Woodruff School of Mechanical Engineering
Physical Processes Affecting the Breakup of Crude Oil-Dispersant Mixtures into Subsurface and Aerosolized Droplets
Dr. Joseph Katz
Johns Hopkins University
Tuesday, March 27, 2018 at 11:00:00 AM
MRDC Building, Room 4211
Dr. Devesh Ranjan
Abstract: A series of laboratory-scale experiments examine the generation of both subsurface and airborne crude oil droplets in several relevant settings, such as breaking waves, raindrop impact, bursting of bubbles, and subsurface plumes with and without cross-flows. For waves, premixing the oil with dispersant (Corexit 9500A) reduces the droplets sizes to the micron- and submicron-scale ranges, and changes the slope of their size distribution. Without dispersant, the characteristic oil droplet diameters can be predicted based on the relevant turbulence scales. Once entrained, the temporal evolution of concentration and size distribution of these droplets can be modeled as a combined effect of turbulent diffusion and buoyant rise. With dispersant, the droplet sizes are much smaller than the turbulence scales, in part due to tip-streaming occurring at the oil-water interface. Furthermore, the droplet fragmentation persists long after the wave breaking. Aerosolization of oil is caused both by the initial splash and by subsequent bubble bursting, as entrained bubbles rise back to the surface. Dispersants increase the airborne nano-droplet concentration by orders of magnitude, raising related health questions to cleanup workers and downstream communities. The general shape of subsurface crude oil plumes in cross flow is affected by the droplet sizes and their interaction with the plume’s counter-rotating vortex pair. Hence, dispersants modify the entire plume geometry and the spatial distribution of droplets in it. The early plume breakup process, which dominates the droplet sizes, is probed by matching the refractive index of silicon oil with that of sugar water. These measurements show that the droplet sizes, location of breakup, and even the plume scales are Reynolds- and Weber-number dependent. The frequent formation of compound droplets containing both oil and water affects their buoyancy and interfacial area.
Short Biography: 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 Fellow of the American Society of Mechanical Engineers (ASME) and the American Physical Society. 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 350 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.
Refreshments will be served.