喷嘴对液固外循环流化床内颗粒循环特性的影响

液固外循环流化床换热器可以用来蒸发浓缩单基药提取硝化棉的提取液.设计了实现液固外循环流化床内颗粒正常循环的关键部件喷嘴,构建了以喷嘴作颗粒循环装置的液固外循环流化床换热器,研究了喷嘴的结构参数及操作参数对起始循环流体流量、全床压降、负压和最大颗粒循环流量等的影响.结果表明,喷嘴的口径比及安装位置对提高颗粒循环效果均存在一个最佳值,为外循环流化床换热器的设计计算提供了依据.     

基于小波变换的气固流化床压力流动信号的分析

将小波分析技术应用于气固流化床压力波动信号的分析中,在不同尺度上提取信号能量特征,由此来对压力波动信号中所含丰富信息进行分析、提出了应用小波分析技术来判别流化床从固定床向鼓泡床转变的新方法,并确定了起始流化速度的范围,初步研究表明,所提取的特征信息反应了气固流化床从固定床向鼓泡床转变的过程,通过此特征信息可以确定流化床的起始流化速度的范围。／     

液固外循环流化床起始外循环液体流量的实验研究

为外循环流化床换热器的设计计算提供依据,以喷嘴为颗粒循环装置的液固外循环流化床换热器为研究对象,考察了颗粒直径、口径比、喷嘴安装位置、颗粒初始加入量及流体粘度对起始外循环液体流量的影响;得出了稳定操作情况下,液固外循环流化床换热器起始外循环液体流量与上述因素之间的经验关联式.结果表明:计算值与实验值吻合较好.     

基于信息熵分析的喷动流化床流动特性

建立了300 mm×30 mm×2000 mm的喷动流化床煤气化炉冷态实验装置和多通道压力信号采集系统,引入压力波动时间序列的Shannon信息熵分析,讨论了不同喷动气速度和流化气流率下各床层区域的Shannon 信息熵,并结合高分辨率数码CCD相机所记录的流动状态,建立了Shannon信息熵与流型之间的联系.床层不同区域的Shannon 信息熵具有较大的差异,不同流型的Shannon 信息熵区分度较好.在较高的喷动气速度或流化气流率下,喷动流化床气固运动周期特性消失,呈现出明显的混沌特性,表现为床层各区域Shannon信息熵的急剧增长和床内不稳定的流动状态的发生.结果表明,Shannon信息熵分析有助于认识喷动流化床复杂的流型及其转变和床内气固两相流动的混沌动力学特性.     

二维流化床光反应器中的光强分布及波动规律

考察了外部平行光源照射下液-固及气-液-固二维流化床中流体流动状况对床层光强分布和波动规律的影响. 采用朗伯-比尔定律建立了两相及三相流化床中光强分布的数学模型，分析了液含率、气含率及气、固相吸光系数对床层光强分布的影响，并采用自制光纤光强传感器测定了床层中的光强分布和波动信号. 二维流化床中床层光强沿径向呈指数衰减，随着液含率和气含率增大而增大，理论计算与实验结果相吻合. 对光强波动信号的功率谱分析表明，液-固流化床中功率谱密度由低频至高频呈规律性衰减，气-液-固三相流化床中由于受气泡的影响功率谱密度出现起伏，在5~12 Hz处出现谱峰，与气泡的产生频率一致. 上述模型可推广应用于其他光源和不同结构流化床光反应器的数学描述.     

含内构件的循环流化床的动态压力特性

针对含内构件的循环流化床,以石英砂为物料,使用动态压力传感器测量了含内构件的流化床中气固两相流的动态压力,分析了床内的瞬时压力特性. 结果表明,在进出口总压降中,文丘里压降最大,占主床压降的60%以上. 表观气速和固体颗粒循环流率共同影响循环流化床内的压力特性. 压力瞬时波动功率谱分析表明,压力波动对应一个主频,表观气速越小、颗粒循环流率越大时,压力波动越大,且循环流化床底部压力波动比上部大. 加入内构件能有效引导气流,使流动更均匀.     

循环流化床颗粒浓度波动信号多重分形测度分析

由于循环流化床气－固两相流动规律相当复杂，使得至今对其流动规律的认知仍不足以直接用于循环流床的工业设计与放大。近十多年来，确定性混沌理论已被用于循环流化床动力学特性的研究，与其密切相关的分形理论也被用于流化床流动特性的研究。然而，这些研究所用均是采用单分形理论，而单分形理论对解释循环流化床复杂的非线性气－固流动行为显得能力不足。为了探讨循环流化床内颗粒流体系统非线性、非均匀性和混沌特性机理。本文引入不同测试多重分形分析的方法，用小波变换模极大值与多重分形测度分析方法相结合，检测循环流化床颗粒浓度波动信号奇异性并得出多重分形奇异谱。结果表明循环流化床颗粒浓度波动信号具有明显的多重分形特性。小波变换多重分形方法可以用来描述床内颗粒流动特性，为探讨循环流化床颗粒流体系统非均匀机制提出了一种新的方法。     

基于小波变换的气固流化床压力波动信号的分析

将小波分析技术应用于气固流化床压力波动信号的分析中,在不同尺度上提取信号能量特征,由此来对压力波动信号中所含丰富信息进行分析,提出了应用小波分析技术来判别流化床从固定床向鼓泡床转变的新方法,并确定了起始流化速度的范围。初步研究表明,所提取的特征信息反应了气固流化床从固定床向鼓泡床转变的过程,通过此特征信息可以确定流化床的起始流化速度的范围。     

气固流化床压力脉动信号的Hilbert-Huang谱分析

首次将Hilbert-Huang变换（HHT）应用于气固流化床压力脉动信号的分析,提取并研究了压力脉动信号中隐含的表征复杂的粒子运动与气泡运动相互调制的非线性特征,以及压力脉动信号高、低阶内禀模态函数（IMF）之间的能量转换与流化床的流化状态相对应的新信息,在此基础上提出了采用压力脉动IMF分量的能量转移现象进行颗粒结块故障判别的新方法.结果表明,应用Hilbert-Huang谱对压力脉动信号分析的新方法能比现有的分析方法提供更多的有用信息,有助于更深入地揭示床内非线性流体动力学特征.     

倒置液固流化床内液固两相流动特性的数值模拟

基于欧拉-欧拉双流体模型,数值模拟倒置液固流化床内液固两相流动行为.数值模拟预测了床内颗粒的速度、浓度分布以及空隙率的变化.研究结果表明颗粒在床内分布呈现非均匀分布,床内形成局部高空隙率的流体团;随着床层高度增加,颗粒轴向速度增大:数值模拟床内空隙率与Renganthan等的实验结果相吻合.     

液固循环流化床换热器中固体颗粒分布

利用CCD图像测量与数据处理系统对多管液固循环流化床换热器中的两相流动特性进行了研究。探讨了下管箱中的分布板结构对固体粒子的体积分数分布、固体粒子的速度分布,以及液固两相流压降的影响。实验结果表明:在循环流化床换热器进口段安装适当结构的多孔板分布器,即多孔板的面积小于床层截面积,且床中心处的遮挡面积大于边缘处的遮挡面积,可以有效地提高固相速度的均匀程度,在较高流速下,能较好地改善固体颗粒在管束中的不均匀分布。     

液固循环流化床两相流动模型

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…     

An analysis of pressure drop fluctuation in a circulating fluidized bed

The characteristics of pressure drop fluctuation in a 5.0 cm I.D.×250cm high circulating fluidized bed with fine polymer particles of PE and PVC were investigated. The measurements of time series of the pressure drop were carried out along the three different axial locations. To determine the effects of coarse particles and relative humidity of air on the flow behavior of polymer powders-air suspension in the riser, we employed deterministic chaos analysis of the Hurst exponent, correlation dimension and phase space trajectories as well as classical methods such as standard deviation, probability density function of pressure drop fluctuation. From a statistical and chaos analysis of pressure fluctuations, the upper dilute region was found to be much more homogenous flow compared to that in the bottom dense region at the same operating conditions. It was also found that the addition of coarse particles and higher humidity of air reduced the pressure fluctuations, thus enhancing flow stability in the riser. The analysis of pressure fluctuations by statistical and chaos theory gave qualitative and the quantitative information of flow behavior in the circulating fluidized bed.     

Investigation on gas–solid flow regimes in a novel multistage fluidized bed

Gas–solid flow regime in a novel multistage circulating fluidized bed is investigated in this study. Pressure fluctuations are first sampled from gas–solid flow systems and then are analyzed through frequency and time–frequency domain methods including power spectrum and Hilbert–Huang transform. According to the flow characteristics obtained from pressure fluctuations, it is found that the gas–solid motions in the multistage circulating fluidized bed exhibit two dominant motion peaks in low and high frequencies. Moreover, gas-cluster motions become intensive for the multistage circulating fluidized bed in comparison with the fast bed. Unlike the traditional methods, the fuzzy C-means clustering method is introduced to objectively identify flow regime in the multistage circulating fluidized bed on the basis of the flow characteristics extracted from bubbling, turbulent, fast, and multistage fluidized beds. The identification accuracy of fuzzy C-means clustering method is first verified. The identification results show that the flow regime in the multistage circulating fluidized bed is in the scope of fast flow regime under examined conditions. Moreover, the results indicate that the consistency of flow regime between two enlarged sections exists. In addition, the transition onset of fast flow regime in the multistage circulating fluidized bed is higher than that in the fast bed.     

AN EXPERIMENTAL STUDY OF LIQUID-PARTICLE FLOW IN CIRCULATING FLUIDIZED BED

A liquid-solid circulating fluidized bed (LSCFB) is operated at high liquid velocity, where particle entrainment is highly significant and between the conventional liquid fluidized bed and the dilute phase liquid transport regimes. LSCFB has potential applications in the fields of food processing, biochemical processing, and petrochemical and metallurgical processing. It is well known that the flow characteristics in a liquid-solid circulating fluidized bed are different from those of a conventional liquid-solid fluidized bed. The limited studies available in literature do not provide complete understanding of the flow structure in this typical regime.

In the present work, experiments were carried out in a 0.0762 m ID and 3 m height laboratory-scale liquid-solid circulating fluidized bed apparatus by using various solid particles and tap water as fluidizing medium. In the experimental setup, two distributors (specially designed) were used to monitor solid circulation rate in the riser. The effects of operating parameters, i.e., primary liquid flow rate in the riser (Up), solid circulation rate (G_s), and particle diameter (dp), were analyzed from the experimental data. Finally, a correlation was developed from the experimental data to estimate average solid holdup in the riser, and it was compared with present experimental and available data in the literature. They agree well with a maximum root-mean-square deviation of 7.83%.     

STOCHASTIC BEHAVIOR OF FLUIDIZED PARTICLES IN A LIQUID-SOLID FLUIDIZED BED

In a liquid-solid fluidized bed, the apparently irregular or stochastic behavior of particles gives rise to various flow regimes depending on parameters such as the particle size, liquid flow rate, static bed height and axial position in the bed. It is highly plausible that this irregular behavior manifests itself as pressure fluctuations; thus, the effects of these parameters on the particle behavior or the particle flow regime were investigated through measurement and spectral analysis of the pressure fluctuations. The results indicate that the amplitude of pressure fluctuations exhibits a maximum and that the decay constant in the autocorrelation function attains its minimum at the intermediate liquid flow rate where the particle flow regime undergoes transition from the cluster circulation to the individual quasi random motion. The model composed of the periodic and stochastic components of pressure fluctuations, is in good accord with the experimental results in terms of both the autocorrelation and power spectral density functions.     

Fractal characteristics of gas-solids flow in a circulating fluidized bed

A fractal approach is adopted to describe the dynamic behavior of a circulating fluidized bed. Two times series, differential pressure fluctuations along the riser height and solids momentum fluctuations along the radial direction, are measured and analyzed in terms of fractal dimensions. The influences of operating conditions and axial/radial positions on the fractal dimension are discussed. Attempts are also made to interpret the flow structure in the bed in terms of the fractal dimension. It is found that fractal analysis can provide a useful tool for understanding the characteristics of gas-solids flow in circulating fluidized beds.     

液固提升管-流化床组合反应器中流化床径向固含率分布的实验研究

在一套新型液固提升管-流化床组合反应器中,以水-玻璃珠为液-固体系,对f500 mm′4000 mm的液固流化床反应器内不同高度颗粒固含率的径向分布进行了实验,考察了表观液速和颗粒循环速率操作条件对颗粒固含率径向分布的影响. 实验表明,液固流化床内流动区域在轴向上可以划分为分布器影响区、过渡区和均匀流化区,径向上可以划分为中心区和环隙区. 这种分布特征主要取决于分布器的结构、尺寸及其流化介质. 本工作还对液固流化床与气固喷动床的三区流动结构进行了比较.