Voidage disturbances

The Hydrodynamic Theory of fluidized bed stability was proposed by Foscolo and Gibilaro who adapted the stability principle of Wallis. They postulated that a fluidized bed is composed of two interpenetrating fluids. One fluid is the gas phase, and the solids phase is also considered as a continuous fluid phase. In this theory, voidage disturbances in the bed propagate as dynamic and kinetic waves. The stability of the fluidized bed depends upon the relative velocities of these two waves. The velocities of the kinetic wave (ue) and the dynamic wave (nj are ... 

Harris, S.E. and Crighton, D.G. (1994). Solitons, solitary waves, and voidage disturbances in gas-fluidized beds. J. Fluid Mech., 266, 243. 

Biesheuvel and Gorrisen (1990) have derived one-dimensional conservation equations for void fraction disturbances in a uniform bubbly fluid. They have studied the features of the propagation of void fraction disturbances and investigated the stability of uniform bubbly flows. They observed that the voidage fraction waves are unstable for void fractions above some critical value (>45%). Their method of approach was similar to that of Batchelor (1988) in many respects. 

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