Showing papers in "Aiche Journal in 2008"
TL;DR: The proposed multimode process monitoring approach based on finite Gaussian mixture model (FGMM) and Bayesian inference strategy is superior to the conventional PCA method and can achieve accurate and early detection of various types of faults in multimode processes.
Abstract: For complex industrial processes with multiple operating conditions, the traditional multivariate process monitoring techniques such as principal component analysis (PCA) and partial least squares (PLS) are ill-suited because the fundamental assumption that the operating data follow a unimodal Gaussian distribution usually becomes invalid. In this article, a novel multimode process monitoring approach based on finite Gaussian mixture model (FGMM) and Bayesian inference strategy is proposed. First, the process data are assumed to be from a number of different clusters, each of which corresponds to an operating mode and can be characterized by a Gaussian component. In the absence of a priori process knowledge, the Figueiredo–Jain (F–J) algorithm is then adopted to automatically optimize the number of Gaussian components and estimate their statistical distribution parameters. With the obtained FGMM, a Bayesian inference strategy is further utilized to compute the posterior probabilities of each monitored sample belonging to the multiple components and derive an integrated global probabilistic index for fault detection of multimode processes. The validity and effectiveness of the proposed monitoring approach are illustrated through three examples: (1) a simple multivariate linear system, (2) a simulated continuous stirred tank heater (CSTH) process, and (3) the Tennessee Eastman challenge problem. The comparison of monitoring results demonstrates that the proposed approach is superior to the conventional PCA method and can achieve accurate and early detection of various types of faults in multimode processes. © 2008 American Institute of Chemical Engineers AIChE J, 2008
452 citations
TL;DR: In this paper, a two-fluid model for gas-particle flows is constructed from a kinetic theory-based model, and a procedure to extract constitutive models for these models through highly resolved simulations of the kinetic theory based model equations in periodic domains is presented.
Abstract: Starting from a kinetic theory based two-fluid model for gas-particle flows, we first construct filtered two-fluid model equations that average over small scale inhomogeneities that we do not wish to resolve in numerical simulations. We then outline a procedure to extract constitutive models for these filtered two-fluid models through highly resolved simulations of the kinetic theory based model equations in periodic domains. Two- and three-dimensional simulations show that the closure relations for the filtered two-fluid models manifest a definite and systematic dependence on the filter size. Linear stability analysis of the filtered two-fluid model equations reveals that filtering does indeed remove small scale structures that are afforded by the microscopic twofluid model. 2008 American Institute of Chemical Engineers AIChE J, 54: 1431–1448, 2008
416 citations
TL;DR: In this paper, the authors focus on the integration of electrodialysis with traditional unit operations and other membranes, and show that such integrations, due to their diversity and practicability, can be versa-tile tools to meet the requirements from chemical, biochemical, food, and pharmaceutical industries.
Abstract: To support a sustainable industrial growth, chemical engineering today faces a cru-cial challenge of meeting the increasing demand for materials and energy. One possi-ble solution is to decrease the equipment size/productivity ratio, energy consumption,and waste generation via process integration and optimization. This review focuses onthe integration of electrodialysis with traditional unit operations and other membraneseparations. Such integrations, due to their diversity and practicability, can be versa-tile tools to meet specific needs from chemical, biochemical, food, and pharmaceuticalindustries.
360 citations
TL;DR: In this article, the H2 storage in the COF and MOF materials assisted by hydrogen spillover, measured at 298 K up to a pressure of 10 MPa, were examined for correlations with their structural and surface features for the first time.
Abstract: Covalent-organic framework COF-1 and metal-organic frameworks HKUST-1 and MIL-101 were synthesized and studied for hydrogen storage at 77 and 298 K. Although MIL-101 had the largest surface area and pore volume among the three materials, HKUST-1 had the highest uptake (2.28 wt %) at 77 K. However, the H2 storage capacity at 298 K and high pressure correlated with the surface area and pore volume. The H2 storage in the COF and MOF materials assisted by hydrogen spillover, measured at 298 K up to a pressure of 10 MPa, have been examined for correlations with their structural and surface features for the first time. By using our simple technique to build carbon bridges, the hydrogen uptakes at 298 K were enhanced significantly by a factor of 2.6–3.2. The net uptake by spillover was correlated to the heat of adsorption through the Langmuir constant. Results on water vapor adsorption at 298 K indicated that COF-1 was unstable in moist air, while HKUST-1 and MIL-101 were stable. The results suggested that MIL-101 could be a promising material for hydrogen storage because of its high heat of adsorption for spiltover hydrogen, large surface area and pore volume, and stability upon H2O adsorption. 2007 American Institute of Chemical Engineers AIChE J, 54: 269–279, 2008
270 citations
TL;DR: The physical properties of the active pharmaceutical ingredient (API) including crystal form, size and shape have the potential to impact bioperformance, particularly for low-solubility compounds, where the rate-limiting step in drug uptake may be the dissolution of the API in the gut.
Abstract: Since the introduction of aspirin in 1899, and more particularly since the advent of antibiotic ‘‘wonder drugs’’ in the 1940s, society has come to rely on the widespread availability of therapeutic drugs at reasonable prices. It was a tremendous challenge to bring penicillin to market and could not have been done without the simultaneous development of both product and process under the inspired leadership of Howard Florey over a 10 year period starting in the early 1930s, as revealed in the riveting story told by Eric Lax. 1 In the interim, much has changed in drug development, but the timelines remain long, and the obstacles to success remain high. For drugs delivered to patients in crystalline form, the physical properties of the active pharmaceutical ingredient (API) including crystal form, size and shape have the potential to impact bioperformance, particularly for low-solubility compounds, where the rate-limiting-step in drug uptake may be the dissolution of the API in the gut. These physical properties of the API are often controlled in the final API crystallization step. Because most small molecule drugs (.90%) are delivered in crystalline form, and currently about 90% of new API’s being pursued are classified as having low solubility in water, a well-controlled crystallization of the API is often a vitally important operation in pharmaceutical manufacturing. Moreover, it is a difficult operation because of uncertainty in the crystal forms that will appear, and because of the many challenges associated with scaling-up crystallizations from laboratory to manufacturing scale. Although great emphasis is placed on the therapeutic and chemical discovery aspects of new APIs, it must be emphasized that the successful entities will eventually need to be manufactured. Pisano 2 has made a detailed study of the strategic value of process development and concludes that the benefits of a superior manufacturing process can include early product launch and consistent, higher product quality. Most companies seek to minimize manufacturing costs and maximize process portability by applying the simplest manufacturing process capable of producing their drug product with desired attributes. Because only 10% of the compounds in development survive the efficacy and safety hurdles in the clinic and become marketed drugs, there is also great value in minimizing R&D costs (including clinical trials), which are estimated to be about $1 billion per launch, with a remaining life protected on-patent of typically only 6–10 years. In this perspective, we describe the state-of-the-art in API crystal product and process design, highlight barriers that currently prevent the production of better, cheaper crystalline products, and give our best estimate of where the field is going and should go during the next decade.
251 citations
TL;DR: In this paper, a screening method is proposed for the molecular design of ionic liquids (ILs) to capture carbon dioxide (CO2), which can reduce efficiently the necessary experimental efforts.
Abstract: A screening method is proposed for the molecular design of ionic liquids (ILs) to capture carbon dioxide (CO2), which can reduce efficiently the necessary experimental efforts. The COSMO-RS method is implemented to predict the Henry's law constants of CO2 in 408 ILs with various combinations of cations and anions. It is found by the screening that the ILs with the anion tris(pentafluoroethyl)trifluorophosphate ([FEP]) show improved capability to capture CO2, compared with other ILs reported in literature. Then, three [FEP]-based ILs are chosen to perform the solubility measurements by the intelligent gravimetric analyzer (IGA 003, Hiden Analytical), with cations of 1-hexyl-3-methylimidazolium ([hmim]), 1-butyl-1-methylpyrrolidinium ([bmpyrr]), and S-ethyl-N,N,N′,N′-tetramethylthiouronium ([ETT]) at 283.2, 298.2, and 323.2 K, up to the pressure of 1.8 MPa. The experimental data show that the solubility of CO2 in [hmim][FEP] is about 15% higher than that in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]), which is in fair agreement with the screening results, indicating the method proposed in this work is reliable. © 2008 American Institute of Chemical Engineers AIChE J, 2008
248 citations
TL;DR: In this work a methodology is presented for the rigorous optimization of nonlinear programming problems in which the objective function and (or) some constraints are represented by noisy implicit black box functions.
Abstract: In this work a methodology is presented for the rigorous optimization of nonlinear programming problems in which the objective function and (or) some constraints are represented by noisy implicit black box functions. The special application considered is the optimization of modular process simulators in which the derivatives are not available and some unit operations introduce noise preventing the calculation of accurate derivatives. The black box modules are substituted by metamodels based on a kriging interpolation that assumes that the errors are not independent but a function of the independent variables. A Kriging metamodel uses non-Euclidean measure of distance to avoid sensitivity to the units of measure. It includes adjustable parameters that weigh the importance of each variable for obtaining a good model representation, and it allows calculating errors that can be used to establish stopping criteria and provide a solid base to deal with “possible infeasibility” due to inaccuracies in the metamodel representation of objective function and constraints. The algorithm continues with a refining stage and successive bound contraction in the domain of independent variables with or without kriging recalibration until an acceptable accuracy in the metamodel is obtained. The procedure is illustrated with several examples. © 2008 American Institute of Chemical Engineers AIChE J, 2008
239 citations
TL;DR: In this article, the authors have modeled and experimentally validated the complex spatially dependent polymerization kinetics and network heterogeneity, and implemented these systems for applications improvement or development in lithography, microdevice fabrication, biomaterials, biodetection, dental materials, and surface coatings.
Abstract: Photopolymerization reactions proceed rapidly at ambient conditions and are able to exhibit both temporal and spatial control, nevertheless their full potential has been limited by a lack of understanding of the polymerization kinetics and polymer network evolution as well as a lack of custom, functional monomers, and polymerization mechanisms For the last 15 years, our group has sought to address these limitations by reaction engineering at both the fundamental and applied levels with a focus on increasing the understanding, potential, and implementation of photopolymerization reactions In particular, we have modeled and experimentally validated the complex spatially dependent polymerization kinetics and network heterogeneity, and we have implemented these systems for applications improvement or development in lithography, microdevice fabrication, biomaterials, biodetection, dental materials, and surface coatings © 2008 American Institute of Chemical Engineers AIChE J, 2008
223 citations
TL;DR: In this paper, the effects of the size and molecular weight of the permeating gases on diffusion and permeation rate for DDR-type zeolite membranes were measured in 25-500°C.
Abstract: DDR-type zeolite membranes were prepared by the secondary growth method on porous α-alumina disk, followed by on-stream counter diffusion chemical vapor deposition modification to eliminate the intercrystalline micropores. Single gas permeation of He, H2, CO2, and CO through this zeolite membrane before and after CVD modification was measured in 25–500°C. Intracrystalline diffusivities for these four gases in DDR-type zeolite were obtained from the permeation data above 300°C to examine the effects of the size and molecular weight of permeating gases on diffusion and permeation rate for this zeolite membrane. For the unmodified DDR-type zeolite membrane with presence of a small amount intercrystalline micropores the diffusivity (or permeance) with a low activation energy depends on both the size and molecular weight of permeating gases. For the CVD-modified DDR-type zeolite membrane with intercrystalline micropores eliminated, the activation energy for diffusion and diffusivity increases with increasing molecular size of the permeating gases. © 2008 American Institute of Chemical Engineers AIChE J, 2008.
192 citations
TL;DR: In this article, the authors address the problem of optimizing corn-based bioethanol plants through the use of heat integration and mathematical programming techniques, which can reduce the operating costs of the plant.
Abstract: In this work, we address the problem of optimizing corn-based bioethanol plants through the use of heat integration and mathematical programming techniques. The goal is to reduce the operating costs of the plant. Capital cost, energy usage, and yields—all contribute to production cost. Yield and energy usage also influence the viability of corn-based ethanol as a sustainable fuel. We first propose a limited superstructure of alternative designs including the various process units and utility streams involved in ethanol production. Our objective is to determine the connections in the network and the flow in each stream in the network such that we minimize the energy requirement of the overall plant. This is accomplished through the formulation of a mixed-integer nonlinear programming problem involving short-cut models for mass and energy balances for all the units in the system, where the model is solved through two nonlinear programming subproblems. We then perform a heat integration study on the resulting flowsheet; the modified flowsheet includes multieffect distillation columns that further reduces energy consumption. The results indicate that it is possible to reduce the current steam consumption required in the transformation of corn into fuel grade ethanol by more than 40% compared to initial basic design. © 2008 American Institute of Chemical Engineers AIChE J, 2008
164 citations
TL;DR: In this paper, the authors present a design framework that comprises four stages of process modeling and multi-objective evaluation considering monetary and non-monetary aspects, and demonstrate on the design of a methyl methacrylate (MMA) process.
Abstract: In recent years, many chemical companies have adopted the concept of sustainable development as a core business value. In this context and with focus on early phases, we present a novel design framework that comprises four stages of process modeling and multiobjective evaluation considering monetary and nonmonetary aspects. Each stage is characterized by the available information as a basis for process modeling and assessment. Appropriate modeling approaches, and evaluation indicators for economy, life-cycle environmental impacts, environment, health, and safety (EHS) hazard, and technical aspects are selected for each defined stage. The proposed framework is demonstrated on the design of a methyl methacrylate (MMA) process: considering 17 synthesis routes, the framework is mimicked step-by-step, to select the route with the best multiobjective performances, and to produce an optimized process flowsheet. As a validation of the framework, evaluation profile of six routes over all stages are compared, and crucial points are identified that should be estimated considerably well in early stages of the framework. © 2008 American Institute of Chemical Engineers AIChE J, 2008
TL;DR: In this paper, the kinetics of gas hydrate growth from binary CH4/C2H6 and CH 4/C3H8 and ternary CH4, C2H 6, C3H 8 gas mixtures were obtained by the gas uptake method in a semibatch stirred vessel at constant pressure and a temperature of 273.7 K. The results were consistent with those obtained by NMR.
Abstract: The kinetics of gas hydrate growth from binary CH4/C2H6 and CH4/C3H8 and ternary CH4/C2H6/C3H8 gas mixtures were obtained by the gas uptake method in a semibatch stirred vessel at constant pressure and a temperature of 273.7 K. These data are of interest for the design of facilities for natural gas storage and transportation in the solid (hydrate) state. During hydrate formation, samples from the gas phase were taken and analyzed by gas chromatography. It was found that the molar composition of CH4 in the vapor phase increased as hydrate crystallization progressed. The observed fractionation effect (enrichment of the hydrate phase with propane) complicates the natural gas storage process. The fractionation effect was also confirmed with molecular-level studies where hydrate from the CH4/C2H6/ C3H8 gas mixture was characterized by powder X-ray diffraction (PXRD), NMR, and Raman spectroscopy. The hydrate phase composition and cage occupancy of each gas were calculated with the help of information obtained by Raman spectroscopy, gas chromatography, and PXRD. The results were consistent with those obtained by NMR. The composition of the gas phase and the hydrate are found to
TL;DR: In this article, a model taking into account of the size of the guest and host particles as well as surface area coverage (SAC) of the coated nano-sized particles is developed to predict the effect of coating on the adhesion reduction of cohesive powders.
Abstract: While it is well known that flow aids such as fumed silica can be added to improve flowability and fluidizability of cohesive powders, the improvements observed depend on how well the flow aids are blended together with the cohesive powders. In this work, dry particle coating is used to deposit a very small amount of nano-sized particles (as low as 0.01 wt %) with a high degree of precision onto the surface of cohesive, Geldart Group C powders to make them fluidize like Group A powders. A model taking into account the effect of the size of the guest and host particles as well as surface area coverage (SAC) of the coated nano-sized particles is developed to predict the effect of coating on the adhesion reduction of cohesive powders. A series of experiments are performed to investigate the improvement in the fluidizability of dry particle coated Group C powders (e.g., cornstarch and aluminum), and the effect of various parameters such as SAC, guest particle size and host particle size are systematically investigated. The results clearly show the effect of each of these parameters on the fluidization behavior of cohesive powders, and also validate the model. The study also indicates that a critical SAC is required to make the coated cornstarch fluidize, which is about 5%; the smaller the guest size, the better its effect on improved fluidizability, although the improvement is reduced if the guest size is smaller than about 10 nm; and if the conditions regarding the SAC and guest size are satisfied, dry particle coating will significantly improve the fluidization of cohesive particles even as small as 5–10 μm. © 2007 American Institute of Chemical Engineers AIChE J, 2008
TL;DR: In this article, the authors proposed a piecewise MILP relaxation approach to solve the under-and overestimation problem for bilinear programs via three systematic approaches, and two segmentation schemes.
Abstract: Many practical problems of interest in chemical engineering and other fields can be formulated as bilinear programs (BLPs). For such problems, a local nonlinear programming solver often provides a suboptimal solution or even fails to locate a feasible one. Numerous global optimization algorithms devised for bilinear programs rely on linear programming (LP) relaxation, which is often weak, and, thus, slows down the convergence rate of the global optimization algorithm. An interesting recent development is the idea of using an ab initio partitioning of the search domain to improve the relaxation quality, which results in a relaxation problem that is a mixed-integer linear program (MILP) rather than LP, called as piecewise MILP relaxation. However, much work is in order to fully exploit the potential of such approach. Several novel formulations are developed for piecewise MILP under- and overestimators for BLPs via three systematic approaches, and two segmentation schemes. As is demonstrated and evaluated the superiority of the novel models is shown, using a variety of examples. In addition, metrics are defined to measure the effectiveness of piecewise MILP relaxation within a two-level-relaxation framework, and several theoretical results are presented, as well as valuable insights into the properties of such relaxations, which may prove useful in developing global optimization algorithms. © 2008 American Institute of Chemical Engineers AIChE J, 2008
TL;DR: In this article, the phase behavior of granular beds of hard spherical particles in a rotating horizontal drum is studied by Discrete Element Method (DEM) simulations, showing strong correlations between flow regime and segregation pattern.
Abstract: The rich phase behavior of granular beds of bidisperse hard spherical particles in a rotating horizontal drum is studied by Discrete Element Method (DEM) simulations. Several flow regimes and various forms of radial segregation, as well as mixing, are observed by systematically varying the operational parameters of the drum, i.e. fill level and angular velocity, over a wide range. Steady states after several dozen revolutions are summarized in two bed behavior diagrams, showing strong correlations between flow regime and segregation pattern. An entropy method quantifies the overall degree of mixing, while density and velocity plots are used to analyze the local properties of the granular bed. The percolation mechanism may provide a qualitative explanation for the distinct segregation processes, and for the transient mixing in nonradially segregated beds. Initially blockwise segregated beds are found to mix before radial segregation sets in. High fill fractions (>65%) show the most intense segregation.
TL;DR: In this article, the performance of limestone-derived CaO during many (>1000 in some cases) calcination and carbonation cycles is reported, and a mechanism for pore evolution during the cyclic capture is proposed consistent with the experimental observations.
Abstract: The performance of limestone-derived CaO during many (>1000 in some cases) calcination and carbonation cycles is reported. After 150 cycles, the calcium utilization during carbonation reached a minimum value between 4 and 17%, with the asymptotic level depending strongly on the carbonation time. With the aid of mechanistic studies including investigations on sorbent surface topology by SEM and mercury intrusion, a mechanism for pore evolution during the cyclic capture is proposed consistent with the experimental observations. © 2008 American Institute of Chemical Engineers AIChE J, 2008
TL;DR: This review covers important developments and discoveries within the laboratory, and the increasing breadth in the scope of the work within the expanding field of tissue engineering is presented.
Abstract: The need for techniques to facilitate the regeneration of failing or destroyed tissues remains great with the aging of the worldwide population and the continued incidence of trauma and diseases such as cancer. A 16-year history in biomaterial scaffold development and tissue engineering is examined, beginning with the synthesis of novel materials and fabrication of 3D porous scaffolds. Exploring cell-scaffold interactions and subsequently cellular delivery using biomaterial carriers, we have developed a variety of techniques for bone and cartilage engineering. In addition to delivering cells, we have utilized growth factors, DNA, and peptides to improve the in vitro and in vivo regeneration of tissues. This review covers important developments and discoveries within our laboratory, and the increasing breadth in the scope of our work within the expanding field of tissue engineering is presented.
TL;DR: In this paper, a modified version of COSMO_LL has been used to predict the liquid-liquid equilibria (LLE) for 32 ternary systems, available in literature, each having an ionic liquid.
Abstract: Ionic liquids with their limitless combination of cations and anions can offer an optimal solvent for a specific purpose. But not all corresponding experimental studies are possible as they will be time consuming and expensive. A judicious screening of the various possible solvents is required to select the proper ionic liquid. Conductor-like screening model (COSMO) along with its extension to real solvents can be used for these predictions. In this work, modified version COSMO_LL has been used to predict the liquid–liquid equilibria (LLE) for 32 ternary systems, available in literature, each having an ionic liquid. A complete dissociation of cations and anions of the ionic liquid has been assumed. The root mean square deviation for all these systems is ∼9% which is excellent when compared with ∼50% obtained for predictions using the nondissociated composite molecule. Additionally, experimental LLE data has been collected for four ternary systems, namely: (a) 1-ethyl-3-methylimidazolium ethylsulphate [Emim] [EtSO4] – Ethanol-Hexene, (b) 1-ethyl-3-methylimidazolium ethylsulphate [Emim] [EtSO4] – Ethanol-Heptene, (c) 1,2-dimethyl-3-ethylimidazolium ethylsulphate [E-2,3-dmim] [EtSO4] – Ethanol-Hexene, and (d) 1,2-dimethyl-3-ethylimidazolium ethylsulphate [E-2,3-dmim] [EtSO4] – Ethanol-Heptene. The tie lines have been estimated using NMR and these have been compared with COSMO_LL predictions giving an average rmsd of ∼6%. © 2008 American Institute of Chemical Engineers AIChE J, 2008
TL;DR: The monitoring of multivariate systems that exhibit non-Gaussian behavior is addressed and the use of principal component analysis (PCA) is proposed to capture the Gaussian and non- Gaussian source signals.
Abstract: The monitoring of multivariate systems that exhibit non-Gaussian behavior is addressed. Existing work advocates the use of independent component analysis (ICA) to extract the underlying non-Gaussian data structure. Since some of the source signals may be Gaussian, the use of principal component analysis (PCA) is proposed to capture the Gaussian and non-Gaussian source signals. A subsequent application of ICA then allows the extraction of non-Gaussian components from the retained principal components (PCs). A further contribution is the utilization of a support vector data description to determine a confidence limit for the non-Gaussian components. Finally, a statistical test is developed for determining how many non-Gaussian components are encapsulated within the retained PCs, and associated monitoring statistics are defined. The utility of the proposed scheme is demonstrated by a simulation example, and the analysis of recorded data from an industrial melter. © 2008 American Institute of Chemical Engineers AIChE J, 2008
TL;DR: In this article, a 3D simulation of the turbulent gas-solid flow in cyclone separators is performed with the lattice-Boltzmann method, and the performance of a Stairmand high efficiency cyclone under various loading conditions is systematically studied.
Abstract: Three-dimensional (3-D), time-dependent Eulerian-Lagrangian simulations of the turbulent gas-solid flow in cyclone separators have been performed. The gas flow is simulated with the lattice-Boltzmann method. It solves the filtered Navier-Stokes equations, where the Smagorinsky subgrid-scale model has been used to represent the effect of the filtered scales. Through this large-eddy representation of the gas flow, solid particles with different sizes are tracked. By viewing the individual particles (of which there are some 10 7 inside the cyclone at any moment in time) as clusters of particles (parcels), the effect of particle-to-gas coupling on the gas-flow and particle behavior at modest mass-loadings (up to 0.2 kg dust per kg air) is studied. The numerical approach is able to capture the effect of mass loading on the swirl intensity as reported in the experimental literature. The performance of a Stairmand high-efficiency cyclone under various loading conditions is systematically studied. The presence of solid particles causes the cyclone to lose swirl intensity. Furthermore, the turbulence of the gas flow gets strongly damped. These two effects have significant consequences for the performance of the cyclone. The pressure drop monotonically decreases with mass loading. The collection efficiency responds in a more complicated manner to the mass loading, with mostly increased cut sizes, and increased overall efficiencies. 2008 American Institute of Chemical Engineers AIChE J, 54: 872–885, 2008
TL;DR: In this paper, a single-channel PEM fuel cell was examined with direct observation of liquid water motion and local current density, and it was shown that flooding is gravity-dependent and the local current densities depend on dynamics of liquid slugs moving through the flow channels.
Abstract: The process of flooding has been examined with a single-channel fuel cell that permits direct observation of liquid water motion and local current density. As product water flows through the largest pores in the hydrophobic GDL, drops detach from the surface, aggregate, and form slugs. Flooding in polymer electrolyte membrane (PEM) fuel cells occurs when liquid water slugs accumulate in the gas flow channel, inhibiting reactant transport. Because of the importance of gravity, we observe different characteristics with different orientations of the flow channels. Liquid water may fall away from the GDL and be pushed out with minimal effect on the local current density, accumulate on the GDL surface and cause local fluctuations, or become a pulsating flow of liquid slugs and cause periodic oscillations. We show that flooding in PEM fuel cells is gravity-dependent and the local current densities depend on dynamics of liquid slugs moving through the flow channels. 2008 American Institute of Chemical Engineers AIChE J, 54: 1313–1332, 2008
TL;DR: In this article, a composite membrane consisting of one fluorite oxide phase (Ce0.8Gd0.2O1.9) for oxygen ionic transport and one perovskite oxide phase (Gd 0.2Sr 0.8FeO3-delta) for electronic transport was investigated, which showed good oxygen permeation stability at 950 C (more than 1100 h).
Abstract: A composite membrane, which comprises of one fluorite oxide phase (Ce0.8Gd0.2O1.9) for oxygen ionic transport and one perovskite oxide phase (Gd0.2Sr0.8FeO3-delta) for both oxygen ionic and electronic transport, was investigated. XRD results revealed that the two oxides are compatible and showed good oxygen permeation stability at 950 C (more than 1100 h). Oxygen flux of the composite membrane was two times higher than that of the Gd0.2Sr0.8FeO3-delta mixed conducting membrane at the same conditions. At steady state, oxygen flux of a 0.5 mm membrane was 0.80 ml/(cm(2) min) under oxygen partial pressure gradient of air/He and similar to 5.0 ml/(cm(2) min) for syngas production at 950 degrees C, respectively. After similar to 440 h operation under syngas conditions, SEM analysis revealed that the syngas side of the membrane still kept dense and the EDX showed the transfer of elements occurred in the depth of a few microns. (c) 2008 American Institute of Chemical Engineers.
TL;DR: Improved KPCA and KICA for multivariate statistical process monitoring (MSPM) are improved and the similarity concept of data in one group is first proposed to capture the nonlinearities.
Abstract: In this article, first, some drawbacks of original Kernel Principal Component Analysis (KPCA) and Kernel Independent Component Analysis (KICA) are analyzed. Then the KPCA and KICA for multivariate statistical process monitoring (MSPM) are improved. The drawbacks of original KPCA and KICA are as follows: The data mapped into feature space become redundant; linear data introduce errors while the kernel trick is used; computation time increases with the number of samples. To solve the above problems, the original KPCA and KICA for MSPM are improved: similarity factors of the observed data in the input and feature space are defined; similar characteristics are measured; similar data are removed according to the similarity measurements; and k-means clustering in feature space is used to isolate different classes. Specifically, the similarity concept of data in one group is first proposed. Applications of the proposed approach indicate that improved KPCA and KICA effectively capture the nonlinearities. © 2008 American Institute of Chemical Engineers AIChE J, 2008
TL;DR: In this paper, a three-phase theory that describes the mass and heat transfer between the air and solids phases is used to develop an understanding of batch fluidized-bed drying, which is a complex air-solids, multiphase process.
Abstract: Mathematical modeling, computational fluid dynamics (CFD) analysis and electrical capacitance tomography (ECT) is used to develop an understanding of batch fluidized-bed drying, which is a complex air-solids, multiphase process. The mathematical model is based on a three-phase theory that describes the mass-and heat-transfer between the air and solids phases. The CFD model is based on a two-fluid model (TFM) approach, in which both phases are considered to be continuous and fully interpenetrating. The hydrodynamic parameters used to model the heat-and mass-transfer between the two phases are determined by a correlation approach, and the estimated parameters are incorporated into a user defined function (UDF) in FLUENT. The moisture diffusion in the air and solids phases is simulated using the user defined scalar (UDS) transport equation in the software package. ECT is used for the online solids concentration and moisture measurement, based on dynamic calibration. Comprehensive comparisons between results from mathematical modeling, CFD simulation and ECT measurement are presented, and are validated using experiment results. Online measurement of moisture content is compared with a static calibration. The mathematical model, CFD and ECT presented are being integrated into an online process control system for a batch fluidized-bed drying application in the pharmaceutical industry. © 2007 American Institute of Chemical Engineers AIChE J, 2008
TL;DR: In this article, natural olivine was used as bed material during the gasification of plastic waste in a pilot-scale bubbling fluidized bed reactor, and the results indicate that it works as an excellent in-situ tar reduction agent, considerably improving the quality of the gas produced, in terms of low tar content, high hydrogen volume fraction and large syngas yield.
Abstract: Natural olivine was used as bed material during the gasification of plastic waste in a pilot-scale bubbling fluidized bed reactor. The results indicate that it works as an excellent in-situ tar reduction agent, considerably improving the quality of the gas produced, in terms of low tar content, high hydrogen volume fraction and large syngas yield. The phenomena concurring to the activation of the catalyst are described together with those that can contribute to deactivate it. A phenomenological description of the different stages occurring during gasification of plastic waste in a fluidized bed of olivine particles is also reported. © 2008 American Institute of Chemical Engineers AIChE J, 2008
TL;DR: In this article, a two-step thermochemical water-splitting cycle based on SnO2/SnO is proposed from the detailed study of the whole tin oxide systems involving three redox pairs.
Abstract: A novel two-step thermochemical water-splitting cycle based on SnO2/SnO is proposed from the detailed study of the whole tin oxide systems involving three redox pairs. The thermal reduction of tin(IV) oxide occurs in the temperature range 1400-1600°C following a zero order kinetic law of Arrhenius with an activation energy of 394.8 kJ mol -1 and a pre-exponential factor of 8.32 X 10 8 g s -1 at atmospheric pressure. The operating conditions that prevent gaseous stannous oxide (SnO) from recombining with O 2 are defined. The effect of a quenching device (water-cooled finger) is negligible whereas operation at low total pressure or low O 2 and SnO partial pressures leads to nearly pure SnO product. The comparison of SnO and metallic tin hydrolysis in a fixed bed reactor reveals a higher reaction rate in the case of SnO. Hydrolysis of these reduced compounds shows nearly complete conversion producing hydrogen by a solid/gas reaction proceeding at moderate temperature, thus easy to implement in a common reactor technology.
TL;DR: In this paper, heat transfer characteristics of microencapsulated phase change material (MPCM) slurry flow in a circular horizontal tube were investigated for water-based slurries using 1-bromohexadecane (C16H33Br) with a mass concentrations varying from 0 to 27.6%.
Abstract: Heat transfer characteristics of microencapsulated phase change material (MPCM) slurry flow in a circular horizontal tube are presented in this paper. Phase change due to the melting is investigated for water-based slurries using microencapsulated 1-bromohexadecane (C16H33Br) with a mass concentrations varying from 0 to 27.6%. The local heat transfer coefficients varied significantly along the test section when PCM particles were melting. The average Nusselt numbers were calculated based on the local heat transfer data and found to be significantly higher than those for single-phase fluid flow. Two new heat transfer correlations, one used for the slurry under laminar condition (0 < Re < 2000) and another used for the slurry under slightly turbulent condition (2200 < Re < 3500), were proposed for predicting the heat transfer behaviors of MPCM slurry in a circular tube. © 2008 American Institute of Chemical Engineers AIChE J, 2008
TL;DR: In this paper, a proportional-integral-derivative (PID) cascaded with a lead-lag compensator is proposed for enhanced disturbance rejection of the second-order stable and unstable processes with time delay.
Abstract: A design method for a proportional-integral-derivative (PID) cascaded with a lead-lag compensator is proposed for enhanced disturbance rejection of the second-order stable and unstable processes with time delay. A two-degree-of-freedom control scheme is used to cope with both regulatory and servo problems. An ideal feedback controller equivalent to internal model control (IMC) is obtained through the IMC design principle, and is further simplified to the PID cascaded with a first-order lead-lag compensator. The simulation is conducted for a broad class of stable and unstable processes and the results are compared with those of recently published PID type controllers to illustrate the superiority of the proposed controller. For a reasonable comparison, the controllers in the simulation study are tuned to have the same degree of robustness by measuring the maximum sensitivity, Ms. The robustness of the controller is also investigated by simultaneously inserting a perturbation uncertainty in all parameters in order to obtain the worst-case model mismatch. The proposed method illustrates greater robustness against process parameter uncertainty. © 2008 American Institute of Chemical Engineers AIChE J, 2008
TL;DR: In this article, the four-point optical probe is applied in a bubble column with an air-water system to investigate the bubble properties (local gas holdup, velocity, chord length, specific interfacial area, and frequency) over a range of gas superficial velocities.
Abstract: The four-point optical probe is applied in a bubble column with an air–water system to investigate the bubble properties (local gas holdup, velocity, chord length, specific interfacial area, and frequency) over a range of gas superficial velocities. Both bubbles moving upward and downward are recorded and measured as opposed to only upward bubbles measured and reported in other studies involving probes. The probe worked efficiently in both bubbly flow and highly churn-turbulent flow at very high superficial gas velocities. Bubble properties at the conditions of churn-turbulent flow are obtained and investigated for the first time. The changes in the bubble velocity distribution, bubble chord length distribution, and specific interfacial area with superficial gas velocity, sparger design, and with axial and radial positions in the column are discussed. © 2007 American Institute of Chemical Engineers AIChE J, 2008
TL;DR: In this article, an adaptive detection observer with a time varying threshold is proposed that provides additional robustness with respect to false declarations of faults and minimizes the fault detection time, and an adaptive diagnostic observer is subsequently utilized in an automated control reconfiguration scheme that accommodates the component and actuator faults.
Abstract: A class of nonlinear distributed processes with component and actuator faults is presented. An adaptive detection observer with a time varying threshold is proposed that provides additional robustness with respect to false declarations of faults and minimizes the fault detection time. Additionally, an adaptive diagnostic observer is proposed that is subsequently utilized in an automated control reconfiguration scheme that accommodates the component and actuator faults. An integrated optimal actuator location and fault accommodation scheme is provided in which the actuator locations are chosen in order to provide additional robustness with respect to actuator and component faults. Simulation studies of the Kuramoto-Sivashinsky nonlinear partial differential equation are included to demonstrate the proposed fault detection and accommodation scheme. © 2008 American Institute of Chemical Engineers AIChE J, 2008