Heat transfer to subcritical and supercritical helium in centrifugal acceleration fields

The effect of centrifugal acceleration on heat transfer from circular flat surfaces (6.1 mm diameter) of copper to helium was investigated by placing the test piece in a small cell revolving about a displaced axis. Free convection data were obtained in the temperature range 4.2 to 4.5 K, and pressure range 0.1 to 0.7 MPa (1 to 7 atm) by imposing centrifugal accelerations of 1 to 300 'g' towards the surface. Data in the nucleate and film boiling regimes were also obtained at near atmospheric pressures. A new correlation is suggested for free convection heat transfer. However, the existing correlations for conventional fluids in the gravity field seem to be also useful for the design work of superconducting generators, once the gravity term in the Rayleigh number is replaced by a centrifugal acceleration. Nucleate boiling heat transfer is found to be little affected by rotation, although increase in the maximum and minimum heat flux were observed. Also, heat transfer in the film boiling regime was improved. (author)