STUDY ON STABILITY OF LIQUID JET FOR LIQUID LITHIUM TARGET OF BORON NEUTRON CAPTURE THERAPY (BNCT)

摘要

For the development of the liquid lithium (Li) jet target system for the boron neutron capture therapy (BNCT), the stability of the Li jet is important. The purpose of the present study is to investigate the characteristics of the disturbances and the droplet formation of a water jet flow at high velocity. The experimental studies for a water jet flow were performed to simulate the liquid Li jet flow. The nozzles in the experiment had a rectangular flow channel with the gap of 0.5 mm and the length of 10 mm and 70 mm. The water flow velocities in these nozzles were 5 m/s, 10 m/s or 15 m/s. The stability of the water jet flow was investigated by the observation of the surface disturbance using a high speed video camera. The formation of water droplet from the water jet flow was detected, and the characteristics of the droplet formation were analyzed using Phase Doppler Anemometry (PDA). Then, the surface disturbance of the jet flow was characterized by the characteristics of the droplet generation. In the experiment with 10mm length of nozzle, a lot of droplets are generated from the jet surface and the surface is considered to be unstable. On the other hand the smooth jet surface and the stable jet are made near nozzle outlet. In the experiment with 70mm length of nozzle, few droplets are generated from the surface of the jet and the surface of the jet is very smooth especially for the place near nozzle outlet. It was concluded that the droplet generation from the surface of the water jet was promoted by the distortion of the jet surface. Also the surfaces of the jet flow made by the nozzle having the length of 70 mm was smoother than those in the tests with the nozzle having the length of 10 mm. The large eddy in the flow must be dumped before the nozzle outlet because the turbulence was fully developed in the nozzle.