气固流化床中侧向射流穿透深度的研究

本文以小米和两种硅胶为物料，在314×25mm的二维射流流化床中，用摄像法研究侧向射流穿透深度，并得到了关联式，误差小于25％．当射流倾角变化范围不大、并忽略射流位置的影响时，可以得到简化公式，误差小于40％使用基于对流体模型的计算机程序进行模拟，分析了射流产生的机理，研究了射流气速、直径、倾角和位置对射流穿透深度的影响．模拟值和实验值较吻合．     

固定床熔渣气化高速射流区气固运动行为研究

为研究固定床熔渣气化炉中气化剂喷嘴安装角度、喷嘴口径、气化剂射流速度与高速射流区深度的关系,利用模化原理对工业级气化炉高速射流区建立50 cm二维冷态模型,采用精密皮托管测量颗粒床层中的气体速度分布,并采用无量纲分析方法,对试验数据进行处理。结果表明:射流穿透深度与喷嘴口径的二次方大致成正比关系;射流深度随喷嘴安装角度的增大呈现先增加后减小的趋势,使得射流深度最大的安装角度为17°~20°;射流深度随射流气速增加呈增大趋势,并拟合出气化剂喷嘴安装角度、射流速度、喷嘴口径与射流区深度的无量纲关系式。     

流化床中射流机制和双射流相互作用

在文献的基础上, 通过实验和模拟的方法研究了射流机制和双射流的相互作用. 采用一个300 mm′51 mm的两维气固流化床,内置两个垂直射流, 使用多路毕托管系统测量射流穿透深度. 使用描述气固流态化的双流体模型进行模拟,用改进的IPSA求解模型方程,通过数值模拟, 讨论了射流产生的机理, 再现了双射流, 并发现双射流的相互作用可分为三类：孤立射流、过渡射流和互作用射流,提出了相应的射流间距判据. 发现影响双射流穿透深度最主要的因素是射流动量、两相间曳力、射流间距和床层表观气速, 建议使用Froude数、Reynolds数、床层表观气速、射流间距和喷口直径来关联不同区域的射流穿透深度. 得到了一个关联式并与文献中的关联式或实验数据做了比较.     

流化床中侧向射流穿透深度的研究

流化床中侧向射流穿透深度的研究李海滨，王洋，张海生（中国科学院山西煤炭化学研究所，太原０３０００１）关键词：流化床，侧向射流，穿透深度１前言气固流化床反应器中，分布板起着气体分布和支持床层物料的作用，分布板区是气体与所处理固体接触最强的区域，在氧化反...     

气固流化床内射流穿透深度的CFD模拟及其实验验证

在经典的Gidaspow无黏性双流体模型中考虑离散颗粒对流体和固体动量守恒方程的影响后,建立了一个具有模拟大规模流化床内气固两相流体动力学特性潜在优势的简化数学模型。在CFX4.4商业化软件平台上通过增加用户自定义子程序考察了二维气固流化床(高2.00 m、宽0.30 m)内射流气速、喷嘴尺寸、环隙气速和静床高度对射流穿透深度的影响,并以树脂颗粒(粒径670 μm、密度1474 kg·m^-3)为研究对象在厚度为0.025 m的矩形床内进行了对比实验。结果表明,选取空隙率为0.8的等高线作为射流边界比较合适;射流穿透深度随射流气速或射流喷口尺寸的增加而增大;射流周围环隙气速由0变到最小流化速度时,射流穿透深度随环隙气速增加而增大,在最小流化速度时达到最大值,然后随环隙气速增加单调减小,当环隙气速大于2.5倍最小流化速度时,射流穿透深度减小程度变缓;在相同射流气速下射流穿透深度随着静床高度的增加而减小,静床高度对射流穿透深度的影响随着射流气速增加呈现扩大的趋势。     

二维射流床空隙率分布

使用ＰＣ－４光导纤维测浓仪测定了二维射流床中的空隙率分布，并考查了静床高、射流管径对空隙率分布的影响，发现在射流喷口上方２．５ｃｍ￣７．５ｃｍ处有一最大空隙率分布区。利用空率分布可定义并求出射流深度，其值与Ｙａｎｇ的关联式计算值吻合。     

悬浮物清除系统的射流器两相紊流数值模拟研究

通过水系统悬浮物清除系统所需射流器建立的三维紊动射流数学模型，对特殊结构形式的射流器进行流场结构和射流紊流动力学性能的研究，通过数学模型计算射流器的紊流流场分布，掌握流场的流体动力学机理，从而获得最接近射流器紊流流场实际状态的描述方法。     

网格尺度、时间步长和颗粒堆积率对射流床CFD模拟的影响

采用欧拉-欧拉双流体模型,在CFX4.4软件上增加用户自定义子程序模拟了高2.0 m、宽0.3 m的二维射流床内空气和玻璃珠体系的流体动力学特性. 考察了网格尺度、最大颗粒堆积率和时间步长对射流的形成及发展过程、射流穿透深度及射流频率的影响,并与实验数据进行了对比. 结果表明,对于本研究的气固体系,当床层下部纵向网格数为100、时间步长0.0005 s时,不仅可以满足网格尺度和时间步长的无关性要求,而且模拟的射流穿透深度和射流频率与实验测量值的误差分别为5.7%和3.8%. 最大颗粒堆积率在本研究范围对模拟结果的影响可以忽略.     

多组分射流床中的射流深度

采用多路毕托管、电磁阀、微压传感器检测技术，考察了气固射流流化床中GeldartB、D类的单一物料及混合物的射流深度．指出物料的平均密度或粒径的增加都会造成射流深度的降低；得到的包括气团惯性准数在内的经验关联式能成功地预测多组分床层的射流深度．     

对气相射流垂直冲击液面过程中射流深度的研究

以空气-水、空气-甘油水溶液两类体系,对气液两相中气体垂直向下喷射的射流深度进行了冷模实验研究。应用计算流体力学的VOF模型和realistic k-ε湍流模型进行模拟计算,模拟结果与实验数据有良好的一致性。结合实验和模拟进行计算分析,结果显示:主导射流深度的主要因素为Fr数和气液密度比;大喷孔和短喷距的组合可得到较大射流深度;表面张力的影响主要存在于浅气穴阶段,当气相射流射穿液面时,其影响骤然消减;液相粘度对射流深度基本无影响。通过数值模拟合理地进行了体系物性扩展,分析结论对于以气相射流为主的两相混合传质传热或反应的工艺设计,具有一定的指导作用。     

Experimental and numerical study of fluid dynamic parameters in a jetting fluidized bed of a binary mixture

The solid circulation pattern, the voidage profile, and the jet penetration height have been investigated experimentally and computationally in a cold-flow model of jetting fluidized beds (JFBs) of a binary mixture in this paper. This rectangular two-dimensional bed is 0.30 m wide and 2.05 m high with a central jet and a conical distributor, which roughly stands for the ash-agglomerating fluidized-bed coal gasifier. A video camera and coloured particle tracer method were employed to explore the fluid dynamics in the bed. In terms of the average physical properties of binary mixtures, a hydrodynamic model describing the gas-solid flow characteristics in a jetting bed is resolved by using a modified Semi-Implicit Method for Pressure-Linked Equation (SIMPLE) algorithm. This paper focuses on three features of the fluid dynamics—solid circulation pattern, voidage profile, and jet penetration height. The solid circulation pattern is composed of three regions: the jetting region, the bubble street, and the annular region. Above the central nozzle the time-averaged isoporosity contours are almost elliptic, while near the walls of the bed, the voidage in high solid concentration region is approximately equal to that at the minimum fluidization state. The jet penetration height increases with increasing jet gas velocity and with decreasing average particle diameter. The increase in weight percentage of the lighter component in the binary system reveals that reduction of average density causes the enlargement of jet penetration height. The simulated results show good agreement with the experimental data.     

流化床射流深度的研究

综述了近三十年来流化床中垂直向上射流、水平射流射流深度的研究状况,结合笔者在多环隙气速、混合物组分射流深度的一系列研究结果,详细论述了射流深度的测试方法、影响因素（射流气速、固体颗粒物性、床层操作压力、环隙气量、放大效应）,同时对诸多射流深度关联式进行了分析,指出了应注意的问题．探讨了射流深度的研究方向．     

CFD simulation of jet behaviors in a binary gas-solid fluidized bed: comparisons with experiments

Based on the experimental observation of the fluidization characteristics of solid mixtures (resin and rapeseed) with different densities and sizes, the jet behaviours of the binary system are simulated in a two-dimensional jetting fluidized bed 0.30 m in width and 2.00 m in height. A simple mathematical model, by introducing two additional force terms in both gas and particle phase momentum equations of Gidaspow’s inviscid two-fluid model, is used to explore the effects of jet gas velocity and mixture combination on the jet penetration depth in the fluidized bed with a binary system. Experimental results show that there is a fluidization velocity interval (u_if-u_ff) for the resin-on-rapeseed (flotsam-on-jetsam) segregated bed. The simulated jet penetration depth increases with the increase of jet gas velocity and the volume fraction of the flotsam (resin), which is in fair agreement with experimental data. The above findings show that the hydrodynamic model of Brandani and Zhang (2006), by introducing the average physical properties from Goossens et al.(1971), can be used to predict the jet behaviors of a well-mixing binary system.     

Horizontal gas and gas/solid jet penetration in a gas–solid fluidized bed

In this paper, the real time, dynamic phenomena of the three-dimensional horizontal gas and gas/solid mixture jetting in a 0.3 m (12 in) bubbling gas–solid fluidized bed are reported. The instantaneous properties of the shape of the jets and volumetric solids holdup are qualified and quantified using the three-dimensional electrical capacitance volume tomography (ECVT) recently developed in the authors’ group. It is found that the horizontal gas jet is almost symmetric along the horizontal axis during its penetration. As the jet width expands, the total volume of the gas jet increases. A mechanistic model is also developed to account for the experimental results obtained in this study. Comparison of jet penetration length and width between the model prediction and ECVT experiment shows that both the maximum penetration length and the maximum width of the horizontal gas jet increase with the superficial gas velocity. When the horizontal gas jet coalesces with a bubble rising from the bottom distributor, it loses its symmetric shape and can easily penetrate into the bed. For the horizontal gas/solid mixture jet penetration in the bed, the tail of the jet at the nozzle shrinks and the jet loses its jet shape immediately when the jet reaches its maximum penetration length, which are different from the characteristics exhibited by the gas jet. The solids holdup in the core region of the gas/solid mixture jet is higher than that in the gas jet. The penetration length of the horizontal gas/solid mixture jet is also larger than that of the gas jet.     

Jet penetration depth in a two-dimensional spout-fluid bed

The jet penetration depth was proposed to be an important parameter to describe the jet action during the chemical process of spout-fluid bed coal gasification. A two-dimensional cold model of a spout-fluid bed coal gasifier with its cross section of and height of 2000 mm was established to investigate the jet penetration depth. Four types of Geldart group D particles were used as bed materials. A multi-channel pressure sampling system and a high-resolution digital CCD camera were employed for experimental investigations. The effects of spouting gas velocity, spout nozzle diameter, static bed height, particle property and fluidizing gas flow rate on the jet penetration depth have been systematically studied by pressure signal analysis and image processing. Experimental results indicate that the jet penetration depth increases with increasing spouting gas velocity and spout nozzle diameter, while it decreases with increasing particle density, particle diameter, static bed height and fluidizing gas flow rate. Additional, a new correlation considered all of the above effects especially static bed height and fluidizing gas flow rate, was developed for predicting the jet penetration depth in spout-fluid beds. The correlation was compared with published experimental data or correlations, which was in well agreement with the present experimental results and some other references.     

Dynamic characteristics of binary mixtures in a two-jet fluidized bed

Aiming to understand biomass-related pyrolysis and gasification processes, which have received particular interests recently due to increasing concerns over fossil fuels and carbon emissions, this work conducts a detailed experimental study of the fluidization characteristics and jet dynamics of biomass mixtures in a fluidized bed. Both single jet and two jets dynamics are investigated, and a parametric study of the influence of particle properties and operational conditions on the dynamic performance of the bed, especially on the jet penetration depth and jet frequency of the binary mixtures, is conducted. Detailed frame-by-frame image analysis coupled with physical parameters reveals many interesting phenomena, which includes multistage flow pattern development and a stochastic nature of jet dynamics, as well as a strong dependence of the jet penetration depth and jet frequency on the bed materials.     

射流流化床中锥形分布板对流动的影响

给出了具有锥形分布板的射流流化床中浓密气固两相流动的多相流体力学基本方程组. 采用二维正交曲线坐标并生成了数值网格,用改进的IPSA方法求解二维正交曲线坐标中的多相流基本方程组,并编制了大型通用程序,流场可视化使用Tecplot软件. 对于给定的模拟计算,计算结果与实验值吻合. 模拟计算中改变了锥形筛板的角度、射流管的直径、床层高度、分布板开孔率的分布、射流气速、床层表观气速等,通过模拟得到床内的流动图像,考察了射流高度及颗粒循环的影响.     

灰熔聚气化装置冷模射流流化床的研究

概述了灰熔聚冷模气固射流流化床的研究现状，内容主要包括：射流形成的条件及流型划分、射流深度、射流势能区、颗粒混合及运动、空隙率分布、气泡行为、分离特性；并预测了今后的研究趋势。     

Fate of solids fed pneumatically through a jet into a fluidized bed

Solid tracer particles were fed pneumatically through a jet into a fluidized bed to simulate the feeding of solids via a pneumatic transport line into a fluidized-bed reactor operating in the slugging-bed mode. The fluidized bed was defluidized instantaneously at different times after the initiation of the tracer particle injection. The bed was then sampled layer by layer to provide the radial and axial concentration profiles of the tracer. Regular and high-speed movies (1,000 frames per second) were taken to study the operation of the fluidized bed and the phenomena of the gas-solid two-phase jet. Experimental results on solid mixing, jet constriction and slugging frequencies, slugging bed height, slug length, jet penetration, and jet half-angle at three nominal jet velocities of 52, 37, and 25 m/s and corresponding solids loadings are presented. Additional experimental results on jet constriction and slugging frequencies, and slug volume (axial slug size) obtained for a wider range of jet velocities confirm the hydrodynamic trends observed during the tracer particle injection experiments. The results indicate that solids mixing increases, and well-mixed conditions are reached earlier, with an increase in jet injection velocity. The obtained mixing times were correlated successfully in terms of the excess gas velocity. The experimental data on jet penetration and slug motion were satisfactorily correlated by modified versions of existing theoretical relations. The modifications included the effect of the injected solids on jet penetration and jet half-angle and also the effect of our semicircular column geometry and single wall-slug configuration on the observed slug motion.