Refrigerator

Abstract: A refrigerator 1 includes a cylinder 2 containing a bed of adsorbent material 3 and a gas, e.g. carbon dioxide. A piston compresses the gas which is adsorbed by the adsorbent material 3 and the heat of adsorption is dissipated by fins 4 to atmosphere. The piston, when retracted, decompresses the gas which desorbs from the adsorbent material 3. Repeated compression and decompression of the gas causes a cold zone to be created within the material 3 which is thermally linked to a location to be refrigerated.

Description: The present invention relates to refrigerators. Refrigeration at about ambient temperature is currently achieved by using the compression cycle with halogenated hydrocarbons such as freon (Registered Trade Mark) gas as the refrigerating medium. Freon gas is compressed and the heat of compression is conducted to atmosphere thereby causing the gas to condense to a liquid. The liquid freon is then passed to the inside of an insulating chamber where it is allowed to expand and evaporate thereby cooling the chamber. The expanded freon gas then returns to a compressor for the cycle to be repeated. Problems appear to arise when these known refrigerators wear out since when they are re-cycled or scrapped it is believed that the freon type gases are released thereby damaging the ionosphere. An alternative cycle is available in domestic refrigeration and is known as the ammonia adsorption cycle. However, it is less efficient and often less reliable being dependent on the containment of hydrogen gas. US-A-4 183 734 discloses a refrigerator comprising a chamber containing a bed of adsorbent material and a compressible gas capable of being adsorbed under pressure by the adsorbent material and desorbed therefrom when the pressure is reduced. Means are provided for alternately compressing the gas within the chamber thus creating a temporary cold zone within the chamber. Thermal connection means are provided for connecting the cold zone to a location to be refrigerated. Unfortunately, such a device is unable to provide a permanent cold zone. It is an aim of the present invention to provide a refrigerator which utilises the cold zone(s) which are created when certain gases are adsorbed by and then desorbed from a bed of adsorbent material. According to one aspect of the present invention a refrigerator comprises a sealed chamber containing a bed of an adsorbent material and a compressible gas capable of being adsorbed under pressure by said adsorbent material and desorbed from said adsorbent material when said pressure is reduced, means for alternately compressing and decompressing the gas within the chamber thus creating a permanent cold zone within the chamber and means for thermally connecting the cold zone to a location to be refrigerated. According to a further aspect of the present invention there is provided a method of refrigeration comprising the steps of: a) compressing a gas within a sealed chamber containing a bed of an adsorbent material such that some at least of the gas is adsorbed by said adsorbent material; b) removing heat generated by the adsorption step; c) decompressing the gas within the chamber such that the gas is desorbed from the adsorbent material; d) repeating steps a), b), and c) until a permanent cold zone is created in the adsorbent material; and e) thermally connecting said cold zone to a location to be refrigerated. An embodiment of the invention will now be described by way of example, reference being made to the Figure of the accompanying diagrammatic drawing which is a schematic sketch of a refrigerator according to the present invention. As shown, a refrigerator 1 includes a chamber in the form of a hollow cylinder 2 within which is located a bed of an adsorbent material 3, for example, a zeolite having a high heat adsorption such as 13X or 5A type. Also located within the cylinder 2 is a pre-selected volume of a gaseous medium such as carbon dioxide which has a high affinity for the adsorbent material 3 and is readily compressible. As shown, the cylinder is arranged vertically and at its lower end and slidably received therein is a piston extending from a compressor 6 preferably of a type totally sealed from the atmosphere. The piston is adapted to seal the carbon dioxide within the cylinder 2 and when reciprocated alternately to compress and decompress the carbon dioxide. Adjacent the lower end of the cylinder 2 there is located thermally connecting means in the form of plates 7 which extend from the outer surface of the cylinder 2 to enter the interior of a compartment 8 which interior is to be cooled. At its upper (as shown) end attached to the cylinder 2 are a plurality of cooling fins 4. In use, the compressor 6 is started and upward (as shown) extended movement of the piston into the interior of the cylinder 2 compresses the carbon dioxide. The carbon dioxide is initially adsorbed by the bed of material 3 at the lower end of the zeolite bed thereby generating heat. The heat generated is carried upward by further incoming carbon dioxide with the result that when the compression stroke of the compressor is completed a heat spot is formed at the extreme upper end of the cylinder 2. This heat spot is dissipated by means of the cooling fins 4 to ambient atmosphere. During downward (as shown) retracted movement of the piston within the interior of the cylinder 2 the decompression of the carbon dioxide takes place which carbon dioxide is desorbed from the adsorbent material 3 leading to a net cooling of the adsorbent material 3. Because some of the heat has been dissipated by means of the cooling fins 4 some of the material 3 will become very cool and it has been found over a number of cycles of the compressor a cold spot is formed within the bed of adsorbent material 3 close to the point of entry of the piston (the lower end of the cylinder 2). This cold spot is thermally linked to the interior of the compartment 8 by plates 7 thereby allowing the interior of the compartment 8 to be refrigerated. Particular advantages of the embodiment described above are (a) the materials employed are all environmentally friendly so that the ultimate disposal of the refrigerator presents no problems; and (b) the system is a closed system requiring no constant replacement of adsorbent or gas.

Claims: A refrigerator (1) comprising a sealed chamber containing a bed of an adsorbent material (3) and a compressible gas capable of being adsorbed under pressure by said adsorbent material (3) and desorbed from said adsorbent material (3) when said pressure is reduced, means for alternately compressing and decompressing the gas within the chamber thus creating a permanent cold zone within the chamber and means (7) for thermally connecting the cold zone to a (8) location to be refrigerated. A refrigerator as claimed in Claim 1, characterised in that the chamber is a cylinder (2) and the means for alternately compressing and decompressing the gas is a piston slidable within the cylinder (2). A refrigerator as claimed in Claim 2, characterised in that the thermally connecting means is a plurality of conductive plates (7) located adjacent the cylinder (2) and in alignment with the cold zone and extending within the interior of a compartment (8) to be refrigerated. A refrigerator as claimed in any one of Claims 1 to 3 , characterised in that the adsorbent material (3) is a zeolite and the compressible gas is carbon dioxide. A refrigerator as claimed in any one of Claims 2 to 4, characterised in that the cylinder (2) is vertically orientated and the piston arranged to be slidable along the lower portion of the cylinder (2). A refrigerator as claimed in Claim 5, characterised in that at the upper end of the cylinder (2) cooling fins (4) are attached to the cylinder (2). A method of refrigeration comprising the steps of: a) compressing a gas within a sealed chamber containing a bed of an adsorbent material (3) such that some at least of the gas is adsorbed by said adsorbent material (3); b) removing heat generated by the adsorption step; c) decompressing the gas within the chamber such that the gas is desorbed from the adsorbent material (2); d) repeating steps a), b), and c) until a permanent cold zone is created in the adsorbent material (2); and e) thermally connecting said cold zone to a location (8) to be refrigerated.

Inventors: GARRETT MICHAEL ERNEST, GARRETT, MICHAEL ERNEST
Applicants: BOC GROUP PLC, THE BOC GROUP PLC
Application year: 1992
Main classification: F25B25
IPC codes: F25B25, F25B17, F25B9