Numerical and experimental studies about the effect of acoustic streaming on ultrasonic processing of metal matrix nanocomposites (MMNCs)

Acoustic streaming is a non-linear physical effect which can assist in effective distribution of nanomaterials in a liquid medium subjected to ultrasonic processing. In this study, a time-dependent non-linear computational model was developed to study the effect of various geometrical configurations of the ultrasonic processing cell on the evolution of acoustic streaming flow. Three different geometrical configurations of a flat-bottomed cylindrical processing cell were analyzed for this study. The most well-developed flow pattern is obtained for the geometrical configuration providing the largest acoustic cavitation zone size. Validation of the computational model was performed by two separate experiments − a sedimentation study and processing of a metal matrix nanocomposite (MMNC) composed of an aluminum alloy mixed with carbon nanofibers (CNFs) and silicon carbide (SiC) microparticles. CNFs sonicated in water using the optimum parameters showed the most stable dispersion after 43 h of observation. Microstructural analysis of a cast MMNC subjected to ultrasonic processing with the optimum parameters showed the effect of acoustic streaming in achieving more uniform distribution of solidified phases along with nanomaterials within the matrix compared to a mechanically stirred sample. Computational analysis showed that irregular bottom shapes of the processing cell significantly influence the acoustic cavitation and streaming flow patterns. These studies lay the groundwork for future research into optimizing the shape of the processing cell for scaling up ultrasonication to process larger volumes of liquid media.