Transport Phenomena in Functional Droplets

Abstract

Liquids containing functional materials are often used in spray systems either to generate surface coating where droplets land on solid substrates or to prepare crystalline and amorphous particles where droplets are dried in-flight and then collected for mass production. Most of these applications involve spraying droplets into a hot environment, whose temperature and velocity vary depending on the application. This allows the liquid to vaporize leading to precipitation and pyrolization of the functional materials, which subsequently attain its final form before being collected or impacted with the substrate. In this chapter, we shall discuss the transport processes inside drying droplets containing functional materials to identify some critical behavior and characteristics. Fundamentally, the life of a sprayed functional droplet is influenced by several competing physical processes such as reaction kinetics, precipitation dynamics, droplet hydrodynamics, and as such a proper balance between the associated characteristic timescales is necessary to achieve desired final product. We shall discuss a large group of experimental and numerical studies performed on single droplets, either levitated or convected, that paved the way to our current understanding. By reviewing these studies on single droplet, the goal of this chapter is to highlight the importance of the thermo-physical phenomena inside the droplets for spray processes involving functional liquids.