Unsteady Heat Transfer and Phase Change Processes within Icing Water Droplets

Abstract

A lifetime-based molecular tagging thermometry (MTT) technique was developed and implemented to achieve simultaneous measurements of droplet size and transient temperature distributions within small water droplets on cold solid surfaces in order to quantify the unsteady heat transfer and phase changing processes within the small icing water droplets. The dynamic changes of the temperature distributions within small water droplets in the course of convective cooling process were quantified clearly from the MTT measurement results. Time evolution of the size change of the small water droplets (in terms of volume, height, contact area and the contact angle of the water droplet) due to evaporation was revealed quantitatively. The MTT technique was also used to visualize the transient behavior of the phase changing process within icing water droplets. Such measurements are highly desirable to elucidate underlying physics to improve our understanding about micro-physical phenomena associate with aircraft icing.