Experimental study on the effect of nozzle surface finishing in high-speed water jet

International Fusion Materials Irradiation Facility (IFMIF) employs a liquid Li jet target being formed by two-dimensional metal contraction nozzle. The Li is corrosive substance and there is the possibility that the Li is corrosive to nozzle surface. Therefore, it is necessary to investigate the effect of nozzle surface finishing on the free surface instabilities, from the viewpoint of useful life and to determine the practical accuracy of finishing. The experiments were performed by two methods, one is the observation of free surface behavior by a high-speed video camera, and the other is the measurement of the velocity profile at the nozzle exit by Laser Doppler Velocimeter (LDV). Two types of nozzles are employed in the present experiment, namely, nozzles with surface finishing of ∇(maximum roughness: 100 μm) and ∇∇∇(maximum roughness: 6.3 μm). In case of the surface finishing of 100 μm, the free surface waves grew growing about 7.5 m/s mean velocity at the nozzle exit, and when the mean velocity is over 15 m/s, many droplets were observed. On the other hand, there was little difference of free surface behavior between surface finishing of 6.3 μm and mirror finishing. These results satisfy the specification required for the IFMIF target nozzle. (author)