Spreading, Splashing and Sparkling: Drop Impingement Phenomena on Pourous Media
Speaker: Cullen Buie, Massachusetts Institute of Technology
Series: MAE Departmental Seminars
Location: Bowen Hall Room 222
Date/Time: Friday, September 20, 2013, 3:30 p.m. - 4:30 p.m.
This study investigates drop impingement on porous media including thin films, paper, and soil. Experiments reveal previously unexplored impingement modes on porous surfaces designated as necking, spreading, and jetting. Dimensional analysis yields a new non-dimensional parameter, denoted the Washburn-Reynolds number, relating droplet kinetic energy and surface energy. The impingement modes correlate with Washburn-Reynolds number variations spanning four orders of magnitude and a corresponding energy conservation analysis for droplet spreading shows good agreement with the experimental results. The simple scaling laws presented will inform the investigation of dynamic interactions between porous surfaces and liquid drops for applications ranging from droplet microfluidics to inkjet printing. In addition, high-speed imaging has revealed evidence of aerosol generation during drop impingement on dry porous media including soils. After impact, tiny gas bubbles form inside the droplet, fed by air escaping the porous media. The tiny bubbles break resulting in microscale jets that quickly break up into droplets. Within a specific range of impact velocity, we observe furious ejection of tiny droplets, producing aerosol clouds above the surface. Aerosol generation can be predicted with knowledge of the surface properties and impact conditions. This work illustrates that aerosols can easily be generated on porous surfaces, with intriguing environmental and engineering implications.
Cullen R. Buie is an Assistant Professor of Mechanical Engineering at MIT. He attended The Ohio State University where he received his B.S. in Mechanical Engineering (2003). After OSU, Cullen attended Stanford University as a National Science Foundation Graduate Research Fellow and obtained his M.S. (2005) and Ph.D. (2009) in Mechanical Engineering. Cullen's Ph.D. research, with Professor Juan Santiago, involved the study of microfluidic pumps to manage liquid water in proton exchange membrane fuel cells. After Stanford Cullen spent a year at UC Berkeley working with Professor Liwei Lin and Professor John Coates as a UC Presidents Postdoctoral Fellow. At MIT his laboratory explores flow physics at the microscale for applications in materials science and microbiology. His research is applicable to a diverse array of problems, from anti-biofouling surfaces and biofuels to energy storage and bacterial infections. Cullen is the recipient of numerous awards for his research and service including the National Science Foundation CAREER Award (2012), the DuPont Young Professor Award (2013), and the DARPA Young Faculty Award (2013).