Implementation of an acoustic levitator experimental setup for the investigation into drying kinetics of single droplets

In recent years, acoustic levitation has increasingly been used to examine single droplets during the drying process. Steady levitation of individual droplets in an ultrasonic field enables the contactless observation during drying. An experimental setup for a levitator is designed and used to determine the drying and levitation behavior of two different material systems. To ensure hot gas flow patterns similar to a falling droplet the ultrasonic reflector has been modified as a multi-hole nozzle through which conditioned hot air is flowing toward the levitated droplet. The surface temperature of the individual droplets is constantly measured via an infrared camera while a CMOS camera is used to track the associated volume change during the drying process. The measured temperature data and volume change from contour data can be used to determine the individual drying rate periods, calculate the heat transfer coefficients and ultimately the drying kinetics with high accuracy over a wide range of parameters. First experimental results for a TiO2 suspension and a Bentonite suspension show good repeatability and prove the suitability of the presented method for determining the drying kinetics of single suspension droplets.