Influence of orientation upon the hydrodynamics of gas-liquid flow for square channels in monolith supports

Monoliths are being used increasingly as catalyst supports for two-phase gas-liquid reactions, yet substantial differences in the mass transfer performance between different configurations have not been thoroughly explained using either mass transfer or hydrodynamic arguments. In this paper, investigations of the differences in hydrodynamics between up-flow and down-flow have been made in a single channel using square glass capillaries of either 1.5 or 2 mm section. The fluids used were either water or 30%_v/v isopropanol/water mixture and air. Predictive flow maps are presented for down-flow: annular, Taylor (slug) flow, bubbly and churn flow were observed. In the Taylor flow regime, slug velocities and lengths measured using an optoelectronic technique were found to be in good agreement with the drift flux model [Zuber, N., Findlay, J.A., 1965. Average volumetric concentration in two-phase flow systems. Journal of Heat Transfer 87, 453-468]. Non-zero drift velocities were obtained. Particle image velocimetry (PIV) was used to investigate the velocity fields within the liquid slugs. For short slugs (slug length less than the tube hydraulic diameter), a flow is developed where the axial velocity component is only a function of position in the tube cross-section. The velocity profile is relatively flat, with the maximum observed velocity at the axis of the tube, V_max, being 0.8-1 times the bubble velocity, V_B. For long slugs, the axial velocity component depends on both the axial position and the position in the tube cross-section. Close to parabolic profiles are developed with V_max/V_B≈1.1-1.7. The location of the centre of the recirculation vortices produced in long slugs was found to be closer to the tube centre in down-flow compared with up-flow. Recirculation times in up-flow were 3 times faster: this has implications for the models used to predict rates of mass transfer and residence time distribution.     

泰勒反应器中流体流动及停留时间分布研究

以水为介质对泰勒反应器中的流动状况和停留时间及其分布(RTD)进行了研究,并应用计算流体力学(CFD)技术对反应器进行了流场模拟和RTD计算。结果表明,在实验范围内,泰勒反应器中停留时间分布受内筒转速、轴向流动速率等因素影响,基于流体力学计算结果与实验结果基本相当。     

基于图像灰度值控制的矿石提纯系统

主要探讨图像处理在工业控制中的一些应用。以图像的灰度值作为检测得目标对象,正确地从图像中提取出目标物体得特征制,是实现许多智能图像系统的基础。基于计算机的图像检验,着眼于检测的图像信息,对洗矿机实行实时控制。     

Experimental investigation of gas-liquid distribution in monolith reactors

The present work investigates the influence of gas and liquid flow rates on inlet liquid distribution across monoliths operating in gas-liquid cocurrent downflow mode. Gas and liquid superficial velocities range from 0 to 68 and 1.4 to 8.5 cm/s, respectively. Gas-liquid distribution was studied using a packed bed liquid distributor and a pipe distributor for the aforementioned range of operating conditions. To determine the liquid distribution over the monolith, gravimetric, time-averaged liquid collection method was applied using a customized collector apparatus. Quantification of the distribution is reported using a suitably defined maldistribution factor. For each liquid velocity, gas velocities are varied and corresponding maldistribution factors are calculated. The results are reported in view of the varying operating conditions.     

喷射式气,液反应器在空气—水系统中的传质特性

在对喷射式气、液反应器中复杂的流动行为进行简化和假定的基础上,导得了传质模型,并以空气-水系统进行实验研究。用光电毛细管法测定喷射管内气泡平均直径 d_(32)和比表面积 a,用氮气解吸水中溶解氧的方法获得体积传质系数 k_La,以确定传质模型中的有关参数。实验获得如下结果:α=9.18×10~2β~(0.74)e~(0.372),k_Lα=0.7206β~(0.88)e~(0.492)。其结果与理论分析较接近,可作为喷射式气、液反应器设计参数。     

Maldistribution susceptibility of monolith reactors: Case study of glucose hydrogenation performance

In this work an ultrafast electron beam X‐ray modality was applied for the first time to characterize the gas–liquid Taylor flow inside each channel of an opaque honeycomb monolith structure ( ) for and . Significant spatial and temporal deviations in the phase holdup as well as in the gas bubble and liquid slug lengths were found. To evaluate the impact of Taylor flow maldistribution on the reactor performance, the data of more than unit cells were used to simulate the reactor productivity in the hydrogenation of glucose. The results verify that a monolith reactor solely designed by using superficial velocities and empirical correlations for gas bubble and liquid slug lengths fails significantly in achieving high product selectivity and the desired conversion. The developed methods are a solid base to design and select proper distributors ensuring the favorable flow configurations for specific chemical processes. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4346–4364, 2016     

Target bounds on reaction selectivity via Feinberg's CFSTR equivalence principle

In this work, we show that the continuous flow stirred tank reactor (CFSTR) equivalence principle, developed by Feinberg and Ellison, can be used to obtain practical upper bounds on reaction selectivity for any chemistry of interest. The CFSTR equivalence principle allows one to explore the attainable reaction region by decomposing any arbitrary, steady‐state reactor‐mixer‐separator system with total reaction volume V > 0 into a new system comprising CFSTRs (where is the number of linearly independent chemical reactions) with the same total reaction volume and a perfect separator system. This work further refines the allowable selectivities by incorporating capacity constraints into the CFSTR equivalence principle to prevent arbitrarily large recycle streams between the CFSTRs and the separators and infinitesimally small CFSTR conversions. These constraints provide practical upper bounds on reaction selectivities of chemistries completely independent of reactor design. We present the methodology and the results for a selection of realistic chemistries. © 2017 American Institute of Chemical Engineers AIChE J, 64: 926–939, 2018     

STEADY LAMINAR FLOW IN TWO SUCCESSIVE BIFURCATIONS

The steady-state vorticity transport equation was solved numerically for inspiratory flow in two-dimensional models of two successive bifurcations. Streamlines and velocity distributions were obtained for Reynolds numbers ranging from 1 to 800. For both symmetric and asymmetric airway models, the calculated axial velocity profiles in the parent channels of the second bifurcations are asymmetric.     

SEMIBATCH PRECIPITATION ACCOMPANYING GAS-LIQUID REACTION

To obtain large particles of insoluble product by precipitation accompanying a gas-liquid reaction, a sparged stirred vessel was operated continuously for the gaseous and liquid reactants but batchwise for the product particles. Except at the beginning of run, most particles formed floes. With increasing concentration of product particles, the average size of floes increased for CaC0₃ but remained unchanged or decreased slightly for SrCO₃ and BaC0₃The effect of agitation on the floc size was significant for CaC03 but scarcely observed for SrC0₃ and BaC0₃ The mass per unit volume of sedimented floes of the three species increased with increasing concentration of product particles, and under the same conditions, they decreased in the following order: CaC0₃ SrC0₃ BaC0₃     

Effect of nozzle diameter and its orientation on the flow pattern and plume dimensions in gas-liquid jet reactors

Gas-liquid jet reactors are widely used in chemical industries in various applications such as feed-water heaters, metal processing, and thermal energy sources, etc. In all these applications, the principal requirement for the design is a prior knowledge of jet shape and dimensions, which primarily depend upon the nozzle type, size, submergence and its orientation. In the present study, CFD simulations of non-reacting (steam-water) and reacting (SF₆-Li) jets have been carried out to understand the variation in plume dimensions of gas-liquid jet reactors. For condensation jet and reaction jet, the criteria have been developed to identify the plume boundary based on the hold-up profile of steam/SF₆ gas and the evaporated fuel. The effect of nozzle diameter and its orientation, nozzle gas velocity and bath temperature on the plume dimensions have been studied for both the types of jets. It was observed that the extent of increase in the plume length is always higher in the case of reaction jet as compared to the condensation jet for all the cases. The analyses also proved that, the availability of reactant is much better with the horizontal orientation which leads to stable plume length. The CFD model has been extended for the prediction of the flow pattern and its effect on the rate of condensation/reaction and plume dimensions for both the jet systems.     

Hydrogenation of 2‐ethylanthraquinone under Taylor flow in single square channel monolith reactors

The hydrogenation of 2‐ethylanthraquinone (EAQ) to 2‐ethylanthrahydroquinone (EAHQ) was carried out under Taylor flow in single square channel monolith reactors. The two opening ends of opaque reaction channel were connected with two circular transparent quartz‐glass capillaries, where Taylor flow hydrodynamics parameters were measured and further used to obtain practical flow state of reactants in square reaction channels. A carefully designed gas‐liquid inlet mixer was used to supply steady gas bubbles and liquid slugs with desired length. The effects of various operating parameters, involving superficial gas velocity, superficial liquid velocity, gas bubble length, liquid slug length, two‐phase velocity and temperature, on EAQ conversion were systematically researched. Based on EAQ conversion, experimental overall volumetric mass transfer coefficients were calculated, and also studied as functions of various parameters as mentioned earlier. The film model, penetration model, and existing semi‐empirical formula were used to predict gas‐solid, gas‐liquid, and liquid‐solid volumetric mass transfer coefficients in Taylor flow, respectively. The predicted overall volumetric mass transfer coefficients agreed well with the experimental ones. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Hydrodynamics of Taylor flow in noncircular capillaries

In this work, volume of fluid (VOF) technique, one computational fluid dynamics (CFD) method, was used to investigate the upward Taylor flow in vertical square and equi-triangular capillaries. For saving computation time, the simulations were carried out in a moving frame of reference attached to Taylor bubbles. The main flow parameters, involving bubble size and shape, liquid film thickness, velocity field and two-phase relative velocity, were studied as functions of capillary number. The numerical simulations were in good agreement with previous reports and showed that the flow in the sides and corners of polygonal capillaries were different. A comparative study was also conducted on Taylor flow in square and equi-triangular capillaries and their circular counterparts, where the influence of capillary geometry on the characteristics of Taylor flow was illustrated clearly.     

ATOMIZATION IN A VENTURI SCRUBBER

High speed motion pictures were made or the breakup of a single jet of water in the throat of a venturi scrubber for various air and water jet velocities and different nozzle diameters. Atomization seemed to occur as the result of several different mechanisms, depending on the flow conditions, the most common mechanisms being breakup due to either capillary or acceleration waves and also breakup by “steady shear,” all of which have been observed by other investigators. The so-called “cloud-type” atomization proposed by Hesketh (1970) was not observed despite several attempts to achieve it. Measured values of pressure drop across the test section of the scrubber compare well with previously published results.     

CONTRIBUTION TO THE ANALYSIS OF THE SELECTIVITY OF GAS-LIQUID REACTIONS PART II: COMPARISON OF EXPERIMENTAL RESULTS WITH MODEL PREDICTIONS

The chlorination of paracresol is used in an experimental study of selectivity in gas-liquid contactors.

Experiments in a batch reactor show the influence on selectivity of the dimensionless numbers presented in Part I and involving competition between mass transfer and chemical reaction together with the hydrodynamics.

The extension of open reactor model presented in Part 1 to the batch reactor permits a comparison between theory and experiments and shows a good agreement     

基于计算机图象处理技术的玻璃等级的动态在线识别

为了识别浮法玻璃生产线上玻璃的等级标记，实现玻璃的自动化分等级堆垛，提出了一种基于数字图象处理技术的机器视觉识别方法。对数字图象的线性变换、平滑处理进行了介绍，提出了运用减影的方法提取等级标记和运用一种基于膨胀的新算法识别等级标记，在此基础上开发出了玻璃等级在线识别系统，并对该系统的应用前景做了展望。