Friction factor correlation with application to the central cooling channel of cable-in-conduit super-conductors for fusion magnets

A correlation has been developed for the turbulent friction factor f of a circular channel with a helical rib roughness of rectangular cross section, which is relevant to the central channel (hole) in two-channel cable-in-conduit conductors. The correlation is based on data we measured on a pipe with three different types of helix. It relates f with the Reynolds number Re and with suitable dimensionless combinations of all relevant geometrical parameters of the problem, i.e., hole diameter and helix gap and thickness. A limited comparison with actual (QUELL) conductor data shows good agreement.