Versatile high-temperature heating system for drying droplets in the TinyLev acoustic levitator

Droplet drying has importance in a range of applications from aerosols and pollutant transport to manufacturing powdered drug formulations. Single droplet drying is often studied to provide insights into the drying process; however, the methods applied are often limited by an inability to dry at high temperatures without the need to attach the droplet to a solid surface-pendant or sessile droplets. This paper discusses the development of an easy to handle and in-expensive acoustic levitator to dry droplets from ambient temperature up to 90 °C. High-temperature drying is rarely achieved using acoustic levitation, apart from a few devices being extensively engineered and expensive. Integrating a TinyLev acoustic levitator, a bespoke compact heating system has been developed, providing stable drying conditions across a range of temperatures. Iterations of the heater design enabled issues of temperature fluctuations to be minimized when the acoustic levitation is triggered, as well as achieving spatial and temporal stability of the temperature field in the levitation zone. Pilot experiments on droplet drying of water and a complex fluid containing surfactants demonstrate the potential of the technique, providing fundamental insights into the drying process across a range of temperatures.