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Apparatus for maintaining the temperature of a component of a gas turbine engine below a predetermined maximum working temperature comprises a reservoir for a cooling fluid having a boiling point below the working temperature and in which the component is immersed or with which it is in contact. At

Apparatus for maintaining the temperature of a component of a gas turbine engine below a predetermined maximum working temperature comprises a reservoir for a cooling fluid having a boiling point below the working temperature and in which the component is immersed or with which it is in contact. At least two heat exchangers are associated with the reservoir and operable to effect condensation of vaporized cooling fluid and return of same to the reservoir. Preferably the apparatus is a closed system incorporating three heat exchangers respectively adapted to effect heat exchange with engine fuel, compressed air derived from a fan or low pressure compressor of the engine and ambient air. Means may advantageously be provided to ensure return of condensed cooling fluid to the reservoir when the attitude of the reservoir is altered as a result of aircraft maneuvers.

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1. Apparatus for maintaining the temperature of a component below a predetermined maximum temperature, the apparatus comprising a reservoir for a cooling fluid having a boiling point below said temperature, said component and said cooling fluid being in heat transferable juxtaposition to one another

1. Apparatus for maintaining the temperature of a component below a predetermined maximum temperature, the apparatus comprising a reservoir for a cooling fluid having a boiling point below said temperature, said component and said cooling fluid being in heat transferable juxtaposition to one another such that heat may transfer therebetween, and two heat exchangers associated with said reservoir and operable to effect condensation of vaporised cooling fluid and return same to said reservoir, the heat exchange capacity of at least one of said heat exchangers being variable between maximum and minimum levels, and the combined heat exchange capacity of the heat exchangers when said variable capacity heat exchanger is operating at its minimum heat exchange capacity being sufficient to maintain the temperature of said component below said predetermined maximum temperature, and wherein the apparatus is used in a gas turbine engine in which one of said heat exchangers is adapted to effect heat exchange with ambient air drawn from around the engine and a second one of said heat exchangers is adapted to effect heat exchange with engine fuel.2. Apparatus according to claim 1 wherein both of said heat exchangers are of variable heat exchange capacity, the minimum combined heat exchange capacity of the heat exchangers being sufficient to maintain the temperature of said component below said predetermined maximum temperature.3. Apparatus according to claim 1 including one or more further heat exchangers of fixed or variable heat exchange capacity, the combined minimum heat exchange capacity of all of said heat exchangers being sufficient to maintain the temperature of said component below said predetermined maximum temperature.4. Apparatus according to claim 1 for use in a gas turbine engine in which one of said heat exchangers is adapted to effect heat exchange with compressed air derived from a low pressure compressor or fan of the engine.5. Apparatus according to claim 1 wherein heat is transferred automatically in whichever one or more of said heat exchangers is operable at a particular point in time.6. Apparatus according to claim 1 wherein said component is disposed adjacent to said reservoir.7. Apparatus according to claim 6 wherein said reservoir comprises an evaporation region of a heat pipe disposed adjacent to said component, said heat pipe also having opposed end regions comprising elements of respective ones of said heat exchangers.8. Apparatus according to claim 1 in which said component is immersed in said cooling fluid.9. Apparatus according to claim 8 including an insulated chamber in fluid communication with the liquid and vapour in said reservoir, said insulated chamber being adapted to extract heat from said component when the cooling effect of said heat exchangers is insufficient to maintain the temperature of said component below said predetermined working temperature.10. Apparatus according to claim 1 including pump means operable to increase the pressure of vapour within any one or more of said heat exchangers.11. Apparatus according to claim 10 including throttle means operable to restrict return flow of condensed vapour from the or each pressurised heat exchanger to said reservoir.12. Apparatus according to claim 11 wherein said throttle means comprises a nozzle disposed adjacent to said component and disposed to discharge returned condensate towards said component.13. Apparatus according to claim 1 wherein said heat exchangers are disposed above said reservoir such that condensed cooling fluid is returned to said reservoir by gravity.14. Apparatus according to claim 1 including means operable to ensure return of condensed cooling fluid to said reservoir when the attitude of the reservoir is altered.15. Apparatus according to claim 14 wherein said means to ensure return of condensed cooling fluid comprises pump means.16. Apparatus according to claim 1 wherein said cooling fluid is selected from water, freon, ammonia and a fluorinated hydrocarbon.17. Apparatus according to claim 16 wherein said cooling fluid comprises a mixture of two or more of said fluids.18. Apparatus according to claim 1 wherein said component comprises a housing containing power electronic devices.19. Apparatus according to claim 1 wherein said component comprises fuel supply line.20. A gas turbine engine including apparatus according to claim 1.21. Apparatus for maintaining the temperature of a component below a predetermined maximum temperature, the apparatus comprising a reservoir for a cooling fluid having a boiling point below said temperature, said component and said cooling fluid being in heat transferable juxtaposition to one another such that heat may transfer therebetween, and two heat exchangers associated with said reservoir and operable to effect condensation of vaporised cooling fluid and return same to said reservoir, the heat exchange capacity of at least one of said heat exchangers being variable between maximum and minimum levels, and the combined heat exchange capacity of the heat exchangers when said variable capacity heat exchanger is operating at its minimum heat exchange capacity being sufficient to maintain the temperature of said component below said predetermined maximum temperature and wherein said apparatus is used in a gas turbine engine in which one of said heat exchangers is adapted to effect heat exchange with compressed air derived from a low pressure compressor or fan of the engine and wherein a second one of said heat exchangers is adapted to effect heat exchange with engine fuel.22. Apparatus according to claim 21 wherein a further one of said heat exchangers is adapted to effect heat exchange with ambient air drawn from around the engine.23. Apparatus for maintaining the temperature of a component below a predetermined maximum temperature, the apparatus comprising a reservoir for a cooling fluid having a boiling point below said temperature, said component and said cooling fluid being in heat transferable juxtaposition to one another such that heat may transfer therebetween, and two heat exchangers associated with said reservoir and operable to effect condensation of vaporised cooling fluid and return same to said reservoir, the heat exchange capacity of at least one of said heat exchangers being variable between maximum and minimum levels, and the combined heat exchange capacity of the heat exchangers when said variable capacity heat exchanger is operating at its minimum heat exchange capacity being sufficient to maintain the temperature of said component below said predetermined maximum temperature and wherein said apparatus is used in a gas turbine engine in which one of said heat exchangers is adapted to effect heat exchange with compressed air derived from a low pressure compressor or fan of the engine and wherein a further one of said heat exchangers is adapted to effect heat exchange with ambient air drawn from around the engine.24. Apparatus for maintaining the temperature of a component below a predetermined maximum temperature, the apparatus comprising a reservoir for a cooling fluid having a boiling point below said temperature, said component and said cooling fluid being in heat transferable juxtaposition to one another such that heat may transfer therebetween, and two heat exchangers associated with said reservoir and operable to effect condensation of vaporised cooling fluid and return same to said reservoir, the heat exchange capacity of at least one of said heat exchangers being variable between maximum and minimum levels, and the combined heat exchange capacity of the heat exchangers when said variable capacity heat exchanger is operating at its minimum heat exchange capacity being sufficient to maintain the temperature of said component below said predetermined maximum temperature and including control means operable to close off communication between one or more of said heat exchangers and said reservoir.25. Apparatus according to claim 24 wherein said control means comprises thermostatic valves.26. Apparatus for maintaining the temperature of a component below a predetermined maximum temperature, the apparatus comprising a reservoir for a cooling fluid having a boiling point below said temperature, said component and said cooling fluid being in heat transferable juxtaposition to one another such that heat may transfer therebetween, and two heat exchangers associated with said reservoir and operable to effect condensation of vaporised cooling fluid and return same to said reservoir, the heat exchange capacity of at least one of said heat exchangers being variable between maximum and minimum levels, and the combined heat exchange capacity of the heat exchangers when said variable capacity heat exchanger is operating at its minimum heat exchange capacity being sufficient to maintain the temperature of said component below said predetermined maximum temperature and wherein said means to ensure return of condensed cooling fluid comprises pump means and wherein at least one of said heat exchangers projects from the reservoir in a direction different to the other or others.27. A method of maintaining the temperature of a component below a predetermined temperature, the method comprising cooling the component by evaporation of a cooling fluid having a boiling point below said temperature, effecting condensation of evaporated cooling fluid by heat exchange with one or more of two heat exchange mediums, the heat exchange capacity of at least one of which is variable between maximum and minimum levels, and maintaining the combined heat exchange capacity of the heat exchange mediums sufficient at all times to maintain the temperature of said component below said predetermined maximum temperature and further including the steps of using the method in a gas turbine engine and wherein one of said heat exchangers exchanges heat with ambient air drawn from around the engine and another one of said heat exchangers exchanges heat with engine fuel.28. A method according to claim 27 wherein heat exchange is effected selectively in one or more of said heat exchange mediums dependent on variation in heat exchange capacity of said variable capacity heat exchange medium.29. A method according to claim 27 wherein heat exchange is effected selectively with one or more of said heat exchange mediums dependent on variation in their respective heat exchange capacities.30. A method according to claim 27 wherein said cooling fluid is selected from water, freon, ammonia and a fluorinated hydrocarbon.31. A method according to claim 27 wherein said component comprises a housing containing power electronic devices.32. A method according to claim 27 wherein said component is a fuel supply line.33. A method of maintaining the temperature of a component below a predetermined temperature, the method comprising cooling the component by evaporation of a cooling fluid having a boiling point below said temperature, effecting condensation of evaporated cooling fluid by heat exchange with one or more of two heat exchange mediums, the heat exchange capacity of at least one of which is variable between maximum and minimum levels, and maintaining the combined heat exchange capacity of the heat exchange mediums sufficient at all times to maintain the temperature of said component below said predetermined maximum temperature and wherein the method is used with a gas turbine engine and one of said heat exchange mediums is maintained in heat exchange relation with the engine fuel.34. A method of maintaining the temperature of a component below a predetermined temperature, the method comprising cooling the component by evaporation of a cooling fluid having a boiling point below said temperature, effecting condensation of evaporated cooling fluid by heat exchange with one or more of two heat exchange mediums, the heat exchange capacity of at least one of which is variable between maximum and minimum levels, and maintaining the combined heat exchange capacity of the heat exchange mediums sufficient at all times to maintain the temperature of said component below said predetermined maximum temperature and wherein a reservoir for said cooling fluid is provided and a control means is provided and including the step of operating said control means to close off communication between said heat exchange mediums and said reservoir.