bluuebunny/crossref_metadata_2025 huggingface dataset:
Cross‐stream migration of bead–spring polymers in nonrectilinear pore flows
Authors: Nitsche Ludwig C.
Published: June 2004

Deterministic 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

A 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

A 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

One 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

The 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

The 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

Improvements 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

Nitrogen‐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

The 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

A 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

A 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.
Washing theory for nonequilibrium stages
Authors: Tosun Ismail
Published: June 2004

A new approach for the determination of concentrations in the case of nonequilibrium washing stages is presented. Each washing stage is assumed to consist of series of mixing cells, and the conservation of solute mass is solved by Laplace transformation. The simplicity of the resulting equations makes this approach more practical than the existing one.
Graphic exergy analysis of processes in distillation column by energy‐utilization diagrams
Authors: Taprap Ruchira , Ishida Masaru
Published: June 2004

The 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

In 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

Modeling 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

The 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

This 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

A 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

During 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

A 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.
Theory of adsorbed solutions: Analysis of one‐dimensional systems
Authors: Chiang Anthony S. T. , Lee C. K. , Wu F. Y.
Published: June 2004

A general formulation for 1‐D multicomponent localized adsorption is presented, as well as a new mixing function that varies with only temperature and spreading pressure. An understanding of this mixing function completely determines the solution thermodynamics of the system. A closed‐form expression for the adsorbed‐phase excess Gibbs energy exhibiting an explicit dependence on the spreading pressure is thus obtained. The empirical expression proposed in the literature for the adsorbed‐phase excess Gibbs energy is found to be consistent with the exact solution obtained in one dimension. The new mixing function further suggests the possibility of considering a binary adsorbed solution as the adsorption of a pseudo adsorbate.
Separation of quaternary conjugate salt systems by fractional crystallization
Authors: Berry David A. , Ng Ka M.
Published: June 2004

A method is presented that synthesizes fractional crystallization separation processes to obtain pure solids from conjugate salt solutions. The method, which includes a procedure to generate phase diagrams by using solubility products, explains how to calculate concentrations of all components in a system given a point on a Jänecke projection. Both multivalent ions and species that exhibit complex‐ionic equilibrium are considered. For solutions from which only simple salts crystallize, three separation classes are identified. The classification is based on the composition of the feed, the characteristics of the phase diagram, and the product salts. Class I separates compatible salts, Class II incompatible salts, and Class III two compatible salts and one incompatible salt. Process paths and design equations for each class are also presented. Guidelines proposed select the separation sequence and the stream compositions based on the effects of the design variables on stream flows and on total annual cost. The method is applicable to systems in which hydrates and double salts are present. An example given shows how to obtain simple salts from these systems.
Feedback regularization and control of nonlinear differential‐algebraic‐equation systems
Authors: Kumar Aditya , Daoutidis Prodromos
Published: June 2004

The feedback control of nonlinear high‐index differential‐algebraic‐equation systems for which the underlying algebraic constraints among the system variables involve the manipulated inputs is addressed in this work. A state‐space realization of such systems cannot be derived independently of the controller design. In view of this fact, a two‐step methodology is proposed for the control of such systems. The first step involves the derivation of a dynamic state‐feedback compensator such that in the resulting system, the underlying constraints are independent of the new inputs. In the second step, a state‐space realization of the feedback modified system is derived and used as the basis for a state‐feedback controller synthesis. Application of the developed control methodology is demonstrated on an interconnection of a two‐phase exothermic reactor and a condenser.
Approximate models for nonlinear process control
Authors: Sentoni G. , Agamennoni O. , Desages A. , Romagnoli J.
Published: June 2004

A methodology is presented to obtain approximate models from input–output data, particularly oriented to implement a model‐predictive control scheme. Causal, time‐invariant nonlinear discrete systems with a certain type of continuity condition called fading memory are dealt with. To synthesize the nonlinear model a finite‐dimensional linear dynamic part (discrete Laguerre polynomials) is used, followed by a nonlinear nonmemory map (single hidden‐layer perceptron). Results of the application to approximate and control a binary distillation column are presented.
One‐dimensional equations governing single‐cavity die design
Authors: Weinstein Steven J. , Ruschak Kenneth J.
Published: June 2004

The 1‐D approximate equations governing flow in a single‐cavity die have been examined in detail. Although the 1‐D momentum equation in the slot and mass conservation equation used in previous studies are generally the same, various forms of the 1‐D momentum equation governing flow in the cavity have been utilized. A rigorous accounting of the origin of the 1‐D cavity equation is given, via asymptotic techniques, integral equations, and the use of approximate velocity fields. Additionally, these techniques are employed to place the slot flow and mass conservation equations, utilized in previous studies, on a firmer theoretical ground. The derived cavity equation and differential equation system is found to be identical to that of Leonard (1985).
Effective diffusion coefficients in square arrays of filament bundles
Authors: Transvalidou Faye , Sotirchos Stratis V.
Published: June 2004

The effects of the polydispersity of the characteristic diffusion length of the pore space of fibrous media on the effective diffusion coefficients of gases are studied by investigating the problem of gaseous diffusion in the Knudsen, transition, and bulk regimes in square arrays of filament bundles, of cylindrical cross section, consisting of unidirectional, freely overlapping cylindrical filaments. Effective diffusion coefficients are computed using a stochastic simulation method based on the computation of the mean square displacement of a large number of molecules (random walkers) diffusing in the pore space. The dependence of effective diffusivity on filament to bundle radius ratio, intrabundle porosity, interbundle porosity, and Knudsen number is investigated in detail. The computed diffusivities are compared to the predictions of analytical or semianalytical formulas based on expressions derived in the literature for two‐phase media or bidisperse pore structures.
Mathematical model of steam drying of wood chips and other hygroscopic porous media
Authors: Fyhr Christian , Rasmuson Anders
Published: June 2004

A model is presented that is focused on the drying kinetics of single wood chips as a function of time and external conditions, such as temperature, pressure and velocity of the superheated steam. A multiphase and 2‐D approach was used to model the coupled transport of water, vapor, air and heat in anisotropic hygroscopic porous media. The model was verified by drying experiments where measurements of the average moisture content, center temperature and pressure in a single wood chip could be performed simultaneously. A comparison between the calculations and the measurements showed that the drying behavior was well predicted. The drying can be divided into three stages: a heat‐up period when condensation on the surface initially increases the moisture content; a period of constant drying rate when the external heat transfer controls the drying rate; and a period of decreasing drying rate when the drying is controlled by internal mass transfer. Many interesting features of the drying could be assigned to the strong anisotropicity of wood, which makes a 2‐D model necessary.
Catalyst bed dilution for improving catalyst wetting in laboratory trickle‐bed reactors
Authors: Al‐Dahhan Muthanna H. , Duduković Milorad P.
Published: June 2004

The catalyst bed dilution technique has found rather widespread applications as a means of producing reliable and reproducible results for successful scale‐up and scale‐down when testing commercially used catalyst particle sizes and alternative feedstocks in small‐scale laboratory trickle‐bed reactors. In such small‐diameter laboratory units when the catalyst used in commercial units is employed as the only packing, low liquid velocities lead to incomplete catalyst utilization due to incomplete external catalyst wetting, liquid maldistribution, and wall effects. Diluting the bed with fines is recommended to remedy these shortcomings. The effect of the bed dilution with fines on catalyst wetting efficiency, pressure drop, and liquid holdup are quantified. At atmospheric pressure, fines improve the catalyst wetting efficiency by increasing both the pressure drop and liquid holdup. At high‐pressure operation, wetting efficiency improves further, whereas pressure drop increases and liquid holdup decreases. In a highly diluted bed (e.g., 2 or more volume fines/1 volume catalyst) the improvement in catalyst wetting efficiency is about the same as that achieved in a bed packed according to our recommended procedure, which is based on filling the voidage of the original bed with fines.
Experimental study of wave propagation dynamics of binary distillation columns
Authors: Hwang Yng‐Long , Graham Glenn K. , Keller George E. , Ting Jack , Helfferich Friedrich G.
Published: June 2004

High‐purity distillation columns are typically difficult to control because of their severely nonlinear behavior reflected by their sharp composition and temperature profiles. The dynamic behavior of such a column, as characterized by the movement of its sharp profile, was elucidated by a nonlinear wave theory established previously. With binary alcohol mixtures, this study provides an experimental observation of such wave‐propagation dynamics of a 40‐tray stripping column and a 50‐tray fractionation column in response to step disturbances of feed composition, feed flow rate, and reboiler heat supply. Our experimental results have verified that the sharp profile in a high‐purity column moves as a constant‐pattern wave and that the nonlinear wave theory predicts its velocity satisfactorily with very simple mathematics. Our results also demonstrate the asymmetric dynamics of the transitions between two steady states.
Frequency‐domain closed‐loop identification of multivariable systems for feedback control
Authors: Li Wei , Lee Jay H.
Published: June 2004

A frequency‐domain identification method for multivariable systems is presented. The method emphasizes accurate identification of the process's gain directionality that is shown to be important for feedback control. The method requires closed‐loop testing in addition to conventional open‐loop testing, and combines open‐loop and closed‐loop data such that the derived model matches both the system's frequency‐response matrix and its inverse accurately. The method is used to identify a model for a nonideal high‐purity distillation column and is shown to capture the gain directionality of the process more accurately than the conventional method.
New approach to constrained predictive control with simultaneous model identification
Authors: Genceli Hasmet , Nikolaou Michael
Published: June 2004

A new framework to closed‐loop process identification is proposed. It relies on simultaneous constrained model predictive control (MPC) and identification (MPCI). MPCI obtains sufficient model information on a process under constrained MPC, while minimally disturbing that process. To select a process input at each time step, MPCI solves a constrained optimization problem on‐line with respect to process input values over a finite moving horizon. These process inputs should satisfy all conventional MPC constraints, as well as additional constraints that assure persistent excitation of the process by these inputs. The persistent excitation constraints can be enabled or disabled, according to process identification needs of the closed loop. An iterative scheme is proposed for the numerical solution of the on‐line optimization problem. At each iteration, that iterative scheme finds a suboptimal feasible solution of the on‐line optimization problem by solving a semidefinite programming problem whose global convergence is guaranteed. The effectiveness of the proposed new methodology is illustrated through simulations on a linear time‐varying process.
Characteristics of a new gas‐induced reactor
Authors: Hsu Yung‐Chien , Huang Chyuan‐Jih
Published: June 2004

A newly developed gas‐induced reactor for gas‐liquid heterogeneous reactions presented here has no baffle on the inner wall of the tank body. Inside the reactor tank, two in‐series 45° pitched blade downward turbines enclosed by a draft tube were employed. As the turbines rotate at high speeds, a central gas vortex is formed downwardly along the central shaft from the free surface of the liquid toward the upper turbine. The gas is then induced by the upper turbine and mixes with the input gas. After that, the mixed gas is broken into bubbles by the lower turbine and dispersed through the liquid vortex. With the formation of gas and liquid vortexes, the reactive gas was able to circulate in the liquid phase to achieve high gas utilization. The experimental studies were on the heterogeneous ozonation reaction of a reactive dye (C.I. Reactive Blue 19). Major experimental parameters, such as impeller speed, input concentration of ozone, input flow rate of ozone and liquid volume, were changed to investigate the characteristics of the gas‐induced reactor. This gas‐induced reactor achieved high gas utilization ratio, short reaction time, and high recovery of the unreactive gas.
Cryocooler development (1995 AIChE Institute Lecture)
Authors: Timmerhaus Klaus D.
Published: June 2004

Increased demand for cryocoolers for aerospace and terrestrial applications has served as an incentive over the past decade to develop units with specific performance parameters. Since many of these units also require a high degree of reliability, considerable effort has been directed toward meeting this goal. The excellent progress that has been made is summarized, and there is every indication that the use of cryocoolers will expand greatly during the next decade, with a rapid transition from present aerospace/military applications to highly civilian uses in such areas as medicine, electronic transmission, environmental control, energy storage, and transportation.
Segregated fermentation model for growth and differentiation of Bacillus licheniformis
Authors: Fordyce Andrew P. , Rawlings James B.
Published: June 2004

This article evaluates the effectiveness of a segregated model for prediction of growth and differentiation of Bacillus licheniformis in a submerged‐culture fermentation system. The segregated model accounts for each of the three morphological forms of the Bacillus life cycle. The sporangium biomass was characterized using an age‐population model to reflect the age‐dependent progress toward spore formation. Constitutive relationships governing the rates of vegetative cell reproduction, spore germination, commitment to sporulation, and substrate consumption are proposed. Based on this model framework, the dynamic cell growth and differentiation equations were developed.

Batch, steady‐state and step‐test fermentation data from a laboratory‐scale fermentor were incorporated into a maximum likelihood parameter estimation scheme for model identification. Confident estimates of growth and differentiation parameters were obtained for the segregated model using biomass measurements. In addition, the model describes successfully growth and differentiation in batch and steady‐state operating modes.
Osmotically activated agent release from electrostatically generated polymer microbeads
Authors: Amsden Brian G.
Published: June 2004

Release of lysozyme from poly(ethylene‐co‐vinyl acetate) microbeads into solution was examined. The lysozyme exists as solid particles dispersed randomly throughout the polymer matrix. Microbeads were prepared in a novel fashion using electrostatics to reduce bead sizes, which ranged from 0.6–0.43 to 1.0–0.85 mm. The release into distilled water was diffusionally controlled, followed by a period of osmotically controlled transport, which lasted for up to 400 hours for 1.0–0.85‐mm microbeads. The osmotically controlled release rate increased as the microbead radius increased, and was time‐ and weakly particle‐size‐dependent, decreasing with time and being initially greater for larger particles, but eventually becoming greater for smaller particles as time progressed. For example, for 0.60–0.43‐mm microbeads, the initial mass fraction release rate from microbeads containing 106–75‐μm particles was 0.0024 h−1, while that of microbeads containing ≤ 53‐μm particles was 0.0068 h−1. At 100 h, however, the release rate from microbeads containing 106–75‐μm particles was 0.0024 h−1, while that of microbeads containing ≤ 53‐μm particles was 0.0029 h−1. The total fraction of agent released from the polymer matrix increased, as the agent particle size increased and as the microbead radius decreased. A mathematical model of the osmotic release mechanism developed was consistent with the experimental observations. This model can be used in the design of controlled release products for pharmaceutical, agricultural and veterinarial applications.
Membrane‐based absorption of VOCs from a gas stream
Authors: Poddar Tarun K. , Majumdar Sudipto , Sirkar Kamalesh K.
Published: June 2004

A regenerative absorption‐based process was developed for removing VOCs from N2 in an inert, nonvolatile, organic liquid flowing in compact hollow‐fiber devices. The process eliminates flooding, loading, and entrainment, and can replace activated carbon adsorption. Two types of holow‐fiber membranes were studied: one with a microporous wall and the other with a highly VOC‐permeable nonporous coating on the outer surface of a microporous hollow fiber. Criteria for nondispersive operation were developed for each case. Experiments were conducted for the absorption of acetone, methylene chloride, toluene, and methanol from the respective VOC‐N2 gas mixture using two absorbents: silicone oil and mineral oil. The highest mass‐transfer coefficient was obtained for toluene followed by methylene chloride, acetone, and methanol. Different resistances making up the overall resistance in VOC absorption were characterized comprehensively to develop a predictive capability and compare the absorption performances of two types of fibers and the two absorbents. The absorbent‐filled porous membrane contributed significantly to the total mass‐transfer resistance. Numerical simulations of governing equations based on a cell model agree well with experimental results.
Phenomenological model of thermal shock propagation in ceramic monolith
Authors: Boshoff‐Mostert L. , Schroeder S. , Van Rensburg N. F. J. , Viljoen H. J.
Published: June 2004

A discrete model is used to study the behavior of shock propagation, crack formation, and crack propagation of a thin ceramic plate. This plate represents a wall of a channel in a monolithic structure. The model involves a spring‐node formulation on a rectangular geometry, which approaches the continuum model correctly when the Poisson ratio is taken as 0.25. Viscous damping is also included. Shock waves originate from perturbations due to local ignition (hot spots), sudden quenching or other changes in operating and driving conditions. The shock wave propagates from the perturbed region. Internodal displacements are used to calculate strains, and the values are compared to a maximum strain associated with failure. Spring constants are set to zero when the maximum strain is exceeded. Reflection of compressional waves from free boundaries as tensional waves leads to enhanced crack formation near the free boundary. Shock waves attenuate much faster when the plate is precracked. Propagation velocities are lower for precracked plates, due to a decrease in (effective) Young's modulus. Velocities of pure compressional and shear waves compare quite well with theoretical values.
Asymptotic models for H2S absorption into single and blended aqueous amines
Authors: Rinker Edward B. , Hanna Owen T. , Sandall Orville C.
Published: June 2004

Asymptotic power series solutions for the mass‐transfer enhancement factor for absorption of a gas component into a liquid where it undergoes irreversible instantaneous chemical reaction(s) with one and two liquid‐phase reactants are developed in this work. The Padé technique is used to extend the region of applicability (accelerate the convergence) of the four‐term asymptotic power series solutions. The resulting modified asymptotic expressions for the enhancement factor show excellent accuracy over a wide range and can be used to predict enhancement factors as low as 2 with an error of about 5% compared to the exact numerical solution. Predictions of these new asymptotic solutions are compared with experimental absorption data for H2S absorption into aqueous methyldiethanolamine and H2S absorption into aqueous mixtures of methyldiethanolamine and diethanolamine obtained in a laminar‐jet absorber. The absolute mean deviations of the predictions from the experimental absorption data for the single and mixed amine solutions were 4.6% and 2.4%, respectively.
Diffusion coefficients of phenol and oxygen in a biofilm of pseudomonas putida
Authors: Beyenal Haluk , Şleker Şlule , Tanyolaç Abdurrahman , Salih Bekir
Published: June 2004

A pure culture of Pseudomonas putida was grown as a film on carbon particles in a differential fluidized bed biofilm reactor, a new experimental system for the application of diffusion‐reaction models. In the active biofilm, effective diffusion coefficients of the essential substrates—phenol and oxygen—were simultaneously calculated. The multisubstrate biokinetic expression used in the model solution was derived by nonlinear regression analysis of the data of continuous system fermenter experiments. The determined biokinetic equations were utilized to solve the diffusion‐reaction model for effective diffusion coefficients in the active biofilm. The ratio of the evaluated effective diffusion coefficient through active biofilm to that of water varied between 17–44% and 9–24% for phenol and oxygen, respectively, for different biofilm densities. Results of the study showed a fair agreement with the literature at low biofilm densities.
Boiling heat transfer of Nitrogen in a thermosyphon condenser‐reboiler
Authors: Sakaue Seiichi
Published: June 2004

An experimental investigation was conducted to determine the boiling heat‐transfer characteristics in a thermosyphon condenser‐reboiler of air‐separation plants. The test section was a plate‐fin heat exchanger of practical size of 0.106 m width and 2.56 m length. The testing fluid was nitrogen. Experiments were carried out within a range of pressure from 150 to 300 kPa, submergence from 1.95 to 2.80 m, and heat flux up to 11 kW/m2 under constant wall‐temperature condition. The liquid superheat at the onset of boiling was rather significant. The boiling heat‐transfer coefficients obtained agreed well with Chen's correlation modified by Colburn's J factor within a mean deviation of 9.3%.
Formation of particle agglomerates after switching fluidizing gases
Authors: Kai Takami , Takahashi Takeshige
Published: June 2004

When a fluidizing gas is switched from a low‐density gas to a high‐density gas, particles in the emulsion phase agglomerate and bubbles disappear. At the same time, channeling occurs and a decrease in the pressure drop over the bed is observed. The disturbance of fluidization is temporary, and normal fluidization is restored after several minutes. The study of mechanisms of the transient phenomena shows that the difference in diffusion rates of the two gases in the emulsion phase caused the agglomeration of particles. Because the mobility of particles was reduced, channels were formed and the fluidizing gas bypassed through them. Effects of the properties of the fluidizing gases and particles on the intensity of the transient phenomena were also studied. The intensity increased with increasing difference in the densities of the two gases. The transient phenomena were considerable for small‐ and light‐particle systems.
Vacuum membrane distillation: Experiments and modeling
Authors: Bandini Serena , Saavedra Aldo , Sarti Giulio Cesare
Published: June 2004

Vacuum membrane distillation is a membrane‐based separation process considered here to remove volatile organic compounds from aqueous streams. Microporous hydrophobic membranes are used to separate the aqueous stream from a gas phase kept under vacuum. The evaporation of the liquid stream takes place on one side of the membrane, and mass transfer occurs through the vapor phase inside the membrane. The role of operative conditions on the process performance is widely investigated in the case of dilute binary aqueous mixtures containing acetone, ethanol, isopropanol, ethylacetate, methylacetate, or methylterbutyl ether. Temperature, composition, flow rate of the liquid feed, and pressure downstream the membrane are the main operative variables. Among these, the vacuum‐side pressure is the major design factor since it greatly affects the separation efficiency. A mathematical model description of the process is developed, and the results are compared with the experiments. The model is finally used to predict the best operative conditions in which the process can work for the case of benzene removal from waste waters.
Thermodynamic consistency of vapor‐liquid equilibrium data at high pressure
Authors: Bertucco Alberto , Barolo Massimiliano , Elvassore Nicola
Published: June 2004

A method for testing the thermodynamic consistency of binary and isothermal vapor‐liquid equilibrium data at moderate and high pressures is proposed, using a ϕ‐ϕ approach. The Redlich‐Kwong‐Soave equation of state with Huron‐Vidal mixing rules at infinite pressure is used in the data‐reduction procedure, and a Margules equation is used to calculate the activity coefficients at infinite pressure. This model is shown to be thermodynamically consistent. The proposed method allows us to check consistency of vapor‐liquid equilibrium data in the presence of components at the gaseous and supercritical states.