Design, CFD validation, and process optimization of a cyclone integrated pilot scale vacuum spray dryer for functional food production

Abstract

Abstract This study presents the design, Computational Fluid Dynamics (CFD) validation, and Reynolds Stress Model (RSM) optimization of a cyclone separator integrated into a pilot-scale vacuum spray dryer for functional food production, comprising (Part A) cyclone design and validation, and (Part B) system-level process optimization. The cyclone was evaluated using Koch-Licht and Enliang-Yingmin theoretical models with gas properties corrected for vacuum operation (4 kPa, 90°C). CFD simulations employing the Reynolds Stress Model with Discrete Phase Model particle tracking characterized swirling flow and separation behavior. The Rosin-Rammler parameters for CFD inlet PSD (d̄ = 4.2 µm, n = 2.1) were estimated from nozzle specifications, while the collected powder PSD measured by laser diffraction yielded Dx(50) = 55.7 ± 0.87 µm (d̄ = 70.7 µm, R2 = 0.984), indicating a ~17-fold size ratio between the collected coarse-powder fraction and the CFD inlet fine particle fraction. Experimental collection efficiency (97.8 ± 0.2%) agreed closely with the Koch-Licht prediction (98.38%). Using the correct vacuum gas density (0.039 kg/m3 at 4 kPa, 90°C), the CFD-predicted pressure drop (156 Pa) was consistent with the theoretical values (153–158 Pa); because pressure drop scales linearly with gas density, the close agreement among the three methods is preserved. For Part B, Central Composite Design optimized six quality responses with R2 values of 0.756-0.987 and non-significant lack-of-fit. Optimal conditions (130 °C, 80 m3/h) produced powders with 3.9% moisture, 93% solid recovery, large particle size (~78 µm), and 89% solubility. Scanning Electron Microscopy (SEM) confirmed spherical morphology (16-56 µm). This integrated approach provides validated engineering data for cyclone design in vacuum spray drying of functional foods.