Stability of wet agglomerates in granular shear flows

Abstract

An agglomerate made of solid particles held together by a viscous liquid phase when sheared in an otherwise dry granular material is observed to deform by stretching. This observation, based on experimental results, is confirmed in the present paper by means of a computer simulation model. Simulations as well as experimental results indicate that the degree of deformation by stretching, a critical factor influencing the stability of such agglomerates, is governed by a dimensionless parameter of the system, called the deformation Stokes number, St_def. Two regimes, involving high and low characteristic degrees of deformation, can be identified based upon the value of this number. Simulation results indicate that for the range of conditions simulated, the value separating the two regimes, the critical deformation Stokes number, St^*_def, is relatively insensitive to the agglomerate size and other parameters of the system. This critical number defines the conditions below which forces inducing agglomerate breakage are low and above which they are high and result in agglomerate break-up. Calculation and/or measurement of this parameter is essential for prediction of equilibrium sizes of agglomerates in industrial granulation operations.