Deposition behavior of spray dried full cream milk, skim milk and whey particles were observed in a pilot scale dryer. Particle surface dominated with fats exhibit gradual decrease in deposition fluxes when transition from the initial adhesion to the subsequent cohesion mechanism. Whey protein, however, displayed significant differences in the adhesion and cohesion fluxes. Reduction of particle deposition on low energy chamber wall surface is more significant for the hydrophobic whey particles. Further analysis shows that the reduction in droplet-wall contact energy is larger for the more hydrophobic droplet, delineating weaker adhesion interaction. The results suggest that the hydrophobicity of the depositing particles in an important consideration when using lower chamber wall with lower surface energy. This is in addition to the effect of particle rigidity and deposition strength as reported previously.
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 )
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