流体流动型态对膜通量影响的实验和计算流体力学研究

This paper reports a study on the role of fluid flow pattern and dynamic pressure on the permeate flux through a micro filtration membrane in laboratory scale. For this purpose, a dead-end membrane cell equipped with a marine type impeller was used. The impeller was set to rotate in the clockwise and counter clockwise directions with the same angular velocities in order to illustrate the effect of rotation direction on permeate flux. Consequently, permeate fluxes were measured at various impeller rotational speeds. The computational fluid dynamics (CFD) pre-dicted dynamic pressure was related to the fluxes obtained in the experiments. Using the CFD modeling, it is proven that the change in dynamic pressure upon the membrane surface has direct effect on the permeate flux.     

基于精细自由基反应机理的丙烷裂解炉炉管CFD模拟(英文)

In the radiant section of cracking furnace, the thermal cracking process is highly coupled with turbulent flow, heat transfer and mass transfer. In this paper, a three-dimensional simulation of propane pyrolysis reactor tube is performed based on a detailed kinetic radical cracking scheme, combined with a comprehensive rigorous computational fluid dynamics（CFD） model. The eddy-dissipation-concept（EDC） model is introduced to deal with turbulence-chemistry interaction of cracking gas, especially for the multi-step radical kinetics. Considering the high aspect ratio and severe gradient phenomenon, numerical strategies such as grid resolution and refinement, stepping method and relaxation technique at different levels are employed to accelerate convergence. Large scale of radial nonuniformity in the vicinity of the tube wall is investigated. Spatial distributions of each radical reaction rate are first studied, and made it possible to identify the dominant elementary reactions. Additionally, a series of operating conditions including the feedstock feed rate, wall temperature profile and heat flux profile towards the reactor tubes are investigated. The obtained results can be used as scientific guide for further technical retrofit and operation optimization aiming at high conversion and selectivity of pyrolysis process.     

搅拌槽内微观混合研究的回顾与展望(英文)

Mixing problems are most likely encountered and sometimes can be severe in scaling-up projects.Micro-mixing is an important aspect for fast or quasi-instantaneous reactions.Poor micro-mixing might produce more undesired by-products,leading to higher purification costs.This paper gives an extensive review and analysis of micro-mixing studies in single-and multiphase stirred tanks.The relevant experiment techniques,micro-mixing models and numerical approaches are critically reviewed and analyzed with remarks and perspectives.The reported studies on two-phase micro-mixing experiments and on the impact of the presence of the dispersed phases on turbu-lence have been limited to a narrow range of conditions.More importantly,disparities widely exist among different reports.Both Lagrangian and Eulerian models are based on oversimplified assumptions,which may lead to uncer-tainties or even unrealistic results.A heuristic model,which is from the perspective of CFD(computational fluid dynamics) and can cover the whole spectrum of scales and also focus on every sub-process,is desired in the future.     

搅拌釜内固-液悬浮体系的CFD-DEM模拟(英文)

Computational fluid dynamics-discrete element method （CFD-DEM） coupled approach was employed to simulate the solid suspension behavior in a Rushton stirred tank with consideration of transitional and rotational motions of millions of particles with complex interactions with liquid and the rotating impeller. The simulations were satisfactorily validated with experimental data in literature in terms of measured particle velocities in the tank. Influences of operating conditions and physical properties of particles （i.e., particle diameter and density） on the two-phase flow field in the stirred tank involving particle distribution, particle velocity and vortex were studied. The wide distribution of particle angular velocity ranging from 0 to 105 r·min-1 is revealed. The Magnus force is comparable to the drag force during the particle movement in the tank. The strong particle rotation will generate extra shear force on the particles so that the particle morphology may be affected, especially in the bio-/polymer-product related processes. It can be concluded that the CFD-DEM coupled approach provides a theoretical way to under-stand the physics of particle movement in micro-to macro-scales in the solid suspension of a stirred tank.     

规整填料塔内两相流动的三维计算流体力学建模(英文)

Characterizing the complex two-phase hydrodynamics in structured packed columns requires a power- ful modeling tool. The traditional two-dimensional model exhibits limitations when one attempts to model the de- tailed two-phase flow inside the columns. The present paper presents a three-dimensional computational fluid dy- namics （CFD） model to simulate the two-phase flow in a representative unit of the column. The unit consists of an CFD calculations on column packed with Flexipak 1Y were implemented within the volume of fluid （VOF） mathe- matical framework. The CFD model was validated by comparing the calculated thickness of liquid film with the available experimental data. Special attention was given to quantitative analysis of the effects of gravity on the hy- drodynamics. Fluctuations in the liquid mass flow rate and the calculated pressure drop loss were found to be quali- tatively in agreement with the experimental observations.     

从超音速蒸汽喷嘴到过冷水直接接触冷凝的数值模拟(英文)

The phenomenon of direct-contact condensation,used in steam driven jet injectors,nuclear reactor emergency core cooling systems and direct-contact heat exchangers,was investigated computationally by introducing a thermal equilibrium model for direct-contact condensation of steam in subcooled water.The condensation model presented was a two resistance model which takes care of the heat transfer process on both sides of the interface and uses a variable steam bubble diameter.The injection of supersonic steam jet in subcooled water tank was simulated using the Euler-Euler multiphase flow model of Fluent 6.3 code with the condensation model incorporated. The findings of the computational fluid dynamics(CFD) simulations were compared with the published experimental data and fairly good agreement was observed between the two,thus validating the condensation model.The results of CFD simulations for dimensionless penetration length of steam plume varies from 2.73-7.33,while the condensation heat transfer coefficient varies from 0.75-0.917 MW·(m 2 ·K) -1 for water temperature in the range of 293-343 K.     

附加湍流器强化陶瓷膜微滤过程的研究

通过在管式陶瓷膜内设置不同结构形式的湍流器，试验和比较了不同主体流速和膜滤压差等工艺条件下的膜滤速率及能耗，分析了湍流器所产生的强化膜滤过程的效果以及试验条件下的一般规律。     

集成反应器微滤过程中湍流促进器的研究

采用湍流促进器对陶瓷膜分离TiO2超细粒子悬浆液微滤过程进行了强化研究。考察了湍流促进器结构参数对强化过程的影响,确定了合适的湍流促进器为螺旋式湍流促进器,其结构参数为螺杆直径2 mm,螺距20 mm;探讨了湍流促进器的强化机理,同时对湍流促进器的有效性进行了实验考察。研究表明,采用这种方法提高了渗透通量。     

湍流促进器强化陶瓷膜微滤CaSO_4悬浆液的研究

研究了湍流促进器对19通道陶瓷膜微滤CaSO4悬浆液过程的影响,优化湍流促进器的优化设计参数。确定螺旋式湍流促进器的强化效果较好。设置方式为内圈螺间距4 mm,外径3.4 mm和外圈螺间距8 mm,外径3.4 mm的组合式,螺旋湍流促进器的强化效果最佳,膜通量提高23.76%,并有效地改善了膜通道内流体流动状态。     

交叉间断肋片与凹槽强化传热的实验与数值研究(英文)

Experimental and numerical investigations have been conducted to study turbulent flow of water and heat transfer characteristics in a rectangular channel with discontinuous crossed ribs and grooves.The tests investigated the overall heat transfer performance and friction factor in ribbed and ribbed-grooved channels with rib angle of 30°.The experimental results show that the overall thermo-hydraulic performance for ribbed-grooved channel is increased by 10%-13.6% when compared to ribbed channel.The investigation on the effects of different rib angles and rib pitches on heat transfer characteristics and friction factor in ribbed-grooved channel was carried out using Fluent with SST(shear-stress transport) k-ω turbulence model.The numerical results indicate that the case for rib angle of 45° shows the best overall thermo-hydraulic performance,about 18%-36% higher than the case for rib angle of 0°.In addition,the flow patterns and local heat transfer characteristics for ribbed and ribbed-grooved channels based on the numerical simulation were also analyzed to reveal the mechanism of heat transfer enhancement.     

陶瓷膜分离CaCO_3悬浆液强化过程的研究

在固定反冲条件下,研究了螺旋型湍流促进器及其螺杆直径、螺间距等参数对19通道无机陶瓷膜分离轻质碳酸钙悬浆液的强化过程,确定了湍流促进器的优化设计参数,并在优化条件下,对操作压力、操作温度、膜面流量和溶液浓度等操作条件进行了研究。     

搅拌萃取塔内单相流动不同雷诺平均湍流模型结果的比较

The flow field of liquid phase (water) of agitated extraction columns is simulated with the help of computational fluid dynamics (CFD). Four kinds of Reynolds-averaged turbulence models, i.e. the standard k-ε model, the RNG (renormaiization group) k-ε model, the realizable k-ε model and the Reynolds stress model, are compared in detail in order to judge which is the best model in terms of the accuracy, less CPU time and memory required. The performance of the realizable k-ε model is obviously improved by reducing the model constant from c2 = 1.90 to c2 = 1.61. It is concluded that the improved realizable k-ε model is the optimal model.     

Experimental and CFD Heat Transfer Studies of Al2Oa-Water Nanofluid in a Coiled Agitated Vessel Equipped with Propeller

This paper presents the heat transfer characteristics of A1203-water nanofluid in a coiled agitated vessel with propeller agitator. The experimental study was conducted using 0.10%, 0.20% and 0.30% volume concentra tion of A1203-water nanofluids. The results showed considerable enhancement of convective heat transfer using the nanofluids. The empirical correlations developed for Nusselt number in terms of Reynolds number, Prandtl number, viscosity ratio and volume concentration fit with the experimental data within ±10%. The heat transfer characteris tics were also simulated using computational fluid dynamics using FLUENT software with the standard ke model and multiple reference frame were adopted. The computational fluid dynamics （CFD） predicted Nusselt number agrees well with the experimental value and the discrepancy is found to be less than ＋8%.     

Novel aeration of a large‐scale flat sheet MBR: A CFD and experimental investigation

Having previously established that the hydrodynamic effect introduced by slug bubbles is more effective and economic in fouling amelioration in flat sheet MBRs (FSMBR) than conventional bubbling, this work is focused on its implementation in a commercial FSMBR. The overall objective is to enhance the hydrodynamic effect on fouling control through the use of two‐stage large‐sized bubble development (coalescence and split). Computational Fluid Dynamics (CFD) was used to predict hydrodynamic features and substantial agreement was observed with experimental measurements. The critical height for bubble development space was determined to be circa 250 mm. Slug bubbles could be introduced into 14 channels, resulting in six‐fold stronger shear stress than that from single bubbles. Energy demand could be reduced by circa 50% compared with industry average usage and the shear stresses developed would, for most applications, be sufficient to ameliorate fouling. Furthermore, the specific air demand per permeate would be halved. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2721–2736, 2018     

纳米ZrO2修饰Al2O3微滤膜处理废冷却液的实验研究

膜分离技术处理含油废水表现出明显的技术优势,其应用还应解决膜表面易被污染,分离效果逐渐下降的问题,主要原因是由于油滴的易变形性引起的膜堵塞。为解决膜渗透通量与膜选择性的矛盾,本文在市售Al2O3微滤膜孔道表面制备纳米ZrO2涂层,利用纳米涂层改变微滤膜的表面亲水憎油性,阻止油滴的变形。研究了陶瓷膜修饰条件和膜过滤操作参数对膜渗透通量的影响,结果表明:纳米涂层能有效提高微滤膜的渗透通量。膜面流速的增加在一定程度上能提高膜渗透通量,但超过一定程度后,增加不明显。当膜面流速为7m/s,修饰陶瓷膜的最大渗透通量为280 L.m-2.h-1,油截留率为96.4%。纳米涂层修饰微滤膜具有良好的抗油滴污染性能,能有效实现稳定含油废水的油水分离。     

微组织组装方法的实验研究及CFD模拟

提出利用微组织组装工程化组织移植物的新思想,并进行了初步实验研究和计算流体力学分析。利用可降解大孔微载体与组织种子细胞共培养,形成大量微组织,然后将微组织置于灌注反应器内培养,使微组织聚集形成功能化大型组织。实验结果表明构建的大型组织在细胞密度、细胞分布以及基质分泌等各方面优于传统方法。模拟分析也说明采用新的方法能够比传统方法获得更好的物质传递效果以及流体力学环境,能够满足组织细胞对氧以及其他营养物质的需求。     

CFD simulation on membrane distillation of NaCl solution

A computational fluid dynamics (CFD) simulation that coupled an established heat and mass transfer model was carried out for the air-gap membrane distillation (AGMD) of NaCl solution to predict mass and heat behaviors of the process. The effects of temperature and flowrate on fluxes were first simulated and compared with available experimental data to verify the approach. The profiles of temperature, temperature polarization factor, and mass flux adjacent to the tubular carbon membrane surface were then examined under different feed Reynolds number in the computational domain. Results show that the temperature polarization phenomena can be reduced, and mass flux can be enhanced with increase in the feed Reynolds number.     

CFD用于机械搅拌生化反应器液固两相混合的研究

运用计算流体力学(CFD)技术对机械搅拌生化反应器中液固两相混合进行数值模拟。应用旋转参考坐标系处理搅拌桨与挡板之间的相对运动,建立液固两相双流体模型,采用有限体积法(FVM)求解流体流动控制方程组。数值计算结果与实验值较为吻合,偏差在10％以下。研究结果对生化反应器的优化设计及放大和混合的基础研究具有参考价值。     

非对称陶瓷膜管渗透性能的CFD模拟研究

陶瓷膜因其化学稳定性好、机械强度大等优点得到广泛应用。计算流体力学(CFD)的快速发展使得计算模拟成为研究和优化陶瓷膜管结构性能的有效手段。为了优化非对称结构陶瓷膜管的结构和操作参数,对其渗透性能进行了CFD计算模拟。针对非对称结构陶瓷膜管的膜层和过渡层的厚度在10 μm级的特点,采用Navier-Stokes方程和Darcy定律来分别描述膜管内和膜多孔介质内的纯水流动,利用多孔介质模型描述膜管的主体支撑层,用多孔跳跃边界简化膜管的膜层和过渡层,利用Konzey-Carmen方程对膜元件各层的渗透率进行估算。计算结果与实验值吻合较好,为优化陶瓷膜管的通道结构提供了便捷的工具。