Gas Fluidisation of Nano-particle Assemblies: Modified Geldart classification to account for multiple- scale fluidisation of agglomerates and clusters

The fluidisation phenomenon is best explained by the balance of short and long range forces evaluated in a given powder assembly. The long range body forces include gravity, solid friction, buoyancy, interstitial fluid drag to include both the viscous (skin) friction and the form drag. The short-range forces, also known as particle surface-active forces can be due to physical (e.g. van der Waals, capillary, electrostatics) or chemical (e.g hydrogen bonding) or electrochemical effects such as electrophoretics. The relative magnitudes of the short-range and longrange forces are in turn determined by the physical properties of the solid particles such as particle size, particle shape and solid density and the properties of the carrier fluid such as fluid density, fluid viscosity and surface tension. It is well-known that with small particles in the sub-millimeter size range, the interstitial fluid effects dominate when the immersed weight becomes of the same order as the fluid drag forces which scale inversely proportionally to particle size.