摘要:

AbstractEnhancement of simultaneous heat and mass transfer due to surface tension gradient‐induced Marangoni convection is studied. The geometry considered is a thin liquid film between a solid phase and a gas phase. In regions where the two Marangoni numbers are of opposite signs (quadrants II and IV), Orr‐Sommerfeld analysis reveals the possibility of oscillatory roll cells. A nonlinear bifurcation study of the amplitude equations indicates that the finite‐amplitude oscillatory rolls are annihilated by steady rolls slightly beyond the oscillatory stability boundary in a heteroclinic bifurcation. Oscillatory rolls are hence restricted to quadrants II and IV. Finite‐amplitude instability due to subcritical bifurcation of the steady rolls is also shown to be limited to these quadrants. In addition to classifying the bifurcations, the numerical study also provides a useful correlation for single‐component flux enhancement,Nh* = 1 + 0.001324Nu0.23Pr0.16(NT−N Tc), which is compared to available expe

ISSN:0001-1541    

DOI:10.1002/aic.690340502

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA heterogeneous electrode surface has been modeled using a regular distribution of circular anodes in a surrounding coplanar cathodic matrix. In the absence of mass transport effects, galvanic currents and potentials have been calculated using finite‐element analysis, with nonlinear electrode kinetics. For a fixed ratio of anodic to cathodic areas on a heterogeneous surface, calculated galvanic currents increase linearly with the active perimeter between cathodic and anodic regions. Furthermore, the current is independent of the shapes and distributions of anodic regions in a surrounding cathodic plane provided that the ratio of overall anodic area to active perimeter is conserved. Thus, due to its longer active perimeter, a surface represented by a large number of tiny anodic islands dispersed in a cathodic sea will exhibit much greater galvanic currents than an equivalent surface represented by a small number of large anodic continent

ISSN:0001-1541    

DOI:10.1002/aic.690340503

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractMonomer partitioning between the aqueous and polymer phases in a latex determines many properties of an emulsion polymerization, such as the reaction rate, molecular weight development and, if operated under refluxing conditions, the reaction temperature. A unique two‐chamber vapor‐liquid equilibrium cell was used during this investigation to obtain anin situseparation of the aqueous phase from the latex, thus permitting a direct determination of the compositions of the aqueous, polymer, and vapor phases in a latex, even under refluxing conditions. Thermodynamic analysis of the vapor‐liquid equilibrium problem allows the prediction of the composition of all phases from measured values of the temperature and pressure only. These predictions agreed well with data from other investigations under nonrefluxing conditions and with the aqueous and vapor phase compositions from this investigation. The polymer phase composition data for vinyl acetate polymers with average molecular weights in excess of 106showed consistently higher polymer volume fractions than predicted. This latter result may be due to crosslinking or strong entanglements resulting from increased chain branching at these high molecular we

ISSN:0001-1541    

DOI:10.1002/aic.690340504

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA prototype of a sodium heat pipe reactor for steam reforming processes has been developed and tested at energy levels up to 6 kW. Both experimental and model simulation data were obtained. Temperature profiles at nonflow and nonreaction flow conditions were used to adjust the parameters of the model, along with an intrinsic rate equation measured in a differential, bench‐scale apparatus.Very good agreement between experiment and model was found for approximately 50 runs under steady state reaction conditions covering a range of process variables. Advantages of the heat pipe as a reactor energy source were confirmed. These include isothermal wall temperatures, energy flux transformation, adjusted flux profiles, and rapid startup. These measurements and computations have provided a model from which optimized configurations have been determine

ISSN:0001-1541    

DOI:10.1002/aic.690340505

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA general physical model of a typical batch extraction system employing liquid surfactant membranes is developed. The model takes into account the continuous‐phase resistance and the interfacial resistance along with permeation through a composite emulsion globule. It also quantifies the loss in extraction efficiencies by leakage of the encapsulated phase due to membrane breakage. The physical model is easily adapted to apply to the case of transport facilitation wherein the solute is reacted in the internal phase to yield products incapable of permeating through the membrane phase. Experimental data on o‐chlorophenol extraction are satisfactorily correlated with the mo

ISSN:0001-1541    

DOI:10.1002/aic.690340506

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe preliminary synthesis of ordinary distillation schemes for separating a single feed into desired products is examined. Nonsharp products are emphasized, i.e., when components are desired in more than one product. Such sets lead naturally to columns with incomplete separation of the key components, including one‐section columns. Stream bypassing around separators and limited stream splitting are permitted. Sequences cannot have separators with identical key components, and only limited product fragmentation is considered. A heuristic ordering of separation options, coupled with a depth‐first application on a pictorial or a matrix representation of a stream, is proposed. Subsequently a best‐first search identifies the few better schemes. Partial sequences are (sub)optimized heuristically. Employing the present methodology on an example problem of four components and products resulted in annual cost savings of 42%, compared to the best sequence isolating the feed compo

ISSN:0001-1541    

DOI:10.1002/aic.690340507

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractExperimental measurements are reported of oil‐water flows in a 20 cm ID pipe at mean velocities between 2.7 and 35 cm/s, at deviation angles θ from vertical between 0 and 65°, and at water flow rate fractions between 30 and 100%. The distribution of the water volume fraction αwacross a pipe section is obtained using local high‐frequency probes. The mean water volume fraction in the section and the slip velocityVsbetween oil and water are also determined. HighVsvalues (up to 50 cm/s) are measured at large deviation angles; they are associated with oil droplet swarms or continuous oil phase zones. Both αwprofiles andVsvalues depend only on the mean water volume fraction and not on the total flow rateQtin the range investigated. At low oil volume fractions αo, all droplets are concentrated close to the upper side of the pipe. At larger αovalues, a slower linear variation of αwwith the distanceyfrom the axis is measured. A model is suggested relating the slope ∂αw/∂yin a vertical plane to the existence of internal density waves in the str

ISSN:0001-1541    

DOI:10.1002/aic.690340508

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA model for the rapid devolatilization of individual coal particles is developed by analogy with a single‐stage equilibrium flash distillation. In the theory, thermal depolymerization of the coal generates aromatic fragments that are widely distributed in size. Conditions for phase equilibrium determine the partitioning of these fragments into intermediates in the condensed phase, which ultimately form char and light gas, and into tar vapor, which escapes in a stream of light gases. Comparison with data shows that the model accurately correlates the yields of noncondensible gas and tar from bituminous coals over wide ranges of temperature and pressure. The predicted molecular weight distributions of tar are also in agreement with measured distributions, and the model yields a mechanistic basis for their observed insensitivity to temperature. The tendency to form lighter tar at higher pressures is also explaine

ISSN:0001-1541    

DOI:10.1002/aic.690340509

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA new approach to represent the deviations from ideality of electrolyte solutions is derived on the basis of the assumptions of specific interactions of Brönsted and of local electroneutrality of Chen. The model consists of two contributions due to long‐range forces, represented by the Debye‐Hückel theory, and to short‐range forces, represented by local compositions through nonrandom factors. With only two adjustable parameters per electrolyte, the model is valid for the whole range of electrolyte concentration, from dilute solution up to saturation. Results are compared with those obtained from two‐parameter or one‐parameter models of Meissner, Bromley, Pitzer, and Chen et al. The model presented in this work consistently produces better results and reproduces the experimental values from the dilute region up to

ISSN:0001-1541    

DOI:10.1002/aic.690340510

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractMixtures of water, oil, and surfactant often form microemulsions where tiny drops of oil (or water) are dispersed in a matrix of water (or oil). A microemulsion is a partially‐ordered fluid in which the surfactant molecules exist in an oriented layer at the boundary between the continuous phase and the discontinuous phase. This work proposes a molecular‐thermodynamic model that is useful for calculating a variety of phase diagrams observed in microemulsion‐forming systems.The model is based on a revised form of Widom's abstract representation of a microemulsion; that representation provides a procedure for calculating essential contributions to the configurational entropy. In Widom's representation, all molecules are difunctional dumbbells such that all the hydrophilic ends are situated together in some lattice sites and all the lipophilic ends are situated together in other sites. A form of Guggenheim's quasichemical theory is used to evaluate the combinatorial contributions that correspond to Widom's picture. Chemical association of surfactant molecules and physical interactions are also taken into account. Minimization of the Gibbs energy yields a distribution function for representing micelle sizes.Calculated ternary phase diagrams are in good agreement with experimental results. Different types of diagrams can be obtained upon changing physically significant model parameters. A study of how these parameters affect phase behavior provides insight on microemulsion stab

ISSN:0001-1541    

DOI:10.1002/aic.690340511

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY