CFD and experimental studies of liquid weeping in the circular sieve tray columns

Sieve trays are widely used in fractionating devices like tray distillation towers existing in separation and purification industries. The weeping phenomenon that has a critical effect on the efficiency of tray towers was studied by a numerical model and some experiments. The experiments were carried out in a pilot scale column with the diameter of 1.22 m that includes two test trays and two chimney trays. Weeping rates and some hydraulic parameters were measured in sieve trays with the hole area of 7.04%. Furthermore, the total weeping rate and weeping rate in inlet and outlet halves of the test tray were determined. It was also used an Eulerian–Eulerian computational fluid dynamics (CFD) method for the present study. The model was able to predict the dry tray pressure drop, total pressure drop, clear liquid height, froth height, and weeping rate simultaneously. Furthermore, the obtained CFD results were in a good agreement with the experimental data in terms of pressure drop and the model properly predicted several hydraulic parameters like the liquid weeping behavior along the tray.     

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.     

Efficiencies of Sieve Tray Distillation Columns by CFD Simulation

A 3‐D two‐fluid CFD model in the Eulerian‐Eulerian framework was developed to predict the hydrodynamics and heat and mass transfer of sieve trays. Interaction between the two phases occurs via interphase momentum and heat and mass transfer. The tray geometries are based on the large rectangular tray of Dribika and Biddulph and FRI commercial‐scale sieve tray of Yanagi and Sakata. In this work a CFD simulation is developed to give predictions of the fluid flow patterns, hydraulics, and mass transfer efficiency of distillation sieve trays including a downcomer. The main objective has been to find the extent to which CFD can be used as a design and prediction tool for real behavior, concentration and temperature distributions, and efficiencies of industrial trays. Despite the use of simple correlations for closure models, the efficiencies obtained are very close to experimental data. The results show that values of point efficiency vary with position on the tray because of variation of affecting parameters, such as velocities, temperature and concentration gradients, and interfacial area. The simulation results show that CFD can be used as a powerful tool in tray design and analysis, and can be considered as a new approach for efficiency calculations and as a new tool for testing mixing models in both phases. CFD can be used as a “virtual experiment” to simulate tray behavior under operating conditions.     

十字旋阀塔板漏液性能

在φ1000mm的圆塔内,以空气-水为介质,对十字旋阀塔板的泄漏率进行了测试,考察了液流强度、出口堰高等因素对泄漏性能的影响,并将其与交错十字旋阀塔板、组合导向浮阀塔板和F1型浮阀塔板的泄漏率进行了对比。结果表明:十字旋阀塔板在气速超过临界阀孔气速且液流强度较小时具有很好的漏液性能,经数据关联,获得了十字旋阀塔板漏液点孔速的关联式。     

微分浮阀塔板的研究和应用

应用空气 -水系统 ,在直径 6 0 0 mm的塔内 ,对微分浮阀塔板的流体力学进行了实验研究 ,测定了临界孔速、塔板压降、雾沫夹带率和液体泄漏率。应用空气 -水 -氧气物系 ,测定了微分浮阀塔板的传质效率。并与 F1型浮阀塔板进行了对比实验研究。实验结果表明 :微分浮阀塔板比 F1型浮阀塔板具有更好的流体力学和传质性能 ,并对实验数据进行了关联 ,获得了计算临界孔速、塔板压降、雾沫夹带率和泄漏点孔速的关联式 ,可用于微分浮阀塔板的设计计算。文中还介绍了微分浮阀塔板的工业应用情况     

Hydrodynamic Characteristics in the Counter‐Flow Total Spray Tray

The capacity of a column is limited by the distribution of gas and liquid, especially in case of large‐diameter cross‐flow trays. In order to solve the bottleneck, a new counter‐flow tray named total spray tray (TST) was put forward. Taking air/water as medium, the hydrodynamic behavior, including the pressure drop, weeping, entrainment, and clear liquid height, was investigated, in comparison with the CTST, which had a higher capacity. Based on experimental data, the correlations of the TST pressure drop were established by regression analysis method. The experimental results show that the TST has a lower wet pressure drop and less weeping. More interestingly, its clear liquid height can be self‐adjusting with the variation of the gas kinetic energy factor, which is beneficial to improving the capacity.     

两种泡罩塔板的流体力学性能研究

应用空气-水系统,在1 000 mm× 400 mm的有机玻璃塔中,测定不同结构的两种泡罩塔板的压降、雾沫夹带、漏液等流体力学性能,对实验测得的结果进行关联,得到了计算泡罩塔板各项流体力学性能的关联式,为今后的设计及应用提供依据.实验结果表明:在正常操作范围内,Ⅱ型泡罩塔板的压降、漏液点、雾沫夹带随板孔动能因子(F0)...     

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.     

网孔塔板的流体力学

木文以空气-水系统在1200×400mm矩形装置内对网孔塔板的流体力学进行了试验研究。试验所采用的塔板参数和操作条件为:塔板开口宽度为3、3.5、4、4.5及4.7mm;塔板开孔率为9.9、12.3、13.2、14.9及15.4％; 挡沫板宽度为150、200、250、300mm;板间距为400、500、600、700及800mm;液流强度为20、30、45、60m~3/m·h;气体空塔速度为0.60—2.8m/s。测定了各有关参数对塔板压降、雾沫夹带和泄漏的影响,并对试验数据进行了关联,得出了计算塔板压降、雾沫夹带、泄漏、上限气速、下限气速及操作弹性等的关系式,以便用于网孔塔板的设计。     

Numerical and Experimental Study of Catalyst Loading and Body Effects on a Gas‐Liquid Trickle‐Flow Bed

The influence of tortuosity and fluid volume fractions on trickle‐flow bed performance was analyzed. Hydrodynamics of the gas‐liquid downward flow through trickle beds, filled with industrial trilobe catalysts, were investigated experimentally and numerically. The pressure drop and liquid holdup were measured at different gas and liquid velocities and in two different loading methods, namely, sock and dense catalyst loading. The effect of sharp corners on hydrodynamic parameters was considered in a bed with rectangular cross section. The reactor was simulated, considering a three‐phase model, appropriate porosity function, and interfacial forces based on the Eulerian‐Eulerian approach. Computational fluid dynamics (CFD) simulation results for pressure drop and liquid holdup agreed well with experimental data. Finally, the velocity distribution in two types of loading and the effect of bed geometry in CFD results demonstrated that pressure drop and liquid holdup were reduced compared to a cylindrical one due to high voidage at sharp corners.     

A CFD‐PBM‐PMLM integrated model for the gas–solid flow fields in fluidized bed polymerization reactors

Although the use of computational fluid dynamics (CFD) model coupled with population balance (CFD‐PBM) is becoming a common approach for simulating gas–solid flows in polydisperse fluidized bed polymerization reactors, a number of issues still remain. One major issue is the absence of modeling the growth of a single polymeric particle. In this work a polymeric multilayer model (PMLM) was applied to describe the growth of a single particle under the intraparticle transfer limitations. The PMLM was solved together with a PBM (i.e. PBM‐PMLM) to predict the dynamic evolution of particle size distribution (PSD). In addition, a CFD model based on the Eulerian‐Eulerian two‐fluid model, coupled with PBM‐PMLM (CFD‐PBM‐PMLM), has been implemented to describe the gas–solid flow field in fluidized bed polymerization reactors. The CFD‐PBM‐PMLM model has been validated by comparing simulation results with some classical experimental data. Five cases including fluid dynamics coupled purely continuous PSD, pure particle growth, pure particle aggregation, pure particle breakage, and flow dynamics coupled with all the above factors were carried out to examine the model. The results showed that the CFD‐PBM‐PMLM model describes well the behavior of the gas–solid flow fields in polydisperse fluidized bed polymerization reactors. The results also showed that the intraparticle mass transfer limitation is an important factor in affecting the reactor flow fields. © 2011 American Institute of Chemical Engineers AIChE J, 58: 1717–1732, 2012     

筛板不均匀漏液的规律及其影响

筛板不均匀漏液的规律及其影响曾爱武刘富善许松林黄洁余国琮（天津大学化学工程研究所，天津３０００７２）关键词筛板不均匀漏液塔板效率１引言塔板漏液是一种导致塔板效率降低的纵向返混。在工程设计中通常以相对漏液１～１０％来决定气相负荷下限，但值得指出的...     

Hydrodynamics of inclined packed beds under flow modulation ‐ CFD simulation and experimental validation

A three‐dimensional unsteady‐state Eulerian multi‐fluid CFD model was developed to simulate the hydrodynamic behavior of inclined gas‐liquid cocurrent downflow packed beds under ON‐OFF liquid, ON‐OFF gas, and gas/liquid alternating cyclic operations. Validation of the CFD simulation results was performed with experimental data provided by electrical capacitance tomography imaging. Incorporation in the Eulerian multifluid CFD model of capillary pressure and mechanical dispersion force was essential to accurately capture the transient spatial heterogeneities arising in tilted packed beds under different cyclic modulation strategies. The applied CFD model was able to satisfactorily predict the values of liquid holdup and pressure drop as well as the morphological characteristics of the traveling waves inside the bed for the examined flow modulations. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4161–4176, 2017     

塔板漏液速率和气速下限的计算

在φ1(?)00试验塔上,以空气-水系统,对φ10大孔(?)板和V型棚板测定了不同工况下的漏液速率,并用多元线性回归拟合得到这两种塔板的漏液速率和气速下限的计算公式,还作了物性修正,可用于工程设计计算。     

Co‐current descending two‐phase flows in inclined packed beds: Experiments versus simulations

The effect of inclination angle of a packed bed on its corresponding gas–liquid flow segregation and liquid saturation spatial distribution was measured in co‐current descending gas–liquid flows for varying inclinations and fluid velocities, and simulated using a two‐phase Eulerian computational fluid dynamics framework (CFD) adapted from trickle‐bed vertical configuration and based on the porous media concept. The model predictions were validated with our own experimental data obtained using electrical capacitance tomography. This preliminary attempt to forecast the hydrodynamics in inclined packed bed geometries recommends for the formulation of appropriate drag force closures which should be integrated in the CFD model for improved quantitative estimation.     

CFD‐Facilitated Flow Field Analysis of Bubble Columns with Concentric Plates for Biological Applications

As the hydrodynamic behavior in bubble columns is difficult to characterize, computational fluid dynamics (CFD) is a useful alternative tool for research and design. An experimental and computational analysis of the macromixing and gas holdup of a bubble column indicates that 3D simulations with CFD using an Eulerian‐Eulerian approximation yield results of the overall velocity field and gas holdup distribution that are suitable for engineering design purposes. Particularly, CFD simulations uncover that the inclusion of concentric solid plates into a bubbling column increase the gas holdup by 79 % and the mixing time by 48 % when compared with a column without plates operating at similar superficial gas velocities.     

CFD simulations and particle image velocimetry measurements in an industrial scale rotating disc contactor

Fluid dynamics of the single‐phase and two‐phase flow in a segment of a rotating disc contactor (RDC) liquid–liquid extraction column with 450 mm inner diameter were studied by performing computational fluid dynamics (CFD) simulations and particle image velocimetry (PIV) measurements. The fluid dynamics were investigated to test the predictivity of CFD at industrial scale. Different turbulence models in conjunction with the Eulerian approach were applied in the single‐phase and two‐phase simulations. The turbulent flow characteristics were analyzed by PIV measurements to validate the CFD simulations. An iso‐optical system composed of CaCl₂/water–butylacetate allows for the two‐phase PIV measurements. Local turbulent energy dissipation was derived from velocity gradients in PIV data. In this connection, the influence of the PIV spatial resolution on the measured energy dissipation was also analyzed, and different fit functions were tested to scale the measured energy dissipation. Simulated velocity fields as well as the energy dissipation were compared with the experimental PIV data. The results from the simulations and experiments are in good agreement. The work shows that CFD can predict hydrodynamic characteristics even at bigger scales but is still subject to some minor restrictions. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

梯形导向浮阀塔板

对梯形导向浮阀塔板的流体力学和传质性能进行了实验研究，对实验数据进行了关联，获得了计算塔板压降，雾沫夹带和泄漏点速的关联式，可供梯形导向浮阀塔板设计计算之用。     

Turbulent flow of hydrates in a pipeline of complex configuration

The present paper describes an experimental study of Freon R11 hydrate transport in a turbulent flow through a model-scale pipeline of complex configuration. The frictional pressure losses as a function of the hydrate phase concentration were determined, and isokinetic sampling was performed for the determination of mean particle size. The experimental rig was modelled using an Eulerian–Eulerian CFD model which was validated with the experimental results. The detailed flow patterns in the pipeline and some other process parameters were determined by the CFD simulations, elucidating further the flow of the slurry in the pipeline. In addition the influence of gravity in densifying the particles under conditions of low Reynolds numbers was studied.