Nonintrusive measurements in micro- and minichannel flows using optical diagnostics can be challenging due to a lack of optical access and spatial resolution. This talk describes two superresolution imaging techniques based on total internal reflection fluorescence and structured illumination, which both yield spatial resolution below classic diffraction limits by exploiting different types of illumination. Total internal reflection fluorescence (TIRF) uses evanescent-wave illumination to visualize fluorescent tracers within a thin (typically less than 500 nm thick) layer next to a refractive index (e.g. fluid-wall) interface. Structured illumination (SI) imaging reconstructs the fluorescence signal from a thin slice of the bulk flow illuminated over its entire volume using multiple images obtained with nonuniform, and usually spatially modulated, illumination. This talk will illustrate the unique capabilities of TIRF and SI particle velocimetry in microchannel flows. Visualizations of liquid-vapor flows poses additional challenges due to the scattering and distortion of light due to the refractive-index difference between the two phases. We are currently developing SI for visualizing flow and pool boiling because it can reduce multiple light scattering and improve optical access in multiphase flows, as demonstrated in recent structured laser illumination planar imaging (SLIPI) of sprays [DOI: 10.1007/s00348-017-2396-9]. The potential of SI visualization will be illustrated by images visualizing the interiors of vapor bubbles in the pool boiling of a fluorescently dyed hydrofluoroether.
Minami Yoda received a BS from Caltech, and a MS and PhD in Aeronautics and Astronautics from Stanford University. Her research interests in experimental fluid mechanics and optical diagnostics include flow boiling, super-resolution imaging, colloid dynamics, and high heat flux plasma-facing components for magnetic fusion energy. Currently Chairperson of Mechanical Engineering and Red Cedar Distinguished Professor at Michigan State University, Dr. Yoda was a Ring Family Professor in the Woodruff School of Mechanical Engineering at Georgia Tech, and a visiting researcher at TU Berlin, the Delft University of Technology, and Tokyo University of Agriculture and Technology. She is former Chair of the American Physical Society (APS) Division of Fluid Dynamics and the American Nuclear Society Fusion Energy Division, editor of Fluid Dynamics Research, and Fellow of APS and ASME.
Event Date: October 31, 2024