A theoretical analysis of channeling in bins and hoppers

The kinematic approach of limit analysis suggested by Drescher [7] is adopted to derive a criterion for channeling in cylindrical bins and conical hoppers. The bulk material is modeled as a perfectly plastic solid with the flow rule associated or non-associated with the Mohr—Coulomb yield condition, which is modified by a tension cut-off. The channeling criterion is derived by examining the stability of bulk material surrounding an empty channel. Partial failure mechanisms are considered, and the influence of the material/wall interface on the stability is discussed.     

The effect of interstitial air pressure gradients on the discharge from bins

This paper presents theoretical and experimental work on the effect of interstitial air pressure on the flow of granular materials from hoppers. In the first part of the paper, a theory is developed for the case of low Reynolds number flow in a conical hopper. In subsequent sections, the theory is extended to cylindrical bunkers, to higher Reynolds numbers, (where inertia effects cannot be neglected) and to cases where the compressibility of the gas is important. In all cases, the theory agrees well with experiment.     

普光气田关井油压恢复异常浅析

普光气田为国内首例开发的超深高酸性气田。单井产能高,关井后油压恢复出现随关井时间延长持续下降的异常情况。通过综合考虑井筒中各种因素,特别是温度的影响,引进井筒效应的概念,从理论上分析了高产纯气井在纯井筒储存和径向流动阶段,产生井口油压动态异常的机理,包括产生的条件及适用范围.研究表明,引起高产气井产生井口油压动态异常的主要原因是关井过程中井筒流体温度的变化和重组分的密度差异引起。因此,在井底压力的计算过程中,必须考虑井筒流体温度和重组份的影响。     

A reassessment of static bin pressure experiments

The experimental studies concerned with Janssen's formulas for bin pressures are reviewed and reassessed. This reassessment is motivated by a recent derivation of Janssen's formulas under less restrictive assumptions. A number of conclusions are drawn and several recommendations formulated as a result of this study. For example, while it is found that much of the published data is reliable, doubt is cast on some of the data presented in the most extensive laboratory investigation undertaken. Recommendations for experimental procedures and procedures for the determination of bin pressures are presented.     

提升管出口T型弯头压降特性的实验分析

在大型循环流化床装置上,以FCC催化剂颗粒为实验物料,针对提升管出口T型弯头用动态压力传感器测量了操作参数和结构尺寸变化对其压降的影响,系统地分析了T型弯头的压降特性。实验结果表明T型弯头的压降与颗粒浓度呈线性关系,与入口速度（提升表观气速）呈二次方关系;T型弯头出口管截面积的减小使得压降显著增大;T型弯头盲管高度的增加可使T型弯头的压降降低,但是当盲管高度增加到一定值时,压降减小不明显。盲管高度对压降的影响是由于盲管高度的增加改变了提升管上部压力的分布,使T型弯头入口压力减小,导致T型弯头的压降降低;同时盲管高度的增加也使提升管出口区域的负压约束区长度增加。盲管所形成的负压约束区构成了对提升管出口的约束作用,T型弯头的盲管高度越大负压约束区越长,约束作用越强。     

CPE成品料仓的改造

为解决氯化聚乙烯物料结块的问题，对其成品料仓进行了改进：(1)在现有设备基础上，增加合适的搅拌方式—螺旋式搅拌；(2)确定高效低噪的传动装置；(3)选择平稳、易于维修、不影响CPE物料质量的双支点机架。经过改造后，达到了预期的目标。     

大差异颗粒静态混合的实验研究

设计了一套混合段内安装挡板锥体内构件的实验装置,采用较大粒径差异的煤与瓷球,通过改变挡锥组数、加料比例等影响因素,对颗粒群的混合行为、混合均匀度的变化趋势与混合机理进行研究。结果表明:在混合段内设置挡板锥体是一种有效的混合方式,可以获得较好的混合均匀度;瓷球/煤的质量比5∶1加料时,混合效果最好;混合机理方面,对流、剪切、扩散共同作用于混合过程。     

Experimental investigations of velocity fields in packed bed static mixers

Experimental investigations of velocity fields have been carried out in static mixers filled by Inzhekhim random packings of various sizes and Rashig rings. Studies have been performed on a laboratory setup by stereoscopic particle image velocimetry using a Polis multiphase flow measurement system. Experimental data have been supplemented by the results of numerical modelling of the hydrodynamics of flow, which were obtained using ANSYS Fluent software.     

Experimental characterization and multi-scale modeling of mixing in static mixers

Mixing in static mixers is studied using a set of competitive-parallel chemical reactions and computational fluid dynamics (CFD) in a wide range of operating conditions. Two kinds of mixers, a wide angle Y-mixer and a two jet vortex mixer, referred to as Roughton mixer, are compared in terms of reaction yields and mixing times. It is found that the Roughton mixer achieves a better mixing performance compared to the Y-mixer. The effect of flow rate ratio on mixing in the Roughton mixer has been studied as well and it is shown that the mixing efficiency is not affected by the flow rate ratio. Moreover, experimental results and model predictions are in good agreement for all mixer geometries and operating conditions. CFD is used to calculate absolute mixing times based on the residence time in the segregated zone and it is shown that mixing times of less than 1 ms can be achieved in the Roughton mixer. In addition, CFD provides insight in local concentrations and reaction rates and serves as a valuable tool to improve or to scale-up mixers.     

选煤厂炼焦精煤采用煤仓脱水的实践

鹤壁六矿选煤厂为合理利用煤炭资源 ,满足市场需要 ,将原洗动力煤的系统改造为洗炼焦煤 ;为保证选煤产品水分达到用户标准 ,结合实际情况 ,增建了精煤贮仓 ,对洗精煤采用煤仓脱水 ,取得了良好效果。     

压力试验时钢制薄壁内压容器模糊静强度的可靠度

应用基于模糊数学与常规可靠性理论相结合的模糊可靠性设计方法,讨论钢制薄壁内压容器模糊静强度在最苛刻的压力试验条件下,有关标准可接受的模糊可靠度范围,为压力容器的模糊可靠性设计从理论走向实用提供了参考依据。     

Sensitivity analysis in static optimization of fermentation plants

Biotechnological processes are often characterized by uncertain model parameters, input variables which are difficult to handle and ill defined cost functions. Nevertheless, it is desirable to define optimal operating points. Starting with a robust approach for numerical optimization, the paper presents three different methods for evaluating the sensitivity of an optimal operating point to uncertain parameters or disturbances of the input variables. It is shown that sensitivity analysis can provide useful guidelines for designing biotechnical plants with invariant optimum operation in the presence of changing inputs or parameters.     

静压法合成人造金刚石晶体生长机理研究进展

文章综述了静压法合成人造金刚石晶体生长机理,但现有理论模型都存在不足,不能圆满解释合成中出现的各种现象.通过综述提出对金刚石晶体生长机理研究的必要性,并对其作出了展望.     

静态混合器中液液分散的实验及CFD模拟

在SK型静态混合器上进行甲苯-水两相混合实验,采用截面直接拍摄法获得分散混合性能指标Sauter平均直径（SMD）。利用Box-Behnken响应面分析设计实验,在Design Expert 7.0平台上拟合实验数据,获得SMD的多项式形式的表达式。建立了与实验相同的静态混合器物理模型,使用Mixture多相流模型、k-ε湍流模型进行了CFD模拟研究,获得了浓度场云图及分布混合指标不均匀系数。模拟所得压降与实验值的相对误差在15%以内,表明模拟结果与实验结果吻合较好。结果表明,静态混合器中液液分散过程是分散混合和分布混合共同作用的结果,两种混合经过6～8个混合单元后共同达到充分发展。充分发展后的SMD受表观流速、分散相分率和静态混合器直径三因素影响,且表观流速的影响最为显著;充分发展后的不均匀系数均达0.05以下,表明静态混合器自身具有较好的分布混合性能。     

A general correlation for pressure drop in a Kenics static mixer

A new pressure drop correlation in a Kenics static mixer has been developed. Pressure drop data were generated from computational fluid dynamics (CFD) calculations, avoiding the experimental limitations in obtaining comprehensive data enough for developing a reliable pressure drop correlation. Dimensional analysis reveals that the pressure drop characteristic of the Kenics static mixer can be described by three dimensionless groups, i.e., the friction factor, Reynolds number (Re), and aspect ratio of a mixing element (AR). A systematic graphical analysis led to a single master curve governing the pressure drop behavior of the Kenics static mixer, which had never been achieved before. We derived a pressure drop correlation fitting well with the obtained master curve in a general form into which the AR effect on the pressure drop is directly incorporated. Unlike the already existing correlations available in the literature, the correlation proposed in this study can cover the whole range of Re from laminar to turbulence. The reliability of the proposed correlation was validated by the comparison with various pressure drop data reported in the literature.     

The vertical force of bulk solids on objects in bins

The vertical force exerted on discs, spheres and horizontal square bars in test bins was measured during gravity flow of bulk solids. Approximate methods for estimating the vertical force on such objects were developed from the equation which expressed the stress in a conical mass flow hopper. With three adjustable parameters, good agreement was obtained between experimental and computed results for discs, provided the disc diameter was more that five times as large as the particle diameter. Identical parameters for a given material were found to be applicable in analyses for spheres and horizontal square bars.     

内置圆盘静态混合器纺丝组件压力降的计算

介绍了纺丝组件内置混合元件的熔体管路几何结构;对应欧姆定律和熔体流动特性方程,根据电路模拟法的计算原理,采用电路模拟法计算内置圆盘静态混合器的纺丝组件压力降.结果表明:以PA6与PE共混纺丝为例,共混物熔体流经喷丝板的压力降为9.80 MPa,远大于流经分配板的压力降0.241 MPa,熔体流经纺丝组件时,主要阻力产生...     

旋流静态混合器内瞬态压力波动信号递归特性

在湍流状态下(Re=1756～3512),为了揭示竖直螺旋上升流中非线性重现结构,采用混沌递归定量分析对(o)100 mm、长径比为2的SK型静态混合器内的瞬态脉动压力时间序列进行表征.通过挖掘静态混合器内压力波动时间序列的递归确定性与阈值系数、采样频率的内在变化规律,确定静态混合递归分析初始优化参数.实验结果表明,静...     

Experimental investigation of a rotating fluidized bed in a static geometry

Rotating fluidized beds in a static geometry are based on the new concept of injecting the fluidization gas tangentially in the fluidization chamber, via multiple gas inlet slots in its cylindrical outer wall. The tangential injection of the fluidization gas fluidizes the particles tangentially and induces a rotating motion, generating a centrifugal field. Radial fluidization of the particle bed is created by introducing a radially inwards motion of the fluidization gas, towards a centrally positioned chimney. Correctly balancing the centrifugal force and the radial gas-solid drag force requires an optimization of the fluidization chamber design for each given type of particles. Solids feeding and removal can be continuous, via one of the end plates of the fluidization chamber.The fluidization behavior of both large diameter, low density polymer particles and small diameter, higher density salt particles is investigated at different solids loadings in a 24 cm diameter, 13.5 cm long non-optimized fluidization chamber. Scale-up to a 36 cm diameter fluidization chamber is illustrated.Provided that the solids loading is sufficiently high, a stable rotating fluidized bed in a static geometry is obtained. This requires to minimize the solids losses via the chimney. With the polymer particles, a dense and uniform bed is observed, whereas with the salt particles a less dense and less uniform bubbling bed is observed. Solids losses via the chimney are much more pronounced with the salt than with the polymer particles.Slugging and channeling occur at too low solids loadings. The hydrostatic gas phase pressure profiles along the outer cylindrical wall of the fluidization chamber are a good indicator of the particle bed uniformity and of channeling and slugging. The fluidization gas flow rate has only a minor effect on the occurrence of channeling and slugging, the solids loading in the fluidization chamber being the determining factor for obtaining a stable and uniform rotating fluidized bed in a static geometry.     

单通道陶瓷膜管低压透水性能实验分析

无机陶瓷膜作为多孔介质具有分离效率高、耐酸、耐碱等优点,被视为在海水淡化、废水处理、气体分离等领域的研究热点。采用Al₂O₃管式单通道陶瓷膜材料构建膜组件,以燃煤电厂自来水、烟气冷凝水、脱硫废水三种不同水质为例,开展低跨膜压差下的膜组件透水性能实验,研究了膜参数、跨膜压差及水体温度等因素对渗透通量、渗透水质的影响,并对引发膜污染的机理过程进行了探讨分析。实验结果表明：陶瓷膜管的结构参数是关键因素,如孔隙率、孔径及厚度等;低跨膜压差下的渗透通量随压力增大呈线性提高,并未发现浓差极化现象,水体温度变化通过改变黏度进而影响渗透通量,同时水质较差时会导致渗透通量降低;陶瓷膜管的孔径是影响渗透水质的核心要素,微滤与纳滤膜对改善悬浮物含量、浊度及色度效果明显,不同孔径对盐度、电导率影响不同;从SEM图可以看出,污染物在膜表面或膜内部发生的沉积、架桥等现象导致严重的膜污染。充分认识影响陶瓷膜管渗透特性的关键因素及污染物的作用机理,对提高无机陶瓷膜的应用前景具有重要意义。