[002] In some cooling applications preference is given to free-piston Stirling coolers with a cooling efficiency coefficient close to that of systems using compressors. Stirling coolers are characterised by a cold surface ensuring the absorption of thermal energy from the external medium, and a hot surface ensuring the rejection of the thermal energy by compression generated by a piston that is reciprocated by a linear engine.

The cold surface absorbs the heat inside the cooler by means of a thermosiphon system, while the hot surface, by means of another thermosiphon system, rejects the absorbed energy outside the cooler. Whereas the heat exchangers are to be set on small surface areas of the cold-and hot sides of a Stirling cooler, larger areas are actually needed for these exchangers to transfer the required energy levels, so that a discrepancy may occur between the ideal surface areas for the heat exchangers and the actual areas available for this purpose. To remedy to this discrepancy, i. e. to improve the heat exchangers'function, the thermal energy inside the cooler is transferred outside by means of a fan-forced heat flow, resulting in increased energy consumption and costs.

[003] In US Patent Application US2002013488 a description is given of a cooling system operated by a Stirling cooler comprising a thermosiphon arrangement with condenser and evaporator endings, where the connection between these endings is achieved by means of one large-diameter and one small-diameter pipes.

[004] In the Japanese Patent Application JP2003075000 a description is given of a heat exchanger mounted on a Stirling cooler, absorbing the thermal energy through its cold surface, and containing a cooling fluid flowing in a hollow region of its body, and cooling fins.

[005] The aim of this invention is the realisation of a cooling device in which the heat exchange between the cold surface of the Stirling cooler, the inner medium of the device, the hot surface of the Stirling cooler, and the external medium where the energy is expulsed, without using additional fan arrangements.

[006] The cooling device realized in order to attain the object of this invention has been illustrated in the attached figures wherein: [007] Fig. 1 is a perspective view of the cooling device; [008] Fig. 2 is a perspective view of a flow pipe; [009] Fig. 3 is an exploded view of a heat exchanger; [010] Fig. 4 is a perspective view of a heat exchanger; [011] Fig. 5 is a frontal view of a heat exchanger; [012] Fig. 6 is a schematic view of a Stirling cooler; [013] Fig. 7 is a perspective view of a Stirling cooler where heat exchangers are mounted on both the cold and hot surfaces; [014] Fig. 8 is a schematic representation of a Stirling cooler with a finned heat exchanger mounted on its hot surface; [015] Fig. 9 is a schematic representation of a Stirling cooler with a finned heat exchanger mounted on its cold surface; [016] Fig. 10 is a schematic representation of a Stirling cooler with its cold surface covered by an insulating material; [017] Fig. 11 is a schematic representation of a Stirling cooler with its hot surface covered by an insulating material; [018] Fig. 12 is a schematic representation of a Stirling cooler with both its cold-and hot surfaces covered by an insulating material; [019] Fig. 13 is a schematic representation of the connection between a heat exchanger and an evaporator; [020] Fig. 14 is a schematic representation of the two evaporators in parallel connection with a heat exchanger.

[021] The components shown in the figures have been enumerated as below: [022] 1. Cooling Device [023] 2. Stirling Cooler [024] 3. Evaporator [025] 4. Condenser [026] 5. Cold Surface [027] 6. Hot Surface [028] 7. Heat Exchanger [029] 8. Contact Surface [030] 9. Joining Surface [031] 10. Flow Channel [032] 11. Flow Pipe [033] 12. Connection Element [034] 13. Finned Heat Exchanger [035] 14. Fan [036] 15. Air Flow Channel [037] 16. Insulating Material [038] 20. Body [039] Cooling devices (1) like refrigerators, deep freezers, beverage containers, etc. contain a body (20); a Stirling cooler (2) achieving the cooling operation; an evaporator (3) in which circulates a cooling fluid flowing freely or activated by a pump, absorbing the thermal energy present in the internal medium of the cooling device (1); and a condenser (4) containing a cooling fluid flowing freely or activated by a pump, rejecting the heat to the outside of the cooling device (1).

[040] The Stirling cooler (2) incorporates a cold surface (5), preferably located inside the body (20), ensuring the absorption of thermal energy from outside during the expansion of the gas contained in the cold side, and a hot surface (6), preferably located outside of the body (20), securing the rejection of the thermal energy during the compression of the gas contained within.

[041] The cooling device (1) using the Stirling cooler (2) comprises a heat exchanger (7) with condensing effect, tightly attached to the cold surface (5) transferring the heat generated in the evaporator (3) to the cold surface (5) by condensing the cooling fluid, and/or a heat exchanger (7) with evaporating effect, tightly attached to the hot surface (6) ) in which flows a cooling fluid and transferring the heat generated at the hot surface (6) by evaporating the cooling fluid coming from the condenser (4).

[042] The Heat exchanger (7) contains one or more flow pipe (11) through which the cooling fluid flows, and one or several connection element (12) designed so as to link the section formed by the flow pipe (11) with the pipes coming from the evaporator (3) or from the condenser (4). The heat exchanger (7) is made, preferably, by superposing flow pipes (11) combined in a way to fully encapsulate the cold surface (5) or the hot surface (6). The connection element (12) could have a single entry and a single outlet or, should more than one evaporator be used, a 3-way or 4-way arrangement could be made.

[043] Where pipes coming from the evaporator (3) and/or from the condenser (4) are connected to the heat exchanger (7) by means of a connection element (12), the section through which the cooling fluid flows is modified, preferably increase, ensuring the spreading of the flow whereby the cooling fluid is redistributed in several flow ways, thus increasing the overall flow area and the contact surfaces where the actual heat exchange takes place.

[044] The flow pipe (11) comprises a contact surface (8) shaped as a semi-circle so as to touch the cold surface (5) or the hot surface (6) of the Stirling cooler (2); two joint surfaces (9), flattened by bending, ensuring connection with other flow pipes (11) located on both sides of the contact surface (8) and one or more flow channel (10) designed to increase the overall heat exchange surface.

[045] In the preferred application the flow pipe (11) is produced by extrusion from aluminium-based material so as to engender e. g. lmm x lmm closely-spaced flow channels (10). Annealed Aluminium, pressed against a mould conceived to generate 10 to 2o flow channels (10) for a desired section, is transformed in a flow pipe (11) when exiting the mould. Flow pipes (11) to be used as parts of heat exchangers (7) could then be cut at desired lengths. Moreover, due to the softness of the material used, the flow pipes could be taken on a shape easily.

[046] The cooling fluid that acquires a liquid state by condensation through the heat exchanger (7) placed on the cold surface (5) of the Stirling cooler (2), acting as a condenser, is then directed to the evaporator (3). The cooling fluid flowing through the evaporator (3) circuit of the cooling device (1) absorbs the heat load in the cabin and is transformed in vapour, reaching the heat exchanger (7) once more, thus completing the cycle.

[047] The cooling fluid that evaporates and passes to a gaseous state during its passage through the heat exchanger (7) placed on the hot surface (6) of the Stirling cooler (2), acting as an evaporator, is then directed to the condenser (4). The cooling fluid flowing through the condenser (4) circuit transfers the heat it carries to the external medium, and reaches the heat exchanger (7) again, thus completing the cycle.

[048] The cooling fluid, condensing in the condenser (4), accumulates in a smaller- diameter pipe when exiting the condenser (4) and forms a column of liquid, and a circulation is initiated in the system due to the differential pressure generated by the column of liquid. The flow rate in the system first increases, until the decrease in the pipe pressure equates the difference of static pressure generated by the column of liquid, and the flow output becomes constant when friction losses due to flow equate the pressure energy of the column of liquid. The cooling liquid circulating inside the evaporator (3) starts evaporating by absorbing thermal energy from inside the cooling device (1). In the vertical line of rotation of the evaporator (3) the cooling fluid appears to be in a gaseous state. The cooling fluid arriving to the heat exchanger (7) located at the cold side entry is distributed to the flow channels (10). Though the flow area of a single flow channel (10) is much smaller than the flow area of the evaporator (3), the total flow output through the combined flow channels (10) equates the flow output from the evaporator (3). The distribution of the flow output to flow channels (10) lowers the speed of the flow, and as this speed reduction is more important than the speed increase linked to the reduction of the flow area (section), there is no noticeable increase in pressure loss, and the circulation continues.

[049] In another application of the invention the cooling device (1) contains, apart from the heat exchanger (7) attached to the hot surface (6) of the Stirling cooler (2), a finned heat exchanger (13) attached to the cold surface (5) of the Stirling cooler (2), an air- blowing fan (14), and an air channel (15) directing the air flow. In this application, while the thermal energy present in the interior (cabin) of the cooling device (1) is transferred by forced flow, by means of the fan (14) and the finned heat exchanger (13), the thermal energy on the hot surface (6) is transferred first to the condenser (4) and then to the external medium through the heat exchanger (7).

[050] In another application of the invention a heat exchanger is mounted on the cold surface (5) of the Stirling cooler (2), and a finned heat exchanger (13) is mounted on the hot surface (6) of the Stirling cooler (2). In this application the heat generated at the hot surface (6) is transferred by forced flow, by means of the fan (14) and the finned heat exchanger (13), while the cold face (5) absorbs the thermal energy by means of the evaporator (7).

[051] In yet another application of the invention the heat exchanger (7) located on the cold face (5), or the heat exchanger (7) located on the hot face (6), or both heat exchangers are covered by an insulating material (16). If the heat exchanger (7) located on the hot surface (6) is external the body (20), it is preferably not covered by insulating material (16), whereas it is covered by insulating material (16) if it is located inside the body (20). The outer surfaces of the heat exchanger (7) are thus isolated from the surrounding medium, thereby increasing the efficiency of the heat transfer process between the cold surface (5) and the hot surface (6) of the Stirling cooler (2) by the cooling fluid circulating in flow pipes (11).

[052] A more efficient cooling is attained as the result of a direct contact between the flow pipe (11) structure contained in heat exchangers (7) and the cold and hot surfaces (5,6) of the Stirling cooler (2). The cooling performance of the cooling device (1) is improved while energy consumption decreases, as heat transfer between the air inside the cooling device (1) and the cooling fluid circulating in the evaporator (3), or between the external air and the cooling fluid circulating in the condenser (4) are realised at low differential temperatures.