A computational fluid dynamic study of a low-humidity co-current spray dryer

Abstract

Because spray drying uses high-temperature gas as the drying medium and the deposits on the wall cannot be avoided in practical spray dryers, the products are subject to degradation by overheating. In order to reduce the degradation of the active components in the dried powder, a low-dew-point (LDP) spray dryer is proposed and evaluated via a computational fluid dynamic (CFD) model. A cylinder-on-cone spray dryer with pressure nozzle is investigated numerically with a commercial CFD code. The effects of low inlet air humidity and temperature on the gas flow patterns, droplet trajectories and overall dryer performance are investigated. The volumetric evaporation rate values, volumetric heat transfer intensity and thermal energy consumption per unit evaporation of water were computed and compared for evaporation of pure water in a spray chamber 2.215 m in diameter with a cylindrical top section 2.0 m high and a bottom cone 1.725 m high. Although a smaller product capacity is obtained compared with the normal spray dryer, it has advantages for drying heat-sensitive materials. © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.