IMMERSION COOLING UNIT OPERATING IN A HUMID ENVIRONMENT

Abstract

The invention relates to an immersion cooling unit (1) comprising an immersion cell defining an internal cavity (3), a bath (5) comprising a dielectric working fluid partially filling the internal cavity and a gaseous phase so as to form a two-phase system; the unit (1) further comprising a condensation device which is positioned in the internal cavity above the electronic component such as not to be immersed in the dielectric working fluid and at least one electronic component (7) which is totally or at least partially immersed in said bath (5); the unit (1) is notable in that the dielectric working fluid comprises perfluoro-4-methyl-2-pentene and in that the gaseous phase comprises a moisture content of at least 20%. Figure for the abstract: Figure 1

Description

Title of the invention: COOLING UNIT WORKING IN A HUMID ENVIRONMENT BY IMMERSION

[0001] The invention relates to the field of dielectric working fluids for immersion cooling, processes employing such working fluids and cooling units comprising them.

[0002] Cooling units are used, for example, for cooling power modules or in data centers, namely locations that house operating computer systems. These systems may include servers, data storage or processing systems, network equipment, backup devices or other network infrastructure, and batteries. Data centers are capable of processing enormous amounts of data, and this process generates significant heat.

[0003] Overheating of equipment can lead to slowdowns, server failures, and interruptions that will directly affect users in terms of efficiency and cost. In order to maintain servers and equipment at a temperature that allows for proper operation, this heat must be dissipated and the equipment cooled.

[0004] Servers are typically stacked in storage racks and kept at a comfortable temperature by air conditioning. This air conditioning is generally achieved through air circulation, using chillers and heat sinks. Water cooling systems can also be used. Air conditioning and cooling systems account for up to 50% of the energy consumption of data centers. However, as the size and density of data centers and the IT systems they contain increase, the need for air conditioning also increases and exceeds the capabilities of conventional air conditioning systems.

[0005] Indeed, increasingly dense circuits present a challenge in terms of cooling. To improve cooling capacity, one technology involves immersing the server or heat-generating electronic component in a dielectric working fluid. The heat from the components is then dissipated by diffusion into the fluid, which significantly improves cooling efficiency. The fluid is then cooled by heat exchange with the external environment or another cooling system. Cooling units of this type are called single-phase cooling systems.

[0006] Another, more compact and efficient technology has been developed: this one uses low-boiling-point dielectric working fluids. At least one electronic component is cooled in a closed circuit. Above a certain temperature, the dielectric working fluid evaporates and recondenses on the walls of the unit or on a condenser before returning to the tank in which the electronic component(s) are immersed. Cooling units of this type are called two-phase cooling units. The low boiling point of the dielectric working fluids is generally below 90°C, which makes it possible to keep the server components at a sufficiently cool temperature for their proper operation while promoting the dissipation of the generated heat via a heat sink.The condensation device may include the walls of the installation, or a condenser, or a condensation coil, or a condensation coil, for example.

[0007] The climate challenge that humanity must face is resulting in an evolution of regulations, particularly concerning the reduction of the production of CO2 equivalents that may be released into the atmosphere.

[0008] In the context of cooling units comprising dielectric working fluids for their cooling, it is necessary to evolve the dielectric working fluids currently used towards working fluids with a lower global warming potential (GWP).

[0009] The GWP is a unit of measurement used to simplify, compare, and interpret the influence of greenhouse gases (GHGs) on global warming. It measures the amount of energy absorbed by one tonne of gas emitted into the atmosphere over a given period. The GWP of a gas always takes carbon dioxide (CO2) as its reference. The GWP of CO2 is therefore equal to 1.

[0010] It is known that perfluorinated liquids, such as Fluoroinert FC-72 and FC-3284, exhibit excellent dielectric properties, such as dielectric constants of 2.0 or less, high volume resistivity on the order of 10¹⁵ ohm-cm, and high dielectric strength. However, these fluids are also generally associated with a high GWP. The GWP of Fluoroinert FC-72 is estimated to be around 9,300. Hydrofluoroethers (HFEs) have lower GWPs but are still not satisfactory and generally have worse dielectric properties than FC-72 and FC-3284. Novec 7100, for example, has a GWP of 297.

[0011] Consequently, there is always a need for working fluids for immersion cooling which satisfy the dielectric applications of the industry while having as low a GWP as possible.

[0012] This is what is proposed, for example, in document WO2023 / 064129 AL. This document concerns an immersion cooling unit comprising a cell An immersion device defines an internal cavity designed to house an electronic component. A dielectric working fluid partially fills the internal cavity and at least partially immerses the electronic component. A condenser coil is positioned above the dielectric working fluid. The dielectric working fluid comprises at least one perfluorohept-2-ene (PFO-161-14myy) and / or one perfluorohept-3-ene (PFO-161-14mcyy).

[0013] Another solution is given by WO2023 / 064123 A1. This document relates to an immersion cooling unit comprising an immersion cell, defining an internal cavity. An energy storage device is positioned in the internal cavity. A dielectric working fluid partially fills the internal cavity and at least partially immerses the energy storage device. A condensing coil is positioned above the dielectric working fluid. The dielectric working fluid comprises at least one of the following: 1,1,1,2,2,5,5,6,6,6-decafluoro-3-hexene (HFO-153-1 Omczz), 1,1,1,4,5,5,5-heptafluoro-4-trifluoromethyl-2-pentene (HFO-153-10mzzy), an azeotropic composition of 1,1,1,2,2,5,5,6,6,6-decafluoro-3-hexene and trans-1,2-dichloroethylene or an azeotropic composition of 1,1,1,4,5,5,5-heptafluoro-4-trifluoromethyl-2-pentene and trans-1,2-dichloroethylene.

[0014] These solutions are promising but require working in a dry environment (i.e., without the presence of water), otherwise corrosion problems may occur. The solution therefore consists of working in a dry environment, but working under such conditions is often difficult. Indeed, liquid water can form through the condensation of residual water molecules present in the free space of the internal cavity of the cooling unit. This water is capable of reacting with certain dielectric heat transfer fluids, for example FK5112, to form acidic compounds, such as propionic acid. This acid, released into the internal cavity of the cooling unit, mixed with the heat transfer fluid, will cause corrosion of the immersed electronic components. A solution therefore remains to be found to overcome this problem.

[0015] The invention aims to address one or more of the problems and drawbacks encountered in the prior art. In particular, the invention aims to provide an immersion cooling unit that allows operation in humid environments while limiting, or even eliminating, corrosion problems related to the presence of water.

[0016] To this end, and according to a first aspect, the invention relates to an immersion cooling unit comprising an immersion cell defining an internal cavity, a bath comprising a dielectric working fluid partially filling the internal cavity, and a gaseous phase so as to form a system biphasic; the unit further comprising a condensation device which is positioned in the internal cavity above the electronic component so as not to be immersed in the dielectric working fluid and at least one electronic component which is totally or at least partially immersed in said bath; the unit is notable in that the dielectric working fluid comprises perfluoro-4-methyl-2-pentene and in that the gaseous phase comprises a moisture content of at least 20%.

[0017] Indeed, it has been found that the presence of water in the cooling unit, whether dissolved in the working fluid, as a film of water supernatant on the dielectric fluid resulting from the condensation of water molecules from the air present in the internal cavity of said unit, or in gaseous form in the gaseous phase of the cavity and measured according to a degree of gaseous phase humidity, does not cause the degradation of perfluoro-4-methyl-2-pentene into an acidic compound and therefore does not lead to corrosion of the electronic components immersed in the working fluid. It has been found that a degree of gaseous phase humidity of at least 20% further encompasses the case in which the dielectric liquid is saturated with water and the cases in which a film or layer of water supernatant is present on the dielectric fluid bath. In other words, a 20% humidity level in the gaseous phase defines operation in a humid environment.

[0018] For example, the gaseous phase shows a degree of humidity of at least 30%, for example of at least 40%, for example of at least 50%.

[0019] For example, the gaseous phase shows a degree of humidity between 20 and 100%, for example between 30 and 90%, for example between 40 and 80% or from 50 to 70%. For example, the gaseous phase shows a degree of humidity between 50 and 100%.

[0020] The cooling unit according to the invention can therefore operate in a humid environment, i.e., in the presence of water, without any risk of corrosion. Furthermore, as shown in the examples, perfluoro-4-methyl-2-pentene exhibits good compatibility with elastomers and offers good performance maintenance over time.

[0021] According to a preferred embodiment, the unit has an operating temperature range of 40 to 70°C.

[0022] Advantageously, the dielectric working fluid has a boiling point between 45 and 70°C.

[0023] Preferably, the dielectric working fluid comprises between 10 and 100% by mass of perfluoro-4-methyl-2-pentene relative to the total mass of the dielectric working fluid, preferably between 20 and 80% by mass.

[0024] According to a preferred embodiment, the dielectric working fluid comprises between 0 and 90% by mass of one or more additives selected from linear hydrocarbons C18-C50, C18-C50 branched hydrocarbons, linear halocarbons, cyclic hydrocarbons, cyclic halocarbons, hydrofluoroolefins, hydrofluorocarbons, carbonates, ketones, halogenated ketones, heptafluorocyclopentane, 1,1,1,2,3,4,4,5,5,5-decafluoropentane, ethyl 3-ethoxypropionate, alcohols, ethers, and halogenated ethers; preferably, the dielectric working fluid comprises one or more additives selected from linear hydrocarbons of Cl8-C50, branched hydrocarbons of Cl8-C50, hydrofluorocarbons, and halogenated ketones.

[0025] Advantageously the volume resistivity of the working fluid at 20°C is at least 1.00 E+13 Q-cm as measured according to standard IEC 60247:2004; preferably, at least 1.00 E+14 Q-cm; preferably even at least 1.00 E+15 Q-cm.

[0026] Advantageously, the working fluid has a global warming potential of less than 200, preferably less than 25.

[0027] Advantageously, the kinematic viscosity at 40°C of the dielectric working fluid is less than 9.0 mm2 / s determined according to ASTM D445-03; preferably, less than 8.0 mm2 / s; more preferably, less than 5.0 mm2 / s; even more preferably, less than 1.0 mm2 / s; or even less than 0.5 mm2 / s.

[0028] For example, the electronic component(s) include elements made of copper, or of an alloy comprising at least one metal selected from copper, aluminum, and mixtures thereof.

[0029] For example, less an electronic component is chosen from microprocessors, wafers used to manufacture semiconductor devices, power control semiconductors, electrical distribution switching equipment, power transformers, printed circuit boards, multichip modules, packaged and unpacked semiconductor devices, laser devices, fuel cells and electrochemical cells.

[0030] According to a preferred embodiment, the unit further comprises one or more components of polymer material selected from ethylene-propylene-diene monomer (EPDM), fluoroelastomers, poly(isobutene), polychloroprene, polyurethane, nitrile-butadiene (NBR), silicone, polyvinylchloride, polypropylene, polytetrafluoroethylene (PTFE), polyamides, styrene-butadiene (SBR), polyethylenes, isobutylene-isoprene copolymers, and polyisoprenes.

[0031] For example, the unit further comprises one or more components made of polymer material selected from a sealing gasket, a protective coating, an element electrical insulation, a tank, a pump, a pipe, a filter, a valve, and an actuator.

[0032] According to a second aspect, the invention relates to the use of a dielectric working fluid in a bath of an immersion cooling unit, the unit further comprising a gaseous phase so as to form a two-phase system, the use being characterized in that the dielectric working fluid comprises perfluoro-4-methyl-2-pentene and in that the gaseous phase comprises a moisture content of at least 20%.

[0033] According to a third aspect, the invention relates to a method of cooling an electronic component comprising the partial or total immersion of said electronic component in a bath of an immersion cooling unit comprising a dielectric working fluid and the transfer of heat from the electrical component to said dielectric working fluid, the unit further comprising a gaseous phase so as to form a two-phase system and a condensation device is positioned in the internal cavity above the electronic component so as not to be immersed in the dielectric working fluid; the method being characterized in that the dielectric working fluid comprises perfluoro-4-methyl-2-pentene and in that the gaseous phase comprises a moisture content of at least 20%. Presentation of the figures

[0034] The invention will be well understood and other aspects and advantages will become clear upon reading the following description, given with reference to the attached figures listed below.

[0035] Figure 1 illustrates an example of an embodiment of a two-phase cooling unit

[0036] Fig. 2 illustrates the device used for corrosion tests.

[0037] Figure 3 shows the comparative results of the corrosion tests a) after 24 hours of immersion, b) after 5 days of immersion, c) after 1 month of immersion. Detailed description

[0038] In the following description, the term "include" is synonymous with "include" and is not limiting in that it permits the presence of other elements in the described installation or other steps in the process to which it relates. It is understood that the term "include" includes the terms "consist of." Throughout the description, the various figures use the same reference numerals to designate identical or similar entities.

[0039] The invention relates to the use of perfluoro-4-methyl-2-pentene as a dielectric working fluid in a humid environment. Said use, the cooling unit, and the cooling method will be described jointly.

[0040] The invention proposes an immersion cooling unit comprising an immersion cell defining an internal cavity, a bath comprising a dielectric working fluid partially filling the internal cavity and a gaseous phase so as to form a two-phase system; the unit further comprising a condensation device which is positioned in the internal cavity above the electronic component so as not to be immersed in the dielectric working fluid and at least one electronic component which is totally or at least partially immersed in said bath; the unit is notable in that the dielectric working fluid comprises perfluoro-4-methyl-2-pentene and in that the gaseous phase comprises a moisture content of at least 20%.

[0041] According to the invention, the cooling unit is two-phase and is intended for cooling electronic components selected from microprocessors, wafers used to manufacture semiconductor devices, power control semiconductors, electrical distribution switching equipment, power transformers, printed circuit boards, multichip modules, packaged and unpacked semiconductor devices, laser devices, fuel cells, electrochemical cells and high-capacity energy storage devices such as batteries, or a combination thereof.

[0042] According to an advantageous embodiment of the invention, the electronic component(s) comprise elements made of copper, or of an alloy comprising at least one metal selected from copper, aluminum, and mixtures thereof.

[0043] Figure 1 illustrates an embodiment of a two-phase cooling unit 1 according to the invention. The immersion cooling unit 1 comprises an immersion cell defining an internal cavity 3, a bath 5 comprising a dielectric working fluid partially filling the internal cavity 3, and at least one electronic component 7 immersed in the bath 5. The electronic component(s) 7 are partially or totally immersed in the bath 5. A condensation device 9 (here a capacitor) is positioned in the upper part of the internal cavity 3 (comprising the gaseous phase), such that it is not immersed in the bath 5. Preferably, the condensation device 9 is located in the gaseous phase directly above the bath 5.

[0044] When the immersion cooling unit 1 is in operation, the heat generated by the electronic component(s) 7 is transferred to said bath 5 either directly or via the heat sinks 11, which are in direct contact with the electronic component(s) 7. The dielectric working fluid of the bath 5 heats up and its temperature approaches its boiling point. The dielectric working fluid partially vaporizes and then recondenses on the A condensation device 9 thus transfers at least some of its heat to the unit. This device, in turn, transfers the heat outside the cooling unit 1 via heat sinks 13, located on the external face of said immersion cooling unit 1. The heat can then be removed, for example by air circulation 15, or via a heat exchanger. Preferably, this heat can be recovered and utilized, for example for heating buildings or domestic hot water, or for energy production via a Rankine cycle.

[0045] According to the invention, the dielectric working fluid is or comprises perfluoro-4-methyl-2-pentene (CAS number 2070-70-4).

[0046] According to the invention, unit 1 may further comprise one or more components made of polymer material in contact with the dielectric fluid in the liquid and / or gaseous state. For example, the component(s) may be selected from a seal, a protective coating, an electrical insulation element, a tank, a pump, a pipe, a filter, a valve, and an actuator.

[0047] For example, the sealing between the components of the unit, such as the evaporator, condenser, dielectric fluid transport pipes, heat exchangers, and pressure regulation components, is achieved by means of polymer seals. In particular, the seals in contact with the gaseous phase of the immersion cell are subjected to high stresses that could degrade them if they are incompatible with the dielectric fluid.

[0048] According to a preferred embodiment of the invention, unit 1 comprises one or more components of polymer material selected from ethylene-propylene-diene monomer (EPDM), fluoroelastomers, poly(isobutene), polychloroprene, polyurethane, nitrile-butadiene (NBR), silicone, polyvinylchloride, polypropylene, polytetrafluoroethylene (PTFE), polyamides, styrene-butadiene (SBR), polyethylenes, isobutylene-isoprene copolymers, and polyisoprenes.

[0049] Indeed, as shown in the examples, these materials show good compatibility with perfluoro-4-methyl-2-pentene.

[0050] Preferably, unit 1 comprises one or more components made of polymer material selected from ethylene propylene diene monomer (EPDM), fluoroelastomers, poly(isobutene), polychloroprene, polyurethane, silicone, polyvinyl chloride, polypropylene, polytetrafluoroethylene (PTFE), polyamides, styrene butadiene (SBR), polyethylenes, isobutylene-isoprene copolymers, and polyisoprenes. More preferably, unit 1 comprises one or more components made of polymer material selected from fluoroelastomers, poly(isobutene), polychloroprene, silicone, polypropylene, polytetrafluoroethylene (PTFE), polyamides, styrene-butadiene (SBR), polyethylenes, isobutylene-isoprene copolymers, and polyisoprenes.

[0051] In one embodiment, the dielectric working fluid is composed solely of perfluoro-4-methyl-2-pentene (i.e., the dielectric working fluid comprises 100% by mass of perfluoro-4-methyl-2-pentene).

[0052] In another embodiment, the dielectric working fluid comprises at least one compound in addition to perfluoro-4-methyl-2-pentene. When the dielectric working fluid comprises a mixture of compounds including perfluoro-4-methyl-2-pentene, the latter is present in the working fluid at a concentration of at least 10% by mass relative to the total mass of the dielectric fluid, preferably at least 12% by mass; preferably at least 15% by mass; preferably at least 18% by mass; preferably at least 20% by mass. Thus, the dielectric working fluid according to the invention comprises between 10 and 100% by mass of perfluoro-4-methyl-2-pentene; preferably from 15 to 90% by mass; more preferably from 20 to 80% by mass.

[0053] According to a preferred embodiment of the invention, the dielectric working fluid comprises between 0 and 90% by mass of one or more additives relative to the total mass of the dielectric fluid. The use of additives can be useful for adjusting the operating temperature range of unit 1. For example, the dielectric working fluid comprises between 1 and 88% by mass of one or more additives; for example, between 5 and 85% by mass; for example, between 8 and 82% by mass; for example, between 10 and 80% by mass.

[0054] Preferably, the additive(s) are chosen from linear hydrocarbons, linear halocarbons from Cl8 to C50, branched hydrocarbons from C18 to C50, cyclic hydrocarbons, cyclic halocarbons, hydrofluoroolefins, hydrofluorocarbons, heptafluorocyclopentane, 1,1,1,2,3,4,4,5,5,5-cafluoropentane, ethyl 3-ethoxypropionate, alcohols (e.g. methanol, ethanol, isopropanol), ethers, halogenated ethers, carbonates, ketones and halogenated ketones. Preferably, the dielectric working fluid comprises one or more additives selected from linear hydrocarbons from Cl8 to C50, branched hydrocarbons from Cl8 to C50, hydrofluorocarbons, and halogenated ketones. More preferably, the dielectric working fluid comprises one or more additives selected from linear hydrocarbons from Cl8 to C22 and branched hydrocarbons from Cl8 to C22.

[0055] Preferably, linear hydrocarbons are chosen from linear hydrocarbons from Cl8 to C22.

[0056] Preferably, the branched hydrocarbons are chosen from among the branched hydrocarbons from Cl8 to C22.

[0057] Preferably, the cyclic hydrocarbons include cyclopentane, cyclohexane, cycloheptane, methyl cyclobutane, and methylcyclopentane. For example, the ethers include diethyl ether; diisopropyl ether; C4F9OCH3; C4F9OCH2CH3; i-C4F9OCH2CH3; (CF3)2CFCF(OCH3)CF2CF3 (73DE); C3F7OCH3; (CF3)2CFCF(OCH2 CH3)CF2CF2CF3 (HFE 7500); 1,1,1,2,3,3-hexafluoro-4-(1,1,2,3,3,3-hexafluoropropoxy)pentane (HFE 7600); furan; 2,3,3,4,4-pentafluorotetrahydro-5-methoxy-2,5-bis[l,2,2,2-tetrafluoro-l- (trifluoromethyl)ethyl]-(HFE 7700); methylperfluoroheptene ethers (Vertrel SF-10).

[0058] Preferably, the ketones and carbonates include dimethyl carbonate, and l,l,l,2,4,4,5,5,5-nonafluoro-(2-trifluoromethyl)-3-pentanone (Novec 1230).

[0059] The aromatic hydrocarbon content of the dielectric working fluid is less than or equal to 2% by mass relative to the total mass of the dielectric fluid, said content being determined by gas chromatography-mass spectrometry (also known as GC / MS). Preferably, the dielectric working fluid is free of aromatic hydrocarbons.

[0060] The dielectric working fluid is selected to undergo a phase transition from the liquid to the gaseous state over the operating temperature range of said unit 1. The presence of at least one additive in addition to perfluoro-4-methyl-2-pentene allows the phase transition temperature of said dielectric working fluid to be modified. For example, hydrocarbon-type additives can help maintain the thermal stability of the fluid, allowing it to operate efficiently over a wide temperature range without significant degradation of its dielectric or cooling properties.

[0061] Advantageously, the dielectric working fluid does not exhibit a flash point, rendering it non-flammable, even in the presence of additives. The flash point measurement is carried out according to ISO 3679 and ISO 3680 standards, rapid closed-cup equilibrium method.

[0062] Advantageously, the kinematic viscosity at 40°C of the dielectric working fluid is less than 9.0 mm2 / s determined according to ASTM D445-03; preferably, less than 8.0 mm2 / s; more preferably, less than 5.0 mm2 / s; even more preferably, less than 1.0 mm2 / s; or even less than 0.5 mm2 / s.

[0063] Regardless of the embodiment, it is advantageous for the operating temperature of the immersion cooling unit 1 to be at least 20°C, preferably at least 30°C, preferably at least 40°C, preferably at least 50°C. Advantageously, the operating temperature of the immersion cooling unit 1 is less than 100°C, preferably less than 90°C, preferably less than 80°C, and preferably less than 70°C.

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[0072] Preferably, the dielectric working fluid is chosen to have a boiling point of at least 40°C, preferably at least 42°C, and more preferably at least 45°C. For example, the dielectric working fluid has a boiling point between 45 and 70°C. Perfluoro-4-methyl-2-pentene is generally found as a mixture of isomers, namely trans-perfluoro-4-methylpent-2-ene (CAS number 3709-71-5), [Chem.l] (CF3hCF^ c=c F CF3 and cis-perfluoro-4-methylpent-2-ene. [Chem. 2] In the mixture of isomers according to the invention, the trans-perfluoro-4-methylpent-2-ene isomer is the major isomer. Thus, perfluoro-4-methylpentene comprises at least 95.0% by mass of the trans-perfluoro-4-methylpent-2-ene isomer based on the total mass of the isomer mixture. Preferably, perfluoro-4-methylpentene comprises at least 95.5% by mass of the trans-perfluoro-4-methylpent-2-ene isomer based on the total mass of the isomer mixture; more preferably, at least 96.0%. Perfluoro-4-methylpentene with a trans / cis ratio of at least 95.0% by mass is commercially available, for example, from 3M. The trans-perfluoro-4-methylpent-2-ene isomer content of the isomer mixture can be determined by 13C and 19F NMR analysis. In some cases the dielectric working fluid according to the invention may include perfluoro-2-methyl-2-pentene. [Chem. 3]

[0073] When this compound is present, its content is advantageously less than or equal to 1 x 10⁻⁴ % by mass relative to the total mass of said dielectric working fluid. The content of perfluoro-2-methyl-2-pentene can be determined by 13C and 19F NMR analysis.

[0074] According to the invention, the cooling unit 1 operates in a humid environment, so the gaseous phase has a humidity level of at least 20%. For example, the gaseous phase has a humidity level of at least 30%, for example, at least 40%, for example, at least 50%. For example, the gaseous phase has a humidity level between 20 and 100%, for example, between 30 and 90%, for example, between 40 and 80%, or from 50 to 100%.

[0075] The invention is remarkable in that it is not necessary to dehumidify the gaseous phase of Unit 1. Indeed, although the presence of a high degree of humidity results in the solubilization of some of this water in the dielectric fluid up to its solubility limit, the presence of water in Unit 1 does not impair the dielectric properties of the working fluid. Furthermore, it has been found that perfluoro-4-methyl-2-pentene does not produce acidic compounds in the presence of water, which minimizes corrosion problems related to the presence of water. The solubility of water in the dielectric fluid is approximately 10 ppm when the dielectric fluid contains no additives (100% perfluoro-4-methyl-2-pentene), but may be different when the dielectric fluid contains one or more additives.

[0076] The dielectric working fluid according to the invention has a high volume resistivity, leading to high electrical resistance and low current leakage. This minimizes the risk of self-discharge in energy storage devices such as batteries. Furthermore, electronic components with different voltage ratings can be assembled more compactly, for a given minimum resistance requirement. Preferably, the volume resistivity of the working fluid is at least 1 x 10¹³ ohm-cm measured according to IEC 60247:2004, preferably at least 1 x 10¹⁴ ohm-cm, and even more preferably at least 1 x 10¹⁵ ohm-cm.

[0077] Remarkably, the dielectric working fluid according to the invention has a global warming potential less than or equal to 200; preferably less than 150; preferably less than 100; preferably less than 80; preferably less than 50; preferably less than 30; preferably less than 25. This low value makes said fluid a very good candidate for replacing dielectric heat transfer fluids such as FC-72, which has a GWP of 9300. It has been found that the addition of additives such as linear or branched hydrocarbons makes it possible to reduce the global warming potential of a dielectric fluid.

[0078] Methods

[0079] The humidity level of the gaseous phase is determined using a hygrometer.

[0080] The boiling point (°C) is determined according to ASTM DI 120-22.

[0081] The heat of vaporization is measured at the boiling point.

[0082] The kinematic viscosity (mm2 / s) is determined according to ASTM D445-03, at 20°C or 40°C.

[0083] The dielectric strength (kV) is determined according to standard NF EN 60156.

[0084] Volume resistivity is measured according to IEC 60247:2004. Examples

[0085] The dielectric working fluid according to the invention has been subjected to various tests with a view to its use in an immersion cooling unit.

[0086] Dielectric working fluids

[0087] IE1 corresponds to the fluid according to the invention and corresponds to a mixture of perfluoro-4-methyl-2-pentene isomers with a trans / cis ratio of 97% (CAS number 2070-70-4).

[0088] IEC is the dielectric working fluid marketed under the name FC-72.

[0089] CE2 is dodecafluoro-2-methylpentan-3-one and is marketed under the trade name FK5112.

[0090] The characteristics of the IE1 and IEC dielectric working fluids are presented in Table 1.

[0091] Table 1: Characteristics of different dielectric working fluids

[0092] [Tables 1] IEC* CE2* IE1 CE3* CAS RN 756-13-8 PRG 9300 <1 20 0 Boiling point (°C) 56 49.2 47 >280 Melting point (°C) -90 -108 -117 -36 Heat of vaporization (kJ / kg) At boiling point 88 88 93 Specific heat (J / kg -K) 25°C 1100 1103 1044 Specific heat (J / kg -K) 40°C 1112 1064 2274(1) Kinematic viscosity (mm² / s) 20°C 0.38 0.40 0.36 Kinematic viscosity (mm² / s) 40°C 0.33 0.3 9.8 Dielectric strength (kV) 20°C 38 >40 79 42 Dielectric constant @ 1kHz 20°C 1.75 1.84 1.88 Volume resistivity (Ω hm-cm) 20°C 11015 11013 11015 11013 Thermal conductivity (W / mK) 20°C 0.06 - 0.0001 1 0.059 0.110 Thermal conductivity (W / mK) 40°C 0.056 0.105 0.142

[0093] * commercial data;

[0094] (1) determined according to ASTM E 1269

[0095] (2) determined according to ASTM D 7896

[0096] IEC and CE2 are comparative dielectric working fluids. CE3 corresponds to an oil marketed under the name Shell S5X. IE1 shows a good combination of characteristics including a low GWP, a boiling point below 50°C, and a volume resistivity of 1x10¹⁵ Ohm-cm.

[0097] Corrosion test

[0098] It is known that CE2 (i.e., FK5112) degrades in the presence of water. The degradation product is an acid that corrodes copper. It was therefore chosen as the comparator fluid in the corrosion test.

[0099] A corrosion test of a copper component was carried out to determine the degradation of electrical fluids. To this end, two containers were prepared. One container held a volume of IE1 fluid and the other held the same volume of CEI fluid. A copper piece was placed at the bottom of each container. The fluid volume and the dimensions of the piece were chosen so that the copper piece was completely immersed in the dielectric fluid to be tested, as illustrated in [Fig. 2]. The same quantity of water was then added to each container. The containers were hermetically sealed and placed in an oven at 50°C. The appearance of the copper pieces was observed after 24 hours, 5 days, and 1 month of immersion, respectively. The results are summarized in Table 2 and [Fig. 3].

[0100] Table 2: Comparative corrosion study of a copper component in the presence of water

[0101] [Tables2] CE2 IE1 24 hours Darker appearance No corrosion 5 days Light corrosion No corrosion 1 month Heavy corrosion No corrosion

[0102] As expected, the copper part in fluid CE2 corroded rapidly, indicating the presence of acidity. Surprisingly, the copper part in fluid IE1 showed no signs of corrosion, even after a month.

[0103] It is therefore possible to conclude that IE1 does not form acid in the presence of water.

[0104] Compatibility test with elastomers.

[0105] The compatibility of the IE1 dielectric working fluid with different elastomers found in electronic components and their connections has been tested.

[0106] The tests performed include dissolution tests and absorption tests, based on the Soxhlet extraction process, as well as on the ISO175:2010 standard.

[0107] Dissolution, one of the most common fluid-material interaction mechanisms, involves the gradual dissolution / escape of materials into the dielectric fluid. This could adversely affect component performance and potentially lead to system failure over time. This phenomenon could also result in a deterioration of the fluid's dielectric properties. Dissolution is generally more severe at higher temperatures, closer to the material's glass transition temperature. The dissolution test determines the percentage by mass extracted from the elastomer.

[0108] Absorption / swelling is another common type of fluid-material interaction in which components absorb the dielectric fluid and swell. This swelling can affect component performance and lead to system failures. Swelling occurs through a diffusion-absorption process, and the rate of swelling is faster at higher temperatures. In the absorption / swelling test, the mass percentage of fluid absorbed by the elastomer is determined.

[0109] Materials that can be directly immersed in the bath are analyzed according to a test based on ISO175:2010.

[0110] The percentage variation of absorbed mass (%ma) or extracted mass (%me) of an elastomer sample is calculated, with %ma=(mf-mi) / mi and respectively %me=(mi-mf) / mi, mf being the mass of the material sample after the test and mi the initial mass of the sample, then is categorized between 1 and 3, i.e. 1 if the variation (%ma or %mi) is less than or equal to 20%; 2 if the variation is between 20% and 30%; 3 if the variation is greater than 30%.

[0111] These results are presented in table 3.

[0112] Table 3: Study of the compatibility of different liquid-phase elastomers with IE1

[0113] [Tables3] Material Method Compatibility EPDM ISO 175 2 Polychloroprene ISO 175 1 Polyurethane ISO 175 1 Nitrile butadiene ISO 175 2 Polypropylene ISO 175 1 Polytetrafluoroethylene ISO 175 1 Polyamide 6 ISO 175 1 Styrene-butadiene ISO 175 1 Polyethylene ISO 175 1 Nitrile ISO 175 1 Isobutylene-isoprene copolymer ISO 175 1 Natural polyisoprene ISO 175 1

[0114] Materials likely to come into contact with the gas phase are analyzed using a test based on the Soxhlet extraction process. The materials are placed in a Soxhlet extractor and then subjected to distillation / condensation steps of the fluid to be tested in a heated flask for at least 48 hours. At the end of the test, the fluid to be tested is evaporated, leaving the extracted residue in the flask. Comparing the mass of the flask before and after the test determines the percentage of mass extracted. Comparing the mass of the material before and after the test determines the percentage of mass absorbed. The percentages of mass extracted (%me) and mass absorbed (%ma) are calculated and categorized from 1 to 3, where 1 is assigned if the variation (%ma or %me) is less than or equal to 15%; 2 if the variation is between 15% and 30%; and 3 if the variation is greater than 30%.

[0115] These results are presented in Table 4.

[0116] Table 4: Study of the compatibility of different gas-phase elastomers with IE1

[0117] [Tables4] Material Method Compatibility EPDM Soxhlet 1 Fluoroelastomer (Viton) Soxhlet 1 Silicone Soxhlet 1 Polyvinyl chloride Soxhlet 2 Butyl sealant (Sikalastomer 51 1) Soxhlet 2 Polyurethane (3M Marine Sealant) Soxhlet 2

[0118] The results are considered acceptable when the score is 1 and considered unacceptable for a score of 3. With a score of 2, the analysis is done on a case-by-case basis.

[0119] Analysis of the results shows very good compatibility with many elastomers.

[0120] Test of performance maintenance over time

[0121] The operation of a two-phase immersion cooling unit whose dielectric fluid comprises 100% by mass of perfluoro-4-methyl-2-pentene was observed under real-world conditions. The tests were carried out on an E3NV type unit, including parts using a butyl sealant (Sikalastomer 511). After 6 months of operation, no contamination or loss of clarity of the working fluid was observed.

Claims

Demands

1. Immersion cooling unit (1) comprising an immersion cell defining an internal cavity (3), a bath (5) comprising a dielectric working fluid partially filling the internal cavity and a gaseous phase so as to form a two-phase system; the unit (1) further comprising a condensation device which is positioned in the internal cavity above the electronic component so as not to be immersed in the dielectric working fluid and at least one electronic component (7) which is totally or at least partially immersed in said bath (5); the unit (1) is characterized in that the dielectric working fluid comprises perfluoro-4-methyl-2-pentene and in that the gaseous phase comprises a moisture content of at least 20%.

2. Unit (1) according to claim 1 characterized in that it has an operating temperature range of 40 to 70°C and / or in that the dielectric working fluid has a boiling point between 45 and 70°C.

3. Unit (1) according to any one of claims 1 or 2 characterized in that the dielectric working fluid comprises between 10 and 100% by mass of perfluoro-4-methyl-2-pentene relative to the total mass of the dielectric working fluid, preferably between 20 and 80% by mass.

4. Unit (1) according to any one of claims 1 to 3 characterized in that the dielectric working fluid comprises between 0 and 90% by mass of one or more additives selected from linear C18-C50 hydrocarbons, branched C18-C50 hydrocarbons, linear halocarbons, cyclic hydrocarbons, cyclic halocarbons, hydrofluoroolefins, hydrofluorocarbons, carbonates, ketones, halogenated ketones, heptafluorocyclopentane, 1,1,1,2,3,4,4,5,5,5-decafluoropentane, ethyl 3-ethoxypropionate, alcohols, ethers, and halogenated ethers; Preferably, the dielectric working fluid comprises one or more additives selected from linear hydrocarbons from Cl8 to C50, branched hydrocarbons from C18 to C50, hydrofluoro hydrocarbons, and halogenated ketones.

5. Unit (1) according to any one of claims 1 to 4 characterized in that the volume resistivity of the working fluid is at least 1.00 E +13 Q-cm as measured according to IEC 60247:200; and / or in that the working fluid has a global warming potential of less than 200.

6. Unit (1) according to any one of claims 1 to 5, characterized in that the kinematic viscosity at 40°C of the dielectric working fluid is less than 9.0 mm2 / s determined according to ASTM D445-03; and / or in that the electronic component(s) comprise elements made of copper, or of an alloy comprising at least one metal selected from copper, aluminum, and mixtures thereof.

7. Unit (1) according to any one of claims 1 to 6, characterized in that at least one electronic component is selected from microprocessors, wafers used to manufacture semiconductor devices, power control semiconductors, electrical distribution switching equipment, power transformers, printed circuit boards, multichip modules, packaged and unpacked semiconductor devices, laser devices, fuel cells and electrochemical cells.

8. Unit (1) according to any one of claims 1 to 6, characterized in that it further comprises one or more components of polymer material selected from ethylene-propylene-diene monomer (EPDM), fluoroelastomers, poly(isobutene), polychloroprene, polyurethane, nitrile-butadiene (NBR), silicone, polyvinylchloride, polypropylene, polytetrafluoroethylene (PTFE), polyamides, styrene-butadiene (SBR), polyethylenes, isobutylene-isoprene copolymers, and polyisoprenes; and / or in that it further comprises one or more components of polymer material selected from a sealing gasket, a protective coating, an electrical insulation element, a tank, a pump, a pipe, a filter, a valve, and an actuator.

9. Use of a dielectric working fluid in a bath (5) of an immersion cooling unit (1), the unit (1) further comprising a gaseous phase so as to form a two-phase system, the use being characterized in that the dielectric working fluid comprises perfluoro-4-methyl-2-pentene and in that the gaseous phase comprises a moisture content of at least 20%.

10. A method for cooling an electronic component comprising the partial or total immersion of said electronic component in a bath (5) of an immersion cooling unit (1) comprising a dielectric working fluid and the transfer of heat from the electronic component to said dielectric working fluid, the unit further comprising a gaseous phase so as to form a two-phase system and a condensation device is positioned in the internal cavity above the electronic component so as not to be immersed in the dielectric working fluid; the method being characterized in that the dielectric working fluid comprises perfluoro-4-methyl-2-pentene and in that the gaseous phase comprises a moisture content of at least 20%.

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