bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surfactants effects on mass transfer during drop‐formation and drop falling stages
Authors: Lee Yuh‐Lang 
Published: April 2004

AbstractThree types of surfactants were used to study their effects on the inhibition of mass transfer in liquid–liquid extraction. A single‐drop extraction apparatus was used to obtain the extraction percentage of acetic acid from dispersed CCl4 droplets to the aqueous phase. By using various lengths of extraction column, the extraction amounts were estimated during the drop‐formation and drop‐falling stages. Effects of these surfactants on the mass transfer during various stages were related to the adsorption behavior of these surfactants. The results of dynamic and equilibrium tensions show that the transport of Triton X‐100 is a diffusion‐controlled mechanism, which shows a fast adsorption kinetic at elevated concentrations. By comparing the effectiveness of the three surfactants in decreasing interfacial tension and in mass‐transfer inhibition, the mass‐transfer inhibition during the drop‐formation and drop‐falling stages can be related, respectively, to the properties of dynamic and equilibrium interfacial tensions. For surfactant concentrations below CMC, a surfactant that is most effective in decreasing the interfacial tension always exhibits the highest effectiveness in mass‐transfer inhibition. When the surfactant concentration is small (about 10−3 mM), the mass‐transfer inhibition of SDS and DTMAC is significant in the drop‐formation stage, but not in the drop‐falling stage. As the concentration is increased, the effectiveness of Triton X‐100 increases more quickly than the others in both the formation and falling stages. The mass‐transfer rate increased slightly when the Triton X‐100 concentration is elevated near CMC, due to the surface remobilization caused by the fast adsorption–desorption rate of Triton X‐100 at elevated concentrations. The mass‐transfer inhibition of surfactant also was caused mainly by the hydrodynamic effect in the drop‐formation stage, but from the obstruction of the barrier layer in the drop‐falling stage.
Modeling particle‐size distribution dynamics in a flocculation system
Authors: Zhang Jian‐jun , Li Xiao‐yan 
Published: April 2004

AbstractFlocculation dynamics accounting for both particle coagulation and aggregate breakage was simulated mathematically by using modified sectional modeling techniques. The methodological improvement included the use of a continuous‐size density function, instead of a characteristic size for each size section, the applications of a comprehensive curvilinear model for the coagulation kinetics, and the fractal scaling relationship for particle aggregates. Simulation results demonstrated that a flocculation system could arrive at a dynamic steady state after a period of flocculation when coagulation and breakage counterbalanced each other, resulting in a stationary size distribution with a unique peak mass concentration. Three distinct breakage distribution functions—binary, ternary, and normal distribution—did not differ considerably based on the simulation results of the steady‐state size distributions. A lower shear rate, breakage rate constant, a higher collision efficiency, and initial particle concentration would result in larger aggregates in a flocculation system. The numerical simulations compared well with the results of the jar‐test flocculation experiments using latex microspheres, suggesting the applicability of the curvilinear–fractal–breakage modeling system for the process simulation of the flocculation units used in water and wastewater treatment.
Thermodynamic solution model for trona brines
Authors: Haynes Henry W. 
Published: April 2004

AbstractA thermodynamics solution model has been developed for concentrated trona brines over temperatures ranging from about 0°C to 200°C. The model was constructed by regressing on solubility data for the temperature‐dependent parameters in Pitzer's activity coefficient model. In addition, the model incorporates published thermochemical data for the solid salts and aqueous species. In some cases it was necessary to estimate solid salt heat capacities, but otherwise no adjustments were made in the thermochemical parameters. With one exception, the model provided an excellent fit to the data. The existence of a high‐temperature trona phase reported earlier cannot be reconciled with the model and is believed to be in error. The phase‐equilibrium diagram generated by the model appears suitable for design purposes.
Heat transfer at the subcooled‐scraped surface with/without phase change
Authors: Qin Frank G. F. , Chen Xiao Dong , Russell Andrew B. 
Published: April 2004

AbstractContinuous heat extraction is important for the process of freeze concentration of aqueous solutions, in which water is removed as solid ice. Three typical unsteady heat transportation patterns were distinguished at the subcooled surface of a scraped‐surface heat exchanger (SSHE) in this study. They were found in different stages of freeze concentration. Experimental measurement of the heat‐transfer coefficient in an SSHE showed that the overall heat‐transfer coefficient of stage III, which was characterized by ice formation on the cooler surface, was about 1.5 times higher than stage I, where no ice formed. Although the ice layer (also known as ice fouling) on a heat exchanger surface may be considered disadvantageous for heat transfer, the initial ice formation actually “boosted up” the heat transportation in an SSHE. The mechanism analysis and mathematical modeling of this phenomenon, however, have not been found in the literature. A mathematical model is developed and a unified expression of the heat‐transfer coefficient in an SSHE with/without phase change is presented. The model predicts a step increase of heat transfer occurs at the onset of ice formation and the maximum heat‐transfer coefficient exists in a narrow range right after reaching the freezing point. These are consistent with the experimental results of this study.
Flow between two coaxial rotating cylinders with a highly water‐repellent wall
Authors: Watanabe Keizo , Takayama Tsukasa , Ogata Satoshi , Isozaki Seiji 
Published: April 2004

AbstractThe torque and velocity profile of a flow between two coaxial cylinders with a highly water‐repellent wall were measured experimentally. Two kinds of highly repellent wall were tested to clarify the surface condition effect of the cylinder on laminar drag reduction with fluid slip. The results of torque measurement showed that laminar drag reduction does not occur for a highly water‐repellent wall with no fine grooves at the wall surface. Fluid slip of Newtonian fluids was clarified by measuring the velocity profile close to the highly water‐repellent wall in a Couette flow by a tracer method for flow visualization. The maximum slip velocity is less than 20% of the wall velocity of the rotating inner cylinder. The result of the drag reduction ratio for the torque was calculated by applying to the slip velocity, and agrees with the experimental result quantitatively. Consequently, the gas trapped in the fine grooves plays an important role in laminar drag reduction with respect to fluid slip. From the flow visualization of laminar Taylor–Couette flow, the intervals of Taylor cells become slightly irregular in the case of the cylinder with a highly water‐repellent wall. The calculation result for the Taylor cell applying the fluid slip boundary condition agrees with the experimental result.
Theoretical analysis of two‐phase bubble formation in an immiscible liquid
Authors: Chen W. B. , Tan Reginald B. H. 
Published: April 2004

AbstractTwo‐phase bubble formation coupled with phase change at a submerged nozzle is studied theoretically. The whole bubble consists of a vapor and a liquid phase. The inner vapor phase is assumed to be surrounded by a thin condensate layer, in which the vapor condenses partially as the two‐phase bubble grows. The interface element approach is applied to describe the dynamics of bubble formation. The effect of heat transfer from bulk vapor within the bubble to the surrounding bulk liquid is related to pressure analysis of vapor within the two‐phase bubble via the mass flux of condensation. The results computed from this model agree well with the experimental data.
Mathematical analysis of physicochemical processes on catalytic surfaces
Authors: Lele Tanmay , Lauterbach Jochen , Ramkrishna Doraiswami 
Published: April 2004

AbstractThe traditional approach followed for mathematically modeling physico‐chemical processes on catalytic surfaces involves the choice of an infinitesimal surface area on the catalyst and formulation of mass balances involving adsorbate surface concentrations. Such a strategy is inadequate when the catalytic surface itself changes dynamically with respect to adsorbate‐dependent surface arrangement of its catalytic atoms (and hence) its characteristic kinetics. A rigorous mathematical framework to model such processes is presented. The basic postulates of the theory are the availability of (1) a length scale over which the local infinitesimal area is of one surface type of another and (2) a time scale in which changes in fractional coverage occurring on the length scale in (1) are deterministically describable by continuous variables. A combination of probability and area‐averaging is used to arrive at a deterministic set of partial differential equations for surface concentrations. The resulting equations include reaction and surface diffusion, and new terms such as dilution/augmentation of surface concentration of species brought about by phase transformation. Such terms are significant in predicting the nonlinear behavior of the system and in extracting the kinetics of surface reactions from dynamic data. An application of the theoretical framework to CO oxidation on Pt(100) is demonstrated and dilution/augmentation terms were identified in the purely temporal model. These terms are shown to be significantly important by simulation.
Bubble injector effect on the gaslift efficiency
Authors: Guet S. , Ooms G. , Oliemans R. V. A. , Mudde R. F. 
Published: April 2004

AbstractAn experimental investigation has been made of the influence of the (initial) bubble size and bubble concentration distribution on the gaslift efficiency for a vertical air–water flow through a pipe of 72‐mm dia. and 18‐m height. Three significantly different bubble injectors were used. It was found that with decreasing bubble size, the liquid production increases at constant gas flow rate and, hence, the gaslift efficiency increases. Also, the initial concentration distribution can be significant, as this distribution can influence the coalescence of bubbles close to the injector. With decreasing bubble size, the transition from bubbly flow to slug flow can be postponed. This is one of the main reasons for the beneficial effect of the bubble size on gaslift efficiency. A theoretical model has been developed to predict the influence of the bubble size on the gaslift efficiency. The agreement is reasonable.
Investigation of impinging‐jet crystallization with a calcium oxalate model system
Authors: Hacherl Jean M. , Paul Edward L. , Buettner Helen M. 
Published: April 2004

AbstractAn impinging‐jet crystallizer was investigated in this work to assess its operational sensitivity and reproducibility for the production of small, monodisperse crystals using calcium oxalate, a model system capable of forming multiple hydrates. The impinging‐jet mixer provides rapid mixing of the reactant solutions through the impingement of two narrow reactant streams at high velocity. Impinging jet linear velocity and postjetting conditions were studied, with the jet operated in nonsubmerged mode. Hydrate form and crystal‐size distribution (CSD) were determined using optical microscopy and image analysis techniques. The impinging jet consistently produced small, monodisperse crystals. However, at a high level of supersaturation, slight variations in the CSD were observed for apparently identical conditions, suggesting a degree of sensitivity in the system that could lead to difficulty in its application. An apparent trend between impinging‐jet linear velocity and crystal size and number was observed, with more small crystals produced at higher linear velocity.
Testing the relative importance of mass and heat resistances in solid catalysts
Authors: Petrus Roman , Szukiewicz Mirosław 
Published: April 2004

AbstractCriteria for isothermal conditions and/or absence of diffusion resistances in catalytic reaction were derived using approximate profiles of reagents concentration and temperature for the important reaction νAA+νBB→νRR and for a power‐law type of the kinetic equation, which are quite often applied in practice. The method can be easily adapted to another type of kinetic rate equation and/or more complicated reaction schemes. The developed criteria were applied to some data from the literature with good result.
Novel method for the fabrication of gradient‐index plastic optical fibers
Authors: Sohn In‐Sung , Park Chang‐Won 
Published: April 2004

AbstractA novel coextrusion method has been introduced for the fabrication of gradient‐index plastic optical fibers (GI‐POFs). In this method, the radial diffusion of a refractive‐index‐modifying dopant in a polymer matrix is enhanced significantly by a new die design concept. A theoretical analysis indicates that this new method can substantially reduce the material residence time required to obtain a smooth refractive‐index profile, thereby increasing the output rate to a much higher level than possible with the conventional methods. An experiment using a poly(methyl methacrylate) (PMMA) with diphenyl sulfide (DPS) and diphenyl sulfoxide (DPSO) as the refractive‐index‐modifying dopants has shown an excellent agreement with the theoretical prediction, suggesting that the new coextrusion method is a viable way to manufacture a GI‐POF with the bandwidth higher than 700 Mbits/s at a distance of 100 m.
Modeling and simulation of propylene polymerization in nonideal loop reactors
Authors: Reginato A. S. , Zacca J. J. , Secchi A. R. 
Published: April 2004

AbstractA dynamic mathematical model for liquid‐phase polymerization in loop reactors was developed and implemented in language C using S‐functions in a MATLAB/SIMULINK environment. It is based on a nonideal continuous stirred‐tank reactor (CSTR) model capable of dealing with multisite copolymerization of olefins. The kinetic scheme includes a specific mechanism for hydrogen effect on rate of polymerization observed on both laboratory experiments and industrial plant trials. A nonideality due to polymer segregation at the reactor output was inserted into the model to better predict reactor slurry density. Polymer moment balances were used to compute resin properties, such as average molecular weights, polydispersity, and melt flow index. Dynamic data from an industrial polypropylene plant were used for parameter estimation and model validation.
Numerical simulation of solids suspension in a stirred tank
Authors: Derksen J. J. 
Published: April 2004

AbstractLarge‐eddy simulations of the turbulent flow driven by a Rushton turbine have been coupled to a Lagrangian description of spherical, solid particles immersed in the flow. The working fluid was water, whereas the solid particles had the properties of glass beads. Simulations were restricted to a lab‐scale tank (volume 10−2 m3), and relatively low solids volume fractions (up to 3.6%). Two sets of particles were considered with particle dia. of 0.30 mm and 0.47 mm, respectively. It has been investigated to what level of detail the particle motion needs to be modeled in order to meet Zwietering's just suspended criterion. It appeared to be essential to take particle‐particle collisions into account, mainly because of their exclusion effect that prevents unrealistic buildup of particle concentrations closely above the bottom. The simulations give detailed insight in the behavior of the particles, and in the way that the liquid flow is altered by the presence of the particles. The frequency and intensity of particle‐particle collisions, and particle‐impeller collisions, have been investigated. Furthermore, it will be demonstrated that the rotational Reynolds numbers of the big (0.47 mm) particles were of the same order of magnitude as their translational counterparts.
Unified model for NOX absorption in aqueous alkaline and dilute acidic solutions
Authors: Patwardhan Janaki A. , Joshi Jyeshtharaj B. 
Published: April 2004

AbstractThe absorption of NOX gases in water and alkalies [NaOH, NH4OH, Ca(OH)2] provides commercially important products nitric acid and salts (nitrates and nitrites), respectively. This complex phenomena of mass transfer with chemical reactions is described quantitatively in terms of [H√(kD)]J values for J = N2O3, N2O4. However, the reported value of H√(kD) for N2O3 absorption in strong alkaline solution was 50 times its value in water. For the intermediate case of NOX absorption in weak alkali Ca(OH)2, it was necessary to have a mathematical model which incorporated the HNO2 decomposition, as well as neutralization by alkali. This led to a unified model for NOX absorption, which can be used for predicting point rates of NOX absorption as well as selectivity, for various gas compositions and liquid‐phase pH. Parametric sensitivity has been reported. A comparison of the model predictions with data from patent on Ca(NO2)2 manufacture has been made to test the model validity.
Chaotic advection in a three‐dimensional stokes flow
Authors: Rodrigo A. J. S. , Mota J. P. B. , Lefevre A. , Leprévost J. C. , Saatdjian E. 
Published: April 2004

AbstractMixing by chaotic advection is studied in a new 3‐D flow geometry. It consists of two confocal elliptic cylinders whose inner and outer boundaries glide circumferentially so that the geometry does not vary with time. Dye advection experiments have been performed and compared to numerical streak lines calculated using the analytical solution of Stokes' equations in elliptical cylindrical coordinates. Experiments show that particle trajectories remain for all practical purposes inside tubes defined by the potential mixing zone during the whole process. For the case where the elliptic cylinders turn time periodically in opposite directions, we examine the effect of the modulation frequency of the boundary displacement protocol by defining appropriate dimensionless control parameters and then numerically monitoring the advection of a passive scalar. It is shown that for a given average axial velocity, there is an optimum modulation frequency that maximizes the mixing enhancement due to chaotic advection.
Flow‐induced particulate separations
Authors: Roberts Brian W. , Olbricht W. L. 
Published: April 2004

AbstractSeparating particles from the liquid in which they are suspended is often an important step in processing multiphase materials such as suspensions and emulsions. We describe a new method to separate neutrally buoyant particles from viscous liquids. The method is based on the low Reynolds number motion of freely‐suspended particles at bifurcations—points where a tube or channel splits into multiple tubes. We show experimentally that the partitioning of particles at a bifurcation differs from the partitioning of the suspending fluid. The effects of particle size, particle volume fraction, and shape of the bifurcation on particle partitioning are examined. Furthermore, we demonstrate that when tubes and bifurcations are arranged in certain ways, the particles can take preferential paths through the network and can be separated from the liquid in which they are suspended. The data show that the particle separation can be enhanced in relatively simple networks consisting of just a few interconnected channels.
Target linearization and model predictive control of polymerization processes
Authors: Bindlish Rahul , Rawlings James B. 
Published: April 2004

AbstractModeling and control of prototypical industrial polymerization processes are presented in the presence of disturbances and plant‐model mismatch. The process model consists of the material balances for the reactor, energy balance for the reactor, and a simplified dynamic model for the downstream flash separator. The process model is used to develop a TLMPC that separates the target calculation from dynamic regulation in a closed‐loop setting. The main feature of the proposed controller (TLMPC) is that the targets are calculated from the nonlinear model, and then used to get the correct linearized model. The linearized model is utilized to calculate the actual control moves for dynamic regulation, and develop an extended Kalman filter for state estimation. The resulting TLMPC controller does not have the computational burdens associated with a full NMPC and gives similar performance to NMPC. The TLMPC shows optimal plant startup, product grade transitions, and regulation around a set point for the polymerization process in comparison to a fixed LMPC. Robustness with respect to incorrect model kinetic parameters, initial state estimates and measured disturbances is also shown for TLMPC, as compared to LMPC.
Novel solar reactor for studying ultrafast gas–solid reactions above 2,000 K
Authors: Steiner E. , Ganz J. , Meier A. , Sturzenegger M. 
Published: April 2004

AbstractA novel solar chemical reactor has been designed and tested for kinetic experiments with μm‐sized metal oxide particles. The solar reactor is essentially a tubular reactor with a continuous feed of particles suspended in a carrier gas. The suspension is electrically preheated in the back part of the solar reactor. Chemical conversion occurs in the high‐temperature zone in the front part of the solar reactor where concentrated solar radiation enters the reactor through a quartz window. Under typical operating conditions, the particle residence time in the high‐temperature zone was estimated to be 50 ms. Reduction of manganese iron oxides showed that flux‐density distributions of 450 to 770 W·cm−2 produced maximum particle temperatures of 2,200 K. Chemical reactivity studies also revealed that quenching is insufficient for very reactive materials. Therefore, an alternative quench device has been tested at room temperature and is discussed here.
New solid equation of state combining excess energy mixing rule for solid–liquid equilibria
Authors: Twu Chorng H. , Tassone Vince , Sim Wayne D. 
Published: April 2004

AbstractCrude oil is a mixture of light and heavy hydrocarbon components. The light components in crude oil keep the heavy components soluble in solution. However, the cooling of crude oil below its solidification point leads to the formation of a solid‐wax phase. A number of thermodynamically based models have been proposed in the literature for the prediction of wax formation in both crude oils and fuels. Some of these models assume ideal liquid solution behavior. Others are a modification of the regular solution theory or the Flory‐Huggins model for activity coefficients, with varying degrees of success. The absence of a proper model in the petroleum industry to describe the liquid‐phase nonideality for mixtures of hydrocarbons with large differences in size is still one of the major problems in solid–liquid equilibrium calculations. A simple methodology is proposed to develop a cubic equation of state (CEOS) for the solid phase to allow the accurate calculation of solid–liquid equilibria. The methodology is successfully applied to the Twu‐Sim‐Tassone (TST) cubic equation of state. The solid TST equation of state is then combined with the TST excess Helmholtz energy mixing rule to handle highly nonideal systems for the accurate prediction of solid–liquid phase equilibria.