Mixed solid/dispersed phase particles in multiphase fluidised beds, Part I: Free energy of stability due to interfacial tension

A theoretical analysis is conducted of the retention of a dispersed phase f luid within a (multiphase) fluidised bed, in terms of the behaviour of mixe d phase particles, or composite particles of the solid and dispersed fluid phases. By analysis of the thermodynamic stability of such particles due to interfacial tension - in the general case considering an "n-plet" (n solid grains surrounding a dispersed phase droplet) - solutions are obtained for the Gibbs free energy of several detachment processes as sets of dimension less equations which are solved numerically. The analysis indicates that al l geometrically possible mixed particles require energy for their rupture, of which the minimum energy rupture process (for a preferentially nonwettin g dispersed phase) is isolated solid particle detachment. Thus, if sufficie nt energy is available, an n-plet will shed solid particles in successive r upture processes, such that if these reach the point at which the n-plet is either buoyant or elutriable, it will be released from the bed. The analys is determines the energy required for mixed-phase particle rupture and the limits of retention of such particles in any given fluidised bed. The deriv ed energy functions are compared to the energy available for mixed particle rupture in Part II (Niven, Khalili & Hibbert, 2000). (C) 2000 Published by Elsevier Science Ltd. All rights reserved.