78th Annual Meeting of the APS Division of Fluid Dynamics (Nov 23 — 25, 2025)

V003: Shattering Shells: Shock-Driven Atomization during various stages of an Evaporating Nanofluid Droplet

This video presents a first-of-its-kind experimental investigation of how a temporally evolving shell in an evaporating nanofluid droplet affects its shock-induced atomization. Understanding the breakup of such droplets under extreme aerodynamic loading is essential for a wide range of applications. In this study, we examine the atomization dynamics of an evaporating acoustically levitated TM-10 nanofluid droplet subjected to shock flow at different stages of evaporation.Droplet evaporation increases nanoparticle concentration, viscosity, and agglomeration, leading to interfacial nanoparticle accumulation. As evaporation progresses, the interface undergoes a sol-gel transition and eventually develops into a solid outer shell at high packing densities. This evolving shell drastically alters the droplet's aerodynamic response.High-speed visualizations reveal that unlike pure liquid droplets, which undergo RT, KH driven breakup, nanofluid droplets with shells exhibit distinct fragmentation behaviors depending on the stage of shell evolution. Gelatinous shell inhibit deformation, producing bags-on-sheet mode, followed by puncture, jetting, and shell delamination, whereas in late-stage solid shell regime brittle fracture dominates, resulting in catastrophic fragmentation. The shell constrains interfacial instabilities and modifies breakup pathways compared to the smooth secondary atomization of pure liquids.These findings demonstrate how shell evolution governs aerodynamic breakup dynamics by linking nanoparticle transport, interfacial transitions, and shock-droplet interactions across multiple timescales. The results have broad implications for sprays involving multicomponent and complex fluids with evolving composites in propulsion, drug delivery, food processing, agricultural spraying, inkjet printing, spray cooling, powder production, coating technologies, and material deposition.