Levich Institute Seminar Announcement, 09/27/2016
Steinman Hall, Room #312
(Chemical Engineering Conference Room)
Professor Chang-Hwan Choi
Stevens Institute of Technology
Department of Mechanical Engineering
"Hydrodynamic Friction Reduction on Superhydrophobic Surfaces"
Patterned hydrophobic (so-called superhydrophobic) surfaces have attracted much interest for the application to hydrodynamic friction reduction for both droplet movement and continuous flow. In droplet movement, the friction is mainly determined by the pinning of a contact line, affected by many surface parameters including chemical heterogeneity, physical structures, and interfacial wetting states. The influence of surface structures on the droplet pinning has been studied from the perspective of both kinetics and dynamics. However, the results are not consistent and the critical factor that would determine the pinning mechanics has not been clearly understood yet. Moreover, the direct mechanism of how the surface structures regulate the depinning dynamics on superhydrophobic surfaces has not been revealed much. In the first half of this talk, our recent study on the pinning/depinning mechanism of a moving droplet on superhydrophobic surfaces will be presented to propose a new physical criterion to evaluate the slipperiness of superhydrophobic surfaces for the droplet movement from the perspective of surface morphology. In the case of continuous flow on superhydrophobic surfaces, the hydrodynamic friction reduction is achieved by using a film or discrete layer of air bubbles entrained at the surface to gain the advantages of the greatly lower viscosity of a near-wall gas. However, most of the experimental studies of the frictional drag reduction on superhydrophobic surfaces have been performed in laminar flow regimes. In the second half of this talk, our recent study on the frictional drag reduction on superhydrophobic surfaces will be presented, covering not only the laminar flow but also turbulent flow. The results presented in this talk would provide valuable insight to understand the friction reduction on superhydrophobic surfaces and pave the way for the engineering of superhydrophobic surfaces for efficient hydrodynamic drag reduction, in both droplet movement and continuous flow.
BRIEF ACADEMIC/EMPLOYMENT HISTORY
Dr. Chang-Hwan Choi is currently working as an Associate Professor in the Department of Mechanical Engineering at the Stevens Institute of Technology. Before he joined Stevens in 2007, Dr. Choi received his PhD in Mechanical Engineering from the University of California at Los Angeles (UCLA) in 2006, specializing in MEMS/Nanotechnology and minoring in Fluid Mechanics and Biomedical Engineering. He earned his MS in Engineering, specializing in Fluids, Thermal, and Chemical Processes from Brown University in 2002. Before he moved to US, he acquired his BS in 1995 and MS in 1997 in Aerospace Engineering from Seoul National University in Korea. He has two-year (1996, 2000) work experience at Korea Aerospace Research Institute and three-year (1997-1999) teaching experience at Chandrakasem Rajabhat University in Thailand. kuj He was a recipient of the 2010 Young Investigator Program (YIP) award by the US Office of Naval Research (ONR) for his work on the development of hydrodynamically-efficient anti-biofouling and anti-corrosion surfaces for naval systems and also highlighted in Nature.
RECENT RESEARCH INTERESTS
His current research activities include large-area nanopatterning and 3D nanofabrication, fluid physics and heat transfer at nanoscale interfaces, microfluidic self-assembly of nanomaterials, nanofluidic energy harvesting, and cell-material interactions, funded by various federal agencies in US (NSF, DARPA, ONR, ARMY, and DOE) and industries.