bluuebunny/crossref_metadata_2025_split huggingface dataset:
Performance analysis of axial‐flow mixing impellers
Authors: Wu Jie , Pullum Lionel 
Published: April 2004

AbstractTheoretical formulations for impeller performance were evaluated based on a blade‐element theory. These enable the calculation of the head and power vs. flow‐rate curves of axial‐flow impellers. The technique uses the lift and drag coefficients of the blade section of an impeller to calculate the spanwise swirl‐velocity distribution. Using the angular‐momentum equation, it is possible to calculate the corresponding spanwise distribution of the energy head of the impeller. Integration of these distributions of head and torque gives the impeller's performance. Parameters including the flow number, the power number, the thrust force number, and the swirl velocity can be found at the impeller operating point, determined using the head curve and an experimentally calibrated resistance curve. A laser Doppler velocimetry (LDV) system was used to measure the velocity distribution for different axial flow impellers in mixing tanks. Calculated flow and power numbers agreed well with the experimental results. Using the blade's spanwise head distribution and a set of calibrated flow‐resistance data, it is also possible to estimate an impeller's outlet axial‐velocity distribution. Predictions compared well with LDV experimental data. The effect of impeller‐blade angle, number of blades, blade camber, and blade thickness on the performance of axial‐flow impellers was investigated using the Agitator software.
Granular flow in a rotating cone partly submerged in a fluidized bed
Authors: Janse Arthur M. C. , Biesheuvel P. Maarten , Prins Wolter , van Swaaij Wim P. M. 
Published: April 2004

AbstractWhen a rotating cone with supply openings near the bottom is partly inserted into a fluidized bed, solid particles are taken up and conveyed spirally over the inner surface. This principle for particle transport was used in a novel reactor for the flash pyrolysis of biomass with several distinct advantages. Particle velocities (up to 5 m/s) were measured, as well as the solids flow rate (up to 1.6 kg/s), as a function of the cone rotational velocity, cone size and cone top angle, the fluidization velocity, and the depth of the cone in the fluidized bed. Three hydrodynamic regimes were recognized, each with its own, specific flow characteristics influencing the particle residence time (distribution) on the cone wall and the solids flow rate. The transition between the regimes could be predicted using a force balance for a single particle. The particle velocity and residence time were modeled successfully for one of the regimes.
Pressure swing adsorption cycles for improved solvent vapor enrichment
Authors: Liu Yujun , Ritter James A. , Kaul Bal K. 
Published: April 2004

AbstractA pressure swing adsorption (PSA)–solvent vapor recovery (SVR) process simulator was used to investigate new PSA cycle configurations designed for higher solvent vapor enrichment. These cycles were modifications of the four‐step Skarstrom cycle used commercially for PSA‐SVR and include the addition of a cocurrent blowdown step, and combinations of cocurrent blowdown and continuous/batch reflux steps. The recovery of gasoline vapor from tank filling operations was simulated with n‐butane, n‐heptane, and nitrogen as representatives of the light and heavy components in gasoline vapor, and carrier gas, respectively. Adding a cocurrent blowdown step increased the solvent vapor enrichment, depending mainly on the step ending pressure, not the step time. Both the continuous and batch reflux steps also increased the solvent vapor enrichment, but at the expense of an increased bed capacity factor. For similar increases in the solvent vapor enrichment, batch reflux led to significantly smaller bed capacity factors compared to continuous reflux and was thus superior for PSA‐SVR. Overall PSA‐SVR process performance improved markedly by adding cocurrent blowdown and batch reflux steps compared to the conventional four‐step cycle.
Design of a carousel process for cesium removal using crystalline silicotitanate
Authors: Hritzko Benjamin J. , Walker D. Douglas , Wang N.‐H. Linda 
Published: April 2004

AbstractA three‐column carousel process based on a pelletized form of CST powder was designed to remove radioactive 137Cs+ from SRS nuclear wastes. A multicomponent ion‐exchange equilibrium model was used to generate cesium loading data, which were fit to the Langmuir equation to obtain effective single‐component cesium isotherm parameters for representative wastes. Mass‐transfer parameters were estimated by analyzing breakthrough curves for two simulated wastes. Simulations based on a pore‐diffusion rate model were performed to determine the lengths of the mass‐transfer zone for different feed compositions and linear velocities. The length of a single segment in the carousel process was the constant‐pattern mass‐transfer zone to ensure consistent high column utilization during startup and cyclic steady state. Analysis of the dimensionless groups in the mass balance equations revealed that the mass‐transfer zone length is proportional to the particle Peclet number. The proportionality constant is a function of the waste composition and the Cs+ concentration in the waste. A higher distribution coefficient and isotherm nonlinearity result in a smaller proportionality constant. With this analysis designs can be easily adjusted for variations in isotherms, feed concentration, particle size, linear velocity, and intraparticle diffusivity.
Double‐slit model for partially wetted trickle flow hydrodynamics
Authors: Iliuta I. , Larachi F. , Al‐Dahhan M. H. 
Published: April 2004

AbstractA double‐slit model developed can predict the frictional two‐phase pressure drop, external liquid holdup, pellet‐scale external wetting efficiency, and gas–liquid interfacial area in cocurrent downflow trickle‐bed reactors operated under partially wetted conditions in the trickle flow regime. The model, an extension of the Holub et al. (1992, 1993) mechanistic pore‐scale phenomenological approach, was designed to mimic the actual bed void by two inclined and interconnected slits: wet and dry slit. The external wetting efficiency is linked to both the pressure drop and external liquid holdup. The model also predicts gas–liquid interfacial areas in partially wetted conditions. An extensive trickle‐flow regime database including over 1,200 measurements of two‐phase pressure drop, liquid holdup, gas–liquid interfacial area and wetting efficiency, published in 1974–1998 on the partial‐wetted conditions, was used to validate the modeling approach. Two new improved slip‐factor functions were also developed using dimensional analysis and artificial neural networks. High‐pressure and ‐temperature wetting efficiency, liquid holdup, pressure drop, and gas–liquid interfacial area data from the literature on the trickle‐flow regime using conventional monosized beds and catalyst bed‐dilution conditions were successfully forecasted by the model.
Modeling constant voltage electrophoretic deposition from a stirred suspension
Authors: González‐Cuenca Mercedes , Biesheuvel P. Maarten , Verweij Henk 
Published: April 2004

AbstractIn electrophoretic deposition, a voltage difference is applied across a suspension, and a layer (“cast” or coating) is formed on one of the electrodes. Based on first principles, cast growth is described in this work for a well‐stirred suspension, a constant voltage difference across the deposition cell, and a nonionic solution. The influence of cast formation on cast growth is implemented, which is a refinement of the model described in 1999 by Biesheuvel and Verweij. Simulation results are compared with experimental data. From the derivation it follows that a smooth cast layer is formed when the particle permittivity is lower than that of the liquid. Catastrophic cast growth occurs when the particle permittivity is higher than that of the liquid.
Thermal effects in dynamic storage of hydrogen by adsorption
Authors: Lamari Malek , Aoufi Asdin , Malbrunot Pierre 
Published: April 2004

AbstractThermal effects in dynamic hydrogen storage by adsorption at room temperature and high pressure are studied theoretically and experimentally. The system of adsorbate–adsorbent used was hydrogen in granular activated carbon. The theoretical analysis was based on heat‐ and mass‐transfer modeling in a packed‐bed adsorber, with particular emphasis on the thermal effects occurring during charge and discharge steps. The influence of gas flow rate and storage pressure (up to 15 MPa) on the total amount stored or delivered was investigated. Operating conditions were compatible with practical application for onboard vehicle storage. The experimental study was carried out in cylindrical 2‐L reservoirs filled with granular activated carbon in which the bed temperature was measured at various positions. The temperature changes during both charge and discharge agreed well with the model predictions.
Mapping the cavitation intensity in an ultrasonic bath using the acoustic emission
Authors: Moholkar Vijayanand S. , Sable Shishir P. , Pandit Aniruddha B. 
Published: April 2004

AbstractA new method for separate identification and determination of the spatial distribution of the two components of the energy intensity in an ultrasound bath (due to the ultrasound waves and cavitation activity) uses two media—cavitating (water) and noncavitating (silicon oil)—under the conditions of the acoustic field in the ultrasound bath. The variation of cavitation intensity in the frequency domain was obtained by subtracting the acoustic emission spectrum of silicon oil from that of water. Measurements at various locations in the bath revealed significant spatial variations in the cavitation intensity in the bath. The local cavitation phenomena in the bath (stable or transient cavitation) were explained based on the spectral characteristics of acoustic emission. The radial dynamics of the bubbles at the location of cavitation intensity measurements was determined using the Gilmore model of bubble dynamics. The bubbles in the region of highest cavitation intensity underwent a transient motion, while the bubbles in the region of lowest cavitation intensity underwent stable/oscillatory motion. The transient collapse of the bubbles that gives rise to local temperature and pressure maxima is at the root of the observed effects of ultrasound on chemical systems. The more violent the collapse of the bubbles, the higher the local cavitation intensity. It was verified using the spectral characteristics of the acoustic emission and simulation of the radial motion of the bubbles.
Pressure swing permeation: Novel process for gas separation by membranes
Authors: Feng Xianshe , Pan Chuen Y. , Ivory John 
Published: April 2004

AbstractA novel process for gas separation, called pressure swing permeation, was investigated to elevate the relatively low permeate pressure by pressurization with high‐pressure feed gas, thereby reducing or eliminating additional permeate compression costs where a pressurized permeate is required. This process uses two or more membrane modules and operates in a cyclic fashion, with each module repeatedly undergoing the sequential steps of feed admission and permeation, residual removal, permeate reception, permeate pressurization, and product withdrawal. The unsteady‐state permeation associated with pressure swing permeation was studied parametrically, and a bench‐scale unit compromising two hollow‐fiber membrane modules in parallel was tested for H2/N2 separation to demonstrate the effectiveness of the process. The permeate product at a pressure as high as the feed pressure can be produced without using a compressor. This is impossible with traditional steady‐state processes where a pressure differential across the membrane must be maintained. The pressure swing permeation is analogous to pressure swing adsorption and has the potential to be synergistically integrated with the pressure swing adsorption process for enhanced separation of gases.
Multistability and hysteresis in an industrial ammonia reactor
Authors: Mancusi E. , Merola G. , Crescitelli S. , Maffettone P. L. 
Published: April 2004

AbstractA model for an industrial ammonia reactor was studied with nonlinear‐analysis tools. This model was recently considered to explain an industrial incident involving the onset of sustained oscillations due to a sudden decrease in the reactor pressure. The analysis was based on the bifurcation diagrams. Both multistability and hysteretic behaviors described here can be useful for an effective plant design, as well as for an adequate plant control and operation.
Fluidization of solids with CO2 at pressures from ambient to supercritical
Authors: Marzocchella Antonio , Salatino Piero 
Published: April 2004

AbstractBeds of two granular materials belonging to groups A‐B and B of the Geldart classification of powders were fluidized by carbon dioxide at 35°C and at 1 to 80 bar. Within this pressure interval, spanning from subcritical to supercritical conditions, the fluid density changes from the values typical of dilute gases to those of liquids. The hydrodynamic behavior of the bed changes accordingly. The bed behavior was investigated by visual inspection of the bed and by analysis of the time series of the pressure drop across the bed and of the heat‐transfer coefficient between the bed and a hot wire probe. The boundaries between different captive fluidization regimes—incipient fluidization, onset of bubbling, and the incipient and fully established turbulent regime—were mapped in gas superficial velocity vs. fluid density phase planes for the two granular materials investigated.
Transport in nanoporous carbon membranes: Experiments and analysis
Authors: Acharya Madhav , Foley Henry C. 
Published: April 2004

AbstractSingle‐component permeances of six gases were measured on three different supported nanoporous carbon membranes prepared by spray coating and pyrolysis of poly(furfuryl alcohol) on porous stainless‐steel disks. Global activation energies were regressed from data collected as a function of temperature. Permeances and global activation energies were correlated to molecular size, assuming that entropic affects dominated the transport. The permeance was best correlated to the minimum projected area of the molecule computed from first principles. The free‐energy barriers to transport within the membranes were derived from the temperature dependence of the permeance data, after accounting for porosity differences between the membranes and differences in molecular adsorption. Using transition‐state theory and an entropic model derived, the free energy, enthalpy, and entropic barriers to transport within the membrane were examined as a function of molecular size. Computed on the basis of size, the entropic component of this barrier did not account for the large differences in the transition‐state free energies. However, when these entropic barrier values were used to compute the enthalpic portion of the barrier free energies, the minimum projected area of each molecule correlated strongly. Furthermore, these enthalpic components of the barriers were fitted nicely by the Everett‐Powl mean field potential, using only the pore size as the adjustable parameter. These results shed light on the underlying mechanism by which shape‐selective transport takes place in the NPC membranes and small molecules are separated.
Flow measurements on a turbulent fiber suspension by laser Doppler anemometry
Authors: Andersson Sven R. , Rasmuson Anders 
Published: April 2004

AbstractThe flow and transition of fiber suspensions to turbulence in a rotary shear tester were studied. Both torque and LDA measurements were performed on a refractive‐index‐matched glass‐fiber suspension in the 3–20 wt. % concentration range. The flow of such suspensions underwent two transitions: the first one coincided with complete agitation, a sharp increase in torque, and fluctuating velocities close to zero. The mean velocities were similar to those of single‐phase flow above this transition. The fluctuation velocities approached those of single‐phase flow with increasing rotational speed, until they were nearly equal. This second transition was interpreted as fully developed turbulent flow. CFD, assuming single‐phase flow, is a helpful tool for describing the flow behavior in this region. The network strength was useful for the study of flow transitions. LDA measurements of the boundary layer at the bottom wall showed that the velocity profile is linear close to the wall even with fibers present. The presence of the fibers also flattened the profiles, indicating an increased momentum transfer.
Design of complex wire‐mesh mist eliminators
Authors: Brunazzi Elisabetta , Paglianti Alessandro 
Published: April 2004

AbstractKnitted wire‐mesh mist eliminators have widespread application in many industrial plants. Despite their extensive use, the open literature regarding them is really limited. Some experimental data and mechanistic models have been published for common knitted wire‐mesh mist eliminators formed from a single metal pad. This type of mist eliminator can be used in most distillation and absorption columns, but because of the poor removal efficiency, cannot be used in operations involving acid mist, fine fog resulting from liquid condensation from a saturated vapor, oil mist from compressed gases, and natural‐gas dehydration applications. Moreover, other possible problems may arise when the separator is fed with high liquid and gas flow rates, because these conditions can induce flooding in the mist eliminator. In both of these cases, common wire‐mesh mist eliminators do not perform satisfactorily, and therefore complex wire‐mesh mist eliminators have to be installed to improve separation efficiency or to increase allowable liquid loadings while avoiding flooding phenomena. This article presents a mechanistic model based on a set of new experimental data obtained by investigating performance of commercial complex eliminators.
Electrodiffusional wall shear rate analysis in scraped surface heat exchanger
Authors: Dumont Eric , Fayolle Francine , Legrand Jack 
Published: April 2004

AbstractAn electrochemical technique was used to measure local and instantaneous wall shear rates in a scraped surface heat exchanger (SSHE). The inner cylinder, equipped with two blades symmetrically opposed, was driven by a stepping motor and the outer cylinder was fixed. Highly viscous Newtonian fluids (Emkarox HV45 solutions) and non‐Newtonian model fluids (aqueous solutions of guar and CMC) were used. The reliability of the electrochemical technique was validated for these fluids in an annular space (SSHE without blades). The evolution of the limiting diffusion current was given by the probes in a scraping situation. In the general case of scraping, the flow was unsteady, and very fast large fluctuations of the limiting diffusion current were measured. The shear rate at the wall of the stator of the SSHE appeared fully controlled by the rotation of the blades. Then, electrodiffusion measurements were interpreted using three different wall shear rate calculating procedures. Wall shear rate in SSHE appeared ten to 100 times more important than in annulus, and the lowest values of the clearance between the edge of the blades and the stator was about 50 × 10−6 m.
Hindered diffusion of dextran and polyethylene glycol in porous membranes
Authors: Shao Jiahui , Baltus Ruth E. 
Published: April 2004

AbstractThe effective diffusion coefficients of dextran and polyethylene glycol in track‐etched polycarbonate membranes were measured using membranes with nominal pore sizes of 0.03 μm, 0.05 μm, and 0.1 μm. Experiments were performed using narrow‐size range fractions of each polymer. When the Stokes‐Einstein radius was used to describe solute size, the observed diffusivities for both polymers agreed closely and were larger than values predicted for rigid spheres, as well as for linear polymers when only steric interactions with the pore wall are assumed. These observations cannot be explained by considering electrostatic interactions between the solute and the pore wall, or solute adsorption on the pore wall. The experimentally measured diffusion coefficients agreed well with a model that treats the polymeric solutes as rigid spheres and includes van der Waals attractive interactions between the solute and the pore wall.
Kinetics of high‐pressure removal of hydrogen sulfide using calcium oxide powder
Authors: Chauk Shriniwas S. , Agnihotri Rajeev , Jadhav Raja A. , Misro Santhosh K. , Fan Liang‐Shih 
Published: April 2004

AbstractSulfidation reaction of CaO at high pressure (up to 2 MPa) and high temperature (up to 900°C) to remove H2S in a coal‐fired gasifier was studied in a high‐pressure and temperature differential‐bed flow‐through reactor. Experimental conditions selected are typical for pressurized gasifiers. Effects of total pressure, H2S partial pressure, reaction temperature, fuel gas composition, and CaO surface area on the extent of sulfur capture and sorbent conversions were determined. The gasifier pressure affected the in‐situ calcination of calcium carbonate particles through reduction in available surface area and pore volume of CaO formed, thus limiting the sulfidation conversion. Time‐resolved conversion data of CaO sulfidation were analyzed using a modified grain model. The model incorporates external and internal diffusion, surface reaction, product layer diffusion, and the structural changes of the sulfiding CaO particle. The activation energy for the reaction was 37 kcal/mol. The estimated product layer diffusivity was 8×10−15 m2/s at 800°C with an associated activation energy of 38.4 kcal/mol—typical of solid state diffusion of ionic species through the product layer. The extent of conversion increased with increasing initial surface area and porosity of CaO particles. The high‐pressure sulfidation reaction data for CaO will be useful in understanding and optimizing the in‐gasifier H2S capture using calcium‐based sorbents.
Analytical solution to an axial dispersion model for the fixed‐bed adsorber
Authors: Liao Hsin‐Tzu , Shiau Ching‐Yeh 
Published: April 2004

AbstractAn axial dispersion model for the operation of a fixed‐bed adsorber with a linear adsorption isotherm was formulated and solved analytically using the separation of variables method. The asymptotic solution for a large Peclet number and/or a small operation time was also obtained using two limiting cases. The results can be used to correlate or to predict both the mass‐transfer zones and the breakthrough curves of a fixed‐bed adsorber. Influence of both the Peclet number and the retardation coefficient on the operation of a fixed‐bed adsorber was also studied. As an example, the axial dispersion model was applied to the experimental data of the removal of phenol from the solution in the activated carbon and the Amberlite resin XAD‐4 fixed‐bed adsorbers.