摘要:

AbstractThe solubility ofL‐serine in water was measured as a function of temperature, and the solubility in methanol‐water solutions was determined as a function of temperature and methanol concentration. Solubility in aqueous solutions was found to be a linear function of temperature. Additionally, a statistical design of experiments was used to identify the kinetic variables that influence the purity ofL‐serine crystals recovered by batch crystallization. Agitation and the rate at which super‐saturation was generated through cooling and methanol addition were found to influence the methanol content of the recovered crystals. The size of the recovered crystals also was found to depend on agitation and the rate at which methanol was added to theL‐serine moth

ISSN:0001-1541    

DOI:10.1002/aic.690370802

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractFor a multitube catalytic reactor in which catalyst occupies the shell side of the cooling tubes, a two‐dimensional model is developed to determine the nonuniform radial distribution of the temperature and concentration. The cross‐section of the fixed bed is divided into a number of equivalent portions proportional to the number of cooling tubes. Each portion is approximated by either an equivalent annular fixed bed or a transformed circular fixed bed in the complex plane. Enthalpy and mass balances are performed on the equivalent annular fixed bed while the radially varying flow distribution and the transport properties are considered in a transformed circular fixed bed. A correlation is developed for the equivalent annular model based on the relationship of the two different approximations. The model can also account for variations in radial porosity, radial velocity, and transport propert

ISSN:0001-1541    

DOI:10.1002/aic.690370803

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractAn emulsion layer model is presented which predicts the thickness of a downward‐moving emulsion layer along the wall of a circulating fluidized bed, the mean solids velocity, and the solids flux in the layer. Also presented is a heat transfer model which, in combination with the emulsion layer model, predicts the low‐temperature data very well. An alternate slab model proposed for the radiative component in a high‐temperature circulating fluidized bed agrees well with experimental data. The heat transfer predictions of the overall model for such operating parameters as solid circulation flux, suspension temperature, length of the heat transfer surface, superficial gas velocity, and mean particle size are in good agreement with the published data for long sur

ISSN:0001-1541    

DOI:10.1002/aic.690370804

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA mathematical model for an ion‐exchange membrane attached to a gas‐fed porous electrode is derived and discussed. The model is applied to simulate the oxygen electrode of a polymer‐electrolyte fuel cell. Our discussion focuses on cell polarization characteristics, water transport, and catalyst utilization—all of which must be considered for fuel‐cell design. Calculated polarization behavior is shown to compare favorably with published experimental data. Our results indicate that if the membrane maintains full saturation, its contribution to the total cell resistance is most significant at higher operating current densities (greater than 200 mA/cm2). Polarization resistance due to the oxygen reduction reaction appears to be important for all practical current densities. Water transport, driven by pressure and electric‐potential forces, is shown to be a complicated function of the cell operating conditions. The utilization and distribution of noble‐metal catalyst

ISSN:0001-1541    

DOI:10.1002/aic.690370805

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA model is presented for a zinc/bromine cell that considers the effects of an increase or a decrease in the cathode channel width due to zinc removal on discharge and zinc deposition on charge, respectively. The model also includes the effect of an organic bromine complexing agent (OCA) on the cell performance. Changes in the channel width affect the catholyte velocity, cathode side pressure drop, mass transfer and potential drop in the cell, while the inclusion of the bromine complexing organic phase shows a marked effect on the available bromine in the aqueous phase.It is shown that during discharge, the release of complexed Bromine by the OCA could degrade the cell performance. A simple equation is derived and used to express the relationship between the total bromine in the organic phase and the bromine in the aqueous phase.

ISSN:0001-1541    

DOI:10.1002/aic.690370806

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractEffective Knudsen diffusion coefficients are presented for fibrous structures consisting of parallel, nonoverlapping or partially overlapping fibers. They are computed by means of a Monte Carlo simulation scheme which is employed to determine the mean square displacement of molecules travelling in the interior of the porous medium for large travel times. The results show that structures of paralle, non‐overlapping fibers have smaller effective diffusion coefficients parallel to the fibers than structures of parallel, randomly overlapping fibers of the same porosity and fiber radius, but larger in directions perpendicular to the fibers. Partially overlapping fiber structures are found to exhibit behavior intermediate to those of the two extreme cases. Molecular trajectory computations are also used to obtain results for the structural properties of partially overlapping fiber structures (e.g., porosity and internal surface area, accessible porosity and internal surface area, and percolation threshold), which are compared with some results of the literature for the equivalent problem of partially overlapping disks on a plan

ISSN:0001-1541    

DOI:10.1002/aic.690370807

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe sorption behavior of water and ethanol on starch material has been investigated in relation to the adsorptive separation of water from ethanol. The adsorption isotherms of water‐starch, ethanol‐starch and water‐ethanol‐starch were measured using a Cahn electrobalance. Careful examination of the many sorption isotherm models resulted in selection of Sircar's model and the potential theory to best represent the isotherm data of water‐starch and ethanol‐starch adsorption. Experimental results showed that ethanol as well as water can adsorb on starch. The adsorption rate of ethanol, however, is much slower than that of water. This suggests that the selective removal of water from ethanol vapor in a packed‐bed adsorber is likely a rate‐dependent, not an equilibrium‐d

ISSN:0001-1541    

DOI:10.1002/aic.690370808

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe influence of various operating and liquid‐phase physical variables on interfacial areaabin cylindrical and spherical gas‐liquid stirred contactors was studied using the sulfite method. Studied were stirring speed, sparger porosity, gas flow rate, liquid‐phase temperature, surface tension, and pH.The results show that the influence of operating variables (gas flow rateQg, stirring speed ω, and the average pore radius of the sparger usedrp) onab, for both types of contactors, can be given by the equation:\documentclass{article}\pagestyle{empty}\begin{document}$$ a_b = Q_g^{0.5} \left({\frac{{k_1 }}{{k_2 }} + \frac{{k_2 }}{{r_p^{1.5} }}\omega } \right) $$\end{document}Dependency ofabon surface tension observed was believed to be caused by a rising rate of bubble coalescence with increased surfactant concentration. The higher the surfactant concentration, the lowerab, tending to a limit that depends on both the type of surfactant and the average size of sparger pore used. Due to the measurement method used, solution pH and temperature were also observed to influ

ISSN:0001-1541    

DOI:10.1002/aic.690370809

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractMelt crystallization manufacturing systems are characterized mathematically and optimized. Directional solidification and sweating are modeled, and the results are correlated to plant data. A nonlinear programming algorithm is constructed to determine the optimal design and operation of a production plant. Process constraints include product purity, process yield, capital cost, phase equilibria, kinetic, and operational factors. An objective function is constructed from scaled yield and capital outlay formulae, and is optimized over a variably constrained feasible space. The dependence of the optima on the separation distribution coefficients and on the constraints is given for specific one‐stage examples for three operational regimes. The one‐stage analyses are applied for the solution of the n‐stage pr

ISSN:0001-1541    

DOI:10.1002/aic.690370810

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA correlation was developed to quantitatively describe the flux in a high‐speed rotating filtration device using a minimum set of parameters. The experimental results were found to be consistent with the concentration polarization (CP) model. Beyond a threshold pressure flux ceases to depend on membrane permeability. The CP model was modified to include the concentration dependence of the diffusivity. This approach was found to be consistent with the strong dependence of flux on pH. Protein concentration in the polarized layer adjacent to the membrane surface was estimated using a procedure that corrects for some of the inconsistencies in the methods usually applied. Four dimensionless numbers were necessary to correlate the experiments with good accuracy. Previously‐reported correlations used only three dimensionless numbers. Usage of four numbers could be justified by dimensional analysis. Finally, the performance of rotary or vortex filtration was compared to that of other configurati

ISSN:0001-1541    

DOI:10.1002/aic.690370811

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY