多层组合桨搅拌槽内气-液分散特性的研究

在直径为0,476m的椭圆底搅拌槽中,采用由六叶半椭圆管叶盘式涡轮桨(HEDT)及四叶宽叶翼型桨的上提(WHU)及下压(WHD)操作组合的六种不同的三层桨,研究了气-液两相体系中的通气功率变化及气含率特性,获得不同桨型的通气搅拌功率及气含率的关联式;结果表明,底桨为HEDT的组合桨通气功率下降幅度最小,相同输入功率时气含率最高,其次为WHD,WHU为底桨时气液分散性能最差。因此,适用于气液两相操作的优化组合桨应以HEDT为底桨。此研究结果可为工业用多层组合桨气液搅拌反应器的设计提供参考。     

搅拌槽内多层组合桨对液-液分散特性的影响

以水-煤油及水-环己烷为体系,研究Rushton涡轮桨(RT),半椭圆管涡轮(HEDT)及翼形轴流式桨(CBY)的6种不同组合桨的液-液分散特性。测定了不同输入功率时分散相体积分率沿轴向及径向的分布。结果表明:当搅拌槽内液位与槽径之比达1.5,在相同输入功率时,三层桨的液液分散性能优于两层桨,功率准数较低的CBY组合桨在输入功率0.8kW/m~3时,槽内的轴向及径向分散相体积分率达到稳定的均匀分布。而功率准数较大的RT组合桨需要在输入功率1.8kW/m~3才能达到槽内分散相的均匀分布。     

搅拌槽内的液-液临界分散

在φ391mm搅拌槽中,分别采用双层Brumagin桨、双层三叶后掠式桨和双层A310桨与7种内构件相组合,在无乳化剂下对油水比(质量比)分别为1∶1.5,1∶2.0的煤油-水体系的液-液临界分散进行了研究。从工业实用的角度出发,对前两种桨找到了一种可替代“轻液挡板”的小挡板及其安装方法:内冷管上均布4块小挡板,B/D=0.08,插入液面深度为0.2D。在φ188mm搅拌槽中,于全挡板条件下,以歧化松香皂为乳化剂,分别采用3种不同几何参数的双层Brumagin桨对油水质量比为1∶1.5的煤油-水体系的临界分散进行了研究。结果表明,与无乳化剂情况相比,液-液临界分散转速(N_c)下降30％～40％,临界分散功耗(P_(cv))下降53％～66％;桨径减小会使N_c和P_(cv)增加。     

双层桨气液搅拌反应槽气液分散特性

采用搅拌功率与氧传质系数方法,对一双层桨搅拌反应槽的自吸分散和表面充气分散性能进行研究.比较了两种桨叶组合在两种分散方式下的气相分散临界转速、搅拌功率及两种桨叶组合自吸分散时的气含率和气液传质系数.结果表明,六叶圆盘直叶桨和六叶圆盘斜叶桨的组合在自吸分散时具有较优的分散性能.     

双层组合桨搅拌槽内气液微观分散特性

采用双电导电极探针法对双层组合桨搅拌槽内气液相界面积特性进行了实验研究,考察了通气量、搅拌转速和桨组合对槽内相界面积的影响。结果表明:对于上层桨为上翻斜叶桨和下层桨为凹叶桨的组合,随着通气量的增加,搅拌槽内大部分区域的相界面积增大,但在槽底区域减小。随着搅拌转速的增加,在叶轮区域的相界面积增加明显,而在槽底和液面区域基本不变化。上下层桨的分散能力和气体分布器结构和操作条件密切相关。对于近壁管式气体分布器搅拌槽,在较低通气量下,上层桨对气液分散起着主要作用,而在高通气量下,下层桨的作用增强,起主要作用。带圆盘的搅拌桨对气体具有良好的阻缓作用,不同气速下均具有优异的气液分散能力。     

组合桨搅拌槽内非牛顿流体的气液分散特性

采用Brookfield黏度仪测量了质量分数为0.5%,1.0%,1.5%的羧甲基纤维素钠(CMC)水溶液在298.15 K的流变特性。在直径为0.48 m的平底搅拌槽中,对搅拌槽内不同的3层组合桨的气液二相的分散特性进行了实验研究,考察了非牛顿流体浓度、桨型组合、通气量和搅拌转速对通气功率、相对功率和气含率的影响规律。结果表明:CMC水溶液为假塑性流体,幂律方程能很好地关联其流变特性。在相同操作条件下,随着浓度的增加气含率减小,功率消耗增加;在相同的功率输入时,下压桨型组合的气含率更高。相对功率(PG/P)、气含率关联式等研究结果对非牛顿流体的气液搅拌器设计和操作具有一定参考价值。     

翼形轴流桨用于液液分散的冷模研究

翼形桨是新一代高效轴向流叶轮。本文将这类叶轮用于液液分散的冷模试验，测定了基本流型及其造成的液滴大小分布，研究了分散特性与搅拌功率的关系，并与传统叶轮比较了搅拌混合的综合性能。     

挡板进气多级搅拌槽内的气—液分散特性

研究了挡板进气多级搅拌槽内的气－液分散流型、临界分散转速、搅拌功率、气含率和气泡停留时间。试验证明，这种结构的搅拌槽，比标准通气式搅拌槽具有更优良的气－液分散特性，并回归得到了搅拌功率、气含率和气泡停留时间的关联式。     

上浮颗粒特性对三相搅拌槽内固-液悬浮及气-液分散的影响

在直径为0.476m(T)的椭圆底有机玻璃搅拌槽中,采用作者此前研究优选的多层组合桨(HEDT WHD WHU),分别选用粒径在0.5至4mm、密度范围在900至955kg(m(3的聚丙烯(PP)颗粒及粉料、低密度聚乙烯(LDPE)颗粒、高密度聚乙烯(HDPE)颗粒作为上浮固体,操作液位为1.5～1.8T,研究了颗粒特性及操作液位对空气-水-上浮固体三相体系的固-液悬浮及气-液分散性能的影响.结果表明:对于同种颗粒,其表面状态对悬浮特性有较大的影响,颗粒表面因含有少量残余溶剂而呈现部分憎水特性时,达到液面处颗粒停留时间不大于1～2秒的临界悬浮状态所需搅拌转速及输入功率显著增加;此时减少上层桨与液面的距离对降低临界悬浮转速及功率有较大贡献.当颗粒种类不同,表面状态及粒径相近时,液固密度差越大,所需悬浮转速越高;但相同输入功率及表观气速时的气含率相差不大.液固密度差相近时,颗粒越小越易被悬浮,但颗粒越小浓度增加使三相体系的气含率降低的幅度越大.对于不同颗粒所得气含率关联式及悬浮特性研究结果可为工业气液固搅拌槽/反应器的优化设计提供参考.     

Local drop size variation in an agitated vessel

The local droplet diameters were measured at two positions inside the circulation region of a stirred tank. The Sauter mean diameter near the top of the vessel was always 1.4 times greater than the one just outside the impeller region for rotational speeds of 250, 300, 350 and 400 rpm and for hold-up fractions of 0.01, 0.025 and 0.05. The drop size distributions at a hold-up fraction 0.01 had one mode for all impeller speeds studied and at both positions. At higher hold-up fractions the distributions usually were bimodal.     

Types of dispersion in agitated liquid-liquid systems

This paper describes phase inversion phenomena in stirred vessels. In particular, the effects of mechanical operating-parameters on dispersion types were investigated. It was found that when the impeller stirring speed was lower than 400 rpm, the aqueous phase became continuous, while when it was higher than 1050 rpm, the phase which had the higher viscosity became dispersed. Surface active agents have strong effects on phase inversion phenomena.     

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。     

搅拌槽中非稳态温度场分布的研究

在对称装有4组垂直加热列管、直径为500mm的搅拌槽中使用长薄叶(CBY)桨进行搅拌,采用液晶(LC)测温技术测量搅拌槽内温度场的分布。分别研究了搅拌槽中轴向温度分布随加热时间、叶轮雷诺数以及桨的安装高度不同而变化的情况。结果表明,列管加热时间的长短对槽内温度分布的趋势没有影响,温度分布的趋势主要取决于所用搅拌桨产生的流型;随着叶轮雷诺数的增加,槽内温度分布相对趋于均匀;搅拌桨的安装高度对温度场的分布影响也很显著。     

Onset of gas self-induction and power consumption after gas induction in an agitated tank

The behavior of inducted gas from liquid surface and the; power requirements in an agitated tank using a mechanical agitator are studied in order to increase the amount of gas self-induction and the gas retention time for gas absorption. A 45° six-blade downward impeller turbine was utilized in this study. Air and water, air and 40 wt% 60 wt%, and 80 wt% of glycerin water, and air and 106 cP silicon oil were employed as gas and liquid phases. Variables which were studied included geometrical factors (immersed depth of impeller, baffle with and diameter of impeller) and the physical properties of the liquid (viscosity, density, and surface tension). The correlations for the onset speed of impeller and power consumption after gas induction in the agitated tank are established from our experimental results. The amount of gas self-induction from the liquid surface in the agitated tank increases with increasing impeller diameter and speed and decreases with increasing baffle width, depth of impeller and viscosity of liquid.     

搅拌罐（釜）的工程放大方法和经济分析

介绍了搅拌罐（釜）的工程放大原理和方法，并通过实例进行了经济分析。     

Determination and correlation of axial-mixing parameters in an agitated liquid-liquid extraction column

Dispersion coefficients were measured in a pilot-plant sized agitated liquid-liquid extraction column of the Kuhni type. Available techniques were considered, and the axial mixing in both phases obtained over a broad range of operating conditions, both with and without mass transfer and with two sets of stator plates. Earlier correlations for backmixing in the continuous phase were checked and improved, the final equation being successfully tested on available published data.     

Onset of gas induction and power consumption in an agitated tank having shortened narrower baffles

The onset speed of gas induction and the power consumption after gas induction were studied in a gas-induced type agitated tank. In such an agitated tank, four unique baffles which were shorter and narrower than the conventional ones were adopted. Two 45° downward pitched blade turbines (PBT) in series were used as impellers. Gas induction could be formed by the dual impellers operated above the onset impeller speed. Several geometric factors and operation parameters were considered by theoretical aspects and the dimensionless analysis to study the onset of gas induction and the power consumption. In all experiments, air and tap water were used as working fluids. Results revealed that a lower agitation speed and less power consumption were needed for the present tank than a narrower full-length baffled agitated tank. In the present tank, the least specific power consumption was found when the liquid level was about 1·9 times the tank diameter. Two correlation equations were obtained to predict, respectively, the onset speed of gas induction and the power consumption after gas induction. Comparison between the present type and various other gas-inducing type agitated tanks were also discussed. © 1998 SCI