CFD Evaluation of Droplet Drying Models in a Spray Dryer Fitted with a Rotary Atomizer

Abstract

Computational fluid dynamics (CFD) modeling of spray dryers requires a simple but sufficiently realistic drying model. This work evaluates two such models that are currently in discussion; reaction engineering approach (REA) and characteristic drying curve (CDC). Two versions of the CDC, linear and convex, drop in drying rate were included. Simulation results were compared to the overall outlet conditions obtained from our pilot-scale experiments. The REA and CDC with a linear drop in drying rate predicted the outlet conditions reasonably well. This is contrary to the kinetics determined previously. Analysis shows that the models exhibit different responses to changes in the initial feed moisture content. Utilizing different models did not result in significantly different particle trajectories. This is due to the low relaxation time of the particles. Despite the slight differences in the drying curves, both models predicted similar particle rigidity depositing the wall. For the first time in a CFD simulation, the REA model was extended to calculate the particle surface moisture, which showed promising results for wet particles. Room for improvement was identified when applying this concept for relatively dry particles.

Keywords:

• CFD
• Droplet drying model
• Rigidity
• Spray drying

ACKNOWLEDGEMENT

This project was funded by the Ministry of Science, Technology and Innovation of Malaysia (Grant number: 03-01-02-SF0046). The first author thanks Dr. Huang Lixin of Research Institute of Chemical Industry of Forrest Products, China, for useful discussions and case studies on the modeling work. Useful suggestions by Dr. Chen Fang Xi CAD-IT Consultants, Singapore, in implementing the drying models are also greatly acknowledged.