GB2467805A

GB2467805A - Sealable module for cooling electrical components

Info

Publication number: GB2467805A
Application number: GB0908156A
Authority: GB
Inventors: Daniel Chester; Peter Hopton
Original assignee: Iceotope Ltd
Current assignee: Iceotope Ltd
Priority date: 2009-05-12
Filing date: 2009-05-12
Publication date: 2010-08-18
Anticipated expiration: 2029-05-12
Also published as: GB2467805C; GB2467805B; GB0908156D0

Abstract

A sealable module comprises a housing and a heat transfer device which defines a first volume. An electronic component (68, 69) is housed in a first volume 66 and immersed in a first cooling liquid. A heat transfer plate 71 closes the first volume and preferably provides a number of fins or pins 76 that intrude into the first volume. A base unit (22) is attached to the heat transfer plate and comprises a number of channels or ducts through which a second cooling flows. In use the component heats the first liquid which in turns heats the heat transfer plate. The second cooling fluid then removes heat from the base plate. In one embodiment the second fluid is pumped to a further heat sink. The flow of the second fluid may be governed according to the temperature of a semi conductor device. The outer housing may be made of a synthetic plastics material. A membrane may also be provided between the semiconductor device and the fluid in the first volume.

Description

COOLED ELECTRONIC SYSTEM

Technical Field of the Invention

This invention relates to a module or capsule for housing an electronic component that generates heat in operation, a method of cooling such an electronic component, a method of cooling an electronic device, a cooled electronic system, and a method of filling a container for an electronic device with a cooling liquid. The invention is particularly applicable, for example, to computer processors and motherboards.

Background to the Invention

Electronic components and in particular computer processors generate heat in operation, which can lead to overheating and consequent damage to the component and other parts of the system. It is therefore desirable to cool the component to transfer the heat away from the component and maintain the component temperature below the maximum operating temperature that is specified for correct and reliable operation of the component.

This issue especially concerns data processing or 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 units contains one or more server board.

A single server board can dissipate many hundreds of watts of electrical power as heat. In existing systems, the energy required to transfer heat continuously so as to maintain correct operation can be of the same order of magnitude as the energy required to operate the servers.

The heat generated can be transferred to a final heat sink external to the building in which the processors are located, for example to the atmospheric air surrounding the building. Current implementations typically rely on air as the transfer medium at one or more stages between the processors and the final heat sink.

However, it is difficult to use air as a transfer medium for such a large quantity of heat, without imposing significant limitations on the building infrastructure. This is because the rate at which heat can be transferred increases with: increasing temperature difference (ST) between the heat source (such as the server boards, in particular the computer processors) and final heat sink; and decreasing thermal resistance of the path or paths thermally connecting the heat source and final heat sink.

Some known technologies for dealing with this difficulty are designed to control the environmental conditions of the location at which the processors are housed. Air handling techniques are currently often used, for example: vapour-compression refrigeration ("air conditioning") of the air that reduces the local air temperature to increase the local temperature difference; and air pressurisation (by the use of fans) to increase the air flow rate and thereby reduce the thermal resistance.

Further heat exchange stages may be used to transfer heat extracted from the local air to a final heat sink, such as atmospheric air.

However, these approaches can be inefficient, as the use of air conditioning can require substantial amounts of electrical power to operate. These approaches can also make the location unpleasant for people, due to the local temperature and noise.

Furthermore, air flow rates and air temperatures may have to be limited, for example maintaining temperature above the "dew point" to prevent water vapour condensing out of air that may damage sensitive electronic components. For these reasons, servers are currently commonly distributed sparsely in order to reduce the heat density and improve local air flow, thereby reducing the thermal resistance.

Cooling the electronic components using a liquid that is brought into contact with the electronic components can be used to increase server density, reduce cooling costs or both.

An existing technique for cooling electronic components using a liquid is described in US-2007/109742 and GB-A- 2432460. A computer processor board is housed inside an airtight container. A coolant liquid, preferably oil, is pumped through the container. The processor board is located at the bottom of the container and an evaporator coil is positioned at the top of the container, such that convection currents are produced in the coolant liquid. The coolant liquid is heated by the processor board and resultant vapour flows into a condenser. The container is positioned such that the circuit board inside lies in a horizontal plane to allow convection of heat from the components.

Using a condenser to provide refrigeration increases the complexity and cost of the system, and introduces further limitations on the system implementation.

WO-2006/133429 and US-2007/034360 describe an alternative known approach for cooling electronic components. The electronic component is sealed inside a container filled with a liqiiid and a thermally conductive plate is provided as part of the container in contact with the liquid. The thermally conductive plate conducts heat from the liquid to the outside of the container. Although this is designed for independent operation, the thermally conductive plate can be coupled to a further heat exchanger for additional cooling of the electronic component.

This alternative arrangement reduces the complexity of the system in comparison with approaches requiring pumped fluids inside the container. However, this does not significantly address the difficulty in reducing the thermal resistance between the heat source and the final heat sink.

Even if the temperature difference is increased, the total thermal resistance will still be significant.

Summary of the Invention

Against this background and in a first aspect, the

present invention provides a sealable module in which one or more heat generating electronic components may be located, the module comprising: a housing; and a heat transfer device having a conduction surface, the housing and the conduction surface together defining a volume in which an electronic component and a first cooling liquid can be located. The heat transfer device further defines a channel for receiving a second cooling liquid, and the conduction surface separates the volume and the channel to allow conduction of heat between the volume and the channel through the conduction surface.

In the preferred embodiment, the sealable module further comprises at least one electronic component which generates heat when in use, and a first cooling liquid, located in the volume.

The second liquid coolant is thereby caused to flow in the channel in direct contact with the conduction surface.

Transferring heat by conduction from a first cooling liquid in the volume to the second cooling liquid in the channel reduces the thermal resistance significantly. This increases the efficiency of heat transfer, making such a system scalable and applicable to systems which generate large quantities of heat, such as data processing centres.

Moreover, the reduced resistance of this system gained by using a conduction surface to transfer heat allows the coolant to be maintained in a liquid state at all times, thereby avoiding the need for vapour-cycle refrigeration that increases the complexity and cost of the system.

Also, the electricity consumption for cooling is reduced by mitigating or even eliminating the need for vapour-compression refrigeration. This also allows the density of electronic components and electronic circuit boards, such as server boards, to be increased.

For a given density of servers and components, a cooling system desirably removes sufficient heat from each component to keep it within its intended operating temperature range, but no more than that. Devices that generate less heat need less cooling than those that generate larger amounts. Cooling below a level necessary for satisfactory operation will normally consume unnecessary additional energy and is therefore less than optimally efficient.

In a second aspect, the present invention provides a method of cooling an electronic component, comprising: providing a module comprising a housing and a heat transfer device having a conduction surface, the housing and the conduction surface together defining a volume; housing the electronic component within the volume; filling the volume with a first cooling liquid; and conducting heat between the S first cooling liquid and a second cooling liquid through the conduction surface, the first cooling liquid and second cooling liquid being located on either side of the conduction surface -Preferably, the step of conducting heat from the first cooling liquid to a second cooling liquid is configured such that the first cooling liquid and second cooling liquid remain in liquid state.

In a third aspect, the present invention may be found in a sealable module in which one or more heat generating electronic components may be located, the module comprising: a housing; a heat transfer device having a conduction surface, the conduction surface and housing together defining a volume in which a first cooling liquid can be located; an electronic component, having an elongate axis and located in the volume; and wherein the heat transfer device defines a channel if or receiving a second cooling liquid, and the conduction surface has an elongate axis arranged in conformity with the elongate axis of the electronic component to allow conduction of heat between the volume and the channel through the conduction surface.

In the preferred embodiment, the sealable module further comprises a first cooling liquid located in the volume.

By conforming the elongate axis of the conduction surface and the elongate axis of the electronic component, conduction of heat from the first cooling liquid in the volume to the second cooling liquid in the channel can occur more efficiently. Moreover, conduction, convection or both can occur through the first cooling liquid even if a small part of volume is not filled by cooling liquid.

Conformity of the elongate axis of the conduction surface and the elongate axis of the electronic component may comprise conformity of one or more of: length; direction; profile; or other characteristics. Preferably, the conduction surface and the electronic component may be arranged parallel to one another. Advantageously, the conduction surface has length and width that are a significant proportion of the length and width of the electronic component. More preferably, the conduction surface has length and width that are at least as great as the length and width of the electronic component.

In the preferred embodiment, the conduction surface separates the volume and the channel to allow conduction of heat between the volume and the channel through the conduction surface.

In a fourth aspect, the present invention may be found in a method of cooling an electronic device having an elongate axis, comprising: housing the electronic device within a container, the container being filled with a first cooling liquid and having an elongate axis which extends in a direction that generally corresponds with the elongate axis of the electronic device; positioning the container such that the electronic device is upright and so that heat generated by the electronic device is transferred to the first cooling liquid; and transferring heat between the first cooling liquid and a second cooling liquid in a heat transfer device. Alternatively, a method of cooling an electronic device may be provided, comprising: housing the electronic device within a container, the container being filled with a first cooling liquid and having a conduction surface for receiving heat generated by the electronic device; positioning the container such that the conduction surface is upright and so that heat generated by the electronic device is transferred to the first cooling liquid; and transferring heat between the first cooling liquid and a second cooling liquid through the conduction surface.

If the container is not completely filled with the first cooling liquid, the surface area of contact between the first cooling liquid and the electronic device may be significantly reduced. By positioning the electronic device or conduction surface upright, any part of the volume that is not filled with the first cooling liquid (and which may be filled with a gas, such as air) does not form a layer between the first cooling liquid and the electronic device or the conduction surface. Advantageously, the electronic device defines a plane and the step of positioning the container such that the electronic device is upright comprises positioning the container such that the plane of the electronic device is upright. Also, when the first cooling liquid becomes heated and expands, this can be accommodated without additional equipment, which might increase the complexity, cost or volume required.

A number of additional features can be applied to the invention as specified by any one of the first, second, third or fourth aspects specified above. These will be described below.

Beneficially, the conduction surface has at least one projection into the first volume for conducting heat between the volume and the channel. The use of at least one projection increases the surface area of the conduction surface and can allow closer conformity between the conduction surface and the shape of the electronic component. These improve the efficiency of heat conduction.

Where the sealable module includes the electronic component, the conduction surface preferably has at least one projection into the first volume for conducting heat between the volume and the channel, the at least one projection being arranged in conformity with the shape of the electronic component. This further improves heat conduction efficiency, by: reducing the space between the component and the conduction surface is reduced; increasing total projection surface area to reduce thermal resistance in the heat flow path; reducing the volume of cooling liquid required for efficient coolingF permit the increased use of materials with poorer conductivity but reduced cost or weight or both (e.g. plastic) . In particular, efficiency of cooling is improved if the cooling liquid comes quickly into contact with the conduction surface.

Optionally, the conduction surface is made from a synthetic plastic material, which is desirably thermally conductive. Additionally or alternatively, the housing may be made from a synthetic plastic material. Preferably, this is thermally insulating. In embodiments, the heat transfer device may be made from a synthetic plastic material.

In some embodiments, the sealable module further comprises a component heat sink coupled to the electronic component, having at least one projection arranged to cooperate with the at least one projection of the conduction surface.

Advantageously, the at least one projection of the conduction surface comprises a fin arrangement.

Alternatively or additionally, the at least one projection -10 -of the conduction surface comprises a pin arrangement. In the preferred embodiment, the at least one projection comprises a pin-fin arrangement.

In the preferred embodiment, the heat transfer device further comprises a base part coupled to the conduction surface and defining the channel for receiving the second cooling liquid.

Advantageously, the sealable module further comprises an insulation layer covering at least part of the housing, exterior to the volume. Additionally or alternatively, the sealable module may comprise an insulation layer covering at least part of the housing, within the volume.

Preferably, more than one electronic component may be located in the volume. In the preferred embodiment, the sealable module comprises a plurality of electronic components, at least one of which generates heat when in use, and further comprising a circuit board holding the plurality of electronic components.

By immersing the circuit board in a carefully selected liquid, it is isolated from damage by airborne pollutants or water that might otherwise condense out of the atmosphere, or leak elsewhere. Pollutants present in air or dissolved in water can readily attack the fine wiring on circuit boards, for example. Also, other heat generating components such as power supplies, DC-DC converters and disk drives can be encapsulated and cooled. Where the at least one electronic component includes a disk drive, the disk drive is preferably a solid state device. Devices with moving parts are undesirable for immersion in a liquid.

The first cooling liquid preferably occupies a portion of the volume of the sealable module, such there is volume available for expansion of the liquid upon heating without -11 -significantly increasing the pressure in the volume.

Preferably, the sealable module further comprises a protective membrane positioned between the circuit board and the housing, the protective membrane being arranged to prevent liquid flow between the housing and the circuit board. This increases the thermal resistance through this undesirable path and reduces the volume of the coolant required to fill the volume, whilst allowing for the presence of small components on the rear of a circuit board.

In the preferred embodiment, the protective membrane is deformable.

In the preferred embodiment, the sealable module further comprises: a filling inlet to the module, located in the housing and through which a liquid can be received into the volume; and a seal to the filling inlet. This allows quick filling or re-filling of the sealable module volume

with cooling liquid in field.

Preferably, the sealable module comprises a pressure relief valve, located in the housing and arranged to allow liquid flow out from the volume when the pressure within the volume exceeds a predefined limit.

A fifth aspect of the invention may be provided by a sealable module in which one or more heat generating electronic components may be located, the sealable module comprising: an inner housing, sealable so as to define a volume in which an electronic component and a first cooling liquid can be located; and an outer housing, defining a channel f or receiving a second cooling liquid, the outer housing being arranged to cooperate with the inner housing to provide an interface between the channel and at least a portion of the inner housing that allows transfer of heat between the volume and the channel.

-12 -The use of an outer housing that defines the channel for receiving a second cooling liquid and which is arranged to cooperate with the inner housing to provide a heat transfer interface advantageously provides a compact module, which allows the width of the channel to be defined or adjusted to meet the heat transfer requirements.

Optionally, the at least a portion of the inner housing that interfaces with the channel defines a conduction surface, the channel having an area of contact with the heat transfer surface defining a channel width, and wherein the minimum channel width is significant in comparison with the dimensions of the heat transfer surface.

Additionally or alternatively, the channel interfaces with the at least a portion of the inner housing along a path having at least one change in direction. Preferably, the path has a straight portion, and wherein the minimum channel width is at least 10% of the length of the straight portion of the path. In other embodiments, the minimum channel width may be at least: 10%; 20%; 30%; 40%; or 50% of the length of the straight portion of the path. Additionally or alternatively, the path comprises a main path and a branch path, the branch path being connected to the main path at at least one point.

Preferably, the inner housing comprises: an interface portion, arranged to cooperate with the outer housing to provide the interface between the channel and at least a portion of the inner housing; and a base portion, arranged to couple to the interface portion so to form the sealable inner housing.

In some embodiments, the at least a portion of the inner housing that interfaces with the channel is made from a synthetic plastic material. Optionally, the inner housing -13 -is made from a synthetic plastic material. Desirably, the outer housing is made from a synthetic plastic material.

The present invention can also be found in a cooled electronic system, comprising: the sealable module according S to the first, second or fifth aspects of the present invention; an electronic component located in the volume; a first cooling liquid located in the volume; a heat sink; a pumping arrangement, arranged to allow a second cooling liquid to flow through the channel of the sealable module to the heat sink at a predetermined flow rate and further arranged to control the portion of the inner housing through which heat is transferred to the channel; a temperature sensor, arranged to determine a temperature of the electronic component; and a controller arranged to control the pumping arrangement, such that the temperature of the electronic component is controlled so as not to exceed a predetermined maximum operating temperature.

Beneficially, the conduction surface has at least one projection into the first volume for conducting heat between the volume and the channel. Where the sealable module includes the electronic component, the conduction surface preferably has at least one projection into the first volume for conducting heat between the volume and the channel, the at least one projection being arranged in conformity with the shape of the' electronic component. In some embodiments, the sealable module further comprises a component heat sink coupled to the electronic component, having at least one projection arranged to cooperate with the at least one projection of the conduction surface. Advantageously, the at least one projection of the conduction surface comprises a fin arrangement. Alternatively or additionally, the at least one projection of the conduction surface comprises a pin -14 -arrangement. In the preferred embodiment, the at least one projection comprises a pin-fin arrangement.

A sixth aspect of the invention may be found in a method of cooling an electronic device, comprising: providing a module comprising a housing and a heat transfer device having a conduction surface, the housing and the conduction surface together defining a volume, the volume being filled with a first cooling liquid and having the electronic device located therein; operating the electronic device within the volume; transferring heat generated by the electronic device from the first cooling liquid to a second cooling liquid through at least a portion of the heat transfer surface; transferring the second cooling liquid to a heat sink; and adjusting one or both of: the flow rate of the second cooling liquid from the conduction surface to the heat sink; and the portion of the conduction surface through which heat is transferred to the second cooling liquid, such that the temperature of the electronic device is controlled so as not to exceed a predetermined maximum operating temperature.

By this adjustment, the thermal resistance can advantageously be increased or reduced as needed to provide the desired temperature difference. This allows the electronic component to be maintained at a temperature no greater than its maximum operating temperature, even if the temperature difference decreases, for example, if the final heat sink temperature increases (such as when an atmospheric final heat sink is used) . Optionally, the conduction surface is made from a synthetic plastic material.

A seventh aspect of the invention may be provided by a method of cooling an electronic device, comprising: operating the electronic device within a container, the -15 -container also comprising a first cooling liquid, such that heat generated by the electronic device is transferred to the first cooling liquid, the container being sealed to prevent leakage of the first cooling liquid; transferring heat between the first cooling liquid and a second cooling liquid in a first heat transfer device; piping the second cooling liquid from the first heat transfer device to a second heat transfer device; transferring heat between the second cooling liquid and a third cooling liquid in the second heat transfer device; and piping the third cooling liquid to a heat sink.

Thus, three stages of liquid cooling are provided, which allows the flow rate and pressure of the second cooling liquid and third cooling liquid to be independently controlled. The pressure of second cooling liquid can therefore be reduced to further mitigate the risk of leakage of this liquid. Since these liquids are in close proximity to the electronic components, leakage is undesirable. Also, the flow rates can advantageously be controlled based upon the level of heat generated to improve the efficiency of heat transfer at each stage.

Preferably, the step of transferring heat between the first cooling liquid and the second cooling liquid is carried out by conduction.

Advantageously, a method of cooling an electronic system is provided, comprising: carrying out the method steps of cooling an electronic device in accordance with this seventh aspect; operating a second electronic device within a second container, the second container also comprising a fourth cooling liquid, such that heat generated by the electronic device is transferred to the fourth cooling liquid, the second container being sealed to prevent -16 -leakage of the fourth cooling liquid; and transferring heat between the fourth cooling liquid and a fifth cooling liquid in a fourth heat transfer device. Optionally, the method further comprises controlling the flow rate of the fifth cooling liquid.

Preferably, the second cooling liquid and the fifth cooling liquid are combined. This allows efficient cooling of multiple electronic devices using separate first cooling stages, but a common second stage of cooling.

Beneficially, the method further comprises controlling the flow rate of the second cooling liquid. In the preferred embodiment, the flow rate is controlled dependent on the temperature of the electronic component or first cooling liquid from which heat is received by the second cooling liquid. This allows the flow rate of second cooling liquid to be matched to the level or rate of heat generation.

Additionally or alternatively, the method further comprises controlling the flow rate of the third cooling liquid.

In some embodiments, where the first heat transfer device comprises a conduction surface, the method may further comprise adjusting one or both of: the flow rate of the second cooling liquid from the first heat transfer device to the second heat transfer device; and the portion of the conduction surface through which heat is transferred to the second cooling liquid, such that the temperature of the electronic component is controlled so as not to exceed a predetermined maximum operating temperature.

In an eighth aspect, the present invention may be found in a cooled electronic system, comprising: a sealed container comprising: a housing; an electronic component; and a first cooling liquid; a first heat transfer device defining a first channel for receiving a second cooling -17 -liquid, the first heat transfer device being configured to transfer heat between the first cooling liquid and the first channel; and a second heat transfer device comprising a second channel for receiving the second cooling liquid from the first channel, and a third channel for receiving a third cooling liquid and coupled to a heat sink, the second heat transfer device being configured to transfer heat between the second channel and the third channel.

Preferably, the first heat transfer device comprises a conduction surface, the housing and the conduction surface together defining a volume in which the electronic component and the first cooling liquid are located. More preferably, the conduction surface separates the volume and the first channel to allow conduction of heat between the volume and the channel through the conduction surface.

Advantageously, the conduction surface has at least one projection for receiving heat from the first cooling liquid.

In the preferred embodiment, the at least one projection is arranged in conformity with the shape of the electronic component. Optionally, the cooled electronic system further comprises a component heat sink coupled to the electronic component and comprising at least one projection arranged to cooperate with the at least one projection of the conduction surface.

Beneficially, the at least one projection of the conduction surface comprises a fin arrangement.

Alternatively or additionally, the at least one projection of the conduction surface comprises a pin arrangement. In the preferred embodiment, the at least one projection comprises a pin-fin arrangement.

In the preferred embodiment, the heat transfer device further comprises a base part coupled to the conduction -18 -surface and defining the channel for receiving the second cooling liquid.

Advantageously, the conduction surface is made from a synthetic plastic material. Additionally or alternatively, the housing may be made from a synthetic plastic material.

In embodiments, the base part of the heat transfer device may be made from a synthetic plastic material.

Optionally, the module further comprises: a filling inlet to the container, through which the first cooling liquid can be received; and a seal to the filling inlet.

Additionally or alternatively, the module further comprises a pressure relief valve, arranged to allow outflow of the first cooling liquid from the container when the pressure within the container exceeds a predefined limit.

Where the electronic component has an elongate axis, the conduction surface preferably has an elongate axis arranged in conformity with the elongate axis of the electronic component to allow conduction of heat between the volume and the channel through the conduction surface.

In some embodiments, the sealed container is a first sealed container, and the cooled electronic system further comprises: a second sealed container comprising: a second housing; a second electronic component; a fourth cooling liquid for receiving heat from the second electronic component; and a fourth heat transfer device comprising a fourth channel for receiving a fifth cooling liquid, the fourth heat transfer device being configured to transfer heat from the fourth cooling liquid to the fourth channel.

Preferably, the first channel and the fourth channel are coupled to combine the second cooling liquid and the fifth cooling liquid.

-19 -In the preferred embodiment, the cooled electronic system further comprises: a controller, arranged to control the flow rate of the second cooling liquid. Additionally or alternatively, the controller is arranged to control the flow rate of the third cooling liquid.

In a seventh aspect, the present invention may be found in a method of filling a container for an electronic device with a cooling liquid, the method comprising: heating the cooling liquid to a filling temperature, the filling temperature being selected such that gases dissolved in the cooling liquid are removed from the cooling liquid; heating the container to the filling temperature; filling the heated container with the heated cooling liquid such that all air in the container is displaced; sealing the container to prevent leakage of the cooling liquid; cooling the sealed container and cooling liquid to an operating temperature.

By heating the container and liquid to a filling temperature and filling the container with the liquid at this temperature, air, moisture and other dissolved gases are removed from the interior of the container. The need for a desiccant in the container is reduced or avoided. This method also increases the volume of the interior space of the container that is filled with liquid under operating conditions, without significantly increasing the pressure within the container. Excessive pressure may result in damage to the container or the electronic component.

Brief Description of the Drawings

The invention may be put into practice in various ways, one of which will now be described by way of example only and with reference to the accompanying drawings in which: -20 -Figure 1 shows a simplified front view of an equipment rack containing multiple equipment modules, each equipment module comprising a sealable module according to the invention; Figure 2 is a simplified cross-sectional side view of the equipment rack shown in Figure 1; Figure 3 illustrates an equipment module, as shown in Figure 1, fitted with a cover; Figure 4 depicts an equipment module with its cover removed, showing two sealable modules according to the invention; Figure 5 is a cross-sectional view of a sealable module comprising a heat generating electronic component according to an embodiment of the invention; Figure 6 is a cross-sectional view of the upper part of the sealable module of Figure 5; Figure 7 shows an embodiment of a two-part cold plate, for use with the sealable module of Figure 5; Figure 8 is a schematic view of a three-stage cooling system comprising a single equipment module according to the invention; Figure 9 is a block diagram showing a three-stage cooling system with multiple equipment modules according to the invention; Figure 10 shows a monitoring and control system for use with the three-stage cooling system of Figure 9; Figure ilA shows a first side view of a second embodiment of a sealable module according to the present invention; Figure 113 shows a second side view of the embodiment shown in Figure ilA; and -21 -Figure 11C shows a more detailed view of the embodiment shown in Figure hA and Figure liB.

Specific Description of a Preferred Embodiment

S

Ref erring first to Figure 5, there is shown a cross-sectional view of a sealable module 60 comprising a heat generating electronic component 69 according to an embodiment of the invention. The sealable module comprises: a housing 41; a conduction surface 71 forming part of a cold plate; a container volume, defined by the housing 41 and conduction surface 71 and filled with a first cooling liquid 66; liquid flow channels 61 adjacent the conduction surface 41; small electronic component 68; and large electronic component 69.

The sealable module further comprises: an electronic circuit board 75; a mounting boss 63 for the electronic circuit board 75; a component heat sink 70 attached to the large electronic component 69; a base part 22 for the cold plate; insulation 73 for the housing 41; an insulating membrane 67; a hold down screw 42 for the housing 41; sealing gaskets 64; hold down screws 72 for the cold plate; and pin-fin projections 76 on the conduction surface 71.

The cold plate is fabricated in two parts. Conduction surface 71 is a pin-finned plate, attached to the cold plate base 22, the two parts together making up a pin-finned cold plate assembly held together by screws 72 or equivalent means. A housing 41 is attached to the pin -finned plate 71, for example using screws 42 in such a way as to provide an internal space for an electronic circuit board 75, the pins of the cold plate and a first cooling liquid 66. A gasket 64 ensures that the assembled capsule is -22 -substantially sealed against liquid loss or ingress of air.

The pin-finned plate is effectively the lid of the assembled capsule -The electronic circuit board 75 carrying components to be cooled is attached to the housing 41 by mounting bosses 63, so as to suspend the board above the cold plate.

Alternatively, the board may be attached to rods extending from the pin-finned conduction surface 71, allowing accurate alignment of the pins of the cold plate with components on the board, prior to attaching the housing.

The pins 76 of the pin-finned conduction surface 71 normally face the component side of the circuit board 75. In some cases, components of significant size may be present on both sides of the board. The housing may then be contoured around the components on the side of the board opposite the pin-tinned conduction surface 71, in order to improve flow of the cooling liquid and reduce the amount of cooling liquid needed.

In the embodiment shown in Figure 5, the cold plate is fabricated in two parts, f or convenience in manufacture. The cold plate base 22 has a flat surface into which channels whose cross section is shown at 61 are manufactured.

The component side of the electronic circuit board 75 faces the pins 76 on the conduction surface 71. A small gap between the ends of the pins and the components is provided.

The pins have an elongated cross-section and the length of the pins varies, so as to maintain a small gap between the variously sized components on the electronics circuit board and the tops of the pins. The faces of the electronic components 68 and 69 project by different amounts from the surface of the board. Small component 68 has a relatively low profile and large component 69 has a much deeper profile -23 -and the corresponding pins 76 have accordingly different heights. This arrangement aids cooling and reduces the total quantity of cooling liquid needed in the capsule.

When the system is in operation, heat generated by the components 68, 69 on the circuit board is transferred to the cooling liquid 66, initially by local conduction and then, as the heated liquid expands and becomes buoyant, by convection. The convecting liquid quickly comes into contact with the pins 76 and other surfaces of the conduction surface 71.

Heat from the pins 76 of the conduction surface 76 is conducted to the circulating second liquid that flows via channels 61, so as to cool the conduction surface 76 and thus cooling liquid 66.

Components on circuit board 75 that generate the largest amount of heat are typically microprocessors. In this case, cooling efficiency for such components may be improved by additionally fitting a finned component heat sink 70, in direct physical and thermal contact with the component, whose fins interleave with the array of pins on the cold plate. The fins of the component heat sink may be partially or fully in physical contact with the pins of the cold plate. When there is partial contact, gaps remain through which the first cooling liquid 66 can flow.

An additional insulating layer 73 covers the housing 41 of the sealable module 60. Additional insulation may also be added to the exterior of the cold plate base 22. The insulation reduces local heat loss into the atmosphere, which can be significant in large installations with many electronic circuit boards, causing room temperature to rise to undesirable levels.

-24 -Electronic circuit board 75 may carry major components only on one side or the other side may carry only small components that generate low amounts of heat in operation.

The operation of the sealable module 60 may then be improved s by excluding liquid flow adjacent to the non-component side of the circuit board 75. A protective membrane 67 is then fitted between the circuit board 75 and the housing 41, which is flexible and can accommodate to the shape of the small components that may be mounted on this side of the board. Convective flow of the cooling liquid 66 is then concentrated in the space between the main component side of the circuit board 75 and the conduction surface 71.

Application of the invention is not limited to computing systems. However, since computing systems generate significant heat, they can benefit from improved cooling. In such systems, one or more microprocessors and several other digital and analogue devices such as memory chips (RAM, RON, PROM, EEPROM and similar devices), specialised integrated circuits (ASIC5) and a range of associated active and passive components are typically mounted on a circuit board, whose function is to act as a major part of a computing system. Although electronic components can be mounted on both sides of the circuit board, it is more usual to mount at least the bulky components on one side only. Other devices are connected to the circuit board by cables, optical means or wireless transmission, the whole forming a computer, computer system or server.

Heat is generated by the various components but, typically, the microprocessor is the highest heat-generating component. An optimally designed cooling system removes sufficient heat from each component to keep it within its designed operating temperature range but no more than that.

-25 -Devices that generate less heat need less cooling than those that generate larger amounts. Cooling below a level necessary for satisfactory operation will normally consume unnecessary additional energy and is therefore less than optimally efficient.

Moreover, packing density of components on computer boards is determined partly by the traditional size of computer housings and the assumption that air-cooling may be employed. In large systems, especially server centres, increasing the packing density of components to reduce overall space occupied is desirable. At the same time, heat generated will be concentrated in a smaller space and needs more effective means of removal. Improving heat removal may enable component packing density to be increased and, more particularly, allow processing power per unit volume to increase.

Referring now to Figure 6, there is shown a cross-sectional view of the upper part of the sealable module 60 of Figure 5. Where the same features are shown, identical reference numerals are used. Figure 6 additionally shows: a filling inlet 44; seal 43; a pressure relief device 45; holes 82 for receiving hold down screw 42; and recesses 83 for receiving the sealing gasket 64. The filling inlet 44 is intended for receiving the first cooling liquid 66 and has a seal 43 to prevent liquid loss once the sealable module 60 is filled. A pressure relief device 45 allows escape of liquid under extreme conditions, outside a normal range of: temperature; pressure; or both.

Referring now to Figure 7, there is shown an embodiment of a two-part cold plate, for use with the sealable module of Figure 5. In addition, the cold plate can be used with a second sealable module. The cold plate comprises -26 -conduction surface 71 and base 22. Base 22 comprises: channels 91 (corresponding with channels 61, shown in Figure 5); first inlet 11 for second cooling liquid; first outlet 12 for second cooling liquid; second inlet 13 for second cooling liquid; second outlet 14 for second cooling liquid; holes 92 for connecting channels 91 to first and second inlets and outlets; and screw hole 98 for attaching housing 41 thereto. Conduction surface 71 comprises long pins 96, short pins 97; screw hole 95.

Channels 91 in the cold plate base form a continuous winding pattern 91 within the boundary of the base 22 and join via holes 92 to tubes in the cold plate base that emerge as inlet and outlet connectors 11, 12, 13, 14. Two separate arrangements of winding channels 91 are shown, each associated with one sealable module 60 and each with its own input and output connector.

The cold plate is completed by conduction surfaces 71, each conduction surface associated with one sealable module and attached to the face of the cold plate base so as to enclose the channels 91, thus creating a tube-like arrangement within the assembled cold plate. The long pins 96 and short pins 97 correspond with projections 76 shown in Figure 5. Not all of the pins comprising projections 76 are shown in Figure 7. The projections 76 project away from the base 22 and into the interior space 66 of the assembled sealable module.

The material used for the cold plate base 22 and conduction surface 71 is chosen to be a good conductor of heat, typically a metal. For ease of fabrication and lower cost in quantity production, a plastic material could be employed with lower but still adequate heat conduction properties. The channels 91 formed within the two-part cold -27 -plate are used to carry a second cooling liquid that circulates through the cold plate and then outside to carry heat away to further cooling stages of the system.

The sealable modules 60 provide a first stage of cooling and form part of equipment modules, each equipment module carrying one or more capsules. At least one and typically many first-stage equipment modules are deployed in a system. The equipment modules may be fitted into any convenient housing but, where large numbers are used in a system, conventional equipment racks would normally be used.

In Figure 4, there is shown an equipment module with its cover removed, showing two sealable modules.

Essentially, Figure 4 shows the assembled cold plate of Figure 7, attached to two upper parts as shown in Figure 6.

Where the same features are shown in Figure 4 as in Figures 6 and 7, identical reference numerals are used. In addition is shown: data transfer cable 46; power cable 47; power and data connector block 48; mounting brackets 49 for the connector block 48; and seal for cable entry 50.

Two sealed modules 60 are shown. Two housings 41 are attached to the conduction plates 71 of the cold plate. The housing 41 for each sealable module 60 is made of plastic or equivalent material, chosen to be an electrical insulator, and to have heat insulating properties, as well as not reacting with the cooling liquid used in the capsule.

Housing 41 is held down by screws 42. Cables 46, 47, carrying electrical power and supporting bi-directional data transmission enter the capsule via entry points 50, sealed to prevent the escape of liquid or the ingress of air.

Cables 46, 47 terminate in a connector block 48 at the rear of the equipment module, supported by brackets 49 or equivalent means of mounting.

-28 -The assembled sealable module 60 is partly or wholly filled with a first cooling 66 via the filling inlet 44 and then sealed with sealing device 43. The filling procedure may take place during factory assembly or during field installation of cooling modules.

During factory filling, the sealable module 60 is partly filled with liquid, the remaining space being occupied by its vapour, air and other contaminants being substantially excluded. One method of achieving this is by heating the liquid and the module to a filling temperature (T11), selected to be high enough to drive dissolved gases from the cooling liquid. The maximum storage temperature of the electronic components is typically much higher than maximum operating temperature, so that Tf ill can be well above Tmax, the highest envisaged operating temperature of the system Sufficient liquid is then added to displace all the air within the sealable module 60 and the sealable module 60 is then sealed with sealing device 43 to prevent liquid escape and ingress of air. The sealable module 60 is then allowed to cool to room temperature. The liquid contracts and leaves a space, occupied by liquid vapour. The filling procedure may take place in two or more steps, allowing time for liquid that has been added to the sealable module 60 in one step to cool partly before adding more.

In field filling, it is preferred to fill with a cool or warm liquid, since there is increased danger of spilling hot liquid. In this case, an air gap is left above the liquid to allow for expansion. Liquid is factory prepared to remove dissolved gases and is then stored in sealed containers. The interior space of the sealable module 60 is filled with dry air and the sealing device fitted. When -29 -filling the sealable module 60 with liquid, the sealing device 43 is removed, a specified amount of de-gassed liquid is poured into the sealable module 60 via the filling inlet 44 and the sealing device 43 is then immediately refitted.

The specified amount of liquid added is sufficient for effective cooling but leaves a remaining space filled with air for expansion of the liquid at temperatures up to Tmax, the highest envisaged operating temperature of the system.

At temperatures below the lowest envisaged room temperature, the liquid may contract further and the electronic circuit board 75 may no longer be fully immersed in liquid. This is envisaged to occur when the module is inactive, in storage or being transported, for example by air, when low external pressure and temperature conditions may occur. The seal 64 between the housing and cold plate is intended to withstand temperature and pressure variations between the limits envisaged for inactivity, storage and transportation and the conditions at Tmax.

Above Tmax, the system would be outside its design temperature range. Although higher temperatures are very unlikely, the pressure relief valve device 45 allows escape of liquid that has exceeded Tmax, the temperature at which the liquid fills or is close to filling the available space inside the module. The pressure relief device may be combined with the seal 43 for the filling inlet 44.

The first cooling liquid 66 is chosen on the basis of a number of desirable characteristics. It should not significantly affect the performance of the electronic circuit board 75 or the transmission of information between the circuit board 75 and other external devices. It should not be corrosive to any component of the cooling module, remain liquid at all operating, storage and transportation -30 -temperatures, have sufficiently good specific heat capacity, in order to carry heat away from the electronic components as efficiently as possible, have a high enough coefficient of expansion and low enough viscosity to aid rapid convection, be low-cost, be safe to use and be non-hazardous in case of leakage One example of a suitable first cooling liquid 66 is a hydrofluoroether chemical. This has all the desirable characteristics, including a high coefficient of expansion and sufficiently high specific heat capacity to provide high mass-flow rate and rapid convection when heated, thus carrying heat quickly away from the hot components.

In Figure 3, there is illustrated the equipment module of Figure 4, fitted with a cover 20 to form an assembled equipment module 2. Equipment module 2 further comprises: clips 21; first data connector 27; second data connector 28; first power connector 29; and second power connector 30.

When housed in a standard equipment rack, the cold plate base 22 is commonly in the vertical plane. The cold plate base 22 carries liquid inlets 11, 13 and outlets 12, 14 each pair being associated with a respective sealable module 60 inside the equipment module 2.

The cover 20 is held in place by clips 21 or equivalent fixings, protects the cooling capsules and other internal parts of the module and gives additional EMC protection. The cover additionally completes an external rectangular box shape that is convenient for sliding into and out of a shelf in a rack for installation, repair or replacement.

Electrical connections are also made at the rear of the module, for power 29,30 and data transfer 27, 28. Standard connectors may be employed to allow connection and disconnection of the module for installation and removal.

-31 -Reference is now made to Figure 1, in which there is shown a simplified front view of an equipment rack containing multiple equipment modules. Equipment rack 1 comprises: equipment module 2; and additional equipment shelves 3. Rack 1 houses a number of cooling modules 2 and has expansion room for further modules in additional equipment shelves 3. The modules are removable for replacement or repair. Figure 1 shows a typical packing density of modules. Only one shelf 3 of the rack 1 is filled with equipment modules 2. The others could be similarly filled with equipment modules 2.

In Figure 2, there is shown a simplified cross-sectional side view of the equipment rack shown in Figure 1.

The front 16, side 15 and rear 17 of the rack 1 are shown.

Liquid connections 11,12,13,14 are also shown on the equipment module 2. These interconnect with a system of pipes in a second liquid cooling stage of the system, which will be described further below. These are normally at the rear 17 of the rack, although in circumstances where rear access is not convenient, they could be at the front 16 of the rack. In this example, the equipment module 2 has two liquid inlets and two liquid outlets, serving two independently cooled sealable modules 60 within each equipment module 2.

Thus, a first stage of cooling electronic components has now been described. The first stage provides a low-cost cooling module, using non-forced cooling (in this case using conduction and convection through a cooling liquid to transport heat) and the ability by some means to detach and replace any faulty module with a module that is working correctly. There may be any number from one to a large number of such modules in a system.

-32 -In the first stage, at least one sealable module 60 is used. Each sealable module 60 houses one or more electronic circuit boards, power supply units, DC to DC power converters or disk drives to be cooled. Heat is removed from the heat-generating electronic components to the first cooling liquid 66 contained within the sealable module and is then transmitted from the first cooling liquid 66 via the conduction surface 71 to a second cooling liquid flowing through the cold plate base 22.

The second cooling liquid is used in a second stage of cooling and a means of circulating the cooling liquid so as to carry heat away from the first stage. A third stage of cooling can also be used to avoid the use of liquids flowing through equipment modules under high pressure.

Further intermediate stages of heat transfer also use liquid to carry heat to a final heat exchanger. Further cooling stages desirably include cooling liquid flow-rate management for the different stages of the system, and pressure management, in order to avoid high cooling liquid pressure in cooling capsules, whilst allowing liquid to be pumped effectively to a final heat sink. The system thereby uses multiple stages of heat transfer using liquids in all stages up to the final heat exchanger.

Sufficient heat is removed to keep components within their specified temperature range but not significantly more than that. Additional heat transfer and lower temperatures that allow alternative operating modes such as "over-clocking" of processors are possible using the system but not necessary in normal operation, since additional energy is consumed in achieving these lower operating temperatures and the alternative modes of operation are not in common use in large scale systems.

-33 -Referring now to Figure 8, there is shown a schematic view of a three-stage cooling system comprising a single equipment module 2. The system further comprises: quick release connectors ill; pipes for second cooling liquid 112; T-junction 113; flow control valves 114; valve controls 115; pump 116; power supply 117; heat exchanger 118; pump 119; power supply 120; pipes for third cooling liquid 126; and heat exchanger 121.

Each internal channel 91 (not shown) of the cold plate 22 (not shown) has input connectors 11, 13 and output connectors 12, 14 for the second cooling liquid. Pipes 112 are joined via quick release devices 111 that also contain a means of isolating the second cooling liquid in the cooling module and pipes. When the cooling module is connected, the liquid can flow normally but when the cooling module is disconnected, these close off the liquid flow and prevent liquid loss from the module or pipes.

The second cooling liquid circulates through the cold plate 22 of the sealable module 60 (not shown) to a heat transfer device 118 and is then returned to the cold plate via a pump 116 supplied with electrical power 117 and a flow control valve 114 which can be adjusted locally or by means of a control signal 115 from an external device. In the illustrated embodiment, the two cooling circuits within the cooling module are connected in parallel via T-junctions 113 in the system of pipes. The flow-rate in each of the parallel circuits can be separately adjusted by means of the flow control valves 114 to take account of different amounts of heat generated in each arm of the cooling system. The direction of liquid flow is shown by arrows.

The heat transfer device 118 has two liquid flow circuits. The heated second cooling liquid from the cooling -34 -module circulates through a first circuit. Cool liquid in the third stage circulates through a second circuit. Heat is transferred from liquid in the first circuit via a heat-conducting interface to liquid in the second circuit, which then flows away through pipes 126 to a final heat exchanger 121. The direction of liquid flow is again shown by arrows.

Heat exchanger 121 comprises: heat exchanger cooling plate 122; fan 123; and power supply 124. This is a conventional device, commonly referred to as a "dry cooler", that may use atmospheric air as the final heat sink medium, this being blown by fan 123 driven by electrical power 124 across a finned cooling plate or equivalent means of heat transfer to cool the circulating third cooling liquid. The cooled liquid is then returned via a pump 119 driven by electrical power 120 to the heat transfer device 118.

The three stages of liquid heat transfer are desirable in situations where the final heat exchanger is located some distance from the equipment to be cooled, for example on the roof of a building. In this case, the pressure difference between liquid circulating through the final heat exchanger 121 and the intermediate heat transfer device 118 may be large. The second stage of heat transfer can use a liquid with a much lower pressure, so that the potential for liquid to leak within the first stage cooling modules and damage the electronic circuit boards is greatly reduced.

Since the second and third cooling liquids are not in contact with the electronic circuit board 75 (not shown), their characteristics are less constrained than those of the first cooling liquid 66. Water, which has he highest specific heat capacity of any common liquid and has very low cost, can be used effectively. An additive to reduce -35 -corrosion and bacterial contamination may optionally be used.

Referring now to Figure 9, there is shown a block diagram showing a three-stage cooling system with multiple S equipment modules according to the invention. This illustrates a larger scale cooling system, comprising: equipment modules 130, 131, 132; pipes 129; flow control valves 133; pumps 134 for second cooling liquid; heat exchanger 135; pump 136 for third cooling liquid; heat exchanger 137; final liquid entry 138 to heat exchanger; and final liquid exit 139 from heat exchanger.

A number of cooling modules 130, 131, 132 are mounted in a housing or rack with an arrangement such as that shown in Figure 1. The liquid flow through the equipment modules 130, 131 and 132 is connected in parallel fashion. Each of the equipment modules 130, 131 and 132 contains one or more sealable modules 60 (not shown) and can be disconnected and removed from the rack separately, using connectors such as those shown in Figure 8, for replacement or repair. The number of cooling modules can be extended, as indicated schematically to a large number.

The second cooling liquid flow is divided amongst the cooling modules by a parallel arrangement of pipes 129, typically with two sets of pipes per cooling module, each serving one of the two sealable modules 60 mounted therein (not shown) . The flow rate to each sealable module 60 can be varied by use of flow control valves 133. The electronic circuit boards 75 (not shown) to be cooled may be in various states of activity, from inactive (or failed) to maximum, with various states of partial activity. As a result, the heat generated in any one sealable module 60 may vary over time.

-36 -A fixed parallel sharing of the second cooling liquid will therefore tend to overcool some capsules and the heated second liquid from different capsules will be at different temperatures. By adjusting the flow rate to each cooling capsule independently, a more efficient system is produced with a more uniform temperature of the heated second cooling liquid from the various cooling capsules.

Pump 134 drives the second cooling liquid through the cooling modules and through heat transfer device 135, from where it is returned to the pump. Pump 134 may be similar to pump 116 of Figure 8, but is desirably of a larger scale to pump liquid to several equipment modules 130, 131, 132 instead of one. Arrows 141 show the direction of liquid flow. Heat transfer device 135 has the same function as the heat transfer device 118 of Figure 8, except that it is desirably of a larger scale to transfer heat from several equipment modules 130, 131, 132 instead of one.

The third stage of the system uses a third cooling liquid to transfer heat from the heat exchange device 135 to a final heat exchanger 137. Pump 136 is used to circulate the liquid. Atmospheric air or cool groundwater, used as the final heat sink medium, enters the heat exchanger at 138 and leaves at 139 In this case, and especially in systems that cool large arrays of servers, the entropy of the liquid carrying the heat may be low enough to be used f or other purposes, rather than be dumped into the environment. It may be used as a source of energy for heating a building for human occupation or the generation of useful amounts of electrical power. In other circumstances, where an unusually high atmospheric temperature would otherwise reduce the temperature difference between the source and final, atmospheric final heat sink to too low a level, excess heat -37 -may be diverted (by diverting some of the final liquid) to air conditioning units, or additional energy might be expended in the final heat exchanger (such as the use of adiabatic "dry coolers", which spray water into the air to increase heat capacity) Figure 9 also shows signal outputs El, E2 En from equipment modules 130, 131 and 132 and control connections Al, A2, A3 2N from flow control valves 133. Also shown are control inputs B and C to pump 134 and pump 135 respectively, and control input D to final heat exchanger 137. These can be used for monitoring and control purposes.

This will be explained in more detail below.

Referring now to Figure 10, there is shown a monitoring and control system 140 for use with the three-stage cooling system of Figure 9. The system comprises: data inputs 146; pump control outputs 145; and flow control valve outputs 144.

A monitoring and control system is used to monitor the temperatures of the electronic devices to be cooled and to adjust the flow rate of the second cooling liquid to each module to provide optimum cooling. Sensors on each electrical circuit board measure the temperature of the electronic components and convert this information to analogue or digital signals. Figure 9 shows signal outputs El, E2 En, where n is the total number of equipment modules that contain temperature-sensing devices, and where each signal contains information about the temperature of the one or more cooling capsules in each module. These outputs are sent to the control system 140.

The control system 140 computes the optimum flow rate of second cooling liquid to each cooling capsule and produces in response a control message Al, A2, A3 AN, -38 -where N=2n, there being two sealable modules 60 per cooling module in the described embodiment. This control message is sent to each flow control valve 133 to adjust the flow rate(s) to the determined levels. In addition, the control system determines whether or not the final heat exchanger needs to adjust its cooling rate, for example by altering the flow level of the final heat sink liquid or air, using control signal D, and is able to turn the circulating pumps 134, 136 on or off or to a different overall flow rate, using control signals B and C, dependent on the total amount of heat to be removed from the cooling modules.

In systems where "run-time hardware abstraction" of processing systems is used (such as with "virtualisation" or "run-time middleware"), the monitoring and control system is particularly important. In systems with hardware abstraction, the multiple electronic circuits boards ("hardware") and multiple computer operating systems are not in one to one correspondence. When one circuit board is under high processing load, some activity can be shared with other boards. Processing is distributed across the items of hardware. As a result, heat generated in different parts of the systems varies from time to time. Cooling rates in different parts of the system may then be adjusted dynamically to align with the changes in amounts of heat generated.

If the first cooling liquid in the sealable module 60 (and thus, the circuit board 75) is to operate at a desired temperature, Tcae, and the final heat sink is at a known temperature Thg, this defines the temperature difference that the cooling system desirably provides, in that LT = Tcase -Ths. Since Tcase is desirably restricted to no -39 -higher than the maximum operating temperature of the circuit board, Tcasemax, then AT �= Tcase,max -Ths Semiconductor manufacturers are increasingly reducing the maximum operating temperature of their processors. This reduces the temperature difference, particularly when refrigeration is not employed to increase the local temperature difference. A further difficulty arises when the final heat sink is at atmospheric temperature, which may be as high as 40 degrees centigrade.

Reducing the thermal resistances in the system can assist to achieve the desired temperature difference.

Systems which transfer heat through fluid flow may result in reduced thermal resistance compared with systems which transfer heat, either in full or in significant part, through static, thermally-coupled bodies or through gases.

For example, the flow rate of the second cooling liquid can be adjusted to reduce the thermal resistance between the sealable module 60 and the heat exchanger 118. Additionally or alternatively, the area of contact between the second cooling liquid flowing through the channels 61 and the conduction surface 71 can be controlled to affect the thermal resistance.

The use of tightly-packed channels 61 increases the pressure drop (i.e. hydraulic pressure losses) in the cold plate which increases the pumping costs for the secondary cooling liquid circuit. The width of the channel can be adjusted to reduce pressure losses and decrease the effect of the conduction surface 71 in the cold plate 22 in transferring heat into water channels.

At one extreme, the channels 61 could be as wide or wider than the dimensions of the housing 41 to present a "flood plain", rather than a "serpentine river", of second -40 -cooling liquid. However, controlling flow of second cooling liquid in such an embodiment may be difficult and features such as eddy currents may cause local build up of heat, which is undesirable as it will reduce rate of heat transfer for adjoining areas of conduction surface 71.

Therefore, the channel 61 width can be less than, but significant in comparison with a dimension of the housing 41. Optimisation of the cross-section of the channels 61 can improve the temperature difference. Channels 61 that are approximately 20% of the length of the longest channel 61 may be defined by baffles that direct flow over specific areas. Also, the flow of the second cooling liquid can be portioned with the channels 61 into sections such that the water is distributed into zones and slowed over areas with greatest heat flux (e.g. processors), the reintroduction of heat back into the primary coolant can be minimised, whilst the entropy of the extracted heat can be minimised.

Whilst a preferred embodiment arid operating modes of the present invention have been described above, the skilled person will recognise that the present invention can be implemented and operated in a number of different ways.

Referring now to Figure hA and Figure hiB, there are shown side views of a second embodiment of a sealable module according to the present invention, which is an alternative to that described above. The sealable module 150 comprises an outer housing 151 and lid 152. Although the second embodiment differs slightly from the first embodiment, the skilled person will appreciate that many features of the two embodiments are interchangeable.

The cold plate 22 is implemented by the outer housing 151, which defines the channels and can be termed a "water jacket", because it dictates the flow of water (as second -41 -cooling liquid) for heat to flow over a heat transfer surface, such as a conduction surface 71.

Referring now to Figure 11C, there is shown a more detailed view of the sealable module according to Figure hA and Figure llB. The sealable module 150 also comprises a heat transfer surface 153, with together with the outer housing 151 defines channels 156. Also, the heat transfer surface 153 and lid 152 (which can be termed a base) define an inner housing with an internal volume for locating the electronic device 153 to be cooled and the first cooling liquid (not shown). Connectors 154 are also shown, for allowing flow of the second cooling liquid through channels 156.

This alternative embodiment of a module may therefore comprise an inner housing, containing the first cooling liquid and one or more motherboards, substantially sealed (except for a filling port) . A heat transfer surface 153 has a gasketed interface with the inner housing and fins facing into the first cooling liquid, shaped to match the profile of the at least one motherboard. The outer housing 151 also has a gasketed interface with the heat transfer surface 153, and contains at least one secondary cooling liquid circuit channel 156, formed with baffles on the heat transfer surface 153 or on the interior surface of the outer housing 151. The at least one channel 156 is optimised to direct the second cooling liquid appropriately over the heat transfer surface 153 with minimised pressure loss. The outer housing 151 has quick-connect hydraulic connectors 154 to enable the channel 156 to be connected to the inlet and the outlet of a rack second cooling liquid supply.

This design allows much tighter integration between the inner housing, heat transfer surface 153 and outer housing -42 - 151 potentially to make a smaller unit, which may allow increased packing density of modules. Fins or baffles may be provided on both sides of heat transfer surface 153. These can, for example, provide additional flow control of second cooling liquid and increase surface area for conduction.

The materials for the present invention can be varied.

Metal materials are good conductors, but expensive. Also, if the heat transfer surface 153 or conduction surface 71 (which can be similar or identical) are made of metal and are large, they may be more likely to warp, putting stress on seals, especially if multiple sealable modules are mounted thereon, meaning areas of potentially different temperature.

In contrast, synthetic plastic materials are inferior conductors in comparison with metal. Known thermally conductive plastics typically conduct 20W/mK compared to l6OW/mK for aluminium. Higher performance thermally conductive plastics are also usually electrically conductive, which is not a desirable characteristic.

However, these materials are less expensive, of lighter weight and are less likely to corrode in the presence of hot water (notwithstanding the possible addition of corrosion inhibitors to the second cooling liquid) than metals.

Optimisation of the temperature difference by control of second cooling liquid flow rates, area of heat transfer and channel cross-section can allow the use of plastic without significant reduction in the temperature difference.

In particular, plastic can be used for the base part 22 of the cold plate or the outer housing ("water jacket") described above. A plastic material reduces the amount of heat transferred through the outer wall of the base part 22 or outer housing 151 and into the local ambient environment, -43 reducing heat lost in this way and increasing efficiency of heat removal into second cooling liquid.

Additionally or alternatively, the conduction surface 71 or heat transfer surface 153 can be made of plastic. This may provide additional expansion capacity for the first cooling liquid within the sealed housing. Such a material might be co-moulded with a rigid central thermal conductive plastic and peripheral ring of flexible non-conductive plastic.

A number of features of the embodiment described above will be understood as optional to the skilled person and might be omitted. These may include insulation 73, quick release connectors ill and protective membrane 67. Also, the skilled person will understand that alternative constructions for the cold plate base 22 or outer housing 151 can be used and that the projections 76 can be of different length and cross-section to that described.

Although an embodiment described above uses an equipment module 2 in which two sealable modules 60 are affixed to a common cold plate base part 22, it will be recognised that only one sealable module 60 might be coupled to a cold plate base part 22, or alternatively more than two sealable modules 60 might be affixed to a cold plate base part 22. Also, equipment modules 2 may be inserted from both back and front of the rack.

The data transmission cables 46 can be replaced by fibre optic cables, optical or infra-red ports or wireless connection between the electronic circuit board and the exterior of the cooling capsule. Power supply connections would normally be wired, even when the data transmission is by other means, although alternative power supplies may be employed, whilst avoiding fluid leakage.

-44 -The second cooling liquid may be distributed via a plenum chamber (a pressure equalisation device) rather than via pipes with individual valves. Also, heat exchanger 121 can alternatively be replaced by cool groundwater or a number of configurations including bypass circuits to transfer some heat to refrigeration systems. To provide resilience and redundancy additional "back-up" pumps and circuits may optionally be provided.

When the final heat sink 121 is close to the equipment to be cooled and the pressure of the cooling liquid circulating in this stage can be lower, a second stage of cooling might be omitted. In this case, the second cooling liquid circulates directly through the final heat exchanger.

Pump 116 and intermediate heat transfer device 118 are omitted. As with the embodiment illustrated in Figure 8, the three-stage system shown in Figure 9 could be reduced to two stages if the liquid pressure in the final stage were low enough.

Claims

-45 -CLAI MS1. A sealable module in which one or more heat generating electronic components may be located, the module comprising: a housing; and a heat transfer device having a conduction surface, the housing and the conduction surface together defining a volume in which an electronic component and a first cooling liquid can be located; and wherein the heat transfer device further defines a channel for receiving a second cooling liquid, the conduction surface separating the volume and the channel to allow conduction of heat between the volume and the channel through the conduction surface.
2. The sealable module of claim 1, further comprising at least one electronic component which generates heat when in use, and a first cooling liquid, located in the volume.
3. A sealable module in which one or more heat generating electronic components may be located, the module comprising: a housing; a heat transfer device having a conduction surface, the conduction surface and housing together defining a volume in which a first cooling liquid can be located; and an electronic component, having an elongate axis and located in the volume; and wherein the heat transfer device defines a channel for receiving a second cooling liquid, and the conduction surface has an elongate axis arranged in conformity with the elongate axis of the electronic component to allow -46 -conduction of heat between the volume and the channel through the conduction surface.
4. The sealable module of claim 3, further comprising a first cooling liquid located in the volume.
5. The sealable module of any preceding claim, wherein the conduction surface has at least one projection into the first volume for conducting heat between the volume and the channel.
6. The sealable module of any of claims 2 to 4, wherein the conduction surface has at least one projection into the first volume for conducting heat between the volume and the channel, the at least one projection being arranged in conformity with the shape of the electronic component.
7. The sealable module of claim 6, further comprising a component heat sink coupled to the electronic component, having at least one projection arranged to cooperate with the at least one projection of the conduction surface.
8. The sealable module of any of claims 5 to 7, wherein the at least one projection of the conduction surface comprises a fin arrangement.
9. The sealable module of any of claims 5 to 8, wherein the at least one projection of the conduction surface comprises a pin arrangement.
10. The sealable module of any preceding claim, wherein the heat transfer device further comprises a base part coupled -47 -to the conduction surface and defining the channel for receiving the second cooling liquid.
11. The sealable module of any preceding claim, further comprising an insulation layer covering at least part of the housing, exterior to the volume.
12. The sealable module of any preceding claim, comprising a plurality of electronic components, at least one of which generates heat when in use, and further comprising a circuit board holding the electronic components.
13. The sealable module off claim 12, further comprising a protective membrane positioned between the circuit board and the housing, the protective membrane being arranged to prevent liquid flow between the protective membrane and the circuit board.
14. The sealable module of any preceding claim, further comprising: a filling inlet to the module, located in the housing and through which a liquid can be received into the volume; and a seal to the filling inlet.
15. The sealable module of any preceding claim, further comprising a pressure relief valve, located in the housing and arranged to allow liquid flow out from the volume when the pressure within the volume exceeds a predefined limit.

-48 -
16. The sealable module of any preceding claim, wherein the conduction surface is made from a synthetic plastic material.
17. A sealable module in which one or more heat generating electronic components may be located, the sealable module comprising: an inner housing, sealable so as to define a volume in which an electronic component and a first cooling liquid can be located; and an outer housing, defining a channel for receiving a second cooling liquid, the outer housing being arranged to cooperate with the inner housing to provide an interface between the channel and at least a portion of the inner housing that allows transfer of heat between the volume and the channel.
18. The sealable module of claim 17, wherein the at least a portion of the inner housing that interfaces with the channel defines a conduction surface, the channel having an area of contact with the heat transfer surface defining a channel width, and wherein the minimum channel width is significant in comparison with the dimensions of the heat transfer surface.
19. The sealable module of claim 17 or claim 18, wherein the channel interfaces with the at least a portion of the inner housing along a path having at least one change in direction.
20. The sealable module of claim 19 when dependent upon claim 17, wherein the path has a straight portion, and -49 -wherein the minimum channel width is at least l0 of the length of the straight portion of the path.
21. The sealable module of claim 19 or claim 20, wherein the path comprises a main path and a branch path, the branch path being connected to the main path at at least one point.
22. The sealable module of any of claims 17 to 21, wherein the inner housing comprises: an interface portion, arranged to cooperate with the outer housing to provide the interface between the channel and at least a portion of the inner housing; and a base portion, arranged to couple to the interface portion so to form the sealable inner housing.
23. The sealable module of any of claims 17 to 22, wherein the at least a portion of the inner housing that interfaces with the channel is made from a synthetic plastic material.
24. The sealable module of any of claims 17 to 23, wherein the outer housing is made from a synthetic plastic material.
25. A cooled electronic system, comprising: the sealable module of any of claims 1, 3 or 17 to 24; an electronic component located in the volume; a first cooling liquid located in the volume; a heat sink; a pumping arrangement, arranged to allow a second cooling liquid to flow through the channel of the sealable module to the heat sink at a predetermined flow rate and further arranged to control the portion of the inner housing through which heat is transferred to the channel; -50 -a temperature sensor, arranged to determine a temperature of the electronic component; and a controller arranged to control the pumping arrangement, such that the temperature of the electronic component is controlled so as not to exceed a predetermined maximum operating temperature.
26. A method of cooling an electronic component, comprising: providing a module comprising a housing and a heat transfer device having a conduction surface, the housing and the conduction surface together defining a volume; housing the electronic component within the volume; filling the volume with a first cooling liquid; and conducting heat between the first cooling liquid and a second cooling liquid through the conduction surface, the first cooling liquid and second cooling liquid being located on either side of the conduction surface.
27. The method of claim 26, wherein the step of conducting heat from the first cooling liquid to a second cooling liquid is configured such that the first cooling liquid and second cooling liquid remain in liquid state.
28. A method of cooling an electronic device, comprising: providing a module comprising a housing and a heat transfer device having a conduction surface, the housing and the conduction surface together defining a volume, the volume being filled with a first cooling liquid and having the electronic device located therein; operating the electronic device within the volume; -51 -transferring heat generated by the electronic device from the first cooling liquid to a second cooling liquid through at least a portion of the heat transfer surface; transferring the second cooling liquid to a heat sink; and adjusting one or both of: the flow rate of the second cooling liquid from the conduction surface to the heat sink; and the portion of the conduction surface through which heat is transferred to the second cooling liquid, such that the temperature of the electronic device is controlled so as not to exceed a predetermined maximum operating temperature.
29. The method of any of claims 26 to 28, wherein the conduction surface is made from a synthetic plastic material.
30. A method of cooling an electronic device having an elongate axis, comprising: housing the electronic device within a container, the container being filled with a first cooling liquid and having an elongate axis which extends in a direction that generally corresponds with the elongate axis of the electronic device; positioning the container such that the electronic device is upright and so that heat generated by the electronic device is transferred to the first cooling liquid; and transferring heat between the first cooling liquid and a second cooling liquid in a heat transfer device.

-52 -
31. A method of cooling an electronic device, comprising: operating the electronic device within a container, the container also comprising a first cooling liquid, such that heat generated by the electronic device is transferred to the first cooling liquid, the container being sealed to prevent leakage of the first cooling liquid; transferring heat between the first cooling liquid and a second cooling liquid in a first heat transfer device; piping the second cooling liquid from the first heat transfer device to a second heat transfer device; and transferring heat between the second cooling liquid and a third cooling liquid in the second heat transfer device; and piping the third cooling liquid to a heat sink.
32. The method of claim 30 or claim 31, wherein the step of transferring heat between the first cooling liquid and the second cooling liquid is carried out by conduction.
33. A method of cooling an electronic system, comprising: carrying out the method steps of cooling an electronic device in accordance with claim 31 or claim 32; operating a second electronic device within a second container, the second container also comprising a fourth cooling liquid, such that heat generated by the electronic device is transferred to the fourth cooling liquid, the second container being sealed to prevent leakage of the fourth cooling liquid; and transferring heat between the fourth cooling liquid and a fifth cooling liquid in a fourth heat transfer device.

-53 -
34. The method of claim 33, further comprising: combining the second cooling liquid and the fifth cooling liquid.
35. The method of any of claims 31 to 34, further comprising: controlling the flow rate of the second cooling liquid.
36. The method of any of claims 31 to 35, further comprising: controlling the flow rate of the third cooling liquid.
37. The method of any of claims 31 to 36, wherein the first heat transfer device comprises a conduction surface, further comprising: adjusting one or both of: the flow rate of the second cooling liquid from the first heat transfer device to the second heat transfer device; and the portion of the conduction surface through which heat is transferred to the second cooling liquid, such that the temperature of the electronic component is controlled so as not to exceed a predetermined maximum operating temperature.
38. A cooled electronic system, comprising: a sealed container comprising: a housing; an electronic component; and a first cooling liquid; a first heat transfer device defining a first channel for receiving a second cooling liquid, the first heat transfer device being configured to transfer heat between the first cooling liquid and the first channel; and a second heat transfer device comprising a second channel for receiving the second cooling liquid from the -54 -first channel, and a third channel for receiving a third cooling liquid and coupled to a heat sink, the second heat transfer device being configured to transfer heat between the second channel and the third channel.
39. The cooled electronic system of claim 38, wherein the first heat transfer device comprises a conduction surface, the housing and the conduction surface together defining a volume in which the electronic component and the first cooling liquid are located.
40. The cooled electronic system of claim 39, wherein the conduction surface separates the volume and the first channel to allow conduction of heat between the volume and the channel through the conduction surface.
41. The cooled electronic system of claim 39 or claim 40, wherein the conduction surface has at least one projection for receiving heat from the first cooling liquid.
42. The cooled electronic system of claim 41, wherein the at least one projection is arranged in conformity with the shape of the electronic component.
43. The cooled electronic system of claim 42, further comprising a component heat sink coupled to the electronic component and comprising at least one projection arranged to cooperate with the at least one projection of the conduction surface.

-55 -
44. The cooled electronic system of any of claims 41 to 43, wherein the at least one projection comprises a fin arrangement.
45. The cooled electronic system of any of claims 41 to 44, wherein the at least one projection comprises a pin arrangement.
46. The cooled electronic system of any of claims 40 to 45, wherein the conduction surface is made from a synthetic plastic material.
47. The cooled electronic system of any of claims 40 to 46, wherein the heat transfer device further comprises a base part coupled to the conduction surface and defining the channel for receiving the second cooling liquid.
48. The cooled electronic system of any of claims 38 to 47, wherein the module further comprises: a filling inlet to the container, through which the first cooling liquid can be received; and a seal to the filling inlet.
49. The cooled electronic system of any of claims 38 to 48, wherein the module further comprises a pressure relief valve, arranged to allow outflow of the first cooling liquid from the container when the pressure within the container exceeds a predefined limit.
50. The cooled electronic system of any of claims 38 to 49, wherein the electronic component has an elongate axis and in which the conduction surface has an elongate axis arranged -56 -in conformity with the elongate axis of the electronic component to allow conduction of heat between the volume and the channel through the conduction surface.
51. The cooled electronic system of any of claims 38 to 50, wherein the sealed container is a first sealed container, and further comprising: a second sealed container comprising: a second housing; a second electronic component; a fourth cooling liquid for receiving heat from the second electronic component; and a fourth heat transfer device comprising a fourth channel for receiving a fifth cooling liquid, the fourth heat transfer device being configured to transfer heat from the fourth cooling liquid to the fourth channel.
52. The cooled electronic system of claim 51, wherein the first channel and the fourth channel are coupled to combine the second cooling liquid and the fifth cooling liquid.
53. The cooled electronic system of any of claims 38 to 52, further comprising: a controller, arranged to control the flow rate of the second cooling liquid.
54. The cooled electronic system of claim 53, wherein the controller is further arranged to control the flow rate of the third cooling liquid.
55. A method of filling a container for an electronic device with a cooling liquid, the method comprising: heating the cooling liquid to a filling temperature, the filling temperature being selected such that gases -57 -dissolved in the cooling liquid are removed from the cooling liquid; heating the container to the filling temperature; filling the heated container with the heated cooling liquid such that all air in the container is disp1aced sealing the container to prevent leakage of the cooling liquid; and cooling the sealed container and cooling liquid to an operating temperature.Amendments to the claims have been filed as follows CL1IMS 1. A method of cooling an electronic device, comprising: providing a module comprising a housing and a heat transfer device having a conduction surface, the housing and the conduction surface together defining a volume, the volume being filled with a first cooling liquid and having the electronic device located therein; operating the electronic device within the volume; transferring heat generated by the electronic device from the first cooling liquid through at least a portion of the conduction surface to a second cooling liquid flowing in a channel; S.... transferring heat from the second cooling liquid to a 15 heat sink; and setting one or both of: the flow rate of the second * cooling liquid over the conduction surface; and the form of *.the channel carrying the second cooling liquid so as to set the portion of the conduction surface through which heat is transferred, such that the temperature of the electronic device is controlled so as not to exceed a predetermined maximum operating temperature.2. The method of claim 1, wherein the step of transferring heat from the first cooling liquid to the second cooling liquid is by conduction through a synthetic plastic material conduction surface.3. The method of claim 1, further comprising: piping the second cooling liquid from the first heat transfer device to a second heat transfer device; and transferring heat between the second cooling liquid and a third cooling liquid in the second heat transfer device; and piping the third cooling liquid to a heat sink; and wherein the container is sealed to prevent leakage of the first cooling liquid.4. A method of cooling an electronic system, comprising: carrying out the method steps of cooling an electronic device in accordance with claim 3; operating a second electronic device within a second container, the second container also comprising a fourth cooling liquid, such that heat generated by the electronic device is transferred to the fourth cooling liquid, the :: 15 second container being sealed to prevent leakage of the fourth cooling liquid; * transferring heat between the fourth cooling liquid and S..a fifth cooling liquid in a fourth heat transfer device; and combining the second cooling liquid and the fifth *:*. 20 cooling liquid.5. The method of claim 3 or claim 4, further comprising: controlling the flow rate of the second cooling liquid.6. The method of any of claims 3 to 5, further comprising: controlling the flow rate of the third cooling liquid.7. A cooled electronic system, comprising: a module, comprising: a housing; and a heat transfer device having a conduction surface, the housing and the conduction surface together defining a volume, the volume being filled with a first cooling liquid and having the electronic device located therein, the heat transfer device being arranged to allow transfer of heat generated by the electronic device from the first cooling liquid to a second cooling liquid through at least a portion of the conduction surface; means for transferring heat from the second cooling liquid to a heat sink; and a controller, arranged to adjust the flow rate of the second cooling liquid over the conduction surface, such that the temperature of the electronic device is controlled so as not to exceed a predetermined maximum operating temperature. * * I...:: 15 8. The cooled electronic system of claim 7: * ** wherein the module is a sealed container; * * S wherein the heat transfer device is a a first heat S..transfer device defining a first channel for receiving the : second cooling liquid; and *:*. 20 the cooled electronic system further comprising a second heat transfer device comprising a second channel for receiving the second cooling liquid from the first channel, and a third channel for receiving a third cooling liquid and coupled to a heat sink, the second heat transfer device being configured to transfer heat between the second channel and the third channel.9. The cooled electronic system of claim 8, wherein the conduction surface separates the volume and the first channel to allow conduction of heat between the volume and the channel through the conduction surface.10. The cooled electronic system of claim 8 or claim 9, wherein the conduction surface has at least one projection for receiving heat from the first cooling liquid.11. The cooled electronic system of claim 10, wherein the at least one projection is arranged in conformity with the shape of the electronic component.12. The cooled electronic system of claim 11, further comprising a component heat sink coupled to the electronic component and comprising at least one projection arranged to cooperate with the at least one projection of the conduction surface. *S.. * S S...:: 15 13. The cooled electronic system of any of claims 10 to 12 * ,. wherein the at least one projection comprises a fin * . e S.. * * arrangement. *SS14. The cooled electronic system of any of claims 10 to 13, . 20 wherein the at least one projection comprises a pin arrangement.15. The cooled electronic system of any of claims 7 to 14, wherein the conduction surface is made from a synthetic plastic material.16. The cooled electronic system of any of claims 8 to 15, wherein the first heat transfer device further comprises a base part coupled to the conduction surface and defining the channel for receiving the second cooling liquid.17. The cooled electronic system of any of claims 7 to 16, wherein the module further comprises: a filling inlet to the container, through which the first cooling liquid can be received; and a seal to the filling inlet.18. The cooled electronic system of any of claims 7 to 17, wherein the module further comprises a pressure relief valve, arranged to allow outflow of the first cooling liquid from the container when the pressure within the container exceeds a predefined limit.19. The cooled electronic system of any of claims 7 to 18, S... wherein the electronic component has an elongate axis and in 15 which the conduction surface has an elongate axis arranged in conformity with the elongate axis of the electronic * component to allow conduction of heat between the volume and 0.5 the channel through the conduction surface. * .* * * S S.. S*. 20 20. The cooled electronic system of any of claims 7 to 19, wherein the sealed container is a first sealed container, and further comprising: a second sealed container comprising: a second housing; a second electronic component; a fourth cooling liquid for receiving heat from the second electronic component; and a fourth heat transfer device comprising a fourth channel for receiving a fifth cooling liquid, the fourth heat transfer device being configured to transfer heat from the fourth cooling liquid to the fourth channel.