The Acoustic Tube Levitator – A Novel Device for Determining the Drying Kinetics of Single Droplets

TLDR: An acoustic tube levitator was developed and used for investigating the drying behavior of single droplets (d D,0 ≃1.0 mm) containing water and a certain fraction of inert, solid material such as glass beads with a mean diameter of d s =30 μm.

Abstract: An acoustic tube levitator was developed and used for investigating the drying behavior of single droplets (d D,0 ≃1.0 mm) containing water and a certain fraction of inert, solid material such as glass beads with a mean diameter of d s =30 μm. A glass tube surrounds the transducer and reflector of the acoustic tube levitator, hence increases the radial stability of the droplet and shields it against disturbances from outside. A CCD camera and a back-light illumination are used to observe the evolution of the droplet diameter and the vertical position of the droplet. Ambient temperature, initial volume and initial solid mass fraction of the droplet were systematically varied. From the measured droplet diameter and the position of the mean density, the moisture content and the mean porosity of the drying droplet/grain can be determined as a function of time.