Dual channel cable in conduit thermohydraulics: Influence of some design parameters

In the framework of the controlled nuclear fusion by magnetic confinement programme, a particular design of a Cable-in-Conduit Conductor (CICC) is being developed, including two parallel cooling channels. The central channel is separated from the strand channel by a spiral structure whose geometry can substantially influence the overall pressure drop. The thermo-hydraulics of this so called dual channel CICC is not well known. Hence various experiments with pressurised nitrogen at room temperature, on straight and curved unit lengths from the ITER toroidal field model coil (TFMC) production, have been performed at both Ansaldo and CEA-Cadarache to characterise the friction factor of the two parallel cooling regions, in a range of representative Reynolds numbers. These experimental results are presented. It has been possible to characterise different kinds of spiral geometries used in the manufacture of the two model coils for ITER: the TFMC and the Central Solenoid Model Coil. A relative assessment of the most suitable spiral for the ITER magnets is presented. This discussion includes: (i) manufacturing aspects with the capability of the spiral to support the cabling process as a function of the geometry of the spiral and the compaction of the cable; (ii) pressure drop considerations, as a function of the spiral geometry which plays an important role in the cooling process and the required cold pump power. Conclusions and recommendations are drawn.