A Fundamental Model of Particle Deposition Incorporated in CFD Simulations of an Industrial Milk Spray Dryer

Abstract

Particle deposition is an important, undesirable problem during the operation of spray dryers. A new mathematical model of particle deposition has been developed and implemented in the computational fluid dynamics (CFD) software FLUENT. The pseudo Ohnesorge number Oh* and Weber number We* have been used to formulate the model to the determine possibility of particle deposition. The reentrainment of the particles back into the dryer chamber was determined according to the wall shear stress. The transient multiphase flow process in an industrial spray dryer that produces around 9 tonnes of milk powder per hour was simulated to validate the deposition model. The numerical results show that reentrainment of particles into the dryer chamber is significant at the chamber walls. The deposition intensity has been found to be higher near the adjunctions of the ceiling wall, the vertical wall, and the conical wall because of smaller wall shear stress. The distribution of wall temperature, Oh* and We*, which has important influence on wall deposition, has been obtained from the numerical results. More experimental and computational work is required for future validations.

Keywords:

• Computational fluid dynamics
• Fluent
• Industrial-scale spray dryer
• Multiphase flow
• Ohnesorge number
• Particle deposition
• Reentrainment
• Weber number

ACKNOWLEDGMENT

This project was sponsored by the Gardiner Foundation and Dairy Innovation Australia Ltd., Melbourne, Australia.