CFD Modeling of Air Flow on Wall Deposition in Different Spray Dryer Geometries

Abstract

Wall deposition is one of the most conventional problems in the spray drying process.The operation of a spray dryer is affected by the wall deposition fluxes inside the equipment. In this study, computational fluid dynamic (CFD) simulation was used to investigate the effect of spray dryer geometry on wall deposition. A CFD model was developed for different geometries of spray dryer with a conical (case A) or a parabolic (cases B and C) bottom. The results implied that the parabolic geometry resulted in a lower deposition rate on the spray dryer walls. A comparison of results using the P-values (F-test) of the air velocity, in the conical and parabolic geometries, showed that there was a significant difference in air stability between them. The flow field in conical geometry case A was significantly more unstable, and parabolic geometry case C produced the most uniform airflow patterns. Moreover, the higher wall shear stress in case C, with lower values of the vorticity, would result in less wall deposition. Downloaded by [Selcuk Universitesi] at 17:49 05 February 2015 2 NOMENCLATURE k G Production of turbulence kinetic energy due to the mean velocity gradients G Production of turbulence kinetic energy due to buoyancy m M Source term in continuity equation F M Source term in momentum equation h M Source term in energy equation i u Gas velocity vector (m/s) i g Gravity component (m 2 /s) k S User defined source term S User defined source term p c Heat capacity (J/kg.K) T Temperature (k) t Time (s) Greek Letters Density (kg/m 3 ) Viscosity (kg/m.s) Downloaded by [Selcuk Universitesi] at 17:49 05 February 2015 3 k The turbulent kinetic energy (m 2 /s 2 ) The energy dissipation rate (m 2 /s 3 ) t The turbulent viscosity (kg/m.s) V Friction velocity (m/s) w Wall shear stress (kg/ms 2 )

Low-Cost Eddy-Resolving Simulation in the Near-Field of an Annular Swirling Jet for Spray Drying Applications

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Numerical Study and Experimental Validation of Skim Milk Drying in a Process Intensified Counter Flow Spray Dryer

“…During the experimental campaign, considerable heat losses were observed from the dryer walls. Numerous studies have relied on fitting a suitable overall heat transfer coefficient by comparing dry runs (without feed spray) and matching the inlet and outlet temperatures [19,27,34,58,59]. The heat loss from the dryer walls was thus estimated following this approach; this was performed by conducting a dry run (no feed injection).…”

CFD Model of Particle Agglomeration in Spray Drying

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