Patent ID: 12199258

In the drawings there is shown a support structure for a duct according to the invention, indicated generally by reference numeral1. InFIG.1the support structure1is illustrated in situ in a battery pack2, in particular, on a lower clamshell of the battery pack2. The support structure1can be used as a guide for a flexible duct3, as shown inFIGS.2to4, in particular, where the duct3changes direction.

The support structure1is used to prevent the duct3kinking, bulging and/or bursting when the duct changes direction. Kinking of the duct3can result in the flexible duct3folding in on itself and creating blockage(s) within the duct3. Blockages due to kinking can be overcome by pressurising the coolant fluid within the duct3sufficiently to overcome the kinking and to force the flexible duct3open. However, use of excessive pressure is undesirable as the pressure required to overcome the kinking effect may cause the flexible duct3to stretch, hence causing the walls of the duct3to thin and potentially burst. Furthermore, the pressure loss within the system due to kinking over a series of multiple bends may be significant, reducing the overall performance of the thermal management arrangement.

The pressure required to overcome the problem of kinking at each bend in a flexible duct3is often in excess of the pressure that the flexible duct3can withstand without bursting. The internal pressure within the duct3is limited by the tensile strength of the inflatable tube and, consequently, its maximum inflated diameter. The support structure1limits the maximum diameter of the duct3and also provides direct mechanical support to the duct3, particularly at places where the duct3changes direction.

Kinking of the duct3is most prone at points where the duct3changes direction. As such, the support structures1are located at the edge of the battery pack2where the flexible duct3emerges from the array of cells4and reverses direction.FIG.1shows the support structures1positioned on the battery pack2at the periphery of the cells4. The support structures1are positioned along opposing sides of the battery pack2at each point the duct2emerges from the array of cells4. As is explained in further detail below, the support structures1can be made from any suitable rigid, semi-rigid or compressible material which has sufficient rigidity to support the flexible duct, for example metal, plastic, rubber, or a potting material such as an epoxy resin or polyurethane foam.

Respective support structures1are positioned at opposing sides of the battery pack2to guide the flexible duct3where the flexible duct3emerges from the array of cells4and changes direction. For this purpose, the support structure1defines a guide path5for the flexible duct3. The guide path5is a slot or channel into which the flexible duct3may be inserted and that the flexible duct3then follows so as to change direction without kinking. The guide path5of the support structure1is defined between an inner supporting face7of an inner guide formation6and an outer supporting face9of an outer guide formation8as shown inFIG.2. A base extends between the inner guide formation6and the outer guide formation8thereby connecting them.

The flexible duct3is first inserted into the support structure1in an uninflated state to follow the guide path5. The guide path5is shaped to accommodate an excess length of the flexible duct3. Providing the flexible duct3with excess length creates some slack that mitigates kinking when the flexible duct3is inflated and so comes under tension. The flexible duct3is inserted into the guide path5in an uninflated state for ease of assembly. However, the skilled reader will appreciate that a small amount of working fluid may be used to pressurise the flexible duct3to give the flexible duct3some stiffness to aid assembly. The working fluid may be, for example, air or a coolant fluid.

The inner guide formation6, more specifically the inner support face7, may be formed from a compressible material such as polymeric foam or rubber, where the duct3contacts the inner guide formation6when inflated. The inner guide formation6is dimensioned such that the bend radius of the inner supporting face7is large enough to guide the flexible duct3smoothly through 180° in successive 90° bends without the duct3kinking. As shown inFIG.2, the inner supporting face7comprises a planar elongate facet10between two radiused edges11. The elongate facet10serves to straighten and support the flexible duct3at the point at which kinking would otherwise be most likely.

Notch-like recesses12in the outer guide formation8opposite the radiused edges11form part of the outer supporting face9to accommodate the slack defined by the excess length of the flexible duct3. Specifically, slack portions of the flexible duct3that bend around the radiused edges11can be pulled or pushed away from the radiused edges11and into the recesses12. Pressing the flexible duct3into the recesses12in this way before inflating the flexible duct3creates slack in the flexible duct3at the radiused edges11. Providing this slack in the flexible duct3before inflation is advantageous as it helps to mitigate kinking of the duct3as it is inflated.

The notch-like recesses12are recesses in the outer supporting face9of the outer guide formation8and may be any shape suitable for partially receiving the duct3to create slack around the radiused edges11.

FIG.3shows the flexible duct3located within the guide path5of the supporting structure1in an uninflated state. When the flexible duct3is first located within the guide path5an elongate rod or tool15may be used to locate the flexible duct3in the recesses12. The elongate rod or tool15pushes the flexible duct3into the recesses12such that slack is created in the flexible duct3.

In particular the slack is created in the region of the radiused edges11such that when the flexible duct3is inflated, thus coming under tension, the flexible duct3does not kink.

FIG.4shows the flexible duct3in an inflated state within the support structure1and cells4. When the duct3is in the inflated state, tension in the flexible duct3takes up any excess slack in the duct3. As the excess slack is taken up in the duct3, the flexible duct3is pulled from the recesses12as shown inFIG.4. In the inflated state the duct3contacts the radiused edges11on the inner supporting face7and is supported by the elongate facet10.

The support structure1is dimensioned such that the cells17positioned on the end of each row of the array have substantially the same thermal contact area with the duct3as cells located in the centre of the array. This is advantageous as it promotes a more even temperature distribution throughout the battery pack2thereby extending the life of the battery pack2. The support structure1achieves this by shielding or thermally insulating a portion of the end cells17from thermal contact with the duct3such that the duct3has substantially the same thermal contact area with the end cells17as cells located within the array.

As shown inFIGS.2to4, the ends of the outer supporting face9abut the end cells17such that the outer bend of the guide path5is defined by the outer supporting face9from the point the duct3emerges from the array to the point that the duct3re-enters the array. The outer supporting face9prevents the duct3expanding such that it wraps around the exterior of the cells17which would cause the end cell17to have an increased thermal contact with the duct3.

Similarly, one end18of the inner supporting face7abuts an end cell17as shown inFIGS.2to4. The end18of the inner supporting face7in abutment with the end cell17provides support to the duct3thereby preventing the duct3bulging and wrapping around the end cell17.

The other end portion19of the inner supporting face7partially follows the surface of another end cell17such that the end portion19wraps around the end cell17to form a thermal insulating barrier. The end portion19of the inner supporting face7partially wraps around the exterior surface of the end cell17such that when the duct3is located within the guide path5the duct3does not contact the end cell17in the region of the end portion19. The skilled reader will understand that the extent to which the portion19extends around the end cell17is dependent upon the thermal contact between the duct3and the cells4. The portion19should extend around the end cell17sufficiently to ensure that the duct3does not contact the end cell17more than any other cell4within the array.

The guide path5defines a channel for the duct3to follow from the point the duct3emerges from the array to the point that the duct3re-enters the array. The guide path5prevents the duct3bulging or thermally contacting the cells17located at the edge of the array any more than a cell located within the array.

Referring now toFIG.5, there is shown a further embodiment of a support structure indicated generally by reference numeral101. The support structure101is formed from a block of solid material, with a plurality of spaced apart guide paths105extending therethrough. The guide paths105are substantially the same shape and size as the guide path5of the embodiment illustrated inFIGS.1to4. As the support structure101comprises a plurality of guide paths105, the duct3can be arranged extending through a first guide path105, along a first row of cells4, back along a second row of cells4adjacent the first row, and into a second guide path105of the same support structure101. Advantageously, a single support structure101can be used to support the duct3in more than one location about the battery pack2as the duct3is arranged around the cells4of the battery pack2.

The support structure101has an inner thermally-insulating block125that is integrally formed with, and extends away from, the inner guide formation106towards the outer cells of the battery pack2when in use, such that the volume between the outer cells of the battery pack2and the inner guide formation106is filled with thermally-insulating material. This further improves the thermal management properties of the duct3. The support structure101further has an outer thermally-insulating block126that is integrally formed with and extends outwardly away from the outer guide formation108. The support structure101thereby supports the duct3in multiple locations and also thermally-insulates the battery pack2.

Referring now toFIGS.6and7there is shown a further embodiment of a support structure according to the invention, indicated generally by reference numeral201. The support structure201of this embodiment has an outer guide formation, an inner guide formation and a guide channel205therebetween. The support structure201is used to prevent a flexible duct from kinking, bulging and/or bursting when the duct changes direction.

The support structure201is dimensioned such that the cells positioned on the end of each row of the array have substantially the same thermal contact area with the duct as cells located in the centre of the array. This is advantageous as it promotes a more even temperature distribution throughout the battery pack thereby extending the life of the battery pack. The support structure201achieves this by shielding or thermally insulating a portion of the end cells from thermal contact with the duct such that the duct has substantially the same thermal contact area with the end cells as cells located within the array.

The outer guide formation of support structure201is formed by the combination of an outer upstand208and the inner surface211of a wall210of the outer pack casing (seeFIG.7). The outer upstand208is located adjacent to at least one cell at the edge of the array of cells. The outer upstand208is a block that has a cell-abutting face235which is curved to match the shape of a cell sidewall, and an outer supporting face209which extends from the cell-abutting face235. The outer upstand208is integrally formed with the lower clamshell237of the battery pack housing236.

The inflatable duct is supported by both the outer supporting face209of the upstand208and the inner surface211of the battery pack wall210. Using the battery pack wall210as part of the outer guide formation removes the need for a larger support structure and therefore reduces the width of, and eliminates dead-space within, the battery pack. Ultimately the battery pack can incorporate more cells within a fixed volume, increasing volumetric and gravimetric energy density of the pack.

The outer supporting face209of upstand208prevents the duct expanding such that it would wrap around the exterior of an end cell, causing the end cell to have an increased thermal contact with the duct.

The inner guide formation of support structure201is formed by a combination of an inner upstand206aand an interface portion206b. The inner upstand206ais similar in construction to the outer upstand208. The inner upstand206ais a block that is integrally formed with the lower clamshell237of battery pack housing238. The inner upstand206ais located on the opposing side of the guide channel205to the outer guide formation. The inner upstand206ahas two curved cell-abutting faces239a,239bfor abutting two adjacent, spaced apart cells.

The inner upstand206afurther has an inner supporting face207that extends between the cell-abutting faces239a,239b. The inner supporting face207of the inner upstand206ahas a substantially planar portion and a substantially curved portion that extends from the substantially planar portion towards the sidewall of a cell. The inner supporting face207provides support to the duct3thereby preventing the duct3bulging and wrapping around an end cell.

The interface portion206bis provided by a compressible pad adhered to the surface of a cell. Specifically, the pad is open-cell polyvinyl chloride (PVC) tape. Alternatively, closed-cell PVC or polyurethane foam could be used, or other suitable compressible material. In use, the interface portion206bof the inner guide formation extends from a cell-abutting face239aof the first part206aand around a portion of the cell to which it is adhered. When the flexible duct (not shown) is inflated it presses against the inner upstand206aand an interface portion206bof the inner guide formation.

The interface portion206bis used to limit the thermal contact between the duct and the peripheral cell to which it is attached. The interface portion206bwraps around the exterior surface of an end cell such that when the duct is located within the guide path205the duct does not contact the end cell in the region of the interface portion206b. The skilled reader will understand that the extent to which the interface portion206bextends around the end cell is dependent upon the required thermal contact between the duct and the cells. The interface portion206bshould extend around the end cell sufficiently to ensure that the duct does not contact the end cell more than any other cell within the array.

The skilled person will appreciate that both of the inner upstand206aand an interface portion206bmay be compressible and/or may be integrally connected to one another. Interface portion206bmay be integrally formed with the lower clamshell237.

Referring now toFIGS.8to10there is shown a yet further embodiment of a support structure according to the invention, indicated generally by reference numeral301. The support structure301of this embodiment has an outer guide formation308, an inner guide formation306and a guide channel305therebetween. The support structure301is used to prevent a flexible duct from kinking, bulging and/or bursting when the duct changes direction.

The support structure301is dimensioned such that the cells positioned on the end of each row of the array have substantially the same thermal contact area with the duct as cells located in the centre of the array. This is advantageous as it promotes a more even temperature distribution throughout the battery pack thereby extending the life of the battery pack. The support structure301achieves this by shielding or thermally insulating a portion of the end cells from thermal contact with the duct such that the duct has substantially the same thermal contact area with the end cells as cells located within the array.

The outer guide formation of support structure301is formed by the combination of a first outer upstand308a, a second outer upstand308band the inner surface311of a wall310of the outer pack casing (seeFIG.9). The first and second upstanding structures308a,308bare spaced apart and both are connected to a support structure base312. The lower clamshell337of the battery pack housing338may include appropriate recesses to accommodate the support structure base312at the edge of the array of cells although in optional embodiments the support structure301may be integrally formed with the lower clamshell337.

The inflatable duct is supported by the first outer upstand308a, the second outer upstand308band the inner surface311of the battery pack wall310. Using the battery pack wall310as part of the outer guide formation removes the need for a larger support structure and therefore reduces the width of, and eliminates dead-space within, the battery pack. Ultimately the battery pack can incorporate more cells within a fixed volume, increasing volumetric and gravimetric energy density of the pack.

The upstanding structures308a,308bare curved and define corners of the guide formation305. The gap between the upstanding structures308a,308bcan be used to pull excess amounts of the duct through the support structure301when arranging the duct in the battery pack.

The first outer upstand308athe second outer upstand308bprevent the duct expanding such that it would wrap around the exterior of an end cell causing the end cell to have an increased thermal contact with the duct.

The inner guide formation306is generally similar to the inner guide formation6shown in e.g.FIGS.2to4and may be attached to the support structure base312or integrally formed with the lower clamshell of the battery pack.

In use, the support structure1,101,201,301is arranged at a location on the battery pack2where the duct3changes direction, such as at the edge of the battery pack2. The uninflated duct3is arranged between the cells4and is inserted into the guide formation5,105,205,305. An elongate tool15such as a screwdriver is inserted into the guide formation5,105,205,305and used to urge the uninflated duct3into the recesses12thereby generating slack within the guide formation5,105,205,305. The duct3is then inflated by pumping a fluid through the duct3. The duct3moves away from the recesses12and extends around the inner guide formation6,106,206,306, which is compressed by the duct3. The support structure1,101,201,301retains the inflated duct away from the outer cells17such that they are not exposed to a greater amount of the duct3than any other cell4in the array. The support structure1,101,201,301further prevents the duct3from kinking as it changes direction where the duct3exits the array and returns back into the array.

Further within the scope of the invention is a battery pack2having a plurality of cells4and a support structure1,101,201,301configured to provide support to a flexible duct3, the flexible duct being arrangeable proximal to (i.e. adjacent to and/or between) the cells4to thermally manage the cells4, and where the support structure1,101,201,301is configured to prevent kinking of the duct3when the duct changes direction.

Yet further within the scope of the invention is a thermal management arrangement30for a battery pack2, wherein the battery pack2has a plurality of cells4and where the thermal management arrangement30has a flexible duct3configured to be placed around the cells4of the battery pack to and carry a fluid to thermally manage the battery pack2. The thermal management arrangement30further has a support structure1,101,201,301configured to provide support to the flexible duct3to prevent the duct3kinking when the duct3changes direction.

The fluid within the duct3can be a coolant fluid used to thermally manage the cells4via heating and/or cooling. The duct3is pressurised by the fluid to an inflated state as shown inFIG.4. When in the inflated state, the duct3is in conformity with the surface of the cells4. This improves the thermal contact between the duct3and the cells4such that the fluid may transfer thermal energy between the fluid and the cells4more efficiently. The duct3further secures the cells4in position when in the inflated state. This improves the connection of the cells4in the battery pack2. Furthermore, when the battery pack2is being used in an automotive or aerospace application where it is subject to vibration, the duct3may reduce the effects of vibrations on the battery pack2by securing the individual cells4in place.

The thermal management arrangement30further involves a potting material231in the form of a thermally insulating foam located within the battery pack. The potting material/thermally insulating foam prevents a high energy thermal event propagating through the battery pack2and reduces the effect of external temperature fluctuations on the battery pack2, helping to ensure that the duct3is the primary controller of thermal energy within the battery pack2.

During construction of the battery pack, the potting material/thermally insulating foam231is poured into the battery pack while the duct is in the inflated state located within the support structures1,101,201,301and between/adjacent to the cells4. The thermally insulating foam is expandable sets rigid such that it secures the cells4and the duct3in position within the battery pack2. This is advantageous as it reduces the effects of vibrations on components within the battery pack2and it acts as a support for the duct3. When the foam sets rigid it surrounds the inflated duct3and provides external support to the duct3thus preventing excessive expansion and potentially, bursting of the duct3. The thermally insulating foam also acts as an adhesive.

The thermal management arrangement30further has an outer casing (not shown) for the battery pack2. The thermally insulating foam secures the outer casing to the battery pack2by adhering the outer casing to the battery pack2. This beneficially reduces or negates the requirement for additional fixings or fasteners which reduces the complexity of the battery pack2and improves the manufacturing process. The thermally insulating foam is polyurethane foam.

The support structures1,101,201,301can be made from any suitable rigid, semi-rigid or compressible material which has sufficient rigidity to support a flexible duct3, for example metal, plastic or rubber. In an important example, the support structures1,101,201,301are made from the potting material used within the battery pack2or possess similar thermal propagation prevention properties as the bulk potting compound. For example, the support structures1,101,201,301can be manufactured by pouring a potting material into a suitable mould, or by cutting out a support structure from e.g. a block of pre-cured thermally insulating foam.

As noted above, the support structures1,101,201,301are used to prevent the duct3kinking, bulging and/or bursting when the duct3is in its inflated state and changes direction. After the duct has been placed within the array of cells and within the support structures1,101,201,301, potting material is poured into the battery pack while the duct is in the inflated state. In cases where the potting material is thermally insulating or polyurethane foam, the potting material expands to surround and support the inflated duct in places where it is not supported by a support structure and/or is not in contact with the sidewall of a cell. In cases where the support structures1,101,201,301are made from thermally insulating foam, once the potting material within the battery pack has cured or hardened then there will be a seamless interface between the support structure and the potting material within the pack. Advantageously, the support structures1,101,201,301and potting material will have the same thermal insulating properties.

In alternatives, the support structure1,101,201,301can be integrally formed with the walls of the battery pack2, for example with either of the upper or lower clamshell. In such examples the support structures1,101,201,301are extrusions from the plastic shells as opposed to an insert within the battery pack2. The lower clamshell and/or upper clamshell can comprise a plurality of circular recesses, each recess being configured to receive an end portion of a respective cylindrical cell. The recesses are arranged in a close-packed array for holding the array of cells in place within the pack. Apertures in the recesses allow the cells to be electrically connected to busbars on the upper and/or lower clamshell.

The duct3is to be formed from an inflatable plastics material such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) or high-density polyethylene (HDPE). An inflatable plastics material is advantageous as the material is intrinsically electrically insulating, lightweight and does not corrode or chemically interact with a coolant such as a glycol water mix. The duct wall is thin thereby allowing good thermal transfer properties between the duct3and the cells4. For example, the duct wall may be between 50 μm and 150 μm thick. The thermal management arrangement has a reservoir (not shown) in fluid communication with the duct3.

The thermal management arrangement30further has a coolant loop (not shown). The coolant loop is in fluid communication with the reservoir. The reservoir contains a coolant fluid and provides hydrostatic pressure to coolant fluid in the coolant loop. The thermal management arrangement further has a pump (not shown) for pumping fluid through the duct3. The pump is configured to pump coolant from the reservoir to the coolant loop to pressurise the coolant loop. Coolant fluid in the reservoir can thereby be used to pressurise the thermal management arrangement30. This allows the pressure to be maintained within the thermal management arrangement30such that the pressure is maintained at a target operating pressure. The thermal management arrangement30has a pressure sensor to monitor the pressure of the fluid such that a target operating pressure is maintained.

The cells4are cylindrical cells, most preferably 18650 or 2170 lithium ion cells. The thermal management arrangement30is well suited for use with cylindrical cells as the duct3can expand and conform to the undulating surface of the cylindrical cells. This is advantageous as it improves the thermal contact between the cells and the duct. The height of the support structures1,101,201,301may be substantially equal to the height of the cells. The height of the duct, in its inflated state, may be equal to or less than the height of the cells.

In example embodiments (not shown), the duct is a multi-lumen duct having two or more lumens along which coolant fluid may flow. A multi-lumen duct may be used in large battery packs where a single lumen duct is not capable of promoting an even temperature distribution. Advantageously, a multi-lumen duct may be used in combination with the support structure1,101,201,301to prevent the multi-lumen duct kinking. Furthermore, the multi-lumen duct may be pressurised such that it expands and conforms to the cells in a similar manner to that of the single lumen duct.

Referring to the drawings and initially toFIGS.11to12, there is shown a duct230/3capable of engaging at least part of a surface area of a heat source17/30, the duct230/3extending along and engageable with at least part of the surface area of the heat source17/30along all or part of the length of the heat source17/30from a first engagement position after inlet52to at least one final engagement position after outlet54between the duct230/3and heat source17/30. A heat transfer fluid flows along an internal conduit of the duct230/3such that heat can be transferred between the duct230/3and the heat source17/30via the heat transfer fluid about the engageable surface areas of the duct230/3and the heat source30/17. The duct230/3is adapted to allow variable thermal transfer via the heat transfer fluid between the engageable surface areas of the duct230/3and the heat source30/17.

The duct230/3is adapted to allow variable thermal transfer via the heat transfer fluid between the engageable surface areas of the duct230/3and the heat source30/17along the length of the duct230/3.

Advantageously, the duct230being adapted to allow variable thermal transfer via the heat transfer fluid between the engageable surface areas of the duct230and the heat source17/30along the length of the duct230compensates for the variation in temperature of the heat transfer fluid as a result of ongoing thermal transfer as the heat transfer fluid flows along the length of the duct230. This ensures uniform thermal transfer between the heat source17/30and the duct230via the heat transfer fluid along the length of the duct230as other parameters such as fluid temperature vary. The heat source17/30comprises a battery pack2comprising a plurality of cells17/30. The duct230is a flexible duct.

The duct230is positioned proximally to the surface of the heat source17/30such that heat can be exchanged between the duct230and the heat source17/30. The duct230is positioned proximally to the surface of the cells17/30such that heat can be exchanged between the duct230and the cells17/30.

In one embodiment, where the duct230/3is a flexible duct3/230, a potting material231seeFIG.13is provided adapted to act as a support for at least a part of the duct230. Advantageously the flexible duct3/230can closely conform to the surface shape of the heat source/cells17/30within the pack2while being reinforced by the potting material231which acts to prevent the flexible duct3/230from over inflation and/or bursting.

The duct3/230is configured to carry the heat transfer fluid from an inlet52to an outlet54to transfer thermal energy between the heat source/cells17/30and the duct3/230at their engageable contact surfaces via the heat transfer fluid and wherein the thermal resistance of the duct230at the inlet52is higher than the thermal resistance of the duct at the outlet54. This is advantageous as varying the thermal resistance of the duct3/230along the length of the duct230promotes a uniform temperature distribution across the heat source/battery pack2. In particular, having a higher thermal resistance at the inlet to the duct230prevents over cooling or heating of heat source/cells17/30located proximal to the inlet52where the temperature differential between the heat transfer fluid and the heat source/cells17/30is at its greatest. The thermal resistance of the duct230/3is varied linearly or non-linearly along the length of the duct230/3such that the thermal resistance of the duct230decreases as the temperature differential between the heat transfer fluid and the heat source/cells17/30also decreases, thereby promoting uniform power dissipation along the length of the duct230.

In one embodiment the wall thickness of the duct230/3may be thicker at the inlet52compared to the outlet54as illustrated inFIG.12where a vertical section through the duct230at the outlet and the inlet is shown illustrating the variation in duct wall thickness. This is advantageous as increasing the wall thickness also increases the thermal resistance of the duct230. As such increasing the wall thickness of the duct230at the inlet also increases the thermal resistance of the duct230.

In an embodiment the wall thickness of the duct may vary linearly along the longitudinal length of the duct3/230. In another embodiment the wall thickness of the duct230may vary non-linearly along the longitudinal length of the duct230. Varying the wall thickness of the duct230along the longitudinal length of the duct230has the effect of varying the thermal resistance of the duct230along its longitudinal length.

In an embodiment the wall thickness may be varied such that a substantially constant power dissipation is achieved along the longitudinal length of the duct230/3. This is advantageous as it promotes an even temperature distribution throughout the array of cells17/30. This may be achieved by increasing the thermal resistance along the length of the duct230.

InFIG.14there is shown a schematic cross section of a battery pack indicated generally by the numeral2000. The battery pack2000includes a duct2011used to thermally manage cells2020. The duct2011comprises flexible duct material2001comprising a matrix2002and a filler2003. The flexible duct carries a fluid2004such as air, water or a water-glycol mixture. Heat is transferred between cells2020and the coolant204via the duct material2001.

The matrix2002is a flexible plastic or polymer material, in this case LDPE, LLDPE, HDPE polyester, silicone or rubber. The matrix2002is electrically insulating. The matrix2002has a thermal conductivity less than 15 Wm−1K−1, ideally less than 10 Wm−1K−1, 5 Wm−1K−1and/or 1 Wm−1K−1.

The filler2003comprises particles of a filler material and these are dispersed throughout the matrix2002. In preferred embodiments the filler2003comprises NANOCYL (RTM) NC7000 series thin multiwall carbon nanotubes however any suitable filler material may be used such as a carbon-based filler material such as carbon, carbon black, graphite, graphite platelets graphene, multi-walled carbon nanotubes or single-wall carbon nanotubes or a ceramic filler material such as aluminium oxide, silicon carbide, boron nitride, silicon nitrate, alumina, aluminium nitride or zinc oxide. The particles of filler material may be elongate and tubular having a diameter of 1-10 nm and a length of 0.5-5 nm. Alternatively the particles of filler may be substantially spherical with an average diameter of between 1 nm and 10 μm.

The thermal conductivity of the filler2003is greater than the thermal conductivity of the matrix2002. Ideally the filler2003has a thermal conductivity greater than 10 Wm−1K−1and/or greater than 100 Wm−1K−1. The duct material2001comprises less than 25% by volume of filler2003, ideally 5-18% by volume of filler or 15% by volume of filler2003. Incorporating a limited amount of filler2003into the matrix provides an increased thermal conductivity while maintaining a low electrical conductivity and favourable mechanical properties (i.e. suitable flexibility for an inflatable duct).

In this example, the duct material2001has a thermal conductivity greater than 0.33 Wm−1K−1at room temperature, ideally greater than 1 Wm−1K−1and/or 10 Wm−1K−1. This means that the heat transfer through the duct material2011is better than a conventional polymer duct. The duct material2001itself is electrically insulating, since the electrical conductivity of the duct material2001is dominated by the electrical properties of the non-conductive matrix2002. The electrically insulating nature of the duct material/matrix significantly reduces the risk of short circuits when compared with a metallic duct.

The duct2011is at least partially surrounded by a potting material2005which acts to reinforce the duct2011at places where it does not contact the wall of a cell2020. Incorporation of filler2003within matrix2002can alter the mechanical properties of the duct2001, particularly for high concentrations of filler2003. Where this leads to any reduction in mechanical strength the reinforcing material5can be used counteract such effects. This embodiment can be used as an alternative or in combination with the variable wall thickness embodiment.

In the preceding discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, coupled with an indication that one of the values is more highly preferred than the other, is to be construed as an implied statement that each intermediate value of the parameter, lying between the more preferred and the less preferred of the alternatives, is itself preferred to the less preferred value and also to each value lying between the less preferred value and the intermediate value.

The features disclosed in the foregoing description or the following drawings, expressed in their specific forms or in terms of a means for performing a disclosed function, or a method or a process of attaining the disclosed result, as appropriate, may separately, or in any combination of such features be utilised for realising the invention in diverse forms thereof as defined in the appended claims.