Rheological behavior of aerated fine powders: modeling the influence of aeration and material properties below the fluidization threshold

Abstract

This study investigates the rheological behavior of marble powder, raw flour, and talc powder in a fluidized bed system equipped with a two-blade mechanical stirrer. Shear tests were conducted below the fluidization threshold (0 < U < U_mf) and at varying bed heights (0 < z < H_mf) to evaluate the influence of key factors on powder rheology. A rheological model, based on Janssen’s analysis, was developed to estimate the torque and normal stress within the particle bed, accounting for powder properties and aeration rate across small-scale bed heights (0 < z < H_mf). The Kozeny–Carman theory for cylindrical and linear pore structures was applied to describe pressure gradient variations. The model produced accurate predictions that aligned well with experimental data across all three powders, within the conditions of “0.1 < ΔP_z/ΔP_mf < 0.6” and “1 cm < z < H_mf.” Results showed that increasing bed height elevates both stress and the required torque, while aeration reduces these values without affecting stress distribution or the overall rheological properties. Notably, each powder exhibited distinct rheological behavior: Talc required the highest torque for stirring, whereas marble powder demonstrated superior flowability and rheological performance under agitation. Key factors influencing powder rheology include particle diameter, bulk density, cohesion, and internal friction angle. Additionally, very smooth and fine particles tend to agglomerate, complicating their flow and separation.