Foam granulation: Liquid penetration or mechanical dispersion?

There have been significant advances in the understanding of wet granulation processes. Foam granulation is the latest development and an emerging area of interest for pharmaceutical manufacturing.Single foam penetration experiments were carried out on static powder beds, followed by short-nucleation experiments (where nuclei are formed by a nucleation-only mechanism) and full foam granulation experiments (where nucleation, growth and breakage are occurring simultaneously). All experiments were performed with lactose monohydrate powder using a 5 L high shear mixer–granulator. The foam penetration/dispersion behaviour was examined and the granule size distributions were investigated as a function of foam quality (83–97% FQ), impeller speed (105–515 rpm) and wet massing period (0–4 min).Nucleation in foam granulation is postulated to undergo either “foam drainage” or “mechanical dispersion” controlled mechanisms. For “foam drainage” mechanism, the foam penetrates the powder bed to form coarse and broad granule size distributions. For “mechanical dispersion” mechanism, the wetting and nucleation conditions are governed by the powder mixing conditions and similar granule size distributions are produced. Regardless of the mechanism, the initial wetting and nucleation behaviour controls the initial nuclei size distribution, and this initial distribution is retained in the final granule size distribution. This work demonstrated the critical importance of the nucleation and binder distribution in determining the granule size distributions for foam granulation process.     

A novel microfluidic mixer using aperiodic perturbation flows

A novel technique is proposed for enhancing the mixing performance of a ‘crisscross’ microfluidic mixer by means of aperiodically-varying perturbation flows. The effects of the perturbation and geometry parameters on the fluid flow characteristics and mixing performance are analyzed numerically. In performing the simulations, the flow field and species concentration field are obtained by solving the two-dimensional time-dependent Navier–Stokes equations and the convection–diffusion equation, respectively. In addition, the oscillating source used to modulate the perturbation flows is modeled using the Sprott system. The results show that the irregularly-alternating flow perturbations cause a repeated stretching and folding of the species streams and enhance the mixing performance as a result. It is shown that an effective improvement in the mixing performance can be obtained through a suitable choice of the Sprott system scaling factor. Moreover, it is shown that having assigned an appropriate scaling factor, the mixing performance can be further improved by specifying suitable values of the geometry and perturbation parameters.     

Expression for turbulent power draw of an in-line Silverson high shear mixer

We report the validation of an expression to accurately describe the power draw of an in-line rotor–stator mixer over a range of flow rates and rotor speeds. The expression consists of a term which reflects the power required to rotate the shaft in response to the liquid resistance and a term to reflect the power convected away from the mixing chamber. A specially commissioned high speed (12,000 rpm), instrumented 150/250 MS Silverson mixer has been developed with power draw determined from both torque and calorimetric measurements. Experiments are carried out using water over a range of independently controlled flow rates and rotor speeds with losses for both techniques carefully accounted for. For the torque measurement the value of the constants for the two terms above are Po_z=0.197 and k₁=9.35, respectively. For the calorimetric technique the measured temperature rise was similar to some of the corrections and losses over a significant range of the experimental space but nevertheless with careful experimentation constants similar to those for the torque technique were obtained, Po_z=0.229 and k₁=7.46. Allowing the calibration of the temperature probes to be a fit parameter in the regression routine increased the value of k₁=8.10 but did not affect the value of Po_z. A simple graphical method is also proposed using a dimensionless form of the expression which yielded slightly higher value of Po_z but a slightly lower value of k₁. The accuracy of both measurement techniques improves with rotor speed and the differences between the constants is attributed to the better accuracy of the torque technique at higher flow rates whereas the calorimetric technique is more accurate at low flow rates where the temperature rise is larger. Several repeats of the calorimetric technique with a reduced set of experimental points show good reproducibility. Finally at low flow rates (<10% of the maximum) the power unexpectantly increases and a modification to the expression is proposed by considering the pumping efficiency.     

Polydisperse granular flows in a bladed mixer: Experiments and simulations of cohesionless spheres

The flow and segregation of polydisperse, spherical particle mixtures in a bladed mixer was investigated using experimental and computational techniques. Discrete element simulations were able to reproduce the qualitative segregation profiles and surface velocities observed experimentally. For a binary system with a 2:1 size ratio, segregation by size occurs due to a sieving mechanism. Segregation in the binary system is fast, with a fully segregated system observed after just 5 revolutions. However, the numerical simulations showed that the extent of segregation in the bladed mixer can be reduced by introducing intermediate particle sizes in between the smallest and the largest particles. Addition of intermediate particle sizes increases convective and diffusive particle motion promoting a mixing mechanism that reduces segregation via the sieving mechanism. Void fraction within the bladed mixer increases as the degree of polydispersity is increased allowing the particles to move more freely throughout the particle bed. Higher void fractions also increase the ability of large particles to penetrate deeper into the particle bed. Normal and shear stresses are also affected by particle size distributions, with lower average values obtained for the system with the largest number of particle species. Differences in the amount of stress generated by each particle species were observed. However, the difference in stresses is reduced as the number of particle species in the system is increased.     

双转子连续混炼机混炼段相似放大初探

基于几何相似准则,分别对3种混炼段构型进行了2倍和10倍放大,用Polyflow软件对放大前后的混炼段流场进行了模拟研究,以1个旋转周期内不同横截面上的平均压力和平均混合指数、物料在混炼段的停留时间分布、混炼段出口截面上的解聚功率密度和修正Lyapunov指数的累积概率函数、比能耗、扭矩和轴向力等为评价指标,分析了几何相似放大对流场特征、混合效果、能耗等的影响。结果表明,采用几何相似准则对不同构型的混炼段进行放大时,在转速不变的情况下,产量均可按几何放大倍数的3次方放大,而混炼段流场特征、混合效果及比能耗保持不变,混炼段转子所受的轴向力和扭矩分别按几何放大倍数的平方和立方增大;在进一步的放大设计中需兼顾热平衡相似,以便在高产量下保证塑化品质。     

空气雾化技术在燃油锅炉上的应用

研究设计内混式高效空气雾化轻柴油燃烧器。针对石油、石化、化工行业中锅炉在开工阶段没有燃料气和蒸汽供应,燃烧器的燃气枪和雾化蒸汽油枪无法投用,因此,锅炉装置不能运行。探讨在原燃烧器的基础上,按尽量不改变原燃烧器结构、燃烧方式和尽量少投入的原则,将原蒸汽雾化燃油枪改用空气雾化方式,开工用燃料油采用0#柴油,其它都不作改动。针对冷态试验结果,讨论了气压和油压对火炬形状的影响,油枪燃烧能量和雾化剂耗量,燃烧火盆与雾化角的关系。使用表明油枪喷嘴喷孔夹角、喷孔数、孔径、燃烧火盆、助燃风设计合理,雾化粒度细,燃烧完全,火焰刚直明亮、集中,喷嘴不结焦,操作性能良好。     

Relationship between droplet size and fluid flow characteristics in miniemulsion polymerization of methyl methacrylate

Static mixer (SM) can be applied for emulsification, but the fundamental understanding of the nature of fluid flow and mixing in static mixers, is however poor. Droplet size is a very important parameter in miniemulsion systems and affects strongly the mechanism of particle formation in polymerization reactions. In this study, static mixer was used as homogenization device for emulsification of methyl methacrylate (MMA). Re number (Re) was obtained for SM inserted tube in different flow rates. It was demonstrated the nature of fluid flow was turbulent under our experimental conditions. The relationship between droplet size—the most important variable in our study—and Weber number (We) was investigated. The results showed that the ratio of the droplet size to the pipe diameter was fit as an exponential function with an order of −0.35. The polymerization of created droplets under certain We values by SM showed that it is possible to obtain a reasonable 1 : 1 copy of droplets to the particles. All these, indicate that using relationship between We and droplet size allow one to obtain acceptable condition of droplet nucleation in miniemulsion polymerization. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

影响密炼机炼胶温度因素的探讨

炼胶温度是决定密炼机生产能力和炼胶质量的重要因素之一。本文主要对影响密炼机的炼胶温度的因素进行了分析，并通过试验机台对转子转速，冷却水温度等因素对炼胶温度的影响进行了实验研究和分析。     

静态混合器在十二烷基硫酸铵生产中应用

介绍了连续生产十二烷基硫酸铵的生产工艺，并与间歇法生产的工艺及产品质量指标作了对比，叙述了利用静态混合器生产十二烷基硫酸铵的优越性。     

双工质塑料冷混机设计研讨

介绍了可提高塑料混合时冷却效率的双工质塑料冷混机，并简要叙述了立式，卧式和立式搅龙双工质冷混机却装置冷却物料的工序。