Spray Dryers: Modeling and Simulation

ABSTRACT This work presents a simulation study of the spray dryer operation using the whole milk suspension as the emulsion to be dried. Two approaches are used to obtain a general description of this operation. The first approach comprises a population balance model, in which drops and particles make up the discrete phase and are distributed into temporal compartments following their residence time in the dryer. Air is the continuous and well-mixed phase. Mass and energy balances are developed for each phase, taking into account their interactions. Constitutive model equations to describe the drop swelling and drying mechanisms as well as the heat and mass transfer between particles and hot air are also analyzed. The set of algebraic-differential equations obtained in this approach is solved by DASSL numerical code. The second approach involves a three-dimensional model solved by a computational fluid dynamic (CFD) code. The continuous air phase follows the time-averaged Navier-Stokes equations coupled with the RNG turbulence model while particle equations are set up in the Lagrangian model using the stochastic method to predict the particle trajectories. Experiments carried out in a pilot spray dryer generate input data for both model approaches. Results are compared to lead to a better understanding of the spray dryer operation.

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