横向旋转磁场对液固流化床中铁磁颗粒成链旋转的影响

<正>朱庆山研究表明,把铁颗粒添加到粘性粉体中,在轴向磁场的作用下,铁颗粒能够成链.Penchev和Hristov研究了横向磁场中铁磁颗粒流态化后,指出横向磁场流态化的一个主要特征也是磁链流态化.不过,这些研究只注重磁场流态化的一些本征特征,没有考虑通过磁场的变化改变磁链长度和磁链运动的方式,进而改善流化的质量.可以设想,如果这样的磁链放在横向均匀旋转磁场中使其自旋,那么自旋的颗粒链就能够对流化的颗粒起到搅拌和混合的作用,因而能够提高流态化的质量.     

不同类型颗粒的振动流态化

在一种新型复合振动流化床中研究了不同振动参数（ｆ＝１０～６０ＨＺ），Ａ＝０．５５×１０（－３）～１．５×１０（－３）ｍ）及不同操作条件对Ｇｅｌｄａｒｔ分类中的Ａ、Ｂ和Ｄ类颗粒起始流化行为的影响。结果发现，振动的引入可以降低颗粒的起始流化速度，对于较细的颗粒降低幅度可达４５％左右；而对于较粗的颗粒，起始流化速度则降低幅度较小。另外，静床高度的增加将使振动效果减弱，使得起始流化速度下降幅度减小。在较宽的实验范围内，提出了振动条件下起始流化速度的经验关联式。     

污泥颗粒与河砂混合流化特性的实验研究

在内径f105 mm、高800 mm的冷态流化床实验装置上进行了污泥颗粒与河砂混合流化特性的实验研究,获得了污泥颗粒水分、污泥颗粒与河砂的质量比对混合物料的流化特性的影响规律. 实验结果表明,污泥颗粒的水分、污泥颗粒与河砂的质量比会影响混合物料的最小流化速度,也影响污泥颗粒与河砂混合的均匀程度. 污泥颗粒的质量比越大,混合物料的最小流化速度越大;污泥颗粒的水分含量越高,混合物料的最小流化速度也越大;污泥颗粒与河砂的质量比越接近1:1,越容易实现充分混合. 在对实验数据进行分析处理的基础上,提出了污泥颗粒与河砂混合物料的最小流化速度经验方程,为流化床污泥颗粒干燥工艺提供基础数据和设计依据.     

粘性SiC颗粒聚团流态化特性

对不同粒径的°SiC粘性颗粒的流态化实验表明,颗粒粒径对流化性能有较大影响,颗粒粒径越小,颗粒间粘附力越大,其流化性能越差;提出了粘性颗粒自然聚团数Ae_n和流态化聚团数Ae_f,用来表征颗粒的流化性能;指出了应开展粘性颗粒聚团流态化的研究。     

生物质焦与煤焦及煤灰的流化特性研究

在φ 115 mm×1 000 mm有机玻璃制成的圆柱型流化床中,对生物质焦、煤焦、煤灰及其混合颗粒的流化特性进行了实验研究.实验结果表明,单一生物质焦颗粒不能正常流化,煤焦和煤灰颗粒可以很好地流化.当煤焦和生物质焦混合颗粒中生物质焦颗粒的质量百分比小于33%时,两者混合颗粒可以达到较好的流化状态,煤焦和生物质焦双组分混合颗粒的最小流化速度随生物质焦质量百分比的增加而减小.生物质焦和煤焦的混合体系中添加煤灰,流化质量可进一步提高,生物质焦、煤焦和煤灰三组分混合颗粒的最小流化速度随着煤灰质量百分比的增加而增大.双组分和三组分混合颗粒的最小流化速度和经验公式预测结果具有良好的一致性.     

横向旋转磁场作用下粘性颗粒流态化质量的改善

本文研究了横向旋转磁场作用下粘性颗粒的气固流态化。研究表明,在粘性颗粒中添加铁磁性颗粒和横向旋转磁场可以明显改善粘性颗粒的流态化质量。     

声场强化微小流化床流动特性研究

在内径4.3mm微小流化床中,考察了声场对FCC及石英砂颗粒流化质量的影响。重点讨论了声压级与频率对微小流化床最小流化速度的影响。结果表明,声场能改善微小流化床流化质量。尤其对于51μm石英砂颗粒,声场可以使其消除沟流,实现稳定流化。声压越大,声场对微小流化床流化质量改善越明显。最小流化速度随声压增高呈单调下降趋势。相同声场条件下,声波对微小流化床最小流化速度数值降低幅度大于大尺度流化床。声场对微小流化床最小流化速度的影响存在最佳频率。但不同颗粒的最佳频率不同。内径4.3mm流化床,51,67,83μm石英砂颗粒与83μmFCC颗粒对应的最佳频率分别为90,90,140和140Hz。在一定的声压与频率下,声场可以降低最小流化速度约9%～21%。对于微小流化床,床径越小,则床层空隙率越大,越有利于实现外场强化,最小流化速度的降低幅度也逐渐增大。     

粘附性颗粒添加组份流态化实验

以不同粒径的ＳｉＣ为物料,考察了表观气速和添加颗粒对其流化性能的影响．实验表明,平均粒径大于１０μｍ的ＳｉＣ物料,可通过增大表观气速使其流化;而小于５μｍ的ＳｉＣ５和ＳｉＣ２物料,不能使用增大表观气速的方法使其流化．添加颗粒能使ＳｉＣ５很好流化,利用流态化聚团准数Ａｅｆ可计算颗粒的最佳添加量ｘｍ．     

含油污泥-石英砂颗粒混合物的混合分离特性

在内径60 mm、高1000 mm的冷态气固流化床实验装置上,研究了含油污泥-石英砂混合颗粒的流化特性.实验结果表明,对于含油污泥含量较高的混合颗粒,随着气速由高到低,含油污泥颗粒与石英砂的流化行为可以分为四个阶段,双组分完全流化、石英砂流化-油泥趋于静止、石英砂趋于静止和固定床阶段；通过两组份分层填装流化实验,发现仅...     

生物质与煤混合颗粒流化特性的实验研究

在 D1 1 5 mm× 1 0 0 0 mm有机玻璃制成的圆柱型流化床中 ,对玉米秆、稻秆、煤及其混合物的流化特性进行了实验研究 .实验结果表明 ,单一生物质颗粒不能形成良好的流化状态 ,而加入一定量煤构成生物质和煤二组分混合颗粒可以实现稳定流化 .当生物质和煤混合颗粒中生物质的质量分率小于 5 0 %时 ,可以达到很好的流化状态 ,生物质和煤二组分混合颗粒的最小流化速度随生物质质量分率的增加而减小 .     

Experimental investigation of a rotating fluidized bed in a static geometry

Rotating fluidized beds in a static geometry are based on the new concept of injecting the fluidization gas tangentially in the fluidization chamber, via multiple gas inlet slots in its cylindrical outer wall. The tangential injection of the fluidization gas fluidizes the particles tangentially and induces a rotating motion, generating a centrifugal field. Radial fluidization of the particle bed is created by introducing a radially inwards motion of the fluidization gas, towards a centrally positioned chimney. Correctly balancing the centrifugal force and the radial gas-solid drag force requires an optimization of the fluidization chamber design for each given type of particles. Solids feeding and removal can be continuous, via one of the end plates of the fluidization chamber.The fluidization behavior of both large diameter, low density polymer particles and small diameter, higher density salt particles is investigated at different solids loadings in a 24 cm diameter, 13.5 cm long non-optimized fluidization chamber. Scale-up to a 36 cm diameter fluidization chamber is illustrated.Provided that the solids loading is sufficiently high, a stable rotating fluidized bed in a static geometry is obtained. This requires to minimize the solids losses via the chimney. With the polymer particles, a dense and uniform bed is observed, whereas with the salt particles a less dense and less uniform bubbling bed is observed. Solids losses via the chimney are much more pronounced with the salt than with the polymer particles.Slugging and channeling occur at too low solids loadings. The hydrostatic gas phase pressure profiles along the outer cylindrical wall of the fluidization chamber are a good indicator of the particle bed uniformity and of channeling and slugging. The fluidization gas flow rate has only a minor effect on the occurrence of channeling and slugging, the solids loading in the fluidization chamber being the determining factor for obtaining a stable and uniform rotating fluidized bed in a static geometry.     

Fluidization of spherical versus elongated particles: Experimental investigation using magnetic particle tracking

In biomass processing fluidized beds are used to process granular materials where particles typically possess elongated shapes. However, for simplicity, in computer simulations particles are often considered spherical, even though elongated particles experience more complex particle– particle interactions as well as different hydrodynamic forces. The exact effect of these more complex interactions in dense fluidized suspensions is still not well understood. In this study we use the magnetic particle tracking technique to compare the fluidization behavior of spherical particles to that of elongated particles. We found a considerable difference between fluidization behavior of spherical versus elongated particles in the time-averaged particle velocity field as well as in the time-averaged particle rotational velocity profile. Moreover, we studied the effect of fluid velocity and the particle's aspect ratio on the particle's preferred orientation in different parts of the bed, which provides new insight in the fluidization behavior of elongated particles.     

Measuring binary fluidization of nonspherical and spherical particles using machine learning aided image processing

The binary fluidization of Geldart D type nonspherical wood particles and spherical low density polyethylene (LDPE) particles was investigated in a laboratory-scale bed. The experiment was performed for varying static bed height, wood particles count, as well as superficial gas velocity. The LDPE velocity field were quantified using particle image velocimetry (PIV). The wood particles orientation and velocity are measured using particle tracking velocimetry (PTV). A machine learning pixel-wise classification model was trained and applied to acquire wood and LDPE particle masks for PIV and PTV processing, respectively. The results show significant differences in the fluidization behavior between LDPE only case and binary fluidization case. The effects of wood particles on the slugging frequency, mean, and variation of bed height, and characteristics of the particle velocities/orientations were quantified and compared. This comprehensive experimental dataset serves as a benchmark for validating numerical models.     

EFFECT OF VARIABLE ACOUSTIC FIELD AND FREQUENCY ON GAS-SOLID SUSPENSION OF FINE POWDER: A REVIEW

Suspensions of fine particles in either Newtonian or non-Newtonian fluids are often encountered in the physical, engineering, and biological sciences. For example, the manufacture of particle-laden products such as reinforced composites, paints, paper, slurries, and cements involves the processing of particle suspensions. Fine particles become difficult to suspend due to interparticle attraction forces like ver der Waals, capillary, and cohesive forces, which are responsible for converting fine particles into aggregates. These aggregates prevent the particles from being suspended uniformly, hence external forces are essential to break these aggregates. External forces include magnetic fields, electrical fields, acoustic fields, and mechanical vibration, which are useful to break aggregates and suspend particle uniformly. This process is termed homogeneous fluidization. This article presents a comprehensive review of sound-assisted fluidized beds for group C, A, and B and binary materials. Furthermore, this review covers the effect of acoustic field intensity and frequency on minimum fluidization velocity and on bubbling.     

Utilizing yield‐stress fluids to suppress chaining during magnetic alignment of microdisks via rotating fields

Inkjet printing can be used to deposit photopolymerizable magnetic inks for the creation of functionalized composites. Anisotropic properties in the composites can be achieved when inkjet printing is combined with external magnetic fields to align magnetically orientable particles (MOPs). When a MOP is induced by an external magnetic field, it will create its own magnetic field that can attract neighboring particles. The coarsening of particles into higher‐order structures like chains and sheets is unwanted in certain areas, such as high‐frequency applications. We show that this particle–particle attraction and subsequent particle migration can be inhibited with the introduction of a yield stress into the suspending medium, while still allowing the alignment of the particle to proceed. For magnetically induced rotational and translational motions for oblate spheroids in a rotating magnetic field, theoretical scalings are presented for the characteristic timescales in a linear fluid and for the characteristic stresses in a yield‐stress fluid. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3215–3226, 2018     

密相流化床中介尺度流动结构的流体力学特性研究

在一套流化床冷模实验装置中对黄沙颗粒和黄沙-硅微粉 （20 μm）混合颗粒进行实验。测量固含率时间序列信号并进行统计分析,提出并建立复杂光纤脉动信号的解耦方法,实现稠密气固流中介尺度流动结构的准确识别。基于统计矩一致性原理提出气泡阈值的计算方法,通过遍历法确定气泡阈值。对气泡阈值变化规律进行分析,发现加入细颗粒有助于改善流化质量,随表观气速的增加,气泡阈值减小。对气泡、乳化和聚团三相的相分率进行统计,发现在黄沙颗粒中加入少量（5%,质量分数）细颗粒能够显著改善流化质量,细颗粒添加量过多时（10%）,对流化质量的改善将减弱。对气泡的流体力学特性进行分析,发现加入10%硅微粉后,气泡弦长增大,频率降低,速度略有降低。对颗粒聚团流体力学特性进行分析,发现随硅微粉含量增加,表观气速对聚团速度的影响减弱,聚团弦长略有减小。加入5%硅微粉后,颗粒聚团的出现频率较小且径向上分布均一。加入10%硅微粉后,聚团频率有所增大,说明加入过多硅微粉会促进聚团的形成。     

Fluidization of fine particles in a sound field and identification of group C/A particles using acoustic waves

Effects of sound field on the fluidization of fine particles have been comprehensively examined by using fine powders (4.8-65 μm average in size) including Al₂O₃, TiO₂, glass beads and FCC catalyst. It is found that the fluidization quality of fine particles can be enhanced with the assistance of a sound field, resulting in higher pressure drops and a lower u_mf. The effect of sound on the fluidization of fine particles is strongly dependent on the particle properties (Geldart type and particle size) as well as the parameters of the sound field such as sound pressure level (or intensity) and frequency. Given a fixed sound frequency, the effect becomes more significant at a higher sound pressure level. For the present sound-aided fluidized bed system, there is a resonant frequency at about 100-110 Hz, at which the effectiveness of the sound wave in improving fluidization of fine particles is most remarkable. In addition, based on the different attenuation features of sonic waves in the gas-solid suspension of group C and A particles, a novel acoustic method is explored to distinguish group C from group A particles.