DESCRIPTION

The present invention relates to apparatus for cooling an object, and particularly but not exclusively apparatus to assist with storing temperature-sensitive medication (e.g. vaccines) without requiring electrical energy.

In many parts of the world, temperature-sensitive medicines must be kept in cold storage to avoid detrimental effects of high ambient temperature or large temperature fluctuations. Such a requirement can be problematic in the more remote parts of the world where electrical energy is not widely available. Whilst solar cells and portable electricity generators may offer a reliable source of electricity in the short term, it is not always appropriate to rely on them in the longer term.

In accordance with a first aspect of the present invention, there is provided apparatus for cooling an object in contact therewith, comprising: a body defining a sealed chamber containing a refrigerant, the sealed chamber having a first part and a second part spaced from the first part, with the second part housing an adsorbent configured to adsorb the refrigerant, wherein the body includes a valve arrangement which is moveable from a closed configuration for isolating liquid refrigerant in the first part when not adsorbed in the adsorbent, to an open configuration for allowing refrigerant vapour to flow from the first part to the second part.

With liquid refrigerant isolated in the first part, a cooling cycle may commence by moving the valve arrangement to the open configuration. Vapour from the liquid refrigerant spreads through the sealed chamber where it is adsorbed by the adsorbent which is preferably a solid. Such adsorption drives further evaporation of liquid refrigerant, inducing cooling in the first part. Once all the liquid refrigerant has evaporated from the first part and/or the adsorbent is unable to adsorb any more vapour from the refrigerant, the cooling cycle stops. However, the apparatus may be reset for a future cooling cycle by heating the second part to desorb adsorbed refrigerant from the adsorbent, and collecting refrigerant in the first part. The present applicant has appreciated that the valve arrangement (when in the closed configuration) enables the apparatus to be stored at ambient temperature in a condition ready to perform the cooling cycle whenever required. Thus, the apparatus may be primed for use when suitable conditions are available, and then stored until cooling is required. This may be extremely useful in the more remote parts of the world, where the energy required to reset the apparatus for a future cooling cycle may not always be readily available.

The sealed chamber may contain substantially no non- condensable gas (such as air) . In other words, the internal volume of the sealed chamber may be filled with refrigerant liquid and vapour alone. In this way, as much of the internal volume as possible is available to receive refrigerant vapour from the liquid refrigerant.

At least a portion of the first part may be lined with a wicking member to promote intimate contact between the first part and liquid refrigerant therein. In this way, the liquid refrigerant is able to draw heat energy from that portion of the first part.

The apparatus may comprise a conduit coupling the first and second parts of the sealed chamber, with the conduit comprising a non-return valve configured to prevent refrigerant vapour flowing from the first part to the second part. The conduit may extend into the first part to define a dip tube with an opening adjacent a bottom surface of the first part. In this way, the opening will be submerged in liquid refrigerant, at least whilst some remains in the first part. For example, the opening may be submerged in liquid refrigerant whilst at least 10% of the total amount of refrigerant remains in the first part. The valve arrangement may include a nonreturn valve configured to prevent refrigerant vapour flowing from the second part to the first part even when the valve arrangement is in the open configuration.

The second part may comprise heat transfer members extending into the adsorbent, the heat transfer members being configured to assist transfer of heat to and from the adsorbent. Efficient heat transfer from the adsorbent to an outer periphery of the second part during adsorption of refrigerant vapour will prevent excessive heat build-up in the second part, and efficient heat transfer to the adsorbent during desorption of adsorbed refrigerant will assist with regeneration of the apparatus for a subsequent cooling cycle. The heat transfer members may be plate-like. The second part may comprise a passageway extending into the adsorbent, with one end of the passageway being open to refrigerant vapour flowing from the first part to the second part. If the heat transfer members are plate-like, the passageway may extend therethrough. The passageway may be lined with a foramenous member, with openings in the foramenous member allowing the vapour substantially unhindered access to the adsorbent. The foramenous member may have a mesh-like structure.

The apparatus may further comprise an insulated member attached to the body. The insulated member may define a handle for lifting the apparatus. This may be useful when moving the apparatus immediately after heating the second part. The valve arrangement may be housed in the insulated member. This may help to protect the valve arrangement, and may also reduce heat flowing from the second part to the first part during a cooling cycle.

The refrigerant may be selected from the group consisting of water, methanol, ethanol, ammonia and mixtures thereof. The adsorbent may be selected from the group consisting of silica gel, calcium chloride, activated carbon and mixtures thereof. In practice, the refrigerant and adsorbent may be selected according to the intended purpose of the apparatus. For example, for refrigeration temperatures (between about 1°C and 8°C) , the adsorbent may be calcium chloride or activated carbon, and the refrigerant may be a mixture of water and methanol or ethanol . For lower temperature applications such as freezing and ice making, a different refrigerant may be selected, such as pure ethanol or ammonia.

Adsorbent selection may be based on the amount of refrigerant it is able to hold at a given temperature, e.g. prevailing ambient temperature. This is because the amount of refrigerant each adsorbent is able to hold varies with temperature. For example, with water as refrigerant, one adsorbent: SWS-IL (calcium chloride in silicagel) has a high water uptake (up to about 80% of its own weight) at temperature below 20%, but a low water uptake (below about 10% of its own weight) at temperatures above 40 ⁰ C) . Different adsorbents have different isosteric properties and adsorbent properties. Another adsorbent: Zeolite X13 will maintain a water uptake of up to about 30% at temperatures in excess of

40 ⁰ C. Other adsorbents may be achieved using a zeolite

(microporous aluminosilicate) or alumina as a porous host matrix and impregnating it with an inorganic salt such as lithium chloride or calcium nitrate.

Refrigerant selection may be based on latent heat of vaporization and the intended operating temperature, e.g. target temperature of the object to be cooled. The latent heat of vaporization is the amount of energy required to convert or vaporize a saturated liquid (i.e. a liquid at its boiling point) into a vapour. The higher the value of the latent heat of vaporization, the higher the duty or cooling capacity of the apparatus for a given quantity of refrigerant. For example, if the apparatus holds 0.4 litres of refrigerant, the theoretical cooling capacity would be about 108OkJ when the refrigerant is water (latent heat of vaporization is 2700kJ/Kg) and about 416kJ when the refrigerant is methanol (latent heat of vaporization is 1300kJ/Kg) . Based on this consideration alone, water would seem to be one of the best refrigerants for all applications. However, the intended operating temperature is another consideration.

With all refrigerants in a closed system temperature is directly related to pressure and all refrigerants have different pressure/temperature comparisons. For example, (in an enclosed system) water (vapour) pressure is 2339 Pascals at 20 ⁰ C at equilibrium. If heat is added to the water, the pressure will rise; e.g. at 25 ⁰ C the pressure will rise to 3170 Pascals. Alternatively, if the pressure is reduced, the temperature will drop; e.g. at 1228 Pascals, the water temperature will be 10 ⁰ C. This is because the water (or refrigerant) will always try to achieve equilibrium. As the pressure reduces, more of the water will vaporize to try to obtain equilibrium; as it evaporates, it adsorbs heat - hence the cooling effect. The purpose of the adsorbent is to adsorb the water (or refrigerant) vapour and reduce the pressure in the system to cause this effect.

Water is generally considered as an unsuitable refrigerant because of its very low (sub atmospheric) operating pressures) . Great care must be taken not to have any leaks on the system. Therefore, generally positive pressure systems using ammonia or methanol might be preferred. Having said that, water may be chosen as the refrigerant for two reasons:

1. The high latent heat value mentioned earlier. This is very useful for a heat storage device where it is important for the apparatus to have as much capacity as possible before it is necessary to recharge it .

2. Water will not evaporate much below 0 ⁰ C. In the absence of any thermostatic control, this is a very useful attribute. For refrigeration applications water is self temperature regulating as it will turn to ice at around 0°C, (even in a vacuum) .

In accordance with another aspect of the present invention, there is provided a kit of parts for cooling an object, comprising apparatus according to the first aspect of the invention, and a device for regenerating the apparatus by desorbing refrigerant adsorbed by the adsorbent when the apparatus is not cooling the object. In one form, the regenerating device may be solar powered, and may comprise a solar collector configured to focus solar radiation on the second part when the apparatus is coupled to the regenerating device.

In another form, the regenerating device may be thermally powered (e.g. by an open fire), and may comprise: a body having a wall defining a pressure chamber for receiving a working liquid, (such as water) , with a part of the wall being configured to transfer thermal energy from inside the pressure chamber to an external surface of the body; and a regulator for regulating pressure of working liquid in the pressure chamber when heated. In use, a working liquid (e.g. water) is poured into the pressure chamber, and the body is exposed to heat from an external high temperature thermal source (e.g. an open fire) in order to boil the working liquid. The regulator regulates the pressure inside the pressure chamber, allowing accurate temperature control of steam generated and hence the part of the wall which is configured to transfer thermal energy to the external surface of the body. For example, a 7.1 bar pressure regulator will accurately control the temperature at about 170 ⁰ C, regardless of the temperature of the thermal source above this temperature.

The body may be elongate, with the said part of the wall being located at one end (hereinafter referred to as the first end) of the elongate body. In this way, the regenerating device may be used with one end in or adjacent the thermal source, with the elongate body extending therefrom such that the first end is furthest from the thermal source. The part of the wall may have a recess with a profile for receiving the second part of the apparatus . The second part of the apparatus may be a snug fit inside the recess, thereby offering efficient transfer of heat therebetween.

The regenerating device may further comprise a ground-engaging support for supporting the body in use. The ground-engaging support may comprise at least one leg, and may be configured to engage the body such that, in use, the regulator remains clear of working liquid in the pressure chamber.

The kit of parts may further comprise a thermally insulated container for storing the object to be cooled. The insulated container may have an external opening configured to releasably receive the first part of the apparatus when cooling an object stored in the insulated container. Once received in the external opening, the first part may extend into or towards an interior of the thermally insulated container to facilitate cooling of the object stored therein. The second part of the apparatus remains outside of the thermally insulated container. The apparatus may be separated from the thermally insulated container when desorbing adsorbed refrigerant from the adsorbent. More than one apparatus according to the first aspect of the invention may be provided to allow sequential use of one after another.

In accordance with another aspect of the present invention, there is provided a method of cooling an object, comprising: providing apparatus according to the first aspect of the present invention, positioning the apparatus such that the first part is thermally coupled to the object to be cooled; and allowing refrigerant vapour to be adsorbed by the adsorbent . The method may further comprise: thermally decoupling the first part and the object to be cooled; heating the second part to desorb refrigerant adsorbed by the adsorbent; and collecting refrigerant in the first part.

An embodiment of the invention will now be described by way of example with reference to the accompanying Figures, in which:

Figure 1 illustrates apparatus embodying the present invention;

Figure 2 illustrates use of the apparatus of Figure 1;

Figure 3 illustrates thermal regeneration of the apparatus of Figure 1 according to one embodiment; and Figure 4 illustrates a device for thermally regenerating the apparatus of Figure 1 according to another embodiment; and

Figure 5 illustrates performance of the apparatus of Figure 1.

Figure 1 shows apparatus 10 comprising a body 12 defining a sealed chamber containing a liquid refrigerant 16. The sealed chamber 14 has a first part 18 and a second part 20 spaced from the first part 18. The second part 20 houses a solid adsorbent 22 which is configured to adsorb vapour from the refrigerant 16.

The body 12 includes a valve arrangement 24 which is movable from a closed configuration for isolating liquid refrigerant in the first part 18 when not adsorbed in the adsorbent, to an open configuration for allowing refrigerant vapour to flow from the first part 18 to the second part 20. The body 12 around the first and second parts 18, 20 of the sealed chamber 14 is made of a metal, such as copper or stainless steel.

In the second part 20, heat transfer members 30 which are disc or plate-like extend into the adsorbent 22. Furthermore, a passageway 32 is provided in the adsorbent 22 and through the heat transfer members 30. The passageway 32 has an end 34 which is open to refrigerant vapour flowing into the second part 22 from the first part 18. The passageway 32 is lined with a foramenous member 36 such as a mesh tube. The heat transfer members 30 and the foramenous member 36 help retain the adsorbent 22 in position. At the same time, the passageway 32 and the foramenous member 36 assist with distribution of refrigerant vapour throughout the adsorbent 22.

A conduit 40 couples the second part 20 to the first part 18. A non-return valve 42 is provided in the conduit 40 to prevent refrigerant vapour flowing therethrough from the first part 18 to the second part 20. Thus, refrigerant vapour can only pass through conduit 40 from the second part 20 to the first part 18. The conduit 40 extends into the first part 18, defining a dip tube 44 with an opening 46 towards a bottom surface 46 of the first part 18. The opening 46 remains submerged in the liquid refrigerant 16, while at least about 10% of the liquid refrigerant remains in the first part 18. A wick 48 lines the first part 18, helping to ensure the liquid refrigerant 16 remains in contact with that part of the body 12, and increasing surface area for vaporisation of liquid refrigerant 16.

The valve arrangement 24 is embedded in a thermally insulating body 50 which defines handle 52. The valve arrangement 24 includes a non-return valve 54 in conduit 56 which is configured to prevent refrigerant vapour flowing therethrough from the second part 20 to the first part 18 even if the valve arrangement 24 is left in the open configuration.

The operation of apparatus 10 will now be described, starting with the cooling cycle. With the apparatus 10 as shown in Figure 1, the valve arrangement 24 is moved to the open configuration, allowing refrigerant vapour in the first part 18 to pass through conduit 56 into the second part 20 where it is adsorbed by the adsorbent 22. Adsorption of the adsorbent 22 causes liquid refrigerant 16 to evaporate, cooling the first part 18. The cooling cycle continues until all the liquid refrigerant 16 has evaporated or the adsorbent 22 is unable to adsorb any more refrigerant, at which point the valve arrangement 24 may be moved to the closed configuration. The apparatus may be recharged by applying heat to the second part 20 to cause desorption of refrigerant from the adsorbent 22. The heat transfer members 30 help transfer the applied heat throughout the adsorbent 22. Desorbed refrigerant vapour travels from the second part 20 through conduit 40 to the first part 18 (the non-return valve 54 preventing passage of desorbed refrigerant vapour through conduit 56 even if valve arrangement 24 is left in the open configuration) . The desorbed refrigerant vapour condenses in the first part 18, with the dip tube 44 helping to condense the vapour at least towards the end of the charging cycle. Once the desorption process is complete, the first part 18 will be full of liquid refrigerant 16. Heating then stops and the second part 20 is allowed to cool to ambient temperature. The liquid refrigerant 16 cannot pass back to the second part 20 until the valve arrangement is moved to the open configuration. In this way, the apparatus 10 may be stored in its "charged" condition, ready to be used to cool an object.

Figures 2 and 3 illustrate schematically a kit of parts which may be used to cool temperature sensitive medicines and the like. In Figure 2, apparatus 50 is functionally equivalent to apparatus 10 and only differs in appearance due to positioning of its valve arrangement. Thus, features in common between apparatus 50 and apparatus 10' share the same reference number. The apparatus 50 is coupled to a thermally insulated container 52, with the first part 18 extending into an interior space 54 whilst the second part 20 remains on the outside of the thermally insulated container 52. More than one individual apparatus 50 may be used with the thermally insulated container 52 at any one time (e.g. three apparatus 50 may be used simultaneously). In this way, the apparatus 50 is able to cool the interior space 54, and any object (e.g. medicine) stored therein, during its cooling cycle. Figure 5 illustrates the difference between ambient temperature (A) and the temperature (B) of the interior space 54 of the thermally- insulated container 52 when cooled with three apparatus 50 over a continuous five day period (the approximate duration of the cooling cycle) . Once the cooling cycle is finished, the spent apparatus 50 may be removed from the thermally insulated container 52 and be replaced by another pre-charged apparatus to continue with cooling any object stored in the interior space 54. The spent apparatus 50 may be charged for re-use in a solar collector 60, which is configured to focus solar radiation to heat the second part 20.

Figure 4 illustrates a device 100 for regenerating the apparatus 10 by desorbing refrigerant adsorbed by the adsorbent 22 in the second part 20. The device 100 comprises an elongate metallic (e.g. steel) body 102 having a wall 104 defining a pressure chamber 106 for receiving a working liquid (not shown) such as water. The elongate body 102 has a first end 110 for positioning in or adjacent a thermal course such as an open fire, and a second end 112 with an external surface 114 defining a recess 116 for receiving the second part 20 of the apparatus 10. The device 100 includes a regulator 120, remote from the first end 110, for regulating pressure in the pressure chamber 106 when the first end 110 is exposed to the thermal source. A valve 130 is provided in the wall 104 to allow the working liquid to enter the pressure chamber 106. Mountings 140 are provided on the body 102 for legs (not shown) to help with positioning the first end 110 of the device 100 in or adjacent a thermal source .

In use, the device 100 is primed by partially filling the pressure chamber 106 with working liquid through the valve 130, and positioning the second part 20 of the apparatus 10 in the recess 116. The elongate body 102 is then positioned with the first end 110 in or adjacent a thermal source (e.g. a fire), with the second end 112 projecting away from the thermal source to protect the apparatus 10 from damage. The working liquid is then allowed to boil transferring heat to the wall 104 and hence to the external surface 114 defining the recess 116. The temperature of the boiling working liquid is controlled by the regulator 120, so as to desorb refrigerant adsorbed by the adsorbent without overheating it. The regulator 120 may be pre-set to boil the working liquid at a predetermined temperature, or may be adjustable and calibrated to boil the working liquid at different temperatures according to the nature of the refrigerant/adsorbent .