L.G. Gibilaro

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

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 model for a segregating gas fluidised bed

A differential equation model is derived to describe particle segregation in a binary mixture of solids fluidised by gas. The model, which is formulated to conform with qualitative descriptions of the mechanism of segregation, yields solutions displaying the unusual features of the steady—state solids—concentration profiles found experimentally and enables appraisals to be made of the relative importance of the contributary mechanisms.

A dynamic response technique for the estimation of gas—liquid mass transfer coefficients in a stirred vessel

Abstract A method is described for evaluating mass transfer coefficients, k L a , in gas sparged stirred vessels. It involves measurement of both liquid and gas concentration responses following a step change in inlet gas concentration, and differs from previously published methods in that the k L a evaluation is independent of the gas residence time distribution . Results are presented that demonstrate the suitability and consistency of the method for a range of gas mixing levels. A modification, that involves only a knowledge of the early liquid concentration response, is suggested as worthy of further consideration.

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

Evaluation of crystal growth kinetics from a desupersaturation curve using initial derivatives

Abstract A technique to evaluate crystal growth kinetics from batch experiments performed in the integral mode is described. The method only requires calculation of the first two derivatives of the desupersaturation curve evaluated at time zero. Results of dissolution experiments can be analyzed in the same way. Kinetic parameters evaluated using this technique compare favourably with those determined using established procedures.

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

Initial response analysis of mass transfer in a gas sparged stirred vessel

Abstract A method for evaluating the mass transfer coefficient, k L a , in a gas sparged stirred vessel from the initial portion of the liquid dynamic response curve is described. The method assumes perfect liquid mixing but is independent of the gas mixing characteristics. Results obtained from two geometrically similar air-water systems (volume ratio 8:1) correlate well over a wide range of operating conditions and are in good agreement with evaluations made on the smaller system using an established and more involved experimental technique.

Particle packing constraints in fluid–particle system simulation

Abstract A procedure is described for limiting the void fraction in fluid particle systems, computed by means of numerical multiphase flow simulation codes, to values which do not fall below those realisable in practice. It is based on a computation of the particle–particle contact forces which come into play only when computed void fractions fall to values below those corresponding to random packing of the particles. The general method is illustrated with reference to the process of sedimentation using a specific fluid-dynamic formulation of the equations of change for fluidization. Without the particle contact force algorithm, the particles compact to the physically meaningless void-fraction of 0.17; with the algorithm the random packing value of 0.4 is achieved.