Abstract
Near-surface velocity measurements are carried out with quantum dot (QD) nanoparticles using evanescent wave illumination. Relying on the small size of QDs, their correspondingly small hydrodynamic radius and high Brownian diffusion coefficient, we consider the situation where the tracer diffusion length over the inter-frame time Δt is large compared to the size of the interrogation region next to the wall. While keeping all other experimental parameters fixed, we systematically increase Δt by as much as a factor of 25, resulting in an increase of the QD diffusion length by a factor of 5. Data indicate a significant overestimation of the “apparent” mean velocity measured experimentally. These results provide a direct confirmation of the phenomenon of diffusion-induced bias described by the simulations of Sadr et al. (2007).
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Acknowledgments
This work was supported by the CRC Program of the National Science Foundation, Grant Numbers CHE-0209898, CHE-0714028, and CHE-0714189.
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Pouya, S., Koochesfahani, M.M., Greytak, A.B. et al. Experimental evidence of diffusion-induced bias in near-wall velocimetry using quantum dot measurements. Exp Fluids 44, 1035–1038 (2008). https://doi.org/10.1007/s00348-008-0491-7
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DOI: https://doi.org/10.1007/s00348-008-0491-7