A simple derivation of the critical condition for the ultrasonic atomization of polymer solutions

A simple model is proposed for the ultrasonic atomization of polymer solutions. In this model, the atomization process is approximated as an equilibrium process. It is shown that the minimum attainable droplet size is determined by two parameters, the (Rayleigh) acoustic pressure acting on the surface of the liquid, and the surface tension of the liquid. Increasing the viscosity of the liquid suppresses the formation of small-sized droplets because of increased attenuation of the sound wave and thus decreased acoustic pressure. Lowering the surface tension of the liquid (e.g., by spreading a surfactant film on the liquid surface) has the opposite effect of enhancing the formation of smaller droplets. Also, there exists a maximum limit for the droplet size, because when the produced droplet is too large, the aspiration flow is unable to carry the droplet against sedimentation. These predictions are supported by experimental observations.