Siloxane heat transfer fluids, apparatuses and methods

Abstract

Heat transfer fluids are described. In particular, siloxane heat transfer fluids having a branched T or Q unit structure wherein each branch comprises a siloxy D unit group are described. These fluids can be used in particular for highly demanding heat transfer applications and are suitable for related heat transfer devices and heat transfer methods.

Description

Technical Field

[0001] This manual relates to heat transfer fluids, heat transfer equipment, and heat transfer methods. Background Technology

[0002] Heat transfer fluids facilitate heat movement between a heat source and a radiator or diffuse heat concentrated in a small area to a larger volume. Associated devices utilize heat transfer fluids to enhance heat transfer. Siloxanes consist of Si-O-Si bonds. Summary of the Invention

[0003] In one aspect, this specification relates to a method for transferring heat. The method includes 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. The heat transfer fluid comprises a branched siloxane having T or Q units, wherein each branch of the branched siloxane comprises a siloxy D-unit group.

[0004] On the other hand, this specification relates to a heat transfer fluid. The heat transfer fluid comprises at least one branched siloxane having T or Q units, each branch having at least one silanoxy D unit group. The heat transfer fluid has a kinematic viscosity of less than 7 centistokes (cSt) at 23°C and a flash point greater than 100°C.

[0005] On the other hand, this specification relates to a method for transferring heat. The method includes providing a heat transfer fluid comprising at least one branched siloxane having T or Q units, wherein each branch of the branched siloxane comprises a silanoxy D-unit group. The heat transfer fluid has a kinematic viscosity of less than 7 cSt at 23°C and a flash point greater than 100°C.

[0006] On the other hand, this specification relates to a heat transfer device. The heat transfer device includes a heat source, a radiator, and a heat transfer fluid in fluid communication with both the heat source and the radiator. The heat transfer fluid comprises branched siloxanes having T or Q units, each branch having a siloxy D-unit group. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of an exemplary heat transfer device.

[0008] Figure 2 This is a schematic diagram of another exemplary heat transfer device. Detailed Implementation

[0009] Silicones are used in a variety of industrial and commercial applications, at least in part because of their oxidative stability over a wide operating temperature range (e.g., -80°C to 250°C). Silicone oils are used as heat transfer fluids; however, conventional silicone heat transfer fluids are primarily based on linear polydimethylsiloxanes, which exhibit either a) low viscosity and low flash point, or b) high viscosity and high flash point. This trade-off is well-known and limits the applications of these conventional silicones. For demanding heat transfer applications, both low viscosity (especially at low temperatures) and a high flash point are required.

[0010] The branched siloxanes described in this application are particularly suitable for heat transfer applications because they exhibit a surprising combination of low viscosity and high flash point. This allows these siloxanes to be used in applications where only fluorinated chemicals were previously considered suitable. The heat transfer siloxanes described herein may be fluorine-free, chlorine-free, or free of all halogens.

[0011] Immersion cooling is a type of heat transfer application where combinations of these properties can find particular utility. For example, large-scale computer server systems perform significant workloads and draw large amounts of power. These servers are typically rack-mounted and air-cooled via internal fans or fans attached to the back of the rack or elsewhere in the server ecosystem. As the demand for higher densities of computer components increases, more efficient conductive cooling mechanisms, such as immersion cooling, are becoming increasingly attractive.

[0012] Other heat transfer applications and devices are applicable to the heat transfer fluids described herein. For example, the branched siloxanes described herein can be used in closed-loop systems where the heat transfer fluid facilitates heat transfer from a heat source to a radiator but never comes into direct contact with the heat source. Conversely, a thermally conductive medium is used to transfer heat between the heat source and the heat transfer fluid; this thermally conductive medium includes one or more of metals, thermal pastes, and thermal interface materials.

[0013] Siloxane structural units are commonly referred to as M, D, T, or Q siloxy units. These correspond to monofunctional, difunctional, trifunctional, and tetrafunctional structural units having 1, 2, 3, or 4 silicon-oxygen bonds, respectively. In some embodiments, the siloxanes described herein may have T or Q units.

[0014] Branched siloxanes suitable as heat transfer fluids as described herein may contain at least one silanoxy D-unit group. In some embodiments, the branched siloxane may contain at least two silanoxy D-unit groups. In some embodiments, each branch of the branched siloxane contains at least one silanoxy D-unit group. In some embodiments, each branch of the branched siloxane contains at least two silanoxy D-unit groups. In some embodiments, the branched siloxanes are symmetrical—meaning that each branch is identical. In some embodiments, the branched siloxane may have a high molecular weight of at least 450 g / mol. In some embodiments, the branched siloxane may contain three branches. In some embodiments, the branched siloxane may contain four branches.

[0015] In some embodiments, the heat transfer fluid containing branched siloxanes as described herein may exhibit a flash point greater than 100°C, greater than 110°C, greater than 120°C, greater than 130°C, greater than 140°C, or greater than 150°C. In some embodiments, the heat transfer fluid containing branched siloxanes as described herein may also exhibit kinematic viscosities less than 20 cSt at 23°C, less than 15 cSt at 23°C, less than 10 cSt at 23°C, less than 7 cSt at 23°C, less than 5 cSt at 23°C, less than 3 cSt at 23°C, or less than 2 cSt at 23°C. In some applications, kinematic viscosity at -60°C may be particularly relevant. The heat transfer fluid containing branched siloxanes described herein may also, or alternatively, exhibit kinematic viscosities less than 100 cSt at -60°C, less than 30 cSt at -60°C, or less than 10 cSt at -60°C.

[0016] In some implementations, branched siloxanes may have one of the forms shown in Formula I or Formula II.

[0017]

[0018] Formula I.

[0019]

[0020] Formula II.

[0021] The synthesis of these branched siloxanes can be accomplished by known techniques such as the Pirers-Rubinsztajn reaction of alkoxysilanes and silyl hydrides (Brook, MAChem.Eur.J. 2018, Vol. 24, pp. 8458-8469), or via the reaction between silanols or silanol salts and chlorosilanes (Katarzhnova, EY et al., Mendeleev Commun. 2021, Vol. 31, pp. 393-396).

[0022] The synthesis of these branched siloxanes can alternatively be accomplished by the following exemplary method. First, a mixture of hexamethyldisiloxane and tetramethyldisiloxane is stoichiometrically balanced using a solid supported acid catalyst, which primarily yields pentamethyldisiloxane (with very little tetramethyldisiloxane remaining). Then, boron Lewis acid-mediated coupling is performed. After distillation of the volatile products and purification of the branched products, more tetramethyldisiloxane is added to the volatile fraction, equilibrated as described above, and reused in the coupling chemistry. This can also be carried out using polymethylhydrosiloxane as the hydride source. Examples of synthetic pathways are shown below:

[0023]

[0024]

[0025] In some implementations, these heat transfer fluids can be incorporated into the heat transfer device. Figure 1This is a schematic diagram of an exemplary heat transfer device. The heat transfer device includes a heat source 110, a heat transfer channel 120 including a heat transfer fluid 122, and a radiator 130. The heat source 110 can be any suitable heat source, including electronic equipment such as a computer or server. The heat source 110 can reach a normal operating temperature of 40°C, 50°C, 60°C, 70°C, 80°C, or higher (in the absence of a cooling system). The heat transfer channel 120 can take any suitable form or be made of any suitable material. For example, the heat transfer channel 120 can be a pipe or cable filled with the heat transfer fluid 122. In some embodiments, the heat transfer channel 120 is directly attached to the heat source 110. In some embodiments, the heat transfer channel 120 is attached to the heat source 110 via thermally conductive adhesive, thermal paste, or a metal connector (such as solder). In some embodiments, the heat transfer channel 120 is similarly attached to the radiator 130. The heat transfer fluid 122 is in fluid communication with both the heat source and the radiator. In some embodiments, the heat transfer fluid 122 circulates without the aid of a pump or other mechanical force. In some embodiments, the heat transfer fluid 122 circulates with the assistance of a pump. The heat transfer fluid 122 contains at least one branched siloxane as described herein. The radiator 130 is configured to release the heat transferred from the heat transfer fluid 122 to the external environment. In some embodiments, the external environment is air. The radiator 130 may be configured with fins or another design to provide a high surface area to volume ratio. This high ratio can help allow maximum heat transfer between the radiator and the external environment.

[0026] Figure 2 This is a schematic diagram of another exemplary heat transfer device. The heat transfer device 200 is similar to... Figure 1 The heat transfer device 100 differs in that the heat transfer fluid 222 is not only in fluid communication with the heat source 210, but also in direct contact with the heat source. The heat transfer channel 220 provides a volume surrounding the heat source 210. The heat transfer fluid 222 is also in fluid communication with the radiator 230. Similar to... Figure 1 The heat transfer device 100, pump, or other mechanism may be used to circulate the heat transfer fluid 222. The heat transfer fluid 222 includes at least one branched siloxane as described herein. Figure 2 An alternative exemplary method is shown, in which the heat source is immersed, i.e., in direct contact with the heat transfer fluid 222.

[0027] right Figure 1 and Figure 2 Modifications and enhancements to the general functional form shown are possible; for example, access doors, support mechanisms, electronic cables and components, monitoring sensors and hardware, pipes and / or tubes, coatings, filters and other mechanisms may be utilized as needed or to suit a particular application.

[0028] Example

[0029] Preparation Example 1: Preparation of a statistical mixture of tetramethyldisiloxane, pentamethyldisiloxane and hexamethyldisiloxane Preparation

[0030] Add 2458 g (15.14 mol, 3217 mL) of hexamethyldisiloxane (Wacker Chemie AG, Munich, Germany), 249.79 g (1.86 mol, 329 mL) of 1,1,3,3-tetramethyldisiloxane (Gelest, Inc., Morrisville, Pa., USA), 13.25 g of DARCO G60 (Thermo Fisher Scientific, Inc., Waltham, Mass., USA), and 2.42 g of concentrated sulfuric acid to a 4 L polypropylene bottle. Seal the bottle and incubate overnight on a shaker. The next day, examine the mixture by gas chromatography for the formation of a new substance: 1,1,3,3,3-pentamethyldisiloxane. The mixture was then filtered through a CELITE 545 (Sigma Aldrich, Burlington, Mass.) pad in a glass sintering funnel to remove the catalyst. The mixture was then collected and used as is.

[0031] Preparation of tri[[dimethyl(trimethylsilyloxy)silyl]oxy]-methyl-silane (Example 1) Preparation

[0032] 220.74 g (1234 mmol, 1.00 equivalent) of triethoxymethylsilane (TCI America Chemical, Portland, Ore.) and 3460.46 g of a statistical mixture of tetramethyldisiloxane, pentamethyldisiloxane, and hexamethyldisiloxane as detailed in Preparation Example 1 (approximately 20% by weight of pentamethyldisiloxane) were added to a 12 L glass reactor equipped with a controller-driven thermocouple (purchased from J-KEM Scientific, St. Louis, Mo., Missouri), a heating mantle, a mechanical stirrer, a glass stirrer converter, a PTFE impeller, a reflux condenser with a nitrogen inlet / outlet and a bubbler, a diaphragm, and a glass bubble tube with a PTFE 24 / 40 adapter. The reactor was then bubbled warmly with nitrogen overnight. The next day, the internal temperature was set to 60°C, bubbling was stopped, and nitrogen was set to flow through the condenser and bubbler.

[0033] In a nitrogen-filled glove box, 100 mg of tris(pentafluorophenyl)borane (TCI America Chemical, Portland, Ore.) was dissolved in 10 mL of toluene, and the solution was removed from the glove box using a syringe with a long stainless steel needle. The catalyst was slowly added through a diaphragm until bubbling was observed, accompanied by exothermic reactions. The internal temperature was maintained below 80°C. Once a small amount of bubbling was observed, even after the addition of additional catalyst, aliquots were taken for further processing. 1 ¹H-NMR analysis indicated the presence of ethoxysilane. After approximately 6.5 hours, the reaction was still not complete. The internal temperature was set to 80°C and stirred overnight. An additional 70 mg of catalyst was administered over 7 hours, followed by... 1 ¹H-NMR and GC analyses indicated that the reaction was essentially complete. The reaction was cooled to room temperature, filtered through a neutral alumina pad in a new 12L glass reactor, and the original reactor was rinsed with two 300mL portions of heptane. The volatiles were then distilled under vacuum.

[0034] After concentration, 1 A small amount of ethoxysilane was observed in the 1H-NMR spectrum. Then, 12.31 g of additional pentamethyldisiloxane was added to a three-necked 2L round-bottom flask equipped with a thermocouple, rubber diaphragm, Claisen adapter with nitrogen bubble tube, T-connector with nitrogen inlet / outlet, and stir bar. The internal temperature was set to 80 °C. 1.3 mL of a toluene solution of 9.5 mg / mL tris(pentafluorophenyl)borane was added to the solution, and a small amount of foaming was observed. Another 0.3 mL was added, but no foaming occurred. Aliquots showed that all the ethoxysilane had been consumed. The reaction was cooled to room temperature, filtered through neutral alumina, washed with heptane, and then the volatiles were stripped under vacuum at approximately 60 °C.

[0035] Distillation of tri[[dimethyl(trimethylsilyloxy)silyl]oxy]-methyl-silane (Example 1) distillation

[0036] 278.38 g of crude tri[[dimethyl(trimethylsilyloxy)silyl]oxy]-methylsilane was added to a single-necked 500 mL distillation flask with a hot well. A short 24 / 40-24 / 40 extender, a short-path distillation head, and a heating mantle with a variable transformer (Variac) were added. The receiver was cooled with a dry ice / isopropanol bath in a Dewar flask. The vacuum source was a 4.31 mTorr Schlenk line. When the system was open, the vacuum was approximately 42 mTorr. Once the head temperature reached 70 °C, the initial fraction was removed. The main fraction was distilled at approximately 18 mTorr and a head temperature of 84 °C. 201.95 g of clear, colorless liquid was collected, with a mass recovery of 72.5%. 1¹H NMR (500MHz, chloroform-d) δ ppm 0.07 (s, 21 H) 0.10 (s, 27 H). 29 Si NMR (99MHz, chloroform-d) δ ppm -67.51 (s, 1 Si) -21.61 (s, 3 Si) 7.29 (s, 3 Si). Quantitative analysis. 13 C NMR (126MHz, chloroform-d) δ ppm -2.49 (s, 1 C) 0.78 (s, 6 C) 1.53 (s, 9 C).

[0037] Preparation and distillation of tetra(dimethyl(trimethylsilyloxy)silyl) ester (Example 2)

[0038] In a nitrogen-filled glove box, 8.99 g (9.646 mL, 43.2 mmol) of tetraethoxy orthosilicate (Sigma Aldrich, Burlington, Mass.) was added to a 500 mL round-bottom flask equipped with a Vigreaux reflux condenser. Then, 31.5463 g of pentamethyldisiloxane (42.163 mL, 216 mmol, Gelest, Morrisville, Pa.) was added via syringe. This reaction can also be carried out using a statistical mixture of tetramethyldisiloxane, pentamethyldisiloxane, and hexamethyldisiloxane as detailed in Preparation Example 1. Both reactants were diluted with 95 g of hexane (Sigma Aldrich, SureSeal). The mixture was placed in a heating block set to 55 °C. Simultaneously, 50 mg of B(C6F5)3 (TCI America) was added to a 20 mL vial and dissolved in 5 mL of toluene. 250 μL of the catalyst solution was added to the reaction mixture; the reaction immediately began to foam and reflux vigorously. After 10 minutes, another 200 μL of the catalyst solution was added, resulting in even more foaming and reflux. Two hours later, aliquots were taken for further processing. 1 H-NMR analysis, 1 ¹H-NMR analysis indicated the total consumption of alkoxysilanes. The crude mixture was cooled, removed from the glove box, and then filtered through a neutral alumina pad. Volatiles were removed on a rotary evaporator. The product was then distilled in two batches on a Kugelrohr still. The product was distilled in a tube furnace at 155 mTorr and 235 °C. A total of 26.83 g of clear, colorless liquid was collected, with a yield of 91%. 1¹H NMR (500MHz, chloroform-d) δ ppm 0.08 (s, 24 H), 0.10 (s, 36 H). 29 Si NMR (99MHz, chloroform-d) δ ppm -109.68 (s, 1 Si) -21.19 (s, 4 Si) 7.37 (s, 4 Si). Quantitative analysis. 13 C NMR (126MHz, chloroform-d) δ ppm 0.75 (s, 8 C) 1.58 (s, 12 C).

[0039] Measurement of physical properties and kinematic viscosity

[0040] Flash point was analyzed using ASTM D-3278-20, "SETAFLASH Series 8 'ACTIVECOOL' Small Closed Cup Apparatus for the Determination of Flash Point of Liquids," which focuses on closed cup flash point.

[0041] Kinematic viscosity was measured using a SCHOTT GERATE AVS 350 viscometer (purchased from Xylem Analytics Germany Sales GmbH & Go.KG, Mainz, Germany). The viscometer was calibrated using a Hagenbach calibration factor.

[0042] The pour point is measured by placing a sealed glass vial containing 1 mL of fluid into a stirred Dewar flask containing a cold isopentane bath. The vial is directly connected to a thermocouple probe. The bath is cooled by bringing a plastic beaker of liquid nitrogen into contact with the bath and cooling until the sample no longer pours. The temperature is increased in 1°C increments until pouring occurs. Pouring is defined as the visible movement of the material during a five-second count. This standard is specified in ASTM D97.

[0043] The characteristics of the comparative example (designated as CE) are derived from the Gelest Silanes and Silicones Handbook 5000-A (purchased from Gelest, Inc., Morrisville, Pa., USA).

[0044]

[0045]

[0046] As can be seen from the test results of the examples and the recorded characteristics of the comparative examples, the examples exhibit a surprising combination of high flash point and low viscosity at low temperature.

[0047] Given that the densities of these materials are close to 1, the kinematic and dynamic viscosities are generally consistent (on the order of magnitude), and the room-temperature dynamic viscosities of the recorded comparative examples indicate that the kinematic viscosities will be similar (though, of course, the units are cSt and cP respectively).

[0048] The extremely low pour point measured for the examples also contrasts with the comparative examples. Since the viscosity is expected to increase dramatically to an unmeasurable point below the pour point, the unacceptable low-temperature viscosity can be reasonably inferred from the recorded pour point and room temperature viscosity of the comparative examples. In other cases, the viscosity at room temperature (23°C) is already excessive and is expected to increase only as the temperature decreases.

Claims

1. A method for transferring heat, the method comprising: Provide a heat source; Provide radiators; Provide a heat transfer fluid in fluid communication with both the heat source and the radiator; The heat transfer fluid comprises a branched siloxane, wherein each branch of the branched siloxane comprises a silanoxy D unit group.

2. The method according to claim 1, wherein the branched siloxane has the form according to formula I, Formula I.

3. The method according to claim 1, wherein the branched siloxane has the form according to formula II, Formula II.

4. The heat transfer fluid according to claim 1, wherein the heat transfer fluid has a kinematic viscosity of less than 10 cSt at 23°C.

5. The heat transfer fluid according to claim 1, wherein the heat transfer fluid has a kinematic viscosity of less than 100 cSt at -60°C.

6. The heat transfer fluid according to claim 1, wherein the heat transfer fluid has a pour point of less than -100°C.

7. The heat transfer fluid according to claim 1, wherein the heat transfer fluid is free of halogens.

8. A heat transfer fluid, said heat transfer fluid comprising: At least one branched siloxane having a T or Q unit, each branch having at least one silanoxy D unit group; The heat transfer fluid has a kinematic viscosity of less than 7 cSt at 23°C and a flash point of greater than 120°C.

9. The heat transfer fluid according to claim 8, wherein the heat transfer fluid has a kinematic viscosity of less than 100 cSt at -60°C.

10. The heat transfer fluid of claim 8, wherein the heat transfer fluid has a kinematic viscosity of less than 50 cSt at -60°C.

11. The heat transfer fluid according to claim 8, wherein the heat transfer fluid has a kinematic viscosity of less than 30 cSt at -60°C.

12. The heat transfer fluid according to claim 8, wherein the heat transfer fluid has a pour point of less than -100°C.

13. The heat transfer fluid of claim 8, wherein the heat transfer fluid is free of halogens.

14. The heat transfer fluid according to claim 8, wherein the branched siloxane has the form according to formula I. Formula I.

15. The heat transfer fluid according to claim 8, wherein the branched siloxane has the form according to formula II. Formula II.

16. A method for transferring heat, the method comprising: A heat transfer fluid is provided, the heat transfer fluid comprising at least one branched siloxane having T or Q units, each branch having a siloxy D unit group, and the heat transfer fluid having a kinematic viscosity of less than 7 cSt at 23°C. Provide at least one surface for conducting heat from or to the at least one surface; The heat transfer fluid is provided such that it is in communication with the surface fluid; The surface is at least 70°C.

17. The heat transfer fluid of claim 16, wherein the heat transfer fluid is free of halogens.

18. A heat transfer device, the heat transfer device comprising: Heat source; heat sink; A heat transfer fluid, wherein the heat transfer fluid is in fluid communication with both the heat source and the radiator; The heat transfer fluid contains branched siloxanes having T or Q units, each branch having a siloxy D unit group.

19. The heat transfer fluid of claim 18, wherein the heat transfer fluid has a kinematic viscosity of less than 100 cSt at -60°C.

20. The heat transfer fluid of claim 18, wherein the heat transfer fluid has a kinematic viscosity of less than 50 cSt at -60°C.

21. The heat transfer fluid of claim 18, wherein the heat transfer fluid has a pour point of less than -100°C.

22. The heat transfer fluid of claim 18, wherein the heat transfer fluid is free of halogens.

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