Mathematical modeling of drying behavior of single emulsion droplets containing functional oil

Abstract

In this study, a mathematical model was developed to study drying behavior of single emulsion droplets containing functional oil. For this aim, drying process was divided into two successive steps by considering a receding emulsion/air interface in the first step and a wet core/crust interface in the second step. A system of differential and algebraic equations was solved numerically using an arbitrary Lagrangian-Eulerian (ALE) framework by considering temperature-dependent thermophysical properties for the droplet/particle constituents. The developed model was then validated using experimental drying data obtained for emulsion droplets containing skim milk powder and walnut oil as wall and core materials, respectively. After validation of the developed model, the effects of drying air temperature (80-140 degrees C), air velocity (0.02-3 m/s), and droplet initial diameter (0.01-0.75 mm) on the droplet/particle drying behavior were systematically investigated. The simulation results agreed fairly well with the experimental data indicating the suitability of the developed model for predicting drying characteristics of liquid droplets containing functional oils. According to the results, drying behavior of emulsion droplets/particles was significantly affected by the variables considered. This work further demonstrated the merits of phenomenological models for tracking and controlling the physicochemical attributes of droplets/particles containing functional ingredients. Accordingly, the developed model could facilitate ongoing attempts to improve the encapsulation quality and to minimize the lipid oxidation in large-scale spray drying systems being employed for microencapsulation of functional oils. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.