Pulsed Pressure Induced Cavitation Erosion in Mercury Narrow Channel under Flowing Conditions

Abstract

In the mercury target for the pulsed neutron source, cavitation is a critical issue to realize a stable and high-power operation of the system, since the cavitation causes severe erosion damage on the mercury enclosure vessel. We have introduced following two techniques to mitigate the cavitation damage. One is the gas microbubbles injection into the flowing mercury, and the other is the double-walled structure with a narrow gap channel at the front part of the vessel. The double-walled structure is expected to mitigate the cavitation damage due to the pressure gradient produced by high-speed flow (~4 m/s) and the narrow gap boundary (2 mm). To quantitatively investigate the effect of double-walled structure on cavitation damage, cavitation damage tests were conducted by parametrically changing the mercury flow velocity in narrow channel and the channel gap width. The results showed that the damage was reduced by increasing the flow velocity whereas the gap width dependency on damage in the range between 1.5 and 2.5 mm was hardly observed under flowing. Experimental results suggested that the damage mitigation effect by high-speed flow was more dominant than that by narrow gap in double-walled structure.