Abstract
This research presents 3D steady-state simulations of a skim milk spray drying process in a counter-current configuration dryer. A two-phase flow involving gas and discrete phase is modeled using the Eulerian–Lagrangian model with two-way coupling between phases. The drying kinetics of skim milk is incorporated using the Reaction Engineering Approach. The model predictions are found to be in accordance with the experimental temperature measurements with a maximum average error of 5%. The validated computational model is employed further to study the effects of nozzle position, initial spray Sauter Mean Diameter (SMD), air inlet temperature, and feed rate on the temperature and moisture profiles, particle impact positions, drying histories, and product recovery at the outlet. The location of the nozzle upwards (≈23 cm) resulted in maximum product recovery and increased the mean particle residence time at the outlet. A similar trend was observed for the highest feed rate of 26 kg/h owing to the increased spray penetration upstream in the chamber. The maximum evaporation zone was detected close to the atomizer (0–10 cm) when the spray SMD is 38 µm, whereas it shifts upstream (40–50 cm) of the dryer for an SMD of 58 µm. The high air inlet temperature resulted in enhanced evaporation rates only in the initial 10–20 cm distance from the atomizer. The results obtained in this study are beneficial for the development of the novel vortex chamber-based reactors with a counter flow mechanism.
Highlights
This study investigates a novel compact dryer for producing skim milk powder based on a counter-current mechanism
The spray dryer operates in a counter flow configuration with feed injected from the bottom, opposite to the direction of the air that enters from the top of the chamber via a small inlet tube
Model validation is completed by comparing numerical results to the experimental Model validation is completed comparing numerical results4.toThe theerror experimental temperature measurements in thebyskim milk test; see Figure bars indicate temperature measurements thedata skim milkitstest; seevalues
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. A process first introduced by Percy in 1870 [1], is the most widely used method for producing milk powders. The process requires atomization of a concentrated liquid feed into tiny droplets (typical 10–200 μm) that undergo evaporation to produce dry solid powder [2,3]. In the Netherlands, milk powder contributes to around 13% of the total dairy exports of the country [4]. While counter-current dryers are thermally more efficient and require lesser energy input, owing to bigger temperature gradients between droplets and the air, than the co-current dryers [5,6], they are limited to thermally resistant materials such as detergents [6,7]
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