Abstract
Simulations of wet fluidized beds of particles in small periodic domains have been carried out using a CFD-DEM approach. A liquid bridge forms upon particle–particle collision, which then ruptures when the particle separation exceeds a critical distance. The simulations take into account only the surface tension force of attraction due to the liquid bridge. Increasing the strength of cohesion leads to larger agglomerates, and correspondingly, higher gas velocities are required to fully support the particles. The slip velocity results from the simulations have been correlated in terms of a Bond number characterizing the strength of cohesion, volume of liquid in the bridge, and particle volume fraction. The CFD-DEM results are systematically coarse-grained to expose the dependence of the filtered drag coefficient on Eulerian filter size, surface tension forces, liquid loading, and solids loading in wet gas–solid fluidized beds.
Highlights
Wet granular flows and fluidization of wet particles by a gas are important in a wide range of industrial processes, in the energy and pharmaceutical industries (Muzzio et al, 2002)
Cohesive interaction between particles due to liquid bridges changes the nature of fluidization; upon increasing cohesion, Geldart group B particles manifest fluidization/defluidization characteristics that are reminiscent of group A particles, and with further increase in cohesion act as group C particles (McLaughlin and Rhodes, 2001; Wormsbecker and Pugsley, 2008; Seville and Clift, 1984)
The work presented in this paper examines how fluidization behavior in wet gas-fluidized beds is affected by liquid bridge characteristics
Summary
Wet granular flows and fluidization of wet particles by a gas are important in a wide range of industrial processes, in the energy and pharmaceutical industries (Muzzio et al, 2002). Very cohesive systems manifest partial, but poor, fluidization above some critical velocity where the pressure drop is considerably smaller than that required to support all the particles in the bed As this velocity is not a good metric to characterize quality of fluidization of very cohesive systems, the notion of full-support velocity where the pressure drop is commensurate with the weight of the bed has been introduced in the literature; this full-support velocity increases with degrees of wetness, or equivalently, the strength of cohesion (Wormsbecker and Pugsley, 2008; D'Amore et al, 1979). It would be valuable to be able to predict this full-support velocity and the flow behavior in wet fluidized beds at even higher gas velocities
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