bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nucleation regime map for liquid bound granules
Authors: Hapgood Karen P. , Litster James D. , Smith Rachel 
Published: April 2004

AbstractNucleation is the first step in granulation where the powder and liquid first contact. Two types of nucleation in wet granulation processes are proposed. Drop controlled nucleation, where one drop forms one nucleus, occurs when drops hitting the powder surface do not overlap (low spray flux Ψa) and the drop must wet quickly into the bed (short drop penetration time tp). If either criterion is not met, powder mixing characteristics will dominate (mechanical dispersion regime). Granulation experiments were performed with lactose powder, water, PEG200, and 7% HPC solution in a 6 L and a 25 L mixer granulator. Size distributions were measured as the drop penetration time and spray flux were varied. At short penetration times, decreasing Ψa caused the nuclei distribution to become narrower. When drop penetration time was high, the nuclei size distribution was broad independent of changes in dimensionless spray flux. Nucleation regime maps were plotted for each set of experiments in each mixer as a function of the dimensionless distribution width δ. The nucleation regime map demonstrates the interaction between drop penetration time and spray flux in nucleation. The narrowest distribution consistently occurred at low spray flux and low penetration time, proving the existence of the drop controlled regime. The nucleation regime map provides a rational basis for design and scale‐up of nucleation and wetting in wet granulation.
Model for temperature profiles in large diameter electrochromatography columns
Authors: Keim Craig , Ladisch Michael 
Published: April 2004

AbstractScale‐up of electrochromatographic separations has been problematic due to electrically induced heating. A two‐dimensional transient temperature model for electrochromatography was developed, which accounts for physical properties of the stationary and mobile phase, and the column wall. The model also accounts for both the temperature effect on the electrical conductivity and a nonuniform, radially variant current density. This model was compared to experimental data from two electrochromatography systems with different cylindrical‐column dimensions, packing materials, and operating conditions. In all cases, the model predicts the temperature to within 3°C of the actual temperature, both for column heatup and cooldown. Separation of a mixture of model proteins on the 3.81‐cm‐ID scale was used as the basis for scale‐up calculations. The model identifies equipment parameters that control heating characteristics and can be scaled up to process 75 mL of sample per run.
Fundamental thermal‐hydraulic pulp digester model with grade transition
Authors: Bhartiya Sharad , Dufour Pascal , Doyle Francis J. 
Published: April 2004

AbstractA detailed fundamental model of a continuous pulp digester was developed for simulation and control. Most modeling efforts in the past had emphasized either reaction kinetics and energy transfer assuming a prescribed flow behavior or modeled digester hydraulics with simplified reaction kinetics. The well‐known extended Purdue model was augmented by incorporating axial momentum transport, of which an immediate consequence is the ability to simulate chip level and its impact on the Kappa number profile, thus enhancing the ability to model chip compaction. Interaction between digester hydraulics and kinetics is illustrated via simulation examples, including scenarios that show incipient plugging of the digester vessel. Higher‐order finite‐difference methods were also used to reduce numerical dissipation and dispersion. The ability to describe chip velocities enables rigorous tracking of a transition front within the digester during feedstock grade transitions. The model explains operational difficulties encountered during hardwood to softwood transition.
Optimal process design with model parameter uncertainty and process variability
Authors: Rooney William C. , Biegler Lorenz T. 
Published: April 2004

AbstractOptimal design under unknown information is a key task in process systems engineering. This study considers formulations that incorporate two types of unknown input parameters, uncertain model parameters, and variable process parameters. In the former case, a process must be designed that is feasible over the entire domain of uncertain parameters, while in the latter case, control variables can be adjusted during process operation to compensate for variable process parameters. To address this problem we extend the two‐stage formulation for design under uncertainty and derive new formulations for the multiperiod and feasibility problems. Moreover, to simplify the feasibility problem in the two‐stage algorithm, we also introduce a KS constraint aggregation function and derive a single, smooth nonlinear program that approximates the feasibility problem. Three case studies are presented to demonstrate the proposed approach.
Fines deposition dynamics in gas–liquid trickle‐flow reactors
Authors: Iliuta Ion , Larachi Faïçal , Grandjean Bernard P. A. 
Published: April 2004

AbstractNonfilterable fines, such as incipient coke particles or fines naturally occurring in oil sands bitumen, are known to be responsible for the severe plugging during the flow of (fine) solid–liquid suspensions in cocurrent gas–liquid trickle‐bed hydrotreating reactors. Accumulating fines in the porous medium causes pressure buildup, and thus the dropoff in hydrogen partial pressure in the bed, overutilizing recycling compressors and shortening the reactor operating cycles. In this work, a 1‐D transient two‐fluid hydrodynamic model based on the macroscopic volume‐average form of the multiphase system transport equations is developed, analyzed, and validated experimentally. The model hypothesizes that plugging occurs via deep‐bed filtration mechanisms. It incorporates physical effects of porosity and effective specific surface‐area changes due to the capture of fines, inertial effects of phases, and coupling effects between the fines filter rate equation and interfacial momentum exchange force terms. It is tested in the trickle‐flow regime for conditions mimicking a hydrotreating trickle‐bed process with spherical and trilobe catalysts. To rationalize deep‐bed filtration phenomena in trickle‐flow reactors, parametric studies are carried out on the effects of liquid velocity and viscosity, gas density and velocity, and fines feed concentration, on the plugging dynamics.
Laminar mixing in different interdigital micromixers: II. Numerical simulations
Authors: Hardt S. , Schönfeld F. 
Published: April 2004

AbstractFlow patterns and mixing properties of micromixing devices described in Part I are investigated by computational fluid dynamics (CFD) and semianalytical methods. The CFD results provide qualitative information on mixing, but, due to numerical artifacts, no quantitative information can be derived in most cases. The geometrical arrangement of liquid lamellae predicted by the CFD simulations explain transmitted‐light experiments reported in Part I. In contrast, the semianalytical method provides a simple model for the mixing devices presented and allows to assess their mixing properties. For two of the four micromixers, mixing times were in the range of milliseconds, thus lending themselves to fast, mass‐transfer‐limited reactions. Experimental data obtained for a specific micromixer support the semianalytical model. Both the model and experiments suggest that geometric focusing of a large number of liquid streams is a powerful micromixing principle.
Experimental analysis of hydrodynamics in a radially agitated tank
Authors: Escudié Renaud , Liné Alain 
Published: April 2004

AbstractA PIV technique is used to analyze the local hydrodynamics generated by a Rushton turbine. Different types of motion coexist in the tank: the mean flow (or global circulation), the periodic fluctuations (or trailing vortices) induced by the blade rotation in the impeller region, and the turbulent fluctuations (that dissipate the kinetic energy). These three kinds of motion can be estimated after experiments as soon as a triple decomposition of the velocity is performed. The mean velocity, the periodically induced stress, and the Reynolds stress are analyzed in the agitated tank, close to the impeller. These data are used for two purposes: to identify and quantify the transfer of kinetic energy between mean flow, periodic flow, and turbulence; and to estimate the dissipation rate of turbulent kinetic energy (TKE) from the balance of TKE, in which each term will be derived from experiments. Characteristics of turbulence are also presented and discussed.
Mechanics of column beds: I. Acquisition of the relevant parameters
Authors: Yew Bee Gaik , Drumm Eric C. , Guiochon Georges 
Published: April 2004

AbstractThe efficiency of chromatographic columns is adversely affected by large‐scale radial variations of the packing density or void ratio of the material used to prepare the bed. This heterogeneity is due to wall friction effects that take place during the preparation of the column and to seepage effects operating during the packing process and the subsequent operation of the column. The dependence of the bed's void fraction on the stress applied during its consolidation was determined, as well as its permeability at various stages of the consolidation process and the coefficient of friction between typical packing materials and the stainless steel wall of chromatographic columns. These results are required to develop and use numerical models of the volumetric response to axial compression of the bed and models of the coupled mechanical‐seepage rheology of particulate materials.
Water‐density effects on phenol oxidation in supercritical water
Authors: Henrikson Jeffrey T. , Savage Phillip E. 
Published: April 2004

AbstractSupercritical water oxidation (SCWO) experiments were performed in a tubular flow reactor at 420–465°C and 141–241 bar. Phenol was the organic reactant. Both pure water and a helium (1/3 by mol)–water mixture served as reaction media. Adding helium to the reaction medium permitted variation of the water concentration and system pressure independently. By decoupling the water concentration from the system pressure, it was shown that the rate of phenol disappearance during SCWO is influenced by the water concentration and not the system pressure. The experiments consistently revealed that adding helium, and thereby decreasing the water concentration at a fixed system pressure, increased the phenol conversion. In addition, experiments showed that lowering the water concentration using pure water as the solvent also increased the phenol conversion. The results suggest that dilution with helium (and perhaps other inert gases) may be a new way to control SCWO reaction rates.
Optimum photolysis in Taylor–Couette flow
Authors: Forney L. J. , Pierson J. A. 
Published: April 2004

AbstractPhotolysis was studied in Taylor–Couette flow, and a similarity law proposed for the formation of a product from a fast photochemical reaction in the presence of laminar Taylor vortices. The concentration of the product formed depended on both the dosage of photons and a reaction‐layer thickness, defined by the radiation penetration depth. In particular, for a given flow rate and radiation intensity, the UV photolysis of iodide produced a maximum concentration of the product triiodide, when the radiation penetration depth was equal to the velocity boundary‐layer thickness. The latter conclusion provides optimum operating conditions to maximize yield in terms of the Taylor number or frequency of rotation.
Monte Carlo simulation of adsorption using 2‐D models of heterogeneous solids
Authors: Cabral V. F. , Tavares F. W. , Castier M. 
Published: April 2004

AbstractA new methodology proposed here correlates the adsorption of pure components and predicts the adsorption of binary and ternary mixtures in homogeneous and heterogeneous solids. This methodology uses the algorithm of molecular simulation in the grand canonical ensemble as an equation of state for the adsorbed phase. In all case studies presented, the simulations described the adsorption characteristics of systems. The results obtained for the adsorption of the binary mixtures of propane–CO2 and propane–H2S, which are strongly nonideal, were quite satisfactory, showing the potential of this technique for the description of real systems.
Diffusing with Stefan and Maxwell
Authors: Amundson Neal R. , Pan Tsorng‐Whay , Paulsen Vern I. 
Published: April 2004

AbstractIn most chemical engineering problems, diffusion is treated as an add‐on to forced advection, and the boundary conditions are the Danckwerts conditions in order to maintain conservation. If we treat problems in which there is no applied advection or chemical reaction for a steady‐state situation and with an ideal gas, it is an equi‐molar process. Because it is considered the natural movement of molecules moving down a concentration gradient, this requires the Stefan‐Maxwell equations. In the standard 1‐D two‐component boundary value problem, analogous to the Dirichlet problem, the solution is direct and is probably the only one there is. In a ternary system, the solution is already not direct and can only be obtained by numerical means, which is not severe. In a quaternary system, it does not appear feasible to obtain a simple procedure like that obtained for the ternary system. A different numerical scheme developed is robust with rapid convergence and works well with an arbitrary number of components, 60 having been used in one problem. As the number of components increases, the solution profiles tend to become linear and the dependence on particular diffusivities is less important. This manifests itself when using diffusivities from a random collection. The problem using a continuous distribution of components is solved, and computationally and theoretically the profiles are probably linear and with a single pairwise diffusion coefficient.
Multiscale resolution of fluidized‐bed pressure fluctuations
Authors: Zhao Gui‐Bing , Yang Yong‐Rong 
Published: April 2004

AbstractPressure fluctuation signals measured from four different axial locations in a bubbling bed 0.3 m in diameter and 3 m in height were analyzed using multiple approaches, including wavelet transform, Hurst analysis, multiscale resolution, and time‐delay embedding. After examining decomposition residuals using different compact support Daubechies wavelets, the Daubechies second‐order wavelet was chosen as an optimal wavelet for decomposing pressure signals. Hurst analysis of the decomposed signals shows that the measured pressure fluctuations can be resolved to three characteristic scales: bifractal mesoscale signals with two distinct Hurst exponents; monofractal micro‐ and macroscale signals with only one characteristic Hurst exponent. Energy profiles of the three scale components confirm that the measured pressure signals mainly reflect the mesoscale component. Time‐delay embedding analysis of three scale signals demonstrates that the microscale dynamics is more complex than the mesoscale dynamics, and the mesoscale dynamics is more complex than the macroscale dynamics. That this result cannot be found solely from Hurst analysis shows the importance of integrating multiple approaches for characterizing the complexity of fluidized systems.
One‐dimensional centrifugation model
Authors: Chan Steven H. , Kiang San , Brown Matthew A. 
Published: April 2004

AbstractA 1‐D theoretical model based on Darcy's law and conservation of mass was used to describe transient filtration on a basket centrifuge for both compressible and incompressible cakes. This filtration model was validated assuming that a liquid layer lay above the surface of the cake. Both the resistance and porosity of the cake were assumed constant throughout the cake at a particular instant in time. A computational algorithm was developed to solve the system of nonlinear equations and to calculate pressure differentials across the cake, location of the slurry front in the basket, cake thickness, filtrate volume, cake resistance, cake porosity, and filtrate flow rate, all as functions of time. Both simulation and experimental results showed the validity of this computational model. A procedure was also developed to use small‐scale lab data, in conjunction with the model, to select the corresponding operating conditions for large‐scale equipment so that cake performance on both scales was dynamically similar. For the situation when the inlet feed had ceased and the liquid layer had fallen below the surface of the cake, the cake deliquoring model proposed by Wakeman and Vince was adopted.
Multiscale SPC using wavelets: Theoretical analysis and properties
Authors: Aradhye Hrishikesh B. , Bakshi Bhavik R. , Strauss Ramon A. , Davis James F. 
Published: April 2004

AbstractMost practical process data contain contributions at multiple scales in time and frequency, but most existing SPC methods are best for detecting events at only one scale. For example, Shewhart charts are best for detecting large, localized changes, while EWMA and CUSUM charts are best for detecting small changes at coarse scales. A multiscale approach for SPC, adaptable to the scale of relevant signal features and developed based on wavelet analysis, detects abnormal events at multiple scales as relatively large wavelet coefficients. Univariate and multivariate multiscale SPC (MSSPC) for detecting abnormal operation are theoretically analyzed, and their properties are compared with existing SPC methods based on their average run lengths. SPC methods are best for detecting features over a narrow range of scales. Their performance can deteriorate rapidly if abnormal features lie outside this limited range. Since in most industrial processes, the nature of abnormal features is not known a priori, MSSPC performs better on average due to its adaptability to the scale of the features and for monitoring autocorrelated measurements since dyadic wavelets decorrelate most stochastic processes. MSSPC with dyadic discretization is appropriate for SPC of highly autocorrelated or nonstationary stochastic processes. If normal measurements are uncorrelated or contain only mild autocorrelation, it is better to use MSSPC with integer or uniformly discretized wavelets. Many existing methods such as MA, EWMA, CUSUM, Shewhart, batch means charts, and their multivariate extensions are special cases of MSSPC.
Development of an inherent safety index based on fuzzy logic
Authors: Gentile Michela , Rogers William J. , Mannan M. Sam 
Published: April 2004

AbstractDuring the past several years, researchers in the U.S. and Europe have developed measurement techniques and analysis tools to estimate the inherent safety of a plant or a processing unit. These tools are based on traditional Boolean mathematical methodologies that are limited by the uncertain and subjective nature of the information analyzed. Preliminary results reported here are on the development of an inherent safety index based on fuzzy logic theory that is an extension of the Boolean theory. The basic ideas of fuzzy logic theory and its application are presented by the inherent safety evaluation of a storage tank. The inherent safety index developed by Heikkila is taken as a base and is compared with the results of the proposed prototype index. It shows the benefits of using fuzzy logic. Strengths and limitations of the proposed methodology are also presented.
Monitoring independent components for fault detection
Authors: Kano Manabu , Tanaka Shouhei , Hasebe Shinji , Hashimoto Iori , Ohno Hiromu 
Published: April 2004

AbstractA chemical process has a large number of measured variables, but it is usually driven by fewer essential variables, which may or may not be measured. Extracting such essential variables and monitoring them will improve the process‐monitoring performance. Independent component analysis (ICA) is an emerging technique for finding several independent variables as linear combinations of measured variables. In this work, a new statistical process control method based on ICA is proposed. For investigating the feasibility of its method, its fault‐detection performance is evaluated and compared with that of the conventional multivariate statistical process control (cMSPC) method using principal‐component analysis by applying those methods to monitoring problems of a simple four‐variable system and a continuous‐stirred‐tank‐reactor process. The simulated results show the superiority of ICA‐based SPC over cMSPC.
Transport of organic components from immobile and bypassed oil in porous media
Authors: Huseby O. , Haugan A. , Sagen J. , Muller J. , Bennett B. , Larter S. , Kikkinides E. S. , Stubos A. K. , Yousefian F. , Thovert J.‐F. , Adler P. M. 
Published: April 2004

AbstractAn experimental study, as well as theoretical and numerical models, are used to validate a methodology to exploit conventional geochemical data with regard to the concentration profiles of organic components occurring naturally in hydrocarbon reservoir oils. The experiment was designed to study transport of organic compounds from bypassed oil during water injection using a homogeneous oil‐filled core sample, which was made heterogeneous by drilling a hole through its central axis and filling it with a highly permeable material. Under the present conditions, diffusion coefficients are the most important parameters controlling the transport, and the effect of partitioning could be accounted for by a simple normalization. The experimental results are well described by a simple 2‐D analytical model that assumes instantaneous removal of solutes from the oil–water interface. The experimental results are also well described by two numerical models, of which one is a full‐featured reservoir scale model, suitable for applications of the methodology to reservoir‐scale cases.
Finite‐element scheme for solution of the dynamic population balance equation
Authors: Rigopoulos Stelios , Jones Alan G. 
Published: April 2004

AbstractA first‐order finite‐element scheme is proposed for solving the 1‐D dynamic population balance equation. The model includes the kinetic processes of nucleation, growth, aggregation, and breakage in a spatially uniform system with or without flow. The numerical scheme features improved stability by taking into account the convective nature of the growth term, and enhanced conservation of moments at nonuniform grids by identifying and mitigating the sources of conservation error in the evaluation of the aggregation source term. Exhaustive benchmarking is carried out against analytical solutions for size‐dependent growth and nucleation, size‐dependent aggregation with a variety of kernels, binary and multiple breakage with uniform and parabolic daughter particle distributions, and combinations of these, respectively. In all cases tested the method proves capable of producing accurate results at a reasonable CPU time, while being relatively simple and easy to implement.