Transient Heat Transfer Characteristics of Liquid Helium in Centrifugal Acceleration Field

Abstract

Transient heat transfer of liquid state helium in centrifugal acceleration fields up to 1300G have been investigated for studying the stability characteristics of the rotor field windings of a superconducting generator. In the experiment, temperature resistive platinum-0.5% cobalt (Pt-Co) thin wire was used as the temperature sensor and heater to measure the heat transfer characteristics. The thermal mass of the Pt-Co wire was small enough to observe the temperature fluctuation due to bubbling in the boiling heat transfer. In this paper, influence of the centrifugal acceleration on the transient heat transfer and its mechanism are discussed based on the experimental results. It was observed that, for step heating with heat flux higher than maximumheat flux at steady state nucleate boiling, quasi-nucleate boiling appeared also in centrifugal acceleration field at the beginning of the heating, and that duration of the quasi-nucleate boiling was not much dependent on the acceleration field for relative high heat flux. This phenomenon was explained by bubble formation process in the boiling heat transfer. In this study, a high speed video camera was used to observe the relation of the bubble formation process and the temperature fluctuation of the Pt-Co wire in the normal gravity.