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이온농도분극에 의한 와류현상에서 관찰된 유동전단응력-이동장벽 효과
곽노균(Rhokyun Kwak),Van Sang Pham,강지윤,한종윤(Jongyoon Han) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Rotating shear flow is a common tool to suppress turbulence and control transport in plasma physics. Despite the desires to apply this phenomenon to other fields, it has rarely been observed in non-ionized fluids. Here, we visualize this effect on a generic neutral-fluid situation in electro-membrane systems: electroconvective vortex (EC) under Hagen-Poiseuille (HP) flow, which initiated by ion concentration polarization (ICP) on ion exchange membranes. This is the first demonstration of “flow-shear-induced transport barrier” in electrochemical systems, which was found only in magnetized flow previously. Combining scaling analysis and experiment, we capture the effect by pinpointing the threshold for shear suppression. Selected by balancing velocity fluctuation (with EC vortices) and flow shear (with noslip walls), the threshold is scaled as the dimensionless EC height dec/w=0.618. Stable EC occurs under the threshold, while chaotic EC occurs over the threshold by velocity fluctuation overwhelming flow shear. The threshold we identify here has wide applications to prevent chaotic flows in various electro-membrane systems.
Fabrication of nanofluidic channels with directed wrinkle/buckling patterns
Seok Chung(정석),Myoung-Woon Moon(문명운),Jeong Hoon Lee(이정훈),Jongyoon Han(한종윤),Roger D. Kamm 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.7
Interest has grown recently in the concept of "unconventional nanofabrication", the creation of nanoscale features by methods that avoid the technical hurdles and high cost of nano-lithographic processes. One of the challenges has been to reliably and inexpensively produce channels of nanometer dimension, as small as 60 ㎚, in the materials commonly used for soft lithography. In this manuscript, we present new approaches based on simple concepts of wrinkle and buckling patterns.