喷动床内气固两相流动进口旋流效应数值模拟

为了研究喷嘴进口气体旋流效应对喷动床内气固两相流动特性的影响规律,采用数值模拟方法进行研究分析。通过欧拉-欧拉双流体模型和颗粒动力学理论对气固两相流动进行模型处理,分别对常规喷动床及带旋流器喷嘴喷动床进行模拟分析与对比。研究表明:喷嘴进口气体旋流效应显著地强化了喷动床内颗粒的径向运动,能有效消除柱锥区的颗粒堆积现象,扩大了低床层区气体喷射区的影响范围,增加了喷动床内气体的湍动能值,从而提高喷动床内颗粒处理的整体效率。存在最佳η(旋流器内径与外径比值)值,即η为0.526时,旋流气体对喷动床环隙区内颗粒堆积的消除作用及气体湍动能值的提升最为显著,同时旋流器喷动床的总体压降达到了峰值。     

喷动床内气固二相流动行为的计算模拟

采用双流体模型结合颗粒动理学理论对喷动床内气固二相流体流动行为进行了计算模拟研究。模型中运用颗粒动理学理论描述颗粒相应力封闭流体控制方程,使用Gidaspow曳力模型描述气固相间作用。喷动床内颗粒在浓相区的体积分数很大,采用Schaeffer′s模型描述颗粒间的摩擦应力。模拟计算结果表明,喷动床内分喷射区、喷泉区、环隙区3个区域,在射流入口处形成一个瓶颈。模拟计算得到的颗粒速度和空隙度分布与实验数据进行比较,计算结果与实验结果吻合较好。     

喷动床内气固两相流动纵向涡流效应数值模拟

为了深入了解纵向涡流对喷动床内气固两相流动特性的影响规律,采用计算流体力学方法对喷动床内气固两相流动的纵向涡流效应进行三维数值模拟。采用RUC曳力系数模型描述气、固相间作用力,通过欧拉-欧拉双流体模型和颗粒动力学理论对气固两相流动进行模型处理。分别对无扰流件、加入一对小球扰流件及加入一对纵向涡流发生器喷动床结构进行了模拟分析及对比。研究表明:加入球体扰流件及纵向涡流发生器之后,喷泉区的喷动高度明显下降,并在球形扰流件及纵向涡流发生器附近产生了二次漩涡。纵向涡流的存在显著地增加了喷动床内环隙区颗粒相的径向速度,增加了喷射区及喷泉区内颗粒体积分数及其密集度,有效增强了喷动床内气体、颗粒沿径向与轴向的湍动能及拟温度值,进而强化了环隙区与喷射区内颗粒、流体两相的横向混合效果及颗粒间的动量交换过程。     

喷动床反应器气固流动模型的研究进展

首先对喷动床流动特征参数关联式进行了扼要介绍,继而着重总结了近年来喷动床内气固流动模型(喷射区气固稀相流模式、环隙区气体渗流模式以及固体颗粒流模式)、以及喷动床放大规律等基础理论研究的进展。最后,提出了未来喷动床流动模型工作的突破点和相应思路。     

喷动床内气固二相流体动力行为颗粒动理学

应用气固二相双流体模型数值模拟了喷动床内流体动力行为,模型中采用稠密固相动力-摩擦应力模型。模型中同时考虑了动理学理论和摩擦应力理论。应用贴体坐标系使得网格与喷动床的倒锥体边界符合良好。模拟得到的喷动床内颗粒速度和浓度实验数据吻合较好。     

整体式多喷嘴喷动-流化床内气固两相流动规律数值模拟

采用双流体模型(TFM)对一种新型整体式多喷嘴喷动-流化床内气固两相流动进行了数值模拟,在喷动床锥体两侧开若干侧喷嘴形成辅助多喷嘴结构,使其在喷动床锥体处产生喷动-流化效果,从而对环隙区锥体边界处堆积颗粒层产生扰流作用。通过CFD数值模拟获得了喷动床内颗粒速度及浓度的分布情况,并与单喷嘴喷动床模拟结果进行对比。研究并优化分析了不同侧喷嘴数量以及侧喷嘴宽度等关键参数对喷动床气固两相流动的影响规律。研究表明,与常规喷动床相比,整体式多喷嘴喷动-流化床结构能有效增强喷动床内环隙区颗粒相运动,特别是强化了喷动床环隙区底部流动死区的颗粒运动,使得锥体边界层颗的粒体积分数显著下降,颗粒体积分数沿径向分布变得更为均匀,同时省略了旁路供气辅助设备。     

锥底喷动床内气固两相流的数值模拟

为了得到喷动床内流场分布的详细信息,给进一步的实验研究和工业放大提供理论依据,对锥底喷动床内气固两相流的流动状况进行数值模拟.使用欧拉模型进行计算,得到稳定的喷动区、环隙区和喷泉区等喷动床典型流动特征.考察喷动床内颗粒相在喷动区、环隙区和喷泉区的速度分布以及空隙率和颗粒体积分率的分布.计算结果同实验观察得到的结果相符.     

三维整体式喷动-流化床结构优化与流动数值模拟

为了对环隙区内的颗粒堆积层产生局部流化作用,提出了一种在喷动床锥体处开一定数量侧喷嘴的整体式多喷嘴喷动-流化床结构,并采用双流体模型(TFM)对三维整体式多喷嘴喷动-流化床内的气固两相流动行为进行了数值模拟。通过计算流体力学(CFD)模拟获得了喷动床内颗粒体积分数、颗粒速度及流场均匀度分布情况,并将模拟结果与传统喷动床进行了对比,同时对锥体处开孔直径等关键参数进行了优化分析。结果表明:与常规喷动床相比,三维整体式多喷嘴喷动-流化床结构能有效增强喷动床环隙区与喷射区颗粒的径向混合,特别是流化了喷动床环隙区底部颗粒的流动死区。颗粒流场均匀度(CV)值随着床层高度的增加而上升,表明多喷嘴对颗粒流场的均匀化效应主要体现在喷动床柱锥区,当A_i/A_z=0.67时,侧喷嘴对喷动-流化床内整体的颗粒流化作用达到最佳。     

新颖环形喷动床颗粒喷动特性实验研究

一种新颖的环形喷动床由内外两个不同内径、同心的垂立圆筒组成,在环形空间底部设置多个喷口,在喷口两侧布置倾斜的导流板.研究颗粒在这种喷动床内的流动特性,探讨喷口结构、颗粒种类以及床内载料量对环形喷动床颗粒喷动特性的影响.实验结果表明:颗粒在环形喷动床内分为三个明显不同的区域,即颗粒填充移动区、密相喷动流化区以及稀相夹带区.当颗粒出现分区喷动后,随床内载料量的增多,填充移动区的高度维持不变,始终等于导流板的高度,而密相喷动区的高度不断增加.风量和颗粒种类对床层最大喷动量、密相喷动高度以及床层压力分布规律有着十分重要的影响.采用不同的喷口结构时,在相同的载料量下,直向喷口的密相喷动区高度更大,而且床内各测点的平均压力大于采用斜向喷口时的相应测点压力.     

喷动床内气固两相流体动力行为的数值模拟

引　言喷动床被广泛应用于不同工业领域中 ,如石油裂解反应 -再生器、煤和农业废弃物气化和燃烧 ,喷动床还被应用于粮食和药品的干燥等[1] .因此 ,喷动床设计应满足不同应用的要求 .喷动床内气相反应物的反应时间和停留时间依赖于床体几何结构和运行参数 .尽管已有许多的实验对喷动床内气固两相流动进行了研究 ,得到了喷射区、环形区和喷泉区内的气固两相流动流体动力特性 ,然而由于喷动床内气固两相流动的复杂性 ,人们对床体几何结构和运行参数对喷动床动力学的影响至今并不清楚 .因此 ,床体几何结构和运行参数等对喷动床动力学的影响成为…     

Numerical simulations of flow behavior of gas and particles in spouted beds using frictional-kinetic stresses model

Flow behavior of gas and particles is simulated in the spouted beds using a Eulerian-Eulerian two-fluid model on the basis of kinetic theory of granular flow. The kinetic-frictional constitutive model for dense assemblies of solids is incorporated. The kinetic stress is modeled using the kinetic theory of granular flow, while the friction stress is from the combination of the normal frictional stress model proposed by Johnson and Jackson (1987) and the frictional shear viscosity model proposed by Schaeffer (1987) to account for strain rate fluctuations and slow relaxation of the assembly to the yield surface. An inverse tangent function is used to provide a smooth transitioning from the plastic and viscous regimes. The distributions of concentration, velocity and granular temperature of particles are obtained in the spouted bed. Calculated particle velocities and concentrations in spouted beds are in agreement with the experimental data obtained by He et al. (1994a, b). Simulated results indicate that flow behavior of particles is affected by the concentration of the transition point in spouted beds.     

粗糙颗粒动理学及流化床内气固流动的数值模拟

基于气体分子动理学和颗粒动理学理论,考虑颗粒旋转流动对颗粒碰撞能量交换和耗散的影响,建立粗糙颗粒动理学。采用Chapman-Enskog颗粒速度分布函数,提出了颗粒相应力、热通量和颗粒碰撞能量耗散计算模型。采用欧拉-欧拉气固双相流模型,数值模拟鼓泡流化床内气体-颗粒两相流动特性。模拟结果得到了床内颗粒相速度和脉动速度分布,与Yuu等实验结果相吻合。分析不同的切向弹性恢复系数对颗粒相拟总温的变化规律,结果表明在低颗粒浓度时颗粒拟总温随切向弹性恢复系数而增加。     

Numerical simulation on dense phase pneumatic conveying of pulverized coal in horizontal pipe at high pressure

A kinetic–frictional model, which treats the kinetic and frictional stresses in an additive manner, was incorporated into the two fluid model based on the kinetic theory of granular flow to simulate three dimensional flow behaviors of dense phase pneumatic conveying of pulverized coal in horizontal pipe. The kinetic stress was modeled by the kinetic theory of granular flow, while the friction stress is from the combination of the normal frictional stress model proposed by Johnson and Jackson [1987. Frictional–collisional constitutive relations for granular materials, with application to plane shearing. Journal of Fluid Mechanics 176, 67–93] and the modeled frictional shear viscosity model proposed by Syamlal et al. [1993. MFIX documentation and theory guide, DOE/METC94/1004, NTIS/DE94000087. Electronically available from http://www.mfix.org], which was modified to fit experimental data. For the solid concentration and gas phase Reynolds number was high, the gas phase and particle phase were all treated as turbulent flow. The experiment was carried out to validate the prediction results by three kinds of measurement methods. The predicted pressure gradients were in good agreement with experimental data. The predicted solid concentration distribution at cross section agreed well with electrical capacitance tomography (ECT) image, and the effects of superficial velocity on solid concentration distribution were discussed. The formation and motion process of slug flow was demonstrated, which is similar to the visualization photographs by high speed video camera.     

Extension of the kinetic theory of granular flow to include dense quasi-static stresses

Fluidized bed technology has diverse industrial applications ranging from the gasification of coal in the power industry to chemical reactions for the plastic industry. Due to their complex chaotic non-linear behaviour understanding the hydrodynamic behaviour in fluidized beds is often limited to pressure drop measurements and a mass balance of the system. Computational fluid dynamics has the capability to model multiphase flows and can assist in understanding gas-solid fluidized beds by modeling their hydrodynamics. The multiphase Eulerian-Eulerian gas-solid model, extended and validated here improves on the kinetic theory of granular flow by including a closure term for the quasi-static stress associated with the long term particle contact at high solid concentrations. Similar quasi-static models have been widely applied to slow granular flow such as chute flow, flow down an incline plane and geophysical flow. However combining the kinetic theory of granular flow and the quasi-static stress model for the application of fluidized beds is limited. The objective of the present paper is to compare two quasi-static stress models to the experimental fluidized bed data of Bouillard et al. [4]. A quasi-static granular flow model (QSGF) initially developed by Gray and Stiles [18] is compared to the commonly used Srivastava and Sundaresan [37]. Both models show good agreement with the experimental bubble diameter and averaged porosity profiles. However only the QSGF model shows a distinct asymmetry in the bubble shape which was documented by Bouillard et al. [4].     

大涡模拟方法模拟鼓泡床内气固两相流动

采用大涡模拟（LES）方法模拟气相湍流,颗粒动理学方法考虑颗粒相碰撞产生的动量和能量传递和耗散,采用颗粒相大涡模拟方法（LESp）模拟颗粒脉动导致的能量耗散,同时考虑介观尺度对颗粒相压力的影响,建立了气体-颗粒LES-θ-LESp双流体模型,研究鼓泡流化床内气固两相流动的特性。数值模拟与文献实测颗粒速度和实测颗粒浓度结果具有相同的变化趋势。     

CFD simulations of bubbling beds of rough spheres

Hydrodynamics of three-dimensional gas-solid bubbling fluidized beds are numerically analyzed. The particle-particle interactions are simulated from the kinetic theory for flow of dense, slightly inelastic, slightly rough sphere proposed by Lun [1991. Kinetic theory for granular flow of dense, slightly inelastic, slightly rough sphere. Journal of Fluid Mechanics 233, 539-559] to account for rough sphere binary collisions and the frictional stress model proposed by Johnson et al. [1990. Frictional-collisional equations of motion for particulate flows and their application to chutes. Journal of Fluid Mechanics 210, 501-535] to consider the frictional contact forces between particles. The present model is evaluated by measured particle distributions and velocities of Yuu et al. [2001. Numerical simulation of air and particle motions in group-B particle turbulent fluidized bed. Powder Technology 118, 32-44] and experimental bed expansion of Taghipour et al. [2005. Experimental and computational study of gas-solid fluidized bed hydrodynamics. Chemical Engineering Science 60, 6857-6867]. Our computed results indicated that the present model gives better agreement with experimental data than the results from original kinetic theory for frictionless slightly inelastic sphere of Ding and Gidaspow [1990. A bubbling fluidization model using kinetic theory of granular flow. A.I.Ch.E. Journal 36, 523-538] with and without solid friction stress model.     

Fluid dynamic simulation in a chemical looping combustion with two interconnected fluidized beds

Flow behavior of gas and particles is simulated in a 2-D chemical-looping combustion (CLC) process with two interconnected fluidized beds. A Eulerian continuum two-fluid model is applied for both the gas phase and the solid phase. Gas turbulence is modeled by using a k-ε turbulent model. The kinetic stress is modeled using the kinetic theory of granular flow, while the friction stress is from the combination of the normal frictional stress model proposed by Johnson and Jackson (1987) and the frictional shear viscosity model proposed by Schaeffer (1987) to account for strain rate fluctuations and slow relaxation of the assembly to the yield surface. Instantaneous and local velocity, concentration of particles and granular temperature are obtained. Predicted time-averaged particle concentrations and velocities reflect the classical core-annular flow structure in the air reactor. Flow behavior of bubbles is predicted in the fuel reactor and pot-seal. Computed leakage qualitatively agrees with experimental data in the fuel reactor and pot-seal.     

水平管加压密相煤粉气力输送数值模拟

针对加压密相气力输送,对现有的颗粒静摩擦力模型进行适当修正,并将其与颗粒动理学理论相结合,建立了可以描述加压密相气力输送的气固湍流流动状况的多相流模型。该模型充分考虑了颗粒间碰撞和摩擦力作用,以及气相和颗粒团湍流脉动之间的相互作用。采用该模型对水平管内加压密相气力输送进行了三维数值模拟研究,模拟得到了气相和固相的速度、浓度和湍流强度分布,以及压降梯度的变化规律,再现了颗粒沉积层的形成和运动的动态过程。并进行了加压密相煤粉气力输送试验研究,预测的压降梯度与试验测量结果相符合。     

提升管内气固流动行为的数值模拟

应用计算流体力学软件Fluent,对空气为连续相、固相为催化裂化反应催化剂的循环流化床提升管内的气固流动行为进行模拟。采用用户自定义函数引入颗粒与壁面的恢复系数和颗粒的镜面反射系数,对颗粒在边壁处的部分滑移运动进行描述。采用不同的计算动力学模型及参数,数值模拟了径向颗粒浓度、轴向床层压降的空间分布,以及用以描述颗粒脉动动能的颗粒温度与固含率的关系,并与文献报道的实验和数值模拟结果进行对比分析。结果表明,选取的颗粒动力学理论模型及参数、颗粒部分滑移边界条件及气固曳力模型,可计算得到合理的颗粒轴向及径向分布,验证了提升管中存在典型的径向环核流动结构和轴向压降分布。进一步分析表明固含率显著影响颗粒温度,当固含率为0.05~0.1,颗粒温度存在转折区。