TEMPERATURE CONTROL MATERIALS

This invention relates to materials for use in garments, and incorporating a system for cooling the body of the wearer of such a garment. It uses technology disclosed in our published International Patent Publication No: WO 2008/053,227, the disclosure of which is incorporated by reference. That publication discloses a material having a cooling system in the form of a refrigeration network in which a fluid is released from a pressurised source to absorb heat as it expands.

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 No: US 2006/0,191,277. These disclosures exploit the ability of a flowing fluid or gas to cool its surroundings. The present invention also exploits this characteristic.

In the present invention, an additional heat transfer device is incorporated in a cooling system of the kind disclosed in our International Patent Publication referred to above. This enables 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. According to the invention, a material has a cooling system in the form of a refrigeration network in which fluid is released from a pressurised source to absorb heat as it evaporates and expands. The cooling system comprises a source of pressurised fluid coupled to a control valve at the proximal end of an elongate evaporator tube; at least one heat exchanger coupled to the evaporator tube and through which the released fluid passes; and a thermoelectric cooler coupled to the heat exchanger.

In preferred materials of the invention a number of miniaturised heat exchangers are spaced along the length of the evaporator tube through which the released fluid 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 enhance the cooling effect of the system, one or more thermoelectric coolers are coupled to the evaporator tube, preferably to the miniaturised heat exchangers. The thermoelectric cooler or coolers are normally fitted to the surface of the respective 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 used in this invention exploit the Peltier effect to transfer heat from one side of the respective device to the other. Thus, when used in a system of the invention, 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 the present 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 25mm ² , 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 systems of the kind referred to, the ratio of gas-liquid mixture in the heat exchanger can be controlled resulting in a significant enhancement of the cooling effect, 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.

In the use of the cooling system in a material of the invention, 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 readily accessible. 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 system.

An embodiment of the invention will now be described by way of example and with reference to the accompanying schematic drawing wherein:

Figure 1 shows an upper body garment fitted with a cooling system embodying the invention;

Figure 2 shows a MHE and a thermoelectric cooling device for use in the system of Figure 1; and

Figures 3 and 4 illustrate different forms of collector that can be coupled to the discharge point at the distal end of the evaporator tube in the network shown in Figure 1.

The material of the garment shown in Figure 1 has an integral cooling system. The cooling system shown has an evaporator tube 2 with one end coupled to a controllable valve 4 to a pressurised fluid cylinder 6. The tube may have a plurality of fine channels for the passage of gas from the source. These may increase in size with

distance from the source. At the distal end the tube is coupled to an accumulator 10, although the gas can be released directly into the atmosphere, for example through a recharge valve. On the path of the tube 2 from the cylinder 6 to the accumulator 10, it is coupled sequentially to 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. Although shown on the garment, it will be understood that normally, 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 fabric of the garment material. The garment material may include heat conductive components, such as thermally conductive fibres, for carrying heat to the evaporator tube.

As shown in Figure 2, the heat exchangers 12 and 14 are each in the form of a panel with substantially parallel surface areas of around 25mm . One of these phases 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-Rl 34a (tetrafluoroethane CH ₂ FCF ₃ ); 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 3 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 4, 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 many applications, typically 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.