WO2018025016A1

WO2018025016A1 - Thermal interface for modular immersion cooling of electronic components

Info

Publication number: WO2018025016A1
Application number: PCT/GB2017/052208
Authority: WO
Inventors: Peter Hopton; Keith Deakin
Original assignee: Iceotope Limited; Kahn, Simon
Priority date: 2016-08-01
Filing date: 2017-07-28
Publication date: 2018-02-08
Also published as: GB201613234D0

Abstract

A module for immersion cooling of one or more electronic components comprises: a housing, defining a sealable volume, configured to contain the one or more electronic components immersed in a coolant liquid, the coolant liquid being for receiving heat generated by the one or more electronic components; and a first thermal interface, arranged to receive heat from the coolant liquid. The housing comprises a plurality of external walls, at least one of which is adapted to expand in use, so that the first thermal interface cooperates with a second thermal interface, external the module, to allow transfer of heat from the first thermal interface. A cooling system is also provided, comprising the module and a module receiving device.

Description

Thermal Interface for Modular Immersion Cooling of Electronic Components

Technical Field of the Invention

The invention concerns a module for immersion cooling of one or more electronic components, a corresponding module receiving device and cooling system comprising both. The one or more electronic components may include a computer processor or motherboard, for example. A method of operating a cooling system is further provided.

Background to the Invention

Electronic components generate heat in operation, which can lead to overheating and consequent damage to the component and other parts of the system. Such electronic components often include motherboards, central processing units (CPUs) and memory modules. It is therefore desirable to cool the component to transfer the heat away from it and maintain the component temperature no higher than the maximum operating temperature that is specified for correct and reliable operation of the component.

This issue especially concerns data processing of computer server centres, where a substantial number of computer processors are co-located and intended for reliable, continuous operation over a long time period. These centres may typically contain many server units, occupying multiple equipment racks and filling one or more rooms. Each server unit contains one or more server boards. A single server board can consume many of hundreds of watts of electrical power, much of which is dissipated as heat.

International patent publication number WO-2010/130993 and US patent publication number 2010/0290190 (both having inventorship in common with this invention) describe a cooling device that uses a sealable module for containing one or more heat generating electronic components, together with a liquid coolant in which the electronic components are immersed. In particular, the coolant in such embodiments is maintained substantially in liquid form, by preventing the coolant from boiling. This is achieved using a second liquid coolant, external the sealable module, which carries heat away from the module. There is therefore a first cooling stage, providing by the first liquid coolant within the module and a second cooling stage, provided by the second liquid coolant. Control of the second liquid coolant stage and/or provision of a third liquid coolant stage (receiving heat from the second liquid coolant) may allow thermal control of the first stage

accordingly. The interface between the first and second stages is provided as part of the module, using a heat exchanger in the form of a cold plate (a conduction surface), having a channel in which the second coolant liquid flows. In use, the module is housed in a rack or cabinet providing connections to corresponding sockets on the module, to allow the second liquid coolant to flow into and out of the module. The connections are designed for quick release, for instance using suitable valves. The modules are normally designed to be inserted and removed from the rack or cabinet (to allow for maintenance, repair and upgrade of the electronic components, for instance).

International patent publication number WO-2014/132085 describes improvements to this system, for instance in which multiple heat exchangers are provided within the module, to allow for redundancy. Should one of the heat exchangers fail, heat transfer from the first to second cooling stages can still be effected using another heat exchanger. The heat exchangers still form part of the module, in this case.

The connections providing the second liquid coolant to the module and carrying it away from the module are a potential failure point in such systems. Moving the heat exchanger out of the module may therefore improve the robustness and durability of the cooling system, but potentially at the expense of the thermal interface between the first and second cooling stages. A thermal bus may be used to provide the thermal interface between the module comprising the first cooling stage and a rack (or similar) having the second cooling stage.

Examples of such thermal buses are known in a variety of contexts and

implementations. For instance, US-6,804,1 17 discusses circuit cards inserted into a rack that mechanically clamps them to a thermal bus. A similar design is shown in

US-2014/036178, having a rack system that clamps a component to a fluid-cooled thermal bus bar. US-8,270,170 relates to a cold plate mounted on an electronic enclosure, in which electronic components are provided. US-7,071 ,408 provides a thermal bus using a planar heat pipe, receiving heat directly from the electronic components. US-6,393,853 describes metal electronics modules mounted between a pair of cooling plates that are pressed against the metal module walls using a mechanical mechanism.

Such existing designs generally do not concern a cooling system with a first liquid cooling stage, in which the electronic components are immersed in a liquid coolant.

Therefore, the challenges in carrying a second liquid coolant discussed above have not been considered. A module and corresponding cooling system design that addresses these issues would therefore be advantageous.

Summary of the Invention

Against this background, there is provided a module for immersion cooling of one or more electronic components in line with claim 1 , a cooling system in accordance with claim 26 and a method of operating a cooling system as defined in claim 42. Further features of the invention are detailed in the dependent claims. Features of the method corresponding with those of the module and/or system may additionally be provided.

A module for immersion cooling of one or electronic components is provided. In such a module, the electronic component or components are provided within a sealable volume, which in use, is immersed in a (liquid) coolant also contained by the volume when sealed. The coolant receives heat generated by the electronic component or components. The module is intended to couple to a second part (a docking device, rack or cabinet, for instance). In order to transfer heat from the coolant to the second part, the module has a first thermal interface (which may simply be a conductor or something more complex) and the second part has a second thermal interface for receiving heat from the first thermal interface. In effect, this may allow the second part to provide a thermal bus. Essentially, the module is allowed to expand in volume (in particular, at least one wall of the module expands), in order that when it is coupled to the second part, the first and second thermal interfaces cooperate (so as to allow the transfer of heat). Beneficially, the volume can contract to allow decoupling.

Advantageously, this allows the module to create a good thermal connection particularly by pressure to allow efficient transfer of heat, especially to a thermal bus provided by the second part. This approach is mechanical straightforward, cost effective and scalable. Moreover, the size of the module may be kept small, especially when not in use. Achieving a good thermal connection by pressure is of significant benefit, which may be enhanced by the use of thermally conductive materials and/or a flexible (or

concertinaed) material either as providing an external surface for the first thermal interface or as additional material sandwiched between two rigid materials forming the first and second thermal interfaces, to provide a thermal interface material (TIM). The TIM may comprise one or more of: silicone; viscous grease; a gel; a tape; a film; a coil or spring; a foam; a metal; and graphite. The TIM may be for one-time use and/or be in the form of a film or spots.

The expansion in volume can be caused by an increase in pressure within the sealable volume, for instance caused by heating of the coolant liquid (as might occur if the dimensions of the sealable volume and the quantity of coolant in it are set appropriately). This requires no additional new parts to the module, simply an adaptation of the module to manage the internal pressure by allowing volume expansion, in contrast with existing approaches. Then, a pressure release mechanism may allow decoupling. Additionally or alternatively, the volume expansion can be effected by an actuator, which may be mechanical (pneumatic, hydraulic actuator, lever, spring and cam, plunger, vacuum-based or tie rod) and/or magnetic.

The module can have an outer housing that is generally cuboid or having tapered sides (a trapezoidal prism), to increase the pressure between the walls of the module and those of the receiving second part, for instance.

The outer housing (or at least part) preferably provides the first thermal interface. More than one wall of the outer housing (and typically opposing walls) may provide some redundancy for this interface. Advantageously, the interface surface and/or an internal surface of the sealable volume has projections and/or grooves (in the form of pins, ribs, fins, dimples and/or spots, for example). The interface surface may also have a coating, which may improve thermal conduction, such as polymerized tetrafluoroethylene (known by the Trade Mark "Teflon"), carbon fibre, spray silicone, graphene, plastic, viscous grease, a gel and/or tape (which may be tear off or one-time use).

A cooling system may comprise a module as described herein together with a module receiving device (the second part). This beneficially provides a space to receive the module. It also provides the second thermal interface, such that insertion of the module into the space and expansion of its volume causes the first and second thermal interfaces to cooperate, for transfer of heat. The second thermal interface is preferably provided by one or more external walls of the receiving device, in particular those defining the space (such as a slot) for receiving the module. The external walls providing the interface may have a coating, for instance comprising a synthetic resin made by polymerizing

tetrafluoroethylene (Trade Mark "Teflon"), carbon fibre, spray silicone, graphene, plastic, viscous grease, a gel and/or tape. Additionally or alternatively, the interface external walls may have projections and/or grooves (in the form of pins, ribs, fins, dimples and/or spots, for example).

The external walls may form part of a cold plate (or multiple cold plates) in embodiments. Each cold plate comprises a channel, in which a second coolant liquid flows. In use, the second coolant liquid receives the heat. The channel may be formed of a semi-flexible material, a metallic material, a non-metallic material, a flexible tube and/or a carbon fibre pipe. In a particular embodiment, the channel is formed in the external wall and expansion of module volume causes the module (and particular its outer surface providing the thermal interface) to seal the channel, thereby allowing the second coolant to flow through the channel and receive it. Where multiple cold plates are provided (for example in opposing external walls defining the space for receiving the module), this may allow redundancy. The external walls may be fixed in place or moveable. For instance, opposing external walls defining the space may be moveable to reduce the size of the space. This may work together with expansion of the module volume to keep the module in place and/or improve pressure to allow better thermal connection.

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 a cross-sectional view of a cooling system in accordance with a first embodiment, comprising a module and a module receiving device;

Figure 2 shows a perspective view of the cooling system shown in Figure 1 ;

Figure 3 illustrates a functional view of the module and a module receiving device shown in Figure 1 , showing two variants in respect of the module;

Figure 4 depicts an exploded view of the module of Figure 1 ;

Figure 5 schematically shows a cross-section of part of the cooling system of Figure 1 in a first variant;

Figure 6 schematically shows a cross-section of part of the cooling system of Figure 1 in a second variant;

Figure 7 schematically shows a cross-section of part of the cooling system of Figure

1 in a third variant;

Figure 8 schematically shows a cross-section of part of a cooling system in accordance with a second embodiment;

Figure 9 schematically illustrates a cross-section of part of a cooling system in accordance with a third embodiment;

Figure 10 shows a perspective view of a cooling system in accordance with a fourth embodiment;

Figure 1 1 schematically shows a cross-section of part of a cooling system in accordance with a fifth embodiment;

Figure 12 depicts a perspective view of a cold plate for use in accordance with a sixth embodiment; and

Figure 13 schematically represents a cross-section of part of a cooling system in accordance with a seventh embodiment. Detailed Description of Preferred Embodiments

Referring first to Figures 1 and 2, there are shown a cross-sectional view and a perspective view respectively of a cooling system in accordance with a first embodiment. The cooling system comprises: a module 20; and a module receiving device 1 . The module 20 (which is commercially termed a "blade") has a housing 3 forming a sealed enclosure or volume 13 that includes one or more electrical components 4, mounted on a Printed Circuit Board (PCB) 2. The sealed volume 13 also holds a high thermal-expansivity dielectric primary coolant. Suitable materials for the primary coolant fluid 13 may include oils (for instance, either natural oils or synthetic oils) as well as fluorine based materials (such as fluoro-octane, hydrofluoroether, hydrofluorolefin, perfluoroketone and

perfluoropolyether). From within the module 20, the PCB 2 passes through a potting 10 and a seal collar with seal 9 in the housing 3 to connect via a connector 8 to a backplane PCB 12.

Two modules 20 are shown as 'docked' in the module receiving device 1 , which has side walls in the form of cold plates. These are formed with channels 1 1 to carry a secondary cooling liquid. In Figure 1 , only two cold plates 1 are shown, but it will be understood that each module 20 may interface with two cold plates 1 , one cold plate 1 on each side of the module 20. The cold plates are therefore provided in a redundant layout (A, B, A, B, etc.).

In operation, the electrical components 4 generate heat which is then passed to the primary coolant in the volume 13. As the primary coolant is heated, the pressure inside the sealed enclosure 13 increases. In turn, this increases pressure on the housing 3, which expands to press against the cold plate 1 and form a joint of increasing thermal conductivity. Pressure within the module 20 is managed through a pressure release area 7 which expands and contracts to fill with coolant to ensure the pressure remains within predetermined design limits. The pressure release area 7 is actuated upon by pulling a handle 6, thereby mechanically releasing pressure from the enclosure to enable the removal of the module 20. The design of the module 20 is for non-phase change cooling, such that the coolant in the sealed volume 13 does not boil and therefore remains substantially in liquid form. The details of this functionality may be found in WO- 2010/130993, for example.

Next referring to Figure 3, there is illustrated a functional view of the module 20 and a module receiving device 1 shown in Figure 1 . In this drawing, the module 20 is shown apart from the module receiving device 1 . Moreover, two variants of the module 20 are shown: in a first variant, module 20a has an outer housing 3a with a relatively smooth or flat surface; and in a second variant, module 20b has an outer housing 3b with a surface having fins and/or grooves 5. The fins and/or grooves 5 extend inside the housing 3b to increase the surface area of contact between the primary coolant and the housing 3b. Corresponding or matching grooves (not shown) are also provided on the module receiving device 1 for receiving the module 20b.

Referring now to Figure 4, there is depicted an exploded view of the module 20. The housing 3 has a side removed for clarity, to show the inside volume and the PCB 2 and the electronic components 4 in more detail. The relative dimensioning of the module 20 and/or the cold plate 1 1 (that is the shape and relative sizes of the sides) may be understood as being possible (and preferable) for most if not all variants and embodiments described herein. It should further be noted that, in these drawings (and all of those shown herein), other connections and components may be included. For example, input/output connections to the electronic component or components in the module may be provided.

A number of different implementations in accordance with this approach will now be discussed. Straightforward combinations of any of the variants or embodiments discussed below with each other and/or the embodiment as discussed above are also possible.

With reference to Figure 5, there is schematically shown a cross-section of part of the cooling system of Figure 1 in a first variant. The cooling system comprises: a module 100; and a cold plate 1 10. In fact, two cold plates 1 10 are shown, on two opposing sides of the module housing 121 and form part of a module receiving device, such as a dock, rack or cabinet. The details of the cold plate 1 10 are similar to those of the cold plate 1 1 , shown with reference to Figures 1 to 4. The module comprises: a housing 121 , formed of thin sheet metal; and heat-generating components 122, mounted on a PCB. The structure of the module 100, with the PCB (a substrate) fixed between two parts of a housing 121 (upper and lower parts) to seal the volume but the PCB extending (slightly) to outside the housing 121 , can also be seen. This type of structure may be implemented in a range of modules, not only those described herein with an expanding volume.

In operation, as the coolant is heated by components 122, the internal pressure of the module 100 increases. This causes an expansion force 123, increasing the volume of the module 100. The housing 121 is designed to direct force 123 as shown, so that the expansion is in the dimension between the cold plates 1 10. This is effected by the concertinaed shape of the sides of the housing 121 , as depicted.

Other implementations along these lines are possible and one such alternative is now discussed as a further example. Referring to Figure 6, there is schematically shown a cross-section of part of the cooling system of Figure 1 in a second variant. Again, the cooling system comprises cold plates 1 10, the details of which are as discussed above. The cooling system further comprises module 200, comprising: two heat-transfer plates 210; a flexible component 220; and a PCB 222 on which heat-generating components are mounted. The heat-transfer plates 210 and flexible component 220 together form the housing and the way that this housing packages the PCB 222 is similar to that shown in Figure 5 above. The housing construction is different from Figure 5, in that it is split into two parts (although in Figure 6, two heat transfer plates are in face shown). Each heat- transfer plate 210, made of metal has an internal surface with grooves, extending into the sealed volume. These are coupled to the flexible component 220, which is designed to extend when force 223 is caused (by expansion of the coolant in the volume).

Referring to Figure 7, there is schematically shown a cross-section of part of the cooling system of Figure 1 in a third variant, in particular showing how the pressure release area 7 of Figure 1 (or a similar pressure release mechanism, for example controlled by means of a valve) in a module 320 might be actuated by means of a handle 300. The action of pulling on the handle 300, in the direction as shown by the arrows, expands the end portion of the module 320 (shown here with a concertinaed wall, but any other variant may equivalently be used). This causes release of the pressure within the module 320 and allows its removal or extraction from the cold plate 1 10.

Although specific embodiments have now been described, the skilled person will appreciate that various modifications and alternations are possible. For instance, a number of alternative ways to implement module expansion and/or contraction may be considered. In one option, an electromechanical implementation may be used to cause expansion and/or contraction of the module side (or sides) or dimensions, so as to provide an electrically controlled "muscle" or clenching means. This may use a piezoelectric material. In another approach, a pneumatic means may be used to mechanically pressurise and/or depressurise (or re-pressurise) the module internal volume and change its external dimensions thereby. A control valve may be used to adjust the pressure accordingly. A hydraulic mechanical approach may also be considered for module expansion and/or contraction, to create a "piston" type arrangement. A diaphragm may be employed to control the hydraulic system in this case.

An additional thermal interface material (TIM) may be provided on the module outer surface, the cold plate (module receiving device) outer surface, both or as a further additional material provided between the module and the cold plate. The TIM may be provided to aid thermal conduction, mitigate damage due to friction between the module and cold plate (for example when the module is removed from the cold plate), to provide electrical insulation between the module and cold plate or a combination of these features. The TIM need not be an electrical insulator. In preferred embodiment, the cold plates and/or module housing would be earth-bonded. The TIM may be different between the module and the cold plate. Additionally or alternatively, the TIM used in conjunction with two opposing sides of the module may be different between the sides. Two or more types of TIM might be used in practice. A PTFE material may be a possible TIM, especially to mitigate friction.

A coating on one or (preferably) both surfaces may be provided as a simple TIM. Although such a coating may be applied in a permanent way to the surface or surfaces of the module and/or cold plate, a one-time usage or degradable coating may be applied, for application on each insertion of the module. This may be in the form or a grease, gel or tape. The coating may be adhered to the surface as the module and cold plate interface. Other forms of TIM may include one or more of: indium micro springs; and a wire wool with a soft filler (for instance, formed using metal foam) to form a soft compressible material with advantageous thermal properties.

Moreover, the principle of this approach may be applied to phase-change cooling as well, where the coolant substantially boils in use. In such an approach, expansion of the volume is more likely. Nevertheless, greater benefits apply to non-phase change cooling, in which the coolant remains in liquid form in use and normally, expansion of the sealed volume would be seen as a difficulty rather than the benefit it is shown to be in this case. Further variants will be discussed below in more general terms, followed by further specific examples.

In one aspect, the invention can be summarised in more general terms as a module for immersion cooling of one or more electronic components. The module comprises a housing, defining a sealable volume, configured to contain the one or more electronic components immersed in a coolant liquid. Advantageously, the coolant liquid is for (typically, configured for) receiving heat generated by the one or more electronic components. The module preferably further comprises a first thermal interface, arranged to receive heat from the coolant liquid. Beneficially, the housing comprises a plurality of external walls, at least one (and possibly more than one) of which is adapted to expand in use. In another sense, the housing may be configured to expand its external volume in at least one dimension. In any such way, the first thermal interface can cooperate with a second thermal interface, external the module, to allow transfer of heat from the first thermal interface. In another (but associated) general sense, there is provided a method of operating a cooling system having method steps corresponding with the operational configuration of a module and/or a cooling system described herein. For instance, such a method may comprise: providing a module having a housing defining a sealable volume, one or more electronic components immersed in a coolant liquid being located within the sealable volume, wherein the housing comprises a plurality of external walls; operating the one or more electronic components such that the one or more electronic components generate heat, the heat being received by the coolant liquid; transferring heat from the coolant liquid to a first thermal interface; and expanding at least one of the plurality of external walls, so that the first thermal interface cooperates with a second thermal interface, external the module, to allow transfer of heat from the first thermal interface. In a further aspect, a corresponding method of manufacturing a module, module receiving device or cooling system may be considered. Further method steps corresponding with any functional configurations of an apparatus features may optionally be provided in relation to either or both method aspects. Some such optional, preferable and/or advantageous features are now discussed with reference to the module and cooling system and others are found throughout this description.

Preferably, the module further comprises one or both of: the one or more electronic components, mounted in the sealable volume; and the coolant liquid, immersing the one or more electronic components within the sealable volume. Typically, the sealable volume is sealed to contain the coolant liquid. Optionally, at least one (and possibly more than one) of the plurality of external walls is configured to contract, to allow decoupling of the first thermal interface and the second thermal interface. This may be same wall or walls as are configured to expand, or different walls. In the preferred embodiment, the housing is generally cuboid in shape. The one or more electronic components may be mounted on a circuit board, which may be generally rectangular and/or elongated in shape. The module housing may be shaped and/or dimensioned in accordance with the circuit board.

As described above, the housing may be formed from a metal, such as aluminium, sheet steel, copper, as sheet, pressed tray or machined. It may also (or alternatively) be formed from a flexible and/or concertinaed material. This may allow expansion.

Additionally or alternatively, the housing comprises (or is formed from) one or more of: a conductive plastic; silicone (framed balloon); carbon (graphite and/or carbon fibre); material additives; kevlar; mylar; and polyurethane (PU). In embodiments, the housing may comprise one or more of: silicone flex; a (metal) spring; and bellows. In the preferred embodiment, at least one of the plurality of external walls is configured to expand, such that at least one external dimension of the housing increases, in response to an increase in pressure within the sealable volume, caused by heating of the coolant liquid. In particular, the coolant liquid may fill at least (in conventional fill level) 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% of the volume within the sealable volume (not occupied by the one or more electronic components).

Preferably, the module further comprises: a pressure release mechanism. This is beneficially configured to cause a reduction in pressure within the sealable volume upon activation. This may thereby cause at least one of the plurality of external walls to contract. This is advantageously achieved by increasing the size of the sealed volume within the module. A pressure release mechanism may further be a coolant displacement

mechanism, for example in that the pressure may be reduced by displacement of the coolant such as by increasing the dimensions of the sealed volume. Another form of pressure release may be provided by increasing size of the air gap in the sealed volume. In particular, the pressure release mechanism may comprise a valve configured selectively, in a first configuration, to close off a part of the sealable volume to the remainder of the sealable volume and thereby maintain a relatively high pressure within the remainder of the sealable volume and, in a second configuration, to open the part of the sealable volume and thereby cause a relatively low pressure within the remainder of the sealable volume. In one embodiment, communication between a second part of internal volume of the housing (which may or may not be part of the sealable volume) and the sealable volume (or part thereof) configured to hold the coolant (and/or in which the coolant is located) may be controlled by the valve, to control the pressure within the housing thereby. Preferably, the module further comprises a release actuator, configured to activate the pressure release mechanism in response to an external force. For example, this may be mechanical such as a handle. Other forms of pressure release actuator are possible, for instance pneumatic, hydraulic, magnetic and/or electrically activated (for instance by means of a motor).

In embodiments, the module may comprise an expansion actuator, configured to cause the at least one of the plurality of walls to expand in response to a trigger event.

This may cause an expansion within the module housing due to pressure or for some other reason. In fact, the volume and/or side wall expansion need not be effected by internal pressure increase. Other options are possible, which may include mechanical, pneumatic, hydraulic, lever-based, spring and cam mechanism, plunge, vacuum-based mechanism, a tie rod mechanism and/or magnetic, for instance. Pneumatic expansion might be achieved using an air bag, for instance. Hydraulic expansion may require some and/or movement of fluid.

In general terms, expansion actuator may comprise (or be) a mechanical expansion actuator, configured mechanically to cause the at least one of the plurality of walls to expand. For example, the mechanical expansion actuator may comprise one or more of: a pneumatic actuator; a hydraulic actuator; a lever; a spring and cam mechanism; a plunger mechanism; a vacuum-based mechanism; and a tie rod mechanism. Additionally or alternatively, the expansion actuator may comprise a magnetic expansion actuator, configured to cause the at least one of the plurality of walls to expand by magnetic attraction or repulsion. In some embodiments, the trigger event may be caused by insertion of the module into a space provided by a module receiving device, the module receiving device providing the second thermal interface.

The first thermal interface is preferably one or more of the external walls of the housing. In this case, the configuration of the first thermal interface may depend on structure of the housing, for instance, if the housing is made of two parts: first walls (which in an elongated, generally cuboid housing may be one or both of the longest and widest external walls) may provide the first thermal interface and cooperate with the second thermal interface; and second walls (which may be some or all of the other walls, particularly those not the longest and widest) may be configured to expand in a direction perpendicular to the first part. In the preferred embodiment, the first thermal interface is formed by first and second external walls on opposing sides of the housing. This may allow redundant operation, as effectively the first and second external walls can transfer heat independently from one another. For instance, if a first part of the first thermal interface formed by the first external wall is unable to transfer a heat amount, the module may be configured to allow a second part of the first thermal interface formed by the second external wall to transfer the heat amount.

Improving the efficiency of heat transfer across the first thermal interface may be significantly advantageous. This may be achieved, for example, if an internal surface of the sealable volume and/or the one or more external walls of the housing providing the first thermal interface comprise projections and/or grooves on a surface (that is the internal surface and/or a surface of the external walls respectively). These projections and/or grooves may be in the form of one or more of: pins; ribs; fins; dimples; and spots. Not all of the surface may be covered by the projections and/or grooves. Optionally, the internal surface of the sealable volume and/or the one or more external walls of the housing providing the first thermal interface may be flat or smooth. Additionally or alternatively, the one or more external walls of the housing providing the first thermal interface may have a coating or a part of all, in particular to improve thermal conduction. The coating may additionally or alternatively allow insertion or removal of the module from a module receiving device. The coating may comprise one of more of: polymerized

tetraf!uoroethylene; carbon fibre; spray silicone; graphene; plastic; viscous grease; a gel; and a tape.

The second thermal interface is beneficially provided by an external surface of a module receiving device. The external surface preferably defines a space for receiving the module. The plurality of external walls of the housing are configured such that, expansion of the at least one of the external walls in use causes some of the plurality of external walls to press against the external surface of the module receiving device. In particular, this is such that the first thermal interface cooperates with the second thermal interface provided by the external surface of the module receiving device. In one preferred embodiment, the first thermal interface comprises two of the external walls of the housing (for instance, as discussed above for redundant operation and/or if the external walls providing the first thermal interface are adjacent). Then, expansion of the at least one of the external walls in use may cause the two external walls of the first thermal interface providing the first thermal interface to press against the second thermal interface provided by the external surface of the module receiving device. Preferably, the two external walls of the housing providing the first thermal interface are on opposite sides of the housing.

In a further general aspect, there may be considered a cooling system, comprising: a module for immersion cooling of one or more electronic components, as disclosed herein; and a module receiving device. The module receiving device may provide a space to receive the module and the second thermal interface, such that insertion of the module into the space and expansion of the at least one of the plurality of external walls of the module in use causes the plurality of external walls to cooperate with the second thermal interface. Optionally, the module receiving device may be provided on its own.

The module receiving device preferably has an external surface defining the space for receiving the module and more preferably also providing the second thermal interface. The external surface may comprise a phase change material (such as gallium, wax) and/or wire wool or a metal foam.

The space defines a slot, advantageously matching the shape of the module, especially when the module has an expanded volume. The slot may be in the form of draw loading slot or "cassette" type slot, in which the module is inserted longitudinally into the slot and then moved laterally within the slot (before or after its volume expansion). In preferred embodiments, the slot is dimensioned to be larger than the housing of the module, for example to allow the volume of the module to expand. Expansion of the at least one of the external walls of the module in use advantageously causes the module to be pushed against the external surface of the module receiving device (in particular one or multiple walls of a slot in which the second thermal interface is located).

The external surface of the module receiving device providing the second thermal interface may have a coating, for example comprising one of more of: polymerized tetrafluoroethylene; carbon fibre; spray silicone; graphene; plastic; viscous grease; a gel; and a tape. Optionally, the coating may be of a tear-off or one-time use type. The coating may aid thermal conduction and/or allow insertion or removal of the module from a module receiving device. Additionally or alternatively, the external surface providing the second thermal interface may comprise projections and/or grooves on the external surface, which may be in the form of one or more of: ribs; pins; fins; dimples; spots. Not all of the external surface providing the second thermal interface may be covered by the projections and/or grooves. The projections and/or grooves may match corresponding grooves and/or projections (respectively) on an outer surface of the module. In other embodiments, the second thermal interface providing the second thermal interface may be smooth or flat.

In the preferred embodiment, the external surface providing the second thermal interface is part of one or more cold plates. Then, the coolant liquid of the module may be considered a first coolant liquid and the one or more cold plates may each comprise a channel, configured to receive a second coolant liquid. In use, the second coolant liquid may receive heat from the second thermal interface. The channel may comprise (or be formed of) one or more of: a semi-flexible material; a metallic material; a non-metallic material; a flexible tube; and a carbon fibre pipe.

The space for receiving the module is preferably at least partly defined by two opposing walls of the external surface. Then, the second thermal interface is beneficially formed by both of the two opposing walls. In this case, a first wall of the two opposing walls may provide a first part of the second thermal interface and a second wall of the two opposing walls may provide a second part of the second thermal interface. The first and second parts may be operated in isolation from one another. Configurations of such types may allow redundant operation, for example where the first part comprises a first cold plate and the second part comprises a second cold plate, isolated from the first. If the first part of the second thermal interface is unable to transfer a heat amount, the module receiving device is configured to allow the second part of the second thermal interface to transfer the heat amount. Optionally, an additional thermal interface material (TIM) may be provided on an outer surface of the module receiving device and/or the module or in the space between the module receiving device and the module. The additional TIM is advantageously configured to one or more of: support heat transfer between the first and second thermal interfaces; mitigate friction between the first and second thermal interfaces; and provide electrical insulation between the first and second thermal interfaces. The additional TIM optionally comprises one or more of: silicone; viscous grease; a gel; a tape; a film; a coil or spring; a foam; a metal; and graphite. The additional TIM may be of one-time use type and/or be formed in spots.

Further specific examples of modules, module receiving devices and/or cooling systems will now be described with reference to additional drawings. Referring next to Figure 8, there is schematically shown a cross-section of part of a cooling system in accordance with a second embodiment. The cooling system comprises: a module 420; and a cold plate formed of rigid plates 400 and a flexible material 410 coupling the plates 400. The module 420 is in accordance with any of those described herein (but less preferably does may not have an expanding wall or volume). In this embodiment, the cold plate is configured to expand in use (as well as the module 420), as allowed by the flexible material 410.

With reference to Figure 9, there is schematically illustrated a cross-section of part of a cooling system in accordance with a third embodiment. In this embodiment, module 520 is again provided between cold plates 1 10 on opposing sides. Again, the module 520 is in accordance with any of those described herein (but optionally may not have an expanding wall or volume). Two cold plates 1 10 are provided adjacent to one another, linked by an expansion device 500 (and without the module therebetween). The expansion device 500 (which may be mechanical, electromechanical, magnetic, pneumatic, hydraulic or other) causes the two cold plates 1 10 to space apart and thereby further compress the module 520 in use, keeping it in place.

Other approaches to expanding the cold plates may be considered. For example, these may be mechanical, using some mechanism to expand the cold plate to push into the module. A pneumatic approach might use some sort of air bag behind the cold plate to actuate it. Additionally or alternatively, a hydraulic implementation might use a flexible cold plate, whereby the pressure is introduced by the secondary coolant circuit's pressure, so that the cold plate is pushed towards the module. Any of the approaches described herein for expanding and/or contracting the module volume could be adapted to be used for cold plate expansion and/or contraction. Referring now to Figure 10, there is shown a perspective view of a cooling system in accordance with a fourth embodiment. Here, two opposing module receiving device walls, in the form of cold plates 610 are provided on either side of a module 620. The module receiving device walls are biased to be pushed together by a hinge 61 1 , thereby making the space between them small. When the module 620 is inserted into the space, the space expands to allow the module 620 to sit within the space defined by the cold plates 610. Secondary coolant connections 612 are also provided to each of the cold plates 610. It will be understood that, in alternative implementations, only one cold plate might be provided in the walls or another form of heat transfer may be used (as discussed below), so that neither wall may comprise a cold plate. This "clamsheH"-type design, with coolant being added to the module receiving device "shell" once sealed, requires electrical input/output connections to the module 620 to be carefully handled and therefore is less advantageous than other designs.

In general terms, in the module receiving device, the space for receiving the module may be at least partly defined by two opposing walls of its external surface. Then, the two opposing walls may be moveable between: a first position, in which the space to receive the module is relatively large; and a second position, in which the space to receive the module is relatively small. This movement may be effected by one or more of: expansion of one or more cold plates provided in the external surface wall; by relative movement of two adjacent walls or cold plate provided on one side of the space (which may be effected by an expansion device or actuator); and by a force (mechanical, electromechanical, magnetic, pneumatic, hydraulic or other) to separate external walls of the module receiving device defining the space on insertion of the module into the space.

Some further possible specific implementations are now presented. Referring to Figure 1 1 , there is schematically shown a cross-section of part of a cooling system in accordance with a fifth embodiment. This comprises: two opposing cold plates 1 10 (similar to the cold plates identified by the same reference numeral described in previous embodiments); a module 720. The module 720 is generally in accordance with any of those described herein, but with an additional further adaptation in its housing 725. The housing 725 is configured to define a void 710 between the module 720 and the cold plate 710, when the module 720 is provided in the space defined by the cold plates 1 10. The housing 725 of the module 720 further comprises a seal 700, such that the void 710 may be filled with a thermally conductive liquid. This occurs only when the module 720 is in contact with the cold plate 1 10 and aids thermal transfer across the housing 725 to the cold plate 1 10. Direct liquid contact of this form with the module 720 (so that the cold plate 1 10 effectively becomes a wall of the module) may therefore rely on a sealed chamber being formed by the void 710 and seal 700, on insertion.

Next with reference to Figure 12, there is depicted a perspective view of a cold plate 800 for use in accordance with a sixth embodiment. Here, the cold plate 800 defines a channel 810 and when the module (not shown, but may be in accordance with any herein described) is not provided adjacent the cold plate 800, the channel is not sealed and therefore open. The cold plate 800 further comprises a seal 820 and when a module is provided adjacent the cold plate 800 and the volume of the module increases (at least one external wall expands), the module presses against the cold plate 800 and seals the channel 810. Once sealed, secondary liquid coolant is pumped through coolant inlet 801 , channel 810 in direct contact with the module external wall and out through coolant outlet 802. In this way, more efficient heat transfer to the secondary coolant may be possible. An alternative to a cold plate 800 as a heat sink in such an embodiment may also be considered.

With reference to the general description herein, the first thermal interface may comprise one or more external walls of the module housing. Then, a channel may be defined by (or formed in) the external surface of the module receiving device. Additionally or alternatively, a channel may be defined by (or formed in) the external surface of the module housing (and in this case, the module housing may further comprise a seal for the channel). In this case, expansion of the at least one of the external walls of the module in use advantageously causes the one or more external walls of the module housing comprising the first thermal interface to seal the channel (formed in the external surface of the module receiving device and/or module housing). The channel may be part of a cold plate structure or it may be in addition to a cold plate structure.

Referring now to Figure 13, there is schematically represented a cross-section of part of a cooling system in accordance with a seventh embodiment. This comprises: a module receiving device formed with cold plates 910; a module 920. The cold plates 910 and module 920 may be in accordance with any herein described, but differ in their shape. As shown, the sides of the module 920 are tapered (to provide a trapezoidal prism shape). The sides of the module receiving device, defined by the cold plates 910 is also tapered, so that the insertion of the module 920 into a space defined by the cold plates 910 creates a locking force that increases the pressure of contact between the external side walls of the module 920 and the cold plates 910. In practice, a volume expansion of the module using this technique would be mechanically actuated, using the tapered module 920. This might be implemented using rows of tapered teeth on the cold plates 910 and the blade being inserted from the front and then down to engage the teeth.

In general terms, the housing of the module may have a shape of a trapezoidal prism. For example, this is such that two opposing externals walls of the housing are non- parallel. The space defined by the module receiving device may have a corresponding shape. Other shapes may be considered.

In all of the embodiments above, the first thermal interface is provided by the walls of the module housing and the second thermal interface is provided by the module receiving device, in the form of a cold plate. This provides a thermal bus. However, other options may be possible. For example, another form of thermal bus (using heat pipes or similar) might be considered. Alternatively, this approach may be used even if a thermal bus is not implemented, for instance with coolant being pumped through the module from the module receiving device (with appropriate connections therebetween). However, the advantages of this approach would be less significant in such scenarios.

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 the invention are applicable to all aspects of the invention and may be used in any combination. Likewise, features described in nonessential combinations may be used separately (not in combination).

Claims

1 . A module for immersion cooling of one or more electronic components, the module comprising:

a housing, defining a sealable volume, configured to contain the one or more electronic components immersed in a coolant liquid, the coolant liquid being for receiving heat generated by the one or more electronic components; and

a first thermal interface, arranged to receive heat from the coolant liquid; and wherein the housing comprises a plurality of external walls, at least one of which is adapted to expand in use, so that the first thermal interface cooperates with a second thermal interface, external the module, to allow transfer of heat from the first thermal interface.

2. The module of claim 1 , wherein at least one of the plurality of external walls is configured to contract to allow decoupling of the first thermal interface and the second thermal interface.

3. The module of claim 1 or claim 2, further comprising:

the one or more electronic components, mounted in the sealable volume; and the coolant liquid, immersing the one or more electronic components within the sealable volume; and

wherein the sealable volume is sealed to contain the coolant liquid.

4. The module of any preceding claim, wherein the at least one of the plurality of external walls is made of a flexible and/or concertinaed material to allow its expansion.

5. The module of any preceding claim, wherein at least one of the plurality of external walls is configured to expand, such that at least one external dimension of the housing increases, in response to an increase in pressure within the sealable volume, caused by heating of the coolant liquid.

6. The module of claim 5, when dependent upon claim 3, wherein the coolant liquid fills at least 80% of the volume within sealable volume not occupied by the one or more electronic components.

7. The module of claim 5 or claim 6, further comprising:

a pressure release mechanism, configured to cause a reduction in pressure within the sealable volume upon activation, causing at least one of the plurality of external walls to contract thereby.

8. The module of claim 7, wherein the pressure release mechanism comprises a valve configured selectively, in a first configuration, to close off a part of the sealable volume to the remainder of the sealable volume and thereby maintain a relatively high pressure within the remainder of the sealable volume and, in a second configuration, to open the part of the sealable volume and thereby cause a relatively low pressure within the remainder of the sealable volume.

9. The module of claim 7 or claim 8, further comprising a mechanical release actuator, configured to activate the pressure release mechanism in response to an external force.

10. The module of any preceding claim, further comprising:

an expansion actuator, configured to cause the at least one of the plurality of walls to expand in response to a trigger event.

1 1 . The module of claim 10, wherein the expansion actuator comprises a mechanical expansion actuator, configured mechanically to cause the at least one of the plurality of walls to expand.

12. The module of claim 1 1 , wherein the mechanical expansion actuator comprises one or more of: a pneumatic actuator; a hydraulic actuator; a lever; a spring and cam

mechanism; a plunger mechanism; a vacuum-based mechanism; and a tie rod mechanism.

13. The module of any one of claims 10 to 12, wherein the expansion actuator comprises a magnetic expansion actuator, configured to cause the at least one of the plurality of walls to expand by magnetic attraction or repulsion.

14. The module of any one of claims 10 to 13, wherein the trigger event is caused by insertion of the module into a space provided by a module receiving device, the module receiving device providing the second thermal interface.

15. The module of any preceding claim, wherein the housing is generally cuboid in shape.

16. The module of any one of claims 1 to 14, wherein the housing has a shape of a trapezoidal prism, such that two opposing externals walls of the housing are non-parallel.

17. The module of any preceding claim, wherein the first thermal interface comprises one or more of the external walls of the housing.

18. The module of claim 17, wherein the first thermal interface is formed by first and second external walls on opposing sides of the housing and wherein if a first part of the first thermal interface formed by the first external wall is unable to transfer a heat amount, the module is configured to allow a second part of the first thermal interface formed by the second external wall to transfer the heat amount.

19. The module of claim 17 or claim 18, wherein an internal surface of the sealable volume and/or the one or more external walls of the housing providing the first thermal interface comprise projections and/or grooves on a surface.

20. The module of any one of claims 16 to 18, wherein the one or more external walls of the housing providing the first thermal interface have a coating.

21 . The module of claim 20, wherein the coating comprises one of more of: polymerized tetrafluoroethylene; carbon fibre; spray silicone; graphene; plastic; viscous grease; a gel; and a tape.

22. The module of any preceding claim, wherein the second thermal interface is provided by an external surface of a module receiving device, the external surface defining a space for receiving the module.

23. The module of claim 22, wherein the plurality of external walls of the housing are configured such that, expansion of the at least one of the external walls in use causes some of the plurality of external walls to press against the external surface of the module receiving device, such that the first thermal interface cooperates with the second thermal interface provided by the external surface of the module receiving device.

24. The module of claim 23, wherein the first thermal interface comprises two of the external walls of the housing, expansion of the at least one of the external walls in use causing the two external walls of the first thermal interface to press against the second thermal interface provided by the external surface of the module receiving device.

25. The module of claim 24, wherein the two external walls of the housing providing the first thermal interface are on opposite sides of the housing.

26. A cooling system, comprising:

a module for immersion cooling of one or more electronic components, in accordance with any preceding claim; and

a module receiving device, providing a space to receive the module and the second thermal interface, such that insertion of the module into the space and expansion of the at least one of the plurality of external walls of the module in use causes the plurality of external walls to cooperate with the second thermal interface.

27. The cooling system of claim 26, wherein the module receiving device has an external surface defining the space for receiving the module and providing the second thermal interface.

28. The cooling system of claim 26, wherein the space defines a slot.

29. The cooling system of claim 28, wherein the slot is dimensioned to be larger than the housing of the module.

30. The cooling system of any one of claims 27 to 29, wherein expansion of the at least one of the external walls of the module in use causes the module to be pushed against the external surface of the module receiving device.

31 . The cooling system of any one of claims 27 to 30, wherein the external surface providing the second thermal interface has a coating.

32. The cooling system of claim 31 , wherein the coating comprises one of more of: polymerized tetraf!uoroethylene; carbon fibre; spray silicone; graphene; plastic; viscous grease; a gel; and a tape.

33. The cooling system of any one of claims 27 to 32, wherein the external surface providing the second thermal interface comprises projections and/or grooves on the external surface.

34. The cooling system of any one of claims 27 to 33, wherein the external surface providing the second thermal interface is part of one or more cold plates.

35. The cooling system of claim 34, wherein the coolant liquid of the module is a first coolant liquid, the one or more cold plates each comprising a channel, configured to receive a second coolant liquid such that in use, the second coolant liquid receives heat from the second thermal interface.

36. The cooling system of claim 35, wherein the first thermal interface comprises one or more external walls of the module housing and wherein the channel is defined by the external surface of the module receiving device, expansion of the at least one of the external walls of the module in use causing the one or more external walls of the module housing comprising the first thermal interface to seal the channel.

37. The cooling system of any one of claims 27 to 36, wherein the space for receiving the module is at least partly defined by two opposing walls of the external surface, the second thermal interface being formed by both of the two opposing walls.

38. The cooling system of claim 37, wherein a first wall of the two opposing walls provides a first part of the second thermal interface and a second wall of the two opposing walls provides a second part of the second thermal interface and wherein if the first part of the second thermal interface is unable to transfer a heat amount, the module receiving device is configured to allow the second part of the second thermal interface to transfer the heat amount.

39. The cooling system of any one of claims 26 to 38, further comprising: an additional thermal interface material, provided on an outer surface of the module receiving device and/or the module or in the space between the module receiving device and the module.

40. The cooling system of claim 39, wherein the additional thermal interface material comprises one or more of: silicone; viscous grease; a gel; a tape; a film; a coil or spring; a foam; a metal; and graphite.

41 . The cooling system of any one of claims 26 to 36, wherein the space for receiving the module is at least partly defined by two opposing walls of the external surface, the two opposing walls being moveable between: a first position, in which the space to receive the module is relatively large; and a second position, in which the space to receive the module is relatively small.

42. A method of operating a cooling system, comprising:

providing a module having a housing defining a sealable volume, one or more electronic components immersed in a coolant liquid being located within the sealable volume, wherein the housing comprises a plurality of external walls;

operating the one or more electronic components such that the one or more electronic components generate heat, the heat being received by the coolant liquid;

transferring heat from the coolant liquid to a first thermal interface; and

expanding at least one of the plurality of external walls, so that the first thermal interface cooperates with a second thermal interface, external the module, to allow transfer of heat from the first thermal interface.