bluuebunny/crossref_metadata_2025_split huggingface dataset:
Self‐tuning control of chip level in a Kamyr digester
Authors: Belanger P. R. , Rochon L. , Dumont G. A. , Gendron S. 
Published: June 2004

AbstractA study is presented of the application of a self‐tuning regulator to the control of the level of wood chips in a Kamyr digester, used in the production of wood pulp. Following an initial phase of experiments and model structure selection, two control schemes were studied, using respectively the blow flow and the outlet device speed as manipulated variables. The approach finally adopted uses the outlet device as the primary control. The control has been in operation for several months and has provided significantly improved control and a high degree of operator acceptance.
Optimal averaging level control
Authors: McDonald K. A. , McAvoy T. J. , Tits André 
Published: June 2004

AbstractAn optimal averaging level control problem is defined and solved for a surge tank system. Two averaging level controllers, the ramp controller and the optimal predictive controller are developed utilizing the optimal control policy. These controllers are compared with previously reported averaging level controllers for step and sinusoidal disturbances in inlet flow rate. The OPC results in improved disturbance filtering characteristics for most of the disturbances considered and is very simple to implement.
A model for flow regime transitions in cocurrent down‐flow trickle‐bed reactors
Authors: Ng K. M. 
Published: June 2004

AbstractA study of the nature of interstitial flows within trickle‐bed reactors is presented. Based on physical concepts, a theory is developed to predict the transition boundaries for various flow regimes for nonfoaming liquids. The effects of factors such as bed porosity, size of monodispersed spherical catalyst particles, interfacial tension, viscosity, density, and the gas and liquid flow rates, on flow transitions are considered. Experimental data in the literature are used to confirm the theory and the agreement is good.
Stage‐wise parameter estimation for stiff differential equations
Authors: Srinivasan V. , Aiken R. C. 
Published: June 2004

AbstractThe use of singular perturbation approximation for estimating parameters in stiff ordinary differential equations is illustrated. A sequential parameter estimation approach, in which the difficult‐to‐estimate parameters are introduced in higher‐order terms of the perturbation solution, is developed and illustrated. This approach is shown to provide excellent initial estimates, to be computationally efficient, and to be insensitive to initial guesses for the parameters. Aspects of data requirements for this problem estimation are discussed.
Automatic synthesis of optimum heat exchanger network configurations
Authors: Floudas C. A. , Ciric A. R. , Grossmann I. E. 
Published: June 2004

AbstractThis paper addresses the problem of automatically generating heat exchanger network configurations that feature minimum investment cost subject to minimum utility cost and fewest number of units. Based on the linear programming and the mixed‐integer linear programming (MILP) transshipment models for heat integration, a superstructure that has embedded many alternative configurations is proposed. This superstructure, which has as units the matches predicted by the MILP transshipment model, includes options for series and parallel matching, as well as stream splitting, mixing, and bypassing. Many of the implied stream connections in the superstructure are reduced to zero flow with a nonlinear programming formulation that leads to realistic and practical designs. Theoretical properties as well as the implementation aspects of the proposed procedure for the automatic generation of networks are presented. The method is illustrated with three example problems.
Evaluation of diffusivities in electrolyte solutions using Stefan‐Maxwell equations
Authors: Pinto N. DeG. , Graham E. E. 
Published: June 2004

AbstractThe Stefan‐Maxwell equations have been used to predict single‐electrolyte diffusion and ternary tracer diffusion in concentrated electrolyte solutions. Variations in diffusivity due to concentration have been shown to be related to the relaxation effect and viscosity changes of solution. Specific equations are presented to evaluate the ion‐ion and ion‐solvent interaction coefficients appearing in the Stefan‐Maxwell equations. These equations, when tested against experimental data, gave an accurate description of the process at up to 4.0 M concentrations and for trace species mobilities differing by a factor of ten.
Bulk separation of multicomponent gas mixtures by pressure swing adsorption: Pore/surface diffusion and equilibrium models
Authors: Doong S.‐J. , Yang R. T. 
Published: June 2004

AbstractA theoretical and experimental study is performed for the bulk separation of a ternary mixture by pressure swing adsorption. Three concentrated products can be obtained by cycling the pressure in the adsorber. Three models are formulated for the cyclic process: equilibrium, Knudsen diffusion, and Knudsen plus surface diffusion. The latter model provides the best results when compared with the experimental data, due to the important contribution of surface flux to the total flux in the sorbent pores.
Dynamic interfacial tensions in acidic crude oil/caustic systems. Part II: Role of dynamic effects in alkaline flooding for enhanced oil recovery
Authors: Borwankar R. P. , Wasan D. T. 
Published: June 2004

AbstractA model for caustic propagation in a core during continuous injection is combined with the considerations of interfacial reactions proposed in Part I in order to examine the role of dynamic effects in continuous alkaline flooding. Axial dispersion of caustic and its reversible uptake by the reservoir rock are taken into account. From this model, the interfacial tension between an isolated oil globule and the surrounding flood water can be predicted as a function of time using the knowledge of the kinetics of interfacial reactions, the rock adsorption equilibria, and the longitudinal dispersion coefficient.
Thermally coupled system of distillation columns: Optimization procedure
Authors: Fidkowski Zbigniew , Krolikowski Lechoslaw 
Published: June 2004

AbstractAn analytical solution of thermally coupled system (TCS) optimization was found. Energy requirements of the TCS were minimized provided that the ternary solution being separated is ideal. The TCS is energetically profitable in comparison with other sequences of distillation columns. The solution method can be used for the synthesis of separation systems and for screening calculations, due to the great simplicity of the result.
Dynamic hydrogenation studies in a catalytic slurry reactor
Authors: Ahn Bum‐Jong , Smith J. M. , McCoy B. J. 
Published: June 2004

AbstractHydrogenation of α‐methyl styrene with Pd/Al2O3 catalyst was studied in a three‐phase stirred slurry reactor. Responses to step inputs of H2 in N2 carrier gas provided temporal moments that allowed estimation of separate values for reversible adsorption and irreversible surface reaction rates for reactant H2. Mass transfer resistances are either estimated from other sources and shown to be small, or are evaluated from the flow rate dependence of the moments. The adsorption equilibrium constant for H2 on the catalyst was measured with reaction product cumene as the solvent. For temperatures between 290 and 322 K adsorption appears to have the dominant influence on the overall rate of hydrogenation. The energy of activation for the adsorption step was found to be 8 kcal/mol.
Reconciliation of process flow rates by matrix projection. Part II: The nonlinear case
Authors: Crowe C. M. 
Published: June 2004

AbstractFlow rate and concentration measurements in a steady state process are reconciled by weighted least squares so that the conservation laws and other constraints are obeyed. Two projection matrices are constructed in turn, in order to decompose the problem into three subproblems to be solved in sequence. The first matrix eliminates all unmeasured component flow rates and concentrations from the equations; the second then removes the unmeasured total flow rates. The adjustments to component flow rates are iteratively determined, starting with guessed values of unmeasured total flow rates.Chi‐square and normal test statistics are derived by linearizing the equations, to allow detection of gross errors in imbalances and adjustments of measurements.
Linear process calculations as convergence accelerators in flowsheet‐sequenced programs
Authors: Milani S. M. , Findley M. E. 
Published: June 2004

AbstractLinear process calculations were developed for use in conjunction with flow‐sheet‐sequenced calculations, as methods of convergence acceleration. Two such methods were compared with the successive substitution and Wegstein methods on relatively simple processes. “Linear Process Simulation,” which requires user‐derived equations, produced the best results.
Electron and hole transport in degenerate semiconductors
Authors: Orazem M. E. 
Published: June 2004

AbstractConcentration‐dependent activity coefficients were used in conjunction with dilute‐solution transport equations to show the effect of degeneracy on the apparent physical properties of semiconductors and on the performance of photovoltaic cells. The approach presented here allows convenient treatment of degenerate semiconductors in a manner that is both thermodynamically consistent and consistent with the Fermi‐Dirac distribution for electrons. These calculations show that neglect of the concentration dependency of the activity coefficients has a large effect on the calculated values for local concentrations in a photovoltaic device, but affects the calculated values of power density and cell potential only slightly. Neglect of the concentration dependency of the activity coefficients does have a significant effect on the calculation of the resistivity of the semiconductor.
Synthesis of decentralized process control structures using the concept of block relative gain
Authors: Manousiouthakis Vasilios , Savage Robert , Arkun Yaman 
Published: June 2004

AbstractThe concept of block relative gain (BRG) is introduced to define a measure of interaction for decentralized control structures. This new theoretical development generalizes the original Bristol's relative gain array (RGA) to block pairing of inputs and outputs that are not necessarily single‐input single‐output pairings. Various properties of BRG are rigorously derived and formulated in a mathematical framework suited to analysis and synthesis. Based on these important properties, a methodology is developed for the systematic generation and selective screening of alternative decentralized control structures. Subsequently, a controller design procedure for the most promising decentralized structures is given. A boiler furnace and a system of heat‐integrated reactors are used to illustrate the significance and the utility of the proposed method for industrial processes.
Computer simulation of turbulent mass transfer at a mobile interface
Authors: McCready M. J. , Vassiliadou Eleni , Hanratty T. J. 
Published: June 2004

AbstractNumerical solutions to the unaveraged mass balance equation for the case of a flat mobile interface reveal that both high‐ and low‐frequency velocity fluctuations can contribute to mass transfer. This is in contrast to transport to a solid boundary where only low‐frequency fluctuations, normal to the wall, are important. The average mass transfer coefficient is found to depend on Schmidt number to the −0.5 power, in agreement with classical theories. It is related to the velocity field in the liquid primarily through the mean‐square value of the gradient of normal velocity fluctuations at the interface.
Fractionating condensation and evaporation in plate‐fin devices
Authors: Tung Hsien‐Hsin , Davis J. F. , Mah R. S. H. 
Published: June 2004

AbstractA model that describes fractionation with condensation and evaporation in a plate‐fin device has been formulated. It is capable of evaluating profiles of composition, temperature, and flow rate for both liquid and vapor streams in an extended surface device. The device may be adiabatic or nonadiabatic and the surface may be incompletely wetted. Compared to experimental measurements, the model predictions showed ± 1 number of transfer unit deviation along the length of the device. The predictions of the top and bottom flow rate ratio showed a 5–10% deviation for adiabatic and condensation runs and a 25% deviation for evaporation runs.
The mutual diffusion coefficient of methanol–n‐hexane near the consolute point
Authors: Clark W. M. , Rowley R. L. 
Published: June 2004

AbstractThe composition and temperature dependence of the mutual diffusion coefficient near the liquid‐liquid critical point of methanol–n‐hexane mixtures has been determined by Gouy interferometry. The critical exponent was found to be 0.685. Constant‐temperature extrapolation to zero diffusivity located the spinodal curve. Spinodal loci calculated from the NRTL model are inconsistent with the experimentally determined values.
Mechanism of potassium‐catalyzed carbon/CO2 reaction
Authors: Sams D. A. , Shadman Farhang 
Published: June 2004

AbstractThe mechanism of potassium‐catalyzed C/CO2 reaction is studied by a temperature and concentration programmed reaction (TCPR) technique. The proposed redox mechanism contains three surface complexes: –CO2K, –COK, and –CK. The oxide groups are the intermediates during C/CO2 gasification. The completely reduced form, –CK, is the end product of catalyst reduction and is the precursor for K loss. The stoichiometries of these surface groups are confirmed by oxygen and potassium balances.
The formation and growth of protein precipitates in a continuous stirred‐tank reactor
Authors: Glatz C. E. , Hoare Michael , Landa‐Vertiz Jaime 
Published: June 2004

AbstractProduct particle size distribution data are obtained for the isoelectric precipitation of protein in a continuous stirred reactor in order to evaluate the kinetics of aggregate growth in processes for protein recovery via precipitation. Data are modeled using population balances to verify the postulated mechanism and provide a basis for evaluating results for other reactor configurations. Aggregate breakage was found to be the dominant phenomenon.
A mathematical model of drying for hygroscopic porous media
Authors: Stanish M. A. , Schajer G. S. , Kayihan Ferhan 
Published: June 2004

AbstractA mathematical model is developed to simulate the drying of hygroscopic porous media and, in particular, of wood. Drying rate experiments were performed using wood specimens and a nonhygroscopic porous ceramic solid and were simulated using the appropriate version of the drying model. Calculated model predictions are in very satisfactory agreement with experimental results. An examination of the relative impacts on drying of the transport mechanisms that comprise the model leads to meaningful interpretations of observed drying behavior. Controlling rate factors can be identified and different types of drying behavior specific to a given material or drying condition can be explained and understood through model simulation studies. Such capability can provide important guidance for drying process design and control.
A receding interface model for the drying of slurry droplets
Authors: Cheong H. W. , Jeffreys G. V. , Mumford C. J. 
Published: June 2004

AbstractA receding interface model of the drying of single drops of slurries of sodium sulfate decahydrate has been developed to describe the drying characteristics of this material and to estimate the drying rates of particulate slurries. The simultaneous heat and mass transfer rate equations have been solved numerically, and the results obtained have been compared with those obtained experimentally by drying single drops suspended on the tip of a glass filament.Single drops of slurries, 1.0 to 1.5 × 10−3 m dia., were suspended on the tip of a flexible glass cantilever inserted in a vertical wind tunnel. A 50μm dia. nickel wire passed through the center of the glass beam and the outer surface was coated with a thin film of copper, thereby forming a thermocouple that measured the temperature of the core of the drop; the deflection of the beam gave the loss in weight during drying. In this way the instantaneous drying rate and drop temperature were determined and compared with those predicted by the receding interface model. In all cases the agreement between the predictions of the model and experimental results was good.
A composite statistical test for detecting changes of steady states
Authors: Narasimhan S. , Mah R. S. H. , Tamhane A. C. , Woodward J. W. , Hale J. C. 
Published: June 2004

AbstractA statistical procedure for determining whether process variables have undergone a change of steady states is developed by using a composite statistical test. Factors influencing the power of the test and the probability of Type I errors were studied through theoretical analysis, computer simulation, and application to plant data. They include the number of variables to be tested together, the number of measurements used in time averaging, the levels of significance of the tests, and the appropriate formulation of the hypotheses. The procedure developed here is useful in process data reconciliation and in applications that require an analysis of process trends.
A new similarity rule for fluidized bed scale‐up
Authors: Horio Masayuki , Nonaka Akira , Sawa Yoshitaka , Muchi Iwao 
Published: June 2004

AbstractA rule of hydrodynamic similarity for a scale change of fluidized beds has been developed based on the governing equations of bubble and interstitial gas dynamics. When geometrically similar scale‐up is to be carried out maintaining hydrodynamic similarity, the proposed similarity rule requires that two conditions be satisfied. The first condition assures a similarity in bubble coalescence. The second assures the similarities in bubble splitting and in the interstitial flow pattern. The present work proves theoretically that these two conditions are the necessary, and almost sufficient, conditions for hydrodynamic similarity. They consider not only bubble coalescence but also bubble splitting. The theory proposed was first tested by previous correlations for bubble diameter and grid zone structure, and second by experiment. It has been proved that as long as the present rule is satisfied, the longitudinal distribution of the average bubble diameter, stochastic variation around it, and the radial distribution of superficial bubble velocity can be maintained similar for a scale change.Application of the present rule to predict the bubbling and solid circulation characteristics in a large‐scale unit by a small‐scale experiment has thus proved promising, at least for Geldart group B particles. In order to further study the possibility of a similarity in mass transfer and chemical reactions, computation was carried out using the three‐phase bubble assemblage model. If the effect of molecular diffusion is negligible, as in the case of fluidized bed combustion, even a chemical similarity is found to be possible.
Kinetics of sodium bicarbonate decomposition
Authors: Hu Wang , Smith J. M. , Doǧu Timur , Doǧu Gülsen 
Published: June 2004

AbstractA thermal gravimetric method was used to measure rates of decomposition of NAHCO3 particles. Such decomposition produces a highly porous Na2Co3 that reacts with SO2 rapidly and completely at moderate temperatures. Hence, NaHCO3 decomposition provides a reactant with attractive features for SO2 removal. The rapid rate of decomposition combined with the high heat effect prevented determining intrinsic rates by constant temperature runs when the temperature level was above 400 K. However, rising‐temperature runs, which allowed time for heat transfer to equilibrate temperatures of the thermocouple and particles, gave reliable results at high temperatures. The activation energy was 102 kJ/mol. Porosimeter data verified the large increase in pore volume (from 0.03 to 0.39 × 10−3 m3/kg) on converting the NaHCO3 particles to Na2CO3. First‐order kinetics were observed up to high conversions, after which the apparent order decreased. However, the sodium bicarbonate could be completely converted to Na2CO3.
Small pore closure and the deactivation of the limestone sulfation reaction
Authors: Simons G. A. , Garman A. R. 
Published: June 2004

AbstractThe sulfation model of Simons and Rawlins (1980) is extended to include the effect of product deposits. The model includes: 1. the plugging of the smallest pores and the subsequent loss in the internal surface area, 2. the diffusion of the SO2 through the product deposits, and 3. the loss of intraparticle diffusion due to the complete plugging of the largest pores. It is shown that the plugging of the smallest pores is generally rate‐controlling.
Molecular thermodynamics for fluids at low and high densities. Part I: Pure fluids containing small or large molecules
Authors: Cotterman R. L. , Schwarz B. J. , Prausnitz J. M. 
Published: June 2004

AbstractA correlation is presented for the thermodynamic properties of pure fluids containing small or large molecules. The residual Helmholtz energy is given in terms of perturbed‐hard‐chain (PHC) theory, extended to polar fluids with a multipolar expansion. The novel feature of this correlation is a separation of the Helmholtz energy into low‐density and high‐density contributions. The low‐density contribution follows from a virial expansion and the high‐density contribution from a perturbation expansion. For intermediate densities, a continuous function is used to interpolate between the two density limits. This modification of PHC theory improves agreement with experimental second virial coefficients, vapor pressures, and saturated liquid densities. Since all molecular parameters used here have a well‐defined physical significance, they can be reliably estimated for high‐molecular‐weight‐fluids where experimental data are scarce. More important, separation into low‐density and high‐density contributions allows separate mixing rules for each density region; this flexibility in mixing rules significantly improves representation of mixture properties, as discussed in Part II.
Hydration of isobutene in liquid‐full and trickle‐bed reactors
Authors: Leung Pak , Zorrilla C. , Recasens F. , Smith J. M. 
Published: June 2004

AbstractRates of hydration of isobutene were measured with Amberlyst‐15 catalyst particles in a differential, liquid‐full recycle reactor operating at atmospheric pressure and 303 to 333 K. Catalysts pretreated in two different ways were studied. Liquid‐to‐particle mass transfer had a small but measurable effect on the rate. Intraparticle diffusion was more significant, as indicated by effectiveness factors from 0.26 for the larger catalyst particles (dp = 1.04 × 10−3 m) at 333 K to 0.84 for the smaller particles (dp = 0.45 × 10−3 m) at 303 K. The intrinsic rate was first‐order in isobutene concentration with an activation energy of 67 kJ/mol. The intraparticle diffusion resistance is due to the macropores surrounding the very small gel‐type microparticles of which the particles were composed.Some data were obtained for reaction rates in trickle‐bed operation. Global rates were somewhat lower in the trickle‐bed operation than in the liquid‐full runs. Using the previously determined intrinsic kinetics and effectiveness factors, the liquid‐to‐particle mass transfer coefficients could be approximated for the trickle‐bed operation.