CFD Modelling of the Evaporation of Biphasic (solid-liquid) Individual Droplets in a Spray Dryer

Abstract

An analysis of the literature shows the capability of Computational Fluid Dynamics to represent the hydrodynamics and heat transfer within spray dryers, as well as the prediction of droplet collision, agglomeration and wall deposition. The literature also reveals that no model published so far describes the drying of individual droplets, the study of which is restricted to experimental methods such as ultrasonic levitation. This article presents an Euler-Lagrange three-phase numerical set-up to simulate the drying of individual droplets within a spray dryer. The defining parameters of both phases, i.e. air and the biphasic (solid-liquid) droplets are taken from a barbotine slurry used for ceramic tile production. A single droplet size has been used—the characteristic Rosin-Rammler droplet size from the distribution generated by an actual spray injector published previously in the literature. The model predicts the theoretical linear evolution of the square diameter according to the D²-law, and the temperature and mass exchange with the environment. This unique numerical set-up allows calculating the Stokes number associated with a given trajectory path as well, providing designers with an accurate degree of control over the fate of individual droplets. The proposed model is therefore a powerful tool intended to support the design and optimization of industrial spray dryers.