A general method for silo classification using rupture plane

A new method is presented for silo classification using the rupture plane in the storage. The proposed method is based on the formula of rupture plane orientation determined by the aspect ratio of specified silos and involves the effects of the conical angle of the storage surface, so it can deal with two cases： the conical angle of the storage surface and the flat storage surface. Compared with the two popular methods based on the silo-aspect ratio and the silo rupture plane, respectively, in current engineering design, the new method can give a range of critical aspect ratios to classify deep silos and squat silos according to the conical angle of the storage surface or the fiat storage surface. Moreover, the range covers the critical aspect ratios obtained from the existing classification methods including the Chinese code based on silo aspect ratios, the German code, Reimbert brothers＇ definition and Liang et al. ＇s definition, so it is a more general method to classify silos and the existing methods can be viewed as special cases of the presented method.

Particulate flow analysis in inclined pipes and transfer chutes using tomography imaging,discrete element simulations and continuum modeling approaches

In particulate material transfer systems,traditional shear test based steady state analysis can provide some insight into the strength of the bulk material and subsequent resistive frictional forces during flow.For fast flowing transfer points,dynamic flow conditions dominate and additional modelling techniques are required to improve design guidance.The research presented shows the evolution of a design solution which utilises two distinct processes;a continuum method and a discrete element method(DEM). Initially,the internal structure of dense granular flow,down vertical and inclined pipes was investigated using a twin sensor,12 electrode electrical capacitance tomography device.Subsequently,DEM simulations were conducted using the commercial software,PFC3D.Initially,two particle types and their flow behaviours were analysed:plastic pellets and sand.The pipe angle was varied between 0°and 45°to the vertical.For both the plastic pellets and the sand,good qualitative agreement was found with the spatial particle concentration analysis.Generally,the flow had a dense particle region at its core with the particle concentration reducing away from this core.As expected,at 0°, the core was centrally located within the pipe for both the plastic pellets and sand.At pipe angles 5°or greater,the dense core of particles was located on or near the pipe wall.Average flow velocity analysis was also conducted using the results of wall friction test analysis.The velocity comparisons also showed good agreement between the ECT image analysis and the DEM simulations. Subsequently,the DEM method was used to analyse a complex transfer system(or chute) with the continuum method providing comparative flow analysis with the DEM flow analysis.

A comparative study on design standards of screw conveyors in China,Germany,and the USA–Part II:Discrete element method

This part of the study aims to evaluate the advantages and disadvantages of technical standards of screw conveyors in China,Germany,and the USA for industrial applications.The source or determination method of empirical coefficients as well as the theoretical foundation of dimensioning-relevant diagrams in these standards is not explicitly documented in the literature.Therefore,instead of less efficient on-site tests,the numerical simulation by discrete element method is conducted.Based on the geometrical and operational designs determined in three standards for horizontal,slightly inclined,and vertical conveyance of three representative bulk solids(barley,lignite,and sand),the potential influencing factors are discussed.With constant particle and contact parameters,the potential deviations caused by particle models are eliminated.Furthermore,the accuracy of power consumption calculation of each standard and the divergence between accessible and required mass flows is comprehensively assessed based on the analysis of simulated outcomes.Two main conclusions are drawn:(1)Particle fall back is barely considered by all three standards and leads to overestimated mass throughput;(2)The decrease in mass throughput caused by an increasing degree of filling can be compensated by slowing down the rotational speed.

INFLUENCE OF AIR HUMIDITY ON THE SUPPRESSION OF FUGITIVE DUST BY USING A WATER-SPRAYING SYSTEM

One of the main origins of fugitive dust emission arises from bulk handling in quarries or mines, in particular, from bulk materials falling from a hopper or a conveyor belt. Water-spraying systems, using two-phase nozzles, are one of the methods to suppress such dust emission. In this work we tried to develop a mathematical model to correlate air humidity, water flux through the nozzle and the dust （in particular PM10） emission, in order to improve the application and efficiency of these systems. Sand from the Yellow River in China was dropped from a conveyor belt into a dust chamber at 1 kg·min^-1, wherefrom the emitted dust was sucked off and quantified via a cascade impactor. A two-phase nozzle was installed in the dust chamber with a water flux through the nozzle of 1.2 to 3 L·h^-1, whereas the relative air humidity changed between 55 and 73%. Dust emission was found to be linearly dependent on relative air humidity. Furthermore model equations were developed to describe the dependence of PM10 emission on water flux and relative air humidity.

Vibration induced flow in hoppers:DEM 2D polygon model

A two-dimensional discrete element model （DEM） simulation of cohesive polygonal particles has been developed to assess the benefit of point source vibration to induce flow in wedge-shaped hoppers. The particle-particle interaction model used is based on a multi-contact principle. The first part of the study investigated particle discharge under gravity without vibration to determine the critical orifice size （Bc） to just sustain flow as a function of particle shape. It is shown that polygonal-shaped particles need a larger orifice than circular particles. It is also shown that Bc decreases as the number of particle vertices increases. Addition of circular particles promotes flow of polygons in a linear manner. The second part of the study showed that vibration could enhance flow, effectively reducing Bc. The model demonstrated the importance of vibrator location （height）, consistent with previous continuum model results, and vibration amplitude in enhancing flow.

A comparative study on design standards of screw conveyors in China,Germany and the USA-PartⅠ:Theoretical calculation and quantitative analysis

Screw conveyors,widely used devices for transporting bulk materials,play an irreplaceable role in the modern industrial system.Despite of their traditional advantages,designers of screw conveyors still heavily rely on their own country's experiments and standards,which are closely related to empirical data.Therefore,the same conveying task often results in different designs.This work aims to compare the design standards of screw conveyors in China,Germany and the USA.Based on related standards acquired from renowned associations in the three countries,the similarities and particularities of these design guidances are compared.With preforming the geometrical and operational designs for horizon-tal,slightly inclined and vertical conveyance of three representative bulk solids(barley,lignite,sand),the advantages and disadvantages of these semi-empirical designs are comprehensively presented.Fur-thermore,the potential influence of empirical coefficients,which are not explicitly documented,are extensively discussed.By analysing all outcomes,the compatibility and applicability of each standard are qualitatively assessed.