Rotating cryostats for heat transfer and fluid flow studies on the helium cooling of superconducting generator rotors

This paper describes the design and construction of two 1 m diameter rotating cryostats for the study of the heat transfer and fluid flow behaviour of helium at 3000 r.p.m. towards the design of refrigeration systems for superconducting a.c. generators. The first LO rotating cryostat has been in continual operation since 1976 and a great deal of basic data has been produced on the high convective heat transfer performance of helium, on the self-pumping capability of helium gas loops and their associated intrinsic instability, on the behaviour of superfluid helium and the He I/He II interface, and on the forward and reverse flows in thermo-siphon loops, together with a wide range of practical experience with rotating helium and instrumentation at 3000 r.p.m., 5000 g or 150 ms −1 tip speed. A second LX rotating cryostat with increased working volume is also described.