Single-Droplet Techniques for Analysis of Evaporation Kinetics and Particle Morphology in Spray Dryers

Barnaby Miles, Lukesh K. Mahato, Rachael E.H. Miles, Emmanuelle Costard, Jewe Schröder, Arend Dubbelboer, JONATHAN P. REID, University of Bristol

     Abstract Number: 151
     Working Group: Aerosol Physics

Abstract
Investigation into the impact of droplet drying kinetics on the morphology of the resultant dried particle is crucial for understanding the spray drying process. Understanding the impact of the drying conditions on the resultant powder properties can help increase the spray dryer efficiency and product quality (Eijkelboom et al. 2024). Experiments in spray dryers have struggled to monitor the drying of the individual droplets directly, whereas single droplet drying (SDD) experiments have been shown to be successful in relating the drying behaviour of single droplets to the resultant particle morphology (Miles et al. 2024). However, SDD techniques struggle to represent the droplet size and temperature profile differences seen in spray dryers (Eijkelboom et al. 2023), so more work is needed to demonstrate if they are relevant for helping increase our understanding of the drying process in spray dryers.

Here, we present novel investigations into the drying kinetics of a range of fat free, dairy-based powders, the impact of their drying behaviour on the final particle morphology and comparative generation of particles in an SDD technique against a small-scale Büchi B290 spray dryer.

An electrodynamic balance was used to characterise the evaporation behaviour of the skimmed milk powders which, coupled with the SADKAT model (Robinson and Hardy (2022)) and the diffusion model reported by Siemons et al. 2019, allowed us to predict the SDD conditions that would reproduce the drying conditions experienced by droplets in a Büchi spray dryer. Using a falling droplet column we then collected samples of particles that had been generated under equivalent drying conditions to those in a Büchi spray dryer (Miles et al. 2025). SEM analysis of the particles showed we had successfully generated comparable morphologies in the SDD and spray dryer samples.