WO2020025717A1

WO2020025717A1 - Liquid cooled server module

Info

Publication number: WO2020025717A1
Application number: PCT/EP2019/070715
Authority: WO
Inventors: Anthony Robinson; Cathal WILSON; Nicolas Baudin; Raphael CAGNIN
Original assignee: The Provost, Fellows, Foundation Scholars and the other members of Board, of the College of the Holy and Undivided Trinity of Queen Elizabeth near Dublin
Priority date: 2018-08-02
Filing date: 2019-07-31
Publication date: 2020-02-06
Also published as: GB2576032A; GB201812595D0; GB2576032B

Abstract

A liquid cooled server module comprising side walls defining an enclosure volume within the module within which electronic components are packaged is described.

Description

Title

Liquid Cooled Server Module

Field

The present application relates to server modules and in particular to a liquid cooled server module. In one aspect the present teaching relates to a sealed liquid cooled server module incorporating an integrated coolant in thermal contact with side walls of the server module.

Background

Data centre server modules are simply computers that are packaged in a slim form factor in order that they can be stacked compactly and thus maximize computing density in a server rack cabinet. In this way, server modules suffer the same thermal management issues as any other computer, though the problem is exacerbated due to the highly integrated packaging and high computing capacity of server modules, which limits the real estate available for thermal management hardware. This is particularly problematic considering that air is still primarily being used as the coolant in data centres.

Figure 1 shows an example of a known typical 1 U server module 100. Server modules such as the module 100 are provided in standard dimensions and the example shown is 19" rack-mountable module, about 44.5mm in thickness. The module comprises side walls 110 defining an enclosure volume 115 within the module within which assorted electronic components 120 are packaged. At a first end of the enclosure 115, a bank of fans 125 is situated which draws cooled air into interior volume forces it to flow over the electronic components 120, providing cooling. As it is seen, a CPU heat sink 130 and RAM modules 135 are aligned parallel to the flow, which is intentional and standardised in that the layout of the components and heat sinks are very specifically located and arranged with the higher power, more crucial components near the fans and aligned in such a way as to reduce blockage (pressure drop) of the air flow. This is the standard configuration of server modules and blade servers though specific components and layouts may differ depending on the required server rack functionality. It will be appreciated that the enclosure volume 115 of such rack modules is intentionally not thermally insulated from the ambient conditions external to the server module. The presence of multiple grills- such as the grills 150- at the end of the rack module is purposeful in that it allows the circulation of active air cooling as effected by the fans 125.

It is acknowledged that air cooling of such server modules in data centres is on its way out. The reason is simple: air is one of the worst heat transfer fluids available. Because of this, high power density electronic components in server modules (e.g. central processing units (CPUs), graphics processing units (GPUs)) require disproportionately large finned metal heat sinks. These heat sinks serve to increase the surface area for heat transfer in order to

compensate for the poor thermal transport properties of air. In a server module 100 such as that shown in Figure 1 , the bank of high powered fans 125 then must force large volumes of air through the module, which are densely packed with thousands of electronic components 120 and many large metal heat sinks 140 (which are attached to very small electronic components). Problematically, the least reliable components in the server module are the fans 125, which paradoxically are the most crucial ones since a lack of coolant causes failure of the entire module. Another major problem with fans is noise. The noise levels are so high that it exceeds health and safety standards.

However, the most problematic issue associated with air cooling is energy consumption. The air which cools the server modules heats up and thus must also be cooled down. In a data centre, this is accomplished by a massive air- conditioning system. To put this into perspective, for every unit of energy used by the server modules to perform their computing services, about the same amount of energy is required to condition the air so that it can be used and reused as a coolant. This is a striking data point considering that experts estimate that the‘business as usual’ model will result in the communications industry using 20% of all the world’s electricity by 2025. Thus, there is a real and more than critical need for viable yet disruptive technological solutions that will significantly curb the escalating energy demand of data centres.

US2009/0262495 uses a heat conducting element to conduct heat away from heat producing components provided within computer equipment to a piped cooling liquid, the piped cooling liquid itself not being piped internally to the computer equipment. It describes using conventional computer equipment cases which are known not to be thermally sealed units, i.e. they are open to ingress and egress of bulk air and liquid through side walls of the cases.

US2014/0096930 describes problems associated with air cooling of servers within data centres and describes a liquid-cooled electronics rack but similarly to US2009/0262495 appears to facilitate air flow through the actual computer cases.

Summary

These and other problems are addressed in accordance with the present teaching by a liquid cooled server module comprising flow channels thermally coupled to side walls of the server module such that the chassis of the server module functions as a heat exchanger. The flow channels are configured to receive a liquid coolant, which operably dissipates heat away from the side walls thereby providing a cooling of components within the internal volume of the server module. In one aspect, the flow channels are integrally formed in the side walls of the server module. In another aspect, the flow channels are provided in a cooling module that is thermally coupled to the side walls of the server module. By providing flow channels within which a liquid coolant may operably flow, the liquid coolant is operably in thermal contact with the side walls with the result that the side walls themselves can be used as a heat sink to which heat generated by electronic components can be transferred and then dissipated away from the server module by the liquid coolant flowing within the flow channels.

As detailed above, in one aspect the server module side walls include integrated flow channels through which a coolant may pass. In another aspect, a cooling module comprising flow channels is provided in intimate thermal contact with the side walls. In both aspects heat present in the side walls is operably dissipated into the liquid coolant within the flow channels through a conduction process.

In one configuration, the server modules are provided as sealed units whose internal volume is isolated from the ambient environment. The unit is configured such that an electronics’ cooling system is enclosed within the module itself with no bulk air or liquid flow into or out of the module. Air or liquid cannot freely pass through the side walls of the module. Such an electronics’ cooling system may comprise an internal liquid cooling system within the sealed unit and using an internal pump, liquid is circulated within the module casing and extracts heat from the electronic components and circulates it to an internally located liquid heat exchanger which is thermally coupled to at least one internal surface of the side walls of the sealed unit. In order to extract the heat and transport it to a remote heat exchanger or other heat dump, an external liquid heat exchanger is thermally coupled - for example mechanically fixed to the side casing in contact with the internal one. The liquid within the flow channels of the external liquid heat exchanger is heated from the heat provided by the internal liquid stream and can be then transported via conventional plumbing away from the server module. This external liquid heat exchanger comprises a dedicated fluid loop which is physically isolated from the internal volume of the server module and hence, in the unlikely event that it leaked, the effect of that leaking would not flood into the sealed server module unit.

In one aspect, liquid from a plurality of individual external liquid heat exchangers is plumbed via a series of manifolds to a common heat drain. In such an arrangement a plurality of individual server modules could be stacked together, in for example a rack configuration, each having its dedicated internal electronics cooling system within the internal volume of the sealed server module unit, each having a dedicated external liquid heat exchanger. The liquid fluid loops from each external liquid heat exchanger could be arranged to interface with a common heat drain. That common heat drain could be specific to the rack, or could be a common heat drain for a plurality of racks. Accordingly, a first embodiment of the application provides a server module as detailed in the claims that follow. The present teaching also provides a server rack as defined in the independent claim directed thereto.

Brief Description of the Drawings

The present application will now be described with reference to the accompanying drawings in which:

Figure 1 is an example of the internal layout of a known server module.

Figure 2 is an example of the internal layout of a server module in accordance with the present teaching.

Figure 3 is an example of another configuration of a server module in accordance with the present teaching.

Figure 4 is an example of another configuration of a server module in accordance with the present teaching.

Figure 5 shows an example of a server rack incorporating a plurality of server modules in accordance with the present teaching.

Figure 6 shows in schematic form a section through a server module in accordance with the present teaching.

Figure 7 shows in schematic form a section through a server module in accordance with the present teaching.

Figure 8 shows a detailed schematic of an exploded portion of Figure 4 with detail on one exemplary heat exchanger interface comprising first and second fluid loops for extracting heat from the internal enclosure volume of the server module

Detailed Description Of The Drawings

Figure 2 shows in schematic form an example of a liquid cooled server module in accordance with one aspect of the present teaching. Similarly to conventional server modules, the server module 200 of Figure 2 comprises a chassis having side walls 210 defining an enclosure volume 215 within the module within which assorted electronic components 220 are packaged. It will be appreciated that the number and shape of these components as illustrated is purely illustrative.

The server module 200 comprises a flow channels 221 , 225 which are thermally coupled to at least one of the side walls 210. The flow channels are arranged in a flow loop comprising a flow line 221 and a return line 225. In this way a liquid coolant can be circulated in thermal proximity to the side wall 210 of the server module and can be used to dissipate heat present in the side wall away from the server module.

The example of Figure 2 shows an overlap region 230 between the flow channels 221 , 225 and interior surfaces of the side walls 210. The efficacy of the thermal transfer from within the volume 215 to the flow channels 221 , 225 can be improved by increasing this contact area. For example, as shown in Figure 3, the overlap region 230 can extend along the entire length of the side walls. In other arrangements, flow channels can be provided in thermal contact with all side walls of the server module.

The material within which the flow channels are defined can be the same as the material used to form the server modules side walls. In another arrangement, the material within which the flow channels are defined has thermal conductivity characteristics that are better than the material used for the overall structure of the side walls. For example, copper could be used as the material within which the flow channels are defined. To improve the thermal transfer from the internal volume 215 through the side walls to the liquid coolant flowing within the side walls, the side walls, at least in the overlap region 230 could be fabricated from the same material within which the flow channels are defined.

By having flow channels thermally coupled to side walls of the server module and having the flow channels configured to receive a liquid coolant which operably dissipates heat away from the side walls the present teaching thereby provides a cooling of electronic components 220 within the internal volume 215 of the server module. In the example of Figures 2 and 3, the flow channels are provided in a cooling module 240 that is thermally coupled to the side walls of the server module. In another aspect, the flow channels are integrally formed in the side walls of the server module. In both aspects heat present in the side walls is operably dissipated into the liquid coolant within the flow channels through a conduction process.

By providing flow channels within which a liquid coolant may operably flow, the liquid coolant is operably in thermal contact with the side walls with the result that the side walls themselves can be used as a heat sink to which heat generated by electronic components can be transferred and then dissipated away from the server module by the liquid coolant flowing within the flow channels.

One mechanism of transferring the heat from the electronic components 220 to the side walls- for subsequent transfer to the liquid flowing within the flow channels, is to locate each of the electronic components on a heat sink that thermally conducts the heat away from the electronic component to the side walls. In another arrangement, the server module may be provided as sealed units whose internal volume is isolated from the ambient environment. The sealed unit in such a configuration will have no bulk air or liquid flow into or out of the module and can therefore be considered a hermetically sealed internal volume. In such an arrangement the internal volume could be filled with a primary coolant which is arranged to absorb heat generated by the electronic components and transfer that heat to the liquid flowing within the flow channels where it is then dissipated away from the server module. The flow channels could be thermally coupled to the side walls such as heretofore described.

Alternatively. The flow channels could pass through the side walls into the internal volume and come into thermal contact with the primary coolant. In either scenario, the efficiency of the thermal transfer by the primary coolant could be improved by actively circulating that coolant within the volume 215, for example by having a circulating pump, which actively moves the liquid within the volume 215. Other arrangements that could be employed with a sealed unit is the choice of liquid for the primary coolant and/or pressurising the unit 200 to vary the heat transfer efficiency. In another configuration the primary coolant is air, not liquid. Again, the air within the hermetically sealed volume is a fixed volume of air- it does not pass through the side walls as the sealed volume is airtight. It does however circulate within the volume and this distribution can be used to move heat away from specific thermal sources - i.e. the electronic components- for subsequent transfer out of the volume using the flow

channels. Figure 4 shows a further modification wherein the server module is again a hermetically sealed unit and comprises an internal liquid cooling system 400 provided within the sealed unit. The liquid cooling system comprises a fluid network 410 within which a liquid coolant can be circulated using an internal pump 420. The flow fluid network 410 facilitates a circulation of the liquid coolant within the module casing 215 and extracts heat from the electronic components 220 and circulates it to an internally located liquid heat exchanger 430 which is thermally coupled to the flow channels which may in some configurations me coupled to at least one internal surface of the side walls 210 of the sealed unit. In order to extract the heat and transport it to a remote heat exchanger or other heat dump, an external liquid heat exchanger 230 is thermally coupled - for example mechanically fixed to the side casing in contact with the internal one. This external liquid heat exchanger is similar in form to that described above in that defines flow channels 221 , 225 within which liquid may operably flow. That liquid is heated from the heat provided by the internal liquid stream 410 and can be then transported via conventional plumbing away from the server module. Each of the internal and external flow networks are separate and distinct in that they are not in fluid communication with one another. As each are provided on respective sides of the side walls 210 of the sealed server module enclosure, any leaking of a liquid from a respective one of the flow networks will not cause a flow of liquid across the side wall.

By provided a sealed unit, the present teaching achieves complete thermal isolation of internal components within a server module from the ambient surroundings within the rack cabinet. The heat generated by the electronics within the server module enclosure is transferred into one or more fluid mediums which is subsequently routed to the compact liquid heat exchanger 430 that is thermally coupled to or forms an integral part of the enclosure casing. In this exemplary arrangement of Figure 4, the server module 400 is sealed, thus enclosing a certain volume of air, which stays contained within the module. This represents a significant departure from the current practice for server cooling which rely on open grates and perforations in the casing in order that internal fans can draw through the module to cool the electronics. In accordance with this aspect of the present teaching, all of the heat generated by the electronics is transferred to internal liquid heat exchangers 410. It is also a departure from liquid-cooled server modules, which use externally supplied liquid (which enters the module itself via fluidic fittings) to cool the high-power components only (CPUs/GPUs), with the rest of the components, accounting for about half of the overall power usage, still relies on a through-flow of large volumes of air. In accordance with this aspect of the invention, the liquid forced by one or more internal pumps 420 circulates a primary coolant, which thermally communicates with the heat generated by all of the electronics. Subsequent to capture of heat into the fluid stream of the primary coolant, the internal liquid is routed to an internally-mounted compact liquid heat exchanger 430. This heat exchange can be provided in tight mechanical contact with or itself forms a portion of the external casing of the server module. In other configurations, the liquid heat exchanger comprises a flow network that passes into the

hermetically sealed volume. This flow network is separate to the fluid that is within the volume- it can be thermally coupled to the internal volume but is not fluidly coupled- there is no fluid exchange between a fluid within the fluid network that passes in and out of the sealed volume and the fluid that is retained within the server volume. This is an important feature of the invention as it completely isolates the internal thermal liquid management system from the external thermal management systems i.e. there are no liquid piping connections to/from the stand-alone module itself, it is sealed.

Related to this, one barrier to the uptake and acceptance of liquid, particularly water, cooling of server modules is leakage. One advantage of sealing the individual modules is that any internal leak within a module will only affect that particular module. At the same time, each module is protected from any external leaks, or other dangerous situations like fire suppression systems. This facilitates arrangements such as shown in Figure 5 which shows a schematic of a server rack cabinet 500, where a plurality of individual modules 400a, 400b ... 400f are tightly stacked vertically to create high computing density per unit floor area. For conventional liquid-cooled modules, which are still vented and partially air-cooled, any leak can potentially damage all the modules in the cabinet, incurring significant expense in terms of replacement cost and down time. In accordance with the present invention, any leak from the internal flow loop(s) for any one module is contained within the modules itself, thus requiring only the replacement or repair of the faulty module. Replacing and/or repairing individual modules is a common practice. Flere it should be mentioned that the internal liquid-based thermal management system can use dielectrics as the working fluid, meaning that any internal leak will not damage the electronic components and require only repair of the cooling system.

The plurality of individual modules 400 can be thermally coupled to their own external heat exchanger 230, which share common flow and return circuits 200,225. The common flow and return loops can be coupled to a shared heat exchanger 530 - i.e. a plurality of individual modules 400 are thermally coupled via a shared loop circuit 200, 225 to a shared server rack heat exchanger 530. This thermal heat exchanger 530 can then be coupled to a further cooling system 550 via a server rack flow 535 and return circuit 540

For the server rack shown in Figure 5, each sealed rack module is connected to its own external compact liquid heat exchanger. This network is arranged hydraulically in parallel and can be circulated to an intermediate compact liquid-liquid heat exchanger, thus having the entire thermal

management system enclosed in the cabinet, as shown. Again, it is possible to circulate a dielectric liquid within this hydraulic network 200/225 to avoid any possible damaging effects of water. Thus, all of the internals of the cabinet can be isolated from the mains water supply 535/540. Importantly, the entire cabinet can be sealed which protects it from any damaging influences/events associated with the external environment and will isolate any noise generated within the enclosure. For the latter, sound absorbing material can be used to line the interior of the cabinet walls.

One technical short falling of conventional air-cooled server modules is that high-powered fans (about 10% of total module power usage) are used to force air flow through the module in order that it cools the electrical

components. Moving air from one end to the other is a considerable task due to the highly integrated and closely packed nature of 1 U server modules. The air heats from the entrance to the exit, which also means that the downstream components are cooled by heated air, making it much less effective. This requires very specialized design in order to ensure all of the components are cooled adequately. The design cycle times and associated cost for new product development are thus considerable. Furthermore, the hot expelled air must be conditioned, cooled and handled at the building level requiring significant infrastructure and energy cost. Current liquid-cooled systems use targeted liquid cooling of the high-powered components (CPUs/GPUs), typically using pressurized external liquid that enters the modules via fluidic fittings. This can capture about half of the thermal energy of the module with the rest handled in the conventional forced air cooling method. Therefore, these liquid cooling systems solve a portion of the energy problem, but do nothing to improve the problem associated with the infrastructure i.e. they still require CRAC/CRAFI systems, hot isles, cold isles etc. Also, having external liquid entering a server module i.e. the negative association of‘plumbing’ fitting on a computer, is a large barrier considering the conservative nature of the industry.

In order to eliminate both the energy and infrastructure problem, all of the heat energy generated by the electronic components in a server module must be transferred into a fluid medium at the server module level; this includes that from the high-power density (CPUs/GPUs) as well as the multitude of low power components. Problematically, supplying liquid cooling to every component is not feasible from both cost and general practicality points of view. Figures 6 and 7 shows two embodiments of the current invention which are configured to address these specific issues. In accordance with this aspect of the present teaching otherwise unused surface area of the top and bottom of the module casing is configured to incorporate ultrathin liquid cold plates 600 as part of the casing structure. Liquid cold plates comprise a plate having a fluid network 610 that defines a flow path that moves liquid under the devices. After the heat is absorbed into the liquid, it is taken out of the plate and into the larger system 430. While water or water/glycol are the most common fluids used in liquid cooling, dielectric oils and refrigerant are other fluids that can be utilized.

Within the internal volume of the server module electronic components 220 such as low power density chips, CPUs and GPUs and other electronic components arranged on one or more PCBs 620 can be provided.

In addition to an internal fluid network 410- such as described above, further air cooling of individual components can be provided. Such air cooling can be effected using an electrohydrodynamic, piezo-electric synthetic or conventional air movers 630 which are arranged to pass air through the internal volume, the heated air ultimately passing the heat into the liquid cold plate network 610 for ultimate passing into the internal heat exchanger 430 and subsequent distribution to an external heat exchanger 230 - such as described above. The separation of the internal volume into distinct regions can be provided by means of cell barriers 635.

Figure 6 and 7 differ from one another in that Figure 6 provides a series of metallic heat fins as heat sinks 640 to extract heat from high power output electronic components 220, examples being CPUs or GPUs. In contrast, Figure 7 shows how such heat can be extracted using a waterblock arrangement 645.

Figure 8 shows an example of a preferred arrangement for the compact liquid heat exchanger 430 that is thermally coupled to or forms an integral part of the enclosure casing as was described with reference to Figure 4. In this arrangement each of the flow networks (410, 221 , 225) on either side of the side walls of the server module enclosure 400 are coupled to a liquid cooled thermal heat sink device 901. In this example, two identical devices 901 are provided on either side of the server module side wall and are arranged on either side of a thermal surface 930. In a preferred arrangement the thermal surface 930 is formed from two distinct parts that are operably brought into thermal contact with one another. In this way, each of the two devices 901 can be separated away from the server module independently of the other.

Each device 901 comprises a housing having a fluid inlet (410a, 221 ) and a fluid outlet (410b, 225) respectively. Each fluid inlet is in fluid communication with a plenum entry chamber 900, the plenum chamber comprising a jet orifice plate 902 which defines a plurality of jet orifices 920 through which a

pressurised liquid can operably exit the plenum entry chamber 900 and contact the thermal surface 930. Each device further comprises at least one exit channel 910, the at least one exit channel being configured to deliver fluid exiting the jet orifices 920 to the fluid outlet.

By providing a plenum chamber which generates a stagnant pressurised flow and then using a plurality of jet orifices 920 to force a pressurised liquid flow onto a thermal surface, it is possible to reduce the actual flow of liquid into the plenum without compromising the overall heat transfer achieved. The heat that is conveyed by the fluid inlet 410A is passed onto the thermal surface 930 where it migrates across to the opposing side of that surface. The consequence of spraying a cooler liquid from the fluid line 221 into the respective plenum 900 and the spraying through the jet orifices 920 onto that surface from outside the server module chamber, effects a drawing of heat away from that thermal surface 930 and the conveying of that heat away through the exit channel 225. Further detail on such a thermal heat sink device can be found in our concurrently filed British Application GB 1812592.2 the content of which is incorporated herein by way of reference.

An arrangement in accordance with the present teaching is advantageous for a number of reasons including:

(i) it facilities novel air and liquid cooling within the enclosure,

(ii) does not have liquid‘plumbing’ fitting entering the module itself- the module is sealed, (iii) by sealing the server module, other server modules are protected in the event that there is an internal leak,

(iv) there is significant, up to 100%, capture of heat into an external ‘mains’ liquid which eliminates the need of air conditioning and handling units, hot and cold isles, false floors etc

It will be appreciated that the present teaching advantageously in certain configurations configures the chassis of the server module to function as a heat exchanger. By providing the chassis as a heat exchanger and/or hermetically and thermally sealing the volume of the server module, it is possible to internally cool electronic components of the server module in a“closed loop” architecture. This can be provided by internally provided liquid loops such as provided by thin cold plates or agitation of the internal air volume using different air movers, such as synthetic jets and EHD blowers, which have no moving parts and thus super high reliability. The displacement of heat away from the electronic components is then extracted from the internal volume using the heat exchanger functionality of the chassis. The liquid loop of the flow channels that can be provided in, or in intimate thermal contact with, the side walls is a closed loop that doesn’t enter the sealed unit of the server module. At the same time, the heat that is extracted by the internal cooling components is only extracted by the thermal interface between those internal cooling components and the flow channels which could be integrated with the side walls. The flow channels provide an indirect cooling effect, the direct cooling effect being provided by the internal cooling components- be those liquid driven or air driven.

The words comprises/comprising when used in this specification are to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims

1. A liquid cooled server module comprising a chassis having side walls defining a thermally sealed enclosure volume within which electronic components are packaged, the thermally sealed enclosure volume being a hermetically sealed internal volume with no bulk air or liquid flow into or out of the volume, the server module further comprising flow channels passing to, or through, the side walls of the server module, the flow channels being configured to receive a liquid coolant which operably dissipates heat away from the hermetically sealed internal volume, thereby providing a cooling of the electronic components within hermetically sealed enclosure volume of the server module.

2. The server module of claim 1 wherein the flow channels are integrally formed in, and thermally coupled to, the side walls of the server module.

3. The server module of claim 1 wherein the flow channels are provided in a cooling module that is thermally coupled to the side walls of the server module.

4. The server module of any preceding claim further comprising an internal coolant module, the internal coolant module being thermally coupled to the flow channels, the internal coolant module being configured to selectively transfer heat generated by electronic components within the internal volume to a location proximal to the flow channels for subsequent transfer away from the server module.

5. The server module of claim 4 wherein the internal coolant module comprise a pump coupled to a fluid network, the fluid network being thermally coupled to individual electronic components and configured such that, as liquid is operably circulated within the fluid network, heat is dissipated away from the electronic components and into the fluid network.

6. The server module of any preceding claims wherein at least a portion of the side walls of the server module is thermally coupled to individual ones of the electronic components and to the flow channels, the at least a portion of the side wall operably providing a heat sink to which heat generated by electronic components can be transferred and then dissipated away from the server module by the liquid coolant flowing within the flow channels.

7. The server module as claimed in any preceding claim comprising one or more heat sinks provided within the hermetically sealed internal volume, the one or more heat sinks being configured to dissipate heat away from the electronic components

8. The server module of any preceding claim wherein the flow channels are in fluid communication with a remote heat exchanger.

9. The server module of any preceding claim wherein the liquid coolant is a dielectric liquid.

10. The server module of any preceding claim further comprising a cold plate integrally formed in the side walls, the cold plate being thermally coupled to the flow channels.

11. The server module of claim 10 comprising at least one air mover arranged to pass air within the hermetically sealed enclosure volume, the air being operably heated by the electronic components, heat from the air passing into the flow channels.

12. The server module of any preceding claim further comprising at least one waterblock thermally coupled to at least one electronic component and to the flow channels.

13. The server module of claim 5 wherein the fluid network of the internal coolant module is coupled to a fluid inlet and a fluid outlet of a first liquid cooled thermal heat sink device, the fluid inlet being in fluid communication with a plenum chamber, the plenum chamber comprising a jet orifice plate, which defines a plurality of jet orifices through which a pressurised liquid can operably exit the plenum chamber and contact a thermal surface, the device further comprising at least one exit channel configured to deliver fluid exiting the jet orifices to the fluid outlet.

14. The server module of claim 13 wherein the server module flow channels which are thermally coupled to the side walls of the server module are coupled to a fluid inlet and a fluid outlet of a second liquid cooled thermal heat sink device, the fluid inlet being in fluid communication with a plenum chamber, the plenum chamber comprising a jet orifice plate which defines a plurality of jet orifices through which a pressurised liquid can operably exit the plenum chamber and contact a thermal surface, the device further comprising at least one exit channel configured to deliver fluid exiting the jet orifices to the fluid outlet, the thermal surface of the second liquid cooled thermal heat sink device being on an opposing side of the side walls of the server module to the thermal surface of the first liquid cooled thermal heat sink device.

15. The server module of claim 14 wherein each of the thermal surfaces of the first and second liquid cooled thermal heat sink devices are thermal contact with one another such that heat transferred to the thermal surface of the first liquid cooled thermal heat sink device is transferred to the thermal surface of the second liquid cooled thermal heat sink device where it is subsequently transferred away from the server module by the server module flow channels.

16. A server rack comprising a plurality of server modules as claimed in any preceding claims, the flow channels from each of the individual server modules being in fluid communication with one another and coupled to common heat exchanger for the server rack.

17. The server rack of claim 16 wherein the common heat exchanger is coupled to a mains liquid supply.