弹状流液弹区含气率分布的试验研究

采用光纤探针法和高速摄影法对垂直上升气液两相弹状流的液弹区含气率分布进行了试验研究,测试管径为15 mm。一种基于机器学习的图像处理技术用来识别气液两相界面,通过搭建气泡边界提取的神经网路系统,使用构建的气泡边界数据库对模型进行多次迭代训练,该方法可以有效地识别多种复杂类型的气泡边界。试验得到了弹状流液弹区的径向含气率分布曲线,结果表明,壁峰分布是液弹区含气率分布的主要形式,其中泰勒气泡的尾迹效应对分布形式有重要影响,尾迹的旋涡中心和含气率分布的峰值相对应。针对弹状流液弹区径向含气率分布的两个主要特征——中心局部含气率和壁峰位置,分别提出了相应的预测公式,且与本文的试验数据吻合良好。     

A comprehensive study on co2-interphase mass transfer in vertical cocurrent and countercurrent gas-liquid flow

Cocurrent and countercurrent absorption and desorption of CO₂ in water was investigated in tall bubble columns (length 440 and 720 cm, diameter 15 and 20 cm, respectively). Operating conditions were applied which provided for high interphase mass transfer rates. Under these circumstances the relative gas holdup varies considerably with axial position whereas the mean bubble diameter measured at two points was found to be approximately constant. The measured data permit the calculation of local values of interfacial areas, superficial gas velocities, and frequency factors for bubble coalescence and break up. A dispersion model which takes into account the hydrostatic head and a variable gas velocity was applied to describe the measured concentration profiles in both phases. If increased mass transfer coefficients at the column bottom and measured local values of the hold up were used a striking agreement between experimental and predicted profiles could be obtained. The findings lead to a more sophisticated picture of the complex behaviour of gas-liquid dispersions at high interphase mass transfer rates.     

Hysteresis effects in countercurrent gas-liquid flow limitations in a vertical tube

New experiments on air-water countercurrent flow limitations in a vertical pipe are presented. The experiments were carried out to investigate the effect of test procedure on the occurrence of the two countercurrent flow limitations; namely the onset of flooding and complete carry-up limits. The results revealed the existence of significant hysteresis effects at both limits particularly for high liquid feed rate. For low liquid feed rate, hysteresis effects were only observed at the complete carry-up limit. Some associated visual observations are reported and the results were empirically correlated and compared with recent data obtained by others.     

An improved stagewise model of countercurrent flow liquid—liquid contactors

An improved stagewise model has been developed to represent more accurately the physical processes occurring in a liquid—liquid extraction column. The influence of drop size distribution is more realistically represented in this model. The model equations have been solved numerically with a range of parameter values in order to predict the extent of the influence of drop size distribution on extraction rates. Drop size distributions, measured in a turbine-agitated column section and inserted into the model equations, gave predictions of a considerable influence of size distribution on extraction column performance.     

Helical liquid flow on a vertical cylinder and its application to gas absorption

An experimental examination of a novel device for enhancing the gas absorption into an aqueous absorbent flowing down the outer wall of a vertical cylinder was reported. This device utilizes flexible strings tightly wound around the cylinder, taking the form of a multiple helix. The absorbent flows along parallel channels partitioned by the strings, maintaining mutual contact with the surrounding gas for a longer time than it would when it flows down the same cylinder wall in the absence of such strings. Both flow‐observation experiments and absorption experiments using water as the absorbent flowing along a single helical channel and carbon dioxide as the gas to be absorbed were carried out. The effectiveness of the helical‐flow device for promoting the absorption was recognized at water flow rates high enough to induce an oscillatory flow mode accompanied by periodical liquid?gas interface deformation. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3109–3118, 2013     

Gas–liquid flows in medium and large vertical pipes

Gas–liquid bubbly flows with wide range of bubble sizes are commonly encountered in many industrial gas–liquid flow systems. To assess the performances of two population balance approaches – Average Bubble Number Density (ABND) and Inhomogeneous MUlti-SIze-Group (MUSIG) models – in tracking the changes of gas volume fraction and bubble size distribution under complex flow conditions, numerical studies have been performed to validate predictions from both models against experimental data of Lucas et al. (2005) and Prasser et al. (2007) measured in the Forschungszentrum Dresden-Rossendorf FZD facility. These experiments have been strategically chosen because of flow conditions yielding opposite trend of bubble size evolution, which provided the means of carrying out a thorough examination of existing bubble coalescence and break-up kernels. In general, predictions of both models were in good agreement with experimental data. The encouraging results demonstrated the capability of both models in capturing the dynamical changes of bubbles size due to bubble interactions and the transition from “wall peak” to “core peak” gas volume fraction profiles caused by the presence of small and large bubbles. Predictions of the inhomogeneous MUSIG model appeared marginally superior to those of ABND model. Nevertheless, through the comparison of axial gas volume fraction and Sauter mean bubble diameter profiles, ABND model may be considered an alternative approach for industrial applications of gas–liquid flow systems.     

General model for prediction of pressure drop and capacity of countercurrent gas/liquid packed columns

A generalized model has been developed for the prediction of pressure drop and flooding in packed columns in which gas and liquid flow countercurrently. The model has been validated for a wide variety of packings, both random and structured. A single mathematical expression is used to describe all flow regimes: dry gas, irrigated gas flow below the load point, loading region, and flooding. The approach to the model development is fundamental in character and is an improvement over models published earlier.     

Liquid-wall shear stress in stratified liquid/gas flow

Stratified liquid/gas flow was experimentally investigated in a horizontal or slightly inclined circular pipe. The polarographic method was used to determine the liquid-wall shear stress. Both the liquid fraction and pressure gradient were also measured. Sixteen wall electrodes were positioned around the tube perimeter. Local liquid-wall shear stress profiles are presented for horizontal and near-horizontal flows. The averaged values are compared with the results obtained from a stratified flow model and models using the experimental data of liquid fraction and pressure drop. This paper was presented at the International Workshop on Electrodiffusion Diagnostics of Flows held in Dourdan, France, May 1993.     

逆流超重机传热的实验研究

主要是通过对逆流超重机传热实验数据的分析,讨论了冷热流体的进口温度、流量、超重机转速等因素对超重机传热的影响.通过实验数据的分析和比较得出超重机作为传热设备明显优于传统设备.     

Experimental study of gas and liquid permeability of a mortar

Eight samples cored from the same mortar were used to investigate their respective gas, ethanol and water permeability. Two gas and liquid permeability cells, using special devices for measuring the injected flow under steady conditions, were designed and presented in this paper. The obtained results showed that water permeability was systematically lower (in an order of magnitude from 1 to 2) than gas permeability whereas ethanol permeability was intermediate between these two values. Nevertheless, ethanol and gas permeabilities were found of the same order and, when gas permeability is corrected from the Klinkenberg (or slippage) effect, the results given by these two fluids are virtually identical and can be considered to be the intrinsic permeability value. Thus, the differences observed between water and gas permeability values have to be explained by other phenomena such as rehydration, dissolution and migration of fine elements or water adsorption in the thinnest pores.     

竖直微肋管内LNG流动沸腾传热特性的分析

实验研究了竖直微肋管内液化天然气(LNG)流动沸腾传热特性,分析热通量、质量流量以及入口压力对LNG两相流动传热特性的影响。针对实验工况分别采用Kim关联式、Koyama关联式以及两种不同F_tp系数的Wellsandt关联式对传热系数进行预测,并将实验结果与预测结果进行比较。结果表明,在整个实验工况范围内,采用Koyama关联式预测准确性最好。     

Experimental and CFD analysis of two-phase cross/countercurrent flow in the packed column with a novel internal

The pressure drop and liquid hold-up for the G-L cross/counter-current flow in a packed column with a novel internal was simulated using a Eulerian/Eulerian two-fluid model solved by a commercial CFD software CFX4.4. Simulation results are in good agreement with the experimental data of pressure drop. The internal significantly increases the gas radial velocity and lower the gas axial velocity, which lowers the pressure drop and improves operational flexibility. To minimize bypass flow caused by the internal, optimum baffle thickness and width of the internal's passage are proposed.     

Mass transfer characteristics of liquid films flowing down a vertical wire in a counter current gas flow

The wetted-wire packing, mainly consisting of a bundle of vertical parallel wires, is a promising concept for the use in separation columns. To investigate the multiphase flow inside the packing in detail and to estimate the performance of the packing, experiments on liquid films on a single vertical wire in a counter current gas flow were carried out. To get information about the interfacial area, an optical measurement of the film thickness was carried out with a digital high speed camera and image recognition tools. By measuring the evaporation of water and aqueous polyvinylpyrrolidone solutions into air, the gas-side mass transfer was determined. The liquid-side mass transfer was examined by measuring the desorption of CO₂ from water into air. The results show that the mass transfer coefficients are comparable to those appearing in common structured packings. When assuming a sufficiently high wire packing density, a specific interfacial area similar to corrugated sheet structured packings can be reached. Previous studies predicted a low pressure drop per packing height and extended capacity limits compared to common packings. In consideration of these results, the wetted wire packing therefore is shown to be suitable especially for absorption processes where a low pressure drop is favourable.     

Longitudinal mixing of the liquid phase in packed columns with countercurrent two phase flow

Axial mixing of the liquid phase in trickle flow through two columns packed with Raschig rings was determined by least square fitting of the experimentally obtained F-curve applying the Fibonacci optimal search method. The Péclet number was found to be independent of the gas flow rate and proportional to the liquid Reynolds number. The one parameter axial dispersed plug flow model was shown to be acceptable in describing axial mixing of the liquid phase. A simple correlation of the Péclet number is proposed for application in mass transfer design calculations     

内插螺旋立式上行管流场及传热性能的实验研究

通过粒子图像测速流场实验与传热实验相结合,研究了内插螺旋立式上行管的螺旋节距、丝径、中径比等结构参数在不同Re下对流场、阻力及传热性能的影响。结果表明,内插螺旋能够有效扰动和混合管内流体,使管内形成多个纵向旋涡的流体结构、增大管壁附近液体涡量,有利于强化传热。当Re相同时,管内平均流速v、Nu和综合换热性能PEC均随丝径增大而增大,随中径比减小而增大;随节距增大,3种参数均出现增大的趋势,节距大于20 mm后开始减小。管内流体的阻力f随丝径和节距增大而减小,随中径比增大而增大。综合比较,在较低Re时,节距p=20 mm、丝径e=1.6 mm、中径比D/d=0.75时综合传热效果最好。     

Adsorption on activated carbon in countercurrent flow: An experimental study

The work describes adsorption experiments from aqueous solutions on activated carbon using a counter-current adsorber. Phenol and paranitrophenol were used for single component adsorption and molasses colour for multicomponent adsorption experiments. Isotherms were determined using simple equilibrium experiments. Three different techniques were used for determination of the kinetics. These were finite bath, infinite bath and fixed bed experiments. A mathematical model for countercurrent adsorption was tested. The model includes the effect of film diffusion and pore diffusion as well as surface diffusion, and can handle systems with a nonlinear isotherms. Kinetic data in the form of an average diffusivity in the carbon determined from the finite bath experiments and isotherm data did not predict the operation of the countercurrent column well. Data from the fixed bed experiments predicted countercurrent column operation much better. This is deemed to be due to inhomogeneities in the carbon used, resulting in a fairly quick initial uptake of the main part of the solute and a slower uptake of a minor amount.     

Numerical study on gas and liquid slugs for Taylor flow in a T-junction microchannel

The rapid development of microfabrication techniques creates new opportunities for applications of microchannel reactor technology in chemical reaction engineering. The extremely large surface-to-volume ratio and the short transport path in microchannels enhance heat and mass transfer dramatically, and hence provide many potential opportunities in chemical process development and intensification. Multiphase reactions involving gas/liquid reactants with a solid as a catalyst are ubiquitous in chemical and pharmaceutical industries. The hydrodynamics of the flow affects the reactor performance significantly; therefore it plays a prominent role in reactor design. For gas/liquid two-phase flow in a microchannel, the Taylor slug flow regime is the most commonly encountered flow pattern. The present study deals with the numerical simulation of the Taylor flow in a microchannel, particularly on gas and liquid slugs. A T-junction empty microchannel with varying cross-sectional width (0.25, 0.5, 0.75, 1, 2 and 3 mm) served as the model micro-reactor, and a finite volume based commercial computational fluid dynamics (CFD) package, FLUENT, was adopted for the numerical simulation. The gas and liquid slug lengths at various operating and fluid conditions were obtained and found to be in good agreement with the literature data. Several correlations in the T-junction microchannel were developed based on the simulation results. The slug flows for other geometries and inlet conditions were also studied.