Experimental validation of particle flow through conveyor transfer hoods via continuum and discrete element methods

Abstract

A critical factor in the design of hood-spoon type conveyor transfers is to match the exit velocity of the material through a conveyor transfer to that of the conveyor belt receiving the material. If particle velocity increases too much issues such as particle attrition, dust generation, chute and belt wear and excessive noise can arise, whereas if particle velocity decreases, stagnation zones can develop, resulting in issues such as spillage or chute blockage. Numerous methods are available to analyse particle flow through a conveyor transfer, including; continuum based analytical methods, the discrete element method (DEM) and experimental analysis. This paper details the findings for these three methods for granular cohesionless materials. The experimental investigations were performed on a conveyor transfer research facility located at the University of Wollongong, using high-speed video to capture the flow and subsequently analysed with Image Pro Plus. Two continuum based analytical analyses were then used to predict the flow through the conveyor transfers. Lastly, the use of DEM provided a third means of quantification and prediction of the particle velocity through the transfer hood with the data further processed using Matlab. These methods were then compared to determine whether continuum or discrete methods allow for accurate prediction of chute flow. (2007) have previously simulated material flow at transfer stations and verified the results experimentally. They primarily investigated the forces generated at an impact plate and the mass flow rates through the transfer station, however DEM validation of the particle velocity through a conveyor transfer is novel. Ilic et al. (2007) have presented comparisons between a continuum method and DEM focussing on a slewing stacker transfer chute, however there was no comparison made to experimental results. Even though there was some agreement between the continuum method and the DEM, there is no certainty that these methods accurately predict reality.The design of conveyor transfers has often relied on trial and error to achieve the desired outcome and has been seen as a 'black art' rather than a science for many years. The development of continuum-based chute flow models, such as that of Roberts (1999;2003) and Korzen (1988), has helped to better understand the flow behaviour of bulk materials. With the advent of DEM comes the possibility that expensive test chutes may no longer need to be constructed to test various designs, with the design process occurring solely on computer workstations. At present there is still some hesitance to rely on DEM alone as it is still considered to be in its infancy with much more validation required before designers put their full trust in it.The presented research examines the inverted chute flow model of Roberts (2003), the continuum method of Korzen (1988) for non-cohesive materials and DEM simulations which are then compared to the results obtained from an experimental conveyor transfer research facility.

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