细颗粒振动流态化行为的二维床观察

本文利用一种新型复合振动充化装置，使在一般操作条件下无法实现正常流化的细颗粒床层处于良好的流化状态。通过观察发现，振动的引入可以破坏沟流的存在而使细颗粒流化；其振动流化有三种存在形式，提出了振动流化的物理模型和流化相同，可以解释细颗流化状态与振动条件及其物性的关系。     

生物质及其与惰性颗粒双组分体系的流化特性

采用MDMDY-300型全自动密度仪和体积法测量了生物质和3种惰性颗粒的颗粒密度和堆密度,在有机玻璃流化床内考察了生物质单组分及其与3种惰性颗粒双组分体系的最小流化空隙率和流化速度。结果表明,单组分颗粒密度随粒径的变化可以忽略,而堆密度却随粒径的增大有所减小;双组分体系的最小流化空隙率随细颗粒组分增加而出现先减小后增大的趋势,最小值出现在细颗粒组分体积分数为30%左右,且颗粒粒径差异越大变化趋势越明显;双组分体系的起始流化速度、最小流化速度和完全流化速度均随细颗粒组分含量增加呈现减小的趋势,当细颗粒体积分数达到30%左右后起始流化速度的下降趋势趋于平缓。     

气固固循环流化反应器的流体力学行为

简单介绍了气固固三相反应设备的研究现状,描述了气固固循环流化反应器的操作特点,实验研究了气固固循环流化反应器的流体力学行为,如气固两相通过填料层的压降、细颗粒的固含率及细颗粒的质量流率等．     

超细颗粒在声场流化床中的流化特性

在内径为130mm的声场流化床中,以原生纳米级SiO2超细颗粒为物料,在声压水平为0～140dB、声波频率为0～500Hz范围内系统地考察了声波对超细颗粒流化特性的影响。结果表明：当声波频率为100～150Hz、声压大于130dB时,声波可以有效地消除节涌、抑制沟流、降低临界流化速度,显著地改善纳米SiO2颗粒的流化质量。在频率一定的情况下,声压越高,超细颗粒的临界流化速度越低,流化质量越好。当频率低于100Hz或高于150Hz时,随着频率的进一步降低或增加,超细颗粒的临界流化速度都增大,甚至又出现节涌和沟流。声波的效果减弱甚至消失。     

超细颗粒流化质量的强化方法

综述了现有文献报道中涉及的辅助细颗粒流化的诸多方法,包括机械振动、离心场、声波、电/磁场扰动、脉冲气流以及添加组分;介绍了各种方法在机理研究和作用效果方面取得的各种进展;并结合各种手段的优缺点给出了一些未来可能的研究方向。分析表明机械振动、离心场、声波、电/磁场扰动等方法更适合于小型化工业生产或实验室研究,脉冲气流以及添加组分有应用于大型化工业生产的可能性,但应用添加组分时如何综合考虑后续分离过程,进而选择合适的添加组分是该种手段成功应用的关键。为超细颗粒流态化研究及工业应用提供指导。     

粒径及声场对SiO2超细颗粒流化行为的影响

采用内径为56 mm的玻璃管流化床,考察了平均粒径分别为5~10 nm(1#), 0.5 mm(2#)及10 mm(3#)的SiO2超细颗粒在无声场及声场存在下的流化行为. 无声场时,1#和2#颗粒可在较高的气速下形成稳定聚团,单位质量颗粒团间作用力与原生颗粒相比显著下降,因而可实现稳定的聚团流化,3#颗粒因颗粒间粘性力较大,无法实现稳定流化. 40~60 Hz的声场对3种超细颗粒的流化行为均可起到一定的改善作用,在此频率范围外,声场的作用不明显. 提高声压级,可以使1#和2#颗粒团发生一定程度的破碎,聚团尺寸减小,最小流化速度降低. 在实验范围内,添加声场无法使3#颗粒实现稳定流化.     

振动流化床临界流化速度理论预测与实验研究

根据振动流化床床层动力学特性,提出了第一、第二流化段,第一、第二临界流化速度的概念.从流化床临界流化速度的定义出发,得出了振动流化床第一临界流化速度数学模型.在二维振动流化床内,以不同粒径的玻璃珠为床料进行实验研究,分析了振动和其它操作条件对临界流化速度的影响,通过实验数据关联得到了振动能量传递系数的数学表达式,并将模型预测与实验结果进行了对比.结果表明振动强度增加,第一、第二临界速度均减小,振动对第一临界流化速度影响更显著,当振动强度超过1.57后,不通气体床层也能流化,第一临界流化速度降为零,模型预测与实验结果有较好的一致性.     

微细粉体振动流化床的流体力学行为研究

本文利用一种振动流化床装置实现了对Ｇｅｌｄａｒｔ２分类中Ｃ类粉体的正常流化，研究了不同振动参数对床膨胀，最小流化等流化行为的影响，提出了振动条件下最小流化速度的经验关联式。     

振动流化床浸没水平管传热特性研究

为了深入研究振动流化床浸没水平管的传热特性,分别以沙子和玉米细颗粒作为实验物料,用水平探头测定了振动流化床中这2种床层颗粒与浸没水平管间的传热系数,分析了操作气速、振动频率、空气进口温度等因素对传热过程的影响。结果表明:在低气速下,振动是影响振动流化床中传热的主要因素,振动的引入可以明显改善流化作用,可以在低气速下得到较好的传热效果,同时达到节能的效果。通过分析实验结果,建立了振动流化床的传热关联式,模型计算值与实测值能较好吻合。研究结果可为干燥膏状物料时确定适宜的操作参数提供参考。     

振动流化床中双组分颗粒流化特性的研究

本文研究了内径为１４８ｍｍ振动圆柱床中等密度和不等密度的双组分颗粒流化特性,考察了不同振动强度对双组分颗粒的床层空隙率、最小流化速度及相图的影响,给出了床层空隙率和最小流化速度的计算式,此计算值与实验值基本相符,且对振动流化床的实际操作和工程设计起到一定的指导作用。     

Parametric study of fine particle fluidization under mechanical vibration

Investigations into the effects of vibration on fluidization of fine particles (4.8-216 μm average in size) show that the fluidization quality of fine particles can be enhanced under mechanical vibration, leading to larger bed pressure drops at low superficial gas velocities and lower values of u_mf. The effectiveness of vibration on improving fluidization is strongly dependent on the properties (Geldart particle type, size-distribution and shape) of the primary particles used and the vibration parameters (frequency, amplitude and angle) applied. The possible roles of mechanical vibration in fine particle fluidization have been studied with respect to bed voidage, pressure drop, agglomeration, and tensile strength of particle bed. Vibration is found to significantly reduce both the average size and the segregation of agglomerates in the bed, thus improving the fluidization quality of cohesive particles. Also, vibration can dramatically reduce the tensile strength of the particle bed. Obviously, vibration is an effective means to overcome the interparticle forces of fine powders in fluidization and enhance their fluidization quality.     

Vibratory Compaction: III, Rate of Entry

A study of the rates at which fine particles can be vibratorily infiltrated into a column matrix of packed coarser particles is reported. Infiltration and compaction rates of angular tetra-hedra, rounded tetrahedra, and spheres were compared. The dependence of infiltration rate on ratio of the sizes of matrix to infiltrating particles and the interparticle void fraction in the matrix were found. The influence of acceleration and frequency of vibration on infiltration rate was also determined.     

EFFECT OF DRYING ON POWDER COATING EFFICIENCY AND AGGLOMERATION IN VIBRO-FLUIDIZED BED

Glass beads of 43 μm were coated in a vibro-fluidized bed by atomizing a fine silica powder together with polyvinyl alcohol aqueous solution. The coating efficiency and weight fraction of the agglomerated particles were measured under various experimental conditions, and their dependencies on the frequency and the direction of vibration were investigated. The coating efficiency and the degree of the agglomeration among core particles correlated well with an index R. The index R was introduced to evaluate quantitatively the drying conditions in a fluidized bed.

Application of vertical vibration on the fluidized bed lowered the coating efficiency somewhat, while it prevented agglomeration. From the experimental results it was confirmed that coating with high quality and high efficiency, where few agglomerates were produced and silica powder was utilized efficiently, was possible in a vibro-fluidized bed with adequate vibration frequency and orientation of the vibration vector.     

EFFECT OF DRYING ON POWDER COATING EFFICIENCY AND AGGLOMERATION IN VIBRO-FLUIDIZED BED

Glass beads of 43 μm were coated in a vibro-fluidized bed by atomizing a fine silica powder together with polyvinyl alcohol aqueous solution. The coating efficiency and weight fraction of the agglomerated particles were measured under various experimental conditions, and their dependencies on the frequency and the direction of vibration were investigated. The coating efficiency and the degree of the agglomeration among core particles correlated well with an index R. The index R was introduced to evaluate quantitatively the drying conditions in a fluidized bed.

Application of vertical vibration on the fluidized bed lowered the coating efficiency somewhat, while it prevented agglomeration. From the experimental results it was confirmed that coating with high quality and high efficiency, where few agglomerates were produced and silica powder was utilized efficiently, was possible in a vibro-fluidized bed with adequate vibration frequency and orientation of the vibration vector.     

Numerical simulation of cohesive particle motion in vibrated fluidized bed

The effect of vibration on the cohesive particle motion in the bed was examined by using discrete element method(DEM). The bed of dried fine particles was treated as the objective of calculation. The van der Waals force was used as the cohesive force because the van der Waals force was considered to be the main cohesive force in this case. Since the actual calculation time was too long, the fine cohesive particle was difficult to be treated. So a relatively large particle (1.0 mm in diameter) was used in calculation and the van der Waals force was assumed that the ratio of gravity force to van der Waals force of particle used in this calculation was equal to that of a fine particle (6.0 μm in diameter), to express the effect of van der Waals force significantly. The calculation results were compared with that case of cohesionless particle.In the case with vibration, the cohesive particle motion in the bed is observed, though no fluidization state appears in the case without vibration, and there is no bubble in the bed even the fluidization state. In the case of cohesive particle, the collision energy between particle and wall caused by vibration gap propagates from the bottom to top of bed, and the particle moves vigorously at the top of bed in the case with vibration. As the vibration gap increases, the effect of vibration on the cohesive particle motion becomes larger, i.e., the low vibration frequency at the same vibration strength or the large vibration strength at the same vibration frequency promotes the fluidization of the bed.     

A study of spray granulation in vibrated fluidized bed with internal heating tubes

The granulation process in a vibrated fluidized bed with immersed horizontal heating tubes was studied in this paper, with small monoammonium phosphate particles as the initial particles and monoammonium phosphate solution sprayed on them. The concrete influences on the granulating performance of the immersed horizontal heating power, fluidizing gas velocity, vibration frequency and amplitude had been analyzed theoretically. The results show that appropriate vibration intensity is a preferred condition for the growth of partials, but the fine dust will become much more along with prolonged vibration. Increasing the heating power is beneficial to raise the growth rate. Particles will grow faster if the fluidizing gas velocity is higher, but this will cause more fine dust. The optimized condition of A = 0.002 m, f = 6.67 Hz, u = 1.4 m/s was given after the analysis of the experimental results. In the end, a semiempirical formula was derived from the experiment data, and the calculation results show good agreement with the experimental data.     

Determination and handling of total mixes in pharmaceutical systems

A method is described for studying the behaviour of homogeneous total mixes in different vibration conditions. Three different total mixes were formed using direct compression tableting excipients and a model drug, potassium chloride. The mixes were vibrated in conditions similar to those encountered during normal pharmaceutical production. Segregation tendencies of the powder mixes were studied according to the deviation in content uniformity of samples removed from different levels in the powder bed following vibration.Certain vibration conditions produced specific segregation patterns based on either percolation or a mechanism analogous to diffusion. Of the three total mixes, Dipac and potassium chloride was found to be most susceptible to segregation in all vibration conditions due to movement of a large proportion of the free fine drug particles. By comparison, Emdex and recrystallised lactose total mixes contained relatively few free drug particles and were resistant to segregation in most conditions.The results suggest that in order to minimise segregation of powders during processing, a drug/excipient combination should be selected to produce optimum interparticle adhesion. Additionally, any vibration occurring during processing should be kept within limits, so that frequencies below approximately 100 Hz and accelerations above approximately 2 G are eliminated.     

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.     

Hold-up of fine particles in the packed dense bed of the multisolid pneumatic transport bed

The hold-up of fine particles in the packed bed of dense particles in the multisolid pneumatic transport bed was experimentally examined. In the experiments, three types of fine particles were used including FCC particles (65 μm), glass beads (105 μm) and fine sand (155 μm), while three types of dense particles were used including aluminum particles (5.50 mm and 6.96 mm) and iron oxide particles (11.08 mm). The hold-up of fine particles in the packed bed of dense particles was found to be higher by a factor as large as 6 compared with that observed in systems without dense particles. An interaction coefficient between fine particles and dense particles was defined based on the momentum balance equation of fine particles in the packed bed. This interaction coefficient, which is empirically correlated, was utilized to account for the hold-up of fine particles in the packed bed.     

Factors affecting methanol photocatalytic oxidation and catalyst attrition in a fluidized-bed reactor

A resolution IV fractional factorial experimental design explored the effects of seven factors on both the methanol photocatalytic oxidation (PCO) rate and the catalyst particle size distribution using a fluidized-bed reactor. The seven factors were as follows: calcination temperature, calcination time, grinding order, particle size, vibration amplitude, carrier gas humidity, and fluidization velocity. Decreasing calcination temperature from 726 to 623 K increased the activity of TiO₂/Al₂O₃ catalysts for methanol PCO. Attrition during fluidization liberated small TiO₂ particles from the bulk catalyst and the rate of attrition increased with gas velocity. Attrition was the primary cause of catalyst elutriation and not the presence of fine particles initially present in the bed from catalyst preparation. Increasing humidity caused agglomeration of fine particles, which reduced the amount of catalyst carryover. Removal of fines from the catalyst bed prior to fluidization caused an increase in catalyst attrition until the amount of fines present in the bed was similar to that of a bed in which fines were not removed.