销钉机筒挤出机螺杆圆周展开面内物料流动与混合的数值分析与实验

在一定简化条件下,对销钉机筒挤出机螺杆圆周展开面内的流场及分布混合效果以及销钉个数对流场和分布混合效果的影响进行了数值与实验研究.提出了流场中某点混合效果、整个流场平均混合效果以及混合效果统计分布的数值计算与评价方法.数值分析结果与实验结果具有较好的一致性.结果表明,销钉及螺棱切槽对物料具有明显的强化流动与混合的作用;6个销钉结构模型混合效果好于3个销钉结构模型,3个销钉结构模型好于有切槽无销钉结构模型,有切槽无销钉结构模型好于无切槽无销钉结构模型;有销钉结构较无销钉结构的平均混合效果提高30%～40%;有销钉结构随着时间的延长,混合效果不断提高,无销钉结构随着时间的延长,当混合效果达到一定值后则不再提高.     

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。     

Experimental study on distributive mixing characteristics of a new type of pin mixing section

To eliminate two shortcomings of normal pin mixing sections, namely, the lack of efficient mixing mechanisms and the formation of dead spots, a new type of pin (pins channeled from top-front to bottom-rear) was previously proposed. As an experimental verification of the effectiveness of this type of pin, a dye decoloration experiment with a visual single screw extruder was carried out. The comparative experiments show that a “//” type pin mixing section (the orientation of holes in the pins is parallel) has the best mixing ability; a 45° angle between the projected line of orientation of holes in the pins and the screw axial line provides maximum mixing; however, a 45° angle between the orientation of the pin array and the screw axial direction results in poor mixing. The effect of density of the pins along the screw circumferential and axial direction on distribution mixing was also investigated experimentally.     

On Gas Separation by Permeation with One-Side Mixing

Abstract

A calculation method for gas separation by permeation with one-side mixing is proposed. Five types of stage flow patterns (one-side mixing, countercurrent flow, cross flow, cocurrent flow, and perfect mixing) are compared with reference to separation of oxygen from air. The calculation results regarding one-side mixing differ from those reported previously     

销钉机筒挤出机螺槽横截面内流体流动与混合的研究

在一定简化条件下，对销钉机筒挤出机螺槽横截面内的流场及混合均化效果以及销钉位置对流场和混合均化效果的影响进行了数值与实验研究。提出了流场中某点混合均化效果、整个流场平均混合均化效果以及混合均化效果统计分布的数值计算与评价方法。数值分析结果与实验结果具有较好的一致性。结果表明，销钉对物料具有明显的强化流动与混合均化的作用：销钉愈接近于螺棱，强化混合均化的效果愈显著：有销钉结构较无销钉结构的平均混合均化效果提高2．5％-5．6％；有销钉结构随着挤出时间的增加，混合均化效果不断提高，无销钉结构随着挤出时间的增加，当混合均化效果达到一定值后则不再提高。     

新型带孔销钉混合段及其分布混合性能

介绍了一种国外开发的用于改善单螺杆挤出机混合性能的新型带孔（或带槽）销钉混合段,与常规销钉混合段相比,其混合能力强,熔体温度 低,当销钉间的轴向距离在11－14mm之间时,有效地加强了熔体的周向汉动,极大地改善了单螺杆挤出机的分布混合性能。     

复合扰流柱的螺旋内构件反应器内流体的宏观混合

在管式反应器内插入复合扰流柱的螺旋型内构件,采用脉冲示踪法测定了反应器内流体的停留时间分布,研究了器内流体的宏观混合特性,分析了该内构件强化混合的机理. 结果表明,复合扰流柱的螺旋型内构件反应器内的流体流动更接近于活塞流,其轴向扩散模型参数Pe为螺旋型内构件反应器的1.02~1.28倍,为不带内构件反应器的1.35~1.77倍. 复合扰流柱的螺旋型内构件能显著增强器内的二次流动,从而强化了宏观混合效果.     

大型塔板的模拟与板效率的研究(Ⅱ)——二维定数混合池模型

为研究大型塔板在复杂流动情况下的浓度分布与板效率计算方法,本文提出二维、固定混合池数、可调整流量的数学模型。此模型可以比较灵活地模拟大型塔板上的各种实际流动现象,并能比较方便地计算出在该流动情况下的塔板浓度分布及板效率值。     

The effect of a new type of pin mixing section on the performance of a single-screw extruder

The effect of a holed-pin mixing section on the performance of a single screw extruder was investigated and compared with a free flight and a normal pin mixing section, using a practical single-screw extruder. The effect of axial distance between two pins in a holed-pin mixing section on performance was also studied. Mixing ability was quantified using the statistical approach of carbon black concentration distribution in the extruded film mixed with a carbon black masterbatch. The results indicate that a free flight gives the lowest melt temperature rise, pressure drop, and driver power, but the worst mixing; a holed-pin mixing section has better mixing ability, lower melt temperature rise, and lower driver power than a normal pin mixing section does; the value of the pressure drop of the two types of pin mixing sections is approximately identical. A longer axial distance between the two pins in a holed-pin mixing section gives better mixing and lower melt temperature rise than a shorter one; however, when the distance is longer than a critical value, the improvement of mixing is not so outstanding; for different axial distances between two pins, no great change in pressure drop was found and the extrusion throughput has almost no great relation to the axial distance.     

A Dynamical Systems Approach to Mixing in Circulating Flows

Circulating flows are found in a variety of mixing equipment such as stirred tanks and airlift loop vessels. This paper presents a different route towards modeling the mixing in circulating flows. This route is based on an innovative use of Poincaré maps and suspended flows, concepts which are found in dynamical systems theory. The mixing model is developed for an arbitrary recirculating flow and uses a circulation time distribution function that is incorporated into the transport equations for an inert tracer injected into the flow system. Two cases are used to study the application of the mixing model in this work. The first case addresses the question of whether the mixing model can be used to study airlift vessels differing in scale and the second case highlights the application of the model to a standard stirred tank. In the first case, model predictions have been compared with experimental data obtained from two geometrically similar airlift systems of different volumes and good agreement is observed. A single parameter correlation for the mixing time is also proposed. In the second case, computational fluid dynamics was used to obtain the flow field of a standard stirred tank fitted with a six bladed Rushton turbine. From the flow field, the distribution of the circulation times is extracted and used to determine the tracer concentration profile in the stirred tank. Good agreement between the model predictions and published experimental data is observed thus indicating that the mixing model shows promise as a technique for studying the mixing in stirred tanks.     

PART Ⅱ TWO DIMENSIONAL FIXED NUMBER MIXING POOL MODEL

A new mathematical model of mixing pool type is proposed for simulating the fluid flow and masstransfer behavior on a large tray.In the proposed model,the whole tray is divided into a number ofsquare (or rectangular)compartments or mixing pools,each of which is assigned to have adjustableflow and baekmixing in both z (along the main flow path) and w(perpendicular to the main flow path)directions.The chief features of present model are: (1) It is two dimensional model instead of usualone dimensional so that more complicated actual flowing condition obtained from hydrodynamic studyon a large tray can be closely simulated by adjusting the flow among mixing pools in both z and wdirections.(2) Since backmixing is taken into account,the number of mixing pools on a tray is fixedinstead of varied as in conventional mixing pool model; thus,the application of matrix computation ispossible.(3) The present model can be reduced to other tray models depending on the number of mixingpools to be chosen in each direction.The application of present model to predict the liquid phase concentration profiles and Murphreeefficiency enhancement on a large tray with complicated flow pattern and velocity distribution as we-observe in our experimental study are demonstrated.The effects of liquid flow rate,nonuniform veloc-.ity field,directional splashing and subsidiary flow are also investigated and discussed.     

塔板上流型变化对板效率影响的计算传质学

利用能够描述塔板上气液两相错流过程的流体力学模型,建立了同时模拟气液两相流动与传质过程的数学模型;通过对气液两相传质方程和流体力学模型方程的联立求解,计算得到了塔板上液相速度分布和气液两相浓度分布的数值解,考察了气相完全混合和气相部分混合两种条件下塔板上的气液两相浓度分布,同时考察了气相完全混合时流型变化对塔板效率的影响.     

销钉机筒挤出机内销钉附近物料流场分析及功率计算

采用当量粘度的方法，基于牛顿流体模型，提出销钉机筒挤出机内销钉附近流场的应力及速度分布数学模型和销钉消耗功率的计算方法。用NR／炭黑混炼胶进行的挤出过程中销钉消耗功率的研究结果表明，实测值与计算值的相对误差只有4％。     

Design of certain fluted mixing sections of extruder screws

A theoretical model is proposed, for certain barrier type fluted mixing sections of extruder screws. Screws with such mixing sections are occasionally used in plasticating extruders. With the aid of this model, these screws can now be quantitatively simulated in the design stage. Specifically the model enables the calculation of pressure change across the section as a function of geometrical configuration of the mixing section and operating conditions. A generalized set of curves, plotted in dimensionless form, for quick manual computation is also given. With its aid, the effect of the design variables on the pressure change is discussed. Finally, mixing section-zones, in reference to the plasticating extrusion theory, and the state of the art of extrusion theory are very briefly discussed.     

Mixing efficiency in a pin mixing section for single‐screw extruders

Non‐Newtonian, non‐isothermal, 3D finite‐element simulation of mixing performance in a pin mixing section with different axial gaps in the pins has been carried out according to their realistic configurations. The quantitative evaluation of mixing ability was based on the theory of kinematics of fluid mixing. To learn and to compare the local mixing performance in a standard screw and a pin mixing section, the local mixing efficiency distribution proposed by Ottino was calculated. Also, the RTDs of these mixers were calculated in an attemt to measure mixing. The integration of the two, namely, the integrating local mixing efficiency along a number of particle pathlines from entrance to exit, together with statistical treatment, which was referred as integral mixing efficiency, then gives a quantitative judgment of the total mixing ability of a continuous mixer. The calculated results showed a nonlinear dependence of the mixing ability of a pin mixing section on the axial gap of the pins. Finally, the calculation results were compared with the experimental ones obtained in our previous study.     

Effect of impeller type on the mixing in torus reactors

Torus reactors are characterized by a homogeneous fluid circulation without dead zones. Torus reactors were used for applications in biotechnology, food processing, polymerization and liquid waste treatments. The relatively simple extrapolation of performances, due to the absence of dead volume, is one of the main advantages of this reactor, with low shear stresses and an effective radial mixing allowing efficient heat dissipation. This study is based on the mixing in order to analyse the fluid circulation, mainly in turbulent flow regime, and to characterize the torus reactor with the axial dispersion plug flow model. The objective of this study is to characterize the flow and the mixing in the torus reactors in batch and continuous modes. The mixing analysis was made according to the flow parameters and to the geometrical characteristics of the reactor and impeller. The mixing in the torus reactor can be characterized by the Péclet number, Pe_D, defined with torus diameter. A representative model based on plug flow with axial dispersion and partial recirculation was proposed.     

RESIDENCE TIME DISTRIBUTION OF RHEOLOGICALLY COMPLEX FLUIDS PASSING THROUGH A SULZER SMX STATIC MIXER

Static mixers are widely used in continuous mixing, heat and mass transfer processes and chemical reactions. However, a proper understanding of the flow pattern is still missing when rheologically complex fluids are involved. This paper presents a study of the Residence Time Distribution (RTD) determination in a Sulzer SMX static mixer. A two-parameter RTD model, based on each mixing element, was proposed to describe the flow pattern of rheologically complex fluids in a such mixer. It was shown that in this model the flowrate fraction across the plug flow component increases with the generalized Reynolds number. However, the volumetric fraction of the plug flow component depends not only on the generalized Reynolds number, but also on the number of mixing elements, apparently due to memory effects of viscoelastic fluids.     

A numerical‐indicator‐based method for design of distributed wastewater treatment systems with multiple contaminants

In the design of distributed wastewater treatment systems with multiple contaminants, it is very important to minimize unnecessary stream mixing to reduce total treatment flow rate as much as possible. A new numerical indicator, total mixing influence potential (TMIP), to reflect the influence of the stream mixing caused by performing a process on the total treatment flow rate of a distributed wastewater system is introduced. In design procedure, the TMIP value is calculated based on pinch principle. The process with the smallest TMIP value will be performed first. The results of a few literature examples show that designs with very low (even minimum) total treatment flow rates can be obtained with the method proposed. In addition, the method proposed is simple and of clear engineering insight. The calculation effort does not increase significantly when the number of streams, contaminants, and/or treatment units increases. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3223–3231, 2015     

A generalized zoning framework for development of CFD-based reduced-order compartment models

While computational fluid dynamics (CFD)-based compartment models have gained popularity as a cost-effective alternative to full CFD modeling of complex mixing systems, model development involves significant trial-and-error efforts. This work presents a generalized zoning framework for the streamlined development of CFD-based compartment models with detailed characterization of the reduced-order representation of the flow physics. With a stirred tank as an illustrative case, reduced-order model for species transport and heat transfer with turbulent flow is derived, followed by introducing the generalized zoning framework to demonstrate how a reduced-order compartment model can be constructed based on a simplified CFD simulation. A test case of mixing two miscible thermal fluids is used to evaluate the CFD-based compartment model. The results demonstrate that the proposed zoning framework exhibits an accurate representation of the CFD simulation of hydrodynamics and demonstrates capabilities of capturing species and heat transfer in turbulent flow systems with complex geometric configurations.