This presentation summaries a series of laboratory studies aimed at characterizing interfacial phenomena affecting the breakup of surface slicks and subsurface plumes of crude oil after an oceanic spill. After entrainment of fresh oil slicks by surface waves, the droplet size distributions are consistent with classical turbulence-based scaling, and their subsequent temporal evolution can be modeled by combining effects of turbulent diffusion and buoyant rise. Premixing the crude oil with dispersant, which drastically reduces the oil-water interfacial tension, causes tip streaming that decreases the droplet sizes to the micron range, orders of magnitude below the turbulence scales. Aerosolization of oil is caused by the initial splash and by subsequent bubble bursting. Premixing with dispersant increases the concentration of airborne oil-containing nano-droplets by one to two orders of magnitude. In contrast, the dispersant causes a reduction in concentration of volatile organic compounds. Extended mixing of oil with seawater generates poly-dispersed water-in-oil emulsions that have two-orders-of-magnitude higher viscosity. Introduction of dispersant generates Marangoni flows, and partially separates the water from the emulsion. Micro emulsions also form as oil droplets rises and cross an oil-water interface. These droplets do not mix with the bulk oil since they remain coated by submicron water films that persist long after crossing. These films eventually break up owing to droplet deformation induced by electrostatic forces. Below the surface, fragmentation of a vertical buoyant oil jet is elucidated by refractive index matching. Compound oil droplets containing water droplets, some with smaller oil droplets, form regularly. Their fraction increases with droplet diameter, reaching 78% for 2mm droplets. While the exterior surfaces of the oil droplets are deformed by the high shear field, the interior interfaces remain spherical, indicating quiescent domains. In the presence of cross flow, entrainment of small droplets into the core of the counter-rotating vortex pair defines the lower boundary of the plume while large droplets escape and define the upper boundary. Hence, reduction of droplet sizes by dispersant increases the fraction of oil entrained into the vortex pair and lowers the upper boundary of the plume.
Joseph Katz
William F. Ward Sr. Distinguished Professor in the Department of Mechanical Engineering, Johns Hopkins University
Joseph Katz received his B.S. degree from Tel Aviv University, and his M.S. and Ph.D. from California Institute of Technology, all in mechanical engineering. He is the William F. Ward Sr. Distinguished Professor of Engineering, and the director and co-founder of the Center for Environmental and Applied Fluid Mechanics at Johns Hopkins University. He is a Member of the National Academy of Engineering, as well as a Fellow of the American Physical Society, American Society of Mechanical Engineers (ASME), and American Society of Thermal and Fluids Engineering. He has served as the Editor of the Journal of Fluids Engineering, and as the Chair of the board of journal Editors of ASME. He has co-authored more than 400 journal and conference papers. Dr. Katz research extends over a wide range of fields, with a common theme involving experimental fluid mechanics, and development of advanced optical diagnostics techniques for laboratory and field applications. His group has studied laboratory and oceanic boundary layers, flows in turbomachines, flow-structure interactions, swimming behavior of marine plankton in the laboratory and in the ocean, as well as cavitation, bubble, and droplet dynamics, the latter focusing on interfacial phenomena associated with oil spills.