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Abstract In this paper, a hermetic and oil-free turbine generator for a cryogenic ORC is suggested and investigated. The generator mainly consists of a high-speed generator, a two-stage supersonic turbine, and magnetic bearings. Based on the hermetic design concept, these components are in a common casing. To upgrade the cooling capability of the generator, heat dissipation fins are installed between the 1st and 2nd stage of the turbine. Performance of the turbine generator was preliminarily investigated by CFD calculations. These results show that the turbine efficiency peaks at 16,000rpm under the design pressure ratio condition. Under the same condition, it is also predicted that comparatively high static pressure recovery coefficient and low total pressure loss can be obtained through the flow path with the fins. Moreover, a series of experimental campaign were conducted on an ORC test rig using −96 deg.C liquid nitrogen and 50 deg.C warm water as cold source and heat source, respectively. These results indicate that the target power output was achieved and the installed heat dissipation fins are effective to enhance the cooling capability of the generator. It was also indicated that under comparatively high loaded conditions, the turbine power output can be increased by heat transferred from the generator.
Tanaka et al. (Mon,) studied this question.