Analytical and experimental study on the feasibility of rotor cooling with thin gas for fully superconducting rotating machines

Abstract

Rotor cooling with thin gas in air gap was considered for fully superconducting rotating machines. This does not require designing coolant channels in the rotor, so the rotor structure can be simplified. The aim of this study is to verify the feasibility of this cooling system with thin gas. In this paper, at first, steady state thermal analysis with the finite element analysis software COMSOL® was conducted to investigate whether it would be possible to observe cooling characteristics of thin gas in our experiment. The analytical result suggests an enhancement of cooling due to convection can be observed in an experiment with liquid-nitrogen cooling by increasing helium gas pressures to 5000 Pa and above. Then an experiment device including a helium gas vessel was fabricated and an experiment without rotation was performed. The temperature of the rotor which was in the vessel cooled by liquid nitrogen was apparently decreasing after feeding helium gas. Therefore, it was confirmed that the rotor was cooled by heat conduction through the helium gas. In the future, to verify whether rotor cooling with thin gas is enhanced by convection, the experiment will be conducted at various rotational speeds and pressures of helium gas.