Buckling of Spray Drying Drops

Abstract

An understanding of the morphological transformations of drying, particle-laden drops, is important for industrial processes such as spray drying, where drops of particulate suspensions dry rapidly to produce granules. The high drying rates during spray drying produce particle-packed shells saturated with liquid, which may buckle, transforming spherical shells into crumpled granules. The morphology of granules depends on the particle’s mechanical properties and size, interparticle interaction, and drying rates. A recent theory has shown that the morphological transformations are controlled by a dimensionless parameter that measures the competition between the compressive stress generated by capillary forces and the elastic strength of the packing. In this work, we perform experiments on a spray dryer with suspensions containing particles of varying sizes and moduli to test the theoretical predictions. We show remarkable agreement with the theory over many orders of magnitude of the dimensionless parameter. The results provide a fundamental understanding of the morphological changes observed in fast-drying drops containing particles and enable the design of buckle-free granules with desired properties.