PA6水解聚合反应数学模型及其实验验证

建立了PA6熔体在VK管中边流动边聚合的聚合反应数学模型,采用流态显示技术和文献报道的测定数据验证了数学模型的可靠性,还研究了熔体在具有优化科挡板内部结构的VK管中流过10块交替排列的挡板过程中停留时间分布、单体的转化率、产物的聚合度的变化规律,并从聚合指标反证了挡板结构的合理性。     

尼龙6聚合管内微分发热量与温度分布

<正>1引言 尼龙6是合成聚酚胺生产中最重要的产品之一[1]，目前工业上多数采用水解聚合。本文涸绕尼龙6聚合反应工程开发的一系列工作都是为这一技术路线国产化提供理论基础。近卫0年来，尼龙6聚合的各种主、副反应精确的动力学数据已有报道[2,3]，目前的重点已转向工业化生产反应器中各种物理过程的模拟，诸如传热、流动、混合、停留时问分布、蒸发脱水以及过程优化控制等领域。     

己内酰胺聚合反应工程CAD软件包——Ⅰ.工业化生产实际值与软件包计算结果的比较

介绍了己内酰胺聚合反应工程 CAD软件包的建立 ,用工厂单 VK管聚合和两步法聚合生产工艺验证了该软件包的可靠性。通过计算可得到单体转化率、聚合物聚合度、相对粘度、相对分子质量分布、环状二聚体含量、反应潜热等重要参数在聚合管中的变化情况     

国内外尼龙6聚合管的差距

针对国内外尼龙６生产厂家所使用的聚合ＶＫ管进行了比较．与国外同行业相比，认为我国的聚合管无论从产量还是产品质量均处于技术落后状态，聚合管内部结构简单，所生产的产品质量差。德国Ｚｉｍｍｅｒ公司设计的ＶＫ管较先进，结构设计合理，当前在技术上处于领先水平。对国产ＶＫ管存在的问题提出一些看法。     

折流板设备中流体停留时间分布与流动形态的对比研究

折流板结构在大空间设备中形成折流通道,以防止短路,从而使流体与换热管和颗粒床等内构件充分接触。停留时间分布(RTD)实验具有简单便捷的优势,针对设备中的短路与如何确定设备合理结构的问题分别设计了几组结构来进行RTD实验与流场数值模拟研究。对比分析结果表明,设备中的短路和死区是相对存在的,通过RTD密度函数曲线的出峰时间及拖尾情况能判断设备中短路与死区的情况,该结论可以为设备设计提供理论依据。利用多釜串联模型的釜数及RTD曲线的出峰时间和方差分析了流量、折流板缺口面积及板距对设备中流体流动形态的影响;研究了设备中的压降,综合考虑设备的能耗和性能,提出了以RTD实验来确定折流板设备合理结构时最合适的釜数、出峰时间及方差。     

尼龙6/纳米蒙脱土复合材料制备及性能研究

利用活化处理的纳米蒙脱土(OMMT),通过原位插层聚合原理,控制聚合温度、压力、时间等,在聚合管实现连续化稳定制备剥离型尼龙6(PA6)/纳米OMMT复合材料;采用熔融纺丝法制得PA6/纳米OMMT复合纤维;利用X射线衍射、透射电镜(TEM)等方法分析复合材料的结构与性能。结果表明:聚合时控制水与己内酰胺质量比为3%～5%,前聚压力不超过0.4 MPa,后聚压力小于-0.040 MPa,聚合温度240～280℃,聚合时间26～30 h,可制得相对分子质量为18 000～18 600,单体质量分数小于1.6%,含水率小于450μg/g的PA6/纳米OMMT切片;TEM分析表明,纳米OMMT在PA6基体均匀分散;复合材料的力学性能有较大幅度的提高,断裂强度达102.15 MPa,比纯PA6提高了12%;PA6/纳米OMMT复合纤维性能优异,适合轮胎骨架材料的制备要求。     

新型湿法除尘系统内气液两相流动的数值模拟

结合湿法除尘及挡板绕流技术,本文设计开发了一种带有挡板结构的新型湿法除尘系统。为探究该系统内挡板结构诱导产生的涡旋流动特性及其内部离散相运动规律,基于计算流体力学（CFD）方法,文章选用重整规划群（RNG）k-ε湍流模型数值对比了不同挡板参数下的涡旋结构、速度分布及压降情况等气相流场特性。同时利用离散相模型（DPM）分析了不同工况下喷淋液滴的运动轨迹、逃逸率及驻留时间表现。结果表明,集尘区内弓形挡板的设置可诱导产生涡旋流动,不仅能够抑制低速“流动死区”,同时还可不同程度改善喷淋液滴逃逸情况、有效延长其在装置内的驻留时间。综合考虑气相入口速度v、挡板安放角θ及喷淋液滴粒径D_p的影响,文章推导获得了液滴逃逸率的计算公式,可较为准确地预测喷淋液滴的运动情况。     

催化裂化沉降器内两端敞开型旋风分离器内气相流动规律

研究考察了催化裂化沉降器内两端敞开型旋风分离器内油气流动规律.用CFX软件采用DSM模型进行了数值模拟,并与用五孔探针测试的流场进行了比较,表明DSM模型有良好的预测精度.在此基础上,采用标量输运方程研究了气体在旋风分离器内的停留时间分布规律.实验和模拟结果均表明,该类旋风分离器内流场与常规旋风分离器的有很大的不同,升气管和料腿均存在回流区,升气管回流区最大可波及分离空间,对分离空间流场有很大干扰.气体示踪模拟结果表明,由入口进入旋风分离器,由升气管、料腿排出的气体的停留时间近似呈对数正态分布;升气管、料腿回流区内气体停留时间呈双峰分布;升气管回流区的存在可使总气体平均停留时间增大约5%～10%;料腿直径的减小以及灰斗的存在均可增大由升气管排出的气量并使升气管、料腿回流区大幅减小,进而减小粗旋风分离器内气体总平均停留时间.     

PA6减压后聚合生产工艺

分析探讨了采用减压后聚合工艺生产ＰＡ６ 的可行性及实施效果。ＰＡ６ 生产中实施减压后聚合工艺能够提高反应后期的排水率、降低中心熔体温度、降低产物的低聚物含量、提高ＶＫ 管生产能力及切片的内在质量。还讨论了真空度的大小对ＰＡ６ 生产的影响。生产中真空度取－ ０．００５～－ ０．０３ Ｍ Ｐａ较为适宜。     

变截面扭曲椭圆管在冷冻脱水器中的应用

应用于四氟乙烯（TFE）生产工艺的传统单弓形折流板式冷冻脱水器存在换热管径大、裂解气冷量分布不均、脱除的冰晶不能有效在脱水器中停留而随裂解气进入下级以及因折流板原因导致的壳程流动阻力大等缺点。为此本文设计了一种新型冷冻脱水器,与传统冷冻脱水器相比,采用变截面扭曲强化传热管代替光滑圆管,使冷冻脱水器管程流体沿扭曲螺旋线流动,低雷诺数下形成非对称扰流,有效破坏边界层,提高了传热效率;管内TFE裂解气中的水分更快冷冻并在气流离心力作用下迅速甩向管壁,凝结成冰,提高脱水效果;并且壳程改为变空间纵向流动,流动阻力低,节省材料。结合案例监测数据,与传统单弓形折流板式冷冻脱水器进行数据对比,冷冻脱水效果较原换热器提高30%。     

Entwurf und Betrieb eines Rohrreaktors mit enger Verweilzeitverteilung

In process engineering the residence time is an important design parameter, and a narrow residence time distribution is advantageous to avoid possible by-products in complex chemical reactions. A good radial mixing with low axial dispersion provides a narrow residence time distribution in a tube reactor. The axial dispersion of laminar flow in a straight tube is very high and generates a wide residence time distribution. However, secondary flows improve the radial mixing, which are investigated in this paper for curved tube reactors. Design notes for good radial mixing and geometric designs of tube reactors with baffles are presented.     

换热器壳程进出口折流区传热温差损失分析

对管壳式换热器壳程进出口折流区的传热温差作了分析,以换热器热流体与冷流体的出口温度比例α表征换热器的换热深度,探讨了换热器换热深度与长径比的关系。采用流路分析方法,对换热器壳程折流区域的传热性能进行了数学分析,并与纯逆流情况作了对比。结果表明:换热器折流区域的传热温差较逆流区域传热温差的偏离量会随α的改变而产生变化,为避免偏移量过大应控制折流区域面积占总传热面积的比例。α1时,为使传热温差偏移小于5%应使折流区域面积占总传热面积的比例小于0.6/R1 a,c。揭示了现有换热器结构大型化之后难以实现α1的原因,并给出一种可以改进传统大型管壳式换热器长径比锐减、换热深度受限的有效结构——壳程多通道结构。     

间断副螺棱结构对挤出机内混沌混合影响的数值模拟

建立了混沌单螺杆挤出机计量段展开螺槽的物理模型及数学模型,根据流体符合Carreau定律,借助Ployflow软件,采用网格叠加技术,对聚合物熔体在插有间断结构副螺棱螺槽内的流动进行了数值模拟分析,从统计学的角度结合粒子示踪技术以停留时间分布、分离尺度、混合效率及累计混合指数为指标来表征螺杆的混合性能。结果表明,当副螺棱间断次数多且高度略低于螺槽高时混沌单螺杆混合性能更好。     

PA6/碳纳米管复合材料的力学性能与结构

研究了碳纳米管的加入对PA6复合材料的力学性能的影响。并用扫描电镜和特性粘数法对结构与性能的关系进行了初步探讨，结果表明，碳纳米管的加入提高了PA6的强度，此时碳纳米管能够以纳米状态均匀地分布在基体中，碳纳米管在原位复合过程中没有对高分子链段的增长带来负面影响，反而使PA6的聚合程度略有增大。     

杆支撑换热器壳程的单元流道模型及流场分布

提出了一种杆支撑换热器壳程的代表性“单元流道”模型,使结构复杂的管壳式换热器数值模拟更加简便而高效,数值分析得到了杆支撑换热器壳程中心区域的单元流道流场、压力场和温度场分布细节信息,为杆支撑换热器的结构完善和研究强化传热机理奠定了理论基础。     

射流循环DTB结晶器内的CFD模拟

采用RNG k-ε湍流模型对实验室级射流循环DTB蒸发结晶器内的单相流流场进行了数值模拟并优化结晶器结构,用欧拉多相流模型对优化的结晶器进行多相流模拟分析。结果表明,导流筒内射流满足线性扩展,其轴向速度分布基本满足高斯分布。刚进入导流筒内的射流段,轴线速度倒数与流程呈良好的线性关系,随射流的发展,轴线速度加速衰减。在入口直径恒定时,循环速率比随导流筒挡板间环隙面积与导流筒横截面积比的增加呈先增大再减小的趋势,存在最优值。优化的实验级DTB结晶器中导流筒内颗粒浓度分布沿径向方向减小,但基本可实现颗粒浓度较为均匀的分布,其循环速率与单相流模拟结果相比较低。     

Screw optimization of a co-rotating twin-screw extruder for a binary immiscible blend

The effect of the screw configuration of a closely intermeshing co-rotating twin-screw extruder on residence time and mixing efficiency was studied for an uncompatibilized immiscible PA6/PP (80:20) bend. Alternative screw configurations were investigated systematically. The residence time distribution (RTD) was found to be a poor indicator of the total mixing efficiency, whereas the mixing intensity function yielded considerably better information. High shear stress, sufficient residence time, and high fill ratio in the melting section of the screw were the most important factors in achieving good dispersion of the minor phase. The evolution of morphology along the screw axis depended strongly on the screw configuration. The downstream flow characteristics after the screw end determined the final morphology of the blend.     

Chaotic mixing in a single‐screw extruder with a moving internal baffle

A geometry in which the mixing of a single‐screw extruder was enhanced by a reciprocating baffle is proposed in this article. The effect of the baffle's amplitude on the mixing kinematics of the screw channel was investigated. A model with the baffle lower than the screw channel and the corresponding mathematical model were developed. The periodic flow and mixing performance of Newtonian fluid in such an extruder were numerically simulated. The finite volume method was used, and the flow domain was meshed by staggered grids with the periodic boundary conditions of the barrier motion being imposed by the mesh supposition technique. Fluid particle tracking was performed by a fourth‐order Runge–Kutta scheme. Distributive mixing was visualized by the evolution of passive tracers initially located at different positions. The growth of the interface stretch of tracers with time and the cumulative residence time distribution were also obtained. Poincaré sections were applied to reveal the geometrical scale of chaotic mixing patterns and the regions with embedded regular laminar flows. For comparison, the mixing performance in a conventional single extruder with fixed baffle was also investigated. POLYM. ENG. SCI., 54:198–207, 2014. © 2013 Society of Plastics Engineers     

The residence time distribution for laminar flow in helically coiled tubes

Sizable errors exist in previously published studies on the residence time distribution for ideal laminar flow in a helically coiled tubes. The numerical methods used to give corrected results are generally useful for flow situations where the projections of the streamlines on the channel cross-section are closed curves.An asymptotic solution, valid at long residence times, has been obtained. This solution confirms the numerical observation that the tail of the distribution is similar to that for laminar flow in a straight tube. If molecular diffusion is ignored, this form of asymptotic behavior is shown to be a general characteristic of all flow systems involving a fixed wall. When diffusion is considered, the asymptotic residence time distribution will be a decaying exponential in time. This confirms the widespread experimental observation that residence time distributions have exponential tails.     

Emulsion polymerization kinetics and reactor design. IV. Continuous-flow operation with recycling

A new mathematical model with a correction for radical capturing efficiency in a continuous emulsion polymerization with recycle flow has been proposed. These performance equations predict the conversion as well as molecular weight distribution of the polymer product during the continuous-flow operation. Experimental results obtained with vigorous mixing associated with a premixer are in best agreement with the theoretical prediction. In certain situations, the recycling provides a means for obtaining a higher degree of back-mixing with a normal flow reactor. However, it is difficult to obtain a high conversion of monomer by a continuous emulsion polymerization operation even with a long residence time. Theoretical and experimental average degrees of polymerization of polymer leaving the reactor are progressively displaced toward smaller values with greater mean residence time. According to the calculations based on our kinetic model the ratio M?_w/M?_n in the continuous emulsion polymerization remains constant regardless of mean residence time.