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Traditionally, when undertaking feasibility studies for designing new storage facilities such as storage silos, engineers will extract design information from experiments and evaluate potential risks associated with health and safety, suitability design for reliable material flow, and quality of products. The simulation approach applied incorporates Computational Fluid Dynamics (CFD), and Discrete Element Modelling (DEM) approaches and experimental tests will be used for validating these simulation results. One important aspect related to handling fine and dusty materials (particles smaller than 100 microns) is the associated risk of dust explosions, which needs to be evaluated before the commissioning of storage silos; to evaluate the accumulation of fines during the silo filling process, simulations and experiments were conducted. Alumina and salt were used here as reference materials for calibration and the validation purposes. The validation efforts are significant due to the fact that the data that is accessible in simulations is vastly different to the accessible data in experiments, which is restricted by measurement techniques and equipment. Such restrictions are observed in the evaluation of particle concentrations in a large confined volume. A new methodology has been developed to evaluate concentrations in both simulations and experiments by employing a non-dimensional factor [k], here called "Concentration Rank Factor" (CRF). A significant finding of this research is that experiments and simulations can be compared using CRF. It has been found to be within 2% of the experiment averaged value of 0.64. [ABSTRACT FROM AUTHOR]

Featured Application: Nanoparticle suspensions are used in a variety of applications involving the transport of reagents and products to and from structured material surfaces. The more efficient alignment of particle layers adjacent to, and in contact with, a reactive surface, such as found in a fuel cell, bio-medical and electrochemical device, is often reliant upon the effective control of the dynamics of particle assembly in narrow conduits. One such control is possible by spectral thermal pulsing to generate a controlled Brownian motion of particles. This is demonstrated by numerical simulation here to be highly effective when particles are conveyed in viscous fluids close to a neutrally buoyant condition. Inter-particle and particle-wall connectivity in suspension flow has profound effects on thermal and electrical conductivity. The spectral impulse generation and the imparting of kinetic energy on the particles is shown through a mathematical analysis to be effective as a means of achieving an approximate equivalent of a Langevin thermostat. However, with dilute suspensions, the quadratic form of the thermal pulse spectra is modified with a damping coefficient to achieve the desired Langevin value. With the dense suspension system, the relaxation time is calculated from the non-linear differential equation, and the fluid properties were supported by the viscosity coefficient. A "smoothed" pulse is used for each time-step of the flow simulation to take care of the near-neighbor interactions of the adjacent particles. An approximate optimal thermostat is achieved when the number of extra pulses introduced within each time step is found to be nearly equal to the co-ordination number of each particle within the assembly. Furthermore, the ratio of the particle kinetic energy and the thermal energy imparted is found to be never quite equal to unity, as they both depend upon the finite values of the pulse duration and the relaxation time. [ABSTRACT FROM AUTHOR]

It is possible for the stratification of poured granular mixtures into layers according to particle size to take place when there is no clear difference in particle shapes within the mixture. It has been established that stratification depends heavily on the fill rate, which determines the overall impact of the incident feed stream on the growing heap. If the angle of repose of the coarse grains is much larger than that of the fine grains, stratification will take place over a wide range of fill rates.

Abstract: Air current segregation (ACS) is one segregation phenomenon that has been identified to contribute significantly to the separation of fines (particles<42 µm) from coarse material during the filling of industrial silos. This paper describes investigations of ACS for alumina powder based on experiments conducted in an industrial silo, in the laboratory and by computation, using the commercial computational fluid dynamics code Fluent. For the industrial silo, the extent of ACS has been measured using the accumulation of fine material at the wall as an indicator. Based on these results, modifications to the feeding system were undertaken which showed that ACS is promoted if the material is fed in a dilute form. Experiments in the laboratory confirmed this effect visually. In order to be able to compare numerically the extend of ACS, a segregation index has been developed. It was found that a dilute particle jet leads to more ACS than dense particle jet. The effects of solids feeding rate and air extraction rate on ACS have been investigated in the laboratory silo and the results clearly show that low solids feeding rates promote ACS. It was further found that an increase in the air extraction rate has a mild effect in suppressing ACS. These effects were confirmed by the Fluent simulations, which showed an unexpectedly good agreement with the experiments. [Copyright &y& Elsevier]