Research Article

Experiments in Fluids

, Volume 52, Issue 3, pp 795-807

First online:

Particle image velocimetry and infrared thermography in a levitated droplet with nanosilica suspensions

  • Abhishek SahaAffiliated withDepartment of Mechanical Materials and Aerospace Engineering, University of Central Florida
  • , Saptarshi BasuAffiliated withDepartment of Mechanical Engineering, Indian Institute of Science
  • , Ranganathan KumarAffiliated withDepartment of Mechanical Materials and Aerospace Engineering, University of Central Florida Email author 

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Preferential accumulation and agglomeration kinetics of nanoparticles suspended in an acoustically levitated water droplet under radiative heating has been studied. Particle image velocimetry performed to map the internal flow field shows a single cell recirculation with increasing strength for decreasing viscosities. Infrared thermography and high speed imaging show details of the heating process for various concentrations of nanosilica droplets. Initial stage of heating is marked by fast vaporization of liquid and sharp temperature rise. Following this stage, aggregation of nanoparticles is seen resulting in various structure formations. At low concentrations, a bowl structure of the droplet is dominant, maintained at a constant temperature. At high concentrations, viscosity of the solution increases, leading to rotation about the levitator axis due to the dominance of centrifugal motion. Such complex fluid motion inside the droplet due to acoustic streaming eventually results in the formation of a ring structure. This horizontal ring eventually reorients itself due to an imbalance of acoustic forces on the ring, exposing larger area for laser absorption and subsequent sharp temperature rise.