Simultaneous Measurements of Droplet Size and Temperature Distribution Within a Water Droplet by using Molecular Tagging Thermometry Technique

摘要

We present the research progress made in developing and implementing a novel lifetime-based molecular tagging thermometry (MTT) technique for achieving simultaneous measurements of droplet size and spatially-and-temporally resolved temperature distribution within small water droplets over solid surfaces for aircraft icing studies. For MTT measurement, a pulsed laser is used to "tag" phosphorescent 1-BrNp M|3-CDROH molecules premixed within a water droplet. Long-lived laser-induced phosphorescence is imaged at two successive times after the same laser excitation pulse. While the size and contact angle of the water droplet can be determined from the acquired phosphorescence images, the temperature measurement is achieved by taking advantage of the temperature dependence of phosphorescence lifetime, which is estimated from the intensity ratio of the acquired phosphorescence image pair. The feasibility and implementation of the lifetime-based MTT technique were demonstrated by conducting simultaneous measurements of droplet size and spatially-and-temporally resolved temperature distribution within a convectively-cooled water droplet over an aluminum test plate to quantify the unsteady mass and heat transfer processes within the small water droplet to elucidate underlying physics to improve our understanding about micro-physical phenomena associated with aircraft icing studies.