John R. Saylor, Ph.D.
Department of Mechanical Engineering
Clemson University
Monday, December 6, 2010
3:10 p.m., 131 Olin Hall
When a drop impacts a flat liquid surface, bubbles can be entrained into the bulk. At relatively low impact velocities, a large number of very small bubbles can form, a process typically referred to as Mesler entrainment. Although this phenomenon has been studied fro over three decades, several basic questions remain unanswered. Among these is the role of surface conditions on the bubble formation process. Virtually all extant work on Mesler entrainment has been conducted in water. While this is a logical choice of working fluid, since many of the applications of Mesler entrainment pertain to its role in the environment (e.g. bubble formation in lakes and oceans during rain), water is nevertheless problematic because its surface is notoriously difficult to keep free of contaminating surfactant monolayers. This difficulty in controlling surface conditions has been hypothesized as the cause of the irreproducibility in Mesler entrainment experiments, a problem experienced by many researchers. In this seminar, data are presented for the first time where silicone oil is used as the working fluid for the study of Mesler entrainment. Silicone oil does not suffer from the contamination problems of water, and the results obtained are very different from those obtained using water. Results for both silicone oil and water are presented where a virtual match between all three of the relevant dimensionless groups is made (the Weber, Froude and Capillary numbers). The difference in the Mesler entrainment behavior, in spite of this match, strongly suggests that surface conditions (specifically the presence of surfactants) is the cause. Via the use of more than one silicone oil, the effect of the Capillary number is also revealed. The potential application of Mesler entrainment to several industrial processes is also discussed.