Bridging the Multiscale Gap: Using CFD Simulations to Translate Spray Drying Process Conditions Into a Single Droplet Drying Setup

The development of industrial spray drying processes often relies on empirical studies of the impact of process and formulation parameters, as limited mechanistic insights can be gained on the morphology development of spray droplets during trials. Understanding the impact of process and formulation parameters on particle morphology is crucial for producing high-quality powder products, as the particle morphology is associated with product properties such as powder flowability. Single droplet drying methods offer the unique opportunity to directly monitor droplets during drying, expanding the mechanistic understanding of morphology development and drying kinetics of droplets. However, a major challenge of single droplet drying setups is their inability to accurately replicate time–temperature histories of droplets in spray dryers, as these histories are unfeasible to determine experimentally. To overcome this challenge, this study uses computational fluid dynamics to simulate the temperature, relative velocity, and residence time of air and particles along the spray tower. The model was validated by experimental data (primarily air outlet temperature, with air outlet velocity as a secondary check) from a pilot-scale spray dryer. Based on the simulation results, a time–temperature history was determined and applied to a hanging-droplet drying platform, allowing the independent investigation of the inlet and outlet air temperature of the spray drying process in a model environment. It was shown that the locking point can be influenced via the inlet air temperature, while final particle morphology is mainly steered by the outlet air temperature. Drying at dynamic temperature conditions is thus assumed to be crucial when investigating phenomena that are closely connected to the locking point, such as agglomeration. This study marks a crucial step toward replicating spray drying–like conditions in single droplet drying.