Quantitative Measurements of Internal Circulation in Droplets Using Flow Tagging Velocimetry

摘要

We demonstrate the use of the photoactivated nonintrnsive tracking of molecular motion flow tagging technique to obtain quantitative velocity measurements in free falling water droplets and in electrohydrodynamic Taylor cones. A simple ray tracing procedure is outlined to remove the optical distortion caused by the droplet surface curvature. This correction is applied to free falling droplet images, and the vertical component of velocity is measured across the droplet. Maximum vertical velocities in the droplet are 15.9_3.3 mm/s. Without ray tracing, the optical distortion is shown to cause errors in the sign of velocity as well as errors of over 100/100 in velocity magnitude. Preliminary velocity measurements in a Taylor cone are also presented. Centerline velocities in the Taylor cone are approximately 4 _/s.