bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic contact angles and flow in vicinity of moving contact line
Authors: Shikhmurzaev Yulii D. 
Published: June 2004

AbstractA previously developed mathematical wetting model is generalized and applied to the following two closely related situations: the spreading of a liquid over a prewet solid surface and the receding contact‐line motion with a microscopic residual film, remaining behind the contact line. An analytical expression for the velocity dependence of the dynamic contact angle is derived. Macroscopic characteristics (the dynamic contact angle and drag force) and the flow field corresponding to the spreading of a liquid over a wet solid surface differ considerably from those calculated for a dry surface. Under certain conditions the flow in the reference frame fixed with respect to the contact line has a region with closed streamlines. The region appears due to the flow‐induced Marangoni effect, the reverse influence of the surface tension gradient along the liquid‐solid interface caused by the flow on the flow, which gives rise to the gradient. The results are compared qualitatively with experimental data.
Cross‐stream migration of bead–spring polymers in nonrectilinear pore flows
Authors: Nitsche Ludwig C. 
Published: June 2004

AbstractDeterministic cross‐stream migration of FENE dumbbells, cyclic trimers and bicyclic tetramers in nonhomogeneous, nonrectilinear flows representative of tortuous pores is analyzed. Identifying the crucial feature of misalignment between a tumbling dumbbell and the surrounding streamlines, Brunn (1983) showed that the dumbbell model requires three reflections in the bead–bead hydrodynamic interaction (HI) for lateral migration to occur: lower‐order approximations of the HI are insufficient because they lead only to alignment with the flow rather than tumbling. In any orientation the trimer (tetramer) has at least two (three) “bonds” out of alignment with the flow. Radial migration in rotary Couette flow between concentric cylinders occurs in the freely draining limit, and the simplest, first‐order HI is sufficient to cause lateral migration in rectilinear tube flow. Flow through a sinusoidally corrugated pore brings a new convective timescale on which the bead–spring entity moves between converging and diverging flow environments. Since this process outpaces the dumbbell's alignment, even a freely draining dumbbell spends most of its time slightly misaligned with the surrounding streamlines, and migrates toward the walls (higher shear). Tumbling occurs on a much longer timescale, with the dumbbell traveling through many wavelengths of the wall corrugations (and fluctuating in orientation) between successive (rapid) end‐for‐end flips in the shear field. The flipping time seems to scale inversely with the length of the dumbbell. The trimer and tetramer rotate largely as in rectilinear shear, and exhibit somewhat stronger migration for the same bond length. As a simple model of pore entrance effects, net drift in an oscillatory Sampson flow through a thin orifice is also considered.
Prediction of polymer‐solvent phase equilibria by a modified group‐contribution EOS
Authors: Lee Byung‐Chul , Danner Ronald P. 
Published: June 2004

AbstractA new group‐contribution lattice–fluid equation of state (GCLF‐EOS), which is capable of predicting the equilibrium properties of polymer–solvent solutions, was developed by modifying the original GCLF‐EOS of High and Danner. The GCLF‐EOS is a group‐contribution form of the Panayiotou–Vera equation of state based on the lattice‐hole theory. Group contributions for the interaction energy and reference volume were developed based only on the saturated vapor pressure and liquid densities of low molecular weight compounds. For a mixture, a binary interaction parameter was introduced into the mixing rules. Group contributions for the binary interaction parameter were developed from the binary vapor–liquid equilibria of low molecular weight compounds. This modified GCLF‐EOS model gives excellent predictions of solvent activity coefficients both at infinite dilution and at finite concentrations. It is significantly better than the original GCLF‐EOS model in its prediction capability. The only input required for the model is the structure of the molecules in terms of their functional groups. No other pure component or mixture properties of the polymer or solvent are needed.
Calcium phosphate decontamination of stainless steel surfaces
Authors: Grant Christine S. , Webb Gregory E. , Jeon Young W. 
Published: June 2004

AbstractA primary constituent in high‐temperature (120–140°C) milk fouling residues is calcium phosphate in the form of calcium phosphate dihydrate (brushite, CaHPO4 · 2H2O) and hydroxyapatite [Ca5(PO4)3OH]. The removal of these mineral‐rich deposits from stainless steel occurs by dissolution and mechanical cleaning. This research uses a novel solid scintillation technique to noninvasively and continuously investigate the removal of P32‐labeled mixtures of calcium phosphate from inner surface of stainless steel tubes. The proposed mass‐transfer model suggests that the film is initialy removed by dissolution, when compared to the experimental results. An alternative first‐order model presented includes the effects of the solvent flow rate and solvent pH on decontamination rates. This model agrees with the experimental cleaning data over the range of pH and flow rates studied.
Effect of disturbances in optimizing control: Steady‐state open‐loop backoff problem
Authors: Bahri Parisa A. , Bandoni Jose A. , Romagnoli Jose A. 
Published: June 2004

AbstractOne of the key components in the operation of chemical plants is the ability to operate over a range of conditions while satisfying performance specifications. A method for determining the necessary open‐loop backoff from a steady‐state nominal optimum is introduced to ensure that disturbances cause no constraint violation. This approach consists of defining a joint optimization‐flexibility problem that can be solved within an optimization framework based on an iterative procedure. By formulating the optimization problem in economic terms, the backoff in the objective function is a measurement of the open‐loop economic penalty that is necessary to be paid to achieve feasible operation over the disturbance range of interest (considering the worst combination). An upper bound on the economic potential available for closed‐loop control can then be established, providing a valid reference for ranking different control schemes. Three examples presented illustrate the application of this approach: (1) a simple linear example, (2) a system of two CSTRs; and (3) an industrial distillation column.
Ignition and extinction in the catalytic oxidation of hydrocarbons over platinum
Authors: Veser Götz , Schmidt Lanny D. 
Published: June 2004

AbstractThe ignition–extinction behavior in the oxidation of methane, ethane, propane and isobutane, as well as of ethylene and propylene over a platinum‐foil catalyst was studied over the entire range of fuel/air ratios at atmospheric pressure. Ignition and extinction of the heterogeneous surface reaction, homogeneous ignition and the autothermal behavior of these fuel–air mixtures were investigated. The results show a common trend in the ignition extinction behavior of the alkanes and a different trend for the olefins. This is discussed in terms of a simple model, which correctly predicts the composition dependence of the surface ignition curve for reasonable values of parameters, indicating a mainly oxygen‐covered surface during ignition of the alkanes and a mainly hydrocarbon‐covered surface in the case of the olefins. Different branches of the complete bifurcation diagrams are discussed separately, allowing qualitative conclusions about the catalytic activity of Pt for the oxidation reactions of different fuels.
Transport properties of water and pentane in Langmuir–Blodgett films
Authors: Hanley C. M. , Quinn J. A. , Vanderlick T. K. 
Published: June 2004

AbstractThe transport of water and pentane vapor in Langmuir–Blodgett (LB) films of arachidic acid is investigated. A quartz crystal microbalance is used to monitor the mass increases of the films upon exposure to the vapor as a function of the pressure. By examining films of different thicknesses, it is shown that it is possible to measure both surface adsorption and solubility. Diffusivity is calculated from the rate of uptake. Water and pentane have Fickian diffusion coefficients of 4 × 10−12 cm2·s−1 and 1 × 10−12 cm2·s−1, respectively. The effect of both aging and annealing of the LB films on the vapor uptake is studied and it is shown that the uptake is sensitive to the state of the film.
Analysis and design of metabolic reaction networks via mixed‐integer linear optimization
Authors: Hatzimanikatis Vassily , Floudas Christodoulos A. , Bailey James E. 
Published: June 2004

AbstractImprovements in bioprocess performance can be achieved by genetic modifications of metabolic control structures. A novel optimization problem helps quantitative understanding and rational metabolic engineering of metabolic reaction pathways. Maximizing the performance of a metabolic reaction pathway is treated as a mixed‐integer linear programming formulation to identify changes in regulatory structure and strength and in cellular content of pertinent enzymes which should be implemented to optimize a particular metabolic process. A regulatory superstructure proposed contains all alternative regulatory structures that can be considered for a given pathway. This approach is followed to find the optimal regulatory structure for maximization of phenylalanine selectivity in the microbial aromatic amino acid synthesis pathway. The solution suggests that from the eight feedback inhibitory loops in the original regulatory structure of this pathway, inactivation of at least three loops and overexpression of three enzymes will increase phenylalanine selectivity by 42%. Moreover, novel regulatory structures with only two loops, none of which exists in the original pathway, could result in a selectivity up to 95%.
Measurement and modeling of N‐atom behavior in the afterglow of a microwave plasma
Authors: Wei Ta‐Chin , Collins Lance R. , Phillips Jonathan 
Published: June 2004

AbstractNitrogen‐atom behavior in a low‐pressure, nonisothermal microwave‐generated nitrogen afterglow was studied. N‐atom flux was measured by chemical titration. It was found that an increase in power or flow rate, or a decrease in pressure resulted in larger productions of N atoms. A one‐dimensional mass‐continuity equation was used to model N atoms' concentration field in the afterglow. The model, with no adjustable parameters, agreed closely with experimental measurements. The model shows that convection, diffusion, and wall recombination play important roles in the afterglow. In contrast, N‐atom generation and homogeneous recombination are of marginal importance. The model was manipulated to assess the impact of the measuring technique, chemical titration, on the N‐atom flux. It was found that the N‐atom flux profile is only slightly impacted, although the concentration profile is strongly modified.
Experimental pressure response for a modified PRC: Well‐stirred binary gas phase
Authors: Soares S. M. S. , Rice R. G. 
Published: June 2004

AbstractThe batch pressure‐response cell provides flexible and accurate means of assessing the kinetics in heterogeneous gas‐liquid reactions. A new model is derived to determine the kinetics of reactions of general (n,m) order using binary gas phase. This model has an important feature that allows the determination of the reaction order with respect to the gas‐phase reactant and the rate constant from a single set of pressure vs. time data through a simple two‐parameter estimation routine. Gas mixing was introduced via a simple modification of the liquid‐phase magnetic stirrer to reduce the gas‐phase mass‐transfer resistance to negligible levels and the parameter estimation problem to only two factors. The heterogeneous cobalt catalyzed sulfite oxidation reaction at low partial pressures of oxygen using a nitrogen‐oxygen mixture was tested to verify the validity of the model. The predicted kinetics were remarkably close to those values in the literature, yielding an oxygen order of 1.98 ± 0.02, which is taken to be second order in oxygen.
Cleaning of solid behenic acid residue from stainless‐steel surfaces
Authors: Grant Christine S. , Perka Alan T. , Thomas William D. , Caton Rashmi 
Published: June 2004

AbstractA rotating disk apparatus was used to study the removal of C14 labeled docosanoic (behenic) acid from stainless steel. The liquid cleaning behavior was studied as a function of temperature, surface morphology, and fluid flow. A mass‐transfer model was proposed to describe the removal of behenic acid from stainless steel using a rotating disk apparatus. The cleaning rates computed from the mass‐transfer model were compared with experimental observations; it was found that at low temperatures the removal was a function of rotation speed. At higher temperatures, however, the removal rate was independent of the disk rotation speed. In some cases the predicted rate of behenic acid removal differed significantly from the observed data. A plausible explanation for these variations is that the residues are removed by the combined effects of dissolution and the shearing of large clusters of solid behenic acid crystals. The temperature‐dependent behavior of the cleaning data was analyzed using an activation‐energy‐based model.
Simulation of noise‐driven wave dynamics on a falling film
Authors: Chang Hsueh‐Chia , Demekhin Evgeny A. , Kalaidin Evgeny 
Published: June 2004

AbstractA numerical model developed simulates inlet noise‐driven wave dynamics on a falling film at relatively high Reynolds numbers. Two parameters, a normalized Reynolds number and a noise index, are sufficient to specify the wave statistics on most channels. Observed phenomena, like wave inception, downstream wave texture coarsening, initial deceleration and subsequent acceleration of wave speeds, are quantitatively reproduced and explained. Statistical analysis from our simulations suggests that beyond a critical Reynolds number this complex noise‐driven spatio‐temporal dynamics can be modeled by a deterministic interaction theory based on stable solitary waves that resemble onehump pulses and a statistical theory with a random‐phase description of noise. The “chaotic” wave dynamics at higher Reynolds number is hence due to both noise amplification/filtering and intrinsic dynamics.
Graphic exergy analysis of processes in distillation column by energy‐utilization diagrams
Authors: Taprap Ruchira , Ishida Masaru 
Published: June 2004

AbstractThe graphical construction called an energy‐utilization diagram (EUD) is adopted for analyses of energy transformation and exergy losses in a distillation column. The overall exergy loss on one plate of a column can be decomposed into six kinds of exergy losses and are represented graphically. Two of them are caused by mixing and cooling in the vapor phase, and the other two by mixing and heating in the liquid phase. To display the remaining two yielded by condensation and evaporation of each component, the concept of the individual energy level is applied. The relationship between the individual energy level and the xy diagram is presented as well as effects of the reflux ratio and the feed location on the EUD for the whole column. Separation of n‐hexane and n‐octane is used to illustrate the methodology.
Application of distributed computing to batch plant design and scheduling
Authors: Subrahmanyam Sriram , Kudva Gautham K. , Bassett Matthew H. , Pekny Joseph F. 
Published: June 2004

AbstractIn designing and scheduling batch plants, engineers strive to choose the ones that maximize economic benefits, subject to constraints imposed by process physics and market demands. Even for relatively small design projects and for experienced engineers, the number of practical alternatives is combinatorially explosive. The formalism of mathematical programming provides a convenient way of organizing alternatives and a rigorous justification of choices. Mathematical modeling of these design problems yields large mixed integer linear programs (MILPs). Thus, the effective use of optimization techniques to formalize the design process relies on the ability to solve large models. Distributed computing can be utilized effectively in the solution of MILPs modeling practical design and scheduling problems. This work demonstrates how large MILPs can be solved using a distributed computing platform. The viability of the distributed computing approach is illustrated by presenting results for problems derived from industrial design case studies.
Mathematical modeling of supercritical extraction of sage oil
Authors: Reverchon E. 
Published: June 2004

AbstractModeling of supercritical CO2 extraction of essential oils from leaves was studied using sage at 90 bar (9 MPa) and 50°C. The fractional separation of the extracts enabled essential oil to be obtained. Four mean sage particle sizes ranging from 0.25 to 3.10 mm were tested. The model proposed was based on differential mass balances performed along the extraction bed. Experimental data suggest that the internal mass transfer was the controlling stage for the extraction process. Different hypotheses were tested on vegetable matter geometry, and their incidence on the model performance was evaluated. The particle shape proved to be a key factor in fitting experimental results, which were fairly good when the conventional spherical geometry was replaced by a realistic slab geometry. Diffusivity of the solute in the solid matrix was used as the only adjustable parameter of the model; its best fit value was 6.0 × 10−13 m2/s. The effect of the introduction of particle‐size distribution into calculations was also tested. To verify if the external mass‐transfer mechanisms influence the extraction process, experiments at two different CO2 flow rates were also performed. Simplified models were also considered, and the extent of approximations was evaluated.
Partial wetting of cylindrical catalytic carriers in trickle‐bed reactors
Authors: Tsamatsoulis D. C. , Papayannakos N. G. 
Published: June 2004

AbstractThe use of a modified Thiele modulus, as a correlating parameter for partially wetted catalyst pellets, is compared with the exact solution of the diffusion and reaction problem. The study of a variety of partially wetted cylindrical catalyst pellets for first‐ and second‐order kinetics indicates that the manner in which particles are externally wetted does not significantly influence the value of the effectiveness factor. External and internal partial wetting of industrial‐size porous extrudates is determined in a bench‐scale hydrotreater at real hydroprocessing conditions by simulating the system response to a step change of feed using the sulfur compounds of a petroleum fraction as tracer molecules. To solve the corresponding mass balances in the interparticle and intraparticle domain, two different numerical methods are compared.
Monte Carlo simulation of size‐enlargement mechanisms in crystallization
Authors: van Peborgh Gooch John R. , Hounslow Michael J. 
Published: June 2004

AbstractThis article outlines a Monte Carlo approach for simulating crystallization processes both as an alternative to solving the population balance equations (PBE) and as a way of conducting multicoordinate simulations that are too complex to be solved as PBEs. First, simple cases with different combinations of nucleation, growth and aggregation are simulated for batch and continuous systems. The comparison of the results of these test cases with analytical and numerical results shows excellent agreement. New results for two cases with simultaneous growth rate dispersion and aggregation are also discussed. From these results, a new hypothesis is proposed to explain the observed reduction in the degree of aggregation for larger crystals in the continuous crystallization of potassium sulfate. The simulations show that this experimental observation may be caused by small, slow‐growing crystals being swallowed by larger, fast‐growing ones.
Rigorous model for ion exchange equilibria of strong and weak electrolytes
Authors: Jansen Marcel L. , Straathof Adrie J. J. , van der Wielen Luuk A. M. , Luyben Karel Ch. A. M. , van den Tweel Will J. J. 
Published: June 2004

AbstractA thermodynamics‐based equilibrium model was developed to describe ion exchange equilibria of strong and weak electrolytes. It is applicable to binary and multicomponent systems, using selectivity coefficients for all ion pairs and distribution coefficients for all neutral species as parameters. The model was successfully tested for a strong‐base anion exchange resin with the strong electrolyte NaCl and the weak electrolytes acetic acid and N‐acetylmethionine in a wide concentration range. Compared to conventional models, this model is more advantageous because it takes into account the uptake of all species, counterions as well coions and neutral species, thus making it possible to calculate the intraparticle pH. Especially when weak electrolytes are involved and when electrolyte concentrations strongly exceed the resin capacity, it is superior to conventional ones, whereas for dilute systems it converges to the conventional stoichiometric displacement model.
Protein separation by continuous‐flow electrophoresis in microgravity
Authors: Clifton Michael J. , Balmann Hélène Roux‐De , Sanchez Victor 
Published: June 2004

AbstractDuring the IML‐2 space shuttle mission, the RAMSES instrument was operated in the Spacelab module. This continuous‐flow electrophoresis device performs separation and purification of protein solutions on a preparative scale. Samples containing artificial mixtures of pure proteins were used to test the capabilities of the device, and useful separations were obtained for proteins having a mobility difference of only 3 × 10−9 m2·V−1·s−1. Operating conditions that cannot be applied on earth were explored for two different sample concentrations, one of which is too high to allow treatment on earth. It agrees well with a previously published numerical model in that the main cause of loss in resolution in this process is the electrohydrodynamic spreading of the protein filaments.
Convective wall‐to‐suspension heat transfer in circulating fluidized bed risers
Authors: Wang X. S. , Gibbs B. M. , Rhodes M. J. , Geldart D. 
Published: June 2004

AbstractA mechanistic model, which incorporates recent findings on the fluid dynamics in the riser of the circulating fluidized bed (CFB), is developed for predicting the suspension‐to‐wall heat‐transfer coefficient in the riser. It is assumed that heat transfer between the gas‐particle suspension and the riser wall takes place by the contact of both particle packets and an emulsion phase on the wall. A characteristic length (L), that is, a sliding distance of the emulsion phase along the heat‐transfer surface, is introduced in the model, enabling the effect of the length of heat‐transfer surface to be evaluated. It is found that the heat‐transfer coefficient decreases with increasing L, but becomes increasingly insensitive to L when L is larger than 1 m. Agreement between model prediction and measurement is encouraging over a range of operating conditions, heat‐transfer surface length, and riser diameters.