bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mixing in a cross‐flow‐impinging jet reactor
Authors: Nadeau Patrice , Berk Dimitrios , Munz Richard J. 
Published: April 2004

AbstractThe mixing of a tracer in a reactor composed of two opposed jets perpendicular to a main stream is studied both experimentally and theoretically. For the experimental conditions, the gas flow was in a transitional state between laminar and turbulent due to the interaction of the mixed streams. Both the measurements and the mathematical model focus on the fluid flow (gas velocity) and the dispersion of a nonreacting species (tracer concentration) injected through one of the reactor streams. Two models are tested against experimental data: a laminar flow model (giving a time‐dependent solution) and a standard k‐ϵ turbulent flow model. These two models give quite different results, both qualitatively and quantitatively. This study demonstrates the importance of the selection of an appropriate mathematical model and computational domain.
MC simulation of aerosol aggregation and simultaneous spheroidization
Authors: Rosner Daniel E. , Yu Suyuan 
Published: April 2004

AbstractA companion article by Tandon and Rosner (1999) showed that Monte‐Carlo (MC) simulation methods can generate joint pdfs of particle volume, v, and surface area, a, for coagulating populations of suspended nonspherical particles simultaneously sintering at finite rates. For continuum‐regime Brownian coagulation at times longer than the characteristic coagulation time, a “self‐preserving” asymptotic pdf shape was shown to extend to these bivariate populations, using the rescaled volume v/v̄(t) and rescaled area a/ā(t) as “similarity” variables. This article considers the corresponding problem of coagulation in the “free‐molecule” limit, relevant to the atmospheric pressure flame experiments of Xing et al. This combination of coagulation‐ and sintering‐rate laws again leads to “self‐preserving” rescaled jpdfs, explicitly time‐independent for an isothermal environment, again dependent on a Damköhler‐like number, Damf (ratio of coagulation time to fusion time). While flames are more complex than our idealized simulations, our present pdfs and associated “mixed moments,” capture important features of experimental results as one approaches the flame, especially evolution of a mean particle “shape factor,” mean number of spherules per aggregate, and narrowness of the spread of spherule sizes. This agreement, coupled with the versatility of MC‐methods for multistate variable particle population balances, encourages extensions leading to a versatile, tractable, formalism for the developing field of sol reaction engineering.
Modeling of a novel vibrospring particle‐size distribution analyzer
Authors: Mahgerefteh Haroun , Shaeri Ali 
Published: April 2004

AbstractThe design and modeling of a novel technique for particle‐size distribution analysis are described. In its most basic form, the unit comprises a horizontally held closed‐coil helical spring that is partly filled with the test powder and sinusoidally vibrated in the transverse direction. Particle‐size distribution data are obtained by stretching the spring to known lengths and measuring the mass of the powder discharged from the spring resonant frequency. The spring's vibration characteristics, including the dynamic vibration profile as well as its first harmonic resonant frequency, are predicted using a viscoelastic model, which is in turn validated by comparison with experimental data. Particle‐size distribution data are reported in conjunction with a variety of powders including glass Ballotini, grit stone, sand, and sawdust in the size range 30–800 μm. A typical reproducibility is ±4%.
Novel sampling approach to optimal molecular design under uncertainty
Authors: Tayal Manish C. , Diwekar Urmila M. 
Published: April 2004

AbstractFor a reliable optimal molecular design, imprecision associated with property‐prediction models cannot be neglected. This study presents a novel sampling approach to stochastic optimization, incorporating property‐prediction uncertainty effects in a robust, generalized optimization framework. Detailed uncertainty analysis addresses, through nine case studies, various issues in computer‐aided molecular design under uncertainty. Results indicate that property‐prediction uncertainty can significantly impact the optimal molecular designs. Additional complex cases with nonlinear or black‐box models, nonlinear objective function and constraints, and nonstable distribution for model parameter uncertainty representation highlight the flexibility and versatility of this approach. Sensitivity analysis of uncertainties in the model parameters was also made possible in this generalized framework. Uncertainties, the focus of any future research, were identified through this critical model. Increased computational efficiency of this approach and wider applicability to solve problems involving various kinds of objective functions and constraints, and different forms of uncertainties, is illustrated in the context of polymer design case studies.
Backone family of equations of state: 2. Nonpolar and polar fluid mixtures
Authors: Weingerl Ulrike , Wendland Martin , Fischer Johann , Müller Andreas , Winkelmann Jochen 
Published: April 2004

AbstractIn the BACKONE equations the Helmholtz energy F is written as the sum F = FH + FA + FD + FQ, where FH is the hard‐body contribution, FA the attractive dispersion force contribution, FD the dipolar, and FQ the quadrupolar contribution. In Part 1 of this article (Müller et al., 1996a) the construction of BACKONE and its application to pure fluids were presented. In the extension to mixtures, for each term of F a specific mixing rule is used. This concept requires only one adjustable state‐independent binary mixture parameter. To demonstrate the feasibility of this approach, predictions of phase equilibria, including a liquid–liquid equilibrium and other thermodynamic properties, are given for 20 binary fluid mixtures from the groups: nonpolar + nonpolar; nonpolar + dipolar; nonpolar + quadrupolar; and polar + polar.
Rheooptical determination of aspect ratio and polydispersity of nonspherical particles
Authors: Vermant J. , Yang H. , Fuller G. G. 
Published: April 2004

AbstractA rheooptical method proposed rapidly determines the aspect ratio and polydispersity of small axisymmetric, nonspherical particles. The time evolution of the average orientation angle of optically isotropic, nonabsorbing particles upon inception of a shear flow was monitored by a polarization modulation method by using dilute suspensions of the particles. Since the orientation angle is a geometric property of the particles, no arbitrary assumptions on the scattering mechanism had to be made to analyze the data. The period of the damped oscillatory response of the orientation angle is related to the average aspect ratio. In the limit of strong flows the damping only depends on dispersion in particle shape. An analytical expression to relate the polydispersity of the equivalent hydrodynamic aspect ratio to the damping function is presented, as well as the applicability of the technique by studying the hydrodynamic aspect ratio and associated polydispersity in a sample containing ellipsoidal hematite particles.
Influence of internal convection during microwave thawing of cylinders
Authors: Basak Tanmay , Ayappa K. G. 
Published: April 2004

AbstractNumerical simulations were carried out for microwave thawing of 2‐D cylinders of pure materials with internal convection in the liquid regions. Enthalpy formulation of the energy balance equation was used with a superficial mushy region around the melting point. Electric field, energy and momentum balance equations were solved using the Galerkin finite‐element method with the penalty finite‐element formulation of the momentum balance equation. Microwave power absorption, temperature, and stream functions were studied for various cases. For samples of diameter D, thawing was contrasted between samples for 0.032 < D/Dp < 3.73 and 0.10 < D/λm < 1.58. These ratios were computed based on the liquid‐phase penetration depth Dp and wavelength of microwave radiation in the medium λm. In all cases, Pr = 0.5 was used and the Rayleigh number varied from 1.067 × 103 for the smallest diameter to 1.33416 × 105 for the largest sample (D = 2 cm). Thawing was contrasted for MWs being incident from the top and bottom faces of the cylinder and with the thawing dynamics in the absence of convection in the liquid. Our simulations indicate that convection plays a small role for D/Dp ≪ 1 and thawing is independent of the direction of MWs. At intermediate values of D/Dp where a strong maximum occurs in the power, the influence of convection with primary and secondary cell formation in the liquid regions was a strong function of the direction of incident microwaves. In the presence of multiple connected thawed regions convection was suppressed.
Controlling bubble coalescence in a fluidized‐bed model using bubble injection
Authors: de Korte Robert Jan , Schouten Jaap C. , van den Bleek Cor M. 
Published: April 2004

AbstractGas–solids fluidized beds are characterized by the presence of gas voids or bubbles causing a mass‐transfer resistance. Enhancing the mass transfer from the bubbles to the emulsion phase by reducing the bubble size can be advantageous for the chemical performance (like the conversion and selectivity) of the reactor. A model using a 2‐D version of the dynamic bubble model of Clift and Grace (1970, 1971) where bubble trajectories are predicted based on an analytic expression for the flow field around a bubble was studied. Bubble coalescence can be reduced by injecting bubbles in certain patterns, which leads to a reduction of the average bubble size higher in the bed. A simple proportional feedback control method to force bubbles on a horizontal line made it possible to generate a bubble injection pattern automatically, leading to smaller bubbles than without the feedback control method. The principle of the controlled bubble injection could lead to improved gas distributor designs.
Kinetics of separating multicomponent mixtures by nondispersive solvent extraction: Ni and Cd
Authors: Ortiz Inmaculada , Galán Berta , Román Fresnedo San , Ibáñez Raquel 
Published: April 2004

AbstractA model for nonsteady metals separation using nondispersive solvent extraction presented explicitly accounts for selective separation of multicomponent solutions and concentration of separated components in a back‐extraction phase. The separation process comprises extraction and back‐extraction steps carried out in two different hollow‐fiber modules, connected through the organic phase, together with three homogenization tanks. The model is based on a set of coupled differential equations describing mass balances of metallic solutes in the fluid phases. To be applied in its simplest form, it requires the knowledge of three characteristic parameters, two parameters related to the chemical reactions, and one mass‐transport parameter. The latter describes the mass‐transport rate through pores of the hollow‐fiber membrane filled with the organic phase. The mathematical model was checked against the kinetic results of the separation of Cd/Ni mixtures working with high‐concentration solutions and obtaining the characteristic parameters of this system.
Design procedure for safe operations in agitated batch reactors
Authors: Fortuin Jan M. H. , Heiszwolf Johan J. , Bildea Costin S. 
Published: April 2004

AbstractAn application‐oriented design procedure is presented for completely mixed liquid reacting systems in batch reactors. These systems can safely be operated by neglecting the heat capacity of the vessel and attributing suitable values to three scale‐independent control parameters: the initial concentration (c0); the inlet coolant temperature (Tc,i); and the Newtonian cooling time (tN). For given dimensionless values of the reaction order n, heat‐transfer capacity βn, and inlet coolant temperature ϵ, the design value α* of the dimensionless adiabatic temperature rise must satisfy α > α* < αm,a. This can help avoid both runaways (α* < αc) and oversteps of the maximum allowable temperature rise (α* < αm,a). A model is derived to calculate αc and αm,a for three different reaction orders. Simulated relationships are verified with experimental results concerning the hydration of 2,3‐epoxypropanol in a 0.27‐L agitated batch reactor.
Analysis of a gap dryer used to produce polymer films and coatings
Authors: Ramesh Narayan , Duda J. L. 
Published: April 2004

AbstractThe ability to predict the drying behavior of thin films and coatings is of great importance to the coating industry and governs the economical production of various polymeric products. In conventional drying processes, a continuous layer of polymer solution is deposited onto a substrate, which is dried in an oven with forced air convection. Recently, a gap dryer was developed that eliminates the need for forced gas flow and provides direct solvent recovery. A model that incorporates simultaneous heat and mass transfer in the bulk polymer and gas phases and jump conditions across the interface is utilized to describe the drying of a binary polymer–solvent system in a gap dryer. Solvent self‐diffusion in the polymer phase is described by the free‐volume theory, and the Flory‐Huggins theory is used to describe polymer–solvent thermodynamics. Simulations indicate the possibility of condensation in the gas phase that can decrease both drying efficiency and coating quality. A method to resolve this problem is proposed, as well as a comparison between the performance of a gap dryer and a conventional convection‐oven dryer.
Particle motion in packed/ebullated beds by CT and CARPT
Authors: Chen Jinwen , Rados Novica , Al‐Dahhan Muthanna H. , Duduković Milorad P. , Nguyen Duyen , Parimi Krishniah 
Published: April 2004

AbstractComputed tomography (CT) and computer‐automated radioactive particle tracking (CARPT) were used to study the gas distribution and incipient particle motion in a packed/ebullated bed in which gas and liquid are in cocurrent upflow. CT scans were performed to evaluate the gas–liquid distributor and gas sparger for the experiments. Using a perforated plate gas–liquid distributor (with 96 1‐mm holes, open area of 0.1%) and a gas sparger (cross‐shaped, with 16 3‐mm holes), the cross‐sectional gas holdup distribution in the packed/ebullated bed was relatively uniform, with gas holdup of about 0.11 in the center and 0.09 near the wall of the bed at superficial gas and liquid velocities of 2 and 0.3 cm/s, respectively. The cross‐sectional averaged gas holdup was 0.095. CARPT experiments were utilized in an air–water–ethanol– (10 wt. %) solids system to identify the operating conditions at which solid particles first start to move in the bed. At a superficial gas velocity of 1.7 cm/s and superficial liquid velocity of 0.3 cm/s, solids particles in the bed started to move and travel long distances in the axial direction. CARPT experiments in the same system at superficial gas velocity of 2.0 cm/s and superficial liquid velocity of 0.3 cm/s showed that the solid particles in the bed were moving significantly throughout the column, generating a recirculation pattern with upflow in the center and downflow near the wall of the column. The time‐averaged maximum upward and downward velocity of the tracer particle was about 0.47 and 0.57 mm/s, respectively.
Review: Developments in distillation and separation technology
Authors: Porter Kenneth E. 
Published: April 2004

AbstractWith the focus on the power of theoretical concepts to enable the creation of new technologies, separation technology is discussed in terms of “intellectual tools” derived from ideas in diffusion accompanied by reaction and from “pinch point” techniques. Ideas are the intellectual tools shaping the changing world (we live not in the information age, but in the intellectual age). Developments in distillation equipment during the last 20 years reveal the importance of business drivers for stimulating change, and why the 1980s was the decade of structured packing and the 1990s of high throughput trays. Because of out inadequate understanding of phase equilibrium (no molecular theory of liquids) and of two‐phase flow (except for when one phase is very dilute), process and equipment design is still essentially empirical. In conclusion it is noted that more might be done to encourage the development of young intellectual tool‐makers. Research in this field might help speed up technical innovation.
Catalytic distillation in structured packings: Methyl acetate synthesis
Authors: Górak Andrzej , Hoffmann Achim 
Published: April 2004

AbstractCatalytic Distillation can improve process design, the design of column internals requires special attention. The catalytic packing MULTIPAK facilitates effective catalysis, high separation efficiency, and a wide loading range simultaneously. In this work the main characteristics of MULTIPAK—pressure drop, loading range, and separation efficiency—are determined experimentally. The developed nonequilibrium stage model developed reflects the complexity of catalytic distillation processes and comprises correlations describing pressure drop and separation efficiency of MULTIPAK as a function of the operating conditions. The model has been implemented in the simulation environment Aspen Custom Modeler, and the simulation results are compared with experimental data for the synthesis of methyl acetate. This model reflects the process behavior, but differences between simulated results and experimental data can still be observed.
Recovery of VOCs from high‐volume, low‐VOC‐concentration air streams
Authors: Wang X. , Daniels R. , Baker R. W. 
Published: April 2004

AbstractHigh‐volume, low‐VOC‐concentration air streams are produced by a broad range of industries. The most widely used treatment technology is carbon adsorption, which produces dilute aqueous waste streams as a secondary waste, is difficult to adapt to particulate‐containing streams, and is too expensive to be applied by some industries. Scrubbing the air with an absorbent liquid is economical, but limited to scrubbing with water due to the expense and difficulty of regenerating nonaqueous scrubbing liquids. A low‐volatility organic scrubbing liquid regenerated by a stripper/membrane vapor‐separation unit was used to remove VOCs from the dilute air stream. The technical and economic feasibility of the scrubbing/stripping/membrane separation hybrid process was evaluated in laboratory tests with a pilot‐scale system. The unit, operated with model‐contaminated gas streams containing 100 to 2,000 ppm methylene/chloride, removed 95% of the methylene chloride in the feed air as a condensed liquid. The experimental data show that the process offers significant cost and operating benefits over other technologies for streams in the 500 to 2,000 ppm VOC concentration range. It can be applied to treating effluent air streams from painting, degreasing, and printing operations.
Millisecond catalytic wall reactors: I. Radiant burner
Authors: Redenius J. M. , Schmidt L. D. , Deutschmann O. 
Published: April 2004

AbstractShort‐contact‐time reactors have potential for high throughput in reactors much smaller than their traditional counterparts. While they operate adiabatically, heat can be exchanged at short contact time by integrating heat exchange into the reactor. Hot effluent of exothermic reaction systems can be redirected over feed gases to recuperate a portion of the sensible heat. Placing catalyst directly on reactor walls eliminates the resistance to heat transfer in the thermal boundary layer so that heat released by combustion can be effectively coupled to an emitter, such as in a radiant burner. A radiant heater was constructed, operated, and simulated incorporating short contact time, energy recuperation, and a catalytic wall. This burner operated stably for many hours at a firing rate from ∼50 to > 160 kW/m2 at a radiant temperature of 950 to 1,150 K at a radiant efficiency of ∼60% with a residence time in the reacting zone of ∼10 ms. This reactor was modeled using 2‐D Navier‐Stokes equations including detailed models for chemistry and heat transport. Temperature and compositions predicted agreed well with experimental measurements.
Intensification of phase transition on multiphase reactions
Authors: Cheng Zhen‐Min , Anter Abdulhakeim M. , Yuan Wei‐Kang 
Published: April 2004

AbstractChemical reactions, generally conducted under full gas or liquid phases, are problematic for volatile liquid reactants. For such reactants, the presence of phase transition can be favorable, since evaporation of the liquid could not only balance the reaction heat but improve the effectiveness factor of the porous catalyst. This principle was applied to engineering applications. Experiment was carried out to investigate effects of catalyst activities, flow directions, operation pressures, gas and liquid flow rates, and reactant concentrations on the reactor behavior. Quench operation with a cold‐injection side stream was initiated to prevent an excessive temperature rise, which was shown to be effective and flexible. With this novel optimizing method, the reactor temperature could be kept around 270°C under 1.0 MPa, even with a benzene concentration of 35%. Research on phase transition of benzene hydrogenation proved successful and could be extended to reaction systems with a similar range of process intensification.
NO/NOx removal with C2 H2 as additive via dielectric barrier discharges
Authors: Chang Moo Been , Yang Shyh Chaur 
Published: April 2004

AbstractEffective reduction and removal of NOx from gas streams by dielectric barrier discharge (DBD) was studied. A laboratory‐scale experimental system was designed and constructed to evaluate the removal efficiency of NO and NOx. Particularly, C2 H2 was added as a reducing agent in the DeNOx plasma process via DBD. Experimental results indicated that the removal efficiency of NO/NOx increased with increasing applied voltage, gas temperature, and H2 O(g) content. As the oxygen content in the gas stream is increased, more CHi radicals will be further oxidized to CO2, thus reducing the removal efficiency of NOx. When sufficient C2 H2 was added to the DBD process, as high as 91.2% of NO and 68.2% of NOx were removed at 140°C for the gas stream containing 500 ppm NO, 1,500 ppm C2 H2, 3.2% H2 O(g), and 5% O2, with N2 as the carrier gas. In addition to N2 and H2 O, the major products found in this process included NO2, N2 O, HNO3, CO2, CO, and HCOOH, depending on H2 O(g) and O2 contents of the gas stream.
New approach for quantifying process feasibility: Convex and 1‐D quasi‐convex regions
Authors: Ierapetritou Marianthi G. 
Published: April 2004

AbstractUncertainities in chemical plants come from numerous sources: internal like fluctuated values of reaction constants and physical properties or external such as quality and flow rates of feedstreams. Accounting for uncertainty in various stages of plant operations was identified as one of the most important problems in chemical plant design and operations. A new approach proposed describes process's feasible region and a new metric for evaluating process flexibility based on the convex hull that is inscribed within the feasible region and determines its volume based on Delaunay Triangulation. The two steps involved are: 1. a series of simple optimization problems are solved to determine points at the boundary of the feasible region; 2. given the set of points at the boundary of the feasible region, the convex hull inscribed within the feasible region is determined. This is achieved by implementing the Quickhull algorithm, an incremental procedure for evaluating the convex hull, and then by computing a Delaunay Triangulation to determine the volume of the convex hull providing a new metric for process flexibility. This approach not only provides another feasibility measure, but an accurate description of the feasible space of the process. It was applied to 1‐D convex problems, and work is in progress to extend it to nonconvex systems.