Concentration fields in evaporating droplets

An analytical solution of the problem of diffusional mass transport inside a spherical binary mixture droplet is presented. The droplet evaporates according to the d(2)-law. Mass fraction profiles of the mixture components are obtained as series expansions in confluent hypergeometric, Legendre and sine/cosine functions. The analytical description is valid for arbitrary ratio of the rate of shrinkage of the sphere surface to the diffusion coefficient in the liquid phase. The results allow for a prediction of the morphology of the dried particles, i.e., whether hollow or solid spheres result from the drying process. The field of application of the results presented is spray drying of solutions of solid substances. (C) 2004 Elsevier Ltd. All rights reserved.