They don’t give much information or video of what’s happening.
With just that shot through the sight glass I can’t guess what’s going on, but they talk about it in a video on YouTube. They’re obviously agitating the liquid some way thats independent of just the evaporation that’s happening, maybe ultrasound.
Someone on here posted a link to a paper about an ultrasonic thin film evaporator for desalination and the authors claimed a pretty dramatic increase in the rate of evaporation with the introduction of ultrasound.
Based on what was said in that paper, there was two reasons for this…
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Ultrasonics increases the rate of evaporation by essentially rattling the solution so fast that it interferes with the formation of large bubbles so you don’t get that bumping effect where large bubbles chaotically grow and pop and jostle the whole solution around. The bubbles formed are much smaller and contain much higher pressure, which allows them to carry more vapor per unit of volume.
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The ultrasonics keeps all the particles moving, increasing the rate of heat transfer. I.e. increases turbulence in the solution.