Levitating water droplets formed by mist particles in an acoustic field

Understanding the physics behind levitation and the flow field around suspended liquid droplets is key to enhancing the drying process of pharmaceuticals and food products. Here an acoustic levitator has been successfully integrated at the Advanced Photon Source for In-situ high-energy x-ray diffraction measurements on particles suspended in an acoustic field. It is demonstrated that acoustic levitation can be utilized to mimic the spray drying amorphization process under controlled conditions. Investigating the velocity field around levitating droplets is also important to understand the forces acting upon the droplets during the levitation process. This paper presents experimental results of the flow field in an acoustic field using Particle Imaging Velocimetry and high-speed imaging and using 3D finite element analysis. The finite element analysis was employed to evaluate the required experimental conditions. The finite element results of acoustically levitated droplets from an ultrasonic wave operating at 22 KHz are compared and discussed. The finite element simulation results are in good agreement with the experimental observations.