Non-Newtonian fluidisation of spherical particles

This work presents the development of a new model based on the submerged object concept in order to characterise the expansion of spherical particles fluidised by non-Newtonian purely viscous liquids, especially at intermediate and high bed void fractions values. In order to take the interactions between the particles into account a parameter called hydraulic tortuosity is introduced which is a function of the Reynolds number and porosity. A method allowing its evaluation is proposed. Based on the test of a lot of experimental data from our laboratory and from previous works, this model is shown to give satisfactory results for porosities values larger than 0.6. In order to cover the entire range of porosities corresponding to the particles expansion a capillary-type model is proposed for the lower values of the porosities. This model is found to give satisfactory results in the range of bed void fraction comprised between the value corresponding to the minimum of fluidisation epsilon(mf) and epsilon = 0.65. The combination of the two models tested on 21 independent sets of data concerning viscoinelastic shear-thinning liquids leads to a mean error of 16%. It is also shown to give accurate predictions for Newtonian liquids. A comparison is also presented with the prediction of some of the widely used equations available in literature. (C) 2002 Elsevier Science Ltd. All rights reserved.