Towards energy-efficient spray drying: Geometric optimization of an ACLR nozzle for atomizing concentrated feeds

Spray drying is a key method for large-scale production of food powders but remains among the most energy-intensive processes in the food industry. Increasing the solids content of liquid feeds can lower thermal energy demand; however, higher viscosities complicate atomization. The Air-Core-Liquid-Ring (ACLR) nozzle presents a promising approach, as it enables atomization of viscous feeds at low pressures (<0.8 MPa) and low air-to-liquid ratios (<1). Nevertheless, existing ACLR designs suffer from internal flow instabilities, leading to fluctuations in liquid lamella thickness and broad droplet size distributions. This study applies a validated CFD model to systematically investigate the influence of key geometric parameters on lamella stability for feeds with up to 54% wt. dry matter (1.33 Pa·s viscosity). The results indicate that a shorter outlet length, a larger chamber inclination, and rounded internal edges promote thinner and more stable lamellas. An optimized design incorporating these features was manufactured and experimentally evaluated, yielding a narrower droplet size distribution than the reference design, even at operating pressures and air-to-liquid ratios reduced by 40%. ... mehrThese findings demonstrate the energetic (of up to 45% when compared to a pressure-swirl nozzle) and operational savings when applying the ACLR nozzle at industrial scale.