Turbine unit with magnetic coupling for use in a Rankin cycle waste heat recovery system
Publication Date: 2013-Oct-23
The IP.com Prior Art Database
The invention pertains to a turbine unit comprising a housing, a turbine, which is rotatably mounted in the housing and located in a space within the housing which is hermetically sealed from the surroundings, a turbine shaft, which is fixed to the turbine in order to rotate together with the turbine and a magnetic coupling for transmitting torque from the turbine shaft to said driven shaft. The magnetic coupling in turn comprises an outer rotor, an inner rotor rotatably mounted within the outer rotor, several first permanent magnets provided on an inner surface of the outer rotor and distributed in the circumferential direction of said inner surface, several second permanent magnets provided on an outer surface of the inner rotor and distributed in the circumferential direction of said outer surface, and a stationary separating member, which is fixed to the housing so as to form a fluid tight seal between the inner rotor and the outer rotor and which comprises a cup-shaped wall arranged in the gap between the inner rotor and the outer rotor, said cup-shaped wall comprising a first layer of thermoplastic material and a second layer of electrically non-conductive DLC or Al2O3 arranged on said first layer. A separating member comprising a layer of thermoplastic material with a coating of DLC or Al2O3 can be made very thin while still fulfilling the requirements with respect to hardness, thermal conductivity etc. imposed by the use in a magnetic coupling of the above-mentioned type.
Page 01 of 9
Turbine unit with magnetic coupling for use in a Rankin
cycle waste heat recovery system
FIELD OF THE INVENTION AND PRIOR ART 5
The present invention relates to a turbine unit for use in a Rankin cycle waste heat recovery system.
A Rankin cycle waste heat recovery system is a well known type of system for recovering energy from waste heat. Such a waste
heat recovery system is for instance previously known from GB 2 406 000 B. In this known system, a working fluid is circulated in a closed circuit, which is sealed from the surroundings in order to prevent escape of the working fluid. The working fluid is heated and vaporized in a vaporizer, for instance
under the effect of exhaust gases from a combustion engine. After exit from the vaporizer, the vaporized working fluid flows into a turbine unit, where it is allowed to expand while driving a turbine, which is rotatably mounted in a housing of the turbine unit. The turbine is located in a in a hermetically sealed space
within the housing. The turbine shaft is connected to a shaft of an alternator through a magnetic coupling, which is configured to transmit torque from the turbine shaft to the alternator shaft. The magnetic coupling disclosed in GB 2 406 000 B comprises an inner rotor and an outer rotor, wherein a cup-shaped separating
member of non-magnetic material, such as for instance stainless steel or plastic, is arranged in the gap between the inner rotor and the outer rotor in order to prevent working fluid to escape from said hermetically sealed space into the surroundings through the magnetic coupling.
For an efficient transfer of magnetic force between the inner and outer rotors of a magnetic coupling of the type disclosed in GB 2 406 000 B, the gap between the rotors should be as small as possible, which in it turn implies that the separating member
between the rotors should be as thin as possible. Furthermore, the separating member must have a sufficient thermal
Page 02 of 9
conductivity to be able to conduct the heat that is developed in the separating member during the rotation of the rotors away to the housing of the turbine unit. If the thermal conductivity of the separating member is too low, the separating member might be damaged by the high temperature.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a turbine unit of the above-mentioned type with an improved magnetic coupling.
According to the invention, this object is achieved by a turbine unit having the features defined in claim 1.
The turbine unit of the invention comprises:
together with the turbine; and
- a magnetic coupling for transmitting torque from the turbine shaft to said driven shaft, wherein the magnetic coupling comprises:
• an outer rotor,
• an inner rotor rotatably mounted within the outer rotor,
• several first permanent magnets provided on an inner surface of the outer rotor and distributed in the circumferential direction of said inner surf...