Transport processes at single droplets in micellar liquid/liquid systems

In many industrial applications, the knowledge of the occurring transport processes in liquid/liquid systems is of great interest to design a multiphase reactor or an extraction column, for instance. All transport processes in liquid/liquid systems are governed by the interface. In some processes surfactants are needed. Surfactants change many interfacial properties which affect the transport processes. In this work, the influence of high surfactant concentrations (micellar systems) on transport processes is regarded. To understand, the occurring reduction of the drop rise velocity and of mass transfer rates experimental investigations of the occurring interfacial phenomena are carried out. Therefore, interfacial tension measurements as well as colloidal probe atomic force measurements of liquid/liquid systems were conducted. It was proved that for high nonionic surfactant concentrations a change of the phase behavior must be taken into consideration to describe transport processes in micellar liquid/liquid systems. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1092–1104, 2015     

Linear and radial marangoni flows of surfactants

The migration velocities of surfactants on the surface of tap water are measured by the tracer method. The results are well reproducible, although the surfactants and the water are used without special purification. A decrease in the surfactant migration velocity with time was observed. It is found that the main cause of the decrease is an increase in the weight of the water adjacent to the surface film. The radial migration after a very short time is characterized by uniform surfactant motion.     

Chromate removal from wastewater using micellar enhanced crossflow filtration: Effect of transmembrane pressure and crossflow velocity

Removal of chromate from wastewater was investigated using Micellar Enhanced Crossflow Microfiltration Technique (MEMF) with cationic surfactant, cetyltrimetylammoniumbromide (CTAB). The variation of chromate, surfactant rejections and permeate flux with time were measured at two different CTAB concentrations as a function of transmembrane pressure drop (ΔP) and crossflow velocity, while CTAB/chromate, membrane pore size, temperature and pH of the feed solution was kept constant. For low CTAB concentration, it was observed that the efficiencies of chromate and surfactant removal increased with increasing ΔP, but decreased with increasing crossflow velocities. It was also observed that the effects of crossflow velocities and ΔPs on the rejections decreased for high CTAB concentration. It was found that fouling of the membrane by surfactant is very rapid at low crossflow velocity and high ΔPs at low CTAB concentration. As a result of this case, both transient permeate flux (J) and steady state permeate flux (J^?) decreased with decreasing crossflow velocity and increasing ΔP for both CTAB concentration. Unlike, modified fouling index (MFI) values increase with decreasing crossflow velocity and increasing ΔP. It was also observed that the effect of surfactant concentration in the 150, 200, and 250 kPa pressure and 3, 4, and 5 m/s crossflow velocity intervals dominates at high surfactant concentration.     

Mechanism of Local Fluidization in Converging Packed Beds

The velocity profile on the bed surface of two‐dimensional linear‐converging beds with 15° and 30° wall angles was measured at different superficial velocities using hot‐wire anemometry. The results of the velocity measurements indicate that local fluidization in the corners is caused by the geometry‐induced maldistribution of fluid flow, and it occurs when the velocity in the corners exceeds the minimum fluidization velocity of particles. The results of pressure measurements within the bed show the same trend as the velocity profile, providing a qualitative verification of the velocity profile measurement. It is shown that the variation of measured pressure drop over the bed with velocity does not agree with the Ergun equation at high superficial velocities due to the severe maldistribution of fluid flow.     

Simulation and experiments of droplet deformation and orientation in simple shear flow with surfactants

The deformation and orientation behavior of three-dimensional (3D) viscous droplets with and without surfactants is studied in simple shear flow using simulations and experiments. Two added amounts of surfactants are considered, along with a range of viscosity ratios and capillary numbers. The numerical method couples the boundary integral method for interfacial velocity, a second-order Runge-Kutta method for interface evolution, and a finite element method for surfactant concentration. The algorithm assumes a bulk-insoluble, nonionic surfactant, and uses a linear equation of state to model the relationship between the interfacial tension and the surfactant concentration on the drop surface. The algorithm was validated by comparison with other numerical results and good agreement was found. The experiments are performed in a parallel-band apparatus with full optical analysis of the droplet. The simulated and measured 3D steady-state shape of the ellipsoidal drops and their orientation are in reasonably good agreement. It was found that the surfactants have a greater effect on drop geometry for smaller viscosity ratios and that the deformation increases as the transport of surfactant becomes more convection dominated. It was also found that surfactants cause the drops to align more in the flow direction and that, for both clean and surfactant-covered drops, this alignment increases with viscosity ratio. Finally, simulations showed a wider distribution of surfactant on the interface for smaller viscosity ratios.     

LASER-BASED FLOW MEASUREMENTS OF DILUTE VERTICAL PNEUMATIC TRANSPORT

Dilute vertical pneumatic transport in a vertical lifter was studied using the sophisticated measurement techniques of laser Doppler anemometry (LDA) and phase Doppler anemometry (PDA). The vertical lifter consisted of a lower fluidized silo, an upper receiving tank, and a connecting vertical transport pipe made of clear glass. The experimental study was performed in order to get detailed information of the complex gas-particle flow behavior in a dilute vertical conveying system. Particle diameter, axial particle, and tangential particle velocities, as well as root mean square velocities, were measured simultaneously for different flow conditions. In addition, overall solid mass fluxes were obtained using weighing cells. Smooth and spherical zirconium oxide (ZrO₂) solids were applied with two different particle size distributions. Measurements were performed using different flow rates of air. The air inlet condition was varied in order to study its effect on the flow behavior. The particle diameter measurements show that no axial or radial segregation by size occurs for this transport condition. The results show that the particle velocity is independent of the particle size as well. The axial velocity profiles at different heights are almost identical and flat, which indicates fully developed turbulent pipe flow. The turbulent velocity measurements show that turbulence is mainly caused by the velocity gradients, and not by particle-particle collisions in dilute flow. The solid mass flux measurements show the importance of optimum inlet condition and how this influences the mass flux.     

Void transport in resin transfer molding

The transport of single drops through a hexagonal cylinder array is used to study the void movement and deformation in a resin transfer molding process. A transparent flow cell is used to visualize the transport of voids through a porous media model. Experiments are conducted with nearly inviscid water drops and viscous glycerol drops with drop sizes ranging from 0.4 to 80 μl, and with both a Newtonian fluid and Boger fluid with average resin velocities ranging from 0.011 to 0.140 cm/s. Two critical capillary numbers, which determine the breakup (Ca_b) and mobilization (Ca*) of drops, are measured to better understand the flow dynamics of voids. As demonstrated by the experiments, there is a critical drop size, below or above which a quite different flow behavior is observed. Such a transition is analyzed with consideration of the geometry characters in the flow field. Results expand the former studies in this area to a significantly larger range of drop sizes and capillary numbers. Particle Tracking Velocimetry is also used to quantify the local velocity, shear stress, extensional stress and energy dissipation in the flow field. Polym. Compos. 25:417–432, 2004. © 2004 Society of Plastics Engineers.     

Transient rise velocity and mass transfer of a single drop with interfacial instabilities - experimental investigations

An experimental study of transient drop rise velocities and mass transfer rates was carried out in the system toluene/acetone/water which is known to show interfacial instabilities. The rise velocity of toluene drops was studied without added solute (acetone) in the diameter range 1-3 mm and with added solute for 2 mm drops. The initial concentration of the transferred solute was varied from 0 to 30 g/L. The transient drop rise velocities were used to quantify the Marangoni effect since the drag coefficient depends on the strength of the Marangoni convection patterns caused by interfacial tension gradients. In addition, mass transfer measurements were carried out in order to determine the modification of the mass transfer rate due to Marangoni convection. Velocity and mass transfer measurements were then correlated via the contact time. Results reveal the existence of a range in which a critical value for the solute concentration can be defined for Marangoni convection.     

LASER-BASED FLOW MEASUREMENTS OF DILUTE VERTICAL PNEUMATIC TRANSPORT

Dilute vertical pneumatic transport in a vertical lifter was studied using the sophisticated measurement techniques of laser Doppler anemometry (LDA) and phase Doppler anemometry (PDA). The vertical lifter consisted of a lower fluidized silo, an upper receiving tank, and a connecting vertical transport pipe made of clear glass. The experimental study was performed in order to get detailed information of the complex gas-particle flow behavior in a dilute vertical conveying system. Particle diameter, axial particle, and tangential particle velocities, as well as root mean square velocities, were measured simultaneously for different flow conditions. In addition, overall solid mass fluxes were obtained using weighing cells. Smooth and spherical zirconium oxide (ZrO₂) solids were applied with two different particle size distributions. Measurements were performed using different flow rates of air. The air inlet condition was varied in order to study its effect on the flow behavior. The particle diameter measurements show that no axial or radial segregation by size occurs for this transport condition. The results show that the particle velocity is independent of the particle size as well. The axial velocity profiles at different heights are almost identical and flat, which indicates fully developed turbulent pipe flow. The turbulent velocity measurements show that turbulence is mainly caused by the velocity gradients, and not by particle-particle collisions in dilute flow. The solid mass flux measurements show the importance of optimum inlet condition and how this influences the mass flux.     

结合吸附模型预测油水液滴的界面流变性质

界面活性分子在油水界面的吸附将改变其界面性质,如界面张力、界面流变性质,从而影响乳状液体系的稳定。通过吸附模型较为准确地描述活性分子在界面上的吸附行为,是定量描述油水界面性质的有效方法之一。以Span80为界面活性物质,模拟油、去离子水为实验介质,研究了低于及超过临界胶束浓度(实验中确定为0.45 mmol·L^-1)下界面张力及界面扩张模量的影响特性,表现为界面扩张模量随Span浓度的增加而先增大后减小的趋势。将描述纯扩散弛豫的Lucassen-van den Tempel模型,同Langmuir、Frumkin、reorientation和rigorous reorientation(严格重排)吸附模型相结合,用于预测含活性分子油水界面张力及扩张流变的性质;结果表明,结合严格重排吸附模型能够准确地预测油水界面张力,界面扩张模量、相角、弹性和黏性模量随浓度、频率的变化趋势。     

Experimental study of kerosene–water two‐phase flow in a vertical pipe using hot‐film and dual optical probes

The local parameters for kerosene–water upward flow are measured in a vertical pipe of 77.8 mm inner diameter at 4200 mm from the inlet (L/D = 54) using hot‐film and dual optical probes. The effect of superficial water velocity and volumetric quality on radial distribution of two‐phase flow parameters is investigated. The results show the following: (i) the profiles of volume fraction and drop frequency are very similar, and increasing superficial water velocity at low volumetric qualities (<18.6%) change the profile from a convex shape with peak at the pipe centreline to uniform then to concave shape with peak near the wall; (ii) the profiles of drop cut chord change from a parabolic shape with peak at centreline for low superficial water velocities to a flat shape at higher superficial water velocity, and the area‐averaged drop diameter decreases with higher superficial water velocities for all volumetric qualities; (iii) velocity profiles for both phases have shapes similar to single phase flow, flatter at higher values of superficial water velocity and volumetric quality and centreline peaked at low superficial water velocities and volumetric qualities; (iv) the slip velocity decreases with radial distance having a peak at centreline and zero values near the wall; (v) introducing kerosene drops into single phase water flow results in a sharp increase in turbulent intensity, particularly at low water velocity, and the difference between the single phase and two‐phase flow turbulence intensities decreases with higher superficial water velocities and (vi) the results show that interfacial area concentration increased with higher volumetric quality and higher number of bubbles thereby increases the contact area between the two phases. © 2012 Canadian Society for Chemical Engineering     

SURFACTANT ADSORPTION TO SPHERICAL PARTICLES: THE INTRINSIC LENGTH SCALE GOVERNING THE SHIFT FROM DIFFUSION TO KINETIC-CONTROLLED MASS TRANSFER

When a drop or bubble of radius b is formed in surfactant solution, surfactant adsorbs, diffuses from solution, and desorbs to establish the equilibrium surface concentration. The transport coefficients for diffusion, adsorption, and desorption are fundamental parameters. However, the transport mechanisms that control the interface far from equilibrium are highly context dependent. Thus, no surfactant has universal “diffusion-controlled” transport. Here we identify a new length scale, R _D-K , that depends on surfactant physicochemistry, and which ranges from roughly 15 to 65 microns. For drops or bubbles with b?R _D-K , mass transfer is kinetically controlled. For b?R _D-K , mass transfer is diffusion controlled. Simulations of adsorption to quiescent spherical interfaces support the importance of R _D-K in determining the controlling transport mechanism for surfactant solutions with concentrations below the critical micelle concentration (CMC). While the case of surfactant adsorbing to a bubble is discussed in detail, the arguments presented are quite general and should apply to adsorption of any solute to any spherical particle.     

Liquid flow pattern around Taylor bubbles in an etched rectangular microchannel

Liquid flow around Taylor bubbles and the motion of bubble interface in a rectangular microchannel etched on a microfluidic chip were investigated using a three-dimensional particle tracking method. The Taylor bubbles were generated by releasing the dissolved air in working the liquid (water) through heating the microfluidic chip to 35–55 °C and had low velocities (15–1500 μm/s). Three-dimensional velocity distributions of liquid recirculation flows surrounding the Taylor bubble head and tail were obtained by tracking submicron fluorescent particles seeded in the working liquid and the motion of the bubble interface was analyzed by monitoring the motions of the particles attached on the bubble interface. The high velocity film flow through the microchannel corners acted as a liquid jet in front of bubble head and drainage into the corners behind the bubble tail to drive the liquid recirculation flows. The bubble interface near the microchannel corners was also moved by the strong liquid shear induced from the high velocity liquid flow in the microchannel corners. This high velocity liquid flow through the corners could be considered to be driven by the pressure drop over the Taylor bubble. The pressure drop resulted from the decrease of bubble surface mobility due to tracer surfactant in the gas–liquid interface.     

Experimental investigation for near-wall lift of coarser particles in slurry pipeline using γ-ray densitometer

Experimental data are collected in 54.9 mm diameter horizontal pipe for concentration profiles using γ-ray densitometer. Two sizes of glass beads with mean diameter and geometric standard deviation of 440 μm and 1.2 and 125 μm and 1.15, respectively, are used. These data are collected for flow velocity up to 5 m/s and overall concentration up to 50% by volume for each velocity. Experimental data measured by sampling probe and pressure gradients in the previous study [D.R. Kaushal, K. Sato, T. Toyota, K. Funatsu, Y. Tomita, Effect of particle size distribution on pressure drop and concentration profile in pipeline flow of highly concentrated slurry, International Journal of Multiphase Flow, 31(7) (2005) 809-823.] are used to compare with γ-ray densitometer measurements and to study slip velocity and near-wall lift of particles in the pipeline. In overall, γ-ray densitometer and sampling probe give quite similar concentration profiles except for few cases of coarser (440 μm) particles at lower flow velocities. Measurements show that, for finer particles, point of maximum concentrations are near the pipe bottom (y/D = 0.1) and for coarser particles, maximum points are relatively away from the pipe bottom with decrease in shift as flow velocity increases. Pressure gradient profiles of equivalent fluid for finer particles are found to resemble with water data except for 50% concentration, however, more skewed pressure gradient profiles of equivalent fluid are found for coarser particles. Experimental results indicate absence of near-wall lift for finer particles due to submergence of particles in the lowest layer into the viscous sublayer and presence of considerable near-wall lift for coarser particles due to impact of viscous-turbulent interface on the bottom most layer of particles and increased particle-particle interactions. It is observed that near-wall lift decreases with increase in flow velocity; however, the effect of slip velocity on pressure drop is greater at lower flow velocities and less at higher flow velocities than near-wall lift of coarser particles in slurry pipeline. For finer particles, the departure from equivalent fluid pressure gradient profile at 50% concentration is attributed to the sudden increase of viscous sublayer thickness.     

Behaviour and removal of fine particles in a liquid-solid spouted bed consisting of binary mixtures

In a liquid-solid spouted bed system containing coarse and fine particles, the entrainment and elutriation of the separated fines were investigated with reference to variations in the pressure drop through the bed. The effect of operating parameters on the velocity corresponding to the beginning of entrainment of fines (U_be) was examined and a dimensionless correlation was proposed. The effect of operating parameters on the elutriation rate coefficient of fines at liquid velocities larger than their terminal settling velocity (U_l) also was studied. An empirical equation was proposed for a column height above TDH, the height of freeboard at which the elutriation rate becomes constant. It was recognized that the elutriation phenomenon was closely related to the length of the stratified particle transport bed when the ascending velocity of the elutriable particles at the top of bed becomes constant.     

Surface Activity and Performance Properties of Gemini Salts of Linear Alkylbenzene Sulfonate in Aqueous Solution

Gemini salts of linear alkylbenzene sulfonate (LABS) were prepared by neutralization of sulfonic acid with a series of low-molecular-weight diamines in aqueous solution. The equilibrium surface activity of Gemini salts of LABS was determined by measuring the surface tension as a function of surfactant concentration to determine the critical micelle concentration (CMC), surface tension at the CMC (γ_CMC), and the area per molecule at the air-water interface (Ų). Electrical conductivity was measured as a function of surfactant concentration to determine the CMC and counterion binding. Dynamic surface tension was measured using a bubble pressure tensiometer to infer the rate at which the surfactant migrates to the air-water interface. Equilibrium interfacial tension against mineral oil was measured using a spinning drop tensiometer. Dynamic interfacial tension was measured using a drop volume tensiometer. The surface tension, CMC, and interfacial tension of Gemini salts of LABS decreased compared to monovalent organic and inorganic salts. The CMC decreases with increasing molecular weight of the diamine spacer group. Dynamic surface and interfacial tension of Gemini salts of LABS are lower than monovalent salts. The foam volume of Gemini salts of LABS was determined using a high shear blender test. The foam volume of Gemini salts of LABS is lower than monovalent salts and depends on the size of the spacer group. Hard-surface cleaning was measured using artificial soil applied to white Formica tiles. Soil removal was determined by optical reflectance as a function of abrasion cycles. Gemini salts of LABS show reduced hard-surface cleaning performance compared to monovalent salts. Detergency of different types of soils on cotton and polyester/cotton fabric was determined by optical reflectance measurements. Gemini salts of LABS show improved cleaning performance compared to monovalent salts. Cleaning performance increases with increasing molecular weight of the diamine spacer group. In situ neutralization of LABS with organic diamines is a simple and efficient way to prepare anionic Gemini surfactants for industrial scale applications.     

On the adsorption kinetics of an eco-friendly surfactant n-decyl-β-D-maltopyranoside

Eco-friendly surfactant alkyl polyglycosides (APGs) have garnered ample interest in the literature. However, the adsorption kinetics of APGs at an air-water interface has not been studied to date. Consequently, this study aimed at investigating the adsorption kinetics of the APG n-decyl-β-D-maltopyranoside (β-C₁₀G₂) at a freshly created air-water interface. The dynamic and equilibrium surface tension (ST) of the aqueous β-C₁₀G₂ solutions were experimentally measured at varying concentrations using a pendant bubble tensiometer and the ST data were examined via theoretical simulations using the Langmuir and Frumkin models. The fitting results revealed that the Frumkin model (with K = −2.9) well-predicted the equilibrium ST data; signifying a considerable cohesive intermolecular force amidst the adsorbed β-C₁₀G₂ molecules. The theoretical mixed-controlled ST profiles (predicted by the Frumkin model) described the dynamic ST data reasonably well, but the adsorption rate constant increased significantly at increasing concentration. A comparison on the ST data of β-C₁₀G₂ and β-C₁₂G₂ (n-dodecyl-β-D-maltopyranoside) was also conducted and a relatively greater surface-activity and lower cmc of the latter alkyl glycoside was observed.     

Microdynamics of the Early Stages of Liquid/Plate Contact under Highly Nonequilibrium Conditions

A microhydrodynamic approach (in which the dissipative coefficients are calculated using the molecular model of lattice gas) is used to study the upward flow of a liquid film over a hydrophilic plate immersed partially in a liquid and to investigate the formation of a meniscus on this plate. The early stages of the unsteady-state transport of a dense fluid over the plate surface (argon–carbon system) are studied numerically. The method enables one to investigate the distributions of molecules and their velocities at different distances from the plate surface. The variation of the concentration fields from the flow origination to the establishment of a quasi-steady state is examined. The contact angle velocity is found (this angle determines the meniscus boundary). It is shown that two types of contact angles can be distinguished in the meniscus-motion dynamics, which correspond to two different molecular scales. The mechanism of the formation of a liquid film and the upward and downward flows of the film on the plate surface at the molecular level (on small spatial scales, where gravity makes no contribution) are discussed. The evolution of a cylindrical drop over the open plate surface is considered.     

Temperature gradients drive radial fluid flow in petri dishes and multiwell plates

Liquid in a Petri dish spontaneously circulates in a radial pattern, even when the dish is at rest. These fluid flows have been observed and utilized for biological research, but their origins have not been well‐studied. Here, particle‐tracking to measure velocities of radial fluid flows, which are shown to be linked to evaporation, is used. Infrared thermal imaging was used to identify thermal gradients at the air‐liquid interface and at the bottom of the dish. Two‐color ratiometric fluorescence confocal imaging was used to measure thermal gradients in the vertical direction within the fluid. A finite‐element model of the fluid, incorporating the measured temperature profiles, shows that buoyancy forces are sufficient to produce flows consistent with the measured particle velocity results. Such flows may arise in other dish or plate formats, and may impact biological research in positive or negative ways. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2227–2233, 2016