, be the same. In some embodiments, each R′ in formula (II) is independently chosen from C1-12 alkyl-substituted phenyl. In further embodiments, one R′ group is C1-12 alkyl-substituted phenyl, and the remaining two R′ groups are unsubstituted phenyl, or two R′ groups are independently chosen from C1-12 alkyl-substituted phenyl and the remaining R′ group is unsubstituted phenyl. In some embodiments, the two R groups chosen from C1-12 alkyl-substituted phenyl are the same.
R as “C6-18 alkyl” in formula (I) may be a straight or branched chain alkyl group having the specified number of carbon atoms. Often, R as “C6-18 alkyl” has at least 8 carbon atoms. Preferably, R as C6-18 alkyl is C6-12 or C6-12 alkyl or C6-10 or C8-10 alkyl. Examples of unbranched alkyl groups include n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, and n-dodecyl. Examples of branched alkyl groups include 2-methylpentyl, 2-ethylbutyl, 2,2-dimethylbutyl, 6-methylheptyl, 2-ethylhexyl, t-octyl, 3,5,5-trimethylhexyl, 7-methyloctyl, 2-butylhexyl, 8-methylnonyl, 2-butyloctyl, 11-methyldodecyl and the like. Examples of linear alkyl and branched alkyl groups also include moieties commonly called isononyl, isodecyl, isotridecyl and the like, where the prefix “iso” is understood to refer to mixtures of alkyls such as those derived from an oxo process.
R′ as “C1-12 alkyl-substituted phenyl” in formula (II) refers to a phenyl group substituted by a C1-12 alkyl group. The alkyl group may be a straight or branched chain alkyl group having the specified number of carbon atoms. More than one alkyl group may be present on the phenyl ring (e.g., phenyl substituted by two alkyl groups or three alkyl groups). Often, however, the phenyl is substituted by one alkyl group (i.e., mono-alkylated). Preferably, the C1-12 alkyl is chosen from C1-10 or C3-10 alkyl, more preferably C1-8 or C3-8 alkyl, or C1-6 or C3-6 alkyl.
Examples of such alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, isopentyl, t-pentyl, 2-methylbutyl, n-hexyl, 2-methylpentyl, 2-ethylbutyl, 2,2-dimethylbutyl, 6-methylheptyl, 2-ethylhexyl, isooctyl, t-octyl, and isononyl, 3,5,5-trimethylhexyl, 2-butylhexyl, isodecyl, and 2-butyloctyl and the like. The alkylating agents may include olefins derived from cracking of naphtha, such as propylene, butylene, diisobutylene, and propylene tetramer. Said alkyl substitution on the phenyl ring may be at the ortho-, meta-, or para-position, or a combination thereof. Often, the alkyl substitution is at the para-position or predominantly at the para-position.
Component (a) may comprise a mixture of phosphate ester compounds of formula (I). For example, component (a) may comprise an isomeric mixture of compounds of formula (I), e.g., such phosphate esters containing branched alkyl isomers, such as derived from a mixture of isomers of branched aliphatic alcohols.
Often, component (b) is a mixture of phosphate esters of formula (II). For example, component (b) may comprise an isomeric mixture of phosphate esters of formula (II), e.g., such phosphate esters containing branched alkyl isomers, such as derived from a mixture of isomers of branched alkylated phenols.
In further embodiments, component (b) comprises an isomeric mixture of phosphate esters of formula (II) containing ortho-, meta-, and/or para-isomers of C1-12 alkyl-substituted phenyl, such as trixylenyl phosphate, tricresyl phosphate and the like.
In many embodiments, component (b) comprises two or more phosphate esters of formula (II) differing in the number of R′ groups that are C1-12 alkyl-substituted phenyl. For example, the mixture of compounds of formula (II) may comprise at least two, often three or all four, from the group chosen from mono(alkylphenyl) diphenyl phosphate, di(alkylphenyl) monophenyl phosphate, tri(alkylphenyl) phosphate, and triphenyl phosphate, where “alkylphenyl” is C1-12 alkyl-substituted phenyl as described herein.
Such mixture of compounds of formula (II) may comprise, for example,
In many embodiments, such mixture of compounds of formula (I) comprises
In many embodiments, such mixture of compounds of formula (I) comprises
The heat transfer fluid of the present disclosure may also include one or more other base oils, such as mineral oils, polyalphaolefins, esters, etc. The other base oil(s) and amounts thereof should be chosen to be consistent with the properties suitable for the circulating immersion cooling fluid as described herein. Typically, the phosphate ester components (a) and (b) collectively make up more than 50% by weight of the heat transfer fluid. For example, in many embodiments, the phosphate ester components (a) and (b) collectively are at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99% by weight of the heat transfer fluid.
The heat transfer fluid of the present disclosure may further comprise one or more performance additives. Examples of such additives include, but are not limited to, antioxidants, metal deactivators, flow additives, corrosion inhibitors, foam inhibitors, demulsifiers, pour point depressants, and any combination or mixture thereof. Fully-formulated heat transfer fluids typically contain one or more of these performance additives, and often a package of multiple performance additives. Often, one or more performance additives are present at 0.0001 wt % up to 3 wt %, or 0.05 wt % up to 1.5 wt %, or 0.1 wt % up to 1.0 wt %, based on the weight of the heat transfer fluid.
The heat transfer fluid may consist essentially of the phosphate ester components (a) and (b) and optionally one or more performance additives. In some embodiments, the heat transfer fluid consists of the phosphate ester components (a) and (b) and optionally one or more performance additives.
The phosphate esters of the present disclosure, including mixtures thereof, are known or can be prepared by known techniques. For example, trialkyl phosphate esters are often prepared by the addition of alkyl alcohol to phosphorous oxychloride or phosphorous pentoxide. Alkylated triphenyl phosphate esters, including mixtures thereof, may be prepared according to a variety of known techniques, such as the addition of alkylated phenol to phosphorous oxychloride. Known processes are described, e.g., in U.S. Pat. Nos. 2,008,478, 2,868,827, 3,859,395, 5,206,404 and 6,242,631.
The phosphate ester components (a) and (b) may be mixed according to any suitable technique for blending such phosphate ester components.
The physical properties of the presently disclosed heat transfer fluid may be adjusted or optimized at least in part based on the extent of alkylation in the phosphate ester components (a) and (b) and/or based on the proportions by weight of the phosphate ester component (a) to the phosphate ester component (b).
Typically, the heat transfer fluid of the present disclosure has a flash point according to ASTM D92 of ≥190° C., preferably ≥200° C.; a kinematic viscosity measured at 40° C. according to ASTM D445 of less than 50 cSt, preferably ≤40 cSt or ≤35 cSt, more preferably ≤30 cSt; a pour point according to ASTM D5950 of ≤−20° C., preferably ≤−25° C., more preferably ≤−30° C.; and a DC resistivity measured at 25° C. according to IEC 60247 of >0.25 GOhm-cm, preferably >0.5 GOhm-cm, >1 GOhm-cm, or >5 GOhm-cm.
For example, in many embodiments, the heat transfer fluid of the present disclosure has a flashpoint according to ASTM D92 of ≥200° C.; a kinematic viscosity measure at 40° C. according to ASTM D445 of ≤30 cSt; a pour point according to ASTM D5950 of ≤−30° C.; and a DC resistivity measured at 25° C. according to IEC 60247 of >1 GOhm-cm or >5 GOhm-cm.
The immersion cooling system of the present disclosure comprises electrical componentry, a heat transfer fluid as described herein, and a reservoir, wherein the electrical componentry is at least partially immersed in the heat transfer fluid within the reservoir, and a circulating system capable of circulating the heat transfer fluid out of the reservoir, through a circulating pipeline of the circulating system, and back into the reservoir.
Electrical componentry includes any electronics that generate thermal energy in need of dissipation for safe usage. Examples include batteries, fuel cells, aircraft electronics, computer electronics such as microprocessors, un-interruptable power supplies (UPSs), power electronics (such as IGBTs, SCRs, thyristors, capacitors, diodes, transistors, rectifiers and the like), invertors, DC to DC convertors, chargers (e.g., within loading stations or charging points), phase change invertors, electric motors, electric motor controllers, DC to AC invertors, and photovoltaic cells.
The system and method of the present disclosure is particularly useful for cooling battery systems, such as those in electric vehicles (including passenger and commercial vehicles), e.g., in electric cars, trucks, buses, industrial trucks (e.g., forklifts and the like), mass transit vehicles (e.g., trains or trams) and other forms of electric powered transportation.
Typically, electrified transportation is powered by battery modules. A battery module may encompass one or more battery cells arranged or stacked relative to one another. For example, the module can include prismatic, pouch or cylindrical cells. During charging and discharging (use) operations of the battery, heat is typically generated by the battery cells, which can be dissipated by the immersion cooling system. Efficient cooling of the battery via the immersion cooling system allows for fast charge times at high loadings, while maintaining safe conditions and avoiding heat propagation and thermal runaway. Electrical componentry in electric powered transportation also include electric motors, which can be cooled by the immersion cooling system.
In accordance with the present disclosure, the electrical componentry is at least partially immersed in the heat transfer fluid within a reservoir. Often, the electrical componentry is substantially immersed or fully immersed in the heat transfer fluid, such as immersing (in the case of a battery module) the battery cell walls, tabs and wiring. The reservoir may be any container suitable for holding the heat transfer fluid in which the electrical componentry is immersed. For example, the reservoir may be a container or housing for the electrical componentry, such as a battery module container or housing.
The immersion cooling system further comprises a circulating system capable of circulating the heat transfer fluid out of the reservoir, through a circulating pipeline of the circulating system, and back into the reservoir. Often, the circulating system includes a pump and a heat exchanger. In operation, for example as shown in
The heat exchanger may be any heat transfer unit capable of cooling the heated heat transfer fluid to a temperature suitable for the particular application. For example, the heat exchanger may use air cooling (liquid to air) or liquid cooling (liquid to liquid). The heat exchanger, for example, may be a shared heat transfer unit with another fluid circuit within the electrical equipment or device, such as a refrigeration/air conditioning circuit in an electric vehicle. The circulation system may flow the heat transfer fluid through multiple heat exchangers, such as air cooling and liquid cooling heat exchangers.
The circulation pipeline of the circulating system may flow the heat transfer fluid to other electrical componentry that generate thermal energy in need of dissipation within the electrical equipment or device. For example, as shown in
The circulating system may also include a heat transfer fluid tank to store and/or maintain a volume of heat transfer fluid. For example, cooled heat transfer fluid from a heat exchanger may be pumped into the heat transfer fluid tank and from the heat transfer fluid tank back into the reservoir.
An example of an immersion cooling system in accordance with the present disclosure is shown in
The depicted flow of the heat transfer fluid 2 over and around the electrical componentry 1 as shown in
While the system and method of the present disclosure is particularly useful for cooling of electrical componentry, such as battery modules, the presently disclosed immersion arrangement of the electrical componentry in the heat transfer fluid also allows the fluid to transfer heat to the electrical componentry to provide temperature control in cold environments. For example, the immersion cooling system may be equipped with a heater to heat the heat transfer fluid, such as shown in
Also disclosed is a method of cooling electrical componentry comprising at least partially immersing electrical componentry in a heat transfer fluid as described herein, and circulating the heat transfer fluid out of the reservoir, through a circulating pipeline of a circulation system, and back into the reservoir.
Further non-limiting disclosure is provided in the Examples that follow.
Heat transfer fluids in accordance with the present disclosure, as well as heat transfer fluids of the Comparative Examples, were evaluated to determine their flash point (ASTM D92), kinematic viscosity measured at 40° C. (ASTM D445), pour point (ASTM D5950), and DC resistivity measured at 25° C. (IEC 60247).
Butylated triphenylphosphate (butylated TPP), which is a mixture of triphenyl phosphate (in the range ≥2.5 to <25 wt %) and a mixture of mono(butylphenyl) diphenyl phosphate, di(butylphenyl) monophenyl phosphate, and tributylphenyl phosphate (in the range of >75 to ≤98.5 wt %), available commercially under the name Durad® 220B, Reolube® Turbofluid 46B, or Reolube® HYD 46B, and tris(2-ethylhexyl) phosphate, available commercially under the name Disflamoll® TOF, at a 90:10 ratio by weight of butylated TPP to tris(2-ethylhexyl) phosphate was evaluated according to the procedures above.
A mixture of butylated TPP and tris(2-ethylhexyl) phosphate at a 75:25 ratio by weight was evaluated according to the procedures above.
A mixture of butylated TPP and tris(2-ethylhexyl) phosphate at a 50:50 ratio by weight was evaluated according to the procedures above.
A mixture of butylated TPP and tris(2-ethylhexyl) phosphate at a 25:75 ratio by weight was evaluated according to the procedures above.
Trimethyl phosphate was evaluated according to the procedures above.
Tri-n-propyl phosphate was evaluated according to the procedures above.
Triisopropyl phosphate was evaluated according to the procedures above.
Tri-n-butyl phosphate was evaluated according to the procedures above.
As shown in the Table above, each of Examples 1a, 1b, 1c and 1d had, in accordance with the present disclosure, a flash point >200° C., a pour point ≤−30° C., a kinematic viscosity at 40° C. of less than 35 cSt, often less than 25 cSt, and a DC resistivity at 25° C. of >5 GOhm-cm. That is, the phosphate ester of Examples 1a, 1b, 1c and 1d had the preferred properties, in a circulating immersion cooling system, of low flammability, low pour point, high electrical resistivity, and low kinematic viscosity for pumpability. In contrast, Comparative Examples 1˜4 each exhibited a low flash point well below 200° C. and a low DC resistivity relative to Examples 1a-1d.
In addition to the Examples 1a-1d above, the mixture of butylated TPP and tris(2-ethylhexyl)phosphate at a 50:50 ratio by weight of Example 1c, with the preferred physical characteristics and properties as described above, was evaluated in a thermal propagation nail test (Example 2) to demonstrate that the heat transfer fluid of the present disclosure, while having excellent viscosity for a circulating immersion cooling system, is effective in maintaining safe conditions and avoiding heat propagation and thermal runaway.
The mixture of butylated TPP and tris(2-ethylhexyl) phosphate at a 50:50 ratio by weight of Example 1c was evaluated in a thermal propagation nail test to simulate thermal runaway conditions. The test was carried out in accordance with standard GB 38031-2020 as per the following: A battery module was packed using 7 cylindrical cells adjacent to one another, with one middle cell and 6 cells surrounding the middle cell. The cells were contained within a battery-like housing filled with the sample fluid, so that the cells were fully immersed in the sample fluid. There was no active cooling of the sample fluid. The middle cell was short circuited by a nail being directly inserted into the middle cell resulting in a temperature rise in the nailed cell and a catastrophic failure of the nailed cell. The surrounding cells were observed to evaluate whether the nailed cell and its associated temperature rise would trigger thermal propagation or potential runaway conditions with respect to the surrounding cells. With the mixture of butylated TPP and tris(2-ethylhexyl) phosphate, no thermal runaway or fire development occurred in the surrounding cells. That is, all of the surrounding 6 cells stayed intact and remained functional and at full voltage. Thus, the mixture of butylated TPP and tris(2-ethylhexyl) phosphate provided effective thermal dissipation and effectively protected the battery module.
A base oil was evaluated in the thermal propagation nail test described in Example 2. The base oil had a flash point of 155° C., pour point of −48° C., and viscosity at 40° C. of 10 cSt. In the presence of the base oil, the failure of the nailed cell transferred enough heat to the surrounding cells to compromise one of the surrounding cells, which lost its voltage. Thus, the base oil did not provide effective thermal dissipation and did not effectively protect the battery module.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21191201.9 | Aug 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/035905 | 7/1/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63219227 | Jul 2021 | US |
