GB2571053A

GB2571053A - Heat sink for immersion cooling

Info

Publication number: GB2571053A
Application number: GB1714304.1A
Authority: GB
Inventors: Edmunds Neil; Young Andrew
Original assignee: Iceotope Ltd
Current assignee: Iceotope Ltd
Priority date: 2017-09-06
Filing date: 2017-09-06
Publication date: 2019-08-21
Anticipated expiration: 2037-09-06
Also published as: GB201714304D0; GB2571053B

Abstract

A heat sink 1 is mountable on a heat-generating electronic device 12 such as an integrated circuit which is immersed in a liquid coolant, is designed for use in a cooling module (blade) 100. The heat sink comprises a base and a retaining wall extending from the base, providing a volume for retaining liquid coolant against the electronic device, and is configured for mounting on top of a heat-transmitting surface of the electronic device 12. Low temperature components 10 and high temperature components 12 may be mounted on circuit boards 15 of the module.

Description

Heat Sink for Immersion Cooling

Technical Field of the Invention

The disclosure concerns a heat sink for an electronic device immersed in a liquid coolant and a cooling module for the electronic device comprising the heat sink.

Background to the Invention

Many types of electrical component generate heat during operation. In particular, electrical computer components such as motherboards, central processing units (CPUs) and memory modules may dissipate substantial amounts of heat when in use. Heating of the electrical components to high temperatures can cause damage, affect performance or cause a safety hazard. Accordingly, substantial efforts have been undertaken to find efficient, high performance systems for cooling electrical components effectively and safely.

One type of cooling system uses liquid cooling. Although different liquid cooling assemblies have been demonstrated, in general the electrical components are immersed in a coolant liquid so as to provide a large surface area for heat exchange between the heat generating electrical components and the coolant.

US-7,905,106 describes a liquid submersion cooling system that cools a number of electronic devices within a plurality of cases connected to a rack system. A housing is filled with a dielectric cooling liquid with heat generating electronic components submerged in the dielectric cooling liquid. The rack system contains a manifold that allows liquid transfer for multiple cases and a pump system for pumping the dielectric cooling liquid into and out of the rack. External heat exchangers allow the heated dielectric cooling liquid to be cooled before being returned to the rack. In areas where there is significant heat, directed liquid flow is used to provide localized cooling. A plurality of tubes extend from a manifold to direct the dielectric cooling liquid to specific targeted hot spots. The ends of the tubes are positioned adjacent the desired hot spots or the tubes can connect to dispersion plenums to help direct the flow of the return liquid to the targeted hot spots. Directing or focusing of the cooling fluid within each case is thereby done at the expense of other components, which may not be cooled as effectively. Moreover, the heat-carrying capacity of the liquid coolant may not be used efficiently. For these reasons, this technique requires a significant quantity of dielectric cooling fluid to be pumped into and out of each case in the rack.

In US-8,305,759, dielectric liquid is used to cool heat-generating electronic components disposed on a circuit board within a case. The liquid is poured or otherwise directed over the electronic components, with gravity assisting the liquid in flowing downward over the components, with the liquid thereafter being collected in a sump for eventual return back to the electronic components. Plenums disposed over the electronic component are provided, to contain the liquid as it flows over the electronic component. This is intended to make more of the liquid contact the component, thereby enhancing the effectiveness of the liquid cooling. Again, this requires a significant quantity of dielectric cooling liquid and relies on gravity-assistance, which can make the system less flexible and introduce other design constraints that may cause the system to be less efficient.

US-8,014,150 describes the cooling of electronic modules in which a cooling apparatus is coupled to a substrate to form a sealed component around an electronic device. Pumps are located within the sealed compartment so that dielectric fluid is pumped towards the electronic device. Cooling occurs by changing the phase of the dielectric fluid from liquid to vapour, which then is caused to condense as it rises towards a liquid-cooled cold plate that is fed by a second fluid. However, this cooling system requires high pressure seals and multiple cooling compartments within a case and so relatively complicated plumbing arrangements for the second cooling fluid.

A more efficient way to use liquid coolant for cooling electronic systems is therefore desired.

Summary of the Invention

Against this background, the invention provides a heat sink for an electronic device immersed in a liquid coolant in accordance with claim 1 and a cooling module for an electronic device as defined by claim 9. Further features of the invention are detailed in the dependent claims and herein. Features a method for manufacturing and/or operating corresponding with those of the heat sink and/or cooling module may additionally be provided.

A heat sink is mountable on a heat-generating electronic device, such as an integrated circuit, computer processor or other electronic component (which generates heat when electrical power is supplied to it in normal operation). The heat sink is designed for use in a cooling module, in which the electronic device is to be immersed in a liquid coolant. It provides a volume for holding or retaining liquid coolant against the heatgenerating electronic device, for example resembling a bath tub or reservoir. In this way, the liquid coolant can be applied more effectively to the place or places where the most heat is generated. Less coolant can therefore be used. Since the coolant is expensive and heavy, reducing the quantity of coolant can improve flexibility, efficiency and reliability (for example, since coolant leakages are less likely and because the coolant in the volume can

-3resist instant temperature changes caused by the failure of other components in the system).

A cooling module for an electronic device has a container, housing the electronic device such that the electronic device can be (at least partially) immersed in the liquid coolant, with the heat sink as disclosed herein, mounted on the electronic device. Typically, the electronic device is planar or mounted on a planar circuit board and the cooling module is configured to be operated such that the plane of the electronic device and/or circuit board is horizontal. The container may be elongated in accordance with the plane of the electronic device and/or circuit board, for example having a shape to match that of the electronic device and/or circuit board.

In respect of the heat sink, the volume for holding or retaining the liquid coolant can be defined by a base and a retaining wall (which may be integral or separate). The base is the part of the heat sink mounted on top of the electronic device (more specifically, a heattransmitting surface of the electronic device) and transfers heat from the heat-transmitting surface. The base typically has a planar surface defining the volume (and the base itself may be planar in shape). Heat transferred (typically conducted) through the base (in particular its surface defining the volume) is transferred to the liquid coolant held in the volume. The retaining wall extends from the base.

One effect of the heat sink is to raise the level of the coolant held within the heat sink’s volume above that external the volume (at least when the cooling module is operated with the plane of the electronic device and/or circuit board horizontal and the quantity of coolant within the container of the cooling module lower than the height of the retaining wall.

Advantageously, the heat sink has projections (such as pins and/or fins) extending from the base (or less preferably, from the retaining wall) within the volume. These projections beneficially extend no further from the base (especially in the direction perpendicular from a plane of the base) as the retaining wall. This may ensure that coolant liquid submerges all the projections. More preferably, the projections extend to substantially the same distance from the base as the retaining wall. This may additionally avoid creating paths within the volume that might bypass the projections. The projections may cause the liquid coolant to spread in a radial direction away from a predetermined point on a surface of the base (for example coincident with a hottest part of the electronic device). In particular, the projections may be formed in a non-linear pattern.

The liquid coolant is advantageously caused to flow within the container, preferably by a pump as part of the cooling module, or less preferably by configuration of the cooling

-4module (for example, to encourage convection). This may cause the liquid coolant to reach the volume of the heat sink. For example, a nozzle arrangement may further be provided, which receives flowing or pumped liquid coolant and directs it to the volume of the heat sink. The nozzle arrangement typically comprises one or more nozzles (which may be push-fit), each of which directs the flowing or pumped liquid coolant to a respective part of the volume of the heat sink, particularly a part of the heat sink’s base. For instance, each nozzle may direct the flowing or pumped liquid coolant to a respective part of the volume of the heat sink adjacent a part of the heat-transmitting surface of the electronic device having a maximum temperature or a temperature above a threshold level (that is, one of the hottest parts of the device). Most preferably, the nozzle arrangement directs the flowing or pumped liquid coolant in a direction perpendicular to the base of the heat sink. This may force the coolant directly into the volume and improve heat dissipation.

Brief Description of the Drawings

The invention may be put into practice in a number of ways and preferred embodiments will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 shows an embodiment of a cooling module in accordance with the disclosure;

Figure 2 depicts an exploded view of the embodiment of Figure 1;

Figure 3 illustrates a first embodiment of a heat sink in accordance with the disclosure;

Figure 4 depicts an exploded view of the embodiment of Figure 3;

Figure 5 shows a cross-sectional view of the heat sink in Figure 3 in operation;

Figure 6 shows a top view of the embodiment of Figure 3, showing a nozzle arrangement;

Figure 7 shows a top view of a first variant of the nozzle arrangement of the embodiment of Figure 3;

Figure 8 shows a top view of a second variant of the nozzle arrangement of the embodiment of Figure 3;

Figure 9 depicts an expanded top view of a part of the embodiment of Figure 3, showing a projection arrangement;

Figure 10 depicts a top view of a first variant of the projection arrangement of the embodiment of Figure 3;

-5Figure 11 depicts a top view of a second variant of the projection arrangement of the embodiment of Figure 3;

Figure 12 depicts a top view of a third variant of the projection arrangement of the embodiment of Figure 3;

Figure 13 illustrates a cross-sectional view of a part of the heat sink in Figure 3, showing a height of the projection arrangement;

Figure 14 illustrates a cross-sectional view of a first variant of the projection arrangement height of the embodiment of Figure 3;

Figure 15 illustrates a cross-sectional view of a second variant of the projection arrangement height of the embodiment of Figure 3;

Figure 16 depicts a cross-sectional view of a second embodiment of a heat sink in accordance with the disclosure;

Figure 17 shows a perspective view of the heat sink of Figure 16;

Figure 18 illustrates an exploded perspective view of a variant of the embodiment of Figures 16 and 17;

Figure 19 shows the exploded view of Figure 18 with a nozzle part removed;

Figure 20 depicts a perspective view of a third embodiment of a heat sink in accordance with the disclosure; and

Figure 21 illustrates an exploded perspective view of a variant of the embodiment shown in Figure 20.

Detailed Description of Preferred Embodiments

With reference to Figure 1, there is shown an embodiment of the cooling module (sometimes termed a ‘blade’) in accordance with the disclosure. Also to be considered is Figure 2, in which there is depicted an exploded view of the embodiment of Figure 1. The cooling module 100 comprises a container 110 (shown without a lid), housing components 12 generating a relatively high temperature and components 10 generating a relatively low temperature. Both low temperature components 10 and high temperature components 12 are mounted on a circuit board 15. In Figures 1 and 2, two such identical circuit boards 15 are shown within the container 110. Heat sinks 1 are mounted on the high temperature components 12. More details regarding heat sinks 1 will be discussed subsequently.

The container 110 is, in operation, filled with a dielectric liquid coolant (not shown), which may be termed a primary coolant. The liquid coolant is not electrically conductive, but is normally thermally conductive and can carry heat by conduction and/or convection. The quantity of liquid coolant inside the container 110 is sufficient to cover or immerse the

-6low temperature components 10 at least partially, but it may not necessarily fully immerse the low temperature components 10. The level of liquid coolant used in operation is discussed below. Pumps 11 cause liquid coolant to flow through pipes 5 and travel to a heat exchanger 19. The heat exchanger 19 receives a secondary liquid coolant (typically water or water-based) and transfers heat from the liquid coolant within the container 110 to this secondary liquid coolant. The secondary liquid coolant is provided to and emerges from the heat exchanger 19 via interface connections 18. The pumps 11 cause the cooled primary liquid coolant to exit the heat exchanger 19 through pipes 5 and emerge through nozzles 2. The pipes 5 and the nozzles 2 are positioned to cause coolant to flow directly onto the heat sinks 1.

The cooling module 100 is typically a rack-mounted module and the electronic components within the container 110 are preferably at least part of a computer server circuitry, for instance comprising a motherboard and associated components. The cooling module may therefore have a height of 1 rack unit (1U, corresponding with 44.45mm) or an integer number of rack units. The cooling module 100 may be configured for installation or installed in a corresponding rack, housing multiple such cooling modules (one, some or all of which may have different internal construction from cooling module 100 disclosed herein). In this configuration, the secondary liquid coolant may be shared between cooling modules in a series or parallel arrangement. A plenum chamber and/or manifold may be provided in the rack to allow this. Other components may be provided in the rack for efficient and safe (such as power regulators, one or more pumps or similar devices).

Referring to Figure 3, there is illustrated a first embodiment of a heat sink in accordance with the disclosure. With reference to Figure 4, there is shown an exploded view of the embodiment of Figure 3. This is a magnified view of the heat sink shown in Figures 1 and 2. The heat sink 1 comprises: a base made up of a mount 16 and a planar substrate 17 fixed to the mount 16; a retaining wall 7 attached to the planar substrate 17; projections (shown in the form of pins) 6; and fixing screws 13, which attach the substrate 17 to the mount 16. In this way, the planar substrate 17 sits directly on the high temperature component 12 and transfers heat from the high temperature component 12 to a volume defined by the planar substrate 17 and the retaining wall 7, in which projections 6 are provided.

The heat sink 1 can be made from a single component, for example by: die cast; lost wax casting; metal injection mould (MIM); additive manufacture; or forged. It could also be machined out of a block of material or skived. The heat sink 1 may be formed from

-7 any material that is thermally conductive, such a metal or other thermal conductor. Some examples may include aluminium, copper or carbon.

Also shown in Figures 3 and 4 are pipe 5 and nozzle 2. The liquid coolant is delivered to the heat sink 1 via the nozzle 2. The nozzle 2 is arranged to direct coolant perpendicular to the plane of the substrate 17. This forces the jet or flow of the liquid coolant directly into the volume defined by the substrate 17 and retaining wall 7 of the heat sink 1. As a consequence, the heat dissipation is improved. This is especially the case in comparison with a system where the coolant is directed to flow over the heat sink, in a direction parallel to the plane of the heat sink substrate, such as in an air cooled system.

In the examples shown in Figures 3 and 4, the nozzle 2 delivers the coolant directly in the centre of the volume defined by substrate 17 and retaining wall 7. In this example, the centre of that volume corresponds with the hottest part of the area of the substrate 17, which is adjacent to (and directly on) the high temperature component 12. This provides a contraflow, such that the coldest coolant is directed to contact the hottest area of the heat sink. The coolant moves out radially from the hottest part.

The nozzle 2 is designed to have a push-fit connection 3 to the pipe 5. This does not require tools, so it can be fitted and removed straightforwardly. Consequently, replacing circuit boards 15, which may be computer motherboards, all the components can be easy and quick. The nozzle is further provided with an earth point 4, which can be coupled to an earth or ground point, to eliminate static build up in the pipe 5 and nozzle 2.

With reference to Figure 5, there is shown a cross-sectional view of the heat sink in Figure 3 in operation. The same features as shown in previous drawings are identified by identical reference numerals. Arrow indicate the flow of coolant within the pipe 5, to provide coolant 8 within the volume defined by the substrate 17 and retaining wall 7 of heat sink 1 and coolant 9 outside the heat sink 1. As indicated previously, coolant emerging from nozzle 2 is directed towards the centre of the volume (corresponding with the centre of the surface area of substrate 17) and from there moves out radially towards the retaining wall 7. Sufficient coolant is pumped via nozzle 2 into the volume, such that it overflows the retaining wall 7 and collects with remaining coolant 9 exterior to heat sink 1.

The retaining wall 7 acting as a side wall enables different levels of coolant. The coolant 8 within the volume of the heat sink 1 is at a relatively high level and the coolant 9, which at least partially immerses the low temperature components 10 (not shown in this drawing), is at a lower level. This allows significantly less liquid coolant to be used than in other similar systems that cover all components at the same height.

-8A number of benefits are thereby realised. Firstly, since less dielectric coolant is being used and this coolant can be expensive, costs can be significantly reduced. Dielectric liquid coolants are typically very heavy. By using less liquid coolant, the cooling module 100 can be more straightforward to install and/or lift. Also, installing the cooling module 100 can require less infrastructure. In addition, the cooling module 100 is easier to handle than similar devices are systems using significantly more primary liquid coolant. The level of the primary liquid coolant 9 within the majority of the container 110 is not close to the top of the container. As a result, spillages during maintenance or exchange of components are less likely. The risk of leakage is also reduced.

The retaining wall 7 creates a weir effect. The coolant 9 at a relatively low level cools the low temperature components 10 that, in the absence of a liquid coolant, would usually be cooled by air. It is not necessary for low temperature components 10 to be fully immersed in liquid coolant.

A further advantage of the volume bound by the substrate 17 and retaining wall 7 is temporary cooling redundancy. If the pump 11 or another component critical to the flow of liquid coolant, breaks down there is a volume of coolant trapped in the volume of heat sink 1. This coolant is sufficient to continue cooling the high temperature component 12, at least for a short time. This will counteract and potentially prevent instant temperature changes on high temperature component 12, thereby reducing show and giving time for these components to shut down.

An aspect of the invention will now be discussed in more general terms. For example, there may be considered a heat sink for an electronic device immersed in a liquid coolant, comprising: a base, configured for mounting on top of a heat-transmitting surface of the electronic device and transferring heat from the heat-transmitting surface; and a retaining wall extending from the base. In particular, the base and retaining wall define a volume for holding some of the liquid coolant, such that heat transferred through the base is transferred to the liquid coolant held in the volume. The volume advantageously allows retains heat adjacent the heat-transmitting surface.

Less dielectric coolant may be used than in existing cooling systems or modules. The base and retaining wall are preferably arranged such that a level of liquid coolant held within the volume is higher than a level of coolant external the volume. For example, this may be implemented by the base comprising a mount, which may cause the volume to be raised above a bottom of the base. The base may further comprise a substrate integral with or attached to the mount, defining a part of the volume. The base and the retaining wall can be separate parts or integral.

-9In the preferred embodiment, a surface of the base defining the volume (such a substrate part of the base) is planar or essentially or substantially planar.

Advantageously, projections extend from the base and/or retaining wall within the volume. In particular, the projections may extend to substantially the same distance from the base (in a direction perpendicular from a plane of the base) as the retaining wall. The projections may comprise pins and/or fins. The projections preferably extend in a direction perpendicular to a plane of the base (the projections are beneficially straight). In particular, the projections may be arranged to cause the liquid coolant to spread in a radial direction away from a predetermined point on a surface of the base (such as a point coincident with or adjacent to a hottest part of the electronic device). The projections are preferably formed in a non-linear pattern. This may allow the coolant to disperse radially from the predetermined point.

In another aspect, there is provided a (sealable) cooling module for an electronic device, comprising: a container, housing the electronic device such that the electronic device can be at least partially immersed in a liquid coolant; and the heat sink as herein described, mounted on the electronic device. The cooling module may further comprise the liquid coolant. The liquid coolant is advantageously a dielectric. It is beneficially thermally conductive and electrically insulating.

The cooling module may be further configured to cause the liquid coolant to flow within the container. In particular, the cooling module may further comprise: a pump for causing the liquid coolant to flow within the container. Additionally or alternatively, the configuration of the cooling module may cause the liquid coolant to flow within the container (for example, by allowing or encouraging convection of the liquid coolant). In any case, the liquid coolant may be a primary coolant. The cooling module may comprise a heat exchanger, configured to receive a secondary liquid coolant and to transfer heat from the primary liquid coolant to the secondary liquid coolant. The heat exchanger is preferably inside the container. The pump may be configured to cause the liquid coolant to flow to and/or from the heat exchanger. Multiple such heat exchangers may optionally be provided.

Beneficially, the cooling module may additionally comprise a nozzle arrangement, arranged to receive flowing or pumped liquid coolant and direct it to the volume of the heat sink. The nozzle arrangement may be arranged to direct the flowing or pumped liquid coolant to a part of the base of the heat sink and/or a part of the volume of the heat sink adjacent the hottest part of the heat-transmitting surface of the electronic device. The

- 10nozzle arrangement is advantageously arranged to direct the flowing or pumped liquid coolant in a direction perpendicular to the base of the heat sink.

The nozzle arrangement preferably comprises one or more nozzles. Each of the one or more nozzles may be configured to direct the flowing or pumped liquid coolant to a respective part of the volume of the heat sink. In some embodiments, the nozzle arrangement comprises a plurality of nozzles. Then, each nozzle may be configured to direct the flowing or pumped liquid coolant to a respective part of the volume of the heat sink adjacent a part of the heat-transmitting surface of the electronic device having a temperature above a threshold level. The threshold level may be set based on the temperature of the hottest part of the heat-transmitting surface of the electronic device, for example based on a percentage or in order to cool a certain number of hottest areas of the heat-transmitting surface.

The cooling module may further comprise at least one pipe, arranged to transport liquid coolant (preferably from the pump, where one is provided) to the nozzle arrangement. Each of the one or more nozzles may then be configured to couple to a respective end of the at least one pipe. Preferably, the coupling is by push-fit. In other words, each nozzle may be push-fit coupled to a respective pipe end.

Referring next to Figure 6, there is shown a top view of the embodiment of Figure 3, showing a nozzle arrangement. As previously discussed, the nozzle 2 (of which the pushfit connection 3 can be seen) coupled to pipe 5. The nozzle 2 is positioned to face the centre of the surface area of the substrate 17 (not shown in this drawing). The radial flow of coolant is shown by arrows in this drawing.

Alternative positions for the nozzle 2 are possible. Some such positions will now be described with reference to Figure 7, in which there is shown a top view of the first variant of the nozzle arrangement of the embodiment of Figure 3 and with reference to Figure 8, in which there is shown a top view of a second variant of the nozzle arrangement of the embodiment of Figure 3. Referring first to Figure 7, the nozzle 2 is shown off-centre. Such an arrangement may be provided if the hottest part of the temperature component 12 is not adjacent the centre of the substrate 17. Referring to Figure 8, two nozzles are shown. The two nozzles 2 are positioned over the surface area of the substrate 17 (not shown) adjacent two of the hottest parts of the high temperature component 12 (not shown) below.

Another generalised aspect of the present disclosure will now be discussed, in which there is provided a cooling module, comprising: a container, housing an electronic device for cooling, such that the electronic device can be at least partially immersed in a liquid coolant; a heat sink, comprising a base mounted on the electronic device; and a nozzle arrangement, arranged to receive liquid coolant and direct it to the base of the heat sink. In particular, the nozzle arrangement may be arranged to direct the received liquid coolant to the heat sink in a direction perpendicular to the base. In some embodiments, the he nozzle arrangement may be arranged to direct the received liquid coolant to the base of the heat sink via an internal (reservoir) volume of the heat sink. Directing the flow of liquid coolant in these ways may promote cooling of the electronic device via the heat sink, since colder liquid coolant may be directed to the hottest parts in an efficient way.

Advantageously, the liquid coolant is caused to flow within the container. In some embodiments, the cooling module further comprises a pump for causing the liquid coolant to flow within the container. The nozzle arrangement may be arranged to receive flowing or pumped liquid coolant. The nozzle arrangement may allow the delivery of coolant directly to the hottest part of the heat sink and thereby may provide a contraflow.

Advantageously, the nozzle arrangement is arranged to direct the flowing or pumped liquid coolant to a part of the heat sink adjacent the hottest part of the electronic device. The nozzle arrangement beneficially comprises one or more nozzles. Then, each of the one or more nozzles may be configured to direct the flowing or pumped liquid coolant to a respective part of the heat sink. In some embodiments, the nozzle arrangement comprises a plurality of nozzles. Then, each nozzle may be configured to direct the flowing or pumped liquid coolant to a respective part of the heat sink adjacent a part of the electronic device having a temperature above a threshold level. The threshold level may be set based on the temperature of the hottest part of the electronic device, for example based on a percentage or in order to cool a certain number of hottest areas of the electronic device.

In the preferred embodiment, the cooling module further comprises: at least one pipe, arranged to transport liquid coolant (preferably from the pump, where one is provided) to the nozzle arrangement. Each of the one or more nozzles may then be configured to couple to a respective end of the at least one pipe. Preferably, the coupling is by push-fit. In other words, each nozzle may be push-fit coupled to a respective pipe end.

The heat sink of this aspect may be the heat sink of the other aspect described above. For example, the base of the heat sink may be configured for mounting on top of a heat-transmitting surface of the electronic device and transferring heat from the heattransmitting surface. The heat sink may further comprise: a retaining wall extending from the base, the base and retaining wall defining a volume for holding some of the liquid coolant, such that heat transferred through the base is transferred to the liquid coolant held in the volume. The base and retaining wall may be arranged such that a level of liquid coolant held within the volume is higher than a level of coolant external the volume. A surface of the base defining the volume is planar. The heat sink volume may be configured such that coolant received in the volume from the nozzle arrangement moves out radially from the part of the volume at which the coolant is received. The heat sink may further comprise projections extending from the base and/or retaining wall within the volume. Preferably, the projections extend to substantially the same distance from the base as the retaining wall. The projections advantageously comprise pins and/or fins. In embodiments, the projections extend in a direction perpendicular to a plane of the base. The projections may be arranged to cause the liquid coolant to spread in a radial direction away from a predetermined point on a surface of the base (such as the hottest part). For instance, they may be formed in a non-linear pattern.

The liquid coolant may be a primary liquid coolant. Then, the cooling module may further comprise: a heat exchanger, configured to receive a secondary liquid coolant and to transfer heat from the primary liquid coolant to the secondary liquid coolant. The pump may be configured to cause the liquid coolant to flow to and/or from the heat exchanger. The nozzle arrangement is advantageously arranged to receive the primary liquid coolant from the heat exchanger. In this way, the coolant directed by the nozzle arrangement to the heat sink may be the coldest coolant. Then, it may beneficially be directed to the hottest part of the heat sink.

The projections 6 (as pin and/or fins) could integrally formed with the rest of heat sink 1 or be made from separate components from the remainder of the heat sink 1. The projections 6 could be tolerance fit, glued or brazed in place. Additionally or alternatively, the retaining wall 7 could be integrally formed or made separately from the rest of the heat sink 1, for example by an extrusion or fabricated sheet metal part. Then, the retaining wall 7 could be tolerance fit, glued in place, brazed or welded.

With reference to Figure 9, there is depicted an expanded top view of part of the embodiment of Figure 3, showing a projection arrangement. As can be seen in this embodiment, the projections 6 are regularly spaced pins.

Although the projections 6 have been shown as pins, other arrangements may be possible and indeed, advantageous. The projections 6 can be fins or a combination of pins and fins. A number of such variants will now be described. For example, the pins and/or fins can be arranged non-linearly (not in straight lines). This may improve the radial flow of coolant. The variants now described are examples of possible alternative implementations, but further options will readily be considered by the skilled person.

- 13With reference to Figure 10, there is depicted a top view of a first variant of the projection arrangement of the embodiment of Figure 3. Here, the projections comprise pins 6 and fins 6’ arranged in a spiral design. These projections again promote radial flow of liquid coolant.

With reference to Figure 11, there is depicted a top view of a second variant of the projection arrangement of the embodiment of Figure 3. The projections comprise pins 6 and fins 6”, arranged in a ‘spider’ design. Like previous designs this further encouraged radial flow.

With reference to Figure 12, there is depicted a top view of a third variant of the projection arrangement of the embodiment of Figure 3, in which the projections comprise pins 6 and pin-fins 6”’. These are arranged in a ‘burst’ design, which likewise promotes radial flow.

Referring next to Figure 13, there is illustrated a cross-sectional view of a part of the heat sink of Figure 3, showing a height of the projection arrangement. As can be seen here, the pins 6 are flush with the height of the retaining wall 7. This has a number of benefits. The retaining wall 7 can ensure that all of the projections 6 are fully wetted. In other words, it is intended that all of the projections 6 (whether pins, fins or a combination thereof) are submerged in coolant 8. This can help to ensure that every possible surface is being used for heat dissipation. Moreover, the coolant cannot bypass or short-cut over the projections 6, since they are the same height as the retaining wall 7. Such designs may be possible however the formation of the projections 6, which need not be as pins shown in Figure 13.

With reference now to Figure 14, there is illustrated a cross-sectional view of the first variant of the projection arrangement height of the embodiment of Figure 3. In this, the projections 6a are at a lower height than the retaining wall 7. This maintains the benefit of projections that are fully wetted, but without the benefit that coolant can bypass the projections. With reference to Figure 15, there is illustrated a cross-sectional view of a second variant of the projection arrangement height of the embodiment of Figure 3, in which the projections 6b are higher than the height of the retaining wall 7. This maintains the benefit that the coolant cannot bypass the projection 6b, but does not benefit from all of the projection 6b being fully wetted.

Reference is again made to Figures 1 and 2. Another part of the cooling module 100 (as shown most clearly in Figure 1) will now be discussed. In the centre of the container 110 sits an electronic device 24. This is typically a power supply. It sits within a separate portion of the container 110 base area from the circuit boards 15, bounded by a

- 14retaining wall 27. With reference now to Figure 16, there is depicted a cross-sectional view of a second embodiment of a heat sink in accordance with the disclosure, which corresponds with a variant of the electronic device 24 and retaining wall 27 shown in Figure 1. Figure 17 shows a perspective view of the heat sink of Figure 16. Figure 17 shows a perspective view of the heat sink of Figure 16.

In this embodiment, a heat sink 20 is provided upon a base 120 of the container 110. The heat sink 20 comprises a base 21 and a retaining wall 27. The electronic device, such as power supply 24, sits on the base 21 of the heat sink 20, within a volume (an internal volume) defined by the base 21 and retaining wall 27. The construction process and/or materials of the heat sink 20 may be equivalent or similar to that used in respect of the previously described heat sink 1.

Coolant is piped into this volume by means of pipe 22. As shown in Figure 16, this coolant flows directly from the end of the tube into a lower portion of the volume defined by base 21 and retaining wall 27. The electronic device 24 is shown as being fully submerged within the coolant. However, it may only be partially submerged depending on the most efficient scenario in terms of heat extraction and volume of coolant.

As with other embodiments in the disclosure, the coolant can flow over the retaining wall 27 allowing for multiple levels of cooling. The same benefits as identified above for this feature equally apply to this embodiment. Moreover, this can provide two levels of cooling, in which low temperature components 10 are cooled by a layer level of coolant than a level of coolant within the volume of the heat sink 20. The benefit of temporary cooling redundancy is also provided.

A cut out 25 is used to create a spout at the other end of the volume from the coolant inlet tube 22. This can give a direction to the flow of coolant and ensure that components are not sat in stagnant coolant as the colder coolant is pumped straight over the side walls.

With reference to Figure 18, there is illustrated an exploded perspective view of a variant of the embodiment of Figure 16 and 17. In this embodiment, the heat sink 20’ includes a volume defined by a base 21 and a retaining wall 27. An electronic device 24 is provided inside this volume. Coolant is delivered to the volume through pipe 22. However, rather than providing this coolant toward a lower portion of the volume, it is provided in an upper portion of the volume via a nozzle attachment 23. This may better control the direction of the coolant flow. A spout 25 at the other end of the volume from the coolant inlet tube 22 may again give direction to the flow of coolant. The other advantages associated with the spout 25 are also provided in this variant. With reference to Figure 19,

- 15there is shown the exploded view of Figure 18 with a nozzle part 3 removed. The nozzle need not be provided and coolant may flow directly from the end of the tube.

Referring to Figure 20, there is depicted a perspective view of a third embodiment of a heat sink in accordance with the disclosure. This is similar to the second embodiment in that it comprises a base 31 and a retaining wall 37 to define a volume in which electronic devices 34 are provided. Coolant arrives in the volume via a pipe 32 and a spout 35 is provided at the other end of the volume from the pipe 32 for coolant to flow.

Figure 21 illustrates an exploded perspective view of a variant of the embodiment shown in Figure 20. Where the same features are shown, identical reference numerals are used. In this variant, the pipe 32 is provided with a nozzle attachment 33 and coolant is provided to an upper part of the volume defined by the base 31 and retaining wall 37. There will be a further variant of this provided, in which the nozzle attachment 33 is omitted.

A further generalised aspect of the present disclosure will now be considered. There may be provided a heat sink for an electronic device located in a cooling module and immersed in a liquid coolant. The heat sink has a wall arrangement to define an internal volume, in which the electronic device is mounted and in which the liquid coolant accumulates around the electronic device in operation, such that heat is transferred from the electronic device to the liquid coolant held in the internal volume. Optionally, the electronic device may further be provided, mounted within the internal volume. In the preferred embodiment, the electronic device is a power supply unit.

Typically, the wall arrangement comprises: a base, configured for mounting the heat sink within the cooling module; and a retaining wall extending from the base, the base and retaining wall defining the internal volume for accumulating the liquid coolant. The wall arrangement may therefore define an open-topped (or partially enclosed) cuboid-shaped or prism-shaped structure. In particular, the base or a surface of the base defining the internal volume is planar. In this way, the surface of the base may lie flat against a surface of a container in which the heat sink is mounted. A planar base surface may also allow the electronic device to lie flat against the base within the internal volume, especially if the electronic device also has a planar surface on which it is mounted.

As described with respect to other aspects or embodiments of the disclosure, the wall arrangement is beneficially arranged such that a level of liquid coolant held within the internal volume is higher than a level of coolant external the internal volume. The advantages (and optionally, the implementation) of this are generally the same as for the other embodiments or aspects.

- 16In the preferred embodiment, the wall arrangement further defines a spout. This may to allow the liquid coolant to flow out of the internal volume. It may also (at least partially) define the flow of liquid coolant through and/or within the internal volume of the heat sink. The spout may be a cut-out in the wall arrangement or retaining wall, for instance.

In addition, there may considered a cooling module for an electronic device, comprising: a container, for housing the electronic device such that the electronic device can be at least partially immersed in a liquid coolant; and the heat sink as described herein with reference to this aspect. The cooling module may be further configured for causing the liquid coolant to flow within the container, in particular by comprising a pump (although alternatives as discussed elsewhere herein may be used instead). In addition, the cooling module may comprise at least one pipe, arranged to receive pumped liquid coolant and having an outlet, from which the flowing or pumped liquid coolant is directed into the internal volume of the heat sink.

The internal volume may be elongated in shape (for example having a rectangular profile). First and second end portions at opposite extremities of the elongated internal volume may thereby be defined. Then, the outlet of the pipe is preferably located at the first end portion and the spout is preferably located at the second end portion. This may promote the flow of liquid coolant along the elongated dimension of the internal volume, to allow more efficient contact with the electronic device.

In some embodiments, the outlet is located in an upper half of a height of the internal volume (in other words, a top half of the internal volume). This may direct the flow of liquid coolant better than if the outlet is located in a lower half. In other embodiments, the outlet is located in a lower half of a height of the internal volume. This may improve efficiency compared with providing the outlet in an upper half, since the coolest coolant may have longer contact with the electronic device. In less preferred embodiments, the outlet is located around halfway of the height of the internal volume.

The outlet of the pipe may comprise one or more nozzles, each nozzle being configured to direct the flowing or pumped liquid coolant to a respective part of the internal volume. For example, this arrangement may resemble (and/or be implemented similarly to) that described with respect to other embodiments or aspects of the disclosure. For instance, each of the one or more nozzles may be configured to push fit couple to a respective end of the at least one pipe.

The liquid coolant is advantageously a primary liquid coolant. Then, the cooling module may further comprise a heat exchanger, configured to receive a secondary liquid

- 17coolant and to transfer heat from the primary liquid coolant to the secondary liquid coolant. Details of the primary and secondary liquid coolants have been discussed above, with reference to other aspects. The pump may be configured to cause the liquid coolant to flow to and/or from the heat exchanger. The one or more nozzles are preferably arranged to receive the primary liquid coolant from the heat exchanger.

Although specific embodiments have now been described, the skilled person will appreciate that various modifications and alternations are possible. The design of the container 110 may be different in shape and/or structure, from that indicated (for example, it may not be cuboid). Any of the thermally conductive parts of the design disclosed herein may be formed using any thermally conductive material, such as copper or aluminium. Different plantings or coatings could be used to improve thermal performance such a gold plating. Different material constructions could be used such as laser sintered, honey cone or foams to increase the surface area.

With reference to the heat sink 1, the base structure may be different. For example, mount 16 may be provided in a different way. Substrate 17 need not be planar. Alternatives to fixing screws 13 may be considered, such as adhesive, rivets or other attachments forms. Retaining wall 17, 37 may be provided as a single (integral) wall or multiple walls. The shape and/or size of retaining wall 17, 37 may also be adjusted.

The design of heat sink 20 may also be varied, with different shapes, sizes and/or implementations. For instance, it may be formed using multiple retaining walls and/or with a non-planar base. The base 120 and retaining wall 27 (or variants thereof) may be integral or separate components. It is typical for electronic devices or components, such as high temperature component 12 and electronic device 24 to have at least one (or some or all) planar surfaces, especially the surface on or to which the heat sink is mounted, placed or fixed (an attachment surface). However, the aspects of the disclosure can readily be adapted to be used with electronic devices and/or components that do not have planar surfaces. For example, the attachment surface can have bumps, be curved, comprise points (for example, shaped as a triangle or other polygonal shape).

Alternative electronic devices from those shown as high temperature component 12 and/or electronic device 24 may be used, for example having different shapes, structures or applications. In some embodiments, no low temperature component 10 may be provided and/or there may be a different design of (or indeed, no) circuit board 15. The layout of circuit boards 15 and/or components may be varied significantly. For instance, the position of electronic device 24 may be different from that shown.

- 18Flow of liquid coolant within the container is preferably achieved using pumps 11. However, there may be more or fewer pumps than shown and indeed, only pump may be provided in some embodiments. Alternatively, the flow of liquid coolant may be achieved and/or encouraged without any pumps. For example, this is possible if the configuration of the container 110 and/or the liquid coolant permits flow of liquid coolant in some other way. One approach is to use the natural consequence of operation of the cooling module: when the electronic components and/or devices are operative, they cause the liquid coolant to heat and convect. Convection of the liquid coolant will cause it to flow. Suitable orientation or design of the container 110 may allow the convective flow of liquid coolant to circulate within the container 110. The flow of liquid coolant may then be further encouraged by baffle plates or other suitable constructions within the container 110. Other designs causing the liquid coolant to flow will also be suitable.

All of the features disclosed herein may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. In particular, the preferred features of each aspect of the disclosure are generally applicable to all aspects of the disclosure and the features of all of the aspects may be used in any combination. Likewise, features described in non-essential combinations may be used separately (not in combination).

A method of manufacturing and/or operating any of the devices disclosed herein is also provided. The method may comprise steps of providing each of features disclosed and/or configuring the respective feature for its stated function.

Claims

1. A heat sink for an electronic device immersed in a liquid coolant, comprising:

a base, configured for mounting on top of a heat-transmitting surface of the electronic device and transferring heat from the heat-transmitting surface; and a retaining wall extending from the base, the base and retaining wall defining a volume for holding some of the liquid coolant, such that heat transferred through the base is transferred to the liquid coolant held in the volume.

2. The heat sink of claim 1, wherein the base and retaining wall are arranged such that a level of liquid coolant held within the volume is higher than a level of coolant external the volume.

3. The heat sink of claim 1 or claim 2, wherein a surface of the base defining the volume is planar.

4. The heat sink of any preceding claim, further comprising projections extending from the base and/or retaining wall within the volume.

5. The heat sink of claim 4, wherein the projections extend to substantially the same distance from the base as the retaining wall.

6. The heat sink of claim 4 or claim 5, wherein the projections comprise pins and/or fins.

7. The heat sink of any one of claims 4 to 6, wherein the projections extend in a direction perpendicular to a plane of the base.

8. The heat sink of any one of claims 4 to 7, wherein the projections are arranged to cause the liquid coolant to spread in a radial direction away from a predetermined point on a surface of the base.

9. The heat sink of any one of claims 4 to 8, wherein the projections are arranged in a non-linear pattern.

10. A cooling module for an electronic device, comprising:

a container, housing the electronic device such that the electronic device can be at least partially immersed in a liquid coolant; and the heat sink of any preceding claim, mounted on the electronic device.

11. The cooling module of claim 10, further configured to cause the liquid coolant to flow within the container and further comprising:

a nozzle arrangement, arranged to receive flowing liquid coolant and direct it to the volume of the heat sink.

12. The cooling module of claim 11, wherein the nozzle arrangement is arranged to direct the flowing liquid coolant to a part of the volume of the heat sink adjacent the hottest part of the heat-transmitting surface of the electronic device.

13. The cooling module of claim 11 or claim 12, wherein the nozzle arrangement comprises one or more nozzles, each of the one or more nozzles being configured to direct the flowing liquid coolant to a respective part of the volume of the heat sink.

14. The cooling module of claim 13, wherein the nozzle arrangement comprises a plurality of nozzles, each nozzle being configured to direct the flowing liquid coolant to a respective part of the volume of the heat sink adjacent a part of the heat-transmitting surface of the electronic device having a temperature above a threshold level.

15. The cooling module of claim 13 or claim 14, further comprising:

a pump configured to cause the liquid coolant to flow within the container.

at least one pipe, arranged to transport liquid coolant from the pump to the nozzle arrangement; and wherein each of the one or more nozzles is configured to push fit couple to a respective end of the at least one pipe.

16. The cooling module of any one of claims 11 to 15, wherein the nozzle arrangement is arranged to direct the flowing liquid coolant in a direction perpendicular to the base of the heat sink.