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.

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.

Investigation of the effects of radial clearance on the screw conveyor performances for different inclinations

Screw conveyors are widely used for bulk material transportation.This study investigates the critical role of radial clearance,the gap between the screw and the conveyor body,on performance across various inclination angles.The Discrete Element Method(DEM)is employed to analyze the effects of different radial clearances on conveyor performance for concrete aggregate and sand as bulk materials.Volumetric efficiencies and capacity losses serve as key performance indicators,quantitatively assessed for each radial clearance and inclination combination.Experimental validation is conducted to corroborate the findings.In the study,the optimal radial clearance was identified as 1.5 to 3 times of the particle size.This optimal clearance minimizes the material jamming and increases the performance for screw conveyors with different inclinations and bulk material types as a result.

Numerical investigation on the spewing mechanism of earth pressure balance shield in a high-pressure water-rich sand stratum

The spewing of a screw conveyor easily occurs from the earth pressure balance(called EPB)shield in a water-rich sand stratum.This may lead to the collapse of the tunnel face and even serious subsidence of the ground surface.To understand the spewing mechanism of the shield screw conveyor and explore the critical hydraulic condition of soil spewing in a shield–soil chamber,a simplified theoretical model for the spewing of the screw conveyor was developed based on the equation of groundwater flow in the screw conveyor under turbulent state.Thus,coupling Darcy's law with Brinkman's equation,this model was implemented within the COMSOL Multiphysics framework.The underground water flow in the shield screw conveyor was simulated so as to obtain its velocity and flow rate.Numerical simulations show that the water pressure distribution is concentrated in the lower part of the soil chamber after the groundwater enters the soil chamber.When the groundwater enters the screw conveyor,its pressure gradually decreases along the direction of the screw conveyor.When the water flow reaches the stratum–shield interface,the flow velocity changes markedly:first increases and concentrates at the entrance of the lower soil chamber,plummets and stabilizes gradually,and increases again at the exit.The soil chamber and screw conveyor are significantly depressurized.It is also found that the soil permeability coefficient can be reduced to k<2.6×10^(−4)cm/s through appropriate soil improvement,which can effectively prevent the occurrence of spewing disasters.

DEM investigation on conveying of non-spherical particles in a screw conveyor

Screw conveyors are extensively used in modern industry such as metallurgy,architecture and pharmaceutical due to their high-efficiency in the transportation of granular materials.And substantial efforts have been devoted to the study of the screw conveyors.Numerical method is an effective way to study screw conveyor.However,previous studies have mainly focused in the regime of spherical particles while the in-depth investigations for non-spherical particles that should be the most encountered in practical applications are still limited.In view of the above situations,discrete element method(DEM),which has been widely accepted in simulating the discrete systems,is utilized to investigate the conveying process of non-spherical particles in a horizontal screw conveyor,with particles being modeled by super-ellipsoids.In addition,a wear model called SIEM(Shear Impact Energy Model)is incorporated into DEM to predict the wear of screw conveyor.The DEM simulation results demonstrate that the particle shape is influential for the flow behaviors of particles and the wear of conveyor.The conveying performance evaluated quantitatively of both mass flow rate and power consumption is subsequently obtained to investigate the effect of sphericity of particle with different operation parameters.Moreover,particle collision frequency and collision energy consumption are acquired to investigate the possible particle breakage between particles and screw blade.The comparisons between particle-particle collision and particle-wall collision reveal that particles with large shape index have more possibility to be damaged in particle-wall impingement.

Application of a screw conveyor with axial tilt blades on a shearer drum and investigation of conveying performance based on DEM

Screw conveyors are widely employed in industrial fields for conveying bulk materials.The shearer drum which uses the screw conveying principle is responsible for excavation and conveying coal particles onto the chain conveyor.Screw conveyor performance is affected by potential factors,such as the blade axial tilt angle and style,core shaft form and diameter.The effect of blade axial tilt angle on the conveying performance was investigated with the help of DEM.In the case of the screw conveyor,the mass flow rate,and particle axial velocity increased with increasing positive axial tilt angle,and declined with increasing negative axial tilt angle.In the case of the drum,the mass flow rate,particle axial velocity,and loading rate first increased and then decreased with increasing positive axial tilt angle,and decreased with increasing negative axial tilt angle.These results can be considered as a benchmark for screw conveyor and drum structural designs with axial tilt screw blades.

Developing a screw conveyor in radio frequency systems to improve heating uniformity in granular products

Radio frequency(RF)treatments have been increasingly studied due to the rapid heating,deep power penetration depth and high energy efficiency.However,the major challenges for commercial RF applications are non-uniform and run-away heating.The purpose of this study was to improve RF heating uniformity in three granular products(soybean,corn,and peanut)using a custom-made screw conveyor with sample movement and mixing.The results showed that soybean,corn and peanut samples in the screw conveyor were RF heated in a similar heating rate under the selected electrode gap and screw rotation speed,and the variations between the highest and lowest temperatures in the three samples were all clearly reduced as compared to the stationary treatments.The RF heating uniformity index was also reduced for soybean,corn,and peanut during and after the RF treatment.Therefore,the screw conveyor could improve RF heating uniformity due to stable,continuous,uninterrupted movement and mixing of samples.The small-scale screw conveyor used in RF systems would provide a solid basis for further large-scale industrial applications.

The fluidesolid coupling analysis of screw conveyor in drilling fluid centrifuge based on ANSYS

In the centrifugal separations of drilling fluid,screw conveyor is a critical component to push and separate the sediment.The work performance and structural parameters of conveyor are immediately related to the production capability,the working life and the separating effect of the centrifuge.The existing researches always use the theoretical calculation of the approximate loads to analyze the strength of conveyor,and it cannot reflect the stress situations accurately.In order to ensure the precise mastery of the working performance,this article obtained pressure distribution under working conditions from CFX evaluation and gained equivalent stress and deformation under several load conditions by using the ANSYS Workbench platform to check the strength of conveyor.The results showed that the influence of centrifugal hydraulic pressure was less than that of centrifugal force on the strength and deformation of conveyor.Besides,the maximum equivalent stress occurred at the inside of the feed opening,while the maximum deformation occurred at the conveyor blade edge of taper extremity.Furthermore,whether considered the feed opening or not,the computing model had a great influence on the analysis results,and the simplified loads had a great influence on the deformation analysis results.The methods and results from this article can provide reference for the design and the improvement of screw conveyor.

Numerical simulation and experiment of grain motion in the conveying system of ratooning rice harvesting machine

The mixtures,grains,and residues in the ratooning rice harvesting machine need to be conveyed forward,backward,upward,and downward.Due to such operations,often accumulation and blockage take place at the intersection of a horizontal-vertical screw conveyor,resulting in low efficiency,high power consumption,and even grain damage.In this study,a CFD-DEM approach was applied to address the above problems.Firstly,a pneumatic conveying device was designed for ratooning rice,and then the motion of the rice grains and airflow field was analyzed in detail.The effects of different cross-sectional heights and lengths of the contraction section related to the mixing cavity were examined.Finally,the three-factor quadratic regression orthogonal rotational combination method was adopted in the experiment,and the fan velocity,filling coefficient,and speed of the horizontal screw conveyor were taken as test factors.The results showed that with the increasing cross-sectional height of the contraction section in the mixing cavity,the grain velocity decreased and the dispersity increased.With increasing length of the contraction section in the mixing cavity,the area of the high-speed airflow zone increased and the diffusion effect was enhanced.At the fan velocity of 2700 r/min,the filling coefficient was 0.41,the speed of the horizontal screw conveyor was 1173 r/min,and the outlet flow optimization index was the highest,which was 45.9%higher than that obtained without airflow.