WO2008053227A1

WO2008053227A1 - Material cooling system

Info

Publication number: WO2008053227A1
Application number: PCT/GB2007/004184
Authority: WO
Inventors: Tilak Dias; Gunathilake Banda Delkumburewatte
Original assignee: Remploy Limited
Priority date: 2006-11-01
Filing date: 2007-11-01
Publication date: 2008-05-08

Abstract

A cooling system for garment material is disclosed. An evaporator tube (2) extends within an absorbent layer (24) between a permeable layer (22) on one surface and an impermeable layer (26) on the other. The evaporator tube is coupled to a source (6) of pressurised fluid at its proximal end, from which fluid is controllably released. As it flows in the evaporator tube it cools its surroundings before leaving the tube from a discharge point (8) at its distal end. A collector (30, 40) may be coupled to the discharge point to receive fluid from the eva orator tube (2).

Description

Material Cooling System

This invention relates to materials for use in garments for use in potentially dangerous environments. It has particular use in CBRN (Chemical Biological and Nuclear Resistant) garments. Such garments need to provide full protection for the wearer against the surrounding atmosphere, while minimising the building up of body heat. Materials of the invention also have use in other fields, such as medicine and physiotherapy. Wound management and the treatment of bed sores are examples.

Current CBRN suits use three independent garments, which are worn on top of each other. The base layer, worn next to the skin, in the form of an underwear garment knitted with a component having a phase change material (e.g. a fabric knitted from Outlast yarn) that absorbs heat during the transition from one phase to another. This enables it to absorb body heat and perspiration. The outer garment is made from a fabric which is substantially impermeable to liquids, and protects the wearer from the external environment, while the middle garment is made from a material which would protect the wearer from harmful gas molecules generally via absorption. CBRN suits comprising such garments are effective, and can typically be worn for periods of up to two hours before the temperature build up becomes uncomfortable.

The human body is self thermo regulating and tries to maintain a constant core body temperature of approximately 37⁰C. Where the temperature of the external environment is less than that of the body an internal source of heat is required to maintain the core temperature. The required heat comes from the body's metabolism. However, if the external temperature is higher than the body temperature, or if the level of physical activity is more than is required for a particular purpose, and the heat produced by the body is not properly dissipated; the body releases liquid (sweats) in an effort to lower the body temperature through evaporation.

For applications where the wearer is under a lot of physical activity and/or heat stress, the evaporation of liquid sweat is the most efficient method of cooling the body. This has served as the primary motivation for an increasing interest in the transport of liquids through clothing systems to facilitate evaporation of sweat to the atmosphere. However, in the case of CBRN protective clothing where the outer layer is completely sealed, the liquid sweat, as well as the heat, cannot be dissipated in this way. This further increases the heat stress on the wearer causing both the temperature and quantity of sweat to accumulate inside the clothing. Currently CBRN clothing design does not provide any facility to remove heat to the outer atmosphere, and limits the time a user can wear the CBRN suit to about two hours.

The present invention is directed at the incorporation of a cooling system into garments of the kind referred to above. Cooling systems for garments are known, and reference is directed to the following US Patent publications, the disclosures of which are hereby incorporated by reference. The US Patents are Nos. 4,188,946; 4,738,119; 4,998,415; and 6,009,713. Reference is also directed to US Patent Application as published under number US 2006/0191277. These disclosures exploit the ability of a flowing fluid or gas to cool its surroundings. The present invention also exploits this characteristic, in a material suitable for use in CBRN suits of the kind referred to above.

Materials in which the invention can be adopted have an impermeable layer at one surface, and a permeable layer at the other surface, which in use would be next to or proximate the skin of the wearer. An absorbent layer is disposed between the permeable and impermeable layers, and a refrigeration network for the material extends within the absorbent layer. The network comprises an evaporator tube extending from a source of pressurised fluid coupled thereto through a control valve, to a discharge point at the distal end of the tube.

In use, when the control valve is opened pressurised fluid is released to pass along the evaporator tube. It will normally be released as a liquid, and progressively change state as it moves along the tube, absorbing heat as it does. The manner in which the evaporator tube extends within the material can be adapted for a particular application, and greater lengths of it can in use be disposed in areas where heat generation is likely to be greatest. The valve controls the passage of gas from the source into the evaporator tube, and thereby the transfer of heat thereto as the gas passes through the tube. It may be adapted to release the gas intermittently and/or in response to sensed conditions. A discharge valve may be disposed at the distal end of the evaporator tube to provide controlled release of gas to the outside atmosphere under higher pressure. Alternatively, the gas may be received in a collector at its distal end. A plurality of collectors may be provided for this purpose, enabling one to be replaced by another when it is saturated. In some applications the discharge point at the distal end of the evaporator tube can be open, allowing vaporised fluid to issue directly into the atmosphere.

The manner in which fluid discharged at the distal end of the evaporator tube is handled will of course depend upon the nature of the fluid itself, and the environment in which the material is being used. Some pressurised fluids can be dangerous, in which case they would have to be collected and confined upon discharge from the evaporator tube. Thus, while nitrogen is readily available, and has good cooling qualities, it would have to be used with great care. Others, such as domestic refrigerants, are more tolerable, and in some applications can be released directly to the atmosphere.

A fluid collector coupled to the discharge point at the distal end of the evaporator tube can take a number of forms. One is a simple reservoir which receives the fluid through a one way valve at the discharge point. Various valving arrangements can be used to ensure that the discharge is contained, and a mechanism can be provided to issue a signal when the collector can no longer accept further fluid. This will normally be a pressure sensor. Flow of fluid into a closed reservoir forming the collector can be enhanced if the interior of the reservoir is initially at less than atmospheric pressure. A preferred arrangement is one in which the reservoir is a collapsible container or bag initially evacuated upon connection to the discharge point at the distal end of the evaporator tube.

The fluid collector will normally be external of the material, and preferably disposed on the impermeable layer at the one surface. Multiple collectors can be provided, each being releasably attachable to the distal end of the evaporator tube. This enables one to be removed and replaced by an empty collector to enable the cooling system to continue operating. It will be appreciated that the source of pressurised fluid at the proximal end of the evaporator tube can also be replaced. In such applications it too will be disposed at an accessible surface of the material.

The evaporator tube itself in material according to the invention can be a rigid structure, but preferably it is flexible and attached to or integrated with the material. To maximise its absorption of heat, the evaporator tube preferably comprises a multitude of fine channels. These can be created in a flexible yarn which can be integrated within the material structure. It can thus be part of a woven or knitted structure within the material. It will also be appreciated that two or more evaporator tubes can be incorporated in the same material, in either the same or independent networks. If they are part of the same network, then the same source of pressurised gas can be used, and the gas can be received in a common collector at the distal ends of the respective evaporator tubes.

Material according to the invention can also include heat conductive components for carrying heat to the evaporator tube or tubes. This feature can be of particular value when the material is used in a garment. In such an application these components can be yarns within garment fabric, which may include a wicking layer for carrying perspiration from the skin to be cooled by the condenser.

Such a garment fabric for facilitating the lateral dissipation of heat, comprises a dissipation layer and an inner layer for engaging the skin. The dissipation layer is liquid absorptive, and the inner layer comprises wicking elements for carrying perspiration from the skin to the dissipation layer. Each layer is preferably a yarn structure, using yarns selected to perform the above functions, but may also comprise a film structure such as a non-woven structure. Multi-filament or spun yarns may be used in the dissipation layer to absorb liquid from the inner layer. The inner layer can be formed from mono-filament yarns to enhance the wicking effect. The dissipation layer will normally be covered by an outer layer providing protection from one or both of chemical and biological hazards, and radiation. Either or both of the dissipation and inner layers may be knitted, and the two layers are preferably integrated. Knitting facilitates such integration, and provides good transfer of liquid from the inner to the dissipation layer. Knitted fabrics, due to their high extensibility under low load, are preferred structures to be worn next to the skin, as they allow a comfortable fit on any part of the body on which they are worn. The dissipation layer can include at the face opposite the inner layer a hydrophobic auxiliary layer to prevent undesired transmission of liquid from the dissipation layer to an outer layer, which will typically contain activated carbon. This auxiliary layer can also be knitted, but usually with a higher stitch density.

The dissipation layer is typically an open yam structure whose volume can be substantially defined by relatively stiff spacer yams. This volume is occupied by absorptive and/or adsorptive elements, preferably yams in a knitted structure which both receive liquid from the inner layer and dissipate it laterally within the fabric. The fabric as a whole can thus comprise a structure established by monofilament yarns forming the inner layer, defining the volume of the dissipation layer, and providing the basis for an hydrophobic auxiliary layer thereover.

The ability of the absorption or dissipation layer to absorb and dissipate liquid can be enhanced by bulking or texturising the yarns in the layer. Multilayer fabrics with such an intermediate layer of spacer yarns are disclosed in US Patent Nos. 5,735,145 and 6,145,348, the contents whereof are hereby incorporated by reference.

The refrigeration network in materials according to the invention can be supplemented by one or more additional heat transfer devices. This can enable the cooling system to be effective over a larger area, and can be adapted to hold the released fluid at lower temperatures in regions closer to the pressurised source. In this embodiment of the invention, a number of miniaturised heat exchangers are disposed spaced along the length of the evaporator tube, and through which the fluid released from the source passes. The or each heat exchanger will normally have an exposed surface, from which heat is progressively absorbed by the flowing fluid, which would result in the development of a gas/liquid mixture along the evaporator tube. The or each heat exchanger can take many forms, such as rectangular or hexagonal box shape; they can be also be cylindrical. At either end of a heat exchanger two connectors can be fitted for attaching the evaporator tube.

In order to further enhance the cooling effect of the system described above, one or more thermoelectric coolers may be coupled to the evaporator tube, preferably to the miniaturised heat exchangers. The thermoelectric cooler or coolers are normally fitted to the surface of the heat exchanger, to effectively control (delay) the cooling effect of the expanding gas. However, they can also be used to control the distribution of the temperature within a cooling garment. Thermoelectric coolers of this type exploit the Peltier effect to transfer heat from one side of the respective device to the other. Thus, when used in the system, the released gas will pass through the "cool" side of the device, and the system will be disposed in a garment with that cool side facing the wearer's body. The transferred heat will dissipate from the other side. The cooler will of course need to be coupled to a source of electrical power, but the power requirement is relatively low and may be provided by a battery as part of the cooling system itself.

Thermoelectric coolers used in this embodiment of the invention may take many forms, and can be adapted to the form of the heat exchanger with which they are to be used in the system. Most simply, the evaporator tube is coupled to a heat exchanger with one cooling surface exposed for contact or juxtaposition with the material surface, and the other engaging the thermoelectric cooler. The area of these surfaces is typically of the order of 25mm², with the heat exchanger and the cooler having a thickness of around 10mm. This compact size enables the cooler and heat exchanger combination to be readily incorporated in cooling systems of the kind referred to above.

By incorporating thermoelectric cooling in refrigeration networks of materials according to the invention, the cooling effect can be significantly enhanced, and importantly the rate of release of fluid from the pressurised source can be reduced. This means that the cooling system can operate for a longer period using fluid from a particular source, and where the cooling system is incorporated in a garment used in dangerous environments, and which has to be substantially sealed, this is of considerable value.

The invention will now be described by way of example and with reference to the accompanying schematic drawings wherein:

Figure 1 is a cross-section of a material which may accommodate a refrigeration network to form material according to the invention;

Figure 2 illustrates a simple form of refrigeration network for incorporation in the material of Figure 1 ;

Figure 3 shows another garment and illustrates how a refrigeration network installed in the garment fabric can extend across different areas;

Figure 4 shows a miniature heat exchanger and thermoelectric cooling device suitable for use in the garment of Figure 3; and

Figures 5 and 6 illustrate different forms of collector that can be coupled to the discharge point at the distal end of the evaporator tube in the network of Figure 2 or that shown in Figure 3.

The fabric shown in Figure 1 has an inner layer 22 for contacting the skin of the wearer. This layer comprises a tightly knitted structure using mono-filament yarns. Such a structure exhibits excellent wicking properties. A dissipation layer 24 overlays the inner layer 22. The dissipation layer 24 is also a knitted structure, but comprises multi-filament or spun yarns. The multiple pores in multi-filament yarns form excellent absorption channels, and capillary action within the channels results also in liquid absorbed from the inner layer 22 dissipating laterally within the layer 24. As a consequence, as different parts of the body of the person wearing a garment comprising the fabric generate different amounts of heat and perspiration, these are dissipated within the garment fabric. In order to enhance the transfer of perspiration from the inner layer 22 to the dissipation layer 24, the two layers can be knitted together. This integration provides maximum contact between the yarns of the two layers, and facilitates transfer of liquid in to and along the yarns of the dissipation layer 24.

The dissipation layer 24 can be formed with heat-shrinking yarns. This enables the pore or capillary size in the yarn structure to be accurately controlled by first creating the yarn structure; for example by knitting, and then heating the structure to shrink the pore or capillary size to the desired level. This can be carried out with the yarn structure of the layer integrated with one or other of the different layers, which need not, of course, comprise heat-shrinking yarns. Mixtures of yarn types, and different treatments such as bulking or texturising, can be employed with different results.

An outer protective layer 26 provides protection from the external environment. This outer layer will be made of a suitably impermeable material, and may contain specifically protective elements such as activated carbon. Such elements can require some protection against liquid in the dissipation layer 24, and this can be provided by a hydrophobic auxiliary layer 28. This auxiliary layer 7 can also be knitted, using hydrophobic yam, and if desired integrated with the dissipation layer 24. In order to provide the requisite defence against the unwanted transmission of liquid to the outer layer 26, a knitted auxiliary layer 28 will be knitted with a relatively high stitch density. Similar yarns can be used for the inner and auxiliary layers 22 and 28, and to define the volume of the dissipation layer 24, and the same yarns can be knitted to form an overall yarn structure into which absorptive and/or adsorptive are integrated to form the dissipation layer 24.

Particular preferred integral knitted fabrics of the kind described above comprise high stretch polyester or polyamide (PA) monofilament yarns for the inner (22) and auxiliary (28) layers, with 100% viscose, 100% lyocel or Oasis SAF adsorbent yarns or blends thereof for the dissipation layer. The liquid uptake by a fibrous assembly such as fabric is complex and involves different processes and parameters. Initially, wetting of a porous medium by the contacting liquid has to take place before it can wick any liquid into the material. The measure of wetting is described by the contact angle, in the range 0 to 90° for any material to take up liquid. Once the fabric is wetted, liquid uptake may occur due to capillary forces (wicking), absorption within fibres (imbibition) and adsorption (adhesion on fibre surface). These processes may occur independently or simultaneously depending upon the properties of the fibrous assembly such as fibre type, yarn structure, fabric structure and porosity. For example, a fabric made of hydrophilic material like cotton or viscose can take up liquid both by wicking and absorption at the same time. On the other hand, hydrophobic material like polyester and polypropylene can only take up liquid by wicking action.

Porosity, both in the fabric structure (between the yarns) and within the yarn (between the yam fibres), plays an important role in liquid uptake. Fabric porosity depends upon the type of the yarn from which it is produced. A fabric made from multi-filament or spun yarn has pores or voids available both within the yam structure (intra-yarn porosity) as well as between the yarns (inter-yam porosity) of a fabric. A mono-filament fabric can only have inter-yarn porosity as there are no voids present within the yarn. A multifilament fabric can therefore wick and retain liquid whereas a monofilament fabric can only wick the liquid without retaining it in its yarn structure.

The highly absorbent nature of the dissipation layer creates a differential driving pressure for liquid in the inner layer to move towards it. This ensures the liquid only moves in the direction towards the dissipation layer. As the dissipation layer slowly saturates, the differential pressure between the layers decreases and ultimately the liquid flow ceases. Since the dissipation layer holds the liquid in the molecular structure of the absorbent fibres, it is difficult for the absorbed liquid to move back in the opposite direction.

The absorbent capacity of materials according to the invention mainly depends upon that of the dissipation layer as the inner layer only facilitates the movement of liquid through its wicking action. The removal of liquid sweat from the wearer's skin is important for CBRN clothing to maintain sensorial and physiological comfort. This objective is accomplished in fabrics of the invention by combining the wicking action of the inner layer of with the absorptive and adsorptive characteristics of the dissipative layer. The fabric thus helps to keep the wearer's skin dry and at the same time will have a high water absorbing capacity, thereby increasing the time a garment made from the fabric can be worn in comfort.

The structure of the inner layer has a dual importance; firstly it should facilitate liquid transfer by means of wicking, and secondly it should preferably prevent the liquid returning to the skin once the dissipative layer is fully saturated. It can be shown by a liquid transport model, based on Washburn's equation, that liquid uptake depends not only on liquid properties (surface tension, viscosity and density), but also on the fabric properties (yarn type and pore size), as well as on fabric-liquid interaction (contact angle). In research using distilled water, the pore size of the fabric (inner layer) and the contact angle were the two significant factors studied. The results demonstrate that as the pore size of the inner layer reduces, the rate of wicking would increase; smaller pores will also retain less liquid within the structure of the inner layer.

To be most effective, the inner layer should have pores as small as possible. In a knitted structure the size of the stitches formed is the key factor which defines the pore size(s). Generally the smallest stitch that can be formed on a knitting machine is defined by the needle type, the needle geometry and the dimensions of the needle hook. The needle used on a knitting machine also defines the machine gauge, which is the distance between two neighbouring needle tricks (the needle pitch) on the needle bed. However, due to the difficulty of remembering the needle pitches of different knitting machines, the industry has become accustomed to defining the number of needles in a unit length (usually the old imperial inch) as the gauge of a knitting machine. Current flat-bed knitting machines are built to medium gauges; eighteen needles per inch (NPI) being the finest machine manufactured today. We have found that the pore size of the structures knitted on flat-bed knitting machines were not sufficiently small. In order to overcome this hurdle high stretch monofilament yarns were used to knit the outer layers. These monofilament yarns would stretch during the stitch formation process, and shrink back to their original length soon after, resulting in smaller stitches thus forming small pores on the outer layers.

Initial knitting trials used a stretch monofilament PA yarn to create the inner layer of the fabric, which resulted in a tighter structure with smaller pore size. The smaller pores helped the inner monofilament layer, and contiguous skin, to stay dry as it retained less moisture. This would also be useful in an auxiliary layer as the basis for an effective application of water impermeable finish or outer layer.

As noted above, a refrigeration network of the kind described below extends within the absorbent layer 24. When the inner layer comprises spacer yams knitted with the inner (22) and outer (26) layers, the knitting can be programmed to create a path for the evaporator tube 2 of the network in the absorbent layer. It is also possible to knit the absorbent layer 24 around the evaporator tube with any attachments, and thereby create a material embodying the invention effectively in a single manufacturing exercise.

Figure 2 shows an elongate evaporator tube 2 whose proximal end is coupled through a controllable valve 4 to a pressurised gas cylinder 6. At the distal end of the evaporator tube is a recharge valve 8. The gas in the cylinder is pressurised to a liquid state, and as it is released it passes along the evaporator tube 2 and absorbs heat within the garment. The recharge valve 8 provides controlled release of the gas into the atmosphere. Alternatively, a collector can be disposed at the distal end to absorb the heated gas. When such a collector creates a back pressure sufficient to inhibit the flow of gas along the evaporator tube, it can be removed and replaced. Gas from a saturated collector can of course be re-pressurised and used again.

The cooling system show in Figure 3 has an evaporator tube 2 with one end coupled to a controllable valve 4 to a pressurised fluid cylinder 6. At the distal end the tube is coupled to an accumulator 10. Although shown on the garment, it will be understood that only the valve 4, the cylinder 6, and the collector 10 will be visible and accessible on the surface. The evaporator tube 2 and its attachments will be within the absorbent layer of the garment material. On the path of the tube 2 from the cylinder 6 to the accumulator 10, it is coupled sequentially to miniature heat exchangers 12 and 14. As the pressurised fluid is released by the valve 4 to pass along the tube 2, it evaporates and expands and in doing so, takes heat from its surroundings. This cooling effect is enhanced by the heat exchangers 12 and 14.

The heat exchangers 12 and 14 are each in the form of a panel with substantially parallel surface areas of around 25mm². One of these surfaces will normally be located in juxtaposition with the body surface of the user. The flat area provides an effective cooling surface. To further enhance the cooling effect, a thermoelectric cooling element 16 is disposed against the other surface of the heat exchanger 12. This cooling element uses the Peltier effect to maintain that other surface at a low temperature, transferring heat to its opposite surface which, in use, will be further remote from the body of the user of the system. Electric current is supplied to the cooling element 16 through terminals 18, 20, from a battery (not shown), which can be mounted for example, on the gas cylinder 6.

While thermoelectric cooling elements 16 could be coupled to each of the heat exchangers in the cooling system, we have found that sufficient benefit can be had by applying thermoelectric cooling only to some of the heat exchangers. In the embodiment shown, it is applied to the heat exchanger 14. The heat exchangers 12, towards the top end of the tube 2, function without any thermo-cooling.

A number of gases can be used to provide the refrigerating medium in materials of the invention. Nitrogen is readily available, and would of course provide excellent cooling qualities, although the storage of liquid nitrogen has to be carefully controlled and monitored. However, it will be appreciated that only a relative small quantity of the pressurised gas will be required, depending upon how long the cooling system is to operate. Another possible gas is the HFC-R134a (tetrafluoroethane CH₂FCF₃); which is a single hydrofluorocarbon or HFC compound. It has no chlorine content, no ozone depletion potential; and only modest global warming potential (ODP - 0 and GWP - 1300. The pressurised cylinder can of course be as readily replaced at the proximal end of the condenser tube as can a collector at the distal end.

It will be appreciated that the system may be adapted to operate at different levels of refrigeration. It may include a sensor, of temperatures or humidity for example, and increase or reduce the cooling effect in response to signals from the sensor. It may also include an internal control affording manual operation. These options can include the possibility of the system being used to freeze perspiration to maximise the cooling effect. A system so adapted can be used in an "ice-pack" for the treatment of various injuries and conditions.

Figure 4 shows a collector in the form of a solid container 30. A one way valve 32 is provided for coupling to the discharge point 8 at the distal end of an evaporator tube (2) which allows fluid from the evaporator tube to enter the container 30. The container is sealed, but has an access duct 34 and a sensor 36 for monitoring the pressure in the container 30. The sensor 36 will generate a signal, normally visible or audible, to indicate when the container is full or saturated and must be replaced. The duct 34 can be used when the container has been removed from the evaporator tube to empty the container and also, to create a negative pressure (relative to atmospheric) in the container when it is coupled to the evaporator tube. This can enhance at least the initial flow of fluid along the evaporator tube, and encourage the initial cooling effect.

In Figure 6, the collector is in the form of a flexible bag 40 shown collapsed and coupled to the one way valve 32. As it received fluid through the valve from the evaporator tube, it progressively expands until full, as shown in dotted outline. It will be evident when the bag is full, that it must be replaced.

It will be appreciated that when a collector must be removed from the discharge point at the distal end of the evaporator tube, the discharge point must be closed. To accomplish this, the coupling between the evaporator tube and the one way valve should be self sealing when the parts are separated. Materials of this invention have been described particularly for use in protective clothing. However, they have other applications where there is a need to dissipate heat and moisture from a surface. Some of these occur in medical and surgical environments, and in wound management. A fabric can be used to keep a wound dry, or at least prevent accumulation of liquid at a wound site. It can also be used in linen to prevent accumulation of perspiration adjacent a patient's body. In these applications an outer protective layer may not be required.

Claims

1. A material having an impermeable layer at one surface and a permeable layer at the other surface with an absorbent layer therebetween; and a refrigeration network for the material comprising an evaporator tube extending within the absorbent layer from a source of pressurised fluid coupled thereto through a control valve, to a discharge point at the distal end of the tube.

2. A material according to Claim 1 including a fluid collector coupled to the discharge point at the distal end of the evaporator tube.

3. A material according to Claim 2 wherein the collector is a closed reservoir coupled to the discharge point through a one way valve.

4. A material according to Claim 3 wherein the reservoir is a flexible bag adapted to expand as it receives fluid from the evaporator tube.

5. A material according to Claim 3 or Claim 4 wherein the collector is provided in a form in which the interior of the reservoir is at less than atmospheric pressure.

6. A material according to any of Claims 2 to 5 wherein the fluid collector is external of the material.

7. A material according to Claim 2 wherein the fluid collector is disposed on the impermeable layer at said one surface.

8. A material according to any of Claims 2 to 7 wherein the network includes a plurality of said collectors, each being releasably attachable to the distal end of the evaporator tube.

9. A material according to any preceding Claim wherein the condenser tube comprises a plurality of fine channels for the passage of gas from the source.

10. A material according to any preceding Claim wherein the absorbent layer includes heat-conductive components for carrying heat to the condenser tube.

11. A material according to Claim 10 wherein the heat-conductive components comprise thermally conductive fibres.

12. A material according to any preceding Claim including a device for operating the control valve.

13. A material according to Claim 12 wherein the device includes a temperature sensor and operates the control valve in response to signals from the sensor.

14. A material according to Claim 12 wherein the device is operated manually.

15. A material according to any preceding Claim wherein the absorbent layer comprises a yarn structure.

16. A material according to Claim 15 wherein the yarn structure comprises knitted yarns.

17. A material according to Claim 16 wherein the yarns are monofilament yarns.

18. A material according to any of Claims 15 to 17 wherein the yarn structure comprises texturised yarns.

19. A material according to any of Claims 15 to 18 wherein the yarns are heat-shrinking yarns, and the structure has been heated to determine the capillary size between and/or within the yarns.

20. A material according to any preceding Claim wherein the permeable and impermeable auxiliary layers, and the absorbent layer form an interconnected knitted yarn structure, with yarns extending between the permeable and impermeable layers defining the absorbent layer.

21. A material according to any preceding Claim including at least one heat exchanger coupled to the evaporator tube and through which the released fluid passes.

22. A material according to Claim 21 wherein each heat exchanger has an exposed surface, from which heat is progressively absorbed by the flowing gas.

23. A material according to Claim 21 or Claim 22 wherein at least one thermoelectric cooler is coupled to the evaporator tube.

24. A material according to Claim 23 wherein each thermoelectric cooler is coupled to a said heat exchanger.

25. A material according to any preceding Claim wherein the source of pressurised fluid is external of the material.

26. A material according to Claim 25 wherein the source of pressurised fluid is disposed on the impermeable layer at said one surface.

27. A fabric comprising material according to any preceding Claim.

28. A medical treatment device comprising material according to any of Claims 1 to 26.

29. A garment comprising material according to any of Claims 1 to 26.