Evolution behavior of cavitation bubble in pure Sn liquid medium with narrow gap under low-amplitude ultrasound.

In this study, a numerical model of cavitation bubble in the narrow-gap pure Sn liquid medium was established by two-dimensional compressible multiphase flow simulation. The effects of the pressure amplitude and the gap size on the shape, size and position of the cavitation bubble were investigated. The calculation results showed that the cavitation bubble in the narrow-gap soldering seam could exist stably after experiencing two stages of the nonlinear oscillation and the near-wall oscillation with the low-amplitude ultrasound and moved directionally on the metal substrate surface. When the pressure amplitude increased or the gap size decreased, the directional motion rate of the cavitation bubble increased and the shape of the bubble was elliptical due to the confinement effect of the substrate wall. The ultrasonic degassing mechanism of the narrow-gap soldering seam under the action of exponential decay ultrasonic vibration was analyzed by comparing the fluid pressure and velocity field variations. The flow field in the center of the soldering seam vibrated stronger than that of the peripheral regions, which could promote the outward motion of the cavitation bubble. Within the calculation time of 0.002 s, the maximum horizontal motion distance of bubble in the narrow-gap soldering seam was 1.13 mm.