Modelling axial dispersion of granular material in inclined rotating cylinders with bulk flow

The axial dispersion of approximately monosized particles in rolling mode in rotating cylinders with bulk flow is examined using a Monte Carlo model and discrete element method (DEM) simulations. The Monte Carlo model predicts that the mean square displacement relative to the mean axial displacement of the bed undergoes oscillations in time. The nature of these oscillations depends on the fill level of the cylinder and the extent of particle mixing during avalanches. When the cylinder is half full the Monte Carlo model predicts undamped oscillations, whereas a filling fraction of 0.26 produces oscillations whose amplitude decreases with time. If mixing during avalanches is assumed to be perfect then the oscillations occur about a linear increase with time. In contrast, if it is assumed that the particles do not mix during avalanching, the oscillations occur about an increase with time which has a gradient which increases with time. There is good qualitative agreement between the Monte Carlo model with perfect mixing and the DEM when the filling fraction is 0.26. For a filling fraction of 0.5 the DEM data show oscillations about a faster than linear increase with time

Effect of periodic boundary conditions on granular motion in horizontal rotating cylinders modelled using the DEM

ISSN:1434-5021ISSN:1434-763

On the occurrence of polygon-shaped patterns in vibrated cylindrical granular beds

We report experimental observations of polygon-shaped patterns formed in a vertically vibrated bed of circular cross-section. A phase map is determined, showing that the polygon pattern is established for Γ = A(2πf)2/g ≳ 10 . The sensitivity of the polygon structure to bed parameters was tested by studying beds of different particle sizes and fill levels. It was hypothesized that the polygon pattern observed in cylindrical beds is the corresponding pattern to the formation of arches in square-shaped beds. The close relationship between these two patterns was demonstrated by two observations: i) the radii of the arches of a corresponding square bed and the inner radius of the cylindrical bed were found to be very similar and ii) the boundary lengths of the two patterns were in good agreement

Comparison of bubble eruption models with two-fluids simulations in a 2D gas-fluidized bed

Two-fluid simulations of gas–solid fluidized beds are performed in this work with a threefold aim: (1) explore the capabilities of two-fluid modelling to reproduce realistically bubble eruption patterns in two-dimensional fluidized beds; (2) compare the results obtained from the two-fluid simulations with particle ejection models; and (3) provide information about the mutual interaction of the gas and particle flows during bubble eruption. To fulfil these aims, results from two-fluid simulations concerning the vertical and horizontal velocities of particles in bubble domes, prior to and during bubble eruption, are reported and compared with previously published experimental data taken from a bed of comparable geometry and operating conditions. The comparison shows excellent quantitative agreement. Particle ejection velocities estimated through semi-empirical and theoretical models proposed in the literature are compared with the particle behaviour in the bubble dome obtained from the two-fluid simulations. The results obtained here indicate that the theory based on the potential flow around a cylinder provides a more accurate prediction for the particle velocities in erupting bubbles than semi-empirical relations. For the data reported here it has been found that the velocity of particles in the bubble dome forms an angle with the vertical direction that is twice the angle formed by the radial direction. This observation is contrary to standard models of 2D bubbles, which assume that the particles are ejected radially outwards from the domeThis work has been partially funded by the Spanish Government (Project DPI2009-10518) and the Autonomous Community of Madrid (Project S2009/ENE-1660)Publicad