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循环流化床气固两相流动数值模拟的研究进展 总被引:1,自引:0,他引:1
对循环流化床气固两相流动数值模拟的研究进展进行介绍,包括传统的欧拉双流体模型、基于颗粒动力学理论的双流体模型、基于拉格朗日坐标系下的颗粒轨道模型、能量最小多尺度模型和小室模型,并对上述模型的原理、发展和优缺点进行了描述。 相似文献
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运用能量最小多尺度 (EMMS)模型 ,推导出滑移速度及颗粒速度的径向分布 ,并进一步计算了径向空隙率、流体速度、团聚物直径、流体对颗粒的悬浮输送能量和颗粒的质量流率等相关的动力学参数 .模型计算结果反映了气固垂直两相流的径向不均匀性 (稀、密两相共存 )及环 /核结构的存在 .计算值与实验结果相吻合 .滑移速度的计算结果表明在核心区内也存在着团聚物 ,并不是呈现单一颗粒运动形态 ,这与实验现象一致 .该模型不仅克服了原有EMMS模型求解困难的问题 ,而且其计算不依赖于核心区半径等任何待定参数 ,只需物性参数、床层截面平均空隙率和操作参数即可 ,方便了实际应用 . 相似文献
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颗粒流体两相流能量最小多尺度作用(EMMS)模型简介 总被引:1,自引:0,他引:1
颗粒流体两相流能量最小多尺度作用模型(EMMS模型)认为,不均匀两相流系统中存在多尺度的相互作用,通常的动量质量守恒条件并不足以确定系统的状态,稳定性条件是必要的。该模型实现了对不均匀两相流状态的定量描述和对聚式散式流态化系统的统一关联,并揭示了不均匀结构、饱和夹带、流型过渡等重要现象的机理。本文简述了该模型的基本思想和要点。 相似文献
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气固流化床反应器是典型的具有多尺度非均匀动态结构的复杂系统。实现对该类反应器定量描述和定向调控的关键是深入了解系统内介尺度结构的形成和演化特征。能量最小多尺度(EMMS)方法为气固非均匀系统的量化表征提供了一种通用的建模思路。首先回顾了EMMS理论在构建曳力本构关系方面的应用,重点介绍了本课题组在EMMS曳力模型普适化方面所做的部分工作;随后对介尺度结构时空动态演化行为的群平衡建模方法进行了论述,并给出了群平衡和结构曳力模型相耦合的连续介质模拟框架;最后讨论了EMMS原理在预测反应器宏尺度动力学方面的应用,包括模型在不同流域的拓展、操作相图的绘制以及循环流化床的全回路稳态建模方法等。 相似文献
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气—固流化床颗粒的内循环流动 总被引:2,自引:0,他引:2
从多尺度范围考察了气-固流化床内尾涡颗粒流和乳化相颗粒流的运动规律,将分散的尾涡颗粒流和乳化相颗粒流连续介质化,从流变学角度定义了颗粒洗粘度,用流体力学方法建立了内循环流动结构的多尺度,连续介质流模型,较好地揭示了颗粒循环循环流动的规律。实验观测支持模型预测结果。 相似文献
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在φ 90 mm×1 000 mm的有机玻璃流化床中,采用PV4A颗粒测速仪测定了不同粒径的河沙、聚氯乙稀(PVC)颗粒在操作气速为0.218~0.524 m/s下不同轴/径向位置的颗粒浓度波动信号,考察了颗粒浓度波动信号多尺度分解的尺度,以及代表颗粒和各不同尺寸气泡运动的细节信号的能量分率与操作条件的关系.研究表明,各尺度下细节信号的能量分率随操作气速、轴向距离增大而增加,随径向距离增大而减小. 相似文献
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将基于能量最小多尺度方法(EMMS)的曳力模型耦合到双流体模型中,并针对循环流化床内的气固两流动进行了模拟研究。采用全滑移壁面边界条件处理颗粒相,考察了3种网格尺度对轴向空隙率和出口颗粒循环量等气固流动特性的影响。计算结果表明,应用EMMS曳力模型处理相间作用力,同时在采用全滑移壁面边界条件处理颗粒相时,双流体模型能够正确预测轴向空隙率分布。采用网格尺寸为2.325 mm×20 mm时,模拟结果和实测数据吻合较好,表明在循环流化床的数值模拟中选择恰当的网格尺度是极为重要的。 相似文献
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综述了循环流化床提升管和下行管气固两相流动模型研究的现状在对这些模型分类评述的基础上,给出了可用于描述下行管反应流动规律的一维两相和地维两相流动模型,为下行管反应器的设计,放在提供了理论依据。 相似文献
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通过颗粒示踪和热示踪两种方法对鼓泡循环流化床中的颗粒循环速度进行了实验研究。实验结果表明:热示踪方法和颗粒示踪方法测量鼓泡循环流化床的移动床中颗粒循环速度在一定范围内是一致的。但热示踪方法还存在一定的局限性,还需要进一步从理论和实验上完善 相似文献
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EFFECTS OF SECONDARY AIR INJECTION ON GAS-SOLID FLOW BEHAVIOR IN CIRCULATING FLUIDIZED BEDS 总被引:3,自引:0,他引:3
Yong Kang Pyung S. Song Jong S. Yun Yi Y. Jeong Sang D. Kim 《Chemical Engineering Communications》2000,177(1):31-47
Effects of secondary air injection on the hydrodynamics such as solid holdup and gas-solid flow behavior were investigated in a circulating fluidized bed. The gas velocity in the riser, the ratio of secondary air velocity to that of primary air, and the solid circulating rate were chosen as operating variables. Fluid cracking catalyst(FCC) with a density of 1840 kg/m3 and a mean diameter of 74 um was employed as the solid phase. The secondary air was fed to the riser radially or tangentially at the wall of the column. Pressure drop fluctuations in the riser were measured and analyzed by adopting the stochastic method to characterize the effects of secondary air injection on the gas-solid flow behavior in the bed.
It has been found that the injection of secondary air into the riser can increase the solid holdup in the riser considerably, and that the tangential injection of secondary air is more effective for the increasing the solid holdup than the radial injection. However, the gas-solid flow behavior has been found to become less persistent with the injection of secondary air; the resultant flow behavior is more complex when the air is injected tangentially than radially. The solid holdups in the primary as well as secondary zones of the riser have been well correlated in terms of not only operating variables but also fractal dimension of the pressure fluctuations. 相似文献
It has been found that the injection of secondary air into the riser can increase the solid holdup in the riser considerably, and that the tangential injection of secondary air is more effective for the increasing the solid holdup than the radial injection. However, the gas-solid flow behavior has been found to become less persistent with the injection of secondary air; the resultant flow behavior is more complex when the air is injected tangentially than radially. The solid holdups in the primary as well as secondary zones of the riser have been well correlated in terms of not only operating variables but also fractal dimension of the pressure fluctuations. 相似文献
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YONG KANG PYUNG S. SONG JONG S. YUN YI Y. JEONG SANG D. KIM 《Chemical Engineering Communications》2013,200(1):31-47
Effects of secondary air injection on the hydrodynamics such as solid holdup and gas-solid flow behavior were investigated in a circulating fluidized bed. The gas velocity in the riser, the ratio of secondary air velocity to that of primary air, and the solid circulating rate were chosen as operating variables. Fluid cracking catalyst(FCC) with a density of 1840 kg/m3 and a mean diameter of 74 um was employed as the solid phase. The secondary air was fed to the riser radially or tangentially at the wall of the column. Pressure drop fluctuations in the riser were measured and analyzed by adopting the stochastic method to characterize the effects of secondary air injection on the gas-solid flow behavior in the bed. It has been found that the injection of secondary air into the riser can increase the solid holdup in the riser considerably, and that the tangential injection of secondary air is more effective for the increasing the solid holdup than the radial injection. However, the gas-solid flow behavior has been found to become less persistent with the injection of secondary air; the resultant flow behavior is more complex when the air is injected tangentially than radially. The solid holdups in the primary as well as secondary zones of the riser have been well correlated in terms of not only operating variables but also fractal dimension of the pressure fluctuations. 相似文献
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循环流化床燃烧数学模型及试验研究 总被引:5,自引:3,他引:2
利用循环流化床内气-固两相流动基础方面的研究成果, 提出床内气固浓-淡流动模型, 建立适用不同结构参数的循环流化床燃烧模型, 考虑了床内气体、固体颗粒的返混、循环过程以及煤燃烧、污染气体的生成和分解、颗粒磨损等过程. 在循环流化床燃烧试验台上进行实验研究, 模型仿真结果和实验数据吻合良好, 表明气固两相浓-淡流动模型所建立的循环流动床燃烧系统模型可以正确地模拟循环流化床的燃烧过程. 相似文献
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引 言流化床换热器具有防、除垢和强化传热等优点 ,在化工、食品、海水淡化、废水处理等领域具有广阔的应用前景[1].目前 ,流化床换热器历经散式流化床、内循环流化床 ,已发展到外循环流化床换热器[2 ],它要求在较稀的颗粒浓度 (颗粒浓度小于 5% )、较高的流速 ( 1~ 3m·s- 1)下操作 .流化床换热器中液体流动及颗粒运动状态的研究对流化床换热器的设计和操作具有重要意义 ,但人们对循环流化床换热器中颗粒运动情况的研究还很缺乏 .考虑到循环流化床换热器中的每根换热管都可作为一个独立的循环流化床对待[3].本文试图建立一滑移速度模型… 相似文献
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This article is devoted to analyzing the mass transfer in heterogeneous gas-solid flow by means of structure and process decomposition. A multi-scale mass transfer model was developed on the basis of the hydrodynamics calculated from the so-called EMMS model. This resulted in the predictions of the steady-state two-dimensional concentration distributions of sublimated substance as well as total mass transfer coefficient for circular concurrent gas-solid contactors. The predictions were validated by experimentally measured (via an on-line HP GC-MS system) axial concentration distributions of sublimated naphthalene in air in a circulating fluidized bed riser 3.0 m in height and 72 mm in diameter. The experiment also obtained mass transfer coefficients comparable to theoretical predictions under conditions with various gas velocities, solid circulation rates, particle sizes, and active material fractions in the particles. Both the theoretical and experimental results demonstrated that the heterogeneous flow structure prevailing in the concurrent gas-solid flow greatly influenced the flow's mass transfer. 相似文献