bluuebunny/crossref_metadata_2025_split huggingface dataset:
A moving‐front transition boiling model
Authors: Kao Y. K. , Weisman J. 
Published: June 2004

AbstractIn accordance with visual observations, a transition boiling model that assumes a quench front which alternately advances and retreats in the water flow direction, is proposed. With appropriate choice of a quench zone width and heat transfer rate when the surface is wet, the model predictions are in the same range as the observed temperature oscillations. An extension of the model leads to heat transfer rate predictions in general agreement with experimental observations.
Aerosol behavior in temperature and concentration gradient fields in nonisothermal tube flow
Authors: Nadkarni A. R. , Mahalingam R. 
Published: June 2004

AbstractA general aerosol dynamics equation is derived for nonisothermal steady flow in cylindrical geometry. A scheme for the numerical solution of this equation is presented and its application is illustrated for a practical case incorporating condensation, nucleation, and thermophoresis effects. Additionally, the results of the numerical computations are compared with laboratory experimental measurements of changes in aerosol concentrations and size distributions for nonisothermal flow through a horizontal circular tube.
A single particle approach for analyzing flow systems. Part III: Multiple fluids
Authors: Rubinovitch Michael , Mann Uzi 
Published: June 2004

AbstractThis paper provides a stochastic model for general flow systems with several inlets and outlets, where different fluids are fed through the various inlets. Several process characteristics are derived and discussed. They include the distribution, mean, and variance of the number of visits and total residence time of the various fluid elements to flow regions and the fraction of each fluid that avoids a flow region or a group of flow regions. It is shown that for any fluid and any specified region, the local flow rate through the region is equal to the product of the net flow rate through the system and the mean number of visits to the region by a fluid element of this type. Expressions are also derived for the compositions of material at the outlet streams and at individual flow regions exits, as well as for the composition of material inside each flow region. These results may be employed to verify flow models of physical systems and to determine model parameters.
Low backmixing in multistage agitated contactors used as reactors
Authors: Vidaurri F. C. , Sherk F. T. 
Published: June 2004

AbstractThe objective of the study was to test the validity of an available backmix correlation in the low backmix regime required by multistage agitated contactors used as reactors. The correlation was found to be inapplicable, and new equation forms were developed to fit the new experimental data. Keys to low backmix rates are a small annular area around the shaft compared to the column cross‐sectional area and an extended annular path length.
A model for parison behavior in the extrusion blow molding process
Authors: Dealy J. M. , Orbey Nese 
Published: June 2004

AbstractA simple, lumped‐parameter model has been developed to predict the length and shape of a parison on the basis of experimental swell data and the storage modulus of the resin. The applicability and limitations of the model are demonstrated by comparing its predictions with experimental observations of parison behavior.
Rapid hydropyrolysis of softening coal particles—A modeling study. Part II: Model predictions and comparison with experimental results
Authors: Schaub Georg , Peters W. A. , Howard J. B. 
Published: June 2004

AbstractThe mathematical model described in Part I is applied to predict CH4 and tar yields in rapid hydropyrolysis of softening coal particles. Predicted effects of pressure and particle size agree with trends previously measured in a screen heater apparatus.
Porosity effects on catalytic char oxidation. Part I: A catalyst deposition model
Authors: Su J. L. , Perlmutter D. D. 
Published: June 2004

AbstractSix char samples generated from two coals were impregnated by solutions with different concentrations of Na2CO3 and /or K2CO3. The catalyst solution penetration was studied, the catalyst uptake was measured, and the effects of impregnation on the char pore structure were determined experimentally. The results indicate that the impregnated catalysts reside only on particle exteriors without significant penetration. The overall rate of reaction is therfore the combination of catalytic reaction on particle exteriors and noncatalytic reaction on the pore surfaces inside the particle. A kinetic model is presented that takes these findings into account.
Effect of pore structure on char oxidation kinetics
Authors: Su J.‐L. , Perlmutter D. D. 
Published: June 2004

AbstractPrior studies have demonstrated that char gasification rates vary with conversion, showing a maximum at an intermediate level. In this work experimentally determined char‐air reaction rates and corresponding pore structures are compared to assess the applicability of a previously proposed random pore model and to extract pertinent chemical and physical parameters. Results on six different chars are presented and analyzed to obtain structure parameters, intrinsic kinetics, and activation energies. Agreement between two independent evaluations of the structure parameters demonstrates the degree of applicability of the random pore model and supports the view that rate variations with conversion are controlled by pore structural changes, even though overall rates also include contributions of intrinsic reactivity.
Incipient fluidization condition for a centrifugal fluidized bed
Authors: Fan L. T. , Chang C. C. , Yu Y. S. , Takahashi Teruo , Tanaka Zennosuke 
Published: June 2004

AbstractA model has been proposed for the condition of incipient fluidization in a centrifugal fluidized bed. The model is based on the balance between the overall forces, including the centrifugal and fluid frictional forces, exerted on the fluidized particles and the overall effective weight of the particles. Equations have been derived from the model for predicting the critical fluidizing velocity and the maximum pressure differential (or pressure drop) through the centrifugal bed. A series of experiments was carried out with different solid particles, bed rotational speeds, and bed heights. The resultant data for the critical fluidizing velocity and the maximum pressure drop of the bed indicate that the proposed model is valid and the derived equations are of practical use.
A model for pressure drop in two‐phase gas‐liquid downflow through packed columns
Authors: Rao V. G. , Drinkenburg A. A. H. 
Published: June 2004

AbstractThe nature of the interaction between the flowing phases in a cocurrent gas‐liquid downflow through packed beds depends on the type of the flow regime. The interaction is poor and geometric in nature in gas‐continuous flow and becomes high and dynamic in pulse flow due to gas dispersion, acceleration, and mixing of the liquid in the pulses. Models to calculate pressure drop in each of the flow regimes are presented, taking into account the respective interactions. Experimental data on pressure drops and liquid holdups were measured in gas‐continuous flow for 3 mm glass spheres and 6 mm Raschig rings. An air‐water system is used. The literature data on pressure drops and the experimental data, covering liquid velocities from 0.001 m/s to 0.029 m/s and gas velocities from 0.097 m/s to 2 m/s, were compared with the calculated values. It was found that the pressure drop due to dynamic interaction can be as low as 10% and as much as 80% of the total pressure drop for the data examined in this work. An empirical correlation for holdup in gas‐continuous flow is given for Rashig rings.
Adsorption equilibrium constants and intraparticle diffusivities in molecular sieves by tracer‐pulse chromatography
Authors: Hyun S. H. , Danner R. P. 
Published: June 2004

AbstractA perturbation chromatography technique using radiotracer gases has been developed to determine the adsorption equilibrium constants and diffusivities in molecular sieves. The ethane and ethylene 13X molecular sieve systems were studied in regions of high concentration. The data obtained by this technique are shown to be in agreement with equilibrium data obtained by static methods and with kinetic data obtained by adsorption uptake and chromatographic methods, but not with kinetic data obtained using NMR techniques. The tracer‐pulse chromatographic technique is much more efficient for obtaining gas adsorption equilibria and intraparticle diffusivities and is considerably easier to adapt to wide pressure and temperature ranges than the conventional methods.
A study of inertial effects in granular bed filtration
Authors: Gal E. , Tardos G. , Pfeffer R. 
Published: June 2004

AbstractThe filtration efficiency of a granular bed filter was investigated in the domain where inertial effects are dominant. A filtration model predicting single sphere and total bed efficiencies based on trajectory calculations of dust particles in the voids of the granular bed was developed. The model uses the flow field in a bed of spheres arranged in a body‐centered cubic array for which the filtration efficiency was found to be a function of a modified Stokes number defined by St′ = St × F where the function F depends only on the Reynolds number. The value of the function F can be found experimentally or predicted from the Ergun correlation to be F = 1 + 0.0157 Re. The filtration efficiency calculated using the model agrees well with experimental results obtained in beds of dense cubic packing of spheres especially at relatively low Reynolds numbers (Re < 200) and relatively high Stokes numbers (St′ > 0.01). The prediction of the theoretical model also agrees well with experimental data for randomly packed beds at low porosities and low Reynolds numbes.
Turbulent flow in stirred tanks. Part I: Turbulent flow in the turbine impeller region
Authors: Placek Jiri , Tavlarides L. L. 
Published: June 2004

AbstractThe concept of the trailing vortex introduced by van't Riet and Smith (1975) is used for evaluation of the mean velocity and intensity of periodic velocity fluctuations in the turbine impeller discharge flow. From the analysis of forces acting on the trailing vortex, it follows that geometric similarity in the impeller discharge flow can be expected for the Reynolds number range Re ε 〈1.5 × 104; 9.0 × 104〉 and for the radial distance up to one‐tenth of the impeller diameter. The calculated profiles of mean velocity and intensity of periodic velocity fluctuations agree with published data and permit the declaration of boundary conditions for the impeller discharge flow for numerical modeling of turbulent fluid flow in turbine impeller agitated tanks.
Relation of oil yield to the structure of the thermal wave in the combustion processing of oil shale
Authors: Hiskakis Miltiadis , Hanratty T. J. 
Published: June 2004

AbstractThe combustion retorting of oil shale is analyzed. By using coordinate systems moving at the same velocity as reaction zones, a model is obtained for the fully developed thermal wave which would exist after the wave has progressed a sufficient distance into the bed. Of particular interest is the interpretation of oil yield in terms of the structure of the wave and of operating variables.
Chemical kinetics of the reaction of carbon dioxide with ethanolamines in nonaqueous solvents
Authors: Sada E. , Kumazawa H. , Han Z. Q. , Matsuyama H. 
Published: June 2004

AbstractThe kinetics of the reaction of carbon dioxide with mono‐ and diethanolamine in such nonaqueous solvents as methanol, ethanol, and 2‐propanol and in water were studied using a stirred tank absorber with a plane gas‐liquid interface at 303 K. The reaction was found to be of first order with respect to carbon dioxide for every solvent. The order of reaction with respect to ethanolamine was found to be unity only for an aqueous solution of monoethanolamine and for the other solutions, ranged from 1.4 to 2, depending on the solvent species. The reaction order was increased in the order of water, methanol, ethanol, and 2‐propanol. The variation of the reaction order with the solvent species could be explained in terms of a reaction scheme via a zwitterion. Almost linear dependence of the logarithm of the reaction rate constant on the solubility parameter of the solvent was derived.
Hot purge gas regeneration of adsorption beds with solute condensation: Experimental studies
Authors: Friday D. K. , LeVan M. D. 
Published: June 2004

AbstractActivated carbon beds with adsorbed n‐octane are regenerated using hot air. Effects of pressure, feed temperature, and initial loading on temperature and concentration breakthrough curves are studied. For moderate and high values of these variables, effluent vapors are found to be saturated with hydrocarbon during part of the heating step, indicating the presence presence of liquid within the bed. Regeneration behavior is predicted with reasonable accuracy using a nonisothermal stage model.
Discrete cell model of fixed‐bed adsorbers with rectangular adsorption isotherms
Authors: Do D. D. 
Published: June 2004

AbstractAdsorption of organics inot activated carbon particles within a fixed‐bed adsorber is modeled using the concept of mixing cells. The adsorption isotherm of these organics is taken to be rectangular because of the commonly observed strong affinity of organics into activated carbons. The model equations are solved by a singular perturbation method, and this results in a graphical procedure similar to that of McCabe and Thiele used in distillation column design. Such a graphical procedure provides a quick means to determine the adsorbate profiles along the adsorber for a given time and also the breakthrough curve, which reflects the performance of the adsorber.
Dynamics of deep‐bed filtration. Part II: Experiment
Authors: Chiang Hsu‐Wen , Tien Chi 
Published: June 2004

AbstractFiltration experiments were conducted using granular beds composed of nearly monosized filter grains and monodispersed suspensions. The experimental data obtained are histories of filtrate quality and pressure drop across the filter bed, from which local filter coefficient and pressure gradient were determined as functions of the specific deposit. The experimental results, together with the results of the analyses of the two limiting situations presented in Part I, were used to develop a general correlation which accounts for the change in filter performance caused by particle deposition.
Evaluating significant economic trade‐offs for process design and steady‐state control optimization problems
Authors: Fisher W. R. , Doherty M. F. , Douglas J. M. 
Published: June 2004

AbstractAn order‐of‐magnitude analysis that evaluates the significant economic trade‐offs for the process design optimization problem allows rapid screening of flowsheet alternatives. The optimization problem is simplified by eliminating all but the most important design variables and by including only the dominant cost functions for each trade‐off. Quantitative parameters are defined which allow a straightforward selection of these elements and identify the incentive for optimization. A new optimization criterion helps to prevent the rigor of the optimization analysis from exceeding the accuracy of the design and economic models used.
Perturbation solution and moment expansion for nonlinear adsorption in a CSTR
Authors: Allal K. , Hinds B. C. , McCoy B. J. 
Published: June 2004

AbstractRegular perturbation theory is applied to determine the response to an impulse input in a continuous‐flow stirred‐tank reactor (CSTR) with nonlinear adsorption. A series expansion for temporal moments is a result of the procedure. This moment expansion allows the usual restriction of linearity in analysis of experimental data by moments to be waived. The response at each order can be expressed as an expansion in Laguerre polynomials involving moments, which, in the present example, converges to the exact solution.
Selectivity modification in electroorganic reactions by periodic current control: Electroreduction of nitrobenzene
Authors: Fedkiw P. S. , Chao J. C. 
Published: June 2004

AbstractThe electroreduction of nitrobenzene in deoxygenated acid solution generates predominantly either p‐aminophenol or aniline via the common electrochemically generated intermediate, phenylhydroxylamine. Square wave current control increases the reaction selectivity for p‐aminophenol, which is produced in a chemical pathway from the intermediate over that obtained at the average current of the oscillation. Data collected under electrokinetic‐controlled reaction conditions on a planar copper electrode in a water‐propanol‐sulfuric acid medium show an order of magnitude increase in selectivity at 100 Hz over that measured at the average direct current. The electrode is depolarized under periodic current control which results in lower rates of undesired electrochemical reactions with a consequential increase in chemical product selectivity. Implications and limitations of periodic electrochemical reaction rate control are discussed.
The surface rejuvenation theory of wall turbulence for momentum, heat and mass transfer: Application to moderate and high schmidt (Prandtl) fluids
Authors: Loughlin K. F. , Abul‐Hamayel M. A. , Thomas L. C. 
Published: June 2004

AbstractThe surface rejuvenation model of the turbulent burst process, already developed for the momentum and heat transfer processes, is applied to the field of mass transfer. The range of applicability of the theory, previously shown to be valid for the Prandtl number range 0.7 to 64 is extended to Schmidt numbers of 6,500 without introducing any new parameters. Concentration and temperature profiles for high Schmidt and Prandtl numbers are in agreement with experimental data. Theoretical expressions for Sherwood and Stanton numbers are calculated and shown to be in agreement with experimental data over five orders of magnitude.
Design of cyclic fixed‐bed adsorption processes. Part II: Regeneration and cyclic operation
Authors: Costa Carlos , Rodrigues Alirio 
Published: June 2004

AbstractRegeneration of polymeric adsorbents saturated with phenol in a fixed bed is modeled by an “equilibrium model” and a “reaction front model.” These models were previously tested over CSTR experiments.A package for the design of cyclic fixed‐bed adsorbers was then prepared by linking the reaction front model for regeneration with a pore‐diffusion model for saturation described in Part I (Costa and Rodrigues, 1985) and a model for washing. Predicted and experimental results were compared in a cyclic run.
Application of the fractional derivatives method to bubble growth/dissolution processes with or without first‐order chemical reaction
Authors: Hong Juan , Woo H. S. 
Published: June 2004

AbstractA new application of the fractional derivatives technique is presented to analyze bubble growth/dissolution processes with or without first‐order chemical reaction. The second‐order partial differentail equation with moving boundary conditions is converted to a first‐order ordinary differential equation using the fractional derivatives technique. The first‐order differential equation can be simplified to the quasistationary and the quasisteady‐state equations under appropriate conditions. The predictions of the fractional derivatives solution (FDS) are in excellent agreement with those by numerical methods over a wide range of the dimensionless parameter Na, which describes the extent of gas saturation. The versatility of FDS encompasses various approximate solutions.
Analysis of deep bed filtration data: Modeling as a birth‐death process
Authors: Fan L. T. , Nassar R. , Hwang S. H. , Chou S. T. 
Published: June 2004

AbstractTo simulate the performance of a deep bed filter in terms of the pressure drop dynamics under a constant flow condition, a fairly general stochastic model, namely, the birth‐death process, which takes into account both blockage of the pores by suspended particles and scouring of deposited particles, is combined with the Carman‐Kozeny equation. This model is relatively simple in that the entire bed is spatially lumped and it contains only two parameters, α and β, which are fairly easy to identify. In spite of this simplicity, the model is capable of representing the majority of the available experimental data.
Diffusion and adsorption of moisture in desiccant sheets
Authors: Raghavan Vaikuntam , Gidaspow Dimitri 
Published: June 2004

AbstractThe simultaneous diffusion and adsorption of water vapor into specially prepared silica gel and activated carbon desiccants was experimentally studied for laminar flow through an isothermally maintained parallel‐plate channel. The equilibrium characteristics and tortuosities of the various desiccant sheets used were experimentally determined.The data were compared with a modified Rosen model. The Rosen model predicts outlet concentrations from the knowledge of adsorption equilibrium constants, diffusion, and mass transfer coefficients. A comparison of computed and measured concentrations as a function of sorption time shows that with independently measured equilibrium and effective diffusion coefficients, the modified Rosen model became completely predictive.
A simultaneous‐modular approach to process flowsheeting and optimization. Part II: Performance on simulation problems
Authors: Chen Hern‐Shann , Stadtherr M. A. 
Published: June 2004

AbstractThe performance of the simultaneous‐modular approach on five simulation problems, ranging in complexity from very simple to moderately complex, is studied. Numerical experiments comparing different computational strategies for implementing the simultaneous‐modular approach are also performed. Full‐block perturbation is found to be the most suitable technique for obtaining the flowsheet‐level Jacobian. On process simulation problems the simultaneous‐modular approach, as implemented in SIMMOD, is found to be as reliable as the sequential‐modular approach, and competitive with or sometimes much better than the sequential‐modular approach in terms of computational efficiency.
A simultaneous‐modular approach to process flowsheeting and optimization. Part III: Performance on optimization problems
Authors: Chen Hern‐Shann , Stadtherr M. A. 
Published: June 2004

AbstractThe performance of the simultaneous‐modular approach on four process optimization problems is studied, and numerical experiments using different computational strategies are also performed. The simultaneous‐modular approach is found to be very effective on process optimization problems, and the strategies used in our implementation SIMMOD are found to be more efficient than those used in previous implementations of the simultaneous‐modular approach for process optimization.
Transient ion exchange and solubilization of limestone in an oil field sandstone: Experimental and theoretical wavefront analysis
Authors: Schweich D. , Sardin M. 
Published: June 2004

AbstractThe competition between calcium‐sodium ion exchange and the solubilization of calcium carbonate is studied in a column packed with a sandstone from an oil field. An equilibrium model accounting for this coupling is described. It is shown that the preflush used to eliminate the exchangeable calcium has only a transient efficiency and that the salinity of the water after the preflush can no longer be decreased to a very low level when the solubilization process occurs.