共查询到19条相似文献,搜索用时 125 毫秒
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引 言大量实验结果[1~ 3]表明 ,循环流化床内气相和颗粒相的两相流体系中 ,颗粒浓度在提升管的横截面上存在显著的非均匀分布 .颗粒在某些条件下聚集于管壁 ,在某些条件下也可能聚集于管中央[4 ].颗粒浓度分布的非均匀性可以分为两种类型 ,一是颗粒层 (Particle -Layering) [5 ],其微观结构近似颗粒固定床 ,颗粒在沿平均速度方向上有排列成床的趋势 ,但仍保持流体特性 ;另为颗粒群(Particle -Packets) [6 ],颗粒群在流化床中的行为如同单相湍流中的流体涡团 ,作无规则运动 ,不断地形成、分解 .催化裂化提… 相似文献
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恒速流加是一种常见的发酵操作方式。通过对该发酵过程动力学的分析,得到反应器有效体积、稀释率以及过程中细胞浓度、底物浓度、产物浓度随时间的变化关系。且提出在发酵后期系统达到拟稳态。该模型的动力学分析为实验室及工业上的应用奠定了一定的理论基础。 相似文献
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张晓如 《硫磷设计与粉体工程》2023,(2):11-13+28+5
针对某电厂转运站煤场输送带头部漏斗堵料问题,通过料性分析和标定试验并结合EDEM离散元软件仿真技术,设定了煤料运行仿真参数,仿真了漏斗堵料状况,并根据仿真结果在漏斗上设置了挡板以解决堵料问题,并以仿真结果验证了改造效果。根据仿真改造模型对头部漏斗进行了改造,实际运行结果证明了改造效果良好,节约了改造时间和成本。 相似文献
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基于离散元法的锥形筒仓中颗粒流体的数学模拟 总被引:2,自引:0,他引:2
采用离散元法对ABS塑料球在筒仓内的流动进行数值模拟,并测定了ABS球的回弹及休止角等微观物性参数,验证了离散元模型中颗粒接触参数的正确性. 基于正交实验法考察了锥形改流体参数对料流的影响,分析了仓壁压力分布规律. 结果表明,锥形改流体参数对物料流型的影响顺序为锥形改流体倾角>锥形改流体距卸料口的高度>锥形改流体高度;锥形改流体倾角<120o时中心流无法转变为整体流. 添加合适的改流体后仓壁所受最大压力减小为原来的一半,最大压力位置上移. 相似文献
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长期以来,工业粉体的动力学研究一直处于空白状态,特别是以粉体为生产目标的水泥行业,这种研究更显得力不从心,最终导致全行业生产中的粉体控制严重落后于对流体和固体原料的控制水平。本文仅以均化库使用中顽症的解决为例,充分说明对粉体性质的研究,十分必要。 相似文献
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天然产物超临界流体萃取过程动力学分析 总被引:1,自引:0,他引:1
对已有超临界流体萃取过程模拟动力学模型提出新的改进。以破碎-完整细胞结构理论为基础,结合植物细胞组织特点建立了基于微分质量守恒方程的动力学模型。通过对萃取过程的分析和必要简化、假设,给出求解模型的初始条件和边界条件。模拟了9种物料的超临界萃取过程。首次得出萃取率和平均粒径的线性关系,利用该关系准确预测了不同平均粒径和流量下的萃取曲线。明确给出萃取过程如何划分为两阶段的方法。重点论述了植物细胞破碎率φf(或平均粒径dP)及内部传质系数ki对萃取过程的影响。 相似文献
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Hydrodynamic and elastoplastic theories are two commonly used continuum approaches for modeling granular materials. Here, the elastoplastic approach is extended to incorporate the rheology of dense granular flow, which therefore allows a quantitative comparison with the hydrodynamic approach under the same setting of rheological laws, material parameters, and numerical method. The flow patterns yielded by two approaches are apparently similar and the discharge rates are close. Yet the elastoplastic approach creates a narrow dome-like flow zone in contrast to the wide cone-like flow zone generated by the hydrodynamic approach. The shear localization is also less prominent in elastoplastic modeling owing to the existence of elastic deformation. The stresses predicted by two approaches match well in flow zones but show significant differences in stagnant zones. The proposed elastoplastic approach incorporating flow rheology can be used generally in both solid and fluid states of granular materials. © 2019 American Institute of Chemical Engineers AIChE J, 65: e16533, 2019 相似文献
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Shape dependence of resistance force exerted on an obstacle placed in a gravity‐driven granular silo flow
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Hiroaki Katsuragi Katha Anki Reddy Keita Endo 《American Institute of Chemical Engineers》2018,64(11):3849-3856
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 相似文献
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Austin B. Isner Paul B. Umbanhowar Julio M. Ottino Richard M. Lueptow 《American Institute of Chemical Engineers》2020,66(5):e16912
Free surface granular flows in bounded axisymmetric geometries are poorly understood. Here, we consider the kinematics and segregation of size-bidisperse flow in a rising conical heap by characterizing the flow of particles in a wedge-shaped silo with frictional sidewalls using experiments and discrete-element-method simulations. We find that the streamwise velocity is largest at the wedge centerline and decreases near the sidewalls, and that velocity profiles in the depthwise and spanwise directions are self-similar. For segregating size bidisperse mixtures, the boundary between small and large particles deposited on the heap is significantly further upstream at the sidewalls than at the centerline, indicating that measurements taken at transparent sidewalls of quasi-2D or wedge-shaped heaps are unrepresentative of an axisymmetric heap. The streamwise velocity and flowing layer depth locally satisfy the scaling relation of Jop et al (J Fluid Mech. 2005;541:167-192) when modified to account for the wedge geometry, highlighting the influence of wall friction on the flow. 相似文献
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在自行设计的有机玻璃流化料仓系统上对粉煤下料过程及其特性进行了实验研究。研究发现,在筒仓段与料斗段连接处上方存在一个临界面。在临界面以上的筒仓段,粉煤以柱塞流形式下料,在临界面以下,粉煤以不定向螺旋运动下料。研究结果表明,料斗下部的流化气对下料稳定性和下料流率有重要影响,存在最佳流化气位置区间和最佳流化气表观气速范围,当流化气补气位置太低,在补气位置附近易形成气压平衡拱。研究还表明,增加料仓压力能提高粉煤下料流率,改善下料稳定性,减弱流化气补气位置及气速对下料的影响,阻止气压平衡拱生成。 相似文献
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筒仓内颗粒流在化工生产中广泛应用,准确描述颗粒流的动力学规律对于调控化工反应过程中的混合和传输效率极为重要。颗粒温度是影响颗粒流的重要参数之一,为此搭建了基于线阵CCD相机的散斑能见度光谱测量装置,选取均值粒径分别为0.94和1.55 mm的球形颗粒进行实验。通过测量卸料过程中筒仓内颗粒流的时变颗粒温度,发现了离散颗粒运动在介尺度条件下具有稳定性。进一步,对比两种粒径颗粒的颗粒温度值,观察到稳态流动中大粒径颗粒具有更高的能量耗散,从而建立了宏观质量流率与介观颗粒温度之间的联系。通过分析筒仓内颗粒温度场的分布特征,发现了孔口附近的离散颗粒存在定向有序的运动。最后,根据筒仓内颗粒流堵塞过程中的颗粒温度变化曲线,揭示了颗粒流堵塞的弛豫变化规律。实验结果揭示的筒仓内颗粒流的运动规律,为完善化工生产中颗粒材料的存储与运输提供了参考数据。 相似文献
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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. 相似文献
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M. Niedostatkiewicz J. Tejchman K. Grudzień Z. Chaniecki 《Chemical Engineering Research and Design》2010
The paper presents results of concentration changes in cohesionless sand during dynamic mass flow in a rectangular model silo composed of a bin and hopper. Electrical capacitance tomography (ECT) was used. Sensors were located outside the silo along both the periphery and height. Local horizontal one-dimensional and cross-sectional two-dimensional evolutions of solid concentrations in dry sand during silo discharge were determined. The first ones were estimated from the raw data and the latter were obtained with the aid of the reconstructed data using a Linear Back Projection algorithm (LBP) to solve an inverse problem. Experiments in a model silo were carried out with two different initial sand densities and wall roughness grades. The measured results with ECT were compared with corresponding ones obtained with a Particle Image Velocimetry (PIV) method. 相似文献
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针对复合移动床反应器内固体颗粒运动,采用离散单元法模型(DEM)考察布料器分别为扇形开口和矩形开口时,布料器转速和开口对颗粒运动的影响,并基于文献结果论证了本文模型的准确性。模拟结果表明:①对于不同布料器,颗粒在移动床中呈现平推流和汇聚流两种流动形态。②随布料器转速及开口的增加,颗粒质量通量非线性增加。③随布料器转速的增加,下落床径向上颗粒分布更均匀;随布料器开口的增大,下落床径向上颗粒分布范围变大,颗粒分布更均匀;对下落床径向上颗粒分布,布料器扇形开口时分布呈U形、矩形开口时分布呈M形。④沿反应器轴向向下,颗粒分布有均匀化趋势;扇形开口布料器对颗粒分布的离散系数大于1,矩形开口布料器对颗粒分布的离散系数约为0.5。 相似文献
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在铜陵海螺两条日产万吨水泥熟料生产线中,设计了4座覫80m圆筒半球库,用于水泥厂原料和燃料的预均化储存,库内采用了混匀堆取料机,该设备的取料机无轨道,这在水泥行业为首次使用。该圆筒半球库由覫80m×14m高圆筒加上半球形网架顶盖组成。由于库内不对称储料和堆料的随机性,加上其直径很大,目前尚无成熟的结构设计理论和经验。设计时采用有限元程序对覫80m圆筒半球库进行了整体力学分析,并依据分析结果进行了结构设计,满足了工艺要求和结构安全稳定性,同时也达到了经济美观的效果。 相似文献