Experimental and computational fluid dynamics modeling of double-partition divided-wall column for flow hydrodynamics and wall heat transfer characteristics

The aim of this study is to investigate the flow hydrodynamics and wall heat transfer characteristics on the tray of a two-staggered walled region in a double-partition divided-wall column (DPDWC). An experimental setup of DPDWC is designed, and a theoretical temperature gradient (TG) model based on Fourier's equation, which describes the wall heat transfer, is proposed. A coupled computational fluid dynamics-TG model is developed to analyze the heat transfer characteristics across partitions of DPDWC. The effects of liquid velocity, gas velocity, and different wall thermal boundary conditions on the flow and temperature fields are studied. The results indicate that the lack of a gas cone near partitions led to few vertical backflows of the liquid phase on the tray. Furthermore, the TGs near the liquid phase outlet increased with an increase in the liquid phase velocity. This work provides a scope for design and operation of DPDWC for industrial implementation.     

A modified model of computational mass transfer for distillation column

The computational mass transfer (CMT) model is composed of the basic differential mass transfer equation, closing with auxiliary equations, and the appropriate accompanying CFD formulation. In the present modified CMT model, the closing auxiliary equations [Liu, B.T., 2003. Study of a new mass transfer model of CFD and its application on distillation tray. Ph.D. Dissertation, Tianjin University, Tianjin, China; Sun, Z.M., Liu, B.T., Yuan, X.G., Liu, C.J., Yu, K.T., 2005. New turbulent model for computational mass transfer and its application to a commercial-scale distillation column. Industrial and Engineering Chemistry Research 44, 4427-4434] are further simplified for reducing the complication of computation. At the same time, the CFD formulation is also improved for better velocity field prediction. By this complex model, the turbulent mass transfer diffusivity, the three-dimensional velocity/concentration profiles and the efficiency of mass transfer equipment can be predicted simultaneously. To demonstrate the feasibility of the proposed simplified CMT model, simulation was made for distillation column, and the simulated results are compared with the experimental data taken from literatures. The predicted distribution of liquid velocity on a tray and the average mass transfer diffusivity are in reasonable agreement with the reported experimental measurement [Solari, R.B., Bell, R.L., 1986. Fluid flow patterns and velocity distribution on commercial-scale sieve trays. AI.Ch.E. Journal 32, 640-649; Cai, T.J., Chen, G.X., 2004. Liquid back-mixing on distillation trays. Industrial and Engineering Chemistry Research 43, 2590-2597]. In applying the modified model to a commercial scale distillation tray column, the predictions of the concentration at the outlet of each tray and the tray efficiency are satisfactorily confirmed by the published experimental data [Sakata, M., Yanagi, T., 1979. Performance of a commercial scale sieve tray. Institution of Chemical Engineers Symposium Series, vol. 56, pp. 3.2/21-3.2/34]. Furthermore, the validity of the present model is also shown by checking the computed results with a reported pilot-scale tray column [Garcia, J.A., Fair, J.R., 2000. A fundamental model for the prediction of distillation sieve tray efficiency. 1. Database development. Industrial and Engineering Chemistry Research 39, 1809-1817] in the bottom concentration and the overall tray efficiency under different operating conditions. The modified CMT model is expected to be useful in the design and analysis of distillation column.     

用X型热膜探针测量筛孔板上液流速度场的方法探索

引　言塔板上的流体力学状况对板式塔的分离效率有很大影响 ,因此准确描述塔板上流体的流动参数和状况对于板式塔精馏过程的模拟与设计具有重要意义 .实验测定塔板上气液两相流的流动特性 ,可以为数学模型中参数的确定、模型的验证以及工程设计提供实验依据 .目前对塔板上液相流速分布的测定方法有两类 :间接法和直接法 .在以往的研究中较多采用的是间接测量法 ,如Ｐｏｒｔｅｒ等[1] 采用的示踪、录像方法 ,余国琮等[2 ] 采用的电导分析法 ,以及张敏卿等[3] 的测温法等 .间接法的主要缺点是准确性不能保证 ,同时仅限于时均流速的测量 .直接…     

塔板上流型变化对板效率影响的计算传质学

利用能够描述塔板上气液两相错流过程的流体力学模型,建立了同时模拟气液两相流动与传质过程的数学模型;通过对气液两相传质方程和流体力学模型方程的联立求解,计算得到了塔板上液相速度分布和气液两相浓度分布的数值解,考察了气相完全混合和气相部分混合两种条件下塔板上的气液两相浓度分布,同时考察了气相完全混合时流型变化对塔板效率的影响.     

大型塔板的模拟与板效率的研究(Ⅱ)——二维定数混合池模型

为研究大型塔板在复杂流动情况下的浓度分布与板效率计算方法,本文提出二维、固定混合池数、可调整流量的数学模型。此模型可以比较灵活地模拟大型塔板上的各种实际流动现象,并能比较方便地计算出在该流动情况下的塔板浓度分布及板效率值。     

筛孔塔板上气相错流对液相流场影响的实验测量

利用热膜流速仪、测量了矩形塔内光板上液体单相流动以及筛孔板上气液两相流动时的液体流速分布，实验主要考察气液两相错流时，气体鼓泡作用对鼓泡区下游液体流速分布的影响，实验结果表明，单相流动时，受壁面效应的影响，靠近塔壁的液体的速度最低，气液两相错流时，受气体阻力作用的影响，靠近壁面液体的速度反而大于远离壁面处液体的速度，气相流量越大对液相流场的影响作用越强。     

Computational fluid dynamic simulation of MVG tray hydraulics

The flow pattern and hydraulics of a Mini V-Grid valve (MVG) tray is predicted by using computational fluid dynamics simulation. A 3-D CFD model in the Eulerian framework was used. The simulation results for MVG tray are compared with that of sieve tray. The sieve tray geometry and operating conditions are based on the Solari and Bell’s sieve tray [1]. The MVG tray differs from that of Solari and Bell’s sieve tray solely by the difference in design of available openings for the flow of gas. The simulation results show that the clear liquid height and the pressure drop of MVG tray are lower than that of sieve tray whereas the liquid velocity is higher and contacts of phases are good. The simulation results of sieve tray are in agreement with the experimental data of Solari and Bell [1].     

PART Ⅱ TWO DIMENSIONAL FIXED NUMBER MIXING POOL MODEL

A new mathematical model of mixing pool type is proposed for simulating the fluid flow and masstransfer behavior on a large tray.In the proposed model,the whole tray is divided into a number ofsquare (or rectangular)compartments or mixing pools,each of which is assigned to have adjustableflow and baekmixing in both z (along the main flow path) and w(perpendicular to the main flow path)directions.The chief features of present model are: (1) It is two dimensional model instead of usualone dimensional so that more complicated actual flowing condition obtained from hydrodynamic studyon a large tray can be closely simulated by adjusting the flow among mixing pools in both z and wdirections.(2) Since backmixing is taken into account,the number of mixing pools on a tray is fixedinstead of varied as in conventional mixing pool model; thus,the application of matrix computation ispossible.(3) The present model can be reduced to other tray models depending on the number of mixingpools to be chosen in each direction.The application of present model to predict the liquid phase concentration profiles and Murphreeefficiency enhancement on a large tray with complicated flow pattern and velocity distribution as we-observe in our experimental study are demonstrated.The effects of liquid flow rate,nonuniform veloc-.ity field,directional splashing and subsidiary flow are also investigated and discussed.     

规整填料塔液相流动的计算流体力学模拟

规整填料因具有诸多优异性能,已在工业上广泛应用,但是至今人们对规整填料内流体流动机理的研究还不是十分透彻,从而限制了其进一步的发展和更新．与散堆填料不同,规整填料在结构上既有规整性又有复杂性,属各向异性,因此对其内流体流动的研究具有一定的难度．而现代计算流体力     

多溢流大型塔板的计算传质学

利用计算传质学方法研究了直径12.6 m的四溢流大型塔板上液相流动结构对塔板效率的影响,建立了描述多溢流塔板上液相流动和传质状况的理论化计算模型。应用该模型,研究了传统等鼓泡面积设计方法条件下单块塔板的速度场和浓度场。结果表明,所模拟四溢流塔板的左侧翼塔板出现返流区,而右侧翼塔板流动结构相对均匀未出现返流区。为进一步优化塔板结构,提高传质效率,对左侧翼塔板提出了加设导流板的改进结构。计算结果表明,改进的塔板结构在一定程度上改善了塔板上液相的流动结构,使得塔板效率较传统设计方法提升了4.53%～9.22%（当Q₁/Q₂=［0.5,1.5］时）。     

Local hydrodynamics of gas–liquid-nanoparticles three-phase fluidization

The laser Doppler anemometer (LDA) and conductivity probes were used for measuring the local hydrodynamic performances such as gas holdup and liquid velocity in a lab-scale gas–liquid–TiO₂ nanoparticles three-phase bubble column. Effects of operating parameters on the local gas holdup and liquid velocity were investigated systematically. Experimental results showed that local averaged axial liquid velocity and local averaged gas holdup increased with increasing superficial gas velocity but decreased with increasing TiO₂ nanoparticles loading and the axial distance from the bottom of the bubble column. A three-dimensional computational fluid dynamic (CFD) model was developed in this paper to simulate the structure of gas–liquid–TiO₂ nanoparticles three-phase flow in the bubble column. The time-averaged and time-dependent predictions were compared with experimental data for model validation. A successful prediction of instantaneous local gas holdup, gas velocity, and liquid velocity were also presented.     

计算传质法预测精馏塔效率(英文)

A computational mass transfer model is proposed for predicting the concentration profile and Murphree efficiency of sieve tray distillation column. The proposed model is based on using modified two equations formulation for closing the differential turbulent mass transfer equation with improvement by considering the vapor injected from the sieve hole to be three dimensional. The predicted concentration distributions by using proposed model were checked by experimental work conducted on a sieve tray simulator of 1.2 meters in diameter for de-sorbing the dissolved oxygen in the feed water by blowing air. The model predictions were confirmed by the ex-perimental measurement. The validation of the proposed model was further tested by comparing the simulated re-sult with the performance of an industrial scale sieve tray distillation column reported by Kunesh et al. for the strip-ping of toluene from its water solution. The predicted outlet concentration of each tray and the Murphree tray effi-ciencies under different operating conditions were in agreement with the published data. The simulated turbulent mass transfer diffusivity on each tray was within the range of the experimental result in the same sieve column re-ported by Cai et al. In addition, the prediction of the influence of sieve tray structure on the tray efficiency by using the proposed model was demonstrated.     

Compartment-model for the simulation of the separation performance of stirred liquid–liquid-extraction columns

For detailed simulation and evaluation of stirred extraction columns a CFD based compartment-model was developed. Instead of simulating all effects in a computational expensive PBE-CFD-model, the velocity field calculation of the continuous phase is decoupled from the calculation of the dispersed phase (one-way coupling). In CFD only the continuous phase is simulated and the resulting velocity profile is used in the compartment-model to simulate the drop movement, coalescence, breakage and mass transfer for a representative number of drops (Monte-Carlo Method). This decoupling has a major impact on the calculated fluid-dynamics. Thus, the velocity profile of the CFD results is modified in the model to account for phase interaction. The compartment-model is applied for the simulation of a Kühni extraction column with the system toluene/water/acetone. The simulation results, namely holdup, drop size and concentration profiles over the column height, are in good agreement with experiments for different loads and different stirrer speeds.     

新型正交波纹板流体力学性能CFD模拟

介绍一种新型穿流塔板--正交波纹板。以欧拉-欧拉两相流模型为基础,建立了正交波纹板上气液两相流场的三维数学模型。CFD模型中主要考虑了气液两相间的曳力作用,相间动量传递源相采用Krishna计算方法。以清液层高度为指标,对CFD模型的可靠性进行了验证。在不同气液负荷下,对正交波纹板的压降、板上液相速度分布及塔内气液分布状况等流体力学性能进行了研究,并与淋降筛板进行对比,结果表明正交波纹板具有更高的操作弹性和更好的操作稳定性。     

单、双溢流塔板液体停留时间分布和板效率的研究

在2米半园筛板试验装置上,用多点电导连续测量和微机数据采集系统研究了单、双溢流塔板的液体停留时间分布和流动型式.得到的等平均停留时间分布图表明,单溢流塔板上液体流动型式相当复杂.在双溢流板中,中央降液管塔板的流动情况与单溢流板的前半部相似;边降液管板的液体流动则要均匀得多.本文建立了由液体等平均停留时间分布曲线计算单、双溢流塔板板效率的数学模型,并给出了关系图.最后,本文提出两种改善液体流动均匀性的新结构,实验证明它们能够明显地提高板效率.     

大型塔板的模拟与板效率的研究(Ⅰ)——不均匀速度场的涡流扩散模型

本文介绍了直径为2m的半圆筛板塔试验装置,并得出塔板上液体流动型式和速度分布的一些实验数据。结果表明塔板上存在着相当复杂的流动和分区。 根据实验结果,在本文描述流动的微分方程中,引入了速度分布函数,并成功地用有限元素法来求解传质问题,从而得出了在不均匀的速度场下大型塔板上的液相浓度分布以及塔板效率。     

湍动浆态床流体力学研究(Ⅱ)轴向浆料速度的径向分布

对高气速、大塔径条件下的湍动浆态床轴向速度进行了实验测定,提出了简化的一维流体力学模型。实验结果表明：固含率对浆料速度的径向分布影响不明显;采用中心速度和塔径作为参考量,则不同条件下的量纲1流速分布相似;高气速下中心速度随塔径的变化可近似用Nottenkamper关联式描述。提出了一维流体力学模型预测浆态床液速分布,模型计算结果与实验数据符合较好,模型较好地反映了浆态床反应器内液速分布随表观气速、固含率及塔径变化的规律。     

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.     

立体传质塔板板上液相流场的三维数值模拟

针对立体传质塔板(CTST)操作时的特点,对1 000 mm的CTST板上液相流场进行了三维计算流体力学(CFD)数值模拟.计算得出了板上液相流场的三维分布特征;实验测量和模拟结果对比,结果吻合较好,说明文中模型有较好的准确度,可以用于CTST板上液相流场的预测.对相同条件下筛板和CTST板上的液相流场分别进行模拟,...     

EXPERIMENTAL AND THEORETICAL INVESTIGATION OF GAS FLOWFIELD ON A ROTATING STREAM TRAY

The rotating stream tray is a new type of column tray operating in the spray regime, through which the gas stream rotates. Combinations, performances and applications of the rotating stream tray are introduced briefly. On a 300 mm diameter rotating stream tray, the gas flowfield was investigated with a DANTEC 55X laser Doppler anemometer. The data of velocity distributions in tangential, axial and radial directions on sections at different heights above the tray were obtained. A numerical model for computing the turbulence flow on the tray was also proposed. The predicted results of three-dimensional velocities and pressures were found to be in qualitative agreement with experimental data. The main gas flow features are clarified.