Heat-transfer fluid, apparatus, and methods

Abstract

Heat-transfer fluids free of halogenated (e.g., fluorinated) molecular species, where such heat-transfer fluids achieve performances that are within the tolerance limits set forth by the industry for nonhalogenated fluids, such heat-transfer fluids comprising an ester, the ester represented by the structure Formula (I), Formula (II), (Formula III), or where R and R' are independently a C4 to C10 hydrocarbyl group; each X and Y is independently hydrogen or a C1 to C2 hydrocarbyl group; n is a whole number from 0 to 6 inclusive; and m is a whole number from 2 to 4 inclusive. Heat transfer apparatuses including the heat transfer fluids and methods of transferring heat are provided.

Description

[0001] HEAT-TRANSFER FLUID, APPARATUS, AND METHODS

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to heat-transfer fluids, heat-transfer apparatuses, and heat- transfer methods.

[0004] BACKGROUND

[0005] Heat-transfer fluids facilitate the movement of heat between a heat source and a heat sink or distribute heat concentrated in a small volume to a larger volume. Associated apparatuses facilitate heat transfer through the use of a heat-transfer fluid.

[0006] SUMMARY

[0007] Disclosed herein are heat-transfer fluids free of halogenated (e.g., fluorinated) molecular species, where such heat-transfer fluids achieve performances that are within the tolerance limits set forth by the industry for nonhalogenated fluids. In one aspect, provided herein are heat-transfer fluid comprising an ester, the ester represented by the structure where R and R' are independently a C4 to CIO hydrocarbyl group; each X and Y is independently hydrogen or a Cl to C2 hydrocarbyl group; n is a whole number from 0 to 6 inclusive; and m is a whole number from 2 to 4 inclusive.

[0008] In another aspect, provided are heat transfer apparatuses comprising a heat source; a heat sink; and a heat transfer fluid in fluid communication with both the heat source and the heat sink; where the heat transfer fluid comprises a heat transfer fluid of the present disclosure.

[0009] In another aspect, provided are methods of transferring heat comprising providing a heat source; providing a heat sink; and providing a heat transfer fluid in fluid communication with both the heat source and the heat sink; where the heat transfer fluid comprises a heat transfer fluid of the present disclosure. As used herein: the term “chiral center” refers to an sp3carbon atom bonded to four different atoms or groups such that it is not superimposable on its mirror image; the term “free of’ means that a particular element, e.g., fluorine, is not present in a molecular structure or refers to an element in a mixture present in a concentration of less than 5 wt.%, less than 4 wt.%, less than 3 wt.%, less than 2 wt.%, less than 1 wt.%, or less than 0.5 wt.%; the term “hydrocarbyl group” refers to a univalent group formed by removing a hydrogen atom from a hydrocarbon, e.g., methyl, ethyl, phenyl., and includes both saturated and unsaturated hydrocarbon species.

[0010] Features and advantages of the present disclosure will be further understood upon consideration of the detailed description as well as the appended claims.

[0011] BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a schematic of a first exemplary heat transfer apparatus.

[0013] FIG. 2 is a schematic of a second exemplary heat transfer apparatus.

[0014] Repeated use of reference characters in the specification and drawings is intended to represent the same or analogous features or elements of the disclosure. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the disclosure. The figures may not be drawn to scale.

[0015] DETAILED DESCRIPTION

[0016] There is significant commercial interest in the development of fluids for use in heat transfer applications. Work in this field has typically focused on the use of highly fluorinated fluids due to the unique properties of highly fluorinated materials such as, for example, their low intermolecular interactions as well as their high to non-existent flash points.

[0017] Immersion cooling is one of the heat-transfer applications where compositions having low viscosity and high flash point may find particular utility. For example, large-scale computer server systems perform significant workloads and draw a considerable amount of power. These servers are conventionally rack mounted and air-cooled via internal fans or fans attached to the back of the rack or elsewhere within the server ecosystem. As the need for higher density of computer components increases, more efficient conductive cooling mechanisms, such as immersion cooling, become increasingly attractive.

[0018] Other heat transfer applications and apparatuses may also be suitable for the heat transfer fluids described herein. For example, the esters described herein may be used in a closed loop system, wherein the heat-transfer fluid facilitates transfer of heat from a heat source to a heat sink but is never directly in contact with the heat source. Instead, a heat-conductive medium is used to transfer heat between the heat source and the heat transfer fluid, including one or more of metals, thermal paste, and thermal interface materials.

[0019] Disclosed herein are heat-transfer fluids free of halogenated (e.g., fluorinated) molecular species, where such heat-transfer fluids achieve performances that are within the tolerance limits set forth by the industry for nonhalogenated fluids. When fluids that are not halogenated are used, they typically require the use of complex and often variable mixtures of molecules to achieve the desired performance. Advantageously, however, the disclosed heat-transfer fluids are generally not mixtures of many different non-halogenated compounds but are instead diastereomeric mixtures that comprise essentially the same few compounds but with different arrangements of the atoms in three-dimensional space.

[0020] In addition to the benefits described above, the nonfluorinated fluids often employed for these cooling applications are frequently obtained from nonrenewable sources, such as, for example, petroleum by-products. In contrast, heat-transfer fluids of the present disclosure may have their raw materials sourced from renewable, biologically based feedstocks. Consequently, heat-transfer fluids of the present disclosure may offer a greener choice for consumers and should allow these fluids to have a high degree of ability to decompose if released into the environment.

[0021] Provided herein are heat-transfer fluids comprising an ester, the ester represented by the structure where R and R' are independently a C4 to CIO, saturated or unsaturated, hydrocarbyl group; each X and Y is independently hydrogen or a Cl to C2 hydrocarbyl group; n is a whole number from 0 to 6 inclusive; and m is a whole number from 2 to 4 inclusive.

[0022] Esters useful in embodiments of the present disclosure may be prepared by methods known to those of ordinary skill in the relevant arts and as described in the Examples below. In some embodiments, the ester may include 1, optionally 2, optionally 3, optionally 4, optionally 5, or optionally 6 chiral centers. In some embodiments the ester may be free of halogens selected from the group consisting of fluorine, chlorine, and combinations thereof.

[0023] Heat transfer fluids of the present disclosure may have an absolute viscosity at 23°C of less than 10 cP, less than 9 cP, less than 8 cP, or less than 7 cP as determined by the Room-Temperature Viscosity Measurement Test. In some embodiments, the heat transfer fluid may have a kinematic viscosity at - 60°C of less than 3000 cSt, less than 2000 cSt, less than 1000 cSt, less than 900 cSt, less than 800 cSt, less than 700 cSt, less than 600 cSt, less than 500 cSt, less than 400 cSt, less than 300 cSt, or less than 200 cSt as determined by the Kinematic Viscosity Measurement Test. In some embodiments, the heat transfer fluid may have a pour point of less than -50 °C, less than -60 °C, less than - 70 °C, less than -80 °C, or less than -90 °C as determined by the Pour Point Measurement Test.

[0024] In some embodiments, heat-transfer fluids of the present disclosure may include a diester represented by the structure

[0025] In some embodiments, heat-transfer fluids of the present disclosure may include an ester represented by the structure

[0026] combinations thereof.

[0027] In some embodiments, heat-transfer fluids of the present disclosure may comprise an ester including a mixture of various constitutional isomers of the CIO acid where the alpha center is quaternary, such esters represented by the structure

[0028]

[0029] In some embodiments, heat-transfer fluids of the present disclosure may include a diester represented by the structure and combinations thereof.

[0030] In some embodiments, the heat transfer fluids disclosed herein may be incorporated into a heat transfer apparatus. FIG. 1 is a schematic of a first exemplary heat transfer apparatus. Referring to FIG. 1, heat transfer apparatus includes heat source 110, heat transfer channel 120 including heat transfer fluid 122, and heat sink 130. Heat source 110 may be any suitable heat source, including, for example, electronic devices such as a computer or a server. In the absence of a cooling system, heat source 110 may reach normal operating temperatures of 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, or higher (e.g., 125 °C) Heat transfer channel 120 may take any suitable form or be made from any suitable material. For example, in some embodiments heat transfer channel 120 may be a pipe or cable filled with heat transfer fluid 122. In some embodiments, heat transfer channel 120 is directly attached to heat source 110. In some embodiments, heat transfer channel 120 is attached to heat source 110 via a thermal adhesive, a thermal paste, a metal joint (e.g., solder), or combinations thereof. In some embodiments, heat transfer channel 120 is similarly attached to heat sink 130. Heat transfer fluid 122 is in fluid communication with both the heat source 110 and the heat sink 130. In some embodiments, heat transfer fluid 122 may be circulated without the aid of a pump or other mechanical forcing. In some embodiments, heat transfer fluid 122 may be circulated with the assistance of a pump. Heat transfer fluid 122 includes at least one diester as described herein.

[0031] Heat sink 130 is configured to release heat transferred from heat transfer fluid 122 to an external environment. In some embodiments, this external environment is air. Heat sink 130 may be configured with fins or another design element known to those of ordinary skill in the relevant arts to provide a high ratio between surface area and volume. This high ratio between surface area and volume of the heat sink 130 may assist in allowing the maximum heat energy to transfer between the heat sink 130 and the external environment.

[0032] FIG. 2 is a schematic of a second exemplary heat transfer apparatus. Heat transfer apparatus 200 is similar to heat transfer apparatus 100 of FIG. 1 except heat transfer fluid 222 is not only in fluid communication with but is also in direct contact with heat source 210. Referring to FIG. 2, heat transfer channel 220 provides a volume that surrounds heat source 210. Heat transfer fluid 222 is also in fluid communication with heat sink 230. As in the case of the heat transfer apparatus 100 in FIG. 1, a pump or other mechanism may be used to circulate heat transfer fluid 222. Heat transfer fluid 222 includes an ester as described herein. FIG. 2 illustrates an alternative exemplary approach wherein the heat source is immersed in, i.e., is in direct contact with, heat transfer fluid 222.

[0033] Modifications and enhancements to the general functional form shown in FIGS. 1 and 2 are contemplated; for example, access doors, support mechanisms, electronic cabling and components, monitoring sensors and hardware, piping and / or tubing, coatings, filters, and other mechanisms can be utilized as necessary or as suited to the particular application.

[0034] Objects and advantages of this disclosure are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure.

[0035] EXAMPLES

[0036] Unless otherwise noted or readily apparent from the context, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. Preparation of Esters Used in the Examples

[0037] Preparation of Esters for Table 1:

[0038] To a solution of the desired diacid or cyclic anhydride (1.00 equiv) and -tohicncsulfonic acid monohydrate (0.01 equiv) in heptane in a round bottom flask with a stir bar was added the desired alcohol (2.08 equiv). A Dean-Stark apparatus and reflux condenser were attached and while stirring the reaction mixture was heated at reflux until the required amount of water was produced. The reaction was cooled to room s temperature and the organic layer was washed with portions of a saturated aqueous solution of NaHCO, until the organic layer was at a neutral pH. The organic layer was dried with MgSOj and the solvent was removed with a rotary evaporator. The concentrated solution was then purified by vacuum distillation to isolate the desired ester as a clear, colorless liquid.

[0039] Preparation of Esters for Table 2:

[0040] Acid Chloride Protocol

[0041] To an oven dried flask equipped with a reflux condenser that had been purged three times was added versatic acid (1.00 equiv) followed by dry DMF (0.005 equiv). The solution was cooled to 0 °C, and then oxalyl chloride (1.02 equiv) was added in a dropwise fashion to minimize the evolution of gas from the solution. Upon complete addition of the oxalyl chloride the reaction was allowed to slowly warm to room temperature and stir overnight. The next day the solution was cooled to 0 °C and then pyridine (2.10 equiv) was added to the reaction in a slow fashion. Upon complete addition of the pyridine the solution was allowed to stir at 0 °C for 20 minutes before the desired alcohol (1.20 equiv) was added in a rapid dropwise fashion. The solution was then warmed to room temperature before being raised to reflux or 100 °C whichever is lower overnight. The next day the reaction is cooled to rt and then the solid is removed via vacuum filtration with washing of the solid with a small portion of dichloromethane. The organic layer was then washed with a 3 M solution of HO until the organic layer was acidic. The organic layer is then washed with a portion of water and then the organic layer is washed to neutral pH with successive washes of a saturated aqueous solution of NaHCO ,. The resulting organic layer was dried with MgSO4 and the solvent was removed with the rotary evaporator to yield an oil which was purified by vacuum distillation to yield the desired material as a clear colorless liquid.

[0042] SN2 Protocol

[0043] To a solution of K2CO3 (1.01 equiv) in DMF (enough DMF to give a concentration of 2 M relative to the acid and DMF) in a round bottom flash equipped with a large stir bar was slowly added the versatic acid (1.00 equiv) over a period of several minutes. The reaction was raised to 100 °C for 1 hour or until the production of CO2 ceased whichever comes later. The desired alkyl halide (1.20 equiv) was then added in a dropwise fashion over a period to maintain the internal temperature within 5 degrees of 100 °C. Upon full addition of the alkyl halide the reaction is heated overnight. After heating overnight, the reaction is cooled to room temperature and then the solid is removed by vacuum filtration retaining the liquid layer. The solvent was removed with the rotary evaporator and the resulting oil was then purified by vacuum distillation to give the desired product as a clear, colorless oil.

[0044] Preparation of Esters for Table 3:

[0045] Fisher Esterification Protocol

[0046] To a solution of the desired diol (1.00 equiv), -tohicncsulfonic acid (0.01 equiv) in toluene (enough toluene to give a concentration of the diol of 10 M relative to the volume of toluene) in a round bottom flask with a stir bar was added the desired carboxylic acid (3.00 equiv). A Dean-Stark apparatus and reflux condenser were attached and while stirring the reaction mixture was heated at reflux until the required amount of water was produced. The reaction was cooled to room temperature and the organic layer was washed with portions of a saturated aqueous solution of NaHCO, until the organic layer was at a neutral pH. The organic layer was dried with MgSOj and the solvent was removed with a rotary evaporator. The concentrated solution was then purified by vacuum distillation to isolate the desired ester as a clear, colorless liquid.

[0047] Acid Chloride Protocol

[0048] To an oven dried 250 mU round bottom flask equipped with a stir bar and a reflux condenser was added the desired carboxylic acid (1.05 equiv) followed by dichloromethane (enough DCM to make the solution 3.3 M relative to the alcohol), and DMF (0.02 equiv). The reaction mixture was cooled to 0 °C with stirring and then the oxalyl chloride (1.04 equiv) was added in a slow dropwise fashion. Upon complete addition, the reaction was allowed to slowly come to room temperature and stir at that temperature overnight. The reaction was then cooled to 0 °C and triethylamine (2.15 equiv) was added in a slow dropwise fashion. More DCM was added to the solution (enough extra DCM to render the final concentration of the alcohol relative to the DCM to be 1.8 M). Upon complete addition of the DCM, the alcohol was added in a slow dropwise fashion and the reaction was allowed to slowly come to room temperature and stir overnight at that temperature. The solution was then vacuum filtered to remove the solid and the liquid filtrated was extracted with 3 M HC1 until the organic layer was acidic, one portion of deionized water, a saturated solution of NaHCO ? until the pH of the organic layer was neutral, and a final portion of deionized water. The resulting organic layer was dried with MgSOr and the solvent was removed with a rotary evaporator yield a colored oil which was purified by vacuum distillation to afford the desired product as a clear colorless oil. Preparation of Esters for Table 4:

[0049] To a round bottom flask was added -tolucncsulfonic acid (0.005 equiv) followed by the desired alcohol (1.00 equiv), carboxylic acid (1.02 equiv) and then heptane or toluene (enough solvent to give a concentration of the alcohol of 10 M relative to the volume of solvent). A Dean-Stark apparatus and reflux condenser were attached and while stirring the reaction mixture was heated at reflux until the required amount of water was produced. The reaction was then cooled to room temperature and then the organic layer was washed with an aqueous saturated solution of NaHCO, until the organic layer was pH 7. The organic layer was dried with MgSOj and then solvent was removed with a rotary evaporator and the resulting oil was then purified by vacuum distillation to yield the desired ester as a clear, colorless liquid.

[0050] Test Methods

[0051] Flash Point Measurement Test

[0052] Sample flash points were analyzed for Closed Cup Flash Point using ASTM D-3278-96 e-1 "Flash Point of Liquids” by SETAFLASH SERIES 8‘ ACTIVECOOL’ Small Scale Closed-Cup Apparatus.

[0053] Kinematic Viscosity Measurement Test

[0054] Between temperature of -20 and -60°C: Samples were measured on an ARES-G2 rheometer, using a 25mm diameter titanium recessed bob in a 27mm cup. Temperature was controlled from -20°C to -60°C at a temperature rate of l°C / min by a forced convection oven in nitrogen atmosphere. The temperature rate was chosen at 1°C to limit thermal lag. Viscosity was measured at a constant shear rate between 20 and 50s'1to increase measure sensitivity depending on instrument measured torque. In some case, a 50s- 1 was used to improve sensitivity even further. The comparison of the data at different shear rate implies that the fluids are expected to be Newtonian in shear.

[0055] Pour Point Measurement Test

[0056] A sealed glass vial containing 1 mL of the target fluid was placed into a stirred Dewar Flask containing cold iso-pentane bath fluid. The vial was attached directly to the thermocouple probe. The bath fluid was chilled by placing a plastic beaker of liquid nitrogen in contact with the bath fluid, cooling until the sample did not pour. Temperature was increased in 1 deg C increments until it poured. Pouring is defined as visible movement of the material during a five second count, as specified in ASTM D97.

[0057] Room-Temperature Viscosity Measurement Test

[0058] Absolute viscosity was measured using a VL- 4000 viscometer (Cambridge Viscosity, Inc., Boston MA, USA) with the piston tuned for the 1 - 20 cP measurement parameter. Results

[0059] Table 1. Properties of Selected Diesters

[0060] Table 2. Properties of Selected Neodecanoate Acid Ester Derivatives

[0061] Table 3. Properties of Selected Diesters Table 4. Properties of Selected Monoesters

[0062] * Mixture of the internal and terminal olefins of “citronelyl” 2-methylbutanoate in an approximate 85: 15 mixture. All cited references, patents, and patent applications in the above application for letters patent are herein incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control. The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be constmed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.

Claims

What is claimed is:

1. A heat-transfer fluid comprising an ester, the ester represented by the structurewhereinR and R' are independently a C4 to CIO hydrocarbyl group; each X and Y is independently hydrogen or a Cl to C2 hydrocarbyl group; n is a whole number from 0 to 6 inclusive; and m is a whole number from 2 to 4 inclusive.

2. The heat-transfer fluid of claim 1, wherein the ester includes 1, optionally 2, optionally 3, optionally 4, optionally 5, or optionally 6 chiral centers.

3. The heat-transfer fluid of claim 1, wherein the heat transfer fluid has as an absolute viscosity at 23°C of less than 10 cP, less than 9 cP, less than 8 cP, or less than 7 cP as determined by the Room- Temperature Viscosity Measurement Test.

4. The heat-transfer fluid of claim 1, wherein the heat transfer fluid has a kinematic viscosity at- 60°C of less than 3000 cSt, less than 2000 cSt, less than 1000 cSt, less than 900 cSt, less than 800 cSt, less than 700 cSt, less than 600 cSt, less than 500 cSt, less than 400 cSt, less than 300 cSt, or less than 200 cSt as determined by the Kinematic Viscosity Measurement Test.

5. The heat-transfer fluid of claim 1, wherein the heat transfer fluid has a pour point of less than -50 °C, less than -60 °C, less than -70 °C, less than -80 °C, or less than -90 °C as determined by the Pour Point Measurement Test.

6. The heat-transfer fluid of claim 1, wherein the ester is free of halogens selected from the group consisting of fluorine, chlorine, and combinations thereof.

7. The heat-transfer fluid of claim 1, wherein the heat transfer fluid includes an ester represented by the structure8. The heat-transfer fluid of claim 1, wherein the heat transfer fluid includes an ester represented by the stmcture9. The heat-transfer fluid of claim 1, wherein the heat transfer fluid includes a diester represented by the stmctureand combinations thereof.

10. A heat transfer apparatus, comprising: a heat source;a heat sink; and a heat transfer fluid in fluid communication with both the heat source and the heat sink; wherein the heat transfer fluid comprises the heat transfer fluid of claim 1.

11. A method of transferring heat, comprising: providing a heat source; providing a heat sink; and providing a heat transfer fluid in fluid communication with both the heat source and the heat sink; wherein the heat transfer fluid comprises the heat transfer fluid of claim 1.

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