Experimental investigations of non‐Newtonian/Newtonian liquid‐liquid flows in microchannels

The plug flow of a non‐Newtonian and a Newtonian liquid was experimentally investigated in a quartz microchannel (200‐µm internal diameter). Two aqueous glycerol solutions containing xanthan gum at 1000 and 2000 ppm were the non‐Newtonian fluids and 0.0046 Pa s silicone oil was the Newtonian phase forming the dispersed plugs. Two‐color particle image velocimetry was used to obtain the hydrodynamic characteristics and the velocity profiles in both phases under different fluid flow rates. The experimental results revealed that the increase in xanthan gum concentration produced longer, bullet‐shaped plugs, and increased the thickness of the film surrounding them. From the shear rate and viscosity profiles, it was found that the polymer solution was in the shear‐thinning region while the viscosity was higher in the middle of the channel compared to the region close to the wall. Circulation times in the aqueous phase increased with the concentration of xanthan gum. © 2017 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 63: 3599–3609, 2017     

Counter‐current gas‐liquid wavy film flow between the vertical plates analyzed using the Navier‐Stokes equations

The article is devoted to a theoretical analysis of counter‐current gas‐liquid wavy film flow between vertical plates. We consider two‐dimensional nonlinear waves on the interface over a wide variation of parameters. The main interest is to analyse the wave structure at the parameter values corresponding to the onset of flooding observed in experiments. We use the Navier‐Stokes equations in their full statement to describe the liquid phase hydrodynamics. For the gas phase equations, we use two models: (1) the Navier‐Stokes system and (2) the simplified Benjamin‐Miles approach where the liquid phase is a small disturbance for the laminar or turbulent gas flow. With the superficial gas velocity increasing and starting from some value of the velocity, the waves demonstrate a rapid decreasing of both the minimal film thickness and the phase wave velocity. We obtain a region of the gas velocity where we have two solutions at one set of the problem parameters and where the flooding takes place. Both the phase wave velocity and the minimal film thickness are positive numbers at such values of the velocity. We calculate the flooding point dependences on the liquid Reynolds number for two different liquids. The wave regime corresponding to the flooding point demonstrates negative u‐velocities in the neighbourhood of the interface near the film thickness maximum. At smaller values of the superficial gas velocity, the negative u‐velocities take place in the neighbourhood of the film thickness minimum. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Analysis of roll wave characteristics under low liquid loading two‐phase flow conditions

An experimental study is conducted using a 0.152‐m ID facility to investigate the wave characteristics of two‐phase stratified wavy flow in horizontal pipelines. The experiments are conducted under low liquid loading condition, which is very commonly observed in wet gas pipelines. The experiments are conducted with water as the liquid phase, and repeated with 51 wt % of monoethylene glycol (MEG) in the aqueous phase to analyze the effects of MEG presence on wave characteristics. The experimental range of this study covers superficial gas velocity, v_Sg, values of 9–23 m/s and superficial liquid velocity, v_SL, values of 0.01–0.02 m/s. Similar test matrices are completed for the cases with and without MEG in the aqueous phase. A conductivity probe system is used to measure the wave characteristics at the liquid–gas interface. These characteristics include the wave celerity, frequency, amplitude, length, and liquid film thickness. The experimental oil–air wave characteristics data of Gawas et al. (Int J Multiphase Flow. 2014;63:93–104) is also used for comparison purposes. The trends in the resulting wave characteristics with respect to input parameters are investigated, for oil, water, or MEG–water mixture as the liquid phase. Common predictive methods for interfacial wave celerity, including shallow water theory, Watson (Proceedings of the 4th International Conference in Multi‐Phase Flows, Nice, France. 1989:495–512), Paras et al. (Int J Multiphase Flow. 1994;20(5):939–956), Al‐Sarkhi et al. (AIChE J. 2012;58(4):1018–1029), and Gawas et al. (Int J Multiphase Flow. 2014;63:93–104) are evaluated in comparison with the experimental data. The results of the wave frequency correlation of Al‐Sarkhi et al. (AIChE J. 2012;58(4):1018–1029) are also compared with the experimental wave frequency data. Lastly, a correlation is developed to predict the relative wave amplitude, as a function of superficial gas Weber number and liquid velocity number. Most of the commonly used two‐phase stratified flow models are developed with the assumption of steady‐state conditions, and neglect the transient wave effects. This study provides valuable experimental results on wave characteristics of stratified wavy flow for different types of liquid phase. Moreover, a comprehensive analysis of the parameters affecting the wave characteristics of stratified wavy flow is presented. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3177–3186, 2017     

Phase separation of gas–liquid two‐phase stratified and plug flows in multitube T‐junction separators

Using air and water as the working fluids, phase separation phenomena for stratified and plug flows at inlet were investigated experimentally, at a simple T‐junction and specifically designed multitube T‐junction separators with two or three layers. The results show that for these two flow patterns the separation efficiency of the two phases for any multitube T‐junction separator is much higher than that of the simple T‐junction. Increasing the number of connecting tubes in the multitube T‐junction separator can increase the separation efficiency. Generally, for stratified flow, complete separation of the two phases can be achieved by the two‐layer multitube T‐junction separator with five or more connecting tubes and by the three‐layer separator; increasing the gas flow rate, the liquid flow rate, or the mixture velocity under plug flow is detrimental to phase separation with a drop in peak separation efficiency. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2285–2292, 2017     

Theoretical and Experimental Studies on Acetylene Absorption in a Polytetrafluoroethylene Hollow‐Fiber Membrane Contactor

The separation of acetylene from a gas mixture was investigated using a polytetrafluoroethylene hollow‐fiber membrane contactor and 1‐methyl‐2‐pyrrolidinone as absorbent. The effects of the gas velocity, the liquid velocity, the feed gas concentration, and the module length on the acetylene mass transfer were investigated. The results showed that the acetylene mass transfer flux increased with increasing liquid velocity, gas velocity, and feed gas concentration, but decreased with increasing membrane module length. A mathematical model was used to predict the wetting extent of the membrane and the mass transfer resistance in the acetylene mass transfer process. The wetting extent of the membrane was found to increase with increasing liquid velocity and to be effectively restrained with increasing gas velocity. The liquid phase resistance and the wetted‐membrane phase resistance controlled the acetylene mass transfer in the acetylene absorption process. The acetylene absorption efficiency was maintained at 90 % for 114 h of the C₂H₂ membrane absorption–thermal desorption cycle process.     

The effect of the size of square microchannels on hydrodynamics and mass transfer during liquid‐liquid slug flow

The present study investigated the influence of square microchannel (MC) size on hydrodynamics and mass transfer in the liquid‐liquid slug flow regime. Three square MCs with the hydraulic diameters of 200, 400, and 600 μm were used. The employed method for estimating mass‐transfer coefficients remarkably increased the accuracy of the results. The findings revealed that decreasing the MC size improved the interfacial area due to plug length enlargement and deteriorated mass‐transfer resistances because of augmented internal circulations, leading to the considerable enhancement of mass‐transfer coefficients. The increasing effect on the overall mass‐transfer coefficient became greater with flow velocity, showing that size effect on mass‐transfer resistances was more profound at higher flow velocities. The influence of size on the interfacial area was significantly greater than that on mass‐transfer resistances due to the significant increment of wall film length with the decrease in channel size. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Relations between the molecular aggregation state and ionic conductivity in photopolymerized crosslinking polymers with oligo(oxyethylene) chains

A mixture of a vinyl monomer and a crosslinking agent was photopolymerized to form a crosslinked polymer film. Methacrylate with pendant oligo(oxyethylene) chain and poly(ethylene glycol) dimethacrylate were used as the vinyl monomer and crosslinking agent, respectively. The ionic conductivity of the film increased with an increasing concentration of LiClO₄ and then decreased. The size of the quasicrystalline aggregation phase composed of pendant and crosslinking chains in the film decreased with an increasing concentration of LiClO₄. The amorphous pendant and crosslinking oxyethylene chains gave rise to increased segmental motion and conductivity. The dissolution was depressed for a decrease in the ionic conductivity at a high LiClO₄ concentration at which the interactions among ions became stronger and the crystal phase of LiClO₄ was formed. The amount of the dissolution of the aggregation phase increased with an increasing crosslinking agent concentration. The quasicrystalline aggregation phase became larger with an increasing length of the pendant chains, and an increase in the size of the aggregation phase resulted in a decrease in the ionic conductivity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1272–1277, 2002     

Characterization of konjac glucomannan–quaternized poly(4‐vinyl‐N‐butyl) pyridine blend films and their preservation effect

Novel polymer blends were prepared from a mixture of 2 wt % konjac glucomannan and 4 wt % quaternized poly(4‐vinyl‐N‐butyl) pyridine (QPVP) in aqueous solution and dried at room temperature for 72 h. Their structure and properties were studied by infrared, wide‐angle X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry. Thermal stability in the dry state was reduced with increasing content of QPVP. Compared with QPVP film, the tensile strength of the films was improved in the dry state. The maximum value of 12.74% tensile break elongation was reached when the content of QPVP was 30%. Structural analysis indicated that clear phase separation was observed when the content of QPVP was only 50%. Results from the filmcoating preservation experiments with lychee showed that this blend film had water‐holding ability. The fruit weight loss rate and rot rate both decreased in various degrees. The potential uses of these novel polymer films could be as preservative films. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1868–1875, 2004     

Optical properties of ethyl‐cyanoethyl cellulose/poly(acrylic acid) cholesteric liquid crystalline composite films

Ethyl‐cyanoethyl cellulose [(E–CE)C]/poly(acrylic acid) (PAA) composite films were prepared by photopolymerizing acrylic acid (AA) in (E–CE)C/AA cholesteric liquid crystalline solutions. With the selection of suitable concentrations, (E–CE)C/PAA composite films showed vivid colors due to the selective reflection property of the cholesteric phase. It was found that the wavelength of reflection was a function of the concentration of (E‐CE)C, and the reflectivity was increased with increasing thickness of the film. The selective reflection of the composite holds well upon heating at temperatures below 160°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 213–217, 2004     

竖直窄矩形通道内环状流的流动传热特性

为了研究竖直窄矩形通道内环状流的流动传热特性,建立了窄矩形通道内环状流的数学物理模型,并进行了实验验证。通过数值求解环状流的数学物理模型得到了环状流区域的压降梯度、沸腾传热系数和液膜内的速度分布。结果表明窄矩形通道内的环状流模型能够很好地预测环状流区域的压降梯度和沸腾传热系数,而且环状流液膜内速度在法向的分布是非线性的,在层流边界层区速度梯度较大。热通量和窄矩形通道的尺寸对液膜的流速有很大影响,随热通量的增加和窄矩形通道尺寸的减小液膜的流速逐渐增加,然而质量流速对液膜流速的影响较小,而且随质量流速的增加液膜的速度逐渐减小。     

Investigating the liquid film characteristics of gas–liquid swirling flow using ultrasound doppler velocimetry

A novel gas–liquid two‐phase flow metering method was proposed. A spiral vane mounted in the inner pipe was used to transform inlet flow patterns into gas–liquid swirling annular flow. The thickness and velocity profile of liquid film were measured by ultrasound Doppler velocimetry. The liquid flow rates were obtained by integrating of velocity profile during the liquid film zone. Experiments were carried out in an air–water two‐phase flow loop and an ultrasonic transducer was installed under the bottom of the test section with the Doppler angle of 70°. The flow patterns included stratified wavy, annular, and slug flows. Compared with non‐swirling flow, the liquid film thickness at the bottom reduces greatly. The measurement accuracy of liquid flow rate was independent of inlet flow patterns, gas and liquid velocities. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2348–2357, 2017     

Role of operating conditions in determining droplet size and viscosity of tackifier emulsions formed via phase inversion

Water‐based pressure‐sensitive adhesives are formulated by combining a polymer latex with a tackifier emulsion. The latter is an oil‐in‐water emulsion made by the process of phase inversion. The phase inversion itself is carried out in a stirred tank fitted with a heating jacket by progressively adding water to a water‐in‐oil emulsion. The point of onset of phase inversion and the characteristics of the emulsion that is formed depend on process conditions; these include temperature, rate of water addition, and agitation speed. The role of these operating conditions is elucidated here. Increasing temperature delayed the onset of phase inversion slightly, but it did not affect emulsion particle size, provided it remained below a critical value. Agitation speed had to be increased upon increasing the water flow rate to prevent increasing the particle size. Finally, the point of onset of phase inversion could be predicted reasonably well using a model available in the literature. © 2010 American Institute of Chemical Engineers AIChE J, 57: 96–106, 2011     

矩形截面螺旋通道内弹状流的流动特性

对水平放置矩形截面螺旋通道内弹状流的流动特性进行了实验研究.通过实验获得了不同周角下的气弹演变过程和局部流动特征,结果表明,其流动特性会随着螺旋周角位置的变化而变化.根据实验数据分析发现,同一工况下,不同转角气弹的运动速度、频率和长度分布不尽相同.重力和离心力的相对大小决定着内外壁面液膜的厚度,给出了同一条件下,不同时刻的液膜厚度的演变过程.最后对下降液膜的运动速度展开了分析研究,在螺旋上升过程中,液膜下降速度逐渐减小,在螺旋下降段,液膜速度明显增大.     

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     

Small‐angle X‐ray scattering analysis of nanophase titanium dioxide,poly[N‐(4‐sulfophenyl)aniline], and their composite

Small‐angle X‐ray scattering and spectroscopic (infrared and ultraviolet–visible) techniques were used to investigate the interactions between titanium dioxide (TiO₂) and the semiconductor polymer poly[N‐(4‐sulfophenyl)aniline] (PSA) in a poly[N‐(4‐sulfophenyl)aniline]/TiO₂ composite (TPSA). The radius of gyration of the cross section, the radius and length of the rodlike particle, the persistence length, the surface fractal dimension, and the PSA layer thickness on TiO₂ in aqueous solutions and in powder form were calculated. The results indicated that the aggregation of TiO₂ particles on drying was reduced by the formation of the composite with the semiconductor polymer. Only the particle length of the TPSA particle (which had a rodlike shape) increased on drying, probably because of increasing void sizes and the formation of aggregation. The persistence length of the TPSA particles decreased with respect to its individual components. The PSA layer thickness on TiO₂ was about 3.6 nm and decreased (to 2.6 nm) on dehydration because of the expulsions of water molecules from the TiO₂/PSA composite. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3183–3187, 2003     

水平管内气液段塞流液塞长度发展规律的实验和模拟研究

In petroleum industry, the slug flow is a fre-quently encountered flow regime in multiphase flowpipeline. For pipeline designers, the liquid slug lengthdistribution is important for the proper design ofdownstream facilities, such as slug catcher and sepa-ration system. However, for its transient and unsteadynature, it is a great challenge for engineers to correctlypredict the flow parameters of slug flow, especiallythe maximum liquid slug length. The unit cell model for slug flow in horizontal…     

Computational Fluid Dynamics Modeling of Gas‐Liquid Two‐Phase Flow around a Spherical Particle

Microscale studies, which can provide basic information for meso‐ and macroscale studies, are essential for the realization of flow characteristics of a packed bed. In the present study, the effects of gas velocity, liquid velocity, liquid‐solid contact angle, and liquid viscosity on the flow behavior were parametrically investigated for gas‐liquid two‐phase flow around a spherical particle, using computational fluid dynamics (CFD) methodology in combination with the volume‐of‐fluid (VOF) model. The VOF model was first validated and proved to be in good agreement with the experimental data. The simulation results show that the film thickness decreases with increasing gas velocity. This trend is more obvious with increasing operating pressure. With increasing liquid velocity, the film thickness tends to be uniform on the particle surface. The flow regime can change from film flow to transition flow to bubble flow with increasing contact angle. In addition, only at relatively high values does the liquid viscosity affect the residence time of the liquid on the particle surface.     

Studies on the mesomorphic properties of ferrocenylene‐based organophosphorous liquid‐crystalline polymers containing phenyl and biphenyl pendant units

The synthesis, mesomorphic character, and effect of spacers in ferrocene‐containing main‐chain liquid‐crystalline polymers are reported in this article. Two different monomers containing ferrocene and phenyl/biphenyl phosphate groups possessing even numbers of spacers from 2 to 10 were prepared and polymerized by polycondensation at room temperature. All the polymers gave birefringent melt except one. The identification of the mesophase was transparent with an increase in spacers. The effect of substitution in the side chain with regard to bulkiness and spacers were studied with thermogravimetric analysis and differential scanning calorimetry. The results reveal that the thermal stability of the polymers increased with the increasing bulkiness of the side chain and decreased with increasing spacer length. The incorporation of the phosphorous moiety also had a considerable effect on the glass‐transition temperature. Char yield of the polymer decreased with increasing methylene chain length, and it did not vary much with the size of the pendent groups. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 831–841, 2002     

Bubble splitting under gas–liquid–liquid three‐phase flow in a double T‐junction microchannel

Gas–aqueous liquid–oil three‐phase flow was generated in a microchannel with a double T‐junction. Under the squeezing of the dispersed aqueous phase at the second T‐junction (T2), the splitting of bubbles generated from the first T‐junction (T1) was investigated. During the bubble splitting process, the upstream gas–oil two‐phase flow and the aqueous phase flow at T2 fluctuate in opposite phases, resulting in either independent or synchronous relationship between the instantaneous downstream and upstream bubble velocities depending on the operating conditions. Compared with two‐phase flow, the modified capillary number and the ratio of the upstream velocity to the aqueous phase velocity were introduced to predict the bubble breakup time. The critical bubble breakup length and size laws of daughter bubbles/slugs were thereby proposed. These results provide an important guideline for designing microchannel structures for a precise manipulation of gas–liquid–liquid three‐phase flow which finds potential applications among others in chemical synthesis. © 2017 American Institute of Chemical Engineers AIChE J, 63: 376–388, 2018     

A one-dimensional model of plug flow pneumatic conveying

A one-dimensional model of pulse or plug flow is proposed. This type of flow is observed at high mass ratios of solids to gas and requires gas velocities orders of magnitude less than dilute phase systems. Plug stability criteria are examined by considering the axial interparticle stresses within single plugs and the effect of the radial transmission of these stresses on wall friction. Establishment of the fluid pressure gradient within the plug and the existence of a settled layer of solids in the interplug space are shown to be important requirements. These concepts are used in the formulation of an empirical pressure drop equation which is used in the correlation of experimental data. Comparison of predicted and experimental values is reasonable for the air-sand system considered. The model should be of value in the planning and interpretation of future experimental studies.