bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory of adsorbed solutions: Analysis of one‐dimensional systems
Authors: Chiang Anthony S. T. , Lee C. K. , Wu F. Y. 
Published: June 2004

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractHigh‐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

AbstractA 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

AbstractA 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

AbstractA 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

AbstractIncreased 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

AbstractThis 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

AbstractRelease 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

AbstractA 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

AbstractA 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

AbstractAsymptotic 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

AbstractA 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

AbstractAn 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

AbstractWhen 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.