Experimental and numerical investigation of acoustic pressures in different liquids.

In an attempt to quantify the instantaneous pressure field in cavitating liquids at large forcing signals, pressures were measured in four different liquids contained in vessels with a frequency mode in resonance with the forcing signal. The pressure field in liquid metal was quantified for the first time, with maximum pressures of the order of 10-15 MPa measured in liquid aluminium. These high pressures are presumed to be responsible for deagglomeration and fragmentation of dendritic intermetallics and other inclusions. Numerical modelling showed that acoustic shielding attenuates pressure far from the sonotrode and it is prominent in the transparent liquids studied but less so in aluminium, suggesting that aluminium behaviour is different. Due to acoustic shielding, the numerical model presented cannot adequately capture the pressure field away from the intense cavitation zone, but gives a good qualitative description of the cavitation activity. The results obtained contribute to understanding the process of ultrasonic melt treatment (UST) of metal alloys, while facilitating further the guidelines formulation and reproducible protocols for controlling UST at industrial levels.