Robert E. Johnson
William D. O'Brien, Jr.
Univ. of Illinois at Urbana--Champaign, Urbana, IL 61801
A model of ultrasonic cleaning of the skin surface is discussed in this presentation. The model assumes that the primary cleaning mechanism is associated with the collapse of cavitation bubble near the skin surface. First, bubble behavior near a deforming surface is briefly reviewed. Based on an available analytical solution, it is shown that when a bubble collapses near the skin surface, a jet formed by the collapsing bubble is directed at the surface. Consequently, it is believed that the flow field induced by bubble jetting plays a central role in the cleaning process. This flow field is modeled as a stagnation point flow and the mean transport of dirt due to this flow field is investigated. Specifically, the removal rate, i.e., mass flux, of dirt from the skin surface is found and is shown to be higher for ideal flows than for viscous flows. Finally, the relation between the stagnation point flow and the Kelvin impulse associated with a single bubble collapse is examined. By assuming a known distribution of bubble sizes, an overall removal rate estimate is obtained.