Heatsink for an immersion cooling system

Abstract

There is provided a heatsink for an immersion cooling system, the heatsink comprising: a plurality of fins for exchanging heat with a dielectric fluid flowing therebetween The spacing between adjacent fins of the plurality of fins is at least 1 mm, and each of the plurality of fins comprises one or more surface disruption features for resetting the thermal boundary layer between the dielectric fluid and the fin downstream of the surface disruption feature.

Description

HEATSINK FOR AN IMMERSION COOLING SYSTEM Field of the invention

[0001] The present invention relates to heatsinks, and particularly, although not exclusively toheatsinks suitable for use in cooling immersion cooling systems.Background

[0002] As the demand for computational processing power has increased (exponentially) over thecourse of the fourth industrial revolution, industrial -scale data centres have been constructed to houselarge-scale computing systems, sometimes including huge numbers of computer processing units(CPUs) and / or graphical processing units (GPUs).

[0003] The power consumed by these processing units can lead to the generation of vast amounts of heat that risks impacting the computational efficiency of the processing units and even risks damaging the processing units and other systems housed within these data centres.

[0004] The present invention has been devised in light of the above considerations.Summary of the Invention

[0005] In a general sense, the present invention provides a configuration for a heatsink that is optimised for use with an immersion cooling system to cool processing units of a data centre. Inparticular, the heatsink comprises a plurality of fins that are sized and spaced in such a way thatoptimises the exchange of heat between the fins and a dielectric fluid flowing therebetween. Previous heatsinks have been optimised for the exchange of heat with air. However, the present inventors have found that the use of a dielectric fluid for heat exchange may beneficially cool the processing units of the data centre more efficiently. Accordingly, the present inventors have designed a reconfiguredheatsink that is optimised for heat transfer with such dielectric fluids.

[0006] In an aspect, there is provided a heatsink for an immersion cooling system. The heatsink includes a plurality of fins for exchanging heat with a dielectric fluid flowing therebetween, where thespacing between adjacent fins of the plurality of fins is at l east 1 mm, and where each of the plurality offins includes one or more surface disruption features for resetting the thermal boundary layer betweenthe dielectric fluid and the fin downstream of the surface disruption feature.

[0007] In this way, the structure and, in particular, the spacing of the fins, of the heatsink may beoptimised for immersion cooling with dielectric fluids.

[0008] The dielectric fluid may be a fluid having a viscosity greater than the viscosity of air. The dimensions of the heatsink, including the dimensions of the plurality of fins (e.g., the spacing between adjacent fins) may be selected so as to allow the dielectric fluid to flow between the fins of the heatsink and efficiently exchange heat with the fins. If the spacing between adjacent fins of the heatsink is lessthan 1 mm, the flow of the dielectric fluid between the fins may be resisted (e.g., due to excess s urfacetension), thereby inhibiting the flow of the dielectric fluid and reducing the efficiency with which heat isexchanged between the plurality of fins and the dielectric fluid.

[0009] The dielectric fluid may, for example, be a dielectric liquid. In other words, the dielectric fluidmay be a liquid that does not conduct electricity.

[0010] Each fin of the plurality of fins may have a thermal boundary layer associated with each face of the corresponding fin that defines a thermal boundary layer between the respective face of thecorresponding fin and the dielectric fluid flowing past the resp ective face. As the dielectric fluid flowsacross the respective face of the corresponding fin and exchanges heat therewith, the thermal boundary layer develops from the respective face of the corresponding fin into the space between the corresponding fin and an adjacent fin. If two thermal boundary layers from the opposing faces of two adjacent fins develop to such an extent that they merge, the efficiency with which the two adjacent finsexchange heat with the dielectric fluid is drastically reduced.

[0011] Accordingly, each of the plurality of fins comprises one or more surface disruption features. Optionally, each of the plurality of fins comprises one or more surface disruption features disposed on each of the faces of the corresponding fin. Each of the one or more surface disruption features may besized and shaped so as to disrupt the flow of the dielectric fluid when the dielectric fluid flows over said^^^^^^^ ^^^^^^^^^^ ^^^^^^^^ ^^^^ ^^^^^^^^^^ ^^ ^^^ ^^^^^^^^^^ ^^^^^^^ ^^^^ ^^^^^^ ^^^ ^^^^^^^ ^^^^^^^^ layerof the corresponding fin downstream of said surface disruption feature such that, immediately^^^^^^^^^^ ^^^^^ ^^^^^^^ ^^ ^^^ ^^^^^^^^^ ^^ ^^^ ^^^^^^^^^^ ^^^^^^^ ^^^^^ ^^ ^^^ ^^^^^^^ ^^^^^^^^^^ ^^^^^^^^^the thermal boundary layer between the respective face of the corresponding fin and the dielectric fluidis reset to be on the respective face of the corresponding fin.

[0012] The heatsink described herein may, for example, comprise a base plate for engagement with a device to be cooled. The device to be cooled may be a unit suitable for use in a data centre ^ for example a CPU or GPU.

[0013] Optionally, the baseplate may include one or more heat transfer components configured to increase the heat transfer efficiency from the base into the plurality of fins. For example, the one ormore heat transfer components may include one or more of: a vapour chamber and / or a heat pipe.

[0014] Optionally, the plurality of fins may extend perpendicularly (or substantially perpendicularly) from a surface of the base plate. In other words, the surface of the base plate may define a horizontal surface, with the plurality of fins extending vertically from the base plate.

[0015] Each of the plurality of fins may, for example, have a common height relative to the base plate.

[0016] The plurality of fins may, for example, be defined by one or more sets of parallel fins. In someparticular examples, all of the plurality of fins may be parallel with each other.

[0017] The plurality of fins may extend in a direction along the surface of the base plate corresponding to a length of the base plate. Correspondingly, the plurality of fins may be spaced apart with the spacing between each pair of adjacent fins extending along a width of the base plate, whereinthe width and length of the base plate may be perpendicular (or at least substantially perpendicular) directions.

[0018] Optionally, adjacent fins of the plurality of fins may be staggered relative to one another. For example, a first fin may extend along a first partial length of the base plate, while a second fin, adjacentto the first fin, may extend along a second partial length of the base plate. The first and second partiallengths may be non-overlapping along the length of the base plate or may be only partially overlapping along the length of the base plate. This non-overlapping (or partial overlapping) along the length of thebase plate may be repeated for each of the other adjacent pairs of fins amongst the plurality of fins.

[0019] In this way, the effective spacing between fins at any given point along the length of the base plate may be increased. This may, in effect, increase the available spacing into which the thermalboundary layer for each fin can extend, thereby improving the heat exchange efficiency of the heatsink.

[0020] Optionally, the fins may be planar. For example, each of the plurality of fins may be defined bya rectangular sheet extending (vertically) from the base plate.

[0021] Each of the plurality of fins may be composed of metal, to improve the heat exchange efficiency between the plurality of fins and the dielectric fluid. Optionally, the dielectric fluid may be a chemically inert fluid ^ in such examples, the plurality of fins need not be composed of an inert material (such as a noble metal). For example, the plurality of fins may be composed of a metal having a highheat exchange efficiency, such as aluminium or copper.

[0022] In some embodiments, for at least one of the plurality of fins, each of the one or more surfacedisruption features may be spaced equidistantly along the corresponding fin.

[0023] In other words, for a given fin of the plurality of fins, the one or more surface disruption features may be spaced equidistantly along the length of the fin (e.g., along a direction parallel to the length of the base plate).

[0024] Optionally, the equidistant spacing of the one or more surface disruption features may be equal on each surface of each of the plurality of fins. In other words, all of the plurality of fins may comprise one or more surface disruption features equidistantly spaced along the lengths of the fins with the same equidistant spacing for each fin.

[0025] Equidistant spacing of the one or more surface disruption features along the fin may facilitate a regular, and predictable heat exchange efficiency for the exchange of heat between each of the corresponding fins and the dielectric fluid. Additionally, a regular equidistant spacing of the one or more surface disruption features along the fin across all of the plurality of fins may reduce the complexityand / or costs associated with manufacturing the heatsinks described herein.

[0026] In some embodiments, for at least one of the plurality of fins, one or more of the one or moresurface disruption features may extend vertically along the corresponding fin.

[0027] In other words, for at least one of the plurality of fins, one or more of the one or more surface disruption features may extend in a direction perpendicular (or at least substantially perpendicular) tothe surface of the base plate from which the pluralit y of fins extends.

[0028] Additionally or alternatively, for at least one of the plurality of fins, one or more of the one or more surface disruption features may extend horizontally along the corresponding fin. In other words, for at least one of the plurality of fins, one or more of the one or more surface disruption features mayextend in a direction parallel to the surface of the base plate from which the plurality of fins extends.

[0029] Additionally or alternatively, for at least one of the plurality of fins, one or more of the one or more surface disruption features may extend at an oblique angle along the corresponding fin. In other words, for at least one of the plurality of fins, one or more of the one or more surface disruption features may extend in a direction that is obliquely angled with respect to the surface of the base plate from which the plurality of fins extends.

[0030] Optionally, for a given fin of the plurality of fins, each of the one or more surface disruption features of said fin may extend in a parallel (or at least substantially parallel) direction. Alternatively, for a given fin of the plurality of fins, each of the one or more surface disruption features of said fin may extend in different directions. In such examples, the one or more surface disruption features may bedefined by a plurality of surface disruption features that can be grouped into subsets of paral lel surfacedisruption features extending in a parallel (or at least substantially parallel) direction.

[0031] Optionally, the one or more surface disruption features for each of the plurality of fins may extend in the same direction. In other words, a pattern of the one or more surface disruption features ofeach of the plurality of fins may be the same across a subset (or i ndeed all) of the plurality of fins.

[0032] Alternatively, as an option, the one or more surface disruption features for each of the plurality of fins may extend in different directions. That is, a pattern of the one or more surface disruption features of each of the plurality of fins may be different between at least some of the plurality of fins. For example, the pattern of one or more surface disruption features may be different between one ormore (or each) pair of adjacent fins.

[0033] In some embodiments, at least one of the one or more surface disruption features may extendalong the full height of the corresponding fin.

[0034] In other words, the at least one of the one or more surface disruption features may extend from a first (bottom) end of the fin in contact with the base plate to a second (top) end of the fin at anend of the fin distal from the base plate.

[0035] By providing a surface disruption feature that extends along the full height of the corresponding fin the disruption of the flow of the dielectric fluid across the respective face of thecorresponding fin can be ensure along the full height of the correspo nding fin, thereby ensuring thecomplete reset of the thermal boundary layer across the full height of the corresponding fin.

[0036] Additionally or alternatively, as an option, at least one of the one or more surface disruption features may extend partially along the height of the corresponding height. In this way, the costs and / or complexity associated with the provision of the one or more surface disruption features may be reduced.

[0037] Optionally, the extent to which each of a plurality of surface disruption features extends along the height of a respective face of the corresponding fin may be the same or may vary. For example, asan option, the extent may alternate for adjacent surface disruption features along the length of the corresponding fin. Alternatively, as an option, each of the surface disruption features on a respectiveface of a corresponding fin may extend fully along the height of the corresponding fin.

[0038] Optionally, the one or more surface disruption features for each of the plurality of fins may extend to the same extent along the height(s) of the corresponding fins. In other words, the extent to which each of the one or more surface disruption features of each of the plurality of fins extend alongthe height of said fins may be the same across a subset (or indeed all) of the plurality of fins.

[0039] Alternatively, as an option, the one or more surface disruption features for each of the plurality of fins may extend to different extents along the height(s) of the corresponding fins. That is, the extentto which each of the one or more surface disruption features of each of the pl urality of fins extend alongthe height of said fins may be different between at least some of the plurality of fins. For example, theextent may be different between one or more (or each) pair of adjacent fins.

[0040] In some embodiments, for at least one of the plurality of fins, the one or more surfacedisruption features may be defined by one or more grooves, notches and / or ridges.

[0041] Optionally, the one or more surface disruption features on each fin may include a variety of types of surface disruption features including one or more features selected from the group of grooves, notches and / or ridges.

[0042] Grooves may be understood to be channel-like recesses in a face of a fin that penetrate partially into the thickness of the fin.

[0043] Notches may be understood as channel-like recesses in a face of a fin that penetrate all theway through the thickness of the fin.

[0044] Ridges may be understood as channel-like protrusions extending from a face of a fin.

[0045] Optionally, each of the surface disruption features on a given fin may be of the same type.

[0046] Optionally, the surface disruption features across the plurality of fins may be of different types for at least some of the plurality of fins. For example, the surface disruption features may be of differenttypes between one or more (or each) pair of adjacent fins.

[0047] Each of the surface disruption features may be sized and arranged to reset the thermal boundary layer between the dielectric fluid and the fin at appropriate intervals so as to improve the heatexchange efficiency of the heatsink, as described above.

[0048] In general terms, the size and spacing of surface disruption features that may be suitable for resetting the thermal boundary layer between heatsink fins and dielectric fluid flowing therethrough may depend on a number of factors including, for example: the viscosity of the dielectric fluid, the temperature of the dielectric fluid, the flow rate of the dielectric fluid, the spacing between the fins of the heatsink, and / or the thermal transport properties of one or both of the dielectric fluid and the fins of the heatsink. The present inventors have found that the sizes, shapes and arrangements described hereinare suitable for resetting the thermal boundary layer between the fins of a h eatsink, as describedherein, and the dielectric fluid having the properties described herein.

[0049] Alternatively, as an option, the surface disruption features across the plurality of fins may beof the same type across a subset (or indeed all) of the plurality of fins.

[0050] In a particular example, the plurality of fins may be a plurality of parallel rectangular fins, eachhaving a plurality of notches etched along the full height of corresponding fin.

[0051] In some embodiments, the position of the one or more surface disruption features in one of the plurality of fins may be staggered relative to the position of the one or more surface disruptionfeatures in an adjacent one of the plurality of fins.

[0052] In other words, the surface disruption features between adjacent pairs of fins may not bealigned along a direction parallel to the length of the base plate.

[0053] Alternatively, as an option, the one or more surface disruption features of each of the plurality of fins may be non-staggered such that each of the surface disruption features is aligned along a direction parallel to the length of the base plate.

[0054] In some embodiments, each of the plurality of fins may have a thickness between 0.5 mm and 1.5 mm.

[0055] Optionally, each of the plurality of fins may have a thickness of 1.5 mm or less, 1.2 mm or less, 1 mm or less, 0.8 mm or less, or 0.7 mm or less.

[0056] Optionally, each of the plurality of fins may have a thickness of 0.5 mm or more, 0.7 mm ormore, 0.8 mm or more, 1 mm or more, or 1.2 mm or more.

[0057] Optionally, each of the plurality of fins may have a thickness between 0.5 and 1.2 mm, 0.5 and 1 mm, 0.5 and 0.8 mm, 0.5 and 0.7 mm, 0.7 and 1.5 mm, 0.7 and 1.2 mm, 0.7 and 1 mm, 0.7 and 0.8mm, 0.8 and 1.5 mm, 0.8 and 1.2 mm, 0.8 and 1 mm, 1 and 1.5 mm, o r 1 and 1.2 mm, In particularexamples, each of the plurality of fins may have a thickness between 0.7 and 0.8 mm.

[0058] Optionally, the base plate may have a thickness of at least 3 mm.

[0059] Optionally, the height of each of the plurality fins relative to the base plate may be at least 20 mm.

[0060] Optionally, the base plate may have an area of at least 6000 mm 2. Optionally, the base platemay be a rectangular base plate having a length of at least 100 mm and a width of at least 60 mm. In particular examples, the base plate may be a rectangular base plate having a length of 119 mm and a width of 79 mm.

[0061] Optionally, an area occupied by the plurality of fins (and the spacing therebetween) maycorrespond to at least 80% of the total area of the base plate.

[0062] In some embodiments, the spacing between adjacent fins may be between 1.5 mm and 2.5 mm.

[0063] The spacing between adjacent fins may be understood as corresponding to the distancebetween adjacent fins in a direction parallel to the width of the base plate from which the fins extend.

[0064] Optionally, the spacing between adjacent fins may be 2.5 mm or less, 2.4 mm or more, 2.2mm or less, 2 mm or less, 1.8 mm or less, or 1.6 mm or less.

[0065] Alternatively, as an option, the spacing between adjacent fins may be 1.5 mm or more, 1.6mm or more, 1.8 mm or more, 2 mm or more, 2.2 mm or more, or 2.4 mm or more.

[0066] Alternatively, as an option, the spacing between adjacent fins may be between 1.5 and 2.4 mm, 1.5 and 2.2 mm, 1.5 and 2 mm, 1.5 and 1.8 mm, 1.5 and 1.6 mm, 1.6 and 2.5 mm, 1.6 and 2.4 mm, 1.6 and 2.2 mm, 1.6 and 2 mm, 1.6 and 1.8 mm, 1.8 and 2.5 mm, 1.8 and 2.4 mm, 1.8 and 2.2 mm, 1.8 and 2 mm, 2 and 2.5 mm, 2 and 2.4 mm, 2 and 2.2 mm, 2.2 and 2.5 mm, 2.2 and 2.4 mm, or 2.4 and 2.5 mm.

[0067] Optionally, the spacing between adjacent fins may be between 1.9 and 2.1 mm, for example 2 mm.

[0068] The spacing between adjacent fins may also be expressed in terms of the number of fins that fit within a width. For example, the adjacent fins may be spaced such that there are between 4 and 6fins per cm in a direction transverse to the surfaces of the fi ns. This may be alternatively expressedbetween 12 and 13 fins per inch in the direction transverse to the surfaces of the fins.

[0069] In some embodiments, for at least one of the plurality of fins, each of the corresponding one or more surface disruption features may have a thickness of up to 5 mm in the direction of flow of the dielectric fluid.

[0070] Each of the one or more surface disruption features may be an elongate feature extending across a respective face of a corresponding fin of the plurality of fins. The thickness of each surface disruption feature may therefore be understood as the extent of the surface disruption feature in adirection transverse to the direction in which said surface disruption feature extends.

[0071] Optionally, the thickness of each surface disruption feature may be 5 mm or less, 4 mm or less, 3 mm or less, or 2 mm or less.

[0072] Alternatively, as an option, the thickness of each surface disruption feature may be 1 mm ormore, 2 mm or more, 3 mm or more, or 4 mm or more.

[0073] Alternatively, as an option, the thickness of each surface disruption feature may be between 1 and 5 mm, 1 and 4 mm, 1 and 3 mm, 1 and 2 mm, 2 and 5 mm, 2 and 4 mm, 2 and 3 mm, 3 and 5 mm,3 and 4 mm, or 4 and 5 mm. In a particular example, the thickness of each surface disruption fe aturemay be between 1 and 2 mm. In the context of the present disclosure, the ranges listed above may beconsidered to be inclusive of their endpoints.

[0074] The present inventors have found that surface disruption features having these sizes may be suitable for disrupting the thermal boundary layer between fins of a heatsink having the arrangementdescribed herein, and dielectric fluids having the properties (e.g., viscosities) described herein.

[0075] In some embodiments, for at least one of the plurality of fins, a feature spacing between adjacent surface disruption features along a corresponding fin may be between 1 mm and 30 mm.

[0076] The present inventors have found that when the feature spacing between adjacent surface disruption features along a fin is within this range, the thermal boundary layer between said fin and thedielectric fluid flowing across the face of the fin is reset before the thermal boundary layer fullydevelops ^ i.e., before the heat exchange efficiency is minimised.

[0077] Optionally, the feature spacing may be 1 mm or more, 5 mm or more, 10 mm or more, 15 mm or more, 20 mm or more, or 25 mm or more. Optionally, the feature spacing may be 30 mm or less, 25mm or less, 20 mm or less, 15 mm or less, 10 mm or less, or 5 mm or less. Option ally, the featurespacing may be between 1 and 25 mm, 1 and 20 mm, 1 and 15 mm, 1 and 10 mm, 1 and 5 mm, 5 and 30 mm, 5 and 25 mm, 5 and 20 mm, 5 and 15 mm, 5 and 10 mm, 10 and 30 mm, 10 and 25 mm, 10 and 20 mm, 10 and 15 mm, 15 and 30 mm, 15 and 25 mm, 15 and 20 mm, 20 and 30 mm, 20 and 25 mm, or 25 and 30 mm.

[0078] Optionally, the number of surface disruption features per fin may be selected to provide feature spacings within the abovementioned ranges. For example, each fin may include 10 or fewersurface disruption features, 7 or fewer surface disruption features, 5 or fewer s urface disruptionfeatures, or 3 or fewer surface disruption features.

[0079] Alternatively, as an option, each fin may include 2 or more surface disruption features, 3 or more surface disruption features, 5 or more surface disruption features, or 7 or more surface disruption features.

[0080] Alternatively, as an option, each fin may include between 2 and 10 surface disruption features, 2 and 7 surface disruption features, 2 and 5 surface disruption features, 2 and 3 surface disruption features, 3 and 10 surface disruption features, 3 and 7 surface disruption features, 3 and 5 surface disruption features, 5 and 10 surface disruption features, 5 and 7 surface disruption features, or 7 and 10 surface disruption features.

[0081] In a particular example, each fin may include 5 surface disruption features.

[0082] In some embodiments, the kinematic viscosity of the dielectric fluid at 40°C may be between 1.5 x 10-6m2s-1and 4 x 10-5m2s-1, and / or the kinematic viscosity of the dielectric fluid at 100°C may be between 5 x 10-7m2s-1and 10-5m2s-1.

[0083] In some embodiments, the kinematic viscosity of the dielectric fluid at 40°C may be between 2 and 6 times greater than the kinematic viscosity of the dielectric fluid at 100°C.

[0084] In some embodiments, the dielectric fluid may include a base oil. The base oil may for example comprise hydrocarbons, wherein less than 90% of the contents of the base oil is defined bysaturated hydrocarbons; and / or the base oil may have a sulphur content of greater than 300 parts permillion, and the viscosity index of the base oil may be between 80 and 120. Such base oils may be^^^^^^^^ ^^ ^^ ^^^^^^ ^^ ^^^^ ^^^^^

[0085] Alternatively, the base oil may comprise hydrocarbons wherein 90% or more of the contents of the base oil is defined by saturated hydrocarbons, and the base oil may have a sulphur content of less than 300 parts per million, and the viscosity index of the base oil may be between 80 and 120. Such^^^^ ^^^^ ^^^ ^^ ^^^^^^^^ ^^ ^^ ^^^^^^ ^^^ ^^^^ ^^^^^

[0086] Alternatively, the base oil may comprise hydrocarbons wherein 90% or more of the contents of the base oil is defined by saturated hydrocarbons, and the base oil may have a sulphur content of lessthan 300 parts per million, and the viscosity index of the base oil may be 120 or more . The base oil mayadditionally or alternatively include gas-to-liquid (GTL) products. All such base oils may be referred to^^ ^^^^^^ ^^^^ ^^^^ ^^^^^

[0087] Alternatively, the base oil may include polyalphaolefins (PAOs). Such base oils may be^^^^^^^^ ^^ ^^ ^^^^^^ ^^^ ^^^^ ^^^^^

[0088] Alternatively, the base oil may include any other base oil. Such base oils may be referred to^^ ^^^^^^ ^^ ^^^^ ^^^^^

[0089] In some embodiments, the dielectric fluid may include a polyolefin, optionally a polyalphaolefin, PAO. PAOs comprise hydrogenated oligomers of decene or, in some cases, hydrogenated oligomers of a mixture of octene, decene and / or dodecane. PAOs comprise complex mixtures of branched hydrocarbons.

[0090] In some embodiments, the dielectric fluid may include a PAO selected from the group consisting of PAO-2, PAO-4, and PAO-6.

[0091] PAO-2 may be a PAO derived from a suitable base oil such as Durasyn ® 162, Spectrasyn ® 2, or Synfluid ® 2. PAO-4 may be a PAO derived from a suitable base oil such as Durasyn ® 164, Spectrasyn ® 4, or Synfluid ® 4. PAO-6 may be a PAO derived from a suitable base oil such asDurasyn ® 166, Spectrasyn ® 6, or Synfluid ® 6. References for datasheets of each of the se base oilsis included below. The contents of these datasheets are incorporated herein by reference.

[0092] Optionally, the dielectric fluid may further comprise one or more additives. The one or more additives may, for example, be selected to reduce oxidation of the dielectric fluid and / or improve thelubricative properties of the dielectric fluid.

[0093] Optionally, the dielectric fluid may have a thermal conductivity between 0.1 and 0.3 W m -1 K-1.

[0094] Optionally, the dielectric fluid may have a specific heat capacity between 1.5 and 4 kJ kg -1 K-1.

[0095] Optionally, the dielectric fluid may have a density between 600 and 1000 kg m -3.

[0096] Optionally, the dielectric fluid may have a flashpoint of at least 100°C, and an autoignition point of at least 200°C.

[0097] Optionally, the dielectric fluid may be an ester or an ether.

[0098] Optionally, the dielectric fluid may be obtainable from a fossil fuel. Alternatively, the dielectricfluid may be obtainable as a refined fluid or a bio-based fluid (e.g., extracted from a vegetable oil).

[0099] Optionally, with any of the dielectric fluids described herein, the dielectric fluid may be mixed and / or combined with one or more antioxidants. The provision of the one or more antioxidants reduce the risk of deterioration (e.g., by rusting) of the component parts of the heatsink, thereby prolonging the lifetime of the heatsink.

[0100] The dielectric fluid may be flowed between the plurality of fins at an input temperature of 45 °Cor less, 35°C or less, 25°C or less, or 15°C or less. Alternatively, the dielectric fluid may be flowedbetween the plurality of fins at an input temperature of 5°C or more, 15°C or more, 25°C or more, or 35°C or more. Alternatively, the dielectric fluid may be flowed between the plurality of fins at an input temperature of between 5°C and 45°C, between 5°C and 35°C, between 5°C and 25°C, between 5°C and 15°C, between 15°C and 45°C, between 15°C and 35°C, between 15°C and 25°C, between 25°C and 45°C, between 25°C and 35°C, or between 35°C and 45°C.

[0101] The dielectric fluid may be flowed between the plurality of fins to have an output temperature of 40°C or more, 50°C or more, 60°C or more, or 70°C or more. Alternatively, the dielectric fluid may be flowed between the plurality of fins to have an output temperature of 80°C or less, 70°C or less, 60°C or less, or 50°C or less. Alternatively, the dielectric fluid may be flowed between the plurality of fins to have an output temperature of between 40°C and 80°C, between 40°C and 70°C, between 40°C and 60°C, between 40°C and 50°C, between 50°C and 80°C, between 50°C and 70°C, between 50°C and 60°C, between 60°C and 80°C, between 60°C and 70°C, or between 70°C and 80°C.

[0102] The dielectric fluid may be flowed between the plurality of fins with a flow rate of 5 litres per minute or more, 7.5 litres per minute or more, 10 litres per minute or more, or 12.5 litres per minute or more. Alternatively, the dielectric fluid may be flowed between the plurality of fins with a flow rate of 15 litres per minute or less, 12.5 litres per minute or less, 10 litres per minute or less, or 7.5 litres perminute or less. Alternatively, the dielectric fluid may be flowed between the plurality of f ins with a flowrate of between 5 and 15 litres per minute, between 5 and 12.5 litres per minute, between 5 and 10 litres per minute, between 5 and 7.5 litres per minute, between 7.5 and 15 litres per minute, between 7.5 and 12.5 litres per minute, between 7.5 litres per minute and 10 litres per minute, between 10 litres per minute and 15 litres per minute, between 10 litres per minute and 12.5 litres per minute, or between 1.5 and 15 litres per minute.

[0103] In another aspect, there is provided a heatsink for an immersion cooling system. The heatsink includes a plurality of fins for exchanging heat with a dielectric fluid flowing therebetween, where the spacing between adjacent fins is at least 1 mm. Optionally, the spacing between adjacent fins may be 2 mm.

[0104] As discussed above, the present inventors have found that the spacing of heatsink fins may be optimised for heat exchange with dielectric fluids. The advantages obtainable by spacing adjacent fins apart with a spacing of at least 1 mm and by providing one or more surface disruption features onrespective faces of corresponding fins may be independently realised. Optionally, a relatively largerspacing between adjacent fins may be provided when the heatsink is used in conjunction with a relatively more viscous dielectric fluid.

[0105] There may be provided a method of cooling a processing unit (e.g., a CPU and / or GPU) using an immersion cooling system. The method may comprise providing one or more heatsinks as described herein attached to the processing unit; and flowing a dielectric fluid, such as those described herein, between the fins of the one or more heatsinks to cool the computing unit.

[0106] The processing unit to be cooled may be a processing unit of a data centre.

[0107] Flowing the dielectric fluid between the fins of the one or more heatsinks may involve passively flowing the dielectric fluid (e.g., by capillary action, gravitational action, or similar) or may involve actively flowing the dielectric fluid (e.g., by pumping the dielectric fluid through the immersioncooling system), or may involve a mixture of actively and passively flowing the dielectric fluid.

[0108] In the context of the present disclosure, the ranges listed above may be considered to be inclusive of their endpoints.

[0109] The invention includes the combination of one or more of the aspects, embodiments and / or preferred features described herein except where such a combination is clearly impermissible or expressly avoided.

[0110] The order of the operations of the methods described herein is exemplary, but the steps may be carried out in any suitable order, or simultaneously where appropriate. Additionally, steps may be added or substituted in, or individual steps may be deleted from any of the methods without departing from the scope of the subject matter described herein. Aspects of any of the examples described abovemay be combined with aspects of any of the other examples described to form further examples.

[0111] It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those thatsolve any or all the stated problems or those that have any or all the s tated benefits and advantages.Variants should be considered to be included into the scope of the invention.Summary of the Figures

[0112] Embodiments and experiments illustrating the principles of the invention will now be discussedwith reference to the accompanying figures, in which:

[0113] FIG. 1 illustrates a heat sink configured to provide cooling as part of an immersion cooling system.

[0114] FIG. 2 illustrates an exemplary arrangement for the plurality of fins for the heatsinks described herein.

[0115] FIG. 3A illustrates an exemplary ridge as a surface disruption feature of a fin of the heatsinks described herein.

[0116] FIG. 3B illustrates an exemplary groove as a surface disruption feature of a fin of the heatsinks described herein.

[0117] FIG. 3C illustrates an exemplary notch as a surface disruption feature of a fin of the heatsinks described herein.

[0118] FIG. 4A illustrates a top view of an exemplary fin arrangement for the heatsinks described herein.

[0119] FIG. 4B illustrates a top view of an alternative exemplary fin arrangement for the heatsinks described herein.

[0120] FIG. 5A illustrates the progression of a thermal boundary layer between adjacent fins that do not include any surface disruption features.

[0121] FIG. 5B illustrates the progression of a disrupted thermal boundary layer between adjacentfins, each comprising one or more surface disruption features.Detailed Description of the Invention

[0122] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. Alldocuments mentioned in this text are incorporated herein by reference.

[0123] FIG. 1 illustrates a heatsink 110 configured to provide cooling as part of an immersion cooling system 100.

[0124] The immersion cooling system 100 comprises a heatsink 110 arranged to provide cooling for a processing unit 120 attached thereto. The processing unit 120 may, for example, be a CPU and / or a GPU.

[0125] The heatsink 110 comprises a base 112 and a plurality of fins 114 extending vertically therefrom. The processing unit 120 comprises a die 122 and a package 124 layered thereon. The processing unit 120 further comprises a thermal interface material 126 arranged in contact with the base 112 of the heatsink 110 such that heat generated by the processing unit 120 is transferred (via conduction through the thermal interface material 126) into the heatsink 110.

[0126] In use, the immersion cooling system 100 may be disposed within a data centre. For example, each processing unit 120 of a data centre may have a respective heatsink 110 attached thereto in the arrangement shown in FIG. 1. In such examples, the data centre may include a coolant circulation system configured to circulate a dielectric fluid therethrough such that the dielectric fluid flows between adjacent fins of the plurality of fins 114 such that the heat transferred into the heatsink 110 from the processing unit 120 is exchanged with the dielectric fluid to cool the immersion cooling system 100.

[0127] FIG. 2 illustrates an exemplary arrangement for the plurality of fins 114 for the heatsinks 110 described herein.

[0128] As can be seen from FIG. 2, the heatsink 110 comprises a base 112 defining a planar surface and a plurality of fins 114 extending away from the base 112 in a direction transverse to the planarsurface. Within the context of this disclosure, the plurality o f fins 114 may be considered to extendvertically from the base 112.

[0129] The plurality of fins 114 are sized and spaced to ensure an efficient heat exchange between each of the plurality of fins 114 and a dielectric fluid flowing therebetween. As will be discussed below in relation to FIG. 5A and FIG. 5B, as the dielectric fluid flows between adjacent fins of the plurality of fins, the respective thermal boundary layers associated with each of an adjacent pair of fins approach each other along the direction of flow of the dielectric fluid until they merge. Once the respective thermal boundary layers have merged, the efficiency of heat exchange between the corresponding fins and the dielectric fluid is significantly reduced.

[0130] To prevent this drop in heat exchange efficiency, each of the plurality of fins 114 comprise one or more surface disruption features 118. For each fin, its respective one or more surface disruption features 118 effectively reset the thermal boundary layer between the fin and the dielectric fluid at a point along the flow downstream of said surface disruption feature 118. In the context of FIG. 2, the oneor more surface disruption features 118 are illustrated as notches that are cut vertically through the f ullheight of each of the plurality of fins 114, although other configurations and arrangements are alsopossible, as is discussed in more detail below in relation to FIG. 3A, FIG. 3B and FIG. 3C.

[0131] The heatsink 110 (i.e., the base 112 and the plurality of fins 114) may be formed from a metal having a suitably high heat exchange efficiency, such as aluminium or copper. The dielectric fluid may be a polyolefin fluid - e.g., a polyalphaolefin such as PAO-2, PAO-4, or PAO-6. The dielectric fluid may be chemically inert, thereby allowing the heatsink 110 to be formed from a metal that is not necessarily a noble metal. In other words, the metal used to form the heatsink 110 can be selected to maximise a high heat exchange efficiency without needing to sacrifice heat exchange efficiency to reduce the risk of a chemical reaction (e.g., oxidation) between the heatsink 110 and the dielectric fluid flowing between the plurality of fins 114.

[0132] Each fin of the plurality of fins 114 has a thickness between 0.5 mm and 1.5 mm or, forexample a thickness between 0.7 mm and 0.8 mm. The spacing between adjacent fins of the plurality of fins 114 is at least 1 mm ^ for example between 1.5 and 2.5 mm or, for example, between 1.9 and 2.1 mm - e.g., 2 mm. Alternatively, the plurality of fins 114 may be spaced such that the fins are arranged with 12 to 13 fins per inch along the base 112.

[0133] The base 112 has a thickness of at least 3 mm ^ for example 4 or 5 mm. The base 112 has an area of at least 6000 mm2. For example, the base 112 may be a rectangular base plate having a length of 119 mm and a width of 79 mm. Each fin of the plurality of fins 114 has a height relative to the base of at least 20 mm. The plurality of fins 114 (and the spacing between the adjacent fins of the plurality offins 114) occupies at least 80% of the total area of the base 112.

[0134] In the example shown in FIG. 2, each of the fins is illustrated with a single surface disruption feature 118. However, each fin may include a plurality of surface disruption features 118 spaced along the fin. For example, each fin may include 5 surface disruption features 118. For each fin, the plurality of surface disruption features 118 may be spaced equidistantly along the fin. Further, in the example shown in FIG. 2, the surface disruption feature 118 on each fin extends vertically along the corresponding fin. However, in other examples, the surface disruption feature(s) 118 may extend in a different direction along the corresponding fin - e.g., horizontally or at an oblique angle. Additionally, in the example shown in FIG. 2, the surface disruption feature 118 on each fin may extend along the full extent (e.g., the full height) of the fin. In other examples, at least one of the one or more surfacedisruption features 118 may extend only partially along the extent (e.g., partially along the full height) o fthe fin. The thickness of each surface disruption feature 118 is up to 5 mm in the direction of flow of thedielectric fluid between the plurality of fins 114 or, in some examples, may be between 1 mm and 2mm.

[0135] The spacing between adjacent surface disruption features 118 along a given fin of the pluralityof fins 114 is between 1 and 30 mm, for example 10, 15, or 20 mm or any spacing between said points.

[0136] As can be seen from FIG. 3A, one or more of the surface disruption features 118 may be defined by a ridge 316a protruding from a surface of a fin 314 of the plurality of fins 114. In the example shown in FIG. 3A, the ridge 316a protrudes symmetrically from both sides of the fin 314, although in other examples, the ridge 316a may only protrude from one side of the fin 314 or may protrude from each side of the fin 314 to different extents. A first ridge may protrude from a first side of the fin 314, while a second ridge may protrude from a second side of the fin 314 at a position along the fin that is offset from the first ridge.

[0137] Meanwhile, as can be seen from FIG. 3B, one or more of the surface disruption features 118 may be defined by a groove 316b etched into a surface of a fin 314 of the plurality of fins 114. In the example shown in FIG. 3B, the groove 316b may be etched symmetrically into both sides of the fin 314, although in other examples, the groove may only be etched into one side of the fin 314 or may be etched into each side of the fin 314 to different extents. A first groove may be etched into a first side of the fin 314, while a second groove may be etched into a second side of the fin 314 at a position along the fin that is offset form the first groove.

[0138] Further, as can be seen from FIG. 3C, one or more of the surface disruption feature 118 maybe defined by a notch 316c etched through a fin 314 of the plurality of fins 114.

[0139] FIG. 4A illustrates a top view of an exemplary fin arrangement for the heatsinks 110 described herein. As can be seen from FIG. 4A, the surface disruption features 118 of adjacent fins from amongst the plurality of fins 114 may be staggered relative to one another in the direction of flow of the dielectric fluid. In other words, the one or more surface disruption features 118 of each fin may not be alignedwith the one or more surface disruption features 118 of the fins adjacent to that fin.

[0140] FIG. 4B illustrates a top view of an alternative exemplary fin arrangement for the heatsinks 110 described herein. As can be seen from FIG. 4B, adjacent fins of the plurality of fins 114 may be staggered relative to one another in the direction of flow of the dielectric fluid. In other words, adjacent fins of the plurality of fins 114 may not be aligned along a direction that is parallel to the direction of flow of the dielectric fluid between the plurality of fins 114.

[0141] FIG. 5A illustrates the progression of a thermal boundary layer 502 between adjacent fins114a, 114b that do not include any surface disruption features.

[0142] For a laminar flow of a fluid over a surface, the thermal boundary layer 502 between the dielectric fluid and a fin 114a, 114b defines the boundary between the dielectric fluid flowing at the coldso-^^^^^^ ^^^^^ ^^^^^^^ ^^^^^^^^^^^ ^^^ ^^^^^^^^^^ ^^^^^ ^^at has been heated by the fin 114a, 114b. Asthe dielectric fluid propagates between the plurality of fins 114, the thermal boundary layers 502 ofadjacent fins approach each other and eventually merge according to the known relationship:^^^^^ ^T ^^ ^^^ ^^^^^^^^^ ^^ ^^^ ^^^^^^^ ^^^^^^^^ ^^^^^ ^^^ ^^^^ ^ ^^^^^ ^^^ ^^^^^ ^^^^^ ^ ^^ ^^^kinematic viscosity of the dielectric fluid, x is the distance along the given fin 114a, 114b in the direction of flow / propagation of the dielectric fluid, u0is the freestream velocity of the dielectric fluid, and Pr is the Prandtl number of the dielectric fluid, wherein the Prandtl number is defined as the ratio betweenthe dielectric fluid's kinematic viscosity and its thermal diffusivity.

[0143] As the thermal boundary layers 502 from two adjacent fins 114a, 114b approach each other and eventually merge, the efficiency of the heat exchange between the two fins 114a, 114b and the dielectric fluid drops dramatically (even so far as dropping to zero once the thermal boundary layers 502 are fully established and merged).

[0144] Meanwhile, FIG. 5B illustrates the progression of a disrupted thermal boundary layer 504between adjacent fins114a, 114b, each comprising one or more surface disruption features 118.

[0145] As can be seen from FIG. 5B, the surface disruption features 118 on each fin disrupts the (laminar) flow of the dielectric fluid between the adjacent fins 114a, 114b and correspondingly disrupts the thermal boundary layers between the fins 114a, 114b and the dielectric fluid resulting in disrupted thermal boundary layers 504. As can be seen from FIG. 5B, the disrupted thermal boundary layers 504 turn and re-approach the fins 114a, 114b downstream of the corresponding surface disruption features 118. In the context of FIG. 5B, the disrupted thermal boundary layers 504 are illustrated as making contact with the fins 114a, 114b downstream of the corresponding surface disruption features 118although, as the skilled person will appreciate, in other examples, the disrupted thermal boundarylayers 504 need not make contact with the fins downstream of the surface disruption features 118, it is only necessary that the disrupted thermal boundary layers 504 are disrupted from their tendencytowards merging along the direction of propagation / flow of the dielectric fluid.

[0146] In other words, each of the surface disruption features 118 of each of the plurality of fins 114 disrupts the development of the thermal boundary layers 502 between each of the fins 114a, 114b and the dielectric fluid resulting in a disrupted thermal boundary layer 504 between each of the plurality of fins 114 and the dielectric fluid that promotes an improved heat exchange efficiency between each ofthe plurality of fins 114 and the dielectric fluid. This consequently improves the cooling efficiency of theheatsink 110 when it is deployed in an immersion cooling system 100, such as that depicted in FIG. 1.

[0147] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0148] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forthabove are considered to be illustrative and not limiting . Various changes to the described embodimentsmay be made without departing from the spirit and scope of the invention.

[0149] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0150] Any section headings used herein are for organizational purposes only and are not to beconstrued as limiting the subject matter described.

[0151] Throughout this specification, including the claims which follow, unless the context requires^^^^^^^^^^ ^^^ ^^^^ ^^^^^^^^^^ ^^^ ^^^^^^^^^^ ^^^ ^^^^^^^^^^ ^^^^ ^^ ^^^^^^^^^^^^ ^^^^^^^^^^^^^ ^^^^^^^^^^^^^^ ^^^^ ^^ ^^^^^^^^^^ ^^ ^^^^^ ^^^ ^^^^^^^^^ ^^ ^ ^^^ ted integer or step or group of integers orsteps but not the exclusion of any other integer or step or group of integers or steps.

[0152] It must be noted that, as used in the specification and the appended claims, the singular forms^^^^ ^^^^^ ^^^ ^^^^^ ^^^^^^^ ^^^^^^ ^^^^^^^^^ ^^^^^^ ^^^ ^^^^^^^ ^^^^^^^ ^^^^^^^^ ^^^^^^^^^^ ^^^^^^ ^^^^^ ^^^^^^^^^ ^^^^^^ ^^ ^^^^ ^^^^^^^ ^^^ ^^^^^^^^^^ ^^^^^ ^ ^^^^^^ ^^ ^^^^^^^ ^^^^^^^ ^^^^^^^^^^ ^^^^^^When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of theantecede^^ ^^^^^^^^ ^^ ^^^^ ^^ ^^^^^^^^^^ ^^^^ ^^^ ^^^^^^^^^^ ^^^^^ ^^^^^ ^^^^^^^ ^^^^^^^^^^ . The term^^^^^^^ ^^ ^^^^^^^^ ^^ ^ ^^^^^^^^^ ^^^^^ ^^ ^^^^^^^^ ^^^ ^^^^^ ^^^ ^^^^^^^ ^^ - 10%.

[0153] ^^^ ^^^^^ ^^^ ^^^ ^^^^^^ ^^ ^^^^ ^^ ^^^ ^^^^^ ^^^^ ^^ ^^^^^ ^^^ ^^^ ^^^^^ ^^^^ ^^^ ^^ ^^^^interchangeably herein.

[0154] ^^^ ^^^^ ^^^^^^^^ ^^ ^^^^ ^^^^^^ ^^ ^^ ^^ ^^^^^ ^^ ^^^^^^^^ ^^^^^^^^^^ ^^ ^^^^ ^^ ^^^^^^^^^^^^^^^ ^^^^^^^^ ^^ ^^^^^^^^^^ ^^^^ ^^ ^^^^^^^ ^^^ ^^ ^^^^ ^^ ^^^ ^^^^^^^ ^^^^^ ^^^ ^^^^ ^^^^^^^^ ^^^^^^ ^^ ^ ^^^^^^ ^^^^ ^^ ^^^ ^ ^^^^^^ ^^ ^^^^^^^^^^^ ^^^^ ^^^ ^ and B and C; A and B; A and C; Band C; A or B or C; A or C; A or C; B or C; only A; only B; and only C.

[0155] ^^^ ^^^ ^^ ^^^ ^^^^ ^^^^^^^^^^ ^^^ ^^^^^^^^^ ^^ ^^^^^ ^^ ^^^ ^^^^^^^^^ ^^ ^^^^^^^^^ ^^^^^ ^^^^^^operations nonetheless also encompasses aspects, examples and embodiments that may be^^^^^^^^^^^ ^^^^^^^^^ ^^^^ ^^^ ^^^^ ^^^^^^^^^ ^^ ^^^^^^^ ^^ ^^^^^ ^^^^^^^ s, steps and / or operations.References

[0156] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of the references is incorporated herein.

[0157] Durasyn ® 162: https: / / www.ineos.com / show- document / ?grade=Durasyn+162&bu=INEOS+Oligomers&documentType=Technical+Data+Sheet&docL anguage=EN&version=4c71f43092636d236a5490e0234d64c3

[0158] Durasyn ® 164: https: / / www.ineos.com / show- document / ?grade=Durasyn+164&bu=INEOS+Oligomers&documentType=Technical+Data+Sheet&docL anguage=EN&version=4c71f43092636d236a5490e0234d64c3

[0159] Durasyn ® 166: https: / / www.ineos.com / show- document / ?grade=Durasyn+166&bu=INEOS+Oligomers&documentType=Technical+Data+Sheet&docL anguage=EN&version=4c71f43092636d236a5490e0234d64c3

[0160] SpectraSyn ® 2: https: / / www.exxonmobilchemical.com / en / chemicals / webapi / dps / v1 / datasheets / 150000000348 / 0 / en

[0161] SpectraSyn ® 4: https: / / www.exxonmobilchemical.com / en / chemicals / webapi / dps / v1 / datasheets / 150000000349 / 0 / en

[0162] SpectraSyn ® 6: https: / / www.exxonmobilchemical.com / en / chemicals / webapi / dps / v1 / datasheets / 150000000352 / 0 / en

[0163] Synfluid ® 2: https: / / www.cpchem.com / sites / default / files / 2020- 04 / Synfluid%2520PAO%25202%2520cSt_0_0.pdf

[0164] Synfluid ® 4: https: / / www.cpchem.com / sites / default / files / 2023- 02 / Synfluid%20PAO%204%20cSt.pdf

[0165] Synfluid ® 6: https: / / www.cpchem.com / sites / default / files / 2023- 02 / Synfluid%20PAO%206%20cSt.pdf

Claims

Claims1. A heatsink for an immersion cooling system, the heatsink comprising:a plurality of fins for exchanging heat with a dielectric fluid flowing therebetween,wherein the spacing between adjacent fins of the plurality of fins is at least 1 mm, and wherein each of the plurality of fins comprises one or more surface disruption features for resetting the thermal boundary layer between the dielectric fluid and the fin downstream of the surface disruption feature.

2. The heatsink of claim 1, wherein, for at least one of the plurality of fins, each of the one or moresurface disruption features is spaced equidistantly along the corresponding fin.

3. The heatsink of claim 1 or 2, wherein, for at least one of the plurality of plurality of fins, one or moreof the one or more surface disruption features extends vertically along the corresponding fin.

4. The heatsink of claim 3, wherein at least one of the one or more surface disruption features extendsalong the full height of the corresponding fin.

5. The heatsink of any one of claims 1 to 4, wherein, for at least one of the plurality of fins, the one ormore surface disruption features are defined by one or more grooves, notches and / or ridges.

6. The heatsink of any one of claims 1 to 5, wherein the position of the one or more surface disruption features in one of the plurality of fins is staggered relative to the position of the one or more surface disruption features in an adjacent one of the plurality of fins.

7. The heatsink of any one of claims 1 to 6, wherein each of the plurality of fins has a thickness between 0.5 mm and 1 mm.

8. The heatsink of any one of claims 1 to 7, wherein the spacing between adjacent fins is between 1.5 mm and 2.5 mm.

9. The heatsink of any one of claims 1 to 8, wherein, for at least one of the plurality of fins, each of the corresponding one or more surface disruption features has a thickness of up to 5 mm in the direction of flow of the dielectric fluid.

10. The heatsink of any one of claims 1 to 9, wherein, for at least one of the plurality of fins, a feature spacing between adjacent surface disruption features along a corresponding fin is between 1 and 30 mm.

11. The heatsink of any one of claims 1 to 10, wherein the kinematic viscosity of the dielectric fluid at 40°C is between 1.5 x 10-6m2s-1and 4 x 10-5m2s-1, and / or wherein the kinematic viscosity of the dielectric fluid at 100°C is between 5 x 10-7m2s-1and 10-5m2s-1.

12. The heatsink of any one of claims 1 to 11, wherein the kinematic viscosity of the dielectric fluid at40°C is between 2 and 6 times greater than the kinematic viscosity of the dielectric fluid at 100°C.

13. The heatsink of any one of claims 1 to 12, wherein the dielectric fluid comprises a polyolefin, optionally a polyalphaolefin, PAO.

14. The heatsink of claim 13, wherein the dielectric fluid comprises a PAO selected from the group consisting of PAO-2, PAO-4, and PAO-6.

15. A heatsink for an immersion cooling system, the heatsink comprising:a plurality of fins for exchanging heat with a dielectric fluid flowing therebetween,wherein the spacing between adjacent fins is at least 1 mm.

Images