Effect of wettability on bubble formation at gas nozzle under stagnant condition

Injection of gas microbubbles into mercury might be effective to mitigate pressure waves generating and propagating in liquid mercury target for MW-class spallation neutron sources. The effect of mitigation is very dependent on the bubble conditions; size, population, etc. It is important to make clear bubble formation behavior from a nozzle for development of making suitable gas microbubbles into mercury. Visualization of microbubbles in mercury was carried out by refraction-enhanced imaging with high-energy synchrotron radiation X-rays at SPring-8 to observe the bubble formation behavior at micro-gas nozzle of 100 μm in inner diameter and 200 μm in outer diameter. The bubble formation behavior in mercury was quite different from that in water. A constant taking account of the wettability and interfacial tension force between liquid and solid metals in an equation of force balance around bubble was identified by visualized bubble size. The bubble size under mercury flowing condition was estimated from the force balance equitation.