Hydrodynamic characteristics of valve tray: Computational fluid dynamic simulation and experimental studies

In order to better understand the hydrodynamics of valve trays, air-water operation in an industrial scale tower with 1.2 m of diameter, consisting of two 14% valve trays, was studied. Experimental results of clear liquid height, froth height, average liquid holdup, dry pressure drop, total pressure drop, weeping and entrainment were investigated, and empirical correlations were presented. Then, a three-dimensional computational fluid dynamics (CFD) simulation in an Eulerian framework for valve tray with ANSYS CFX software was done. The drag coefficient, which was used in the CFD simulations, was calculated from the data obtained in the experiments. The simulation results were found to be in good agreement with experimental data at this industrial scale. The objective of the work was to study the extent to which experimental and CFD simulations must be used together as a prediction and design tool for industrial trays.     

立体旋流筛板空间气相流场的CFD模拟

应用STAR-CCM+软件,采用Realizable k-ε模型,对立体旋流筛板空间气相流场特性进行了数值模拟研究。结果表明:立体旋流筛板空间主要存在贴近筛板壁面的穿孔流动与两筛板间的旋流流动2种方式,气体经立体旋流筛板的流动过程分起旋阶段与旋流发展阶段。在贴近筛板壁面的区域,由内筒外壁至外筒内壁方向,穿孔流动速度在各流动阶段均呈增加的趋势;在两筛板间区域,起旋阶段,由内筒外壁至外筒内壁方向旋流流动速度值变化较小,沿旋流方向靠近下一块筛板区域的速度值较大;旋流发展阶段,由内筒外壁至外筒内壁方向旋流流动速度值呈先降低再增加的趋势,沿旋流方向靠近上一块筛板区域的速度值较大。在轴向不同高度区域,贴近筛板壁面的穿孔速度为中部最大、上部次之、下部最小;两筛板间的旋流流动速度为上部较小,中、下部较大。各区域速度值随着气相动能因子的增加而增加。     

Computational fluid dynamic simulation of fluid flow in a rotating packed bed

Rotating packed bed (RPB) has been widely used in absorption, desorption, distillation, oxidation, crystallization, precipitation, polymerization, and production of nanoparticles. RPB utilizes centrifugal acceleration to intensify the mixing and mass-transfer processes. Under high-gravity, molecule diffusions are much faster than under normal gravity. With the centrifugal force generated by rotation, RPBs have considerable high mass-transfer and micromixing performance. However, because of the complexity of fluid flow inside the RPB, the flow experiments do not easily lead to the deeper understanding on the fluid dynamics in an RPB. In this paper, computational fluid dynamics model and two-, three-dimensional physical models have been developed to describe the RPB. Numerical simulation of the fluid flow and pressure drop in dry bed in an RPB using commercial software, Fluent, as a computational platform has been carried out. Different fluid flow rates, rotator speeds and gas flow rates have been systematically investigated. The preliminary simulation results show that the models used to describe the RPB can give rise to better understanding of the flow in an RPB.     

F1型浮阀塔板两相流场的CFD模拟

利用FLUNENT软件采用欧拉(Euler)两相流模型模拟计算了FI型浮阀塔板在阀片全开状态时的气液两相流流场.模拟选用清液层高度作为衡量非稳态流场收敛判别标准,模拟的结果和实验测得的数据二者吻合较好,证明CFD方法是一种很有效的辅助浮阀塔板设计的手段.     

Computational fluid dynamics on the hydrodynamic characteristics of the conical cap tray

This paper addresses an investigation on the hydrodynamic behavior of a new type of cap trays called conical cap tray (ConCap tray). A 3-D computational fluid dynamics model was developed to predict the hydrodynamics of the ConCap tray which is operated in the spray regime. The model considers two phase flow of gas and liquid in a VOF-like code framework. The homogeneous multiple size group model (MUSIG model) and shear stress transport (SST) turbulence model were implemented. Detailed insights into the hydrodynamic behavior of the inside of the cones were obtained. The relation between velocity, pressure and cross section area of the flow inside the cone also was formulated. The computational fluid dynamic (CFD) results show that the pressure variation in the cones forces the liquid on the tray to be highly turbulent, which leads to deform the interface to break up. Effect of different riser heights was also studied by CFD simulations. The results show that the riser height has a significant role in the hydrodynamics of the tray, especially in uniform gas distribution in the tray and reducing weeping rates.     

Computational fluid dynamic simulation of gas-liquid flow in rotating packed bed:A review

The rotating packed bed (RPB) has been widely used in gas-liquid flow systems as a process intensifica-tion device,exhibiting excellent mass transfer enhancement characteristics.However,the complex inter-nal structure and the high-speed rotation of the rotor in RPB bring significant challenges to study the intensification mechanism by experiment methods.In the past two decades,Computational fluid dynam-ics (CFD) has been gradually applied to simulate the hydrodynamics and mass transfer characteristics in RPB and instruct the reactor design.This article covers the development of the CFD simulation of gas-liquid flow in RPB.Firstly,the improvement of the simulation method in the aspect of mathematical mod-els,geometric models,and solving methods is introduced.Secondly,new progress of CFD simulation about hydrodynamic and mass transfer characteristics in RPB is reviewed,including pressure drop,veloc-ity distribution,flow pattern,and concentration distribution,etc.Some new phenomena such as the end effect area with the maximum turbulent have been revealed by this works.In addition,the exploration of developing new reactor structures by CFD simulation is introduced and it is proved that such new struc-tures are competitive to different applications.The defects of current research and future development directions are also discussed at last.     

Computational fluid dynamic simulation of ethylene hydrogenation in a fluidised bed of porous catalyst particles

Computational fluid dynamics (CFD) is used to study the flow behaviour and conversion in a freely bubbling bed of porous cracking catalyst particles fluidised by a mixture of ethylene and hydrogen on the in‐house code FLOTRACS‐MP‐3D. The solid phase viscosity and pressure are modelled on the basis of kinetic theory of granular flows (KTGF). An effective solid density is calculated to account for the inherent porosity of particles. The cohesive inter‐particle forces are incorporated into the CFD model by using an empirical approach proposed in literature. Qualitatively, the CFD model captures the flow behaviour and heat transfer in the bed quite well. On the quantitative front, the variation of conversion with gas velocity is predicted fairly well with the deviation between the predicted and measured conversion remaining within 20%. © 2011 Canadian Society for Chemical Engineering     

Computational fluid dynamic (CFD) simulation of a pilot-scale annular bubble column photocatalytic reactor

The behavior of an 18-l pilot-scale photocatalytic reactor has been investigated using a computational fluid dynamic (CFD) approach. The granular Eulerian model was used to describe the multiphase flow system. Solid recirculation was predicted while liquid velocity vectors were influenced by the gas flow. The companion radiation transport equation was iteratively solved using a finite-volume-based discrete ordinate method. The first-order photodegradation kinetics of spent Bayer liquor previously studied in the same reactor was used to evaluate the CFD simulation. A Pearson correlation coefficient 0.974 between simulated and experimental data is indicative of model adequacy.     

新型固定阀塔板的流体力学和传质性能研究

提供了一种阀盖两侧具有向下弯曲折边的新型固定阀。在内径为500mm的有机玻璃塔内,以空气水为物系,研究了其流体力学性能;在内径为300mm的不锈钢塔内,以乙醇水为物系,常压全回流情况下,研究了其传质性能。研究结果表明:新型固定阀塔板的板压降略高于筛孔塔板,比F1 浮阀塔板小得多,雾沫夹带量小,雾沫夹带液泛点阀(筛)孔动能因子均比筛孔塔板、F1 浮阀塔板大,漏液量较小,漏液点阀(筛)孔动能因子比筛孔塔板低,比F1 浮阀塔板高,传质效率与F1 浮阀塔板相当。     

生物反应器内不同桨叶组合计算流体力学模拟

运用计算流体力学(CFD)数值模拟方法研究在相同工况下(搅拌桨转速为400 r/min、通气速度为0.86 vvm和操作温度为15 ℃),4种不同桨叶组合方式对5 L气液生物反应器流场、氧传质系数kLα、空气体积分数、气含率(体积分数)和功率的影响,评判各桨叶组合综合性能.计算结果表明:1号方案上下档均为径向桨,具有最...     

Computational fluid dynamics simulation of a novel bioreactor for sophorolipid production

This paper describes three-dimensional computational fluid dynamics(CFD) simulations of gas–liquid flow in a novel laboratory-scale bioreactor contained dual ventilation-pipe and double sieve-plate bioreactor(DVDSB)used for sophorolipid(SL) production. To evaluate the role of hydrodynamics in reactor design, the comparisons between conventional fed-batch fermenter and DVDSB on the hydrodynamic behavior are predicted by the CFD methods. Important hydrodynamic parameters of the gas–liquid two-phase system such as the liquid phase velocity field, turbulent kinetic energy and volume-averaged overall and time-averaged local gas holdups were simulated and analyzed in detail. The numerical results were also validated by experimental measurements of overall gas holdups. The yield of sophorolipids was significantly improved to 484 g·L~(-1)with a 320 h fermentation period in the new reactor.     

Computational fluid dynamic simulations of coal-fired utility boilers: An engineering tool

The objective of this study was to develop an engineering tool by which the combustion behavior of coals in coal-fired utility boilers can be predicted. We presented in this paper that computational fluid dynamic (CFD) codes can successfully predict performance of- and emission from- full-scale pulverized-coal utility boilers of various types, provided that the model parameters required for the simulation are properly chosen and validated. For that purpose we developed a methodology combining measurements in a 50 kW pilot-scale test facility with CFD simulations using the same CFD code configured for both test and full-scale furnaces. In this method model parameters of the coal processes are extracted and validated. This paper presents the importance of the validation of the model parameters which are used in CFD codes. Our results show very good fit of CFD simulations with various parameters measured in a test furnace and several types of utility boilers. The results of this study demonstrate the viability of the present methodology as an effective tool for optimization coal burning in full-scale utility boilers.     

Computational fluid dynamic simulations of chemical looping fuel reactors utilizing gaseous fuels

A computational fluid dynamic (CFD) model for the fuel reactor of chemical looping combustion technology has been developed, with special focus on accurately representing the heterogeneous chemical reactions. A continuum two-fluid model was used to describe both the gas and solid phases. Detailed sub-models to account for fluid–particle and particle–particle interaction forces were also incorporated. Two experimental cases were analyzed in this study (Son and Kim, 2006; Mattison et al., 2001). Simulations were carried out to test the capability of the CFD model to capture changes in outlet gas concentrations with changes in number of parameters such as superficial velocity, metal oxide concentration, reactor temperature, etc. For the experiments of Mattisson et al. (2001), detailed time varying outlet concentration values were compared, and it was found that CFD simulations provided a reasonable match with this data.     

Computational fluid dynamic modelling of flow patterns in an oscillatory baffled column

Numerical simulations to date within the context of oscillatory flow in a baffled column have been limited to flows in a symmetrical regime, i.e. eddies are generated symmetrical to the central line of the column where the oscillatory Reynolds numbers are below 400. In this paper, 3-D computational fluid dynamic (CFD) simulation of flow patterns of oscillatory flow in a baffled column has, for the first time, been carried out and the results extended to all regimes of oscillatory Reynolds numbers covering from symmetric to asymmetric flows. The flow patterns simulated have also been validated by both direct flow visualisation and by digital particle image velocimetry measurements. The success of such CFD simulations opens doors for many potential studies, from optimisation of geometry for plug flow to suspension of particles, and from droplet breakage and coalescence to mass/heat transfer of particles.     

不同搅拌系统气液氧传递的计算流体力学模拟

研究了搅拌槽中搅拌桨组合形式对气液氧传递特性的影响,主要采用Garcia-Ochoa和Gomez基于Higbie渗透理论提出的气液氧传递理论模型,在ANSYS CFX11.0软件基础上开发了用于模拟搅拌生物反应器中氧传递过程的方法。通过模拟比较了不同搅拌桨组合的气液氧传递系数,以及在有氧消耗和无氧消耗情况下反应器内饱和氧浓度的分布,发现上层为轴流式的三宽叶搅拌桨底层为径流式的六弯叶圆盘透平桨的组合形式氧供应能力最强,体积氧传递系数与桨的形式没有直接关系,同样的搅拌桨安装在不同的桨组合中或在不同的操作条件下所形成的体积氧传递系数是有差别的。     

Computational fluid dynamics simulation of virtual impactor performance: Comparison to experiment

Computational fluid dynamics (CFD) simulations were performed on a slit virtual impactor (SVI). A full-section planar model of the critical zone (nozzle) was constructed based on the measured values of geometrical dimensions of the SVI. Simulation was performed for a flow rate of 20.33 SCFH (standard cubic feet per hour) that corresponded to a Reynolds number value of 448 in the experiment. Impactor efficiency curve was computed and compared to experimental data. Details of internal wall losses were characterized and the wall loss curve was generated. Performance characteristics obtained from simulation results are in good agreement to the observed experimental trend over the complete range of Stokes numbers and the exact value of the cut-point Stokes number. Tracks for lower Stokes number particles faithfully reproduce the trend observed in the experiment, namely the regional demarcation of particle origin in the inlet nozzle, based on their final destination. Further, the effect of crossing trajectories that was visualized in the experiment for higher Stokes number particles of value of ~ 50 was captured. Additional details from the simulation results indicated that the onset of effect of crossing trajectories occurred for particles larger than a Stokes number of 6 and the collection efficiency for the above device was nearly unity over a wide range of Stokes number (Stk ~ 2 to 125) values.     

CFD gas-liquid simulation of oriented valve tray

Computational fluid dynamics (CFD) has recentlyemerged as an effective tool for the investigation of the hydraulic parameters and efficiency of tray towers. The computation domain was established for two types of oriented valves within a tray and meshed into two parts with different grid types and sizes. The volume fraction correlation concerning inter-phase momentum transfer source was fitted based on experimental data, and built in UDF for simulation. The flow pattern of oriented valve tray under different operating conditionswas simulated under Eulerian-Eulerian framework with realizable k-ε model. The predicted liquid height from CFD simulation was in good agreement with the results of pressure drop and volume fraction correlations. Meanwhile, the velocity distribution and volume fraction of the two phases were demonstrated and analyzed, which are useful in design and analysis of the column trays.     

Computational fluid dynamic study of polycaprolactone nanoparticles precipitation in a co-flow capillary micro-tube

Polycaprolactone nanoparticles (NPs) were produced in the co-flow glass capillary device with $250\mathrm{\mu m}$ tip dimension. NPs size was 990 nm for continuous phase velocity, and $u_c=0.05\mathrm{m}/\mathrm{s}$ and 426 nm for $u_c=0.2\mathrm{m}/\mathrm{s}$. The droplet formation process in the co-flow microchannel was also simulated using computational fluid dynamic (CFD). Employing a digital image analysis technique, a cut-off value of 0.81 for the dispersed phase volume fraction was proposed for the determination of droplet size. A scenario was expressed for NP formation from micro-droplets. Moreover, after conducting 27 CFD simulations, a dimensionless exponential form correlation was proposed for droplet size estimation. In this generalized map, there were three distinct regions based on the relative capillary numbers of continuous to dispersed phases. It was revealed that at a constant dispersed phase velocity, by increasing the continuous phase velocity, more small NPs are formed. The results show that the ratio of micro-droplets to NPs size was between 735 and 755.     

Computational fluid dynamics simulation of polymer electrolyte membrane fuel cells operating on reformate

Carbon monoxide (CO) can extremely diminish the polymer electrolyte membrane fuel cell (PEMFC) performance since it is preferentially absorbed on the platinum catalyst layer blocking and reducing the number of catalyst sites available for the hydrogen oxidation reaction. To gain a good insight of CO poisoning characteristics so as to provide a remedial solution for CO-poisoned PEMFCs, a two-dimensional, isothermal, and single phase CO poisoning numerical model taking into account the transport phenomena, electrochemical reactions and multi-component gas mixture transport is developed for such purpose. Linear and bridged-bonded adsorbed CO modes were considered to occur in parallel on the highly dispersed nano-crystalline Pt/C and PtRu/C catalysts. By performing computational fluid dynamics numerical simulations, this study clearly demonstrates the CO poisoning mechanisms and characteristics of PEMFCs. The numerical results obtained are in reasonably good agreement with the experimental data showing the predictive capability of the model.