Solvent evaporation kinetics in spray drying and how to consider heat loss

Real (diabatic) spray drying processes have heat loss that affects drying kinetics. The heat loss depends on process parameters and on the type of spray drying equipment. Practically, heat loss can be determined by evaporating the solvent of a specific spray drying process with measurement of the outlet temperature after process equilibration. In this work, models to calculate the droplet evaporation time from an adiabatic (perfectly insulated) spray drying process are further developed to take heat loss into account. Comparison of different calculation models from water evaporation trials on a modified Buchi lab spray dryer with results from ANSYS 13.0 CFD simulations, show a good agreement for the introduced equations where heat loss is considered. The advantage of knowing the droplet evaporation time is that it condenses all relevant parameters of a specific spray drying process including material properties of the solvent to one single parameter affecting evaporation kinetics. The knowledge of the droplet evaporation time is of significant importance for scale-up activities, process transfers and optimizations as well as for particle engineering purposes.