Molecular tagging thermometry for transient temperature mapping within a water droplet.

We present the progress made in developing a molecular tagging thermometry (MTT) technique for achieving spatially and temporally resolved temperature measurements within a small water droplet over a solid surface. For MTT measurement, a pulsed laser is used to tag phosphorescent 1-BrNp.Mbeta-CD.ROH molecules premixed with water. Long-lived laser-induced phosphorescence is imaged at two successive times after the same laser excitation pulse. The temperature measurement is achieved by taking advantage of the temperature dependence of the phosphorescence lifetime, which is estimated from the intensity ratio of the acquired phosphorescence image pair. The measured transient temperature distributions can be used to quantify the unsteady heat transfer process inside convectively cooled water droplets over smooth or rough surfaces.