S.P. Waldram

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 unified model for particulate expansion of fluidised beds and flow in fixed porous media

Abstract A model is derived for a fluidised bed that enables its steady state particulate expansion to be predicted as a function of superficial velocity from the initial (packed bed) condition to the final fully expanded (single suspended particle) state. These predictions are in good agreement with the empirical correlations and functional dependencies found by Richardson and Zaki[1,2] over the full range of flow conditions. The derivations incorporat revisions in the form of the pressure drop correlations for flow in porous media that are justified on theoretical and empirical grounds.

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.

A simple mechanistic description of the unsteady state expansion of liquid fluidised beds

On considere les forces agissant sur une particule seule du lit, la force de trainee particulierement

On the Kennedy and Bretton model for mixing and segregation in liquid fluidized beds

Abstract The foundations and applications of the Kennedy and Bretton model for mixing and segregation in liquid fluidized beds containing two sizes of equal density particles are critically examined. A direct method of solution that avoids all the difficulties and pitfalls of previous methods is presented.

Fluidization quality: A criterion for indeterminate stability

Abstract Voidage inhomogeneities in fluidized beds may rapidly decay or grow to result respectively in unambiguously stable (particulate) or unstable (aggregate) behaviour. Where growth or decay rates are small, disturbances may propagate through the bed at effectively constant amplitude. This phenomenon is examined in the light of a predictive model of the fluidized state; this provides a general criterion for indeterminate stability, in good agreement with both new and previously published observations, that leads to a global map for the quality of fluidization by ambient water.

Dynamic compensation of transient responses and the evaluation of system moments

Abstract A dynamic measurement technique is proposed in which the datum against which the measurement is made is itself a function of time. A general analysis, in terms of the system moments, demonstrates the advantages of the method which is further illustrated by analogue simulations of particular examples.

A REVIEW OF APPLICATIONS OF A FLUID-PARTICLE INTERACTION MODEL TO PREDICTIONS OF FLUIDISED BED BEHAVIOUR

A simple hydrodynamic model for the interaction of particles with a fluid has been applied to a number of problems in fluidisation. It leads to quantitative predictions, in good agreement with experimental findings, of the onset of aggregate (bubbling) behaviour in both gas and liquid beds, and inversion phenomena and concentration profiles in binary liquid beds.

Some general observations on the recycle flow model

Abstract Recycle around a plug flow reactor is considered for all possible recycle rates, both positive and negative. For a first order reaction in such a system performance predictions are made. System behaviour as the recycle rate tends to infinity is discussed.