假塑性流体搅拌槽内停留时间分布

在直径φ500 mm和高350 mm的无挡板半球底有机玻璃槽中,采用45°斜叶桨研究了流量、搅拌功率、全槽平均表观牯度和物料流变特性对停留时间分布(RTD)的影响.结果表明,对于假塑性流体(流变指数为0.654)和牛顿流体,流量对RTD的影响两者差别不大,搅拌功率的增加更容易改变假塑性流体的RTD,使其更趋于全混流;对于牛顿流体,当搅拌功率大到一定程度后,再增加搅拌功率收效不大.假塑性流体的相对全混釜数随着全槽平均表观粘度的增加而增加,在全槽平均表观粘度相同时,假塑性流体的相对全混釜效大于牛顿流体,随着流体假塑性的增强,假塑性流体与牛顿流体相对全混釜数的差值显著增大.     

锚式搅拌槽中高粘弹性流体的流速分布及其功率消耗

用照相法测定了锚式搅拌槽中高粘弹性流体的流型和流速分布,另测定了搅拌功率消耗,结果发现:1.与牛顿流体相比,在低Re数下,粘弹性流体的切向速度较大,而径向速度则较小.2.转速相同时,在高剪切率区域,粘弹性流体的剪切率大于牛顿流体.由CEF方程导出功率计算式N_pRe_af_s~(1-n)=k_pf_vf_s~2[1+F_1avf_s~(m-n-3)Wi/K_s~2]用实验数据确定f_(?)和F_(1av),得到可适用于牛顿流体、假塑性流体和粘弹性流体的普适功率计算式,计算结果与实验值比较接近.     

PIV技术测试聚合物流体拉伸流动的实验研究

针对低相对分子质量、低黏度的牛顿流体（如聚异丁烯）和非牛顿流体（如3 %苯甲酸钠溶液）,采用粒子成像速度仪（PIV）系统测试了2种流体在同一流率下流经渐变收缩流道时的速度分布,并研究比较了壁面处的纯剪切流动与流道中心轴线上的拉伸流动。通过实验测试与有限元模拟比较发现,牛顿流体和非牛顿流体的速度分布形态具有一定的差异。在确定速度分布的情况下,根据渐变收缩流动的特点,可以得到流体流动时中心轴线上的拉伸速率和边界处的剪切速率。     

基于四参数流变模式的旋流分离流场特性分析

利用四参数流变模式描述钻井液的非牛顿流动特性,结合雷诺应力模型(RSM),研究钻井液非牛顿性对旋流分离流场的影响. 得到3种流体介质的速度场和压力场分布规律. 结果表明,流场模拟结果与实验结果吻合,模拟结果可靠. 虽然3种流体流场分布趋势相同,但同一位置非牛顿流体的静压力(4.02和3.77 MPa)和轴向速度(11.9和12.4 m/s)大于牛顿流体(3.22 MPa和11.7 m/s),切向速度(42.5和39.7 m/s)小于牛顿流体(47.5 m/s);四参数流体的静压力(3.77 MPa)和压力降(4.51 MPa)小于幂律流体(4.02和4.79 MPa),能量损失降低0.28 MPa,四参数流体的切向速度比幂律流体小2.8 m/s,且其零轴速包络面更靠近器壁,不利于流体介质分离.     

流变学的应用与发展

简要说明了流变学研究的内容和非牛顿流体的概念,介绍了非牛顿流体的流变特性及其在生产和生活中的一些应用,分析了流体流变学研究的发展现状,并对我国流变学研究所面临的热点、难点和发展趋势进行了展望.     

聚合反应工程——第5章 非牛顿流体的传递过程(二)

5.2 非牛顿流体的搅拌功率 在高分子材料等工业生产中,经常需操作属非牛顿性流体的物料,因而对非牛顿流体搅拌功率的计算,为化学工程技术人员所广泛重视。 对牛顿流体的搅拌功率,一般可关联为     

非牛顿流体幂指式流变模型的实验验证

用 30 #机械油加聚异丁烯高分子添加剂构成非牛顿流体 ,选用幂指式流变模型作为这种流体的本构方程。并在改进的MPV 15 0 0试验机上进行了这种非牛顿流体的流变性能试验。对于试验数据用幂指式 (τ =m γn)模型进行线性回归。 8组数据处理得到的最小相关系数Rh=0 .996 3,在 0 .0 1信度下是高度显著的。充分证明幂指式流变模型完全符合这种流体的本构方程。从而为这种非牛顿流体在摩擦学中的应用提供了理论分析基础     

非牛顿流体中的气泡行为

非牛顿流体广泛存在于各学科领域（如化工、食品和生物医学等），也与许多工业过程及人类的生命过程密切相关。非牛顿流体中的气泡行为直接影响流体传质、传热及化学过程的快慢。因此，了解和研究非牛顿流体中的气泡行为具有重要意义。本文分别从气泡生成、聚并和破裂3个方面对非牛顿流体中气泡行为的研究进展进行评述。     

非牛顿流体薄膜流中质量传递的实验研究

本文通过实验,研究非牛顿流体层流降膜流中质量传递过程.实验系采用温壁塔测定二氧化碳在高分子水溶液中吸收速率.这些溶液符合幂律模型.实验证明非牛顿幂律流体降膜流中考虑速度分布的微分方程精确解是正确的;对拟塑性流体,用无因次长度Z<0.1作为渗透论适用范围的判据是合适的,而精确解则不受此范围的限制.     

柴油低温粘温特性和流变性研究

考察了柴油加入低温流动改进剂前后的低温粘温特性和流变特性。结果表明,随着温度降低,柴油的表观粘度和粘流活化能增大,稠度系数增大．流动特性指数减小,柴油的流变特性越来越偏离牛顿流体,非牛顿性越来越强,柴油在低温下为假塑性非牛顿型流体。加入低温流动性改进剂T1804 后,柴油的低温表现粘度和粘流活化能显著降低,柴油的流动特性指数值增大,稠度系数值减小,与未加剂柴油相比,更接近于牛顿流体。     

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.     

Residence Time Distribution Models Derived from Non‐Ideal Laminar Velocity Profiles in Tubes

The theoretical E‐curve for the laminar flow of non‐Newtonian fluids in circular tubes may not be accurate for real tubular systems with diffusion, mechanical vibration, wall roughness, pipe fittings, curves, coils, or corrugated walls. Deviations from the idealized laminar flow reactor (LFR) cannot be well represented using the axial dispersion or the tanks‐in‐series models of residence time distribution (RTD). In this work, four RTD models derived from non‐ideal velocity profiles in segregated tube flow are proposed. They were used to represent the RTD of three tubular systems working with Newtonian and pseudoplastic fluids. Other RTD models were considered for comparison. The proposed models provided good adjustments, and it was possible to determine the active volumes. It is expected that these models can be useful for the analysis of LFR or for the evaluation of continuous thermal processing of viscous foods.     

循环浆态床气体停留时间分布的研究

研究了循环浆态床气流段的气流量和液体循环量对气体停留时间分布的影响。实验结果表明,减小气流量或者增加液体循环量,气体返混程度变大,气体平均停留时间增长。建立模型模拟循环浆态床气流段气体停留时间分布,得到停留时间分布密度函数和物料分率p与射流相似准数Ct和气液动量比准数Cr的关联式。从关联式看出,气液动量比准数Cr越小,物料分率p越大,表明循环液体流量越大,气体停留时间分布越接近于全混流。这一结论与实验结果相符。     

THE RESIDENCE TIME DISTRIBUTION FOR LAMINAR FLOW OF NON-NEWTONIAN LIQUIDS THROUGH HELICAL TUBES

The residence time distribution in a helically coiled tubular reactor is computed for laminar flow of inelastic non-Newtonian liquid at small Dean number. Effect of pseudoplasticity on the residence time distribution is explored. It was found that pseudoplaslicity of the liquid makes the residence time distribution narrower. The effect of dialalant fluid behavior is opposite but very small in magnitude. The results of numerical integrations are correlated with power law index, allowing predictions over a wide range of the index. The results could be used to predict conversion of reactions in a coiled reactor, such as continuous polymerization or fermentation reactors, where the reaction mixtures are likely to be non-Newtonian in nature. Results will be also useful in characterization of coiled chromatographic columns.     

旋转填料床与盘管组合反应器中的流动特性

以饱和的NaCl水溶液为示踪剂,采用脉冲法考察了液体流量、转子转速对旋转填料床与盘管组合反应器停留时间分布(RTD)曲线的影响。用轴向扩散模型对流动状况和返混程度进行了表征。结果表明,组合反应器内的流体流动型态与盘管相同,接近活塞流,且流量越大,平均停留时间越短。旋转填料床转子转速对组合反应器停留时间分布影响很小。     

An input/output approach to the optimal transition control of a class of distributed chemical reactors

An input/output approach to the optimal concentration transition control problem of a certain type of distributed chemical reactors is proposed based on the concept of residence time distribution, which can be determined in practice by using data from experimental measurements or computer simulations. The main assumptions for the proposed control method to apply are that the thermal and fluid flow fields in the reactor are at pseudo-steady-state during transition and that the component whose concentration is to be controlled participates only in first-order reactions. Using the concept of cumulative residence time distribution, the output variable is expressed as the weighted sum of discretized inputs or input gradients in order to construct an input/output model, on the basis of which a constrained optimal control problem, penalizing a quadratic control energy functional in the presence of input constraints, is formulated and solved as a standard least squares problem with inequality constraints. The effectiveness of the proposed optimal control scheme is demonstrated through a continuous-stirred-tank-reactor (CSTR) network and a tubular reactor with axial dispersion and a first-order reaction. It is demonstrated through computer simulations that the proposed control method is advantageous over linear quadratic regulator (LQR) and proportional-integral (PI) control in terms of control cost minimization and input constraint satisfaction.     

Residence Time Distribution of a Capillary Microreactor Used for Pharmaceutical Synthesis

The main drivers for application of small-scale reactors in the pharmaceutical industry are the possibility of rapid synthesis and screening of novel drugs as well as the readiness of the scale-up. The characterization of fluid flow pattern was performed through step-up and step-down residence time distribution experiments using a tracer at six different flow rates. Four single-parameter models were considered for representing deviations from ideal plug flow and ideal laminar flow in tubes. The model that provided the best results was the axial dispersion model and the Peclet and Reynolds numbers could be well correlated. Obtained Peclet values from 44 to 244 were close to Pe > 100, in which axial dispersion can be neglected and the reactor can be considered as plug flow reactor.     

Residence Time Characteristics of the Novel Archimedean Screw Crystallizer/Reactor

This work presents a novel design of a continuous crystallizer, the Archimedean screw crystallizer reactor (ASKR) with integrated Archimedean screw as conveying element. By the screw, the axial motion of the product solution is initiated, and an undesired axial mixing is restricted. This structure results in a narrow residence time distribution and, thus, promotes a defined product quality. In order to quantitatively assess the flow characteristics of the crystallizer and to highlight the influence of variable operating parameters such as rotational speed and volumetric flow, investigations of the residence time behavior with variation of the operating parameters are reported.     

Reactor dynamics and molecular weight distributions: Some aspects of continuous polymerisation in tubular reactors

A study was made of the effect of residence time distribution and thermal nonuniformities on molecular weight dispersion in continuous nonchain and chain polymerizations, respectively. The analyses were conducted with the aid of the assumption of microsegregation, which facilitated and unified the computational approach. Holdback was examined and found to be a good criterion for characterizing the importance of residence time distribution. Power-law flow index was found to have a direct effect on molecular weight dispersion in isothermal nonchain polymerizations as well as an indirect influence in chain polymerizations via its role as a parameter for thermal sensitivity. It was concluded that the isothermal, segregated, continuous stirred tank reactor has a greater effect on molecular dispersion in nonchain-type polymerizations than the worst isothermal tubular reactor, as correctly predicted by holdback, and temperature nonuniformities have a profound influence on molecular dispersion in chain-type polymerizations.     

Influence of the meandering channel geometry on the thermo-hydraulic performances of an intensified heat exchanger/reactor

In the global context of process intensification, heat exchanger/reactors are promising apparatuses to implement exothermic chemical syntheses. However, unlike heat exchange processes, the implementation of chemical syntheses requires to control the residence time to complete the chemistry. A way to combine the laminar regime (i.e. enough residence time) with a plug flow and the intensification of both heat and mass transfers is the corrugation of the reaction path.In this work, the experimental set-up is based on plate heat exchanger/reactor technology. 7 milli-channel corrugated geometries varying the corrugation angle, the curvature radius, the developed length, the hydraulic diameter and the aspect ratio have been designed and experimentally characterized (heat transfer, mixing times, pressure drops, RTD). The objectives were to assess their respective performances to derive some correlations depending on the channel design.The results confirmed the benefits of the reaction channel corrugation. Heat and mass transfers have been intensified while maintaining a plug flow behaviour in the usually laminar flow regime. Moreover, whatever the meandering channel's curvature radius, the results highlighted the relevance of considering the Dean number as the scale-up parameter. This dimensionless number, more than the Reynolds number, seems to govern the flow in the wavy channels.