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Abstract
This article investigated the influence of drying rate on the shrinkage behavior of skim milk (SMP) droplets during convective drying, behavior which was then mapped using the Peclet number, Pe. The objective was to demonstrate the potential use of the Peclet number to predict the particle formation pathway during drying by defining a material-specific perfect shrinkage threshold using only the knowledge of initial process conditions and droplet characteristics. The shrinkage mapping was undertaken by drying relatively large and statically suspended droplets through adjustment of the drying air humidity. Its influence on droplet shrinkage behavior was observed through droplet diameter profile. Analysis of lactose, a non-skin-forming material, revealed perfect shrinkage behavior. Experiments with SMP, a skin-forming material, revealed that deviation from perfect shrinkage behavior occurred beyond the Peclet number threshold of 0.23–1.27 when droplets and the solid diffusion front were modelled as an equivalent sphere. The developed threshold was further used to predict the shrinkage behavior of atomized SMP droplets undergoing rapid drying in a spray tower.