bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal integration of processes with heat engines and heat pumps
Authors: Swaney Ross E. 
Published: June 2004

AbstractAn extended transportation array representation is developed for the design of process heat recovery networks incorporating heat engines and heat pumps. The formulation automatically accounts for the relocation of pinches in the integrated system. The optimal heat flow pattern is determined based on simple economic criteria. Simplified models of heat engine and heat pump systems are developed that permit integration options to be identified on the basis of heat flows without requiring specific cycle designs. The solution array identifies design alternatives and provides a decision framework to guide in selecting the final design topology.
Dynamics and control of quasirational systems
Authors: Ramanathan S. , Curl R. L. , Kravaris C. 
Published: June 2004

AbstractSystems having transfer functions of the form

where P1(s), P2(s) and Q(s) are polynomials, are called quasirational distributed systems (QRDS). They are encountered in processes modeled by hyperbolic partial differential equations. QRDS can have an infinity of right half‐plane zeros which causes large phase lags and can result in poor performance of the closed‐loop system with PID controllers. Theory on the asymptotic location of zeros of quasipolynomials is used to predict the nonminimum phase characteristics of QRDS and formulas are presented for factoring QRDS models into minimum and non‐minimum phase elements.A generalized Smith predictor controller design procedure for QRDS, based on this factorization, is derived. It uses pole placement to obtain a controller parameterization that introduces free poles which are selected to satisfy robustness specifications. The use of pole placement allows for the design of robust control systems in a transparent manner. Controller selection is generally better, simpler and more direct with this procedure than searching for optimal PID controller settings.
Adjustable solute distribution between polymers and supercritical fluids
Authors: Shim Jae‐Jin , Johnston Keith P. 
Published: June 2004

AbstractThe sorption of toluene, dilute in CO2, and likewise the distribution coefficient of toluene between silicone rubber and CO2 have been explored from gaseous to supercritical fluid conditions. Sorption and desorption isotherms were determined by frontal analysis using a new inverse supercritical fluid chromatography technique at 35 and 70°C up to 250 bar. Complementary swelling data are presented for pure CO2 in silicone rubber up to 315 bar. A new result is that the sorption of toluene goes through a maximum and is highly adjustable over a continuum in the highly compressible region of carbon dioxide. This behavior is explained physically and predicted quantitatively with the Flory equation and the Peng‐Robinson equation of state using only information from binary systems. These results are useful for a wide variety of applications including impregnation of polymers with pharmaceuticals, fragrances and other additives, and polymer purification.
Partial internal wetting of catalyst particles with a distribution of pore size
Authors: Bhatia S. K. 
Published: June 2004

AbstractThe recent model of partial internal wetting of catalyst particles (Bhatia, 1988) is extended to allow for pore‐size distribution, multicomponent diffusion, and nonlinear kinetics for spherical particles exposed to condensible vapor undergoing an exothermic reaction. Profiles of liqid filling of the pores are computed, and the influence on mass transfer and effectiveness factor is determined. Under certain circumstances, the effectiveness factor has a maximum with respect to the mole fraction of condensible component suggesting an optimum vapor‐phase composition. As the bulk vapor approaches saturation the effectiveness factor and particle temperature can drop sharply because of precipitious increase in liquid filling. However, a significant fraction of the pore space is still dry in contradiction to prior models assuming complete internal wetting of catalyst particles. The new model is more realistic than earlier attempts and lays the framework for proper representation of the physical phenomena involved.
Phase equilibria for supercritical fluid process design
Authors: Brennecke Joan F. , Eckert Charles A. 
Published: June 2004

AbstractSupercritical fluids (SCF's) are powerful solvents with many unique properties. They have great potential for many extraction processes, but reliable and versatile mathematical models of the phase equilibrium thermodynamics are needed for their use in process design and economic feasibility studies. This paper reviews existing experimental data and analytical methods and attempts to delineate their strengths and limitations. Also discussed are new data needs and possible new directions for a better fundamental understanding of the molecular processes in SCF solutions.
A MIMO cautious self‐tuning controller
Authors: Papadoulis Apostolos V. , Svoronos Spyros A. 
Published: June 2004

AbstractThis paper presents a simple linear model based self‐tuning controller (STC) for MIMO systems. The controller, namely the cautious selftuning controller (CSTC), features enhanced robustness characteristics in the case of unmodeled nonlinearities and / or dynamics. The controller structure is that of a linear quadratic, minimizing a single‐step cost function, and with time varying input penalization. The CSTC can be applied to open‐loop stable and minimum‐phase systems. Application to a simulated distillation column demonstrates its effectiveness.
Gas‐particle flow in a vertical pipe with particle‐particle interactions
Authors: Sinclair J. L. , Jackson R. 
Published: June 2004

AbstractA theory is presented for the fully‐developed flow of gas and particles in a vertical pipe. The relation between gas pressure gradient and the flow rates of the two phases is predicted, over the whole range of cocurrent and countercurrent flows, together with velocity profiles for both phases and the radial concentration profile for the particles. The gas and the particles interact through a drag force depending on their relative velocity, and there are mutual interactions between pairs of particles through inelastic collisions. This model is shown to account for marked segregation of gas and particles in the radial direction, and the predicted relation between the pressure gradient and the flow rates of the two phases is surprisingly complex.
A phenomenological correction to an equation of state for the critical region
Authors: Chou Grace F. , Prausnitz John M. 
Published: June 2004

AbstractThis work presents a phenomenological correction to improve a classical equation of state for representing phase equilibria and densities in the vapor‐liquid critical region. This correction consists of two steps. The first step is a volume translation which locates the correct critical point; this volume translation also improves density predictions for pure fluids and mixtures. The second step provides a near‐critical contribution to the residual Helmholtz energy which accounts for aomalous behavior near the critical point. For pure fluids, the near‐critical contribution flattens the coexistence curve and pressure‐density isotherms near the critical point. For mixtures, the near‐critical contribution has only a small effect on the calculated coexistence curve; this effect is often masked by the choice of binary parameters in the classical equation which have a more profound effect on the calculated results.
Deadtime compensation for nonlinear processes
Authors: Kravaris Costas , Wright Raymond A. 
Published: June 2004

AbstractMany industrially important processes feature both nonlinear system dynamics and a process deadtime. Powerful deadtime compensation methods, such as the Smith predictor structure in state space for linear systems is presented first and then directly extended to nonlinear systems. When combined with input/output linearizing state feedback, this Smith‐like predictor makes a nonlinear system with deadtime behave like a linear system with deadtime. The control structure is completed by adding an external linear controller, which provides integral action and compensates for the deadtime in the input/output linear system, and an open‐loop state observer. Conditions for robust stability with respect to errors in the deadtime and more general linear unstructured multiplicative uncertainties are given. Computer simulations for an example system demonstrate the high controller performance that can be obtained using the proposed method.
A reaction engineering approach to the problem of concrete carbonation
Authors: Papadakis V. G. , Vayenas C. G. , Fardis M. N. 
Published: June 2004

AbstractSteel bars in reinforced concrete are protected from corrosion by the high pH environment of the surrounding concrete. This alkaline environment is destroyed by the reaction of atmospheric CO2 with the Ca(OH)2 of the concrete mass. When this process, called carbonation of concrete, reaches the reinforcing bars, corrosion of the latter may commence. In this paper, the physiochemical processes in this phenomenon are presented and modeled mathematically. The mathematical model is fairly complex, but certain simplifying assumptions are possible, which lead to the formation of a “carbonation front” and to a simple analytical expression for the evolution in time of this front, in terms of the composition parameters of cement and concrete and of the environmental conditions. This simple expression is in very good agreement with experimental results obtained in this and in previous studies. The effect of some parameters on the carbonation front propagation is also discussed.
Diffusion in zeolites containing mixed cations
Authors: Yeh Y. T. , Yang R. T. 
Published: June 2004

AbstractExperimental results are reported for equilibrium adsorption and diffusivities of CH4, C2H6 and CO2 in type A zeolite containing mixed Na and K cations ranging from 0 to 100% in composition, at two temperatures and 1 atm. Two simple theoretical solutions are given for the diffusivity. One is for diffusion with pore (aperture) blocking using the effective medium approximation, which is readily available from the literature on percolation theory. The other is a kinetic solution derived in this work for cavities containing heterogeneous sites, which is a case where the percolation theory is not applicable. The equilibrium adsorption results show that K+ has a preference for the aperture (or pore‐blocking) sites (site type II), and these results are interpreted by the bond percolation theory. The diffusivity results are successfully interpreted by the poreblocking theory in zeolites containing less than 25% K+ and by the kinetic theory for zeolites with higher K+ contents.
Suspension‐to‐Surface heat transfer in a circulating‐fluidized‐bed combustor
Authors: Wu Richard L. , Grace John R. , Lim C. Jim , Brereton Clive M. H. 
Published: June 2004

AbstractHeat transfer coefficients were measured for ciculating beds of sand particles of mean size 222 to 299 μm at temperatures of 340–880° C. Transfer coefficients were obtained for both a 1.22‐m‐long, 12.7‐mm‐OD vertical tube and a 1.59‐m‐long, 148‐mm‐wide membrane wall near the top of a 152‐mm‐square by 7.32‐m‐tall combustion column. For both surfaces and all temperatures, average heat transfer coefficients increased almost linearly with local suspension density which ranged from 0 to 70 kg/m3. Radiation played a significant role, especially at high temperatures and low suspension densities. Heat transfer coefficients also varied significantly with the lateral position of the tube. The vertical length of heat transfer surface is shown to be an important parameter allowing seemingly discrepant published results to be reconciled.
Aggregation kinetics in salt‐induced protein precipitation
Authors: Przybycien Todd M. , Bailey James E. 
Published: June 2004

AbstractThe kinetics of protein aggregation in salt‐induced precipitation processes were studied as a function of salt type, salt concentration, temperature and protein concentration. α‐chymotrypsin (αCT) was used as a model protein. Stopped‐flow turbidimetry was used to monitor the progress of precipitations. Analysis of the linear portions of the turbidity trajectories indicates that temperature and salt concentration effects are related to protein solubility; the protein concentration dependence is well described by the Smoluchowski collision equation. The aggregation kinetics of partially‐inhibited αCT exhibit poisoning behavior, underscoring the importance of dimerization and monomer addition in the precipitation of αCT. Solute particle radius distributions determined via dynamic laser light scattering for low salt and supernatant αCT solutions indicated that significant aggregation does not occur in the absence of supersaturation. A detailed population balance model was proposed that accounted for specific and nonspecific interactions and monomer addition. The model is expected to find general application to protein aggregation phenomena, in particular for proteins that have specific quaternary interactions.
The pressure field in an unsteady‐state fluidized bed
Authors: Foscolo Piero U. , Felice Renzo Di , Gibilaro Larry G. 
Published: June 2004

AbstractAn assumption commonly, but by no means universally, made in the stability analysis of the homogeneously fluidized state is that the pressure field may be well approximated by its gravitational component alone. This assumption is critically examined: the results indicate that it is valid for most cases of practical interest but can lead to significant discrepancies for liquid fluidization of low‐density particles.
Gas diffusion in random‐fiber substrates
Authors: Melkote Rajesh R. , Jensen Klavs F. 
Published: June 2004

AbstractA Monte Carlo (MC) technique involving explicit calculation of molecular trajectories in fibrous media is used to obtain effective transport coefficients in the Knudsen regime of gas diffusion. A fully penetrable cylinders (FPC) model is used to represent a fibrous substrate during the course of densification, as in composite fabrication processes such as chemical vapor infiltration (CVI). The calculated Knudsen permeabilities are in excellent agreement with available data. Accessible porosities are computed as a function of total porosity and are shown to depend on the fiber number density. The nonfiber phase is shown to percolate at ϕ ≈ 0.095, but the threshold is sensitive to the boundary conditions employed.
Modeling phenol degradation in a fluidized‐bed bioreactor
Authors: Livingston Andrew G. , Chase Howard A. 
Published: June 2004

AbstractA study was made of phenol degradation by bacteria immobilized onto particles of calcined diatomaceous earth in a draft‐tube, three‐phase fluidized‐bed reactor.A mathematical model is used to describe simultaneous diffusion and reaction of oxygen and phenol in the reactor. Kinetic parameters for the growth of nonsupported cells were obtained in batch and chemostat experiments. Liquid‐solid mass transfer coefficients were determined experimentally and showed good agreement with literature values for conventional three‐phase fluidized beds. Experimental steady‐state degradation data were used to calculate biofilm substrate diffusivities. These were found to decrease as the biofilm density increased.The transition from phenol to oxygen‐limiting biofilm kinetics predicted by the model was shown to exist experimentally. A critical ratio of phenol/dissolved oxygen concentration was found at which this transition occurred. This provides a criterion for establishing whether increased aeration will increase the volumetric degradation rate.
Simulation of ceramic particle formation: Comparison with in‐situ measurements
Authors: Zachariah M. R. , Semerjian H. G. 
Published: June 2004

AbstractCeramic particle formation processes have been studied using SiO2 as a model compound. Silica particles have been synthesized in a counterpropagating diffusion flame reactor, in which in‐situ measurements of particle size and number density have been made. In addition, the time‐temperature history of the particle field has been calculated from a flame simulation. Numerical simulations using moment and sectional methods for particle formation have been applied and compared to the experimental measurements. The simulations for the particle formation assume a kinetically‐constrained approach, allowing a simple representation of nucleation, surface growth and coagulation. The results suggest that, if the source rates are known well enough, particle formation of low vapor pressure species can be predicted. Both models do well in predicting the gross features of particle formation (number density and mean particle size), although the moment solution does a poor job of predicting the polydispersity effects during periods of high monomer generation rates.
Closure models for turbulent reacting flows
Authors: Dutta A. , Tarbell J. M. 
Published: June 2004

AbstractIn this paper, a simple procedure based on fast and slow reaction asymptotics has been employed to derive first‐order closure models for the nonlinear reaction terms in turbulent mass balances from mechanistic models of turbulent mixing and reaction. The coalescence‐redispersion (CRD) model, the interaction by exchange with the mean (IEM) model, the three‐environment (3E) model, and the four‐environment (4E) model have been used to develop closure equations. The closure models have been tested extensively against experimental data for both single and multiple reactions. The closures based on slow asymptotics for the CRD, 3E and 4E models provide very good predictions of all of the experimental data, while other models available either in the literature or derived here are not adequate. The simple new closure equations developed in this paper may be useful in modeling systems involving turbulent mixing and complex chemical reactions.
Calculation of the compression zone height in continuous thickeners
Authors: Font R. 
Published: June 2004

AbstractA method to calculate the compression zone height in continuous thickeners is presented. With this method, it is necessary to know the variations of the pulp‐supernatant interface and the sediment height vs. time in a batch test. This method is discussed considering the following aspects: relationship between the settling rate of solids and their concentration in the settling zone; and the compression of solids due to the squeeze transmitted by the upper layers—unbuoyed weight of particles minus force of friction due to the Darcian flow. When the variation of the sediment height vs. time becomes linear, it is possible to calculate the maximum solids concentration which can be reached by sedimentation. The change of the solids matrix permeability and its influence on the method proposed are also analyzed.
Fluidized bed drying of solids
Authors: Chandran A. N. , Rao S. Subba , Varma Y. B. G. 
Published: June 2004

AbstractA kinetic model is developed for the drying of solids in fluidized beds, assuming a falling rate period following a constant rate period. Experimental data obtained using batch and continuous single and spiral fluidized beds are satisfactorily matched with the assumed drying kinetics and the residence time distribution of solids appropriate for the type of dryer.
The backfill cycle of the pressure swing adsorption process
Authors: Liow Jong‐Leng , Kenney C. N. 
Published: June 2004

AbstractThe backfill cycle in the pressure swing adsorption (PSA) separation of air to produce an enriched oxygen product using a zeolite 5A molecular sieve was studied theoretically and experimentally. The effects of the backfill cycle, cycle configuration, backfill rate, pressurisation rate, and product rate were studied. The theory agreed well with the experimental results in predicting the product oxygen concentration over a wide range of backfill pressures, thus giving a basic understanding of the bed dynamics of the backfill cycle. The theory showed that the backfill rate and adsorption capacity of the adsorbent were the most important parameters governing the efficiency of the PSA process. We showed that, given an adequate backfill pressure, a separate pressurization step could be omitted by incorporating it with the product release step with no detrimental effect on the product oxygen concentrations while increasing adsorbent productivity.
The stability analysis of nonlinear feedback systems
Authors: Khambanonda Tanes , Palazoglu Ahmet , Romagnoli Jose A. 
Published: June 2004

AbstractA stability condition is developed for multivariable, nonlinear feedback systems. The method is based on a modified sector condition and is combined with a polynomial expansion of the nonlinear system to create viable approximations that can be exploited within the sector bound setting. An example demonstrates the utility of the method in defining stable operating regimes for chemical processes.
The fluid dynamics of reverse roll coating
Authors: Coyle D. J. , Macosko C. W. , Scriven L. E. 
Published: June 2004

AbstractThe flow in the metering gap of a reverse roll coater is examined by experiments and finite element solutions of the Navier‐Stokes equations. At high speed ratios and capillary numbers, the metered film flow deviates strongly from predictions of lubrication theory: the wetting line moves through the gap center and the metered film thickness passes through a minimum. The two flow instabilities found are ribbing, a sinusoidal cross‐web waviness extending smoothly down‐web; and cascade, an irregular V‐shaped cross‐web wave, repeated quasiperiodically down‐web. Experimental operability diagrams define parameter ranges where these instabilities and the steady two‐dimensional flow are encountered. Ribbing behavior is understood by consideration of the pressure gradient at the free surface. The mechanism of cascade is the intrusion through the gap of the wetting line, which causes the metered film to thicken and eventually reattach to the metering roll in a cyclical manner.
Estimation of multiple specific growth rates in bioprocesses
Authors: Pomerleau Yves , Perrier Michel 
Published: June 2004

AbstractAn on‐line estimation technique for multiple specific growth rates is proposed. Time‐varying tuning parameters are used to obtain constant estimation error dynamics in spite of strongly varying process dynamics commonly encountered in bioprocesses. This approach simplifies the tuning of the algorithm to a pole placement procedure. Application of the method is illustrated through the study of the baker's yeast fedbatch process. Guidelines for selection of measured state variables are given in relation to the performance of the estimation method.
Thermoflow multiplicity in a cooled tube
Authors: Stroh Friedemann , Pita Jorge , Balakotaiah Vemuri , Luss Dan 
Published: June 2004

AbstractThe coupling between the momentum and energy balances and the change of physical properties with temperature can give rise to situations in which the pressure drop vs. flow rate curve is nonmonotonic. This can lead to thermoflow multiplicity—the existence of different flow rates in a tube under the same overall pressure drop. A two‐dimensional model is used to analyze the conditions leading to thermoflow multiplicity for an incompressible non‐Newtonian fluid flowing in a cooled tube. First, the multiplicity features of various limiting models are determined. These results are later used to gain an understanding of the asymptotic multiplicity features of the general model. The results show that the temperature sensitivity of the viscosity necessary for thermoflow multiplicity to occur decreases with increasing Brinkman number or β (modified Stanton number), or with decreasing cooling temperature, Biot number, or power law parameter. Multiple flow rates for a prescribed pressure drop are unlikely to occur in heat exchangers in which the Brinkman numbers are usually low and Biot numbers are high but may be found in polymer processing applications.