Spray drying of highly viscous feeds: Modeling the internal flow of an ACLR atomizer for non-Newtonian liquid feeds with high dry-matter contents

Spray drying is a widely used method for producing food powders in large quantities, but it also has a high energy demand. To address this, researchers aim to increase the dry-matter content of liquid feeds, which poses the challenge of having to atomize high-viscosity liquids into fine droplets. The Air-Core-Liquid-Ring (ACLR) nozzle offers a solution by inducing an internal annular flow, though it can present internal instabilities. This study numerically investigates how high feed viscosities, of up to 1.3 Pa · s, influence the internal flow conditions. We confirmed that, even at this viscosity range, the internal instabilities can be strongly reduced while maintaining air-to-liquid ratios below 1 and pressures below 1 MPa. This is much lower than pressures of pressure-swirl nozzles and ALRs of external-mixing nozzles, which are both more commonly used in the industry. A CFD model was successfully adapted to predict the internal flow behavior and it can be used to evaluate process conditions outside experimental capabilities.