双螺杆中啮合块、螺杆元件混合过程及混合性能的研究

以双螺杆挤出机中的啮合块、螺杆元件作为研究对象,对其混合过程及混合性能进行研究,分析物料与添加剂的相互运动及变化过程。利用网格重叠技术和Ployflow软件对啮合块、螺杆元件的混合性能进行仿真,研究螺杆元件及不同转速下啮合块对应流体区域内的最大剪切应力,粒子在流体区域内的停留时间分布、分布指数、分离尺度等。结果表明:在啮合块流道内的混合过程中,啮合区域的两种粒子进行分布混合,其他区域的粒子在轴向运动到第2片啮合块时开始被带入啮合区,与另一种粒子进行分布混合;在相同转速下,啮合块的混合性能优于螺杆元件,随着转速的提高,啮合块的分散混合性能逐渐增强。     

Determining a value for mixing: Mixing degree

We have developed a new method to determine the degree of mixing for a given system. The method assumes knowledge of the locations of all or some studied particles both before and after mixing. The method is scalable and gives comparable results for systems with varying shapes and sizes of the mixing space. It can also be used to determine the mixing of only a part of the space studied. Due to the information needed, the method is best suited for simulations, but in some cases it might be possible to use it with real laboratory experiments.     

Steering of Liquid Mixing Speed in Interdigital Micro Mixers – From Very Fast to Deliberately Slow Mixing

Very fast mixing in the range of milliseconds as well as deliberately slow mixing was realized by specially adjusted interdigital micro mixers made of glass or stainless steel. The corresponding micro mixers are presented including experimental and theoretical investigations of the respective mixing process. Fast mixing was realized by combination of flow multilamination by interdigital microstructured feeding structures with geometric focusing. Details on the microfabrication, achievable throughputs and hydrodynamics are discussed. To prevent clogging of microsized feeding structures in the case of precipitation reactions, mixing was deliberately slowed down by separating the reactant solutions at the outlet by additional layers of inert liquids.     

聚烯烃重力掺混料仓及其评价

介绍了聚烯烃掺混料仓的常用形式和工作原理,并对5种常用掺混料仓的特点和性能进行了综合评价,提出了掺混料仓选用的原则。     

混炼工艺对NBR/PVC发泡材料性能的影响

研究了密炼和开炼两种混炼方式及不同的密炼温度对丁腈橡胶(NBR)/聚氯乙烯(PVC)发泡材料性能的影响。结果表明,混炼温度相同时,密炼工艺比开炼工艺的塑化共混效果更好,胶料的门尼黏度更高,发泡材料性能更优;在130～160℃的密炼温度范围内,密炼温度为150℃时得到的发泡材料密度最低、硬度较高。     

Mixing of viscous liquid mixtures

When a quiescent binary mixture is instantaneously brought from two- to one-phase region of its phase diagram, the resulting mixing process is driven both by diffusion and by convection. Applying the diffuse interface model, here we show by numerical simulation that the bulk motion that is induced during phase transition effectively slows down the mixing process. In fact, in our model convection is induced by a non-equilibrium body force that is proportional to the chemical potential gradients, expressing the tendency of the demixing system to minimize its free energy. In liquid systems, as this driving force induces a material flux which is much larger than that due to pure molecular diffusion, drops tend to coalesce and form larger domains which eventually must dissolve by diffusion. Therefore, in the absence of any external agitation, mixing is slower in mixtures with larger viscosities, contrary to common thinking. In addition, as expected, the mixing rate decreases as the Margules parameter Ψ increases, where Ψ describes the relative weight of enthalpic versus entropic forces.     

Characterization of the Mixing Quality in Micromixers

The laminar flow patterns and mixing performance of two different micromixers have been investigated and quantified using CFD. The micromixer geometries consist of a channel with either diagonal or asymmetric herringbone grooves on the channel floor. The numerical results show that a single helical flow is produced for the diagonal mixer, whereas the herringbone mixer creates a double helical flow, composed of an alternating large and small vortex. Particle tracking of a tracer shows that very little convective mixing occurs in the diagonal mixer. However, in the herringbone mixer, very good mixing occurs. Quantitative analysis methods that are traditionally used for characterizing macro‐scale static mixers have been employed. Calculation of the variance of tracer dispersion and the stretching has shown to be well adapted for quantifying the mixing in the micromixers. However, methods based on the deformation rate appear to be less suitable. The results are in excellent agreement with previous experimental findings.     

Coagulation of Particles Through Rapid Mixing

As is often assumed, rapid mix effectively distributes the dosed coagulant in suspension to promote subsequent flocculation of suspended particles and coagulant molecules. This study determined that the role of rapid mix is considerably more complex than conventionally assumed. Particles in the raw water samples from the Banxing Water Works of Taipei City were coagulated at high shear environment, during which flocs of size 40–70 μm were produced. The produced floc interior was compacted, and residual turbidity and the amount of dissolved natural organic matter (NOM) in suspension were substantially reduced. The subsequent stage of rapid mix slightly reduces floc size, further compacts the floc interior, and expels fine particles and some adsorbed NOM from the flocs. A sudden reduction in shearing rate produced large sized flocs with not so compact structures. Moreover, this action released fine particles from flocs into the suspension and enhanced adsorption of NOM onto solid surfaces.     

Coagulation of Particles Through Rapid Mixing

As is often assumed, rapid mix effectively distributes the dosed coagulant in suspension to promote subsequent flocculation of suspended particles and coagulant molecules. This study determined that the role of rapid mix is considerably more complex than conventionally assumed. Particles in the raw water samples from the Banxing Water Works of Taipei City were coagulated at high shear environment, during which flocs of size 40-70 μm were produced. The produced floc interior was compacted, and residual turbidity and the amount of dissolved natural organic matter (NOM) in suspension were substantially reduced. The subsequent stage of rapid mix slightly reduces floc size, further compacts the floc interior, and expels fine particles and some adsorbed NOM from the flocs. A sudden reduction in shearing rate produced large sized flocs with not so compact structures. Moreover, this action released fine particles from flocs into the suspension and enhanced adsorption of NOM onto solid surfaces.     

Mixing of concrete or mortars: Dispersive aspects

This article describes an experimental methodology offering mixing efficiency criteria for granular materials in terms of their dispersion capability. This methodology is based on the analysis of the dispersion kinetics of colored, cohesive, tracer particles that progressively disagglomerate during stirring. The effects of certain critical parameters such as the mixer speed and the type of mixer are described. In terms of the mix design, the contribution of the largest particles to the dispersion kinetics, and therefore to the mixing efficiency, is highlighted. A simple comparison of the mixing efficiency of mixer/mix design/procedure sets is finally provided for such cementitious granular materials.     

Mixing of concrete or mortars: Distributive aspects

This article describes an experimental methodology offering efficiency criteria for granular materials in terms of their mixing distributive capability. The methodology is based on analyzing the distribution kinetics of colored tracer particles which were demonstrated to respond similar to cement particles during mixing. The effect of certain critical parameters such as the mixer type, the volume and the mixer speed are investigated. The influence of mix design characteristics on distribution is also presented for several mixer types. Finally, a comparison of the dispersive versus the distributive capability is achieved for several (mixer, mix design) systems, which opens opportunities for defining rules for transfer and extrapolation.     

重力掺混料仓中颗粒混合效果的实验研究

通过实验介绍了颗粒物料在料仓中的流动形式及颗粒混合机理，提出了粒料通过垂直管开孔的流率计算方程，针对重力掺混的特性，确立了评价颗粒混合效果的混合指数计算模型，用于中试实验，证明了中试重力掺混仓设计的合理性。     

城市煤气多气种掺混技术的应用

介绍了多气种掺混的气质持性及符合7R气质特性的“三气”掺混最佳比；提出了以烟道气替代两段炉贫煤气进行掺混的思路，并对原商品煤气中两种“三气”掺混技术的经济效巢进行了比较。     

关于混炼理论的探讨

本文对橡胶混炼理论进行了探讨,给出了表达混炼理论三要求与物理性能关系的数学公式。对两段混炼、混炼温度、开炼机和密炼机、混炼加药顺序等关键因素作了理论分析。     

振动力场作用下聚合物填充体系挤出混合特性

本文利用一种新型毛细管动态流变仪,对碳酸钙填充聚丙烯体系进行了实验性研究。发现质量百分比为８５／１５的ＰＰ／ＣａＣＯ３填充体系,在一较佳振动条件下动态挤出时,振动场的存在对ＣａＣＯ３在ＰＰ熔体中的分散有促进作用,大大改善了混合料的混合程度。     

Mixing studies of non-Newtonian fluids in an anchor agitated vessel

The success of any mixing operation involving liquid–liquid, gas–liquid and gas–liquid–solid systems depends mainly on the geometry of the vessel and impeller, operating conditions and properties of the system. Transformation of laboratory results to commercial scale unit is very difficult due to the complexity of flow phenomena and the scale up is being done by adopting a conservative approach which is based on the geometric, kinematic and dynamic similarities. This approach does not take into account the non-ideal flow behavior of the fluid and the design of commercial unit will be more rational if this information is included in the design of the unit.     

Unsteady Mixing Characteristics in a Vessel with Forward‐Reverse Rotating Impeller

Usually, mixing is carried out in a vessel with four baffles and a single impeller. In some applications, however, the use of a baffled vessel is not recommended. One of the stirring methods used instead is unsteady agitation with forward‐reverse rotating impellers. The aim of this work was to characterize the agitation characteristics in a baffled and an unbaffled vessel with a turbine impeller. Mixing time and mixing power were evaluated in relation to the presence of baffles and the frequency of forward‐reverse rotation. It was found that the frequency of oscillation does not affect either the mixing time and mixing power values or the drag and added mass coefficients. Power requirements and mixing time were higher compared to the steady mixing conditions in a baffled vessel. The results showed that it is not recommended to use baffles because they have no influence on unsteady mixing.     

无塔混合成型工艺生产浓缩洗衣粉

本文介绍了无塔混合成型技术生产浓缩或超浓缩洗衣粉的方法,给出了原料配方和具体操作步骤。