Continuous Liquid Phase Research Articles

DEM‐simulation of the magnetic field enhanced cake filtration

AbstractUsing the discrete element method, we simulate numerically the cake formation and growth in magnetic field enhanced cake filtration to give further insight on the mechanisms of the structuring of the filter cake due to the interaction of magnetic, hydrodynamic, and mass forces. The motion of the discrete particles is obtained by applying the three‐dimensional Newton's equations to individual particles, allowing for both external forces (gravity, applied magnetic field) and particle–particle interactions calculated using the modified DLVO‐theory. Continuous liquid phase flow is assumed as one‐dimensional. The simulation results compare favorably with reported experimental data,1 and can be used to delineate the regimes associated with different liquid flow and magnetic field effects that are observed experimentally. © 2012 American Institute of Chemical Engineers AIChE J, 2012

Least Squares Higher Order Method for the Solution of a Combined Multifluid-Population Balance Model: Modeling and Implementation Issues

Abstract In this paper we attempt to highlight the main challenges of the implementation of the presented combined Eulerian multifluid-Population balance model for bubbly flows as applied to simulate the behavior of vertical bubble column reactor. The 1–D steady-state model equations for the bubble column with water as the liquid continuous phase and air bubbles of diameter as a dispersed phase, constitutes the liquid continuity and momentum equations and the dispersed phase population balance equation and the dispersed phase momentum equation. In addition, the ideal gas law, two moments of the distribution (void and SMD), and a set of constitutive equations are required.

Study of a new multi channel foam and emulsion generator

ABSTRACTThis work describes the design and operation of two microfluidic emulsion and foam generators. The difference between the two devices consists in the geometry of the output channel - in one case, we used a straight microchannel, whereas in the second case we implemented a fractal channel output geometry. While both devices can produce highly monodisperse foams and emulsions at high throughput (coefficient of variation CV≈1.5% and production frequency of up to 2.5kHz per channel with a total of 256 micro channels capable, in theory, of operating in parallel), the actual CV at the exit of the device was significantly higher due to interactions between adjacent droplets or bubbles. Using a combination of high-viscosity continuous phase liquid and low-solubility gas phase resulted in improved monodispersity. In these conditions, the fractal output channel geometry resulted in the lowest overall CV (≈3%) at the exit of the device for both foam and emulsion production, due to an inhibition of aging and coalescence phenomena as compared to the straight channel.

CFD simulations of dense solid–liquid suspensions in baffled stirred tanks: Prediction of suspension curves

Mixing of solid particles into liquids within contactors mechanically agitated by stirrers is a topic of primary importance for several industrial applications. A great research effort has been devoted to the assessment of the minimum impeller speed ( N js ) able to guarantee the suspension of all particles. Conversely, only little attention has been paid so far to the evaluation of the amount of solid particles that are suspended at impeller speeds lower than N js . In some cases the loss in available interfacial area between particles and liquid could be reasonably counterbalanced by a decreased mechanical power, making it of interest to evaluate the percentage of suspended solids at different impeller speeds < N js in order to quantify the possible economical advantage of adopting an incomplete suspension (filleting) regime inside the stirred tank. The present work deals with computational fluid dynamics simulations of dense solid–liquid partial suspensions in baffled stirred tanks and particularly focuses on the prediction of the amount of suspended particles at agitation speeds encompassing both the filleting and the complete suspension regime. An Eulerian–Eulerian Multi Fluid Model coupled with a standard k– ɛ turbulence model for the continuous (liquid) phase only was adopted for CFD simulations. Both the Sliding Grid (SG) and the Multiple Reference Frame (MRF) approaches were employed to simulate the impeller-tank relative rotation. Different turbulence corrections to the fluid-particle drag correlation were considered. Experimental evidence was used for validation purposes: data collected by using the Pressure Gauge Technique (PGT) [1] and snapshots of the simulated tank. Comparison between CFD predictions and all experimental data showed a satisfactory agreement; for large particle diameters the drag coefficient correlation due to Pinelli et al. [2] gave the best results. The influence of the impeller motion treatment was found to be negligible.

Bimodal model for predicting the emulsion-hydrate mixture viscosity in high water cut systems

For many production operations, particularly deepwater fields, those requiring long tiebacks, water flooded and mature reservoirs (where water cuts can be very high), the traditional techniques to prevent hydrate problem may not be economical and/or logistically practical. Thus the industry needs improved techniques to tackle flow assurance problems for such challenging conditions.Preventing hydrate agglomeration and transportation of hydrate slurry could be a new solution. The rheological behaviour of hydrate slurry has mainly been investigated in low water cut systems where water is the limiting factor. In high water cut systems, hydrate former components are the limiting factor and therefore the rheological behaviour of hydrate slurry has to be study in water–oil emulsion and this has a significant role on the viscosity of the system.In this communication, a model to predict the viscosity of water–oil emulsion in the presence of hydrate particles in high water cut systems using the concept for a bimodal mixture is proposed. In the model, water–oil emulsion and hydrate particles in the liquid continuous phase are treated separately as unimodal models. In addition, a modification has been applied to the Mills (1985) model to calculate the viscosity of unimodal hydrate suspensions. The model has been validated using experimental data for high water cut systems (above 50%) in the presence of different anti-agglomerant (AA) concentrations. The predictions of the proposed model are in good agreement with experimental data for both oil-in-water and water-in-oil hydrate mixtures.

Analysis of suspension and heat transfer characteristics of Al 2O 3 nanofluids prepared through ultrasonic vibration

Nanofluids that contain nanoparticles with excellent heat transfer characteristics dispersed in a continuous liquid phase are expected to exhibit superior thermal and fluid characteristics to those in a single liquid phase primarily because of their much greater collision frequency and larger contact surface between solid nanoparticles and the liquid phase. One of the major challenges in the use of nanofluids to dissipate the heat generated in electronic equipment such as LEDs is nanoparticles’ precipitation due to their poor suspension in the fluid after periods of storage or operation, thereby leading to deterioration in the nanofluids’ heat transfer rate. In this study, ultrasonic vibration was employed to prepare Al 2O 3 nanofluids with a surfactant, a dispersant, and a combination of the two to evaluate their suspension and heat transfer characteristics. The experimental results show the Al 2O 3 nanofluid prepared with a non-ionic surfactant with a hydrophile lipophile balance (HLB) value of 12 to have the lowest nanoparticle precipitation rate and, accordingly, the highest degree of emulsification stability. Moreover, the nanofluids prepared with both the dispersant and surfactant had the greatest dynamic viscosity and lowest degree of thermal conductivity. Both the precipitation rate and dynamic viscosity of the nanoparticles increased, and their thermal conductivity coefficient decreased, the longer they remained in the Al 2O 3 nanofluids. Further, an increase in operating temperature caused an increase in the thermal conductivity coefficients of all of the Al 2O 3 nanofluids considered.

Multidimensional population balance model for the simulation of turbulent gas–liquid systems in stirred tank reactors

The prediction of turbulent gas–liquid systems, and in general of multiphase flows, has been historically performed with the implicit assumption of separately considering fluid dynamics issues from the evolution of the dispersed phase (i.e., the gas bubbles). These two aspects can be simultaneously accounted for by means of a multidimensional population balance model, able to describe the interactions between the continuous liquid phase and the gas bubbles, as well as the interactions among different gas bubbles (e.g., coalescence and break-up), both in terms of momentum and mass coupling. The model has to quantify the effects of these interactions on the population of dispersed bubbles and has to estimate the distributions of bubble velocity, size and composition, as well as the state of the continuous phase. A novel approach based on the direct quadrature method of moments is here formulated, tested on several simplified cases and adopted to describe the evolution of the gas bubble in a realistic gas–liquid stirred tank reactor. Results are eventually validated through comparison with experimental data from the literature.

Effect of a dispersed immiscible liquid phase on the hydrodynamics of a bubble column and ebullated bed

Secondary undesired reactions in ebullated bed resid hydroprocessors can generate an additional dispersed liquid phase, referred as mesophase, which is denser and more viscous than the continuous liquid phase and affects the operation and transport phenomena of the fluidized bed. This study investigates the effect of a dispersed immiscible liquid phase on the overall phase holdups, bubble properties, and fluidization behavior in a bubble column and ebullated bed. The experimental system consisted of biodiesel as the continuous liquid phase, glycerol as the dispersed liquid phase, 1.3 mm diameter glass beads, and nitrogen. The addition of dispersed glycerol reduced the gas holdups in the bubble column for the studied gas and liquid superficial velocities. Dynamic gas disengagement profiles reveal a rise in the large bubble population and reductions to the small and micro bubble holdups when increasing the glycerol concentration. Liquid–liquid–solid bed expansions at various liquid flowrates confirm particle agglomeration in the presence of a more viscous dispersed liquid phase. Overall phase holdups in a gas–liquid–liquid–solid ebullated bed were obtained while varying the gas and liquid flowrates as well as the glycerol concentration. A coalesced bubble flow regime was observed in the bed region without glycerol whereas the addition of glycerol resulted in the dispersed bubble flow regime due to particle clustering and a greater apparent particle size. The resulting bubble flow regime increased the bed and freeboard region gas holdups due to enhanced bubble break-up. Observations of the fluidized bed behavior following the addition of the dispersed glycerol are also discussed.

Intermediate scales between simulation and modeling of two-phase flows

Phenomena related to two-phase flows in an experiment in which air is injected in the lower part of a tank filled with water are investigated, via the SIMMER-IV software. The Reynolds and Weber numbers of the bubbly flow have high values. Small scale phenomena, related to small bubbles behavior or turbulence in the liquid continuous phase, are modeled via classical closure laws. An attempt to represent the formation of individual large bubbles, close to the injector, via direct simulation is done. In a first calculation, the large bubbles break-up is not represented. This phenomenon, the space scale of which is close to the cell size, cannot be simulated, with the present computational resources. Nevertheless, relatively fine meshes are used, for an accurate description of hydrodynamical phenomena, and these phenomena are too large to be modeled via closure laws. The case is therefore useful to underline some basic limits in the potentialities of direct simulation and modeling and to propose an attempt to face the problem. The breakup of bubbles is now represented. Finally the validity of the approach is checked directly by simulating a single bubble experiment. The problem of the convergence between multiphase codes and direct simulation ones is pointed.

점성슬러리 기포탑에서 작은 기포의 체류량 특성

점성슬러리 기포탑에서 작은 기포의 체류량 특성에 대해 고찰하였다. 정압 강하방법(Static pressure drop method)에 의해 구한 기포탑 내부전체 기포체류량과 이중저항탐침법(dual resistivity probe method)에 의해 구한 큰 기포의 체류량으로부터 기포탑 내부에 체류하는 작은 기포의 체류량을 구할 수 있었다. 기체유속, 연속액상의 점도 그리고 슬러리 상중에 포함된 고체입자의 분율이 전체 기체체류량, 큰 기포의 체류량 그리고 작은 기포의 체류량에 미치는 영향을 검토하였다. 점성슬러리 기포탑에서 작은 기포의 체류량은 기체의 유속이 증가하면 증가하였으나 연속액상의 점도와 슬러리상에 포함된 고체입자의 분율이 증가하면 감소하였다. 기포탑 내부에 체류하는 전체 기포 체류량 중 작은 기포 체류량의 분율은 기체유속이 증가하면 증가하였으나 연속액상의 점도와 슬러리상에 포함된 고체입자의 분율이 증가하면 감소하였다. 기포탑 내부에 체류하는 작은 기포는 큰 기포의 상승속도에 영향을 미치지 못하였다. Holdup characteristics of small bubbles were investigated in a viscous slurry bubble column. The phase holdup of small bubbles was obtained from the knowledge of total bubble(gas) holdup and large bubble holdup, which were measured by mean of static pressure drop method and dual resistivity probe method, respectively. Effects of gas velocity, viscosity of continuous liquid phase and solid fraction in the slurry phase on the small bubble holdup as well as holdups of total bubble(gas) and large bubble in a viscous slurry bubble column. The small bubble holdup increased with increasing gas velocity but decreased with increasing liquid viscosity or solid fraction in the slurry phase. In addition the fraction of small bubble in the total bubble(gas) holdup increased with increasing gas velocity but decreased with increasing liquid viscosity or solid fraction in the slurry phase. It was revealed that the rising velocity of large bubble did not related to the holdup of small bubble in a viscous slurry bubble column.

Competition Between Viscoelasticity and Surfactant Dynamics in Flow Focusing Microfluidics

AbstractThe goal of this work is to quantify the impact of viscoelasticity on a tipstreaming phenomenon observed in flow focusing microfluidic devices. Tipstreaming, or thread formation, is a phenomenon caused by surfactant transport to, from, and along, deforming interfaces that leads to long filaments in microfluidic devices. Viscoelasticity also leads to stable filaments, so possible synergies are investigated here. The ability to generate extremely long and thin filaments that will break up via interfacial instabilities will lead to the formation of droplets much smaller than the device lengthscales. Viscoelastic Boger fluids are used as the dispersed phase liquid in a flow focusing device and surfactant is added to the continuous phase liquid. We find a region of operating space in which viscoelasticity appears to couple with surfactant transport to form long threads. The phenomenon is described qualitatively and is related to fluid relaxation times. magnified image

An inexpensive thread-based system for simple and rapid blood grouping

This study investigates the use of thread as a flexible and low-cost substrate for the rapid grouping of blood. The use of a capillary substrate such as thread for blood grouping utilises the sensitivity of the flow resistance of large particles in narrow capillary channels to separate agglutinated red blood cells (RBCs) from plasma. Large and discrete particles formed in a continuous liquid phase do not provide capillary wicking driving force and fall behind the capillary wicking front, leading to their separation from the wicking liquid. The capillary substrate therefore provides a very promising but different mechanism for the separation of the agglutinated RBCs and the blood serum phase compared to most existing blood grouping methods. The principle of chromatographic separation is also exploited in this study via the use of suitable dyes to enhance the visual detection of the agglutinated RBCs and the serum phase; surprising and encouraging outcomes are obtained. Using a thread-based device, the ABO and Rh groups can be successfully determined with only 2μL of whole blood from a pricked finger tip within 1min and without pre-treatment of the blood sample. It is hoped that a new, inexpensive, rapid and simple method may provide an easy-to-use blood grouping platform well suited to those in developing or remote regions of the world.

Enhancement of Sieve Tray Efficiency using Computational Fluid Dynamics

High degree of competitiveness associated with petroleum leads to the exhaustive search for new technologies that enable greater efficiency in the related processes. A three-dimensional mathematical homogeneous biphasic model was implemented in the commercial code of Computational Fluid Dynamics (CFD), FLUENT package to predict concentration and temperature distributions on sieve trays of distillation columns and good simulation results are obtained. The tray geometries and operating conditions are based on the experimental works of Indian oil corporation limited (R&D). The dispersed gas phase and continuous liquid phase are modelled in the mixture model for two interpenetrating phases with inter phase momentum, heat and mass transfer. The main objective of this study has been to find the extent to which CFD can be used as a prediction tool for real behaviour, and concentration and temperature distributions of sieve trays. The simulation results are shown that CFD is a powerful tool in tray design, analysis and trouble shooting, and can be considered as a new approach for efficiency calculations.

Spatially and chemically resolved measurement of intra- and inter-particle molecular diffusion in a fixed-bed reactor

This work demonstrates for the first time the ability to spatially and chemically resolve inter- and intra-particle apparent diffusion coefficients in a packed bed during reaction using Nuclear Magnetic Resonance. The measurements were performed using a diffusion preconditioned one-dimensional chemical shift imaging pulse sequence; all the data are recorded within a single measurement. The reaction studied was the continuous liquid phase esterification of acetic acid and ethanol to form ethyl acetate and water over an ion-exchange resin at ambient temperature and pressure. Inter- and intra-particle apparent diffusivities of the hydrocarbons were resolved at four different spatial positions along the length of the catalyst bed. Absolute composition measurements were obtained of the liquid in the inter-particle space of the bed. Relative concentration measurements of the chemical species in the intra-particle space are also reported. The development of these measurement methods advances our ability to characterise mass transfer limitations in situ within a working fixed-bed reactor.

Brownian dynamics of emulsion film formation and droplet coalescence

We analyze the evolution in thickness and radius of the film formed during the collision of two deformable emulsion Brownian droplets. These variables exhibit random fluctuations due to thermal disturbances from the continuous liquid phase. As a result, the system probes a random trajectory in the configurational space until it reaches a critical film thickness, at which point the droplets coalesce. Therefore, the film is modeled as a disk with thicknesses and radi that can fluctuate. Our analysis is based on a Langevin-Brownian dynamics approach, which accounts for the thermodynamic and hydrodynamic interactions in the lubrication approximation. We examine the effect of parameters such as droplet size, interfacial mobility, and electrolyte concentration on the coalescence of small Brownian droplets. The results suggest that the coalescence times depend on a complex interplay between the thermodynamic and hydrodynamic interactions.

The velocity and shape of convected elongated liquid drops in narrow gaps

The motion and shape of a liquid drop through another continuous liquid phase (conveying phase) in a Hele-Shaw cell with two different apertures were investigated experimentally. Eight different liquid–liquid systems were tested. In all cases, the continuous phase was more viscous and wetted the bounding walls. In the capillarity-dominated region, the irregular shape of the discontinuous phase changed with time and distance, with much lower velocity than that of the conveying phase. At higher capillary number, three different shapes of stabilized elongated drops were observed. The conditions that lead to the appearance of stabilized elongated drops are discussed. In contrast to gas–liquid systems, the velocity of these stabilized elongated drops was 2 to 4.7 times higher than that of conveying liquid. Two new correlations are derived from dimensionless analysis and the experimental data to predict the elongated drop shape and velocity as a function of the dimensionless parameters governing the system.

Trends in Atomization Theory

Sprays are widely used in industry for combustion, coating, painting, and a number of other applications. They have in common the principle of dividing a continuous liquid phase into a dispersed phase made of numerous droplets. Among all the techniques employed to atomize liquids, very few are fully described by a model or a convenient theory. We summarize in this work the main trends and principles of spray and atomization models. The mechanisms identified as being at the origin of atomization, such as aerodynamic drag, cavitation, turbulence, electrostatic forcing, etc., are listed and the appropriate models are described. Linear instability theory, cavitation models, electrostatic equations, along with Eulerian models, and statistical descriptions of sprays are presented. The need for intense work and improvement of knowledge is brought out in the conclusion.

Correlating Obstructed Diffusion with Obstacle Morphology using Single Molecule Tracking and AFM in Supported Lipid Bilayers

Biophysical research has shown that membrane phospholipids and proteins diffuse not only under normal Brownian diffusion, but with confined and anomalous behavior. We are motivated to understand this anomalous diffusion because it may be involved in many cell functions. We have used single molecule tracking on phase separated, supported lipid bilayers to investigate the origin of this unusual diffusion. DSPC forms ∼250 nm, gel phase domains that act as obstacles to diffusion in the DOPC continuous liquid phase.

The Velocity and Shape of Convected Elongated Liquid Drops in Vertical Narrow Gaps

Abstract The motion and shape of a liquid drop through another continuous liquid phase (conveying phase) in a vertical Hele-Shaw cell with two different apertures were investigated experimentally. Two different liquid/liquid systems were tested. In all cases, the continuous phase was more viscous and wetted the bounding walls. In the capillarity-dominated region, the irregular shape of the discontinuous phase changed with time and distance, with much lower velocity than that of the conveying phase. In contrast to gas/liquid systems, the velocity of these stabilized, elongated drops was 2.5 to almost 5 times higher than that of conveying liquid. Despite the similarities between flow in vertical and horizontal Hele-Shaw cells, the velocity of droplets in a vertical fracture is different from that of a horizontal fracture. A new correlation is derived from dimensionless analysis and the experimental data to predict the elongated drop velocity as a function of the dimensionless parameters governing the system. Introduction Two-phase flow in micro-fractures is fundamental to many different fields of advanced science and technology, such as chemical process engineering, bioengineering, medical and genetic engineering, as well as petroleum engineering. For instance, understanding the flow of two-phase fluids in near-parallel gaps through fractured rocks has a significant effect on design of different recovery methods for naturally fractured reservoir. The flow pattern of two-phase immiscible flow in a fracture depends on the flow rates of the phases, the geometry, aperture, roughness of the fracture, the flow properties of the phases and interfacial tension between the phases. The flow patterns in a fracture are different from that in macro-sized rectangular ducts or pipes because of the small aperture, which can enhance capillary effects. The flow structure in the fracture affects the flow and transport through the surrounding porous matrix blocks. The slug flow pattern in a fracture, which occurs over a wide range of parameters, is frequently encountered in oil-wet fractured reservoirs during the immiscible displacement of viscous oil. It also occurs in natural gas reservoirs during displacement of water during gas production.

Quantification of the velocity acceleration factor for colloidal transport in porous media using NMR

Nuclear magnetic resonance (NMR) techniques were used to quantify the transport of colloids through porous media. This was achieved via the application of chemically-resolved pulsed field gradient (PFG) methods, hence probing the displacement (probability distribution) propagators of both the colloidal and continuous liquid phase. A dilute decane-in-water emulsion was used with flow through a random glass sphere packing being considered. The acquired propagators allowed for quantification of both colloidal entrapment and the velocities of both the continuous phase and the flowing colloids. The flowing colloids were found to experience a velocity acceleration factor (VAF) increase of 1.08 relative to the continuous phase. This was found to be independent of displacement observation time or flowrate. It was speculated to be a consequence of radial exclusion due to the finite size of the colloids. Simulations of the colloidal transport were also performed using a lattice Boltzmann platform and a Lagrangian particle-tracking algorithm which incorporated colloidal radial exclusion. Reasonable agreement was observed between the simulation and the experimental data.