共查询到17条相似文献,搜索用时 187 毫秒
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稠密气固两相流动过程模拟的改进模型与应用 总被引:2,自引:0,他引:2
提出了模拟稠密气固两相流动的改进模型。湍流流场采用改进的k-ε-εe模型,颗粒的聚合效应采用聚合力的当量直径折算模型计算。将颗粒团作为离散相,研究颗粒团的运动、碰撞、破碎与合并。应用上述模型数值模拟了循环流化床内的稠密气固两相流动。得到了床内气相速度、颗粒团分布、颗粒浓度分布及颗粒团大小分布等详细两相流场信息。计算结果合理,与前人实验结果相符。模拟结果详细揭示了循环流化床内稠密气固两相流动的基本特征。图8表2参8 相似文献
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高通量循环流化床提升管中气固两相流动的研究 总被引:1,自引:0,他引:1
发展清洁煤炭利用、煤炭多联产和IGCC迫切需求研发先进的煤气化技术。循环流化床(CFB)提升管内的气固两相流动对循环流化床气化技术有重要影响。在f 0.187′10 m的冷态实验台上考察密相CFB提升管内气固两相流动。基于能量最小多尺度原理(EMMS)提出了改进的曳力修正系数表达式,并嵌入到双流体模型中,完成了冷态实验台的三维数值模拟。结果展现了CFB提升管内典型的环核结构和壁面颗粒返混现象,同时捕捉到了颗粒团的形成与破裂运动。通过与Gidaspow曳力模型计算结果的比较证实,提出了曳力修正系数可以较好地模拟浓相CFB提升管内的气固两相运动。 相似文献
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本文基于气固两相欧拉-欧拉双流体模型,对多孔布风鼓泡流化床内气固两相流流动特性进行了数值模拟,研究了床内压力分布,气泡的运动行为,以及气相和颗粒相速度的分布情况,并将模拟结果与相应实验数据进行比较。结果表明所用模型能较好的预测流化床内气固两相流的流动特性,模拟结果与实验结果吻合较好。 相似文献
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宽筛分流化床气—固两相流动结构离散颗粒模型 总被引:5,自引:0,他引:5
建立了适合描述宽筛分流化床气 固两相流动结构的离散颗粒模型。颗粒的运动满足牛顿第二定律 ,流体相的运动规律由局部平均的纳维 斯托克斯方程求解 ,两相间的耦合由牛顿第三定律决定。对宽筛分流化床中气泡的形成、颗粒的流化过程进行了数值模拟 ,结果与实验现象相符合 ;模拟结果还发现单颗粒的运动速度表现出不可预测特性 ,颗粒的总体速度不完全满足正态分布。 相似文献
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鼓泡流化床流动特性的欧拉-离散单元方法模拟 总被引:5,自引:2,他引:5
利用欧拉—离散单元方法对气固射流流化床内的流体动力学特性进行了数值模拟。在模型中把气相作为连续介质处理,采用欧拉方法建立其动量及质量守恒方程;对固体颗粒相则采用属于拉格朗日范略的离散单元方法(DEM)模拟;气固两相之间的相互作用采用DiFelice经验关系式反映。利用该模型模拟了流化床内初始阶段的气固两相流动特性。此外,由于气泡特性对流化床的流化质量具有重要的影响,故利用频谱分析理论对床内的模拟压力信号时间序列进行了分析,得出了在几个典型入口气速下的气泡统计生成频率,数值模拟结果与有关实验结果定性一致。 相似文献
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为了研究喷动流化床煤部分气化炉的气-固流动特性,采用三维欧拉多相流模型和颗粒动能理论相结合的数学模型,对一台直径100 mm的喷动流化床试验台进行了数值模拟研究.研究内容包括喷动流化床不同工况下内部射流的发展、气-固流动特性、典型工况下气体速度分布、颗粒速度分布以及由于颗粒碰撞引起的颗粒相压力分布.模拟结果表明:典型工况下,当喷动风与总风的比例为50%时,流场有利于煤气化;气体曳力和颗粒碰撞对环形区颗粒特别是靠墙区颗粒的运动影响很大.为了验证模型的合理性,采用文献中的试验工况进行计算,计算结果和文献中的测量值吻合较好. 相似文献
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Xue-yao Wang Fan Jiang Xiang Xu Sheng-dian Wang Bao-guo Fan Yun-han Xiao 《热科学学报(英文版)》2009,18(2):137-141
Gas-solid flow in dense CFB (circulating fluidized bed)) riser under the operating condition, superficial gas 15.5 m/s and
solid flux 140 kg/m2s using Geldart B particles (sand) was investigated by experiments and CFD (computational fluid dynamics)
simulation. The overall and local flow characteristics are determined using the axial pressure profiles and solid concentration
profiles. The cold experimental results indicate that the axial solid concentration distribution contains a dilute region
towards the up-middle zone and a dense region near the bottom and the top exit zones. The typical core-annulus structure and
the back-mixing phenomenon near the wall of the riser can be observed. In addition, owing to the key role of the drag force
of gas-solid phase, a revised drag force coefficient, based on the EMMS (energy-minimization multi-scale) model which can
depict the heterogeneous character of gas-solid two phase flow, was proposed and coupled into the CFD control equations. In
order to find an appropriate drag force model for the simulation of dense CFB riser, not only the revised drag force model
but some other kinds of drag force model were used in the CFD. The flow structure, solid concentration, clusters phenomenon,
fluctuation of two phases and axial pressure drop were analyzed. By comparing the experiment with the simulation, the results
predicted by the EMMS drag model showed a better agreement with the experimental axial average pressure drop and apparent
solid volume fraction, which proves that the revised drag force based on the EMMS model is an appropriate model for the dense
CFB simulation. 相似文献
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Mohammad A. Dehnavi Shahrokh Shahhosseini S. Hassan Hashemabadi S. Mehdi Ghafelebashi 《International Communications in Heat and Mass Transfer》2010
The hydrodynamics and temperature of a two-dimensional gas–solid fluidized bed of gas phase olefin polymerization reactor had been studied. A two-fluid Eularian Computational Fluid Dynamics (CFD) model with closure relationships according to the kinetic theory of granular flow has been applied in order to simulate the gas–solid flow. Fluidization regime and gas–solid flow pattern were investigated using three different drag models. Model predictions of bed pressure drop were compared with corresponding experimental data reported in the literature to validate the model. The predicted values were in reasonable agreement with the experimental data. The temperature behavior of fluidized bed with various drag models was investigated. The temperature gradient in the primary section of the bed was much larger than the gradient in other sections and the effect of all drag models on temperature gradient along the bed was approximately similar. 相似文献
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利用循环流化床内气-固两相流动等基础方面的研究成果,根据本文床内气固浓-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、NO的生成和分解、颗粒磨损等因素。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化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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循环床锅炉沿床高的烟气浓度及燃烧份额分布测试结果证明,鼓泡流化床和循环流化床的重要差异表现为密相区燃烧行为的根本不同,由于床料平均粒径较低,循环床密相区的流动不同于鼓泡床,导致气固两相之间的传质阻力增加,从而影响燃烧反应,密相区的燃烧行为表现为欠氧。循环床锅炉沿床高乃至分离器都有燃烧反应发生,建立了考虑气固相间传质阻力的流化床密相区燃烧模型,并与实际循环流化床锅炉的测试数据比较,计算结果与测试值比较吻合。 相似文献
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Numerical simulation of gas-solid flow behaviors in a rectangular fluidized bed is carried out three dimensionally by the
discrete element method (DEM). Euler method and Lagrange method are employed to deal with the gas phase and solid phase respectively.
The collided force among particles, striking force between particle and wall, drag force, gravity, Magnus lift force and Saffman
lift force are considered when establishing the mathematic models. Soft-sphere model is used to describe the collision of
particles. In addition, the Euler method is also used for modeling the solid phase to compare with the results of DEM. The
flow patterns, particle mean velocities, particles’ diffusion and pressure drop of the bed under typical operating conditions
are obtained. The results show that the DEM method can describe the detailed information among particles, while the Euler-Euler
method cannot capture the micro-scale character. No matter which method is used, the diffusion of particles increases with
the increase of gas velocity. But the gathering and crushing of particles cannot be simulated, so the energy loss of particles’
collision cannot be calculated and the diffusion by using the Euler-Euler method is larger. In addition, it is shown by DEM
method, with strengthening of the carrying capacity, more and more particles can be schlepped upward and the dense suspension
upflow pattern can be formed. However, the results given by the Euler-Euler method are not consistent with the real situation. 相似文献