抄録
A mercury target system will be installed in Japan Proton Accelerator Research Complex (J-PARC) for MW class neutron sources. High intense proton beams injected into the target will induce cavitation by pressure waves. Injection of microbubbles with 50 to 200 μm in diameter into mercury may be effective to reduce cavitation damage. Bubble generation in mercury is difficult because of its poor wettability. Therefore, we artificially change wetting condition in water to simulate bubble formation in poor wetting conditions. Experimentally, visualization of bubble growth at an orifice type nozzle of 100 μm in diameter was done by a high-speed CCD camera. Wetting condition on the orifice surface was worsen by coating it with a water-repellent. Computational Fluid Dynamics (CFD) simulation was carried out under stagnant water to understand the effect of wettability on bubble formation from the orifice nozzle. It was found that the bubble diameter depends on contact angle and it increases as wetting conditions become worse, i.e. large contact angle.
