The effect of mixer properties and fill level on granular flow in a bladed mixer

Abstract

in Wiley InterScience (www.interscience.wiley.com).The discrete element method was used to study the effect of mixer properties and fill level on the granular flow of monodisperse, cohesionless spheres in a bladed mixer. For fill levels just covering the span of the blades, a three-dimensional (3-D) recirculation zone develops in front of the blades, which promotes vertical and radial mixing. Increasing fill level reduces the size of the recirculation zone, decreases bed dilation and hinders particle diffusivities. However, above a critical fill level, the behavior of the particles within the span of the blade is found to be invariant of fill level. At lowfill levels, the pressure within the particle bed varies linearly with bed height and can be approximated by hydrostatics. At higher fill levels, a constant pressure region develops within the span of the blades due to the angled pitch of the blades. Cylinder wall friction is shown to significantly influence granular behavior in bladed mixers. At low-wall friction, the 3-D recirculation zone observed for high-wall friction conditions does not develop. High-wall friction leads to an increase in convective and diffusive particle mixing. Shear stresses are shown to be a function of wall friction. Blade position along the vertical axis is shown to influence flow patterns, granular temperature and stress. The effect of increasing the mixer diameter at a constant particle diameter was also studied. When the mixer diameter is larger than a critical size such that wall effects are minimized, the observed granular behavior follows simple scaling relations. Particle velocities and diffusivities scale linearly with mixer size and blade speed. Normal and shear stress profiles are found to scale linearly with the total weight of the particle bed.

The internal loads, moments, and stresses in rod-like particles in a low-speed, vertical axis mixer

“…The limited blade speed dependence is reasonable considering that the particle-particle and particle-wall interactions depend on their relative velocities, not the absolute velocities. As has been found in previous studies (e.g., Remy et al, 2010), the internal particle stresses are more influenced by the weight of the supported material.…”

“…17. The mean and median of the max(|σ 1 |, |σ 3 |) distributions increase with dimensionless bed height, as is expected since it has been observed that the stresses in an AFD geometry are due largely to the weight of the material in the device (Remy et al, 2010). The fitting parameter b is nearly independent of H/H B and approximately equal to 0.5, and the parameter a decreases in a nearly linear manner with increasing H/H B .…”

Continuous quantitative monitoring of powder mixing dynamics by near-infrared spectroscopy

“…Since it is well known that the filling protocol of blenders has a strong impact on mixing performance, we performed lab-scale mixing experiments with different powder filling sequences and fill levels. Furthermore, we analyzed experimentally the convective and diffusive mixing properties of the binary pharmaceutical powder blend based on recent simulation studies of the mixing process [39].…”

Monitoring Blending of Pharmaceutical Powders with Multipoint NIR Spectroscopy

“…Overcoming the problems associated with differences between calibration and measurement has been discussed in the literature (20,21). Moreover, the dynamics of blending processes have been studied theoretically as well (22,23) and experimentally using model substances (24) and pharmaceutical powders (25). However, using one probe in the same position usually does not provide a reliable assessment of the blending process (21,26).…”