A fuel rod of VHTR (Very High Temperature gas-cooled Reactor) which is planed by JAREI has rectangular projection parts, called "Spacer ribs", to make the coolant flow in a concentric annular channel. To investigate the effect of a spacer rib on heat transfer characteristic, the surface temperature distribution was measured using thermosensitive liquid-crystal-film adhered on the heating plane, under the laminar, transitional and turbulent flow conditions.
