The design and performance of a vane mixer based on extensional flow for polymer blends

A new laboratory‐scale mixing device called the “Vane Mixer” was designed, built, and tested. The vane mixer consists of three vane plasticizing and conveying unit. In comparison with the existing laboratory mixers, material flow in this vane mixer is characterized by a high contribution from extensional flow. As the mixer has mixing chamber of very simple geometry, the cleaning is very easy and the material lost is very small. The influences of mixing time and rotor speed on dispersed phase size were characterized and discussed. Morphology data on model immiscible polystyrene/high density polyethylene (PS/HDPE) blend have proved the high distributive and dispersive mixing efficiency. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41551.     

Characterization of mixing in an optimized designed T-T mixer with cylindrical elements

Passive micromixers are preferred over active mixers for many microfluidic applications due to their relative ease in integration into complex systems and operational flexibility. They also incur very low cost of manufacturing. However, the degree of mixing is comparatively low in passive mixers than active mixers due to the absence of disturbance in the flow by external forces and the inherent laminar nature of microchannel flows. Various designs of complex channel structures and three-dimensional geometries have been investigated in the past to obtain an efficient mixing in passive mixers. But the studies on mixing enhancement with simple planar geometries of passive mixers have been few and limited. The present work aims to investigate the possibility of mixing enhancement by employing simple planar type designs, such as T-mixer and T-T mixer with cylindrical elements placed in the mixing channel. The mixing performance has been evaluated in the Reynolds number range of 6 to 700. Numerical results have shown that T-T mixer with cylindrical elements performed significantly well and obtained very good mixing quality over basic T-mixer for the entire range of Reynolds number (6 to 700). The device has also shown better mixing as compared to basic T-T mixer and T-mixer with cylindrical elements. A larger pair of vortices formed in the stagnation area due to the presence of a cylindrical element in the junction. Cylindrical elements downstream caused significant enhancement in mixing due to splitting and recombining action. The size of the cylindrical element in the T-T mixer has been optimized to obtain better mixing performance of the device. Remarkable improvement in mixing quality by T-T mixer with cylindrical elements has been obtained at the expense of small rise in pressure drop as compared to other passive designs considered in this study. Therefore, the current design of T-T mixer with cylindrical elements can act as an effective and simple passive mixing device for various micromixing applications.     

Foam generation in a rotor—stator mixer: schaumerzeugung in einem rotor—stator mischer

The foaming process of an aqueous liquid system with surface active agents and thickeners in a rotor-stator mixer has been studied.The foaming capacity of a rotor—stator mixer may be represented by a so-called mixing characteristic. The foamabilities of several liquid systems have been measured as a function of the mixer geometry and the rotational speed.The hydrodynamics in a rotor-stator mixer is characterized by a Newton—Reynolds relationship. The mechanism of foaming and the dependence of several mixing parameters are different for the turbulent and laminar flow regions. The mixing process is evaluated in both regimes. In the transition region from turbulent to laminar the foaming is very poor in comparison with that in the turbulent and laminar flow regimes.     

Sources of irreversibilities in a perfectly Axisymmetric geometry at low Reynolds numbers

In plastic industry, a large variety of polymeric materials are obtained by liquid–liquid mixing. Recently, a new type of mixer (later called RMX)—based on a convergent/divergent unit which favors elongational flow—was developed with improved efficiency in polymer blending compared to traditional shear flow‐based devices such as internal mixers or extruders. The present study aims at identifying the possible origins of the higher dispersive and distributive mixing capability of this device. An experimental study, including flow visualization, and numerical simulations of creeping flows induced by this original device was carried out for Newtonian, shear‐thinning and viscoelastic fluids. The predictedmixing capability is based on length stretch and Lyapunov exponent methods. Calculation results show a good agreement with experiments and highlight some fundamental mixing mechanisms, such as striation, for viscoelatic fluids. POLYM. ENG. SCI., 54:2046–2056, 2014. © 2013 Society of Plastics Engineers     

Flow field analysis of a cavity transfer mixer

The cavity transfer mixer (CTM) was primarily designed as a distributive mixing device to be used as an add-on unit to existing extruders. In determining the CTM overall mixing efficiency as well as its potential use for various applications, the flow patterns/characteristics within this mixer must be well understood. In this work, a fluid dynamics analysis package, FIDAP, based on the finite element method was employed to simulate the flow patterns in a CTM with 6 rows and 4 cavities per row. A 3D, isothermal flow analysis was carried out and the fluid of choice was a flexible polyvinylchloride whose rheological behavior is described by a power-law model fluid. The flow field was characterized in terms of velocity profiles, pressure distributions, shear rates/shear stresses generated and a parameter λ quantifying the elongational flow components. The results of the flow simulations were compared with experimental data. The CTM potential use for dispersive mixing was discussed.     

Characterization of continuous convective powder mixing processes

The Process Analytical Technology (PAT) initiative has encouraged the development of new technology to improve upon the current manufacturing paradigm. As a result substantial attention has recently focused on continuous processing due to the ability to control disturbances online, avoiding the loss of processing materials and enabling effective process scale-up. In this paper, a pharmaceutical formulation is blended using a continuous flow “high shear” mixer utilizing different operating and design parameters. The mixing efficiency is characterized by extracting samples at the discharge of the blender, and analyzing them using Near Infrared Spectroscopy to determine compositional distribution. Operational conditions such as the inclination angle of the mixer and impeller rotation rate were investigated and showed to affect the mean residence time. The effects of mixer angle, agitation speed, number of blades, blade angle, number of passes through the mixer on the mixing performance of a powder continuous convective mixer are also examined and shown to affect mixing performance whereas the cohesive properties of the material did not significantly affect the mixing operation.     

圆排波瓣喷管引射器高效掺混流场数值计算

采用贴体曲线坐标、SIMPLEC算法和完全压力修正,在非正交性非常大的结构型同位网格上求解了圆排波瓣喷管引射器内流场的不可压Navier-Stokes方程,湍流采用标准k-ε涡黏模型.计算得到了引射器中热混合效率沿混合管轴向的变化规律和流向涡的演变规律.混合管中的流向涡阵列大大强化了主次流的掺混.但该型引射器的总体热混合效率不高,实验的3种主流温度下最大热混合效率为0.874.将混合管出口截面速度分布和温度分布的数值模拟结果与实验值比较,两者比较一致;模拟结果与混合管沿轴向的静压系数分布规律实验值也基本相同.     

脉冲式气流混合机的设计与应用

设计了新型脉冲式气流混合机。该混合机具有混合效率高、快速混合、大型化、单位能耗低等特点。     

Processing of nanocomposites PLA/graphite using a novel elongational mixing device

Expanded graphite (EG) was added to polylactic acid (PLA) and then fully mixed in a novel elongational mixing device (RMX) to obtain PLA/EG nanocomposites. The operation of the new mixer device is based on the induced multiple passages of material (by means of reciprocating pistons) at different flow speeds through a short capillary die, thus creating convergent/divergent elongational flows. Highly homogeneous materials were obtained at all mixing conditions and particle size ranged from hundred to several hundreds of nanometers. Also, X‐ray diffractograms showed different intensity of the characteristic peak of EG (3% wt/wt EG was kept constant), suggesting partial exfoliation. Furthermore, the molecular weight of processed neat PLA samples was assessed in order to correlate the PLA degradation to morphology and reinforcement mechanisms in the nanocomposites, as a function of the RMX parameters. As well, final flow properties of neat PLA and EG compounds were obtained by dynamic rheology. Thermo‐mechanical degradation of PLA was found to play a major role in the rheology of mixing. On the other hand, PLA nanocomposites presented a storage modulus between 20 and 40% higher than neat PLA. Finally, morphology comparison between the RMX and an internal mixer, at the same mixing energy input, demonstrated a higher dispersive mixing efficiency for the RMX. POLYM. ENG. SCI., 55:214–222, 2015. © 2014 Society of Plastics Engineers     

Pressure drop and mixing behaviour of non‐Newtonian fluids in a static mixing unit

Static or motionless mixers have received wide application in chemical and allied industries due to their low cost and high efficiency. The pressure drop and mixing behaviour of such mixers have been widely studied. However, the available information for non‐Newtonian fluids is scanty. The results of pressure drop and mixing studies conducted with a locally made motionless mixer (MALAVIYA mixer) and four non‐Newtonian fluids—aq. CMC, PVA, and PEG solutions are reported in this article. The new mixer causes less pressure drop compared to some of the commercial mixers. Mixing behaviour of the unit is more closer to plug flow and a two‐parameter model correlates the dispersion data.     

Effects of embedded streamwise vorticity on turbulent mixing

This work concerns the characterization of turbulent flow underlying mixing in the presence of streamwise vorticity. An experimental test section made of a cylindrical tube equipped with seven rows of streamwise vortex generators was designed and constructed for this study. Each row is composed of four vortex generators fixed symmetrically on the tube wall. This new type of mixer, called a high-efficiency vortex (HEV) mixer, generates coherent structures in the form of longitudinal counter-rotating vortices. The resulting flow enhances radial mass transfer and thus facilitates particle dispersion and mixing. The energy cost of this mixer used as an emulsifier has been evaluated as up to a thousand times less than that of other static mixers for a given interface area generation (Lemenand et al. [1] and [2]).The aim of this work is to study experimentally and numerically the turbulence structure and mixing properties of the flow composed of streamwise vortices superimposed on a turbulent flow, in particular the more energetic structures present in the base flow. Experiments were carried out in the test section in a flow loop by measuring instantaneous velocities by laser Doppler anemometry. Numerical simulations of the velocity distribution and turbulence field inside the flow were conducted for various turbulence models using a computational fluid dynamic CFD package. Attention is focused on the evolution and distribution of turbulent kinetic energy dissipation as the underlying mechanism for turbulent mixing. Mean and turbulent quantities are compared with experimental results.Both laboratory experiments and numerical simulations show a vortex zone behind each tab that could explain the efficiency of the HEV mixer. This study provides a basis for understanding the physical mechanisms in the mixing and homogenizing of the flow and therefore the efficiency of the mixer.     

双转子连续混炼机中的混沌混合行为研究

双转子连续混炼机是一种具有优异分散与分布混合特性的连续混炼设备。本文运用混沌流动理论,对双转子连续混炼机混炼流场的混沌流动特性进行了分析研究,提出了采用以物料停留时间为基准的修正Lyapunov指数来描述混合过程中发生的拉伸应变,并借助于有限元计算,得出流场绝大部分区域的修正Lyapunov指数大于零,并发现混炼流场中存在非常有利于拉伸、折叠流动的涡旋流动,赋予了双转子连续混炼机优异的分散与分布混合特性。     

Production of commercial dyes via impingement-sheet mixing: Part I. Testing of a device suitable for industrial application

Impingement-sheet mixing is a proven technique for the rapid mixing of liquids on the laboratory scale. In this paper a practical mixer design for use on the industrial scale is presented. The industrial impingement-sheet mixer was tested at flow rate ratios typical of commercial applications and, compared with earlier laboratory results, only a slight loss in mixing speed was noted. At flow rates of the order of liters/minute and pressure drops up to 1.5 bar, the micromixing times of the industrial impingement-sheet mixer are of the order of tens of milliseconds for reactant stoichiometric ratios near 1.00. If one of the reactants is present in at least a 10% excess, then the micromixing time of the limiting reagent is reduced to several milliseconds.     

Developing mechanistic understanding of granular behaviour in complex moving geometry using the Discrete Element Method: Part B: Investigation of flow and mixing in the Turbula® mixer

As a consequence of increasing computer power and more readily useable commercial codes, the Discrete Element Method is being used in an increasing range of applications to simulate increasingly complex processes, often for evaluation of machinery prototypes. This presents the additional challenge of analysis of results, in particular to extract flow and mixing mechanisms with a view to improving design or operation.The Turbula mixer is a laboratory scale mixer, which is widely used in industry for the development or testing of new granular products. It comprises a simple vessel geometry (cylinder) that moves with a complex, yet regular, 3D motion giving rise to rapid and thorough mixing of the contents. The mixer presents an ideal system for evaluation of the power of DEM to simulate complex processes and to develop protocols for processing the results of the simulation. Initial results of this investigation, presented in this paper, show that mixing behaviour changes non-monotonically as a function of mixer speed. For the system of monodisperse glass spheres it is shown that mixing rate (in terms of number of mixer revolutions to achieve complete mixing) initially decreases with increasing speed and subsequently increases. The behaviour is suggestive of a transition in the flow process and is the subject of further investigation.     

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.     

Performance of Kenics static mixer over a wide range of Reynolds number

The present study deals with the numerical simulation of flow patterns and mixing behaviour in Kenics static mixer over a wide range of Reynolds number. Three different sets of Kenics mixer (aspect ratio = 1.5) comprised of 3, 9 and 25 elements each have been characterized. The Reynolds number was varied in the range of 1 to 25,000 (i.e., from laminar to turbulent flow regime). The numerical approach takes into account the aspects of the fluid flow at higher Reynolds number values including circumferential velocity profiles at different cross-sections within the Kenics mixer, which were neglected in previous studies. It was observed that cross-sectional mixing in the turbulent flow regime takes place up to 30% of each element length at element-to-element transition; beyond that velocity profiles were uniform. The experiments were also carried out to measure the circumferential and axial velocity profiles and pressure drop in three different Kenics Mixers using air as fluid. The pressure drop per unit element (ΔP/η) was found to be independent of the number of Kenics mixing elements used in the system. The total pressure drop across Kenics mixer obtained by CFD simulations were compared with the experimental pressure drop values and correlations available in the literature. The numerical results were found in good agreement with the experimental as well as the results reported in the literature. A new pressure drop correlation in the Kenics static mixer has been developed.     

Comparative analysis of different static mixers performance by CFD technique: An innovative mixer

The flow and mixing behavior of two miscible liquids has been studied in an innovative static mixer by using CFD,with Reynolds numbers ranging from 20 to 160. The performance of the new mixer is compared with those of Kenics, SMX, and Komax static mixers. The pressure drop ratio(Z-factor), coefficient of variation(CoV), and extensional efficiency(α) features have been used to evaluate power consumption, distributive mixing, and dispersive mixing performances, respectively, in all mixers. The model is firstly validated based on experimental data measured for the pressure drop ratio and the coefficient of variation. CFD results are consistent with measured data and those obtained by available correlations in the literature. The new mixer shows a superior mixing performance compared to the other mixers.     

涡轮喷射混合器中错流射流混合性能研究

采用示踪法研究了涡轮喷射混合器内错流射流混合特征。探讨了射流的流动状态如射流的附壁效应、穿透率、动量比及雷诺数等对混合的影响,并对混合时间进行了分析。研究结果表明,涡轮喷射混合器是能够满足混合均匀度要求高、介质体积比高和喷嘴能有效防堵的快速混合装置。     

The recirculating screw mixer: A new small-volume mixer for the polymer laboratory

The recirculating screw mixer (RSM), a new small-volume intensive mixer for the polymer laboratory, is designed, built, modeled, and tested. This type of batch mixer is intended for the mixing of 1 to 30 cm³ of viscous material at high shear rates. A material element in the mixer experiences alternating screw pump and tubular flows with reorientation between these flows. A mixer with a 10 cm³ sample capacity is built for testing and evaluation. Flow visualization experiments are used to investigate the quality of the distributive mixing achieved. The flows in the mixer are modeled for the cases of a Newtonian fluid and a power law fluid. The Newtonian model accurately predicts the recirculation time for particles suspended in Newtonian silicone oils. The power law model accurately predicts the screw torque obtained with a polystyrene and polyethylene. A method for the measurement of fluid rheology from the operating conditions of the RSM is proposed and tested. The mixing achieved by the RSM is compared to that obtained by a batch mixer with roller blades. Both mixers are used to prepare blends of ethylene-propylene rubber in polystyrene. The morphologies of the resultant blends are compared and differences in the mixing action are discussed. The mixers are also used to prepare composites of fumed silica in polyethylene. The quality of mixing obtained in the RSM compares quite favorably with that obtained in the batch mixer with roller blades for polystyrene/ethylene-propylene rubber reactive blends and polyethylene/silica composites.