This is where my mind is at... The most important effect of ultrasound in crystallizing systems is the cavitation, the opening and subsequent implosion of gas or vapour bubbles with a typical diameter of 10-15 μm. The primary effect of ultrasound on a continuum fluid is to impose an oscillatry pressure on it. At low intensity this pressure wave will induce motion and mixing with in the fluid, this process is known as acoustic streaming. At higher intensities, the local pressure in the expansion phase of the cycle falls below the vapour pressure of the fluid, causing minute bubbles or cavities to grow.

Nice to see you @theMac