摘要:

AbstractThe introduction of reactant gas into a fluidized‐bed chemical reactor as a jet is a common design practice. However, the shape and extent of the void formed by a jet into a fluidized bed and the manner in which the void breaks up into bubbles have still not been described well.An experimental study of a horizontal jet into a 15 cm by 38 cm cross‐section fluidized bed was carried out using an X‐ray system. Instantaneous solid fraction averaged along 15‐cm chords across the bed were measured. The mean value and the fluctuating component of solid fraction were determined for two initial jet diameters, 0.64 and 1.27 cm, and three initial jet velocities, 23, 46 and 69 m/s. Maps of the mean solid fraction and of statistical properties of the fluctuating component show that there are three discernible regions in the jet‐influenced area of the bed. These are a coherent void, bubble trains, and a surrounding compac

ISSN:0001-1541    

DOI:10.1002/aic.690391202

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe dispersion of particles in turbulent duct flow under the influence of electrostatic fields is studied using direct numerical simulation. In this new approach, particles are moved in the temporally and spatially varying turbulent flow field under the influence of electrostatic and gravitational body forces, as well as fluid dynamic drag. The simulations agree well with previously performed experiments (done in geometries typical of wire‐plate and plate‐plate electrostatic precipitators) not only in the overall collection efficiency of particles, but in particle concentration profiles at various axial locations in the flow direction. This gives confidence in the technique that may be used to study different precipitator geometries and flow field configurations, supplementing costly and difficult experiments. Furthermore, information is obtained at a much more detailed level than is possible via experiments, allowing insights into the mechanisms dominating particle collect

ISSN:0001-1541    

DOI:10.1002/aic.690391203

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThis experimental work concerns the multivariable nonlinear control of a continuous stirred‐tank polymerization reactor. The globally linearizing control (GLC) method is implemented to control conversion and temperature in the reactor in which the solution polymerization of methyl methacrylate takes place. Control of conversion and temperature is achieved by manipulating the flow rate of an inlet initiator stream and two coordinated heat input variables. Conversion is inferred from on‐line measurements of density and temperature. A reduced‐order state observer is utilized to estimate the concentrations of monomer, initiator and solvent in the reactor. The concentration estimates are used in the control law. This study demonstrates the considerable computational efficiency of the nonlinear controller, which is implemented on a microcomputer. The experimental results show the excellent performance of the controller in the presence of active state and input constraints. A systematic approach is also given for the synthesis of output feedback controllers within the GLC framework for processes with secondary ou

ISSN:0001-1541    

DOI:10.1002/aic.690391204

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractControl structure (strategy) selection consists of the selection and pairing of manipulated and measured variables. This article outlines a procedure that uses such tools as the existence of right half plane (RHP) transmission zeros, the relative gain array, the performance relative gain array, and the closed‐loop disturbance gain. The regulatory control system for the fluid catalytic cracking process is used as an example. Several authors found the Kurihara control structure to be preferable to the conventional control structure. The reason is that RHP transmission zeros limit the achievable bandwidth for the conventional control structure. Two other control structures, however, have better controllability characteristics than both the conventional and the Kurihara control structures. The sensitivity of the measurement selection and variable pairing with respect to changes in the operating point and parametric uncertainty is examined, as well as the general objectives of the regulatory control level and its interaction with the higher levels in the control hierarch

ISSN:0001-1541    

DOI:10.1002/aic.690391205

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractSufficient conditions for robust closed‐loop stability of a class of dynamic matrix control (DMC) systems are presented. The l1‐norm is used in the objective function of the on‐line optimization, thus resulting in a linear programming problem. The ideas of this work, however, are expandable to other DMC‐type controllers. The keys to the stability conditions are: to use an end‐condition in the moving horizon on‐line optimization; to have coefficients of the move suppression term in the objective function of the on‐line optimization satisfy certain inequalities; and to express the uncertainty as deviations in the unit pulse response coefficients of the nominal plant. These deviations and disturbances must also satisfy certain inequalities.An off‐line tuning procedure for robust stability and performance of a class of DMC controllers is also included, which determines an optimal moving horizon length and optimal values for coefficients of the move suppression term. The applicability of our approach is elucidated through numeri

ISSN:0001-1541    

DOI:10.1002/aic.690391206

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractTwo cationic, copper metal complexes with different ligands were synthesized: ethylenediamine (en) [Cu(C2N8N2) (ClO4)2] and diethanolamine (Deta) {[Cu‐C8H21N2O4]ClO4}. These complexes were mounted on Cab‐O‐Sil using nonaqueous impregnation techniques, and the loadings were determined at which multilayers formed. These samples were analyzed for copper, carbon, nitrogen and hydrogen content to determine if ligand dissociation occurred during the impregnation. Samples were decomposed in a thermal gravimetric apparatus to determine the kinetics of the thermolysis reaction in air, and the evolved gases were analyzed by gas chromatograph‐mass spectrometry to determine the products of the thermolysis reaction. The results of these and earlier studies are summarized in a model that describes the effects of molecular structure upon complex‐support interactions. Complexes with the ability to form hydrogen bond interactions between the ligand and the support form strong interactions with the surface of silica, whereas complexes without such hydrogen bond interactions are only weakly attracted to the silica surface. Strong interactions with the surface may also arise as a result of ligand dissociation and direct interaction of the metal ion with the surface oxygens. The charge on the complex and its shape play less important roles in determining the affinity of the metal complex with t

ISSN:0001-1541    

DOI:10.1002/aic.690391207

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractWe report experimental data showing the effect of temperature on polymer partitioning in the dextran (DEX500)‐polyethylene glycol (PEG8000)‐water system. Increasing temperature increases the concentration of PEG in the top phase and decreases the concentration of DEX in the bottom phase. A solution thermodynamic model based on local compositions with temperature‐dependent parameters correlates the experimental data well, and an efficient Gibbs‐free energy minimization algorithm for phase equilibrium calculations is described. The partial molar enthalpies and entropies of each of the solutes, calculated with the model, are negative and decrease in magnitude as temperature in

ISSN:0001-1541    

DOI:10.1002/aic.690391208

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractComputer simulation results are presented for the residual chemical potential μ 1r, local solvent density enhancement Δρloc, and average solute potential energy u1of a solute molecule immersed in afluid very close to its critical point. The simulation algorithm involves the Monte Carlo method in conjunction with free energy perturbation ideas. A number of ideas related to the feasibility of computer simulations in near‐critical solvents are investigated. Due to long‐range correlations near the critical point, it is not clear that simulations in this regime can be expected to yield accurate results using ensemble sizes of the magnitude typically used in simulations. Examination of system size and number of sampling steps on the simulations shows that the accuracy of the results depend to a large extent on the nature of the thermodynamic property being investigated. The solute chemical potential is suited particularly to simulation since it depends primarily on short‐range structure in the system. A comparison of the simulation results with integral equation theory calculations shows both approaches agree well with

ISSN:0001-1541    

DOI:10.1002/aic.690391209

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractActive cell migration is essential in many physiological processes and in the function of some bioartificial tissues. Therefore, several investigators have recently attempted to quantitatively characterize random cell movement on isotropic substrata in vitro. A popular approach is to fit a theoretical expression for mean‐squared cell displacement deriving from correlated random walk models to cell tracking data, yielding three objective cell movement indices: root‐mean‐squared speed, directional persistence time, and random motility coefficient (analogous to a molecular diffusion coefficient). The data are obtained typically by averaging cell displacements over a cell track composed of cell positions measured at equal time increments and frequently by further pooling such displacement data from tracks of different cells from the same population. We identify pitfalls introduced if an ordinary nonlinear least‐squares regression analysis is used to fit the theoretical expression to the data as is commonly done and propose a generalized least‐squares regression analysis as a remedy. This method estimates the cell movement indices and associated uncertainties much more accurately. It also predicts the precision of the indices based on their assumed true values and provides a means to address such issues as optimal sampling methods for data acquisition from cell tracks and handling errors associated with measuring cell

ISSN:0001-1541    

DOI:10.1002/aic.690391210

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe time‐dependent electrical resistance of human cadaver skin was shown to be bound by an upper limit at equilibrium and a lower limit at steady state. The time to reach steady state from any initial condition by applying a current was much shorter than the recovery to equilibrium, due to different driving forces. The ratio of the equilibrium to the solution resistances increased with the salt concentration in free solution. This equilibrium relative resistance was sensitive to skin variability, primarily due to its dependence on porosity and pore geometry. A model was developed relating the equilibrium relative resistance to the structural properties of skin. The estimated pore radius of 25 × 10−10m from the equilibrium resistance data is consistent with the average pore radius of human skin reported in the literature. In contrast, the steady‐state resistance could be several orders of magnitude lower than the equilibrium resistance and depended on current density and salt concentration but not on the history of prior exposures of a skin sample to a current. This difference can greatly reduce the power requirement for iontophoresis and can make this technology more practical. A linear relationship was found between the logarithm of the steady‐state relative resistance (skin/solution resistances) and the logarithm of the current density divided by the salt concentration. The slope of −0.65 was in excellent agreement with the theoretical slope of −2/3 that was derived for the convective transport of ions in a charged pore under a cons

ISSN:0001-1541    

DOI:10.1002/aic.690391211

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY