bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling and optimization of a novel membrane reformer for higher hydrocarbons
Authors: Chen Zhongxiang , Yan Yibin , Elnashaie Said S. E. H. 
Published: April 2004

AbstractA novel circulating fast fluidized‐bed membrane reformer efficiently carries out simultaneous steam and oxidative reforming of heptane over nickel catalysts. A plug‐flow reactor model was developed to investigate effects of the operating parameters. The cases with palladium hydrogen membranes and/or dense perovskite oxygen membranes are investigated. The simulations show that high purity hydrogen can be efficiently produced using hydrogen membranes, which “break” the thermodynamic equilibrium barriers. The perovskite oxygen selective membranes supply oxygen along the length (or height) of the reformer for oxidative reforming of hydrocarbons, providing the heat necessary for the highly endothermic steam reforming reaction. The combination of these two membranes with the characteristics of the fast fluidization reformer makes this process not only an efficient hydrogen producer but also an energy efficient process. The fast continuous flow of catalyst makes the effect of carbon deposition on catalyst activity negligible in the novel process. Process optimization for the maximum hydrogen yield is conducted using the flexible tolerance optimization method.
Modeling transient stresses in spherical vessels during blowdown under fire attack
Authors: Falope G. B. O. , Mahgerefteh H. 
Published: April 2004

AbstractThe development of a rigorous mathematical model for simulating the failure risk of pressurized spherical hydrocarbon containing vessels during blowdown under fire attack is described. Accounting for the important thermodynamic and interfacial mass and heat transfer processes taking place during blowdown, the model simulates the thermal and pressure stresses in the vessel wall in both the radial and tangential directions. Failure is assumed to take place when the sum of these two stresses in either direction exceeds the vessel material of construction yield strength. Application of the model to the blowdown of a condensable hydrocarbon mixture indicates that failure occurs in the vapor space due to thermal weakening of the vessel wall. Finally, the risks associated with blowdown during fire attack for a cylindrical as opposed to a spherical vessel of the same volume and prevailing conditions are compared and contrasted.
Modeling the hydration of foodstuffs: Temperature effects
Authors: Weerts A. H. , Lian G. , Martin D. R. 
Published: April 2004

AbstractTo assess the impact of hydration kinetics of dried foodstuffs on their sensory property and release of functional molecules, it is necessary to be able to predict the temperature effect. Based on the dynamics of capillary flow in partially saturated porous media, a finite‐element model is developed to directly predict the infiltration of water into dried food materials as a function of temperature. The transfer properties are derived from physically based constitutive relationships of water adsorption and permeation. This is in contrast to the semiempirically fitted transfer properties often used in the heat‐ and mass‐transfer models of foods based on Fick's diffusion theory. Rehydration of green tea at different temperatures has been measured using the NMR method. The rehydration process also has been simulated using the capillary model, and the predictions are in good agreement with experimental data.
Separation performance predictions of a Stairmand high‐efficiency cyclone
Authors: Derksen J. J. 
Published: April 2004

AbstractLarge‐eddy simulations (LES) were performed on the gas flow in a Stairmand high‐efficiency cyclone at Re = 280,000. The LES realistically represent the 3‐D, time‐dependent flow, including phenomena such as vortex core precession, and vortex breakdown. Quantitatively good agreement with measured velocity profiles is observed, for both the time‐averaged velocities and the velocity fluctuation levels. The single‐phase LES formed the starting point for modeling solid particle motion in the cyclone based on one‐way coupling between the gas flow and the particles. It is shown that some details of the flow in the relatively small region in the vicinity of the inlet have strong influence on the separation process. Due to the long residence times of particles inside the cyclone, the concurrent simulation of gas flow and particle motion is a lengthy computational process. Therefore, three alternative ways of modeling particle motion were explored: a frozen‐field approach, an eddy‐lifetime model, and a periodic‐flow approach. The results of these approaches are compared to the results of the concurrent simulation.
Experimental and simulation studies of heat transfer in polymer melts
Authors: Chen Hongbing , Sundararaj Uttandaraman , Nandakumar K. 
Published: April 2004

AbstractThe heat transfer of a single solid cylindrical poly(ether imide) (PEI) pellet in polyethylene (PE) melt under simple shear flow was studied using experiments and numerical simulations. This included two approximate 2‐D representations of the geometry, and a rigorous 3‐D geometry matching the experimental conditions. A generalized power‐law viscosity model for PE melt, and temperature‐dependent conductivity and specific heat were used for PEI in the models. Viscous dissipation was included in the simulations. From the experimental temperature history, the mean heat‐transfer coefficient h̄ was determined to be 370 W/m2·K, with the assumption of a uniform convective environment. From the simulation, h̄ was determined to be 1,160 W/m2·K and 420 W/m2·K in the 2‐D simulations with circular and rectangular pellet, respectively, and 250 W/m2·K for the 3‐D simulation. Results from the 3‐D simulation proved that the uniform convection assumption used to calculate h̄ for the experiment was not acceptable.
Novel multifunctional optical‐fiber probe: I. Development and validation
Authors: Liu Jinzhong , Grace John R. , Bi Xiaotao 
Published: April 2004

AbstractBy combining aspects of optical fiber probes used to determine local particle concentrations and local particle velocities and by rapid signal processing, it is shown that a single probe can determine local instantaneous particle fluxes. Providing a transparent cover to prevent a “blind zone” is shown to be critical in improving the probe performance and linearity. A simple mechanistic model is successful in predicting the performance of the optical system. The results of the probe are validated using particles glued onto both a rotating disk and a flat vibrating surface.
Attainable reaction and separation processes from a superstructure‐based method
Authors: Linke Patrick , Kokossis Antonis 
Published: April 2004

AbstractGeneric technology for the synthesis and optimization of integrated reaction and separation systems uses rich superstructure formulations comprising two types of generic synthesis units with flexible representation modes. A reactor/mass exchanger unit enables a detailed representation of the reaction and mass exchange phenomena. A conceptual representation of separation systems is facilitated through separation task units. All possible process designs featuring reaction, reactive separation, and separation are embedded in the superstructure formulations as combinations of generic units and their features. The design options are explored using stochastic optimization techniques suitable for this class of problems. The flexible representation framework enables technology applications to general process design, as well as design subproblems including reactor and reactive separator design. Four case studies demonstrate the ability of the methodology to address a wide variety of process systems and to deliver design novelty.
Optimal measurement system design for chemical processes
Authors: Muske Kenneth R. , Georgakis Christos 
Published: April 2004

AbstractA procedure for the optimal determination of measured variables in chemical processes is presented. This procedure is based on quantifying the trade‐off between the process information that can be obtained and the total cost of the sensors making up the measurement system. The resulting trade‐off is specified as a Pareto optimization problem. The optimal measurement systems that should be considered for installation are determined from the set of solutions to this Pareto optimization problem. The approach is demonstrated using a CSTR process example.
Viscoelastic model for particle fragmentation in olefin polymerization
Authors: Kittilsen Pål , Svendsen Hallvard F. , McKenna Timothy F. 
Published: April 2004

AbstractThe catalyst particle fragmentation process is an important step in determining the final morphology of olefin polymer particles. Understanding the different phenomena that influence it is, therefore, essential in optimizing polymerization processes and in obtaining the desired quality of polymer. A new viscoelastic model of the fragmentation process developed is demonstrated. The model relates the magnitude and generation rate of physical forces and the physical characteristics of the polymer and support. In this way, the effects of different parameters, such as reaction rate, polymer properties, and support characteristics, can be related to changes in the morphology of polymer particles. A faster reaction rate makes the particle become more porous, and a more viscous polymer will make particles with less porosity. It is discussed why larger pores will break before smaller on the same catalyst.
Interfacial protein networks and their impact on droplet breakup
Authors: Jones Daniel B. , Middelberg Anton P. J. 
Published: April 2004

AbstractConventional theories for predicting droplet disruption are based on a dimensionless capillary number and fail when a protein emulsifier is present at moderate concentration. In this study, droplet disruption is examined in simple shear and, in parallel, novel equipment is used to define conditions under which an interfacial stress‐transmitting protein network forms at an oil/water interface. Capillary number predictions fail when a rigid interfacial protein network forms. Complete stress‐strain curves, to high material deformation, are presented for these networks. This work demonstrates that droplets destabilized by interfacially adsorbed protein should be viewed as deformable capsules or cells surrounded by a stress‐transmitting network. Deformation and disruption could then be predicted by existing theories for such systems, using the constitutive data provided by the stress‐strain tests. Such an approach is expected to be superior to existing methods based solely on interfacial energy.
Sensitivity study on interfacial closure laws in two‐fluid bubbly flow simulations
Authors: Oey R. S. , Mudde R. F. , van den Akker H. E. A. 
Published: April 2004

AbstractThe two‐fluid formulation with closure models for interfacial forces and turbulence is applied to the evaluation of a meandering plume in a rectangular bubble column. In literature there is some discussion about how precisely the models should be in order to capture the dynamics as is observed experimentally. Furthermore, this type of flow has shown to be quite sensitive for the degree of diffusion (physical and numerical) introduced in the model equations. The focus is on the necessity and influence of certain interfacial closure models in above type of bubbly flow. The influence of the drag, turbulent diffusive, and added mass force will be highlighted. TVD schemes are used for the computations to obtain accurate results against low costs, that is, coarse grid approximation and to reduce the amount of numerical diffusion as much as possible. Still these schemes have to be “tuned” in their properties in order to obtain the desired accuracy. Nonproper choice of certain parameters, that is, “flux‐limiters” introduces errors in the final solution, with the same order of magnitude as physical phenomenon, which are introduced by interfacial forces.
Characterization of asphaltenes aggregation and fragmentation in a shear field
Authors: Rahmani Nazmul H. G. , Masliyah Jacob H. , Dabros Tadeusz 
Published: April 2004

AbstractAggregation and breakup of asphaltenes flocs in a Couette flow device are studied for various values of shear rate (G), volume fraction of particles (φ), and solvent composition (ratio of toluene to n‐heptane in the solution Xs). The number average asphaltene aggregate size initially increases before achieving a maximum size and then decreases until reaching a steady‐state value that reflects a balance between aggregation and fragmentation. Increasing the applied shear rate leads to higher aggregation and fragmentation rates, reducing the steady‐state average aggregate size and the characteristic relaxation time required to achieve a steady state. For a fixed value of G, when either φ is increased or Xs is decreased, the steady‐state floc size increases. The kinetics of the aggregation‐fragmentation process and the attainment of steady state by asphaltenes aggregates were modeled using a population balance approach. The model describes the time evolution of the average floc size using fitted parameters (the breakup coefficient for shear fragmentation, b and the porosity of the aggregates ϵ). Binary breakage was included in calculations and collision efficiency was assumed to be equal to one.
Numerical study of the packing of wet coarse uniform spheres
Authors: Yang R. Y. , Zou R. P. , Yu A. B. 
Published: April 2004

AbstractThe discrete‐element method was extended to investigate the effect of liquid addition on the packing of monosized spheres. By explicitly taking into account the interaction forces between particles, such as contact forces and capillary force, the packing of wet spheres can be simulated by the method. Simulations are performed under the so‐called poured packing, where a different amount of water is added to spheres of different sizes. Comparison with data in the literature shows that the simulations yield a satisfactory agreement in the relationship between porosity and moisture content, macroscopically verifying the proposed model. The packing structure is then analyzed in terms of microscopic properties such as the radial distribution function and coordination number and are shown to vary with liquid content for a given particle size. The relationship between porosity and capillary force is finally quantified, which confirms those derived based on macroscopic assumptions.
Flocculation of biological cells: Experiment vs. theory
Authors: Han Binbing , Akeprathumchai S. , Wickramasinghe S. R. , Qian X. 
Published: April 2004

AbstractFlocculation of biological cells is important in the biotechnology industry, as it could lead to improved efficiencies for bioreactor harvesting operations such as microfiltration. Experimental studies for flocculation of yeast and CHO cells using cationic polyelectrolytes suggest the existence of a steady‐state, self‐similar floc size distribution. The experimentally determined floc size distributions were modeled using a population balance approach. For flocculated yeast suspensions, the variation of the floc volume fraction with dimensionless particle diameter is predicted by the population balance model assuming a binary breakage distribution function. However, the variation of floc number fraction with dimensionless particle diameter is better predicted assuming a log normal fragment distribution function probably due to the presence of submicron‐sized yeast cell debris. For CHO cell flocs, the floc volume and number fractions are predicted using a log normal fragment distribution function. CHO cells are far more fragile than yeast cells. Thus, individual CHO cells in a CHO cell floc can lyse leading to the formation of a number of small particles.
Design of alternative refrigerants via global optimization
Authors: Sahinidis Nikolaos V. , Tawarmalani Mohit , Yu Minrui 
Published: April 2004

AbstractAccurate and fast enumeration of large, combinatorial search spaces presents a central conceptual challenge in molecular design. To address this challenge, an algorithm is developed that guarantees globally optimal solutions to a mixed‐integer nonlinear programming formulation for molecular design. The formulation includes novel structural feasibility constraints, while the algorithm provides all feasible solutions to this formulation through the implicit enumeration of a single branch‐and‐reduce tree. This algorithm is used to provide the complete solution set to a refrigerant design problem posed elsewhere. In addition to rediscovering CFCs, the proposed methodology identifies a number of novel potential replacements of Freon 12.
Probabilistic model for sensor fault detection and identification
Authors: Mehranbod Nasir , Soroush Masoud , Piovoso Michael , Ogunnaike Babatunde A. 
Published: April 2004

AbstractA new Bayesian belief network (BBN) model with discretized nodes is proposed for fault detection and identification in a single sensor. The single‐sensor model is used as a building block to develop a BBN model for all sensors in the process considered. A new fault detection index, a fault identification index, and a threshold setting procedure for the multisensor model are introduced. The fault detection index exploits the probabilistic information of the multisensor model, which, along with the proposed threshold setting procedure, leads to effective detection of faulty sensors. The fault identification index uses only the probabilistic information of the faulty sensor to determine in a discretized fashion the size of faults that should be analyzed within a moving time window to identify the fault type. Single‐sensor model design parameters (prior and conditional probability data) are optimized to achieve maximum effectiveness in detection and identification of sensor faults. The single‐sensor model and optimal values of design parameters are used to develop a multisensor BBN model for a polymerization reactor at steady‐state conditions. Its capabilities to detect and identify bias, drift, and noise in sensor readings are illustrated for single and simultaneous multiple faults by several case studies.
Diagnostic nonlinear analysis of Fischer‐Tropsch synthesis in stirred‐tank slurry reactors
Authors: Song Hyun‐Seob , Ramkrishna Doraiswami , Trinh Sinh , Wright Harold 
Published: April 2004

AbstractMultiplicity of steady states was experimentally observed, somewhat sporadically, for Fischer–Tropsch (FT) synthesis in stirred tank slurry reactors in the reactor originally at the wax‐producing (normal) steady state suddenly jumping to a high‐temperature (methane‐producing) steady state for some time and eventually returning to the normal steady state. A diagnostic nonlinear analysis showed a plausible interpretation of this nonlinear behavior under two settings: 1. assuming that the controlled system is stable and motivated by simplicity, as it obviates the inclusion of an energy balance for the cooler, thus reducing the dimension of the problem; 2. examining the more realistic problem by discarding the foregoing assumption, thus having to increase the analysis level. The first approach showed that the Stanton number for heat transfer (StH) and the Damköhler number (Da) could be two key process parameters accounting for the observed multiplicity characteristics of FT synthesis. The decrease in StH, attributable to deteriorating performance of the cooler, is the likely cause for the sudden jump of the reactor from the normal to high‐temperature steady state. The eventual recovery of the original steady state is, spurred by a decrease in Da, possibly attributable to catalyst deactivation. Depending on the initial conditions and/or startup history from the initial to the target conditions, the multiplicity behaviors of FT synthesis may or may not be observed, which is why the observation of multiplicity is sporadic. The second approach incorporating the cooler's energy balance increases the region of multiplicity over that with the first. Simple proportional control law is applied to the system to examine the effect of the control parameter settings on reactor behavior. Except for this feature, the findings from the two analysis modes are in harmony.
Kinetics of microwave‐assisted oxidative degradation of polystyrene in solution
Authors: Sivalingam G. , Agarwal Nitin , Madras Giridhar 
Published: April 2004

AbstractThe kinetics of the oxidative degradation of polystyrene in dichlorobenzene in the presence of benzoyl peroxide was studied in a microwave reactor. Solutions with peroxide concentration ranging from 15 to 40 kg/m3 were irradiated by microwave of 700 W and frequency of 2.45 MHz with a different cycle heating period ranging from 20 to 45 s. The molecular‐weight distributions were measured as a function of reaction time by gel permeation chromatography. Because the temperature of the system continuously varies with reaction time, a radical mechanism for oxidative degradation based on continuous distribution kinetics with time/temperature‐dependent rate coefficients was proposed. The activation energy of 46.4 kJ/mol for the microwave‐assisted oxidative degradation of polystyrene was obtained by nonlinearly regressing the experimental data.
Spanning the flow regimes: Generic fluidized‐bed reactor model
Authors: Abba I. A. , Grace J. R. , Bi H. T. , Thompson M. L. 
Published: April 2004

AbstractProbabilistic averaging is used to model fluidized‐bed reactors across the three fluidlization flow regimes most commonly encountered in industry (bubbling, turbulent, and fast fluidization), extending earlier work, which introduced this approach to bridge the bubbling and turbulent regimes of fluidization. In extending this concept to the fast fluidization regime, the probabilities of being in each of the three regimes are represented as probability density functions derived from regime boundary transition data. The three regime‐specific models—a generalized version of a two‐phase bubbling bed model at low gas velocities, a dispersed flow model for turbulent beds at intermediate velocities, and a generalized version of a core‐annulus model at higher velocities—are employed, leading to improved predictions compared with any of the individual models, while avoiding discontinuities at the regime boundaries. Predictions from the new integrated model are in good agreement with available ozone decomposition data over the full range of applicability covered elsewhere.
Reconstruction of the O2 uptake rate and CO2 evolution rate on a time scale of seconds
Authors: Bloemen H. H. J. , Wu L. , van Gulik W. M. , Heijnen J. J. , Verhaegen M. H. G. 
Published: April 2004

AbstractThe reconstruction is addressed of the dynamics of the microbial oxygen uptake rate (OUR) and carbon dioxide evolution rate (CER) from off‐gas concentration measurements and dissolved oxygen measurements during highly dynamic conditions, encountered, for example, during a substrate‐pulse experiment. The reconstruction of the OUR and CER is done by fitting a model for the mass transport to the measured data using smoothing techniques. Most of the parameters of the mass‐transport model, including the sensor dynamics, are derived from physical knowledge. A few remaining parameters that cannot be derived from physical knowledge are computed by fitting the model to an identification data set. It is demonstrated that the net gas production or consumption can have a significant impact on the estimated OUR, and, therefore, is included in the model. Besides the reconstruction of the OUR and the CER, the reconstruction algorithm also incorporates the monitoring of the mass‐transfer coefficient kla.