bluuebunny/crossref_metadata_2025_split huggingface dataset:
Internally staged permeator prepared from annular hollow fibers for gas separation
Authors: Li K. , Wang Dongliang , Li Dongfei , Teo W. K. 
Published: April 2004

AbstractA polysulfone/polyethersulfone annular hollow‐fiber (tube) membrane was prepared using a phase‐inversion process, which is useful for further preparation of an internally staged permeator (ISP) for gas separation. This study focused on the techniques of fabricating the polysulfone/polyethersulfone annular‐hollow‐fiber membranes and its membrane permeators for gas enrichment. Two homogeneous polymer solutions comprising polysulfone/DMAc and polyethersulfone/NMP/water, respectively, were prepared and extruded with a triple‐orifice spinneret into an annular‐hollow‐jiber membrane that possesses two distinct skin layers and is capable of providing two separation stages internally for gas separation. The performance of the ISP fabricated from the prepared annular hollow‐fiber membrane was evaluated theoretically and experimentally under co/countercurrent and countercurrent flow patterns for various binaly gas mixtures. The mathematical models generally describe satisfactorily the observed experimental results. A parametric study reveals that while, in general, better separation is available at lower values of overall stage cuts, highly purified permeate products could be achieved at higher values of overall stage cuts if the concentration of a permeating component in the feed stock is relatively high.
Back mixing in a reciprocating plate column with stable density gradients
Authors: Rao Nadella V. Rama , Baird Malcolm H. I. 
Published: April 2004

AbstractAxial dispersion coeficients were measured in an aqueous phase flowing downward through a 5.08‐cm‐dia. Karr‐type reciprocating plate column. The steady tracer injection method was used, in which the concentration profile was measured upstream of tracer injection. The tracer solution was a strong (150–170 g/L) solution of sodium chloride, whereby a significant stable density gradient (density decreasing with height) was created in the upstream section. The operating variables included frequency (0 to 7.1 Hz), amplitude (0.7 to 1.4 cm), and plate spacing (2.65 to 7.65 cm). Some data were also obtained under two‐phase conditions with a refined kerosene (Isopar M) dispersed in the aqueous phase as droplets. Some control experiments were done using a neutrally buoyant tracer solution containing sodium chloride and methanol. There was no evidence that the stable density gradient had any effect in reducing the values of the axial dispersion coejjicient, although earlier published work had shown that an unstable density gradient did increase axial miring.
Synchronization of batch trajectories using dynamic time warping
Authors: Kassidas Athanassios , MacGregor John F. , Taylor Paul A. 
Published: April 2004

AbstractThe application of dynamic time warping (DTW) to the analysis and monitoring of batch processes is presented. This dynamic‐programming‐based technique has been used in the area of speech recognition for the recognition of isolated and connected words. DTW has the ability to synchronize two trajectories by appropriately translating, expanding, and contracting localized segments within both trajectories to achieve a minimum distance between the trajectories. Batch processes often are characterized by unsynchronized trajectories, due to the presence of batch‐to‐batch disturbances and the existence of physical constraints. To compare these batch histories and apply statistical analysis one needs to reconcile the timing differences among these trajectories. This can be achieved using DTW with only a minimal amount of process knowledge. The combination of DTW and a monitoring method based on Multiway PCA/PLS is used for both off‐line and on‐line implementation. Data fiom an industrial polymerization reactor are used to illustrate the implementation and the performance of this method.
Investigation of a complex reaction network: I. Experiments in a high‐pressure trickle‐bed reactor
Authors: Khadilkar M. R. , Jiang Y. , Al‐Dahhan M. , Duduković M. P. , Chou S. K. , Ahmed G. , Kahney R. 
Published: April 2004

AbstractA high‐pressure trickle‐bed reactor was used to achieue high productivity and selectivity for the manufacture of a key herbicide intermediate (α‐aminomethyl‐2‐furanmethanol) (amino alcohol, AA) from α‐nitromethyl‐2‐furanmethanol (nitro alcohol, NA). Raney Nickel catalysts of varying activity were prescreened for suitability in tricklebed operation. The effect of operating parameters such as reactant feed concentration, liquid mass uelocity, and temperature on the yield of amino alcohol (A) for RNi‐a are discussed. The superiority of trickle‐bed reactors ouer others such as semibatch and batch sluny systems is demonstrated. The AA yield increases with decrease in feed reactant concentration and liquid mass velocity, as well as with lowering of the operat ing temperature. A maximum product yield of 90.1% was obtained at 8.3 wt. % feed concentration of nitroalcohol (NA), while at the highest feed concentration of 40 wt. % NA, the maximum product yield was 58%. The volumetric productivity of AA was significantly higher at higher reactant feed concentrations, even though the yield was lower under these conditions. The operating temperature was also an important parameter, with a lower temperature being preferable for trickle‐bed experiments. Bed dilution with inert fines improued catalyst utilization and increased the AA yield and productivity in the laboratory‐scale trickle‐bed reactor.
Investigation of a complex reaction network: II. Kinetics, mechanism and parameter estimation
Authors: Jiang Y. , Khadilkar M. R. , Al‐Dahhan M. , Duduković M. P. , Chou S. K. , Ahmed G. , Kahney R. 
Published: April 2004

AbstractConventional strategies for discrimination of intrinsic and apparent kinetics from crushed‐ and whole‐catalyst‐pellet experimental data, respectively, do not yield satisfactory results for the reaction network in the manufacture of (α‐aminomethyl‐2‐furanmethanol) (aminoalcohol) from αnitromethyl‐2‐furanmethanol (nitroalcohol). Laboratory trickle‐bed reactor tests in the range of concentration and product yield of commercial interest are utilized to yield a reasonable set of kinetic parameters, which are otherwise unobtainable. This is accomplished by proposing a reaction network, a plausible mechanism, and optimizing the kinetic parameters based on the reactor‐model‐generated peformance data to fit experimental output concentrations of all species for the entire set of experiments. A complex reaction network for the key reactions in the system is developed based on the reaction scheme in Part I. Fitting of trickle‐bed reactor data to this model is attempted to yield an insight into the actual kinetics. The results show promise of obtaining an overall network kinetic model, even with the limited data available.
Structural stability of kinetic models: Anomalies due to irreversible adsorption
Authors: Nibbelke Rob H. , Hoebink Jozef H. B. J. , de Croon Mart H. J. M. , Marin Guy B. 
Published: April 2004

AbstractThe assumption of irreversible adsorption of a reactant can lead to a structurally unstable kinetic model. The structural instability is caused by the fact that two steadystate solutions intersect in the bifurcation diagram o j for example, the degree of surface coverage of one of the adsorbates us. the partial pressure of one of the reactants. One of the two solutions is a trivial solution, corresponding to a catalyst surface completely covered with the irreversibly adsorbing reactant. The intersection point is a transcritical bifurcation point. A structurally stable kinetic model is obtained i f an arbitrarily small desorption rate coefficient is introduced. Two examples are discussed in which a transcritical bifurcation point is encountered, that is, the total oxidation of ethene in three‐way catalysis and the chemical vapor deposition of refractory metals. The consequences of the existence of a transcritical bifurcation point for kinetic parameter estimation and reactor simulation are emphasized.
Study of the morphological hysteresis in immiscible polymer blends
Authors: Minale Mario , Mewis Jan , Moldenaers Paula 
Published: April 2004

AbstractThe effect of processing conditions (essentially the flow conditions) on the mophology of incompatible, immiscible polymer blends was investigated. In simple shear flow the steady‐state mophology, that is, droplet size, of such blends is a single‐valued finction of the shear rate whenever a critical shear rate is exceeded. Below this critical value it becomes uely dificult to reach a dynamic equilibrium between droplet breakup and coalescence, which gives rise to a hysteresis region for the size of the inclusions. Such regions were identified and studied for model‐blend systems. The critical shear rate decreases with increasing concentration of the droplet phase. A large ratio of droplet over matrix viscosity seems to have the opposite effect. The hysteresis region is bounded by the critical curues for droplet breakup and coalescence. The accessibility of this re gion can therefore be used to evaluate models for the said phenomena in nondilute systems. Droplet breakup is nearly independent of droplet concentration, while elasticity of the dispersed phase seems to facilitate breakup. As expected, coalescence is enhanced by higher concentrations. Droplet elasticity induces a certain degree of “rigidity” to the interface, and therefore the mobile interface model for coalescence is not suitable for such systems.
Droplet size evolution during coalescence in semiconcentrated model blends
Authors: Vinckier I. , Moldenaers P. , Terracciano A. M. , Grizzuti N. 
Published: April 2004

AbstractThe droplet‐size evolution in polymer blends, due to flow‐driven coalescence, is nvestigated both experimentally and theoretically. In the experiments, preshearing at a high rate is applied to generate a fine morphology in the blend; subsequently, the shear rate is suddenly decreased to induce coalescence, and the resulting growth in droplet size is measured. It is demonstrated that rheological as well as microscopic techniques can be used for an in‐situ determination of the size evolution of the droplets. Effects of shear rate, step‐down ratio, and blend concentration were studied systematically. A master curve for the droplet growth at each step ratio can be obtained by plotting the relative increase in droplet diameter us. the strain after step‐down in shear rate, multiplied by the fraction of the disperse‐phase squared. To model the droplet‐size evolution the strategy of Chesters is followed. It is implemented here for semiconcentrated blends, resulting in a one‐parameter model equation that correctly describes the experimental observations.
Modeling and simulation of shell and tube heat exchangers under milk fouling
Authors: Georgiadis Michael C. , Rotstein Guillermo E. , Macchietto Sandro 
Published: April 2004

AbstractA mathematical model for single shell and tube heat exchangers under milk fouling is presented. A fouling model based on a reaction/mass‐transfer scheme is detailed in which the main factors during milk heat treatment are quantified in a formal way. This model is coupled with a detailed dynamic model of a shell‐and‐tube heat exchanger where both radial and axial domains are taken into account. An analytical procedure for the calculation of key parameters provides the means to achieve more accuracy. The simulation results agree well with available experimental work. Four different heat exchanger arrangements are then considered to illustrate their impact on the fouling behavior. The results are encouraging enough to validate current operating industrial techniques for fouling mitigation. For a given thermal duty, short heat exchangers are more prone to fouling due to high‐temperature requirements and milk should be heated 11s gradually as possible to minimize fouling. The results show that there are main tradeoffs between design and operation issues.
Filtration of particulate suspensions in acoustically driven porous media
Authors: Gupta Sanjay , Feke Donald L. 
Published: April 2004

AbstractRetention of suspended solids within a porous medium subjected to resonant ultrasonic fields was studied experimentally. In laboratory tests, 325 mesh polystyrene particles were collected with high (typically > 80%) single‐pass efficiency using a polyester foam mesh with pores more than two orders of magnitude larger than the particles retained. Deactivation of the acoustic field allows the retained particles to be flushed from the porous medium. The effects on filtration efficiency of processing variables (suspension flow rate, solids concentration in the feed, intensity of the acoustic field, and frequency of the acoustic field) are reported. A simplified analysis of particle trajectories toward cylindrical collectors in response to acoustic and hydrodynamic forces provides insight into the fundamental physical phenomena that govern the acoustically enhanced filtration process.
Mixing and particle dispersion in the wavy vortex regime of Taylor–Couette flow
Authors: Rudman Murray 
Published: April 2004

AbstractFluid flow and particle dispersion were investigated numerically in the wavy vortex regime of Taylor‐Couette flow. The flow field for wavy vortex flow is stationary when viewed in a frame rotating with the azimuthal wave velocity. These steady flow fields are used to track fluid particles and to estimate the effective axial difision resulting from chaotic fluid aduection. The effective diffusion coefficient for a fixed wave state is a function of the Reynolds number. Particle dispersion is a strong function of wave state, showing that a universal relationship between dispersion and Reynolds number cannot be found in this regime of cylindrical Taylor‐Couette flow. The effectiue Schmidt number of chaotic advection is less than unity for all wavy vortex flows examined, indicating that chaotic advection plays an important role in fluid mixing in these flow regimes. Fluid particle retention in the cores of the wavy vortices is also predicted for some parameter regimes, although not all. Particles trapped in vortex cores are only poorly mixed within the core and play no role in global mixing. A preliminary examination of inertial particle settling suggests that the fluid flow does not prevent settling in the mean, although the magnitude of the settling velocity significantly affects the dispersion of inertial particles.
Critical criteria for ignition of combustible fluids in insulation materials
Authors: Brindiey J. , Grifiths J. F. , Zhang J. , Hafiz N. A. , McIntosh A. C. 
Published: April 2004

AbstractThe possibility of a combustion hazard, when a flammable liquid leaks into insulation materials, is determined by the surface temperature, the volatility and loading of the fluid, the exothermicity of the combustion process, and the porosity of the matrix. Whether or not there is asymmetric heating is also influential. The oxygen diffusion rate or a reduction in its ambient concentration have a limited effect. A dimensionless, analytical, criticality criterion (u∞) for ignition of flammable liquids dispersed within a hot inert matrix is compared with a dimensionless parameter (u∞) based on the classic Frank‐Kamenetskii ignition criterion. The relationship between u∞, and uFK is explored numerically over wide ranges of conditions and the switch as a monitor of safe operating practice are calculated assuming uniform surface heating. The application of u∞, is most appropriate with a high loading of a relatively high volatility fluid dispersed within a matrix that presents a very high internal surface area, and the reaction is not very exothermic. The application of uFK is appropriate to other circumstances. It was also found that certain classes of compounds may be capable of bonding to insulation in a way that suppresses their normal evaporative loss. This may signify a hitherto unrecognized problem that certain combinations of liquids and pipe insulating materials enhance combustion hazards.
Large‐scale DAE optimization using a simultaneous NLP formulation
Authors: Cervantes A. , Biegler L. T. 
Published: April 2004

AbstractThe differential‐algebraic equation (DAE) optimization problem is transformed to a nonlinear programming problem by applying collocation on finite elements. The resulting problem is solved using a reduced space successive quadratic programming (rSQP) algorithm. Here, the variable space is partitioned into range and null spaces. Partitioning by choosing a pivot sequence for an LU factorization with partial pivoting allows us to detect unstable modes in the DAE system, which can now be stabilized without imposing new boundary conditions. As a result, the range space is decomposed in a single step by exploiting the overall sparsity of the collocation matrix; which performs better than the two‐step condensation method used in standard collocation solvers. To deal with ill‐conditioned constraints, we also extend the rSQP algorithm to include dogleg steps for the range space step that solves the collocation equations. The performance of this algorithm was tested on two well known unstable problems and on three chemical engineering examples including two reactive distillation columns and a plug‐flow reactor with free radicals. One of these is u batch column where an equilibrium reaction takes place. The second reactive distillation problem is the startup of a continuous column with competitive reactions. These optimization problems, which include more than 150 DAEs, ure solved in less than 7 CPU minutes on workstation class computers.
Product design through multivariate statistical analysis of process data
Authors: Jaeckle Christiane M. , Macgregor John F. 
Published: April 2004

AbstractA methodology is developed for finding a window of operating conditions within which one should be able to produce a product having a specified set of quality characteristics. The only information assumed to be available is that contained within historical data on the process obtained during the production of a range of existing product grades. Multivariate statistical methods are used to build and to invert either linear or nonlinear empirical latent variable models of the existing plant operations to obtain a window of operating conditions that are capable of yielding the desired product and that are still consistent with past operating procedures and constraints. The methods and concepts are illustrated using a simulated high‐pressure tubular reactor process for producing low‐density polyethylene.
Activated carbon production from low ash subbituminous coal with CO2 activation
Authors: Teng Hsisheng , Lin Hung‐chi 
Published: April 2004

AbstractActivated carbon was prepared by physical activation in CO, from a low‐ash subbituminous coal. The preparation process consisted of carbonization of the coal in N, followed by activation of the resulting chars in CO2. The activation temperature ranged from 700 to 950°C. Experimental results revealed that the surface area, pore volume and average pore diameter of the activated carbon generally increased with the amount of carbon burnoff carried out at the same temperature. These surface characteristics were also influenced by the variation of the activation temperature. It was found that the porosity of the carbon passed through a maximum at a temperature of 750°C. The activation energy for the carbon gasification in CO2 was calculated to be in a range of 130 180 kJ/mol, based on the assumption that the reaction rate was proportional to the surface area of the carbon. The apparent order with respect to CO2 partial pressure for the gasification was found to be within the range of 0.15–0.25.
Thermodynamic consistency test for equilibria involving cross‐linked polymers
Authors: Hillaire A. , Favre E. 
Published: April 2004

AbstractThe implications of the peculiarities of equilibria involving a cross‐linked polymer network and a solvent were examined in the derivation of a thermodynamic consistency test. While strict application to a binary system achieves no tangible result, it is shown that a simple expression can be obtained from the Gibbs‐Duhem equation, if several sets of data, including both binary and ternary, are combined. The expression derived was applied to previously reported multicomponent data. The results and further developments of the newly proposed test are discussed.
Trailing vortices around a 45° pitched‐blade impeller
Authors: Schäfer M. , Yianneskis M. , Wächter P. , Durst F. 
Published: April 2004

AbstractThe trailing vortex system near impeller blades has been identified as the major flow mechanism responsible for mixing and dispersion in stirred vessels, and high turbulence levels in the vortices have an important impact on such phenomena as drop breakup and cell damage in bioreactors. Numerical computations of the flows require more detailed information on the velocity characteristics generated by different impeller designs than is available in the literature. Our study on the mean flow and turbulence structure generated by a pitched‐blade turbine with four 45° inclined blades found that single trailing vortex is formed around each turbine blade. The vortex axis spread out radially by less than 0.0015 T and was inclined at 20° to the horizontal plane. The vortices merged into the bulk flow structure at around 135° behind each blade. Periodicity of the mean flow due to the crossing of the individual blades and high levels of kinetic energy of turbulence (k) are contained within a radial distance of around r/T = 0.23 from the axis and a vertical distance of z/T = 0.07–0.46 from the bottom of the vessel. The k levels decay to nearly‐uniform and low values outside this region. The results are compared with earlier investigations, and their implications for mixing processes and CFD predictions of the flows are discussed. The data identify flow regions accurately where intense turbulence is present and thus give useful indications for the optimization of mixing processes.
Model elastic liquids with water‐soluble polymers
Authors: Dontula P. , Macosko C. W. , Scriven L. E. 
Published: April 2004

AbstractModel liquids with nearly constant viscosity and adjustable elasticity are needed to resolve the role of elasticity in coating and other free‐surface flows. Available Boger liquids are not well suited to free‐surface flows, because they are solutions in organic solvents and their viscosities exceeding 1 Pa · s fall on the high side. Aqueous liquids are preferred in laboratory studies partly due to environmental hazards. Aqueous polymer solutions with constant shear viscosity and adjustable elasticity were prepared by adding small amounts of a high‐molecular‐weight polymer to a more concentrated aqueous solution of the same polymer but of a much lower molecular weight. Up to 0.2 wt. % of high‐molecular weight poly(ethylene oxide) (PEO, Mw from 400,000 to 4 million g/mol) was added to almost inelastic solutions of low‐MW polyethylene glycol (PEG, Mn = 8,000 g/mol). PEG concentrations in these solutions varied between 16.7 and 42.9 wt. %. Shear viscosities of these solutions ranged from about 0.02 to 0.3 Pa · s and were constant up to shear rates of 100 s−1. The stress ratio is one measure of the elasticity of the liquid. Stress ratios up to 0.2 were estimated from small‐amplitude oscillatory measurements. Terminal behavior (elastic modulus rising with the square of the frequency) was not observed even at 10−2 rad/s. Viscosity and elasticity of the liquids can be manipulated over a wide range by varying the amounts and molecular weights of PEG and PEO within the unentangled and dilute regions of the concentration–molecular weight diagram, respectively. Fits of experimental data to candidate differential and integral constitutive equations are also discussed.