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Abstract: The cyclic variation of the mean residence time of the liquid phase is investigated in a trickle-bed reactor operated with a liquid feed rate modulated in a periodic square wave pattern. Experiments made using a salt tracer method are compared to a residence time model, based on the concept of continuity shock waves. The model predicts accurately the mean residence times and their cyclic variation in case of a non-zero base liquid flow rate. A particular application of the model is the adjustment of the feed cycle parameters in order to obtain a constant residence time of the liquid, no matter the moment at which it enters the bed. This particular cycle duration depends, among others, on the feed rates, but also on the bed length. [Copyright &y& Elsevier]

The axial segregation behavior of a binary mixture made of spherical and non-spherical particles is studied experimentally and numerically using Discrete Element Methods (DEM). Two different shape approximations are used for modeling cylindrical particles: the equivalent sphere and the multisphere approximation. The coefficients required by DEM are calibrated partly by separate experiments, partly by geometrical considerations. The main objective is to dispose of a simple procedure to characterize the friction coefficients and to evaluate the main changes imposed by shape in an axial segregated rotating tumbler. The simulations match with the experimental observations in the multisphere case, the transient behavior is caught with accuracy with both approximations. [ABSTRACT FROM AUTHOR]

A horizontal rotating tumbler provided with internal baffles and containing a mixture of two types of particles is investigated by discrete element method (DEM) simulations. The main objective of this study is to characterize the dynamics of a rotary kiln containing spherical steel balls and wood particles, investigating the effect of internal baffles and wood chip particle shape on segregation. The results show that the presence of baffles imposes a cyclic behavior to the solid bed and that the magnitude of this cyclic behavior depends on the solid holdup. The wood particle shape effects are analyzed considering two different approaches: a spherical approximation and a multisphere approximation. The differences between these two approaches are mitigated at relatively high velocity. This type of simulation can also serve for baffle sizing. [ABSTRACT FROM AUTHOR]

The drift flux concept has been used to describe and analyse some hydrodynamic parameters such as the flow regimes and the retention phases in three-phase fluidised and fixed bed reactors. The effects of the gas, liquid and solid properties and the characteristics of the apparatus (distributor quality) on the hydrodynamics have been studied. Two hydrodynamic data banks as well as experimental results have been used to study the influence of the coalescence inhibiting behaviour of liquids and to determine flow regime transitions and phase retentions. In heterogeneous regime, the ratio of the drift flux density to the superficial gas velocity tends to a limit, approximately independent on the liquid velocity in both fixed and fluidised beds. Two correlations of the drift flux have been developed by this analysis; the first of which is valid in the three-phase fluidised beds and the other in the three-phase fixed beds. [Copyright &y& Elsevier]