| The significance of powder flow properties is apparent, since a wide variety of products are manufactured and processed in the form of powder across many industries. Powder flow properties are mainly correlated closely to both powder physical properties and mechanical properties, in addition to the material properties of the primary comprised particles. They also depend on the physical properties of the interstitial gas and the degrees of interaction between the gas and particles, leading to various powder states. Among these factors, powder size has a great effect on powder flow properties. In general, fine powders (with particle size smaller than 25--30 microm) are cohesive and tend to exhibit problematic flow such as arching, discontinuous transportation and poor fluidization. The poor flow properties of fine powders are mainly attributed to their relatively larger interparticle forces and challenge the applications of fine powders in recent years, for example, powder coating.;Another achievement of this study was the development of a new type of fluidized bed based on the special fluidization behaviors of fine powders in a rotating drum. This new fluidized bed requires no external gas supply, leading to an advantageous gasless fluidized bed which combines the advantages of a traditional fluidized bed and zero gas consumption. Several aspects of the new gasless fluidized bed were studied. First, the fluidization mechanism in the gasless fluidized bed was revealed. Second, comprehensive experiments identified 5 possible flow regimes for a fine powder in the gasless fluidized bed. Third, it was found that fluidization in the gasless fluidized bed can be improved by increasing wall-powder friction. Lastly, some specially designed baffles were employed to promote gasless powder fluidization, leading to a more practical baffled gasless fluidized bed. These studies prepare the new gasless fluidized bed to replace the traditional fluidized bed for suitable applications.;Keywords: fine powder; flow property; fluidization; nanoparticle; flow additive; rotating drum; gasless fluidized bed; powder coating;As the need to improve flow properties of fine powders increases, various flow aids have been developed. One of the widely used flow aids is additive which modifies the surface of fine particles so that the interparticle forces decrease and the flow properties of fine powders thus improve. In this study, fine powders of a wide range of flow properties were engineered using three types of nanoparticles as flow additives, allowing for a comprehensive study regarding the effects of nanoparticles on improving the flow properties of fine powders. This led to several achievements: first, an optimization of nanoparticle effects on fine powder flow was found by employing a series of powder characterization techniques. In particular, optimized formulations and concentrations of the nanoparticles were ascertained for powder coating. This can practically guide the usage of flow additives in powder coating and could also benefit other applications where flow additives are used. Second, by comprehensively investigating the flow characteristics of the fine powders with improved properties, a new fluidization characteristic gas velocity, Ubf, was proposed to characterize fluidization of fine powders based on powder bed expansion. Its estimation and validity has been thoroughly discussed. In addition, it was attempted to study a powder's interparticle forces at the microscale using an interfacial force microscope. |
