Spray drying: Influence of developing drop morphology on drying rates and retention of volatile substances. 2. Modeling

Two numerical models simulating the drying of a drop containing dissolved solids are presented. The first is a simple model, to predict the drying rate and temperature history of a drying drop during the period of morphological development. The model assumes that the drying rate is controlled by the rate of heat transfer from the drying gas to the drop. The second model utilizes the convective diffusion equations for a drop containing SF6 (a model volatile component), water, and sucrose. Concentration profiles in the liquid are treated as radially symmetric. A single, centrally located bubble containing water vapor, SF6, and an inert gas is included to simulate the effects of morphological development. This bubble never ruptures. The model predicts a net inward flux of SF6 from a sufficiently negative value of the cross-diffusion coefficient after the drop surface is sufficiently dry. The model predictions are in good agreement with experimental data.