垂直惰性阳极铝电解槽内的析气行为

垂直惰性阳极铝电解槽内,析气行为会影响氧化铝浓度分布和电流效率。利用新设计的透明电解槽进行了电解试验,观察了大尺寸惰性阳极气泡的析出及逸出过程。试验结果表明：在阳极底掌下,气泡进行周期性的生长、长大、并聚和脱离,但大尺寸阳极上气泡的滑动和并聚过程与小尺寸阳极上的不同。阳极工作面上则形成了气泡群,新形成的气泡迅速脱离。紧贴着阳极的气泡运行速度慢,外层的气泡运动速度快。所有气泡最终都经液面逸出,大部分气泡到达液面时立即逸出,少部分未及时逸出的气泡随着电解质做一段水平运动后才逐步逸出。测量到的惰性阳极的气泡运动速度为0.006~0.445 m·s^-1,底部的气泡运动速度分布范围宽,然而,受电解质的限制,中上部的范围窄。     

垂直惰性阳极铝电解槽内的析气行为

垂直惰性阳极铝电解槽内,析气行为会影响氧化铝浓度分布和电流效率。利用新设计的透明电解槽进行了电解试验,观察了大尺寸惰性阳极气泡的析出及逸出过程。试验结果表明:在阳极底掌下,气泡进行周期性的生长、长大、并聚和脱离,但大尺寸阳极上气泡的滑动和并聚过程与小尺寸阳极上的不同。阳极工作面上则形成了气泡群,新形成的气泡迅速脱离。紧贴着阳极的气泡运行速度慢,外层的气泡运动速度快。所有气泡最终都经液面逸出,大部分气泡到达液面时立即逸出,少部分未及时逸出的气泡随着电解质做一段水平运动后才逐步逸出。测量到的惰性阳极的气泡运动速度为0.006~0.445 m·s~(-1),底部的气泡运动速度分布范围宽,然而,受电解质的限制,中上部的范围窄。     

高温铝牺牲阳极在油田污水中的性能测试

牺牲阳极保护是阴极保护应用的一种重要方式 ,已广泛用于船舶、港口设施、海洋工程、埋地管线以及石化、电力、市政等领域。原油贮罐底部常常沉淀有一定量的原油污水 ,这类原油污水中往往含有大量电解质 ,极易对罐体产生腐蚀 ,所以采用牺牲阳极对其进行阴极保护十分必要。另外 ,由于原油贮罐在贮油过程中 ,根据工艺需要 ,常需要加温 ,而普通牺牲阳极在高温条件下 ,电流效率低 ,发生电流小 ,不能满足保护要求。青岛海洋腐蚀研究所新研制成功的高效铝牺牲阳极 ,具有电流效率高、电位分布均匀等特点 ,适用于原油贮罐罐底内壁在高温环境下的阴极…     

铝用炭素材料(续6)

1 1 8侧插自焙阳极 (ｈｏｒｚｏｎｔａｌｓｏｄｅｒｂｅｒｇａｎｏｄｅ)侧插自焙阳极是阳极导电棒从侧部插入的连续自焙阳极。它是侧插自焙阳极铝电解槽的重要部件 ,在电解过程中 ,强大的直流电由侧插钢棒通过炭素阳极导入铝电解槽 ,在炭素阳极底部发生分解氧化铝的复杂电化学反应。随着电解过程的进行 ,炭阳极底部不断地消耗 ,每天消耗高度平均为 1～ 2ｃｍ ,要定期向阳极框架内添加阳极糊以保持阳极、阳极锥体高度及连续正常工作。侧插自焙阳极的下部浸在电解质里 ,阳极四周的两大面或四面通常钉有多排阳极棒 ,整个阳极的温度从下至上逐渐…     

氧化铝在冰晶石熔体中溶解的研究方法评述

氧化铝溶解度和溶解速率的高低将直接影响电解铝工业的生产是否正常运行,因此它们是电解铝工业的重要指标。本文将对冰晶石熔体中氧化铝溶解度和溶解速度的研究方法进行综合评述,为下一步新型低温电解质的研究提供参考。     

石英质高温涂料的研究与应用

1 研究匣钵涂料的意义与目的在陶瓷生产中,为防止制品在高温焙烧时与匣钵内钵底发生粘连和防止匣钵之间粘连,普遍采用的办法是在匣钵内钵底以及匣钵口部涂一层以工业氧化铝粉为主要原料制备的一种高温浆,简称氧化铝浆。此法虽然使用效果较好,但也存在明显的不足。     

SOFC氧离子导体电解质材料的研究进展及性能优化策略

典型的固体氧化物燃料电池(SOFC)由致密电解质、多孔阴极和阳极三部分构成。其中,电解质介于阴极和阳极之间,是一种具有全固态结构的氧化物陶瓷材料。电解质是SOFC的核心部件之一,是电池工作温度和电池性能的决定性因素。目前,对于高温电解质材料的研究与应用已经相对成熟。但是,在电池高温运行条件下,会导致电极和电解质界面反应、密封困难及使用寿命变短等问题。因此,SOFC电解质的发展逐渐趋向于中温化。但随着工作温度的降低,电解质欧姆阻抗(Ro)势必增大,使得电池的电导率下降。基于此,电解质在中温下的性能提升以及优化近年来备受关注。文中综述了几种不同类型的氧离子导体电解质最新研究进展,并论述了SOFC中低温运行条件下电解质性能提升的主要优化策略。     

镍铁尖晶石基金属陶瓷惰性阳极的电解腐蚀行为

采用粉末冶金法制备了10%Ag-NiFe2O4/NiO金属陶瓷惰性阳极,阳极为圆柱形,直径50 mm,高15 mm. 在960℃下进行电流密度为0.8 A/cm2的铝电解实验,电解时间为10 h. 研究了阳极在Na3AlF6-5%CaF2-5%Al2O3熔体中的腐蚀行为. 电解后的阳极外观尺寸略有变化,但没有发生阳极肿胀及阳极表面起层、剥离的现象,表现出较好的耐腐蚀性. 计算得到阳极腐蚀率为1.5′10-4 g/(cm2·h),折算为13 mm/a. 电解所得铝的纯度在92%~93%之间. 对腐蚀后阳极的表面分析发现,陶瓷相中Ni和Fe组元并不以化学计量数溶解,陶瓷组元的Fe2O3比NiO优先溶解进入电解质. 正对阴极的阳极表面和背对阴极的阳极表面氧元素的含量不同,前者中氧元素多于后者,说明在阳极正对阴极的表面发生析氧反应更剧烈一些,一部分新生态的氧与阳极表面的金属发生氧化反应生成Ag3O4. 对腐蚀后阳极断面进行分析发现,电解质渗透进入阳极内部,与陶瓷基体离解产生的Fe2O3发生反应,生成FeF3沉积在阳极的空隙中.     

阳极氧化电压对多孔氧化铝膜生长过程的影响

以草酸溶液为电解质,采用两步电化学阳极氧化法制备了氧化铝有序多孔膜,研究了阳极氧化电压对多孔膜生长过程及形貌的影响. 结果表明,电流密度、生长速率及孔径、孔间距随电压的升高而增大,而膨胀因子与电压呈线性关系. 氧化铝膜的孔隙率保持在12%左右,与电压基本无关.     

草酸溶液中多孔氧化铝的制备及机理研究

以草酸溶液为电解质,采用两次电化学阳极氧化法制备氧化铝有序多孔膜,研究了不同阶段孔洞的形态结构以及孔洞的排布,发现自组织过程主要是在第一次阳极氧化的过程中实现的,第二次阳极氧化只是在第一次的基础上实现孔的有序定向生长。     

Effects of anode-cathode distance on the cell potential and electrical bath resistivity in an aluminium electrolysis cell with a sloping TiB2 composite cathode

A study of the effects of anode-cathode distance (ACD) on the cell potential and electrical bath resistivity in a laboratory scale cell that utilizes a sloping TiB₂ composite cathode shows an increasing bath resistivity as the ACD decreases, due to a simultaneously increasing gaseous phase fraction in the electrolyte. The effective bath resistivity was found to increase rapidly after ACD=10 mm and was proportional to the inverse of ACD within this low ACD range studied (2–10 mm). Addition of NaCl to the electrolyte (5.5 wt%) lowered the electrical resistivity by increasing the conductivity of the electrolyte, and at low ACD it also lowered the bubble contribution to the bath resistivity, most likely due to changes in the hydrodynamic properties of the system. Lowering the cryolite ratio (i.e. molar ratio of NaF to AlF₃) resulted in a higher electrical resistivity in the electrolyte by decreasing the conductivity of the melt, as well as by changing the hydrodynamic properties of the melt, leading to an increased bubble contribution to bath resistivity at low ACD. An increase in temperature resulted in a reduced bubble contribution at low ACD in a similar manner as the NaCl addition. From these results, it is clear that for a commericial process, reduction of the ACD and optimization of process conditions to reduce the effect of bubbles should allow significant savings in the energy requirements of the Hall-Heroult process.     

On the second-order moment turbulence model for simulating a bubble column

Two versions of the second-order moment two-phase turbulence model are proposed in this study for simulating bubble-liquid two-phase turbulent velocity fluctuations and their interactions in bubble-liquid flows under the dispersed bubble regime. One of them is a full transport equation model; the other is an algebraic stresses model. The proposed model is used to simulate liquid and gas mean velocities, gas volume fraction, liquid and gas Reynolds stresses and turbulent kinetic energy in a 2-D bubble column. Furthermore, the bubble and liquid velocities, Reynolds stresses and gas volume fraction are measured using the PIV. The simulation results are in good agreement with the PIV results and experimental data in the literature. The studies reveal the liquid recirculation and bubble up-rising flow patterns, and anisotropic liquid and bubble normal Reynolds stresses. Bubble fluctuation is observed to be stronger than liquid fluctuation. Moreover, both the liquid velocity gradient and bubble-liquid interaction are important for the generation of liquid turbulence.     

Measurements and numerical predictions of gas vortices formed by single bubble eruptions in the freeboard of a fluidised bed

Gas vortices generated in the freeboard of a bubbling fluidised bed have become the centre of increasingly more research due to the advances in experimental technology. The behaviour of gas flow in the freeboard of a bubbling fluidised bed is of interest for applications such as the gasification of coal where reactions of gas mixtures, as well as gas–particle heat and mass transfer take place. Knowledge of the hydrodynamics of the gas within the freeboard can be hard to characterise, especially the detailed behaviour of gases escaping from bubbles that erupt at the bed surface. In the present study, experiments were conducted on a rectangular three-dimensional gas–solid fluidised bed. The experiments used a particle imaging velocimetry (PIV) measurement technique to visualise and measure the gas flow within the freeboard after a single bubble eruption. A computational study was carried out using Eulerian–Eulerian, kinetic theory of granular flow approach with a quasi-static flow model and with LES used to account for gas turbulence. Results from a three dimensional simulation of the experimental fluidised bed were compared with experimental velocity profiles of gas flow in the freeboard of the gas–solid fluidised bed after a bubble eruption. The CFD simulations showed a qualitative agreement with the formation of the gas vortices as the bubble erupted. Consistent with experimental findings the CFD simulations showed the generation of a pair of vortices. However, the simulations were unable to demonstrate downward flow at the centre of the freeboard due to particles in free fall after a bubble eruption event was observed in the experiments. Velocity profiles from the CFD data are in reasonably good agreement with the characteristic trends observed in the experiments, whereas the CFD model was able to predict the gas vortices phenomena and the velocity magnitudes were over-predicted.     

二维鼓泡床内气液流动特性实验与数值模拟

采用高速摄像法测量了0.20 m×0.02 m×2.00 m拟二维床内气泡尺寸分布和流型等变化规律,结果表明,随着表观气速的增大,鼓泡床内依次呈现均匀鼓泡区、过渡区和湍动区3种形式,以气泡个数概率表示的气泡尺寸分布呈对数正态分布。以计算流体力学软件ANSYS CFX 10.0为平台,采用k-ε湍流模型和GRACE曳力模型对气液鼓泡床内流体动力学行为展开了数值模拟,其结果与实验值比较吻合。研究表明,从多相流理论出发的计算流体力学模拟方法可以用来预报鼓泡床内流型过渡等流体动力学特性。     

鼓泡床内气泡-液体两相湍流代数应力模型的数值模拟

现有的气泡 -液体两相流动的数值模拟中 ,或者不考虑湍流 ,或者仅仅考虑液体湍流 ,但是直接模拟和PIV测量结果都表明气泡由于尾迹的作用有强烈的湍流脉动 .本文首次推导和封闭了同时模拟气泡湍流脉动和液体湍流脉动的二阶矩输运方程两相湍流模型 ,并在此基础上建立了代数应力气泡 -液体两相湍流模型 .用代数应力模型模拟了二维矩形断面鼓泡床内气泡 -液体两相流动 .预报结果给出了气泡和液体两相速度场、两相Reynolds应力及湍动能分布和气泡体积分数分布 .模拟结果与PIV测量结果符合很好 ,表明了模型的合理性 .研究结果表明 ,原先静止的液体在气泡因浮力而产生的上升运动的作用下产生回流流动 ,而气泡则只有上升运动 .气泡速度始终大于液体速度 .在床内气泡湍流脉动确实始终很强烈 .液体则由于气泡的作用以及自身速度梯度产生的双重作用而发生湍流脉动 .气泡的脉动显著地大于液体的脉动 .两相湍流脉动都是各向异性的 ,而且气泡湍流脉动的各向异性比液体的更强烈     

鼓泡床内气液两相流动的二阶矩模型与代数应力模型的模拟比较

A full second-order moment(FSM) model and an algebraic stress (ASM) two-phase turbulence model are proposed and applied to predict turbulent bubble-liquid flows in a 2D rectangular bubble column.Predication gives the bubble and liquid velocities,bubble volume fraction,bubble and liquid Reynolds stresses and bubble-liquid velocity correlation.For predicted two-phase velocities and bubble volume fraction the is only silight difference between these two models,and the simulation results using both two models are in good agreement with the particle image velocimetry(PIV) measurements.Although the predicted two-phase Reynolds stresses using the FSM are in somewhat better agreement with the PIV measurements than those predicted using the ASM,the Reynolds stresses predicted using both two models are in general agreement with the experiments.Therefore,it is suggested to use the ASM two-phase turbulence model in engineering application for saving the computation time.     

Measurement and CFD simulation of single-phase flow in solvent extraction pulsed column

A CFD (computational fluid dynamics) model of a solvent extraction pulsed column has been developed and run with a single water phase. The results are compared with experimental measurements taken on a pilot scale column using PIV (particle image velocimetry).The pulsed column investigated had disk-doughnut internals and was operated under pulsing intensities ranging from 10 to 32.5 mm/s. PIV measurements of velocity were used to validate the CFD model and to characterise the pulsing flow of a single phase through the column. The CFD modelling was performed for the same geometry and operating conditions using a 2D computational grid and a low Reynolds Number k-ε turbulence model. An improved velocity prediction was achieved by adding a gap between the doughnut internal and the pulsed column wall. The combined measurements and predictions give insight into the effect of the geometry internals on the flow hydrodynamics in the pulsed column.     

Study on flow fields in a bioreactor with perforated blades

Flow fields of a gas–liquid fluid in a bioreactor with perforated blades were evaluated with the computational fluid dynamics and particle image velocimetry (PIV). The flow pattern of the fluid was the complex turbulence, and the fluid had preferable flow fields for fermentations. Using a rotating coordinate system and a sliding mesh method, a mesh of 24 × 16 × 80 (X × Y × Z) was selected due to its high accuracy and appropriate workload. The numerical results of the two‐phase flow model agreed well with the experimental results of the PIV, such as flow field characteristics and data curves. The RNG k–ε model was adopted, which could precisely simulate anisotropic flow fields around higher‐speed blades. Whole deviations of X‐, Y‐ and Z‐direction velocities ranged only from 5.4% to 10.5%, and continuous turbulence models could effectively simulate transfer procedures of the fluid. Because of its low cost, simplicity and easy of scale‐up, the bioreactor with perforated blades and its models mechanism of fluid microelements are expected to be efficient for its industrial amplification and application in food industry. © 2012 Canadian Society for Chemical Engineering     

Study on gas-liquid flow characteristics in stirred tank with dual-impeller based on CFD-PBM coupled model

Study on gas-liquid flow in stirred tank with two combinations of dual-impeller (six-bent-bladed turbine(6BT)+six-inclined-blade down-pumping turbine (6ITD),the six-bent-bladed turbine (6BT)+six-inclined-blade up-pumping turbine (6ITU)) was conducted using computational fluid dynamics (CFD) and popula-tion balance model (PBM) (CFD-PBM) coupled model.The local bubble size was captured by particle image velocimetry (PIV) measurement.The gas holdup,bubble size distribution and gas-liquid interfacial area were explored at different conditions through numerical simulation.The results showed that the 4 mm bubbles accounted for the largest proportion of 33％ at the gas flow rates Q =0.76 m3·h-1 and 22％ at Q =1.52 m3·h-1 for combined impeller of 6BT + 6ITU,while the bubbles of 4.7 mm and 5.5 mm were the largest proportion for 6BT + 6ITD combination,i.e.25％ at Q =0.76 m3·h-1 and 22％ at Q =1.52 m3·h-1,respectively,which indicated that 6BT + 6ITU could reduce bubble size effectively and promote gas dispersion.In addition,the gas holdup around impellers was increased obviously with the speed compared with gas flow rate.So it was concluded that 6ITU impeller could be more conductive to the bubble dispersion with more uniform bubble size,which embodied the advantages of 6BT + 6ITU combination in gas-liquid mixing.