P.U. Foscolo

A fully predictive criterion for the transition between particulate and aggregate fluidization

A simple general model for the interaction between a particle and the fluid in a fluidized suspension, enables a hydrodynamic criterion for the onset of bubbling in fluidized beds to be formulated in a compact and fully predictive form. Excellent agreement is found between the proposed criterion and experimental observations reported in the literature for liquid beds and gas fluidized systems operating under both ambient and elevated pressure condi

Generalized friction factor and drag coefficient correlations for fluid-particle interactions

Abstract The pressure drop correlation: proposed on the basis of theoretical considerations, is compared with published experimental results obtained from high voidage fixed beds of spheres and is shown to represent a significant improvement over the established Ergun equation. It is used to produce drag coefficient correlations for individual particles in the bed which in turn yield a general and fully predictive expression for the drag force on a particle in a fluidized suspension.

A predictive model for the equilibrium composition and inversion of binary-solid liquid fluidized beds

Abstract The concept of complete segregation of a binary-solid particulate fluidized bed is generalized to accommodate cases where the bottom zone contains an equilibrium mixture of the two solid components. The model is fully predictive and provides a complete explanation of the “inversion phemonenon” in close agreement with recently published experimental studies.

The influence of temperature on the quality of gas fluidization

Abstract Results are presented of an experimental study of the effect of temperature (up to 910°C) on the fluidization characteristics of three powders, chosen to span the fine-to-moderate size range. The major conclusions are that: the onset of bubbling, as measured by the minimum bubbling voidage, is progressively delayed with increasing temperature—in good agreement with theoretical predictions; and the quality of fluidization in the bubbling regime, quantified in terms of the standard deviation of bed pressure fluctuations, may be predicted for elevated-temperature systems from experiments conducted under ambient conditions.

On the minimum bubbling voidage and the Geldart classification for gas-fluidised beds

Abstract Reported experimental findings for the effect of systematic variation of all the relevant variables on the bubbling point of gas-fluidised beds are shown to be in agreement with the predictions of a general fluid dynamic stability criterion for fluidisation. The criterion is also applied to the evaluation of the stabilising effect of fines addition and, somewhat speculatively, to the prediction of the boundary between the Geldart Group A and Group C powders.

Dynamic similarity rules: Validity check for bubbling and slugging fluidized beds

Abstract An experimental verification is reported on the validity of scale-up rules for fluidized beds, which were proposed and discussed previously [6]. Five different gas-solid systems were investigated: three of them dynamically similar, the fourth one characterized by non-spherical particles, and the last one completely out of scale. The minimum fluidizing velocity, as well as the bed expansion and the instantaneous pressure fluctuations inside the bed, were measured at different gas flow rates. The analysis of the experimental data confirms the applicability of the scaling rules when the fluidized beds exhibit bubbling behaviour. However, for increased aspect ratio, so that the slugging regime prevails, all the dimensionless values of the frequency and standard deviation of the pressure signal differ significantly.

Fluid pressure loss in slugging fluidised beds

The pressure drop across a slugging fluidised bed increases with increasing gas velocity above the value representing the weight of suspended particles; this is in contrast to the situation for bubbling and homogeneously fluidised systems. The phenomenon appears to be largely due to the transformation, and eventual dissipation, of the potential energy developed by the rising solid slugs; it is fully quantifiable on this basis, and appears to be independent of the extent of particle-particle and particle-wall frictional interactions, both of which can play significant roles in other aspects of slugging behaviour. A mechanism is proposed for the energy transformation chain that gives rise to the observed pressure loss in the fluid.

Scaling relationships for fluidisation: the generalised particle bed model

The purpose of this communication is to present scaling relationships based on a formulation of the equations of change that encorporates fully quantifiable expressions for the primary fluid-particle interaction terms, including the effect of particle pressure

STEADY-STATE EXPANSION CHARACTERISTICS OF MONOSIZE SPHERES FLUIDISED BY LIQUIDS

Abstract Velocity-voidage experiments conducted on beds of truly monosized and spherical plastic particles fluidised by solutions of glycerol, enable the change of behaviour at high expansion conditions to be correlated with the unhindered particle Reynolds number.

The experimental determination of one-dimensional wave velocities in liquid fluidized beds

Abstract Three experimental investigations into one-dimensional wave propagation in liquid fluidized beds are reported: dynamic wave velocity measurements under incipient fluidisation conditions confirm the predictions of a theoretical expression that has been successfully applied to fluidization stability studies; continuity wave velocity determinations confirm a long established relationship; and bed collapse experiments on bubbling liquid fluidized beds lead to the evaluation of the dense phase void fraction and bubble hold-up.