半圆柱形液固导向管喷动流化床流型的研究

本文以平均粒径为0．9mm的玻璃珠为流化颗粒,常温水为流化介质,在直径为97mm的半圆柱形液固导向管喷动流化床中,通过对喷动区和环隙区单位床高压降-流速曲线的分析并结合实验现象的观察,确定了喷动区和环隙区的流型及流型转变速度,在此基础上提出了液固导向管喷动流化床的流型图。研究结果表明,环隙达到流态化后,在较大的喷动液流速范围内,颗粒层能维持在较低的膨胀牢状态下。这对流化床电极非常有利;液固导向管喷动流化床有较大的操作弹性。     

带纵向涡发生器喷动床内颗粒流动特性PIV实验

针对喷动床内环隙区颗粒缺少横/径向运动的特点,通过实验将纵向涡流发生器及纵向涡流效应引入喷动床。采用粒子图像测速技术研究了在内径为152 mm的喷动床内纵向涡流及颗粒设计参数对喷动床内喷射区及环隙区颗粒相径向速度的影响,研究结果表明,纵向涡发生器在扰流元件上方横截面内颗粒相运动出现大量二次涡流,相比较于无纵向涡流扰流件情况,喷动床内的颗粒径向速度得到了显著增加,表明纵向涡发生器能够增强颗粒相在喷射区及环隙区的径向运动能力。在喷动床稳定喷动范围内,颗粒直径及颗粒密度越小,纵向涡流对颗粒相径向运动的强化效果越佳。     

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。     

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.     

纵向涡流发生器喷动床颗粒流动特性研究

探究纵向涡流对喷动床内喷射区及环隙区颗粒相径向速度的影响。采用粒子图像测速技术对内径D=152mm的喷动床进行实验研究,分析对比了不同扰流元件外形,尺寸及安装间距等重要参数对喷动床内颗粒运动的影响。研究结果表明:加入纵向涡发生器后,在扰流元件上方横截面内颗粒相运动出现了大量二次涡流,并且纵向涡发生器增强颗粒相在喷射区及环隙区的径向运动能力。在相同直径尺寸下,球体扰流元件较圆柱体扰流件对喷动床内颗粒径向运动的强化效果更好。存在一个最佳的扰流元件直径及布置间距使得纵向涡流对颗粒径向运动的强化效果达到最佳。     

液固导向管喷动流化床中颗粒流动特性的数值模拟

为获得优化床层结构及操作条件,采用双流体模型对导向管喷动流化床进行了数值模拟。研究考察了进口喷动液流速和流化液流速对颗粒流动规律的影响,结果表明:喷动液流速对颗粒的浓度分布及速度分布影响较小,只能使颗粒在环隙区与导向管内的循环加快;流化液流速对颗粒的浓度分布及速度分布影响较大,随着流化液速度的增大,颗粒在环隙区分布更均匀,浓度降低,颗粒更容易被卷吸进入导向管内,颗粒循环速度加快。     

带纵向涡发生器喷动床内颗粒流动特性PIV实验

针对喷动床内环隙区颗粒缺少横/径向运动的特点,通过实验将纵向涡流发生器及纵向涡流效应引入喷动床。采用粒子图像测速技术研究了在内径为152 mm的喷动床内纵向涡流及颗粒设计参数对喷动床内喷射区及环隙区颗粒相径向速度的影响,研究结果表明,纵向涡发生器在扰流元件上方横截面内颗粒相运动出现大量二次涡流,相比较于无纵向涡流扰流件情况,喷动床内的颗粒径向速度得到了显著增加,表明纵向涡发生器能够增强颗粒相在喷射区及环隙区的径向运动能力。在喷动床稳定喷动范围内,颗粒直径及颗粒密度越小,纵向涡流对颗粒相径向运动的强化效果越佳。     

纳米TiO_2颗粒在声场导向管喷动流化床中的流化特性

在内径120 mm的半圆柱型声场导向管喷动流化床中,以平均粒径290 nm的TiO_2颗粒为原料,高速空气射流为喷动气,考察了操作条件、声参数(频率和声压)对纳米颗粒在声场导向管喷流床中的流态化特性的影响。结果表明:声波可以有效抑制沟流,改善环隙流化质量,防止射流旁路,从而促使粉体稳定循环,加快循环速率;同时声波可以显著地降低纳米TiO_2颗粒的最小喷动速度,声波频率一定时,最小喷动速度随声压的增加而减小;声压一定时,最小喷动速度在声波频率为80 Hz时达到最小值,低于或者高于80 Hz,最小喷动速度都会增大。     

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。     

Hydrodynamics of a gas-driven gas-liquid-solid spouted bed with a draft tube

A cylindrical gas-liquid-solid spouted bed, driven exclusively by gas flow, has been developed with a high potential for use in biochemical processes, such as a biological wastewater treatment. A plexiglass column with a 152 mm inner diameter was used in combination with a 53 mm inner diameter plexiglass draft tube. Three particle types were studied with densities ranging from 1044 kg/m³-1485 kg/m³ and average particle sizes ranging from 0.7-2.5 mm. Four flow regimes were observed when increasing the gas velocity, including fixed bed, semispouted bed, full spouted bed, and internal circulating fluidized bed. The transition gas velocities between those regimes were experimentally measured and termed as minimum spouting velocity, full spouting velocity, and minimum circulating velocity, respectively. A measurement of the downward particle flux in the annulus was used to identify the minimum spouting velocity, while the particle velocity and dense phase retraction in the annulus were monitored for the full spouting and minimum circulating velocities. All regime transition velocities increased with more dense particles and longer draft tubes. The minimum spouting velocity and full spouting velocity were not affected when varying the nozzle-tube gap, while the minimum circulating velocity increased with longer nozzle-tube gaps. Experiments without a draft tube were carried, though the spouting stability was significantly reduced without the draft tube.     

Hydrodynamics of a spouted bed with an impermeable draft tube for binary particle systems

A spouted bed with an impermeable draft tube was employed to obtain fundamental data of binary mixtures of glass beads for both the operating conditions and the design factors. These data were compared with those for the coarser particle system only. From this view point, minimum spouting velocity, pressure drop, hold-up of solid particles within a draft tube, upward gas flow rate within the annulus and solids circulation rate were determined by changing the total gas flow rate and mass fraction of finer particles as operating parameters and by changing distance of entrainment zone and draft tube diameter as geometric parameters.     

双喷嘴矩形喷动床流动性能实验研究

在120 mm×240 mm的双喷嘴矩形不锈钢床内,对新型双喷嘴矩形导流管喷动床的最小喷动速度和喷动高度进行了研究,考察了喷动气速、粒径、静床层高度、导流管直径、导流管安装位置对最小喷动速度和喷动高度的影响。结果表明:最小喷动速度随颗粒直径、导流管直径、导喷距的增大而增大,随静床层高度的增大而减小;喷动高度随喷动气速的增大而增大,随导流管直径的增大而减小,受静床层高度和导喷距的影响不大,并得出了最小喷动速度的关联式。     

Hydrodynamic simulations of gas–solid spouted bed with a draft tube

Flow behavior of particles in a two-dimensional spouted bed with a draft tube is studied using a continuous kinetic-friction stresses model. The kinetic stress of particles is predicted from kinetic theory of granular flow, while the friction stress is computed from a model proposed by Johnson et al. (1990). A stitching function is used to smooth from the rapid shearing viscous regime to the slow shearing plastic regime. The distributions of concentration and velocities of particles are predicted in the spouted bed with a draft tube. Simulated results compare with the vertical velocity of particles (Zhao et al., 2008) measured and in the spout bed with draft plates and solid circulation rate (Ishikura et al., 2003) measured in the spouted bed with a draft tube. The impact of the friction stress of particles on the spout, annulus, fountain and entrancement regions is analyzed in gas–solid spouted bed with a draft tube. Numerical results show that the gas flow rate through the annulus increases with the increase of the entrainment zone. The solids circulation rate decreases with the decrease of inlet gas velocity and the height of the entrainment zone. The effect of spouting gas velocity on distributions of concentration, velocity and particle circulation is discussed.     

Hydrodynamics of a spouted bed with a porous draft tube containing a small amount of finer particles

A small-size spouted bed with a porous draft tube was employed to obtain hydrodynamic data of binary mixtures of glass beads for a range of operating conditions and design factors. In this case, a small amount of finer particles was added mostly to the large majority of coarser particles. Under this condition, minimum spouting velocity, bed pressure drop, hold-up of solid particles within a draft tube, gas flow rate through the annulus and solids circulation rate were determined by changing the total gas flow rate and the mass fraction of finer particles as operating parameters, and by changing the height of the entrainment zone and the draft tube diameter as geometric parameters. The results show that the gas flow rate through the annulus increases by increasing the distance between the gas inlet nozzle and the bottom of the draft tube, that is, the height of the entrainment zone, but decreases with increasing draft tube diameter and mass fraction of finer particles. The porous draft tube shows a higher gas flow rate through the annulus than the non-porous draft tube, particularly in the case of the low height of the entrainment zone. The solids circulation rate increases with increasing gas velocity, the height of the entrainment zone and the porous draft tube diameter. Moreover, the porous draft tube leads to a higher solids circulation rate than the non-porous draft tube.     

双喷嘴矩形导流管喷动床喷动压降

引言 传统的柱锥形喷动床(CSBs)的应用受到一些因素的限制,例如处理物料能力、起始压力大及难以放大等,为此,Romankov等[1]最早提出了长方形截面的矩形喷动床结构,来克服CSBs的缺点.此后,Rocha等[2]用矩形喷动床进行了片剂包衣的研究.     

Grain Drying in a Paraboloid-Based Spouted Bed with and without Draft Tube

In this study, grain drying in a spherical-based spouted bed (SBSB), a cone-based spouted bed (CBSB), and a paraboloid-based spouted bed (PBSB) with and without draft tube was investigated. Spouted-bed bases with the same volume in different shapes—spherical, cone, and paraboloid—were used for the drying experiments to investigate the effect of the spouted-bed base shape on drying. The drying experiments were carried out with perforated and solid draft tubes. The effects of the distance between the gas inlet nozzle and the bottom of the draft tube (entrainment zone height) and the draft tube diameter as geometric parameters on drying were also investigated. It was seen that the geometrical shape of the contactor base influenced the drying time. The highest drying rate was achieved for drying in a paraboloid-based spouted bed. The results also showed that using a draft tube caused a significant increase in drying time. Because the perforated draft tube allows a higher gas flow rate through the annulus, it decreases the drying time when compared with the solid draft tube. Drying time decreased slightly with the decreasing height of the entrainment zone but draft tube diameter did not have a considerable effect on drying.     

Effects of Draft Tubes on Particle Velocity Profiles in Spouted Beds

The vertical particle velocity profiles in a full‐column cylindrical conical spouted bed, with or without a draft tube, are measured using a fibre optic probe system. The profiles have different characteristics for a draft tube spouted bed (DTSB) than for a conventional spouted bed (CSB). The spout of a CSB consists of a central flow where particle velocities fit exponential distributions, and a boundary layer where particle velocities are nearly uniform. The spout of a DTSB has no boundary layer and its radial particle velocity profiles are approximately linear. The particle velocities in the spout of a DTSB increase when superficial gas velocity increases, draft tube diameter decreases, or when entrainment height decreases. A kinematic model has been used to simulate the granular flow in the annulus of a CSB and DTSB, and they are compared with the experiments. The particle velocities in the annulus of a DTSB are much lower than that of a CSB. Their radial profiles are also different with a CSB. The dependence of particle velocities in the annulus of a DTSB on superficial gas velocity, draft tube diameter, and entrainment height are also discussed. One concludes that the draft tube diameter and entrainment height are two key factors for the solid circulation rate of a DTSB.     

Fluid and particle flow characteristics in a draft tube spouted bed with modified fluid outlet

Glass particles, 0.54-1.39 mm in diameter, are spouted with air in a half-cylindrical draft tube spouted bed with modified fluid outlet to investigate the flow characteristics of the fluid and particles in the annulus. Using the measured pressure distribution and particle velocity and pathline in the annulus, the fluid streamlines, fluid and particle residence time distributions are obtained. Effects of the spoul inlet fluid flowrate, distance between the draft lube and spout inlet and the modified fluid outlet on the flow fields are also discussed.