组合桨搅拌器的宏观混合特性

分别以浓度为１％，２％，３％，３．５％的羧甲基纤维素溶液为实验，采用测温法，测定了正交双层三角桨－单螺带桨，正交双层三角桨－内外单螺带桨．锚式桨－三叶推进器．锚式桨－内外单螺带４种组合桨拌器的宏观混合时间，无量钢数Ｃ１，Ｃ２，Ｃ３，Ｃ４综合评判了它们的宏观混合性能，实验证明，前２种组合桨搅拌器在不同流域内都使搅拌介质达到良好的宏观混合，且功率消耗低，混合效率高，具有明显的节能优势，对搅拌变粘度体系     

刚柔组合搅拌桨与刚性桨调控流场结构的对比

高黏度流体处于层流状态时,普遍存在的混合隔离区,降低了流体的混合效率。减小或消除隔离区,是实现流体高效混合的基本途径。采用实验研究与数值模拟相结合的方法,对刚性六直叶涡轮桨(刚性桨)和刚柔组合六直叶涡轮桨(组合桨)的流场结构进行研究,对比分析了两种桨叶在相同功耗(3 kW·m-3)时的轴向、径向和切向的速度矢量图、速度云图以及速度分布散点图。结果表明,刚性桨的能量集中在桨叶尖端部分,远离桨叶区域的流体速度很小甚至为0 m·s-1;而组合桨可将能量从桨叶尖端扩散至全槽,使槽内流体均具有一定的流速,提高了混合效率,且显色实验与数值模拟结果一致,组合桨体系的混合隔离区在短时间内就可消除,混合良好,而刚性桨体系的混合隔离区始终存在,混合效果不佳。     

刚柔组合搅拌桨与刚性桨调控流场结构的对比

高黏度流体处于层流状态时,普遍存在的混合隔离区,降低了流体的混合效率。减小或消除隔离区,是实现流体高效混合的基本途径。采用实验研究与数值模拟相结合的方法,对刚性六直叶涡轮桨（刚性桨）和刚柔组合六直叶涡轮桨（组合桨）的流场结构进行研究,对比分析了两种桨叶在相同功耗（3 kW·m^-3）时的轴向、径向和切向的速度矢量图、速度云图以及速度分布散点图。结果表明,刚性桨的能量集中在桨叶尖端部分,远离桨叶区域的流体速度很小甚至为0 m·s^-1;而组合桨可将能量从桨叶尖端扩散至全槽,使槽内流体均具有一定的流速,提高了混合效率,且显色实验与数值模拟结果一致,组合桨体系的混合隔离区在短时间内就可消除,混合良好,而刚性桨体系的混合隔离区始终存在,混合效果不佳。     

组合桨的混合性能研究

用模拟合成橡胶的粘稠介质研究了组合桨的宏观与微观混合性能，以及组合桨的匹配，提出组合桨（螺带／透平）是改善粘稠介质快速混合的有效途径。     

组合桨搅拌槽内高黏流体混合特性的数值模拟

利用计算流体力学数值模拟方法,对直段桨为双螺带式和Paravisc式以及底桨为锚式和变径双螺带式的组合桨功率和混合时间进行了研究,并对其中最优桨型进行了放大规律的探索。通过数值模拟得到了4种组合桨中各单桨及组合桨的功率准数关联式,提出组合桨中各桨之间功率上的反作用关系。在10种组合桨中,Paravisc-锚式组合桨达到完全混合时所转圈数最少,且在相同转速下量纲一剪切量较大,混合特性最优,将其从体积为100 L的搅拌槽内放大至200 L和500 L搅拌槽中,发现其符合桨端线速度的放大准则。文中对各桨型的功率特性、混合特性和放大规律的分析,可为工业设计和优化高黏度流体组合桨参数提供重要参考。     

偏心组合桨搅拌槽内层流混合过程的数值模拟

目前,处理高黏流体和对剪切敏感介质的层流搅拌槽的报道并不多见。本文建立了描述双层组合桨搅拌槽内高黏非牛顿流体层流流动、混合过程的数学模型,利用Laminar模型、多重参考系法（MRF）和示踪剂浓度法对其流场特性、示踪剂扩散过程进行数值模拟,分析搅拌槽内轴向速度曲线、示踪剂浓度响应曲线和混合时间。结果表明：中心搅拌中间面将介质阻隔在各自的半层内运动,偏心搅拌介质作全局运动,轴向混合能力突出;转轴中心搅拌依靠上下半层浓度差的增大向下扩散,转轴偏心搅拌通过不对称结构扩散示踪剂,叶轮相对转轴偏心搅拌则利用叶片的不对称分布;距离加料点较近和较远的监测点浓度响应曲线因振荡和调整,混合时间较长,处于中间面的监测点拥有最短的混合时间。     

组合螺带桨搅拌槽内粉体的混合性能

在直径0.48 m的立式搅拌槽内研究了4种组合式螺带搅拌桨的粉体混合性能,考察了搅拌转速、粉体物料装填高度和搅拌桨型对粉体混合性能的影响,分析了径向与轴向上的粉体混合情况. 结果表明,搅拌转速是影响粉体混合的重要因素,增加搅拌转速能明显缩短混合时间,转速44.0 r/min时的混合因子π3比转速8.7及26.5 r/min时下降50%及30%以上;在搅拌桨内部附加较小的内桨使功率略有增加,但可显著缩短混合时间,转速44.0 r/min时能使π3下降50%,提高混合效率.     

组合桨聚合釜内非牛顿流体的混合特性

在φ476mm的椭圆底有机玻璃聚合釜中,以羧甲基纤维素-甘油水溶液(前者质量分数为1.3％)为实验物系。利用酸碱中和法测定了9种不同的搅拌桨直径与聚合釜直径比接近于1的组合搅拌桨沿聚合釜轴向及径向的混合特性。结果表明：内外螺带-锚式组合桨的轴向混合最强,但径向混合较差。框板式搅拌桨的轴向混合较内外螺带-锚式组合桨弱,但比改进偏框式桨强,其径向混合较后者弱。改进偏框桨的7种不同组合方式沿径向的混合良好,多数组合桨沿轴向的混合较前2种组合桨弱,更接近于平推流。     

翼形桨搅拌槽内混合过程的数值模拟

采用FLUENT软件的多重参考系(MRF)及标准k-ε模型,将速度场与浓度场方程分开进行求解,对单层轴流式三叶CBY翼形桨搅拌槽内的混合过程进行了数值模拟,所得的混合时间的模拟结果与实验值相吻合。同时采用数值模拟的方法研究了不同的示踪剂加料点、监测点位置及操作条件对混合时间的影响规律;模拟结果表明,混合过程主要由搅拌槽内的流体流动所控制,混合时间与示踪剂加料点及监测点位置密切相关。上述的研究结果对于工业搅拌反应器的优化具有一定的参考意义。     

轴流式搅拌桨搅拌槽内混合时间的数值模拟

利用计算流体力学软件FLUENT 6.0程序计算了单层CBY搅拌槽内流体混合过程的速度场和浓度场,讨论了加料点位置和监测点位置对混合时间的影响。结果表明,拌槽内物料的混合过程主要由槽内的流体流动所控制;混合时间与加料点位置有关,在桨叶附近区域加料时混合时间比在液体表面加料时的混合时间短,应尽量在搅拌反应器的桨叶尖端处加料;不同的监测点位置对混合时间有很大的影响,在靠近槽底部进行监测所得到的混合时间最短。     

管壳式换热器壳程流体流动与换热的数值模拟

为了研究纵向多螺旋流管壳式换热器壳程流体湍流流动与换热的工作机理,文中利用FLUENT软件,在壳程流体流速设定值不断改变的情况下,对纵向多螺旋流管壳式换热器壳程湍流流动与换热进行了三维数值模拟。得到了多螺旋流管壳式换热器在不同的壳程流体流速下的温度场、速度场、质点迹线图、壳程传热膜系数分布图等。根据模拟得到的结果,从多个方面对纵向多螺旋流管壳式换热器壳程湍流流动与强化传热进行了探讨。模拟结果与实验结果进行了比较,二者误差约在±11%以内,吻合良好。     

An analytical model for the prediction of power consumption for shear-thinning fluids with helical ribbon and helical screw ribbon impellers

An approximate analytical model has been developed to predict power consumption for the mixing of shear-thinning fluids with helical ribbon and helical screw ribbon impellers in the laminar flow regime. Extensive data on power input measurements embracing a wide range of flow behaviour index, with strong (n<0.4) and weak (0.4<n<1) shear-thinning fluid characteristics, available in the literature have been used to demonstrate the applicability of the present model for a wide range of helical ribbon mixer configurations. The model is able to explain the differences in the data reported in the existing literature and to successfully predict the complex dependence of power consumption on the fluid properties and the system geometry. Finally, the proposed correlation only requires a knowledge of the flow behaviour index of the fluid and of the geometrical parameters of the mixing systems (wall clearance, number of ribbons, pitch and width of the ribbons) and one characteristic parameter K_p of the mixing system which can be obtained from a single measurement of power for Newtonian liquids in the laminar regime.     

Solids suspension with up-pumping pitched-blade and high-efficiency impellers

The use of axial-flow impellers in the up-pumping mode has been increasing, but little performance and design information is available. Up-pumping pitched-blade and high-efficiency impellers have been studied in solids suspension applications, and their performance has been compared to and contrasted with that of the more conventional down-pumping mode. Just-suspended speed data has been interpreted in terms of two literature correlations that can be used for design purposes. Just-suspended torque and power requirements are presented, as well as turbulent power number and flow pattern data. In general, the just-suspended torque and power requirements of up-pumping pitched-blade and high-efficiency impellers are substantially higher than those of the down-pumping mode. However, if a large impeller diameter is required to avoid critical speed limitations or to achieve sufficient power inputs at high solids loadings, then up-pumping impellers may be a viable option.     

多层翼形桨搅拌槽内混合过程的CFD模拟

The mixing process in a stirred tank of 0.476m diameter with single, dual and triple 3-narrow blade hydrofoil CBY impellers was numerically simulated by using computational fluid dynamics （CFD） package FLU-ENT6.1. The multi-reference frame （MRF） and standard k-ε turbulent model were used in the simulation. The shaft power and the mixing time predicted by CFD were in good agreement with the experiment. The effects of tracer feeding and detecting positions on mixing time were investigated. The results are of importance to the optimum design of industrial stirred tank/reactors.     

Turbulent forward–reverse mixing characteristics in vessel with multiple‐turbine impellers

BACKGROUND: Mixing in unbaffled vessel with multiple‐turbine impellers was studied. The mixing time and mixing power were evaluated in relation to the distance between impellers and the number of impellers. RESULTS: It has been confirmed that frequency of oscillation has no influence on the mixing time and mixing power values or on drag and added mass coefficients. The coefficients were greater when distance between impellers was smaller. Moreover added mass coefficient was dependent on Reynolds number (n_i > 2). Compared with unidirectional mixing conditions, for systems with one type of impeller, the power requirement was about 38% higher for forward‐reverse mixing. Despite the fact that the power demand was greater, the mixing time was not shorter, but about 30% higher than unidirectional mixing in a baffled vessel. However, the forward‐reverse mixing mode exhibits a higher level of homogeneity which it achieved faster than unidirectional mixing. CONCLUSION: The power requirements and mixing time for forward‐reverse mixing mode were higher in comparison with unidirectional mixing. Despite this, higher values of homogeneity were achieved faster. Higher levels of shear rate and better homogeneity indicate that forward‐reverse mixing can be beneficial for multi‐phase mixing in vessels with multiple impellers. © 2012 Society of Chemical Industry     

搅拌桨组合数值模拟优化及在谷氨酰胺转胺酶发酵中的应用

搅拌是影响发酵过程的主要因素之一,组合不同类型搅拌桨、发挥其各自优势,势必能够优化搅拌性能、提高微生物发酵生产效率。本研究采用计算流体力学（CFD）方法,模拟六直叶涡轮桨（DT）和DT、DT和抛物线桨（BT6）、六斜叶桨（CM6）和DT以及CM6和BT6四种搅拌桨组合对流场和混合时间的影响。对模拟得到的混合时间进行实验验证。结果表明,最优组合为：上桨叶为CM6桨,下桨叶为BT6桨。吸水链霉菌WSH03-13产谷氨酰胺转胺酶（TG）的发酵实验结果表明：CM6和BT6桨组合可获得最高的谷氨酰胺转胺酶活性和生物量,分别为4.7U/mL和42.9g/L,较优化前（DT和DT桨）分别提高了53%和40.9%,说明优化后的搅拌桨组合更有利于微生物生长和发酵。研究结果为组合搅拌桨在微生物发酵过程中的应用提供了借鉴。     

Characterisation of three different impellers using the LDV-technique

A characterisation of three commonly used impellers was made in this study by measuring local mean velocities and the fluctuations of these velocities with the LDV technique. The data was used to estimate volumetric flow, velocity fluctuations and turbulent intensity in the impeller region of the tank. The impellers investigated were a high flow impeller, a pitched blade turbine and a Rushton turbine. The cylindrical vessel used was made of Perspex, had a dished bottom (DIN 28013), was equipped with four baffles and had an inner diameter of 0.45 m. It was found that the bulk velocities could be scaled with the tip-speed of the impeller (ND). The flow rate at constant impeller speed increased in the order high flow impeller — Rushton turbine — pitched blade turbine. The corresponding order for the turbulence fluctuation is: high flow impeller — pitched blade turbine — Rushton turbine. The velocity profile of the flow out from the high flow impeller was furthermore, not as smooth as could be expected.     

煤浆混合槽混合性能的数值模拟

利用计算流体力学(CFD)方法研究煤浆混合槽的混合性能。采用Fluent 6.2计算软件,选用多重参考系法(MRF)、RNGk-ε湍流模型以及混合物多相流模型,对卧式煤浆混合槽的内部流动情况进行数值模拟,得到了湍流强度、湍动能、压力、速度分布以及出口各相分布等混合性能。模拟结果与实验结果进行了初步比较,吻合较好。研究结果表明,混合时在挡板和搅拌浆叶之间产生漩涡,有利于防止物料堆积,使混合更均匀。     

折流板间距对换热器性能影响的数值研究

采用CFD数值模拟方法,研究了简化模型下弓形折流板和螺旋折流板换热器,对应于不同间距/螺距时,流动参量的变化对换热器整体流动与传热性能的影响。结果表明,两种结构对应的壳程压力损失和换热系数均随壳程流量的增加而增大,而螺旋折流板结构单位压降下换热系数大于弓形折流板,并且其性能受折流板螺距变化的影响较小,体现了螺旋折流板结构的优越性。计算结果与现有实验结论吻合较好。     

密封点挥发性有机物（VOCs）排放速率的数值模拟及实测应用

目前对设备与管线组件密封点挥发性有机物（VOCs）排放速率的研究尚停留经验估算的阶段,本文以连接件密封点为典型代表,对乙醇生产装置中所涉密封点VOCs排放速率进行数值模拟和实测应用研究。利用直接测量包扎法对连接件进行包扎密封,将其所形成的包袋内流通空间类比为石油化工反应器,引入化工单元混合时间和空时的概念,通过计算流体力学数值模拟的方法,对比包袋内速度场、浓度场和压力场的分布情况,定量分析出包扎法系统中惰性载气吹扫流量和包袋体积之间的关系,优选合理的操作参数,现场实测并推算出连接件VOCs排放速率。研究结果表明：适当减小包袋体积可增加混合强度,缩短混合时间;在保持袋内微正压条件下,合理选择吹扫流量以匹配不同的包袋体积,吹扫时间大于袋内混合空时的2倍可基本达到近稳态;建立新的连接件密封点VOCs泄漏浓度和泄漏排放速率之间的幂函数关系式,用以评估核算VOCs年排放量更准确。