Layer Inversion and Bed Contraction in Down‐Flow Binary‐Solid Liquid‐Fluidized Beds

Experiments were carried out on downward-flow water-fluidized binary mixture of spheres selected for possible layer inversion. With the two binaries tested (relatively high-density large particles mixed with lower-density smaller particles), only one of the five possible steps of the layer inversion progression was clearly identified for the higher liquid velocities, a mixed layer being observed at the top of the column close to the distributor. This layer manifested a bed contraction so large that its bulk density was lower than those of its constituent mono-components at the same liquid velocity, which determined its location within the column. The voidage of the mixed layer could be predicted with good accuracy (<0.7%) by regression of the Westman packed bed equation with one adjustable parameter. Des experiences ont ete menees sur un melange binaire fluidise par de l'eau et a ecoulement descendant, comprenant des spheres selectionnees pour une inversion possible des couches. Avec les deux binaires testees (de grosses particules de masse volumique relativement elevee melangees a de petites particules de faible masse volumique), seulement une des cinq etapes possibles menant a l'inversion des couches est clairement identifiee pour les vitesses de liquide les plus elevees, une couche mixte etant observee dans la partie superieure de la colonne pres du distributeur. Cette couche montre une contraction du lit si grande que sa masse volumique globale est plus faible que celle de ses composants individuels constitutifs a la meme vitesse de liquide, ce qui determine sa position dans la colonne. Le degre de vide de la couche mixte a pu etre predit avec une bonne precision (<0,7%) en effectuant une regression sur l'equation de lit garni de Westman avec un parametre ajustable.

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