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L'ajout d'eau liquide à des lits de particules de polystyrène de plus de 3 mm de diamètre améliore le jaillissement en causant une diminution de la vitesse de jaillissement minimale. Alors que le degré d'amélioration est du point de vue quantitatif comparable à ce que nous avons indiqué antérieurement pour des lits fl uidisés à larges particules hydrophobes légères, le mécanisme est différent. L'amélioration du jaillissement se produit parce que le liquide s'agglomère à l'interface jet-espace annulaire, formant un tube d'aspiration quasi imperméable effi cace, ce qui a pour effet d'accroître la vitesse du gaz en haut du jet.

When liquid is added to large-particle gas-uidized beds where the liquid density is similar to the particle density, the liquid addition can cause a dramatic increase in the velocity range and intensity of uidization. In this paper it is shown that this also leads to strong enhancement of the heat transfer between the bed and an immersed tube. Experiments were carried out using a heated tube of outer diameter 25 mm in air-uidized beds of polystyrene particles or glass beads to which small quantities of water (typically equivalent to 10 per cent of the bed volume) were added. The results from the heat transfer experiments are explained with the aid of observations of the tube surface using an industrial endoscope located inside the tube. The key factors underlying the enhancement of heat transfer are identi ed to be heat conduction to liquid-solid aggregates, convection to the liquid phase, convection to the gas phase and vaporization.

The effects of tube bank configuration on forces and heat transfer were investigated for both two-dimensional and three-dimensional gas fluidized beds. Effective dynamic forces and heat transfer coefficients were measured for several tube bank configurations, and it was found that the average forces are smaller than for a single tube. The heat transfer coefficient can be increased by providing sufficient space for particles to descend around both sides of the tube bank. The results provide useful guidelines for optimizing the configuration of tube banks to achieve high heat transfer coefficients while reducing tube erosion due to dynamic forces.

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