Patent Description:
Cooling is essential to enable telecommunications and computing systems to function properly. Efficient cooling systems that consume less energy, reduce any active control and lower costs are therefore advantageous.

<CIT> relates to a spacecraft modular system with two components of a cooling system, allowing for an expanded and a non-expanded configuration according to the preamble of claim <NUM>.

According to the invention, there is provided a heat exchanger comprising: a plurality of channels configured for flow of working fluid wherein the plurality of channels are configured to move between a non-expanded configuration and an expanded configuration such that, in the non-expanded configuration the plurality of channels are sized so as to allow for movement of the heat exchanger relative to one or more heat sources and in the expanded configuration the plurality of channels are sized so as to restrict movement of the heat exchanger relative to the one or more heat sources, wherein the plurality of channels are configured so that changes in internal pressure of the working fluid causes the plurality of channels to move between the non-expanded configuration and the expanded configuration.

The plurality of channels may be substantially flat.

The plurality of channels may be configured to fit between substantially flat heat sources.

The heat exchanger may be configured so that when the plurality of channels are in the non-expanded configuration and positioned between the one or more heat sources a gap is provided between the heat sources and the plurality of channels.

The heat exchanger may be configured so that when the plurality of channels are in the expanded configuration and positioned between the one or more heat sources the plurality of tubes grip the heat sources.

A thermal interface material may be coupled to the plurality of channels.

The plurality of channels comprise a plurality of internal walls configured to provide a plurality of sub-channels and wherein the plurality of internal walls comprise means for enabling expansion of the internal walls as the plurality of channels are moved between the non-expanded configuration and the expanded configuration. The heat exchanger may comprise at least one header configured to enable cooling of one or more heat sources.

According to various, but not necessarily all, examples of the disclosure there may be provided a cooling system comprising a plurality of heat exchangers as described herein.

The cooling system may be for cooling hardware components.

The cooling system may comprise one or more intermediate heat exchangers comprising a reservoir for storing working fluid.

The reservoir may be coupled to an outlet of the intermediate heat exchanger.

The heat exchangers may be removably coupled to the cooling system.

The cooling system may be coupled to an air-cooling system.

The air-cooling system may comprise one or more fans configured to drive air flow through the air-cooling system towards a two-phase cooling system.

The two-phase cooling system may be configured to enable heat to be recovered from the air-cooling system.

<FIG> schematically shows an example of passive two-phase cooling system <NUM> that can comprise evaporators <NUM> according to examples of the disclosure. It is to be appreciated that the cooling systems disclosed in this disclosure are also compatible with active single- and two-phase implementations where pumps or other mechanical drivers are used to circulate the working fluid.

In the example of <FIG> the two-phase cooling system <NUM> comprises a thermosyphon loop that is driven by gravity rather than a pump. The example heat exchangers and evaporators <NUM> disclosed herein can be provided within other types of two-phase cooling system <NUM> in other examples of the disclosure.

The thermosyphon loop shown in <FIG> comprises an evaporator <NUM>, a condenser <NUM>, a downcomer <NUM> and a riser <NUM>. A working fluid <NUM> is provided within the thermosyphon loop. When the thermosyphon loop is in use the working fluid <NUM> circulates through the components of the thermosyphon loop.

The evaporator <NUM> is provided at the bottom of the thermosyphon loop so that the working fluid flows down the downcomer <NUM> into the evaporator <NUM> under the force of gravity as indicated by the arrow <NUM>. The height and inner diameter of the downcomer <NUM> can be selected to set the driving force of the thermosyphon that causes the fluid to flow through the evaporator <NUM>, riser <NUM> and condenser <NUM>. The working fluid <NUM> is in the liquid phase <NUM> at the inlet of the evaporator <NUM>.

The evaporator <NUM> comprises any means for transferring heat from a heat source <NUM> into the working fluid <NUM>. The evaporator <NUM> is thermally coupled to the heat source <NUM>. A thermal interface material could be used to enable the evaporator <NUM> to be thermally coupled to the heat source <NUM>. The heat source <NUM> could comprise an electronic device that generates unwanted heat during operation. The electronic device could be a server, router, network switch, storage device or any other suitable type of device. In some examples the heat sources can comprise a plurality of electronic devices that could provide a data centre, telecommunication equipment room, or network, a communication room, a computer room, a network room or any other suitable arrangement.

Heat is transferred from the heat source <NUM> to the working fluid <NUM> in the evaporator <NUM> as indicated by the arrows <NUM>. This heat transfer causes a partial evaporation of working fluid <NUM> within the evaporator <NUM> and converts the working fluid <NUM> from a liquid phase <NUM> into a mixture of liquid and vapour phase. In particular, the evaporator <NUM> causes some of the working fluid <NUM> to be converted into the vapour phase <NUM> while some remains in a liquid phase <NUM> so that the fluid expelled from the outlet of the evaporator <NUM> is a two-phase mixture. The heat transfer in the evaporator <NUM> is a combination of sensible and latent heat. The mass fraction of vapor <NUM> at the outlet of the evaporator <NUM> is identified by the vapor quality. The two-phase mixture can comprise droplets of vapour entrained within the liquid or other flow regimes depending on the design of the thermosyphon loop, heat load, filling ratio and any other suitable parameter.

The evaporator <NUM> is coupled to the riser <NUM> so that the working fluid expelled from the evaporator <NUM> flows into the riser <NUM>. This working fluid comprises a two-phase mixture where the vapour phase <NUM> is less dense than the liquid phase <NUM>. The working fluid <NUM> within the thermosyphon loop rises through the riser <NUM>, as indicated by the arrows <NUM>. The passive flow in the thermosyphon loop is driven by the density difference between the working fluid <NUM> in the liquid phase in the downcomer <NUM> and the working fluid <NUM> in the two-phase mixture in the riser <NUM>.

The evaporator <NUM> can comprise structures that enable efficient transfer from the evaporator <NUM> into the working fluid <NUM>. For example, the evaporator <NUM> could comprise wick structures, micro-channels, arrays of evaporator fins, a serpentine arrangement of macro- / micro-channels or any suitable combination of such features.

The condenser <NUM> is provided at the top of the thermosyphon loop. The condenser <NUM> is positioned above the evaporator <NUM> so that the working fluid <NUM> flows upwards from the evaporator <NUM> to the condenser <NUM>.

The condenser <NUM> is coupled to the riser <NUM> so that the working fluid <NUM> in the two-phase mixture (vapour phase <NUM> and liquid phase <NUM>) flows from the riser <NUM> into the condenser <NUM>. The condenser <NUM> can comprise any means for cooling the working fluid <NUM>. For example, the condenser <NUM> could be air-cooled or liquid-cooled. A liquid-cooled condenser <NUM> could comprise a tube-in-tube heat exchanger, a shell- and-tube heat exchanger, a plate heat exchanger or any other suitable heat exchanger configuration or arrangement. An air-cooled condenser could comprise a louvered-fin flat tube heat exchanger, a tube-and-fin heat exchanger or any other suitable heat exchanger configuration or arrangement. The condenser <NUM> can comprise any suitable geometry that enables heat to be removed efficiently from the working fluid.

The condenser <NUM> is thermally coupled to a coolant <NUM>. A thermal interface material could be used to enable the condenser <NUM> to be thermally coupled to the coolant <NUM>. The latter implementation can be also used to enable hardware hot-swappability by installing a reworkable thermal interface material that connects the two streams of the condenser <NUM>. In other examples the coolant <NUM> can be directly integrated in the condenser <NUM> with a wall interface separating the stream of thermosyphon working fluid <NUM> from the stream of coolant <NUM>. The wall interface can comprise a highly-conductive metal or metal alloy, such as copper, aluminum, brass, or any other suitable metal. In some examples the wall interface can comprise highly-conductive ceramics such as Aluminum Nitride (AIN), or polymers such as filled polymer composites.

The condenser <NUM> enables heat to be transferred from the working fluid <NUM> to the coolant <NUM> as indicated by the arrows <NUM>. This heat transfer causes the working fluid <NUM> to condense, at least partly, back into the liquid phase <NUM>. The working fluid <NUM> at the outlet of the condenser <NUM> can be therefore in the liquid phase <NUM> or in the two-phase mixture (vapour phase <NUM> and liquid phase <NUM>).

The condenser <NUM> is coupled to the downcomer <NUM> so that the working fluid <NUM> can flow down the downcomer <NUM> by gravity and be returned to the inlet of the evaporator <NUM>.

<FIG> schematically show a heat exchanger <NUM> according to examples of the disclosure. In this example the heat exchanger <NUM> is an evaporator <NUM>. The evaporator <NUM> can be used in cooling systems such as the two-phase cooling system <NUM> shown in <FIG>. It is to be appreciated that the evaporator <NUM> shown in <FIG> can be also used in active single- and two-phase cooling systems where pumps or other mechanical drivers are used to circulate the working fluid.

The evaporator <NUM> can be used to cool memory boards, GPU cards and/or other flat, or substantially flat components of hardware or other heat sources. The components that are being cooled can be used in telecommunications systems, computing systems or any other suitable systems. In the examples of <FIG> the evaporator <NUM> is shown in position adjacent to the memory boards <NUM>. In the example shown in <FIG> the evaporator <NUM> is configured to enable cooling of a stack of memory boards <NUM>. A space is provided between adjacent memory boards <NUM> and sections of the evaporator <NUM> are configured to be fitted into the spaces between adjacent memory boards <NUM>.

The evaporator <NUM> comprises a plurality of channels <NUM>. The channels <NUM> are configured to enable flow of working fluid <NUM>. The channels <NUM> can provide a conduit or a plurality of conduits for the working fluid <NUM> between the inlet manifold and the outlet manifold. In this example the inlet manifold is the downcomer <NUM> of a two-phase cooling system <NUM> and the outlet manifold is the riser <NUM> of the two-phase cooling system <NUM>. In the examples of <FIG> the working fluid <NUM> flows through the channels <NUM> in the direction indicated by the arrows <NUM>.

The plurality of channels <NUM> are configured to enable heat from one or more heat sources <NUM> to be transferred into the working fluid <NUM> within the plurality of channels <NUM>. In the example of <FIG> the memory boards <NUM>, and the components on the memory boards <NUM> provide the heat sources <NUM> (indicated in <FIG>). The plurality of channels <NUM> are sized and shaped so that they can be positioned close enough to the memory boards <NUM> to enable heat from the memory boards <NUM> to be transferred into the working fluid <NUM> within the channels <NUM>.

The channels <NUM> can be flat, or substantially flat. The channels <NUM> can be shaped so that the height of the channels <NUM> is much less than the width of the channels <NUM>. This can provide for efficient transfer of heat from the memory boards <NUM> into the working fluid <NUM> within the channels <NUM>. This can also enable the plurality of channels <NUM> to be fitted into the gaps between adjacent memory boards <NUM>.

The channels <NUM> can be sized so that they cover, or substantially cover, the surfaces of the memory boards <NUM>. In some examples the channels <NUM> can be sized and shaped so that the surface area of the flat surface of the channels <NUM> covers, or substantially covers, the memory boards <NUM>. This can enable heat from a plurality of different components on the memory boards <NUM> to be transferred into the working fluid <NUM>.

In examples of the disclosure the plurality of channels <NUM> are expandable so that they can move between a non-expanded configuration and an expanded configuration. <FIG> shows the evaporator <NUM> with the plurality of channels <NUM> in the non-expanded configuration. In this example, in the non-expanded configuration the working fluid pressure is slightly higher than ambient pressure. In other examples, in the non-expanded configuration the working fluid pressure could be the same, or substantially the same, as the ambient pressure. <FIG> shows the plurality of channels <NUM> in the expanded configuration. In this example, in the expanded configuration the working fluid pressure is much higher than ambient pressure.

The external walls of the plurality of channels <NUM> can be configured to expand and contract to allow the plurality of channels <NUM> to move between the expanded and non-expanded configurations. The external walls of the plurality of channels <NUM> can be formed from any suitable material that enables the expansion of the plurality of channels <NUM>.

As shown in <FIG> when the plurality of channels <NUM> are in the non-expanded configuration the plurality of channels <NUM> are sized so as to allow for movement of the evaporator <NUM> relative to the memory boards <NUM> or other heat sources <NUM>. In this non-expanded configuration, a gap <NUM> is provided between the plurality of channels <NUM> and the memory boards <NUM>. This gap <NUM> provides a clearance between the channels <NUM> and the memory boards <NUM> and allows the evaporator <NUM> to be inserted into position and/or removed from position adjacent to the memory boards <NUM>.

When the evaporator <NUM> is in use, and thus is cooling the heat sources <NUM> on the memory boards <NUM>, heat is transferred into the working fluid <NUM> within the plurality of channels <NUM>. This increases the pressure of the working fluid <NUM> within the plurality of channels <NUM>. When the internal pressure of the working fluid <NUM> is greater than the ambient temperature fluid pressure this will cause expansion of the channels <NUM>. This causes the channels <NUM> to move from the non-expanded configuration shown in <FIG> to the expanded configuration shown in <FIG>.

As shown in <FIG> when the evaporator <NUM> is in the expanded configuration, the plurality of channels <NUM> are sized to ensure good heat transfer between the heat sources <NUM> of the memory boards <NUM> and the working fluid <NUM> flowing in the evaporator <NUM>. The expanded channels <NUM> can also restrict movement of the evaporator <NUM> relative to one or more heat sources <NUM> and memory boards <NUM>.

As shown in <FIG> there is no gap between the channels <NUM> and the memory boards <NUM> in the expanded configuration. In this configuration the channels <NUM> can be in direct contact with the memory boards so that the channels <NUM>, or at least part of the channels, touch the memory boards <NUM>. This causes the channels <NUM> to grip the memory boards <NUM> or other heat sources <NUM> and so restricts the movement of the evaporator <NUM> relative to the memory boards <NUM>.

The channels <NUM> of the evaporator <NUM> can revert back to the non-expanded configuration. For example, if the memory boards <NUM> are not in use and heat is not being transferred into the working fluid <NUM> this will cause a drop in the pressure of the working fluid <NUM>. This causes the channels <NUM> to contract back to the non-expanded configuration when the evaporator <NUM> is disconnected from the thermosyphon loop <NUM>. This could then enable the evaporator <NUM> to be removed from the memory stack, for maintenance, repair or any other suitable purpose.

In the example shown in <FIG> a thermal interface material <NUM> is coupled to the plurality of channels <NUM>. The thermal interface material <NUM> is coupled to the external walls of the channels <NUM> and therefore is provided between the memory boards <NUM> and the channels <NUM>. The thermal interface material <NUM> can comprise a phase change material, a reworkable gad pad or any other suitable thermally conductive material.

The thermal interface material <NUM> can be provided over the flat, or substantially flat, surface of the channels <NUM> to provide good thermal conductivity across the surface area of the memory boards <NUM>.

It is to be appreciated that the evaporator <NUM> can comprise components that are not shown in <FIG>. For example, the evaporator <NUM> can comprise an inlet header and/or an outlet header. The inlet header and outlet header can be configured to enable even flow distribution and stable heat transfer performance from the inlet to the outlet of the evaporator <NUM>. The inlet header and outlet header can be designed to enable the evaporator <NUM> to meet power requirements and can take into account geometry and space constraints of the hardware being cooled. The inlet and outlet header of the evaporator <NUM> can have a circular, rectangular or any other cross-sectional area and/or shape. The evaporator <NUM> can have dedicated headers when cooling one heat source or shared headers when cooling multiple heat sources.

<FIG> show example channels <NUM> that could be used in the evaporators <NUM> illustrated in <FIG> or in any other suitable evaporators <NUM> or heat exchangers <NUM>.

<FIG> shows an example of channel <NUM> that can be configured to be moved between an expanded and a non-expanded configuration. The channel <NUM> is flat, or substantially flat. The height "h" of the channel <NUM> is much less than the width "w" of the channel <NUM>. This provides a low-profile channel <NUM> that can enable efficient heat transfer from the memory boards <NUM> or other heat sources <NUM> into the working fluid <NUM> within the channels <NUM>. This can also enable the plurality of channels <NUM> to be fitted into the gaps in a stack of memory boards <NUM>.

The channel <NUM> comprises an external wall <NUM>. The external wall <NUM> provides a closed channel through which the working fluid <NUM> can flow. The external wall <NUM> can comprise a thermally conductive material to enable heat to be effectively transferred into the working fluid <NUM>. The external wall <NUM> can also comprise a material that is flexible enough to allow the channel <NUM> to be moved between the non-expanded configuration and the expanded configuration. In some examples the external wall <NUM> can comprise copper, aluminum, brass or any other suitable material or combination of materials.

The channel <NUM> can also comprise a plurality of internal walls <NUM>. The internal walls <NUM> extend vertically across the hight "h" of the channel <NUM>. The internal walls <NUM> subdivide the channel <NUM> into a plurality of sub-channels <NUM>. The sub-channels <NUM> provide more efficient flow of the working fluid <NUM> within the channel <NUM> due to the lower pressure drops and thus enable efficient heat transfer. In the example shown in <FIG> the internal walls <NUM> are distributed evenly across the width "w" of the channel so that the sub-channel <NUM> all have the same or similar sizes. In other examples different configurations of the internal walls <NUM> and sub-channels <NUM> could be used for optimizing, or substantially optimizing, the flow distribution.

<FIG> show how the channel <NUM> that can be configured to enable movement between a non-expanded configuration and an expanded configuration. <FIG> show a cross section of the channel <NUM> in different stages of fabrication.

<FIG> shows the cross section of the channel <NUM> as shown in <FIG>. In this example the channel <NUM> comprises a multiport tube. This channel <NUM> comprises external walls <NUM> and a plurality of internal channels <NUM> where the internal channels <NUM> are formed from internal walls <NUM>. In <FIG> the channel <NUM> is in the expanded configuration.

In this expanded configuration the side edges <NUM> of the channel <NUM> have a convex shape so that the side edges <NUM> curve outwards.

In <FIG> the internal walls <NUM> are configured with means for enabling expansion of the internal walls <NUM> as the plurality of channels <NUM> are moved between the non-expanded configuration and the expanded configuration. In the example of <FIG> a section of the internal walls <NUM> is removed to create a gap <NUM> between sections of an internal wall <NUM>. This gap <NUM> can allow movement of the lower section of the internal walls <NUM> relative to the upper section of the internal walls <NUM> and so allows for the expansion and contraction of the channel <NUM>.

The gap <NUM> can be sized so as to allow for relative movement of the sections of the internal walls <NUM> while still providing for efficient flow of the working fluid <NUM> through the channel <NUM>. The gaps <NUM> in the internal walls <NUM> can be formed using any suitable method.

Once the gaps <NUM> or other means for enabling expansion of the internal walls <NUM> are provided within the internal walls <NUM>, forces can be applied to the channel <NUM> to cause contraction of the channel into the non-expanded configuration. In the example of <FIG> a horizontal force is applied at the side edges <NUM> of the channel <NUM> and a vertical force is applied at upper edges of the channel <NUM>.

The applied forces cause the channel <NUM> to be contracted into the non-expanded configuration as shown in <FIG>. In this non-expanded configuration, the side edges of the channel <NUM> are provided into a folded configuration <NUM>. This reduces the height of the channel <NUM> and provides a lower profile for the channel <NUM>. When the channel <NUM> is in the non-expanded configuration the size of the gap <NUM> between sections of the internal walls <NUM> is decreased as the upper edges of the channel <NUM> are closer together.

When the channel <NUM> is in the configuration as shown in <FIG> it can be moved into position relative to memory boards or other similar heat sources <NUM>. During hardware operation, heat from the source is transferred into the working fluid <NUM> within the channel <NUM> causing the increase in pressure within the working fluid which, in turn, causes expansion of the channel <NUM> back into an expanded configuration. In the expanded configuration the folded side edges are, at least partially, unfolded.

<FIG> shows an example two-phase cooling system <NUM> that can comprise an evaporator <NUM> with a plurality of channels <NUM> as shown in <FIG>. The two-phase cooling system <NUM> can be configured to be thermally coupled to a secondary cooling system. For example, the two phase-cooling system <NUM> can provide server-level cooling while the secondary cooling system can provide rack and/or room-level cooling. The two-phase cooling system <NUM> can be fluidically isolated from the secondary cooling system to enable the use of two different working fluids within the respective cooling systems. The two-phase cooling system <NUM> can be generally used for cooling any device that generates unwanted heat in a telecommunication system, computing system or in any other suitable type of system.

The two-phase cooling system <NUM> shown in <FIG> is a low-height thermosyphon loop. The thermal performance of the thermosyphon loop can be controlled by selecting an appropriate working fluid <NUM>. The selection of an appropriate working fluid can be based on the trade-off between thermal performance, cost and robust operation.

The evaporator <NUM> of the two-phase cooling system <NUM> is thermally coupled to a heat source <NUM>. The heat source <NUM> could comprise one or more memory boards <NUM> and/or any other suitable heat generating components such as CPUs, GPUs, TPUs, or any other suitable components. The evaporator <NUM> can comprise a plurality of expandable channels <NUM> or wick structures, micro-channels, arrays of evaporator fins, a serpentine arrangement of macro-/micro-channels or any suitable combination of such features. These are not shown in <FIG> for clarity, however they can be incorporated in the evaporator <NUM>.

The evaporator <NUM> is coupled between the downcomer <NUM> and the riser <NUM> of the two-phase cooling system <NUM> so that the working fluid <NUM> can flow from the downcomer <NUM> through the channels <NUM> of the evaporator <NUM> and into the riser <NUM> as indicated by the arrow.

The two-phase cooling system <NUM> also comprises an intermediate heat exchanger <NUM>. The intermediate heat exchanger <NUM> enables the two-phase cooling system to be coupled to a secondary cooling system. The intermediate heat exchanger <NUM> can comprise means that enables heat from the two-phase cooling system <NUM> to be transferred to a secondary cooling system. The secondary cooling system can be an air-cooled or a liquid-cooled system.

In the example of <FIG> the intermediate heat exchanger <NUM> comprises a condenser <NUM> and a rack-level evaporator <NUM>. In the intermediate heat exchanger <NUM>, the working fluid <NUM> from the two-phase cooling system <NUM> is condensed by the condenser <NUM> on the primary side. This causes heat to be transferred to the rack-level evaporator <NUM> on the secondary side of the intermediate heat exchanger <NUM>.

The rack-level evaporator <NUM> forms part of a rack-level cooling loop. The rack-level cooling loop can be an active single-phase or two-phase cooling system, or another passive two-phase cooling system as shown in <FIG>. As mentioned above, the thermosyphon loop and rack-level cooling systems can have the same type working fluid <NUM> or different types of working fluids <NUM>.

The intermediate heat exchanger <NUM> can be positioned directly above the evaporator <NUM> as shown in <FIG>. In other examples the intermediate heat exchanger <NUM> can be positioned in a different position. The position of the intermediate heat exchanger <NUM> relative to the evaporator <NUM> can be determined by the hardware that is being cooled. The location of the intermediate heat exchanger <NUM> relative to the evaporator <NUM> dictates the geometry (diameter and length) of the downcomer <NUM> and riser <NUM>.

The condenser <NUM> is coupled between the riser <NUM> and the downcomer <NUM>. In this example the condenser <NUM> is a low-profile condenser <NUM> so that it has a flat, or substantially flat, shape. In this example the condenser <NUM> also comprises a reservoir <NUM>. The reservoir <NUM> can be configured to store working fluid <NUM> and optimize, or substantially optimize, thermal performance. The reservoir <NUM> can be machined directly in the outlet header of the condenser <NUM> or incorporated along the downcomer <NUM>. The reservoir can have a circular, rectangular or any other cross-sectional area and/or shape.

The rack-level evaporator <NUM> can comprise any means that enables heat to be transferred from the condenser <NUM> to a secondary cooling system. The condenser <NUM> can comprise a plurality of wick structures, micro-channels, arrays of evaporator fins, a serpentine arrangement of macro-/micro-channels or any suitable combination of such features.

<FIG> show an example condenser <NUM> in more detail. The example condensers <NUM> could be provided within a two-phase cooling system <NUM> as shown in <FIG> or within any other suitable type of cooling system.

<FIG> shows the intermediate heat exchanger <NUM> comprising the condenser <NUM> and the rack-level evaporator <NUM>, <FIG> shows a top view of the condenser <NUM> and <FIG> shows a bottom view of the condenser <NUM>.

In the example of <FIG> the rack-level evaporator <NUM> comprises an inlet <NUM> and an outlet <NUM>. The inlet <NUM> and the outlet <NUM> are provided on opposing sides of the rack-level evaporator <NUM> so as to enable working fluid <NUM> to flow through the rack-level evaporator <NUM>. In the example of <FIG> the inlet <NUM> and the outlet <NUM> are configured to extend in a horizontal direction so as to allow for flow of the working fluid <NUM> in a horizontal direction. This also provides the rack-level evaporator <NUM> with a low profile which reduces the form factor of the intermediate heat exchanger <NUM>. The profile provides a more versatile cooling system that can be used with a wider range of devices. Other configurations and arrangements for the inlet tube <NUM> and outlet tube <NUM> can be used depending on the hardware that is to be cooled.

The condenser <NUM> also comprises an inlet port <NUM> and an outlet port <NUM> for the flow of working fluid <NUM>.

The condenser <NUM> comprises a reservoir <NUM> for storing working fluid <NUM>. In the examples of <FIG> the reservoir <NUM> is coupled to an outlet header of the condenser <NUM>. Positioning the reservoir <NUM> in the outlet header of the condenser <NUM> rather than within the downcomer <NUM> can make the cooling system <NUM> easier to fabricate. Positioning the reservoir <NUM> in the outlet header also ensures that the reservoir <NUM> is in the highest position within the cooling system <NUM> providing optimal thermal performance. <FIG> also show that the reservoir <NUM> can be designed with a filling port <NUM> in order to charge the cooling system <NUM> before operation.

The reservoir <NUM> of the condenser <NUM> can reduce sub-cooling of the working fluid <NUM>. This can help to prevent flooding of the condenser <NUM> which would reduce the thermal efficiency of the cooling systems.

<FIG> shows an evaporator <NUM> coupled to a rack manifold <NUM>. The rack manifold <NUM> enables the evaporator <NUM> to be fluidically coupled to a condenser <NUM> and other components of a cooling system. The evaporator <NUM> could comprise a plurality of channels <NUM> as shown in <FIG> or could be manufactured with any other suitable type of structures to enhance heat transfer. The evaporator <NUM> can be thermally coupled via a thermal interface material (not shown in <FIG>) to a heat source <NUM>. The heat source could be a memory board <NUM>, heat generating components such as CPUs, GPUs, TPUs, or any other suitable heat sources.

The evaporator <NUM> is coupled to the rack manifold <NUM> that comprises a downcomer <NUM> and a riser <NUM>. The downcomer <NUM> and the riser <NUM> are configured so as to allow for the flowing of working fluid <NUM> between the condenser <NUM> (not shown in <FIG>) and the evaporator <NUM>.

In the example shown in <FIG> means for removably coupling the evaporators <NUM> to the rack manifold <NUM> are provided in both the downcomer <NUM> and the riser <NUM>. In this example the means are represented by quick couplings provided in both the downcomer <NUM> and the riser <NUM>. Other means and/or type of couplings could be used in other examples of the disclosure. The means could enable the evaporator <NUM> to be removed from the rest of the cooling system <NUM> while the hardware is in use. This can provide for a hot-swappable evaporator <NUM> or other heat exchangers <NUM>.

The quick couplings <NUM> that can be used are schematically shown in more detail in <FIG>. The quick couplings <NUM> comprise an adapter plug <NUM>, a valve <NUM> and a housing <NUM>. Depending on the operating conditions and system geometry the quick couplings can be either blind-mate or hand-mate.

<FIG> schematically show the layout of a cooling system for multiple components to be cooled within a targeted hardware <NUM>. The cooling system can use passive two-phase flow as shown in <FIG> The cooling system comprises a plurality of evaporators <NUM> comprising a plurality of channels <NUM> as shown in <FIG>. In some examples the evaporators <NUM> can comprise wick structures, micro-channels, arrays of evaporator fins a serpentine arrangement of macro-/micro-channels or any suitable combination of such features.

In the example of <FIG> the hardware <NUM> comprises memory units <NUM> and processing units <NUM>. In this example the hardware <NUM> comprises four memory units <NUM> and two processing units <NUM>. Other arrangements and configurations of the components in the hardware <NUM> could be used in other examples of the disclosure.

The memory units <NUM> can comprise stacks of memory boards <NUM>. The expandable channels <NUM> of the evaporators <NUM> can be fitted into gaps between adjacent memory boards <NUM>. This can provide efficient cooling of the memory boards <NUM>. Additional evaporators <NUM> can also be provided on the processing units <NUM>.

In the example of <FIG> the two-phase cooling system <NUM> is configured so that the evaporators <NUM> are connected in series. The evaporators <NUM> are connected in series so that working fluid <NUM> from the outlet of a first evaporator <NUM> is then provided to the inlet of the next evaporator <NUM> within the series. In this series arrangement the working fluid <NUM> passes through each of evaporators <NUM> sequentially.

In the example shown in <FIG> the two-phase cooling system <NUM> comprises two series loops. A first series loop comprises the evaporators <NUM> for cooling the memory units <NUM> and a second series loop comprises the evaporator <NUM> for cooling the processing units <NUM>. Depending on the hardware configuration and thermal design power of the different components, other arrangements could be used in other examples of the disclosure.

In the example of <FIG> the two-phase cooling system <NUM> is configured so that the evaporators <NUM> are connected in parallel. The evaporators <NUM> are connected in parallel so that the inlets and the outlets of each evaporator <NUM> share common server-level manifolds. In this example the server-level inlet manifold has the working fluid <NUM> coming from the downcomer <NUM>, while the server-level outlet manifold has the working fluid <NUM> going to the riser <NUM>. Depending on the hardware configuration and thermal design power of the different components, other arrangements could be used in other examples of the disclosure.

<FIG> shows an example evaporator <NUM> that can be used in cooling systems operating in single- and two-phase flow, as well as in active and passive mode. For example, it could be used in the two-phase cooling system <NUM> of <FIG>.

The example evaporator <NUM> comprises a base plate <NUM> and a plurality of evaporator fins <NUM>. The evaporator <NUM> would also comprise a cover plate (not shown in <FIG>) arranged to cover the base plate <NUM> and evaporator fins <NUM>.

The base plate <NUM> comprises a flat or substantially flat surface. The base plate <NUM> can comprise a thermally conductive material. When the evaporator <NUM> is in use the base plate <NUM> can be thermally coupled to a heat source to enable heat to be transferred from the heat source into working fluid <NUM> within the evaporator <NUM>.

The plurality of evaporator fins <NUM> extend out of the surface of the base plate <NUM>. The evaporator fins <NUM>, at least partially, define flow paths for the working fluid <NUM> through the evaporator <NUM>.

In the example of <FIG> the evaporator fins <NUM> comprise elongate structures that extend perpendicularly, or substantially perpendicularly, out of the base plate <NUM>. In the example shown in <FIG> the evaporator fins <NUM> comprise elongate plates that extend in parallel, or substantially parallel, across the surface of the base plate <NUM>.

The evaporator fins <NUM> can comprise any suitable thermally conductive material. The evaporator fins <NUM> can comprise the same material as the base plate <NUM> and the cover plate.

<FIG> show another cooling system arrangement that could be used for the cooling of a targeted hardware <NUM>. In this example the hardware <NUM> comprises four memory units <NUM> and two processing units <NUM>. Other hardware configurations701 could be used in other examples of the disclosure.

In the example hardware <NUM> shown in <FIG> evaporators <NUM> are provided on the processing units <NUM>, while the memory units <NUM> and other low-power components on the server board are cooled via air-cooling heat sinks <NUM>. The evaporators <NUM> could comprise a plurality of wick structures, micro-channels, arrays of evaporator fins, a serpentine arrangement of macro-/micro-channels or any suitable combination of such features. <FIG> shows example micro-channels that can be used.

The hardware <NUM> shown in <FIG> comprises a hybrid cooling system, as the two processing units <NUM> are two-phase cooled, while the other components, such as the memory units <NUM>, board, and secondary chips, are cooled by an air-cooling system.

The air-cooling system is configured to draw in cold air at the front of the hardware <NUM> as indicated by the arrow <NUM>. The air then flows through the different air-cooling heat sinks <NUM> located on the hardware components and it increases its temperature thanks to the heat dissipation from the memory units <NUM> and other heat sources <NUM>. The heated air is then expelled from the back of the hardware <NUM> as indicted by the arrow <NUM>.

In the example shown in <FIG> the hardware <NUM> comprises a baffle <NUM>. The baffle <NUM> can be an adjustable baffle and is provided around the memory units <NUM> and other heat sources <NUM>. The baffle <NUM> provides means for directing the air flow over the memory units <NUM> and other air-cooled components in order to reduce pressure drop and maximize, or substantially maximize, the heat transfer provided by the air cooling. The arrows and baffle shown in <FIG> show a uniform air flow over the hardware components. In other examples additional baffles, or other means for guiding air flow, can be installed in the hardware <NUM> so as to provide for increased air flow over the air-cooled components compared to other components, which can be two-phase cooled or do not require specific cooling. Control of the air flow can be beneficial to improve energy efficiency and reduce noise level.

A plurality of fans <NUM> are also provided at the rear of the hardware <NUM>. The plurality of fans <NUM> are configured to draw the air through the hardware <NUM>. In the example of <FIG>, three fans <NUM> are provided. Other numbers of fans, locations of fans and air flow directions can be used in other examples of the disclosure.

In the example of <FIG> the hardware <NUM> also comprises an additional cooling system <NUM>. In this example the additional cooling system <NUM> can comprise a passive two-phase cooling system <NUM> as shown in <FIG>. The additional cooling system <NUM> is configured to enable cooling of the heated air that has been drawn over the memory units <NUM> and any other air-cooled components. The two-phase cooling system is therefore configured to enable heat to be recovered from the air-cooling system. The additional cooling system <NUM> is provided at the rear of the hardware <NUM> so that the air from the air-cooling system can be cooled before exiting the hardware <NUM> and entering the surrounding environment.

The additional cooling system <NUM> can comprise an evaporator <NUM> positioned between a downcomer <NUM> and a riser <NUM>. <FIG> shows a section of the additional cooling system <NUM> and evaporator <NUM> in more detail. The evaporator <NUM> can be connected to a rack manifold as described above or by using any other suitable connection.

The evaporator <NUM> of the additional cooling system <NUM> is provided at the rear of the hardware <NUM> and comprises an inlet <NUM> that is coupled to the downcomer <NUM>. The inlet <NUM> enables the single-phase working fluid <NUM> to be provided to the evaporator <NUM>.

The working fluid <NUM> flows through the evaporator <NUM> as indicated by the arrow <NUM>. This causes the working fluid <NUM> to be heated by the air that is drawn across the evaporator <NUM>. The air can be drawn across the evaporator <NUM> by the plurality of fans within the fan tray <NUM>. In this example three fans <NUM> are provided within the fan tray <NUM>. Other numbers of fans <NUM>, locations of fans and air flow directions can be used in other examples of the disclosure.

Due to the heat transfer between the heated air and the working fluid <NUM>, the working fluid <NUM> is partially boiled and the two-phase working fluid <NUM> is then expelled from the evaporator <NUM> through the outlet <NUM> and provided to the riser <NUM>.

The additional cooling system <NUM> therefore enables additional heat to be removed from the data centre <NUM>. This heat could be recovered and transferred elsewhere for heating or reused in waste heat recovery applications. This can provide for more energy efficient hardware <NUM>. The example shown in <FIG> is suitable for use in datacenters, and other hardware environments, that operate with traditional cooling methods, such as direct expansion, chilled water, evaporative free cooling, or any other traditional cooling method.

The additional cooling system <NUM> can also help to mitigate hot spots that can appear when upgrading hardware with additional IT, telecom and computing capabilities in existing datacenters in which room-level cooling infrastructures have been sized for a given cooling capacity.

In the example shown in <FIG> the cooling system <NUM> is shown as being provided in addition to the evaporators <NUM> used on the processing units <NUM>. In other examples the additional cooling system <NUM> could be provided in hardware <NUM> without these primary evaporators <NUM> or in any other suitable configuration.

In the example shown in <FIG> the additional cooling system <NUM> is configured to cool the air before it is expelled from the hardware <NUM> into the surrounding environment. In other examples the additional cooling system <NUM> can be configured to enable the cooled air to be recirculated within the hardware <NUM> rather than exiting the hardware <NUM>. In such examples, baffles or any other suitable means for guiding air flow can be provided within the hardware <NUM>. Recirculating the air within the hardware <NUM> can reduce the heat expelled into the environment surrounding the hardware <NUM> and can allow more efficient cooling and reduced overall energy consumption.

If it is intended to use `comprise' with an exclusive meaning then it will be made clear in the context by referring to "comprising only one.

The use of the term 'example' or `for example' or 'can' or 'may' in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus `example', `for example', `can' or 'may' refers to a particular instance in a class of examples.

The term 'a' or 'the' is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use 'a' or 'the' with an exclusive meaning then it will be made clear in the context. In some circumstances the use of `at least one' or 'one or more' may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning.

The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result.

Claim 1:
A heat exchanger (<NUM>) comprising:
a plurality of channels (<NUM>) configured for flow of working fluid wherein the plurality of channels (<NUM>) are configured to move between a non-expanded configuration and an expanded configuration such that, in the non-expanded configuration the plurality of channels (<NUM>) are sized so as to allow for movement of the heat exchanger (<NUM>) relative to one or more heat sources (<NUM>) and in the expanded configuration the plurality of channels (<NUM>) are sized so as to restrict movement of the heat exchanger (<NUM>) relative to the one or more heat sources (<NUM>), wherein the plurality of channels (<NUM>) are configured so that changes in internal pressure of the working fluid causes the plurality of channels (<NUM>) to move between the non-expanded configuration and the expanded configuration,
characterised in that
the plurality of channels (<NUM>) comprise a plurality of internal walls (<NUM>) configured to provide a plurality of sub-channels (<NUM>) and wherein the plurality of internal walls (<NUM>) comprise means for enabling expansion of the internal walls (<NUM>) as the plurality of channels (<NUM>) are moved between the non-expanded configuration and the expanded configuration.