Experimental investigation of liquid–liquid flow in an inclined pipe using dimensionless numbers

Two-phase flow is a common phenomenon in the energy industry, where flow patterns significantly affect heat transfer and pressure drop in different systems. However, there is no unique or comparable flow map because of its dependency on dimensional parameters. Therefore, an analysis using dimensionless numbers makes the results comprehensive. To do so, a series of liquid–liquid flow experiments (1296 experiments) were conducted in a transparent pipe at the different velocities of the phases. The flow patterns were captured using a high-speed camera. The experiments were performed at eight different inclinations within the range of −20 to +20 degrees. Six flow patterns are observed at different inclinations; stratified flow with mixing at the interface (STMI), dispersion of water in oil (Dw/o), dispersion of oil in water (Do/w), dual continuous (DC), slug, and wavy stratified (WST), where the first five flow patterns are presented in the upward flow and the two last flow patterns disappear in some of the downward flow. The pattern of boundaries for each flow pattern in the upward flow shows dependency on inclination, while in the downward flow condition, a rather general format can be applied to most of the patterns. The analysis illustrates that gravity and buoyancy forces are the dominating forces in the system compared to other forces, such as viscous, inertia, and interfacial tension, which are due to the inclination of the pipe.     

水平与微倾斜管内间歇流中长气泡的形态特征

利用双平行探针技术和摄像方法对水平和近水平微倾斜管内长气泡的形态特征进行了实验研究.实验结果表明气泡头部以及气泡体的形态特征取决于气液混合Froude数和管道倾角,而尾部特征还与气泡长度有关;小气泡通过单纯水跃面的长气泡尾部向液塞区弥散,而具有阶梯状尾部结构的长气泡并不向液塞区弥散小气泡,所以气泡尾部结构特征的变化决定了弹状流向段塞流的转变;管道倾角对长气泡形态特征有显著的影响,下倾管内的长气泡在低Froude数时出现头尾倒置现象,同时下倾管内的长气泡比上倾管更易保持阶梯状的尾部结构,所以下倾管的弹状流区比上倾管宽.     

Flow pattern transition for vertical downward two phase flow

Experiments of flow pattern for vertical downward gas—liquid flow are reported. In addition theoretically based transition criteria for the flow pattern are presented. The experimental results compare resonably well with the theoretical model for the prediction of flow pattern in vertical downward flow.     

Bubble evolution and necking at a submerged orifice for the complete range of orifice tilt

Bubble formation at an inclined orifice has been studied numerically using coupled‐diffused interface‐smoothed particle hydrodynamics. The simulation covers the entire range of orifice inclination, starting from upward facing (0^°) to downward facing (180^°) orientation for a moderate air flow (30 cm³/s). Bubble at the orifice mouth becomes asymmetric as the plate gets tilted. The asymmetry maximizes at vertical orientation but with downward facing orifices symmetry restores. The local hydrodynamic structure reveals that the internal circulation cells in bubble become stronger as the inclination increases making the growing bubble asymmetric. Interestingly, bubble volume for downward facing orifice is 4.75 times higher than the bubble released at upward facing orifice. Observations from the present simulations suggest that bubble frequency and shape can be controlled by allowing appropriate inclination in the orifice mouth. © 2012 American Institute of Chemical Engineers AIChE J, 59: 630–642, 2013     

Hydrodynamic characteristics of gas-liquid slug flow in a downward inclined pipe

Gas-liquid slug flow in a downward inclined pipe was studied experimentally by employing a wire-mesh sensor that enables quantitative measurements of the cross-sectional void fraction distribution. Processing of the wire-mesh sensor data was applied to carry out a statistical analysis of characteristic parameters of downward slug flow, such as bubble and liquid slug length distributions, as well as to determine the ensemble-averaged shapes of the bubble nose, liquid film and bubble tail. It was found that the pipe inclination affects mainly the bubble length, while variation in the gas flow rate affects both bubble and slug length. The bubble nose shape is more sensitive to the flow conditions than the bubble tail. The 3D structure of an elongated bubble in downward slug flow was reconstructed from the wire-mesh sensor data.     

Flow regimes,hold–up and pressure drop for two phase flowin helical coils

Experimental results on flow pattern, hold–up and pressure drop are presented for cocurrent upward and downward air water flow in helical coils. A tube of 0.01 m internal diameter was used and the ratio of coil to tube diameter was varied from 11 to 156.5. Water flow rate was varied from 4.9 × 10-⁶ m³/s to 92 × 10-⁶ m³/s while the range of gas flow rate covered was 83 × 10-⁶ m³/s to 610 × 10-⁶ m³/s. A new mechanistic approach is proposed to correlate pressure drop data in coils. The proposed model retains the identity of each phase and separately accounts for the effects of curvature and tube inclination resulting from the torsion of the tube. This makes it possible to use a single model to predict pressure drop for both upward and downward two–phase flow in coiled tubes. Required correlations for hold–up, interfacial friction factor and friction factors for individual phases are provided.     

Influence of tube inclination on the flow regime boundaries of condensing steam

Flow regime data of condensing steam inside an inclined 13.4 mm ID tube are presented. The effect of upward and downward inclinations within ± 10° on the different transition lines is discussed. In all test runs, complete condensation has been achieved inside the condenser, with or without full tube at exit depending on the total mass flow rate and inclination angle. It is shown that the zones occupied by the wavy and slug regimes experience significant shifts, whereas the effect on the annular flow boundary appears to be insignificant at the present small inclination angles. The present data sets are compared with adiabatic gas-liquid flow regime maps developed analytically and experimentally for horizontal and inclined tubes. Deviations due to the condensation process are observed; however, consistent trends are identified among the two types of flow.     

气液向下并流填料塔的流型和压降

本文提供了气液向下并流填料塔内的流型转变点数据和压降数据,并对文献中提出的几个流型图和压降公式进行了验证。     

垂直管内向上气液流动的分析(Ⅰ)——弹状气泡与下落液膜流动

弹状流是垂直管内气液两相上升流中的一种重要流型。本文从相对坐标系的质量与动量衡算出发,对弹状气泡与下落液膜流动进行分析,建立了相应的计算公式。本文也是完整的弹状流数学模型的一部分。     

封闭腔内水自然对流换热数值模拟

为了揭示封闭腔内非Boussinesq流体在浮力驱动下所特有的流动换热现象和形成机理,采用CFD软件Fluent对封闭腔内水的自然对流进行数值模拟,得到矩形封闭腔高宽比、Rayleigh数、倾斜角度、壁面温度差对流动和传热的影响规律。研究结果表明：由于水的密度在3.98℃达到最大,两竖壁面温度跨越这一点时会引起流动图像反转;具有流动反转的双涡结构降低了对流换热平均Nusselt数;相同Rayleigh数下,高宽比为1对应对流换热平均Nusselt数最大值;倾斜角度对平均Nusselt数影响与Rayleigh数和温度边界条件有关。     

倾斜下降管内油气水三相流流型转变的实验研究

对倾斜下降管倾角变化对油气水三相流流型转变的影响进行了研究 ,通过大量实验得到流型图 ,发现倾角对流型转变有重大影响 :倾角增大到 3 0°时 ,增大气流量 ,泡状流已不再转变为间歇流 ,而是分层流 ;倾角变化对环状流和间歇流之间的转变影响显著。得到的界限方程规律与实验现象及流型图符合良好     

Modeling of low viscosity oil-water annular flow in horizontal and slightly inclined pipes: Experiments and CFD simulations

To characterize the effect of pipe inclination, low viscosity, flow rate and inlet water cut on annular flow pattern, a low viscosity oil-water two-phase annular flow in horizontal and slightly inclined (+1°, +3° and +5°) pipes with diameter of 20 mm has been experimentally investigated. A modified VOF model based on the CFD software package FLUENT was used to predict the in-situ oil fraction and pressure drop. The experimental data indicate that annular flow appears at a medium-high water cut. The slip ratio increases with flow rate increase but decreases with increasing water cut. The changes are more significant as the degree of inclination increases. Pressure drop is strongly dependent on flow rate, as it increases rapidly as inlet flow rate increase. Good agreement between the experimental data and calculated results of slip ratio and pressure drop was obtained.     

下倾管中活塞流液塞长度波动特性

通过采集下倾管中活塞流的差压信号,应用互相关法分析得到液塞长度时间序列.利用统计理论与分形理论分析液塞长度时间序列来揭示液塞长度波动特性.结果表明：气相折算速度对液塞长度的影响远大于液相折算速度.液相折算速度较大时,随着混合速度的增加,液塞长度波动的混沌程度增加;而液相折算速度较小时,随着混合速度的增加,液塞长度波动的混沌程度减小.在管线下倾角较大的情况下,液塞长度分布集中在较小的范围内.管线下倾角越大,液塞长度波动的长程相关性越好.     

Adiabatic two-phase flow in narrow channels between two flat plates

Adiabatic cocurrent flow of air and water through a narrow passage between two flat plates 240 mm long and 99mm wide with gap-widths of 0.778 mm and 1.465 mm was investigated for six different orientations: Vertically upward and downward, 45^° inclined upward and downward, and horizontal flows between horizontal plates and between vertical plates. Except for horizontal flow between vertical plates, the effects of gap width and flow channel orientation on flow pattern, void fraction and friction pressure drop were found to be small in narrow channels. The void fraction and two-phase friction multiplier data could also be reasonably correlated in terms of the Martinelli parameter. For horizontal flow between vertical plates, both the void fraction and friction multiplier data showed strong mass velocity effects. Several friction pressure drop correlations were tested for applicability to the narrow channels including a separated flow model proposed in this work.     

负压差立管下料过程压力脉动的传递性实验与分析

在高13m大型循环流化床装置上,对φ150 mm×900 mm负压差立管内气固两相流的动态压力进行了轴向多点测量,并用标准偏差进行了分析,主要研究立管下料过程的动态传递特性.实验表明负压差立管内存在明显的压力脉动现象,这种压力脉动具有一定的传递性.颗粒质量流率比较小时是稀密两相共存流态,稀相区的压力脉动主要受进料流量振荡的影响,向下传递;密相区的压力脉动主要受立管的波动性排料影响,向上传递;随着颗粒质量流率的增加达到浓相输送流态时,上部是连续式浓相输送流态,下部是密相波浪式输送流态,立管的压力脉动主要受进口流量振荡和排料过程压缩气体作用,向下传递.对立管的压力脉动进行标准偏差分析表明脉动压力传递沿颗粒的流动方向上具有幅值增大特性.在立管内流态从稀密两相共存流态转变为浓相输送流态时,由于颗粒压缩气体分量最大,压力脉动幅值最大,减小或增加颗粒质量流率,压力脉动幅度均降低.     

Effect of pipe orientation on dense-phase transport in inclined upward and downward flows

A physical model is presented to describe the flow characteristics of cocurrent two-layer upflow and downflow through inclined tubes. The influence of inclination angle on these two kinds of flow patterns has been investigated. For inclined upflow, the solids/gas velocity ratio is less than unity and decreases slightly with the increase of inclination angle, whereas for inclined downflow, this velocity ratio is, in general, greater than unity and increases with the inclination angle. The average voidage increases as the inclination angle decreases for inclined upflow while an opposite trend exists for inclined downflow. The pressure gradient is invariably negative for inclined upflow at various inclination angles and for inclined downflow of low inclination; however, the gradient becomes positive for inclined downflow at higher inclination angles. A flow regime map has also been presented. The present predictions agree well with the existing published experimental results.     

EFFECT OF PIPE ORIENTATION ON DENSE-PHASE TRANSPORT IN INCLINED UPWARD AND DOWNWARD FLOWS

A physical model is presented to describe the flow characteristics of cocurrent two-layer upflow and downflow through inclined tubes. The influence of inclination angle on these two kinds of flow patterns has been investigated. For inclined upflow, the solids/gas velocity ratio is less than unity and decreases slightly with the increase of inclination angle, whereas for inclined downflow, this velocity ratio is, in general, greater than unity and increases with the inclination angle. The average voidage increases as the inclination angle decreases for inclined upflow while an opposite trend exists for inclined downflow. The pressure gradient is invariably negative for inclined upflow at various inclination angles and for inclined downflow of low inclination; however, the gradient becomes positive for inclined downflow at higher inclination angles. A flow regime map has also been presented. The present predictions agree well with the existing published experimental results.     

板式换热器相变流动的传热及压降特性

建立了三维单流道模型,模拟了波纹倾角和波纹节距对相变流动传热和压降特性的影响。结果表明,沸腾传热和压降特性同时受到流动形式和触点影响,"曲折型"流动有利于液膜蒸发增强传热,触点对气相的扰动作用小于液相,因此在气相体积分数较高的区域的触点处气液相变转化现象不明显。传热系数随波纹倾角的增加而增大,随波纹节距的增加而减小,但在相同入口Reynolds数下波纹节距λ=16 mm比14 mm的传热系数大,主要是因为流动形式的改变在某种程度上减弱了触点数目减少对传热的影响。β=75°和λ=10 mm时传热性能最好。沸腾流动的压降随波纹倾角的增大先升高后降低,在β=65°左右达到峰值,随着波纹节距的增大而降低。     

IDENTIFICATION OF LIQUID-LIQUID FLOW PATTERN IN A HORIZONTAL PIPE USING ARTIFICIAL NEURAL NETWORKS

Identification of flow pattern during the simultaneous flow of two immiscible liquids requires knowledge of the flow rate of each fluid as well as knowledge of other physical parameters like conduit inclination, pipe material, pipe diameter, viscosity of the oil, wetting characteristics of the pipe, design of the entry mixer, and fluid-fluid interfacial tension. This article presents an artificial neural network (ANN)-based novel technique to determine the liquid-liquid flow regime. This approach uses phase superficial velocities as input parameters, which are obtained from a specific set of data obtained from experimental investigations. Both experimental and ANN-based determinations of liquid-liquid flow pattern have been undertaken for a common data set and the results are compared to prove the effectiveness of ANNs in pattern recognition. A unique ANN architecture is identified with three hidden layers, and the inputs and outputs are modeled into binary form. Levenberg-Marquardt (LM) learning algorithm is used for training this neural network. The design details of the ANN, parameter modeling, and training aspects are presented.