Measurement of Dean flow in a curved micro-tube Using micro digital holographic particle tracking velocimetry

Abstract

Digital micro holographic particle tracking velocimetry (HPTV) was used to measure the three-dimensional (3D) velocity field of a laminar flow in a curved micro-tube with a circular cross-section. The micro HPTV system consists of a high-speed camera and a single laser with an acoustic optical modulator (AOM) chopper. We obtained the temporal evolution of the instantaneous velocity field of water flow within curved micro-tubes with inner diameters of 100 and 300 mu m. The 3D mean velocity-field distribution was obtained quantitatively by statistically averaging the instantaneous velocity fields. At low Dean numbers (De), a secondary flow was not generated in the curved tube; however, with increasing Dean number a secondary flow consisting of two large-scale counter-rotating vortices arose due to enhanced centrifugal force. To reveal the flow characteristics at high Dean numbers, the trajectories of fluid particles were evaluated experimentally from the 3D velocity-field data measured using the HPTV technique. The present experimental results, especially the 3D particle trajectories, are likely to be helpful in understanding mixing phenomena in curved sections of various 3D curved micro-tubes or micro-channels, as well as in the design of such structures.