6种常规搅拌器的剪切性能研究

不同搅拌工况下剪切性能的需求是选用搅拌器的一个重要指标,文中基于对常规的6种搅拌器流场的CFD模拟,计算了搅拌器各自的剪切性能量纲一数C_3,分析了搅拌流场中剪应力的累计概率分布及统计平均结果。二者对比发现:从宏观平均效果上看,搅拌器剪切性能满足直叶桨>斜叶桨,圆盘涡轮>开启涡轮>桨式;而剪应力极大值影响作用则是直叶圆盘涡轮>斜叶圆盘涡轮>直叶桨式>斜叶开启涡轮>直叶开启涡轮>斜叶桨式。因此,对剪切作用敏感的搅拌过程,在采用常规的搅拌器剪切性能评价的基础上,还需要充分考虑搅拌流场中剪应力极大值的影响,合理选用搅拌器。     

双层搅拌器组合的气液分散性能研究

系统研究和比较了径流桨和径流桨组合、径流桨和斜叶桨组合以及斜叶桨和斜叶桨组合3类不同的双层搅拌器组合,在气液分散搅拌过程中的优劣。小通气量时径流桨和斜叶桨组合(DT PTD和PTU DT)在相同的单位体积搅拌功率下气含率最高,而在大通气量时,双层上翻式斜桨组合(PTU PTU)气含率最高,并发现大通气量时,下层桨不宜采用下压式斜叶桨。     

新型同心双轴搅拌器功率与混合特性的数值模拟

基于同心双轴搅拌器的结构与运行特点,建立了兼顾其流动、混合过程的三维数学模型,并以过程工业应用较多的两种不同尺寸双层组合桨作为内桨、框式桨作为外桨构成的同心双轴搅拌器为研究对象,数值模拟了其在中高黏牛顿流体中同向及反向转动模式的功率特性、流场特性及混合特性。模拟结果表明,同向转动模式下,整个系统的搅拌功耗更小、混合效率更高;外桨功耗受内桨影响较大,一般随内桨转速的增大,恒速外桨的功耗同向转动时会减小、反向转动时会增大;对由桨式搅拌器构成的组合式内桨而言,当内桨直径与釜体直径之比为0.35左右时,相同Reynolds数下的单位体积混合能更小;中高黏牛顿流体中,同心双轴搅拌器的内桨采用上层六斜叶桨+下层六直叶桨的组合形式时更高效节能,仅在体系Reynolds数小于36时,上层二斜叶桨+下层二直叶桨的内桨组合形式才具有相对优势。     

新型组合桨混合特性研究

根据聚合反应的特定工艺过程要求,提出了一种新型搅拌桨,对其混合性能进行了研究并与常规桨型进行对比。结果表明,该桨在高粘度流体内混合时间、排液量、混合效率等方面较常规桨型好,能在较短的时间内实现全罐的均匀混合。     

双层桨自吸式搅拌槽气-液分散性能

对一双层桨自吸式搅拌槽内气液分散性能进行了研究,在有无定子两种情况下,对比了不同桨型组合的搅拌功率、相对功率消耗、气含率和容积传氧系数。结果表明:自吸式搅拌槽可以有效降低功率消耗;6P-6PDTU(抛物线型桨与六叶上斜叶桨)组合的功率消耗小于6DT-6PDTU(六直叶圆盘桨与六叶上斜叶桨)组合,相对功率消耗更接近于1;气含率和容积传氧系数小于6DT-6PDTU组合。研究表明,虽然6DT-6PDTU组合的搅拌功率较大,且不利于气液分散和混合,但吸气量和气液两相之间的传质效果较好。     

搅拌器在工业合成醋酸反应器中的应用

详细分析了工业合成醋酸反应器中的机械搅拌过程,描述了气液分散搅拌过程中搅拌桨叶的选择和计算。对醋酸反应器这样复杂的气-液反应混合过程,必须采用合适的机械搅拌器。目前采用最多的是径向流和轴向流相结合的多层搅拌桨叶组合形式的搅拌器。搅拌桨的计算和设计对保证醋酸反应中充分的气-液分散混合并达到良好的气-液传质过程十分重要。不同大小醋酸反应釜的搅拌器必须根据不同生产处理量和醋酸装置的工艺条件进行设计和选型。     

气液混合搅拌器组合的优化

研究了由3种基本搅拌桨类型(圆盘涡轮、上翻斜叶涡轮和下压斜叶涡轮)组成的9种搅拌桨组合在搅拌槽中的气液分散能力,得到了不同气体流速下优化的搅拌桨组合.     

几种单层桨搅拌槽内宏观混合特性的比较

为了丰富对向心桨的混合特性的认识,比较了向心桨、Rushton桨、三斜叶桨和穿流桨的单层桨搅拌槽内的宏观混合特性,考察了搅拌转速、桨叶离底高度对搅拌槽混合时间和功率特性的影响。结果表明,四种桨的宏观混合时间均随着搅拌转速的增加而减少,搅拌功率均随转速的增加逐渐增大。当转速相同时,四种桨型中Rushton桨的功率消耗最大,三斜叶桨功率消耗最小,向心桨的功率消耗仅仅比三斜叶桨高。桨叶离底高度的变化对四种桨型的混合时间和功率的影响不尽相同。混合效率的影响因素大小顺序为：搅拌转速>桨型>桨叶离底高度。在考察的四种桨型中,向心桨的混合效率最高。研究成果可为向心桨等新型搅拌桨的工业应用积累实验数据,为其优化设计和放大提供理论依据。     

筒式搅拌器性能试验研究

介绍了获得实用新型专利的筒式搅拌器的结构和工作原理,对筒式搅拌器的搅拌性能进行了试验研究和分析,并与推进式搅拌器和涡轮式搅拌器进行了比较。试验结果表明,3种搅拌器在同等条件下,筒式搅拌器的能耗最小,且其排液量和循环流量最大。     

两层桨搅拌釜内混合过程的新二维单元串联模型

在直径为 1 86mm的立式搅拌釜内 ,利用热电偶—温差法测量了两层组合桨搅拌釜内的液相混合时间 ,试验中采用的搅拌桨有直叶圆盘涡轮和斜叶涡轮 (上推式斜叶涡轮 PTU和下压式斜叶涡轮 PTD) ;根据激光多谱勒测速仪对流场的测量结果 ,提出了一种新的二维单元串联模型 ,用该模型对两层组合桨搅拌釜内的混合过程进行了模拟 ,发现模拟值和实验值吻合较好。     

THE GROWTH OF CAVERNS FORMED AROUND ROTATING IMPELLERS DURING THE MIXING OF A YIELD STRESS FLUID

The growth of caverns, formed around rotating impellers in a yield stress fluid during mixing in a stirred vessel, has been studied by observing impeller speeds at which fluid motion was first observed at the vessel's wall and base, and at the free liquid surface. The effect of impeller geometry has been studied with a disk turbine (DT), a two bladed paddle (2BP), a pitched blade turbine (PBT) and a marine propeller (MP).

The presence of four baffles (10%) was found to increase the impeller speed at which the cavern reaches the vessel wall by 9% on average over that observed without baffles. After the cavern has reached the vessel walls, impeller type had a small effect upon the vertical expansion of the cavern with increasing impeller speed. Radial flow impellers (DT and 2BP), on average, performed better than an axial flow impeller (MP), with a mixed flow impeller (PBT) in between. Baffles significantly reduce the rate of this vertical expansion of the cavern. Clearance of the impeller from the vessel base had little effect upon the growth of the cavern above the impeller.     

THE GROWTH OF CAVERNS FORMED AROUND ROTATING IMPELLERS DURING THE MIXING OF A YIELD STRESS FLUID

The growth of caverns, formed around rotating impellers in a yield stress fluid during mixing in a stirred vessel, has been studied by observing impeller speeds at which fluid motion was first observed at the vessel's wall and base, and at the free liquid surface. The effect of impeller geometry has been studied with a disk turbine (DT), a two bladed paddle (2BP), a pitched blade turbine (PBT) and a marine propeller (MP).

The presence of four baffles (10%) was found to increase the impeller speed at which the cavern reaches the vessel wall by 9% on average over that observed without baffles. After the cavern has reached the vessel walls, impeller type had a small effect upon the vertical expansion of the cavern with increasing impeller speed. Radial flow impellers (DT and 2BP), on average, performed better than an axial flow impeller (MP), with a mixed flow impeller (PBT) in between. Baffles significantly reduce the rate of this vertical expansion of the cavern. Clearance of the impeller from the vessel base had little effect upon the growth of the cavern above the impeller.     

LIQUID FLOW IN IMPELLER REGION OF AN UNBAFFLED AGITATED VESSEL WITH UNSTEADILY FORWARD-REVERSE ROTATING IMPELLER

For an unbaffled agitated vessel with an unsteadily forward-reverse rotating impeller whose rotation proceeds with repeated acceleration, deceleration, and stop-reverse processes, the liquid flow in the impeller region was studied based on photographs showing path lines of tracer particles. An image series taken during one cycle of the forward-reverse rotation was analyzed to characterize the internal stream inside the impeller rotational region and the discharge stream outside its region when a disk turbine impeller with six flat blades was rotated unsteadily. Because of the unsteady flow generated inside the impeller rotational region, the velocity vector of outflow from its region fluctuated periodically with the change of the impeller rotation rate. The circumferential velocity was almost in phase with the impeller rotation rate, oscillating periodically. The radial velocity exhibited larger values in the process for the impeller from decelerating to stopping and reversal. The radial flow, whose velocity decreased downstream outside the impeller rotational region, was clarified to be transformed into upward and downward axial flows that are almost uniform in the circumferential direction throughout the region near the vessel wall.     

LIQUID FLOW IN IMPELLER REGION OF AN UNBAFFLED AGITATED VESSEL WITH UNSTEADILY FORWARD-REVERSE ROTATING IMPELLER

For an unbaffled agitated vessel with an unsteadily forward-reverse rotating impeller whose rotation proceeds with repeated acceleration, deceleration, and stop-reverse processes, the liquid flow in the impeller region was studied based on photographs showing path lines of tracer particles. An image series taken during one cycle of the forward-reverse rotation was analyzed to characterize the internal stream inside the impeller rotational region and the discharge stream outside its region when a disk turbine impeller with six flat blades was rotated unsteadily. Because of the unsteady flow generated inside the impeller rotational region, the velocity vector of outflow from its region fluctuated periodically with the change of the impeller rotation rate. The circumferential velocity was almost in phase with the impeller rotation rate, oscillating periodically. The radial velocity exhibited larger values in the process for the impeller from decelerating to stopping and reversal. The radial flow, whose velocity decreased downstream outside the impeller rotational region, was clarified to be transformed into upward and downward axial flows that are almost uniform in the circumferential direction throughout the region near the vessel wall.     

冷却水循环泵抗汽蚀性能改造

针对大流量冷却水循环泵叶累的严重汽蚀问题，利用研究所高性能离心泵设计计算系统重新设计制造叶轮与并投入运行，叶轮的抗汽蚀性能大为提高。     

高粘性非牛顿流体搅拌的研究

本文研究了双螺带搅拌器和另外两种新型搅拌器(收缩桨式、交叉桨式)在非牛顿流体中的搅拌特性,试验比较认为,交叉桨为比较理想的桨叶形式。利用回归组合设计,找出了交叉桨式搅拌器无因次混合时间与几个设备参数之间的关系,通过优化运算得到了最佳参数,并研究了交叉桨在粘弹性流体中的搅拌特性。     

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。     

EFFECT OF IMPELLER DESIGN ON LIQUID PHASE MIXING IN MECHANICALLY AGITATED REACTORS

Liquid phase mixing time (θ_mix) was measured in mechanically agitated contactors of internal diameter 0.57 m, 1.0 m and 1.5 m. Tap water was used as the liquid phase. The impeller speed was varied in the range of 0.4-9.0 r/s. Three types of impellers, namely disc turbine (DT), pitched blade downflow turbine (PTD) and pitched-blade upflow turbine (PTU) were employed. The ratio of impeller diameter to vessel diameter (D/T) and the ratio of impeller blade width to impeller diameter (W/D) were varied over a wide range. The effects of impeller clearance from the tank bottom (C), the blade angle (φ), the number of blades (n_b), the blade thickness (k) and the total liquid height (H/T) were studied in detail. Mixing time was measured using the conductivity method.

Mixing time was found to have a strong dependance on the flow pattern generated by the impeller. Mixing time was found to decrease by decreasing the impeller clearance in the case of DT and PTU. However in the case of PTD it increases with a decrease in the impeller clearance. Similar trend of the effect of impeller clearance on θ_mix, was observed for all the other PTD impellers with different diameter, number of blades and blade angle (except 60^° and 90^°). All the impeller designs were compared on the basis of power consumption and on this basis optimum design recommendations have been made. For PTD impellers, a correlation has been developed for the dimensionless mixing time.     

NUMERICAL SIMULATION OF TURBULENT FLOW OF AGITATED LIQUID WITH PITCHED BLADE IMPELLER

The turbulent flow field in an agitated system with baffles was solved numerically using the standard k-e model, an algebraic Reynolds stress model (ASM) and a differential Reynolds stress model (RSM). The commercial software FLOW3D (CFDS, Harwell Laboratories, 1991) was used for this purpose. The aim of the study was to investigate the influence of the impeller boundary conditions and turbulence models to the agreement with experimentally obtained laser-Doppler anemometry data. The boundary conditions for the impeller discharge used in the numerical calculations were obtained as whole-cycle-ensemble averages from experimental LDA-measurements (Fort et al., 1992). Since measurements of the rate of dissipation of turbulent kinetic energy ( ε) was not available the dissipation rate per unit mass in the impeller discharge was estimated from the expression:

where k is the turbulent kinetic energy per unit mass and L the macroscale of turbulence in the pitched blade impeller discharge. The macroscale of turbulence (L) in the impeller boundary condition for e was varied in order to optimize the fit of theoretically obtained profiles of turbulent kinetic energy with experimental data. The constant A was fixed to 0.85 according to Wu and Patterson (1989). The optimal values of L for the different turbulence models were compared with the projected height of the impeller blade (h). All three components of the mean velocity were compared with experimental data for the optimal ratio of L/h for six radial cross-sections in the tank.

The mean velocity field obtained from simulations showed good agreement with experimental data for all models, with somewhat better agreement for the k — e model. An optimal value of the ratio L/h was found to be equal to 2.0 for the k — ε model and 1.3 for the ASM. However, no such optimal value for the RSM could be determined in this study.     

生产羧基丁苯胶乳聚合釜的放大规律

根据羧基丁苯胶乳合成工艺的特点，乳液均成核机理和低皂聚合原理，拟定了聚合釜的放大规律应遵循的依据。通过冷模试验和工业性试验，推荐聚合釜适宜的搅拌器为改进四叶斜桨和四叶斜桨；回归试验数据得到改进四叶斜桨搅拌功能Ｎｐ＝２．７９（ＨＬ／Ｄ）｛（ｄ／Ｄ）＾－１４（ｂ２／Ｄ）＾０．８３－」（ｄ２－ｂ１）／Ｄ「＾－１４「（ｂ２－ｂ１）／Ｄ」＾０．８３×「（３－２ｂ１）／ｄ」＾５｝聚合釜。