Heat transfer and flow instability in a superconducting machine rotating at 3000 rpm

Heat transfer measurements have been carried out on the liquid He⁴ in a side arm rotating at a speed of 3000 rpm. The heat transfer cell consists of a copper disc mounted perpendicularly to the radial direction at a radial distance of 0.41 m. A correlation of the type: $\text{Nu/(1 + S}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{)}\text{= 0.17}\text{R}{}_{\mathrm{a}}{}^{0.3}$ where S is the stratification factor, has been obtained.The flow pattern of He⁴-gas through a U-tube under a self-pumping system in a rotating frame has been studied analytically. It can be demonstrated that the flow polarity is influenced by the velocity gradient of the friction factor in the region, between stream-line and turbulent motions, which can lead to flow instability of the kind observed experimentally recently. It has been explained that the instability may occur in both increasing and decreasing speed modes or heat inputs.