Pressure drop measurements on supercritical helium cooled cable in conduit conductors

For extensive projects such as the International Thermonuclear Experimental Reactor design cooperation it is essential to know the pressure drops to be expected from different conductor geometries and operating conditions. To measure these drops a flow loop was constructed to circulate supercritical helium through different conductors. The loop is surrounded by a 5-K radiation shield to allow for stable operation at the required temperatures. A coil heat exchanger immersed in a helium bath is used to remove the heat generated by the pump. Pressure drops are measured across 1-m lengths of the conductors for various mass flow rates. Plots of friction factor versus Reynolds number are used to correlate the data. Supercritical helium flow through the two cable-in-conduit conductors tested in the 3 K to 7 K temperature range appears to undergo laminar to turbulent transition at Reynolds numbers varying from 1000 to 7000. It is concluded that flow area and cooled perimeter alone do not adequately correlate the observed pressure drop along the conductors