基于整体流型的粉体料仓设计分析

介绍了各种料仓流型,分析了影响料仓流型的因素,并应用到整体流料仓设计,在料斗形式、曲线、材料的选择以及改流体的设置上,作了详细的分析比较。     

粉体料仓的设计

介绍了料仓设计的基本方法, 包括流型选择、流型设计以及卸料口尺寸的确定方法等, 最后给出一个应用实例。     

料仓设计中物料阻流问题的探析

本文通过分析料仓中物料的流型、阻流原因、提出设计中的考虑因素及预防措施。     

料仓流型及改善贮料流动性分析

本文介绍了各种料仓流型,并详细分析了影响料仓流型的因素,尤其是装料形式、改流体对料仓流型的影响,为料仓设计、选择流型和改善散体流动措施提供了参考。     

粉体料仓下料不畅的原因及解决方法

本文从主观设计和客观生产因素两方面全方位分析了卸料口堵塞的原因，并有针对性的提出了防止料仓卸料口堵塞的方法。     

粉体料仓的设计与安全防护

简要介绍了粉体料仓的结构和流动状态,指出了料仓设计需要考虑的各种因素,分析了粉体料仓在使用中易出现的问题,如流动不稳定、搭桥、堵塞等,提出了一系列预防结拱、破拱措施,以及防止储存物料损失、污染环境、危害人员和设备安全的安全防护措施。     

粉体料仓的卸料问题

<正>料仓能否保持连续、平稳和顺畅卸料是水泥生产正常运行的基础,更是下级给料计量设备稳定运行和准确计量控制的关键影响因素。但在工程设计中却常常不被重视,由于下料仓问题导致计量设备不能正常工作的现象较为常见,尤其对于煤粉和粉煤灰系统更为突出。本文对此进行讨论,希望为料仓的设计和选用提供有益的参考。1料仓中物料卸料的主要形态粉体物料在料仓中实际卸料流动状态往往比较     

料仓中粉体流动数学模型分析

对料仓中粉体流动进行模拟可以获得粉体流动的压力、流动速度、相组分和相浓度分布。模拟料仓中粉体流动有3种数学模型:有限元素模型、离散元素模型和混合模型,每种模型各自适用于不同的流动区域,混合模型集合了前2种模型的优点,是模拟料仓中粉体流动的最先进模型。     

影响粉体料仓卸空率的因素分析

正0前言粉体料仓是建材生产的重要设备,用于储存粉体物料、均化物料性能及平衡工艺物流等,是粉体工艺过程中各种单元操作之间必不可少的设备。粉体料仓卸空率是指排出物料的量与其仓容量的比值。该指标衡量的是粉体料仓的有效容积和残料量的变化关系,是粉体料仓主要技术性能指标之一,是粉体料仓价值在使用功能上的体现。1关于粉体料仓卸空率的认识对于卸空率的看法,应该是一个衡量粉体料仓是否具有先进性的指标,而不仅作为一个日常使用     

料仓中粉体的流动现象及受力研究

在大规模、连续化利用粉体或生产粉体的相关生产作业中,原料、半成品以及成品数量和重量巨大。生产过程中需要利用各种输送与仓储设备使粉体在各工序之间有序地、不间断地进行输送和储存,以保证生产正常进行,进而实现生产的自动化。为了更好地实现自动化控制,研究了粉体在料仓中的流动化现象以及受力情况,论述了料仓中粉体的两种不同流动方式及各自特点,分析了粉体在投入料仓时以及静止状态和运动状态下粉体的压力分布及交替应力的产生和分布。     

Influence of inherent particle characteristics on hopper flow rate

The inherent factors influencing the shear strength of particulate materials are also believed to influence the flow rate through a hopper. These inherent particle characteristics include particle size, particle-size distribution, particle shape, angularity, hardness, and surface roughness. To determine the effect of inherent particle characteristics on flow rate and pluviated void ratio, a wide range of materials were tested. These materials ranged from manufactured sands and glass beads to natural sands. Determination of particle size, particle-size distribution, and hardness was achieved by conducting conventional tests such as sieve analyses and specific gravity tests. Quantification of the shape and angularity parameter is more difficult due to the nonavailability of any standard techniques. To achieve the objective of quantifying shape and angularity, a new technique was developed utilizing the image analyzer. Two shape parameters, namely, Shape Factor and Angularity Factor, were determined for various materials. Shape and Angularity Factors were correlated with flow rate as well as the pluviated void ratio. Overall, the results indicate that as shape and angularity of particles increase, the flow rate decreases, and pluviated void ratio increase. A good correlation between drained shear strength properties and the flow rates measured in the cone was also found to exist. Therefore, index tests such as flow rate through a flow cone (hopper) can be used to estimate the drained monotonic strength of particulate materials.     

Heat transfer and flow pattern in vertical liquid-solids flow

Wall-to-bed heat transfer in hydraulic transport of spherical glass particles of diameter 1.20, 1.94 and 2.98 mm and in single-phase flow regime was studied. Experiments were performed by transporting the spherical glass particles with water in a 25.4 mm I.D. copper tube equipped with a steam jacket.In the runs without particles, the tube Reynolds number varied between 2280 and 21,300, while in hydraulic transport runs, the tube Reynolds number varied between 3300 and 20,150. The loading ratio (G_p/G_f) was between 0.07 and 0.328, and the fluid superficial velocity was between 0.29·U_t and 2.86·U_t, where U_t represents the single particle terminal velocity. For these ratios, the voidage ranged from 0.715 to 0.895.The data for the heat transfer factor (j_H) in single-phase flow are correlated using a general form j_H=f(Re). The data for wall-to-bed heat transfer in the hydraulic transport of particles show that an analogy between heat and momentum transfer exists. The data were correlated by treating the flowing fluid-particle suspension as a pseudofluid, by introducing a modified suspension-wall friction coefficient (f_w) and a modified Reynolds number (Re_m).     

入口流速对间断微通道内流型演变及流量分配特性影响

微通道内气液两相流动规律是影响微通道换热器换热系数和流场温度均匀性的主要因素。以N2和H2O为工质，对间断、并联矩形微通道换热器内气液两相流型的起始、发展、稳定过程的演化以及并联通道内流量分配不均匀特性进行了数值模拟研究。结果表明，不同的进口Re对微通道内流型的演变过程和流动周期有重要影响，当进口Re为450时，气相工质在均流腔内以离散的散团状形态脉动扩散至微通道中，并联通道内气相工质从弹状流型态逐渐转变为泡状流型态；当进口Re增至为1600时，气相工质在均流腔内以较连续的椭圆状型态扩散至微通道中，并联通道内气相工质从环状流型态逐渐转变为泡状流型态。通道结构还将影响并联通道间的流量分配的均匀性，间断微腔的存在使微通道内工质质量流量分布均匀性提升38.7%，通过研究通道内压力分布规律，发现通道内静压的分布不均匀是导致两相工质从均流腔进入微通道时发生不均匀分配的重要原因。     

On the development of flow pattern in a bubble column reactor: Experiments and CFD

A comprehensive analysis of the development of flow pattern in a bubble column reactor is presented here through extensive LDA measurements and CFD predictions. In the LDA measurements, the simultaneous measurements of 2D velocity-time data were carried out at several radial locations and many axial cross-sections of the column for two different spargers. The profiles of mean axial liquid velocity, fractional gas hold-up and bubble slip velocity showed excellent agreement between the predictions and the experimentally measured values. The experimental results showed that the mean tangential velocity varies systematically in the radial as well as along the axial co-ordinates. The turbulence parameters viz. turbulent kinetic energy, energy dissipation rate and eddy diffusivity were also analysed. The estimated values of local energy dissipation rate obtained using eddy isolation model were used for establishing the energy balance in the column. The experimental data were used for the estimation of normal and shear stress profiles. For the case of single point sparger, just above the sparger region, the bubble plume was seen to have a strong tangential component of motion thereby yielding higher gas hold-up slightly away from the centre. This visual observation was well captured in profiles of all the hydrodynamic parameters obtained from the experimental data. CFD simulations of the mean velocities, gas hold-up and turbulent kinetic energy compared well with the experimental results.     

GPU-based discrete element simulation on flow stability of flat-bottomed hopper

In this study, the flow stability of the flat-bottomed hopper was investigated via GPU-based discrete element method(DEM) simulation. With the material height inside the hopper reducing, the fluctuation of the flow rate indicates an unstable discharge. The flow regions of the unstable discharge were compared with that of the stable discharge, a key transformation zone, where the voidage showed the largest difference between unstable and stable discharge, was revealed. To identify the relevance of the key transformation zone and the hopper flow stability, the voidage variation of the key transformation zone with material height reducing was studied.A sharp increase in the voidage in the key transformation zone was considered to be the standard for judging the unstable hopper flow, and the ‘Top–Bottom effect' of the hopper was defined, which indicated the hopper flow was unstable when the hopper only had the top area and the bottom area, because the voidage of particles in the top area and the bottom area were both variables.     

Rotated, circular arc models of stress in silos applied to core-flow and vertical rat-holes

Rotated, circular arc geometry models have been developed to describe core-flow and vertical rat-holes in cylindrical hoppers and silos.The conceptual problem of the variation of incremental element thickness has been overcome, resulting in models of greater theoretical rigour.Models have been developed in an average stress and point stress form. Analysis shows that stresses vary with vessel radius through an arc angle parameter, ε, as well as with bed depth.The models indicate that conditions at a rat-hole annulus wall are quite different from the mean stress or wall stress and this has implications for stability and flow.A modified failure criterion, based upon azimuthal stress has been used to assess the stability of deep rat-holes, and a range of rat-hole stability determined, which is dependent upon material properties and vessel diameter.Predicted stress distributions are functions of assumed internal stress distribution relationships. More physical data are required in this area to enable reliable modelling.     

Consolidation and flow of cohesive bulk solids

The strength and the flow properties of bulk solids can be determined by performing shear tests. A shear test always consists of two parts, consolidation and measurement of strength. The measured strength depends on the way and degree of consolidation. During consolidation a stress history is impressed on the bulk solid sample which only vanishes after steady state flow. Since the consolidation is normally done nonhydrostatically, the strength will depend on the direction of stress application (anisotropy). Thus, the strength of a bulk solid sample strongly depends on its stress history and it can show anisotropic behaviour. These effects have to be considered when comparing available shear testers.     

The shape of the cohesive arch in hoppers and silos — Some theoretical considerations

Models of the cohesive arch have been developed in order to predict arch shape and test the circular arc hypothesis first proposed by Enstad [‘On the theory of arching in mass flow hoppers’, Chem. Eng. Sci., 1975, 30, 10, 1273-1283].A 2-dimensional arch was modelled. Vertical and horizontal force balances described the system, with 2 unknown: arch stress, σ_arc, and vertical arch co-ordinate y. A rotationally symmetrical system was also modelled and included the azimuthal stress σ_az. σ_az was related to σ_arc by a Mohr-Coulomb yield type of equation. These equations were solved numerically by an Euler method.A least squares fit was used to predict the equivalent circular arc radius R and circular arc co-ordinate y_circ. The square of deviation from the circle Σ(y − y_circ)² was used as a statistical measure of the goodness of fit to the circular arc.The arch shape was generally an excellent approximation to the circular arc. However, the arch diverged from the circular as arch span increased.A dimensionless group was defined: the Stress-Radius Number, N_SR, which incorporates the ratio of equivalent circular arc radius to the arch stress at the apex. N_SR was constant for a given set of conditions and was ideally equal to 1 for a 2-dimensional arch and 2 for a rotationally symmetrical arch with no overpressure.Arch thickness models had little effect upon arch shape but had a great influence upon stress. This affected the critical outlet dimension for flow.Rotationally symmetrical arches were very sensitive to the relation between azimuthal and arch stresses. This affected both arch shape and stresses.A critical outlet dimension was calculated and showed great variation dependent upon assumptions made. Jenike's approach of an arch of constant thickness with no overpressure yielded a conservative value.     

Discrete element method modeling of non-spherical granular flow in rectangular hopper

Discrete element method (DEM) was developed to simulate the corn-shaped particles flow in the hopper. The corn-shaped particle was described by four overlapping spheres. Contact force and gravity force were considered when establishing the model. In addition, the velocity distribution and voidage variance of corn-shaped and spherical particles were investigated. The results show that the vertical velocity difference between centre and side wall and the horizontal velocity of corn-shaped particles are relatively larger than that of spherical particles. The mean voidage for corn-shaped particles is smaller than for spherical particles in any hopper. And the mean voidage values decrease with the increase of the ratio of width and length (D/L) and the ratio of height and width (H/D) for both corn-shaped and spherical particles. The local voidage profiles in hoppers with different D/L were also studied. It demonstrates that the wall effect on the voidage of spherical particles is more remarkable than that of the corn-shaped particles. The voidage fluctuations of corn-shaped and spherical particles decrease obviously with increasing D/L when the particles are far away from the wall. And when the particles are discharging, the wall effect on the spherical particles is more remarkable than the condition of packing naturally.     

重力对垂直相分离冷凝管内流型调控的影响

随着重力的降低,冷凝换热性能急剧恶化,特别在微重力条件下,流型与传热极不协同,所需的冷凝长度要比地面常规重力情况大一个数量级。基于非能动相分离概念的适用于不同重力条件的新型相分离冷凝管,促进了流型与传热的协同,极大强化了冷凝换热。在地面常规重力、小重力和微重力情况下,数值研究了新型冷凝管内垂直上升的空气-水两相流型的调控过程。通过研究得出:在三种不同重力条件下,均呈现“气在壁面,液在中心”的全新分布模式,特别是在微重力情况下,环隙区域内完全被气体占据,液体完全在核心区域内流动;重力越小,调控后液膜厚度减小幅度越大,特别在微重力条件下,减薄到1/32;重力越小,调控后薄液膜主导的冷凝换热量提高幅度越大,特别在微重力条件下,调控后提高到57.4倍,极大地强化了冷凝换热。总体来说,重力越小,流型调控过程越有利于强化冷凝换热。