(423e) Particle Circulation Motions in an Evaporating Droplet

Particle deposition inside evaporating droplets has various applications including bioassays, spray drying, and microelectronics. In an evaporating particle-laden droplet, transport of particles influences the particle deposition pattern. Evaporative cooling of the droplets results in Marangoni currents near the droplet surface, and the Marangoni currents together with the internal edgeward flow form circulations inside the droplet. The direction of the Marangoni flow has been shown to change for various conditions. Hu and Larson (2005) found the direction of the Marangoni flow reverses at a critical contact angle. Ristenpart (2007) showed that the critical contact angle is related to the thermal conductivity of droplet and of the substrate respectively. Furthermore, Xu (2007) observed a stagnation point where the surface flow has opposite directions on either side. Recently, Barash (2015) showed that a multi-cellular flow exists inside the droplet by numerical simulation. In this work, we model the evaporating particle-laden droplet using the finite element method. Simulations show the variation of flow structures under various heating conditions, and can be used to predict deposition patterns.