Flow Channel Boundaries in Silos

The critical slip planes at the silo filling state are compared with the flow channel boundary during silo discharge for semi‐mass flows. The static critical slip planes are determined by using the dynamic programming method based on the stress field of granular solids stored in silos at the filling state. The flow channel boundary is estimated through the finite element analysis of the silo discharge. The results indicate that the critical slip line lies above the flow channel boundary. This characteristic can be attributed to the changeover of major principal stress directions of granular solids from the silo filling to the silo discharge. The analysis demonstrates that the silo wall friction tends to lift up the critical slip plane and flow boundary. A simple correlation is developed between the positions of critical slip planes and flow boundaries and is experimentally verified.     

Numerical study on the behavior of funnel flow silos with and without inserts through a continuum hydrodynamic approach

In this paper the results from simulations performed using a hydrodynamic model proposed by Artoni et al. [Chem. Eng. Sci. 64 (2009a) 4040–4050] have been compared with published data of an extensive experimental investigation carried out at the Tel-Tek Research Institute in Porsgrunn, Norway. The experiments collected several data and observations on the wall stresses and the flow patterns observed during discharge of a full-scale funnel flow silo with and without inserts. The comparison between simulation and experiments showed the ability of the model to capture quantitatively the main features of both the flow and of the wall stress profiles when flow corrective inserts are put in the hopper of the silo in order to convert the discharge regime to a mass flow regime. Moreover information such as the stresses on the internals, which are difficult or impossible to get experimentally, have been collected from the simulations and discussed.     

Shape dependence of resistance force exerted on an obstacle placed in a gravity‐driven granular silo flow

Resistance force exerted on an obstacle in a gravity‐driven slow granular silo flow is studied by experiments and numerical simulations. In a two‐dimensional granular silo, an obstacle is placed just above the exit. Then, steady discharge flow is made and its flow rate can be controlled by the width of exit and the position of obstacle. During the discharge of particles, flow rate and resistance force exerting on the obstacle are measured. Using the obtained data, a dimensionless number characterizing the force balance in granular flow is defined by the relation between the discharge flow rate and resistance‐force decreasing rate. The dimensionless number is independent of flow rate. Rather, we find the weak shape dependence of the dimensionless number. This tendency is a unique feature for the resistance force in granular silo flow. It characterizes the effective flow width interacting with the obstacle in granular silo flow. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3849–3856, 2018     

基于离散元的落地熟料库贮料压力分析

采用离散元EDEM软件,建立大直径落地熟料库偏心卸料动态力学模型,模拟熟料库在使用过程中的卸料状况;研究熟料颗粒流动引起的仓壁动态压力效应;指出在熟料作用下库底廊道顶部纵向压力的不对称性,以及廊道侧壁高度范围内侧贮料压力的不均匀性;从而找出仓壁和廊道的不同受力特点。     

Austragorgane und Austraghilfen

Feeders and Discharge Aids. Feeders and discharge aids have an influence on the flow behaviour of bulk solids in silos. Together with the geometric form of the silo, they are responsible for the operating conditions of a silo. Therefore, feeders and discharge aids have to be chosen and installed under consideration of the flow properties of the bulk solid to be stored. The necessary information is obtained by using the silo design method due to Jenike. This method yields the geometrical data of the hopper (wall steepness, outlet diameter) necessary for a troublefree operation (no doming and ratholing; mass flow; no segregation; uniform flow). Furthermore, the design of feeders and discharge aids plays an important role in determining their function. For example, stagnant zones will build up and cause flow problems on protruding edges and on walls which are not steep enough. For the correct function of the hopper/feeder combination it is important to make sure that the feeder fully activates the hopper outlet and stagnant zones cannot build up. This can be ensured by an appropriate feeder design (increasing capacity in direction of conveying). The driving power of a feeder has to be calculated also on the basis of the flow properties of the bulk solid to be stored.     

Rushton搅拌釜内的气含率分布及其流动特性的模拟

利用雷诺应力模型结合多参考系法模拟了Rushton气液搅拌釜内的气液流动特性,得到了不同截面处气含率大小分布规律,并与γ射线CT实验所测得的结果做了比较,发现除排出流区CFD模拟值与实验值相差较大外,上循环区与下循环区都吻合得较好;结果表明排出流区的气含率最高,在搅拌桨高速旋转下,流体沿叶片端面急速排出,湍动也十分强烈...     

The simulation and experimental study of granular materials discharged from a silo with the placement of inserts

The simulation method of DEM and experimental method are used to investigate the flow pattern of the filling and discharging process for two-dimensional plane silos. Two kinds of inserts (conical insert and BINSERT®) are used in the silo to change the flow fields of the silo. The placement of inserts improves the flow behaviors of funnel flow type to mass flow type during discharging. The wall normal stresses are influenced by the change of the flow type. The effects of using differently shaped inserts on the flow pattern and wall stress are analyzed in this study. The controlling parameters include the silo half-angle, the orifice width, the shape of the insert and the properties of the granular materials. The simulation and experimental results are in good agreement.     

大直径浅圆仓缩尺模型试验研究

大直径浅圆仓在生产过程中,由于仓底的偏心卸料使筒仓仓壁产生不均受力,会给筒仓结构的使用带来安全隐患。通过对浅圆仓缩尺模型试验,模拟筒仓生产过程的卸料状况,并对筒仓仓壁及仓底廊道顶部进行压力测试,将测试结果与理论计算进行对比,从而得出偏心卸料与静载状态的超压系数,为大直径浅圆仓设计提供依据。     

Flow pattern measurement in a full scale silo containing iron ore

The flow pattern in a silo is important because it affects both the recovery of solids and the pressures on the silo wall during discharge. Wherever mass flow is not achieved, the boundary of the flow channel has significant implications for both the functional and structural design of the silo. Many techniques have been used for the study of flow patterns in model silos, but most cannot be used at full scale, and very few quality measurements at full scale have ever been made. This paper outlines a full scale experimental study in which the patterns of solids flow and the flow channel boundaries are reliably quantified.The full scale silo was specially designed, constructed and instrumented to exhibit funnel flow and to make observations of the solids flow pattern and the silo wall pressures. It had three outlets: one concentric, one fully eccentric and one in between. Three materials were used: iron ore pellets, slag fines and crushed basalt. This paper describes experiments involving iron ore pellets. The silo was seeded with radio frequency tags whose residence times were measured by detecting them on exit during discharge. The residence time data were studied to deduce the discharge flow pattern. This paper presents the results of three different flow pattern interpretation techniques: the best of them (mass-time relationships) is shown to give a very clear identification of the solids flow pattern and the flow channel boundary.     

基于离散元的中心椎体筒仓偏心卸料侧压力分析

利用EDEM建立中心锥体筒仓缩尺试验模型,通过EDEM软件模拟得出中心锥体筒仓仓壁及锥体侧压力,对比EDEM模拟值、试验值和相关的Janssen公式值.验证EDEM软件模拟的合理性.然后进行中心锥体筒仓单孔卸料模拟,提取部分与试验传感器位置的仓壁及锥体侧压力,得出侧压力超压系数,与试验值进行对比.     

A new load cell for measuring normal and shear stresses

A special stress measuring device for determining the normal and shear stresses acting on silo walls was developed and tested. The load cell can be used for measuring simultaneously the normal stress as well as the intensity and direction of the shear stress.     

补气料仓中宽筛分粒煤的下料特性

在自行设计的有机玻璃补气料仓系统上对宽筛分粒煤下料特性进行了实验研究,结果表明,料仓出口直径、粒煤粒径和外水分对宽筛分粒煤在补气料仓中的下料特性有显著影响.宽筛分粒煤的下料流率随料仓出口直径的增大而增加,但增加量随着补气量的增加而减小.增加宽筛分粒煤的平均粒径使料仓出口有效尺寸减小,导致物料下料流率减小.增加宽筛分粒煤...     

Three‐dimensional numerical analysis of injection‐compression molding process

Injection‐compression molding (ICM) process, combining conventional injection molding (CIM) process with compression molding, has been widely used in the manufacturing of optical media and optical lenses. Most of previous numerical studies regarding ICM process employ the Hele‐Shaw approximation, which is appropriate for thin cavity geometry only. This work presents a three‐dimensional numerical analysis system using a stabilized finite element method (FEM) and an arbitrary Lagrangian‐Eulerian (ALE) method for more rigorous modeling and simulation of ICM process of three‐dimensional geometry. The developed system is verified by comparing the results with existing experimental data as well as simulation data obtained from commercial software. Then, the system is adopted for simulations of ICM process of an optical lens, which is a practical example of three‐dimensional geometry. According to the simulation results, three‐dimensional flow characteristics are found to be significant especially during compression stage because of the squeezing nature of the flow. The results are then compared with those of CIM process, showing that ICM process results in reduced and more uniform distributions of the generalized shear rate and shear stress of the final part. Basic parametric studies are also carried out to understand effects of processing conditions, such as compression velocity and compression gap. POLYM. ENG. SCI.,2011. © 2011 Society of Plastics Engineers     

Simulation of Orifice Flow Influenced by Lateral Flow in a Trough‐Type Liquid Distributor

A computational fluid dynamics (CFD) simulation is performed to investigate the influence of lateral flow on the orifice flow in a trough‐type liquid distributor. The discharge coefficients from the simulation are in good agreement with the experimental values, indicating that the CFD simulation is accurate in describing the outflow through orifices. The lateral flow near an orifice can change the velocity and pressure distributions of flow regions in front of this orifice, causing a decrease in the discharge coefficient. This phenomenon is supported by the theory of flow past a blunt body. An important implication derived from this finding is that the influence of lateral flow should be minimized in the design of a trough‐type liquid distributor, because the decrease in the discharge coefficient leads to non‐uniform outflow. The structure of a trough‐type liquid distributor is optimized to improve the liquid distribution performance by reducing the influence of lateral flow.     

Determination of bulk solid concentration changes during granular flow in a model silo with ECT sensors

Experiments in a cylindrical model silo were carried out with different initial densities of sand and silo wall roughness. Solid concentration changes during granular flow in the model silo were measured with electrical capacitance tomography (ECT) sensors. During silo flow, strong dynamic effects connected with booming sound occurred. Local one-dimensional (1D) and cross-sectional 2D evolutions of solid concentrations in dry sand during silo discharge were observed. The 1D phenomena were estimated from the raw data and the 2D phenomena were obtained from the reconstructed data by solving an inverse problem with a linear back projection algorithm.     

Simulation of dense granular flows: Comparison with experiments

A comparison of the predictions of a rheological model that we recently developed with experimental results of stress and flow profiles in a pilot scale silo is presented in this work. Experiments were performed to collect information on the flow field by means of a tracer method and on wall normal stresses at several different positions along the vessel. The silo (2.5 m high, 0.5 m wide) had the possibility of inserting internal devices; the model was first validated on data without internals and then used to predict the profiles for the case with them. Both stress and flow profiles with and without internals agree with the experimental results within the experimental error that locally could be rather significant due to the difficulty of large scale experiments with granular materials.     

Investigation of wall stress and outflow rate in a flat-bottomed bin: A comparison of the DEM model results with the experimental measurements

The present paper provides a discrete element method (DEM) analysis of the filling and discharge processes of granular material in a 3D flat-bottomed bin. A granular aggregate of nearly round particles (20,400 pea grains, 7.2-7.8 mm in diameter) is considered. The numerical results are compared with the experimental data. The DEM analysis provides an accurate prediction of wall stress distribution and the outflow rate of discharge throughout the bottom orifice. The stress distribution developed within the granular material after filling and during the discharge phase is considered, and the transition from the active to passive stress state is discussed. This analysis aims to quantitatively predict the flow parameters related to the careful identification of the material parameters. The investigation presented may be useful for the ongoing development of DEM.     

多点卸料浅筒仓力学性能检测

结合实际工程，通过现场测试和实验分析结果，结合原型的数值模拟逆解验算，确定多点卸料特大型浅筒仓的负荷大小及分布，提供了力学参量的现场检测分析结果和长期的监测技术研究成果。此项成果填补了国内外多点卸料浅筒仓研究的空白。