Fluidized bed rheology for granular media

摘要

Granular media, bulk solids and in particular dry granular fluidized beds are used in a variety of industries. Suspension rheology and the rheology of fluidized beds share certain similarities such as classification as two phase systems and the complex interplay between particle-particle interaction, bulk viscosity of the non-solid phase and the frictional and collisional parts of the solid phase. Simultaneous probing of rheology and fluidization of granular beds has been challenging and difficult. Despite the difficulty, characterization of powder flow is necessary for proper process design, quality control of the powder themselves and especially for proper reactor design and other fluidized bed applications. A high precision air bearing rheometer for characterization is introduced which is capable of measuring not only basic properties such as cohesion strength but also true powder rheology in the fluidized state via rotational and oscillatory tests augmented through the use of a classical pressure drop device attached to a rotational rheometer. Being able to measure small torques in a reproducible manner enables a proper rheological study of fluidized beds similar to the rheology of complex fluids in fluidized as well as consolidated states. The combination of a rotational rheometer with a fluidization setup allows real rheological measurements over a range of shear rates and shear stress on powder systems in a well-defined fluidization state.