Experimental Studies on Suspension of Solid Particles in a Low‐Shear Stirred Vessel

A low‐shear stirred vessel was explored. Experimental studies on the suspension of solid particles in solid‐liquid and gas‐solid‐liquid systems were conducted to examine the performance of this new reactor. The method based on the power number curve was modified to determine the critical impeller speeds required for just complete off‐bottom suspension of solids under non‐gassed (N_js) and gassed conditions (N_jsg) in this reactor, and a PC‐6A fiber‐optic probe for the measurement of solid distribution was used to complementarily validate this method. A more homogeneous flow field was gained with a draft tube installed, so that the standard deviations of average shear rate and maximal shear rate are reduced. The modified power consumption method can determine N_js and N_jsg, and the values of N_js with a draft tube are much lower than those without it. N_jsg increases slightly with increasing gas flow rate, and N_jsg with a higher solid weight fraction is larger in this lower‐shear reactor.     

Effect of Gravity on the Hydrodynamics in an Unbaffled Stirred Vessel

The hydrodynamics in an unbaffled stirred vessel were simulated in order to highlight the effect of gravity on pressure and velocity distributions. Two fluids with different viscosity were studied for the laminar and turbulent flow regimes, respectively. The simulation results were compared with experimental data from the literature. Results indicate that for the higher‐viscosity fluid, gravity only affects static pressure and that the effects of gravity on velocity and dynamic pressure are negligible. For the lower‐viscosity fluid, however, gravity imposes a pronounced impact on static pressure, dynamic pressure, velocity, and turbulent kinetic energy. These findings indicate that careful consideration is necessary for the role that gravity plays in the study of free‐surface hydrodynamics in unbaffled stirred vessels.     

Optical Measurement Method of Particle Suspension in Stirred Vessels

Suspending particles in liquids is an important and versatile case for industrial stirring processes. By using advanced optical, non‐invasive measurement techniques like particle image velocimetry (PIV), it is possible to gain deep insights into the involved fluid dynamics without affecting the flow. However, for suspensions, the application of PIV is not trivial since both, suspended and tracer particles are present and need to be discerned during experiments. The here presented method development solves this problem and thus leads to a better insight into turbulent kinetic energy distribution, which can be utilized for process optimization through improved stirred vessel design.     

Energy Dissipation Rates of Newtonian and Non‐Newtonian Fluids in a Stirred Vessel

Energy dissipation rates of water and glycerol as Newtonian fluids and carboxyl methyl carbonate solution as non‐Newtonian fluid in a stirred vessel are investigated by 2D particle image velocimetry and compared. Mean velocity profiles reflect the Reynolds (Re) number similarity of two flow fields with different rheological properties, but the root mean square velocity profiles differ in rheology at the same Re‐number. Energy dissipation rates are estimated by direct calculation of fluctuating velocity gradients. The varying energy dissipation rates of Newtonian and non‐Newtonian fluids result from the difference in fluid rheology and apparent viscosity distribution which decides largely the flow pattern, circulation intensity, and rate of turbulence generation.     

A Langrangian Study of Solids Suspension in a Stirred Vessel by Positron Emission Particle Tracking (PEPT)

A technique of Positron Emission Particle Tracking (PEPT) was used to obtain information on the flow behavior of coarse particles suspended in pseudoplastic liquids agitated by axial‐hydrofoil Lightnin impellers A320 and A410. PEPT enables the position of a 600 μm radioactive particle tracer inserted inside one of the suspended particles to be detected many times per second and its full trajectory followed inside the vessel. Particle trajectory analysis yielded information on particle circulation, velocity distribution, and spatial occupancy. The minimum speed for complete particle suspension, N_js, was also determined. The well‐known Zwietering correlation failed to predict the measurements by a substantial margin, suggesting that it is inadequate for viscous non‐Newtonian liquids.     

Positron Emission Particle Tracking for Liquid-Solid Mixing in Stirred Tanks

Mixing in stirred tanks is vital to a wide range of industrial processes, typically requiring solids to be fully suspended and evenly distributed. The quality of suspension and mixing is typically measured visually. Such measurements are thus subject to human interpretation and can only feasibly be conducted in transparent systems – an uncommon condition in industrial systems. Visual measurements of homogeneity must also infer full 3D distributions of particles solely from the observation of a limited section thereof. This work details methods by which a system's homogeneity and state of suspension may be measured and quantified with no human interpretation, which can extract information from opaque systems and consider full 3D data acquired throughout the interior of a given system.     

Flow Fields in Stirred Vessels Depending on Different Internal Heat Exchangers and Vessel Bottoms

This study provides the influence of different heat exchanger internals (helical pipe coils, heating plugs, pipe registers) and reactor bottom shapes (torispherical/dished (Kloepper‐shape), hemispherical, and flat) on the flow field, the turbulent kinetic energy, and the ratio of tangential flow in stirred vessels, based on extensive stereo PIV measurement series in refractive index‐matched, optically completely accessible systems. The investigations impressively show advantages and disadvantages of the various equipment, which have a massive influence on both heat transport and the flow.     

CFD Prediction of Flow and Homogenization in a Stirred Vessel: Part II Vessel with Three and Four Impellers

This article deals with CFD simulations of flow inside stirred vessels equipped with three and four radial or axial impellers mounted on the same shaft. A comparison was made between simulated data and experiments for one‐ and two‐impeller systems and was presented in Part I [1]. The effect of the lowest impeller off‐bottom clearance, number of impellers used, and impeller type on the tracer distribution was studied. The simulations were mainly focused on the grid size and type and the analysis of the concentration curves in each impeller section. The predicted velocity fields, power and pumping numbers, concentration curves, and mixing times were validated with experimental data. The simulation results show the significant influence of the grid density on the velocity profiles and power and pumping numbers in contrast to the low impact on the concentration curves. A better prediction of the concentration curves was reached when radial impellers were used; the mixing times were generally over‐predicted.     

CFD Prediction of Flow and Homogenization in a Stirred Vessel: Part I Vessel with One and Two Impellers

A simulation of flow field and tracer homogenization was performed using the commercial CFD software FLUENT 6.1. The aim is to investigate the potential of CFD software to predict concentration distribution of added tracer in cylindrical vessels. The calculated results – dimensionless velocity profiles, power and pumping numbers, dimensionless concentration curves, and mixing times – were compared with experiments in stirred vessels. In Part I, the study was performed for vessels agitated by one or two impellers on a centric shaft. Two different impellers were used – a 6‐bladed 45° pitched blade turbine and a standard Rushton turbine. The standard k‐? turbulence model and multiple reference frames method were used for the simulations. The influence of the grid type was also investigated; three types of grid – a structured, unstructured and a special user‐defined grid – were studied.     

搅拌槽内的气泡尺寸分布

在槽径分别为Φ０．２８７ｍ、Φ０．４９５ｍ、Φ１．１００ｍ三个几何相似的搅拌槽内，采用双电导探针法测定了搅拌槽内上、下循环区及叶轮区的气泡尺寸分布，研究了单位液体体积搅拌功率、表现气速及搅拌槽放大过程对气泡尺寸的影响规律以及气泡尺寸的空间分布规律，并得到了相应的经验关联式，为气－液搅拌槽的设计放大提供参考。     

纯碱颗粒级配对平板玻璃熔制质量的影响

纯碱是平板玻璃生产中的一种重要原料 ,其粒度大小对玻璃的熔制存在明显的影响。通过大量的熔化、澄清实验研究纯碱的不同粒度以及颗粒级配对玻璃熔化、澄清质量的影响 ,从而确定符合生产需要的纯碱颗粒级配的优化范围 ,并从理论上加以探讨。过粗的纯碱颗粒不利于玻璃的熔制 ,其上限应控制在 2 6目左右 ,而纯碱细粉的含量则应控制在合适的范围内。     

Comparison of Experimental and Computational Particle Trajectories in a Stirred Vessel

A particle trajectory in a turbulent flow is measured by a 3-dimensional tracking technique and compared with the pattern calculated by a Lagrangian model. The geometry chosen is a standard vessel provided with a Rushton turbine. First, the flow field is simulated using the commercial Fluent package. The impeller global performance is determined. The dimensionless numbers are calculated: t_c, N_QP, N_P. These results are validated by LDV data. The numerical particle trajectory is compared to the experimental trajectory, and the reliability of the numerical trajectory is proved. Finally, some news tools for analyzing the flow are presented. Useful information is included in the long particle trajectory, which enables one to compute a probability of presence. The fluid dynamic behavior is visualized by Poincaré sections.     

移动容器加热结构对流体分布影响的研究

利用数值模拟的方法,研究了一种典型的移动式压力容器外置式加热管连接处开孔对管内流动性能的影响。开孔的目的是为了均衡不同纵向加热管内的流量,充分发挥每根加热管的传热性能。分析了不同小孔直径对加热管内流量和压降的影响。结果表明,孔径的减小使流体分布更加对称,但同时也使管内压降剧增。因此孔径的选取需要综合考虑流量和压降两种因素的影响。     

分别粉磨对矿渣水泥颗粒分布以及性能的影响

本文从矿渣和熟料的易磨性和粉磨动力学方面,解释了共同粉磨和分别粉磨的矿渣水泥颗粒分布产生差异的原因,总结并分析了两种不同工艺对矿渣水泥和混凝土性能的影响。     

乙氧基镁催化剂粉末粒度及粒度分布测定的研究

用乙醇做分散介质,用激光粒度测定仪测定四个乙氧基镁催化剂粉末试样的粒度及粒度分布,测试快速、准确。试验结果显示乙氧基镁（德国）催化剂粉末粒度最小,粒度分布集中,在四个样品中质量最好,试验结果令人满意。     

双层翼型桨搅拌槽内流动特性的PIV研究

在直径0.476 m的搅拌槽内,采用粒子图像测速技术对双层三叶CBY翼型桨搅拌槽内的流场进行了研究,考察了层间距、浸没深度和离底高度等参数对流场分布的影响. 结果表明,层间距H2≤0.6T(T为搅拌槽直径)时,槽内可形成整体的轴向循环流动,H2≥0.7T时槽内将产生分区流动现象. 浸没深度对桨叶排出流区域的速度影响很小. 降低下层桨的离底高度能加强下层桨的径向流动,并增大上层桨叶轮区和循环区流体的轴向流动.     

搅拌槽内固液两相流的数值模拟及功率计算

使用计算流体动力学的方法对搅拌槽中的流场进行模拟,得到搅拌槽中液体的流动状况和体积分数分布。对流场分布规律、固体颗粒体积分数特点加以分析,进而利用模拟出的数据计算搅拌轴的功率,为搅拌器的设计提供参考。     

Development of a networks-of-zones fluid mixing model for an unbaffled stirred vessel used for precipitation

Reactive acid-alkali tracers have been deployed to capture the macromixing and partial segregation behaviour in an unbaffled stirred vessel. This configuration is often used in precipitators to avoid inadvertent solid accretions on vessel internals. The macromixing behaviour for semi-batch addition with visualisation of reactive (acid-alkali) tracers has been acquired via video images which are rendered visible using phenolphthalein as indicator. By means of visual reality modelling, in which computer graphics are used to reconstruct and closely mimic the experimentally visualised fluid mixing “scenes”, the parameters for a networks-of-zones mixing model for the unbaffled semi-batch case have been established. The model can then be used for predicting precipitation behaviour for single-jet and other modes of operation. Some illustrative examples for barium sulphate, showing the underlying supersaturation fields in 3-D and the consequent time evolving particle size distributions, are presented and discussed for a single jet case.     

焦油渣含量及其粒度分布测定方法的研究

采用离心———抽提相结合的方法测定焦油渣含量,并运用激光粒度分析技术测定焦油渣粒度分布。结果表明,焦油中焦油渣以<10μm微粒组成为主,占总渣量88%～97%。     

A Multi‐Block Approach to Obtain Angle‐Resolved PIV Measurements of the Mean Flow and Turbulence Fields in a Stirred Vessel

Two‐dimensional Particle Image Velocimetry (PIV) measurements have been used to characterize the complex turbulent flow generated by a T/3 45° pitched‐blade down‐flow turbine, operated at Re ≈ 5 · 10⁴, in a fully turbulent stirred vessel. To maintain high spatial resolution when viewing the whole vessel, a multi‐block approach has been developed, which combines data from different fields of view into a composite flow map. Using 500 measurements of instantaneous u and v velocity fields, angle‐resolved mean velocity maps and turbulence properties, such as the RMS velocities and the turbulence kinetic energy, have been estimated near to the blade, as well as in the bulk of the vessel, at a spatial resolution of between 1 and 2 mm. Vorticity maps have also been calculated to help visualize the trailing vortex structures close to the impeller blades and integral length scales have been estimated from the two‐dimensional spatial auto‐correlation function. It is shown than the common assumption that the integral length scale is about half the blade width is an overestimate close to the impeller and an underestimate far from the impeller.