bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solution of material balances for flowsheets modelled with elementary modules: The unconstrained case
Authors: Sood Mohinder K. , Reklaitis G. V. , Woods J. M. 
Published: June 2004

AbstractA study is made of the structure and properties of material balance simulation problems, and a technique is developed for their efficient solution. The method requires neither simultaneous solution of all balance equations nor iterative convergence methods. Instead, for each stream mixing point in the flow sheet, a vector balance equation is developed which contains as unknowns only mixer output streams. This unique set of vector equations is sequenced for solution by using precedence ordering and substitution techniques. It is shown that only as many vector equations need to be solved simultaneously as there are streams which would require iteration in the conventional sequential approach. Once the mixer output streams are calculated, the remaining intermediate process streams are evaluated directly with no further equation solving. Computational results are presented showing the efficiency of the method.
Enhancement of heat transfer and thermal homogenity with motionless mixers
Authors: Nauman E. B. 
Published: June 2004

AbstractMotionless mixers are well suited to augment heat transfer and to provide a uniform thermal environment in laminar flow reactors. Heat transfer performance can be characterized with the Nusselt number, while the degree of thermal homogeneity can be characterized using the thermal time distribution which is the nonisothermal analogue of the residence time distribution. Theoretical results, calculations, and design strategies are presented for a variety of mixer types including flow inverters as well as the more common flow dividers. Two‐channel, partial flow inversion is an excellent, near optimal, strategy for cooling or other situations such as polymerizations which give elongated velocity profiles. For flattened velocity profiles, perfect mixing can sometimes give better results. In practice, however, partial inverters can be expected to outperform those motionless mixers which are primarily flow dividers.
A population balance approach to the modeling of solid phase reactions
Authors: Bhatia Suresh K. , Perlmutter D. D. 
Published: June 2004

AbstractA population balance approach is used to model solid phase reactions in terms of nuclei of the product phase dispersed in the reactant matrix. A conversion‐time relationship is obtained by the solution of a set of moment equations derived from the population balance. Some previously known solutions for both homogeneous and heterogeneous nucleation are developed by this approach to demonstrate the relative ease of solution when compared with previously used integral techniques. A model for nucleus impingement at low conversions is formulated and applied to published data on the oxidation of cuprous iodide to illustrate the practical use of this technique. The classical Avrami model (Avrami, 1939, 1940, 1941) is modified to include the initial volume of a nucleus, and it is shown that insensitivities in the original model are removed by this improvement. The need for direct measurements of nucleation and growth rates is emphasized.
Effective interfacial area determination by gas absorption accompanied by second‐order irreversible chemical reaction
Authors: Matheron Erik R. , Sandall Orville C. 
Published: June 2004

AbstractOxygen and carbon dioxide were absorbed by aqueous sodium hydroxide solutions in an agitated vessel, and the experimental results were interpreted in terms of the surface renewal theory in order to deduce effective interfacial areas. The simultaneous physical and chemical absorption experiments permitted a determination of the enhancement factor under identical physicochemical and hydrodynamic conditions. It was found that for the unbroken interface case, the effective areas for physical and chemical absorption are equal when the Danckwerts parameter γ is approximately unity. γ is defined as the ratio of the increase in absorption capacity of the liquid to the enhancement factor. For the case where the gas is sparged through the liquid, it was found that the effective interfacial area is a strong function of agitator speed (above a critical speed) and gas flow rate, whereas the mass transfer coefficient was found to be nearly independent of agitator speed and gas sparge rate.
Turbulence characteristics and mass transfer at air‐water surfaces
Authors: Davies John T. , Lozano Francisco J. 
Published: June 2004

AbstractThe turbulence intersities and spectra in water very close to an air interface have been measured with a hot wire anemometer. The turbulence in the water has been induced in three ways: with a stirrer, by a submerged jet, and by flow of a thin film of water over inclined plates, both rough and smooth.We find that the root‐mean‐square fluctuation velocity Ṽx′ shows for the first system no regular trend with the distance y below the surface, while for the second system Ṽx′ increases markedly as the surface is approached. In water films over the rough plates, Ṽx′ can be as high as four times the shear stress velocity.The turbulence energy spectra close to the surfaces in the first and second systems show (Figure 6) no extended region of slope −5/3, whereas for flow over the plates, there is an appreciable subrange of this slope (Figures 8 and 9).Intensities of turbulence in the surface region are as high as 30 to 50% in the first system, up to 100% in the second system, and 17% over smooth plates and up to 60% over rough plates.These turbulence characteristics can be related to the rates of mass transfer for oxygen absorbing into water by comparing plots of k/D1/2 with the square roots of the different eddy frequencies. The Levich treatment [interpreted by Equation (15)] gives good agreement with the stirred cell and jet results. For the smooth and rough plates, mass transfer depends on eddies intermediate in size between the x directional and the y directional large eddies. In all cases, the Kolmogoroff eddy frequencies are much too high to correlate with mass transfer rates.Further, the energy spectra show that 60 to 80% of the total eddy energy lies in the larger eddies, with only 1% (or less) in the Kolmogoroff range.We conclude that the Prandtl sized eddies, and even larger eddies, determine mass transfer rates at a free surface.Direct measurement of concentration fluctuation frequencies, using platinum microelectrodes, was found to be unsatisfactory because of the poor frequency response of the amplified signals.
Staged approach of percolation processes
Authors: Rodrigues Alírio E. , Beira Eduardo C. 
Published: June 2004

AbstractSorption processes in a perfectly mixed reactor are analyzed by using two models: The equilibrium model and a kinetic model which considers the effect of the external mass transfer resistance. In both cases, a general non‐linear equilibrium isotherm is considered.The influence of the different model parameters on the response of the perfectly mixed sorber and their effect on a design parameter (the breakthrough time) are discussed.A criterium is derived in order to predict when the equilibrium model is valid.
Growth of ice in a saltwater drop falling in an organic phase
Authors: Bustany S. T. , Harriott Peter , Wiegandt H. F. 
Published: June 2004

AbstractData on the ice formation rate are presented for a salwater drop suspended by drag forces in a flowing cold organic liquid. The effects of refrigerant undercooling, salt concentration, drop size, and time were studied. Ice formation rates in drops of 3 wt % sodium chloride solution were two to three times lower than in pure water drops. A parallel plate model was used to correlate the data and predict ice formation rates for other drops and refrigerants.Dispersing drops of brine or fruit juices in a countercurrent cold organic refrigerant is a method of desalination (or freeze concentration) that deserves further study.
Fully developed viscous flow and heat transfer in curved semicircular sectors
Authors: Masliyah Jacob H. , Nandakumar K. 
Published: June 2004

AbstractThe Navier‐Stokes equation in stream function‐vorticity form and the energy equation are solved numerically for a fully developed flow of a Newtonian fluid in coiled circular sectors having zero pitch. Two heat transfer cases are studied: axially uniform heat flux with uniform peripheral temperature and axially uniform temperature with mixed conditions along the periphery. Solutions are presented for curvature ratios in the range of 5 to 30, Prandtl numbers in the range of 0.7 to 100, and Dean numbers up to 300. In all cases studied, the heat transfer performance for the curved tubes was superior to that of a straight tube geometry.
Concentration forcing of catalytic surface rate processes: Part I. Isothermal carbon monoxide oxidation over supported platinum
Authors: Cutlip Michael B. 
Published: June 2004

AbstractPeriodic feed switching between carbon monoxide/argon and oxygen/argon mixtures to a gradientless reactor has been found to significantly increase the average reaction rate as compared to the steady state rate, when the time averaged feed concentrations in both cases are stoichiometric. The rate enhancement achieved during periodic reactor operation is attributed to the attainment of more desirable surface concentrations on the platinum catalyst which dramatically increase the surface rate processes leading to carbon dioxide production.
Numerical analysis of variable property heat transfer to a single sphere in high temperature surroundings
Authors: Sayegh N. N. , Gauvin W. H. 
Published: June 2004

AbstractA theoretical study has been conducted to investigate the effects of large temperature differences on the rate of pure heat transfer from a very hot gas to stationary spheres.In the numerical analysis, the momentum and energy equations for variable property flow past a sphere were solved simultaneously, using finite difference techniques. Results were obtained for Reynolds numbers up to 50 and surface temperature to gas temperature ratios varying between 0.25 and unity. These ranges cover most of the conditions commonly encountered in heterogeneous plasmas, transferred arc, and other high temperature chemical engineering processes. The flow behavior, drag coefficients, and Nusselt number were calculated for each case.The constant property solutions were in excellent agreement with numerical and experimental results reported in the literature, thus justifying the validity of the model and of the underlying assumptions. In general, the effect of variable properties was to drastically increase the flow velocity, vorticity, and temperature and vorticity gradients near the surface.A generalized heat transfer correlation was derived which, in addition to constant property conditions, included the effect of large variations in the physical properties of the fluid as a result of large temperature differences.
Equilibrium and kinetics studies of hydrogen isotope exchange on vanadium hydride
Authors: Wong Y. W. , Hill F. B. 
Published: June 2004

AbstractChromatography experiments and pressure‐composition isotherm measurements were carried out on the vanadium‐hydrogen system in order to obtain an understanding of the equilibrium and kinetic factors affecting hydrogen isotope exchange. Analysis of the results yielded values of the hydrogen equilibrium distribution coefficient, the tritium‐protium separation factor, the rate of the gas‐solid exchange reaction, and the axial dispersion coefficient.
Surface ablation in the impingement region of a liquid jet
Authors: Swedish Michael J. , Epstein Michael , Linehan John H. , Lambert George A. , Hauser George M. , Stachyra Larry J. 
Published: June 2004

AbstractA theoretical and experimental investigation of a water jet impinging on a melting solid surface has been carried out. Ice, octane, p‐xylene, and olive oil served as the meltable solid materials, comprising a Prandtl number range of 5 to 2 800. An available laminar stagnation flow model was utilized to describe melting heat transfer in the jet impingement region. Melting rate measurements were found to agree quite well with the values predicted with this model.
Mass transfer between a flowing fluid and a solid wavy surface
Authors: Thorness Charles B. , Hanratty Thomas J. 
Published: June 2004

AbstractThis paper considers the transfer of mass or heat between a fluid and a small amplitude solid wavy surface. A periodic variation of the transfer rate can occur because of wave induced variations of the normal convective flow and of the properties of the turbulence. Solutions of the mass balance equations are presented for the laminar flow at a large Schmidt number or Prandtl number and for turbulent flow at large and small wave numbers. For turbulent flows at intermediate wave numbers, the prediction is limited by inadequacies of present theories that model the wave induced variation in the turbulent diffusion of heat or mass. In order to provide guidance for this modeling, new measurements on the variation of the mass transfer rate along a solid wavy surface are presented for a Schmidt number of 729. An analogy between momentum and mass transfer is explored as a means for evaluating the turbulent diffusion terms.The amplitude of the function describing the mass transfer variation is found to decrease with decreasing wave number and the phase to increase with decreasing wave number. The phase angle and the amplitude of the variation in the mass transfer rate relative to the average mass transfer rate are insensitive to changes in Schmidt number or Prandtl number. For turbulent flows, the phase change can be large enough that the maximum in the mass transfer rate can exist somewhere in the trough of the wave. This result is of considerable significance in interpreting wavelike dissolution patterns.
Estimation of phase diagrams and solubilities for aqueous multi‐ion systems
Authors: Kusik C. L. , Meissner H. P. , Field E. L. 
Published: June 2004

AbstractCalculation of the phase diagram for saturated aqueous multi‐ion solutions of strong electrolytes, based upon use of the thermodynamic solubility products, is illustrated for the four‐ion system: Na+, K+, Mg++, SO4=. Solid phases are identified along with the ion concentrations of the associated saturated solutions.
Calculation of sulfate and nitrate levels in a growing, reacting aerosol
Authors: Peterson Thomas W. , Seinfeld John H. 
Published: June 2004

AbstractThe temporal variation of particle size and chemical composition of a marine aerosol exposed to SO2, NH3, NO, NO2, H2SO4 and H2O vapor is studied to determine the effect of these parameters on the sulfate and nitrate levels in the particle. Results show that, for gas phase SO2 oxidation to sulfate, and liquid phase nitrate formation, those parameters that enhance sulfate formation tend to inhibit nitrate formation, and vice versa. Further, for the situation considered, the ratio predicted for sulfate and nitrate ions to ammonium ions is very nearly that found if all these ions were present in the form of NH4NO3 and (NH4)2SO4. This compares favorably with data on sulfate, nitrate and ammonium levels in the Los Angeles area. The model used is capable of representing a general growing, reacting aerosol; other cases studied by this approach are briefly outlined. Limitations of its use are discussed.
Effects of acceleration, deceleration and particle shape on single‐particle drag coefficients in still air
Authors: Marchildon E. K. , Gauvin W. H. 
Published: June 2004

AbstractMeasurements were made of the drag coefficients of smooth solid particles moving singly through still air at Reynolds numbers in the range of 103 to 104. Spheres were observed during acceleration, deceleration and at terminal velocity. Discs were tested during acceleration and at steady velocity. Other particles in the shapes of discs, circular cylinders and rectangular parallelepipeds were tested at steady velocity in their preferred and, in some cases, non‐preferred orientations. The effects of non‐steady velocity and of particle form were determined. An unexpected influence of particle density was observed for some of the particles.
Diffusivities of low‐volatility species in light gases
Authors: Ravindran Periasamy , Davis E. J. , Ray A. K. 
Published: June 2004

AbstractGas‐phase diffusivities for high boiling point organics in common gases are determined by evaporating a single submicron aerosol droplet of the organic species, while it is suspended in an electric field in the path of a polarized laser beam. The droplet size is measured as a function of time by using Mie theory to determine the size from the light scattering data of intensity versus angle. In addition to diffusivities, the Lennard‐Jones molecular interaction potential parameter, ϵii, and the collision diameter σii, are found, by applying the molecular theory of gases to interpret the evaporation rate data. Results are compared with available empirical and semi‐theoretical correlations for diffusivities and Lennard‐Jones parameters. The low vapor pressure organics used here are dioctyl phthalate (DOP), dibutyl sebacate (DBS) and dibutyl phthalate (DBP), and the carrier gases are helium, nitrogen and carbon dioxide.
Sweetening of sour natural gases by mixed‐solvent absorption: Solubilities of ethane, carbon dioxide, and hydrogen sulfide in mixtures of physical and chemical solvents
Authors: Rivas O. R. , Prausnitz J. M. 
Published: June 2004

AbstractSolubilities of ethane, carbon dioxide, and hydrogen sulfide have been measured in propylene carbonate, N‐methyl‐2‐pyrrolidone and tetramethylene sulfone (sulfolane); and in mixtures of these physical solvents with monoethanolamine and diglycolamine, in the range −10 to 100°C. Thermodynamically consistent equations are given for gas absorption with chemical reaction at equilibrium. Henry's law describes physical equilibrium between the acidic gas in the vapor phase and free acid solute in the liquid phase. Equilibrium constants describe chemical equilibria for the absorbed gas and the chemical solvent.Preliminary design calculations for sweetening natural gases by absorption with mixed solvents suggest that, under some circumstances, mixed‐solvent absorption may be more economical than using conventional aqueous alkanolamine.
Computation of phase and chemical equilibrium: Part I. Local and constrained minima in Gibbs free energy
Authors: Gautam Rajeev , Seider Warren D. 
Published: June 2004

AbstractSeveral methods are reviewed for determining compositions in multiphase, reacting mixtures at equilibrium. Wolfe's quadratic programming algorithm is applied and results compared with the Rand method (Dluzniewski and Adler 1972), NASA method (Gordon and McBride 1971) and the George et al. (1976) implementation of Powell's method. For poor guesses in compositions, local and constrained minima in Gibbs free energy may arise, giving incorrect phase distributions.
A thermodynamic‐combinatorial approach to the design of optimum heat exchanger networks
Authors: Flower John R. , Linnhoff Bodo 
Published: June 2004

AbstractThis article describes a novel approach to the systematic synthesis of heat exchanger networks. For a given synthesis problem, this approach leads to a complete listing of all solutions which exist, using a prescribed degree of energy recovery, the minimum number of exchangers, heaters and coolers, and no split streams. The approach is combinatorial, with a variety of thermodynamic criteria used to minimize the problem size by preventing infeasible solutions being generated. Two examples (5SPI and 6SPI) are discussed to illustrate complete solution by hand.
Moving‐bed solids flow in an inclined pipe leading into a fluidized bed: Part II. The solids flow properties
Authors: Chen Te‐Yu , Walawender Walter P. , Fan L. T. 
Published: June 2004

AbstractThe purpose of part II of this paper is to theoretically analyze and experimentally examine moving‐bed solids flow in an inclined pipe connecting a fluidized bed and a solids storage vessel. The macroscopic momentum balance equation is simplified and applied to the present system. A friction factor correlation is developed. Based on the flow curves constructed, we found that the power law model is suitable for describing moving‐bed solids flow.
Analysis of the phase inversion characteristics of liquid‐liquid dispersions
Authors: Arashmid M. , Jeffreys G. V. 
Published: June 2004

AbstractCorrelations of the collision frequency and the coalescence frequency of an agitated dispersion are combined with models relating drop sizes and hold‐up to agitator speed, to predict the ambivalence range and phase inversion composition of liquid‐liquid dispersions. Our model was tested by comparing predicted and experimental phase invesrion compositions of the system toluene‐water ad carbontetrachloride‐water. In addition, the predicted results have been compared ith published results for the system kerosene‐water, and in all cases, agreemet between predicted and experimental resutls are excellent.
Effectiveness and deactivation of a diluted catalyst pellet
Authors: Varghese Philip , Wolf Eduardo E. 
Published: June 2004

AbstractIn this article, we analyze the performance of a dluted catalyst pellet consisting of inert and active particles under diffusion influenced conditions and pore‐mouth poisoning. First, we establish the requirements for validty of the analytical soltuions of the diluted pellet equations. Secondly, we show that, under pore‐mouth poisoning conditions, a diluted pellet can display considerably longer lifetimes than a uniformly impregnated catalyst. Conversely, for the same lifetime, use of a diluted pellet can result in savings of the catalytic agent. These advantages are not offset by difficulties in catalyst manufacture, as is the case for previous designs.
Structural analysis of multicomponent reaction models: Part I. Systematic editing of kinetic and thermodynamic values
Authors: Sorensen Jan P. , Stewart Warren E. 
Published: June 2004

AbstractThe consistency of a chemical reaction scheme depends in part on the numerical values given for its kinetic and thermodynamic constants. Part I of the present two‐part treatment provides (1) a systematic procedure to reduce the given values to a self‐consistent form, and (2) a proper selection of parameters whenever the values are to be improved by a subsequent regression analysis. Various completeness and consistency tests are described, including a search for illegal reaction loops arising from assumptions of irreversibility. The procedure is implemented on a computer and is illustrated with two examples.
The facilitated transport of carbon monoxide through cuprous chloride solution
Authors: Smith Douglas R. , Quinn John A. 
Published: June 2004

AbstractThe facilitated transport of carbon monoxide through thin, immobilized films of cuprous chloride solutions is investigated, using a tracer C14O technique. Steady‐state tracer flux measurements are used to determine the second‐order forward rate constant and equilibrium constant for the reversible reaction of CO with cuprous ion. The enchanced results at low CO partial pressures can be interpreted in terms of a consecutive reaction model. The cuprous ion is remarkably effective as a carrier for CO. The CO permeation rate in the presence of cuprous ion can be increased by two orders of magnitude over the nonfacilitated flux. As such, the cuprous ion is an attractive facilitating agent for use in a membrane separation system.
The effect of an expanded section on slugging
Authors: Yang W.‐C. , Keairns D. L. 
Published: June 2004

AbstractSlugging experiments were performed in a semicircular Plexiglas column 5.6 m in height to study the effect of an expanded section on slugging. The bottom section of the column (3.05 m long) is 28.6 cm in inside diameter and the expanded section 40.6 cm. Both the bed height and the fluidizing velocity were varied during the study, and the results were successfully correlated with a theoretically derived equation. The implications in designing a bed with an expanded section to reduce the slugging effectively are also discussed.