固体推进剂同向双螺杆元件混合性能模拟

首先设计了4种固体推进剂用螺杆元件,并进行了固体推进剂药浆的流变性能测试,通过使用Polyflow软件对4种螺杆元件的流场进行数值模拟。对各螺杆元件流场的剪切速率、加权平均剪切应力、平均回流系数、累积停留时间分布等表征螺杆元件混合性能以及流场特性的指标进行分析,对比4种螺杆元件的分散和分布混合性能,并建立了螺杆元件混合性能的评价体系。结果表明,KB元件和S型元件对药浆有较好的综合混合性能,有利于固体推进剂的混合。     

螺杆构型对PLA/PTW共混物性能影响的研究

选用剪切元件（KB元件）、拉伸元件（S元件）、常规螺纹元件（SE元件）和混合元件（SME元件）设计了4种啮合同向双螺杆挤出机混合段螺杆构型，模拟研究了螺杆构型对聚乳酸/乙烯-丙烯酸丁酯-甲基丙烯酸缩水甘油酯共聚物（PLA/PTW）共混体系混合效果的影响，分别通过出入口压差、加权平均剪切应力、累积最大剪切应力、回流系数和累积停留时间表征了螺杆构型的正向输送能力、分散混合能力和分布混合能力，并采用实验方法研究了复合材料的力学性能。结果表明，KB元件和SME元件分散布置时具有较强的分散混合和分布混合能力，PLA/PTW共混体系的混合效果更好，且能在PLA/PTW共混物拉伸强度基本不变的情况下进一步提高其冲击强度，同时，模拟结果和实验结果吻合，表明模拟可为混合段螺杆构型的优化提供指导。     

螺杆转速对热熔挤出吲哚美辛混合性能的影响

热熔挤出技术已成为一种制备药物固体分散体的新方法，螺杆转速作为挤出过程中的工艺参数对药物的混合具有重要影响。以吲哚美辛(INM)和聚乙二醇(PEG10000)为原料，设计了挤出机混合段螺杆构型，采用Polyflow进行数值模拟，基于加权平均剪切应力、累积最大剪切应力分布、累计停留时间分布和平均回流系数，分析螺杆转速对INM混合性能的影响。同时，以INM为原料药，采用热熔挤出技术制备了不同螺杆转速下的挤出样品，使用扫描电子显微镜(SEM)和溶出实验对样品进行表征。结果表明，在一定范围内，随着螺杆转速的增大，药物的分散混合和分布混合性能增强，但是，螺杆转速较大会导致药物分布混合性能降低，不利于药物的混合。     

啮合同向双螺杆3种构型的模拟分析和实验研究

通过数值模拟方法对3种含捏合盘元件螺杆构型的剪切速率、停留时间和回流量等指标进行了分析,通过实验对3种螺杆构型的混合性能进行了对比。结果表明,90°捏合盘元件与反向捏合盘元件组合可以达到较好的分布混合效果,45°捏合盘元件与反向捏合盘元件的组合可以达到较好的分散混合能力,捏合段加入反向螺纹元件并不能提高分布混合能力,但可以延长停留时间。     

新型偏心双螺杆挤出机流域混合特性

基于非对称流场的混沌混合理论,设计了一种新型的偏心双螺杆挤出机。通过对比传统普通螺杆元件与新型偏心螺杆元件,偏心距不仅决定了螺杆的端面形状,也改变了螺槽形状,使同一导程内的2个独立的C型室螺槽形成一个ω型室螺槽。利用Polyflow软件分别对传统双螺杆挤出机与3种不同偏心距螺杆元件的新型双螺杆挤出机进行模拟仿真,分析了压力场、速度场与混合指数分布规律,计算了4种双螺杆挤出机流场的停留时间分布、分离尺度、最大剪切应力等混合表征系数。结果表明,与传统双螺杆挤出机相比,偏心双螺杆挤出机压力分布不均匀,正负压压力值增大,因此,压力差增大,使熔体回流速度增大,混合效果更佳;拉伸流区域增大,混合能力增强;熔体在流体域内的总体停留时间缩短,混合效果更佳;分离尺度数值下降较快,混合效率较高;偏心螺杆元件对流体的剪切应力增大,分散混合能力增强。     

三螺杆挤出机啮合块混合特性的数值模拟

利用流场分析软件Polyflow对啮合块在不同参数下的等温稳态流场进行数值模拟。同时引入加权平均剪切应力,加权平均剪切、拉伸速率和回流系数等不同的评价指标以表征倒三角形三螺杆挤出机的混合性能。深入分析不同因素对啮合块混合特性的影响。结果表明:啮合块具有优异的分布和分散混合性能。啮合盘厚度增加导致流场中拉伸作用增强。增大错列角会使正向啮合块的剪切降低,拉伸增强,反向啮合块的趋势则与之相反;为啮合块的设计提供了依据。     

三螺杆、双螺杆挤出机及其啮合块混合性能的比较

利用Polyflow聚合物流体分析软件,对三螺杆和双螺杆挤出机及不同参数啮合块的流道模型进行了等温数值模拟。经过统计后处理,引入加权平均剪切速率和剪切应力、回流系数等评价指标,深入分析了流场的混合行为。同时对倒三角形三螺杆挤出机和双螺杆挤出机的混合能力进行了对比,以此对三螺杆和双螺杆挤出机混合性能的优劣性加以探讨。     

同质回流在农村污水处理一体化装置中的应用研究

现有农村污水处理一体化装置,为节省成本非曝气区通常不安装搅拌装置,造成处理效果差、出水不达标等问题。本文利用回流泵富余能力在非曝气区进行同质回流,解决了泥水混合问题,提高了COD和总氮处理效率。研究表明当布水口流速≥2.4 m/s,单个布水口服务面积≤0.35 m2,非曝气区水流上升流速≥16 m/h时,同质回流混合效果更好。     

A2/O工艺处理混合污水脱氮中试研究

采用A2/O工艺处理生活污水和粪便的混合污水,进行了不同HRT、DO、混合液回流比和污泥回流比等条件下的脱氮效果的研究,进行了6种不同工况下的脱氮和有机物去除效果的研究.结果表明,当好氧池水力停留时间(HRT)为5 h、好氧池DO为3 mg·L-1、混合液回流比R为120%和污泥回流比r为80%时,A2/O工艺能获得较好的脱氮效果和有机物去除效果.     

顶置七喷嘴气化炉冷态速度场研究

为研究顶置七喷嘴气化炉流场情况,基于相似准则设计并模拟工业规模干粉气化炉条件,采用激光多普勒动态分析仪(PDA)在高4 000 mm、直径800 mm的模型炉中测定了顶置七喷嘴的速度场分布,并与单喷嘴速度场进行对比。结果表明:单喷嘴偏向于中心射流,而顶置七喷嘴轴向速度沿径向分布速度剪切小,更倾向于平推流,且顶置七喷嘴中心轴向速度衰减快,颗粒不易"短路"。此外,相比单喷嘴而言,顶置七喷嘴回流区域更小且中心气固混合效果更好。而通过计算出的回流比结果表明,顶置七喷嘴在喷嘴出口附近的回流比较高,能有效促进气化剂与燃料的混合,提高气化碳转化率。     

卧式双轴自清洁反应器粘性体系停留时间分布

在粘性体系中以茜素红为示踪剂,采用紫外光测试技术研究了卧式双轴自清洁反应器中的停留时间分布(RTD),利用返混模型对实验条件下的RTD及返混系数进行了模拟计算,得到了返混系数与雷诺数的关联式。结果表明,反应器的RTD受物料流速、搅拌速率及物料粘度等因素的影响,体系粘度增加返混系数减小;在实验范围内,基于返混模型的计算结果与实验结果基本相符。     

Flow patterns and mixing mechanisms in the screw mixing element of a co‐rotating twin‐screw extruder

Non‐Newtonian and non‐isothermal flow simulations based on 3‐D FEM were applied to a special and conventional elements of a twin‐screw extruder. The screw mixing element (SME), a kind of special element, was a distributive mixing promoter consisting of a standard screw profile with slots cut across the flight tip to increase leakage flow. The full flight screw (FF) and the kneading block (KB) were examined as conventional elements in order to contrast the mixing behavior with the SME. The accuracy of numerical results was verified by experimentally measuring pressure and temperature. Additionally, marker particle tracking analysis was carried out to evaluate the distributive and dispersive mixing. Using the above analyses, the following results were obtained: The pumping capability of the SME was smaller than that of the FF and was the same as for the KB. The SME suppressed heat generation and showed the lowest temperature distribution of the three elements. For distributive mixing, the SME showed the best performance judging from the mixing coefficient G, residence time distribution, and area stretch distribution based on a laminar mixing mechanism. A higher rotational speed achieved better distributive mixing performance. For dispersive mixing defined by stress distribution, the SME showed the second best performance next to the KB. It also showed better dispersive mixing performance with increasing rotational speed. The SME had the advantages of low heat generation and good distributive mixing.     

静态混合器中液液分散的实验及CFD模拟

在SK型静态混合器上进行甲苯-水两相混合实验,采用截面直接拍摄法获得分散混合性能指标Sauter平均直径（SMD）。利用Box-Behnken响应面分析设计实验,在Design Expert 7.0平台上拟合实验数据,获得SMD的多项式形式的表达式。建立了与实验相同的静态混合器物理模型,使用Mixture多相流模型、k-ε湍流模型进行了CFD模拟研究,获得了浓度场云图及分布混合指标不均匀系数。模拟所得压降与实验值的相对误差在15%以内,表明模拟结果与实验结果吻合较好。结果表明,静态混合器中液液分散过程是分散混合和分布混合共同作用的结果,两种混合经过6～8个混合单元后共同达到充分发展。充分发展后的SMD受表观流速、分散相分率和静态混合器直径三因素影响,且表观流速的影响最为显著;充分发展后的不均匀系数均达0.05以下,表明静态混合器自身具有较好的分布混合性能。     

ANALYSIS OF AXIAL MIXING IN A GAS-LIQUID RECIPROCATING PLATE COLUMN

Axial mixing in the continuous phase in a Landau reciprocating-plate column (LRPC) has been investigated for both single-phase and two-phase gas-liquid flow conditions. A hydrodynamic model is proposed in which axial mixing is described as a process consisting of a backflow through the plate plus longitudinal mixing within the stage. The region in the proximity of the plates is almost perfectly mixed, beyond which there is a low-intensity mixing zone that varies in height and degree of mixing depending on phase velocities as well as the plates design and oscillation velocity. The presence of the dispersed phase affects axial mixing in both the well- and poorly mixed regions of each stage in two opposite ways: it decreases the backflow between the stages due to the hindrance effect caused by the presence of gas bubbles, and it increases the axial dispersion coefficient in the second stage by increasing the turbulence and phase entrainment caused by circulation and bubbles rising. The model adjustable parameters were determined from an experimentally measured dispersion coefficient over a wide range of operating conditions using the transient tracer injection method. The predictions of the model compare favorably with experimental data and can be applied for describing axial mixing in the continuous phase in an LRPC with±14% accuracy.     

Numerical investigation of gas mixing in gas‐solid fluidized beds

Gas mixing in a tall narrow fluidized bed operated in the slugging fluidization regime is simulated with the aid of computational fluid dynamics. In the first part, a parametric study is conducted to investigate the influence of various parameters on the gas mixing. Among the parameters studied, the specularity coefficient for the partial‐slip solid‐phase wall boundary condition had the most significant effect on gas mixing. It was found that the solid‐phase wall boundary condition needs to be specified with great care when gas mixing is modeled, with free slip, partial slip and no‐slip wall boundary conditions giving substantial differences in the extent of gas back mixing. Axial and radial tracer concentration profiles for different operating conditions are generally in good agreement with experimental data from the literature. Detailed analyses of tracer back mixing are carried out in the second part. Two parameters, the tracer backflow fraction and overall gas backflow fraction, in addition to axial profiles of cross‐sectional averaged tracer concentrations, are evaluated for different flow conditions. Qualitative trends are consistent with reported experimental findings. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Relationship between local residence time and distributive mixing in sections of a twin‐screw extruder

Local residence time and distributive mixing were measured in conveying sections and kneading blocks of a twin screw‐extruder. The residence time measurements were completed using carbon black as the tracer and an infrared temperature probe to detect the temperature decrease caused by the changing surface emissivity. The validity of this experimental technique was extensively evaluated. A mixing limited interfacial reaction between polymer tracers was used to directly measure the distributive mixing in the twin‐screw extruder. Possible relationships between mixing and residence time in the sections of the twin‐screw extruder were investigated by combining these two measurements. Distributive mixing in conveying sections was related to the local average residence time and the fill. In contrast, distributive mixing in kneading blocks was related to the local average number of screw revolutions experienced by the polymer. Forward stagger kneading discs achieved the greatest amount of distributive mixing, which was attributed to a combination of local stagnant flow regions and more frequent interfacial reorientation.     

螺杆构型对PA6/PE-LD共混体系性能的影响

在啮合同向双螺杆挤出机中,研究了熔体输送段分布混合元件和分散混合元件先后布置、交错/集中布置以及不同元件相同布置方式对聚酰胺6/低密度聚乙烯（PA6/PE-LD）共混体系性能的影响。结果表明,混合元件交错布置的螺杆构型混合能力优于混合元件集中布置的螺杆构型的混合能力;交错布置的螺杆构型获得的共混体系力学性能也优于混合元件集中布置的螺杆构型获得的共混体系的力学性能。     

同向双螺杆挤出机中齿形元件的流动和混合模拟

应用POLYFLOW软件,采用三维非等温、Cross模型,对高聚物熔体在双螺杆挤出机齿形元件和断裂螺纹元件中的流动和混合过程进行了数值模拟,并用示踪粒子法研究了不同颜色粒子的流迹和停留时间、剪切速率、剪切应力、拉伸速率的分布。在此基础上,对两种元件的分布性混合和分散性混合性能进行的量化分析对比发现,与断裂螺纹元件相比,齿形元件有着弱的输送能力和建压能力,强的轴向温升能力,强的分布性混合能力和分散性混合能力。     

双转子连续混炼机混沌型转子混合性能的研究

在提出一种新型混沌型转子结构的基础上,运用Polyflow软件对其混炼过程进行三维非牛顿等温模拟,并借助于粒子示踪法对物料所经历的流场特性进行统计学分析;分析了转子结构和工艺参数对转子混合性能的影响,同时通过共混改性实验,对转子的混合效果进行了评估和表征。结果表明,高混沌型转子的分布混合能力有较大的提高,同时保持着良好的分散混合能力;混沌型转子制备的复合材料力学性能优于经典转子;转子转速的提高可以增强混沌转子的分散及分布混合能力,适当的加料速率是保证取得较好混合效果的关键因素。