Spray Drying Drop Morphology: Experimental Study

The objective of this study was to develop the capabilities to determine the effect of operational parameters on the morphology of powders produced by spray drying. A device used for monitoring morphological characteristics of a single suspended droplet was constructed. It allowed for monitoring and recording the images of a drying droplet as a function of time. The experimental drying was carried out for a number of systems that highlighted the effects of different controlling parameters, such as drying temperature and initial solute concentration. The experiments demonstrated that the shell structure of a drying droplet played an important role in determining the final dried particle morphology. In addition, the shell structure of a drying droplet varies from material to material, which increases the difficulty in the modeling prediction. Several materials with different physical properties, such as solubility and latent heat of crystallization, were investigated. Two sets of experiments, Ca(C 2 H 3 O 2 ) 2 versus NaC 2 H 3 O 2 and K 2 CO 3 versus Na 2 CO 3 , were run to examine the effect of material solubility. The effect of latent heat of crystallization was examined by experiment with NH 4 Cl versus NaCl. In summary, low drying temperature and material with high latent heat of crystallization (i.e., endothermic crystallization) were favorable for small, dense, and regularly-shaped particles. Materials that formed an elastic shell structure such as ammonium chloride led to hollow particle formation. Material with high solubility led to small, dense, irregularly-shaped particles. A higher initial solute concentration was favorable for the formation of a large dense particle.