Analysis of transient thermally-induced convection of supercritical helium in a conduit

This work investigates the thermally-induced transient flow and heat transfer in cable-in-conduit conductors (CICC) cooled with initially stagnant supercritical helium. Prior studies have demonstrated that thermally-induced flow results in a high heat transfer coefficient and a large thermal stability margin. Accurate prediction of the stability margin requires a quantitative description of the variation of heat transfer with heat flux. This study focuses on the heat transfer/heat flux relationship and on the basic mechanisms governing the early stages of transient heating. The present modeling divides the problem into two parts: a low-heat flux regime and a high-heat flux regime. Results from the present models indicate that the heat transfer coefficient exhibits a minimum, as observed experimentally in a previous study, and that, in general, heat transfer can be considerably enhanced by using a highly compressible fluid like supercritical helium.