Molecular Tagging Technique for the Simultaneous Measurements of Flow Velocity and Temperature Fields

Abstract

We report recent improvements to the Molecular Tagging Velocimetry and Thermometry (MTV&T) technique for the simultaneous measurements of velocity and temperature fields in fluid flows. Instead of using tiny particles, specially-designed phosphorescent molecules, which can be turned into long-lasting glowing molecules upon excitation by photons of appropriate wavelength, are used as tracers for both velocity and temperature measurements. A pulsed laser is used to tag the tracer molecules in the regions of interest, and the movements of the tagged molecules are imaged at two successive times within the photoluminescence lifetime of the tracer molecules. The measured Lagrangian displacement of the tagged molecules between the two image acquisitions provides the estimate of the fluid velocity vector. The simultaneous temperature measurement is achieved by taking advantage of the temperature dependence of phosphorescence lifetime, which is estimated from the intensity ratio of the tagged molecules in the two images. The implementation and application of the MTV&T technique are demonstrated by conducting simultaneous velocity and temperature measurements in the wake region of a heated circular cylinder and a transient electroosmotic flow (EOF) inside a microchannel.