Fundamentals of dry coating in fluidized bed

This thesis is devoted to the study of a novel dry coating method in fluidized bed - Dry Coating of Particles in Spouted bed (DCPS). The main objectives of this work were to study the feasibility of the process, both quantitatively and qualitatively, and to compare the results with coating by conventional mechanical mixing. Aerosol mechanics is applied to account for the following: 1) collision between the guest and host particles in a spouted bed (analysis of guest-host particle inertial fluid-dynamic interaction), and 2) to show how collision efficiency of guest particles with host particles affects the coating efficiency. An equation for relating coating efficiency to collision efficiency was derived. This equation predicts high coating efficiency for large-size guest aggregates and low coating efficiency for small-size guest aggregates. The experimental results confirmed the above predictions. It was established that large-size guest aggregates deformed during collision in the spouted bed resulting in patches over the surface of the host. This deposition mode results in large surface coverage. It was also established that the relative variation of coating among coated host particles by this method was very low. The relative variation of patches over the coated host surface was very low and from literature survey it was found that single particle coating resulted in non-uniform distribution over host particle surface [10]. Dry coating, by conventional mechanical mixing was investigated and compared with the novel dry coating method proposed in this thesis. This investigation demonstrated that coating by mechanical mixing resulted in non-uniform coating and harmful manifestation of guest particle agglomeration during the mixing process