Simulation of a single spherical droplet drying considering shrinking and temperature profiles: first drying stage

Abstract

A model including simultaneous droplet heating and water evaporation is proposed to simulate temperature, shrinking and mass profiles of a spherical droplet subjected to convective drying, being valid for the first drying stage. Experimental data on drying skim milk and colloidal silica obtained in the literature were used for validation, but there is no restriction in the model that prevents it from being suitable for other materials. There were not significant differences observed concerning to the droplet components (dissolved or insoluble materials). The initial heating time of the particle upon reaching the constant temperature is relatively short ($\Delta t\approx7s$) for both simulated materials and water evaporation during the first drying stage occurs mostly at the wet bulb temperature of the air. Discrepancy between simulated and experimental values did not exceed $9\%$ for skim milk and $7\%$ for colloidal silica in this first stage, indicating good applicability of the model. Considering the applicability of the model in a more generic way, Whitaker correlation evaluated at the film temperature showed better results. Finally, the small discrepancy found is discussed and some improvements are proposed.

Key words
Critical moisture; differential-algebraic equations; first drying stage; single droplet drying; spray drying